Method for sieving lithium carbonate powder

Abstract

This invention discloses a method for sieving lithium carbonate powder, belonging to the field of lithium carbonate powder processing technology. The method includes: mixing lithium carbonate raw material powder with fumed nano-silica at a mass ratio of 100:0.5-2.0 in an inert gas atmosphere, reacting with hexamethyldisilazane vapor at 70-120°C; stopping the hexamethyldisilazane supply, purging with high-purity nitrogen to obtain hydrophobic passivated powder; sieving with a gradient pressure pulsed airflow to obtain undersize powder; placing the undersize powder in a sodium carbonate aqueous solution, treating at 60-80°C for 15-30 minutes, filtering, and then washing with 4-5 stages of countercurrent flow and vacuum drying to obtain lithium carbonate powder. This method, through endpoint control of ammonia gas produced by silanization, temporary coating sieving, and multi-stage decoating washing, improves anti-agglomeration, moisture resistance, and flowability while reducing lithium loss, silicon residue, and sodium residue.

Description

Technical Field

[0001] This invention belongs to the field of lithium carbonate powder processing technology, and specifically relates to a method for sieving lithium carbonate powder. Background Technology

[0002] Lithium carbonate is a key raw material for the cathode material and electrolyte of lithium-ion batteries. Battery-grade lithium carbonate has strict requirements for particle size distribution, with a typical indicator being D. 50 3-8μm, D 90 ≤15μm, D max ≤45μm. Excessively wide or uneven particle size distribution will directly affect the compaction density, electrochemical uniformity, and battery cycle life of the cathode material.

[0003] Currently, the main methods for screening lithium carbonate powder are mechanical vibration screening and air classification, but the following prominent problems are encountered in actual production: (1) Severe electrostatic agglomeration. During the processing and transportation of lithium carbonate powder, the electrostatic attraction between particles is much greater than the gravity due to frictional charging, forming strong agglomerates. The agglomerates cannot be effectively dispersed on the screen surface, causing screen hole blockage and low screening efficiency.

[0004] (2) Surface deterioration due to moisture absorption. Although lithium carbonate itself is not hygroscopic, industrial lithium carbonate powder may contain trace amounts of alkaline impurities such as LiOH introduced during the manufacturing process. After absorbing moisture, these impurities form a water film and liquid bridging forces on the surface, which exacerbates particle agglomeration. When water and CO2 are present at the same time, Li2CO3 may also be converted into LiHCO3, which has higher solubility.

[0005] (3) Lack of endpoint control for ammonia byproduct of silanization. When hexamethyldisilazane reacts with the silanol groups on the surface of silica, it can release NH3. The accumulation of NH3 and ammonia-containing condensate in the closed reactor will change the pH and ionic composition of the powder interface. When residual moisture and trace amounts of CO2 are present, ammonium salts may also be formed, increasing the fluctuation of the subsequent water washing system.

[0006] (4) Controlling sodium impurities is quite difficult. Sodium carbonate solution can reduce the dissolution loss of Li2CO3 through the common ion effect of carbonate, but the mother liquor carried by the wet filter cake after filtration will introduce Na. + .

[0007] (5) Traditional processing methods have shortcomings. Existing methods for modifying fatty acids or fatty acid salts are prone to introducing organic residues; mechanical vibrating screens with ultrasonic assistance have energy consumption and screen life issues in continuous production. More fundamentally, traditional screening aids are usually permanently retained on the powder surface, making it difficult to balance screening effect and product purity.

[0008] Therefore, the industry urgently needs an industrial screening method that can suppress electrostatic agglomeration and hygroscopic bridging during the screening stage, quantitatively remove ammonia after silanization, and remove silicon coating and sodium ions through controlled multi-stage washing after screening. Summary of the Invention

[0009] The purpose of this invention is to provide a method for sieving lithium carbonate powder, which solves the problems of electrostatic agglomeration, moisture bridging, sieve clogging and low sieving yield in the process of sieving lithium carbonate fine powder, as well as the lack of endpoint control for silanization by-product ammonia, temporary coating and sodium carbonate mother liquor residue leading to fluctuations in product purity and yield.

[0010] The objective of this invention can be achieved through the following technical solutions: A method for sieving lithium carbonate powder includes the following steps: S1. Under the protection of inert gas, lithium carbonate raw material powder and fumed nano-silica are mixed and stirred evenly at a mass ratio of 100:0.5-2.0, so that the nano-silica is dispersed and attached to the surface of lithium carbonate particles to form a temporary silica-based isolation layer, thus obtaining pre-coated powder. S2. The pre-coated powder is placed in a sealed reactor and reacted with hexamethyldisilazane vapor at 70-120°C, so that hexamethyldisilazane reacts with the silanol groups on the surface of nano-silica to form a temporary hydrophobic passivation layer containing trimethylsilane groups; after stopping the supply of hexamethyldisilazane, the reaction temperature is maintained and the mixture is purged with high-purity nitrogen gas with a purity of not less than 99.999% and a water and CO2 volume fraction of not more than 5 ppm for 60-90 minutes, and the purging is stopped when the NH3 volume fraction at the outlet is not more than 10 ppm, to obtain the hydrophobic passivation powder; S3. The hydrophobic passivated powder is fed into an airflow sieving device and sieved sequentially through a low-pressure fluidization stage, a medium-pressure deagglomeration stage, a high-pressure crushing stage, and a low-pressure recovery stage to collect the undersize powder. The undersize powder is placed in a 3-8 wt% sodium carbonate aqueous solution and treated at 60-80℃ with stirring for 15-30 minutes to convert the amorphous nano-silica component into soluble silicate or desorb it from the powder surface, and to reduce the solubility of Li2CO3 in the liquid phase by utilizing the carbonate common ion. After filtration, it is washed with 4-5 stages of countercurrent washing with deionized water at 60-80℃, with the mass ratio of deionized water to wet filter cake in each stage being 0.4:1-0.8:1, and the Na+ in the final washing solution is used as the washing solution. + The washing endpoint was set at a concentration not exceeding 10 mg / L, followed by vacuum drying to obtain lithium carbonate powder.

[0011] In a preferred embodiment of the present invention, in step S1, the fumed silica nanoparticles are hydrophilic fumed silica with a specific surface area of ​​150-300 m². 2 / g, with an original particle size of 7-40nm.

[0012] As a preferred embodiment of the present invention, in step S1, the stirring speed is 1500-3000 rpm.

[0013] As a preferred embodiment of the present invention, in step S2, the amount of hexamethyldisilazane used is 0.2%-1.0% of the mass of the pre-coated powder.

[0014] As a preferred embodiment of the present invention, in step S2, the amount of hexamethyldisilazane used is 0.3%-0.5% of the mass of the pre-coated powder.

[0015] As a preferred technical solution of the present invention, the cumulative replacement amount of high-purity nitrogen after silanization is 5-8 times the effective gas phase volume of the reactor. The NH3 concentration of the purging tail gas is continuously detected and treated with acidic absorption liquid. The time and the outlet NH3 concentration constitute a dual endpoint to avoid batch-to-batch differences in residual ammonia caused by purging only at a fixed time.

[0016] As a preferred technical solution of the present invention, step S2 further includes spray modification of the powder after contact reaction, specifically: while the powder after contact reaction is stirred at 60-80°C, a titanate coupling agent solution is applied to the surface of the powder by atomization spray, and after spraying, stirring is continued and the temperature is raised to solidify, to obtain hydrophobic passivated powder, which further enhances the moisture resistance and low friction of the temporary coating during the sieving stage.

[0017] As a preferred embodiment of the present invention, the titanate coupling agent solution refers to a titanate coupling agent solution with a concentration of 1.0-3.0 wt% prepared by dissolving a monoalkoxy type titanate coupling agent in isopropanol; the amount of the monoalkoxy type titanate coupling agent is 0.02%-0.10% of the mass of the hydrophobic passivation powder.

[0018] As a preferred embodiment of the present invention, the stirring and heating curing refers to stirring for 10-20 minutes and heating to 100-120°C for 15-30 minutes.

[0019] As a preferred embodiment of the present invention, in step S3, the pulse pressure of the low-pressure fluidization stage is 0.2-0.3 MPa, the pulse pressure of the medium-pressure depolymerization stage is 0.5-0.7 MPa, the pulse pressure of the high-pressure crushing stage is 0.8-1.0 MPa, and the pulse pressure of the low-pressure recovery stage is 0.2-0.3 MPa; the pulse duration of each stage is 0.5-2.0 s, and the pulse interval is 1.5-5.0 s.

[0020] In a preferred embodiment of the present invention, in step S3, the mass ratio of the sieved refined powder to the sodium carbonate aqueous solution is 1:5-10; the filtered filter cake is subjected to 4-5 stages of countercurrent washing with deionized water at 60-80℃, with the mass ratio of deionized water to wet filter cake in each stage being 0.4:1-0.8:1, and the final washing solution contains Na... + Not exceeding 10 mg / L; after washing, vacuum dry for 1-3 h at 100-140℃ and a vacuum gauge reading of -0.085 MPa to -0.095 MPa.

[0021] As a preferred embodiment of the present invention, the lithium carbonate powder has a total silicon residue of no more than 30 ppm (Si), which translates to no more than 64 ppm of SiO2; a Na residue of no more than 50 ppm; a Li2CO3 main content of no less than 99.5%, and D... 90 Not higher than 15μm.

[0022] The beneficial effects of this invention are: This invention uses a temporary composite coating to replace a permanent surface-modified coating. Combined with the endpoint control of ammonia gas byproduct of silanization, gradient airflow sieving, sodium carbonate coating removal, and multi-stage countercurrent sodium removal washing process, it plays an anti-agglomeration, anti-hygroscopic and low-friction role in the sieving stage, and reduces silicon, sodium and volatile residues after sieving. The use of fumed silica nanoparticles to form a particle-spaced structure reduces van der Waals interactions, mechanical interlocking, and electrostatic agglomeration. Hexamethyldisilazane is used to convert silanol groups into trimethylsilyl hydrophobic end groups, and high-purity nitrogen is used for dual-endpoint purging to remove NH3 and residual volatiles, reducing interfacial composition fluctuations caused by the combined effects of ammonia condensate, residual moisture, and trace amounts of CO2. Low-dosage spray repair with titanate coupling agent further reduces moisture absorption and friction. Gradient pressure pulsed airflow screening employs staged control of low-pressure fluidization, medium-pressure deagglomeration, high-pressure crushing, and low-pressure recovery to gradually deagglomerate agglomerates with different binding strengths, balancing screening throughput and fine powder yield. Sodium carbonate treatment facilitates the entry of the temporary silica-based coating into the liquid phase and reduces the bulk dissolution loss of Li₂CO₃ by utilizing carbonate co-ions; subsequent countercurrent hot water washing with defined stages, liquid-to-solid ratio, and final stage wash endpoint enhances the Na₂CO₃ concentration. + The stability was removed, and the lithium loss caused by additional water washing was controlled by utilizing the characteristic that the solubility of Li2CO3 decreases with increasing temperature. Detailed Implementation

[0023] The claims of the present invention will be further described in detail below with reference to specific embodiments, but this does not constitute any limitation on the present invention. Any limited modifications made by any person within the scope of protection of the claims of the present invention are still within the scope of protection of the claims of the present invention.

[0024] The lithium carbonate raw material powder D used in the embodiments of the present invention 50 It is 12.6 μm, D 90 The silica nanoparticles have a diameter of 28.4 μm, a moisture content of 0.42 wt%, and an angle of repose of 45°. The fumed silica nanoparticles are hydrophilic and have a specific surface area of ​​approximately 200 m². 2 / g, with an original particle size of approximately 12nm; the purity of hexamethyldisilazane is not less than 99.0%; the monoalkoxy titanate coupling agent is triisostearoyl titanate isopropyl ester; and the sodium carbonate is anhydrous sodium carbonate.

[0025] Example 1

[0026] 10.0 kg of lithium carbonate raw material powder and 0.10 kg of fumed nano silica were added to a high-speed mixer and mixed at 2000 rpm for 10 min under nitrogen protection. The mixture was then cooled in a jacket to ensure that the material temperature did not exceed 35°C, thus obtaining pre-coated powder.

[0027] The pre-coated powder was transferred into a closed reactor, purged with nitrogen until the oxygen content reached 65 ppm, and heated to 90°C. Hexamethyldisilazane vapor was introduced at 100 rpm with 30 g of hexamethyldisilazane. After purging for 30 min, the reaction was maintained for 40 min. The supply of hexamethyldisilazane was stopped, and the temperature was maintained at 90°C. The mixture was then purged with high-purity nitrogen for 90 min to obtain hydrophobic passivated powder.

[0028] Dry nitrogen was used for gradient pressure pulsed airflow sieving, with screens of 325 mesh, 400 mesh, 500 mesh, and a collection tray from top to bottom. The low-pressure fluidization stage had a pressure of 0.25 MPa, a pulse duration of 0.8 s, a pulse interval of 2.5 s, and was repeated 4 times; the medium-pressure depolymerization stage had a pressure of 0.60 MPa, a pulse duration of 1.2 s, a pulse interval of 1.8 s, and was repeated 4 times; the high-pressure crushing stage had a pressure of 0.90 MPa, a pulse duration of 0.8 s, a pulse interval of 2.5 s, and was repeated 2 times; and the recovery stage had a pressure of 0.25 MPa, a pulse duration of 1.5 s, a pulse interval of 4.0 s, and was repeated once.

[0029] The first screening yielded 8.48 kg of 500-mesh undersize material, with a relative yield of 84.8% based on the initial lithium carbonate raw material mass. The residues from the 325-mesh, 400-mesh, and 500-mesh sieves were combined and subjected to a second screening, yielding 0.81 kg of undersize material. The combined undersize concentrate yielded 9.29 kg, with a total relative yield of 92.9%.

[0030] 9.29 kg of sieved refined powder was added to 55.7 kg of 5 wt% sodium carbonate aqueous solution and treated at 70℃ and 150 rpm for 20 min. After filtration, it was washed with 65℃ deionized water in four stages of countercurrent washing, with the mass ratio of deionized water to wet filter cake in each stage being 0.6:1. The final washing solution contained Na+ The endpoint was set at 10 mg / L, followed by drying at 120 °C and a vacuum gauge reading of -0.09 MPa for 2 h. The resulting lithium carbonate powder weighed 9.12 kg, with a Li₂CO₃ content of 99.67%, total silicon (Si) of 15 ppm, residual Na of 48 ppm, and D... 50 It is 8.33 μm, D 90 The thickness is 14.87 μm, and the water content is 0.042%.

[0031] Example 2

[0032] The difference from Example 1 is as follows: 10.0 kg of lithium carbonate raw material powder and 0.20 kg of fumed nano silica were added to the high-speed mixer; the amount of hexamethyldisilazane was 50 g; the silanization temperature was 110°C, and the reaction was maintained for 30 min after purging with gas for 30 min; after stopping the feeding, the temperature was maintained at 110°C and purged with high-purity nitrogen as in Example 1 for 60 min; after filtration, a 5-stage countercurrent washing was performed, and the remaining operations remained unchanged.

[0033] The first sieving yielded 8.73 kg of material through a 500-mesh sieve, with a relative yield of 87.3%. The residues from the 325-mesh, 400-mesh, and 500-mesh sieves were combined and subjected to a second sieving, yielding 0.72 kg of material through a 500-mesh sieve. The combined undersize concentrate yielded 9.45 kg, with a total relative yield of 94.5%.

[0034] 9.45 kg of the sieved refined powder was added to 56.7 kg of a 5% sodium carbonate aqueous solution and treated at 70℃ and 150 rpm for 20 min. After filtration, it was washed with deionized water at 65℃ in five stages of countercurrent washing, with a deionized water to wet filter cake mass ratio of 0.6:1 in each stage. It was then dried at 120℃ and a vacuum gauge reading of -0.09 MPa for 2 h. The resulting lithium carbonate powder weighed 9.25 kg, with a Li₂CO₃ content of 99.63%, total silicon (Si) of 18 ppm, residual Na of 48 ppm, and D... 50 It is 7.96 μm, D 90 The thickness is 14.03 μm, and the moisture content is 0.052%.

[0035] Example 3:

[0036] The difference from Example 1 is that the number of cycles in the medium-pressure depolymerization stage of the gradient pressure pulse airflow screening is adjusted to 3, the pressure in the high-pressure crushing stage is adjusted to 1.00 MPa, and the number of cycles in the high-pressure crushing stage is adjusted to 3, while the other operations and steps remain unchanged.

[0037] The first sieving yielded 8.61 kg of material under 500 mesh, with a relative yield of 86.1%. The residues from the 325 mesh, 400 mesh, and 500 mesh sieves were combined and subjected to a second sieving, yielding 0.77 kg of material under 500 mesh. The combined undersize concentrate yielded 9.38 kg, with a total relative yield of 93.8%.

[0038] 9.38 kg of the sieved refined powder was added to 56.3 kg of a 5% sodium carbonate aqueous solution and treated at 70℃ and 150 rpm for 20 min. After filtration, it was washed with deionized water at 65℃ in four stages of countercurrent washing, with a deionized water to wet filter cake mass ratio of 0.6:1 in each stage. It was then dried at 120℃ and a vacuum gauge reading of -0.09 MPa for 2 h. The resulting lithium carbonate powder weighed 9.17 kg, with a Li₂CO₃ content of 99.62%, total silicon (Si) of 17 ppm, total silicon (Na) of 49 ppm, and total silicon (D) of 49 ppm. 50 It is 7.96 μm, D 90 It has a thickness of 14.13 μm and a moisture content of 0.068%.

[0039] Example 4:

[0040] The difference from Example 1 is that the pre-coated powder was transferred to a closed reactor, nitrogen was used to replace the oxygen content to 65 ppm, the temperature was raised to 90°C, and hexamethyldisilazane vapor (30 g) was introduced while stirring at 100 rpm. After purging for 30 min, the reaction was maintained for 40 min. The feeding was stopped and the reactor was purged with high-purity nitrogen as in Example 1 for 70 min. Then the temperature was lowered to 65°C and stirred at 100 rpm. 5.0 g of triisostearoyl titanate isopropyl ester was dissolved in 245.0 g of isopropanol to prepare a 2.0% titanate coupling agent solution, which was then applied to the powder surface by atomization spray. After spraying, the temperature was maintained at 65°C and stirred for 15 min. The temperature was then raised to 110°C and cured for 20 min to obtain hydrophobic passivated powder. The atomizing gas was dry nitrogen at a pressure of 0.5 MPa and the spraying time was 5 min. The remaining operations were the same as in Example 1.

[0041] A single sieving process yielded 9.05 kg of material through a 500-mesh sieve, with a relative yield of 90.5%. The residues from the 325-mesh, 400-mesh, and 500-mesh sieves were combined and subjected to a second sieving process, yielding 0.57 kg of material through a 500-mesh sieve. The combined undersize concentrate yielded 9.62 kg, with a total relative yield of 96.2%. Coated undersize concentrate D 50 It is 7.24 μm, D 90 The thickness is 12.81 μm, the water content is 0.024%, the 24-hour moisture absorption rate is 0.027%, the static water contact angle is 126°, and the angle of repose is 23°.

[0042] 9.62 kg of sieved refined powder was added to 57.7 kg of a 5% sodium carbonate aqueous solution and treated at 70℃ and 150 rpm for 20 min. After filtration, it was washed with 65℃ deionized water in a 5-stage countercurrent process, with a deionized water to wet filter cake mass ratio of 0.6:1 in each stage. The final washing solution contained Na... + The endpoint was set at 10 mg / L, followed by drying at 120 °C and a vacuum gauge reading of -0.09 MPa for 2 h. The resulting lithium carbonate powder weighed 9.47 kg, with a Li₂CO₃ content of 99.72%, total silicon (Si) of 12 ppm, residual Na of 40 ppm, and D... 50 It is 7.28 μm, D 90 It has a thickness of 12.94 μm and a moisture content of 0.037%.

[0043] Comparative Example 1 Take 10.0 kg of lithium carbonate raw material powder from the same batch and directly sieve it using a conventional vibrating screen with a mesh size of 500 for 30 minutes.

[0044] A single sieve yielded 5.23 kg of material through a 500-mesh sieve, representing a relative yield of 52.3%.

[0045] The obtained undersize material D 50 It is 18.62 μm, D 90 The size is 42.14 μm, the angle of repose is 48°, the moisture content is 0.44%, and the 24-hour moisture absorption rate is 1.05%.

[0046] Comparative Example 2 Take 10.0 kg of lithium carbonate raw material powder from the same batch and sieve it using the gradient pressure pulse airflow sieving process described in Example 1.

[0047] A single sieve yielded 6.85 kg of material through a 500-mesh sieve, representing a relative yield of 68.5%.

[0048] The obtained undersize material D 50 It is 14.23 μm, D 90 The size is 31.68 μm, the angle of repose is 44°, the moisture content is 0.43%, and the 24-hour moisture absorption rate is 0.96%.

[0049] Comparative Example 3 Take 10.0 kg of lithium carbonate raw material powder from the same batch, add 0.10 kg of fumed nano silica, and process it according to the pre-coating steps in Example 1. Do not perform hexamethyldisilazane passivation and titanate coupling agent spray reinforcement. Then, use a conventional rotary vibrating screen to sieve at 500 mesh for 30 min.

[0050] A single sieve yielded 5.87 kg of material through a 500-mesh sieve, representing a relative yield of 58.7%.

[0051] The obtained undersize material D 50 It is 16.54 μm, D 90 The micrometer diameter is 36.27 μm, the angle of repose is 38°, the moisture content is 0.40%, and the 24-hour moisture absorption rate is 0.62%.

[0052] Comparative Example 4 Take 10.0 kg of lithium carbonate raw material powder from the same batch, without adding fumed nano silica, and directly introduce hexamethyldisilazane vapor under stirring conditions of 90℃ and 100 rpm. The amount of hexamethyldisilazane is 30 g. After purging for 30 min, maintain the reaction for 40 min. After stopping the feeding, purge under the high-purity nitrogen conditions of Example 1, and then use a conventional vibrating screen to sieve at 500 mesh for 30 min.

[0053] A single sieve yielded 5.42 kg of material through a 500-mesh sieve, representing a relative yield of 54.2%.

[0054] The obtained undersize material D 50 It is 17.83 μm, D 90 The nanometer diameter is 39.51 μm, the angle of repose is 42°, the moisture content is 0.39%, and the 24-hour moisture absorption rate is 0.55%.

[0055] Comparative Example 5 Take 10.0 kg of lithium carbonate raw material powder from the same batch, add 0.10 kg of fumed nano silica, and passivate it by passing hexamethyldisilazane vapor. The amount of hexamethyldisilazane used is 30 g. The pre-coating and passivation conditions are the same as in Example 1. After treatment, instead of gradient pressure pulse airflow sieving, conventional rotary vibrating screen is used for 500 mesh sieving for 30 min.

[0056] A single sieve yielded 6.24 kg of material through a 500-mesh sieve, representing a relative yield of 62.4%.

[0057] The obtained undersize material D 50 It is 15.35μm, D 90 The size is 33.82 μm, the angle of repose is 29°, the moisture content is 0.081%, and the 24-hour moisture absorption rate is 0.097%.

[0058] Comparative Example 6 Take 10.0 kg of lithium carbonate raw material powder from the same batch, add 0.10 kg of fumed nano silica, and process it according to the pre-coating steps of Example 1. Do not perform hexamethyldisilazane passivation and titanate coupling agent spray reinforcement. Then, use the gradient pressure pulse airflow sieving process of Example 1 for sieving.

[0059] A single sieve yielded 7.31 kg of material passing through a 500-mesh sieve, representing a relative yield of 73.1%.

[0060] The obtained undersize material D 50 It is 13.54 μm, D 90 The nanometer diameter is 29.48 μm, the angle of repose is 37°, the moisture content is 0.38%, and the 24-hour moisture absorption rate is 0.33%.

[0061] Comparative Example 7 Take 10.0 kg of lithium carbonate raw material powder from the same batch, without adding fumed nano silica, and directly introduce hexamethyldisilazane vapor under stirring conditions of 90℃ and 100 rpm. The amount of hexamethyldisilazane is 30 g. After purging for 30 min, maintain the reaction for 40 min. After stopping the feeding, purge with high-purity nitrogen under the conditions of Example 1 until the volume fraction of NH3 at the outlet is not higher than 10 ppm. Then, use the gradient pressure pulse airflow sieving process of Example 1 for sieving.

[0062] A single sieve yielded 7.08 kg of material passing through a 500-mesh sieve, representing a relative yield of 70.8%.

[0063] The obtained undersize material D 50 It is 13.94 μm, D 90 The micrometer diameter is 30.87 μm, the angle of repose is 40°, the moisture content is 0.36%, and the 24-hour moisture absorption rate is 0.28%.

[0064] Comparative Example 8 Take 10.0 kg of lithium carbonate raw material powder from the same batch, add 0.10 kg of fumed nano silica, and process it according to the pre-coating steps in Example 1; then, use a solution of γ-aminopropyltriethoxysilane ethanol instead of hexamethyldisilazane vapor for surface treatment; wherein, the amount of γ-aminopropyltriethoxysilane is 30 g, the amount of anhydrous ethanol is 500 g, stir and react at 80°C for 60 min, remove ethanol under reduced pressure, and solidify at 120°C for 30 min; after treatment, use the gradient pressure pulse airflow sieving process in Example 1 for sieving.

[0065] A single sieve yielded 7.16 kg of material passing through a 500-mesh sieve, representing a relative yield of 71.6%.

[0066] The obtained undersize material D 50 It is 13.27 μm, D 90 It has a diameter of 28.63 μm, an angle of repose of 35°, a moisture content of 0.15%, and a 24-hour moisture absorption rate of 0.26%.

[0067] Comparative Example 9 The difference from Example 4 is that no titanate coupling agent was sprayed for reinforcement, and the effect of the titanate coupling agent spraying reinforcement step on improving the moisture resistance and powder sieving performance of the temporary coating was tested. Specifically, 10.0 kg of lithium carbonate raw material powder and 0.10 kg of fumed nano-silica are added to a high-speed mixer for pre-coating treatment; then passivation is performed using hexamethyldisilazane vapor, with 30 g of hexamethyldisilazane used; and then gradient pressure pulse airflow sieving is performed.

[0068] The results showed that 8.48 kg of material was obtained from the first sieve screening, with a relative yield of 84.8%; after the second sieve screening, 9.29 kg of fine powder was obtained by combining the sieve undersize particles, with a total relative yield of 92.9%.

[0069] The resulting coated undersize powder D 50 It is 8.22 μm, D 90 The size is 14.65 μm, the angle of repose is 26°, the moisture content is 0.06% by mass, and the 24-hour moisture absorption rate is 0.06%.

[0070] Comparative Example 10 The difference from Example 4 is that 50.0g of triisostearoyl titanate isopropyl ester was dissolved in 245.0g of isopropanol to prepare a titanate coupling agent solution with a total mass of 295.0g and a mass fraction of 16.95%. The rest of the operation is the same as in Example 4.

[0071] A single sieve yielded 8.78 kg of material passing through a 500-mesh sieve, representing a relative yield of 87.8%.

[0072] The obtained undersize material D 50 It is 7.58 μm, D 90 It has a diameter of 13.56 μm, an angle of repose of 26°, a moisture content of 0.05%, and a 24-hour moisture absorption rate of 0.05%.

[0073] When the titanate coupling agent is in excess, the organic layer on the surface of the powder thickens, which is not conducive to the thorough sieving of fine powder.

[0074] Comparative Example 11 10.0 kg of lithium carbonate raw material powder from the same batch was taken and treated directly according to the titanate coupling agent spray reinforcement conditions in Example 4 without pre-coating with fumed silica or passivating with hexamethyldisilazane. Specifically, 5.0 g of triisostearoyl titanate isopropyl ester was dissolved in 245.0 g of isopropanol to prepare 250.0 g of a 2% (w / w) isopropanol solution of triisostearoyl titanate isopropyl ester; under stirring conditions of 65°C and 100 rpm, it was atomized with 0.5 MPa dry nitrogen for about 5 min, and after spraying, it was stirred at 65°C for 15 min, and then heated to 110°C for 20 min to solidify. After treatment, it was subjected to a gradient pressure pulse airflow sieving process.

[0075] A single sieve yielded 6.92 kg of material passing through a 500-mesh sieve, representing a relative yield of 69.2%.

[0076] The obtained undersize material D 50 It is 14.06 μm, D 90 The micrometer diameter is 31.28 μm, the angle of repose is 43°, the moisture content is 0.41%, and the 24-hour moisture absorption rate is 0.82%.

[0077] Titanate coupling agents are difficult to exert an effective reinforcing effect on their own when fumed nano silica and hexamethyldisilazane passivation are lacking.

[0078] Comparative Example 12 The difference from Example 4 is that the sodium carbonate solution treatment, water washing and drying purification steps are omitted, that is, the coated undersize powder is directly used as the final product after sieving.

[0079] The first sieving yielded 9.05 kg of 500-mesh sieve undersize, with a relative yield of 90.5%. After the second sieving, the combined undersize powder yielded 9.62 kg, with a total relative yield of 96.2%.

[0080] The coating removal step is omitted, and the resulting powder D 50 It is 7.24 μm, D 90 The particle size is 12.86 μm, the moisture content is 0.02% by mass, the 24-hour moisture absorption rate is 0.02%, and the angle of repose is 23°. Testing revealed that the product contains 98.42% Li₂CO₃, 4768 ppm total silicon (calculated as Si), and 48 ppm residual Na.

[0081] Comparative Example 13 The difference from Example 4 is that the 5% sodium carbonate aqueous solution in the coating removal step was replaced with an equal mass of deionized water at 25°C. Subsequently, the five-stage countercurrent washing and drying were still performed as in Example 4 to evaluate lithium loss in the absence of carbonate common ion protection.

[0082] The first sieving yielded 9.05 kg of 500-mesh sieve undersize, with a relative yield of 90.5%. After the second sieving, the combined undersize powder yielded 9.62 kg, with a total relative yield of 96.2%.

[0083] After pure water treatment, five-stage countercurrent washing, and drying, 9.07 kg of lithium carbonate powder was obtained, with a Li₂CO₃ content of 99.34%, total silicon (Si) of 786 ppm, residual Na of 45 ppm, and D... 50 It is 7.37 μm, D 90 The thickness is 13.35 μm, and the moisture content is 0.042%.

[0084] The results indicate that pure water is insufficient to remove the silica component from the temporary composite coating, and the lithium carbonate dissolution increases when there is a lack of common ion protection from carbonate ions.

[0085] Comparative Example 14 10.0 kg of lithium carbonate raw material powder from the same batch was used for surface modification with hydrophobic fumed silica treated with hexamethyldisilazane and isopropyl triisostearoyl titanate. Specifically, 0.10 kg of the hydrophobic fumed silica treated with hexamethyldisilazane and 5.0 g of isopropyl triisostearoyl titanate were used, dissolved in 245.0 g of isopropanol to prepare a 2% (w / w) isopropanol solution of isopropyl triisostearoyl titanate. After treatment, the sample was directly subjected to gradient pressure pulsed airflow sieving, without a step of directional removal of the temporary coating using sodium carbonate solution.

[0086] The first sieving yielded 8.76 kg of 500-mesh sieve undersize, with a relative yield of 87.6%. After the second sieving, the combined undersize powder yielded 9.41 kg, with a total relative yield of 94.1%.

[0087] The obtained powder D 50 It is 7.63 μm, D 90 The particle size is 13.58 μm, the moisture content is 0.03% by mass, the 24-hour moisture absorption rate is 0.03%, and the angle of repose is 25°. Testing revealed that the product contains 98.55% Li₂CO₃, 4582 ppm total silicon (Si), and 52 ppm residual Na.

[0088] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, features in the embodiments of the present invention can be combined with each other unless otherwise specified.

Claims

1. A method for sieving lithium carbonate powder, characterized in that, Includes the following steps: S1. Under inert gas protection, lithium carbonate raw material powder and fumed nano-silica are mixed and stirred evenly at a mass ratio of 100:0.5-2.0 to obtain pre-coated powder; S2. The pre-coated powder is placed in a sealed reactor and reacted with hexamethyldisilazane vapor at 70-120°C. After the hexamethyldisilazane supply is stopped, the reactor is purged with high-purity nitrogen to obtain hydrophobic passivated powder. S3. The hydrophobic passivated powder is fed into an airflow sieving device and sieved sequentially through a low-pressure fluidization stage, a medium-pressure deagglomeration stage, a high-pressure crushing stage, and a low-pressure recovery stage. The undersized fine powder is collected, placed in a sodium carbonate aqueous solution, and treated at 60-80℃ with stirring for 15-30 minutes. After filtration, it is washed countercurrently and dried to obtain lithium carbonate powder.

2. The method for sieving lithium carbonate powder according to claim 1, characterized in that, In step S1, the fumed silica nanoparticles are hydrophilic fumed silica with a specific surface area of ​​150-300 m². 2 / g, with an original particle size of 7-40nm.

3. The method for sieving lithium carbonate powder according to claim 1, characterized in that, In step S1, the stirring speed is 1500-3000 rpm.

4. The method for sieving lithium carbonate powder according to claim 1, characterized in that, In step S2, the amount of hexamethyldisilazane used is 0.2%-1.0% of the mass of the pre-coated powder.

5. The method for sieving lithium carbonate powder according to claim 1, characterized in that, Step S2 further includes spraying the powder after the contact reaction, specifically: while stirring the powder at 60-80℃, a titanate coupling agent solution is applied to the surface of the powder by atomization spraying, and after spraying, stirring is continued and the temperature is raised to solidify, to obtain hydrophobic passivated powder.

6. The method for sieving lithium carbonate powder according to claim 5, characterized in that, The titanate coupling agent solution refers to a titanate coupling agent solution with a concentration of 1.0-3.0 wt% prepared by dissolving a monoalkoxy type titanate coupling agent in isopropanol; the amount of the monoalkoxy type titanate coupling agent is 0.02%-0.10% of the mass of the hydrophobic passivation powder.

7. The method for sieving lithium carbonate powder according to claim 5, characterized in that, The stirring and heating curing refers to stirring for 10-20 minutes and heating to 100-120℃ for 15-30 minutes to cure.

8. The method for sieving lithium carbonate powder according to claim 1, characterized in that, In step S3, the pulse pressure of the low-pressure fluidization stage is 0.2-0.3 MPa, the pulse pressure of the medium-pressure depolymerization stage is 0.5-0.7 MPa, the pulse pressure of the high-pressure crushing stage is 0.8-1.0 MPa, and the pulse pressure of the low-pressure recovery stage is 0.2-0.3 MPa; the pulse duration of each stage is 0.5-2.0 s, and the pulse interval is 1.5-5.0 s.

9. The method for sieving lithium carbonate powder according to claim 1, characterized in that, In step S3, the mass ratio of the sieved refined powder to the sodium carbonate aqueous solution is 1:5-10; the filtered filter cake is washed with deionized water at 60-80℃ for 4-5 stages of countercurrent washing, with the mass ratio of deionized water to wet filter cake in each stage being 0.4:1-0.8:1, and the sodium ion concentration in the final washing solution is not higher than 10mg / L; then it is vacuum dried for 1-3h at 100-140℃ and a vacuum gauge reading of -0.085MPa to -0.095MPa.

10. The method for sieving lithium carbonate powder according to claim 1, characterized in that, The lithium carbonate powder has a total silicon residue of no more than 30 ppm (Si); a sodium residue of no more than 50 ppm; a Li₂CO₃ content of no less than 99.5%; and a D content of no more than 50%. 90 Not higher than 15μm.