Modelling Metal Complexation in Solvent Extraction Systems

CURTIN UNIVERSITY Modelling Metal Complexation in Solvent Extraction Systems by Sergey Lunkov A thesis submitted in partial fulfillment for the degree of Doctor of Philosophy in the Faculty of Science and Engineering Department of Chemistry October 2013 Declaration of Authorship I, Sergey Lunkov, declare that this thesis titled, `Modelling Metal Complexation in Synergistic Solvent Extraction Systems' and the work presented in it are my own. To the best of my knowledge and belief this thesis contains no material previously published by any other person except where due acknowledgement has been made. This thesis contains no material which has been accepted for the award of any other degree or diploma in any university. I confirm that: This work was done wholly or mainly while in candidature for a research degree at this University. Where any part of this thesis has previously been submitted for a degree or any other qualification at this University or any other institution, this has been clearly stated. Where I have consulted the published work of others, this is always clearly at- tributed. Where I have quoted from the work of others, the source is always given. With the exception of such quotations, this thesis is entirely my own work. I have acknowledged all main sources of help. Where the thesis is based on work done by myself jointly with others, I have made clear exactly what was done by others and what I have contributed myself. Signed: Date: i \Knowledge is knowing a tomato is a fruit; Wisdom is not putting it in a fruit salad." Brian Gerald O'Driscoll CURTIN UNIVERSITY Abstract Faculty of Science and Engineering Department of Chemistry Doctor of Philosophy by Sergey Lunkov Quantum mechanical studies of the Z/E acetoin oxime interconversion have been con- ducted using both density functional theory (DFT) and ab initio post-Hartree-Fock methods in order to understand the thermodynamic and kinetic properties of the syn/anti isomerisation of 5,8-diethyl-7-hydroxydodecan-6-oxime. This molecule is the active reagent in LIX63, a commercial material used in hydrometallurgical solvent extraction (SX). Based on calculated data and experimental results, for Z/E 5,8-diethyl-7-hydroxydodecan-6-oxime interconversion and the IR spectra of its pure anti isomer, it has been shown that the active reagent in LIX63 favours an oligomeric form. Theoretically, it has been found that higher order oligomers are energetically more favourable. Based on this it has been suggested that at high concentrations hydroxyoximes exist in the form of polymeric rings and/or chains. The effect of different R groups on the thermodynamic and kinetic properties of aliphatic α-hydroxyoxime syn/anti interconversion has also been studied. Theoretically, it has been shown that using R=C3H8 on both ends of the oxime is the minimum sub- stituent size required to obtain a good description of thermodynamics and kinetics in comparison to experimental data for LIX63. Further increases in the size of the R group does not have any significant effect on either thermodynamics or kinetics of the syn/anti isomerisation (except via an inversion mechanism, where the effect of the size of the hydrocarbon side-chain is still quite significant in going from R=C2H5 to R=C3H8). Lastly, potential energy surfaces of Ni2+, Co2+, Cu2+, Zn2+ and Mn2+ transition metal complexes with acetoin oxime and acetic acid have been studied at the M06/6-31G(d,p)/LanL2DZ level of theory using different stoichiometries. The theoretically determined order in which metal ions are extracted agrees well with experiment for the case when 1:2:2 metal:hydroxyoxime:carboxylic acid complexes are formed. The synergistic effect of addition of hydroxyoxime to the system of metal ions and carboxylic acid has been shown. The theoretically determined lowest energy conformation for the Ni:hydroxyoxime:carboxylic acid 1:2:2 stoichiometry complex agrees well with that ob- served experimentally. Acknowledgements This thesis is built on the shoulders of more people than I could ever name in this space, for I feel I should thank all of the people who have had a hand in shaping my intellectual and personal growth to this point. However, I would be remiss if I did not single out a few people for special thanks. I thank my main supervisor and first reader, Prof. Julian Gale from the De- partment of Chemistry at Curtin University, for encouraging me to be strategic at all times, for constantly feeding me with the most useful ideas and advice without which my thesis would not be even half as good as it is and for inviting me to be part of the project that introduced me to The Parker Cooperative Research Centre for Integrated Hydrometallurgy Solutions in the first place. Thank you to Prof. Kate Wright, my co- supervisor, for putting me on a track that turned scattered ideas and observations into a single thesis. To Dr. Keith Barnard, my associate supervisor and second reader from the Parker Centre, who provided us with the latest experimental data on the synergistic solvent extraction of transition metal ions with the mixture of LIX63 hydroxyoxime and Versatic10 carboxylic acid. To Prof. Mark Ogden, my chairperson from the Depart- ment of Chemistry at Curtin University, who pointed out some key points in studying hydroxyoxime oligomerisation and provided me with the facilities for analysing the IR spectra of the anti isomer of LIX63 hydroxyoximme. A big thank you to the iVEC and National Computational Infrastructure (NCI) for giving me chance to use their facilities and providing me with an impressive amount of computing time without which it would not be possible to perform all these calculations. I would like to express my great appreciations to my family and friends for their inspiration and support. I gratefully acknowledge the financial support from Curtin University and Parker Centre. Finally I would like to thank Curtin University for its existence as without it I would not have met all these great people and spent this wonderful time of conducting such exciting research. iv Contents Declaration of Authorshipi Abstract iii Acknowledgements iv List of Figures viii List of Tables xv Abbreviations xxi Physical Constants xxii Symbols xxiii 1 Solvent Extraction1 1.1 Introduction...................................1 1.2 Overview of Extractive Metallurgy......................2 1.3 Solvent Extraction...............................6 1.3.1 Extractants available for the Solvent Extraction of Transition Metals 10 1.3.2 Synergistic Solvent Extraction.................... 14 1.4 References.................................... 17 2 Computational Chemistry 21 2.1 Introduction to Quantum Mechanics..................... 21 2.2 The Born-Oppenheimer Approximation................... 28 2.3 Hartree-Fock Theory.............................. 29 2.3.1 Electron Correlation Methods..................... 31 2.4 Density Functional Theory.......................... 32 2.4.1 Local Density Approximation..................... 34 2.4.2 Generalised Gradient Approximation Methods........... 35 2.4.3 Meta-GGA Methods.......................... 36 2.4.4 Hybrid Methods............................ 37 2.4.5 Hybrid-Meta-GGA Methods...................... 38 v Contents vi 2.5 Semi-empirical Methods............................ 39 2.6 Molecular Mechanics.............................. 40 2.7 Methods Selection............................... 41 2.8 Thermochemistry................................ 42 2.9 References.................................... 43 3 Syn/anti Isomerisation of a Model Hydroxyoxime 47 3.1 Introduction................................... 47 3.2 Methodology.................................. 53 3.3 Results and Discussion............................. 55 3.3.1 Thermodynamics of Syn/Anti Acetoin Oxime Equilibrium..... 56 3.3.2 Kinetics of Syn/Anti Hydroxyoxime Equilibrium.......... 70 3.4 Conclusions................................... 79 3.5 References.................................... 80 4 Effect of the Hydrocarbon Side-chains on the Syn/Anti Equilibrium and Kinetics of Hydroxyoxime Isomerisation 86 4.1 Introduction................................... 86 4.2 Methodology.................................. 87 4.3 Results and Discussion............................. 88 4.3.1 Thermodynamics of the Syn/Anti Hydroxyoxime Equilibrium... 89 4.3.2 Kinetics of the Syn/Anti Hydroxyoxime Equilibrium........ 110 4.4 Conclusions................................... 115 4.5 References.................................... 116 5 DFT Study of Hydroxyoxime Oligomerisation 118 5.1 Introduction................................... 118 5.2 Methodology.................................. 119 5.3 Results and Discussion............................. 120 5.3.1 Thermodynamics of Syn/Anti Aceoin Oxime Dimerisation..... 121 5.3.2 Thermodynamics of Formation of Acetoin Oxime Trimers..... 133 5.3.3 Thermodynamics of Formation of Aceoin Oxime Tetramers.... 137 5.3.4 Kinetics of Syn/Anti Isomerisation of Hydroxyoxime Oligomers.. 143 5.3.5 Conclusion............................... 144 5.4 References.................................... 145 6 Modelling Metal Complexation in Solvent Extraction Systems 147 6.1 Introduction................................... 147 6.1.1 Coordination Chemistry of The Transition Metal-Hydroxyoxime- Carboxylic Acid Complexes...................... 149 6.2 Methodology.................................. 151 6.3 Results and Discussion............................. 152 6.3.1 Thermodynamics of M(OxH)2(Ac)2 and M(Ox)2(AcH)2 Transi- tion Metal Complexes with Acetoin Oxime and Acetic Acid

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