A small-particle-size lithium fluoride and its preparation method

Abstract

This invention belongs to the field of new energy and discloses a method for preparing small-particle-size lithium fluoride, including step 3, which specifically involves: adjusting the pH of the lithium hydrogen fluoride solution with lithium hydroxide to cause the lithium fluoride to precipitate and precipitate; the lithium hydroxide is continuously added to the lithium hydrogen fluoride solution over a period of 0.5 to 1 hour. This method reduces the particle size of lithium fluoride and narrows the particle size distribution range by controlling the duration of lithium hydroxide addition to the lithium hydrogen fluoride solution. This invention also discloses a lithium fluoride.

Description

Technical Field

[0001] This invention relates to the field of new energy, specifically to a small-particle-size lithium fluoride and its preparation method. Background Technology

[0002] Lithium fluoride, as an important raw material for lithium hexafluorophosphate, has wide applications in many fields. With the rapid development of the new energy industry, higher requirements have been placed on the market supply and product quality of lithium fluoride.

[0003] CN111606336A discloses a method for preparing lithium fluoride with a particle size greater than 130 μm; CN101723415A discloses a new process for producing battery-grade lithium fluoride with an average particle size of approximately 71.42 μm.

[0004] In the existing technology, there are very few relevant documents that propose methods for preparing lithium fluoride products with small particle size and narrow particle size distribution.

[0005] Therefore, the technical problem to be solved in this case is: how to prepare lithium fluoride products with small average particle size and narrow particle size distribution. Summary of the Invention

[0006] The main objective of this invention is to provide a method for preparing small-particle-size lithium fluoride. This method reduces the particle size of lithium fluoride and narrows the particle size distribution range of lithium fluoride by controlling the time when lithium hydroxide is added to the lithium hydrogen fluoride solution.

[0007] In addition, the present invention also discloses a lithium fluoride.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for preparing small-particle-size lithium fluoride includes step 3, wherein step 3 specifically involves: adjusting the pH of the lithium hydrogen fluoride solution with lithium hydroxide to cause the lithium fluoride to precipitate and precipitate; the lithium hydroxide is continuously added to the lithium hydrogen fluoride solution over a period of 0.5 to 1 hour.

[0010] In some embodiments of the present invention, the lithium hydroxide is added at a time of 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, or 1.0h.

[0011] By controlling the addition time of lithium hydroxide, this invention can control the particle size of lithium fluoride to an average particle size (D50) of 12-26 μm.

[0012] In this invention, among the various factors affecting lithium fluoride, the duration of lithium hydroxide addition is the most significant. If the addition rate is too slow, the density of the crystal nuclei formed in the early stages will be low, and the crystal nuclei will continue to grow, resulting in a larger particle size. If the addition rate is too fast, the crystal nuclei will aggregate in the later stages as the density increases, leading to rapid crystal growth at the end of the reaction, resulting in a larger particle size. Furthermore, the aggregation of crystal nuclei makes it easier to trap impurities, increasing the impurity content in the lithium fluoride product.

[0013] In the above-described method for preparing small-particle-size lithium fluoride, the following steps are included before step 3:

[0014] Step 1: Prepare a carbonized solution containing lithium bicarbonate using lithium carbonate;

[0015] Step 2: Use hydrofluoric acid to convert lithium bicarbonate in the carbonization solution into lithium hydrogen fluoride to obtain a lithium hydrogen fluoride solution.

[0016] In the above-described method for preparing small-particle-size lithium fluoride, the lithium hydroxide is added to the lithium hydrogen fluoride solution at a decreasing rate.

[0017] This means that the lithium hydroxide of the present invention can be added to the solution in a uniformly decelerated manner, or it can be added to the solution in multiple stages, with each subsequent stage being added at a slower rate than the previous stage; for example, it can be divided into 2 stages, 3 stages, 4 stages, or 5 stages.

[0018] Based on the results of actual research, two stages are sufficient to meet customers' needs for product performance. Therefore, this invention will focus on further research using a two-stage approach. Undoubtedly, adding more stages or gradually decreasing speeds will yield even better results.

[0019] It should be further noted that the lithium carbonate of the present invention can be 3N grade (99.9% purity) lithium carbonate, 4N grade (99.99% purity) lithium carbonate, or industrial grade lithium carbonate.

[0020] In the actual research process, we use industrial-grade lithium carbonate, which generally refers to lithium carbonate with a purity of no more than 99.4 wt%, especially lithium carbonate with a purity of 98.0 wt% to 99.4 wt%.

[0021] All embodiments in this invention are based on industrial-grade lithium carbonate; undoubtedly, if industrial-grade lithium carbonate can achieve the effects of this invention, then 3N or 4N grade lithium carbonate can also achieve the effects of this invention. This is because the oxalic acid and complexing agent used in steps 1, 2, and 3 of the embodiments of this invention are for better removal of impurities in the carbonization liquid, thus facilitating impurity control of lithium fluoride.

[0022] In the above-described method for preparing small-particle-size lithium fluoride, the lithium hydroxide is added in a first stage and a second stage; the first stage precedes the second stage; and the addition rate of lithium hydroxide in the first stage is greater than the addition rate of lithium hydroxide in the second stage.

[0023] Preferably, the lithium hydroxide is added at a rate that is 1.5 to 3 times faster in the first stage than in the second stage.

[0024] In the above-mentioned method for preparing small-particle-size lithium fluoride, in step 3, after adding lithium hydroxide, the stirring speed is maintained at 500-1000 r / min, and / or the reaction temperature is controlled at room temperature to 80℃; and / or, after the addition of lithium hydroxide is completed, the reaction continues for 0.5-1 h.

[0025] In some embodiments of the present invention, the stirring speed is 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min or 1000 r / min;

[0026] The reaction temperature is controlled at 20℃, 30℃, 40℃, 50℃, 60℃, 70℃ or 80℃;

[0027] In some embodiments of the present invention, after the addition of lithium hydroxide, the reaction continues for 0.5h, 0.6h, 0.7h, 0.8h, 0.9h or 1.0h.

[0028] Preferably, in step 3, after adding lithium hydroxide, the stirring speed is maintained at 500-800 r / min, and / or the reaction temperature is controlled at room temperature to 60°C.

[0029] Temperature and stirring speed are other factors that affect the particle size of lithium fluoride. The faster the stirring speed, the larger the particle size. The higher the temperature, the faster the crystal nucleation rate. Under a suitable crystal nucleation density, the smaller the particle size.

[0030] In the above-described method for preparing small-particle-size lithium fluoride, the pH of the lithium hydrogen fluoride solution is adjusted to 7-10 using lithium hydroxide; preferably, the pH of the lithium hydrogen fluoride solution is adjusted to 8-10 using lithium hydroxide.

[0031] In some embodiments of the present invention, the pH of the solution after adjustment with lithium hydroxide is 7, 7.5, 8, 8.5, 9, 9.5 or 10;

[0032] pH is another factor affecting the particle size of lithium fluoride. The higher the pH, the smaller the particle size. This is because the lower the pH, the smaller the amount of lithium hydroxide used, the fewer the crystal nuclei, and the more significant the particle size increase, resulting in a larger particle size. However, the pH cannot be greater than 10. If it exceeds 10, in the presence of a complexing agent, soluble complexes will precipitate or complexes that have already bound metal ions will dissociate and release metal ions, thereby increasing the impurities in the product and increasing the particle size.

[0033] In the above-described method for preparing small-particle-size lithium fluoride, step 1 specifically comprises:

[0034] Step 11: Prepare a carbonization solution containing lithium bicarbonate using industrial-grade lithium carbonate, and remove some metal ions from the carbonization solution using oxalate.

[0035] Step 12: Use a complexing agent to complex some of the metal ions in the solution obtained in Step 1.

[0036] This invention does not exclude the use of complexing agents to remove impurities, but this would result in a large amount of complexing agent being used, and the high concentration of complexes could cause soluble complexes to precipitate or cause complexes that have already complexed with metal ions to dissociate and precipitate metal ions during the pH adjustment process of lithium hydroxide solution, thereby increasing the amount of impurities in the product.

[0037] This invention does not exclude the use of oxalate alone to remove impurities, but the problem with this is that impurities cannot be completely removed, resulting in a high impurity content in the product.

[0038] Therefore, the present invention preferably removes most of the metal ions by first removing them with oxalate, and then complexes the remaining small amount of metal ions with a complexing agent to achieve a higher purity of the product.

[0039] In some cases of the present invention, it has been found that the presence of impurities has a slight negative impact on particle size and particle size distribution. Therefore, the present invention preferably removes impurities from the carbonization liquid.

[0040] In the above method for preparing small-particle-size lithium fluoride, step 11 specifically includes:

[0041] Industrial-grade lithium carbonate is added to water to prepare a slurry, and carbon dioxide is introduced until the lithium carbonate is converted into lithium bicarbonate.

[0042] The oxalate ions are added to the slurry before, during, or after the conversion of lithium carbonate to lithium bicarbonate.

[0043] In the above-mentioned method for preparing small-particle-size lithium fluoride, the oxalate is added to the slurry before carbon dioxide is introduced, and the solid-to-water ratio in the slurry is 1:20-30.

[0044] In some embodiments of the present invention, the solid-to-water ratio in the slurry is 1:20, 1:21, 1:22, 1:23, 1:24, 1:25, 1:26, 1:27, 1:28, 1:29 or 1:30;

[0045] If oxalate is added to the solution before lithium carbonate is converted to lithium bicarbonate, most of the impurities in the lithium carbonate solution during carbonation and dissolution are metal ions that can form soluble bicarbonates, such as calcium and magnesium ions. Once these metal ions are converted to soluble bicarbonates, they will immediately react with the oxalate in the carbonation solution to form a precipitate. Meanwhile, metal ions that cannot form soluble bicarbonates during carbonation will exist as carbonate or hydroxide precipitates, or will be chelated by oxalic acid during lithium carbonate carbonation. Adding oxalic acid or oxalate after carbonation allows for a longer and more thorough combination with the free metal ions. The effect is limited. Furthermore, carbonate or hydroxide precipitates, once settled, are difficult to fully chelate with oxalic acid and oxalate. These unchelated carbonate or hydroxide precipitates, being very fine, are difficult to filter out and will also affect the uniformity of the crystal grains during lithium fluoride formation. Compared to adding oxalic acid or oxalate after carbonation, adding oxalic acid or oxalate before carbonation has the advantage of: it can more thoroughly and for a longer time form oxalate precipitates with metal ions. Simultaneously, it can chelate and form precipitates as soon as the carbonate or hydroxide precipitates separate from lithium carbonate. Overall, it has a higher ability to remove impurity metal ions, and combined with the subsequent complexation process, it significantly improves product purity.

[0046] In the above-mentioned method for preparing small-particle-size lithium fluoride, the oxalate ion exists in the form of oxalic acid and / or oxalate, and / or the oxalate is sodium oxalate and / or potassium oxalate;

[0047] And / or, the complexing agent is one or more combinations of polyacrylic acid, hydrolyzed polymaleic anhydride, sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, citric acid, gluconic acid, tartaric acid, iminodisuccinic acid, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, glutamic acid diacetate, sodium ethylenediamine diophenylacetate, tetrasodium glutamic acid diacetate, ethylenediamine diophenylacetate, and disodium ethylenediamine diophenylacetate.

[0048] And / or, the mass of the oxalic acid or oxalate is equivalent to 0.1% to 1% of the mass of the carbonization liquid;

[0049] And / or, the amount of complexing agent added is equivalent to 0.02% to 0.5% of the weight of the carbonization liquid.

[0050] In some embodiments of the present invention, the mass of the oxalic acid or oxalate is equivalent to 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1% of the mass of the carbonization liquid;

[0051] In some embodiments of the present invention, the amount of complexing agent added is equivalent to 0.02%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4% or 0.5% of the weight of the carbonized liquid.

[0052] In the above method for preparing small-particle-size lithium fluoride, the hydrofluoric acid is added to step 2 in the form of a hydrofluoric acid solution with a concentration of 40 wt% to 99 wt%; the lithium hydroxide is added to step 3 in the form of a lithium hydroxide solution with a concentration of 5 wt% to 20 wt%.

[0053] And / or, the pH value of the lithium hydrogen fluoride solution is 3 to 4.

[0054] In this invention, the concentration of hydrofluoric acid and the concentration of lithium hydroxide used have no substantial impact on the reaction results.

[0055] Finally, the present invention also discloses a lithium fluoride prepared by any of the methods described above, which has a purity of over 99.9 wt% and an average particle size of 12–26 μm.

[0056] One of the above-described technical solutions of the present invention has at least one of the following advantages or beneficial effects:

[0057] 1. This invention reduces the particle size of lithium fluoride by controlling the addition time of lithium hydroxide, thereby narrowing the particle size distribution range of lithium fluoride.

[0058] 2. By further optimizing the difference in the rate of addition of lithium hydroxide before and after the addition, this invention can make the crystal nucleus formation rate faster in the early stage, so as to reach a suitable crystal nucleus density as soon as possible. Then, the addition rate is reduced in the later stage, so that the crystal nuclei can continue to increase while maintaining a steady growth. This controls the average particle size and reduces the particle size distribution range.

[0059] 3. By further adjusting the final pH value of the solution with lithium hydroxide, this invention can prevent the crystal nucleus density from being too high or too low, thus avoiding an increase in particle size.

[0060] 4. The present invention preferably uses industrial-grade lithium carbonate as raw material, which is inexpensive and has a purity of over 98%, making it particularly suitable for the process of the present invention.

[0061] 5. By optimizing the configuration of the impurity removal agent, this invention can further improve the purity of the product and optimize the control of the particle size of lithium fluoride. Detailed Implementation

[0062] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0063] Example 1

[0064] (1) Mix industrial-grade lithium carbonate with pure water to form a slurry. The mass of industrial-grade lithium carbonate is 100g, the mass of pure water is 2500g, the solid-liquid ratio is 1:25 (weight ratio, the same below), the stirring speed is 400r / min, and carbon dioxide is introduced at a gas flow rate of 3L / min for carbonization. After carbonization for 2.5h, filter to obtain carbonized liquid. The content of each substance of industrial-grade lithium carbonate is shown in Table 1 below.

[0065] Table 1 Raw Material Information Table

[0066]

[0067] (2) Add 0.25% oxalic acid (by mass of carbonized liquid) to the carbonized liquid obtained in step one, stir at 400 r / min for 20 min at room temperature, and filter to obtain carbonized liquid 2.

[0068] (3) Add disodium ethylenediaminetetraacetate equivalent to 0.02% of the solution mass to carbonized liquid 2, and stir at 400 r / min for 20 min at room temperature to obtain carbonized liquid 3;

[0069] (4) Take carbonized liquid 3, add 40wt% hydrofluoric acid to pH 4, stir at 500r / min for 2h, add 8wt% lithium hydroxide solution (370g) to adjust pH to 9, add lithium hydroxide solution at a constant rate for 1h, the reaction temperature is room temperature, after adding lithium hydroxide solution, react for another 1h, the stirring speed remains unchanged throughout the process, solid-liquid separation to obtain LiF wet material, take the separated LiF wet material and add pure water for stirring and washing, separate and dry to obtain LiF product.

[0070] In the subsequent examples and comparative examples, unless otherwise specified, the reaction temperature is room temperature, which is assumed to be 25°C.

[0071] Example 2

[0072] (1) Mix industrial grade lithium carbonate with pure water to form a slurry. The mass of industrial grade lithium carbonate is 100g, the mass of pure water is 2000g, the solid-liquid ratio is 1:20, the stirring speed is 400r / min, and carbon dioxide is introduced at a gas flow rate of 3L / min for carbonization. After carbonization for 2.5h, filter to obtain carbonized liquid.

[0073] (2) Add 0.1% oxalic acid (by mass of carbonization solution) to the carbonization solution obtained in step one, stir at 400 r / min for 20 min at room temperature, and filter to obtain carbonization solution 2.

[0074] (3) Add 0.05% of ethylenediamine di-o-phenylacetic acid (EDTA) to carbonized liquid 2 and stir at 400 r / min for 20 min at room temperature to obtain carbonized liquid 3.

[0075] (4) Take carbonized liquid 3, add hydrofluoric acid with a concentration of 40wt% to pH 3, and stir at a speed of 500r / min for 1h; under the condition of reaction temperature of 40℃, add lithium hydroxide solution with a concentration of 10wt% (730g) to adjust pH to 10. Lithium hydroxide is added to the solution at a constant rate for 0.75h. After the lithium hydroxide solution is added, react for another 0.5h. Stir at a speed of 800r / min. Solid-liquid separation is used to obtain LiF wet material. Take the separated LiF wet material and add pure water for stirring and washing. After separation and drying, LiF product is obtained.

[0076] Example 3

[0077] (1) Mix industrial grade lithium carbonate with pure water to form a slurry. The mass of industrial grade lithium carbonate is 100g, the mass of pure water is 3000g, the solid-liquid ratio is 1:30, the stirring speed is 600r / min, and carbon dioxide is introduced at a gas flow rate of 3L / min for carbonization. After carbonization for 4h, filter to obtain carbonized liquid.

[0078] (2) Add sodium oxalate equivalent to 1% of the mass of the carbonized liquid to the carbonized liquid obtained in step one, stir at 600 r / min for 40 min at room temperature, and filter to obtain carbonized liquid 2.

[0079] (3) Add 0.5% of the solution mass of disodium ethylenediamine di-o-phenylacetate to carbonized liquid 2 and stir at 400 r / min for 20 min at room temperature to obtain carbonized liquid 3;

[0080] (4) Take carbonized liquid 3, add hydrofluoric acid with a concentration of 40wt% to pH 3.5, stir at a speed of 500r / min for 1h, and add lithium hydroxide solution with a concentration of 20wt% (520g) to adjust pH to 8 at a reaction temperature of 80℃. The lithium hydroxide solution is added to the solution at a constant rate for 0.5h. After the lithium hydroxide solution is added, react for another 1h while stirring at a speed of 1000r / min. Solid-liquid separation is performed to obtain wet LiF material. Take the separated wet LiF material and add pure water for washing. After separation and drying, LiF product is obtained.

[0081] Example 4

[0082] The process is largely the same as in Example 1, except that the lithium hydroxide solution is added in two continuous and sequential stages. The first stage takes 5 minutes and the amount added is equivalent to 21 wt% of the total lithium hydroxide solution. The second stage takes 55 minutes and the amount added is equivalent to 79 wt% of the total lithium hydroxide solution. The ratio of the feeding rates of the first and second stages is 2.92.

[0083] Example 5

[0084] The process is largely the same as in Example 1, except that the lithium hydroxide solution is added in two continuous and sequential stages. The first stage takes 10 minutes and the amount added is equivalent to 30 wt% of the total lithium hydroxide solution. The second stage takes 50 minutes and the amount added is equivalent to 70 wt% of the total lithium hydroxide solution. The ratio of the feeding rates of the first and second stages is 2.14.

[0085] Example 6

[0086] The process is largely the same as in Example 1, except that the lithium hydroxide solution is added in two continuous and sequential stages. The first stage takes 15 minutes and the amount added is equivalent to 33 wt% of the total lithium hydroxide solution. The second stage takes 45 minutes and the amount added is equivalent to 67 wt% of the total lithium hydroxide solution. The ratio of the feeding rates of the first and second stages is 1.48.

[0087] Example 7

[0088] The process is largely the same as in Example 3, except that the lithium hydroxide solution is added in two continuous and sequential stages. The first stage takes 2.5 minutes and the amount added is equivalent to 21 wt% of the total lithium hydroxide solution. The second stage takes 27.5 minutes and the amount added is equivalent to 79 wt% of the total lithium hydroxide solution. The ratio of the feeding rates of the first and second stages is 2.92.

[0089] Example 8

[0090] The process is largely the same as in Example 3, except that the lithium hydroxide solution is added in two continuous and sequential stages. The first stage takes 5 minutes and the amount added is equivalent to 30 wt% of the total lithium hydroxide solution. The second stage takes 25 minutes and the amount added is equivalent to 70 wt% of the total lithium hydroxide solution. The ratio of the feeding rates of the first and second stages is 2.14.

[0091] Example 9

[0092] The process is largely the same as in Example 3, except that the lithium hydroxide solution is added in two continuous and sequential stages. The first stage takes 7.5 minutes and the amount added is equivalent to 33 wt% of the total lithium hydroxide solution. The second stage takes 22.5 minutes and the amount added is equivalent to 67 wt% of the total lithium hydroxide solution. The ratio of the feeding rates of the first and second stages is 1.48.

[0093] Example 10

[0094] The process is largely the same as in Example 1, except that the lithium hydroxide solution is added in three consecutive stages. The first stage takes 5 minutes and the amount added is equivalent to 21 wt% of the total lithium hydroxide solution. The second stage takes 20 minutes and the amount added is equivalent to 35 wt% of the total lithium hydroxide solution. The third stage takes 30 minutes and the amount added is equivalent to 35 wt% of the total lithium hydroxide solution. The ratio of the feeding rates of the first, second, and third stages is 3:1.75:1.17.

[0095] Example 11

[0096] (1) Mix industrial grade lithium carbonate with pure water to form a slurry with a solid-liquid ratio of 1:25 (by weight, the same below). Add 0.25% oxalic acid equivalent to the mass of the solution. Stir at 400 r / min and introduce carbon dioxide at a gas flow rate of 3 L / min for carbonization. After carbonization for 2.5 h, filter to obtain carbonized liquid 1.

[0097] (2) Add disodium ethylenediaminetetraacetate equivalent to 0.02% of the solution mass to carbonization solution 1, and stir at 400 r / min for 20 min at room temperature to obtain carbonization solution 2;

[0098] (3) Take carbonized liquid 2, add hydrofluoric acid with a concentration of 40wt% to adjust the pH to 4, stir at a speed of 500r / min for 2h, add lithium hydroxide solution with a concentration of 8wt% (41g) to adjust the pH to 9. The lithium hydroxide solution is added in two continuous and sequential stages. The first stage takes 5min and the amount added is equivalent to 21wt% of the total lithium hydroxide solution; the second stage takes 55min and the amount added is equivalent to 79wt% of the total lithium hydroxide solution. The ratio of the feeding rates of the first and second stages is 2.92. The reaction temperature is room temperature. After the lithium hydroxide solution is added, the reaction continues for 1h. The stirring speed remains unchanged throughout the process. Solid-liquid separation yields wet LiF material. Take the separated wet LiF material, add pure water for washing, and after separation and drying, obtain the LiF product.

[0099] Example 12

[0100] The process is largely the same as in Example 11, except that the lithium hydroxide solution is added in two continuous and sequential stages. The first stage takes 10 minutes and the amount added is equivalent to 30 wt% of the total lithium hydroxide solution. The second stage takes 50 minutes and the amount added is equivalent to 70 wt% of the total lithium hydroxide solution. The ratio of the feeding rates of the first and second stages is 2.14.

[0101] Example 13

[0102] The process is largely the same as in Example 11, except that the lithium hydroxide solution is added in two continuous and sequential stages. The first stage takes 15 minutes and the amount added is equivalent to 33 wt% of the total lithium hydroxide solution. The second stage takes 45 minutes and the amount added is equivalent to 67 wt% of the total lithium hydroxide solution. The ratio of the feeding rates of the first and second stages is 1.48.

[0103] Example 14

[0104] The process is largely the same as in Example 1, except that in step 4, lithium hydroxide is used to adjust the pH to 7.

[0105] Example 15

[0106] The process is largely the same as in Example 1, except that in step 4, lithium hydroxide is used to adjust the pH to 11.

[0107] Comparative Example 1

[0108] The process is largely the same as in Example 1, except that in step 4, lithium hydroxide is added to the solution all at once within 1 minute.

[0109] Comparative Example 2

[0110] The process is largely the same as in Example 1, except that in step 4, lithium hydroxide is added over a period of 2 hours at a constant rate.

[0111] Analysis and Testing

[0112] Test item 1: Lithium fluoride purity, test method: difference subtraction method.

[0113] Test item 2: Impurity elements in lithium fluoride, test method: ICP.

[0114] Test item 3: Average particle size of lithium fluoride, which is represented by D50 in this invention; the particle size is tested by laser particle size analyzer.

[0115] Test Item 4: The particle size distribution of lithium fluoride is represented by testing D10 and D90. D10 indicates that the material with a particle size smaller than this accounts for 10% of the total material, and D90 indicates that the material with a particle size smaller than this accounts for 90% of the total material. By measuring D10 and D90, the particle size difference between D10 and D90 can be determined, which can indirectly represent the particle size distribution.

[0116] The test results are shown in Table 2.

[0117] Table 2. Particle size, purity, and impurity element content of lithium fluoride (particle size unit: μm)

[0118]

[0119] Results analysis:

[0120] 1. As can be seen from Examples 1-3 and Comparative Examples 1 and 2, the method of the present invention can control D50 within the range of 14-28 μm, and the particle size distribution range (difference between D90 and D10) within 22-36 μm. This demonstrates that by controlling the addition time of lithium hydroxide, the particle size of lithium fluoride can be effectively controlled. This proves that when the nucleus concentration is within a suitable range, particle size growth is controllable and the distribution range is narrow. Adding lithium hydroxide all at once or continuously for up to 2 hours will result in a significant increase in particle size.

[0121] 2. As can be seen from Examples 1 and 4-6, D50 can be controlled within the range of 14-18 μm, and the particle size distribution range (difference between D90 and D10) is 19-26 μm. By adding lithium hydroxide in stages, the crystal nucleus concentration is rapidly increased in the early stage and then maintained to increase slowly and steadily in the later stage, which is conducive to further optimization of lithium fluoride particle size.

[0122] 3. As can be seen from Examples 3 and 7-9, D50 can be controlled within the range of 16-21 μm, and the particle size distribution range (difference between D90 and D10) is 24-30 μm. By adding lithium hydroxide in stages, the crystal nucleus concentration is rapidly increased in the early stage and then maintained to increase slowly and steadily in the later stage, which is conducive to further optimization of lithium fluoride particle size.

[0123] 4. As can be seen from Examples 1, 5 and 10, adding lithium hydroxide in stages can improve the particle size and particle size distribution to a certain extent.

[0124] 5. As can be seen from Examples 1, 4-6, and 11-13, through Examples 11-13, D50 can be controlled within the range of 13-14 μm, and the particle size distribution range (difference between D90 and D10) is 18-25 μm. By adding lithium hydroxide in stages and adding oxalic acid during carbonization, the solution purity is higher, which is more conducive to optimizing the lithium fluoride particle size, indicating that impurities will affect the particle size distribution to a certain extent.

[0125] 6. As can be seen from Examples 1, 14, and 15, the pH should be controlled within the range of 7-10. The lower the pH, the smaller the amount of lithium hydroxide used, the fewer the crystal nuclei, and the more obvious the particle size increase, resulting in a larger particle size. When the pH reaches 11, and in the presence of a complexing agent, soluble complexes will precipitate or complexes that have already bound metal ions will dissociate and precipitate metal ions, thereby increasing the impurities in the product and increasing the particle size.

[0126] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing small-particle-size lithium fluoride, characterized in that, The preparation method includes the following steps: Step 1: Prepare a carbonized solution containing lithium bicarbonate using lithium carbonate; Step 2: Use hydrofluoric acid to convert lithium bicarbonate in the carbonization solution into lithium hydrogen fluoride to obtain a lithium hydrogen fluoride solution; Step 3: Adjust the pH of the lithium hydrogen fluoride solution with lithium hydroxide to cause lithium fluoride to precipitate and precipitate; the lithium hydroxide is continuously added to the lithium hydrogen fluoride solution over 0.5 to 1 hour; the pH of the lithium hydrogen fluoride solution is adjusted to 8 to 10 using lithium hydroxide. Step 1 further includes steps 11 and 12. Step 11: Prepare a carbonization solution containing lithium bicarbonate using industrial-grade lithium carbonate, and remove some metal ions from the carbonization solution using oxalate. Step 12: Use a complexing agent to complex some of the metal ions in the solution obtained in Step 11; Step 11 specifically involves: adding industrial-grade lithium carbonate to water to prepare a slurry, then introducing carbon dioxide until the lithium carbonate is converted into lithium bicarbonate; the oxalate ions are added to the slurry before the lithium carbonate is converted into lithium bicarbonate. The lithium hydroxide was added to the lithium hydrogen fluoride solution at a decreasing rate.

2. The method for preparing small-particle-size lithium fluoride according to claim 1, characterized in that, The lithium hydroxide is added in two stages: a first stage and a second stage. The first stage occurs before the second stage. The rate at which lithium hydroxide is added in the first stage is greater than the rate at which it is added in the second stage. The rate at which lithium hydroxide is added in the first stage is 1.5 to 3 times the rate at which it is added in the second stage.

3. The method for preparing small-particle-size lithium fluoride according to claim 1, characterized in that, After adding lithium hydroxide, maintain the stirring speed at 500–1000 r / min, and / or control the reaction temperature in step 3 at room temperature to 80°C; and / or continue the reaction for 0.5–1 h after the lithium hydroxide is added.

4. The method for preparing small-particle-size lithium fluoride according to claim 3, characterized in that, After adding lithium hydroxide, maintain the stirring speed at 500-800 r / min, and / or control the reaction temperature in step 3 at room temperature to 60℃.

5. The method for preparing small-particle-size lithium fluoride according to claim 1, characterized in that, The oxalate ions are added to the slurry before carbon dioxide is introduced, and the solid-to-water weight ratio in the slurry is 1:20-30.

6. The method for preparing small-particle-size lithium fluoride according to claim 1, characterized in that, The oxalate ion exists in the form of oxalic acid and / or oxalate, wherein the oxalate is sodium oxalate and / or potassium oxalate. And / or, the complexing agent is one or more combinations of polyacrylic acid, hydrolyzed polymaleic anhydride, sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, citric acid, gluconic acid, tartaric acid, iminodisuccinic acid, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, glutamic acid diacetate, sodium ethylenediamine diophenylacetate, tetrasodium glutamic acid diacetate, ethylenediamine diophenylacetate, and disodium ethylenediamine diophenylacetate. And / or, the mass of the oxalic acid or oxalate is equivalent to 0.1% to 1% of the mass of the carbonization liquid; And / or, the amount of complexing agent added is equivalent to 0.02% to 0.5% of the mass of the carbonized liquid.

7. The method for preparing small-particle-size lithium fluoride according to claim 1, characterized in that, The hydrofluoric acid is added to step 2 in the form of a hydrofluoric acid solution with a concentration of 40 wt% to 99 wt%; the lithium hydroxide is added to step 3 in the form of a lithium hydroxide solution with a concentration of 5 wt% to 20 wt%. The pH value of the lithium hydrogen fluoride solution is 3-4.

8. A lithium fluoride, characterized in that, The material was prepared by any one of the methods described in claims 1 to 7, and its purity reached more than 99.9 wt%; the average particle size was 12 to 26 μm.

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