Raman studies of technetium in borosilicate waste glass

Abstract

The characterization of technetium (Tc) environments in borosilicate glasses is important with regard to the long-term isolation of Tc in nuclear wastes from the environment by waste vitrification. In this study, Raman spectroscopy was used to detect Tc in various borosilicate waste glass formulations in which Tc valence and average coordination environment were previously characterized by X-ray absorption spectroscopy. Raman spectral comparisons between chemically equivalent Tc-containing and Tc-free borosilicate glass pairs indicate Tc-dependent features near 320 and 910 cm−1 resulting from internal vibrational modes of pertechnetate tetrahedral (Tc7+ in TcO4 −), similar to those observed for pertechnetate aqueous solutions. Initial observations of the pertechnetate Tc–O symmetric stretch mode near 910cm−1 indicate a peak area dependence on pertechnetate concentration and a detection limit near 50 ppm Tc7+ in borosilicate glass. Pertechnetate Tc–O symmetric stretch mode frequency versus composition relationships for the borosilicate waste glasses suggest that pertechnetate tetrahedra are surrounded by network-modifying cations. However, Raman spectroscopy is insensitive to six-coordinated Tc4+ species in borosilicate glasses.