A green and efficient liquid–liquid extraction system was developed for the separation of lithium isotopes by using hydrophobic ionic liquids (ILs = [C 4,6,8,10 mim] + [NTf 2 ] − ) as extraction organic phase and benzo-15-crown-5 (B15C5) as complexing agent. The maximum single-stage separation factor α of 6 Li/ 7 Li obtained in this study was 1.029 ± 0.001, indicating 6 Li was enriched in ionic liquid phase while 7 Li was concentrated in the aqueous phase. The lithium ion was extracted into the ionic liquid in the formation of 1:2 complex [Li + (B15C5) 2 ]. The negative data of thermodynamic parameters (∆ H 0 and ∆ G 0 ) suggest that the extraction system was a spontaneous exothermic process . In addition, effective lithium isotopes separation factor and the extraction efficiency of lithium ions can be gained in the condition of lower temperature with softer counter anions in the novel extraction system.
A novel liquid–liquid extraction system was investigated for the selective separation of lithium isotopes using ionic liquids (ILs = [C 6,8,10,12 mim] + [PF 6 ] － ) as extraction solvent and benzo-15-crown-5 (B15C5) as extractant. The effects of the concentration of lithium salt , counter anion of lithium salt, initial pH of aqueous phase, and extraction temperature on the lithium isotopes separation were studied. The maximum single-stage separation factor α of 6 Li/ 7 Li obtained in the present study was 1.038 ± 0.002, indicating the lighter isotope 6 Li was enriched in organic phase while the heavier isotope 7 Li was concentrated in the aqueous phase. The formation of 2:1 complex Li(B15C5) 2 + in the IL phase was determined on the basis of slope analysis method. The large value of the free energy change (− G 0 = 77.87 J mol −1 ) indicated the high separation capability of the lithium isotopes by B15C5/30%CH 3 Cl-70% C 6 mimPF 6 mixture extraction system. Lithium in Li(B15C5) 2 + complex was stripped by 0.5 mol·L −1 HCl solution. The extraction system offers high efficiency, simplicity application prospect to separation lithium isotope separation from LiCl solution.
Li Cui,Ren Gao,Qiaowei Zhang,Kun Jiang,Hongyan He,Wei-Lu Ding,Fangqin Cheng
Crown ethers (CEs) are promising materials for lithium isotope (6Li and 7Li) separation for their unique cavity structure and size effect, but the low partitioning of Li+ makes the practical implementation not applicable. The loss of CE molecules is also a critical problem. In this work, benzo-15-crown-5 functionalized imidazolium ionic liquids with different alkyl chain lengths ([Cn(B15C5)mim][NTf2], n = 6, 8, 10) are synthesized. The association constants of [Cn(B15C5)mim][NTf2] and Li+, Li+ partition, and the separation factor of 6Li and 7Li using [Cn(B15C5)mim][NTf2] were investigated. Compared with the B15C5 monomer, the covalent bonding of B15C5 onto the cation of imidazolium ILs contributes to the dramatic increase of binding ability toward Li+. The association constants of [Cn(B15C5)mim][NTf2] with Li+ increase with the elevation of the alkyl chain length due to the flexibility changes. However, [C8(B15C5)mim][NTf2] delivers the most outstanding partition coefficient of Li+ up to 7.59 with a separation factor of 1.033 (273 K), exceeding those reported for CE-based materials. The increased hydrophobicity of [Cn(B15C5)mim][NTf2] enables sustainable and robust use in the separation process. Both molecular dynamics simulations and interfacial tension experiments confirm that [C8(B15C5)mim][NTf2] exhibits the best affinity to the interfaces of dichloroethane/water. The coordination environment of Li+ can be tuned by regulating the length of the alkyl chains, resulting in different isotopic effects. This study offers a promising system for the effective and sustainable separation of 6Li and 7Li.
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