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Bioreduction of the well-crystallized ferric oxyhydroxide gamma-FeOOH lepidocrocite was investigated in batch cultures using Shewanella putrefaciens bacterium (strain CIP 8040) at initial pH 7.5 in bicarbonate buffer. The cultures were performed with formate as electron donor without phosphate, in the presence or absence of anthraquinone-2,6-disulfonate (AQDS) as electron shuttle. During lepidocrocite reduction, the iron(II,III) hydroxycarbonate green rust GR(CO32-) was characterized by X-ray diffraction, transmission electron microscopy, and transmission Mössbauer spectroscopy. The AQDS accelerated the kinetics of GR formation. GR was the major end product when bacterial reduction was not stopped by lack of electron donor, and between 55 and 86% of the iron from gamma-FeOOH precipitated in GR(CO32-). However, when the bacterial reduction was stopped by freezing/thawing or the electron donor was exhausted, the large quantity of remaining lepidocrocite induced a transformation of GR into magnetite. This confirms that GR is metastable with respect to magnetite in the presence of gamma-FeOOH.

Electron transfer at the mineral/water interface: Selenium reduction by ferrous iron sorbed on clay. Geochimica et Cosmochimica Acta, Elsevier, 2007, 71 (23) , selenite was sorbed as outer-sphere sorption complex, covering only part of the positive edge sites, as verified by a structure-based MUSIC model and Se K-edge XAS (X-ray absorption spectroscopy). When selenite was added to montmorillonite previously equilibrated with Fe 2+ solution however, slow reduction of Se and formation of a solid phase was observed with Se K-edge XANES (x-ray absorption near-edge spectroscopy) and EXAFS (extended x-ray absorption finestructure) spectroscopy. Iterative transformation factor analysis of XANES and EXAFS spectra suggested that only one Se reaction product formed, which was identified as nano-particulate Se(0). Even after one month, only 75% of the initially sorbed Se(IV) was reduced to this solid species. Mössbauer spectrometry revealed that before and after addition and reduction of Se, 5% of total sorbed Fe occurred as

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