title: Iron-monosulfide oxidation in natural sediments: resolving microbially mediated S transformations using XANES, electron microscopy, and selective extractions.
abstract: Iron-monosulfide oxidation and associated S transformations in a natural sediment were examined by combining selective extractions, electron microscopy and S K-edge X-ray absorption near-edge structure (XANES) spectroscopy, The sediment examined in this study was collected from a waterway receiving acid-sulfate soil drainage. It contained a high acid-volatile sulfide content (1031 micromol g(-1)), reflecting an abundance of iron-monosulfide. The iron-monosulfide speciation in the initial sediment sample was dominated by nanocrystalline mackinawite (tetragonal FeS). At near-neutral pH and an 02 partial pressure of approximately 0.2 atm, the mackinawite was found to oxidize rapidly, with a half-time of 29 +/- 2 min. This oxidation rate did not differ significantly (P < 0.05) between abiotic versus biotic conditions, demonstrating that oxidation of nanocrystalline mackinawite was not microbially mediated. The extraction results suggested that elemental S (S8(0)) was a key intermediate S oxidation product Transmission electron microscopy showed the S8(0) to be amorphous nanoglobules, 100-200 nm in diameter. The quantitative importance of S8(0) was confirmed by linear combination XANES spectroscopy, after accounting for the inherent effect of the nanoscale S8(0) particle-size on the corresponding XANES spectrum. Both the selective extraction and XANES data showed that oxidation of S8(0) to SO4(2-) was mediated by microbial activity. In addition to directly revealing important S transformations, the XANES results support the accuracy of the selective extraction scheme employed here.
authors.affiliation: A Centre for Acid Sulfate Soil Research, Southern Cross GeoScience, Southern Cross University, Lismore, NSW 2480, Australia. ed.burton@scu.edu.au
authors.forename: E D
authors.initials: ED
authors.lastname: Burton
authors.forename: R T
authors.initials: RT
authors.lastname: Bush
authors.forename: L A
authors.initials: LA
authors.lastname: Sullivan
authors.forename: R K
authors.initials: RK
authors.lastname: Hocking
authors.forename: D R G
authors.initials: DR
authors.lastname: Mitchell
authors.forename: S G
authors.initials: SG
authors.lastname: Johnston
authors.forename: R W
authors.initials: RW
authors.lastname: Fitzpatrick
authors.forename: M
authors.initials: M
authors.lastname: Raven
authors.forename: S
authors.initials: S
authors.lastname: McClure
authors.forename: L Y
authors.initials: LY
authors.lastname: Jang
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D001673:Biodegradation, Environmental; D005296:Ferrous Compounds / Q000737:chemistry* / Q000302:isolation & purification*; D019015:Geologic Sediments / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008854:Microscopy, Electron; D010084:Oxidation-Reduction; D013057:Spectrum Analysis; D013455:Sulfur / Q000378:metabolism*
chemical_list: D005296:Ferrous Compounds; D013455:Sulfur; C022597:ferrous sulfide