TECHNETIUM SPECIATION IN CEMENT WASTE FORMS DETERMINED BY X-RAY-ABSORPTION FINE-STRUCTURE SPECTROSCOPY

The chemistry of technetium in cement waste forms has been studied wit h X-ray absorption fine structure (XAFS) spectroscopy. Using the Tc K- edge X-ray absorption near-edge structure (XANES) as a probe of the te chnetium speciation, our results show that partial reduction of the pe rtechnetate ion, TcO4-, takes place in the presence of the cement addi tive, blast furnace slag (BFS). The addition of the reducing agents Fe S, Na2S, and NaH2PO2 produces more extensive reduction of TcO4-, while the compounds FeO, Fe3O4, and Mn3O4 are observed to be unreactive. Th e extended X-ray absorption fine structure (EXAFS) data for the BFS, N a2S, and FeS treated cements indicate the presence of Tc clusters poss essing first shell S coordination. For the Na2S and FeS additives, Tc- Tc interactions are detected in the EXAFS demonstrating an extended st ructure similar to that of TcS2. The EXAFS spectrum of the NaH2PO2 tre ated cement reveals Tc-O and Tc-Tc interactions that resemble those fo und in the structure of TcO2.