KAGAKU KOGAKU RONBUNSHU, Vol.40, No.2, 90-97, 2014
Effect of Ionic Strength, Temperature on Equilibrium and Kinetics of Arsenic Adsorption using Magnetite
Effect of ionic strength and temperature on the equilibrium and kinetics of arsenic adsorption on magnetite prepared by precipitation were investigated. The adsorption of As(III) was independent of ionic strength. After the adsorption of As(III), the zeta potential decreased and the point of zero charge (PZC) of the magnetite shifted to the acidic side. The adsorption of As(III) was considered to be the result of inner-sphere complex formation because of the endothermic reaction and the positive entropy change in the As(III) adsorption reaction. The adsorption of As(V) increased with increasing ionic strength at higher pH than the PZC, and a shift of the PZC was observed after the adsorption of As(V). The exothermic reaction and the positive entropy change of the reaction indicated that the As(V) adsorption occurred by the mechanism of outer-and inner-sphere complex formation. The presence of phosphate and silicate greatly decreased the adsorption of As(III) and As(V). The rate-controlling step in the adsorption of As(III) and As(V) was found to be the intraparticle diffusion process, since the kinetics of As(III) and As(V) adsorptions can be explained by the Dunwald-Wagner equation.