Effect of carbon coatings on gold dissolution in the presence of sulphide and lead

Abstract

The role of sulphide and lead in gold dissolution in a cyanide medium has been investigated for pure gold with elemental carbon coatings. Sulphide reduced the dissolution of gold with or without carbon coatings to almost the same extent and this effect became more pronounced at a higher sulphide concentration. The carbon coating slightly reduced the negative effect of sulphide on gold dissolution at around 0.2–5 mg S 2−/L. The negative effect of sulphide on gold dissolution decreased with increasing cyanide concentration. Lead increased the dissolution of gold with or without carbon coatings at a concentration up to 2 mg Pb 2+/L with the beneficial effect declining over this concentration range. The carbon coating reduced the beneficial effect of lead on gold dissolution. Gold dissolution was retarded at around 5 mg Pb 2+/L. The positive effect of lead on gold dissolution became more prominent with increasing cyanide concentration. SEM analysis revealed much less erosion of gold occurring with the addition of sulphide. The gold surface showed highly corroded spots scattered across relatively less corroded areas during leaching with the addition of lead, while the gold surface was smooth after leaching with a carbon coating. An XPS investigation indicated the formation of AuS x at the gold surface with the addition of sulphide. Metallic lead or AuPb alloys and lead hydroxide were detected at the gold surface after leaching with the addition of lead. The carbon coating hindered the diffusion of lead to the gold surface and hence reduced the beneficial effect of lead on gold dissolution.