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Froth flotation has been used to concentrate minerals for over a century (Finch and Dobby, 1990) and it is essential for the economical recovery of metals which are present at low concentrations. The traditional flotation cell consists of a stirred tank incorporating air injection. In recent decades columns have appeared to offer advantages for platinum flotation. This project is a comparative study of the use of column and mechanical cells as cleaners for the flotation of an UG-2 (Upper Group 2) platinum ore. A laboratory column cell, 1.8 m high and 60 mm in diameter, was constructed to have the same volume as a conventional 5L Denver mechanical cell. Batch cleaning tests were used to compare the two types of cells, while varying the depressant dosage and conditioning technique. The performance of the column cell when the pulp was recycled was also compared. Finally the effect of doubling the column height, whilst maintaining the same mass percent of solids as in the original column, was investigated. Samples were subjected to acid digestion to determine Copper (Cu) and Nickel (Ni) recovery as an indicator of platinum recovery. Platinum Group Metals and Gold (PGM+Au) assays were performed on samples from a final series of tests that used a different but similar ore sample. The investigations showed that the mechanical cell performed better than the column. The PGM grade in the mechanical cell was 6.5ppm higher for a common recovery of 80% PGM in both cells. The performance of the column cell was only marginally improved when the pulp was recycled. Mass recovery data indicated that the column cell required less depressant for reducing the mass recovery. The corresponding grade recovery curves showed that for a 10 g/t depressant addition, the grade of the concentrate produced in the column cell doubled whilst that of the mechanical cell revealed no significant change. It was suggested in literature (Whitney and Yan, 1996) that the depressant was more effective in a column cell, due to the absence of agitation by an impeller. Platinum recovery data from the final series did not confirm the interesting trend observed with the preliminary tests (Cu/Ni) at a low depressant dosage (10g/t), but marginal improvements were noted at higher dosages. The effect of agitation during conditioning with depressant was also investigated. Gentle conditioning of the depressant, prior to column flotation, resulted in a higher grade and recovery of PGM as compared to conditioning by means of the recirculation pump. The PGM grade when gentle conditioning was employed was 9 ppm higher for a common PGM recovery of 80% for both conditioning techniques. Finally it was found that increasing the column height improved the grade-recovery relationship. The PGM grade obtained by the longer column was 8 ppm higher for a common PGM recovery of 75% in both columns. The performance of the longer column was similar to that of the mechanical cell. Tests were also conducted at a platinum concentrator, to compare the performance of a 378L pilot-plant column (5.5m high and 0.3m diameter), to that of a pilot-plant consisting of six mechanical cells. The pilot test rig of mechanical cells (FCTR) achieved a significantly better recovery than a pilot column. However, by decreasing the column feed flowrate and thereby increasing the residence time, a substantial improvement in the PGM grade and recovery was obtained by the column cell. / Thesis (M.Sc.Eng.)--University of KwaZulu-Natal, Durban, 2012.

Distinctive fine-structure due to ³⁵Cl/³⁷Cl isotopologue and isotopomer effects is resolved at high magnetic fields for ¹⁹⁵Pt and ¹⁰³Rh NMR signals, resulting in a unique NMR “finger-print”, with which it is possible to uniquely identify all chlorido containing Pt(IV) and Rh(III) complexes. In this study, these isotope shifts are computed from first principles in order to provide a solid theoretical framework for the empirical observations. Use is made of DFT to calculate the ³⁵/³⁷Cl and ¹⁶/¹⁸O induced isotope shifts in the ¹⁹⁵Pt NMR spectra of [Pt³⁵Cl₆]²⁻ and [Pt³⁷Cl₆]²⁻, for the [Pt³⁵Cl n ³⁷Cl₅₋ n(H₂O)]⁻ (n=0-5), cis-Pt³⁵Cln³⁷Cl₍₄₋n₎(H₂O)₂ (n=0-4), and fac-[Pt³⁵Cl n³⁷Cl₍₃₋ n₎(H₂O)₃]⁺ (n=0-3) series. The computational protocol is extended to calculate the ³⁵/³⁷Cl and ¹⁶/¹⁸O induced isotope shifts in [Pt³⁵Cl n³⁷Cl₍₅₋ n₎(OH)]²⁻ (n=0-5), cis- [Pt³⁵Cln³⁷Cl₍₄₋ n₎(OH)₂]²⁻ (n=0-4), fac-[Pt³⁵Cln³⁷Cl₍₃₋ n₎(OH)₃] ²⁻ (n=0-3), cis- [Pt³⁵Cl n³⁷Cl₂₋n(OH)₄]²⁻ (n=0-2) and [Pt³⁵Cl n³⁷Cl₍₁₋ n₎(OH)₅]²⁻ (n=0-1). For Rh(III), the ³⁵Cl/³⁷Cl isotope shifts in the ¹⁰³Rh NMR spectra of [Rh³⁵Cl n³⁷Cl₅₋ n(H₂O)] ²⁻ (n=0-5), cis-[Rh³⁵Cl n³⁷Cl₍₄₋ n₎(H₂O)₂]⁻ (n=0-4), and fac-Rh³⁵Cl n³⁷Cl₍₃₋ n₎(H₂O)₃ (n=0-3) were calculated. The ¹⁹⁵Pt and ¹⁰³Rh NMR chemical shifts computed for these species reproduce the order of magnitude of the observed effect reasonably well, up to ca. 1 ppm. In most cases, general trends are also captured qualitatively, thus providing the first theoretical basis for the origin of subtle isotope shifts in ¹⁹⁵Pt NMR spectra. Neither simple polarizable continuum models nor small, microsolvated complexes lead to improved isotope shifts for the series investigated, however, valuable insight into the degree of solvent interaction was gained. Using the polarized continuum model to calculate shielding/bond-length derivatives together with gas-phase zero-point corrections to estimate shieldings, it was shown that the contraction of the coordination sphere in the hydroxide complexes cause the Pt-Cl bonds to become magnetically equivalent, justifying why their isotopomers aren't resolved. In this study, theoretical modelling of structural effects on NMR parameters extends to the smallest scale, distance changes of a few femtometers upon isotopic substitution.

A kinetic study on polycrystalline platinum (Pt) in sulphuric acid is presented. An electrochemical kinetic mechanism of Pt oxide reduction and surface oxide structures are proposed. The reduction reaction was studied by cyclic voltammetry (CV) and various potential programs that combine sweep and hold periods by an assembled analog instrumentation. The reduction peak was studied under three surface conditions: same oxide coverage θ and same potential E, different θ and same E, and same θ but different E, to determine the influence of θ and E on the peak potential and peak shape. The double-layer charge measured previously by dynamic electrochemical impedance spectroscopy (dEIS) was used to correct the CV baseline. Differential-equation-based models as a function of θ and E were investigated to simulate the oxide reduction and oxidation, and estimate kinetic parameters. A simple mechanism combining desorption and multi-layer growth mechanisms showed good fit with both the spread-out oxidation peak and the sharp reduction peak. A microscopic surface oxide growth model was proposed to explain the surface oxides reduction mechanism. / Graduate

ABSTRACT Background: There is a paucity of empirical data on the impact of HIV/AIDS on mortality in the mining industry in the pre-ART era. Such data will provide a baseline against which the efficacy of antiretroviral treatment can be measured into the future. Objectives: To measure all-cause mortality in a population of platinum miners between 1992 and 2002, the impact of HIV/AIDS on mortality in this group and to determine the pattern of other cause-specific mortality. Methods: This was a primary analysis of mortality in an open cohort of male semi- and unskilled workers at a platinum mine. Using Poisson regression, all-cause, HIV/AIDSrelated and other cause-specific mortality rates and rate ratios were calculated by age and calendar year. Results: There were 1986 deaths in the cohort of 29954 subjects who contributed 200657 person years of follow up over the 11 year period of the study. Crude all-cause mortality increased from a base of 5.1 per 1000 person years at risk (pyar) (95% CI 4.2- 6.2) in 1992 to 20.4 per 1000 pyar (95% CI 18.3-22.8) in 2002. Age-adjusted all-cause mortality increased more than three-fold from 1992 to 2002 (RR 3.2, 95% CI 2.5-4.0). The excess mortality was attributed to HIV/AIDS-related deaths which increased from 0% in 1992-1994 to 5.1% of total deaths in 1995 and reached 63.3 % of deaths in 2002. Mortality due to other communicable diseases, non-communicable diseases and injuries remained stable throughout the study period. Conclusion: The impact of the HIV/AIDS epidemic on mortality in this group of platinum mine workers has been profound and comparable to that experienced by the general South African population. The data reported here provide a baseline to measure the impact of antiretroviral treatment on the future course of mortality due to the epidemic.

Lam Wai-yean. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1978. / Bibliography: leaves 108-109.

This work aims to develop solvent extractants to recover platinum and palladium from highly acidic chloride solutions bearing other platinum group metals (PGMs). In general, metal values can be recovered by solvent extraction through three different mechanisms: metal cation extraction (1); metalate anion extraction (2); or metal salt extraction (3). Mn- + n(LH)(org) ⇌ [M(L)n](org) + nH+ (1) MClx n- + nL(org) + nH+ ⇌ [MClx(LH)n](org) (2) MClx + nL(org) ⇌ [MClxLn](org) (3) The main objective of this thesis is to establish whether ditopic extractants can be developed which have chemical functionalities that allow both mechanisms (2) and (3) to operate, co-extracting Pt(IV) and Pd(II) as their chloridometalates in an outer sphere binding site (2) and allowing their separation by raising pH to transfer the more kinetically labile Pd(II) to an inner sphere binding site (3) and releasing H2PtCl6 to the aqueous strip solution. A review of the literature is presented in Chapter 1, noting current commercially available extractants and the processes in which they are, or have been, applied. Particular attention is paid to the mode of action of the reported extractants and whether they extract metal cations, anions or metal salts. This chapter also outlines the proposed solvent extraction circuit in which new reagents developed in this thesis would be incorporated and the methods applied during the screening of candidate extractants. Chapter 2 deals exclusively with the use of reagents with inner-sphere binding sites for the selective extraction of palladium over platinum. Work on a series of oxime reagents synthesised for palladium extraction as part of preliminary MSci research (Andrew M. Wilson, MSci Thesis, University of Edinburgh, 2011) is reviewed. Studies of the hydrolytic stability of oximes indicate that they are unsuitable for incorporation into ditopic reagents for use in a circuit with a highly acidic feed solution. Thioethers were studied as alternatives as they show high kinetic selectivity for palladium over platinum and are more stable under acidic conditions. The synthesis and extraction properties of model reagents (largely arylalkyl thioethers) are reported and compared with those of the commercially available di-n-hexylsulfide. Incorporation of a polar group such as an amide provides phase transfer catalysis, accelerating the rate of transport of Pd(II) into the organic phase, but reducing selectivity over Pt(IV). The identification of functionalities that operate as receptors for chloridometalates by forming outer-sphere assemblies is explored in Chapter 3. The synthesis of amine, amide and amino-amide extractants from acid chloride streams and the effects of variations of functional groups on the extraction of PtCl6 2− are described. Secondary amides were found to be stronger extractants than tertiary amides, and aliphatic amides also show better metalate extraction than aromatic amides. The interactions between protonated aminoamide reagents and PtCl6 2− werre analysed by X-ray crystallography, noting that C-H∙∙∙Cl interactions with the “soft” chloridometalate anion are more common than with the “hard” chloride ion which shows a preference for more conventional N-H∙∙∙Cl interactions. Chapter 4 combines the reagent types explored in Chapters 2 and 3, in ditopic extractants that have both inner- and outer sphere binding sites. The synthesis and characterisation of a series of thioether amide reagents are reported and the selective extraction of platinum and palladium over other PGMs are discussed. In-house screenings of aryl- and alkylthioetheramide extractants showed selective co-extraction of Pd(II) and Pt(IV), rejecting Ir(III). Pt(IV) can be selectively water-stripped followed by ammonia-stripping of Pd(II). Industrial screenings at Johnson Matthey Technology Centre further exemplified the selectivity of these extractants over Ru(III) and Rh(III), although third phases were formed when the reagents were used for recovery from highly concentrated metal-feed solutions. The mode of action of the ditopic extractants is discussed, based on DFT calculations, crystal structure determinations and NMR studies, which support the formation of outersphere metalate assemblies and inner-sphere palladium complexes. Chapter 5 describes new difunctional (inner + outer sphere complexation) extraction by a single chemical entity, in this case an unsaturated N-heterocycle (an azole). The synthesis and characterisation of a series of hydrophobic azoles are described. These have basicities which allow protonation when contacted with strongly acidic solutions (2), but can be deprotonated in contact with water to allow their neutral forms to form inner-sphere complexes with Pd(II). Triazole-based reagents show the selective co-extraction of Pt(IV) and Pd(II) and, as with the ditopic thioetheramide reagents reported in Chapter 4, allow the selective water stripping of Pt(IV) and subsequent ammonia stripping of Pd(II).