The design and development of a water-soluble heterocyclic ligand are believed to be an alternative way for improving the separation efficiency of actinides from lanthanides. Herein, we designed and synthesized a novel hydrophilic multidentate ligand: disulfonated N,N′-diphenyl-2,9-diamide-1,10phenanthroline (DS-Ph-DAPhen) with soft and hard donor atoms, as a masking agent in aqueous solutions for Am(III) separation. The combination of N,N,N′,N′-tetraoctyldiglycolamide in kerosene and DS-Ph-DAPhen in aqueous phases could separate Am(III) from Eu(III) across a range of nitric acid concentrations with very high selectivity. The coordination behaviors of Eu(III) with DS-Ph-DAPhen in aqueous solutions were studied by UV−vis titration, electrospray ionization mass spectrometry, and Fourier transform infrared spectra. The results indicated that Eu(III) ions could form both 1:1 and 1:2 complexes with the DS-Ph-DAPhen ligand in aqueous solution. Density functional theory calculation suggests that there are more covalent characters for Am−N bonds than that for Eu−N bonds in the complexes, which supports the better selectivity of the DS-Ph-DAPhen ligand toward Am(III) over Eu(III). This work demonstrates a feasible alternative approach to separating trivalent actinides from lanthanides with high selectivity.
Although 1,10-phenanthroline-based ligands have recently shown vast opportunities for the separation of trivalent actinides (Ans(III)) from lanthanides (Lns(III)), the optimization and design of the extractant structure based on the phenanthroline framework remain hotspots for further improving the separation. Following the strategy of hard and soft donor atom combination, for the first time, the quinoline group was attached to the 1,10-phenanthroline skeleton, giving a lipophilic ligand, 2,9-diacyl-bis((3,4-dihydroquinoline-1((2H)-yl)-1),10-phenanthroline (QL-DAPhen)), for Am(III)/Eu(III) separation. In the presence of sodium nitrate, the ligand can effectively extract Am(III) over Eu(III) in HNO 3 solution, with the separation factor (SF Am/Eu ) ranging from 29 to 44. The coordination chemistry of Eu(III) with QL-DAPhen was investigated by slope analysis, NMR titration, UV−vis titration, Fourier transform infrared spectroscopy, electrospray ionization-mass spectrometry, and theoretical calculations. The experimental results unanimously confirm that the ligand forms both 1:1 and 1:2 complexes with Eu(III), and the stability constants (log β) of each of the two complexes were obtained. Density functional theory calculations show that the Am−N bonds have more covalent characteristics than the Eu−N bonds in the complexes, which reveals the reason why the ligand preferentially bonds with Am(III). Meanwhile, the thermodynamic analysis reveals that the 1:1 complex is more thermodynamically stable than the 1:2 complex. The findings of this work have laid a solid theoretical foundation for the application of phenanthrolinebased ligands in the separation of An(III) from practical systems.
The extraction of Eu(iii), U(vi), and Pu(iv) from 0.1-3 M HNO solutions by using N,N-di(2-ethyl-hexyl)-diglycolamic acid (HDEHDGA) is presented. In contrast to common organic acid extractants, such as long-chain carboxylic acids, organophosphorus acids, and derivatives of beta-diketones, losing extractability, HDEHDGA exhibits a strong ability to extract lanthanide and actinide ions from high HNO solutions.
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