The effect of Cl⁻, PO₄ ³⁻, and SiO₃ ²⁻ on the adsorption of As(V) and As(III) on bauxite in water

Abstract

The adsorption performance of bauxite for the removal of As(V) and As(III) from contaminated water was investigated. The effect of initial pH, contact time, and the presence of silicate, phosphate and chloride, at concentrations typically found in the ground drinking water in India/Bangladesh, were investigated. As(V) is adsorbed at a rapid initial rate (>96% adsorption within 1 minute) followed by a slow process, reaching a steady state within 6 hours. In comparison the adsorption of As(III) is slow, only 40% is adsorbed within the first minute that gradually rises to 85% in 6 hours. The presence of chloride has insignificant effect on both As(III) and As(V) adsorption. Silicate and phosphate both significantly affect adsorption of both the arsenic ions. Phosphate affects adsorption more strongly than silicate and their effect on As(III) is higher than As(V). When silicate and phosphate are present together, the adsorption of As(V) is almost the same as for the individual ions. However, the As(III) adsorption is significantly affected. The adsorption is 61% as compared to 73% for silicate and 71% for phosphate when individually present. While chloride alone has insignificant effect on the adsorption of the arsenic ions, it has some influence when present together with silicate or phosphate. Chloride + Phosphate combination increases As(V) adsorption by 3% and As(III) by 8%. Chloride + Silicate combination increases As(V) adsorption by 9% but decreases As(III) by almost the same percentage. As compared to the influence of silicate + phosphate, the combination of the three ions together, lowers the As(V) adsorption by 4% and increases As(III) by 4%.

Keywords: Arsenic removal; Bauxite; Coexisting ions; Adsorption