A method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate

Abstract

This invention provides a method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate, belonging to the field of lithium fluoride preparation technology. The method includes: preparing industrial-grade lithium carbonate, water, and calcium oxide into a slurry for a causticization reaction; after the reaction, separating the solid and liquid phases to obtain a lithium hydroxide solution and calcium carbonate slag; recrystallizing the lithium hydroxide solution to obtain lithium hydroxide monohydrate crystals and a mother liquor; redissolving the lithium hydroxide monohydrate crystals and filtering to obtain a high-purity lithium hydroxide solution and an insoluble filter residue; spray-drying the high-purity lithium hydroxide solution under a hydrogen fluoride hot atmosphere to generate high-purity nano-sized lithium fluoride. Furthermore, the insoluble filter residue is washed with water and then added to the mother liquor; the tail gas generated during the spray-drying reaction undergoes a neutralization reaction with the mother liquor to prepare conventional lithium fluoride. This invention, based on causticization, recrystallization, and spray-drying steps, produces battery-grade lithium fluoride that balances high purity and nano-particle size, and also includes a neutralization reaction to recover the waste materials generated during the reaction process.

Description

Technical Field

[0001] This invention belongs to the field of lithium fluoride preparation technology, and specifically relates to a method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate. Background Technology

[0002] Lithium fluoride, as one of the essential basic materials for lithium-based batteries, is a key lithium source for the synthesis of lithium hexafluorophosphate, a core material in lithium-ion battery electrolytes. The main technologies for preparing high-purity lithium fluoride include direct preparation, extraction preparation, and ion exchange methods. Most publicly available methods focus on the purification techniques of the lithium and fluorine sources. Controlling the particle size of lithium fluoride to the nanoscale can significantly improve the reactivity of the synthesis of lithium hexafluorophosphate from lithium fluoride.

[0003] Industrial-grade lithium carbonate is the most basic lithium salt product on the market, with good storage and transportation performance, making it the best raw material for synthesizing battery-grade high-purity lithium salts. In addition, the direct preparation method has become the main method for synthesizing lithium fluoride due to its simple principle. This method involves directly reacting a lithium source (mainly lithium carbonate) with a fluorine source to produce lithium fluoride. The main synthesis routes are as follows:

[0004] (1) Liquid-liquid wet process: First, high-purity lithium carbonate is prepared by hydrogenation pyrolysis, and then it is reacted with hydrofluoric acid to prepare battery-grade lithium fluoride. The disadvantage of this process is that it generates a large amount of carbon dioxide gas, which is difficult to recycle.

[0005] (2) Gas-liquid wet process: high-purity lithium carbonate is prepared by the carbide-hydrogenation reaction of lithium carbonate and lithium hydroxide, and then hydrogen fluoride is introduced to prepare lithium fluoride. Although carbon dioxide can be recovered in this process, there is a problem that the particle size of the product is difficult to control. Therefore, mechanical sieving is required at the end to obtain fine and large particles of lithium fluoride.

[0006] (3) Solid-solid dry process: high-purity lithium fluoride is obtained by mixing and roasting battery-grade lithium carbonate and solid ammonium fluoride. However, the solid-phase mixing method has low reaction efficiency, high energy consumption and cannot effectively control the size of the grains.

[0007] In summary, current direct synthesis methods for lithium fluoride cannot simultaneously address the shortcomings and defects in purity and particle size. Therefore, the high-purity lithium salt market urgently needs a method for preparing high-purity nanoscale lithium fluoride from industrial-grade lithium carbonate. Summary of the Invention

[0008] Therefore, the present invention aims to provide a method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate, in order to solve at least one of the technical problems in the background art.

[0009] This invention is implemented as follows:

[0010] A method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate, the method comprising the following steps:

[0011] Industrial-grade lithium carbonate, water, and calcium oxide are mixed into a slurry and subjected to a causticization reaction. After the reaction is completed, solid-liquid separation is performed to obtain lithium hydroxide solution and calcium carbonate slag.

[0012] Lithium hydroxide solution is recrystallized to obtain lithium hydroxide monohydrate crystals and mother liquor; the lithium hydroxide monohydrate crystals are redissolved and filtered to obtain high-purity lithium hydroxide solution and insoluble filter residue.

[0013] High-purity lithium hydroxide solution is spray-dried under a hot atmosphere of hydrogen fluoride to produce high-purity nano-sized lithium fluoride.

[0014] Furthermore, the high-purity lithium hydroxide solution is spray-dried under a hot atmosphere of hydrogen fluoride to generate high-purity nano-sized lithium fluoride, as follows:

[0015] In the spray drying tower, high-purity lithium hydroxide solution is atomized into mist droplets by centrifugal atomization and enters the tower. Hydrogen fluoride enters the tower in the form of hot gas. The two react with heat in the tower to generate high-purity nano-sized lithium fluoride.

[0016] Furthermore, the centrifugal atomization frequency is 400Hz~600Hz, the feed rate of the high-purity lithium hydroxide solution is 60mL / h~300mL / h, the air flow rate of the hydrogen fluoride is 0.05L / min~0.5L / min, and the spray drying reaction temperature is 100℃~150℃.

[0017] Furthermore, the spray drying tower lining and the hydrogen fluoride inlet pipe lining are made of PTFE.

[0018] Furthermore, the recrystallization operation specifically includes: first evaporating and concentrating at 100℃~110℃, and then cooling to 35℃~45℃ for crystallization.

[0019] Furthermore, the mass concentration of the high-purity lithium hydroxide solution is 3.5% to 7%.

[0020] Furthermore, in the causticizing reaction, the molar ratio of industrial-grade lithium carbonate to calcium oxide is 1:1.02~1.5; the liquid-to-solid ratio of the slurry is 8~12:1; the temperature of the causticizing reaction is 80℃~90℃; and the time of the causticizing reaction is 1h~10h.

[0021] Furthermore, in the causticizing reaction, the purity of industrial-grade lithium carbonate is ≥98.5%, and the purity of calcium oxide is ≥90%.

[0022] Further, the insoluble filter residue is washed with water and then added to the mother liquor; then the tail gas generated by the spray drying reaction is neutralized with the mother liquor to prepare lithium fluoride.

[0023] Furthermore, the neutralization reaction is carried out at a stirring rate of 100 rpm to 300 rpm, the reaction temperature is 25℃ to 45℃, and the tail gas flow rate is 0.1 L / min to 5 L / min.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. This invention is based on causticization, recrystallization and spray drying steps to obtain battery-grade lithium fluoride with both high purity and nanoparticle size. At the same time, a neutralization reaction is added to recover the three wastes generated during the reaction process.

[0026] 2. Compared with current methods for preparing lithium fluoride, the spray drying method provided by this invention can not only greatly improve the reaction rate of lithium hydroxide solution and hydrogen fluoride, but also optimize the product particle size; by controlling the spray drying parameters, high-purity lithium fluoride with nanoscale and uniform particle size distribution can be prepared.

[0027] 3. Compared with the current method of preparing high-purity lithium fluoride using industrial-grade lithium carbonate, this invention uses inexpensive and common calcium oxide and conventional recrystallization to synthesize high-purity lithium hydroxide solution from lithium carbonate and effectively remove impurities, thereby improving the purity of lithium fluoride products. The reaction between lithium hydroxide and hydrogen fluoride does not generate a large amount of waste gas, the reaction rate is fast, and the production efficiency is high.

[0028] 4. This invention provides a treatment solution for the three wastes generated during the synthesis of high-purity nano-grade lithium fluoride. The overall process has the advantages of short process flow, simple operation, high controllability, and green environmental protection. The four main processes involved, namely causticization, recrystallization, spray drying, and neutralization, are easy to scale up production. Therefore, this invention has considerable industrial application prospects. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0030] To facilitate understanding of the present invention, a more comprehensive and detailed description of the invention will be provided below in conjunction with the accompanying drawings and preferred embodiments. However, the scope of protection of the present invention is not limited to the specific embodiments described below. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0031] A method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate, the process is as follows: Figure 1As shown, it includes the following steps:

[0032] (1) Industrial grade lithium carbonate, water and calcium oxide are prepared into a slurry for causticization reaction. After the reaction is completed, solid-liquid separation is performed to obtain lithium hydroxide solution and calcium carbonate slag.

[0033] The purity of industrial-grade lithium carbonate is ≥98.5%, and the purity of calcium oxide is ≥90%. In specific implementation, the molar ratio of industrial-grade lithium carbonate to calcium oxide is 1:1.02~1.5; the liquid-to-solid ratio in the slurry is 8~12:1; the temperature of the causticizing reaction is 80℃~90℃, and the time of the causticizing reaction is 1h~10h.

[0034] In this step (1), calcium oxide reacts with water to form calcium hydroxide, which then reacts with lithium carbonate. Calcium oxide should be added in excess to improve the conversion rate and remove impurities of industrial-grade lithium carbonate. The reaction equation is: Li2CO3(slurry) + Ca(OH)2(slurry) = LiOH(aq) + CaCO3(s).

[0035] (2) The lithium hydroxide solution was recrystallized to obtain lithium hydroxide monohydrate crystals and mother liquor; the lithium hydroxide monohydrate crystals were redissolved and filtered to obtain high-purity lithium hydroxide solution and insoluble filter residue;

[0036] In order to accelerate the evaporation rate and increase the crystallization yield, according to the law of the change of solubility of lithium hydroxide with temperature, step (2) is based on the recrystallization method to obtain lithium hydroxide monohydrate crystals and mother liquor. The main component of the mother liquor is saturated lithium hydroxide solution.

[0037] The recrystallization process specifically includes: first, evaporating and concentrating the solution at 100℃~110℃, then cooling it to 35℃~45℃ for crystallization; as the solution temperature decreases, lithium hydroxide gradually precipitates from the solution to form crystals.

[0038] The mass concentration of the high-purity lithium hydroxide solution after redissolution is 3.5%~7%.

[0039] (3) High-purity lithium hydroxide solution is spray-dried under a hot atmosphere of hydrogen fluoride to produce high-purity nano-sized lithium fluoride;

[0040] The reaction in step (3) is carried out in a spray drying tower. Hydrogen fluoride gas is filtered and heated, and the hot gas enters the tower from the top in a spiral shape. The high-purity lithium hydroxide solution is atomized into extremely fine mist droplets by atomization (preferably centrifugal atomization) and enters the tower from the bottom. The two react rapidly in parallel flow in the tower and can be dried into high-purity nano-grade lithium fluoride in a very short time. The finished lithium fluoride is output from the tower through a cyclone separator, and the tail gas is discharged by a fan.

[0041] In specific implementation, the frequency of centrifugal atomization is 400Hz~600Hz, the feed rate of high-purity lithium hydroxide solution is 60mL / h~300mL / h; the air flow rate of hydrogen fluoride is 0.05L / min~0.5L / min; the spray drying reaction temperature is 100℃~150℃; the reaction equation for the spray drying process described in step (3) is:

[0042] LiOH(aq) + HF(g) = LiF(s) + H2O(g);

[0043] LiOH(aq) + CO2(g) = Li2CO3(aq) + H2O(g);

[0044] Li2CO3(aq) + 2HF(g) = CO2(g) + 2LiF(s)+H2O(g);

[0045] Lithium hydroxide solution is atomized into droplets by centrifugal atomization and introduced into a spray drying tower with a hydrogen fluoride atmosphere. This significantly increases the contact area between the lithium hydroxide solution and hydrogen fluoride, accelerating the reaction rate and shortening the crystal growth time. Even if lithium carbonate is generated due to the presence of a small amount of carbon dioxide in the spray drying tower, it will be converted into lithium fluoride in the atmosphere of hydrogen fluoride and water vapor, thus eliminating the need for an inert atmosphere. To better achieve the above process, it is necessary to control the appropriate centrifugal atomization frequency, spray drying temperature, solution injection rate, and hydrogen fluoride airflow. The selection of these four factors is related to the parameters of the spray drying equipment, and the operating conditions may be altered due to changes in parameters such as the size of the spray drying equipment. These modifications are also within the scope of protection of this invention.

[0046] The high-purity nano-sized lithium fluoride obtained in this step has a purity ≥99.9% and an average particle size D. 50 ≤1μm.

[0047] To prevent corrosion from hydrogen fluoride, the spray drying tower and pipeline linings should be coated with anti-corrosion paint. Specifically, the spray drying tower lining and the hydrogen fluoride inlet pipeline lining should be PTFE lining.

[0048] (4) The insoluble filter residue is washed with water and then added to the mother liquor; then the tail gas generated by the spray drying reaction is neutralized with the mother liquor to prepare lithium fluoride;

[0049] The purpose of step (4) is to process the waste residue (filter residue), waste liquid (mother liquor), and waste gas (tail gas) generated in the previous steps to obtain conventional lithium fluoride; the tail gas generated in step (3) mainly consists of air and hydrogen fluoride, the mother liquor generated in step (2) mainly consists of saturated lithium hydroxide solution, and the insoluble filter residue generated in step (2) is lithium carbonate generated by the carbonization reaction of lithium hydroxide during the redissolution process; therefore, the three wastes (lithium carbonate, saturated lithium hydroxide solution, and hydrogen fluoride) generated in steps (1) to (3) directly undergo a neutralization reaction in this step to prepare lithium fluoride. However, due to the high impurity content in the crystallization mother liquor, this step can only obtain conventional lithium fluoride products, whose purity is lower than that of the high-purity nano-sized lithium fluoride obtained in step (3), and the particle size is larger than that of the high-purity nano-sized lithium fluoride. The lithium fluoride obtained in this step has a purity ≥99% and an average particle size D 50 ≥5μm;

[0050] Specifically, the neutralization reaction is carried out at a stirring rate of 100 rpm to 300 rpm, a reaction temperature of 25°C to 45°C, and a tail gas flow rate of 0.1 L / min to 5 L / min.

[0051] Because industrial-grade lithium carbonate contains high levels of impurities such as calcium and sulfate, this invention first uses inexpensive calcium oxide as an auxiliary material to convert industrial-grade lithium carbonate into a lithium hydroxide solution and remove impurities such as calcium, magnesium, and calcium phosphate. Then, it uses recrystallization to obtain lithium hydroxide monohydrate and redissolves it in water to obtain a high-purity lithium hydroxide solution. Next, the high-purity lithium hydroxide solution is spray-dried in a hydrogen fluoride atmosphere. Spray drying significantly expands the contact area between reactants, increases the reaction rate, and helps to reduce the particle size of the product, thus obtaining high-purity nano-sized lithium fluoride. Finally, this invention also includes a neutralization treatment method for the mother liquor and hydrogen fluoride tail gas to obtain lithium fluoride, achieving solid, liquid, and gaseous waste treatment.

[0052] Example 1

[0053] A method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate includes the following steps:

[0054] (1) Prepare a slurry with industrial grade lithium carbonate (98.5%), water and calcium oxide (94%) with a Li2CO3:CaO molar ratio of 1:1.02 and a liquid-solid ratio of 8:1. Causticize the slurry at 80℃ for 1 hour. After the reaction is completed, filter the slurry through a plate and frame filter to obtain lithium hydroxide solution and calcium carbonate slag.

[0055] (2) The lithium hydroxide solution was evaporated and concentrated at 100°C and cooled and crystallized at 35°C to obtain lithium hydroxide monohydrate and mother liquor. The lithium hydroxide monohydrate was dissolved in water and then solid-liquid separation was performed to obtain a high-purity lithium hydroxide solution (LiOH content of 3.5%) and insoluble filter residue.

[0056] (3) The high-purity lithium hydroxide solution was centrifuged and atomized into the spray drying tower at a feed rate of 60 mL / h and a frequency of 400 Hz. The temperature inside the spray drying tower was maintained at 100 ℃, and the air flow rate of hydrogen fluoride (heated to 100 ℃) was 0.05 L / min. High-purity nano-sized LiF was obtained by bag dust collection and labeled as LiF1-1.

[0057] (4) The filter residue generated in step (2) is washed with water and added to the mother liquor. It is then neutralized with the tail gas generated in step (3) at 25°C. The stirring rate during the reaction is 100 rpm and the tail gas flow rate is 0.1 L / min. LiF is obtained and labeled as LiF1-2.

[0058] The purity and particle size of the products from steps (3) and (4) above were tested, and the results are shown in Table 1.

[0059] Example 2

[0060] A method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate includes the following steps:

[0061] (1) Prepare a slurry with industrial grade lithium carbonate (98.5%), water and calcium oxide (94%) with a Li2CO3:CaO molar ratio of 1:1.5 and a liquid-solid ratio of 12:1. Causticize the mixture at 90℃ for 10h. After the reaction is completed, filter the mixture through a plate and frame filter to obtain lithium hydroxide solution and calcium carbonate slag.

[0062] (2) The lithium hydroxide solution was evaporated and concentrated at 110°C and cooled and crystallized at 45°C to obtain lithium hydroxide monohydrate and mother liquor. The lithium hydroxide monohydrate was dissolved in water and then solid-liquid separation was performed to obtain a high-purity lithium hydroxide solution (LiOH content of 7%) and insoluble filter residue.

[0063] (3) The high-purity lithium hydroxide solution was centrifuged and atomized into the spray drying tower at a feed rate of 300 mL / h and a frequency of 600 Hz. The temperature inside the spray drying tower was maintained at 150 ℃, and the air flow rate of hydrogen fluoride (heated to 150 ℃) was 0.5 L / min. High-purity nano-sized LiF was obtained by bag dust collection and labeled as LiF2-1.

[0064] (4) The filter residue generated in step (2) is washed with water and added to the mother liquor. It is then neutralized with the tail gas generated in step (3) at 45°C. The stirring rate is 300 rpm and the tail gas flow rate is 5 L / min to obtain LiF, which is labeled as LiF2-2.

[0065] The purity and particle size of the products from steps (3) and (4) above were tested, and the results are shown in Table 1.

[0066] Example 3

[0067] A method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate includes the following steps:

[0068] (1) Prepare a slurry with industrial grade lithium carbonate (98.5%), water and calcium oxide (94%) in a Li2CO3:CaO molar ratio of 1:1.1 and a liquid-solid ratio of 10:1. Causticize the mixture at 85℃ for 3 hours. After the reaction is completed, filter the mixture through a plate and frame filter to obtain lithium hydroxide solution and calcium carbonate slag.

[0069] (2) The lithium hydroxide solution was evaporated and concentrated at 105°C and cooled and crystallized at 40°C to obtain lithium hydroxide monohydrate and mother liquor. The lithium hydroxide monohydrate was dissolved in water and then solid-liquid separation was performed to obtain a high-purity lithium hydroxide solution (LiOH content of 5%) and insoluble filter residue.

[0070] (3) The high-purity lithium hydroxide solution was centrifuged and atomized into the spray drying tower at a feed rate of 150 mL / h and a frequency of 500 Hz. The temperature inside the spray drying tower was maintained at 130 ℃, and the air flow rate of hydrogen fluoride (heated to 130 ℃) was 0.2 L / min. High-purity nano-sized LiF was obtained by bag dust collection and labeled as LiF3-1.

[0071] (4) The filter residue generated in step (2) is washed with water and added to the mother liquor. It is then neutralized with the tail gas generated in step (3) at 30°C. The stirring rate is 250 rpm and the tail gas flow rate is 0.2 L / min to obtain LiF, which is designated as LiF3-2.

[0072] The purity and particle size of the products from steps (3) and (4) above were tested, and the results are shown in Table 1.

[0073] Comparative Example 1

[0074] This comparative example is a method for preparing lithium fluoride from industrial-grade lithium carbonate. The difference between this method and Example 3 is step (3). In step (3) of this comparative example, the lithium hydroxide solution and hydrogen fluoride gas are reacted using a conventional gas-liquid mixture. The other steps and reaction parameters are the same as in Example 3. The steps of this comparative example are as follows:

[0075] (1) Same as step (1) in Example 3;

[0076] (2) Same as step (2) in Example 3;

[0077] (3) A high-purity lithium hydroxide solution was fed into the spray drying tower at a feed rate of 150 mL / h. The temperature inside the spray drying tower was maintained at 130℃, the hydrogen fluoride air flow rate was 0.2 L / min, and LiF was obtained by bag dust collection and labeled as LiF4-1.

[0078] (4) Same as step (4) in Example 3, the obtained LiF is designated as LiF4-2.

[0079] The purity and particle size of the products from steps (3) and (4) above were tested, and the results are shown in Table 1.

[0080] Comparative Example 2

[0081] This comparative example is a method for preparing lithium fluoride from industrial-grade lithium carbonate. The difference between this method and Example 3 is the deletion of the recrystallization and resolution steps in step (2), and the deletion of step (4) based on the reaction in step (2). The steps in this comparative example are as follows:

[0082] (1) Same as step (1) in Example 3;

[0083] (2) The lithium hydroxide solution was centrifuged and atomized into the spray drying tower at a feed rate of 150 mL / h and a frequency of 500 Hz. The temperature inside the spray drying tower was maintained at 130 ℃, the hydrogen fluoride air flow rate was 0.2 L / min, and the dust was collected by bag filter to obtain LiF, which was numbered as LiF5-1.

[0084] The purity and particle size of the tested products are shown in Table 1.

[0085] Comparative Example 3

[0086] This comparative example is a method for preparing lithium fluoride from industrial-grade lithium carbonate. The difference between this method and Example 3 is the centrifugal atomization frequency in step (3). This comparative example is set to 300Hz, while the other steps and reaction parameters are the same as in Example 3.

[0087] The LiF obtained in step (3) of this comparative example is designated as LiF6-1, and the LiF obtained in step (4) is designated as LiF6-2. The purity and particle size of the products were tested, and the results are shown in Table 1.

[0088] Comparative Example 4

[0089] This comparative example is a method for preparing lithium fluoride from industrial-grade lithium carbonate. The difference between this method and Example 3 is the spray drying temperature in step (3), which is set to 90°C in this comparative example. Other steps and reaction parameters are the same as in Example 3.

[0090] The LiF obtained in step (3) of this comparative example is designated as LiF7-1, and the LiF obtained in step (4) is designated as LiF7-2. The purity and particle size of the products were tested, and the results are shown in Table 1.

[0091] Comparative Example 5

[0092] This comparative example is a method for preparing lithium fluoride from industrial-grade lithium carbonate. The difference between this method and Example 3 is the feed rate of high-purity lithium hydroxide solution and the air flow rate of hydrogen fluoride in step (3). In this comparative example, the high-purity lithium hydroxide solution is set to 50 mL / h and the air flow rate of hydrogen fluoride is 0.04 L / min. Other steps and reaction parameters are the same as in Example 3.

[0093] The LiF obtained in step (3) of this comparative example is designated as LiF8-1, and the LiF obtained in step (4) is designated as LiF8-2. The purity and particle size of the products were tested, and the results are shown in Table 1.

[0094] Comparative Example 6

[0095] This comparative example is a method for preparing lithium fluoride from industrial-grade lithium carbonate. The difference between this method and Example 3 is the feed rate of high-purity lithium hydroxide solution and the air flow rate of hydrogen fluoride in step (3). In this comparative example, the high-purity lithium hydroxide solution is set to 350 mL / h and the air flow rate of hydrogen fluoride is 0.55 L / min. Other steps and reaction parameters are the same as in Example 3.

[0096] The LiF obtained in step (3) of this comparative example is designated as LiF9-1, and the LiF obtained in step (4) is designated as LiF9-2. The purity and particle size of the products were tested, and the results are shown in Table 1.

[0097] Table 1

[0098]

[0099] As shown in Table 1, the high-purity nano-sized LiF prepared in the embodiments of the present invention has a purity ≥ 99.9% and an average particle size D. 50 The purity is ≤1μm. Furthermore, the solid, liquid, and gaseous waste generated during the synthesis process is recycled to produce conventional LiF with a purity ≥99%, thus avoiding environmental pollution and waste of raw materials.

[0100] In Comparative Example 1, the high-purity lithium hydroxide solution and hydrogen fluoride gas were reacted using a conventional gas-liquid mixing reaction. As can be seen from the data in Table 1, compared with the spray drying reaction of the present invention, the LiF prepared in Comparative Example 1 has deficiencies in both purity and particle size, and the product quality is far inferior to that of Example 3.

[0101] In Comparative Example 2, industrial-grade lithium carbonate reacts with calcium oxide to generate lithium hydroxide solution, which is then directly spray-dried with hydrogen fluoride gas. As shown in Table 1, compared with the present invention, which recrystallizes and redissolves the lithium hydroxide solution, the LiF obtained in Comparative Example 2 has low purity and the product quality is far inferior to that of Example 3. Furthermore, the hydrogen fluoride tail gas generated in the process will also pollute the environment.

[0102] In Comparative Example 3, the spray drying reaction was controlled at a lower centrifugal atomization frequency, resulting in poor atomization effect of the high-purity lithium hydroxide solution. The droplets formed by the high-purity lithium hydroxide solution were larger, which reduced the reaction efficiency with hydrogen fluoride gas. As can be seen from the data in Table 1, the particle size of its product was larger than that of Example 3, and the purity was lower than that of Example 3.

[0103] In Comparative Example 4, the spray drying reaction temperature was controlled at 90°C. As can be seen from the data in Table 1, the particle size of its product was larger than that of Example 3, and the purity was lower than that of Example 3. The reason is that the spray drying temperature is lower, which easily leads to untimely evaporation of water, resulting in a higher water content in the product and more residual lithium hydroxide impurities, which reduces the purity and increases the particle size.

[0104] In Comparative Example 5, the feed rate of high-purity lithium hydroxide solution and hydrogen fluoride gas in the spray drying reaction was reduced. As can be seen from the data in Table 1, the particle size of the product was larger than that of Example 3, and the purity was lower than that of Example 3. The reason is that the lower feed rate and air volume led to incomplete reaction, incomplete reaction between hydrogen fluoride gas and lithium hydroxide solution, higher lithium hydroxide impurity content in the product, reduced lithium fluoride purity, and larger particle size.

[0105] In Comparative Example 6, the feed rate of high-purity lithium hydroxide solution and hydrogen fluoride gas in the spray drying reaction was increased. As can be seen from the data in Table 1, the particle size of the product was larger than that of Example 3, and the purity was lower than that of Example 3. The reason is that the excessive feed rate or air volume caused droplets of hydrogen fluoride and lithium hydroxide solution in the tail gas to enter the product collection device, contaminating the product, reducing the purity of the product, and increasing the particle size of the product.

[0106] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate, characterized in that, The method includes the following steps: Industrial-grade lithium carbonate with a purity ≥98.5%, water, and calcium oxide with a purity ≥90% were prepared into a slurry and subjected to a causticization reaction. After the reaction was completed, solid and liquid were separated to obtain a lithium hydroxide solution and calcium carbonate slag. The lithium hydroxide solution is recrystallized to obtain lithium hydroxide monohydrate crystals and mother liquor; the recrystallization operation is specifically as follows: first, evaporate and concentrate at 100℃~110℃, and then cool to 35℃~45℃ for crystallization. Lithium hydroxide monohydrate crystals were redissolved and then filtered to obtain a high-purity lithium hydroxide solution and an insoluble filter residue; the mass concentration of the high-purity lithium hydroxide solution was 3.5%~7%; High-purity lithium hydroxide solution is spray-dried under a hot atmosphere of hydrogen fluoride to produce high-purity nano-sized lithium fluoride; specifically including: In a spray drying tower, a high-purity lithium hydroxide solution is atomized into droplets by centrifugal atomization and enters the tower. Hydrogen fluoride enters the tower as a hot gas, and the two react in the tower to generate high-purity nano-sized lithium fluoride. The frequency of centrifugal atomization is 400Hz~600Hz, the feed rate of the high-purity lithium hydroxide solution is 60mL / h~300mL / h, the air flow rate of the hydrogen fluoride is 0.05L / min~0.5L / min, and the spray drying reaction temperature is 100℃~150℃.

2. The method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate according to claim 1, characterized in that, The spray drying tower lining and the hydrogen fluoride inlet pipe lining are made of PTFE.

3. The method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate according to claim 1, characterized in that, In the causticizing reaction, the molar ratio of industrial-grade lithium carbonate to calcium oxide is 1:1.02~1.5; the liquid-to-solid ratio of the slurry is 8~12:1; the temperature of the causticizing reaction is 80℃~90℃; and the time of the causticizing reaction is 1h~10h.

4. The method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate according to claim 1, characterized in that, The insoluble filter residue is washed with water and then added to the mother liquor; then the tail gas generated by the spray drying reaction is neutralized with the mother liquor to prepare lithium fluoride.

5. The method for preparing high-purity nano-sized lithium fluoride from industrial-grade lithium carbonate according to claim 4, characterized in that, The neutralization reaction was carried out at a stirring rate of 100 rpm to 300 rpm, a reaction temperature of 25℃ to 45℃, and a tail gas flow rate of 0.1 L / min to 5 L / min.

Images