Adsorption of Au(III) and Au(I) complexes on δ-MnO2

Abstract

The sorption of AuCl4−,AuCl2− and Au(S2O3)3- on δ-MnO2 was investigated at pH2–11.6, 0.01 mol/L and 0.1 mol/L NaNO3 solutions. At pH 4 in two electrolyte strength solutions, Au sorption densities on δ-MnO2 are 0.18–0.21 and 0.28μmoL/m2 for AuCl4− and Au(S2O3)23-, respectively, and the Au surface coverage is approximate to or lower than 1%. This adsorption of the two Au complexes decreases as the solution pH increases, which conforms to the sorption regularity of the anion on δ-MnO2. The Au sorption decreases in the sequence of Au(S2O3)23- >AuCl4− >AuC12−. The intrinsic equilibrium constants (logKint) of the three Au complexes are 1.17–2.7, much higher than those of Cu and Cd. The hydrolysis products of AuCl4- are preferentially adsorbed by δ-MnO2 and the inner-sphere Au-surface complexes are formed on the surface.