Interaction of carbonate and organic anions with sulfate and selenate adsorption on an aluminum oxide
2000
Wijnja, H. | Schulthess, C.P.
The presence of anionic cosolutes often influences anion adsorption on soil mineral surfaces. The possible effect of common solutes, such as CO3 species, on the adsorption of other anions on metal (hydr)oxides is poorly understood. Accordingly, we determined the effect of CO3, formate, acetate, oxalate, and citrate on the adsorption of SO4 and SeO4 on Al oxide. Carbonate markedly promotes the adsorption of SO4 and SeO4 between pH 6 and 8. The maximum effect occurs at relatively low CO3 concentrations (0.3 mM) and the promotive effect decreases with further increase in CO3 adsorption. Formate and acetate also promote adsorption of SO4 and SeO4, 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, CO3 may promote the adsorption of other oxyanions by forming extra reactive protonated sites that exist with the adsorbed CO3. 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 PO4. Finally, the adsorptive properties of Al oxide, as we know it from simple model systems, can significantly be altered in soils, where CO3 and organic anions are ubiquitous solutes. For example, the adsorption maximum of SO4 > SeO4 became SO4 = SeO4 in the presence of CO3.
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