A method for preparing anhydrous lithium iodide

Abstract

The application provides a preparation method of anhydrous lithium iodide, and belongs to the field of new energy solid-state batteries. The method comprises the following steps in sequence: mixing a lithium source and an iodine source, obtaining a mixed solution after reaction, removing impurities by filtration to obtain a filtrate; the filtrate is subjected to frozen impurity separation, and after filtration, the liquid is a frozen clear solution, and the solid is a sodium salt or a potassium salt; the frozen clear solution is heated and evaporated to concentrate, when the solid content is 50%-70%, heating is stopped, lithium iodide concentrated slurry is obtained, the lithium iodide concentrated slurry is cooled to room temperature under stirring to obtain lithium iodide one-evaporation crystal slurry, after centrifugation, one-evaporation wet product and primary mother liquor are obtained; the one-evaporation wet product is dissolved in water and filtered, and then the heating and evaporation concentration process of step c is repeated to obtain two-evaporation wet product and secondary mother liquor; the two-evaporation wet product is heated and self-dissolved, and after spray drying, anhydrous lithium iodide is obtained. The anhydrous lithium iodide prepared by the method has a purity greater than or equal to 99.9%, and can be applied to the field of solid-state batteries.

Description

Technical Field

[0001] This invention relates to the field of new energy solid-state batteries, specifically to a method for preparing anhydrous lithium iodide. Background Technology

[0002] Anhydrous lithium iodide is a white solid, readily soluble in water, methanol, ethanol, and acetone. When melted, it is corrosive to glass and ceramics. Solid anhydrous lithium iodide is hygroscopic, and the product is mostly lithium iodide trihydrate, with the molecular formula LiI·3H₂O, a white crystalline solid with a density of 3.494 g / cm³. 3 It must be stored in a sealed container.

[0003] Anhydrous lithium iodide is an important lithium compound widely used in pharmaceuticals, batteries, organic synthesis, and functional materials. In the pharmaceutical field, anhydrous lithium iodide is a key raw material for the synthesis of dopamine-like drugs. In the lithium battery field, anhydrous lithium iodide is widely used in lithium battery electrolytes; lithium batteries using anhydrous lithium iodide as the electrolyte are already used in pacemakers, offering advantages such as high energy density, low loss, long lifespan, good sealing performance, and prevention of bodily fluid inflow. Adding anhydrous lithium iodide to solid electrolytes can increase lithium-ion conductivity and battery stability. As an electrolyte for high-end lithium-ion power batteries, the quality of anhydrous lithium iodide determines the safety and reliability of lithium-ion power batteries. The water content and stability of the product are key factors affecting lithium-ion power batteries. Furthermore, some industry professionals have suggested that smaller particle sizes can reduce electro-ionic resistance, increase capacity, and reduce mechanical stresses related to volume changes. With the continued rise in the penetration rate of new energy electric vehicles and the gradual release of high-end power battery production capacity, the development of anhydrous lithium iodide for next-generation high-end lithium-ion power batteries has significant practical implications.

[0004] Currently, lithium iodide preparation technologies can be mainly categorized into two main types: liquid-phase methods and solid-phase methods. Liquid-phase methods include: ① the neutralization reaction of hydroiodic acid with lithium hydroxide (CN102030345A); ② the reaction of lithium hydroxide with elemental iodine in a hydrazine hydrate system (CN113735140A). Although some companies have achieved annual production scales of tons using liquid-phase methods, it is still not the most cost-effective route. Solid-phase methods refer to the direct reaction of metallic lithium with elemental iodine (CN 107473243A). The product has low water content, but the reaction is incomplete, resulting in lower product purity. It requires purification using organic solvents and involves high-temperature, high-pressure containers, posing a risk of explosion. Furthermore, the drying and dehydration of trihydrate lithium iodide remains a challenge for the industry. High-end anhydrous lithium iodide can be used in lithium batteries. According to patent CN104261440B, the best overall battery performance is achieved when the moisture content is controlled below 150 ppm. Therefore, breaking through key core technologies and accelerating the realization of significant cost reduction and efficiency improvement is the biggest challenge in coping with current market competition. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing anhydrous lithium iodide. This method uses materials containing lithium sulfate or lithium chloride as raw materials, first obtaining lithium iodide hydrate crystals, and then dewatering to obtain anhydrous lithium iodide products suitable for high-end lithium-ion batteries.

[0006] The technical solution of the present invention is as follows: This invention provides a method for preparing anhydrous lithium iodide, comprising the following steps: a. Mix lithium source and iodine source, react to obtain a mixed solution, filter to remove impurities and obtain filtrate; b. Freeze the filtrate obtained in step a to remove impurities. After filtration, the liquid is a clear cryosol and the solid is a sodium or potassium salt. c. Heat and evaporate the frozen liquid obtained in step b to concentrate it. When the solid content is 50%-70%, stop heating to obtain lithium iodide concentrated slurry. Cool the lithium iodide concentrated slurry to room temperature under stirring to obtain lithium iodide first-evapor crystal slurry. After centrifugation, obtain first-evapor wet product and primary mother liquor. d. The first-distilled wet product obtained in step c is dissolved in water and filtered. Then the heating, evaporation and concentration process in step c is repeated to obtain the second-distilled wet product and the secondary mother liquor. e. The second-distilled wet product obtained in step d is heated to self-dissolve, and after spray drying, anhydrous lithium iodide is obtained; The lithium source is a lithium sulfate solution or a lithium chloride solution; The iodine source is a sodium iodide solution or a potassium iodide solution.

[0007] In step a, mixing the lithium source and the iodine source involves slowly adding the iodine source into the lithium source.

[0008] In this invention, if the anhydrous lithium iodide obtained in step e is defective, the defective anhydrous lithium iodide can be returned to the water dissolution process in step d for resolution and the subsequent steps can be continued until the prepared anhydrous lithium iodide meets the requirements for qualified products.

[0009] In one specific embodiment, the lithium source is a lithium sulfate solution, and the molar ratio of sodium iodide or potassium iodide to lithium sulfate is 2.0:1-2.2:1; preferably, the molar ratio of sodium iodide or potassium iodide to lithium sulfate is 2:1.

[0010] In one specific embodiment, the lithium sulfate solution is a lithium sulfate solution from a lithium salt production workshop, and its preparation process includes the following steps: (1) After calcining the lithium ore at 1100-1380℃, sulfuric acid is added at a mass ratio of acid material to lithium ore of 1:4-7 to carry out acidification treatment to obtain acidification treatment solution; (2) In the acidification treatment solution, add water or recycled filtrate at a mass ratio of 2-3:1 between the added liquid and lithium ore, adjust the pH to 5.7-6.2, let stand and filter to obtain mother liquor 1; (3) Adjust the pH of mother liquor 1 to 8.5-9.7, let it stand and filter to obtain mother liquor 2; (4) Adjust the pH of mother liquor 2 to 10-10.8, let it stand, and filter to obtain mother liquor 3; (5) Detection of Ca in mother liquor 3 2+ To determine the concentration, add an equimolar amount of sodium carbonate, stir, let stand, and then filter to obtain mother liquor 4. After evaporation and concentration, obtain a lithium sulfate solution.

[0011] The main components of the lithium sulfate solution in the lithium salt production workshop are as follows:

[0012] In one specific embodiment, the lithium source is a lithium chloride solution, and the molar ratio of sodium iodide or potassium iodide to lithium chloride is 1.0:1-1.2:1, preferably, the molar ratio of sodium iodide or potassium iodide to lithium chloride is 1:1.

[0013] In one specific embodiment, the lithium chloride solution is a lithium chloride solution from a lithium salt production workshop, and its preparation process includes the following steps: ① After calcining the lithium ore at 1100-1380℃, sulfuric acid is added at a mass ratio of acid solution to lithium ore of 1:4-7 to carry out acidification treatment, and the acidification treatment solution is obtained. ② In the acidification solution, add water or recycled filtrate at a liquid-to-lithium ore mass ratio of 2-3:1, then adjust the pH to 5.7-6.2, let stand, filter, and obtain mother liquor 1; ③ Adjust the pH of mother liquor 1 to 8.5-9.7, let it stand, filter, and obtain mother liquor 2; ④ Adjust the pH of mother liquor 2 to 10-10.8, let it stand, filter, and obtain mother liquor 3; ⑤ Detection of Ca in mother liquor 3 2+ To determine the concentration, add an equimolar amount of sodium carbonate, stir, let stand, and then filter to obtain mother liquor 4. ⑥ Add calcium chloride to mother liquor 4 according to the molar ratio of sulfate to calcium of 1.05-1.1:1 for conversion. After conversion and filtration, evaporate and concentrate the filtrate to obtain lithium chloride solution.

[0014] The main components of the lithium chloride solution in the lithium salt production workshop are as follows:

[0015] In one specific implementation, the reaction time in step a is 15-45 min.

[0016] In one specific embodiment, in step b, the freezing temperature for precipitation is -15℃ to 0℃, and the time is 30-60 min; the iodine source is a sodium iodide solution, and the concentration of sodium ions in the frozen solution is less than or equal to 35 g / L, and the concentration of sulfate ions is less than or equal to 25 g / L; the iodine source is a potassium iodide solution, and the concentration of potassium ions in the frozen solution is less than or equal to 50 g / L, and the concentration of sulfate ions is less than or equal to 40 g / L.

[0017] When the lithium source is lithium sulfate and the iodine source is sodium iodide, the number of freezing purification cycles depends on the concentrations of sodium ions and sulfate ions in the cryosol. Specifically, the sodium ion concentration must be less than or equal to 35 g / L and the sulfate ion concentration must be less than or equal to 25 g / L. If the concentration of the cryosol does not meet this requirement after the first freezing purification, the cryosol can be subjected to a second freezing purification. This process can be repeated multiple times until the sodium ion concentration is less than or equal to 35 g / L and the sulfate ion concentration is less than or equal to 25 g / L.

[0018] When the lithium source is lithium sulfate and the iodine source is potassium iodide, the number of freezing precipitation cycles depends on the concentrations of potassium ions and sulfate ions in the cryosol. Specifically, the potassium ion concentration must be less than or equal to 50 g / L and the sulfate ion concentration must be less than or equal to 40 g / L. If the concentration of the cryosol does not meet this requirement after the first freezing precipitation, the cryosol can be subjected to a second freezing precipitation. This process can be repeated multiple times until the potassium ion concentration is less than or equal to 50 g / L and the sulfate ion concentration is less than or equal to 40 g / L.

[0019] In one specific embodiment, in step b, the freezing temperature for precipitation is -15℃ to 0℃, and the time is 30-60 min; the iodine source is a sodium iodide solution, and the sodium ion concentration in the frozen solution is less than or equal to 90 g / L, and the chloride ion concentration is less than or equal to 160 g / L; the iodine source is a potassium iodide solution, and the potassium ion concentration in the frozen solution is less than or equal to 140 g / L, and the chloride ion concentration is less than or equal to 160 g / L.

[0020] When the lithium source is lithium chloride and the iodine source is sodium iodide, the number of freezing precipitation cycles depends on the concentrations of sodium ions and chloride ions. Specifically, the sodium ion concentration must be less than or equal to 90 g / L and the chloride ion concentration must be less than or equal to 160 g / L. If the concentration of the clear liquid after the first freezing precipitation does not meet this requirement, the clear liquid can be subjected to a second freezing precipitation. This process can be repeated multiple times until the sodium ion concentration is less than or equal to 90 g / L and the chloride ion concentration is less than or equal to 160 g / L.

[0021] When the lithium source is lithium chloride and the iodine source is potassium iodide, the number of freezing precipitation cycles depends on the concentrations of potassium ions and chloride ions. Specifically, the potassium ion concentration must be less than or equal to 140 g / L and the chloride ion concentration must be less than or equal to 160 g / L. If the concentration of the cryo-liquid after the first freezing precipitation does not meet this requirement, the cryo-liquid can be subjected to a second freezing precipitation. This process can be repeated multiple times until the potassium ion concentration is less than or equal to 140 g / L and the chloride ion concentration is less than or equal to 160 g / L.

[0022] In one specific embodiment, in step b, the method for processing and reusing sodium or potassium salt is as follows: the sodium or potassium salt is redissolved in water at a ratio of 1:2 to 2:1, then evaporated and centrifuged. The solid is dried again to obtain the corresponding sodium or potassium salt by-product, and the liquid is returned to the freezing and impurity removal process in step b, and frozen and impurity removed together with the filtrate obtained in step a.

[0023] In one specific embodiment, in step c, the primary mother liquor is returned to the filtration process of step a and filtered together with the mixture from step a.

[0024] In one specific embodiment, during step d, the mass ratio of the first-distilled wet product to water is 2:1 during the process of dissolving the first-distilled wet product in water.

[0025] In one specific embodiment, in step d, the filtration of the first-distilled wet product after dissolving it in water is carried out by precision filtration to remove solid particles larger than or equal to 0.3 μm.

[0026] In one specific embodiment, in step d, the secondary mother liquor is returned to the heating, evaporation, and concentration process in step c, where it is heated, evaporated, and concentrated together with the frozen clear liquid from step c.

[0027] In one specific embodiment, in step e, the temperature at which the second-distilled wet product undergoes self-dissolution upon heating is greater than or equal to 73°C; the temperature for spray drying is 300°C.

[0028] In one specific embodiment, the preparation method further includes: f, pulverization and packaging: the anhydrous lithium iodide from step e is pulverized by ball milling to obtain anhydrous lithium iodide product.

[0029] In one specific embodiment, the ball mill rotates at 300-600 rpm for 1-8 hours.

[0030] In one specific embodiment, in step f, the anhydrous lithium iodide product has a particle size of less than or equal to 25 μm and a purity of greater than or equal to 99.9%.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Using lithium sulfate solution or lithium chloride solution directly from the lithium salt production workshop as raw material saves raw material costs and facilitates large-scale production.

[0032] (2) The static drying and dehydration process was adopted, which solved the problems of wall adhesion and low yield during the drying of lithium iodide.

[0033] (3) The preparation method of the present invention uses lithium sulfate purified solution as raw material, and obtains the product through freezing precipitation and evaporation crystallization.

[0034] The anhydrous lithium iodide product also incorporates a ball milling process, resulting in an anhydrous lithium iodide product with a particle size ≤25um and a purity greater than or equal to 99.9%. It can be applied in the field of solid-state batteries, especially as a key raw material in the synthesis of lithium metal battery electrolyte additives, lithium-oxygen battery anion additives, and sulfur-based solid electrolytes. Attached Figure Description

[0035] Figure 1 This is a flowchart illustrating the lithium iodide preparation process of the present invention; Figure 2 The image shows an SEM image of the anhydrous lithium iodide product prepared in Example 1. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0037] Example 1

[0038] This embodiment provides a method for preparing anhydrous lithium iodide, including the following steps: (1) Take 3L of lithium sulfate leaching solution with a concentration of 40g / L based on Li2O (the lithium sulfate leaching solution is the lithium sulfate solution in the lithium salt production workshop, which contains a small amount of sodium, potassium, calcium, magnesium and other ion impurities). Its main components are shown in Table 1.

[0039] (2) Freezing and purification: Weigh about 1.40 L of sodium iodide solution with an iodine content of 800 g / L according to the molar ratio of sodium iodide to lithium sulfate = 2.2:1, slowly add it to the purified lithium sulfate solution, stir at room temperature for 15 minutes and then filter. Take the filtrate, cool it to -5℃, keep it at the temperature for 40 minutes, filter off the white solid, continue to cool the filtrate to -10℃, keep it at the temperature for 40 minutes, filter off the insoluble matter, freeze it again to -15℃, keep it at the temperature for 40 minutes, filter off the insoluble matter, and obtain the lithium iodide cryopure solution.

[0040] Table 1. Solution composition before and after freezing

[0041] (3) Evaporation and concentration: The lithium iodide cryopreservation liquid is heated and evaporated. When the cryopreservation liquid begins to become turbid and some crystals precipitate, the Li2O concentration is ≥180g / L. Evaporation continues. When the solid content reaches 50%, heating is stopped. The liquid is cooled to room temperature under stirring to obtain lithium iodide first-evaporation crystal slurry. After centrifugation analysis, the first-evaporation wet product is obtained. The first-evaporation wet product is then dissolved in a solid-liquid ratio of 2:1 and filtered through a precision filter. The filtrate is then evaporated and concentrated again to obtain the second-evaporation wet product.

[0042] (4) After heating the second-distilled wet product to 73°C to dissolve it, spray-dry it at 300°C to obtain 819 grams of qualified lithium iodide.

[0043] (5) Ball milling: The qualified lithium iodide product is ball milled in a ball mill at a speed of 300 rpm for 8 hours to obtain anhydrous lithium iodide product with a particle size of less than 25 μm.

[0044] The SEM image of the anhydrous lithium iodide product prepared in this embodiment is shown below. Figure 2 As shown.

[0045] Example 2

[0046] This embodiment provides a method for preparing anhydrous lithium iodide, including the following steps: (1) Take 3L of lithium sulfate leaching solution with a concentration of 60g / L based on Li2O (the lithium sulfate leaching solution is the lithium sulfate solution in the lithium salt production workshop, which contains a small amount of sodium, potassium, calcium, magnesium and other ion impurities). Its main components are shown in Table 2.

[0047] (2) Freezing and purification: Weigh 1.52 L of sodium iodide solution with iodine content of 1000 g / L according to the molar ratio of sodium iodide and lithium sulfate of 2:1, slowly add it to the lithium sulfate solution, stir at room temperature for 45 minutes, cool the mixture to -5℃, keep it at the temperature for 40 minutes, filter out the white solid, continue to cool the filtrate to -10℃, keep it at the temperature for 40 minutes, filter out the insoluble matter, and freeze it again to -15℃ to obtain the lithium iodide cryo-clarified solution.

[0048] Table 2. Solution composition before and after freezing

[0049] (3) Evaporation and concentration: The neutralized lithium iodide cryosol is heated and evaporated. When the cryosol begins to become turbid and some crystals precipitate, the Li2O concentration is ≥180g / L. Evaporation continues until the solid content reaches 70%. The first-evaporated lithium iodide crystal slurry is obtained. After centrifugation analysis, the first-evaporated wet product is obtained. The first-evaporated wet product is then dissolved in a solid-liquid ratio of 2:1 and filtered through a precision filter. The filtrate is then evaporated and concentrated again to obtain the second-evaporated wet product.

[0050] (4) After heating the second-distilled wet product to 100°C to dissolve it, spray-dry it at 300°C to obtain 1265.5 g of qualified lithium iodide.

[0051] (5) Ball milling: The qualified lithium iodide product is ball milled in a ball mill at a speed of 600 rpm for 1 hour to obtain anhydrous lithium iodide product with a particle size of less than 25 μm.

[0052] Example 3

[0053] This embodiment provides a method for preparing anhydrous lithium iodide, including the following steps: (1) Take 3L of lithium sulfate leaching solution with a concentration of 50g / L based on Li2O (the lithium sulfate leaching solution is the lithium sulfate solution in the lithium salt production workshop, which contains a small amount of sodium, potassium, calcium, magnesium and other ion impurities). Its main components are shown in Table 3.

[0054] (2) Freezing and purification: Weigh 1.11 L of sodium iodide solution with iodine content of 1200 g / L according to the molar ratio of sodium iodide and lithium sulfate of 2.1:1, slowly add it to the purified lithium sulfate solution, stir at room temperature for 30 minutes, cool the mixture to -5℃, keep it at the temperature for 40 minutes, filter off the white solid, continue to cool the filtrate to -10℃, keep it at the temperature for 40 minutes, filter off the insoluble matter, and freeze it again to -15℃ to obtain the purified lithium iodide cryosol.

[0055] Table 3. Solution composition before and after freezing

[0056] (3) Evaporation and concentration: The lithium iodide cryopreservation liquid is heated and evaporated. When the cryopreservation liquid begins to become turbid and some crystals precipitate, the Li2O concentration is ≥180g / L. Evaporation continues until the solid content reaches 60%. Heating is stopped to obtain lithium iodide first-evaporation crystal slurry. After centrifugation analysis, the first-evaporation wet product is obtained. The first-evaporation wet product is then dissolved in a solid-liquid ratio of 2:1 and filtered through a precision filter. The filtrate is then evaporated and concentrated again to obtain the second-evaporation wet product.

[0057] (4) After heating the second-distilled wet product to 85°C to dissolve it, spray-dry it at 300°C to obtain 1003.8 g of qualified lithium iodide.

[0058] (5) Ball milling: The qualified lithium iodide product is ball milled in a ball mill at a speed of 500 rpm for 2 hours to obtain anhydrous lithium iodide product with a particle size of less than 25 μm.

[0059] Example 4

[0060] This embodiment provides a method for preparing anhydrous lithium iodide, including the following steps: (1) Take 3L of lithium chloride purification solution with a concentration of 200g / L based on Li2O (the lithium chloride purification solution is the lithium chloride solution in the lithium salt production workshop, which contains a small amount of anionic impurities such as sulfate and carbonate). Its main components are shown in Table 4.

[0061] (2) Freezing to remove impurities: According to the molar ratio of sodium iodide and lithium chloride 1:1, measure 4.23L of sodium iodide solution with iodine content of 1200g / L and slowly add it to the lithium sulfate solution. Freezing to remove impurities is not required. After filtration, the filtrate is ready for use.

[0062] Table 4. Solution composition before and after freezing

[0063] (3) Evaporation and concentration: The above filtrate is heated and evaporated. When the filtrate begins to become turbid and some crystals precipitate, evaporation continues. When the solid content reaches 60%, heating is stopped to obtain lithium iodide slurry. After centrifugation analysis, the first-evaporated wet product is obtained. The first-evaporated wet product is then dissolved in a solid-liquid ratio of 2:1 and filtered through a precision filter. The filtrate is then evaporated and concentrated again to obtain the second-evaporated wet product.

[0064] (4) After heating the second-distilled wet product to 85°C to dissolve it, spray-dry it at 300°C to obtain 2176 grams of qualified lithium iodide.

[0065] (5) Ball milling: The qualified lithium iodide product is ball milled in a ball mill at a speed of 500 rpm for 2 hours to obtain anhydrous lithium iodide product with a particle size of less than 25 μm.

[0066] Example 5

[0067] This embodiment provides a method for preparing anhydrous lithium iodide, including the following steps: (1) Take 3L of lithium chloride purification solution with a concentration of 280g / L based on Li2O (the lithium chloride purification solution is the lithium chloride solution in the lithium salt production workshop, which contains a small amount of anionic impurities such as sulfate and carbonate). Its main components are shown in Table 5.

[0068] (2) Freezing and purification: According to the molar ratio of sodium iodide and lithium chloride 1.1:1, 7.8L of sodium iodide solution with iodine content of 1000g / L was measured and slowly added to the lithium chloride solution. After stirring at room temperature for 15 minutes, the mixture was cooled to -5℃ and kept for 40 minutes. The white solid was filtered off, and the filtrate was further cooled to -10℃ and kept for 40 minutes. After filtering off the insoluble matter, it was frozen again to -15℃ to obtain lithium iodide cryo-clarified solution.

[0069] Table 5. Solution composition before and after freezing

[0070] (3) Evaporation and concentration: The above-mentioned lithium iodide frozen clear liquid is heated and evaporated. When the filtrate begins to become turbid and some crystals precipitate, evaporation continues. When the solid content reaches 50%, heating is stopped to obtain lithium iodide first-evaporation crystal slurry. After centrifugation analysis, the first-evaporation wet product is obtained. The first-evaporation wet product is then dissolved in a solid-liquid ratio of 2:1 and filtered through a precision filter. The filtrate is then evaporated and concentrated again to obtain the second-evaporation wet product.

[0071] (4) After heating the second-distilled wet product to 73°C to dissolve it, spray-dry it at 300°C to obtain 3024 grams of qualified lithium iodide.

[0072] (5) Ball milling: The qualified lithium iodide product is ball milled in a ball mill at a speed of 600 rpm for 1 hour to obtain anhydrous lithium iodide product with a particle size of less than 25 μm.

[0073] Example 6

[0074] This embodiment provides a method for preparing anhydrous lithium iodide, including the following steps: (1) Take 3 L of lithium chloride purification solution with a concentration of 220 g / L based on Li2O (the lithium chloride purification solution is the lithium chloride solution in the lithium salt production workshop, which contains a small amount of anionic impurities such as sulfate and carbonate). Its main components are shown in Table 6.

[0075] (2) Freezing and purification: According to the molar ratio of sodium iodide and lithium chloride 1.2:1, 8.38L of sodium iodide solution with iodine content of 800g / L was measured and slowly added to the lithium chloride solution. After stirring at room temperature for 15 minutes, the mixture was cooled to -5℃ and kept warm for 40 minutes. The white solid was filtered off, and the filtrate was further cooled to -10℃ and kept warm for 40 minutes. After filtering off the insoluble matter, it was frozen again to -15℃ to obtain lithium iodide cryo-clarified solution.

[0076] Table 6. Solution composition before and after freezing

[0077] (3) Evaporation and concentration: The above-mentioned lithium iodide frozen clear liquid is heated and evaporated. When the filtrate begins to become turbid and some crystals precipitate, evaporation continues. When the solid content reaches 70%, heating is stopped to obtain lithium iodide first-evaporation crystal slurry. After centrifugation analysis, the first-evaporation wet product is obtained. The first-evaporation wet product is then dissolved in a solid-liquid ratio of 2:1 and the filtrate is filtered through a precision filter. The evaporation and concentration operation is repeated once to obtain the second-evaporation wet product.

[0078] (4) After heating the second-distilled wet product to 73°C to dissolve it, spray-dry it at 300°C to obtain 3096 grams of qualified lithium iodide.

[0079] (5) Ball milling: The qualified lithium iodide product is ball milled in a ball mill at a speed of 300 rpm for 8 hours to obtain anhydrous lithium iodide product with a particle size of less than 25 μm.

[0080] Example 7

[0081] This embodiment provides a method for preparing anhydrous lithium iodide, including the following steps: (1) Take 3L of lithium sulfate leaching solution with a concentration of 40g / L based on Li2O (the lithium sulfate leaching solution is the lithium sulfate solution in the lithium salt production workshop, which contains a small amount of sodium, potassium, calcium, magnesium and other ion impurities). Its main components are shown in Table 7.

[0082] (2) Freezing and purification: Weigh about 1.12 L of potassium iodide solution with iodine content of 1000 g / L according to the molar ratio of potassium iodide and lithium sulfate = 2.2:1, slowly add it to the purified lithium sulfate solution, stir at room temperature for 15 minutes and then filter. Take the filtrate, cool it to -5℃, keep it warm for 40 minutes, filter off the white solid, continue to cool the filtrate to -10℃, keep it warm for 40 minutes, filter off the insoluble matter, freeze it again to -15℃, keep it warm for 40 minutes, filter off the insoluble matter, and obtain the lithium iodide cryopure solution.

[0083] Table 7. Solution composition before and after freezing

[0084] (3) Evaporation and concentration: The lithium iodide cryopreservation liquid is heated and evaporated. When the cryopreservation liquid begins to become turbid and some crystals precipitate, the Li2O concentration is ≥180g / L. Evaporation continues. When the solid content reaches 50%, heating is stopped. The liquid is cooled to room temperature under stirring to obtain lithium iodide first-evaporation crystal slurry. After centrifugation analysis, the first-evaporation wet product is obtained. The first-evaporation wet product is then dissolved in a solid-liquid ratio of 2:1 and filtered through a precision filter. The filtrate is then evaporated and concentrated again to obtain the second-evaporation wet product.

[0085] (4) After heating the second-distilled wet product to 73°C to dissolve it, spray-dry it at 300°C to obtain 915 grams of qualified lithium iodide.

[0086] (5) Ball milling: The qualified lithium iodide product is ball milled in a ball mill at a speed of 300 rpm for 8 hours to obtain anhydrous lithium iodide product with a particle size of less than 25 μm.

[0087] Example 8

[0088] This embodiment provides a method for preparing anhydrous lithium iodide, including the following steps: (1) Take 3L of lithium chloride purification solution with a concentration of 280g / L based on Li2O (the lithium chloride purification solution is the lithium chloride solution in the lithium salt production workshop, which contains a small amount of anions such as sulfate and carbonate). Its main components are shown in Table 8.

[0089] (2) Freezing and purification: According to the molar ratio of potassium iodide and lithium chloride 1.1:1, about 7.82L of potassium iodide solution with iodine content of 1000g / L was slowly added to the lithium chloride solution. After stirring at room temperature for 15 minutes, the mixture was cooled to -5℃ and kept warm for 40 minutes. The white solid was filtered off, and the filtrate was further cooled to -10℃ and kept warm for 40 minutes. After filtering off the insoluble matter, it was frozen again to -15℃ to obtain lithium iodide cryo-clarified solution.

[0090] Table 8. Solution composition before and after freezing

[0091] (3) Evaporation and concentration: The above-mentioned lithium iodide frozen clear liquid is heated and evaporated. When the filtrate begins to become turbid and some crystals precipitate, evaporation continues. When the solid content reaches 50%, heating is stopped to obtain lithium iodide first-evaporation crystal slurry. After centrifugation analysis, the first-evaporation wet product is obtained. The first-evaporation wet product is then dissolved in a solid-liquid ratio of 2:1 and filtered through a precision filter. The filtrate is then evaporated and concentrated again to obtain the second-evaporation wet product.

[0092] (4) After heating the second-distilled wet product to 73°C to dissolve it, spray-dry it at 300°C to obtain approximately 3250 grams of qualified lithium iodide.

[0093] (5) Ball milling: The qualified lithium iodide product is ball milled in a ball mill at a speed of 600 rpm for 1 hour to obtain anhydrous lithium iodide product with a particle size of less than 25 μm.

[0094] Comparative Example 1

[0095] This comparative example provides a method for preparing anhydrous lithium iodide, which is basically the same as the steps in Example 2, except that: after freezing and precipitation, the sodium ion concentration in the clear liquid is >35g / L and the sulfate ion concentration is >25g / L. The specific contents are shown in Table 9.

[0096] Table 9. Solution composition before and after freezing

[0097] Comparative Example 2

[0098] This comparative example provides a method for preparing anhydrous lithium iodide, which is basically the same as the steps in Example 4, except that: after freezing and precipitation, the sodium ion concentration in the clear liquid is >90g / L and the chloride ion concentration is >160g / L, and the specific contents are shown in Table 10.

[0099] Table 10. Solution composition before and after freezing

[0100] Comparative Example 3

[0101] This comparative example provides a method for preparing anhydrous lithium iodide, which is basically the same as the steps in Example 2, except that the heating and evaporation concentration process is stopped when the solid content reaches 45%.

[0102] The final yield was 687.5 grams of qualified lithium iodide, with a low first-pass yield.

[0103] Comparative Example 4

[0104] This comparative example provides a method for preparing anhydrous lithium iodide, which is basically the same as the steps in Example 2, except that the heating and evaporation concentration process is stopped when the solid content reaches 75%.

[0105] Comparative Example 5

[0106] This comparative example provides a method for preparing anhydrous lithium iodide, which is basically the same as the steps in Example 4, except that the heating and evaporation concentration process is stopped when the solid content reaches 45%.

[0107] The final yield was 1388 grams of qualified lithium iodide, with a low first-pass yield.

[0108] Comparative Example 6

[0109] This comparative example provides a method for preparing anhydrous lithium iodide, which is basically the same as the steps in Example 4, except that the heating and evaporation concentration process is stopped when the solid content reaches 75%.

[0110] Table 11. Test data of anhydrous lithium iodide products in Examples 1-8 and Comparative Examples 1-6

[0111] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing anhydrous lithium iodide, characterized in that, Includes the following steps: a. A lithium source and an iodine source are mixed and reacted to obtain a mixed solution. The solution is then filtered to remove impurities, yielding a filtrate. The lithium source is a lithium sulfate solution or a lithium chloride solution, and the iodine source is a sodium iodide solution or a potassium iodide solution. When the lithium source is a lithium sulfate solution, the molar ratio of sodium iodide or potassium iodide to lithium sulfate is 2.0:1-2.2:1; when the lithium source is a lithium chloride solution, the molar ratio of sodium iodide or potassium iodide to lithium chloride is 1.0:1-1.2:

1. b. The filtrate obtained in step a is subjected to freeze purification. After filtration, the liquid is a clear cryosol, and the solid is a sodium or potassium salt. The freeze purification temperature is -15℃ to 0℃, and the time is 30-60 min. When the iodine source is sodium iodide solution and the lithium source is lithium sulfate solution, the sodium ion concentration in the clear cryosol is less than or equal to 35 g / L, and the sulfate ion concentration is less than or equal to 25 g / L. When the iodine source is potassium iodide solution and the lithium source is lithium sulfate solution, the potassium ion concentration in the clear cryosol is less than or equal to 50 g / L, and the sulfate ion concentration is less than or equal to 40 g / L. When the iodine source is sodium iodide solution and the lithium source is lithium chloride solution, the sodium ion concentration in the clear cryosol is less than or equal to 90 g / L, and the chloride ion concentration is less than or equal to 160 g / L. When the iodine source is potassium iodide solution and the lithium source is lithium chloride solution, the potassium ion concentration in the clear cryosol is less than or equal to 140 g / L, and the chloride ion concentration is less than or equal to 160 g / L. c. Heat and evaporate the frozen liquid obtained in step b to concentrate it. When the solid content is 50%-70%, stop heating to obtain lithium iodide concentrated slurry. Cool the lithium iodide concentrated slurry to room temperature under stirring to obtain lithium iodide first-evapor crystal slurry. After centrifugation, obtain first-evapor wet product and primary mother liquor. d. After dissolving the first-distilled wet product obtained in step c in water, use precision filtration to filter out solid particles larger than or equal to 0.3 μm. Then repeat the heating, evaporation and concentration process in step c to obtain the second-distilled wet product and secondary mother liquor. e. The second-distilled wet product obtained in step d is heated to a self-dissolution temperature greater than or equal to 73°C, and then spray-dried at 300°C to obtain anhydrous lithium iodide.

2. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that, When the lithium source is a lithium sulfate solution, the molar ratio of sodium iodide or potassium iodide to lithium sulfate is 2:

1.

3. A method for preparing anhydrous lithium iodide according to claim 1 or 2, characterized in that, The lithium sulfate solution is a lithium sulfate solution from a lithium salt production workshop, and its preparation process includes the following steps: (1) After calcining the lithium ore at 1100-1380℃, sulfuric acid is added at a mass ratio of acid material to lithium ore of 1:4-7 to carry out acidification treatment to obtain acidification treatment solution; (2) In the acidification treatment solution, add water or recycled filtrate at a mass ratio of 2-3:1 between the added liquid and lithium ore, adjust the pH to 5.7-6.2, let stand and filter to obtain mother liquor 1; (3) Adjust the pH of mother liquor 1 to 8.5-9.7, let it stand and filter to obtain mother liquor 2; (4) Adjust the pH of mother liquor 2 to 10-10.8, let it stand, and filter to obtain mother liquor 3; (5) Detection of Ca in mother liquor 3 2+ To determine the concentration, add an equimolar amount of sodium carbonate, stir, let stand, and then filter to obtain mother liquor 4. After evaporation and concentration, obtain a lithium sulfate solution.

4. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that, When the lithium source is a lithium chloride solution, the molar ratio of sodium iodide or potassium iodide to lithium chloride is 1:

1.

5. A method for preparing anhydrous lithium iodide according to claim 1 or 4, characterized in that, The lithium chloride solution is a lithium chloride solution from a lithium salt production workshop, and its preparation process includes the following steps: ① After calcining the lithium ore at 1100-1380℃, sulfuric acid is added at a mass ratio of acid solution to lithium ore of 1:4-7 to carry out acidification treatment, and the acidification treatment solution is obtained. ② In the acidification treatment solution, add water or recovered filtrate at a mass ratio of liquid to lithium ore of 2-3:1, then adjust the pH to 5.7-6.2, let stand, filter, and obtain mother liquor 1; ③ Adjust the pH of mother liquor 1 to 8.5-9.7, let it stand, filter, and obtain mother liquor 2; ④ Adjust the pH of mother liquor 2 to 10-10.8, let it stand, filter, and obtain mother liquor 3; ⑤ Detection of Ca in mother liquor 3 2+ To determine the concentration, add an equimolar amount of sodium carbonate, stir, let stand, and then filter to obtain mother liquor 4. ⑥ Add calcium chloride to mother liquor 4 according to the molar ratio of sulfate to calcium of 1.05-1.1:1 for conversion. After conversion and filtration, evaporate and concentrate the filtrate to obtain lithium chloride solution.

6. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that, In step a, the reaction time is 15-45 min.

7. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that, In step b, the method for processing and reusing sodium or potassium salt is as follows: the sodium or potassium salt is redissolved in water at a ratio of 1:2 to 2:1, then evaporated and centrifuged. The solid is dried again to obtain the corresponding sodium or potassium salt by-product. The liquid is returned to the freezing and impurity removal process in step b and frozen and impurity removed together with the filtrate obtained in step a.

8. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that, In step c, the mother liquor is returned to the filtration process of step a and filtered together with the mixture from step a.

9. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that, In step d, during the process of dissolving the first-distilled wet product in water, the mass ratio of the first-distilled wet product to water is 2:

1.

10. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that, In step d, the secondary mother liquor is returned to the heating, evaporation and concentration process in step c, where it is heated, evaporated and concentrated together with the frozen clear liquid from step c.

11. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that, The preparation method further includes: f, pulverization and packaging: the anhydrous lithium iodide from step e is pulverized by ball milling to obtain the anhydrous lithium iodide product.

12. The method for preparing anhydrous lithium iodide according to claim 11, characterized in that, The ball mill operates at a speed of 300-600 rpm for 1-8 hours.

13. The method for preparing anhydrous lithium iodide according to claim 11, characterized in that, In step f, the anhydrous lithium iodide product has a particle size of less than or equal to 25 μm and a purity of greater than or equal to 99.9%.

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