Adsorption of As by γ-Fe₂O₃ and the Effect of Temperature

Abstract

In recent years, contamination of groundwater by arsenic has become an environmental problem around the world, since arsenic is carcinogenic. It is present in groundwater predominantly as inorganic arsenite (As(III)) and arsenate (As(V)). To remove arsenic from water, adsorption is an effective technology, because adsorptive methods are generally simple to operate at low cost. We performed adsorption experiments with various metal oxides in order to remove arsenic from aqueous solution. The adsorbent γ-Fe₂O₃, which is inexpensive and safe for human health, was prepared by varying the molar ratio of Fe³⁺ and Fe²⁺, and the effect of pH on removal of arsenic was examined with the synthesized γ-Fe₂O₃. The adsorption of As(III) and As(V) was found to be strongly dependent on pH. As(III) present as a neutral species at below pH 7 is thought to be adsorbed by physical bonding through, for example, van der Waals forces, or by chemical reaction, while the adsorption of As(V) present as anionic species in aqueous solution over pH 1 is affected by electrostatic repulsion at higher pH than its IEP with a change in zeta potential after adsorption. We investigated the adsorption of arsenic at different temperatures and found that the adsorption of As(V) is more strongly dependent on the temperature than that of As(III).