A method for producing large-grain lithium fluoride crystals

Abstract

This invention provides a method for preparing large-particle lithium fluoride crystals, relating to the field of chemical engineering crystallization technology, aiming to solve the problem of small particle size in existing lithium fluoride crystals. The key technical points are: first, lithium fluoride seed crystals are added to pure water to obtain a lithium fluoride crystal slurry; then, the lithium fluoride crystal slurry is placed in a crystallization vessel, stirring is started, and lithium hydroxide aqueous solution and hydrofluoric acid aqueous solution are simultaneously and uniformly added dropwise; after the addition is complete, the crystal slurry is filtered to obtain a filter cake, the filter cake is washed with deionized water, and the filter cake is dried to obtain D. 50 The lithium fluoride seed crystals are large-particle lithium fluoride crystals with a size of 170-190 μm; the D of the lithium fluoride seed crystals... 50 The particle size is 2-50 μm, and the dropping time is 5-48 h. This invention balances the generation and consumption of supersaturation by precisely controlling the reaction system and dropping method, inhibiting nucleation and promoting crystal growth, and is suitable for the preparation of large-particle lithium fluoride.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering crystallization technology, and in particular to a method for preparing large-particle lithium fluoride crystals. Background Technology

[0002] Lithium fluoride, as an important inorganic functional material, has wide applications in fields such as lithium-ion battery electrolytes, optical crystals, high-temperature fluxes, and special ceramics.

[0003] Currently, the mainstream industrial methods for preparing lithium fluoride mostly involve reacting lithium sources such as lithium carbonate and lithium hydroxide with fluorine-containing raw materials such as hydrofluoric acid or ammonium fluoride. However, these routes generally suffer from complex raw material systems and a variety of byproducts. Taking the ammonium fluoride route as an example, the reaction inevitably releases ammonia gas, which not only puts pressure on environmental protection but also introduces impurity ions such as ammonium ions. Subsequent purification and washing processes are required to meet high purity requirements, making the process cumbersome and the production cost high.

[0004] A more prominent issue lies in particle size control. Traditional processes typically involve directly mixing two reactant solutions. In this mode, the local concentration within the system increases instantaneously, and supersaturation accumulates rapidly, easily triggering explosive nucleation. During the nucleation-dominated crystallization process, the formation of numerous small crystal nuclei consumes the vast majority of the solute, resulting in a large number of nuclei but insufficient growth drive for individual crystals. Consequently, the resulting lithium fluoride products generally have small particle sizes, irregular crystal shapes, and a wide particle size distribution.

[0005] For example, invention patent CN 104291363 A discloses a method for preparing lithium fluoride. First, 0.001-0.01% (by weight) of a purification agent is added to a soluble lithium salt aqueous solution with a concentration of 5-150 g / L, and the mixture is stirred and filtered. Then, 50 μm lithium fluoride seed crystals are added to the filtrate under stirring conditions of 0-150℃ and 0-600 rpm. Subsequently, a fluoride aqueous solution with a concentration of 10-300 g / L (fluoride to lithium salt weight ratio 1:0.5-1) is added at a flow rate of 0.01-100 L / min. After reacting at this temperature for 1-300 min, solid-liquid separation is performed. The solid material is dried at 100-150℃ for 2-5 h to obtain D. 50 Lithium fluoride products with a diameter greater than 0.12 mm.

[0006] For example, invention patent CN 117800369 A discloses a method for continuous production of lithium fluoride. First, high-purity lithium carbonate is mixed with pure water and carbonized with CO2 to obtain a lithium bicarbonate solution. Then, pure water and hydrogen fluoride gas are added to the reactor to adjust the pH to 0.5-0.8. Subsequently, the lithium bicarbonate solution and 49% hydrofluoric acid are simultaneously added dropwise at 20-25°C to form crystal nuclei. Next, the temperature is increased to 45-50°C at 1-2°C / min, and the feed flow rate is adjusted to promote crystal growth. After continuous feeding and discharge, the product is centrifuged, washed with deionized water, and dried at 100°C to obtain a product with a purity of 99.97% and a particle size D. 50 Lithium fluoride products with a diameter of 101-110 μm.

[0007] Analysis of existing patents reveals several problems with current lithium fluoride preparation technologies: The raw material system is complex, often involving multiple fluorine and lithium compounds, which not only increases raw material and management costs but also produces byproducts such as ammonia and carbon dioxide, leading to cumbersome subsequent processing and potential introduction of impurities; the preparation process is lengthy, often requiring multiple conversion steps (such as the carbonation and dissolution of lithium carbonate) or purification with impurity removal agents, resulting in numerous steps, high energy consumption, and many control points, making it difficult to improve production efficiency and product consistency; the physical properties of the product are poor, with the resulting lithium fluoride crystals generally having small particle sizes and uneven distribution, leading to low bulk density and poor flowability, directly affecting the processing performance and material uniformity of downstream applications.

[0008] The negative impacts of excessively small particle size permeate the entire production and application chain. On the production side, finely powdered lithium fluoride exhibits high filtration resistance, low washing efficiency, and high drying energy consumption, and is highly prone to generating dust, posing safety hazards and severely restricting production efficiency and operational safety. On the application side, low bulk density and poor flowability directly affect the metering accuracy and processing uniformity of the material, making it even more difficult to meet the requirements of high-end applications with specific requirements for raw material particle size and physical morphology.

[0009] Therefore, developing a simple process that can effectively control the crystallization process and prepare lithium fluoride with large particle size and uniform particle size distribution is of great practical significance. Summary of the Invention

[0010] In view of this, the present invention provides a method for preparing large-particle lithium fluoride crystals. The present invention achieves a supply-demand balance between the generation and consumption of supersaturation within the system by simultaneously and uniformly adding an aqueous solution of lithium hydroxide and an aqueous solution of hydrofluoric acid to a pre-prepared lithium fluoride crystal slurry, and by precisely controlling the reaction concentration and the dropping method. This effectively suppresses primary and secondary nucleation, promoting the solute to be primarily used for crystal growth. It has good prospects for efficient industrial production and applications in high-end fields such as lithium battery electrolytes and optical materials.

[0011] The present invention provides a method for preparing large-particle-size lithium fluoride crystals, comprising the following steps: S1. Add lithium fluoride seed crystals to pure water to obtain lithium fluoride crystal slurry; S2. Place the lithium fluoride slurry from S1 into a crystallization vessel, start stirring, and simultaneously and uniformly add lithium hydroxide aqueous solution and hydrofluoric acid aqueous solution to the crystallization vessel. After the addition is complete, filter the slurry to obtain a filter cake. Rinse the filter cake with deionized water, and after the pH of the rinsing solution is measured to be 6.5-7.0, dry the filter cake to obtain D. 50 It consists of large-particle lithium fluoride crystals with a size of 170-190 μm.

[0012] Preferably, in step S1, the mass ratio of pure water to lithium fluoride seed crystals is 1:(0.0002-0.1), more preferably 1:(0.005-0.0125); the D of the lithium fluoride seed crystals... 50 The size ranges from 2 to 50 μm.

[0013] Preferably, in step S2, the concentration of the lithium hydroxide aqueous solution is 50-120 g / L; the concentration of the hydrofluoric acid aqueous solution is 5%-40%; the system solution temperature during the dropwise addition is 10-50℃, more preferably 20-30℃; the volume ratio of the lithium hydroxide aqueous solution to the hydrofluoric acid aqueous solution is 1:(0.2-1), more preferably 1:(0.3-0.5); the volume ratio of the lithium fluoride crystal slurry to the lithium hydroxide aqueous solution is 1:(1-5), more preferably 1:(1.5-2.5); the dropwise addition time is 5-48 h, more preferably 8-40 h; and the drying temperature is 60℃, and the drying time is 12 h.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention uses only pure water, lithium hydroxide, and hydrofluoric acid as the core reaction system, which not only simplifies the process steps but also produces water as the only byproduct. This system cuts off the introduction of complex impurities at the source, allowing for the production of extremely high-purity (e.g., electronic-grade) lithium fluoride chemicals without the need for additional impurity removal agents.

[0015] This invention creatively employs a reaction crystallization mode of "crystal slurry base liquid + double drop addition". By pre-placing seed crystals and precisely controlling the addition rate and concentration of lithium ions and fluoride ions, the system is maintained in a metastable range, so that the supersaturation generated by the reaction is directed for crystal growth rather than secondary nucleation, thereby stably preparing large-particle-size, regularly morphologically regular blocky lithium fluoride crystals.

[0016] Thanks to the significant improvement in crystal grain size, the bulk density and flowability of the product of this invention have been significantly improved, providing high-quality raw materials for the preparation of high-performance functional materials and showing good application prospects. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings.

[0018] Figure 1 A physical image of the lithium fluoride product obtained based on Example 1 of the method of the present invention; Figure 2 SEM image of the lithium fluoride product obtained based on Example 1 of the method of the present invention; Figure 3 SEM image of the lithium fluoride product obtained based on Example 2 of the method of the present invention. Detailed Implementation

[0019] 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.

[0020] Unless otherwise specified, all experiments were repeated three times, and the results are expressed as averages.

[0021] Example 1: A method for preparing large-particle lithium fluoride by crystallization, comprising the following steps: S1. Preparation of lithium fluoride crystal slurry: First, add 0.3 g of lithium fluoride seed crystals (D) to 50 ml of pure water. 50 (30 μm), to obtain lithium fluoride crystal slurry; S2. Place 50 ml of the lithium fluoride slurry obtained in S1 into a crystallization vessel, start stirring, control the solution temperature to 20℃, and simultaneously and uniformly add 95 ml of 90 g / L lithium hydroxide aqueous solution and 35 ml of 20% hydrofluoric acid aqueous solution. After the addition is completed in 24 h, filter the slurry to obtain a filter cake. Rinse the filter cake with deionized water, and after the pH of the rinsing solution reaches 7.0, dry the filter cake at 60℃ for 12 h. After drying, obtain D. 50 It is a 181 μm lithium fluoride crystal product.

[0022] Example 2 The difference from Example 1 is that: in S1, the amount of pure water used is 40 ml; in S2, the solution temperature is 30°C, the concentration of lithium hydroxide aqueous solution is 50 g / L, the volume of hydrofluoric acid aqueous solution is 29 ml, and the dropping time is 10 h. After drying at 60°C for 12 h, D is obtained. 50 It is a 173 μm lithium fluoride crystal product.

[0023] Example 3 The difference from Example 1 is that the amount of lithium fluoride seed crystals used in S1 is 0.25 g, and the amount of lithium fluoride seed crystals D is... 50The sample size was 45 μm; the hydrofluoric acid concentration in S2 was 5%, and the dropping time was 14 h. After drying at 60℃ for 12 h, D was obtained. 50 It is a 190 μm lithium fluoride crystal product.

[0024] Example 4 The difference from Example 1 is that: in S1, the amount of pure water used is 60 ml, the amount of lithium fluoride seed crystals used is 0.8 g, and the amount of lithium fluoride seed crystals D is... 50 The concentration was 50 μm; the volume of lithium hydroxide aqueous solution in S2 was 100 ml, and the volume of hydrofluoric acid aqueous solution was 30 ml, with a dropping time of 8 h. After drying at 60℃ for 12 h, D was obtained. 50 It is a 183 μm lithium fluoride crystal product.

[0025] Example 5 The difference from Example 1 is that the amount of lithium fluoride seed crystals used in S1 is 0.5 g, and the amount of lithium fluoride seed crystals D is... 50 The sample size was 10 μm; in S2, the volume of lithium hydroxide aqueous solution was 90 ml with a concentration of 95 g / L, and the volume of hydrofluoric acid aqueous solution was 40 ml with a concentration of 40%, with a dropping time of 40 h. After drying at 60℃ for 12 h, D was obtained. 50 It is a 172 μm lithium fluoride crystal product.

[0026] Example 6 The difference from Example 1 is that: in S1, the amount of pure water used is 40 ml, the amount of lithium fluoride seed crystals used is 0.5 g, and the amount of lithium fluoride seed crystals D is... 50 The sample size was 2 μm, and the dropping time in S2 was 10 h. After drying at 60℃ for 12 h, D was obtained. 50 It is a 171 μm lithium fluoride crystal product.

[0027] Comparative Example 1 The difference from Example 1 is that in S2, 95 ml of 90 g / L lithium hydroxide aqueous solution is added all at once, followed by 35 ml of 20% hydrofluoric acid aqueous solution added dropwise over 14 hours. Subsequent steps include filtration, rinsing (pH 7.0), and drying at 60°C for 12 hours to obtain D. 50 It is a 32μm lithium fluoride crystal product.

[0028] Comparative Example 2 The difference from Example 1 is that: in S1, no lithium fluoride seed crystals were added, and only 50 ml of pure water was used as the reaction medium; in S2, the dropping time was 24 h. Subsequent filtration, rinsing (pH 7.0), and drying at 60°C for 12 h yielded D. 50 It is a 47μm lithium fluoride crystal product.

[0029] Comparative Example 3 The difference from Example 1 is that the dropping time in S2 is 4 hours. Subsequent filtration, rinsing (pH 7.0), and drying at 60°C for 12 hours yielded D. 50 It is a 45 μm lithium fluoride crystal product.

[0030] Comparative Example 4 The difference from Example 1 is that in S2, the lithium hydroxide aqueous solution and the hydrofluoric acid aqueous solution were not added synchronously and uniformly, but were added asynchronously and uniformly. The hydrofluoric acid aqueous solution was added in 4 hours and the lithium hydroxide aqueous solution was added in 12 hours.

[0031] Drying at 60℃ for 12 h yielded D. 50 It is a 36 μm lithium fluoride crystal product.

[0032] Comparative Example 5 The difference from Example 1 is that the lithium fluoride seed crystal D added in S1 50 The size is 3 μm, and the amount added is 0.002 g.

[0033] Drying at 60℃ for 12 h yielded D. 50 It is a 44 μm lithium fluoride crystal product.

[0034] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. 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 all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing large-particle-size lithium fluoride crystals, characterized in that, Includes the following steps: S1. Add lithium fluoride seed crystals to pure water to obtain lithium fluoride crystal slurry; S2. Place the lithium fluoride slurry from S1 into a crystallization vessel, start stirring, and simultaneously and uniformly add lithium hydroxide aqueous solution and hydrofluoric acid aqueous solution to the crystallization vessel. After the addition is complete, filter the slurry to obtain a filter cake, rinse the filter cake with deionized water, and then dry the filter cake to obtain D. 50 It consists of large-particle lithium fluoride crystals with a size of 170-190 μm; The D of the lithium fluoride seed crystal 50 The thickness is 2-50 μm, and the dropping time is 5-48 h.

2. The method for preparing large-particle-size lithium fluoride crystals according to claim 1, characterized in that, In step S1, the mass ratio of pure water to lithium fluoride seed crystals is 1:(0.0002-0.1).

3. The method for preparing large-particle-size lithium fluoride crystals according to claim 1, characterized in that, In step S2, the concentration of the lithium hydroxide aqueous solution is 50-120 g / L.

4. The method for preparing large-particle-size lithium fluoride crystals according to claim 1, characterized in that, In step S2, the concentration of the hydrofluoric acid aqueous solution is 5%-40%.

5. The method for preparing large-particle-size lithium fluoride crystals according to claim 1, characterized in that, In step S2, the temperature of the system solution is 10-50℃ during the dropwise addition process.

6. The method for preparing large-particle-size lithium fluoride crystals according to claim 1, characterized in that, In step S2, the volume ratio of the lithium hydroxide aqueous solution to the hydrofluoric acid aqueous solution is 1:(0.2-1).

7. The method for preparing large-particle-size lithium fluoride crystals according to claim 1, characterized in that, In step S2, the volume ratio of the lithium fluoride slurry to the lithium hydroxide aqueous solution is 1:(1-5).

8. The method for preparing large-particle-size lithium fluoride crystals according to claim 1, characterized in that, In step S2, the dripping time is 8-40 h.

Images