Separation of rate earth elements by continuous stripping with DTPA from DIDPA solvent

Continuous stripping of rare earth elements (REs) with the diethylenetriaminepentaacetic acid (DTPA) solution from the diisodecylphosphoric acid (DIDPA) solvent was examined with lab-scale mixersettlers to develop a process for the separation of trivalent actinides (An(III)) from the mixture of An (III) and REs. DIDPA is an extractant applied to separate transuranic elements from high-level liquid waste in the 4-Group Partitioning Process developed in Japan Atomic Energy Research Institute (presently: Japan Atomic Energy Agency). The experiment on continuous stripping with the DTPA solution of a little higher pH than an appropriate pH for selective stripping of An (III) showed that Nd could be selectively stripped from the DIDPA solvent containing La and Nd. The stripping yield of Nd was found to be higher than 99.8%, whereas 97.6% of La was left in the solvent. The pH of the DTPA solution decreased in the stages near the solvent feed, which was explained by the extraction of ammonium ion. These findings make it possible to predict quantitatively the behavior of An(III) and REs in the various conditions of the DIDPA-DTPA continuous stripping system. (author)