A STUDY ON THE BIOOXIDATION OF AN ARSENICAL GOLD SULPHIDE CONCENTRATE WITH EXTREME THERMOPHILIC MICROORGANISMS

Biooxidation of sulphide minerals has become an important method for the pretreatment of refractory gold ores. Moreover, bioleaching of the minerals with thermophilic microorganisms is attracting increasing interest as a promising alternative process. In this study, the biooxidation of an arsenical refractory gold sulphide concentrate using extreme thermophiles is examined. The concentrate contained 100.84 g/t Au, 31.8% pyrite (FeS2), 10.9% arsenopyrite (FeAsS), 0.2% chalcopyrite (CuFeS2), 37.3% quartz (SiO2) and 19.8% gangue. Biooxidation experiments were conducted in Erlenmeyer flasks at 150 rpm and 68 degrees C. Highest sulphide oxidation with 60.8% over 432 h was achieved in the presence of the mixed culture, EXTM containing two strains (Acidianus brierleyi and Sulfolobus metallicus). EXTM mixed culture was shown to biooxidize the concentrate more rapidly and extensively than the pure cultures. Compared with the control test in the absence of microorganisms, the dissolution of iron and arsenic was enhanced by 11.8-38.1% and 16.4-60.5% respectively in the presence of the archaeal strains. The increase in the pulp density was shown to adversely influence the biooxidation activity of the strains. After 24 h leaching time by direct cyanidation, low gold recovery was obtained (less than 20% Au). On the other hand, a high gold recovery was achieved for the biooxidized residues: after 24 h cyanidation gold dissolution reached about 77.1% Au.