The interfacial reactivity of arsenic species with green rust sulfate (GRSO4)

Arsenic (As) contamination in groundwater is a significant health and environmental concern worldwide because of its wide distribution and toxicity. The fate and mobility of As is greatly influenced by its interaction with redox-active mineral phases, among which green rust (GR), an Fe-II-Fe-III layered double hydroxide mineral, plays a crucial role. However, the controlling parameters of As uptake by GR are not yet fully understood. To fill this gap, we determined the interfacial reactions between GR sulfate (GR(SO4)) and aqueous inorganic As(III) and As(V) through batch adsorption experiments, under environmentally-relevant groundwater conditions. Our data showed that, under anoxic conditions, GR(SO4) is a stable and effective mineral adsorbent for the removal of As(III) and As(V). At an initial concentration of 10 mg L-1, As(III) removal was higher at alkaline pH conditions (similar to 95% removal at pH 9) while As(V) was more efficiently removed at near-neutral conditions (>99% at pH 7). The calculated maximum As adsorption capacities on GR(SO4) were 160 mg g(-1) (pH 8-9) for As(III) and 105 mg g(-1) (pH7) for As(V). The presence of other common groundwater ions such as Mg2+ and PO43- reduces the efficiency of As removal, especially at high ionic strengths. Long-term batch adsorption experiments (up to 90 days) revealed that As-interacted GR(SO4) remained stable, with no mineral transformation or release of adsorbed As species. Overall, our work shows that GR(SO4) is one of the most effective As adsorbents among iron (oxyhydr) oxide phases. (C) 2018 Elsevier B.V. All rights reserved.