Interaction of Carbonate and Organic Anions with Sulfate and Selenate Adsorption on an Aluminum Oxide

Abstract

The presence of anionic cosolutes often influences anion adsorption on soil mineral surfaces. The possible effect of common solutes, such as CO 3 species, on the adsorption of other anions on metal (hydr)oxides is poorly understood. Accordingly, we determined the effect of CO 3 , formate, acetate, oxalate, and citrate on the adsorption of SO 4 and SeO 4 on Al oxide. Carbonate markedly promotes the adsorption of SO 4 and SeO 4 between pH 6 and 8. The maximum effect occurs at relatively low CO 3 concentrations (0.3 m M ) and the promotive effect decreases with further increase in CO 3 adsorption. Formate and acetate also promote adsorption of SO 4 and SeO 4 , while oxalate and citrate have a competitive effect, especially at lower pH values. Based on existing Fourier transformed infrared (FTIR) spectroscopic data and new electrophoretic mobility data, CO 3 may promote the adsorption of other oxyanions by forming extra reactive protonated sites that exist with the adsorbed CO 3 Acetate and formate presumably interact through the same mechanism. This promotive mechanism was ineffective in the case of adsorption of a high affinity anion such as PO 4 Finally, the adsorptive properties of Al oxide, as we know it from simple model systems, can significantly be altered in soils, where CO 3 and organic anions are ubiquitous solutes. For example, the adsorption maximum of SO 4 > SeO 4 became in the presence of CO 3