An economic analysis of coal desulpharisation by froth flotation to prevent acid rock drainage (ARD) and an economic review of capping covers and ARD treatment processes

Master Thesis


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University of Cape Town

Acidic drainage as a result of mining and mineral processing activities is a growing concern. The effects of Acid Rock Drainage (ARD) include environmental pollution in the affected areas and beyond. As South Africa has water challenges, the potential threat of continual depletion of useable water resources through their contamination by ARD and other mining activities may affect economic productivity, as well as quality of life. Currently used ARD remediation measures are variable and costly, not only in South Africa but worldwide. End of pipe approaches such as treatment by neutralisation fail to reduce the risk of ARD generation and provide long term solutions. Further it fails to address the limited resource utilisation of the byproduct materials, currently disposed of as ARD forming wastes. The Department of Chemical Engineering, at UCT, has focused research onto the prevention of ARD generation and minimisation of waste. One approach proposed is the two stage froth flotation process for separating sulphides, responsible for ARD formation, from the remaining tailings, leaving these benign with respect to ARD. Testwork results have proven its technical feasibility using porphyry copper tailings, fine coal and more recently gold tailings. Historically, ultrafine coal was not treated by most collieries in South Africa, but disposed as waste. Oxidation of the pyrite in the coal leads to generation of acidic water. In this project, an economic analysis of the coal two stage flotation process for the mitigation of ARD formation is considered. This project proposes ARD prevention by desulphurisation of sulphide rich waste coal material as an in-process approach which can be incorporated into mineral process flowsheets or as an add-on process for desulphurisation of old workings. The two stage flotation may yield a valuable mineral or coal product, as well as a low volume sulphide rich fraction which can be processed further to yield sulphuric acid or disposed of with containment and a benign tailings fraction which can be used as cover material or disposed conventionally.

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