The mechanism of enhanced gold extraction from ores in the presence of activated carbon

Carbon-in-leach (CLL) is a common process alternative to carbon-in-pulp (CIP) when an ore is preg-robbing. The activated carbon will compete with the preg-robbing on constituents in the leach tanks, with gold cyanide more selectively adsorbing onto the carbon due to its stronger adsorptive capacity. However, other mechanisms may also play a role in enhancing the extraction of gold from an ore in the presence of activated carbon. There may be an equilibrium effect in solution, where the gold concentration is decreased due to adsorption onto activated carbon, resulting in a greater driving force for further dissolution of gold, according to Le Chatelier's Principle. In this paper the use of activated carbon to improve gold dissolution from a number of ores of different mineralogy was investigated. Plant work, batch experimentation and diagnostic leaching were used to research this effect. An appreciable improvement in gold extraction was found when activated carbon was used. Both of the suggested mechanisms were found to play a role in enhancing gold extraction, with the controlling mechanism most strongly dependent on the ore's mineralogy. The Dreg-robbing characteristics of the ore and the cyanide concentration used for gold leaching were also important factors in the enhancement of gold extraction. (C) 2000 Elsevier Science B.V. All rights reserved.