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SCHOOL OF MATERIALS AND MINERAL RESOURCES ENGINEERING UNIVERSITI SAINS MALAYSIA

CARBOTHERMAL REDUCTION OF RUTILE By

AINI NAZIHAH BINTI JIMAT Supervisor: Dr. Norlia Binti Baharun

Co-Supervisor: Dr. Sheikh Abdul Rezan Bin Sheikh Abdul Hamid

Dissertation submitted in partial fulfillment of the requirements for the degree of Bachelor of Engineering with Honours

(Mineral Resources Engineering) Universiti Sains Malaysia

JUNE 2016

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DECLARATION

I hereby declare that I have conducted, completed the research work and written the dissertation “Carbothermal Reduction of Rutile”. I also declare that it has not been previously submitted for the award of any degree or diploma or diploma or other similar

title of this for any other examining body or University.

Name of Student: Aini Nazihah binti Jimat Signature:

Date:

Witness by

Supervisor: Dr. Norlia binti Baharun Signature:

Date:

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ACKNOWLEDGEMENT

First of all, I would like to express the deepest gratitude to Allah S.W.T for giving me such a great chance of handling a final year project and completing my thesis during this year. I will remember all the things that happened during my thesis until my end life and also took it as an experience in my life. I wish to thank Universiti Sains Malaysia (USM) and Ministry of Education (MOE) of Malaysia for supporting this work. This work was supporting by three grants which is from my supervisor, co-supervisor and Dr.

Muhamad Fared Murshed, lecturer in Water and Environmental Engineering from School of Civil Engineering.

Next, this project would not be a success without the motivation and supervision from my supervisor and co-supervisor, Dr. Norlia Baharun and Dr. Sheikh Abdul Rezan bin Sheikh Abdul Hamid who helped me a lot. My sincere gratitude goes to both of them for their great support and accepted all my weakness during complete this work. A good co-operation goes to Prof Ahmad Fauzi for giving permission on using Lenton furnace.

And also for all the technician of PPKBSM especially Mr Sharul, Mr Safik, Mrs Mahani, Mrs Haslina, Mr Rashid, Mr Zaini, Mr Khairi, Mr Junaidi and Mr Kemuridan.

Lastly, I would like to thank with my family especially my parents, Mr Jimat bin Sidek and Mrs Kamisah binti Alip, siblings and friends for giving me support mentally and emotionally. Especially for Shaik Abdul Rahman, Najwa Ibrahim, Hafizah Kamaruzaman, Nur Fatehah Amiera, Eltefat Ahmadi, Nur Atiqqah, Law and Kin Choong. They had listening to my problems and trying to reduce my stress. Without them, I would not have the strength to complete my thesis. Thank you very much for help and support.

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TABLE OF CONTENTS

PAGE

TITLE OF THESIS i

DECLARATION ii

ACKNOWLEDGEMENTS iii

TABLE OF CONTENTS iv

LIST OF TABLES ix

LIST OF FIGURES xi

LIST OF SYMBOLS AND ABBREVIATIONS xiv

ABSTRAK xvii

ABSTRACT xviii

CHAPTER 1 : INTRODUCTION

1.1 Introduction 1

1.2 Application of Titanium Metal and Titania Pigment 2

1.3 Early Method of Processing Rutile 3

1.4 The Becher Process 7

1.5 Problem Statement 8

1.6 Objectives 10

1.7 Thesis Outline 10

CHAPTER 2 : LITERATURE REVIEW

2.1 Introduction 12

2.2 Carbothermal Reduction of Rutile 13

2.3 Reaction Mechanism of Carbothermal Reduction 14

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2.4 Phase Development in Carbothermal Reduction 17

2.5 Effect of Raw Material Characteristic on the Carbothermal Reduction of TiO2

18

2.6 Reducing Agent 19

2.6.1 Polystyrene (PS) 19

2.6.2 Mukah Coal 20

2.7 The Aeration Step of the Becher Process 21

2.8 Application of Catalyst for Accelerating the Aeration Step 24

2.9 Effect of Experimental Parameter 27

2.9.1 Effect of Raw Material Characteristic on the Carbothermal Reduction of TiO2

27

2.9.2 Effect of Gas Atmosphere on Carbothermal Reduction 27 2.9.3 Effect of Temperature on the Rate of Reduction 28

2.9.4 Effect of Temperature on Iron Removal 29

2.9.5 Effect of Dissolved Oxygen and pH on Iron Removal 32

2.10 Full Factorial Design of Experiment (DOE) 32

CHAPTER 3 : MATERIALS AND RESEARCH METHODOLOGY

3.1 Introduction 34

3.2 Raw Materials 34

3.2.1 Rutile 35

3.2.2 Mukah Coal 36

3.2.3 Polystyrene (PS) 37

3.2.4 Other Materials 38

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3.3 Flowchart of Research Work 39

3.4 Raw Material Preparation 40

3.5 Raw Material Characterization 41

3.6 Sample Mixing 41

3.7 Oxidation Test 43

3.8 Thermodynamic Studies 43

3.9 Carbothermal Reduction 44

3.9.1 Variables for Carbothermal Reduction 46

3.9.2 Extent of Reduction (XO) 47

3.9.3 Extent of Nitridation (XN) 48

3.10 Aeration Leaching (NH4Cl solution) 49

3.11 Leaching (H2SO4 solution) 52

3.12 Characterization Methods 54

3.12.1 X-ray Diffraction (XRD) 55

3.12.2 X-ray Flourescent (XRF) 57

3.12.3 Thermal Gravimetric Analysis (TGA) 57

3.12.4 Scanning Electron Microscopy (SEM) / Energy Dispersive X- ray Spectrometry (EDX) Analysis

59

3.12.5 Inductively Coupled Plasma (ICP) Technique 60

3.12.6 CHNS Analysis 60

3.13 Full Factorial Design of Experiment (DOE) of Aeration Leaching 61 CHAPTER 4 : RESULTS AND DISCUSSION

4.1 Introduction 63

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4.2 Thermodynamic Studies on Rutile Sample 63

4.2.1 Gibbs Free Energy 64

4.2.2 Equilibrium Composition and TPP Diagram 66

4.2.3 Eh-pH or Pourbaix Diagram 68

4.3 Characterization Analysis 69

4.3.1 X-ray Flourescence (XRF) Analysis 70

4.3.1.1 Raw Material 70

4.3.2 X-ray Diffraction (XRD) Analysis 71

4.3.2.1 Raw Material 71

4.3.2.2 Carbothermal Reduction and Nitridation of Malaysian Rutile Ore

73

4.3.2.3 Aeration Leaching (NH4Cl) 74

4.3.2.4 Leaching Process by using H2SO4 solution 77 4.3.3 Thermal Gravimetric Analysis (TGA) of Carbon Sources 77 4.3.4 Scanning Electron Microscope (SEM)/ Energy-dispersive X-

ray Spectrometry (EDX) Analysis

79

4.3.4.1 Raw Material 79

4.3.4.2 Carbothermal Reduction and Nitridation of Malaysian Rutile Ore

80

4.3.4.3 Aeration Leaching (NH4Cl solution) 84 4.3.4.4 Aeration Leaching (H2SO4 solution) 86 4.3.5 Inductively Coupled Plasma (ICP) Technique 86 4.3.5.1 Percentage of Iron Extracted (XFe) by using NH4Cl 86

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viii solution

4.3.5.2 Percentage of Iron Extracted (XFe) by using H2SO4

solution

88

4.4 Oxidation Test 89

4.5 Other Techniques used for Calculation 90

4.5.1 Extent of Reduction (XO) for CTRN 90

4.5.2 Extent of Nitridation (XN) for CTRN 91

4.5.3 Full Factorial Design of Experiment (DOE) of Leaching Conditions

94

4.5.4 Statistical Analysis of Response for Leached Sample 96 CHAPTER 5 : CONCLUSION AND RECOMMENDATION

5.1 Conclusion 104

5.2 Recommendation for Future Work 105

REFERENCES 106

APPENDICES 110

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LIST OF TABLES

Table 3.1 Properties of rutile ores 35

Table 3.2 Proximate analysis of Mukah coal 36

Table 3.3 Ultimate analysis of Mukah coal 37

Table 3.4 General properties of polystyrene plastic 38

Table 3.5 CHNS analysis for 2 types of carbon sources 42 Table 3.6 The ranges of process variable for carbothermal reduction 47 Table 3.7 Range of process variables of aeration leaching 52 Table 3.8 The parameter used in leaching with sulphuric acid solution 53 Table 4.1 The Gibbs free energy function and the equilibrium

temperature

64

Table 4.2 XRF analysis of raw rutile 70

Table 4.3 ICSD numbers for phases on XRD analysis 72

Table 4.4 Fe concentration and % Fe extracted 87

Table 4.5 Fe concentration from ICP and percentage of Fe extracted 88 Table 4.6 Weight loss of three samples after oxidation test 89 Table 4.7 Extent of reduction calculated from weight loss method 90

Table 4.8 CHNS results of nitrided rutile 91

Table 4.9 Extent of nitridation calculated from CHNS analysis 92 Table 4.10 Summary of Rwp, GoF, phases, XN andXO of three samples. 94

Table 4.11 DOE of aeration leaching 95

Table 4.12 High, low and control parameter conditions for DOE 96

Table 4.13 Standard deviation and R-squared value. 96

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Table 4.14 Summary of Fe extracted (ppm) and the factors. 97

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LIST OF FIGURES

Figure 1.1 Leaching of titanium slag for pigment production 4 Figure 1.2 The early method for treating ilmenite for pigment production 6 Figure 1.3 Production of synthetic rutile from high grade ilmenite 7 Figure 2.1 Schematic of reaction mechanism of carbothermal reduction for

TiO2

15

Figure 2.2 Calculated predominance area diagram for stable phases at 1573 K in Ti-C-N system

16

Figure 2.3 Plot of time versus % iron removal during rusting 25 Figure 2.4 Effect of concentration of AQ-2,6 or AQ-2 on iron removal during

aeration of reduced ilmenite in 2% w/v NH4Cl

26

Figure 2.5 Arrhenius plots 31

Figure 3.1 Overall process flowchart of the experimental procedure 39 Figure 3.2 Horizontal tube furnace for carbothermal reduction process 45

Figure 3.3 Isothermal heating profile 46

Figure 3.4 Schematic diagram for aeration leaching 50

Figure 3.5 Mechanism for leaching with sulfuric acid solution 53

Figure 3.6 Summary of characterization methods 54

Figure 3.7 Heating profile of TGA 58

Figure 4.1 Plot of G° versus temperature 65

Figure 4.2 Equilibrium composition of TiN formation 66

Figure 4.3 TPP or predominance diagram for Ti-O-N system 67 Figure 4.4 Eh-pH diagram for Fe-S-H2O system at 70 68

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Figure 4.5 Eh-pH diagram for Fe-Cl-H2O system at 70 69

Figure 4.6 XRD plots of raw rutile sample 72

Figure 4.7 The differences of three samples and raw rutile after carbothermal reduction

74

Figure 4.8 XRD plots for sample Run 2 ( >32 m) 75

Figure 4.9 XRD plots for sample Run 8 ( >32 m) 75

Figure 4.10 XRD plots for sample of Run 9 ( >32 m) 76 Figure 4.11 XRD plots for sample after leaching with H2SO4 solution 77

Figure 4.12 TGA curve for PS 78

Figure 4.13 TGA curve of Mukah coal 79

Figure 4.14 SEM photomicrograph of raw rutile powder 80

Figure 4.15 SEM image of PS85C15 after carbothermal reduction 81 Figure 4.16 SEM image of PS90C10 after the carbothermal reduction 81 Figure 4.17 SEM image of PS95C05 after the carbothermal reduction 82 Figure 4.18 SEM/EDX analysis for sample of PS85C15 showing the Ti as the

major peak

82

Figure 4.19 SEM/EDX analysis for sample of PS90C10 showing the Ti as the major peak

83

Figure 4.20 SEM/EDX analysis for sample of PS99C05 showing the Ti as the major peak

83

Figure 4.21 SEM/EDX analysis for sample of Run 8 (>32 m) showing the Ti as the major peak and Fe is the least element

84

Figure 4.22 SEM/EDX analysis for sample of Run 2 (>32 m) showing the Ti 85

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as the major peak and Fe is the least element

Figure 4.23 SEM/EDX analysis for sample of Run 9 (>32 m) showing the Ti as the major peak and Fe is the least element

85

Figure 4.24 SEM/EDX analysis for sample of aeration leaching with H2SO4 solution

86

Figure 4.25 Predicted vs. Actual graph of Fe extracted (ppm) 99

Figure 4.26 Pertubation plot for Fe extracted (ppm) 100

Figure 4.27 Cube plot of Fe extracted (ppm) 101

Figure 4.28 3D surface plot of Fe extracted (ppm) 102

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LIST OF SYMBOLS AND ABBREVIATIONS

SYMBOLS

Degree Celcius Degree Fahrenheit

% Percent m Micrometer

m2 Meter cube cm2 Centimeter cube

G Gram

In Inches kcal Kilo calories

λ Wavelength of the incident X-rays N “order” of reflection

d Interplanar spacing of the crystal Angle of incidence

kN Kilo Newton L Liter

min Minute at time, t Wf Final weight of sample Wi Initial weight of sample Oi Initial oxygen wt%

K Kelvin

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xv atm Atmosphere

G Gibb free energy

J Joule

Wt Weight

H Hour

XO Extent of reduction XN Extent of nitridation ppm Part per million

- Lowest level + Highest level Rp Profile factor

Rwp Weight profile factor GoF Goodness of fit

A Catalyst wt%

B PS to Mukah coal ratio C Leaching time

ABBREVIATIONS

XRF X-ray Fluorescence XRD X-ray Diffraction

CHNS Carbon Hydrogen Nitrogen Sulphur SEM Scanning Electron Microscope

EDX Energy-dispersive X-ray Spectrometry ICP Inductively Coupled Plasma

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xvi DOE Design of Experiment

PS Polystyrene

CTRN Carbothermal Reduction and Nitridation

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PENURUNAN KARBOTERMA RUTIL

ABSTRAK

Penurunan karboterma adalah satu proses untuk mengurangkan sebatian bahan dengan menggunakan karbon sebagai agen penurunan. Rutil adalah sampel yang dipilih dalam kajian ini yang merupakan komposisi titanium adalah sekitar 60-70% berbanding dengan rutil sintetik yang mempunyai melebihi 90% komposisi titanium. Komposisi Ferum juga berbeza iaitu rutil mempunyai lebih Ferum berbanding rutile sintetik. Penurunan karboterma dan penitridaan itu dilakukan dengan menggunakan tiub relau elektrik pada 1250 dalam suasana gas H2-N2 dan selama 3 jam. Tiga sampel disediakan oleh nisbah yang berbeza daripada polistirena (PS) dan Mukah arang batu telah digunakan sebagai ejen penurunan dan karbon kepada oksigen dikurangkan dalam rutil telah ditetapkan pada nisbah mol 4.5: 1. Sejauh mana pengurangan (XO) dan sejauh mana penitridaan (XN) sampel PS95C05 adalah yang tertinggi iaitu 25.82% dan 8.72% masing-masing. Larut lesap pengudaraan rutil nitrida telah dijalankan pada 0.37 M NH4Cl untuk penyingkiran logam besi. Parameter lain digunakan seperti jumlah pemangkin (formaldehid), masa larut lesap dan nisbah PS / C sampel. 11 kali larut lepas dilakukan oleh perisian DOE. Dalam kajian ini, TiN tidak kuat dikesan oleh analisis XRD kerana peratusan nitrogen dalam penurunan karbotermal adalah rendah (<5.00%) telah dilakukan oleh analisis CHNS. Dari itu, karbon dalam sampel tidak sepenuhnya ditukar kepada gas karbon monoksida. Dari pegiraan peratusan Fe diekstrak, nilai tertinggi telah disampaikan oleh sampel PS85C15 iaitu 45.94%. Walau bagaimanapun, sampel akan diteruskan dengan ujian larut lesap oleh larutan asid sulfuric untuk pembandingan antara dua method.

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xviii

CARBOTHERMAL REDUCTION OF RUTILE

ABSTRACT

Carbothermal reduction is a process of reducing a compound of substance by using carbon as the reducing agent. Rutile is the selected sample in this research which is the composition of titanium is around 60-70% compared to synthetic rutile that have above 90% composition of titanium. The composition of iron also different which is rutile have more than iron compared to synthetic rutile. Carbothermal reduction and nitridation was done in a horizontal electric tube furnace at 1250 in H2-N2 gas atmosphere and 3 hours for soaking time. Three sample are prepared by different ratios of polystyrene (PS) and Mukah coal was used as the reductant and carbon to oxygen reducible in the rutile was set at molat ratio 4.5:1. The extent of reduction (XO) and the extent of nitridation (XN) of sample PS95C05 was the highest that is 25.82% and 8.72% respectively. The aeration leaching of nitride rutile was carried out in 0.37 M NH4Cl solution for metallic iron removal. Other parameters was used such as the amount of catalyst (formaldehyde), leaching time and the PS/C ratio of the sample. 11 runs was done by DOE software. The highest catalyst used is 1.0 wt% while the lowest is 0.1 wt%. PS/C ratio did not affect Fe extracted (ppm) from perturbation analysis via DOE software. In this research, TiN is not strongly detected by XRD analysis because the percentage of nitrogen in the carbothermal reduction is low (<5.00%) was done by CHNS analysis. From that, the carbon in the sample was not completely converted to carbon monoxide gas. From the percentage of Fe extracted calculation, the highest value was presented by sample PS85C15 that is 45.94%.

However , samples will be forwarded to the test leaching by sulfuric acid solution for comparison between the two methods.

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CHAPTER 1

INTRODUCTION

1.1 Introduction

Rutile is the major phase in synthetic rutile. The differences between rutile and synthetic rutile which was the rutile have 60-70% of TiO2 while synthetic rutile have more than 90% of TiO2. The composition of Fe in rutile also low compared to Fe composition in ilmenite. Rutile have yellowish metal compared to synthetic rutile which is the golden yellow color. Pseudorutile, Fe2Ti3O9 was produced rutile and ilmenite from heating process of sample to 623K (Sheikh Abdul Rezan et al., 2012). The formation of rutile is generally from reduced ilmenite and iron removal.

Ilmenite is a raw mineral that is easily searchable and can be processed in various ways. Based on Barksdale (1968), it is an important source of titanium, a metal which is being used in most industries for its high resistance to corrosion. The world reserves of titanium are 90% in the form of ilmenite, FeTiO3, and only 10% in the form of rutile, TiO2

(Habashi, 2014). Rutile is relatively simple to be treated into titanium compared to ilmenite, which will go through several complex processes (Habashi, 2014).

The main products of ilmenite treatment are titania pigment and titanium metal. The ore processing of ilmenite is very complex due to its mineralogical complexity. There are

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several methods used in processing ilmenite. From the early method of concentrated sulphuric acid treatment to pyrometallurgical treatment, ilmenite treatment had been progressively improved to obtain the best condition in producing titania pigments and titanium metal.

1.2 Application of Titanium metal and Titania Pigments

Titanium metal have their exclusive properties such as high tensile strength to density ratio and high corrosive resistance. This properties were reduced the pollutant to be occurred. Other than that, titanium alloy widely used in aircraft and marine purpose. These properties make titanium perfect for use in marine and corrosion resistance applications (Hanson, B.H., 1986).

Besides, titanium also applied to consumer and architectural. For example, titanium is used in automotive applications because titanium have high strength and rigidity properties. Titanium also used in sporting good likes tennis racket, golf ball, cricket and many else. Therefore, titanium have more application for consumer and daily life as a human.

According to the properties, titanium is bio-compatible (non-toxic and is not rejected by the body), medical applications are used titanium for surgical implements and implants, such as hip balls and sockets (joint replacement). This property is also useful for

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orthopedic implant applications. Titanium is also used for the surgical instruments used in image-guided surgery, including wheelchairs, crutches, and any other products where high strength and lightly.

In order to produce titanium metal from ilmenite, titanium tetrachloride (TiCl4) was needed. Chlorination of nitrided ilmenite was important step to enable low temperature chlorination (Rezan et al., 2010). Achieving this can be reality if metallic iron was removed fron nitride ilmenite by a hydrometallurgical process. Titanium tetrachloride produced from metallic titanium and titania white pigment by carbochlorination of natural or synthetic rutile at 800-1100 .

1.3 Early Method of Processing Rutile

According to Habashi, ilmenite ore is treated with concentrated sulphuric acid, H2SO4 at temperature 110 to 120 was one of the part in early method of titania pigment production. The reaction in this method are represent as Equation 1.1.

FeTiO3 + 4 (1.1)

The production of ferrous and titanyl sulphates was also used this process because it easily to separate by filtration and precipitation. Unfortunately, this process were not

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suitable for environmental because it consume the pollutant problem which is producing dilute acid and ferrous sulphate and hard to be disposed it. Although it have the problems, the new technology or method were produced by using hydrometallurgical and pyrometallurgical routes, by removing the iron in ore in the first step.

For the hydrometallurgical routes, iron was leached from ilmenite. High grade ilmenite was decomposed in autoclaves by 20 wt % hydrochloric acid at 120 with a pressure of 200 kPa. Then, iron was appears as ferrous chloride and leaving as a solid containing about 93% TiO2. After that, the Equation 1.2 was formed.

FeTiO3 + 2 (1.2)

Figure 1.1: Leaching of titanium slag for pigment production (Habashi, 2014)

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The impure synthetic rutile will proceed to treat by chlorine gas to prepare TiCl4 or titanium metals are produced without pollution problems. However, this method is suitable for the high grade ilmenite because it contain high silicates gangue composition which will remain in the synthetic rutile and can be decreasing its separation during chlorination process.

For the secondly routes that is pyrometallurgy method, the ilmenite was mixed with a certain amount of anthracite which is one of the carbon sources in sufficient enough to reduce the iron oxide component in the ilmenite ore (Habashi, 2014). Then the mixed compound will be charged in an electric furnace at temperature 1650 where the iron oxide is reduced to metal while titanium is separated as a slag. The reaction is represented as Equation 1.3 and 1.4.

FeTiO3 + C (1.3)

Fe2O3 + 3C (1.4)

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Figure 1.2: The early method for treating ilmenite for pigment production (Habashi, 2014) Then, the synthetic rutile is treated from rutile mineral which is the composition of titanium oxide in synthetic rutile is higher than rutile. This experimental was used for the rutile mineral by using sulphuric acid which is certain concentration and the supporting parameters such as temperature of surrounding, weight of the sample and the leaching time.

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Figure 1.3: Production of synthetic rutile from high grade ilmenite (Habashi, 2014)

1.4 The Becher Process

Becher process is basically a process of producing synthetic rutile from ilmenite ores. This process is suitable for weathered ilmenite that has low concentrations of magnesium and chromium. There are three main steps in the Becher process, namely reduction, aeration and acid leach steps.

Reduction step or specifically known as carbothermal reduction of ferrous and ferric iron in ilmenite to metallic iron is done in a kiln at high temperature. Reduction step is done on the blend of ilmenite, coal and sulphur which is heated to temperature of greater than 1200°C. This reaction will convert ilmenite to reduced ilmenite (RI), in which fine-grained

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metallic iron is dispersed throughout a reticulated matrix of titanium dioxide. The reactions involved in the reduction step are:

4FeTiO3 (s) + O2 (g) 2Fe2O3.TiO2 (s) + 2TiO2 (s) (1.5) Fe2O3.TiO2 (s) + 3CO (g) 2Fe (s) + TiO2 (s) + 3CO2 (g) (1.6)

The second step of the Becher process is the aeration step. This step is the main focus of this project. Aeration involves the removal of metallic iron created during the reduction step by ‘rusting’ it out. It involves agitating the RI in 1% ammonium chloride ( ) solution while air is being introduced through the pulp. The iron will then rust and precipitate out of solution, away from the titanium dioxide portion in the form of a slime.

4Fe (s) + 3O2 (g) 2Fe2O3 (1.7)

The final step in the Becher process is the acid leach step. Acid leaching of the RI is done using 0.5 M sulfuric acid, which is to remove most of the residual iron and other impurities to form synthetic rutile. (Shaik, 2015)

1.5 Problem Statements

Based on the costing of Titania white pigments and titanium metal production is high cost, the usage of titanium metal has become limited. This also includes the processing

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of ilmenite to titanium tertrachloride production. The commercial chlorination process in the production of titanium metal or titania pigment requires 800 to 1100 to occur (Mostert et al., 1992). Titanium oxycarbonitride produced from carbothermal reduction in H2 – N2 gas mixtures will allow low temperature chlorination (Adipuri et al., 2011). The product of titanium tetrachloride, TiCl4 is important starting material for the production of titanium and high grade titania pigment.

However the existence of metallic iron within the titanium oxycarbonitride structure will affect the formation of TiCl4. Iron will react more readily with chlorine gas during chlorination process to form FeCl3. This will retard the formation of TiCl4 or increase chlorine gas consumption. Therefore, aeration leaching method was used to remove the metallic iron in nitride ilmenite to increase the efficiency of the titanium tetrachloride production process. Aeration leaching takes a long time to complete, thus catalyst was used and many other parameters were varied in accelerating the dissolution of iron.

Therefore the higher formation of TiCl4 can be done by chlorination of titanium oxycarbonitrate at lower temperature in the range of 200 to 350 after removing iron (Ostrovski et al., 2011). Chlorination of ilmenite’s impurities will be selective at lower temperature compared to high temperature chlorination. This permits selective chlorination of titanium oxycarbonitride, decreases the chlorine consumption and waste generation, and makes the whole technology of ilmenite processing more efficient and environmental

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friendly. Low temperature of chlorination will lower the cost of production of titanium metal.

1.6 Objectives

There are some objectives in this project that is concern. The objectives are listed below:

1. To compare the best process of iron removal in nitride Malaysian rutile by aeration leaching process in between ammonium chloride or sulfuric acid solution.

2. To determine the best combination of parameters such as type of catalyst, agitation speed, concentration, leaching time and temperature.

3. To determine the best sample for Becher process.

1.7 Thesis Outline

This thesis contains five chapters. Chapter 1, starts with introduction of the research background of the raw material and also the objectives and the problem statements of this project. Chapter 2, reviews the literature from the previous project that are related to this project and studies the carbothermal reduction of rutile, synthesis of titanium oxycarbonitride and the aeration leaching of rutile mineral. Chapter 3, explains the materials and experimental methods of the research. These include material selection, sample preparation, sample characterization, experimental setup and statistical design.

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Then, Chapter 4 discussed the data analysis and interpretation. The data were obtained from the result of XRD, XRF, SEM, ICP, and TGA. Finally, Chapter 5 shows the conclusion for this project and provides the recommendations for improvement in future research.

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12 CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

In this chapter, there was several research for carbothermal reduction of rutile mineral. Reduction of ilmenites and synthetic rutile in hydrogen-nitrogen mixture was much faster than in pure nitrogen (Sheikh Abdul Rezan et al., 2012).

Carbon can be used to reduce various types of oxides such as Cu2O, PbO, Fe3O4, ZnO, MnO and TiO2. According to the study by Das et al. (2002) on synthesis routes of TiC, the chemical reaction that governs the overall reaction rate was represented by Equation 2.1.

2C + O2 = 2CO (2.1)

In carbothermal reduction, the reaction occurs in an inert atmosphere for carbide and oxycarbide. The driving force is Equation which is sometimes called the Boudouard reaction. Nitrogen or nitrogen-containing atmospheres using carbothermal reduction was produced nitrides, carbonitrides and oxycarbonitrides (Berger et al., 1999).

From previous literatures, the experimental results have contradictions and these have led to different interpretations of the reaction mechanism to take place (Berger et al.,

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1999). Thus, a further study should be done, according to different parameters which affect the mechanism of carbothermal reduction. These parameters include reduction temperature, soaking time and carbon to oxide molar ratio.

2.2 Carbothermal Reduction of Rutile

Carbothermal reduction is a process of reducing a compound or substance, usually metal oxides by using carbon as its reducing agent. Rutile, TiO2 is one of the product while the carbothermal reduction occur on raw ilmenite. Besides, there was pseudobrookite (Fe2Ti3O9), hematite (Fe2O3) when the ilmenite reduced at a minimum temperature of 800 for 2 hours. While the reduction is up to 850 , the sample forms TiO2 and Fe2O3

and when it up to 900 , ferric pseudobrookite will be formed. The main phase are TiO2

and Fe2TiO5 (Zhao, 2010). The reason that absence of pseudobrookite at 900 because it was affected by both amount of impurities and reduction time.

In some cases, pseudorutile Fe2Ti3O9 was converted to ilmenite and rutile while heating a sample to 350 (Sheik Abdul Rezan, 2012). Iron in synthetic rutile was in the metallic state, while the reduction of rutile were converted to titanium suboxides at temperatures below 850 .

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2.3 Reaction Mechanism of Carbothermal Reduction

The mechanism of carbothermal reduction using TiO2 and ZrO2 was investigated (Berger, Gruner et al. 1999). The proposed is shown in Equation 2.2.

Oxide (s) + C (s) Carbide (s) + CO (g) (2.2)

The mechanism included two solid state reactants, one solid state and one gaseous product. Hence, the reaction was interpreted as mass transport mechanism, where one of the solid raw materials as precursor, whereby the solid product is formed from two gaseous intermediate products (Berger, Gruner et al. 1999).

Furthermore in (Berger, Gruner et al. 1999) research, the routes of mass transport and product formation is investigated. There are three possible ways of mass transport, which is the first is based on the reduction of oxide by CO with regeneration of CO from reaction of CO2 with C. Thus, the precursor is oxides particles. Next, the route of mass transport is the formation of gaseous oxide intermediates, which is the carbon particles became precursor for carbide formation. While the third way is reaction between oxide and carbon by solid state reaction. In the mechanism, the CO is considered as gaseous reaction and no mass transfer function (Berger, Gruner et al. 1999). The Figure 2.1 shows the stages of the reaction in carbothermal reduction of TiO2.

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15

Figure 2.1: Schematic of reaction mechanism of carbothermal reduction for TiO2 (Berger, Gruner et al. 1999)

From the Figure 2.1 shows that three step in carbothermal reduction for TiO2. The first step (1) the formation of CO gas by solid state reaction of oxide and carbon or by destruction of oxygen-containing functional groups at carbon surface. For reducing the TiO2, the CO is used as reducing agent to suboxides (TinO2n-1). The end of this stage will results in formation of Ti2O3 based on the removal of oxygen in TiO2. But in Rezan and Zhang at el. (2011) shows that the formation Ti2O3 was not observed in reduction process of TiO2.

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This situation can be explained by thermodynamic stability in predominance diagram. Figure 2.2 shows the predominance diagram of Ti3O5 can thermodynamically coexist with TiN (Jha and Yoon et al. 1999). The low O2 potential is required for TiO2 to coexist.

Figure 2.2: Calculated predominance area diagram for stable phases at 1573 K in Ti-C-N system (Jha and Yoon, 1999)

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17

2.4 Phase Development in Carbothermal Reduction

Understanding of phase development is very crucial to ensure the formation of product with controlled composition, carbon content and nitrogen content in TiOxCyNz. The phase evolution in carbothermal reduction was represented by Equation 2.3 (Rezan et al., 2012).

Fe2Ti3O9 + FeTiO3 FeTiO3 + TiO2 Fe + TiO2 Fe + Ti3O5 Fe +TiOxCyNz (2.3)

Another phase transformation in reduction of pure TiO2 (Rezan, Zhang et al., 2011) which was in Equation 2.4.

TiO2 Ti5O9 Ti4O7 Ti3O5 TiOxCyNz (2.4)

Monteverade et al., (2001) shows a simplified phase transformation route using nanosized TiO2 and nanosized carbon sources, which is nanosized carbon black and activated carbon. The evolution is:

TiO2 TinO2n-1 Ti3O5 TiOxCyNz (2.5)

The phase development was investigated using nanosized anatase and carbon black (Xiang et al., 2008). There are two routes of phase transformation discovered which are:

TiO2 (anatase) TiO2 (rutile) Ti5O9 Ti4O7 Ti3O5 Ti(N,O) TiN Ti(C,N) (2.6)

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TiO2 (anatase) TiO2 (rutile) Ti5O9 Ti4O7 Ti2O3 Ti(C,N,O) Ti (C,N) (2.7)

According to Xiang et al., (2007) another phase transformation route which included the formation of Ti10O19.

TiO2 Ti10O19 Ti3O5 TiOxNy TiN (2.8)

This proposed that the reaction rate of transformation from Ti3O5 to TiOxNy is very rapid. Hence, it supports that the formation of Ti2O3 is undetectable. If the formation of Ti2O3 is detected, the carbothermal reduction might be has leaking along the tube.

2.5 Effect of Raw Material Characteristic on the Carbothermal Reduction of TiO2

The mixture of TiO2 powder and 100% anatase phase structure shows a higher titanium carbide (TiC) formation ability than the titanium dioxide powders with the mixed phase structure of the anatase and rutile phase structures (Gil-Geun Lee et al., 2003).

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19 2.6 Reducing Agent

2.6.1 Polystyrene (PS)

Generally, the properties of polystyrene are clear, in pallets size, hard, brittle and low resistance with high temperature. Polystyrene might be rigid or foamed. Polystyrene is a synthetic aromatic polymer that are made from the styrene monomer, a liquid petrochemical. Polystyrene is one of the most widely used plastic and the scale of its production had reached several billion kilogram per year. Polystyrene are made into a foamed material which is expanded polystyrene (EPS) or extruded polystyrene (XPS) that is valued for cushioning properties. The melting point of the polystyrene was 240-270 .

The formula of polystyrene is (C8H8)n where there is carbon element in it. From the previous study, this polymer can be used to partially replace coke as the carbon source in reduction process and make the low cost of electricity and also carbon usage (Zaharia et al., 2009). In carbothermal reduction process, carbon and hydrogen have the potential to be used. Coke making is the one of the largest sources of greenhouse gas emission in the reduction process (Khanna et al., 2007). Thus, it is difficult that make sure the coke consumption should be decreased further to avoid the emission of greenhouse gases.

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20

For the next studies of polystyrene, when this polymer are made of plastic, it might be have higher hydrogen content than coke/coal. Therefore, the CO2 emission can be reduced. Slag foaming in FeO reduction can be enhanced while the coke and plastic are mixed together (Sahajwalla et al., 2012). According to carbothermal reduction method, there must not have any leaking of nitrogen and hydrogen gas to make the process will be produced a good result.

Polystyrene can be applied in many field such as automotives, electronics, food packaging, insulation and also in medical. Styrene also occurs in naturally in food such as strawberries, cinnamon, beef and coffee. Polystyrene also can be make as product by adding some colorant. As a thermoplastic polymer, polystyrene is in a solid (glassy and clearly) state at room temperature but melting at the temperature above 100 If the original structure is pallet form, it might be flat and yellowish color if there are some friction with steel. That is because the steel such as ring mill is quickly hot temperature.

Therefore, there must have a suitable method or machine to make it fine size.

2.6.2 Mukah Coal

Abundant coal resources were found in Sarawak and Sabah. In this research, the Mukah coal were reacted as a carbon source and the reducing agent for carbothermal reduction of rutile. From the previous study, the coal does not have definite physical

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21

properties because it is dependent on the geological settings and the type of the coal it bears. Furthermore, the properties of coal also depends on the mine site.

Sarawak is endowed with more than one billion tonnes of inferred coal reserves.

According to the statistical, with some 550 million tonnes in the Mukah/Balingian belt.

While the another 470 million tones are found in the Merit-Pila area in the Kapit Division where the Sarawak Energy Bhd (SEB) has a long-term pelan to build another coal-fired power plant (The Star, 2013).

2.7 The Aeration Step of the Becher Process

There are three steps in Becher process that is oxidation test, carbothermal reduction and last step is aeration leaching. In this step, the aeration leaching used ammonium chloride as the enhance solution to leached the iron metal in the sample.

Becher process is a corrosion reaction where iron is oxidized by dissolved oxygen to ferrous ions. The equation shows the reaction.

Fe Fe2+ + 2e- (2.9)

O2 + 4H+ + 4e- 2H2O (2.10)

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The ferrous ions is further oxidised precipitating as a variety of oxides or oxyhydroxides including magnetite, Fe3O4, hematite, Fe2O3 and lepidocrocite, -FeOOH.

The effect of pulp density, temperature, type and concentration of catalyst, and pressure on the aeration of reduced ilmenite was investigated by Becher et al. 1965. The best aeration condition was at weight ratios of water to reduced ilmenite between 10:1 and 2:1. The total pressure at 791 kPa, aeration went five times faster than at atmospheric pressure. At this pressure also occurred the aeration rate was constant between 50 and 150 . From that, in addition to oxidation by dissolved oxygen, some acid oxidation of metallic iron was noticed at high temperature. It was observed that temperature about 55 were ideal and nothing happen when gaining by increasing the temperature to 75 . This is for aerations at atmosphere pressure. Aeration process took 6.5 hours to complete.

The oxidation of iron powder was dissolved oxygen in dilute NaCl and NH4Cl solution (Mandyczewsky et al). The buffering action of NH4+ was recognized as important in preventing pessivation. He concluded that oxidation proceeds in two stage:

i. Electrochemical oxidation of metallic iron to ferrous ions.

ii. Oxidation of ferrous ions to hydrated ferric oxides.

Arvaamides et al. (1996) investigated the effect of air flow rate at “high” and “low”

pulp densities and also investigated the effect of NH4Cl concentration. The aeration rate is

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not further increase while the air flow rates above 0.3 L min-1 at low pulp density and 0.5 L min-1 at high pulp density. Aeration also complete at 5 to 7 hours. The faster aeration when the pulp density is higher and the oxygen utilization also increased. NH4Cl concentration of 0.5 – 1.0% (w/v) produced similar aeration times and residual iron levels.

Since the NH4Cl solution is above 1.0%, the aeration rate was slow slightly and possible due to lower dissolved oxygen levels at higher salt concentration. While below 0.5% the aeration rate also a little lower indicating that NH4Cl does directly influence corrosion of iron in reduced ilmenite (Avraamides et al,. 1996).

Based on the Adipuri wt al., (2011), he had proved his work by applying the best conditions for aeration leaching which were:

i. Temperature : 70 .

ii. Concentration of NH4Cl solution : 0.37M iii. Air flow rate : 2.5 L min -1

iv. Leaching time: 5 hours

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2.8 Application of Catalyst for Accelerating the Aeration Step

The aeration step of the Becher process involve in agitating the reduced ilmenite and ammonium chloride, NH4Cl solution while the air is also supplied by vacuum pump.

Aeration step has limitation in its efficiency because it is a batch process (Warren J.

Bruckard et al., 2004) which can take maximum 22 hours to complete the leaching.

Ammonium chloride is a white crystalline solid which is soluble in water and react as the medium for enhancing the aeration leaching because it is acid to neutralize bases. This will consume more than 50% of the total electrical energy used in the overall Becher process.

Thus, to improve the efficiency of aeration step means to enhance the economics measure of this process.

As an initiative, several workers had investigated the utilization of catalysts to accelerate the aeration step. They have considered of using reagents included multidentate ligands, which form complexed with Fe(Ш) such as citric and tartaric acid, pyrogallol, saccharin, starch and formaldehyde, and other carbonyl compounds such as glyoxal, glucose and sucrose (Warren J. Bruckard et al., 2004).

The iron oxide of ilmenite is reduced to the metallic state using coal, which is then catalytisally converted to solid iron oxide, which can be easily separated (Becher et al., 1965). The product obtained is synthetic rutile containing around 92% TiO2. While the other research that is developed by RRL, Trivandrum, reduced ilmenite is the first

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subjected to catalytic aeration followed by acid wash which gives a high grade synthetic rutile containing up to 96% TiO2 (Mohan Das et al., 1997). It can be conclude that both process have slowest aeration step where is taking up to 16 hours for completion.

Figure 2.3: Plot of time versus % iron removal during rusting (Kumari et.,al, 2001)

The Figure 2.3 shows that the iron removed in reduced ilmenite is higher when using carbonyl compound (sucrose, glucose ang glyoxal) as the catalyst compared to without any catalyst. There was a different in time when the % iron removal is 20%, which

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is the aeration leaching with catalyst is much lower than without catalyst. This proves that carbonyl compound is a suitable reagent for accelerating the aeration step of the Becher process. But they have never been used in a commercial operation (Bruckard et al., 2004).

Figure 2.4 is the one of the example from previous research by using AQ-2 as the catalyst.

Figure 2.4: Effect of concentration of AQ-2,6 or AQ-2 on iron removal during aeration of reduced ilmenite in 2% w/v NH4Cl (Bruckard et al., 2004).

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27 2.9 Effect of Experimental Parameter

From the research, there are several parameters were be considered to this experiment. From that, there are also effect of some gas atmosphere on carbothermal reduction stage, effect of temperature on the rate of reduction, the effect in set up of the some analysis, and the effect of dissolved oxygen and pH on iron removal.

2.9.1 Effect of Raw Material Characteristic on the Carbothermal Reduction of TiO2

The mixture of TiO2 powder and 100% anatase phase structure shows a higher titanium carbide (TiC) formation ability than the titanium dioxide powders with the mixed phase structure of the anatase and rutile phase structures (Gil-Geun Lee et al., 2003).

2.9.2 Effect of Gas Atmosphere on Carbothermal Reduction

Gas atmosphere influences reduction reaction because the reaction involved in carbothermal reduction is a reaction between solid oxides with gas. From the study by Jha and Yoon (1999), different gas atmosphere are used to investigate the influence of gases on carbothermal reduction. Extent of reduction (X) was higher under N2 atmosphere than under gas mixture of (CO + N2 + H2) (Jha and Yoon, 1999). This is due to excess CO reversing the Boudouard reaction.

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In the study by Rezan et al. (2011) on carbothermal reduction and nitridation, the effect of gas atmosphere was investigated using 50-50 vol% of nitrogen and hydrogen. The results showed the presence of H2 gas encouraged faster and higher extent of reduction.

Besides that, the effect of gas atmosphere on the purity of TiO2 was discussed. The rate of reduction in H2-N2 gas mixture was higher when ilmenite grade was decreasing whereas the opposite happened when N2 gas was used (Rezan et al., 2012).

The effect of gas atmosphere is also studied using H2, argon (Ar) and helium (He) gases. The effects of these gases are investigated on the rate of generation of CO, reduction temperature and reduction rate. In this research, H2 gas enabled reduction of TiO2 to start at lower temperature compared to argon gas and helium gas (Dewan et al., 2009). The rate of reduction was higher when using H2 since it is reacting with TiO2 to form suboxides compared to inert argon and helium gas.

2.9.3 Effect of Temperature on the Rate of Reduction

Generally, the rate and extent of reduction is increased with increasing the temperature. Effect of temperature on the rate of reduction was strong in the range 1000°C - 1400°C (1000°C - 1250°C in particular) and quite minor in the range of 1400°C to 1600°C (Rezan, 2011).

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Titanium oxycarbonitride started to form at 1000°C. The sample reduced at 1000°C to 1150°C contained titanium suboxides with poor crystal structure. After 10 minutes of reduction, at 1150°C, titania was converted to suboxides Ti5O9, Ti4O7 and Ti3O5. After another 10 minutes of reduction, Ti4O7 disappeared, leaving Ti3O5 as the only detectable titanium suboxide, and titanium oxycarbonitride started to form. For further reduction until 90 minutes, Ti3O5 and titanium oxycarbonitride oxycarbonitride coexisted (Rezan, 2011).

As the reaction continued, the amount of oxycarbonitride increased with Ti3O5

decreased. Oxygen in the oxycarbonitride was replaced with nitrogen. After 120 minutes of reduction, titanium oxides became undetectable by XRD. Further reduction involved a slow replacement of oxygen in the oxycarbonitride by nitrogen. Extent of reduction increased to 91.9% after 300 minutes of reduction, producing titanium oxycarbonitride containing 16 mol% TiO and 84 mol% TiN. TiC content was always low in titanium oxycarbonitride.

2.9.4 Effect of Temperature on Iron Removal

Investigations of the effect of temperature on rusting show that there is a variation in trend between NH4C1 and the other compounds. In the case of NH4Cl, alone an increase in temperature was found to favour the reaction (Farrow et al., 1987). Experiments carried out at 25, 30, 35 and 40°C show that iron removal increases with temperature up to 70°C.

Experiments were carried out only up to 40°C, as the optimum in the case of carbonyl compounds was found to be less than 40°C. When glyoxal, glucose or sucrose is added to

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the system the removal of iron increases with temperature up to 35°C, after which it decreases, indicating an optimum temperature of 35°C.

Activation energies of the reaction were calculated using the following equations (Han et al., 1997):

1 – (1-x) 1/3 = K’t (2.11)

K’ = 1/Ro (2.12)

K’ = CAKC / ρRo (2.13)

Analysis showed that the rate determining step was not controlled by the diffusion process, surface chemical reaction being found to be the rate determining step. The plots of time versus 1 - (1 - x) 1/3 calculated for all the systems gave straight lines. The activation energies are calculated from the Arrhenius plots, shown in Figure 2.5.

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Figure 2.5: Arrhenius plots (Kumari et al., 2001)

The activation energies are 28.07, 41.78, 46.36 and 63.82 KJ/mol for NH4Cl+ (glyoxal, glucose and sucrose) and NH4Cl alone respectively. There is a decrease in the activation energy when organic compounds are added to NH4CI. When glyoxal was added, the activation energy was found to be less than half of that with NH4C1 alone. When the inverse of K’ vs % is plotted, a straight line is obtained as expected from Equation which also supports the chemical reaction limiting hypothesis.

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2.9.5 Effect of Dissolved Oxygen and pH on Iron Removal

The dissolved oxygen decreases in the initial stages up to 2 hours by using NH4Cl solution, remaining more or less at about 3.7 ppm thereafter. In the other cases it increases rapidly in a random manner, being higher than NH4Cl alone at any given time except at zero time (Kumari et al., 2009)

In the case of NH4Cl, the pH increases gradually up to 6.2 at 8 hours, while in the case of glyoxal after an initial increase up to 2 hours it decreases with a final value of 3.9 at 8 hours due to the formation of free acids in the system during the reaction. Further, the concentration of free acids formed varied irregularly during the reaction in the case of all the three compounds, which was confirmed through estimations of free acids by titration with standard alkali at regular intervals during the progress of the reaction (Kumari et al., 2001).

2.10 Full Factorial Design of Experiment (DOE)

Full Factorial Design of Experiment is the most efficient software to do any experiment. In factorial design, each complete trial or replication of the experiments with all possible combination of the factors interest will be investigated. The effect of each parameter involves being change in response produced by the variation in the level of

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factor. The parameters involve wil be denoted as ‘+’ and ‘-‘ as high and low levels (Montgomery, 2001).

When there are three factors being involves, factorial design will be implemented. Using the notations of ‘+’ and ‘-‘ signs indicate low and high levels of factors, eight runs of experiment will be conducted. In other word, the design can also be presumed as a design matrix. In addition, three different symbols are widely used for the runs in the designs. The first ‘+’ and ‘-‘ notations, often called the geometric notation.

Secondly, the use of lowercase letter labels to identify the treatment combinations. Lastly, the notations may also use 1 and 0 to denote as high and low factors levels, respectively, instead of + and – sign.

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34 CHAPTER 3

MATERIALS AND RESEARCH METHODOLOGY

3.1 Introduction

In this chapter will be present the determination of the suitable parameters for accelerating the aeration leaching in step of Becher process. From the previous research, the three parameters were used that is leaching time, weight percent of catalyst and the molar ratio of Polystyrene and Mukah coal. In this research, three sample will be prepared to do the experiment. In addition, to study the behavior and reactions that took place under the influence of different combination of parameters.

3.2 Raw Materials

In starting of study of the raw materials is very details and much more effort for reading the journal. That is because every material have their behavior and properties so that the method selected must be suitable on it. Thus, in this chapter the raw materials used are rutile, polystyrene and Mukah coal.

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35 3.2.1 Rutile

Table 3.1 shows some properties of rutile ores (Enc. Of Minerals, 2nd ed., 1990).

Most rutile mined for the production of titanium dioxide. That is because the rutile is the main ore used for the production of titanium metal about 60-70%. Rutile is a crystalline iron titanium oxide (FeTiO3) and it crystallizes in a form of trigonal system. Furthermore, according to classification of rocks this rutile is come from primary mineral in igneous rock. In this research, Malaysian rutile was provided by Ooi Cheng Huat Sdn. Bhd.

Table 3.1: Properties of rutile ores (Enc. Of Minerals, 2nd ed., 1990)

Properties Identification

Color Blood red, Bluish, Brownish yellow, Brown red, Violet.

Streak Grayish black

Specific gravity 4.70-4.79

Crystal system Trigonal

Fracture Conchoidal to subconchoidal Chemical classification Oxide

Tenacity Brittle

Mohr scale hardness 6-6.5

Luster Sub-metallic

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36 3.2.2 Mukah Coal

There are two sources of carbon which is Mukah coal and polystyrene (PS). The coal was supplied by Panoramio Coal Mining, Mukah, Sarawak. The average size of the Mukah coal was 1 mm. Based on Department of Mineral and Geoscience Sarawak (JMG) report, coal characterization was done by two methods, which was proximate and ultimate analysis. Proximate analysis gives the physical properties whereas ultimate analysis gives the composition of Carbon, Hydrogen, Nitrogen and Sulphur content in the coal.

Table 3.2 shows the proximate analysis of Mukah coal as stated by JMG Sarawak (JMG Sarawak: Coal and Coke Report, 2012). The moisture content of Mukah coal was about 9.4 wt% while the ash content was 8.9 wt %. Volatile matter for Mukah coal was 37.6 wt%. This shows that the coal main composition (>50 wt%) was removed during the gasification process as the temperature used was high (>1000 ). While the Table 3.3 shows the ultimate analysis of Mukah coal.

Table 3.2: Proximate analysis of Mukah coal Moisture (wt%) Ash content (wt%) Volatile

matter (wt%)

Fixed carbon (wt%)

9.4 8.9 37.6 44.6

Sources: 1) Departments of Minerals and Geoscience Sarawak (2012)

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Table 3.3: Ultimate analysis of Mukah coal Carbon (wt%) Hydrogen

(wt%)

Nitrogen (wt%)

Sulphur (wt%) Oxygen (wt%)

74.75 5.38 2.02 1.35 0

Sources: 1) Departments of Minerals and Geoscience Sarawak (2012)

3.2.3 Polystyrene (PS)

Basically, the polystyrene is a clear, colorless polymer used extensively for low-cost applications. The hardness of polystyrene is quietly high and hard to liberate it into small size. It is usually form in both pallet and sheet form. In this research, the polystyrene in form of pallets was used. It is also not able to liberate by using the ring mill because the polystyrene much easier to melting cause of friction between their surface to ring mill’s surface. Table 3.4 shows the general properties of polystyrene plastic.

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Table 3.4: General properties of polystyrene plastic

Properties Units Values

Specific gravity g/ 1.03 – 1.06

Apparent density g/ 0.60 – 0.65

Water absorption % 0.03 – 0.10

Tensile strength MN/ 34.5 – 48.3

Deflection In 0.15 – 0.35

Hardness Rockwell scale M45 – M60

3.2.4 Other Materials

In addition for other material are hydrogen and nitrogen gas. This materials were used in carbothermal reduction step. It is importance for creating a hydrogen-nitrogen gas mixture atmosphere in the tube furnace. The ratio between both gas is 50:50. There was another reason the hydrogen and nitrogen is used that is to inhibit the formation of methane, CH4 where it is important in converting titanium suboxides into titanium oxycarbide or titanium oxycarbonitride (Rezan, Zhang & Ostrovski, 2012). The hydrogen were chosen because it is one of the inert behavior.

Reasons for used nitrogen in carbothermal reduction is to prevent the oxidation of titanium oxide, TiO2 into titanium suboxides such as Ti3O5. That is because the formation

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will be retarded in titanium oxycarbonitride formation and also consumed to change the nitrogen atom into it for TiOxCyNz formation.

3.3 Flowchart of Research Work

To achieve the objectives of this research, a flowchart needs to be done precisely and practically with laboratory equipment. Figure 3.1 shows the overall process flowchart of the project undertaken.

Figure 3.1: Overall process flowchart of the experimental procedure RAW MATERIALS PREPARATION

Grind ilmenite, PS and Mukah coal until size -75µm.

SAMPLE MIXING

Use the roller bottle to mixing all the raw materials based on carbon mixing calculation.

carbon to reducible oxygen molar ratio is 4.5:1

OXIDATION TEST

To determine the carbon content in sample by heating in horizontal tube furnace with 850ºC

for 6 hours and open air.

CARBOTHERMAL REDUCTION

To produce nitrided rutile by heating in horizontal tube furnace with 1250ºC for 3

hours and presence of H2-N2 gas.

AERATION LEACHING

Based on DOE software to do this step. Formaldehyde catalyst was used in mixture of 2.5g of nitrided in rutile, 100 ml of 0.37 M ammonium chloride as the solution with fixed temperature 70ºC.

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40 3.4 Raw Material Preparation

The sample of mineral rutile was taken from Ooi Cheng Huat Sdn. Bhd. Company.

Ring mill is used for liberation the size of the sample until -75 m. The ring mill was chosen because to grind it quickly. To make the constant size of ore, the sieve mesh of size 75 m is used and send it to TGA, XRF, and XRD analysis.

For preparing the polystyrene, mini grinder is used for getting the size of -75 m.

The ring mill is not suitable for PS sample because of it properties which is PS are not resistance in high temperature. While the coal are prepared by using agate mortar and -75 m mesh sieve. That is because the coal is softer and easier to reduce the size.

Next, the sample is prepared by mixing the three materials with different ratio of polystyrene and mukah coal which is the carbon sources. Both are reducing agent for carbothermal reduction process. All sample are prepared in dry condition to ensure the moisture content is constant.

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41 3.5 Raw Material Characterization

This stage is important to understand the characteristic of the material. Before do any process on it, the characterization of material must be analyse first so that the method is suitable for the sample. Thermal Gravimetric Analysis (TGA) is used for Mukah coal and polystyrene for knowing the changes of physical structure in certain temperature. While the raw rutile mineral is proceed at XRD, XRF, and SEM/EDX analysis to identify the phases existed in the sample.

3.6 Sample Mixing

In this research, the sample mixing were calculated by using mixing calculation with a carbon to oxygen molar ratio of 4.5:1. The oxygen mole was determined from the amount of reducible oxygen in rutile based on XRF analysis results. The carbon mole was set three times greater than of the mole of oxygen. This is to ensure the more excessive amount of carbon in samples and thus to ensure the reduction is complete change from titanium to titanium oxycarbonitride.

Three sample with different ratio of polystyrene and Mukah coal is prepared and label as PS85C15, PS90C10, and PS95C05 which have same mass (50g). From the labeling, the first sample have 85% of polystyrene while 15% is Mukah coal. The second sample is control sample which is 90% of polystyrene and 10% of Mukah coal. Last but not least, the higher ratio of polystyrene were in sample PS95C05 which is 95% and 5% of

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Mukah coal. According to Muhammad Fuad (2014), iron oxides can be removed as much as possible from titanium oxides lattice when using high amount PS.

CHNS was done on Mukah coal and Polystyrene sample to determine the content of carbon, hydrogen, nitrogen and sulphur in the sample. Table 3.5 shows the results of the CHNS analysis. The calculation for weight percentage of carbon and reducible oxygen molar ratio are shown in APPENDIX A.

Table 3.5: CHNS analysis for 2 types of carbon sources Carbon

Sources

Ultimate %

C H N S

Polystyrene 91.12 5.84 0 0.16

Mukah coal 74.75 5.38 2.02 1.35

The raw materials were dry mixed with polystyrene and Mukah coal in the polypropylene(PP) bottle. The bottle will be rolled on roller in 1 hour to ensure all the material were mixed well.

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