Method for preparing high-purity lithium carbonate through deep purification and gradient carbonization

Abstract

The invention relates to a method for preparing high-purity lithium carbonate through deep purification and gradient carbonization. According to the method, industrial-grade (or lower-quality) lithium hydroxide is adopted as a main raw material, battery-grade lithium hydroxide is refined from the industrial-grade lithium hydroxide, and 5N lithium carbonate can be prepared at most through secondary hydrogenation. The high-purity lithium carbonate prepared by the method meets the industrial standard of lithium carbonate, the process method is simple, the raw materials are all industrial-grade, the production cost can be greatly reduced, the operation is continuous, the requirement on equipment is low, and the method is suitable for mass production and large-scale popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of high-purity material preparation, and particularly relates to a method for preparing high-purity lithium carbonate by deep purification and gradient carbonization. Background Art

[0002] Lithium carbonate (Li2CO3) is the basic raw material for the production of secondary lithium salts and lithium metal products, and thus becomes the lithium product with the largest consumption in the lithium industry. It can also be used as a raw material to prepare various lithium salts and their compounds with high added value, and is widely used in fields such as lithium batteries, catalysts, medicine, and semiconductors.

[0003] According to the industry standard "High-Purity Lithium Carbonate" YS / T 546-2021, high-purity lithium carbonate refers to a lithium carbonate product with a lithium carbonate (Li2CO3) content reaching or exceeding 99.9%. In addition, high-purity lithium carbonate can be further subdivided into different purity grades, for example:

[0004] · 99.9% (3N): Suitable for some mid- to high-end application fields;

[0005] · 99.99% (4N): Suitable for higher-demand electronic materials, high-end battery cathode materials, etc.;

[0006] · 99.999% (5N): It is ultra-high-purity lithium carbonate, mainly used for manufacturing surface acoustic wave device lithium tantalate and lithium niobate single crystals, etc.

[0007] In the electronic industry, as the cathode material and electrolyte raw material of lithium-ion batteries, it can also be used to produce high-purity lithium salts such as lithium chloride and lithium bromide. With the continuous expansion of the application market of upstream products in lithium-ion batteries and electronic information materials, the high-purity Li2CO3 industry has continuously shown new growth, and its development and application prospects are broad.

[0008] CN110117020A discloses a method for treating lithium-containing minerals by mineral element phase transfer. After the mineral element phase transfer, the obtained mixture is subjected to subsequent treatment to obtain a lithium-containing product, including adding carbonate and / or introducing CO2 into the leaching solution after the mineral element phase transfer for lithium precipitation, and obtaining lithium carbonate and mother liquor after solid-liquid separation; and refining the obtained lithium carbonate by methods such as lithium carbonate recrystallization method, causticization method, electrolysis method, or carbonization method to obtain high-purity lithium carbonate.

[0009] CN207608328U relates to a three-in-one system device for preparing high-purity lithium carbonate, which integrates three preparation methods: the furnace stone method, the brine method, and the waste lithium extraction method. After filtering the wastewater in the brine method, it is collected through a water delivery pipeline and sent to each water-using device, and the waste materials generated in the three preparation methods are collected and reacted to be used as new raw materials.

[0010] Existing methods for preparing high-purity lithium carbonate include the recrystallization method, electrolysis method, and salt lake brine method used in the aforementioned prior art. Their disadvantages include high requirements for raw material quality, high energy consumption, complex equipment, and environmental impacts, etc., resulting in difficulties in reducing the production cost of high-purity lithium carbonate and achieving 5N purity of lithium carbonate. Therefore, there is an urgent need for a method for preparing high-purity lithium carbonate with a simple process, low requirements for equipment, and the ability to significantly reduce costs. Summary of the Invention

[0011] To solve the deficiencies of the prior art, the present invention provides a method for preparing high-purity lithium carbonate by deep purification and gradient carbonization. Compared with the existing methods for preparing high-purity lithium carbonate, the present invention uses industrial-grade (or lower-quality) lithium hydroxide as the main raw material, refines industrial-grade lithium hydroxide into battery-grade lithium hydroxide, and then through secondary hydrogenation, 5N lithium carbonate can be obtained at most. The high-purity lithium carbonate prepared by this method meets the lithium carbonate industry standard (YS / T 546-2021), has a simple process method, all raw materials are industrial-grade, can significantly reduce the production cost, has continuous operation, and has low requirements for equipment, and is suitable for mass production and large-scale promotion.

[0012] To achieve the above object, the present invention proposes the following technical solutions.

[0013] A method for preparing high-purity lithium carbonate by deep purification and gradient carbonization, the method comprising the following steps:

[0014] (1) Purify and remove impurities from industrial-grade lithium hydroxide, and recrystallize to obtain battery-grade lithium hydroxide;

[0015] (2) React the aqueous solution of battery-grade lithium hydroxide with carbon dioxide to carry out a carbonization reaction to obtain a lithium carbonate slurry. After solid-liquid separation, wash with hot water to obtain 3N lithium carbonate;

[0016] (3) React the 3N lithium carbonate slurry with carbon dioxide to carry out a primary hydrogenation reaction to generate a first lithium bicarbonate solution. After primary filtration, carry out primary pyrolysis to obtain 4N lithium carbonate;

[0017] (4) React the 4N lithium carbonate slurry with carbon dioxide to carry out a secondary hydrogenation reaction to generate a second lithium bicarbonate solution. After secondary filtration, carry out secondary pyrolysis to obtain 5N lithium carbonate.

[0018] In the technical solution of the present application, the industrial-grade lithium hydroxide refers to lithium hydroxide with a purity of 95% to <99.0%; the battery-grade lithium hydroxide refers to lithium hydroxide with a purity of ≥99.0% (see YS / T 1568-2022).

[0019] Furthermore, the water used in the method is high-purity water; the carbon dioxide used is industrial-grade carbon dioxide.

[0020] The high purity water refers to water that has been treated by various water treatment technologies to remove electrolytes, colloids, organic matter, and microbial contamination in the water, making it water of extremely high purity. The content of impurities in it is less than 0.1 mg / L, the conductivity at 25 °C is less than 0.1 μS / cm, and the pH is between 6.8 and 7.0.

[0021] The purity of the industrial-grade carbon dioxide reaches over 99%, meeting the national standard GB / T6052 - 2011.

[0022] In one embodiment, in step (1), the impurity content in the industrial-grade lithium hydroxide is as follows: Na ≤ 0.11%, K ≤ 0.066%, Fe ≤ 0.042%, Ca ≤ 0.011%, Cu ≤ 0.0024%, Mg ≤ 0.0052%, Mn ≤ 0.001%, Si ≤ 0.62%, Cl - ≤ 0.82%, SO4 2- ≤ 0.0072%, CO3 2- ≤ 0.9%, B ≤ 0.015%, acid-insoluble substances ≤ 0.33%;

[0023] The impurity content in the battery-grade lithium hydroxide is as follows: Na ≤ 0.0018%, K ≤ 0.001%, Fe ≤ 0.001%, Ca ≤ 0.0015%, Cu ≤ 0.0001%, Mg ≤ 0.001%, Mn ≤ 0.0001%, Si ≤ 0.003%, Cl - ≤ 0.002%, SO4 2- ≤ 0.005%, CO3 2- ≤ 0.6%, B ≤ 0.00005%, acid-insoluble substances ≤ 0.005%.

[0024] The acid-insoluble substances refer to substances that are insoluble in dilute hydrochloric acid (10% - 20% hydrochloric acid), generally referring to some insoluble impurity substances brought in from raw materials, such as it can include Al2O3, Fe2O3, Mn3O4, SiO2, insoluble silicates, carbides, etc.

[0025] Furthermore, in step (1), the purification and impurity removal is to use impurity removal agents to remove some impurities in the industrial-grade lithium hydroxide. The impurity removal agents include: barium hydroxide, oxalic acid, and EDTA; the recrystallization is to remove the impurities enriched in the lithium hydroxide mother liquor through evaporation recrystallization to obtain battery-grade lithium hydroxide.

[0026] Furthermore, in step (2), the aqueous solution of the battery-grade lithium hydroxide is a saturated solution; the end point pH of the carbonization reaction is 9 - 11.

[0027] In one embodiment, in step (2), the hot water washing is carried out by stirring with hot water, and the number of washing times is 3 times. The temperature of the hot water can be 85-100 °C.

[0028] Further, in step (3), the 3N lithium carbonate slurry is obtained by dispersing 3N lithium carbonate in water, and the solid-liquid ratio is 1:(25-30). In the dispersion process, stirring equipment such as a stirring paddle, a magnetic stirrer and / or ultrasonic dispersion can be used to gradually disperse the lithium carbonate solid in water to form a slurry. The dispersion time is generally determined according to the particle size and dispersion degree of lithium carbonate. For example, the dispersion time is 10-30 min.

[0029] Further, in step (3), the end point pH of the first hydrogenation reaction is 7-8. At this time, the solution is clear and the first hydrogenation reaction terminates; the first filtration adopts the nanofiltration method, and its purpose is to remove impurities. The pore size of the microporous filter membrane is 0.10-0.45 μm; the first pyrolysis adopts microwave pyrolysis, and the time is 1-1.5 h.

[0030] Among them, the reaction time of the first pyrolysis is 60-90 min. And during the pyrolysis process, stirring and decompression operations (such as -0.04 to -0.06 MPa) can be accompanied to promote the uniform distribution of heat, prevent local overheating, and accelerate the escape of gases such as carbon dioxide.

[0031] Further, in step (4), the 4N lithium carbonate slurry is obtained by dispersing 4N lithium carbonate in water, and the solid-liquid ratio is 1:(30-35). Stirring equipment such as a stirring paddle, a magnetic stirrer and / or ultrasonic dispersion can be used to gradually disperse the lithium carbonate solid in water to form a slurry; the dispersion time is 30-40 min.

[0032] Further, in step (4), the end point pH of the second hydrogenation reaction is 7-8. At this time, the solution is clear and the second hydrogenation reaction terminates; the second filtration adopts the nanofiltration method and combines ion adsorption to remove impurities. The pore size of the microporous filter membrane is 0.01-0.10 μm, and the ion adsorption is carried out by using an ion exchange resin; the second pyrolysis adopts microwave or ultrasonic pyrolysis, and the time is 1-1.5 h.

[0033] Among them, the ion exchange resin can be, for example, Purolite S930Plus and Purolite A520E of the Purolite Group. In the ion adsorption, metal ion adsorption mainly adsorbs metal ions such as Mn, Cd, Cr, Cu, Zn, etc.; anion adsorption can adsorb anions such as SO4 2- , Cl - and so on.

[0034] Among them, the reaction time of the secondary pyrolysis is 70-80 min. During the pyrolysis process, stirring and decompression operations can be accompanied (for example, -0.04 to -0.06 MPa) to promote the uniform distribution of heat, prevent local overheating, and accelerate the escape of gases such as carbon dioxide.

[0035] Furthermore, the 5N lithium carbonate obtained in step (4) of the method can be further washed with hot water and dried. The hot water washing is carried out by stirring with 100°C hot water three times; the drying temperature is 120°C and the time is 4-5 h.

[0036] The advantages of the present invention over the prior art include:

[0037] 1. The present invention uses industrial-grade lithium hydroxide as the main raw material. By refining industrial-grade (or lower-quality) lithium hydroxide into battery-grade lithium hydroxide and then performing secondary hydrogenation, highly purified lithium carbonate with deep purification can be obtained. And gradient carbonization can be carried out sequentially according to actual needs, and 5N lithium carbonate can be prepared at most.

[0038] 2. The highly purified lithium carbonate prepared by this method meets the lithium carbonate industry standard (YS / T 546-2021). The process method is simple, the raw materials are all industrial-grade, the production cost can be greatly reduced, the operation is continuous, and the requirements for equipment are low, which is suitable for mass production and large-scale promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic process flow diagram for preparing highly purified lithium carbonate from industrial-grade lithium hydroxide in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] In order to better understand the above technical solutions, the exemplary embodiments of the present invention will be described in more detail below with reference to the drawings.

[0041] Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more clear and thorough understanding of the present invention and to be able to convey the scope of the present invention completely to those skilled in the art.

[0042] As Figure 1 shown, it is a schematic process flow diagram for preparing highly purified lithium carbonate from industrial-grade lithium hydroxide in an embodiment of the present invention. The following examples and comparative examples specifically analyze the process and results of preparing 3N-5N highly purified lithium carbonate.

[0043] Example 1

[0044] Dissolve industrial-grade LiOH in high-purity water to prepare a saturated solution, and successively use impurity removers including oxalic acid, barium hydroxide, and EDTA to filter and remove impurities such as Ca 2+ , Mg 2+ , Fe 3+ and other partial impurities, and remove the mother liquor and enrich the impurities by evaporation and recrystallization to obtain battery-grade LiOH with higher purity.

[0045] The impurity contents in the used industrial-grade LiOH include: Na 0.11%, K 0.066%, Fe 0.042%, Ca 0.011%, Cu 0.0024%, Mg 0.0052%, Mn 0.001%, Si 0.62%, Cl - 0.82%, SO4 2- 0.0072%, CO3 2- 0.9%, B 0.015%, acid-insoluble substances 0.33%.

[0046] The impurity contents in the obtained battery-grade LiOH include: Na 0.0018%, K 0.001%, Fe 0.001%, Ca 0.0015%, Cu 0.0001%, Mg 0.001%, Mn 0.0001%, Si 0.003%, Cl - 0.002%, SO4 2- 0.005%, CO3 2- 0.6%, B≤0.00005%, acid-insoluble substances 0.005%.

[0047] Then, completely dissolve the battery-grade LiOH in high-purity water to obtain a saturated solution, introduce industrial-grade CO2 for carbonization reaction, stop the reaction when the pH value is 9-10, obtain a lithium carbonate slurry, filter the slurry for solid-liquid separation, wash it 3 times with 100°C hot water, and dry it at 120°C for 2 h to obtain 3N lithium carbonate.

[0048] Example 2

[0049] The difference from Example 1 is that when preparing 3N lithium carbonate from battery-grade LiOH, stop the reaction when the pH value is 10-11.

[0050] Comparative Example 1

[0051] The difference from Example 1 is that when preparing 3N lithium carbonate from battery-grade LiOH, stop the reaction when the pH value is 11-12.

[0052] Comparative Example 2

[0053] The difference from Example 1 is that when preparing 3N lithium carbonate from battery-grade LiOH, the reaction is stopped when the pH value is 8-9.

[0054] Example 3

[0055] Add the 3N lithium carbonate obtained in Example 1 to high-purity water with a solid-liquid ratio of 1:25, and obtain a lithium carbonate slurry through magnetic stirring and ultrasonic dispersion for 30 min; continuously stir the lithium carbonate slurry and introduce industrial-grade CO2 for a primary hydrogenation reaction until the pH value of the solution reaches 7-8 to obtain a lithium bicarbonate solution.

[0056] The solution is filtered once by nanofiltration, and the pore size of the microporous filter membrane is 0.40 μm; then after microwave pyrolysis for 1 h, lithium carbonate precipitates out, and the pyrolysis process is accompanied by stirring and depressurization operations; the separated lithium carbonate precipitate is stirred and washed 3 times with hot water at 100 °C and dried at 120 °C for 3 h to obtain 4N lithium carbonate.

[0057] Example 4

[0058] The difference from Example 3 is that when preparing the lithium carbonate slurry with 3N lithium carbonate, the solid-liquid ratio is 1:30.

[0059] Comparative Example 3

[0060] The difference from Example 3 is that when preparing the lithium carbonate slurry with 3N lithium carbonate, the solid-liquid ratio is 1:20.

[0061] The impurity contents of the 3N lithium carbonate obtained in the above Examples 1-2 and Comparative Examples 1-2 and the 4N lithium carbonate obtained in Examples 3-4 and Comparative Example 3 are shown in Table 1 below.

[0062] Table 1

[0063]

[0064]

[0065] For the preparation of 3N lithium carbonate, it is necessary to determine the end point of the carbonization reaction of LiOH and CO2. Examples 1-2 and Comparative Examples 1-2 show that when the pH is in the range of 9-11, the carbonization reaction is relatively complete; when the pH > 11, the carbonization reaction is incomplete, and the unreacted LiOH will become the main impurity, and the impurities in the raw materials will also reduce the opportunity for co-precipitation or adsorption removal due to incomplete reaction; when the pH < 9, the excessive CO2 will further react with Li2CO3 to form soluble lithium bicarbonate, and the excessive CO2 will retain more anionic impurities.

[0066] When preparing 4N lithium carbonate, the solid-liquid ratio of the 3N lithium carbonate slurry affects the impurity content. Examples 3-4 show that when the solid-liquid ratio is 1:(25-30), the ion removal effect is relatively ideal; but when the solid-liquid ratio is 1:20, it is speculated that it has an adverse effect on the hydrogenation reaction, resulting in an increase in the impurity concentration.

[0067] Example 5

[0068] Add the 4N lithium carbonate obtained in Example 4 to high-purity water with a solid-liquid ratio of 1:30, and obtain a lithium carbonate slurry through magnetic stirring and ultrasonic dispersion for 40 min; continuously stir the lithium carbonate slurry and introduce industrial-grade CO2 for secondary hydrogenation reaction until the pH value of the solution is 7-8 and the solution is completely clear, then the secondary hydrogenation reaction terminates to obtain a second lithium bicarbonate solution.

[0069] Filter and remove impurities from the second lithium bicarbonate solution using a 0.10 μm filter membrane, adsorb metal ions using the ion exchange resin Purolite S930Plus, and then use Purolite A520E to adsorb anions; then after microwave pyrolysis for 80 min, lithium carbonate precipitates out, and the pyrolysis process is accompanied by stirring and depressurization operations; wash the separated lithium carbonate precipitate 3 times with hot water at 100 °C and dry it at 120 °C for 4 h to obtain 5N lithium carbonate.

[0070] Example 6

[0071] The difference from Example 5 is that for the second lithium bicarbonate solution after ion adsorption by the resin, ultrasonic pyrolysis is carried out for 80 min to precipitate lithium carbonate.

[0072] Comparative Example 4

[0073] The difference from Example 5 is that the second lithium bicarbonate solution is filtered and purified using a 10 μm filter paper, and the ions are not adsorbed using an exchange resin.

[0074] Comparative Example 5

[0075] The difference from Example 5 is that the second lithium bicarbonate solution is filtered and purified using a 0.45 μm filter membrane, and the ions are not adsorbed using an exchange resin.

[0076] Comparative Example 6

[0077] The difference from Example 5 is that the ions are not adsorbed using an exchange resin.

[0078] The impurity contents in the 5N lithium carbonate obtained in the above Examples 5-6 and the 4N lithium carbonate obtained in Comparative Examples 4-6 (the purity did not reach 5N due to process limitations) are shown in Table 2 below.

[0079] Table 2

[0080]

[0081]

[0082] For the preparation of 5N lithium carbonate, selecting a nanofiltration membrane with a suitable pore size and simultaneously using an ion adsorption resin can achieve good results. When a nanofiltration membrane with an inappropriate pore size is not used, or an ion adsorption resin is not used, it is relatively difficult to achieve lithium carbonate with a purity of 5N.

[0083] The technical solution of the present invention uses industrial-grade lithium hydroxide as the main raw material. By refining industrial-grade lithium hydroxide into battery-grade lithium hydroxide, and then subjecting the battery-grade lithium hydroxide to secondary hydrogenation, 5N lithium carbonate can be prepared at most. For each purity level from 3N to 5N, there are factors in its preparation process that can significantly affect the final result. The disclosure of the present invention provides a solution for preparing up to 5N lithium carbonate from industrial-grade raw materials, and the process method is simple, the operation is continuous, the requirements for equipment are low, and it is suitable for industrial production.

[0084] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limitations of the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing high-purity lithium carbonate by deep purification and gradient carbonization, characterized in that, The method includes the following steps: (1) Purify and remove impurities from industrial-grade lithium hydroxide, and recrystallize to obtain battery-grade lithium hydroxide; (2) Carry out a carbonization reaction between the aqueous solution of battery-grade lithium hydroxide and carbon dioxide to obtain a lithium carbonate slurry. After solid-liquid separation, wash with hot water to obtain 3N lithium carbonate; (3) Carry out a primary hydrogenation reaction between the 3N lithium carbonate slurry and carbon dioxide to generate a first lithium bicarbonate solution. After primary filtration, carry out primary pyrolysis to obtain 4N lithium carbonate; (4) Carry out a secondary hydrogenation reaction between the 4N lithium carbonate slurry and carbon dioxide to generate a second lithium bicarbonate solution. After secondary filtration, carry out secondary pyrolysis to obtain 5N lithium carbonate.

2. The method according to claim 1, wherein The water used in the method is high-purity water with a conductivity less than 0.1 μS / cm; the carbon dioxide used is industrial-grade carbon dioxide.

3. The method according to claim 1 or 2, characterized in that, In step (1), the impurity contents in the industrial lithium hydroxide are as follows: Na ≤ 0.11%, K ≤ 0.066%, Fe ≤ 0.042%, Ca ≤ 0.011%, Cu ≤ 0.0024%, Mg ≤ 0.0052%, Mn ≤ 0.001%, Si ≤ 0.62%, Cl - ≤ 0.82%, SO4 2- ≤ 0.0072%, CO3 2- ≤ 0.9%, B ≤ 0.015%, acid-insoluble substances ≤ 0.33%; The impurity contents in the lithium hydroxide for battery grade are: Na ≤ 0.0018%, K ≤ 0.001%, Fe ≤ 0.001%, Ca ≤ 0.0015%, Cu ≤ 0.0001%, Mg ≤ 0.001%, Mn ≤ 0.0001%, Si ≤ 0.003%, Cl - ≤ 0.002%, SO4 2- ≤ 0.005%, CO3 2- ≤ 0.6%, B ≤ 0.00005%, acid insoluble substances ≤ 0.005%.

4. The method according to claim 3, wherein In step (1), the purification and impurity removal is to use an impurity remover to remove some impurities in the industrial-grade lithium hydroxide. The impurity remover includes: barium hydroxide, oxalic acid and EDTA; the recrystallization is to remove the impurities enriched in the lithium hydroxide mother liquor by evaporation recrystallization to obtain battery-grade lithium hydroxide.

5. The method according to claim 1 or 2, characterized in that, In step (2), the aqueous solution of battery-grade lithium hydroxide is a saturated solution; the end point pH of the carbonization reaction is 9-11.

6. The method according to claim 5, wherein In step (2), the hot water washing is carried out by means of hot water stirring and washing, and the number of washing times is 3 times.

7. The method according to claim 1 or 2, characterized in that, In step (3), the 3N lithium carbonate slurry is obtained by dispersing 3N lithium carbonate in water, and the solid-liquid ratio is 1:(25-30); the dispersion time is 10-30 min.

8. The method according to claim 7, wherein In step (3), the end point pH of the primary hydrogenation reaction is 7-8; the primary filtration adopts nanofiltration, and its purpose is to remove impurities, and the pore size of the microporous membrane is 0.10-0.45 μm; the primary pyrolysis adopts microwave pyrolysis, and the time is 1-1.5 h.

9. The method according to claim 1 or 2, characterized in that, In step (4), the 4N lithium carbonate slurry is obtained by dispersing 4N lithium carbonate in water, and the solid-liquid ratio is 1:(30-35); the dispersion time is 30-40 min.

10. The method according to claim 9, characterized in that, In step (4), the end point pH of the secondary hydrogenation reaction is 7-8; the secondary filtration adopts nanofiltration combined with ion adsorption for impurity removal, the pore size of the microporous filter membrane is 0.01-0.10 μm, and the ion adsorption is carried out by using an ion exchange resin; the secondary pyrolysis adopts microwave or ultrasonic pyrolysis, and the time is 1-1.5 h.

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