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A DGA-arm-grafted macrocyclic aza-crown ether ligand (Cr6DGA) was synthesized, and its solvent extraction behavior toward trivalent americium and europium in nitric acid medium was studied. The effects of various parameters such as the contact time, temperature, concentration of the extractant, and acidity on the extraction by Cr6DGA were investigated. It was found that in 3 mol/L HNO3, the SFEu/Am value was about 2. The complexation energies calculated by DFT showed that the Eu­(III) complexes were more stable than the corresponding Am­(III) complexes in gas, aqueous, and organic phases. Furthermore, the coordination study showed that the metal/ligand ratio of the extracted species was 1:2 by mass spectrometry (MS) analysis. The time-resolved laser-induced fluorescence spectra (TRLFS) further proved that the extracted species contained one water molecule, and so the composition of the extracted complexes may be [EuL2NO3(H2O)]2+ or [EuL2(NO3)2(H2O)]+. Finally, DFT calculations revealed that [EuL2(NO3)2(H2O)]+ is a more stable species and the binding energy of Eu­(III) with the DGA unit is lower than that with the crown unit.

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Three octyl-extended bis-triamide extractants (L1–L3) were designed and synthesized for the selective solvent extraction of Th­(IV) over U­(VI) in a kerosene–HNO3 system. L1 and L2 exhibited good extraction property and selectivity toward Th­(IV) over U­(VI) and reached extraction equilibrium within 10 min. In a wide range of a HNO3 concentration from 0.1 to 3.0 M, the separation factor of Th­(IV) over U­(VI) (SFTh/U) of L1 and L2 ranged from 12.1 ± 1.6 to 123.0 ± 20.2 and 15.2 ± 2.4 to 88.1 ± 14.9, respectively. Slope analysis indicated that Th­(IV) was extracted as different species under different HNO3 concentrations, in which the slopes were 2.08 ± 0.20, 1.61 ± 0.03, and 1.54 ± 0.03 for L1 and 2.37 ± 0.22, 2.07 ± 0.17, and 1.76 ± 0.18 for L2 under 0.1, 1.0, and 3.0 M HNO3, respectively. A continuous variation method (Job plot) illustrated a 1.5:1 ligand/thorium (L/Th) ratio in a methanol phase, indicating that L1/L2 and Th­(IV) could form mixed 1:1 and 2:1 L/Th extracted complexes. Extended X-ray absorption fine structure (EXAFS) and density functional theory (DFT) calculations revealed that the extracted complexes of L1 and L2 with Th during the extraction process at 0.1 M HNO3 were [2L1·Th·3­(NO3)]+ and [2L2·Th·3­(NO3)]+.

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