Effects of metal cation substitution on hexavalent chromium reduction by green rust
Autor: | Knud Dideriksen, Marco C. Mangayayam, Liane G. Benning, Elisabeth Eiche, Andrew N. Thomas, Thomas Neumann, Helen M. Freeman, Jörg Göttlicher, Ralph Steininger, Dominique J. Tobler |
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Jazyk: | angličtina |
Rok vydání: | 2020 |
Předmět: |
Chromium
Geography & travel Inorganic chemistry chemistry.chemical_element Remediation 02 engineering and technology 010501 environmental sciences engineering.material 01 natural sciences Metal lcsh:Chemistry chemistry.chemical_compound Chromium Green rust X-ray absorption spectroscopy Remediation Geochemistry and Petrology Hexavalent chromium Sulfate lcsh:Environmental sciences 0105 earth and related environmental sciences ddc:910 lcsh:GE1-350 In situ chemical reduction Chromate conversion coating Green rust X-ray absorption spectroscopy 021001 nanoscience & nanotechnology Feroxyhyte chemistry lcsh:QD1-999 13. Climate action visual_art Reagent visual_art.visual_art_medium engineering 0210 nano-technology Research Article |
Zdroj: | Geochemical Transactions, Vol 21, Iss 1, Pp 1-16 (2020) Geochemical transactions, 21 (1), Art. Nr.: 2 Thomas, A N, Eiche, E, Göttlicher, J, Steininger, R, Benning, L G, Freeman, H M, Tobler, D J, Mangayayam, M, Dideriksen, K & Neumann, T 2020, ' Effects of metal cation substitution on hexavalent chromium reduction by green rust ', Geochemical Transactions, vol. 21, no. 1, 2, pp. 1-16 . https://doi.org/10.1186/s12932-020-00066-8 Geochemical Transactions |
ISSN: | 1467-4866 |
Popis: | Chromium contamination is a serious environmental issue in areas affected by leather tanning and metal plating, and green rust sulfate has been tested extensively as a potential material for in situ chemical reduction of hexavalent chromium in groundwater. Reported products and mechanisms for the reaction have varied, most likely because of green rust’s layered structure, as reduction at outer and interlayer surfaces might produce different reaction products with variable stabilities. Based on studies of Cr(III) oxidation by biogenic Mn (IV) oxides, Cr mobility in oxic soils is controlled by the solubility of the Cr(III)-bearing phase. Therefore, careful engineering of green rust properties, i.e., crystal/particle size, morphology, structure, and electron availability, is essential for its optimization as a remediation reagent. In the present study, pure green rust sulfate and green rust sulfate with Al, Mg and Zn substitutions were synthesized and reacted with identical chromate (CrO42−) solutions. The reaction products were characterized by X-ray diffraction, pair distribution function analysis, X-ray absorption spectroscopy and transmission electron microscopy and treated with synthetic δ-MnO2 to assess how easily Cr(III) in the products could be oxidized. It was found that Mg substitution had the most beneficial effect on Cr lability in the product. Less than 2.5% of the Cr(III) present in the reacted Mg-GR was reoxidized by δ-MnO2 within 14 days, and the particle structure and Cr speciation observed during X-ray scattering and absorption analyses of this product suggested that Cr(VI) was reduced in its interlayer. Reduction in the interlayer lead to the linkage of newly-formed Cr(III) to hydroxyl groups in the adjacent octahedral layers, which resulted in increased structural coherency between these layers, distinctive rim domains, sequestration of Cr(III) in insoluble Fe oxide bonding environments resistant to reoxidation and partial transformation to Cr(III)-substituted feroxyhyte. Based on the results of this study of hexavalent chromium reduction by green rust sulfate and other studies, further improvements can also be made to this remediation technique by reacting chromate with a large excess of green rust sulfate, which provides excess Fe(II) that can catalyze transformation to more crystalline iron oxides, and synthesis of the reactant under alkaline conditions, which has been shown to favor chromium reduction in the interlayer of Fe(II)-bearing phyllosilicates. |
Databáze: | OpenAIRE |
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