Preparation method of lithium carbonate tertiary crystallization and application thereof

Abstract

A three-stage crystallization method for preparing lithium carbonate and its application includes: S1 First-stage cooling crystallization: heating the lithium carbonate mother liquor to 80-90℃, and gradually lowering the temperature of the lithium carbonate mother liquor to 25-30℃; the temperature decrease rate is 0.5-2℃ / min; separating lithium carbonate crystals by centrifugation or filtration; S2 Second-stage vacuum flash crystallization: preheating the lithium carbonate mother liquor after the separation of lithium carbonate crystals in S1 to 40-50℃ and sending it into a vacuum flash evaporator, performing three-stage crystallization and separating lithium carbonate crystals by centrifugation or filtration; S3 Third-stage cryogenic cooling crystallization: transferring the lithium carbonate mother liquor after the separation of lithium carbonate crystals in S2 to a cryogenic system for cryogenic cooling crystallization, lowering the temperature of the lithium carbonate mother liquor to -20 to -30℃; separating lithium carbonate crystals by centrifugation or filtration. This method can prepare high-purity lithium carbonate and improve the efficiency and speed of lithium carbonate crystallization and mother liquor separation.

Description

Technical Field

[0001] This invention relates to the field of lithium carbonate preparation technology, and in particular to a method for preparing lithium carbonate through tertiary crystallization and its application. Background Technology

[0002] With the rapid development of lithium battery technology, the demand for high-purity lithium carbonate continues to grow. Traditional lithium carbonate manufacturing processes suffer from numerous problems, such as low purity, high energy consumption, and severe environmental pollution. In particular, the purification process is inefficient in removing potassium-sodium mixed salts and trace metal impurities from lithium sulfate solutions, leading to unstable final product quality. Traditional lithium carbonate preparation typically involves a single addition of the extractant without proper temperature control; moreover, it usually employs a simple linear cooling process without temperature coils or circulating cooling systems, resulting in poor temperature control and uniformity, ultimately leading to low lithium carbonate yield and poor particle size uniformity. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned technical defects and provide a method for preparing lithium carbonate through tertiary crystallization and its application.

[0004] In a first aspect, this application provides a method for preparing lithium carbonate through tertiary crystallization, comprising:

[0005] S1 primary cooling crystallization:

[0006] The lithium carbonate mother liquor is heated to 80-90℃, and then gradually reduced to 25-30℃; the temperature reduction rate is 0.5-2℃ / min; the lithium carbonate crystals are separated by centrifugation or filtration.

[0007] The separated lithium carbonate crystals were washed and dried to obtain primary lithium carbonate crystals.

[0008] S2 secondary vacuum flash crystallization:

[0009] The lithium carbonate mother liquor after separating lithium carbonate crystals in S1 is preheated to 40-50℃ and sent to a vacuum flash evaporator. After three-stage crystallization, the lithium carbonate crystals are separated by centrifugation or filtration.

[0010] The separated lithium carbonate crystals were washed and dried to obtain secondary lithium carbonate crystals;

[0011] S3 Level 3 Cryogenic Cooling Crystallization:

[0012] After separating the lithium carbonate crystals in S2, the lithium carbonate mother liquor is transferred to a cryogenic system for cryogenic cooling and crystallization, so that the lithium carbonate mother liquor is cooled to -20 to -30℃.

[0013] Lithium carbonate crystals are separated by centrifugation or filtration.

[0014] The separated lithium carbonate crystals were washed and dried to obtain tertiary lithium carbonate crystals.

[0015] In one embodiment, the lithium carbonate mother liquor in step S1 has a lithium carbonate mass fraction of 20-60%.

[0016] In one embodiment, in step S1, the primary cooling crystallization, the washing is performed with deionized water; the drying temperature is 60-80°C, and the drying time is 6-12 hours.

[0017] In one embodiment, in step S2, the secondary vacuum flash crystallization, the tertiary crystallization includes sequentially performing first-stage crystallization, second-stage crystallization, and third-stage crystallization on the lithium carbonate mother liquor;

[0018] The temperature of the lithium carbonate mother liquor controlled during the first-stage crystallization was 33-37℃, the pressure was 75-85mbar, and the flow rate was 20L / min.

[0019] The temperature of the lithium carbonate mother liquor for the second-stage crystallization is controlled at 23-27℃, the pressure at 55-65mbar, and the flow rate at 15L / min.

[0020] The third-stage crystallization process controls the temperature of the lithium carbonate mother liquor to be 13-17℃, the pressure to be 15-25mbar, and the flow rate to be 10L / min.

[0021] In one embodiment, in step S2, the secondary vacuum flash crystallization, the cooling rate of the first-stage crystallization is 2°C / h, and the pressure reduction rate is 10 mbar / min.

[0022] The second-stage crystallization cooling rate is 1.5℃ / h, and the pressure reduction rate is 10mbar / min;

[0023] The cooling rate of the third-stage crystallization is 1℃ / h, and the pressure reduction rate is 10mbar / min.

[0024] In one embodiment, in step S2, secondary vacuum flash crystallization, the washing is performed with deionized water; the drying temperature is 60-80℃, and the drying time is 6-12h.

[0025] In one embodiment, in step S2, the secondary vacuum flash crystallization, the vacuum flash evaporator is a horizontal vacuum multi-stage flash crystallizer.

[0026] In one embodiment, in step S2, secondary vacuum flash crystallization, the lithium carbonate mother liquor is temperature controlled by a temperature-controlled liquid, which is a 20% ethylene glycol aqueous solution or a 20% sodium chloride aqueous solution.

[0027] In one embodiment, the 20% ethylene glycol aqueous solution has a freezing point of -10°C, a viscosity of 2.5 mPa·s, and a thermal conductivity of 0.52 W / (m·K).

[0028] The 20% sodium chloride aqueous solution has a freezing point of -5℃, a viscosity of 1.2 mPa·s, and a thermal conductivity of 0.6 W / (m·K).

[0029] In one embodiment, in step S3, the three-stage cryogenic cooling crystallization, the cryogenic system uses a ThermoFisher Scientific DF100 cryostat, which is equipped with an industrial-grade refrigeration system to achieve efficient low-temperature cycling.

[0030] In one embodiment, in step S3, the cryogenic cooling crystallization, the cryogenic system uses a low-temperature heat transfer oil as the cryogenic fluid; preferably, the cryogenic fluid is a low-temperature heat transfer oil produced by BASF, with an operating temperature range of -60°C to -100°C and a thermal conductivity ≥0.15W / (m·K).

[0031] In one embodiment, in step S3, the three-stage cryogenic crystallization, the cooling rate is 0.5-1℃ / min. Within this temperature range, the lithium carbonate solution can be highly supersaturated, which is beneficial for generating high-purity large crystals. Controlling a stable cooling rate also ensures uniform crystal growth.

[0032] In one embodiment, in step S3, the three-stage cryogenic cooling crystallization, the washing is performed with deionized water; the drying temperature is 60-80℃, and the drying time is 6-12h.

[0033] Secondly, this application also provides the application of the above-mentioned three-stage crystallization method for preparing lithium carbonate in the preparation of high-purity lithium carbonate.

[0034] The present invention has the following beneficial effects

[0035] The present invention provides a three-stage crystallization method for preparing lithium carbonate. This method involves primary cooling crystallization, secondary vacuum flash crystallization, and tertiary cryogenic cooling crystallization of lithium sulfate mother liquor. This process enables the preparation of high-purity lithium carbonate while simultaneously increasing the reaction rate and reducing production energy consumption. By controlling the final temperature and cooling rate of the tertiary cryogenic cooling crystallization, a high degree of supersaturation of the lithium carbonate solution can be achieved within this temperature range, which is beneficial for generating large, high-purity crystals. Controlling the cooling rate also ensures uniform crystal growth. Furthermore, by controlling the cooling rate and avoiding excessively rapid cooling that could lead to uneven lithium carbonate crystallization, the formation of lithium carbonate crystals can be better controlled, improving the efficiency and speed of separation between the lithium carbonate crystals and the mother liquor. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to the embodiments and examples. It should be understood that these embodiments and examples are for illustrative purposes only and are not intended to limit the scope of the invention. The purpose of providing these embodiments and examples is to make the disclosure of the present invention more thorough and complete. It should also be understood that the present invention can be implemented in many different forms and is not limited to the embodiments and examples described herein. Those skilled in the art can make various modifications or alterations without departing from the spirit of the present invention, and the equivalent forms obtained also fall within the protection scope of this application. Furthermore, numerous specific details are set forth in the following description to provide a fuller understanding of the present invention. It should be understood that the present invention can be implemented without one or more of these details.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for descriptive purposes only and is not intended to be limiting of the invention.

[0038] the term

[0039] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0040] In this document, terms such as "preferred," "better," "more suitable," and "ideal" are merely descriptions of more effective implementation methods or embodiments and should be understood not to limit the scope of protection of this invention. If multiple "preferred" terms appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" term shall be independent.

[0041] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features. It should be understood that when the chemical composition of a substance is described in a limiting manner, the substance may contain impurities present in normal amounts, including but not limited to impurities inevitably introduced due to the preparation process.

[0042] In this invention, numerical intervals (i.e., numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the aforementioned numerical intervals are considered continuous and include the two endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints. In this document, this is equivalent to directly listing every integer. For example, if t is an integer selected from 1 to 10, it means that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Furthermore, when multiple ranges are provided to describe features or characteristics, these ranges can be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0043] The raw materials used in the embodiments and comparative examples of this invention are as follows:

[0044] Lithium carbonate mother liquor 1: Lithium carbonate mass fraction is 20%.

[0045] Lithium carbonate mother liquor 2: Lithium carbonate mass fraction is 60%.

[0046] Cryogenic System: DF100 Freezer, Thermo Fisher Scientific

[0047] Coolant: Duratherm LT Heat Transfer Fluid, operating temperature range -60℃ to -100℃, thermal conductivity ≥0.15W / (m·K), BASF

[0048] Vacuum flash evaporator: Horizontal vacuum multi-stage flash crystallizer CMSMPR

[0049] Temperature control fluid 1: 20% ethylene glycol aqueous solution, freezing point -10℃, viscosity 2.5 mPa·s, thermal conductivity 0.52 W / (m·K).

[0050] Temperature control liquid 2: 20% sodium chloride aqueous solution with a freezing point of -5℃, viscosity of 1.2 mPa·s, and thermal conductivity of 0.6 W / (m·K).

[0051] Examples 1-3: Preparation method of high-purity lithium carbonate:

[0052] S1 primary cooling crystallization:

[0053] The lithium carbonate mother liquor is heated to 85°C and then gradually reduced to 30°C; the temperature reduction rate is 0.5-2°C / min; the lithium carbonate crystals are separated by centrifugation or filtration.

[0054] The separated lithium carbonate crystals were washed and dried at 70°C for 10 hours to obtain primary lithium carbonate crystals.

[0055] S2 secondary vacuum flash crystallization:

[0056] The lithium carbonate mother liquor after separating lithium carbonate crystals in S1 is preheated to 45°C and sent to a vacuum flash evaporator. After three-stage crystallization, the lithium carbonate crystals are separated by centrifugation or filtration.

[0057] The separated lithium carbonate crystals were washed and dried at 70°C for 10 hours to obtain secondary lithium carbonate crystals.

[0058] The three-stage crystallization includes sequentially performing first-stage crystallization, second-stage crystallization, and third-stage crystallization on the lithium carbonate mother liquor;

[0059] The temperature of the lithium carbonate mother liquor for the first-stage crystallization is controlled at 33-37℃, the pressure at 75-85mbar, and the flow rate at 20L / min. The temperature of the lithium carbonate mother liquor is controlled by a temperature-controlled liquid, and the cooling rate of the first-stage crystallization is 2℃ / h, and the pressure reduction rate is 10mbar / min.

[0060] The temperature of the lithium carbonate mother liquor for the second-stage crystallization is controlled at 23-27℃, the pressure at 55-65mbar, and the flow rate at 15L / min. The temperature of the lithium carbonate mother liquor is controlled by a temperature-controlled liquid. The cooling rate of the second-stage crystallization is 1.5℃ / h, and the pressure reduction rate is 10mbar / min.

[0061] The third-stage crystallization process controls the temperature of the lithium carbonate mother liquor to be 13-17℃, the pressure to be 15-25mbar, and the flow rate to be 10L / min. The temperature of the lithium carbonate mother liquor is controlled by a temperature-controlled liquid, and the cooling rate of the third-stage crystallization process is 1℃ / h, and the pressure reduction rate is 10mbar / min.

[0062] S3 Level 3 Cryogenic Cooling Crystallization:

[0063] After separating the lithium carbonate crystals in S2, the lithium carbonate mother liquor is transferred to a cryogenic system for cryogenic cooling and crystallization, cooling the lithium carbonate mother liquor to -20 to -30°C; the cryogenic cooling and crystallization cooling rate is 0.5-1°C / min.

[0064] Lithium carbonate crystals are separated by centrifugation or filtration.

[0065] The separated lithium carbonate crystals were washed and dried at 70°C for 10 hours to obtain tertiary lithium carbonate crystals.

[0066] Comparative Examples 1-3: Preparation methods of high-purity lithium carbonate:

[0067] S1 primary cooling crystallization:

[0068] The lithium carbonate mother liquor is heated to 85°C, and then the temperature is gradually reduced to 30°C; the rate of temperature reduction is controlled; and the lithium carbonate crystals are separated by centrifugation or filtration.

[0069] The separated lithium carbonate crystals were washed and dried at 70°C for 10 hours to obtain primary lithium carbonate crystals.

[0070] S2 secondary vacuum flash crystallization:

[0071] The lithium carbonate mother liquor after separating lithium carbonate crystals in S1 is preheated to 45°C and sent to a vacuum flash evaporator. After three-stage crystallization, the lithium carbonate crystals are separated by centrifugation or filtration.

[0072] The separated lithium carbonate crystals were washed and dried at 70°C for 10 hours to obtain secondary lithium carbonate crystals.

[0073] The three-stage crystallization includes sequentially performing first-stage crystallization, second-stage crystallization, and third-stage crystallization on the lithium carbonate mother liquor;

[0074] The temperature, pressure, and flow rate of the lithium carbonate mother liquor are controlled during the first-stage crystallization process. The temperature of the lithium carbonate mother liquor is controlled by a temperature-controlled liquid, with the first-stage crystallization cooling rate being 2℃ / h and the pressure reduction rate being 10mbar / min.

[0075] The temperature, pressure, and flow rate of the lithium carbonate mother liquor are controlled during the second-stage crystallization process. The temperature of the lithium carbonate mother liquor is controlled by a temperature-controlled liquid, with a cooling rate of 1.5℃ / h and a pressure reduction rate of 10mbar / min during the second-stage crystallization process.

[0076] The temperature, pressure, and flow rate of the lithium carbonate mother liquor are controlled by the third-stage crystallization control liquid; the temperature of the lithium carbonate mother liquor is controlled by the temperature control liquid, and the cooling rate of the third-stage crystallization is 1℃ / h, and the pressure reduction rate is 10mbar / min.

[0077] S3 Level 3 Cryogenic Cooling Crystallization:

[0078] The lithium carbonate mother liquor after separating the lithium carbonate crystals in S2 is transferred to a cryogenic system for cryogenic cooling and crystallization to cool the lithium carbonate mother liquor; the cooling rate of the cryogenic cooling and crystallization is controlled.

[0079] Lithium carbonate crystals are separated by centrifugation or filtration.

[0080] The separated lithium carbonate crystals were washed and dried at 70°C for 10 hours to obtain tertiary lithium carbonate crystals.

[0081] Comparative Example 4

[0082] The lithium carbonate mother liquor 1 is heated to 85°C, and then the temperature of the lithium carbonate mother liquor is gradually reduced to 30°C; the temperature reduction rate is 5°C / min; the lithium carbonate crystals are separated by centrifugation or filtration.

[0083] The separated lithium carbonate crystals were washed and dried at 70°C for 10 hours to obtain lithium carbonate crystals.

[0084] Comparative Example 5

[0085] S1: Heat the lithium carbonate mother liquor 1 to 85°C, and gradually reduce the temperature of the lithium carbonate mother liquor to 30°C; the temperature reduction rate is 1°C / min; separate the lithium carbonate crystals by centrifugation or filtration.

[0086] The separated lithium carbonate crystals were washed and dried at 70°C for 10 hours to obtain lithium carbonate crystals.

[0087] S2: The lithium carbonate mother liquor after separating the lithium carbonate crystals in S1 is transferred to a cryogenic system for cryogenic cooling and crystallization, so that the lithium carbonate mother liquor is cooled to 10°C; the cryogenic cooling and crystallization cooling rate is 2°C / min.

[0088] Lithium carbonate crystals are separated by centrifugation or filtration.

[0089] The separated lithium carbonate crystals were washed and dried at 70°C for 10 hours to obtain lithium carbonate crystals.

[0090] The lithium carbonate crystals obtained from S1 and S2 were mixed to obtain the lithium carbonate crystals obtained in Comparative Example 5.

[0091] The differences between the preparation methods of the examples and the comparative examples are shown in the table below.

[0092]

[0093]

[0094] The primary, secondary, and tertiary lithium carbonate crystals obtained in Examples 1-4 and Comparative Examples 1-3 were collected and mixed to obtain the lithium carbonate crystals obtained in each example or comparative example, and were tested using the following various test methods:

[0095] 1. Lithium carbonate purity detection method: The purity of the crystal is analyzed using atomic absorption spectrometry (AAS) or inductively coupled plasma mass spectrometry (ICP-MS).

[0096] 2. Yield detection method: Calculate the lithium carbonate yield of the examples and comparative examples, that is, the ratio of the amount of lithium carbonate produced to the amount of raw materials consumed;

[0097] 3. Lithium carbonate particle size distribution test: The size distribution of crystals was measured using a laser particle size analyzer; the uniformity CU adopted the industrially accepted definition: CU = percentage of crystal mass within the target particle size range.

[0098]

[0099]

[0100] As can be seen from the above embodiments, the present invention can prepare high-purity lithium carbonate through primary cooling crystallization, secondary vacuum flash crystallization, and tertiary cryogenic cooling crystallization, which can improve the reaction rate and reduce production energy consumption; by controlling the cooling rate, uneven lithium carbonate crystallization caused by excessively rapid cooling can be avoided.

Claims

1. A method for preparing lithium carbonate through tertiary crystallization, characterized in that, include: S1 primary cooling crystallization: The lithium carbonate mother liquor is heated to 80-90℃, and then the temperature is gradually reduced to 25-30℃ at a rate of 0.5-2℃ / min. The lithium carbonate crystals are then separated by centrifugation or filtration. The separated lithium carbonate crystals were washed and dried to obtain primary lithium carbonate crystals. S2 secondary vacuum flash crystallization: The lithium carbonate mother liquor after separating lithium carbonate crystals in S1 is preheated to 40-50℃ and sent to a vacuum flash evaporator. After three-stage crystallization, the lithium carbonate crystals are separated by centrifugation or filtration. The separated lithium carbonate crystals were washed and dried to obtain secondary lithium carbonate crystals; S3 Level 3 Cryogenic Cooling Crystallization: After separating the lithium carbonate crystals in S2, the lithium carbonate mother liquor is transferred to a cryogenic system for cryogenic cooling and crystallization, so that the lithium carbonate mother liquor is cooled to -20 to -30℃. Lithium carbonate crystals are separated by centrifugation or filtration. The separated lithium carbonate crystals were washed and dried to obtain tertiary lithium carbonate crystals; In step S2, the secondary vacuum flash crystallization, the tertiary crystallization includes sequentially performing first-stage crystallization, second-stage crystallization, and third-stage crystallization on the lithium carbonate mother liquor; the first-stage crystallization controls the temperature of the lithium carbonate mother liquor to be 33-37℃, the pressure to be 75-85mbar, and the flow rate to be 20L / min. The temperature of the lithium carbonate mother liquor for the second-stage crystallization is controlled at 23-27℃, the pressure at 55-65mbar, and the flow rate at 15L / min. The temperature of the lithium carbonate mother liquor controlled during the third-stage crystallization process is 13-17℃, the pressure is 15-25mbar, and the flow rate is 10L / min. In step S2, the secondary vacuum flash crystallization process, the cooling rate of the first-stage crystallization is 2℃ / h, and the pressure reduction rate is 10mbar / min. The second-stage crystallization cooling rate is 1.5℃ / h, and the pressure reduction rate is 10mbar / min; The cooling rate of the third-stage crystallization is 1℃ / h, and the pressure reduction rate is 10mbar / min; Step S3 is a three-stage cryogenic cooling crystallization process, wherein the cryogenic cooling crystallization cooling rate is 0.5-1℃ / min.

2. The method for preparing lithium carbonate by three-stage crystallization according to claim 1, characterized in that, In step S1, the primary cooling crystallization, the washing is performed with deionized water; the drying temperature is 60-80℃, and the drying time is 6-12 hours.

3. The method for preparing lithium carbonate by three-stage crystallization according to claim 1, characterized in that, In step S2, the secondary vacuum flash crystallization, the temperature of the lithium carbonate mother liquor is controlled by a temperature-controlled liquid, which is a 20% ethylene glycol aqueous solution or a 20% sodium chloride aqueous solution; the vacuum flash evaporator is a horizontal vacuum multi-stage flash crystallizer.

4. The method for preparing lithium carbonate by three-stage crystallization according to claim 3, characterized in that, The 20% ethylene glycol aqueous solution has a freezing point of -10℃, a viscosity of 2.5 mPa·s, and a thermal conductivity of 0.52 W / (m·K). The 20% sodium chloride aqueous solution has a freezing point of -5℃, a viscosity of 1.2 mPa·s, and a thermal conductivity of 0.6 W / (m·K).

5. The method for preparing lithium carbonate by three-stage crystallization according to claim 1, characterized in that, Step S3 involves three-stage cryogenic cooling and crystallization. The cryogenic system uses a low-temperature heat transfer oil as the cryogenic fluid.

6. The method for preparing lithium carbonate by three-stage crystallization according to claim 1, characterized in that, Step S3 involves three-stage cryogenic cooling crystallization, with washing performed using deionized water; the drying temperature is 60-80℃, and the drying time is 6-12 hours.

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