Pyrrhotite bioleaching for gold recovery: a complete scheme of treatment

The aim of the present work was to investigate the biooxidation of a refractory gold-bearing pyrrhotite in order to increase the gold recovery during the subsequent conventional cyanidation. Bacterial coltures utilised in the biological test consisted predominantly of Thiobacillus genus. Tests were carried out at laboratory scale. The gold content of the ore sample - coming from South America - was of 9 g/t Au. After 48 hours leach time low gold recovery has been obtained by direct cyanidation (<30% Au). A high gold recovery was achieved for the biooxidated samples: after 48 hours cyanidation gold dissolution reached about 93% Au. Experimental results have shown the technical feasibility of the biooxidative pretreatment prior to the conventional leaching. A complete process flowsheet has been developed considering also the subsequent steps for gold recovery by carbon adsorption-desorption and electrowinning.