Determination of Sulfur Environments in Borosilicate Waste Glasses Using X-ray Absorption Near-Edge Spectroscopy
Sulfur can be the waste-loading limiting constituent for vitriﬁcation of sulfur-bearing radioactive wastes due to low solubility in silicate melts. Methods to improve sulfur loading would beneﬁt from improved understanding of the structural aspects of sulfur incorporation in borosilicate and other glasses. To this end, sulfur XANES spectra were collected for eight crystalline standards and twenty-four glasses, including borosilicate, phosphate, and borate compositions. Spectra for the standards show a systematic energy shift of the sulfur K-edge from 2469 to 2482 eV, as sulfur valence increases from 2- (in sulﬁdes) to 6+ (in sulfates). Most crucible glasses investigated have simple edges near 2482 eV that indicate sulfur in the form of sulfate only. Other glasses, some synthesized under reducing conditions, have complicated edges, indicating sulfate, sulﬁte, and more reduced species that may include S, S–S doublets, or short polysulﬁde chains. Sulﬁde species (S2-) were not dominant in any of the samples over the range of redox conditions investigated. These results indicate that sulfur incorporation is considerably more complex than would be suggested by the conventional interpretation of the redox-dependence of sulfur solubility, which considers only sulfate and sulﬁde species. Raman data indicate that several of the glasses investigated are not homogeneous with regard to all sulfur species.
Analytical Chemistry | Atomic, Molecular and Optical Physics | Biological and Chemical Physics | Physical Chemistry
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McKeown, D. A.,
Muller, I. S.,
Pegg, I. L.,
Stolte, W. C.
Determination of Sulfur Environments in Borosilicate Waste Glasses Using X-ray Absorption Near-Edge Spectroscopy.
Journal of Non-Crystalline Solids, 333