Method for producing lithium carbonate

Abstract

The invention discloses a method for producing lithium carbonate. The method comprises the following steps: S1, obtaining a lithium bicarbonate solution; s2, evaporating and pyrolyzing the lithium bicarbonate solution in a crystallizer to generate lithium carbonate slurry and a CO2-containing gas phase; the pyrolysis temperature is 40-70 DEG C, and the pressure in the crystallizer is 20-90 kPa; s3, performing liquid-solid separation on the lithium carbonate slurry to obtain a lithium carbonate solid; water vapor of the gas phase part is condensed and then is collected and recycled as condensate water, and CO2 gas is discharged or collected and recycled. The lithium bicarbonate solution is evaporated and pyrolyzed under the negative pressure and low temperature conditions, efficient production of lithium carbonate is achieved, the method has the advantages of being low in energy consumption, small in lithium loss, capable of reducing scaling and the like, meanwhile CO2 can be recycled, and the resource utilization rate is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium carbonate and relates to a method for producing lithium carbonate. Background Art

[0002] Lithium carbonate is the most important lithium salt among lithium compounds and a key raw material for the preparation of other high-purity lithium compounds and lithium alloys. As a core raw material for lithium-ion batteries, battery-grade lithium carbonate (purity ≥99.5%) is used to prepare cathode materials such as lithium cobalt oxide and ternary materials. Its high energy density (170 mAh / g) and thermal stability support the development of new energy vehicles and energy storage systems. With the rapid development of new energy technologies, lithium-ion batteries have made significant progress and breakthroughs in the transportation sector, becoming a core energy source for new energy vehicles and playing a decisive role in their development. Lithium batteries made with battery-grade lithium carbonate offer advantages in quality and performance, reducing external interference, thereby extending the battery's lifespan and increasing the actual driving time of new energy vehicles, significantly promoting the development of the new energy vehicle industry. Furthermore, lithium-ion batteries are widely used in the energy storage sector, where lithium carbonate also plays a vital role, providing support for building a sustainable energy storage and utilization system.

[0003] Lithium carbonate is also widely used in industrial manufacturing. Glass and ceramic industry: Lithium carbonate can be used to manufacture high-borosilicate glass, high-temperature stable ceramics, etc., and can improve the strength, thermal stability, and optical properties of glass and ceramics. For example, in glass manufacturing, it can react with substances such as silicon dioxide and potassium oxide to produce optical glass with advantages such as high refractive index and low dispersion, which is used in optical instruments, television screens, and other fields; in ceramic manufacturing, it reacts with substances such as aluminum oxide to produce high-performance ceramics used in aviation, aerospace, military, and other fields. Metallurgical industry: In the aluminum smelting process, lithium carbonate can be used as an electrolytic bath additive and can also be used to produce aluminum-lithium alloys, significantly improving the mechanical properties and corrosion resistance of the metal, making aluminum alloys more widely used in fields such as aerospace. Lithium carbonate can be used to produce acoustic-grade single crystals and optical-grade single crystals, and is also used in synthetic rubber, dyes, semiconductors, military defense industry, televisions, atomic energy, and other fields.

[0004] Lithium carbonate preparation methods can be categorized by raw material source into lithium ore preparation, brine preparation, and other methods. Lithium ore preparation can be further divided into spodumene sintering and sulfuric acid methods, while brine preparation can be further divided into precipitation, adsorption, extraction, and membrane separation methods.

[0005] CN110656239B discloses a method for extracting lithium by separation and purification by extraction-strip extraction, comprising the following steps: (1) extracting and separating a lithium-containing solution at pH = 10-13 using an extraction system containing a composite extractant to obtain a lithium-loaded organic phase; (2) subjecting the lithium-loaded organic phase obtained in step (1) to a gas-liquid-liquid three-phase phase extraction to obtain a lithium-loaded strip solution; and (3) heat-treating and separating the strip solution obtained in step (2) to obtain a lithium product and a separated mother liquor.

[0006] CN118724028A discloses a method for preparing lithium carbonate using lepidolite, comprising the following steps: S1, mixing lepidolite with sulfate, and sequentially performing roasting, grinding, drying, and countercurrent leaching to obtain a lepidolite leachate; S2, mixing the lepidolite leachate with water in a set ratio, and adding calcium hydroxide to obtain a mixed solution; S3, filtering calcium and magnesium ions from the mixed solution; S4, mixing the mixed solution obtained in step S3 from which calcium and magnesium ions have been filtered with a lithium-extracting organic extractant, and then extracting the solution to obtain a lithium-loaded extractant; S5, mixing the lithium-loaded extractant with water, and washing the solution to obtain a clean lithium-loaded extractant; S6, combining the lithium-loaded extractant obtained in step S5 with water and carbon dioxide, and then performing back extraction to obtain a lithium bicarbonate solution; and S7, removing oil and calcium and magnesium ions from the lithium bicarbonate solution using a resin, and then performing pyrolysis, and then centrifuging the pyrolysis solution to obtain lithium carbonate.

[0007] CN118754166A discloses a method for leaching battery-grade lithium carbonate, the preparation steps of which include: (1) grinding lithium mica, sieving, keeping the sieved powder at 600°C for 2h in a mixed gas atmosphere of hydrogen and argon, cooling, and adding potassium fluoride powder; roasting; leaching with sulfuric acid solution, and solid-liquid separation to obtain a leachate and a leach residue; (2) adding a composite solution of C-undecylcalix[4]hydroquinone and valinomycin in dimethyl sulfoxide to the leachate, and adding anhydrous sodium carbonate to obtain crude lithium carbonate; (3) adding the crude lithium carbonate to deionized water, stirring evenly to form a suspension, passing carbon dioxide gas, filtering to obtain a clear liquid, and evaporating and crystallizing the clear liquid at 80°C in an evaporating dish to obtain the battery-grade lithium carbonate.

[0008] CN119911941A discloses a novel process for preparing battery-grade lithium carbonate from lithium precipitation mother liquor, which comprises mixing quicklime and lithium precipitation mother liquor to adjust the base and remove fluorine; filtering calcium ions in the mixed liquor, calcining the filtered calcium residue, and then supplementing quicklime and carbon dioxide; mixing the obtained filtrate with an organic extractant for extraction; mixing the obtained loaded organic phase with pure water for washing; stripping the obtained washed loaded organic phase; degreasing the obtained stripping solution; decalcifying the degreasing stripping solution through a resin; pyrolyzing the obtained stripping solution and filtering and drying it to obtain battery-grade lithium carbonate.

[0009] Lithium carbonate aqueous solution can be converted into lithium bicarbonate after the introduction of carbon dioxide. Lithium bicarbonate is unstable and only exists in the solution; heating the lithium bicarbonate solution can precipitate lithium carbonate. This reversible reaction is used in the lithium carbonate purification process. The technical solutions of the above-mentioned prior art ultimately obtain lithium carbonate by pyrolyzing the lithium bicarbonate solution. In the existing technical solution, the pyrolysis of the lithium bicarbonate solution is carried out under normal pressure, and the pyrolysis temperature is about 90°C. The high pyrolysis temperature leads to high energy consumption, and a large amount of circulating water is required for cooling after pyrolysis; at the same time, the solubility of lithium carbonate decreases with increasing temperature, and pyrolysis at high temperature can easily lead to scaling of the pyrolysis container. There is an urgent need to improve the preparation process of lithium carbonate and solve these technical problems. Summary of the Invention

[0010] The purpose of the present invention is to provide a method for producing lithium carbonate. In the step of preparing lithium carbonate by pyrolysis of lithium bicarbonate solution, a negative pressure low-temperature pyrolysis method is adopted to reduce the pyrolysis temperature. On the one hand, it can reduce the energy consumption of the pyrolysis process and reduce the amount of circulating water used in the cooling process; on the other hand, the pyrolysis temperature is reduced, and the solubility of lithium carbonate is increased, which is conducive to reducing scaling in the pyrolyzer and forming lithium carbonate solids with larger crystalline particles. The method provided by the present invention is applicable to the preparation of lithium carbonate from various raw materials such as brine, lithium ore, and waste lithium batteries, or the preparation of high-purity lithium carbonate by purification of crude lithium carbonate, as long as lithium carbonate is ultimately prepared by pyrolysis of lithium bicarbonate solution. The purpose of the present invention is achieved through the following technical solutions.

[0011] A method for producing lithium carbonate comprises the following steps: S1 obtains lithium bicarbonate solution; S2 causes the lithium bicarbonate solution to evaporate and pyrolyze in the crystallizer to generate lithium carbonate slurry and a gas phase containing CO2; the pyrolysis temperature is 40-70°C and the pressure in the crystallizer is 20-90kPa; S3 separates the lithium carbonate slurry into a liquid-solid state to obtain lithium carbonate solid and pyrolysis mother liquor; the water vapor in the gas phase is condensed and collected for reuse as condensed water, and the CO2 gas is discharged or collected for reuse.

[0012] The method for producing lithium carbonate provided by the present invention reduces the pyrolysis temperature by using a negative pressure low-temperature pyrolysis method. On the one hand, this can reduce the energy consumption of the pyrolysis process and the amount of circulating water used in the cooling process. On the other hand, the reduced pyrolysis temperature increases the solubility of lithium carbonate, which is beneficial to reducing scaling in the pyrolyzer and forming lithium carbonate solids with larger crystalline particles.

[0013] Furthermore, in step S2, the pyrolysis temperature is 50-60°C and the pressure in the crystallizer is 30-70 kPa. Within this temperature and pressure range, a better balance between energy consumption and pyrolysis efficiency is achieved, reducing the risk of equipment scaling.

[0014] Furthermore, the lithium bicarbonate solution of step S1 is continuously fed into the crystallizer, and the lithium carbonate slurry generated in step S2 is continuously extracted by a forced circulation pump; a portion of the extracted lithium carbonate slurry enters step S3 for liquid-solid separation, and the remainder is returned to the outlet pipe of the crystallizer. By continuously feeding the lithium bicarbonate solution and continuously extracting it by the forced circulation pump, continuous production is achieved and production efficiency is improved; by returning a portion of the lithium carbonate slurry to the crystallizer, sufficient thermal decomposition of the lithium bicarbonate is ensured.

[0015] Preferably, the flow rate of the lithium carbonate slurry in the forced circulation pump is 1.5-5 m / s. Within this flow rate range, crystal deposition can be prevented and continuous discharge stability can be ensured.

[0016] Preferably, the average residence time of the lithium bicarbonate solution and lithium carbonate slurry (collectively referred to as materials) in the crystallizer is 1 to 3 hours. If the residence time is too long, the energy consumption is too high; if the residence time is too short, the lithium bicarbonate pyrolysis is incomplete. The average residence time of the materials is determined by controlling the effective volume and pyrolysis capacity of the crystallizer. For example, the pyrolysis capacity of the crystallizer is 3m 3 / h, effective volume is 9m 3 , then the average residence time of the material is 9÷3=3 (h).

[0017] Furthermore, the method for obtaining the lithium bicarbonate solution in step S1 is: extracting the lithium-containing solution with an extractant to obtain a loaded organic phase, stripping the loaded organic phase with a stripping agent to obtain a stripping solution, and removing impurities from the stripping solution to obtain the lithium bicarbonate solution; the stripping agent is CO2 and water or cooled pyrolysis mother liquor, or carbonic acid.

[0018] Preferably, the lithium-containing solution is salt lake brine, waste lithium battery leachate, lithium ore leachate or lithium precipitation mother liquor, and the CO2 gas in step S3 is collected and returned to step S1 for stripping.

[0019] Furthermore, the method for obtaining the lithium bicarbonate solution in step S1 is: leaching the lithium-containing solid material (lithium ore or waste lithium batteries) with sulfuric acid or roasting it with sulfate to obtain a lithium sulfate solution, adding carbonate to the lithium sulfate solution to obtain lithium carbonate, and then introducing CO2 to convert the lithium carbonate into lithium bicarbonate.

[0020] Furthermore, the method for obtaining the lithium bicarbonate solution in step S1 is: adding water to crude lithium carbonate to form a slurry, and introducing CO2 into the slurry to convert the lithium carbonate into lithium bicarbonate.

[0021] Furthermore, the average particle size of the lithium carbonate crystals in the lithium carbonate slurry generated in step S2 is ≥10 μm. Low-temperature pyrolysis of lithium carbonate has high solubility, which is conducive to forming lithium carbonate solids with larger crystal particles, thereby improving product purity and filtration efficiency.

[0022] The present invention has the following beneficial technical effects: the pyrolysis temperature is lowered by adopting a negative pressure low-temperature pyrolysis method, which can, on the one hand, reduce the energy consumption of the pyrolysis process and reduce the amount of circulating water used in the cooling process; on the other hand, the pyrolysis temperature is lowered, and the solubility of lithium carbonate is increased, which is conducive to reducing scaling in the pyrolyzer and forming lithium carbonate solids with larger crystalline particles; the applicability is strong, and it can be applied whether lithium carbonate is prepared from various raw materials such as brine, lithium ore, waste lithium batteries, etc., or high-purity lithium carbonate is prepared by purifying crude lithium carbonate, as long as lithium carbonate is ultimately prepared by pyrolysis of a lithium bicarbonate solution. DETAILED DESCRIPTION

[0023] The following is a clear and complete description of the technical solution of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention. Example 1

[0024] A method for producing lithium carbonate comprises the following steps: S1: extracting salt lake brine with an extractant to obtain a loaded organic phase, and subjecting the loaded organic phase to a gas-liquid-liquid three-phase phase extraction, wherein the gas phase is CO2 gas, the first liquid phase is the product of cooling the pyrolysis mother liquor obtained in step S3, and the second liquid phase is the loaded organic phase to obtain a lithium-loaded strip solution, and the strip solution is refined after deoiling, removing calcium and magnesium to obtain a lithium bicarbonate solution.

[0025] S2 The lithium bicarbonate solution obtained in step S1 is continuously input into the crystallizer, and the lithium bicarbonate solution is evaporated and pyrolyzed in the crystallizer to generate lithium carbonate slurry and a gas phase containing CO2. The pyrolysis temperature is 40°C and the pressure in the crystallizer is 20kPa. The lithium carbonate slurry is continuously extracted by a forced circulation pump, and the flow rate of the lithium carbonate slurry in the forced circulation pump is 2 m / s. 50% of the extracted lithium carbonate slurry is returned to the crystallizer, and the rest enters step S3 for liquid-solid separation. The residence time of the material in the crystallizer is 3h.

[0026] S3: Separating the lithium carbonate slurry into solid and lithium carbonate solid and pyrolysis mother liquor; condensing the water vapor in the gas phase and collecting it as condensed water for reuse; collecting the CO2 gas and returning it to step S1 for stripping. Example 2

[0027] A method for producing lithium carbonate comprises the following steps: S1 Lepidolite is mixed with sulfate and then roasted. The roasted sand is leached with water to obtain a leachate. The leachate is cleaned to obtain a lithium sulfate solution. Sodium carbonate is added to obtain lithium carbonate. CO2 is introduced to convert the lithium carbonate into lithium bicarbonate to obtain a lithium bicarbonate solution.

[0028] S2 The lithium bicarbonate solution obtained in step S1 is continuously input into the crystallizer, and the lithium bicarbonate solution is evaporated and pyrolyzed in the crystallizer to generate lithium carbonate slurry and a gas phase containing CO2. The pyrolysis temperature is 50°C and the pressure in the crystallizer is 30kPa. The lithium carbonate slurry is continuously extracted by a forced circulation pump, and the flow rate of the lithium carbonate slurry in the forced circulation pump is 3 m / s. 40% of the extracted lithium carbonate slurry is returned to the crystallizer, and the rest enters step S3 for liquid-solid separation. The residence time of the material in the crystallizer is 2.5h.

[0029] S3: Separating the lithium carbonate slurry into a liquid-solid state to obtain lithium carbonate solid; the water vapor in the gas phase is condensed and collected as condensed water for reuse, and the CO2 gas is collected and returned to step S1 for reuse. Example 3

[0030] A method for producing lithium carbonate comprises the following steps: S1: Mix the waste lithium battery positive electrode material with sulfate and then add sulfuric acid. The mixed material is calcined under a nitrogen atmosphere. The calcined material is soaked in water to obtain a leachate. Sodium sulfide is added to the leachate to remove nickel and cobalt. Calcium hydroxide solution is then added to separate the liquid and solid to obtain a lithium sulfate solution. Sodium carbonate is added to the lithium sulfate solution to obtain lithium carbonate. CO2 is introduced to convert the lithium carbonate into lithium bicarbonate to obtain a lithium bicarbonate solution.

[0031] S2 The lithium bicarbonate solution obtained in step S1 is continuously input into the crystallizer, and the lithium bicarbonate solution is evaporated and pyrolyzed in the crystallizer to generate lithium carbonate slurry and a gas phase containing CO2. The pyrolysis temperature is 60°C and the pressure in the crystallizer is 70kPa. The lithium carbonate slurry is continuously extracted by a forced circulation pump, and the flow rate of the lithium carbonate slurry in the forced circulation pump is 4 m / s. 30% of the extracted lithium carbonate slurry is returned to the crystallizer, and the rest enters step S3 for liquid-solid separation. The residence time of the material in the crystallizer is 2h.

[0032] S3: Separating the lithium carbonate slurry into a liquid-solid state to obtain lithium carbonate solid; the water vapor in the gas phase is condensed and collected as condensed water for reuse, and the CO2 gas is collected and returned to step S1 for reuse. Example 4

[0033] A method for producing high-purity lithium carbonate comprises the following steps: S1: Crude lithium carbonate is added with water to form a slurry, CO2 is introduced to convert the lithium carbonate into lithium bicarbonate, and insoluble impurities are removed by filtration to obtain a lithium bicarbonate solution.

[0034] S2 The lithium bicarbonate solution obtained in step S1 is continuously input into the crystallizer, and the lithium bicarbonate solution is evaporated and pyrolyzed in the crystallizer to generate lithium carbonate slurry and a gas phase containing CO2. The pyrolysis temperature is 70°C and the pressure in the crystallizer is 90kPa. The lithium carbonate slurry is continuously extracted by a forced circulation pump, and the flow rate of the lithium carbonate slurry in the forced circulation pump is 5 m / s. 20% of the extracted lithium carbonate slurry is returned to the crystallizer, and the rest enters step S3 for liquid-solid separation. The residence time of the material in the crystallizer is 1 hour.

[0035] S3: Liquid-solid separation of the lithium carbonate slurry to obtain high-purity lithium carbonate solid; water vapor in the gas phase is condensed and collected as condensed water for reuse, and CO2 gas is collected and returned to step S1 for reuse.

[0036] Although the embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art may make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention. The scope of protection of the present invention is defined by the claims and their equivalents.

Claims

1. A method for producing lithium carbonate, characterized in that, The following steps are involved: S1 obtains lithium bicarbonate solution; S2 causes the lithium bicarbonate solution to evaporate and pyrolyze in the crystallizer to generate lithium carbonate slurry and a gas phase containing CO2; the pyrolysis temperature is 40-70°C and the pressure in the crystallizer is 20-90kPa; S3 separates the lithium carbonate slurry into a liquid-solid state to obtain lithium carbonate solid and pyrolysis mother liquor; the water vapor in the gas phase is condensed and collected for reuse as condensed water, and the CO2 gas is discharged or collected for reuse.

2. The method according to claim 1, characterized in that In step S2, the pyrolysis temperature is 50-60° C., and the pressure in the crystallizer is 30-70 kPa.

3. The method according to claim 1, characterized in that The lithium bicarbonate solution in step S1 is continuously fed into the crystallizer, and the lithium carbonate slurry generated in step S2 is continuously extracted by a forced circulation pump; a portion of the extracted lithium carbonate slurry enters step S3 for liquid-solid separation, and the rest is returned to the crystallizer.

4. The method according to claim 3, wherein The flow rate of lithium carbonate slurry in the outlet pipe of the forced circulation pump is 1.5~5 m / s.

5. The method according to claim 3, characterized in that The average residence time of lithium bicarbonate solution and lithium carbonate slurry in the crystallizer is 1 to 3 hours.

6. The method according to claim 1, characterized in that The method for obtaining the lithium bicarbonate solution in step S1 is as follows: extracting the lithium-containing solution with an extractant to obtain a loaded organic phase, stripping the loaded organic phase with a stripping agent to obtain a stripping solution, and removing impurities from the stripping solution to obtain the lithium bicarbonate solution; the stripping agent is CO2 and water or cooled pyrolysis mother liquor, or carbonic acid.

7. The method according to claim 6, characterized in that The lithium-containing solution is salt lake brine, waste lithium battery leachate, lithium ore leachate or lithium precipitation mother liquor. The CO2 gas in step S3 is collected and returned to step S1 for stripping.

8. The method according to claim 1, characterized in that The method for obtaining the lithium bicarbonate solution in step S1 is as follows: leaching the lithium-containing solid material with sulfuric acid or roasting it with sulfate to obtain a lithium sulfate solution, adding carbonate to the lithium sulfate solution to obtain lithium carbonate, and then introducing CO2 to convert the lithium carbonate into lithium bicarbonate.

9. The method according to claim 1, characterized in that The method for obtaining the lithium bicarbonate solution in step S1 is: adding water to crude lithium carbonate to form a slurry, and introducing CO2 into the slurry to convert the lithium carbonate into lithium bicarbonate.

10. The method according to claim 1, wherein The average particle size of the lithium carbonate crystals in the lithium carbonate slurry generated in step S2 is ≥10 μm.