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

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The objectives of this project have been to characterise the biooxidation of an auriferous pyrite/arsenopyrite flotation concentrate, and to interpret laboratory batch and continuous pilot plant data in the light of the logistic model. Furthermore, the possibility of predicting continuous biooxidation plant performance from batch data was considered. The batch testing was carried out on five narrowly sized fractions of Fairview concentrate, as well as on the bulk concentrate. Extents of removal of iron, arsenic and sulphide-sulphur were described by the logistic equation and values of the kinetic parameters obtained. Maximum rates of removal of these components, predicted by the logistic parameters, correlated well with experimentally determined rates of removal obtained from the linear portions of the fractional removal versus time curves. Bibliography: pages 93-98.

Thesis (MTech (Chemical Engineering))--Cape Technikon, Cape Town, 1999 / Carbon-in-pulp (CIP) and carbon-in-leach (CIL) remain the most effective, and widely used processes for gold recovery from cyanided pulps. The extensive use of carbon in such processes have prompted many researchers to investigate the mechanism of metal cyanide adsorption. Not only has this provided many viable theories in the understanding of the mechanism, but it has also led to an improved understanding of the effects of the various operating conditions on the CIP circuit. However, the declining gold price has made gold producers aware of the need to either further optimise existing circuits or find alternative means of operation so as to improve efficiency. It is therefore the aim of this study to investigate the factors which influence the metal extraction circuit. In this study the effects of parameters such as gold and carbon concentrations, slurry density and stirring speed on the adsorption process were investigated. It was found that the effects of gold and carbon concentrations could be determined directly, that is, a definite linear relationship exists between these two parameters and adsorption rate. However, slurry density and stirring speed (power input) have a twofold effect on the process. For this reason two distinct terms called the "blinding" and "mixing" numbers have been identified. It has been shown that all the parameters investigated influences the rate of adsorption during the constant rate adsorption period. However, only solution concentration, carbon concentration and carbon loading influence the process during the diminishing rate of adsorption. This confirmed the belief that intraparticle diffusion is the rate controlling factor during the diminishing rate period. Furthermore, the point at which constant rate adsorption is replaced by the diminishing rate of adsorption is mainly a function of solution concentration.

Thesis (MTech (Chemical Engineering))--Cape Technikon, Cape Town, 2000 / In a typical gold-recovery plant, it is estimated that a substantial amount of the gold in residues may be in the form that is recoverable by cyanidation. The gold in residues can be ascribed broadly to (l) the presence of cyanicides, which consume the cyanide radical and thus inhibit dissolution of gold, (2) refractory gold resulting from coatings on some gold particles, (3) large gold particles incompletely dissolved due to inadequate contact time, (4) unliberated gold as a result of too coarse a milled product, and (5) gold dissolved during leaching, then adsorbed by other minerals or by carbonaceous matter in the pulp. This study focuses on the latter, where dissolved gold is pregrobbed during leaching by adsorbent materials in the ore. The term pregrobbing refers to the active adsorption ofgold from cyanide pregnant solutions by components ofthe ore. It has been suggested that gold already dissolved by cyanide may be adsorbed by other minerals and by carbonaceous matter in the pulp. The presence ofcarbonaceous matter in gold ores presents a two-fold problem namely, the poor release of gold from the carbonaceous matrix and the uptake of dissolved gold by the carbonaceous leach residues. Studies by several other investigators using ores from various parts of the world have similarly shown that the natural carbonaceous matter associated with refractory gold ores often behaves like activated carbon when in contact with aurocyanide solutions. Some debate also exists over the extent to which gold may be adsorbed onto the surfaces of minerals. Different authors have identified that minerals such as' pyrite, copper sulphides, quartz and layered silicates, such as kaolin, phlogopite and ilIite exhibit gold adsorbing properties. Activated carbon was first used as a model pregrobber in batch kinetic adsorption experiments in the presence of a gold selective strong base anion-exchange resin.

M.Tech. / The study presented, investigated the acid leaching behavior of calcines emanating from conventional roasting and microwave assisted roasting of sulphide ores. The aim was to investigate a possible change in the mineral composition of the calcine produced and to investigate the leaching behavior of the calcine produced by conventional and microwave assisted roasting. Two sulphide concentrates were received, pyrite concentrate from OTJIHASE concentrator and sphalerite concentrate from ZINCOR. The mineralogical study was done using the XRD (PANalytical X-PertPro X-Ray diffractometer) to determine the mineral composition of the concentrate and the head grade of each concentrate was determined with an Atomic Absorption Spectrometry (AAS) machine for copper, iron and zinc. The concentrates were wet screened at 500, 355, 212, 150, 106 and 75 μm screens for size distribution and for the purpose of the study it was required that 80% of concentrate should pass the 75 μm screen since after roasting, the calcine obtained were to be acid leached. Conventional roasting was carried out at temperatures of 500oC, 700oC, 850oC and 1000oC at durations of 5min, 10min, 20min, 30min, 1hour and 2hours, while microwave assisted roasting carried out at powers of 200W, 400W, 600W, 800W and time intervals of 3s, 10s, 30s, 30min and 1hour

The full text of this thesis/dissertation is not available online. Pending permission from the author/supervisor access may be provided on <a href="mailto:upetd@up.ac.za">request.</a> Read the abstract in the section 00front of this document. / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2006. / Materials Science and Metallurgical Engineering / unrestricted