Abstract
Raw algal lipids (RALs) and their derivatives (fatty acid methyl esters; FAMEs) were investigated as biocollectors for the recovery of coal from ash-rich fine coal waste by froth flotation. Testing was done on fine coal discards from two South African sites—a high ash (50%), high sulphur (5.7%) sample and a lower ash (26%), low sulphur (0.91%) sample. The yield and recovery of combustibles on using biocollectors was similar to, or better than, with oleic acid, a polar collector demonstrated as a good collector in previous research. The RALs and FAMEs reduced the ash and sulphur content of the combustible fraction of the high ash-high sulphur sample to between 23–28% and 1.9–3.3%, respectively. The chemical modification of RALs to FAMEs provided potential for improving the selectivity of the recovery of combustibles. It also resulted in a change of the optimum operating pH, with RALs yielding better results at the natural pH of the sample (pH 2.7), while FAMEs performed best at pH 7.
Highlights
At the current rate of coal extraction, South Africa generates around 60 million tonnes of coal waste annually, with over a billion tonnes of coal waste already accumulated [1]
The biocollectors performed significantly better when compared to oleic acid and dodecane at the same fixed dosage of 2.79 kg/t
Raw algal lipids proved to be a good biocollector for the flotation of both high-ash, high-sulphur and low-ash, low-sulphur fine coal waste from two different geographical locations in South Africa
Summary
At the current rate of coal extraction, South Africa generates around 60 million tonnes of coal waste annually, with over a billion tonnes of coal waste already accumulated [1]. This waste has a large footprint on land that could be used for other productive purposes. A study by Chugh and Behum [5] in the United States showed that some coal wastes that were produced from the cleaning process had as high as 6.85% sulphur (sulphur is a proxy for pyrite content in coal characterisation).
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