Mössbauer spectroscopic study on chemical changes of iron compounds with the aid of sulfate-reducing bacteria

Abstract

⁵⁷Fe Mössbauer spectra were measured of reaction products formed during an incubation experiment with sulfate-reducing bacteria, which were isolated from estuarine sediments of the Tama River in Tokyo. The spectrum of the product incubated for several days showed some overlapping sextets. This product had a different chemical form from amorphous iron monosulfide produced by inorganic reaction between ferrous and sulfide ions. It was estimated that the structure of nearest neighbor of iron in this product was similar to that of pyrrhotite (Fe_1−x S). After several months of incubation, other singlet and doublet appeared successively on the spectrum, corresponding to mackinawite (FeS_1−x ) and new sulfide, respectively. Both values of isomer shift and quadrupole splitting of new sulfide increased with increasing incubation time and approached those of pyrite (FeS₂). Extended X-ray absorption fine structure (EXAFS) showed that iron atoms were coordinated by sulfur in the incubation product.