A method for purifying lithium carbonate

Abstract

The application discloses a purification method of lithium carbonate, which comprises the following steps: mixing industrial-grade lithium carbonate with water according to a certain proportion and stirring to carry out beating; under the stirring condition, carbon dioxide is introduced into the solution after beating to carry out a reaction, so that a lithium bicarbonate solution is obtained; after the reaction is completed, barium hydroxide is added dropwise into the lithium bicarbonate solution, and then filtration is carried out; a small amount of hydrofluoric acid is added dropwise into the obtained filtrate, and then filtration is carried out; the obtained lithium bicarbonate filtrate is subjected to a cation exchange column, so that a relatively pure lithium bicarbonate solution is obtained; the obtained lithium bicarbonate filtrate is subjected to pyrolysis crystallization, lithium carbonate crystals are obtained after filtration; the obtained lithium carbonate crystals are stirred with a certain amount of ultrapure water, and then filtration and washing are carried out, so that high-purity lithium carbonate is obtained. The application can obtain high-purity lithium carbonate with a purity of greater than or equal to 99.99%, the amount of hydrofluoric acid added in the process is smaller, the purpose of impurity removal can be achieved, and the influence on the product yield is reduced as much as possible.

Description

Technical Field

[0001] This invention belongs to the field of lithium carbonate purification technology, specifically relating to a technical process for purifying industrial-grade lithium carbonate to prepare high-purity lithium carbonate. Background Technology

[0002] Lithium carbonate, as an upstream product in the lithium industry, has a wide range of applications and can also be used as a raw material to prepare various lithium industrial products. Therefore, due to its unique position and properties, it has become an irreplaceable compound in the lithium salt industry. China has relatively abundant lithium resources, but the purity is relatively low. Currently, the application of high-purity lithium salts in high-tech fields such as new energy and new materials is constantly expanding, especially in the lithium battery industry, where its application is particularly prominent. The variety of products is constantly being innovated, and the output is increasing year by year, demonstrating the growing importance of lithium as an energy metal. On the other hand, with the rapid development of industries such as electrochemistry and new energy vehicles, the industrial applications of high-purity lithium carbonate are becoming more widespread. For example, high-purity lithium carbonate can be used to synthesize electrolyte lithium salts such as lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium tetrafluoroborate. These lithium salts have high requirements for the quality of lithium carbonate products. Therefore, developing high-purity lithium carbonate (99.9-99.99%) from industrial-grade lithium carbonate (98.5-99.4%) as raw material has great industrial application prospects.

[0003] Most existing technologies purify industrial lithium carbonate to battery-grade lithium carbonate. However, the resulting battery-grade lithium carbonate has a high sodium and potassium ion content, making it difficult to meet the production requirements of lithium salts such as lithium bis(fluorosulfonyl)imide. Furthermore, to remove the abundant calcium and magnesium ions in industrial lithium carbonate, hydrofluoric acid, barium hydroxide, and barium bicarbonate are typically introduced as precipitants to remove divalent impurity ions. However, the excessive use of hydrofluoric acid and barium salts can easily introduce fluoride and barium ions, generating new, difficult-to-remove impurities. Some patents can prepare high-purity lithium carbonate from industrial lithium carbonate, but this involves multiple ion exchange resin processes and washing, significantly reducing the lithium carbonate yield. This patent combines the washing filtrate and the pyrolysis crystallization filtrate as a mother liquor, which is then mixed with the raw lithium carbonate to form a slurry. This allows for the reuse of lithium carbonate dissolved in the mother liquor, reducing lithium carbonate loss.

[0004] Therefore, this patent does not rely entirely on adding precipitants to remove impurity metal ions. Instead, it combines the addition of small amounts of barium hydroxide and hydrofluoric acid as precipitants to remove divalent impurity ions with ion exchange resin. This reduces the introduction of new impurity ions and relatively reduces the yield loss caused by the number of times the filtrate passes through the ion exchange column, which is of great significance for industrial production. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method for purifying industrial lithium carbonate to high-purity lithium carbonate. The technical solution of this invention is as follows:

[0006] A method for purifying high-purity lithium carbonate includes the following steps:

[0007] (1) Mix industrial lithium carbonate with water, stir and slurry;

[0008] (2) Under stirring conditions, a certain amount of carbon dioxide is introduced into the pulping solution to react under controlled temperature. After a certain reaction time, lithium bicarbonate solution A is obtained.

[0009] (3) Based on the sulfate content in the raw material industrial lithium carbonate obtained by testing, add an appropriate amount of barium hydroxide to the lithium bicarbonate solution to remove magnesium ions and sulfate ions. The reaction time is 20-120 min, and the purity of barium hydroxide is 99.9%. After the reaction is completed, filter to obtain filtrate B.

[0010] (4) Add a small amount of hydrofluoric acid solution to filtrate B, stir for 10-60 min and then filter to obtain filtrate C;

[0011] (5) Pass the filtrate C obtained above through a chromatography column and repeat the process several times to obtain filtrate D.

[0012] (6) After heating the filtrate D to the set temperature, it is subjected to pyrolysis crystallization. After reacting for a certain time, it is filtered to obtain solid lithium carbonate and filtrate E. Filtrate E is stored as the mother liquor for the next batch of industrial-grade lithium carbonate for recycling.

[0013] (7) The solid lithium carbonate obtained above is pulped and washed, and then filtered to obtain lithium carbonate and filtrate F. After the lithium carbonate is dried for a certain period of time, high-purity lithium carbonate with a purity of 99.99% is obtained. Filtrate F and crystallization filtrate E are combined and used as mother liquor for mixing and pulping with the next batch of raw material lithium carbonate, which greatly reduces the discharge of waste liquid and the cost of environmental protection treatment. At the same time, the lithium carbonate dissolved in the mother liquor is recovered, and the yield is improved.

[0014] Preferably, the pulping operation in step (1) includes: the ratio of industrial-grade lithium carbonate to high-purity water is 1:(10-20), and the stirring speed is 300-500 r / min.

[0015] Preferably, the stirring speed in step (2) is 350-500 r / min, the reaction temperature is controlled at 0-15℃, the carbon dioxide flow rate is 0.5-2.0 L / min, and the reaction time is 2-4 h.

[0016] Preferably, the amount of barium hydroxide added in step (3) is 0.1 g / L to 0.3 g / L in the lithium bicarbonate solution.

[0017] Preferably, the reaction time after adding barium hydroxide in step (3) is 20-40 min.

[0018] Preferably, the reaction temperature after adding barium hydroxide in step (3) is 10-20℃.

[0019] Preferably, the hydrofluoric acid mentioned in step (4) is hydrofluoric acid with a mass fraction of 40-49%.

[0020] Preferably, the ratio of the mass of hydrofluoric acid added in step (4) to the mass of the raw material lithium carbonate is in the range of 1:(10-100).

[0021] Preferably, the reaction time after adding hydrofluoric acid in step (4) is in the range of 20-30 min.

[0022] Preferably, the reaction temperature after adding hydrofluoric acid in step (4) is 10-20℃.

[0023] Preferably, the ion exchange resin in step (5) is a mixed resin formed by LSC-500 resin, D451 resin and S930 resin in a mass ratio of 2-4:4-8:1-3; in some preferred embodiments, the mixed mass ratio of the resins LSC-500, D451 and S930 is 3:6:1.

[0024] The resin is packed into a chromatography column with a diameter of 2.0-2.5 cm, a height of 30-40 cm, and an aspect ratio of 16:1. The resin flows through the chromatography column at a flow rate of 0.4-2.0 L / h.

[0025] In some preferred configurations, the chromatography column has a diameter of 2.5 cm and an aspect ratio of 16:1.

[0026] Preferably, in step (5), the flow rate of the lithium bicarbonate filtrate through the exchange column is 0.5-1.0 L / h.

[0027] Preferably, in step (5), the lithium bicarbonate filtrate is passed through the cation exchange column 1-2 times.

[0028] Preferably, the reaction temperature in step (6) is 80-95℃.

[0029] Preferably, the reaction time in step (6) is 2-4 hours.

[0030] Preferably, the mother liquor synthesized from the pyrolysis crystallization filtrate and the pulping and washing filtrate in step (6) is mixed with industrial lithium carbonate as a raw material. The mother liquor is suitable to be reused 5 times in this process.

[0031] Preferably, in step (7), the mass ratio of ultrapure water to lithium carbonate during pulping and washing is 1:(5-10).

[0032] Preferably, during the pulping and washing process in step (7), the mechanical stirring rate is 300-500 r / min.

[0033] Preferably, the pulping temperature in step (7) is 70-90℃ during pulping and washing.

[0034] Preferably, the stirring time during pulping and washing in step (7) is 60-90 min.

[0035] Preferably, the filter membrane used for filtration in steps (3), (4), (6), and (7) is an acetate nitrocellulose filter membrane with a pore size of 3-5 μm.

[0036] Preferably, the drying temperature of solid lithium carbonate in step (7) is 80-100℃.

[0037] Preferably, the drying time of solid lithium carbonate in step (7) is 8-10 hours.

[0038] The final drying yields high-purity lithium carbonate with a purity of 99.99%, wherein the contents of sodium, potassium, calcium, and magnesium ions are ≤10ppm, the contents of iron, copper, nickel, lead, and aluminum ions are ≤5ppm, and the contents of sulfate and chloride ions are ≤20ppm.

[0039] Compared with the prior art, the technical solution provided by the present invention has the following technical advantages:

[0040] 1. The raw material used in this invention is industrial lithium carbonate, which is readily available and low in cost. The final purified lithium carbonate has a purity of 99.99%, which can meet the requirements of certain fields such as electrolyte lithium salts that have high purity requirements for lithium carbonate.

[0041] 2. This invention recycles and reuses the mother liquor obtained from the pyrolysis reaction process and the mother liquor obtained from pulping and washing, which can improve the total yield of lithium carbonate. The process also has the advantages of strong impurity removal ability and low wastewater discharge.

[0042] 3. This invention combines the use of precipitants for impurity removal with the use of ion exchange resins for metal ion removal. First, a small amount of hydrofluoric acid and barium hydroxide are used to initially remove large amounts of calcium, magnesium, and sulfate ions. More importantly, a mixed resin formed by D451 (macroporous urea-formaldehyde chelating resin), LSC-500 (macroporous aminophosphonic acid chelating resin), and S930 (macroporous polystyrene chelating resin) is used to further remove sodium, potassium, calcium, magnesium, zinc, copper, nickel, and other metal ions. Then, a final pulping and washing step continues to remove difficult-to-remove monovalent impurity ions such as sodium and potassium ions. This process ultimately purifies industrial-grade lithium carbonate raw materials to a high purity of 99.99% lithium carbonate.

[0043] This invention employs three types of chelating resins. Chelating resins have a wider pH range and are suitable for both weakly acidic and weakly alkaline environments. They are applicable to the removal of impurities from lithium bicarbonate in a weakly alkaline environment as described in this invention. Furthermore, chelating resins have a certain removal effect on sodium ions, which can specifically solve the problem of high sodium ion content during the purification process of lithium carbonate, making it difficult to remove sodium ions. Among them, D451 chelating resin has a good removal effect on sodium and potassium ions, LSC-500 chelating resin has a good removal effect on calcium, magnesium, sodium and potassium ions, and S930 chelating resin has a good removal effect on heavy metal ions such as copper, lead, nickel, zinc, cobalt and manganese ions. In addition, the three chelating resins still have good stability when used in combination, allowing their respective removal performance to be brought into play. They can remove metal impurity ions such as sodium, potassium, calcium, magnesium, copper, lead and nickel ions in one step. Compared with a single resin, more ions are removed in one step, avoiding the need for multi-stage resin removal and reducing the removal cost in the production process. Furthermore, when the usage ratio of the three chelating resins is adjusted, different impurity removal effects will be achieved on metal impurity cations. In order to solve the problem that sodium ions are prone to excessive levels during the purification of lithium carbonate, followed by calcium ions and magnesium ions with slight excesses, and heavy metal ions with occasional excesses, this invention focuses on increasing the usage ratio of D451 resin, using LSC-500 resin in moderation, and using a small amount of S930 resin. Attached Figure Description

[0044] Figure 1 This is a flow chart of the lithium carbonate purification process of the present invention. Detailed Implementation

[0045] To fully demonstrate the synergistic effect between different resins in this invention, which has a better impurity removal effect than a single resin, and to demonstrate the influence of using resins in different ratios on the impurity removal effect, the invention will be described in detail through the following specific embodiments. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments.

[0046] Example 1

[0047] 200g of industrial lithium carbonate (99% purity) was weighed and mixed with water at a ratio of 1:15, and the mixture was pulped at a stirring speed of 400 rpm. Carbon dioxide was introduced into the pulped solution at a flow rate of 0.6 L / min, and the reaction temperature was 5℃. After 2 hours of reaction, lithium bicarbonate solution A was obtained. 0.4g of barium hydroxide (99.9%) was added to the lithium bicarbonate solution. The reaction temperature was 15℃, and the reaction was stopped and filtered after 30 minutes to obtain filtrate B. 4g of 49% hydrofluoric acid was added dropwise to filtrate B, and the mixture was stirred at 10℃ for 30 minutes at a stirring speed of 450 rpm. After the reaction was completed, the mixture was filtered to obtain filtrate C. The filtrate was passed through a chromatography column (the ion exchange resins were LSC-500, D451, and S930 mixed in a ratio of 3:4:3, and this resin was packed into the chromatography column, which had a diameter of 2.5 cm, a height of 40 cm, and an aspect ratio of 16:1, and flowed through the column at a rate of 1.0 L / h). The flow was repeated twice. The resulting filtrate D was subjected to pyrolysis crystallization at 95°C for 3 hours. After filtration and washing, sub-high-purity lithium carbonate and filtrate E were obtained. Solid lithium carbonate was then mixed with ultrapure water at a ratio of 1:5 and slurried at 80°C and a stirring speed of 400 r / min for 2 hours. This slurry was then filtered to obtain high-purity lithium carbonate wet material and filtrate F. The wet lithium carbonate was dried in an oven at 80°C for 8 hours to obtain the high-purity lithium carbonate product, with a yield of 70.5%.

[0048] Example 2

[0049] Weigh 150g of industrial lithium carbonate (99% purity), and then weigh 2700g of the mother liquor formed from filtrate E and filtrate F. Mix the industrial lithium carbonate with the mother liquor, add 300g of ultrapure water, and then start stirring, controlling the mechanical stirring speed at 400 rpm. Introduce carbon dioxide gas into the mixed solution, controlling the carbon dioxide flow rate at 0.6 L / min, and maintain the reaction temperature at 5°C. After reacting for 2 hours, obtain lithium bicarbonate solution A. Add 0.4g of barium hydroxide to the lithium bicarbonate solution, maintain the reaction temperature at 15°C, and stop the reaction after 30 minutes, then filter to obtain filtrate B. Add 4g of 49% hydrofluoric acid dropwise to filtrate B, and then stir at 10°C for 30 minutes at a speed of 450 rpm. After the reaction is complete, filter to obtain filtrate C. The filtrate was passed through a chromatography column (ion exchange resins LSC-500, D451, and S930 were mixed in a ratio of 3:6:1 and packed into the column; the column diameter was 2.5 cm, height 40 cm, aspect ratio 16:1, and flow rate was 1.0 L / h). The filtrate was passed through the column twice. The resulting filtrate D was subjected to pyrolysis crystallization at 95°C for 3 hours. After filtration and washing, sub-high-purity lithium carbonate and filtrate E were obtained. Solid lithium carbonate was then mixed with ultrapure water at a ratio of 1:5 and slurried at 80°C and a stirring speed of 400 r / min for 2 hours. This slurry was then filtered to obtain high-purity lithium carbonate wet material and filtrate F. The wet lithium carbonate was dried in an oven at 80°C for 8 hours to obtain the high-purity lithium carbonate product, with a yield of 89.1%.

[0050] Example 3

[0051] The method and steps are the same as in Example 2, except that the ion exchange resins LSC-500, D451 and S930 are mixed in a ratio of 2:6:2, and the yield is 90.8%.

[0052] Example 4

[0053] The method and steps are the same as in Example 2, and the ratio of the three ion exchange resins is also the same as in Example 2. The difference is that the ion exchange resins were reused for 3 days, and the yield obtained was 90.8%.

[0054] Example 5

[0055] The method and steps are the same as in Example 2, and the ratio of the three ion exchange resins is also the same as in Example 2. The difference is that the ion exchange resins were reused for 6 days, and the yield obtained was 90.8%.

[0056] Example 6

[0057] The method and steps are the same as in Example 2, and the ratio of the three ion exchange resins is also the same as in Example 2. The difference is that the ion exchange resins were reused for 9 days, and the yield obtained was 90.8%.

[0058] Example 7

[0059] The method and steps are the same as in Example 2, except that the ion exchange resins D451 and S930 are mixed in a ratio of 6:1, and the yield is 90.3%.

[0060] Example 8

[0061] The method and steps are the same as in Example 2, except that the ion exchange resins D451 and LSC-500 are mixed in a ratio of 6:3, and the yield is 92.7%.

[0062] Example 9

[0063] The method and steps are the same as in Example 2, except that the ion exchange resins S930 and LSC-500 are mixed in a ratio of 1:3, and the yield is 91.4%.

[0064] Comparative Example 1: 200g of industrial lithium carbonate (99% purity) was weighed and mixed with water at a ratio of 1:15, and the mixture was pulped at a stirring speed of 400 rpm. Carbon dioxide was introduced into the pulped solution, with a flow rate of 0.6 L / min and a reaction temperature of 5°C. After 2 hours of reaction, lithium bicarbonate solution A was obtained. 0.4g of barium hydroxide (99.9%) was added to the lithium bicarbonate solution. The reaction temperature was 15°C, and the reaction was stopped and filtered after 30 minutes to obtain filtrate B. 4g of 49% hydrofluoric acid was added dropwise to filtrate B, and the mixture was stirred at 10°C for 30 minutes at a stirring speed of 450 rpm. After the reaction was completed, the mixture was filtered to obtain filtrate C. The above filtrate C was subjected to pyrolysis crystallization at 95℃ for 3 hours, followed by filtration and washing to obtain sub-high-purity lithium carbonate and filtrate D. Solid lithium carbonate was then mixed with ultrapure water at a 1:5 ratio and slurried at 80℃ and a stirring speed of 400 r / min for 2 hours. This mixture was then filtered to obtain high-purity lithium carbonate wet material and filtrate E. The wet lithium carbonate material was dried in an oven at 80℃ for 8 hours to obtain the high-purity lithium carbonate product, with a yield of 69.8%.

[0065] The contents of cationic and anionic impurities in lithium carbonate obtained in Examples 1-9 and Comparative Example 1 were tested, and the results are shown in Table 1.

[0066] Table 1. Impurity content in lithium carbonate purified in Examples 1-9 and Comparative Example 1.

[0067]

[0068] Based on the yield results of Examples 1-5 and the detection results of cationic impurities in the purified lithium carbonate in Table 1, it can be seen that the lithium carbonate prepared by the process used in this invention achieves a purity of 99.99%, with metal cationic impurity content <10ppm and chloride and sulfate ion content <20ppm. Examples 1-3 show that when the three resins are mixed in different proportions, the resin with LSC-500, D451, and S930 mixed in a ratio of 3:6:1 exhibits better filtration performance for impurity ions in the lithium bicarbonate solution, and removes sodium, potassium, calcium, and magnesium ions more effectively. Examples 4-6 show that after using a mixture of LSC-500, D451, and S930 resins for a certain period, the mixture can remain stable for about 6 days. Continued use reduces its ability to remove metal impurity ions, leading to excessive sodium, potassium, and calcium ion content in the product. As shown in Examples 7-9, the new filled resin obtained by mixing two of the three resins LSC-500, D451, and S930 all have certain defects in filtering metal impurities and cannot completely and effectively reduce sodium ions, potassium ions, calcium ions, magnesium ions, and heavy metal ions to a reasonable range. In Comparative Example 1, when the same hydrofluoric acid and barium hydroxide were added, without the special ion exchange resin column of this invention, sodium ions, potassium ions, calcium ions, and magnesium ions were difficult to remove completely. Compared with the traditional hydrofluoric acid process, this invention adds a special ion exchange resin column and pulping and washing, making the removal of metal ions such as sodium and potassium ions more thorough. Then, the crystallization filtrate and pulping and washing filtrate are reused, reducing the loss of lithium carbonate in the process. The yield after mother liquor reuse reaches up to 92.7%, proving that this process has good prospects for industrial application. In summary, the new resin obtained by mixing LSC-500, D451 and S930 resins in a certain proportion has a significant synergistic effect, with no obvious interference between them, and can be used stably for several days. Moreover, when LSC-500, D451 and S930 are mixed in a ratio of 3:6:1, this synergistic effect is even better, and the metal impurity ions can be reduced to a very low level.

[0069] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for purifying lithium carbonate, characterized in that, include: (1) Mix industrial lithium carbonate with water, stir and slurry; (2) Under stirring conditions, carbon dioxide is introduced to carry out the reaction at a controlled temperature. After a certain reaction time, lithium bicarbonate solution A is obtained; (3) Barium hydroxide is added dropwise to lithium bicarbonate solution A to remove magnesium ions and sulfate ions. After the reaction is completed, the solution is filtered to obtain lithium bicarbonate solution B. (4) Add a small amount of hydrofluoric acid to the above filtrate B to remove calcium ions. After the reaction is complete, filter to obtain filtrate C. (5) Pass the above-obtained filtrate C through a chromatography column to obtain filtrate D; the ion exchange resin used in the chromatography column is a mixed resin formed by LSC-500 type resin, D451 resin and S930 resin in a mass ratio of 2-4:4-8:1-3. (6) After heating and crystallizing the filtrate D, filter it to obtain solid lithium carbonate and filtrate E; (7) The above solid lithium carbonate is dried to obtain lithium carbonate.

2. The method for purifying lithium carbonate according to claim 1, characterized in that, The pulping operation in step (1) includes: the ratio of industrial-grade lithium carbonate to high-purity water is 1:(5-25), the stirring speed is 200-600r / min, the purity of industrial-grade lithium carbonate is 98.5-99.4%, and the conductivity of ultrapure water is ≤0.2us / cm.

3. The method for purifying lithium carbonate according to claim 1, characterized in that, The stirring speed in step (2) is 200-500 r / min, the reaction temperature is controlled at 0-20℃, the carbon dioxide flow rate is 0.2-10.0 L / min, and the carbon dioxide aeration time is 1-6 h.

4. The method for purifying lithium carbonate according to claim 1, characterized in that, In step (3), the amount of barium hydroxide added is 0.05 g / L to 2.0 g / L in lithium bicarbonate solution, the reaction temperature is 0 to 25°C, the reaction time after adding barium hydroxide is 20 to 120 min, and the purity of barium hydroxide is 99.9%.

5. The method for purifying lithium carbonate according to claim 1, characterized in that, In step (4), the ratio of the amount of hydrofluoric acid added to the mass of the raw material lithium carbonate is 1:(10-100), the mass concentration of hydrofluoric acid is 40-49%, the reaction temperature is 0-25℃, and the reaction time after adding hydrofluoric acid is 10-60 min.

6. The method for purifying lithium carbonate according to claim 1, characterized in that, The resin is packed into a chromatography column with a diameter of 2.0-2.5 cm, a height of 30-40 cm, and an aspect ratio of 16:

1. The resin flows through the chromatography column at a flow rate of 0.4-2.0 L / h.

7. The method for purifying lithium carbonate according to claim 1, characterized in that, The reaction temperature in step (6) is 70-100℃ and the reaction time is 0.5-4h.

8. The method for purifying lithium carbonate according to claim 1, characterized in that, The mixing ratio of lithium carbonate and water in step (7) is 1:(3-10), the stirring rate after mixing is 200-500 r / min, the stirring time is 30-120 min, and the temperature of pulping and washing is 50-90℃.

9. The method for purifying lithium carbonate according to claim 1, characterized in that, The filter membrane used in steps (3), (4), (6), and (7) is an acetic acid nitrocellulose filter membrane with a pore size ≤ 5 μm; the lithium carbonate obtained after filtration in step (7) is dried at a temperature of 70-150℃ for 8-15 hours.

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