ACTINIDE-ALUMINATE SPECIATION IN ALKALINE RADIOACTIVE WASTE
Highly alkaline radioactive waste tanks contain a number of transuranic species, in particular U, Np, Pu, and Am--the exact forms of which are currently unknown. Knowledge of actinide speciation under highly alkaline conditions is essential towards understanding and predicting their solubility and sorption behavior in tanks, determining whether chemical separations are needed for waste treatment, and designing separations processes. Baseline washing of tank sludges with NaOH solutions is being proposed to reduce the volume of HLW. Alkaline pretreatment of HLW will be needed to remove aluminum [as NaAl(OH){sub 4}] because it significantly reduces the HLW volume; however, aluminate [Al(OH){sub 4}{sup -}] enhances actinide solubility via an unknown mechanism. Thus, alkaline wash residues may require an additional treatment to remove actinides. The results of this research will determine the nature TRU (Np, Pu, Am) speciation with aluminate anions under alkaline, oxidizing tank-like conditions. Specific issues to be addressed include solubility of these actinides, speciation in aluminate-containing alkaline supernatants, the role of actinide redox states on solubility, and partitioning between supernatant and solid phases, including colloids. Studies will include thermodynamics, kinetics, spectroscopy, electrochemistry, etc. It is already known, for example, that certain high valent forms of NF and Pu are very soluble under alkaline conditions due to the formation of anionic hydroxo complexes, AnO{sub 2}(OH){sub 4}{sup 2-} and AnO{sub 2}(OH){sub 5}{sup 3-}. The presence of aluminate ions causes the actinide solubilities to increase, although the exact species have only been determined during this program. We are continuing to characterize high-valent TRU elements bound to oxo, water, OH{sup -}, under waste-like and sludge washing conditions. These conditions are in the range of 1-3 M excess hydroxide, {approx}0.2 M carbonate, {approx}0.5 M aluminate, for a total sodium of 2-4 mols/kg. Molecular structure-specific probes include vibrational (IR and Raman), multinuclear nuclear magnetic resonance (NMR), extended X-ray absorption fine structure (EXAFS), luminescence, optical absorption (UV-Vis-conventional and photoacoustic) spectroscopies. We anticipate that the knowledge gained during this project will impact on clean-up approaches to significantly reduce costs, schedules, and risks.
- Research Organization:
- DOE (US)
- Sponsoring Organization:
- USDOE Office of Environmental Management (EM) (US)
- DOE Contract Number:
- FG07-98ER14940
- OSTI ID:
- 833174
- Report Number(s):
- EMSP-65318-2001; R&D Project: EMSP 65318; TRN: US0406437
- Resource Relation:
- Other Information: PBD: 1 Jun 2001
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
54 ENVIRONMENTAL SCIENCES
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ACTINIDES
ALUMINATES
ALUMINIUM
ANIONS
COLLOIDS
ELECTROCHEMISTRY
FINE STRUCTURE
KINETICS
LUMINESCENCE
NUCLEAR MAGNETIC RESONANCE
RADIOACTIVE WASTES
SODIUM
SPECTROSCOPY
THERMODYNAMICS
WASTE PROCESSING