Mechanism of adsorption of gold and silver species on activated carbons

Abstract

The adsorption characteristics of gold and silver cyanide anionic species on a suite of active carbons derived from coal, coconut shell and polyacrylonitrile have been investigated. The gold and silver cyanide adsorption capacities for both coconut shell and coal derived carbons correlate with total pore volume. Nitric acid treatment of the carbon was detrimental to gold adsorption in spite of the incorporation of oxygen into the carbon through oxidation. The influence of nitrogen functional groups in the carbon structure on gold and silver adsorption was investigated using carbons with very high nitrogen contents derived from polyacrylonitrile. The addition of ethanol and butanol to the solution had an adverse effect on gold adsorption. Adsorption of silver cyanide ionic species on the active carbon was suppressed in the presence of excess free cyanide ions in solution whereas gold cyanide adsorption was not greatly affected. The results are discussed in terms of the mechanism of adsorption, equilibria in solution and the bonding in metal cyanide complexes adsorbed on the carbon surface.