| Description |
The industrial use of activated carbon for gold adsorption from alkaline cyanide leach solutions has been a major development in gold hydrometallurgy which was commercialized during the last part of the 20th century. In the gold industry, activated carbon is most often used to adsorb gold from dilute alkaline cyanide solutions. The gold is dissolved as the Au(CN)2 - complex and is recovered from the solution by Carbon-in- Pulp (CIP) or Carbon-in-Leach (CIL) processes. Activated carbon loaded with gold must be treated by an elution step to desorb the gold for subsequent recovery. In this way, a smaller volume of higher grade gold solution is produced, suitable for final gold recovery by electrowinning. The gold elution efficiency can be increased by the use of hydro-alcoholic solution and high temperature. The effect of particle size on gold elution has not been studied. In this regard, experiments have been performed with different size fractions of activated carbon to study the stripping characteristics of activated carbon for gold elution. It has been observed that it is difficult to elute gold from fine activated carbon which is quite contrary to fundamental expectations. From a technological point of view, it is necessary to develop improved methods of stripping for enhanced gold recovery from alkaline cyanide solutions. As part of this work, to overcome the problem of gold elution from fine carbon, alternative elution procedures have been developed and discussed. These include, use of hydro-alcoholic solutions, use of vacuum degassing prior to stripping, and application of external pressure. Research on this topic is carried out to enhance the understanding of the science involved in the elution of gold from fine activated carbon. Hence, current research focuses on finding a plausible explanation to explain the difficulty of eluting gold from fine activated carbon. The emphasis of this research is to address the stripping by experimentation and with the aid of computational chemistry tools. Since activated carbon consists of a cryptocrystalline graphitic structure which contributes significantly to gold adsorption, research on HOPG (highly oriented pyrolytic graphite) is in progress to determine the nature of graphite surfaces, their wetting characteristics, and their significance in gold adsorption / desorption from alkaline cyanide solutions. Computational chemistry analysis of adsorbed aurodicyanide anions at graphite surfaces are being done to understand the nature of gold adsorption/desorption from alkaline cyanide solutions by activated carbon. Current results from these surface chemistry studies are used to discuss the state of gold cyanide at activated carbon surfaces and the anomalous elution dependence on particle size. |
