Faculty of Forestry, Geosciences and Hydrosciences Institute of Waste Management and Contaminated Sites Chair in Waste Management Prof. Dr.-Ing. habil. B. Bilitewski

Mineral phases of steel industry slags used in a landfill cover construction

MASTER THESIS

TECHNISCHE UNIVERSITÄT DRESDEN

Submitted by: Silvia Diener

Matriculation number: 2800 264

Tutors: Dr.-Ing. Lale Andreas, Division of Waste Science & Technology,

Luleå University of Technology, Sweden.

Prof. Dr.-Ing. habil. Bernd Bilitewski, Institute of Waste Management

and Contaminated Sites, Technische Universität Dresden, Germany.

Dresden, the 21st of March 2006

I

Aufgabenstellung für die Diplomarbeit

Thema: Mineralphasen in Stahlschlacken beim Einsatz

in der Dichtungsschicht einer Deponieoberflächenabdichtung

(Mineral phases of steel industry slags used in a landfill cover construction)

Pfannenschlacke und Elektroofenschlacke sind Abfallprodukte aus der Stahlindustrie.

Die derzeitige Praxis besteht in einer Deponierung dieser Stahlschlacken. Je nach

Stahlwerk fallen jährlich Tausende Tonnen verschiedener Schlacketypen an.

Der Einsatz dieser Schlacken beispielsweise als alternative Baustoffe im Deponiebau

wird in Zukunft stärkere Bedeutung und Akzeptanz erfahren.

Durch die zementähnlichen Eigenschaften von Pfannenschlacke nach Zugabe von

Wasser und anschließender Verdichtung rücken Einsatzgebiete bei denen hohe Dichte,

niedrige Permeabilität und mechanische Stabilität vonnöten sind, in den Vordergrund,

beispielsweise in der Dichtungsschicht einer Deponieoberflächenabdichtung. Die zu

untersuchenden Stahlschlacken stammen von Uddeholm Tooling AB, einem Stahlwerk

in Hagfors, Schweden.

Zielsetzung:

1) die Untersuchung der Abbindeeigenschaften von Pfannenschlacke, Elektro-

ofenschlacke und Mischungen aus denselbigen durch kalorimetrische Messungen,

2) die Untersuchung der kristallinen und amorphen Mineralzusammensetzung der

Schlackeproben mit Hilfe IR-Spektroskopie und Röntgenbeugung,

3) die Auswertung der Ergebnisse im Hinblick auf Langzeitverhalten und Stabilität

der Mineralphasen sowie

4) die Analyse einer möglichen Korrelation zwischen Abbindeeigenschaften und Mi-

neralzusammensetzung der Materialien.

TABLE OF CONTENTS

II

TABLE OF CONTENTS LIST OF ABBREVIATIONS .......................................................... III

LIST OF FIGURES........................................................................... V

LIST OF TABLES ......................................................................... VII

TERMINOLOGY .................................................................................... VIII

SUMMARY ............................................................................................. XIII

1 INTRODUCTION...................................................................................... 1

2 MATERIAL AND METHODS ................................................................. 2

2.1 Material ....................................................................................................................... 2

2.2 Methods ...................................................................................................................... 5

2.2.1 Calorimetry ...................................................................................................... 6

2.2.3 X-ray diffraction .............................................................................................. 7

3 RESULTS................................................................................................... 8

3.1 Calorimetry ................................................................................................................. 8

3.2 IR spectroscopy........................................................................................................... 9

3.3 X-ray diffraction ....................................................................................................... 13

4 DISCUSSION .......................................................................................... 15

5 CONCLUSIONS...................................................................................... 22

6 REFERENCES......................................................................................... 25

APPENDICES

APPENDIX I Sample preparation and Measurement Data APPENDIX II Steel slags - General data, mineralogical composition

and suitable analysis methods for determining heat of hydration and mineral phases - Literature Review

APPENDIX III Extended summary in German -

Mineralphasen in Stahlschlacken beim Einsatz in der Dichtungsschicht einer Deponieoberflächenabdichtung

LIST OF ABBREVIATIONS

III

LIST OF ABBREVIATIONS AOD Argon Oxygen Decarburisation

BF Blast Furnace

BOF Basic Oxygen Furnace (LD converter)

CEN Comité Européen de Normalisation

(European Committee for Standardization)

DRIFTS Diffuse Reflectance Infrared Fourier Transform Spectroscopy

DTA Differential Thermal Analysis

EAF Electric Arc Furnace

EDX Energy Dispersive X-Ray Analysis

FEhS FEhS - Institut für Baustoff-Forschung e.V.

(former „Forschungsgemeinschaft Eisenhüttenschlacken“;

German research institute for building materials)

FTIR Fourier Transform Infrared (Spectroscopy)

KBr Potassium Bromide

MID-IR Mid range of infrared radiation

IR Infrared (Spectroscopy)

MSWI Municipal Solid Waste Incineration

NMR Nuclear Magnetic Resonance

OECD Organisation for Economic Co-operation and Development

OPC Ordinary Portland Cement

SEM Scanning Electron Microscopy

TG/TGA Thermal Gravimetric Analysis

XRD X-Ray Diffraction

A special cement nomenclature, called cement chemist notation (CCN) is used to

simplify cement formulas. Important abbreviations are:

C = CaO lime (calcium oxide)

S = SiO2 silica (silicon oxide)

A = Al2O3 aluminate (aluminium oxide)

F = Fe2O3 ferrite (iron oxide)

S = SO3 sulphate (sulphur oxide)

LIST OF ABBREVIATIONS

IV

H = H2O in cement: hydrated water

C-S-H Calcium silicate hydrate

C-A-H Calcium aluminate hydrate

With the help of that nomenclature, formulas as for the mineral ettringite

6CaO*Al2O3*3SO3*32H2O can be written simpler as C6A S 3H32.

LIST OF FIGURES

V

LIST OF FIGURES Figure 1. EAF slag ............................................................................................................ 2

Figure 2. Ladle slag .......................................................................................................... 2

Figure 3. Chemical composition of EAF slag and ladle slag............................................ 3

Figure 4. Particle size distribution of EAF 1, EAF 2 and ladle slag

(Herrmann et al., 2005) ..................................................................................... 4

Figure 5. Sample cup in the calorimeter ........................................................................... 6

Figure 6. Temperature changes per gram slag during hydration measured with

calorimetry ........................................................................................................ 8

Figure 7. IR spectra of 100 % ladle slag (hydrated sample)............................................. 9

Figure 8. FTIR spectra of two hydrated slags and three hydrated slag mixtures ........... 10

Figure 9. Comparison of area ratio of peaks caused by absorption of OH-bonds.......... 11

Figure 10. Diffraction pattern of 100 % ladle slag and 100 % EAF slag ....................... 13

APPENDIX I Figure 1. IR spectra for all hydrated slag samples (LS = ladle slag)................................ 8

Figure 2. IR spectra for hydrated ladle slag and non hydrated ladle slag......................... 9

Figure 3. IR spectra of 100 % EAF slag and 100 % ladle slag (hydrated) ....................... 9

Figure 4. Diffraction pattern of 100 % ladle slag and 100 % EAF slag ......................... 10

APPENDIX II Figure 1. Flow chart of the steel making process at Uddeholm Tooling Ltd.

(Beskow and Du Sichen; 2004)......................................................................... 3

Figure 2. Types of steel slags generated in Europe 2004

(Euroslag, 2006) ................................................................................................ 5

Figure 3. Utilisation of steel slags in Europe 2004 (Euroslag, 2006)............................... 6

Figure 4. Reuse of steel slags in Germany in 2004 (FEhS, 2005).................................... 7

Figure 5. Layers and their functions in a cover construction with a mineral liner;

examples for possible alternative materials (Andreas et al., 2005)................... 8

Figure 6. Changes in cement microstructure during hydration (Wenk and Bulakh, 2004)

........................................................................................................................................ 15

Figure 7. Phase diagram of CaO–SiO2–Al2O3 system.................................................... 17

LIST OF FIGURES

VI

Figure 8. Differential calorimetric analyses of CA, CA2 and corresponding mixtures

(Möhmel et al., 1998)...................................................................................... 19

Figure 9. Compilation of literature data about main elements in EAF slags

(BMU data [6])................................................................................................ 21

Figure 10. Composition of Uddeholm ladle slag and BMU data about ladle slag [6].... 23

Figure 11. Mineralogical evolution taking place during weathering of MSWI

bottom ash (Piantone et al., 2004)................................................................... 26

Figure12. The rate of heat evolution of cement hydration at 25 °C

(Mostafa and Brown, 2005) ............................................................................ 30

Figure 13. X-ray diffraction of EAF sample (Shen et al., 2004) .................................... 34

Figure 14. Vibration modes of the CO2 molecule .......................................................... 37

Figure 15. Schematical draw of the Michelson interferometer ...................................... 39

Figure 16. Comparison of interferogram and spectrum.................................................. 40

Figure 17. Sample accessory of the DRIFTS method .................................................... 40

Figure 18. Model spectrum for explaining fundamental terms

(Günzler and Gremlich, 2002) ........................................................................ 42

LIST OF TABLES

VII

LIST OF TABLES

Table 1. Annual slag generation at Uddeholm Tooling Ltd (Herrmann et al., 2005)....... 3

Table 2. Mixtures of EAF and ladle slag used in the experiments ................................... 4

APPENDIX I Table 1. Sample data......................................................................................................... 2

Table 2. Recorded data of 100 % ladle slag sample ......................................................... 2

Table 3. Recorded data of 35 % EAF slag sample ........................................................... 3

Table 4. Recorded data of 50 % EAF slag sample ........................................................... 3

Table 5. Recorded data of 65 % EAF slag sample ........................................................... 3

Table 6. Recorded data of 100 % EAF slag sample ......................................................... 4

Table 7. Mixtures for preparation of specimens ............................................................... 5

Table 8. Data of the cylinder ............................................................................................ 5

Table 9. Data of modified Proctor device......................................................................... 5

Table 10. Main IR peaks of 100 % EAF slag, 50 % EAF slag and the two ladle slag

samples including literature data .................................................................................... 11

APPENDIX II Table 1. Steel slag generation in EU, Germany and Sweden ........................................... 6

Table 2. Clinker and mineral phases in OPC according to Knoblauch

and Schneider (1992).......................................................................................... 12

Table 3. Main mineral phases in cement with chemical compounds and corresponding

cement nomenclature.......................................................................................... 14

Table 4. Hydraulic behaviour or different materials (Röhling et al., 2000) ................... 16

Table 5. Chemical composition of certain materials used in cement industry

(according to Knoblauch and Schneider, 1992) ................................................. 17

Table 6. Chemical composition of two EAF slags (Motz and Geiseler, 2001) .............. 20

Table 7. Predominant mineral phases associated with steel slag

(Murphy et al., 1997).......................................................................................... 22

Table 8. Regions of Infrared radiation............................................................................ 35

TERMINOLOGY

VIII

TERMINOLOGY

Amorphous Minerals that have no crystal lattice, i.e. no structure consisting

of crystal units. The antonym is crystalline.

Blast furnace In a blast furnace, iron ore is reduced to iron in the form of pig

iron. Raw materials are coke and iron ore. Furthermore, air is

blown into the furnace. Products of this continuous process are

molten iron and blast-furnace slag.

Carbonation Chemical reaction leading to formation of carbonates. An

example is the reaction of calcium hydroxide with carbon

dioxide in the air to calcite.

Cash minerals Minerals that have the ability to incorporate heavy metals in

their crystal structure (also called reservoir minerals). They can

be formed by thermal processes (primary cash minerals) or by

hydraulic reactions (secondary cash minerals). Certain cement

phases, carbonates and iron-hydroxides are known as cash

minerals.

Curing Hardening of cement due to hydration.

Diffraction When a beam of light is directed towards a crystal, light is

diffracted under a certain conditions, e.g. that distances

between the crystal lattice are equivalent to the wavelength of

the light beam. Diffraction means that the light of the original

light beams is scattered, many beams are formed that all have a

regular pattern including information about the crystal

structure.

TERMINOLOGY

IX

Fly ash Artificial puzzolan originating from coal combustion or MSWI

incineration. Fly ash is collected in electric filters and bag

filters.

Hydration1 The curing of cement and cementitious materials directly after

addition of water is based on the chemical and physical

integration of water in the structure of hydraulic minerals.

Chemically bound water cannot evaporate and belongs to the

hardened cement paste, whereas physically bound water present

in e.g. capillary pores can evaporate.

Ladle A vessel for transporting molten steel or metals.

Latent hydraulic Property of calcium silicate aluminate compounds. After

addition of water, hydration takes place but just in presence of

an activator, e.g. Ca(OH)2. An example for a material

consisting of calcium silicate compounds is blast furnace slag.

The cause for this property is a defective (metastable) lattice

structure (Knoblauch, 1992).

Liner A liner is a designed containment layer. It can be built from

natural or synthetic materials. Here, the term is used for a part

in the top cover construction of a landfill, also called the barrier

layer.

Mineral phase A phase is any part of a system that is physically homogeneous

within itself and is mechanically separable from the other parts.

Any pure mineral is a single phase; any rock is a system in

which the phases are the individual minerals. In cement for

example the main mineral phases are tricalcium silicate,

dicalcium silicate, tricalcium aluminate and tetracalcium

alumino ferrite.

1 German: Hydratation

TERMINOLOGY

X

Molecular vibrations The chemical bonds of a molecule will vibrate, if a molecule

absorbs infrared radiation. The bonds can perform different

vibrations. They can stretch, bend and contract. Therefore,

infrared spectroscopy belongs to the methods of vibrational

spectroscopy.

Puzzolanic materials Natural or artificial materials that - together with water and the

activator calcium hydroxide (slaked lime) - form cement stone

similar products. Beneath alumina, puzzolans generally contain

silica amounts between 50 and 80%. The silica is present in an

amorphous state, otherwise no reaction would occur. Puzzolans

just form a hydraulic binder after the chemical reaction with

calcium hydroxide. The activator calcium hydroxide is needed

for the hydraulic reaction of puzzolanic materials even if there

is enough calcium oxide present in the material to build the

same hydration products.

They are therefore distinguished from hydraulic or latent

hydraulic substances. The reaction rate for a puzzolanic

reaction is slower than for a hydration reaction (Grübl et al.

2001).

Solid solution2 According to IUPAC (1997), a solid solution is a mixed crystal.

Another constituent - apart from the ones belonging to the

original crystal - must be present that fits into the crystal

structure and is distributed in the host crystal.

Steel slags Also called steelmaking slags. The term includes EAF slags,

ladle slags and AOD slags. They are formed during steel

production by adding slag formers. The slag formers react with

the undesirable elements, e.g. carbon, silicon, sulphur or

phosphorous. These elements are oxidised and rise to the

2 German: Mischkristall

TERMINOLOGY

XI

surface of the molten steel, where they are removed

(deslagging).

Tapping of steel Here: The process of pouring the steel from the EAF furnace

into the ladle.

Uphill casting For solidification, different steel casting processes exist. The

typical ingot mould casting process is known as uphill casting,

in which molten metal fills a mould from the bottom.

Vacuum degassing After the steel has been treated in the ladle, the ladle is brought

to a degassing station where it is put under a vacuum lid. The

vacuum treatment and the additional stirring with injected

argon gas or blowing of oxygen shall a. o. reduce several

elements as e.g. hydrogen in the steel.

PREFACE

XII

PREFACE

I would like to express my gratitude to Dr. Lale Andreas for giving me not only the

opportunity to write this thesis at Luleå University of Technology (LTU), but also for

helpful answers to all my questions, the organization of my stay, the supervision of this

thesis and her efforts to make me settle in.

I thank Prof. Dr.-Ing. habil. Bernd Bilitewski for being my supervisor in Dresden.

I also thank Inga Herrmann for her help, for her correction tips and last but not least for

bailing me out at Christmas 2005.

The master thesis was performed in co-operation with the division of process

metallurgy at LTU. For the laboratory analyses, data interpretation and sharing their

knowledge about metallurgy and minerals, I especially thank Margareta Lidström

Larsson and Fredrik Engström.

I really enjoyed my stay at the division of Waste Science and Technology in Luleå and

always felt a very friendly atmosphere there. Therefore, I want to thank Roger Lindfors,

Ulla Brit Uvemo, Igor Travar, Lisa Dahlén, Dr. Holger Ecke and Prof. Dr. Anders

Lagerkvist.

Furthermore, I got to know a lot of friends in Luleå who tried to make me see the things

besides work and studies.

I also thank Rita Ougolnikova and Irene Schneider for last comments on this work.

I thank my family, for their continual support in everything that I do. I will always be

grateful to you.

SUMMARY

XIII

SUMMARY In 2004, the European steel industry generated about 15.2 million tonnes of different

steel slags. Out of these, electric arc furnace (EAF) slags and secondary metallurgical

slags account for almost 6 million tonnes (Euroslag, 2006). Steel slags can potentially

be reused, e.g. as construction material in landfill liners or cover constructions. Their

physical and chemical properties have been investigated by e.g. Herrmann et al. (2005),

Shen H. et al. (2004), Shi (2002), Motz and Geiseler (2001) and Fällman (1997).

However, not much is known with regard to their long-term behaviour. The presented

project deals with alterations of the mineralogical composition of steel slags as a base

for estimations of the long-term stability.

Two types of steel slags, electric arc furnace (EAF) slag and ladle slag were mixed in

different proportions and analysed with calorimetry, infrared (IR) spectroscopy and X-

ray diffraction (XRD). In the mixture ladle slag reacts with water by hydration, while

the EAF slag works as filler.

The study focused on the cement reaction as well as on the mineralogical composition.

The cement reaction was tested with the aid of calorimetry, whereas IR spectroscopy

(FTIR spectrometer) and XRD were used to analyse the amorphous and crystalline

mineral phases. A method for preparing specimens was developed.

The temperature development of the different mixtures of EAF and ladle slag recorded

by the calorimeter showed an activation of the mixture by Al-rich ladle slag: higher

portions of ladle slag resulted in an increased development of heat. However, higher

portions of ladle slag also involve a delay of the maximum heat build-up.

The IR analyses showed that changes in the sample spectra were proportional to the

content of EAF slag. Additionally, one IR analysis of non-hydrated (dry) ladle slag was

performed. During qualitative analysis of the IR spectra, absorption bands were

identified in the wave number ranges of inorganic carbonates, calcium silicates and

aluminium oxide. The biggest differences between the samples could be seen in the

region from 3500 to 3200 cm-1. Ladle slag showed clear absorption peaks, while EAF

slag did not. This wave number range represents the absorption of O-H bonds and

therewith the integration and absorption of water molecules in the mineral structure.

SUMMARY

XIV

With the help of XRD, the main minerals in a 100 % ladle slag were identified as

γ - Calcium silicate (γ -Ca2SiO4) and Mayenite (Ca12Al14O33), whereas Merwinite

(CaMgSiO4) and Monticellite (Ca3Mg(SiO4)2) were most common in 100 % EAF slag.

New mineral phases after mixing both slag types could not be detected with XRD.

Mineralogy determines steel slag properties and liner performance. Mineral alterations

include the formation of secondary minerals through weathering of the analysed

primary minerals. Estimations for these aging reactions of primary minerals are

outlined.

INTRODUCTION

1

1 INTRODUCTION

Electric arc furnace (EAF) slag and ladle slag are by-products of steel produced in an

electric arc furnace and the following secondary metallurgy processes in a ladle vessel.

Their reuse is not only of environmental benefit as natural aggregates do not have to be

exploited, but also of economical benefit as many landfills in Europe need a final cover

in the future.

In order to assess if EAF slag and ladle slag can be utilised as construction materials in

the liner barrier of a landfill, their physical and chemical properties have to be known,

as well as their environmental impact and long-term behaviour. The mechanical and

chemical stability of the construction is an important question.

The aims of the study are to estimate the reactivity of the slags after water addition, to

determine amorphous and crystalline mineral phases in the slags and slag mixtures, and

to evaluate the stability of the major mineral phases. Another question is the formation

of new mineral phases after mixing EAF slag with ladle slag and water.

The reactivity of the slags after water addition is together with the gradient of heat

generation over time an indicator for the formation of more or less stable mineral phases

during the curing process. The stability of the steel slag minerals is important for the

prediction of mineral transformations that may occur in a landfill environment and

therewith affect the stability and long-term behaviour of the cover construction itself.

The suitability of the analysis methods calorimetry, IR spectroscopy and X-ray

diffraction (XRD) for answering the above stated research questions was assessed in a

literature review (Appendix II). A method to prepare samples for IR and XRD analyses

was developed and is described in Appendix I, together with the sample preparation for

the calorimetric experiments and the collected data.

MATERIAL AND METHODS

2

2 MATERIAL AND METHODS

In the following chapter, the well-known properties of the steel slags are reported about.

In addition, the measuring procedure of the various analytical techniques is described.

2.1 Material

Five steel slags were sampled from Uddeholm Tooling Ltd., a company producing a. o.

high-alloyed tool steel. The slags were investigated at the Division of Waste Science

and Technology at Luleå University of Technology (LTU) during autumn and winter

2004/05. The results of these investigations are published in Herrmann et al. (2005) and

Andreas et al. (2005) yet those results being important for the understanding of this

study are shortly described in the following.

Two EAF slags and one ladle slag were investigated in this study, whereas both EAF

slags (called type 1 and 2) are mixed in equal shares due to their similar chemical

composition. Figure 1 and 2 show the two steel slag types.

Figure 1. EAF slag

Figure 2. Ladle slag

The investigated EAF slag and ladle slag had some major differences in their chemical

composition, which is presented in Figure 3. Not only does ladle slag contain 26 %

more calcium oxide and 47 % more aluminate, it also reaches only 39 % of the silicate

content of EAF slag.

MATERIAL AND METHODS

3

0

5

10

15

20

25

30

35

40

45

CaO SiO2 Al2O3 MgO MnO Fe2O3 FeO

cont

ent [

wt.-

%]

Electric Arc Furnace slag 1/2

Ladle slag

Figure 3. Chemical composition of EAF slag and ladle slag

EAF 1 was produced under reducing conditions while there was still a high silicon

content in the steel melt. EAF 2 was formed under a reducing atmosphere as well, but

with addition of silicon and iron chromate (FeCr). Furthermore, oxygen was blown into

the melt.

The ladle slag was tapped after the secondary steelmaking process at the ladle furnace

station. In the ladle, a. o. processes as deoxidisation with aluminium, addition of slag

formers (dolomite and lime) and alloys take place. The production steps in the EAF and

in the ladle are further explained in Appendix II (Chapter 2).

Uddeholm Tooling Ltd. is a small steel mill. The annual slag output can be seen from

table 1.

Table 1. Annual slag generation at Uddeholm Tooling Ltd (Herrmann et al., 2005)

EAF 1 EAF 2 LS

amount per year

[ton] 5200 2000 1300

After tapping, the slag is stored indoor and just cooled by air contact. The slag types are

piled separately. A representative sample was taken from every heap in summer 2004.

EAF 1 and 2 were crushed to a size smaller than 20 mm. They contain much coarser

particles than the ladle slag which disintegrates into fine powder because of the high

Ca/Si ratio. As can be seen in Figure 4, two thirds of the ladle slag consists of particles

smaller than 0.25 mm, while only 18 to 24 % of the EAF slag particles are below that

size.

CaO SiO2 Al2O3 MgO MnO Fe2O3 FeO

MATERIAL AND METHODS

4

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.001 0.01 0.1 1 10 100particle size [mm]

pass

ed a

mou

nt

EAF 1

EAF 2

Ladle

Figure 4. Particle size distribution of EAF 1, EAF 2 and ladle slag (Herrmann et al., 2005)

Curing, a special feature of materials with cementitious properties occurred after mixing

the slags with water. This hardening of the material originates from the hydration

reaction and is further explained in Appendix II.

Hardening tests described in Herrman et al. (2005) showed that ladle slag hardens very

quickly in contrast to EAF slag. In order to be able to use it as a construction material,

EAF slag 1 and 2 can be added “to decelerate the hardening process” that there is at

least one day time for construction. Curing of the material originates from hydration

which is further explained in chapter 4 of Appendix II. All three types if steel slags,

EAF slag 1, 2 and ladle slag, have been categorised as “non hazardous waste” according

to EU legislation (EU, 2002). The mixtures of ladle slag and EAF slag 1 and 2 (in equal

shares) used in all measurements are shown in table 2.

Table 2. Mixtures of EAF and ladle slag used in the experiments EAF slag [%] 100 0 35 50 65

Ladle slag [%] 0 100 65 50 35

MATERIAL AND METHODS

5

2.2 Methods

In order to quantify the heat release during hydration, the slags are mixed with water

and analysed in a calorimeter. The method of IR spectroscopy was taken to observe

changes in the chemistry of the hydrated slags, in case of a major part of amorphous

minerals in the slags. Furthermore IR spectra are easier to analyse than e.g. X-ray

diffractograms. The spectra can be analysed without the use of databases, but

identification of a compound is usually not done only with IR analyses. The most

certainty is achieved by combining information derived from IR spectra with knowledge

of the chemical composition, i.e. other analysis methods. About combinations of IR

spectroscopy with other analysis methods has been reported about in Appendix II.

In combination with IR spectroscopy, XRD was applied. XRD is especially of use for

phase identification of crystalline solids. It is therewith possible to distinguish, e.g. two

minerals with the same chemical composition but different crystal structure. The

detailed applied methods of IR spectroscopy and XRD are explained in chapter 6 and 7

of Appendix II.

Before analyses, the slags were sieved. From EAF slags, the fraction 8 < x > 19 mm and

from ladle slag, the fraction < 19 mm was taken and analysed. For the calorimetry

measurements, the slag was taken in the original state. Slag samples for IR and XRD

analyses were prepared. Each sample was mixed with 10 % of water and compacted in

three layers. This water content was determined as optimum water content for a

compacted slag mixture with a maximum density. The corresponding Proctor-

experiment is found in Herrmann et al. (2005).

The specimens were stored in a bucket with 100 % humidity for two days in order to

allow hydration of as many minerals as possible during these two days. A complete

hydration of the material would take much longer, but not more time than one week of

sample preparation was available. After that, the specimens were dried for five days in

an exsiccator. It is important that he samples for the IR measurements are dry because

otherwise, water would absorb IR radiation and the spectra would be altered. After

drying the samples were grinded (particle size required for IR and XRD: < 200 µm) and

iron particles were removed by a magnet (see also Appendix I for preparation of

MATERIAL AND METHODS

6

specimens). One ladle slag sample (100%) was analysed with IR spectroscopy without

mixing it with water before. Therefore, this sample is called non hydrated ladle slag.

2.2.1 Calorimetry

The experiments were carried out with a Parr 1455 Solution Calorimeter. The sample

chamber shown in Figure 5 is a fully silvered glass dewar within a stainless steel air

can. For isolation the whole assembly is surrounded by a block of plastic foam which

lies in a rugged aluminium case. Temperatures are measured with a temperature probe,

which has to be immersed to the water in the dewar. The calorimeter is connected to a

strip chart recorder. The anticipated temperature range was fixed with the help of the

key functions of the calorimeter. The temperature change is simultaneously measured

and recorded on a paper sheet. The measurement was cancelled when the temperature

decreased up to the initial temperature. The heat outputs of the slags are compared by

relating the temperature change to the mass of the slag in the calorimeter.

The water in the dewar (ca. 40 ml) and the water later mixed with the sample (water

content ca. 30 %) should both have approximately room temperature. The high water

content was taken to have an excess of water, because hydration is limited by water

content. The water is filled in the measurement assembly before sample addition to

record the initial temperature. When the initial temperature is stable, sample is added

and mixed with water.

Figure 5. Sample cup in the calorimeter

water in dewar

thermometer

slag sample in plastic containerwater

MATERIAL AND METHODS

7

2.2.2 IR spectroscopy

The samples were taken from the same material which has been prepared for the XRD

analyses, except of an additional grinding with a mortar before IR analyses. Before

measuring the actual samples, a background spectrum needs to be recorded. For this,

Potassium bromide (KBr) is used as a so called window material, because it does not

absorb in the MID-IR, i.e. it is infrared transparent. To not take up humidity from the

air, KBr is stored in an exsiccator. It has to be grinded with a mortar in a bowl as well.

The spectrometer automatically subtracts the background spectra of KBr from all

measured spectra. The performance of a quantitative analysis was not undertaken. For a

quantitative analysis, the analysis has to be performed with a standard included in the

sample.

2.2.3 X-ray diffraction

For the diffraction experiments, a powder diffractometer was used. A powder

diffractometer uses a detector to register the positions of the scattered X-rays. The

detector is moved around the sample on a circular plane. Each lattice plane of a crystal

in the sample can diffract X-rays at all angles that fulfil the Bragg-equation (see chapter

6.1, Appendix II) and therewith produces a diffraction cone. These diffraction cones

consist of very close beams diffracted by crystallites in the powder and are recorded by

the detector. Consequently, the received powder diffractogram is determined by the

crystal structure and unique for each material.

RESULTS

8

3 RESULTS

In the following, analyses results of calorimetry, IR spectroscopy and XRD are

presented. Further IR spectra are displayed in Appendix I.

3.1 Calorimetry

The heat development of the different slag mixtures is shown in Figure 6 below. The

x-axis shows the time, the y-axis the temperature difference per gram slag. The heat

released decreases with increasing EAF slag content. For one sample with 100 % EAF

slag, the heat development over 60 hours was recorded and it showed a continuous heat

release. However, the temperature change was only 0.22 °C.

0.00

0.05

0.10

0.15

0.20

0.25

0 5 10 15 20 25 30 35time [hrs]

[dT/g]100%LS

35%EAF

50%EAF

65%EAF

100%EAF

Figure 6. Temperature changes per gram slag during hydration measured with

calorimetry

The diagram shows that the heat development in the dewar occurred under partly

adiabatic3 conditions. One part of the released heat of hydration leads to heating of the

slag sample, another part is evolved to the environment (depending on isolation

properties) and the third part increases the temperature in the calorimeter. At the

beginning, conditions are almost adiabatic. Heat generation and heat outflow are in

equilibrium at the maximum of the reaction (Zement-Taschenbuch, 2000).

3 Adiabatic conditions: no heat exchange between sample and environment

RESULTS

9

3.2 IR spectroscopy

The IR results are compiled in chapter 3 of Appendix I. The IR spectra of EAF and ladle

slag plus the spectra of three mixtures of them, i.e. 35 / 50 / 65 % and one additional

sample of non hydrated ladle slag were recorded. The IR spectrum of 100 % (hydrated)

ladle slag is given as an example in Figure 7. The two below explained peaks A1 and

A2 are marked.

4000.0 3000 2000 1500 1000 500 400.0

0.000

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.900

cm-1

K-M

36233526 3318

1656

1422

970

929919

866

818

568

523

476

442426411

Figure 7. IR spectra of 100 % ladle slag (hydrated sample) The spectrum in Figure 6 is shown in the form wave number vs. Kubelka-Munk units.

For qualitative interpretation, just the relation of the peaks is of interest, not the

respective Kubelka-Munk value of each peak itself (see chapter 7.4, Appendix II). The

range on the x-axis comprises the wave numbers 40,000 to 400 cm-1. In Figure 8, a

compilation of all sample spectra is presented.

peak with area A2 peak with area A1

RESULTS

10

Figure 8. FTIR spectra of two hydrated slags and three hydrated slag mixtures

The biggest difference between all spectra is seen in the wave number range from 3500-

3200 cm 1− . The spectrum of hydrated ladle slag shows several peaks, at e.g. 3623 and

3526 cm 1− , whereas the 100 % EAF slag has none there. This wave number range

reflects the vibrations of O-H bonds, which can be bound to several components.

During the hydration reaction, the water molecules took up spaces in the crystal lattice.

If an OH- ion is bound at a different place of the molecule or mineral after reacting with

the water, the O-H bond absorbs IR radiation at a slightly different frequency.

The mixtures show similar peaks as the ladle slag, but these peaks are not as intense as

the ladle slag peak at 1600-1300 cm-1. The latter one is explained further down but the

decrease of the ratio between the two peaks is evaluated in Figure 9 below. It shows,

that the more ladle slag the sample contains, the more intense is the peak A1 from 3750-

2450 cm-1 compared to peak A2 from 1600-1300 cm-1.

4000 3000 2000 1500 1000 500 400

wave number/cm-

1

K-M

3299 1462

983 905

653

590

523

866

865

3526 3338

1660

1418

978 951

653

524

3528 1655

1415

867

817 669

525

3622 3527

3328 1655

1418

972

929

919867

818

524

3623 3526 3318

1656

1422

970

929

919

866

818568

523

100%EAF, 0% LS

65%EAF, 35% LS

50%EAF, 50% LS

35%EAF, 65% LS

0%EAF, 100% LS

RESULTS

11

0

35

65100

0

1

2

3

4

5

6

0 20 40 60 80 100ladle slag [%]

A1/

A2

Figure 9. Comparison of area ratio of peaks caused by absorption of OH-bonds A1 = area below the graph from 3750-2450 cm-1 A2 = area below the graph from 1600-1300 cm-1

There is also a broad band around 3200 cm-1 (accompanied with a weak peak at

1655 cm-1), which is caused by physically bound water respectively its asymmetric

stretches. That means that water molecules are absorbed to some compound.

A general rule is that the lower the wave number, the stronger the bond. The reason is

that atoms having a larger mass, e.g. metals, result in higher bond forces and absorb at a

lower frequency, i.e. wave number.

DRIFTS (Diffuse Reflectance Infrared Fourier Transform spectroscopy) measures the

radiation scattered at the surface of a material. Therefore small impacts of the surface,

can be seen clearly in the spectrum. But also changes of the air, respectively atmosphere

in the sample compartment during the analysis can influence the spectrum. Same

spectra, as the one of ladle slag slag show a smaller peak at 2359 cm-1 for example. CO2

is known for having an antisymmetric C=O stretching at 2349 cm-1 (from the rotational

spectrum). Probably, the small peak in the steel slag represents the changing CO2

content in the atmosphere during the recording of the KBr as background spectrum and

the sample itself.

In that so called fingerprint region (from 1500 to 650 cm-1), “a spectrum may have

hundred or more absorption bands present”, but according to Günzler and Gremlich

(2002) “only the most intense bands serve as indicators”. Therefore, only the most

intense peaks can be assigned to a bond. For the other ones, often overlapped by each

other, assumptions can be made.

RESULTS

12

A broad band present in all spectra lies at 1500-1350 cm-1, originating from C-O

stretching vibrations in the functional group CO3 of inorganic carbonates as CaCO3

(further bands at 880 and 710 cm-1).

Also, calcium silicate and calcium aluminate phases are likely to be present. Generally,

they show bands from 1100 to 800 cm-1 (CaxSiyOz) as well as from 600 to 500 cm-1

(CaxAlyOz). One problem of analysing them with certainty is that many bounds show

absorption in that area. Resolving the broad (overlapping) bands of spectra is

complicated. However, the 970 cm-1 is considered to be originated from calcium silicate

phases as this peak can be seen rather clearly. The stretching vibration of the Si-O bond

in calcium silicates absorbs in the region 1100-800 cm-1 as well as from 600 to

500 cm-1.

Anhydrous calcium silicates – anhydrous refers to “no crystalline water” – absorb at

920 cm-1, 536-526 and 464-458 cm-1 (Gomes and Ferreira, 2005). Furthermore, they are

known for having puzzolanic properties. Hydrated ladle slag shows the 920 cm-1 band.

But with an increasing amount of EAF, this peak is getting harder to identify.

Because oxides of iron, aluminium and small amounts of magnesium are present in the

slags, those are worth to look for as well. Al-O stretching vibrations occur in the region

from 950-800 cm-1 and the strong peak at 866 cm-1 in the ladle slag spectrum is

probably due to Al-O stretching vibration. This peak is shifted towards 860 cm-1 in the

non hydrated ladle slag and also present at the 100 % EAF slag samples, but with much

lower intensity. The aluminium peak is much weaker in the EAF spectra, because ladle

slag has a three times higher aluminium content than EAF slag. Possible compounds

containing aluminium can be calcium alumino silicate hydrates (C-A-S-H).

Speaking about differences in the spectra, it can be said, that the relation of the peak

around 866 cm-1 and the peak around 970 cm-1 changes with EAF content. The more

EAF the sample contains, the higher is the intensity of the around 970 cm-1 compared to

the peak around 866 cm-1. As said before, the first peak is assumed to be aluminium

while the second is related to calcium silicates.

Another peak shifting between hydrated and non hydrated ladle slag has occurred from

568-576 cm-1. Possible compounds causing these bands are again aluminium or iron

oxides (610-520 cm-1 and 580-560 cm-1), whereas magnesium oxide bands should be

RESULTS

13

placed at slightly lower wave numbers (~560-550 cm-1). But calcium silicates and

aluminates absorb in this range as well. Molecules absorbing at wave numbers lower

than 700 cm-1 cannot be identified with certainty.

3.3 X-ray diffraction

Steel slags are a very complex material, which means they can contain a variety of

minerals. The XRD measurements showed that most of the minerals are present as

crystals, i.e. very few amorphous phases have been detected. The presence of

amorphous structures can be detected with XRD as an increase of the baseline from

2Ө (2-Theta) = 20 on. But the pattern produced of an amorphous phase cannot be

assigned to a compound.

For identification, the diffractogram is compared with minerals in a database. If a

sample consists of more than one mineral, as it is the case for steel slags, the different

peaks of each substance overlap each other and get harder to identify. A mineral only

can be detected if the sample contains more than 4 % of it. EAF slag and ladle slag

consist of different minerals.

In Figure 10, the diffraction pattern of 100 % ladle slag and 100 % EAF slag are shown.

X-ray diffraction pattern of steelslags

10 20 30 40 50 60 70 80 90

2 - Theta - Scale

Inte

nsity 100 % EAF

100 % Ladle

Figure 10. Diffraction pattern of 100 % ladle slag and 100 % EAF slag

100 % ladle slag

100 % EAF slag

RESULTS

14

The mixtures of EAF and ladle slag only contained mixtures of the minerals of both

samples indicating that no new minerals have been formed.

The minerals detected have been:

Ladle slag

Periclase MgO

Dicalcium silicate γ - Ca2SiO4

Iron Fe

Spinel MgAl2O4

Mayenite Ca12Al14O33

Dicalcium Silicate α - Ca2SiO4

EAF slag

Iron Fe

Merwinite Ca3Mg(SiO4)2

Monticellite CaMgSiO4

Clinoenstatite MgSiO3

Dicalcium Silicate Ca2SiO4

Magnesium Aluminium Oxide MgAl2O4

Out of these, the main minerals were

γ - Dicalcium silicate (γ - Ca2SiO4) and Mayenite in ladle slag and

Merwinite and Monticellite in EAF slag.

The minerals have different properties considering their hydraulic behaviour. Periclase

for example forms hydraulic minerals under addition of water.

In XRD analysis, the peaks of high intensity can be assigned to a certain mineral. The

strong peak in the EAF slag diffractogram for example originates from periclase.

Furthermore, different phases of dicalcium silicate have been recorded. They are formed

during cooling of the molten slag. Each of the five polymorphs of Calcium silicate has a

different crystal structure and different properties.

DISCUSSION

15

4 DISCUSSION

Method development for preparing sample specimens

For the IR and XRD analyses, a method of sample preparation including hydration of

slags and compaction was developed. Five different slag specimens according to five

mixtures were prepared. They were stored in a 100 % humid atmosphere for two days

(see description in chapter 2 of Appendix I). This short period of time restricts the

curing processes since the hydration is limited by the water content. If water is

available, the hydration will continue until all silica molecules have reacted with the

OH- ions. The short curing time affected certainly the results of the mineralogical

analyses but the time for preparing samples was limited by external circumstances and,

also, the study had a survey character, i.e. the results are considered sufficient for a first

overview and more investigations are planned.

Analysis methods

The common area for the application of IR spectroscopy is analysis of the chemical

structure of organic compounds. However, no reason could be identified - by studying

the literature (Appendix II) - to not use IR spectroscopy for inorganic compounds as

well. Furthermore, the possible presence of a considerable amount of amorphous mate-

rial in the slags suggested the IR method.

The evaluation of the IR spectra of steel slags was based on personal experience and

literature data. However, available databases for IR data were difficult to use because

steel slags are very complex and contain a broad variety of minerals. Absorption data

from databases mostly refer to pure chemical compounds.

IR measurements of such complex materials as steel slags can not give evidence for the

presence of a compound with absolute certainty. Together with the knowledge of the

chemical composition and the absorption data, it only allows statement s like that the

present elements and functional groups absorb in a certain wave number range. If

absorption in that wave number range was measured, it can originate from the assumed

compound, but it also can originate from the absorption of other compounds or

influences as sample preparation or changing conditions while the analyses were

performed. A quantitative analysis has not been performed. In such an analysis a

standard is measured together with the window material (KBr) and the slag.

DISCUSSION

16

The analyses of hydrated and non hydrated ladle slag proved the integration of hydra-

tion water in the slag structure. The absorption bands below 1000 cm-1 and particularly

below 700 cm-1 are difficult to assign to a chemical compound as not only carbonates,

calcium silicates and calcium aluminates absorb in that range but also iron, aluminium

and magnesium compounds.

The differentiation of mineral phases as calcium silicates as tricalcium silicate and

dicalcium silicate is not possible with IR measurements.

Furthermore, conditions in the atmosphere of the sample compartment in the apparatus,

as for example CO2 and air humidity can have an influence on the measurements. This

is because water vapour and carbon dioxide absorb in the MIR. If the atmospheric

conditions in the sample compartment are the same during the analysis of both the

sample and the background, the instrument will ratio out these bands and they are not

seen anymore in the final spectra (Smith, 1996). The IR spectrometer had to be moved

to another room between the first experiments (including measurement of background)

and the repeated analyses of 50 % EAF slag and non hydrated ladle slag. However, only

a little disturbance around 2350 cm-1 has been caused by this.

The investigation of the crystal structures was done by XRD analyses. Even if it is not

possible to identify amorphous phases with XRD, the diffractogram of a sample contai-

ning amorphous phases shows a hump of the background in the range 2θ (2 Theta) ~ 20

to 40. In the diffractograms, this hump was very low. Hence, the majority of the

minerals in the slags are present in a crystalline state. The time for crystallisation after

tapping of the slag is determined by the slag treatment. The Uddeholm slags have been

stored and cooled by air contact and could therefore crystallise during storage.

As diffraction occurs at the sample surface, the diffracted X-rays only contain

information about the minerals detected at the surface. For that reason the sample

preparation has to be very careful, so that crystals are evenly distributed in the sample.

The information about the main minerals in the EAF slag and ladle slag was attained by

thermo dynamic calculations. The diffractograms were evaluated by a database. Except

of some very intensive, clear peaks, it is impossible to analyse them visually, because of

the number of peaks caused by each mineral. XRD as well as IR peaks can overlap each

DISCUSSION

17

other, the peaks can be shifted on the x-axis or they can differ in intensity from sample

to sample.

Some compounds have very similar diffraction patterns. They can consist of the same

crystalline phase but include different irregularities in their crystal structure. This

phenomenon is called solid solution. Under certain conditions, minerals can exchange

atoms. For example calcium silicate phases as Ca(Mn)Si2O6 can have iron atoms at

some places in the crystal structure. XRD is not able to detect those small differences at

the atomic level.

XRD analyses further proved that no mineral formations were induced by mixing EAF

and ladle slag. Only minerals that were present in the pure slags could be detected in the

mixtures. One possible explanation is that no new phases have been formed (at the

present conditions, e.g. 25 °C), but it is also possible, that new formed phases were

below the detection limit of 4 wt-%. As only the surface is scanned by X-rays, small

varieties of the particle distribution originating from the sample preparation could cause

errors too.

Heat generation and curing behaviour

The curing properties and the released heat of hydration have been analysed with the

calorimeter. The heat generation was highest for pure ladle slag while pure EAF slag

released no or very little heat. The ladle slag specimen hardened very fast and, looking

at the different mixtures, curing was the faster the higher the portions of ladle slag.

Ladle slag has a CaO/SiO2 ratio of 3 and hence, is considered as a hydraulic material.

The larger this ratio, the higher is the hydraulic reactivity of the material.

Even if aluminate activates the hydration and the formation of cement phases, the

maximum heat output occurred slightly later, the more ladle slag, i.e. aluminate, the

sample contained. The hydration reaction of pure ladle slag occurs 5 hours later

compared to the mixture containing 65 % EAF slag. Probably, the presence of a cement

activator can retard the time of maximum heat release.

The function of aluminate in the mixtures of EAF and ladle slag was weak not just

because of a lower amount of ladle slag but also because of the low amount of reactive

DISCUSSION

18

lime and high silica in EAF slag4 (see composition in chapter 2). That means that EAF

slag of that composition can be seen as a latent hydraulic material even though almost

no heat output has been recorded.

From cementitious materials it is known that a slow curing process with heat output

over longer period leads to higher long-term stability. For answering the question,

whether the reaction of the samples containing EAF slag proceeds faster but stops

earlier, or if the low reaction rate leads to a continuous reaction, longer measurements

would be needed.

Strength and stability of phases

Although ladle slag released the most heat of hydration, it is not sure that the sample

develops the highest final strength during curing.

The strength developing characteristics depend primarily on the mineral phases: they

contribute either to early strength (e.g. tricalcium silicate) due to higher heat of

hydration or to later strength (e.g. dicalcium silicate) due to less heat of hydration

(Dobrowolski, 1998).

It has been observed during sample handling that the cured specimen consisting of

100 % ladle slag collapsed when touched after three months. It had been stored in a

room together with the other samples. As the sample with 100 % EAF slag did not cure,

it had not formed a stable specimen after hydration. All specimens consisting of slag

mixtures were still stable after three months. The alumina content of ladle slag of

23 wt-% is compared to EAF slag relatively high. The instability of the ladle slag

specimen asserts the hypothesis of very low final strength of cementitious materials

containing high aluminate (see Appendix II, chapter 4.1).

Aluminous cement shows a (compared to OPC) fast and intensive hydration reaction

with monocalcium aluminate being the main mineral phase. Low final strength of

aluminous cement is caused by mineral transformations of monocalcium aluminate

during curing. The minerals developed at the end of the hydration reaction (e.g.

dicalcium aluminate hydrate) have a different crystal structure and are less stable than

4 CaO/SiO2 ratio EAF slag = 0.9

DISCUSSION

19

monocalcium aluminate. The same hydration products could have been formed in ladle

slag and instead of reacting with silicates, calcium could have reacted with aluminate,

which in the following could have caused low final strength.

Another possible reason for the disintegration of the ladle slag specimen could be the

expansion of mineral phases. As been detected with XRD analyses, a substantial

amount of periclase is present in ladle slag. Periclase is known for expansion after

hydration. Also, the phase γ - Dicalcium silicate (γ -Ca2SiO4) was measured. This

phase is formed of α - Ca2SiO4 during cooling of the molten slag. The different phases

of dicalcium silicate all have a different crystal structure. During phase transformation,

the change in the crystal structure leads to a disintegration of the mineral. This also can

be a reason for the fine structure of ladle slag. However, no complete explanation of the

observation can be provided.

Mineral alterations

Even though no long-term behaviour has been measured in this study, some additional

observations after three months of storage could be made.

The colour of the three months old specimens was lighter than directly after the

preparation which could be caused by carbonation and calcite formation on the surface.

The formation of carbonates and hence the development of a high buffer capacity is one

assumption for mineral alterations in a liner consisting of steel slags.

The mineral alterations that are estimated for slags consisting of calcium silicates and

calcium aluminates also include the formation of C-S-H and C-A-H phases. These

phases have a good adsorption capacity for heavy metals due to their large reaction

surface (see Appendix II, chapter 4.3). Other types of so called cash minerals that could

hinder the release of contaminants are iron and aluminium phosphates/hydrates/hy-

droxides and silicates.

It is hard to draw conclusion from literature data of ashes and slags regarding mineral

alterations. How much of a material will be transformed and which secondary phases

are developed, has to be investigated for each type of material separately. Ashes and

slags can differ very much in their composition which is reflected also in the literature

where considerable variations of data for mineral alterations of MSWI ashes are

reported.

DISCUSSION

20

Application of steel slags in a liner

As ladle slag adds the reactive compounds to a mixture and addition of EAF slag leads

to higher long-term stability, both slag types have their own function and are necessary

in construction applications. The 50/50 mixture is most favoured in a liner application

because its hydraulic behaviour, curing time and stability showed to be the best for the

target function.

Principally, the chemical and mineralogical composition encourages the application of

steel slags in a top cover construction of a landfill. Through compaction, an increase in

buffer capacity will be achieved, as gas and water fluxes need more time to reach the

reactive surface of the material. Furthermore, construction materials containing

carbonates have advantages considering the expected chemical and mineralogical

changes.

Future experiments

Further analyses with regard to the stability of mineral phases, the formation of

secondary mineral phases and the long time behaviour need to be done. Humidity and

carbon dioxide influence these mineral alterations. Hypotheses about possible

secondary mineral phases have been outlined in the literature review. The expansion of

free CaO and MgO due to late hydration is one problem of applying steel slags as a

construction material. If a construction material does not have sufficient volume

stability, the stability of the whole construction is endangered.

If longer measurements will be performed, much more efforts are necessary. A bigger

number of specimens (including parallels) has to be stored under defined conditions,

e.g. fixed CO2 content and humidity, and more IR and XRD measurements have to be

performed after different periods of sample storage. There are good reasons to assume

that the described mineral alterations can be detected with these two analyses methods.

Quantitative IR as well as XRD measurements should be considered. If possible, the

quantitative methods should be favoured. Suggested time spans for sample storage are

30 days, half a year and one year.

Furthermore, SEM analyses could complete the picture about the mineralogical slag

structure as phases below 4 wt-% and non crystalline material cannot be measured with

XRD. The presence of crystalline structures could be unveiled by this type of

DISCUSSION

21

microscopy. One could illustrate the topography of the surface. Simultaneously, data of

the crystal units are measured.

Models estimating the time for decomposition of ash layers consisting of carbonates by

carbonation result often in time spans of thousands of years (Ecke, 2003). Results of

models performed with steel slag compositions, layer thickness and climate data would

be interesting. Also, further investigations about the stability of the estimated secondary

phases under landfill conditions are necessary. At present thermo dynamical data and

secondary mineral phases are not available for all of the measured minerals.

CONCLUSIONS

22

5 CONCLUSIONS

Calorimetry, IR spectroscopy, XRD as well as sample handling and experiences with

preparing slag specimens provided the following findings.

In Europe steel slags are often landfilled or temporarily stored, although

applications for their reuse already exist (e.g. as additives in a road construction).

The target of nowadays research is to identify further applications for reusing steel

slags and to investigate the environmental impact that steel slags would have. The

conditions present in the liner have to be estimated before using alternative

construction materials as steel slags.

Up to today, the long-term behaviour is still unknown. It is affected by processes as

weathering, including carbonation (carbonic acid weathering) and pH changes,

leaching, aging of mineral phases and therewith stability changes of the minerals.

XRD and IR spectroscopy are suitable methods to analyse the mineral phases of

steel slags. The reaction of the slags under addition of water is called hydration

which has been described in this literature review. To determine the heat

development and conditions of this reaction, calorimetry is a suitable technique.

Ladle slag releases the most heat during hydration, while the heat release of EAF

slag is very little. The maximum heat output occurred the later the more ladle slag

was in the mixture.

The ladle slag specimen cured fastest. The EAF slag sample was not curing to a

rock-like compound and developed no mechanical strength.

A conclusion regarding the correlation of curing behaviour and mineral phases

formed is possible in the way that a high amount of certain mineral phases as

dicalcium silicates results in limited cementitious properties. Such mineral phases

have been recorded by XRD in both slag types.

CONCLUSIONS

23

The heat release during hydration does not necessarily correlate to the stability of

the hydration products, i.e. there is no correlation between heat of hydration and

developed final strength.

Ladle slag showed a higher reactivity than EAF slag, but probably has a lower final

strength, which is concluded from the high alumina content and the properties of

similar cement types. However, the investigation of the final strength after curing

was not part of the measurements.

A mixture of EAF slag and ladle slag is recommended for a landfill cover.

A sample preparation method was developed for mineral analyses, which worked

well and can be applied in further tests. With this method explained in Appendix I

the mineral phases after hydration could be measured by IR and XRD analyses.

IR spectroscopy revealed the different chemical bonds and compounds formed after

hydration. The IR spectra and the intensities of the peaks changed proportional to

the ladle slag content in the mixture. For example, the detection of hydrated water

was the lower; the more ladle slag was present.

Both steel slags consist predominantly of crystalline phases. It is likely that solid

solutions are formed during slag cooling. However, these irregularities of the

crystalline phases cannot be detected with XRD. According to the XRD analyses,

no new minerals have been formed after mixing the two steel slag types.

Further research

Slag storage and how slag properties change with different storage methods or slag

treatments should be investigated more detailed. The stability of mineral phases present

in steel slags, e.g. merwinite, monticellite, mayenite and phases consisting of calcium

silicate, ferrite, magnesia and aluminate is mainly influenced by humidity, carbon

dioxide and pH changes. Humidity and carbonation are assumed to be correlated but

this has not been analysed for steel slags up to now.

CONCLUSIONS

24

Secondary mineral phases of the analysed phases are assumed to be carbonates and

bicarbonates. The formation of carbonates will be a short-term process, while

bicarbonates are formed over very long time periods (in the range of thousands of

years). The amount of minerals that will react and be transformed into secondary phases

is unknown. Compaction will increase the buffer capacity and contribute to longer

reaction times.

More knowledge of stability and long-term behaviour of mineral phases of steel slags

can be achieved with long-term experiments and by modelling and further thermo dyna-

mical data about the analysed minerals.

REFERENCES

25

6 REFERENCES

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Dobrowolski, J. A. (1998). Concrete Construction Handbook. 4th ed., Mc Graw-Hill

Inc., New York, p.1.15, 1.17 et seq.

Ecke, H. (2003). Sequestration of metals carbonated in municipal solid waste incine-

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Fällman, A-M. (1997). Charaterisation of Residues – Release of contaminants from

slags and ashes. Doctoral Thesis – Linköping University, Sweden, p. 9.

Gadsden, J. A. (1975). Infrared Spectra of Minerals and Related Inorganic Compounds.

London, Butterworth, p. 6et seq., 23et seq., 62.

Gomes, C. E. M.; Ferreira, O. P. (2005). Analyses of Microstructural Properties of

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Tecnologia, vol. 15, n° 3, p. 193-198.

Günzler, H.; Gremlich, H-U. (2002). IR Spectroscopy - An Introduction. WILEY-VCH

Verlag GmbH, Weinheim, Germany, p. 176.

REFERENCES

26

Herrmann, I.; Lidström Larsson, M.; Andreas, L. (2005). Användning av stalslagg i

sluttäckningen av Hagfors kommunala deponin. Delrapport, MIMER, Luleå

Tekniska Universitet, Sweden.

Hirschmann, G. (1999). Langzeitverhalten von Schlacken aus der thermischen

Behandlung von Siedlungsabfällen. Fortschr. – Ber. VDI Reihe 15 Nr. 220.

VDI Verlag, Düsseldorf, p. 153.

IUPAC (1997). Compendium of Chemical Terminology. 2nd Edition. Blackwell

Science. International Union of Pure and Applied Chemistry – IUPAC.

Online version of IUPAC compendium:

http://www.chemsoc.org/cgi-shell/empower.exe?DB=goldbook

Knoblauch, H.; Schneider, U. (1992). Bauchemie. Werner-Verlag GmbH, Düsseldorf,

p. 126, 160.

Krenkler, K. (1980). Chemie des Bauwesens. Band 1: Anorganische Chemie. Springer-

Verlag, Berlin, Heidelberg, p. 405.

Motz, H. and Geiseler, J. (2001). Products of steel slags as an opportunity to save

natural resources. Waste Management, Vol. 21, p. 285-293.

Shen, H. et al. (2004). Physicochemical and minerological properties of stainless steel

slags oriented to metal recovery. Resources, Conservation and Recycling 40,

p.245-271.

Shi, C. (2002). Characteristics and cementitious properties of ladle slag fines from steel

production. Cement and Concrete Research vol. 32, p. 459-462.

Smith, B. C. (1996). Fundamentals of Fourier transform infrared spectroscopy. CRC

Press LLC, Boca Raton, Florida, USA, p. 30.

Zement-Taschenbuch (2000). Verein Deutscher Zementwerke e.V. (ed.). 49th ed. Verlag

Bau+Technik GmbH, Düsseldorf, Germany, p. 322.

APPENDIX I

APPENDIX I

SAMPLE PREPARATION AND MEASUREMENT DATA

1 CALORIMETRY....................................................................................... 2

2 PREPARATIONS OF SPECIMENS FOR IR SPECTROSCOPY AND

XRD EXPERIMENTS.................................................................................. 4

2.1 Sample preparation............................................................................................ 4

2.2 Storage of specimens and grinding.................................................................... 6

2.3 Observations ...................................................................................................... 7

3 IR SPECTROSCOPY ................................................................................ 7

4 X-RAY DIFFRACTION.......................................................................... 10

5 REFERENCES......................................................................................... 12

APPENDIX I

2

1 CALORIMETRY

The EAF slag was already crushed to a size smaller than 20 mm at Uddeholm Tooling

AB. Sieving at 20 mm for ladle slag was planned, but a 20 mm sieve was not available

at the university laboratory. That is why EAF 1, EAF 2 and ladle slag (sample no. 5)

were sieved with a 19 mm sieve to remove the fraction > 19 mm. Furthermore, the

fraction < 8 mm of EAF slag 1 and 2 was removed by sieving. Each slag type was

homogenised and reduced. EAF slag 1 and 2 were mixed in equal shares to form the

EAF fraction. These slag fractions were used for all performed measurements. The

exact data of the mixtures measured in the calorimeter are presented in table 1.

Table 1. Sample data

EAF fraction 0 (ladle slag) 35 50 65 100

in [%] mass EAF slag in [g] - 10.44 15.75 19.54 30.32 mass ladle slag in [g] 30.04 19.48 15.72 10.54 - mass of water in plastic container in [g]

10.27 10.04 10.47 10.57 10.52

mass of water in dewar in [g]

40.66 40.11 40.52 40.10 40.22

The recorded values measured by the calorimeter for each sample are presented in table

2 to 6.

Table 2. Recorded data of 100 % ladle slag sample time T dT dT/g slag [hrs] [°C] [°C] [°C/g] 0 21.25 0 0.00 5 22.95 1.70 0.06 10 23.35 2.10 0.07 15 24.75 3.50 0.12 20 27.35 6.10 0.20 21 27.4 6.15 0.20 25 26.43 5.18 0.17 30 24.92 3.67 0.12 35 23.65 2.40 0.08

APPENDIX I

3

Table 3. Recorded data of 35 % EAF slag sample time T dT dT/g slag [hrs] [°C] [°C] [°C/g] 0 22.94 0 0 2.5 23.35 0.41 0.01 5 23.94 1.00 0.03 7.5 24.2 1.26 0.04 10 24.3 1.36 0.05 15 25.25 2.31 0.08 20 26.68 3.74 0.13 25 26.08 3.14 0.10 30 24.95 2.01 0.07 35 24.05 1.11 0.04

Table 4. Recorded data of 50 % EAF slag sample time T dT dT/g slag [hrs] [°C] [°C] [°C/g] 0 21.98 0 0.00 5 22.83 0.85 0.03 10 23.00 1.02 0.03 15 24.74 2.76 0.09 17.5 25.24 3.26 0.10 20 25.00 3.02 0.10 25 24.07 2.09 0.07 30 23.17 1.19 0.04 35 22.58 0.60 0.02

Table 5. Recorded data of 65 % EAF slag sample time T dT dT/g slag [hrs] [°C] [°C] [°C/g] 0 21.88 0.00 0.00 5 22.65 0.77 0.03 10 23.23 1.35 0.04 15 24.19 2.31 0.08 20 23.80 1.92 0.06 25 23.07 1.19 0.04 30 22.80 0.92 0.03 35 22.55 0.67 0.02

APPENDIX I

4

Table 6. Recorded data of 100 % EAF slag sample time T dT dT/g slag [hrs] [°C] [°C] [°C/g] 0 21.45 0.00 0.00 5 21.72 0.27 0.01 10 21.68 0.23 0.01 15 21.64 0.19 0.01 20 21.93 0.48 0.02 25 22.12 0.67 0.02 30 21.90 0.45 0.01 35 21.70 0.25 0.01

2 PREPARATIONS OF SPECIMENS FOR IR SPECTROSCOPY AND

XRD EXPERIMENTS

Specimens for IR and XRD analyses had to be prepared in order to detect the chemical

and mineral structure of the hydrated samples. The used spectroscopic method was the

DRIFTS method which cannot be applied for wet samples, because the water absorbs

radiation and the spectra would be altered.

2.1 Sample preparation

The sieving of the original slag fractions has been explained above (see chapter 1,

Appendix I). They were further used for preparation of specimens. The different

mixtures shown in table 7 were formed and the corresponding mass of each sample

fraction was recorded. The mass of EAF and ladle slag needed for e.g. the specimen

consisting of the 100 % mixture differed because the density of EAF slag is less than for

ladle slag. The height of all specimens was about 4.7 cm.

APPENDIX I

5

Table 7. Mixtures for preparation of specimens

sample no. fraction of EAF

slag mass of EAF

slag mass of ladle

slag mass of water

in [%] in [g] in [g] in [g]

1 0 - 144.32 14.43

2 35 63.85 117.51 19.43

3 50 78.86 78.86 16.18

4 65 117.14 63.44 18.18

5 100 198.54 - 16.15

Each slag sample was separated in three equal parts, mixed with about one third of the

corresponding amount of water and compacted. The necessary knocks of one layer with

the proctor device were calculated according to the following.

Calculation

The sample compaction was carried out according to SS 02 71 09 (SIS, 1994) except

that a different proctor device (than the standard proctor device) was used. The number

of beats from the proctor device was calculated according to equation 1 below in order

to compact the samples with a certain energy. The energy applied was assumed to be

2.5 Nm/cm3 (according to SS 0271 09).

Table 8. Data of the cylinder height [cm] 9.0

height of sample [cm] 4.7

diameter [cm] 5.0

sample volume [cm3] 92.28 Table 9. Data of modified Proctor device height [m] 0.295

falling weight [kg] 2.099

diameter of knock area [cm] 3.0

energy applied [Nm/cm3] 2.5

APPENDIX I

6

The following formula was used to calculate the necessary knocks with the proctor

device for the requested energy input of 2.5 Nm/cm3.

Equation 1 for calculating energy input with proctor devise:

EV

hgmnn=

**** 21

Before getting the necessary knocks for obtaining the stated energy input, unit

conversion was done. The result was again multiplied with a factor of 0.82, because the

relation of cylinder diameter to diameter of knock area of the standard proctor device

(102mm/50mm) in SS 02 71 09 is bigger than the one of the used proctor devise

(50mm/30mm). Therefore 12.6 * 0.82 ≈ 10 knocks with the bearable proctor device had

to be applied for specimen compaction.

2.2 Storage of specimens and grinding

The specimens were stored in a bucket with 100 % humidity to allow a full hydration

reaction over this time. However, the reaction will not continue if there is no humid

atmosphere. For a longer hydration reaction, a longer storage time with 100 % humidity

must be taken. For these measurements, not more time than one week of sample

preparation was available.

After two days in the bucket, the specimens were put in an exsiccator. This was done

because the sample material for the IR measurements had to be dry. After, five days of

curing in the exsiccator, the specimens were taken out.

One day before X-ray measurements, the specimens were pulverized. At first, some

material was scratched off the specimen with big pliers. This material was put in a

grinding apparatus. Before starting the grinding process, a magnet was held over the

n1 number of slag layers in specimen

n2 number of knocks with proctor devise

m mass of falling weight at Proctor devise[kg]

g acceleration due to gravity [m/s2)]

h height of falling weight before compaction [m]

V sample volume [cm3]

E applied energy [Nm/cm3]

APPENDIX I

7

sample and small iron particles were taken out. Then grinding started. It was also

possible to look inside the apparatus and adjust the grinder. Between several grinding

steps, the apparatus was opened and the magnetic fraction was removed again.

Otherwise, these particles could disturb the analyses. After grinding, the sample was put

in a little plastic bag.

2.3 Observations

It was observed from earlier compaction experiments that the 100 % EAF slag specimen

had a crumble consistency after curing. The specimens containing both EAF and ladle

slag exhibited higher strength after standing in room conditions for three months. The

100 % ladle slag specimen became less stable over this time. This indicates that EAF is

basically stabilizing the whole structure, e.g. as aggregate in cement. However, no

strength measurements were performed.

3 IR SPECTROSCOPY The five slag samples were grinded with a mortar in a bowl a second time. The non

hydrated ladle slag and the KBr, which was used as a background material, were

grinded in that way as well.

For the measurements, the samples were diluted in KBr (3.5 % of sample). The material

was weighed and mixed with the KBr by using a little piece of paper. The material is

diluted because only a small sample amount (in the range of some mg) is needed. A

particle size of 2 µm (Gadsden, 1975) is to be preferred. Afterwards, the KBr and the

slag sample are carefully put in the sample cup. As for the XRD measurements as well,

shaking or pressing of material has to be avoided. Instead, a small spatula is pushed

over the plane of the sample cup. If no even surface was obtained, the sample cup has to

be filled again.

The sample cup (filled with about 20 to 25 mg of material) is than put in the specimen

holder and the data (e.g. sample name, scanning range) are given into the computer.

Before starting the measurement, waiting of five minutes was necessary to have stable

atmosphere conditions in the sample compartment. The measurement itself included

130 scans of the sample and took about 20 minutes. After each measurement, the

sample cup was cleaned with cotton wool.

APPENDIX I

8

The spectra of the five hydrated slag samples is shown in Fig. 1, whereas the

comparison between hydrated and non hydrated ladle slag performed by IR

spectroscopy is shown in Figure 2.

Figure 1. IR spectra for all hydrated slag samples (LS = ladle slag)

4000 3000 2000 1500 1000 500 400wave number/cm-1

K-M

3299 1462

983 905

653 590

523 866

865

3526 3338

1660

1418

978 951 653

524

3528 1655

1415

867 817 669

525

3622 3527

3328

1655

1418

972 929 919 867

818

524

3623 3526 3318

1656

1422

970

929 919 866

818 568 523

100%EAF, 0% LS

65%EAF, 35% LS

50%EAF, 50% LS

35%EAF, 65% LS

0%EAF, 100% LS

APPENDIX I

9

Figure 2. IR spectra for hydrated ladle slag and non hydrated ladle slag

Figure 3. IR spectra of 100 % EAF slag and 100 % ladle slag (hydrated)

4000 3000 2000 1500 1000 500 400wave number/cm-1

K-M

3299 1462

983 905

653 590

523

866

3623 3526 3318

1656

1422

970 929 919

866

818 568 523

100%EAF, 0% LS

0%EAF, 100% LS

4000 3000 2000 1500 1000 500 400

K-M 3623 3526 3318

1656

1422

970 929 919

866

818 568

523

476

3300

1459

973 928 919

860

818 576

521492473

hydrated ladle slag

non hydrated ladle slag

APPENDIX I

10

4 X-RAY DIFFRACTION

For X ray diffraction analysis just a small amount of the solid sample is needed. Before

putting the sample in the diffractometer, the sample was put in a small round deepening

of a thin plastic plate. The difficulty is to have an even sample surface but not to press

or shake the material in the plate. This would change the result, because the premise of

the analysis is that the crystals are randomly orientated over the surface. The flat plate

with the sample is than put on the circumference of an X-ray focusing circle. One

analysis took approximately 1.5 hours.

X-ray diffraction pattern of steelslags

10 20 30 40 50 60 70 80 90

2 - Theta - Scale

Inte

nsity 100 % EAF

100 % Ladle

Figure 4. Diffraction pattern of 100 % ladle slag and 100 % EAF slag

100 % ladle slag

100 % EAF slag

11

Table 10. Main IR peaks of 100 % EAF slag, 50 % EAF slag and the two ladle slag samples including literature data slag type and wave number Literature [cm- author corresponding possible compounds date of measurement vibration (nh = non hydrated) 100%EAF (12.12.) 3300 3500-3400 Smith (1999) Silanol SiO-H stretch silica (Si-OH bonds) 100%EAF (21.12.) 3468 ~3440 O-H stretches combined and adsorbed 50%EAF (21.12.) 3528 3700-3200 water of C-S-H and 100%LS (12.12.) 3526 3440-3446 Gomes and Ferreira (2005) aluminate phases 100%LS_nh (21.12.) 3300 (ancl.1640-

100%EAF (12.12.) 1458 1436-1424 Gomes and Ferreira (2005) C-O stretch carbonate phases 100%EAF (21.12.) 1459 1510-1410 Smith (1999) C-O stretch inorganic carbonates 50%EAF (21.12.) 1415 ~1463 Smith (1999) antisymm. CO3 carbonate 100%LS (12.12.) 1422 1520-1320 Günzler and Williams (2001) stretching vibrat. in inorganic salts 100%LS_nh (21.12.) 1459

100%EAF (12.12.) 982 880 + 710 Gomes and Ferreira (2005) C-O stretch carbonate phases 100%EAF (21.12.) 983 874-880 and Gomes and Ferreira (2005) C-O stretch 50%EAF (21.12.) 867 920 Gomes and Ferreira (2005) anhydrous calcium silicates 100%LS (12.12.) 866 880-860 Smith (1999) C-O out of plane bend inorganic carbonates 100%LS_nh (21.12.) 860 920-800 Socrates (1994) AlO2- Al-ion (also 670-620, etc)

986-970 Gomes and Ferreira (2005) calcium silicates ~940 Smith (1999) silanol Si-O stretch silica ~805 Smith (1999) Si-O-Si symm. stretch

100%EAF (12.12.) 521 536-526 Gomes and Ferreira (2005) anhydrous calcium silicates 100%EAF (21.12.) 522 50%EAF (21.12.) 525 100%LS (12.12.) 523 100%LS_nh (21.12.) 521

APPENDIX I

12

5 REFERENCES Dobrowolski, J. A. (1998). Concrete Construction Handbook. 4th ed., Mc Graw-Hill,

Inc., p. 1.15.

Gomes, C. E. M.; Ferreira, O. P. (2005). Analyses of Microstructural Properties of

VA/VeoVA Copolymer Modified Cement Pastes. Polímeros: Ciência e

Tecnologia, vol. 15, n° 3, p. 193-198.

Günzler, H.; Williams, A. (2001). Handbook of Analytical Techniques. Vol.1. WILEY-

VCH Verlag, Weinheim, Germany, p. 471

Socrates, G. (1994). Infrared characteristic group frequencies. 2nd ed.

Smith, B. C. (1999). Infrared Spectral Interpretation - A systematic approach. CRC

Press LLC, Boca Raton, Florida, USA, p. 165

Svensk Standard SS 02 71 09, 1994. Geotekniska provningsmetoder – Kornfördelning –

Siktning. SIS – Standardiseringskommisionen i Sverige.

APPENDIX II

APPENDIX II

STEEL SLAGS

–

GENERAL DATA, MINERALOGICAL COMPOSITION AND

SUITABLE ANALYSIS METHODS FOR DETERMINING HEAT OF

HYDRATION AND MINERAL PHASES

– LITERATURE REVIEW –

APPENDIX II

II

TABLE OF CONTENTS 1 INTRODUCTION...................................................................................... 1

2 ORIGINS AND FORMATION OF ELECTRIC ARC FURNACE AND

LADLE SLAG .............................................................................................. 2

2.1 Electric Arc Furnace slag (EAF-slag) ............................................................... 2

2.2 Ladle slag........................................................................................................... 2

3 REUSE OF STEEL SLAGS ...................................................................... 3

3.1 Generation and utilisation of steel slags in Europe ........................................... 5

3.2 Utilisation of steel slags in a landfill cover construction .................................. 8

4 MINERAL PHASES................................................................................ 10

4.1 Mineral phases of cement ................................................................................ 11

4.2 Mineral phases of steel slags ........................................................................... 20

4. 3 Alteration of mineral phases........................................................................... 24

5 CALORIMETRY..................................................................................... 29

6 X-RAY DIFFRACTION.......................................................................... 31

6.1 Physical background and sample preparation ................................................. 32

6.2 Interpretation of one X-ray diffractogram of steel slag................................... 33

7 IR SPECTROSCOPY .............................................................................. 34

7.1 Physical background of Vibrational Spectroscopy.......................................... 35

7.2 Technique of the FTIR Spectrometer .............................................................. 39

7.3 The DRIFTS method ....................................................................................... 40

7.4 Interpretation of IR spectra.............................................................................. 41

8 DISCUSSION .......................................................................................... 44

9 CONCLUSIONS...................................................................................... 47

10 LITERATURE CITED .......................................................................... 48

APPENDIX II

1

1 INTRODUCTION

Many landfills in Europe have to be closed due to the regulations in the EU landfill

directive (1999/31/EC). Construction material for the final cover construction of these

sites is scarce due to the high amounts needed and the demands of the respective landfill

class. The estimated need comprises 100 million tonnes only in Sweden (Andreas et al.,

2005). Therefore the use of secondary construction materials from different industries is

explored. Especially steel industry slags seem to be suitable for applications in

geotechnical constructions as for example landfill cover constructions for non-

hazardous waste landfills. This is assumed to their high bulk density, low permeability

and high strength (Motz and Geiseler, 2001). Investigations of the leaching behaviour

by Motz and Geiseler (2001) have shown that only the pH-value had an environmental

impact. Significant leaching of elements could not be proved.

Steel slags are easily accessible. Different slags are produced during steel production

from which electric arc furnace (EAF) slag and ladle slag are investigated in this study.

The aim of this literature review is to determine possible mineral phases occurring in

steel slags, the formation of these phases and under which conditions transformations

can occur. Factors influencing these alterations shall be outlined.

Furthermore, analytical methods to measure mineral phases are proposed, explained and

discussed if they can be used for these investigations. Among other things cement

reaction, and crystal and amorphous structures of the minerals shall be examined.

Special focus is put on X-ray diffraction (XRD) and Infrared (IR) Spectroscopy. What

and how much information about mineral phases of steel slags can be gained by using

these analysis methods?

Finally, desirable properties are defined that steel slags should have when used in a

landfill cover construction.

Possible advantages as well as disadvantages of the analysis methods are discussed and

literature data about steel slag analyses are collected.

Finally, an attempt of defining desirable properties of the steel slags with regard to their

use in a cover construction will be undertaken.

APPENDIX II

2

2 ORIGINS AND FORMATION OF ELECTRIC ARC FURNACE AND

LADLE SLAG

Different slags arise as a by-product during the production of different steels types. The

steel industry tries to minimize the generation of slags but they are not completely

avoidable.

2.1 Electric Arc Furnace slag (EAF-slag)

EAF slags originate from steel mills where the manufacturing process is based on scrap

metal and an electric arc furnace is used. The electric arc furnace contains scrap, iron,

alloys and slag formers (Beskow et al; 2004). In Figure 1, the steel production process

by the scrap route is shown. The power of three graphite electrodes producing electric

arcs is used to melt the material and to form steel. Removal of phosphorous, sulphur and

silicon as well as reduction of carbon is initiated by lancing oxygen into the melt [4].

Slag formers are added to the furnace from below and from the sides. The formed slag

products, consisting basically of oxides, will rise to the surface due to their lower

density. The deoxidisation products are integrated in the slag. These refining processes

would take long time, if not an excess of oxygen is provided for the reactions. Later this

excess oxygen has to be removed again. The steel is tapped into the ladle (also called

converter), which is a vessel used to transport the molten steel to the ladle station.

There, further processes are initiated to increase steel quality (secondary metallurgy).

2.2 Ladle slag

After being treated in the EAF furnace, tapped in the ladle and slag being removed from

the ladle (tapping of EAF slag), the steel is further treated at the ladle station. In the

ladle the chemical composition of the steel is adjusted, the temperature and composition

of the melt are homogenised and further removal of phosphor, sulphur and other

disturbing trace elements is performed.

Steel containing excess oxygen will form gas bubbles during solidification leading to

internal holes. To avoid this, the steel is deoxidised with aluminium wire or bars.

Aluminium and silicon (in the form of ferro silicon) have a high oxygen affinity and are

APPENDIX II

3

therefore used for deoxidisation. After that, slag formers (dolomite and lime) and

aluminate are added again. Depending on the steel type various alloys are given to the

steel. The steel is heated up to about 1925 K and stirred at the degassing station under

vacuum conditions (Figure 1) to ensure homogeneity and to remove nitrogen and

hydrogen. Stirring is done by induction and through circulation of argon gas. Due to

further refining the steel is treated by inductive stirring a second time during which

inclusions grow and are removed (Beskow et al., 2004). In the last manufacturing

process, called uphill casting, the hot steel is casted in moulds for solidification. The

melt in the moulds rises from the bottom to improve the cooling process of the steel.

Figure 1. Flow chart of the steel making process at Uddeholm Tooling Ltd. (a) electric arc furnace (b) ladle furnace (c) vacuum degassing (d) uphill casting (Beskow and Du Sichen; 2004)

3 REUSE OF STEEL SLAGS

As for other secondary materials, the reuse of steel slags helps to conserve natural

construction materials and to prevent emissions to the atmosphere. But for the time

being, industrial by-products as steel slags are classified as waste in Europe. The

definition of waste is constituted in the Council Directive 75/442/EC and amended by

the Council Directive 91/156/EC. That definition complicates the marketing and use of

slag as a product. Nevertheless, there is a discussion going on about such terms as “end-

of-waste” and future definitions in regulations. This discussion is necessary and

probably a never-ending process, because due to research new treatment methods are

developed. Innovations in material science help to conserve the environment and lead to

APPENDIX II

4

new application fields of materials. It is intended to change the definition of waste in the

way that slags will be considered as by-products and are not classified as waste

anymore. Slags from steel industry have found fields of application nowadays. If slags

are treated further, e.g. by different cooling methods, stabilization methods or crushing,

their properties can be optimized. Different treatments of slags lead to different slag

types that are likely to have differences in their properties (Tossavainen, 2005a).

Respective treatment techniques are:

quenching rapid cooling

air cooling slow cooling

granulation

pelletisation

foaming

proper solidification with a specified heat treatment

separation, crushing, sieving and milling.

Tossavainen (2005a) concludes that the cooling conditions (as well as the chemical

composition) determine the formation of a crystalline or amorphous mineral structure,

which furthermore influences durability, solubility and reactivity of the slags (see

chapter 4.2). Interestingly, steel slags, which have been treated by one or more of the

above listed treatment techniques are not included in the European Waste Catalogue

(EWC) established by the Commission Decision 2000/532/EC according to a position

paper of the European Slag Association called Euroslag (2006). The EWC assigns a

number to all types of materials which can be seen as waste. However, a material stated

in the EWC is only defined as waste, if the definition of waste stated in the above

mentioned Council directives applies.

APPENDIX II

5

3.1 Generation and utilisation of steel slags in Europe The chemical and physical properties determined by the production process in the steel

mill and will influence the possibilities for utilisation. For instance, the type of slag

formers added to the melt (e.g. dolomite or lime) highly influences the chemical

composition. This means that different steel production processes result in different

slags.

On the other hand Motz and Geiseler (2001) state that “BOF5 and EAF slags from

different sources within Europe […] are generally comparable and independent of their

producers”. This indicates that nowadays steel manufacturers make big efforts for slag

treatment so that desirable properties are achieved.

Figure 2 shows that steel slags in Europe comprise mainly BOF slags and EAF slags but

also 9 % of secondary steel slags to which ladle slag and argon oxygen decarburisation

(AOD) slags belong to.

Figure 2. Types of steel slags generated in Europe 2004

(Euroslag, 2006)

The amount of generated steel slags in the EU, Germany and Sweden is shown in table

1. According to these data, Germany produced about 40 % of all steel slags in 2004.

5 Basic Oxygen Furnace

BOF slag 62 %

EAF slag 29 %

Secondary steel slag 9 %

APPENDIX II

6

Table 1. Steel slag generation in EU, Germany and Sweden

Year Amount

[million tonnes] Reference

EU 2004 15.2 Euroslag (2006)

Germany 2004 6.22 FEhS (2005)

Sweden 2002 0.896 Moosberg-Bustnes [5]

The most common reuse of steel slags is as aggregates in road constructions, e.g.

ashaltic or unbound layers according to data from Euroslag (2006) shown in Figure 3.

Almost one fifth of steel slags are interim, i.e. temporarily stored which is done mainly

to observe their properties over time but also because no industrial consumer who wants

to reuse the material has been found yet. 11 % of the slags in the EU are finally

deposited on landfills. To a small extend slags are also applied in the production of lime

fertilizer and hydraulic engineering.

45%

17%

14%

11%6% 3% 3% 1%

road production interim storage internal recycling

final deposit others fertilizer

hydraulic engineering cement production

Figure 3. Utilisation of steel slags in Europe 2004 (Euroslag, 2006)

The amount of reused steel slags varies considerably from country to country, due to

differences in chemical composition of the slags and national environmental

regulations. Motz and Geiseler (2001) reported that 35 % of the 12 million tonnes of

produced steel slags were still dumped in Europe in 2001. In 2004, only 11 % of the

15.2 million tonnes produced steel slags were dumped. If one adds the 17 % interim

stored steel slags, about 28 % of the European steel slags do not have found any field of

application yet.

APPENDIX II

7

Conditions as relatively abundant resources of high-quality rock material as in Sweden

are playing a major role in reuse of slags. According to Moosberg-Bustnes [5], in

Sweden 44 % of steel slags were “finally deposited” in 2002.

In Germany, data are collected by the FEhS-institute being a research association for

building materials (former “Forschungsgemeinschaft Eisenhüttenschlacken e. V.”).

Utilisation data for 2004 are given in Figure 4 below. According to FEhS (2005), 54 %

of steel slags are used as building material in roads, hydraulic engineering, earth-works

etc., 17 % are landfilled and further 4 % are interim stored.

12%5%

54% 8%

4%

17%

internal recycling/circuitry fertilizerbuidling materials othersinterim storage final deposit

Figure 4. Reuse of steel slags in Germany in 2004 (FEhS, 2005)

In Germany the development of utilizing slags for construction purposes begun very

early. Already, in 1936 a motor highway in Saxony, has been build with Portland

cement mixed with slag (note of the author: probably blast-furnace slag) as an additive.

It showed a very good durability under all conditions (Ylipekkala, 2005).

If slags shall be used in road construction, they have to fulfil certain mechanical and

environmental requirements. The required properties and the corresponding test

methods are stipulated in European standards for aggregates and road materials by the

European committee of Standardisation (e.g. tests for chemical properties of aggregates

- CEN EN 1744). A decisive property for the reuse in road construction is volume

stability, which expresses the volume increase during and after the construction process.

Several treatment methods to assure sufficient volume stability are shortly described in

Motz and Geiseler (2001).

APPENDIX II

8

Fine milled quenched slag powders are also applicable as additives in cement industry

(Ylipekkala, 2005), but mostly BF slags are used for this application. As shown in Fig.

3, only 1 % of steel slags are used as additive in cement.

3.2 Utilisation of steel slags in a landfill cover construction

The landfill cover construction tested in the Hagfors/Uddeholm project at Luleå

University of Technology is shown in Figure 5 (Andreas et al., 2005).

• ~ 0,3 m Vegetation layer: plant colonization, water magazine, protection against erosion

• ≥ 1.5 m Protection layer: water magazine, protection against desiccation, freezing, root penetration, erosion of the layers below

• Geomembrane (~ 0,5-5 mm): layer separation• ~ 0.4 m Drainage layer: collection and discharge of percolation

water, prevent water standing on liner• Geomembrane

• ≥ 1.0 m Barrier layer, liner: minimize gas and water transport

• Geomembrane• ≥ 0.5 m Gas drainage, foundation layer: surface adjust-

ment, load distribution, gas transport

• ~ 0,3 m Vegetation layer: plant colonization, water magazine, protection against erosion

• ≥ 1.5 m Protection layer: water magazine, protection against desiccation, freezing, root penetration, erosion of the layers below

• Geomembrane (~ 0,5-5 mm): layer separation• ~ 0.4 m Drainage layer: collection and discharge of percolation

water, prevent water standing on liner• Geomembrane

• ≥ 1.0 m Barrier layer, liner: minimize gas and water transport

• Geomembrane• ≥ 0.5 m Gas drainage, foundation layer: surface adjust-

ment, load distribution, gas transport

• ~ 0,3 m Vegetation layer: plant colonization, water magazine, protection against erosion

• ≥ 1.5 m Protection layer: water magazine, protection against desiccation, freezing, root penetration, erosion of the layers below

• Geomembrane (~ 0,5-5 mm): layer separation• ~ 0.4 m Drainage layer: collection and discharge of percolation

water, prevent water standing on liner• Geomembrane

• ≥ 1.0 m Barrier layer, liner: minimize gas and water transport

• Geomembrane• ≥ 0.5 m Gas drainage, foundation layer: surface adjust-

ment, load distribution, gas transport

POSSIBLE MATERIALS

SOIL, COMPOST

SOIL, DIGESTED SEWAGE SLUDGE MIXED WITH THE FINER FRACTION OF SLAG

COARSE SLAG (EAF), CRUSHED CONSTRUCTION DEBRIS

LADLE SLAG MIXED WITH EAF SLAG

COARSE SLAG (EAF)

Figure 5. Layers and their functions in a cover construction with a mineral liner; examples for possible alternative materials (Andreas et al., 2005)

The most critical element of a landfill top cover construction is the liner layer (also

called barrier layer). Prevention of water and oxygen infiltration into the waste and

uncontrolled leakage of gas out of the landfill are the main tasks a liner has to fulfil.

According to the recommendations of the Swedish Environmental Agency (RVF,

2002), the liner has to have a thickness of at least 0.5 m, whereas the whole cover

construction should have a thickness of at least 2.5 m.

The prevention of water infiltration shall be reached through

minimizing percolation of water through the cover system by impeding

infiltration through it (direct function) and

promoting storage or drainage of water in the overlying layers (indirect

function). Runoff, evapotranspiration and internal drainage impede water from

reaching the liner.

APPENDIX II

9

Critical aspects affecting the performance of the liner are quoted from Koerner and

Daniel (1997). According to them, cover performance is limited by:

“cracking due to desiccation, deformations from waste settlement, or seismic

motions (e.g., with clay),

root penetration,

resistance to gas migration,

slope stability,

creep of all materials (clay, bentonite, geomembrane, asphalt) and

service life (geomembranes and asphalt)”.

The liner material has different functions (Tham et al., 2003). As a high dense cover, the

used construction material must have a low hydraulic conductivity and a high dry

density. A high density can also be achieved if coarse and fine materials are mixed

according to the Fuller curve and compacted. The liner material should not contribute to

an increased contamination of the leachate. The atmosphere in a landfill can contain

CO2 up to about 50 vol.-%. This leads to a carbonation of the cover material and may

decrease its permeability. Todorovic and Ecke (2005) investigated carbonation as an

important weathering process for MSWI ash and the effect of it on the release of critical

components. They reported that alkaline waste materials are unstable under atmospheric

conditions. Hence, weathering will change their mineralogy.

According to Tham et al. (2003), the most critical factors for liner performance of

secondary construction materials as e.g. incineration residuals are “chemical

interactions” and “the resistance to different settlements”. If the construction material

contains hydraulic minerals, the hardening during curing can cause shrinkage.

To reach a low permeability, a liner material should be easily compactable, i.e. an even

grain size distribution is necessary (Herrmann et al., 2005). Clays, bentonite mats or

sand-bentonite mixtures are materials often used. Geo membranes serve to separate the

different layers of the cover construction.

Steel slags could be used in the protection layer, the drainage layer, the liner and the gas

drainage layer. Of course, each layer has different requirements to the construction

material. For fulfilling the functions of the protection layer (e.g. water storage,

prevention of desiccation, freezing and erosion) the material needs to have a fine

APPENDIX II

10

structure and contain some organic material. In contrast to the protection layer, both of

the drainage layers require a coarse fraction of steel slag. Therefore, EAF slag shall

come into use as a part of the protection layer (fine fraction), both of the drainage layers

(coarse fraction) and in the liner in mixture with ladle slag (fine fraction).

Liner materials as ashes or slags often contain a high amount of carbonates, which are

formed after hydration and carbonation of calcium compounds. Afterwards, the

dissolution of formed carbonates while reacting with water that have percolated through

the overlaying layers can become important in landfills (Marfunin, 1998). The molds of

the dissolved carbonates will become additional pore spaces for gases evaporating

through the cover. Additionally, CO2 can break up new flow channels leading to an

increasing permeability. This is called fracing.

4 MINERAL PHASES

A phase is any portion of a system that is physically homogeneous within itself and is

mechanically separable from the other portions. A pure mineral consists of a single

phase; a rock is a system of mineral phases, i.e. the phases are the individual minerals.

In this study mineral phases of steel slags shall be investigated. Up to now, little

literature is available directly focusing on mineral phases of steel slags. Furthermore, an

overview shall be given not just about the mineral phases but also about their influence

on slag properties. Steel slags are known for having similar chemical compositions as

cementitious material (Shi and Qian, 2000; Bävermann, 1997; Fällmann, 1997) and

Portland cement, a special cement type (Murphy et al., 1997). Both steel slags and

cement contain lime, silica, aluminate and magnesia. That is why steel slags “can be

regarded as a weak Portland cement clinker” (Shi, 2000) and cement phases play a

major role in slag chemistry.

The different fractions lime, silica, aluminate and magnesia will differ for different steel

slags. Shi also concluded that the variation of the mineral composition of steel slags

origins from the “highly variable” chemical composition of steel slags.

APPENDIX II

11

The occurrence of minor elements in steel slags depends on the production process in

the steel mill, i.e. which type of steel was produced and from which part of the

manufacturing process the slag has been tapped (Caley and McDonald, 2001).

It is also possible to calculate the mineral composition by knowing the chemical

compounds. An example for cement is given in Czernin (1964). But with this method,

just assumptions are possible, as already marginal variances in the chemical

composition can cause strong displacements in the mineral composition.

4.1 Mineral phases of cement

Cement is a hydraulic binder. Binders are finely ground mineral substances, that after

mixing with water cure to a rock-like, water-resistant material. The term ´hydraulic´

points out that the binder not just cures and develops strength by being abandoned to

air, but also under water. A very common type of cement, used widely in manufacturing

of concrete, is Ordinary Portland cement (OPC). It is produced by heating a mixture of

limestone and clay in a rotary kiln at temperatures of 1450 to 1550° C.

One reaction in the kiln producing so called quick lime is decarbonation of calcite, also

called lime burning.

CaCO3 CaO + CO2

Calcite quick lime gas

The compounds formed during the high temperatures are called clinker minerals. After

the kiln, the material is cooled, 5 % of gypsum is added and the material is ground to

OPC. Under normal temperature conditions only CaSiO3 would form. But the high

temperatures induce the attachment of further lime to silica.

The clinker and mineral phases, their properties and the associated fraction in OPC are

presented in table 2 below. The contents of free lime and free magnesium oxide have to

be limited in a construction material, because volume stability is very important under

these applications. Expansion after contact with water in steel slags is “most likely”

caused by these two compounds. (Tossavainen, 2005b).

APPENDIX II

12

Table 2. Clinker and mineral phases in OPC according to Knoblauch and Schneider (1992)

Clinker phase

(mineral phase)

Cement

nomenclature Properties

Mass fraction (%) in

cement clinker

Tricalcium

silicate C3S

Fast curing, high heat of

hydration, high strength 45 - 80

Dicalcium

silicate C2S

Slow, continuous curing

Low heat of hydration,

high strength

0 - 32

Tricalcium

aluminate C3A

Fast reaction with H2O

High heat of hydration,

low strength,

susceptible to sulphate

waters

7 - 15

Tetracalcium

aluminate

ferrite

C4AF

Little and slow curing,

resistant to sulphate

waters

4 - 14

Free CaO

(free lime) C

If high amounts present

internal expansion 0.1 - 3

Free MgO

(periclase) M

If high amounts present

internal expansion 0.5 - 4.5

During all cement production processes, large amounts of CO2 are released. According

to Wenk and Bulakh (2004), 8 % of the world’s industrial production of CO2 is emitted

by the cement industry.

Hydration

While mixing cement with water, the cement converts to a fluid, plastic suspension

called cement-paste. Paste refers to a mixture of cement and water in such proportions,

that setting and hardening (also called curing) occurs. The chemical reactions occurring

between water and cement are referred to as hydration. The water is taken up and

integrated in the solid structure. These reactions continue over a long time up to years

and with time, the strength of the cement increases. The most important changes in

APPENDIX II

13

mineral composition and microstructure shall be illustrated shortly. One exemplary

hydration process, called lime slaking, is shown below.

CaO + H2O Ca(OH)2

The hydration of lime and silica leading to calcium silicates is:

CaO + SiO2 + H2O CaSiO2(OH)2

Both of these reactions are proceeding during the hydration of cement minerals. The

hydration of tricalcium silicate shall serve as an example.

2 Ca3SiO5 + 7 H2O 3 CaO.2SiO2.4H2O + 3 Ca(OH)2 + 173.6kJ

Tricalcium silicate water Calcium silicate hydrate Calcium hydroxide heat

One reaction product is hydrated lime (calcium hydroxide). Hydrated lime takes up 20

% more space than CaCO3. That causes disruption of the whole structure and the

material falls apart. Depending on the amount of water, it either turns into a powder or a

suspension (lime water). Hydration is an exothermic process. The heat of hydration of

lime is 280 cal/g, i.e. one gram of lime can raise the temperature of 280 g of water about

1 °C (Czernin, 1964). Some further comments about the hydration process and the heat

development are explained in Chapter 5.

The most important mineral phases in cement as well as the hydration products are

presented in table 3.

APPENDIX II

14

Table 3. Main mineral phases in cement with chemical compounds and corresponding cement nomenclature

Clinker phase

(mineral phase) Mineral name Chemical compound

Cement

nomenclature

Tricalcium silicate Alite 3CaO*SiO2 C3S

Dicalcium silicate Belite 2CaO*SiO2 C2S

Tricalcium

aluminate - 3CaO*Al2O3 C3A

Tetracalcium

aluminoferrite

Celite or

Brownmillerite 4CaO*Al2O3*Fe2O3 C4AF

Calcium sulphate

dehydrate Gypsum CaO*SO3*2H2O C S H2

Calcium hydrate Portlandite CaO*H2O CH

Calcium silicate

hydrate -

No well defined compound

(changing composition) C-S-H

Tricalcium

aluminate

trisulfate hydrate

(Trisulfate)

Ettringite

3CaO*Al2O3*3CaSO4*32H2O

or

6CaO*Al2O3*3SO3*32H2O

C3A*3C S*H 32

or

C6A S 3 H 32

During the first minutes of the hydration reaction, the oversaturated lime-compounds

(formed during high temperatures) – in OPC mainly tricalcium silicate and dicalcium

silicate – go into solution. The solution becomes saturated and large crystals of calcium

hydroxide (portlandite) and needle-shaped crystals of ettringite are formed. This is

illustrated in Figure 6. The possible subdivision of the curing process in dormant period,

setting and hardening period can be explained by the mineral changes.

APPENDIX II

15

Figure 6. Changes in cement microstructure during hydration (Wenk and Bulakh, 2004)

Because portlandite crystals take up 20-25 % of the volume, strength and durability of

the paste decreases. Afterwards, small crystals of calcium silicate hydrates (C-S-H) are

formed by the disintegration of calcium silicates. The particles size decreases and

colloids are developed which have a much higher specific surface. The C-S-H does not

only take up hydration water (in its structure), but also binds water on the surface by

adsorption (Krenkler, 1980). Such substances are called gels, because of the high

amount of adsorption water compared to the small size of the particle itself. The

composition of C-S-H varies with temperature, age of hydration and the water/cement

ratio (Wenk and Bulakh, 2004).

Factors influencing the rate of cement hardening are identified by Dobrowolski (1998)

as the following ones:

Chemical and physical properties

Curing conditions (e.g. temperature, moisture during curing, time)

Water/cement ratio (affecting the ultimate strength)

According to Dobrowolski (1998), “a high water/cement ratio produces a paste of high

porosity and low strength“. After the main hydration reactions, the hardened cement

paste not only contains chemical bound hydration water, but also physical bound gel-

water and free capillary water (Grübl et al., 2001).

The clinker minerals (see table 1) are present in certain modifications. For example, the

mineral belite (C2S) can exist as α -C2S, β -C2S and γ -C2S, each of them having

slightly different crystal dimensions. Which form is present depends on the temperature.

APPENDIX II

16

During cooling of a melt, the α -phase present at very high temperatures changes to the

β - phase and further to the γ -phase (Röhling et al., 2000).

The main parameters determining the development of strength according to Grübl et al.

(2001) are the chemical-mineralogical composition and the grinding fineness. The

chemical-mineralogical composition and the grinding fineness interact with each other.

If a material contains less reactive calcium silicates, grinding can provide a larger

reactive surface and the reaction rate increases (Röhling et al., 2000). However, Czernin

(1964) states that the chemical composition is of minor importance for the final

strength.

The hydraulic behaviour of materials used in cement industry can be very different.

Often, additives are given to the cement in order to influence properties as for example

curing behaviour (acceleration or retardation of curing), workability and strength. The

hydraulic behaviour depends on the CaO/SiO2 ratio. Röhling et al. (2000) describe a

material as puzzolanic if it has a CaO/SiO2 ratio of at most 0.5 (table 4).

Table 4. Hydraulic behaviour or different materials (Röhling et al., 2000)

CaO/SiO2 ratio Hydraulic behaviour

Puzzolanic 0 - 0.5 Very low, needs an

activator

Latent–hydraulic 0.5 – 1.5 Low, needs an activator

Hydraulic 1.5 – 2.5

2.5 – 4.0

Slow curing

Fast curing

Puzzolans can be of natural origin, e.g. high silica and/or high alumina soils of volcanic

origin. Artificial puzzolans have a hydraulic reactivity developed through thermal

processes including fly ash which comes in use in cement production as an additive.

Cement additives used are for example fly ash, silica fume, blast furnace slag, oil shale

and limestone (Röhling et al., 2000). Often gypsum is added to various cement types.

APPENDIX II

17

A comparison of the chemical compositions of the some of the materials mentioned

above can help in further understanding possible similarities in their properties. It is

necessary for classifying materials and for distinguishing them in a phase diagram. The

chemical compositions of OPS, BF slag and fly ash are shown in table 5. The main

oxide is marked by a grey background.

Table 5. Chemical composition of certain materials used in cement industry (according to Knoblauch and Schneider, 1992)

Chemical

compounds

(mass-%)

OPC

(incl. SO3, Mn2O3)

BF slag

(water–quenched)

Fly ash

from black coal

combustion

(incl. SO3, Cl)

SiO2 18 - 24 32 - 40 45 - 55

Al2O3 4 - 8 10 - 16 25 - 30

CaO 61 - 69 40 - 45 2 - 6.5

Fe2O3 1 - 4 - 5 - 10

MgO 0.5 - 4 up to 5 23

Alkalis - - 3 - 6

With the help of table 5, OPC can be classified as hydraulic material with a fast curing

behaviour, BF slag as latent hydraulic and fly ash as puzzolan of artificial origin.

Another type of comparing material compositions are phase diagrams. Figure 7 shows

the ternary phase diagram of the CaO–SiO2–Al2O3 system.

Figure 7. Phase diagram of CaO–SiO2–Al2O3 system

SiO2 Al2O3

CaO

APPENDIX II

18

Each axis of the phase diagram shows a different binary system, i.e. the three binary

systems CaO–SiO2, CaO–Al2O3 and Al2O3–SiO2 are included. The little sketch at the

right presents which compound of the binary system of each axis increases. Mineral

phases can be associated to a point on the axis. For example, the binary system CaO–

SiO2 includes the phases 100 % CaO, C3S, C2S, C3S2, CS and 100 % SiO2 (Caley and

MacDonald, 2001). In the phase diagram, fly ash is orientated further right compared to

slags or Portland cement. The region around that part is presented by the puzzolans,

while slags as basic BF slag have a higher CaO/SiO2 ratio and therefore are latent

hydraulic. Slags with relatively high silica content are acids.

Aluminious cement contains up to 50 % of alumina and therefore mainly consists of

calcium aluminates, instead of calcium silicates as the other cement types. This cement

type has a very fast hydration process and can bind about twice as much water as other

cements (Grübl et al., 2001). Mixtures of aluminous cement with calcium hydroxide

(slaked lime) or OPC have only moderate final strength after curing (Karsten, 1997).

The main mineral phase of aluminous cement is calcium aluminate which after

hydration forms calcium aluminate hydrate. Dicalcium aluminate hydrate is responsible

for the fast hydration and fast curing, but it is not a stable hydration product. Under

warm and humid conditions (over 22° C), aluminate hydrate and water are separated,

dicalcium aluminate hydrate forms, strength and volume decrease and porosity

increases. Gases and water can react easily with the cement, therefore pH and final

strength decrease. For load-bearing components, it is not allowed to use aluminious

cement (Knoblauch and Schneider, 1992).

Möhmel et al. (1998) stated that the hydraulic properties of cement to a large part

depend on the ratio of calcium aluminate phases. Mixtures of synthesised calcium

monoaluminate (CA) and calcium dialuminate (CA2) have been analysed with

differential calorimetry analysis (DCA), XRD and nuclear magnetic resonance (Al-

NMR). The question of this study was how hydration of one aluminate phase influences

the second phase if they are mixed in different ratios. Measurements included heat

development during hydration over 28 days, strength, specific surface, rate of reaction

and hydration products of 100 % CA and CA2 and three mixtures (20/80; 50/50; 80/20).

One result was that the specific surface of hydrated CA2 is much larger than for CA.

That probably explains the long reaction period of CA2 during hydration in Figure 8. As

APPENDIX II

19

acc. to Möhmel et al. (1998) a high specific surface indicates “a good penetratable

product layer around the calcium aluminate particles, which allows their further

hydration6”.

Figure 8. Differential calorimetric analyses of CA, CA2 and corresponding mixtures

(Möhmel et al., 1998)

Another interesting fact resulting from specific surface analyses was that the hydration

behaviour of the pure phases did not correlate with the behaviour of the mixtures. The

CA2-rich mixture had only a relatively small specific surface.

Hydration products furthermore included amorphous as well as crystalline hydration

products from which especially the high amount of amorphous phases influenced the

reaction rate. The XRD experiments lead to the conclusion that after hydration of CA

CaH10 was formed, whereas hydration of CA2 rather induced formation of Al(OH)3. The

CA reaction rate increased in the mixtures compared with the pure CA. The opposite

applied to CA2.

In the next chapter, the chemical composition and mineral phases of steel slags are

investigated.

6 German quotation: „Eine hohe spezifische Oberfläche ist nämlich ein Zeichen für eine gut penetrierbare Produktschicht um die Calciumaluminatkörner, die deren weitere Hydratation erlaubt.“

duration of hydration [hrs] duration of hydration [hrs]

APPENDIX II

20

4.2 Mineral phases of steel slags

As stated in the terminology chapter, the term ´steel slags´ includes EAF slags, ladle

slag and AOD slags. But because only EAF and ladle slag are included in this study, the

chapter is restricted to the mineral phases of EAF and ladle slag.

Studies focusing on mineral phases of EAF slags were performed by

Murphy et al. (1997), Motz and Geiseler (2001), Shen H. et al. (2004) and

Tossavainen (2005a). These studies also reported about BF slags (Murphy et al.,

Tossavainen), BOF slags (Motz and Geiseler) and natural rock materials (Motz and

Geiseler, Tossavainen).

Motz and Geiseler (2001) classified EAF slags as “calciumsilicatic” with an CaO con-

tent in the range of 25-40 % and a SiO2 content of 12-17 %. Additionally, free MgO and

free lime (CaO) is present. They outline MgO and free CaO as a “key criterion” for the

application of steel slags in civil engineering.

The main mineral phases of EAF slags – as well as for BOF slags – are dicalcium

silicate (C2S), dicalcium ferrite (C2F) and wustite (FeO) (Motz and Geiseler, 2001). The

chemical composition of two different EAF slags is given in table 6.

Table 6. Chemical composition of two EAF slags (Motz and Geiseler, 2001)

EAF slag with low MgO

[%]

EAF slag with high MgO

[%]

CaO 30 - 40 25 - 35

SiO2 12 - 17 10 - 15

Al2O3 4 - 7 4 - 7

MgO 4 - 8 8 - 15

MnO <6 <6

P2O5 <1.5 <1.5

Fetotal 18 - 28 20 - 29

CaOfree <3 <3

APPENDIX II

21

The manufacturing of different steel types leads to different slag types. The chemistry of

steel slags depends not just on the amount of alloys given to the steel, but also which

slag forming agent is used.

A compilation of the chemical composition of different EAF slags found in literature is

shown in Figure 9.

0

5

10

15

20

25

30

35

Ca Si Al Mg Mn Fe

wt - %

Uddeholm (EAF) Fällman/Hartlén (EAF) Murphy (EAF)Caley/Mac Donald (EAF) Shen (EAF) BMU (EAF l-a)BMU (EAF h-a) Motz (EAF-low MgO) Motz (EAF-high MgO)

Figure 9. Compilation of literature data about main elements in EAF slags (BMU data [6])

The differences between OPC and steel slags are explained by Murphy et al. (1997).

The author states that steel slags contain more iron oxide than OPC. The valence state

of iron oxide determines the morphology and cementitious properties. The iron is

present in the form of divalent and trivalent iron. Furthermore, steel slags consist of

higher amounts of free lime. Free MgO and CaO are hydraulic phases and will lead to

expansion of the structure after contact with water (fluid or gaseous). Expansion of free

CaO is occurring earlier than that of free MgO (Murphy et al., 1997). The MgO content

of EAF slags can be higher compared to BOF-slags due to the reaction with the

refractory lining but also depends on the eventual use of dolomite as slag forming agent.

Murphy et al. (1997) investigation results of EAF mineral phases are presented in

table 7.

l-a … slag from low alloyed steel h-a …slag from high alloyed steel

APPENDIX II

22

Table 7. Predominant mineral phases associated with steel slag (Murphy et al., 1997) Melting

Formula Name Synonym point (°C)

3CaO*SiO2 Alite Tricalcium silicate 1900

2CaO* SiO2 Belite Dicalcium silicate 2130

β -2CaO*SiO2 Belite (Larnite*)

α -2CaO*SiO2 Bredigite

2CaO*Fe2O3 Dicalcium ferrite Calcium ferrite 1430

4CaO*Al2O*Fe2O3 Brown millerite 1410

FeO Wustite Iron oxide

MgO Periclase Magnesia 2800

CaO Lime Calcia 2570

*β -Ca2OSiO4 = Larnite (Tossavainen, 2005a)

Additionally, the melting points of some phases are given to indicate which mineral

phases solidify first when the melt in the converter is cooled down. Solidification of

periclase happens first while brown millerite solidifies at last.

Murphy et al. (1997) conclude that the limited cementitious properties of steel slags

result from a lack of tricalcium silicate and a surplus of wustite, which has the ability of

taking up calcium. Therefore, calcium is not available for the formation of tricalcium

silicate anymore. Wustite solid solutions (see Terminology) are the main mineral phases

in steel slags according to Murphy et al. These phases do not occur in Portland cements

and do not form hydraulic minerals. Therefore, they have no cementitious properties.

The matter is different with the ferritic minerals, e.g. calcium ferrite, calcium aluminate

ferrite. They are formed by the mineral phase hematite (Fe2O3) and are hydraulic.

In their studies, Shi and Qian (2000) summarised the relationship of basicity, reactivity

and mineral phases of steel slags. According to their findings, the reactivity of steel

slags as well as the content of free CaO increases with basicity, i.e. the CaO/SiO2 ratio.

Slags with a low reactivity contained olivine (0.9 < CaO/SiO2 < 1.5) and merwinite

(1.5 < CaO/SiO2 < 2.7). Medium reactive slags (CaO/SiO2 < 2.7) consisted of dicalcium

silicate while high reactive slags with a CaO/SiO2 ratio > 2.7 were build of tricalcium

APPENDIX II

23

silicate.

With orientation towards metal recovery, Shen H. et al. (2004) analyzed the mineral

phases of EAF slag. The author found bredigite (Ca7Mg(SiO4)4), merwinite

(Ca3Mg(SiO4)2), akermanite (Ca2MgSi2O7) and gehlenite (Ca2Al(AlSi)O7) being the

main minerals. Also magnetite and chromite (Fe, Cr and Ni phases) were recorded after

magnetic separation of the original sample. These results were also recorded by

analyses of Tossavainen (2005b), who besides other minerals (included in table 4)

identified Merwinite and Larnite (β -Ca2OSiO4) as the main phases of the EAF slag

samples. All slags contained hydraulic minerals and glass, which together with aqueous

solutions tend to form stable hydrated phases.

Tossavainen (2005b) also found an increasing number of mineral phases as cooling time

and therewith other influencing factors increase. As a result of this, a more homogenous

slag with few phases is formed after rapid cooling e.g., by water granulation. Krenkler

(1980) also reports that a rapid cooling leads to a glassy structure (of BF slag) while

slow cooling supports crystal growth. This example shows that appropriate treatment

techniques make it possible to control the properties of slag materials.

05

101520253035

Ca Si Al Mg Mn Fe

wt - %

Uddeholm - ladle slag BMU - ladle slag

Figure 10. Composition of Uddeholm ladle slag and BMU data about ladle slag [6]

Mineralogical compositions of ladle slag have been investigated by Caley and

MacDonald (2001). One ladle slag with additional fluorspar (CaF2) and one ladle slag

with nepheline syenite (igneous rock containing the mineral nephelite, which has the

formula (Na, K)AlSiO2) were looked at. SEM analyses showed the presence of cement

phases as tri- and dicalcium silicate in the fluorspar slag and the minerals merwinite and

monticellite in the nepheline syenite slag.

APPENDIX II

24

4. 3 Alteration of mineral phases

Alteration of minerals in nature occurs mainly due to weathering processes. A primary

mineral undergoes transformation and a secondary mineral is formed. This is also called

mineral aging. Factors as temperature, pressure, the chemical, physical and biological

environment and also humidity influence these alterations. The application of steel slags

in a liner construction will lead to alterations of the primary mineral phases over time.

An assessment of resulting secondary mineral phases shall be made in this chapter. For

this, a simplification of the expected surrounding conditions is necessary.

The reaction rate of mineral transformations can differ according to the present

conditions. This is especially the case in a liner, as there are no evenly distributed

conditions, for example a changing water content in the pores over time and place.

Again, mineral transformations of well ascertained similar materials can be adjuvant to

assess secondary phases of steel slags.

In the liner, the main gases influencing the alteration processes of minerals are

considered to be CO2 and CH4. Carbonation and methane oxidation are the respective

processes expected to occur in the cover construction of a landfill.

Also, the humidity, i.e. the water vapour is of interest for the forming of secondary

minerals. The pore solution (including percolates) will react with the (initially present)

primary minerals of the liner material. The pore solution gets oversaturated with respect

to a certain compound and the primary minerals will become unstable, because of

changes in pH, buffering capacity, salinity and redox potential. A certain compound can

precipitate and a new secondary mineral will be formed (Marfunin, 1998). From the

estimation of the water balance it is expected that 5 % of the precipitation infiltrate

through the liner and reach the foundation layer. A quantification of expected methane

values cannot be given for the liner itself.

About mineral phases of slags, Tossavainen (2005c) states that these minerals “probably

react with moisture, CO2, etc. during storage und to some degree undergo phase

transformations”. The author further emphasises the effect of weathering processes and

crystal structure on leaching behaviour. Leaching reactions of amorphous slags will

differ from the reaction of crystalline slags.

APPENDIX II

25

The reaction of calcium silicate phases with carbon dioxide and moisture is known from

cement chemistry. In presence of moisture, carbon dioxide in the air forms carbonic

acid (H2CO3).

H2O + CO2 H2CO3

The hardening of lime according to the formula

Ca(OH)2 + CO2 CaCO3 + H2O

or more precisely presented by

Ca(OH)2 + H2CO3 CaCO3 + 2H2O (exothermal reaction)

is also called carbonation. The carbon dioxide originates mainly from the air (air content

about 0.03 %). But the carbonation process does not take place in absence of water

(vapour or liquid). The base calcium hydroxide only reacts with carbon dioxide in the

form of carbonic acid. Due to the very low carbon dioxide content in the air,

carbonation of the whole bulk of a material takes long time. Karsten (1997) states, that

for cement, carbonation (hardening of lime) occurring on the surface is finished after

about one year. The process is accelerated by a high CO2 concentration in the

surrounding air and humidity. However, too high moisture content retards the reaction.

Carbonation is proceeding optimally under the influence of heat, good circulation of air,

high pressure and high reaction surface (Karsten, 1997).

Studies focused on mineral transformations of MSWI ashes were performed by

Zevenbergen et al. (1998), Knorr et al. (1999), Hirschmann (1999) and a. o. summarized

by Piantone et al. (2004). During weathering of MSWI ashes, reservoir minerals are

formed that comprise phases of ettringite, calcium monosulphate, calcium silicate

hydrate (C-S-H), brucite (Mg(OH)2) and calcite (see Figure 11).

APPENDIX II

26

Figure 11. Mineralogical evolution taking place during weathering of MSWI

bottom ash (Piantone et al., 2004)

After two years of weathering, the primary minerals of MSWI bottom ash were

transformed into zeolites, after 12 years into clays. However, chemical composition and

hydraulic behaviour of the minerals present in MSWI ash vary considerably from steel

slags. Less calcium, higher silicon and higher metal fractions are the main differences

(Hirschmann, 1999). The hydraulic reaction of MSWI ash is very low and carbonation

plays a minor role in the first 20 years. Heavy metals as zinc and lead can be bound to

carbonates and get immobilized (Huber et al., 1996). But regardless the differences of

the steel slags and MSWI ashes, fig. 10 shows that hydration and hydrolysis reactions as

well as mineral alterations occur. Hydrolysis refers to the chemical reaction of minerals

with H+ and OH- ions of dissociated water molecules. Mainly carbonates and silicates

are broken down by hydrolysis.

Particularly, the stability regions of primary and secondary minerals depending on pH

are given in Figure 11 above. As mentioned before, dissolved carbon dioxide and L/S

ratio (liquid/solid) influence these alterations. Cement phases for example – the

presented stability region is from pH 9 to 13 – are shown as secondary phases. The

origin of C-S-H (calcium silicate hydrates) is lime, which in fig. 10 is referred to as

primary phase. Nevertheless, in this study, calcium silicate hydrates are referred to as

primary minerals in steel slags, i.e. primary phases after hydration.

Some theses about mineral alterations of steel slags shall be inferred. Steel slags are

mainly consisting of calcium silicates. As it is a basic construction material, the buffer

APPENDIX II

27

capacity (acid neutralisation capacity) of carbonates is expected to play a major role in

the beginning of the leaching process. Some important buffering reactions of

carbonates, silicates and aluminium hydroxides according to Scheffer and Schacht-

schabel (1998) are:

Carbonates CaCO3 + H+ HCO3- + Ca2+ pH 8 … 6.5

Bicarbonates HCO3- + H+ CO2 + H2O pH 7 … 4.5

Primary silicates –(SiO)M + H+ – (SiOH) + M+ pH < 7

[M+ = 0.5Ca, 0.5 Mg, K, Na]

Al-hydroxides Al(OH)3 + 3H+ Al3+ + 3H2O pH 4.8 … 3

Because of their high specific surface of 10-50 m²/g, C-S-H phases also have a high

sorption capacity. As mentioned in Hirschmann (1999), the sorption capacity depends

on the Ca/Si ratio. Sorption capacity increases with silica content. Concerning this

matter, Piantone et al. (2004) writes that “carbonate and Fe oxide phases […] can take

up metals very efficiently”. Hirschmann furthermore attributes a “substantial” metal

uptake to C-S-H and C-A-H phases (Knorr et al., 1999). The buffer is generated by

carbonation and metal complexes are incorporated in the lattice of the minerals.

If the carbonate buffer is used up and pH decreases, a higher solubility of calcium and a

higher heavy metal content can occur in the leachate. The possibility of a release of

certain metals already before the buffer capacity is used up, has been investigated by

Kersten (1996). The solubility and release of heavy metals is controlled by processes as

complexation, ion exchange, precipitation, formation of solid solutions and adsorption

(Kersten, 1996).

The destruction of carbonates by dissolution of calcium (also called decalcification)

through weathering can be assessed by chemical models. Therefore, assumptions are

made for parameters as thickness of the slag layer (consisting of carbonates),

precipitation in a certain area, infiltration rate in the ground, carbonation rate and

calcium content of the slag layer. The solubility rate of calcium is in the range of 16-60

g/m³ of leachate (Hirschmann, 1999).

APPENDIX II

28

Different authors (a. o. Lahl, 1992; Ecke, 2003b) reported about a period of several

thousand years until the carbonate buffer of an assumed slag layer is used up.

In how far, aging processes lead to expansion of phases through hydration of free MgO

or CaO or clay formation is still unknown. It is probable that chemical compounds

preserved in the matrix of the material will get in contact with air and water etc. after

some of the matrix already has been diluted. Than, also this CaO or MgO can undergo

hydration reactions. According to the theses of Huber et al. (1996), the following

processes occur during the alteration of MSWI ash:

- hydration

- carbonation

- microbiological and anorganic oxidation

- weathering and crystallization.

The focus in the study of Huber et al. was laid at the alterations of MSWI ash. But about

alterations of carbonates, i.e. carbonatic material, the author made preditions as well. It

was stated that during aging, hydroxids are transformed into carbonates (1st step), e.g.

calcium hydroxide into calcite. Afterwards, while the carbonate buffer is reduced,

carbonates are transformed into bicarbonates (2nd step).

CaCO3 + CO2 + H2O Ca(HCO3)2

Knorr et al. (1999) assumes that only a minor part of the minerals (about 10 to 20 m.-%)

will be carbonated at all. However, Huber et al. (1996) resulted that due to artificial

carbonation 80 % of the analysed MSWI ashes have been carbonated. The rest did not

transform into carbonates, because, a rest of carbonates were integrated in slag particles

or glassy compounds. Even if the carbon dioxide content has been increased in the

laboratory, the rest of the material did not form into carbonates. Instead, the already

present carbonates were transformed into bicarbonates. But the author furthermore

assumes that in a landfill over a long time period also these 20 % could get carbonated.

As the steel slags from Uddeholm AB investigated in this study are already hydrated

after the liner is build, the formation of carbonates of at least a part of the material is

expected. As stated before, it takes probably several thousands of years until the

carbonate buffer is used up bicarbonates are formed. Huber et al. also suggests pH value

as the crucial parameter for estimation of long-term processes.

APPENDIX II

29

5 CALORIMETRY

It is known from past investigations (Shi, 2002), that the slags have curing properties,

i.e. which while mixing with water heat due to hydration is released (exothermic

reaction). The slag hardens during a certain time depending on the respective

composition. The knowledge of heat development after mixing EAF-slag and ladle slag

is unknown. This plays an important role not only for the construction time of the liner,

but also is assumed to influence the mineral formation (e.g. melting points, solution, and

crystallisation).

Calorimetry means measuring heat. Here the term “heat” refers to all kinds of energies

that can be exchanged between two systems. A calorimeter is a device for measuring

heat, i.e. energy changes.

The heat released during a chemical reaction in a liquid media can be measured in a

calorimeter. It can be used as an indicator for the heat of hydration released from the

system to the environment. A calorimeter measures the energy exchange between the

reaction system and its environment. The reaction system is the ongoing chemical

process and the environment is presented by the calorimeter and its contents itself. To

be able to fulfil the assumption of negligible heat flow between the calorimeter and the

surrounding, the calorimeter has to be very well isolated. Under this condition, the

energy change during the reaction is equivalent to the heat uptake (respectivily heat

loss).

The basic equation of calorimetry is

dQ = C * dT or

Q = C * ∆T = c * m * ∆T

Q......Heat, i.e. energy change [KJ]

C......Heat capacity [KJ*K 1− ] or [KJ*°C 1− ]

∆T ...Temperature change [K] or [°C]

c.......specific heat capacity [KJ*kg 1− *K 1− ] or [KJ* kg 1− *°C 1− ]

m .....mass [kg]

APPENDIX II

30

To calculate the energy change in a calorimeter, the heat capacity of the calorimeter

itself is required. It has to be experimentally determined by a standardization procedure

where chemicals with a known release or absorption of energy are reacting.

With the energy change known, one can further calculate the change in enthalpy ∆H.

∆H = -Q / m

An example of heat evolution during cement curing is shown in Figure 12. It can be

seen that the reaction of pure Portland cement occurs in five stages with the highest heat

released in the first stage.

Figure12. The rate of heat evolution of cement hydration at 25 °C (Mostafa and Brown, 2005) (1) the initial reaction (2) the induction period (3) the acceleratory period (4) the deceleratory period (5) the period of slow continued

The mechanism of hydration is further explained in Glasser (1996) who states that it is

similar for all “glassy” materials as slag, fly ash and glass [2]. These materials contain

Si-O-Si bonds (silanol bonds) which are hydrolysed by OH- ions. Through this first step

of alkaline hydrolysis, the network of the glassy material breaks apart. The material

reacts with activators as e.g. Ca(OH)2 in cement. Precipitation of the reaction products

occurs and the gel-like matrix solidifies.

Motz and Geiseler (2001) summarize the hydration of slag as reaction between water

vapour and free CaO and/or free MgO forming hydroxides. Depending on the amount

of CaO and MgO a volume increase, disintegration of slag pieces and a loss of strength

are possible consequences. Tossavainen (2005a) also mentions expansion as a

APPENDIX II

31

consequence of hydration of CaO and MgO. The hydration of MgO takes thereby more

time than that of free lime.

The heat of hydration for the main clinker phases are given in Knoblauch and Schneider

(1992). For the mineral phase C2S, heat of hydration after full hydration is 250 J/g,

while it is 525 J/g for C3S. Also, Portland cement releases 375-525 J/g, while aluminous

cement releases 545-585 J/g.

Tossavainen (2005b) reported about calorimetric measurements of cement mixed with

20 % ladle slag. Untreated ladle slag has been found to “retard the heat development

curve severely”. If the slag was granulated, hydraulic reactivity was higher. The author

also concluded that “the reactivity of a slag is increased with an increase in the glassy

content”. Furthermore, water granulation has increased volume-stability.

More hydration characteristics analysed with differential thermal analysis of systems of

Portland cement and mineral additives (e.g. BF slag) have been reported by Sharma and

Pandey (1999).

Adjustment of the curing process is important as construction must be finished before

curing stops. Mixing EAF and ladle slag is one possibility to do this, as curing time

depends on the composition. In cement industry, this problem is solved by adding

calcium sulphate and therewith retarding curing. Cement additives generally have to be

adjusted to the chemical-mineralogical composition (Grübl et al., 2001).

6 X-RAY DIFFRACTION

X-ray diffraction is also referred to as crystal structure analysis, because the

prerequisite, for being able to use this analysis method, is a crystalline sample.

The best results are obtained with single crystals, but also crystal powder can be used.

The information obtained from the spectrum is the measurements of the unit cell (i.e.

the smallest repeating array of atoms in a crystal) and the detailed position of all atoms

in the crystal. Therewith the crystal- and molecule symmetry can be derived (Mortimer,

2003).

APPENDIX II

32

6.1 Physical background and sample preparation

To avoid absorption, the XRD method (combined with the powder method) uses

monochromatic X-ray beams, i.e. light with a single wavelength. The X-ray beams fall

on the crystal planes under a certain angle and are reflected i.e. diffracted according to

the Bragg-equation.

n * λ = 2 * d * Ө

with n order of diffraction [1,2,3,...]

λ wavelength

d distance between the crystal layers

Ө angle of incidence / angle of diffraction

(Mortimer, 2003)

To diffract X-rays, a lattice plane of the crystal has to be in a reflection position. The

short wavelengths of X-rays make them ideal for crystal analysis because their

wavelengths (0.1-5 Å) correspond to the distance between the lattice planes in

crystalline minerals which is roughly 0.3 nm or 3 Å (Jones, 1987). The distance

between two lattice planes is called interplanar spacing or d-spacing. For diffraction, the

scattered X-rays must not interfere destructively with each other, what is the case at one

particular angle Ө, called Bragg angle, of the incident beam. At this angle, determined

by the distance between similar atomic planes, the path-length difference of the X-rays

scattered at different atomic planes are integers (n frequently 1) or in other words “the

path lengths of the scattered rays differ from each other by exact multiples of the

incident monochromatic X-ray wavelength” (Jones, 1987). As a result, the scattered

rays are in phase and interfere constructively. Constructive interference means, that

when two waves are in phase, there is a perfect overlap of crests with crests and troughs

with troughs. This leads to an intense light beam. The resulting X-ray intensity,

measured as 2Ө, is represented by a peak in the diffractogram. The Ө angle represents

the angle where constructive interference has occurred.

APPENDIX II

33

Sample powders can be used instead of single crystals as well. The first step of sample

preparation is to ground the pure specimen into particles of less than about 50 µm in

size (Jones, 1987). Diffraction occurs because lattice planes are randomly distributed in

the powder, so that at least some crystals of each plane fulfil the Bragg-equation. The

X-ray beam falls onto the plane with the Bragg-angle and is diffracted.

With the help of a magnet, metallic particles – which can cause disturbances while

analysing – are taken away. The sample is carefully filled in the sample cup. The

surface of the sample has to be as even as possible. The sample cup is put in the XRD

device.

The elements in the mineral are identified with the help of the characteristic wavelength

of the diffracted X-ray. The intensity of the radiation states the concentration of the

element if quantitative analysis is performed (Jones, 1987).

6.2 Interpretation of one X-ray diffractogram of steel slag

Diffraction patterns of steel slags as shown in Figure 12 are very complex and a variety

of mineral phases can exist in the sample. Steel slags can contain crystalline and

amorphous phases. Amorphous structures cannot be identified, but the amount of the

amorphous fraction can be estimated from a hump of the background of the diffraction

pattern at about 2θ (2-Theta) from 20 to 40.

If a sample measured with XRD contains several minerals, peaks of one mineral will

overlap with the peaks of the other minerals. Many crystalline phases are detected and

the specimen gives all the diffraction beams simultaneously. This makes the

identification procedure of each mineral taking part in the diffraction pattern more

complicated. Every crystal phase has its characteristic diffraction pattern. Diffraction

patterns of single minerals are recorded in tables and databases. But in a sample,

together with other minerals, this diffractogram is modified the more, the more other

minerals are present (Jones, 1987).

In Figure 13 almost every peak in this diffractogramm of steel slag is caused by more

than one mineral (the main peak for example by bredigite and merwinite).

APPENDIX II

34

Figure 13. X-ray diffraction of EAF sample (Shen et al., 2004)

The two variables obtained from the computer analysis of the diffraction pattern are the

peak position with which the interplanar spacing (d-value) can be calculated and the

intensity of the peak.

Further examples of XRD patterns originating from steel slag, fly ash and ordinary

Portland cement (OPC) can be found for instance in Murphy (1997), Sharma and

Pandey (1999) and Shen H. et al. (2004).

7 IR SPECTROSCOPY

The infrared radiation is a part of the electromagnetic radiation. Its range is between the

visible part and the microwaves. The most important infrared region in analytical

spectroscopy is the mid-infrared region, because there the fundamental vibrations of

molecules are observed (table 8). Rotations are possible modes as well. Nevertheless, in

fluids and solids rotations are suppressed and only a few compounds exhibit rotational

bands.

APPENDIX II

35

Table 8. Regions of Infrared radiation

Range Wave number [cm-

1] Wavelength [µm]

Near Infrared 13300 ... 4000 0.75 ... 2.5

Mid Infrared 4000 ... 400 2.5 ... 25

Far Infrared 400 ... 10 25 ... 1000

7.1 Physical background of Vibrational Spectroscopy

Some basic principles shall be explained first. If light interacts with matter, three

processes are occurring simultaneously, that are reflection, transmission and absorbtion.

The intensity of a light beam I0 includes information of all three processes.

I0 = Ir + It+ Ia

The transmittance of a sample is the ratio of the intensity of monochromatic radiation

entering a sample related to the intensity transmitted by the sample:

T = I/Io

The absorbance A and the transmittance are logarithmically related. Absorbance

changes linearly with changes in concentration of an absorbing sample.

A = log (1/T) = log (Io/I) = e * c * L

Io = Intensity of incident radiation

I = Intensity of transmitted radiation

e = molar extinction coefficient (= absorbtivity a)

c = concentration (mole/l)

L = sample pathlength (cm) (= thickness of the sample b)

APPENDIX II

36

The absorbance of a sample written as

A = a * b * c

is called Bouguer-Lambert-Beer law or commonly Beer´s law. This is the fundamental

equation for spectrometric quantative analysis.

Infrared light is absorbed by a molecule or a functional group if a change in the dipole

moment occurs as a result of optical excited vibrations in the molecule. To absorb

radiation is equivalent with reaching a higher energy state and “the associated energy is

converted into these types of motions” of the chemical bonds (Sherman Hsu, 1997).

The dipole moment describes the unequal distribution of the electric charges of a

molecule considering their distance. The larger the change in the dipole moment, the

stronger is the absorption. The relation between the intensity of the infrared absorption

and the dipole moment µ is given by:

IIR ~ 2

⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

qµ

The absorption intensity is proportional to the square of the change in the dipole

moment µ, with respect to the change in the normal coordinate q, which describes the

molecular vibrations induced. Molecular vibrations can be imagined by a model. One

can consider a complex molecule as a system of coupled inharmonic oscillators

(Günzler and Williams, 2001). The internal degrees of freedom correspond to the

number of independent normal modes of vibrations. If there are N atomic nuclei in the

molecule, a nonlinear molecule will have 3N-6 and a linear molecule 3N-5 internal

degrees of freedom, i.e. modes of vibration.

Water for example has a static dipole moment, where positive and negative electric

charges are not equally distributed in the molecule. When an electromagnetic field

affects the dipole, it orientates itself towards the direction of the field, i.e. the charges

experience a static force leading to rotation of the molecule and vibrations in the

boundary length. The molecule takes up rotational and vibrational energy from the

electromagnetic field. Excitation only takes place, if the vector of the electromagnetic

field is not perpendicular to the vector of the dipole moment. The frequency of the

APPENDIX II

37

exciting IR radiation has to correspond to the frequency of a certain molecular vibration.

Than radiation is absorped by the molecule (Sherman Hsu, 1997).

Unlike water, carbon dioxide has no static dipole moment. The charges are linearly

situated (linear molecule), so that the polarizations cancel each other. Nevertheless the

carbon dioxide molecule can be excited to vibrations with infrared radiation, so that a

dynamic change in the dipole moment occurs.

This change in the dipole moment is induced, e.g. during antisymmetric vibrations (Fig.

14). Vibrations, as for example symmetric ones in the CO2 molecule, leading to no

change in dipole moment, are infrared inactive. This means they do not absorb infrared

radiation.

Figure 14. Vibration modes of the CO2 molecule (a) symmetrical stretching (b) asymmetrical stretching (c) bending

As can be seen in Figure 13, a stretching vibration means that the distance between two

atoms increases or decreases, whereas an atom bends if it leaves its position on the

original bond axis. The CO2 molecule has four normal modes of vibration (three of

them IR active) from which one mode is not shown in the figure above.

(a) (b) (c)

APPENDIX II

38

The unit widely used for IR radiation is the wave number. It is proportional to the

frequency and therewith also to the energy of the electromagnetic field.

ν~ = λ1 =

cν

ν~ ...........wave number [cm-1]

λ ...........wavelength [cm]

ν ............frequency [s-1]

C.............speed of light [km* s-1]

The majority of the investigations with IR spectroscopy focus on organic compounds.

The spectra of inorganic substances show few, wide and intense absorption bands

(Günzler and Gremlich, 2002) and in contradiction to organic molecules they are further

characterized by absence of C-H stretching and bending bands (Smith, 1999).

Smith states that “infrared bands of metal atoms […] often appear below 400 cm-1” and

that “it is usually impossible to tell from a mid-infrared spectrum what metal atoms are

present in a sample” if the spectrometer does not reach this wave number range. As

examples, the author names metal-oxygen stretching and bending vibrations. Also

Günzler and Williams (2001) name this problem by stating that “the fundamentals occur

in the mid-infrared range, which is the most important infrared region”, but

simultaneously “the fundamentals of heavy, single-bonded atoms and the absorptions of

inorganic coordination compounds are found in the far-infrared region”. More

information of the infrared spectra of carbonates can be found in Gadsden (1975).

As summarized by Smith (1999) “inorganic spectra consist of high intensity, low wave

number vibrations characterized by the lack of C-H stretches and the occasional

presence of water bands.” However, many inorganic compounds can be identified with

IR as well. Often, samples consist of a positively charged metal ion and a negatively

charged ion. Due to the high partial positive and negative charges in this ionic bond, the

dipole moment is large, and strong infrared bands are obtained (Smith, 1999).

APPENDIX II

39

7.2 Technique of the FTIR Spectrometer

The Fourier Transform Infrared (FTIR) method is a spectroscopic method used to get

structural information on materials. The spectrometer contains a device called

interferometer. The so called Michelson interferometer is most often used (Figure 15).

Figure 15. Schematical draw of the Michelson interferometer

The interferometer is an optical instrument to split one beam coming from a source into

two beams, to shift them sterically by mirrors against each other and to interfere, i.e.

recombine them at a beam splitter. From there just one beam is directed towards the

sample. After having interacted with the sample, the beam is detected. The detector

measures the intensity of the radiation depending on the optical path difference of the

two beams. The result is the interferogramm. To calculate a spectrum, the FTIR

spectrometer transforms the interferogramm by using the cosine Fourier-transformation.

The interferogram is a function of time domain, whereas the spectrum is a function of

frequency domains as shown in Figure 16. With the Fourier transformation, time and

frequency data can be interconverted.

APPENDIX II

40

Figure 16. Comparison of interferogram and spectrum

For a detailed understanding, literature about FTIR data processing, e.g. Gronholz and

Herres (1984) is recommended.

7.3 The DRIFTS method

To measure infrared spectra of powders and other solid materials, Diffuse Reflectance

Infrared Fourier Transform Spectroscopy (DRIFTS) is used. Diffuse reflectance means

that the incoming radiation is reflected in all directions. The DRIFTS accessory consists

of flat mirrors, an ellipsoidal mirror and a sample slide mount where the sample cup is

placed in (Figure 17). The IR beam is directed from the flat mirrors onto the ellipsoidal

focusing mirror and from there onto the sample. The sample consisting of the slag/KBr

mixture reflects the radiation diffusively. The scattered light is collected by the mirrors

again and redirected to the IR detector. A high quality DRIFTS spectrum is the results

of 10 to 100 sample scans.

Figure 17. Sample accessory of the DRIFTS method

APPENDIX II

41

The material to be examined, consisting of a part of the cured steel slag specimen, is

grinded to a very fine powder from which approximately 3 mg of sample are taken and

dispersed homogeneously in an appr. 200 mg KBr matrix. Grinding is done by hand

with pestle and mortar. The preffered particle size would be the one below the

wavelength of the used radiation, to avoid a loss of energy due to scattered radiation.

Scattering is recognized in a sloping of the baseline (Smith, 1996).

The reason for using potassium bromide is given by the cut-off-frequency of around

300 cm-1 stating there is no absorption of MIR radiation with pure ionic bonds (infrared

transparent).

7.4 Interpretation of IR spectra

The first step evaluating a spectrum is to look for measurement parameters as

resolution, possible irregularities as spectral manipulations (e.g. baseline correction) and

features showing mistakes in the analysis procedure. This can be for instance too much

or too less sample, a poorly pulverized sample (for solid samples), unequal distribution

of the sample in the KBr or water absorption bands.

If a sample consists of a mixture of different molecules, the spectrum gets more

complex, similar to a XRD diffractogram. A possible method to simplify the spectrum

is purification of the sample. Another method, called spectral subtraction, is used if for

instance water absorption bands shall be removed of a spectrum. Another tool for

simplifying interpretation is the mathematical comparison of the measured spectrum

with a collection of known spectra from a library or a database. The fitting of two

similar spectra can be expressed by the hit quality index (HQI). Furthermore, methods

of manipulating spectra can be used. Therewith, hidden features can appear, by for

instance increasing the resolution of the spectra. A combination of these methods is also

applicable (Smith, 1999). However, due to the variety of molecular design and

therewith recordable spectra, the molecular structure often can only be explained

partially.

APPENDIX II

42

A 10-step approach for interpretation of spectra is given in Smith (1999), from which

some advices have already been mentioned above. Further, detailed interpretation help

is given in Günzler and Gremlich (2002). In Figure 18, the terms needed for

interpretation are shown within an example. Terms as absorption maximum and

shoulder are also used in data tables, where no spectra are given.

Figure 18. Model spectrum for explaining fundamental terms

(Günzler and Gremlich, 2002) 1) Baseline 2) Area between baseline and transmittance 1: background absorption or

reflection losses on e.g. on cell windows 3) Absorption maximum, i.e. transmittance minimum and absorption

maximum, respectively, of the vibrational bands: all of these synonymous terms serve for labelling the position of maximum uptake of radiation energy in the spectrum by the molecule.

4) Shoulder: two non-separated bands. 5) Disturbances by absorption of CO2 and H2O of the air.

An IR spectrum can be plotted in two ways, first transmittance vs. wave number and

second absorbance vs. wave number, as shown on the axes of Figure 17.

For the DRIFTS method another transformation from transmittance into Kubelka-Munk

units needs to be done, because the law of Lambert-Beer is not valid for diffusive

reflection.

APPENDIX II

43

The Kubelka-Munk function is:

f (R) = RR

2)²1( − =

sk

R......capability of diffusive reflection

k ......absorption coefficient

s .......scattering coefficient

Therefore, the y-axis of spectra recorded with the DRIFTS method is in Kubelka-Munk

units, which are linear to concentration. If one performs a quantitative analysis of an IR

spectra measured using the DRIFTS method, one can relate the radiation intensity to the

sample concentration via the Kubelka-Munk function.

APPENDIX II

44

8 DISCUSSION

As steel slags and BF slags have cementitious properties, they have been used as filler

material for cement (Shi and Qian, 2000; Bävermann, 1997; Fällmann, 1997). That

changes the properties of the cement and is the reason why a lot of research of slags is

orientated towards this application. A similarity of cement and slags is the presence of

hydraulic minerals and the hydration process induced by adding water (Glasser, 1996).

However, the hydration reaction is very low compared to cement. Steel slags can

contain many different minor elements depending on the steel, i.e. alloys from were it is

tapped (Caley and MacDonald, 2001). Therefore, they have to be analysed before

applying them as a construction material.

Literature about the long-term behaviour of steel slags has not been available in the

form of measurements. Therefore, factors for assessing the alteration and ageing

processes of the material have been outlined. The focus of this work is put on the

mineral phases. They are a. o. influenced by the chemical composition and the slag

treatment after the steel tapping. Slow cooling leads to a more crystalline slag, whereas

rapid cooling results in more amorphous phases. The slags of Uddeholm have been air-

cooled and should therefore contain minerals in a crystalline form. But no analyses of

the mineral structure have to been performed up to now. Analyses of other slags a.o. by

Shen H. et al. (2004) have found minerals in a crystalline form as merwinite,

akermanite, gehlenite and bredigite.

Granulation of slags can increase the reactivity according to Tossavainen (2005b). But

again, this result has been taken from a study where ladle slag was mixed with cement

(1:5) leading to “nucleation and growth rates”, which “are almost the same as for pure

cement”. If this is transferable to mixtures of steel slags is unknown.

After EAF and ladle slag are mixed in the ratio1:1 they are supposed to react with water

(water content about 10 %) to a stable, hardly permeable matrix. Nevertheless, settle-

ments of a landfill, gases leaking out through the top cover and slope stability can

represent severe problems for the liner material. Volume stability, i.e. the control of ex-

pansion during hydration, is done in all applications of hydraulic construction material.

APPENDIX II

45

What is known about hydration is that the mineral phases react with water to more

stable phases. However, the hydraulic properties of steel slags are in every case less

than for MSWI ashes (Huber et al., 1996). One reason is the absence of organic material

in steel slags.

It is known from cement chemistry that the strength development during curing, i.e.

setting after hydration, is the larger the longer this transformation of the minerals takes.

If this knowledge is applied towards slag chemistry, a slow curing reaction would be

favourable, because construction of the top cover only can take place if the slag is not

hardened completely.

For analysing the mineral phases, calorimetry, IR spectroscopy and XRD are suitable,

but using these methods also includes some disadvantages. XRD reveals peaks in a

diffractogram only if the mineral is present in a crystallized state. But the crystallinity of

the hydration products of cement (Haga et al., 2002) and cementitious materials is often

low. For this reason, it is common in material science to combine the XRD technique

with other methods.

For example, combinations with NMR, IR spectroscopy (Haga et al., 2002), SEM

(Piantone et al., 2004; Shen H. et al., 2004; Murphy et al., 1997) and Differential

Thermal Analysis DTA (Sharma and Pandey, 1999) have been found in the literature.

Additionally, improved results of XRD analyses can be achieved if applying magnetism

as with EDX (Shen H. et al., 2004, Murphy et al., 1997) to separate the sample in a low

and a high magnetic fraction. Elementary analysis is of course included in all

investigations as the basic method to estimate the chemical composition.

About the recording of infrared bands from inorganic molecules especially from metals

Smith (1999) suggests to analyze existing metals not with MID-IR but with atomic

spectroscopy instruments because certain stretching and bending vibrations appear

below 400 cm-1 and cannot be recorded with MID-IR. However, he states that

“vibrations such as C-O, N-O and S=O stretching and bending give rise to good

inorganic group wave numbers in the mid-infrared”. Furthermore, IR enables

distinguishing minerals that have the same chemical composition but a different crystal

structure (e.g. calcite and aragonite) because they cause different infrared spectra.

APPENDIX II

46

Considering the limitations stated above, MID-IR spectroscopy and XRD are

appropriate analytical tools for this investigation as they can complete each other.

However, the interpretation of diffractograms as well as IR spectra requires experience

and care.

The investigations of hydration mechanism and heat release in past studies have mostly

been directed towards hydration reactions of cement with blending agents. The main

calorimetrical tools used for this purpose have been DTA/TGA (Haga et al., 2002;

Pane and Hansen, 2005) and isothermal calorimetry (Pane and Hansen, 2005).

The assessment of the stability features and the possible presence of secondary minerals

as well as the attempt of predicting the aging processes occurring in a landfill liner are

the main reasons for investigating steel slags. The main slag aging processes are

summarized in Huber et al. (1996). With focus on ashes from municipal solid waste

incineration (MSWI), the authors point out hydration, carbonation, remaining biological

activity, oxidation of elementary metals, oxidation of sulphides and weathering pro-

cesses as well as crystallization as the main aging processes.

As materials as MSWI ashes and steel slags are alkaline, they behave as buffers for the

neutralisation of acids. Huber et al. (1996) is stating the above processes leading to a

decrease of buffering capacity and pH and a rise of redox potential. If the pH drops

below the neutral point, leaching of certain heavy metals can occur.

The prediction of a transformation of hydroxides into carbonates and - connected to a

decrease of the carbonate buffer - the transformation of carbonates into bicarbonates

seems to be transferable towards steel slags. Under landfill conditions these processes

probably take centuries or up to thousands of years, according to some models

performed about decalcification. The actual reaction time of these processes and the

appearing equilibria are still unknown.

APPENDIX II

47

9 CONCLUSIONS

In Europe steel slags are often landfilled or temporarily stored, although

applications for their reuse already exist (e.g. as additives in a road construction).

The target of nowadays research is to identify further applications for reusing steel

slags and to investigate the environmental impact that steel slags would have. The

conditions present in the liner have to be estimated before using alternative

construction materials as steel slags.

Up to today, the long-term behaviour of steel slags is still unknown. It is affected by

processes as weathering, including carbonation (carbonic acid weathering) and pH

changes, leaching, aging of mineral phases and therewith stability changes of the

minerals.

XRD and IR spectroscopy are suitable methods to analyse the mineral phases of

steel slags. The reaction of the slags under addition of water is called hydration

which has been described in this literature review. To determine the heat

development and conditions of this reaction, calorimetry is a suitable technique.

XRD is applicable for determining the structure of crystalline solid samples using

the diffraction angles and the intensity recorded in a diffractogram.

Infrared radiation originates from the vibration and rotation of bonds and ions of

molecules. Also amorphous structures as for instance glassy mineral phases, which

are common in certain steel slags, can be identified with IR spectroscopy.

With the results from these analyses, predictions of possible aging processes and the

long-term behaviour can be done. The secondary phases formed during mineral

aging are assumed to consist mainly of carbonates. A landfill layer of this type is

expected to be stable for a long time, at least some hundred years until the carbonate

buffer is used up and potentially bicarbonates form.

APPENDIX II

48

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FEhS (2005). Report of the FEhS institute, no. 1/2005. Institut für Baustoff-Forschung

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Gadsden, J. A. (1975). Infrared Spectra of Minerals and Related Inorganic Compounds.

London, Butterworth, p. 6 et seq., 23 et seq., 62

Glasser, F. P. (1996). Properties of cement waste composites. Waste Management, Vol.

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Grübl, P.; Weigler, H.; Karl, S. (2001). Beton-Arten, Herstellung und Eigenschaften.

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künstlicher Alterung. Endbericht des Forschungsprojektes „Alterungsverhalten

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Date: 2005-11-10

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künstlicher Alterung. Research report, Universität für Bodenkultur, Wien.

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Date: 2005-11-10

[4] Lecture notes. Division of Building Materials and Building Technology. Katholieke

Universitet Leuven (BE).

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Date: 2005-10-31

[5] Moosberg-Bustnes, H. Industrial by-products in the concrete industry.

Swedish Cement and Concrete Institute.

Internet: www.byggforsk.no/visVedlegg. aspx?vedleggID=204&dokumentID=1129

Date: 2006-01-13

[6] BMU – Bundesumweltamt (Federal Ministry for the Environment, Nature Conserva-

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Standards and directives

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The Council of the European Union, Brussels.

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och deponering (Deponiehandbok). RVF – Svenska Renhallnings- verksför-

eningen, Malmö, Sweden.

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APPENDIX III

APPENDIX III

EXTENDED SUMMARY IN GERMAN

Mineralphasen in Stahlschlacken beim Einsatz

in der Dichtungsschicht einer Deponieoberflächenabdichtung

APPENDIX III

1

Zusammenfassung

Elektroofenschlacke und Pfannenschlacke (auch Konverterschlacke genannt) sind

Nebenprodukte der Stahlproduktion im Elektrolichtbogenofen und der darauf folgenden

sekundärmetallurgischen Prozesse in einer sog. Pfanne. Insgesamt wurden 2004 in

Europa 15, 2 Mio. Tonnen Stahlschlacken (d.h. Schlacken aus dem Sauerstoff-

blasverfahren, Elektroofenschlacke und Pfannenschlacke) produziert (Euroslag, 2006).

Die Weiterverwendung von Stahlschlacken u. a. im Strassen-, Wasser- und Erdbau, als

Düngemittel für kalkarme Böden und als Zementzuschlagsstoff ist in einzelnen

europäischen Ländern sehr unterschiedlich ausgeprägt und hängt u. a. von der

Verfügbarkeit natürlicher Rohstoffe ab. Die Nutzung dieser Schlacken ist dabei nicht

nur von ökologischem Nutzen, indem der Abbau natürlicher Rohstoffe vermieden wird,

sondern auch von ökonomischem Vorteil, da der Bedarf an Baustoffen für den Bau

einer Deponieoberflächenabdichtung durch Deponieschließungen in Zusammenhang

mit der EU Deponierichtlinie 1999/31/EC steigen wird.

Um eine Abschätzung bezüglich der Verwendung von Stahlschlacken als Baumaterial

in der Dichtungsschicht einer Deponie vornehmen zu können, bedarf es der Kenntnis

ihrer physikalischen und chemischen Eigenschaften, als auch einer Einschätzung des

Umwelt- und Langzeitverhaltens. Die mechanische und chemische Stabilität einer

solchen Konstruktion ist hierbei von besonderer Bedeutung.

Die Ziele dieser Arbeit sind die Abschätzung der Reaktivität der Schlacken nach

erfolgter Wasserzugabe, die Bestimmung der amorphen und kristallinen Mineralphasen

in den Schlacken und Mischungen aus denselbigen und die Bestimmung der Stabilität

der Hauptmineralphasen. Die mögliche Bildung neuer Minerale nach dem Mischen von

Elektroofenschlacke und Pfannenschlacke unter Wasserzugabe soll ebenfalls untersucht

werden.

Die Reaktivität der Schlacken nach Wasserzugabe ist zusammen mit dem zeitlichen

Verlauf der Wärmeentwicklung ein Indikator für die Bildung mehr oder weniger sta-

biler Mineralphasen während des Abbindeprozesses. Die Stabilität der in den Stahl-

schlacken enthaltenen Minerale ist bedeutsam für Mineralumwandlungen, welche unter

den Bedingungen in einer Dichtungsschicht geschehen können. Diese Mineraltrans-

formationen werden auch als Alterungsprozesse der Minerale bezeichnet Die sich

APPENDIX III

2

bildenden sekundären Mineralphasen bestimmen die Stabilität und das Langzeit-

verhalten der gesamten Oberflächenabdichtung.

Eine Einschätzung zur Tauglichkeit der Analysemethoden Kalorimetrie, Infrarot-

Spektroskopie (IR-Spektroskopie) und Röngtendiffraktometrie (XRD) zur

Beantwortung der oben genannten Fragen wurde in der Literaturstudie vorgenommen

(Anhang II). Eine Methode zur Probenkörperherstellung für die IR- and XRD-Analysen

wurde entwickelt und ist in Anhang I beschrieben, zusammen mit der

Probenvorbereitung der Kalorimetrieversuche und der Zusammenstellung der gesamten

Messdaten.

Aus der Literaturstudie geht hervor, dass Lösungskalorimetrie, XRD und IR-Spek-

troskopie geeignete Methoden zur Messung der Mineralphasen sowie deren Hydratation

von Stahlschlacken darstellen. Die Hydratationsreaktion der Schlacken nach

Wasserzugaben ist ebenfalls erläutert worden. Es soll u. a. die Wärmeentwicklung und

der Verlauf der Hydratation von Elektroofenschlacke und Pfannenschlacke sowie

verschiedener Schlackemischungen bestimmt werden.

XRD-Analysen sind u. a. zur Strukturbestimmung fester kristalliner Proben geeignet.

Die Röntgenstrahlen werden von den einzelnen Gitterebenen der Kristalle unter

bestimmten Winkeln, welche die Bragg-Gleichung erfüllen, gebeugt und die Intensität

der gebeugten Strahlung wird vom Detektor erfasst.

Die Infrarot-Spektroskopie hingegen beruht auf Atomschwingungen in Molekülen,

welche durch die einfallende Strahlung angeregt werden. Es können sowohl

Schwingungen und Rotationen von Bindungen als auch von Ionen im Molekül

detektiert werden. Gemessen wird hierbei, welcher Teil der einfallenden

Infrarotstrahlung von der jeweiligen Probe absorbiert wird. Die Absorption und das

dazugehörige Energieniveau im Absorptionsspektrum können dann der Frequenz einer

Molekülschwingung zugeordnet werden. Mit Hilfe der IR-Spektroskopie können auch

amorphe Mineralphasen gemessen werden. Amorphe Phasen können beispielsweise

glasartige Phasen sein, welche sich aufgrund plötzlicher Abkühlung der Schlacken-

schmelze bilden.

Der zeitliche Verlauf der Wärmeentwicklung der im Kalorimeter gemessenen

Mischungen zeigte eine Aktivierung der Hydratationsreaktion durch Aluminium. Je

höher der Anteil an Pfannenschlacke in der Mischung, desto größer war der gemessene

APPENDIX III

3

Temperaturunterschied, d.h. die abgegebene Wärmemenge. Allerdings führte ein

größerer Anteil an Pfannenschlacke in der Mischung zu einer zeitlichen Verzögerung

der maximalen Wärmefreisetzung, d. h. der maximale Reaktionsumsatz geschah später.

Die Spektroskopiemessungen ergaben, dass die Änderungen in den Spektren der

einzelnen Mischungen proportional zum Anteil an Elektroofenschlacke sind. Außer den

Mischungen und der zwei reinen Proben von Elektroofenschlacke und Pfannenschlacke

wurde zusätzlich eine spektroskopische Messung von nicht hydratisierter Pfannen-

schlacke durchgeführt, um dessen Spektrum mit der hydratisierten Schlackenform

vergleichen zu können.

Mithilfe einer qualitativen Analyse der Spektren wurden Absorptionsbanden von

anorganischen Karbonaten, Kalziumsilikaten und Aluminiumoxid identifiziert. Der

größte Unterschied zwischen allen Proben befand sich in der Wellenzahl-Region von

3500-3200 cm-1. Die gemessene Probe aus 100 % (hydratisierter) Pfannenschlacke

zeigte deutliche Absorptionsbanden in diesem Bereich, wohingegen dies bei

Elektroofenschlacke und nicht hydratisierter Pfannenschlacke nicht der Fall war. In dem

genannten Wellenzahl-Bereich absorbieren O-H Bindungen die einfallende Strahlung.

Durch die Absorptionsmessung dieser Bindungen konnte der Einbau und die

Absorption von Wassermolekülen in die Mineralstruktur durch Hydratation

nachgewiesen werden. Diese Absorptionsbanden sind also nur bei einer entsprechend

ausgeprägten Hydratation erkennbar. Das hydraulische Verhalten wird vor allem durch

chemischen und mineralogischen Eigenschaften bestimmt.

Mit der Methode der Röntgenbeugung wurden die Hauptphasen aller Schlackeproben

inklusive der Schlackenmischungen gemessen. Dabei ergab sich, dass die

Schlackemischungen die gleichen Minerale wie reine Pfannen- bzw. Elektroofen-

schlacke besaßen. Es konnten keine Mineralneubildungen bei den Mischungen

gemessen werden. Dies kann zum einen daran liegen, dass es keine Neubildungen von

Mineralphasen gab. Es kann aber auch am Messgerät liegen, welches eine Phase nur

detektiert, wenn sie mehr als 4 wt-% am Anteil der Gesamtprobe beträgt. Die Haupt-

minerale von Pfannenschlacke sind γ - Dikalziumsilikat (γ - Ca2SiO4) und Mayenit.

Bei Elektroofenschlacke sind Merwinit und Monticellit am häufigsten vertreten. Diese

Ergebnisse beruhen auf thermodynamischen Modellen. Beide Schlacken bestehen

APPENDIX III

4

vorwiegend aus kristallinen Phasen. Dies lässt sich mit der langsamen Abkühlung der

Schlackenschmelze im Stahlwerk erklären.

Eine Schlussfolgerung hinsichtlich einer Korrelation zwischen Abbindeverhalten und

Mineralphasen ist nur begrenzt möglich. Bestimmte Mineralphasen wie

Dikalziumsilikat besitzen nur geringe hydraulische Eigenschaften. Deren Hydratation

und Abbindeverhalten wird entsprechend gering ausfallen. Es herrscht keine Korrelation

zwischen Hydratationswärmefreisetzung und Stabilität einer bestimmten Mineralphase.

Es kann somit Phasen geben, die bei hoher Wärmefreisetzung geringe Endfestigkeiten

nach dem Abbinden entwickeln.

Da Pfannenschlacke einen Beitrag zur Hydratationsreaktion liefert, da mehr reaktives

Kalziumoxid vorhanden ist und Elektroofenschlacke die Festigkeiten der Mischungen

positiv beeinflusst, wird eine Mischung beider Schlacken zu gleichen Anteilen in der

Dichtungsschicht einer Deponieoberflächenabdichtung als optimal angesehen.

Das Langzeitverhalten der Schlacken ist zurzeit noch nicht bekannt und kann daher nur

abgeschätzt werden. Es wird durch Faktoren wie Verwitterung (eingeschlossen darin ist

die Karbonatisierung), Feuchtigkeit, pH Veränderungen und Redoxpotential sowie die

Pufferkapazität der Minerale beeinflusst. Die Karbonatisierung wird dabei vor allem

vom CO2 - Gehalt und der Feuchtigkeit beieinflusst. Aufgrund der Literaturrecherche

und Beobachtungen an den Probekörper nach einer dreimonatigen Lagerungszeit wird

angenommen, dass die sich bildenden sekundären Phasen aus Stahlschlacken vor allem

aus Karbonaten bestehen. Allerdings werden nicht alle Mineralphasen verwittern und

sekundäre Phasen bilden. Nach hinreichend langen Zeiträumen von mehreren Tausend

Jahren können sich ebenfalls Hydrogenkarbonate bilden, allerdings muss die

Pufferkapazität der Schlackeschicht aus Karbonaten vorher hinreichend gesunken sein.

Forschungsbedarf ist vor allem im Bereich der Schlackealterung während verschiedener

Lagerungsbedingungen und der thermodynamischen Eigenschaften der Minerale zu

sehen. Experimente und Modelle zur Vorhersage von chemischen und strukturellen

Veränderungen der Minerale können hier einen Betrag zur Klärung des

Langzeitverhaltens liefern. Bei experimentellen Versuchen wird versucht diese

Langzeitprozesse künstlich zu beschleunigen. Diese Forschungen sind unerlässlich, um

Stahlschlacken Baumaterial einsetzen zu können.

Eidesstattliche Erklärung Hiermit erkläre ich an Eides statt, dass ich die vorliegende Arbeit

selbstständig und ohne fremde Hilfe angefertigt habe. Sämtliche benutzten

Informationsquellen sowie das Gedankengut Dritter wurden im Text als

solche kenntlich gemacht und im Literaturverzeichnis angeführt. Die Arbeit

wurde bisher nicht veröffentlicht und keiner Prüfungsbehörde vorgelegt.

Dresden, den 21. März 2006