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Faculty for Biology, Chemistry, and Earth Sciences

Environmental Geochemistry Group - Prof. Dr. Britta Planer-Friedrich

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Master Thesis

Ferrous iron oxidation in the presence of antimonate: Mutual effects on iron mineral products and antimony sequestration

Laura Wegner (10/2020-10/2020)

Support: Kerstin Hockmann

Antimony is a contaminant of increasing scientific interest. Although it is already known that Sb mobility is greatly influenced by Fe hydroxides, this study is the first to investigate its effect on the product of the oxidation of Fe(II) containing solutions. The products of the rapid oxidation of Fe(II) in aerated solutions at pH 7 at molar ratios of Fe:Sb of 100:1, 25:1, 10:1, 4:1 and a Sb free control treatment were identified as lepidocrocite at higher and as feroxyhyte at lower Fe:Sb ratios via XRD and TEM measurements. Additional PO43- extractions and a desorption experiment using the dried solids originating from the oxidation experiment verified the hypothesis that instead of surface adsorption, up to up to 16.21 mol% of the Fe(III) had been substituted by Sb(V) in the crystal structure. This caused structural disorder in the lepidocrocite crystals and resulted in the switch to feroxyhyte as reaction product at ratios of Fe:Sb 10:1 and lower. An additional desorption experiment revealed a very low remobilization due to the incorporation into the crystal structure. This is the first evidence of feroxyhyte formation from Fe(II) oxidation, and the high degree of substitution introduces coprecipitation as a promising new approach for the treatment of Sb-contaminated waters.

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