MSc Project title Comparison of froth flotation and gravity separation of the Waterberg and Witbank coal ultrafines in terms of mitigating ARD potential
(Duration: Feb 2013 to June 2015)
In South Africa, over 10 million tons of ultrafine coal wastes are discarded every year, typically in the form of ultrafine slurries. The high calorific value of these discards leads to a waste of energy that could be harnessed and used, while the high sulfur content contributes to adverse environmental effects such as acid rock drainage (ARD). Desulfurization is a useful means of completely eliminating the threat of ARD. UCT has developed a two-stage flotation process, which involves coal flotation in the first stage and sulfide flotation in the second stage. On the other hand, gravity separation, particularly reflux classification, has shown great promise in coal beneficiation.
This thesis presents the results obtained in the combination of flotation and reflux classification for the effective removal of sulfide minerals from two South African coal ultrafines, whilst recovering valuable coal, and comparing the results with the UCT two-stage flotation process. Two process routes were investigated: (i) froth flotation followed by reflux classification of tailings, and (ii) reflux classification followed by froth flotation of overflow. Both process routes were hypothesized to perform better than the UCT two-stage process because they take advantage of the natural hydrophobicity of coal and the large density difference between coal and pyrite. This comparison was based on the recovery of valuable coal, benign tailings and sulfide-rich concentrate. The results show that reflux classifier is indeed capable of separating pyrite from coal (90 % sulfur reduction). The UCT two-stage process also showed great separation performances, with up to 60 % sulfur reduction.
Iroala O., Franzidis J-P., Harrison S. 2013. Comparison of froth flotation and gravity separation of the Waterberg and Witbank coal ultrafines in terms of mitigation ARD potential. Poster presented at 31st Annual SAIMM Mineral Processing Conference, 6-7 August, Cape Town, South Africa.
Iroala, O.J., Franzidis, J.-P., Harrison, S.T.L., Campbell, Q. and Le Roux, M. 2014. Comparison of froth flotation and gravity separation of coal ultrafines in terms of mitigating ARD potential. 20th Fossil Fuel Foundation Coal, Energy and Sustainability Conference, 27-28 November, Cape Town, South Africa. Also presented at the 32nd annual SAIMM Mineral Processing Conference, 7-8 August, Cape Town.