Separation Of Lithium Isotopes By Ionic Liquids-Electromigration Method

The common lithium isotopes in nature are Li-6 and Li-7,with natural abundances of 7.58%and 92.42%respectively.Li-6 and Li-7 both have important applications in the nuclear industry.Over 30%of Li-6 can be used in the process of civil controlled fusion,over 90%of Li-6 can be used in the military process of uncontrolled fusion,while over99.99%of⁷Li OH can be used as p H regulator of pressurized water reactor,over 99.995%of⁷Li₂Be F₄can be used as coolant of molten salt reactor.Therefore,it is very important to research the separation of Li-6 and Li-7 from natural abundance of lithium products.At present,lithium amalgam method is only one way of lithium isotope separation for industrial application reported in public,but there is a large amount of metal mercury is used in this method,which will bring environmental risk and pose a threat to health.Therefore,with more and more attention to environmental issues,it is increasingly ur-gent to find an alternative method of lithium amalgam.Ionic liquids-electromigration method is an environmentally friendly method for the separation of lithium isotopes by the electromigration of lithium ions in the ionic liquids phase.In this paper,some work has been done on the separation of lithium isotopes by ionic liquids-electromigration method.（1）By studying the concentration of anions and cations of ionic liquids migrate to the electrode solution,the law of the ions transfer from the ionic liquids to the electrode solution is studied.The conclusions are as follows:1?The migration of ionic liquids anions and anions in the system is influenced by the interaction of three forces,namely,electromigration force,diffusion force and back-dissolution force.The electromigra-tion force drives the anions and cations of ionic liquids to migrate to the anode aqueous solution and cathode aqueous solution respectively,while the diffusion force drives the anions and cations of ionic liquids to migrate to the anode aqueous solution and cathode aqueous solution at the same time.The back-dissolution force drives the migration to the anions and cations of ionic liquids in the electrode solution to the ionic liquids phase.2?With the increase of the current,the electromigration effect is gradually enhanced,so that the migration amount of ionic liquids cations to the cathode solution increases and the migration amount to the anode solution decreases.At the same time,the migra-tion of anions from ionic liquids to anode solution increased,while that from cathode solution decreased.It is shown that the directional migration behavior of ionic liquids anions under the action of electric field and the migration amount of ionic liquids anions are directly related to the strength of electric field.3?When the electrode solution is alkaline or dissolved Li N（CF₃SO₂）₂,the ionic liquids cations and solution anions form a new hydrophobic ionic liquids,and then the ionic liquids phase is dissolved back into the ionic liquids phase,resulting in a significant decrease in the amount of cations trans-ferred into the electrode solution.4?When dissolve Li N（CF₃SO₂）₂into ionic liquids,the ionic liquids cationic migration amount was significantly inhibited,and lithium ions replaced part of ionic liquids cations migration into the electrode solution.Therefore,it can be inferred that the conductive mechanism of ionic liquids phase in the system may be the directional migration of ionic and negative ions in the ionic liquids phase and the directional migration of lithium ions in the ionic liquids phase under the action of electric field.（2）By measuring the concentration of lithium ions in cathode solution after apply-ing electric field,the migration of lithium ions in the binary system of ionic liquids/aqueous solution in the process of separation of lithium isotopes by ionic liquids-electromigration method was studied.The results show that:1?Lithium ions cannot directly migrate from the anode aqueous solution through the ionic liquids/anode aque-ous solution interface into the ionic liquids phase.2?The lithium ions directly dissolved into the ionic liquids can be electromigrated into the cathode solution.3?The lithium ions dissolved in dimethyl sulfoxide can be electromigrated from the anode solution into the cathode solution through the ionic liquids phase.It is speculated that the hydrated lithium ions in aqueous solution is difficult to cross the hydrophobic ionic liquids/an-ode aqueous solution interface,and the lithium ions dissolved in dimethyl sulfoxide has fewer water molecules without binding or complexing,so it can cross the interface due to less resistance at the hydrophobic ionic liquids/dimethyl sulfoxide interface.The de-tection of the lithium isotopic value in the cathode solution in this process proves that this method has a weak effect on the separation of lithium isotopes.（3）Lithium ions were loaded into the ionic liquids-crown ether system through the extraction process,and then the electric field was applied to the system of ionic liq-uids crown ether to make lithium ions partially migrate out of the ionic liquids-crown ether system,so as to study the isotope separation effect in the process of lithium ions electromigration.The results show that the electric field can make lithium ions migrate from the organic phase consisting of ionic liquids-crown ether system into the cathode aqueous solution,and the process can realize the separation of lithium isotopes.The results show that at low voltage,Li-7 preferentially migrates from the organic phase to the cathode aqueous solution,while at high voltage,Li-6 preferentially migrates from the organic phase to the cathode aqueous solution.In the two-stage process,the elec-tromigration makes the lithium isotope value from-7.6 to-21.5;in the three-stage process,the lithium isotope value of cathode solution is from-5.7 to-16.1,while the lithium isotope value of anode solution after the whole electromigration process is 6.4.It is proved that this method has obvious separation effect of lithium isotopes.