Goethite dissimilatory reduction

In the sorption experiments of Icopini et al. (2004), the measured isotopic contrast between Fe(II)aq and the goethite starting material was -0.8%o after Fe(II) had sorbed to the surface over 24 hours in this case, the isotopic fractionation between sorbed Fe(II) and Fe(II)aq is not the 0.8%o measured difference, but is approximately +2.1%o based on an inferred 8 Fe value for the sorbed component as calculated from Fe mass balance (Fig. 4), as was noted in that study. Measured differences in Fe isotope compositions between ferric oxide/hydroxide and Fe(II)aq during dissimilatory Fe(III) reduction and photosynthetic Fe(II) oxidation have been proposed to reflect fractionation between soluble Fe(II) and Fe(III) species, where the soluble Fe(III) component is postulated to be bound to the cell and is not directly measured (Beard et al. 2003a Croal et al. 2004). In the case of dissimilatory Fe(III) reduction, assuming a static model simply for purposes of illustration, if 50% of the Fe in a pool that is open to... 

Flynn GJ, Sutton SR (2002) An assessment of the chemical heterogeneity of individual 3 pm fragments from an L2011 cluster . Supplement to Met Planet. Sci. 37 5012 Fredrickson JK, Zachara JM, Kennedy DW, Duff MC, Goiby YA, Li Shu-Mei W, Krupka KM (2000) Reduction of U(VI) in goethite (a-FeOOH) suspension by a dissimilatory metal-reducing bacterium. Geochim. Cosmochim. Acta 64 3085-309... 

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