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

The sorption of AuCl4-,AuCl2- and Au(S2O3)(2)(3-) on delta-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 delta-MnO2 are 0.18-0.21 and 0.28 mu moL/m(2) for AuCl4- and Au(S2O3)(2)(3-), 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 delta-MnO2. The Au sorption decreases in the sequence of Au(S2O3)(2)(3-) >AuCl4- > AuCl2-. The intrinsic equilibrium constants (logK(int)) 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 delta-MnO2 and the inner-sphere Au-surface complexes are formed on the surface.