LAUSR

Abstract The effect of biooxidation (BIOX) pre-treatment of refractory gold concentrates using mixotrophic and chemolithotrophic bacteria on the gold extraction during cyanidation of the concentrates at neutral pH was studied. A series of biooxidation and cyanidation of the biooxidized concentrates was carried out using three strains of bacteria; two mixotrophic bacteria of SKC1 and SKC2 and a chemolithotrophic bacteria Acidithiobacillus ferrooxidans (AC). Two distinct types of refractory gold concentrates with high sulfur content (i.e. S > 20%) and low sulfur content (i.e. S   5.0 which is not a suitable living environment for the bacteria. Cyanide consumption for cyanidation of the biooxidized concentrates with both mixotrophic bacteria was significantly increased due to reactions of sulfur and iron species that were precipitated during the biooxidation step with cyanides to form thiocyanate and ferrocyanide ions.