Study On Lithium Isotopic Separation Of Different Ionic Liquid-Crown Ether Extraction Systems

With the depletion of oil,coal,natural gas,etc.,human being need to explore new energy nuclear fusion energy without pollution and environmental protection.Lithium isotopes are important raw material for the development of the nuclear industry.⁶Li is an essential nuclear fusion reactor material.⁷Li is used as a core condensing agent for thermal fusion reactors and a heat-conducting heat carrier.The application of lithium isotopes are of great significance.The separation of lithium isotope has attracted the attention of researchers all over the world.Four aspects of lithium isotope separation in the ionic liquid-crown ether extraction systems were studied.First,the mechanism of ionic liquids as co-extractants for extracting lithium ions in the lithium isotopes separation process was investigated.The obtained hydrophobic ionic liquid[BMIm][NTf₂]has the best synergistic effect though the application of sixteen kinds of ionic liquids in the extraction of lithium ions.The extraction rate and distribution coefficient of lithium ions in the extraction system containing[BMIm][NTf₂]were 26.35%and 0.358,respectively.The experimental rasults were shown that the hydrophobicity and steric hindrance of ionic liquids had gone up with the increasing side chain of ionic liquids,which was beneficial for lithium extraction.The shorter the side chain of ionic liquid was,the greater the hydrophilicity of ionic liquid was.When the side chain of ionic liquid reaches a certain length,the extraction of lithium can achieve the best effect.The concentration of[BMIm]⁺in the aqueous phase before and after extraction was determined by the obtained standard curve of[BMIm]⁺in aqueous solution.Results were shown that the cation exchange behavior between lithium ion in the aqueous phase and[BMIm]⁺in the organic phase was observed after extraction.In order to further measure the effect of ionic liquid on lithium extraction,the organic phase structure after lithium isotope separation was investigated by infrared spectroscopy,which indicated that the anion of ionic liquid has an influence on the chelate cation formed by lithium ion and crown ether.Secondly,study on the separation of lithium isotopes by the[BMIm][NTf₂]/4'-acetylbenzo-15-crown-5.The values of lithium extraction efficiency were arranged in order from largest to smallest:butyl acetate>dichloromethane>anisole>chloroform.In general,cation extraction was promoted in non-polar solvents that were helped for ion mass transfer,which was beneficial to improve lithium extraction rate.The exchange reaction of ⁶Li and ⁷Li increased with improving lithium extraction rate in the liquid-liquid extraction system.In addition,butyl acetate has the ability to extract lithium,which was no exchange behavior of⁶Li and ⁷Li and influenced severely the exchange of ⁶Li and ⁷Li with crown ether.The neutral or weak acidity of aqueous solution was beneficial to lithium extraction and isotopes separation in the system.When the initial pH values of aqueous phase was acidity,H⁺and Li⁺competed in the process of combining crown ethers.When the initial pH values of aqueous phase was alkaline,OH^-made the structure of the Li⁺complexation unstable.The concentrations of lithium salt,ionic liquids and corwn ether in certain range can promote the separation of lithium isotopes.But the extraction rate of lithium goes up with the increasing concentration of crown ether.The complex ratio of crown ether molecules to lithium ions was obtained by the slope method.And two configurations of complex formed by lithium ions and crown ether molecules were optimized by Gaussian software.The results were shown that regardless of the stability of the complex or the Gibbs free energy,the complex formed by the crown ether molecule and the lithium ion 1:1 is better,which is consistent with the experimental results.Thirdly,The extraction kinetics of lithium ions were studied by the[BMIm][NTf₂]/Acb15c5-dichloromethane extraction system.The extraction process is a mixed control kinetic process occurring in the interface region.The extraction kinetic equation?_Li,0=10^{-3.843±0.0001}·[Li⁺]^0.9071·[[BMIm]⁺]^0.8328·[AcB15C55]⁰.8555.8555 of lithium ion can be obtained by the influence of differen initial concentrations of LiNTf₂,AcB15c5 and[BMIm][NTf₂]on the mass transfer rate of Li⁺.The steady state approximation method was used to analyze the formation of complexe at the two-phase interface.The kinetic mechanism of lithium ion was deduced,which is consistent with the experimental results.At last,the thermodynamics of lithium extractionin and the exchange behavior of ⁶Li and ⁷Li were studied by Van't Hoff equation and thermodynamic formula.The extraction process of lithium ions with a new type of crown ether or AcB15C5 as the extractant is a spontaneous exothermic reaction at 293.15 K.Beside,the extraction process of lithium ions with AcB15C5 as the extractant is a spontaneous exothermic reaction at 293.15 K.Based on the above studies,the crown ether-ionic liquids extraction system has a good application prospect for lithium isotope separation.