MSc Project title Mitigation of acid rock drainage risks associated with coal slurry by means of froth flotation techniques
(Supervisors: Prof J-P Franzidis; Prof S Harrison and Dr J Broadhurst) Graduated: 2011
The South African coal processing sector currently generates more than 12 million tons of ultrafine slurry per annum, the majority of which is disposed of in slimes dams. These ultrafine coal wastes contain sulphide-bearing minerals, particularly pyrite, which oxidize and give rise to acid rock drainage (ARD) under conventional disposal conditions. The release of salt and heavy metal bearing ARD to the surrounding environment results in extensive and prolonged contamination of local ground and surface waters. Currently, South African coal mining and processing operations still emphasise an end-of-pipe approach in their management of AMD, with the focus being largely on chemical and/or biological treatment techniques.
This study, which was commenced in 2010, investigated the technical feasibility of separating pyritic sulphur from coal ultrafines using a two stage flotation process, aimed at simultaneously eliminating ARD risks and recovering valuable coal. Laboratory-scale batch flotation tests were conducted on a coal fine-to-utrafine sample for a selected case study to determine the effects of key parameters on (i) the extent of sulphide sulphur removal in a desulphurization (reverse) float; and (ii) the extent of coal recovery in a direct coal float. The results showed that a low-sulfur tailings (0.38% S) can be produced, together with a clean coal stream with a low ash content (13.54%) and a low volume sulfide-rich fraction (2.68% total sulfur).The low sulfur tailings produced were found to have low ARD potential. The coal ultrafine concentrate stream produced has added value because of its reduced ash content.
Peer-reviewed journal publications
Kazadi Mbamba, C., Franzidis, J.-P., Harrison, S.T.L. and Broadhurst, J.L. 2013. Flotation of coal and sulphur from South African ultrafine colliery wastes. Journal of the Southern African Institute of Mining and Metallurgy, 113: 399-405
Kazadi Mbamba, C., Harrison, S.T.L., Franzidis, J.-P. and Broadhurst, J.L. 2012. Mitigating acid rock drainage risks while recovering low-sulfur coal from ultrafine colliery wastes using froth flotation. Minerals Engineering, 29: 13-21
Oral conference presentations
Kazadi Mbamba C., Harrison S.T.L., Franzidis J-P. and Broadhurst J. 2011. Mitigating rock drainage risks while recovering low-sulphur coal from ultrafine colliery wastes using froth flotation. SAIMM Mineral Processing Conference, Cape Town, 4-5 August 2011
Kazadi Mbamba, C., Harrison, S.T.L., Franzidis J-P and Broadhurst, J. 2011. Mitigating acid rock drainage risks while recovering low-sulphur coal from ultrafine colliery wastes using froth flotation. Sustainability through Resource Conservation & Recycling (SRCR ’11), Falmouth, UK, 10-12 May, 2011
Kazadi Mbamba, C. 2010. Mitigation of acid rock drainage risks associated with coal slurry by means of froth flotation techniques, 15th Southern African Conference in Coal, Carbon and Energy Technology, Johannesburg, 17-18 November 2010.