Effects of hydrogen-peroxide supply rate on schwertmannite microstructure and chromium(VI) adsorption performance.

Schwertmannite has attracted increasing interest for its excellent sorption for pollutants such as arsenite [As(III)] and arsenate [As(V)]. Limited studies were conducted with hexavalent chromium [Cr(VI)], especially for schwertmannite synthesized through Fe2+ oxidation. The effect of the hydrogen-peroxide (H2O2) supply rate on the structural characteristics and Cr(VI) adsorption capacity of schwertmannite is unclear. The morphology, crystallinity, specific surface area (SSA), pore volume and Cr(VI) adsorption of schwertmannite through Fe2+ oxidation at different H2O2 supply rates were analyzed. A slow H2O2 supply could improve the schwertmannite SSA and pore volume. Schwertmannite changed from nanoparticle aggregates (169.31 m2/g SSA, 0.20 cm3/g pore volume) to ball-with-whisker-shaped particles (228.75 m2/g SSA, 0.30 cm3/g pore volume) with a lower H2O2 supply rate. The Cr(VI) adsorption capacity increased by 6.25%-11.70% at different given Cr(VI) concentrations. The maximum Cr(VI) adsorption capacity of schwertmannite was 1.89 mmol/g at pH 6.0. Cr(VI) adsorption onto schwertmannite may be attributed mainly to ion exchange with the structural SO42-. More than 91% of the original Cr(VI) adsorption capacity was maintained after four recycles. This study provides novel insights into the effects of H2O2 supply rate on the microstructure of schwertmannite and its adsorption capacity for Cr(VI) in aqueous medium.