Enhanced Leaching of Arsenopyrite Concentrates as a Pretreatment for Gold Refractory Ores

Dr. Oscar G. Olvera, Dr. Yeonuk Choi, Dr. Peter Kondos

Refractory sulfidic ores consist of materials in which gold occurs finely disseminated within metallic sulfides or forming solid solutions, with pyrite and arsenopyrite being the two sulfides most commonly associated with gold. Given that gold in this type of ores is not readily accessible to leaching solutions, typical cyanide operations yield poor performance and oxidative pretreatments are usually required to increase gold recovery in these ores.

Due to the characteristics of refractory sulfidic ores, in order to increase gold recovery it is necessary to break or modify the sulfide matrix encapsulating the gold. Pretreatment alternatives include ultra-fine grinding, roasting, pre-aeration, acidic and alkaline high pressure oxidation, and bacterial oxidation. The presence of arsenic, however, introduces a serious disadvantage to the use of roasting and bacterial leaching, while high pressure oxidation involves high capital costs.

In this work we have evaluated the addition of a carbon resin as an elemental sulfur collector upon the oxidation of an arsenopyrite-pyrite sulfidic concentrate under atmospheric tank leaching (ATL) conditions. The ATL residues were further tested for gold recovery under standard cyanide carbonin-leach (CIL) and calcium thiosulfate (CaTS) leaching conditions.