MECHANISM OF ADSORPTION OF GOLD AND SILVER SPECIES ON ACTIVATED CARBONS

The adsorption characteristics of gold and silver cyanide anionic spec ies 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 ox ygen into the carbon through oxidation. The influence of nitrogen Func tional groups in the carbon structure on gold and silver adsorption wa s investigated using carbons with very high nitrogen contents derived from polyacrylonitrile. The addition of ethanol and butanol to the sol ution had an adverse effect on gold adsorption. Adsorption of silver c yanide ionic species on the active carbon was suppressed in the presen ce of excess free cyanide ions in solution whereas gold cyanide adsorp tion was not greatly affected. The results are discussed in terms of t he mechanism of adsorption, equilibria in solution and the bonding in metal cyanide complexes adsorbed on the carbon surface. (C) 1998 Elsev ier Science Ltd. All rights reserved.