X-ray absorption studies of the local strontium environments in borosilicate waste glasses

X-ray absorption spectra were collected and analyzed to characterize the strontium environments in borosilicate glass formulations developed for the immobilization of nuclear wastes. Sr can become a major constituent in some radioactive wastes because of the use of Sr-compounds in waste pretreatment processes. Data are presented for 13 borosilicate glasses that are used to simulate the anticipated waste glass compositions, where SrO concentrations range from approximately 2 to 30 wt%. The XANES data are statistically identical for all glasses investigated, and indicate divalent strontium. The EXAFS data for both crystalline standards and glasses appear to provide information only about the inner four to six coordinating oxygens that surround Sr. The data and analyses for all glasses show that the inner coordination environments around Sr have average Sr–O distances near 2.53 A, which are statistically invariant with respect to glass composition and to various synthesis conditions. Sr–O distances determined for the glasses are within the shorter end of the range of individual Sr–O distances in the SrCO3 and haradaite (SrVSi2O7) crystalline standards.