Method for preparing battery-grade lithium phosphate from salt lake high-impurity lithium carbonate and agricultural phosphate fertilizer

Abstract

A method for preparing battery-grade lithium phosphate by using salt lake high-impurity lithium carbonate and an agricultural phosphate fertilizer relates to the technical field of battery materials, and comprises the following steps: sequentially washing and acidolysis the salt lake high-impurity lithium carbonate to remove soluble and insoluble impurities in the salt lake high-impurity lithium carbonate, mixing the salt lake high-impurity lithium carbonate with the agricultural phosphate fertilizer, and carrying out secondary impurity removal and lithium precipitation processes to obtain the battery-grade lithium phosphate. And preparing the lithium phosphate required by the lithium ion battery. According to the method, high-value utilization of the two raw materials is well realized, and the raw material cost of the lithium source and the phosphorus source of the lithium ion battery is also effectively reduced. And the problem of excessive phosphate fertilizer is solved, the development of the lithium battery industry is promoted, and the lithium battery has better practical value.

Description

Technical Field

[0001] The invention relates to the field of battery materials, and in particular to a method for preparing battery-grade lithium phosphate by utilizing salt lake high-mix lithium carbonate and agricultural phosphate fertilizer. Background Art

[0002] With the development of society, China has transformed from a major importer of phosphate fertilizer to a major manufacturer of phosphate fertilizer. In 2007, my country has achieved a net export of phosphate fertilizer, with a total output of 13.51 million tons, and has maintained a considerable output since then. However, as the output of phosphate fertilizer becomes larger and larger, there is now a clear pressure to destock, so phosphate fertilizer products urgently need to be reformed in the direction of diversified products and high-value products.

[0003] On the other hand, salt lake high-impurity lithium carbonate refers to lithium carbonate extracted from salt lake brine and containing high impurities. There are many salt lakes distributed in my country. These salt lakes have rich lithium resources and are an important source of raw materials for extracting lithium carbonate. These lithium carbonates contain impurity elements such as sodium, potassium, magnesium, and calcium, and often require a lot of resources to purify before they can be put into use.

[0004] With the rapid popularity of the new energy industry, lithium iron phosphate and lithium iron manganese phosphate materials have become more and more popular, which has also led to a surge in the prices of upstream raw materials such as lithium and phosphorus. This has not only increased the production costs of enterprises, but also hindered the country's efforts to vigorously promote the industrialization of new energy.

[0005] On one hand, there is the overcapacity of agricultural phosphate fertilizers that need to be destocked, and the high-impurity lithium carbonate in salt lakes that needs to be purified due to high impurity content. On the other hand, there is the urgent need for lithium and phosphorus sources in the new energy industry. Faced with these two supply and demand contradictions, how to reuse the excess agricultural phosphate fertilizers and high-impurity lithium carbonate in salt lakes as phosphorus and lithium sources in the new energy industry has become a focus of current attention. Summary of the invention

[0006] The object of the present invention is to provide a method for preparing battery-grade lithium phosphate using salt lake high-mix lithium carbonate and agricultural phosphate fertilizer, which can use agricultural phosphate fertilizer and salt lake high-mix lithium carbonate as phosphorus source and lithium source, thereby realizing high-value utilization of the two raw materials and reducing the raw material costs of lithium source and phosphorus source of lithium-ion batteries.

[0007] The embodiment of the present invention is achieved as follows: A method for preparing battery-grade lithium phosphate using salt lake high-mix lithium carbonate and agricultural phosphate fertilizer, comprising: S1. Dissolve the salt lake high-mix lithium carbonate in water, collect the precipitate by filtration, and obtain crude lithium carbonate; S2. The crude lithium carbonate is dissolved with acid, and impurities are removed by filtration to obtain a first filtrate; S3. The first filtrate and the agricultural phosphate fertilizer are mixed, and the impurities are removed by filtration to obtain a second filtrate; S4. The second filtrate and the impurity removal agent are mixed and filtered to obtain a lithium phosphorus solution; S5. Adjust the pH of the lithium-phosphorus solution to 8-12, collect the precipitate by filtration, and obtain battery-grade lithium phosphate after drying.

[0008] The beneficial effects of the embodiments of the present invention are: The embodiment of the present invention provides a method for preparing battery-grade lithium phosphate using high-impurity lithium carbonate from salt lakes and agricultural phosphate fertilizer. The high-impurity lithium carbonate from salt lakes is washed and acid-lyzed to remove soluble and insoluble impurities therein, and then mixed with agricultural phosphate fertilizer, and the lithium phosphate required for lithium-ion batteries is prepared through secondary impurity removal and lithium precipitation processes. This method well realizes the high-value utilization of the two raw materials and effectively reduces the raw material costs of lithium sources and phosphorus sources for lithium-ion batteries. It not only solves the problem of excess phosphate fertilizer, but also promotes the development of the lithium battery industry, and has good practical value. DETAILED DESCRIPTION

[0009] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0010] The following is a detailed description of a method for preparing battery-grade lithium phosphate using salt lake high-mix lithium carbonate and agricultural phosphate fertilizer according to an embodiment of the present invention.

[0011] The present invention provides a method for preparing battery-grade lithium phosphate by using salt lake high-mix lithium carbonate and agricultural phosphate fertilizer, which comprises: S1. Dissolve the salt lake high-mix lithium carbonate in water, collect the precipitate by filtration, and obtain crude lithium carbonate; S2. The crude lithium carbonate is dissolved with acid, and impurities are removed by filtration to obtain a first filtrate; S3. The first filtrate and the agricultural phosphate fertilizer are mixed, and the impurities are removed by filtration to obtain a second filtrate; S4. The second filtrate and the impurity removal agent are mixed and filtered to obtain a lithium phosphorus solution; S5. Adjust the pH of the lithium-phosphorus solution to 8-12, collect the precipitate by filtration, and obtain battery-grade lithium phosphate after drying.

[0012] As the output of phosphate fertilizers becomes larger and larger, there is now a clear pressure to destock. On the other hand, salt lakes are rich in lithium resources and are an important source of raw materials for extracting lithium carbonate. These lithium carbonates contain impurities such as sodium, potassium, magnesium, and calcium, and often require a lot of resources to purify before they can be put into use. If there is a way to make use of these two methods at the same time, it will bring huge social value.

[0013] Agricultural phosphate fertilizers include at least one of monoammonium phosphate, diammonium phosphate and calcium hydrogen phosphate. The biggest problem with using agricultural phosphate fertilizers as a phosphorus source is the metal ions such as potassium and sodium they contain. These ions have high solubility and cannot be completely removed by recrystallization during the preparation of agricultural phosphate fertilizers, and will remain in the agricultural phosphate fertilizer products. As for the highly impure lithium carbonate in salt lakes, it is used as a lithium source. When purifying lithium carbonate, the existing technology usually uses fluoride to remove magnesium and calcium, and fluoride combines with lithium to form lithium fluoride precipitation, which will cause a large loss of lithium.

[0014] In view of the above situation, the inventor cleverly combined agricultural phosphate fertilizer and salt lake high-mix lithium carbonate. The method directly uses salt lake high-mix lithium carbonate that has not been pre-purified, avoiding the loss of lithium during the purification process. It adopts a reasonable processing sequence to complete the removal of impurity elements such as sodium, potassium, magnesium, and calcium during the mixed use of agricultural phosphate fertilizer and salt lake high-mix lithium carbonate. It not only effectively reduces the cost of raw materials, but also has a simple process, low requirements on equipment, reduces production costs, and has better social benefits.

[0015] Furthermore, in step S1, the mass ratio of the salt lake high impurity lithium carbonate to water is 1:0.5-10; after the salt lake high impurity lithium carbonate is dissolved in water, it is stirred and dissolved at 25-120° C. Under this condition, the soluble impurities in the salt lake high impurity lithium carbonate, such as potassium and sodium salts, can be fully dissolved, thereby removing most of the soluble impurities.

[0016] In step S2, the crude lithium carbonate is first mixed with 2 to 15 times the mass of water, and then 0.8 to 3 times the mass of acid is added to dissolve, stirred for reaction for 2 to 24 hours, and then filtered. Under the above conditions, the lithium carbonate in the salt lake high-mix lithium carbonate can be fully dissolved and filtered to remove insoluble impurities. Optionally, the acid includes at least one of sulfuric acid, nitric acid and hydrochloric acid.

[0017] In step S3, the amount of agricultural phosphate fertilizer added is calculated according to the molar ratio of lithium to phosphorus of 1:2.5-3.5; after adding the agricultural phosphate fertilizer, the mixture is stirred and reacted for 2-6 hours, and then filtered. Under the above conditions, the phosphate or hydrogen phosphate in the agricultural phosphate fertilizer can be used to complex lithium to avoid the loss of lithium, thereby further removing insoluble impurities.

[0018] In step S4, the mass ratio of the second filtrate to the impurity removal agent is 1:0.01~0.1; after the second filtrate and the impurity removal agent are mixed, the reaction is stirred for 2~24 hours and then filtered. Under the above conditions, the impurity removal agent can cause calcium, magnesium and other ions in the second filtrate to form a precipitate, thereby separating them from the second solution to obtain a relatively pure lithium phosphorus solution. Optionally, the impurity removal agent includes at least one of ammonia water, hydrogen fluoride, ammonium bifluoride, sodium hydroxide, potassium hydroxide, hydrofluoric acid, and fluorosilicic acid.

[0019] Furthermore, in step S5, the reaction temperature is 20-120°C and the reaction time is 2-24 h. Under the above conditions, lithium phosphate in the lithium-phosphorus solution can be precipitated and then separated from the solution by filtration, while the remaining small amount of impurity ions remain in the solution and are further removed.

[0020] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0021] Example 1 This embodiment provides a method for preparing battery-grade lithium phosphate using salt lake high-mix lithium carbonate and agricultural phosphate fertilizer, which comprises: S1. Preliminary impurity removal: Add 10 times the mass of water to the salt lake high-impurity lithium carbonate, then heat it to 80°C and stir it, so that some metal ion impurities in the lithium carbonate are removed in the form of soluble salts. After filtering, the lithium carbonate solid with preliminary impurity removal is obtained.

[0022] S2. Acid leaching: Add 5 times the mass of water to the lithium carbonate preliminarily removed from the impurities in step S1, and then add 2 times the mass of sulfuric acid, react for 6 hours to substantially dissolve the solid, and then filter to obtain insoluble residue and clarified filtrate.

[0023] S2. Supplementing the lithium source: adding solid phosphate fertilizer to the clarified filtrate obtained in step S2, controlling the molar concentration ratio of lithium to phosphorus to be 1:3, stirring for 4 hours and then filtering to remove insoluble impurities to obtain a clarified filtrate.

[0024] S4. Deep purification: Add 0.05 times the mass ratio of the impurity removal agent to the clarified filtrate obtained in step S3, react for 12 hours and filter to obtain a lithium-phosphorus solution after impurities are removed.

[0025] S5. Preparation of lithium phosphate: nitrogen is introduced into the lithium phosphate solution obtained in step S4 to control the pH value at 10, and then the solution is reacted at 90° C. for 12 hours and then filtered. The filter residue is dried and crushed to obtain a battery-grade lithium phosphate product.

[0026] Example 2 This embodiment provides a method for preparing battery-grade lithium phosphate using salt lake high-mix lithium carbonate and agricultural phosphate fertilizer, which comprises: S1. Preliminary impurity removal: Add 5 times the mass of water to the salt lake high-impurity lithium carbonate, then heat it to 80°C and stir it, so that some metal ion impurities in the lithium carbonate are removed in the form of soluble salts. After filtering, the lithium carbonate solid with preliminary impurity removal is obtained.

[0027] S2. Acid leaching: Add 5 times the mass of water to the lithium carbonate preliminarily removed from the impurities in step S1, and then add 2 times the mass of sulfuric acid, react for 6 hours to substantially dissolve the solid, and then filter to obtain insoluble residue and clarified filtrate.

[0028] S3. Supplementing the lithium source: adding solid phosphate fertilizer to the clarified filtrate obtained in step S2, controlling the molar concentration ratio of lithium to phosphorus to be 1:3, stirring for 4 hours and then filtering to remove insoluble impurities to obtain a clarified filtrate.

[0029] S4. Deep purification: Add 0.05 times the mass ratio of the impurity removal agent to the clarified filtrate obtained in step S3, react for 12 hours and filter to obtain a lithium-phosphorus solution after impurities are removed.

[0030] S5. Preparation of lithium phosphate: nitrogen is introduced into the lithium phosphate solution obtained in step S4 to control the pH at 8, and then the solution is reacted at 90° C. for 12 hours and filtered. The filter residue is dried and crushed to obtain a battery-grade lithium phosphate product.

[0031] Example 3 This embodiment provides a method for preparing battery-grade lithium phosphate using salt lake high-mix lithium carbonate and agricultural phosphate fertilizer, which comprises: S1. Preliminary impurity removal: Add 10 times the mass of water to the salt lake high-impurity lithium carbonate, then heat it to 80°C and stir it, so that some metal ion impurities in the lithium carbonate are removed in the form of soluble salts. After filtering, the lithium carbonate solid with preliminary impurity removal is obtained.

[0032] S2. Acid leaching: Add 5 times the mass of water to the lithium carbonate preliminarily removed from the impurities in step S1, and then add 2 times the mass of sulfuric acid, react for 6 hours to substantially dissolve the solid, and then filter to obtain insoluble residue and clarified filtrate.

[0033] S3. Supplementing the lithium source: adding solid phosphate fertilizer to the clarified filtrate obtained in step S2, controlling the molar concentration ratio of lithium to phosphorus to be 1:2, stirring for 4 hours and then filtering to remove insoluble impurities to obtain a clarified filtrate.

[0034] S4. Deep purification: Add 0.05 times the mass ratio of the impurity removal agent to the clarified filtrate obtained in step S3, react for 12 hours and filter to obtain a lithium-phosphorus solution after impurities are removed.

[0035] S5. Preparation of lithium phosphate: nitrogen is introduced into the lithium phosphate solution obtained in step S4 to control the pH value at 10, and then the solution is reacted at 90° C. for 12 hours and then filtered. The filter residue is dried and crushed to obtain a battery-grade lithium phosphate product.

[0036] Comparative Example 1 This comparative example provides a method for preparing battery-grade lithium phosphate using salt lake high-impurity lithium carbonate and agricultural phosphate fertilizer, which is basically the same as the method in the embodiment, except that in step S4, no impurity removal agent is added.

[0037] Comparative Example 2 This comparative example provides a method for preparing battery-grade lithium phosphate using salt lake high-impurity lithium carbonate and agricultural phosphate fertilizer, which is basically the same as the method in the embodiment, except that step S1 is eliminated and the method starts directly from step S2.

[0038] Comparative Example 3 This comparative example provides a method for preparing battery-grade lithium phosphate using salt lake high-mix lithium carbonate and agricultural phosphate fertilizer, which is basically the same as the method in the embodiment, except that in step S3, the molar concentration ratio of lithium and phosphorus is controlled at 1:5.

[0039] Comparative Example 4 This comparative example provides a method for preparing battery-grade lithium phosphate using salt lake high-mix lithium carbonate and agricultural phosphate fertilizer, which is basically the same as the method in the embodiment, except that in step S3, the molar concentration ratio of lithium and phosphorus is controlled to be 1:1.

[0040] Test example The methods provided in Examples 1 to 3 and Comparative Examples 1 to 4 were used to detect the impurity removal rates after different preliminary impurity removals and deep purifications, and the final products were analyzed for components. The analysis results are shown in Tables 1 to 2.

[0041] Table 1. Test results of product impurity removal effect Initial cleaning Deep purification Example 1 85% 99.5% Example 2 85% 99.2% Example 3 82% 99.6% Comparative Example 1 83% 97.4% Comparative Example 2 / 82.6% Comparative Example 3 83% 98.3% Comparative Example 4 84% 97.7% Table 2. Product component analysis results (unit: ppm) Al Ca K Mg Na S Mn High impurity lithium carbonate raw materials 8310.01 95054.72 222930.48 31167.40 123425.55 15855.20 496.11 Agricultural phosphate fertilizer raw materials 4002.29 12262.32 4237.67 7627.47 2123.32 53343.9 638.23 Example 1 23.25 38.65 41.49 15.78 21.45 20.46 11.56 Example 2 35.78 27.46 45.61 23.87 27.46 50.46 13.49 Example 3 52.32 31.26 39.81 35.21 30.56 62.49 30.47 Comparative Example 1 249.56 154.16 40.56 46.55 26.44 146.46 97.89 Comparative Example 2 1378.28 979.6 368.4 574.1 187.2 598.1 263.4 Comparative Example 3 32.57 31.46 104.9 21.97 99.34 57.12 35.18 Comparative Example 4 128.74 104.31 51.35 98.36 76.14 40.79 129.4 As can be seen from Table 1, by using the methods of Examples 1 to 3 of the present invention, in the preliminary impurity removal stage, the impurity removal rate can reach more than 82%, and most of the impurities in the salt lake high-mix lithium carbonate can be removed. In the deep purification stage, the impurity removal rate reached more than 99.2%, and the product purity was guaranteed. As can be seen from Table 2, the main impurity ions in the product are well controlled, meeting the requirements of electronic grade lithium phosphate.

[0042] In contrast, in Comparative Example 1, no impurity removal agent was used, and it can be seen that the content of impurities such as Al, Ca, S, and Mn has increased significantly. In Comparative Example 2, the preliminary impurity removal in step S1 was cancelled. It can be seen from Table 1 that the impurity removal rate after deep purification only reached 82.6%, and it can also be seen from Table 2 that a large amount of impurity ions still remain.

[0043] In Comparative Example 3, the amount of agricultural phosphoric acid was increased, and the excess phosphoric acid remained, resulting in a significant increase in the content of soluble ions such as Na and K. In Comparative Example 4, the amount of agricultural phosphoric acid was reduced, the content of high-mix lithium carbonate in the salt lake was too high, and a large amount of impurity ions remained. At the same time, due to the low content of phosphate, the lithium could not be completely complexed, resulting in a large amount of lithium loss.

[0044] In summary, the embodiment of the present invention provides a method for preparing battery-grade lithium phosphate using high-impurity lithium carbonate from salt lakes and agricultural phosphate fertilizer. The high-impurity lithium carbonate from salt lakes is washed and acid-lyzed in succession to remove soluble and insoluble impurities therein, and then mixed with agricultural phosphate fertilizer, and the lithium phosphate required for lithium-ion batteries is prepared through secondary impurity removal and lithium precipitation processes. This method well realizes the high-value utilization of the two raw materials, and also effectively reduces the raw material costs of lithium-ion batteries in lithium sources and phosphorus sources. It not only solves the problem of excess phosphate fertilizer, but also promotes the development of the lithium battery industry, and has good practical value. .

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing battery-grade lithium phosphate using salt lake high-mix lithium carbonate and agricultural phosphate fertilizer, characterized in that: include: S1. The salt lake high impurity lithium carbonate is dissolved in water, and the precipitate is collected by filtration to obtain crude lithium carbonate; S2. dissolving the crude lithium carbonate with an acid, filtering to remove impurities, and obtaining a first filtrate; S3. The first filtrate and the agricultural phosphate fertilizer are mixed, and impurities are removed by filtration to obtain a second filtrate; S4. The second filtrate and the impurity removal agent are mixed and filtered to obtain a lithium phosphorus solution; S5. Adjust the pH of the lithium-phosphorus solution to 8-12, collect the precipitate by filtration, and obtain the battery-grade lithium phosphate after drying.

2. The method according to claim 1, characterized in that In step S1, the mass ratio of the salt lake high-mix lithium carbonate to water is 1:0.5-10; after dissolving the salt lake high-mix lithium carbonate in water, the solution is stirred at 25-120°C.

3. The method according to claim 1, characterized in that In step S2, the crude lithium carbonate is first mixed with 2 to 15 times the mass of water, and then 0.8 to 3 times the mass of acid is added to dissolve it, and the reaction is stirred for 2 to 24 hours, and then filtered.

4. The method according to claim 3, characterized in that The acid includes at least one of sulfuric acid, nitric acid and hydrochloric acid.

5. The method according to claim 1, characterized in that: In step S3, the amount of the agricultural phosphate fertilizer added is calculated according to the molar ratio of lithium to phosphorus of 1:2.5-3.5; after adding the agricultural phosphate fertilizer, the mixture is stirred for reaction for 2-6 hours and then filtered.

6. The method according to claim 5, characterized in that The agricultural phosphate fertilizer includes at least one of monoammonium phosphate, diammonium phosphate and calcium hydrogen phosphate.

7. The method according to claim 1, characterized in that In step S4, the mass ratio of the second filtrate to the impurity-removing agent is 1:0.01-0.1; after the second filtrate and the impurity-removing agent are mixed, they are stirred for reaction for 2-24 hours and then filtered.

8. The method according to claim 7, characterized in that The impurity removal agent includes at least one of ammonia water, hydrogen fluoride, ammonium bifluoride, sodium hydroxide, potassium hydroxide, hydrofluoric acid, and fluorosilicic acid.

9. The method according to claim 8, characterized in that In the step S5, the reaction temperature is 20-120° C., and the reaction time is 2-24 h.