Includes bibliographical references. / The use of microorganisms for the regeneration of leach agents in the heap leaching of mineral sulfide ores is finding increasing application as a hydrometallurgical unit operation applicable to the treatment of the increasing low grade ores. These same microorganisms contribute to the formation of acid rock drainage (ARD) through the oxidation of base metal sulfides, particularly pyrite. In this research, the effect of intermittent irrigation on the extraction of copper and iron from a low grade chalcopyrite ore in the heap bioleaching system is investigated and compared with the effect under abiotic conditions. As a secondary investigation, the effect of the introduction of layers of fines, which may develop during the course of the operation of heaps, on copper extraction in heap bioleaching systems was also researched.

Includes bibliographical references (leaves 81-87). / Microbial oxidation rates catalysed by the acidophilic micro-organisms mediating mesophilic and thermophilic bioleaching of mineral sulphides have been well characterised under conditions typical of active tank leaching processes in the mineral industry. However, with the increasing need to beneficiate low grade ores, heap bioleaching processes are increasingly of interest. The physicochemical conditions within the heap bioleach differ considerably from the tank leaching system in terms of typical iron concentration, presence of dissolved salts and dissolved gases. This study focuses particularly on the kinetic description of the microbial ferrous oxidation rate and the microbial growth rate of the Leptospirillum species under conditions where the supply of carbon dioxide is limited.

Includes synopsis. / Includes bibliographical references. / The aim of this thesis is to establish and understand the location of glucose oxidase (GO) in fungi Aspergillus niger NRRL-3 and Penicillium sp. CBS120262 to inform the enzyme recovery. GO was chosen to be a model system and the outcomes obtained in this study could then be applied to other enzyme and microbial systems in which product location has been shown to be influenced by operating conditions.

Includes bibliographical references (p. 122-129). / Efficient intracellular product release from yeast is required for the recovery of many bioproducts, recombinant or other. Traditionally such product release is achieved by non-selective, energy demanding mechanical disruption. The fine debris resulting from mechanical disruption is also challenging in the solid-liquid separation in downstream process. This study investigates the effect of the pretreatment on the energy efficiency of cell disruption, the extent of product release and its selective product release. Saccharomyces cerevisiae and Kluyveromyces lactis were used as the model microorganisms while disruption following pretreatment was achieved on exposure to ultrasound or passing through the high pressure homogenisation (HPH). Pretreatments were selected for their ability to weaken the yeast cell wall, rather than to permeabilise the cell. This allowed product release to be concentrated into the disruption step only, not distributed between the disruption and pretreatments steps. Rapid temperature treatment at 40 to 60CC, pH shock across the range pH 9 to 11 and osmotic pressure between 0.5 MPa and 5 MPa were used as single pretreatment. Combined pretreatments were also considered. These were affected by diluting the yeast suspension into a pre-warmed pH or high osmolarity buffer. On dilution, the temperature was increased rapidly to 40CC, while the pH or osmotic pressure was increased to pH 10 or 1 MPa.

Includes abstract. / Includes bibliographical references. / Bubble column reactors are extensively used in the petro-chemicals industry due to the combined advantages of high rates of heat and mass transfer coupled with low operating and maintenance costs. The complex hydrodynamics brought about by the multiphase nature of such systems offer significant challenges in modelling, analysis and operation, thus making experimental measurement of system response of special importance. One such measurement technique is Electrical Resistance Tomography (ERT). In this study, the development of an experimental bubble column reactor fitted with 8 rings of 16 electrodes for ERT measurements using an instrument developed at the University of Cape Town (UCT) is described.

Includes synopsis. / Includes bibliographical references. / In 2004, Mintek recognised the gold mining industry‘s need for an online free and WAD cyanide measurement device and went about extending the existing free cyanide analyser,the Cynoprobe to include WAD cyanide measurement. The WAD cyanide analysis technique was to be based on ligand exchange, which required the selection of an appropriate reagent,with amperometric finish. Thereafter, the technique was validated in the laboratory to include the capabilities of the prototype instrument in terms of accuracy and precision (0.5-100 ppm WAD CN). Various local trials were conducted in order to validate the measurement and the robustness of the instrument in an industrial environment. Successful trials (<10% error with respect to laboratory analysis) led to international application and exposure to complex ore types and process solutions.

Includes abstract. / Includes bibliographical references (leaves 81-95). / This study focuses on newly synthesized polyphenolic compounds which were expected to be antioxidants in vivo. Antioxidants are compounds which at low concentrations can prevent or reduce the deleterious effects caused by reactive oxygen species (ROS) induced by UVA exposure of the skin. This study focuses on developing methods required to measure the effects of these synthesized compounds in ultraviolet radiation-exposed cultured skin cells. Biocatalytic synthesis of polyphenolic compounds was carried out using isolated enzymes, tyrosinase from Agaricus biosporus, and laccase from Trametes pubescens to produce oxidized oligomeric products.

Includes abstract. / Includes bibliographical references. / Hydrometallurgical methods are increasingly considered as alternatives to conventional pyrometallurgical techniques for extraction of metals from mineral ores. Chalcopyrite is a key copper mineral due to its abundance on earth. However, due to its refractory nature in sulfate leaching systems, a viable hydrometallurgical route for its extraction remains elusive...The work in this present thesis is presented as an initial study to commission the potentiostat instrument, investigate the common trends that are observed in running potential controlled (voltammetric) studies of chalcopyrite and compare them to those reported in literature, and investigate the electrochemical behaviour under different reaction conditions.

Includes abstract. / Includes bibliographical references (leaves 140-161). / The overall objective of this study was to characterise, functionally, Dunaliella species naturally inhabiting Sua Pan solar saltworks evaporation ponds in Botswana and to evaluate the species for potential application in commercial production of ß-carotene. The main goal was to establish if the species are of commercial value with regard to massive accumulation of carotenoids, specifically ß-carotene. The study assessed the productivity of the environmental isolates by means of growth and carotenoid biosynthesis properties at indoor laboratory scale...

An electrochemical study was conducted on a stationary, synthetically produced, covellite electrode in acidic, chloride solutions at ambient conditions to investigate the dissolution behaviour of the mineral over a surface potential range from the open circuit potential (OCP) to about 0.62 V (vs. SHE). The electrode was mounted in an apparatus, which was designed to resemble leaching of the mineral under conditions applicable to heap leaching of whole ores, where the mineral occurs in cracks or pores in the gangue matrix or is covered (or partially covered) by reaction products.