Development of Fundamental Data on Chemical Speciation and Solubility for Strontium and Americium in High-Level Waste: Predictive Modeling of Phase Partitioning During Tank Processing
In this project, Pacific Northwest National Laboratory (PNNL) and Florida State University (FSU) are investigating the speciation of Sr and Am/Cm in the presence of selected organic chelating agents over ranges of hydroxide, carbonate, ionic strength, and competing metal ion concentrations present in high-level waste (HLW) stored in tanks at Hanford and other U.S. Department of Energy (DOE) sites. The chelating agents that are being studied are EDTA (ethylenediaminetetraacetic acid), HEDTA (N-(2-hydroxyethyl)ethylenediaminetriacetic acid), NTA (nitrilotriacetic acid), IDA (iminodiacetic acid), citrate, and oxalate. The project comprises integrated research tasks that approach the problem of chemical speciation using macroscopic thermodynamic measurements of metal-ligand competition reactions, molecular modeling studies to identify structures or complexes of unusual stability, and mass spectrometry measurements of complex charge/mass ratio that can be applied to mixed metalchelate systems. This fundamental information then is used to develop thermodynamic models designed to predict changes in chemical speciation and solubility resulting from various tank processing conditions. In this way we can develop new approaches that address fundamental problems in aqueous speciation and, at the same time, provide useful and practical information needed for tank waste processing. Current strategies for reducing the total volume of radioactive tank waste requiring disposal at Hanford and other DOE sites call for the development of methods that can be used to selectively dissolve and remove non-radioactive elements, such as Al, P, and Cr, while retaining or precipitating the radioactive elements, including Sr and the actinide elements, in the tank sludge. This partitioning between solids and precipitates is fundamentally dependent on the chemical speciation of the elements present in the tank processing solutions. Of particular importance is separation of the radioactive and hazardous actinide elements and fission products from the sludge and supernatants, particularly from supernatants containing high concentrations of strong chelating agents that can act to dissolve the actinides and fission products as well as interfere with subsequent metal ion extraction processes. Specifically, the fundamental understanding of chemical speciation reactions gained from these studies will help us identify other potential mechanisms (e.g., competition, displacement, or other reactions) that could be used for removing Sr and Am/Cm from organic chelates present in the HLW.
- Research Organization:
- Pacific Northwest National Lab., Richland, WA; The Florida State University, Tallahassee, FL (US)
- Sponsoring Organization:
- USDOE Office of Environmental Management (EM) (US)
- DOE Contract Number:
- FG07-02ER63222
- OSTI ID:
- 833734
- Report Number(s):
- EMSP-73749-2002; R&D Project: EMSP 73749; TRN: US200430%%1769
- Resource Relation:
- Other Information: PBD: 1 Jun 2002
- Country of Publication:
- United States
- Language:
- English
Similar Records
Chemical Speciation of Americium, Curium and Selected Tetravalent Actinides in High Level Waste
Chemical speciation of strontium, americium, and curium in high-level waste: Predictive modeling of phase partitioning during tank processing. 1997 annual progress report