High-temperature FeS-FeS{sub 2} solid-state transitions: Reactions of solid mackinawite with gaseous H{sub 2}S
- Schuit Institute of Catalysis, Eindhoven University of Technology, 5600 MB Eindhoven (Netherlands)
Phase transitions and reactions of non-oxidized and surface-oxidized mackinawite (FeS) in helium and H{sub 2}S gas were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT). DFT was used to obtain optimized structures of the iron-sulfur phases mackinawite, hexagonal pyrrhotite, greigite, marcasite and pyrite and to determine the thermochemical properties of reactions of mackinawite with H{sub 2}S to these phases. The phase transitions of mackinawite to hexagonal pyrrhotite are endothermic, while reactions to greigite, marcasite and pyrite are exothermic. The experiments show that non-oxidized mackinawite converts into hexagonal pyrrhotite (Fe{sub 9}S{sub 10} first and then Fe{sub 7}S{sub 8}) in He and also in H{sub 2}S but at a lower temperature. No further reactions can be observed under these conditions. In the case of surface-oxidized mackinawite, the extent of surface oxidation determines the course and the final product of the reaction with H{sub 2}S. If the extent of surface oxidation is low, only Fe{sup 2+} is oxidized to Fe{sup 3+}. Under these conditions mackinawite converts into the mixed-valence thiospinel compound greigite. In case of pronounced surface oxidation all surface Fe centers are oxidized to the Fe{sup 3+} state and S{sup 2-} is oxidized to SO{sub 4}{sup 2-}. Oxidation of sulfur is a prerequisite for the formation of pyrite. - Graphical abstract: Reactions of mackinawite (FeS) with H{sub 2}S. In the absence of electron acceptors the system remains in the Fe{sup 2+}/S{sup 2-} regime and endothermic pyrrhotite phases form (upper pathway). Only in the presence of electron acceptors, FeS phases with iron or sulfur in higher oxidation states can form and FeS reacts under these conditions exothermic to pyrite (FeS{sub 2}) via greigite (Fe{sub 3}S{sub 4}) as intermediate (lower pathway)
- OSTI ID:
- 21212116
- Journal Information:
- Journal of Solid State Chemistry, Vol. 181, Issue 11; Other Information: DOI: 10.1016/j.jssc.2008.08.024; PII: S0022-4596(08)00451-9; Copyright (c) 2008 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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