Ion-exchange adsorption of zinc and copper ions on silica

Abstract

Ion-exchange adsorption of zinc and copper ions on silica were examined in 2 M NH 4Cl solution containing ZnO or ZnCl 2 and in 1 M NH 4Ac containing 0·05 M CuCl 2 respectively. The ion-exchange adsorption attains equilibrium in about 2 hr at 25°C. The adsorption of zinc ion increases with the pH of the solution up to pH 7·12, then decreases. Between pH 5·48 and 6·38 the mole-ratio of H + released/Zn 2+ adsorbed is constant at about 3·0. Zinc ion adsorption on heated silica decreases markedly with increase in the heating temperature. For copper ion adsorption, the mole-ratio, H + rel./Cu 2+ ads., is 4·0. The infra-red absorption spectra of silica samples, heated silica and silica treated with Zn, 2+ Cu 2+ and Na + solutions, were taken. A decrease in the absorption intensities for the bending vibration of -OH groups on the silica is discussed. A surface complex mechanism for metal ion adsorption of silica is proposed and it is concluded that the silica surface is acting as tridentate ligands for the zinc ion adsorption. A new method for determination of the surface acid and the surface area of silica is suggested.