Application of a high-surface-area schwertmannite in the removal of arsenate and arsenite

Schwertmannite is a poorly crystalline Fe(III) hydroxide, which always shows high sorption capacities to pollutants. In this study, schwertmannite synthesized from the Fe³⁺ hydrolyzation method showed a hedgehog-like shape, with a specific surface area of 325.5 m² g^-1, which was much higher than that of the sphere-like schwertmannite synthesized from the Fe²⁺ oxidation method, with a specific surface area of 48.2 m² g^-1. The former was then used to evaluate its sorption performance to As(V) and As(III). Sorption of As(V) and As(III) could reach equilibrium in 200 min, and the maximum sorption capacities of As(V) and As(III) were 182.86 and 45.50 mg g^-1 at pH 3.0, respectively, and 143.25 and 217.85 mg g^-1 at pH 7.0, respectively. Sorption capacity was dependent on pH and more As(V) adsorbed on schwertmannite at lower pH, while As(III) sorption increased with the increase of pH. Our results also indicated that the presence of sulfate reduced the sorption of As(V) from 85.4 to 67.6 mg g^-1 as sulfate concentration increased from 0.2 to 6 g L^-1, while such an effect was not apparent in As(III) sorption. Nitrate and chloride did not show significant interference on the sorption of both As(V) and As(III). Schwertmannite showed better repeated uses in the removal of As(V) and As(III) after seven repeated using cycles with removal percentages of 95.3 % at pH 3.0 and 63.9 % at pH 7.0 to As(V), and 31.0 % at pH 3.0 and 81.6 % at pH 7.0 to As(III).