Method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method

Abstract

The present invention provides a method for preparing high-purity metallic lithium by molten vacuum thermal reduction-distillation method, which belongs to the technical field of preparation of metallic lithium, and the method includes: lithium chloride and metallic aluminum are vacuum heat-treated to a molten state respectively; in a vacuum reduction tank after preheating, the molten metallic aluminum is stirred and mixed with the molten lithium chloride in batches for vacuum thermal reduction reaction; the temperature is raised after stopping stirring, and the gasified lithium product in the vacuum reduction tank is transferred to a heat-insulated reactor for collection; high-purity hydrogen is introduced into the reactor to reduce and purify the gasified lithium product; the temperature in the reactor is slowly reduced to 200°C to 300°C, and the gasified lithium product is liquefied into molten lithium, and high-purity metallic lithium is obtained after cooling. Under the vacuum and high-temperature conditions of the present invention, the molten metallic aluminum in batches is used to implement efficient reduction of lithium chloride, and the lithium gas generated by the reduction is deeply reduced and purified in combination with hydrogen, and ultra-high-purity metallic lithium is successfully obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of metal lithium preparation, and in particular relates to a method for preparing high-purity metal lithium by using a molten vacuum thermal reduction-distillation method. Background Art

[0002] Lithium metal is an important light alkali metal, the lightest metal element in nature, with extremely high electrical and thermal conductivity. With the rapid development of new energy, new materials and other industries, the demand for lithium metal in the fields of batteries, alloys, nuclear industry, etc. continues to grow, and its strategic position is becoming increasingly prominent. In particular, in the fields of new energy vehicles, energy storage systems, etc., the demand for lithium metal as a key raw material for batteries is growing particularly rapidly.

[0003] The main methods for preparing metallic lithium include melt electrolysis, vacuum thermal reduction, chemical deposition, ion exchange, etc. Among them, electrolysis is one of the most commonly used methods. The melt electrolysis method is the earliest method for preparing metallic lithium for large-scale production. It is to melt the lithium salt and then electrolyze it through an electrolytic cell to precipitate lithium metal on the cathode. However, it has high energy consumption, complex process, and will produce toxic and harmful gases such as chlorine, which is difficult to handle, and other problems, which has led to its gradual elimination. The technologies of chemical deposition method, ion exchange method and other methods are not yet mature and are still in the laboratory stage, and have not been applied in large-scale production.

[0004] The most commonly used method nowadays is thermal reduction, which uses a reducing agent to reduce lithium compounds to metallic lithium under high temperature conditions. It has safer reaction conditions and lower energy consumption, but because it is a solid-phase reaction, it has the limitations of low product purity and low production efficiency. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for preparing high-purity metallic lithium using a molten vacuum thermal reduction-distillation method, aiming to solve at least one technical problem in the background technology.

[0006] The present invention is achieved in that:

[0007] A method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method, the method comprising the following steps:

[0008] Weighing lithium chloride and metallic aluminum in a preset ratio, and performing vacuum heat treatment to form molten lithium chloride and metallic aluminum respectively, with the heat treatment temperature being 700° C. to 800° C.;

[0009] In the preheated vacuum reduction tank, the molten aluminum metal is mixed with the molten lithium chloride in batches and stirred to perform a vacuum thermal reduction reaction at a temperature of 800°C to 1000°C;

[0010] After the vacuum thermal reduction reaction is completed, stirring is stopped, the temperature is raised to 1350°C to 1550°C, and the gasified lithium product in the vacuum reduction tank is transferred to the heat-insulating reactor for collection;

[0011] High-purity hydrogen is introduced into the reactor to reduce and purify the gasified lithium product;

[0012] The temperature in the reactor is slowly lowered to 200°C to 300°C, and the gasified lithium product is liquefied into molten lithium. After the gas is discharged, the molten lithium is cooled to room temperature along with the furnace to obtain a high-purity metallic lithium product.

[0013] Furthermore, the vacuum thermal reduction reaction is specifically performed as follows:

[0014] Preheat the vacuum reduction tank to a temperature of 700°C to 800°C;

[0015] Mixing all the molten lithium chloride and 1 / 3 of the weight of molten metal aluminum in a vacuum reduction tank;

[0016] After the vacuum in the vacuum reduction tank is evacuated to below 30Pa, heating is started to raise the internal temperature to 800°C to 1000°C, and vacuum thermal reduction reaction is carried out at a constant temperature for 1h to 2h with the assistance of continuous mechanical stirring and ultrasonic vibration;

[0017] Add 1 / 3 weight of molten lithium metal and continue the vacuum thermal reduction reaction for 2h to 3h;

[0018] Add 1 / 3 of molten metallic lithium and continue the vacuum thermal reduction reaction for at least 4 hours.

[0019] Furthermore, during the entire vacuum thermal reduction reaction, the aluminum chloride gas generated in the reduction tank is continuously extracted to maintain the vacuum reaction environment, and the aluminum chloride gas is introduced into a double-layer condensation container in an inert gas environment at the same temperature for collection, and the interlayer is cooled by circulating water to condense the aluminum chloride gas into a solid state.

[0020] Furthermore, during the entire vacuum thermal reduction reaction, the mechanical stirring speed is 30 rpm to 50 rpm; and the ultrasonic vibration frequency is 40 KHz to 80 KHz.

[0021] Furthermore, the molar ratio of lithium chloride to metallic aluminum is controlled to be 3:1.2-1.6;

[0022] When lithium chloride and aluminum metal are completely converted into molten state, keep them warm for more than 20 minutes for preliminary impurity removal;

[0023] The vacuum heat treatment is performed in a flowing inert atmosphere.

[0024] Furthermore, before the reactor collects the gasified lithium product, sufficient nitrogen is introduced into the reactor to remove oxygen and carbon dioxide therein; the temperature inside the reactor is 1350°C to 1550°C.

[0025] Furthermore, in the reduction purification, the molar ratio of the introduced hydrogen to the initial lithium chloride is controlled to be between 2.5 and 5:1.

[0026] Furthermore, during the reduction and purification, the reactor is continuously mechanically stirred at a speed of 300 rpm to 500 rpm.

[0027] Furthermore, the gas discharged from the reactor after cooling is mixed with ultrapure water at room temperature to remove a small amount of hydrogen chloride gas impurities in the hydrogen, and the impurity-free gas is reused as reduced and purified hydrogen.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. Under vacuum and high temperature conditions, the present invention uses batches of molten metal aluminum to efficiently reduce lithium chloride, and combines hydrogen to perform deep secondary reduction and purification on the lithium gas generated by the reduction, thereby successfully obtaining ultra-high purity metallic lithium.

[0030] 2. The present invention processes the reaction raw materials into a molten liquid state before vacuum thermal reduction. The use of liquid reactants greatly increases the reaction contact area and significantly improves the reaction rate and conversion rate.

[0031] 3. The present invention introduces hydrogen circulation, and performs a second reduction treatment on the lithium chloride gas that has not fully reacted in the initial reduction, and further purifies it, thereby obtaining ultra-high purity metallic lithium with a purity higher than 99.99%.

[0032] 4. The present invention complies with green environmental protection requirements, avoids the generation of waste residues and waste liquids, recycles hydrogen, and produces aluminum chloride and industrial-grade hydrochloric acid with economic value as by-products, effectively realizing resource recycling. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific implementation cases described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] The method for preparing high-purity metallic lithium by using a molten vacuum thermal reduction-distillation method comprises steps S1 to S5.

[0035] S1: Accurately weigh a certain mass of lithium chloride and metallic aluminum, and control the molar ratio of lithium chloride to metallic aluminum at 3:1.2-1.6; respectively place the weighed lithium chloride and metallic aluminum in a vacuum melting furnace, pre-evacuate to a pressure below 30Pa, and then gradually increase the temperature of the vacuum melting furnace to 700°C-800°C to ensure that the lithium chloride and metallic aluminum are completely converted into a molten state, and maintain the temperature for more than 20 minutes (preferably 20 minutes-40 minutes) after the target temperature is raised for preliminary impurity removal, during which the process is carried out in a flowing inert atmosphere (the inert atmosphere is one or more of argon, nitrogen or helium).

[0036] S2: all the molten lithium chloride and 1 / 3 of the weight of the molten metal aluminum are mixed and placed in a preheated (same temperature as step S1) vacuum reduction tank, the air pressure in the reduction tank is evacuated to below 30Pa by a rotary vane vacuum pump, and then heating is started, the temperature is further increased to 800°C to 1000°C, the mechanical stirring speed is turned on (30rmp to 50rmp) and ultrasonic vibration (40KHz to 80KHz) is turned on simultaneously to assist, and the reduction reaction is carried out at a constant temperature. After reacting for 1h to 2h, 1 / 3 of the weight of the molten metal lithium is added for the first time, and then the remaining 1 / 3 of the weight of the molten metal lithium is added again after reacting for 2h to 3h, and the reaction is continued for more than 4h, and the vacuum thermal reduction reaction is terminated; during this period, the aluminum chloride gas generated in the vacuum reduction tank needs to be continuously evacuated to maintain the vacuum reaction environment, and the aluminum chloride gas is introduced into a double-layer condensation container in an inert gas environment at the same temperature for collection, and the interlayer is cooled by circulating water to condense the aluminum chloride gas into a solid state.

[0037] S3: Stop mechanical stirring and further increase the temperature in the vacuum reduction tank to 1350°C-1550°C to vaporize the small amount of molten lithium chloride and molten lithium that have not reacted completely; collect lithium gas and lithium chloride gas in a high-temperature reactor. Before collection, introduce sufficient nitrogen into the reactor to remove oxygen and carbon dioxide therein, and preheat to 1350°C-1550°C to maintain a constant temperature; the residual metal aluminum in the vacuum reduction tank that has not participated in the reaction is cooled with the furnace and then returned to step S1 for reuse.

[0038] S4: In 10 minutes, an excess of high-purity hydrogen (purity ≥ 99.999%) is introduced into the reactor for reduction and purification reaction, and the hydrogen reacts with molten lithium chloride at high temperature to produce metallic lithium and hydrogen chloride gas; the molar ratio of hydrogen to the lithium chloride added in step S1 is controlled between 2.5 and 5:1; the temperature is maintained for the reduction reaction for more than 1 hour, during which the gas in the reactor is continuously mechanically stirred at a speed of 300 rpm to 500 rpm to form a gas vortex to accelerate the reaction rate, so as to further purify the metallic lithium.

[0039] S5: After the reduction and purification reaction is completed, the temperature in the reactor is slowly lowered to 200°C-300°C, and the gas and molten lithium metal in the reactor are collected separately; the gas is passed into ultrapure water at room temperature and then collected to remove a small amount of hydrogen chloride gas in the hydrogen, and returned to step S4 for recycling; after the molten lithium is cooled to room temperature with the furnace, a high-purity lithium metal product can be obtained.

[0040] The present invention overcomes the problems of high energy consumption of electrolysis and low reaction efficiency of traditional solid-state metal thermal reduction. It innovatively uses molten metal aluminum to efficiently reduce lithium chloride under vacuum and high temperature conditions. Subsequently, the generated lithium gas is deeply reduced and purified by hydrogen to successfully obtain ultra-high purity metallic lithium.

[0041] In the vacuum thermal reduction process of the present invention, the use of liquid reactants greatly increases the reaction contact area, significantly improving the reaction rate and conversion rate. The present invention also creatively introduces hydrogen circulation, and the lithium chloride gas that is not fully reacted in the initial reduction is subjected to a second reduction treatment for further purification. In the product composition of the present invention, in addition to the main product ultra-high purity metallic lithium, aluminum chloride and industrial-grade hydrochloric acid with economic value are also produced as by-products, which improves the economic benefits of the entire production process. In addition, the present invention does not produce waste residues and waste liquids, and meets green environmental protection requirements.

[0042] Example 1

[0043] A method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method comprises the following steps:

[0044] S1. Weigh 900 g of lithium chloride (21.23 mol, 1.0 eq) and 229 g of metallic aluminum (8.48 mol, 0.4 eq) and place them in a vacuum melting furnace. Pre-evacuate the furnace to a pressure below 30 Pa, then gradually increase the temperature of the vacuum melting furnace to 700 ° C to ensure that the lithium chloride and metallic aluminum are completely converted into a molten state. After the temperature is increased to the target temperature, keep it for 20 minutes for preliminary impurity removal, which is carried out in flowing nitrogen.

[0045] S2. All molten lithium chloride and 1 / 3 molten metal aluminum are mixed and placed in a vacuum reduction tank preheated to 550°C. The air pressure in the vacuum reduction tank is pumped to below 30Pa by a rotary vane vacuum pump and then heating is started. The temperature is further increased to 800°C. The mechanical stirring speed is turned on at 30rmp and ultrasonic vibration 40KHz is turned on simultaneously to assist. The reduction reaction is carried out at a constant temperature. After 2 hours of reaction, 1 / 3 molten metal lithium is added for the first time. Then, after 3 hours of reaction, 1 / 3 molten metal lithium is added again. After the reaction is continued for 4 hours, the thermal reduction reaction ends. During this period, the aluminum chloride gas generated in the vacuum reduction tank needs to be continuously removed to maintain the vacuum reaction environment, and the aluminum chloride gas is introduced into a double-layer condensation container in an inert gas environment at the same temperature for collection. The interlayer is cooled by circulating water to condense the aluminum chloride gas into a solid state.

[0046] S3, stop mechanical stirring, further increase the temperature in the vacuum reduction tank to 1350 ° C, so that the small amount of molten lithium chloride and molten lithium that have not reacted completely are gasified. The lithium gas and lithium chloride gas are collected in a high-temperature reactor. Before collection, sufficient nitrogen needs to be introduced into the reactor to exclude oxygen and carbon dioxide therein, and the reactor is preheated to 1350 ° C to maintain a constant temperature. The residual metal aluminum that does not participate in the reaction in the vacuum reduction tank is cooled with the furnace and returned to step S1 for reuse.

[0047] S4. A certain amount of high-purity hydrogen (purity ≥ 99.999%, 53.07 mol, 2.5 eq) is introduced into the reactor within 20 min. The temperature is maintained for a reduction reaction for 1 hour, during which the gas in the reactor is continuously mechanically stirred at a speed of 300 rpm to form a gas vortex to accelerate the reaction rate, so as to further purify the metallic lithium.

[0048] S5. After the reduction and purification reaction is completed, the temperature in the reactor is slowly lowered to 200°C. The gas and molten lithium metal in the reactor are collected separately. The gas is passed through ultrapure water at room temperature and then collected to remove a small amount of hydrogen chloride gas in the hydrogen, and then returned to step S4 for recycling. After the molten lithium is cooled to room temperature with the furnace, a high-purity lithium metal product can be obtained.

[0049] Example 2

[0050] A method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method comprises the following steps:

[0051] S1. Weigh 900 g of lithium chloride (21.23 mol, 1.0 eq) and 268 g of metallic aluminum (9.93 mol, 0.47 eq) and place them in a vacuum melting furnace. Pre-evacuate the furnace to a pressure below 30 Pa, then gradually increase the temperature of the vacuum melting furnace to 750°C to ensure that the lithium chloride and metallic aluminum are completely converted into a molten state. After the temperature is increased to the target temperature, keep it for 30 minutes for preliminary impurity removal, which is carried out in flowing nitrogen.

[0052] S2. All molten lithium chloride and 1 / 3 molten metal aluminum are mixed and placed in a vacuum reduction tank preheated to 625°C. The air pressure in the vacuum reduction tank is pumped to below 30Pa by a rotary vane vacuum pump and then heating is started. The temperature is further increased to 900°C. The mechanical stirring speed is turned on at 40rmp and ultrasonic vibration is turned on at 60KHz to assist. The reduction reaction is carried out at a constant temperature. After 1.5 hours of reaction, 1 / 3 molten metal lithium is added for the first time. Then, after 2.5 hours of reaction, 1 / 3 molten metal lithium is added again. After the reaction is continued for 4 hours, the thermal reduction reaction ends. During this period, the aluminum chloride gas generated in the vacuum reduction tank needs to be continuously removed to maintain the vacuum reaction environment, and the aluminum chloride gas is introduced into a double-layer condensation container in an inert gas environment at the same temperature for collection. The interlayer is cooled by circulating water to condense the aluminum chloride gas into a solid state.

[0053] S3, stop mechanical stirring, further increase the temperature in the vacuum reduction tank to 1450 ° C, so that the small amount of molten lithium chloride and molten lithium that have not reacted completely are gasified. The lithium gas and lithium chloride gas are collected in a high-temperature reactor. Before collection, sufficient nitrogen needs to be introduced into the reactor to exclude oxygen and carbon dioxide therein, and the reactor is preheated to 1450 ° C to maintain a constant temperature. The residual metal aluminum in the vacuum reduction tank that does not participate in the reaction is cooled with the furnace and returned to step S1 for reuse.

[0054] S4. A certain amount of high-purity hydrogen (purity ≥ 99.999%, 79.60 mol, 3.75 eq) is introduced into the reactor within 20 min; the temperature is maintained for reduction reaction for 1 hour, during which the gas in the reactor is continuously mechanically stirred at a speed of 400 rpm to form a gas vortex to accelerate the reaction rate, so as to further purify the metallic lithium.

[0055] S5. After the reduction and purification reaction is completed, the temperature in the reactor is slowly lowered to 250°C. The gas and molten lithium metal in the reactor are collected separately. The gas is passed through ultrapure water at room temperature and then collected to remove a small amount of hydrogen chloride gas in the hydrogen, and then returned to step S4 for recycling. After the molten lithium is cooled to room temperature with the furnace, a high-purity lithium metal product can be obtained.

[0056] Example 3

[0057] A method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method comprises the following steps:

[0058] S1. Weigh 900 g of lithium chloride (21.23 mol, 1.0 eq) and 306 g (11.33 mol, 0.53 eq) of metallic aluminum and place them in a vacuum melting furnace. Pre-evacuate the furnace to a pressure below 30 Pa, then gradually increase the temperature of the vacuum melting furnace to 800°C to ensure that the lithium chloride and metallic aluminum are completely converted into a molten state. After the temperature is increased to the target temperature, maintain it for 40 minutes for preliminary impurity removal in flowing helium.

[0059] S2. All molten lithium chloride and 1 / 3 molten metal aluminum are mixed and placed in a vacuum reduction tank preheated to 625°C. The air pressure in the vacuum reduction tank is pumped to below 30Pa by a rotary vane vacuum pump and then heating is started. The temperature is further increased to 1000°C. The mechanical stirring speed is turned on at 50rmp and ultrasonic vibration 80KHz is turned on simultaneously to assist. The reduction reaction is carried out at a constant temperature. After 1h of reaction, 1 / 3 of molten metal lithium is added for the first time. Then, after 2h of reaction, 1 / 3 of molten metal lithium is added again. After the reaction is continued for 4h, the thermal reduction reaction ends. During this period, the aluminum chloride gas generated in the vacuum reduction tank needs to be continuously removed to maintain the vacuum reaction environment, and the aluminum chloride gas is introduced into a double-layer condensation container in an inert gas environment at the same temperature for collection. The interlayer is cooled by circulating water to condense the aluminum chloride gas into a solid state.

[0060] S3, stop mechanical stirring, further increase the temperature in the vacuum reduction tank to 1550 ° C, so that the small amount of molten lithium chloride and molten lithium that have not reacted completely are gasified. The lithium gas and lithium chloride gas are collected in a high-temperature reactor. Before collection, sufficient nitrogen needs to be introduced into the reactor to exclude oxygen and carbon dioxide therein, and the reactor is preheated to 1550 ° C to maintain a constant temperature. The residual metal aluminum in the vacuum reduction tank that does not participate in the reaction is cooled with the furnace and returned to step S1 for reuse.

[0061] S4. A certain amount of high-purity hydrogen (purity ≥ 99.999%, 106.13 mol, 5 eq) is introduced into the reactor within 20 minutes. The temperature is maintained for a reduction reaction for 1 hour, during which the gas in the reactor is continuously mechanically stirred at a speed of 500 rpm to form a gas vortex to accelerate the reaction rate, so as to further purify the metallic lithium.

[0062] S5. After the reduction and purification reaction is completed, the temperature in the reactor is slowly lowered to 200°C. The gas and molten lithium metal in the reactor are collected separately. The gas is passed through ultrapure water at room temperature and then collected to remove a small amount of hydrogen chloride gas in the hydrogen, and then returned to step S4 for recycling. After the molten lithium is cooled to room temperature with the furnace, a high-purity lithium metal product can be obtained.

[0063] Comparative Example 1

[0064] This comparative example uses a molten vacuum thermal reduction-distillation method to prepare high-purity metallic lithium. The only difference from Example 1 is the method of adding metallic aluminum in step S2, which is adjusted from adding metallic aluminum in equal amounts in three times to adding it all at once, and the heating reaction is carried out for a total of 9 hours.

[0065] Comparative Example 2

[0066] This comparative example uses a molten vacuum thermal reduction-distillation method to prepare high-purity metallic lithium, which differs from Example 1 only in that the hydrogen reduction purification step in step S4 is not performed.

[0067] Comparative Example 3

[0068] This comparative example uses a vacuum thermal reduction-distillation method to prepare high-purity metallic lithium. The only difference between this comparative example and Example 1 is that step S1 is not performed, the melting treatment of the raw materials lithium chloride and metallic aluminum before the reaction is deleted, and the solid lithium chloride and metallic aluminum are directly subjected to a vacuum thermal reduction reaction.

[0069] Calculate the yield of lithium in the entire reaction of Example 1 to Example 3 and Comparative Example 1 to Comparative Example 3, yield = (m Li ×C Li ) / (m LiCl ×C LiCl ×M Li / M LiCl )×100%; where m Li is the total mass of finished lithium metal, C Li is the purity of finished lithium metal, m LiCl is the total mass of raw material lithium chloride, C LiCl is the lithium chloride content of the raw material, M Li 、M LiCl is the relative molecular mass of lithium and lithium chloride.

[0070] A certain amount of the product metal lithium was dissolved in ultrapure water and its purity was determined by inductively coupled plasma emission spectrometry. The yield and purity results are shown in Table 1.

[0071] Table 1

[0072] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Yield / % 99.985 99.995 99.989 95.263 98.973 98.576 purity / % 99.993 99.997 99.995 99.987 98.890 99.457

[0073] It can be seen from the data in Table 1 that the present invention utilizes the molten vacuum thermal reduction-distillation method to prepare metallic lithium, which has the advantages of high yield and high purity, and its purity is greater than 99.99%.

[0074] By comparing Example 1 with Comparative Example 1, it can be seen that when lithium chloride and metallic aluminum are subjected to vacuum thermal reduction, the metallic aluminum is mixed with lithium chloride for reaction at one time, and the metallic lithium yield and purity are greatly reduced. The reason is that adding a large amount of aluminum at one time may cause the reaction to be too violent, resulting in local overheating or uneven reaction, thereby affecting the yield and purity of lithium.

[0075] By comparing Example 1 with Comparative Example 2, it can be seen that after the vacuum thermal reduction of lithium chloride and metallic aluminum, a small amount of lithium chloride still does not participate in the reaction, resulting in a significant reduction in yield and purity. In Example 1, high-purity hydrogen is added, which reacts with lithium chloride at high temperature to generate lithium and hydrogen chloride, thereby improving the yield and purity.

[0076] By comparing Example 1 with Comparative Example 3, it can be seen that the yield and purity of metallic lithium in Comparative Example 3 are lower than those in Example 1. The reason is that in the vacuum thermal reduction reaction, direct liquid-liquid reaction occurs, the contact surface between the two is higher, the reaction rate is higher, and thus the thermal reduction reaction is more complete.

[0077] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method, characterized in that: The method comprises the following steps: Weighing a preset ratio of lithium chloride and metallic aluminum, respectively, and vacuum heat treating them to form molten lithium chloride and metallic aluminum, the heat treatment temperature being 700° C. to 800° C.; In the preheated vacuum reduction tank, the molten aluminum metal is mixed with the molten lithium chloride in batches and stirred to perform a vacuum thermal reduction reaction at a temperature of 800°C to 1000°C; After the vacuum thermal reduction reaction is completed, stirring is stopped, the temperature is raised to 1350°C to 1550°C, and the gasified lithium product in the vacuum reduction tank is transferred to the heat-insulating reactor for collection; High-purity hydrogen is introduced into the reactor to reduce and purify the gasified lithium product; The temperature in the reactor is slowly lowered to 200°C to 300°C, and the gasified lithium product is liquefied into molten lithium. After the gas is discharged, the molten lithium is cooled to room temperature along with the furnace to obtain a high-purity metallic lithium product.

2. The method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method according to claim 1, characterized in that: The specific operation of the vacuum thermal reduction reaction is as follows: Preheat the vacuum reduction tank to a temperature of 700°C to 800°C; Mixing all the molten lithium chloride and 1 / 3 of the weight of molten metal aluminum in a vacuum reduction tank; After the vacuum in the vacuum reduction tank is evacuated to below 30Pa, heating is started to raise the internal temperature to 800°C to 1000°C, and vacuum thermal reduction reaction is carried out at a constant temperature for 1h to 2h with the assistance of continuous mechanical stirring and ultrasonic vibration; Add 1 / 3 weight of molten lithium metal and continue the vacuum thermal reduction reaction for 2h to 3h; Add 1 / 3 of molten metallic lithium and continue the vacuum thermal reduction reaction for at least 4 hours.

3. The method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method according to claim 2, characterized in that: During the entire vacuum thermal reduction reaction, the aluminum chloride gas generated in the reduction tank is continuously extracted to maintain the vacuum reaction environment, and the aluminum chloride gas is introduced into a double-layer condensation container in an inert gas environment at the same temperature for collection. The interlayer is cooled by circulating water to condense the aluminum chloride gas into a solid state.

4. The method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method according to claim 2, characterized in that: During the entire vacuum thermal reduction reaction, the mechanical stirring speed is 30 rpm to 50 rpm; and the ultrasonic vibration frequency is 40 KHz to 80 KHz.

5. The method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method according to claim 1, characterized in that: The molar ratio of lithium chloride to metallic aluminum is controlled to be 3:1.2-1.6; When lithium chloride and aluminum metal are completely converted into molten state, keep them warm for more than 20 minutes for preliminary impurity removal; The vacuum heat treatment is performed in a flowing inert atmosphere.

6. The method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method according to claim 1, characterized in that: Before the reactor collects the gasified lithium product, sufficient nitrogen is introduced into the reactor to remove oxygen and carbon dioxide therein; the temperature inside the reactor is 1350°C to 1550°C.

7. The method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method according to claim 1, characterized in that: During the reduction purification, the molar ratio of the introduced hydrogen to the initial lithium chloride is controlled to be between 2.5 and 5:

1.

8. The method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method according to claim 1 or 7, characterized in that: During the reduction and purification, the reactor is continuously mechanically stirred at a speed of 300 rpm to 500 rpm.

9. The method for preparing high-purity metallic lithium by melt vacuum thermal reduction-distillation method according to claim 1, characterized in that: The gas discharged from the reactor after cooling is mixed with ultrapure water at room temperature to remove a small amount of hydrogen chloride gas impurities in the hydrogen, and the impurity-free gas is reused as reduced and purified hydrogen.