Interaction of Synthetic Sulfate Green Rust with Antimony(V)

Green rusts (GRs), which are mixed ferrous/ferric hydroxides, occur in many suboxic soils and sediments and are thought to play an important role in the fate and transport of many inorganic contaminants. In this study, the interaction of Sb with sulfate GR (GRSO(4)) was investigated using multitechnique approaches such as X-ray absorption fine structure (XAFS), XRD, and BET analyses. XANES analyses show that the oxidation states of Sb(V) sorbed on GRSO(4) is dominantly Sb(V), suggesting that GRSO(4) does not work as a strong reductant in the system of the present study. The sorption experiment, EXAFS, and XRD results suggested that there are two bonding modes for Sb(V) sorption on GRSO(4), (i) the sorption to edge sites with inner-sphere complex and (ii) to interlayer surface with outer-sphere complex. In addition, it was found that fraction (i) is dominant for Sb(V) sorption on GRSO(4). The transformation of metastable GRSO(4) was inhibited by the presence of Sb(V). The transformed products of GRSO(4), such as magnetite and Fe(OH)(2), have larger surface areas and higher capacities as adsorbent for Sb(V) than GRSO(4), and the fraction of the transformed product largely affects the distribution of Sb between water and solid, a mixture of GRSO(4), magnetite, and Fe(OH)(2).