Competitive adsorption of molybdate, chromate, sulfate, selenate, and selenite on γ-Al2O3

Competitive adsorption of molybdate, selenite, selenate, chromate, and sulfate onto γ-Al2O3 was investigated in the present study. Binary-solute systems of MoO42−/SeO32−, CrO42−/SO42−, and CrO42−/SeO42− as well as single anion systems were evaluated for the relative influence on competitive adsorption on oxide surface. As would be expected, the adsorption density of each anion in the binary-solute systems decreases, as compared to the respective density in a single anion system. Furthermore, MoO42− inhibits SeO32− adsorption in acidic condition and that SO42− or SeO42− depresses CrO42−. The order of the relative retainment of anions on oxide surface is molybdate>selenite>selenate∼sulfate>chromate, which corresponds to the magnitude of the overall proton coefficient of the corresponding anions.