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Asta M.P.,CSIC - Institute of Environmental Assessment And Water Research | Ayora C.,CSIC - Institute of Environmental Assessment And Water Research | Roman-Ross G.,University of Girona | Cama J.,CSIC - Institute of Environmental Assessment And Water Research | And 3 more authors.
Chemical Geology | Year: 2010

Acid waters and sediments of the Tinto Santa Rosa acid stream (Iberian Pyritic Belt; SW, Spain) were analysed to determine the role of sedimentary phases in the behaviour of arsenic. Aqueous arsenic and iron concentrations decreased markedly from the adit mouth to 300 m downstream indicating iron minerals precipitation as well as arsenic sorption onto these newly-formed phases. This was confirmed by the high arsenic concentrations observed in bed-stream precipitates, which play a major role in controlling arsenic mobility. To unravel the complex nature of the AMD sediments a combination of techniques including X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), total solid digestions, X-Ray Fluorescence (XRF) and X-Ray Absorption Spectroscopy (XAS) were employed. Results showed that (1) arsenic was present predominantly in its pentavalent state; (2) upstream arsenic was sorbed onto the main phase, schwertmannite, whereas downstream it was chiefly associated with goethite and jarosite; and (3) changes in arsenic speciation with depth were observed in the consolidated terrace sediments, where arsenic appeared primarily associated with schwertmannite in the upper part of the terraces, but with goethite at depth. Arsenic mobilization was controlled by sorption onto newly formed precipitates (schwertmannite, goethite and jarosite), causing natural arsenic attenuation. © 2009 Elsevier B.V. All rights reserved.


Byrne J.M.,Williamson Research Center for Molecular Environmental Science | Byrne J.M.,University of Tübingen | Coker V.S.,Williamson Research Center for Molecular Environmental Science | Moise S.,Keele University | And 9 more authors.
Journal of the Royal Society Interface | Year: 2013

Cobalt-doped magnetite (CoxFe32xO4) nanoparticles have been produced through the microbial reduction of cobalt-iron oxyhydroxide by the bacterium Geobacter sulfurreducens. Thematerials produced, asmeasured by superconducting quantum interference device magnetometry, X-ray magnetic circular dichroism, Mo?ssbauer spectroscopy, etc., show dramatic increases in coercivity with increasing cobalt content without a major decrease in overall saturation magnetization. Structural andmagnetization analyses reveal a reduction in particle size to less than 4 nm at the highest Co content, combined with an increase in the effective anisotropy of the magnetic nanoparticles. The potential use of these biogenic nanoparticles in aqueous suspensions formagnetic hyperthermia applications is demonstrated. Further analysis of the distribution of cations within the ferrite spinel indicates that the cobalt is predominantly incorporated in octahedral coordination, achieved by the substitution of Fe2 site with Co2, with up to 17 per cent Co substituted into tetrahedral sites © 2013 The Author(s) Published by the Royal Society. All rights reserved.

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