Improvements in gold ore cyanidation by

It is known that the presence of sulphidic minerals in the cyanidation of gold ores may cause significant consumption of oxygen supplied in the injected air. This may result in dissolved oxygen starvation for the oxidative leaching of the gold, and ultimately it will reduce the maximum attainable recovery of gold from the ore. In addition, the presence of sulphides leads to extra consumption of the cyanide-leaching agent, NaCN, due to the formation of thiocyanate, therefore increasing costs. These types of gold sulphidic ores may be pre-treated prior to cyanidation by means of an oxidation step, converting the sulphides to oxides or sulphates, which can enhance gold recovery. The leaching circuit comprises an initial three-tanks-in-series alkaline pre-oxidation step using only compressed air and lime, followed by a train of fourteen aerated and mechanically-agitated tanks for cyanidation. The ore feeding the leaching circuit averages 1.70 g Au/t, and the main oxygen-consuming component is the sulfide mineral pyrrhotite (FeS). In previous internal studies, it was found that up to 30% of gold reporting in the tailings was still leachable and not being recovered due to process kinetics.