Products of pertechnetate radiolysis in highly alkaline solution: structure of TcO2 x xH2O.
The chemistry of technetium in certain high-level nuclear waste (HLW) tanks at the Hanford Site complicates the treatment and vitrification of HLW. A major problem is the presence, in certain tanks, of unidentified, lower-valent technetium species, which are difficult to remove from the waste by current separation processes. Radiolytic reduction of TcO4- in alkaline solutions containing selected organic compounds, approximating the conditions in HLW, was investigated to determine the classes of compounds that can be formed under these conditions. Insoluble TcO2 x xH2O is the primary radiolysis product with the majority of organic compounds investigated, including citrate, dibutyl phosphate, and aminopolycarboxylates. X-ray absorption fine structure (XAFS) measurements show that TcO2 x xH2O has a one-dimensional chain structure consisting of edge-sharing TcO6 octahedra with bridging oxide and trans water ligands. When diols, such as ethylene glycol, are present, only soluble, Tc(IV) alkoxide compounds are produced. The XAFS and UV-visible spectra of these compounds provide evidence for a binuclear structure similar to (H2EDTA)2Tc2(mu-O)2. The properties of the Tc(IV) alkoxide complexes were determined and are consistent with those observed for the soluble, lower-valent technetium complexes that complicate the treatment of HLW at the Hanford site.
Lukens
Wayne W
WW
Chemical Sciences Division, The Glenn T. Seaborg Center, Ernest O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA. WWLukens@lbl.gov
Bucher
Jerome I
JI
Edelstein
Norman M
NM
Shuh
David K
DK
D010100:Oxygen / Q000737:chemistry; D011850:Radioactive Waste; D019275:Radiopharmaceuticals / Q000737:chemistry*; D012037:Refuse Disposal / Q000379:methods; D013670:Sodium Pertechnetate Tc 99m / Q000737:chemistry*; D017556:Technetium Compounds / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D011850:Radioactive Waste; D019275:Radiopharmaceuticals; D017556:Technetium Compounds; D014867:Water; D013670:Sodium Pertechnetate Tc 99m; D010100:Oxygen