Heap Biooxidation - Bioleachingofa Refractory Gold-Bearing Ore

Abstract

A refractory pyrite/arsenopyrite ore containing 3.7 g/ton of gold finely disseminated in the sulphide matrix was subjected to microbial leaching in a heap containing 120 tons of ore crushed to minus 15 mm. The ore was initially leached by means of acidophilic chemolithotrophic bacteria to oxidize the sulphide minerals and to liberate the gold. About 50% of the sulphide sulphur was oxidized within 90 days. Previous laboratory experiments had shown that such degree of sulphide oxidation resulted in a high gold extraction during the subsequent leaching of the pretreated ore. After the bacterial pretreatment the ore was washed with water and was treated by alkaline solutions until the pH of the heap effluents was established in the range of 9- 10. Then the leaching of the gold was started with solutions containing amino acids of microbial origin and thiosulphate as gold-complexing agents as well as some ions participating in the oxidation and/or complexation of the gold. 70.7% of the gold was leached within 12 days in this way. Silver was leached together with gold. The pregnant solutions were treated by cementation with metallic zinc to precipitate the dissolved precious metals.