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 with X-ray absorption fine structure (XAFS) spectroscopy. Using the Tc /f-edge X-ray absorption near-edge structure (XANES) as a probe of the technetium speciation, our results show that partial reduction of the pertechnetate ion, TcOj, takes place in the presence of the cement additive, blast fumace slag (BFS). The addition of the reducing agents FeS, NazS, and NaHjPOz produces more extensive reduction of TcOl, while the Compounds FeO, Fe304, and MnjOi are observed to be unreactive. The extended X-ray absorption fine structure (EXAFS) data for the BFS, Na^S, and FeS treated cements indicate the presence of Tc Clusters possessing first shell S coordination. For the Na2S and FeS additives, Tc-Tc interactions are detected in the EXAFS demonstrating an extended structure similar to that of TcSa. The EXAFS spectrum of the NaHzPOj treated cement reveals T c O and Tc-Tc interactions that resemble those found in the structure of TcO,.

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