Thesis (Ph. D.)--University of Wisconsin--Madison, 1976. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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).

Universiẗat, Diss., 2001--Osnabrück.

Thesis (Ph.D.)(Geology)--University of Pretoria, 2006. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

Ph.D. (Chemistry) / The effect of crystal defects on the adsorption and flotation properties of zinc sulphides was examined. Flotation experiments were restricted to collectorless flotation, that is to the flotation of untreated and copper-activated samples. The effect of cyanide treatment was examined only so that an explanation could be found for the bonding characteristics of the adsorbed copper on regions where the crystallography was undisturbed and on those where it was distorted. The electrochemical method for the determination of copper permitted continuous and highly sensitive monitoring of the copper adsorption on the sphalerites. The first part of the thesis concerns the adsorption of copper on synthetic zinc sulphide crystals and natural sphalerites. It is stated that the degree of adsorption depends on the defect structure. Structure etching, gamma-ray irradiation, and selective grinding experiments are shown to justify the conclusions reached. The second part of the thesis describes the flotation of the samples. The adsorption characteristics of the samples are defined in the first part and the adsorption and flotation properties are correlated.

No description available.

This work constitutes a fundamental study of the interaction between soluble sulphide,copper (II) oxide and cerussite particles in the presence of Ca²⁺ ,Mg²⁺ starch , gum arabic and Triton X- IOO . A detailed investigation of the effect of pH of the system on the rate of sulphide uptake was made . In addition , the structural form of the surface precipitat.es were determined with the aid of scanning electron microscopy . On the basis of these results , it was concluded that adsorption of sulphide on cerussite in the presence or absence of Ca²⁺ starch, gum arabic and Triton X-IOO could either lead to the formation of a non-uniform or a uniform sulphide layer depending on the experimental conditions . However , the interaction of copper (II) · oxide wi th soluble sulphide in the presence or absence of the above mentioned species always led to the formation or a non-uniform sulphide layer . Preliminary experiments of the interaction between xanthate and sulphidized surface showed that oxide surface covered with metal sulphide layer reacts with less xanthate than the free oxide surface.

In order to elucidate the mechanism of hydrogen sulphide oxidation, the photo-oxidation and thermal oxidation of hydrogen sulphide were studied, using gas chromatography for the analysis of final products. Photo-oxidation was studied at 130° and 150°C. Products found were sulphur dioxide, hydrogen, water and sulphur. Production of sulphur dioxide was found to be inhibited by an increase in surface area. Whether in photo- or thermal oxidation, the yield of sulphur dioxide increased drastically with slight increases in (O₂)/H₂S) ratio. This was also observed in the yield of hydrogen in photo-oxidation. Thermal oxidation was studied at 160°, 170°, 190°, 210°, 225°, 240°, and 260°C. Products were sulphur dioxide, water, and sulphur. No hydrogen was found. An expression for the production of sulphur dioxide was obtained: [formula omitted] = k (H₂S)⁻¹→⁺¹ (O₂)³ The overall activation energy was found to be 21.2±2k.cal./mole. Comparison with previously reported works was made and a mechanism proposed. / Science, Faculty of / Chemistry, Department of / Graduate

The applicability of microbiological oxidation for the recovery of zinc from a high-grade zinc sulfide concentrate has been investigated using a pure strain of Thiobacillus ferrooxidans. Factors affecting the bacterial activity and consequently the rate and extent of zinc extraction were studied. These factors were: temperature, pH, nutrient and substrate concentrations, solid particle size and surface area. The effect of carbon dioxide concentration in the air supplied to the oxidation was also studied. Larger scale experiments were carried out to simulate more closely possible industrial conditions. The optimum temperature was found to be 35°C, the optimum pH 2.3. Nutrient levels of 89 mg phosphate P/l and 636 mg ammonia N/1 were sufficient to avoid rate limitation and provide for maximum extraction, respectively. Increasing the particle surface area, the pulp density, or the total surface per unit volume of leach liquor increased the rate of zinc extraction up to a point beyond which further increases were not effective. Increasing the carbon dioxide content of the air had a similar effect. The larger scale experiments gave similar extraction rates to those observed in shake flasks but the extent of zinc extraction was significantly higher. The final concentration of zinc in leach solutions reached levels currently-employed in commercial electrowinning procedures. A form of the generalized logistic equation was shown to be capable of representing the complete extraction curve under a variety of experimental conditions. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

The impact of the Deepwater Horizon blowout on coastal wetlands can be understood through investigating carbon loading and microbial activity in salt marsh sediments. Carbon influx causes pore water sulfide to increase in wetland sediment, making it toxic and inhospitable to marsh vegetation. High sulfide levels due to increased microbial activity can lead to plant browning and mortality. Preliminary analyses at Marsh Point, Mississippi indicated that sulfate reducing bacteria are more active in contaminated marsh, producing sulfide concentrations 100x higher than in noncontaminated marsh. Sediment electrode profiles, hydrocarbon contamination, and microbial community profiles were measured at three additional locations to capture the spatial sedimentary geochemical processes impacting salt marsh dieback. Findings indicate that response to contamination is variable due to physical and biogeochemical processes specific to each marsh. Temporal evaluation indicates that there is a lag in maximum response to contamination due to seasonal effects on microbial activity.