Corrosion marine des aciers: rôle des interactions rouille verte sulfatée/bactéries sulfato-réductrices

Abstract

The corrosion of steel in marine media leads to the formation of the Fe(II-III) hydroxysulphate green rust GR(SO42-), that forms initially the inner part of the rust layer. This compound is rapidly oxidised into Fe(III) oxyhydroxides, mainly α- and γ-FeOOH, that constitute the outer part of the rust layer. After 6-12 months of exposure to the marine environment, an additional inner layer of iron sulphide is present under the green rust layer, as the result of the metabolic activity of sulphate-reducing bacteria (SRB). So it can be assumed that SRB can use the sulphate ions present inside the GR(SO42-) crystals as electron acceptor, and this study was focused on the evolution with time of systems including GR(SO42-) samples and SRB. The considered SRBs, Desulfovibrio desulfuricans subsp.aestuarii ATCC 29578, were added with GR(SO42-) to a Starkey culture medium modified specifically for the study. Four conditions were envisioned, corresponding to various concentrations of bacteria (107 or 109 bact. mL-1) and various sources of sulphate (FeSO4 + GR(SO 42-) or GR(SO42-) only). Cells were counted by epifluorescence microscopy using DAPI fluorochrome. The evolution with time of the GR(SO42-)/SRB systems after 15 and 30 days in anaerobic conditions proved to be independent of these conditions. In any case, the iron sulphide generated by bacterial activity, characterised by X-ray diffraction and Raman spectroscopy, proved to be Fe(III)-containing mackinawite. © EDP Sciences.