Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, ETH Zurich, Universitätstrasse 16, CHN, CH-8092 Zurich, Switzerland.
Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, ETH Zurich, Universitätstrasse 16, CHN, CH-8092 Zurich, Switzerland.
J Hazard Mater. 2021 Jan 15;402:123425. doi: 10.1016/j.jhazmat.2020.123425. Epub 2020 Jul 21.
Arsenic-contaminated waters affect millions of people on a daily basis. Because the toxicity of As is dependent on the redox state, understanding As biogeochemistry, particularly in reducing environments, is critical to addressing the environmental risk that As poses. Sorption of As to Fe(III)-(oxyhydr)oxides is an important mechanism for As removal from solution under anoxic conditions. However, dissolved ferrous Fe (Fe(II)) also occurs under anoxic conditions, and the impact that Fe(II)-catalyzed recrystallization of crystalline Fe minerals has on As sorption mechanisms is not clear. Our research investigates the potential for non-stoichiometric magnetite, a commonly occurring mixed-valence Fe oxide in anoxic aquifers, to adsorb and/or incorporate inorganic As species during Fe(II)-catalyzed recrystallization at neutral pH, with particular focus on the impact of mineral stoichiometry (Fe(II):Fe(III) = 0.23 and 0.0) and varying Fe(II) concentrations. By following aqueous As concentrations and speciation over time coupled with As K-edge X-ray absorption spectroscopy, our results demonstrate that the presence of Fe(II) substantially enhanced As removal from solution. In addition, we highlight a Fe(II)-induced mechanism through which highly mobile, toxic As(III) species are oxidized on the mineral surface to form As(V). Furthermore, the presence of Fe(II) promotes the structural incorporation of As(V) into the non-stoichiometric magnetite and maghemite structures. These results highlight the potential of Fe(II)-reacted non-stoichiometric magnetite or maghemite as pathways for long-term As sequestration in anoxic environments.
砷污染水每天都会影响数百万人。由于砷的毒性取决于其氧化还原状态，因此了解砷的生物地球化学特性，尤其是在还原环境中，对于解决砷带来的环境风险至关重要。在缺氧条件下，砷与三价铁（氢氧）氧化物的吸附是从溶液中去除砷的重要机制。然而，溶解的二价铁（Fe(II)）也会在缺氧条件下出现，而 Fe(II)催化的结晶铁矿物再结晶对砷吸附机制的影响尚不清楚。我们的研究调查了非化学计量磁铁矿（在缺氧含水层中普遍存在的混合价态氧化铁）在中性 pH 值下 Fe(II)催化再结晶过程中吸附和/或掺入无机砷物种的潜力，特别关注矿物化学计量（Fe(II):Fe(III) = 0.23 和 0.0）和变化的 Fe(II)浓度的影响。通过随时间推移监测水溶液中砷浓度和形态，以及砷 K 边 X 射线吸收光谱，我们的结果表明，Fe(II)的存在大大增强了溶液中砷的去除。此外，我们强调了一种 Fe(II)诱导的机制，通过该机制，高度移动的有毒 As(III)物种在矿物表面被氧化形成 As(V)。此外，Fe(II)的存在促进了 As(V)在非化学计量磁铁矿和磁赤铁矿结构中的结构掺入。这些结果突出了 Fe(II)反应的非化学计量磁铁矿或磁赤铁矿作为缺氧环境中砷长期固定的途径的潜力。
