This thesis focuses on platinu'm group element (PGE) mineralization in the Unki Section of the Selukwe Subchamber of the Great Dyke (Zimbabwe), and is based on drill hole intersections and underground and surface exposures of the Main Sulphide Zone (MSZ) which hosts significant concentrations of PGE. The petrological and geochemical data presented are part of a broader study currently underway and the present are restricted to the 2m section of the PGE-rich MSZ encountered in drill hole MR126. The PGE-rich MSZ at Unki is unique in having a shear, locally referred to as the Footwall Shear, developed at or close to its base . It is however, similar to the other PGE occurrences on the Great Dyke (MSZ) in having its hanging-wall restricted to within 1m of the websterite/bronzitite contact. Slight axial tilting to t he west is indicated by steeper dips on the eastern flank. The sulphide concentration wit hin the MSZ can be used as a rough guide to the PGE-rich zone, but is not sufficiently precise to be used in stope control. The visual identification of the potentially mineable zone remains a problem that is unlikely to be solved. Based on petrological evidence, the bulk of the sulphides with which the PGE are associated, are cumulus in status. This provides unequivocal evidence for an orthomagmatic origin of the MSZ. The dominant platinum group mineral (PGM) phase is the Arsenide/Sperrylite group which is most commonly found at the contact zones between base metal sulphides (BMS) and gangue. The PGM range up to 90 ~m in length. Geochemical evidence from the analyses of cumulate orthopyroxenes through the 2m PGE-rich MSZ interval at Unki reveals a trend of arked Fe enrichment upwards which corresponds to an enrichment in sulphide. This indicates that precipitation of sulphide was caused by fractionation with lowering of temperature in the magma. The Fe enrichment is followed by a reversal in Mg# of orthopyroxene which corresponds to the decrease in sulphide content, suggest i ng that the termination of the PGE-rich MSZ was due to an increase in temperature associated with an influx of new magma. Coupled with these magmatic events are a complex interplay of chemical and physical processes occurring at a critical stage in the overall fractionation of the Great Dyke magma chamber. The overall persistence and continuity of t he PGE zone as observed in the Unki area is consistent with the inferred orthomagmatic origin of the mineralization

Please read the abstract in the section 03back of this document / Dissertation (MSc (Applied Mineralogy))--University of Pretoria, 2005. / Mathematics and Applied Mathematics / unrestricted

The aim of this thesis was to investigate the properties of novel platinum compounds with possible potential as anticancer agents, and to determine how their behaviour could lead to a better understanding of the chemistry involved. The final criteria were improvement of their anticancer behaviour. Since many questions are still unanswered as to the role of sulfur in anticancer action, studies were undertaken to synthesize novel platinum(II) complexes having non-leaving groups consisting of a combination of an aromatic nitrogen and thioetherial sulfur capable of forming a five membered ring upon coordination. The structural unit was 1-methyl-2-methylthioalkyl/aryl. Numerous complexes formed by these ligands each having chloro, bromo, iodo and oxalato leaving groups were then fully characterized. The results obtained by the various synthetic methods were compared and explained in terms of the chemistry involved. The role of the sulfur donor was indicated in both the halo- and oxalato-complexes and proved to be strongly influenced by the nature of the leaving groups. Their differences are reflected in their anticancer behaviour. The study was extended to mononitroplatinum(IV) complexes, in view of the kinetically stable platinum(IV) compounds and advantages related to this. A specific mononitroplatinum(IV) complex which proved to have good anticancer and STAT 3 properties could according to the literature not be synthesized successfully in a good yield and a high degree of purity. The results of extensive studies showed that the main problem centred around the simultaneous reactions in equilibrium during the synthesis. A number of these species formed as a result of side reactions could be identified and their close separation factors indicated chromatographically. The mechanism of these reactions and the unstable intermediate species involved could be rationalized and compared to analogues in the literature. All the complexes studied were characterized by spectral and thermal methods both in solution as well as the solid state. Their anticancer behaviour towards three anticancer cell lines (Hela, MCF 7, Ht 29) were determined and acted as a guide towards possible structural modifications for their improved capability. Three crystal structures of platinum(II) complexes were determined. The extent of the ionization of the platinum(II) complexes as well the redox potentials (Pt(II) / Pt(IV)) of the platinum(IV) complexes were particularly important factors pertaining to their anticancer action.

The fluorides of platinum have been reinvestigated. Attempts to prepare a difluoride were unsuccessful. It is suggested that this is-due to it being unstable towards disproportionation. X-ray Crystallographic evidence is presented as evidence for a trifluoride of platinum although a pure sample has not been isolated. This trifluoride is shown to be isostructural with the rhombohedital trifluorides of palladium, iridium and rhodium. Platinum tetrafluoride has been reinvestigated. It was found to be diamagnetic and to have a lattice of slightly-distorted, tetragonal uranium tetrachloride type. The adducts of platinum tetrafluoride with bromine trifluoride and selenium tetrafluoride were investigated further and found to be diamagnetic. The platinum tetrafluoride, selenium tetrafluoride adduct was shown to be isostructural with the corresponding palladium and germanium compounds. An ionic lattice is suggested for these compounds. Bromine trifluoride adducts do not form a similar-series and this, combined with their physical properties lead to the suggestion that these compounds are more covalent in nature. The previously unknown pentapositive state of platinum has been established. Platinum pentafluoride is a deep-red, reactive solid which readily disproportionates on heating. It gives rise to 1:1 adducts with iodine pentafluoride and chlorine trifluoride. These, like the bromine trifluoride adducts, are low-melting solids. Potassium fluoroplatinate (V) was prepared as a deep-yellow solid, crystallizing with the rhombohedral potassium fluorosmate lattice. A pentapositive oxyfluoride, platinum oxytrifluoride was found, it is suggested that this is polymeric. Platinum hexafluoride has been briefly investigated. A very reactive oxyfluoride, of formula PtO₂F₆, has been prepared and investigated. It is a deep-red solid which can be sublimed at 90° in a vacuum. It melts with decomposition at 219°. It is paramagnetic and crystallizes in a cubic lattice. Many of its chemical properties were studied. It is suggested that this compound is platinum peroxidehexafluoride. The crystal structures of the tetrafluorides of platinum rhodium, tin and lead were investigated. No similarity in structure was found. A brief investigation into the fluorides of rhodium has lead to the suggestion that a pentafluoride, in addition to a tetrafluoride, exists. / Science, Faculty of / Chemistry, Department of / Graduate

Platinum pentafluoride has been prepared, by a new preparative method, in a more stable, pure and crystalline form than the material already described. It has been shown, by x-ray powder photography, to be isomorphous with other noble metal pentafluorides and almost isodimensional with rhodium pentafluoride. A tetrameric structural unit like that observed in ruthenium pentafluoride is also assumed for platinum pentafluoride. Its magnetic properties have been shown to be representative of a third transition series d⁵ ion in a distorted octahedral environment. The nature of the bonding in germanium difluoride is discussed in the light of the crystal structure, which has been deduced from data obtained from single crystals prepared in this work. The products of interaction of chlorine or bromine with the difluoride are consistent with the structural findings. The ¹⁹F n.m.r. spectra of the mixed chlorofluorides (GeFCl₃, GeF₂Cl₂, GeF₃CI, GeF₄ ) and bromofluorides, indicate that intermolecular exchange between these compounds must be extremely slow, at least in the absence of a catalyst. It has been shown that germanium difluoride is so strong a reducing agent that it reduces iodine pentafluoride to iodine below room temperature. The powerful reducing properties of the difluoride were also illustrated by the reduction of platinum tetrafluoride to the metal at room temperature. Attempts to reduce tungsten hexafluoride at 300° led to the formation of Ge₂WF₈. In glass the germanium difluoride reacted with tungsten hexafluoride and the container to yield WO₂F. / Science, Faculty of / Chemistry, Department of / Graduate

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ABSTRACT Background: In association with other occupational exposures like silica dust and radon, cigarette smoking impacts on the health of miners, especially with regard to the risk of developing COPD, PTB and lung cancer. These compensable diseases place a great burden on both miners and mines. The prevalence of smoking among black miners in South Africa is unknown and data for white miners are not recent. Objectives: To determine the prevalence of smoking and smoking trends in miners in a platinum mining company from 1998 to 2002 and to describe some important factors associated with their smoking habits. Methods: This was a cross-sectional study using medical surveillance data about employees of a platinum mining company from 1998 to 2002. Results: Over 80000 repeated records of over 25000 miners were studied over the five-year period. The prevalence of smokers was 44.4%. Miners were less likely to smoke in 2002 than in 1998 (OR 0.23, CI 0.21 – 0.25). Over this period, smoking prevalence dropped from 43.3% to 31.3%. The decrease was evident in most socio-demographic groups. There was also a decrease in cigarette consumption over time (p<0.001). Multivariable analysis showed that whites were more likely to “always” and/or “ever” smoke than blacks (adjusted OR=2.4, CI 1.79 – 3.20 and OR 2.5, CI 1.98 – 3.27, respectively). Conclusion: Even though there has been a decline in smoking prevalence since 1998, the relatively higher prevalence in platinum miners compared to that of the general population, and the additional effect of occupational exposures, are still a public health concern. There is need to establish smoking cessation and prevention programmes and to continue collecting detailed smoking information during annual surveillance programmes that could be used to monitor the effectiveness of such programmes.

Water is a vital transport and process medium used in mineral processing. Fresh water is substantially utilized as an ideal flotation media in the froth flotation process (Rao et al., 2016). However, the mining sector is impelled to save on the consumption of fresh water and reduce waste discharge owing to limited freshwater supply (Ridoutt and Pfister, 2010), stringent environmental regulations (Amezaga et al., 2011) and the increase in water demand among multiple users (Rijsberman, 2006). To improve water efficiency, the use of impure primary water supplies, and process water recycling has been implemented in flotation circuits. Generally, the recycling of process water is executed from tailings dams, thickener overflows, and dewatering and filtration units. The recycling of process water has been considered to be advantageous as it reduces freshwater consumption, lowers waste discharge and reduces volumes of reagents required in flotation circuits (Muzenda, 2010). However, recycled process water has been found to exhibit increased concentrations of typical contaminants such as colloidal matter, metal ions, sulphates, sulphites, thiosalts, calcium, magnesium, sodium, potassium, and residual floatation reagents. These contaminants affect the process water quality, which plays a vital role in flotation efficiency. Though a significant amount of work has been done on the effects of water quality on the flotation of valuable minerals, many studies have focussed on base metal sulphides and the use of benchscale techniques. Literature speculates that ions in process water hinder the interaction between xanthate collectors and valuable minerals, hence, contributing to a decrease in flotation recoveries (Kirjavainen et al., 2002, Boujounoui et al., 2015). The findings in literature have been deduced without an understanding of the underlying mechanisms of interaction between xanthate collectors and mineral surfaces in the presence of ions. Accordingly, literature still holds a lack of understanding on how ions affect the adsorption of xanthate collectors on mineral surfaces. This study, therefore, seeks to unpack the underlying mechanisms of interfacial interactions between ions with PGMs and the subsequent adsorption kinetics of a xanthate collector. This study investigated the effects of Ca2+, Mg2+, SO4 2- , S2O3 2- and Na+ ions at increasing ionic strength, on the adsorption of SIBX on synthetic PdS and PdTe2 minerals. The selection of the minerals was based on the need to give an insight into the differences in reactivities of the very floatable minerals (PdS) and the difficult-to-float minerals (PdTe2), with SIBX in the presence of ions. The mechanisms in question were examined by electrochemical techniques at laboratory scale. Rest potential measurements were used to determine the interactions of ions and/or SIBX on the PGM surfaces. Cyclic voltammetry was employed to determine the redox reactions that occur on the PGM surfaces in the absence and presence of ions and SIBX. Ultimately, electrochemical impedance spectroscopy was used to demonstrate the adsorption mechanisms of SIBX in the absence and presence of the investigated ions. The rest potential measurements generally displayed an increase in the extent of interactions between the investigated ions with the palladium minerals, with an increase in ionic strength. An inverse relationship was exhibited on the extent of interactions between the ions and PdS, and the extent of interaction between SIBX and PdS. Divalent ions displayed higher interactions with the palladium minerals than the monovalent ions investigated. All salts were found to demonstrate a decrease in the rest potential for PdS at all concentrations except for MgSO4, which increased the rest potential at 5 SPW and 10 SPW. Final rest potentials for most conditions were observed to be above the equilibrium potential of dixanthogen formation except for Na2S2O3 at 3 SPW, 5 SPW and 10 SPW, and CaCl2 at 1 SPW. Dixanthogen formation was most likely favoured on PdS for the conditions with final rest potentials above the equilibrium potential of dixanthogen formation. With regard to the PdTe2 mineral, it was found that most ions enhanced the interaction between SIBX and PdTe2. Contrary to the findings of PdS, it was found that most salts exhibited an increase in rest potential on PdTe2 except for Na2S2O3. Final rest potentials for all conditions investigated were observed to occur above the equilibrium potential of dixanthogen formation except for Na2S2O3 at all ionic strengths, MgCl2 at 10 SPW and NaCl at ionic strengths of 3 SPW, 5 SPW and 10 SPW. The latter conditions show that the formation of a metal-xanthate on PdTe2 was favoured. Generally, for both minerals, NaCl displayed the least interaction. It was found that increasing the ionic strength of salts, generally decreased the rate of dixanthogen formation on PdS. On the contrary, SIBX interacted more with PdTe2 at an increase in the ionic strength of salts. This observation favoured the formation of either a metal-xanthate or dixanthogen at a slower rate. Additionally, it was determined that the adsorption of ions investigated occurred via interfacial charge transfer kinetics, where an ion exchange mechanism has been proposed in the case of the divalent anions. In the case of divalent cations, it was presumed that the ions dissociate in solution and precipitate upon their interaction with the palladium minerals to hydroxides and/or carbonates. This study has shown that the mechanism of adsorption of ions on palladium minerals is heavily influenced by the type of mineral surface onto which the ions adsorb. The extent of interaction of ions with palladium minerals together with their corresponding oxidation products can be determined by the mineral type and the salt type and its ionic strength. Moreover, it was denoted that an electrochemical system that consists of salts at the palladium mineral surfaces can best be described by a resistor, Rs in series with a parallel circuit of a capacitor, Cdl, representing the electrical double layer and a resistor indicating Rct. For an electrochemical system with both salt and SIBX, it has been surmised that an equivalent circuit consisting of a resistor, Rs, in series with a parallel circuit of a capacitor, Cc, representing a coating layer formed on the palladium surfaces as a result of the adsorption and oxidation od SIBX and a capacitor, Cdl. This work has shown that the mechanisms of interactions between xanthates and PGMs in the absence and presence of salts can be successfully determined using electrochemical techniques. An understanding of such mechanisms developed from the interactions of Ca2+, Mg2+, SO4 2- , S2O3 2- and Na+ ions with SIBX on PGM minerals will help alleviate flotation problems caused by the troublesome ions. An understanding of the mechanisms proposed by this study will act as a diagnostic tool for developing flotation strategies that will maximize flotation recoveries where water quality is concerned

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