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-robbi ng behavior of Goldstrike ore and the leaching behavior of carbonaceous mat ter within the ore. Carbonaceous matter obtained by acid demineralization o f Goldstrike ore was leached using either an ammoniacal thiosulfate system or a sodium cyanide system. Leaching of the carbonaceous matter was conduct ed in batch experiments, as well as in columns at various flow rates to com pare the mass of gold leached from the carbonaceous matter to its initial g old content. Ammoniacal thiosulfate leaching of carbonaceous matter from au toclaved Goldstrike ore resulted in 90-100% solubilization of the gold init ially present regardless of the preg-robbing behavior of the parent ore. Fo r carbonaceous matters from non-autoclaved ores, ammoniacal thiosulfate lea ching only solubilized about 40% of the gold initially present in the carbo naceous matter, indicating that approximately 60% of the gold was encapsula ted in sulfides. The percentage of gold leached by ammoniacal thiosulfate w as found to depend on the initial gold content of the carbonaceous matter s ince an equivalent, small amount of gold was taken up by all carbonaceous m atters examined. Gold leaching was primarily limited by the volume of lixiv iant contacting the carbonaceous matter; however, a slight kinetic limitati on was observed in ammoniacal thiosulfate leaching at higher flow rates. Th e percentage of gold leached by sodium cyanide from carbonaceous matter dem ineralized from autoclaved Goldstrike ore was inversely related to the preg -robbing behavior of the parent ore, suggesting that preg-robbing is contro lled by the retention of gold by carbonaceous matter during leaching. Simil arities between the naturally occurring carbon and commercial activated car bon suggest that the mechanism of gold retention by the naturally occurring carbon during leaching is the same as gold cyanide complex adsorption by c ommercial 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 o f the ore. (C) 2001 Elsevier Science B.V. All rights reserved.