Discussion of Mackinawite Formation During Microbial Corrosion

摘要

The discussion of the technical note, mackinawite Formation During MicrobialCorrosion, by McNeill and Little, takes exception to the authors' assertion that the presence of mackinawite, and especially the presence of mackinawite altering to smythite or greigite, on iron or carbon steel corroding in the biosphere, is an indication that the corrosion is influenced by sulfatereducing bacteria (SRB). The criticism is based on two published papers 1.2 in which tetragonal iron sulfides FeS,.,) were produced on carbon steel specimens exposed to H 2 S in abiotic aqueous environments. The compounds were identified as closely related compounds of the same symmetry as natural mackinawite but slightly different lattice parameters. All H a and 2 are unstable in environments above the sulfide S concentrations used in the experiments cited in references 1 fence with the possible exception of the lowest H2 S concentration, 1 at which no kansite (the term used for tetragonal iron sulfide) was detected. This is outside the region of biosphere waters, even in environments isolated from the atmosphere.3 Accordingly, the experiments in the discussion all replicate conditions that, in the biosphere, can only exist with a continuously acting, distributed hydrogen.