Thesis (Ph.D.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 417-523) Also available in print.

Thesis (M.Phil.) - University of Queensland, 2006. / Includes bibliography.

Thesis (M.S.)--Humboldt State University, 2007. / Includes bibliographical references (leaves 20-22). Also available via Humboldt Digital Scholar.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

M.Tech. (Extraction Metallurgy) / Please refer to full text to view abstract

Chalcopyrite (CuFeS2) is the most abundant of the copper sulfides and also one of the most refractory for leaching. Several processing routes have been proposed to overcome drawbacks associated with environmental problems related to copper extraction from this mineral. Atmospheric leaching in acidic ferric sulfate is regarded as being particularly attractive over other hydrometallurgical systems. However, the challenge has been to overcome the problem of slow extraction rates due to passivity encountered at high solution potentials in this system. This highlights the need to investigate better operating conditions to optimize copper extraction and prevent the problem of passivation, and to develop suitable modeling tools to assess and diagnose leaching performance. In this work, a dissolution rate expression for chalcopyrite leaching in acidic ferric sulfate media is proposed accounting for effects in the active and passive regions under potentials from 415 to 550 mV (Ag/AgCl). A model of chemical speciation in the bulk solution elucidates the idea of passivation caused by precipitation of ferric species and their consequent adsorption onto the chalcopyrite surface. Electrochemical studies on massive samples of chalcopyrite involving characterization and modeling of the anodic and cathodic half-cell reactions of chalcopyrite leaching together with mixed potential considerations lead to the development of the mathematical expression for dissolution rate. The mathematical model was calibrated with electrochemical parameters and results are in good agreement with real leaching data from batch tests for solution potential regions where passivity is not observed. On the other hand, the passive region was modeled by means of adjusting parameters related to adsorption energies of the passivating species. Results of the model for this region deviate from real data as potential becomes higher probably due to diffusion resistance through a layer composed of ferric complexes. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

No description available.

The kinetics of dissolution of ilmenite, containing haematite, in aqueous solutions of sulphuric acid have been studied. Iron was found to leach from the mineral complex at a faster rate than titanium. The rates of solution of both iron and titanium increased, up to certain limiting values, upon abrading the mineral during leaching and were found to be related to the hydrogen ion activity of the leaching solution by a first order dependency. The results have been interpreted in terms of preferential and possibly diffusion-controlled leaching of the haematite with ilmenite being removed both by slow leaching and tearing out from the specimen surface. / Applied Science, Faculty of / Materials Engineering, 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

Microbiological leaching of sulfide minerals in fermenters is believed to have commercial potential. The oxygen transfer rate has been assumed to be one of the most important factors affecting the leach rate. The mass-transfer rate at various solution pH's was studied by using an unsteady gassing out process. The sulfite-oxidation process was also studied in an attempt to explain the absorption mechanism. A 7.5 inch I.D. methyl methacrylate tank with 4 baffles and a 4-inch diameter paddle type impeller were used. The impeller was driven by a motor mounted on a dynamometer which allowed measurement of the power used in agitation. All the experiments were carried out under highly turbulent conditions and covered the liquid temperature range 25°C to 40°C. The results showed that pH had no effect on mass-transfer coefficient. The values of K[subscript L]a increased as temperature increased. The relationship between K[subscript L]a, power input and superficial gas velocity was found to be of the form: K[subscript L]a = c(HP/V)[superscript x] (V[subscript s])[superscript y] A comparison of the K[subscript L]a observed in an unsteady gassing out process and that in a sulfite-oxidation process showed that the interfacial area/unit volume of liquid, a, is directly proportional to (V[subscript s])º‧⁵º which coincides with Calderbank's result. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate