| Abstract
| - The chemistry of technetium in certain high-level nuclearwaste (HLW) tanks at the Hanford Site complicates thetreatment and vitrification of HLW. A major problem is thepresence, in certain tanks, of unidentified, lower-valenttechnetium species, which are difficult to remove from thewaste by current separation processes. Radiolyticreduction of TcO4- in alkaline solutions containing selectedorganic compounds, approximating the conditions inHLW, was investigated to determine the classes of compoundsthat can be formed under these conditions. InsolubleTcO2·xH2O is the primary radiolysis product with the majorityof organic compounds investigated, including citrate,dibutyl phosphate, and aminopolycarboxylates. X-rayabsorption fine structure (XAFS) measurements show thatTcO2·xH2O has a one-dimensional chain structureconsisting of edge-sharing TcO6 octahedra with bridgingoxide and trans water ligands. When diols, such as ethyleneglycol, are present, only soluble, Tc(IV) alkoxide compoundsare produced. The XAFS and UV−visible spectra ofthese compounds provide evidence for a binuclear structuresimilar to (H2EDTA)2Tc2(μ-O)2. The properties of theTc(IV) alkoxide complexes were determined and areconsistent with those observed for the soluble, lower-valent technetium complexes that complicate the treatmentof HLW at the Hanford site.
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