Noncyanide leaching of an auriferous pyrite ore from Ecuador

Gold leaching of an auriferous pyrite ore from the Portovelo deposit in Ecu ador indicates that noncyanide leaching systems, such as thiocyanate and th iourea, are not as effective as the traditional cyanide system. For example , whereas approximately 95% of the gold can be leached from the ore with cy anide, only about 50% gold dissolution can be achieved with a thiocyanate l eaching system. Electrochemical measurements indicate that gold is not cath odically protected by pyrite in these systems. Based on the results of prel iminary diagnostic experiments, it appears that gold dissolution in thiocya nate and thiourea systems is limited by passivation due to the formation of either elemental sulfur or sulfur compounds on the gold surface.