Bio-reduction of elemental sulfur to increase the gold recovery from enargite

The mineral enargite can be of interest to the mining industry as a copper and precious metal source. The mineral has a refractory character towards oxidation, which is attributed to the formation of elemental sulfur that seals off the mineral surface. In this study it was investigated whether elemental sulfur resulting from oxidation during industrial milling can be converted into hydrogen sulfide via bio-reduction. The removal of elemental sulfur in this process will clean the mineral surfaces for subsequent oxidation, prevent interference with the gold extraction process and reduce consumption of chemicals such as cyanide.HPLC analysis confirmed that indeed elemental sulfur was formed during industrial milling of an enargite–pyrite gold concentrate. Removal of elemental sulfur via bio-reduction was successful and improved the gold leachability from 48.9% to 69.6%. The combination of milling and bio-reduction was therefore concluded to be a possible route to liberate metals. Further research is necessary to investigate if the enargite to sulfur conversion can be improved to obtain economically satisfactory (> 90%) gold recoveries.

► Industrial milling of enargite results in the formation of elemental sulfur.
► Elemental sulfur can be removed via bio-reduction producing hydrogen sulfide.
► Bio-reduction of elemental sulfur increases the gold recovery from enargite.