Arsenic(V) removal behavior of schwertmannite synthesized by KMnO₄ rapid oxidation with high adsorption capacity and...

Adsorption is a simple and efficient way for arsenic contamination purification in water, with a pressing challenge to find a cheap and efficient adsorbent. As a poorly crystalline Fe(III)-oxyhydroxy sulfate mineral, schwertmannite can be As(V) adsorbent because of its tunnel structure and low cost. However, the schwertmannite synthesized commonly by H₂O₂ rapid oxidation suffers from the low Fe utilization and limited As(V) adsorption capacity. In this research, the schwertmannite is synthesized by KMnO₄. The results show that the Fe utilization can be improved from 40% to 56%, with the As(V) adsorption capacities double times better than those synthesized by H₂O₂ at pH 7 and 2. The As(V) adsorption mechanisms at different pHs and the reason for the improvement of As(V) adsorption capacity are thoroughly investigated. The FTIR and EDS images confirm that As(V) adsorption exchange with SO₄^2- is the dominant mechanism at pH 7 and 2. At pH 11, the As(V) is mainly removed by surface complexation because the surface SO₄^2- is exchanged by OH^-. The intraparticle diffusion model fitting and XPS results further reveal that the tunnel structure built by Fe-SO₄ in the KMnO₄ oxidized schwertmannite is more stable, possibly resulting in the better As(V) adsorption performance.