A method for preparing high-purity lithium phosphate using lithium precipitation mother liquor from salt lake brine

Abstract

This invention discloses a method for preparing high-purity lithium phosphate using lithium precipitation mother liquor from salt lake brine. The method includes: placing the lithium precipitation mother liquor from salt lake brine and a dispersant in a closed reaction apparatus and heating to 70℃-95℃; then introducing a phosphoric acid solution and performing a crystallization lithium precipitation reaction followed by aging to obtain crude lithium phosphate; wherein the dispersant includes an ethylene glycol polymer; purifying and drying the crude lithium phosphate to obtain high-purity lithium phosphate. The method provided by this invention features simple process, high lithium yield, controllable crystallization process, high product purity, single raw material usage, economic rationality, and environmental friendliness, which is beneficial for the high-value, efficient, and sustainable development and utilization of salt lake resources.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology, specifically relating to a method for preparing high-purity lithium phosphate using lithium precipitation mother liquor from salt lake brine. Background Technology

[0002] Lithium, as the lightest and least dense metal, possesses unique physical and chemical properties, earning it the nickname "industrial MSG." It has long been widely used in glass, ceramics, optoelectronics, metallurgy, catalysis, lubrication, and pharmaceuticals. Since the advent of the industrial age, the large-scale use of fossil fuels has led to global environmental pollution and an energy crisis. To address this issue, the new energy industry has developed rapidly in recent years, with lithium finding further applications, particularly as a fundamental raw material for lithium-ion batteries. Global demand for lithium is enormous, leading it to be hailed as a "new energy darling of the 21st century."

[0003] Globally, lithium exists primarily in three forms: brine deposits, pegmatite deposits, and sedimentary deposits. Lithium-bearing brine deposits account for approximately 60% of global lithium resources, pegmatite deposits for about 30%, and sedimentary deposits for about 10%. The lithium precipitation mother liquor produced during lithium extraction is a complex brine mixture system, in which Li... + The concentration is approximately 1-2 g / L, and it contains a large amount of Cl. - CO3 2- SO4 2- Al 3+ Ca 2+ Na + K + Mn 2+ Mg 2+ Fe 3+ If the lithium precipitation mother liquor is directly discharged into the environment, it will cause a large loss of lithium resources. If it is discharged into the lithium precipitation recycling system, it will lead to an increase in Cl in the system. - CO3 2- SO4 2- Na + Enrichment of lithium in lithium salt products can lead to excessive levels of impurities, affecting product quality. Therefore, finding an economical, green, and efficient way to recover lithium from lithium precipitation mother liquor is a solution to the current global lithium resource supply and demand imbalance.

[0004] With the rapid development of the new energy industry, the market demand for lithium iron phosphate (LFP), a cathode material for lithium batteries, is booming. Lithium phosphate contains both phosphorus and lithium, and under specific preparation processes, the manufacturing cost of LFP can be reduced. Therefore, lithium phosphate, as an important raw material, is widely used in the production of LFP. In recent years, some companies and research institutions have been working on recovering lithium from lithium precipitation mother liquor using phosphates, ultimately obtaining products such as lithium phosphate and lithium dihydrogen phosphate.

[0005] For example, patents CN201610295111.9 and CN201510374978.9 describe methods for preparing lithium salts using lithium precipitation mother liquor. These methods involve multiple pH adjustments to the reaction system, consuming large amounts of acid and alkali, and using various chemical reagents. This not only increases production costs and the difficulty of on-site management but also introduces other impurity ions into the reaction system, affecting the quality of the lithium salt product. Patent CN202010208353.6 describes a five-step process for preparing battery-grade lithium phosphate, including phosphate decarbonization, EDTA complexation precipitation, pH adjustment with alkaline solution, purification with lithium hydroxide solution, and pressure washing under an inert gas atmosphere. This method uses more than four chemical reagents and requires pressure washing under an inert gas atmosphere, resulting in an overly lengthy process, low lithium recovery rate, and significantly increased production costs due to the complex raw material system and pressure equipment. Patent CN201110190405.2 describes a six-step process for preparing high-purity lithium dihydrogen phosphate, including preliminary lithium precipitation, deep lithium precipitation, separation and washing, acid dissolution, concentration and recrystallization, and dehydration rinsing. The process is complex. The alkaline lithium precipitation mother liquor is acidified to lower the pH from 12-14 to around 5-7. After lithium precipitation, alkali is added to adjust the pH to around 10.0. During the dissolution process, phosphoric acid is added to lower the pH to between 1.5 and 2.0, consuming large amounts of phosphoric acid and sodium hydroxide. Furthermore, the dissolution and recrystallization process not only consumes large amounts of pure water but also requires heating to 130℃. Most lithium extraction enterprises in my country's salt lakes are located in high-altitude regions such as Qinghai and Tibet. Heating the aqueous solution to this temperature is extremely energy-intensive, and freshwater resources are extremely scarce in these areas. Therefore, this method is too costly and has limited economic benefits.

[0006] Furthermore, due to limitations in ore mining and lithium separation and extraction technologies, the early exploitation and utilization of lithium resources primarily relied on solid lithium ore. Brine lithium extraction technology has only gradually matured in the last five years, and is currently being industrialized on a large scale in regions such as Qinghai and Tibet in China. Early technologies for recovering lithium precipitation mother liquor mostly focused on the mother liquor produced by ore-based lithium extraction processes. The phase composition, impurity ion types, and salt concentrations of the mother liquor produced by ore-based and brine-based lithium extraction processes differ significantly. In addition to 1-2 g / L of lithium, the mother liquor from ore-based lithium extraction also contains a large amount of CO3. 2- SO4 2- Na +Al 3+ Mn 2+ Fe 3+ Elements such as Al. A common method for treating the mother liquor from lithium extraction from ore involves freezing to precipitate sodium, separating Na₂SO₄·10H₂O, then concentrating the mother liquor to precipitate Li₂CO₃. The solution after solid-liquid separation is returned to the initial mother liquor, which is then frozen again to precipitate sodium, achieving a self-circulating process. This method reduces the lithium recycling process, but the lithium yield is low, the freezing and concentration processes are energy-intensive, and because Al... 3+ Mn 2+ Fe 3+ Elements constantly circulate within the reaction system, ultimately leading to high or even excessive levels of impurities in lithium products. Furthermore, the main components of the mother liquor in the brine lithium extraction method are Li₂CO₃ and NaCl. The solubility of NaCl does not change significantly with temperature, making the freezing and sodium precipitation process ineffective in removing Na₂CO₃. + When phosphate salts are reacted directly with lithium precipitation mother liquor, severe agglomeration and peritectic phenomena occur, resulting in a large amount of Na. + The brine is entrained in agglomerates that cannot be removed by subsequent washing. In addition, the resulting product has a wide particle size distribution, which cannot meet the needs of downstream enterprises.

[0007] In recent years, methods developed for lithium recovery from lithium precipitation mother liquor produced by lithium extraction from salt lake brine have included methods such as the use of hydrogen fluoride to prepare lithium fluoride, which produces tail liquid containing large amounts of fluoride ions, causing significant environmental pollution and failing to meet current environmental protection requirements. The phosphate precipitation-lithium hydroxide purification-pressurized washing technology has an overly lengthy process flow, low lithium recovery rate, and requires a variety of acids and alkalis, resulting in high consumption and excessive production costs. Furthermore, the pressurized equipment is not conducive to enterprise production safety management or industrial scale-up. Multi-stage lithium precipitation-concentration recrystallization technology has a complex process flow, large acid and alkali consumption, long production cycle, high energy consumption, and high freshwater consumption, resulting in limited economic benefits and low enterprise enthusiasm for recovery. Therefore, considering production costs, economic benefits, technological scale-up feasibility, and environmental protection, the above technologies cannot yet achieve economical, green, and efficient recovery of lithium resources from lithium precipitation mother liquor. Summary of the Invention

[0008] The main objective of this invention is to provide a method for preparing high-purity lithium phosphate using lithium precipitation mother liquor from salt lake brine, thereby overcoming the shortcomings of existing technologies.

[0009] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0010] This invention provides a method for preparing high-purity lithium phosphate using lithium precipitation mother liquor from salt lake brine, comprising:

[0011] Lithium precipitation mother liquor from salt lake brine and a dispersant are placed in a closed reaction device and heated to 70℃-95℃. Then, a phosphoric acid solution is introduced and a crystallization lithium precipitation reaction and aging treatment are carried out to obtain crude lithium phosphate. The dispersant includes ethylene glycol polymer.

[0012] Furthermore, the crude lithium phosphate is purified and dried to obtain high-purity lithium phosphate.

[0013] In some more specific implementations, the high-purity lithium phosphate contains more than 97 wt% lithium phosphate.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] (1) The crystallization process in this invention is controllable, the product has high purity, and the prepared lithium phosphate has good dispersibility, concentrated particle size distribution, and low impurity content.

[0016] (2) The method provided by the present invention is a green and energy-saving low-temperature crystal structure control technology. By adding PEG, lithium phosphate crystals are oriented to grow along the (120) crystal plane, thereby achieving precise control of crystal form and morphology.

[0017] (3) The method provided by this invention has an advanced synthesis concept and is green and environmentally friendly. By adopting the environmental protection concept of designing without using harmful substances and manufacturing without introducing harmful substances, the synthesis process uses only one raw material, which greatly reduces the consumption of acid and alkali. The preparation process achieves zero emission of toxic and harmful substances, and eliminates the risk of secondary pollution to the salt lake environment during the recycling process.

[0018] (4) The reaction equipment used in this invention has a high degree of automation, precise control of reaction conditions, and high recovery efficiency. The fully automatic antisolvent crystallization screening instrument used in this invention has a high degree of automation and can monitor the reaction process and display the reaction trend in real time through pre-programming. The high-sensitivity detector can precisely control the reaction conditions, making the recovery process more refined. The multi-channel reactor supports multiple sets of experiments to be carried out simultaneously, which greatly improves the synthesis efficiency.

[0019] (5) The reaction conditions of this invention are mild, the process is simple and the production cost is low, which is conducive to the economical, green and efficient recovery of lithium from lithium precipitation mother liquor;

[0020] (6) The lithium phosphate product prepared by this invention has high purity and high lithium recovery rate. It achieves efficient lithium precipitation in one step in lithium precipitation mother liquor with high salt concentration and low lithium concentration. The lithium recovery rate is greater than 82%, and the lithium phosphate purity is as high as 97% or more. The obtained product can be directly used for the synthesis of lithium iron phosphate. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a process flow diagram of preparing high-purity lithium phosphate using lithium precipitation mother liquor from salt lake brine in a typical embodiment of the present invention;

[0023] Figure 2 This is a SEM image of lithium phosphate prepared without PEG in Example 2 of the present invention;

[0024] Figure 3 This is a SEM image of lithium phosphate prepared using PEG in Example 2 of this invention;

[0025] Figure 4 These are XRD comparison images of lithium phosphate prepared without PEG and prepared with PEG in Example 2 of this invention;

[0026] Figure 5 This is a comparison chart of laser particle size analysis of lithium phosphate prepared with and without PEG in Comparative Example 1 of this invention. Detailed Implementation

[0027] In view of the deficiencies of existing technologies, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. It mainly uses lithium precipitation mother liquor from salt lake brine as raw material, polyethylene glycol (PEG) as a polymeric dispersant, and a fully automated antisolvent crystallization screening instrument to synthesize high-purity lithium phosphate in one step. This method includes three main steps: lithium crystallization precipitation, washing and purification, and separation and drying. The lithium crystallization precipitation process utilizes the programming function of the fully automated antisolvent crystallization screening instrument to automatically and precisely control the reaction conditions and monitor the reaction trend and progress in real time. This method uses phosphoric acid as the phosphorus source, simultaneously achieving the effects of lithium crystallization precipitation and carbon removal purification. Furthermore, a trace amount of dispersant is added during the crystallization process to inhibit product agglomeration and peritectic phenomena, achieving crystal morphology and crystal form control. This one-step synthesis of high-purity lithium phosphate greatly simplifies the process flow and overcomes the disadvantages of traditional processes, such as lengthy processes, large amounts of acid and alkali used, and harsh reaction conditions. This method features simple process, high lithium yield, high product purity, single raw material usage, economic rationality, and environmental friendliness, which is conducive to the high-value, efficient, and sustainable development and utilization of salt lake resources.

[0028] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Specifically, as one aspect of the technical solution of this invention, a method for preparing high-purity lithium phosphate using lithium precipitation mother liquor from salt lake brine includes:

[0030] Lithium precipitation mother liquor from salt lake brine and a dispersant are placed in a closed reaction device and heated to 70℃-95℃. Then, a phosphoric acid solution is introduced and a crystallization lithium precipitation reaction and aging treatment are carried out to obtain crude lithium phosphate. The dispersant includes ethylene glycol polymer.

[0031] Furthermore, the crude lithium phosphate is purified and dried to obtain high-purity lithium phosphate.

[0032] This invention utilizes low-lithium-concentration brine from salt lakes as raw material to synthesize high-purity lithium phosphate in a single step. This significantly shortens the lengthy process of traditional methods, which involve repeated pH adjustments, recrystallization, and acidification. This greatly improves production efficiency and provides a feasible solution for the economical and rational treatment of lithium phosphate mother liquor. Traditional lithium phosphate crystallization processes often result in peritectic formation and agglomeration due to the rapid crystallization reaction between phosphate and lithium ions, leading to high impurity content in the product, which is difficult to remove through subsequent washing processes. This invention addresses this by adding a trace amount of dispersant, allowing the high-molecular-weight PEG to fully adsorb onto the surface of lithium phosphate crystals. Utilizing its steric hindrance effect, it effectively inhibits crystal agglomeration, resulting in high-purity lithium phosphate with good dispersibility, concentrated particle size distribution, and low impurity content. Meanwhile, the presence of polymeric dispersants increases the viscosity of the reaction system solution, inhibits the violent reaction between phosphate and lithium, prolongs the sedimentation time, reduces peritectic phenomena during crystallization, and further reduces the impurity content in the product; in addition, lithium phosphate synthesized by traditional methods is β-Li3PO4, which is more prone to peritectic phenomena during the growth process and needs to be transformed into γ-Li3PO4 by dissolution and recrystallization or high-temperature calcination above 450℃. This invention adds PEG to make lithium phosphate crystals grow along the (120) crystal plane at a relatively low temperature of 70-95℃, thereby achieving precise control of its crystal form and morphology, thus obtaining γ-Li3PO4. This method has low energy consumption, short process, and is more energy-efficient and environmentally friendly; this invention is designed With its advanced concept and environmentally friendly synthesis process, this invention addresses the previous technical solutions for synthesizing lithium phosphate from lithium precipitation mother liquor. These solutions relied heavily on acids, alkalis, and complexing agents to improve lithium yield and product purity. The invention adopts an environmentally friendly approach that avoids the use and introduction of harmful substances during design and manufacturing. The synthesis process uses only one raw material, significantly reducing acid and alkali consumption. The preparation process achieves zero emissions of toxic and harmful substances, eliminating the risk of secondary pollution to the salt lake environment during recycling. Existing methods for treating lithium precipitation mother liquor ignore the realities faced by most lithium extraction enterprises in high-altitude, remote areas with inconvenient transportation, scarce freshwater resources, and limited energy infrastructure. These methods involve the use of numerous raw materials, high consumption, high energy consumption, and high freshwater consumption, resulting in high overall recycling costs. This invention utilizes a single raw material, mild reaction conditions, a simple process, and low production costs, which is beneficial for the economical, green, and efficient recovery of lithium from lithium precipitation mother liquor. The lithium recovery rate of this invention is as high as 82% or more, and the prepared lithium phosphate product has a main content of >97%, sodium content <0.5%, magnesium content <0.005%, calcium content <0.003%, and potassium content <0.003%. This invention uses a fully automated anti-solvent crystallization screening instrument for lithium recovery from lithium precipitation mother liquor. This equipment differs from conventional crystallization reaction devices, featuring a high degree of automation, programmable operation, no need for personnel to be on duty during the reaction process, and the ability to monitor the reaction progress in real time and record reaction data. The reaction detector has high sensitivity, and the reaction conditions are precisely controlled, allowing for a more refined synthesis process.

[0033] In some preferred embodiments, the dispersant comprises ethylene glycol polymers with different degrees of polymerization.

[0034] In some preferred embodiments, the method specifically includes: placing the lithium precipitation mother liquor from salt lake brine and a dispersant in a closed reaction apparatus and heating it to 70℃-95℃, then adding a phosphoric acid solution at a rate of 3ml / min-20ml / min, and continuing the crystallization lithium precipitation reaction for 10min-120min at a temperature of 70℃-95℃ and a stirring speed of 100rpm-600rpm.

[0035] Furthermore, the closed reaction device can be a fully automatic antisolvent crystallization screening instrument or a heating and stirring device that meets the requirements.

[0036] In some preferred embodiments, the molar ratio of phosphorus in the phosphoric acid solution to lithium in the lithium precipitation mother liquor of the salt lake brine is 0.90:1-2.00:1.

[0037] In some preferred embodiments, the mass ratio of the dispersant to the lithium precipitation mother liquor from the salt lake brine is 1:100 to 10:100.

[0038] In some preferred embodiments, the lithium precipitation mother liquor from the salt lake brine comprises the following components calculated by mass percentage:

[0039]

[0040] In some preferred embodiments, the degree of polymerization of the ethylene glycol polymer is 200-10000.

[0041] In some preferred embodiments, the aging process is carried out at an aging temperature of 30°C-90°C and for a aging time of 30 min-240 min.

[0042] In some preferred embodiments, the method specifically includes: performing solid-liquid separation on the crude lithium phosphate, and then mixing the obtained solid with hot water for washing and separation treatment.

[0043] Furthermore, the mass ratio of the hot water to the solid material is 10:1 to 2:1.

[0044] Furthermore, the temperature of the hot water is 30℃-90℃.

[0045] Furthermore, solid-liquid separation equipment such as sand core funnels, filter presses, or centrifuges are used for solid-liquid separation.

[0046] In some preferred embodiments, the method specifically includes: drying the purified product under vacuum at 100℃-300℃ for 4h-12h.

[0047] In some preferred embodiments, the high-purity lithium phosphate contains more than 97 wt% lithium phosphate.

[0048] Furthermore, the sodium content in the high-purity lithium phosphate is less than 0.5 wt%, the magnesium content in the high-purity lithium phosphate is less than 0.005 wt%, the calcium content in the high-purity lithium phosphate is less than 0.003 wt%, and the potassium content in the high-purity lithium phosphate is less than 0.003 wt%.

[0049] In some preferred embodiments, the process flow diagram for preparing high-purity lithium phosphate using lithium precipitation mother liquor from salt lake brine in this invention is as follows: Figure 1 As shown.

[0050] In some more specific embodiments, the method for preparing high-purity lithium phosphate using lithium precipitation mother liquor from salt lake brine includes:

[0051] (a) Lithium crystallization precipitation: This invention uses a fully automated antisolvent crystallization screening instrument as the crystallization reaction device. First, the reaction program is set via control software, including heating rate, reaction temperature, reaction time, feeding rate, stirring speed, aging temperature, and aging time. Then, the lithium precipitation mother liquor and an appropriate amount of dispersant are added to a closed reactor. After the mother liquor is heated to the set temperature, a phosphoric acid solution is automatically and uniformly pumped into the reactor from the feed port at a certain metering ratio. The lithium crystallization precipitation reaction is carried out under stirring. After the predetermined reaction time is reached, the next step of heat preservation and aging is automatically initiated. After aging, the material in the reactor cools naturally.

[0052] (b) Washing and purification: The material obtained in reaction step (a) is subjected to solid-liquid separation using a sintered glass funnel. The separated solid powder is added to a beaker, and then an appropriate amount of hot water is added. After stirring at room temperature for a certain period of time, solid-liquid separation is performed using a sintered glass funnel. During separation, the material is rinsed with an appropriate amount of deionized water.

[0053] (c) Separation and drying: The powder material obtained after washing in reaction step (b) is vacuum dried at a certain temperature, and the final product is high-purity lithium phosphate.

[0054] Preferably, the reaction temperature used in the lithium deposition step is 70℃-95℃.

[0055] Preferably, the feeding rate in the lithium deposition step is 3 ml / min-20 ml / min.

[0056] Preferably, the molar ratio of phosphoric acid to lithium in the lithium precipitation mother liquor during the lithium precipitation step is P / Li = 0.90-2.00.

[0057] Preferably, the dispersant in the step is an ethylene glycol polymer with a degree of polymerization of 200-10000 and an addition amount of 1wt%-10wt%.

[0058] Preferably, the reaction time in the lithium deposition step is 10 min to 120 min.

[0059] Preferably, the stirring speed in the lithium deposition step is 100rpm-600rpm.

[0060] Preferably, the aging time in the aging step is 30 min to 240 min.

[0061] Preferably, the aging temperature in the aging step is 30℃-90℃.

[0062] Preferably, the hot water temperature in the washing step is 30℃-90℃.

[0063] Preferably, the hot water liquid-solid ratio in the washing step is 10:1 to 2:1.

[0064] Preferably, the drying temperature in the drying step is 100℃-300℃.

[0065] Preferably, the drying time in the drying step is 4h-12h.

[0066] Preferably, after the material is processed through the above steps, the final target product lithium phosphate can be obtained, with a main content >97%, sodium content <0.5%, magnesium content <0.005%, calcium content <0.003%, and potassium content <0.003%.

[0067] This invention addresses the limitations of early lithium extraction processes using ore-based lithium precipitation mother liquor recovery, as well as the problems of low lithium recovery rates, severe product agglomeration, high impurity content, cumbersome processes, environmental unfriendliness, and high recovery costs in existing salt lake brine-based lithium extraction processes. It employs a fully automated anti-solvent crystallization and screening instrument, using salt lake brine lithium precipitation mother liquor as raw material, and controls the crystallization process by adding a dispersant to synthesize high-purity lithium phosphate in one step. This method utilizes highly automated equipment with precise reaction condition control; the process flow is simple, the raw material is singular, the process conditions are mild, production costs are low, and it is environmentally friendly; the lithium recovery rate is high, the product has good dispersibility, and high purity, which is conducive to the high-value, efficient, and sustainable development and utilization of salt lake resources.

[0068] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and provides detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0069] Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0070] Example 1

[0071] The lithium precipitation mother liquor from lithium carbonate production in a salt lake in Qinghai was selected as raw material. The main ion content and some physical properties of the mother liquor were tested and are shown in Table 1.

[0072] Table 1. Main ion concentrations in L1 lithium precipitation mother liquor

[0073]

[0074] 350.04 g of L1 mother liquor was weighed and added to the reactor of an automated antisolvent crystallizer. Magnetic stirring was turned on and the speed was controlled at 250 rpm. Then, 5 wt% PEG-200 solution was added, and the temperature was raised to 90℃ at a rate of 1.5℃ / min. The peristaltic pump speed was then adjusted, and a certain amount of phosphoric acid solution (the molar ratio of phosphoric acid to lithium in the lithium precipitation mother liquor, P / Li = 1.45) was added dropwise. After the phosphoric acid solution was added, the reaction was stirred continuously for 15 min. After the reaction was completed, the magnetic stirring was turned off, and the mixture was aged at 90℃ for 60 min. After aging, the system was allowed to cool naturally to room temperature. The reaction mixture was filtered using a dry, clean sintered sand funnel fitted with a 0.45 μm aqueous microporous membrane. During filtration, the weight of the filter bottle and the filtrate were weighed and recorded, the density of the filtrate was measured, and the lithium content of the filtrate was tested by ICP. Based on the test results, the lithium yield in the lithium precipitation mother liquor was calculated to be 82.94%. The filtered powder was scraped into a dry, clean beaker and weighed. Hot water was added at a solid-liquid ratio of 1:2, and the mixture was stirred at 60°C for 30 minutes. The material was then filtered again using a dry, clean sand-core funnel fitted with a 0.45μm aqueous microporous membrane, and rinsed with an appropriate amount of deionized water. The resulting powder was dried in a vacuum oven at 120°C for 6 hours to obtain high-purity lithium phosphate. The test results are shown in Table 2.

[0075] Table 2 Chemical analysis results of lithium phosphate samples

[0076]

[0077] The process is simple, the reaction conditions are mild, and it is easy to scale up to an industrial scale. It uses a single raw material, and the lithium yield in the lithium precipitation mother liquor is as high as 82%. It is green and environmentally friendly, and has good economic benefits. The purity of lithium phosphate is as high as 97.07%, which meets the quality requirements of downstream battery companies for raw materials.

[0078] Example 2

[0079] The lithium precipitation mother liquor from lithium carbonate production in a salt lake in Qinghai was selected as raw material. The main ion content and some physical indicators of the mother liquor were tested and are shown in Table 3.

[0080] Table 3. Main ion concentrations in L2 lithium precipitation mother liquor

[0081]

[0082] 350.46 g of L2 mother liquor was weighed and added to the reactor of an automated antisolvent crystallizer. Magnetic stirring was turned on and the speed was controlled at 250 rpm. Then, 1 wt% PEG-1000 solution was added, and the temperature was raised to 80℃ at a rate of 1.5℃ / min. The peristaltic pump speed was then adjusted, and a certain amount of phosphoric acid solution (the molar ratio of phosphoric acid to lithium in the lithium precipitation mother liquor, P / Li = 1.45) was added dropwise. After the phosphoric acid solution was added, the reaction was stirred continuously for 60 min. After the reaction was completed, the magnetic stirring was turned off, and the mixture was aged at 80℃ for 60 min. After aging, the system was allowed to cool naturally to room temperature. The reaction mixture was filtered using a dry, clean sintered sand funnel fitted with a 0.45 μm aqueous microporous membrane. During filtration, the weight of the filter bottle and the filtrate were weighed and recorded, the density of the filtrate was measured, and the lithium content of the filtrate was tested by ICP. Based on the test results, the lithium yield in the lithium precipitation mother liquor was calculated to be 86.47%. The filtered powder was scraped into a dry, clean beaker and weighed. Hot water was added at a solid-liquid ratio of 1:1, and the mixture was stirred at 70°C for 30 minutes. The material was then filtered again using a dry, clean sand-core funnel fitted with a 0.45μm aqueous microporous membrane, and rinsed with an appropriate amount of deionized water. The resulting powder was dried in a vacuum oven at 100°C for 12 hours to obtain high-purity lithium phosphate. The test results are shown in Table 4.

[0083] Table 4 Chemical analysis results of lithium phosphate samples

[0084]

[0085] This process is simple, with mild reaction conditions, and is easy to scale up industrially. It uses a single raw material, achieves a lithium yield of up to 86% in the lithium precipitation mother liquor, is environmentally friendly, and offers good economic benefits. The lithium phosphate purity is as high as 96.74%, meeting the quality requirements of downstream battery manufacturers. (See attached image) Figure 2 , Figure 3 , Figure 4As shown, scanning electron microscopy revealed significant changes in the morphology and crystal form of lithium phosphate prepared after the addition of PEG. After the addition of PEG, the lithium phosphate changed from a spindle shape to a distinct columnar shape, with crystals growing in the same direction and the crystal particles growing from about 10 μm to 30 μm. X-ray diffraction tests showed that the crystal structure of lithium phosphate changed significantly before and after the addition of PEG. Lithium phosphate without PEG was β-Li3PO4 with space group Pmnb, while lithium phosphate with PEG was γ-Li3PO4 with space group Pmn21.

[0086] Example 3

[0087] The lithium precipitation mother liquor from lithium carbonate production in a salt lake in Qinghai was selected as raw material. The main ion content and some physical properties of the mother liquor were tested and are shown in Table 5.

[0088] Table 5. Main ion concentrations in L3 lithium precipitation mother liquor

[0089]

[0090] 351.33 g of L3 mother liquor was weighed and added to the reactor of an automated antisolvent crystallizer. Magnetic stirring was turned on and the speed was controlled at 600 rpm. Then, 3 wt% PEG-4000 solution was added, and the temperature was raised to 90℃ at a rate of 1.5℃ / min. The peristaltic pump speed was then adjusted, and a certain amount of phosphoric acid solution (the molar ratio of phosphoric acid to lithium in the lithium precipitation mother liquor, P / Li = 1.75) was added dropwise. After the phosphoric acid solution was added, the reaction was stirred continuously for 60 min. After the reaction was completed, the magnetic stirring was turned off, and the mixture was aged at 90℃ for 120 min. After aging, the system was allowed to cool naturally to room temperature. The reaction mixture was filtered using a dry, clean sintered sand funnel fitted with a 0.45 μm aqueous microporous membrane. During filtration, the weight of the filter bottle and the filtrate were weighed and recorded, the density of the filtrate was measured, and the lithium content of the filtrate was tested by ICP. Based on the test results, the lithium yield in the lithium precipitation mother liquor was calculated to be 87.23%. The filtered powder was scraped into a dry, clean beaker and weighed. Hot water was added at a solid-liquid ratio of 1:1, and the mixture was stirred at 40°C for 30 minutes. The material was then filtered again using a dry, clean sand-core funnel fitted with a 0.45μm aqueous microporous membrane, and rinsed with an appropriate amount of deionized water. The resulting powder was dried in a vacuum oven at 160°C for 4 hours to obtain high-purity lithium phosphate. The test results are shown in Table 6.

[0091] Table 6 Chemical analysis results of lithium phosphate samples

[0092]

[0093] The process is simple, the reaction conditions are mild, and it is easy to scale up to an industrial scale. It uses a single raw material, and the lithium yield in the lithium precipitation mother liquor is as high as 87%. It is green and environmentally friendly, and has good economic benefits. The purity of lithium phosphate is as high as 97.12%, which meets the quality requirements of downstream battery companies for raw materials.

[0094] Example 4

[0095] The lithium precipitation mother liquor from lithium carbonate production in a salt lake in Qinghai was selected as raw material. The main ion content and some physical indicators of the mother liquor were tested and are shown in Table 7.

[0096] Table 7. Main ion concentrations in L4 lithium precipitation mother liquor

[0097]

[0098] 349.62 g of L4 mother liquor was weighed and added to the reactor of an automated antisolvent crystallizer. Magnetic stirring was turned on and the speed was controlled at 350 rpm. Then, 5 wt% PEG-10000 solution was added, and the temperature was raised to 70℃ at a rate of 1.5℃ / min. The peristaltic pump speed was then adjusted, and a certain amount of phosphoric acid solution (the molar ratio of phosphoric acid to lithium in the lithium precipitation mother liquor, P / Li = 1.15) was added dropwise. After the phosphoric acid solution was added, the reaction was stirred continuously for 30 min. After the reaction was completed, the magnetic stirring was turned off, and the mixture was aged at 70℃ for 120 min. After aging, the system was allowed to cool naturally to room temperature. The reaction mixture was filtered using a dry, clean sintered sand funnel fitted with a 0.45 μm aqueous microporous membrane. During filtration, the weight of the filter bottle and the filtrate were weighed and recorded, the density of the filtrate was measured, and the lithium content of the filtrate was tested by ICP. Based on the test results, the lithium yield in the lithium precipitation mother liquor was calculated to be 71.66%.

[0099] The filtered powder was scraped into a dry, clean beaker and weighed. Hot water was added at a solid-liquid ratio of 1:1, and the mixture was stirred at 40°C for 30 minutes. The material was then filtered again using a dry, clean sand-core funnel fitted with a 0.45μm aqueous microporous membrane, and rinsed with an appropriate amount of deionized water. The resulting powder was dried in a vacuum oven at 200°C for 4 hours to obtain high-purity lithium phosphate. The test results are shown in Table 8.

[0100] Table 8 Chemical analysis results of lithium phosphate samples

[0101]

[0102] The process is simple, the reaction conditions are mild, and it is easy to scale up to an industrial scale. It uses a single raw material, and the lithium yield in the lithium precipitation mother liquor is as high as 71%. It is green and environmentally friendly, and has good economic benefits. The purity of lithium phosphate is as high as 97.65%, which meets the quality requirements of downstream battery companies for raw materials.

[0103] Comparative Example 1

[0104] The lithium precipitation mother liquor from lithium carbonate production in a salt lake in Qinghai was selected as raw material. The main ion content and some physical indicators of the mother liquor were tested and are shown in Table 9.

[0105] Table 9. Main ion concentrations in L1 lithium precipitation mother liquor

[0106]

[0107] 350.00 g of L1 mother liquor was weighed and added to the reactor of an automated antisolvent crystallizer. Magnetic stirring was turned on, and the speed was controlled at 250 rpm. The temperature was increased to 90℃ at a rate of 1.5℃ / min. Then, the peristaltic pump speed was adjusted, and a certain amount of phosphoric acid solution (the molar ratio of phosphoric acid to lithium in the lithium precipitation mother liquor, P / Li = 1.45) was added dropwise. After the phosphoric acid solution was added, the reaction was stirred continuously for 15 min. After the reaction was completed, the magnetic stirring was turned off, and the mixture was aged at 90℃ for 60 min. After aging, the system was allowed to cool naturally to room temperature. The reaction mixture was filtered using a dry and clean sintered sand funnel fitted with a 0.45 μm aqueous microporous membrane. During filtration, the weight of the filter bottle and the weight of the filtrate were weighed and recorded, the density of the filtrate was measured, and the lithium content of the filtrate was tested by ICP. Based on the test results, the lithium yield in the lithium precipitation mother liquor was calculated to be 80.18%. The filtered powder was scraped into a dry, clean beaker and weighed. Hot water was added at a solid-liquid ratio of 1:1, and the mixture was stirred at 40°C for 30 minutes. The material was then filtered again using a dry, clean sand-core funnel fitted with a 0.45μm aqueous microporous membrane, and rinsed with an appropriate amount of deionized water. The resulting powder was dried in a vacuum oven at 120°C for 6 hours to obtain high-purity lithium phosphate. The test results are shown in Table 10.

[0108] Table 10 Chemical analysis results of lithium phosphate samples

[0109]

[0110] Whether or not PEG is added during the lithium phosphate preparation process has a significant impact on the particle size of the product, as shown in Table 11 and... Figure 5 As shown, the average D(50) of the sample prepared without PEG was about 69.578 and the average D(100) was about 238; the average D(50) of the sample prepared with PEG was about 43.757 and the average D(100) was about 151. It can be seen that the average particle size of lithium phosphate products is smaller and the particle size distribution is more concentrated after adding PEG, and the products are more uniform.

[0111] Table 11 Results of laser particle size analysis of lithium phosphate samples

[0112]

[0113] Although the overall lithium yield of lithium phosphate prepared without the addition of PEG did not change significantly, chemical analysis revealed that the product contained a high Na content of 1.5338 wt%, a Ca content of 0.5061 wt%, and a B2O3 content of 0.0953 wt%, with a purity of only 95.07% and uneven particle size distribution, which could not meet the quality requirements of downstream battery companies for raw materials.

[0114] Comparative Example 2

[0115] The lithium precipitation mother liquor from lithium carbonate production in a salt lake in Qinghai was selected as raw material. The main ion content and some physical indicators of the mother liquor were tested and are shown in Table 12.

[0116] Table 12 Main Ion Concentrations in L1 Lithium Precipitating Mother Lithium Solution

[0117]

[0118] 350.04 g of L1 mother liquor was weighed and added to the reactor of an automated antisolvent crystallizer. Magnetic stirring was turned on and the speed was controlled at 250 rpm. Then, 5 wt% PEG-200 solution was added, and the temperature was increased to 60℃ at a rate of 1.5℃ / min. The peristaltic pump speed was then adjusted, and a certain amount of phosphoric acid solution (the molar ratio of phosphoric acid to lithium in the lithium precipitation mother liquor, P / Li = 1.45) was added dropwise. After the phosphoric acid solution was added, the reaction was stirred continuously for 15 min. After the reaction was completed, the magnetic stirring was turned off, and the mixture was aged at 60℃ for 60 min. After aging, the system was allowed to cool naturally to room temperature. The reaction mixture was filtered using a dry, clean sintered sand funnel fitted with a 0.45 μm aqueous microporous membrane. During filtration, the weight of the filter bottle and the weight of the filtrate were weighed and recorded, the density of the filtrate was measured, and the lithium content of the filtrate was tested by ICP. Based on the test results, the lithium yield in the lithium precipitation mother liquor was calculated to be 63.14%. The filtered powder was scraped into a dry, clean beaker and weighed. Hot water was added at a solid-liquid ratio of 1:1, and the mixture was stirred at 60°C for 30 minutes. The material was then filtered again using a dry, clean sand-core funnel fitted with a 0.45μm aqueous microporous membrane, and rinsed with an appropriate amount of deionized water. The resulting powder was dried in a vacuum oven at 120°C for 6 hours to obtain high-purity lithium phosphate. The test results are shown in Table 13.

[0119] Table 13 Chemical analysis results of lithium phosphate samples

[0120]

[0121] The process is simple, the reaction conditions are mild, and it is easy to scale up industrially. However, the lithium yield in the lithium precipitation mother liquor is only 63.14% under the reaction conditions of 60℃. Under these conditions, the lithium recovery rate is low, the economic benefits are low, and it is not conducive to the comprehensive and efficient recycling of salt lake resources.

[0122] It should be understood that the technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made to the technical solutions of the present invention without departing from the spirit and scope of the claims are within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity lithium phosphate by using a lithium precipitation mother liquor of salt lake brine, characterized in that, The application comprises the following steps: The lithium precipitation mother liquor of salt lake brine and dispersant are put into a closed reaction device and heated to 70-95℃, then the phosphoric acid solution is input at a rate of 3-20 ml / min, and the crystallization lithium precipitation reaction is continued at 70-95℃ and 100-600 rpm for 10-120 min to make the lithium phosphate crystals grow along the (120) crystal face, then the aging treatment is carried out to obtain the crude lithium phosphate, which is crude γ-Li3PO4; wherein the dispersant is selected from ethylene glycol polymer; The crude lithium phosphate is purified and dried to obtain high-purity lithium phosphate, which is high-purity γ-Li3PO4; the content of lithium phosphate in the high-purity lithium phosphate is more than 97wt%; the content of sodium in the high-purity lithium phosphate is less than 0.5wt%, the content of magnesium in the high-purity lithium phosphate is less than 0.005wt%, and the contents of potassium and calcium in the high-purity lithium phosphate are both less than 0.003wt%.

2. The method of claim 1, wherein: The molar ratio of phosphorus in the phosphoric acid solution to lithium in the lithium precipitation mother liquor of salt lake brine is 0.90:1-2.00:

1.

3. The method of claim 1, wherein: The mass ratio of the dispersant to the lithium precipitation mother liquor of salt lake brine is 1:100-10:

100.

4. The method of claim 1, wherein: The molecular polymerization degree of the ethylene glycol polymer is 200-10000.

5. The method of claim 1, wherein, The aging temperature in the aging treatment is 30-90℃, and the aging time is 30-240 min.

6. The method of claim 1, wherein Specifically comprising: The crude lithium phosphate is subjected to solid-liquid separation, then the obtained solid is mixed with hot water for washing and separation treatment.

7. The method of claim 6, wherein: The mass ratio of the hot water to the solid is 10:1-2:1, and the temperature of the hot water is 30-90℃.

8. The method of claim 1, wherein Specifically comprising: The product obtained by the purification treatment is vacuum dried at 100-300℃ for 4-12 h.

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