Ion-Exchange Equilibria for [Au(CN)2]-/Cl- and [Au(CN)2]-/SCN- on Purolite A500 in Mixed Solvents at 303 K

Abstract

Ion-exchange equilibria are presented for [Au(CN)2]-/Cl- and [Au(CN)2]-/SCN- in dimethyl sulfoxide (DMSO) + water and N-methyl-2-pyrrolidone (NMP) + water mixed solvents at 303 K, using Purolite A500 as the ion-exchanger. The effects of mixed-solvent composition and the type of counterion on the selectivity of the ion-exchange resin for [Au(CN)2]- is discussed in terms of the degree of solvation of the various anions in the mixed solvents. The effect of the mixed solvent on the exchange capacity of the resin is also considered. The experimental data are correlated using the law of mass action, modified with activity coefficients, to determine the equilibrium constant for each binary system. It is shown that the selectivity of the resin for [Au(CN)2]- decreases significantly with an increase in the composition of organic solvent in the mixed solvent. The particular combination of Cl- in NMP−water mixtures is remarkably effective for reducing the loading of [Au(CN)2]- on Purolite A500. The fitted values of ...