The use of tetra-alkylcarbamides as novel ligands: N,N-butyl-N’,N’-hexylurea (L1: ABHU), and N,N-butyl-N’,N’-pentylurea (L2: ABPU), for the solvent extraction and complexation behaviors of uranium(VI) was synthesized and investigated in this study. The effects of HNO3and NO3−concentrations in the aqueous phase on the distribution ratio of U(VI) were examined. Under 5 mol/L HNO3concentration,DUreached 5.02 and 4.94 respectively without third-phase formation. During the extraction, slope measurements and IR spectral analysis revealed that the U(VI) complexes are a form of UO2(NO3)2·2Lfor both ligands. In addition, thermodynamic studies showed that the uranium extraction reaction was a spontaneous exothermic reaction. The deep structural analysis of the complexes was realized with DFT calculation. The bond length, bond properties, and topology of the complexes were discussed in detail to analyze the extraction behavior. This study enriches the coordination chemistry of U(VI) by tetra-alkylcarbamides, which may offer new clues for the design and synthesis of novel ligands for the separation, enrichment, and recovery of uranium in the nuclear fuel cycle.Keywords:uranium;extraction;tetra-alkylcarbamides;DFT calculation
In this work, the solvent extraction and complexation behaviors of U(VI) by two novel asymmetrical tetra-alkylcarbamides, N,N’-butyl-N,N’-hexylurea ( L1 : SBHU ) and N,N’-butyl-N,N’-pentylurea ( L2 : SBPU ) in HNO 3 media were systematically investigated. Both two ligands extract U(VI) more effectively than other metals such as Pu(IV), Np(IV), and Th(IV) in a wide range of acidity. Under 5 mol/L HNO 3 , D U reached 5.25, while D Pu = 1.08, D Np = 0.11, D Th = 0.13.. Additionally, no third-phase was present by the extraction of highly uranium concentration solution with SBHU even under 7 mol/L HNO 3 after four cycles demonstrating good acid resistance and resistance to the formation of the third phase. Slope analyses and FT-IR indicate that the U(VI) complexes are a form of UO 2 (NO 3 ) 2 ·2 L for the two ligands during the extraction. Additionally, based on the DFT calculations, the NBO analysis, and topological analysis were analyzed in detail. The results demonstrate that the interactions between ligands and U(VI) are shown mainly as ionic characteristics, and the ligand-to-metal charge transfer was also observed. This study enriches the coordination chemistry of actinides: Th(IV), U(VI), Np(IV), Am(III), and Pu(IV) by tetra-alkylcarbamides, which may shed light on the design and synthesis of novel U(VI) selective ligands.
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