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Analysis of the Major Fe Bearing Mineral Phases in Recent Lake Sediments by EXAFS Spectroscopy

Spadini, Lorenzo ; Bott, Markus ; Wehrli, Bernhard ; Manceau, Alain

In: Aquatic Geochemistry, 2003, vol. 9, no. 1, p. 1-17

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    Title
    • Analysis of the Major Fe Bearing Mineral Phases in Recent Lake Sediments by EXAFS Spectroscopy
    Author
    • Spadini, Lorenzo. Environmental Geochemistry Group, LGIT-IRIGM, University of Grenoble and CNRS, BP 53, 38041, Grenoble, France Cedex 9
    • Bott, Markus. Limnological Research Center, Swiss Federal Institute for Environmental Science and Technology (EAWAG) and Swiss Federal Institute of Technology (ETH), CH-6047, Kastanienbaum, Switzerland
    • Wehrli, Bernhard. Limnological Research Center, Swiss Federal Institute for Environmental Science and Technology (EAWAG) and Swiss Federal Institute of Technology (ETH), CH-6047, Kastanienbaum, Switzerland
    • Manceau, Alain. Environmental Geochemistry Group, LGIT-IRIGM, University of Grenoble and CNRS, BP 53, 38041, Grenoble, France Cedex 9
    Document Type
    • Postprint
    OAI-PMH Identifier
    • oai:doc.rero.ch:319895
    Summary
    Extended X-ray absorption fine structure (EXAFS) spectroscopy and chemical analyses were combined to determine the Fe bearing minerals in recent lake sediments from Baldeggersee (Switzerland). The upper section of a laminated sediment core, deposited under eutrophic conditions, was compared to the lower part from an oligotrophic period. Qualitative analysis of FeK EXAFS agreed well with chemical data: In the oligotrophic section Fe(II)-O and Fe(III)-O specieswere present, whereas a significant fraction of Fe(II)-S sulfides was strongly indicated in the eutrophic part. A statistical analysis was performed by least square fitting of normalized reference spectra. The set of reference minerals included Fe(III) oxides and Fe(II) sulfides, carbonates and phosphates. In the oligotrophic regime no satisfying fit was obtained using the set of reference spectra, indicating that siderite (FeCO3) was not present in a significant amount in these carbonate-rich sediments. Simulated EXAFS spectra for a(Cax, Fe1-x)CO3solid solution allowed reconstructing the specificfeatures of the experimental spectra, suggesting that this phase was the dominant Fe carrier in the oligotrophic section of the core. In the eutrophic part, mackinawite was positively identified and represented the dominant Fe(II) sulfide phase. This finding agreed with chemical extraction, which indicated that18-40 mol% of Fe was contained in the acid volatile iron sulfide fraction. EXAFS spectra of the eutrophic section were best fitted by considering the admixture of mackinawite and the Fe-Ca carbonate phase inferred to be predominant in the oligotrophic regime