Adsorption kinetic properties of As(III) on synthetic nano Fe-Mn binary oxides

Abstract

The adsorptive removal of arsenic by synthetically-prepared nano Fe-Mn binary oxides (FM) was investigated. A novel method using potassium permanganate and ferric chloride as raw materials was used to synthesise FM. The molar ratio of Fe and Mn in the synthetic Fe-Mn binary oxides was 4: 3. The FM-1 and FM-2 (prepared at different activation temperatures) having high specific surface areas (358.87 and 128.58 m2/g, respectively) were amorphous and of nano particle types. The amount of arsenic adsorbed on FM-1 was higher than that adsorbed on FM-2 particles. After adsorption by FM-1, residual arsenic concentration decreased to less than 10 µg/L. The adsorption kinetics data were analyzed using different kinetic models including pseudo first-order model, pseudo second-order model, Elovich model and intraparticle diffusion model. Pseudo second-order kinetic model was the most appropriate model to describe the adsorption kinetics. The adsorption percentage of As(III) increased in the pH range of 2–3 while it decreased with the increase of pH (3<pH<10). The effects of coexisting anions on As(III) removal using FM-1 and FM-2 were also studied and the order of the effects is as follows: NO3 -, Cl-, F-<SO4 2-, HCO3 -<H2PO4 -, indicating that H2PO4 - is the major competitor with As(III) for adsorptive sites on the surface of the adsorbents. The higher adsorption capacity of FM-1 makes it potentially attractive adsorbent for the removal of As(III) from groundwater.