A method for preparing lithium fluoride and products and applications thereof

Abstract

The application discloses a preparation method of lithium fluoride, and products and applications of the lithium fluoride, and relates to the following steps: 1) simultaneously starting to add a fluorine-containing alkaline solution and a lithium hydroxide solution in a reaction bottom solution; controlling the adding speed of the fluorine-containing alkaline solution and the lithium hydroxide solution, so that the fluorine-containing alkaline solution and the lithium hydroxide solution are simultaneously added; continuing to react after the feeding is completed, so as to obtain lithium fluoride slurry; 2) performing solid-liquid separation on the lithium fluoride slurry obtained in the step 1), collecting a solid phase obtained through the solid-liquid separation; and washing and drying, so as to obtain finished lithium fluoride. The preparation method is simple in process, the lithium fluoride crystal prepared has a regular shape and a uniform particle size distribution, and can be directly used as a crystal seed for preparation of a chemical product and growth of an optical crystal.

Description

Technical Field

[0001] This invention relates to the field of new material preparation technology, specifically to a method for preparing lithium fluoride, its products, and its applications. Background Technology

[0002] Lithium fluoride, with a cubic crystal structure, is a white powder at room temperature. It is slightly soluble in water but insoluble in organic solvents such as ethanol. Lithium fluoride has wide applications in many fields, such as: as a neutron shielding material in the nuclear industry; as a heat transfer fluid for storing solar radiation in aerospace technology; as a flux in lava reactors; and in the battery industry for preparing the electrolyte lithium hexafluorophosphate. Lithium fluoride possesses a wide transmission band and high transmittance, making it an excellent optical crystal material, commonly used in the fabrication of optical windows, lenses, prisms, and refractive elements in the ultraviolet-visible-infrared range.

[0003] Currently, the main method for synthesizing lithium fluoride is the direct synthesis method, which involves directly mixing and stirring a fluorine source and a lithium source. For example, finished lithium carbonate or lithium hydroxide can be used as the lithium source and directly reacted with hydrofluoric acid, sodium fluoride, or ammonium fluoride. Conventional methods produce lithium fluoride crystals with coarse morphology and concentrated particle size distribution, which is detrimental to subsequent crystal growth and processing. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing lithium fluoride, which is simple and produces lithium fluoride crystals with regular shape and uniform particle size distribution.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing lithium fluoride includes the following steps:

[0007] 1) Simultaneously add a fluorinated alkaline solution and a lithium hydroxide solution to the reaction substrate; control the addition rate of the fluorinated alkaline solution and the lithium hydroxide solution to ensure that they are added at the same time; after the addition is complete, continue the reaction to obtain a lithium fluoride slurry;

[0008] 2) Perform solid-liquid separation on the lithium fluoride slurry obtained in step 1), collect the solid phase obtained from the solid-liquid separation; wash and dry to obtain the finished lithium fluoride product.

[0009] Preferably, the fluorine content in the fluorinated alkaline solution is 30–90 g / L; and the concentration of the lithium hydroxide solution is 10%–25%.

[0010] Preferably, the addition time of the fluorine-containing alkaline solution and the lithium hydroxide solution is 30-75 min; after the addition is completed, the reaction continues for 20-40 min.

[0011] Preferably, the reaction substrate is Zn. 2+ Solution and / or Mn 2+ Solution; the concentration of the reaction substrate is 0.04–0.1 mol / L.

[0012] Preferably, the fluorine-containing alkaline solution is wastewater containing fluorine and ammonium generated during the tantalum-niobium metallurgy process; the volume ratio of the reaction base liquid to the fluorine-containing alkaline solution is 1:(0.5-1.5).

[0013] Furthermore, the fluorine-containing alkaline solution and the lithium hydroxide solution are added simultaneously through conduits; at least one of the conduit openings for the fluorine-containing alkaline solution and the lithium hydroxide solution is immersed in the reaction substrate, or both the conduit openings for the fluorine-containing alkaline solution and the lithium hydroxide solution are located above the surface of the reaction substrate.

[0014] Furthermore, it also includes the step of sieving the obtained lithium fluoride product and collecting the lithium fluoride crystals on the sieve.

[0015] Furthermore, it also includes recycling treatment, in which the undersize material obtained after sieving is added back to the reaction base liquid for reuse.

[0016] Another object of the present invention is to provide a lithium fluoride, which is prepared by a lithium fluoride preparation method provided in the first object of the present invention.

[0017] Another object of the present invention is to provide an application of lithium fluoride prepared by the lithium fluoride preparation method provided in the first object of the present invention in chemical products and optical components.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] The lithium fluoride preparation method provided by this invention is simple to operate. In a system containing a reaction substrate, by controlling the addition rate of raw materials, the fluorine-containing alkaline solution and the lithium hydroxide solution are added simultaneously and completely. After the reaction, a lithium fluoride product with regular crystal shape, smooth surface, good flowability, and uniform particle size distribution can be obtained. The prepared lithium fluoride crystals have a regular structure and are easy to sieve to obtain crystals with uniform particle size, which can be directly used as seed crystals for chemical product preparation and optical crystal growth. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the feeding method for a lithium fluoride preparation method provided by the present invention.

[0021] Figure 2 Images of lithium fluoride crystals under a 1000X scanning electron microscope are shown, where (a) is an image of commercially available AR-grade LiF crystals and (b) is an image of the LiF crystals in Example 2.

[0022] Figure 3 The images show the particle size distribution of lithium fluoride crystals obtained by laser particle size analyzer, where (a) is the particle size distribution of commercially available AR-grade LiF crystals, and (b) is the particle size distribution of LiF crystals in Example 2. Detailed Implementation

[0023] The specific embodiments of the present invention are discussed in detail below with reference to the accompanying drawings. Obviously, this is only for illustrative purposes, and the described embodiments are only some embodiments, not all embodiments.

[0024] This invention provides a method for preparing lithium fluoride, comprising the following steps:

[0025] 1) Simultaneously add a fluorinated alkaline solution and a lithium hydroxide solution to the reaction substrate; control the addition rate of the fluorinated alkaline solution and the lithium hydroxide solution to ensure that they are added at the same time; after the addition is complete, continue the reaction to obtain a lithium fluoride slurry;

[0026] 2) Perform solid-liquid separation on the lithium fluoride slurry obtained in step 1), collect the solid phase obtained from the solid-liquid separation; wash and dry to obtain the finished lithium fluoride product.

[0027] In existing technologies, lithium fluoride is typically precipitated by adding solid lithium carbonate or lithium hydroxide to a hydrogen fluoride solution. While this method is simple, the product has a coarse morphology, poor flowability, and it is difficult to obtain crystals with uniform particle size, making it unsuitable for direct use as a raw material for chemical product preparation or optical crystal growth. This invention addresses this by first adding a reaction substrate to a reactor, followed by the simultaneous addition of a fluorine-containing alkaline solution and a lithium hydroxide solution, controlling the addition rate to ensure simultaneous dripping. This allows for more uniform nucleation and growth of the resulting lithium fluoride, yielding lithium fluoride crystals with a more ideal structure.

[0028] In one embodiment, the fluorine content in the fluorinated alkaline solution is 30–90 g / L, specifically 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, or any value between 30 and 90 g / L; the concentration of the lithium hydroxide solution is 10%–25%, specifically 10%, 13%, 16%, 19%, 22%, 25%, or any value between 10% and 25%.

[0029] In one embodiment, the feeding time of the fluorine-containing alkaline solution and the lithium hydroxide solution is 30 to 75 minutes, specifically 30 minutes, 45 minutes, 60 minutes, 75 minutes or any value between 30 and 75 minutes; after the feeding is completed, the reaction continues for 20 to 40 minutes, specifically 20 minutes, 30 minutes, 40 minutes or any value between 30 and 40 minutes.

[0030] If the feeding time is too long, impurities are easily adsorbed on the crystal surface, which reduces the binding energy of the crystal surface and causes uneven crystal growth. If the feeding time is too short, the fluorine-containing alkaline solution and lithium hydroxide cannot react fully, resulting in a low reaction yield and small lithium fluoride particle size.

[0031] In one embodiment, the reaction substrate is Zn 2+ Solution and / or Mn 2+ The concentration of the reaction substrate is 0.04–0.1 mol / L, specifically 0.04 mol / L, 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, or any value between 0.04 and 0.1 mol / L.

[0032] Preferably, the reaction substrate is Zn 2+ Solution and / or Mn 2+ Solution, add Mn 2+ Zn 2+ This will greatly increase the solubility of lithium fluoride due to the salt effect, common ion effect, and counter ion effect. Molecular dynamics simulations indicate that the essence of these effects is the interaction between cations and anions in the solution and F... — The association between them is directly related to F. — When Mn forms associated ions, it is subject to electrostatic attraction, which increases the energy barrier that needs to be overcome. 2+ Zn 2+ The cations exhibited strong hydration capabilities. The maximum solubilities of zinc fluoride and manganese fluoride at room temperature were 0.156 mol / Kg and 0.954 mol / Kg, respectively. More preferably, the concentration of the reaction substrate was controlled between 0.04 mol / L and 0.1 mol / L. At lower concentrations and without exceeding the maximum solubility, no precipitation of zinc fluoride and manganese fluoride occurred, which further improved the purity of lithium fluoride.

[0033] In one embodiment, the fluorine-containing alkaline solution is fluorine- and ammonium-containing wastewater generated during tantalum-niobium metallurgy; the volume ratio of the reaction base liquid to the fluorine-containing alkaline solution is 1:(0.5-1.5), specifically any value between 1:0.5, 1:0.7, 1:0.9, 1:1.1, 1:1.3, 1:1.5 or 1:(0.5-1.5).

[0034] The ammonium fluoride wastewater generated during tantalum and niobium metallurgy mainly contains F - SO4 2- NH4 + Plasma, F in wastewater - SO4 2- The low content of F content hinders resource utilization. The conventional treatment method in existing technologies is to use lime precipitation.- and SO4 2- Then, ammonia nitrogen is stripped off, but the mixed waste residue of CaF and CaSO4 produced by this method is classified as hazardous waste.

[0035] The preparation method provided by this invention is preferably more suitable for ammonium fluoride-containing wastewater systems. Before the reaction between the fluoride-containing alkaline solution and the lithium hydroxide solution, Zn is first used... 2+ Solution and / or Mn 2+ Using the solution as the reaction substrate, and combining it with the feeding method described in the aforementioned examples, can dissolve the F in the fluoride-containing alkaline solution. - Clusters, and Li + Lithium fluoride crystals are precipitated. The reaction equation is LiOH + NH4F = LiF + NH3·H2O, where Zn 2+ and Mn 2+ The electrostatic interaction between lithium fluoride and LiF molecules lowers the free energy for molecular cluster formation, and because lithium fluoride has strong polarity, lithium fluoride molecules tend to... 2+ and Mn 2+ Nucleation and growth occur nearby.

[0036] The method of this invention can also be used to treat ammonium fluoride-containing wastewater generated during tantalum and niobium metallurgy, thereby achieving the removal of F from the tantalum and niobium ammonium fluoride-containing wastewater. - The utilization of resources also alleviates the wastewater treatment problem in the tantalum and niobium industry, resulting in good economic and social benefits.

[0037] In one embodiment, such as Figure 1 As shown, Figure 1 This is a schematic diagram of the feeding method for a lithium fluoride preparation method provided by the present invention. A fluorine-containing alkaline solution and a lithium hydroxide solution are added simultaneously through conduits. At least one of the conduit openings for the fluorine-containing alkaline solution and the lithium hydroxide solution is immersed in the reaction base liquid, or both the conduit openings for the fluorine-containing alkaline solution and the lithium hydroxide solution are located above the surface of the reaction base liquid.

[0038] At least one of the conduits for the fluorinated alkaline solution and the lithium hydroxide solution is immersed in the reaction solution. This method of addition increases the contact reaction time between the fluorinated alkaline solution and the lithium hydroxide solution, thereby reducing the nucleation rate of the crystals, slowing down the diffusion rate, and increasing the crystal growth time. The number of critical nuclei formed per unit time decreases, and the critical nucleus size increases. These few nuclei will continue to grow until they come into contact with each other, resulting in large lithium fluoride crystals. The nuclei can grow freely in the liquid, with a roughly uniform growth rate in all directions, forming regularly shaped crystals that are less prone to aggregation. This ensures complete and sufficient reaction of the reactants, improving the yield of lithium fluoride products.

[0039] In one embodiment, the method further includes a step of sieving the obtained lithium fluoride product and collecting the lithium fluoride crystals on the sieve.

[0040] In one embodiment, the method further includes a recycling process, in which the undersize material obtained after sieving is added to the reaction substrate for reuse.

[0041] It is understandable that the sieve mesh size can be determined according to actual needs. Large lithium fluoride crystals on the sieve that meet the requirements can be used directly, such as as raw materials for crystal growth. Small lithium fluoride crystals that fall off the sieve are added back into the reaction solution for recrystallization to obtain crystals with larger particle sizes.

[0042] The present invention also provides a lithium fluoride, which is prepared by a lithium fluoride preparation method provided in the above embodiments.

[0043] The present invention also provides an application of lithium fluoride prepared by the method for preparing lithium fluoride provided in the above embodiments in chemical products and optical components.

[0044] The specific embodiments of the present invention are described in detail below.

[0045] Some of the equipment used in the examples: beaker, Changzhou Aohua JJ-1A digital display electric stirrer, YCJ120 / 4-3 speed-regulating motor, Shenchen YZ1515x peristaltic pump, SHZ-D(III) circulating water vacuum pump, Buchner funnel, 101-1AS drying oven, DP-LDJ-G6609 angle of repose measuring instrument, laser particle size analyzer, and Phenom Pure electron microscope.

[0046] Example 1

[0047] (1) Transfer 1250 ml of 0.08 mol / L ZnSO4 solution into the reactor as the reaction base liquid. The volume ratio of the reaction base liquid to the fluorine-containing alkaline solution is 1:0.8. Start stirring.

[0048] (2) While stirring the bottom liquid, add 1000ml of fluorine- and ammonium-containing wastewater (90g / L fluorine content) and 900ml of 25% lithium hydroxide solution to the reactor. The conduit for the fluorine-containing alkaline solution should be submerged in the bottom liquid, while the conduit for the lithium hydroxide solution should be above the bottom liquid. Control the addition rate of the fluorine-containing tantalum-niobium wastewater and lithium hydroxide solution so that the raw materials are added simultaneously in about 30 minutes. Continue the reaction for 40 minutes to obtain lithium fluoride slurry, and let it stand for 1 hour.

[0049] (3) After the reaction in step (2) is completed, the lithium fluoride slurry is filtered to obtain a lithium fluoride filter cake. The lithium fluoride filter cake is added to 700 ml of deionized water and stirred and washed for 30 min, filtered, and then placed in a drying oven and dried at 105 °C for 8 h to obtain the finished lithium fluoride product.

[0050] (4) The lithium fluoride product was sieved using a 300-mesh sieve. The particles that passed through the sieve were collected, while the particles that passed through the sieve were added back into the reactor for reuse. According to statistics, the +300 mesh fraction accounted for 60.12% of the lithium fluoride product, the total lithium yield was 96.29%, and the angle of repose was determined to be 36° using an angle of repose measuring instrument.

[0051] Example 2

[0052] (1) Transfer 2000 ml of 0.1 mol / L MnSO4 solution into the reactor as the reaction base liquid. The volume ratio of the reaction base liquid to the fluorine-containing alkaline solution is 1:1. Start stirring.

[0053] (2) While stirring the bottom liquid, add 2000ml of fluorine- and ammonium-containing wastewater (70g / L fluorine content) and 2300ml of 10% lithium hydroxide solution to the reactor. The conduit for the fluorine-containing alkaline solution should be above the bottom liquid, while the conduit for the lithium hydroxide solution should be submerged in the bottom liquid. Control the addition rate of the fluorine-containing tantalum-niobium wastewater and lithium hydroxide solution so that the raw materials are added simultaneously in about 60 minutes. Continue the reaction for 30 minutes to obtain lithium fluoride slurry, and let it stand for 1 hour.

[0054] (3) After the reaction in step (2) is completed, the lithium fluoride slurry is filtered to obtain a lithium fluoride filter cake. The lithium fluoride filter cake is added to 800 ml of deionized water and stirred and washed for 30 min, filtered, and then placed in a drying oven and dried at 105 °C for 15 h to obtain the finished lithium fluoride product.

[0055] (4) The lithium fluoride product was sieved using a 300-mesh sieve. The particles that passed through the sieve were collected, while the particles that passed through the sieve were added back into the reactor for reuse. According to statistics, the +300 mesh fraction accounted for 62.82% of the lithium fluoride product, the total lithium yield was 97.06%, and the angle of repose was determined to be 35° using an angle of repose measuring instrument.

[0056] Example 3

[0057] (1) Transfer 3200 ml of 0.04 mol / L ZnSO4 solution into the reactor as the reaction base liquid. The volume ratio of the reaction base liquid to the fluorine-containing alkaline solution is 1:0.5. Start stirring.

[0058] (2) While stirring the bottom liquid, add 1600 ml of fluorine- and ammonium-containing wastewater (fluorine content 30 g / L) generated during tantalum-niobium metallurgy and 1600 ml of 15% lithium hydroxide solution to the reactor. The inlet of the fluorine-containing alkaline solution and the inlet of the lithium hydroxide solution should be above the bottom liquid. Control the addition rate of the fluorine-containing tantalum-niobium wastewater and lithium hydroxide solution so that the raw materials are added simultaneously in about 45 min. Continue the reaction for 35 min to obtain lithium fluoride slurry, and let it stand for 1 h.

[0059] (3) After the reaction in step (2) is completed, the lithium fluoride slurry is filtered to obtain a lithium fluoride filter cake. The lithium fluoride filter cake is added to 600 ml of deionized water and stirred and washed for 30 min, filtered, and then placed in a drying oven and dried at 105 °C for 12 h to obtain the finished lithium fluoride product.

[0060] (4) The lithium fluoride product was sieved using a 300-mesh sieve. The particles that passed through the sieve were collected, while the particles that passed through the sieve were added back into the reactor for reuse. According to statistics, the +300 mesh fraction accounted for 61.39% of the lithium fluoride product, the total lithium yield was 96.32%, and the angle of repose was determined to be 34° using an angle of repose measuring instrument.

[0061] Example 4

[0062] (1) Transfer 800 ml of 0.06 mol / L ZnSO4 solution and 800 ml of 0.06 mol / L MnSO4 solution into the reactor as the reaction base liquid. The volume ratio of the reaction base liquid to the fluorine-containing alkaline solution is 1:1.5. Start stirring.

[0063] (2) While stirring the bottom liquid, add 2400ml of fluorine- and ammonium-containing wastewater (50g / L fluorine content) and 1200ml of 20% lithium hydroxide solution to the reactor. The conduit for the fluorine-containing alkaline solution and the conduit for the lithium hydroxide solution should be submerged in the bottom liquid. Control the addition rate of the fluorine-containing tantalum-niobium wastewater and lithium hydroxide solution so that the raw materials are added simultaneously in about 75 minutes. Continue the reaction for 20 minutes to obtain lithium fluoride slurry, and let it stand for 1 hour.

[0064] (3) After the reaction in step (2) is completed, the lithium fluoride slurry is filtered to obtain a lithium fluoride filter cake. The lithium fluoride filter cake is added to 500 ml of deionized water and stirred and washed for 30 min, filtered, and then placed in a drying oven and dried at 105 °C for 15 h to obtain the finished lithium fluoride product.

[0065] (4) The lithium fluoride product was sieved using a 300-mesh sieve. The particles that passed through the sieve were collected, while the particles that passed through the sieve were added back into the reactor for reuse. According to statistics, the +300 mesh fraction accounted for 60.63% of the lithium fluoride product, the total lithium yield was 95.38%, and the angle of repose was determined to be 36° using an angle of repose measuring instrument.

[0066] Performance Comparison

[0067] Using commercially available AR-grade lithium fluoride crystals as comparative examples, scanning electron microscopy (SEM), angle of repose (ARR), and laser particle size analysis were performed on the finished lithium fluoride crystals in Example 2 of this invention. The results are shown in Table 1 below. Figures 2-3 As shown, where Figure 2 Images obtained using scanning electron microscopy (SEM). Figure 3 This is a particle size distribution diagram for laser particle size analysis.

[0068] Table 1

[0069]

[0070] Based on the above data comparison, it can be seen that the lithium fluoride crystals prepared by the lithium fluoride preparation method provided by this invention have a more uniform particle size distribution and larger crystal size compared to lithium fluoride crystals prepared by conventional methods. The angle of repose measurement instrument analysis shows that the angle of repose is >30°, indicating good fluidity. Under a 1000X scanning electron microscope, the crystals are regular in shape, granular, and not prone to agglomeration.

[0071] In the above embodiments, lithium fluoride was prepared using ammonium fluoride-containing wastewater and lithium hydroxide generated during tantalum-niobium metallurgy as raw materials through the lithium fluoride preparation method provided by this invention. The total lithium yield reached over 95%, the angle of repose was around 35°, and the fluidity was good. Simultaneously, the method for preparing lithium fluoride from tantalum-niobium wastewater was also achieved. - Its resource utilization has good economic value.

[0072] In practical applications, the above embodiments can be reasonably modified based on the inventive concept of this invention to achieve the desired effect, according to actual needs. The above embodiments are merely preferred embodiments of this invention and should not be construed as limiting the scope of protection of this invention. Any non-substantial changes and substitutions made by those skilled in the art based on this invention are within the scope of protection claimed by this invention.

Claims

1. A method for preparing lithium fluoride, characterized in that, Includes the following steps: 1) Simultaneously add a fluorinated alkaline solution and a lithium hydroxide solution to the reaction substrate; control the addition rate of the fluorinated alkaline solution and the lithium hydroxide solution to ensure that they are added at the same time; after the addition is complete, continue the reaction to obtain a lithium fluoride slurry; 2) Perform solid-liquid separation on the lithium fluoride slurry obtained in step 1), collect the solid phase obtained from the solid-liquid separation; wash and dry to obtain the finished lithium fluoride product; The reaction substrate is Zn 2+ Solution and / or Mn 2+ Solution; the concentration of the reaction substrate is 0.04~0.1 mol / L.

2. The method for preparing lithium fluoride according to claim 1, characterized in that, The fluorine content in the fluorine-containing alkaline solution is 30~90 g / L; the concentration of the lithium hydroxide solution is 10%~25%.

3. A method for preparing lithium fluoride according to claim 1 or 2, characterized in that, The addition time for the fluorine-containing alkaline solution and the lithium hydroxide solution is 30~75 min; after the addition is completed, the reaction continues for 20~40 min.

4. The method for preparing lithium fluoride according to claim 1, characterized in that, The fluorine-containing alkaline solution is wastewater containing fluorine and ammonium generated during the tantalum-niobium metallurgical process; the volume ratio of the reaction base liquid to the fluorine-containing alkaline solution is 1:(0.5~1.5).

5. The method for preparing lithium fluoride according to claim 1, characterized in that, The fluorinated alkaline solution and the lithium hydroxide solution are added simultaneously through separate conduits; at least one of the conduit openings for the fluorinated alkaline solution and the lithium hydroxide solution is immersed in the reaction substrate, or both the conduit openings for the fluorinated alkaline solution and the lithium hydroxide solution are located above the surface of the reaction substrate.

6. The method for preparing lithium fluoride according to claim 1, characterized in that, It also includes the step of sieving the obtained lithium fluoride product and collecting the lithium fluoride crystals on the sieve.

7. The method for preparing lithium fluoride according to claim 6, characterized in that, It also includes recycling, where the undersize material obtained after sieving is added back to the reaction solution for reuse.

8. A lithium fluoride, characterized in that, The lithium fluoride is prepared by a method for preparing lithium fluoride according to any one of claims 1 to 7.

9. The application of lithium fluoride prepared by any one of claims 1 to 7, or the lithium fluoride of claim 8, in chemical products and optical components.

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