Modeling Competitive Adsorption of Molybdate,Sulfate, and Selenate on #gamma#-Al_2O_3 by the Triple-Layer Model

摘要

Competitive adsorption of molybdate, sulfate, and selenate onto y-AI2OJ was investigated in the present study. Binary solute sys- tems of MoO_4~(2-) + SO_4~(2-),MoO_4~(2-) + SeO_4~(2-),and SO_4~(2-) + SeO_4~(2-) and a ternary solute system of MoO_4~(2-) + SO_4~(2-) + SeO_4~(2-) were evaluated to determine their relative effects on competitive adsorption on the y-A120J surface. Anionic competitive adsorption efficiency was pH dependent. The higher the pH, the lower the efficiency of MoO~- in preventing S~- and SeO~- adsorption; similar results were found in SeO~- depressing SO~- 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 y-AI2OJ surface is composed of many groups of binding sites. Be- cause of the heterogeneity of adsorption sites, the triple-layer model (TLM) predicted the competitive effects qualitatively but not quan- titatively. TLM gave reasonable descriptions of molybdate adsorp- tion in the presence of sulfate and selenate, indicating that the model may be useful in predicting molybdate adsorption on #gamma#-Al_O_3.