This thesis involves the design and development of reagents for the recovery of base metals (specifically zinc, nickel and cobalt) in hydrometallurgical solvent extraction processes. The work aims to demonstrate how ligand design can affectively tune the strength and selectivity of extractants to achieve efficient recovery of the desired base metals. Chapter 1 reviews current solvent extraction processes used in extractive metallurgy, encompassing both the well established technologies developed for sulfate streams as well as those more recently explored for treating chloride streams. Also reviewed, is the nature of the chemical binding involved in the three key modes of extraction; namely cation transport, anion transport and metal salt transport. Chapter 2 summarises the methodologies that have been established during this research for the appropriate testing of these reagents. Chapter 3 deals exclusively with the processing of zinc sulfide ores with an aim to design reagents to achieve concentration and separation of zinc in chloride hydrometallurgical circuits. The amido functionalised reagents that are reported have a common structural feature with ligands that have been previously studied by the Tasker group (Ross J. Ellis Thesis, University of Edinburgh, 2009). A six membered chelate ring is formed by a protonated amino nitrogen atom and an amido oxygen atom in a sequence of the type R2HN+-CH2-NR-CO-R. This differs from those previously studied which have a sequence of the type R2HN+-CH2-CHR-CO-NR2. The pro-ligands (L) operate via an anion exchange mechanism (Equation 1) whereby two protonated ligands (LH+) coordinate to the outersphere of anionic zinc(II) or iron(III) chloridometalates from acid chloride solutions using both N-H and C-H hydrogen-bond donors. pH dependent solvent extraction experiments have concluded that this reagent series achieves zinc(II) loading with pH0.5 values that are competitive with the previous ligand series (Ross J. Ellis Thesis, University of Edinburgh, 2009). Chloride concentration dependent solvent extraction experiments have demonstrated that the reagents show an unusually good selectivity for ZnCl4 2- over chloride or FeCl4 - in equilibrium of the type; yLorg + yH+ +MClx y- ⇌ [(LH)yMClx](org) (1) The development of bidentate and tridentate pyrazolone-based pro-ligands for the extraction of nickel and cobalt from mixed metal sulfate streams is considered in Chapters 4 and 5. These reagents (LH) operate via metal cation transport, where an inner-sphere complex of nickel(II) or cobalt(II) is formed with the ligand (L-) see Equation 2. A combination of N, O and S donors has been incorporated into 1-phenyl-3-methyl-4- acylpyrazol-5-ones and their respective 4-acylpyrazolone oximes in order to tune the bidentate ligands (L-) for optimal coordination with nickel(II) or cobalt(II). Substituent effects have also been investigated, by synthesising a series of 1-(2-X-phenyl)-3-methyl-4- acylpyrazol-5-one oximes [X = Cl, H]. Substitution in the 3-position of the phenol group in phenolic oximes has been reported to increase extractant strength for copper by two orders of magnitude (Ross S. Forgan Thesis, University of Edinburgh, 2008). Similar improvements were not observed in this study. The nature of this effect has been attributed to buttressing of hydrogen-bonds, where the substituent forms a stabilising, bifurcated hydrogen-bond between the oximic hydrogen and the pyrazolonic oxygen. yLHorg + My+ ⇌ [(L)yM]org + yH+ (2) Tridentate analogues of the oxime reagents above have been prepared as imines derived from anilines contained o-O, S or N donor atoms. It was hoped that these would give high spin octahedral nickel(II) complexes in extraction processes. They proved to be weak extractants. Chapter 6 focuses of the development of bidentate pyrazolethiones for the selective extraction of cobalt from manganese in acidic sulfate streams. These reagents have been designed to favour coordination to metals in a tetrahedral geometry as shown by L. Emeleus and A. Smith for copper and zinc (Lucy Emeleus Thesis, University of Edinburgh 1999 and Andrew Smith Thesis, University of Edinburgh 2000).

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering (Metallurgy and Materials Engineering), May 2016 / The solvent extraction of iron and titanium from solution generated by the two-step sulphuric acid leaching of coal fly ash by Primene JMT was investigated. The influence of hydrogen ion concentration, Primene JMT concentration, aqueous to organic volume phase ratio and temperature on the extraction of iron and titanium was determined by the use of Design of Experiments. Hydrogen ion concentration and the interaction between the aqueous to organic volume phase ratio with Primene JMT concentration had a significant effect on the extraction of iron while temperature did not. Hydrogen ion concentration and temperature did not have a significant effect on the extraction of titanium, while the interaction between Primene JMT concentration and aqueous to organic volume phase ratio had a significant effect. Extraction improvement tests showed that at a hydrogen ion concentration of 0.28M, 88% iron and 99% extraction of titanium from coal-fly ash leach solution could be achieved. Construction of a McCabe-Thiele diagram showed that a four-stage solvent extraction system with Primene JMT could reduce the iron and titanium concentration in the coal fly ash leach solutions to below 0.05g/L / GS2016

Nenhuma / Foi realizado neste trabalho o estudo da recuperação de európio e ítrio de monitores de computadores sucateados por meio de técnicas hidrometalúrgicas. O trabalho foi composto de três etapas: (i) lixiviação ácida do pó de revestimento da tela de monitores CRT; (ii) separação dos elementos de interesse por extração por solventes em escala de bancada testes descontínuos e (iii) otimização da etapa (ii) em escala micro piloto testes contínuos. Na etapa de lixiviação ácida investigou-se a influência do agente lixiviante, da relação ácido/amostra, tempo e temperatura de reação na porcentagem de solubilização de európio e ítrio do resíduo em estudo. Obteve-se um máximo de solubilização destes (98% p/p) com o emprego de H2SO4 na relação ácido/amostra 1250g/kg em temperatura ambiente (25 C), 10% de sólidos e com agitação mecânica por 30 minutos. O licor obtido no processo de lixiviação, contendo 11,9 g/L de ítrio e 0,72 g/L de európio, foi submetido a testes descontínuos de extração por solventes com a finalidade de separação dos dois íons metálicos. Investigou-se o desempenho dos seguintes extratantes orgânicos no rendimento de extração das espécies de interesse: DEHPA, IONQUEST 801, CYANEX 272 e PRIMENE JMT. O DEHPA na concentração de 1,0 mol/L mostrou-se mais eficiente na separação do par Y/Eu, fator de separação igual a 111,4 na relação de fase A/O = 1 e agitação mecânica por 10 minutos. A partir da isoterma de extração e construção do diagrama McCabe-Thiele, observou-se que dois estágios de extração na relação A/O = 1,1 são suficientes para extrair todo o ítrio da fase aquosa para a fase orgânica, enquanto que o európio fica na fase aquosa. Na lavagem do orgânico carregado, uma solução de H2SO4 0,75 mol/L na relação de fase O/A = 5 foi suficiente para retirar todas as espécies coextraídos na etapa de extração. No processo de reextração, obteve-se 67% de reextração de ítrio da fase orgânica para a fase aquosa com o emprego de HCl 5,0 mol/L na relação de fase O/A = 1. A partir da curva de equilíbrio de reextração, determinou-se que são necessários no mínimo 12 estágios de reextração para se reextrair todo o ítrio da fase orgânica. Após definidas as melhores condições de extração, lavagem e reextração na etapa descontínua, realizou-se cinco ensaios contínuos de extração por solventes em escala micro piloto até se atingir a condição ótima de separação dos elementos em estudo. A melhor separação foi alcançada quando o circuito operou com três estágios de extração, sete de lavagem e quinze de reextração. Ao final do processo obteve-se um rafinado com 0,55 g/L de Eu, 16,7 g/L de Zn e concentração de Y menor que 0,001 g/L. No reextrato, a concentração de Y é de 41,4 g/L e 0,06 g/L de Eu, enquanto que a concentração de Zn foi menor que 0,001 g/L. / This work deals with the study of the recovery of europium and yttrium from discarded computer monitors through hydrometallurgical techniques. It comprises three phases: (i) acid leaching of the coating powder of the monitor screens CRT; (ii) separation of the concerning elements through solvent extraction in a laboratory bench scale discontinuous tests, and (iii) optimisation of phase ii in a micro pilot scale continuous tests. In the acid leaching phase, it was investigated the influence of the leaching agents, the relation acid/sample, time and temperature of the reaction in the percentage of solubilisation of europium and yttrium from the studied residue. The maximum solubilisation achieved (98 w/t%) occurred when H2SO4 in an acid/sample relation of 1250g/kg at room temperature (25 C), 10% of solids and mechanical agitation for 30 minutes were used. The liquor obtained in the leaching process, containing 11.9 g/L of yttrium and 0.72 g/L of europium, was submitted to solvent extraction discontinuous experiments aiming at the separation of the two metallic ions. The behaviour of the following organic extractants - DEHPA, IONQUEST 801, CYANEX 272 and PRIMENE JMT was investigated in relation to the performance of the extraction of the concerned species. DEHPA in concentration of 1.0 mol/L showed to be more efficient in the separation of the pair Y/Eu, with a separation factor equal to 111,4 for phase relation A/O =1, under mechanical agitation for 10 minutes. Based on the McCabe-Thiele diagram, it could be observed that two extraction stages in the relation A/O =1.1 were enough to extract all the yttrium in the aqueous phase to the organic phase, whereas the europium remains in the aqueous phase. In the loaded organic scrubbing, a H2SO4 0.75 mol/L solution in the relation phase O/A of 5 proved to be sufficient to remove all the co-extracted species in the extraction phase. In the stripping phase, 67% of the yttrium extraction was obtained from the organic phase to the aqueous phase by employing HCl 5.0 mol/L in the relation phase O/A = 1. From the stripping isotherm, it was determined that at least 12 stages of stripping are necessary in order to extract all the yttrium in the organic phase. After defining the best extraction, scrubbing and stripping conditions in the discontinuous phase, five continuous solvent extraction experiments were carried out in a micro pilot scale, until the optimum condition for separation of the elements under study was achieved. This degree of separation was attained when the circuit operated with three separation stages, seven washing stages and fifteen stripping phases. At the end of the process, a raffinate containing 0,55 g/L of Eu and 16,7 g/L of Zn and a pregnant stripping solution with 41,4 g/L of Y and 0,06 g/L of Eu was achieved.

O urânio é geralmente recuperado de seus minérios através da lixiviação com ácido sulfúrico seguido de extração líquido-líquido (ELL) para produzir o concentrado de urânio (yellow cake). Essa rota é usada pelas Indústrias Nucleares do Brasil S/A - INB, em Caetité/BA, Brasil, que utiliza a amina terciária Alamine 336 para extrair urânio do licor sulfúrico e como reextratante utiliza o cloreto de sódio (NaCl). Devido à escassez de água na região em que se situa essa unidade, toda água utilizada no processo é recirculada após tratamento com cal. Como nesse tratamento o íon Cl- não é removido, sua concentração aumenta a cada ciclo de reutilização da água, diminuindo a eficiência de extração do urânio, causando queda na produção de concentrado de urânio e perdas financeiras. Eventualmente a INB é obrigada a adicionar água nova no processo para reduzir o teor de Cl-. Este trabalho apresenta uma avaliação comparativa entre os seguintes sistemas de extração de urânio: U-H2SO4-Alamine 336 e U-H2SO4-Cl-Alamine 336. No primeiro sistema, a concentração de urânio variou entre 0,4 e 2,1 g/L. No segundo sistema, a concentração de urânio foi fixada em 2,0 g/L e a concentração de íons cloreto variou de 1,0 a 7,0 g/L. A concentração de Alamine 336 variou de 0,05 a 0,20 mol/L e a de sulfato (SO42-) de 0,24 a 1,05 mol/L nos dois sistemas. Exxsol D100 e tridecanol 5% v/v foram usados como diluente e modificador, respectivamente. Comparando os resultados obtidos, observa-se que a presença de cloreto na solução de alimentação tem impacto negativo sobre a extração de urânio com Alamine 336. Na ausência de cloreto atinge-se 90% de extração quando a concentração do extratante é de 0,10 mol/L ou maior, para todas as concentrações de sulfato e urânio utilizadas. Na presença de cloreto, o mesmo percentual é atingido apenas com concentrações de 0,20 mol/L do extratante e em concentração de cloreto abaixo de 3,0 g/L. Ou seja, a porcentagem de extração de urânio é reduzida drasticamente na presença de cloreto em altas concentrações, enquanto em baixas concentrações tal efeito negativo pode ser inibido aumentando a concentração de Alamine 336 ou diminuindo a concentração de sulfato. Para explicar o efeito negativo da presença do cloreto, dois prováveis mecanismos de extração para esses sistemas são apresentados: a competição entre o cloreto e o sulfato durante a protonação da amina e a extração do cloreto pelo complexo sulfato-amina, competindo com o trissulfatouranilato VI. Esses mecanismos podem ocorrer simultaneamente. / Uranium is usually recovered from ores by sulphuric acid leaching followed by solvent extraction in order to produce a uranium ore concentrate. Such route is used by Indústrias Nucleares do Brasil S/A - INB, at Caetité/BA, Brazil, which uses the tertiary amine Alamine336 to extract uranium from the sulphuric liquor and a sodium chloride solution as stripping agent. Due to water scarcity in this region, all water used in the process is recirculated after treatment with lime. At this treatment the chloride ion (Cl-) is not removed, causing the increase in Cl- concentration with each recirculation of water, reducing the efficiency of extraction of uranium, causing a drop in production of uranium concentrate and financial losses. Eventually the INB Company is required to add new water in the process to reduce the content of Cl-. In this work, a comparative evaluation between the following uranium extraction systems is carried out: U-H2SO4-Alamine 336 and U-H2SO4-Cl-Alamine 336. In the first system, the uranium concentration ranged from 0.4 to 2.1 g/L. In the second system, the uranium concentration was set at 2.0 g/L and chloride ion concentration ranged from 1 to 7 g/L. In both systems the concentration of Alamine 336 ranged from 0.05 to 0.20 mol/L and the sulphate (SO42-) concentration from 0.24 to 1.05 mol/L. Exxsol D100 and tridecanol 5% v/v were used as diluent and modifier, respectively. The comparison of the results showed that chloride ions have a negative impact on the uranium extraction with Alamine 336. In the absence of chloride ions, 90% of extraction is achieved for extractant content of 0.10 mol/L or higher, for all sulphate and uranium concentrations studied. In the presence of chloride ions, the same extraction efficiency is reached solely for extractant content of 0.20 mol/L and for chloride ions content lower than 3.0 g/L. The percentage on the uranium extraction is drastically reduced at high chloride concentrations, whereas at low chloride concentrations such negative effect may be inhibited by increasing the Alamine336 concentration or decreasing sulphate concentration. In order to explain the negative impact of chloride ions on uranium extraction, two probable mechanisms of extraction for both reaction systems are shown: competition between chloride and sulphate in amine protonation and the chloride extraction by amine-sulphate complex, competing with uranium (VI) oxide sulphate. These mechanisms may occur simultaneously.

This thesis investigates the mode of action of cationic reagents in the recovery of platinum group metals (PGMs) by anion exchange solvent extraction. Industry uses a range of extractants to achieve efficient concentration and separation of PGMs in hydrometallurgical processes, but an understanding of the processes at a molecular level is limited and restricts the options to improve efficiency. The research, sponsored in part by Johnson Matthey and Anglo American, explores two different aspects of the mode of action of reagents used to recover chloride and platinum. Chapter 1 reviews the extraction of chloridometalates in hydrometallurgy and other methods used to recover PGMs. The chapter also covers current ideas on whether formation of outer-sphere anion-cation molecular assemblies or whether larger supramolecular aggregates are responsible for the extraction of PGMs. These two separate routes of study can be investigated by various computational and experimental methods, which are discussed in Chapter 2. In Chapter 3, the model systems chosen to develop the methodologies utilised throughout the thesis are presented. The development involves the extraction of chloride ions by tributyl-phosphate (TBP) and then is extended to extraction of PGM chloridometalates in Chapter 4. Computational methods are used to probe the atomistic and supramolecular theories in predicting the most likely assemblies which will be formed in the transfer of anions between the aqueous and organic phase. Slope analysis and the determination of the contents of the organic phase is used to validate computational models, along with spectroscopic techniques to determine shape and size of assemblies formed during extraction. The application of these methodologies to an amide extractant is discussed in Chapter 5. Computational methods predict the probability of formation of specific complex assemblies during the extraction of PtCl62- by protonated forms of the amide. Determination of the stoichiometry involved in formation of the complex assemblies by slope analysis is reported along with analysis of water, metal and chloride content to confirm the computational model. Final conclusions on all systems explored within the thesis and suggestions for future work are presented in the final chapter. The combination of experimental and computational methods are shown to be very efficient in defining mechanisms of extraction, involving determination of structures formed during the process and how and why they form.

This work aims to define the modes of action of a series of metal extraction ligands with particular focus on how these depend on the formation of supramolecular assemblies. Though solvent extraction processes are well established industrially often the understanding, particularly of the metal coordination chemistry, is less so. A greater understanding of a variety of solvent extraction systems can lead to the development of stronger and more specific extractants. Chapter 2 examines the role of inter-ligand interactions in the extraction of copper by phenolic oximes and pyrazoles. Computational methods are used to understand the importance of inter-ligand outer-sphere interactions in square-planar copper complexes. It is shown that functionalisation at different positions on the phenol ring can either stabilise or destabilise the copper complex and it is possible to predict the strength of extractants from DFT calculations. Substitution ortho to the phenolic oxygen in the oximes and pyrazoles can have a major effect of enhancing the strength of extractants by “buttressing” the H-bonding between ligands. However, in the amino-methyl substituted oximes buttressing is so strong that is has an adverse effect on complex formation. Crystal structures are confirmed by both ENDOR EPR spectroscopy and DFT structures. A series of 6-X-4-methyl-2-(5-alkyl-1H-pyrazol-3-yl)- phenols (X = H, OMe, Br and NO2) was synthesised and characterised (X = H, OMe, Br and NO2) and the copper extractant found to be 6-nitro-4-methyl-2-(5-(1,3,5-tri-methyl-pentyl)- 1H-pyrazol-3-yl)-phenol extractants. Computational DFT studies in the gas phase were carried out to calculate the formation energies of analogous phenolic pyrazole copper complexes. The predicted order of these energies followed the same trend shown by experimental solvent extraction studies. Studies also showed that substitution can affect not only complex stability through inter-ligand interactions through hydrogen bonding in the outer-sphere but also the strength of metal-ligand bonds. Chapter 3 looks at synergistic solvent extraction systems: where more than one extractant works together to provide additional strength and selectivity. Combinations of neutral N and O donor ligands with carboxylic, phosphinic and sulfonic acids were studied by solvent extraction, crystallographic and computational methods. Crystal structures and DFT-optimised structures show that ligands and acid form pseudo-tridentate ligands where both the neutral ligand and the deprotonated acid are coordinated directly to the metal centre with inter-ligand hydrogen bonding allowing for a more flexible backbone than a classic tridentate system. Although synergistic extractions systems often utilise carboxylic acids many of the structures show the similarities with systems containing phosphinic acids and it was shown experimentally that some extraction systems show greater synergism with phosphinic than carboxylic acid in the recovery of nickel. Chapter 4 deals with the extraction of molybdenum with commercial phosphinic acid extractant Cyanex 600. The propensity for molybdenum to form oxo clusters in aqueous solutions and the influence pH in both the speciation of the Mo species and extraction conditions contributes to a complex extraction profile. The pH dependence of extraction shows that different mechanisms operate at low (pH < 0) and high (pH > 0) pH. The extraction curve shows a conventional S-curve between pH 0 and 1.5 and slope analysis within this pH range gives a value very close to two but identification of structures which match this profile is complex. Maximum pH extraction is see at ~ pH 1.5. ESMS studies identified very similar species in the organic phase despite the variation seen in the S-curve. A survey of the structures of metal complexes of phosphinate ligands suggests that molybdenum-phosphinate complexes can often form cubane-like structure and negative ion ESMS data supports the concept of cluster formation in the organic phase. A common feature of the spectra are tetra- tri- and bi-metal- oxo species and spectra show a large number of peaks. It is very probable that the extraction of molybdenum(VI) with phosphinic acids is a dynamic system as extraction is influenced by the molybdenum speciation in the aqueous phase which is in turn influenced by both the pH and the molybdenum concentration both of which change over the course of a conventional extraction.

This thesis focuses on development of new regents which are suitable for recovering nickel, cobalt and copper from laterite leach solutions, specifically focusing on reagent requirements for novel base metal flowsheets developed by Anglo American. The work aims to design reagents which can extract nickel(II), cobalt(II) and copper(II) from a highly acidic aqueous sulfate solutions whilst showing selectivity over iron(II) and iron(III). Chapter 1 reviews current extractive metallurgy processes for separating and concentrating metals in laterite ores and describes new flowsheets proposed by Anglo American. Chapter 2 considers whether single reagent molecules with sets of tridentate donor atoms can generate sufficiently stable nickel(II) complexes to allow selective extraction of nickel from an aqueous sulfate solution. The salicylaldimines, 3-X-4-alkyl-6-(quinolin-8-imino)phenol, 3-X-4-alkyl-6-(2- methoxyphenylimino)phenol and 3-X-4-alkyl-6-(2-thiomethoxyphenylimino)phenol (alkyl = tert-butyl or tert-octyl; X = H, Br or NO2), were selected for study. The synthesis and characterisation of these proligands and their nickel(II) complexes are reported. XRD structures of Br-substituted salicylaldimines and their nickel(II) complexes are compared and discussed. The 4-tert-octylsalicylaldimines were used to extract nickel(II) from an aqueous sulfate solution with a pH > 2.8 and 3- nitro-4-tert-octyl-6-(quinolin-8-imino)phenol was found to be the strongest extractant in the series with a pH0.5 of 3.5. Computational studies of an analogous series of salicylaldimine proligands in the gas phase calculated the formation energies of their nickel(II) complexes and the predicted trend follows the experimentally determined solvent extraction results. Chapter 3 investigates modifications to phenolic pyrazoles, which are known copper(II) extractants. A series of 6-X-4-methyl-2-(5-alkyl-1H-pyrazol-3-yl)-phenols (X = H, OMe, Br and NO2) was synthesised and characterised. Varying the 6-X-substituent of the phenolic pyrazole altered the strength of copper extraction and 6-nitro-4-methyl-2-(5-(1,3,5-tri-methyl-pentyl)-1H-pyrazol-3-yl)-phenol was found to be the strongest extractant in the series. Analysis of XRD structures of related phenolic pyrazoles and their copper(II) complexes showed evidence of inter- and intra-molecular hydrogen bonding. Computational DFT studies in the gas phase were carried out to calculate the formation energies of analogous phenolic pyrazole copper complexes. The predicted order of these energies followed the same trend shown by experimental solvent extraction studies. The double deprotonation of 4-tert-butyl-(pyrazol-3-yl)-phenol at high pH forms a polynuclear complex in the organic phase with a copper(II) to ligand ratio of 1:1, thereby increasing the mass transport efficiency of copper by the reagent. The synthesis and characterisation of the [Cu16(4-tert-butyl-(pyrazol-3-yl)- phenolate)16(EtOH)4(H2O)2] wheel complex was carried out to demonstrate how such polynuclear copper(II) complexes could be formed under solvent extraction conditions. Chapter 4 explores the solvent extraction of nickel(II) and cobalt(II) by novel combinations of neutral nitrogen-donor heterocyclic ligands with organic acids, such as dinonylnaphthelenesulfonic acid (DNNSAH). The synthesis and characterisation of 2,6-bis(5-alkyl-1H-pyrazol-3-yl)-pyridine, 2-(5- alkyl-1H-pyrazol-3-yl)-pyridine and 5,5'-alkyl-3,3'-bi-1H-pyrazole (alkyl = tert-butyl or nonyl) and their nickel(II) complexes were reported. Also reported are synthesis and 6-N-alkyl-2-(2-pyridinyl)- benzothiazole (alkyl = n-butyl or n-decyl) and 2-(1-Isopropyl-benzimidazol-2-yl)-pyridine. The extraction of nickel(II) from highly acidic mixed metal aqueous sulfate solutions by some of these ligands was studied. These synergistic mixtures demonstrated remarkable strength and selectivity for nickel(II), and cobalt(II) over iron(II). XRD structures of nickel(II) complexes of 2,6-bis(5-tert-butyl- 1H-pyrazol-3-yl)-pyridine, 2-(5-tert-butyl-1H-pyrazol-3-yl)-pyridine and 5,5'-tert-butyl-3,3'-bi-1Hpyrazole with sulfonates or perchlorates as ion-pairs have intermolecular hydrogen bonding interactions between the inner-sphere ligands and the counterions.

Protactinium (Pa) is an actinide with chemical properties that are unique among the actinide elements. While the properties of other actinides are to a large extent understood, much of the chemistry of Pa remains a mystery. This thesis aims to illuminate new understanding of Pa chemistry through behavioral analysis using analytical techniques including liquid-liquid extraction (LL); extraction chromatography (ExC); and spectroscopic studies. Applications of radioanalytical chemistry and Pa: Through the research presented in this dissertation, we have developed a new way to separate uranium (U), thorium (Th), and Pa from complex environmental samples. The approach has been demonstrated for U-series dating of materials by alpha spectrometry. The method can be applied to geochronology, as well as to nuclear-forensic analysis of uranium-containing materials. In studies presented here, samples from a Paleolithic lake (Lake Bonneville, Utah USA) were analyzed for the radioactivity concentration of 230Th, 231Pa, 234U, 235U, and 238U by isotope dilution alpha spectrometry. Radioactivities were used to estimate of the time period of formation of the deposit from which the samples were collected. Ages were determined from the isotopics ratios; i.e., 231Pa/235U (40 ka); and 230Th/238U (39.5 ka) we found to be concordant with radiocarbon-14 dates (37 ka) obtained by collaborators at Brigham Young University. These studies inspired the development of a novel ExC resin to facilitate preparation of highly pure tracer isotope (233Pa) from a neptunium-237 (237Np) source. The material used for this development comprised 1-octanol adsorbed to a semi-porous resin material. The new approach greatly improved the yield and purity of 233Pa used for these chronometric analyses Developing an understanding of the chemistry of Pa at trace concentrations: The new-improved analytical described above led to the hypothesis that analytical separations approaches could be used to develop a more detailed understanding of Pa chemistry. Toward this goal, experiments were conducted to understand how the extraction of Pa is impacted by solution acidity [H+], anion concentration [A-; Cl-, NO3-], and extractant concentration ([2,6-dimethyl-4-heptanol, DIBC]). A full-factorial experimental design was employed to create a model that would allow for predictions in Pa behavior, as well as describe the nature of the observations. This model generated a multivariate equation that relates the distribution coefficient ([Pa] organic phase/ [Pa] aqueous phase) to each of the parameters ([H+], [A-], and [DIBC]). Further studies expanded to other alcohols (ROH) used as extractants (1-octanol, (2,6)-dimthyl-4-heptanol, and 2-ethyl-hexanol); and the results were analyzed using the slope analysis and comparative extraction studies using the model and compared to other actinide elements (Th, U, Np, americium (Am)) by both LL and ExC systems. These experiments revealed unique chemical behavior of Pa with respect to the other actinides. For example, it was found that Pa was the only actinide element to be extracted into the organic phase under acidic conditions (HCl and HNO3). Slope analysis experiments elucidated the stoichiometric identity of Pa species, with respect to the anion and extractant. Future studies will aim to identify the oxygen stoichiometry and species by X-ray absorption techniques. Investigations of the organic phase: In the final sections of this thesis, experiments are presented that are intended to determine if aggregation plays a key role in the extraction of Pa in systems containing 1-octanol and 2-ethyl-hexanol. This work is done in the absence of metal ions to control the dynamics of the organic phase, and are analyzed by tensiometry and Karl Fisher titrations with small angle X-ray scattering and molecular dynamic simulations. A key novel finding of these studies in that ROH molecules arrange in nanoscale aggregates that decrease the interfacial tension between the phases and extract a significant amount of water into the aggregates stabilized by a network of H-bonding. These studies lead to the hypothesis for future studies that Pa extraction is likely facilitated by solvation into the organic phase via ROH aggregates. The sum of the findings and observations of this dissertation provide insight into the chemical nature of Pa: (1) Novel extraction methods to obtain radiochemically pure fractions show that Pa can be efficiently extracted and separated from complex matrices to aid in chronometric analysis for geochronology or nuclear forensics; (2) Statistical modeling to develop a better understanding of the main effects of solvent extraction parameters; (3) Equilibrium analysis to improve our understanding of chemistry of Pa and how it is unique to the actinides; (4) Aggregation analysis to demonstrate a solvent centric understanding of extraction studies, these results lead to future experiments to investigate how organic phase aggregation can influence solvent extraction selectivity.

Approximately 70% of the western world's known nickel reserves are contained in laterite ores, but only 30% of the world's nickel production comes from these ores. This is due to the lack of economically viable technology to extract the nickel from these ores. However, recent advances in pressure acid leaching technology have resulted in new commercial attempts to extract nickel and its valuable by-product, cobalt, from laterite ores. The commissioning of three nickel laterite projects in Western Australia in the late 1990s represents the first of these new generation nickel operations, with several other projects; in Australia and overseas, in various stages of development. Unfortunately, several technical issues have hindered full production in these new refineries. Some of these problems are directly attributable to the mixer-settler contactors used in the solvent extraction process. This has highlighted a need to develop alternative contactors for industrial use. Electrostatic Pseudo Liquid Membrane (ESPLIM) is an alternative, novel technique to conduct the solvent extraction process. It combines the basic principles of solvent extraction, liquid membrane and electrostatic dispersion into a simple, compact reactor that utilises many advantages of each technique. The aim of this study w as to develop a method of extracting and separating cobalt from an acidic nickel laterite leach solution using ESPLIM. Bench scale tests using synthetic and actual leach solutions have shown that: the design and construction materials of the baffle plate and electrodes have a significant effect on the performance of the reactor; an AC power supply provided better droplet dispersion than a DC power supply; an increase in the applied electric field strength above a critical value resulted in a decrease in the aqueous droplet size and an increase in residence tune. / These effects increased the extraction efficiency and the concentration of the loaded strip solution. However, further increases in applied electric field strength decreased efficiency due to excessive levels of swelling and leakage; the known extraction isotherms for cobalt and nickel apply in the ESPLIM technique; salts of soluble organic acids influence extraction efficiency by changing the aqueous pH and interfacial tension; the use of ammonia was found to be effective as a replacement for salts of soluble organic acids; the ESPLIM reactor can cope with large changes in the flow rates of both feed and strip solutions. However, an increase in the feed flow rate should be accompanied by a relative increase in the ship flow rate to maintain high extraction efficiencies; the baffle design has a significant impact on the levels of swelling and leakage; provided the electrostatic field strength is maintained and flow rates are increased proportionately to the size of the reactor, no significant scale-up issues were observed, indicating that the data generated in bench scale studies could be applied to plant scale contactors. The optimum conditions, devised as a result of this investigation, to extract cobalt from an acidic nickel laterite leach solution using the ESPLIM technique are as follows: an applied electric field strength of 5.5 kV/cm. a raffinate pH of 5.5, a solvent containing 10% Cyanex 272 with 5% TBP in Solvent HF diluent, a feed to strip flow ratio of approximately 5 and a 1 M H[subscript]2S0[subscript]4 strip solution. At these conditions, almost complete cobalt extraction is achieved after only two extraction stages. A comparable extraction using conventional mixer-settlers could only be achieved after five stages.

The bulk of the world's known nickel reserves are contained in laterite ores but sulphidic ores remain the main source of the Western world's nickel production. With the continuing increase in nickel consumption and the depletion of sulphidic ores, the traditional source of nickel, the extraction of nickel from lateritic ores has been the subject of research interest worldwide. Advances in pressure acid leaching (PAL) technology have resulted in significant commercial attempts to extract nickel from these ores. Leaching the ore with sulphuric acid at elevated temperatures and pressures allows almost complete dissolution of the nickel and cobalt, a valuable byproduct of these ores, but yields highly contaminated pregnant leach solutions. Separating and purifying the nickel and cobalt from these solutions remains a hindrance to full commercial production. Several purifying techniques have been commercialised but all suffer from continuing technical problems. Among them, however, the direct solvent extraction (DSX) technique offers several advantages. Direct solvent extraction involves the separation of the nickel and cobalt directly from the partially neutralised pregnant liquor stream (PLS) by solvent extraction with Cyanex(R) 272 as the extractant. However certain contaminants adversely affect the solvent extraction process. Among them is chromium and little is known about the solvent extraction behaviour of this metal. The present work investigated the solvent extraction of chromium with Cyanex(R) 272. It was found that the solvent extraction behaviour of chromium(III) and chromium(VI), both of which could be found in PAL-generated PLS, are distinctly different. / For chromium(III), solvent extraction tests showed that (a) it is extracted in the pH range 4-7; (b) the extraction is partly influenced by diffusion; (c) the apparent equilibration time is significantly longer than most transition metals; (d) increases in temperature from 22 to 40 C resulted in increases in the extraction; (e) the pH0.5 increases in the order nitrate < chloride < sulphate in the presence of these anions; (f) the presence of acetate depresses extraction of chromium(III) when the solution is allowed to stand before extraction; (g) in the PLS, chromium(III) precipitated at lower pH than that predicted by the solubility product principle; and (h) the pH0.5 decreases as the Cyanex(R) 272 concentration increases. Chromium(III) is initially extracted by solvation of its inner sphere complex, which then undergoes further reaction in the organic phase leading to the formation of a much more stable species that is difficult to strip. A reaction scheme together with a description of both the initially extracted and resulting stable species is proposed. Extraction of chromium(VI), on the other hand, (a) occurs at pH less than 2 by solvation of chromic acid; (b) is independent of the aqueous phase composition; (c) does not occur in the pH range (3-6) used in the separation of nickel and cobalt. The latter is irrespective of temperature up to 40 C, the use of industrial PLS as the aqueous phase or the presence of an anti-oxidant in the organic phase. The stripping of chromium(III) from a loaded organic phase can be achieved using 1-4 mol L-1 mineral acids provided the stable organic species have not formed making industrial scale stripping of chromium(III) from Cyanex(R) 272 difficult. The exact composition of the aqueous phase during extraction affects the stripping efficiency.