Method for preparing high-purity nanoscale lithium fluoride from industrial grade lithium carbonate

Abstract

The invention provides a method for preparing high-purity nanoscale lithium fluoride from industrial-grade lithium carbonate, and belongs to the technical field of lithium fluoride preparation.The method comprises the steps that the industrial-grade lithium carbonate, water and calcium oxide are prepared into slurry to be subjected to causticization reaction, and after the reaction is finished, solid-liquid separation is conducted to obtain a lithium hydroxide solution and calcium carbonate residues; recrystallizing the lithium hydroxide solution to obtain lithium hydroxide monohydrate crystals and mother liquor; re-dissolving the lithium hydroxide monohydrate crystal, and filtering to obtain a high-purity lithium hydroxide solution and insoluble filter residues; and carrying out spray drying reaction on the high-purity lithium hydroxide solution in a hydrogen fluoride hot atmosphere to generate the high-purity nanoscale lithium fluoride. In addition, washing insoluble filter residues with water, and adding mother liquor; the tail gas generated by the spray drying reaction and the mother liquor are subjected to neutralization reaction to prepare the conventional lithium fluoride. On the basis of causticization, recrystallization and spray drying steps, the battery-grade lithium fluoride with high purity and nano particle size is prepared, and meanwhile, a neutralization reaction is added to recycle three wastes generated in the reaction process.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium fluoride preparation, and particularly relates to a method for preparing high-purity nanometer-level lithium fluoride from industrial-grade lithium carbonate. Background Art

[0002] As one of the important basic materials of lithium-based materials, lithium fluoride is a key lithium source for the synthesis of lithium hexafluorophosphate, which is the core material of lithium-ion battery electrolyte. The preparation technologies of high-purity lithium fluoride mainly include direct preparation method, extraction preparation method and ion exchange method. Most of the published methods focus on the purification technology of lithium and fluorine sources. Controlling the particle size of lithium fluoride at the nanometer level can significantly improve the reaction activity of lithium fluoride in the synthesis of lithium hexafluorophosphate.

[0003] Industrial-grade lithium carbonate is the most basic lithium salt product on the market. It has good storage and transportation performance and is 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. It is to directly react a lithium source (mainly lithium carbonate) with a fluorine source to generate lithium fluoride. The main synthesis routes are as follows:

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

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

[0006] (3) Solid-solid dry process, which uses battery-grade lithium carbonate and solid ammonium fluoride to mix and react to obtain high-purity lithium fluoride. However, the solid-phase mixing method has low reaction efficiency, high energy consumption and cannot effectively control the grain size.

[0007] In summary, the current direct preparation method for synthesizing lithium fluoride cannot simultaneously take into account the shortcomings and defects of purity and particle size. Therefore, the high-purity lithium salt market urgently needs a method for preparing high-purity nano-scale lithium fluoride from industrial-grade lithium carbonate. Summary of the invention

[0008] In view of this, the object of the present invention is to provide a method for preparing high-purity nano-scale lithium fluoride from industrial-grade lithium carbonate, aiming to solve at least one technical problem in the background technology.

[0009] The present invention is achieved in that:

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

[0011] Industrial-grade lithium carbonate, water and calcium oxide are prepared into a slurry for causticization reaction, and after the reaction, solid-liquid separation is performed to obtain lithium hydroxide solution and calcium carbonate slag;

[0012] The lithium hydroxide solution is subjected to a recrystallization operation to obtain lithium hydroxide monohydrate crystals and a mother liquor; the lithium hydroxide monohydrate crystals are redissolved and then filtered to obtain a high-purity lithium hydroxide solution and an insoluble filter residue;

[0013] High-purity lithium hydroxide solution is spray-dried in a hot hydrogen fluoride atmosphere to generate high-purity nano-scale lithium fluoride.

[0014] Furthermore, the high-purity lithium hydroxide solution is spray-dried in a hot atmosphere of hydrogen fluoride to generate high-purity nano-scale lithium fluoride, and the specific operation is as follows:

[0015] In the spray drying tower, high-purity lithium hydroxide solution is atomized into mist-like liquid droplets by centrifugal atomization and enters the tower, and hydrogen fluoride enters the tower in the form of hot gas. The two are heated and reacted in the tower to generate high-purity nano-level lithium fluoride.

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

[0017] Furthermore, the spray drying tower lining and the hydrogen fluoride air intake pipe lining are PTFE lined.

[0018] Furthermore, the recrystallization operation specifically includes: first evaporating and concentrating at 100°C to 110°C, and then cooling to 35°C to 45°C 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-solid ratio of the slurry is 8-12:1; the temperature of the causticizing reaction is 80°C-90°C, 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] Furthermore, the insoluble filter residue is washed with water and then added to a mother liquor; then the tail gas generated by the spray drying reaction undergoes a neutralization reaction 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, a reaction temperature of 25° C. to 45° C., and an intake rate of tail gas of 0.1 L / min to 5 L / min.

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

[0025] 1. The present invention is based on the steps of causticization, recrystallization and spray drying to produce battery-grade lithium fluoride with high purity and nanometer particle size, and also adds a neutralization reaction to recover the three wastes generated during the reaction.

[0026] 2. Compared with the current method for preparing lithium fluoride, the spray drying method provided by the present 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 nanometer scale 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, the present invention uses cheap and common calcium oxide and conventional recrystallization method to synthesize high-purity lithium hydroxide solution from lithium carbonate and effectively remove impurities, thereby improving the purity of lithium fluoride product. The reaction of 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. The present invention provides a treatment scheme for the three wastes in the process of synthesizing high-purity nano-scale lithium fluoride. The overall process has the advantages of short process, simple operation, high controllability, and green environmental protection. The four main processes of causticizing, recrystallization, spray drying, and neutralization involved are easy to expand production. Therefore, the present invention has considerable industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0030] For the convenience of understanding the present invention, the present invention will be described more comprehensively and meticulously in conjunction with the accompanying drawings and preferred embodiments below, but the protection scope of the present invention is not limited to the following specific embodiments. Unless otherwise defined, all professional terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or can be prepared by existing methods.

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

[0032] (1) industrial-grade lithium carbonate, water, and calcium oxide are prepared into a slurry for causticization reaction, and after the reaction, solid-liquid separation is performed to obtain a 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 a specific implementation, the molar ratio of industrial-grade lithium carbonate to calcium oxide is 1:1.02-1.5; the liquid-solid ratio in the slurry is 8-12:1; the temperature of the causticizing reaction is 80°C-90°C, and the time of the causticizing reaction is 1h-10h;

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

[0035] (2) performing a recrystallization operation on 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;

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

[0037] The recrystallization operation specifically includes: first evaporating and concentrating at 100°C to 110°C, then cooling to 35°C to 45°C 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% to 7%.

[0039] (3) spray drying high-purity lithium hydroxide solution in a hot atmosphere of hydrogen fluoride to generate high-purity nano-scale lithium fluoride;

[0040] The reaction in step (3) is carried out in a spray drying tower. The hydrogen fluoride gas is filtered and heated, and the hot gas enters the tower evenly 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 are rapidly contacted and reacted in parallel in the tower, and can be dried into a finished product of high-purity nano-grade lithium fluoride in a very short time; the finished product lithium fluoride is output from the tower through a cyclone separator, and the tail gas is discharged by a fan;

[0041] In the 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 volume of hydrogen fluoride is 0.05L / min-0.5L / min; the spray drying reaction temperature is 100°C-150°C; the reaction equation occurring in the spray drying process of 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] The lithium hydroxide solution is atomized into mist droplets by centrifugal atomization and introduced into the spray drying tower in the hydrogen fluoride atmosphere, which greatly increases the contact area between the lithium hydroxide solution and the hydrogen fluoride, accelerates the reaction rate, and shortens the grain growth time; even if lithium carbonate is generated due to 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, so no inert atmosphere protection is required. In order to better realize the above process, it is necessary to control the appropriate centrifugal atomization frequency, spray drying temperature, solution injection rate, and hydrogen fluoride air intake. The selection of these four factors is related to the parameters of the spray drying equipment. The operating conditions may change due to changes in parameters such as the size of the spray drying equipment. These changes are also within the scope of protection of the present invention;

[0046] The purity of the high-purity nano-scale lithium fluoride prepared in this step is ≥99.9%, and the average particle size is D 50 ≤1μm.

[0047] In order to prevent corrosion from hydrogen fluoride, the spray drying tower and the pipeline lining should adopt anti-corrosion coating. Specifically, the spray drying tower lining and the hydrogen fluoride intake pipeline lining should adopt PTFE lining.

[0048] (4) washing the insoluble residue with water and adding the mother liquor; then neutralizing the tail gas generated by the spray drying reaction with the mother liquor to prepare lithium fluoride;

[0049] The function of step (4) is to process the waste residue (filter residue), waste liquid (mother liquor) and waste gas (tail gas) produced in the previous steps to obtain conventional lithium fluoride; the tail gas produced in step (3) is mainly composed of air and hydrogen fluoride, the main component of the mother liquor produced in step (2) is saturated lithium hydroxide solution, and the insoluble filter residue produced in step (2) is lithium carbonate generated by carbonization reaction of lithium hydroxide during the re-dissolution process; therefore, the three wastes (lithium carbonate, saturated lithium hydroxide solution, hydrogen fluoride) produced in steps (1) to (3) are directly neutralized 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, the purity of which is lower than the high-purity nano-scale lithium fluoride obtained in step (3), and the particle size is larger than the above-mentioned high-purity nano-scale lithium fluoride. The purity of the lithium fluoride obtained in this step is ≥99%, and the 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 an intake rate of tail gas of 0.1 L / min to 5 L / min.

[0051] Since industrial-grade lithium carbonate contains relatively high levels of impurities such as calcium and sulfate, the present invention first uses cheap calcium oxide as an auxiliary material to transform industrial-grade lithium carbonate into lithium hydroxide solution and removes impurities such as calcium, magnesium, and calcium phosphate therein; then, monohydrate lithium hydroxide is obtained by recrystallization and redissolved in water to obtain a high-purity lithium hydroxide solution; then, the high-purity lithium hydroxide solution is subjected to a spray drying reaction in a hydrogen fluoride atmosphere, and the spray drying significantly expands the contact area between the reactants, increases the reaction rate, and helps to reduce the particle size of the product, thereby obtaining high-purity nano-scale lithium fluoride; finally, the present invention also uses a neutralization treatment method for the mother liquor and hydrogen fluoride tail gas to obtain lithium fluoride, thereby realizing the treatment of solid, liquid, and gas wastes.

[0052] Example 1

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

[0054] (1) industrial-grade lithium carbonate (98.5%), clean water, and calcium oxide (94%) are prepared into a slurry with a molar ratio of Li2CO3:CaO = 1:1.02 and a liquid-to-solid ratio of 8:1, and the mixture is causticized at 80° C. for 1 hour. After the reaction is completed, the lithium hydroxide solution and calcium carbonate slag are obtained by plate and frame filtration;

[0055] (2) evaporating and concentrating the lithium hydroxide solution at 100° C. and cooling and crystallizing at 35° C. to obtain lithium hydroxide monohydrate and a mother liquor, dissolving the lithium hydroxide monohydrate in water and then performing solid-liquid separation to obtain a high-purity lithium hydroxide solution (LiOH content of 3.5%) and an insoluble filter residue;

[0056] (3) High-purity lithium hydroxide solution was centrifugally atomized into a spray drying tower at a feed rate of 60 mL / h and a frequency of 400 Hz. The temperature in the spray drying tower was maintained at 100° C. The air flow rate of hydrogen fluoride (heated to 100° C.) was 0.05 L / min. The dust was collected by a bag to obtain high-purity nano-scale LiF, which was numbered as LiF1-1;

[0057] (4) The filter residue produced in step (2) is washed with water and then added to the mother liquor, and then neutralized with the tail gas produced in step (3) at 25° C. During the reaction, the stirring rate is 100 rpm and the amount of tail gas introduced is 0.1 L / min to obtain LiF, which is numbered as LiF1-2.

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

[0059] Example 2

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

[0061] (1) industrial-grade lithium carbonate (98.5%), clean water, and calcium oxide (94%) are prepared into a slurry with a molar ratio of Li2CO3:CaO = 1:1.5 and a liquid-to-solid ratio of 12:1, and the mixture is causticized at 90° C. for 10 h. After the reaction is completed, a lithium hydroxide solution and calcium carbonate slag are obtained by plate and frame filtration;

[0062] (2) evaporating and concentrating the lithium hydroxide solution at 110° C. and cooling and crystallizing at 45° C. to obtain lithium hydroxide monohydrate and a mother liquor, dissolving the lithium hydroxide monohydrate in water and then performing solid-liquid separation to obtain a high-purity lithium hydroxide solution (LiOH content of 7%) and an insoluble filter residue;

[0063] (3) High-purity lithium hydroxide solution was centrifugally atomized into a spray drying tower at a feed rate of 300 mL / h and a frequency of 600 Hz. The temperature in the spray drying tower was maintained at 150° C. The air flow rate of hydrogen fluoride (heated to 150° C.) was 0.5 L / min. The dust was collected by a bag to obtain high-purity nano-scale LiF, which was numbered as LiF2-1.

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

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

[0066] Example 3

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

[0068] (1) industrial-grade lithium carbonate (98.5%), clean water, and calcium oxide (94%) are prepared into a slurry with a molar ratio of Li2CO3:CaO = 1:1.1 and a liquid-to-solid ratio of 10:1, and subjected to causticizing reaction at 85° C. for 3 h. After the reaction is completed, a lithium hydroxide solution and calcium carbonate slag are obtained by plate and frame filtration;

[0069] (2) evaporating and concentrating the lithium hydroxide solution at 105° C. and cooling and crystallizing at 40° C. to obtain lithium hydroxide monohydrate and a mother liquor, dissolving the lithium hydroxide monohydrate in water and then performing solid-liquid separation to obtain a high-purity lithium hydroxide solution (LiOH content of 5%) and an insoluble filter residue;

[0070] (3) High-purity lithium hydroxide solution was centrifugally atomized into a spray drying tower at a feed rate of 150 mL / h and a frequency of 500 Hz. The temperature in the spray drying tower was maintained at 130° C. The air flow rate of hydrogen fluoride (heated to 130° C.) was 0.2 L / min. The dust was collected by a bag to obtain high-purity nano-scale LiF, which was numbered as LiF3-1;

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

[0072] The purity and particle size of the products of step (3) and step (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 comparative example and Example 3 is step (3). In step (3) of this comparative example, the lithium hydroxide solution and the hydrogen fluoride gas adopt a conventional gas-liquid mixing reaction. The other steps and reaction parameters are the same as those of Example 3. The steps of this comparative example are:

[0075] (1) The same as step (1) of Example 3;

[0076] (2) The same as step (2) of Example 3;

[0077] (3) High-purity lithium hydroxide solution is fed into a spray drying tower at a feed rate of 150 mL / h, the temperature in the spray drying tower is maintained at 130° C., the hydrogen fluoride air flow rate is 0.2 L / min, and LiF is obtained by bag dust collection, which is numbered as LiF4-1;

[0078] (4) The same as step (4) of Example 3, the LiF obtained is numbered as LiF4-2.

[0079] The purity and particle size of the products of step (3) and step (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 comparative example and Example 3 is that the recrystallization and redissolution steps of step (2) are deleted, and step (4) based on the reaction of step (2) is also deleted. The steps of this comparative example are:

[0082] (1) The same as step (1) of Example 3;

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

[0084] The purity and particle size of the product were tested and the results 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 comparative example and Example 3 is that the centrifugal atomization frequency in step (3) is set to 300 Hz. The other steps and reaction parameters are the same as those in Example 3.

[0087] The LiF prepared in step (3) of this comparative example is numbered as LiF6-1, and the LiF prepared in step (4) is numbered 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 comparative example and Example 3 is that the spray drying temperature in step (3) is set to 90°C. The other steps and reaction parameters are the same as those in Example 3.

[0090] The LiF prepared in step (3) of this comparative example is numbered as LiF7-1, and the LiF prepared in step (4) is numbered 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 comparative example and Example 3 is the feed amount of high-purity lithium hydroxide solution and the air flow rate of hydrogen fluoride in step (3). In this comparative example, the feed amount of high-purity lithium hydroxide solution is set to 50 mL / h, and the air flow rate of hydrogen fluoride is 0.04 L / min. The other steps and reaction parameters are the same as those in Example 3.

[0093] The LiF prepared in step (3) of this comparative example is numbered as LiF8-1, and the LiF prepared in step (4) is numbered 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 comparative example and Example 3 is the feed amount of high-purity lithium hydroxide solution and the air intake amount of hydrogen fluoride in step (3). In this comparative example, the feed amount of high-purity lithium hydroxide solution is set to 350 mL / h, and the air intake amount of hydrogen fluoride is 0.55 L / min. The other steps and reaction parameters are the same as those in Example 3.

[0096] The LiF prepared in step (3) of this comparative example is numbered as LiF9-1, and the LiF prepared in step (4) is numbered 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]

[0100] From the data in Table 1, it can be seen that the purity of the high-purity nano-scale LiF prepared in the embodiment of the present invention is ≥99.9%, and the average particle size D 50 ≤1μm, and the solid, liquid and gaseous wastes generated during the synthesis process are recycled to produce conventional LiF with a purity of ≥99%, avoiding environmental pollution and waste of raw materials.

[0101] In Comparative Example 1, the high-purity lithium hydroxide solution and the hydrogen fluoride gas adopt a conventional gas-liquid mixing reaction. It can be seen from the data in Table 1 that, compared with the spray drying reaction of the present invention, the LiF prepared in Comparative Example 1 has insufficient defects in terms of purity and particles, and the product quality is far inferior to that of Example 3.

[0102] In Comparative Example 2, industrial-grade lithium carbonate reacts with calcium oxide to generate a lithium hydroxide solution, which is directly spray-dried with hydrogen fluoride gas. From the data in Table 1, it can be seen that compared with the present invention, the lithium hydroxide solution is recrystallized + redissolved, and the LiF prepared in Comparative Example 1 has low purity, and the product quality is far inferior to that of Example 3. In addition, the hydrogen fluoride tail gas generated in the process will also pollute the environment.

[0103] 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 efficiency of its contact reaction with hydrogen fluoride gas. It can be seen from the data in Table 1 that the particle size of the product is larger than that of Example 3, and the purity is lower than that of Example 3.

[0104] In Comparative Example 4, the spray drying reaction temperature was controlled at 90°C. From the data in Table 1, it can be seen that the particle size of the product is larger than that of Example 3, and the purity is lower than that of Example 3. The reason is that the spray drying temperature is low, which easily leads to untimely evaporation of water, a high water content of the product, and more residual lithium hydroxide impurities, which reduces the purity and increases the particle size.

[0105] In Comparative Example 5, the feed rates of high-purity lithium hydroxide solution and hydrogen fluoride gas in the spray drying reaction are reduced. It can be seen from the data in Table 1 that the particle size of the product is larger than that of Example 3, and the purity is lower than that of Example 3. The reason is that the lower feed rate and air intake lead to incomplete reaction, incomplete reaction of hydrogen fluoride gas and lithium hydroxide solution, and a high content of lithium hydroxide impurities in the product, which reduces the purity of lithium fluoride and increases the particle size.

[0106] In Comparative Example 6, the feed rate of high-purity lithium hydroxide solution and hydrogen fluoride gas in the spray drying reaction was increased. From the data in Table 1, it can be seen that the particle size of the product is larger than that of Example 3, and the purity is lower than that of Example 3. The reason is that the excessive feed rate or air intake causes droplets of hydrogen fluoride and lithium hydroxide solution in the tail gas to enter the product collecting device, contaminating the product, reducing the purity of the product, and increasing the particle size of the product.

[0107] 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 nano-scale lithium fluoride from industrial-grade lithium carbonate, characterized in that: The method comprises the following steps: Industrial-grade lithium carbonate, water and calcium oxide are prepared into a slurry for causticization reaction, and after the reaction, solid-liquid separation is performed to obtain lithium hydroxide solution and calcium carbonate slag; The lithium hydroxide solution is recrystallized to obtain lithium hydroxide monohydrate crystals and mother liquor; The lithium hydroxide monohydrate crystals are redissolved and then filtered to obtain a high-purity lithium hydroxide solution and an insoluble filter residue; High-purity lithium hydroxide solution is spray-dried and reacted in a hot atmosphere of hydrogen fluoride to generate high-purity nano-scale lithium fluoride.

2. The method for preparing high-purity nano-scale lithium fluoride from industrial-grade lithium carbonate according to claim 1, characterized in that: The high-purity lithium hydroxide solution is spray-dried in a hot atmosphere of hydrogen fluoride to generate high-purity nano-scale lithium fluoride, specifically comprising: In the spray drying tower, high-purity lithium hydroxide solution is atomized into mist-like liquid droplets by centrifugal atomization and enters the tower, and hydrogen fluoride enters the tower in the form of hot gas. The two are heated and reacted in the tower to generate high-purity nano-level lithium fluoride.

3. The method for preparing high-purity nano-scale lithium fluoride from industrial-grade lithium carbonate according to claim 2, characterized in that: The frequency of the centrifugal atomization is 400 Hz to 600 Hz, the feed rate of the high-purity lithium hydroxide solution is 60 mL / h to 300 mL / h; the air intake volume of the hydrogen fluoride is 0.05 L / min to 0.5 L / min; and the spray drying reaction temperature is 100° C. to 150° C.

4. The method for preparing high-purity nano-scale lithium fluoride from industrial-grade lithium carbonate according to claim 2 or 3, characterized in that: The spray drying tower lining and the hydrogen fluoride air inlet pipe lining are PTFE lined.

5. The method for preparing high-purity nano-scale lithium fluoride from industrial-grade lithium carbonate according to claim 1, characterized in that: The recrystallization operation specifically includes: first evaporating and concentrating at 100° C. to 110° C., and then cooling to 35° C. to 45° C. for crystallization.

6. The method for preparing high-purity nano-scale lithium fluoride from industrial-grade lithium carbonate according to claim 1, characterized in that: The mass concentration of the high-purity lithium hydroxide solution is 3.5% to 7%.

7. The method for preparing high-purity nano-scale 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°C-90°C, and the time of the causticizing reaction is 1h-10h.

8. The method for preparing high-purity nano-scale lithium fluoride from industrial-grade lithium carbonate according to claim 1 or 7, characterized in that: In the causticizing reaction, the purity of the industrial-grade lithium carbonate is ≥98.5%, and the purity of the calcium oxide is ≥90%.

9. The method for preparing high-purity nano-scale 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 undergoes a neutralization reaction with the mother liquor to prepare lithium fluoride.

10. The method for preparing high-purity nano-scale lithium fluoride from industrial-grade lithium carbonate according to claim 9, characterized in that: 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 an intake amount of tail gas of 0.1 L / min to 5 L / min.

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