Method for preparing battery-grade lithium dihydrogen phosphate from sodium lithium sulfate potassium salt and battery-grade lithium dihydrogen phosphate

Abstract

The invention relates to the field of battery materials, and provides a method for preparing battery-grade lithium dihydrogen phosphate from sodium lithium sulfate potassium salt, which comprises the following steps: S1, preparing the sodium lithium sulfate potassium salt into a mixed solution, adding a purifying agent to adjust the pH value for reaction, and filtering to obtain a purified solution and purified slag; s2, adding a chelating agent into the purified liquid, then adding monopotassium phosphate mother liquor for precipitation reaction, and filtering to obtain crude lithium phosphate and sulfate primary mother liquor; s3, mixing the crude lithium phosphate and phosphoric acid in proportion, adding the barium salt slurry, filtering, and concentrating and crystallizing a liquid phase to obtain battery-grade lithium dihydrogen phosphate; s4, performing fractional separation on the primary sulfate mother liquor to extract a mixed salt of by-products potassium sulfate, sodium sulfate and ammonium sulfate; and S5, extracting lithium from the ammonium sulfate secondary mother liquor to recover the lithium element and sulfate mother liquor. The method can realize low-cost preparation of battery-grade lithium dihydrogen phosphate, has high economic benefit of the whole process, and can be suitable for industrial popularization and application.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, provides a method for preparing battery-grade lithium dihydrogen phosphate from sodium potassium lithium sulfate and the battery-grade lithium dihydrogen phosphate. Background Technology

[0002] With the rapid development of the new energy industry, the electric vehicle industry has experienced rapid growth, with a market penetration rate of nearly 50% and enormous future growth potential. As the core of the new energy vehicle industry, battery development is crucial. Lithium iron phosphate batteries, with their advantages of long lifespan, high discharge capacity, high safety, non-toxicity, and wide availability of raw materials, are key to the sustainable development of the new energy industry.

[0003] The ferrous oxalate process for preparing lithium iron phosphate is a key research area in the industry, second only to the iron phosphate process. In the ferrous oxalate process, the iron source, ferrous oxalate, possesses both "Fe... 2+ Its dual function as a "supply agent" and "reducing agent," coupled with its loose crystal structure, eliminates the need for adding a reducing agent during preparation and makes it easier to ball-mill into fine and uniform particles. This results in lithium iron phosphate products with a larger specific surface area, significantly improved low-temperature discharge performance, and high rate capability, making them particularly suitable for scenarios requiring wide temperature range and short-term high-power discharge.

[0004] Lithium dihydrogen phosphate, as the core precursor for the production of lithium iron phosphate using the ferrous oxalate process, can provide a stable source of phosphorus and lithium for lithium iron phosphate, and the elemental ratio is stable and controllable, which plays a decisive role in the performance of lithium iron phosphate.

[0005] The production technology of lithium dihydrogen phosphate is relatively limited. It is mostly produced by neutralizing battery-grade lithium carbonate and lithium hydroxide with phosphoric acid. The high cost of lithium source has a certain impact on the large-scale promotion and application of lithium dihydrogen phosphate. To reduce costs, technical teams in related fields have proposed several methods for preparing lithium dihydrogen phosphate from crude lithium salts, aiming to obtain battery-grade lithium dihydrogen phosphate from non-battery-grade raw materials and thus reduce lithium source costs. Patents such as CN113044820A, CN119551638A, CN113387338A, CN116495712A, and CN108147384A disclose different low-cost methods for preparing lithium dihydrogen phosphate using crude lithium salts. These methods involve using different low-cost lithium raw materials and undergoing a series of impurity removal and conversion processes to ultimately prepare battery-grade lithium dihydrogen phosphate. However, these methods suffer from problems such as numerous and low-value byproducts, low lithium utilization, complex reaction processes, and high difficulty in process control. Consequently, their industrialization prospects are poor, and they have failed to achieve further industrial-scale promotion.

[0006] Furthermore, none of these existing technologies specifically address the use of lepidolite as a lithium source for the preparation of battery-grade lithium dihydrogen phosphate. The aforementioned methods exhibit poor adaptability to lepidolite as a lithium source. This is because lepidolite, as a primary raw material for supplying lithium from ore, has a relatively low lithium content, high impurity element content, and high levels of associated potassium and aluminum. Moreover, due to the characteristics of its production process, a large amount of potassium and sodium ions enter the solution along with the lithium leaching, increasing the process difficulty and material consumption for the preparation of battery-grade lithium dihydrogen phosphate, resulting in high costs.

[0007] Therefore, solving the problem of efficient and low-cost preparation of lithium dihydrogen phosphate from lepidolite, while making efficient use of associated elements, is one of the effective ways to reduce the preparation cost of lithium dihydrogen phosphate. At the same time, it will effectively promote the low-cost and large-scale application of lepidolite ore and further stabilize the supply of lithium resources. Summary of the Invention

[0008] To address the aforementioned shortcomings in the existing technology, the core objective of this invention is to provide a method for preparing battery-grade lithium dihydrogen phosphate from sodium and potassium lithium sulfate, as well as the battery-grade lithium dihydrogen phosphate itself. This method enables the direct preparation of battery-grade lithium dihydrogen phosphate from lepidolite leachate, resulting in low raw material costs, high by-product value, high utilization rate of valuable elements, and high overall economic benefits. It is suitable for industrial promotion and application.

[0009] This invention is achieved through the following technical solution: A method for preparing battery-grade lithium dihydrogen phosphate from sodium potassium lithium sulfate includes the following steps: S1 Lithium sulfate sodium and potassium salt purification: Prepare a mixed solution of lithium sulfate sodium and potassium salt, add a purifying agent to the mixed solution, adjust the pH value, mix and react, and then filter to obtain a purified liquid and a purified residue; The lithium sulfate sodium potassium salt is a mixed salt solution obtained by water leaching / acid leaching after high-temperature calcination of lepidolite, or a concentrated crystallized product of the mixed salt solution; the purifying agent is one or more of lithium phosphate, ammonium phosphate, potassium phosphate, or sodium phosphate. S2 Crude lithium phosphate precipitation: A chelating agent is added to the purified solution obtained in step S1, followed by the addition of potassium dihydrogen phosphate mother liquor; the pH value is then adjusted to obtain lithium phosphate salt precipitation, followed by filtration to obtain crude lithium phosphate and sulfate primary mother liquor; The potassium dihydrogen phosphate mother liquor is the potassium dihydrogen phosphate mother liquor produced by multiple crystallizations of potassium dihydrogen phosphate in the ammonium method for producing potassium dihydrogen phosphate. S3 Preparation of electronic-grade lithium dihydrogen phosphate: The crude lithium phosphate obtained in step S2 and phosphoric acid are mixed in proportion and dissolved in water to obtain a mixed solution. A precipitant is added to the mixed solution and reacted uniformly. After the reaction is completed, the mixture is filtered and separated. After liquid phase concentration and crystallization, battery-grade lithium dihydrogen phosphate is obtained. S4 Multi-stage separation and recovery of by-products from sulfate mother liquor: The pH value of the primary sulfate mother liquor obtained in step S2 is adjusted back, the mother liquor is concentrated and crystallized to obtain potassium sulfate crystals, the liquid phase concentration is adjusted, the temperature is lowered and crystallized to obtain sodium sulfate crystals, the ammonium sulfate mixed salt crystals are concentrated and separated again, and the remaining liquid phase is the secondary sulfate mother liquor. S5 Secondary mother liquor lithium extraction: The ammonium sulfate secondary mother liquor obtained in step S4 is added to the potassium dihydrogen phosphate mother liquor from step S2. A neutralizing agent is used to raise the pH value to precipitate lithium phosphate. After solid-liquid separation, solid-phase lithium phosphate and liquid-phase sulfate tertiary mother liquor are obtained. The solid-phase lithium phosphate is returned to step S1 as a purification agent, and the liquid-phase sulfate tertiary mother liquor is returned to step S2 and mixed with the sulfate primary mother liquor for recycling.

[0010] This invention uses leaching solution of calcined lepidolite or concentrated salt of leaching solution as initial raw material. By designing a process route, impurities are removed at specific stages of the process to obtain battery-grade lithium dihydrogen phosphate. Furthermore, through a reasonable recycling route design, the utilization rate of lithium is greatly improved, and all by-products are high-value by-products. The entire process route is simple and economically efficient.

[0011] More importantly, this invention creatively incorporates the potassium dihydrogen phosphate mother liquor, a byproduct of the ammonium process for producing potassium dihydrogen phosphate, into the route design of this invention. Since the main components of the potassium dihydrogen phosphate mother liquor are elements such as phosphorus, potassium, sodium, and nitrogen, introducing it into the reaction system of this invention can not only serve as a phosphorus source for the preparation of lithium dihydrogen phosphate, but also the impurities such as potassium, sodium, and nitrogen are the same as the impurities sodium and potassium and the nitrogen introduced by the neutralizing agent in this application. These impurities can be entered together into the subsequent sulfate mother liquor fractionation and purification process to obtain a high-value-added byproduct.

[0012] In the production of potassium dihydrogen phosphate using the ammonium process, the resulting potassium dihydrogen phosphate mother liquor mainly contains elements such as phosphorus, potassium, sodium, and nitrogen. After the mother liquor reaches a certain concentration through recycling, impurities accumulate, making it difficult to produce high-purity potassium dihydrogen phosphate products. Therefore, it is often directly discharged and used as a raw material for compound fertilizers, resulting in the waste of high-value elements and affecting the economic benefits of enterprises. This invention uses it as a raw material for the production of lithium dihydrogen phosphate. Furthermore, it reacts with lithium sodium and potassium sulfate solutions to prepare crude lithium phosphate, which is then converted into lithium dihydrogen phosphate. This process design not only avoids affecting the purity of lithium dihydrogen phosphate products due to impurities in the potassium dihydrogen phosphate mother liquor, but also allows the impurities in the potassium dihydrogen phosphate mother liquor to enter the ammonium sulfate primary mother liquor together with the impurities in the lithium sodium and potassium sulfate for subsequent fractional purification and reuse, thus enabling the high-value utilization of this byproduct, the potassium dihydrogen phosphate mother liquor.

[0013] The design of steps S1-S5 in this invention involves first adding phosphate to sodium and potassium lithium sulfate (a water / acid leaching solution of lepidolite after high-temperature calcination) to raise the pH value, removing impurities such as calcium, magnesium, manganese, and iron from the solution, and separating the solid and liquid phases to obtain a purified solution and a purified residue. A chelating agent is added to the purified solution to chelate the trace elements. Then, potassium dihydrogen phosphate mother liquor is added dropwise to the purified solution to adjust the pH value, and the reaction generates crude lithium phosphate and a primary mother liquor of sulfate. Subsequently, the crude lithium phosphate is added with phosphoric acid to prepare battery-grade lithium dihydrogen phosphate. The ammonium sulfate mother liquor is further processed to sequentially separate and purify high-purity potassium sulfate, sodium sulfate, and a mixed ammonium sulfate salt. The resulting secondary mother liquor is further used for lithium extraction. The extracted solid-phase lithium phosphate is returned to the system as the purifying agent in step S1, and the liquid-phase sulfate tertiary mother liquor is returned to the system as a mixed recycling of the sulfate primary mother liquor in step S2.

[0014] Preferably, the present invention further employs phosphoric acid leaching to extract and adjust the slurry of the purified residue obtained in step S1, and finally adjusts the pH value to <9, filters for solid-liquid separation, and returns the obtained filtrate to step S1 for reuse, and mixes it with the lithium sulfate sodium potassium salt mixed solution in step S1, and the resulting solid phase is used as a calcium salt product; the calcium salt product meets the requirements of feed-grade calcium phosphate.

[0015] Preferably, in step S1, the concentration of the mixed solution is 5-30%.

[0016] Preferably, in step S1, the amount of purifying agent added is based on adjusting the pH value of the solution to 8.0~10.0, the purification reaction time is 0.5~2.0h, and the purification reaction temperature is 60~80℃.

[0017] Preferably, in step S2, the chelating agent is one or more of EDTA, DTPA, MGDA, ATMP, and HEDP, and the amount used is 0.01 to 0.1% of the mass of the mixed solution in step S1.

[0018] Preferably, in step S2, the content of each component in the potassium dihydrogen phosphate mother liquor satisfies the following: Na2O content 3~5%, K2O content 12~17%, and P2O5 content 20~30%.

[0019] Preferably, in step S2, the amount of potassium dihydrogen phosphate mother liquor added satisfies the following conditions: the molar mass of phosphorus in the potassium dihydrogen phosphate mother liquor is 0.34 to 0.38 times the molar mass of lithium in the purified liquid; the pH value is adjusted to 9.0 to 11.0 using a neutralizing agent to obtain lithium phosphate precipitate; the neutralizing agent is selected from at least one of ammonia water, liquid ammonia, and ammonia gas.

[0020] Preferably, in step S3, crude lithium phosphate and phosphoric acid are mixed at a molar ratio of 1:2.0~2.5, and water is added to adjust the solution concentration to 20~50%. The phosphoric acid is 85% industrial phosphoric acid.

[0021] Preferably, in step S3, the precipitant is a barium salt, preferably barium carbonate prepared into a slurry and added, and the amount of barium carbonate added is 1.0 to 1.5 times the molar amount of sulfate in the mixed solution in step S3.

[0022] Through the above-described process control, the lithium dihydrogen phosphate product obtained by this invention has a purity greater than 99.5% and impurity elements less than 50 ppm, which meets the requirements for raw materials in battery material production.

[0023] Preferably, in step S4, the concentration of the primary sulfate mother liquor is adjusted to 5-30%, preferably 20-30%, and the pH value is controlled to 6.0-8.0; the temperature is lowered to 30-50℃ to crystallize and obtain potassium sulfate crystals; then the liquid phase concentration is adjusted to 50%-60%, and the temperature is lowered to -5-5℃ to crystallize and obtain sodium sulfate crystals; the ammonium sulfate mixed salt crystals are then separated by evaporation and concentration.

[0024] Through the design and optimization of the above-mentioned separation and purification process, this invention can achieve a potassium sulfate purity of 95-99%, a sodium sulfate purity of 90-98%, and an ammonium sulfate mixed salt purity of 70-80%, potassium sulfate 5-10%, and sodium sulfate 10-20%. This achieves high-value recovery of each sulfate.

[0025] Preferably, in step S5, the amount of potassium dihydrogen phosphate mother liquor added satisfies the following conditions: the molar mass of phosphorus in the potassium dihydrogen phosphate mother liquor is 0.4 to 0.6 times the molar mass of lithium in the sulfate secondary mother liquor; the pH value is adjusted to 9.0 to 11.0 using a neutralizing agent to obtain lithium phosphate precipitate; the neutralizing agent is selected from at least one of ammonia water, liquid ammonia, and ammonia gas.

[0026] This invention enables each process step to be implemented according to the designed route by strictly setting the reaction parameters of each process step. It can achieve efficient removal of impurities, effective assurance of product quality, high lithium yield, and high-value conversion of by-products. Ultimately, the entire system can meet product quality requirements while achieving high economic benefits, thereby promoting its industrialization.

[0027] The present invention also provides a battery-grade lithium dihydrogen phosphate, which is prepared by the above-described method for preparing battery-grade lithium dihydrogen phosphate from sodium potassium lithium sulfate.

[0028] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects: (1) The sodium and potassium lithium sulfate used in this invention are low-concentration leaching solutions or crystals after the decomposition of lepidolite as raw materials. There is no need to purify them to obtain purified lithium sulfate monohydrate. When the low-concentration leaching solution is used directly as raw material, the concentration cost of this process can be effectively reduced and energy consumption can be significantly reduced. At the same time, as a source of low-grade lithium ore, lepidolite can be used directly as raw material without going through complicated processes to convert it into battery-grade lithium carbonate or battery-grade lithium hydroxide, which greatly reduces the cost of raw materials and expands the high-value utilization pathways of lepidolite.

[0029] (2) This invention uses potassium dihydrogen phosphate mother liquor as the phosphorus source of the entire reaction system. By designing the process route and process conditions in a reasonable way, it can not only ensure the quality of lithium dihydrogen phosphate products, but also recover the potassium and sodium elements associated with potassium dihydrogen phosphate mother liquor and lithium sodium potassium salt and convert them into potassium sulfate, sodium sulfate and other products, thereby maximizing the value of potassium and sodium elements and solving the problem of recycling potassium dihydrogen phosphate mother liquor.

[0030] (3) The multi-stage separation and purification technology proposed in this invention, through the optimization of the concentration and crystallization process, can obtain potassium sulfate, sodium sulfate and ammonium sulfate mixed salt with high purity in stages. Potassium sulfate can be used directly as potassium fertilizer, sodium sulfate can be returned to the phosphorus chemical system as a defluorinating agent, and ammonium sulfate mixed salt can provide nutrients such as nitrogen and potassium as raw materials for compound fertilizer.

[0031] (4) This invention mainly uses ammonia as a pH adjusting agent, which effectively avoids the influence of sodium elements caused by using soda ash or caustic soda for neutralization. The added value of the by-product ammonium sulfate is much higher than that of sodium sulfate, and it can be widely used in the fertilizer field, making it more economical.

[0032] (5) The present invention uses sodium potassium lithium sulfate as raw material, completely eliminating the use of lithium carbonate. The reaction process does not produce carbon dioxide emissions. Based on a scale of 10,000 tons / year of lithium dihydrogen phosphate, it reduces carbon dioxide emissions by 2,100 tons / year compared to conventional processes, resulting in good emission reduction benefits. Attached Figure Description

[0033] Figure 1 This is a process flow diagram of the method for preparing battery-grade lithium dihydrogen phosphate using sodium potassium lithium sulfate according to Example 1 of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the present invention will be further described below in conjunction with specific embodiments. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents used, or any products for which the manufacturer is not specified, are all commercially available conventional products. All features disclosed in this specification, except for mutually exclusive features and / or steps, may be combined in any manner.

[0035] The following embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way.

[0036] In the following embodiments of this application, the sodium and potassium lithium sulfate salts are concentrated crystals of the acid leaching extract from the same batch of calcined lepidolite, the specific composition of which is shown in Table 1. These crystals are adjusted to a mixed solution with a concentration of 20% for use in the following embodiments.

[0037] Table 1. Composition of concentrated crystals from the acid leaching solution of calcined lepidolite used in the embodiments of this application.

[0038] In the following embodiments of this application, the potassium dihydrogen phosphate mother liquor used is the potassium dihydrogen phosphate mother liquor after multiple crystallizations of potassium dihydrogen phosphate in the ammonium method for producing potassium dihydrogen phosphate. The specific contents of each component in the mother liquor are 3.6% Na2O, 13.8% K2O, and 25.2% P2O5.

[0039] Example 1 This embodiment provides a method for preparing battery-grade lithium dihydrogen phosphate from sodium potassium lithium sulfate, including the following steps: S1 Lithium sulfate sodium and potassium salt purification: Prepare a 20% mixed solution of lithium sulfate sodium and potassium salt, add lithium phosphate to the mixed solution to adjust the pH to 9.0, mix and react at 70℃ for 1 hour, then let stand and filter to obtain purified liquid and purified residue; S2 Crude lithium phosphate precipitation: Add chelating agent EDTA to the purified solution obtained in step S1. The amount of EDTA added is 0.05% of the mixed solution in step S1 by mass. Then add potassium dihydrogen phosphate mother liquor to the purified solution, and adjust the pH value to 9.0 with ammonia water. React at 70℃ for 1 hour to obtain lithium phosphate precipitate. Then filter to obtain crude lithium phosphate and sulfate primary mother liquor. The above-mentioned addition of potassium dihydrogen phosphate mother liquor satisfies the following condition: the molar mass of phosphorus in the potassium dihydrogen phosphate mother liquor is 0.34 times the molar mass of lithium in the purified liquid; S3 Preparation of electronic-grade lithium dihydrogen phosphate: The crude lithium phosphate obtained in step S2 and phosphoric acid are mixed at a molar ratio of 1:2.0 and dissolved in water to obtain a 30% mixed solution. Barium carbonate slurry is added to the mixed solution and reacted uniformly at a temperature of 70℃ for 1 hour. After the reaction is completed, the mixture is filtered and separated. After liquid phase concentration and crystallization, battery-grade lithium dihydrogen phosphate is obtained. The amount of barium carbonate slurry added is 1.3 times the molar amount of sulfate in the mixed solution in this step. S4 Multi-stage separation and recovery of by-products from sulfate mother liquor: The primary sulfate mother liquor obtained in step S2 is evaporated and concentrated to 25%, the pH value is adjusted to 5.0 with sulfuric acid, and the temperature is lowered to 30°C to crystallize potassium sulfate crystals. The liquid phase concentration is adjusted to 35%, and the temperature is lowered to 0°C to crystallize sodium sulfate crystals. The liquid phase is evaporated, concentrated and separated again to obtain ammonium sulfate mixed salt crystals. The remaining liquid phase is the secondary sulfate mother liquor. S5 Lithium Extraction from Secondary Mother Liquor: The potassium dihydrogen phosphate mother liquor from step S2 is added to the ammonium sulfate secondary mother liquor obtained in step S4. The amount of potassium dihydrogen phosphate mother liquor added satisfies the following condition: the molar mass of phosphorus in the potassium dihydrogen phosphate mother liquor is 0.4 times the molar mass of lithium in the sulfate secondary mother liquor. Ammonia water is used to raise the pH to 9.0 for lithium phosphate precipitation. The reaction is carried out at 80℃ for 0.5 h. After solid-liquid separation, solid-phase lithium phosphate and liquid-phase sulfate tertiary mother liquor are obtained. The solid-phase lithium phosphate is returned to step S1 as a purifying agent according to the required amount in step S1. The liquid-phase sulfate tertiary mother liquor is returned to step S2 and mixed with the sulfate primary mother liquor for recycling. S6 Secondary lithium extraction from purification residue: The purification residue obtained in step S1 is leached with 40% phosphoric acid, the slurry concentration is adjusted to 20%, lime milk is added to adjust the pH to 7.0, and solid-liquid separation is performed by filtration. The filtrate is returned to step S1 for reuse and mixed with the lithium sulfate sodium potassium salt mixed solution in step S1. The resulting solid phase is feed-grade dicalcium phosphate.

[0040] Repeat steps S1-S6 once for one cycle of reaction.

[0041] Example 2 This embodiment provides a method for preparing battery-grade lithium dihydrogen phosphate from sodium potassium lithium sulfate. The difference from Embodiment 1 is that steps S1-S6 are repeated three times in a cyclic reaction.

[0042] Example 3 This embodiment provides a method for preparing battery-grade lithium dihydrogen phosphate from sodium potassium lithium sulfate. The difference from Embodiment 1 is that steps S1-S6 are repeated five times in a cyclic reaction.

[0043] Example 4 This embodiment provides a method for preparing battery-grade lithium dihydrogen phosphate from sodium potassium lithium sulfate. The difference from Example 1 is that in step S1, lithium phosphate is added to the mixed solution to adjust the pH to 10.0, and the mixture is reacted at 80°C for 0.5 hours, followed by standing and filtration to obtain a purified solution and a purified residue. In step S2, the amount of EDTA added is 0.01% by mass of the mixed solution in step S1. The remaining reactions are exactly the same as in Example 1.

[0044] Example 5 This embodiment provides a method for preparing battery-grade lithium dihydrogen phosphate from sodium potassium lithium sulfate. The difference from Example 1 is that in step S1, lithium phosphate is added to the mixed solution to adjust the pH to 10.0, and the mixture is reacted at 80°C for 0.5 hours, followed by standing and filtration to obtain a purified solution and a purified residue. In step S2, the amount of EDTA added is 0.1% by mass of the mixed solution in step S1. The remaining reactions are exactly the same as in Example 1.

[0045] Example 6 This embodiment provides a method for preparing battery-grade lithium dihydrogen phosphate from sodium potassium lithium sulfate. The difference from Example 1 is that the amount of potassium dihydrogen phosphate mother liquor added in step S3 satisfies the following conditions: the molar mass of phosphorus in the potassium dihydrogen phosphate mother liquor is 0.38 times the molar mass of lithium in the purified solution; and the pH value is adjusted to 11.0 with ammonia. The remaining reactions are exactly the same as in Example 1.

[0046] Example 7 This embodiment provides a method for preparing battery-grade lithium dihydrogen phosphate from sodium potassium lithium sulfate. The difference from Example 1 is that in step S3, crude lithium phosphate and phosphoric acid are mixed at a molar ratio of 1:2.5 and dissolved in water to obtain a 50% mixed solution. The remaining reactions are exactly the same as in Example 1.

[0047] Example 8 This embodiment provides a method for preparing battery-grade lithium dihydrogen phosphate from sodium and potassium lithium sulfate. The difference from Example 1 is that in step S4, the primary mother liquor of sulfate obtained in step S2 is concentrated to 30%, the pH is adjusted to 7.0 with sulfuric acid, the concentrated mother liquor is cooled to 40°C to crystallize potassium sulfate crystals, the liquid phase concentration is adjusted to 50%, and the liquid phase is cooled to 5°C to crystallize sodium sulfate crystals. The ammonium sulfate mixed salt crystals are then separated by further concentration, and the remaining liquid phase is the secondary mother liquor of sulfate. The remaining reactions are exactly the same as in Example 1.

[0048] Example 9 This embodiment provides a method for preparing battery-grade lithium dihydrogen phosphate from sodium and potassium lithium sulfate. The difference from Example 1 is that in step S4, the primary mother liquor of sulfate obtained in step S2 is concentrated to 10%, the pH is adjusted to 6.0 with sulfuric acid, the concentrated mother liquor is cooled to 30°C to crystallize potassium sulfate crystals, the liquid phase concentration is adjusted to 40%, and the liquid phase is cooled to -5°C to crystallize sodium sulfate crystals. The ammonium sulfate mixed salt crystals are then separated by further concentration, and the remaining liquid phase is the secondary mother liquor of sulfate. The remaining reactions are exactly the same as in Example 1.

[0049] Example 10 This embodiment provides a method for preparing battery-grade lithium dihydrogen phosphate from sodium potassium lithium sulfate. The difference from Embodiment 1 is that in step S5, the amount of potassium dihydrogen phosphate mother liquor added satisfies the following conditions: the molar mass of phosphorus in the potassium dihydrogen phosphate mother liquor is 0.6 times the molar mass of lithium in the secondary mother liquor of sulfate; and the pH value is adjusted to 11.0 using ammonia water to obtain lithium phosphate precipitate.

[0050] Experimental Example The final product lithium dihydrogen phosphate obtained after the experiments in Examples 1-10 (after the last cycle), and the mixed salt of potassium sulfate, sodium sulfate, and ammonium sulfate recovered in step S4 were taken respectively. Their performance was measured, and the utilization rate of lithium was calculated based on the mass of raw materials, the lithium content in raw materials, the mass of products, and the lithium content in products. The results are shown in Table 2. Table 2 Properties of products and byproducts in each embodiment

[0051] As can be seen from the results in Table 2, the preparation method of the present invention can produce lithium dihydrogen phosphate products that meet battery-grade requirements, and the quality of the products can still meet the requirements after multiple cycles. In addition, the by-products potassium sulfate and sodium sulfate obtained by the present invention have high purity. Potassium sulfate can be used directly as potassium fertilizer, sodium sulfate can be used as a defluorinating agent, and ammonium sulfate mixed salt can be used as nitrogen and potassium fertilizer, all of which can form high value-added products.

[0052] In summary, the method of this invention, through the design of the overall process route, achieves low-cost preparation of battery-grade lithium dihydrogen phosphate. The entire preparation process has low energy consumption, low raw material costs, and high added value of by-products, and has great industrial application value.

[0053] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

Claims

1. A method for preparing battery-grade lithium dihydrogen phosphate from sodium and potassium lithium sulfate, characterized in that, Includes the following steps: S1 Lithium sulfate sodium and potassium salt purification: Prepare a mixed solution of lithium sulfate sodium and potassium salt, add a purifying agent to the mixed solution, adjust the pH value, mix and react, and then filter to obtain a purified liquid and a purified residue; The lithium sulfate sodium potassium salt is a mixed salt solution obtained by water leaching / acid leaching after high-temperature calcination of lepidolite, or a concentrated crystallized product of the mixed salt solution; the purifying agent is one or more of lithium phosphate, ammonium phosphate, potassium phosphate, or sodium phosphate. S2 Crude lithium phosphate precipitation: A chelating agent is added to the purified solution obtained in step S1, followed by the addition of potassium dihydrogen phosphate mother liquor; the pH value is then adjusted to obtain lithium phosphate salt precipitation, followed by filtration to obtain crude lithium phosphate and sulfate primary mother liquor; The potassium dihydrogen phosphate mother liquor is the potassium dihydrogen phosphate mother liquor after multiple crystallizations of potassium dihydrogen phosphate in the ammonium method for producing potassium dihydrogen phosphate. S3 Preparation of electronic-grade lithium dihydrogen phosphate: The crude lithium phosphate obtained in step S2 and phosphoric acid are mixed in proportion and dissolved in water to obtain a mixed solution. A precipitant is added to the mixed solution and reacted uniformly. After the reaction is completed, the mixture is filtered and separated. After liquid phase concentration and crystallization, battery-grade lithium dihydrogen phosphate is obtained. S4 Multi-stage separation and recovery of by-products from sulfate mother liquor: The pH value of the primary sulfate mother liquor obtained in step S2 is adjusted back, the mother liquor is concentrated and crystallized to obtain potassium sulfate crystals, the liquid phase concentration is adjusted, the temperature is lowered and crystallized to obtain sodium sulfate crystals, the ammonium sulfate mixed salt crystals are concentrated and separated again, and the remaining liquid phase is the secondary sulfate mother liquor. S5 Secondary mother liquor lithium extraction: The ammonium sulfate secondary mother liquor obtained in step S4 is added to the potassium dihydrogen phosphate mother liquor from step S2. A neutralizing agent is used to raise the pH value to precipitate lithium phosphate. After solid-liquid separation, solid-phase lithium phosphate and liquid-phase sulfate tertiary mother liquor are obtained. The solid-phase lithium phosphate is returned to step S1 as a purification agent, and the liquid-phase sulfate tertiary mother liquor is returned to step S2 and mixed with the sulfate primary mother liquor for recycling.

2. The method for preparing battery-grade lithium dihydrogen phosphate from sodium and potassium lithium sulfate according to claim 1, characterized in that, In step S1, the concentration of the mixed solution is 5-30%.

3. The method for preparing battery-grade lithium dihydrogen phosphate from sodium and potassium lithium sulfate according to claim 1, characterized in that, In step S1, the amount of purifying agent added is based on adjusting the pH value of the solution to 8.0~10.0, the purification reaction time is 0.5~2.0h, and the purification reaction temperature is 60~80℃.

4. The method for preparing battery-grade lithium dihydrogen phosphate from sodium and potassium lithium sulfate according to claim 1, characterized in that, In step S2, the chelating agent is one or more of EDTA, DTPA, MGDA, ATMP, and HEDP, and the amount used is 0.01~0.1% of the mass of the mixed solution in step S1.

5. The method for preparing battery-grade lithium dihydrogen phosphate from sodium and potassium lithium sulfate according to claim 1, characterized in that, In step S2, the content of each component in the potassium dihydrogen phosphate mother liquor meets the following requirements: Na2O content 3~5%, K2O content 12~17%, and P2O5 content 20~30%.

6. The method for preparing battery-grade lithium dihydrogen phosphate from sodium and potassium lithium sulfate according to claim 1, characterized in that, In step S2, the amount of potassium dihydrogen phosphate mother liquor added satisfies the following conditions: the molar mass of phosphorus in the potassium dihydrogen phosphate mother liquor is 0.34 to 0.38 times the molar mass of lithium in the purified liquid; the pH value is adjusted to 9.0 to 11.0 using a neutralizing agent to obtain lithium phosphate precipitate; the neutralizing agent is selected from at least one of ammonia water, liquid ammonia, and ammonia gas.

7. The method for preparing battery-grade lithium dihydrogen phosphate from sodium and potassium lithium sulfate according to claim 1, characterized in that, In step S3, crude lithium phosphate and phosphoric acid are mixed at a molar ratio of 1:2.0~2.5, and water is added to adjust the solution concentration to 20~50%.

8. The method for preparing battery-grade lithium dihydrogen phosphate from sodium and potassium lithium sulfate according to claim 1, characterized in that, In step S4, the concentration of the primary sulfate mother liquor is 5-30%, and the pH value is adjusted to 6.0-8.0; The crystallization temperature for obtaining potassium sulfate crystals from the mother liquor of sulfate is 30-40℃; then the liquid concentration is adjusted to 30%-50%, and the temperature is lowered to -5-5℃ to obtain sodium sulfate crystals. The ammonium sulfate mixture was then evaporated and concentrated again to separate the crystals.

9. The method for preparing battery-grade lithium dihydrogen phosphate from sodium and potassium lithium sulfate according to claim 1, characterized in that, In step S5, the amount of potassium dihydrogen phosphate mother liquor added satisfies the following conditions: the molar mass of phosphorus in the potassium dihydrogen phosphate mother liquor is 0.4 to 0.6 times the molar mass of lithium in the sulfate secondary mother liquor; the pH value is adjusted to 9.0 to 11.0 using a neutralizing agent to obtain lithium phosphate precipitate; the neutralizing agent is selected from at least one of ammonia water, liquid ammonia, and ammonia gas.

10. A battery-grade lithium dihydrogen phosphate, characterized in that, It is prepared by the method for preparing battery-grade lithium dihydrogen phosphate from sodium potassium lithium sulfate according to any one of claims 1 to 9.

Images