On the solution chemistry of cyanidation of gold and silver bearing sulphide ores. A critical evaluation of thermodynamic calculations

Abstract

The use of thermodynamic calculations for cyanidation of gold/silver and their minerals is reviewed. In literature there are a number of studies based on thermodynamic calculations to describe the chemistry of cyanide leaching of gold and/or silver from sulphide minerals. Disagreements between computational and experimental results are usually significant. In the present study, a critical evaluation of thermodynamic calculations, including the authors' own recalculations, for cyanide leaching of gold/silver are carried out in order to interpret the experimental results. The solution chemistry of the leaching process is discussed with reference to both computational and experimental results. The competition of cyanide complexation of gold, silver and other metals, especially copper and iron, as well as the influence of sulphide, during cyanide leaching is particularly considered. It is demonstrated that the oxidation rate (kinetics) of sulphide determines the characteristics of the cyanide leaching sulphide, the different metal species precipitate, as cyanide is consumed during leaching, in the order of FeOOH(s) > Cu(OH) 2(s) > AgCN(s) > Ag 2O(s) > Au(s). In the case of incomplete oxidation of sulphide, the precipitation order is Ag 2S(s) > FeOOH(s) > Cu(OH) 2(s) > Au(s). Based on these calculations, experimental results of cyanide leaching can be now well interpreted.