Mobility of toxic antimony during aeration of Fe(II)-rich waters

Laura Wegner1, Edward D. Burton2, Catherine McCammon3, Andreas C. Scheinost4, Stefan Peiffer5, Britta Planer-Friedrich6, Kerstin Hockmann5
1 University of Bayreuth, Department of Hydrology, 95440 Bayreuth, Germany,
2 Southern Cross University, Southern Cross GeoScience, Lismore NSW 2480, Australia
3 University of Bayreuth, Bayerisches Geoinstitut, 95440 Bayreuth, Germany
4 The Rossendorf Beamline at European Synchrotron Radiation Facility, 38043 Grenoble, France, and HZDR Institute for Resource Ecology, 01314 Dresden, Germany, and Institute of Geological Sciences, 3012 Bern, Switzerland
5 University of Bayreuth, Department of Hydrology, 95440 Bayreuth, Germany
6 University of Bayreuth, Environmental Geochemistry Group, 95440 Bayreuth, Germany

O 3.2 in What goes around comes around - Biogeochemical cycling of Iron, Sulfur & Carbon in the Environment

14.10.2021, 14:45-15:00, H 36

In redox-variable environments, the mobility of antimony (Sb), a toxic metalloid of increasing concern, is closely linked to the biogeochemical cycling of iron (Fe). Microbial production of soluble Fe(II) has been shown to release co-associated Sb under anaerobic conditions typical of wetland soils. In contrast, Sb-Fe interactions during aerobic Fe(II) oxidation and subsequent Fe(III) precipitation have received little attention. We investigated the effect of Fe(II) oxidation in the presence of environmentally relevant Sb(V) concentrations on the nature of the resulting Fe(III) precipitates and the mobility of Sb. Oxidation experiments were carried out in oxygen-saturated solutions (pH 7) containing an initial concentration of 1 mM Fe(II) and dissolved Sb(V) at Sb:Fe molar ratios of 0, 1:100, 1:25, 1:10, and 1:4. Iron and Sb concentrations in solution were monitored during the oxidation reaction and the precipitates were characterized using a combination of microscopic, spectroscopic and wet chemical extraction techniques.

Iron(II) quickly oxidized (within ~10 min) to Fe(III) after it had been added to the aerated solutions and precipitated. Aqueous Sb was removed from the solution in parallel with Fe(II). In absence and at low levels of Sb(V), lepidocrocite was the only solid-phase oxidation product. Interestingly, higher Sb:Fe molar ratios (1:10 and 1:4) inhibited lepidocrocite precipitation, and resulted in the formation of feroxyhyte, a rather uncommon Fe(III) oxide. Phosphate-extractions, together with Mössbauer and X-ray absorption spectroscopy, showed that >99% of the co-precipitated Sb was incorporated into the structure of the newly formed Fe(III) oxides, making it rather inaccessible for remobilization.

Our results are important for a safe management of Sb-contaminated sites and for the development of engineered solutions that harness Fe(II) oxidation reactions for water treatment.

Keywords: Oxidation, Antimony, Iron Oxides

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