Abiotically or microbially mediated transformations of magnetite by sulphide species: The unforeseen role of nitrate-reducing bacteria

In the anoxic conditions of nuclear waste deep geological repository, the main iron corrosion products formed at the surface of the carbon steel overpacks are siderite (FeIICO3) and magnetite (FeIIFeIII2O4) that form a rather protective layer. The originality of this work is the consideration of the bacterial metabolism of nitrate-reducing bacteria (NRB), often overlooked in corrosion processes. Klebsiella mobilis was used as a model of NRB and incubated with ferrous carbonates/magnetite corrosion bilayers under anoxic conditions. As a consequence of a combination of biotic and abiotic processes magnetite was reduced to mackinawite (FeIIS) and subsequently transformed to greigite (FeIIFeIII2S4).