Method for preparing battery-grade lithium phosphate from lithium carbonate mother liquor obtained after lithium extraction of salt lake brine

Abstract

The invention discloses a method for preparing battery-grade lithium phosphate from lithium carbonate mother liquor after lithium extraction from salt lake brine. The method comprises the following steps: providing lithium carbonate mother liquor after lithium extraction from salt lake brine; adjusting the pH value of the lithium carbonate mother liquor to 11-14, then adding sodium phosphate, and carrying out nucleation, aging and separation treatment to prepare crude lithium phosphate; and carrying out acid dissolution treatment on the crude lithium phosphate, then adjusting the pH value to 11-14, adding a dispersing agent, and then carrying out aging, filtering, sizing and washing and drying treatment to prepare the battery-grade lithium phosphate. According to the method, the lithium resource in the lithium carbonate mother liquor is separated and extracted by utilizing a coprecipitation method and is converted into the crude lithium phosphate, the crude lithium phosphate is purified to prepare the battery-grade lithium phosphate, meanwhile, the salt lake resource is comprehensively utilized by the method provided by the invention, and the resource utilization efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of comprehensive utilization of salt lake resources, and specifically relates to a method for preparing battery-grade lithium phosphate by utilizing lithium carbonate mother liquor obtained after lithium extraction from salt lake brine. Background Art

[0002] Lithium (Li) is the lightest metal element in nature. It is silvery white and has unique physical and chemical properties such as high specific heat, high electrical conductivity and strong chemical activity. It has a wide range of uses. At present, the application of metallic lithium and its compounds in traditional industrial fields such as glass ceramics, electrolytic aluminum, grease, air conditioning and refrigeration, organic synthesis, metallurgy, chemical industry, medicine and reagents continues to grow. Its application in aluminum-lithium alloys, lithium batteries and nuclear fusion and other energy, military industry, aerospace, nuclear industry and other fields has also expanded rapidly. Therefore, it is known as "industrial MSG" and is also regarded as an important strategic material by many countries. Because of its application in lithium batteries, it is known as "the energy metal that promotes the progress of the world". In nature, lithium resources are mainly found in solid ores and liquid brines. The important position of brine lithium resources in the development of lithium resources in the world has been established for nearly 30 years. It has attracted the attention of the lithium resource development industry in terms of application and extraction of lithium compounds. The trend of lithium salt production in the world is to extract lithium from salt lakes as the main method, supplemented by ore extraction. In my country, due to the advantages of large resources and low cost in lithium extraction from salt lake brine, and with the increasing depletion of solid lithium ore resources, salt lake brine has gradually become the main source of lithium resources. At present, the mainstream processes for lithium extraction from salt lakes with high magnesium-lithium ratio mainly include: salt field process, magnesium-lithium separation, impurity removal of lithium-containing solution, precipitation and conversion of lithium carbonate and other process steps. The precipitation conversion of lithium carbonate is to add sodium carbonate solution to lithium-rich solution to prepare lithium carbonate through precipitation reaction. The solution after solid-liquid separation is called lithium carbonate mother liquor. The lithium content in lithium carbonate mother liquor is still 1-2g / L, which is an important lithium resource.

[0003] With the rapid development of the new energy industry, the market demand for lithium iron phosphate, a positive electrode material for lithium batteries, is strong. Lithium phosphate contains two elements, phosphorus and lithium. Under a specific preparation process, it can reduce the manufacturing cost of lithium iron phosphate. Therefore, lithium phosphate, as an important raw material, will be widely used in the production process of lithium iron phosphate. The existing method of utilizing the mother liquor after lithium extraction from salt lake brine is complicated. It is necessary to first use hydrochloric acid to remove the carbonate ions, and then add alkali to adjust its pH, which consumes acid and alkali. The evaporation and concentration process of lithium has high energy consumption and high cost. Extracting lithium in the form of lithium phosphate has a mild reaction and simple equipment, which is suitable for large-scale and efficient utilization of lithium resources in lithium carbonate mother liquor. There are no reports on the preparation of battery-grade lithium phosphate using lithium carbonate mother liquor. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for preparing battery-grade lithium phosphate using lithium carbonate mother liquor obtained after lithium extraction from salt lake brine, so as to overcome the shortcomings of the prior art.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes: The embodiment of the present invention provides a method for preparing battery-grade lithium phosphate using lithium carbonate mother liquor obtained after lithium extraction from salt lake brine, which comprises: Provide lithium carbonate mother liquor after lithium extraction from salt lake brine; wherein Li + The concentration is 1~2g / L, CO 3 2- The concentration is 10~30g / L, OH - The concentration is 5~25g / L; The pH value of the lithium carbonate mother solution is adjusted to 11-14, and then sodium phosphate is added and nucleation, aging and separation are performed to obtain crude lithium phosphate; And, the crude lithium phosphate is subjected to acid dissolution treatment, and then the pH value is adjusted to 11-14 and a dispersant is added, and then the crude lithium phosphate is subjected to aging, filtering, pulp washing and drying treatment to obtain battery-grade lithium phosphate.

[0006] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses lithium carbonate mother liquor as raw material and adopts co-precipitation method to separate and extract lithium resources from lithium carbonate mother liquor. The present invention uses lithium carbonate mother liquor as raw material and adopts co-precipitation method to separate and extract lithium resources from lithium carbonate mother liquor. The lithium is first converted into crude lithium phosphate, and then acid dissolution and dispersant purification treatment are adopted to obtain battery-grade lithium phosphate products. (2) The method provided by the present invention enables the comprehensive utilization of salt lake resources and improves the efficiency of resource utilization. At the same time, the technology has the advantages of being green, efficient, energy-saving, requiring small investment, low energy consumption, and having little pollution. In addition, the process equipment is simple, the operation process is short, and it is easy to control, making it suitable for industrial promotion. DETAILED DESCRIPTION

[0007] In view of the defects of the prior art, the inventors of this case have proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution is mainly achieved by adjusting the pH value of the lithium carbonate mother liquor, adding phosphoric acid or sodium phosphate solution to the lithium carbonate mother liquor with adjusted pH value under certain temperature and rotation speed conditions to carry out co-precipitation reaction, and obtaining solid crude lithium phosphate through the steps of nucleation, aging, filtration, washing, drying and the like; acid-dissolving the crude lithium phosphate, adding alkaline solution under certain temperature conditions to adjust the pH so that the lithium phosphate is crystallized and precipitated again, filtering, washing and drying to obtain a battery-grade lithium phosphate product.

[0008] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0009] Specifically, as one aspect of the technical solution of the present invention, a method for preparing battery-grade lithium phosphate using lithium carbonate mother liquor after lithium extraction from salt lake brine comprises: Provide lithium carbonate mother liquor after lithium extraction from salt lake brine; wherein Li + The concentration of CO is 1~2g / L, 3 2- The concentration is 10~30g / L, OH - The concentration is 5~25g / L; The pH value of the lithium carbonate mother solution is adjusted to 11-14, and then sodium phosphate is added and nucleation, aging and separation are performed to obtain crude lithium phosphate; And, the crude lithium phosphate is subjected to acid dissolution treatment, and then the pH value is adjusted to 11-14 and a dispersant is added, and then the crude lithium phosphate is subjected to aging, filtering, pulp washing and drying treatment to obtain battery-grade lithium phosphate.

[0010] In some preferred embodiments, the lithium carbonate mother liquor is the mother liquor obtained by preparing lithium carbonate using salt lake brine, wherein Li + The concentration of CO is 1.3~1.7g / L, 3 2- The concentration is 15~25g / L, OH - The concentration is 10~20g / L.

[0011] In some preferred embodiments, the method specifically includes: adjusting the pH value of the lithium carbonate mother liquor to 11-14 with an alkaline solution, then adding a sodium phosphate solution at 80-110° C. and performing a nucleation reaction for 40-90 minutes at a stirring rate of 50-200 rpm, and then performing aging, solid-liquid separation, secondary slurry washing, and drying to obtain crude lithium phosphate.

[0012] Furthermore, the molar number of sodium phosphate and lithium after reaction is 10%-30% excess, preferably 15-25%.

[0013] Further, the alkaline solution includes sodium hydroxide solution and / or potassium hydroxide solution, but is not limited thereto.

[0014] Furthermore, the concentration of the alkaline solution is 20-30wt%.

[0015] Furthermore, the concentration of the sodium phosphate solution is 5-15wt%.

[0016] Furthermore, the main content of lithium phosphate in the crude lithium phosphate is ≥90.0wt%.

[0017] Furthermore, the method specifically includes: adding sodium phosphate solution at 90-100° C. and performing a nucleation reaction at a stirring rate of 100-150 rpm.

[0018] Furthermore, the addition time of the sodium phosphate solution is 20 to 50 minutes.

[0019] Furthermore, the aging temperature is 80-110°C.

[0020] Furthermore, the aging time is 20 to 90 minutes.

[0021] In some preferred embodiments, the method specifically comprises: Dissolving the crude lithium phosphate with an inorganic acid to form a crude lithium phosphate solution; Also, the crude lithium phosphate solution is heated to 80-110° C. and the pH value is adjusted to 11-14 with an alkaline solution, and then a dispersant is added and reacted at 80-110° C. for 40-90 minutes, and then aged, filtered, three-time pulp washing, and dried to obtain battery-grade lithium phosphate.

[0022] Furthermore, the inorganic acid includes any one or more combinations of hydrochloric acid, sulfuric acid, and phosphoric acid, but is not limited thereto.

[0023] Furthermore, the concentration of the inorganic acid is 2-6 mol / L.

[0024] Furthermore, the dispersant includes any one or more combinations of PEG-200, polyethylene glycol 9000, and hydroxyethyl cellulose, but is not limited thereto.

[0025] Furthermore, the method specifically comprises: heating the crude lithium phosphate solution to 90-100° C. and adjusting the pH value with an alkaline solution, and then adding a dispersant and reacting at 90-100° C.

[0026] Furthermore, the aging temperature is 80-110°C.

[0027] Furthermore, the aging time is 20 to 90 minutes.

[0028] Furthermore, the liquid-to-solid ratio (mass ratio) of the three pulp washings is 2:1~5:1.

[0029] Furthermore, the drying temperature is 80-120°C.

[0030] In some preferred embodiments, the main content of lithium phosphate in the battery-grade lithium phosphate is ≥99.5wt%, the total content of Na and K is ≤500ppm, the total content of Ca and Mg is ≤200ppm, B is ≤200ppm, and the lithium yield is >80%.

[0031] In some more specific embodiments, the method for preparing battery-grade lithium phosphate using lithium carbonate mother liquor after lithium extraction from salt lake brine comprises: (1) adding a sodium hydroxide solution of a certain concentration to the lithium carbonate mother liquor to adjust the pH value of the lithium carbonate mother liquor; (2) Adding sodium phosphate solution dropwise to the lithium carbonate mother liquor with adjusted pH value, carrying out nucleation reaction under stirring at a certain temperature, and then aging after the nucleation reaction.

[0032] (3) After aging, solid-liquid separation is performed, and the solid phase is subjected to secondary pulp washing, and after washing, it is dried to obtain a crude lithium phosphate product (4) Adding acid to dissolve the crude lithium phosphate, adding sodium hydroxide solution to the solution, adjusting the pH value, and adding a dispersant until all the lithium phosphate is precipitated, aging, filtering, slurry washing three times, and drying to obtain a battery-grade lithium phosphate product.

[0033] In some more specific embodiments, the method for preparing battery-grade lithium phosphate using lithium carbonate mother liquor after lithium extraction from salt lake brine comprises: (1) Add a sodium hydroxide solution of a certain concentration to the lithium carbonate mother liquor to adjust the pH value of the lithium carbonate mother liquor. The lithium carbonate mother liquor is the mother liquor obtained by preparing lithium carbonate using salt lake brine, wherein Li + The concentration is 1-2 g / L, preferably 1.3-1.7 g / L, CO 3 2- The concentration is 10-30 g / L, preferably 15-25 g / L, OH - The concentration is 5-25 g / L, preferably 10-20 g / L; the pH value of the lithium carbonate mother liquor is adjusted to 11-14 using a sodium hydroxide solution with a mass fraction of 30%.

[0034] (2) Sodium phosphate solution is added dropwise to the lithium carbonate mother liquor with adjusted pH value, and a nucleation reaction is carried out under stirring at a certain temperature, and then aging is carried out. The mass concentration of sodium phosphate is 5-15%; the amount of sodium phosphate is 10-30% excess, preferably 15-25%; the stirring rate is 50-200rpm, preferably 100-150rpm; the reaction temperature is 80-110℃, preferably 90-100℃; the reaction time is 40-90min, wherein the feeding time is 20-50min, and the aging time is 20-90min. After aging, solid-liquid separation is carried out, and the solid phase is subjected to secondary slurry washing, and then dried after washing to obtain a crude lithium phosphate product, wherein the main content of the prepared crude lithium phosphate is ≥90.0%.

[0035] (3) Add acid to dissolve the crude lithium phosphate, add sodium hydroxide solution to the solution at a certain temperature and stirring speed to adjust the pH value, and add a dispersant until all the lithium phosphate is precipitated, then age, filter, wash three times, and dry to obtain a battery-grade lithium phosphate product. The acid dissolution is hydrochloric acid, sulfuric acid or phosphoric acid, with a concentration of 2~6 mol / L; the reaction temperature is 80~110℃, preferably 90~100℃; the reaction time is 40~90min, wherein the aging time is 20~90min, the dispersant is PEG-200, polyethylene glycol 9000 and hydroxyethyl cellulose; the pH value is 11~14. The liquid-to-solid ratio of the three washings is 2:1~5:1; the temperature after drying is 80~120℃, and the main content of the obtained battery-grade lithium phosphate is ≥99.5%, Na+K≤500ppm, Ca+Mg≤200ppm, and B≤200ppm.

[0036] The present invention utilizes a co-precipitation method to separate and extract lithium resources from lithium carbonate mother liquor, and converts the lithium resources into crude lithium phosphate, and purifies the crude lithium phosphate to prepare battery-grade lithium phosphate. The method provided by the present invention enables comprehensive utilization of salt lake resources and improves resource utilization efficiency. At the same time, there are no reports on converting lithium resources in lithium carbonate mother liquor into crude lithium phosphate and then purifying it.

[0037] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments. This embodiment is implemented on the premise of the technical solution of the invention, and provides a detailed implementation method and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0038] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0039] Example 1 The lithium carbonate mother liquor used in this embodiment comes from the mother liquor after lithium extraction from a salt lake in Qinghai. + The concentration is 1.3 g / L, CO 3 2- Concentration 15g / L, OH - The concentration is 5g / L; Weigh 2000g of the mother liquor, adjust the pH of the lithium precipitation mother liquor to 11 with a 30% sodium hydroxide solution, heat the solution to 80°C, add an excess of 10% of a 5% sodium phosphate solution by mass, control the stirring speed to 50rpm, and the reaction time to 40min. After the reaction, age at 80°C for 20min, and obtain a crude lithium phosphate product by filtering, washing, and drying; The crude lithium phosphate product was completely dissolved with 2 mol / L hydrochloric acid, and the dissolved solution was heated to 80°C. A 30% mass fraction sodium hydroxide solution was added thereto to adjust the pH to 14, and PEG-200 was added. The reaction time was 40 min. After the reaction, it was aged at 110°C for 90 min and filtered. After filtration, the filter cake was washed three times with a liquid-to-solid ratio controlled at 2:1. The filter cake was separated and dried at a drying temperature of 80°C. The main content of the obtained battery-grade lithium phosphate was 99.6%, Na+K was 500 ppm, Ca+Mg was 100 ppm, B was 200 ppm, and the lithium yield was 85%.

[0040] Example 2 The lithium carbonate mother liquor used in this embodiment comes from the mother liquor after lithium extraction from a salt lake in Qinghai. + The concentration is 1g / L, CO 3 2- Concentration 10g / L, OH - The concentration is 20g / L; Weigh 2000g of the mother liquor, adjust the pH of the lithium precipitation mother liquor to 14 with a 30% potassium hydroxide solution, heat the solution to 110°C, add an excess of 30% sodium phosphate solution with a mass fraction of 15% thereto, control the stirring speed to 200rpm, and the reaction time to 140min. After the reaction, age at 110°C for 90min, filter, wash, and dry to obtain a crude lithium phosphate product; The crude lithium phosphate product was completely dissolved with 6 mol / L phosphoric acid, and the dissolved solution was heated to 110°C. A 30% mass fraction sodium hydroxide solution was added thereto to adjust the pH to 11, and polyethylene glycol 9000 was added. The reaction time was 40 minutes. After the reaction, it was aged at 80°C for 20 minutes and filtered. After filtration, the filter cake was washed three times with a liquid-to-solid ratio controlled at 5:1. The filter cake was separated and dried at a drying temperature of 120°C. The main content of the obtained battery-grade lithium phosphate was 99.5%, Na+K was 400ppm, Ca+Mg was 200ppm, B was 100ppm, and the lithium yield was 82%.

[0041] Example 3 The lithium carbonate mother liquor used in this embodiment comes from the mother liquor after lithium extraction from a salt lake in Qinghai. + The concentration is 2g / L, CO 3 2- Concentration 30g / L, OH - The concentration is 25g / L; Weigh 2000g of the mother liquor, adjust the pH of the lithium precipitation mother liquor to 12 with a 30% sodium hydroxide solution, heat the solution to 100°C, add an excess of 15% sodium phosphate solution with a mass fraction of 10%, control the stirring speed to 100rpm, and the reaction time to 90min. After the reaction, age at 100°C for 50min, filter, wash, and dry to obtain a crude lithium phosphate product; The crude lithium phosphate product was completely dissolved with 3 mol / L phosphoric acid, and the dissolved solution was heated to 100°C. A 30% mass fraction sodium hydroxide solution was added thereto to adjust the pH to 13, and hydroxyethyl cellulose was added. The reaction time was 90 minutes. After the reaction, the mixture was aged at 90°C for 60 minutes and filtered. After filtration, the filter cake was washed three times with a liquid-to-solid ratio of 4:1, separated and dried at a drying temperature of 100°C. The main content of the obtained battery-grade lithium phosphate was 99.8%, Na+K was 350ppm, Ca+Mg was 180ppm, B was 160ppm, and the lithium yield was 86%.

[0042] Example 4 The lithium carbonate mother liquor used in this embodiment comes from the mother liquor after lithium extraction from a salt lake in Qinghai. + The concentration is 1.7 g / L, CO 3 2- Concentration 25g / L, OH - The concentration is 10g / L; Weigh 2000g of the mother liquor, adjust the pH of the lithium precipitation mother liquor to 13 with a 30% potassium hydroxide solution, heat the solution to 90°C, add an excess of 25% of a 10% sodium phosphate solution by mass, control the stirring speed to 150rpm, and react for 80min. After the reaction, age at 100°C for 50min, filter, wash, and dry to obtain a crude lithium phosphate product; The crude lithium phosphate product was completely dissolved with 4 mol / L phosphoric acid, and the dissolved solution was heated to 90°C. A 30% mass fraction sodium hydroxide solution was added thereto to adjust the pH to 12, and hydroxyethyl cellulose was added. The reaction time was 80 minutes. After the reaction, the mixture was aged at 90°C for 60 minutes and filtered. After filtration, the filter cake was washed three times with a liquid-to-solid ratio of 3:1, separated and dried at a drying temperature of 90°C. The main content of the obtained battery-grade lithium phosphate was 99.7%, Na+K was 250ppm, Ca+Mg was 140ppm, B was 180ppm, and the lithium yield was 84%.

[0043] Comparative Example 1 The method is the same as in Example 1, except that the pH value of the mother solution is adjusted to 9; The lithium carbonate mother liquor used in this embodiment comes from the mother liquor after lithium extraction from a salt lake in Qinghai. +The concentration is 1.3 g / L, CO 3 2- Concentration 15g / L, OH - The concentration is 5g / L; Weigh 2000g of the mother liquor, adjust the pH of the lithium precipitation mother liquor to 9 with a 30% sodium hydroxide solution, heat the solution to 80°C, add an excess of 10% of a 5% sodium phosphate solution by mass, control the stirring speed to 50rpm, and the reaction time to 40min. After the reaction, age at 80°C for 20min, and obtain a crude lithium phosphate product by filtering, washing, and drying; The crude lithium phosphate product was completely dissolved in 2 mol / L hydrochloric acid, and the dissolved solution was heated to 80°C. A 30% mass fraction sodium hydroxide solution was added thereto to adjust the pH to 9, and PEG-200 was added. The reaction time was 40 min. After the reaction, it was aged at 1100°C for 90 min and filtered. After filtration, the filter cake was washed three times with a liquid-to-solid ratio controlled at 2:1. The filter cake was separated and dried at a drying temperature of 80°C. The main content of the obtained battery-grade lithium phosphate was 99.6%, Na+K was 500 ppm, Ca+Mg was 100 ppm, B was 200 ppm, and the lithium yield was 65%.

[0044] Comparative Example 2 The method is the same as in Example 1, except that the temperature of the nucleation reaction is 50°C; The lithium carbonate mother liquor used in this embodiment comes from the mother liquor after lithium extraction from a salt lake in Qinghai. + The concentration is 1.3 g / L, CO 3 2- Concentration 15g / L, OH - The concentration is 5g / L; Weigh 2000g of the mother liquor, adjust the pH of the lithium precipitation mother liquor to 11 with a 30% sodium hydroxide solution, heat the solution to 50°C, add an excess of 10% of a 5% sodium phosphate solution by mass, control the stirring speed to 50rpm, and the reaction time to 40min. After the reaction, age at 50°C for 20min, and obtain a crude lithium phosphate product by filtering, washing, and drying; The crude lithium phosphate product was completely dissolved with 2 mol / L hydrochloric acid, and the dissolved solution was heated to 50°C. A 30% mass fraction sodium hydroxide solution was added thereto to adjust the pH to 14, and PEG-200 was added. The reaction time was 40 min. After the reaction, it was aged at 50°C for 90 min and filtered. After filtration, the filter cake was washed three times with a liquid-to-solid ratio controlled at 2:1. The filter cake was separated and dried at a drying temperature of 80°C. The main content of the obtained battery-grade lithium phosphate was 99.6%, Na+K was 500 ppm, Ca+Mg was 100 ppm, B was 200 ppm, and the lithium yield was 50%.

[0045] Comparative Example 3 The method is the same as in Example 1, except that the temperature of the nucleation reaction is 130°C; this only differs in energy consumption. Modified to: The method is the same as Example 1, except that the pulping is not performed. The lithium carbonate mother liquor used in this embodiment comes from the mother liquor after lithium extraction from a salt lake in Qinghai. + The concentration is 1.3 g / L, CO 3 2- Concentration 15g / L, OH - The concentration is 5g / L; Weigh 2000g of the mother liquor, adjust the pH of the lithium precipitation mother liquor to 9 with a 30% sodium hydroxide solution, heat the solution to 80°C, add an excess of 10% of a 5% sodium phosphate solution by mass, control the stirring speed to 50rpm, and the reaction time to 40min. After the reaction, age at 80°C for 20min, and obtain a crude lithium phosphate product by filtering, washing, and drying; The crude lithium phosphate product was completely dissolved with 2 mol / L hydrochloric acid, and the dissolved solution was heated to 80°C. A 30% mass fraction sodium hydroxide solution was added thereto to adjust the pH to 9, and PEG-200 was added. The reaction time was 40 min. After the reaction, it was aged at 1100°C for 90 min and filtered. After filtration, the filter cake was dried at 80°C. The main content of the obtained battery-grade lithium phosphate was 95.6%, Na+K was 2000ppm, Ca+Mg was 1000ppm, B was 1000ppm, and the lithium yield was 85%.

[0046] Comparative Example 4 The method is the same as in Example 1, except that the dispersant is absent; The lithium carbonate mother liquor used in this embodiment comes from the mother liquor after lithium extraction from a salt lake in Qinghai. + The concentration is 1.3 g / L, CO 3 2- Concentration 15g / L, OH - The concentration is 5g / L; Weigh 2000g of the mother liquor, adjust the pH of the lithium precipitation mother liquor to 11 with a 30% sodium hydroxide solution, heat the solution to 80°C, add an excess of 10% of a 5% sodium phosphate solution by mass, control the stirring speed to 50rpm, and the reaction time to 40min. After the reaction, age at 80°C for 20min, and obtain a crude lithium phosphate product by filtering, washing, and drying; The crude lithium phosphate product was completely dissolved with 2 mol / L hydrochloric acid, and the dissolved solution was heated to 80°C. A 30% by mass sodium hydroxide solution was added thereto to adjust the pH to 14. The reaction time was 40 min. After the reaction, it was aged at 1100°C for 90 min and filtered. After filtration, the filter cake was washed three times with a liquid-to-solid ratio controlled at 2:1. The filter cake was separated and dried at a drying temperature of 80°C. The main content of the obtained battery-grade lithium phosphate was 97.5%, Na+K was 2000ppm, Ca+Mg was 500ppm, B was 500ppm, and the lithium yield was 85%.

[0047] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments with other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0048] It should be understood that the technical solution of the present invention is not limited to the above-mentioned specific implementation cases. Any technical deformation made according to the technical solution of the present invention without departing from the scope of protection of the purpose of the present invention and the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing battery-grade lithium phosphate using lithium carbonate mother liquor obtained after lithium extraction from salt lake brine, characterized in that: include: Provide lithium carbonate mother liquor after lithium extraction from salt lake brine; wherein Li + The concentration is 1~2g / L, CO3 2- The concentration is 10~30g / L, OH - The concentration is 5~25g / L; The pH value of the lithium carbonate mother solution is adjusted to 11-14, and then sodium phosphate is added and subjected to nucleation, aging and separation treatment to obtain crude lithium phosphate; And, the crude lithium phosphate is subjected to acid dissolution treatment, and then the pH value is adjusted to 11-14 and a dispersant is added, and then the crude lithium phosphate is subjected to aging, filtering, pulp washing and drying treatment to obtain battery-grade lithium phosphate.

2. The method according to claim 1, characterized in that: The lithium carbonate mother liquor is the mother liquor obtained by preparing lithium carbonate using salt lake brine. + The concentration is 1.3~1.7g / L, CO3 2- The concentration is 15~25g / L, OH - The concentration is 10~20g / L.

3. The method according to claim 1, characterized in that Specifically include: The pH value of the lithium carbonate mother liquor is adjusted to 11-14 by using an alkaline solution, and then a sodium phosphate solution is added at 80-110° C. and a nucleation reaction is carried out for 40-90 minutes at a stirring rate of 50-200 rpm, followed by aging, solid-liquid separation, secondary slurry washing, and drying to obtain crude lithium phosphate.

4. The method according to claim 3, characterized in that: The alkaline solution includes sodium hydroxide solution and / or potassium hydroxide solution; and / or, the concentration of the alkaline solution is 20-30wt%; And / or, the concentration of the sodium phosphate solution is 5-15wt%; And / or, the main content of lithium phosphate in the crude lithium phosphate is ≥90.0wt%.

5. The method according to claim 3, characterized in that: Specifically, the method comprises: adding a sodium phosphate solution at 90-100° C. and performing a nucleation reaction at a stirring rate of 100-150 rpm; And / or, the addition time of the sodium phosphate solution is 20 to 50 minutes; And / or, the aging temperature is 80-110°C; And / or, the aging time is 20 to 90 minutes.

6. The method according to claim 1, characterized in that Specifically include: Dissolving the crude lithium phosphate with an inorganic acid to form a crude lithium phosphate solution; Also, the crude lithium phosphate solution is heated to 80-110° C. and the pH value is adjusted to 11-14 with an alkaline solution, and then a dispersant is added and reacted at 80-110° C. for 40-90 minutes, and then aged, filtered, three-time pulp washing, and dried to obtain battery-grade lithium phosphate.

7. The method according to claim 6, characterized in that: The inorganic acid includes any one or more combinations of hydrochloric acid, sulfuric acid, and phosphoric acid; And / or, the concentration of the inorganic acid is 2-6 mol / L; And / or, the dispersant includes any one or more combinations of PEG-200, polyethylene glycol 9000, and hydroxyethyl cellulose.

8. The method according to claim 6, characterized in that Specifically include: The crude lithium phosphate solution is heated to 90-100°C and the pH value is adjusted with an alkaline solution, and then a dispersant is added and reacted at 90-100°C.

9. The method according to claim 6, characterized in that: The aging temperature is 80-110°C; And / or, the aging time is 20 to 90 minutes; And / or, the liquid-to-solid ratio of the three washings is 2:1 to 5:1; And / or, the drying temperature is 80-120°C.

10. The method according to claim 1, characterized in that: The main content of lithium phosphate in the battery-grade lithium phosphate is ≥99.5wt%, the total content of Na and K is ≤500ppm, the total content of Ca and Mg is ≤200ppm, B is ≤200ppm, and the lithium yield is >80%.