Institut de Mineralogie et de Physique des Milieux Condenses (IMPMC), UMR 7590, CNRS, Universite Paris 6 (UPMC), Universite Paris 7 (UPD), IPGP, 140, rue de Lourmel, 75015 Paris, France.
Environ Sci Technol. 2010 Jan 1;44(1):109-15. doi: 10.1021/es901627e.
The knowledge of arsenic speciation at the surface of green rusts (GRs), Fe(II)((1-x))Fe(III)(x) (OH)(2) (CO(3), Cl, SO(4))(x-), is environmentally relevant because arsenic sorption onto GRs could contribute to arsenic retention in anoxic environments (hydromorphic soils, marine sediments, etc.). The nature of arsenic adsorption complexes on hydroxychloride green rust 1 (GR1Cl) at near-neutral pH under anoxic conditions was investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy at the As K-edge. Sorption data indicate that As(V) sorbs more efficiently than As(III) at the studied As loadings (0.27 micromol m(-2) and 2.7 micromol m(-2)). EXAFS results indicate that arsenite [As(III)] and arsenate [As(V)] form inner-sphere complexes on the surface of GR1Cl at arsenic surface coverages of 0.27 and 2.70 micromol m(-2), with distinct types of As(III) and As(V) sorption complexes, which change in relative concentration as a function of arsenic loading. For As(V), the EXAFS-derived As-Fe distances (3.34 +/- 0.02 and 3.49 +/- 0.02 A) suggest the presence of binuclear bidentate double-corner complexes ((2)C) and monodentate mononuclear corner-sharing complexes ((1)V). For As(III), EXAFS-derived As-As distance (3.32 +/- 0.02 A) and As-Fe distances (3.49 +/- 0.02 and 4.72 +/- 0.02 A) are consistent with the presence of dimers of As(III) pyramids binding to the edges of the GR1Cl layers by corner sharing with FeO(6) octahedra. However, (2)C and (1)V As(III) complexes cannot be excluded. These results improve our knowledge of the mode of As(V) and As(III) inner-sphere adsorption on green rusts, which will help to constrain sorption modeling of arsenic in soils, sediments, and aquifers.
绿锈（GRs）表面的砷形态知识与环境相关，因为砷在 GRs 上的吸附可能有助于缺氧环境（水成型土壤、海洋沉积物等）中砷的保留。在缺氧条件下，使用扩展 X 射线吸收精细结构（EXAFS）光谱法在砷 K 边研究了近中性 pH 下羟基氯化物绿锈 1（GR1Cl）上砷吸附络合物的性质。吸附数据表明，在所研究的砷负载（0.27 µm 和 2.7 µm）下，砷（V）比砷（III）更有效地吸附。EXAFS 结果表明，砷（III）和砷（V）在 GR1Cl 表面上形成内圈络合物，砷表面覆盖率为 0.27 和 2.70 µm，具有不同类型的砷（III）和砷（V）吸附络合物，其浓度随砷负载的变化而变化。对于 As(V)，EXAFS 衍生的 As-Fe 距离（3.34 +/- 0.02 和 3.49 +/- 0.02 A）表明存在双核双齿双顶角络合物（(2)C）和单核单齿顶角共享络合物（(1)V）。对于 As(III)，EXAFS 衍生的 As-As 距离（3.32 +/- 0.02 A）和 As-Fe 距离（3.49 +/- 0.02 和 4.72 +/- 0.02 A）与 As(III)金字塔的二聚体的存在一致，这些二聚体通过与 GR1Cl 层边缘的 FeO(6)八面体顶角共享来结合。然而，不能排除（2)C 和（1)V As(III)络合物。这些结果提高了我们对绿锈中 As(V)和 As(III)内圈吸附模式的认识，这将有助于约束土壤、沉积物和含水层中砷的吸附模型。
