CITRATE-BASED TALSPEAK ACTINIDE-LANTHANIDE SEPARATION PROCESS

Lanthanide elements are produced in relatively high yield by fission o f U-235. Almost all the lanthanide isotopes decay to stable nonradioac tive lanthanide isotopes in a relatively short time. Consequently, it is highly advantageous to separate the relatively small actinide fract ion from the relatively large quantities of lanthanide isotopes. The T ALSPEAK process (Trivalent Actinide Lanthanide Separations by Phosphor us-reagent Extraction from Aqueous Complexes) is one of the few means available to separate the trivalent actinides from the lanthanides. Pr evious work based on the use of lactic or glycolic acid has shown dele terious effects of some impurity ions such as zirconium(IV), even at c oncentrations on the order of 10(-4) M. Other perceived problems were the need to maintain the pH and reagent concentrations within a narrow range and a significant solubility of the organic phase at high carbo xylic acid concentrations. Our cold experiments showed that replacing the traditional extractants glycolic or lactic acid with citric acid e liminates or greatly reduces the deleterious effects produced by impur ities such as zirconium. An extensive series of batch tests was done u sing a wide range of reagent concentrations at different pH values, te mperatures, and contact times. The results demonstrated that the citra te-based TALSPEAK can tolerate appreciable changes in pH and reagent c oncentrations while maintaining an adequate lanthanide extraction. Exp eriments using a three-stage glass mixer-settler showed a good lanthan ide extraction, appropriate phase disengagement, no appreciable delete rious effects due to the presence of impurities such as zirconium, exc ellent pH buffering, and no significant loss of organic phase.