Technetium-99 is a fission product of 235U and has a half-life of 2.13 × 105 years. Past radioactive waste management practices have led into Tc-99 being released in the environment in several DOE sites such as Savannah River and Hanford. The redox chemistry of technetium plays a large role in its mobility in the environment. Pertechnetate is highly mobile, however, reduced forms of Tc-99, such as TcO2 and Tc2S7 can be considered for the immobilization of Tc-99 in the environment. The immobilization of technetium is key for remediation efforts. The objective of this project is to compare dissolution kinetics of technetium oxides and technetium sulfides, as immobilization forms in the environment, under oxidizing conditions. Batch dissolution experiments were performed on benchtop where each sample comprised of 2 mg of TcO2 or Tc2S7 suspended in 10 mM bicarbonate at a pH of 8. The samples were in triplicate. The dissolution of technetium(IV) phases was monitored by measuring soluble pertechnetate in the aqueous phase by using Liquid Scintillation Counting. The results showed a complete re-oxidation of technetium oxide within four days, whereas technetium sulfides oxidized at ~50% within a month, indicating that this is a much more recalcitrant reduced form of Tc-99, and hence more appropriate for longer term environmental remediation.

Comparative dissolution kinetics of technetium oxides and technetium sulfides under oxidizing conditions

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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