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Ion-exchange equilibria are presented for [Au(CN) 2 ] -/Cl -, [Au(CN) 2 ] -/SCN -, and SCN -/Clin acetone + water mixtures at 303 K using Purolite A500 as the ion exchanger. The effect of the composition of acetone in the external solution on the ion-exchange isotherm for each binary system is 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 Purolite A500 is highly dependent on the composition of the external solution. The selectivity of the resin for [Au(CN) 2 ] -, in particular, decreases markedly with an increase in the composition of acetone. The fitted values of the equilibrium constants are consistent with the trends observed in the corresponding ionexchange isotherms.

Ion-exchange equilibria are presented for [Au(CN) 2 ] -/Cland [Au(CN) 2 ] -/SCNin 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 Clin NMP-water mixtures is remarkably effective for reducing the loading of [Au(CN) 2 ]on Purolite A500. The fitted values of the equilibrium constants are consistent with the trends observed in the corresponding ion-exchange isotherms.

Ion-exchange equilibria are presented for Au(CN) 2 -/Cl -, Au(CN) 2 -/SCN -, and SCN -/Clin aqueous solution at 303 K using Purolite A500 as the ion exchanger. The effect of the total solution concentration on the ion-exchange isotherm for each binary system is 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 isotherm for each binary system is independent of the total solution concentration, within the range of concentration considered. The selectivity of Purolite A500 for a given ion increases in the order Cl -< SCN -< Au(CN) 2 -. The fitted values of the equilibrium constants are in qualitative agreement with the selectivity of the resin for the various ionic species.