Interactions between sulphides and manganese dioxide in thiosulphate leaching of gold ores

The interactions between manganese dioxide and pyrite or chalcopyrite were investigated in both the ammoniacal and ammoniacal thiosulphate leaching systems. Pyrite and chalcopyrite dissolved at enhanced rates in the presence of manganese dioxide in both ammoniacal and ammoniacal thiosulphate solutions. The interactions between manganese dioxide and sulphides were also applied in the thiosulphate leaching of gold from a pyrite concentrate and a sulphide ore. The addition of a small amount of manganese dioxide in the thiosulphate leaching of the sulphide bearing gold ores improved both the kinetics and the overall gold extractions without much impact on thiosulphate consumption.A pre-treatment process with copper ammoniacal solutions enhanced gold extractions from the sulphide bearing ores and reduced thiosulphate consumption to a large extent. The sulphides partially degraded in the pre-treatment process likely exposing gold to leach solutions. SEM images of the surface corrosion of pyrite and chalcopyrite in contact with manganese dioxide showed that the pre-treatment with manganese dioxide enhanced the degradation of the sulphide matrices, thus achieved a better gold leaching from the sulphide bearing ores.