Includes abstract. / Includes bibliographical references (p. [191]-204). / The objective of this work was to investigate the effects of a wide range of solution conditions,namely: temperature, pH, dissolved Al and Mg, and the effect of total iron concentration on the kinetics of microbial ferrous-iron oxidation by Leptospirillum ferriphilum, with a view to developing a comprehensive rate equation.

Includes bibliographical references (leaves 127-136). / The coal biosolubilisation processes may be used to convert low rank coal to either a clean, cost-effective energy source or to value-added products. This can lead to increased utilisation of low-rank coal. Low-rank coal is currently under-utilised because of its low calorific value, high moisture and sulphur content. Most research on coal biosolubilisation has centred on pre-treated coal. Little work is reported on naive coal. Low yields of solubilised coal products are currently reported in the literature. This may be due to further degradation of the soluble processes or to limitation of solubilisation step. These products have potential as starting materials for biotransformation to value-added products. However, to date, small volumes of solubilised coal products are available to assess their potential for further biotransformation owing to current biosolubilisation of low-rank coal being widely carried out as a small scale Petri dishes or Erlenmeyer flask of volume. This dissertation presents the results of the investigation of biosolubilisation of low-rank coal in slurry systems using Trichoderma alroviride. Its main objectives were to investigate key operating variables influencing untreated low rank coal biosolubilisation and degradation of soluble products, and to study different reactor configurations for coal biosolubilisation

Includes abstract. / Includes bibliographical references. / The technical feasibility of the ammonia leaching process of a Platreef flotation concentrate was investigated in different reactor settings i.e. shake flasks, columns and batch stirred tank reactors, respectively. The process investigated aims to use either a heap leaching environment or tank leaching of untreated low-grade concentrates under ambient conditions and mild temperatures. This process is proposed as an alternative primary treatment method for the recovery of base metal sulphides from a PGM containing concentrate that cannot be extracted economically by conventional milling, smelting and refining methods.

Includes abstract. / Includes bibliographical references. / Thus, this study focused on the determination of antioxidant activity and the extraction of phenolic antioxidants from fruit processing wastewaters obtained from fruit processors in the Western Cape region of South Africa, using various extraction techniques. The chemical analysis of the fruit processing wastewaters showed that the silage water SW had the highest concentration of total phenols of 399.52 mgIL gallic acid equivalents (GAE) and apple wastewater AWl had the lowest concentration of 7.61 mg/L GAE. The fruit processing wastewaters also contained sugars and complex carbohydrates.

Includes bibliography. / The objectives of this work were to provide rigorous kinetic information on the effects of feed sulphate concentration and temperature on the anaerobic sulphate reduction process and to develop a kinetic model to explain this dependency. These objectives were addressed by performing batch and continuous sulphate reduction experiments using a mixed sulphate reducing microbial culture with acetate as the organic carbon and electron donor source. Sulphate concentration, acetate concentration and biomass concentration was used to determine the metabolic activity of the microorganisms and the rate of sulphate conversion.

Includes abstract. / Includes bibliographical references. / Mine wastewaters are presently generated at working and abandoned mining operations, both within South Africa and internationally. Currently, active treatment systems are being utilised to treat the voluminous quantities of acid rock drainage that are being generated within South Africa, largely as a result of groundwater rebound through abandoned workings. However these technologies are not economically viable for the treatment of smaller discharges from diffuse sources, such as coal spoil heaps, overburden and waste rock dumps, over a long period of time. In addition, they are questionable from a sustainability perspective. The Integrated managed passive (IMPI) treatment system is a semi-passive biological process, which was developed for the treatment of sulphate-laden mine water discharges. The system consists of modular sulphate reduction and sulphide oxidation units. A demonstration-scale plant was constructed at BHP Billiton’s Middelburg Colliery, however the sulphide oxidation unit, the linear flow channel reactor (LFCR) did not perform efficiently. This study was conducted to develop a greater understanding of the physical, chemical and biological processes occurring within the reactor. Data generated during previous studies were critically evaluated and a number of unsubstantiated assumptions and experimental deficiencies were identified.

Includes abstract. / Includes bibliographical references (leaves 96-99). / The bubble column reactor is commonly used in industry, although the fluid dynamics inside are not well understood. The challenges associated with solving multi phase flow problems arise from the complexity of the governing equations which have to be solved, which are typically mass, momentum and energy balances. These time-dependent problems need to include effects of turbulence and are computationally expensive when simulating the hydrodynamics of large bubble columns. In an attempt to reduce the computational expense in solving bubble column reactor models, a "cell" model is proposed which predicts the velocity flow field in the vicinity of a single spherical bubble. It is intended that this model would form the fundamental building block in a macroscale model framework that does predict the flow of multiple bubbles in the whole column. The non-linear Navier-Stokes (NVS) equations are used to model fluid flow around the bubble. This study focusses on the Reynolds number range where the linear Stokes equations can be used to accurately predict the flow around the bubble. The Stokes equations are mathematically easier to solve than the NVS equations and are thus less computationally expensive. The validity of the NVS model was tested against experimental data for the flow of water around a solid sphere and was found to be in close agreement for the Reynolds number range 25 to 80. The simulation results from the Stokes flow model were compared with those from the NVS flow model and were similar at Reynolds numbers below 1. The application is then in the partitioning of the bubble column into regions governed by either Stokes or NVS equations.

Includes abstract. / Includes bibliographical references. / Anglo American Platinum’s expansion project, which aimed at increasing platinum production to 3.5 million oz per annum, necessitated an expansion in the Rustenburg Base Metal Refinery (RBMR) to accommodate the associated increase in the production of base metals (Cu, Ni, and Co). RBMR’s name plate capacity increased from 21 000 to 33 000 tonnes of nickel per annum. The expansion project involved various brownfield and greenfield installations and was completed in 2011. The new circuit and various process additions posed a significant risk to the nickel cathode quality with regard to zinc contamination. Mass balancing of the pre-expansion circuit showed that as much as 50% of the zinc entering the plant would exit through the nickel cathode, thus making it the major bleed for zinc from the circuit. The expansion circuit mass balance showed that although a portion of the zinc would exit through the pressure iron removal residue, this small bleed stream would not be sufficient to ensure that the nickel cathode does not exceed 50 ppm (LME specification). Another factor contributing to the zinc problem was the fact that more Platreef ore, with higher zinc levels, was being mined. These factors indicated that a dedicated zinc removal section was required to ensure a sustainable nickel cathode production containing less than 50 ppm zinc.

Secondary leach concentrate (SLC) is an important bleed stream for minor elements from Anglo Platinum’s Base Metal Refinery (BMR) which produces copper nickel and cobalt sulphate. It contains mainly sulphur, iron jarosites, unleached base metals and platinum group metals (PGMs), which makes the treatment of SLC necessary. The SLC is currently toll-refined at Umicore’s Hoboken smelter and refinery to recover revenue from entrapped valuable metals. This method of treatment results in excessively high costs due to high transport and toll refining expenses as well as penalties. Thus, an in-house method of treatment by Anglo Platinum itself would prove beneficial in that it would eliminate these excessive costs and also provide a method of treatment in the event of residues exporting becoming banned or strongly penalised in future. Therefore, a method for treating SLC in-house is investigated. The first stage of the proposed treatment method involves a pyrometallurgical process where the removal of amphoterics by oxidative fuming, followed by reduction to recover base metals from the slag takes place. The PGMs are reported mainly to the metal alloy phase along with the base metals during this process. The project discussed in this report deals with the treatment of this furnace alloy which is referred to as Cu alloy. The Cu alloy is used to produce anodes to be applied to an electrorefining application for the recovery of Cu as a Cu cathode and PGMs in the form of anode slimes. Spent electrolyte from the BMR copper electrowinning section adjusted to specific pH and Cu concentration is used as electrolyte to which dissolvable metals (such as Ni and Fe) are recovered.

Includes bibliography. / The objectives of this research thesis were to understand and quantify biological responses to hydrodynamic stress by investigating the activity of the yeast Saccharomyces cerevisiae, cultivated in the presence of a range of solid loadings, solid sizes and agitation rates. The influence of inoculum size, inoculum age and type of agitator were also investigated. This study was carried out with the intention of identifying biological responses to hydrodynamic stress and modelling observed effects on microbial activity.