A method for preparing battery-grade lithium carbonate by using salt lake lithium carbonate

Abstract

The present application relates to the technical field of lithium carbonate preparation, in particular to a method for preparing battery-grade lithium carbonate by using salt lake lithium carbonate, comprising the following steps: adding purified water and ethanolamine to crude lithium carbonate from salt lake brine, wet ball milling, then adding sodium hydroxide solution for alkali washing, adopting purified water to make slurry of the obtained filter residue A, carbonizing to obtain filter liquor B, adding magnesium chloride and sodium oxalate in sequence for impurity removal, pyrolyzing and crystallizing, drying the obtained lithium carbonate wet product to obtain battery-grade lithium carbonate. The method has the advantages of high purification process treatment efficiency and high lithium recovery rate, and the prepared lithium carbonate product can meet the requirements of battery-grade lithium carbonate.

Description

Technical Field

[0001] This invention relates to the field of lithium carbonate preparation technology, and more specifically to a method for preparing battery-grade lithium carbonate using lithium carbonate from salt lakes. Background Technology

[0002] With the rapid development of the global new energy vehicle and energy storage industries, the demand for lithium resources, as a core raw material for power batteries, is experiencing explosive growth. Lithium carbonate is a key precursor for preparing cathode materials for lithium-ion batteries. Battery-grade lithium carbonate has strict requirements for product purity, impurity content, and particle size distribution, as its quality directly affects the battery's energy density and cycle life. Currently, lithium resources mainly come from lithium-bearing ores and salt lake brines, with salt lake brines becoming the primary source of future lithium supply due to their large reserves and low extraction costs. However, due to the complex composition of salt lake brines, lithium carbonate prepared using them suffers from low purity and high levels of calcium, boron, and silicon. The presence of these impurities severely restricts the preparation efficiency and product quality of battery-grade lithium carbonate. Therefore, developing a method for efficiently purifying salt lake lithium carbonate to prepare battery-grade lithium carbonate is of great significance. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing battery-grade lithium carbonate using lithium carbonate from salt lakes. This method addresses the issues of low purity and high levels of calcium, boron, and silicon impurities in lithium carbonate from salt lakes, offering advantages such as high purification process efficiency and high lithium recovery rate. Furthermore, the prepared lithium carbonate product meets the requirements for battery-grade lithium carbonate.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] This application provides a method for preparing battery-grade lithium carbonate using lithium carbonate from salt lakes, comprising the following steps:

[0006] S1. Add purified water and ethanolamine (2-4 times the molar amount of silicon in the crude lithium carbonate) to the crude lithium carbonate from the salt lake brine, and perform wet ball milling to prepare crude lithium carbonate slurry. Add sodium hydroxide to the slurry after ball milling until the sodium hydroxide concentration in the slurry is 20-40%. Stir and react at 70-80℃ for 60-90 min. Filter and wash while hot to obtain filtrate A and filter residue A.

[0007] S2. Prepare lithium carbonate slurry by using purified water to filter residue A. Introduce carbon dioxide into the lithium carbonate slurry and react for 120-150 min at a pressure of 0.2-0.5 MPa and a temperature of 30-40℃ to obtain carbonized liquid. Filter the carbonized liquid to obtain filter residue B and filtrate B.

[0008] S3. Determine the Si content in filtrate B. Add magnesium chloride to filtrate B according to the molar ratio of Si to Mg of 1:2-4. Stir and react for 20-30 minutes, then filter to obtain filtrate C and filter residue C.

[0009] S4. Determine the Ca content in filtrate C. Add sodium oxalate at 1.1-1.3 times the molar amount of Ca in filtrate C, stir and react for 90-120 min, and filter the reaction solution to obtain filtrate D and filter residue D.

[0010] S5. Pyrolysis crystallization of filtrate D, and hot filtration and washing of pyrolysis slurry to obtain wet lithium carbonate and lithium precipitation mother liquor.

[0011] S6. The wet lithium carbonate is dried to obtain battery-grade lithium carbonate.

[0012] Crude lithium carbonate from salt lake brine has low purity and high levels of Si, Ca, and B impurities. Furthermore, silicon exists as a composite of silicates and colloidal silica, which is trapped and encapsulated within the lithium carbonate particles, hindering the removal of other impurities and impeding subsequent carbonization. This makes it difficult to obtain battery-grade lithium carbonate using conventional methods. In this application, crude lithium carbonate from salt lake brine is wet-milled with ethanolamine. The electrostatic bonding between ethanolamine and silica allows silica to be separated and dispersed from the lithium carbonate particles. Strongly alkaline sodium hydroxide is added to the milled slurry. As the charge strength of ethanolamine decreases, silica dissociates from it and reacts with sodium hydroxide at high temperature to form soluble sodium silicate. Filtration under high temperature conditions removes most of the silicon impurities from the crude lithium carbonate. On the other hand, sodium hydroxide also promotes the dissolution of boron impurities to form sodium borate, further removing boron from the raw material. Hot filtration and hot water washing reduce the viscosity of sodium silicate, facilitating filtration. Since lithium carbonate has low solubility in hot water, hot filtration reduces lithium loss.

[0013] After the purification process in S1, a large amount of silicon and boron impurities in the crude lithium carbonate are removed, and the purity of the crude lithium carbonate is improved. When carbon dioxide is introduced, the lithium carbonate reacts with the carbon dioxide to be converted into lithium bicarbonate, which has higher solubility.

[0014] After carbonization, magnesium chloride is used to further remove impurities from the lithium bicarbonate solution. Magnesium reacts with silicate ions to form a sparingly soluble magnesium silicate precipitate; adding excess magnesium ensures complete precipitation of silicon impurities. Calcium is then removed by oxalate ions in sodium oxalate, and the resulting sodium salt is washed away with water during subsequent pyrolysis. The purified lithium bicarbonate solution decomposes upon heating to form lithium carbonate. Lithium carbonate has very low solubility in hot water; high-temperature pyrolysis ensures reaction efficiency, ultimately achieving the preparation of battery-grade lithium carbonate.

[0015] Furthermore, the wet ball milling process in S1 is as follows: the material-to-water ratio is controlled at 1:1.2-1.5. Purified water is added to the crude lithium carbonate, and then ethanolamine with a molar amount of 2-4 times that of silicon in the crude lithium carbonate is added. The material-to-ball ratio is 1:1.5-1.8, and the mixture is ball-milled at 20-30 rpm for 6-8 hours.

[0016] Further, in S1, the sodium hydroxide is a sodium hydroxide solution with a concentration of 40-70%.

[0017] Furthermore, S1 also includes purifying filtrate A and returning it to S1 for use in preparing sodium hydroxide solution.

[0018] Furthermore, the purification method in S1 involves determining the silicon and boron content in filtrate A and calculating the required Ca. 2+ Add lime slurry to filtrate A at 1.05-1.2 times the theoretical dosage, stir at 200-300 rpm for 90-120 min, let stand for 30-60 min after the reaction is complete, and then filter to obtain purified filtrate A.

[0019] Furthermore, in S2, the method for preparing lithium carbonate slurry using purified water for filter residue A is as follows: filter residue A and purified water are added to the carbonation reactor at a mass ratio of 1:20-30, and stirred at 200-300 rpm for 5-10 minutes to obtain a uniform lithium carbonate slurry.

[0020] Further, in S5, the pyrolysis crystallization method is as follows: the filtrate D is pumped into the pyrolysis crystallizer, and at a stirring speed of 300-350 rpm, the temperature is first raised to 70-75℃ and reacted for 60-90 min, and then the temperature is raised to 90℃-95℃ and reacted for 30-60 min. The pyrolysis slurry is filtered while hot and washed with hot water at 90-95℃ to obtain lithium carbonate wet product and lithium precipitation mother liquor.

[0021] Furthermore, S5 also includes the detection of Na in the lithium precipitation mother liquor. + The content of Na in the lithium precipitation mother liquor + If the concentration is <20g / L, the lithium precipitation mother liquor will be returned to S2 to replace purified water for the preparation of lithium carbonate slurry, thus realizing a closed-loop circulation of the lithium precipitation mother liquor.

[0022] If Na in the lithium precipitation mother liquor + For concentrations >20g / L, pump the lithium precipitation mother liquor into an evaporator to concentrate it to 30-40% of its original volume. Then, pump the concentrate into a cooling crystallizer to cool it to 20-30℃ to precipitate salt. After filtration to remove salt, return the mother liquor to the S2 cycle.

[0023] Furthermore, S5 also includes the collection of carbon dioxide released during the pyrolysis crystallization process. The collected carbon dioxide is dehydrated by condensation and then pressurized to 0.8-1.2 MPa before being returned to the carbonization process of S2 for recycling.

[0024] Furthermore, in S6, the drying method is to send the wet lithium carbonate product into a vacuum dryer and dry it at a vacuum degree below 100Pa and a temperature of 80-95℃ until the moisture content is ≤0.2% to obtain battery-grade lithium carbonate.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] This application addresses the issues of low purity and high silicon, calcium, and boron content in crude lithium carbonate derived from salt lake brine. It proposes a method for purifying and preparing lithium carbonate products from salt lake lithium carbonate by using ethanolamine electrostatic adsorption combined with alkaline washing to remove silicon and boron, followed by carbonation dissolution, deep impurity removal, and pyrolysis precipitation. This purification process boasts high efficiency, high lithium recovery rate, and the prepared lithium carbonate product meets the requirements for battery-grade lithium carbonate content. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the preparation of battery-grade lithium carbonate using lithium carbonate from salt lakes in this application. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The crude lithium carbonate used in the embodiments and comparative examples of this invention is derived from salt lake brine, and its composition is as follows: lithium carbonate content 77.54%, Na 6.35%, Ca 1544.01ppm, Mg 23.61ppm, Fe 11.39ppm, K 213.06ppm, Si 862.53ppm, Al 22.06ppm, Mn 0.84ppm, Zn 2.52ppm, Pb 0.23ppm, Cu 0.004ppm, Ni 0.008ppm, B 57.36ppm, SO42- 2- 241.21ppm, Cl - 80.57ppm;

[0030] Unless otherwise specified, all methods described herein are conventional methods, and all raw materials described herein are available from publicly available commercial sources.

[0031] Example 1

[0032] This embodiment provides a method for preparing battery-grade lithium carbonate using lithium carbonate from salt lakes, including the following steps:

[0033] S1. Crude lithium carbonate from salt lake brine and purified water were fed into a ball mill at a mass ratio of 1:1.3. Ethanolamine, which was three times the molar amount of silicon in the crude lithium carbonate, was added to the mill. The ball milling was carried out at 30 rpm for 7 hours with a material-to-ball ratio of 1:1.6. The slurry after ball milling was pumped into a reaction vessel. A 50% sodium hydroxide solution was added to the slurry until the sodium hydroxide concentration in the slurry was 30%. The temperature was raised to 75°C and the mixture was stirred at 200 rpm for 80 minutes. The mixture was filtered while hot and washed with 75°C hot water to obtain filtrate A and filter residue A.

[0034] After purification, filtrate A is returned to S1 for the preparation of sodium hydroxide solution. The specific method involves determining the silicon and boron content in filtrate A and calculating the required Ca content. 2+ Add 20% lime slurry to filtrate A at 1.1 times the theoretical dosage, stir at 200 rpm for 100 min, let stand for 45 min after the reaction is complete, and filter using a plate and frame filter press to obtain purified filtrate A.

[0035] S2. Add filter residue A and purified water into the carbonization reactor at a mass ratio of 1:25, stir at 200 rpm for 10 min to obtain a uniform lithium carbonate slurry, continuously introduce carbon dioxide into the lithium carbonate slurry, and react at a pressure of 0.4 MPa and a temperature of 35℃ for 135 min. After the reaction is completed, filter the carbonization liquid through a plate and frame filter press to obtain filter residue B and filtrate B.

[0036] S3. Pump filtrate B into the primary impurity removal vessel, determine the Si content in filtrate B, add magnesium chloride to filtrate B according to the molar ratio of Si to Mg of 1:3, stir at 200 rpm, react for 30 min, and then filter through a plate and frame filter press to obtain filtrate C and filter residue C.

[0037] S4. Pump filtrate C into the secondary impurity removal reactor and determine the Ca content in filtrate C. 2+ To determine the content, sodium oxalate was added at 1.2 times the molar amount of calcium ions in filtrate C. The mixture was stirred at 200 rpm for 120 min. The resulting liquid was filtered through a plate and frame filter press to obtain filtrate D and filter residue D.

[0038] S5. Pump the filtrate D into the pyrolysis crystallizer. At a stirring speed of 300 rpm, first heat it to 70°C and react for 90 min, then raise the temperature to 90°C and react for 60 min. Carbon dioxide is recovered throughout the process. The pyrolysis slurry is filtered while hot by a leaf filter. The wet product is washed with 90°C hot water to obtain lithium carbonate wet product and lithium precipitation mother liquor.

[0039] Carbon dioxide and lithium precipitation mother liquor can be reused using the following methods;

[0040] The method for recycling lithium precipitation mother liquor involves detecting the Na content in the lithium precipitation mother liquor.+ The content of Na in the lithium precipitation mother liquor + <20g / L, the above lithium precipitation mother liquor can be returned to S2 to replace purified water for preparing lithium carbonate slurry, realizing a closed-loop circulation of lithium precipitation mother liquor; if the Na content in the lithium precipitation mother liquor is ... + For concentrations >20g / L, the lithium precipitation mother liquor is pumped into an evaporator to concentrate it to 35% of its original volume. The concentrate is then pumped into a cooling crystallizer to cool it to 25°C to precipitate salt. After filtration to remove salt, the mother liquor is returned to the S2 cycle.

[0041] The method for carbon dioxide recycling is to collect the carbon dioxide released during the pyrolysis crystallization process, remove water by condensation, and then pressurize it to 1 MPa to return it to the carbonization process of S2 for recycling.

[0042] S6. The wet lithium carbonate product is fed into a vacuum dryer and dried at 90°C under a vacuum of less than 100 Pa until the moisture content is ≤0.2% to obtain battery-grade lithium carbonate.

[0043] Example 2

[0044] This embodiment provides a method for preparing battery-grade lithium carbonate using lithium carbonate from salt lakes, including the following steps:

[0045] S1. Crude lithium carbonate from salt lake brine and purified water were added to a reactor at a mass ratio of 1:1.2. Ethanolamine, at a molar ratio of 4 times that of silicon in the crude lithium carbonate, was added. The mixture was ball-milled at 20 rpm for 8 hours using a material-to-ball ratio of 1:1.5. The ball-milled slurry was pumped into the reactor, and a 40% sodium hydroxide solution was added to the slurry until the sodium hydroxide concentration in the slurry reached 20%. The temperature was raised to 70°C, and the mixture was stirred at 300 rpm for 60 minutes. The mixture was then filtered while hot and washed with 70°C hot water to obtain filtrate A and filter residue A.

[0046] After purification, filtrate A is returned to S1 for the preparation of sodium hydroxide solution. The specific method involves determining the silicon and boron content in filtrate A and calculating the required Ca content. 2+ Add 20% lime slurry to filtrate A at 1.2 times the theoretical dosage, stir at 300 rpm for 90 minutes, let stand for 60 minutes after the reaction is complete, and filter using a plate and frame filter press to obtain purified filtrate A. Add solid sodium hydroxide to adjust the sodium hydroxide concentration in filtrate A to 60%.

[0047] S2. Add filter residue A and purified water to the carbonation reactor at a mass ratio of 1:20 and stir at 300 rpm for 10 min to obtain a uniform lithium carbonate slurry. Continuously introduce carbon dioxide into the lithium carbonate slurry and react at a pressure of 0.5 MPa and a temperature of 30°C for 120 min until the lithium carbonate dissolves into lithium bicarbonate. After the reaction is completed, filter the carbonation liquid through a plate and frame filter press to obtain filter residue B and filtrate B.

[0048] S3. Pump filtrate B into the primary impurity removal vessel, determine the Si content in filtrate B, add magnesium chloride to filtrate B according to the molar ratio of Si to Mg of 1:2, and react for 20 minutes under stirring at 300 rpm. Then filter through a plate and frame filter press to obtain filtrate C and filter residue C.

[0049] S4. Pump filtrate C into the secondary impurity removal reactor and determine the Ca content in filtrate C. 2+ To determine the content, sodium oxalate was added at 1.1 times the molar amount of calcium ions in filtrate C. The mixture was stirred at 300 rpm for 90 min. The resulting liquid was then filtered through a plate and frame filter press to obtain filtrate D and filter residue D.

[0050] S5. Pump the filtrate D into the pyrolysis crystallizer. At a stirring speed of 300 rpm, heat it to 75°C and react for 60 min. Then raise the temperature to 95°C and react for 30 min. Recover carbon dioxide throughout the process. Filter the pyrolysis slurry while it is hot through a leaf filter. Wash the wet product with 95°C hot water to obtain lithium carbonate wet product and lithium precipitation mother liquor.

[0051] Carbon dioxide and lithium precipitation mother liquor can be reused using the following methods;

[0052] The method for recycling lithium precipitation mother liquor involves detecting the Na content in the lithium precipitation mother liquor. + The content of Na in the lithium precipitation mother liquor + <20g / L, the above lithium precipitation mother liquor can be returned to S2 to replace purified water for preparing lithium carbonate slurry, realizing a closed-loop circulation of lithium precipitation mother liquor; if the Na content in the lithium precipitation mother liquor is ... + For concentrations >20g / L, the lithium precipitation mother liquor is pumped into an evaporator to concentrate it to 40% of its original volume. The concentrate is then pumped into a cooling crystallizer to cool it to 20°C to precipitate salt. After filtration to remove salt, the mother liquor is returned to the S2 cycle.

[0053] The method for carbon dioxide recycling is to collect the carbon dioxide released during the pyrolysis crystallization process, remove water by condensation, and then pressurize it to 1.2 MPa to return it to the carbonization process of S2 for recycling.

[0054] S6. The wet lithium carbonate product is fed into a vacuum dryer and dried at 95°C under a vacuum of less than 100Pa until the moisture content is ≤0.2% to obtain battery-grade lithium carbonate.

[0055] Example 3

[0056] This embodiment provides a method for preparing battery-grade lithium carbonate using lithium carbonate from salt lakes, including the following steps:

[0057] S1. Crude lithium carbonate from salt lake brine and purified water were added to a ball mill at a mass ratio of 1:5. Ethanolamine, at a molar ratio of twice that of silicon in the crude lithium carbonate, was added. The ball milling was carried out at 20 rpm for 8 hours with a material-to-ball ratio of 1:1.8. The slurry after ball milling was pumped into a reaction vessel. A 70% sodium hydroxide solution was added to the slurry until the sodium hydroxide concentration in the slurry reached 40%. The temperature was raised to 80°C, and the mixture was stirred at 200 rpm for 90 minutes. The mixture was filtered while hot and washed with 80°C hot water to obtain filtrate A and filter residue A.

[0058] After purification, filtrate A is returned to S1 for the preparation of sodium hydroxide solution. The specific method involves determining the silicon and boron content in filtrate A and calculating the required Ca content. 2+ Add 20% lime slurry to filtrate A at 1.05 times the theoretical dosage, stir at 200 rpm for 120 min, let stand for 30 min after the reaction is complete, and filter using a plate and frame filter press to obtain purified filtrate A. Add solid sodium hydroxide to adjust the sodium hydroxide concentration in filtrate A to 50%.

[0059] S2. Add filter residue A and purified water to the carbonation reactor at a mass ratio of 1:30 and stir at 200 rpm for 5 min to obtain a uniform lithium carbonate slurry. Continuously introduce carbon dioxide into the lithium carbonate slurry and react at a pressure of 0.2 MPa and a temperature of 40℃ for 150 min until the lithium carbonate dissolves into lithium bicarbonate. After the reaction is completed, filter the carbonation liquid through a plate and frame filter press to obtain filter residue B and filtrate B.

[0060] S3. Pump filtrate B into the primary impurity removal vessel, determine the Si content in filtrate B, add magnesium chloride to filtrate B according to the molar ratio of Si to Mg of 1:4, stir at 200 rpm, react for 30 min, and then filter through a plate and frame filter press to obtain filtrate C and filter residue C.

[0061] S4. Pump filtrate C into the secondary impurity removal reactor and determine the Ca content in filtrate C. 2+ To determine the content, sodium oxalate was added at 1.3 times the molar amount of calcium ions in filtrate C. The mixture was stirred at 200 rpm for 120 min. The resulting liquid was filtered through a plate and frame filter press to obtain filtrate D and filter residue D.

[0062] S5. Pump the filtrate D into the pyrolysis crystallizer. At a stirring speed of 350 rpm, heat it to 70°C and react for 90 min. Then raise the temperature to 90°C and react for 60 min. Recover carbon dioxide throughout the process. Filter the pyrolysis slurry while it is hot through a leaf filter. Wash the wet product with 90°C hot water to obtain lithium carbonate wet product and lithium precipitation mother liquor.

[0063] Carbon dioxide and lithium precipitation mother liquor can be reused using the following methods;

[0064] The method for recycling lithium precipitation mother liquor involves detecting the Na content in the lithium precipitation mother liquor. + The content of Na in the lithium precipitation mother liquor + <20g / L, the above lithium precipitation mother liquor can be returned to S2 to replace purified water for preparing lithium carbonate slurry, realizing a closed-loop circulation of lithium precipitation mother liquor; if the Na content in the lithium precipitation mother liquor is ... + For concentrations >20g / L, the lithium precipitation mother liquor is pumped into an evaporator to concentrate it to 30% of its original volume. The concentrate is then pumped into a cooling crystallizer to cool it to 30°C to precipitate salt. After filtration to remove salt, the mother liquor is returned to the S2 cycle.

[0065] The method for carbon dioxide recycling is to collect the carbon dioxide released during the pyrolysis crystallization process, remove water by condensation, and then pressurize it to 0.8 MPa to return it to the carbonization process of S2 for recycling.

[0066] S6. The wet lithium carbonate product is fed into a vacuum dryer and dried at 85°C under a vacuum of less than 100Pa until the moisture content is ≤0.2% to obtain battery-grade lithium carbonate.

[0067] Comparative Example 1

[0068] The method in Example 1 differs in that the crude lithium carbonate from the salt lake brine is not treated in S1 but directly enters S2, that is, the crude lithium carbonate from the salt lake brine is carbonized by preparing a lithium carbonate slurry with purified water.

[0069] Comparative Example 2

[0070] The method of Example 1 differs in that, in S1, crude lithium carbonate from salt lake brine and purified water are added to a ball mill at a mass ratio of 1:1.3, with a material-to-ball ratio of 1:1.6, and the mixture is ball-milled at 30 rpm for 7 hours. The ball-milled slurry is then pumped into a reaction vessel, and a 50% sodium hydroxide solution is added to the resulting slurry until the sodium hydroxide concentration in the slurry is 30%. The temperature is raised to 75°C, and the mixture is stirred at 200 rpm for 80 minutes. The mixture is then filtered while hot, and washed with 75°C hot water to obtain filtrate A and filter residue A.

[0071] Comparative Example 3

[0072] The method of Example 1 differs in that, in S1, crude lithium carbonate from salt lake brine and purified water are fed into a ball mill at a mass ratio of 1:1.3. Ethanolamine, which is three times the molar amount of silicon in the crude lithium carbonate, is added to the ball mill. The ball-to-material ratio is 1:1.6. The ball milling is carried out at 30 rpm for 7 hours. The slurry after ball milling is pumped into a reaction vessel. A 50% sodium hydroxide solution is added to the slurry until the sodium hydroxide concentration in the slurry is 30%. The mixture is stirred at 200 rpm at room temperature for 80 minutes. After filtration, the mixture is washed with purified water to obtain filtrate A and filter residue A.

[0073] Comparative Example 4

[0074] The method is the same as in Example 1, except that magnesium chloride is added to filtrate B in S3 at a molar ratio of Si to Mg of 1:1.

[0075] Comparative Example 5

[0076] The method of Example 1 is different in that S4 is not involved, and the filtrate D of S3 is directly pyrolyzed according to the method in S5.

[0077] Comparative Example 6

[0078] The method of Example 1 is different in that the pyrolysis method in S5 is as follows: the filtrate D is pumped into the pyrolysis crystallizer, and the temperature is raised to 90°C for 150 min at a stirring speed of 300 rpm. Carbon dioxide is recovered throughout the process. The pyrolysis slurry is filtered while hot by a leaf filter and the wet product is washed with 90°C hot water to obtain lithium carbonate wet product and lithium precipitation mother liquor.

[0079] Test case

[0080] The lithium carbonate prepared in the examples and comparative examples was tested for content and impurities according to YS / T582-2023. The lithium carbonate recovery rate was calculated as follows: lithium carbonate recovery rate = (mass of battery-grade lithium carbonate × purity) / (mass of crude lithium carbonate from salt lake × purity) × 100%. The results are shown in Table 1 below.

[0081] Table 1: Test results for preparing battery-grade lithium carbonate from lithium carbonate in salt lakes

[0082]

[0083] As can be seen from the above, the method provided in this application embodiment is used to prepare battery-grade lithium carbonate from lithium carbonate in salt lakes. It can be well used for the purification of crude lithium carbonate in salt lakes. The lithium carbonate content and impurities prepared meet the quality requirements of battery-grade lithium carbonate (Li2CO3-D1), and the lithium carbonate recovery rate is high.

[0084] In Comparative Example 1, the crude lithium carbonate from the salt lake brine was not treated with S1. The resulting lithium carbonate had a low main content and the removal of many impurities was not ideal. This indicates that directly purifying the crude lithium carbonate from the salt lake brine using carbonation, impurity removal and pyrolysis processes is not very effective.

[0085] In Comparative Example 2, no ethanolamine was added during the ball milling process of S1, and the main lithium carbonate content and many impurities were still high. This indicates that alkaline washing with sodium hydroxide solution before carbonation helps to purify crude lithium carbonate from salt lake brine, but the impurity removal effect is still not good, and the prepared lithium carbonate product does not meet the requirements for battery-grade lithium carbonate.

[0086] In Comparative Example 3, S1 was added to a sodium hydroxide solution and reacted at room temperature. The main lithium carbonate content was low and many impurities were still high, indicating that the alkaline washing and impurity removal effect was not good under room temperature conditions. The prepared lithium carbonate product did not meet the requirements for battery-grade lithium carbonate.

[0087] In Comparative Example 4, magnesium chloride was added to filtrate B in S3 at a molar ratio of Si to Mg of 1:1. The main content of lithium carbonate and Si did not meet the requirements for battery-grade lithium carbonate.

[0088] In Comparative Example 5, the filtrate D prepared in S3 was not purified again by sodium oxalate in S4 and was directly pyrolyzed in S5. The resulting lithium carbonate had a lithium carbonate content and Ca content that did not meet the requirements for battery-grade lithium carbonate.

[0089] In Comparative Example 6, S5 was directly heated to 90℃ for thermal desorption of lithium, resulting in a reduced lithium carbonate recovery rate and the main lithium carbonate content not meeting the requirements for battery-grade lithium carbonate.

[0090] The particle size of the battery-grade lithium carbonate prepared in Examples 1-3 was further measured. The particle size D of the battery-grade lithium carbonate prepared in Example 1 was... 10 It is 2.5μm, D 50 It is 5.1 μm, D 90 The particle size D of the battery-grade lithium carbonate prepared in Example 2 is 12.4 μm. 10 It is 3.1 μm, D 50 It is 7.6 μm, D 90 The particle size D of the battery-grade lithium carbonate prepared in Example 3 is 14.8 μm. 10 It is 2.9 μm, D 50 It is 6.3 μm, D 90 The particle size of the battery-grade lithium carbonate prepared in the above examples is 13.7 μm, which meets the requirements.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit them; although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of this application or equivalent substitutions can be made to some technical features, all of which should be covered within the scope of the technical solutions claimed in this application.

Claims

1. A method for preparing battery-grade lithium carbonate from lithium carbonate in salt lakes, characterized in that, Includes the following steps: S1. Add purified water and ethanolamine (2-4 times the molar amount of silicon in the crude lithium carbonate) to the crude lithium carbonate from the salt lake brine, and perform wet ball milling to prepare crude lithium carbonate slurry. Add sodium hydroxide to the slurry after ball milling until the sodium hydroxide concentration in the slurry is 20-40%. Stir and react at 70-80℃ for 60-90 min. Filter and wash while hot to obtain filtrate A and filter residue A. S2. Prepare lithium carbonate slurry by using purified water to filter residue A. Introduce carbon dioxide into the lithium carbonate slurry and react for 120-150 min at a pressure of 0.2-0.5 MPa and a temperature of 30-40℃ to obtain carbonized liquid. Filter the carbonized liquid to obtain filter residue B and filtrate B. S3. Determine the Si content in filtrate B. Add magnesium chloride to filtrate B according to the molar ratio of Si to Mg of 1:2-4. Stir and react for 20-30 minutes, then filter to obtain filtrate C and filter residue C. S4. Determine the Ca content in filtrate C. Add sodium oxalate at 1.1-1.3 times the molar amount of Ca in filtrate C, stir and react for 90-120 min, and filter the reaction solution to obtain filtrate D and filter residue D. S5. Pyrolysis crystallization of filtrate D, and hot filtration and washing of pyrolysis slurry to obtain wet lithium carbonate and lithium precipitation mother liquor. S6. Dry the wet lithium carbonate to obtain battery-grade lithium carbonate; S1 also includes purifying filtrate A and returning it to S1 for use in preparing sodium hydroxide solution. The purification method in S1 involves determining the silicon and boron content in filtrate A and calculating the required Ca. 2+ Add lime slurry to filtrate A at 1.05-1.2 times the theoretical dosage, stir at 200-300 rpm for 90-120 min, let stand for 30-60 min after the reaction is complete, and then filter to obtain purified filtrate A. S5 also includes the detection of Na in lithium precipitation mother liquor. + The content of Na in the lithium precipitation mother liquor + If the concentration is <20g / L, the lithium precipitation mother liquor will be returned to S2 to replace purified water for the preparation of lithium carbonate slurry, thus realizing a closed-loop circulation of the lithium precipitation mother liquor. If Na in the lithium precipitation mother liquor + For concentrations >20g / L, pump the lithium precipitation mother liquor into an evaporator to concentrate it to 30-40% of its original volume. Then, pump the concentrate into a cooling crystallizer to cool it to 20-30℃ to precipitate salt. After filtration to remove salt, return the mother liquor to the S2 cycle.

2. The method for preparing battery-grade lithium carbonate from lithium carbonate in salt lakes according to claim 1, characterized in that, The wet ball milling process in S1 is as follows: the material-to-water ratio is controlled at 1:1.2-1.

5. Purified water is added to the crude lithium carbonate, and then ethanolamine with a molar amount of 2-4 times that of silicon in the crude lithium carbonate is added. The material-to-ball ratio is 1:1.5-1.8, and the mixture is ball-milled at 20-30 rpm for 6-8 hours.

3. The method for preparing battery-grade lithium carbonate from lithium carbonate in salt lakes according to claim 1, characterized in that, In S1, the sodium hydroxide is a sodium hydroxide solution with a concentration of 40-70%.

4. The method for preparing battery-grade lithium carbonate from lithium carbonate in salt lakes according to claim 1, characterized in that, In S2, the method for preparing lithium carbonate slurry using purified water for filter residue A is as follows: filter residue A and purified water are added to the carbonation reactor at a mass ratio of 1:20-30, and stirred at 200-300 rpm for 5-10 minutes to obtain a uniform lithium carbonate slurry.

5. The method for preparing battery-grade lithium carbonate from lithium carbonate in salt lakes according to claim 1, characterized in that, In S5, the pyrolysis crystallization method is as follows: the filtrate D is pumped into the pyrolysis crystallizer, and the temperature is first raised to 70-75℃ for 60-90 min at a stirring speed of 300-350 rpm, and then the temperature is raised to 90℃-95℃ for 30-60 min. The pyrolysis slurry is filtered while hot and washed with hot water at 90-95℃ to obtain lithium carbonate wet product and lithium precipitation mother liquor.

6. The method for preparing battery-grade lithium carbonate from lithium carbonate in salt lakes according to claim 1, characterized in that, S5 also includes the collection of carbon dioxide released during the pyrolysis crystallization process. The collected carbon dioxide is dehydrated by condensation and then pressurized to 0.8-1.2 MPa before being returned to the carbonization process of S2 for recycling.

7. A method for preparing battery-grade lithium carbonate from lithium carbonate in salt lakes according to claim 1, characterized in that, In S6, the drying method is to send the wet lithium carbonate product into a vacuum dryer and dry it at a vacuum degree below 100 Pa and a temperature of 80-95°C until the moisture content is ≤0.2% to obtain battery-grade lithium carbonate.

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