SELECTIVE SEPARATION OF URANYL-ION FROM TRUS IN A COMBINED SOLVENT-EXTRACTION PROCESS USING TETRAHYDROFURAN-2,3,4,5-TETRACARBOXYLIC ACID

Selective partitioning of uranyl from transuranic elements in a solven t extraction system which employs a neutral organophosphorus extractan t and an aqueous complexant has been demonstrated in a previous report . The extractant solution combines tyl(phenyl)-N,N-diisobutylcarbamoyl methylphosphine oxide (CMPO), diamyl(amyl)phosphonate (or tributylphos phate), and di(t-butylcyclohexano)-18-crown-6 in Isopar L, and is desi gned for simultaneous removal of strontium, technetium, lanthanides an d actinides from radioactive wastes. The aqueous complexant is tetrahy drofuran-2,3,4,5-tetracarboxylic acid (THFTCA). In this report, the se paration of UO22+ 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 pote ntiometric 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 pa rtially accounts for the selectivity. Ternary complexes involving UO22 + CMPO, and THFTCA in the extractant phase also appear to play a role.