Dissolution of Technetium(IV) Oxide by Natural and Synthetic Organic Ligands Under both Reducing and Oxidizing Conditions
- ORNL
- Lawrence Berkeley National Laboratory (LBNL)
- Washington State University
Technetium-99 (Tc) in nuclear waste is a significant environmental concern due to its long half-life and high mobility in the subsurface. Reductive precipitation of Tc(IV) oxides [TcO2(s)] is an effective means of immobilizing Tc, thereby impeding its migration in groundwater. However, TcO2(s) is subject to dissolution by oxidants and/or complexing agents. In this study we ascertain the effects of a synthetic organic ligand, ethylenediaminetetraacetate (EDTA), and two natural humic isolates on the dissolution and solubility of Tc(IV) oxides. Pure synthetic TcO2(s) (0.23 mM) was used in batch experiments to determine dissolution kinetics at pH ~6 under both reducing and oxidizing conditions. All organic ligands were found to enhance the dissolution of Tc(IV) oxides, increasing their solubility from ~10-8 M (without ligands) to 4 10-7 M under strictly anoxic conditions. Reduced Tc(IV) was also found to re-oxidize rapidly under oxic conditions, with an observed oxidative dissolution rate approximately an order of magnitude higher than that of ligand-promoted dissolution under reducing conditions. Significantly, oxidative dissolution was inhibited by EDTA but enhanced by humic acid compared with experiments without any complexing agents. The redox functional properties of humics, capable of facilitating intra-molecular electron transfer, may account for this increased oxidation rate under oxic conditions. Our results highlight the importance of complex interactions for the stability and mobility of Tc, and thus for the long-term fate of Tc in contaminated environments.
- Research Organization:
- Oak Ridge National Laboratory (ORNL)
- Sponsoring Organization:
- SC USDOE - Office of Science (SC)
- DOE Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1018617
- Journal Information:
- Environmental Science & Technology, Journal Name: Environmental Science & Technology Journal Issue: 11 Vol. 45; ISSN 0013-936X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CHELATING AGENTS
DISSOLUTION
EDTA
ELECTRON TRANSFER
FUNCTIONALS
HALF-LIFE
HUMIC ACIDS
KINETICS
OXIDATION
OXIDES
OXIDIZERS
PRECIPITATION
Pertechnetate
RADIOACTIVE WASTES
SOLUBILITY
STABILITY
TECHNETIUM 99
mobilization
organic matter
oxidation
reduction