Research on leaching of carbonaceous gold ore with copper-ammonia-thiosulfate solutions

Abstract For carbonaceous gold ore and its concentrates, gold extraction by direct cyanidation is usually low due to the known preg-robbing effect. The leaching behavior of a carbonaceous gold ore with a high content of dolomite in copper-ammonia-thiosulfate solutions was investigated. A gold extraction of 74% was achieved in a copper-ammonia-thiosulfate leaching solution. Thiosulfate consumption increased with an increase of Cu 2+ and S 2 O 3 2− concentration as well as with leaching temperature, but decreased with increasing ammonia concentration and initial pH. The effect of microwave roasting pre-treatment on gold extraction was examined. The gold extraction increased to 90% after the ore was microwave roasted for 30 min at 500 °C. The increase in gold extraction after microwave roasting pre-treatment was caused by the formation of surface cracks, which facilitated the transport of the thiosulfate lixiviant to otherwise encapsulated gold. The microwave roasting also reduced the organic carbon content of the ore, thus enabling cyanidation.