SOLVENT EXTRACTION SEPARATIONS OF TRiVALENT LANTHANIDE AND ACTINIDE IONS USING AN AQUEOUS AMINOMETHANE-DIPHOSPHONIC ACID

摘要

The possibility of separating the trivalent lanthanides, represented by Eu~(3+), and actinides, represented by Cf~(3+), using bis-(2-ethylhexyl)phosphoric acid (HDEHP) in toluene and an aqueous phase containing N-piperidinomethane-l,l-diphosphonic acid (PMDPA), has been investigated. This modified aqueous phase offers potential advantages over the diethylenetriaminepentaacetic acid based TALSPEAK process because of the improved complexation properties of PMDPA in acidic solutions, and the ability to decompose PMDPA before disposal. Extraction experiments were conducted at 25°C in 2 M NaClO_4 between -log [H~+] 1 and 2. The studies enabled us to derive the aqueous phase speciation, the stability constants of the aqueous complexes, and the Cf/Eu separation factors. Despite the presence of an amino group in PMDPA that should favor the retention of the actinides in the aqueous phase, the Cf/Eu separation factors are near unity under the conditions studied.