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Early oxidation processes on the Greigite Fe₃S₄(001) surface by water: A density functional theory study

Santos Carballal, David, Roldan Martinez, Alberto and de Leeuw, Nora 2016. Early oxidation processes on the Greigite Fe₃S₄(001) surface by water: A density functional theory study. The Journal of Physical Chemistry C 120 (16) , pp. 8616-8629. 10.1021/acs.jpcc.6b00216

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Abstract

Greigite (Fe₃S₄), the sulfide counterpart of the spinel-structured oxide material magnetite (Fe₃O₄), is a mineral widely identified in anoxic aquatic environments and certain soils, which can be oxidised, thereby producing extremely acid solutions of sulfur-rich wastewaters, so-called acid mine drainage (AMD) or acid rock drainage (ARD). Here we report a computational study of the partial replacement of sulfur (forming H₂S) by oxygen (from H₂O) in the Fe₃S₄(001) surface, derived from density functional theory calculations with on-site Coulomb approach and long-range dispersion corrections (DFT+U–D2). We have proposed three pathways for the oxidation of the surface as a function of H₂O coverage and pH. Different pathways give different intermediates, some of which are followed by a solid-state diffusion of the O atom towards its most stable position. Low levels of H₂O coverage, and especially basic conditions, seem to be essential, leading to the most favourable energetic landscape for the oxidation of the Fe₃S₄(001) surface. We have derived the thermodynamic and kinetic profile for each mechanism and plotted the concentration of H₂S and protons in aqueous solution and thermodynamic equilibrium with the stoichiometric and partially oxidized Fe₃S₄(001) surface as a function of the temperature. Changes in the calculated vibrational frequencies of the adsorbed intermediates are used as a means to characterise their transformation. We have taken into account statistical entropies for H₂S and H₂O and other experimental parameters, showing that this mineral may well be among those responsible for the generation of AMD.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Advanced Research Computing @ Cardiff (ARCCA)
Chemistry
Subjects: Q Science > QD Chemistry
Uncontrolled Keywords: spinels; surface science; oxidation-corrosion; catalysis; sulfides
Additional Information: PDF uploaded in accordance with publisher's policies at http://www.sherpa.ac.uk/romeo/issn/1932-7447/ (accessed 31.3.16).
Publisher: ACS Publications
ISSN: 1932-7447
Funders: Engineering & Physical Sciences Research Council (EPSRC) grant EP/G036675, Engineering & Physical Sciences Research Council (EPSRC) grant EP/K035355/2, Engineering & Physical Sciences Research Council (EPSRC) grant EP/L000202
Date of First Compliant Deposit: 30 March 2016
Date of Acceptance: 28 March 2016
Last Modified: 23 May 2019 05:21
URI: http://orca.cf.ac.uk/id/eprint/88312

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