Effects of Quebracho Tannin on Recovery of Colloidal Gold from Bioleached Wash Liquor

Abstract

Gold occurs in some concessions as submicron particles in pyrite and arsenopyrite, which is processed in a flotation concentration to obtain gold enriched sulphide concentrate. The concentrate is then treated in a biological oxidation step to oxidize the sulphides, liberate the occluded gold and make them amenable for cyanidation. The oxidized sulphide concentrate with high acidic content is washed in Counter-Current Decantation (CCD) thickeners to obtain thickened slurry, from which gold is recovered by cyanidation and wash liquor which is considered as tailings. The wash liquor from the CCD thickeners of a typical BIOX plant in Ghana, Golden Star Resources Limited, carries away 0.57 g/L of gold to tailings. This paper considered effects of Quebracho Tannin (QT) on recovery of gold from the oxidized flotation concentrate wash liquor. The effect of Quebracho Tannin on Total Suspended Solids (TSS) was also established. This research established that the gold lost to tailings was not soluble in the effluent but was mainly in the form of colloidal particles. Application of Quebracho Tannin to CCD effluent showed a substantial decrease in the loss of gold to tailings. About 0.13 g of gold was recovered from the CCD effluent per tonne of ore treated. An optimum QT dose of 0.05 g/l was determined from laboratory test giving a 21.25 % reduction in the Total Suspended Solids (TSS) and a 45.79 % reduction in the gold loss to tailings. When the 0.05 g/l dose was applied on the plant the TSS reduced by 53.51 %.

Keywords: Quebracho Tannin, Pyrite, Arsenopyrite, Gold processing, Colloidal particles.