IMPACT OF IRON(II)-INDUCED TRANSFORMATION OF IRON(III) (HYDR)OXIDES ON MOLYBDENUM MOBILITY IN GROUNDWATER
Qin, Kaixuan 1990-
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Elevated concentrations of molybdenum (Mo) in groundwater are a growing concern at mines worldwide. However, information on geochemical controls of Mo mobility within mining environments are limited. Sorption onto Fe(III) (hydr)oxides is an important control on the mobility of metal(loid)s in soils, sediments and aquifers and is, therefore, an important mechanism of Mo attenuation within mine wastes and associated groundwater systems. However, sorption effectiveness depends on Mo speciation, pH, and redox conditions. There is potential for re-partitioning and release of associated Mo during Fe(II)-induced transformation of Fe (hydr)oxides. Column experiments were conducted to examine: (1) adsorption behaviour of molybdate (MoO42-) on ferrihydrite [Fe2O3·nH2O], goethite [α-FeOOH], and hematite [α-Fe2O3]; and (2) Mo re-partitioning during Fe(II)-induced reductive transformation of ferrihydrite and goethite. Results demonstrated that MoO42- sorption capacity at circumneutral pH followed the general order: ferrihydrite > goethite > hematite. Subsequent reductive transformation by dissolved Fe(II) led to Mo re-partitioning without a substantial increase in Mo mobility. The extent of Mo mobilization was, however, greater at low (0.2 mM) compared to high (2.0 mM) Fe(II) concentrations. Furthermore, ferrihydrite generally exhibited stronger retention ability during reductive transformation – both for low and high Fe(II) concentrations – compared to goethite. Raman spectroscopy and scanning electron microscopy suggested that lepidocrocite [γ-FeOOH] was the major transformation product in the goethite and ferrihydrite columns. X-ray absorption spectroscopy (XAS) indicated that the Mo coordination environment changed from tetrahedral to octahedral during reduction, which suggests Mo might be incorporated into the transformed Fe phases with a disordered structure. This research improves our understanding of relationships between redox conditions, mineral transformations, and Mo mobility, which is critical for the development of Mo management and remediation strategies in mining environments.
DegreeMaster of Science (M.Sc.)
CommitteeChen, Ning; Derek, Peak; Butler, Samuel; Grosvenor, Andrew
Copyright DateOctober 2016
Fe(III (hydr)oxides, molybdenum, reductive transformation