XANES evidence for sulphur speciation in Mn-, Ni- and W-bearing silicate melts
Access Status
Authors
Date
2009Type
Metadata
Show full item recordCitation
Source Title
ISSN
Faculty
Remarks
The link to the journal’s home page is: http://www.elsevier.com/wps/find/journaldescription.cws_home/212/description#description. Copyright © 2009 Elsevier B.V. All rights reserved
Collection
Abstract
S K edge XANES and Mn, W and Ni XANES and EXAFS spectra of silicate glasses synthesised at 1400 degrees C and 1 bar with compositions in the CaO-MgO-Al2O3-SiO2-S plus MnO, NiO, or WO3 systems were used to investigate sulphur speciation in silicate glasses. S K-edge spectra comprised a composite peak with an edge between 2470 and 2471.4 eV, which was attributed to S2-, and a peak of variable height with an edge at 2480.2 to 2480.8 eV, which is consistent with the presence of S+6. The latter peak was attributed to sample oxidation during sample storage. W-rich samples produced an additional lower energy peak at 2469.8 eV that is tentatively attributed to the existence of S 3p orbitals hybridised with the W 5d states. Deconvolution of the composite peak reveals that the composite peak for Mn-bearing samples fits well to a model that combines three Lorentzians at 2473.1, 2474.9 and 2476.2 eV with an arctan edge step. The composite peak for W-bearing samples fits well to the same combination plus an additional Lorentzian at 2469.8 eV. The ratio of the proportions of the signal accounted for by peaks at 2473.1eV and 2476.2eV correlates with Mn:Ca molar ratios, but not with W:Ca ratios. Spectra from Ni-bearing samples were qualitatively similar but S levels were too low to allow robust quantification of peak components. Some part of the signal accounted for by the 2473.1 eV peak was therefore taken to record the formation of Mn-S melt species, while the 2469.8 peak is interpreted to record the formation of W-S melt species. The 2474.9 eV and 2476.2 eV peaks were taken to be dominated by Ca-S and Mg-S interactions. However, a 1:1 relationship between peak components and specific energy transitions is not proposed. This interpretation is consistent with known features of the lower parts of the conduction band in monosulphide minerals and indicates a similarity between sulphur species in the melts and the monosulphides. S XANES spectra cannot be reproduced by a combination of the spectra of the component element monosulphides. Mn-, W- and Ni- XANES and EXAFS for synthetic glasses without sulphide exsolution did not show any sensitivity to the presence of sulphur, which is unsurprising as S:O ratios were sufficiently low that metals would be mostly co-ordinated by O. Mn EXAFS spectra were consistent with divalent Mn in 5 co-ordinated Mn-O melt species. W spectra were consistent with tetrahedrally co-ordinated hexavalent W, most likely in scheelite-like melt species, and Ni spectra were consistent with [4] co-ordinated divalent Ni. These results indicate lower coordinations for both W and Ni than those inferred by some previous workers. Cation coordination may reflect the proportion of non-bridging oxygens, which is lower in the Ca-rich and Al-poor samples investigated here than for previous studies.
Related items
Showing items related by title, author, creator and subject.
-
Sandison, Carolyn M. (2001)The importance of organic sulphur fixation in the preservation of organic matter in humic coal-forming environments is demonstrated in this thesis. The transgression of coal depositional systems by marine waters during ...
-
Motta, Rafael ; Fitzsimons, Ian ; Moraes, R.; Johnson, Tim ; Schuindt, S.; Benetti, B.Y. (2021)Mineral assemblages that are diagnostic of ultrahigh-temperature (>900 °C) metamorphism are generally restricted to Mg- and Al-rich rocks. However, in many metamorphic terrains such compositions do not occur, and the rocks ...
-
Evans, Katy; O'Neill, H.; Mavrogenes, J. (2008)Sulphur solubility and immiscibility relationships in silicate melts as a function of the concentrations of Cu,Mn, Ni and W were measured for melts synthesised at 1400 C and 1 bar. Relationships between fS2, fO2 andthe S ...