Gold and silver extraction by ammoniacal thiosulfate leaching from a rhyolite ore

Abstract An investigation has been carried out to identify the parameters of importance in the dissolution of gold and silver values from an ore using ammoniacal thiosulfate solutions containing copper. The chemistry of the dissolution process has been analyzed through the construction of E H −pH diagrams. The experimental results show that it is possible to solubilize about 70% of silver and 90% of gold values in one hour. The leaching process is quite sensitive to thiosulfate and ammonia concentrations. Maintenance of proper E h and pH conditions is necessary to prevent precipitation of copper as Cu 2 S with concomitant loss of silver values from solution.