The feasibility of using supercritical carbon dioxide as a substitute extraction solvent in nuclear reprocessing was tested by the extraction of lanthanide ions from acidic solution.Lanthanides were extracted from 6 HN03-3 M LiN03 solutions using tributyl phosphate-(TBP-) modified CO2.Synergistic effects were also investigated using a combination of thenoyltrifluoroacetone (TTA) and TBP-modified COj as the extractant. It was found that near-quantitative extraction ofSm3+, Eu3*, Gd3*, and Dy3* was achieved while the extraction efficiencies for La3+, Ce3+, Yb3+, and Lu3+ were much lower. The light lanthanides extracted as Ln(N03)3-3TBP and the heavy lanthanides extracted as Ln(N03)3-2TBP when TBPmodified CO2 was used as the extractant, while Ln(TTA)3• 3TBP and Ln(TTA)3-2TBP adducts were extracted when TTA was added to TBP-modified CO2.Trivalent lanthanides and actinides are byproducts of nuclear processes and must be separated from dissolved fuel solutions during reprocessing operations. One drawback to such processing systems is the generation of large amounts of organic waste in the form of spent solvents. It may be possible to minimize the generation of liquid wastes by substituting a less expensive, easily recyclable, and generally nontoxic supercritical fluid such as CO2 in nuclear waste and fuel processing schemes. In addition, extractions using supercritical CO2 are generally more efficient in terms of speed as compared to conventional solvent extraction due to the more favorable mass transport properties of a supercritical fluid.* 1Since the direct extraction of metal ions using supercritical CO2 is inefficient due to weak van der Waals interactions and due to the need for cationic charge neutralization, it has been suggested that a chelating agent be introduced into the supercritical fluid extraction stream in order to extract metals.2 While research involving the extraction of metal ions using supercritical CO2 containing a dissolved ligand is in its infancy, the extraction of transition metals from aqueous and solid materials2•3 and f-block elements from solid matrices4 using a dissolved ligand in the CO2 phase has been accomplished.The extraction of metal ions using this in situ chelation and extraction method has been shown to be more efficient with the use of alcohol-modified CO2; however, it may be possible to use a modifier which is itself a complexing agent. One such modifier that has been used in the supercritical fluid
Hydrogen evolution from 6°C o r-and 3 H ,B-irradiated molecular sieve SA adsorbing HTO was measured. The results showed an additional evolution of H 2 (HT) gas due to energy transfer from molecular sieve to adsorbed water in both r-and ,8-irradiations, and the yield at a given irradiation dose was higher than that from radiolysis of liquid HTO but lower than that in the silica gel-HTO system. The additional yield was formulated as a function of the amount of adsorbed water and irradiation dose. However a large difference in hydrogen yields was observed between r-and ,8-irradiations contrary to silica gel-HTO system. A possible reason is considered.
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