X-ray absorption studies of manganese valence and local environment in borosilicate waste glasses

Abstract

X-ray absorption data were collected and analyzed to characterize the manganese environments in borosilicate glass formulations to be used for immobilization of nuclear wastes. Mn can become a significant constituent in some radioactive wastes, because of the use of Mn-compounds in waste pretreatment processes. Sixteen borosilicate glasses were investigated, which were synthesized to simulate the Mn environments in the anticipated waste glasses, where MnO concentrations range from 0.4 to 13.6 wt%. The X-ray absorption near edge structure (XANES) for all glasses investigated indicate that most of the manganese within these samples is divalent. The extended X-ray absorption fine structure (EXAFS) analysis results for the glasses show average Mn–O distances near 2.07 Å, coordination numbers between 4.3 and 5.2, and large first-shell Debye–Waller factors. The EXAFS findings indicate that Mn 2+ in borosilicate glass is most likely within a distribution of environments that include 4- and 5-coordinated sites. EXAFS data and fitting results also show that the average manganese environments in these glasses are statistically invariant with respect to composition as well as to synthesis conditions.