Preparatory Bioleaching to the Conventional Cyanidation of Arsenical Gold Ores

Cyanide leaching is the wide-spread process for the extraction of gold from primary raw-materials. However when gold is associated with metal sulphides, an oxidative thermal or a chemical pretreatment is often needed to access precious metal particles. Bacterial oxidative leaching may be an interesting alternative - low cost and environmentally friendly - to liberate gold from the sulphide matrix and then make it amenable to cyanidation. Bioleachh~g with Thiobacillus ferrooxidans has been investigated at 30°C at bench scale on a gold-bearing arsenopyrite (2 g/t Au) ore coming from Golcuck Mine in Turkey. The study was concerned with the influence of the age of the inoculum, pH, pulp density and time of the bacterial leaching at 30°C on the recovery of gold during the subsequent standard cyanide attack. Direct cyanide leaching of the arsenopyrite ground to- 74 pm showed no gold dissolution at all, but with fine grinding to -30 pm, gold recovery increased to about 55. 3 % after 48 hours of cyanidation. On the contrary, cyanidation performed for 2 days on a bioleached arsenopyrite allowed 90% of gold to be solubilized in 2 hours.