Antimony mobility and influence on secondary mineral pathways during iron(II)-catalyzed transformation of ferrihydrite
Sara Schlagenhauff (11/2018-09/2019)
Betreuer: Kerstin Hockmann, Britta Planer-Friedrich
Antimony mobility during transformation of iron oxides is an area of environmental concern. However, the effect of Sb on iron transformation pathways is poorly understood. In this study, Fe(II)-catalyzed transformation of ferrihydrite in three different ratios of Fe(III):Sb(V) was investigated via reactor experiments. The solid material was examined with x-ray diffraction (XRD), 1 M HCl and 1 M PO43- extractions, and the aqueous phases were analyzed by ICP-MS. In the Fe(II)-supplied reactors, the XRD diffractograms showed formation of crystalline secondary phases by day one which varied based on the initial concentration of Sb(V). At a ratio of Fe(III):Sb(V) = 0.016 the kinetics of ferrihydrite transformation to goethite were enhanced as goethite became the dominant phase six days earlier than lower Sb treatments. Feroxyhyte formed in the highest treatment (Fe(III):Sb(V) = 0.08) and remained stable during the experiment. Dissolved Fe decreased in the HCl-extractions by 75-91% by day one with the highest percentage lost in the high-Sb treatment. Dissolved Sb was below the detection limit (DL 0.16 µmol Sb L-1) in the zero and low-Sb treatments and fell below the DL in the mid and high treatments by day one. The PO43- extractable Sb, which represents Sb adsorbed to the solid phase, also decreased at day one from ~20% to ~5%. Since adsorbed and aqueous Sb decreased, Sb was likely incorporated into the crystal lattice during transformation. Incorporated Sb is less mobile and so this mechanism has potential for remediation of Sb polluted sites.