Biotic Fe(III) reduction of magnetite coupled to H2 oxidation: Implication for radioactive waste geological disposal

• Structural Fe(III) of magnetite is bioavailable for hydrogenotrophic iron-reducing bacteria.
• Extent of Fe(III) bioreduction depends on the H2 content in the gas phase.
• Vivianite (a ferrous phosphate) was identified as the sole biogenic mineral.
• Fe(III) bioreduction may affect the passivating properties of magnetite.

We report the first results on microbial Fe(III) reduction of magnetite in the presence of H2 (4%, 10%, or 60% H2) as the sole electron donor. The H2 concentration is the parameter likely to control both chemical and biological dissolution of magnetite, and a direct correlation between H2 concentration, bacterial activity, and the extent of Fe(III) bioreduction was observed. Vivianite was identified as a secondary mineral phase as a consequence of the increase in dissolved Fe(II) and the presence of phosphate in the experimental solutions. In the context of metal corrosion, Fe(III) bioreduction coupled to H2 oxidation may affect the passivating properties of oxide layers made of magnetite.

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