A method for producing battery-grade lithium dihydrogen phosphate from lithium-containing brine

Abstract

A method for producing battery-grade lithium dihydrogen phosphate using lithium-containing brine includes the following steps: (1) adding sodium hydroxide solution to lithium-containing mother liquor, adding the mixed solution to sodium dihydrogen phosphate solution, maintaining the pH of the system at 9-11, reacting, separating the solid and liquid phases to obtain lithium phosphate precipitate and mother liquor; (2) adjusting the slurry, adding concentrated sulfuric acid to react, separating the solid and liquid phases to obtain a mixed solution of liquid-phase lithium dihydrogen phosphate and lithium sulfate; (3) vacuum cooling and crystallization separation to obtain lithium dihydrogen phosphate crystals. This invention achieves efficient recovery of lithium ions from low-concentration lithium-containing brine, eliminating the need for conventional processes such as electrodialysis and MVR for further concentration of lithium-containing mother liquor. It also avoids the use of phosphoric acid in the acidification process, saving raw material costs, reducing the amount of water added in the acidification process, and reducing energy consumption in the crystallization separation process. The resulting battery-grade lithium dihydrogen phosphate is of stable quality, uniformly distributed, and bright white in color, suitable for preparing lithium-ion battery cathode materials, and has a low cost.

Description

Technical Field

[0001] This invention relates to a method for treating low-concentration lithium-containing brine, and more particularly to a method for producing battery-grade lithium dihydrogen phosphate using low-concentration lithium-containing brine. Background Technology

[0002] Lithium dihydrogen phosphate (LDH) is a crucial raw material in the production of lithium iron phosphate (LFP). Compared to other processes, LFP produced via LDH (ferrous oxalate process) boasts advantages such as high compaction density, high energy density, and excellent cycle performance, making it the primary choice for third- and fourth-generation LFP. Traditional processes use lithium hydroxide or lithium carbonate as the lithium source, combined with phosphoric acid as the phosphorus source, resulting in persistently high raw material costs. In particular, the price of battery-grade lithium hydroxide fluctuates significantly, substantially impacting production cost control. Furthermore, the reaction process generates substantial amounts of phosphorus-containing wastewater, posing significant challenges for environmental treatment. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a low-cost method for producing battery-grade lithium dihydrogen phosphate using lithium-containing brine, and the resulting battery-grade lithium dihydrogen phosphate product has relatively stable quality.

[0004] The technical solution adopted by this invention to solve its technical problem is a method for producing battery-grade lithium dihydrogen phosphate using lithium-containing brine, comprising the following steps:

[0005] (1) A certain amount of sodium hydroxide solution was added to the lithium-containing mother liquor, and then the mixed solution was slowly added to the sodium dihydrogen phosphate solution. The pH of the system was kept at 9~11. After reacting for a period of time, lithium phosphate slurry was obtained. Solid-liquid separation was performed to obtain lithium phosphate precipitate and mother liquor.

[0006] (2) Add water or lithium-containing mother liquor obtained in step (3) to the lithium phosphate precipitate obtained in step (1) to adjust the slurry, and then add a certain amount of concentrated sulfuric acid to react and obtain a slurry containing lithium sulfate monohydrate solid. The solid-liquid separation yields a liquid phase mixed solution of lithium dihydrogen phosphate and lithium sulfate and a solid phase of lithium sulfate monohydrate.

[0007] (3) The mixed solution of liquid lithium dihydrogen phosphate and lithium sulfate obtained in step (2) is subjected to vacuum cooling and crystallization separation to obtain lithium dihydrogen phosphate crystals and lithium-containing mother liquor.

[0008] The purity of the obtained lithium dihydrogen phosphate crystals is >99.5%.

[0009] Furthermore, in step (1), the lithium-containing mother liquor is lithium-containing brine that has been purified by removing calcium and magnesium.

[0010] Furthermore, in step (1), the lithium-containing brine is at least one of salt lake brine, underground brine, etc.

[0011] Furthermore, in step (1), the lithium ion concentration in the purified lithium-containing brine after calcium and magnesium removal is not less than 5 g / L, the calcium ion content is not higher than 5 mg / L, and the magnesium ion content is not higher than 5 mg / L. Existing technologies require a high lithium ion content in the lithium source, but this invention is applicable to brine with both high and low lithium ion content, thus reducing the cost of the lithium source.

[0012] Furthermore, in step (1), the amount of sodium dihydrogen phosphate added is such that the molar ratio of phosphate ions to lithium ions in the lithium-containing mother liquor is 0.9~1.3:3.

[0013] Furthermore, in step (1), the reaction temperature is 10~70℃ and the reaction time is 10~60 minutes.

[0014] Furthermore, in step (2), the solid content of the system is maintained at 30~50wt% after slurry preparation.

[0015] Furthermore, in step (2), the reaction temperature is 60~90℃, and the reaction time is 10~60 minutes. Too low a reaction temperature affects the single-batch yield of lithium dihydrogen phosphate and increases the recycling rate, while too high a reaction temperature wastes energy.

[0016] Further, in step (2), the concentration of the sulfuric acid solution is 70~100wt%. The molar ratio of sulfuric acid to lithium phosphate in the added sulfuric acid solution is 1~1.15:1. In step (2), the lithium phosphate acidification does not require the addition of phosphoric acid; it reacts directly with the sulfuric acid solution. In step (2), a certain amount of concentrated sulfuric acid is directly added to the mixed solution after slurry preparation. The heat of dilution is used to increase the reaction rate, improve the solubility of lithium dihydrogen phosphate, and reduce the solubility of lithium sulfate.

[0017] Furthermore, in step (2), the lithium phosphate precipitate does not need to be washed and reacts directly with the sulfuric acid solution.

[0018] Furthermore, in step (3), the separation of lithium dihydrogen phosphate and lithium sulfate does not require evaporation and crystallization, but rather utilizes the difference in solubility between co-saturated lithium sulfate and lithium dihydrogen phosphate at different temperatures to separate lithium dihydrogen phosphate.

[0019] Furthermore, in step (3), the temperature of the vacuum crystallization separation is 30~50℃, and the reaction time is 10~60 minutes. Vacuum crystallization is a vacuum cooling process in which the mixed solution is cooled from 90℃ to 40℃ under vacuum conditions.

[0020] Furthermore, in step (2), the collected lithium sulfate monohydrate crystals are used for the production of lithium hydroxide.

[0021] The lithium-containing mother liquor in step (3) is reused for the dilution of sulfuric acid in step (2), so that lithium ions can be recycled and reused, thereby increasing the yield of lithium dihydrogen phosphate.

[0022] This invention provides a method for producing battery-grade lithium dihydrogen phosphate using lithium-containing brine. The method directly uses lithium-containing brine instead of lithium hydroxide or lithium carbonate; uses sulfuric acid of a certain concentration instead of phosphoric acid; and uses vacuum crystallization to precipitate lithium dihydrogen phosphate by taking advantage of the difference in solubility of lithium dihydrogen phosphate and lithium sulfate when co-saturated under cooling conditions. At the same time as the precipitation of lithium dihydrogen phosphate, lithium sulfate monohydrate is not precipitated.

[0023] The principle of this invention is as follows: Sodium dihydrogen phosphate is added to lithium-containing brine that has been purified by removing calcium and magnesium, and sodium hydroxide is added to adjust the pH value to obtain lithium phosphate precipitate (the reaction process is shown in reaction formula 1 using sodium dihydrogen phosphate as an example). The lithium phosphate precipitate is separated, and then reacted with sulfuric acid solution to generate a mixture of lithium dihydrogen phosphate and lithium sulfate (the reaction process is shown in reaction formula 2). Since lithium dihydrogen phosphate has a high solubility, while lithium sulfate has a low solubility, and the solubility of lithium sulfate decreases with increasing temperature, the difference in solubility between lithium dihydrogen phosphate and lithium sulfate is utilized to control the reaction temperature and concentration of lithium phosphate and sulfuric acid, so that lithium dihydrogen phosphate is fully dissolved in the liquid phase and its solubility is less than its saturation solubility, while lithium sulfate cannot be completely dissolved, and lithium sulfate monohydrate crystals precipitate.

[0024] The reaction formulas involved are as follows:

[0025] 3Li + +NaH2PO4+2NaOH→Li3PO4↓+3Na + +2H₂O (Reaction 1)

[0026] Li3PO4 + H2SO4 + H2O → LiH2PO4 + Li2SO4·H2O (Reaction 2)

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention uses lithium-containing brine instead of lithium hydroxide or lithium carbonate, which reduces the cost of raw materials; and uses sulfuric acid instead of phosphoric acid, which only requires that the sulfuric acid does not introduce heavy metal impurities, thus reducing the cost.

[0029] (2) The lithium-containing brine used in this invention can be a low-concentration lithium-containing brine, which can be purified by nanofiltration reverse osmosis and calcium and magnesium removal processes without the need for further concentration by electrodialysis and MVR process, thus shortening the existing process route and ensuring that the lithium ion yield is the same as that of the existing process.

[0030] (3) The present invention uses vacuum crystallization, which utilizes the difference in solubility between lithium dihydrogen phosphate and lithium sulfate under cooling conditions to precipitate lithium dihydrogen phosphate. This method has lower energy consumption than the evaporation method proposed by similar processes. The lithium dihydrogen phosphate crystals produced are larger in particle size than those produced by the evaporation process, making them easier to separate. Their thermal response performance is more sensitive, which can reduce the capacity efficiency of the pre-burning process in the subsequent lithium iron phosphate production process.

[0031] (4) By adding high concentration of sulfuric acid, the present invention makes full use of the heat of dissolution of sulfuric acid and further reduces energy consumption.

[0032] (5) The present invention produces lithium hydroxide from the produced lithium sulfate. The lithium sulfate is purified and concentrated. Compared with the existing processes of producing lithium sulfate from salt lake brine and producing lithium sulfate from ore, the solvent evaporation process is omitted, which effectively saves energy. The mother liquor after separating lithium dihydrogen phosphate is recycled for dilution of sulfuric acid, which effectively improves the lithium ion yield of the cycle, reduces the amount of recycling, and further reduces the production cost.

[0033] This invention achieves efficient recovery of lithium ions from low-concentration lithium-containing brine, eliminating the need for conventional processes such as electrodialysis and MVR (Medium-Volume Reduction) to further concentrate the lithium-containing mother liquor. It also avoids the use of phosphoric acid in the acidification process, saving raw material costs and reducing water addition. The crystallization separation process has low energy consumption, thus optimizing the high energy consumption problem of existing evaporation crystallization processes. The resulting battery-grade lithium dihydrogen phosphate is stable, uniformly distributed, and bright white, making it suitable for preparing lithium-ion battery cathode materials. Its cost is significantly lower than existing processes, resulting in substantial economic and social benefits. Attached Figure Description

[0034] Figure 1 This is a graph showing the weight changes of self-made lithium dihydrogen phosphate and purchased lithium dihydrogen phosphate prepared in Example 1 of this invention as a function of temperature.

[0035] Figure 2 This is a graph showing the heat absorption data of the self-made lithium dihydrogen phosphate and the purchased lithium dihydrogen phosphate prepared in Example 1 of this invention as a function of temperature. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments.

[0037] The lithium-containing brine used in the embodiments of this specification after calcium and magnesium removal purification is lithium-containing mother liquor, which is salt lake brine after the nanofiltration reverse osmosis-calcium and magnesium removal process. Its main components are shown in Table 1 below.

[0038] Table 1

[0039]

[0040] Example 1

[0041] The method for producing battery-grade lithium dihydrogen phosphate using lithium-containing brine in this embodiment includes the following steps:

[0042] (1) Add 300 mL of 10% sodium hydroxide solution to 1000 g of lithium-containing mother liquor. Slowly add the mixed solution to 137 g of 30% sodium dihydrogen phosphate solution. Keep the system temperature at 40 °C and control the pH of the system after complete mixing to 10.5, which is conducive to the precipitation of lithium phosphate. The main reaction in the turbid liquid is reaction one. The reaction time is 30 minutes to obtain lithium phosphate slurry. After solid-liquid separation, 37.9 g of lithium phosphate precipitate and 1399.1 g of low-lithium mother liquor are obtained. The average particle size of lithium phosphate is 135.5 μm and the purity is 98.53%.

[0043] (2) Add 37.9g ​​of solid lithium phosphate to the reactor without washing. Add 13.9g of water and 113.8g of lithium dihydrogen phosphate mother liquor obtained in step (3) at 40℃ to the reactor. Adjust the slurry and keep the solid content of the system at 23wt%. Slowly add 36.1g of 98wt% concentrated sulfuric acid (the molar ratio of sulfuric acid to lithium phosphate in the sulfuric acid solution is 1~1.15:1) to keep the acid in excess. The reaction time is 60 minutes to allow the lithium phosphate to react fully. At 90℃, convert lithium dihydrogen phosphate according to the second reaction process and completely dissolve it so that its solubility is less than the saturated solubility and it will not precipitate. At the same time, lithium sulfate is obtained during the reaction. Due to the inhibition of lithium sulfate dissolution by the co-saturated system, a small part of lithium sulfate 4.0g is in the liquid phase, and most of the lithium sulfate 31.4g precipitates in the form of lithium sulfate monohydrate. A slurry containing solid lithium sulfate monohydrate is obtained. Solid-liquid separation is performed to obtain a mixed solution of liquid lithium dihydrogen phosphate and lithium sulfate and a solid lithium sulfate monohydrate.

[0044] (3) Cool the mixed solution of lithium dihydrogen phosphate and lithium sulfate obtained in step (2) at 90°C to 40°C, filter to obtain 10.2g of lithium dihydrogen phosphate crystals (purity of 99.6%), recrystallize to obtain battery-grade lithium dihydrogen phosphate, and return the cooled lithium dihydrogen phosphate mother liquor to step (2). The vacuum cooling crystallization separation time is 20 minutes.

[0045] (4) The lithium sulfate monohydrate crystals obtained in step (2) are washed again, the amount of washing water is controlled, and the washed water is reused to continue washing the lithium sulfate monohydrate crystals. After the lithium dihydrogen phosphate in the solution reaches a certain concentration, it is returned to step (1) for lithium precipitation. The obtained lithium sulfate monohydrate crystals are purified and concentrated to produce lithium hydroxide.

[0046] According to the test results, in this embodiment, the lithium precipitation rate in the lithium-containing mother liquor is 97.9% (lithium in lithium phosphate ÷ lithium content in lithium-containing mother liquor) = 6.85 ÷ 7 = 97.9%.

[0047] Example 2

[0048] The difference between Example 2 and Example 1 is that in step (2), the acidification step does not involve adding mother liquor to adjust the slurry, but instead adds water, which is the initial reaction condition without circulating mother liquor. Specifically, it includes the following steps:

[0049] (1) Add 300 mL of 10% sodium hydroxide solution to 1000 g of lithium-containing mother liquor. Slowly add the mixed solution to 137 g of 30% sodium dihydrogen phosphate solution. Keep the system temperature at 40 °C and control the pH of the system after complete mixing to 10.5, which is conducive to the precipitation of lithium phosphate. The main reaction formula in the turbid liquid is reaction one. The reaction time is 30 minutes to obtain lithium phosphate slurry. After solid-liquid separation, 38.1 g of lithium phosphate precipitate and 1398.2 g of low lithium-containing mother liquor are obtained. The average particle size of lithium phosphate is 133.1 μm and the purity is 98.33%.

[0050] (2) 38.1g of solid lithium phosphate was added to the reactor without washing, and 23.8g of water was added to the reactor to prepare the slurry. 34.1g of 98wt% concentrated sulfuric acid (the molar ratio of sulfuric acid to lithium phosphate in the sulfuric acid solution was 1~1.15:1) was slowly added to maintain excess acid so that the lithium phosphate could react fully. The reaction time was 30 minutes. At 90℃, lithium dihydrogen phosphate was converted according to the second reaction process and completely dissolved so that its solubility was less than the saturated solubility and it would not precipitate. At the same time, lithium sulfate was obtained during the reaction. Due to the inhibition of lithium sulfate dissolution by the co-saturated system, a small portion of 1.1g was in the liquid phase, and the majority of 37.1g precipitated in the form of lithium sulfate monohydrate. A slurry containing solid lithium sulfate monohydrate was obtained. Solid-liquid separation was performed to obtain a liquid phase mixed solution of lithium dihydrogen phosphate and lithium sulfate and a solid phase of lithium sulfate monohydrate.

[0051] (3) Cool the mixed solution of lithium dihydrogen phosphate and lithium sulfate obtained in step (2) at 90°C to 40°C, filter to obtain 10.7g of lithium dihydrogen phosphate crystals (purity 99.5%), wash and dry to obtain battery-grade lithium dihydrogen phosphate, and return the cooled lithium dihydrogen phosphate mother liquor to step (2) for diluting sulfuric acid. The vacuum crystallization separation time is 30 minutes.

[0052] (4) Washing step (2) The lithium sulfate monohydrate crystals obtained are washed again by controlling the amount of washing water. The resulting washing water is reused to continue washing the lithium sulfate monohydrate crystals. After purification and concentration, it is used to produce lithium hydroxide.

[0053] According to the test results, in this embodiment, the lithium precipitation rate in the lithium-containing mother liquor is 97.4% (lithium in lithium phosphate ÷ lithium content in lithium-containing mother liquor) = 6.81 ÷ 7 = 97.4%.

[0054] Comparative Example 1

[0055] The difference between this comparative example and Example 1 is that in step (1), the lithium precipitation step involves adding 137g of 30% sodium dihydrogen phosphate solution to 1000g of lithium-containing mother liquor (with a lithium ion content of 7g / L), maintaining the system temperature at 40°C, and slowly adding 300mL of 10% sodium hydroxide solution to the system. Other reaction conditions remain unchanged, as follows:

[0056] The lithium phosphate obtained from the lithium precipitation step has an average particle size of 12.6 μm, making solid-liquid separation difficult, and the purity is 85.99%.

[0057] (1) Add 137g of 30% sodium dihydrogen phosphate solution to 1000g of lithium-containing mother liquor (where the lithium ion content is 7g / L), keep the system temperature at 40℃, and slowly add 300mL of 10% sodium hydroxide solution to the system to make the pH of the system 10.5, which is conducive to the precipitation of lithium phosphate. The main reaction formula in the turbid liquid is reaction one. The reaction time is 30 minutes, and lithium phosphate precipitate and low lithium-containing mother liquor are obtained.

[0058] (2) 44.5g of lithium phosphate precipitate and 1390.1g of low-lithium mother liquor obtained in step (1), wherein the average particle size of lithium phosphate is 13.9μm and the purity is 85.93%;

[0059] (3) 113.8g of lithium dihydrogen phosphate mother liquor at 40℃ was quantitatively added to the reactor. 44.5g of lithium phosphate solid was added to the reactor without washing to prepare the slurry. After preparation, the solid content of the system was kept at 23wt%. 36.1g of 98wt% concentrated sulfuric acid (the molar ratio of sulfuric acid to lithium phosphate in the sulfuric acid solution was 1~1.15:1) was slowly added to keep the acid in excess so that the lithium phosphate could react fully. The reaction time was 60 minutes. At 90℃, lithium dihydrogen phosphate was converted according to the second reaction process and completely dissolved so that its solubility was less than the saturated solubility and it would not precipitate. At the same time, lithium sulfate was obtained during the reaction. Due to the inhibition of lithium sulfate dissolution by the co-saturated system, a small portion of 3.9g was in the liquid phase, and the majority of 38.0g precipitated in the form of lithium sulfate monohydrate. A slurry containing lithium sulfate monohydrate solid was obtained. Solid-liquid separation was performed to obtain a liquid phase mixed solution of lithium dihydrogen phosphate and lithium sulfate and a solid phase of lithium sulfate monohydrate.

[0060] (4) Separate the lithium sulfate monohydrate obtained in step (2), wash the lithium sulfate monohydrate crystals in the separation equipment, control the amount of washing water, separate again, and reuse the washing water to continue washing the lithium sulfate monohydrate crystals.

[0061] (5) Cool the lithium dihydrogen phosphate mother liquor obtained in step (4) from 90℃ to 40℃ and perform vacuum crystallization separation for 20 minutes. Filter to obtain 10.5g of lithium dihydrogen phosphate crystals (purity 99.2%), wash and dry to obtain battery-grade lithium dihydrogen phosphate, and return the cooled lithium dihydrogen phosphate mother liquor to step (3) for diluting sulfuric acid.

[0062] (6) The solid lithium sulfate monohydrate obtained in step (4) is purified and concentrated to produce lithium hydroxide.

[0063] According to the test results, in this embodiment, the lithium precipitation rate in the lithium-containing mother liquor is 97.4% (lithium in lithium phosphate ÷ lithium content in lithium-containing mother liquor) = 6.81 ÷ 7 = 97.4%.

[0064] Comparative Example 2

[0065] The difference between this comparative example and Example 1 is that the lithium ion content of the lithium-containing brine used for lithium precipitation is 3 g / L, and the amount of other components added is adjusted according to the theoretical value. Other conditions remain unchanged, as follows.

[0066] (1) Add 200 mL of 10% sodium hydroxide solution to 1000 g of lithium-containing mother liquor. Slowly add the mixed lithium-containing mother liquor to 55.3 g of 30% sodium dihydrogen phosphate solution. Keep the system temperature at 40 °C and control the pH of the system after complete mixing to 10.5, which is conducive to the precipitation of lithium phosphate. The main reaction formula in the turbid liquid is reaction one. The reaction time is 30 minutes, and lithium phosphate precipitate and low lithium-containing mother liquor are obtained.

[0067] (2) Separate 15.3 g of lithium phosphate precipitate and 1275.0 g of low-lithium mother liquor obtained in step (1), wherein the average particle size of lithium phosphate is 119.1 μm and the purity is 97.91%;

[0068] (3) 2.4g of water and 45.7g of lithium dihydrogen phosphate mother liquor at 40℃ were quantitatively added to the reactor. 15.3g of lithium phosphate solid was added to the reactor without washing to prepare the slurry. After preparation, the solid content of the system was kept at 24wt%. 14.0g of 98wt% concentrated sulfuric acid (the molar ratio of sulfuric acid to lithium phosphate in the sulfuric acid solution was 1~1.15:1) was slowly added to keep the acid in excess. The reaction time was 60 minutes to allow the lithium phosphate to react fully. At 90℃, the lithium dihydrogen phosphate was converted according to the second reaction process and completely dissolved so that its solubility was less than the saturated solubility and it would not precipitate. At the same time, lithium sulfate was obtained during the reaction. Due to the inhibition of lithium sulfate dissolution by the co-saturated system, a small portion of 3.3g was in the liquid phase, and the majority of 13.6g precipitated in the form of lithium sulfate monohydrate. A slurry containing lithium sulfate monohydrate solid was obtained. Solid-liquid separation was performed to obtain a liquid phase mixed solution of lithium dihydrogen phosphate and lithium sulfate and a solid phase of lithium sulfate monohydrate.

[0069] (4) Separate lithium sulfate monohydrate, wash lithium sulfate monohydrate crystals in the separation equipment, control the amount of washing water, separate again, and reuse the obtained washing water to continue washing lithium sulfate monohydrate crystals. After the lithium dihydrogen phosphate in the solution reaches a certain concentration, return to step (1) for lithium precipitation.

[0070] (5) Cool the lithium dihydrogen phosphate mother liquor obtained in step (4) from 90℃ to 40℃ and perform vacuum crystallization separation for 20 minutes. Filter to obtain 4.10g of lithium dihydrogen phosphate crystals (purity of 99.5%), wash and dry to obtain battery-grade lithium dihydrogen phosphate, and return the cooled lithium dihydrogen phosphate mother liquor to step (3) for diluting sulfuric acid.

[0071] (6) The solid lithium sulfate monohydrate obtained in step (4) is purified and concentrated to produce lithium hydroxide.

[0072] According to the test results, in this embodiment, the lithium precipitation rate in the lithium-containing mother liquor is 91.7% (lithium in lithium phosphate ÷ lithium content in lithium-containing mother liquor) = 2.75 ÷ 3 = 91.7%.

[0073] The particle size of the lithium phosphate obtained by this invention was measured. Table 2 compares the specific particle size data of lithium phosphate obtained in Example 1 and Comparative Example 1. Table 3 compares the specific particle size data of the self-made lithium dihydrogen phosphate prepared in Example 1 of this invention and the purchased lithium dihydrogen phosphate. The purchased lithium dihydrogen phosphate was analytical grade and manufactured by Hubei Shengwei New Materials Co., Ltd. As shown in Tables 2 and 3, the lithium dihydrogen phosphate crystals of this invention have a larger particle size and are easier to separate than those obtained by the evaporation process.

[0074] Table 2 Comparison of specific particle size data of lithium phosphate obtained in Example 1 and Comparative Example 1

[0075]

[0076] Table 3 Comparison of specific particle size data between self-made lithium dihydrogen phosphate and purchased lithium dihydrogen phosphate

[0077]

[0078] Figure 1 , 2 The data provided are TG-DSC values ​​for the self-made lithium dihydrogen phosphate and the purchased lithium dihydrogen phosphate prepared in Example 1 of this invention. Figure 1 This is a graph showing the weight changes of self-made lithium dihydrogen phosphate and purchased lithium dihydrogen phosphate prepared in Example 1 of this invention as a function of temperature. Figure 2 This is a graph showing the endothermic data of the self-made lithium dihydrogen phosphate and the purchased lithium dihydrogen phosphate prepared in Example 1 of this invention as a function of temperature. The self-made lithium dihydrogen phosphate loses water more easily, indicating that it participates in the reaction more readily. As can be seen from the graph, the endothermic peak of the self-made lithium dihydrogen phosphate is more concentrated, and the mid-stage dehydration rate is faster, indicating that its thermal response performance is more sensitive.

Claims

1. A method for producing battery-grade lithium dihydrogen phosphate using lithium-containing brine, characterized in that, Includes the following steps: (1) A certain amount of sodium hydroxide solution was added to the lithium-containing mother liquor, and then the mixed solution was slowly added to the sodium dihydrogen phosphate solution. The pH of the system was kept at 9~11. After reacting for a period of time, lithium phosphate slurry was obtained. Solid-liquid separation was performed to obtain lithium phosphate precipitate and mother liquor. (2) Add water or lithium-containing mother liquor obtained in step (3) to the lithium phosphate precipitate obtained in step (1) to adjust the slurry, and then add a certain amount of concentrated sulfuric acid to react and obtain a slurry containing lithium sulfate monohydrate solid. The solid-liquid separation yields a liquid phase mixed solution of lithium dihydrogen phosphate and lithium sulfate and a solid phase of lithium sulfate monohydrate. (3) The mixed solution of liquid lithium dihydrogen phosphate and lithium sulfate obtained in step (2) is subjected to vacuum cooling crystallization separation to obtain lithium dihydrogen phosphate crystals and lithium-containing mother liquor.

2. The method for producing battery-grade lithium dihydrogen phosphate using lithium-containing brine according to claim 1, characterized in that, The purity of the obtained lithium dihydrogen phosphate crystals is >99.5%.

3. The method for producing battery-grade lithium dihydrogen phosphate from lithium-containing brine according to claim 1 or 2, characterized in that, In step (1), the lithium-containing mother liquor is lithium-containing brine that has been purified by removing calcium and magnesium.

4. The method for producing battery-grade lithium dihydrogen phosphate from lithium-containing brine according to claim 1 or 2, characterized in that, In step (1), the lithium-containing brine is at least one of salt lake brine and underground brine.

5. The method for producing battery-grade lithium dihydrogen phosphate from lithium-containing brine according to claim 1 or 2, characterized in that, In step (1), the lithium ion concentration in the lithium-containing brine after calcium and magnesium removal is not less than 5 g / L, the calcium ion content is not higher than 5 mg / L, and the magnesium ion content is not higher than 5 mg / L.

6. The method for producing battery-grade lithium dihydrogen phosphate from lithium-containing brine according to claim 1 or 2, characterized in that, In step (1), the amount of sodium dihydrogen phosphate added is such that the molar ratio of phosphate ions to lithium ions in the lithium-containing mother liquor is 0.9~1.3:3; and / or, in step (1), the reaction temperature is 10~70℃ and the reaction time is 10~60 minutes.

7. The method for producing battery-grade lithium dihydrogen phosphate from lithium-containing brine according to claim 1 or 2, characterized in that, In step (2), the solid content of the system is maintained at 30~50wt% after slurry preparation.

8. The method for producing battery-grade lithium dihydrogen phosphate from lithium-containing brine according to claim 1 or 2, characterized in that, In step (2), the reaction temperature is 60~90℃ and the reaction time is 10~60 minutes.

9. The method for producing battery-grade lithium dihydrogen phosphate from lithium-containing brine according to claim 1 or 2, characterized in that, In step (2), the concentration of the sulfuric acid solution is 70~100wt%; and / or the molar ratio of sulfuric acid to lithium phosphate in the added sulfuric acid solution is 1~1.15:

1.

10. The method for producing battery-grade lithium dihydrogen phosphate from lithium-containing brine according to claim 1 or 2, characterized in that, In step (3), the temperature of the vacuum crystallization separation is 30~50℃, and the reaction time is 10~60 minutes.

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