Iron-monosulfide oxidation in natural sediments : Resolving microbially mediated S transformations using XANES, electron microscopy, and selective extractions
- Authors: Burton, Edward , Bush, Richard , Sullivan, Leigh , Hocking, Rosalie , Mitchell, David , Johnston, Scott , Fitzpatrick, Rob W. , Raven, Mark , McClure, Stuart , Jang, Lingyun
- Date: 2009
- Type: Text , Journal article
- Relation: Environmental Science and Technology Vol. 43, no. 9 (2009), p. 3128-3134
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- Description: 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 S0 8 to be amorphous nanoglobules, 100-200 nm in diameter. The quantitative importance of S0 8 was confirmed by linear combination XANES spectroscopy, after accounting for the inherent effect of the nanoscale S0 8 particle-size on the corresponding XANES spectrum. Both the selective extraction and XANES data showed that oxidation of S0 8 SO4 2- 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. © 2009 American Chemical Society.
Fe and S K-edge XAS determination of iron-sulfur species present in a range of acid sulfate soils : Effects of particle size and concentration on quantitative XANES determinations
- Authors: Morgan, Kate , Burton, Edward , Cook, Perran , Raven, Mark , Fitzpatrick, Rob W. , Bush, Richard , Sullivan, Leigh , Hocking, Rosalie
- Date: 2009
- Type: Text , Conference paper
- Relation: 14th International Conference on X-ray Absorption Fine Structure (XAFS14); Camerino, Italy; 26th-31st July 2009. Vol. 190, p. 1-5
- Full Text: false
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- Description: Acid sulfate soils (ASS) are soils and soft sediments in which sulfuric acid may be produced from iron sulfides or have been produced leaving iron oxyhydroxysulfates in amounts that have a long lasting effect on soil characteristics. If soil material is exposed to rotting vegetation or other reducing material, the Fe-oxyhydroxysulfates can be bacterially reduced to sulfides including disulfides (pyrite and marcasite), and Monosulfidic Black Ooze (MBO) a poorly characterised material known to be a mixture of iron sulfides (especially mackinawite) and organic matter. The chemistry of these environments is strongly affected by Fe and S cycling processes and herein we have sought to identify key differences in environments that occur as a function of Fe and S concentration. In addition to our chemical results, we have found that the effects of particle size on self absorption in natural sediments play an important role in the spectroscopic identification of the relative proportions of different species present. © 2009 IOP Publishing Ltd.