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An Investigation Into Aqueous Titanium

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An Investigation Into Aqueous Titanium An Investigation into Aqueous Titanium Speciation Utilising Electrochemical Methods for the Purpose of Implementation into the Sulfate Process for Titanium Dioxide Manufacture Samala Shepherd, BSc. (Hons) Masters of Philosophy in Chemistry University of Newcastle March, 2013 STATEMENT OF ORIGINALITY This thesis contains no material which has been accepted for the award of any other degree or diploma in any university or other tertiary institution and, to the best of my knowledge and belief, contains no material previously published or written by another person, except where due reference has been made in the text. I give consent to this copy of my thesis, when deposited in the University Library**, being made available for loan and photocopying subject to the provisions of the Copyright Act 1968. **Unless an Embargo has been approved for a determined period. Samala L. Shepherd i Acknowledgements There are many people who have helped me and contributed to my work in a number of ways and I’d like to thank them. I’d like to thank BHP Billiton Newcastle Technology Centre for making this project possible. The ARC for support and funding. Dr. Scott Donne for the vast knowledge he provided me with and the friendship and support. Thank you to Carolyn Freeburn, Vicki Thompson, and Stephen Hopkins for the ‘store/equipment room’ when I was in need. Thank you to Dianna Brennan for keeping me supplied. Michael Fitzgerald for his continued support. Last but not least a big thanks to my family, they are stuck with me but bare the burden with smiles and support and I thank them greatly. ii Declaration To the World of Chemistry. May you never stop amazing people! iii Table of Contents STATEMENT OF ORIGINALITY ................................................................ i Acknowledgements ......................................................................................... ii Declaration ..................................................................................................... iii Table of Figures .............................................................................................. 5 Abstract ........................................................................................................... 9 1 Introduction to Titanium and its Electrochemistry ................................ 10 1.1. The Sulfate Process ....................................................................... 10 1.2. Aqueous Titanium Chemistry ....................................................... 15 1.2.1. Introduction ............................................................................. 15 1.2.2. Aqueous Titanium(II) Chemistry ........................................... 17 1.2.3. Aqueous Titanium(III) Chemistry .......................................... 18 1.2.4. Aqueous Titanium(IV) Chemistry .......................................... 19 1.2.4.1. Monomeric Species of Titanium(IV) .................................. 20 1.2.4.2. Oligomeric species of Titanium(IV) ................................... 23 1.2.5. Mixed Oxidation State, Ti(III) and Ti(IV) Species ................ 25 1.3. Aqueous Titanium(IV) Electrochemistry ..................................... 27 1.3.1. Thermodynamics .................................................................... 27 1.3.2. Redox Mechanisms ................................................................. 28 1.3.3. The CE or ECE Mechanism ................................................... 29 1 1.3.3.1. Low Acid Concentration Mechanisms ................................ 29 1.3.3.2. High Acid Concentration Mechanisms ............................... 31 1.4. Electroactivity of Various Ti(IV) Species .................................... 32 1.5. Polarography of Titanium(IV) ...................................................... 35 1.6. Constant Current Electrolysis of Titanium containing solutions .. 37 1.7. Hydrogen Evolution Reaction (HER) ........................................... 38 1.7.1. Proton Diffusion ..................................................................... 38 1.7.2. Kinetics ................................................................................... 39 1.7.3. Cathodic Substrate Effects ...................................................... 40 1.8. Leachate Impurities of Ilmenite .................................................... 42 1.9. Design ........................................................................................... 42 1.10. References ..................................................................................... 43 2 Experimental .......................................................................................... 46 2.1. Solution Preparation ...................................................................... 46 2.2. Cyclic Voltammetry Measurements ............................................. 47 2.3. Impedance Spectroscopy (EIS) Measurements ............................ 49 2.4. Rotating Disc Electrode Voltammetry .......................................... 51 2.5. Electrochemical Protocol for Polarography .................................. 52 2.6. References ..................................................................................... 54 3 Electrochemistry Results ....................................................................... 55 2 3.1. Cyclic Voltammetry ...................................................................... 55 3.1.1. Cathodic Substrate .................................................................. 55 3.1.2. Titanium Concentration Effects .............................................. 55 3.1.3. Sulfuric Acid Concentration Effects ....................................... 61 3.1.4. Kinetic Information ................................................................ 65 3.1.5. Solution Age Effects ............................................................... 69 3.2. Electrochemical Impedance Spectroscopy (EIS) .......................... 72 3.3. Rotating Disc Electrode (RDE) Voltammetry .............................. 82 3.4. Conclusions ................................................................................... 88 3.5. References ..................................................................................... 89 4 Polarography .......................................................................................... 90 4.1. Polarographic Behaviour............................................................... 90 4.2. Effect of H2SO4 Concentration ..................................................... 97 4.3. Effect of Electrolyte Age .............................................................. 99 4.4. Effect of Different Acid Media ................................................... 103 4.4.1. Backgrounds ......................................................................... 103 4.4.2. Different Supporting Electrolytes ......................................... 103 4.4.3. Titanium Metal ..................................................................... 105 4.4.4. Titanyl oxysulfate Addition to Various Acid Media ............ 107 4.5. Conclusions ................................................................................. 110 3 4.6. References ................................................................................... 110 5 Sulfate Process Implementation ........................................................... 112 5.1. Overview of Electrochemical Techniques .................................. 112 5.2. Implementation ........................................................................... 112 5.3. Industrial Design ......................................................................... 115 5.4. References ................................................................................... 115 6 Appendix A .......................................................................................... 116 7 Appendix B .......................................................................................... 118 8 Appendix C .......................................................................................... 131 4 Table of Figures Figure 1-5. Curves of Ti(IV) in SWV, with forward scan ∆I < 0 and reverse scan ∆I > 0. The numbers on the curves are the concentrations of H2SO4 (M) [28]. ............................................... 31 Figure 1-6. Curves of Ti(IV) in SWV, with forward scan ∆I < 0 and reverse scan ∆I > 0. The numbers on the curves are the concentrations of H2SO4 (M) [28]. ............................................... 34 -6 2 -1 Figure 1-7. Diffusion coefficients, D, of Ti(IV) in H2SO4 at 25°C. D0 = 4.2 x 10 cm s [28].... 36 Figure 1-8. The exchange current densities for hydrogen evolution on several cathodic substrates [41]. Data points are the negative logarithm of the exchange current densities in Am-2. .............. 41 Figure 2-1. An example of three full cycles from cyclic voltammetry of a solution containing 0.0 2+ M TiO in 0.1 M H2SO4, at 21 ± 1°C. .......................................................................................... 48 Figure 2-5. An example of a Lorentzian lineshape graph. ............................................................ 54 Figure 3-1. Cathodic sweep only from the cyclic voltammogram, of solutions containing different 2+ TiO concentrations in 0.1 M H2SO4 at a scan rate of 5 mV/s using a Pb cathode, at 21 ± 1°C. The numbers in bold brackets, (1) – (4) are explained in the text. ................................................ 56 Figure 3-2. The maximum peak currents corresponding to peaks (1) – (4) from Figure
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