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- Author or Editor: N. C. Schroeder x
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Summary
A significant amount of technetium in Hanford waste exists as unidentified, stable, reduced technetium complexes. In order to facilitate the identification of these non-pertechnetate species we have developed a separation scheme which involves three major steps: (1) pretreatment of the sample with Zn2+, (2) cation-exchange to remove gross activity (90Sr), and (3) size exclusion chromatography to remove residual activity and separate the technetium fractions. Addition of Zn2+ is used to compete for the complexants that bind strontium without perturbing the pH of the sample. Technetium recovery was ~50%. One technetium fraction was obtained free of residual gross activity.
Summary
The autoreduction of pertechnetate (99TcO4 -) to Tc(IV/V) alkoxide complexes in aqueous, alkaline, solutions is described. Solutions of sodium pertechnetate (0.01M) reacted with nitrogen and oxygen donor ligands (1.0M) in 2M sodium hydroxide. Solutions containing nitrogen donor ligands (e.g., EDTA) showed the initial formation of lightly colored complexes followed by rapid decomposition in air. In contrast, stable, reduced complexes were formed within minutes of mixing pertechnetate with mono- and disaccharides in strong base, as indicated by a persistent color change. Chemical yields of these reactions were determined by thin layer chromatography or paper chromatography and radiochemically assayed with a Bioscan imaging scanner. Analysis by UV-vis spectroscopy suggested that Tc(IV) or Tc(V) complexes were produced, with the oxidation state dependent on the reducing ligand. These experiments may help explain the reduction of pertechnetate to the soluble complexes that have been found in the Hanford nuclear waste tanks.
Abstract
More than 50% of the technetium in Hanford 101-SY and 103-SY tank waste is not pertechnetate (TcO4 –). These non-pertechnetate species (TcN) are stable, soluble, reduced complexes of technetium. In order to remediate these waste, it will be necessary to oxidize these species to TcO4 –. For radioanalytical purposes, oxidation requires digestion in Ce(IV)/16M HNO3. Many oxidants are ineffective. Sodium peroxydisulfate, sodium peroxydisulfate/silver(I), and ozone oxidize all of the technetium species to pertechnetate.
