Synthesis and extraction studies with a rationally designed diamide ligand selective to actinide(iv) pertinent to the plutonium uranium redox extraction process.

A new class of conformationally constrained oxa-bridged tricyclo-dicarboxamide (OTDA) ligand was rationally designed for the selective extraction of tetravalent actinides pertinent to the Plutonium Uranium Redox EXtraction (PUREX) process. Two of the designed diamide ligands were synthesized and extraction studies were performed for Pu(iv) from HNO3 medium. The mechanism of extraction was investigated by studying various parameters such as feed HNO3, NaNO3 and OTDA concentrations. The nature of the extracted species was found to be [Pu(NO3)4(OTDA)]. One of the OTDA ligands was elaborately tested and showed the selective extraction of Pu(iv) and Np(iv) over other actinide species, viz., U(vi), Np(v), Am(iii), lanthanides and fission products contained in a nuclear waste from the PUREX process. DFT calculations predicted the charge density on each of the coordinating 'O' atoms of OTDA supporting its high Pu(iv) selectivity over other ions studied and also provided the energy optimized structure of OTDA and its Pu(iv) complex.

Design, synthesis and extraction studies of a new class of conformationally constrained (N,N,N',N'-tetraalkyl)7-oxabicyclo[2.2.1]heptane-2,3-dicarboxamides.

A new class of conformationally constrained 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxamides (OBDA) of three secondary amines was synthesized, and their extraction behavior for trivalent and tetravalent actinides in HNO3 medium was studied. Amongst the diamides, N,N-bis-2-ethylhexyl substituted diamide showed the best results for actinide extraction. This diamide also exhibited a very low level of extraction for Sr(ii) and Ru(iii) which is desirable, thus providing higher selectivity for actinides. The stripping of extracted metal ions was achieved using 0.1 M oxalic acid for Pu(iv) or pH ∼ 2 solution for Am(iii). Third phase formation was not observed for the OBDA ligand even for a higher concentration of Eu up to 5 g L(-1) with retention of good DEu. The tridentate nature of the OBDA ligand was ascertained by studying the IR and NMR spectra of the Eu(iii) complex with the ligand. The OBDA showed the formation of a mixture of mono- and di-solvated species of Eu(iii) as indicated by the slope analysis method and ESI-MS. Density functional theoretical (DFT) study was carried out to determine the energy optimized structure of the free ligand and its Am(3+) complex.