Biological Preoxidation Of A Pyrite Gold Concentrate

Gold and silver often occur finely disseminated in sulphide minerals such as pyrite. The use of biological leaching to dissolve pyrite and liberate gold has been extensively studied for a concentrate from the Porgera deposit, Papua New Guinea. The successful operation of a continuous bioleach circuit has been demonstrated. Bioleach residues were cyanide leached to extract gold and silver, and unreacted pyrite recovered for recycle to the bioleach. A 26 day steady state continuous bioleach test on a concentrate assaying 14.3 g/tonne Au and 87.0 g/tonne Ag produced residues with an average 73.5% weight loss and a pyrite oxidation of 88%. Cyanidation and recovery of pyrite from the cyanide residues for recycle gave overall recoveries of 92.1% gold and 74.6% silver. A proportion of the remaining precious metals was found in the bioleach solutions and may be recoverable. Losses to tails were 3.0% gold and 8.1% silver. Final tails represented 14.3% of the feed weight and averaged 1.84 g/tonne Au. A description of the continuous bioleach circuit and bioleach residue handling procedures, and the results of the study are presented. The features and advantages of biological oxidation as a pretreatment for refractory precious metal ores and concentrates are discussed.