Ammoniacal thiosulfate and sodium cyanide leaching of preg-robbing Goldstrike ore carbonaceous matter

The aim of this work was to establish a relationship between the preg-robbing behavior of Goldstrike ore and the leaching behavior of carbonaceous matter within the ore. Carbonaceous matter obtained by acid demineralization of Goldstrike ore was leached using either an ammoniacal thiosulfate system or a sodium cyanide system. Leaching of the carbonaceous matter was conducted in batch experiments, as well as in columns at various flow rates to compare the mass of gold leached from the carbonaceous matter to its initial gold content. Ammoniacal thiosulfate leaching of carbonaceous matter from autoclaved Goldstrike ore resulted in 90–100% solubilization of the gold initially present regardless of the preg-robbing behavior of the parent ore. For carbonaceous matters from non-autoclaved ores, ammoniacal thiosulfate leaching only solubilized about 40% of the gold initially present in the carbonaceous matter, indicating that approximately 60% of the gold was encapsulated in sulfides. The percentage of gold leached by ammoniacal thiosulfate was found to depend on the initial gold content of the carbonaceous matter since an equivalent, small amount of gold was taken up by all carbonaceous matters examined. Gold leaching was primarily limited by the volume of lixiviant contacting the carbonaceous matter; however, a slight kinetic limitation was observed in ammoniacal thiosulfate leaching at higher flow rates. The percentage of gold leached by sodium cyanide from carbonaceous matter demineralized from autoclaved Goldstrike ore was inversely related to the preg-robbing behavior of the parent ore, suggesting that preg-robbing is controlled by the retention of gold by carbonaceous matter during leaching. Similarities between the naturally occurring carbon and commercial activated carbon suggest that the mechanism of gold retention by the naturally occurring carbon during leaching is the same as gold cyanide complex adsorption by commercial activated carbon. Similar to leaching with ammoniacal thiosulfate, kinetics of sodium cyanide leaching also depended primarily on the volume of lixiviant contacting the carbonaceous matter; however, the kinetics of sodium cyanide leaching were also influenced by the preg-robbing behavior of the ore.