Removal of arsenic from acidic liquors using chemical and autotrophic and mixed heterotrophic bacteria-produced biogenic schwertmannites.

Arsenic penetrates human society through a variety of geological and anthropogenic processes, posing significant health hazards. Acid mine drainage, which contains high concentrations of heavy metals and sulfate, is formed by the biological oxidation of pyrite and other metal-containing sulfidic minerals and is a significant environmental hazard. Adsorption is a simple and effective method for removing arsenic from water. In this study, co-precipitation and adsorption of arsenic with biogenic and chemically produced iron-containing settleable precipitates, i.e. schwertmannites were studied. Autotrophic Leptospirillum ferrooxidans and heterotrophic mixed culture of Alicyclobacillus tolerans and Acidiphilium cryptum oxidized iron at rates from 18 to 23 mg/(L.h) in the presence of 5 and 10 mg/L As, and both cultures tolerated up to 100 mg As/L although Fe oxidation rates decreased to 3-4 mg/(L.h). At Fe/As ratios of ≥20, As removal efficiencies of ≥95% were obtained by co-precipitation with Fe at pH 3.5-4.5. Because schwertmannite precipitates produced by the heterotrophic culture formed crystals, it was studied for adsorptive removals of As and As and compared with chemically synthesized schwertmannites. As (100 mg/L) adsorption onto biogenic and chemical schwertmannite were 25 and 44%, respectively, at pH 4. At 100 mg As/L, adsorption capacity and efficiency onto biogenic schwertmannite were 47 mg/g and 50%, respectively. At 300 mg As/L, adsorption capacity and efficiency onto chemical schwertmannite were 169 mg/g and 56%, respectively. In summary, biogenic schwertmannite has potential for As removal via co-precipitation with Fe at pH 3.5-4.5 and Fe/As ratios of ≥20 due to low production cost from acidic mine drainage. In contrast to the schwertmannite generation methods, which are usually performed with autotrophic acidophilic bacteria in the literature, this efficient and modular schwertmannite production process and its evaluation on arsenic adsorption is an important potential in acidic mine drainage treatment containing arsenic.