Effective treatment of thioantimonates-bearing waters by nanocrystalline iowaite, an iron-based layered double hydroxide

Elevated concentrations of antimony (Sb) in the environment originating from natural and anthropogenic sources are of global concern due to their high toxicity and mobility. Notably, the formation of thioantimony species (e.g. tri- and tetra-thioantimonates) enhances Sb release into aquatic systems, and they may dominate Sb species in reducing environments, such as sulfidic geothermal waters. In this study, batch sorption experiments were conducted to investigate thioantimonates removal from aqueous solution by nanocrystalline iowaite, a sorbent suitable for incorporating hazardous anions but not used for treating thioantimonates-bearing waters up to now. Based on the fits of kinetics and isotherm sorption models as well as the structural comparison of iowaite before and after its reaction with thioantimonates-bearing solutions by use of XRD and XPS analyses, both the anion exchange between thioantimonates in solution and chloride in the interlayer regions of iowaite and the inner-sphere complexation of sorbed thioantimonates with iron atoms located in iowaite layers were found to be responsible for the efficient removal of aqueous thioantimonates by iowaite. Moreover, the presence of common anions (SO₄²⁻, Cl⁻, and NO₃⁻) or Sb oxyanions (antimonite and antimonate) over a wide range of concentrations had little effect on thioantimonates sorption, whereas the addition of arsenic oxyanions (arsenite and arsenate) with high concentrations exhibited a clear inhibition of thioantimonates removal. Nevertheless, iowaite is still a strong scavenger of thioantimonates under environmentally relevant conditions and therefore holds promise for future large-scale treatment of geothermal waters, anoxic groundwaters, and mining wastewaters that are potentially rich in thioantimonates.