Browsing by Author "Bush, RT"

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    Divergent Fe and S mineralization pathways during the oxidative transformation of greigite, Fe3S4
    (Elsevier, 2017-09-30) Moon, EM; Bush, RT; Gibbs, DHM; Mata, JP
    The iron sulfide mineral greigite, Fe3S4, has previously been identified in the surface layers of the intertidal zone of a partially remediated acid sulfate soil wetland, representing an end-member in an iron sulfide mineralization pathway distinct from that of pyrite. The persistence of greigite is important for the stability of the remediated landscape, but the response of greigite to periods of oxygenation (for example, during a neap tide) is poorly understood. In this study, we employ X-ray absorption spectroscopy to identify the Fe and S speciation and mineralogy resulting from the oxidative disintegration of synthetic greigite under physiochemical solution conditions consistent with a partially remediated acid sulfate soil wetland. Results indicate divergent Fe and S mineralization pathways culminating in elemental sulfur and iron (hyr)oxide minerals. No sulfate-containing minerals were identified, and under all conditions tested, residual greigite remains. The oxidation products, and the presence of sulfur reducing bacteria, provide the right chemical environment for the reformation of greigite during the sub-oxic conditions of the rest of the tidal cycle. This likely explains the persistence of greigite in the intertidal zone, and implies that the oxidation of greigite is not detrimental to the long term stability of the acid sulfate soil remediation process. © 2017 Elsevier B.V.
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    Iron-monosulfide oxidation in natural sediments: resolving microbially mediated S transformations using XANES, electron microscopy, and selective extractions
    (American Chemical Society, 2009-05-01) Burton, ED; Bush, RT; Sullivan, LA; Hocking, RK; Mitchell, DRG; Johnston, SG; Fitzpatrick, RW; Raven, M; McClure, S; Jang, LY
    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 μmol 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 O2 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 (S08) 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 to SO42− 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. © 2009, American Chemical Society
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    Mobilisation, alternation, and redistribution of monosulfidic sediments in inland river systems
    (Academic Press Ltd- Elsevier Science Ltd, 2012-12-15) Cheetham, MD; Wong, VN; Bush, RT; Sullivan, LA; Ward, NJ; Zawadzki, A
    The accumulation of monosulfidic sediments in inland waterways is emerging as a major environmental issue. Mobilisation and suspension of monosulfidic sediments can result in deoxygenation, acidification of the water column and mobilisation of trace metals. The controls on monosulfidic sediment mobilisation and the critical thresholds for its scour and entrainment have not been established. This study examines the effect of a minor flood event (average return interval of 5 years) on sulfidic sediment scour in the Wakool River in southern NSW, Australia. Five profiles were sampled within a small (similar to 300 m) reach before and after a minor flood event to determine the degree of sediment scour and transport. The results indicate substantial scour of both monosulfidic sediments and underlying bed sediments (approximately 2100 m(3)). Changes in the sediment geochemistry suggest large concentrations of monosulfidic sediments had been suspended in the water column, partially-oxidised and redeposited. This is supported by Pb-210 results from one of the profiles. These results suggest that these monosulfidic sediments can move as bed load during minor flood events. (C) 2012 Elsevier Ltd. All rights reserved.
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    Resolving the holocene alluvial record in southeastern Australia using luminescence and radiocarbon techniques.
    (Wiley-Blackwell, 2010-10) Cheetham, MD; Keene, AF; Erskine, WD; Bush, RT; Fitzsimmons, KE; Jacobsen, GE; Fallon, SJ
    A previous assessment of radiocarbon (14C) dates from alluvial units in southeastern Australia revealed a gap in the geochronological record that coincides with the Holocene climatic optimum. This gap in the alluvial record can be further refined using optically stimulated luminescence (OSL). The chronology of Holocene river terraces on Widden Brook, a sandy alluvial stream in southeastern Australia, was established using 14C and OSL techniques. Combined use of these independent techniques allows for a more rigorous assessment of the alluvial record. The robust chronology, consisting of 38 14C and 11 OSL samples, permitted identification of significant depositional variation within the catchment, resulting from localised geomorphic processes. The three terrace sequences identified yielded distinct chronologies, suggesting alluvial deposition at different times. The sequences exhibited a continuous chronology, which indicated continuous deposition throughout the Holocene. The chronology of terrace sequences within this catchment suggests that terrace formation can be attributed to localised geomorphic processes rather than climatic forcing. © 2010, Wiley-Blackwell.