Despite recent advances, effective actinide (An) -lanthanide (Ln) separation in used nuclear fuel (UNF) by solvent extraction remains a challenge. In order to assist in overcoming this challenge, a new hydroxypyridinone (HOPO) type ligand, 1-(1,2-HOPO)-decyl (1), was synthesized and compared with the known 4-LI(1,2-HOPO) (2) and the 3,4,3-LI(1,2-HOPO) (3) analogs for Ln(III) complexation. The ultimate goal of the project is to achieve selective An/Ln separation by liquid-liquid extraction by either selectively forming complexes with An vs. Ln in the organic phase, or by selective holdback in the aqueous phase. The complexation properties of these ligands with several Ln were studied via UV-Visible, fluorescence, and NMR titrations with logβ1:2 M(1)2 values of 10.1±0.3 for La(III), 9.8±0.1 for Eu(III), and 9.3±0.4 for Sm(III) in MeOH via UV-Vis titrations and non-linear regression analysis of the binding curves. NMR titrations of 2 in D2O showed clear evidence of complexation with distinct observed resonances for the formed complex in slow exchange with the ones of the free ligand, and a determined binding constant (from the integral ratios) of logβ1:2 = 7.88±0.08 for LuIII(2)2. The electrochemical behavior of 2 with Eu(III) was also studied in 0.1 M HNO3. The ligand demonstrated both surface-based and solution-based redox chemistry with altered redox behavior, when complexed to Eu(III). Extraction studies also showed potential application of 1 as an f-element extractant from alkaline solutions, with 99.5±2.5% Sm(III) extraction from pH 10.0 into CHCl3 (0.02 M of 1), followed by 99.1±3.8 % Sm(III) recovery in 3 M HNO3 after stripping.

Hydroxypyridinone-derived chelators for f-element complexation in used nuclear fuel conditions

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