Iron-monosulfide oxidation in natural sediments: Resolving microbially mediated S transformations using XANES, electron microscopy, and selective extractions

E. D. Burton, R. T. Bush, L. A. Sullivan, R. K. Hocking, D. R G Mitchell, S. G. Johnston, R. W. Fitzpatrick, M. Raven, S. McClure, L. Y. Jang

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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 μ mol 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 O 2 partial pressure of ∼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 (S0 8) was a key intermediate S oxidation product. Transmission electron microscopy showed the S08 to be amorphous nanoglobules, 100-200 nm in diameter. The quantitative importance of S08 was confirmed by linear combination XANES spectroscopy, after accounting for the inherent effect of the nanoscale S08 particle-size on the corresponding XANES spectrum. Both the selective extraction and XANES data showed that oxidation of S08 SO42- was madiated by microbial activity. In addition to directly revealing important S transformations, the XANES results support the accuracy of the selective extraction scheme employed here.

Original languageEnglish
Pages (from-to)3128-3134
Number of pages7
JournalEnvironmental Science and Technology
Volume43
Issue number9
DOIs
Publication statusPublished - 1 May 2009
Externally publishedYes

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