X-ray absorption studies of vanadium valence and local environment in borosilicate waste glasses using vanadium sulfide, silicate, and oxide standards

X-ray absorption spectroscopic data were collected and analyzed to characterize vanadium in borosilicate glasses used for immobilization of sulfur-containing nuclear wastes. Data are presented for borosilicate glasses, some with and some without sulfur, that have V2O5 concentrations as high as 12 wt%, and for the sulfides: sulvanite and patronite, the silicates: cavansite, hadaraite, and roscoelite, and the oxide: vanadinite. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data for the glasses have no sulfur dependent features, but do show changes that parallel various redox conditions for the corresponding melts. EXAFS, data for the glasses indicate V-O distances near 1.70 Angstrom that are considerably shorter than typical V-S distances found in the sulfides. Both XANES and EXAFS indicate that most or all vanadium in these glasses is in the form of V5+O4 tetrahedra; glasses synthesized under reducing conditions can have penta-coordinated V4- populations up to approximately 20-25% of all vanadium present. (C) 2002 Elsevier Science B.V. All rights reserved.