The extraction of metal cyanides by crosslinked polydiallylamine

Abstract

The extraction of Au(CN) 2 −, Ni(CN) 4 −, Cu(CN) 2 − and Ag(CN) 2 − by polydiallylamine (PDAA) was examined. Crosslinking was found to have a major effect on monovalent/divalent anion selectivity. PDAA with a low degree of crosslinking displays a clear preference for Ni(CN) 4 − over Au(CN) 2 − under most conditions, with the gold species only favoured at high pH. Increasing the degree of crosslinking significantly lowers the distribution of nickel by limiting the flexibility of the resin chains, thereby reducing its ability to orient functional groups around the divalent anion. Selective extraction of gold may therefore be achieved at a lower pH. X-ray photoelectron spectroscopy (XPS) shows that Ni(CN) 4 − and Cu(CN) 2 − are adsorbed intact and that Ag(CN) 2 − adsorbs with a stoichiometry of Ag(CN) 1.5 x− . This contrasts to earlier results for Au(CN) 2 − which indicate decomposition to an AuCN species.