Method for preparing battery-grade lithium dihydrogen phosphate
By using lithium phosphate as an intermediate, the process for preparing battery-grade lithium dihydrogen phosphate has been simplified, solving the problems of long process, high cost and low purity in the existing technology, and achieving efficient and safe lithium-ion recovery and purity improvement.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-11
- Publication Date
- 2026-04-03
AI Technical Summary
Existing technologies for preparing battery-grade lithium dihydrogen phosphate have long process flows, high costs, low product purity, and low lithium-ion recovery rates, and also pose equipment safety hazards and material loss problems.
Using lithium phosphate as a key intermediate, a pH-adjusted precipitation reaction is carried out by mixing lithium-rich purification solution and phosphate solution, followed by water washing, acid hydrolysis and two evaporation crystallization processes. This simplifies the process, improves product purity and increases lithium-ion recovery rate.
This has shortened the process flow, reduced costs, improved product purity and lithium-ion recovery rate, simplified equipment operation, reduced energy and material consumption, and avoided safety hazards caused by gas generation.
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Figure BDA0005735604440000191
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium extraction technology from salt lakes, specifically to a method for preparing battery-grade lithium dihydrogen phosphate. Background Technology
[0002] Lithium dihydrogen phosphate (LiH2PO4) is an important chemical raw material with wide applications in lithium-ion batteries, the glass and ceramics industry, chemical synthesis, and biomedicine. Salt lake brines are a significant source of lithium resources. Currently, the mainstream process for extracting lithium from salt lake brines involves preparing lithium carbonate, and then using lithium carbonate or lithium hydroxide prepared from it as a raw material to react with phosphoric acid to produce battery-grade lithium dihydrogen phosphate.
[0003] However, this traditional process has several significant drawbacks: Firstly, the process is lengthy and costly, as it involves the synthesis, calcination, and multiple subsequent dissolution and purification steps of lithium carbonate, resulting in high energy and material consumption. Secondly, in the preparation of lithium dihydrogen phosphate, the reaction between lithium carbonate and phosphoric acid releases a large amount of carbon dioxide gas, which can easily cause material spillage and foam entrainment in the equipment, leading to material loss and safety hazards, and placing stringent requirements on the design of the reaction equipment. At the same time, the solubility of lithium carbonate is relatively low during the lithium precipitation process, and the lithium ions in the mother liquor require further treatment, which lengthens the process.
[0004] Currently, the industry lacks a mature solution that can directly connect to the existing lithium extraction front end of salt lakes (to obtain lithium-containing purified liquid), minimize modifications to existing lithium carbonate production lines, and continuously, stably, and efficiently produce battery-grade lithium dihydrogen phosphate. Summary of the Invention
[0005] The purpose of this invention is to overcome the problems of long process flow, high cost, low product purity and low lithium ion recovery rate in the preparation of battery-grade lithium dihydrogen phosphate in the existing technology, and to provide a method for preparing battery-grade lithium dihydrogen phosphate. This technical solution uses lithium phosphate as a key intermediate, shortens the process flow, reduces process cost, improves product purity, and improves the primary recovery rate of lithium ions.
[0006] To achieve the above objectives, the present invention provides a method for preparing battery-grade lithium dihydrogen phosphate, the method comprising the following steps:
[0007] (1) Mix the lithium-rich purification solution and the phosphate solution and control the pH value to 9-12 with a pH adjuster to carry out a precipitation reaction to obtain a slurry. Then separate the solid phase from the slurry to obtain lithium phosphate solid.
[0008] (2) The obtained lithium phosphate solid was washed with water in a certain proportion to remove soluble impurities;
[0009] (3) The lithium phosphate solid is mixed with water, and the resulting mixture is subjected to acid hydrolysis reaction with phosphoric acid. The pH value of the solution obtained after acid hydrolysis reaction is controlled to be 2-4 to obtain lithium dihydrogen phosphate solution.
[0010] (4) The lithium dihydrogen phosphate solution is subjected to a first evaporation crystallization to obtain a crystallization slurry. Then, the crystallization slurry is subjected to solid-liquid separation to obtain crude lithium dihydrogen phosphate and a first evaporation mother liquor. The first evaporation mother liquor is returned to step (1) for reuse as at least part of the lithium-rich purified liquid.
[0011] (5) Prepare the crude lithium dihydrogen phosphate into a solution, mix it with phosphoric acid and adjust the pH value to 3-4. Perform a second evaporation crystallization on the obtained solution to obtain a concentrated slurry. Then, perform solid-liquid separation on the concentrated slurry to obtain lithium dihydrogen phosphate and secondary evaporation mother liquor. Return the secondary evaporation mother liquor as at least part of the lithium dihydrogen phosphate solution to step (3) for reuse.
[0012] Preferably, the lithium ion content in the lithium-rich purification solution is 8-25 g / L.
[0013] Preferably, in step (1), the phosphate solution contains at least one of sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate.
[0014] Preferably, in step (1), the concentration of phosphate in the phosphate solution is 180-250 g / L.
[0015] Preferably, in step (1), the pH adjuster is an aqueous solution of sodium hydroxide and / or ammonia.
[0016] Preferably, in step (1), the molar ratio of the amount of lithium-rich purification solution to the amount of phosphate solution is 1:(1.1-1.3), wherein the lithium-rich purification solution is calculated as lithium ions and the phosphate solution is calculated as phosphate ions.
[0017] Preferably, in step (1), the conditions for the precipitation reaction include: a temperature of 70-95°C and a time of 0.5-1.5h.
[0018] Preferably, in step (2), the mass ratio of the lithium phosphate solid to water is 1:(2-3.5).
[0019] Preferably, in step (2), the conditions for the acidolysis reaction include: a temperature of 20-80℃ and a time of 0.3-1h.
[0020] Preferably, in step (3), the conditions for the first evaporation crystallization include: a temperature of 75-90°C and a vacuum degree of -0.09 to -0.06 MPa.
[0021] Preferably, in step (4), the specific process of preparing the crude lithium dihydrogen phosphate into a solution includes: mixing the crude lithium dihydrogen phosphate and water at 75-90°C.
[0022] Preferably, in step (4), the conditions for the second evaporation crystallization include: a temperature of 75-90°C and a vacuum degree of -0.09 to -0.06 MPa.
[0023] Compared with the prior art, the present invention has the following technical effects:
[0024] (1) The method described in this invention can directly utilize existing salt lake lithium carbonate production lines. It only requires changing "adding sodium carbonate to prepare lithium carbonate" to "adding phosphate to prepare lithium phosphate" and adding subsequent evaporation equipment to realize the transformation of the production line. The transformation cost is low and the implementation speed is fast. This invention has process compatibility and transformation convenience.
[0025] (2) The method described in this invention eliminates the complex steps of calcination and carbon dioxide treatment in the subsequent lithium carbonate to lithium dihydrogen phosphate process, simplifies the process flow, significantly reduces energy and material consumption, and thus reduces production costs.
[0026] (3) The lithium dihydrogen phosphate product prepared by the method of the present invention has high purity. Specifically, through the "lithium phosphate precipitation" step and the front-end impurity removal equipment, most of the sodium ions and potassium ions and other impurities in the solution can be effectively separated. In the key "two-stage evaporation and crystallization" step, the first evaporation can effectively remove some of the impurity ions that cannot be removed by washing during the lithium precipitation process, creating conditions for obtaining a high-purity product by the second crystallization.
[0027] (4) The method described in this invention uses the reaction of lithium phosphate with phosphoric acid as a liquid-solid phase reaction, which does not produce gas. The reaction process is stable, easy to control and operate, and the equipment is highly safe.
[0028] (5) The lithium ion yield of the method described in this invention is high. Compared with the lithium carbonate process, lithium phosphate has a lower solubility and the subsequent evaporation mother liquor can be reused. The lithium ion yield can reach more than 92% in the process of preparing lithium dihydrogen phosphate product from lithium-rich refined liquid. Detailed Implementation
[0029] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.
[0030] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0031] The method for preparing battery-grade lithium dihydrogen phosphate according to the present invention includes the following steps:
[0032] (1) Mix the lithium-rich purification solution and the phosphate solution and control the pH value to 9-12 with a pH adjuster to carry out a precipitation reaction to obtain a slurry. Then separate the solid phase from the slurry to obtain lithium phosphate solid.
[0033] (2) The lithium phosphate solid is mixed with water, and the resulting slurry is subjected to acid hydrolysis reaction with phosphoric acid. The pH value of the solution obtained after acid hydrolysis reaction is controlled to be 2-4 to obtain lithium dihydrogen phosphate solution.
[0034] (3) The lithium dihydrogen phosphate solution is subjected to a first evaporation crystallization to obtain a crystallization slurry. Then, the crystallization slurry is subjected to solid-liquid separation to obtain crude lithium dihydrogen phosphate and a first evaporation mother liquor. The first evaporation mother liquor is returned to step (1) for reuse as at least part of the lithium-rich purified liquid.
[0035] (4) Prepare the crude lithium dihydrogen phosphate into a solution, mix it with phosphoric acid and adjust the pH value to 3-4, and perform a second evaporation crystallization on the obtained solution to obtain a concentrated slurry. Then, perform solid-liquid separation on the concentrated slurry to obtain lithium dihydrogen phosphate and secondary evaporation mother liquor. Return the secondary evaporation mother liquor as at least part of the lithium dihydrogen phosphate solution to step (3) for reuse.
[0036] According to the method described in this invention, lithium phosphate is prepared by using a lithium-rich purification solution and a phosphate solution, and then subjected to two evaporation crystallization processes. This shortens the process flow, reduces process costs, improves product purity, and increases the primary recovery rate of lithium ions.
[0037] In the method described in this invention, the method may further include preparing the lithium-rich purified solution by enriching and purifying lithium ions in the brine of a salt lake. The enrichment and purification can be achieved through at least one of adsorption, membrane separation, and extraction. The adsorption can be carried out using a lithium-ion adsorbent, employing adsorption methods conventionally used in the art; various commercially available lithium-ion adsorbents can achieve the same performance. The membrane separation can be carried out using anion and cation exchange membranes and / or nanofiltration membranes, employing membrane separation methods conventionally used in the art (e.g., electrodialysis); various commercially available anion and cation exchange membranes and nanofiltration membranes can achieve the same performance. The extraction can be carried out using an extractant, employing extraction methods conventionally used in the art; the extractant can be at least one of di(2-ethylhexyl)phosphoric acid (D2EHPA), trioctylphosphine oxide (TOPO), and 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP); various commercially available extractants can achieve the same performance.
[0038] In the method described in this invention, the lithium ion content in the lithium-rich purification solution can be 8-25 g / L, preferably 15-20 g / L.
[0039] In the method described in this invention, in step (1), in order to effectively separate most of the sodium and potassium ions and other impurities in the solution, the phosphate solution preferably contains at least one of sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate, more preferably disodium hydrogen phosphate. The concentration of phosphate ions in the phosphate solution can be 180-250 g / L, preferably 200-220 g / L.
[0040] In the method described in this invention, in step (1), the pH adjuster can be an aqueous solution of sodium hydroxide and / or ammonia, preferably an aqueous solution of sodium hydroxide. The concentration of the aqueous solution of sodium hydroxide can be 20-40 wt%, preferably 25-35 wt%. The concentration of the ammonia can be 20-40 wt%, preferably 30-40 wt%.
[0041] In the method described in this invention, in order to improve the recovery rate of lithium ions, in step (1), the molar ratio of the amount of lithium-rich purification solution to the amount of phosphate solution is preferably 1:(1.1-1.3), more preferably 1:(1.15-1.2), wherein the lithium-rich purification solution is calculated as lithium ions and the phosphate solution is calculated as phosphate ions.
[0042] In the method described in this invention, in order to improve the recovery rate of lithium ions, the conditions for the precipitation reaction include: the temperature can be 70-95℃, preferably 85-90℃; the time can be 0.5-1.5h, preferably 0.7-1.2h.
[0043] In some embodiments, the specific process of mixing the lithium-rich purification solution and the phosphate solution and controlling the pH value to 9-12 with a pH adjuster to carry out the precipitation reaction includes: mixing the lithium-rich purification solution and the phosphate solution, then adding a pH adjuster while stirring and controlling the pH value to 9-12, and then carrying out the precipitation reaction at 70-95°C for 0.5-1.5 hours.
[0044] In the method described in this invention, the solid phase can be separated from the slurry by filtration. The method may further include washing the solid phase separated in step (1) with water 2-4 times. In each washing process, the mass ratio of the solid phase separated in step (1) to water can be 1:(4-6). The method may further include separating the liquid phase from the slurry obtained in step (1) to obtain lithium precipitation mother liquor, and discharging the lithium precipitation mother liquor into the salt field system after a phosphorus treatment process.
[0045] In the method described in this invention, in step (2), the mass ratio of the lithium phosphate solid to water can be 1:(2-3.5), preferably 1:(2.5-3). The specific process of mixing the lithium phosphate solid and water can involve adding water to the lithium phosphate solid and then pulping it.
[0046] In the method described in this invention, in order to improve the purity of lithium dihydrogen phosphate, in step (2), the phosphoric acid is preferably electronic-grade phosphoric acid and / or food-grade phosphoric acid. The conditions for the acid hydrolysis reaction include: a temperature of 20-80℃, preferably 40-80℃; and a time of 0.3-1h, preferably 0.5-1h. No gas is generated during the acid hydrolysis reaction, the reaction process is stable, and it is easy to control and operate.
[0047] In the method described in this invention, the conditions for the first evaporation crystallization in step (3) include: a temperature of 75-90°C, preferably 75-85°C; and a vacuum of -0.09 to -0.06 MPa, preferably -0.08 to -0.07 MPa. To ensure the quality of the lithium dihydrogen phosphate product, the specific process of step (3) preferably includes: performing a first evaporation crystallization on the lithium dihydrogen phosphate solution, concentrating and crystallizing it at a temperature of 75-90°C and a vacuum of -0.09 to -0.06 MPa until lithium dihydrogen phosphate crystals precipitate, obtaining a crystallization slurry; then performing solid-liquid separation on the crystallization slurry to obtain crude lithium dihydrogen phosphate and a first evaporation mother liquor; returning the first evaporation mother liquor as at least part of the lithium-rich purified liquid to step (1) for reuse. In the first evaporation mother liquor, the concentration of sodium ions can be below 1 g / L, preferably 0-0.5 g / L. Solid-liquid separation of the crystallization slurry can be performed by centrifugation. In this document, the vacuum is atmospheric pressure minus absolute pressure. The first evaporation crystallization effectively removes some of the impurity ions that cannot be removed by washing during the lithium precipitation process.
[0048] In the method described in this invention, the specific process of preparing the crude lithium dihydrogen phosphate solution in step (4) may include: mixing the crude lithium dihydrogen phosphate and water at 70-85°C. In step (4), the crude lithium dihydrogen phosphate is dissolved in water to prepare a near-saturated or saturated solution in the solution prepared by the method.
[0049] In the method described in this invention, in step (4), the conditions for the second evaporation crystallization include: the temperature can be 75-90℃, preferably 75-85℃; the vacuum degree can be -0.09 to -0.06MPa, preferably -0.08 to -0.07MPa.
[0050] In the method described in this invention, to ensure the quality of lithium dihydrogen phosphate products, the specific process of step (4) preferably includes: mixing the crude lithium dihydrogen phosphate and water at 75-90°C to prepare a solution, then adding phosphoric acid to adjust the pH value to 3-4, subjecting the obtained solution to a second evaporation crystallization, concentrating the solution at a temperature of 75-90°C and a vacuum degree of -0.09 to -0.06 MPa until crystals precipitate out, obtaining a concentrated slurry, and then performing solid-liquid separation on the concentrated slurry to obtain lithium dihydrogen phosphate and a secondary evaporation mother liquor; the secondary evaporation mother liquor is returned to step (3) as at least a portion of the lithium dihydrogen phosphate solution for reuse. In step (4), the solid-liquid separation of the concentrated slurry can be performed by centrifugation. In step (4), the phosphoric acid can be electronic grade phosphoric acid and / or food grade phosphoric acid. Returning the secondary evaporation mother liquor as at least a portion of the lithium dihydrogen phosphate solution for reuse in step (3) ensures product quality and controls the sodium ion content in the product to meet battery-grade standards.
[0051] In the method described in this invention, the method may further include: drying the solid phase obtained by solid-liquid separation of the concentrated slurry. The drying conditions include: a temperature of 80-110℃, preferably 90-110℃; and a time of 1-3 hours, preferably 1.5-3 hours.
[0052] In some embodiments, the method for preparing battery-grade lithium dihydrogen phosphate according to the present invention includes the following steps:
[0053] (1) Mix the lithium-rich purification solution with a phosphate solution of 180-250 g / L (calculated as phosphate ions), then add a pH adjuster under stirring and control the pH value to 9-12, and carry out a precipitation reaction at 70-95℃ for 0.5-1.5 h to obtain a slurry. Then separate the solid phase from the slurry by filtration. Wash the solid phase obtained in step (1) with water 2-4 times to obtain lithium phosphate solid. Separate the liquid phase from the slurry obtained in step (1) to obtain lithium precipitation mother liquor. Discharge the lithium precipitation mother liquor into the salt field system after phosphorus treatment.
[0054] (2) Add water to the lithium phosphate solid and slurry it. Add phosphoric acid dropwise to the mixture under stirring and carry out acid hydrolysis reaction at 20-80℃ for 0.3-1h. Control the pH value of the solution obtained after acid hydrolysis reaction to be 2-4 to obtain lithium dihydrogen phosphate solution.
[0055] (3) The lithium dihydrogen phosphate solution is subjected to a first evaporation crystallization at a temperature of 75-90℃ and a vacuum degree of -0.09 to -0.06 MPa until lithium dihydrogen phosphate crystals precipitate, resulting in a crystallization slurry. The crystallization slurry is then subjected to solid-liquid separation by centrifugation to obtain crude lithium dihydrogen phosphate and a first evaporation mother liquor. The first evaporation mother liquor is returned to step (1) as at least a portion of the lithium-rich purified liquid.
[0056] Reuse in the middle;
[0057] (4) The crude lithium dihydrogen phosphate and water are mixed at 75-90℃ to prepare a solution, which is then mixed with phosphoric acid and the pH value is adjusted to 3-4. The resulting solution is subjected to a second evaporation crystallization. The solution is concentrated at a temperature of 75-90℃ and a vacuum degree of -0.09 to -0.06MPa until crystals precipitate out to obtain a concentrated slurry. The concentrated slurry is then subjected to solid-liquid separation by centrifugation to obtain a solid phase and a secondary evaporation mother liquor. The secondary evaporation mother liquor is returned to step (3) as at least part of the lithium dihydrogen phosphate solution for reuse. The solid phase obtained by solid-liquid separation of the concentrated slurry is dried at 80-110℃ for 3-6 hours to obtain lithium dihydrogen phosphate.
[0058] In the lithium-rich purification solution, the lithium ion content is 8-25 g / L, the sodium ion content is 8-15 g / L, the total calcium and magnesium ion content is less than 1 mg / L, and the borate content is mainly B. 3+ Calculated as below 5 mg / L;
[0059] In the phosphate solution, the phosphate is at least one of sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate;
[0060] The pH adjuster is an aqueous solution of sodium hydroxide and / or ammonia; the concentration of the aqueous solution of sodium hydroxide is 20-40 wt%; the concentration of the ammonia is 20-40 wt%.
[0061] The molar ratio of the lithium-rich purification solution to the phosphate solution is 1:(1.1-1.3), wherein the lithium-rich purification solution is calculated as lithium ions and the phosphate solution is calculated as phosphate ions.
[0062] In each washing process, the mass ratio of the solid phase separated in step (1) to the water is 1:(4-6);
[0063] In step (2), the mass ratio of the lithium phosphate solid to water is 1:(2-3.5);
[0064] In step (2), the phosphoric acid is electronic grade phosphoric acid and / or food grade phosphoric acid.
[0065] The following examples further illustrate the method for preparing battery-grade lithium dihydrogen phosphate according to the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.
[0066] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples are commercially available. The phosphoric acid used in the examples and comparative examples is electronic-grade phosphoric acid with a concentration of 85 wt%.
[0067] Example 1
[0068] (1) Take 1L of lithium-rich purified solution (the lithium-rich purified solution is obtained by enriching and purifying lithium ions 1 in salt lake brine to obtain lithium chloride purified solution, in which the lithium ion content is 25g / L, the sodium ion content is 15g / L, the calcium ion content is 0.5mg / L, the magnesium ion content is 0.5mg / L, and the borate content is B) 3+A mixture of 5 mg / L lithium-rich purified solution and 200 g / L sodium dihydrogen phosphate aqueous solution (calculated as phosphate) was prepared (the molar ratio of the lithium-rich purified solution to the sodium dihydrogen phosphate aqueous solution was 1:1.2, wherein the lithium-rich purified solution was calculated as lithium ions and the sodium dihydrogen phosphate aqueous solution was calculated as phosphate). A 30 wt% sodium hydroxide solution was added under stirring, and the pH of the precipitation reaction solution was controlled to be 9. The precipitation reaction was carried out at 85°C for 1 h to obtain a slurry. The solid phase was then separated from the slurry by filtration. The solid phase obtained in step (1) was washed with water 3 times (the mass ratio of the solid phase obtained in step (1) to water was 1:5 in each washing process) to obtain wet filter cake lithium phosphate (lithium precipitation yield was 85%). The liquid phase was separated from the slurry obtained in step (1) to obtain lithium precipitation mother liquor. The lithium precipitation mother liquor was discharged into the salt field system after a phosphorus treatment process.
[0069] (2) Water (the mass ratio of the lithium phosphate solid to water is 1:2.5) is added to the wet filter cake lithium phosphate and pulped. Then, electronic grade phosphoric acid (concentration of 85wt%) is added dropwise to the mixture under stirring. Acid hydrolysis is carried out at 30°C for 0.5h, and the pH value of the acid hydrolysis solution is controlled to be 3.0 to obtain lithium dihydrogen phosphate solution.
[0070] (3) The lithium dihydrogen phosphate solution is subjected to a first evaporation crystallization, and concentrated crystallization is carried out at a temperature of 85°C and a vacuum degree of -0.08MPa until lithium dihydrogen phosphate crystals precipitate to a volume ratio of 30% in the solid-liquid mixture, and a crystallization slurry is obtained. The crystallization slurry is separated into solid and liquid by centrifugation to obtain crude lithium dihydrogen phosphate and a first evaporation mother liquor; the first evaporation mother liquor is returned to step (1) for reuse as at least part of the lithium-rich purified liquid;
[0071] (4) Mix 100g of the crude lithium dihydrogen phosphate and 0.2L of water at 85°C to prepare a solution. Then add electronic grade phosphoric acid (concentration of 85wt%) to adjust the pH value to 3.0. Perform a second evaporation crystallization on the obtained solution. Concentrate the solution at 85°C and a vacuum of -0.08MPa until crystals precipitate out, until the volume ratio of crystals in the solid-liquid mixture is 30%, to obtain a concentrated slurry. Separate the concentrated slurry into solid and liquid by centrifugation to obtain a solid phase and a secondary evaporation mother liquor. Return the secondary evaporation mother liquor as at least part of the lithium dihydrogen phosphate solution to step (3) for reuse. Dry the solid phase obtained by solid-liquid separation of the concentrated slurry at 100°C for 2 hours to obtain a lithium dihydrogen phosphate product. The purity of the product is 99.71% as analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The contents of key impurity elements Na, K, Ca, Mg and Fe are all lower than the requirements of battery-grade material standards. The specific contents and yields of each component are recorded in Table 1.
[0072] Example 2
[0073] (1) Take 1L of lithium-rich purified solution (the lithium-rich purified solution is obtained by enriching and purifying lithium ions 1 in salt lake brine to obtain lithium chloride purified solution, in which the lithium ion content is 25g / L, the sodium ion content is 15g / L, the calcium ion content is 0.5mg / L, the magnesium ion content is 0.5mg / L, and the borate content is B) 3+ A mixture of 5 mg / L lithium-rich purified solution and 200 g / L sodium dihydrogen phosphate aqueous solution (calculated as phosphate) was prepared (the molar ratio of the lithium-rich purified solution to the sodium dihydrogen phosphate aqueous solution was 1:1.3, wherein the lithium-rich purified solution was calculated as lithium ions and the sodium dihydrogen phosphate aqueous solution was calculated as phosphate). A 30 wt% sodium hydroxide solution was added under stirring, and the pH of the precipitation reaction solution was controlled to 10. The precipitation reaction was carried out at 85°C for 1 h to obtain a slurry. The solid phase was then separated from the slurry by filtration. The solid phase obtained in step (1) was washed with water 3 times (the mass ratio of the solid phase obtained in step (1) to water was 1:5 in each washing process) to obtain wet filter cake lithium phosphate (lithium precipitation yield was 96%). The liquid phase was separated from the slurry obtained in step (1) to obtain lithium precipitation mother liquor. The lithium precipitation mother liquor was discharged into the salt field system after a phosphorus treatment process.
[0074] (2) Water (the mass ratio of the lithium phosphate solid to water is 1:2) is added to the wet filter cake lithium phosphate and pulped. Then, electronic grade phosphoric acid (concentration of 85wt%) is added dropwise to the mixture under stirring. Acid hydrolysis is carried out at 50°C for 1 hour, and the pH value of the solution obtained after acid hydrolysis is controlled to be 3.0 to obtain lithium dihydrogen phosphate solution.
[0075] (3) The lithium dihydrogen phosphate solution is subjected to a first evaporation crystallization, and concentrated crystallization is carried out at a temperature of 85°C and a vacuum degree of -0.08MPa until lithium dihydrogen phosphate crystals precipitate to a volume ratio of 30% in the solid-liquid mixture, and a crystallization slurry is obtained. The crystallization slurry is separated into solid and liquid by centrifugation to obtain crude lithium dihydrogen phosphate and a first evaporation mother liquor; the first evaporation mother liquor is returned to step (1) for reuse as at least part of the lithium-rich purified liquid;
[0076] (4) Mix 100g of the crude lithium dihydrogen phosphate and 0.2L of water at 80°C, then add electronic grade phosphoric acid (concentration of 85wt%), adjust the pH to 3.0, and perform a second evaporation crystallization on the resulting solution. Concentrate the solution at 85°C and a vacuum of -0.08MPa until crystals precipitate out, until the volume ratio of crystals in the solid-liquid mixture is 30%, to obtain a concentrated slurry. Separate the concentrated slurry into solid and liquid phases by centrifugation to obtain a solid phase and a secondary evaporation mother liquor. Return the secondary evaporation mother liquor as at least part of the lithium dihydrogen phosphate solution to step (3) for reuse. Dry the solid phase obtained by solid-liquid separation of the concentrated slurry at 100°C for 2 hours to obtain a lithium dihydrogen phosphate product. According to ICP-MS analysis, the purity of the product is 99.68%, and the contents of key impurity elements Na, K, Ca, Mg, and Fe are all lower than the requirements of battery-grade material standards. The specific contents and yields of each component are recorded in Table 1.
[0077] Example 3
[0078] (1) Take 1L of lithium-rich purified solution (the lithium-rich purified solution is obtained by enriching and purifying lithium ions 1 in salt lake brine to obtain lithium chloride purified solution, in which the lithium ion content is 12g / L, the sodium ion content is 8g / L, the calcium ion content is 0.5mg / L, the magnesium ion content is 0.5mg / L, and the borate content is B) 3+ A mixture of 5 mg / L lithium-rich purified solution and 180 g / L disodium hydrogen phosphate aqueous solution (calculated as phosphate) was prepared (the molar ratio of the lithium-rich purified solution to the disodium hydrogen phosphate aqueous solution was 1:1.1, wherein the lithium-rich purified solution was calculated as lithium ions and the disodium hydrogen phosphate aqueous solution was calculated as phosphate). A 30 wt% sodium hydroxide solution was added under stirring, and the pH of the precipitation reaction solution was controlled to 10. The precipitation reaction was carried out at 85°C for 1 h to obtain a slurry. The solid phase was then separated from the slurry by filtration. The solid phase obtained in step (1) was washed with water 3 times (the mass ratio of the solid phase obtained in step (1) to water was 1:5 in each washing process) to obtain wet filter cake lithium phosphate (lithium precipitation yield was 95%). The liquid phase was separated from the slurry obtained in step (1) to obtain lithium precipitation mother liquor. The lithium precipitation mother liquor was discharged into the salt field system after a phosphorus treatment process.
[0079] (2) Water (the mass ratio of the lithium phosphate solid to water is 1:2) is added to the wet filter cake lithium phosphate and pulped. Then, electronic grade phosphoric acid (concentration of 85wt%) is added dropwise to the mixture under stirring and acid hydrolysis is carried out at 50°C for 0.3h. The pH value of the solution obtained after acid hydrolysis is controlled to be 3.0 to obtain lithium dihydrogen phosphate solution.
[0080] (3) The lithium dihydrogen phosphate solution is subjected to a first evaporation crystallization, and concentrated crystallization is carried out at a temperature of 90°C and a vacuum degree of -0.09MPa until lithium dihydrogen phosphate crystals precipitate to a volume ratio of 30% in the solid-liquid mixture, to obtain a crystallization slurry. Then, the crystallization slurry is subjected to solid-liquid separation by centrifugation to obtain crude lithium dihydrogen phosphate and a first evaporation mother liquor. The first evaporation mother liquor is returned to step (1) for reuse as at least part of the lithium-rich purified liquid.
[0081] (4) Dissolve 100g of the crude lithium dihydrogen phosphate and 0.2L of water at 90°C, then add electronic grade phosphoric acid (concentration of 85wt%) to adjust the pH to 3.0. Perform a second evaporation crystallization on the resulting solution at 90°C and a vacuum of -0.09MPa until lithium dihydrogen phosphate crystals precipitate to a volume ratio of 30% in the solid-liquid mixture. Stop evaporation to obtain a concentrated slurry. Perform solid-liquid separation on the concentrated slurry by centrifugation to obtain a solid phase and a secondary evaporation mother liquor. Return the secondary evaporation mother liquor as at least part of the lithium dihydrogen phosphate solution to step (3) for reuse. Dry the solid phase obtained by solid-liquid separation of the concentrated slurry at 100°C for 2 hours to obtain a lithium dihydrogen phosphate product. According to ICP-MS analysis, the product purity is 99.75%. The contents of key impurity elements Na, K, Ca, Mg and Fe are all lower than the requirements of battery-grade material standards. The specific contents and yields of each component are recorded in Table 1.
[0082] Example 4
[0083] (1) Take 1L of lithium-rich purified solution (the lithium-rich purified solution is obtained by enriching and purifying lithium ions 1 in salt lake brine to obtain lithium chloride purified solution, wherein the lithium ion content is 8g / L, the sodium ion content is 5g / L, the calcium ion content is 0.5mg / L, the magnesium ion content is 0.5mg / L, and the borate content is B) 3+ A mixture of 5 mg / L lithium-rich purified solution and 250 g / L sodium phosphate aqueous solution (calculated as phosphate) was prepared (the molar ratio of the lithium-rich purified solution to the sodium phosphate aqueous solution was 1:1.3, wherein the lithium-rich purified solution was calculated as lithium ions and the sodium phosphate aqueous solution was calculated as phosphate ions). A 30 wt% ammonia aqueous solution was added under stirring, and the pH of the precipitation reaction solution was controlled to 12. The precipitation reaction was carried out at 85°C for 1 h to obtain a slurry. The solid phase was then separated from the slurry by filtration. The solid phase obtained in step (1) was washed with water 3 times (the mass ratio of the solid phase obtained in step (1) to water was 1:4 in each washing process) to obtain wet filter cake lithium phosphate (lithium precipitation yield was 98%). The liquid phase was separated from the slurry obtained in step (1) to obtain lithium precipitation mother liquor. The lithium precipitation mother liquor was discharged into the salt field system after a phosphorus treatment process.
[0084] (2) Water (the mass ratio of the lithium phosphate solid to water is 1:3.5) is added to the wet filter cake lithium phosphate and pulped. Then, electronic grade phosphoric acid (concentration of 85wt%) is added dropwise to the mixture under stirring and acid hydrolysis is carried out at 80°C for 0.3h. The pH value of the solution obtained after acid hydrolysis is controlled to be 2.0 to obtain lithium dihydrogen phosphate solution.
[0085] (3) The lithium dihydrogen phosphate solution is subjected to a first evaporation crystallization. The concentration and crystallization are carried out at a temperature of 75°C and a vacuum degree of -0.06MPa until the lithium dihydrogen phosphate crystals precipitate to a volume ratio of 30% in the solid-liquid mixture. Evaporation is stopped to obtain a crystallization slurry. The crystallization slurry is separated into solid and liquid by centrifugation to obtain crude lithium dihydrogen phosphate and a first evaporation mother liquor. The first evaporation mother liquor is returned to step (1) for reuse as at least part of the lithium-rich purified liquid.
[0086] (4) Mix 100g of the crude lithium dihydrogen phosphate and 0.2L of water at 75°C, then add electronic grade phosphoric acid (concentration of 85wt%) to adjust the pH to 3.0. Perform a second evaporation crystallization on the obtained solution. Concentrate the solution at 75°C and a vacuum of -0.06MPa until crystals precipitate out, until the volume ratio of crystals in the solid-liquid mixture is 30%. Stop evaporation to obtain a concentrated slurry. Separate the concentrated slurry into solid and liquid phases by centrifugation to obtain a solid phase and a secondary evaporation mother liquor. Return the secondary evaporation mother liquor as at least part of the lithium dihydrogen phosphate solution to step (3) for reuse. Dry the solid phase obtained by solid-liquid separation of the concentrated slurry at 80°C for 4h to obtain the lithium dihydrogen phosphate product. According to ICP-MS analysis, the purity of the product is 99.80%. The contents of key impurity elements Na, K, Ca, Mg and Fe are all lower than the requirements of battery-grade material standards. The specific contents and yields of each component are recorded in Table 1.
[0087] Example 5
[0088] The method was implemented according to Example 1, except that the aqueous solution of ammonium dihydrogen phosphate was replaced with an aqueous solution of ammonium dihydrogen phosphate. The lithium precipitation yield was 85%, and lithium dihydrogen phosphate product was obtained. ICP-MS analysis showed that the product purity was 99.75%. The contents of key impurity elements Na, K, Ca, Mg and Fe were all lower than the requirements of battery-grade material standards. The specific contents and yields of each component are recorded in Table 1.
[0089] Comparative Example 1
[0090] The method was carried out according to Example 1, except that the pH value of the solution obtained after the precipitation reaction was controlled to be 6. The specific steps are as follows:
[0091] (1) Take 1L of lithium-rich purified solution (the lithium-rich purified solution is obtained by enriching and purifying lithium ions 1 in salt lake brine to obtain lithium chloride purified solution, in which the lithium ion content is 25g / L, the sodium ion content is 15g / L, the calcium ion content is 0.5mg / L, the magnesium ion content is 0.5mg / L, and the borate content is B) 3+ A mixture of 5 mg / L lithium-rich purified solution and 200 g / L sodium dihydrogen phosphate aqueous solution (calculated as phosphate) was prepared (the molar ratio of the lithium-rich purified solution to the sodium dihydrogen phosphate aqueous solution was 1:1.2, wherein the lithium-rich purified solution was calculated as lithium ions and the sodium dihydrogen phosphate aqueous solution was calculated as phosphate ions). A 30 wt% sodium hydroxide solution was added under stirring, and the pH of the precipitation reaction solution was controlled to be 6. The precipitation reaction was carried out at 85°C for 1 h to obtain a slurry. The solid phase was then separated from the slurry by filtration. The solid phase obtained in step (1) was washed with water 3 times (the mass ratio of the solid phase obtained in step (1) to water was 1:5 in each washing process) to obtain wet filter cake lithium phosphate (lithium precipitation yield was 45%). The lithium precipitation mother liquor required a high lithium ion content and needed to be recycled twice. The liquid phase was separated from the slurry obtained in step (1) to obtain the lithium precipitation mother liquor. The lithium precipitation mother liquor was discharged into the salt field system after passing through a phosphorus treatment process.
[0092] (2) Water (the mass ratio of the lithium phosphate solid to the water is 1:2) is added to the wet filter cake lithium phosphate and pulped. Then, electronic grade phosphoric acid (concentration of 85wt%) is added dropwise to the mixture under stirring and acid hydrolysis is carried out at 30°C for 0.5h. The pH value of the solution obtained after acid hydrolysis is controlled to be 3.0 to obtain lithium dihydrogen phosphate solution.
[0093] (3) The lithium dihydrogen phosphate solution is subjected to a first evaporation crystallization. The concentration and crystallization are carried out at a temperature of 85°C and a vacuum of -0.08MPa until the lithium dihydrogen phosphate crystals precipitate to a volume ratio of 30% in the solid-liquid mixture. Evaporation is stopped to obtain a crystallization slurry. The crystallization slurry is separated into solid and liquid by centrifugation to obtain crude lithium dihydrogen phosphate and a first evaporation mother liquor. The first evaporation mother liquor is returned to step (1) for reuse as at least part of the lithium-rich purified liquid.
[0094] (4) Dissolve 100g of the crude lithium dihydrogen phosphate and 0.2L of water at 80°C, then add electronic grade phosphoric acid (concentration of 85wt%) to adjust the pH to 3.0. Perform a second evaporation crystallization on the resulting solution at 80°C and a vacuum of -0.08MPa until lithium dihydrogen phosphate crystals precipitate to a volume ratio of 30% in the solid-liquid mixture. Stop evaporation to obtain a concentrated slurry. Perform solid-liquid separation on the concentrated slurry by centrifugation to obtain a solid phase and a secondary evaporation mother liquor. Return the secondary evaporation mother liquor as at least part of the lithium dihydrogen phosphate solution to step (3) for reuse. Dry the solid phase obtained by solid-liquid separation of the concentrated slurry at 100°C for 2 hours to obtain the lithium dihydrogen phosphate product. The purity of the product is 99.80% as analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The specific content and yield of each component are recorded in Table 1.
[0095] Comparative Example 2
[0096] The method described in Example 1 was followed, except that hydrochloric acid was used to acidify lithium phosphate. The specific steps are as follows:
[0097] (1) Take 1L of lithium-rich purified solution (the lithium-rich purified solution is obtained by enriching and purifying lithium ions 1 in salt lake brine to obtain lithium chloride purified solution, in which the lithium ion content is 25g / L, the sodium ion content is 15g / L, the calcium ion content is 0.5mg / L, the magnesium ion content is 0.5mg / L, and the borate content is B) 3+ A mixture of 5 mg / L lithium-rich purified solution and 200 g / L sodium dihydrogen phosphate aqueous solution (calculated as phosphate) was prepared (the molar ratio of the lithium-rich purified solution to the sodium dihydrogen phosphate aqueous solution was 1:1.2, wherein the lithium-rich purified solution was calculated as lithium ions and the sodium dihydrogen phosphate aqueous solution was calculated as phosphate). A 30 wt% sodium hydroxide solution was added under stirring, and the pH of the precipitation reaction solution was controlled to be 9. The precipitation reaction was carried out at 85°C for 1 h to obtain a slurry. The solid phase was then separated from the slurry by filtration. The solid phase obtained in step (1) was washed with water 3 times (the mass ratio of the solid phase obtained in step (1) to water was 1:5 in each washing process) to obtain wet filter cake lithium phosphate (lithium precipitation yield was 92%). The liquid phase was separated from the slurry obtained in step (1) to obtain lithium precipitation mother liquor. The lithium precipitation mother liquor was discharged into the salt field system after a phosphorus treatment process.
[0098] (2) Water (the mass ratio of the lithium phosphate solid to the water is 1:2) is added to the wet filter cake lithium phosphate and the mixture is slurried. Then, hydrochloric acid (concentration of 30wt%) is added dropwise to the mixture under stirring. The mixture is acidified at 50°C for 0.5h and the pH of the solution obtained after the acidification reaction is controlled to be 3.0 to obtain lithium dihydrogen phosphate solution.
[0099] (3) The lithium dihydrogen phosphate solution is subjected to a first evaporation crystallization, and concentrated crystallization is carried out at a temperature of 85°C and a vacuum degree of -0.08MPa until lithium dihydrogen phosphate crystals precipitate to a volume ratio of 30% in the solid-liquid mixture, to obtain a crystallization slurry. Then, the crystallization slurry is subjected to solid-liquid separation by centrifugation to obtain crude lithium dihydrogen phosphate and a first evaporation mother liquor. The first evaporation mother liquor is returned to step (1) for reuse as at least part of the lithium-rich purified liquid.
[0100] (4) Dissolve 100g of the crude lithium dihydrogen phosphate and 0.2L of water at 80°C, then add hydrochloric acid (concentration of 30wt%) to adjust the pH to 3.0. Perform a second evaporation crystallization on the obtained solution. Concentrate the solution at 85°C and a vacuum of -0.08MPa until crystals precipitate and the volume ratio of crystals in the solid-liquid mixture reaches 30% to obtain a concentrated slurry. Then, separate the solid and liquid phases of the concentrated slurry by centrifugation to obtain a solid phase and a secondary evaporation mother liquor. Return the secondary evaporation mother liquor as at least part of the lithium dihydrogen phosphate solution to step (3) for reuse. Dry the solid phase obtained by solid-liquid separation of the concentrated slurry at 100°C for 2 hours to obtain the lithium dihydrogen phosphate product. ICP-MS analysis showed that the product purity was 98.52%, and the chloride ion content exceeded the standard. The specific content and yield of each component are recorded in Table 7.
[0101] Comparative Example 3
[0102] (1) Take 1L of lithium-rich purified solution (the lithium-rich purified solution is obtained by enriching and purifying lithium ions 1 in salt lake brine to obtain lithium chloride purified solution, in which the lithium ion content is 25g / L, the sodium ion content is 15g / L, the calcium ion content is 0.5mg / L, the magnesium ion content is 0.5mg / L, and the borate content is B) 3+ A lithium carbonate aqueous solution with a concentration of 5 mg / L and a concentration of 200 g / L (calculated as carbonate) was mixed (the molar ratio of the lithium-rich purification solution to the lithium carbonate aqueous solution was 1:1.2, wherein the lithium-rich purification solution was calculated as lithium ions and the lithium carbonate aqueous solution was calculated as carbonate ions). A sodium hydroxide solution with a concentration of 30 wt% was added under stirring, and the pH value of the precipitation reaction solution was controlled to 12. The precipitation reaction was carried out at 85°C for 1 h to obtain a slurry. Then, the solid phase was separated from the slurry by filtration. The solid phase obtained in step (1) was washed with water 3 times (the mass ratio of the solid phase obtained in step (1) to water was 1:5 in each washing process) to obtain wet filter cake lithium carbonate (lithium precipitation yield of 82%). The liquid phase was separated from the slurry obtained in step (1) to obtain lithium precipitation mother liquor. The lithium precipitation mother liquor was discharged into the salt field system after phosphorus treatment.
[0103] (2) Add water to the wet lithium carbonate obtained in step (2) (the mass ratio of the lithium carbonate solid to water is 1:2) and slurry it. Then, add electronic grade phosphoric acid (concentration of 85wt%) dropwise to the mixture under stirring, adjust the pH of the solution to 3, and collect the filtrate containing lithium dihydrogen phosphate. During this process, a large amount of carbon dioxide is generated and the solution foams severely.
[0104] (3) The filtrate containing lithium dihydrogen phosphate from step (2) was evaporated and concentrated, then cooled and crystallized. The lithium dihydrogen phosphate was collected and dried at 100°C for 2 hours to obtain the lithium dihydrogen phosphate product. The purity of the product was 99.75% according to ICP-MS analysis. The specific content and yield of each component are recorded in Table 1.
[0105] Table 1
[0106]
[0107] As can be seen from the results in Table 1, the embodiments using the method for preparing battery-grade lithium dihydrogen phosphate described in this invention have higher purity of lithium dihydrogen phosphate product and higher lithium-ion recovery rate. The contents of key impurity elements Na, K, Ca, Mg, and Fe are all lower than the requirements of battery-grade material standards, and the process flow is shortened, reducing process costs. Although Comparative Examples 1 and 3 have higher purity of lithium dihydrogen phosphate product, their lithium-ion recovery rates are lower than those of the embodiments.
[0108] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.
Claims
1. A method for preparing battery-grade lithium dihydrogen phosphate, characterized in that, The method includes the following steps: (1) Mix the lithium-rich purification solution and the phosphate solution and control the pH value to 9-12 with a pH adjuster to carry out a precipitation reaction to obtain a slurry. Then separate the solid phase from the slurry to obtain lithium phosphate solid. (2) The lithium phosphate solid is mixed with water, and the resulting slurry is subjected to acid hydrolysis reaction with phosphoric acid. The pH value of the solution obtained after acid hydrolysis reaction is controlled to be 2-4 to obtain lithium dihydrogen phosphate solution. (3) The lithium dihydrogen phosphate solution is subjected to a first evaporation crystallization to obtain a crystallization slurry. Then, the crystallization slurry is subjected to solid-liquid separation to obtain crude lithium dihydrogen phosphate and a first evaporation mother liquor. The first evaporation mother liquor is returned to step (1) for reuse as at least part of the lithium-rich purified liquid. (4) Prepare the crude lithium dihydrogen phosphate into a solution, mix it with phosphoric acid and adjust the pH value to 3-4, and perform a second evaporation crystallization on the obtained solution to obtain a concentrated slurry. Then, perform solid-liquid separation on the concentrated slurry to obtain lithium dihydrogen phosphate and secondary evaporation mother liquor. Return the secondary evaporation mother liquor as at least part of the lithium dihydrogen phosphate solution to step (3) for reuse.
2. The method according to claim 1, characterized in that, In the lithium-rich purification solution, the lithium ion content is 8-25 g / L.
3. The method according to claim 1 or 2, characterized in that, In step (1), the phosphate solution contains at least one of sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate. Preferably, in step (1), the concentration of phosphate in the phosphate solution is 180-250 g / L.
4. The method according to any one of claims 1-3, characterized in that, In step (1), the pH adjuster is an aqueous solution of sodium hydroxide and / or ammonia.
5. The method according to any one of claims 1-4, characterized in that, In step (1), the molar ratio of the amount of lithium-rich purification solution to the amount of phosphate solution is 1:(1.1-1.3), wherein the lithium-rich purification solution is calculated as lithium ions and the phosphate solution is calculated as phosphate ions.
6. The method according to any one of claims 1-5, characterized in that, In step (1), the conditions for the precipitation reaction include: a temperature of 70-95℃ and a time of 0.5-1.5h.
7. The method according to any one of claims 1-6, characterized in that, In step (2), the mass ratio of the lithium phosphate solid to water is 1:(2-3.5); Preferably, in step (2), the conditions for the acidolysis reaction include: a temperature of 20-80℃ and a time of 0.3-1h.
8. The method according to any one of claims 1-7, characterized in that, In step (3), the conditions for the first evaporation crystallization include: a temperature of 75-90°C and a vacuum degree of -0.09 to -0.06 MPa.
9. The method according to any one of claims 1-8, characterized in that, In step (4), the specific process of preparing the crude lithium dihydrogen phosphate into a solution includes mixing the crude lithium dihydrogen phosphate and water at 75-90°C.
10. The method according to any one of claims 1-9, characterized in that, In step (4), the conditions for the second evaporation crystallization include: a temperature of 75-90°C and a vacuum degree of -0.09 to -0.06 MPa.