Selective Complexation and Separation of Uranium(VI) from Thorium(IV) with New Tetradentate N,O-Hybrid Diamide Ligands: Synthesis, Extraction, Spectroscopy, and Crystallographic Studies

Abstract

An unmet challenge in the thorium-uranium fuel cycle is the efficient separation of uranium from thorium. Herein, two new tetradentate N,O-hybrid ligands, N,N′-diethyl-N,N′-di-p-tolyl-2,2′-bipyridine-6,6′-dicarboxamide (Et-Tol-BPDA) and N,N′-diethyl-N,N′-di-p-tolyl-2,2′-bipyrimidine-4,4′-dicarboxamide (Et-Tol-BPymDA), comprising a bipyridine or bipyrimidine core and amide moieties were designed and synthesized for selectively complexing and separating U(VI) from Th(IV). The high U(VI)/ Th(IV) extraction selectivity was achieved by Et-Tol-BPDA (SF U/Th = 33 at 3 M HNO 3 ) and Et-Tol-BPymDA (SF U/Th = 73 at 3 M HNO 3 ) in nitric acid solutions. The extraction process for U(VI) or Th(IV) with these two ligands primarily proceeded through the solvation mechanism, as evidenced by slope analyses. Thermodynamic studies for the extraction of U(VI) and Th(IV) revealed a spontaneous process. Results from UV−vis spectroscopic titration and slope analyses demonstrated that U(VI) and Th(IV) each form a 1:1 complex with the two ligands both in the monophasic organic solution and the biphasic extraction system. The stability constants of the 1:1 complexes of Et-Tol-BPDA or Et-Tol-BPymDA with U(VI) were found to be larger than those with Th(IV), which coincide well with the high U(VI)/Th(IV) extraction selectivity. The solid-state structures of Et-Tol-BPDA, Et-Tol-BPymDA, and 1:1 complexes of the two ligands with U(VI) or Th(IV) were analyzed by X-ray diffraction technique. The results from this work implicate the potential of bipyridine-and bipyrimidinederived diamide ligands for uranium/thorium separation.

Kinetic features of solvent extraction by N,O-donor ligands of f-elements: a comparative study of diamides based on 1,10-phenanthroline and 2,2′-bipyridine

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Palladium recovery from acidic solution with phenanthroline-based covalent organic polymers as adsorbents for efficient heterogeneous catalysis

“…Nuclear energy is deemed as a greener and safer energy source than traditional fossil fuels, with almost negligible CO 2 emission but much higher energy output than other emerging options including solar, wind, tidal, etc . 1,2 Nuclear power has contributed approximately 11% of the total electricity in the world, and the proportion is still increasing fast with the explosively rapid development of contemporary industries and the global energy shortage. 3 However, the associated radioactive nuclear wastes have brought severe threats to the environmental system, which are of high priority to deal with for sustainable development and public acceptance of nuclear energy.…”

First Report on a 1-Cycle Solid-Phase Extraction Method for Selective Separation of Am3+ and Eu3+: Use of BTP-Grafted Silica Decorated on Activated Carbon

“…The separation of trivalent actinides and lanthanides is one of the most difficult tasks in separation chemistry due to their similar chemical properties. − Although much progress has been made concerning the development of extractants, the liquid–liquid extraction process has certain drawbacks, such as excess utilization of volatile organic compound (VOC)-based solvents, secondary waste accumulation, emulsion formation between phases, and multistage extraction processes, which will affect the economic performance of the process in large-scale practical applications. Alternatively, solid-phase extraction technique has been considered as a relatively “green” separation method with high separation efficiency due to the possibility of column mode operation and easy scale-up options.…”