ON THE SOLUTION CHEMISTRY OF CYANIDATION OF GOLD AND SILVER BEARING SULFIDE ORES - A CRITICAL-EVALUATION OF THERMODYNAMIC CALCULATIONS

The use of thermodynamic calculations for cyanidation of gold/silver a nd their minerals is reviewed. In literature there are a number of stu dies based on thermodynamic calculations to describe the chemistry of cyanide leaching of gold and/or silver from sulphide minerals. Disagre ements between computational and experimental results are usually sign ificant. In the present study, a critical evaluation of thermodynamic calculations, including the authors' own recalculations, for cyanide l eaching of gold/silver are carried out in order to interpret the exper imental results. The solution chemistry of the leaching process is dis cussed with reference to both computational and experimental results. The competition of cyanide complexation of gold, silver and other meta ls, 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 charact eristics 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)> Ag2O(s)> Au(s). In the case of incomp lete oxidation of sulphide, the precipitation order is Ag2S(s)> FeOOH( s)> Cu(OH)(2)(s)> Au(s). Based on these calculations, experimental res ults of cyanide leaching can be now well interpreted. (C) 1997 Elsevie r Science B.V.