-
Journal of Hazardous Materials 231 232 (2012) 114 119
Contents lists available at SciVerse ScienceDirect
Journal of Hazardous Materials
j our na l ho me p age: www.elsev ier .com
Effect o ero
Cilai TanCollege of Reso
h i g h l
The select Ammoniu The result
a r t i c l
Article history:Received 29 March 2012Received in revised form
21 June 2012Accepted 21 June 2012Available online 29 June 2012
Keywords:Zero-valent iroNitrate reductSoil and grounLoess
soilCationsAnions
le reafor soil and groundwater nitrate remediation under acidic
or near neutral conditions. But few studies havebeen reported about
it and the effects of coexistent ions under alkaline conditions. In
this study, nitratereduction by Fe0 was evaluated via batch tests
in the presence of alkaline soil and common cation (Fe2+,Fe3+ and
Cu2+) and anion (citrate, oxalate, acetate, SO42, PO43, Cl and
HCO3). The results showed thatcation signicantly enhanced nitrate
reduction with an order of Fe3+ > Fe2+ > Cu2+ due to
providing Fe2+
3
1. Introdu
The loesinant terra6.24 105 kresource issource for the
industrindustrial wtilizer to imincreasinglyinvestigatiobasin (a
typthat nitratethe drinking[2]. Excessivdiseases [3
CorresponE-mail add
0304-3894/$ http://dx.doi.oniondwater remediation
directly or indirectly. Most anions enhanced nitrate reduction,
but PO4 behaved inhibition. The pro-motion decreased in the order
of citrate > acetate > SO42 > Cl HCO3 oxalate PO43.
Ammoniumwas the major nal product from nitrate reduction by Fe0,
while a little nitrite accumulated in the begin-ning of reaction.
The nitrogen recovery in liquid and gas phase was only 5678% after
reaction due toammonium adsorption onto soil. The solution pH and
electric conductivity (EC) varied depending on thespecic ion added.
The results implied that PRB based Fe0 is a potential approach for
in situ remediationof soil and groundwater nitrate contamination in
the alkaline conditions.
2012 Elsevier B.V. All rights reserved.
ction
s plateau, an arid or semi-arid region, is the predom-in in the
northwest of China, comprising an area ofm2. Loess soil is an
alkaline soil. In this area, water
scarce and groundwater is the predominant waterpeople living,
agricultural and industrial use. But asial and agricultural
development, nitrogen-containingaste efuent discharge, excessive
use of nitrogen fer-prove food output for increasing population
induced
nitrate contamination in the groundwater [1]. Ann on sub-aqueous
nitrate contamination in Guanzhongical loess plateau), Shaanxi
Province in China, indicated
concentration in most groundwater markedly exceeded water
standard (GB 5749-2006) of China (10 mg N L1)e nitrate in drinking
water can cause cancer and other
]. Loess soil is an alkaline soil that has an average pH
ding author.ress: [email protected] (Z. Zhang).
value above 8.0, and HCO3, SO42, Cl, Na+, Ca2+, and K+ are
themajor ions in the soil and groundwater [4].
Many studies have shown that nitrate reduction by Fe0 was
anacid-driven and surface-mediated process, which was
spontaneousunder acidic condition, or near neutral condition with
the help ofcatalysts [58]. Permeable reactive barrier (PRB) based
Fe0 has beensuccessfully used for in situ groundwater contamination
remedi-ation, including nitrate, under acidic or near neutral
conditions[9]. But no study has been reported whether or not it
could workunder alkaline condition, such as in alkaline loess
plateau. Granu-lar iron reactivity is predominantly controlled by
the groundwatergeochemistry (e.g., coexistent ion and pH) [10,11].
The coexistentions behaved different impacts on Fe0 reactivity
depending on thetarget pollutants [12,13]. Fe2+, Fe3+ and
corresponding hydroxidesare the oxidative products from Fe0
corrosion. Lots of previousstudies showed that Fe2+ or Fe3+
enhanced Fe0 degradation of pen-tachlorophenol [14], chromate [15]
and nitrate [16,17]. Cu(II) wasusually added as a catalyst for
enhancing pollutants removal by Fe0
[6,14]. Cations (Fe2+, Fe3+ and Cu2+) without soil have been
provedto promote nitrate reduction by Fe0 but there were no
distinct effectby Ca2+, Na+ and K+ based on the former studies
[17]. Therefore, we
see front matter 2012 Elsevier B.V. All rights
reserved.rg/10.1016/j.jhazmat.2012.06.042f common ions on nitrate
removal by z
g, Zengqiang Zhang , Xining Sunurces and Environment, Northwest
A&F University, Yangling, Shannxi 712100, China
i g h t s
ed cations and anions enhance nitrate reduction by Fe0 in
alkaline soil.m is major nal product from nitrate reduction.s prove
the feasibility of using Fe0 for groundwater nitrate
remediation.
e i n f o a b s t r a c t
Zero-valent iron (Fe0)-based permeab/ locate / jhazmat
-valent iron from alkaline soil
ctive barrier (PRB) technology has been proved to be
effective
-
C. Tang et al. / Journal of Hazardous Materials 231 232 (2012)
114 119 115
also investition by Fe0
inorganic ioexistent orgselected to
The objeions in soilpresence ofpractical apin the loess
2. Materia
2.1. Materi
Unless ograde and water.
Nitrate sstock solutsodium salting Industrapproximatwith a
spec[18] calculder = 0.762/as m. Irolarge amoudegassed ddried in
vacfrom no.1 Aversity, ChiSoil sample1.0 mm nyloas: pH
(soil:organic car3.68%, totalN 0.018 mgSO42 75 m
copper were not detectable. All processes were performed as
themethods for the examination of water and wastewater of China(4th
edition).
perim
eredrth-cven r weecic
V/Wtermg N
n conealed
at 20st wintai
suspssedllectiniti5.0 mge, f, nito detactioove 2)
weactieasualyseC.
alyt
sca obtae nitred ul con
usinFig. 1. SEM photograph of iron grains.
gated the effects of Fe2+, Fe3+ and Cu2+ on nitrate reduc-in the
presence of loess soil. Moreover, the commonns such as Cl, HCO3,
SO42, PO43 and potential co-anic ions such as citrate, oxalate and
acetate have beenevaluate their effects on nitrate removal by
Fe0.ctive of this study was to evaluate the effects of common
and groundwater on nitrate reduction by Fe0 in the alkaline
soil, aiming to give some possible guidance toplication of PRB
technology for in situ removal of nitrate
plateau area in the future.
ls and methods
als
therwise indicated, all chemicals used were reagent
2.2. Ex
Tapsoil (Easoil (opowdeand spto soilthe deof 60 ma aniowere
sshakertrol teonly coa littleand pawas coas the about a
syrinnitrateorder tafter reto remgas (Nafter rand mthe an24 1
2.3. An
Theused toder. Thmeasuthermaminedall aqueous solutions were
prepared with deionized
olution was prepared using NaNO3. Cation and anionions were
prepared with corresponding chloride ands, respectively. The iron
particle (Tianjin Zonghengx-ial &Trading Chemical Reagent Co.,
China) size wasely 50100 m in diameter (Fig. 1), irregular in
shape,ic surface area 0.01520.0076 m2 g1, following Liaosating
method, i.e. the specic surface of iron pow-D m2 g1, D represents
the iron diameter, reportedn powder was pretreated with 0.5 mol L1
HCl untilnts of gas escaped (about 35 min), then washed
witheionized water to remove the residual HCl and thenuum container
for further use. The soil was obtainedgricultural Experiment
Station of Northwest A & F Uni-na, air-dried and sieved via a
2.0 mm nylon screen.s used for chemical analysis additionally
sieved via an screen. The properties of the soil can be
summarized
water = 1:2.5 w/v) 8.35 0.12, moisture content 5.21%,bon 1.71%,
total N (Kjeldahl-N) 523 mg kg1, total iron
copper 29.05 mg kg1, nitrate-N 0.94 mg kg1, nitrite- kg1,
ammonium-N 0.595 mg kg1, Cl 96 mg kg1,g kg1, HCO3 82 mg kg1,
dissolvable iron and
a DDS-307respectivelspectrophospectrophoreduction mits
reactionnitroprussiFe2+ was dtotal dissolhydroxylamaverage val
3. Results
3.1. Effect o
As illustremoval. NiFe0 at 144 h49.6% remobe becausede and
oxsmelled duents
ask (250 mL) was used as the reactor. 42.2 g raw
loessumuli-Orthic Anthrosoles), corresponding to 40.00 g drydry at
105 C), and 5.00 g (in excess) pretreated ironre added into each
reactor, followed by adding nitrate
ion stock solutions, resulting in a nal ratio of liquid = 5:1 (a
national standard of water and soil ratio forination of soluble
ions in soil), a nitrate concentrationL1, a cation concentration of
1.0 mM and 2.0 mM, orcentration of 1.0 mM and 3.0 mM. Then the
reactors
tightly with rubber stopple, and placed in a complanate0 rpm.
The headspace was air. At the same time a con-thout iron powder and
ions and another control testning iron powder were prepared. After
shaking 1 min,ension was extracted from the reactor using a
syringe,
through a 0.45 m ber lter membrane. The ltrateed for pH and EC
measurement, which was recordedal values. Subsequently, at the
designed time intervall of suspension was extracted from the
reactor withollowed by lter. The ltrate was collected for pH,
EC,rite, ammonium, and dissolved iron measurement. Inect the gas
phase constitute in the headspace of reactorn, the reactors were
ashed using argon gas (>99.99%)air in the headspace in the
beginning of reaction. Theas collected and analyzed using gas
chromatographon. The NH3 was collected in 0.10 M NaOH solutionred
as NH4+. All tests were conducted in duplicate ands were nished
within 24 h at room temperature of
ical methods
nning electron microscopy (SEM, Hitachi S-450) wasin the
microstructure and size information of iron pow-rogen gas in the
headspace in reactor after reaction wassing gas chromatograph
(GC-7800, Agilent) equippedductivity detector. The solution pH and
EC were deter-g a pHS-3 C model exact pH meter (Lei-ci, China)
and
model Electric Conductivity Detector (Lei-ci, China),y. Nitrate
measurement was achieved by the ultraviolettometric method at 220
nm and 275 nm using a UV1102tometer [19]. Nitrite was analyzed by
the hydrazineethod at 540 nm, and ammonium was measured using
with phenol and hypochlorite and catalyzed sodiumde to form
indophenol at 636 nm [19]. The dissolvedetermined as phenanthroline
method at 510 nm. Theved iron was analyzed as Fe2+ after its
reduction usingine hydrochloride [19]. All results presented are
theue of duplicate.
and discussion
f cations
rated in Fig. 2a, acid pretreated Fe0 enhanced nitratetrate
removal rate of 69.2% was achieved by pretreated. By contrast, it
was tend to constant after 120 h and onlyval was observed using raw
Fe0 alone at 144 h. It might
acid pretreated removed the passive layer (e.g., sul-ide
(Fe2O3)) on the Fe0 surface. A rotten-egg smell wasring acid
pretreatment. Previous studies also showed
-
116 C. Tang et al. / Journal of Hazardous Materials 231 232
(2012) 114 119
50
60
70
/L
blank
Fe0
acidFe0
a
10
12b
Fig. 2. Nitrate en, (bwas a nitrate s
that acid prand perchloicantly pro92% and 98presence ofCu2+,
respewithin 30 hrespectivelydue to the rimplied thavious studiunder
acidition (pH > 8Fe0/cation, 20 h and themainly occuFe0
reactionconsistent wciency of Feby ultrasouucts (mainlCaCO3,
FeCOwhich decrreduction [such as Fe2
tial for nitroxide lm reducing nietry of 0.75under neuttion
would could acceleformation iand enhanc
occureact
Fe0
Fe0 0
10
20
30
40
250 50 75 100 125 150 175 200
Nit
rate
-Nm
g
Time (h)
1.0mM Fe2+
2.0mM Fe2+
1.0mM Fe3+
2.0mM Fe3+
1.0mM Cu2
2.0mM Cu2
0
2
4
6
8
0
pH
0
1
2
3
4
5
6
500 100 15 0 200
Nitri
te-N
(mg
/L)
Time (h)
c
Blank Acid Fe 0
1.0 mM Fe2+ 2.0 mM Fe2+
1.0 mM Fe3+ 2.0 mM Fe3+
1.0 mMCu2+ 2.0 mM Cu2+
0
5
10
15
20
25
0
Am
mo
nia
-N
mg
/L
reduction by Fe0 in the presence of loess soil and different
cation: (a) nitrate nitrogolution without Fe0 and additional
cation. The same means in the Figs. 3 and 4.
etreatment enhanced Fe0 reactivity toward nitrate [20]rate [21]
reduction. The introduction of cation signif-moted nitrate
reduction by pretreated Fe0. 96%, 99%,% of nitrate removal were
observed after 144 h in the
1.0 mM Fe2+, 2.0 mM Fe2+, 1.0 mM Cu2+ and 2.0 mMctively. But
complete removal of nitrate was achieved
might redox
2Fe3+ +
Cu2+ +
and 20 h in the presence of 1.0 mM and 2.0 mM Fe3+,. The pH in
most systems was above 8.0 after 3.0 helease of OH from iron
corrosion (Fig. 2b). The resultst nitrate reduction by Fe0 could
occur at pH > 8.0. Pre-es showed that nitrate reduction by Fe0
was effectivec condition (pH < 7.0) but neglectable in alkaline
condi-.0) [7,8,22]. In the systems including pretreated Fe0 orthe
added nitrate was removed rapidly in the beginningn gradually
decreased. It implied that nitrate reductionrred in the presence of
fresh Fe0. It was well known that
with pollutants was surface mediated [23]. This wasith former
researches that the decontamination ef-
0 was fast in the beginning of reaction or polished Fe0
nd [24,25]. As the reaction process, iron corrosion prod-y as
hydroxide and iron oxides) and precipitates (e.g.,3) deposited on
the surface of Fe0 due to increasing pH,
eased Fe0 reactivity and restrained the further nitrate26]. On
the other hand, some iron corrosion products+, Fe(OH)+, Fe(OH)2,
and green rust have great poten-ate reduction [27]. Huang et al.
[28] reported that theon the surface of Fe0 could not prevent the
iron fromtrate if plenty of Fe2+ was available with a
stoichiom-
mol Fe2+ for 1.0 mol nitrate reduction to ammoniumral
conditions. Once the Fe2+ was depleted, the reac-stop immediately.
Another study also showed that Fe2+
rate iron corrosion and facilitate passive oxides trans-nto
conductor (Fe3O4), which favored electron transfered nitrate
reduction by Fe0 [16]. The key role of Fe2+
The addFe3+ > Fe2+ >addition of (2)). Althouadsorbed
Fereported Cunitrate reducatalytic efited due to(e.g., iron ox6 mg
N L1
Cu2+ additiafter 16 h areported threduction cduced. Lessand
subseqIt might beto nitrite bu[30], whichthe reactionto
precipitathe accumuFe0 or corro
In the sytivity (EC) dstabilized asumption o25 50 75 100 12 5
150
Time (h)
Blank Acid Fe 0
1.0 mM Fe2+ 2.0 mM Fe2+
1.0 mM Fe3+ 2.0 mM Fe3+
1.0 mM Cu2+ 2.0 mM Cu2+
05 100 150 200
Time (h)
Fe0
Acid Fe0
1 mMFe2+
2 mMFe2+
1 mMFe3+
2 mMFe3+
1 mMCu2+
2 mMCu2+
d
) pH, (c) nitrite nitrogen, and (d) ammonia nitrogen. Blank
treatment
r in this study, because Fe2+ could be produced fromion after
external cation was added as below:
3Fe2+ (1)
Cu0 + Fe2+ (2)ed cation enhanced nitrate reduction with an order
of Cu2+ in the same concentration. Apparently, the directFe2+ is
better than indirect from Cu2+ replacement (Eq.gh dissolved Fe2+
was not detectable, Fe(OH)2 or surface2+ might contribute the
enhancement. Previous studies0 could accelerate electron transfer
and then increasection by Fe0 as a catalyst [6,14]. But in this
study itsciency in enhancing electron transfer might be inhib-
passivation by non-conducting soils and precipitatesides,
hydroxide). Nitrite accumulated sharply to nearlyin the rst 10 h
with the effect of Cu2+ (Fig. 2c). Moreon favored nitrite
accumulation. But nitrite decreasednd less than 1.0 mg N L1 in 30
h. An et al. [29] alsoat FeCu nanoparticles signicantly enhanced
nitrateomparing with nano-Fe alone, but more nitrite was pro-
than 2.0 mg N L1 nitrite accumulated in the beginninguently
decreased rapidly in the presence of Fe2+ or Fe3+.
because Cu2+ or Cu0 could catalyze nitrate reductiont it was
weak or not in catalyzing nitrite to ammonia
led to the accumulation of nitrite at the beginning of.
Subsequently, Cu2+ or Cu0 lost its catalytic activity duetion and
passivation by nonconducting substances. Butlated nitrite
disappeared later due to the reduction ofsion products [27].stems
with external addition of cation, electric conduc-ecreased rapidly
in the beginning of reaction and thenfter 16 h (data not shown).
This was due to the con-f nitrate and adsorption/co-precipitation
of ions on the
-
C. Tang et al. / Journal of Hazardous Materials 231 232 (2012)
114 119 117
50
60
70
Blank
AcidFe0
chloride
A (1.0 mM )
50
60
L
Blank
Acid Fe 0
chloride
sulfate
B (3.0 mM)
Fig. 3. NitrateCH3COO .
corrosion padsorption systems cofrom nitratthe system in liquid
ph(NH3) was 5ammoniumheadspace and stirringdetected inhigh pH
(8solved iron adsorbed an
3.2. Effect o
As shownitrate redution. The into cation, nslowed dowlibrium
compretreated 0
10
20
30
40
250 50 75 100 125 150 175
Nitra
te-N
mg/L
Time(h)
sulfate
bicarbonat e
oxalate
citrate
phosphate
acetate
0
10
20
30
40
0
Nitra
te-N
mg/
400
500
600
700
800
900
8.5
8.9
9.3
9.7
10.1
10.5
200 40 60 80 100 120C
on
du
ctivity (
us/c
m)
pH
Time (h)
a
pH
Conductivity
8
8.5
9
9.5
10
10.5
11
0
pH
700
10.5
c10.2400
500
600
8
8.5
9
9.5
10
200 40 60 80 100 120
Co
nd
uctivity (
us/c
m)
pH
Time(h)
pH
Conductivity
8.2
8.6
9
9.4
9.8
20
pH
reduction by Fe0 as affected by different external anions: (A)
1.0 mM; (B) 3.0 mM, and
roducts of iron. Finally, both the reduction reaction andreached
equilibrium and then EC kept constant. In allntaining Fe0, ammonium
was the major nal producte reduction (Fig. 2d). More ammonia was
detected inwith more nitrate removal. The total nitrogen
recoveryase (i.e., NO3-N, NO2-N and NH4+-N) and gas phase673% (data
not shown). It was due to the adsorption of
onto soil and precipitates. NH3 gas was observed in theof
reactor after reaction due to relative high pH (>8.0). But no N2
and other nitrogen oxide compounds were
headspace. Ammonia volatilization in the system with9) was also
observed in previous studies [31,32]. Dis-and copper were
undetectable in the system because ofd deposited in high pH.
f anions
ed in Fig. 3A and B, all anions except PO43 enhancedction by
Fe0. Contrarily, PO43 inhibited nitrate reduc-uence was favored at
higher concentration. Similaritrate decreased sharply during the
rst 16 h and thenn. But it took longer time before they reached
equi-paring with cation. In the control treatment (i.e., onlyiron
without external anion addition) 72.5% of nitrate
removal w84.7% in thof Cl, resammoniuminsignicanThe enhancthe
promotstrength bythe premisintermediaeasily conv[27,34]. The124 h
in thThe externaerated ironstrength thenhancemethe promotof surface
rtion of greewas also efthat both Gichiometricsystem ext25 50 75
100 12 5 150 175
Time(h)
bicarbonate
oxalate
citrate
phosphat e
acetate
300
500
700
900
1100
20 40 60 80 100 120
Conductivity (
us/c
m)
Time (h)
b
pH
Conductivity
750d350
450
550
650
0 40 60 80 100 120
Conductivity (
us/c
m)
Time (h)
pH
Conductivity
the pH and EC of 3.0 mM anions: (a) Cl , (b) SO42 , (c) HCO3 ,
(d)
as observed after 124 h. But it increased to 76.6% ande presence
of 1.0 mM and 3.0 mM external additionpectively (Fig. 3A, B). The
corresponding increase of
was also observed (data not shown). Nevertheless,t nitrite
accumulated and nearly disappeared after 60 h.ement of nitrate
reduction by Fe0 might result fromion of iron pitting corrosion and
the increase of ionic
Cl [33]. Iron corrosion and electron release wase of pollutants
degradation by Fe0 [23]. Nitrite, as thete product from nitrate
reduction, was not stable anderted to ammonium by Fe0 and iron
corrosion products
nitrate removal efciency was 84.4% and 92.9% aftere presence of
1.0 mM and 3.0 mM SO42, respectively.l addition of ion increased
ionic strength and then accel-
corrosion. Distinctly, sulfate contributed stronger ionan
chloride with the same concentration. Hence, itsnt was better.
Moreover, previous studies indicated thation of SO42 and Cl might
contribute to the increaseeactivity or sorption capacity of Fe0 and
the produc-n rust (e.g., [Fe4IIFe2III(OH)12SO4yH2O], GRSO42 ),
whichfective for nitrate reduction [10,27,35]. It was provedRSO42
and Fe4.5Fe1.5(OH)12Cl1.5xH2O (GRCl ) could sto-ally reduce nitrate
to ammonium [27]. Thus, in theernally adding Cl and SO42, nitrate
reduction was
-
118 C. Tang et al. / Journal of Hazardous Materials 231 232
(2012) 114 119
650
10
10.2
/cm
)
a
12
650
700
10
10.5
2
s/c
m)
b
anion
probably paThe promottration, respresence ofand GRCl , [36]. A
greein the systeintroductioand 93.4% itive effectCH3COO >and the
othin pH and Eincreased aand then kiron corrosby Fe0 contquent
ammof other ionIt implied thwould be re
The nitrthe systemtively. The not shown)and inner-scorrosion
aphosphate cthe competnitrate rem84.2%) (Fig.motion to nnitrate
(>95and 3.0 mMat the last pbeginning o
nions adsn thie theoug
redulutiother d asd th450
550
9
9.2
9.4
9.6
9.8
200 40 60 80 100 120
Conductivity (
us
pH
Time(h)
pH
Conductivity
8
8.5
9
9.5
10
200 40 60 80 100
pH
Time(h)
c
pH
Conductivity
8.5
9
9.5
0
pH
Fig. 4. The time course of pH and EC in the presence of 3.0
mM
rtially resulted from green rusts (GRCl ) and GRSO42 .ion of
HCO3 was similar to Cl at the same concen-ulting in a nitrate
removal of 76.4% and 85.7% in the
1.0 mM and 3.0 mM, respectively. Similar to GRSO42the GRHCO3
also had potential for nitrate reductionn color was observed after
settling during experimentsm with externally adding Cl, SO42 and
HCO3. Then of 1.0 mM and 3.0 mM CH3COO achieved 88.25%nitrate
removal, respectively. As a whole, the pos-s of the four anions
above decreased in the order:
other aused aeffect idissolv
AlthnitrateThe soeach obehavetion, an SO42 > Cl HCO3.
Although the rst ion was organicers were inorganic, they exhibited
similar variationC during the whole reaction period. The solution
pHnd EC decreased signicantly within the rst 40 h,ept stable (Fig.
3a, b, c, d). Both alkaline release fromion and acidity consumption
from nitrate reductionributed to pH increase. Nitrate reduction and
subse-onium adsorption, the adsorption and co-precipitations onto
iron hydroxides all contributed to EC decrease.at other co-existent
contaminants (e.g., heavy metals)moved simultaneously by adsorption
and precipitation.ate removal rate was 62.4% and 60.9% (Fig. 3A, B)
in
externally adding 1.0 mM and 3.0 mM PO43, respec-nitrogen
recovery was the highest in all anions (data. Phosphate has been
reported to form co-precipitationphere complexes on the surface of
iron inhibited ironnd electron transfer [37,38]. Although the
addition ofould increase ion strength and promote iron
corrosion,itive adsorption was stronger. Oxalate achieved
similaroval rate as Cl in the same concentration (76.3% and
3A, B). Among all anions, citrate achieved the best pro-itrate
reduction by Fe0. Almost complete removal of%) was observed after
124 h in the presence of 1.0 mM
citrate. The reactors containing citrate were very cleareriod of
the experiment, though they were turbid in thef reaction as other
systems. But the reactors containing
low pH led ions, whichprecipitatiodecreased tsimultaneohigher
conc
In conctive effectsloess soil. rate > acetacation, nitrotion
was obdetected af
4. Fe0-bas
Accordinby Fe0 fromanions (Cl
to the promof green runicantly ereduced to cess whichMore iron
concentrati700
800
900
1000
1100
0
Conductivity (
us/c
m)
500
550
600
0 40 60 80 100 120
Conductivity (
u
Time(h)
pH
Conductivity
: (a) PO43 , (b) C2O42 , (c) citrate.
s were always turbid. Considering citrate was usuallyorbent or
chelator in industry, it might have the sames study. Citrate as a
chelator could destabilize and nally
passive oxide layer on the surface of iron [37].h PO43, oxalate
and citrate behaved differently onction, they exhibited similar
variation in pH and EC.n pH and EC varied repetitive and showed
opposite to(Fig. 4). A possible explanation was that the added
ion
a buffer alone or together with some ions in soil solu-us they
prevented the solution pH from uctuating. The
to dissolve the precipitates and/or desorb the adsorbed
caused a rise of EC. Contrarily, the high pH
inducedn/co-precipitation and then more adsorption, whichhe EC.
Consequently, the solution pH and EC changedusly and exhibited a
uctuant situation, especially withentration.lusion, all anions
excluding PO43 revealed posi-
on nitrate reduction by Fe0 in the presence ofThe promotion
effect decreased in the order: cit-te > SO42 > Cl HCO3
oxalate PO43. Similar togen recovery was only 6178%. Some nitrite
accumula-served in the beginning, but less than 1.0 mg N L1 waster
reaction in all systems with different anion present.
ed PRB implication in the loess plateau area
g to the above results, reductive removal of nitrate an alkaline
(pH > 8) soil was possible. The major
, SO42, HCO3) can accelerate nitrate reduction dueotion of iron
corrosion and the possible occurrence
sts. The Fe0 corrosion products, Fe(II) and Fe(III), sig-nhanced
nitrate reduction. Moreover, nitrate can benitrogen gas by
hydrogenotrophic denitrication pro-
consumed H2 deriving from iron corrosion [39,40].powder may be
consumed in the regions where theon of PO43 is higher. Some organic
ligands (e.g.,
-
C. Tang et al. / Journal of Hazardous Materials 231 232 (2012)
114 119 119
citrate, acetate and oxalate) would promote not only
nitratechemical reduction by Fe0 but also microorganism
denitrication.For example, the denitrication rates decreased in the
of orderacetate > H2 > S > thiosulphate > ferrous iron
in microcosm [41]. Cer-tainly, therenvironmenThe iron in
rpassivationfor the reacFe0 [42]. Thtion and relBut it is stilwater
nitradeveloped i
5. Conclus
The resuline loess plreduction recould be acanions (citrsame
concein the ordeorder of citOnly PO43
Ammoniumreduction. Nwas less threcovery inDissolved iring on the
potential tenitrate cont
Acknowled
We acknResearch LaResearch DrD. Strahm, Seattle, U.Sthe
professence, Northanonymous
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Effect of common ions on nitrate removal by zero-valent iron
from alkaline soil1 Introduction2 Materials and methods2.1
Materials2.2 Experiments2.3 Analytical methods
3 Results and discussion3.1 Effect of cations3.2 Effect of
anions
4 Fe0-based PRB implication in the loess plateau area5
ConclusionsAcknowledgementsReferences
