High-purity lithium carbonate production process

Abstract

A high-purity lithium carbonate production process for producing high-purity lithium carbonate that can be used in new energy lithium battery applications, belonging to the technical field of lithium carbonate production. The high-purity lithium carbonate production process comprises the following steps: slurry preparation, carbonation, crude purification, pipeline demagnetization, fine purification, pyrolysis, centrifugal dewatering, stirring and washing, and drying. Directed at the problems existing in a current production process of preparing high-purity lithium carbonate, such as low efficiency, high cost, low purity, process complexity and high pollution, the present production process, by means of performing optimization and improvement, achieves preparation of lithium carbonate having a purity of up to 99.99%. The production process has a short flow and high efficiency, and realizes recovery and reuse of a mother liquor, which is beneficial to improving product yield, reducing production costs and wastewater treatment costs, and reducing environmental pollution.

Description

A high-purity lithium carbonate production process Technical Field

[0001] The present invention belongs to the technical field of lithium carbonate production, specifically to the production of high-purity lithium carbonate that can be used in new energy lithium batteries, and more particularly to a high-purity lithium carbonate production process. Background Art

[0002] Electrochemical energy storage technology, as a core energy storage technology, continues to deepen and innovate. Lithium-ion batteries account for 86.3% of electrochemical energy storage and have the advantages of high operating voltage, high energy density, long cycle life, and low environmental pollution. They are widely used in military equipment, aerospace, electric vehicles, digital products and other fields. They are one of the most promising new generation energy storage devices. High-purity lithium carbonate is one of the core raw materials for lithium-ion batteries. It is mainly used in the preparation of high-end lithium-ion battery positive electrode materials and battery-grade lithium fluoride. At present, the main methods for preparing high-purity lithium carbonate are recrystallization, electrolysis, Zinfl-Harder-Dauth method, causticization carbonization method and precipitation method.

[0003] Recrystallization method: The lithium carbonate recrystallization method is based on the inverse solubility of lithium carbonate and the characteristic that the amount of solubility of impurity salts increases with increasing temperature, so as to achieve the purpose of removing impurities and purifying lithium carbonate. Lithium carbonate is dissolved in deionized water, the temperature is increased to dissolve, and then vacuum filtered and cooled to crystallize, thereby obtaining high-purity lithium carbonate. This method has simple steps, can be operated continuously, has low cost, and can effectively remove impurities in lithium carbonate. However, due to the low solubility of lithium carbonate in water and the slow dissolution rate, a large amount of solvent is required for recrystallization, the production cycle is long, the efficiency is low, and it is not suitable for application in actual production.

[0004] Electrolysis: The anode solution is LiCl solution, the cathode solution is LiOH solution, and the electrolysis process is carried out using an ion exchange membrane as a diaphragm. After complete electrolysis, hydrochloric acid is generated in the anode chamber, and a high-purity lithium hydroxide solution is generated in the cathode chamber. CO2 is introduced into the cathode solution and reacts to produce lithium carbonate. Compared with traditional electrolysis, this method eliminates the step of generating alkaline solution. The production process does not involve strong acids or strong bases, simplifying the process flow and reducing the risk of equipment corrosion. However, the toxic chlorine gas generated at the anode can worsen the working environment. Furthermore, the electrolysis process is energy-intensive and the ion exchange membranes used are expensive, increasing production costs and hindering industrial production.

[0005] Zinfl-Harder-Dauth method: dissolve crude lithium carbonate in acetic acid and then precipitate Ca with (NH4)2C2O4 2+ , using Ba(OH)2 to precipitate Mg 2+ , add H2SO4 to remove Ba 2+The mixture is filtered and evaporated to dryness, and the ammonium salts are removed by heating. The resulting solid is dissolved in HCl and purified (NH4)2CO3 is added to obtain purified lithium carbonate. The Zinfl-Harder-Dauth method is a traditional method for purifying lithium carbonate, which involves a large number of reagents and still fails to meet high purity requirements.

[0006] Causticization carbonation method: Use refined lime milk to causticize crude lithium carbonate to form LiOH solution, and Ca 2+ Mg 2+ Then they are precipitated in the form of CaCO3 and Mg(OH)2 respectively. After filtering and cooling, a small amount of LiOH·H2O will be precipitated from the solution. Then a certain amount of CO2 is introduced into the remaining solution to precipitate Ca 2+ After filtration and impurity removal, the filtrate is carbonized to obtain purified Li2CO3. The causticizing carbonization method can effectively remove calcium and magnesium impurities, and recycling the mother liquor can reduce Li loss. However, this method has high requirements for lime milk and strict control of parameters such as temperature. It is difficult to operate in practice, and the loss rate of lithium included in the precipitate is high.

[0007] Precipitation method: Lower-purity Li2CO3 is slurried with deionized water. CO2 is added to form water-soluble LiHCO3, which is then filtered to remove insoluble impurities. LiOH is then added to the filtrate to form higher-purity Li2CO3. This method produces higher-purity Li2CO3 and makes it easier to control the purity and particle size of the product. However, it requires higher-purity LiOH, which is more expensive, requires a more robust reaction ratio, and requires strict reaction conditions.

[0008] Therefore, there is an urgent need to develop a high-purity lithium carbonate preparation process that is efficient, low-cost, simple in process, highly operable, and has low environmental pollution. Chinese patent [CN 116903005 A] provides a method for preparing high-purity lithium carbonate from crude lithium carbonate. The crude lithium carbonate is subjected to external field coupled slurry mixing, water washing, shear carbonization, ion exchange, impurity removal, and shear thermal decomposition to produce high-purity lithium carbonate, thereby achieving high-value utilization of lithium-containing resources. This method is simple in process and has outstanding advantages such as strong raw material adaptability, high impurity removal efficiency, low reagent consumption, high metal recovery rate, and clean and environmentally friendly. However, how to screen out ion exchange resins that chelate specific functional groups to achieve selective and efficient removal of impurity ions in LiHCO3 solution becomes the main cost limitation of this method. The carbonization decomposition method involves slurrying crude lithium carbonate with deionized water. CO₂ gas is introduced under stirring to convert the slightly soluble Li₂CO₃ into soluble LiHCO₃. Impurities that are not hydrogenated are removed by filtration. The purified filtrate is then placed in another container, stirred, and heated. The LiHCO₃ gradually converts to precipitated Li₂CO₃, which is then filtered to obtain purified Li₂CO₃. This method can remove most impurities and is highly operational. However, the lithium carbonate produced by the traditional carbonization decomposition method has low purity, making it difficult to meet the requirements for battery cathode materials and battery-grade lithium fluoride. Furthermore, the traditional carbonization decomposition method directly evaporates and concentrates the pyrolysis mother liquor, significantly increasing production costs and placing a certain burden on the environment. Summary of the Invention

[0009] In view of the problems of low efficiency, high cost, low purity, complex process and high pollution in the current production process for preparing high-purity lithium carbonate, the present invention optimizes and improves the production process of lithium carbonate to achieve the preparation of lithium carbonate with a purity of up to 99.99%. The production process is short and efficient, and the mother liquor is recovered and reused, which is conducive to improving product yield, reducing production costs and wastewater treatment costs, and reducing pollution to the environment.

[0010] The present invention provides a high-purity lithium carbonate production process, which comprises the following steps:

[0011] S1 slurrying: add industrial lithium carbonate to pure water or the mother liquor separated by centrifugation, stir and slurry at a stirring speed of 500-2000 r / min for 8-12 hours to fully disperse;

[0012] S2 Carbonization: Add the slurry liquid into the carbonization kettle, continuously introduce carbon dioxide gas, and stir the slurry liquid at a stirring speed of 500-1000 r / min. Lithium carbonate reacts with carbon dioxide to generate a soluble lithium bicarbonate solution until the slurry liquid changes from a white suspension state to a relatively clear liquid state;

[0013] S3 crude purification: the generated lithium bicarbonate solution is passed into a plate and frame filter for filter pressing to remove and collect insoluble impurities such as iron, manganese, and silicon in the lithium bicarbonate solution and send it to acid dissolution purification for lithium precipitation;

[0014] S4 Pipeline Demagnetization: Pre-immerse the pipeline through which lithium bicarbonate will flow in a dilute hydrochloric acid solution with a concentration of 0.01-0.1 M for 2-5 hours, then rinse the pipeline with clean water until there is no obvious solid impurities in the cleaning solution to remove magnetic substances in the pipeline;

[0015] S5 fine purification: The roughly purified lithium bicarbonate solution flows into a precision filter through a demagnetization pipe for fine purification, and the concentrations of lithium ions, sodium ions, potassium ions, chloride ions, and sulfate ions in the lithium bicarbonate solution are detected and controlled;

[0016] S6 Pyrolysis: The finely purified lithium bicarbonate solution is transferred to a pyrolysis kettle and heated with steam to decompose the lithium bicarbonate solution to produce lithium carbonate and carbon dioxide. The reaction is complete until no obvious bubbles are present. The lithium ion concentration in the lithium bicarbonate solution is detected and controlled.

[0017] S7 Centrifugal Drying: The pyrolyzed liquid is transferred to a centrifuge for solid-liquid separation. The centrifuged liquid is collected as the mother liquor and used as the bottom liquid of the front-stage raw material slurry tank or as washing water for the battery-grade lithium carbonate line.

[0018] S8: The solids after centrifugation are put into the stirring and washing tank and stirred with pure water to remove potassium and sodium impurities on the surface of the solids. The slurry after stirring and washing in the stirring and washing tank is transferred to the centrifuge for solid-liquid separation. The solids are packed in ton bags to obtain high-purity lithium carbonate wet products. The washing liquid is collected as the mother liquor and transferred to the front-stage raw material slurry tank as the bottom liquid or the washing water for the battery-grade lithium carbonate line;

[0019] S9 Drying: Put the high-purity lithium carbonate wet product into the dryer, set the temperature, and dry it to obtain a high-purity lithium carbonate product.

[0020] In some embodiments, the mass ratio of industrial lithium carbonate to pure water or the mother liquor separated by centrifugation in step S1 is 1:25-30.

[0021] In some embodiments, the flow rate of the carbon dioxide gas in step S2 is 100-300 m3 / min.

[0022] In some embodiments, the filtration pressure of the plate and frame filter in step S3 is 0.3-0.5 MPa.

[0023] In some embodiments, the control indicators of the concentrations of lithium ions, sodium ions, potassium ions, chloride ions, and sulfate ions in the lithium bicarbonate solution in step S5 are: lithium ions are 7.6-9 g / L, potassium ions are not higher than 0.3 g / L, sodium ions are not higher than 0.5 g / L, chloride ions are not higher than 0.5 g / L, and sulfate ions are not higher than 0.5 g / L.

[0024] In some embodiments, in step S6, the temperature of the lithium bicarbonate solution is raised to 90-100⁰C using steam.

[0025] In some embodiments, the concentration of lithium ions in the lithium bicarbonate solution in step S6 is controlled to be no higher than 2.5 g / L.

[0026] In some embodiments, the centrifugal speed of the centrifuge in step S7 is 7000-10000 r / min.

[0027] In some embodiments, the mass ratio of solid to pure water in step S8 is 1:3-5.

[0028] In some embodiments, the temperature of the drying machine in step S9 is set to 90-120⁰C, and the drying time is 3-6 hours.

[0029] (1) The preparation process of the present invention is simple and does not require the use of additional chemical reagents, which can greatly reduce production costs and reduce environmental pollution;

[0030] (2) The present invention collects and recycles the pyrolysis mother liquor and the cleaning liquid as the slurry bottom liquid without evaporation and concentration, which can reduce the use of steam and thus reduce production costs. The cost per ton of pyrolysis mother liquor and cleaning liquid can be reduced by more than 1,000 yuan;

[0031] (3) The present invention removes insoluble impurities in the lithium carbonate solution step by step through processes such as crude purification, pipeline demagnetization and fine purification, so that the purity of the prepared lithium carbonate is relatively high, reaching above 99.999%;

[0032] (4) The present invention can improve the yield of lithium carbonate product by recollecting insoluble impurities for acid dissolution and collecting mother liquor and washing liquid as new slurry, and the yield can reach more than 90%. Implementation Method

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings, technical process steps, specific implementation conditions and materials in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example 1

[0035] Add industrial lithium carbonate to pure water or mother liquor separated by centrifugation. The mass ratio of industrial lithium carbonate to pure water or mother liquor separated by centrifugation is 1:25. Stir and mix the mixture for 12 hours at a stirring speed of 2000 r / min to fully disperse the mixture. Add the slurry into the carbonization kettle and continue to introduce carbon dioxide gas at a flow rate of 100 m 3 / min, stir the slurry at a stirring speed of 1000 r / min, and the lithium carbonate reacts with carbon dioxide to generate a soluble lithium bicarbonate solution until the slurry solution changes from a white suspended state to a relatively clear liquid state. The generated lithium bicarbonate solution is filtered into a plate and frame filter with a pressure of 0.5 MPa to remove and collect insoluble impurities such as iron, manganese, and silicon in the lithium bicarbonate solution and send it to acid dissolution for purification and lithium precipitation. The pipeline through which lithium bicarbonate needs to flow in the subsequent process is pre-soaked with a dilute hydrochloric acid solution with a concentration of 0.1 M for 2 hours, and then the pipeline is cleaned with clean water until there is no obvious solid impurities in the cleaning liquid to remove the magnetic substance in the pipeline. The crudely purified lithium bicarbonate solution is passed through a demagnetization pipe and into a precision filter for fine purification. The concentrations of lithium ions, sodium ions, potassium ions, chloride ions, and sulfate ions in the lithium bicarbonate solution are measured as follows: lithium ion 8.1 g / L, potassium ion 0.12 g / L, sodium ion 0.31 g / L, chloride ion 0.29 g / L, and sulfate ion 0.37 g / L. The finely purified lithium bicarbonate solution is transferred to a pyrolysis kettle and heated to 95°C with steam. This decomposes the lithium bicarbonate solution, producing lithium carbonate and carbon dioxide. The reaction is complete until no bubbles are noticeable. The lithium ion concentration in the lithium bicarbonate solution is measured at 2.44 g / L. The pyrolysis liquid is transferred to a centrifuge for solid-liquid separation at a centrifugal speed of 7000 r / min. The centrifuge liquid is collected as the mother liquor and used as the bottom liquid in the upstream raw material slurry tank or as washing water for the battery-grade lithium carbonate line. The solid after centrifugation is put into a stirring and washing tank and stirred and washed with pure water. The mass ratio of pure water to solid is 1:3. The potassium and sodium impurities on the surface of the solid are removed. The slurry after stirring and washing in the stirring and washing tank is transferred to a centrifuge for solid-liquid separation. The solid is packed in ton bags to obtain a high-purity lithium carbonate wet product. The washing liquid is collected as a mother liquor and transferred to the front-end raw material slurry tank as a bottom liquid or battery-grade lithium carbonate line washing water. The high-purity lithium carbonate wet product is put into a dryer, set the temperature to 100⁰C, and dried for 5 hours to obtain a high-purity lithium carbonate product. The obtained high-purity lithium carbonate is subjected to various performance tests (test results are shown in Table 1), and its purity is measured to be 99.9993%. The impurity content of potassium, sodium, calcium, and magnesium is less than the national standard YS / T 546-2021 standard for high-purity lithium carbonate. It is calculated that the lithium carbonate yield of the method of this embodiment 1 is 93.1%.

[0036] Table 1 Test results of high-purity lithium carbonate prepared in Example 1

[0037] Example 2

[0038] Add industrial lithium carbonate to pure water or mother liquor separated by centrifugation, the mass ratio of industrial lithium carbonate to pure water or mother liquor separated by centrifugation is 1:30, stir and slurry for 8 hours at a stirring speed of 500 r / min to fully disperse. Transfer the slurry liquid into the carbonization kettle, and continuously introduce carbon dioxide gas at a flow rate of 300 m 3 / min, stir the slurry at a stirring speed of 1000 r / min, and the lithium carbonate reacts with carbon dioxide to generate a soluble lithium bicarbonate solution until the slurry solution changes from a white suspended state to a relatively clear liquid state. The generated lithium bicarbonate solution is filtered into a plate and frame filter with a pressure of 0.4 MPa to remove and collect insoluble impurities such as iron, manganese, and silicon in the lithium bicarbonate solution and send it to acid dissolution for purification and lithium precipitation. The pipeline through which lithium bicarbonate needs to flow in the subsequent process is pre-soaked with a dilute hydrochloric acid solution with a concentration of 0.05 M for 4 hours, and then the pipeline is cleaned with clean water until there is no obvious solid impurities in the cleaning liquid to remove the magnetic substance in the pipeline. The crudely purified lithium bicarbonate solution is passed through a demagnetization pipe and into a precision filter for fine purification. The concentrations of lithium ions, sodium ions, potassium ions, chloride ions, and sulfate ions in the lithium bicarbonate solution are measured as follows: lithium ion 8.9 g / L, potassium ion 0.09 g / L, sodium ion 0.22 g / L, chloride ion 0.18 g / L, and sulfate ion 0.31 g / L. The finely purified lithium bicarbonate solution is transferred to a pyrolysis kettle and heated to 100°C with steam. This decomposes the lithium bicarbonate solution, producing lithium carbonate and carbon dioxide. The reaction is complete until no bubbles are noticeable. The lithium ion concentration in the lithium bicarbonate solution is 2.48 g / L. The pyrolysis liquid is transferred to a centrifuge for solid-liquid separation at a centrifugal speed of 10,000 r / min. The centrifuge liquid is collected as the mother liquor and used as the bottom liquid in the upstream raw material slurry tank or as washing water for the battery-grade lithium carbonate line. The solid after centrifugation is put into a stirring and washing tank and stirred and washed with pure water. The mass ratio of pure water to solid is 1:4. Potassium and sodium impurities on the surface of the solid are removed. The slurry after stirring and washing in the stirring and washing tank is transferred to a centrifuge for solid-liquid separation. The solid is packed in ton bags to obtain a high-purity lithium carbonate wet product. The washing liquid is collected as a mother liquor and transferred to the front-end raw material slurry tank as a bottom liquid or battery-grade lithium carbonate line washing water. The high-purity lithium carbonate wet product is put into a dryer, set the temperature to 110⁰C, and dried for 4 hours to obtain a high-purity lithium carbonate product. The obtained high-purity lithium carbonate is subjected to various performance tests (test results are shown in Table 2), and its purity is measured to be 99.9994%. The impurity content of potassium, sodium, calcium, and magnesium is less than the national standard YS / T 546-2021 standard for high-purity lithium carbonate. It is calculated that the lithium carbonate yield of the method of this embodiment 2 is 92.4%.

[0039] Table 2 Test results of high-purity lithium carbonate prepared in Example 2

[0040] Example 3

[0041] Add industrial lithium carbonate to pure water or mother liquor separated by centrifugation. The mass ratio of industrial lithium carbonate to pure water or mother liquor separated by centrifugation is 1:28. Stir and mix the mixture for 10 hours at a stirring speed of 500 r / min to fully disperse the mixture. Add the slurry mixture into the carbonization kettle and continue to introduce carbon dioxide gas at a flow rate of 200 m 3 / min, stir the slurry at a stirring speed of 800 r / min, and the lithium carbonate reacts with carbon dioxide to generate a soluble lithium bicarbonate solution until the slurry solution changes from a white suspended state to a relatively clear liquid state. The generated lithium bicarbonate solution is filtered into a plate and frame filter with a pressure of 0.5 MPa to remove and collect insoluble impurities such as iron, manganese, and silicon in the lithium bicarbonate solution and send it to acid dissolution for purification and lithium precipitation. The pipeline through which lithium bicarbonate needs to flow in the subsequent process is pre-soaked with a dilute hydrochloric acid solution with a concentration of 0.08 M for 5 hours, and then the pipeline is cleaned with clean water until there is no obvious solid impurities in the cleaning liquid to remove the magnetic substance in the pipeline. The crudely purified lithium bicarbonate solution is passed through a demagnetization pipe and into a precision filter for fine purification. The concentrations of lithium ions, sodium ions, potassium ions, chloride ions, and sulfate ions in the lithium bicarbonate solution are measured as follows: lithium ion 8.7 g / L, potassium ion 0.11 g / L, sodium ion 0.27 g / L, chloride ion 0.28 g / L, and sulfate ion 0.43 g / L. The finely purified lithium bicarbonate solution is transferred to a pyrolysis kettle and heated to 100°C with steam. This decomposes the lithium bicarbonate solution, producing lithium carbonate and carbon dioxide. The reaction is complete until no bubbles are noticeable. The lithium ion concentration in the lithium bicarbonate solution is 2.49 g / L. The pyrolysis liquid is transferred to a centrifuge for solid-liquid separation at a centrifugal speed of 8000 r / min. The centrifuge liquid is collected as the mother liquor and used as the bottom liquid of the upstream raw material slurry tank or as washing water for the battery-grade lithium carbonate line. The solid after centrifugation is put into a stirring and washing tank and stirred and washed with pure water. The mass ratio of pure water to solid is 1:5 to remove potassium and sodium impurities on the surface of the solid. The slurry after stirring and washing in the stirring and washing tank is transferred to a centrifuge for solid-liquid separation. The solid is packed in ton bags to obtain a high-purity lithium carbonate wet product. The washing liquid is collected as the mother liquor and transferred to the front-end raw material slurry tank as the bottom liquid or the battery-grade lithium carbonate line washing water. The high-purity lithium carbonate wet product is put into the dryer, the temperature is set to 110⁰C, and it is dried for 4 hours to obtain a high-purity lithium carbonate product. The obtained high-purity lithium carbonate is subjected to various performance tests (the test results are shown in Table 3), and its purity is measured to be 99.9991%, and the content of impurities such as potassium, sodium, calcium and magnesium is less than the national standard YS / T 546-2021 standard for high-purity lithium carbonate. It has been calculated that the lithium carbonate yield of the method in Example 3 is 91.9%

[0042] Table 3 Test results of high-purity lithium carbonate prepared in Example 3

[0043] Example 4

[0044] Add industrial lithium carbonate to pure water or mother liquor separated by centrifugation. The mass ratio of industrial lithium carbonate to pure water or mother liquor separated by centrifugation is 1:29. Stir and mix the mixture at a stirring speed of 1500 r / min for 10 hours to fully disperse the mixture. Add the slurry mixture into the carbonization kettle and continuously introduce carbon dioxide gas at a flow rate of 200 m 3 / min, stir the slurry at a stirring speed of 800 r / min, and the lithium carbonate reacts with carbon dioxide to generate a soluble lithium bicarbonate solution until the slurry solution changes from a white suspended state to a relatively clear liquid state. The generated lithium bicarbonate solution is filtered into a plate and frame filter with a pressure of 0.5 MPa to remove and collect insoluble impurities such as iron, manganese, and silicon in the lithium bicarbonate solution and send it to acid dissolution for purification and lithium precipitation. The pipeline through which lithium bicarbonate needs to flow in the subsequent process is pre-soaked with a dilute hydrochloric acid solution with a concentration of 0.06 M for 5 hours, and then the pipeline is cleaned with clean water until there is no obvious solid impurities in the cleaning liquid to remove the magnetic substance in the pipeline. The crudely purified lithium bicarbonate solution is passed through a demagnetizing pipe and into a precision filter for fine purification. The concentrations of lithium ions, sodium ions, potassium ions, chloride ions, and sulfate ions in the lithium bicarbonate solution are measured as follows: lithium ion 8.9 g / L, potassium ion 0.15 g / L, sodium ion 0.37 g / L, chloride ion 0.15 g / L, and sulfate ion 0.46 g / L. The finely purified lithium bicarbonate solution is transferred to a pyrolysis kettle and heated to 100°C with steam. This decomposes the lithium bicarbonate solution, producing lithium carbonate and carbon dioxide. The reaction is complete until no bubbles are noticeable. The lithium ion concentration in the lithium bicarbonate solution is 2.47 g / L. The pyrolysis liquid is transferred to a centrifuge for solid-liquid separation at a centrifugal speed of 9000 r / min. The centrifuge liquid is collected as the mother liquor and used as the bottom liquid in the upstream raw material slurry tank or as washing water for the battery-grade lithium carbonate line. The solid after centrifugation is put into a stirring and washing tank and stirred and washed with pure water. The mass ratio of pure water to solid is 1: 4. The potassium and sodium impurities on the surface of the solid are removed. The slurry after stirring and washing in the stirring and washing tank is transferred to a centrifuge for solid-liquid separation. The solid is packed in ton bags to obtain a high-purity lithium carbonate wet product. The washing liquid is collected as a mother liquor and transferred to the front-end raw material slurry tank as a bottom liquid or battery-grade lithium carbonate line washing water. The high-purity lithium carbonate wet product is put into a dryer, set the temperature to 120⁰C, and dried for 3 hours to obtain a high-purity lithium carbonate product. The obtained high-purity lithium carbonate is subjected to various performance tests (test results are shown in Table 4), and its purity is measured to be 99.9995%. The impurity content of potassium, sodium, calcium, and magnesium is less than the national standard YS / T 546-2021 standard for high-purity lithium carbonate. It is calculated that the direct yield of lithium carbonate of the method of this embodiment 4 is 92.7%.

[0045] Table 4 Test results of high-purity lithium carbonate prepared in Example 4

[0046] Example 5

[0047] Add industrial lithium carbonate to pure water or mother liquor separated by centrifugation. The mass ratio of industrial lithium carbonate to pure water or mother liquor separated by centrifugation is 1:30. Stir and slurry are prepared at a stirring speed of 1800 r / min for 9 hours to fully disperse. Transfer the slurry liquid into the carbonization kettle and continuously introduce carbon dioxide gas. The flow rate of carbon dioxide gas is 150 m 3 / min, stir the slurry at a stirring speed of 1000 r / min, and the lithium carbonate reacts with carbon dioxide to generate a soluble lithium bicarbonate solution until the slurry solution changes from a white suspended state to a relatively clear liquid state. The generated lithium bicarbonate solution is filtered into a plate and frame filter with a pressure of 0.3 MPa to remove and collect insoluble impurities such as iron, manganese, and silicon in the lithium bicarbonate solution and send it to acid dissolution for purification and lithium precipitation. The pipeline through which lithium bicarbonate needs to flow in the subsequent process is pre-soaked with a dilute hydrochloric acid solution with a concentration of 0.05 M for 5 hours, and then the pipeline is cleaned with clean water until there is no obvious solid impurities in the cleaning liquid to remove the magnetic substance in the pipeline. The crudely purified lithium bicarbonate solution is passed through a demagnetization pipe and into a precision filter for fine purification. The concentrations of lithium ions, sodium ions, potassium ions, chloride ions, and sulfate ions in the lithium bicarbonate solution are measured as follows: lithium ion 8.6 g / L, potassium ion 0.188 g / L, sodium ion 0.25 g / L, chloride ion 0.11 g / L, and sulfate ion 0.42 g / L. The finely purified lithium bicarbonate solution is transferred to a pyrolysis kettle and heated to 100°C with steam. This decomposes the lithium bicarbonate solution, producing lithium carbonate and carbon dioxide. The reaction is complete until no bubbles are noticeable. The lithium ion concentration in the lithium bicarbonate solution is measured to be 2.45 g / L. The pyrolysis liquid is transferred to a centrifuge for solid-liquid separation at a centrifugal speed of 10,000 r / min. The centrifuge liquid is collected as the mother liquor and used as the bottom liquid in the upstream raw material slurry tank or as washing water for the battery-grade lithium carbonate line. The solid after centrifugation is put into a stirring and washing tank and stirred and washed with pure water. The mass ratio of pure water to solid is 1:4 to remove potassium and sodium impurities on the surface of the solid. The slurry after stirring and washing in the stirring and washing tank is transferred to a centrifuge for solid-liquid separation. The solid is packed in ton bags to obtain a high-purity lithium carbonate wet product. The washing liquid is collected as a mother liquor and transferred to the front-end raw material slurry tank as a bottom liquid or battery-grade lithium carbonate line washing water. The high-purity lithium carbonate wet product is put into a dryer, set the temperature to 120⁰C, and dried for 3 hours to obtain a high-purity lithium carbonate product. The obtained high-purity lithium carbonate is subjected to various performance tests (test results are shown in Table 5), and its purity is measured to be 99.9993%. The content of impurities such as potassium, sodium, calcium and magnesium is less than the national standard YS / T 546-2021 standard for high-purity lithium carbonate. It is calculated that the lithium carbonate yield of the method in this embodiment 5 is 92.9%.

[0048] Table 5 Test results of high-purity lithium carbonate prepared in Example 5

[0049] Example 6

[0050] Add industrial lithium carbonate to pure water or mother liquor separated by centrifugation. The mass ratio of industrial lithium carbonate to pure water or mother liquor separated by centrifugation is 1:29. Stir and mix the mixture for 11 hours at a stirring speed of 1600 r / min to fully disperse the mixture. Add the slurry mixture into the carbonization kettle and continuously introduce carbon dioxide gas at a flow rate of 240 m 3 / min, stir the slurry at a stirring speed of 900 r / min, and the lithium carbonate reacts with carbon dioxide to generate a soluble lithium bicarbonate solution until the slurry solution changes from a white suspended state to a relatively clear liquid state. The generated lithium bicarbonate solution is filtered into a plate and frame filter with a pressure of 0.4 MPa to remove and collect insoluble impurities such as iron, manganese, and silicon in the lithium bicarbonate solution and send it to acid dissolution for purification and lithium precipitation. The pipeline through which lithium bicarbonate needs to flow in the subsequent process is pre-soaked with a dilute hydrochloric acid solution with a concentration of 0.09 M for 4 hours, and then the pipeline is cleaned with clean water until there is no obvious solid impurities in the cleaning liquid to remove the magnetic substance in the pipeline. The crudely purified lithium bicarbonate solution is passed through a demagnetization pipe and into a precision filter for fine purification. The concentrations of lithium ions, sodium ions, potassium ions, chloride ions, and sulfate ions in the lithium bicarbonate solution are measured as follows: lithium ion 8.77 g / L, potassium ion 0.11 g / L, sodium ion 0.24 g / L, chloride ion 0.22 g / L, and sulfate ion 0.44 g / L. The finely purified lithium bicarbonate solution is transferred to a pyrolysis kettle and heated to 100°C with steam. This decomposes the lithium bicarbonate solution, producing lithium carbonate and carbon dioxide. The reaction is complete until no bubbles are noticeable. The lithium ion concentration in the lithium bicarbonate solution is measured to be 2.49 g / L. The pyrolysis liquid is transferred to a centrifuge for solid-liquid separation at a centrifugal speed of 9000 r / min. The centrifuge liquid is collected as the mother liquor and used as the bottom liquid of the upstream raw material slurry tank or as washing water for the battery-grade lithium carbonate line. The solid after centrifugation is put into a stirring and washing tank and stirred and washed with pure water. The mass ratio of pure water to solid is 1:4 to remove potassium and sodium impurities on the surface of the solid. The slurry after stirring and washing in the stirring and washing tank is transferred to a centrifuge for solid-liquid separation. The solid is packed in ton bags to obtain a high-purity lithium carbonate wet product. The washing liquid is collected as a mother liquor and transferred to the front-end raw material slurry tank as a bottom liquid or battery-grade lithium carbonate line washing water. The high-purity lithium carbonate wet product is put into a dryer, set the temperature to 120⁰C, and dried for 4 hours to obtain a high-purity lithium carbonate product. The obtained high-purity lithium carbonate is subjected to various performance tests (test results are shown in Table 6), and its purity is measured to be 99.9996%. The impurity content of potassium, sodium, calcium, and magnesium is less than the national standard YS / T 546-2021 standard for high-purity lithium carbonate. It is calculated that the lithium carbonate yield of the method in this embodiment 6 is 94.1%.

[0051] Table 6 Test results of high-purity lithium carbonate prepared in Example 6

[0052] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A production process for high-purity lithium carbonate, characterized in that, The high-purity lithium carbonate production process includes the following steps: S1 Pulping: Add industrial lithium carbonate into pure water or the mother liquor separated by centrifugation, and stir and adjust the pulp at a stirring speed of 500 - 2000 r / min for 8 - 12 hours to fully disperse it; S2 Carbonization: Transfer the adjusted pulp liquid into the carbonization kettle, continuously introduce carbon dioxide gas, stir the adjusted pulp liquid at a stirring speed of 500 - 1000 r / min, and react lithium carbonate with carbon dioxide to generate a soluble lithium bicarbonate solution until the adjusted pulp liquid changes from a white suspension state to a relatively clear liquid state; S3 Coarse purification: Feed the generated lithium bicarbonate solution into a plate and frame filter press for pressure filtration, remove and collect insoluble impurities such as iron, manganese, and silicon in the lithium bicarbonate solution, and send them to acid dissolution, purification, and lithium precipitation; S4 Magnetic removal from pipelines: Pre-soak the pipelines through which the subsequent process of lithium bicarbonate needs to flow with a dilute hydrochloric acid solution with a concentration of 0.01 - 0.1 M for 2 - 5 hours, and then wash the pipelines with clean water until there are no obvious solid impurities in the washing liquid to remove magnetic substances in the pipelines; S5 Fine purification: Feed the lithium bicarbonate solution after coarse purification into a precision filter through a magnetic removal pipeline for fine purification, and detect and control the concentrations of lithium ions, sodium ions, potassium ions, chloride ions, and sulfate ions in the lithium bicarbonate solution; S6 Pyrolysis: Transfer the finely purified lithium bicarbonate solution into a pyrolysis kettle, heat it with steam to decompose the lithium bicarbonate solution, generating lithium carbonate and carbon dioxide, fully react until there are no obvious bubbles, and detect and control the lithium ion concentration in the lithium bicarbonate solution; S7 Centrifugal dewatering: Transfer the pyrolyzed slurry into a centrifuge for solid-liquid separation, collect the centrifugate as the mother liquor, and transfer it to be used as the bottom liquid of the front-stage raw material pulping tank or the washing water for the battery-grade lithium carbonate line; S8 Stirring and washing: Put the centrifuged solid into a stirring and washing tank, wash it with pure water to remove potassium and sodium impurities on the surface of the solid. After the slurry in the stirring and washing tank is washed, transfer it to a centrifuge for solid-liquid separation. Pack the solid in a ton bag to obtain a high-purity lithium carbonate wet product. Collect the washing liquid as the mother liquor and transfer it to the front-stage raw material pulping tank as the bottom liquid or the washing water for the battery-grade lithium carbonate line; S9 Drying: Put the high-purity lithium carbonate wet product into a dryer, set the temperature, and conduct drying to obtain a high-purity lithium carbonate product.

2. The high-purity lithium carbonate production process according to claim 1, characterized in that, In the step S1, the mass ratio of industrial lithium carbonate to pure water or the mother liquor separated by centrifugation is 1:25 - 30.

3. The high-purity lithium carbonate production process according to claim 1, characterized in that, The flow rate of carbon dioxide gas in the step S2 is 100~300 m 3 / min.

4. The high-purity lithium carbonate production process according to claim 1, characterized in that, In the step S3, the filtration pressure of the plate and frame filter press is 0.3 - 0.5 MPa.

5. The high-purity lithium carbonate production process according to claim 1, characterized in that, In the step S5, the control indexes for the concentrations of lithium ions, sodium ions, potassium ions, chloride ions, and sulfate ions in the lithium bicarbonate solution are respectively: lithium ions are 7.6 - 9 g / L, potassium ions are not higher than 0.3 g / L, sodium ions are not higher than 0.5 g / L, chloride ions are not higher than 0.5 g / L, and sulfate ions are not higher than 0.5 g / L.

6. The high-purity lithium carbonate production process according to claim 1, characterized in that, In the step S6, use steam to heat the temperature of the lithium bicarbonate solution to 90 - 100 °C.

7. The high-purity lithium carbonate production process according to claim 1, characterized in that, In the step S6, the control index for the lithium ion concentration in the lithium bicarbonate solution is not higher than 2.5 g / L.

8. The high-purity lithium carbonate production process according to claim 1, characterized in that, In the step S7, the centrifugation speed of the centrifuge is 7000 - 10000 r / min.

9. The high-purity lithium carbonate production process according to claim 1, characterized in that, In the step S8, the mass ratio of the solid to pure water is 1:3 - 5.

10. The high-purity lithium carbonate production process according to claim 1, characterized in that, In the step S9, the temperature of the dryer is set at 90 - 120 °C, and the drying time is 3 - 6 h.

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