High abundance 6Li and 7Li are essential materials for the nuclear industry. In this article, the lithium isotope separation effect and lithium-ion transport of a “lithium salt aqueous solution (anolyte)|crown ethers–ionic liquid organic solution|ammonium chloride aqueous solution (catholyte)” electromigration system with B12C4, B15C5 and B18C6 as phase transfer catalysts were investigated systematically. The results show that separation factors can reach 1.028 (B12C4), 1.024 (B15C5) and 1.011 (B18C6), respectively, when LiCl solution is used as the anolyte. The separation effect mainly originated from interfaces between anolytes and organic solutions, and was less affected by an electric field. The separation effect between organic solution and catholytes was greatly affected by the electric field for B12C4 and B15C5 systems, which converted from 7Li-enrichment to 6Li-enrichment with increased voltage. For the B18C6 system it was less affected. Furthermore, lithium ion transport in B12C4, B15C5 and B18C6 systems was greatly promoted by the electric field, with the Li+ concentration in catholytes of B12C4, B15C5 and B18C6 systems increased from 0.088 mg L−1, 0.286 mg L−1 and 0.778 mg L−1 to 8.321 mg L−1, 7.422 mg L−1 and 4.631 mg L−1 respectively as the voltage increased from 2 V to 16 V. The B12C4 system has been confirmed as the optimal solution considering both the Li+ transport and isotope separation effect.
Lithium isotopes play an essential role in the nuclear industry. The extraction method with crown ethers as extractants is considered as one of the promising methods for lithium isotope separation with good application prospects. However, the effects of crown ethers with different cavity sizes in the system containing ionic liquids on isotope enrichment in organic solution/aqueous solution have not been systematically investigated. With three typical benzo crown ethers (B12C4, B15C5 and B18C6) as extractants and the mixtures of ionic liquids and anisole as solvents, the effect of crown ethers on the extraction rate of Li+, separation factor and δ7Li variation in organic solution/aqueous solution was investigated with varied solvent composition, lithium salts and concentration of crown ethers. The order of extraction rates was: B15C5 (40.88%) > B18C6 (38.12%) > B12C4 (23.35%) and the order of isotope separation factors was: B15C5 (1.024) > B12C4 (1.023) > B18C6 (1.010) under optimized conditions. The δ7Li in aqueous solution of B15C5 systems was higher than those corresponding to the B12C4 and B18C6 system while the δ7Li in the organic solution of the B12C4 systems was more negative than those corresponding to the B15C5 and B18C6 system. So, B12C4 systems achieve better 6Li enrichment in the organic phase and B15C5 systems achieve better 7Li enrichment in the aqueous phase.
Lianjing Mao,Xiaolong Zhou,Tianyu Zheng,Xiao Li,Xiufang Wang,Zhiyu Zhao,Wei Sun,Pengrui Zhang,Jinhe Sun
The metal ion extraction process is usually accompanied by the removal of coordinated water molecules and the change of water content in the extraction phase. However, hierarchical methodologies on water research are incredibly sparse, restricting a thorough knowledge of the extraction mechanism. It was clarified the diversity of water occurrence forms in the extraction phase and quantitative relationship between water, Li + and crown ether based on the (B12C4/B15C5/B18C6-[EMIm][NTf 2 ])-LiNTf 2 solvent extraction system. While the complexation mechanism between hydrated Li + and crown ether was discussed carefully. Firstly, it demonstrated that the water content of the extraction phase: B18C6 > B15C5 > B12C4. Secondly, the water in the extraction phase is mainly collected by solvent and crown ether, with the latter catching water primarily via Li + coordination and weak interactions. In the end, focusing on the water captured by the crown ether through Li + coordination, slope analysis and DFT calculations found that Li (H 2 O) 4 + was removed three water molecules to complex with B12C4 or B15C5, whereas B18C6 tends to remove two water molecules. It is precious for a thorough grasp of the mechanism and procedure of Li + extraction by crown ethers. What’s more, it offers novel strategies for investigating water content and transfer mechanisms in extraction systems.
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