Substituted malonamides as extractants for partitioning of actinides from nuclear waste solutions

Pentaalkyl malonamides are suggested as alternatives to organophosphorous reagents for the extraction of actinides from high level liquid waste generated during the reprocessing of irradiated fuels. With a view to study the extraction behaviour of these actinides from nitric acid medium, four diamides namely (1) N,N,N′,N′-tetrabutyl undecyl malonamide (TBUDMA), (2) N,N,N′,N′-tetrabutyl tetradecyl malonamide (TBTDMA), (3) N,N′-dimethyl-N,N′-dibutyl undecyl malonamide (DMDBUDMA) and (4) N,N′-dimethyl-N,N′-dibutyl tetradecyl malonamide (DMDBTDMA) were prepared by substitution on the basic skeletons of N,N,N′,N′-tetraalkyl-2-alkyl malonamides. The substituted diamides showed good extractability towards Am, Pu, Np and U into n-dodecane from nitric acid solutions of concentrations ranging from 3 to 8 M except for DMDBUDMA which showed third phase formation beyond 2 M HNO3. Extraction maxima for Am with TBUDMA and TBTDMA were seen at 6–7 M whereas DMDBTDMA showed maximum extraction at 5 M nitric acid. Am(III) and Pu(IV) extracted as trisolvates whereas U(VI) was extracted as disolvate. Distribution behaviour of fission products using DMDBTDMA was also investigated. DMDBTDMA was found to be a promising alternative to the TRUEX solvent for the actinide partitioning from simulated High Level Waste (HLW).