Microbial iron reduction in clay minerals: new insights from stable iron isotopes

Monday, June 28, 2021

The paper entitled “Consecutive Fe redox cycles decrease bioreducible Fe(III) and Fe isotope fractionations by eliminating small clay particles” was published in the journal Geochimica et Cosmochimica Acta by ERG researchers Bingjie Shi, Christina Smeaton, Chris Parsons and Philippe Van Cappellen in collaboration with colleagues from the University of Wisconsin-Madison.  The paper presents the very first experimental data on the changes in iron (Fe) isotope fractionation of a Fe-rich clay mineral during successive redox cycles.

In each of the redox cycles, the ferric iron (Fe3+) in the clay mineral was reduced by a known metal reducing bacterium and then re-oxidized by oxygen via aeration. The isotope fractionation between aqueous ferrous iron (Fe2+) and structural Fe3+ was found to decrease in the consecutive redox cycles. The results imply a progressive loss in the amount of bioreducible clay-bound Fe due to the preferential reductive dissolution of Fe3+ from the smallest clay particles. Hence, in redox-dynamic environments, such as the vadose zone of soils, the fraction of clay-bound Fe that is potentially renewable for use by Fe-reducing microorganisms is a function of the evolving size distribution of the clay particles.        

The paper can be accessed at LINK.

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