Thesis (M.Sc.). / Written for the Dept. of Earth and Planetary Sciences. Title from title page of PDF (viewed 2008/05/14). Includes bibliographical references.

A dissertation submitted to the Faculty of Engineering and the Built Environment at the University of Witwatersrand, Johannesburg, in part fulfillment of the requirements for the degree of Master of Science in Engineering, 17 May 2018 / Traditionally, copper and cobalt are extracted from oxidised ores via hydrometallurgical processing route. The ore is leached in sulphuric acid in reducing conditions. This method co-extracts impurity metal values like iron and manganese, necessitating downstream solution purification, which causes significant valuable losses. Pregnant leach solution purification is performed through step-wise oxidation and acid neutralisation of the leach solution. Cobalt is the most affected component in this process due to high losses incurred during the precipitation stages. Moreover, because the lixiviant is not recycled, the method consumes ominously high quantities of sulphuric acid. As a result, the process must be accompanied by readily available and cost-effective acid-making plant. In the event of an increase in the price of sulphuric acid raw materials or a decline in the ore grade, a source of 50% of the world’s cobalt might be rendered impracticable. This work investigates the viability of using ammoniacal solution as an alternative lixiviant to sulphuric acid. Ammoniacal solution forms soluble complexes with copper and cobalt at pH and potential where iron, manganese and other impurities tend to form precipitates. Because of the preferential leaching, downstream solution purification can be circumvented, thereby reducing valuable losses. Furthermore, because there is no solution altering, multi-step solution purification required, the leach solution retains its initial pre-leaching properties, making it fully recyclable. The recyclable nature of the lixiviant thus reduces lixiviant costs. Furthermore, an advantage of leaching in ammonia is lower equipment costs because ammonia is less corrosive than acid. The feed material used in this study was an oxidised copper-cobalt ore sourced from Katanga Region in the DRC. A size fraction analysis was undertaken in order to determine the deportation of the copper and cobalt metals in the feed material. In the leaching tests conducted, the effect of particle size, temperature, concentration of the reducing agent and concentrations of ammonia and ammonium carbonate were investigated. The results showed that a +63-75μm size fraction had the highest grade of copper and cobalt and was thus used for all the experiments undertaken. The results also indicated that cobalt and copper extraction was highly influenced by temperature. It was found that working at ambient temperature results in poor extraction of the value metal species while raising the temperature to 80°C significantly improves the extraction of both value metals if premature depressurising of the leach vessel is avoided. The results also showed that there was no significant extraction advantage gained from milling finer than -63μm. Moreover, it was found that at 80°C, 2.0M ammonia solution, 0.4M ammonium carbonate, 300rpm, 0.4M reducing agent and 60 minutes pre-treatment and leach time, a peak extraction of 90% could be realised for copper. It was also noted that even better extraction efficiencies could be obtained for copper in the absence of a reducing agent. Optimum cobalt extraction of 85% was obtained at 80°C, 2.0M ammonia solution, 2.0M ammonium carbonate solution, 0.4M ammonium sulphite, 60 minutes pre-treatment time and 60 minutes leaching time. This compares well to about 40-60% recovery reported when leaching in acid. These findings point to the conclusion that ammoniacal solution is a viable alternative to sulphuric acid for hydrometallurgical processing of the copper-cobalt ore. / MT 2018

Investigations have been carried out for a number of cobalt deposits in Australia including three from the Mt Isa Block in Queensland, several deposits in New South Wales, and one deposit each in the Northern Territory and South Australia, with respect to the identification of cobalt-bearing mineralisation and possible modes of formation. The deposits studied cover a range of deposit and mineralisation types including hydrothermal (e.g., cobaltite, Esperanza, Queensland; arsenopyrite, Dome Rock, South Australia) and sedimentary (secondary mineralisation such as the manganese wads at Bungonia, New South Wales). Deposits that were studied previously by the author (MSc thesis) in the Mt Isa Block have been used for comparison of mineralisation and temperatures of formation. The determination of the temperatures of formation of mineralisation, in particular with respect to cobaltite and arsenopyrite, by means of the application of the FeAsSCoAsS-NiAsS ternary phase diagram and the arsenopyrite geothermometer, has helped lead to deductions concerning the modes of deposition. Other deposit features such as structural constraints and associated mineralisation aided in the formalisation of conclusions. Many of the deposits are hydrothermal in nature and contain high temperature phases including molybdenite and uraninite. The latter represent geochemical and mineralogical clues which show that many of the ores were emplaced by igneous processes associated with granites. The findings of this study suggest that despite high percentages of substituting species in arsenopyrite, derived temperatures, from the application of the binary and ternary geothermometers, are comparable. It was noted that the presence of pyrrhotite and/or löllingite to act as buffers in the system is an important constraint on the comparability of derived temperatures. Potential processing applications for the extraction of cobalt from ores are briefly discussed, with respect to the type and cobalt content of mineralisation identified. The Esperanza and the Selwyn copper-gold deposits show the greatest potential for economic cobalt recovery. / Doctor of Philosophy (PhD)

Thesis (Ph.D. (Physics)) --University of Limpopo, 2013 / The intention of the current study is to investigate structure, ion transport and reactivity of various forms of the cobalt pentlandite, Co9S8, at different temperatures using atomistic simulation methods with the support of electronic structure calculations. The first interatomic potentials of Co9S8 were derived with input data as structure and elastic properties from experiment and electronic structure calculations respectively. The potentials were validated by running energy minimization and molecular dynamics calculations. Structure, elastic properties and phonon spectra were well reproduced, together with the complex high temperature transformations and melting of Co9S8 as deduced from crystal structure, radial distribution functions, density profiles and diffusion coefficients. Amongst the high symmetry surfaces {111}, {101} and {101} atomistic surface energy calculations proposed the {111} surface of Co9S8 as the most stable in agreement with experimental morphologies, and water adsorption energies on the such surfaces which mostly agreed with those from electronic structure calculations. The structural and ion transport variations with temperature were investigated and predicted surface melting at lower temperatures than the bulk. The effects of hydration on the surfaces at low and high temperatures were also studied. The structural and ion transport properties of Co9S8 nanoparticles of varying sizes, covered by high symmetry surfaces {111}, {101} and {100} were predicted using molecular dynamics method based on our derived interatomic potentials. The structural and ion transport properties of Co9S8 nanoparticles of varying sizes, covered by high symmetry surfaces {111}, {101} and {100} were predicted using molecular dynamics method based on our derived interatomic potentials. Generally for {111}, {101} nanoparticles, high temperature transitions were abrupt for smaller nanoparticles and these tended to disintegrate and form voids. However, for larger nanoparticles the transitions were more gradual. Transitions in the {100} bound nanoparticles were less dramatic for all sizes and the formation of voids was reduced at high temperatures. Generally, the melting temperatures of different sizes of nanoparticles increases with the particle size hence approach the bulk limit. The interaction of nanoparticles with water was investigated. / Anglo Platinum, National Research Foundation (South Africa), and The Royal Society (UK)