SUBSTITUTED MALONAMIDES AS EXTRACTANTS FOR PARTITIONING OF ACTINIDES FROM NUCLEAR WASTE SOLUTIONS

Pentaalkyl malonamides are suggested as alternatives to organophosphor ous reagents for the extraction of actinides from high level liquid wa ste 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 malonami de (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 prepar ed by substitution on the basic skeletons of N,N,N',N'-tetraalkyl-2-al kyl malonamides. The substituted diamides showed good extractability t owards 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 T BUDMA and TBTDMA were seen at 6-7 M whereas DMDBTDMA showed maximum ex traction at 5 M nitric acid. Am(III) and Pu(IV) extracted as trisolvat es whereas U(VI) was extracted as disolvate. Distribution behaviour of fission products using DMDBTDMA was also investigated. DMDBTDMA was f ound to be a promising alternative to the TRUEX solvent for the actini de partitioning from simulated High Level Waste (HLW). (C) 1998 Elsevi er Science Ltd. All rights reserved.