Reduction of antimony by nano-particulate magnetite and mackinawite

The speciation of antimony is strongly influenced by its oxidation state (V, III, 0 -III). Redox processes under anaerobic groundwater conditions may therefore greatly after the environmental behaviour of Sb. Employing X-ray absorption and photoelectron spectroscopy, we show here that Sb(\/) is reduced to Sb(III) by magnetite and mackinawite, two ubiquitous Fe(II)-containing minerals, while Sb(III) is not reduced further. At the surface of magnetite, Sb(III) Forms a highly symmetrical sorption complex at the position otherwise Occupied by tetrahedral Fe(III). The Sb(V) reduction increases with pH, and at pH values >6.5 Sb(V) is completely reduced to Sb(III) within 30 clays. In contrast, at the mackinawite surface, Sb(V) is completely reduced across a wide pH range and within I h. The Sb(V) reduction proceeds solely by oxidation of surface Fe(II), while the oxidation state of sulphide is conserved. Independent of whether Sb(V) or Sb(III) was added, all amorphous or nano-particulate SbS3-like solid formed.