Immobilization of arsenate in water and sediments using schwertmannite synthesized by persulfate oxidation

Schwertmannite (SCH), an iron-hydroxyl sulfate mineral, has been widely applied for arsenic adsorption and immobilization. In this study, persulfate was used in chemical oxidation procedure of SCH synthesis instead of hydrogen peroxide (H2O2). The properties of SCH synthesized by persulfate oxidation (SCH-S) and its immobilization efficiency with respect to arsenate [As(V)] in water and sediments were investigated. The results show that persulfate can be used as an effective oxidizer in SCH synthesis instead of H2O2. The absence of side re-actions and a high solution pH facilitated Fe3+ precipitation for SCH-S formation in persulfate oxidation compared to SCH synthesized by H2O2 oxidation (SCH-H). SCH-S particles also exhibited a non-spherical structure with a higher proportion of SO42- and a larger specific surface area (63.7 m(2)/g). The As(V) adsorption capacity of SCH-S was greater than that of SCH-S, and the As(V) adsorption process followed the pseudo-second-order and Langmuir models. Under acidic and neutral conditions, the As(V) adsorption capacities of SCH-S were 63.1 and 54.7 mg/g, respectively, mainly through As(V) exchange with SO42-. Under alkaline conditions, physical mechanisms resulting in low As(V) adsorption by SCH-S. More than 99.5% of the As(V) in sediments was immobilized by 3.0% SCH-S over 10 d. Bioavailable As(V) in sediments was converted to stable amorphous and crystalline hydrous oxide-bound fractions, which effectively decreased leachability and bio-accessibility. These results indicate that persulfate oxidation is a promising method of SCH synthesis, and SCH-S can be an effective material for the remediation of As contamination.