Gold recovery enhancement from complex sulphide ores through combined bioleaching and cyanidation

The recent discovery of gold finely intergrown with the complex metal sulphides in the Tertiary volcanites of the Serrenti-Furtei district in central and southern Sardinia, prompted the investigation of gold extraction methods that are both economically viable and environmentally friendly. Here two types of integrated processes for gold extraction are compared: roasting plus cyanidation and bioleaching plus cyanidation. With the first process, overall gold recoveries as high as 85% are achieved, whereas with a variant of the second, total gold recovered does not exceed 77%. Both types of processes investigated are described in detail. The findings of the investigation suggest that the advantages offered by the biohydrometallurgical processes—especially from the environmental viewpoint—may compensate the lower gold recovery they yield.