Preg-robbing phenomena in the cyanidation of sulphide gold ores

The ability of pyrite and chalcopyrite to adsorb gold was examined. Experim ents were conducted in cyanide deficient solutions with and without activat ed carbon. Chalcopyrite was shown to be very strongly preg-robbing. It comp eted with activated carbon to remove the majority of gold from solution. Py rite was also strongly preg-robbing, and in cyanide deficient solutions ads orbed the majority of the gold in preference to activated carbon. The degre e of adsorption onto the ore or the activated carbon was a function of the kinetics of the adsorption process. The role of the cyanide complexes of copper, silver, zinc, nickel and iron was also examined. It was found that these complexes counteract preg-robbin g, and serve to stabilise the aurocyanide complex by precipitating prior to gold precipitation. When cyanide or cyanide-species were present in soluti on, the adsorption onto activated carbon was found in general to take prefe rence to the adsorption onto the minerals. The ability of a sulphide ore to adsorb Au(CN)(2)(-) from solution was found to be a function of how rapidl y the ore consumed cyanide and precipitated metal-cyanide complexes. A mechanism was proposed where the gold is reduced at the chalcopyrite surf ace through the formation of an adsorbed intermediate. The gold was reduced , along with the oxidation of chalcopyrite to form copper-cyanide complexes in solution. Reduction of gold on the pyrite was observed to occur with th e release of zinc as an impurity into solution, and a mechanism for this re action was proposed. (C) 2000 Elsevier Science B.V. All rights reserved.