Formation and Redox Reactions of Green Rusts under

Diss ETH No 15492

Formation and Redox Reactions of Green Rusts under Geochemical Conditions found

in Natural Soils and Sediments

A dissertation submitted to the

SWISS FEDERAL INSTITUTE OF TECHNOLOGY

for the degree of

DOCTOR OF NATURAL SCIENCES

presented by

MARIANNE ERBS

MSc in environmental chemistry

born January 13 1973

in Haderslev Denmark

Accepted on recommendation of

Prof Dr Rene P Schwarzenbach examiner

Prof Dr Stefan B Haderlein co-examiner

Prof Dr Hans CB Hansen co-examiner

Zuumlrich 2004

In fond memory of my mother

Esther Kristine Erbs (1949-2002)

who taught me how to be strong feel joy and bear compassion

I dedicate this work to her Without her support care and love

I would never have been the person I am today

To dare is to lose ones footing momentarily Not to dare is to lose oneself

Soslashren Kierkegaard

Acknowledgements

I would like to thank Stefan Haderlein Hans Christian B Hansen and Rene

Schwarzenbach for their supervision of this work Without the encouragement and

confidence of HCB Hansen and former colleagues at the Royal Veterinary and

Agricultural University in Copenhagen I would never have pursued a PhD and

without the understanding of Rene Schwarzenbach after the tragic death of my

mother I would not have had the time necessary to finish it

I thank Christian Bender Koch Hanne Nancke-Krogh Susanne Guldberg and

Henrik T Andersen (Royal Veterinary and Agricultural University Denmark) for

their valuable contribution to my work I would also like to express my gratitude to

former and present members of the Contaminant Hydrology Group from whom I

have received many benefits I mourn the loss of Denis Mavrocordatos (EAWAG)

who provided technical assistance in the electron microscopy lab and I will always

keep the sunny hours in his company in fond memory Finally I would like to

thank Kristina Straub and Bernhard Schink (University of Constance Germany)

who welcomed me in their lab for a week and taught me how to work with strict

anaerobic bacteria

I gratefully acknowledge the grant which I received from the Danish Research

Agency

Table of Contents

Table of Contents Zusammenfassung I Summary V 1 General Introduction 1 11 Iron cycling in the subsurface 1 12 Green rusts 3 13 Microbial formation of green rusts 7 14 Redox reactions of green rusts 8 15 Outline of the thesis 10 References 11 2 Solid State Oxidation of Vivianite by Anaerobic

Denitrifying Fe(II)-Oxidizing Bacteria 17 Abstract 17 21 Introduction 17 22 Materials and methods 22

221 Microorganisms and media 22 222 Characterisation of precipitates 23 223 Biooxidation experiments 24 224 Analytical methods 25

23 Results and discussion 25 231 Identification of solid iron-containing phases 25 232 Factors controlling the rate and extent of Fe(II) biooxidation 34 233 Morphology of solid iron phases 37

24 Conclusions 38 References 39 3 Formation of Layered Iron Hydroxides by

Microbial Fe(III) Reduction 43 Abstract 43 31 Introduction 44 32 Materials and methods 47

321 Preparation of iron oxide coatings 47 322 Mineral characterisation 48 323 Culture conditions and cell preparation 48 324 Bioreduction experiments 49

Table of Contents

325 Analytical methods 50 33 Results and discussion 50

331 Fe(II) production and suspension colour changes 50 332 Identification of solid iron phases 55 333 Factors controlling the identity of the secondary iron minerals 58 334 Factors controlling the rate and extent of Fe(III) bioreduction 59

34 Conclusions 60 References 61 4 Reduction of Nitroaromatic Probe Compounds by Sulphate

Green Rust The Effect of Probe Compound Charge 65 Abstract 65 41 Introduction 66 42 Materials and methods 71

421 Synthesis of GR-SO4 71 422 Mineral characterisation 72 423 Lyophilization and determination of specific surface area 72 424 Estimation of the one-electron reduction potential for 4-NPA 73 425 Kinetic experiments 74 426 Analytical methods 74

43 Results and discussion 75 431 Product formation and reaction kinetics 75 432 Comparison of rate constants for the different NACs 79 433 Factors influencing the reaction rate 82 434 Comparison with rate constants obtained for other Fe(II) containing

mineral systems 83 435 Depletion of reactive sites 85 436 The role of external and internal reactive sites 86

44 Conclusions 89 References 91 5 Reductive Transformation of Trichloroacetate in Abiotic

Fe(II)-Fe(III) Mineral Systems 97 Abstract 97 51 Introduction 98 52 Materials and methods 101

521 Synthesis of GRs and magnetite 102 522 Preparation of iron oxide coatings 102 523 Mineral characterisation 103 524 Kinetic experiments 103

Table of Contents


531 Product formation and reaction kinetics 105 532 Comparing rate constants obtained for the various Fe(II)-Fe(III)

mineral systems 109 533 Comparing with rate constants obtained for other chlorinated

aliphatic compound 112 534 Factors controlling the reactivity of surface-bound Fe(II) 114 535 Comparison with biotic and other abiotic systems 118

54 Conclusions 119 References 120 6 Conclusions and Outlook 125 References 128 7 Supporting Information I 71 Estimation of the one-electron reduction potential for 4-NPA I 72 The rate-limiting step IV 721 Mass transfer (diffusion) limited kinetics V

722 Surface saturation limited kinetics IX 73 External surface area of GR-SO4 and GR-CO3 XI 74 Van der Waals radii XIV 75 Adsorption of Fe(II) onto Fe(III) oxides XVI References XVIII Curriculum Vitae

Zusammenfassung I

Zusammenfassung Geschichtete Fe(II)-Fe(III)-Hydroxide (Gruumlner Rost) gehoumlren zur Gruppe der

Fe(II)-haltigen Mineralsysteme (zB Magnetit (Fe3O4) Siderit (FeCO3) Vivianit

(Fe2(PO4)2sdot8H2O) Fe(II)-Sulfide sowie an die Oberflaumlche von Fe(III)-Oxiden und

Tonmineralien gebundenes zweiwertiges Eisen) die die Aktivitaumlt von Fe(II) in

suboxischen und anoxischen Boumlden und Sedimenten kontrollieren Gruumlner Rost

Phasen (GRs) bestehen aus planaren positiv geladenen trioktaedrischen Fe(II)-

Fe(III)-Hydroxidschichten die durch hydratisierte Anionen in den

Zwischenschichten ausgeglichen werden Ihre generelle Zusammensetzung ist

[FeII(6-x)FeIII

x(OH)12]x+[(A)xnmiddotyH2O]x- wobei x = 09 - 42 ist A entspricht einem n-

valenten Anion (zB CO32- Clndash oder SO4

2-) und y repraumlsentiert die Anzahl

Wassermolekuumlle in der Zwischenschicht GRs sind wichtige intermediaumlre Phasen

die durch unvollstaumlndige Oxidation von Fe(II) oder teilweise Reduktion von Fe(III)

gebildet werden koumlnnen Sie koumlnnen in suboxischen nicht-sauren eisenhaltigen

natuumlrlichen wie auch technischen Systemen auftreten so wie in Wasser gesaumlttigten

Boumlden und interstitiellen Sedimenten Rohrleitungen in der

Trinkwasserversorgung Stahlpfosten in marinen Sedimenten Stahlbeton und in

reaktiven durchlaumlssigen Waumlnden aus nullwertigem Eisen zur in-situ Sanierung von

Altlasten und Aquiferen Aufgrund ihrer Schichtstruktur den anionischen

Zwischenschichten und der hohen spezifischen Oberflaumlchen sind GRs reaktive

Ionentauscher und Sorbentien von Anionen Des Weiteren wurde gezeigt dass

GRs eine Reihe anorganischer und organischer Schadstoffe reduzieren koumlnnen

Durch Immobilisierung und Transformation koumlnnen GRs somit eine wichtige Rolle

fuumlr das Abbauverhalten und den Transport solcher Schadstoffe in suboxischen

Boumlden und Sedimenten spielen Die Resultate dieser Dissertation tragen zum

Verstaumlndnis uumlber die Bildung und Reaktivitaumlt von Fe(II)-haltigen Mineralsystemen

wie GRs Vivianit Magnetit und an Goethit (α-FeOOH)- und Lepidokrozit (γ-

FeOOH)-Oberflaumlchen gebundenes Fe(II) in der Natur bei

II Zusammenfassung

Um die Rolle von Bakterien bei der Bildung von GRs in natuumlrlichen Boumlden und

Sedimenten aufzuklaumlren wurden Eisenminerale untersucht die als Folge der

Aktivitaumlt von eisenrespirierenden Bakterien gebildet wurden Kapitel 2 beschreibt

die Untersuchungen von eisenhaltigen Produkten die von anaeroben autotrophen

denitrifizierenden Fe(II)-oxidierenden Bakterien (FeOB) gebildet wurden Ein

Bikarbonat- und Phosphat-reiches Kulturmedium bot den nitratreduzierenden

FeOB optimale Bedingungen Fe(II) lag zu Anfang der Reaktion als weisses

Fe(II)-Hydroxyphosphat (Vivianit) und als geloumlstes Fe(II) vor Die Ergebnisse

zeigten dass die denitrifizierenden FeOB amorphen Goethit via ein gruumlnes Fe(III)-

angereichertes Vivianit-Zwischenprodukt bildeten Die Analyse mit Moumlssbauer

Spektroskopie deutet nicht auf eine Bildung von GR hin

In Kapitel 3 werden jene Eisenmineralien beschrieben die waumlhrend der Reduktion

verbreiteter Fe(III)-Oxide durch anaerobe dissimilative Fe(III)-reduzierende

Mikroorganismen Shewanella algae BrY gebildet wurden Um natuumlrliche

Zustaumlnde zu simulieren wurden Fe(III)-Oxide als Beschichtungen auf

Silikatpartikel (Modellsystem fuumlr Sandboumlden) oder Calcitpartikel (CaCO3

Modellsystem fuumlr kalkhaltige Boumlden) aufgetragen sowie synthetische

Elektronencarrier und hochkonzentrierte kuumlnstliche pH-Puffer ausgeschlossen

Die erforschten Mineralsysteme umfassten GoethitCalcit- LepidokrozitCalcit-

und FerrihydritSand-Suspensionen S algae BrY reduzierte beachtliche Mengen

des eingesetzten Fe(III) und es bildeten sich gruumlne und schwarze Festphasen

innerhalb von 1-2 Wochen nach der Animpfung Moumlssbauer Spektroskopie der

gruumlnen und schwarzen Praumlzipitate zeigte dass sich diese aus GR und Vivianit

zusammensetzen

Die Reaktivitaumlt synthetischer GRs gegenuumlber reduzierbaren organischen

Schadstoffen wurde erkundet um die potentielle Bedeutung von GR-Phasen fuumlr

das Schicksal solcher Verbindungen abzuschaumltzen Zu diesem Zweck wurden

Nitroaromaten (NACs) und Chloracetate als Modellverbindungen benutzt um

Zusammenfassung III

umweltrelevante Redoxreaktionen zu studieren In Kapitel 4 wurde die relative

Reaktivitaumlt von aumlusseren und inneren reaktiven Stellen in synthetischem Sulfat-

Gruumlnem Rost (GR-SO4) anhand von strukturaumlhnlichen ldquoreaktiven

Sondenmolekuumllenrdquo mit unterschiedlichen Ladungen untersucht Als reaktive

Sondenmolekuumlle wurden Nitrobenzen 2-Nitrophenol 4-Nitrotoluen 4-

Chlornitrobenzen und 4-Nitrophenylessigsaumlure verwendet Die Ergebnisse zeigen

dass GR-SO4 die NACs vollstaumlndig zu den entsprechenden Anilinen reduzierte

Die Reaktionen folgten einer pseudo 1 Ordnungs Kinetik bezuumlglich NAC und die

auf Oberflaumlche normalisierten pseudo 1 Ordnungs Geschwindigkeitskonstanten

(Anfangsraten) waren 016ndash465middot10-4 s-1middotm-2middotL fuumlr [Fe(II)GR]0 = 103-1260 mM

[NAC]0 = 20-102 microM und pH 84-86 Weder durch Einbezug von

Massentransferlimitierung noch von Oberflaumlchensaumlttigungskinetik war es moumlglich

die aumlhnlichen Oberflaumlchennormalisierten pseudo 1 Ordnungs

Geschwindigkeitskonstanten fuumlr die Reduktion der neutralen und anionischen

NACs durch GR-SO4 zu erklaumlren Dieser Umstand laumlsst vermuten dass die

Reaktion zwischen NAC und GR-SO4 an den externen reaktiven Fe(II)-Stellen

stattfindet Bei niedrigen Fe(II)GR-Anfangskonzentrationen wurden die externen

reaktiven Fe(II)-Stellen aufgebraucht und die Regenerierung von neuen externen

reaktiven Stellen haben schliesslich die Geschwindigkeit der Reduktion von NACs

durch GR-SO4 kontrolliert

In Kapitel 5 wurde die Reaktivitaumlt von verschiedenen umweltrelevanten Fe(II)-

Fe(III)-Mineralsystemen gegenuumlber Trichloressigsaumlure (TCA) und

Dichloressigsaumlure (DCA) in Batchexperimenten die natuumlrliche Bedingungen

imitierten untersucht Die Fe(II)-Fe(III)-Systeme umfassten Sulfat-Gruumlner Rost

Carbonat-Gruumlner Rost Magnetit Fe(II)Goethit und Fe(II)Lepidokrozit TCA

wurde von allen Fe(II)-haltigen Mineralien zu DCA reduziert Die Reaktionen

folgten einer pseudo 1 Ordnungs Kinetik bezuumlglich TCA und die auf Oberflaumlche

normalisierten pseudo 1 Ordnungs Geschwindigkeitskonstanten betrugen 033ndash

76middot10-5 min-1middotm-2middotL bei [Fe(II)]0 = 025ndash116 mM [TCA]0 = 15ndash1000 microM und pH

IV Zusammenfassung

70ndash87 Die Ergebnisse zeigen keine signifikanten Unterschiede zwischen den

verschiedenen Fe(II)-Fe(III)-Systemen bezuumlglich Produkteverteilung und

oberflaumlchen-normalisierten pseudo 1 Ordnungs Geschwindigkeits-konstanten In

keinem der Systeme wurde DCA innerhalb des experimentellen Zeitraums zu

Monochloressigsaumlure oder Essigsaumlure weiter reduziert

Die Ergebnisse die in dieser Dissertation praumlsentiert werden zeigen dass

mikrobiologische Prozesse fuumlr die Oxidation von Vivianit-Phasen im Untergrund

verantwortlich sein koumlnnen Zudem wurde nachgewiesen dass GRs bei tiefen

Kohlenstoff- und Fe(III)-Konzentrationen sowie durch Ausschluss von

kuumlnstlichen Elektronencarriern und pH-Pufferung mikrobiell gebildet werden

koumlnnen Ferner zeigten Befunde dass GRs eine bedeutende Rolle fuumlr die reduktive

Transformation von NACs und TCA in natuumlrlichen Boumlden und Sedimenten spielen

koumlnnen

Summary V

Summary

Layered iron(II)-iron(III)-hydroxides (green rusts) belong to the group of Fe(II)-

bearing mineral systems eg magnetite (Fe3O4) siderite (FeCO3) vivianite

(Fe2(PO4)2sdot8H2O) Fe(II) sulfides as well as Fe(II) associated with Fe(III) oxide

and clay mineral surfaces that control the Fe(II) activity in suboxic and anoxic

soils and sediments Green rusts (GRs) consist of plane positively charged

trioctahedral Fe(II)-Fe(III) hydroxide sheets balanced by hydrated anions in the

interlayers and hold the general formula [FeII(6-x)FeIII

x(OH)12]x+[(A)xnmiddotyH2O]x-

where x = 09 - 42 A is an n-valent anion eg CO32- Clndash or SO4

2- and y is the

number of water molecules in the interlayer GRs are important intermediate

phases formed by partial oxidation of Fe(II) or partial reduction of Fe(III) and they

have been found in suboxic non-acid iron-rich natural environments such as

hydromorphic soils and intertidal sediments and in engineering systems including

pipeline distribution systems for drinking water steel sheet piles in marine

sediments reinforced concrete and permeable reactive barriers of zero-valent iron

implemented for on-site remediation of contaminants Due to their layered

structures anionic interlayers and high specific surface areas GRs represent

reactive ion exchangers and sorbents of anions In addition GRs have been shown

to reduce a range of inorganic and organic pollutants Thus through sequestration

and reductive transformation GRs may play an important role in the fate and

transport of contaminants in suboxic soils and sediments The work presented in

this dissertation adds to the understanding of how Fe(II)-bearing minerals like

GRs vivianite magnetite and Fe(II) associated with goethite (α-FeOOH) and

lepidocrocite (γ-FeOOH) may form and react in nature

In order to elucidate the role of bacteria in the formation of GRs in natural soils

and sediments we studied the iron mineral phases forming as a result of the

activity of iron-respiring bacteria In the study described in chapter 2 the Fe-

containing products formed by anaerobic autotrophic denitrifying Fe(II)-oxidizing

VI Summary

bacteria (FeOB) were examined The culture medium applied contained high levels

of bicarbonate and phosphate and is typically used in this kind of studies as it

provides excellent conditions for the nitrate-reducing FeOB Fe(II) was present

initially as a whitish solid Fe(II) hydroxy phosphate (vivianite) and as soluble

Fe(II) The results obtained demonstrate that the denitrifying FeOB produce poorly

crystalline goethite via a greenish Fe(III)-enriched vivianite intermediate

Moumlssbauer spectroscopic analyses provided no significant evidence of green rust

formation

In chapter 3 the Fe-containing products formed during reduction of common

Fe(III) oxides by the anaerobic dissimilatory Fe(III)-reducing microorganism

Shewanella algae BrY are discussed In order to simulate natural conditions

Fe(III) oxides were applied as coatings on silica (model system for sandy soils) or

calcite (CaCO3) particles (model system for calcareous soils) and synthetic

electron shuttles as well as highly concentrated artificial pH buffers were excluded

The mineral systems studied include goethitecalcite lepidocrocitecalcite and

hydrous ferric oxidesand suspensions S algae BrY reduced substantial amounts

of the initial Fe(III) and green and blackish mineral phases were produced within

1-2 weeks after inoculation Moumlssbauer spectroscopic analyses showed that the

green and black precipitates consisted of GR and vivianite

The reactivity of synthetic GRs towards reducible organic pollutants was

investigated in order to asses the potential significance of GR phases for the fate of

such compounds To this end we used nitroaromatic compounds (NACs) and

chlorinated acetates as suitable model compounds for studying environmentally

relevant redox reactions In the work described in chapter 4 the relative reactivity

of outer and inner Fe(II) reactive sites in synthetic sulfate green rust (GR-SO4) was

studied using a series of structurally closely related compounds with different

charge properties as ldquoreactive probesrdquo The probe compounds included

nitrobenzene 2-nitrophenol 4-nitrotoluene 4-chloronitrobenzene and 4-

Summary VII

nitrophenylacetic acid The results show that NACs are completely reduced to their

corresponding anilines by GR-SO4 The reactions followed pseudo 1 order

kinetics with respect to NAC and the surface area-normalised pseudo 1 order rate

constants (initial rates) obtained were 016ndash465middot10-4 s-1middotm-2middotL at [Fe(II)GR]0 = 103-

1260 mM [NAC]0 = 20-102 microM and pH 84-86 Neither mass transfer control nor

surface saturation kinetics could explain the similarity of the surface-normalised

pseudo 1 order rate constants obtained for the reduction of the neutral and anionic

NACs by GR-SO4 These observations suggest that the reaction between NAC and

GR-SO4 takes place at the external reactive Fe(II) sites At low initial Fe(II)GR

concentrations the external reactive Fe(II) sites were depleted and the regeneration

of new external reactive sites eventually controlled the reduction of the NACs by

GR-SO4

Finally the reactivity of various Fe(II)-Fe(III) mineral systems towards

trichloroacetic acid (TCA) and dichloroacetate (DCA) has been investigated in

laboratory batch experiments imitating natural conditions (Chapter 5) The Fe(II)-

Fe(III)-systems investigated included GR-SO4 carbonate green rust magnetite

Fe(II)goethite and Fe(II)lepidocrocite TCA was readily reduced to DCA by all

Fe(II)-containing minerals The reactions followed pseudo 1 order kinetics with

respect to TCA and the surface area-normalised pseudo 1 order rate constants

obtained were 033ndash76middot10-5 min-1middotm-2middotL at [Fe(II)]0 = 025ndash116 mM [TCA]0 =

15ndash1000 microM and pH 70ndash87 Our results showed no significant differences

regarding product distribution and surface area-normalised reaction rate constants

between the Fe(II)-Fe(III)-systems DCA was not further reduced to

monochloroacetate (MCA) or acetate in any of the systems within the time frame

in our experiments

The results presented in chapter 2 indicate that microbiological processes may be

responsible for the oxidation of vivianite phases in natural subsurface

environments In chapter 3 we demonstrated that GRs may be produced

VIII Summary

microbially at conditions including low carbon and Fe(III) concentrations as well

as the exclusion of synthetic electron shuttles and pH buffers The results obtained

in chapter 4 and 5 show that GRs transform NACs and TCA readily The reductive

transformation of NACs and TCA by GRs is relevant to understanding the

processes responsible for their degradation in the subsurface and the development

of innovative technologies for their remediation

General Introduction 1

1 General Introduction

11 Iron cycling in the subsurface

Iron is the fourth most abundant element (4-5 mass) and the most abundant redox

sensitive element in the Earthrsquos crust It is found as Fe(II) and Fe(III) in a number

of minerals in rocks soils and sediments Under anoxic conditions solid Fe(III)-

containing minerals can be reduced to soluble Fe(II) once the more energetically

favoured electron donors - nitrate and manganese(IV) oxides - have been

consumed Dissolved Fe(II) can be reoxidized to insoluble Fe(III) microbially or

abiotically upon exposure to oxygen Due to this ready alternation between the

Fe(II) and Fe(III) redox states iron plays a major role in controlling the redox

potential and the carbon cycling in subsurface environments (Nealson amp Saffarini

1994)

Nonenzymatic processes were previously considered to account for most of the

Fe(III) reduction in subsurface environments The significance of bacteria in the

biogeochemical cycling of iron has been broadly recognized over the past two

decades Dissimilatory Fe(III)-reducing bacteria (DIRB) that gain energy by

coupling the oxidation of hydrogen or organic compounds to the reduction of

Fe(III) oxides have been known for many years but their biogeochemical

importance was only widely acknowledged about a decade ago (reviewed by

Lovley 1997) Fe(III) bioreduction accounts for a major fraction of the carbon

oxidation in many different anoxic environments and in the presence of sufficient

amounts of reactive Fe(III) microbial Fe(III) reduction may even inhibit sulphate

reduction and methanogenesis (King 1990 Lovley amp Phillips 1986) In fact most

of the Fe(III) reduction in the Fe(III) reduction zone of aquatic sediments and

aquifers is enzymatically catalyzed by microorganisms (Lovley et al 1991) A

wide diversity of DIRB distributed among several different phylogenetic groups

2 Chapter 1 is known today The two most studied DIRB are the obligate anaerobic Geobacter

spp and the facultatively anaerobic Shewanella spp (Figure 11)

Aerobic oxidation of Fe(II)-containing minerals by lithotrophic acidophilic and

neutrophilic bacteria has been known for many years but their broad significance

in the biogeochemical cycling of iron has only been recognized over the past two

decades Both acidophilic (Thiobacillus ferrooxidans) and neutrophilic

(Gallionella ferruginea Leptothrix ochracea Sphaerotilus natans) aerobic Fe(II)-

oxidizing bacteria (FeOB) have been isolated (Hanert 1992 Kuenen et al 1992

Mulder amp Deinema 1992)

Figure 11 The microbial iron cycle

Anaerobic Fe(II) oxidation by phototrophic purple non-sulfur bacteria utilizing

Fe(II) as an electron donor in the light was recognized only a decade ago (Widdel

et al 1993) Subsequently it was demonstrated that the biological oxidation of

Fe(II) in the absence of oxygen is possible by light-independent chemotrophic

microorganisms using nitrate as the electron acceptor (Straub et al 1996) Thus

the microbial iron cycle includes anaerobic Fe(III)-reducing microorganisms and

aerobic as well as anaerobic Fe(II)-oxidizing bacteria (Figure 11)


12 Green rusts

Iron oxides iron hydroxides and iron oxyhydroxides (collectively termed iron

oxides or Fe(III) oxides) are ubiquitous in the pedosphere where they originate

from aerobic weathering of surface magmatic rocks such as ferromagnesium

silicates and pyrite (Cornell amp Schwertmann 1996) Goethite (α-FeOOH)

lepidocrocite (γ-FeOOH) ferrihydrite (Fe5HO8sdot4H2O) hematite (α-Fe2O3)

magnetite (Fe3O4) maghemite (γ-Fe2O3) and akageneite (β-FeOOH) constitute the

most important iron oxides in soils and sediments (Schwertmann amp Cornell 1991)

The formation and transformation of iron oxides depend on pH solution

composition redox potential temperature rate of oxidationreduction and degree

and rate of hydrationdehydration Iron oxides are important to many soil

properties such as colour pH and redox buffer capacity aggregation with other

soil particles as well as retention of anions and cations (Cornell amp Schwertmann

1996) A number of Fe(II)-bearing minerals including Fe(II)-containing clays (eg

smectites vermiculites and micas) magnetite siderite (FeCO3) vivianite

(Fe2(PO4)2sdot8H2O) Fe(II) sulphides and green rusts (layered Fe(II)-Fe(III)

hydroxides) may be present in soils and sediments under suboxic and anoxic

conditions Green rusts are believed to play a central role as metastable

intermediates in the redox cycling of iron at circumneutral pH in aquatic and

terrestrial environments

Green rusts (GRs) are layered iron(II)-iron(III)-hydroxides consisting of plane

positively charged trioctahedral Fe(II)-Fe(III) hydroxide sheets balanced by

hydrated anions in the interlayers (cf Figure 41 this work) GRs belong

structually to the pyroaurite-sjoumlgrenite group of layered hydroxides and they hold

the general formula [FeII(6-x)FeIII

x(OH)12]x+[(A)xnmiddotyH2O]x- where x = 09 - 42 A is

an n-valent anion eg CO32- Clndash or SO4

2- and y is the number of water molecules

in the interlayer The three most common and investigated green rust forms include

chloride GR (GR-Cl) sulphate GR (GR-SO4) and carbonate GR (GR-CO3)

Generally GRs are crystallographically classified into the GRI (rhombohedral

4 Chapter 1 GR-Cl and GR-CO3) and GRII (hexagonal GR-SO4) crystal systems The GR

interlayer thickness is a function of both the size and the charge of the interlayer

anion Tetrahedrally coordinated anions like sulphate lead to larger interlayer

distances than smaller monoatomic anions like chloride or planar ions like

carbonate (Mendiboure amp Schoumlllhorn 1986) Not only size but also charge density

plays a role for the interlayer spacing That is for anions having the same number

of valence electrons anions with smaller ionic radii (higher electron density) are

bound more strongly and therefore result in smaller interlayer spacings The

interlayer in GR-SO4 is composed of two consecutive planes of anions and water

whereas GR-Cl and GR-CO3 interlayers consist of only one single plane (Simon et

al 2003)

GRs are important intermediate phases formed by partial oxidation of Fe(II) or

partial reduction of Fe(III) In neutral and weakly alkaline solutions the oxidation

of dissolved Fe(II) always passes through solid GR phases (Bernal et al 1959)

GRs may also form during oxidation of zero-valent iron and as a result of the

combination of Fe(II) and Fe(III) at circumneutral pH (Figure 12)

Figure 12 Formation and transformation of GRs Fe3O4 = magnetite γ-Fe2O3 = maghemite α-

FeOOH = goethite γ-FeOOH = lepidocrocite akageneite = β-FeOOH


Oxidation of GR-CO3 usually produces goethite and magnetite-maghemite

whereas GR-Cl and GR-SO4 transform into lepidocrocite and magnetite-

maghemite depending on pH and oxidation rate (Bernal et al 1959 Taylor 1980

Carlson amp Schwertmann 1990) The brown δ-FeOOH is formed by vigorous

oxidation of GR using air or a 30 aqueous solution of hydrogen peroxide (Bernal

et al 1959 Misawa et al 1974) Black ferromagnetic magnetite forms by slow

oxidation of GR whereas lepidocrocite forms at high oxidation rates (Misawa et

al 1974) The presence of chloride is a prerequisite for the formation of

akageneite (Bernal et al 1959 Refait amp Genin 1997)

A substantial amount of work has been conducted in order to estimate the free

energies of formation of green rusts The free energies of formation reported for

the carbonate and sulphate GRs fall in the range 4234ndash4384 kJsdotmol-1 as determined

from solution data monitored during anoxic alkalimetric titrations and from

reduction potential (Eh) and pH recordings monitored during oxidation of GRs in

aqueous solution (Hansen et al 1994 Drissi et al 1995 Genin et al 1996) The

free energies of formation provided allow for estimation of the stability domains of

GRs in Eh-pH phase diagrams (Drissi et al 1995 Genin et al 1996) As

evidenced from such diagrams (Figure 13) the stability domain of GR-SO4 lies

within pH 6-8 and Eh -700 ndash -400 mV depending on the activities of Fe(II) and

sulphate (compare Figures 13aampb) This agrees with the natural GR occurrences

found in suboxic non-acid iron-rich environments such as hydromorphic soils and

intertidal sediments (Al-Agha et al 1995 Trolard et al 1996 Genin et al 1998)

In addition GRs have been found as corrosion products in numerous engineering

systems including a pipeline distribution system for drinking water steel sheet

piles in marine sediments reinforced concrete (ferro-concrete) and permeable

reactive barriers of zero-valent iron implemented for on-site remediation of organic

and inorganic contaminants (Tuovinen et al 1980 Nielsen 1976 Genin et al

1991 Roh et al 2000)

6 Chapter 1

Figure 13 Eh-pH phase diagrams of GR-SO4 a) a = 10+2Fe-3 = 10minus2

4SOa -3 and b) a = 10+2Fe-2

= 10minus24SOa -1

The stability domains of GR-Cl and GR-CO3 are similar to the stability domain of

GR-SO4 At Fe(II) and sulphate activities lower than depicted in Figure 13b the

stability domain of GR-SO4 will be situated at higher pH and lower Eh Other

dissolved species present at anoxic conditions such as phosphate sulphide

carbonate and organic ligands may exert considerable effects on the availability of

Fe(II) and Fe(III) At anoxic and circumneutral conditions vivianite

(Fe2(PO4)2sdot8H2O) controls the Fe(II) activity even at very low phosphate

concentrations (Nriagu amp Dell 1974) The formation of solid Fe(II) sulphides and

siderite (FeCO3) as well as the complexation of Fe(II) and Fe(III) by organic

ligands may also control the activity of Fe(II) in the subsurface and thereby

interfere with the formation of GRs

Due to their layered structures anionic interlayers and high specific surface areas

GRs represent reactive ion exchangers and sorbents of environmentally concerning

anions eg arsenate and selenate (Myneni et al 1997 Randall et al 2001) In

addition GRs may incorporate divalent transition metal cations like Ni2+ Zn2+

Cd2+ Co2+ and Mg2+ by isomorphic substitution for Fe2+ in the hydroxide layers


(Tamaura 1985 Tamaura 1986 Refait et al 1994 Parmar et al 2001 Refait et

al 2001) Furthermore GRs have been shown to reduce a range of inorganic

contaminants such as nitrite nitrate selenate chromate uranyl pertechnetate and

the transition metals AgI AuIII CuII and HgII as well as organic pollutants

including halogenated ethanes ethenes and methanes (Hansen et al 1994 Hansen

et al 1996 Myneni et al 1997 Erbs et al 1999 Loyaux-Lawniczak et al 1999

Cui amp Spahiu 2002 Lee amp Batchelor 2002b Heasman et al 2003 OrsquoLoughlin et

al 2003aampb Pepper et al 2003 Elsner et al 2004 OrsquoLoughlin amp Burris 2004)

Thus through sequestration and reductive transformation GRs may play an

important role in the fate and transport of contaminants in suboxic soils and

sediments It should be noted that the rate constants reported for the reduction of

these inorganic and organic pollutants by GRs cannot be directly compared as the

various studies were conducted at very different experimental conditions

13 Microbial formation of green rusts

Generally one would expect that biogenic minerals have chemical compositions

and crystal habits similar to those produced by nonenzymatic processes as they are

governed by the same equilibrium principles In fact since the latter stages of

mineralization are abiotically driven and since the secondary Fe(II)-containing

minerals are formed indirectly by electron transfer outside the bacterial cell and not

directly inside the bacterial cell the type of iron mineral formed is a function of the

environmental conditions in which the bacteria live ie the same microorganism

form different minerals in different environments

The microbial formation of GRs resulting from bioreduction of various Fe(III)

oxides including ferrihydrite goethite and lepidocrocite by strains of the

anaerobic dissimilatory DIRB Shewanella putrefaciens has been reported

repeatedly over the last years (Fredrickson et al 1998 Kukkadapu et al 2001

Parmar et al 2001 Ona-Nguema et al 2002aampb Glasauer et al 2003)

However no evidence of biogenic formation of GRs at natural geochemical

8 Chapter 1 conditions have been offered and it is still unknown whether this process may take

place at natural conditions comprising low nutrient levels low iron concentrations

and the absence of synthetic electron shuttles and highly concentrated artificial pH

buffers Moreover the biotic formation of GRs by anaerobic denitrifying Fe(II)-

oxidizing bacteria has been suggested but the phases still need to be properly

identified (Chaudhuri et al 2001) In order to elucidate the role of bacteria in the

formation of GRs in natural soils and sediments we studied the iron mineral

phases forming as a result of the activity of iron-respiring bacteria (Chapters 2 and

3)

14 Redox reactions of green rusts

Fe(II) is one of the most abundant reductants present in aquatic and terrestrial

environments under suboxic and anoxic conditions (Lyngkilde amp Christensen

1992 Ruumlgge et al 1998) In these environments Fe(II) may be present as soluble

organic and inorganic complexes as surface complexes and as a host of Fe(II)-

bearing minerals Although aqueous Fe(II) complexes may reduce a number of

contaminants Fe(II) associated with mineral surfaces and structural Fe(II) present

in the mineral lattice in Fe(II)-containing minerals are often more powerful

reductants Fe(II)-bearing minerals including GRs magnetite siderite Fe(II)

sulphides as well as Fe(II)-carrying Fe(III) oxide and clay mineral surfaces have

been shown to reduce a number of organic and inorganic contaminants such as

nitroaromatic compounds chlorinated aliphatics chromate uranyl pertechnetate

nitrate monochloramine and carbamate pesticides (Klausen et al 1995 Cui amp

Eriksen 1996 Butler amp Hayes 1998amp1999 Erbs et al 1999 Liger et al 1999

Loyaux-Lawniczak et al 1999 Amonette et al 2000 Hwang amp Batchelor 2000

Hansen et al 2001 Gander et al 2002 Lee amp Batchelor 2002aampb Pecher et al

2002 Vikesland amp Valentine 2002 Hofstetter et al 2003 OrsquoLoughlin et al

2003aampb Strathmann amp Stone 2003 Elsner et al 2004 OrsquoLoughlin amp Burris

2004) However only few comparative studies on the reactivity of Fe(II)-bearing

minerals exist (Lee amp Batchelor 2002b Elsner et al 2004) When examining the


reaction rates of the reductive transformation of NACs and chlorinated aliphatics

by GRs and other Fe(II)-bearing minerals reported in these studies the rate

constants for GRs are mostly among the highest rates reported and in some cases

even higher than the rate constants for Fe(II) sulphides Thus GRs may play an

important role in the transformation of reducible contaminants in the subsurface

Nitroaromatic compounds (NACs) are widely applied as explosives herbicides

insecticides solvents and intermediates in the synthesis of dyes and pesticides

(Hartter 1985 Rosenblatt et al 1991) NACs are ubiquitous in the subsurface

environment and pose a health risk due to their toxicity (Rickert 1985) In anoxic

environments reduction of the nitro group is generally the first step during abiotic

or microbial transformation of the NACs (Macalady et al 1986) The

transformation reaction generally produces the corresponding aromatic amines and

minor amounts of intermediates (hydroxylamines and nitroso compounds) as well

as coupling products (azo and azoxy compounds) These products may be of

similar or even greater environmental concern

Trichloroacetic acid (TCA) is ubiquitous in soils and the concentrations reported

range from lt005 to 380 microgkg (Euro Chlor 2001 McCulloch 2002 Ahlers et al

2003) On account of its phytotoxicity suspected human carcinogenicity and

widespread occurrence TCA is of considerable environmental concern especially

in the terrestrial compartment (Ahlers et al 2003) Moreover the daughter

compounds of TCA - dichloroacetic acid (DCA) and monochloroacetic acid

(MCA) - are also toxins and suspected human carcinogens as well as widespread in

the environment (Reimann et al 1996 Berg et al 2000 Ahlers et al 2003 and

references therein) In this work the reactivity of synthetic green rusts towards

nitroaromatic compounds (NACs) and the reactivity of various Fe(II)-Fe(III)

mineral systems including synthetic GRs towards chlorinated acetates have been

studied (Chapters 4 and 5)

10 Chapter 1 15 Outline of the thesis

An examination of the Fe-containing products produced during solid state

oxidation of vivianite by anaerobic autotrophic denitrifying Fe(II)-oxidizing

bacteria is presented in chapter 2 The Fe(II)-oxidizing bacteria were cultured in a

mineral medium containing high levels of bicarbonate and phosphate which is

typically used in this kind of studies as it provides excellent conditions for the

nitrate-reducing FeOB The solid iron phases forming were investigated by

transmission Moumlssbauer spectroscopy infrared spectroscopy and scanning electron

microscopy

Chapter 3 includes a study on the Fe-containing products formed during reduction

of common Fe(III) oxides by the anaerobic dissimilatory Fe(III)-reducing

microorganism Shewanella algae BrY In order to simulate natural conditions


calcite particles (model system for calcareous soils) and synthetic electron shuttles

as well as highly concentrated artificial pH buffers were excluded The mineral

systems studied include goethitecalcite lepidocrocitecalcite and hydrous ferric

oxidesand suspensions The solid iron phases produced were examined by

transmission Moumlssbauer spectroscopy

A study on the relative reactivity of outer and inner Fe(II) sites in synthetic GR-

SO4 by using a series of structurally closely related compounds with different

charge properties as ldquoreactive probesrdquo is presented in chapter 4 The probe

compounds included nitrobenzene 2-nitrophenol 4-nitrotoluene 4-

chloronitrobenzene and 4-nitrophenylacetic acid

In chapter 5 an investigation of the reactivity of various Fe(II)-Fe(III) mineral

systems towards TCA and DCA is presented The study included laboratory batch

experiments imitating natural conditions The Fe(II)-Fe(III)-systems investigated

included GR-SO4 carbonate green rust magnetite Fe(II)goethite and


Fe(II)lepidocrocite The reactivities of the Fe(II)-Fe(III) mineral systems were

examined by comparing their surface-normalized rate constants

The results and environmental implications of this work are summarized in chapter

6 References Ahlers J Regelmann J Riedhammer C (2003) Environmental risk assessment of airborne trichloroacetic acid - a contribution to the discussion of the significance of anthropogenic and natural sources Chemosphere 52 531-537 Al-Agha MR Burley SD Curtis CD Esson J (1995) Complex cementation textures and authigenic mineral assemblages in recent concretions from the Lincolnshire Wash (east coast UK) driven by Fe(0) to Fe(II) oxidation Journal of the Geological Society 152 157-171 Amonette JE Workman DJ Kennedy DW Fruchter JS Gorby YA (2000) Dechlorination of carbon tetrachloride by Fe(II) associated with goethite Environmental Science and Technology 34 4606-4613 Berg M Muumlller SR Muumlhlemann J Wiedmer A Schwarzenbach RP (2000) Concentrations and mass fluxes of chloroacetic acids and trifluoroacetic acid in rain and natural waters in Switzerland Environmental Science and Technology 34 2675-2683 Bernal JD Dasgupta DR Mackay AL (1959) The oxides and hydroxides of iron and their structural inter-relationships Clay Minerals Bulletin 4 15-30 Butler EC Hayes KF (1998) Effects of solution composition and pH on the reductive dechlorination of hexachloroethane by iron sulfide Environmental Science and Technology 32 1276-1284 Butler EC Hayes KF (1999) Kinetics of the transformation of trichloroethylene and tetrachloroethylene by iron sulfide Environmental Science and Technology 33 2021-2027 Carlson L Schwertmann U (1990) The effect of CO2 and oxidation rate on the formation of goethite versus lepidocrocite from an Fe(II) system at pH 6 and 7 Clay Minerals 25 65-71 Chaudhuri SK Lack JG Coates JD (2001) Biogenic magnetite formation through anaerobic biooxidation of Fe(II) Applied and Environmental Microbiology 67 2844-2848 Cornell RM Schwertmann U (1996) The iron oxides Structure properties reactions occurrence and uses VCH Verlagsgesellschaft mbH Weinheim Cui D Eriksen TE (1996) Reduction of pertechnetate by ferrous iron in solution influence of sorbed and precipitated Fe(II) Environmental Science and Technology 30 2259-2262

Cui D Spahiu K (2002) The reduction of U(VI) on corroded iron under anoxic conditions Radiochemica Acta 90 623-628

12 Chapter 1 Drissi SH Refait Ph Abdelmoula M Geacutenin JMR (1995) The preparation and thermodynamic properties of Fe(II)-Fe(III) hydroxide-carbonate (green rust I) Pourbaix diagram of iron in carbonate-containing aqueous media Corrosion Science 37 2025-2041 Elsner M Haderlein SB Schwarzenbach RP (2004) Reactivity of Fe(II)-bearing minerals towards reductive transformation of organic contaminants Environmental Science and Technology 38 799-807 Erbs M Hansen HCB Olsen CE (1999) Reductive dechlorination of carbon tetrachloride using iron(II)iron(III)-hydroxide-sulphate (green rust) Environmental Science and Technology 33 307-311 Euro Chlor (2001) Trichloroacetic acid in the environment a dossier Euro Chlor Brussels and the European Chlorinated Solvent Association Fredrickson JK Zachara JM Kennedy DW Dong H Onstott TC Hinman NW Li S (1998) Biogenic iron mineralization accompanying the dissimilatory reduction of hydrous ferric oxide by a groundwater bacterium Geochimica et Cosmochimica Acta 62 3239-3257 Gander JW Parkin GF Scherer MM (2002) Kinetics of 111-trichloroethane transformation by iron sulfide and a methanogenic consortium Environmental Science and Technology 36 4540-4546 Geacutenin JMR Bourrieacute G Trolard F Abdelmoula M Jaffrezic A Refait Ph Maitre V Humbert B Herbillon A (1998) Thermodynamic equilibria in aqueous suspensions of synthetic and natural Fe(II)-Fe(III) green rusts Occurrences of the mineral in hydromorphic soils Environmental Science and Technology 32 1058-1068 Geacutenin JMR Olowe AA Benbouzid-Rollet ND Prieur D Confente M Resiak B (1991) The simultaneous presence of green rust 2 and sulfate reducing bacteria in the corrosion of steel sheet piles in a harbour area Hyperfine Interactions 69 875-878 Geacutenin JMR Olowe AA Refait Ph Simon L (1996) On the stoichiometry and Pourbaix diagram of Fe(II)-Fe(III) hydroxy-sulphate of sulphate-containing green rust 2 An electrochemical and Moumlssbauer spectroscopy study Corrosion Science 38 1751-1762 Glasauer S Weidler PG Langley S Beveridge TJ (2003) Controls on Fe reduction and mineral formation by a subsurface bacterium Geochimica et Cosmochimica Acta 67 1277- 1288 Hanert HH (1992) The genus Gallionella In The Prokaryotes Balows A Truper HG Dworkin M Harder W Schleifer KH (eds) Springer Verlag 4082-4088 Hansen HCB Borggaard OK Soslashrensen J (1994) Evaluation of the free energy of formation of iron(II)iron(III)-hydroxidesulphate (Green Rust) and its reduction of nitrite Geochimica et Cosmochimica Acta 58 2599-2608 Hansen HCB Guldberg S Erbs M Koch CB (2001) Kinetics of nitrate reduction by green rusts ndash effects of interlayer anion and Fe(II)Fe(III) ratio Applied Clay Science 18 81-91


Hansen HCB Koch CB Nancke-Krogh H Borggaard OK Soslashrensen J (1996) Abiotic nitrate reduction to ammonium Key role of green rust Environmental Science and Technology 30 2053-2056 Hartter DR (1985) The use and importance of nitroaromatic chemicals in the chemical industry In Toxicity of nitroaromatic compounds Rickert DE (ed) Hemisphere Publishing Corporation 1-13 Heasman DM Sherman DM Ragnarsdottir KV (2003) The reduction of aqueous Au3+ by sulfide minerals and green rust phases American Mineralogist 88 725-738 Hofstetter TB Schwarzenbach RP Haderlein SB (2003) Reactivity of Fe(II) species associated with clay minerals Environmental Science and Technology 37 519-528 Hwang I Batchelor B (2000) Reductive dechlorination of tetrachloroethylene by Fe(II) in cement slurries Environmental Science and Technology 34 5017-5022 King GM (1990) Effects of added manganic and ferric oxides on sulfate reduction and sulfide oxidation in intertidal sediments FEMS Microbiology Ecology 73 131-138 Klausen J Troumlber SP Haderlein SB Schwarzenbach RP (1995) Reduction of substituted nitrobenzenes by Fe(II) in aqueous mineral suspensions Environmental Science and Technology 29 2396-2404 Kuenen JG Robertson LA Tuovinen OH (1992) The genera Thiobacillus Thiomicrospira and Thiosphaera In The Prokaryotes Balows A Truper HG Dworkin M Harder W Schleifer KH (eds) Springer Verlag 2618-2624

Kukkadapu RK Zachara JM Smith SC Fredrickson JK Liu C (2001) Dissimilatory bacterial reduction of Al-substituted goethite in subsurface sediments Geochimica et Cosmochimica Acta 65 2913-2924 Lee W Batchelor B (2002a) Abiotic reductive dechlorination of chlorinated ethylenes by iron- bearing soil minerals 1 Pyrite and magnetite Environmental Science and Technology 36 5147- 5154 Lee W Batchelor B (2002b) Abiotic reductive dechlorination of chlorinated ethylenes by iron-bearing soil minerals 2 Green rust Environmental Science and Technology 36 5348- 5354 Liger E Charlet L Van Cappellen P (1999) Surface catalysis of uranium (VI) reduction by iron(II) Geochimica et Cosmochimica Acta 63 2939-2955 Lovley DR (1997) Microbial Fe(III) reduction in subsurface environments FEMS Microbiology Reviews 20 305-313 Lovley DR Phillips EJP (1986) Organic matter mineralization with reduction of ferric iron in anaerobic sediments Applied and Environmental Microbiology 51 683-689 Lovley DR Phillips EJP Lonergan DJ (1991) Enzymatic versus nonenzymatic mechanisms for Fe(III) reduction in aquatic sediments Environmental Science and Technology 25 1062-1067

14 Chapter 1 Loyaux-Lawniczak S Refait Ph Lecomte P Ehrhardt J Geacutenin JMR (1999) The reduction of chromate ions by Fe(II) layered hydroxides Hydrology and Earth System Sciences 3 593-599 Lyngkilde J Christensen TH (1992) Redox zones of a landfill leachate pollution plume (Vejen Denmark) Journal of Contaminant Hydrology 10 273-289 Macalady DL Tratnyek PG Grundl TJ (1986) Abiotic reduction reactions of anthropogenic organic chemicals in anaerobic systems A critical review Journal of Contaminant Hydrology 1 1-28 McCulloch A (2002) Trichloroacetic acid in the environment Chemosphere 47 667-686 Mendiboure A Schoumlllhorn A (1986) Formation and anion exchange reactions of layered transition metal hydroxides [Ni1-xMx](OH)2(CO3)x2(H2O)z (M = Fe Co) Revue de Chimie Mineacuterale 23 819-827 Misawa T Hashimoto K Shimodaira S (1974) The mechanism of formation of iron oxide and oxyhydroxides in aqueous solutions at room temperature Corrosion Science 14 131-149 Mulder EG Deinema MH (1992) The sheathed bacteria In The Prokaryotes Balows A Truper HG Dworkin M Harder W Schleifer KH (eds) Springer Verlag 2618-2624 Myneni SCB Tokunaga TK Brown Jr GE (1997) Abiotic selenium redox transformations in the presence of Fe(IIIII) oxides Science 278 1106-1109 Nealson KH Saffarini D (1994) Iron and manganese in anaerobic respiration Environmental significance physiology and regulation Annual Review of Microbiology 48 311-343 Nielsen A (1976) Hvid groslashn og sort rust Beskrivelse af en korrosionsskade paring et svoslashmmebassin Nordisk Betong 2 21-24 Nriagu JO Dell CI (1974) Diagenetic formation of iron phosphates in recent lake sediments American Mineralogist 59 934-946 OLoughlin EJ Burris DR (2004) Reduction of halogenated ethanes by green rust Environmental Toxicology and Chemistry 23 41-48 OLoughlin EJ Kelly SD Cook RE Csencsits R Kemner KM (2003a) Reduction of uranium(VI) by mixed iron(II)iron(III) hydroxide (green rust) Formation of UO2 nanoparticles Environmental Science and Technology 37 721-727 OLoughlin EJ Kelly SD Kemner KM Csencsits R Cook RE (2003b) Reduction of AgI AuIII CuII and HgII by FeIIFeIII hydroxysulfate green rust Chemosphere 53 437-446 Ona-Nguema G Abdelmoula M Jorand F Benali O Gehin A Block J-C Geacutenin JMR (2002a) Iron (IIIII) hydroxycarbonate green rust formation and stabilization from lepidocrocite bioreduction Environmental Science and Technology 36 16-20 Ona-Nguema G Abdelmoula M Jorand F Benali O Gehin A Block J-C Geacutenin JMR (2002b) Microbial reduction of lepidocrocite γ-FeOOH by Shewanella putrefaciens The


formation of green rust Hyperfine Interactions 139140 231-237 Parmar N Gorby YA Beveridge TJ Ferris FG (2001) Formation of green rust and immobilization of nickel in response to bacterial reduction of hydrous ferric oxide Geomicrobiology Journal 18 375-385 Pecher K Haderlein SB Schwarzenbach RP (2002) Reduction of polyhalogenated methanes by surface-bound Fe(II) in aqueous suspensions of iron oxides Environmental Science and Technology 36 1734-1741 Pepper SE Bunker DJ Bryan ND Livens FR Charnock JM Pattrick RAD Collison D (2003) Treatment of radioactive wastes An X-ray absorption spectroscopy study of the reaction of technetium with green rust Journal of Colloid and Interface Science 268 408- 412 Randall SR Sherman DM Ragnarsdottir KV (2001) Sorption of As(V) on green rust (Fe4(II)Fe2(III)(OH)12SO4

3H2O) and lepidocrocite (γ-FeOOH) Surface complexes from EXAFS spectroscopy Geochimica et Cosmochimica Acta 65 1015-1023 Refait Ph Abdelmoula M Trolard F Geacutenin JMR Ehrhardt JJ Bourrieacute G (2001) Moumlssbauer and XAS study of a green rust mineral the partial substitution of Fe2+ by Mg2+ American Mineralogist 86 731-739 Refait Ph Drissi SH Marie Y Geacutenin JMR (1994) The substitution of Fe2+ ions by Ni2+ ions in green rust one compounds Hyperfine Interactions 90 389-394 Refait Ph Geacutenin JMR (1997) The mechanisms of oxidation of ferrous hydroxychloride β- Fe2(OH)3Cl in aqueous solution The formation of akaganeite vs goethite Corrosion Science 39 539-553 Reimann S Grob K Frank H (1996) Chloroacetic acids in rainwater Environmental Science and Technology 30 2340-2344 Rickert DE (1985) Toxicity of nitroaromatic compounds Hemisphere Publishing Corporation 1-13 Roh Y Lee SY Elless MP (2000) Characterization of corrosion products in the permeable reactive barriers Environmental Geology 40 184-194 Rosenblatt DH Burrows EP Mitchell WR Parmer DL (1991) Organic explosives and related compounds In The Handbook of Environmental Chemistry Anthropogenic compounds Hutzinger O (Ed) Springer-Verlag 195-234 Ruumlgge K Hofstetter TB Haderlein SB Bjerg PL Knudsen S Zraurig C Mosbaeligk H Christensen TH (1998) Characterization of predominant reductants in an anaerobic leachate- affected aquifer by nitroaromatic probe compounds Environmental Science and Technology 32 23-31 Schwertmann U Cornell RM (1991) Iron oxides in the laboratory Preparation and characterization VCH Verlagsgesellschaft mbH Weinheim Simon L Francois M Refait Ph Renaudin G Lelaurain M Geacutenin JMR (2003)

16 Chapter 1 Structure of the Fe(II-III)-layered double hydroxysulphate green rust two from Rietveld analysis Solid State Sciences 5 327-334 Strathmann TJ Stone AT (2003) Mineral surface catalysis of reactions between FeII and oxime carbamate pesticides Geochimica et Cosmochimica Acta 67 2775-2791 Straub KL Benz M Schink B Widdel F (1996) Anaerobic nitrate-dependent microbial oxidation of ferrous iron Applied and Environmental Microbiology 62 1458-1460 Tamaura Y (1985) ZnII-bearing green rust II and its spontaneous transformation into ZnII- bearing ferrite in aqueous solution Bulletin of the Chemical Society of Japan 58 2951-2954 Tamaura Y (1986) Ni(II)-bearing green rust II and its spontaneous transformation into Ni(II)- bearing ferrites Bulletin of the Chemical Society of Japan 59 1829-1832 Taylor RM (1980) Formation and properties of Fe(II)Fe(III)-hydroxycarbonate and its possible significance in soil formation Clay Minerals 15 369-382 Trolard F Abdelmoula M Bourrieacute G Humbert B Geacutenin JMR (1996) Mise en eacutevidence dun constituant de type rouilles vertes dans les sols hydromorphes Proposition de lexistence dun nouveau mineacuteral la fougeacuterite Geacuteosciences de surface Comptes Rendus de LrsquoAcademie des Sciences 323 1015-1022 Tuovinen OH Button KS Vuorinen A Carlson L Mair DM Yut LA (1980) Bacterial chemical and mineralogical characteristics of tubercles in distribution pipelines Journal of the American Water Works Association 72 626-635 Vikesland PJ Valentine RL (2002) Iron oxide surface-catalyzed oxidation of ferrous iron by monochloramine implications of oxide type and carbonate on reactivity Environmental Science and Technology 36 512-519 Widdel F Schnell S Heising S Ehrenreich A Assmus B Schink B (1993) Ferrous iron oxidation by anoxygenic phototrophic bacteria Nature 362 834-836

Solid State Oxidation of Fe(II) in Vivianite by Anaerobic Denitrifying Fe(II)-Oxidizing Bacteria 17

2 Solid State Oxidation of Fe(II) in Vivianite by Anaerobic Denitrifying Fe(II)-Oxidizing Bacteria

Abstract

This work investigated the Fe-containing products formed by anaerobic

autotrophic denitrifying Fe(II)-oxidizing bacteria in a specific bicarbonate buffered

(30 mM HCO3- pH 70) culture media containing 10 mM Fe(II) 4 mM nitrate and

4 mM phosphate Fe(II) was present initially as a whitish vivianite-like

(Fe3(PO4)2middot8H2O) precipitate and as soluble Fe(II) The initial phase of the

oxidation produced a greenish metavivianite-like ((FeII3-xFeIII

x)(PO4)2(OH)xmiddot(8-

x)H2O x gt 12) phase In the late oxidation phase a reddish precipitate of poorly

crystalline goethite (α-FeOOH) dominated the colour of the media in coexistence

with Fe(II)-containing siderite (FeCO3) The increasing amounts of Fe(III) present

in the ldquovivianiterdquo and ldquometavivianiterdquo structures were accompanied by an

increasing intensity in the green colour as the Fe(II) biooxidation progressed This

colour development has produced the idea of biogenic green rusts (layered Fe(II)-

Fe(III) hydroxides) in several studies on nitrate-dependent Fe(II) biooxidation

However in this work no evidence of green rust formation mediated by anaerobic

denitrifying Fe(II)-oxidizing bacteria was obtained

21 Introduction




decades Aerobic Fe(II)-oxidizing bacteria (FeOB) have been isolated from acidic

ecosystems (Thiobacillus ferrooxidans) neutral eutrophic systems (Sphaerotilus

natans Leptothrix ochracea) and neutral oligotrophic systems (Gallionella

ferruginea) (Hanert 1992 Kuenen et al 1992 Mulder amp Deinema 1992) At

neutral pH Fe(II) is unstable in the presence of oxygen and is rapidly oxidized to

the insoluble Fe(III) Hence the only pH neutral environments where soluble

18 Chapter 2

Fe(II) is available for aerobic FeOB are at interfaces between oxic and anoxic

conditions The aerobic neutrophilic FeOB (Leptothrix ochracea Gallionella

ferruginea and Sphaerotilus natans) live at such interfaces and are usually

associated with the yellowishreddish ferric deposits formed there

Over the past several years there has been a growing recognition that other less

readily detectable types of bacteria are involved in Fe(II) oxidation in ecosystems

at circumneutral pH For example it has been reported that neutrophilic FeOB are

abundant at the Loihi seamount hydrothermal vents and play a major role in the

Fe(III) oxide deposition (Emerson amp Moyer 2002) Similarly unidentified

neutrophilic obligate lithotrophic FeOB have been isolated from the rhizosphere of

wetlands plants where they are closely associated with deposits of amorphous

Fe(III) oxides (Emerson et al 1999) It was previously believed that Fe(III) oxide

deposits associated with sheaths were produced biologically whereas Fe(III) oxide

deposits not associated with cells were produced abiotically Recently the

formation of amorphous Fe(III) oxide in gradient tubes has been attributed to the

action of FeOB (Sobolev amp Roden 2001) The authors attribute 90 of the

oxidation to biological processes and indicated that the organisms seem to produce

a mobile form of Fe(III) that diffuses away from the cells before being

precipitated thereby avoiding encrustation of the cells They suggest that such

soluble Fe(III) complexes might be substrates for closely associated Fe(III)-

reducing bacteria Such an arrangement might allow close coupling between

microbial Fe(II) oxidation and Fe(III) reduction within millimeters of the oxic-

anoxic interface





microbial activity using nitrate as the electron acceptor (Straub et al 1996) In


addition studies conducted in gradient cultures revealed that nitrate-reducing

strains could also oxidize Fe(II) with molecular oxygen (Benz et al 1998) Hence

these Fe(II)-oxidizing strains may use nitrate as well as oxygen as electron

acceptors The microbial oxidation of Fe(II) was coupled to stoichiometric

reduction of nitrate to N2 and only one strain produced traces of N2O as a by-

product (Straub et al 1996 Benz et al 1998) The authors proposed the formation

of 2-line ferrihydrite as the end product of Fe(II) biooxidation The chemical

reduction of nitrate by Fe(II) requires a catalyst eg at least 10 microM Cu2+ in order

to take place at significant rates and may thus be considered insignificant under the

conditions applied in our study (Moraghan amp Buresh 1976) The chemical

oxidation of Fe(II) with nitrous oxide has not been observed However nitrite can

oxidize Fe(II) chemically (Moraghan amp Buresh 1977 Straub et al 1996) but this

process is considered insignificant at the conditions applied here No denitrifying

Fe(II)-oxidizing enrichment culture has been found to produce ammonium from

nitrate

Both lithoheterotrophic (depending on organic cosubstrates such as acetate) and

strictly lithoautotrophic nitrate-reducing FeOB have been found in various marine

and freshwater sediments However most isolates depend on organic cosubstrates

for cell biosynthesis (Benz et al 1998) Most probable number estimations

showed that denitrifying FeOB accounted for 00006-08 of the acetate-oxidizing

denitrifying microbial population Lithotrophic FeOB accounted for less than

00001 of the total bacterial community Attempts to isolate CO2-fixing nitrate-

dependent FeOB from lithotrophic cultures have failed (Straub amp Buchholz-

Cleven 1998) Mixotrophic FeOB accounted for 0004-004 of the total bacterial

community In addition microbial nitrate-dependent Fe(II) oxidation was

demonstrated in a flooded paddy soil as well as in activated sludge from a

wastewater treatment plant (Nielsen amp Nielsen 1998 Ratering amp Schnell 2001)

Since the activity is not restricted to sunlight exposed habitats microbial nitrate-

dependent Fe(II) oxidation is supposedly more important on a global scale than

20 Chapter 2

anaerobic Fe(II) oxidation by phototrophic bacteria Furthermore it has been

reported that anaerobic denitrifying FeOB aptly oxidize biogenic Fe(II) minerals

formed by bioreduction of synthetic goethite and ferrihydrite and that anaerobic

Fe(III)-reducing bacteria readily reduce Fe(III) minerals formed by biooxidation of

Fe(II) (Weber et al 2001 Straub et al 1998) Hence autotrophic denitrifying

FeOB may play a significant role in the nitrogen and iron cycles in subsurface

environments where the nitrate and the Fe(II) zones overlap and organic carbon

supply is limited (Figure 21)

Figure 21 The microbial iron cycle linking the carbon and nitrogen cycles

Phosphate is released into the environment through natural processes such as rock

weathering and decomposition of dead organic material and anthropogenic

activities eg wastewater effluents and application of manure and fertilizers in

horti- and agriculture In anoxic soils and sediments phosphate may be sequestered

by sorption onto Fe(III) oxides (Williams et al 1971 Patrick amp Khalid 1974)

Phosphate strongly influences the type morphology and properties of Fe(III)

oxides formed by oxidation and hydrolysis of Fe(II) salts as well as the degree of

their transformation (Kandori et al 1992 Cumplido et al 2000 Benali et al

2001) Phosphate may also be retained by precipitation of Fe(II) phosphates such

as the monoclinic vivianite (Fe3(PO4)2middot8H2O) which is the most important stable

Fe(II) orthophosphate solid encountered in the subsurface under most conditions

(Nriagu 1972) At anoxic and circumneutral conditions the whitish vivianite


controls the Fe(II) activity even at very low phosphate concentrations (Nriagu amp

Dell 1974) Vivianite occurs as a secondary mineral in the gossans of metallic ore

deposits and as a weathering product of primary iron-manganese phosphates in

pegmatites (Gaines et al 1997) Moreover natural vivianite occurrences have

been identified in a number of lake and river sediments (Zwaan amp Kortenbout van

der Sluys 1971 Nriagu amp Dell 1974 Postma 1981 Nembrini et al 1983

Henderson et al 1984 Dodd et al 2003 House 2003 and references therein)

Vivianite is also found in sewage sludge as a result of the wastewater treatment

where iron salts are added in order to remove phosphate (Seitz et al 1973) It is

however still indefinite how ubiquitous vivianite is in nature Furthermore only

little is known about the mechanism of vivianite formation and the role played by

sedimentary Fe(III) oxides Anaerobic Fe(III)-reducing microorganisms may

reduce Fe(III) oxides thereby releasing the iron as soluble Fe(II) and mobilizing

the phosphate adsorbed to the Fe(III) oxides (Lovley 1997) It has been suggested

that vivianite is formed by precipitation following reductive dissolution of Fe(III)

oxides (Manning et al 1981 Manning amp Jones 1982) However it has also been

proposed that the transformation of Fe(III) oxides to vivianite occurs topotactically

and not via reductive dissolution (Nembrini et al 1983) Vivianite was shown to

form microbially as a result of the activity of the anaerobic Fe(III)-reducing

bacteria Shewanella putrefaciens in the presence of high Fe(III)-citrate and

phosphate concentrations (Jorand et al 2000) Moreover vivianite formation by

bioreduction of Fe(III) in hydrous ferric oxide and in smectite has been reported

(Fredrickson et al 1998 Dong et al 2003)

Only little is known about the oxidation products of vivianite Metavivianite a

greenish triclinic iron hydroxy phosphate mineral was first described by Ritz et al

(1974) and it was later found to coexist with vivianite in several natural sediment

samples (Henderson et al 1984) Once the Fe(III) content became evident the true

composition of metavivianite ((FeII3-xFeIII

x)(PO4)2(OH)x

22 Chapter 2

middot(8-x)H2O x gt 12)) was established (Rodgers amp Johnston 1985 Rodgers 1986

and references therein) The formation of intermediate greenish precipitates during

oxidation of fluffy colourless Fe(II) precipitates by anoxic phototrophic

microorganisms and nitrate-dependent FeOB have been reported (Ehrenreich amp

Widdel 1994 Chaudhuri et al 2001) Since both studies were conducted in

bicarbonate buffered mineral media (22-30 mM HCO3ndash pH 70-72) containing

37-5 mM phosphate we assume that the initial fluffy whitish precipitates

consisted mainly of vivianite Chaudhuri et al (2001) proposed that the

intermediate green phases produces by the denitrifying FeOB consist of carbonate

green rust (GR-CO3) but no convincing evidence of this biogenic GR-CO3 has been

provided yet The major objective of this work was to examine the Fe-containing

products forming during the course of biooxidation of vivianite by non-

phototrophic anaerobic denitrifying Fe(II)-oxidizing bacteria

2 2 Materials and methods

All handling and sampling of solutions and suspensions were carried out under

sterile and strict anoxic conditions All chemicals were pa quality

221 Microorganisms and media

Enrichment cultures of nitrate-reducing FeOB taken from town ditches (Bremen

Germany) were grown in anoxic bicarbonate-buffered (30 mM HCO3ndash 90

N210 CO2 pH 70) mineral media containing 4 mM phosphate as well as

essential trace elements and vitamins (Table 21 Straub amp Buchholz-Cleven

1998) Ammonium was omitted from the media in order to facilitate detection of

ammonium possibly produced by reduction of nitrate The techniques used for

preparation of media and cultivation of bacteria under anoxic conditions have been

described by Widdel amp Bak (1992) 05 M aqueous stock solutions of FeCl2 or

FeSO4 were prepared in 100 mL glass flasks by reacting 65 mmol of iron powder

(particle size 10 microm Merck) with 100 mL deoxygenated 10 M HCl or 05 M


H2SO4 respectively The solutions were magnetically stirred and heated (~80degC)

during reaction until the H2(g) production had ceased (ge 1 hour) The FeCl2 and

FeSO4 stock solutions were stored under a small Ar overpressure at 5degC

Table 21 Composition of the mineral medium (adopted from Straub amp Buchholz-Cleven

(1998))

Components Concentration (M) KH2PO4 15middot10-3

K2HPO4 25middot10-3

MgSO4middot7H2O 10middot10-3

CaCl2middot2H2O 50middot10-4

H3BO3 56middot10-5

ZnSO4middot7H2O 10middot10-6

Na2MoO4middot2H2O 40middot10-6

CuSO4middot5H2O 20middot10-7

MnSO4middotH2O 10middot10-6

Na2SeO4 12middot10-5

CoCl2middot6H2O 50middot10-6

NiCl2middot6H2O 80middot10-6

NaCl 10middot10-5

NaHCO3ndash 30middot10-2

Cyanocobalamine (vitamin B12) 37middot10-8

p-aminobenzoic acid (vitamin Hrsquo) 36middot10-7

D(+)-biotin (vitamin H) 41middot10-8

Nicotinic acid (Niacin) 81middot10-7

Ca-D(+)-pantothenate (vitamin B5) 52middot10-8

Pyridoxamine dihydrochloride 96middot10-7

Thiaminechloridehydrochloride (vitamin B1) 15middot10-7

NaNO3 40middot10-3

FeSO4 or FeCl2 0010

222 Characterisation of precipitates

In order to optimize the characterization and distinction between the spectral

components transmission Moumlssbauer spectra were obtained at temperatures

between 5 K and 250 K and in external magnetic fields of 4 T (parallel to the γ-ray

direction) using a conventional constant acceleration spectrometer and a source of 57Co in Rh The spectrometer was calibrated using a 125 microm foil of α-Fe at room

temperature and isomer shifts are given relative to the centroid of the spectrum of

this absorber The spectra were fitted using simple Lorentzian line shape Infrared

(IR) spectra were obtained using a Perkin Elmer FT-IR 2000 spectrometer and the

24 Chapter 2

KBr pellet technique Scanning electron microscopy (SEM) was carried out in

order to study the morphology and composition of the precipitates Specimens for

SEM were prepared by depositing suspended particles onto an aluminum stub

coated with a carbon sticker The stub was quickly transferred into a sputtering

chamber and coated with a thin Pt film (~20 nm) In order to avoid interfering Pt

signals in the energy dispersive spectra the stubs were in some cases not coated

with Pt but quickly transferred to the SEM chamber for evacuation Measurements

were performed using a Philips XL30 equipped with a LaB6 source and an

accelerating voltage of 20 kV and an EDAX eDXi X-ray dispersive spectrometer

223 Biooxidation experiments

The biooxidation experiments were conducted in 50-400 mL butyl rubber

stoppered bottles with a 90 N210 CO2 headspace constituting 10 of the total

volume Prior to inoculation 4 mM NaNO3 was added as the electron acceptor and

10 mM Fe2+ (as chloride or sulphate) as the electron donor to the mineral media

Control experiments were performed in the same media only they were not

inoculated Addition of ferrous iron to the media induced an immediate

precipitation of a solid whitish material The whitish precipitate was collected on

022 microm polyvinylidendifluorid (Durapore Millipore) filters and stored in an

anoxic atmosphere until further measurements Old outgrown media suspensions

that had turned reddish in color due to a precipitate produced by the denitrifying

FeOB were used as inocula Inoculum volume was kept lt1 of the culture volume

in order to prevent the reddish inoculum from dominating over the initial whitish

precipitate Cultures were incubated in the dark at room temperature and gently

agitated once every day Typical color successions for the media were initial

whitish precipitates turning first more and more greenish over time and then finally

turning reddish (see Fig 22) The color developed uniformly without any

indications of multiple phases in the precipitate At different time intervals

suspension samples were withdrawn using 90 N210 CO2-flushed polyethylene

syringes The precipitates were collected on 022 microm polyvinylidendifluorid


(Durapore Millipore) filters and analyzed by Moumlssbauer spectroscopy and SEM

Nonfiltered suspension samples were digested in 01 M HCl and chemically

analyzed for Fe(II) NO3- and NH4

+

224 Analytical methods

Fe2+ was determined using a modified phenanthroline method (Fadrus amp Maly

1975) Nitrate was quantified by ion chromatography (Morales et al 2000) and

ammonium was measured photometrically using the indophenol reaction (Rossum

amp Villarruz 1963)

23 Results and discussion

231 Identification of solid iron-containing phases

In most cases the mineral media for cultivating denitrifying FeOB contained 10

mM FeCl2 or FeSO4 4 mM NO3ndash 4 mM total phosphorus and 30 mM HCO3

- at pH

70 ([HCO3-] = 2138middot[CO3

2-] at pH 70) Whitish flocs precipitated immediately at

these initial conditions when Fe(II) was added to the media (Figure 22a) Such

colourless flocs have been reported to precipitate in similar mineral media (10 mM

Fe(II) 37-5 mM phosphate 22-30 mM HCO3ndash pH 70-72) (Ehrenreich amp

Widdel 1994 Chaudhuri et al 2001) Our Fe(II) measurements showed that 20-

50 of the total Fe(II) added was present in this initial white precipitate

26 Chapter 2

a

210- Figure 22 Colour of suspended material in the growth media during Fe(II) biooxidation a)

Initial whitish precipitate prior to inoculation b) Inte1mediate greenish phase fo1med within 2-3

days after inoculation c) reddish precipitate at late stage of biooxidation (gt5-6 days)

The precipitates were filtered and investigated by Mossbauer and IR spectroscopy

The transmission Mossbauer spectra obtained for the initial whitish precipitate at

temperatures between 20 and 250 K are shown in Figure 23 The spectrum

measured at 250 K consists of two fairly well-resolved Fe(II) doublets (see

parameters in Table 22) The change in line-overlap with decreasing temperature

is primarily ascribed to differences in the temperature dependence of the

quadrupole splitting of the two components From the spectra at 10 and 6 K

(Figure 24) it can be concluded that magnetic ordering takes place between these

two temperatures and that only one transition occurs (indicating the presence of

only one phase) The parameters of one of the Fe(II) doublets at 250 K (designated

B in Table 22) are in very good agreement with previously published values for

the vivianite Fe(Il)8 site at room temperature (eg McCammon amp Burns 1980)

and the ordering temperature also agrees well with an assignment as vivianite

(Forsyth et al 1970) However the second Fe(II) doublet in the initial colourless

precipitate (Table 22) has parameters that deviate from previously reported values

by having a smaller quadrupole splitting (indicating a less distorted coordination)

and a significantly higher relative intensity and line width These effects might be

due to the presence of numerous defects in the vivianite crystal lattice particularly


affecting the Fe(II)A sites It should be noted that further components may be added

to the fit in order to improve its statistics Nevertheless we decided to include no

further components as suggested by the finding of one magnetic ordering only

Accordingly our interpretation of the Moumlssbauer results for the initial white

precipitate suggests a highly defective vivianite having a distribution of local

coordination environments particular in the A site This assignment is further

supported by a major absorption band due to phosphate anions in the infrared

spectrum at approximately 1000 cm-1 and the absence of other complex anions

(data not shown) Thus the whitish precipitate is referred to as a vivianite-like

(ldquovivianiterdquo) precipitate

0

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

3

2

1

0

80 K

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

2 5

2 0

1 5

1 0

0 5

0 0

250 K

Figure 23 Transmission Moumlssbauer spectra measured between 250 and 20 K of the initial

whitish precipitate prior to inoculation (see Fig 22a) Fitting components (and their sum) are

shown as full lines

28 Chapter 2

Table 22 Selected Mossbauer parameters of the doublet components in the spectra obtained for

different precipitates

Precipitates Temperature Isomer shift Quadrupole Line width Area (K) (mms-1) splitting (mms-1) (mms-1) ()

Whitish Fe(II)B 250 127 309 035 38

Fe(II)A 250 128 181 051 62

Dark greenish Fe(II)B 250 126 305 023 17

Fe(II)A 250 132 238 051 44

Fe(III) 250 036 085 040 38

Reddish-orange 40 138 244 094 67 Fe(II) Hyperfine parameters are generally given with uncertainties of 003 mms- the spectral area with an uncertainty of 3

1005

1000

0995

0990

- 0985 ~ e c 0980 0

-~ 0975 E c nl b 1000 g ~ Qi 0995 0

0990

0985

0980 -12 -8

~ -~

bullbull bull Ibull bull bullbull bull bull ~ bull bull ~

It

10 K

bull bull bull bull (J ~ i~ 6K bullmiddotf bull bull

~ bull bull bull

-4 0 4 8 12

Velocity (mmls)

Figure 24 Transmission Mossbauer spectra measured at 10 and 6 K of the initial whitish

precipitate prior to inoculation (see Fig 22a)

In general the color of the media suspension changed from whitish into light green

color within 2-3 days after inoculation (Figure 22b ) This transformation occurred


without dissolving the initial whitish precipitate or preserving the whitish

precipitate as a separate phase implying some kind of solid state transformation

Two identical media suspensions were inoculated simultaneously but at the

sampling time they had distinctly different intensities of the green color

designated light and dark green respectively Moumlssbauer spectra of the dark green

sample are shown in Figure 25 The spectra of this sample are all fitted using three

doublet components (two Fe(II) and one Fe(III)) and the parameters of the

spectrum measured at 250 K are given in Table 22

30

25

20

15

10

05

00

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

35

30

25

20

15

10

05

00

80 K

30

25

20

15

10

05

00

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

25

20

15

10

05

00

250 K

Figure 25 Transmission Moumlssbauer spectra measured between 250 and 20 K of the dark

greenish precipitate formed during biooxidation Fitting components (and their sum) are shown

as full lines

No magnetic ordering of the dark green precipitate was observed at temperatures

above 20 K but ordering occurred around 10 K (not shown - due to very thin

30 Chapter 2

samples this was not investigated in details) The two greenish samples had very

similar parameters only differing in the relative intensity of Fe(III) 26 and 38

in the light greenish and dark greenish samples respectively Assuming the

spectral area of a component to be proportional to the abundance of the species in

the solid these results indicate a correlation between the intensity of the green

color and the content of Fe(III) in the precipitate The parameters of the Fe(II)

doublets in the dark green precipitate (Table 22) were in very good agreement

with previously published values for vivianite with a non-negligible Fe(III) content

(McCammon amp Burns 1980) whereas the Fe(III) component in particular had a

higher quadrupole splitting The observation that magnetic ordering of both Fe(II)

and Fe(III) occurred at similar temperature for the light green phase (Figure 26) is

a strong indication that they both belong to the same phase The absence of the

component with the low quadrupole splitting in the spectra of both green samples

might indicate that the initial vivianite-like phase crystallized into a more well-

defined vivianite over time However freshly prepared and long-term aged (gt1

year) suspensions of the initial vivianite-like precipitate did not differ significantly

Hence we suggest that the recrystallization of the vivianite-like precipitate can be

explained by Fe(II) biooxidation

Solid State Oxidation ofFe(II) in Vivianite by Anaerobic Denitrifying Fe(II)-Oxidizing Bacteria

0

2

3

- 4

~ 5 c ~ 6 e-0 7 -2 nl Q) 00 gt ~ 05 Qi 0 10

15

20

25

30

35

bullbullbull hi 6~

bullbullbullbull bull bull bullbull bull 10 K bull bull

bull bull bull bull bull bull bull

~~ ~~ lf 6K bull bull bullbull middot bull bull r bull

bull bull bull bull bull bullbull bull bull bull - 12 -a -4 0 4 8 12

Velocity (mms)

31

Figure 26 Transmission Mossbauer spectrn measured at 6 and 10 K of the light greenish

precipitate fonned during biooxidation

The solid state oxidation of monoclinic vivianite to triclinic metavivianite is well-

known (McCammon amp Bums 1980 Pratesi et al 2003 and references therein)

The vivianite crystal structure contains Fe(II) ions in both isolated Fe(II)A and

paired Fe(Il)8 octahedra Mossbauer spectroscopic analyses have shown that the

Fe(Il)8 Fe(II)A ratio increases with increasing Fe(III) concentration suggesting that

the remaining Fe(II)A ions are more readily oxidized than the Fe(II)a ion of an

Fe(Il)8 -Fe(III)8 pair (McCammon amp Bums 1980) The mechanism of oxidation of

Fe(II) in vivianite involves conversion of H20 ligands to OH- ions producing a

progressive collapse of the vivianite structure due to the elimination of hydrogen

bonds (Moore 1971) The exact oxidation limits between which the triclinic lattice

is stable are somewhat disputed as the results obtained for synthetic and natural

vivianites oxidized chemically in the laboratory and naturally oxidized natural

vivianite specimens do not agree completely (Rodgers 1986 and references

therein) Taking all reports into account the monoclinic structure of vivianite is

supposedly maintained until 40-50 of total iron is oxidized Further oxidation

32 Chapter 2

leads to the formation of the triclinic metavivianite in which the FeA site is fully

oxidized whereas the oxidation of the FeB ranges from 20 to almost 100 Thus

the triclinic metavivianite structure persists close to complete oxidation of total

iron The Moumlssbauer results obtained in this study are consistent with the vivianite

solid state oxidation mechanism reported by McCammon amp Burns (1980) Thus

we propose that the intermediate greenish precipitate is a metavivianite-like

(ldquometavivianiterdquo) phase It should be noted that a minor oxidation of dissolved

Fe(II) may have occurred even though the solid state oxidation of Fe(II) was

predominant

Within 5-6 days after inoculation the greenish intermediate was transformed into a

reddish product (Figure 22c) The magnetically ordered sextet in the spectrum of

the red phase (Figure 27) measured at 40 K was due to goethite (α-FeOOH)

(magnetic hyperfine field of 470 T and a quadrupole shift of -01 mms-1 cp

Moslashrup et al 1983) The sextet deviated from ideal goethite by its asymmetric line

shape and its low ordering temperature (around 100 K ndash data not shown) and thus

the goethite was poorly crystalline It is very likely that the presence of phosphate

in the media retarded the crystal growth of goethite The unusual reddish colour of

the goethite might also be explained by the presence of phosphate The spectrum at

40 K was however dominated by a Fe(II) doublet (Table 22) that ordered

magnetically between 40 and 20 K (Figure 27) The hyperfine parameters and the

magnetic ordering temperature indicated that this component was due to siderite

(FeCO3) having a magnetic ordering temperature of 38 K (Jacobs 1963) The

siderite component may have formed as a result of the microbial activity changing

the chemistry of the solution and precipitating a major part of the remaining

dissolved Fe(II) at this stage The characteristic vivianite Fe(II) doublet with large

quadrupole splitting was not detected in this sample The reddish precipitate

contained considerably less Fe(III) than the greenish precipitate (only 33 as

estimated from the spectral area) None of the components in the reddish sample

Solid State Oxidation ofFe(II) in Vivianite by Anaerobic Denitrifying Fe(II)-Oxidizing Bacteria 33

could be detected in freshly inoculated samples indicating that carryover of mineral

precipitates by inoculation of the culture media was negligible

0

2

- 3

~4 c

Q 5

e 6 0

~ 7 g

0 3l Q)

a 1

2

3

4

5

-12 a

40K

bull bull (

4 0 4 8 12 Velocity (mms)

Figure 27 Transmission Mossbauer spectra measured at 20 and 40 K of the reddish precipitate

fo1med during the late biooxidation stage Fitting components (and their sum) are shown as full

lines

Strengite (FeP04middot2H20) was not detected at any time during oxidation

Santabarbaraite a new amorphous F e(III) hydroxy phosphate mineral

(Fe3(P04)i(OH)3middot5H20) was reported in a recent study (Pratesi et al 2003) The

brownish mineral was a result of the solid state oxidation of vivianite through

metavivianite However no Mossbauer data have been provided for this new

mineral yet and therefore we cannot give an account of whether santabarbaraite

forms in our system or not Thus goethite was the dominating end product and we

propose the reaction path depicted in Figure 28 for the nitrate-dependent

biooxidation of Fe(II) in our systems

34 Chapter 2

Fe3(PO4)2middot8H2O (FeII3-xFeIII

x)(PO4)2(OH)xmiddot(8-x)H2O α-FeOOH

NO3- N2 NO3

- N2

ldquoVivianiterdquo ldquoMetavivianiterdquo Goethite

Figure 28 Proposed reaction path and iron-containing minerals forming during solid state

oxidation of vivianite by denitrifying FeOB at the experimental conditions applied in this study

The biotic formation of layered Fe(II)-Fe(III) hydroxides (green rusts) by

anaerobic denitrifying Fe(II)-oxidizing bacteria has been suggested but proper

identification of these phases still lacks (Chaudhuri et al 2001) We cannot rule

out that small amounts of green rusts (GRs) perhaps a phosphate intercalated GR

(Hansen amp Poulsen 1999) might have been present here during the greenish

intermediate ldquometavivianiterdquo oxidation stage When present in low concentrations

especially in mixtures including other iron minerals it is very difficult to identify

GRs even with Moumlssbauer spectroscopy At least two complementary methods

such as X-ray diffraction (XRD) and Moumlssbauer spectroscopy are required for

proper identification and characterization of GRs However the precipitates

collected in this work were poorly crystalline and did not allow for XRD analysis

Electron micrographs including energy dispersive X-ray spectroscopy suspension

colour and mineral stability calculations do not suffice as evidence Hence no

convincing evidence of GR formation facilitated by denitrifying FeOB has been

provided so far The blue-green colours of metavivianite and green rust minerals

originate from Fe(II)-Fe(III) charge transfer between adjacent Fe(II) and Fe(III)

ions in edge-shared octahedra (Faye et al 1968) The greenish suspension colour

occurring during the intermediate phase has incited the idea of biogenic GRs in

studies on nitrate-dependent Fe(II) biooxidation (Chaudhuri et al 2001 Lack et

al 2002aampb) However our results indicate that this reasoning is misleading

232 Factors controlling the rate and extent of Fe(II) biooxidation

Generally it was found that maximally 20-64 of the initial Fe(II) amount was

oxidized to Fe(III) (Figure 29) This indicates some limitations in the accessibility


of Fe(II) in the system Based solely on stoichiometry considerations the

microorganisms are expected to oxidize 5 mol Fe(II) for every 1 mol nitrate

reduced to dinitrogen However as exemplified in Figure 28 this ratio was mostly

lt4 which can be explained by the consumption of nitrogen as a result of microbial

growth At initial [Fe(II)][NO3ndash] ratios lt5 nitrate is in excess and should not limit

the extent of the biooxidation Thus the lack of complete biooxidation could not be

due to exhaustion of nitrate Furthermore all growth essential nutrients were more

than sufficiently applied hence the incomplete Fe(II) biooxidation was not caused

by lack of nutrients The most reasonable explanation therefore seems to be that an

increasingly limited access to the electron donor over time inhibits complete long-

term Fe(II) biooxidation At least four mechanisms may cause this inhibition 1)

the Fe(II) becomes isolated within the structure of the mixed Fe(II)-Fe(III)

minerals forming during biooxidation or underneath a passive Fe(III)-bearing

surface film on the initial Fe(II) precipitates 2) the FeOB cell surface becomes

covered with a passive Fe(III)-bearing surface film 3) the Fe(II) biooxidation is

controlled by the rate of dissolution of the initial Fe(II) minerals or 4) the reaction

proceeds primarily by biooxidation of dissolved Fe(II) whose concentration

gradually decreases due to changes in solid phase composition The actual

mechanisms whereby the surface-associated Fe(III) can inhibit Fe(II) biooxidation

are unknown but they may involve both kinetic and thermodynamic constraints on

the electron transfer The Moumlssbauer results obtained in this work strongly suggest

that the Fe(II) biooxidation occurred mainly in the solid state of the initial

ldquovivianiterdquo phase However we cannot rule out that some dissolved Fe(II) was

oxidized as well

36 Chapter 2

Figure 29 Concentration profiles of total Fe(II) and nitrate as a function of time during Fe(II)

biooxidation

No Fe(II) oxidation took place in cultures where nitrate had been omitted

confirming that the microbial Fe(II) oxidation is nitrate-dependent (data not

shown) No Fe(II) oxidation was detected in the non-inoculated control

experiments within the duration of the experiments and thus the chemical

oxidation of dissolved Fe(II) by nitrate catalyzed by vitamins or trace elements

(eg Cu(II)) can be neglected Ammonium did not form in detectable amounts

during Fe(II) biooxidation (data not shown) and therefore dinitrogen was assumed

to be the end product as reported previously (Straub et al 1996 Benz et al 1998)

The absence of ammonium formation does indirectly support the absence of

biologically induced green rust formation as synthetic green rust is known to

convert nitrate into ammonium in purely chemical reactions (Hansen et al 1996)

It was visually observed that the phosphate concentration in the media exerted a

control on the microbial Fe(II)-oxidation At phosphorus concentrations le 2 mM

no Fe(II)-oxidation took place However the solubility product for vivianite (Ksp =

171middot10-36 at 25degC (Al-Borno et al 1994)) was still by far exceeded under these

conditions It is not known whether this phosphate limiting effect is due to growth

constraints in the mixed bacterial community or whether specific Fe(II) phosphate


precipitates are prerequisites of the Fe(II) biooxidation to take place Experiments

are currently underway in our laboratory in order to elucidate the role of specific

initial Fe(II) precipitates It should be noted that the growth of the denitrifying

FeOB could not be estimated as they were present in highly heterogeneous

suspensions containing both solid iron phases as well as other bacteria (enrichment

culture)

233 Morphology of solid iron phases

The morphology of the various precipitates was studied by SEM The initial

whitish precipitate consisted of a web-like structure (Figure 21 Oa and background

in Figure 21 Ob) whereas more distinct hexagonally shaped rosettes with particle

size ~20 microm (Figure 2lObampc) formed during Fe(II) biooxidation The energy

dispersive spectroscopic element analyses showed that other than iron the initial

whitish precipitate and the rosettes contained mainly phophorus

Figure 210 Scanning electron micro graphs of precipitates fo1med at various stages of the

experiment a Initial whitish precipitate bampc Rosettes observed in the intennediate greenish

precipitate d Reddish precipitate sampled during the late biooxidation stage

38 Chapter 2

These observations are interpreted as vivianite forming a web-like morphology in

the initial whitish precipitate and partly transforming into hexagonal particles in

the greenish colored stage The interpretations are supported by similar vivianite

morphologies reported including pseudo-hexagonal vivianite crystals of low

symmetry resulting from microbial Fe(III) reduction of HFO and platy rosettes of

vivianite crystals formed during bioreduction of Fe(III) in smectite (Fredrickson et

al 1998 Dong et al 2003) It was not possible to associate the morphology

observed in the reddish precipitate with the minerals identified in this phase

(Figure 210d)

24 Conclusions

This work demonstrated that anaerobic autotrophic denitrifying Fe(II)-oxidizing

bacteria produce poorly crystalline goethite by solid state oxidation of ldquovivianiterdquo

via a ldquometavivianiterdquo intermediate The increasing amount of Fe(III) forming in the

vivianite structure was accompanied by an increasing intensity in the green colour

as the Fe(II) biooxidation progressed Moumlssbauer spectroscopic analyses provided

no significant evidence of green rust formation The finding of microbially

oxidized vivianite in this study raises the question of the oxidation state of

vivianite specimens from natural sediments Vivianite is generally believed to be

an ideal Fe(II) hydroxy phosphate mineral and the presence of Fe(III) is explained

by aerial oxidation upon sampling The results presented here indicate that

microbiological processes may be responsible for the oxidation of vivianite and

metavivianite in natural subsurface environments Acknowledgments

We would like to thank Dr K Straub for providing and advising us how to culture the nitrate-

reducing FeOB Furthermore we thank Dr C B Koch for performing the Moumlssbauer analyses

and Dr D Mavrocordatos for performing the SEM analyses


References Al-Borno A Tomson MB (1994) The temperature dependence of the solubility product constant of vivianite Geochimica et Cosmochimica Acta 58 5373-5378 Benali O Abdelmoula M Refait Ph Geacutenin JMR (2001) Effect of orthophosphate on the oxidation products of Fe(II)-Fe(III) hydroxycarbonate The transformation of green rust to ferrihydrite Geochimica et Cosmochimica Acta 65 1715-1726 Benz M Brune A Schink B (1998) Anaerobic and aerobic oxidation of ferrous iron at neutral pH by chemohetorotrophic nitrate-reducing bacteria Archives of Microbiology 169 159-165 Chaudhuri SK Lack JG Coates JD (2001) Biogenic magnetite formation through anaerobic biooxidation of Fe(II) Applied and Environmental Microbiology 67 2844-2848 Cumplido J Barron V Torrent J (2000) Effect of phosphate on the formation of nanophase lepidocrocite from Fe(II) sulfate Clays and Clay Minerals 48 503-510 Dodd J Large DJ Fortey NJ Kemp S Styles M Wetton P Milodowski A (2003) Geochemistry and petrography of phosphorus in urban canal bed sediment Applied Geochemistry 18 259-267 Dong H Kostka JE Kim J (2003) Microscopic evidence for microbial dissolution of smectite Clays and Clay Minerals 51 502-512 Ehrenreich A Widdel F (1994) Anaerobic oxidation of ferrous iron by purple bacteria a new type of phototrophic metabolism Applied and Environmental Microbiology 60 4517-4526 Emerson D Moyer CL (2002) Neutrophilic Fe-oxidizing bacteria are abundant at the Loihi seamount hydrothermal vents and play a major role in Fe oxide deposition Applied and Environmental Microbiology 68 3085-3093 Emerson D Weiss JV Megonigal JP (1999) Iron-oxidizing bacteria are associated with ferric hydroxide precipitates (Fe-plaque) on the roots of wetland plants Applied and Environmental Microbiology 65 2758-2761 Fadrus H Maly J (1975) Suppression of iron(III) interference in the determination of iron(II) in water by the 110-phenanthroline method The Analyst 100 549-554 Faye GH Manning PG Nickel EH (1968) The polarized optical absorption spectra of tourmaline cordierite chloritoid and vivianite ferrous-ferric electronic interaction as a source of pleochroism American Mineralogist 53 1174-1201 Forsyth JB Johnson CE Wilkonson C (1970) The magnetic structure of vivianite Fe3(PO4)2middot8H2O Journal of Physics Part C Solid State Physics 3 1127-1139 Fredrickson JK Zachara JM Kennedy DW Dong H Onstott TC Hinman NW Li S (1998) Biogenic iron mineralization accompanying the dissimilatory reduction of hydrous ferric oxide by a groundwater bacterium Geochimica et Cosmochimica Acta 62 3239-3257 Gaines RV Skinner HCW Foord EE Mason B Rosenzweig A (1997) Danas new

40 Chapter 2 mineralogy 8th ed John Wiley amp Sons Inc Hanert HH (1992) The genus Gallionella In The Prokaryotes Balows A Truper HG Dworkin M Harder W Schleifer KH (eds) Springer Verlag 4082-4088 Hansen HCB Koch CB Nancke-Krogh H Borggaard OK Soerensen J (1996) Abiotic nitrate reduction to ammonium Key role of green rust Environmental Science and Technology 30 2053-2056 Hansen HCB Poulsen IF (1999) Interaction of synthetic sulphate green rust with phosphate and the crystallization of vivianite Clays and Clay Minerals 47 312-318 Henderson GS Black PM Ridgers KA Rankin PC (1984) New data on New Zealand vivianite and metavivianite New Zealand Journal of Geology and Geophysics 27 367-378 House WA (2003) Geochemical cycling of phosphorus in rivers Applied Geochemistry 18 739-748 Jacobs IS (1963) Metamagnetism of siderite (FeCO3) Journal of Applied Physics 34 1106-1107 Jorand F Appenzeller BMR Abdelmoula M Refait Ph Block J-C Geacutenin JMR (2000) Assessment of vivianite formation in Shewanella putrefaciens culture Environmental Technology 21 1001-1005 Kandori K Uchida S Kataoka S Ishikawa T (1992) Effects of silicate and phosphate ions on the formation of ferric oxide hydroxide particles Journal of Materials Science 27 719-728 Kuenen JG Robertson LA Tuovinen OH (1992) The genera Thiobacillus Thiomicrospira and Thiosphaera In The Prokaryotes Balows A Truper HG Dworkin M Harder W Schleifer KH (eds) Springer Verlag 2618-2624 Lack JG Chaudhuri SK Chakraborty R Achenbach LA Coates JD (2002a) Anaerobic biooxidation of Fe(II) by Dechlorosoma suillum Microbial Ecology 43 424-431 Lack JG Chaudhuri SK Kelly SD Kemner KM OConnor SM Coates JD (2002b) Immobilization of radionuclides and heavy metals through anaerobic bio-oxidation of Fe(II) Applied and Environmental Microbiology 68 2704-2710 Lovley DR (1997) Microbial Fe(III) reduction in subsurface environments FEMS Microbiology Reviews 20 305-313 Manning PG Birchall T Jones W (1981) Ferric hydroxides in surficial sediments of the great lakes and their role in phosphorus availability a Moumlssbauer spectral study Canadian Mineralogist 19 525-530 Manning PG Jones W (1982) The binding capacity of ferric hydroxides for non-apatite inorganic phosphorus in sediments of the depositional basins of Lakes Erie and Ontario Canadian Mineralogist 20 169-176 McCammon CA Burns RG (1980) The oxidation mechanism of vivianite as studied by Moumlssbauer spectroscopy American Mineralogist 65 361-366 Moore PB (1971) The Fe2+

3(H2O)n(PO4)2 homologous series crystal-chemical relationships


and oxidized equivalents American Mineralogist 56 1-17 Moraghan JT Buresh RJ (1976) Chemical reduction of nitrate by ferrous iron Journal of Environmental Quality 5 320-325 Moraghan JT Buresh RJ (1977) Chemical reduction of nitrite and nitrous oxide by ferrous iron Journal of American Soil Science Society 40 47-50 Morales JA de Graterol LS Mesa J (2000) Determination of chloride sulfate and nitrate in groundwater samples by ion chromatography Journal of Chromatography A 884 185-190 Mulder EG Deinema MH (1992) The sheathed bacteria In The Prokaryotes Balows A Truper HG Dworkin M Harder W Schleifer KH (eds) Springer Verlag 2618-2624 Moslashrup S Madsen MB Franck J Villadsen J Koch CJW (1983) A new interpretation of Moumlssbauer spectra of microcrystalline goethiterdquosuper-ferromagnetismrdquo of ldquosuper-spin-glassrdquo behaviour Journal of Magnetism and Magnetic Materials 40 163-174 Nembrini GP Capobianco JA Viel M Williams AF (1983) A Moumlssbauer and chemical study of the formation of vivianite in sediments of Lago Maggiore (Italy) Geochimica et Cosmochimica Acta 47 1459-1464 Nielsen JL Nielsen PH (1998) Microbial nitrate-dependent oxidation of ferrous iron in activated sludge Environmental Science and Technology 32 3556-3561 Nriagu JO (1972) Stability of vivianite and ion-pair formation in the system Fe3(PO4)2-H3PO4- H2O Geochimica et Cosmochimica Acta 36 459-470 Nriagu JO Dell CI (1974) Diagenetic formation of iron phosphates in recent lake sediments American Mineralogist 59 934-946 Patrick Jr WH Khalid RA (1974) Phosphate release and sorption by soils and sediments Effect of aerobic and anaerobic conditions Science 186 53-55 Postma D (1981) Formation of siderite and vivianite and the pore-water composition of a recent bog sediment in Denmark Chemical Geology 31 225-244 Pratesi G Cipriani C Giuli G Birch WD (2003) Santabarbaraite a new amorphous phosphate mineral European Journal of Mineralogy 15 185-192 Ratering S Schnell S (2001) Nitrate-dependent iron(II) oxidation in paddy soil Environmental Microbiology 3 100-109 Ritz C Essene EJ Peacor DR (1974) Metavivianite Fe3(PO4)2middot8H2O a new mineral American Mineralogist 59 896-899 Rodgers KA (1986) Metavivianite and kerchenite a review Mineralogical Magazine 50 687- 691 Rodgers KA Johnston JH (1985) Type metavivianite Moumlssbauer evidence for a revised composition Neues Jahrbuch fuumlr Mineralogie-Monatshefte 12 539-542

42 Chapter 2 Rossum JR Villarruz PA (1963) Determination of ammonia by the indophenol method Journal of American Water Works Association 55 657-658 Seitz MA Riedner RJ Malhotra SK Kipp RJ (1973) Iron-phosphate compound identification in sewage sludge residue Environmental Science and Technology 7 354-357 Sobolev D Roden EE (2001) Suboxic deposition of ferric iron by bacteria in opposing gradients of Fe(II) and oxygen at circumneutral pH Applied and Environmental Microbiology 67 1328-1334 Straub KL Benz M Schink B Widdel F (1996) Anaerobic nitrate-dependent microbial oxidation of ferrous iron Applied and Environmental Microbiology 62 1458-1460 Straub KL Buchholz-Cleven BEE (1998) Enumeration and detection of anaerobic ferrous iron-oxidizing nitrate-reducing bacteria from diverse European sediments Applied and Environmental Microbiology 64 4846-4856 Straub KL Hanzlik M Buchholz-Cleven BEE (1998) The use of biologically produced ferrihydrite for the isolation of novel iron-reducing bacteria Systematic and Applied Microbiology 21 442-449 Weber KA Picardal FW Roden EE (2001) Microbially catalyzed nitrate-dependent oxidation of biogenic solid-phase Fe(II) compounds Environmental Science and Technology 35 1644-1650 Widdel F Bak F (1992) Gram-negative mesophilic sulfate-reducing bacteria In The Prokaryotes (Balows A Truumlper HG Dworkin M Harder W Schleifer K-H (eds)) Springer 2nd ed 3352-3378

Widdel F Schnell S Heising S Ehrenreich A Assmus B Schink B (1993) Ferrous iron oxidation by anoxygenic phototrophic bacteria Nature 362 834-836 Williams JDH Syers JK Shukla SS Harris RF Armstrong DE (1971) Levels of inorganic and total phosphorus in lake sediments as related to other sediment parameters Environmental Science and Technology 5 1113-1120

Zwaan PC Kortenbout van der Sluys G (1971) Vivianite crystals from Hare Noord Brabant Province The Netherlands Scripta Geology 6 1-7

Formation of Layered Iron Hydroxides by Microbial Fe(III) Reduction 43

3 Formation of Layered Iron Hydroxides by Microbial Fe(III)

Reduction Abstract

Many inorganic and organic pollutants may be degraded by microorganisms in the

subsurface However a wide range of contaminants including chromate nitrate

radionuclides nitroaromatic compounds chlorinated aliphatics and carbamate

pesticides may also be chemically transformed by reduction reactions involving

layered iron(II)-iron(III)-hydroxides (green rusts) Hence green rusts (GRs) may

play a potentially important role in the fate and transport of pollutants in iron-rich

suboxic soils and sediments Yet only little is known about the formation of GRs

in these environments The biotic formation of GRs mediated by the anaerobic

dissimilatory Fe(III)-reducing bacteria Shewanella spp has been reported and

proposed in several studies However the experimental conditions applied were

mostly not natural and the evidence of GR formation provided may be questioned

This work investigated the Fe-containing products formed by the facultatively

anaerobic Fe(III)-reducing microorganism Shewanella algae BrY in culture

media containing 4-10 mM formate or lactate and 8-27 mM Fe(III) In order to

simulate natural conditions Fe(III) oxides were applied as coatings on silica

(model system for sandy soils) or calcite particles (model system for calcareous

soils) and synthetic electron shuttles as well as highly concentrated artificial pH

buffers were excluded S algae BrY reduced 19-72 of the initial Fe(III) when

grown in goethitecalcite lepidocrocitecalcite or hydrous ferric oxidesand mineral

systems and green or blackish mineral phases were produced within 1-2 weeks

after inoculation Moumlssbauer spectroscopic analyses indicated that the green and

blackish precipitates were dominated by vivianite (Fe3(PO4)2sdot8H2O) and green rust

44 Chapter 3

31 Introduction

The significance of bacteria in the biogeochemical cycling of iron has been broadly

recognized over the past two decades Chemical processes were previously

considered to account for most of the Fe(III) reduction in subsurface environments

Dissimilatory Fe(III)-reducing bacteria (DIRB) that gain energy by coupling the

oxidation of hydrogen or organic compounds to the reduction of Fe(III) oxides

have been known for many years but their biogeochemical importance was

acknowledged only a decade ago (reviewed by Lovley 1997) DIRB transfer

electrons to extracellular Fe(III) without assimilating the iron Fe(III) bioreduction

accounts for a major fraction of the carbon oxidation in many different

environments and in the presence of high amounts of reactive Fe(III) microbial

Fe(III) reduction may even inhibit sulfate reduction and methanogenesis (King

1990 Lovley amp Phillips 1986) In fact most of the Fe(III) reduction in the Fe(III)

reduction zone of aquatic sediments and aquifers is thought to be enzymatically

catalyzed by microorganisms (Lovley et al 1991) However the relative

importance of microbial and chemical processes involved in the Fe(III) reduction

are still somewhat disputed among microbiologists and geochemists

A wide diversity of Fe(III)-reducing bacteria which fall in a number of different

phylogenetic groups is known today Both organisms growing by respiration and

by fermentation have been isolated and identified (Lovley 1991 Nealson amp

Saffarini 1994) Hydrogen short- and long-chained fatty acids amino acids

sugars and aromatic compounds may serve as electron donors for Fe(III)

bioreduction The enzymes responsible for dissimilatory Fe(III) reduction are outer

membrane associated ferric reductases (Lower et al 2001 and references therein)

Iron reducing bacteria may utilize alternative electron acceptors such as O2 nitrate

S0 sulfate humic substances contaminant metals and metalloids as well as

chlorinated solvents The first organism shown to couple respiratory growth to

dissimilatory iron reduction was Pseudomonas ferrireductans now known as

Shewanella oneidensis but previously classified as Alteromonas putrefaciens and


Shewanella putrefaciens (Venkateswaran et al 1999) Various DIRB including

the obligate anaerobic Geobacter sp and the facultatively anaerobic Shewanella

sp have been isolated from both marine and freshwater sediments soil and

aquifers (Thamdrup 2000 and references therein)

The redox potentials of oxidized and reduced iron couples and thus the energy

yield available from Fe(III) reduction depend strongly on the specific iron phases

involved In soil and aquatic environments Fe(III) oxides mainly occur in

association with other sediment particles as aggregates or coatings Amorphous

and poorly crystalline Fe(III) oxides usually make up 20 or less of the iron

content in a sediment (Thamdrup 2000) They are the main products of abiotic and

biotic Fe(II) oxidation in sediments and they constitute the most important phases

for microbial Fe(III) reduction Until recently it was generally believed that DIRB

reduced insoluble Fe(III) oxides only by direct contact with the Fe(III) oxide

thereby allowing electron transfer from the cell to the Fe(III) oxide surface

However over the past several years there has been a growing recognition that

DIRB may use different strategies in order to access the solid Fe(III) oxides These

strategies include solubilization of Fe(III) by synthetic or natural Fe(III) chelators

and Fe(III) reduction via electron shuttling with soluble humic substances or

microbially produced electron shuttles (Nevin amp Lovley 2002 and references

therein Turick et al 2003) The Fe(III) complexing agents may also stimulate

Fe(III) oxide reduction indirectly by chelation and thus removal of Fe(II) from

the cell and the Fe(III) oxide surfaces Both chelated Fe(III) and soluble electron

shuttles are more accessible to Fe(III) reductases than solid Fe(III) oxides In

contrast to Geobacter metallireducens S algae produces and releases extracellular

electron shuttling compounds (Nevin amp Lovley 2000) However in the absence of

soluble electron shuttles reversible adhesion is required for reduction of solid

Fe(III) oxides by S algae BrY (Das amp Caccavo 2000) Shewanella algae BrY

adheres readily and preferentially to a range of solid Fe(III) oxides such as

ferrihydrite goethite and hematite (Das amp Caccavo 2001) The adhesion

46 Chapter 3

mechanisms are not completely understood but recent results suggest that the

adhesion is mediated by cell surface proteins and independent of cell motility

(Caccavo amp Das 2002)



anaerobic DIRB Shewanella putrefaciens has been reported repeatedly over the

last years (Fredrickson et al 1998 Kukkadapu et al 2001 Liu et al 2001



conditions have been offered and it is still unknown whether this process may take

place at natural conditions comprising low carbon and iron concentrations as well

as the absence of synthetic electron shuttles and highly concentrated artificial pH

buffers GRs are layered iron(II)-iron(III)-hydroxides with anionic interlayers and

they hold the general formula [FeII(6-x)FeIII

x(OH)12]x+[(A)xnmiddotyH2O]x- where x = 09 -

42 A is an n-valent anion eg CO32- Clndash or SO4

2- and y is the number of water

molecules in the interlayer In circumneutral solutions the oxidation of dissolved

Fe(II) always passes through solid GR phases (Bernal et al 1959) This agrees

with the natural GR occurrences found in suboxic nonacid iron-rich environments

such as hydromorphic soils and intertidal sediments (Al-Agha et al 1995 Trolard

et al 1996 Genin et al 1998) In addition GRs have been found as corrosion

products in numerous engineering systems eg in a pipeline distribution system

for drinking water steel sheet piles in marine sediments reinforced concrete

(ferro-concrete) and permeable reactive barriers of zero-valent iron implemented

for on-site remediation of organic and inorganic contaminants (Tuovinen et al

1980 Nielsen 1976 Genin et al 1991 Roh et al 2000) Through sequestration


transport of organic and inorganic pollutants in suboxic iron-rich soils and

sediments (see Chapters 4 amp 5 in this work and references therein)


The major goal of this work was to examine the iron minerals forming during the

course of Fe(III) bioreduction of hydrous ferric oxide goethite and lepidocrocite

Two model systems simulating sandy and calcareous soils in subsurface

environments were designed in order to investigate the formation of iron minerals

at conditions including low carbon levels low Fe(III) concentrations applied as

Fe(III) oxide coatings on sand or calcite no electron shuttle and no synthetic pH

buffers

32 Materials and methods

All handling and sampling of solutions and suspensions were carried out at strict

anoxic conditions Standard sterile techniques were used throughout (Hungate

1969 Miller amp Wolin 1974) Only the iron oxide coatings were not autoclaved in

order to avoid the iron oxides from transforming Goethite (acicular particles with

size 01 times 06 microm specific surface area 16 m2g) and lepidocrocite (acicular

particles with size 005 times 03 microm specific surface area 18 m2g) were purchased as

fine powders from Bayer (Bayferrox 910 and 943) Calcite (grain size 170-350 microm

Pluumlss-Staufer AG) and sea sand (dominantly quartz grain size 01-03 mm Riedel-

de Haeumln) were used as Fe(III) oxide coating bearing minerals

321 Preparation of iron oxide coatings

Two grams of goethite (goe) or lepidocrocite (lep) and 100 g calcite were

combined with 200 mL deionized water (DIW) in a 500 mL polyethylene flask

Hydrous ferric oxide (HFO) was synthesized by dissolving 4 g Fe(NO3)3middot9H2O in

70 mL DIW followed by slow neutralization under magnetic stirring till pH 7 with

approximately 30 mL 1 M NaOH (method modified after Schwertmann amp Cornell

1991) The HFO coating was made by combining 100 mL freshly precipitated

HFO with 900 mL deionized water and 50 g sea sand in a polyethylene bottle The

suspensions containing the iron oxide coatings were gently agitated on a

reciprocating shaker for 24 h and left to stand for another 24 h Excess Fe(III)

oxides and salts were removed from the coated material by repeated decantation

48 Chapter 3

and washing with 003 M NaNO3 followed by washing with DIW until clear

runoff Finally the coatings were collected on folding filters and air dried The

amount of HFO goethite and lepidocrocite coated onto sand and calcite after

washing and drying was quantified to 7-11 mg Fe(III)g sand or calcite

322 Mineral characterisation

The identity and purity of the HFO synthesized were examined by means of X-ray

diffraction (XRD) measurements The XRD analyses were performed on a Scintag

XDS 2000 using Co Kα radiation (45 kV 40 mA) using divergence scatter and

receiving slits of 1deg 05deg and 02 mm respectively Samples were scanned

between 6 and 80 deg2θ with a scan speed of 1 deg2θmin Mineral suspension samples

for transmission Moumlssbauer spectroscopic analysis were collected on 02 microm filters

in an anoxic glove box (Coy Laboratory Products Inc) transferred to Perspex

capsules and stored in liquid nitrogen until measurement Moumlssbauer spectra were

obtained between 250 and 5 K using a conventional constant acceleration

spectrometer and a source of 57Co in Rh The spectrometer was calibrated using a

125 microm foil of α-Fe at room temperature and isomer shifts are given relative to

the centroid of this absorber The spectra were fitted using simple Lorentzian line

shape and it was assumed that all positions have identical f-factors

323 Culture conditions and cell preparation

Shewanella algae BrY is a motile gram-negative rod which was isolated first from

anoxic estuary sediments (Caccavo et al 1992) S algae BrY was grown

aerobically in tryptic soy broth (30 gL CASO-bouillon Merck) at 28degC on a rotary

shaker at 150 rpm for 16-18 h Cells were harvested by centrifugation (6000 rpm times

g 4ordmC 15 min) during the late exponential ndash early stationary growth phase at

OD660 ~ 06 Optimal Fe(III) reductase activity is expressed at this stage of growth

(Roden amp Zachara 1996) The cells were washed twice in oxic 50 mM PIPES

[piperazine-NNacute-bis(2-ethanesulfonic acid)] buffer (pH 70) and resuspended in

culture medium containing no Fe(III) and no carbon source Washed cell


suspensions were used as inocula for Fe(III) reduction experiments Oxygen was

expelled from the inoculum by extensive purging with 100 N2(g) (9999999

purity) Working stock cultures of S algae BrY were maintained aerobically on

tryptic soy agar plates at ambient temperature

324 Bioreduction experiments

All anaerobic incubations were carried out in anoxic serum vials (25 mL) or test

tubes (13 mL) sealed with thick (10-13 mm) butyl rubber stoppers and aluminum

crimp caps or plastic screw caps The basal culture medium (Table 31) was

prepared according to Kostka amp Nealson (1998) but with a phosphate

concentration of 2 mM and the exclusion of Fe(II) and EDTA

(ethylenediaminetetraacetic acid) The medium was amended with 4-10 mM

lactate or formate and 8-27 mM Fe(III) The Fe(III) was applied as Fe(III) oxide

coatings on sand or calcite The suspensions were purged extensively with 100

N2(g) (HFOsand suspensions) or 995 N205 CO2(g) (goecalcite and

lepcalcite suspensions) prior to inoculation The calcareous systems were buffered

at pH ~ 76 through a natural buffer system (CaCO3(s) + 995 N205 CO2(g))

whereas the sandy systems contained no pH buffer (100 N2(g) pH 55-60)

Inoculum size made up 5 of the total volume Cultures were incubated dark at

room temperature and gently agitated once every day At different time intervals

suspension samples for Fe(II) and Moumlssbauer analysis were withdrawn from the

reaction mixture using 100 N2(g) or 995 N205 CO2(g)-flushed sterile

disposable syringes and hypodermic needles Suspension samples for Fe(II)

analysis were digested in 01 M HCl for 30 min

50 Chapter 3

Table 31 Composition of the mineral medium (modified from Kostka amp Nealson (1998))

Components Concentration (M)

(NH4)2SO4 00143 KH2PO4 73middot10-4

K2HPO4 13middot10-3



H3BO3 56middot10-5








NaCl 10middot10-5

L-arginine 11middot10-4

L-serine 19middot10-4

L-glutamic acid 14middot10-4

Lactate or formate 4-10middot10-3

Fe(III) 8-27middot10-3


Fe(II) was determined using a modified phenanthroline method (Fadrus amp Maly

1975) The total amount of Fe(III) coated on calcite and sand was determined by

atomic absorption spectroscopy following dissolution in 6 M HCl(aq) for 24 h


331 Fe(II) production and suspension colour changes

Strongly chelating agents such as EDTA were omitted from the culture medium in

order to prevent complexation of Fe(II) and Fe(III) which interferes with

precipitation of Fe(II) and Fe(II)-Fe(III) mineral phases Within 1-2 weeks after

inoculation Shewanella algae BrY produced green mineral phases in media

suspensions containing lepidocrocite and goethite as coatings on calcite and 4-10

mM formate or lactate (Figure 31) The formation of the green precipitates was

generally slower for the lepidocrocite coating than for the goethite coating The


blue-green colours of the phases produced most likely originate from Fe(II)-Fe(III)

charge transfer between adjacent Fe(II) and Fe(III) ions in edge-shared octahedra

(Faye et al 1968) Dark brown and blackish products were formed when the

bacteria were inoculated on HFO coated sand (Figure 32)

Figure 31 Culture tubes containing a) goethite and b) lepidocrocite coated calcite in culture

medium The left tubes of the pair were not inoculated whereas the right tubes were

photographed 5 months after inoculation with S algae BrY Experimental conditions [formate]0

= 4 mM [Fe(III)]0 = 8 mM 995 N205 CO2(g) pH 76

52 Chapter 3

Figure 32 Culture tubes containing HFO coated sand in culture medium Tubes 1 and 2 to the

left were not inoculated whereas tubes 3-5 to the right were photographed a) 13 days and b) 21

days after inoculation with S algae BrY Experimental conditions [lactate]0 = 10 mM [Fe(III)]0

= 25 mM 100 N2(g) pH 55-60

The green and black colours did not change to other colours (observed for gt1

year) indicating that the microbial Fe(III) reduction ceased at these mineral stages

The concentrations of dissolved ferrous iron (Fe(II)sol) estimated during Fe(III)

bioreduction were generally low (Figure 33) When comparing the final Fe(II)sol

amounts produced and the slopes of the Fe(II)sol formation curves for HFO

goethite and lepidocrocite in Figure 33 it can be seen that the final Fe(II)sol

amount and the Fe(II)sol production rate both follow the order HFO gt goethite gt

lepidocrocite at similar cell densities regardless of the carbon source applied This

suggests that bioreduction by S algae BrY is more facile for HFO than for goethite

and lepidocrocite at the experimental conditions employed here It should be noted

that the final Fe(II)sol amounts and the Fe(II)sol production rates reported in this

work have not been normalised with respect to the specific surface areas of the iron

oxides and coating-bearing solids applied The reactivity trend is consistent with

previous findings demonstrating higher reducibility of natural and poorly


crystalline Fe(III) oxides as compared to synthetic crystalline Fe(III) oxides

(Zachara et al 1998) The authors ascribed these differences in reducibility to

differences in particle size surface area and crystal defects of the Fe(III) oxides In

some cases the dissolved Fe(II) concentration decreased again with time (Figure

33 b-d) This indicates that the Fe(II) formed was incorporated into solid phases

forming andor adsorbed onto the calcite sand or Fe(III) oxide surfaces The solid

Fe(II) concentrations were not estimated spectrophotometrically The solid

material was generally low in total iron and therefore saving it for Moumlssbauer

spectroscopic analysis was given highest priority

54 Chapter 3

Figure 33 Time course of dissolved Fe(II) production during bioreduction of HFOsand

goethitecalcite and lepidocrocitecalcite by S algae BrY Experimental conditions [Fe(III)]0 =

25 mM [formate]0 = 10 mM (a-c) or [lactate]0 = 10 mM (d-f)

No color change and no Fe(II) production were observed in mineral suspensions

lacking either a carbon source or S algae BrY cells (data not shown)


332 Identification of solid iron phases

The purity of the Fe(III) oxides used in the experiments were investigated by

transmission Mossbauer spectroscopy (Figure 34) Single (or strongly dominating)

sextets in the spectra with magnetic hyperfine fields of 48 1 505 and 45 5 Tat 5 K

demonstrated the purity of the HFO goethite and lepidocrocite samples

respectively A minor impurity of goethite in the lepidocrocite sample was

resolved in the spectrum measured at 80 K (not shown for pure sample but can be

seen as a magnetically ordered sextet in Figure 35c) No Fe(II)-containing

components were detected

a)

c)

middot 12 -8 -4 4 8 12

Velocity (mmls

bull middot12 -8 -4 0 4 12

Velocity (mmls)

b)

middot12 -8 -4 4 8 12

Velocity (mmls

Figure 34 Transmission Mossbauer spectra measured at 5 K of a) HFO (magnetic hyperfine

field of 481 T isomer shift of 048 1nrns-1 negligible quadrupole shift and line width of outer

lines 110 rmns-1) b) goethite (magnetic hyperfine field of 505 T isomer shift of 049 rmns-1

quadmpole shift of -013 1nrns-1 and line width of outer lines 042 rnrns-1

) and c) lepidocrocite

56 Chapter 3

(magnetic hyperfine field of 455 T isomer shift of 050 mms-1 quadrupole shift of ndash001 mms-1

and line width of outer lines 060 mms-1) prior to inoculation Simple Lorenztian fits are shown

The oxidation state and coordination of Fe in the microbially reduced HFO

goethite and lepidocrocite samples were also examined by transmission Moumlssbauer

spectroscopy (Figure 35) The bioreduced HFO goethite and lepidocrocite samples

cultured on formate contained Fe(II) holding similar coordination as inferred from

the similarity of the hyperfine parameters (see legend in Figure 35) but different

relative intensities (72 19 and 71 respectively) The major part of the Fe(III)

remaining in the bioreduced samples were coordinated similarly to the Fe(III)

present in the initial Fe(III) oxide The coordination of Fe(II) in the bioreduced

lepidocrocite samples cultured on lactate was slightly different (a smaller

quadrupole splitting of 288 mms-1 for the ferrous component dominates ndash data not

shown) The exact mineralogy of the Fe(II) present in the green phases was not

fully resolved but its coordination is very akin to one of the Fe(II) sites in vivianite

(see Chapter 2 this work) and synthetic green rusts (Koch 1998) These findings

agree with other reports on the bioformation of vivianite and green rusts by

Shewanella putrefaciens CN32 although the evidence provided may be discussed

(Fredrickson et al 1998 Glasauer et al 2003 Parmar et al 2001) Our

Moumlssbauer data on the green phases did not allow for a detailed account of the type

of green rust produced However when considering solution composition (see

Table 31) and the high affinity of GR interlayers for carbonate it is reasonable to

assume that carbonate GR was formed (Hansen amp Taylor 1991) Due to the high

amounts of Fe(III) in the oxides present in the experiments it was difficult to probe

a possible content of Fe(III) in the vivianite with certainty The differences in the

number of Fe(II) positions in the Moumlssbauer spectra and particular the different

temperatures at which magnetic ordering takes place can be employed in order to

distinguish between green rust and vivianite Preliminary Moumlssbauer data obtained

for the blackish precipitates formed in the HFOsand suspensions indicate that they

hold no resemblance to magnetite eventhough the colour suggests so On the

contrary the black precipitates seemed to be more similar to synthetic green rusts


Mossbauer spectroscopic measurements are currently underway in order to resolve

the Fe(II) coordinations in the greenish and blackish phases

a) b)

c c g Q e- e 0 0 1l 1l

-~ bull ~

iii ~ Qi bull a bull

-12 -8 4 0 4 12

4 -3 -2 -1 0 1 2 4 Velocity (mmts) Velocity ( rmis)

c)

-12 -8 4 8 12

v elocity (m mis)

Figure 35 Transmission Mossbauer spectra of the black and green phases fo1med within 1-2

weeks after inoculation of a) HFO (measured at 130 K) b) goethitecalcite (measured at 80 K)

and c) lepidocrocitecalcite (measured at 80 K) with S algae BrY Experimental conditions

[fo1m ate]0 = 4 mM [Fe(III)]o = 8 mM 995 Ni05 C02(g) pH 76 The quadrnpole

splittings and isomer shifts for the Fe(II) components in the three systems are a) 293 nnns-1 and

126 mmsmiddot1 b) 308 rmnsmiddot1 and131 rmnsmiddot1 and c) 322 mmsmiddot1 and 132 mmsmiddot1 Simple Lorenztian

fits are shown

The evidence provided in many of the studies proposing biogenic GRs is not all

too convincing but it strongly suggests the probability of microbially produced GR

being present The challenge encountered is that when present in low

58 Chapter 3

concentrations especially in mixtures including other iron minerals it is very

difficult to identify GRs using conventional solid phase analysis methods even

with Moumlssbauer spectroscopy At least two complementary methods such as XRD

and Moumlssbauer spectroscopy are required for proper identification and

characterization of GRs However in this work the solid materials were generally

too low in total iron to allow for XRD analysis Moreover the highly

heterogeneous suspensions were dominated by the coating-bearing sand and calcite

solids Electron micrographs including energy dispersive X-ray spectroscopy

suspension colour and mineral stability calculations do not suffice as evidence The

most convincing evidence provided so far involves an atypical GR-CO3 with an

Fe(II)Fe(III) ratio of 1 (Ona-Nguema et al 2002aampb) This GR-CO3 was formed

as a result of lepidocrocite reduction by Shewanella putrefaciens CIP 8040 at

conditions comprising high nutrient levels (50-75 mM formate) high Fe(III)

concentrations (80-300 mM) and a synthetic electron shuttle (100 microM

anthraquinone-26-disulfonate (AQDS)) at initial pH 75 Hence the results

reported during recent years suggest that microbial formation of GR may be

possible The results presented here indicate that GRs may be produced


as the exclusion of synthetic electron shuttles and pH buffers

333 Factors controlling the identity of the secondary iron minerals

In general one would expect that biogenic minerals have chemical compositions



mineralization are inorganically driven and the secondary Fe(II)-containing




form different minerals in different environments The key factors controlling the

identity of the secondary iron minerals include medium composition electron


donor and electron acceptor concentrations mineral aging as well as adsorbed ions

(Zachara et al 2002) The main factor controlling the nature of the secondary

mineral products are the respiration-driven biogenic Fe(II) supply rate and

magnitude and its surface reaction with the residual oxide and other sorbed ions

(Zachara et al 2002) Especially solution and medium composition have a strong

impact on the nature of the Fe(II)-containing biomineralization products forming

Accordingly siderite (FeCO3) and magnetite (Fe3O4) were the secondary solid

phases resulting from the bioreduction of ferrihydrite by Shewanella putrefaciens

CN32 in bicarbonate buffered medium (pH 71) containing no phosphate whereas

siderite and vivianite were the secondary iron minerals dominating in bicarbonate

buffered medium (pH 74) containing 4 mM phosphate (Zachara et al 2002) This

is explained by the inhibiting effect of phosphate on crystallization of magnetite

(Couling amp Mann 1985 Fredrickson et al 1998)

334 Factors controlling the rate and extent of Fe(III) bioreduction

In this study the extent of Fe(III) bioreduction was estimated to 19-72 by

transmission Moumlssbauer measurements In fact complete microbial reduction of

crystalline Fe(III) minerals has never been observed in laboratory batch culture

studies (Roden amp Urrutia 2002) It has been found that Fe(II) does not inhibit

Fe(III) reductase activity through an enzyme inhibition mechanism (Roden amp

Urrutia 2002) Hence other chemical andor physiologic factors control the

bioavailability of solid Fe(III) phases and thus the extent of their microbial Fe(III)

reduction The initial rate and long-term extent of microbial reduction of

amorphous and crystalline Fe(III) oxides including HFO goethite and hematite

were linearly correlated with oxide surface area (Roden amp Zachara 1996)

Association of biogenic Fe(II) with Fe(III) oxide and DIRB cell surfaces reduced

the long-term extent of crystalline Fe(III) oxide bioreduction (Roden amp Urrutia

2002) These results were explained by Fe(II) surface complexes andor

precipitates creating a passive Fe(II)-bearing surface film providing direct physical

interference with the electron transfer from the DIRB cells to Fe(III) However the

60 Chapter 3

real mechanisms whereby the surface-associated Fe(II) inhibits Fe(III) oxide

bioreduction are unclear but they most likely involve both kinetic and

thermodynamic constraints on the electron transfer Culture medium composition

in particular the presence and the concentration of phosphate as well as Fe(II)

chelating ligands also exert an influence on the extent of the microbial reduction

of Fe(III) oxides The extent of Fe(III) bioreduction was inhibited by high

phosphate concentrations which favoured surfacebulk precipitation processes

(Urrutia et al 1998) The carbon sources most frequently applied in Fe(III)

bioreduction studies include malate citrate and other di- and tricarboxylic acids

which are not only easily metabolizable carbon sources but also eminent Fe(II) and

Fe(III) chelators In this study we employed formate and lactate as carbon sources

since they are the weakest complexing agents of Fe(II) and Fe(III) among the C1-

C3 monocarboxylic acids (Martell 1964) Thus we expect less dissolution of

prevailing precipitates by complexation as compared to other studies

34 Conclusions

This work demonstrated that Shewanella algae BrY reduced 19-72 of initial

Fe(III) when grown in culture media containing 4-10 mM formate or lactate and 8-

27 mM Fe(III) applied as goethite or lepidocrocite coatings on calcite (pH 76) or

HFO coatings on sand (pH 55-60) Within 1-2 weeks after inoculation green

mineral phases were produced in the goethitecalcite and lepidocrocitecalcite

mineral systems whereas black precipitates formed in the HFOsand suspensions

Moumlssbauer spectroscopic analyses indicated that the greenish and blackish phases

most likely were mineral mixtures dominated by vivianite and green rust Thus the

results indicate that GRs may be produced microbially at conditions including low

carbon and Fe(III) concentrations as well as the exclusion of synthetic electron

shuttles and pH buffers

Acknowledgments

We would like to thank Dr R Gerlach for providing us the Shewanella algae BrY culture and

Dr C B Koch for performing the Moumlssbauer analyses


References Al-Agha MR Burley SD Curtis CD Esson J (1995) Complex cementation textures and authigenic mineral assemblages in recent concretions from the Lincolnshire Wash (east coast UK) driven by Fe(0) to Fe(II) oxidation Journal of the Geological Society 152 157-171 Bernal JD Dasgupta DR Mackay AL (1959) The oxides and hydroxides of iron and their structural inter-relationships Clay Minerals Bulletin 4 15-30 Caccavo Jr F Blakemore RP Lovley DR (1992) A hydrogen-oxidizing Fe(III)-reducing microorganism from the Great Bay Estuary New Hampshire Applied and Environmental Microbiology 58 3211-3216 Caccavo Jr F Das A (2002) Adhesion of dissimilatory Fe(III)-reducing bacteria to Fe(III) minerals Geomicrobiology Journal 19 161-177 Couling SB Mann S (1985) The influence of inorganic phosphate on the crystallization of magnetite (Fe3O4) from aqueous solution Journal of the Chemical Society Chemical Communications 1713-1715 Das A Caccavo Jr F (2000) Dissimilatory Fe(III) oxide reduction by Shewanella alga BrY requires adhesion Current Microbiology 40 344-347

Das A Caccavo Jr F (2001) Adhesion of the dissimilatory Fe(III)-reducing bacterium Shewanella alga BrY to crystalline Fe(III) oxides Current Microbiology 42 151-154 Fadrus H Maly J (1975) Suppression of iron(III) interference in the determination of iron(II) in water by the 110-phenanthroline method The Analyst 100 549-554 Faye GH Manning PG Nickel EH (1968) The polarized optical absorption spectra of tourmaline cordierite chloritoid and vivianite ferrous-ferric electronic interaction as a source of pleochroism American Mineralogist 53 1174-1201 Fredrickson JK Zachara JM Kennedy DW Dong H Onstott TC Hinman NW Li S (1998) Biogenic iron mineralization accompanying the dissimilatory reduction of hydrous ferric oxide by a groundwater bacterium Geochimica et Cosmochimica Acta 62 3239-3257 Geacutenin JMR Olowe AA Benbouzid-Rollet ND Prieur D Confente M Resiak B (1991) The simultaneous presence of green rust 2 and sulfate reducing bacteria in the corrosion of steel sheet piles in a harbour area Hyperfine Interactions 69 875-878 Geacutenin JMR Bourrieacute G Trolard F Abdelmoula M Jaffrezic A Refait Ph Maitre V Humbert B Herbillon A (1998) Thermodynamic equilibria in aqueous suspensions of synthetic and natural Fe(II)-Fe(III) green rusts Occurrences of the mineral in hydromorphic soils Environmental Science and Technology 32 1058-1068 Glasauer S Weidler PG Langley S Beveridge TJ (2003) Controls on Fe reduction and mineral formation by a subsurface bacterium Geochimica et Cosmochimica Acta 67 1277- 1288 Hansen HCB Taylor RM (1991) The use of glycerol intercalates in the exchange of CO3

2- with SO4

2- NO3- or Cl- in pyroaurite-type compounds Clay Minerals 26 311-327

62 Chapter 3

Hungate RE (1969) A roll tube method for cultivation of strict anaerobes Methods in Microbiology 3B 117-132 King GM (1990) Effects of added manganic and ferric oxides on sulfate reduction and sulfide oxidation in intertidal sediments FEMS Microbiology Ecology 73 131-138 Koch CB (1998) Structures and properties of anionic clay minerals Hyperfine Interactions 117 131 -157 Kostka J Nealson KH (1998) Isolation cultivation and characterization of iron- and manganese reducing bacteria In Techniques in Microbial Ecology Burlage RS Atlas R Stahl D Geesey G Sayler G (eds) Oxford University Press Inc 58-78 Kukkadapu RK Zachara JM Smith SC Fredrickson JK Liu C (2001) Dissimilatory bacterial reduction of Al-substituted goethite in subsurface sediments Geochimica et Cosmochimica Acta 65 2913-2924

Liu C Zachara JM Gorby YA Szecsody JE Brown CF (2001) Microbial reduction of Fe(III) and sorptionprecipitation of Fe(II) on Shewanella putrefaciens strain CN32 Environmental Science and Technology 35 1385-1393 Lovley DR (1991) Dissimilatory Fe(III) and Mn(IV) reduction Microbiological Reviews 55 259-287 Lovley DR (1997) Microbial Fe(III) reduction in subsurface environments FEMS Microbiology Reviews 20 305-313 Lovley DR Phillips EJP (1986) Organic matter mineralization with reduction of ferric iron in anaerobic sediments Applied and Environmental Microbiology 51 683-689 Lovley DR Phillips EJP Lonergan DJ (1991) Enzymatic versus nonenzymatic mechanisms for Fe(III) reduction in aquatic sediments Environmental Science and Technology 25 1062-1067 Lower SK Hochella Jr MF Beveridge TJ (2001) Bacterial recognition of mineral surfaces Nanoscale interactions between Shewanella and α-FeOOH Science 292 1360-1363 Martell AE (1964) Stability constants of metal-ion complexes Part 2 Organic including macromolecule ligands The Chemical Society London 2 ed Miller TL Wolin MJ (1974) A serum bottle modification of the Hungate technique for cultivating obligate anaerobes Applied Microbiology 27 985-987 Nealson KH Saffarini D (1994) Iron and manganese in anaerobic respiration Environmental significance physiology and regulation Annual Review of Microbiology 48 311-343 Nevin KP Lovley DR (2000) Lack of production of electron-shuttling compounds or solubilization of Fe(III) during reduction of insoluble Fe(III) oxide by G metallireducens Applied and Environmental Microbiology 66 2248-2251 Nevin KP Lovley DR (2002) Mechanisms for Fe(III) oxide reduction in sedimentary


environments Geomicrobiology Journal 19 141-159 Nielsen A (1976) Hvid groslashn og sort rust Beskrivelse af en korrosionsskade paring et svoslashmmebassin Nordisk Betong 2 21-24 Ona-Nguema G Abdelmoula M Jorand F Benali O Gehin A Block J-C Geacutenin JMR (2002a) Iron (IIIII) hydroxycarbonate green rust formation and stabilization from lepidocrocite bioreduction Environmental Science and Technology 36 16-20 Ona-Nguema G Abdelmoula M Jorand F Benali O Gehin A Block J-C Geacutenin JMR (2002b) Microbial reduction of lepidocrocite γ-FeOOH by Shewanella putrefaciens The formation of green rust Hyperfine Interactions 139140 231-237 Parmar N Gorby YA Beveridge TJ Ferris FG (2001) Formation of green rust and immobilization of nickel in response to bacterial reduction of hydrous ferric oxide Geomicrobiology Journal 18 375-385 Roden EE Urrutia MM (2002) Influence of biogenic Fe(II) on bacterial crystalline Fe(III) oxide reduction Geomicrobiology Journal 19 209-251 Roden EE Zachara JM (1996) Microbial reduction of crystalline iron(III) oxides Influence of oxide surface area and potential for cell growth Environmental Science and Technology 30 1618-1628 Roh Y Lee SY Elless MP (2000) Characterization of corrosion products in the permeable reactive barriers Environmental Geology 40 184-194 Schwertmann U Cornell RM (1991) Iron oxides in the laboratory Preparation and characterization VCH Verlagsgesellschaft mbH Weinheim Thamdrup B (2000) Bacterial manganese and iron reduction in aquatic sediments In Advances in Microbial Ecology (Schink B ed) Kluwer AcademicPlenum Publishers New York 41-84 Trolard F Abdelmoula M Bourrieacute G Humbert B Geacutenin JMR (1996) Mise en eacutevidence dun constituant de type rouilles vertes dans les sols hydromorphes Proposition de lexistence dun nouveau mineacuteral la fougeacuterite Geacuteosciences de surface Comptes Rendus de LrsquoAcademie des Sciences 323 1015-1022 Tuovinen OH Button KS Vuorinen A Carlson L Mair DM Yut LA (1980) Bacterial chemical and mineralogical characteristics of tubercles in distribution pipelines Journal of the American Water Works Association 72 626-635 Turick CE Caccavo Jr F Tisa LS (2003) Electron transfer from Shewanella algae BrY to hydrous ferric oxide is mediated by cell-associated melanin FEMS Microbiology Letters 220 99-104 Urrutia MM Roden EE Fredrickson JK Zachara JM (1998) Microbial and surface chemistry controls on reduction of synthetic Fe(III) oxide minerals by the dissimilatory iron- reducing bacterium Shewanella alga Geomicrobiology 15 269-291 Venkateswaran K Moser DP Dollhopf ME Lies DP Saffarini DA MacGregor BJ Ringelberg DB White DC Nishijima M Sano H Burghardt J Stackebrandt E

64 Chapter 3

Nealson KH (1999) Polyphasic taxonomy of the genus Shewanella and description of Shewanella oneidensis sp nov International Journal of Systematic Bacteriology 49 705-724 Zachara JM Fredrickson JK Li S Kennedy DW Smith SC Gassman PL (1998) Bacterial reduction of crystalline Fe3+ oxides in single phase suspensions and subsurface materials American Mineralogist 83 1426-1443

Zachara JM Kukkadapu RK Fredrickson JK Gorby YA Smith SC (2002) Biomineralization of poorly crystalline Fe(III) oxides by dissimilatory metal reducing bacteria (DMRB) Geomicrobiology Journal 19 179-207

Reduction of Nitroaromatic Probe Compounds by Sulphate Green Rust 65

4 Reduction of Nitroaromatic Probe Compounds by Sulphate Green Rust The Effect of Probe Compound Charge

Abstract

Layered iron(II)-iron(III)-hydroxides (green rusts) may play an important role in

controlling the fate and transport of many organic and inorganic contaminants in

iron-rich suboxic soils and sediments Unlike most other iron oxides green rusts

(GRs) contain not only external Fe(II) reactive sites at the basal planes and at the

edges but also internal sites in the space between consecutive Fe(II)-Fe(III)

hydroxide layers The GR interlayer thickness is a function of both the size and the

charge of the interlayer anion Whether a given oxidant has access to the internal

sites in GRs is dependent on its charge We investigated the reductive

transformation of nitroaromatic compounds (NACs) by GR-SO4 and studied the

effect of NAC charge on the reactivity towards GR-SO4 A series of structurally

closely related compounds with different charge properties including nitrobenzene

4-nitrotoluene 4-chloronitrobenzene and 4-nitrophenylacetic acid were used as

probe compounds The NACs were completely reduced to their corresponding

anilines by GR-SO4 The reactions followed pseudo 1 order kinetics with respect

to NAC and the surface area-normalised pseudo 1 order rate constants obtained

were 016ndash465middot10-4 s-1middotm-2middotL at [Fe(II)GR]0 = 103-1260 mM [NAC]0 = 20-102

microM and pH 84-86 Neither mass transfer control nor surface saturation kinetics

could account for the rather unexpected similarity of the surface area-normalised


NACs by GR-SO4 These observations suggest that the anionic NACs did not have

an enhanced access to the inner or outer Fe(II)-GR reactive sites as compared to

the neutral NACs Hence the reaction between NAC and GR-SO4 primarily took

place at the edges of GR-SO4

66 Chapter 4

41 Introduction

Layered iron(II)-iron(III)-hydroxides (green rusts) are intermediate phases formed

by partial oxidation of Fe(II) or partial reduction of Fe(III) In neutral and weakly

alkaline solutions the oxidation of dissolved Fe(II) always passes through solid

green rust (GR) phases (Bernal et al 1959) This agrees with the natural GR

occurrences found in suboxic non-acid iron-rich environments such as

hydromorphic soils and intertidal sediments (Al-Agha et al 1995 Trolard et al

1996 Genin et al 1998) In addition GRs have been found as corrosion products

in numerous engineered systems ie a pipeline distribution system for drinking

water steel sheet piles in marine sediments reinforced concrete (ferro-concrete)

and permeable reactive barriers of zero-valent iron implemented for on-site

remediation of organic and inorganic contaminants (Tuovinen et al 1980 Nielsen

1976 Genin et al 1991 Roh et al 2000) Furthermore the microbial formation

of GRs resulting from bioreduction of Fe(III) oxides by strains of the anaerobic

dissimilatory Fe(III) reducing bacteria Shewanella putrefaciens has been reported

increasingly over the last 5 years (Fredrickson et al 1998 Kukkadapu et al 2001

Parmar et al 2001 Ona-Nguema et al 2002 Glasauer et al 2003) Moreover

the biotic formation of GRs by anaerobic denitrifying Fe(II) oxidizing bacteria has

been proposed but proper identification of the GR phases still lacks (Chaudhuri et

al 2001) All these indications of microbial GR formation infer the importance of

GRs as a link between geochemical and biological processes in natural systems

GRs form platy crystals with the general formula [FeII(6-

x)FeIIIx(OH)12]x+[(A)xnmiddotyH2O]x- where x = 09 - 42 A is an n-valent anion eg

CO32- Clndash or SO4

2- and y is the number of water molecules in the interlayer The

crystal structure consists of positively charged hydroxide sheets with Fe(II) and

Fe(III) cations having octahedral hydroxyl coordination The Fe(III) in the

hydroxide layers creates a net positive charge which is balanced by hydrated

anions in the interlayers (Figure 41) The interlayers have a higher affinity for


divalent anions than for monovalent anions (Miyata 1983) Among the 3 most

common GR forms the affinity follows the order CO32- gt SO4

2- gt Clndash The extreme

preference shown for carbonate hinders further access and exchange except under

certain conditions (Hansen amp Taylor 1991) Non-carbonate forms are readily

exchanged with other anions when dispersed in a solution containing the

exchanging anion (Mendiboure amp Schoumlllhorn 1986)

c

ba

Figure 41 Green rust layer structure The hydroxide layers and the interlayers are connected by

hydrogen bonds (not shown) The GR-SO4 crystal structure is characterised by the hexagonal

unit cell having a = b = 055 nm and c = 110 nm (Simon et al 2003) The unit cell consists of

one double layer (a double layer is a hydroxide layer and an interlayer) ie the hydroxide layer

constitutes 049 nm and the interlayer 061 nm in GR-SO4

The GR interlayer thickness (extending in the c axis direction Figure 41) is a

function of both the size and the charge of the interlayer anion Tetrahedrally

coordinated anions like sulphate lead to larger interlayer distances than smaller

monoatomic anions like chloride or planar ions like carbonate (Mendiboure amp

Schoumlllhorn 1986) Not only size but also charge density plays a role for the

interlayer spacing That is for anions having the same number of valence

electrons anions with smaller ionic radii (higher electron density) are bound more

strongly and therefore result in smaller interlayer spacings


GRs represent reactive ion exchangers and sorbents of anions eg arsenate

selenate and phosphate (Myneni et al 1997 Hansen amp Poulsen 1999 Randall et

al 2001) In addition GR may incorporate heavy metal cations by isomorphic

68 Chapter 4

substitution into the GR hydroxide layers (Tamaura 1985 Tamaura 1986)

Furthermore GRs have been shown to reduce a range of inorganic contaminants

such as nitrite nitrate selenate chromate uranyl pertechnetate and the transition

metals AgI AuIII CuII and HgII as well as organic pollutants including halogenated

ethanes ethenes and methanes (Hansen et al 1994 Hansen et al 1996 Myneni et

al 1997 Erbs et al 1999 Loyaux-Lawniczak et al 1999 Cui amp Spahiu 2002

Lee amp Batchelor 2002b Heasman et al 2003 OrsquoLoughlin et al 2003a amp 2003b

Pepper et al 2003 Elsner et al 2004 OrsquoLoughlin amp Burris 2004) Thus through

sequestration and reductive transformation GRs may play an important role in

controlling the fate and transport of contaminants in suboxic soils and sediments

In a previous study the effects of interlayer anion and Fe(II)Fe(III) ratio in GRs

on the reduction rate of nitrate were investigated (Hansen et al 2001) It was

found that the rate of nitrate reduction to ammonium increased with increasing

Fe(II)Fe(III) ratio and decreased when exchanging a monovalent interlayer anion

(chloride) with a divalent anion (sulphate) The results suggest that for anionic

oxidants like nitrate Fe(II) within the hydroxide layer is available from the outside

basal planes and from the edges as well as through the interlayer under certain

conditions (Figure 42) However oxidants with different charge properties

(cations neutral molecules) may exhibit different affinities for the various reactive

Fe(II) sites present in GR

As the reactive sites are located inat the Fe(II)-Fe(III) hydroxide layers the rate of

reaction depends on the hydroxide layer area which can be accessed by the

oxidant If the oxidant can exchange with the interlayer anion reaction can take

place both at outer and inner surfaces of the GR particles and in total more

reactive sites are available for the reaction However it was found that nitrate

cannot penetrate the interlayer when carbonate or sulphate constitutes the

interlayer anions (Hansen amp Koch 1998) This agrees with the fact that the

interlayers have a lower affinity for monovalent anions than for divalent anions


(Miyata 1983) However when nitrate was forced into the interlayer by extracting

the interlayer sulphate through precipitation of barium sulphate outside the GR

particles the observed 40 fold increase in rate of nitrate reduction almost equalled

the increase in exposed surface area of the Fe(II)-Fe(III) hydroxide layers (Hansen

amp Koch 1998) From these observations it is expected that the rate of reaction

depends on the particular GR form the crystallite size and the ease with which an

oxidant can exchange with An- in the GR interlayer (Figure 42) Due to

electrostatic interactions we expect anions to be attracted to the positively charged

outer and inner surfaces to a higher degree than cations and neutral compounds If

this theory holds we may expect oxidants with similar intrinsic reactivity (similar

one-electron reduction potentials) to react in the following order anionic gt non-

charged gt cationic (Figure 43) granting that we do not normalise the rate

constants with respect to the amount of oxidant sorbed

Figure 42 Reaction of a probe compound at basal planes at edges and in the interlayer of GR

The hypothesis only holds in cases where the oxidants possess the same intrinsic

reactivities If the relative reactivities of the probe compounds differ greatly from

what would be expected when considering only their reduction potentials

70 Chapter 4

compound specific effects such as charge properties might explain this and the

relative reactivities may follow a pattern like the one depicted in Figure 43

Figure 43 Hypothetical plot of observed reaction rate constants for the reactions between

cationic neutral and anionic probe compounds and GR-SO4 assuming that the oxidant charge

controls its reactivity towards GR

In this work we investigated the reductive transformation of NACs by GR-SO4

Furthermore the effect of NAC charge on the rate of reaction and the possible

access to the internal reactive sites in GR-SO4 were assessed When quantifying

Fe(II) in GRs by means of acid digestion it is not possible to distinguish between

the reactive sites accessible from the outside (at the basal planes or at the edges) or

through the interlayer However we designed an indirect method to gain insight

into the relative importance of the various reactive sites by using a series of

structurally closely related compounds with different charge properties as ldquoreactive

probesrdquo Neutral and anionic probes were needed in order to access all Fe(II)

reactive sites According to our hypothesis cationic and non-charged oxidants

should provide information about the reactivity of the outer Fe(II) reactive sites in

GR whereas the anionic oxidants should provide information about the reactivity


of both outer and inner Fe(II) reactive sites We chose five nitro aromatic

compounds (NACs) - representing an important group of reducible organic

pollutants - as probe compounds (Figure 43) This class of compounds is not only

of great environmental concern but also comprises suitable model compounds for

studying redox reactions potentially relevant in the environment Moreover they

react readily with Fe(II) surface species associated with iron oxides or clay

minerals transforming them into well-defined easily detected products allowing

mass and electron balances to be established (Hofstetter et al 2003 Klausen et al

1995 Schultz amp Grundl 2000) Our main goals were to establish the rate law and

estimate the surface area-normalised reaction rates for the reaction of the probe

compounds with GR-SO4 in order to assess the importance of the Fe(II) reactive

sites accessible through the interlayer relative to the Fe(II) reactive sites accessible

at the outer surface in GR-SO4



strict anoxic conditions All chemicals were pa quality or better Methanolic stock

solutions (5 mM) of nitrobenzene (NB) 4-nitrotoluene (4-NT) 4-

chloronitrobenzene (4-CNB) and 4-nitrophenylacetic acid (4-NPA) were prepared

in deoxygenated methanol Several attempts to synthesize the cationic probe

compound 4-(NNN-trimethylammonium)-nitrobenzene failed and therefore the

study had to be carried out with only neutral and anionic oxidants The sulphate

GR form was chosen as it is the most stable form and thus the easiest to work

with in the lab

421 Synthesis of GR-SO4

GR-SO4 was synthesized by controlled air oxidation of an FeSO4 solution at a

constant pH of 700 according to the procedure given by Koch amp Hansen (1997)

The GR-SO4 suspension was washed with deoxygenated deionised water and

72 Chapter 4

separated on a folding filter redispersed in deoxygenated 25 mM Na2SO4(aq) in

order to stabilize the GR-SO4 and prevent it from transforming into magnetite

spontaneously Washing separation and redispersion of the GR-SO4 suspension

were conducted in an anoxic glove box (Coy Laboratory Products Inc) All

suspensions and solutions were deoxygenated by Ar-purging (999998 Ar

Carbagas)


The identity and purity of the GR-SO4 suspensions were examined by means of X-

ray diffraction measurements The XRD analyses were performed on a Scintag

XDS 2000 using Cu Kα radiation (45 kV 40 mA) Glycerol smears made

according to Hansen (1989) were scanned between 6 and 80 deg2θ with a scan speed

of 1 deg2θmin

423 Lyophilization and determination of specific surface area

Simple air-drying of the GR mineral in the glove box resulted in big flakes with

very low surface areas hence a more suitable lyophilization method was adopted

from Elsner et al (2004) The GR-SO4 suspensions were lyophilised using

Schlenk-type glassware The set-up consisted of a 1 L round bottom flask and a

200 mL glass finger connected by a crescent-shaped bridge equipped with an

evacuation outlet and a stopcock All ground joints and fittings were attached using

high-vacuum grease The washed and resuspended GR-SO4 suspensions were

filled into the glass finger and the freeze-drying apparatus was assembled and

closed before taking it out of the glove box The suspension was frozen by

carefully submerging the lower part of the glass finger into liquid nitrogen for a

few hours Subsequently the evacuation outlet was connected to a vacuum pump

by a metal hose Following a short evacuation of the metal hose the lyophilization

apparatus was evacuated for several minutes by gently opening the stopcock The

evacuation was terminated by closing the stopcock and disconnecting the vacuum

pump The apparatus position was now reversed by removing the glass finger from


and immersing the round bottom flask into liquid nitrogen As any other

lyophilization method this method depends on sublimation of the ice from the

frozen sample and its recondensation on a cool surface in this case the round

bottom flask Generally it took 1-2 d for the mineral to dry The apparatus was

disassemled in the glove box and the fine powder stored under anoxic conditions

The specific surface area (SSA) of GR-SO4 was determined by the BET multi-

point method using N2 adsorption (Brunauer et al 1938) Powder samples were

filled into sample burettes in the glove box and the generously greased stopcocks

closed Samples and burettes were evacuated prior to connecting them to the BET-

instrument (Sorptomatic 1990 Fisons)

424 Estimation of the one-electron reduction potential for 4-NPA

Kinetic experiments in 100 mL Viton stoppered and alu-crimp capped serum vials

were carried out under the exclusion of oxygen as described by Hofstetter et al

(1999) The homogeneous aqueous solutions contained 50 mM KH2PO4 buffer

(pH = 660) 5 mM Na2S redox buffer and 20 microM juglone (8-hydroxy-14-

naphthoquinone) added as deoxygenated 20 mM methanolic stock solution The

solutions were equilibrated at least one day prior to 4-NPA addition To start the

reaction 50 microM 4-NPA was added as deoxygenated 20 mM methanolic stock

solution The vials were agitated on a roller apparatus in the dark at 21ordmC Control

experiments were prepared similarly except for the addition of juglone At

different time intervals aqueous samples were withdrawn with a syringe and

collected in 18 mL HPLC vials containing 100 microL 1 M HCl The sample vials

were sealed with Teflon-coated silicone septa and plastic screw caps and vortexed

for 10 s The samples were stored at -20degC and analysed without further treatment

For comparison experiments with 4-NT were also conducted See Supporting

Information 71 for more information on the one-electron reduction potentials

74 Chapter 4

425 Kinetic experiments

All reactions took place at pH 84-86 where GR-SO4 tends to stabilize and buffer

itself Samples for Fe(II) and XRD analysis were withdrawn prior to reaction Due

to the fast reactions the experiments were conducted in 10 mL single-use

polyethylene syringes (BD Plastipak) in the glove box To start reaction 40-200

microL 5 mM methanolic stock solutions of NAC were quickly added to 10 mL GR-

SO4 suspension (1-12 mM Fe(II)GR) washed and resuspended in 25 mM

Na2SO4(aq) A Teflon filter (25 mm x 02 microm BGB Analytik) was quickly

mounted on the tip of the syringe and the syringe was vigorously shaken between

sampling At different time intervals filtered suspension samples were collected in

18 mL HPLC vials The HPLC vials were sealed with Teflon-coated silicone septa

and plastic screw caps The samples were stored at -20degC and analysed without

further treatment Absorption of NAC in the syringe and in the Teflon filter

evaluated in blank experiments with NAC added to 25 mM Na2SO4(aq) was found

to be negligible


Initial total and aqueous Fe(II) were determined using a modified phenanthroline

method (Fadrus and Maly 1975) In order to determine [Fe(II)aq] and [Fe(II)total] 1

mL filtered (022 microm) and 1 mL unfiltered GR-SO4 suspension samples were

withdrawn and each treated with 18 mL 01 M HCl for at least 30 min From these

acid digests 01 mL was added to 05 mL Fe(II)-reagent and 19 mL deionised

water (DIW) added up The Fe(II) content in GR-SO4 was estimated as the

difference [Fe(II)GR] = [Fe(II)total] - [Fe(II)aq] The NACs and their corresponding

intermediates and products formed during reduction by GR-SO4 were quantified by

reversed-phase HPLC Separation was performed on a LiChrospher 100 RP-18 (5

microm 125 times 4 mm ID) reversed-phase column coupled with a LiChroCART 100 RP-

18 (4 times 4 mm ID) precolumn Analytical conditions were isocratic and the eluent

consisted of 10 mM hydroxylammonium chloride in various DIWCH3OH

mixtures (vv 3565 and pH 70 for 4-NT and 4-CNB 955 and pH 60 for


4-NPA) The injection volume was 20 microLand the flow-rate 10 mLmin HPLC

analyses were performed using a Gynkotek High Precision Pump M480 Gynkotek

Gina 50 autosampler and a diode array UV detector (340s Gynkotek) UV-VIS

detection was carried out at the wavelengths of maximum absorption for the

various nitro aromatic and aniline analytes


431 Productformation and reaction kinetics

The reduction of the aromatic nitro group occurs via nitroso- and hydroxylamino-

intermediates where 2 electrons are transferred in each reaction step (Figure 44)

0 --0 H OH H H --0 N N N N

2e- 2H+ H20 + 2e-~ 2e- 2H+ H20

~ ~ R R R

Nitro benzene Nitrosobenzene Hydroxylamine Aniline

Figure 44 Reductive transfonnation pathway of NA Cs

Thus in order to reduce 1 Ar-N02 completely to Ar-NH2 6 electrons

corresponding to 6 mol Fe(II) are needed As magnetite was the major iron phase

formed during reaction (XRD results not shown) we assume the following

reaction stoichiometry

The aniline product was not formed at the same rate as the nitro compound

degraded which is consistent with the detection of early eluting hydroxylamine

intermediates during the course of the reaction (Figure 45a amp 45c) No traces of

76 Chapter 4

nitrosobenzene intermediates or side products such as azoxy- azo- or

hydrazobenzene were found In Figure 45 pseudo 1 order kinetic plots and ln

[Ar-NO2]t[Ar-NO2]0) versus time plots for the neutral probe compounds 4-CNB

and 4-NT are shown as examples The plots for NB and 4-NPA look similar

Figure 45 a Concentration versus time plots for reaction of GR-SO4 with 4-CNB ([Fe(II)GR]0 =

126 mM [4-CNB]0 = 30 microM) b ln [Ar-NO2]t[Ar-NO2]0) versus time plots for reaction of GR-

SO4 with 4-CNB ([Fe(II)GR]0 = 126 mM + [4-CNB]0 = 30 microM [Fe(II)GR]0 = 63 mM + [4-

CNB]0 = 50 microM) c Concentration versus time plots for reaction of GR-SO4 with 4-NT

([Fe(II)GR]0 = 131 mM [4-NT]0 = 20 microM) d ln [Ar-NO2]t[Ar-NO2]0) versus time plots for

reaction of GR-SO4 with 4-NT ([Fe(II)GR]0 = 131 mM [4-NT]0 = 20 microM [Fe(II)GR]0 = 131

mM [4-NT]0 = 50 microM) The hydroxylamino intermediate shown in microM equals the deficit in the

mass balance and in abs equals the detector response (peak area) Solid lines represent 1 order

kinetic fits (a amp c) and ln [Ar-NO2]t[Ar-NO2]0) versus time fits (d) whereas symbols and dotted

lines represent actual data


At intial Fe(II)GR concentrations in large excess of initial Ar-NO2 concentration

we found a pseudo 1 order rate law for the degradation of Ar-NO2 by GR-SO4

[ ] [ ] [ b 2

a GR

2 ArNOFe(II) ArNOsdotsdot=minus k

dtd ]

where a = 1 b = 1 and the observed pseudo 1 order rate constant kobs = k middot

[Fe(II)GR] At high [Fe(II)GR]0[Ar-NO2]0 ratios the nitro compound was

transformed completely into the aniline product within reaction duration and the

degradation curves of the nitro compound were shaped according to pseudo 1

order kinetics (data points follow solid line in Figure 45a) In some instances ie

at low [Fe(II)GR]0[Ar-NO2]0 ratios the reactions did not follow pseudo 1 order

kinetics for the whole duration of reaction (data points deviate from solid line in

Figure 45c) Hence in order to allow comparison all the pseudo 1 order rate

constants were calculated as initial rates (ie max first two half-lives) from linear

fits of (time ln [Ar-NO2]t[Ar-NO2]0)-plots (Figure 45b amp 45d) Surface area-

normalised pseudo 1 order rate constants are shown in Table 41

Tabl

e 4

1 S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

4-n

itrot

olue

ne (4

-NT)

4-

chlo

roni

trobe

nzen

e (4

-CN

B) a

nd 4

-nitr

ophe

nyla

cetic

aci

d (4

-NPA

) by

GR

-SO

4

Exp

erim

ent

Age

GR

(d

) [F

e(II

) GR] 0

(mM

) [N

AC

] 0 (micro

M)

[Fe(

II) G

R] 0

[N

AC

] 0∆[

ArN

O2]

(microM

) af b

k obs

(s-1

) ck o

bs (s

-1middotm

-2middotL

) d

GR

-SO

4 + 4

-NT

3 1

103

20

51

5

109

54

5

7

65middot1

0-46

95middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

50

20

6

174

34

8

7

41middot1

0-46

74middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

10

0 10

3

214

21

4

2

63middot1

0-42

39middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

55

18

7

177

32

2

4

21middot1

0-43

83middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

10

2 10

1

165

16

2

2

37middot1

0-42

15middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

25

412

9

7 38

8

4

82middot1

0-44

38middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

46

224

9

9 21

5

6

37middot1

0-45

79middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

100

103

13

7

137

196

middot10-4

178

middot10-5

GR

-SO

4 + 4

-NT

2 15

1

31

20

655

5

4 27

0

6

74middot1

0-44

82middot1

0-5

GR

-SO

4 + 4

-NT

2 15

1

31

50

262

9

7 19

4

5

89middot1

0-44

21middot1

0-5

GR

-SO

4 + 4

-NT

4 2

126

0 50

25

2 49

1

982

110

middot10-2

817

middot10-5

GR

-SO

4 + 4

-NT

4 2

630

50

12

6 42

6

852

186

middot10-3

276

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

126

0 30

42

0 29

0

967

925

middot10-3

687

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

630

50

12

6 38

0

760

136

middot10-3

202

middot10-5

GR

-SO

4 + 4

-NPA

2

2 12

60

40

315

371

92

8

5

96middot1

0-34

43middot1

0-5

GR

-SO

4 + 4

-NPA

2

2 6

30

45

140

273

60

7

1

09middot1

0-31

62middot1

0-5

a A

mou

nt o

f NA

C re

duce

d by

GR

-SO

4 at r

eact

ion

term

inat

ion

b F

ract

ion

of in

itial

ly a

dded

NA

C tr

ansf

orm

ed b

y G

R-S

O4 a

t rea

ctio

n te

rmin

atio

n c

Pse

udo

1

orde

r rat

e co

nsta

nts c

alcu

late

d as

initi

al ra

tes

ie m

ax f

irst t

wo

half-

lives

d S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

The

are

a of

GR

-SO

4 per

L

su

spen

sion

was

cal

cula

ted

as frac14

middot[Fe

(II)

GR] 0middot

600

gmiddotm

ol-1

middot71

2 m

2 middotg-1


432 Comparison of rate constants for the different NACs

Even for NACs holding very different one-electron transfer reduction potentials

( ) their reactivities differed only little in Fe(II)-Fe(III) systems such as the

Fe(II)goethite system (slope a = 06 for linear free energy relationship (LFER)

between k

1hE

obs and Hofstetter et al 1999) and the Fe(II)magnetite system

(LFER slope a = 034 Klausen et al 1995) When considering only the for the

reductive transformation reactions of the NACs applied in this study (Table 42)

we expect the surface area-normalised pseudo 1 order rate constants for the

reduction of the NACs to follow the order 4-CNB gt NB gt 4-NT gt 4-NPA Based

on log k

1hE

1hE

obs versus correlations obtained in Fe(II)goethite systems we expect 4-

CNB to react 6 times faster than 4-NPA (Hofstetter et al 1999)

1hE

Table 42 One-electron reduction potentials and relative reactivities in Fe(II)-magnetite and GR-

SO4 systems for the nitro aromatic probe compounds

Compound pKa Eh1

acute (mV) krel (Fe3O4) cd krel (GR-SO4) ce

4-Chlornitrobenzene - -450 a 122 148

Nitrobenzene - -486 a 1 1

4-Nitrotoluene - -500 a 057 176

4-Nitrophenylacetic acid 385 -543 b - 123 a Values from references cited in Hofstetter et al 1999 b Estimated at pH 660 using a LFER (Hofstetter et al 1999 see Supporting Information 71) c Reactivity relative to NB d Values from Klausen et al 1995 e Values from this work

A comparison of the relative rate constants of the NACs obtained for their

transformation by GR-SO4 (this work) and by magnetite (Klausen et al 1995)

shows that they do not differ significantly from each other in any of the mineral

systems (Table 42) When considering charge effects we expect the anionic probe

compounds to react faster with GR-SO4 than the neutral probe compounds

provided that they sorb preferentially within the GR-SO4 interlayers and that Fe(II)

in the interlayers are equally or more reactive than external Fe(II) sites Still the

surface area-normalised kobs values obtained for NB 4-NT 4-CNB and 4-NPA

under various experimental conditions did not differ significantly from each other

80 Chapter 4

(Figure 46 Table 41) The anionic probe compound 4-NPA did not react

significantly faster with GR-SO4 than the neutral probe compounds NB 4-NT and

4-CNB This may indicate that 4-NPA does not significantly interact with reactive

Fe(II) sites in the interlayer Alternatively the negative charge carried by 4-NPA

may be compensating for the lower intrinsic reactivity as compared to the neutral

probe compounds thus explaining the similarity in rate constants for 4-NPA and

the neutral probe compounds Finally other factors than intrinsic reactivity or

charge of the probe compounds such as regeneration of reactive sites or formation

of the magnetite phases may control the overall reactivity of the system

Figure 46 Actual plot of surface area-normalised pseudo 1 order rate constants for the reactions

between neutral and anionic probe compounds and GR-SO4

In heterogeneous reactions mass transfer in bulk solution becomes the rate-

limiting step when the surface reaction is much faster than the diffusion of the

reacting species to the reactive surface In cases where mass transfer controls the

overall rate of reaction the observed pseudo 1 order rate constant kobs ge kLmiddota

where kL is the calculated mass transfer coefficient (mmiddots-1) and a is the ratio of the

external (geometric) specific surface area to volume of solution (m-1) (see


Supporting Information 72) Mass transfer controlled reactions between GR-SO4

particles and the NACs in bulk solution would explain the similar pseudo 1 order

rate constants obtained for the NACs in this work However when comparing our

estimates of kLmiddota with kobs (see Supporting Information 72) we found that the rates

of mass transfer for all 4 NACs exceed the observed rate constants by at least 3

orders of magnitude at every initial Fe(II)GR concentration Thus the reactions of

the given NACs with GR-SO4 are not likely to be mass transfer limited under the

experimental conditions applied here

Since mass transfer in bulk solution does not control the reaction between GR-SO4

and NACs the overall reaction rate may be surface saturation controlled During

the reductive transformation of NACs not only the parent compound but also

various intermediates forming may compete for the restricted number of reactive

sites present in GR-SO4 This competition may constitute the rate limiting step in

the overall reactivity and may even be enhanced if the number of reactive sites is

depleted during reaction However surface saturation kinetics would not explain

the unexpected similarity of the pseudo 1 order rate constants obtained for the

NACs but it could explain the bent curves observed at low initial Fe(II)GR

concentrations (Figure 45d) The kinetically deviating cases at low [Fe(II)GR]0

were evaluated according to Langmuir-Hinshelwood kinetics (see Supporting

Information 72) Our experimental data did not agree with the Langmuir-

Hinshelwood rate law for any of the NACs (regression results not shown)

Simplifying the rate law by assuming that the aniline product or the

hydroxylamino intermediate or both did not compete for the reactive sites did not

improve the regression Thus the Langmuir-Hinshelwood model cannot explain

the deviations from pseudo 1 order kinetics observed at [Fe(II)GR]0 in our GR-SO4

system and it does not suffice as the correct reaction mechanism nor as the rate-

limiting step

82 Chapter 4

If the adsorption follows a saturation-type sorption isoterm (eg Langmuir) the

sorbate (oxidant) concentration at the surface will vary non-linearily with the total

amount of oxidant added This dependence will have to be taken into account when

establishing rate laws for the heterogeneous reactions and when testing the

hypothesis that the reaction rates depend on the sorbed concentration of the

oxidants However at the high reaction rates observed here we could not quantify

sorption Since the measured initial NAC concentrations corresponded to the

nominal amount of NAC added we assume that transformation and not sorption

was responsible for the consumption of NAC

433 Factors influencing the reaction rate

In general numerous compound- and system-specific factors influence redox

reactions One very important factor is pH which influences the speciation of

dissociable compounds as well as the stability of GR and the formation of other

iron minerals in the system pH has a strong impact on the sorption and therefore

the availability of ionisable oxidants such as carboxylic acids At pH ~ 84 where

our experiments were conducted 4-NPA (pKa = 385) is completely dissociated

Our experiments conducted with GR-SO4 and NB showed that pH was constant

during reaction In addition solution pH has an effect on the surface speciation

From other Fe(II)-Fe(III) systems such as Fe(II) surface species associated with

iron oxides or clay minerals it is well-known that other reactive hydroxylated

Fe(II)-Fe(III)-hydroxo surface complexes can form at higher pH (Charlet et al

1998 Liger et al 1999) Williams amp Scherer (2001) reported a small decrease (5

fold) in the reduction rate of chromate with GR-CO3 when increasing pH from 50

to 90 This decrease may be due to the alternating speciation of the Fe(II) surface

sites on GR-CO3 and of chromate in solution (pKa (H2CrO4) = 08 pKa (HCrO4ndash) =

65) when raising pH (Williams amp Scherer 2001) In contrast other studies have

reported small increases (4 fold) in the reduction rates of nitrate and

trichloroethene with GR-SO4 when increasing pH from 71 to 84 and from 68 to

101 respectively (Koch amp Hansen 1997 Lee amp Batchelor 2002b)


In this work all experiments were carried out in the presence of 25 mM

Na2SO4(aq) in order to minimize GR-SO4 dissolution and spontaneous

transformation into magnetite Preliminary results from experiments conducted

with NB show that the bulk concentration of Na2SO4 has only a very small impact

on the rate ie increasing the concentration of Na2SO4(aq) in the GR-SO4

suspension from 5 to 25 mM reduced the observed rate constant by a factor of 2

At Na2SO4 concentrations above 25 mM the effect leveled off and therefore

[Na2SO4] = 25 mM was chosen for this work Portions of the same GR-SO4

suspension were used for kinetic experiments over a period of two weeks No

significant aging effects eg rate constants decreasing as a function of GR age

were observed within this time frame

434 Comparison with rate constants obtained for other Fe(II) containing

mineral systems

A recent study compared the reactivity of various Fe(II) containing iron mineral

systems towards organic probe compounds representing different classes of

pollutants (Elsner et al 2004) The reductive transformation of 4-CNB was

investigated for the Fe(III) minerals goethite (α-FeOOH) lepidocrocite (γ-

FeOOH) and hematite (α-Fe2O3) as well as for the Fe(II)-Fe(III) oxide magnetite

(Fe3O4) All experiments were conducted in the presence of 1 mM dissolved Fe(II)

at pH 72 As seen from the surface area-normalised pseudo 1 order rate constants

in Figure 47 the reduction of 4-CNB by the Fe(II)-amended goethite

lepidocrocite and magnetite systems was up to 40 times faster than its reduction by

GR-SO4 The reduction rate obtained for the Fe(II)hematite system was only

slightly higher than the rate for the blank containing no iron mineral but aqueous

Fe(II) solely

84 Chapter 4

Figure 47 Surface area-normalised pseudo 1 order rate constants for the degradation of 4-CNB

by GR-SO4 (open square this work) and various Fe(II) containing mineral systems (solid circles

Elsner et al 2004) Experimental conditions applied by Elsner et al 1 mM aqueous Fe(II) pH

72 25 m2 mineral surface areaL GR-SO4 = green rust sulphate α-FeOOH = goethite Fe3O4 =

magnetite γ-FeOOH = lepidocrocite α-Fe2O3 = hematite

The experiments with GR-SO4 in our study were carried out at pH 84 whereas the

experiments comprising the other systems in Figure 47 were conducted at pH 72

As the reactivity of GR is expected to increase with pH (Lee amp Batchelor 2002b

Koch amp Hansen 1997) the lower of GR-SO4 compared to other Fe(II) systems

cannot be explained by differences in pH values GR-SO4 might just contain fewer

or less reactive surface sites than Fe(II)-amended goethite lepidocrocite and

magnetite suspensions These findings contrast those of other studies which found

higher surface area-normalised pseudo 1 order rate constants for dechlorination

reactions for GR-SO4 than for magnetite (Lee amp Batchelor 2002a amp 2002b Elsner

et al 2004) The different reactivity orders of the Fe(II)-bearing minerals found

for chlorinated aliphatics and nitro aromatics suggest that effects other than pH and


the intrinsic reduction potentials of the reacting species play a role for the

reactivity of these Fe(II)-bearing minerals

435 Depletion of reactive sites

Assuming that the platy hexagonal GR-SO4 crystals hold an average width of 1 microm

and an average particle thickness of 35 nm (Hansen amp Koch 1998) the ratio of

outer surface area to total surface area AouterAtotal ~ 131 (see Supporting

Information 73) This means that only 3 of the total surface area in GR-SO4 is

available at the external surface Thus as the interlayer sulphate in GR-SO4 is not

readily exchanged with the anionic NAC applied we conclude that 4-NPA and

other NACs only react with the Fe(II) sites at the external GR-SO4 surface In

Table 43 the actual amounts of NAC reduced by GR-SO4 during reaction is

compared with the amount of NAC which theoretically can be reduced by the

initial amount of external reactive Fe(II) sites in GR-SO4 at AouterAtot ~ 131

Table 43 The actual amounts of NAC reduced by GR-SO4 during reaction ∆[NAC]act

compared with the amount of NAC which stoichiometrically should be reduced by the initial

amount of external reactive Fe(II) sites in GR-SO4 ∆[Ar-NO2]theory (calculated as

[Fe(II)GR]0(31middot6) assuming an even distribution of Fe(II) throughout the GR-SO4 structure)

Calculated for [NAC]0 ~ 50 microM

[Fe(II)GR]0 (mM)

∆[Ar-NO2]theory(microM)

∆[4-NT]act (microM)

∆[4-CNB]act (microM)

∆[4-NPA]act (microM)

103 55 174 177 99

63 339 426 380 273

As seen in Table 43 the actual amounts of NAC reduced by GR-SO4 during

reaction are in most cases higher than the amount of NAC which should be

reduced at the given [Fe(II)GR]0 according to reaction stoichiometry This indicates

that new external reactive sites were regenerated eg the Fe(III) phases produced

peel off the GR surface exposing new Fe(II) sites or that outermost internal

86 Chapter 4

reactive sites in close vicinity to the edges are available for reaction as well Lee

and Batchelor (2000b) also found the experimentally observed reduction capacity

of GR-SO4 for chlorinated ethylenes to be 2-3 orders of magnitudes lower than the

estimated reduction capacity including all Fe(II) in GR-SO4

At low initial Fe(II)GR concentrations only a fraction of NAC was reduced within

the reaction time observed (Figure 45c) even though there was stoichiometric

excess of Fe(II)-GR present The fraction of initial Ar-NO2 reduced by GR-SO4 at

reaction termination decreased as [Fe(II)GR]0 decreased (Table 41) and was

accompanied by a change in apparent rate laws with time (compare Figures 45b amp

d) In order to explain these observations we propose that the NACs react only at

external reactive Fe(II) sites and that the regeneration of new external reactive sites

is much slower than the reduction of NAC by GR-SO4 Thus the fast reduction of

NAC taking place at the external reactive sites represents the pseudo 1 order

behaviour whereas depletion of external reactive sites and their slow regeneration

are represented by the second bent part of the (time ln [Ar-NO2]t[Ar-NO2]0)-

curves deviating from pseudo 1 order kinetics Hence at low [Fe(II)GR]0 the

regeneration of reactive sites will eventually control the overall reaction rate

Depletion of available Fe(II) was also observed during the fast reduction of

chromate by GR-CO3 when the initial chromate concentration was increased or

when the GR-CO3 suspension was respiked with chromate repeatedly (Williams amp

Scherer 2001)

436 The role of external and internal reactive sites

It is reasonable to assume that GRs hold adsorption properties similar to other

layered double hydroxides such as hydrotalcites The sorption of 246-

trinitrophenol (TNP) and 245-trichlorophenol (TCP) on chloride and carbonate

intercalated hydrotalcites (HT-Cl = Mg3Al(OH)8ClmiddotyH2O HT-CO3 =

Mg6Al2(OH)16CO3middotyH2O) has been investigated (Hermosin et al 1993 Ulibarri et

al 1995 Ulibarri et al 2001) The authors found that the adsorption of TCP on


HT-CO3 was very low and that TCP adsorbs only on the external surface sites of

HT-CO3 (Hermosin et al 1993) Furthermore is was reported that the adsorption

of TNP on HT was dramatically affected by the nature of the interlayer anion ie

the adsorption of TNP was considerably higher on HT-Cl than on HT-CO3

(Ulibarri et al 2001) For HT-Cl interlayer anion exchange of chloride with TNP

was detected by XRD analysis and an expansion of the characteristic basal d003

spacing from 79 Ǻ to 132 Ǻ confirmed the presence of TNP in the HT interlayer

(Ulibarri et al 1995) Collating the results reported for HTs with GRs it is not

likely that the divalent SO42- in GR-SO4 is exchanged with the monovalent 4-NPA

Chacirctelet et al (1996) investigated the adsorption of mono- and divalent anions

onin the outer and inner adsorption sites in HT by varying the zetapotential with

pH in the presence of various electrolytes The authors found that SO42- adsorbs on

the external HT surfaces by formation of outer-sphere complexes whereas chloride

hardly adsorbed on HT Moreover it was reported that the adsorption of sulphate

onto HT was not strongly affected by the presence of chloride while sulphate on

the contrary inhibited the adsorption of chloride on HT Studies applying

spectroscopic analyses have investigated the sorption of oxyanions at external and

internal GR-SO4 surfaces (Myneni et al 1997 Randall et al 2001) Selenate was

adsorbed only on the outer GR-SO4 surface when added after GR formation

whereas it was primarily coprecipitated into the interlayer when present during GR

formation Thus for selenate its presence during GR formation is a prerequisite of

its incorporation in the GR interlayer Selenate is readily reduced by GR-SO4 and

the rates of reduction of coprecipitated selenate were very similar to the reduction

rates of selenate adsorbed at the outer GR surface (Myneni et al 1997) This

finding suggests that the outer and inner reactive Fe(II) sites in GR-SO4 hold

similar reactivities

Results based on electron microscopy reported that the reduction of uranyl took

place primarily at the edges of hexagonal GR-SO4 particles (OrsquoLoughlin et al

2003a) In another recent study XRD characterization of the GR-SO4 crystals

88 Chapter 4

during reaction with trichloroacetate (TCA) indicated that TCA did not enter the

GR-SO4 interlayer during reaction (Chapter 5 this work) The average GR-SO4

particle thickness perpendicular to the basal plane was constant during reaction

implying that TCA reacts only at the edges and not at the basal planes Assuming

that the platy hexagonal GR-SO4 crystals hold an average width of 1 microm and an

average particle thickness of 35 nm (Hansen amp Koch 1998) the ratio of edge

surface area to outer surface area is AedgeAouter ~ 130 (see Supporting Information

73) Hence only 3 of the outer surface area in GR-SO4 is available at the edges

Once more the regeneration of new external reactive sites is strongly inferred as

the actual amounts of NAC reduced by GR-SO4 during reaction are much higher

than the amount of NAC which may be reduced by the reactive edge sites present

initially Assuming that the NACs react at the edges only and if employing the

AedgeAouter in the estimation of the rate constants the surface area-normalised

pseudo 1 order rate constants for GR-SO4 would be 30 times higher than the rate

constants depicted in Figure 47 Thus the reactivity of GR-SO4 normalised to its

reactive surface area is higher than the reactivity normalised to its outer surface

area determined by the BET method (N2 adsorption)

The reduction of chromate has been examined in the presence of all the common

GR forms (Bond amp Fendorf 2003 Loyaux-Lawniczak et al 1999 Loyaux-

Lawniczak et al 2000 Williams amp Scherer 2001) The results reported by Bond

amp Fendorf (2003) confirm that not only the surface area of GR but also the

interlayer spacing (interlayer anion size) and interlayer anion charge play an

important role for the reaction rate Hence it follows that coordination (size) and

charge of the oxidant determine its access to the internal sites in GRs

The results obtained for all 4 NACs support what has been reported for nitrate and

TCA At [Fe(II)GR]0 = 2-10 mM and [NO3-]0 = 143 mM pseudo 1 order rate

constants for the reduction of nitrate by GR-SO4 were 158middot10-7 s-1middotm-2middotL (Hansen

et al 2001) This reaction rate increased 40 times by adding barium nitrate instead


of sodium nitrate thereby precipitating the interlayer sulphate as barium sulphate

and enhancing access to the interlayer Though barium addition changes the GR-

SO4 system dramatically it indicates the importance of interlayer anion exchange

(Hansen amp Koch 1998) The rate constant reported for nitrate (no barium added) is

100-1000 smaller than the rate constants obtained for the NACs in this work

Moreover the reaction kinetics for nitrate did not deviate from pseudo 1 order

kinetics At [Fe(II)GR]0 = 025-104 mM and [TCA]0 = 50 microM-1 mM pseudo 1

order rate constants for the reduction of TCA by GR-CO3 or GR-SO4 were 65middot10-7

s-1middotm-2middotL (Chapter 5 this work) The rate constant for TCA is 10-1000 smaller than

the rate constants for the NACs and the reaction kinetics for TCA did not deviate

from pseudo 1 order kinetics This suggests that the overall reductive

transformation of slowly reacting oxidants such as nitrate and TCA is not

controlled by the rate of regeneration of external Fe(II) reactive sites Altogether

the results reported for selenate chromate and nitrate clearly demonstrate that

these anionic oxidants react primarily with external reactive sites in GR-SO4 Only

under certain conditions ie adding the oxidant prior to GR-SO4 formation or

extracting the interlayer sulphate through precipitation with barium outside the

GR-SO4 particles do the oxidants have access to the interlayer Our findings

suggest that both the neutral and anionic nitro aromatic probe compounds applied

here also react exclusively with the external reactive sites in GR-SO4 Supposedly

the neutral and monovalent charge states of the NACs hinder their access to the

GR-SO4 interlayer A divalent anionic nitro aromatic probe compound might

exchange with the interlayer sulphate more readily and gain access to the inner

Fe(II) reactive sites in GR-SO4 only divalent anionic NACs are not commercially

available

44 Conclusions

This work demonstrates that NACs are completely reduced to their corresponding

anilines by GR-SO4 The surface area-normalised pseudo 1 order rate constants

obtained for the reduction of the neutral and anionic NACs by GR-SO4 under

90 Chapter 4

various experimental conditions did not differ significantly from each other despite

their different charges Neither mass transfer control nor surface saturation kinetics

could account for the similarity of the pseudo 1 order rate constants obtained for

the NACs These observations suggest that the anionic NACs do not have an

enhanced access to inner or outer Fe(II)-GR reactive sites as compared to the

neutral NACs Based on our estimations of the molecular sizes of the NACs we

propose that the charge and not the size of the NACs controls their access to the

internal reactive sites in GRs Hence the reaction between NAC and GR-SO4 takes

place primarily at the external reactive Fe(II) sites This work further demonstrated

that the reduction of the NACs by GR-SO4 only followed pseudo 1 order kinetics

throughout the whole reaction at high initial Fe(II)GR concentrations At low initial

Fe(II)GR concentrations the NACs were not reduced completely within the reaction

time observed though according to reaction stoichiometry the total Fe(II)-GR

present should be sufficient to reduce the whole amount of NAC This means that

at some point during the reaction the external reactive Fe(II) sites were depleted

and the regeneration of new external reactive sites was much slower than the

reduction of the NACs by GR-SO4 The reduction of 4-CNB by GR-SO4 reported

here was 10-100 times slower than its reduction by other Fe(II)-Fe(III) systems

such as goethite lepidocrocite and magnetite suspensions amended with Fe(II)

(Elsner et al 2004)

The results obtained in this work infer that under natural geochemical conditions

where GR-SO4 presumably forms in low concentrations the rate of regeneration of

external Fe(II) reactive sites may control the overall reductive transformation of

fast reacting pollutants by GR-SO4 Thus not only abiotic processes such as

interchanging redox conditions created by water level alterations but also the direct

microbial formation through Fe(III)-reducing bacteria may govern the formation of

GRs and the renewal of external Fe(II) reactive sites in GRs This holds both for

natural systems like iron-rich suboxic soils and sediments as well as engineered


systems like permeable reactive barriers of zero-valent iron implemented for on-

site remediation of organic and inorganic contaminants

Acknowledgments

We would like to thank Henrik T Andersen for performing the NB kinetic experiments and

Hanne Nancke-Krogh for technical assistance in the laboratory

References

Al-Agha MR Burley SD Curtis CD Esson J (1995) Complex cementation textures and authigenic mineral assemblages in recent concretions from the Lincolnshire Wash (east coast UK) driven by Fe(0) to Fe(II) oxidation Journal of the Geological Society 152 157-171 Bernal JD Dasgupta DR Mackay AL (1959) The oxides and hydroxides of iron and their structural inter-relationships Clay Minerals Bulletin 4 15-30 Bond DL Fendorf S (2003) Kinetics and structural constraints of chromate reduction of green rusts Environmental Science and Technology 37 2750-2757 Brunauer S Emmett PH Teller E (1938) Adsorption of gases in multimolecular layers Journal of American Chemical Society 60 309-319 Charlet L Silvester E Liger E (1998) N-compound reduction and actinide immobilisation in surficial fluids by Fe(II) The surface FeIIIFeIIOH0 species as major reductant Chemical Geology 151 85-93 Chacirctelet L Bottero JY Yvon J Bouchelaghem A (1996) Competition between monovalent and divalent anions for calcined and uncalcined hydrotalcite anion exchange and adsorption sites Colloids and Surfaces A Physicochemical and Engineering Aspects 111 167-175 Chaudhuri SK Lack JG Coates JD (2001) Biogenic magnetite formation through anaerobic biooxidation of Fe(II) Applied and Environmental Microbiology 67 2844-2848 Cui D Spahiu K (2002) The reduction of U(VI) on corroded iron under anoxic conditions Radiochemica Acta 90 623-628 Elsner M Haderlein SB Schwarzenbach RP (2004) Reactivity of Fe(II)-bearing minerals towards reductive transformation of organic contaminants Environmental Science and Technology 38 799-807 Erbs M Hansen HCB Olsen CE (1999) Reductive dechlorination of carbon tetrachloride using iron(II)iron(III)-hydroxide-sulphate (green rust) Environmental Science and Technology 33 307-311 Fadrus H Maly J (1975) Suppression of iron(III) interference in the determination of iron(II) in water by the 110-phenanthroline method The Analyst 100 549-554 Fredrickson JK Zachara JM Kennedy DW Dong H Onstott TC Hinman NW Li S

92 Chapter 4 (1998) Biogenic iron mineralization accompanying the dissimilatory reduction of hydrous ferric oxide by a groundwater bacterium Geochimica et Cosmochimica Acta 62 3239-3257 Geacutenin JMR Bourrieacute G Trolard F Abdelmoula M Jaffrezic A Refait Ph Maitre V Humbert B Herbillon A (1998) Thermodynamic equilibria in aqueous suspensions of synthetic and natural Fe(II)-Fe(III) green rusts Occurrences of the mineral in hydromorphic soils Environmental Science and Technology 32 1058-1068

Geacutenin JMR Olowe AA Benbouzid-Rollet ND Prieur D Confente M Resiak B (1991) The simultaneous presence of green rust 2 and sulfate reducing bacteria in the corrosion of steel sheet piles in a harbour area Hyperfine Interactions 69 875-878 Glasauer S Weidler PG Langley S Beveridge TJ (2003) Controls on Fe reduction and mineral formation by a subsurface bacterium Geochimica et Cosmochimica Acta 67 1277- 1288 Hansen HCB (1989) Composition stabilization and light absorption of Fe(II)Fe(III) hydroxycarbonate (green rust) Clay Minerals 24 663-669 Hansen HCB Borggaard OK Soslashrensen J (1994) Evaluation of the free energy of formation of iron(II)iron(III)-hydroxidesulphate (Green Rust) and its reduction of nitrite Geochimica et Cosmochimica Acta 58 2599-2608 Hansen HCB Guldberg S Erbs M Koch CB (2001) Kinetics of nitrate reduction by green rusts ndash effects of interlayer anion and Fe(II)Fe(III) ratio Applied Clay Science 18 81-91 Hansen HCB Koch CB (1998) Reduction of nitrate to ammonium by sulphate green rust Activation energy and interlayer reaction mechanism Clay Minerals 33 87-101 Hansen HCB Koch CB Nancke-Krogh H Borggaard OK Soerensen J (1996) Abiotic nitrate reduction to ammonium Key role of green rust Environmental Science and Technology 30 2053-2056 Hansen HCB Poulsen IF (1999) Interaction of synthetic sulphate green rust with phosphate and the crystallization of vivianite Clays and Clay Minerals 47 312-318 Hansen HCB Taylor RM (1991) The use of glycerol intercalates in the exchange of CO3

2- with SO4


Heasman DM Sherman DM Ragnarsdottir KV (2003) The reduction of aqueous Au3+ by sulfide minerals and green rust phases American Mineralogist 88 725-738 Hermosin MC Pavlovic I Ulibarri MA Cornejo J (1993) Trichlorophenol adsorption on layered double hydroxide a potential sorbent Journal of Environmental Science and Health A28 1875-1888 Hofstetter TB Heijmann CG Haderlein SB Holliger C Schwarzenbach RP (1999) Complete reduction of TNT and other (poly)nitroaromatic compounds under iron-reducing subsurface conditions Environmental Science and Technology 33 1479-1487 Hofstetter TB Schwarzenbach RP Haderlein SB (2003) Reactivity of Fe(II) species associated with clay minerals Environmental Science and Technology 37 519-528


Klausen J Troumlber SP Haderlein SB Schwarzenbach RP (1995) Reduction of substituted nitrobenzenes by Fe(II) in aqueous mineral suspensions Environmental Science and Technology 29 2396-2404 Koch CB Hansen HCB (1997) Reduction of nitrate to ammonium by sulphate green rust Advances in GeoEcology 30 373-393 Kukkadapu RK Zachara JM Smith SC Fredrickson JK Liu C (2001) Dissimilatory bacterial reduction of Al-substituted goethite in subsurface sediments Geochimica et Cosmochimica Acta 65 2913-2924 Lee W Batchelor B (2002a) Abiotic reductive dechlorination of chlorinated ethylenes by iron- bearing soil minerals 1 Pyrite and magnetite Environmental Science and Technology 36 5147- 5154 Lee W Batchelor B (2002b) Abiotic reductive dechlorination of chlorinated ethylenes by iron-bearing soil minerals 2 Green rust Environmental Science and Technology 36 5348- 5354 Liger E Charlet L Van Cappellen P (1999) Surface catalysis of uranium (VI) reduction by iron(II) Geochimica et Cosmochimica Acta 63 2939-2955 Loyaux-Lawniczak S Refait Ph Ehrhardt J Lecomte P Geacutenin JMR (2000) Trapping of Cr by formation of ferrihydrite during the reduction of chromate ions by Fe(II)-Fe(III) hydroxysalt green rusts Environmental Science and Technology 34 438-443 Loyaux-Lawniczak S Refait Ph Lecomte P Ehrhardt J Geacutenin JMR (1999) The reduction of chromate ions by Fe(II) layered hydroxides Hydrology and Earth System Sciences 3 593-599 Mendiboure A Schoumlllhorn A (1986) Formation and anion exchange reactions of layered transition metal hydroxides [Ni1-xMx](OH)2(CO3)x2(H2O)z (M = Fe Co) Revue de Chimie Mineacuterale 23 819-827 Miyata S (1983) Anion-exchange properties of hydrotalcite-like compounds Clays and Clay Minerals 31 305-311 Myneni SCB Tokunaga TK Brown Jr GE (1997) Abiotic selenium redox transformations in the presence of Fe(IIIII) oxides Science 278 1106-1109 Nielsen A (1976) Hvid groslashn og sort rust Beskrivelse af en korrosionsskade paring et svoslashmmebassin Nordisk Betong 2 21-24 OLoughlin EJ Burris DR (2004) Reduction of halogenated ethanes by green rust Environmental Toxicology and Chemistry 23 41-48 OLoughlin EJ Kelly SD Cook RE Csencsits R Kemner KM (2003a) Reduction of uranium(VI) by mixed iron(II)iron(III) hydroxide (green rust) Formation of UO2 nanoparticles Environmental Science and Technology 37 721-727

94 Chapter 4 OLoughlin EJ Kelly SD Kemner KM Csencsits R Cook RE (2003b) Reduction of AgI AuIII CuII and HgII by FeIIFeIII hydroxysulfate green rust Chemosphere 53 437-446 Ona-Nguema G Abdelmoula M Jorand F Benali O Gehin A Block J-C Geacutenin JMR (2002) Iron (IIIII) hydroxycarbonate green rust formation and stabilization from lepidocrocite bioreduction Environmental Science and Technology 36 16-20 Parmar N Gorby YA Beveridge TJ Ferris FG (2001) Formation of green rust and immobilization of nickel in response to bacterial reduction of hydrous ferric oxide Geomicrobiology Journal 18 375-385 Pepper SE Bunker DJ Bryan ND Livens FR Charnock JM Pattrick RAD Collison D (2003) Treatment of radioactive wastes An X-ray absorption spectroscopy study of the reaction of technetium with green rust Journal of Colloid and Interface Science 268 408- 412 Randall SR Sherman DM Ragnarsdottir KV (2001) Sorption of As(V) on green rust (Fe4(II)Fe2(III)(OH)12SO4

3H2O) and lepidocrocite (γ-FeOOH) Surface complexes from EXAFS spectroscopy Geochimica et Cosmochimica Acta 65 1015-1023 Roh Y Lee SY Elless MP (2000) Characterization of corrosion products in the permeable reactive barriers Environmental Geology 40 184-194 Schultz CA Grundl TJ (2000) pH dependence on reduction rate of 4-Cl-nitrobenzene by Fe(II)montmorillonite systems Environmental Science and Technology 34 3641-3648 Simon L Francois M Refait Ph Renaudin G Lelaurain M Geacutenin JMR (2003) Structure of the Fe(II-III)-layered double hydroxysulphate green rust two from Rietveld analysis Solid State Sciences 5 327-334 Tamaura Y (1986) Ni(II)-bearing green rust II and its spontaneous transformation into Ni(II)- bearing ferrites Bulletin of the Chemical Society of Japan 59 1829-1832 Tamaura Y (1985) ZnII-bearing green rust II and its spontaneous transformation into ZnII- bearing ferrite in aqueous solution Bulletin of the Chemical Society of Japan 58 2951-2954 Trolard F Abdelmoula M Bourrieacute G Humbert B Geacutenin JMR (1996) Mise en eacutevidence dun constituant de type rouilles vertes dans les sols hydromorphes Proposition de lexistence dun nouveau mineacuteral la fougeacuterite Geacuteosciences de surface Comptes Rendus de LrsquoAcademie des Sciences 323 1015-1022 Tuovinen OH Button KS Vuorinen A Carlson L Mair DM Yut LA (1980) Bacterial chemical and mineralogical characteristics of tubercles in distribution pipelines Journal of the American Water Works Association 72 626-635 Ulibarri MA Pavlovic I Barriga C Hermosin MC Cornejo J (2001) Adsorption of anionic species on hydrotalcite-like compounds effect of interlayer anion and crystallinity Applied Clay Science 18 17-27 Ulibarri MA Pavlovic I Hermosin MC Cornejo J (1995) Hydrotalcite-like compounds as potential sorbents of phenols from water Applied Clay Science 10 131-145


Williams AGB Scherer MM (2001) Kinetics of chromate reduction by carbonate green rust Environmental Science and Technology 35 3488-3494

Reductive Transformation of Trichloroacetate in Abiotic Fe(II)-Fe(III) Mineral Systems 97

5 Reductive Transformation of Trichloroacetate in Abiotic Fe(II)-Fe(III) Mineral Systems

Abstract

Trichloroacetate (TCA) is a widespread environmental contaminant with proven

phytotoxicity and suspected human carcinogenicity In order to assess the global

cycling of TCA and to predict its fate in subsurface environments information

regarding the reactivity and product distribution of TCA degradation is needed

Due to the high oxidation state of TCA conditions for oxidative transformation

pathways in soils and groundwater are unfavorable However in suboxic soils and

sediments Fe(II)-bearing minerals are potential reactants for reductive

dehalogenation reactions of TCA as has been demonstrated for other halogenated

contaminants We examined the reactivity of various Fe(II)-Fe(III) mineral

systems towards TCA and dichloroacetate (DCA) its expected transformation

product in laboratory batch experiments imitating natural conditions ie low

initial Fe(II) Fe(III) and TCADCA concentrations and no artificial buffer The

Fe(II)-Fe(III)-systems investigated included sulfate green rust (GR-SO4) carbonate

green rust (GR-CO3) magnetite Fe(II)goethite and Fe(II)lepidocrocite

Trichloroacetate was readily reduced to DCA by all Fe(II)-bearing minerals The

reactions generally followed pseudo 1 order kinetics with respect to TCA The

surface area-normalised pseudo 1 order rate constants obtained (035ndash76middot10-5 min-

1middotm-2middotL at [Fe(II)]0 = 020ndash122 mM [TCA]0 = 15ndash1000 microM and pH 70ndash87)

showed no striking differences regarding product distribution and surface area-

normalised reaction rate constants between the Fe(II)-Fe(III)-systems The

stoichiometrically formed DCA was not further reduced to monochloroacetate

(MCA) or acetate in any of the systems within the time frame in our experiments

To our knowledge this is the first published report on abiotic transformation of

TCA by Fe(II)-bearing minerals Our results imply that processes involving

reactive Fe(II)-bearing minerals may play a significant role in controlling the fate

98 Chapter 5

of TCA in natural subsurface environments and that DCA found in the subsurface

may be formed by such processes

51 Introduction

Trichloroacetic acid (TCA) has been applied as a herbicide for many years until its

use was banned in the late 1980acutes (Berg et al 2000) Today TCA is mainly used

as an etching agent in the metal industry as a swelling solvent in the plastic

production and as a bleaching agent in the paper and pulp manufacture (Muumlller et

al 1996) Other anthropogenic sources include formation of TCA as a result of the

chlorine based disinfecting process used in drinking water treatment and the

atmospheric photooxidation of chlorinated solvents including tetrachloroethene

and 111-trichloroethane (McCulloch 2002) Only very little information is

available on the TCA production volumes and even less is known about the

amount of TCA released into the environment as a result of its industrial

applications Due to its low volatility and high aqueous solubility TCA is easily

washed out of the atmosphere into the aquatic and terrestrial biospheres As TCA

is found in almost every ecosystem around the globe including non-urban and

non-industrial sites the relative contributions from anthropogenic and natural

sources are currently being debated (McCulloch 2002 Ahlers et al 2003)

Trichloroacetic acid is omnipresent in soils and the concentrations reported are

very variable ranging from lt005 microgkg to 380 microgkg (Euro Chlor 2001

McCulloch 2002 Ahlers et al 2003) Both abiotic and enzymatically catalyzed

formation of TCA from humic acids have been demonstrated in laboratory studies

(Haiber et al 1996 Hoekstra et al 1999b Fahimi et al 2003) Furthermore the

in situ natural formation of TCA from anthropogenic or natural tetrachloroethene

or 111-trichloroethane in biota has been suggested (Hoekstra et al 1999a

McCulloch 2002) Such natural sources may explain part of the TCA

concentrations found in soils but their environmental significance is still unknown


On account of its phytotoxicity suspected human carcinogenicity and widespread

occurrence TCA is of considerable environmental concern especially in the

terrestrial compartment The TCA concentrations found in soil air and water in

pre-industrial times were far below the present ones (Jordan amp Frank 1999 Ahlers

et al 2003) Based on the current TCA concentrations detected in soils the

European Commission proposed risk reduction measures concerning

tetrachloroethene - a precursor of TCA - to be taken immediately (Ahlers et al

2003 and references therein) Occurrences of monochloroacetic acid (MCA) and

dichloroacetic acid (DCA) reported include surface waters marine waters

precipitation ice (glaciers) and air (Reimann et al 1996 Berg et al 2000 Scott et

al 2000 Scott et al 2002) Based on the concentrations reported for the aquatic

environments it is reasonable to assume that MCA and DCA are omnipresent in

soils as well Sources of MCA and DCA include production in the chemical

industry photooxidation of chlorinated aliphatics in the atmosphere and reductive

transformation of TCA (Reimann et al 1996 Ahlers et al 2003 and references

therein) MCA and DCA are also toxins and suspected human carcinogens (Kuumlhn

amp Pattard 1990) hence not only TCA but also its daughter compounds are

pollutants of environmental concern

In subsurface environments TCA may be removed by sorption seepage chemical

transformation microbial degradation and plant uptake followed by metabolic

degradation andor physical removal at harvest (Foy 1975) There is little or no

evidence of abiotic transformations of TCA in the literature Only one recent study

demonstrated the reductive dechlorination of TCA to MCA by Fe(0) (Hozalski et

al 2001) It has been reported that the degradation of TCA in soil is slow and

mainly mediated by microorganisms but only little is known about the bacteria and

processes involved (Lignell et al 1984) Biodegradation of TCA has been found at

both oxic and anoxic conditions An aerobic microorganism capable of growing on

TCA as the sole carbon and energy source has been characterised (Yu amp Welander

1995) Moreover anaerobic bacteria coupling co-metabolic growth to reductive

100 Chapter 5

dechlorination of TCA have been isolated (Weightman et al 1992 De Wever et

al 2000) However more information regarding the abiotic and biotic

transformation of TCA is needed in order to assess the fate and transport of TCA in

natural subsurface environments

It is well-known that Fe(II) present in minerals or associated with mineral surfaces

is a much stronger reductant than Fe(II) in solution The enhanced reactivity of a

structural or surface-bound Fe(II) center can be rationalized by the increased

electron density donated by hydroxyl ligands and a stabilization of the Fe(III)

oxidation state by the hydroxyl ligands (Luther 1990) Fe(II)-bearing minerals

including layered Fe(II)-Fe(III) hydroxides (green rusts) magnetite (Fe3O4)

siderite (FeCO3) Fe(II) sulfides as well as Fe(II)-carrying Fe(III) oxides and clay

minerals have also been shown to reduce a range of organic and inorganic

contaminants such as nitro aromatic compounds chlorinated aliphatics chromate

uranyl pertechnetate nitrate monochloramine and carbamate pesticides (Chapter

4 this work Klausen et al 1995 Cui amp Eriksen 1996 Erbs et al 1999 Liger et

al 1999 Loyaux-Lawniczak et al 1999 Amonette et al 2000 Hansen et al

2001 Pecher et al 2002 Vikesland amp Valentine 2002 Hofstetter et al 2003

OrsquoLoughlin and Burris 2003 OrsquoLoughlin et al 2003a amp 2003b Strathmann amp

Stone 2003 Elsner et al 2004a) Laboratory and field studies showed that even in

geochemically highly heterogeneous anoxic aquifer sediments Fe(II) adsorbed to

Fe(III) (hydr)oxide surfaces was the dominant reductant of nitroaromatic and

halogenated contaminants (Ruumlgge et al 1998 Hofstetter et al 1999 Kenneke amp

Weber 2003) Only little is known about the nature of the Fe(II) species associated

with Fe(III) oxide surfaces but reactive hydroxylated Fe(II)-Fe(III)-hydroxo

surface complexes associated with hematite and magnetite above pH 65 have been

proposed (Charlet et al 1998aampb Liger et al 1999) Due to the presence of

structural Fe(II) within the mineral lattice the reactivity of Fe(II) associated with

mixed valent Fe(II)-Fe(III) minerals such as green rusts magnetite and reduced

ferruginous clay minerals may hold another reactivity than Fe(II) associated with


pure Fe(III) oxides However Fe(II) adsorbed on Fe(III) oxides such as goethite

hematite and lepidocrocite may also hold different reactivities as the Fe(III) oxides

contain different crystal and surface structures

Since chlorinated ethanes and ethenes such as hexachloroethane 111-

trichloroethane tetrachloroethene and trichloroethene are susceptible to chemical

reduction by a range of Fe(II)-bearing minerals including magnetite GR-SO4

Fe(II) sulfides and Fe(II)-carrying Fe(III) oxides (Butler amp Hayes 1998 amp 1999

Hwang amp Batchelor 2000 Gander et al 2002 Lee amp Batchelor 2002aampb Elsner

et al 2004a) we hypothesized that TCA may be transformed by Fe(II)-bearing

minerals as well The main goals of this work were to study such reactions and

establish product distribution and surface area-normalised reaction rates for the

reductive dechlorination of TCA by Fe(II)-Fe(III) mineral systems common in

nature


No synthetic buffers were applied and iron concentrations were kept low The

calcareous systems were pH-controlled at 76 through a natural buffer system

(CaCO3(s) + 995 N205 CO2(g)) All handling and sampling of solutions and

suspensions were carried out under strict anoxic conditions Goethite (acicular

particles with size 01 times 06 microm specific surface area 16 m2g) and lepidocrocite

(acicular particles with size 005 times 03 microm specific surface area 18 m2g) were

purchased as fine powders from Bayer (Bayferrox 910 and 943) Calcite (grain size

170-350 microm Pluumlss-Staufer AG) was used as a buffer or as a Fe(III)-oxide-bearing

mineral In order to simulate natural conditions the iron minerals were applied as

coatings on calcite particles (model system for calcareous soils) in some

experiments Trichloroacetic acid dichloroacetic acid and monochloroacetic acid

were pa quality (Fluka)

102 Chapter 5

521 Synthesis of GRs and magnetite

GR-CO3 was synthesized by controlled air oxidation of an FeCl2 solution at a

constant pH of 700 (titrated with 1 M Na2CO3) according to the procedure given

by Hansen amp Koch (1997) 05 M aqueous stock solutions of FeCl2 were prepared

in 100 mL glass flasks by reacting 65 mmol of iron powder (particle size 10 microm

Merck) with 100 mL deoxygenated 10 M HCl The solutions were magnetically

stirred and heated (~80degC) during reaction until the H2(g) production had ceased (ge

2 hours) The FeCl2 solutions were stored in the dark under a small Ar

overpressure at 5degC The GR-CO3 suspensions were washed with deoxygenated

deionised water (DIW) separated on a folding filter (medium filtration rate cotton

linterhigh alpha pulp Schleicher amp Schuell) and redispersed in deoxygenated

DIW Washing separation and redispersion of the GR-CO3 suspension were

conducted in an anoxic glove box (92 N28 H2 Coy Laboratory Products Inc)

All suspensions and solutions were deoxygenated by Ar-purging (999998 Ar

Carbagas) Magnetite was synthesized by further aerial oxidation of GR-CO3 at pH

700 until consumption of 1 M Na2CO3 ceased GR-SO4 was synthesized by

controlled air oxidation of an FeSO4 solution at a constant pH of 70 according to

the procedure given by Koch amp Hansen (1997) The GR-SO4 suspension was

washed with deoxygenated DIW separated on a glass filter funnel (pore size 4

Duran) and redispersed in deoxygenated DIW Washing separation and

redispersion of the GR-SO4 suspension were conducted in an anoxic glove bag

(999995 Ar Aldrich)



combined with 200 mL DIW in a 500 mL polyethylene flask The suspension was

gently agitated on a reciprocating shaker for 24 h and left to stand for another 24 h

Excess Fe(III) oxides and salts were removed from the coated material by repeated

decantation and washing with DIW in polyethylene flasks until clear runoff

Finally the coatings were collected on folding filters and air dried The amount of


goethite and lepidocrocite coated onto calcite after washing and drying was

quantified to 10-11 mg Fe(III)g calcite


The identity and purity of the GR-CO3 GR-SO4 and magnetite suspensions were

examined by means of X-ray diffraction (XRD) The XRD analyses were

performed on a Scintag XDS 2000 using Co Kα radiation (45 kV 40 mA) or a

Siemens D5000 XRD applying Co Kα radiation (40 kV 40 mA) Glycerol smears

made according to Hansen (1989) were scanned between 6 and 80 deg2θ with a scan

speed of 1 deg2θmin The specific surface area (SSA) of calcite was determined by

the BET multi-point method using N2 adsorption (Brunauer et al 1938) Powder

samples were filled into sample burettes in the glove box and the generously

lubricated stopcocks closed Samples and burettes were evacuated prior to

connecting them to the BET-instrument (Sorptomatic 1990 Fisons)


All reactions were carried out in 25-100 mL serum vials sealed with stoppers

(Viton or Teflon coated rubber) and aluminum crimp caps Kinetic experiments

were conducted with GR-SO4 GR-CO3 magnetite Fe(II)goethite and

Fe(II)lepidocrocite at room temperature In most cases pH was controlled through

the carbonate-bicarbonate buffer system by adding calcite to suspensions

containing the iron minerals solely or by adding the iron minerals as coatings on

calcite Furthermore the calcite containing suspensions were deoxygenated with

05 CO2995 N2(g) thereby attaining an initial pH of 76-77 The GR-CO3 and

magnetite suspensions were deoxygenated with 100 N2(g) and no additional pH

buffer was added The goethite and lepidocrocite suspensions were amended with

300-1000 microM FeCl2(aq) and equilibrated gt 20 h prior to TCADCA addition See

Table 51 for more details on the experimental conditions To start the reaction 50

microM - 1 mM TCA or DCA was added to the mineral suspensions from aqueous

anoxic stock solutions The reaction vials were agitated gently on a roller apparatus

104 Chapter 5

or a shaking table (35 rpm) in order to minimize abrasion of the iron oxide mineral

coatings At appropriate time intervals suspension samples were withdrawn using

Ar(g)- 100 N2(g)- or 995 N205 CO2(g)-flushed sterile disposable syringes

and hypodermic needles The suspension samples were filtered (02 microm Teflon)

and collected for quantification of chloride and the chlorinated acetic acids The

samples were stored at -20degC and analysed without further treatment


Total and aqueous Fe(II) were determined using a modified phenanthroline method

(Fadrus and Maly 1975) For determining [Fe(II)aq] and [Fe(II)total] 1 mL filtered

(02 microm Teflon) and 1 mL unfiltered mineral suspension were added to 18 mL 01

M HCl respectively and allowed to dissolve for 30 min From these acid digests

01 mL was added to 05 mL Fe(II)-phenanthroline-buffer-reagent and 19 mL

DIW added up Estimates of the structural or adsorbed Fe(II) in the Fe(II)-Fe(III)

mineral systems were estimated as the difference [Fe(II)solid] = [Fe(II)total] -

[Fe(II)aq] The total amount of Fe(III) coated on calcite was determined by atomic

absorption spectroscopy following dissolution in 6 M HCl(aq) for 24 h At low

initial TCA concentrations (le 50 microM) the chlorinated acetic acids were quantified

by means of a modified ion interaction (or paired-ion) chromatographic method

(Sarzanini et al 1999) Separation was performed on a LiChrospher 100 RP-18 (5



consisted of 50 aqueous solution of 35 mM cetyltrimethylammonium chloride

(pH 50) and 50 CH3CN The injection volume was 20 microL and the flow-rate 10

mLmin HPLC analyses of the chloroacetates were performed using a Gynkotek

Pump M480 Gynkotek Gina 50 auto sampler and a diode array UV detector (340s

Gynkotek) UV-VIS detection was carried out at 200 nm At higher initial TCA

concentrations the chlorinated acetic acids were quantified by a modified HPLC

method (Husain et al 1992) Separation was performed on a ChromSphere C-18

(10 microm 250 times 46 mm ID) reversed-phase column Analytical conditions were


isocratic and the eluent consisted of 015 M (NH4)2SO4(aq) pH 55 The injection

volume was 20 microL and the flow-rate 10 mLmin HPLC analyses were performed

using a Series 10 Liquid Chromatographic Pump (Perkin-Elmer) and a SPD-10 A

VP UV-VIS detector (Shimadzu) UV-VIS detection was carried out at 210 nm

Chloride was determined in the GR-SO4 kinetic experiments using a flow injection

system with spectrophotometric detection (Cheregi amp Danet 1997)


531 Product formation and reaction kinetics

Trichloroacetate was readily reduced to DCA by all the Fe(II)-bearing minerals

examined Only DCA was detected within the reaction time in all the Fe(II)-Fe(III)

mineral systems Experiments conducted with the various Fe(II)-Fe(III) mineral

systems and DCA confirmed that no significant reduction of DCA took place (data

not shown) Hence it is reasonable to assume that the further hydrogenolysis of

DCA to MCA is too slow to be detected within the experimental time frame here

The mass balance of TCA and DCA was almost complete in all suspensions ruling

out any alternative reaction pathways to reductive dechlorination Decarboxylation

of TCA producing chloroform and carbon dioxide requires high temperatures and

is therefore assumed not to take place at the experimental conditions applied here

(Atkins et al 1984) Based on these results we propose that the reductive

dechlorination of TCA by Fe(II)-bearing minerals proceeds via hydrogenolysis

(replacement of halogen by hydrogen) as reported for the transformation of TCA

by zero-valent iron (Hozalski et al 2001) Thus in order to reduce TCA to DCA

2 electrons corresponding to 2 Fe(II) are needed (Figure 51)

106 Chapter 5

Cl3CC

O

O- Cl2HCC

O

O-

2e- H+ Cl-

TCA DCA Figure 51 Proposed reductive transformation pathway of TCA

In the Fe(II)goe and Fe(II)lep systems we detected no TCA transformation in the

absence of either aqueous Fe(II) or pure or calcite-associated goethite and

lepidocrocite These results strongly indicate that reactive Fe(II) species associated

with the goethite and lepidocrocite surfaces are the reductants for TCA in these

systems The Fe(III) phases forming in the mineral suspensions were not

characterised and therefore the reaction stoichiometry cannot be assessed

At initial Fe(II) concentrations in large excess of initial TCA concentration we

found a pseudo 1 order rate law for the degradation of TCA by Fe(II)

[ ] [ ] [ b a TCAFe(II) TCA

sdotsdot=minus kdt

d ]

where a = 1 b = 1 and the observed pseudo 1 order rate constant kobs = k middot [Fe(II)]

At all [Fe(II)]0[TCA]0 ratios studied (6-738) TCA was transformed almost

quantitatively into DCA and the reaction kinetics followed pseudo 1 order kinetics

with respect to TCA (Figure 52) The observed pseudo 1 order rate constants for

the transformation of TCA by the various Fe(II)-Fe(III) mineral systems were

calculated as initial rates (ie max first two half-lives) from linear fits of (time ln

[TCA]t[TCA]0)-plots (Table 51) The amount of chloride produced during

reaction with GR-SO4 was always equivalent to the amount of TCA transformed

into DCA (Figure 52c) This also indicates that no significant further reduction of

DCA took place in GR-SO4 suspensions


Figure 52 Time course of TCA consumption and DCA and chloride production for a)

Fe(II)Goe ([Fe(II)tot]0 = 095 mM) b) Fe(II)Lep ([Fe(II)tot]0 = 091 mM) c) GR-SO4

([Fe(II)GR]0 = 962 mM) d) GR-CO3 ([Fe(II)tot]0 = 633 mM) and e) Magnetite ([Fe(II)tot]0 = 350

mM) Solid lines represent 1 order kinetic fits whereas symbols and dotted lines represent actual

data = TCA = DCA = Clndash

T

able

51

Exp

erim

enta

l con

ditio

ns a

nd p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

TC

A b

y va

rious

Fe(

II)-

Fe(I

II) c

onta

inin

g m

iner

al sy

stem

s

Syst

em

Susp

ensi

on a

ge

(d)

[Fe(

II)] s

olid

a (m

M)

[Fe(

II)] a

q b

(mM

) [T

CA

] 0 (micro

M)

pHin

itcpH

endd

k obs

e (min

-1)

Surf

ace

area

(m

2 L)

k obs

f

(min

-1m

-2middotL

)

Fe(I

I)aq

1

0

030

434

nd

76

gn

dn

dn

d

Fe(I

I)G

oe

1

002

024

429

nd

78

g1

021

0-47

1 i

143

10-5

Fe(I

I)G

oe

1

013

094

543

77

70

225

10-4

71

i3

161

0-5

Fe(I

I)G

oe

coat

ing

1

023

40

066

484

765

80

g6

401

0-454

0 j

119

10-5

Fe(I

I)G

oe

coat

ing

1

0

150

8048

6n

d7

6 g12

43

10-4

540

j2

301

0-5

Fe(I

I)L

ep

1

0

020

2315

7n

d7

8 g0

751

0-48

0 i

094

10-5

Fe(I

I)L

ep

coat

ing

1

016

30

137

470

765

80

g2

821

0-454

0 j

052

10-5

Fe(I

I)L

ep

coat

ing

1

0

100

8141

7n

d7

7 g8

311

0-454

0 j

154

10-5

Fe3O

41

3

380

1251

38

107

8g

830

10-4

16

k5

311

0-4

Fe3O

477

112

56

556

70

70

153

10-4

52

k2

951

0-5

GR

-CO

31

5

940

3950

37

658

4g

761

10-4

419

l1

821

0-5

GR

-CO

32

7

60

147

88

568

2940

81

0-453

6 l

761

10-5

GR

-CO

332

73

003

563

85

80

490

10-4

515

l0

951

0-5

GR

-CO

314

2

3

530

005

629

nd

87 g

513

10-4

249

l2

061

0-5

GR

-SO

41

5

17-1

217

086

-13

910

5n

dn

d3

601

0-492

6 m

039

10-5

GR

-SO

41

6

22-1

027

093

-14

527

0n

dn

d3

761

0-488

1 m

043

10-5

GR

-SO

41

7

05-1

014

077

-17

950

0n

dn

d3

741

0-4 9

18

m0

411

0-5

GR

-SO

41

5

17-1

051

060

-16

510

00n

dn

d2

891

0-483

7 m

035

10-5

n

d =

not

det

ecte

d a

Ini

tial s

truct

ural

or a

dsor

bed

Fe(I

I) e

stim

ated

as [

Fe(I

I)to

tal]

ndash [F

e(II

) aq]

b In

itial

dis

solv

ed F

e(II

) mea

sure

d c

Sus

pens

ion

pH p

rior t

o TC

A a

dditi

on d

Sus

pens

ion

pH a

t rea

ctio

n

te

rmin

atio

n e

Pse

udo

1 o

rder

rate

con

stan

ts fo

r the

con

sum

ptio

n of

TC

A c

alcu

late

d fr

om in

itial

rate

s (m

ax f

irst t

wo

half-

lives

) f

Surf

ace

area

-nor

mal

ised

pse

udo

1 o

rder

rate

con

stan

ts g

pH

con

trol

th

roug

h pu

re C

aCO

3 and

05

C

O2(g

) h

pH

con

trol t

hrou

gh F

e(II

I) o

xide

-coa

ted

calc

ite a

nd 0

5

CO

2(g)

i Es

timat

ed u

sing

the

SSA

of t

he F

e(II

I) o

xide

app

lied

j E

stim

ated

usi

ng th

e SS

A o

f cal

cite

~1

m2 g

k E

stim

ated

ass

umin

g SS

A =

4 m

2 g (S

chw

ertm

ann

amp C

orne

ll 1

991)

frac12middot[

Fe(I

I) sol

id] 0middot

232

gmiddotm

ol-1

middot4 m

2 middotg-1

l E

stim

ated

ass

umin

g SS

A =

47

m2 g

(Will

iam

s amp S

cher

er 2

001)

frac14middot[F

e(II

) GR] 0middot

600

gmiddotm

ol-1

middot47

m2 middotg

-1 m

Est

imat

ed a

s in l

but u

sing

SSA

= 7

12

m2 middotg

-1 (C

hapt

er 4

thi

s wor

k)


532 Comparing rate constants obtained for the various Fe(II)-Fe(III) mineral

systems

Data for the systems containing iron oxide coated calcite were very similar to the

data obtained for the pure iron oxides (not shown in Figure 53) Since no SSA was

determined for magnetite in this study a SSA of 4 m2g was assumed

(Schwertmann amp Cornell 1991) However it should be noted that the magnetite

synthesized by Schwertmann and Cornell (1991) was prepared differently (ie

oxidation of Fe(II) by nitrate in a heated alkaline solution) from the magnetite

applied in this study The surface area-normalised pseudo 1 order kobs values

obtained for GR-CO3 GR-SO4 Fe(II)goethite and Fe(II)lepidocrocite were all

within the same order of magnitude (Figure 53a)

Figure 53 Average surface area-normalised pseudo 1 order rate constants for the degradation of

a) TCA (this work) b) hexachloroethane (Elsner et al 2004a) and c) carbon tetrachloride

(Amonette et al 2000 Pecher et al 2002 OrsquoLoughlin et al 2003c Elsner et al 2004b) by

GR-SO4 GR-CO3 (suspension age 1 d) Fe3O4 Fe(II)α-FeOOH and Fe(II)γ-FeOOH

Experimental conditions applied in this work [Fe(II)tot]0 = 025-107 mM in the goethite and

lepidocrocite suspensions [Fe(II)tot]0 = 025-116 mM in the GR-SO4 and GR-CO3 suspensions

pH 70-86 71-926 m2 mineral surface areaL Experimental conditions applied by Elsner et al

1 mM aqueous Fe(II) 25 m2 mineral surface areaL Experimental conditions applied in

references employed in c) [Fe(II)tot]0 = 1-83 mM 25-275 m2 mineral surface areaL GR-SO4 =

110 Chapter 5

sulfate green rust GR-CO3 = carbonate green rust Fe3O4 = magnetite α-FeOOH = goethite γ-

FeOOH = lepidocrocite

When comparing the rate constants for the Fe(II)-Fe(III) mineral systems found for

reduction of TCA in this study (Figure 2a) mixed valent Fe(II)-Fe(III) minerals

such as green rusts and magnetite containing structural Fe(II) within the mineral

lattice do not seem to be significantly more reactive than Fe(II)-Fe(III) mineral

systems containing Fe(II) associated with pure Fe(III) oxides Unlike most other

iron oxides GRs contain not only external Fe(II) reactive sites at the surface but

also internal sites in the space between consecutive Fe(II)-Fe(III) hydroxide layers

The GR interlayer thickness is a function of both the size and the charge of the

interlayer anion For solutes the Fe(II) within the GR hydroxide layer is accessible

at the outside basal planes and at the edges as well as through the interlayer under

certain conditions (see Figure 42 Chapter 4 this work) Due to electrostatic

forces oxidants holding different charge properties (anions cations neutral

molecules) may exhibit different affinities for the various reactive Fe(II) sites

present in GR As the reactive sites are located inat the Fe(II)-Fe(III) hydroxide

layers the rate of reaction depends on the hydroxide layer area which can be

accessed by the oxidant If the oxidant is able to exchange with the interlayer

anion reaction can take place both at outer and inner surfaces of the GR particles

and in total more reactive sites are available for the reaction Thus oxidant size

and charge primarily control its access to the internal sites in GRs XRD

characterization of the GR-SO4 crystals during reaction with TCA demonstrated

that the GR-SO4 interlayer spacing did not vary during reaction (Table 52) This

may indicate that TCA did not enter the GR-SO4 interlayers

Reductive Transformation of Trichloroacetate in Abiotic Fe(II)-Fe(III) Mineral Systems 111 Table 52 Diffraction angle d-spacing and width at half peak height (Wfrac12) for the 001 GR-SO4

diffraction peak as a function of time during reaction with TCA ([Fe(II)GR]0 = 4 mM [TCA]0 = 1

mM)

Time (min) Angle (deg2θ)

d001-spacing(nm)

Wfrac12(degθ)

0 9483 10821 0273

10 9494 10809 0287

215 9522 10777 0263

330 9550 10745 0273

510 9524 10775 0277

855 9509 10791 0253

1160 9467 10839 0268

We roughly estimated the molecular size of TCA by summing the covalent radii of

the individual atoms (see Supporting Information 74) When comparing the

molecular size of TCA with the GR-SO4 interlayer spacing of 061 nm it can be

concluded that only when the C-C bond is oriented perpendicular to the interlayer

plane does the size of TCA exceed the GR-SO4 interlayer spacing In contrast the

size of TCA exceeds the GR-CO3 interlayer spacing (026 nm) regardless of its

orientation Hence if TCA was intercalated in the GR-CO3 interlayer we would

expect the interlayer spacing to expand The same holds for intercalation of a

vertically oriented TCA in the GR-SO4 interlayer Supposedly both the low charge

and the size of TCA impeded its access to the GR-SO4 and GR-CO3 interlayers ie

the divalent sulphate and carbonate in the GR interlayers did not readily exchange

with the monovalent TCA since GR interlayers generally have a higher affinity for

divalent anions than for monovalent anions (Miyata 1983) Thus TCA did neither

access nor react with internal Fe(II) reactive sites in GR-SO4 which means that the

reaction between TCA and GR-SO4 took place at the external reactive Fe(II) sites

solely It is reasonable to assume that the same holds for the reaction between TCA

and GR-CO3 No significant aging effects eg rate constants varying as a function

of GR age were observed within 142 days (see Table 51) However the SSAs of

112 Chapter 5

the GR suspensions holding ages up to 142 days were not measured but estimated

assuming that the GR SSA did not decrease within the time frame

According to the Scherrer formula the width at half peak height (Wfrac12) of a

diffraction peak is inversely proportional to the average crystal dimension

perpendicular to the given crystal plane (Klug amp Alexander 1974) The average

GR-SO4 particle thickness perpendicular to the basal plane (Wfrac12 Table 52) was

constant during reaction implying that TCA reacts only at the edges and not at the

basal planes Assuming that the platy hexagonal GR-SO4 and GR-CO3 crystals

hold an average width of 1 microm and an average particle thickness of 35 nm (Hansen

and Koch 1998) the ratio of edge surface area to outer surface area is AedgeAouter ~

130 for GR-SO4 and 121 for GR-CO3 (see Supporting Information 73) This

means that only 3 of the outer surface area in GR-SO4 and 5 of the outer

surface area in GR-CO3 are available at the edges Assuming that TCA reacts at the

edges only and if employing the AedgeAouter in the estimation of the rate constants

the surface area-normalised pseudo 1 order rate constants for GR-SO4 and GR-

CO3 would be 20-30 times higher than the rate constants depicted in Figure 53a

Thus the reactivity of GRs normalised to their reactive surface area is much higher

than the reactivity normalised to their total surface area

533 Comparing with rate constants obtained for other chlorinated aliphatic

compounds

Though care must be taken when comparing kinetic parameters obtained at

different experimental conditions (eg pH [Fe(II)]0[TCA]0 ratios surface area to

volume ratios etc) it is interesting to compare our results to those reported for

hexachloroethane (Figure 53b data from Elsner et al 2004a) The reductive

transformation of hexachloroethane was investigated for various Fe(II)-bearing

minerals including Fe(II)goethite Fe(II)lepidocrocite and GR-SO4 in the presence

of 1 mM dissolved Fe(II) and 25 m2 mineral surface areaL at pH 72 except for the

GR-SO4 suspensions in which the dissolved Fe(II) concentrations were slightly


higher and pH = 8 The pseudo 1 order rate constants reported for

hexachloroethane are in the range 18middot10-4 ndash 75middot10-3 h-1middotm-2middotL (Elsner et al 2004a)

When comparing Figure 53a with Figure 53b it can be seen that the differences

in intrinsic reactivity of the Fe(II)-bearing mineral systems are more pronounced

for hexachloroethane than for TCA

Caution should also be advised to the different reaction mechanisms by which

hexachloroethane and TCA react The transfer of a single electron and the

formation of an alkyl radical upon removal of a chlorine atom constitute the first

and in most cases the rate-limiting step in the reduction of chlorinated aliphatic

compounds (Vogel et al 1987) Depending on the chemical structure of the

chlorinated aliphatic compound the resulting free alkyl radical may undergo

hydrogenolysis chloroelimination or dimerizationcoupling In the case of TCA

the free dichloroacetate radical most likely undergoes hydrogenolysis The almost

quantitative transformation of TCA to DCA confirms that hydrogenolysis is the

prevalent reaction mechanism in our mineral systems The pentachloroethyl radical

formed from hexachloroethane may undergo hydrogenolysis (producing

pentachloroethane) or dichloroelimination (producing tetrachloroethene) Elsner et

al (2004a) found that hexachloroethane was transformed quantitatively into

tetrachloroethylene for all minerals which strongly indicates that

dichloroelimination was the dominating reaction mechanism Another

polychlorinated aliphatic compound transformed mainly by hydrogenolysis under

reducing conditions is carbon tetrachloride Several studies have investigated the

reductive dechlorination of carbon tetrachloride by various Fe(II)-bearing minerals

including Fe(II)goethite and GR-SO4 and reported pseudo 1 order rate constants

in the order 152middot10-4 ndash 640middot10-4 h-1middotm-2middotL for Fe(II)goethite and 864middot10-4 h-1middotm-2middotL

for GR-SO4 (Amonette et al 2000 Pecher et al 2002 OLoughlin et al 2003c

Elsner et al 2004b) When comparing Figure 53a with Figure 53c it can be seen

that the range of magnitude of the rate constants and the differences in intrinsic

114 Chapter 5

reactivity of the Fe(II)-bearing mineral systems are similar for carbon tetrachloride

and TCA

534 Factors controlling the reactivity of surface-bound Fe(II)

The reactivity of an oxidant towards Fe(II) surface species cannot be predicted

from the reduction potentials of the redox couple alone In heterogeneous systems

processes such as mass transfer and adsorptiondesorption may have a rate-limiting

effect on the overall reaction rate If the adsorption follows a saturation-type

sorption isotherm (eg Langmuir) the sorbate (oxidant) concentration at the

surface will vary non-linearly with the total amount of oxidant added This

dependence will have to be taken into account when establishing rate laws for the

heterogeneous reactions and when testing the hypothesis that the reaction rates

depend on the sorbed concentration of the oxidants pH has a strong impact on the

sorption and thereby on the availability of ionizable oxidants At the pH values

applied here the chloroacetates are fully dissociated (pKa (TCA) = 066 pKa

(DCA) = 135 pKa (MCA) = 287) However we found the sorption of TCA to be

negligible in suspensions of pure calcite goethitecalcite and lepidocrocitecalcite

at pH 76-77 Moreover the mass balance of TCA and DCA was almost complete

in all suspensions and therefore loss of TCA or DCA due to adsorption at mineral

surfaces or incorporation in the GR anion interlayers can be ruled out Calcite has a

much lower adsorption capacity than most iron oxides hence we anticipate that

goethite and lepidocrocite control the adsorption of TCA and DCA in both the pure

FeOOH and the FeOOHcalcite suspensions This was supported by our

experimental results demonstrating that the presence of a calcite surface - either

pure or as a support for goethite and lepidocrocite coatings - did not exert any

noticeable effect on the reaction rates (see Table 51) In addition the surface area-

normalised rate constants for mineral systems containing goethite or lepidocrocite

in pure form and mineral systems containing goethite or lepidocrocite as coatings

on calcite were very similar In heterogeneous reactions mass transfer in bulk

solution becomes the rate-limiting step when the surface reaction is much faster


than the diffusion of the reacting species to the reactive surface However at the

low rate constants obtained here the reaction of TCA with the Fe(II)-bearing

minerals is not likely to be mass transfer limited (see Supporting Information 72)

One very important factor affecting heterogeneous redox reactions is pH which

influences the speciation of the complexes in solution and at mineral surfaces as

well as the stability of the more soluble Fe(II)-containing minerals such as GRs In

contrast to aqueous Fe(II) complexes it is not possible to predict the reactivity of

Fe(II) surface species as their reduction potentials are unknown In the absence of

specifically adsorbing solutes other than H+ the surface charge of the Fe(III)

oxides goethite and lepidocrocite is determined by the surface densities of the

charged surface species equivFeOH2+ and equivFeOndash whereas the surface charge of calcite

is determined by the density of the surface species equivCO3ndash equivCaOH2

+ and equivCaOndash

(Stumm 1992 Van Cappellen et al 1993) The point of zero charge (pHpzc) of

pure calcite is in the pH range 7-11 and depends on the partial pressure of carbon

dioxide pCO2 The higher the pCO2 the lower the pHpzc At the experimental

conditions applied here (05 = 0005 atm CO2(g)) the pHpzc = 82 for calcite

(Table 53) As only 10-11 mg Fe(III) of goethite and lepidocrocite was coated

onto calcite we assumed a pHpzc of 82 for the goethite and lepidocrocite coated

calcite particles as well The pHpzc values for green rusts are unknown

116 Chapter 5

Table 53 Specific surface areas and point of zero charge of the various iron minerals in pure form as well as goethite and lepidocrocite coated onto calcite

Mineral Structural formula SSA (m2g) pHpzc

GR-SO4 FeII4FeIII

2(OH)12SO4middot3H2O 71 a -

GR-CO3 FeII4FeIII

2(OH)12CO3middot3H2O 47 b -

Magnetite Fe3O4 - 69 e

Goethite α-FeOOH 16 c 85 f

Lepidocrocite γ-FeOOH 18 c 73 e

Calcite CaCO3 le 1 d 82 g

Goe coating - le 1 d 82 h

Lep coating - le 1 d 82 h

a Chapter 4 this work b Williams amp Scherer 2001 c Product information by Bayer d The SSA of calcite was

quantified to le 1 m2g The detection limit of our BET method was 1 m2g e Charlet et al 1998a f Liger et al

1999 g Van Cappellen et al 1993 h Same as for calcite

The surface hydroxyl groups on iron oxides may be both singly (equivFe-OH) doubly

(equivFe2-OH) triply (equivFe3-OH) and geminally (equivFe-(OH)2) coordinated (Cornell amp

Schwertmann 1996 Stumm 1992) The differently coordinated surface hydroxyl

groups are not equally reactive Adsorption reactions involve only singly

coordinated surface groups and therefore only this kind of hydroxyl groups on iron

oxides will be considered here (Cornell amp Schwertmann 1996) Hence the

predominant surface sites available for adsorption in pure suspensions of Fe(III)

oxides are equivFeOH0 equivFeOH2+ and equivFeOndash In the presence of dissolved Fe(II)

equivFeIIIOFeIIOH0 equivFeIIIOFeIIOndash and equivFeIIIOFeII+ constitute the main reactive sites at

the Fe(III) oxide surfaces (Liger et a 1999) Assuming that Fe2+ and other cationic

Fe(II) species are the dominating adsorbates on the mineral surfaces in our

experiments we expect the actual pHpzc to be higher than the pHpzc of the pure

oxides listed in Table 53 Hence at pHlt82 where most of our experiments were

conducted all the mineral surfaces presumably carry net positive charges

At pH 70 where Fe2+ is still the predominant Fe(II) species in solution (~50) we

expect that equivFeIIIOFeIIOH equivFeIIIOFeIIOndash and equivFeIIIOFeII+ constitute the main


reactive sites at the Fe(III) oxide surfaces as suggested by Liger et a 1999 As pH

increases from 70 to 87 the Fe(II) carbonate complexes become increasingly

important in solution at the expense of the Fe2+ FeCl+ FeSO40 and FeOH+ species

(King 1998) Fe(II) carbonate complexes do not bind at the oxide surface as

readily as the aquo or hydroxo complexes of Fe(II) but carbonate itself sorbs

readily to Fe(III) oxide surfaces through which the Fe(III) oxide surface is coated

by inner-sphere monodentate equivFeIIIOCOOH0 surface complexes (Villalobos amp

Leckie 2000 amp 2001) The presence of carbonate shifted the sorption edge for the

Fe(II) adsorption on goethite from pH 58 to 78 and the authors hypothesized this

to be a result of the formation of aqueous and surface Fe(II)-carbonate complexes

and to competition between carbonate and Fe(II) for Fe(III) oxide surface sites

(Vikesland amp Valentine 2002) Similarly monodentate surface complexes like

equivFeIIICl0 and equivFeIIIOSO3ndash as well as ternary monodentate surface complexes like

equivFeIIIOFeIICl0 and equivFeIIIOFeIIOSO3ndash and ternary bidentate surface complexes such

as (equivFeIIIO)2FeIIOSO3 may form at Fe(III) oxide surfaces when Fe(II) chloride and

sulfate are present in solution (Ostergren et al 2000 Kim et al 2004) However

the effects of anionic ligands such as chloride and sulfate on Fe(II) adsorption at

Fe(III) oxide surfaces and the reactivity of Fe(II) carbonate chloride and sulfate

surface sites are still unknown and need to be evaluated (see Supporting

Information 75) Thus we do not know whether chloride and sulfate decrease or

increase the Fe(II) sorption in our mineral systems We can only report that we did

not detect any significant differences in the rate of TCA transformation between

the mineral suspensions containing carbonate chloride and sulfate respectively

Hence we anticipate that equivFeIIIOFeIIOH equivFeIIIOFeIIOndash and equivFeIIIOFeII+ constitute

the main reactive sites at the Fe(III) oxide surfaces within the whole pH range 70-

87 This might also explain why we did not detect any obvious systematic pH

effect in the Fe(II)-Fe(III)-systems (see Table 51) In the case of

hexachloroethane the reactivity order GR-SO4gtgoethitegtmagnetitegtlepidocrocite

may be rationalized by the variations in surface site densities and total amount of

118 Chapter 5

Fe(II) sorbed on the iron minerals (see Supporting Information 75) as well as the

different speciations and reactivities of the Fe(II) surface sites on the iron minerals

535 Comparison with biotic and other abiotic systems

Only one report on abiotic transformation of TCA is found in the literature and the

study demonstrates the reductive dechlorination of TCA to MCA by Fe(0)

(Hozalski et al 2001) The authors reported a pseudo 1 order rate constant of

60middot10-4 min-1middotm-2middotL for the transformation of TCA to DCA and a pseudo 1 order

rate constant of 225middot10-4 min-1middotm-2middotL for the transformation of DCA to MCA at

[Fe(0)]0 = 025 M [TCA]0 = 100-200 microM and pH 36-62 The rate constant for

TCA reduction by Fe(0) is 10-300 times faster than the rate constants reported for

the Fe(II)-bearing mineral systems here

There is abundant evidence that soil microorganisms and fungi can dechlorinate

TCA but only little is known about the bacteria and processes involved in the

biodegradation of TCA Biotransformation of TCA has been found at both oxic

and anoxic conditions Most of the microorganisms isolated grow feebly on TCA

as a sole source of carbon (Foy 1975 Weightman et al 1992 De Wever et al

2000) Only one bacterium capable of growing on TCA as the sole carbon and

energy source has been characterized (Yu amp Welander 1995) In addition

anaerobic bacteria coupling co-metabolic growth to reductive dechlorination of

TCA have been isolated (Weightman et al 1992 De Wever et al 2000) The

inability to grow on the less chlorinated acids DCA and MCA is a notable feature

of both the aerobic and anaerobic bacteria Complete transformation of TCA to

methane and carbon dioxide has only been found when abiotic and biotic processes

were combined (Egli et al 1989) The abiotic transformation of TCA to DCA

occurred spontaneously in the presence of sterile activated charcoal whereas the

DCA formed was further degraded to methane and carbon dioxide by a mixed

culture of methanogenic bacteria However the abiotic reductant(s) responsible for

the transformation of TCA to DCA was not reported (Egli et al 1989)


The rate constants obtained in this work suggest that the Fe(II)-bearing mineral

systems may be important reductants of TCA in natural suboxic environments In

natural iron-rich soils holding specific surface areas of 22 m2g (Kenneke amp

Weber 2003) average bulk densities of 265 gcm3 and porosities of 25 and

containing 2 iron oxides a rough estimation of the half-life of TCA amounts to

47 minutes when applying the average surface area-normalised rate constant

obtained for all the Fe(II)-Fe(III) mineral systems in this work (1middot10-3 h-1middotm-2middotL)

This estimation is based on the assumption that enough reactive Fe(II) is available

in these soils The natural iron-reducing sediment investigated by Kenneke and

Weber (2003) contained 80 microM Fe(II) in the soil solution and 315 micromole Fe(II) per

g sediment At such low Fe(II) concentrations the overall rate of abiotic

transformation of TCA in natural soils and sediments is most likely limited by the

regeneration of reactive Fe(II) Hence the continuous regeneration of reactive

Fe(II) surface sites by adsorption of abiotically or microbially produced Fe(II) may

further the long-term abiotic transformation of TCA in such environments

54 Conclusions

This work demonstrates that various Fe(II)-Fe(III) minerals systems including GR-

SO4 GR-CO3 magnetite Fe(II)goethite and Fe(II)lepidocrocite readily transform

TCA to DCA Dichloroacetate was not further reduced to MCA or acetate by any

of the Fe(II)-bearing minerals The surface area-normalised pseudo 1 order rate

constants obtained for the reductive transformation of TCA by the various Fe(II)-

bearing minerals did not differ significantly from each other The results obtained

in this work infer that under natural geochemical conditions Fe(II)-bearing mineral

systems may play an important role in the overall transformation of TCA Thus

not only microbial degradation but also abiotic reductive transformation of TCA by

Fe(II)-bearing minerals may govern the fate of TCA in natural subsurface

environments This holds both for natural systems like iron-rich suboxic soils and

sediments as well as engineered systems like permeable reactive barriers of zero-

120 Chapter 5

valent iron implemented for on-site remediation where both Fe(0) and solid or

surface-bound Fe(II) corrosion intermediates may transform TCA

Acknowledgments

We would like to thank Susanne Guldberg for performing the experimental work comprising

GR-SO4

References

Ahlers J Regelmann J Riedhammer C (2003) Environmental risk assessment of airborne trichloroacetic acid - a contribution to the discussion of the significance of anthropogenic and natural sources Chemosphere 52 531-537 Amonette JE Workman DJ Kennedy DW Fruchter JS Gorby YA (2000) Dechlorination of carbon tetrachloride by Fe(II) associated with goethite Environmental Science and Technology 34 4606-4613 Atkins PJ Gold V Marsh R (1984) The decarboxylation of trichloroacetic acid and the reactions of the trichloromethyl anion with 135-trinitrobenzene and with hydrogen ions kinetic measurements in dimethyl sulphoxide solution Journal of the Chemical Society Perkin Transactions 2 7 1239-1245 Berg M Muumlller SR Muumlhlemann J Wiedmer A Schwarzenbach RP (2000) Concentrations and mass fluxes of chloroacetic acids and trifluoroacetic acid in rain and natural waters in Switzerland Environmental Science and Technology 34 2675-2683 Brunauer S Emmett PH Teller E (1938) Adsorption of gases in multimolecular layers Journal of American Chemical Society 60 309-319 Butler EC Hayes KF (1998) Effects of solution composition and pH on the reductive dechlorination of hexachloroethane by iron sulfide Environmental Science and Technology 32 1276-1284 Butler EC Hayes KF (1999) Kinetics of the transformation of trichloroethylene and tetrachloroethylene by iron sulfide Environmental Science and Technology 33 2021-2027 Charlet L Liger E Gerasimo P (1998a) Decontamination of TCE- and U-rich water by granular iron Role of sorbed Fe(II) Journal of Environmental Engineering 124 25-30 Charlet L Silvester E Liger E (1998b) N-compound reduction and actinide immobilisation in surficial fluids by Fe(II) the surface FeIIIFeIIOH0 species as major reductant Chemical Geology 151 85-93 Cheregi M Danet AF (1997) Flow injection determination of chloride ions with spectrophotometric detection Analytical Letters 30 2847-2858 Cornell RM Schwertmann U (1996) The iron oxides Structure properties reactions occurrence and uses VCH Verlagsgesellschaft mbH Weinheim

Reductive Transformation of Trichloroacetate in Abiotic Fe(II)-Fe(III) Mineral Systems 121 Cui D Eriksen TE (1996) Reduction of pertechnetate by ferrous iron in solution influence of sorbed and precipitated Fe(II) Environmental Science and Technology 30 2259-2262

Egli C Thuumler M Suter D Cook AM Leisinger T (1989) Monochloro- and dichloroacetic acids as carbon and energy sources for a stable methanogenic mixed culture Archives of Microbiology 152 218-223 Elsner M Haderlein SB Schwarzenbach RP (2004a) Reactivity of Fe(II)-bearing minerals towards reductive transformation of organic contaminants Environmental Science and Technology 38 799-807 Elsner M Haderlein SB Kellerhals T Luzi S Zwank L Angst W Schwarzenbach RP (2004b) Mechanisms and products of surface-mediated reductive dehalogenation of carbon tetrachloride by Fe(II) on goethite Environmental Science and Technology 38 2058-2066 Erbs M Hansen HCB Olsen CE (1999) Reductive dechlorination of carbon tetrachloride using iron(II)iron(III)-hydroxide-sulphate (green rust) Environmental Science and Technology 33 307-311 Euro Chlor (2001) Trichloroacetic acid in the environment a dossier Euro Chlor Brussels and the European Chlorinated Solvent Association Fadrus H Maly J (1975) Suppression of iron(III) interference in the determination of iron(II) in water by the 110-phenanthroline method The Analyst 100 549-554 Fahimi IJ Keppler F Schoumller HF (2003) Formation of chloroacetic acids from soil humic acid and phenolic moieties Chemosphere 52 513-520 Foy CL (1975) The chlorinated aliphatic acids In Herbicides Chemistry degradation and mode of action Kearney PC Kaufman DD (eds) Marcel Dekker Inc 399-452 Gander JW Parkin GF Scherer MM (2002) Kinetics of 111-trichloroethane transformation by iron sulfide and a methanogenic consortium Environmental Science and Technology 36 4540-4546 Haiber G Jacob G Niedan V Nkusi G Schoumller HF (1996) The occurrence of trichloroacetic acid (TCAA) ndash indications of a natural production Chemosphere 33 839-849

Hansen HCB (1989) Composition stabilization and light absorption of Fe(II)Fe(III) hydroxycarbonate (green rust) Clay Minerals 24 663-669 Hansen HCB Guldberg S Erbs M Koch CB (2001) Kinetics of nitrate reduction by green rusts ndash effects of interlayer anion and Fe(II)Fe(III) ratio Applied Clay Science 18 81-91 Hansen HCB Koch CB (1997) A comparison of nitrate reduction by carbonate and sulphate forms of green rust Kodama H Mermut A R Torrance J K (eds) Proceedings of the 11th International Clay Conference Ottawa Canada Clays for our future 11 295-302 Hoekstra EJ de Leer EWB Brinkman UATh (1999a) Mass balance of trichloroacetic acid in the soil top layer Chemosphere 38 551-563 Hoekstra EJ de Leer EWB Brinkman UATh (1999b) Findings supporting the natural

122 Chapter 5

formation of trichloroacetic acid in soil Chemosphere 38 2875-2883 Hofstetter TB Heijman CG Haderlein SB Holliger HC Schwarzenbach RP (1999) Complete reduction of TNT and other (poly)nitroaromatic compounds under iron-reducing subsurface conditions Environmental Science and Technology 33 1479-1487 Hofstetter TB Schwarzenbach RP Haderlein SB (2003) Reactivity of Fe(II) species associated with clay minerals Environmental Science and Technology 37 519-528 Hozalski RM Zhang L Arnold WA (2001) Reduction of haloacetic acids by Fe0 Implications for treatment and fate Environmental Science and Technology 35 2258-2263 Husain S Narsimha R Alvi SN Rao RN (1992) Monitoring the effluents of the trichloroacetic acid process by high-performance liquid chromatography Journal of Chromatography 600 316-319 Hwang I Batchelor B (2000) Reductive dechlorination of tetrachloroethylene by Fe(II) in cement slurries Environmental Science and Technology 34 5017-5022 Jordan A Frank H (1999) Trifluoroacetate in the environment Evidence for sources other than HFCHCFCs Environmental Science and Technology 33 522-527 Kenneke JF Weber EJ (2003) Reductive dehalogenation of halomethanes in iron- and sulfate-reducing sediments 1 reactivity pattern analysis Environmental Science and Technology 37 713-720 Kim CS Rytuba JJ Brown Jr GE (2004) EXAFS study of mercury(II) sorption to Fe- and Al-(hydr)oxides II Effects of chloride and sulphate Journal of Colloid and Interface Science 270 9-20 King DW (1998) Role of carbonate speciation on the oxidation rate of Fe(II) in aquatic systems Environmental Science and Technology 32 2997-3003 Klausen J Troumlber SP Haderlein SB Schwarzenbach RP (1995) Reduction of substituted nitrobenzenes by Fe(II) in aqueous mineral suspensions Environmental Science and Technology 29 2396-2404 Klug PH Alexander LE (1974) X-ray diffraction procedures John Wiley amp Sons Inc Koch CB Hansen HCB (1997) Reduction of nitrate to ammonium by sulphate green rust Advances in GeoEcology 30 373-393 Kuumlhn R Pattard M (1990) Results of the harmful effects of water pollutants to green algae (Scenedesmus subspicatus) in the cell multiplication inhibition test Water Research 24 31-38 Lee W Batchelor B (2002a) Abiotic reductive dechlorination of chlorinated ethylenes by iron- bearing soil minerals 1 Pyrite and magnetite Environmental Science and Technology 36 5147- 5154 Lee W Batchelor B (2002b) Abiotic reductive dechlorination of chlorinated ethylenes by iron-bearing soil minerals 2 Green rust Environmental Science and Technology 36 5348- 5354

Reductive Transformation of Trichloroacetate in Abiotic Fe(II)-Fe(III) Mineral Systems 123 Liger E Charlet L Van Cappellen P (1999) Surface catalysis of uranium (VI) reduction by iron(II) Geochimica et Cosmochimica Acta 63 2939-2955 Lignell R Heinonen-Tanski H Uusi-Rauva A (1984) Degradation of trichloroacetic acid (TCA) in soil Acta Agriculturae Scandinavia 34 3-8 Loyaux-Lawniczak S Refait Ph Lecomte P Ehrhardt J Geacutenin JMR (1999) The reduction of chromate ions by Fe(II) layered hydroxides Hydrology and Earth System Sciences 3 593-599 Luther III GW (1990) The Frontier-Molecular-Orbital theory approach in geochemical processes in W Stumm Ed Aquatic Chemical kinetics John Wiley and Sons New York pp 173-198 McCulloch A (2002) Trichloroacetic acid in the environment Chemosphere 47 667-686 Miyata S (1983) Anion-exchange properties of hydrotalcite-like compounds Clays and Clay Minerals 31 305-311 Muumlller SR Zweifel H-R Kinnison DJ Jacobsen JA Meier MA Ulrich MM Schwarzenbach RP (1996) Occurrence sources and fate of trichloroacetic acid in Swiss lakes Environmental Toxicology and Chemistry 15 1470-1478 OLoughlin EJ Burris DR (2003) Reduction of halogenated ethanes by green rust Environmental Toxicology and Chemistry 23 41-48 OLoughlin EJ Kelly SD Cook RE Csencsits R Kemner KM (2003a) Reduction of uranium(VI) by mixed iron(II)iron(III) hydroxide (green rust) Formation of UO2 nanoparticles Environmental Science and Technology 37 721-727 OLoughlin EJ Kelly SD Kemner KM Csencsits R Cook RE (2003b) Reduction of AgI AuIII CuII and HgII by FeIIFeIII hydroxysulfate green rust Chemosphere 53 437-446 OLoughlin EJ Kemner KM Burris DR (2003c) Effects of AgI AuIII and CuII on the reductive dechlorination of carbon tetrachloride by green rust Environmental Science and Technology 37 2905-2912 Ostergren JD Brown Jr GE Parks GA Persson P (2000) Inorganic ligand effects on Pb(II) sorption to goethite (α-FeOOH) II Sulfate Journal of Colloid and Interface Science 225 483-493 Pecher K Haderlein SB Schwarzenbach RP (2002) Reduction of polyhalogenated methanes by surface-bound Fe(II) in aqueous suspensions of iron oxides Environmental Science and Technology 36 1734-1741 Reimann S Grob K Frank H (1996) Chloroacetic acids in rainwater Environmental Science and Technology 30 2340-2344 Ruumlgge K Hofstetter TB Haderlein SB Bjerg PL Knudsen S Zraurig C Mosbaeligk H Christensen TH (1998) Characterization of predominant reductants in an anaerobic leachate- affected aquifer by nitroaromatic probe compounds Environmental Science and Technology 32

124 Chapter 5

23-31 Sarzanini C Bruzzoniti MC Mentasti E (1999) Preconcentration and separation of haloacetic acids by ion chromatography Journal of Chromatography A850 197-211 Schwertmann U Cornell RM (1991) Iron oxides in the laboratory Preparation and characterization VCH Verlagsgesellschaft mbH Weinheim Scott BF Mactavish DC Spencer C Strachan WMJ Muir DCG (2000) Haloacetic acids in Canadian lake waters and precipitation Environmental Science and Technology 34 4266-4272 Scott BF Spencer C Marvin CH Mactavish DC Muir DCG (2002) Distribution of haloacetic acids in the water columns of the Laurentian Great Lakes and Lake Malawi Environmental Science and Technology 36 1893-1898 Strathmann TJ Stone AT (2003) Mineral surface catalysis of reactions between FeII and oxime carbamate pesticides Geochimica et Cosmochimica Acta 67 2775-2791 Stumm W (1992) Chemistry of the solid-water interface John Wiley amp Sons Inc Van Cappellen P Charlet L Stumm W Wersin P (1993) A surface complexation model of the carbonate mineral-aqueous solution interface Geochimica et Cosmochimica Acta 57 3505- 3518 Vikesland PJ Valentine RL (2002) Iron oxide surface-catalyzed oxidation of ferrous iron by monochloramine implications of oxide type and carbonate on reactivity Environmental Science and Technology 36 512-519 Villalobos M Leckie JO (2000) Carbonate adsorption on goethite under closed and open CO2 conditions Geochimica et Cosmochimica Acta 64 3787-3802 Villalobos M Leckie JO (2001) Surface complexation modeling and FTIR study of carbonate adsorption to goethite Journal of Colloid and Interface Science 235 15-32 Vogel TM Criddle CS McCarty PL (1987) Transformations of halogenated aliphatic compounds Environmental Science and Technology 21 722-736 Weightman AL Weightman AJ Slater JH (1992) Microbial dehalogenation of trichloroacetic acid World Journal of Microbiology and Biotechnology 8 512-518 De Wever H Cole JR Fettig MR Hogan DA Tiedje JM (2000) Reductive dehalogenation of trichloroacetic acid by Trichlorobacter thiogenes gen nov spnov Applied and Environmental Microbiology 66 2297-2301 Williams AGB Scherer MM (2001) Kinetics of chromate reduction by carbonate green rust Environmental Science and Technology 35 3488-3494 Yu P Welander T (1995) Growth of an aerobic bacterium with trichloroacetic acid as the sole source of energy and carbon Applied Microbiology and Biotechnology 42 769-774

Conclusions and Outlook 125

6 Conclusions and Outlook The work presented in this dissertation adds to the understanding of how Fe(II)-

bearing minerals like green rusts (GRs) vivianite (Fe2(PO4)2sdot8H2O) magnetite

(Fe3O4) and Fe(II) associated with goethite and lepidocrocite may form and react in

nature In order to elucidate the role of bacteria in the formation of GRs in natural

soils and sediments we studied the iron mineral phases forming as a result of the

activity of iron-respiring bacteria In chapter 2 the Fe-containing products formed

by anaerobic autotrophic denitrifying Fe(II)-oxidizing bacteria (FeOB) were

examined The culture medium applied contained high levels of bicarbonate and

phosphate and is typically used in this kind of studies as it provides excellent

conditions for the nitrate-reducing FeOB Fe(II) was present initially as a whitish

solid Fe(II) hydroxy phosphate (vivianite) and as soluble Fe(II) The results

obtained demonstrate that the denitrifying FeOB produce poorly crystalline

goethite via a greenish Fe(III)-enriched vivianite intermediate Moumlssbauer

spectroscopic analyses provided no evidence of green rust formation At low

phosphate concentrations where vivianite does not control the Fe(II) activity it is

reasonable to assume that siderite (FeCO3) precipitates initially and that carbonate

GR phases may form during biooxidation At low bicarbonate concentrations we

would expect Fe(II) sulfate or chloride species to dominate initially (depending on

the Fe(II) source applied) and sulfate GR or chloride GR to form during

biooxidation In chapter 3 we investigated the Fe-containing products formed

during reduction of common Fe(III) oxides by the anaerobic dissimilatory Fe(III)-

reducing microorganism Shewanella algae BrY S algae BrY reduced substantial

amounts of the initial Fe(III) and green and blackish mineral phases were produced

within 1-2 weeks after inoculation Moumlssbauer spectroscopic analyses showed that

the green and black precipitates consisted of green rust and vivianite

We studied the reactivity of synthetic GRs towards reducible organic pollutants in

order to asses the potential significance of GR phases for the fate of such

126 Chapter 6

compounds To this end we used nitroaromatic compounds (NACs) and

chlorinated acetates as suitable model compounds for studying redox reactions

potentially relevant in the environment In chapter 4 we investigated the relative

reactivity of outer and inner Fe(II) reactive sites in synthetic sulfate green rust

(GR-SO4) by using a series of structurally closely related compounds with different



nitrophenylacetic acid Our results demonstrated that NACs are completely

reduced to their corresponding anilines by GR-SO4 The reactions followed pseudo

1 order kinetics with respect to NAC and the surface area-normalised pseudo 1

order rate constants obtained were 016ndash465middot10-4 s-1middotm-2middotL at [Fe(II)GR]0 = 103-


surface saturation kinetics could account for the similarity of the surface-

normalised pseudo 1 order rate constants obtained for the reduction of the neutral

and anionic NACs by GR-SO4 These observations suggest that the reaction

between NAC and GR-SO4 takes place at the external reactive Fe(II) sites At low

initial Fe(II)GR concentrations the external reactive Fe(II) sites were depleted and

the regeneration of new external reactive sites eventually controlled the reduction

of the NACs by GR-SO4 In chapter 5 we examined the reactivity of various

Fe(II)-Fe(III) mineral systems towards trichloroacetic acid (TCA) and

dichloroacetate (DCA) in laboratory batch experiments imitating natural

conditions The Fe(II)-Fe(III)-systems investigated included GR-SO4 carbonate

green rust magnetite Fe(II)goethite and Fe(II)lepidocrocite TCA was readily

reduced to DCA by all Fe(II)-containing minerals The reactions followed pseudo

1 order kinetics with respect to TCA and the surface area-normalised pseudo 1

order rate constants obtained were 033ndash76middot10-5 min-1middotm-2middotL at [Fe(II)]0 = 025ndash

116 mM [TCA]0 = 15ndash1000 microM and pH 70ndash87 Our results showed no

significant differences regarding product distribution and surface area-normalised

reaction rate constants between the Fe(II)-Fe(III)-systems DCA was not further


reduced to monochloroacetate (MCA) or acetate in any of the systems within the

time frame in our experiments

As suggested in chapters 2 and 3 sufficient evidence must be provided and caution

should be exercised when proclaiming new biogenic minerals The study of

microbially produced GRs is still in its infancy and more research is needed in

order to elucidate the role of bacteria in the formation of GRs in natural soils and

sediments The results presented in chapter 2 indicate that microbiological

processes may be responsible for the oxidation of vivianite and metavivianite

((FeII3-xFeIII

x)(PO4)2(OH)xmiddot(8-x)H2O x gt 12) in natural subsurface environments

In chapter 3 we demonstrated that GRs may be produced microbially at conditions

including low carbon and Fe(III) concentrations as well as the exclusion of

synthetic electron shuttles and pH buffers The role of microbial processes in the

redox cycling of iron in the subsurface and the ways in which these processes can

be coupled to contaminant remediation are currently active areas of research Zero-

valent iron has been the most extensively studied reductant for the treatment of

many inorganic and organic contaminants and is currently the most commonly

used material for the construction of permeable reactive barriers (PRB) but a

detailed understanding of the processes involved in the reduction of these

pollutants by Fe(0) is lacking (Scherer et al 2000) Potentially reactive Fe(II)-

bearing corrosion products identified in iron metal columns and barriers include

magnetite siderite Fe(II) sulfides green rusts as well as Fe(II) sorbed to mineral

surfaces (Gu et al 1999 Roh et al 2000) The formation of reactive Fe(II)-

bearing minerals like GRs may explain the effective long-term operation of zero-

valent iron PRBs despite the formation of thick oxide films Thus natural in situ

PRBs might be created by stimulating the activity of anaerobic dissimilatory

Fe(III)-reducing bacteria and the subsequent formation of Fe(II) species such as

GRs Furthermore suspensions of synthetic GRs which are easily prepared from

relatively inexpensive commodity chemicals may also be injected and dispersed

into the subsurface

128 Chapter 6

The reductive transformation of NACs and TCA by GRs is relevant to

understanding the processes responsible for their degradation in the subsurface and

the development of innovative technologies for their remediation The results

obtained in chapters 4 and 5 indicate that GRs may play a significant role in the

reductive transformation of NACs and TCA in natural subsurface environments

Furthermore our results suggest that mainly the outer Fe(II) sites in GRs are

utilized in the reaction with neutral and monovalent anionic compounds and that

these sites may be replenished eg by reduction of the oxidized surface sites or

adsorption of Fe(II) from solution The continuous restoration of Fe(II) surface

sites in GRs may promote their long-term reactivity towards reducible

contaminants

References

Gu B Phelps TJ Liang L Dickey MJ Roh Y Kinsall BL Palumbo AV Jacobs GK (1999) Biochemical dynamics in zero-valent iron columns Implications for permeable reactive barriers Environmental Science and Technology 33 2170-2177 Roh Y Lee SY Elless MP (2000) Characterization of corrosion products in the permeable reactive barriers Environmental Geology 40 184-194 Scherer MM Richter S Valentine RL Alvarez PJJ (2000) Chemistry and microbiology of permeable reactive barriers for In Situ groundwater clean up Critical Reviews in Environmental Science and Technology 30 363-411

Supporting Information I

7 Supporting Information


The one-electron reduction potential of the half-reaction for a given NAC 1hE

ArNO2 + e- ArNO2

can be used for comparing reduction rates of different NACs in a given system

The formation of the nitroaryl radical is the rate-determining step in the overall rate

of the reduction of a NAC to the corresponding aniline The difference between the

of a NAC and a given reductant is proportional to the change in standard free

energy for the transfer of the first electron ∆G

1hE

1degrsquo If a linear relationship between

the free energy of activation and ∆G1degrsquo is assumed the values of various NACs

can be a measure of their relative reactivity with a given reductant

1hE

As neither the one-electron reduction potential for 4-nitrophenylacetic acid (4-

NPA) nor the Hammett constant for the acetic acid substituent could be found in

the literature the one-electron reduction potential for 4-NPA was estimated by

application of a linear free energy relationship (LFER) to experimental data

Kinetic experiments were conducted in order to obtain the pseudo 1 order rate

constant for the reduction of 4-NPA by a model hydroquinone (reduced

juglone (8-hydroxy-14-naphthoquinone) in the presence of HS

minusHJUGk

ndash) The reduction of

a NAC by juglone follows the rate law

[ ] [ ] [ ] [ ] [ ] [ ]2222 ArNOJUGfkArNOHJUGkArNOk

dtArNOd

totHJUGHJUGHJUGobs sdotsdotsdot=sdotsdot=sdot=minus minusminusminusminus

and the was deducted from a LFER 1hE

II Chapter 7

bEak hHJUG +sdot=minus 059160

log1

for which a and b values have been established for a range of NACs with known

values (Hofstetter et al 1999) An excellent correlation of and log

has been found to exist over a range of 250 mV corresponding to more than 5 order

of magnitude for This is due to the fact that the actual transfer of the first

electron is the rate-determining step under the experimental conditions chosen

1hE 1

hE minusHJUGk

minusHJUGk

For comparison experiments with 4-nitrotoluene (4-NT) were also conducted The

pseudo 1 order rate constants for the reduction of 4-NPA with juglone were

corrected for the reduction of 4-NPA with only HSndash (control experiments

containing no juglone)

[ ]minuslowast

minusminus

minus

minus=

HJUGkk

k HSHJUGHJUG

where (MminusHJUGk -1middots-1) is the rate constant for a compound in the presence of only

juglone (slowastminusHJUGk -1) is the pseudo 1 order rate constant for a compound in the

presence of both juglone and HSndash (sminusHSk -1) is the pseudo 1 order rate constant for

the control reaction in the presence of only HSndash and [HJUGndash] (M) is the

concentration of the reactive dissociated HJUG- form (nondissociated

hydroquinone species are very nonreactive as compared to the monophenolate

species)

Supporting Information III

OH 0 OH OH

+ e- + H+ = + e- + H+ =

0 0

pl(( ox) = 8 00 PK1 (red) = 6 60

JUG HJUG

OH OH

OH

pKa2(red) = 10 60

Figure 7 1 Oxidized and reduced juglone fo1m s

Kinetic experiments in homogeneous anoxic aqueous solutions contained 5 mM

HS- 20 microM total juglone 50 mM KH2P04 buffer and were conducted at pH =

660 corresponding to a concentration of the reactive dissociated juglone form

[HJUG] = 10 microM

By using the LFER

E1 logkHJUG- = 125 middot 005~16 + 923

the following values were obtained

(Hofstetter et al 1999)

NAC k (M-1 -1) HJUG- middots log kHJUG- E~ (mV)

4-NT

4-NPA

311 middot10middot7

164middot10middot7

847middot 10-8

116middot 10middot7

226middot10middot2

489middot10middot3

-165

-231

-515

-546

IV Chapter 7

lowast

minusHJUGk -values are averages of triplicates whereas -values are averages of

duplicates The determined for 4-NT in this work (-515 mV) differs 3 from

the -value of -500 mV reported in the literature (Meisel amp Neta 1975

Wardman 1989) Hence it is assumed that the -value determined for 4-NPA

also differs by 3

minusHSk

1hE

1hE

1hE

Note that even for NACs holding very different values the difference in their

reactivities are much less pronounced in Fe(II)-Fe(III) systems such as the

Fe(II)goethite system (LFER slope a = 06 Hofstetter et al 1999) and the

Fe(II)magnetite system (LFER slope a = 034 Klausen et al 1995) as compared

to the jugloneH

1hE

2S system (a = 125) Furthermore it should be noted that all

LFERs mentioned here were established for neutral NACs and in this work we

have simply assumed that the LFERs are also valid for anionic NACs

72 The rate-limiting step

The overall rate of a reaction is equal to the rate of the slowest step in the

mechanism In heterogeneous reactions eg a compound reacting at the surface of

suspended particles in bulk solution the overall process by which the

heterogeneous reactions proceed may be broken down into a sequence of

individual diffusion steps and reaction steps 1) Mass transfer (diffusion) of the

reactant from the bulk fluid to the external surface of the solid phase 2)

Adsorption of reactant onto the solid surface 3) Reaction on the solid surface 4)

Desorption of the products from the solid surface 5) Mass transfer of the products

from the external solid surface to the bulk fluid Hence the rate of reaction of a

compound reacting at the surface of suspended particles in bulk solution may be

either mass transfer adsorptiondesorption or surface reaction limited When the

diffusion steps are much faster than the reaction steps the mass transfer or

diffusion steps do not affect the overall reaction rate However if the reaction steps

Supporting Information V

are very fast compared with the diffusion steps mass transport affects the reaction

rate Here only the external mass transfer is considered ie the diffusion of

reactants or products between the bulk fluid and the external surface of the solid

phase The additional internal mass transfer resistance for particles containing

substantial internal surface area is not addressed

721 Mass transfer (diffusion) limited kinetics

The overall rate constant can be represented by a system of resistances in series

(Fogler 1999 Arnold et al 1999)

⎟⎟⎠

⎞⎜⎜⎝

⎛+=

minusgeomSALobs kkak1111

where kobs is the observed rate constant kL is the mass transfer coefficient (mmiddots-1) a

is the ratio of the external (geometric) specific surface area to volume of solution

(m-1) and kSA-geom is the intrinsic rate constant of the reaction normalized to the

external specific surface area rather than the BET specific surface area By

comparing kLmiddota with kobs one can estimate the role of mass transfer on the rate of

reaction Thus if kLmiddota gtgt kobs mass transfer is so fast that it has no impact on the

reaction rate whereas if kLmiddota le kobs mass transfer is the rate limiting step

In fluid dynamics the Reynolds number Re is used for determining whether a

flow is laminar or turbulent

νtp ud sdot

=Re

where dp is the particle diameter (m) ut is the terminal particle settling velocity

(mmiddots-1) and ν is the kinematic fluid viscosity (m2middots-1) ν = η ρ where η is the

(absolute) dynamic fluid viscosity in centipoise (1 centipoise = 1 mPamiddots = 10-3

kgmiddotm-1middots-1) and ρ is the fluid density (kgmiddotm-3)

VI Chapter 7

At Re lt 1 we can apply Stokersquos particle settling velocity Stokersquos law is an

equation relating the terminal settling velocity of a smooth rigid sphere in a

viscous fluid of known density and viscosity to the diameter of the sphere when

subjected to a known force field

( )η

ρρsdot

minussdotsdot=

18

2pp

t

dgu (mmiddots-1)

where g = 981 mmiddots-2 is the gravitational constant ρp is the particle density (kgmiddotm-3)

The Sherwood number is the main parameter for prediction of the mass transfer

process

in fluid dynamics

3121 ScRe602Sh sdotsdot+=sdot

=lowast

lowast

iw

pL

Ddk

where Diw is the diffusion coefficient of the compound i in water (m2middots-1) is the

minimum (uncorrected) value of the mass transfer coefficient and Sc is the

Schmidt number This relation is often referred to as the Froumlssling correlation The

particle diameter is a key parameter in the Froumlssling correlation and the external

mass transfer coefficient varies with square of the particle size for smaller

particles

lowastLk

The Schmidt number is the ratio of the kinematic fluid viscosity and the diffusion

coefficient of the compound i in water

iwDν

=Sc

Supporting Information VII

According to Harriott (1962) the actual mass transfer coefficient kL is 15 times

greater than the minimum value of the mass transfer coefficient The

uncertainty in k

lowastLk

Lmiddota associated with particle sphericity and roughness issues are

believed not to exceed a factor of 2

The diffusion coefficient of a compound i in water can be estimated as (Hayduk amp

Laudie 1974)

5890141

9102613

iiw

VD

sdot

sdot=

minus

η (m2middots-1)

where iV is the molar volume of the compound i (cm3middotmol-1) estimated according

to Fuller et al 1966

Assuming spherical particles the external (geometric) specific surface area and the

particle diameter are calculated from the measured BET specific surface area Atot

assuming that our GR-SO4 has a AtotAouter ~ 30 similar to the one reported by

Hansen amp Koch (1998)

( ) ( ) ( )pppp

p

pp

p

dd

dV

SAAρρπ

πρ 1000

6

100061100030

SA3

2tot

geom sdot=

sdotsdot

sdot=

sdot== (m2middotg-1)

In our aqueous GR-SO4 system the density ρ = 1000 kgmiddotm-3 the absolute dynamic

viscosity η = 10-3 Pamiddots and the kinematic viscosity ν = 10-6 m2middots-1 for water The

GR-SO4 particle specific parameters used is found below

VIII Chapter 7

GR-SO4

Atot (m2g) 712

SAgeom (m2g) 237

Particle density ρp (kgm3) 1500

Particle diameter dp (m) 169middot10-6

Settling velocity ut (ms) 778middot10-7

Reynolds number 132middot10-6

The molar volumes the diffusion coefficients in water and the Schmidt numbers

for the NACs including 4-chloronitrobenzene (4-CNB) and nitrobenzene (NB)

were

Compound iV (cm3middotmol-1) Diw (m2middots-1) Sc

4-NT 1260 768middot10-10 1302

4-CNB 1230 779middot10-10 1284

4-NPA 1535 684middot10-10 1462

NB 1055 853middot10-10 1173

The ratio of the external (geometric) specific surface area to volume of solution

were calculated for GR-SO4 at the various concentrations applied

[Fe(II)GR]0 (mM) a (m-1)

103 366middot102

63 224middot103

126 448middot103

60 213middot103

The uncorrected mass transfer coefficients were estimated for the NACs using the

Froumlssling correlation

Supporting Information IX

[Fe(II)GR]0 (mM) lowastLk (mmiddots-1)

4-NT 912middot10-4

4-CNB 925middot10-4

4-NPA 812middot10-4

NB 101middot10-3

Finally kLmiddota was calculated and compared with the experimental 1 order rate

constants kobs obtained for the NACs

Compound [Fe(II)GR]0 (mM) kLmiddota (s-1) kobs (s-1) a

4-NT 103 050 420middot10-4

63 307 140middot10-3

126 613 590middot10-3

4-CNB 103 051 740middot10-4

63 311 170middot10-3

126 622 460middot10-3

4-NPA 103 045 640middot10-4

63 273 109middot10-3

126 546 473middot10-3

NB 60 324 137middot10-3 b

a Experimental pseudo 1 order rate constant at 50 microM [Ar-NO2]0 b Experimental pseudo 1 order rate constant at 10 microM [Ar-NO2]0

When comparing kLmiddota with kobs it can be seen that the rates of mass transfer for all

3 NACs exceed the observed rate constants by at least 3 or 4 orders of magnitude

at every initial Fe(II)GR concentration Thus the reaction of the given NACs with

GR-SO4 is not subject to mass transfer limitations under the experimental

conditions applied here

722 Surface saturation limited kinetics

More than 75 of all heterogeneous reactions that are not diffusion-limited are

surface-reaction-limited rather than adsorption- or desorption-limited We now

X Chapter 7

look at the reaction A = B = C where an intermediate B is formed In our system

A = Ar-NO2 B = Ar-NHOH and C = Ar-NH2 In this case the surface reaction is

assumed to be a single-site mechanism where only the site S on which A or B is

adsorbed is involved in the reaction forming B or C

KA

Adsorption 1 A + S = AmiddotS

kS1

Surface reaction 1 AmiddotS = BmiddotS

KB-1

Desorption 1 BmiddotS = B + S

KB

Adsorption 2 B + S = BmiddotS

kS2

Surface reaction 2 BmiddotS = CmiddotS

KC-1

Desorption 2 CmiddotS = C + S

The rate law for this surface-reaction limited single-site mechanism involving an

intermediate follows Langmuir-Hinshelwood kinetics (adopted from Fogler 1999)

CCBBAA

AAsitesSA

CKCKCKCKCk

dtdC

sdot+sdot+sdot+sdotsdotsdot

=minus1

1

Supporting Information XI

where kS1 is the intrinsic rate constant of the surface reaction transforming A into

the intermediate B Csites is the concentration of reactive sites S on the solid

surface KA KB and KC are the adsorption constants for A B and C at the reactive

surface sites and CA CB and CC are the concentrations of A B and C in the bulk

fluid Two major assumptions of the Langmuir isotherm imply that there is a fixed

number of localised surface sites present on the surface and that the activity of the

surface towards adsorption desorption or surface reaction is independent of

surface coverage

Hence fitting -∆CA∆t to CA CB and CC using a nonlinear curve fitting software

such as SigmaPlot may provide one with the intrinsic rate constant and the

adsorptions constants If KB and KC gtgt KA the intermediate and the product are

strongly competing with the reactant for vacant reactive surface sites

Our data was not fitted successfully by the Langmuir-Hinshelwood rate law

(regression results not shown) Simplifying the rate law by excluding either the

term KCmiddotCC or KBmiddotCB or both (assuming that the aniline product or the

hydroxylaniline intermediate or both did not compete for the reactive sites) did not

improve the regression The Langmuir-Hinshelwood rate law for a dual-site

mechanism did not fit our data either Thus Langmuir-Hinshelwood kinetics

cannot explain the reaction mechanism of the given NACs in our GR-SO4 system

73 External surface area of GR-SO4 and GR-CO3

The GR-SO4 unit cell consists of one double layer (d001 = 11 nm) ie one

hydroxide layer (049 nm ) and one interlayer (061 nm) Hexagonal GR-SO4

particles holding an average width of 1 microm (Figure 72) an average particle

thickness of 35 nm (Hansen amp Koch 1998) and a hydroxide layer thickness of

049 nm have a surface area of the basal plane

Abasal = 1 microm middot 1 microm ndash 2 middot 05 microm middot 025 microm = 075 microm2

XII Chapter 7

and a surface area of the edges

Aedge = (2 middot 05 microm + 4 middot 056 microm) middot 000049 microm = 00016 microm2

Figure 72 The hexagonal platy morphology of GR particles holding an average width of 1 microm

The particle thickness is the mean crystal thickness perpendicular to the 003 plane

as determined from the 003 reflections in an X-ray diffractogram A GR-SO4

particle holding a thickness of 35 nm contains 35 nm11 nm = 318 double layers

The GR-CO3 unit cell consists of one double layer (d001 = 075 nm) ie one

hydroxide layer (049 nm ) and one interlayer (026 nm) Hence a GR-CO3 particle

holding a thickness of 35 nm contains 35 nm075 nm = 467 double layers

The outer surface area of a GR-SO4 particle including outer basal planes and

edges is

Aouter = 222 microm 155microm 00016318microm 0752 =sdot+sdot

and the total surface area of a GR-SO4 particle including both inner and outer

basal planes as well as edges is

Supporting Information XIII

Atot = 222 microm 478)microm 00016microm 0752(318 =+sdotsdot

Hence the ratio of outer surface area to total surface area is

131microm 478microm 155

AA

2

2

tot

outer asymp=

Furthermore the ratio of edge surface area to outer surface area is

130microm 155

microm 00016318AA

2

2

outer

edge asympsdot

=

For GR-CO3 the outer surface area including outer basal planes and edges is


and the total surface area of a GR-CO3 particle including both inner and outer





AA

2

2

tot

outer asymp=


121microm 157

microm 00016467AA

2

2

outer

edge asympsdot

=

XIV Chapter 7

74 Van der Waals radii

The size of polyatomic molecules can be estimated by summing the van der Waals

radii of the

individual atoms Van der Waals radii or nonbonded radii can be pictured as the

radii of hard spherical atoms (Figure 73)

Figure 73 Schematic of neighboring nonbonded atoms with van der Waals radii rA and rB

Assuming that the spheres of neighboring nonbonded atoms just touch (Figure

73) the highest possible ion or molecule size Ms can be estimated as the sum of

the van der Waals radii

Ms = 2middotrA + 2middotrB + (1)

Taking Paulingrsquos rule for nonmetals into account we can estimate the real size of

polyatomic ions bound by covalent bonds (Pauling 1960) The van der Waals

radius is larger than the covalent radius because it involves the interposition of two

electron pairs between the atoms rather than one The rule states that the van der

Waals radius of an atom exceeds its covalent radius by ~008 nm (overlap in

Figure 74)

Figure 74 Schematic of atoms undergoing covalent bonding

Supporting Information XV

Thus the size of polyatomic ions bound by covalent bonds Ms can now be

estimated as the sum of the van der Waals radii subtracted by 008 nm

Ms = 2middot(rA - 008 nm) + 2middot(rB - 008 nm) + (2)

We estimated the molecular size of the NACs (Table 72) by means of equation (2)

and the van der Waals radii of the atoms in Table 71

Table 71 Van der Waals radii of various atoms Values from Pauling 1960

Atom vdW radii (nm)

H 0120

O 0140

N 0150

C 0170

Cl 0181

S 0185

In order to make the calculations it was assumed that all atoms were spherical and

that all bond angles were 90deg or 180deg (linear structures) In addition no distinctions

were made between single and double bonds The molecular sizes of the NACs

were estimated with the benzene ring representing the xy plane

Table 72 Molecular sizes of the NACs a Thickness z of the xy plane

Compound Ms (x) (nm) Ms (y) (nm) Ms (z) (nm)a

NB 054 080 036

4-NT 054 106 036

4-CNB 054 100 036

4-NPA 054 136 036

XVI Chapter 7

Note that the molecular sizes in Table 72 are only rough estimations

For comparison with the GR-SO4 interlayer spacing (061 nm) we consider three

possible orientations of the NACs in the GR-SO4 interlayer 1) The NAC xyz

coordination is equivalent to the crystal abc coordination (z = c = 036 nm) 2) the

NAC xy plane is parallel to the crystal bc plane (z = a = 054 nm) and 3) the NAC

xy plane is parallel to the crystal ac plane (z = b = 080-136 nm) Hence the sizes

of the NACs do not hinder their access to the GR-SO4 interlayer Only when

oriented vertically do the sizes of the NACs (z = b = 080-136 nm) exceed the GR-

SO4 interlayer spacing

The molecular size of trichloroacetate (TCA) was also estimated by means of

equation (2) and the atomic van der Waals radii in Table 71 When the TCA

aliphatic chain is assumed to represent the x direction (Ms (x) = 066 nm) the

molecular size in the y and z directions ranges from 045-053 nm depending on the

free rotation of the C-C bond Thus only if the C-C bond is oriented perpendicular

to the crystal ab plane does the size of TCA exceed the GR-SO4 interlayer spacing

(061 nm) In contrast the size of TCA exceeds the GR-CO3 interlayer spacing

(026 nm) regardless of its orientation

75 Adsorption of Fe(II) onto Fe(III) oxides

As seen from the Fe(II) sorption isotherms Fe(II) sorption varies widely between

the Fe(III) oxides as a function of solution pH (Figure 75) Average surface

densities of approximately 2 singly coordinated sitesnm2 iron oxide have been

suggested for goethite and lepidocrocite (Cornell amp Schwertmann 1996) The

similar surface site densities of goethite and lepidocrocite might explain their

similar Fe(II) adsorption isotherms (Figure 75)

Supporting Information XVII

Figure 75 Fe(II) adsorption edges for ferrihydrite goethite hematite lepidocrocite and

magnetite in the absence of other specifically adsorbing cations and anions (from Vikesland amp

Valentine 2002 and references therein) The total number of surface sites was in excess of the

total Fe(II) concentrations in all experiments

Dissolved cations or anions may specifically adsorb at the calcite and Fe(III) oxide

surfaces by exchanging for H+ or OHndash at the equivCO3H0 equivCaOH0 equivFeOH0 and

equivFeIIIOFeIIOH0 surface sites At the experimental conditions applied here within a

pH range 70-87 the dominant species of interest in solution are Fe2+ HCO3ndash

CO32ndash Clndash SO4

2ndash (only in the GR-SO4 systems) and the anionic TCA and DCA In

addition Fe2+ readily forms aqueous complexes with hydroxide carbonate

chloride and sulfate whereby the species FeOH+ FeHCO3+ Fe(OH)(CO3)ndash

FeCO30 Fe(CO3)2

2ndash FeCl+ and FeSO40 may occur (Millero amp Hawke 1992) At

pH 70-87 we expect the Fe(II) species Fe2+ FeCO30 Fe(OH)(CO3)ndash FeOH+ and

Fe(CO3)22ndash to dominate in the GR-CO3 and CaCO3(s)CO2(g) buffered magnetite

suspensions In the goecalcite and lepcalcite suspensions we expect the FeCl+

species to dominate as well whereas the Fe2+ FeSO40 and FeOH+ species most

XVIII Chapter 7

likely dominate in the GR-SO4 suspensions Anionic inorganic ligands like

carbonate chloride and sulfate can lower or enhance the adsorption of Fe(II) due to

a) formation of stable nonadsorbing Fe(II) ligand aqueous complexes b) formation

of Fe(II) ligand Fe(III) oxide surface complexes which can lead to surface

precipitation at high Fe(II) and ligand concentrations c) competitive ligand

sorption to the Fe(III) oxide surface blocking reactive sorption sites at the surface

and d) diminution of the positive charge at the Fe(III) oxide surface (at pH levels

below the point of zero charge (pHpzc) of the Fe(III) oxide) thereby decreasing the

electrostatic repulsion of cations by the Fe(III) oxide surface Specifically adsorbed

cations increase the pHpzc whereas specifically adsorbed anions decrease the pHpzc

References Arnold WA Ball WP Roberts AL (1999) Polychlorinated ethane reaction with zero-valent zinc Pathways and rate control Journal of Contaminant Hydrology 40 183-200 Cornell RM Schwertmann U (1996) The iron oxides Structure properties reactions occurrence and uses VCH Verlagsgesellschaft mbH Weinheim Fogler HS (1999) Elements of chemical reaction engineering 3rd ed Prentice Hall Fuller EN Schettler PD Giddings JC (1966) A new method for prediction of binary gas-phase diffusion coefficients Industrial and Engineering Chemistry 58 19-27 Hansen HCB Koch CB (1998) Reduction of nitrate to ammonium by sulphate green rust Activation energy and interlayer reaction mechanism Clay Minerals 33 87-101 Harriott P (1962) Mass transfer to particles Part I Suspended in agitated tanks AIChE Journal 8 93-102 Hayduk W Laudie H (1974) Prediction of diffusion coefficients for nonelectrolytes in dilute aqueous solutions AIChE Journal 20 611-615 Hofstetter TB Heijmann CG Haderlein SB Holliger C Schwarzenbach RP (1999) Complete reduction of TNT and other (poly)nitroaromatic compounds under iron-reducing subsurface conditions Environmental Science and Technology 33 1479-1487 Klausen J Troumlber SP Haderlein SB Schwarzenbach RP (1995) Reduction of substituted nitrobenzenes by Fe(II) in aqueous mineral suspensions Environmental Science and Technology 29 2396-2404 Meisel D Neta P (1975) One-electron redox potentials of nitro compounds and radiosensitizers Correlation with spin densities of their radical anions Journal of the American Chemical Society 97 5198-5203

Supporting Information XIX

Millero FJ Hawke DJ (1992) Ionic interactions of divalent metals in natural waters Marine Chemistry 40 19-48 Pauling L (1960) The nature of the chemical bond 3rd ed Cornell University Press Ithaca Vikesland PJ Valentine RL (2002) Iron oxide surface-catalyzed oxidation of ferrous iron by monochloramine implications of oxide type and carbonate on reactivity Environmental Science and Technology 36 512-519 Wardman P (1989) Reduction potentials of one-eletron couples involving free radicals in aqueous solution The Journal of Physical Chemistry Reference Data 18 1637-1755

Curriculum Vitae 13011973 Born in Haderslev Denmark 1988-1991 Mathematical high school Haderslev Katedralskole Denmark 1991-1992 Sabbatical year 1992-1995 B Sc in environmental chemistry University of Copenhagen

(KU) Denmark B Sc thesis 1995 ldquoMethane oxidizing bacteria in soilrdquo

1995-1998 M Sc in environmental chemistry University of Copenhagen

Denmark 1997-1998 diploma thesis ldquoReductive dechlorination of carbon tetrachloride and chloroform in presence of iron(II)iron(III)-hydroxides (green rust)rdquo

1998-1999 Research and teaching assistant at the Chemistry Department

The Royal Veterinary amp Agricultural University (KVL) Denmark

1999-2004 PhD in environmental sciences Swiss Federal Institute of

Technology Zuumlrich (ETHZ) and Swiss Federal Institute for Environmental Science and Technology (EAWAG) Switzerland Docoral thesis ldquoFormation and redox reactions of green rusts under geochemical conditions found in natural soils and sedimentsrdquo

2000-2002 Teaching assistent at the Swiss Federal Institute of Technology

Zuumlrich and supervision of diploma students 2002 Microbial Diversity summer course (7 weeks) at the Marine

Biological Laboratory Woods Hole Massachusetts USA

In fond memory of my mother

Esther Kristine Erbs (1949-2002)

who taught me how to be strong feel joy and bear compassion

I dedicate this work to her Without her support care and love

I would never have been the person I am today

To dare is to lose ones footing momentarily Not to dare is to lose oneself

Soslashren Kierkegaard

Acknowledgements
















anaerobic bacteria


Agency

Table of Contents








Table of Contents











Table of Contents







Zusammenfassung I









[FeII(6-x)FeIII





















II Zusammenfassung
























zusammensetzen





Zusammenfassung III






























IV Zusammenfassung













koumlnnen

Summary V

Summary










2- and y is the




















VI Summary








formation





















Summary VII












GR-SO4













in our experiments




VIII Summary



















1994)

































12 Green rusts









































al 2003)




































1991 Roh et al 2000)

6 Chapter 1


4SOa -3 and b) a = 10+2Fe-2

= 10minus24SOa -1






















































3)

























































microscopy




































Abstract

















21 Introduction










18 Chapter 2























anoxic interface





















nitrate















20 Chapter 2



















































x)(PO4)2(OH)x

22 Chapter 2

































(1998))


K2HPO4 25middot10-3



H3BO3 56middot10-5








NaCl 10middot10-5









NaNO3 40middot10-3

FeSO4 or FeCl2 0010









24 Chapter 2


































+





amp Villarruz 1963)





- at pH

70 ([HCO3-] = 2138middot[CO3







26 Chapter 2

a

































0

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

3

2

1

0

80 K

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

2 5

2 0

1 5

1 0

0 5

0 0

250 K



shown as full lines

28 Chapter 2




Whitish Fe(II)B 250 127 309 035 38

Fe(II)A 250 128 181 051 62


Fe(II)A 250 132 238 051 44

Fe(III) 250 036 085 040 38


1005

1000

0995

0990

- 0985 ~ e c 0980 0

-~ 0975 E c nl b 1000 g ~ Qi 0995 0

0990

0985

0980 -12 -8

~ -~


It

10 K


~ bull bull bull

-4 0 4 8 12

Velocity (mmls)














30

25

20

15

10

05

00

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

35

30

25

20

15

10

05

00

80 K

30

25

20

15

10

05

00

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

25

20

15

10

05

00

250 K



as full lines



30 Chapter 2




















0

2

3

- 4

~ 5 c ~ 6 e-0 7 -2 nl Q) 00 gt ~ 05 Qi 0 10

15

20

25

30

35

bullbullbull hi 6~





Velocity (mms)

31


















32 Chapter 2









predominant























0

2

- 3

~4 c

Q 5

e 6 0

~ 7 g

0 3l Q)

a 1

2

3

4

5

-12 a

40K

bull bull (




lines










34 Chapter 2



NO3- N2 NO3

- N2



















































oxidized as well

36 Chapter 2


biooxidation
























culture)











38 Chapter 2









(Figure 210d)

24 Conclusions



























Reduction Abstract























44 Chapter 3

31 Introduction



























































46 Chapter 3






































buffers






















48 Chapter 3





















































50 Chapter 3




K2HPO4 13middot10-3



H3BO3 56middot10-5








NaCl 10middot10-5




























52 Chapter 3




= 25 mM 100 N2(g) pH 55-60

























54 Chapter 3
















a)

c)

middot 12 -8 -4 4 8 12

Velocity (mmls

bull middot12 -8 -4 0 4 12

Velocity (mmls)

b)

middot12 -8 -4 4 8 12

Velocity (mmls






56 Chapter 3


































a) b)

c c g Q e- e 0 0 1l 1l

-~ bull ~


-12 -8 4 0 4 12


c)

-12 -8 4 8 12

v elocity (m mis)







fits are shown




58 Chapter 3




























































60 Chapter 3















34 Conclusions












Acknowledgments






2- with SO4


62 Chapter 3





64 Chapter 3





Abstract
























66 Chapter 4

41 Introduction





































c

ba


















68 Chapter 4















































70 Chapter 4









































with in the lab





72 Chapter 4






Carbagas)






of 1 deg2θmin












































74 Chapter 4















to be negligible

























0 --0 H OH H H --0 N N N N

2e- 2H+ H20 + 2e-~ 2e- 2H+ H20

~ ~ R R R










76 Chapter 4


















[ ] [ ] [ b 2

a GR


dtd ]












Tabl

e 4

1 S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

4-n

itrot

olue

ne (4

-NT)

4-

chlo

roni

trobe

nzen

e (4

-CN

B) a

nd 4

-nitr

ophe

nyla

cetic

aci

d (4

-NPA

) by

GR

-SO

4

Exp

erim

ent

Age

GR

(d

) [F

e(II

) GR] 0

(mM

) [N

AC

] 0 (micro

M)

[Fe(

II) G

R] 0

[N

AC

] 0∆[

ArN

O2]

(microM

) af b

k obs

(s-1

) ck o

bs (s

-1middotm

-2middotL

) d

GR

-SO

4 + 4

-NT

3 1

103

20

51

5

109

54

5

7

65middot1

0-46

95middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

50

20

6

174

34

8

7

41middot1

0-46

74middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

10

0 10

3

214

21

4

2

63middot1

0-42

39middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

55

18

7

177

32

2

4

21middot1

0-43

83middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

10

2 10

1

165

16

2

2

37middot1

0-42

15middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

25

412

9

7 38

8

4

82middot1

0-44

38middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

46

224

9

9 21

5

6

37middot1

0-45

79middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

100

103

13

7

137

196

middot10-4

178

middot10-5

GR

-SO

4 + 4

-NT

2 15

1

31

20

655

5

4 27

0

6

74middot1

0-44

82middot1

0-5

GR

-SO

4 + 4

-NT

2 15

1

31

50

262

9

7 19

4

5

89middot1

0-44

21middot1

0-5

GR

-SO

4 + 4

-NT

4 2

126

0 50

25

2 49

1

982

110

middot10-2

817

middot10-5

GR

-SO

4 + 4

-NT

4 2

630

50

12

6 42

6

852

186

middot10-3

276

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

126

0 30

42

0 29

0

967

925

middot10-3

687

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

630

50

12

6 38

0

760

136

middot10-3

202

middot10-5

GR

-SO

4 + 4

-NPA

2

2 12

60

40

315

371

92

8

5

96middot1

0-34

43middot1

0-5

GR

-SO

4 + 4

-NPA

2

2 6

30

45

140

273

60

7

1

09middot1

0-31

62middot1

0-5

a A

mou

nt o

f NA

C re

duce

d by

GR

-SO

4 at r

eact

ion

term

inat

ion

b F

ract

ion

of in

itial

ly a

dded

NA

C tr

ansf

orm

ed b

y G

R-S

O4 a

t rea

ctio

n te

rmin

atio

n c

Pse

udo

1

orde

r rat

e co

nsta

nts c

alcu

late

d as

initi

al ra

tes

ie m

ax f

irst t

wo

half-

lives

d S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

The

are

a of

GR

-SO

4 per

L

su

spen

sion

was

cal

cula

ted

as frac14

middot[Fe

(II)

GR] 0middot

600

gmiddotm

ol-1

middot71

2 m

2 middotg-1






between k

1hE






on log k

1hE

1hE



1hE



Compound pKa Eh1















80 Chapter 4













































limiting step

82 Chapter 4











































mineral systems












Fe(II) solely

84 Chapter 4




































[Fe(II)GR]0 (mM)





103 55 174 177 99

63 339 426 380 273






86 Chapter 4





















Scherer 2001)






































88 Chapter 4






















































available

44 Conclusions




90 Chapter 4




















(Elsner et al 2004)












Acknowledgments



References




2- with SO4











Abstract


























98 Chapter 5



51 Introduction























































100 Chapter 5











































nature














102 Chapter 5






















(999995 Ar Aldrich)





































104 Chapter 5






















































106 Chapter 5

Cl3CC

O

O- Cl2HCC

O

O-

2e- H+ Cl-











sdotsdot=minus kdt

d ]

















T

able

51

Exp

erim

enta

l con

ditio

ns a

nd p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

TC

A b

y va

rious

Fe(

II)-

Fe(I

II) c

onta

inin

g m

iner

al sy

stem

s

Syst

em

Susp

ensi

on a

ge

(d)

[Fe(

II)] s

olid

a (m

M)

[Fe(

II)] a

q b

(mM

) [T

CA

] 0 (micro

M)

pHin

itcpH

endd

k obs

e (min

-1)

Surf

ace

area

(m

2 L)

k obs

f

(min

-1m

-2middotL

)

Fe(I

I)aq

1

0

030

434

nd

76

gn

dn

dn

d

Fe(I

I)G

oe

1

002

024

429

nd

78

g1

021

0-47

1 i

143

10-5

Fe(I

I)G

oe

1

013

094

543

77

70

225

10-4

71

i3

161

0-5

Fe(I

I)G

oe

coat

ing

1

023

40

066

484

765

80

g6

401

0-454

0 j

119

10-5

Fe(I

I)G

oe

coat

ing

1

0

150

8048

6n

d7

6 g12

43

10-4

540

j2

301

0-5

Fe(I

I)L

ep

1

0

020

2315

7n

d7

8 g0

751

0-48

0 i

094

10-5

Fe(I

I)L

ep

coat

ing

1

016

30

137

470

765

80

g2

821

0-454

0 j

052

10-5

Fe(I

I)L

ep

coat

ing

1

0

100

8141

7n

d7

7 g8

311

0-454

0 j

154

10-5

Fe3O

41

3

380

1251

38

107

8g

830

10-4

16

k5

311

0-4

Fe3O

477

112

56

556

70

70

153

10-4

52

k2

951

0-5

GR

-CO

31

5

940

3950

37

658

4g

761

10-4

419

l1

821

0-5

GR

-CO

32

7

60

147

88

568

2940

81

0-453

6 l

761

10-5

GR

-CO

332

73

003

563

85

80

490

10-4

515

l0

951

0-5

GR

-CO

314

2

3

530

005

629

nd

87 g

513

10-4

249

l2

061

0-5

GR

-SO

41

5

17-1

217

086

-13

910

5n

dn

d3

601

0-492

6 m

039

10-5

GR

-SO

41

6

22-1

027

093

-14

527

0n

dn

d3

761

0-488

1 m

043

10-5

GR

-SO

41

7

05-1

014

077

-17

950

0n

dn

d3

741

0-4 9

18

m0

411

0-5

GR

-SO

41

5

17-1

051

060

-16

510

00n

dn

d2

891

0-483

7 m

035

10-5

n

d =

not

det

ecte

d a

Ini

tial s

truct

ural

or a

dsor

bed

Fe(I

I) e

stim

ated

as [

Fe(I

I)to

tal]

ndash [F

e(II

) aq]

b In

itial

dis

solv

ed F

e(II

) mea

sure

d c

Sus

pens

ion

pH p

rior t

o TC

A a

dditi

on d

Sus

pens

ion

pH a

t rea

ctio

n

te

rmin

atio

n e

Pse

udo

1 o

rder

rate

con

stan

ts fo

r the

con

sum

ptio

n of

TC

A c

alcu

late

d fr

om in

itial

rate

s (m

ax f

irst t

wo

half-

lives

) f

Surf

ace

area

-nor

mal

ised

pse

udo

1 o

rder

rate

con

stan

ts g

pH

con

trol

th

roug

h pu

re C

aCO

3 and

05

C

O2(g

) h

pH

con

trol t

hrou

gh F

e(II

I) o

xide

-coa

ted

calc

ite a

nd 0

5

CO

2(g)

i Es

timat

ed u

sing

the

SSA

of t

he F

e(II

I) o

xide

app

lied

j E

stim

ated

usi

ng th

e SS

A o

f cal

cite

~1

m2 g

k E

stim

ated

ass

umin

g SS

A =

4 m

2 g (S

chw

ertm

ann

amp C

orne

ll 1

991)

frac12middot[

Fe(I

I) sol

id] 0middot

232

gmiddotm

ol-1

middot4 m

2 middotg-1

l E

stim

ated

ass

umin

g SS

A =

47

m2 g

(Will

iam

s amp S

cher

er 2

001)

frac14middot[F

e(II

) GR] 0middot

600

gmiddotm

ol-1

middot47

m2 middotg

-1 m

Est

imat

ed a

s in l

but u

sing

SSA

= 7

12

m2 middotg

-1 (C

hapt

er 4

thi

s wor

k)



systems



















110 Chapter 5



























mM)


d001-spacing(nm)

Wfrac12(degθ)

0 9483 10821 0273

10 9494 10809 0287

215 9522 10777 0263

330 9550 10745 0273

510 9524 10775 0277

855 9509 10791 0253

1160 9467 10839 0268



















112 Chapter 5




















compounds






































114 Chapter 5


and TCA









































+ and equivCaOndash








116 Chapter 5



GR-SO4 FeII4FeIII


GR-CO3 FeII4FeIII

























































118 Chapter 5













































54 Conclusions













120 Chapter 5



Acknowledgments


GR-SO4

References





122 Chapter 5



124 Chapter 5






























126 Chapter 6







































((FeII3-xFeIII





















into the subsurface

128 Chapter 6











contaminants

References






ArNO2 + e- ArNO2






1hE




1hE








minusHJUGk




dtArNOd



II Chapter 7


log1






1hE 1

hE minusHJUGk

minusHJUGk





[ ]minuslowast

minusminus

minus

minus=

HJUGkk

k HSHJUGHJUG







species)


OH 0 OH OH

+ e- + H+ = + e- + H+ =

0 0

pl(( ox) = 8 00 PK1 (red) = 6 60

JUG HJUG

OH OH

OH

pKa2(red) = 10 60





[HJUG] = 10 microM

By using the LFER





4-NT

4-NPA

311 middot10middot7

164middot10middot7

847middot 10-8

116middot 10middot7

226middot10middot2

489middot10middot3

-165

-231

-515

-546

IV Chapter 7

lowast





also differs by 3

minusHSk

1hE

1hE

1hE





to the jugloneH

1hE



























⎟⎟⎠

⎞⎜⎜⎝

⎛+=











νtp ud sdot

=Re





VI Chapter 7





( )η

ρρsdot

minussdotsdot=

18

2pp

t

dgu (mmiddots-1)



process

in fluid dynamics


=lowast

lowast

iw

pL

Ddk






particles

lowastLk



iwDν

=Sc




uncertainty in k

lowastLk




Laudie 1974)

5890141

9102613

iiw

VD

sdot

sdot=

minus

η (m2middots-1)







( ) ( ) ( )pppp

p

pp

p

dd

dV

SAAρρπ

πρ 1000

6

100061100030

SA3

2tot

geom sdot=

sdotsdot

sdot=





VIII Chapter 7

GR-SO4

Atot (m2g) 712

SAgeom (m2g) 237







were


4-NT 1260 768middot10-10 1302

4-CNB 1230 779middot10-10 1284

4-NPA 1535 684middot10-10 1462

NB 1055 853middot10-10 1173




103 366middot102

63 224middot103

126 448middot103

60 213middot103





4-NT 912middot10-4

4-CNB 925middot10-4

4-NPA 812middot10-4

NB 101middot10-3




4-NT 103 050 420middot10-4

63 307 140middot10-3

126 613 590middot10-3

4-CNB 103 051 740middot10-4

63 311 170middot10-3

126 622 460middot10-3

4-NPA 103 045 640middot10-4

63 273 109middot10-3

126 546 473middot10-3

NB 60 324 137middot10-3 b










X Chapter 7





KA


kS1


KB-1


KB


kS2


KC-1




CCBBAA

AAsitesSA

CKCKCKCKCk

dtdC


=minus1

1









surface coverage



















XII Chapter 7











edges is








AA

2

2

tot

outer asymp=


130microm 155

microm 00016318AA

2

2

outer

edge asympsdot

=








AA

2

2

tot

outer asymp=


121microm 157

microm 00016467AA

2

2

outer

edge asympsdot

=

XIV Chapter 7



radii of the













Figure 74)









Atom vdW radii (nm)

H 0120

O 0140

N 0150

C 0170

Cl 0181

S 0185







NB 054 080 036

4-NT 054 106 036

4-CNB 054 100 036

4-NPA 054 136 036

XVI Chapter 7






































FeCO30 Fe(CO3)2






XVIII Chapter 7

























Acknowledgements
















anaerobic bacteria


Agency

Table of Contents








Table of Contents











Table of Contents







Zusammenfassung I









[FeII(6-x)FeIII





















II Zusammenfassung
























zusammensetzen





Zusammenfassung III






























IV Zusammenfassung













koumlnnen

Summary V

Summary










2- and y is the




















VI Summary








formation





















Summary VII












GR-SO4













in our experiments




VIII Summary



















1994)

































12 Green rusts









































al 2003)




































1991 Roh et al 2000)

6 Chapter 1


4SOa -3 and b) a = 10+2Fe-2

= 10minus24SOa -1






















































3)

























































microscopy




































Abstract

















21 Introduction










18 Chapter 2























anoxic interface





















nitrate















20 Chapter 2



















































x)(PO4)2(OH)x

22 Chapter 2

































(1998))


K2HPO4 25middot10-3



H3BO3 56middot10-5








NaCl 10middot10-5









NaNO3 40middot10-3

FeSO4 or FeCl2 0010









24 Chapter 2


































+





amp Villarruz 1963)





- at pH

70 ([HCO3-] = 2138middot[CO3







26 Chapter 2

a

































0

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

3

2

1

0

80 K

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

2 5

2 0

1 5

1 0

0 5

0 0

250 K



shown as full lines

28 Chapter 2




Whitish Fe(II)B 250 127 309 035 38

Fe(II)A 250 128 181 051 62


Fe(II)A 250 132 238 051 44

Fe(III) 250 036 085 040 38


1005

1000

0995

0990

- 0985 ~ e c 0980 0

-~ 0975 E c nl b 1000 g ~ Qi 0995 0

0990

0985

0980 -12 -8

~ -~


It

10 K


~ bull bull bull

-4 0 4 8 12

Velocity (mmls)














30

25

20

15

10

05

00

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

35

30

25

20

15

10

05

00

80 K

30

25

20

15

10

05

00

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

25

20

15

10

05

00

250 K



as full lines



30 Chapter 2




















0

2

3

- 4

~ 5 c ~ 6 e-0 7 -2 nl Q) 00 gt ~ 05 Qi 0 10

15

20

25

30

35

bullbullbull hi 6~





Velocity (mms)

31


















32 Chapter 2









predominant























0

2

- 3

~4 c

Q 5

e 6 0

~ 7 g

0 3l Q)

a 1

2

3

4

5

-12 a

40K

bull bull (




lines










34 Chapter 2



NO3- N2 NO3

- N2



















































oxidized as well

36 Chapter 2


biooxidation
























culture)











38 Chapter 2









(Figure 210d)

24 Conclusions



























Reduction Abstract























44 Chapter 3

31 Introduction



























































46 Chapter 3






































buffers






















48 Chapter 3





















































50 Chapter 3




K2HPO4 13middot10-3



H3BO3 56middot10-5








NaCl 10middot10-5




























52 Chapter 3




= 25 mM 100 N2(g) pH 55-60

























54 Chapter 3
















a)

c)

middot 12 -8 -4 4 8 12

Velocity (mmls

bull middot12 -8 -4 0 4 12

Velocity (mmls)

b)

middot12 -8 -4 4 8 12

Velocity (mmls






56 Chapter 3


































a) b)

c c g Q e- e 0 0 1l 1l

-~ bull ~


-12 -8 4 0 4 12


c)

-12 -8 4 8 12

v elocity (m mis)







fits are shown




58 Chapter 3




























































60 Chapter 3















34 Conclusions












Acknowledgments






2- with SO4


62 Chapter 3





64 Chapter 3





Abstract
























66 Chapter 4

41 Introduction





































c

ba


















68 Chapter 4















































70 Chapter 4









































with in the lab





72 Chapter 4






Carbagas)






of 1 deg2θmin












































74 Chapter 4















to be negligible

























0 --0 H OH H H --0 N N N N

2e- 2H+ H20 + 2e-~ 2e- 2H+ H20

~ ~ R R R










76 Chapter 4


















[ ] [ ] [ b 2

a GR


dtd ]












Tabl

e 4

1 S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

4-n

itrot

olue

ne (4

-NT)

4-

chlo

roni

trobe

nzen

e (4

-CN

B) a

nd 4

-nitr

ophe

nyla

cetic

aci

d (4

-NPA

) by

GR

-SO

4

Exp

erim

ent

Age

GR

(d

) [F

e(II

) GR] 0

(mM

) [N

AC

] 0 (micro

M)

[Fe(

II) G

R] 0

[N

AC

] 0∆[

ArN

O2]

(microM

) af b

k obs

(s-1

) ck o

bs (s

-1middotm

-2middotL

) d

GR

-SO

4 + 4

-NT

3 1

103

20

51

5

109

54

5

7

65middot1

0-46

95middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

50

20

6

174

34

8

7

41middot1

0-46

74middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

10

0 10

3

214

21

4

2

63middot1

0-42

39middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

55

18

7

177

32

2

4

21middot1

0-43

83middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

10

2 10

1

165

16

2

2

37middot1

0-42

15middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

25

412

9

7 38

8

4

82middot1

0-44

38middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

46

224

9

9 21

5

6

37middot1

0-45

79middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

100

103

13

7

137

196

middot10-4

178

middot10-5

GR

-SO

4 + 4

-NT

2 15

1

31

20

655

5

4 27

0

6

74middot1

0-44

82middot1

0-5

GR

-SO

4 + 4

-NT

2 15

1

31

50

262

9

7 19

4

5

89middot1

0-44

21middot1

0-5

GR

-SO

4 + 4

-NT

4 2

126

0 50

25

2 49

1

982

110

middot10-2

817

middot10-5

GR

-SO

4 + 4

-NT

4 2

630

50

12

6 42

6

852

186

middot10-3

276

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

126

0 30

42

0 29

0

967

925

middot10-3

687

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

630

50

12

6 38

0

760

136

middot10-3

202

middot10-5

GR

-SO

4 + 4

-NPA

2

2 12

60

40

315

371

92

8

5

96middot1

0-34

43middot1

0-5

GR

-SO

4 + 4

-NPA

2

2 6

30

45

140

273

60

7

1

09middot1

0-31

62middot1

0-5

a A

mou

nt o

f NA

C re

duce

d by

GR

-SO

4 at r

eact

ion

term

inat

ion

b F

ract

ion

of in

itial

ly a

dded

NA

C tr

ansf

orm

ed b

y G

R-S

O4 a

t rea

ctio

n te

rmin

atio

n c

Pse

udo

1

orde

r rat

e co

nsta

nts c

alcu

late

d as

initi

al ra

tes

ie m

ax f

irst t

wo

half-

lives

d S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

The

are

a of

GR

-SO

4 per

L

su

spen

sion

was

cal

cula

ted

as frac14

middot[Fe

(II)

GR] 0middot

600

gmiddotm

ol-1

middot71

2 m

2 middotg-1






between k

1hE






on log k

1hE

1hE



1hE



Compound pKa Eh1















80 Chapter 4













































limiting step

82 Chapter 4











































mineral systems












Fe(II) solely

84 Chapter 4




































[Fe(II)GR]0 (mM)





103 55 174 177 99

63 339 426 380 273






86 Chapter 4





















Scherer 2001)






































88 Chapter 4






















































available

44 Conclusions




90 Chapter 4




















(Elsner et al 2004)












Acknowledgments



References




2- with SO4











Abstract


























98 Chapter 5



51 Introduction























































100 Chapter 5











































nature














102 Chapter 5






















(999995 Ar Aldrich)





































104 Chapter 5






















































106 Chapter 5

Cl3CC

O

O- Cl2HCC

O

O-

2e- H+ Cl-











sdotsdot=minus kdt

d ]

















T

able

51

Exp

erim

enta

l con

ditio

ns a

nd p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

TC

A b

y va

rious

Fe(

II)-

Fe(I

II) c

onta

inin

g m

iner

al sy

stem

s

Syst

em

Susp

ensi

on a

ge

(d)

[Fe(

II)] s

olid

a (m

M)

[Fe(

II)] a

q b

(mM

) [T

CA

] 0 (micro

M)

pHin

itcpH

endd

k obs

e (min

-1)

Surf

ace

area

(m

2 L)

k obs

f

(min

-1m

-2middotL

)

Fe(I

I)aq

1

0

030

434

nd

76

gn

dn

dn

d

Fe(I

I)G

oe

1

002

024

429

nd

78

g1

021

0-47

1 i

143

10-5

Fe(I

I)G

oe

1

013

094

543

77

70

225

10-4

71

i3

161

0-5

Fe(I

I)G

oe

coat

ing

1

023

40

066

484

765

80

g6

401

0-454

0 j

119

10-5

Fe(I

I)G

oe

coat

ing

1

0

150

8048

6n

d7

6 g12

43

10-4

540

j2

301

0-5

Fe(I

I)L

ep

1

0

020

2315

7n

d7

8 g0

751

0-48

0 i

094

10-5

Fe(I

I)L

ep

coat

ing

1

016

30

137

470

765

80

g2

821

0-454

0 j

052

10-5

Fe(I

I)L

ep

coat

ing

1

0

100

8141

7n

d7

7 g8

311

0-454

0 j

154

10-5

Fe3O

41

3

380

1251

38

107

8g

830

10-4

16

k5

311

0-4

Fe3O

477

112

56

556

70

70

153

10-4

52

k2

951

0-5

GR

-CO

31

5

940

3950

37

658

4g

761

10-4

419

l1

821

0-5

GR

-CO

32

7

60

147

88

568

2940

81

0-453

6 l

761

10-5

GR

-CO

332

73

003

563

85

80

490

10-4

515

l0

951

0-5

GR

-CO

314

2

3

530

005

629

nd

87 g

513

10-4

249

l2

061

0-5

GR

-SO

41

5

17-1

217

086

-13

910

5n

dn

d3

601

0-492

6 m

039

10-5

GR

-SO

41

6

22-1

027

093

-14

527

0n

dn

d3

761

0-488

1 m

043

10-5

GR

-SO

41

7

05-1

014

077

-17

950

0n

dn

d3

741

0-4 9

18

m0

411

0-5

GR

-SO

41

5

17-1

051

060

-16

510

00n

dn

d2

891

0-483

7 m

035

10-5

n

d =

not

det

ecte

d a

Ini

tial s

truct

ural

or a

dsor

bed

Fe(I

I) e

stim

ated

as [

Fe(I

I)to

tal]

ndash [F

e(II

) aq]

b In

itial

dis

solv

ed F

e(II

) mea

sure

d c

Sus

pens

ion

pH p

rior t

o TC

A a

dditi

on d

Sus

pens

ion

pH a

t rea

ctio

n

te

rmin

atio

n e

Pse

udo

1 o

rder

rate

con

stan

ts fo

r the

con

sum

ptio

n of

TC

A c

alcu

late

d fr

om in

itial

rate

s (m

ax f

irst t

wo

half-

lives

) f

Surf

ace

area

-nor

mal

ised

pse

udo

1 o

rder

rate

con

stan

ts g

pH

con

trol

th

roug

h pu

re C

aCO

3 and

05

C

O2(g

) h

pH

con

trol t

hrou

gh F

e(II

I) o

xide

-coa

ted

calc

ite a

nd 0

5

CO

2(g)

i Es

timat

ed u

sing

the

SSA

of t

he F

e(II

I) o

xide

app

lied

j E

stim

ated

usi

ng th

e SS

A o

f cal

cite

~1

m2 g

k E

stim

ated

ass

umin

g SS

A =

4 m

2 g (S

chw

ertm

ann

amp C

orne

ll 1

991)

frac12middot[

Fe(I

I) sol

id] 0middot

232

gmiddotm

ol-1

middot4 m

2 middotg-1

l E

stim

ated

ass

umin

g SS

A =

47

m2 g

(Will

iam

s amp S

cher

er 2

001)

frac14middot[F

e(II

) GR] 0middot

600

gmiddotm

ol-1

middot47

m2 middotg

-1 m

Est

imat

ed a

s in l

but u

sing

SSA

= 7

12

m2 middotg

-1 (C

hapt

er 4

thi

s wor

k)



systems



















110 Chapter 5



























mM)


d001-spacing(nm)

Wfrac12(degθ)

0 9483 10821 0273

10 9494 10809 0287

215 9522 10777 0263

330 9550 10745 0273

510 9524 10775 0277

855 9509 10791 0253

1160 9467 10839 0268



















112 Chapter 5




















compounds






































114 Chapter 5


and TCA









































+ and equivCaOndash








116 Chapter 5



GR-SO4 FeII4FeIII


GR-CO3 FeII4FeIII

























































118 Chapter 5













































54 Conclusions













120 Chapter 5



Acknowledgments


GR-SO4

References





122 Chapter 5



124 Chapter 5






























126 Chapter 6







































((FeII3-xFeIII





















into the subsurface

128 Chapter 6











contaminants

References






ArNO2 + e- ArNO2






1hE




1hE








minusHJUGk




dtArNOd



II Chapter 7


log1






1hE 1

hE minusHJUGk

minusHJUGk





[ ]minuslowast

minusminus

minus

minus=

HJUGkk

k HSHJUGHJUG







species)


OH 0 OH OH

+ e- + H+ = + e- + H+ =

0 0

pl(( ox) = 8 00 PK1 (red) = 6 60

JUG HJUG

OH OH

OH

pKa2(red) = 10 60





[HJUG] = 10 microM

By using the LFER





4-NT

4-NPA

311 middot10middot7

164middot10middot7

847middot 10-8

116middot 10middot7

226middot10middot2

489middot10middot3

-165

-231

-515

-546

IV Chapter 7

lowast





also differs by 3

minusHSk

1hE

1hE

1hE





to the jugloneH

1hE



























⎟⎟⎠

⎞⎜⎜⎝

⎛+=











νtp ud sdot

=Re





VI Chapter 7





( )η

ρρsdot

minussdotsdot=

18

2pp

t

dgu (mmiddots-1)



process

in fluid dynamics


=lowast

lowast

iw

pL

Ddk






particles

lowastLk



iwDν

=Sc




uncertainty in k

lowastLk




Laudie 1974)

5890141

9102613

iiw

VD

sdot

sdot=

minus

η (m2middots-1)







( ) ( ) ( )pppp

p

pp

p

dd

dV

SAAρρπ

πρ 1000

6

100061100030

SA3

2tot

geom sdot=

sdotsdot

sdot=





VIII Chapter 7

GR-SO4

Atot (m2g) 712

SAgeom (m2g) 237







were


4-NT 1260 768middot10-10 1302

4-CNB 1230 779middot10-10 1284

4-NPA 1535 684middot10-10 1462

NB 1055 853middot10-10 1173




103 366middot102

63 224middot103

126 448middot103

60 213middot103





4-NT 912middot10-4

4-CNB 925middot10-4

4-NPA 812middot10-4

NB 101middot10-3




4-NT 103 050 420middot10-4

63 307 140middot10-3

126 613 590middot10-3

4-CNB 103 051 740middot10-4

63 311 170middot10-3

126 622 460middot10-3

4-NPA 103 045 640middot10-4

63 273 109middot10-3

126 546 473middot10-3

NB 60 324 137middot10-3 b










X Chapter 7





KA


kS1


KB-1


KB


kS2


KC-1




CCBBAA

AAsitesSA

CKCKCKCKCk

dtdC


=minus1

1









surface coverage



















XII Chapter 7











edges is








AA

2

2

tot

outer asymp=


130microm 155

microm 00016318AA

2

2

outer

edge asympsdot

=








AA

2

2

tot

outer asymp=


121microm 157

microm 00016467AA

2

2

outer

edge asympsdot

=

XIV Chapter 7



radii of the













Figure 74)









Atom vdW radii (nm)

H 0120

O 0140

N 0150

C 0170

Cl 0181

S 0185







NB 054 080 036

4-NT 054 106 036

4-CNB 054 100 036

4-NPA 054 136 036

XVI Chapter 7






































FeCO30 Fe(CO3)2






XVIII Chapter 7

























Table of Contents








Table of Contents











Table of Contents







Zusammenfassung I









[FeII(6-x)FeIII





















II Zusammenfassung
























zusammensetzen





Zusammenfassung III






























IV Zusammenfassung













koumlnnen

Summary V

Summary










2- and y is the




















VI Summary








formation





















Summary VII












GR-SO4













in our experiments




VIII Summary



















1994)

































12 Green rusts









































al 2003)




































1991 Roh et al 2000)

6 Chapter 1


4SOa -3 and b) a = 10+2Fe-2

= 10minus24SOa -1






















































3)

























































microscopy




































Abstract

















21 Introduction










18 Chapter 2























anoxic interface





















nitrate















20 Chapter 2



















































x)(PO4)2(OH)x

22 Chapter 2

































(1998))


K2HPO4 25middot10-3



H3BO3 56middot10-5








NaCl 10middot10-5









NaNO3 40middot10-3

FeSO4 or FeCl2 0010









24 Chapter 2


































+





amp Villarruz 1963)





- at pH

70 ([HCO3-] = 2138middot[CO3







26 Chapter 2

a

































0

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

3

2

1

0

80 K

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

2 5

2 0

1 5

1 0

0 5

0 0

250 K



shown as full lines

28 Chapter 2




Whitish Fe(II)B 250 127 309 035 38

Fe(II)A 250 128 181 051 62


Fe(II)A 250 132 238 051 44

Fe(III) 250 036 085 040 38


1005

1000

0995

0990

- 0985 ~ e c 0980 0

-~ 0975 E c nl b 1000 g ~ Qi 0995 0

0990

0985

0980 -12 -8

~ -~


It

10 K


~ bull bull bull

-4 0 4 8 12

Velocity (mmls)














30

25

20

15

10

05

00

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

35

30

25

20

15

10

05

00

80 K

30

25

20

15

10

05

00

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

25

20

15

10

05

00

250 K



as full lines



30 Chapter 2




















0

2

3

- 4

~ 5 c ~ 6 e-0 7 -2 nl Q) 00 gt ~ 05 Qi 0 10

15

20

25

30

35

bullbullbull hi 6~





Velocity (mms)

31


















32 Chapter 2









predominant























0

2

- 3

~4 c

Q 5

e 6 0

~ 7 g

0 3l Q)

a 1

2

3

4

5

-12 a

40K

bull bull (




lines










34 Chapter 2



NO3- N2 NO3

- N2



















































oxidized as well

36 Chapter 2


biooxidation
























culture)











38 Chapter 2









(Figure 210d)

24 Conclusions



























Reduction Abstract























44 Chapter 3

31 Introduction



























































46 Chapter 3






































buffers






















48 Chapter 3





















































50 Chapter 3




K2HPO4 13middot10-3



H3BO3 56middot10-5








NaCl 10middot10-5




























52 Chapter 3




= 25 mM 100 N2(g) pH 55-60

























54 Chapter 3
















a)

c)

middot 12 -8 -4 4 8 12

Velocity (mmls

bull middot12 -8 -4 0 4 12

Velocity (mmls)

b)

middot12 -8 -4 4 8 12

Velocity (mmls






56 Chapter 3


































a) b)

c c g Q e- e 0 0 1l 1l

-~ bull ~


-12 -8 4 0 4 12


c)

-12 -8 4 8 12

v elocity (m mis)







fits are shown




58 Chapter 3




























































60 Chapter 3















34 Conclusions












Acknowledgments






2- with SO4


62 Chapter 3





64 Chapter 3





Abstract
























66 Chapter 4

41 Introduction





































c

ba


















68 Chapter 4















































70 Chapter 4









































with in the lab





72 Chapter 4






Carbagas)






of 1 deg2θmin












































74 Chapter 4















to be negligible

























0 --0 H OH H H --0 N N N N

2e- 2H+ H20 + 2e-~ 2e- 2H+ H20

~ ~ R R R










76 Chapter 4


















[ ] [ ] [ b 2

a GR


dtd ]












Tabl

e 4

1 S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

4-n

itrot

olue

ne (4

-NT)

4-

chlo

roni

trobe

nzen

e (4

-CN

B) a

nd 4

-nitr

ophe

nyla

cetic

aci

d (4

-NPA

) by

GR

-SO

4

Exp

erim

ent

Age

GR

(d

) [F

e(II

) GR] 0

(mM

) [N

AC

] 0 (micro

M)

[Fe(

II) G

R] 0

[N

AC

] 0∆[

ArN

O2]

(microM

) af b

k obs

(s-1

) ck o

bs (s

-1middotm

-2middotL

) d

GR

-SO

4 + 4

-NT

3 1

103

20

51

5

109

54

5

7

65middot1

0-46

95middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

50

20

6

174

34

8

7

41middot1

0-46

74middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

10

0 10

3

214

21

4

2

63middot1

0-42

39middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

55

18

7

177

32

2

4

21middot1

0-43

83middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

10

2 10

1

165

16

2

2

37middot1

0-42

15middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

25

412

9

7 38

8

4

82middot1

0-44

38middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

46

224

9

9 21

5

6

37middot1

0-45

79middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

100

103

13

7

137

196

middot10-4

178

middot10-5

GR

-SO

4 + 4

-NT

2 15

1

31

20

655

5

4 27

0

6

74middot1

0-44

82middot1

0-5

GR

-SO

4 + 4

-NT

2 15

1

31

50

262

9

7 19

4

5

89middot1

0-44

21middot1

0-5

GR

-SO

4 + 4

-NT

4 2

126

0 50

25

2 49

1

982

110

middot10-2

817

middot10-5

GR

-SO

4 + 4

-NT

4 2

630

50

12

6 42

6

852

186

middot10-3

276

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

126

0 30

42

0 29

0

967

925

middot10-3

687

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

630

50

12

6 38

0

760

136

middot10-3

202

middot10-5

GR

-SO

4 + 4

-NPA

2

2 12

60

40

315

371

92

8

5

96middot1

0-34

43middot1

0-5

GR

-SO

4 + 4

-NPA

2

2 6

30

45

140

273

60

7

1

09middot1

0-31

62middot1

0-5

a A

mou

nt o

f NA

C re

duce

d by

GR

-SO

4 at r

eact

ion

term

inat

ion

b F

ract

ion

of in

itial

ly a

dded

NA

C tr

ansf

orm

ed b

y G

R-S

O4 a

t rea

ctio

n te

rmin

atio

n c

Pse

udo

1

orde

r rat

e co

nsta

nts c

alcu

late

d as

initi

al ra

tes

ie m

ax f

irst t

wo

half-

lives

d S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

The

are

a of

GR

-SO

4 per

L

su

spen

sion

was

cal

cula

ted

as frac14

middot[Fe

(II)

GR] 0middot

600

gmiddotm

ol-1

middot71

2 m

2 middotg-1






between k

1hE






on log k

1hE

1hE



1hE



Compound pKa Eh1















80 Chapter 4













































limiting step

82 Chapter 4











































mineral systems












Fe(II) solely

84 Chapter 4




































[Fe(II)GR]0 (mM)





103 55 174 177 99

63 339 426 380 273






86 Chapter 4





















Scherer 2001)






































88 Chapter 4






















































available

44 Conclusions




90 Chapter 4




















(Elsner et al 2004)












Acknowledgments



References




2- with SO4











Abstract


























98 Chapter 5



51 Introduction























































100 Chapter 5











































nature














102 Chapter 5






















(999995 Ar Aldrich)





































104 Chapter 5






















































106 Chapter 5

Cl3CC

O

O- Cl2HCC

O

O-

2e- H+ Cl-











sdotsdot=minus kdt

d ]

















T

able

51

Exp

erim

enta

l con

ditio

ns a

nd p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

TC

A b

y va

rious

Fe(

II)-

Fe(I

II) c

onta

inin

g m

iner

al sy

stem

s

Syst

em

Susp

ensi

on a

ge

(d)

[Fe(

II)] s

olid

a (m

M)

[Fe(

II)] a

q b

(mM

) [T

CA

] 0 (micro

M)

pHin

itcpH

endd

k obs

e (min

-1)

Surf

ace

area

(m

2 L)

k obs

f

(min

-1m

-2middotL

)

Fe(I

I)aq

1

0

030

434

nd

76

gn

dn

dn

d

Fe(I

I)G

oe

1

002

024

429

nd

78

g1

021

0-47

1 i

143

10-5

Fe(I

I)G

oe

1

013

094

543

77

70

225

10-4

71

i3

161

0-5

Fe(I

I)G

oe

coat

ing

1

023

40

066

484

765

80

g6

401

0-454

0 j

119

10-5

Fe(I

I)G

oe

coat

ing

1

0

150

8048

6n

d7

6 g12

43

10-4

540

j2

301

0-5

Fe(I

I)L

ep

1

0

020

2315

7n

d7

8 g0

751

0-48

0 i

094

10-5

Fe(I

I)L

ep

coat

ing

1

016

30

137

470

765

80

g2

821

0-454

0 j

052

10-5

Fe(I

I)L

ep

coat

ing

1

0

100

8141

7n

d7

7 g8

311

0-454

0 j

154

10-5

Fe3O

41

3

380

1251

38

107

8g

830

10-4

16

k5

311

0-4

Fe3O

477

112

56

556

70

70

153

10-4

52

k2

951

0-5

GR

-CO

31

5

940

3950

37

658

4g

761

10-4

419

l1

821

0-5

GR

-CO

32

7

60

147

88

568

2940

81

0-453

6 l

761

10-5

GR

-CO

332

73

003

563

85

80

490

10-4

515

l0

951

0-5

GR

-CO

314

2

3

530

005

629

nd

87 g

513

10-4

249

l2

061

0-5

GR

-SO

41

5

17-1

217

086

-13

910

5n

dn

d3

601

0-492

6 m

039

10-5

GR

-SO

41

6

22-1

027

093

-14

527

0n

dn

d3

761

0-488

1 m

043

10-5

GR

-SO

41

7

05-1

014

077

-17

950

0n

dn

d3

741

0-4 9

18

m0

411

0-5

GR

-SO

41

5

17-1

051

060

-16

510

00n

dn

d2

891

0-483

7 m

035

10-5

n

d =

not

det

ecte

d a

Ini

tial s

truct

ural

or a

dsor

bed

Fe(I

I) e

stim

ated

as [

Fe(I

I)to

tal]

ndash [F

e(II

) aq]

b In

itial

dis

solv

ed F

e(II

) mea

sure

d c

Sus

pens

ion

pH p

rior t

o TC

A a

dditi

on d

Sus

pens

ion

pH a

t rea

ctio

n

te

rmin

atio

n e

Pse

udo

1 o

rder

rate

con

stan

ts fo

r the

con

sum

ptio

n of

TC

A c

alcu

late

d fr

om in

itial

rate

s (m

ax f

irst t

wo

half-

lives

) f

Surf

ace

area

-nor

mal

ised

pse

udo

1 o

rder

rate

con

stan

ts g

pH

con

trol

th

roug

h pu

re C

aCO

3 and

05

C

O2(g

) h

pH

con

trol t

hrou

gh F

e(II

I) o

xide

-coa

ted

calc

ite a

nd 0

5

CO

2(g)

i Es

timat

ed u

sing

the

SSA

of t

he F

e(II

I) o

xide

app

lied

j E

stim

ated

usi

ng th

e SS

A o

f cal

cite

~1

m2 g

k E

stim

ated

ass

umin

g SS

A =

4 m

2 g (S

chw

ertm

ann

amp C

orne

ll 1

991)

frac12middot[

Fe(I

I) sol

id] 0middot

232

gmiddotm

ol-1

middot4 m

2 middotg-1

l E

stim

ated

ass

umin

g SS

A =

47

m2 g

(Will

iam

s amp S

cher

er 2

001)

frac14middot[F

e(II

) GR] 0middot

600

gmiddotm

ol-1

middot47

m2 middotg

-1 m

Est

imat

ed a

s in l

but u

sing

SSA

= 7

12

m2 middotg

-1 (C

hapt

er 4

thi

s wor

k)



systems



















110 Chapter 5



























mM)


d001-spacing(nm)

Wfrac12(degθ)

0 9483 10821 0273

10 9494 10809 0287

215 9522 10777 0263

330 9550 10745 0273

510 9524 10775 0277

855 9509 10791 0253

1160 9467 10839 0268



















112 Chapter 5




















compounds






































114 Chapter 5


and TCA









































+ and equivCaOndash








116 Chapter 5



GR-SO4 FeII4FeIII


GR-CO3 FeII4FeIII

























































118 Chapter 5













































54 Conclusions













120 Chapter 5



Acknowledgments


GR-SO4

References





122 Chapter 5



124 Chapter 5






























126 Chapter 6







































((FeII3-xFeIII





















into the subsurface

128 Chapter 6











contaminants

References






ArNO2 + e- ArNO2






1hE




1hE








minusHJUGk




dtArNOd



II Chapter 7


log1






1hE 1

hE minusHJUGk

minusHJUGk





[ ]minuslowast

minusminus

minus

minus=

HJUGkk

k HSHJUGHJUG







species)


OH 0 OH OH

+ e- + H+ = + e- + H+ =

0 0

pl(( ox) = 8 00 PK1 (red) = 6 60

JUG HJUG

OH OH

OH

pKa2(red) = 10 60





[HJUG] = 10 microM

By using the LFER





4-NT

4-NPA

311 middot10middot7

164middot10middot7

847middot 10-8

116middot 10middot7

226middot10middot2

489middot10middot3

-165

-231

-515

-546

IV Chapter 7

lowast





also differs by 3

minusHSk

1hE

1hE

1hE





to the jugloneH

1hE



























⎟⎟⎠

⎞⎜⎜⎝

⎛+=











νtp ud sdot

=Re





VI Chapter 7





( )η

ρρsdot

minussdotsdot=

18

2pp

t

dgu (mmiddots-1)



process

in fluid dynamics


=lowast

lowast

iw

pL

Ddk






particles

lowastLk



iwDν

=Sc




uncertainty in k

lowastLk




Laudie 1974)

5890141

9102613

iiw

VD

sdot

sdot=

minus

η (m2middots-1)







( ) ( ) ( )pppp

p

pp

p

dd

dV

SAAρρπ

πρ 1000

6

100061100030

SA3

2tot

geom sdot=

sdotsdot

sdot=





VIII Chapter 7

GR-SO4

Atot (m2g) 712

SAgeom (m2g) 237







were


4-NT 1260 768middot10-10 1302

4-CNB 1230 779middot10-10 1284

4-NPA 1535 684middot10-10 1462

NB 1055 853middot10-10 1173




103 366middot102

63 224middot103

126 448middot103

60 213middot103





4-NT 912middot10-4

4-CNB 925middot10-4

4-NPA 812middot10-4

NB 101middot10-3




4-NT 103 050 420middot10-4

63 307 140middot10-3

126 613 590middot10-3

4-CNB 103 051 740middot10-4

63 311 170middot10-3

126 622 460middot10-3

4-NPA 103 045 640middot10-4

63 273 109middot10-3

126 546 473middot10-3

NB 60 324 137middot10-3 b










X Chapter 7





KA


kS1


KB-1


KB


kS2


KC-1




CCBBAA

AAsitesSA

CKCKCKCKCk

dtdC


=minus1

1









surface coverage



















XII Chapter 7











edges is








AA

2

2

tot

outer asymp=


130microm 155

microm 00016318AA

2

2

outer

edge asympsdot

=








AA

2

2

tot

outer asymp=


121microm 157

microm 00016467AA

2

2

outer

edge asympsdot

=

XIV Chapter 7



radii of the













Figure 74)









Atom vdW radii (nm)

H 0120

O 0140

N 0150

C 0170

Cl 0181

S 0185







NB 054 080 036

4-NT 054 106 036

4-CNB 054 100 036

4-NPA 054 136 036

XVI Chapter 7






































FeCO30 Fe(CO3)2






XVIII Chapter 7

























Table of Contents











Table of Contents







Zusammenfassung I









[FeII(6-x)FeIII





















II Zusammenfassung
























zusammensetzen





Zusammenfassung III






























IV Zusammenfassung













koumlnnen

Summary V

Summary










2- and y is the




















VI Summary








formation





















Summary VII












GR-SO4













in our experiments




VIII Summary



















1994)

































12 Green rusts









































al 2003)




































1991 Roh et al 2000)

6 Chapter 1


4SOa -3 and b) a = 10+2Fe-2

= 10minus24SOa -1






















































3)

























































microscopy




































Abstract

















21 Introduction










18 Chapter 2























anoxic interface





















nitrate















20 Chapter 2



















































x)(PO4)2(OH)x

22 Chapter 2

































(1998))


K2HPO4 25middot10-3



H3BO3 56middot10-5








NaCl 10middot10-5









NaNO3 40middot10-3

FeSO4 or FeCl2 0010









24 Chapter 2


































+





amp Villarruz 1963)





- at pH

70 ([HCO3-] = 2138middot[CO3







26 Chapter 2

a

































0

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

3

2

1

0

80 K

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

2 5

2 0

1 5

1 0

0 5

0 0

250 K



shown as full lines

28 Chapter 2




Whitish Fe(II)B 250 127 309 035 38

Fe(II)A 250 128 181 051 62


Fe(II)A 250 132 238 051 44

Fe(III) 250 036 085 040 38


1005

1000

0995

0990

- 0985 ~ e c 0980 0

-~ 0975 E c nl b 1000 g ~ Qi 0995 0

0990

0985

0980 -12 -8

~ -~


It

10 K


~ bull bull bull

-4 0 4 8 12

Velocity (mmls)














30

25

20

15

10

05

00

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

35

30

25

20

15

10

05

00

80 K

30

25

20

15

10

05

00

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

25

20

15

10

05

00

250 K



as full lines



30 Chapter 2




















0

2

3

- 4

~ 5 c ~ 6 e-0 7 -2 nl Q) 00 gt ~ 05 Qi 0 10

15

20

25

30

35

bullbullbull hi 6~





Velocity (mms)

31


















32 Chapter 2









predominant























0

2

- 3

~4 c

Q 5

e 6 0

~ 7 g

0 3l Q)

a 1

2

3

4

5

-12 a

40K

bull bull (




lines










34 Chapter 2



NO3- N2 NO3

- N2



















































oxidized as well

36 Chapter 2


biooxidation
























culture)











38 Chapter 2









(Figure 210d)

24 Conclusions



























Reduction Abstract























44 Chapter 3

31 Introduction



























































46 Chapter 3






































buffers






















48 Chapter 3





















































50 Chapter 3




K2HPO4 13middot10-3



H3BO3 56middot10-5








NaCl 10middot10-5




























52 Chapter 3




= 25 mM 100 N2(g) pH 55-60

























54 Chapter 3
















a)

c)

middot 12 -8 -4 4 8 12

Velocity (mmls

bull middot12 -8 -4 0 4 12

Velocity (mmls)

b)

middot12 -8 -4 4 8 12

Velocity (mmls






56 Chapter 3


































a) b)

c c g Q e- e 0 0 1l 1l

-~ bull ~


-12 -8 4 0 4 12


c)

-12 -8 4 8 12

v elocity (m mis)







fits are shown




58 Chapter 3




























































60 Chapter 3















34 Conclusions












Acknowledgments






2- with SO4


62 Chapter 3





64 Chapter 3





Abstract
























66 Chapter 4

41 Introduction





































c

ba


















68 Chapter 4















































70 Chapter 4









































with in the lab





72 Chapter 4






Carbagas)






of 1 deg2θmin












































74 Chapter 4















to be negligible

























0 --0 H OH H H --0 N N N N

2e- 2H+ H20 + 2e-~ 2e- 2H+ H20

~ ~ R R R










76 Chapter 4


















[ ] [ ] [ b 2

a GR


dtd ]












Tabl

e 4

1 S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

4-n

itrot

olue

ne (4

-NT)

4-

chlo

roni

trobe

nzen

e (4

-CN

B) a

nd 4

-nitr

ophe

nyla

cetic

aci

d (4

-NPA

) by

GR

-SO

4

Exp

erim

ent

Age

GR

(d

) [F

e(II

) GR] 0

(mM

) [N

AC

] 0 (micro

M)

[Fe(

II) G

R] 0

[N

AC

] 0∆[

ArN

O2]

(microM

) af b

k obs

(s-1

) ck o

bs (s

-1middotm

-2middotL

) d

GR

-SO

4 + 4

-NT

3 1

103

20

51

5

109

54

5

7

65middot1

0-46

95middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

50

20

6

174

34

8

7

41middot1

0-46

74middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

10

0 10

3

214

21

4

2

63middot1

0-42

39middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

55

18

7

177

32

2

4

21middot1

0-43

83middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

10

2 10

1

165

16

2

2

37middot1

0-42

15middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

25

412

9

7 38

8

4

82middot1

0-44

38middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

46

224

9

9 21

5

6

37middot1

0-45

79middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

100

103

13

7

137

196

middot10-4

178

middot10-5

GR

-SO

4 + 4

-NT

2 15

1

31

20

655

5

4 27

0

6

74middot1

0-44

82middot1

0-5

GR

-SO

4 + 4

-NT

2 15

1

31

50

262

9

7 19

4

5

89middot1

0-44

21middot1

0-5

GR

-SO

4 + 4

-NT

4 2

126

0 50

25

2 49

1

982

110

middot10-2

817

middot10-5

GR

-SO

4 + 4

-NT

4 2

630

50

12

6 42

6

852

186

middot10-3

276

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

126

0 30

42

0 29

0

967

925

middot10-3

687

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

630

50

12

6 38

0

760

136

middot10-3

202

middot10-5

GR

-SO

4 + 4

-NPA

2

2 12

60

40

315

371

92

8

5

96middot1

0-34

43middot1

0-5

GR

-SO

4 + 4

-NPA

2

2 6

30

45

140

273

60

7

1

09middot1

0-31

62middot1

0-5

a A

mou

nt o

f NA

C re

duce

d by

GR

-SO

4 at r

eact

ion

term

inat

ion

b F

ract

ion

of in

itial

ly a

dded

NA

C tr

ansf

orm

ed b

y G

R-S

O4 a

t rea

ctio

n te

rmin

atio

n c

Pse

udo

1

orde

r rat

e co

nsta

nts c

alcu

late

d as

initi

al ra

tes

ie m

ax f

irst t

wo

half-

lives

d S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

The

are

a of

GR

-SO

4 per

L

su

spen

sion

was

cal

cula

ted

as frac14

middot[Fe

(II)

GR] 0middot

600

gmiddotm

ol-1

middot71

2 m

2 middotg-1






between k

1hE






on log k

1hE

1hE



1hE



Compound pKa Eh1















80 Chapter 4













































limiting step

82 Chapter 4











































mineral systems












Fe(II) solely

84 Chapter 4




































[Fe(II)GR]0 (mM)





103 55 174 177 99

63 339 426 380 273






86 Chapter 4





















Scherer 2001)






































88 Chapter 4






















































available

44 Conclusions




90 Chapter 4




















(Elsner et al 2004)












Acknowledgments



References




2- with SO4











Abstract


























98 Chapter 5



51 Introduction























































100 Chapter 5











































nature














102 Chapter 5






















(999995 Ar Aldrich)





































104 Chapter 5






















































106 Chapter 5

Cl3CC

O

O- Cl2HCC

O

O-

2e- H+ Cl-











sdotsdot=minus kdt

d ]

















T

able

51

Exp

erim

enta

l con

ditio

ns a

nd p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

TC

A b

y va

rious

Fe(

II)-

Fe(I

II) c

onta

inin

g m

iner

al sy

stem

s

Syst

em

Susp

ensi

on a

ge

(d)

[Fe(

II)] s

olid

a (m

M)

[Fe(

II)] a

q b

(mM

) [T

CA

] 0 (micro

M)

pHin

itcpH

endd

k obs

e (min

-1)

Surf

ace

area

(m

2 L)

k obs

f

(min

-1m

-2middotL

)

Fe(I

I)aq

1

0

030

434

nd

76

gn

dn

dn

d

Fe(I

I)G

oe

1

002

024

429

nd

78

g1

021

0-47

1 i

143

10-5

Fe(I

I)G

oe

1

013

094

543

77

70

225

10-4

71

i3

161

0-5

Fe(I

I)G

oe

coat

ing

1

023

40

066

484

765

80

g6

401

0-454

0 j

119

10-5

Fe(I

I)G

oe

coat

ing

1

0

150

8048

6n

d7

6 g12

43

10-4

540

j2

301

0-5

Fe(I

I)L

ep

1

0

020

2315

7n

d7

8 g0

751

0-48

0 i

094

10-5

Fe(I

I)L

ep

coat

ing

1

016

30

137

470

765

80

g2

821

0-454

0 j

052

10-5

Fe(I

I)L

ep

coat

ing

1

0

100

8141

7n

d7

7 g8

311

0-454

0 j

154

10-5

Fe3O

41

3

380

1251

38

107

8g

830

10-4

16

k5

311

0-4

Fe3O

477

112

56

556

70

70

153

10-4

52

k2

951

0-5

GR

-CO

31

5

940

3950

37

658

4g

761

10-4

419

l1

821

0-5

GR

-CO

32

7

60

147

88

568

2940

81

0-453

6 l

761

10-5

GR

-CO

332

73

003

563

85

80

490

10-4

515

l0

951

0-5

GR

-CO

314

2

3

530

005

629

nd

87 g

513

10-4

249

l2

061

0-5

GR

-SO

41

5

17-1

217

086

-13

910

5n

dn

d3

601

0-492

6 m

039

10-5

GR

-SO

41

6

22-1

027

093

-14

527

0n

dn

d3

761

0-488

1 m

043

10-5

GR

-SO

41

7

05-1

014

077

-17

950

0n

dn

d3

741

0-4 9

18

m0

411

0-5

GR

-SO

41

5

17-1

051

060

-16

510

00n

dn

d2

891

0-483

7 m

035

10-5

n

d =

not

det

ecte

d a

Ini

tial s

truct

ural

or a

dsor

bed

Fe(I

I) e

stim

ated

as [

Fe(I

I)to

tal]

ndash [F

e(II

) aq]

b In

itial

dis

solv

ed F

e(II

) mea

sure

d c

Sus

pens

ion

pH p

rior t

o TC

A a

dditi

on d

Sus

pens

ion

pH a

t rea

ctio

n

te

rmin

atio

n e

Pse

udo

1 o

rder

rate

con

stan

ts fo

r the

con

sum

ptio

n of

TC

A c

alcu

late

d fr

om in

itial

rate

s (m

ax f

irst t

wo

half-

lives

) f

Surf

ace

area

-nor

mal

ised

pse

udo

1 o

rder

rate

con

stan

ts g

pH

con

trol

th

roug

h pu

re C

aCO

3 and

05

C

O2(g

) h

pH

con

trol t

hrou

gh F

e(II

I) o

xide

-coa

ted

calc

ite a

nd 0

5

CO

2(g)

i Es

timat

ed u

sing

the

SSA

of t

he F

e(II

I) o

xide

app

lied

j E

stim

ated

usi

ng th

e SS

A o

f cal

cite

~1

m2 g

k E

stim

ated

ass

umin

g SS

A =

4 m

2 g (S

chw

ertm

ann

amp C

orne

ll 1

991)

frac12middot[

Fe(I

I) sol

id] 0middot

232

gmiddotm

ol-1

middot4 m

2 middotg-1

l E

stim

ated

ass

umin

g SS

A =

47

m2 g

(Will

iam

s amp S

cher

er 2

001)

frac14middot[F

e(II

) GR] 0middot

600

gmiddotm

ol-1

middot47

m2 middotg

-1 m

Est

imat

ed a

s in l

but u

sing

SSA

= 7

12

m2 middotg

-1 (C

hapt

er 4

thi

s wor

k)



systems



















110 Chapter 5



























mM)


d001-spacing(nm)

Wfrac12(degθ)

0 9483 10821 0273

10 9494 10809 0287

215 9522 10777 0263

330 9550 10745 0273

510 9524 10775 0277

855 9509 10791 0253

1160 9467 10839 0268



















112 Chapter 5




















compounds






































114 Chapter 5


and TCA









































+ and equivCaOndash








116 Chapter 5



GR-SO4 FeII4FeIII


GR-CO3 FeII4FeIII

























































118 Chapter 5













































54 Conclusions













120 Chapter 5



Acknowledgments


GR-SO4

References





122 Chapter 5



124 Chapter 5






























126 Chapter 6







































((FeII3-xFeIII





















into the subsurface

128 Chapter 6











contaminants

References






ArNO2 + e- ArNO2






1hE




1hE








minusHJUGk




dtArNOd



II Chapter 7


log1






1hE 1

hE minusHJUGk

minusHJUGk





[ ]minuslowast

minusminus

minus

minus=

HJUGkk

k HSHJUGHJUG







species)


OH 0 OH OH

+ e- + H+ = + e- + H+ =

0 0

pl(( ox) = 8 00 PK1 (red) = 6 60

JUG HJUG

OH OH

OH

pKa2(red) = 10 60





[HJUG] = 10 microM

By using the LFER





4-NT

4-NPA

311 middot10middot7

164middot10middot7

847middot 10-8

116middot 10middot7

226middot10middot2

489middot10middot3

-165

-231

-515

-546

IV Chapter 7

lowast





also differs by 3

minusHSk

1hE

1hE

1hE





to the jugloneH

1hE



























⎟⎟⎠

⎞⎜⎜⎝

⎛+=











νtp ud sdot

=Re





VI Chapter 7





( )η

ρρsdot

minussdotsdot=

18

2pp

t

dgu (mmiddots-1)



process

in fluid dynamics


=lowast

lowast

iw

pL

Ddk






particles

lowastLk



iwDν

=Sc




uncertainty in k

lowastLk




Laudie 1974)

5890141

9102613

iiw

VD

sdot

sdot=

minus

η (m2middots-1)







( ) ( ) ( )pppp

p

pp

p

dd

dV

SAAρρπ

πρ 1000

6

100061100030

SA3

2tot

geom sdot=

sdotsdot

sdot=





VIII Chapter 7

GR-SO4

Atot (m2g) 712

SAgeom (m2g) 237







were


4-NT 1260 768middot10-10 1302

4-CNB 1230 779middot10-10 1284

4-NPA 1535 684middot10-10 1462

NB 1055 853middot10-10 1173




103 366middot102

63 224middot103

126 448middot103

60 213middot103





4-NT 912middot10-4

4-CNB 925middot10-4

4-NPA 812middot10-4

NB 101middot10-3




4-NT 103 050 420middot10-4

63 307 140middot10-3

126 613 590middot10-3

4-CNB 103 051 740middot10-4

63 311 170middot10-3

126 622 460middot10-3

4-NPA 103 045 640middot10-4

63 273 109middot10-3

126 546 473middot10-3

NB 60 324 137middot10-3 b










X Chapter 7





KA


kS1


KB-1


KB


kS2


KC-1




CCBBAA

AAsitesSA

CKCKCKCKCk

dtdC


=minus1

1









surface coverage



















XII Chapter 7











edges is








AA

2

2

tot

outer asymp=


130microm 155

microm 00016318AA

2

2

outer

edge asympsdot

=








AA

2

2

tot

outer asymp=


121microm 157

microm 00016467AA

2

2

outer

edge asympsdot

=

XIV Chapter 7



radii of the













Figure 74)









Atom vdW radii (nm)

H 0120

O 0140

N 0150

C 0170

Cl 0181

S 0185







NB 054 080 036

4-NT 054 106 036

4-CNB 054 100 036

4-NPA 054 136 036

XVI Chapter 7






































FeCO30 Fe(CO3)2






XVIII Chapter 7

























Table of Contents







Zusammenfassung I









[FeII(6-x)FeIII





















II Zusammenfassung
























zusammensetzen





Zusammenfassung III






























IV Zusammenfassung













koumlnnen

Summary V

Summary










2- and y is the




















VI Summary








formation





















Summary VII












GR-SO4













in our experiments




VIII Summary



















1994)

































12 Green rusts









































al 2003)




































1991 Roh et al 2000)

6 Chapter 1


4SOa -3 and b) a = 10+2Fe-2

= 10minus24SOa -1






















































3)

























































microscopy




































Abstract

















21 Introduction










18 Chapter 2























anoxic interface





















nitrate















20 Chapter 2



















































x)(PO4)2(OH)x

22 Chapter 2

































(1998))


K2HPO4 25middot10-3



H3BO3 56middot10-5








NaCl 10middot10-5









NaNO3 40middot10-3

FeSO4 or FeCl2 0010









24 Chapter 2


































+





amp Villarruz 1963)





- at pH

70 ([HCO3-] = 2138middot[CO3







26 Chapter 2

a

































0

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

3

2

1

0

80 K

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

2 5

2 0

1 5

1 0

0 5

0 0

250 K



shown as full lines

28 Chapter 2




Whitish Fe(II)B 250 127 309 035 38

Fe(II)A 250 128 181 051 62


Fe(II)A 250 132 238 051 44

Fe(III) 250 036 085 040 38


1005

1000

0995

0990

- 0985 ~ e c 0980 0

-~ 0975 E c nl b 1000 g ~ Qi 0995 0

0990

0985

0980 -12 -8

~ -~


It

10 K


~ bull bull bull

-4 0 4 8 12

Velocity (mmls)














30

25

20

15

10

05

00

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

35

30

25

20

15

10

05

00

80 K

30

25

20

15

10

05

00

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

25

20

15

10

05

00

250 K



as full lines



30 Chapter 2




















0

2

3

- 4

~ 5 c ~ 6 e-0 7 -2 nl Q) 00 gt ~ 05 Qi 0 10

15

20

25

30

35

bullbullbull hi 6~





Velocity (mms)

31


















32 Chapter 2









predominant























0

2

- 3

~4 c

Q 5

e 6 0

~ 7 g

0 3l Q)

a 1

2

3

4

5

-12 a

40K

bull bull (




lines










34 Chapter 2



NO3- N2 NO3

- N2



















































oxidized as well

36 Chapter 2


biooxidation
























culture)











38 Chapter 2









(Figure 210d)

24 Conclusions



























Reduction Abstract























44 Chapter 3

31 Introduction



























































46 Chapter 3






































buffers






















48 Chapter 3





















































50 Chapter 3




K2HPO4 13middot10-3



H3BO3 56middot10-5








NaCl 10middot10-5




























52 Chapter 3




= 25 mM 100 N2(g) pH 55-60

























54 Chapter 3
















a)

c)

middot 12 -8 -4 4 8 12

Velocity (mmls

bull middot12 -8 -4 0 4 12

Velocity (mmls)

b)

middot12 -8 -4 4 8 12

Velocity (mmls






56 Chapter 3


































a) b)

c c g Q e- e 0 0 1l 1l

-~ bull ~


-12 -8 4 0 4 12


c)

-12 -8 4 8 12

v elocity (m mis)







fits are shown




58 Chapter 3




























































60 Chapter 3















34 Conclusions












Acknowledgments






2- with SO4


62 Chapter 3





64 Chapter 3





Abstract
























66 Chapter 4

41 Introduction





































c

ba


















68 Chapter 4















































70 Chapter 4









































with in the lab





72 Chapter 4






Carbagas)






of 1 deg2θmin












































74 Chapter 4















to be negligible

























0 --0 H OH H H --0 N N N N

2e- 2H+ H20 + 2e-~ 2e- 2H+ H20

~ ~ R R R










76 Chapter 4


















[ ] [ ] [ b 2

a GR


dtd ]












Tabl

e 4

1 S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

4-n

itrot

olue

ne (4

-NT)

4-

chlo

roni

trobe

nzen

e (4

-CN

B) a

nd 4

-nitr

ophe

nyla

cetic

aci

d (4

-NPA

) by

GR

-SO

4

Exp

erim

ent

Age

GR

(d

) [F

e(II

) GR] 0

(mM

) [N

AC

] 0 (micro

M)

[Fe(

II) G

R] 0

[N

AC

] 0∆[

ArN

O2]

(microM

) af b

k obs

(s-1

) ck o

bs (s

-1middotm

-2middotL

) d

GR

-SO

4 + 4

-NT

3 1

103

20

51

5

109

54

5

7

65middot1

0-46

95middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

50

20

6

174

34

8

7

41middot1

0-46

74middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

10

0 10

3

214

21

4

2

63middot1

0-42

39middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

55

18

7

177

32

2

4

21middot1

0-43

83middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

10

2 10

1

165

16

2

2

37middot1

0-42

15middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

25

412

9

7 38

8

4

82middot1

0-44

38middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

46

224

9

9 21

5

6

37middot1

0-45

79middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

100

103

13

7

137

196

middot10-4

178

middot10-5

GR

-SO

4 + 4

-NT

2 15

1

31

20

655

5

4 27

0

6

74middot1

0-44

82middot1

0-5

GR

-SO

4 + 4

-NT

2 15

1

31

50

262

9

7 19

4

5

89middot1

0-44

21middot1

0-5

GR

-SO

4 + 4

-NT

4 2

126

0 50

25

2 49

1

982

110

middot10-2

817

middot10-5

GR

-SO

4 + 4

-NT

4 2

630

50

12

6 42

6

852

186

middot10-3

276

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

126

0 30

42

0 29

0

967

925

middot10-3

687

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

630

50

12

6 38

0

760

136

middot10-3

202

middot10-5

GR

-SO

4 + 4

-NPA

2

2 12

60

40

315

371

92

8

5

96middot1

0-34

43middot1

0-5

GR

-SO

4 + 4

-NPA

2

2 6

30

45

140

273

60

7

1

09middot1

0-31

62middot1

0-5

a A

mou

nt o

f NA

C re

duce

d by

GR

-SO

4 at r

eact

ion

term

inat

ion

b F

ract

ion

of in

itial

ly a

dded

NA

C tr

ansf

orm

ed b

y G

R-S

O4 a

t rea

ctio

n te

rmin

atio

n c

Pse

udo

1

orde

r rat

e co

nsta

nts c

alcu

late

d as

initi

al ra

tes

ie m

ax f

irst t

wo

half-

lives

d S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

The

are

a of

GR

-SO

4 per

L

su

spen

sion

was

cal

cula

ted

as frac14

middot[Fe

(II)

GR] 0middot

600

gmiddotm

ol-1

middot71

2 m

2 middotg-1






between k

1hE






on log k

1hE

1hE



1hE



Compound pKa Eh1















80 Chapter 4













































limiting step

82 Chapter 4











































mineral systems












Fe(II) solely

84 Chapter 4




































[Fe(II)GR]0 (mM)





103 55 174 177 99

63 339 426 380 273






86 Chapter 4





















Scherer 2001)






































88 Chapter 4






















































available

44 Conclusions




90 Chapter 4




















(Elsner et al 2004)












Acknowledgments



References




2- with SO4











Abstract


























98 Chapter 5



51 Introduction























































100 Chapter 5











































nature














102 Chapter 5






















(999995 Ar Aldrich)





































104 Chapter 5






















































106 Chapter 5

Cl3CC

O

O- Cl2HCC

O

O-

2e- H+ Cl-











sdotsdot=minus kdt

d ]

















T

able

51

Exp

erim

enta

l con

ditio

ns a

nd p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

TC

A b

y va

rious

Fe(

II)-

Fe(I

II) c

onta

inin

g m

iner

al sy

stem

s

Syst

em

Susp

ensi

on a

ge

(d)

[Fe(

II)] s

olid

a (m

M)

[Fe(

II)] a

q b

(mM

) [T

CA

] 0 (micro

M)

pHin

itcpH

endd

k obs

e (min

-1)

Surf

ace

area

(m

2 L)

k obs

f

(min

-1m

-2middotL

)

Fe(I

I)aq

1

0

030

434

nd

76

gn

dn

dn

d

Fe(I

I)G

oe

1

002

024

429

nd

78

g1

021

0-47

1 i

143

10-5

Fe(I

I)G

oe

1

013

094

543

77

70

225

10-4

71

i3

161

0-5

Fe(I

I)G

oe

coat

ing

1

023

40

066

484

765

80

g6

401

0-454

0 j

119

10-5

Fe(I

I)G

oe

coat

ing

1

0

150

8048

6n

d7

6 g12

43

10-4

540

j2

301

0-5

Fe(I

I)L

ep

1

0

020

2315

7n

d7

8 g0

751

0-48

0 i

094

10-5

Fe(I

I)L

ep

coat

ing

1

016

30

137

470

765

80

g2

821

0-454

0 j

052

10-5

Fe(I

I)L

ep

coat

ing

1

0

100

8141

7n

d7

7 g8

311

0-454

0 j

154

10-5

Fe3O

41

3

380

1251

38

107

8g

830

10-4

16

k5

311

0-4

Fe3O

477

112

56

556

70

70

153

10-4

52

k2

951

0-5

GR

-CO

31

5

940

3950

37

658

4g

761

10-4

419

l1

821

0-5

GR

-CO

32

7

60

147

88

568

2940

81

0-453

6 l

761

10-5

GR

-CO

332

73

003

563

85

80

490

10-4

515

l0

951

0-5

GR

-CO

314

2

3

530

005

629

nd

87 g

513

10-4

249

l2

061

0-5

GR

-SO

41

5

17-1

217

086

-13

910

5n

dn

d3

601

0-492

6 m

039

10-5

GR

-SO

41

6

22-1

027

093

-14

527

0n

dn

d3

761

0-488

1 m

043

10-5

GR

-SO

41

7

05-1

014

077

-17

950

0n

dn

d3

741

0-4 9

18

m0

411

0-5

GR

-SO

41

5

17-1

051

060

-16

510

00n

dn

d2

891

0-483

7 m

035

10-5

n

d =

not

det

ecte

d a

Ini

tial s

truct

ural

or a

dsor

bed

Fe(I

I) e

stim

ated

as [

Fe(I

I)to

tal]

ndash [F

e(II

) aq]

b In

itial

dis

solv

ed F

e(II

) mea

sure

d c

Sus

pens

ion

pH p

rior t

o TC

A a

dditi

on d

Sus

pens

ion

pH a

t rea

ctio

n

te

rmin

atio

n e

Pse

udo

1 o

rder

rate

con

stan

ts fo

r the

con

sum

ptio

n of

TC

A c

alcu

late

d fr

om in

itial

rate

s (m

ax f

irst t

wo

half-

lives

) f

Surf

ace

area

-nor

mal

ised

pse

udo

1 o

rder

rate

con

stan

ts g

pH

con

trol

th

roug

h pu

re C

aCO

3 and

05

C

O2(g

) h

pH

con

trol t

hrou

gh F

e(II

I) o

xide

-coa

ted

calc

ite a

nd 0

5

CO

2(g)

i Es

timat

ed u

sing

the

SSA

of t

he F

e(II

I) o

xide

app

lied

j E

stim

ated

usi

ng th

e SS

A o

f cal

cite

~1

m2 g

k E

stim

ated

ass

umin

g SS

A =

4 m

2 g (S

chw

ertm

ann

amp C

orne

ll 1

991)

frac12middot[

Fe(I

I) sol

id] 0middot

232

gmiddotm

ol-1

middot4 m

2 middotg-1

l E

stim

ated

ass

umin

g SS

A =

47

m2 g

(Will

iam

s amp S

cher

er 2

001)

frac14middot[F

e(II

) GR] 0middot

600

gmiddotm

ol-1

middot47

m2 middotg

-1 m

Est

imat

ed a

s in l

but u

sing

SSA

= 7

12

m2 middotg

-1 (C

hapt

er 4

thi

s wor

k)



systems



















110 Chapter 5



























mM)


d001-spacing(nm)

Wfrac12(degθ)

0 9483 10821 0273

10 9494 10809 0287

215 9522 10777 0263

330 9550 10745 0273

510 9524 10775 0277

855 9509 10791 0253

1160 9467 10839 0268



















112 Chapter 5




















compounds






































114 Chapter 5


and TCA









































+ and equivCaOndash








116 Chapter 5



GR-SO4 FeII4FeIII


GR-CO3 FeII4FeIII

























































118 Chapter 5













































54 Conclusions













120 Chapter 5



Acknowledgments


GR-SO4

References





122 Chapter 5



124 Chapter 5






























126 Chapter 6







































((FeII3-xFeIII





















into the subsurface

128 Chapter 6











contaminants

References






ArNO2 + e- ArNO2






1hE




1hE








minusHJUGk




dtArNOd



II Chapter 7


log1






1hE 1

hE minusHJUGk

minusHJUGk





[ ]minuslowast

minusminus

minus

minus=

HJUGkk

k HSHJUGHJUG







species)


OH 0 OH OH

+ e- + H+ = + e- + H+ =

0 0

pl(( ox) = 8 00 PK1 (red) = 6 60

JUG HJUG

OH OH

OH

pKa2(red) = 10 60





[HJUG] = 10 microM

By using the LFER





4-NT

4-NPA

311 middot10middot7

164middot10middot7

847middot 10-8

116middot 10middot7

226middot10middot2

489middot10middot3

-165

-231

-515

-546

IV Chapter 7

lowast





also differs by 3

minusHSk

1hE

1hE

1hE





to the jugloneH

1hE



























⎟⎟⎠

⎞⎜⎜⎝

⎛+=











νtp ud sdot

=Re





VI Chapter 7





( )η

ρρsdot

minussdotsdot=

18

2pp

t

dgu (mmiddots-1)



process

in fluid dynamics


=lowast

lowast

iw

pL

Ddk






particles

lowastLk



iwDν

=Sc




uncertainty in k

lowastLk




Laudie 1974)

5890141

9102613

iiw

VD

sdot

sdot=

minus

η (m2middots-1)







( ) ( ) ( )pppp

p

pp

p

dd

dV

SAAρρπ

πρ 1000

6

100061100030

SA3

2tot

geom sdot=

sdotsdot

sdot=





VIII Chapter 7

GR-SO4

Atot (m2g) 712

SAgeom (m2g) 237







were


4-NT 1260 768middot10-10 1302

4-CNB 1230 779middot10-10 1284

4-NPA 1535 684middot10-10 1462

NB 1055 853middot10-10 1173




103 366middot102

63 224middot103

126 448middot103

60 213middot103





4-NT 912middot10-4

4-CNB 925middot10-4

4-NPA 812middot10-4

NB 101middot10-3




4-NT 103 050 420middot10-4

63 307 140middot10-3

126 613 590middot10-3

4-CNB 103 051 740middot10-4

63 311 170middot10-3

126 622 460middot10-3

4-NPA 103 045 640middot10-4

63 273 109middot10-3

126 546 473middot10-3

NB 60 324 137middot10-3 b










X Chapter 7





KA


kS1


KB-1


KB


kS2


KC-1




CCBBAA

AAsitesSA

CKCKCKCKCk

dtdC


=minus1

1









surface coverage



















XII Chapter 7











edges is








AA

2

2

tot

outer asymp=


130microm 155

microm 00016318AA

2

2

outer

edge asympsdot

=








AA

2

2

tot

outer asymp=


121microm 157

microm 00016467AA

2

2

outer

edge asympsdot

=

XIV Chapter 7



radii of the













Figure 74)









Atom vdW radii (nm)

H 0120

O 0140

N 0150

C 0170

Cl 0181

S 0185







NB 054 080 036

4-NT 054 106 036

4-CNB 054 100 036

4-NPA 054 136 036

XVI Chapter 7






































FeCO30 Fe(CO3)2






XVIII Chapter 7

























Zusammenfassung I









[FeII(6-x)FeIII





















II Zusammenfassung
























zusammensetzen





Zusammenfassung III






























IV Zusammenfassung













koumlnnen

Summary V

Summary










2- and y is the




















VI Summary








formation





















Summary VII












GR-SO4













in our experiments




VIII Summary



















1994)

































12 Green rusts









































al 2003)




































1991 Roh et al 2000)

6 Chapter 1


4SOa -3 and b) a = 10+2Fe-2

= 10minus24SOa -1






















































3)

























































microscopy




































Abstract

















21 Introduction










18 Chapter 2























anoxic interface





















nitrate















20 Chapter 2



















































x)(PO4)2(OH)x

22 Chapter 2

































(1998))


K2HPO4 25middot10-3



H3BO3 56middot10-5








NaCl 10middot10-5









NaNO3 40middot10-3

FeSO4 or FeCl2 0010









24 Chapter 2


































+





amp Villarruz 1963)





- at pH

70 ([HCO3-] = 2138middot[CO3







26 Chapter 2

a

































0

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

3

2

1

0

80 K

3 5

3 0

2 5

2 0

1 5

1 0

0 5

0 0

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

2 5

2 0

1 5

1 0

0 5

0 0

250 K



shown as full lines

28 Chapter 2




Whitish Fe(II)B 250 127 309 035 38

Fe(II)A 250 128 181 051 62


Fe(II)A 250 132 238 051 44

Fe(III) 250 036 085 040 38


1005

1000

0995

0990

- 0985 ~ e c 0980 0

-~ 0975 E c nl b 1000 g ~ Qi 0995 0

0990

0985

0980 -12 -8

~ -~


It

10 K


~ bull bull bull

-4 0 4 8 12

Velocity (mmls)














30

25

20

15

10

05

00

20 K

Velocity (mms)

Rel

ativ

e ab

sorp

tion

()

35

30

25

20

15

10

05

00

80 K

30

25

20

15

10

05

00

150 K

-5 -4 -3 -2 -1 0 1 2 3 4 5

25

20

15

10

05

00

250 K



as full lines



30 Chapter 2




















0

2

3

- 4

~ 5 c ~ 6 e-0 7 -2 nl Q) 00 gt ~ 05 Qi 0 10

15

20

25

30

35

bullbullbull hi 6~





Velocity (mms)

31


















32 Chapter 2









predominant























0

2

- 3

~4 c

Q 5

e 6 0

~ 7 g

0 3l Q)

a 1

2

3

4

5

-12 a

40K

bull bull (




lines










34 Chapter 2



NO3- N2 NO3

- N2



















































oxidized as well

36 Chapter 2


biooxidation
























culture)











38 Chapter 2









(Figure 210d)

24 Conclusions



























Reduction Abstract























44 Chapter 3

31 Introduction



























































46 Chapter 3






































buffers






















48 Chapter 3





















































50 Chapter 3




K2HPO4 13middot10-3



H3BO3 56middot10-5








NaCl 10middot10-5




























52 Chapter 3




= 25 mM 100 N2(g) pH 55-60

























54 Chapter 3
















a)

c)

middot 12 -8 -4 4 8 12

Velocity (mmls

bull middot12 -8 -4 0 4 12

Velocity (mmls)

b)

middot12 -8 -4 4 8 12

Velocity (mmls






56 Chapter 3


































a) b)

c c g Q e- e 0 0 1l 1l

-~ bull ~


-12 -8 4 0 4 12


c)

-12 -8 4 8 12

v elocity (m mis)







fits are shown




58 Chapter 3




























































60 Chapter 3















34 Conclusions












Acknowledgments






2- with SO4


62 Chapter 3





64 Chapter 3





Abstract
























66 Chapter 4

41 Introduction





































c

ba


















68 Chapter 4















































70 Chapter 4









































with in the lab





72 Chapter 4






Carbagas)






of 1 deg2θmin












































74 Chapter 4















to be negligible

























0 --0 H OH H H --0 N N N N

2e- 2H+ H20 + 2e-~ 2e- 2H+ H20

~ ~ R R R










76 Chapter 4


















[ ] [ ] [ b 2

a GR


dtd ]












Tabl

e 4

1 S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

4-n

itrot

olue

ne (4

-NT)

4-

chlo

roni

trobe

nzen

e (4

-CN

B) a

nd 4

-nitr

ophe

nyla

cetic

aci

d (4

-NPA

) by

GR

-SO

4

Exp

erim

ent

Age

GR

(d

) [F

e(II

) GR] 0

(mM

) [N

AC

] 0 (micro

M)

[Fe(

II) G

R] 0

[N

AC

] 0∆[

ArN

O2]

(microM

) af b

k obs

(s-1

) ck o

bs (s

-1middotm

-2middotL

) d

GR

-SO

4 + 4

-NT

3 1

103

20

51

5

109

54

5

7

65middot1

0-46

95middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

50

20

6

174

34

8

7

41middot1

0-46

74middot1

0-5

GR

-SO

4 + 4

-NT

3 1

103

10

0 10

3

214

21

4

2

63middot1

0-42

39middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

55

18

7

177

32

2

4

21middot1

0-43

83middot1

0-5

GR

-SO

4 + 4

-CN

B 1

1

103

10

2 10

1

165

16

2

2

37middot1

0-42

15middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

25

412

9

7 38

8

4

82middot1

0-44

38middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

46

224

9

9 21

5

6

37middot1

0-45

79middot1

0-5

GR

-SO

4 + 4

-NPA

1

1 1

03

100

103

13

7

137

196

middot10-4

178

middot10-5

GR

-SO

4 + 4

-NT

2 15

1

31

20

655

5

4 27

0

6

74middot1

0-44

82middot1

0-5

GR

-SO

4 + 4

-NT

2 15

1

31

50

262

9

7 19

4

5

89middot1

0-44

21middot1

0-5

GR

-SO

4 + 4

-NT

4 2

126

0 50

25

2 49

1

982

110

middot10-2

817

middot10-5

GR

-SO

4 + 4

-NT

4 2

630

50

12

6 42

6

852

186

middot10-3

276

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

126

0 30

42

0 29

0

967

925

middot10-3

687

middot10-5

GR

-SO

4 + 4

-CN

B 2

2

630

50

12

6 38

0

760

136

middot10-3

202

middot10-5

GR

-SO

4 + 4

-NPA

2

2 12

60

40

315

371

92

8

5

96middot1

0-34

43middot1

0-5

GR

-SO

4 + 4

-NPA

2

2 6

30

45

140

273

60

7

1

09middot1

0-31

62middot1

0-5

a A

mou

nt o

f NA

C re

duce

d by

GR

-SO

4 at r

eact

ion

term

inat

ion

b F

ract

ion

of in

itial

ly a

dded

NA

C tr

ansf

orm

ed b

y G

R-S

O4 a

t rea

ctio

n te

rmin

atio

n c

Pse

udo

1

orde

r rat

e co

nsta

nts c

alcu

late

d as

initi

al ra

tes

ie m

ax f

irst t

wo

half-

lives

d S

urfa

ce a

rea-

norm

alis

ed p

seud

o 1

ord

er ra

te c

onst

ants

The

are

a of

GR

-SO

4 per

L

su

spen

sion

was

cal

cula

ted

as frac14

middot[Fe

(II)

GR] 0middot

600

gmiddotm

ol-1

middot71

2 m

2 middotg-1






between k

1hE






on log k

1hE

1hE



1hE



Compound pKa Eh1















80 Chapter 4













































limiting step

82 Chapter 4











































mineral systems












Fe(II) solely

84 Chapter 4




































[Fe(II)GR]0 (mM)





103 55 174 177 99

63 339 426 380 273






86 Chapter 4





















Scherer 2001)






































88 Chapter 4






















































available

44 Conclusions




90 Chapter 4




















(Elsner et al 2004)












Acknowledgments



References




2- with SO4











Abstract


























98 Chapter 5



51 Introduction























































100 Chapter 5











































nature














102 Chapter 5






















(999995 Ar Aldrich)





































104 Chapter 5






















































106 Chapter 5

Cl3CC

O

O- Cl2HCC

O

O-

2e- H+ Cl-











sdotsdot=minus kdt

d ]

















T

able

51

Exp

erim

enta

l con

ditio

ns a

nd p

seud

o 1

ord

er ra

te c

onst

ants

for t

he re

duct

ive

trans

form

atio

n of

TC

A b

y va

rious

Fe(

II)-

Fe(I

II) c

onta

inin

g m

iner

al sy

stem

s

Syst

em

Susp

ensi

on a

ge

(d)

[Fe(

II)] s

olid

a (m

M)

[Fe(

II)] a

q b

(mM

) [T

CA

] 0 (micro

M)

pHin

itcpH

endd

k obs

e (min

-1)

Surf

ace

area

(m

2 L)

k obs

f

(min

-1m

-2middotL

)

Fe(I

I)aq

1

0

030

434

nd

76

gn

dn

dn

d

Fe(I

I)G

oe

1

002

024

429

nd

78

g1

021

0-47

1 i

143

10-5

Fe(I

I)G

oe

1

013

094

543

77

70

225

10-4

71

i3

161

0-5

Fe(I

I)G

oe

coat

ing

1

023

40

066

484

765

80

g6

401

0-454

0 j

119

10-5

Fe(I

I)G

oe

coat

ing

1

0

150

8048

6n

d7

6 g12

43

10-4

540

j2

301

0-5

Fe(I

I)L

ep

1

0

020

2315

7n

d7

8 g0

751

0-48

0 i

094

10-5

Fe(I

I)L

ep

coat

ing

1

016

30

137

470

765

80

g2

821

0-454

0 j

052

10-5

Fe(I

I)L

ep

coat

ing

1

0

100

8141

7n

d7

7 g8

311

0-454

0 j

154

10-5

Fe3O

41

3

380

1251

38

107

8g

830

10-4

16

k5

311

0-4

Fe3O

477

112

56

556

70

70

153

10-4

52

k2

951

0-5

GR

-CO

31

5

940

3950

37

658

4g

761

10-4

419

l1

821

0-5

GR

-CO

32

7

60

147

88

568

2940

81

0-453

6 l

761

10-5

GR

-CO

332

73

003

563

85

80

490

10-4

515

l0

951

0-5

GR

-CO

314

2

3

530

005

629

nd

87 g

513

10-4

249

l2

061

0-5

GR

-SO

41

5

17-1

217

086

-13

910

5n

dn

d3

601

0-492

6 m

039

10-5

GR

-SO

41

6

22-1

027

093

-14

527

0n

dn

d3

761

0-488

1 m

043

10-5

GR

-SO

41

7

05-1

014

077

-17

950

0n

dn

d3

741

0-4 9

18

m0

411

0-5

GR

-SO

41

5

17-1

051

060

-16

510

00n

dn

d2

891

0-483

7 m

035

10-5

n

d =

not

det

ecte

d a

Ini

tial s

truct

ural

or a

dsor

bed

Fe(I

I) e

stim

ated

as [

Fe(I

I)to

tal]

ndash [F

e(II

) aq]

b In

itial

dis

solv

ed F

e(II

) mea

sure

d c

Sus

pens

ion

pH p

rior t

o TC

A a

dditi

on d

Sus

pens

ion

pH a

t rea

ctio

n

te

rmin

atio

n e

Pse

udo

1 o

rder

rate

con

stan

ts fo

r the

con

sum

ptio

n of

TC

A c

alcu

late

d fr

om in

itial

rate

s (m

ax f

irst t

wo

half-

lives

) f

Surf

ace

area

-nor

mal

ised

pse

udo

1 o

rder

rate

con

stan

ts g

pH

con

trol

th

roug

h pu

re C

aCO

3 and

05

C

O2(g

) h

pH

con

trol t

hrou

gh F

e(II

I) o

xide

-coa

ted

calc

ite a

nd 0

5

CO

2(g)

i Es

timat

ed u

sing

the

SSA

of t

he F

e(II

I) o

xide

app

lied

j E

stim

ated

usi

ng th

e SS

A o

f cal

cite

~1

m2 g

k E

stim

ated

ass

umin

g SS

A =

4 m

2 g (S

chw

ertm

ann

amp C

orne

ll 1

991)

frac12middot[

Fe(I

I) sol

id] 0middot

232

gmiddotm

ol-1

middot4 m

2 middotg-1

l E

stim

ated

ass

umin

g SS

A =

47

m2 g

(Will

iam

s amp S

cher

er 2

001)

frac14middot[F

e(II

) GR] 0middot

600

gmiddotm

ol-1

middot47

m2 middotg

-1 m

Est

imat

ed a

s in l

but u

sing

SSA

= 7

12

m2 middotg

-1 (C

hapt

er 4

thi

s wor

k)



systems



















110 Chapter 5



























mM)


d001-spacing(nm)

Wfrac12(degθ)

0 9483 10821 0273

10 9494 10809 0287

215 9522 10777 0263

330 9550 10745 0273

510 9524 10775 0277

855 9509 10791 0253

1160 9467 10839 0268



















112 Chapter 5




















compounds






































114 Chapter 5


and TCA









































+ and equivCaOndash








116 Chapter 5



GR-SO4 FeII4FeIII


GR-CO3 FeII4FeIII

























































118 Chapter 5













































54 Conclusions













120 Chapter 5



Acknowledgments


GR-SO4

References





122 Chapter 5



124 Chapter 5






























126 Chapter 6







































((FeII3-xFeIII





















into the subsurface

128 Chapter 6











contaminants

References






ArNO2 + e- ArNO2






1hE




1hE








minusHJUGk




dtArNOd



II Chapter 7


log1






1hE 1

hE minusHJUGk

minusHJUGk





[ ]minuslowast

minusminus

minus

minus=

HJUGkk

k HSHJUGHJUG







species)


OH 0 OH OH

+ e- + H+ = + e- + H+ =

0 0

pl(( ox) = 8 00 PK1 (red) = 6 60

JUG HJUG

OH OH

OH

pKa2(red) = 10 60





[HJUG] = 10 microM

By using the LFER





4-NT

4-NPA

311 middot10middot7

164middot10middot7

847middot 10-8

116middot 10middot7

226middot10middot2

489middot10middot3

-165

-231

-515

-546

IV Chapter 7

lowast





also differs by 3

minusHSk

1hE

1hE

1hE





to the jugloneH

1hE



























⎟⎟⎠

⎞⎜⎜⎝

⎛+=











νtp ud sdot

=Re





VI Chapter 7





( )η

ρρsdot

minussdotsdot=

18

2pp

t

dgu (mmiddots-1)



process

in fluid dynamics


=lowast

lowast

iw

pL

Ddk






particles

lowastLk



iwDν

=Sc




uncertainty in k

lowastLk




Laudie 1974)

5890141

9102613

iiw

VD

sdot

sdot=

minus

η (m2middots-1)







( ) ( ) ( )pppp

p

pp

p

dd

dV

SAAρρπ

πρ 1000

6

100061100030

SA3

2tot

geom sdot=

sdotsdot

sdot=





VIII Chapter 7

GR-SO4

Atot (m2g) 712

SAgeom (m2g) 237







were


4-NT 1260 768middot10-10 1302

4-CNB 1230 779middot10-10 1284

4-NPA 1535 684middot10-10 1462

NB 1055 853middot10-10 1173




103 366middot102

63 224middot103

126 448middot103

60 213middot103





4-NT 912middot10-4

4-CNB 925middot10-4

4-NPA 812middot10-4

NB 101middot10-3




4-NT 103 050 420middot10-4

63 307 140middot10-3

126 613 590middot10-3

4-CNB 103 051 740middot10-4

63 311 170middot10-3

126 622 460middot10-3

4-NPA 103 045 640middot10-4

63 273 109middot10-3

126 546 473middot10-3

NB 60 324 137middot10-3 b










X Chapter 7





KA


kS1


KB-1


KB


kS2


KC-1




CCBBAA

AAsitesSA

CKCKCKCKCk

dtdC


=minus1

1









surface coverage



















XII Chapter 7











edges is








AA

2

2

tot

outer asymp=


130microm 155

microm 00016318AA

2

2

outer

edge asympsdot

=








AA

2

2

tot

outer asymp=


121microm 157

microm 00016467AA

2

2

outer

edge asympsdot

=

XIV Chapter 7



radii of the













Figure 74)









Atom vdW radii (nm)

H 0120

O 0140

N 0150

C 0170

Cl 0181

S 0185







NB 054 080 036

4-NT 054 106 036

4-CNB 054 100 036

4-NPA 054 136 036

XVI Chapter 7






































FeCO30 Fe(CO3)2






XVIII Chapter 7

























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Formation and Redox Reactions of Green Rusts under