Method for preparing low-sulfur low-sodium battery-grade lithium carbonate in one step by freezing semi-carbonization process

Abstract

The invention relates to the technical field of lithium salt preparation, and discloses a method for one-step preparation of low-sulfur low-sodium battery-grade lithium carbonate by a freezing semi-carbonization process, the process of preparing a finished liquid by concentrating a purified liquid in a traditional process is omitted, a carbonizer is added into the purified liquid, sodium sulfate is separated out after freezing, and lithium sulfate is converted into lithium bicarbonate, so that the lithium carbonate is prepared. The concentration of sulfate ions and sodium ions in the purification liquid is greatly reduced, then the nucleation rate is controlled by adjusting the concentration and dosage of the precipitator, the production of the low-sulfur and low-sodium battery-grade lithium carbonate is realized, the production process of the lithium carbonate is simplified, the energy consumption and production cost of the battery-grade lithium carbonate are reduced, and the production cost of the battery-grade lithium carbonate is reduced. And the low-sulfur and low-sodium battery-grade lithium carbonate is prepared.

Description

Technical Field

[0001] The invention relates to the field of lithium salt preparation, and in particular to a method for preparing low-sulfur and low-sodium battery-grade lithium carbonate in one step using a freezing semi-carbonization process. Background Art

[0002] With the rapid development of new energy vehicles and energy storage in recent years, the demand for lithium batteries has increased year by year, and the demand for lithium resources has become more and more urgent. As an important raw material for the positive electrode material of lithium-ion batteries, the quality of lithium carbonate directly affects the performance of the battery. Therefore, the preparation of high-purity, low-impurity battery-grade lithium carbonate is the key to the lithium-ion battery industry. At present, my country's traditional ore lithium extraction technology is that spodumene is roasted, crushed, screened, acidified, and leached to obtain a leachate, alkalized to remove calcium and magnesium to obtain a purified liquid, evaporated and concentrated to obtain a finished liquid, and then the finished liquid and soda ash react to precipitate lithium, stir, wash, rinse, dry, and crush to prepare battery-grade lithium carbonate. In order to improve the yield, the lithium precipitation mother liquor is usually partially slurried after freezing and sodium precipitation, and partially removed from the soda ash solution, resulting in some sulfate ions circulating in the system. This process has been very mature after many years of production practice, but the sulfate content of the prepared battery-grade lithium carbonate is usually between 0.06% and 0.075%, and the sodium index is usually between 0.007 and 0.015%, which meets the standard requirements but is still relatively high. In particular, the new industry standard for battery-grade lithium carbonate was released and implemented, dividing battery-grade lithium carbonate into three grades. The first-grade product has the sulfate index set at 0.04% and the sodium ion index set at 0.005%. It is difficult for traditional processes to meet these requirements.

[0003] At present, the method for enterprises to produce low-sulfur and low-sodium battery-grade lithium carbonate is usually through secondary lithium precipitation, that is, lithium sulfate is leached by sulfuric acid method, crude lithium carbonate is obtained after one-step lithium precipitation, crude lithium carbonate is carbonized and converted into lithium bicarbonate, and finally heated and decomposed to obtain battery-grade lithium carbonate. Or purchase crude lithium carbonate or crude lithium hydroxide, and obtain low-sulfur and low-sodium battery-grade lithium carbonate after carbonization, impurity removal and thermal decomposition. This process is complicated and costly.

[0004] In addition, the process of freezing and precipitation of mirabilite is often used in the lithium industry, the purpose of which is to reduce the sodium sulfate content so that the mother liquor can be recycled. However, due to the solubility of sodium sulfate, it is impossible to completely precipitate the sodium sulfate, not to mention the sulfate ions inherent in the lithium sulfate system. Therefore, as long as the mother liquor is recycled, the sulfate content of the battery-grade lithium carbonate produced will be maintained between 0.06% and 0.075%. This is also the reason why most manufacturers have to use secondary carbonization to precipitate lithium.

[0005] The patent with publication number CN112573546A adopts the "reverse feeding, non-circulating mother liquor" and "efficient desorption" processes, which can reduce the sulfate ion of industrial-grade lithium carbonate to 0.03%, increase the main content to 2.5N, and reduce the battery-grade sulfate ion to 0.010%-0.008%, and stabilize the main content to 3N or even reach the 3.5N4N limit.

[0006] This existing technology process does not require the mother liquor to be circulated, which is unrealistic for most lithium salt production companies that use yield as their core competitiveness. In addition, high-temperature and high-pressure reactors are used for efficient desorption, which increases equipment investment and operational risks.

[0007] Therefore, a new technical solution is needed to solve the above technical problems. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing low-sulfur and low-sodium battery-grade lithium carbonate in one step by a freezing semi-carbonization process, reducing the content of sulfate ions and sodium ions in the battery-grade lithium carbonate, adding a carbonizing agent to a purified liquid, precipitating sodium sulfate after freezing, converting lithium sulfate into lithium bicarbonate, greatly reducing the concentration of sulfate ions and sodium ions in the purified liquid, and then adjusting the concentration of a precipitant to achieve the production of low-sulfur and low-sodium battery-grade lithium carbonate. The present invention precipitates sodium sulfate decahydrate by freezing to carry away part of the water, thereby increasing the concentration of lithium oxide in the purified liquid; and the purified liquid contains a large amount of bicarbonate ions after freezing and semi-carbonization, which can further reduce the amount and concentration of pure alkali solution, save the process of concentrating the purified liquid to prepare a finished liquid in the traditional process, reduce energy consumption and production costs, and achieve the preparation of low-sulfur and low-sodium battery-grade lithium carbonate synthesized in one step by freezing and semi-carbonizing the purified liquid.

[0009] The technical solution adopted by the present invention is: The method for preparing low-sulfur and low-sodium battery-grade lithium carbonate in one step by a freezing semi-carbonization process comprises the following steps: Step 1: crush the lithium ore and grind it into fine powder, calcine it at a temperature of 1000-1200°C, then acidify, slurry mix, leach, alkalize and remove impurities, and remove impurities with resin to obtain a purified liquid; Step 2: After heating the purified liquid, add the carbonizing agent and stir until it becomes clear or nearly clear to obtain a pre-carbonized liquid; Step 3: The pre-carbonized liquid is frozen to precipitate the mirabilite, and the finished liquid is obtained after centrifugation. The finished liquid is added with a buffer to prepare a finished liquid slurry; Step 4: pump in lithium precipitation mother liquor, add washing water or pure water or a mixed solution of the two to prepare the base liquid; Step 5: Add the precipitant to the above base liquid, stir and clarify, then heat to 90-100°C, and add lithium carbonate seed crystals; Step 6: Slowly pump the finished liquid slurry obtained in step 3 into the mixed liquid obtained in step 5 to perform lithium precipitation reaction, control the feeding time, and control the insulation time after the feeding is completed, then centrifuge, stir, wash, rinse, dry, and crush to prepare battery-grade lithium carbonate; Step 7: Most of the lithium precipitation mother liquor can be returned to the front end for slurry preparation, and a small amount can be used to prepare the bottom liquid to achieve the recycling of the mother liquor.

[0010] By adopting the above process, sodium sulfate decahydrate is precipitated by freezing to take away part of the water, thereby increasing the concentration of lithium oxide, eliminating the evaporation and concentration steps of the purified liquid, reducing equipment investment, lowering energy consumption and production costs, and only requiring changes to the pipeline route in the original traditional process without purchasing other equipment to achieve the preparation of low-sulfur and low-sodium battery-grade lithium carbonate.

[0011] Preferably, in step 2, the purified liquid is heated to 25-48°C.

[0012] Preferably, in step 2, the carbonizing agent is sodium bicarbonate or a mixture of sodium bicarbonate and sodium carbonate, and the amount of sodium carbide in the mixture does not exceed 5% of the sodium bicarbonate.

[0013] Preferably, in step 2, the amount of carbonizing agent added is 7%-15% of the weight of the purified liquid.

[0014] Preferably, in step 3, freezing is performed once, and the freezing temperature is controlled to be 2°C~-7°C.

[0015] Preferably, in step 3, two freezings are performed, the temperature of the first freezing is controlled at 5-10 degrees Celsius, the freezing liquid after centrifugation is heated to 10-15°C, and sodium bicarbonate is added, the amount of which is 3%-6% of the weight of the first freezing liquid, and then a second freezing is performed, the temperature of the second freezing is controlled at 2°C~-7°C, and then sodium sulfate is separated by centrifugation, and the mother liquor is the finished liquid.

[0016] By adopting the above process, the operation can adopt single freezing or double freezing. During the secondary freezing, sodium bicarbonate needs to be added to provide sufficient sodium ions to ensure the precipitation of mirabilite and reduce the sulfate ions in the purified liquid to a sufficiently low level.

[0017] Preferably, in step 3, the buffer is sodium bicarbonate, and the amount of the buffer solvent added is 10-30% by weight of the finished solution.

[0018] Preferably, in step 4, the total volume of the base liquid is 40% of the volume of the finished liquid, of which the volume of the lithium precipitation mother liquid is 10%-15% of the volume of the finished liquid, and the rest is supplemented with washing water or pure water.

[0019] Preferably, in step 5, the precipitant is sodium carbonate or a mixture of sodium carbonate and sodium bicarbonate, which is added to the base liquid to control the concentration of soda ash in the base liquid to be 150-190 g / L and the concentration of sodium bicarbonate to be less than 30 g / L.

[0020] Preferably, in step 6, the insulation time is 40 min-120 min.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. The process of the present invention prepares a method for preparing low-sulfur and low-sodium battery-grade lithium carbonate in one step through a freezing semi-carbonization process, thereby reducing the content of sulfate ions and sodium ions in battery-grade lithium carbonate.

[0022] 2. The process of the present invention precipitates sodium sulfate decahydrate by freezing to carry away part of the water, thereby increasing the concentration of lithium oxide in the purified liquid, eliminating the evaporation and concentration process, and reducing energy consumption.

[0023] 3. The process of the present invention adds a carbonizing agent to the purified liquid, precipitates sodium sulfate after freezing, converts part of the lithium sulfate into lithium bicarbonate, and reduces the concentration of sulfate ions and sodium ions in the purified liquid.

[0024] 4. The process of the present invention freezes and semi-carbonizes the purified liquid so that the finished liquid contains a large amount of bicarbonate ions, which can reduce the amount and concentration of pure alkali solution, so as to control the nucleation rate during lithium precipitation and further reduce the sulfate ion and sodium ion content in the product. DETAILED DESCRIPTION Example

[0025] Step 1: crush 2.5 kg of lithium concentrate into fine powder, calcine at 1100 ° C, acidify, slurry, leaching, alkalize and remove impurities, and remove impurities with resin to obtain a purified liquid; Table 2. Purification liquid data, g / L

[0026] Step 2: After the purified liquid is heated to 48°C, 400g of sodium bicarbonate is added and stirred until the solution is almost clear to obtain a pre-carbonized liquid; Step 3: After the pre-carbonized liquid is frozen to -7°C, it is centrifuged to obtain about 840 kg of mirabilite and 2.92 L of finished liquid. 300 g of sodium bicarbonate is added to the finished liquid to prepare a finished liquid slurry for standby use; Table 3. Finished liquid data, g / L

[0027] Table 4. Sodium Sulfate Data, %

[0028] Step 4: Take 300 ml of lithium precipitation mother liquor, add 900 ml of pure water to make a bottom liquid, add 220 g of sodium carbonate to the bottom liquid, stir to clarify, heat to 95°C, and add 10 g of lithium carbonate seed crystals; Step 5: After the liquid slurry is completed, it is slowly pumped into the bottom liquid to carry out lithium precipitation reaction, which takes 200 minutes. After the feeding is completed, it is kept warm for 60 minutes, followed by centrifugation, stirring, washing, rinsing and drying operations.

[0029] Table 5. Battery grade lithium carbonate data, % Example

[0030] Step 1: crush 2.5 kg of lithium concentrate into fine powder, calcine at 1100 ° C, acidify, slurry, leaching, alkalize and remove impurities, and remove impurities with resin to obtain a purified liquid; Table 6. Purification liquid data, g / L

[0031] Step 2: After the purified liquid is heated to 40°C, 300g of sodium bicarbonate and 15g of sodium carbonate are added, and stirring is started until the solution is almost clear to obtain a pre-carbonized liquid; Step 3: After the pre-carbonized liquid is frozen to -2°C, it is centrifuged to obtain about 720 kg of mirabilite and 2.98 L of finished liquid. 200 g of sodium bicarbonate is added to the finished liquid to prepare a finished liquid slurry for standby use; Table 7. Finished liquid data, g / L

[0032] Table 8. Sodium Sulfate Data, %

[0033] Step 4: Take 300 ml of lithium precipitation mother liquor, add 900 ml of pure water to make a bottom liquid, add 220 g of sodium carbonate to the bottom liquid, stir to clarify, heat to 95°C, and add 10 g of lithium carbonate seed crystals; Step 5: After the liquid slurry is completed, it is slowly pumped into the bottom liquid to carry out lithium precipitation reaction, which takes 180 minutes. After the feeding is completed, it is kept warm for 50 minutes, followed by centrifugation, stirring, washing, leaching and drying operations.

[0034] Table 9. Battery grade lithium carbonate data, % Example

[0035] Step 1: crush 2.5 kg of lithium concentrate into fine powder, calcine at 1100 ° C, acidify, slurry, leaching, alkalize and remove impurities, and remove impurities with resin to obtain a purified liquid; Table 10. Purification liquid data, g / L

[0036] Step 2: After the purified liquid is heated to 35°C, 400g of sodium bicarbonate is added and stirred until the solution is almost clear to obtain a pre-carbonized liquid; Step 3: After the pre-carbonized liquid is frozen to -7°C, centrifuge and separate. The separated filtrate is heated to 14°C in a water bath, and then 100 g of sodium bicarbonate is added. After stirring until it is almost clear, it is further frozen to -7°C and centrifuged to obtain about 1020 g of mirabilite and 2.87 L of finished liquid. 200 g of sodium bicarbonate is added to the finished liquid to prepare a finished liquid slurry for standby use. Table 11. Finished liquid data, g / L

[0037] Table 12. Sodium Sulfate Data, %

[0038] Step 4: Take 300 ml of lithium precipitation mother liquor, add 900 ml of pure water to make a bottom liquid, add 200 g of sodium carbonate to the bottom liquid, stir to clarify, heat to 95°C, and add 10 g of lithium carbonate seed crystals; Step 5: The completed liquid slurry is slowly pumped into the bottom liquid to carry out lithium precipitation reaction, which takes 220 minutes. After the feeding is completed, it is kept warm for 80 minutes, followed by centrifugation, stirring, washing, leaching and drying operations.

[0039] Table 13. Battery grade lithium carbonate data, % Example

[0040] Step 1: 2.5 kg of lithium concentrate was crushed and ground into fine powder, calcined at 1100° C. and then acidified, 3 L of lithium precipitation mother liquor produced in Example 3 was transferred to prepare pulp, leached, alkalized and impurity-removed, and resin impurity-removed to obtain purified liquid; Table 14. Purification liquid data, g / L

[0041] Step 2: After the purified liquid is heated to 42°C, 450 g of sodium bicarbonate is added and stirred until the solution is almost clear to obtain a pre-carbonized liquid; Step 3: After the pre-carbonized liquid is frozen to -5°C, it is centrifuged to obtain about 810 g of mirabilite and 2.95 L of finished liquid. 150 g of sodium bicarbonate is added to the finished liquid to prepare a finished liquid slurry for later use; Table 15. Finished liquid data, g / L

[0042] Table 16. Sodium Sulfate Data, %

[0043] Step 4: Take 300 ml of lithium precipitation mother liquor, add 500 ml of pure water and 300 ml of wash water produced in Example 3 to prepare a base liquid, add 180 g of sodium carbonate to the base liquid, stir to clarify, heat to 95° C., and add 10 g of lithium carbonate seed crystals; Step 5: After the liquid slurry is completed, it is slowly pumped into the bottom liquid to carry out lithium precipitation reaction, which takes 150 minutes. After the feeding is completed, it is kept warm for 60 minutes, followed by centrifugation, stirring, washing, rinsing and drying operations.

[0044] Table 17. Battery grade lithium carbonate data, %

[0045] Compared with the traditional process, the process of the present invention requires evaporation and concentration of the purified liquid to prepare a finished liquid with a high lithium oxide concentration to improve the lithium precipitation yield and reduce the generation of mother liquor. This process freezes and precipitates sodium sulfate decahydrate to take away part of the water, improves the lithium oxide concentration, omits the evaporation and concentration steps of the purified liquid, reduces equipment investment, and reduces energy consumption and production costs; compared with the traditional process in which the finished liquid first precipitates lithium to prepare lithium carbonate, and the lithium carbonate is then carbonized with carbon dioxide and then heated and decomposed to prepare low-sulfur and low-sodium battery-grade lithium carbonate, this process omits the step of carbonizing lithium carbonate, reduces equipment investment, simplifies the process flow, and reduces production costs; compared with the traditional process in which the soda ash base liquid needs to be configured with 250g / L to improve the lithium precipitation yield, this process uses 160- 190g / L pure ash solution is used as the base liquid, and sodium bicarbonate is added as a buffer. By reducing the concentration of reactants and controlling the nucleation rate, the preparation of low-sulfur and low-sodium battery-grade lithium carbonate is finally achieved. Compared with the traditional process in which the lithium precipitation mother liquor is first frozen to precipitate Glauber's salt, and the sodium precipitation mother liquor is then reused for slurry preparation, the lithium precipitation mother liquor produced by this process is directly reused for slurry preparation, and only the purified liquid needs to be frozen, so the amount of solution required for freezing treatment in the process can be reduced. Compared with the traditional process in which the lithium precipitation mother liquor needs to be frozen twice to precipitate Glauber's salt, this process can be frozen once or twice. During the second freezing, sodium bicarbonate needs to be added to provide sufficient sodium ions to ensure the precipitation of Glauber's salt, so that the sulfate ions in the purified liquid are reduced to a sufficiently low level. Compared with the traditional process, although the concentration of the finished liquid and the concentration of the pure ash base liquid are reduced, the yield of lithium precipitation is not reduced, and the output of the mother liquor is almost the same as that of the traditional process. The process only needs to change the pipeline line on the original traditional process, and does not need to purchase other equipment to achieve the preparation of low-sulfur and low-sodium battery-grade lithium carbonate.

[0046] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by those skilled in the art should be included in the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing low-sulfur and low-sodium battery-grade lithium carbonate in one step by a freezing semi-carbonization process, characterized in that: The following steps are involved: Step 1: crush the lithium ore and grind it into fine powder, calcine it at a temperature of 1000-1200°C, then acidify, slurry mix, leach, alkalize and remove impurities, and remove impurities with resin to obtain a purified liquid; Step 2: After heating the purified liquid, add the carbonizing agent and stir until it becomes clear or nearly clear to obtain a pre-carbonized liquid; Step 3: The pre-carbonized liquid is frozen to precipitate the mirabilite, and the finished liquid is obtained after centrifugation. The finished liquid is added with a buffer to prepare a finished liquid slurry; Step 4: pump in lithium precipitation mother liquor, add washing water or pure water or a mixed solution of the two to prepare the base liquid; Step 5: Add the precipitant to the above base liquid, stir and clarify, then heat to 90-100°C, and add lithium carbonate seed crystals; Step 6: Slowly pump the finished liquid slurry obtained in step 3 into the mixed liquid obtained in step 5 to perform lithium precipitation reaction, control the feeding time, and control the insulation time after the feeding is completed, then centrifuge, stir, wash, rinse, dry, and crush to prepare battery-grade lithium carbonate; Step 7: Most of the lithium precipitation mother liquor can be returned to the front end for slurry preparation, and a small amount can be used to prepare the bottom liquid to achieve the recycling of the mother liquor.

2. The method for preparing low-sulfur and low-sodium battery-grade lithium carbonate by a one-step freezing semi-carbonization process according to claim 1, characterized in that: In step 2, the purified liquid is heated to 25-48°C.

3. The method for preparing low-sulfur and low-sodium battery-grade lithium carbonate by a one-step freezing semi-carbonization process according to claim 1, characterized in that: In step 2, the carbonizing agent is sodium bicarbonate or a mixture of sodium bicarbonate and sodium carbonate, and the amount of sodium carbide in the mixture does not exceed 5% of the sodium bicarbonate.

4. The method for preparing low-sulfur and low-sodium battery-grade lithium carbonate by a one-step freezing semi-carbonization process according to claim 1, characterized in that: In step 2, the amount of carbonizing agent added is 7%-15% of the weight of the purified liquid.

5. The method for preparing low-sulfur and low-sodium battery-grade lithium carbonate by a one-step freezing semi-carbonization process according to claim 1, characterized in that: In the step 3, freezing is performed once, and the freezing temperature is controlled to be 2°C to -7°C.

6. The method for preparing low-sulfur and low-sodium battery-grade lithium carbonate by a one-step freezing semi-carbonization process according to claim 1, characterized in that: In the step 3, two freezings are performed, the temperature of the first freezing is controlled at 5-10 degrees Celsius, the freezing liquid after centrifugation is heated to 10-15°C, and sodium bicarbonate is added, the amount of which is 3%-6% of the weight of the first freezing liquid, and then a second freezing is performed, the temperature of the second freezing is controlled at 2°C~-7°C, and then sodium sulfate is separated by centrifugation, and the mother liquor is the finished liquid.

7. The method for preparing low-sulfur and low-sodium battery-grade lithium carbonate by a one-step freezing semi-carbonization process according to claim 1, characterized in that: In step 3, the buffer is sodium bicarbonate, and the amount of the buffer solvent added is 10-30% of the weight of the finished solution.

8. The method for preparing low-sulfur and low-sodium battery-grade lithium carbonate in one step by the freezing semi-carbonization process according to claim 1, characterized in that: In step 4, the total volume of the base liquid is 40% of the volume of the finished liquid, of which the volume of the lithium precipitation mother liquid is 10%-15% of the volume of the finished liquid, and the rest is supplemented with washing water or pure water.

9. The method for preparing low-sulfur and low-sodium battery-grade lithium carbonate by a one-step freezing semi-carbonization process according to claim 1, characterized in that: In step 5, the precipitant is sodium carbonate or a mixture of sodium carbonate and sodium bicarbonate, which is added to the base liquid to control the concentration of soda ash in the base liquid to be 150-190 g / L and the concentration of sodium bicarbonate to be less than 30 g / L.

10. The method for preparing low-sulfur and low-sodium battery-grade lithium carbonate by a one-step freezing semi-carbonization process according to claim 1, characterized in that: In step 6, the insulation time is 40 min-120 min.

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