Gold recovery from a refractory pyrrhotite ore by biooxidation

The aim of the present investigation was to study the biooxidation of a refractory gold-bearing pyrrhotite, in order to increase the gold recovery during the subsequent conventional cyanidation. Bacterial cultures utilised in the biological test consisted predominantly of Thiobacillus genus. Tests were conducted at laboratory scale. The gold content of the ore sample, coming from Bolivia, was of 10 g t-1 Au. After 24 h leaching time by direct cyanidation, low gold recovery was obtained (<20% Au), with a high reagent consumption. On the other hand, a high gold recovery was achieved for the biooxidated samples: After 24 h cyanidation gold dissolution reached about 91% Au. Experimental results have shown the technical feasibility of the biooxidative pretreatment prior to conventional leaching and a complete circuit of treatment, on laboratory scale, has been developed considering also the subsequent gold recovery by carbon adsorption/desorption and electrowinning. A gold extraction yield of about 86% was determined in the whole process for gold extraction from pyrrhotite (biooxidation, solid-liquid separation, cyanidation, adsorption, desorption, electrowinning).