Abstract
It has long been recognized that sulfate reducing bacteria (SRB) found in natural and industrial waste waters promote microbiologically influenced corrosion (MIC) of certain metals and alloys. Corrosion may be enhanced biologically, through direct enzymatic action of the bacteria, or abiotically, as a result of reaction with metabolic byproducts or changes in local conditions (for example, pH) brought about by bacterial activity. In this study, X-ray photoelectron spectroscopy (XPS) is utilized in conjunction with conventional microbiological and quantitative chemical analytical techniques to analyze the effects of localized environmental conditions similar to those found near the surface of a passive stainless steel on the behavior of SRB, and to determine the ability of these bacteria to alter local environmental conditions in such a way as to create conditions that accelerate corrosion. Specifically, the interactions of Fe, Cr, Ni and Mo ions with Desulfovibrio sp. under anoxic conditions were studied in order to determine the influence of passive dissociation products on the extent of sulfate reduction and to determine the resulting speciation of the metal ions and sulfur. In all cases, XPS revealed the presence of multiple reduced sulfur species (SC2-3, elemental S and S2), as well as reduction of both the molybdate and ferric ions. Localized reduction in pH due to SRB metabolic activity was presumed to play a role in the formation of stable molybdenum disulfide and ferrous species.
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