THE OPTIMIZATION OF AN IMPREGNATED CARBON SYSTEM TO SELECTIVELY RECOVER CYANIDE FROM DILUTE-SOLUTIONS

Cyanide is used extensively in the mining industry to dissolve gold an d silver from slimy pulps. In this study a coconut shell carbon was im pregnated with different metals, and then used for the recovery of fre e cyanide. The metal impregnated carbon outperformed the virgin carbon both kinetically and in the final cyanide loading. It is proposed tha t the free cyanide adsorbed onto the metal impregnated carbon via two mechanisms, viz. [a] free cyanide is oxidised catalytically, and [b] t he metal is leached from the impregnated carbon, followed by the forma tion of a metal cyanide complex, and the subsequent adsorption of the complex on the carbon. It was found that the silver (as silver nitrate ) impregnated carbon yielded higher free cyanide loadings when compare d to silver (as silver cyanide) and copper (as copper(ll)chloride) imp regnated carbons. Furthermore, the presence of silver cyanide in solut ion did not influence the adsorption of free cyanide on silver impregn ated carbon. Moreover, the atmosphere during impregnation did not affe ct the performance of metal impregnated carbon, with respect to free c yanide adsorption. An optimum impregnation procedure is proposed which allowed maximum free cyanide recovery. (C) 1997 Elsevier Science Ltd.