Method for extracting iron phosphate from waste residue after extracting lithium from lithium iron phosphate

Abstract

The application provides a method for extracting iron phosphate from lithium extraction waste residue of lithium iron phosphate, and belongs to the field of new energy battery recycling. The method realizes higher efficiency in the extraction process through accurate detection of iron and phosphorus elements in the lithium extraction waste residue of lithium iron phosphate. The method realizes efficient removal of aluminum and other impurities in the lithium extraction waste residue of lithium iron phosphate by adsorbing magnetic substances onto magnetic bodies and taking the aluminum ions and other impurities away by the magnetic substances, so that the subsequent extraction process is more effective. The method realizes more effective extraction of iron phosphate by adding a chelating agent, and realizes efficient, high-value and high-purification "three-high" recycling of the iron phosphate residue in the lithium extraction waste residue of lithium iron phosphate through the above three steps of "three effects".

Description

Technical Field

[0001] This invention relates to the field of new energy battery recycling, specifically to a method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate. Background Technology

[0002] In recent years, with the rapid development of the global electric vehicle and energy storage industries, lithium iron phosphate (LFP) batteries have been more widely promoted and applied due to their numerous advantages, such as high specific capacity, stable structure, safe performance, and long service life. At the same time, considering the current lifespan of lithium-ion batteries is generally 3-5 years, there is a significant problem of large-scale disposal of LFP batteries now and in the future. It is estimated that after 2023, the amount of discarded power batteries in my country will reach 120,000 to 170,000 tons. A large number of LFP batteries urgently need recycling and processing. Firstly, failure to recycle and reuse discarded LFP batteries poses a significant threat to the environment and human health. Secondly, LFP batteries are rich in lithium and iron phosphate; from the perspective of resource recycling and environmental protection, the effective and selective recovery of valuable metals such as lithium from LFP batteries is particularly important.

[0003] Currently, the recycling of waste lithium iron phosphate is mainly handled through wet processing. The main steps include battery discharge, dismantling, crushing, and sorting to obtain black powder, which is then recovered and reused through leaching, elemental separation and purification, and product regeneration. Lithium has a high recovery value, and the process of recovering lithium from waste lithium iron phosphate into high-value lithium carbonate or lithium hydroxide products is relatively mature.

[0004] Some of the waste residue from lithium iron phosphate extraction contains a large amount of valuable reusable iron, which can be further processed to produce iron phosphate. However, this waste residue also contains impurities such as aluminum, and current aluminum removal processes for iron phosphate face numerous challenges, including lengthy processes, poor deep aluminum and impurity removal efficiency, and low product purity and yield. How to achieve efficient, high-value, and highly purified recycling of iron phosphate residue is a significant challenge currently facing the recycling of waste lithium iron phosphate batteries. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate. The method mainly consists of three steps: detection, magnetic separation, and refining of the waste residue after lithium extraction from lithium iron phosphate. This method achieves the technical effect of efficient, high-value, and highly purified recycling of iron phosphate residue from the waste residue after lithium extraction from lithium iron phosphate.

[0006] This invention discloses a method for extracting iron phosphate from lithium iron phosphate (LFP) residue. By precisely detecting the iron and phosphorus elements in the LFP residue, the refining process becomes more efficient. By adsorbing magnetic materials onto a magnetic substrate, impurities such as aluminum ions are carried away, thus removing these impurities from the LFP residue and making subsequent refining more effective. Furthermore, the addition of a chelating agent results in a higher-performance refining method, further enhancing the efficiency of iron phosphate extraction. These three steps, known as the "three-efficiency" approach, achieve highly efficient, high-value, and highly purified recycling of iron phosphate residue from LFP residue. This invention also provides a more environmentally friendly refining method, ensuring an alternative solution for situations with stringent environmental requirements.

[0007] Specifically, the technical solution of the present invention provides a method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate, characterized in that the waste residue after lithium extraction from lithium iron phosphate is first pre-selected by magnetic separation, and then refined to obtain battery-grade anhydrous iron phosphate product. The specific steps are as follows:

[0008] S21 involves drying and crushing the waste residue after lithium extraction from lithium iron phosphate, grinding it in an elliptical ball mill, and then passing it through a 200-220 mesh sieve to obtain lithium iron phosphate waste residue powder with a particle size of 0.065-0.074 mm.

[0009] S22, the waste residue powder after lithium extraction from lithium iron phosphate is conveyed to a magnetic separator by a conveyor belt for magnetic separation, and the magnetic flux density of the magnetic separator is set to 9000-10000GS.

[0010] S23, repeat step S22 above 4-5 times to obtain the initially selected iron phosphate powder C;

[0011] S31, mix the iron phosphate powder C initially selected in S23 with ammonia water with a concentration of 20% at a mass ratio of 1:3 to form a slurry;

[0012] S32, add chelating agent to the above slurry, mix and add to the reaction vessel, wherein the chelating agent and the initially selected iron phosphate refining powder C are mixed in a mass percentage ratio of 0.05:1;

[0013] S33 was stirred at 200-400 r / min for 2-3 hours at 80-90℃. After the reaction was completed, it was filtered immediately to obtain ammonium phosphate filtrate and ferric hydroxide filter residue.

[0014] S34, Cool the ammonium phosphate filtrate from S33 at room temperature, and place the ferric hydroxide filter residue in a drying oven and dry it at a temperature of 40-80°C for 2-3 hours;

[0015] S35, put the dried ferric hydroxide filter residue and a 45% sulfuric acid solution into a container at a mass ratio of 1:4, and stir at a rate of 600 r / min for 1-2 hours at room temperature of 25-30℃.

[0016] S36, add polyvinylpyrrolidone as a dispersant, the mass ratio of the dispersant to the added ferric hydroxide filter residue is 1:20, and at the same time, heat to 60°C and continue stirring in an inert gas atmosphere for 30 minutes. While stirring, add the cooled ammonium phosphate filtrate from step S34 dropwise.

[0017] S37, after stirring at 50-60℃ for 4-5 hours, cool to room temperature and filter to obtain filtrate containing ammonium sulfate and ferric phosphate dihydrate filter residue;

[0018] S38. The ferric phosphate dihydrate filter residue is washed 2-3 times with anhydrous ethanol, then rinsed and washed 3-4 times with distilled water, and dried in a drying oven at 110-170℃ for 8-10 hours to obtain pure ferric phosphate dihydrate.

[0019] S39, calcining the ferric phosphate dihydrate at 600°C in an inert gas atmosphere for 1-2 hours yields battery-grade anhydrous ferric phosphate.

[0020] Specifically, the technical solution of the present invention provides a method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate, characterized in that, before the magnetic separation step, a step is included to detect the iron and phosphorus content in the waste residue after lithium extraction from lithium iron phosphate, specifically:

[0021] S10, take 100 grams of lithium iron phosphate residue after lithium extraction, grind it into powder A, and control the particle size of powder A to be between 300-325 mesh.

[0022] S11, add powder A into a 250ml wide-mouth polypropylene bottle;

[0023] S12, add 100ml of ethanol, put it in an ultrasonic cleaner and clean for 20-30 seconds, repeat 2-3 times;

[0024] S13, add 150 ml of weakly acidic ionized water with a pH value between 6.6 and 6.9, put it in an ultrasonic cleaner and clean for 30 seconds, repeat 4-5 times, filter out the water to get powder B;

[0025] S14, add 10 ml of aqua regia to a wide-mouth polypropylene bottle containing the above powder B to form a solution, and add pure water to the 200 ml mark.

[0026] S15, heat the solution to 80-90℃ and maintain for 10-20 minutes;

[0027] S16, cool the solution to room temperature of 25-27°C, and add pure water to the 200ml mark;

[0028] S17, the iron and phosphorus content in the solution was detected by ICP-MS.

[0029] Preferably, an embodiment of the present invention provides a method for refining iron phosphate from lithium iron phosphate residue after lithium extraction, wherein the lithium iron phosphate residue after lithium extraction, which has an iron content of more than 20% by mass and a phosphorus content of more than 10% by mass as determined by ICP-MS, is selected as the raw material for refining iron phosphate.

[0030] Preferably, an embodiment of the present invention provides a method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate. In step S32, the chelating agent is selected from at least one of hydroxyethylidene diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, or 2-hydroxyphosphonoacetic acid (HPAA).

[0031] Preferably, an embodiment of the present invention provides a method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate, wherein in S33, the iron hydroxide filter residue exists in the form of Fe2O3·3H2O.

[0032] Preferably, an embodiment of the present invention provides a method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate, wherein the polyvinylpyrrolidone added in S36 is one or more of PVP-K15, PVP-K30, PVP-K60 and PVPK90.

[0033] Alternatively, embodiments of the present invention provide a method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate, characterized in that the waste residue after lithium extraction from lithium iron phosphate is first pre-selected by magnetic separation, and then refined to obtain battery-grade anhydrous iron phosphate product, specifically as follows:

[0034] S21 involves drying and crushing the waste residue after lithium extraction from lithium iron phosphate, grinding it in an elliptical ball mill, and then passing it through a 200-220 mesh sieve to obtain lithium iron phosphate waste residue powder with a particle size of 0.065-0.074 mm.

[0035] S22, the waste residue powder after lithium extraction from lithium iron phosphate is conveyed to a magnetic separator by a conveyor belt for magnetic separation, and the magnetic flux density of the magnetic separator is set to 9000-10000GS.

[0036] S23, repeat step S22 above 4-5 times to obtain the preliminary selected iron phosphate powder C rich in phosphorus ions and iron ions.

[0037] S31', the initially selected ferric phosphate powder C and water are mixed at a mass ratio of 1:10 and added to the reactor. The mixture is continuously heated and stirred at a rate of 200-400 r / min for 2-3 hours at a temperature of 80-90℃. After filtration, filter residue D and ferric phosphate solution dissolved in hot water are obtained. After cooling to room temperature, precipitate and filter to obtain solid ferric phosphate dihydrate product E1 and filtrate F1.

[0038] S32', filter residue D and 30% hydrogen peroxide are mixed at a mass ratio of 1:3, and the temperature is raised to 50°C at a rate of 8°C / min. After stirring thoroughly, the mixture is kept at this temperature for 1 hour, and then filtered to obtain solid product E2 of ferric phosphate dihydrate and filtrate F2.

[0039] S33', ferric phosphate dihydrate solid product E1 and ferric phosphate dihydrate solid product E2 are rinsed and washed 3-4 times with distilled water, and then dried in a drying oven at 110-170℃ for 8-10 hours to obtain pure ferric phosphate dihydrate.

[0040] S34', by calcining the ferric phosphate dihydrate at 600°C for 1-2 hours, battery-grade anhydrous ferric phosphate product can be obtained.

[0041] Specifically, embodiments of the present invention provide a method for extracting iron phosphate from waste residue after lithium extraction from lithium iron phosphate, characterized in that it further includes a step of detecting the iron and phosphorus content in the waste residue after lithium extraction from lithium iron phosphate, specifically:

[0042] S10, take 100 grams of lithium iron phosphate residue after lithium extraction, grind it into powder A, and control the particle size of powder A to be between 300-325 mesh.

[0043] S11, add powder A into a 250ml wide-mouth polypropylene bottle;

[0044] S12, add 100ml of ethanol, put it in an ultrasonic cleaner and clean for 20-30 seconds, repeat 2-3 times;

[0045] S13, add 150 ml of weakly acidic ionized water with a pH value between 6.6 and 6.9, put it in an ultrasonic cleaner and clean for 30 seconds, repeat 4-5 times, filter out the water to get powder B;

[0046] S14, add 10 ml of aqua regia to a wide-mouth polypropylene bottle containing the above powder B to form a solution, and add pure water to the 200 ml mark.

[0047] S15, heat the solution to 80-90℃ and maintain for 10-20 minutes;

[0048] S16, cool the solution to room temperature of 25-27°C, and add pure water to the 200ml mark;

[0049] S17, the iron and phosphorus content in the solution was detected by ICP-MS.

[0050] Furthermore, the iron phosphate prepared by the method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate according to the embodiments of the present invention.

[0051] Furthermore, a method for manufacturing a lithium iron phosphate battery, wherein the lithium iron phosphate battery is prepared by refining iron phosphate from the waste residue after lithium extraction from lithium iron phosphate according to the method described in the embodiments of the present invention.

[0052] It should be understood that the description in the Summary of the Invention is not intended to limit the key or essential features of the embodiments of the present invention, nor is it intended to restrict the scope of the invention. Other features of the invention will become readily apparent from the following description. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. 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.

[0054] The technical solution of the present invention will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0055] This invention proposes a method for high-value recovery of iron phosphate from lithium iron phosphate extraction waste residue. The method mainly consists of three steps: detection, magnetic separation, and refining of the waste residue after lithium iron phosphate extraction. The aim is to achieve efficient, high-value, and highly purified "three-high" recovery treatment of iron phosphate residue from lithium iron phosphate extraction waste residue.

[0056] Step 1: Detection of iron and phosphorus content in the waste residue after lithium iron phosphate extraction.

[0057] Neither existing wet nor dry processes can guarantee the consistent quality of the waste residue after lithium iron phosphate (LFP) extraction. The chemical composition of this waste residue varies considerably. To improve efficiency and reduce costs, it is essential to first test the waste residue and then select only those meeting refining requirements for iron phosphate extraction. This quantitative approach allows for scientific evaluation and enables the effective selection of the optimal refining technology in subsequent processes. Therefore, testing the waste residue before refining is a crucial step in improving the efficiency and quality of iron phosphate extraction from LFP waste residue.

[0058] The specific steps taken in this invention are as follows:

[0059] S10, take 100 grams of lithium iron phosphate residue after lithium extraction and grind it into powder A using a ceramic mortar and pestle. The particle size of powder A is controlled between 300-325 mesh. The mortar and pestle are also made of ceramic material, or hardwood material.

[0060] S11, add powder A into a pure 250ml wide-mouth PP bottle (polypropylene bottle);

[0061] S12, add 100ml of ethanol to the wide-mouth PP bottle (polypropylene bottle), and place it in an ultrasonic cleaner for 20-30 seconds, repeating 2-3 times.

[0062] S13, add 150 ml of weakly acidic ionized water with a pH value between 6.6 and 6.9 to the wide-mouth PP bottle, put it in an ultrasonic cleaner for 30 seconds, repeat 4-5 times, and filter out the water to obtain powder B.

[0063] S14, add 10 ml of aqua regia (the mass ratio of HCl to HNO3 is 3:1 during the preparation process) to a wide-mouth PP bottle containing the above powder B to form a solution, and add pure water to the 200 ml mark.

[0064] S15, heat the solution to 80-90℃ and maintain for 10-20 minutes;

[0065] S16, cool the solution to room temperature of 25-27°C and add pure water to the 200ml mark;

[0066] S17, the iron and phosphorus content in the solution was detected by ICP-MS.

[0067] In the next refining process, the waste residue from lithium iron phosphate extraction, which has an iron content of more than 20% by mass and a phosphorus content of more than 10% by mass after detection by ICP-MS, is used as the raw material for refining iron phosphate.

[0068] Specifically, the refining value of waste residue after lithium extraction from lithium iron phosphate with an iron content of less than 20% by mass and a phosphorus content of less than 10% by mass is generally low, and it is not considered as a preferred raw material for lithium iron phosphate extraction in this invention.

[0069] In the technical solution of this invention, the purpose of selecting a polypropylene bottle in S12 is because it has the advantages of being corrosion-resistant, lightweight, sealable, and hygienic. Its continuous operating temperature can reach 110-120℃, which can maximize the completeness and interference-free nature of the testing process.

[0070] In the technical solution of this invention, the ionized water in S13 is filtered through a water purifier using activated carbon as a filter layer to purify tap water to meet standards. Then, it is electrolyzed through a diaphragm to generate two types of active water, namely ionized water. The water flowing out from the cathode is alkaline ionized water (for drinking); the water flowing out from the anode is acidic ionized water (for external use). Ionized water does not include water with added substances such as physiological saline. Compared with ordinary water, ionized water differs in osmotic pressure, molecular cluster size, solubility, conductivity, pH value, surface tension, density, thermal conductivity, and oxygen content.

[0071] It is worth mentioning that the main purpose of using weakly acidic ionized water with a pH value between 6.6 and 6.9 in step S13 of this invention is to better clean impurities for effective ICP-MS detection.

[0072] Step 1 is implemented and verified through the following two specific examples.

[0073] Example 1:

[0074] In one embodiment of the present invention, the main components of the waste residue after lithium iron phosphate extraction from a selected sample, as determined by the ICP-MS detection method described in the present invention, are as follows:

[0075] Table 1

[0076]

[0077] After testing with ICP-MS, the iron content was found to be over 20% (32.5%) and the phosphorus content was over 10% (18.3%). Therefore, the waste residue after lithium extraction from lithium iron phosphate can be used as raw material for the next step of refining iron phosphate.

[0078] Example 2:

[0079] In another embodiment of the present invention, the main components of the waste residue after lithium iron phosphate extraction from one sample, as determined by the ICP-MS detection method described in the present invention, are as follows:

[0080] Table 2

[0081]

[0082] After testing with ICP-MS, the iron content was found to be over 20% (34.7%) and the phosphorus content was over 10% (18.9%). Therefore, the waste residue after lithium extraction from lithium iron phosphate can be used as raw material for the next step of refining iron phosphate.

[0083] Step 2: Magnetic separation to remove aluminum and other impurities

[0084] In existing technologies, methods for removing impurities such as aluminum from the waste residue after lithium extraction from lithium iron phosphate generally employ alkaline leaching or acid leaching to remove aluminum. However, due to the mutual influence between aluminum and iron in acidic and alkaline solutions, not only does this increase the cost of impurity removal, but it also results in low purity and yield of the iron phosphate product during the refining process.

[0085] Step two primarily utilizes magnetic separation to adsorb magnetic materials onto a magnetic body, carrying away impurities such as aluminum ions, thereby removing aluminum and other impurities from the waste residue after lithium iron phosphate extraction. Magnetic separation offers a low-cost, highly automated method for material separation, efficiently removing impurities, especially at high production volumes, thus improving material grade and increasing the economic value per unit of the waste residue after lithium iron phosphate extraction.

[0086] S21. After the sample testing in step one above is completed, the solid lithium iron phosphate residue that meets the requirements is dried, crushed, ground into powder by an elliptical ball mill, and then passed through a 200-220 mesh sieve to obtain lithium iron phosphate residue powder with a particle size of 0.065-0.074mm.

[0087] S22, the lithium iron phosphate residue powder obtained in step S21 is conveyed to a magnetic separator via a conveyor belt, preferably a permanent magnet roller separator. The magnetic flux density of the magnetic separator is set to 9000-10000GS. Under the action of the magnetic field, magnetic mineral particles containing impurities such as aluminum agglomerate to form "magnetic clusters" or "magnetic chains". The "magnetic clusters" or "magnetic chains" are attracted to the magnetic poles by the magnetic force in the slurry and are adsorbed onto the cylinder. Since the polarity of the magnetic poles is alternately arranged along the rotation direction of the cylinder and remains stationary during operation, the "magnetic clusters" or "magnetic chains" generate a magnetic stirring phenomenon due to the alternating magnetic poles as the cylinder rotates. The non-magnetic minerals trapped in the "magnetic clusters" or "magnetic chains" fall off during the agitation. The "magnetic clusters" that are finally adsorbed on the surface of the cylinder are the impurities such as aluminum, and the rest are components rich in phosphorus ions and iron ions.

[0088] S23. Repeat step S22 4-5 times to obtain the selected primary iron phosphate powder C, which is rich in phosphorus and iron ions.

[0089] The reason for selecting an elliptical ball mill in step S21 is that the elliptical balls in the elliptical ball mill also have antistatic and moisture-proof properties, which can reduce the adsorption of fine powder and reduce the occurrence of over-grinding.

[0090] Specifically, step two is verified through two specific embodiments corresponding to step one.

[0091] Example 3:

[0092] In a specific application of step two, a waste residue sample after lithium extraction from lithium iron phosphate in Example 1 of the present invention is selected, wherein the mass percentages of Fe, P, Li, Ni, Al, Mn, Cu, Co, and V are 32.5%, 18.3%, 3.25%, 0.11%, 0.79%, 0.12%, 0.41%, 0.11%, and 0.17%, respectively.

[0093] The solid lithium iron phosphate residue after lithium extraction in Example 1 was dried, crushed, ground into powder by an elliptical ball mill, and then passed through a 220-mesh sieve to obtain lithium iron phosphate residue powder with a particle size of less than 0.065 mm.

[0094] After lithium extraction from lithium iron phosphate, the waste residue powder is conveyed to a magnetic separator via a conveyor belt. A permanent magnet roller magnetic separator is preferred. The modulation magnetic flux density of the magnetic separator is set to 9000GS. The "magnetic clusters" that are finally attracted to the surface of the cylinder are impurities such as aluminum, and the rest are components rich in phosphorus ions and iron ions.

[0095] Repeat the magnetic separation step 5 times to obtain a finely selected iron phosphate powder rich in phosphorus and iron ions.

[0096] Table 3

[0097]

[0098] Using the method in step two, after detecting with ICP-MS and comparing with the waste residue after lithium iron phosphate extraction before magnetic separation, as shown in Table 3, it can be found that while the aluminum content is significantly reduced, impurities such as Ni, Mn, V, Co, and Cu are also reduced accordingly, and the mass ratio of Fe and P will also increase accordingly.

[0099] Example 4:

[0100] In another specific application of step two, a waste residue sample after lithium extraction from lithium iron phosphate in Example 2 of the present invention was selected, wherein the mass percentages of Fe, P, Li, Cr, Al, Zn, Mg, Co, and Cd were 34.7%, 18.9%, 0.25%, 0.01%, 0.79%, 0.02%, 0.07%, 0.01%, and 0.001%, respectively.

[0101] The solid lithium iron phosphate residue from Example 2 was dried, crushed, ground in an elliptical ball mill, and then passed through a 200-mesh sieve to obtain residue powder with a particle size of less than 0.074 mm.

[0102] After lithium extraction from lithium iron phosphate, the waste residue powder is conveyed to a magnetic separator via a conveyor belt. A permanent magnet roller magnetic separator is preferred. The modulation magnetic flux density of the magnetic separator is set to 10000GS. The "magnetic clusters" that are finally attracted to the surface of the cylinder are impurities such as aluminum, and the rest are components rich in phosphorus ions and iron ions.

[0103] Repeat the magnetic separation step four times to obtain a finely selected iron phosphate powder rich in phosphorus and iron ions.

[0104] Using the method in step two, after detecting with ICP-MS and comparing with the waste residue after lithium iron phosphate extraction before magnetic separation, as shown in Table 4, it can be found that while the aluminum content is significantly reduced, impurities such as Zn, Mg, Cr, Co, and Cd are also reduced accordingly, and the mass ratio of Fe and P will also increase accordingly.

[0105] Table 4

[0106]

[0107] Step 3: Refining Ferric Phosphate

[0108] S31, mix the iron phosphate powder C initially selected in step two with 20% ammonia water at a mass ratio of 1:3 to form a mixed slurry;

[0109] S32, then the slurry is mixed with a specific chelating agent and added to the reactor, wherein the chelating agent and iron phosphate refining powder are added in a mass percentage of 0.05:1;

[0110] S33, continuously heat and maintain the temperature at 80-90℃, stir at a rate of 200-400r / min for 2-3 hours, filter immediately after the reaction is completed to obtain ammonium phosphate filtrate and ferric hydroxide filter residue;

[0111] S34, the ammonium phosphate filtrate is cooled to room temperature, and the ferric hydroxide filter residue is placed in a drying oven and dried at 40-80°C for 2-3 hours, so that it exists in the form of Fe2O3·3H2O;

[0112] S35, dry Fe2O3·3H2O and 45% sulfuric acid solution are placed in a container at a mass ratio of 1:4. Stir at 600r / min for 1-2 hours at room temperature of 25-30℃ to disperse and form a suspension.

[0113] S36, then add polyvinylpyrrolidone as a dispersant to prevent precipitation. The mass ratio of the dispersant to the added Fe2O3·3H2O is controlled at 1:20. At the same time, the temperature is raised to 60°C and stirred for 30 minutes in an inert gas atmosphere. The role of the inert gas atmosphere is to prevent iron ions from being oxidized. While stirring, the ammonium phosphate filtrate from step S34 is added dropwise.

[0114] S37, then maintain the temperature at 50-60℃ and continue stirring for 4-5 hours, cool to room temperature and filter to obtain filtrate containing ammonium sulfate and ferric phosphate dihydrate (H4FeO6P) filter residue;

[0115] S38. Taking advantage of the fact that the dispersant polyvinylpyrrolidone is easily soluble in alcohol, the filter residue of ferric phosphate dihydrate is washed with anhydrous ethanol 2-3 times, then rinsed with distilled water 3-4 times, and dried in a drying oven at 110-170℃ for 8-10 hours to obtain pure ferric phosphate dihydrate.

[0116] S39, calcining the ferric phosphate dihydrate at 600°C in an inert gas atmosphere for 1-2 hours yields battery-grade anhydrous ferric phosphate.

[0117] In step S32, the specific chelating agent is selected from at least one of hydroxyethylidene diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, or 2-hydroxyphosphonoacetic acid (HPAA), mainly utilizing its good scale inhibition properties to prevent unwanted precipitation during the reaction process.

[0118] In step S36, polyvinylpyrrolidone is used as a dispersant and as a high molecular weight surfactant. In different dispersion systems, polyvinylpyrrolidone can be used as a dispersant, emulsifier, thickener, leveling agent, particle size regulator, anti-reprecipitation agent, coagulant, solubilizer and detergent.

[0119] In this invention, polyvinylpyrrolidone can be one or more of PVP-K30, PVP-K60, PVPK90 and PVP-K15. The larger the molecular weight, the greater the viscosity. For example, the molecular weight of PVPK30 is about 40,000, while the molecular weight of PVPK90 is about 1.3 million. PVPK30 is preferred in this invention.

[0120] In this invention, polyvinylpyrrolidone, as a dispersant, inhibits aggregation in solution mainly through three mechanisms:

[0121] 1) It reduces the surface tension of the interface through adsorption;

[0122] 2) Through the action of the adhesive groups, a liquid film is formed on the surface of the particles to prevent the particles from getting close to each other;

[0123] 3) It utilizes the steric hindrance effect. Therefore, controlling the appropriate pH value, temperature, concentration, and adding a suitable amount of dispersant or electrolyte during the liquid phase reaction stage can keep the particles in a highly dispersed state, which is beneficial for reducing agglomeration.

[0124] In S39, the inert gas atmosphere can be one or both of nitrogen and argon.

[0125] In addition, after step S37, the filtrate containing ammonium sulfate can be dried simultaneously to obtain ammonium fertilizer, which becomes a fertilizer powder suitable for various soils and crops.

[0126] It should be noted that in the specific operation of this invention, step one, as a detection step, can be performed independently, while steps two and three need to be performed in conjunction. This will be explained below through specific embodiments.

[0127] Example 5:

[0128] The first step involves selecting the waste residue from lithium iron phosphate extraction, which has been verified through testing in Example 1 of this invention. The mass percentages of Fe, P, Li, Ni, Al, Mn, Cu, Co, and V are 32.5%, 18.3%, 3.25%, 0.11%, 0.79%, 0.12%, 0.41%, 0.11%, and 0.17%, respectively.

[0129] The second step involves drying and crushing 100 kg of solid lithium iron phosphate residue after lithium extraction, grinding it in an elliptical ball mill, and then passing it through a 220-mesh sieve to obtain residue powder with a particle size of less than 0.065 mm. The residue powder is then conveyed to a magnetic separator via a conveyor belt, preferably a permanent magnet roller separator. The magnetic flux density of the separator is set to 9000 GS. The "magnetic clusters" attracted to the surface of the cylinder are impurities such as aluminum, while the remaining components are rich in phosphorus and iron ions. The magnetic separation step is repeated 5 times to obtain the selected primary iron phosphate powder C, which is rich in phosphorus and iron ions.

[0130] The third step involves mixing the ferric phosphate powder C selected in step two with 20% ammonia water at a mass ratio of 1:3 to form a slurry. Then, 2-phosphonobutane 1,2,4-tricarboxylic acid is added to the slurry, and the mixture is added to a reaction vessel. The mass ratio of 2-phosphonobutane 1,2,4-tricarboxylic acid and ferric phosphate powder C is 0.05:1. The mixture is continuously heated and stirred at 200-400 r / min for 2-3 hours at a temperature of 80-90℃. After the reaction is complete, the mixture is immediately filtered to obtain an ammonium phosphate solution and ferric hydroxide residue. Testing revealed that the iron recovery rate in this embodiment was 95.1%, and the phosphate recovery rate was 95.3%.

[0131] The ammonium phosphate filtrate was cooled to room temperature, and the ferric hydroxide filter residue was placed in a drying oven and dried at 40-80°C for 2-3 hours, existing as Fe2O3·3H2O. The dried Fe2O3·3H2O and a 45% sulfuric acid solution were added to a container at a mass ratio of 1:4. The mixture was stirred at 600 r / min for 1-2 hours at room temperature (25-30°C) to ensure thorough dispersion and the formation of a suspension. Then, polyvinylpyrrolidone K-30 was added at a mass ratio of 1:20 to Fe2O3·3H2O, and the temperature was raised to 60°C under argon atmosphere. Continue stirring for 30 minutes in an inert gas atmosphere, adding ammonium phosphate filtrate dropwise while stirring; then maintain the temperature at 50-60℃ and continue stirring for 4-5 hours, cool to room temperature and filter to obtain a filtrate containing ammonium sulfate and ferric phosphate dihydrate (H4FeO6P) filter residue; wash the ferric phosphate dihydrate filter residue 2-3 times with anhydrous ethanol, then rinse with distilled water 3-4 times, and dry in a drying oven at 110-170℃ for 8-10 hours to obtain pure ferric phosphate dihydrate; calcine the ferric phosphate dihydrate at 600℃ in an inert gas atmosphere of nitrogen for 1-2 hours to obtain battery-grade anhydrous ferric phosphate product.

[0132] Example 6:

[0133] The first step involves selecting the waste residue from lithium iron phosphate extraction in Example 2 of this invention, wherein the mass percentages of Fe, P, Li, Cr, Al, Zn, Mg, Co, and Cd are 34.7%, 18.9%, 0.25%, 0.01%, 0.79%, 0.02%, 0.07%, 0.01%, and 0.001%, respectively.

[0134] The second step involves drying and crushing 100 kg of solid lithium iron phosphate residue after lithium extraction, grinding it in an elliptical ball mill, and then passing it through a 200-mesh sieve to obtain lithium iron phosphate residue powder with a particle size of less than 0.074 mm. The lithium iron phosphate residue powder is then conveyed to a magnetic separator via a conveyor belt, preferably a permanent magnet roller separator. The magnetic flux density of the separator is set to 10000 GS. The "magnetic clusters" attracted to the surface of the cylinder are impurities such as aluminum, while the remaining components are rich in phosphorus and iron ions. The magnetic separation step is repeated four times to obtain the selected primary iron phosphate powder C, which is rich in phosphorus and iron ions.

[0135] The third step involves mixing the ferric phosphate powder C selected in step two with 20% ammonia water at a mass ratio of 1:3 to form a slurry. Then, hydroxyethylidene diphosphonic acid is added to the slurry, and the mixture is added to a reaction vessel at a mass ratio of 0.05:1. The mixture is continuously heated and stirred at 200-400 r / min for 2-3 hours at a temperature of 80-90℃. After the reaction is complete, the mixture is immediately filtered to obtain an ammonium phosphate solution and ferric hydroxide residue. Testing revealed that the iron recovery rate in this embodiment was 96.3%, and the phosphate recovery rate was 96.8%.

[0136] The ammonium phosphate filtrate was cooled to room temperature, and the ferric hydroxide filter residue was placed in a drying oven and dried at 40-80°C for 2-3 hours, existing as Fe2O3·3H2O. The dried Fe2O3·3H2O and a 45% sulfuric acid solution were added to a container at a mass ratio of 1:4. The mixture was stirred at 600 r / min for 1-2 hours at room temperature (25-30°C) to ensure thorough dispersion and form a suspension. Polyvinylpyrrolidone was then added as a dispersant to prevent precipitation. The mass ratio of the dispersant to the added Fe2O3·3H2O was controlled at 1:20, and the temperature was simultaneously raised to 60°C. The mixture is stirred for 30 minutes in an inert nitrogen atmosphere while ammonium phosphate filtrate is added dropwise. Afterward, the mixture is stirred for 4-5 hours at 50-60°C, then cooled to room temperature and filtered to obtain a filtrate containing ammonium sulfate and ferric phosphate dihydrate (H4FeO6P) filter residue. The ferric phosphate dihydrate filter residue is washed 2-3 times with anhydrous ethanol, then rinsed 3-4 times with distilled water, and dried in a drying oven at 110-170°C for 8-10 hours to obtain pure ferric phosphate dihydrate. The ferric phosphate dihydrate is calcined at 600°C in an inert nitrogen atmosphere for 1-2 hours to obtain battery-grade anhydrous ferric phosphate product.

[0137] Furthermore, this invention also provides an environmentally friendly process as an alternative solution in specific environments. This refining process is more environmentally friendly, but the efficiency of obtaining iron phosphate is relatively reduced. The specific process steps are as follows:

[0138] S31', the initially selected ferric phosphate powder C and water are mixed at a mass ratio of 1:10 and added to the reactor. The mixture is continuously heated and stirred at a rate of 200-400 r / min for 2-3 hours at a temperature of 80-90℃. After filtration, filter residue D and ferric phosphate solution dissolved in hot water are obtained. The mixture is cooled to room temperature and precipitated and filtered to obtain solid ferric phosphate dihydrate product E1 and filtrate F1.

[0139] Ferric phosphate (FePO4) is not readily soluble in water at room temperature, but it can partially dissolve at high temperatures, although this requires a certain temperature and time. In hot water, the solubility of ferric phosphate increases with increasing temperature, thus requiring a certain amount of time to dissolve.

[0140] S32': Filter residue D and 30% hydrogen peroxide are mixed at a mass ratio of 1:3, and the mixture is heated to 50°C at a rate of 8°C / min. After thorough stirring, the mixture is kept at this temperature for 1 hour, and then filtered to obtain solid product E2 of ferric phosphate dihydrate and filtrate F2.

[0141] When ferrous dihydrogen phosphate solution comes into contact with hydrogen peroxide, a redox reaction occurs, producing ferric phosphate and sodium hydroxide solution.

[0142] S33', ferric phosphate dihydrate solid product E1 and ferric phosphate dihydrate solid product E2 are rinsed and washed 3-4 times with distilled water, and then dried in a drying oven at 110-170℃ for 8-10 hours to obtain pure ferric phosphate dihydrate.

[0143] S34', by calcining the ferric phosphate dihydrate at 600°C for 1-2 hours, battery-grade anhydrous ferric phosphate product can be obtained.

[0144] This invention discloses a method for extracting iron phosphate from lithium iron phosphate residue after lithium extraction. By testing the residue, the extraction process is made more efficient. Physical magnetic separation removes some impurities, further improving the extraction efficiency. A higher-performance extraction method makes iron phosphate extraction more effective, resulting in higher leaching rates of iron and phosphorus. A more environmentally friendly extraction method ensures alternative solutions are available when environmental requirements necessitate them. Therefore, through these three steps, the "three-efficiency" approach achieves efficient, high-value, and highly purified recycling of iron phosphate residue from lithium iron phosphate extraction waste.

[0145] Furthermore, the iron phosphate prepared according to the method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate according to the embodiments of the present invention.

[0146] Furthermore, according to the embodiments of the present invention, the application of iron phosphate prepared by the method of extracting iron phosphate from the waste residue after lithium extraction of lithium iron phosphate in lithium iron phosphate batteries is proposed, and a method for manufacturing lithium iron phosphate batteries is proposed. The iron phosphate prepared by the method of extracting iron phosphate from the waste residue after lithium extraction of lithium iron phosphate according to the embodiments of the present invention is used to manufacture lithium iron phosphate batteries.

[0147] It should be noted that in the description of this invention, the term "embodiment," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment or comparative example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0148] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate, characterized in that, First, the waste residue after lithium extraction from lithium iron phosphate is pre-selected through magnetic separation, and then refined to obtain battery-grade anhydrous iron phosphate product. The specific steps are as follows: S21 involves drying and crushing the waste residue after lithium extraction from lithium iron phosphate, grinding it in an elliptical ball mill, and then passing it through a 200-220 mesh sieve to obtain lithium iron phosphate waste residue powder with a particle size of 0.065-0.074 mm. S22, the waste residue powder after lithium extraction from lithium iron phosphate is conveyed to a magnetic separator by a conveyor belt for magnetic separation, and the magnetic flux density of the magnetic separator is set to 9000-10000Gs; S23, repeat step S22 above 4-5 times to obtain the initially selected iron phosphate powder C; S31, mix the iron phosphate powder C initially selected in S23 with ammonia water with a concentration of 20% at a mass ratio of 1:3 to form a slurry; S32, add chelating agent to the above slurry, mix and add to the reaction vessel, wherein the chelating agent and the initially selected iron phosphate refining powder C are mixed in a mass percentage ratio of 0.05:1; S33 was stirred at 200-400 r / min for 2-3 hours at 80-90℃. After the reaction was completed, it was filtered immediately to obtain ammonium phosphate filtrate and ferric hydroxide filter residue. S34, Cool the ammonium phosphate filtrate from S33 at room temperature, and place the ferric hydroxide filter residue in a drying oven and dry it at a temperature of 40-80°C for 2-3 hours; S35, put the dried ferric hydroxide filter residue and a 45% sulfuric acid solution into a container at a mass ratio of 1:4, and stir at a rate of 600 r / min for 1-2 hours at room temperature of 25-30℃. S36, add polyvinylpyrrolidone as a dispersant, the mass ratio of the dispersant to the added ferric hydroxide filter residue is 1:20, and at the same time, heat to 60°C and continue stirring in an inert gas atmosphere for 30 minutes. While stirring, add the cooled ammonium phosphate filtrate from step S34 dropwise. S37, after stirring at 50-60℃ for 4-5 hours, cool to room temperature and filter to obtain filtrate containing ammonium sulfate and ferric phosphate dihydrate filter residue; S38. The ferric phosphate dihydrate filter residue is washed 2-3 times with anhydrous ethanol, then rinsed and washed 3-4 times with distilled water, and dried in a drying oven at 110-170℃ for 8-10 hours to obtain pure ferric phosphate dihydrate. S39, calcining the ferric phosphate dihydrate at 600°C in an inert gas atmosphere for 1-2 hours yields battery-grade anhydrous ferric phosphate.

2. The method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate according to claim 1, characterized in that, Prior to the magnetic separation step, a step is also included to detect the iron and phosphorus content in the waste residue after lithium iron phosphate extraction, specifically: S10, take 100 grams of lithium iron phosphate residue after lithium extraction, grind it into powder A, and control the particle size of powder A to be between 300-325 mesh. S11, Add powder A to a 250ml wide-mouth polypropylene bottle; S12, add 100ml of ethanol, put it in an ultrasonic cleaner and clean for 20-30 seconds, repeat 2-3 times; S13, add 150ml of weakly acidic ionized water with a pH value between 6.6 and 6.9, put it in an ultrasonic cleaner and clean for 30 seconds, repeat 4-5 times, filter out the water to get powder B; S14, add 10 ml of aqua regia to a wide-mouth polypropylene bottle containing the above powder B to form a solution, and add pure water to the 200 ml mark. S15, heat the solution to 80-90℃ and maintain for 10-20 minutes; S16, cool the solution to room temperature of 25-27°C, and add pure water to the 200ml mark; S17, the content of iron and phosphorus in the solution was detected by ICP-MS.

3. The method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate according to claim 2, characterized in that, The waste residue from lithium iron phosphate extraction, which has an iron content of over 20% by mass and a phosphorus content of over 10% by mass after ICP-MS analysis, is used as the raw material for refining iron phosphate.

4. The method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate according to claim 1, characterized in that, In step S32, the chelating agent is selected from at least one of hydroxyethylidene diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, or 2-hydroxyphosphonoacetic acid.

5. The method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate according to claim 1, characterized in that, In S33, the ferric hydroxide filter residue exists in the form of Fe2O3·3H2O.

6. The method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate according to claim 1, characterized in that, The polyvinylpyrrolidone added to S36 is one or more of PVP-K15, PVP-K30, PVP-K60 and PVPK90.

7. A method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate, characterized in that, First, the waste residue after lithium extraction from lithium iron phosphate is pre-selected through magnetic separation, and then refined to obtain battery-grade anhydrous iron phosphate product, specifically as follows: S21 involves drying and crushing the waste residue after lithium extraction from lithium iron phosphate, grinding it in an elliptical ball mill, and then passing it through a 200-220 mesh sieve to obtain lithium iron phosphate waste residue powder with a particle size of 0.065-0.074 mm. S22, the waste residue powder after lithium extraction from lithium iron phosphate is conveyed to a magnetic separator by a conveyor belt for magnetic separation, and the magnetic flux density of the magnetic separator is set to 9000-10000Gs; S23, repeat step S22 above 4-5 times to obtain the initially selected iron phosphate powder C; S31', the initially selected ferric phosphate powder C and water are mixed at a mass ratio of 1:10 and added to the reactor. The mixture is continuously heated and stirred at a rate of 200-400 r / min for 2-3 hours at a temperature of 80-90℃. After filtration, filter residue D and ferric phosphate solution dissolved in hot water are obtained. After cooling to room temperature, precipitate and filter to obtain solid ferric phosphate dihydrate product E1 and filtrate F1. S32', filter residue D and 30% hydrogen peroxide are mixed at a mass ratio of 1:3, and heated to 50°C at a rate of 8°C / min. After thorough stirring, the mixture is kept at this temperature for 1 hour, and then filtered to obtain solid product E2 of ferric phosphate dihydrate and filtrate F2. S33', ferric phosphate dihydrate solid product E1 and ferric phosphate dihydrate solid product E2 are rinsed and washed 3-4 times with distilled water, and then dried in a drying oven at 110-170℃ for 8-10 hours to obtain pure ferric phosphate dihydrate. S34', by calcining the ferric phosphate dihydrate at 600°C for 1-2 hours, battery-grade anhydrous ferric phosphate product can be obtained.

8. The method for extracting iron phosphate from the waste residue after lithium extraction from lithium iron phosphate according to claim 7, characterized in that, It also includes a step for detecting the iron and phosphorus content in the waste residue after lithium iron phosphate extraction, specifically: S10, take 100 grams of lithium iron phosphate residue after lithium extraction, grind it into powder A, and control the particle size of powder A to be between 300-325 mesh. S11, Add powder A to a 250ml wide-mouth polypropylene bottle; S12, add 100ml of ethanol, put it in an ultrasonic cleaner and clean for 20-30 seconds, repeat 2-3 times; S13, add 150ml of weakly acidic ionized water with a pH value between 6.6 and 6.9, put it in an ultrasonic cleaner and clean for 30 seconds, repeat 4-5 times, filter out the water to get powder B; S14, add 10 ml of aqua regia to a wide-mouth polypropylene bottle containing the above powder B to form a solution, and add pure water to the 200 ml mark. S15, heat the solution to 80-90℃ and maintain for 10-20 minutes; S16, cool the solution to room temperature of 25-27°C, and add pure water to the 200ml mark; S17, the content of iron and phosphorus in the solution was detected by ICP-MS.

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