3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Recovery of PGMs from an oxide ore by flotation and leaching(2018) Sefako, Relebohile BasilFroth flotation is the process used in the Platinum Group Metal industry to upgrade the run-of-mine ore for subsequent processes such as smelting and hydrometallurgical PGM refining. The PGM concentrator plants achieve high PGM recoveries (>85%) when treating prestine (unweathered) sulphide ores. However, the depletion of prestine sulphide PGM bearing minerals has triggered interest in exploration of techniques for PGM recovery from near surface oxidised PGM ores. All earlier attempts to process the oxidised PGM ores by conventional flotation methods achieved poor recoveries (typically less than 50 %) hindering the commercial exploitation of these resources. The characterisation of the non-sulphide PGM ore used in this study indicated that the ore is enriched in oxide iron minerals as a result of weathering. In the flotation work, the maximum PGM flotation recoveries achieved using the sulphide co-collector schemes were 55.1% 3E (Pt, Pd and Au). Application of the hydroxamate oxide collector improved the flotation performance to recoveries of 74.7% 3E. The superior PGM recoveries achieved with hydroxamates probably lies in their ability to form complexes with metals such as iron. Hydroxamates co-collectors have been proven to improve recoveries without any adverse effects on performance of primary collectors such as SIBX. In this study the non-sulphide PGM ROM ore was leached directly using different acids. Low PGM extractions were recorded for hydrochloric acid (36.6% Pt and 8.8% Pd) and nitric acid (34.5% Pt and 7.1% Pd). The best leaching results of 48% Pt and 24.5% Pd were obtained using aqua regia solution though it is non-selective. Leaching of ROM ore is generally not preferable as it leads to high reagent consumptions. In this study it was postulated that leaching of low grade flotation concentrate would be preferred. Experiments were conducted to leach the concentrate that had the highest PGM recovery with sulphuric acid in order to target the base metals and further concentrate the PGMs in the residue. The base metal recovery from flotation concentrate using sulphuric acid was only efficient for copper and nickel while poor iron recoveries were achieved.Item Development of a high pressure hydrometallurgical process for the extraction of iron from iron oxide bearing materials(2016) Rolfe, WesleyThe feasibility of extracting iron from iron(III) oxide bearing materials with acetylacetone has been under investigation for many years. This is an alternate, environmentally friendly process for the recovery of iron compared to conventional processes that are energy intensive, have numerous costly process steps and produce large quantities of greenhouse gases. Iron(III) oxide bearing waste materials can be used in this process which reduces its environmental impact as it would not require waste storage. This study investigated the feasibility of reducing the reaction time of the liquid phase extraction of iron from iron ore fines by performing the extraction at elevated pressures and temperatures. It was found that that the extraction under pressure was dependent on temperature, pressure, particle size and solid to liquid ratio. It was found that at high temperatures and long extraction times, an unknown secondary reaction occurs that consumes the desired product, iron(III) acetylacetonate, and inhibits the recovery of these crystals. This results in lower extraction yields. It was found that the side reaction was largely dependent on the temperature of the system and the amount of iron(III) acetylacetonate present. The effects of the side reaction could be limited by lower operating temperatures and reducing the total reaction times. An optimum conversion of iron(III) oxide to iron(III) acetylacetonate of 47.2% was achieved for synthetic iron (III) oxide (> 95 wt% Fe2O3) at a total extraction time of 4 h, 160 °C, 0.025 g:1 mL, operating pressure of 1700 kPa, initial N2 feed pressure of 1010 kPa and 375 rpm stirrer speed. The optimum extraction of iron from iron ore fines (> 93 wt% Fe2O3) to iron(III) acetylacetonate was found to be 20.7% at 4 h, 180 °C, 0.025 g:1 mL and operating pressure of 1900 kPa, initial N2 feed pressure of 1010 kPa and 375 rpm stirrer speed. These are the optimum conditions where the side reaction is limited to improve the recovery and desired reaction conversion capabilities of the process. The operation under pressure yielded lower conversions than that of the atmospheric leaching process developed by Tshofu (acetylacetone water system under reflux). It was also found that it was not possible to reduce the extraction time and achieve comparable extractions when operating at higher temperatures and pressures. The formation of an additional unwanted product would also lead to unnecessary treatment costs in an industrial process. Hence, it was found that pressure leaching as an alternative is not currently viable due to the lower yields and associated high costs. Atmospheric leaching seems to be the most economically feasible option until a better alternative is found.