Thesis (M.Sc.(Physics)) --University of Limpopo, 2006 / Platinum group minerals are abundant in South Africa. Platinum is of great significance in catalytic applications and many other medical and pharmaceutical industries. Our studies of PtSb2 and PtBi2 were carried out using Density Functional Techniques, including LDA and GGA methods. We investigated the pressure dependences of lattice parameters and bond lengths of the materials. All these properties were shown to decrease with increasing pressure, in a linear fashion. Other features that were studied are the electronic properties like density of states (DOS) and optical properties to determine the type of material being studied. A set of interatomic potentials has been derived for the study of bulk and surface properties of PtSb2 using the GULP code (General Utility Lattice Program). These potentials have proved to be reliable since they reproduced bulk properties of PtSb2 such as lattice parameters and elastic constants. As there are no experimental studies on surfaces we have been able, for the first time, to calculate surface energies for the low index surfaces and found out that the most stable surface is the {100} Sb terminated one, with the energy of 0.933 J.m-2 and the least stable is the {111} Sb terminated surface with the energy of 2.586 J.m-2.

No description available.

Thesis (MScIng)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1957. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph.D.(Geology))--Univerisity of Pretoria,2001. / Summaries in Afrikaans and English. Includes bibliographical references.

Report (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 53-61). Also available via the Internet.

In this thesis, the preparation of a number of halomethyl complexes of rhodium, platinum, and palladium is described. Complexes of the type trans-[Rh(CH2X)X(P4)]+ (X = Cl, Br, I, P = PMe3, dmpe) were found to be unstable, decomposing in situ to give a mixtures of dihalo, trihalo, and phosphine ylide species. Platinum and palladium species of the type trans-M(CH2X)X(PEt3)2 (X = Cl, I, M = Pt, Pd), which were formed by the reaction between M(PEt3)3 CH2XY were also unstable. In the case of platinum, phosphine ylide species were isolated from reaction mixtures, whilst the palladium halomethyl species decomposed over a number of days to give dihalide complexes. However, palladium iodomethyl species prepared via reactions involving 2 moles of phosphine per mole of metal were found to be stable. Neutral rhodium halomethyl complexes were also found to be far more stable than their cationic counterparts. The synthesis and characterisation of trans-RhCl(CO)(CH2l)I(P)2/ (P = PMe3, PEt3, or Et2PPh), prepared by oxidative addition of CH2I2 to RhCl(CO)(P)2 is described. When less basic phosphines (such as PPh3) or the sterically hindered phosphine PCy3 were used, no evidence of any reaction between the rhodium complex and the CH2I2 was observed. The molecular structure of trans-RhCl(CO)(CH2l)I(PEt3)2 has been studied by X-ray diffraction analysis. This complex proved to be inert to substitution at the iodomethyl carbon atom by neutral nucleophiles such as H2O, CH3OH, and PEts, but prone to substitution by Cl-. The lability of iodomethyl (and chloromethyl) ligands towards CO insertion has also been studied. There is evidence to suggest that an iodoacyl platinum complex may form in solution after the complex cis-Pt(CH2l)I(PPh3)2 had been left under 1 atm CO for 24 hours. However, in the case of trans-Pd(CH2l)I(PCy3)2 this same reaction took 7 days under 70 atm pressure of CO. All of the rhodium iodomethyl complexes prepared were also inert to CO insertion at ambient temperature and 1 atm CO, but excellent evidence for CO insertion having taken place in irflns-RhCl(CO)(CH2l)I(PEt3)2 was observed at 70°C and 35 atm of CO. Evidence for CO insertion into a rhodium-chloromethyl bond was also observed under the more forcing conditions of 100°C and 70 atm CO. This insertion reaction may prove to be extremely useful in catalytic systems. A report of some preliminary catalytic studies involving the production of diethylmalonate from CH2I2 and C2-products from the hydroformylation of (CH2O)[sub]n under very mild conditions is also presented. It is thought that these catalytic reactions proceed via carbonyl insertion into a rhodium-iodomethyl bond.

The voltammetric behaviour of I-cysteine and other organic compounds such as hydrazine, hydroxylamine and methionine has been studied on GCE modified with phthalocyanine complexes of osmium, rhodium and ruthenium. For cysteine oxidation, the catalytic activity of the electrode was dependent the nature of the axial ligand. When cyanide and dimethylsulphoxide (DMSO) were used as axial ligands, giving (DMSO)(Cl)Rh(III)Pc, [(CN)₂Rh(III)Pc], (DMSO)₂0S(II)Pc and [(DMSO)₂Ru(II)Pc].2DMSO complexes, the peak current increased with repetitive scanning, indicating the increase in catalytic activity of the electrode after each scan. This behaviour was not observed when pyridine was used as axial ligand. The improvement of the catalytic activity of the GCE after the first scan has been attributed to the formation of the dimeric π-cation radical species at the electrode surface. Water soluble phthalocyanine complex ([(CN)₂Os(II)Pc]²⁻) and the tetramethyltetra-pyridinoporphyrazine complexes of Pd(II) and Pt(II), ([Pd(II)2,3Tmtppa(-2)]⁴⁺, [Pd(II)3,4Tmtppa(-2)]⁴⁺, [Pt(II)2,3Tmtppa(-2)]⁴⁺ and [Pt(II)3,4Tmtppa(-2)⁴⁺) have been prepared. [(CN)₂Os(II)Pc]²⁻ is soluble in water at pH greater 4 without the formation of dimers. The [M(II)Tmtppa(-2)]⁴⁺ (M = Pd or Pt) show high solubility in water and are stable only in acidic pHs. The cyclic voltammetry of the MPc and [M(II)Tmtppa(-2)]⁴⁺ complexes prepared, is also reported. The interactions of amino acids I-histidine and I-cysteine with the [M(II)Tmtppa(-2)]⁴⁺ complexes of Pd(II) and Pt(ll) were studied. All the [M(Il)Tmtppa(-2)]⁴⁺ are readily reduced to the monoanion species [M(Il)Tmtppa(-3)]³⁻ in the presence of histidine and cysteine. The rate constants for the interaction of [M(Il)Tmtppa(-2)]⁴⁺ complexes ofPt(II) and Pd(II), with histidine and cysteine range from approximately 2 x 10⁻³ to 0.26 dm³ mol⁻¹ s⁻¹. Kinetics of the interaction of [Co(Il)TSPc]⁴⁻ with amino acids, histidine and cysteine in pH 7.2 buffer were studied. The rate constants were found to be first order in both [Co(II)TSPc]⁴⁻ and the amino acid. The formation of [Co(III)TSPc]³⁻ in the presence of histidine occurred with the rate constant of 0.16 dm³ mol⁻¹ s⁻¹, whereas the formation of the [Co(I)TSPc]⁵⁻ species in the presence of cysteine gave the rate constant of 2.2 dm³ mo⁻¹ s¹. The relative quantum yield (QΔ) for singlet oxygen production by [(CN)₂Os(Il)Pc]²⁻, and [(CN)⁴Ru(II)Pc]²⁻ in DMF using diphenylisobenzofuran (DPBF) and a chemical quencher were determined. The quantum yield values were obtained as 0.39 ± 0.05 , and 0.76 ± 0.02 for [(CN₂Os(II)Pc]²⁻ and [(CN)₂Ru(II)Pc]²⁻ respectively. The differences in quantum yield values have been explained in terms of donor abilities of both the central metal and the axial ligands.

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

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