Tuning the extraction mechanism of uranyl ion in bicyclooctanium, propylpyridinium, piperidinium and imidazolium based ionic liquids: First ever evidence of 'cation exchange', 'anion exchange' and 'solvation' mechanism

A novel diamide ligand, 5-bromo-N1, N3-diisopropylisophthalamide has been synthesized and characterized by FTIR, H-1 NMR, and C-13 NMR. The extraction mechanism of uranyl ion with the diamide ligand has been studied in unexplored ionic liquid families. For the same metal-ligand system; cation exchange, anion exchange, and solvation mechanism can be predominately achieved by changing the ionic liquid system. The experimental results suggest that the change in extraction mechanism is induced by the cations of the ionic liquids. In bicyclooctanium ionic liquid, the extracted species was [UO2(NO3)(3)L-2](-); In piperidinium and pyridinium-based ionic liquid, the species were UO2(NO3)(2)L and UO2(NO3)(2)L-2 respectively. In imidazolium-based ionic liquid, the species was [UO2(NO3)L](+). Though the extraction efficiency in methylpyridinium and bicyclooctanium based ionic liquids are better, the pipiredinium and imidazolium-based ionic liquids exhibited a high degree of radiological stability. The aqueous solution of sodium carbonate is found to be better in the back extraction of uranyl ions from the ionic liquids relative to EDTA and oxalic acid. However, the efficacy of back extraction differs largely on the ionic liquid system. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

A novel diamide ligand, 5-bromo-N1, N3-diisopropylisophthalamide, was synthesized and characterized, and its extraction mechanism with uranyl ions in various ionic liquid families was studied. Changing the ionic liquid system can achieve different extraction mechanisms, predominantly influenced by the cations of the ionic liquids. The study found that the back extraction of uranyl ions from the ionic liquids is better with sodium carbonate compared to EDTA and oxalic acid, but the efficacy varies among different ionic liquid systems.