School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332-0340, USA.
J Hazard Mater. 2011 May 30;189(3):647-52. doi: 10.1016/j.jhazmat.2011.02.029. Epub 2011 Feb 17.
Recent evidence suggests that the oxidation of arsenite by zero-valent sulfur (S(0)) may produce stable aqueous arsenate species under highly reducing conditions. The speciation of arsenic (As) in reducing soils, sediments and aquifers may therefore be far more complex than previously thought. We illustrate this by presenting updated E(h)-pH diagrams of As speciation in sulfidic waters that include the most recently reported formation constants for sulfide complexes of As(III) and As(V). The results show that the stability fields of As(III) and As(V) (oxy)thioanions cover a large pH range, from pH 5 to 10. In particular, As(V)-S(-II) complexes significantly enhance the predicted solubility of As under reducing conditions. Equilibrium calculations further show that, under conditions representative of sulfidic pore waters and in the presence of solid-phase elemental sulfur, the S(0)((aq))/HS(-) couple yields a redox potential (E(h))∼ 0.1 V higher than the SO(4)(2-)/HS(-) couple. S(0) may thus help stabilize aqueous As(V) not only by providing an electron acceptor for As(III) but also by contributing to a more oxidizing redox state.
最近的证据表明，亚砷酸盐在零价硫（S(0)）的作用下氧化可能会在高度还原的条件下产生稳定的水合砷酸盐。因此，还原土壤、沉积物和含水层中的砷（As）的形态可能比以前想象的要复杂得多。我们通过呈现最新报告的 As(III)和 As(V)的硫化物络合物形成常数的硫化水的更新 E(h)-pH 图来说明这一点。结果表明，As(III)和 As(V)（氧）硫代阴离子的稳定性场覆盖了很大的 pH 范围，从 pH 5 到 10。特别是，As(V)-S(-II)络合物显著提高了在还原条件下预测的 As 溶解度。平衡计算进一步表明，在代表硫化孔隙水的条件下，并存在固相元素硫的情况下，S(0)((aq))/HS(-)偶联产生的氧化还原电位（E(h)）比 SO(4)(2-)/HS(-)偶联高约 0.1 V。因此，S(0)不仅可以通过为 As(III)提供电子受体来帮助稳定水合的 As(V)，还可以有助于更氧化的氧化还原状态。
