Desulphurization of Ferronickel Alloy Using a Waste ... · Desulphurization of Ferronickel Alloy Using a Waste Material from Alumina Production By Xinqiang Men Master of Applied Science

Desulphurization of Ferronickel Alloy Using a Waste

Material from Alumina Production

by

Xinqiang Men

A thesis submitted in conformity with the requirements for the degree of

Master of Applied Science

Graduate Department of Materials Science and Engineering

University of Toronto

Copyright by Xinqiang Men, 2012

ii

Desulphurization of Ferronickel Alloy Using a Waste

Material from Alumina Production

By

Xinqiang Men

Master of Applied Science

Department of Materials Science and Engineering

University of Toronto

2012

ABSTRACT

Red mud is a waste product of alumina production and has an adverse effect on environment.

About 90 million tonnes of red mud are produced annually throughout the world and little is

recycled for useful applications. The world nickel reserves consist of approximately 30%

sulphide ores and 70% oxide ores. Despite the relative abundance of oxide ores, 55% of

nickel and nickel alloys produced today are derived from sulphide ores. However, with the

production of nickel and its alloys from low-grade oxide ores becoming increasingly

important, a major concern is high sulphur level in the resultant alloy. For this reason,

desulphurization of the ferronickel becomes an important consideration. In the present study,

experiments were conducted to determine if red mud could be used as a major ingredient of

custom designed fluxes for the desulphurization of ferronickel alloy. Factors investigated

included desulphurization rates, contact angle measurements and flux-refractory interactions.

iii

ACKNOWLEDGEMENTS

I would like to express my sincerest appreciation to my supervisor Prof. A.McLean, Dr. Y.D.

Yang, Dr. Soda, Prof. M. Barati for their continual guidance, support and encouragement.

I would like to thank for the help from Paul, Karim, Yuki and other members of our research

group. Appreciation is also expressed to Allan from Ryerson University for his help in

preparing materials for me.

I express my thanks to Process Research Ortech (PRO) for in-kind support and the Centre for

Chemical Process Metallurgy (CCPM) together with NSERC for financial support through a

CRD Grant. In addition, I would like to thank the Department of Materials Science and

Engineering, and University of Toronto for support.

Finally, I would like to thank my family and friends in China for their unending support and

encouragement throughout my study.

iv

TABLE OF CONTENTS

ABSTRACT ............................................................................................................................. ii

ACKNOWLEDGEMENTS ..................................................................................................... iii

TABLE OF CONTENTS ......................................................................................................... iv

LIST OF TABLES ................................................................................................................. viii

LIST OF FIGURES ................................................................................................................. ix

LIST OF SYMBOLS ............................................................................................................... xi

LIST OF APPENDICES ........................................................................................................ xiv

CHAPTER ONE: INTRODUCTION....................................................................................... 1

1.1 Background ..................................................................................................................... 1

1.2 References ....................................................................................................................... 4

CHAPTER TWOLITERATURE REVIEW ......................................................................... 5

2.1 The Production of Alumina and Red Mud ...................................................................... 5

2.1.1 Bayer Process............................................................................................................ 5

2.1.2 Sintering Process ...................................................................................................... 9

2.1.3 Combined Process .................................................................................................. 12

2.2 Physical and Chemical Properties of Red Mud ............................................................. 16

2.2.1 Physical Properties of Red Mud ............................................................................. 16

2.2.2 Chemical Properties of Red Mud ........................................................................... 16

2.3 Negative Influence Caused by Red Mud ...................................................................... 17

2.4 Means to Recycle Red Mud .......................................................................................... 18

2.4.1 Utilization of Red Mud as Building Materials ....................................................... 18

2.4.1.1 Producing cement ............................................................................................. 18

2.4.1.2 Producing glass-ceramic .................................................................................. 19

2.4.1.3 Producing bricks............................................................................................... 19

2.4.1.4 Producing pigment ........................................................................................... 20

2.4.2 Recovery of Valuable Elements from Red Mud ..................................................... 20

2.4.2.1 Recovery of Al2O3 and Na2O ........................................................................... 21

2.4.2.2 Recovery of Fe2O3 ............................................................................................ 22

2.4.2.3 Recovery of TiO2.............................................................................................. 23

v

2.4.3 Utilization of Red Mud as Environmental Materials .............................................. 24

2.4.3.1 Water treatment ................................................................................................ 24

2.4.3.2 Gas cleaning ..................................................................................................... 28

2.4.3.3 Soil amelioration .............................................................................................. 28

2.5 Problems in Recycling Red Mud .................................................................................. 29

2.6 References ..................................................................................................................... 30

CHAPTER THREE: EXPERIMENTAL ASPECTS .............................................................. 36

3.1 Materials ........................................................................................................................ 36

3.1.1 Solid Materials ........................................................................................................ 36

3.1.2 Gas Material............................................................................................................ 38

3.1.3 Liquid Material ....................................................................................................... 38

3.2 Scanning Electron Microscopy (SEM) ......................................................................... 38

3.2.1 Basic Principles of SEM ......................................................................................... 38

3.2.2 Sample Preparation ................................................................................................. 39

3.3 X-ray Diffraction (XRD) ............................................................................................... 39

3.3.1 Basic Principles of XRD ......................................................................................... 39


3.4 X-ray Fluorescence (XRF) ............................................................................................ 41

3.4.1 Basic Principles of XRF ......................................................................................... 41


3.5 Thermogravimetric Analysis (TGA or TG) ................................................................... 42

3.5.1 Basic Principles of TGA ......................................................................................... 42


3.6 Desulphurization Experiments ...................................................................................... 43

3.6.1 Experimental Equipment ........................................................................................ 43


3.6.3 Experimental Procedure.......................................................................................... 45

3.6.4 Sulphur Analysis of Samples .................................................................................. 45

3.7 Contact Angle Experiments........................................................................................... 45



vi


3.7.4 Measurement of Contact Angle .............................................................................. 49

3.8 Corrosion Experiment ................................................................................................... 49




3.8.4 Corrosion Effect Analysis ....................................................................................... 50

3.9 References ..................................................................................................................... 51

CHAPTER FOUR: RESULTS AND DISCUSSION ............................................................. 52

4.1 Characterization of Red Mud ........................................................................................ 52

4.1.1 XRF Study of Red Mud .......................................................................................... 52

4.1.2 XRD and TG Study of Red Mud ............................................................................ 53

4.1.2.1 XRD and TG Study of Red Mud S1 ................................................................ 53

4.1.2.2 XRD and TG Study of Red Mud B1 ................................................................ 56

4.1.2.3 XRD and TG Study of Red Mud B2 ................................................................ 58

4.2 Desulphurization Experiments ...................................................................................... 60

4.2.1 Evaluation of desulphurization results ................................................................... 60

4.2.2 Effect of some factors on the desulphurization reaction ........................................ 61

4.2.2.1 Effect of nickel content in the alloy ................................................................. 61

4.2.2.2 Effect of aluminum addition in the flux ........................................................... 63

4.2.2.3 Effect of iron oxide addition ............................................................................ 64

4.2.2.4 Effect of temperature variation ........................................................................ 66

4.2.2.5 Effect of carbon content ................................................................................... 67

4.3 Result of Contact Angle Experiment............................................................................. 68

4.3.1 Hemispherical Temperature of Refining Flux ........................................................ 68

4.3.2 Contact Angle Measurements ................................................................................. 69

4.3.2.1 The Change of Contact Angle as a Function of Time and Temperature .......... 71

4.3.2.2 The Change of Contact Angle as a Function of Nickel Content ...................... 74

4.4 Result of Corrosion Test ................................................................................................ 75

4.5 References ..................................................................................................................... 79

CHAPTER FIVE: CONCLUSIONS ...................................................................................... 80

vii

APPENDICES ........................................................................................................................ 82

Appendix A: The results for desulphurization experiments ................................................ 82

Appendix B: The results for contact angle experiments ..................................................... 85

Appendix C: The photos of crucibles before and after corrosion experiments ................... 86

Appendix D: The XRD and TG results of B3, B4 and B5 .................................................. 88

viii

LIST OF TABLES

Table 2.1 The main chemical composition of red mud......17

Table 3.1 The chemical composition of AISI 1117 low carbon steel........36

Table 3.2 The chemical composition of nickel-based alloy...36

Table 3.3 The chemical composition of stainless steel substrates.....37

Table 3.4 The schedule of desulphurization experiment...44

Table 3.5 The schedule of contact angle experiment.....48

Table 3.6 The schedule of corrosion experiment...50

Table 4.1 The chemical composition of red mud......52

ix

LIST OF FIGURES

Figure 1.1 Flow chart of nickel oxide ores processing...2

Figure 2.1 Flow chart of Bayer process......7

Figure 2.2 Flow chart of sintering process....10

Figure 2.3 Flow chart of parallel process..13

Figure 2.4 Flow chart of serial process.....14

Figure 2.5 Flow chart of mixed process....15

Figure 3.1 EDX analysis of refractory brick.....37

Figure 3.2 Schematic diagram of a Scanning Electron Microscope.....39

Figure 3.3 Bragg's Law.....40

Figure 3.4 Schematic diagram of desulphurization experiment....43

Figure 3.5 Schematic diagram of contact angle equipment......47

Figure 3.6 Image of the software to measure contact angle..49

Figure 4.1 XRD result of red mud S1.......54

Figure 4.2 TG result of red mud S1..55

Figure 4.3 XRD result of red mud B1..56

Figure 4.4 TG result of red mud B1...,.57

Figure 4.5 XRD result of red mud B2..58

Figure 4.6 TG result of red mud B2.....59

Figure 4.7 Effect of nickel content in alloy on desulphurization reaction...62

Figure 4.8 Effect of nickel content in alloy on apparent desulphurization

rate constant ......62

Figure 4.9 Effect of aluminum addition in flux on desulphurization reaction..63

Figure 4.10 Effect of aluminum addition in flux on apparent desulphurization rate

constant...64

Figure 4.11 Effect of iron oxide addition in flux on desulphurization reaction...65

http://serc.carleton.edu/research_education/geochemsheets/BraggsLaw.html

x

Figure 4.12 Effect of iron oxide addition in flux on apparent desulphurization rate

constant......65

Figure 4.13 Effect of temperature variation on desulphurization reaction..66

Figure 4.14 Effect of temperature variation on apparent desulphurization rate

constant......66

Figure 4.15 Effect of carbon content on desulphurization reaction....67

Figure 4.16 Hemispherical temperature of refining flux.69

Figure 4.17 Contact angle with 5% nickel substrate as a function of time.71

Figure 4.18 Contact angle with 10% nickel substrate as a function of time...71

Figure 4.19 Contact angle with 15% nickel substrate as a function of time...72

Figure 4.20 Contact angle with 5% nickel substrate as a function of temperature.72

Figure 4.21 Contact angle with 10% nickel substrate as a function of temperature...73

Figure 4.22 Contact angle with 15% nickel substrate as a function of temperature...73

Figure 4.23 Contact angle as a function of nickel contents when CaO content is

fixed...74

Figure 4.24 EDX result of refractory brick sample after corrosion test.....76

Figure 4.25 The relation between CaO content in flux and corrosion depth..76

Figure 4.26 SEM result of No. 1 test...77






Figure 4.32 SEM result of No. 7 test......78

xi

LIST OF SYMBOLS

aq: aqueous solution.

A : the total reaction area between molten slag and liquid alloy.

AC: activated carbon.

A/S: the weight ratio between alumina and silicon oxide in bauxite.

B1: the first kind of red mud from Bayer process in USA.

B2: the second kind of red mud from Bayer process in USA.

B3: the first kind of red mud from Bayer process in Canada.

B4: the second kind of red mud from Bayer process in Canada.

B5: the red mud from Bayer process in China.

2Cs : sulphide capacity of the slag.

CCD : counter current decantation.

d: the interplanar spacing.

EDX: energy-dispersive X-ray spectroscopy.

fs : the sulphur activity coefficient.

k : Etvs constant, which is valid for almost all substances and its value is 2.1 x 107 [J K1

mol2/3

].

aK : the apparent desulphurization rate constant .

Ks : the sulfur mass transfer coefficient.

SL : sulphur distribution ratio between molten slag and liquid metal.

xii

n: an integer.

OPC: ordinary Portland cement.

2PO : the partial oxygen pressure.

: the partial sulphur pressure.

r : the roughness ratio.

RMGA: red mud granular adsorbents.

iS][ : the initial sulphur content in the ferronickel alloy.

fS][ : the final sulphur content in the ferronickel alloy.

tS][ : the sulfur content in liquid metal at any sampling time.

)%( Swt : the weight percent of sulphur in the slag.

]%[ Swt : the weight percent of sulphur in the alloy.

SEM: scanning electron microscopy.

t : time.

T : temperature.

TC : the critical temperature and corresponds to the temperature at which the surface tension

is zero.

TBP: tri-butyl phosphate.

TGA: thermogravimetric analysis.

V : the molar volume of a substance.

V : the volume of liquid alloy.

WHIMS: wet high intensity magnetic separation.

xiii

XRD: x-ray diffraction.

XRF: x-ray fluorescence.

: surface tension.

ls : the interfacial tension between liquid and solid.

sg : the interfacial tension between gas and solid.

lg : the interfacial tension between liquid and gas.

S : desulphurization degree.

: the angle of incident X-rays.

* : the apparent contact angle which corresponds to the stable equilibrium state.

: Youngs contact angle as defined for an ideal surface.

: the wavelength of X-rays.

xiv

LIST OF APPENDICES

Appendix A: The results for desulphurization experiments ................................................ 82

Appendix B: The results for contact angle experiments ..................................................... 85

Appendix C: The photos of crucibles before and after corrosion experiments ................... 86

Appendix D: The XRD and TG results of B3, B4 and B5 .................................................. 88

1

CHAPTER ONE: INTRODUCTION

1.1 Background

Nickel is a very important metal that finds a variety of applications including consumer

products, building, automotive and electronics. There are two kinds of ores containing nickel,

namely oxide and sulphide ores. Anthony and Flett [1] reported that about 55% of the

worlds nickel production originates from sulphide ores while the balance is derived from

oxide ores. However, oxide ores count for about 70% of the worldwide reserves. Apparently,

oxide ores will play a significant role in the production of nickel in the future. Nickel oxide

ores can be classified two kinds --- limonite ore and saprolite ores in terms of mineralogy.

Limonite ore usually contains high MgO content and low FeO content which is treated by

pyrometallurgy to form ferronickel or matte. However, saprolite ore contains high FeO

content and low MgO content which prefers hydrometallurgy to recover nickel and cobalt.

The flow chart showing the treatment of nickel oxide ores is shown in Figure 1.1.

2

Figure 1.1 Flow chart of nickel oxide ores processing [2]

Most of nickel produced using oxide ores is from pyrometallurgical processes namely

ferronickel smelting or matte smelting. So, we can draw such a conclusion that using nickel

oxide ores to produce ferronickel will become more and more important in the future. Before

being used to make stainless steel or other materials, the ferronickel needs pretreatment to

remove impurities especially sulphur and phosphorus that will cause negative influence on

the properties of steel product.

Red mud is a by-product during alumina production. Usually, about 1 to 1.5 tonnes of red

mud will be produced when we get 1 tonne of alumina. About 90 million tonnes of red mud

are produced every year in the world [3]. Red mud is deemed as a toxic industrial waste

which needs treatment before discharge because of alkalinity and chemical and mineralogical

properties. Until now, the main means to deal with red mud are to store it in impoundments

or dump it in the sea depending on local environment. Nowadays, how to recycle red mud

3

has become an important topic around the world. The last 40 years have witnessed a lot of

patent applications concerning the ways of red mud utilization. However, a little amount of

red mud is consumed until now due to the limitations of recycling red mud.

So, based on the information above, to use red mud to remove sulphur in ferronickel seems

to be a promising method of recycling red mud. The objectives in this study include:

1) To characterize several kinds of red mud.

2) To study desulphurization of ferronickel using fluxes made from red mud.

3) To study the interfacial phenomena between fluxes made from red mud and ferronickel.

4) To study whether fluxes made from red mud will attack the refractory materials.

4

1.2 References

[1] M.T. Anthony, D.S. Flett. Nickel processing technology: A review. Nickel: 1996

Commodity Meeting. Minerals Industry International. pp. 2642.

[2] T. Norgate , S. Jahanshahi. Assessing the energy and greenhouse gas footprints of nickel

laterite processing. Minerals Engineering. 24, 2011, pp. 698707.

[3] S.B. Wang, H.M. Ang, M.O. Tade. Novel application of red mud as coagulant, adsorbent

and catalyst for environmentally benign processes. Chemosphere. 72, 2008, pp.1621-1653.

5

CHAPTER TWOLITERATURE REVIEW

2.1 The Production of Alumina and Red Mud

Last decades have witnessed the prosperity of alumina industry. The annual yield of alumina

across the world continues to go up. A lot of residue, red mud, is also produced at the same

time. Usually, about 1 to 1.5 tonnes of red mud will be produced with 1 tonne of alumina.

About 90 million tonnes of red mud are produced every year in the world [1]. Nowadays,

most of alumina is produced from bauxite through three means including Bayer process,

sintering process and combined process [2]. What kind of method should be used to produce

alumina is mainly decided by the category of bauxite. In fact, the criterion to evaluate the

quality of bauxite is based on its mineralogical and chemical characteristics. We can classify

bauxites by their mineralogical characteristics so that there are four kinds of bauxites in

nature including gibbsite bauxite, boehmite bauxite, diasporic bauxite and combined bauxite

[3]. Usually, gibbsite bauxite is the easiest kind of bauxite to digest compared to boehmite

bauxite and diasporic bauxite which is the most difficult kind of bauxite to digest. Another

aspect influencing the quality of bauxite is the chemical characteristics. We usually use A/S,

which means the weight ratio between alumina and silicon oxide in bauxite, to judge the

quality of bauxite. The quality of bauxite goes up with the increase of A/S. Nowadays, Bayer

process usually demands gibbsite bauxite or boehmite bauxite whose A/S should be more

than 7. On the contrary, sintering process is used to deal with diasporic bauxite whose A/S is

usually below 3.5.

2.1.1 Bayer Process

Bayer process was invented by Karl Josef Bayer, an Austrian, in 1889. Since then, it has been

the most popular method to produce alumina in that it is quite suitable to deal with gibbsite

bauxite or boehmite bauxite which exists in most countries producing alumina. In addition,

6

Bayer process also includes a variety of merits such as low energy consumption, high-quality

product, excellent economic benefits, and relatively simple flow chart. So, most alumina

nowadays is produced by Bayer process in the world. The flow chart is displayed in Figure

2.1.

7

Figure 2.1 Flow chart of Bayer process

8

As can be seen from Figure 2.1, firstly, bauxite and lime will be ground. After that, they will

be mixed with recycled alkaline solution in a wet ball mill to form slurry. Next, the slurry is

pumped to digester where digestion takes place under suitable pressure and temperature. The

main reaction in digestion is shown below.

Al2O3 (1 or 3)H2O+2NaOH+aq 2NaAlO2+aq (2.1)

In addition, SiO2 also reacts with alkali to form Na2O Al2O3 x SiO2y H2O finally. The

slurry flowing out of the digester consists of sodium aluminate solution and insoluble residue

including Na2O Al2O3 x SiO2y H2O and red mud. Sodium aluminate solution will be

purified by filters to get rid of remaining residue. Next, sodium aluminate solution will be

cooled and diluted. Then, it will be decomposed by mixing with Al2O33H2O seed. The main

reaction in decomposition is shown below.

2NaAlO2 + 4H2O + aq Al2O33H2O + 2 NaOH + aq (2.2)

After decomposition, slurry flowing out of decomposers contains recycled alkaline solution

and Al2O33H2O crystals that will be classified according to size. The big Al2O33H2O

crystals will be changed to Al2O3 by roasting. However, the small ones will return to the

decomposers as seed. Moreover, recycled alkaline solution is evaporated to remove extra

water and used to digest new bauxite. During this process, some Na2CO3H2O crystals will

form and react with lime milk to produce NaOH which will be added into the recycled

alkaline solution to adjust its concentration. The separated red mud is counter-current washed

using hot water several times in order to recover Al2O3 and Na2O before disposed in landfills.

How many times the red mud will be washed is decided by the utilization of red mud

produced. If the red mud will be sent to sintering process in a combined process as a sort of

raw material still containing certain amount of alumina, it usually will be washed for 3 or 4

times. However, if it will be deposited in landfills directly, at least 6 times should be

employed to retrieve Al2O3 and Na2O as much as possible.

9

2.1.2 Sintering Process

Sintering process is mainly employed by a few countries to deal with bauxite containing

diaspore. Compared with Bayer process, this method has a variety of disadvantages such as

sophisticated flow chart, high energy consumption. However, the most vital advantage of this

method is that it can use low-quality bauxite to produce alumina. With the continuous

decrease of high-quality bauxite in the world, a conclusion that sooner or later sintering

process will be more popular than now can be drawn. The flow chart is displayed in Figure

2.2.

10

Figure 2.2 Flow chart of sintering process

11

Unlike Bayer process, sintering process uses soda ash and lime to mix with ground bauxite to

form slurry. Then, the slurry is injected into rotary kiln to form agglomerated material whose

main compositions are Na2O Al2O3, 2CaO SiO2, and Na2O Fe2O3. The main reactions in the

rotary kiln are as follows.

Na2CO3 + Al2O3 Na2O Al2O3 + CO2 (2.3)

2CaO + SiO2 2CaO SiO2 (2.4)

Na2CO3 + Fe2O3 Na2O Fe2O3 + CO2 (2.5)

Next step is digestion in which agglomerated material will be ground in mills with alkaline

solution to form sodium aluminate solution and red mud. In this process, several reactions

take place as follows.

Na2O Al2O3 + 4 H2O + aq 2NaAl(OH)4+aq (2.6)

Na2O Fe2O3 + 4 H2O + aq 2NaOH + Fe2O33H2O+aq (2.7)

2CaO SiO2 + 2NaOH + aq Na2 SiO3 + 2Ca(OH)2+ aq (2.8)

2CaO SiO2 + 2 Na2CO3 + aq Na2 SiO3 + 2NaOH + 2Ca CO3+ aq (2.9)

The result of digestion is that useful materials including Na2O and Al2O3 are transferred into

solution but waste materials such as SiO2 and Fe2O3 will enter solid residue named red mud.

At the same time, some SiO2 will reenter into the solution which is the main impurity of

sodium aluminate solution that needs to be purified. During desilication, CaO will be added

into sodium aluminate solution to get rid of most of SiO2. The main reactions are shown

below.

xNa2SiO3+2NaAl(OH)4 + aq Na2O Al2O3 x SiO2y H2O+ 2xNaOH + aq (2.10)

3Ca(OH)2 + 2 NaAl(OH)4 + aq 3CaO Al2O6H2O+ 2NaOH + aq (2.11)

3CaOAl2O6H2O + x Na2 SiO3+ aq 3CaOAl2OxSiO2yH2O+ 2xNaOH + aq (2.12)

12

Then, sodium aluminate solution will be decomposed by CO2 gas to produce Al2O33H2O

which will be changed to Al2O3 by roasting. The reactions are shown below.

2 Na Al(OH)4 + CO2 + aq Na2CO3 + Al2O33H2O (2.13)

Al2O33H2O Al2O3 + 3H2O (2.14)

In addition, red mud produced will be deposited in landfills after washed by hot water for 6

to 8 times to recover Al2O3 and Na2O.

2.1.3 Combined Process

Combined process, as its name shows, contains Bayer process and sintering process at the

same time. If there exist gibbsite bauxite (A/S7) and diaspore bauxite (A/S4)

simultaneously or bauxite whose quality is moderate (7A/S4) in a region, combined

process is better to deal with these bauxites in comparison to Bayer process or sintering

process separately. Generally, combined process contains three various flow charts including

parallel process, serial process, mixed process.

Parallel process is employed to deal with gibbsite bauxite and diaspore bauxite at the same

time. The flow chart for parallel process is displayed in Figure 2.3.

13

Figure 2.3 Flow chart of parallel process

As can be seen from Figure 2.3, there exist some advantages in parallel process. First, it can

make full use of different bauxite resources simultaneously in a region. Second, Na2CO3H2O

crystals produced from evaporation in Bayer process will be directly used in sintering

process so that causticization reaction is not necessary in Bayer process. In addition, some

organic impurities absorbed by Na2CO3H2O crystals will be burned in sintering process. So,

the negative effects caused by organic impurities can be eliminated in Bayer process. Third,

the loss of NaOH in Bayer process can be compensated by cheap Na2CO3. However, there

14

also exist some disadvantages in parallel process. The first one is that mixing green solution

will result in the increase of alkali circulation in Bayer process which will influence some

technical conditions. Second, the production capacity of Bayer process is dependant on that

of sintering process to some extent. Third, the flow chart of parallel process is a little

complicated.

Serial process is good at dealing with moderate bauxite whose A/S is located between 4 and

7. The flow chart of serial process is displayed in Figure 2.4.

Figure 2.4 Flow chart of serial process

In serial process, bauxite is firstly dealt with by Bayer process. After that, the red mud

produced in Bayer process will be sent to sintering process as a material to recover the

remnant Al2O3 and alkali. A part of green solution is sent to Bayer process to decompose.

The merits in serial process are apparent. First of all, the bauxite will be treated by two

15

processes, which will increase the overall alumina yield. Next, most product is from Bayer

process so that the production cost is low. But, the demerits of serial process cannot be

ignored. Firstly, the sintering temperature range of red mud from Bayer process is quite

limited. This makes the operation of sintering kiln very tough. Secondly, how to balance the

production of these two processes is a little difficult. Sometimes, as long as the production of

Bayer process is not stable, which will affect the operation of sintering process. Also, if the

amount of Fe2O3 in bauxite is not enough so that to compensate the loss of alkali in Bayer

process becomes very difficult.

Mixed process makes some improvements of serial process and is popular in China. The

flow chart of mixed process is displayed in Figure 2.5.

Figure 2.5 Flow chart of mixed process

16

In mixed process, the red mud produced in Bayer process will be mixed with certain amount

of diaspore bauxite (A/S is around 4 ) to increase the sintering temperature range. Thus, the

sintering process will produce enough green solution. Most of it will be decomposed in

sintering process by CO2, the rest is sent to Bayer process to compensate the loss of alkali

there. A big advantage of mixed process is that it is easy to balance the production of two

systems. In addition, it also consumes some low-grade bauxite. Its demerit is that the whole

flow chart is long and needs a lot of equipment.

2.2 Physical and Chemical Properties of Red Mud

Red mud widely differs in physical and chemical properties due to various bauxites and

processing methods.

2.2.1 Physical Properties of Red Mud

Red mud is a powder material whose color presents red or gray because of various contents

of iron oxide. Its specific gravity varies from 2840-2870 g/m3; average particle size is below

75 m; specific surface area is 64.09-186.9 m2/g ; plasticity index is 17.0-30.0; void ratio is

2.53-2.95 [4].

2.2.2 Chemical Properties of Red Mud

In red mudit mainly contains six kinds of oxides including CaO, Al2O3 , Na2O, Fe2O3, SiO2

and TiO2. In addition, it also contains some quantities of MgO, K2O and some trace elements

such as Zr, P, Sr, Cr, Ba, Mn [5]. Moreover, red mud is a highly alkaline waste material with

pH 10-12.5.

The main chemical compositions of several kinds of red mud from different countries are

displayed in Table 2.1.

17

Table 2.1 The main chemical composition of red mud (wt%)

CaO MgO Na2O K2O Fe2O3 TiO2 Al2O3 SiO2

USA 3.91 0.09 9.59 0.04 44.45 7.63 18.73 10.92

Canada

D1 10.07 0.18 7.35 33.98 5.86 17.37 12.21

Canada

D2 3.28 0.28 10.09 0.05 39.38 6.54 20.56 16.3

China 29.65 1.12 6.01 0.80 9.97 2.85 4.78 14.20

2.3 Negative Influence Caused by Red Mud

Red mud is deemed as a toxic industrial waste which needs treatment before discharge

because of alkalinity and chemical and mineralogical properties [6]. Until now, the main

means to deal with red mud are to store it in impoundments [7] or dump it in the sea

depending on local environment [8]. However, these means will result in a variety of

negative influences on environment including: 1) conventional disposal needs a lot of areas

to hold it; 2) some chemicals in red mud, such as sodium hydroxide and sodium carbonate,

will contaminate local ground water, soil and sea; 3) fine dust will form during storage which

will be absorbed by animals and human beings; 4) it will also cause adverse impacts on local

tourism due to esthetic and stigma problems [9]. So, to dump red mud in the sea directly is

not permitted in many countries because of environmental requirements. In addition, storing

red mud in impoundments also needs to meet a lot of prerequisites including land and

technology availability, climatic and geographic conditions, logistics and regulatory

requirements.

18

2.4 Means to Recycle Red Mud

Nowadays, how to recycle red mud has become a critical topic around the world. The last 40

years have witnessed more than 285 patent applications concerning ways for red mud

utilization [10]. However, little amount of red mud is consumed until now.

2.4.1 Utilization of Red Mud as Building Materials

Nowadays, red mud is used for materials such as cement, glass-ceramic, bricks and pigment.

2.4.1.1 Producing cement

Some papers focus on using red mud from Bayer process to produce cement. For instance,

Tsakiridis et al. [11] studied the properties of ordinary Portland cement (OPC) produced by

adding red mud. The result demonstrated that 3.5% (weight percent) addition of red mud did

not negatively affect the quality of the produced cement. Singh et al. [12, 13] described the

performance of three cements that were made from lime + red mud + fly ash; lime + red mud

+ bauxite; lime + red mud + bauxite + gypsum respectively. The strengths of the cements

made from lime + red mud + bauxite and lime + red mud + bauxite + gypsum were

comparable or better to OPC. Vangelatos et al. [14] mixed red mud that was dewatered by

means of a filter press with limestone and sandstone. They produced various clinkers by

adding 1, 3 and 5 wt% red mud respectively. The results shown that OPC they made

displayed good mechanical properties. Many years ago in China, some companies used red

mud from sintering process to produce OPC. Due to the high content of 2CaOSiO2 in this

red mud, it is suitable for producing cement. The addition of red mud in process for

producing cement has some advantages. First, it can lower the consumption of other raw

materials including limestone and iron powder. Second, it also can improve the yield of kiln

[15]. However, no matter what kind of red mud will be used to produce cement, there exist

several problems. First, the alkali in red mud will cause negative influence on the

performance of cement. In addition, the chemical compositions of red mud are quite difficult

19

to remain stable because of the fluctuation of alumina production. Moreover, the total energy

consumption is very high because of the large amount of water in red mud. Especially in

recent years, an increasing number of companies choose Dry Process to produce cement. So,

the amount of red mud added to cement has decreased significantly.

2.4.1.2 Producing glass-ceramic

Some researchers studied the way to produce glass-ceramic using such materials as fly ash

and blast furnace slag [16-18]. However, few papers were concerned with glass-ceramic

based on red mud. Because red mud usually contains a certain amount of CaO, Al2O3 and

SiO2, it is suitable to produce CaO-Al2O3-SiO2 glass-ceramics. Peng et al. [19] used red mud

from a company in China to produce two nano-crystal glass-ceramics through suitable

thermal treatment. Both glass-ceramics exhibited good mechanical properties. H.Z. Yang et

al. [20] made double-layer glass-ceramic/ceramic tile using bauxite tailings and red mud

whose amount reached 56% of the total weight. The product shown good macroscopic

appearance, microstructure, and mechanical properties. J.K. Yang et al. [21] studied the

feasibility of using red mud from sintering process and fly ash collected from electrostatic

precipitator in a power plant to produce glasses and glass-ceramic. His work demonstrated

that the total weight of red mud and fly ash could be up to 85%. In addition, according to the

research of Erol et al. [22], the addition of red mud did not affect the properties of glass-

ceramic made from fly ash and silica fume.

2.4.1.3 Producing bricks

In China, Yang and Xiao [23] employed red mud from sintering process to make unsintered

bricks. They found the optimum proportion of red mud brick (weight percent) could be 25-40%

red mud, 18-28% fly ash, 30-35% sand, 8-10% lime, 1-3% gypsum and about 1% Portland

cement. After evaluation, the bricks reached the Chinese criterion of first-class brick. Wu et

al. [24] made a variety of ceramic simple bricks containing various amounts of red mud. First,

they mixed red mud from sintering process with other materials such as fly ash and shale.

20

Then, the samples were fired at different temperatures. Next, properties of samples were

analyzed. They found material containing 70% (weight percent) red mud displayed the best

performance after firing at 1100C, which was capable of substituting clay bricks in

construction. Kavas [25] used boron waste and red mud from Turkey to make red mud bricks.

He added 5%, 10% and 15wt% boron waste respectively into the red mud to make six bricks.

Then, these bricks were fired at 700C, 800C, 900C separately. Next, samples were

analyzed in terms of mineralogical and mechanical properties. The result demonstrated that

the adulteration of 15% boron waste not only decreased firing temperature of red mud brick

but also increased mechanical performance of them.

2.4.1.4 Producing pigment

Pera et al. [26] used red mud from Bayer process to make pozzolanic pigment. According to

their research, 11% burnt red mud could be mixed with other materials to obtain the final

product.

Despite so many published papers related with using red mud to produce building materials,

there does not appear to be any large-scale production in this field. First, some pretreatment

steps of red mud including dewatering, drying, sintering are necessary. All these processes

will increase the energy consumption and cost of final product. Second, these new methods

are facing competition from existing processes. Third, some uncertainties with health risk

about red mud brick still exist. For instance, Somlai et al. [27] made a conclusion that the use

of red mud as building material was limited based on the study of 226

Ra and 232

Th activity in

red mud from Hungarian bauxite.

2.4.2 Recovery of Valuable Elements from Red Mud

How to extract useful materials from industrial waste is a popular topic because of the

exhaustion of natural resources. Red mud contains some valuable materials such as Al2O3,

Na2O, Fe2O3, and TiO2. In addition, it also contains some quantities of MgO, K2O and some

21

other trace elements such as Zr, P, Sr, Cr, Ba, Mn. So, it is important to study the

possibilities to recover these materials.

2.4.2.1 Recovery of Al2O3 and Na2O

Cresswell et al. [28] used sulphur dioxide to digest red mud in the presence of water. In this

step, soda, alumina and silica were dissolved in solution. Next step was to selectively

precipitate silica to produce the liquor containing soda and alumina. Then, the liquor was

causticized with lime to produce calcium sulphite, which was separated firstly and then

calcined to regenerate lime and sulphur dioxide for recycle. The purified sodium aluminate

was returned to Bayer process. However, this method has three demerits. First, it has

complicated flow chart, which will increase the investment of equipment and cost of product.

Second, the acid solution will cause corrosion of equipment. Third, a lot of sulphur dioxide

will be consumed due to the high alkalinity of red mud. The second way to recover Al2O3 and

Na2O of red mud from Bayer process is to send it to a sintering process. This is combined

process mentioned in 2.1.3. In 1982, Cresswell and Milne [29] described a hydrothermal

method to recover Al2O3 and Na2O of red mud from Bayer process. They mixed red mud

slurry with a strong caustic solution and lime. The mixture was heated to 290-310 C for 0.5-

2 hours under 4-9 MPa. The result was the recovery of typically 95% of soda and better than

70% of alumina into the solution phase. The crystallized sodium aluminate was dissolved

and returned to Bayer process after desilication. Zhong et al. [30] also studied the recovery

of Al2O3 and Na2O from red mud. They leached red mud with different amounts of 40-60%

NaOH solution and lime milk at 120-210 C for 3.5 hours. Then, the leaching liquor and

residue were separated by filtration. The residue was leached with 7% NaOH solution and

lime milk at 170C for 2 hours. The result shown that 87.8% Al2O3 and 96.4% Na2O in the

red mud could be recovered. The measures mentioned above have some disadvantages. First,

red mud must be treated under high temperatures and pressures, which means a lot of energy

is needed. Second, strong caustic solution is needed which will result in corrosion of

equipment.

22

2.4.2.2 Recovery of Fe2O3

Fe2O3 is another material in red mud that has attracted a number of researchers. Until now,

there are three means to recover iron from red mud: smelting, solid-state reduction and

magnetic separation. In smelting process, red mud is charged into blast furnace or rotary

furnace with a reducing agent. Then, iron oxide in red mud is reduced to generate pig iron

that can be used in steel production. Erag and Apak [31] mixed red mud from Turkey with

dolomite and coke. After pelletized and sintered at 1100C for 1 hour in a furnace, the

mixture was finally smelted at 1550C to produce pig iron and a slag that was used to

produce pigment-grade TiO2. However, smelting process has some demerits. High energy

and capital costs are associated with blast furnace (BF) operation because scale of operation

is high. Red mud must be mixed with some good-grade iron ore to maintain the minimum

grade of the charge to BF. In addition, titanium reacts with other constituents of the slag to

form multiple oxides that are difficult to leach [32]. In the solid-state reduction process, the

mud is mixed with a reducing agent or contacted with a reducing gas to produce metallic iron

[33]. The product can be an input either in a steel-making furnace or a conventional blast

furnace. Compared to smelting process, solid-state reduction process consumes less energy.

But, it also has some disadvantages. First, the metallic iron produced is quite difficult to

separate from the rest of product. So, it is easily polluted by gangue materials. Second, the

product is in a very fine form. Then, it needs agglomeration before transportation [32].

Magnetic separation is also an attractive way to recycle iron from red mud. According to the

study of Jamieson et al. [34], they employed wet high intensity magnetic separation

(WHIMS) to get a magnetic fraction containing around 56% (weight percent) Fe2O3 and a

non-magnetic fraction of less than 4% Fe2O3 (weight percent). In China, Shandong

Aluminum Company also used WHIMS to produce iron ore containing 56%-75.92% (weight

percent) Fe2O3. The recovery rate of Fe2O3 was 45% (weight percent) [35]. Another means is

to convert hematite or goethite in red mud to magnetite firstly, which is followed with

magnetic separation. Obviously, this process is more complex than magnetic separation

http://www.sciencedirect.com/science?_ob=RedirectURL&_method=outwardLink&_partnerName=27983&_origin=article&_zone=art_page&_linkType=scopusAuthorDocuments&_targetURL=http%3A%2F%2Fwww.scopus.com%2Fscopus%2Finward%2Fauthor.url%3FpartnerID%3D10%26%20

23

directly. But it also has some advantages. First, goethite is easier to separate magnetically

and needs less energy to reduce compared to hematite. So, the extra cost of reducing hematite

to magnetite can be compensated by the energy difference between reducing hematite and

magnetite to metallic iron [32]. Xiang et al. [36] employed low temperature reduction

(

24

Despite considerable work on extracting metals from red mud, no large-scale process has

been fulfilled [40]. For instance, combined process in China is facing a dilemma. Sintering

part in combined process can recover Al2O3 and Na2O present in red mud from Bayer process.

However, the high energy consumption increases the cost of product significantly. Magnetic

separation to recover iron from red mud seems popular in China now. But, the product

contains low Fe2O3 content which cant compete with virgin iron ore. In addition, some

methods employed acid to leach red mud. Apparently, a large amount of acid will be

consumed due to the high alkalinity of red mud and how to recycle the acid is also a problem.

Generally speaking, an integrated process for recovering various metals from red mud

simultaneously should decrease the waste output as much as possible and show technical and

economic viability in the future.

2.4.3 Utilization of Red Mud as Environmental Materials

In recent years, people also have found some applications of red mud in water treatment, gas

cleaning and soil amelioration due to its special properties such as high alkalinity and high

content of oxide component.

2.4.3.1 Water treatment

The first impurity in water that has drawn much attention is phosphate, which will result in

the algal and hydrophytic boom and rapid deterioration of water quality. Li et al. [41] studied

the effect of acidification and heat treatment of raw red mud and fly ash on the sorption of

phosphate in parallel experiments. First, red mud undergoing acidification and heat treatment

displayed better result in removal of phosphate than red mud without any treatment. Second,

result also displayed that red mud stirred with 0.25 mol/L HCl for 2 hours performed the

maximum removal of phosphate (99% removal of phosphate) compared to red mud treated

with 0.5, 1 and 2 mol/l HCl . The reason was that dilute HCl improved the surface areas of

the red mud, which enhanced the phosphate removal. In addition, another red mud sample

25

prepared by heating the red mud at 700 C for 2 h performed better phosphate removal (99%

removal of phosphate) than other samples heated at 200, 500, 600, 800, 900, 1000 C. This

could be explained by the effect of temperature on water removal and sintering. During

heating at 500 C, the surface area of red mud was enlarged initially because the expulsion of

water resulted in the development of porosity. After this, the phosphate removal process was

most efficient at 700 C and then became less efficient with the increase of temperature or

time. This was because the decomposition of some hydroxyl groups, calcite and the sintering

shrinkage of materials. According to their study, initial pH would also affect the sorption

capacity significantly. Zhu et al. [42] produced adsorbents based on red mud to remove

phosphate from aqueous solution. The results shown that phosphate removal efficiency was

97 % with optimal reaction conditions initial phosphate concentration 100 mg/ L, red mud

dosage 10 g/L, pH 2.0, respectively. The phosphate removal efficiency of the red mud

adsorbents decreased with the increase of pH. Yue et al. [43] studied the characteristics of red

mud granular adsorbents (RMGA) for phosphate removal from aqueous solution. RMGA

were produced with different mass ratio of three raw materials (red mud, bentonite and starch)

and sintered at various temperatures. Their performance was evaluated by adsorption

capacity on phosphate. The adsorption experiments were directed with the selected operating

parameters (stirring speed of 100 rpm, reaction time of 5 h, adsorbent dosage of 4 g/L, initial

pH of 3.00 and initial phosphate concentration of 50 mg/L) under certain aquatic

temperatures. The result displayed that red mud ratio and sintering temperatures affected the

characteristics of RMGA greatly, and that the optimum parameters, under which the largest

adsorption capacities could be achieved, varied with different aquatic temperatures. This

phenomenon was caused by the chemical reactions that occurred gradually in RMGA with

the increase of sintering temperature, which led to diversification of surface characteristics

and a decrease of the amount of effective components for adsorption, so the adsorption of

phosphate on RMGA was affected by these interactions.

26

Nitrate is also a pollutant material in water. Ho et al. [44] studied the removal of nitrogen and

phosphorus from sewage effluent by passage through sand amended with red mud. The result

demonstrated that the removal efficiency decreased with the drop of red mud content in the

sand. For example, an average of 24% nitrogen removal was obtained with 30% red mud, 9%

removal with 20% red mud and very little removal with 10% red mud. At the same time, the

corresponding phosphorus removals were 91%, 63% and 50% respectively. The reason was

that the drop of red mud content in the sand also decreased the adsorption capacity of

amended sand and increased the infiltration rate. engelolu et al. [45] employed the original

and activated red mud in batch adsorption technique to remove nitrate from aqueous solution.

They found the red mud activated using 20% HCl for 20 minutes was better than original red

mud. The nitrate saturation capacities of activated and original red mud were 5.858 mmol

nitrate/g dry wt. of red mud and 1.859 mmol nitrate/g dry wt. of red mud, respectively.

Another notable impurity in water is fluoride. The accumulation of fluoride in human body

will damage the function of bones and cause fractures. In addition, fluoride is also a

carcinogen [46]. engelolu et al. [47] studied removal of fluoride from aqueous solution by

using the original and activated red mud in a batch equilibration technique. Influence of pH,

adsorbent dose and contact time on the adsorption were investigated. The fluoride adsorption

capacity of activated form was found to be higher than that of the original form. The

maximum removal of fluoride ion was obtained at pH 5.5. Activated red mud performed

better than original red mud. About 82% fluoride could be removed by activated red mud

based on the experimental result.

Sometimes, wastewater contains some trace elements that are also a potential danger to

human beings and environment. Orecanin et al. [48] produced coagulant based on red mud

from an Alumina plant. First, the red mud was mixed with diluted sulphuric acid (30%

weight) with solid /liquid ratio 1:10. Then, the liquor was separated from the residual red

27

mud by centrifugation or filtration through the filter press. Next, the acid red mud (pH 0) was

neutralized with waste base to pH 8. The coagulant was in gel-like state and suitable for

heavy metals and turbidity removal from industrial wastewater. They employed the coagulant

to treat waste water generated from pressure washing of boats coated with antifouling paints

containing high amounts of Cu2+

, Zn2+

, Pb2+

, Ti4+

, and Cr3+

. The result shown that the

coagulant based on red mud could get rid of heavy metals successfully. For instance, the

concentrations of Cu2+

, Zn2+

, Pb2+

, and Cr3+

decreased from

4260 ng/g, 10900 ng/g, 5350

ng/g, 3970 ng/g to 81.4 ng/g, 43.5 ng/g, 31 ng/g, 290 ng/g respectively. Santona et al. [49]

investigated the heavy metal adsorption of red mud with and without acid treatment. The

results shown that adsorption capacity of the red mud without treatment for the three heavy

metals was ZnPb > Cd. Acid treatment with HCl decreased the red muds capacity to absorb

the heavy metals by 30%. They believed that acid treatments dissolved a portion of the

cancrinite which played a significant role in adsorbing heavy metals and also varied the

structure of the red mud. Altundoan et al. [50] found acid treatment could increase arsenic

adsorption capability of red mud. Batch adsorption studies have shown that activated red

mud in dosages ranging from 20 to 100 g/l can be used effectively to remove arsenic from

aqueous solutions. The process is pH dependent, the optimum range being 5.87.5 for As (III)

and 1.83.5 for As (V). The maximum removals are 96.52% for As (V) and 87.54% for As

(III) for solutions with a final pH of 7.25 and 3.50, respectively, for the initial arsenic

concentration of 133.5 mol/ l (10 mg/ l), activated red mud dosage of 20 g /l, contact time

of 60 min and temperature of 25 C. Gen-Fuhrman [51] investigated the arsenic adsorption

capability of seawater-neutralized red mud through acid treatment, combined acid and heat

treatment. The results shown that acid treatment increased the removal efficiency. The

activated red mud pretreated by acid and heat could remove about 100% arsenate at pH 4.5

when the initial arsenate concentration is 2 mg/l. In addition, no pollutants were released

after adsorption process.

28

Besides the pollutants mentioned above, some researchers also studied the possibilities of

using red mud to remove other pollutants such as dye stuff, organics and bacteria in

wastewater [52-54].

2.4.3.2 Gas cleaning

A lot of gases including CO2, H2S, SOx and NOx are produced from industries every day. All

these gases will cause negative influences on environment. Jones et al. [55] employed an

investigation on carbon dioxide capture using raw and neutralized red mud for carbonation. It

was found that hydroxide alkalinity consumption was 85% on raw red mud and 89% on red

mud after only 5 min of carbonation. Based on the experiments, they calculated that the

amount of carbon dioxide that could be removed annually at aluminum refineries in Australia

is potentially 15 million tons.

2.4.3.3 Soil amelioration

Feigl et al. [56] studied the effectiveness of red mud in stabilizing contaminated mine waste

and agricultural soil. The whole process lasted for two years. First, the result shown that a 5%

(by weight) red mud addition decreased the highly mobile, water-extractable amount of Cd

and Zn by 57% and 87%, respectively, in the agricultural soil and by 73% and 79%,

respectively, in the mine waste. Second, addition of red mud did not increase the toxicity of

the treated mine waste and soil and decreased the Cd and Zn uptake of Sinapis alba test

plants by 1829%. These results indicated that red mud applied to agricultural soil had no

negative effects on plants and soil microbes and decreased the amounts of mobile metals,

thus indicating its value for soil remediation. Liu and Luo [57] investigated effects of

granulated red mud addition on the fractionation of Pb and Zn in soil and plants growth.

Results shown the concentrations of Pb and Zn decreased by adding granulated red mud. 5%

granulated red mud addition decreased the concentrations of Pb and Zn by 41.03% and 26.55%

respectively. Moreover, they found 1% addition of granulated red mud addition could help

growth of leeks.

29

Although red mud has found some usage in environmental materials, there still some obvious

demerits. First, red mud requires pretreatment such as acidification or thermal treatment in

order to gain better performance. This will increase the cost of using red mud. Second, the

amount of red mud used in environmental materials is very limited.

2.5 Problems in Recycling Red Mud

Until now, a large number of papers have discussed various ways to recycle red mud.

However, few of them are commercially implemented. This can be explained by reasons

below [58].

1) The unique properties of red mud limit its recovery and utilization. For example, the high

water content and high alkalinity of red mud usually require pretreatment before it is used.

2) Red mud has found quite limited consumption in many aspects. For instance, the addition

amount of red mud in cement production decreases significantly due to the advance of

technology.

3) The safety of using red mud impedes its utilization. For example, some researchers worry

about radioactive damage caused by red mud. In addition, people still have a lot of work

to make sure whether recycling red mud will result in negative impacts on environment.

4) The product based on red mud cant compete with those from existing processes in terms

of quality. For instance, iron ore made by magnetic separation of red mud contains less

Fe2O3 compared to traditional product.

Thus, researchers should make effort to find an increasing number of measures to recover red

mud in the future. An ideal means to recover red mud should be both technically and

economically viable. At the same time, high-quality product should be produced by

consuming large amount of red mud and harmless to either environment or human beings.

30

2.6 References

[1] S. Wang, H.M. Ang, M.O.Tade. Novel application of red mud as coagulant, adsorbent and

catalyst for environmentally benign processes. Chemosphere. 72, 2008, pp. 1621-1653 .

[2] Y. Liu, C. Lin, Y. Wu. Characterization of red mud derived from a combined Bayer

process and bauxite calcinations method. Journal of Hazardous Materials. 146, 2007, pp.

255-261.

[3] R.K. Paramguru, P.C. Rath, V.N. Misra. Trends in red mud utilization- A review, Mineral

Processing and Extractive Metallurgy Review. 26:1, 2005, pp. 1-29.

[4] X.L. Nan, T.A. Zhan, Y. Liu, Z.H. Dou. Analysis of comprehensive utilization of red mud

in China, The Chinese Journal of Process Engineering. 10, 2010, pp. 264-270.

[5] Na zhang , X.M. Liu , H.H. Sun , L.T. Li . Evaluation of blends bauxite- calcinations-

method red mud with other industrial wastes as a cementitious material: Properties and

hydration characteristics, Journal of Hazardous Materials. 185, 2001, pp. 329-335.

[6] A.R. Hind, S.K. Bhargava, S.C. Grocott. The surface chemistry of Bayer process solids: a

review. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 146 (13), 1999,

pp. 359374.

[7] C. Brunori, C. Cremisini, C. Massanisso, P. Pinto, V. Torricelli. Reuse of a treated red

mud bauxite waste: studies on environmental compatibility. Journal of Hazardous Materials.

117 , 2005, pp. 5563.

[8] R.K. Paramguru, P.C. Rath, V.N. Misra. Trends in red mud utilization a review.

Mineral Processing & Extractive Metallurgy Review. 26 (1), 2004, pp. 129.

[9] Y.J. Liu, R. Naidu , H. Ming. Red mud as an amendment for pollutants in solid and liquid

phases. Geoderma. 163, 2011, pp. 112.

[10] M. Saternus. Bayerns method of Al2O3 production- possibilities of red mud disposal

and utilization. Solid State Phenomina. 176, 2011, pp. 11-12.

[11] P.E. Tsakiridis, S. Agatzini-Leonardou, P. Oustadakis. Red mud addition in the raw meal

for the production of Portland cement clinker. Journal of Hazardous Materials. 116, 2004, pp.

31

103-110.

[12] M. Singh, S.N. Upadhayay, P.M. Prasad. Preparation of special cements from red mud.

Waste Management.16, 1996, pp. 665-670.

[13] M. Singh, S.N. Upadhayay, P.M. Prasad. Preparation of iron rich cements using red mud.

Cement and Concrete Research. 27, 1997, pp. 1037-1046.

[14] I. Vangelatos, G.N. Angelopoulos, D. Boufounos. Utilization of ferroalumina as raw

material in the production of Ordinary Portland Cement. Journal of Hazardous Materials. 168,

2009, pp. 473478.

[15] J. Yu, Y.P. Jia, S.H. Zhu. Production of cement using waste from aluminum industry(red

mud). Cement Engineering. No.6, 1996, pp. 34-36.

[16] Y.J. Park, S.O. Moon, J. Heo. Crystalline phase control of glass ceramics obtained from

sewage sludge fly ash. Ceramics International. 29, 2003, pp. 223227.

[17] M. Alonso, E. Sainz, F.A. Lopez. Preparation of glass-forming materials from

granulated blast furnace slag. Metallurgical and Materials Transactions. B27, 1996, pp. 801

809.

[18] G.A. Khater. The use of Saudi slag production of glass-ceramic materials. Ceramics

International. 18 (1), 2002, pp. 5967.

[19] F. Peng, K.M. Liang, H. Shao, A.M. Hu. Nano-crystal glass-ceramics obtained by

crystallization of vitrified red mud. Chemosphere. 59, 2005, pp. 899903.

[20] H.Z. Yang, C.P. Chen, L.J. Pan, H.X. Lub, H.W. Sun, X. Hu. Preparation of double-layer

glass-ceramic/ceramic tile from bauxite tailings and red mud. Journal of the European

Ceramic Society. 29, 2009, pp. 18871894.

[21] J.K. Yang, D.D. Zhang, J. Hou , B.P. He , B. Xiao. Preparation of glass-ceramics from

red mud in the aluminum industries. Ceramics International. 34, 2008, pp. 125130.

[22] M. Erol , S. Kkbayrak, A. Ersoy-Meriboyu. Production of glass-ceramics obtained

from industrial wastes by means of controlled nucleation and crystallization. Chemical

Engineering Journal. 132, 2007, pp. 335343.

32

[23] J.K. Yang , B. Xiao. Development of unsintered construction materials from red mud

wastes produced in the sintering alumina process. Construction and Building Materials. 22,

2008, pp. 2299-2307.

[24] J.F. Wu, F.Y. Zhang, H.L. Li, B.Z. Fang, X.H. Wu. Preparation and reaction mechanism

of red mud based ceramic simple bricks. Journal of Wuhan University of technology-Materal

Science. 2010, pp. 1001-1005.

[25] T. Kavas. Use of boron waste as a fluxing agent in production of red mud brick.

Building and Environment. 41, 2006, pp. 1779-1783.

[26] J. Pera, R. Boumaza, J. Ambroise. Development of a pozzolanic pigment from red mud.

Cement and Concrete Research. 27, 1997, pp. 1513-1522.

[27] J. Somlai, V. Jobbagy, J. Kovacs, S. Tarjan, T. Kovacs. Radiological aspects of the usability

of red mud as building material additive. Journal of Hazardous Materials. 150 (3), 2008, pp.

541545.

[28] P.J. Cresswell, I.L. Grayson, A.M. Smith. Recovery of sodium aluminate from Bayer

process red mud. US Patent 4668485 , 1987.

[29] P.J. Cresswell, D.J. Milne. Production of alumina. US Patent 4483830, 1984.

[30] L. Zhong, Y.F. Zhang, Y. Zhang. Extraction of alumina and sodium oxide from red mud

by a mild hydro-chemical process. Journal of Hazardous Materials. 172, 2009, pp. 1629-

1634.

[31] E. Erag, R. Apak. Furnace smelting and extractive metallurgy of red mud: Recovery

of TiO2, Al2O3 and pig iron. Journal of Chemical Technology and Biotechnology. 1997, pp.

241-246.

[32] R.K. Paramguru, C. Rath , V.N. Misra. Trends in red mud utilization- A Review. Mineral

Processing and Extractive Metallurgy Review. 26:1, 2004, pp. 1-29.

[33] P. Liu, Z. Huo, S. Gu. Magnetic dressing iron mineral concentrate from Bayer red mud.

Light Metals. 1995, pp. 149-153.

[34] E. Jamiesona, A. Jonesa, D. Coolinga, N. Stockton. Magnetic separation of red sand to

33

produce value. Minerals Engineering . 19, Issue 15, 2006, pp. 1603-1605.

[35] Technical report of Shandong Aluminum Company. 2008.

[36] Q. Xiang, X. Liang, M.E. Schlesinger, J.L. Watson. Low temperature reduction of ferric

iron in red mud. Light Metals. 2001, pp. 157-162.

[37] E. ayan, M. Bayramolu. Statistical modeling of sulphuric acid leaching of TiO2,

Fe2O3 and Al2O3 from red mud. Process Safety and Environmental Protection. 79, Issue 5,

2001, pp. 291-296.

[38] M. Ochsenkuhn-Petropoulou, K. Hatzilyberis, L. Mendrinos, C. Salmas. Pilot plant

investigation of the leaching process for the recovery of scandium from red mud. Industry

and Engineering Chemistry Research. 41 (23), 2002, pp. 57945801.

[39] H.L. Zhou, D.Y. Li, Y.J. Tian, Y.F. Chen. Extraction of scandium from red mud by

modified activated carbon and kinetics study. RARE METALS. 27(3), 2008, pp. 223-227.

[40] C. Klauber , M. Grfe, G. Power. Bauxite residue issues: II. options for residue

utilization. Hydrometallurgy. 108 , 2011, pp. 11-32.

[41] Y.Z. Li, C.J. Liu, Z.K. Luan, X.J. Peng. Phosphate removal from aqueous solutions

using raw and activated red mud and fly ash. Journal of Hazardous Materials. 137(1), 2006,

pp. 374-383.

[42] X.F. Zhu, H.Y. Liu, P.H. Shi, J.F. Wu, Y.F. Guo. Removal of phosphate from aqueous

solution by using red mud. Advanced Materials Research. 291-294, 2011, pp. 1804-1807.

[43] Q.Y. Yue, Y.Q. Zhao, Q. Li, W.H. Li, B.Y. Gao, S.X. Han, Y.F. Qi, H. Yu. Research on

the characteristics of red mud granular adsorbents (RMGA) for phosphate removal. Journal

of Hazardous Materials. 176, 2010, pp. 741748.

[44] G.E. Ho, K. Mathew, R.A. Gibbs. Nitrogen and phosphorus removal from sewage

effluent in amended sand columns. Water Research. 26, 1992, pp. 295300.

[45] Y. Cengelolu, A. Tor, M. Ersz , G. Arslan. Removal of nitrate from aqueous solution

by using red mud. Separation and Purification Technology. 51, 2006, pp. 374378.

[46] B.D. Turner, P. Binning, S.L.S. Stipp. Fluoride removal by calcite: evidence for fluorite

34

precipitation and surface adsorption. Environmental Science and Technology. 39, 2005, pp.

95619568.

[47] Y. engelolu, E. Kir, M. Ersz. Removal of fluoride from aqueous solution by using

red mud. Separation and Purification Technology. 28 , 2002, pp. 8186.

[48] V. Orecanin, K. Nad, V. Valkovic, N. Mikulic, O. Metrovic. Red mud and waste base:

Raw materials for coagulant production. Journal of Trace and Microprobe Techniques. 19:3,

2001, pp. 419-428.

[49] L. Santona, P. Castaldi, P. Melis. Evaluation of the interaction mechanisms between red

muds and heavy metals. Journal of Hazardous Materials. 136, 2006, pp. 324329.

[50] H.S. Altundoan, S. Altundoan, F. Tmen, M. Bildik. Arsenic adsorption from aqueous

solutions by activated red mud. Waste Management. 22, 2002, pp. 357363.

[51] H. Gen-Fuhrman, J.C. Tjell, D. McConchie. Increasing the arsenate adsorption

capacity of neutralized red mud (Bauxsol). Journal of Colloid and Interface Science. 271,

2004, pp. 313320.

[52] C. Namasivayam, D.J.S.E. Arasi, Removal of Congo red from wastewater by adsorption

onto waste red mud. Chemosphere. 34, 1997, pp. 401417.

[53] A. Tor, Y. engelolu, M.E. Aydin, M. Ersz. Removal of phenol from aqueous phase

by using neutralized red mud. Journal of Colloids and Interface Science. 300, 2006, pp. 498

503.

[54] G.E. Ho, R.A. Gibbs, K. Mathew. Bacteria and virus removal from secondary effluent in

sand and red mud columns. Water Science and Technology. 23, 1991, pp. 261270.

[55] G. Jones, G. Joshi, M. Clark, D. McConchie. Carbon capture and the aluminum industry:

preliminary studies. Environmental Chemistry. 3, 2006, pp. 297303.

[56] V. Feigl, A. Anton , N. Uzigner , K. Gruiz. Red mud as a chemical stabilizer for soil

contaminated with toxic metals. Water, Air and Soil Pollution. 2011, pp. 1-11.

[57] Y. Liu , L. Luo. Effects of granulated red mud on Lead-Zinc waste soil remediation and

leeks growth. International Conference on Computer Distributed Control and Intelligent

35

Environmental Monitoring. Changsha, Hunan China. 2011, pp. 1202-1206.

[58] W.C. Liu, J.K. Yang, B. Xiao. Review on treatment and utilization of bauxite residues in

China. International Journal of Mineral Processing. 93, 2009, pp. 220231.

36

CHAPTER THREE: EXPERIMENTAL ASPECTS

3.1 Materials

3.1.1 Solid Materials

Three kinds of red mud S1, B1and B2, from sintering process and Bayer process

respectively are used in experiments. Some other chemicals were used to make various

fluxes. Among these chemicals, the purities of Al2O3, CaO, SiO2, Fe2O3, Na2CO3 are 99.8%,

99.95%, 99.8%, 99% and 99.5% respectively. Pure nickel and aluminum (purity greater than

99.9%) and AISI 1117 low carbon steel whose chemical composition is shown in Table 3.1

were mixed to form an alloy. Another type of alloy was the nickel-based alloy whose

chemical composition is shown in Table 3.2. The compositions of stainless steel substrates

are shown in Table 3.3.

Table 3.1 The chemical composition of AISI 1117 low carbon steel

Element C Mn P S

Weight(%) 0.14-0.20 1.0-1.3 0.04 0.08-0.13

Table 3.2 The chemical composition of nickel-based alloy

Element chemical composition (%)

C S Al As Ca Cr Fe Ni P Si Balance

Weight(%) 0.42 0.39 0.08 0.6 0.01 0.15 9.03 50.2 9.1 2.54 27.48

37

Table 3.3 The chemical composition of stainless steel substrates

Stainless

Steel

chemical composition (%)

Cr Ni C Mg Cu Mo Si S P other

1 15-17.5 3-5 0-0.07 0-1 3-5 0 0-1 0-0.03 0-0.04

Cb and Ti

0.15-0.45

2 17-19 8-10 0-0.15 0-2 0-1 0-1 0-1 0-0.15 0-0.2 0

3 16-18 0-0.75 0.95-1.2 0-1 0-0.5 0-0.75 0-1 0-0.03 0-0.04 0

4 16-18 10-15 0-0.08 0-2 0-0.75 0-3 0-1 0.03 0-0.045 N 0-0.1

5 13.5-16 24-27 0-0.08 0-2 0 1-1.5 0-1 0-0.025 0-0.025

Al 0.15 ;

Ti 0-2.35

The size, roughness and thickness of substrates were about 2.54 x 2.54 cm, 0.3m and 5mm

respectively. Before use, substrates were degreased in acetone and ultrasonically cleaned. For

corrosion experiments, crucibles made from refractory bricks were used. Their composition

was analyzed by EDX and is shown in Figure 3.1, which shows the main chemical materials

in refractory bricks are MgO and Cr2O3.

Figure 3.1 EDX analysis of refractory brick

38

3.1.2 Gas Material

The purity of Argon gas used for the experiments was 99.5%.

3.1.3 Liquid Material

Acetone was used to clean the substrates to get rid of grease on the surface.

3.2 Scanning Electron Microscopy (SEM)

3.2.1 Basic Principles of SEM

Scanning Electron Microscopy (SEM) is widely employed to reveal information of

samples such as texture, chemical composition, and crystalline structure and orientation of

materials combined with EDX (Energy-dispersive X-ray spectroscopy). SEM uses a beam

of accelerated electrons to scan the surface of a sample. Through the interactions between

sample and electrons, signals including secondary electrons, visible light, characteristic X-

rays, backscattered electrons, and diffracted backscattered electrons will be generated. By

using various detectors, a variety of information about the sample can be produced. For

instance, secondary electrons are mainly employed to display morphology and topography

of the sample; characteristic x-rays can be used to determine chemical composition. The

SEM system contains six parts including electron source (gun), electron lens, sample stage,

detectors, display/data output devices, infrastructures that consists of vacuum system,

cooling system and power system. A typical SEM system is shown in Figure 3.2.

http://serc.carleton.edu/research_education/geochemsheets/electroninteractions.html

39

Figure 3.2 Schematic diagram of a Scanning Electron Microscope [1]

3.2.2 Sample Preparation

Samples for SEM analysis were obtained from the corrosion experiments. First, crucibles

used for these experiments would be cut in half. Then, small pieces of samples around the

slag line were taken from each crucible. Next, each sample was put into a mould, which was

charged with resin and hardener in the ratio of 2 to 1. After several hours, the samples were

fastened in hard resin cylinders. The samples were dried and cleaned and the surface coated

with a thin carbon film.

3.3 X-ray Diffraction (XRD)

3.3.1 Basic Principles of XRD

XRD is a non-destructive analytical technique to characterize crystalline materials. When a

beam of X-rays whose wavelength is known passes through a crystalline sample to be

examined, the interaction of the incident rays with the sample results in constructive

http://en.wikipedia.org/wiki/Thermogravimetric_Analysis#cite_note-0#cite_note-0

40

interference when conditions satisfy Bragg's Law. This law relates the wavelength of

electromagnetic radiation to the diffraction angle and the lattice spacing in a crystalline

sample. These diffracted X-rays are then detected, processed and counted. By scanning the

sample through a variety of 2 angles, all possible diffraction directions of the lattice should

be attained due to the random orientation of the powdered material. The material can be

identified by changing the diffraction peaks to d-spacings in that each crystalline material has

a set of unique d-spacings, which is achieved through comparing d-spacings with standard

reference patterns. The principle of this technique is based on Bragg's Law (n = 2 d sin),

which could be explained by Figure 3.3.

Figure 3.3 Bragg's Law [2]

http://serc.carleton.edu/research_education/geochemsheets/BraggsLaw.htmlhttp://serc.carleton.edu/research_education/geochemsheets/BraggsLaw.htmlhttp://serc.carleton.edu/research_education/geochemsheets/BraggsLaw.htmlhttp://en.wikipedia.org/wiki/Thermogravimetric_Analysis#cite_note-0#cite_note-0

41

When the top beam strikes the top layer at atom z, the second beam continues to the next

layer where it is scattered by atom B. The second beam must travel the extra distance AB +

BC, which must be an integral (n) multiple of the wavelength () since the phases of the two

beams remain the same. So,

n = AB +BC (3.1).

In triangle ABz, we can relate d and to the distance (AB + BC).

AB = d sin (3.2).

Because AB = BC, we have,

n = 2 d sin (3.3)

and Bragg's Law has been derived. Where n is an integer is the wavelength of X-raysd

is the interplanar spacing and is the angle of incident X-rays.


Each sample is ground to pass a 270 mesh sieve. After that, about 0.4 g sample is charge into

a glass holder cavity. Next, sample is packed tightly and extra material removed using a glass

slide. A Philips PW 1830 X-ray diffractometer is employed to scan samples with CuK

radiation at 40 kV and 40 mA. The range of 2 is changed from 20 to 65 degree and software

is used to analyze the results.

3.4 X-ray Fluorescence (XRF)

3.4.1 Basic Principles of XRF

When a sample is illuminated by an intense X-ray beam, atoms in the sample will gain

energy from the incident X-ray by ionizing so that electrons located on lower energy orbital

42

will transfer to higher energy orbital. The positions left by these electrons will be occupied

by electrons from higher energy orbital. During this process, energy is released in the form of

characteristic X-rays because of the energy difference between the inner electron orbital and

the outer one. Since each element has unique atomic structure, the change of intensity of

characteristic X-rays emitted can permit determination of the chemical composition of a

sample. The intensity of the energy measured by detectors in an X-ray fluorescence (XRF)

spectrometer is proportional to the amount of the element in the sample. The exact value of

this proportionality for each element is derived by comparison with standards whose

composition is known from prior analyses by other techniques.


Each sample is ground to pass 270 mesh sieve. During grinding, a device called desk mill is

employed. Boric acid is used as a binder when the sample is compressed with a pressure of 5

tons per square inch. Samples were analyzed using a Philips 2404 sequential X-ray

fluorescence spectrometer. Philips software was used to scan the entire X-ray spectrum and

provide the final data results.

3.5 Thermogravimetric Analysis (TGA or TG)

3.5.1 Basic Principles of TGA

Thermogravimetric Analysis is a test to study changes in weight in relation to change in

temperature. TGA has found a variety of uses in describing characteristics of materials such

as water of crystallisation, degradation of materials, reaction kinetics, oxidation and

reduction. The equipment has a high-precision balance with a pan (generally platinum) to

hold the sample. Sometimes a quartz crystal microbalance is used for measuring smaller

samples on the order of a microgram (versus milligram with conventional TGA).[3] A

http://en.wikipedia.org/wiki/Weighthttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Thermogravimetric_Analysis#cite_note-0#cite_note-0

43

thermocouple is employed to accurately monitor the temperature. The temperature in many

testing methods routinely reaches 1000C or greater. The atmosphere may be controlled with

an inert gas to prevent oxidation or other undesired reactions. The whole process can be

controlled by a computer.


Firstly, 40 mg sample is charged into a platinum crucible. The sample holder is placed into a

high temperature oven. With the increase of temperature, changes of sample weight are

measured continuously. Heating rate was 10 C per minute; the temperature varied from

25C to 1100C; atmosphere for the test was dry air.

3.6 Desulphurization Experiments

3.6.1 Experimental Equipment

The experimental system used for desulphurization studies included a 30KW high frequency

induction furnace, crucibles made of either graphite or magnesium oxide, and two Pt/Pt -10%

Rh thermocouples. A diagram demonstrating this experimental system is shown in Figure 3.4.

Figure 3.4 Schematic diagram of desulphurization experiment

http://en.wikipedia.org/wiki/Thermocouplehttp://en.wikipedia.org/wiki/Inert_gas

44


Before use, red mud and CaO are dehydrated by heating at 600 and 200 respectively.

The flux powder was pressed to a small cylinder before use so that it was convenient to put it

into the crucible at high temperatures. The desulphurization schedule is shown in Table 3.4.

Table 3.4 The schedule of desulphurization experiment

Exp Flux Ni content(wt%) Temperature(K)

1 45.5gS1+4.5gCaO+10%Al 0 1673

2 45.5gS1+4.5gCaO+10%Al 10 1673

3 45.5gS1+4.5gCaO+10%Al 20 1673

4 45.5gS1+4.5gCaO+10%Al 30 1673

5 45.5gS1+4.5gCaO+10%Al 40 1673

6 45.5gS1+4.5gCaO+10%Al 50 1673

7 40g B1 + 10% Al 10 1673

8 40g B1 + 5% Al 10 1573

9 40g B1 + 5% Al 10 1673

10 40g B1 + 5% Al 10 1773

11 40g B1 + 0% Al 10 1673

12 40g B1 + 8% Al 10 1673

13 30g

50 1673 CaO:Al2O3:SiO2=50:40:10

14

30g

50 1673 CaO:Al2O3:SiO2=50:40:10

20% Fe2O3

15

30g

50 1673 CaO:Al2O3:SiO2=50:40:10

40% Fe2O3

16 45.5gS1+4.5gCaO+10%Al

10 1673 C: 4%

17 45.5gS1+4.5gCaO+10%Al

10 1673 C: 2.57%

45

3.6.3 Experimental Procedure

For every experiment, certain amount of alloy is placed in the reaction crucible, which is

placed in the induction furnace. The main function of two thermocouples was to monitor the

temperatures of hot metal bath and graphite lining crucible. The temperature difference

between these two thermocouples was 100C. When the hot metal temperature reached the

required value, a suction tube that was made of quartz was used to extract the first metal

sample which was to be analyzed to obtain the initial sulphur level. After the first sample, the

flux was charged into the reaction crucible and this was taken as