ToF-SIMS analysis of abiotic and biotic iron sulfide layers formed in aqueous conditions on iron surfaces

Abstract

An approach for the identification of the origin of iron sulfides formation on iron surfaces using Time-of-Flight Secondary Ions Mass Spectrometry (ToF-SIMS) is reported here in. Two different sulfidation processes of iron surfaces are presented (both at room temperature): the first abiotic procedure was carried out using chronoamperometry (E = −0.8 V/SCE) of pure iron in 10 mM of Na2S,9H2O (pH = 11) while the second biotic procedure was accomplished by immersing a pure iron sample in a medium containing HS− ions produced by a sulfate-reducing bacterium (SRB) of the genus Desulfovibrio at an open circuit potential (OCP). A surface analytical method using Time-of-Flight Secondary Ions Mass Spectrometry (ToF-SIMS) coupled with ToF-SIMS spectra peak-fitting and data processing was developed to calculate an accurate sulfur isotopic fractionation δ34SV-CDT on iron sulfide layers formed on iron surfaces, thus allowing to discriminate between abiotically versus biotically generated sulfides. This approach contributes to a better understanding of iron surface interactions with sulfur containing environmental species of abiotic or biotic origin.