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The thesis deals with the modification of salicylaldoxime-based reagents used in hydrometallurgical extraction, addressing rational ligand design to tune copper(II) extractant strengths and also the development of reagents which are capable of transporting transition metal salts. Chapter 1 reviews current solvent extractant technology for metal recovery, including the limited knowledge of the effect of substituents on extractive efficacy. Advances in leaching technology have led to systems wherein increases in process efficiency could be obtained using reagents which can transport both a transition metal cation and its attendant anion(s), and the potential advantages of metal salt extractants are discussed. The problems encountered when trying to extract hydrophilic anions selectively into organic media are also considered. Chapter 2 discusses techniques used in industry to tune reagent properties, many of which depend on the importance of H-bonding in non-polar solvents. Synthesis of a series of 5-alkyl-3-X-2-hydroxybenzaldehyde oximes (X = a range of substituents) is described and copper extraction experiments are reported. 3-Substitution is found to alter reagent strength by two orders of magnitude, with 3-bromo-5-tert-butyl-2- hydroxybenzaldehyde oxime the strongest extractant. An analysis of X-ray structures of several ligands and copper(II) complexes is given in an attempt to establish whether trends in the solid state structures can account for variations in extractant strength. A more detailed analysis of the hydrogen bonding in salicylaldoximato copper(II) complexes and ligand dimers is carried out in Chapter 3, with the aim of defining how substituent effects could be used to design reagents with appropriate extractive behaviour. 3-X-2-Hydroxybenzaldehyde oximes with no 5-alkyl substituent are synthesised and subjected to a detailed study by X-ray crystallography and computational techniques, which, alongside evidence provided by CID-MS experiments, suggest that the dominant substituent effect in determining extractant strength is the ability to “buttress” the pseudomacrocyclic hydrogen bonding motif involving the oximic hydrogen and phenolic oxygen. Ligands with 3-substituents capable of accepting H-bonds were found to be stronger extractants than those which could not, and the steric hindrance afforded by bulky substituents made 3,5-di-tert-butyl-2-hydroxybenzaldehyde oxime the weakest extractant. Ligand acidity is also noted to have a significant effect on reagent strength, with electronwithdrawing substituents lowering the pKa of the phenolic proton and increasing extractive efficacy. Chapter 4 focuses on metal salt extraction, and the development of selective, robust and hydrolytically stable reagents. Six novel extractants, based on a salicylaldoxime scaffold with a pendant dialkylaminomethyl arm, are described. Only 5-tert-butyl-3- dihexylaminomethyl-2-hydroxybenzaldehyde oxime and 3-tert-butyl-5- dihexylaminomethyl-2-hydroxybenzaldehyde oxime have sufficient solubility to be effective reagents. The former extracts CuCl2 and ZnCl2 in a highly efficient manner, with one mole of metal salt extracted per mole of ligand, twice the expected capacity. X-ray structure determination of complexes of the related ligand 5-tertbutyl- 2-hydroxy-3-piperidin-1-ylmethylbenzaldehyde oxime defines the binding mode, with the chloride anions bound to the inner sphere of the metal cations. Loading and stripping experiments show it to be an extractant with potential commercial application. Cation and anion selectivity of the two extractants defined above is the focus of Chapter 5, which begins with an overview of techniques and attempts to attenuate the Hofmeister bias, the main factor in the selective extraction of hydrophilic anions into organic media. pH loading profiles show the 3- dihexylaminomethyl isomer to be an effective CuCl2 and CuSO4 extractant, but the cation extractive efficacy of the 5-isomer is hampered by the 3-tert-butyl group. Both ligands are found to be selective for Cl- > SO4 2-, following the Hofmeister bias. Further information on anion binding is provided by solid state structures of copper salt complexes, showing that in all cases the copper(II) cation interacts in some way with the anion. Cation extraction is affected significantly by the anion present, with FeIII selectively extracted against CuII in the presence of SO4 2- which is consistent with cation-anion interactions having great influence on the overall stability of the ligand-metal salt assembly.

Selective coordination to zinc over other members of the first row transition metal series is important for the commercial application of lipophilic ligands for the hydrometallurgic recovery of the metal. In order to achieve selectivity for zinc(n) over other ions, particularly copper(II) and iron(III), ligands have to be designed which take advantage of zinc's preferred tetrahedral coordination geometry and the borderline donor atom preference of the metal. With such ligands in mind, three new classes of ligand system have been designed and synthesised based on the benzimidazole, quinoline and pyridine ring systems with appended phosphinic and thiophosphinic acid anionic donor groups. Benzimidazole ligands which bind zinc in a 2:1 manner in solution have been made and their complexation ability assessed by ESMS, (^31)p NMR, liquid-liquid extraction, fluorescence and UV absorption spectroscopic methods. A bisbenzimidazole ligand with a C(_3) spacer in the 2,2' position was synthesised and shown to bind zinc initially in a 2:1 manner, at low metal concentrations, and predominantiy as a 1:1 species at higher metal concentrations. The formation constant for the ML complex was shown to be logK(_ML)=5 by analysis of the NMR titration curve, which was in close agreement with the value obtained from liquid-liquid extraction studies. A directly linked 2,2'- bisbenziraidazole system was also synthesised as an extension to previous work, however isolation of the target ligand proved to be difficult due to the insolubility of the desired bis-acid.8-(Quinolinyl)phenylphosphinic acid and 8-(2-metiiylquinolinyl)phenylphosphinic acid were also synthesised and their solution complexation behaviour studied in detail. The unsubstituted ligand appeared to form 1:1 complexes with zinc at all the metal concentrations studied, and the absence of the methyl substituent does not inhibit coordination to the ferric ion. In contrast the metiiyl substituted ligand initially forms a 2:1 L:M complex, and 1:1 complexes at higher metal concentrations. The initial ML(_2) complex probably involves coordination of two of the phosphinic acid moieties. Three pyridyl derived ligand systems were also synthesised varying the bulk of the C-6 substituent and the effect of the phosphinic versus the thiophosphinic acid moiety towards zinc coordination was examined. Both of the methyl appended ligands were shown to bind zinc in a 2:1 manner, with the thiophosphinic acid exhibiting a greater avidity for zinc. In contrast, the unsubstituted ligand predominantly forms 1:1 complexes at all metal concentrations.

Solution density modelling is important in hydrometallurgical processes as accurate predictions of single and mixed electrolytes can be used in the design of equipment and their sizing, heat transfer calculations and choosing of materials for construction. This research project entails modeling of electrolyte solutions by extending the Laliberte and Cooper (compound level) model to ionic level where an electrolyte solution is modeled as a mixture of cations, anions and water molecules. This modeling predicts single and mixed electrolyte density as a function of electrolyte temperature in degrees Celsius; water, cation and anion apparent volumes in cubic centimeters; and their respective concentrations in the electrolyte as mass fractions. The model was developed by fitting single electrolyte density data reported in literature using the least squares method in Microsoft Excel®. The following 26 single electrolyte solutions were used in the fitting exercise: Al2(SO4)3, BaCl2, CaCl2, CdSO4, CoCl2, CuSO4, FeCl3, FeSO4, HCl, HCN, HNO3, K2CO3, LiCl, MgSO4, MnCl2, Na2SO3, NaF, NaI, NaOH, (NH4)2SO4, NiCl2, SrCl2, ZnCl2, ZnBr2, (NH4)2C2O4 and KNO2. The above electrolytes attributed to the following ions: Al3+, Ba2+, Ca2+ Cd2+, Co2+, Cu2+, Fe3+, Fe2+, H+1, K+1, Li+1, Mg2+, Mn+2, Na+1, NH4+1, Ni2+, Sr+2, Zn2+, SO42-, Cl-1, CN-1, NO3-1, CO32-, OH-1, SO32-, Br-1, F-1, I-1, C2O4-2 and NO2-1. This translated to a combination of at least 216 single electrolyte solutions which could be feasibly modeled, and a solution with at most 10 anions for mixed electrolytes, which is comparable with practical hydrometallurgical solutions. A database of volumetric parameters was generated comprising a total of 18 cations and 12 anions. The validation of the developed model was done by predicting densities for both single and mixed electrolytes not used in the fitting exercise. The average density error i.e. the difference between experimental and model density for the single electrolyte solutions was 22.62 kg m-3 with a standard deviation of 39.66 kg m-3. For the mixed electrolytes, the average density error was 12.34 kg m-3 with a standard deviation of 24.48 kg m-3. These calculated errors translated to a maximum percentage average error of less than 4% for single electrolyte solutions and maximum average percentage of less than 3% for mixed electrolyte solutions.

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Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 271-303).

The kinetics of zinc extraction from perchlorate solutions with di(2-ethylhexyl) phosphoric acid in n-heptane have been measured using the rotating diffusion cell technique. The extraction of zinc is controlled by the mass transfer of reactants (Zn²⁺ and D2EHPA) to the interface. At low zinc concentrations, the system is controlled by the aqueous transport of Zn²⁺ to the interface; at higher zinc concentrations transport of D2EHPA becomes rate controlling. For the range of D2EHPA concentrations examined, the transport of D2EHPA is rate controlling. Bulk pH has a negligible effect, except perhaps at the lowest pH values examined, where there may be a slight decrease in extraction rate. This decrease was attributed to less favourable thermodynamics at low interfacial pH values. It appears that the chemical reaction rate is fast enough that it has a negligible effect on the overall extraction rate. A basic mathematical model was developed which is adequate for predicting the extraction rate under variable conditions of zinc concentration, D2EHPA concentration, and pH. The effect of using a partially loaded organic extractant was also investigated, and the system was found to be mass transfer controlled. An extended mathematical model was developed which predicts that the speciation of organic complexed zinc changes with increasing preload, and at high loadings the direction of ZnL₂HL and ZnL₂(HL)₂ flux reverses, with these species providing extractant to the interface. At very high loadings, ZnL₂HL provides almost all the extractant to the interface. Experimental studies of the effect of temperature on the rate of zinc extraction resulted in a calculation of the activation energy which was consistent with a diffusion controlled mechanism. Finally, the effect of different filter pore sizes on extraction was examined. The extraction rate decreases significantly with a very small filter pore size, while there appeared to be little or no effect for larger filter pore sizes. For the filter pore size used in this study, it was therefore concluded that the filter pores do not pose an additional resistance to mass transfer. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

In recent years a significant amount of research has gone into the development of a feed pretreatment process for the concentrate refined at Anglo American Platinum's Precious Metals Refiners (PMR). Such a process has the potential to significantly simplify the downstream refining process and reduce the number of unit processes required for purification. One of the considered options involves a high temperature oxidative roast process followed by a high temperature hydrochlorination process to volatilise base metal chlorides and other impurities. The resulting precious group metal (PGM) concentrate is cleaner and thus requires significantly less process steps to final product. The off-gas from hydrochlorination contains predominantly silver, copper, nickel and iron. This off-gas undergoes a quench-scrub to condense the base metal chlorides. The quench-scrub liquor undergoes a dechlorination process with sulfuric acid to precipitate AgCl(s). The filtrate from this process then undergoes an electrochemical reduction process to recover copper metal concentrate. The objectives of this study were to: i. Determine the operating conditions for an electrochemical reduction process aimed at recovering copper as a copper powder from a sulfuric acid stream containing copper, nickel and iron. ii. Develop a conceptual flowsheet for a batch electrochemical process and estimate the capital cost and operating cost.