Study On 15-Crown-5 Derivative Extraction And Separation Of Lithium Isotope

The construction of clean energy as the main energy system has become a common global goal.As a low-carbon,safe,and efficient clean energy,nuclear energy plays an important role in alleviating energy shortages,ecological environmental protection,and pollution prevention.Lithium has two stable isotopes（⁶Li and ⁷Li）in nature,and their relative abundances are 7.53%and 92.47%,respectively,which play a pivotal role in the nuclear industry.⁷Li is an important component of coolant and heat carrier in nuclear power system of thorium molten salt reactor,and ⁶Li is the source of tritium（T）in nuclear fusion reactor material.The development of separation technology of ⁷Li and⁶Li is of great significance to national defense and energy industry in China.However,due to their similar physical and chemical properties,it is extremely difficult to separate lithium isotopes.In this paper,the 15-crown-5 derivative extraction system was carried out to study the separation of lithium isotopes,and the abundance of ⁶Li was increased from the natural abundance to 9.52%.The specific research content is as following:（1）Choose the electron-donating group 4-amino-benzo-15-crown-5（4-NB）as the extractant,and hydrophobic room temperature ionic liquids and traditional organic solvents anisole are used as solvents,the system was constructed to study the extraction and separation of lithium isotope,and the effects of factors such as the content of ionic liquid and extraction temperature on the extraction and separation of lithium isotope were analyzed.The results showed that the medium of ionic liquid and temperature extraction had a significant effect on the separation of lithium isotope.After extraction and separation,⁷Li and ⁶Li are respectively enriched in the aqueous phase and the organic phase,respectively.（2）In order to improve the stability of the extraction and separation system and the effect of extraction and separation,a set of experimental equipment that can achieve low-temperature extraction and separation of lithium isotopes has been designed and established.The influence of hydrodynamic parameters such as gas holdup,bubble size and gas-liquid flow pattern on the extraction separation effect during the reaction process was investigated.Under the same conditions,the separation of lithium isotopes by vibration and air flotation complex extraction methods was compared,and it was found that the separation of lithium isotopes by air flotation complex extraction methods can not only reduce the loss of extractant,improve the stability of the extraction system,but also increase the lithium isotope.The extraction separation effect.The factors affecting the extraction and separation process of lithium isotopes were discussed and optimized.The maximum single-stage separation factor（α）is 1.037.Theδ⁷Li and relative abundance of ⁶Li in the enriched organic phase after single-stage extraction is-42.15 and 7.90%,respectively.（3）The thermodynamics and kinetics of extraction of lithium isotopes by crown ether/ionic liquid system were studied.Thermodynamic studies demonstrate that the extraction and separation of lithium isotopes by crown ether/ionic liquid system are all spontaneous exothermic processes.Therefore,lower temperature is beneficial to improve the extraction and separation effect of lithium isotopes.The kinetic results showed that the diffusion resistance in organic phase was greater than that in water phase,and the activation energy of the extraction process was 24.50 k J·mol^-1 based on the Arrhenius equation,indicating that the extraction kinetics of the system was controlled by the mixture of diffusion and chemical kinetics.（4）The degree of single-stage extraction and separation of lithium isotopes is limited.A multi-stage cascade separation method is used to study lithium isotope separation.The results show that the stacked cross-flow multi-stage method gets a better separation and enrichment trend.As the number of separation stages increases.The relative abundance of 6Li in the enriched organic phase gradually increased.On this basis,an experimental device that can achieve multi-stage cascade cycle extraction and separation was established to extract and separate lithium isotopes and showed a good enrichment effect.After separation,the relative abundance of ⁶Li in the enriched phase increased to 9.52%.（5）DFT method was used to calculate the electron density difference diagram,mean local ionization energy,lone-pair electronic isosurface and surface electrostatic potential of crown ether extractant under the B3LYP/6-31G（d,p）base theory level.Combined with the force constant theory of the chemical bond,the separation mechanism of lithium isotope in crown ether extractant system was preliminaries explained.The interaction energy（ΔE）of the complexation between the extractant and⁶Li⁺is-47.72 kcal·mol^-1 by theoretical calculation,indicating that the extraction separation process is exothermic reaction,and the extraction separation effect of lithium isotope can be improved by lowering the temperature.The reason why the ionic liquid[BMIm][NTf₂]improved the extraction and separation effect of lithium isotope in the system was analyzed by ultraviolet spectroscopy and cavity theory.