Effect of alkyl chain length on the extraction properties of U and Th using novel CnmimNTf2/isophthalamide systems

An attempt was made to investigate the structural modification of CnmimNTf2 ionic liquid in combination with a novel ligand, 5-bromo-N1,N3-bis(1-methyl-1H-pyrazol-3-yl)isophthalamide on the extraction properties of tetra and hexavalent actinides. In C4mimNTf2, C6mimNTf2, the extraction processes predominantly followed the ‘cation exchange’ mechanism involving the species: [UO2(NO3)L]+ and [Th(NO3)2L]2+, whereas, in C8mimNTf2, the ‘solvation’ mechanism was found to be predominant involving neutral species UO2(NO3)2L2 and Th(NO3)4L3. The speciation was further confirmed by investigating the participation of imidazolium cation in extraction. In ionic liquid, the extraction processes were slower compared to that in the molecular diluent. The time required to attain the equilibrium D values followed the trend: C4mimNTf2 C8mimNTf2, which was ascribed to the enhancement in organophilicity of the cation on increasing the length of the side chain and hence the effect on their dissolution in water. Three cycles of 1 mM aqueous sodium carbonate solution and four cycles of 1 mM oxalic acid solution were sufficient for almost quantitative back extraction of U and Th, respectively.C8mimNTf2 based systems were better radio-resistant compared to the lower homologue. •Novel isophthalamide in Ionic liquid for efficient extraction of UO22+, Th4+.•The structural modification in ionic liquid changes the mechanism from ‘cation exchange’ to ‘solvation’.•Structural modification in ionic liquid influences speciation, extraction kinetics, efficiency and radiolytic stability.•Slower kinetics in ionic liquid pertaining to high viscosity coefficient.•C8mimNTf2 based solvent system showed better stability than that of C4mimNTf2 and C6mimNTf2.