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

Abstract

A novel diamide ligand, 5-bromo-N1, N3-diisopropylisophthalamide has been synthesized and characterized by FTIR, 1H NMR, and 13C 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)3L2]-; In piperidinium and pyridinium-based ionic liquid, the species were UO2(NO3)2L and UO2(NO3)2L2 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.