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Includes bibliographical references (leaves 80-82). / An Excel-based mathematical model simulating the Base Metal's Refinery Secondary Leach operation is developed in this thesis. Fundamental building blocks of batch leach data, equipment specifications, process conditions and feed characteristics are used to develop the model. The aim of which is to develop a tool to verify actual plant performance against theoretical performance and assist with troubleshooting in the plant or serve as a basis for future autoclave design. In the present study the model is specifically used to investigate the cause of the reduced leach efficiencies that the plant is experiencing.

Includes bibliographical references. / Although heap leaching is by now a well-established technology choice in the mining industry, the process remains limited by low recoveries and long extraction times. It is becoming increasingly clear that the successful application of heap leaching technology will ultimately depend on having a comprehensive understanding of the underlying fundamental processes for optimisation to take place...The subject of this research was, therefore, to understand more clearly the diffusion reaction phenomena of reagents through large particles and to provide true and reliable physical parameters to formulate the relevant modelling approaches to large particle leaching. A combination of standard optical microscopy, SEM, QEMSCAN and X-ray CT techniques has been used for the characterization of crack networks and mineral dissemination in the ore particles, which are important characteristics that determine the diffusion of reagents into and out of particles and the reactions within.

Includes bibliographical references. / In this thesis, it is hypothesized that in bioleaching flow reactor systems, high reaction rate regions exist that can be maintained by application of biological stress trajectories. Reactor models are developed for the purpose of optimising plant operation, understood here as maximising the production rate. Complicating this attempt are a) the non-linear dynamics associated with the kinetics and b) the primary reaction's being multiphase. Mathematical models are developed to establish which particle parameters are necessary to describe reactor performance using the method of segregation. The models are distinguished by the combination of either particle residence time or age and/or particle size distributions. The models evaluated at steady state are validated against pilot plant data obtained from the Fairview Mine in South Africa and were found to be in good agreement with the data. As the model was developed using a segregation approach and thus incorporates age distributions in the model formulation, the model could be extended to unsteady state operation.

AD technology is well developed, cost efficient and can be easily implemented in developing countries. Biogas production has become a very topical subject, with many European nations introducing initiatives to increase biogas production. AD of algal biomass was studied in detail during the 1980’s, however, with the current drive toward cleaner technology processes, there has been a renewed interest in the technology. This study investigated the feasibility of using algal biomass as a feedstock for AD.

In the present study a methodology and a spreadsheet model were developed with the aim of integrating techno-economic and environmental objectives simultaneously during decision making. The model was developed specifically for the copper industry, mainly due to the wide array of different processing technologies and operational synergies that exist in this industry.

Every aspect of the modern day life relies on combustion, be it in motor vehicles, industrial equipment or power generation. The downside to the extensive use of combustion technology is the environmental pollution produced by the process. The lack of fast solving models to simulate combustion hampers the investigation into the optimisation of combustion processes. In this study, the compartment approach in developing a fast and accurate simulation is used to investigate combustion systems. A chemical reactor network (CRN) is proposed for the simulation of the combustion of iso-octane. The compartmentalisation of a combusting system involves proposing a reactor network based on the flow fields predicted by computational fluid dynamics (CFD). The first step in the development of such a model involves using of a reduced kinetic model representing thousands of combustion steps in a few elementary steps by lumping species. The reduced kinetic model used in this study consists of a five-step mechanism involving four pseudo species. The thermodynamic properties of the pseudo species in the system were regressed against experimental data and successfully validated using the plug flow and continuous stirred tank reactor sub-models. The reduced kinetic model was also further validated using Rapid Compression Machine data. The current study also modified the methodology for developing a CRN in order to make the CRN more predictive as compared to previous studies. This was achieved by incorporating non-isothermal sub-models into the network instead of isothermal sub-models that rely on the CFD temperature field. The network parameters were also correlated to the inlet Reynolds number in order to further increase the predictive nature of the network for industrial applications and to allow for the systems performance to be predicted over a wide range of input conditions. The investigation begins by conducting a CFD simulation of iso-octane combustion in a furnace and double inlet reactor assuming a one-step global reaction. On the basis of the CFD flow fields, a CRN was proposed and coupled to the reduced kinetics.

Includes bibliographical references. / A high filtration resistance has been found to hinder the dewatering of the antagonistic biocontrol yeast Crytococcus albidus. Throught literature a hypothesis was developed that the extracellular polysaccharide produced by C. albidus is the major cause of hindrance to the filtration process. Microscopic analysis of C. albidus cultures illustrated cell-bound extracellular capsule. Viscosity measurements and visual observations of precipitation of the polysaccharide with ethanol were evidence extracellular polysaccharide suspended in the surrounding media. In this study, alteration of the composition of the growth medium and various pre-filtration treatments of the yeast harvest were investigated to improve filterability. The treatments included washing the yeast to remove suspended macromolecules, exposing the yeast suspension to a high shear environment to reduce the quantity of cell-bound polysaccharide, and varying suspension temperature. Us of Saccharomyces cerevisiae (Baker's yeast) and diatomaceous earth (DAE) as filter aids were investigated as a means of further improving filterability.

Bibliography: leaves 70-79. / The current focus of research in the UCT Minerals Bioprocessing Research Unit is to develop an understanding of the chalcopyrite bioleaching sub-processes. This thesis forms part of the greater study on bioleaching, investigating the ferric leaching subprocess. The objective of this thesis was two-folds. Firstly, a detailed literature review was undertaken to develop a better understanding of the ferric leaching of chalcopyrite and the cause of passivation during chalcopyrite leaching. Secondly, leach experiments on pyrite were used to establish the applicability and reproducibility of measuring the rate of ferric leaching at a constant redox potential, using the methodology developed by Kametani and Aoki (1985). Following this, chalcopyrite ferric leach experiments were conducted to obtain the redox potential range where chalcopyrite leaching occurs. The rate of chalcopyrite leaching in a sulfate media decreases with time due to the formation of a passivating layer. This has been described by many researchers as parabolic kinetics (Dutrizac, 1982; Beckstead et al., 1976; Munoz et al., 1979 and Dutrizac and Mac Donald, 1974). The nature of the passivating layer is still under considerable debate. Current theories of passivation include either the formation of jarosite, ferric hyroxy sulfate, sulfur or iron deficient polysulfide like covellite (Klauber et al. , 2001 , Parker et al., 1981 , Munoz et al, 1976, Warren et al., 1985 and Parker et al., 1981). Recent research has suggested that different passivating layers are formed during the various stages of chalcopyrite leaching. These include a ferric hydroxy sulfate layer followed by jarosite over extended period of time (Klauber etal., 2001 and Parker et al., 2001 ). Current investigations are underway to establish whether semiconductor properties of the mineral affects the type of passivating layer formed. To date, most of the work has been performed at temperatures higher than those at which chalcopyrite bioleaching occurs and with varying pH and redox potentials. There has been little consideration of the potential difference between the suspended particles surface and the solution. This problem can be overcome by conducting experiments at a constant solution redox potential. Kametani and Aoki (1985) first presented a method of maintaining a constant redox potential by using potassium permanganate as an oxidant to continuously re-oxidise ferrous-iron to ferric-iron. This method was then adopted by our research group to determine the initial rates of chalcopyrite leaching. Preliminary rates of chalcopyrite leaching were presented in the thesis by Furamera (2000). Further work was required to firmly establish the rates of chalcopyrite leaching and the optimal redox potential range within which chalcopyrite leach occurs. This involved optimising the redox potential control system to obtain better redox potential control during the chalcopyrite leach experiment.

Includes bibliographical references. / Bioleaching is an established technology for the treatment of refractory gold ores and concentrates. The bioleaching of sulphide minerals is a complex process in which bacterial and chemical oxidation processes occur simultaneously. Recent studies has provided convincing evidence that the bioleaching of pyrite occurs via a two-step mechanism (Boon, 1996).