SELECTIVE SEPARATION OF URANYL ION FROM TRU'S IN A COMBINED SOLVENT EXTRACTION PROCESS USING TETRAHYDROFURAN-2,3,4,5-TETRACARBOXYLICACID

Abstract

Selective partitioning of uranyl from transuranic elements in a solvent extraction system which employs a neutral organophosphorus extractant and an aqueous complexant has been demonstrated in a previous report. The extractant solution combines octyl(phenyl)-N,N-diisobutylcarbamoylrnethylphosphine oxide (CMPO), diamyt(amyl)phosphonate (or tributylphosphate), and di(t-butylcyclohexano)-18-crown-6 in Isopar L, and is designed for simultaneous removal of strontium, technetium, lanthanides and actinides from radioactive wastes. The aqueous complexant is tetrahydrofuran-2,3,4,5-tetracarboxylic acid (THFTCA). In this report, the separation of UO₂ ²⁺ from Np(IV), Eu(III), Am(III), and Pu(IV) using the Combined Process Solvent has been optimized. Potentiometric titration and NMR spectroscopic results describe the distribution of THFTCA into the organic phase as a function of acidity and [THFTCA]. Further potentiometric titration experiments have determined the stoichiometry and stability of uranyl complexes in the aqueous phase. The thermodynamic data indicate that the uranyl complexes are anomalously weak which partially accounts for the selectivity. Ternary complexes involving, UO₂ ²⁺ CMPO, and THFTCA in the extractant phase also appear to play a role.