Lithium carbonate seed crystal, method for preparing the same and use thereof

Abstract

This application discloses a lithium carbonate seed crystal, its preparation method, and its uses, relating to the field of lithium carbonate preparation technology. The method for preparing the lithium carbonate seed crystal includes: preparing a lithium salt solution containing a dispersant; mixing the lithium salt solution containing the dispersant with a carbonate solution, and performing a pressure reaction at 180℃~220℃ and 0.8 MPa~2.2 MPa to obtain lithium carbonate microcrystals; subjecting the pressure-reacting system to gradient depressurization and aging to allow the lithium carbonate microcrystals to grow into lithium carbonate seed crystals; and filtering, washing, and drying the aged system to obtain the lithium carbonate seed crystals. The preparation method proposed in this application, through pressure reaction under specific high-temperature and high-pressure conditions, utilizing a dispersant and subsequent gradient depressurization and aging steps, prepares high-purity lithium carbonate seed crystals.

Description

Technical Field

[0001] This application relates to the field of lithium carbonate preparation technology, and in particular to a lithium carbonate seed crystal, its preparation method and uses. Background Technology

[0002] In the production process of lithium carbonate, seed crystals are often used to guide and control the crystallization process to obtain high-quality lithium carbonate products. Currently, a common method is to return some of the screen residue and recycled material from the production process to the lithium deposition system as seed crystals. However, using such recycled material as seed crystals has significant drawbacks: its particle size distribution is uneven, making it easy for fine powder to induce secondary nucleation during crystallization, affecting the stability of the product's particle size distribution; at the same time, the recycled material usually contains high levels of impurities such as sodium, potassium, and sulfate, which can enter the final product and affect the purity of lithium carbonate. Especially in high-purity applications such as battery-grade lithium carbonate, such seed crystals are difficult to meet the requirements.

[0003] Therefore, there is an urgent need to develop a method for preparing lithium carbonate seeds with high purity, controllable particle size, and good stability. Summary of the Invention

[0004] The main purpose of this application is to propose a lithium carbonate seed crystal, its preparation method and application, which aims to solve or at least partially alleviate the problems of low purity, uneven particle size and poor stability of lithium carbonate products caused by the use of recycled materials as seed crystals in the prior art.

[0005] To achieve the above objectives, in a first aspect, this application proposes a method for preparing lithium carbonate seed crystals, comprising the following steps: Step S1: Prepare a lithium salt solution containing a dispersant; Step S2: The lithium salt solution containing the dispersant is mixed with the carbonate solution and subjected to a steam pressure reaction at 180℃~220℃ and 0.8 MPa~2.2 MPa to obtain lithium carbonate microcrystals; Step S3: The system after the steam pressure reaction is subjected to gradient depressurization and aged to allow the lithium carbonate microcrystals to grow into lithium carbonate seed crystals. Step S4: The aged system is filtered, washed, and dried to obtain the lithium carbonate seed crystals.

[0006] In some embodiments, in step S1, the concentration of lithium ions in the lithium salt solution is 15 g / L to 35 g / L; and / or The lithium salt solution includes at least one of lithium sulfate solution and lithium-containing brine solution.

[0007] In some embodiments, in step S1, the dispersant includes at least one of ethylenediaminetetraacetic acid and polyethylene glycol; and / or The amount of dispersant added is 0.1 g / L to 0.5 g / L.

[0008] In some embodiments, step S1 further includes the following step before preparing the lithium salt solution containing the dispersant: Sodium hydroxide was added to the lithium salt solution to adjust the pH to 12-13. After clarification and filtration, sodium carbonate was added to remove calcium, and then the solution was filtered again. Wherein, the molar ratio of calcium ions to carbonate ions in the solution after the addition of sodium carbonate is (0.8~0.9):1.

[0009] In some embodiments, in step S2, the carbonate solution includes at least one of sodium carbonate solution and potassium carbonate solution; and / or The concentration of carbonate ions in the carbonate is 1 mol / L to 3 mol / L.

[0010] In some embodiments, in step S2, after mixing the lithium salt solution containing the dispersant with the carbonate solution, the molar ratio of lithium ions to carbonate ions in the solution is 1:(1.05~1.2).

[0011] In some embodiments, in step S2, the lithium salt solution is placed in a high-pressure reactor, and a carbonate solution is pumped into the high-pressure reactor. The pumping time is 1.5 h to 2 h, and the amount of carbonate pumped per minute is 0.8% to 1.2% of the total volume of the carbonate solution.

[0012] In some embodiments, in step S2, the autoclaving reaction process is subjected to stirring at a speed of 200 r / min to 400 r / min; and / or The autoclaving reaction time is 30 min to 90 min.

[0013] In some embodiments, step S3, the gradient depressurization includes: reducing the pressure to 0.5 MPa to 1 MPa over 20 to 40 minutes, and then reducing the pressure to 0.1 MPa to 0.3 MPa over 30 to 60 minutes.

[0014] In some embodiments, in step S3, the aging temperature is 140°C to 200°C, and the time is 60 min to 100 min; and / or The stirring speed during aging is 150 r / min to 300 r / min.

[0015] In some embodiments, in step S4, the filtration is hot filtration, with an outlet temperature of 60°C to 80°C; and / or The washing process involves washing 2-3 times with deionized water at 60℃~90℃ until the sum of chloride and sulfate ion concentrations in the wash water is less than 50 ppm; and / or The drying process involves vacuum drying at 150℃~200℃ for 2 h~5 h.

[0016] Secondly, this application also proposes a lithium carbonate seed crystal, which is prepared by the preparation method proposed in the first aspect of this application.

[0017] In some embodiments, the lithium carbonate seed crystals satisfy at least one of the following conditions: D50 ranges from 3 μm to 8 μm; SPAN less than 1.15; The purity of Li2CO3 is not less than 99.95%; The combined content of calcium and magnesium ions is less than 10 ppm; The combined sodium and potassium ion content is less than 50 ppm.

[0018] Thirdly, this application also proposes the use of the lithium carbonate seed crystals proposed in the second aspect of this application in the lithium carbonate crystallization precipitation process.

[0019] In some embodiments, the lithium carbonate crystallization precipitation process is a continuous evaporation crystallization process; The lithium carbonate seed crystals are returned to the continuous evaporation crystallization process for recycling as crystallization seed crystals.

[0020] The method for preparing lithium carbonate seeds proposed in this application involves a steam-pressure reaction under specific high-temperature and high-pressure conditions (180℃~220℃, 0.8MPa~2.2 MPa) to create a stable supersaturated environment. This promotes uniform nucleation of lithium carbonate, forming microcrystals and avoiding the problems of rapid, irregular nucleation and excessive fine powder caused by excessively high local concentrations under normal pressure or instantaneous reactions. This fundamentally solves the defects of traditional recycled seed crystals, such as uneven particle size and easy secondary nucleation. Simultaneously, the addition of a dispersant effectively inhibits abnormal aggregation of crystal nuclei and the adsorption or entry of impurity ions into the crystal lattice on the crystal surface, thus improving the purity of the product. Furthermore, in the gradient depressurization and aging steps, the supersaturation of the system is slowly released, providing mild growth conditions for the microcrystals, enabling them to grow directionally and stably. This further reduces internal stress and defects in the crystals, improving the sphericity, dispersibility, and crystal integrity of the seeds. Finally, filtration, washing, and drying effectively remove impurity ions adsorbed and encapsulated on the crystal surface, significantly improving the purity of the lithium carbonate seeds.

[0021] Therefore, the lithium carbonate seed crystals prepared by this method have uniform particle size distribution (D50 of 3 μm to 8 μm, SPAN less than 1.15), high purity (Li2CO3 purity not less than 99.95%, extremely low impurity ion content), and good crystal quality (quasi-spherical, well-dispersed, and with complete crystal form). This overcomes the drawbacks of using traditional recycled materials as seed crystals, and can improve the product quality and process stability of subsequent lithium carbonate crystallization precipitation processes. It is especially suitable for continuous evaporation crystallization processes and can realize the recycling of seed crystals. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the content shown in these drawings without creative effort.

[0023] Figure 1 A schematic flowchart illustrating the method for preparing lithium carbonate seed crystals provided in this application; Figure 2 A physical image of the seed crystals prepared in Example 1 of this application; Figure 3 A magnified micrograph of the seed crystals prepared in Example 1 of this application.

[0024] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0026] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0027] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution that simultaneously satisfies A and B. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0028] Currently, some of the screen residue and recycled material are returned to the lithium precipitation system to assist in crystallization during the lithium carbonate production process. However, the particle size of the seed crystals is unstable, and fine powder can easily lead to secondary nucleation. In addition, the recycled material has high impurities, containing high levels of sodium, potassium, and sulfate ions, which affects the quality of the produced lithium carbonate.

[0029] Based on the above issues, please refer to Figure 1 In a first aspect, embodiments of this application propose a method for preparing lithium carbonate seed crystals, comprising the following steps: S1. Prepare a lithium salt solution containing a dispersant; S2. A lithium salt solution containing a dispersant is mixed with a carbonate solution and subjected to a steam pressure reaction at 180℃~220℃ and 0.8 MPa~2.2 MPa to obtain lithium carbonate microcrystals. S3. The system after the autoclaving reaction is subjected to gradient depressurization and aging to allow lithium carbonate microcrystals to grow into lithium carbonate seed crystals. S4. The aged system is filtered, washed, and dried to obtain lithium carbonate seed crystals.

[0030] By performing a steam-pressure reaction under specific high-temperature and high-pressure conditions (180℃~220℃, 0.8 MPa~2.2 MPa) in S2, a stable supersaturated environment is constructed, promoting uniform nucleation of lithium carbonate and forming microcrystals. This avoids the problems of rapid, irregular nucleation and excessive fine powder caused by excessively high local concentrations under normal pressure or instantaneous reactions. This fundamentally solves the defects of traditional recycled seed crystals, such as uneven particle size and easy secondary nucleation. At the same time, the addition of dispersants effectively inhibits the abnormal aggregation of crystal nuclei and the adsorption of impurity ions on the crystal surface or into the crystal lattice, thereby improving the purity of the product. Furthermore, in S3, through gradient depressurization and aging steps, the supersaturation of the system is slowly released, providing mild growth conditions for microcrystals, enabling them to grow in a directional and stable manner. This further reduces internal stress and defects in the crystals, improving the sphericity, dispersibility, and crystal integrity of the seed crystals. Finally, in S4, filtration, washing, and drying effectively remove impurity ions adsorbed and encapsulated on the crystal surface, significantly improving the purity of the lithium carbonate seed crystals.

[0031] In some embodiments, in step S1, the lithium salt solution includes at least one of lithium sulfate solution and lithium-containing brine solution. The concentration of lithium ions in the lithium salt solution is 15 g / L to 35 g / L.

[0032] Lithium sulfate solutions are typically obtained from lithium extraction from ores such as spodumene, and their composition is relatively simple and controllable. Lithium-containing brines (such as salt lake brines or the liquid after lithium extraction from lepidolite) have complex compositions, often containing various impurity ions such as sodium, potassium, calcium, and magnesium, which can easily enter subsequent systems. Therefore, in some embodiments, step S1, before preparing the lithium salt solution containing the dispersant, includes the following step: S11. Add sodium hydroxide to the lithium salt solution to adjust the pH to 12-13. After clarification and coarse filtration using a plate and frame filter press, add sodium carbonate to remove calcium, and then filter through a cartridge-type precision filter. The molar ratio of calcium ions to carbonate ions in the solution after adding sodium carbonate is (0.8-0.9):1.

[0033] In some preferred embodiments, the concentration of lithium ions in the lithium salt solution is 25~35 g / L.

[0034] Under strongly alkaline conditions (pH 12-13), divalent and trivalent metal ions such as magnesium, iron, and manganese in the solution form insoluble hydroxide precipitates, which can be effectively separated by clarification and filtration. This step preferentially removes most non-lithium metal ions, preventing them from competing with subsequently added sodium carbonate for precipitation. Specifically, the added sodium carbonate reacts with calcium ions to form calcium carbonate precipitate. The amount of carbonate ions is controlled to slightly exceed the stoichiometric level of calcium ions (molar ratio 0.8-0.9:1) to remove calcium ions by precipitation, reducing the calcium content in the solution to 0.015 g / L.

[0035] In some embodiments, in step S1, the dispersant includes at least one of ethylenediaminetetraacetic acid and polyethylene glycol; the amount of dispersant added is 0.1 g / L to 0.5 g / L.

[0036] Ethylenediaminetetraacetic acid (EDTA) can selectively form stable, soluble chelates with trace amounts of divalent or polyvalent metal ions (such as calcium and magnesium) in solution, preventing impurity ions from adsorbing onto lattice sites during lithium carbonate crystal growth. Simultaneously, EDTA molecules can coat the crystal nucleus surface, providing steric hindrance. Polyethylene glycol (PEG), a nonionic polymeric surfactant, has long-chain molecules that adsorb onto the surface of crystal particles to form a hydration film, preventing particle aggregation and agglomeration through steric repulsion. Both ensure the monodispersity of the microcrystals formed during the autoclaving reaction, resulting in a narrow particle size distribution (low SPAN value) in the final lithium carbonate seed crystals.

[0037] In some preferred embodiments, EDTA is selected as the dispersant, and the addition amount is 0.2 g / L to 0.5 g / L.

[0038] In some embodiments, in step S2, the carbonate solution includes at least one of sodium carbonate solution and potassium carbonate solution; the concentration of carbonate ions in the carbonate is 1 mol / L to 3 mol / L.

[0039] Sodium carbonate is the most commonly used precipitant, reacting directly to produce lithium carbonate and sodium sulfate, resulting in a simple system. Controlling the carbonate ion concentration in the carbonate solution between 1 mol / L and 3 mol / L balances production efficiency and reaction process controllability. If the carbonate ion concentration is below 1 mol / L, the solution volume is too large, leading to insufficient supersaturation, weak nucleation driving force, and affecting product yield and particle size uniformity. If the carbonate ion concentration is above 3 mol / L, localized supersaturation is likely to occur upon addition, inducing explosive nucleation and producing a large number of uncontrollable fine crystallites, resulting in a widened particle size distribution (increased SPAN value) and particle agglomeration.

[0040] In some preferred embodiments, sodium carbonate is used as the carbonate.

[0041] In some embodiments, in step S2, after mixing the lithium salt solution containing the dispersant with the carbonate solution, the molar ratio of lithium ions to carbonate ions in the solution is 1:(1.05~1.2), and a slight excess of carbonate ions can make the lithium react more fully.

[0042] In some embodiments, in step S2, the lithium salt solution is placed in a high-pressure reactor, and a carbonate solution is pumped into the high-pressure reactor; the pumping time is 1.5 h to 2 h, and the amount of carbonate pumped in per minute is 0.8% to 1.2% of the total volume of carbonate.

[0043] The use of pumping instead of a single pouring method allows the precipitant to be dispersed in time and space, enabling its slow and uniform introduction into the vigorously stirred lithium salt solution. This maintains the supersaturation of the entire system within a metastable region suitable for controlled nucleation and growth. Furthermore, by precisely controlling the pumping rate and time, the system pH is stabilized, avoiding localized supersaturation and ensuring uniform nucleation during the autoclaving reaction.

[0044] To ensure uniform mass and heat transfer within the reactor and avoid localized concentration and temperature gradients, in some embodiments, the autoclaving process in step S2 is stirred at a speed of 200 r / min to 400 r / min; the autoclaving time is 30 min to 90 min. Stirring at this speed effectively disperses the pumped carbonate solution, maintaining uniform temperature and ion concentration throughout the reactor. In some preferred embodiments, the autoclaving time is 45 min to 75 min.

[0045] In some implementations, step S3, gradient depressurization includes: reducing the pressure to 0.5 MPa to 1 MPa over 20 to 40 minutes, and then reducing the pressure to 0.1 MPa to 0.3 MPa over 30 to 60 minutes.

[0046] The first stage of depressurization (reducing to 0.5 MPa~1 MPa) involves the gradual release of some supersaturation under higher pressure, providing the main material source for microcrystal growth. At this stage, the temperature is high, and the crystal growth rate is rapid. If this stage lasts less than 20 minutes, the supersaturation release is too rapid, potentially triggering secondary nucleation; if it lasts longer than 40 minutes, production efficiency decreases. The second stage of depressurization (reducing to 0.1 MPa~0.3 MPa) further releases residual supersaturation under lower pressure, refining the crystal faces and repairing the sphericity of the microcrystals, while also promoting the release of internal stress. If this stage lasts less than 30 minutes, crystal defects may not be adequately repaired; if it lasts longer than 60 minutes, it is unnecessary. This phased, gentle depressurization, replacing direct, rapid depressurization, effectively avoids crystal breakage or internal crack formation due to sudden environmental changes, and is key to obtaining high sphericity, low stress, and narrow-distribution seed crystals.

[0047] In some embodiments, in step S3, the aging temperature is 140℃~200℃, the time is 60 min~100 min, and the stirring speed during aging is 150 r / min~300 r / min.

[0048] By controlling the aging temperature at 140℃~200℃, stable crystal growth can be achieved within 60 min~100 min. In addition, stirring at 150 r / min~300 r / min maintains good suspension of crystal particles in the solution, prevents sedimentation and agglomeration, and ensures that each crystal grain is in full contact with the supersaturated solution layer to achieve uniform growth.

[0049] After aging, the crystals need to be quickly separated from the high-temperature mother liquor to terminate the growth process and prevent impurities from precipitating on the crystal surface during cooling. In some embodiments, in step S4, filtration is performed while the crystals are still hot, with an outlet temperature of 60°C to 80°C. The filter cake obtained after filtration still retains a high concentration of impurity ions from the mother liquor; therefore, it is washed 2-3 times with deionized water at 60°C to 90°C until the sum of chloride and sulfate ions in the wash water is less than 50 ppm, ensuring that soluble impurity ions adsorbed on the seed crystal surface and trapped in the interstitial spaces are thoroughly removed. After washing, drying is performed under vacuum at 150°C to 200°C for 2-5 hours.

[0050] This application also provides a lithium carbonate seed crystal, prepared by the method described above. Specifically, in some embodiments, the lithium carbonate seed crystal satisfies at least one of the following conditions: D50 ranges from 3 μm to 8 μm; SPAN less than 1.15; The purity of Li2CO3 is not less than 99.95%; The combined content of calcium and magnesium ions is less than 10 ppm; The combined sodium and potassium ion content is less than 50 ppm.

[0051] The term "D50" refers to the particle size at which the cumulative particle size distribution percentage of a sample reaches 50%. Physically, it means that 50% of the particles are larger than D50, and 50% are smaller. D50 is often used to represent the average particle size of powders. "SPAN" is a measure of particle size distribution width, calculated as SPAN = (D90 - D10) / D50, where D90 and D10 represent the particle sizes at which the cumulative particle size distribution percentage reaches 90% and 10%, respectively. A smaller SPAN value indicates a narrower particle size distribution and more uniform particle size.

[0052] This application also proposes a use of the lithium carbonate seed crystals described above in a lithium carbonate crystallization precipitation process. In some embodiments, the lithium carbonate crystallization precipitation process is a continuous evaporation crystallization process. The lithium carbonate seed crystals are recycled back into the continuous evaporation crystallization process as crystallization seed crystals.

[0053] In continuous evaporation crystallization processes, stable seed crystal circulation is crucial for maintaining steady-state system operation. This particular seed crystal features uniform particle size, high sphericity, good mechanical strength, and extremely high purity. It maintains its shape without breakage during system circulation, shearing, and pumping, preventing the generation of fine powder that induces secondary nucleation, thus ensuring long-term stability in the number and particle size distribution of seed crystals within the system. Simultaneously, its ultra-high purity ensures that impurities such as sodium and potassium do not accumulate in the system during long-term circulation, guaranteeing the consistent quality of the entire continuous evaporation crystallization process product (battery-grade lithium carbonate) and enabling the recycling of high-value seed crystals.

[0054] The following specific examples provide further details.

[0055] Example 1 (1) Prepare an industrial grade lithium sulfate (Li2SO4, purity >95%) solution with a lithium ion concentration of 20 g / L, add 0.3 g / L of dispersant ethylenediaminetetraacetic acid (EDTA), stir to dissolve, and obtain a lithium salt solution containing dispersant.

[0056] (2) Transfer the above solution into a high-pressure reactor, seal and stir and heat to 200°C, with the pressure inside the reactor corresponding to 1.50 MPa and the stirring speed set to 300 r / min.

[0057] (3) Slowly pump a sodium carbonate (Na2CO3) solution with a concentration of 2.0 mol / L into the reactor for 1.67 hours (about 100 min). Control the total molar ratio of lithium ions to carbonate ions in the reactor after feeding to be 1:1.1. Continue to steam and pressurize the reaction under stirring at 300 r / min for 60 min to obtain lithium carbonate microcrystalline slurry.

[0058] (4) Gradual depressurization and aging: In the first stage, the pressure was reduced from 1.5 MPa to 1.0 MPa in about 30 min, while the temperature was slowly reduced to 160℃; in the second stage, the pressure was reduced from 1.0 MPa to 0.2 MPa in about 45 min, while the temperature was slowly reduced to 170℃. The stirring speed was maintained at 200 r / min throughout the process, and the total aging time was 75 min.

[0059] (5) Cool the system to 70°C, filter while hot, and wash the filter cake twice with deionized water at 80°C. Detect the sum of chloride and sulfate ions in the last wash water as 25 ppm, and stop washing. Place the filter cake in a vacuum drying oven at 200°C and dry for 3 h to obtain the final product, lithium carbonate seed crystals.

[0060] After testing, such as Figure 2 and Figure 3As shown, the seed crystals obtained in this embodiment have a D50 of 5.6 μm, a SPAN of 1.10, a lithium carbonate purity of 99.97%, a combined calcium and magnesium ion content of 7 ppm, a sodium ion content of 22 ppm, a potassium ion content of 8 ppm, and a yield of 82%. The product is spherical, has good dispersibility, and exhibits no agglomeration.

[0061] Example 2 The difference between this embodiment and Embodiment 1 is that the lithium ion concentration of the lithium salt solution in step (1) is 25 g / L, while all other conditions are the same.

[0062] Testing showed that the purity of the seed crystals obtained in this embodiment was 99.96%, the yield was 88%, the product was spherical, had good dispersibility, and no agglomeration.

[0063] Example 3 The difference between this embodiment and embodiment 1 is that (1) uses lithium-containing brine as the lithium source and adds a raw material liquid purification pretreatment step. The specific operation and parameters are as follows: (1) Take the lithium-containing brine solution after lithium extraction from lepidolite. Its composition is as follows: Li + 15.32 g / L, Na + 20.24 g / L, K + 30.24 g / L, Ca² + 0.21 g / L, Mg² + 0.01 g / L, Mn² + 0.12 g / L. Add sodium hydroxide to adjust the pH to 12.5, and then perform coarse filtration using a plate and frame filter press (filter cloth pore size 8 μm) to remove hydroxide precipitates.

[0064] (2) Sodium carbonate was added to the filtrate at a molar ratio of calcium ions to carbonate ions of 0.85:1. After stirring and reacting, the solution was filtered through a precision filter with a filter element pore size of 0.5 μm to obtain a purified lithium salt solution. The composition of the solution was determined to be: Li + 15.02 g / L, Na + 30.17 g / L, K + 28.93 g / L, Ca² + <0.01 g / L, Mg² + <0.001g / L, Mn² + <0.001 g / L.

[0065] (3) Add 0.3 g / L of dispersant polyethylene glycol (PEG) to the purification solution and stir to dissolve.

[0066] (4) Transfer the solution to a high-pressure reactor, heat it to 210°C, pressurize it to 2.1 MPa, stir it at 400 r / min, and perform the remaining operations as in Example 1. The reaction time is 90 min.

[0067] (5) Gradual depressurization and aging: In the first stage, the pressure was reduced from 2.1 MPa to 1.0 MPa in about 30 min, while the temperature was slowly reduced to 160℃; in the second stage, the pressure was reduced from 1.0 MPa to 0.2 MPa in about 45 min, while the temperature was slowly reduced to 130℃. The stirring speed was maintained at 200 r / min throughout the process, and the total aging time was 75 min.

[0068] (6) Cool the system to 70°C, filter while hot, and wash the filter cake twice with deionized water at 80°C. Detect the sum of chloride and sulfate ions in the last wash water as 25 ppm, and stop washing. Place the filter cake in a vacuum drying oven at 200°C and dry for 3 h to obtain the final product, lithium carbonate seed crystals.

[0069] Testing revealed that the seed crystals obtained in this embodiment had a D50 of 6.0 μm, a SPAN of 1.12, a lithium carbonate purity of 99.96%, a combined calcium and magnesium ion content of 9 ppm, a sodium ion content of 29 ppm, and a potassium ion content of 20 ppm. The product exhibited a near-spherical shape, good dispersibility, and no agglomeration.

[0070] Example 4 The difference between this embodiment and embodiment 3 is that the autoclaving reaction temperature in step (4) is adjusted to 220°C, while the other conditions are the same as in embodiment 3.

[0071] Testing showed that the purity of the seed crystals obtained in this embodiment was 99.96%, the product was spherical, had good dispersibility, and had very little agglomeration.

[0072] Example 5 The difference between this embodiment and embodiment 1 is that the autoclaving reaction pressure in steps (2) and (3) is adjusted to 0.8 MPa (the corresponding temperature is about 170°C), while the other conditions are the same as in embodiment 1.

[0073] Testing showed that the purity of the seed crystals obtained in this embodiment was 99.96%, the product was spherical, had good dispersibility, and had very little agglomeration.

[0074] Example 6 The difference between this embodiment and Example 1 is that the dispersant is 0.1 g / L EDTA, while all other conditions are the same as in Example 1.

[0075] Testing showed that the purity of the seed crystals obtained in this embodiment was 99.96%, the product was spherical, had good dispersibility, and had a very small amount of agglomeration.

[0076] Example 7 The difference between this embodiment and Example 1 is that the dispersant is 0.5 g / L EDTA, while all other conditions are the same as in Example 1.

[0077] Testing showed that the purity of the seed crystals obtained in this embodiment was 99.96%, the product was spherical, had good dispersibility, and no agglomeration.

[0078] Example 8 The difference between this embodiment and embodiment 1 is that in step (2), a sodium carbonate (Na2CO3) solution with a concentration of 1 mol / L is slowly pumped into the reactor, while other conditions are the same as in embodiment 1.

[0079] Testing showed that the purity of the seed crystals obtained in this embodiment was 99.97%, the product was spherical, had good dispersibility, and no agglomeration.

[0080] Example 9 The difference between this embodiment and embodiment 1 is that in step (2), a sodium carbonate (Na2CO3) solution with a concentration of 3 mol / L is slowly pumped into the reactor, while the other conditions are the same as in embodiment 1.

[0081] Testing showed that the purity of the seed crystals obtained in this embodiment was 99.96%, the product was spherical, had good dispersibility, and no agglomeration.

[0082] Example 10 The difference between this embodiment and Embodiment 1 is that the total aging time is 60 minutes, while all other conditions are the same as in Embodiment 1.

[0083] Testing showed that the purity of the seed crystals obtained in this embodiment was 99.96%, the product was spherical, had good dispersibility, and no agglomeration.

[0084] Example 11 The difference between this embodiment and Embodiment 1 is that the total aging time is 100 min, while all other conditions are the same as in Embodiment 1.

[0085] Testing showed that the purity of the seed crystals obtained in this embodiment was 99.96%, the product was spherical, had good dispersibility, and no agglomeration.

[0086] Comparative Example 1 The difference between this comparative example and Example 1 is that the reaction and crystallization are carried out under normal pressure instead of steam pressure. Specifically: (1) Prepare a lithium salt solution containing the same dispersant as in Example 1; (2) In an atmospheric pressure reactor, heat the solution to 90°C, pump in sodium carbonate solution with stirring, and react at atmospheric pressure for 60 min; (3) After the reaction, without gradient depressurization and aging, directly cool, filter, wash and dry.

[0087] The results showed that the obtained product had a large particle size, with a D50 of 12.3 μm and a SPAN as high as 1.62, indicating severe particle agglomeration. Furthermore, the lithium carbonate purity was only 98.7%, far inferior to that of Example 1. This demonstrates that the autoclaving conditions of this application are crucial for obtaining seed crystals with uniform particle size, high purity, and good dispersibility.

[0088] Comparative Example 2 The difference between this comparative example and Example 1 is that step (4) does not involve gradient depressurization and aging, but instead, after the steam pressure reaction is completed, the depressurization valve is opened directly and quickly to reduce the pressure to atmospheric pressure, followed by cooling, filtration, washing, and drying.

[0089] The results showed that the obtained product had extremely uneven particle size, distributed over a wide range of 2–15 μm, with severe crystal breakage and poor sphericity. This indicates that gradient decompression and aging play a decisive role in protecting the crystal structure and achieving particle size uniformity.

[0090] Comparative Example 3 The difference between this comparative example and Example 1 is that the lithium ion concentration of the lithium salt solution in step (1) is 10.23 g / L, while all other conditions are the same.

[0091] The results showed that the product yield of this comparative example was only 72%, while the yield of Example 1 was 82% and the yield of Example 2 (lithium ion concentration 25 g / L) was 88%. This indicates that when the lithium ion concentration is below 15 g / L, the number of nuclei is insufficient, resulting in a significant decrease in yield.

[0092] Comparative Example 4 The difference between this comparative example and Example 1 is that the lithium ion concentration of the lithium salt solution in step (1) is 38.80 g / L.

[0093] The results showed that after the reaction, a large number of flaky crystals appeared on the inner wall of the autoclave, and there were obvious hard lumps in the product. Testing revealed that the sulfate impurity content in the crystals exceeded 2%, severely affecting the product purity. This indicates that a lithium ion concentration higher than 35 g / L induces abnormal crystal morphology and increases impurity encapsulation.

[0094] Comparative Example 5 The difference between this comparative example and Example 3 is that the autoclaving reaction temperature in step (4) is adjusted to 135°C, while the other conditions are the same as in Example 3.

[0095] The results showed that the product contained a large number of coarse particles with a D50 significantly greater than 15 μm and uneven particle size distribution. This indicates that when the temperature is below 150℃, the balance between nucleation and growth rates is disrupted, tending to form a small number of coarse crystals that do not meet the particle size requirements for seed crystals.

[0096] Comparative Example 6 The difference between this comparative example and Example 1 is that the autoclaving reaction temperature in steps (2) and (3) is adjusted to 250°C, while all other conditions are the same.

[0097] The results showed that a large amount of flocculent material appeared in the autoclave during the reaction, seriously affecting normal production. This indicates that when the temperature exceeds 220℃, the reaction environment of the system changes adversely, making it impossible to obtain qualified lithium carbonate seed crystals.

[0098] Comparative Example 7 The difference between this comparative example and Example 1 is that the autoclaving reaction pressure in steps (2) and (3) is adjusted to 0.6 MPa (the corresponding temperature is about 160°C), while all other conditions are the same.

[0099] The results showed that the obtained product crystals were severely broken and had poor sphericity. This indicates that when the pressure is below 0.8 MPa, the vapor environment is insufficient to construct a stable supersaturated system, the crystal growth process is disturbed, and the product quality is significantly reduced.

[0100] The above description is merely an exemplary embodiment of this application and does not limit the patent scope of this application. Any equivalent transformations made based on the technical concept of this application and the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for preparing lithium carbonate seed crystals, characterized in that, Includes the following steps: Step S1: Prepare a lithium salt solution containing a dispersant; Step S2: The lithium salt solution containing the dispersant is mixed with the carbonate solution and subjected to a steam pressure reaction at 180℃~220℃ and 0.8 MPa~2.2 MPa to obtain lithium carbonate microcrystals; Step S3: The system after the steam pressure reaction is subjected to gradient depressurization and aged to allow the lithium carbonate microcrystals to grow into lithium carbonate seed crystals. Step S4: The aged system is filtered, washed, and dried to obtain the lithium carbonate seed crystals.

2. The preparation method according to claim 1, characterized in that, In step S1, the concentration of lithium ions in the lithium salt solution is 15 g / L to 35 g / L; and / or The lithium salt solution includes at least one of lithium sulfate solution and lithium-containing brine solution.

3. The preparation method according to claim 1, characterized in that, In step S1, the dispersant includes at least one of ethylenediaminetetraacetic acid and polyethylene glycol; and / or The amount of dispersant added is 0.1 g / L to 0.5 g / L.

4. The preparation method according to claim 1, characterized in that, In step S1, before preparing the lithium salt solution containing the dispersant, the following step is also included: Sodium hydroxide was added to the lithium salt solution to adjust the pH to 12-13. After clarification and filtration, sodium carbonate was added to remove calcium, and then the solution was filtered again. Wherein, the molar ratio of calcium ions to carbonate ions in the solution after the addition of sodium carbonate is (0.8~0.9):

1.

5. The preparation method according to claim 1, characterized in that, In step S2, the carbonate solution includes at least one of sodium carbonate solution and potassium carbonate solution; and / or The concentration of carbonate ions in the carbonate is 1 mol / L to 3 mol / L.

6. The preparation method according to claim 5, characterized in that, In step S2, after mixing the lithium salt solution containing the dispersant with the carbonate solution, the molar ratio of lithium ions to carbonate ions in the solution is 1:(1.05~1.2).

7. The preparation method according to claim 6, characterized in that, In step S2, the lithium salt solution is placed in a high-pressure reactor, and a carbonate solution is pumped into the high-pressure reactor. The pumping time is 1.5 h to 2 h, and the amount of carbonate pumped per minute is 0.8% to 1.2% of the total volume of the carbonate solution.

8. The preparation method according to claim 1, characterized in that, In step S2, the autoclaving reaction process is subjected to stirring at a speed of 200 r / min to 400 r / min; and / or The autoclaving reaction time is 30 min to 90 min.

9. The preparation method according to claim 1, characterized in that, In step S3, the gradient depressurization includes: reducing the pressure to 0.5 MPa to 1 MPa over 20 to 40 minutes, and then reducing the pressure to 0.1 MPa to 0.3 MPa over 30 to 60 minutes.

10. The preparation method according to claim 1, characterized in that, In step S3, the aging temperature is 140℃~200℃, and the time is 60 min~100 min; and / or The stirring speed during aging is 150 r / min to 300 r / min.

11. The preparation method according to claim 1, characterized in that, In step S4, the filtration is hot filtration, with an outlet temperature of 60℃~80℃; and / or The washing process involves washing 2-3 times with deionized water at 60℃~90℃ until the sum of chloride and sulfate ion concentrations in the wash water is less than 50 ppm; and / or The drying process involves vacuum drying at 150℃~200℃ for 2 h~5 h.

12. A lithium carbonate seed crystal, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 11.

13. The lithium carbonate seed crystals as described in claim 12, characterized in that, The lithium carbonate seed crystals satisfy at least one of the following conditions: D50 ranges from 3 μm to 8 μm; SPAN less than 1.15; The purity of Li2CO3 is not less than 99.95%; The combined content of calcium and magnesium ions is less than 10 ppm; The combined sodium and potassium ion content is less than 50 ppm.

14. The use of the lithium carbonate seed crystal as described in claim 12 or 13 in the lithium carbonate crystallization precipitation process.

15. The use as described in claim 14, characterized in that, The lithium carbonate crystallization precipitation process is a continuous evaporation crystallization process. The lithium carbonate seed crystals are returned to the continuous evaporation crystallization process for recycling as crystallization seed crystals.

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