Experimental and Theoretical Insight into Biphasic Extractive Mass Transfer of Thorium into Ionic Liquid Phase Using Chloroamide Ligands

2-chloro-N-methyl-N-phenylacetamide (L1) and 2-chloro-N-(3-methylpyridin-2-yl)acet amide (L2) have been explored for the efficient separation of tetravalent thorium ion (Th4+) from aqueous phase to the ionic liquid phase. Due to the positive inductive effect (+I effect) of alkyl group, the electron density on N in L1 was more compared to that in L2; as evidenced from the distribution ratio values of Th4+ (D-L1(Th) similar to 180 and D-L2(Th) similar to 107 at 1 M HNO3). The extraction proceeds via 'cation exchange' mechanism involving 1:3 metal ligand stoichiometry for both the ligands. Each thorium complex was associated with three nitrate ions; thus, making the complex uni-positive in nature. The charge compensation during extractive mass transfer was done by dissolution of one hexyl methylimidazolium cation from ionic liquid phase to aqueous phase. The mass transfer followed slower kinetics, which was attributed to the high viscosity coefficient of ionic liquid. The extraction processes were spontaneous (Delta G(L1)(300K) similar to -16.31kJ mol(-1) and Delta G(L2)(300K) similar to -15.75kJ mol(-1)) and endothermic in nature with a significant enhancement in the entropy (Delta S-L1(300K) similar to -107.98 kJ mol(-1)K(-1) and Delta S-L2(300K) similar to -103.54 kJ mol(-1)K(-1)). Density functional theory (DFT) calculation revealed the presence of two types of Th-O bond associated with nitrate ion and ligands (Th-O-nitrate(L1) similar to 2. 511 angstrom, Th-O-nitrate(L1) similar to 2.411 angstrom, Th-O-nitrate(L2) similar to 2.518 angstrom and Th-O-nitrate(L2) similar to 2.422 angstrom. The higher extraction efficiency of Th4+ for L1 was corroborated from the negative DG values calculated for L1 in gas and ionic liquid phase compared to that for L2. (c) 2022 Elsevier B.V. All rights reserved.