Includes bibliographical references. / Acid mine drainage (AMD) is one of the major environmental challenges facing the South African mining sector. Acid mine drainage has received significant public attention in recent years. South Africa's long mining history has led to a growing concern that coal-related AMD from these mines (both operational and defunct) will continue for centuries to come. Pyrite bearing fine waste, generated during coal preparation and beneficiation, is thought to carry a significant amount of AMD pollution risk. Coal-related AMD generation has not been afforded the same exposure as AMD generation from high sulphide minerals such as gold and copper ores. This is exacerbated by the growing concern over water quality degradation in the Mpumalanga region of South Africa. The development of integrated solutions to address the management of coal-related AMD requires an understanding of the principle causes behind coal-related AMD. To date, most of the prediction methods described in literature have been derived for the prediction of AMD in metal bearing ores. Furthermore, some of these methods are based on assumptions and do not take into consideration the various sulphur species present. Additionally, some of these methods have limited applicability to coal due to the high total organic carbon content (TOC) of the material. This research project attempts to address these short comings and uncertainties by developing a systematic and meaningful framework for the characterisation of South African coal and coal waste. The research project contributes to the knowledge of coal-related AMD with particular emphasis on the characterisation methods responsible for sulphur speciation and mineralogy for coal. The approach entails carrying out a case study assessment aimed at empirically assessing a coal tailings sample according to: particle size distribution, textural reference, mineralogical characteristics, and how the aforementioned factors influence the acid potential in coal. The approach intends to address key factors which include: identifying the sulphur bearing organic and inorganic constituents related AMD generation in coal, assessing how the mineralogy, texture and particle size distribution contribute to AMD potential in coal tailings, and then identifying suitable analytical techniques and test methods which can provide data. The combination of these key outcomes will seek to provide a systematic and meaningful framework for the characterisation of coal and coal waste streams. The characterisation methods used in this case study outlined a framework focusing on four main areas of acid mine drainage characterisation for coal wastes, these included: chemical characterisation, mineralogical characterisation, sulphur speciation and AMD prediction. This comprehensive approach employed a suite of techniques, including: petrography, quantitative x-ray diffraction (QXRD) and quantitative evaluation of minerals by scanning electron spectrometry (QEMSCAN).

Includes bibliographical references / Rising global energy demands and global warming concerns from fossil derived fuels are two major problems affecting future generations. Bioenergy from algae offers a part solution that is both attractive and sustainable, by supplementing energy demands from a renewable energy source (the sun) and consuming carbon dioxide in the process. Bioenergy from algae is a proven concept (e.g algal biodiesel), yet the low productivities and high costs of existing processes limit their ability to make a significant contribution. Algae production occurs in specially designed photobioreactors, which are typically light limited. Hence, optimization of light supply to algae is key. A mathematical model of a photobioreactor is useful to aid in the design and optimization process. A model enables the prediction of productivities as a function of changing model inputs and hence allows optima to be predicted. While these are typically validated experimentally, this greatly reduces the number of experiments required, thereby saving cost and time. For this work, the production of algal biodiesel using airlift photobioreactors was used as the case study for the model development. Scenedesmus sp. was chosen as the model species owing to its comparatively high lipid productivity, a desirable trait for the production of biofuels. Although many parameters affect algal growth and lipid productivity, this project focused on one critical parameter, that of light provision.

Bibliography: leaves [177]-191. / Cell damage from hydrodynamic stress is an important consideration in biological systems since it can result in the growth and function of the cell becoming impaired (Toma et al. 1991, Lilly et al. 1992). In the extreme case of cell damage, cell disruption occurs. This dissertation presents the results of an investigation into the disruption of stationary-phase microbial cells in a stirred tank reactor when agitated in the presence of biologically inert solid particles in the absence of aeration. Applications of biological processes, where cells and solid particles are used, include bead mills, minerals bioprocessing, soil bioremediation and immobilised biocatalysts. An understanding of the rate, extent and mechanisms of cell disruption in these systems will facilitate the design of bioreactors to minimise or maximise microbial cell disruption, depending on the application. The primary objectives were to quantify and model the effect of incompletely and completely suspended solids on the kinetics of cell disruption, as a function of the solids concentration, agitation intensity and impeller flow pattern. Saccharomyces cerevisiae was used as model micro-organism and silica as the solid particles. Modelling the cell disruption enabled its prediction as a function of the operating parameters and further allowed the cell disruption mechanisms to be elucidated. A final objective was to quantify the solids suspension as a function of the operating parameters.

Includes bibliographical references. / Gold-bearing refractory sulphidic ores require a pretreatment process before extraction of the valuable metal, may be carried out. Bioleaching of the mineral may be used as pretreatment. Further mineral bioleaching may be used to liberate base metals such as copper from refractory sulphidic ores. The microorganisms used in the high intensity tank-based commercial biohydrometallurgy processes are mainly mesophiles, although moderate thermophiles are currently used at Youanmi Mine in Australia (Brierley, 1997). Extreme thermophiles have been found to exhibit enhanced oxidation kinetics in terms of rate of reaction and extent of solubilisation (Duarte et al, 1993; Norris and Barr, 1988; Konishi et al., 1995). However, these thermophiles appear to be sensitive to hydrodynamic conditions (Clark and Norris, 1996) and the presence of solids (Le Roux and Wakerley, 1988; Nemati and Harrison, 2000). An understanding of this sensitivity would be useful in developing systems to utilise extreme thermophiles in commercial biohydrometallurgy processes. The main objective of this study was to determine the effect of the solid particulate phase on the bioleaching performance of the extreme thermophile Sulfolobus metallicus. The hypothesis of the thesis was as follows: Archae involved in bioleaching are susceptible to damage in agitated aerated vessels, especially with increasing pulp density.

World-wide, acid rock drainage (ARD) is one of the biggest environmental challenges facing environments with current or previously active mining activities. Formed from the exposure of sulphide mineral to both water and air, and catalyzed by naturally occurring iron- and sulphur-oxidizing micro-organisms, ARD pollution is predominantly associated with the mining of sulphidic ores and coal. Of particular concern are the large volumes of mining wastes from which the generation of ARD and the associated pollution effects often persist over tens to hundreds of years after mining operations have ceased. Current ARD management strategies focus on the prevention of ARD through mineral waste deposition or remediation options once ARD has formed. These strategies, however, do not remove the risk of ARD generation in the future. The aim of this study was to investigate the removal of the potential for ARD generation from a low-grade copper waste rock through the accelerated removal of the sulphur components via reaction. The three waste rock samples used in this investigation had total sulphur grades of between 2.20 and 3.20 % with the majority of the sulphide present as pyrite, chalcopyrite and galena. Significant quantities of non-sulphide associated iron minerals, predominantly magnetite, were also present in the three samples. The waste rock samples were sourced from mining operations in Chile and South Africa and had a D80 of approximately 0.8 cm. All three waste rock samples were potentially ARD generating.

Production of biofuel from microalgae is an attractive and sustainable option for meeting rising global energy demands and mitigating global warming. However, for commercial production of microalgae to be economically feasible, high biomass productivities and low auxiliary energy inputs must be achieved in large photobioreactors. According to literature, one of the main factors limiting growth is the inefficiency of light utilization (Posten, 2009; Janssen et al., 2003; Carvalho et al., 2006). In a photobioreactor, as biomass concentration and depth of culture increase, the amount of light that is able to penetrate the culture decreases exponentially. This occurs because of mutual shading of algal cells via adsorption of pigments or via scattering of cells. The purpose of this study was to optimize biomass productivity and biomass concentration by developing a thorough understanding of the microalgal response to light. In particular, the effects of light source, light intensity, configuration (internal and external), reactor design and the related variation in light/dark cycling were investigated.

Solar energy, particularly electricity generated from the solar resource, has long been thought to be amongst the most expensive energy products. However, in a climate of electricity shortages and pressures on industries to reduce energy-related greenhouse gas emissions, many previous truths are being challenged. In the solar energy field there have emerged several technical and market innovations, thus making it more attractive. This could be of interest to many mining operations which are located in desert-type environments with high solar insolation and far from electricity grids. The objective of this dissertation is to evaluate the use of the available solar energy technologies at utility scale to supply the high energy demand of selected minerals processing industries by co-locating a solar power plant with a minerals processing operation. The effect on how the use of a utility scale solar energy use affects fuel transportation energy and conversion and transmission line losses is assessed. The study analyses the energy usage of different typical minerals processing operations, to identify the processing areas that are likely to benefit from the use of solar energy. Comminution, hot leaching processes and electrowinning circuits are shown to be the most energy intensive areas. Comminution requires high voltage AC power which can be supplied by the solar thermal (ST) technology which converts solar heat to steam which then drives a turbine. Process steam generation can also be achieved directly from ST technology. Electrowinning on the other hand requires low voltage DC electrical output, which can be generated directly using Photovoltaic (PV) technology. Five minerals processing operations, chosen to represent a range of different types of processes and energy supply scenarios, are profiled and their energy requirements quantified as a basis for establishing the extent to which solar energy can augment energy supply in different cases in this industry.

This project identified the possibility of manipulating rejection mechanisms in flotation to produce passivated pyrrhotite tailings. Passivation enables surface coating of the sulfide thus inhibiting attack by oxidising agents. Promotion of passivation of pyrrhotite during flotation to produce un-reactive tailings has not been explored to date. Polyethylene polyamines (DETA/TETA), which are already used as depressants in flotation, have been proved to be effective coating agents, significantly reducing the oxidation of pyrrhotite and pyrite in both abiotic and biotic systems. However, passivation by polyethylene polyamines (DETA and TETA) has only been explored on waste rock and pristine pyrrhotite. Furthermore, studies of the mechanism of oxidation of pyrrhotite have observed the formation of a hydrophilic ferric oxyhydroxide layer which enables depression of pyrrhotite during flotation. This layer has been reported in literature to inhibit the further oxidation of the pyrrhotite surface. Thus passivation can also take advantage of the formation of the ferric oxyhydroxide layer to inhibit further oxidation of the mineral.

Amidases are hydrolytic enzymes that catalyze the hydrolysis of amides to their corresponding carboxylic acids and ammonia. Amidases are ubiquitous in nature, and they have been isolated from a wide range of microorganisms, the most common source being bacteria. Amidases are recognized as potential industrial biocatalysts in processes that involve the synthesis of chiral compounds, mostly used in the pharmaceutical, agrochemical and food industries. The discovery of amidases from extremophiles has increased the potential for application of these enzymes for the development of new processes. In nonaqueous media, amidases have the ability to synthesize enantiopure amides due to the shift in thermodynamic equilibrium towards synthesis. For synthesis to occur, an acyl donor and an acyl acceptor are required, in which the acyl acceptor acts as a nucleophile. The applicability of amidases in non-aqueous media opens new possibilities for processes in which the enzyme can be used for the industrial synthesis of commercially relevant new products. A novel amidase was previously isOlated from a thermophilic Geobacillus species, and the amidase was cloned and expressed in an Escherichia coli BL21 strain. Also in previous studies, it was shown that the enzyme exhibits both amide hydrolysis and acyl transfer activities. The highest activity of the G. pallidus RAPc8 amidase was observed at 50°C in the presence of acetamide and substrate preference was towards aliphatic, short chain amides. Furthermore, the enzyme displayed enantioselectivity towards lactamide, which is a chiral compound. The amidase compound showed selectivity towards the D-isomer of lactamide and no detectable activity on the L-isomer. This study presents the investigation and development of a novel biocatalytic process that involves the synthesis of enantiopure amides in non-aqueous media, using the G. pal/idus RAPc8 amidase. The amidase was produced and expressed in E. coli BL21.

Bibliography: pages [167]-176. / In large scale brewing operations, process efficiency and beer quality rely on consistent fermentations. Improper handling of yeast may result in slow or incomplete fermentations and beer of unacceptable quality. The maintenance of yeast quality during yeast handling is therefore crucial. Current guidelines for yeast handling, plant design and equipment specifications are based predominantly on empirical knowledge. The effects of different equipment, flow conditions and physical conditions to which brewery yeast is exposed are largely unknown. Hence, South African Breweries (SAB) requested a study on the possible damage to yeast (loss of yeast quality) during mechanical handling in a brewery. The investigation detailed in this thesis was limited to mechanical handling of yeast during cropping (the transfer of yeast from a fermentation vessel to a storage vessel for re-use) and had the following objectives: to assess the potential for a loss of yeast quality during the mechanical handling in a brewery, to select and validate analytical techniques for the identification, characterisation and quantification of a loss of yeast quality, to characterise and quantify the loss of yeast quality during yeast cropping in a brewery.