Effects of Common Competing Anions on the Adsorption of As(III) by d-MnO2 and Goethite

Abstract

Batch experiments had been conducted to study the effects of PO₄^3–, HPO₄^2–, H₂PO₄^–, SiO₃^2–, SO₄^2– and Cl^– on the adsorption of As(III) by the d-MnO₂ and the goethite. Moreover, the influential mechanisms of anions had been discussed. First, when the concentration of As(III) was low (10 mg/L), the effects of PO₄^3– and SiO₃^2– on the adsorption of As(III) by the d-MnO₂ were notable and relative small effects of HPO₄^2– and H₂PO₄^– were suggested. PO₄^3–, SiO₃^2– and H₂PO₄^– could affect the adsorption of As(III) by the goethite and the effect of HPO₄^2– could be negligible. Both SO₄^2– and Cl^– had negligible competing adsorption to As(III) by the d-MnO₂ and the goethite. The effects of anions on the As(III) adsorption by the d-MnO₂ were more severe than that by the goethite. Then, when the concentration of As(III) varied from 0-85 mg/L, compared to the blank, all the anions performed their effects to As(III) absorption by the d-MnO₂ and the goethite and the effects were more severe in high concentration than that in low concentration. The effects to the goethite were also obvious than that to the d-MnO₂ in high concentration. Lastly, for the d-MnO₂ and the goethite, SiO₃^2– magnified the effect of PO₄^3–. For the goethite, the combined effect of SiO₃^2– and PO₄^3– was more remarkable. The difference was decided by the structure characteristic of sorbent themselves, the d-MnO₂ had more adsorptive capacity while the goethite had strong adsorptive affinity to As(III).