Abstract
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.
Highlights
Spent nuclear fuel reprocessing is becoming a necessity in the generation of nuclear energy
Partitioning and transmutation (P&T) strategy is becoming vital for the management of high-level liquid waste (HLLW).2
Three OBDAs 1a–c having different amine components have been synthesized from commercially available starting materials as shown in Scheme 1
Summary
Spent nuclear fuel reprocessing is becoming a necessity in the generation of nuclear energy. The acidic raffinate produced is known as high-level liquid waste (HLLW), which contains significant amounts of trivalent lanthanides and minor actinides (Am, Cm and Np) It contains a small amount of Pu and fission products (137Cs, 90Sr, 106Ru etc.). The increase in chain length from one carbon to two carbons between the central ether oxygen atom and the amide moieties in ODPA has been attempted but with poor extraction abilities.7b As. mentioned above, the only reported diglycolamides on a rigidified tetrahydrofuran platform (as a mixture of cis and transisomers) have been reported by Iqbal et al.7a We were curious to develop tridentate diamide based ligands 1 based on conformationally constrained 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid, where the ether–oxygen is positioned at the bridgehead and a chain of two carbon atoms lies between the ether oxygen and the amide moieties (Fig. 2). We describe the synthesis of three conformationally constrained bridged 7-oxabicyclo[2.2.1]heptane-2,3dicarboxamides 1a–c (OBDA 1a–c) and their extraction properties for 241Am(III), (152+154)Eu(III), 239Pu(IV), 233U(VI) from the nitric acid medium using 15% isodecyl alcohol (IDA)/ n-dodecane as a diluent mixture
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