Department of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
Environ Sci Technol. 2013 Jun 4;47(11):5652-9. doi: 10.1021/es3049724. Epub 2013 May 13.
Sorption to iron (Fe) minerals determines the fate of the toxic metalloid arsenic (As) in many subsurface environments. Recently, thiolated As species have been shown to dominate aqueous As speciation under a range of environmentally relevant conditions, thus highlighting the need for a quantitative understanding of their sorption behavior. We conducted batch experiments to measure the time-dependent sorption of two S-substituted arsenate species, mono- and tetrathioarsenate, and compared it to the sorption of arsenite and arsenate, in suspensions containing 2-line ferrihydrite, goethite, mackinawite, or pyrite. All four As species strongly sorbed to ferrihydrite. For the other sorbents, binding of the thiolated As species was generally lower compared to arsenate and arsenite, with the exception of the near instantaneous and complete sorption of monothioarsenate to pyrite. Analysis of the X-ray absorption spectroscopy (XAS) spectra of sorbed complexes implied that monothioarsenate binds to Fe oxides as a monodentate, inner-sphere complex. In the presence of Fe sulfides, mono- and tetrathioarsenate were both unstable and partially reduced to arsenite. Adsorption of the thiolated As species to the Fe sulfide minerals also caused the substitution of surface sulfur (S) atoms by As and the formation of As-Fe bonds.
铁（Fe）矿物的吸附作用决定了有毒类金属砷（As）在许多地下环境中的命运。最近的研究表明，在一系列与环境相关的条件下，巯基取代的砷物种主导了水溶液中砷的形态，因此需要定量了解它们的吸附行为。我们进行了批量实验，以测量两种 S 取代的砷酸盐物种，单硫代砷酸盐和四硫代砷酸盐，在含有 2 线水铁矿、针铁矿、磁黄铁矿或黄铁矿的悬浮液中，随时间变化的吸附行为，并将其与亚砷酸盐和砷酸盐的吸附行为进行了比较。所有四种 As 物种都强烈地吸附在水铁矿上。对于其他的吸附剂，与砷酸盐和亚砷酸盐相比，巯基取代的砷物种的结合通常较低，除了单硫代砷酸盐几乎瞬时和完全吸附在黄铁矿上。对吸附络合物的 X 射线吸收光谱（XAS）分析表明，单硫代砷酸盐与 Fe 氧化物结合形成单齿内圈络合物。在 Fe 硫化物存在下，单硫代砷酸盐和四硫代砷酸盐都不稳定，部分还原为亚砷酸盐。巯基取代的砷物种吸附到 Fe 硫化物矿物上，也会导致表面硫（S）原子被 As 取代，并形成 As-Fe 键。
