Modeling Competitive Adsorption of Molybdate, Sulfate, and Selenate on gamma-Al(2)O(3) by the Triple-Layer Model

Competitive adsorption of molybdate, sulfate, and selenate onto gamma-Al(2)O(3) was investigated in the present study. Binary solute systems of MoO(2-)(4)+SO(2-)(4), MoO(2-)(4)+SeO(2-)(4), and SO(2-)(4)+SeO(2-)(4) and a ternary solute system of MoO(2-)(4)+SO(2-)(4)+SeO(2-)(4) were evaluated to determine their relative effects on competitive adsorption on the gamma-Al(2)O(3) surface. Anionic competitive adsorption efficiency was pH dependent. The higher the pH, the lower the efficiency of MoO(2-)(4) in preventing SO(2-)(4) and SeO(2-)(4) adsorption; similar results were found in SeO(2-)(4) depressing SO(2-)(4) adsorption. This research found that more sites are occupied in mixed anionic adsorbate systems than when either ion is present alone. The results suggest that the gamma-Al(2)O(3) surface is composed of many groups of binding sites. Because of the heterogeneity of adsorption sites, the triple-layer model (TLM) predicted the competitive effects qualitatively but not quantitatively. TLM gave reasonable descriptions of molybdate adsorption in the presence of sulfate and selenate, indicating that the model may be useful in predicting molybdate adsorption on gamma-Al(2)O(3). Copyright 2001 Academic Press.