The Stability of Selected Sulfide Minerals in Sulfuric Acid and Acidic Thiocyanate Solutions

The stability of pyrite, chalcopyrite, chalcocite, covellite, bornite and enargite at pH 2 in the absence and presence of thiocyanate has been determined by linear sweep voltammetry and chronoamperometry under conditions pertaining to the thiocyanate leaching of gold (pH 2 and 602-702 mV vs. SHE). Electrochemical measurements indicated that the decomposition rate of all sulfide minerals increased with an increase in oxidation potential with pyrite and chalcopyrite being the least reactive and chalcocite and bornite being the most reactive of the examined sulfides. The oxidation rate of covellite and enargite was higher than that of pyrite and chalcopyrite but much lower than that of chalcocite and bornite. It was found that the variation of pH from pH 1 to pH 3 has minimal effect on the oxidation rate of pyrite and chalcopyrite. In the presence of 0.05 M thiocyanate at pH 2 and in the potential range of interest for gold leaching (602-702 mV vs. SHE), the effect of thiocyanate was not significant on the oxidation of selected sulfides