Separation Of Lithium Isotopes By Electromigration

There are two stable lithium isotopes in nature:~6Li and ~7Li,with natural abundances of 7.5%and 92.5%respectively.High abundance of ~6Li and ~7Li products play an important role in the nuclear industry.The relatively high abundance of ~6Li is a key feedstock in the production of nuclear fusion reactor fuel,and high abundance of ~7Li can be used as p H regulator of PWR and coolant of molten salt reactor.Therefore,the industrial production of high abundance lithium isotope is an essential step for large-scale application of nuclear fusion reactor and new nuclear fission reactor.At present,COLEX process is the only method to achieve large-scale industrial application of lithium isotope separation,but it is harmful to the environment.The lack of efficient separation method and process of lithium isotope without mercury is one of the bottlenecks restricting the sustainable development of nuclear industry.Based on the previous work of the research group,this paper constructed the system of aqueous solution│ionic liquid-crown ether organic phase│aqueous solution,and the separation of lithium isotopes by electromigration was studied based on this system.Furthermore,the synergistic effect of various functions in the separation of lithium isotopes is preliminarily explored.The specific research results are as follows:(1)Separation of lithium isotopes by two-section electromigrationA two-section system of"lithium ion-crown ether anode solution│cathode aqueous solution"was constructed.The ionic liquid-crown ether system loaded with lithium ions after extraction was used as anode solution,the lithium ions moving into the cathode aqueous solution are enriched by ~7Li at 1 V and 2 V,and too high voltage(2～4 V)will lead to organic phase decomposition.With 15-crown-5 loaded lithium ions as anode solution,the separation effect of lithium ions and lithium isotopes in cathode aqueous solution is weak.With lithium salt solution added 15-crown-5 as the anode solution,the lithium ions migrating into the cathode aqueous solution are enriched in ~6Li at the low voltage of 4 V and below,and the lithium ions migrating into the cathode aqueous solution are enriched in ~7Li at the high voltage of 8 V and above.(2)Separation of lithium isotopes by three-section electromigrationA three-section system of"aqueous solution│ionic liquid-crown ether organic phase│aqueous solution"was constructed.When lithium ions were introduced into the organic phase by extracting,both the aqueous solution of anode and cathode were enriched in ~7Li and the organic phase was enriched in ~6Li under low voltage(2 V,4 V).When lithium ions were introduced into the system with lithium salt solution as anode solution,the anode aqueous solution was enriched in ~7Li,while the organic and cathodic aqueous solutions were enriched in ~6Li under high voltage(8 V,16 V).The enrichment effect of ~6Li in the cathode aqueous solution is gradually weakened with time.The method of introducing lithium ions from anode aqueous solution has better lithium isotope separation effect than that of introducing lithium ions from organic phase.(3)Synergistic effect of multiple actions in electromigration separation of lithium isotopesA series of comparative experiments were designed to study the effects of lithium ion diffusion,electric field force and organic phase extraction on lithium ion migration and lithium isotope separation,as well as the interactions among the three effects.The effects of electric field and crown ether on lithium ion migration and lithium isotope enrichment are discussed.It is found that the driving force of diffusion is the difference of lithium ion concentration in different parts of the system,and the enrichment direction of ~6Li is the same as the diffusion direction of lithium ion.The electric field will affect the structure and properties of the ionic liquid as well as the stability of the lithium ion-crown ether chelate,and then affect the ability of the organic phase to retain lithium ions.~6Li migrates and enriches from anode to cathode direction.The introducing of crown ether in the organic phase greatly enhanced the lithium ion transport capacity and the separation effect of lithium isotopes,and the extraction capacity of lithium ions and the selective enrichment ability of ~6Li decreased with the increase of the concentration of lithium ions in the organic phase.The enrichment of lithium isotopes in the"aqueous solution│ionic liquid-crown ether organic phase│aqueous solution"system under the action of electric field is a dynamic process.Under different conditions,the enrichment position of ~6Li can change correspondingly.