A method for lithium isotope separation

Abstract

This invention belongs to the field of isotope separation technology, specifically disclosing a method for lithium isotope separation. Addressing the significant risks to the ecological environment and occupational health posed by existing lithium amalgam methods due to the use of large quantities of highly toxic metallic mercury, and the limitation of insufficient mercury availability hindering large-scale production to meet the increasing demand for lithium isotope products, this invention proposes a safe, efficient, and industrially viable non-mercury-based lithium isotope separation method. This method is a liquid-liquid extraction method based on isotope exchange reactions between molten salt and liquid metal. The basic principle utilizes two stable isotopes of lithium. 6 Li and 7 The difference in the partition coefficient of Li between the liquid metal phase and the molten salt phase. The single-stage separation coefficient α of this method can meet the requirements of the single-stage separation factor for the industrialization of chemical exchange method (α≥1.02), and can be realized by laboratory heating furnace or scaled up by high-temperature extraction tower, providing a new technical route for lithium isotope separation.

Description

Technical Field

[0001] This invention belongs to the technical field of isotope separation, specifically relating to a new method for lithium isotope separation based on liquid-liquid extraction of molten salt phase and liquid metal phase, which is safe, efficient and has industrial application prospects. Background Technology

[0002] Developing nuclear energy is an important measure for my country's sustainable development, and lithium isotopes play a crucial role in the nuclear industry. Lithium exists in nature in two stable isotopic forms, namely… 6 Li (natural abundance approximately 7.42%) and 7 Li (natural abundance approximately 92.58%). 6 Li and 7 Lithium (Li) has important applications in the nuclear industry. (Li+) with an abundance of over 30% 6 Li can be used in civilian controlled nuclear fusion processes, with an abundance of over 90%. 6 Li can be used in uncontrolled nuclear fusion processes for military applications; and 7 Li abundance above 99.99% 7 LiOH can be used as a pH adjuster in pressurized water reactors. 7 Li abundance greater than 99.995% 7 Li₂BeF₄ can be used as a coolant in molten salt reactors. Therefore, separating high-abundance lithium isotope products from naturally abundant lithium products is of great significance for the stable supply of raw materials for the nuclear industry. The separation and enrichment of lithium isotopes are key technologies that must be solved in nuclear energy development.

[0003] 6 Li and 7 Li has an identical electron configuration and very similar chemical properties, making its separation extremely difficult. Since the 1930s, researchers worldwide have focused on this issue. 6 Li / 7 Extensive research has been conducted on the separation of lithium isotopes, leading to the development of a series of methods, primarily including lithium amalgamation, solvent extraction, ion exchange chromatography, and molten salt electrolysis. However, solvent extraction suffers from problems such as solvent loss and difficulty in achieving multi-stage separation; ion exchange chromatography suffers from low single-stage separation coefficients, long equilibrium times, and discontinuous operation; and molten salt electrolysis suffers from low efficiency, high energy consumption, and difficulty in achieving continuous multi-stage separation. These limitations hinder the industrial application of these methods.

[0004] The lithium amalgam method, due to its large single-stage separation factor (~1.05), fast isotope exchange reaction rate (~several seconds), stable two-phase structure, and ease of interconversion facilitating cascade formation, as well as the ease of forming two-phase convection which benefits process design and scale-up, is currently the only reported method for lithium isotope separation that has achieved industrial application. However, the lithium amalgam method requires the use of large amounts of heavy metal mercury, whose high toxicity can easily cause persistent environmental pollution during production and wastewater treatment, directly threatening the health of operators. Furthermore, equipment corrosion and mercury leakage risks further exacerbate safety hazards. Simultaneously, limited by the scale of mercury supply and the prospect of a future ban on mercury production, this method is unlikely to meet the huge future demand for lithium isotopes from the nuclear energy industry. Therefore, the development of a safe, efficient, and industrially viable non-mercury-based lithium isotope separation method is becoming increasingly urgent. Summary of the Invention

[0005] This invention aims to provide a novel, green, efficient, and easily industrialized method for lithium isotope separation based on a metal-ion migration and exchange mechanism. It innovatively uses a liquid metal phase and a molten salt phase to replace the lithium amalgam phase and aqueous phase, respectively, avoiding the use of highly toxic mercury. This method is environmentally friendly, uses readily available raw materials, has a high single-stage separation factor, facilitates continuous operation, and easily forms two-phase convection, which is beneficial for process design and scale-up. It has promising industrial application prospects and is expected to meet the massive demand for lithium isotopes from the future nuclear energy industry. This method effectively solves the severe environmental risks, occupational health hazards, and raw material mercury production bottlenecks of existing industrialized lithium isotope separation technologies, as well as the problems of low separation factors, unsatisfactory efficiency, or the use of harmful reagents in other methods such as solvent extraction.

[0006] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0007] A method for separating lithium isotopes includes the following steps:

[0008] S1. Preparation of molten salt phase: Mix lithium salt and inorganic salt in a certain proportion, heat to melt, and react to obtain a uniform molten salt phase. When the water content of the molten salt phase is less than 1000 ppm, step S2 can be omitted.

[0009] S2. Preparation of a deep dehydration molten salt phase: The prepared molten salt phase is mixed with metallic lithium, heated to melt it, and after the reaction, excess metallic lithium is removed to obtain a deep dehydration molten salt phase with a water content of less than 1000 ppm;

[0010] S3. Preparation of liquid metal phase: Use metallic lithium heated to a molten state as the liquid metal phase; or, mix metallic lithium with liquid metal, heat to melt it, and react to obtain the liquid metal phase;

[0011] S4. Lithium Isotope Ion Migration and Exchange: The molten salt phase (which can be the molten salt phase with a water content of less than 1000 ppm obtained in step S1, or the deeply dehydrated molten salt phase with a water content of less than 1000 ppm obtained in step S2) is mixed with the liquid metal phase. The reaction time is not more than 36 h within the temperature range of 300~700℃. After the reaction is completed, the mixture is allowed to stand and cool to achieve phase separation. The separated solid molten salt phase and solid metal phase are collected separately. The molten salt phase is enriched. 7 Li, enriched in metallic phase 6 Li.

[0012] Preferably, in step S1, the lithium salt is any one or more of lithium halide, lithium nitrate, lithium carbonate, and lithium sulfate;

[0013] Further, in step S1, the self-preparation method of the lithium salt is as follows: in a glove box filled with an inert atmosphere, metallic lithium and acid are mixed in proportion to obtain a lithium-containing aqueous solution. The pH value of the lithium-containing aqueous solution is adjusted using the same acid, and the water is removed by heating and evaporation to obtain solid lithium salt.

[0014] The acid used in the self-preparation method of the lithium salt is any one of hydrochloric acid, nitric acid, and sulfuric acid;

[0015] In the self-preparation method of the lithium salt, the acid concentration is 1~10 mol / L; the mass ratio of metallic lithium to acid is 1:(15~25); the lithium ion concentration of the lithium-containing aqueous solution is 1~10 mol / L; the pH value is adjusted to less than 7; the heating temperature is 100~700 ℃, and the reaction time is 1~36 h.

[0016] Preferably, in step S1, the inorganic salt includes one or a mixture of several of the following: halogen salts, carbonates, sulfates, and nitrates.

[0017] Preferably, in step S1, the molar ratio of the lithium salt to the inorganic salt is 1:(1~4); the heating temperature is 100~700 ℃, and the reaction time does not exceed 36 h.

[0018] Preferably, in step S2, the mass ratio of the molten salt phase to metallic lithium is (5000~200):1; the heating temperature is 300~700 ℃; and the reaction time does not exceed 36 h.

[0019] Preferably, in step S3, the liquid metal is one or a mixture of potassium, gallium, indium, tin and bismuth; the molar ratio of lithium metal to liquid metal is the liquid phase range molar ratio in the alloy phase diagram (less than 1:1); the heating temperature after mixing is 100~700 ℃; and the reaction time does not exceed 36 h.

[0020] Furthermore, in step S3, the liquid metal phase includes elemental lithium metal and an alloy formed by lithium metal and liquid metal.

[0021] Preferably, in step S4, the mass ratio of the liquid metal phase to the molten salt phase is 1:(15~50).

[0022] Preferably, in step S4, the equipment used for the lithium isotope ion migration and exchange process is a heating furnace or a high-temperature extraction tower equipped with a stirring device. The stirring device rotates at a speed not exceeding 1000 rpm; the high-temperature extraction tower covers all types of extraction towers, such as pulse sieve plate towers, packed towers, and rotary disc extraction towers, and can be any one or more combinations thereof.

[0023] Furthermore, the lithium isotope ion migration and exchange process uses a high-temperature extraction tower that maintains an inert atmosphere for protection, operates at a slightly positive pressure of 0.1~10 kPa, has 1~800 stages, a single-stage residence time of 0.1~8 hours, and a two-phase flow ratio of molten salt phase: liquid metal phase = (15~50):1.

[0024] Furthermore, the high-temperature extraction tower used in the lithium isotope ion migration and exchange process is made of any one of stainless steel, nickel-based alloy, boron nitride ceramic, or graphite.

[0025] The present invention has the following beneficial effects:

[0026] 1. This invention uses environmentally friendly molten salt and non-toxic liquid metal as the lithium exchange phase, avoiding the environmental pollution, ecological risks, and occupational health hazards caused by the use of large amounts of heavy metal mercury in traditional lithium amalgam processes, thus conforming to green and environmentally friendly principles. The Li / Li exchange phase is promoted under heating and stirring conditions. + Efficient migration and exchange between molten salt and liquid metal phases, based on 6 Li and 7 The differences in vibrational frequencies and migration rates caused by variations in the mass of Li enable the effective separation of lithium isotopes between two phases. This method exhibits a high separation factor, meeting the requirements for a single-stage separation factor (α≥1.02) for industrial-scale chemical exchange methods, and achieves enrichment of the molten salt phase. 7 Li, enriched in liquid metallic phase 6 Li showed a clear separation effect.

[0027] 2. The method of the present invention has simple steps, controllable parameters, readily available raw materials, low energy consumption and cost, mild operating conditions, can be scaled up using a high-temperature extraction tower and is easy to apply industrially. It overcomes the bottleneck of the lithium amalgam method being limited by mercury production and can meet the huge demand for lithium isotopes in the nuclear energy industry.

[0028] 3. This invention provides a new technical path for lithium isotope separation. Based on the metal-ion migration and exchange mechanism, it overcomes the limitations of existing lithium amalgam methods and other separation technologies, such as high energy consumption, low separation factor, unsatisfactory efficiency, or the use of harmful reagents. This invention promotes the advancement of isotope separation technology and has important scientific and application value. Attached Figure Description

[0029] Figure 1 This is a flowchart of the self-prepared lithium salt process of the present invention.

[0030] Figure 2 This is a flowchart of a lithium isotope separation process according to the present invention.

[0031] Figure 3 This is a flow chart for multi-stage countercurrent extraction of heavy metal phase and light molten salt phase according to the present invention. It is applicable to systems in which the density of the metal phase is greater than that of the molten salt phase, with the metal phase entering from the top and exiting from the bottom, and the molten salt phase entering from the bottom and exiting from the top.

[0032] Figure 4 This is a flow chart for multi-stage countercurrent extraction of light metal phase and heavy molten salt phase according to the present invention. It is applicable to systems in which the density of the metal phase is less than that of the molten salt phase, with the metal phase entering from the bottom and exiting from the top, and the molten salt phase entering from the top and exiting from the bottom. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Unless otherwise specified, the equipment and reagents involved in the following embodiments are all commercially available conventional equipment and reagents, and the experimental operations involved are all conventional operations in the art unless otherwise specified.

[0034] Example 1

[0035] This embodiment provides a method for lithium isotope separation, including steps of preparing a molten salt phase, preparing a deeply dehydrated molten salt phase, preparing a liquid metal phase, and lithium isotope ion migration and exchange. The flowchart for preparing the molten salt phase is shown below. Figure 1 As shown, the equipment used in the lithium isotope ion migration and exchange step is a heating furnace equipped with a stirring device. In this embodiment, the heating furnace was purchased from Zibo Jiuchen Energy Saving Technology Co., Ltd., model: JC-A220. In actual applications, any heating equipment is acceptable. The specific operation is as follows:

[0036] In an Ar-atmospheric glove box, 50 mL of hydrochloric acid and 3 g of metallic lithium were added to a 100 mL beaker to obtain a lithium-containing aqueous solution. The pH was adjusted to 1 using hydrochloric acid, and the mixture was placed in a furnace at 150 °C for 12 h to obtain a solid lithium salt. A mixture of lithium salt and potassium chloride at a molar ratio of 1:1 was placed in a 100 mL boron nitride crucible and placed in a furnace at 600 °C for 24 h to obtain a molten salt phase. The prepared molten salt phase was mixed with metallic lithium at a mass ratio of 1:0.001 and placed in a boron nitride crucible. The mixture was then reacted at 600 °C for 24 h to remove excess metallic lithium, yielding a deeply dehydrated molten salt phase with a water content of less than 1000 ppm. Elemental lithium heated to a molten state was used as the liquid metal phase. 50 g of deeply dehydrated molten salt phase and 1 g of liquid lithium metal phase were added to a boron nitride crucible, mixed, and reacted in a furnace at 380 °C and 500 rpm for 12 h with stirring. After the reaction was complete, the two phases were separated by cooling to obtain a solid molten salt phase and a solid metallic phase. The abundance of lithium isotopes in the molten salt phase and the metallic phase before and after the reaction showed that the molten salt phase was enriched. 7 Li, enriched in metallic phase 6 Li has a single-level separation factor of 1.033.

[0037] Example 2

[0038] This embodiment provides a method for lithium isotope separation, including preparing a molten salt phase, preparing a deeply dehydrated molten salt phase, preparing a liquid metal phase, and lithium isotope ion migration and exchange steps. The lithium isotope ion migration and exchange step utilizes a heating furnace equipped with a stirring device. Specific operations are as follows:

[0039] In an Ar-atmospheric glove box, 50 mL of hydrochloric acid and 4 g of metallic lithium were added to a 100 mL beaker to obtain a lithium-containing aqueous solution. The pH was adjusted to 2 using hydrochloric acid, and the mixture was placed in a furnace at 500 °C for 24 h to obtain a solid lithium salt. A mixture of lithium salt, lithium bromide, and lithium iodide in a molar ratio of 1:1:3 was placed in a 100 mL boron nitride crucible and placed in a furnace at 600 °C for 12 h to obtain a molten salt phase. The prepared molten salt phase was mixed with metallic lithium in a mass ratio of 500:1 and placed in a boron nitride crucible. The mixture was reacted at 600 °C for 24 h to remove excess metallic lithium, yielding a deeply dehydrated molten salt phase with a water content of less than 1000 ppm. A mixture of metallic lithium and metallic bismuth in a molar ratio of 1:5 was reacted at 500 °C for 12 h, and then cooled to obtain a liquid metallic phase. 50 g of deeply dehydrated molten salt phase and 2 g of liquid lithium metal phase were added to a boron nitride crucible, mixed, and reacted in a furnace at 430 °C and 500 rpm for 24 h with stirring. After the reaction was complete, the two phases were separated by cooling to obtain a solid molten salt phase and a solid metallic phase. The abundance of lithium isotopes in the molten salt phase and the metallic phase before and after the reaction showed that the molten salt phase was enriched.7 Li, enriched in metallic phase 6 Li has a single-level separation factor of 1.024.

[0040] Example 3

[0041] This embodiment provides a method for lithium isotope separation, including preparing a molten salt phase, preparing a deeply dehydrated molten salt phase, preparing a liquid metal phase, and lithium isotope ion migration and exchange steps. The lithium isotope ion migration and exchange step utilizes a heating furnace equipped with a stirring device. Specific operations are as follows:

[0042] In an Ar-atmospheric glove box, 50 mL of hydrochloric acid and 5 g of metallic lithium were added to a 100 mL beaker to obtain a lithium-containing aqueous solution. The pH was adjusted to 3 using hydrochloric acid, and the mixture was placed in a furnace at 500 °C for 24 h to obtain a solid lithium salt. A mixture of lithium salt and potassium chloride at a molar ratio of 1:1 was placed in a 100 mL boron nitride crucible and placed in a furnace at 600 °C for 24 h to obtain a molten salt phase. The prepared molten salt phase was mixed with metallic lithium at a mass ratio of 200:1 and placed in a boron nitride crucible. The mixture was then reacted at 600 °C for 24 h to remove excess metallic lithium, yielding a deeply dehydrated molten salt phase with a water content of less than 1000 ppm. Finally, metallic lithium and potassium chloride were mixed at a molar ratio of 1:19 and reacted at 500 °C for 12 h. After cooling, a liquid metallic phase was obtained. 50 g of deeply dehydrated molten salt phase and 2 g of liquid lithium metal phase were added to a boron nitride crucible, mixed, and reacted in a furnace at 430 °C and 500 rpm for 36 h with stirring. After the reaction was complete, the two phases were separated by cooling to obtain a solid molten salt phase and a solid metallic phase. The abundance of lithium isotopes in the molten salt phase and the metallic phase before and after the reaction showed that the molten salt phase was enriched. 7 Li, enriched in metallic phase 6 Li has a single-level separation factor of 1.022.

[0043] Example 4

[0044] This embodiment provides a method for lithium isotope separation, including preparing a molten salt phase, preparing a deeply dehydrated molten salt phase, preparing a liquid metal phase, and lithium isotope ion migration and exchange steps. The lithium isotope ion migration and exchange step utilizes a heating furnace equipped with a stirring device. Specific operations are as follows:

[0045] In an Ar-atmospheric glove box, 50 mL of hydrochloric acid and 4 g of metallic lithium were added to a 100 mL beaker to obtain a lithium-containing aqueous solution. The pH was adjusted to 2 using hydrochloric acid, and the mixture was placed in a furnace at 500 °C for 24 h to obtain a solid lithium salt. A mixture of lithium salt and potassium chloride at a molar ratio of 1:1 was placed in a 100 mL boron nitride crucible and placed in a furnace at 600 °C for 24 h to obtain a molten salt phase. The prepared molten salt phase was mixed with metallic lithium at a mass ratio of 200:1 and placed in a boron nitride crucible. The mixture was then reacted at 600 °C for 24 h to remove excess metallic lithium, yielding a deeply dehydrated molten salt phase with a water content of less than 1000 ppm. Elemental lithium heated to a molten state was used as the liquid metal phase. 50 g of deeply dehydrated molten salt phase and 3 g of liquid lithium metal phase were added to a boron nitride crucible, mixed, and reacted in a furnace at 480 °C and 500 rpm for 36 h with stirring. After the reaction was complete, the two phases were separated by cooling to obtain a solid molten salt phase and a solid metallic phase. The abundance of lithium isotopes in the molten salt phase and the metallic phase before and after the reaction showed that the molten salt phase was enriched. 7 Li, enriched in metallic phase 6 Li has a single-level separation factor of 1.021.

[0046] Example 5

[0047] This embodiment provides a method for lithium isotope separation, including preparing a molten salt phase, preparing a liquid metal phase, and lithium isotope ion migration and exchange steps. The lithium isotope ion migration and exchange step utilizes a high-temperature extraction tower. Specific operations are as follows:

[0048] Molten salt phase preparation: Commercially available LiCl and KCl were mixed in a 1:1 molar ratio and melted at 450 °C for 12 hours to prepare a molten salt phase with a lithium ion concentration of 4 mol / L and a water content of less than 1000 ppm. The processing capacity was 200 g / day. Liquid metal phase preparation: Metallic lithium and metallic bismuth were mixed in a 1:6 molar ratio and melted at 400 °C for 12 hours to prepare a Li-Bi alloy containing approximately 0.6 wt% lithium. The molten salt phase and liquid metal phase were subjected to lithium isotope ion migration and exchange using a small-scale device consisting of a two-stage high-temperature extraction tower. Each stage of the tower had a diameter of DN40 and a height of 800 mm. The tower type was a pulse sieve plate tower. Since the density of the Li-Bi alloy phase was greater than that of the molten salt phase in this embodiment, the metallic phase, as the heavier phase, entered from the top of the tower and flowed out from the bottom, while the molten salt phase, as the lighter phase, entered from the bottom of the tower and flowed out from the top, forming a countercurrent contact. Figure 3As shown; Operating conditions: operating temperature 430 ± 3 ℃, single-stage residence time 4 hours, molten salt phase to liquid metal phase flow ratio 15:1. The system uses high-purity argon gas for protection, maintaining a slight positive pressure of 0.5 kPa. The online monitoring and control system uses a PLC system to monitor parameters such as temperature, flow rate, pressure, and isotope abundance in real time. Operating results: After two stages of countercurrent extraction, the molten salt phase... 7 Li abundance increased from 92.58% to approximately 93.1% in the metallic phase. 6 Li abundance increased from 7.42% to approximately 8.5%. The single-stage separation factor reached 1.025, and the total two-stage separation factor was approximately 1.050.

[0049] Example 6

[0050] This embodiment provides a method for lithium isotope separation, including preparing a molten salt phase, preparing a liquid metal phase, and lithium isotope ion migration and exchange steps. The lithium isotope ion migration and exchange step utilizes a heating furnace equipped with a stirring device. Specific operations are as follows:

[0051] In an Ar-atmospheric glove box, commercially available lithium chloride and potassium chloride were mixed in a 1:1 molar ratio and placed in a 100 mL boron nitride crucible. The mixture was then placed in a furnace at 600 °C and reacted for 24 h to obtain a molten salt phase with a water content of less than 1000 ppm. Molten lithium metal was used as the liquid metal phase. 50 g of the molten salt phase and 1 g of the liquid lithium metal phase were added to the boron nitride crucible, mixed, and reacted in a furnace at 380 °C and 500 rpm for 24 h with stirring. After the reaction was complete, the two phases were separated by cooling to obtain a solid molten salt phase and a solid metal phase. The abundance of lithium isotopes in the molten salt phase and the metal phase before and after the reaction showed that the molten salt phase was enriched. 7 Li, enriched in metallic phase 6 Li has a single-level separation factor of 1.024.

[0052] The metallic phase and molten salt phase products obtained by this invention using a high-temperature extraction tower or heating furnace can be further recycled as materials (example flow diagram as shown). Figure 2 As shown in the figure, a cascading effect can be achieved, which can improve the isotope separation factor.

[0053] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. Any changes made by those skilled in the art after reading the specification of the present invention, as long as they are within the scope of the claims of the present invention, will be protected by patent law.

Claims

1. A method for separating lithium isotopes, characterized in that, Includes the following steps: S1. Preparation of molten salt phase: Mix lithium salt and inorganic salt in a certain proportion, heat to melt, and react to obtain a uniform molten salt phase. Step S2 can be omitted when the water content of the molten salt phase is less than 1000 ppm. The lithium salt is any one or more of lithium halide, lithium nitrate, lithium carbonate, and lithium sulfate, and the inorganic salt includes one or more of halogen salts, carbonates, sulfates, and nitrates. S2. Preparation of a deep dehydration molten salt phase: The prepared molten salt phase is mixed with metallic lithium, heated to melt it, and after the reaction, excess metallic lithium is removed to obtain a deep dehydration molten salt phase with a water content of less than 1000 ppm; S3. Preparing a liquid metal phase: using elemental lithium heated to a molten state as the liquid metal phase; or, mixing lithium metal with a liquid metal, heating it to melt, and reacting to obtain a liquid metal phase; wherein the liquid metal is one or a mixture of potassium, gallium, indium, tin, and bismuth; S4. Lithium isotope ion migration and exchange: The molten salt phase with a water content of less than 1000 ppm obtained in step S1 or S2 is mixed with the liquid metal phase. The reaction is carried out at a temperature range of 300~700℃ for no more than 36 hours. After the reaction is completed, the mixture is allowed to stand and cool to achieve phase separation. The separated solid molten salt phase and solid metal phase are collected separately. The molten salt phase is enriched. 7 Li, enriched in metallic phase 6 Li.

2. The method for lithium isotope separation according to claim 1, characterized in that, In step S1, the molar ratio of lithium salt to inorganic salt is 1:(1~4); the heating temperature is 100~700 ℃, and the reaction time does not exceed 36 h.

3. The method for lithium isotope separation according to claim 1, characterized in that, In step S1, the lithium salt is either commercially available or self-prepared. The self-preparation method of the lithium salt is as follows: in a glove box filled with an inert atmosphere, metallic lithium and acid are mixed in a certain proportion to obtain a lithium-containing aqueous solution. The pH value of the lithium-containing aqueous solution is adjusted using the same acid. The water is removed by heating and evaporation to obtain solid lithium salt. The acid used in the self-preparation method of the lithium salt is any one of hydrochloric acid, nitric acid, and sulfuric acid.

4. The method for lithium isotope separation according to claim 3, characterized in that, In step S1, the acid concentration in the self-preparation method of the lithium salt is 1~10 mol / L; the mass ratio of metallic lithium to acid is 1:(15~25); the lithium ion concentration in the lithium-containing aqueous solution is 1~10 mol / L; the pH value is adjusted to less than 7; the heating temperature is 100~700 ℃; and the reaction time is 1~36 h.

5. The method for lithium isotope separation according to claim 1, characterized in that, In step S2, the mass ratio of the molten salt phase to lithium metal is (5000~200):1; the heating temperature is 300~700 ℃; and the reaction time does not exceed 36 h.

6. The method for lithium isotope separation according to claim 1, characterized in that, In step S3, the molar ratio of lithium metal to liquid metal is less than 1:1, the heating temperature after mixing is 100~700 ℃, and the reaction time does not exceed 36 h.

7. The method for lithium isotope separation according to claim 1, characterized in that, In step S4, the mass ratio of the liquid metal phase to the molten salt phase is 1:(15~50).

8. The method for lithium isotope separation according to claim 1, characterized in that, In step S4, the equipment used for the lithium isotope ion migration and exchange process is a heating furnace or a high-temperature extraction tower equipped with a stirring device.

9. The method for lithium isotope separation according to claim 8, characterized in that, In step S4, the high-temperature extraction tower is kept under an inert atmosphere, the operating pressure is a slight positive pressure of 0.1~10 kPa, the number of stages is 1~800, the residence time of a single stage is 0.1~8 hours, and the two-phase flow ratio is molten salt phase: liquid metal phase = (15~50):

1.

10. The method for lithium isotope separation according to claim 8, characterized in that, In step S4, the high-temperature extraction tower is made of any one of stainless steel, nickel-based alloy, boron nitride ceramic, or graphite.

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