Recycling method of lithium iron phosphate battery waste

Abstract

The invention relates to the technical field of recycling of waste battery materials, and discloses a recycling method of lithium iron phosphate battery waste, which comprises the following steps: carrying out sufficient acid leaching on the lithium iron phosphate battery waste, and carrying out solid-liquid separation to obtain a leachate; adding a sufficient amount of iron ion complexing agent competing with phosphate radicals and a sufficient amount of lithium precipitation inhibitor competing with lithium ions into the leachate, and diluting to obtain a mixed solution; the temperature is controlled to be 20-50 DEG C, alkali liquor is gradually added into the mixed solution, when the pH value of the solution reaches 3.5-4.5, the alkali liquor continues to be added, oxygen is introduced into the solution at the same time, when ferrous iron in the solution is oxidized to 30-40%, oxygen introduction is stopped, the condition is maintained for 8-12 min, after it is detected that a ferroferric oxide product appears in a system, the pH value of the solution is rapidly adjusted to 7.5-8.5, and the ferroferric oxide product is obtained. Fully aging to obtain slurry containing ferroferric oxide; and ferroferric oxide is extracted from the slurry. According to the method, ferroferric oxide with relatively high purity can be recovered and obtained.

Description

Technical Field

[0001] This invention relates to the field of recycling technology for waste battery materials, and more specifically, to a method for recycling waste lithium iron phosphate batteries. Background Technology

[0002] With the widespread adoption of new energy vehicles and portable electronic devices, the application scope of lithium-ion batteries is expanding daily. Lithium-ion batteries, especially those using lithium iron phosphate (LFP) as the cathode material, occupy a crucial position in electric vehicles and energy storage batteries due to their high energy density, long cycle life, and excellent safety performance. However, as these batteries reach the end of their lifespan, the disposal of used LFP batteries has become a pressing issue. This not only relates to the effective utilization of resources but also to the prevention and control of environmental pollution. Currently, recycling methods for used LFP batteries mainly include high-temperature solid-phase recycling, high-temperature solid-phase remediation, liquid-phase wet recycling, bioleaching recycling, and high-energy mechanical-chemical activation recycling. Each of these methods has its limitations. For example, high-temperature solid-phase recycling suffers from high energy consumption, the generation of toxic gases, and low product purity; liquid-phase wet recycling generates large amounts of wastewater and cannot achieve full component recycling; bioleaching and mechanical-chemical activation recycling suffer from long cycles and low efficiency. Furthermore, existing recycling methods often require fine grinding and drying, which not only increases process complexity but also contradicts the principles of reducing carbon emissions and green production. Therefore, developing a method for the efficient, environmentally friendly, and economical recycling of spent lithium iron phosphate batteries, especially achieving the efficient extraction and purification of valuable metals, is of significant practical importance and application value. This can not only reduce resource waste but also alleviate the pressure of lithium resource imports, providing strong support for the healthy development of my country's new energy industry. Furthermore, optimizing the recycling process to reduce energy consumption and environmental impact aligns with the concepts of green manufacturing and sustainable development.

[0003] To this end, many patents have made innovative efforts, for example: CN113443640A discloses a method for preparing battery-grade lithium carbonate and iron phosphate from waste lithium iron phosphate black powder. This method involves acid leaching to extract lithium under oxidative conditions and then precipitating lithium, followed by a second acid leaching of the iron-phosphorus slag to precipitate iron. This method can efficiently separate and recover iron, lithium, and phosphorus elements. However, with industry development, the market for iron phosphate products is saturated, and lithium carbonate is also under pressure. Furthermore, due to changes in the raw materials required for fourth-generation high-pressure lithium iron phosphate, lithium phosphate and lithium dihydrogen phosphate are gradually gaining market favor. CN117303330A discloses a method for preparing battery-grade lithium dihydrogen phosphate from lithium iron phosphate waste. The method first adds lithium iron phosphate powder to an oxalic acid solution, followed by stirring, filtration, EDTA complexation, heating, and filtration to obtain a purified lithium dihydrogen phosphate solution. Battery-grade lithium dihydrogen phosphate is then obtained through evaporation and cooling crystallization. This method selectively removes iron from lithium iron phosphate and recovers lithium and phosphorus. However, oxalic acid, as a moderately strong acid, has poor leaching efficiency for elements in lithium iron phosphate, requiring a larger theoretical acid dosage, increasing costs, adjusting pH, and the precipitation of impurities along with ferrous oxalate, resulting in low iron utilization.

[0004] Therefore, in the existing lithium iron phosphate recycling routes, the market for the products iron phosphate and lithium carbonate is approaching saturation, and lithium phosphate is gradually showing its value. However, the process focuses on the recovery of phosphorus and lithium elements, while iron elements are not effectively utilized. Iron elements become solid waste along with carbon slag, or generate iron oxide red and iron-containing products with low purity, resulting in low iron element utilization.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for recycling waste lithium iron phosphate batteries, aiming to improve at least one of the problems mentioned in the background art.

[0007] This invention is implemented as follows: This invention provides a method for recycling waste lithium iron phosphate batteries, comprising: The waste lithium iron phosphate battery material is thoroughly acid-leached, and the leachate is obtained after solid-liquid separation. Add sufficient iron ion complexing agent that competes with phosphate and sufficient lithium precipitation inhibitor that competes with lithium ions to the leachate, and dilute to avoid precipitation in the solution to obtain a mixed solution. Control the temperature of the mixed liquor at 20~50℃, gradually add alkali solution to the mixed liquor, and when the pH of the solution reaches 3.5~4.5, continue to add alkali solution and simultaneously introduce oxygen into the solution. When the ferrous iron in the solution is oxidized to 30~40%, stop the oxygen introduction and maintain for 8~12 minutes. After that, when the presence of ferric oxide products is detected in the system, adjust the pH of the solution to 7.5~8.5 within 10 minutes. After sufficient aging, a slurry containing ferric oxide is obtained. Ferric oxide was extracted from the slurry.

[0008] In an optional embodiment, the iron ion complexing agent is selected from at least one of sodium citrate, sodium tartrate, and disodium ethylenediaminetetraacetate; And / or, the lithium precipitation inhibitor is selected from at least one of sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, sodium nitrate, and potassium nitrate; Alternatively, alkali solution may be added slowly to the mixture, ensuring that the pH of the solution reaches 3.5-4.5 within at least 30 minutes.

[0009] In an optional embodiment, the acid used in the acid leaching step is at least one of sulfuric acid, nitric acid, and hydrochloric acid; Optionally, when the acid used for acid leaching is sulfuric acid, the sulfuric acid and lithium iron phosphate battery waste are fed in a molar ratio of H2SO4:Li of 1.0~2.0:1. Optionally, the concentration of sulfuric acid used for acid leaching is 1.0~2.0 mol / L. Optionally, when the acid used for acid leaching is hydrochloric acid, the hydrochloric acid and lithium iron phosphate battery waste are fed in a molar ratio of HCl:Li of 2.5~3.5:1. Optionally, the concentration of hydrochloric acid used for acid leaching is 0.6~1.4 mol / L; Optionally, when the acid used for acid leaching is nitric acid, the nitric acid and lithium iron phosphate battery waste are fed in an HNO3:Li molar ratio of 2.5 to 3.5:1. Optionally, the concentration of nitric acid used for acid leaching is 1.4~2.8 mol / L.

[0010] In an optional embodiment, the solid-liquid ratio during acid leaching is 1:3 to 6.

[0011] In an optional embodiment, the dosage of the iron ion complexing agent is 0.1~0.6 mol / L; And / or, the dosage of lithium precipitation inhibitor is 1.0~2.0 mol / L.

[0012] In an optional implementation, dilution is performed to avoid precipitation in the solution as follows: Dilute the solution containing iron ion complexing agents and lithium precipitation inhibitors by 2 to 10 times the volume.

[0013] In an optional implementation, the method for extracting ferric oxide from the slurry includes: The slurry was treated with magnetic separation to obtain primary iron oxide and lithium liquid; The initial product of ferric oxide was washed with dilute acid for 1-15 minutes and then the solid and liquid were separated to obtain a solid and a filtrate. The solid was washed multiple times with pure water and then dried to obtain the ferric oxide product. Optionally, the dilute acid is selected from at least one of hydrochloric acid, citric acid, sulfuric acid, nitric acid, oxalic acid, and acetic acid; Optionally, the concentration of the dilute acid is 0.01~0.04 mol / L.

[0014] In an optional implementation, after obtaining the lithium liquid: Concentrate the lithium liquid 2 to 10 times to obtain a concentrated solution; The concentrate was frozen at -15~-10℃ to precipitate sulfate impurities, and the solid-liquid separation yielded lithium precipitation solution. Lithium hydroxide was added to the lithium precipitation solution according to the stoichiometric ratio of lithium to phosphorus in lithium phosphate or a ratio range close to that of phosphorus. The solution was then heated to precipitate the precipitate. Lithium hydroxide was added again until the pH was 11-12. The solution was then fully aged to obtain a slurry containing lithium phosphate. The slurry containing lithium phosphate is subjected to solid-liquid separation to obtain a solid, which is then washed and dried to obtain anhydrous lithium phosphate.

[0015] In an optional embodiment, the temperature is raised to 70~100°C to precipitate the precipitate; Optionally, the aging time after precipitation is 1.5 to 2.5 hours.

[0016] In an optional embodiment, after the slurry containing lithium phosphate is subjected to solid-liquid separation to obtain a solid, the solid is washed with hot water at a temperature of 70~100°C. Optionally, after washing, the product is dried at a temperature of 180~220℃ for 5~7 hours.

[0017] The present invention has the following beneficial effects: The method for recycling lithium iron phosphate battery waste provided in this invention involves adding a complexing agent to the acid leaching solution to complex iron ions, creating a competitive relationship with phosphate ions and inhibiting the formation of precipitation by combining iron and phosphate ions. In the lithium precipitation inhibitor, positively valent ions can combine with phosphate and hydrogen phosphate ions, competing with lithium ions. Simultaneously, the presence of positively valent ions reduces the activity of lithium ions, hindering their combination with phosphate and hydrogen phosphate ions to form precipitation. The addition of the inhibitor increases the ionic strength of the solution, resulting in a large number of positively valent ions and negatively valent ions such as Na+ in the solution. + and SO4 2- Forming an ionic atmosphere to shield Li + With anions (such as PO4) 3- HPO4 2- Electrostatic attraction between the two is utilized. After adding an iron ion complexing agent and a lithium precipitation inhibitor, dilution is performed to ensure that the low concentration does not form a precipitate. After obtaining the mixture, the initial pH is adjusted to 3.5-4.5 at low temperature to prevent excessively high local pH when adding alkaline solution, which could lead to the formation of ferrous hydroxide precipitate before iron(III) oxide (Fe3O4) is formed. 30-40% of ferrous ions are slowly oxidized to prevent over-oxidation and the formation of ferric hydroxide precipitate, while maintaining this oxidation for a certain period to ensure complete oxidation of ferrous ions. Once iron(III) oxide (Fe3O4) is formed, the pH of the solution is further adjusted to ensure continued formation of Fe3O4. The reaction is carried out at low temperature to inhibit the nucleation and growth of lithium phosphate and lithium dihydrogen phosphate, ensuring product purity.

[0018] Therefore, the recycling method provided by this invention can recover iron from waste lithium iron phosphate batteries and generate iron(III) oxide with high purity. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A process flow diagram of the recycling method provided by the present invention; Figure 2 The X-ray diffraction pattern of the iron(III) oxide prepared in Example 1 is shown below. Figure 3 The image shows the X-ray diffraction pattern of lithium phosphate prepared in Example 1. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0023] This invention provides a method for recycling waste lithium iron phosphate batteries, comprising: The waste lithium iron phosphate battery material is thoroughly acid-leached, and the leachate is obtained after solid-liquid separation. Add sufficient iron ion complexing agent that competes with phosphate and sufficient lithium precipitation inhibitor that competes with lithium ions to the leachate, and dilute to avoid precipitation in the solution to obtain a mixed solution. Control the temperature of the mixed liquor at 20~50℃, gradually add alkali solution to the mixed liquor, and when the pH of the solution reaches 3.5~4.5, continue to add alkali solution and simultaneously introduce oxygen into the solution. When the ferrous iron in the solution is oxidized to 30~40%, stop the oxygen introduction and maintain for 8~12 minutes. After that, when the presence of ferric oxide products is detected in the system, adjust the pH of the solution to 7.5~8.5 within 10 minutes. After sufficient aging, a slurry containing ferric oxide is obtained. Ferric oxide was extracted from the slurry.

[0024] The method for recycling lithium iron phosphate battery waste provided in this invention involves adding a complexing agent to the acid leaching solution to complex iron ions, creating a competitive relationship with phosphate ions and inhibiting the formation of precipitation by combining iron and phosphate ions. In the lithium precipitation inhibitor, positively valent ions can combine with phosphate and hydrogen phosphate ions, competing with lithium ions. Simultaneously, the presence of positively valent ions reduces the activity of lithium ions, hindering their combination with phosphate and hydrogen phosphate ions to form precipitation. The addition of the inhibitor increases the ionic strength of the solution, resulting in a large number of positively valent ions and negatively valent ions such as Na+ in the solution. + and SO4 2- Forming an ionic atmosphere to shield Li + With anions (such as PO4) 3- HPO4 2- Electrostatic attraction between the two is utilized. After adding an iron ion complexing agent and a lithium precipitation inhibitor, dilution is performed to ensure that the low concentration does not form a precipitate. Once the mixture is obtained, the initial pH is adjusted to 3.5-4.5 at low temperature to prevent excessively high local pH when adding alkali, which could lead to the formation of ferrous hydroxide precipitate before iron(III) oxide (Fe3O4) is formed. 30-40% of the ferrous ions are slowly oxidized to prevent over-oxidation and the formation of ferric hydroxide precipitate, while maintaining this oxidation for a certain period to ensure complete oxidation of the ferrous ions. Once iron(III) oxide (Fe3O4) is formed, the pH of the solution is further adjusted to ensure continued formation of Fe3O4. The reaction is carried out at low temperature to inhibit the nucleation and growth of lithium phosphate and lithium dihydrogen phosphate, ensuring product purity.

[0025] Specifically, such as Figure 1 As shown, the recycling method is as follows: S1, Acid Immersion (1) Mix the lithium iron phosphate battery waste with acid to fully dissolve the substances in the lithium iron phosphate battery waste that can be dissolved in the acid, and then perform solid-liquid separation to obtain leachate and carbon residue.

[0026] Optionally, the acid used in the pickling step is at least one of sulfuric acid, nitric acid, and hydrochloric acid.

[0027] When sulfuric acid is used for acid leaching, the sulfuric acid and lithium iron phosphate battery waste are fed in a molar ratio of H2SO4:Li of 1.0~2.0:1.

[0028] Optionally, the molar ratio of H2SO4:Li is selected from any value of 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.7, 1.8, 1.9, 2.0 or a range between the two. Preferably, it is 1.8:1.

[0029] Optionally, the concentration of sulfuric acid used for acid leaching is 1.0~2.0 mol / L.

[0030] Optionally, the sulfuric acid concentration is selected from any value or a range between 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.9 mol / L, and 2.0 mol / L.

[0031] (2) When the acid used for acid leaching is hydrochloric acid, the hydrochloric acid and lithium iron phosphate battery waste are fed in a molar ratio of HCl:Li of 2.5~3.5:1.

[0032] Optionally, the molar ratio of HCl:Li is any value selected from 2.5, 2.6, 2.7, 2.8, 2.9, 3.1, 3.2, 3.3, 3.4, 3.5, or a range between the two. Preferably, it is 3.2:1.

[0033] Optionally, the concentration of hydrochloric acid used for acid leaching is 0.6~1.4 mol / L.

[0034] Optionally, the hydrochloric acid concentration is any value or a range between 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, and 1.4 mol / L.

[0035] (3) When the acid used for acid leaching is nitric acid, the nitric acid and lithium iron phosphate battery waste are fed in a molar ratio of HNO3:Li of 2.5~3.5:1.

[0036] Optionally, the molar ratio of HNO3:Li is any value selected from 2.5, 2.6, 2.7, 2.8, 2.9, 3.1, 3.2, 3.3, 3.4, and 3.5, or a range between both. Preferably, it is 3.1:1.

[0037] Optionally, the concentration of nitric acid used for acid leaching is 1.4~2.8 mol / L.

[0038] Optionally, the nitric acid concentration is selected from any value or a range between 1.4 mol / L, 1.5 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, 2.7 mol / L, and 2.8 mol / L.

[0039] Optionally, the solid-liquid ratio in the acid leaching process is 1:3 to 6.

[0040] Furthermore, in the acid leaching process, the solid-liquid ratio is selected from any value or a range between 1:3, 1:3.2, 1:3.5, 1:3.8, 1:4, 1:4.5, 1:4.8, 1:5, 1:5.2, 1:5.5, 1:5.9, and 1:6.

[0041] Preferably, the solid-liquid ratio is 1:3. This solid-liquid ratio ensures that the water consumption is not excessive and that the viscosity is suitable, preventing problems with uneven dispersion.

[0042] S2, Leachate Preparation Add sufficient amounts of an iron ion complexing agent that competes with phosphate and a lithium precipitation inhibitor that competes with lithium ions to the leachate, and dilute it to ensure that its concentration is low enough to prevent precipitation.

[0043] Optionally, the iron ion complexing agent is selected from at least one of sodium citrate, sodium tartrate, and disodium EDTA.

[0044] Optionally, the dosage of the iron ion complexing agent is 0.1~0.6 mol / L (0.1~0.6 mol per liter of leachate). At this dosage, it can be ensured that the iron ions are fully complexed and iron precipitation is avoided.

[0045] Optionally, the concentration of the complexing agent is selected from any value or a range between 0.1 mol / L, 0.12 mol / L, 0.15 mol / L, 0.2 mol / L, 0.24 mol / L, 0.26 mol / L, 0.28 mol / L, 0.3 mol / L, 0.31 mol / L, 0.32 mol / L, 0.33 mol / L, 0.35 mol / L, 0.37 mol / L, 0.38 mol / L, 0.4 mol / L, 0.41 mol / L, 0.42 mol / L, 0.44 mol / L, 0.45 mol / L, 0.47 mol / L, 0.48 mol / L, 0.5 mol / L, 0.52 mol / L, 0.54 mol / L, 0.55 mol / L, 0.56 mol / L, 0.59 mol / L, and 0.6 mol / L.

[0046] Preferably, the concentration of the complexing agent is 0.5 mol / L. This dosage ensures better chelation of iron ions and effectively prevents residues from entering subsequent products.

[0047] Optionally, the lithium precipitation inhibitor is selected from at least one of sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, sodium nitrate, and potassium nitrate.

[0048] Optionally, the dosage of the lithium precipitation inhibitor is 1.0~2.0 mol / L (1.0~2.0 mol per liter of leachate) with an H2SO4:Li molar ratio of [value missing]. At this dosage, lithium ion precipitation can be sufficiently suppressed.

[0049] Optionally, the concentration of the lithium precipitation inhibitor is selected from any value or a range between 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, and 2.0 mol / L.

[0050] Optionally, the concentration of the lithium precipitation inhibitor is 1.6 mol / L. At this concentration, lithium precipitation can be effectively inhibited, while avoiding the difficulty of subsequent cleaning and impurity removal by adding excessive amounts of the inhibitor.

[0051] Optionally, the dilution factor can be 2 to 10 times the volume. This dilution factor ensures that the concentrations of lithium, phosphorus, and iron in the mixture are at a low level.

[0052] Optionally, the dilution factor is selected from any value of 2, 3, 4, 5, 6, 7, 8, 9, and 10, or a range between both. Preferably, the dilution factor is 5.

[0053] S3, Sinking Iron Control the temperature of the mixed liquor at 20~50℃, slowly add alkali solution to the mixed liquor, and ensure that the pH of the solution reaches 3.5~4.5 after at least 30 minutes. When it reaches 3.5~4.5, continue to add alkali solution and simultaneously introduce oxygen into the solution. When the ferrous iron in the solution is oxidized to 30~40%, stop the oxygen introduction and maintain it for 8~12 minutes. After that, after the appearance of ferric oxide products in the system is detected, adjust the pH of the solution to 7.5~8.5 within 10 minutes. After sufficient aging, a slurry containing ferric oxide is obtained.

[0054] In this step, temperature control, pH control at each stage, and the point at which oxygen supply is stopped are all crucial factors affecting whether iron(III) oxide is formed.

[0055] Adding alkali at low temperatures slows the reaction rate, and gradually adjusting the pH to 3.5-4.5 further ensures a slower reaction. Oxygen is introduced only when the pH reaches this range to oxidize ferrous iron. Introducing oxygen too early will over-oxidize ferrous iron, easily forming ferric hydroxide; introducing oxygen too late will reach the pH required for ferrous iron precipitation, forming ferrous hydroxide. Oxygen introduction is stopped when ferrous iron is oxidized to 30-40% to prevent over-oxidation and ferric hydroxide precipitation. After stopping oxygen introduction, maintain the solution for a certain period to ensure complete oxidation of ferrous iron to form magnetite (Fe3O4) without forming ferric iron (Fe3O4). When magnetite forms, the pH is rapidly adjusted to ensure continued magnetite formation. The entire reaction is carried out at low temperatures to inhibit the nucleation and growth of lithium phosphate and lithium hydrogen phosphate, ensuring product purity. Excessively high pH can lead to the formation of insoluble lithium phosphate; therefore, pH adjustment must be rapid (within 10 minutes) while maintaining a slightly alkaline solution.

[0056] Optionally, the pH of the solution can be adjusted to 7.5-8.5 within 10 minutes. The specific pH can be any value among 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4 and 8.5 or a range between the two.

[0057] S4, pickling The slurry obtained from S3 was subjected to magnetic separation to obtain primary iron oxide and lithium liquid.

[0058] The initial ferric oxide product was washed with dilute acid for 1-15 minutes, followed by solid-liquid separation to obtain a solid and a filtrate. The solid was washed multiple times with pure water and then dried to obtain the ferric oxide product.

[0059] This step involves briefly stirring the initial iron oxide product with dilute acid, which dissolves solid impurities of lithium and phosphorus compounds adhering to the surface of the iron oxide, thereby purifying the iron oxide.

[0060] Optionally, the dilute acid is selected from at least one of hydrochloric acid, citric acid, sulfuric acid, nitric acid, oxalic acid, and acetic acid.

[0061] Optionally, the concentration of the dilute acid is 0.01~0.04 mol / L.

[0062] Optionally, the concentration of the dilute acid is selected from any value or a range between 0.01 mol / L, 0.012 mol / L, 0.015 mol / L, 0.016 mol / L, 0.018 mol / L, 0.02 mol / L, 0.022 mol / L, 0.024 mol / L, 0.026 mol / L, 0.028 mol / L, 0.029 mol / L, 0.03 mol / L, 0.031 mol / L, 0.032 mol / L, 0.035 mol / L, 0.037 mol / L, 0.039 mol / L, and 0.04 mol / L.

[0063] Optionally, dilute acid washing can convert the small amount of sparingly soluble lithium phosphate and dilithium hydrogen phosphate generated on the product surface into soluble lithium dihydrogen phosphate, achieving solid-liquid separation. The solid is then washed with pure water to improve purity.

[0064] Optionally, the mass ratio of dilute acid to iron(III) oxide is 2 to 5:1 (e.g., 2:1, 3:1 or 5:1, or a range of the aforementioned values).

[0065] S5, Lithium precipitate (1) Concentrate the lithium liquid obtained in step S3 by 2 to 10 times to obtain a concentrated solution.

[0066] Optionally, the concentration factor is selected from any value of 2, 3, 4, 5, 6, 7, 8, 9, and 10 times, or a range between both. Preferably, the concentration factor is 5 times.

[0067] (2) The concentrate is frozen at -15~-10℃ to precipitate sulfate impurities, and the solid-liquid separation yields lithium precipitation solution. The obtained sulfate impurities can be returned as lithium precipitation inhibitors.

[0068] Optionally, the freezing temperature is any value or a range between -15°C, -14°C, -13°C, -12°C, -11°C, and -10°C.

[0069] (3) Add lithium hydroxide to the lithium precipitation solution according to the stoichiometric ratio of lithium to phosphorus in lithium phosphate or the ratio range near it, then raise the temperature to precipitate the precipitate, continue to add lithium hydroxide until the pH is 11~12 to reach the reaction endpoint, and fully age to obtain a slurry containing lithium phosphate.

[0070] Optionally, the lithium-phosphorus ratio is 2.90~3.15:1.

[0071] Optionally, the lithium-phosphorus molar ratio is selected from any value or a range between 2.90:1, 2.91:1, 2.92:1, 2.93:1, 2.94:1, 2.95:1, 2.96:1, 2.97:1, 2.98:1, 2.99:1, 3.00:1, 3.10:1, 3.12:1, 3.13:1, 3.14:1, and 3.15:1. Preferably, the lithium-phosphorus molar ratio is 3.10:1.

[0072] Optionally, the temperature can be raised to 70~100℃ to precipitate the precipitate.

[0073] Optionally, the heating temperature is selected from any value or a range between 70°C, 71°C, 72°C, 76°C, 78°C, 80°C, 81°C, 83°C, 85°C, 87°C, 88°C, 90°C, 91°C, 92°C, 94°C, 95°C, 97°C, 98°C, 99°C, and 100°C. Preferably, lithium deposition is performed at a temperature of 90°C.

[0074] The slurry containing lithium phosphate is subjected to solid-liquid separation to obtain a solid, which is then washed and dried to obtain anhydrous lithium phosphate.

[0075] Optionally, lithium hydroxide is added to a pH value of any one of 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, and 12.0, or a range between both.

[0076] If the pH of the endpoint reaction is too low, lithium dihydrogen phosphate is easily formed, and the precipitation is incomplete. If the pH is too high, the reaction vessel is easily corroded, and the amount of raw materials used is increased. Therefore, it is necessary to reasonably control the pH value of the endpoint reaction. If the reaction temperature is too low, lithium phosphate nucleation and growth are difficult, and the reaction rate is low. High temperature is beneficial to increase the reaction rate. Therefore, the lithium precipitation process is carried out at high temperature. Because of the presence of the complexing agent, impurities such as calcium, magnesium and iron are in the solution and are not mixed into the lithium phosphate solid. Soluble positive salts are easily soluble in hot water and can be removed by stirring and washing. At the same time, due to the precipitation of impurities by freezing, the sulfate content is reduced, so the lithium phosphate with high purity is obtained.

[0077] Optionally, the aging time after precipitation is 1.5 to 2.5 hours.

[0078] Optionally, the aging time is selected from any value of 1.5h, 1.8h, 2h, 2.3h and 2.5h or a range between the two.

[0079] (4) After the slurry containing lithium phosphate is separated into solid and liquid, the solid is washed with hot water at a temperature of 70~100℃ (e.g., 70℃, 80℃, 90℃ or 100℃, or a range of the above values).

[0080] Optionally, after washing, the product is dried at a temperature of 180~220℃ (e.g., 180℃, 190℃, 200℃ or 220℃, or a range of the above values) for a time of 5~7h (e.g., 5h, 6h or 7h, or a range of the above values).

[0081] Example 1 S1. Provide lithium iron phosphate waste powder and add 1.75 mol / L dilute sulfuric acid solution at a solid-liquid ratio of 1:5. The molar ratio of H2SO4:Li is approximately 1.5:1. Mix evenly and allow it to react fully for 3 hours. Filter to obtain leachate and carbon slag.

[0082] S2. Add iron ion complexing agents to the leachate, namely 0.5 mol / L sodium citrate and 0.2 mol / L disodium ethylenediaminetetraacetate, and add a lithium precipitation inhibitor, 1.6 mol / L sodium sulfate solution. Dilute the mixed solution 5 times to obtain a mixed solution.

[0083] S3. Heat the mixture to 40°C and slowly add 0.02 mol / L sodium carbonate solution. About 30 minutes after adding the sodium carbonate solution, bring the pH of the solution to about 4.0. At this time, continue to pass sodium carbonate solution through the bubble, and at the same time, slowly bubble oxygen into the solution at 50 mL / min to partially oxidize ferrous ions. When 40% of the ferrous ions are oxidized, stop bubbling oxygen to avoid excessive oxidation and the formation of ferric hydroxide precipitate. Maintain this for 10 minutes. After the product of ferric oxide appears, add alkali solution within 10 minutes to quickly adjust the pH of the solution to about 8.5 to ensure that the raw materials react completely. Aging for 2 hours yields a slurry containing ferric oxide.

[0084] S4. Perform magnetic separation on the slurry to obtain primary iron oxide and lithium liquid.

[0085] The obtained Fe3O4 primary product was added to twice its mass of 0.04 mol / L HCl solution and stirred to remove lithium-containing precipitate. It was then washed three times with 10 times its volume of pure water and then vacuum dried at 60°C for 6 hours to obtain the Fe3O4 product.

[0086] S5. Evaporate and concentrate the lithium liquid by 5 times to obtain concentrated liquid, and cool it to room temperature; The concentrate was placed in a freezer at -10°C to precipitate crystals. After centrifugation, sulfate crystals were obtained, which can be used to subsequently formulate lithium precipitation inhibitors. Lithium hydroxide was added to the liquid obtained from the previous centrifugation step to adjust the lithium-phosphorus molar ratio to 3.10:1. The mixture was stirred continuously and heated to 90°C, resulting in precipitation. A small amount of lithium hydroxide was added to adjust the pH of the solution to 12 to avoid the formation of dilithium hydrogen phosphate in the product at low pH, which would lead to product impurity. The mixture was aged for 2 hours, and then the solid and liquid were separated. The mixture was washed with hot water and dried at 200°C for 6 hours to obtain anhydrous lithium phosphate.

[0087] Example 2 S1. Provide lithium iron phosphate waste powder and add 1.0 mol / L dilute sulfuric acid solution at a solid-liquid ratio of 1:3. The molar ratio of H2SO4:Li is approximately 1:1. Mix evenly and allow it to react fully for 3 hours. Filter to obtain leachate and carbon slag.

[0088] S2. Add iron ion complexing agents to the leachate, namely 0.25 mol / L sodium citrate, 0.2 mol / L disodium ethylenediaminetetraacetate, and 0.1 mol / L sodium tartrate, and add a lithium precipitation inhibitor, 1.0 mol / L sodium sulfate solution. Dilute the mixed solution by 2 times to obtain a mixed solution.

[0089] S3. Heat the mixture to 50°C and slowly add 0.05 mol / L potassium hydroxide solution. After about 40 minutes of adding sodium carbonate solution, bring the pH of the solution to about 4.0. At this time, continue to pass sodium carbonate solution through the solution and simultaneously slowly bubble oxygen into the solution at 100 mL / min to partially oxidize ferrous ions. When 40% of ferrous ions are oxidized, stop bubbling oxygen to avoid excessive oxidation and the formation of ferric hydroxide precipitate. Maintain this for 10 minutes. After the appearance of ferric oxide product, add alkali solution within 10 minutes to quickly adjust the pH of the solution to about 8.0 to ensure complete reaction of the raw materials. Aging for 2 hours yields a slurry containing ferric oxide.

[0090] S4. Perform magnetic separation on the slurry to obtain primary iron oxide and lithium liquid.

[0091] The obtained Fe3O4 primary product was added to 5 times its mass of 0.01 mol / L HCl solution and stirred to remove lithium-containing precipitate. It was then washed three times with 10 times its volume of pure water and then vacuum dried at 60°C for 6 hours to obtain the Fe3O4 product.

[0092] S5. Evaporate and concentrate the lithium liquid by 2 times to obtain concentrated liquid, and cool it to room temperature; The concentrate was placed in a freezer at -10°C to precipitate crystals. After centrifugation, sulfate crystals were obtained, which can be used to subsequently formulate lithium precipitation inhibitors. Lithium hydroxide was added to the liquid obtained from the previous centrifugation step to adjust the lithium-phosphorus molar ratio to 2.90:1. The mixture was stirred continuously and heated to 90°C, resulting in precipitation. A small amount of lithium hydroxide was added to adjust the pH of the solution to 11 to avoid the formation of dilithium hydrogen phosphate in the product at low pH, which would lead to product impurity. The mixture was aged for 2 hours, and then the solid and liquid were separated. The mixture was washed with hot water and dried at 200°C for 6 hours to obtain anhydrous lithium phosphate.

[0093] Example 3 S1. Provide waste lithium iron phosphate powder and add it at a solid-liquid ratio of 1:4. 2Mix 0 mol / L dilute sulfuric acid solution with H2SO4:Li molar ratio of approximately 1.7:1 until homogeneous and allow to react fully for 3 hours. Filter to obtain leachate and carbon residue.

[0094] S2. Add iron ion complexing agents to the leachate, namely 0.3 mol / L sodium citrate, 0.1 mol / L disodium ethylenediaminetetraacetate, and 0.2 mol / L sodium tartrate, and add a lithium precipitation inhibitor, 2.0 mol / L sodium sulfate solution. Dilute the mixed solution 10 times to obtain a mixed solution.

[0095] S3. Heat the mixture and maintain it at 20°C. Slowly add 0.01 mol / L potassium hydroxide solution. About 50 minutes after adding sodium carbonate solution, adjust the pH of the solution to about 3.5. At this time, continue to pass sodium carbonate solution through the solution and simultaneously slowly bubble oxygen into the solution at 40 mL / min to partially oxidize ferrous ions. When 40% of ferrous ions are oxidized, stop bubbling oxygen to avoid excessive oxidation and the formation of ferric hydroxide precipitate. Maintain this for 10 minutes. After the appearance of ferric oxide product, add alkali solution within 10 minutes to quickly adjust the pH of the solution to about 7.5 to ensure complete reaction of the raw materials. Aging for 2 hours yields a slurry containing ferric oxide.

[0096] S4. Perform magnetic separation on the slurry to obtain primary iron oxide and lithium liquid.

[0097] The obtained Fe3O4 primary product was added to 3 times its mass of 0.03mol / L citric acid solution and stirred to remove lithium-containing precipitate. It was then washed three times with 10 times its volume of pure water and then vacuum dried at 60℃ for 6 hours to obtain the Fe3O4 product.

[0098] S5. Evaporate and concentrate the lithium liquid by 2 times to obtain concentrated liquid, and cool it to room temperature; The concentrate was placed in a freezer at -10°C to precipitate crystals. After centrifugation, sulfate crystals were obtained, which can be used to subsequently formulate lithium precipitation inhibitors. Lithium hydroxide was added to the liquid obtained from the previous centrifugation step to adjust the lithium-phosphorus molar ratio to 3.01:1. The mixture was stirred continuously and heated to 90°C, resulting in precipitation. A small amount of lithium hydroxide was added to adjust the pH of the solution to 11.5 to avoid the formation of dilithium hydrogen phosphate in the product at low pH, which would lead to product impurity. The mixture was aged for 2 hours, and then the solid and liquid were separated. The mixture was washed with hot water and dried at 200°C for 6 hours to obtain anhydrous lithium phosphate.

[0099] Example 4 S1. Provide lithium iron phosphate waste powder and add 1.4 mol / L dilute sulfuric acid solution at a solid-liquid ratio of 1:3. The molar ratio of H2SO4:Li is approximately 1.3:1. Mix evenly and allow it to react fully for 3 hours. Filter to obtain leachate and carbon slag.

[0100] S2. Add iron ion complexing agents to the leachate, namely 0.5 mol / L sodium citrate and 0.2 mol / L disodium ethylenediaminetetraacetate, and add a lithium precipitation inhibitor, 2.0 mol / L sodium sulfate solution. Dilute the mixed solution three times to obtain a mixed solution.

[0101] S3. Heat the mixture and maintain it at 40°C. Slowly add 0.02 mol / L potassium hydroxide solution. About 60 minutes after adding sodium carbonate solution, adjust the pH of the solution to about 4.5. At this time, continue to pass sodium carbonate solution through the bubbler and simultaneously slowly bubble oxygen into the solution at 40 mL / min to partially oxidize ferrous ions. When 35% of ferrous ions are oxidized, stop bubbling oxygen to avoid excessive oxidation and the formation of ferric hydroxide precipitate. Maintain this for 10 minutes. After the appearance of ferric oxide product, add alkali solution within 10 minutes to quickly adjust the pH of the solution to about 8.5 to ensure complete reaction of the raw materials. Aging for 2 hours yields a slurry containing ferric oxide.

[0102] S4. Perform magnetic separation on the slurry to obtain primary iron oxide and lithium liquid.

[0103] The obtained Fe3O4 primary product was added to 4 times its mass of 0.01 mol / L HCl solution and stirred to remove lithium-containing precipitate. It was then washed three times with 10 times its volume of pure water and then vacuum dried at 60°C for 6 hours to obtain the Fe3O4 product.

[0104] S5. Evaporate and concentrate the lithium liquid three times to obtain a concentrated liquid, and cool it to room temperature; The concentrate was placed in a freezer at -10°C to precipitate crystals. After centrifugation, sulfate crystals were obtained, which can be used to subsequently formulate lithium precipitation inhibitors. Lithium hydroxide was added to the liquid obtained from the previous centrifugation step to adjust the lithium-phosphorus molar ratio to 3.10:1. The mixture was stirred continuously and heated to 90°C, resulting in precipitation. A small amount of lithium hydroxide was added to adjust the pH of the solution to 12 to avoid the formation of dilithium hydrogen phosphate in the product at low pH, which would lead to product impurity. The mixture was aged for 2 hours, and then the solid and liquid were separated. The mixture was washed with hot water and dried at 200°C for 6 hours to obtain anhydrous lithium phosphate.

[0105] Example 5 S1. Provide lithium iron phosphate waste powder and add 2.3 mol / L dilute sulfuric acid solution at a solid-liquid ratio of 1:3. The molar ratio of H2SO4:Li is approximately 2:1. Mix evenly and allow it to react fully for 3 hours. Filter to obtain leachate and carbon slag.

[0106] S2. Add iron ion complexing agents to the leachate, namely 0.3 mol / L sodium citrate, 0.2 mol / L disodium ethylenediaminetetraacetate, and 0.2 mol / L sodium tartrate solution, and add lithium precipitation inhibitor 2.0 mol / L sodium sulfate solution. Dilute the mixed solution by 2 times to obtain a mixed solution.

[0107] S3. Heat the mixture to 40°C and slowly add 0.05 mol / L sodium bicarbonate solution. About 30 minutes after adding the sodium carbonate solution, adjust the pH of the solution to around 4.5. At this point, continue to pass sodium carbonate solution through the bubbler while simultaneously slowly blowing oxygen into the solution at 40 mL / min to partially oxidize ferrous ions. When 30% of the ferrous ions have been oxidized, stop blowing oxygen to avoid excessive oxidation and the formation of ferric hydroxide precipitate. Maintain this for 10 minutes. After the appearance of ferric oxide products, add alkali solution within 10 minutes to quickly adjust the pH of the solution to around 8.0 to ensure complete reaction of the raw materials. Aging for 2 hours yields a slurry containing ferric oxide.

[0108] S4. Perform magnetic separation on the slurry to obtain primary iron oxide and lithium liquid.

[0109] The obtained Fe3O4 primary product was added to 3 times its mass of 0.02mol / L HCl solution and stirred to remove lithium-containing precipitate. It was then washed three times with 10 times its volume of pure water and then vacuum dried at 60℃ for 6 hours to obtain the Fe3O4 product.

[0110] S5. Evaporate and concentrate the lithium liquid by 2 times to obtain concentrated liquid, and cool it to room temperature; The concentrate was placed in a freezer at -10°C to precipitate crystals. After centrifugation, sulfate crystals were obtained, which can be used to subsequently formulate lithium precipitation inhibitors. Lithium hydroxide was added to the liquid obtained from the previous centrifugation step to adjust the lithium-phosphorus molar ratio to 3.06:1. The mixture was stirred continuously and heated to 90°C, resulting in precipitation. A small amount of lithium hydroxide was added to adjust the pH of the solution to 12 to avoid the formation of dilithium hydrogen phosphate in the product at low pH, which would lead to product impurity. The mixture was aged for 2 hours, and then the solid and liquid were separated. The mixture was washed with hot water and dried at 200°C for 6 hours to obtain anhydrous lithium phosphate.

[0111] Example 6 This comparative example is basically the same as Example 1, except that no freezing and impurity removal is performed during the lithium precipitation process.

[0112] Example 7 This comparative example is basically the same as Example 1, except that the final pH of lithium hydroxide added during the lithium precipitation process is 9.

[0113] Example 8 This comparative example is basically the same as Example 1, except that the reaction temperature is controlled at 30°C after adding lithium hydroxide during the lithium precipitation process.

[0114] Comparative Example 1 This comparative example is basically the same as Example 1, except that no iron ion complexing agent is added.

[0115] Comparative Example 2 This comparative example is basically the same as Example 1, except that no lithium precipitation inhibitor is added.

[0116] Comparative Example 3 This comparative example is basically the same as Example 1, except that the temperature of the mixed solution is controlled at 60°C during the iron sludge deposition process.

[0117] Comparative Example 4 This comparative example is basically the same as Example 1, except that the pH was directly adjusted to 8.5 during the iron precipitation process.

[0118] Comparative Example 5 This comparative example is basically the same as Example 1, except that oxygen is introduced from the beginning of the iron precipitation process, and alkali solution is added while oxygen is introduced until the solution pH is 8.5.

[0119] Comparative Example 6 This comparative example is basically the same as Example 1, except that oxygen is stopped when the iron precipitation process is oxidized to 60% of ferrous iron.

[0120] Comparative Example 7 This comparative example is basically the same as Example 1, except that during the iron precipitation process, the pH is adjusted to 9 within 10 minutes after the appearance of iron(III) oxide.

[0121] Experimental Example 1 X-ray diffraction patterns of the iron(III) oxide prepared in each embodiment were prepared, as follows: Figure 2 As shown in the figure, the method provided by the present invention produces iron(III) oxide.

[0122] The X-ray diffraction pattern of lithium phosphate prepared in the example is shown below. Figure 3 As shown, the lithium phosphate prepared in Example 1 can be seen.

[0123] Experiment Example 2 The various properties of the iron(III) oxide prepared in each embodiment and comparative examples 1-7 were tested and recorded in Table 1.

[0124] Table 1. Indicators of Fe3O4

[0125] As can be seen from Examples 1-5 in Table 1, the recovered Fe3O4 has a purity of over 99% and a low content of metal impurity ions.

[0126] Comparing Comparative Example 1 with Example 1, the purity of iron oxide in Comparative Example 1 is significantly lower, indicating that without the addition of an iron ion complexing agent, during the precipitation process of the raw material solution, iron ions combine with phosphate ions to form a precipitate, reducing the purity of the product. Comparing Comparative Example 2 with Example 1, the Fe3O4 solution of Comparative Example 2 has a lower purity, indicating that without the addition of lithium precipitation inhibitor, lithium combines with phosphate to form precipitate during the raw material precipitation process, reducing the purity of the product. Comparing Comparative Example 3 with Example 1, the purity of the iron oxide solution in Comparative Example 3 was lower, indicating that increasing the reaction temperature is more conducive to the formation of lithium and phosphate ions into precipitates. Therefore, the process of recovering iron oxide needs to be kept at low temperature or room temperature. Comparing Comparative Example 4 with Example 1, the purity of Fe3O4 was significantly lower, indicating that the rapid oxidation and pH change during the iron precipitation process would produce products such as ferric hydroxide, ferric phosphate, and lithium phosphate, which would affect the purity of the product. Comparing Comparative Example 5 with Example 1, the purity of Fe3O4 in Comparative Example 5 was significantly lower, indicating that if oxygen is introduced from the beginning, ferric hydroxide will be produced. Comparing Comparative Example 6 with Example 1, the purity of Fe3O4 in Comparative Example 6 is significantly lower, indicating that if too much ferrous iron is oxidized before oxygen is introduced, the source of ferrous iron in the reaction will be reduced, and the product will be more likely to form hydroxides. Comparing Comparative Example 7 with Example 1, the significantly lower purity of iron(III) oxide in Comparative Example 7 indicates that if iron(III) oxide is present and the pH is adjusted to a range beyond that defined in this invention, ferrous hydroxides of divalent and trivalent iron will be produced.

[0127] Experimental Example 3 The various test indicators of lithium phosphate prepared in each embodiment were measured, and the test results were recorded in Table 2.

[0128] Table 2. Detection Indicators of Lithium Phosphate

[0129] As can be seen from Examples 1-5 in Table 2, the purity of the recovered lithium phosphate product is above 99.20%, and the content of impurity ions is low. Comparing Example 6 with Example 1, the lithium phosphate purity in Example 6 was lower, indicating that the lack of impurity removal led to an increase in sodium and sulfur impurity ions to 0.22% and 0.70%, respectively. Comparing Example 7 with Example 1, the lithium phosphate in Example 7 has lower purity, indicating that the low endpoint reaction pH leads to the presence of lithium hydrogen phosphate, which affects the product purity. Comparing Example 8 with Example 1, the lithium phosphate in Example 8 has lower purity, indicating that a lower reaction temperature makes it easier for sulfate impurities to enter the product via peritectic processes.

[0130] Therefore, in order to obtain high-quality lithium phosphate products, the lithium precipitation process requires impurity removal, a suitable endpoint reaction pH, and a suitable reaction temperature.

[0131] In summary, the recycling method provided by this invention can recover iron from spent lithium iron phosphate batteries to generate iron(III) oxide. In a preferred embodiment, lithium can also be recovered to obtain lithium phosphate.

[0132] The above description is merely a preferred embodiment of the present invention and is not intended to limit the 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 recycling lithium iron phosphate battery waste, characterized by, The application relates to a method for extracting ferroferric oxide from lithium iron phosphate battery waste. The lithium iron phosphate battery waste is sufficiently acid-leached, and after solid-liquid separation, an leaching solution is obtained; A sufficient amount of an iron ion complexing agent competing with phosphate and a sufficient amount of a lithium precipitation inhibitor competing with lithium ions are added into the leaching solution, and the solution is diluted to avoid precipitation in the solution, so that a mixed solution is obtained; The temperature of the mixed solution is controlled to be 20-50 DEG C, alkali liquor is gradually added into the mixed solution, when the pH of the solution reaches 3.5-4.5, the alkali liquor is continuously added into the solution, oxygen is simultaneously introduced into the solution, when the divalent iron in the solution is oxidized to 30-40%, the oxygen introduction is stopped, the solution is maintained for 8-12 min, then the pH of the solution is adjusted to 7.5-8.5 within 10 min after the appearance of ferroferric oxide in the system is detected, and after sufficient aging, a slurry containing ferroferric oxide is obtained; The ferroferric oxide is extracted from the slurry.

2. The recycling method according to claim 1, characterized in that, The iron ion complexing agent is at least one selected from sodium citrate, sodium tartrate and disodium ethylenediaminetetraacetate; And / or, the lithium precipitation inhibitor is at least one selected from sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, sodium nitrate and potassium nitrate; Optionally, the alkali liquor is slowly added into the mixed solution, and it is ensured that the pH of the solution reaches 3.5-4.5 after at least 30 min.

3. The recycling method according to claim 1, characterized in that, The acid used in the acid leaching step is at least one selected from sulfuric acid, nitric acid and hydrochloric acid; Optionally, when the acid used in the acid leaching is sulfuric acid, the sulfuric acid and the lithium iron phosphate battery waste are added according to an H2SO4:Li molar ratio of 1.0-2.0:1; Optionally, the concentration of the sulfuric acid used in the acid leaching is 1.0-2.0 mol / L; Optionally, when the acid used in the acid leaching is hydrochloric acid, the hydrochloric acid and the lithium iron phosphate battery waste are added according to an HCl:Li molar ratio of 2.5-3.5:1; Optionally, the concentration of the hydrochloric acid used in the acid leaching is 0.6-1.4 mol / L; Optionally, when the acid used in the acid leaching is nitric acid, the nitric acid and the lithium iron phosphate battery waste are added according to an HNO3:Li molar ratio of 2.5-3.5:1; Optionally, the concentration of the nitric acid used in the acid leaching is 1.4-2.8 mol / L.

4. The recycling method according to claim 3, characterized in that, The solid-liquid ratio during the acid leaching is 1:3-6.

5. The recycling method according to claim 4, characterized in that, The adding amount of the iron ion complexing agent is 0.1-0.6 mol / L; And / or, the adding amount of the lithium precipitation inhibitor is 1.0-2.0 mol / L.

6. The recycling method according to claim 3, characterized in that, The way of diluting to avoid precipitation in the solution is: The solution added with the iron ion complexing agent and the lithium precipitation inhibitor is diluted by 2-10 times in volume.

7. The recycling method according to claim 3, characterized by, The way of extracting the ferroferric oxide from the slurry includes: The slurry is treated by magnetic separation to obtain ferroferric oxide and lithium liquid; The ferroferric oxide is stirred in dilute acid for 1-15 min, then solid-liquid separation is conducted to obtain solid and filtrate, the solid is washed with pure water for multiple times, then dried to obtain ferroferric oxide product; Optionally, the dilute acid is at least one selected from hydrochloric acid, citric acid, sulfuric acid, nitric acid, oxalic acid and acetic acid; Optionally, the concentration of the dilute acid is 0.01-0.04 mol / L.

8. The recycling method according to claim 7, characterized in that, After the lithium liquid is obtained: The lithium liquid is concentrated by 2-10 times to obtain a concentrated solution; The concentrated solution is frozen at -15 ~ -10 ℃ to precipitate sulfate impurities, and solid-liquid separation is performed to obtain a lithium precipitation solution; According to the stoichiometric ratio of lithium and phosphorus in lithium phosphate or a ratio range close thereto, lithium hydroxide is added to the lithium precipitation solution, and then the temperature is raised to precipitate a precipitate. The lithium hydroxide is continuously added until the pH is 11-12, and the slurry containing lithium phosphate is sufficiently aged to obtain a slurry containing lithium phosphate; The slurry containing lithium phosphate is subjected to solid-liquid separation to obtain a solid, and then the obtained solid is washed and dried to obtain anhydrous lithium phosphate.

9. The recycling method according to claim 8, characterized in that, The temperature is raised to 70-100 ℃ to precipitate a precipitate; Optionally, the aging time after the precipitate is precipitated is 1.5-2.5 h.

10. The recycling method according to claim 8, characterized in that, After the slurry containing lithium phosphate is subjected to solid-liquid separation to obtain a solid, the solid is stirred with hot water, and the temperature of the hot water is 70-100 ℃; Optionally, after stirring, drying is performed, the drying temperature is 180-220 ℃, and the drying time is 5-7 h.

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