Study On Extraction And Separation Of Lithium Isotope From Different Side Chain Crown Ether-Ionic Liquids

The common lithium isotopes in nature are ⁶Li and ⁷Li,with natural abundances of 7.42%and 92.58%respectively.Lithium isotopes occupy an important position in the nuclear industry.Tritium（T）is produced by ⁶Li after bombarded by thermal neutrons.It is an indispensable fusion fuel for a controlled thermonuclear fusion reactor.⁷Li compounds play an important role in the regulation of nuclear fission reaction and equipment maintenance.For example,ultra-pure ⁷LiF can be used as an important component of a new generation of molten salt reactor coolant,⁷LiOH can be used to adjust the PWR pH and reduce the corrosion of container equipment.At the same time,with the rapid development of the global economy,Environmental issues and the energy crisis have become increasingly serious,green and efficient nuclear fusion energy has become the focus of development in all countries in the world.Therefore,the separation and utilization of the raw material lithium isotopes have attracted the attention of many researchers and are also of great significance.In this paper,ionic liquid and anisole are used as a synergist and solvent,crown ether be used as extractant to build a green and efficient extraction and separation of lithium isotope system,to explore its ability to separate lithium isotopes,the specific research are as follows:（1）Study on the Extraction of Lithium Isotopes from Different Side Crown Ethers:4-nitrobenzo-15-crown-5（4-NO₂-B15C5）,4-aminobenzo-15-crown-5（4-NH₂-B15C5）and benzo-15-crown-5（B15C5）were used as the extractant,anisole and 1-butyl-3-methylimidazolium bis（trifluoromethanesulfonyl）imide were used as diluent and co-solvent,1 mol/L LiCl solution was used as extraction solvent to construct a green-efficient crown Ether-ionic liquid/lithium salt solution solvent extraction system.The effects of crown ether concentration,anion effect and crown ether side groups on the separation of lithium isotopes were investigated.All the experiments were carried out at room temperature.The results show that three crown ethers have a good ability to separate lithium isotopes.Lithium ions and crown ethers are extracted into the organic phase at a molar ratio of 2:1.Under the optimal experimental conditions,the single-stage separation coefficients are above 1.03,⁶Li is enriched in the organic phase.The order of the extraction rate（E%）is as follows:4-NH₂-B15C5>B15C5>4-NO2-B15C₅,but the degree of enrichment of ⁶Li is opposite to the above order.（2）Study on the Separation of Lithium Isotopes from a new type of benzo-15-crown-5 crown ether:Based on the above experimental phenomena and results,a new class of benzotrope-15-crown-5 chelators was selected as the extractant.And anisole and 1-butyl-3-methylimidazolium bis（trifluoromethanesulfonyl）imide were used as diluent and co-solvent,1 mol/L LiCl solution was used as extraction solvent,1 mol/L LiCl solution was used as extraction solvent to build a new system for the extraction and separation of lithium isotopes,The effects of crown ether concentration and anion on the separation of lithium isotopes were investigated.All experiments were performed at room temperature.The results show that the new crown ether has a good ability of separating lithium isotopes.The complex formed by lithium ion and crown ether in a molar ratio of 2:1 is extracted into the organic phase.Under the optimal experimental conditions,the single-stage separation coefficient can reach 1.036,⁶Li is enriched in the organic phase,and the new crown ether shows good hydrophobicity throughout the extraction process.（3）Multistage countercurrent extraction for the separation of lithium isotopes:a new type hydrophobic benzotrope-15-crown-5 chelators was used as the extractant,anisole and 1-butyl-3-methylimidazolium bis（trifluoromethanesulfonyl）imide were used as diluent and co-solvent,1 mol/L LiCl solution was used as extraction solvent.The 5th and 20th stages of countercurrent extraction and separation of lithium isotopes were constructed under laboratory conditions.The experimental results show that after 5 stages of countercurrent extraction,the separation coefficient also increases to 1.065,the abundance of ⁶Li increases from 7.42%of natural abundance to about 7.85%.And then,after 20 multistage countercurrent extraction experiments,the separation factor and the abundance values of ⁶Li appear to increase first and then decrease,with the highest values being 1.077 and 7.93%,respectively.At the same time,the solid compounds produced during the experiment can also enrich ⁶Li.The overall experimental results show that the new crown ether system has a good prospect of the separation of lithium isotopes.