Waste lithium iron phosphate battery recovery method

Abstract

A waste lithium iron phosphate battery recovery method. The method comprises selective leaching, deep purification and battery-grade iron phosphate preparation. By means of selective leaching, lithium and ferrophosphorus materials are separated in one step, and leaching conditions are optimized to prevent difficulty in leaching ferrophosphorus and inability to dissolve impurities caused by transformation of a ferrophosphorus crystal form; obtained ferrophosphorus graphite slag is used as a raw material for synthesizing iron phosphate, and is subjected to further purification and impurity removal (deep purification) by means of a dilute strong acid and an alkali solution, thereby reducing subsequent complex processes such as liquid phase impurity removal of ferrophosphorus liquid, and finally, the purified ferrophosphorus graphite slag is subjected to acid leaching to obtain high-purity filtrate containing phosphorus and iron which can be used for directly synthesizing battery-grade iron phosphate. In the whole process, a small amount of acid is used, a high-impurity-content battery material can be treated, the impurity element removal efficiency is high, the process is short, and the economic benefit is high.

Description

Recycling method of waste lithium iron phosphate batteries

[0001] Cross-references

[0002] This application claims priority to a Chinese patent application filed with the Patent Office of China, with application number 202311619925.X, application date November 30, 2023, and invention name “Method for Recycling Waste Lithium Iron Phosphate Batteries”. The entire contents of the application are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of green recycling of waste lithium-ion batteries, and in particular to a method for recycling waste lithium iron phosphate batteries. Background Art

[0004] Lithium iron phosphate (LiFePO4, LFP) is considered one of the most promising cathode materials for lithium-ion batteries due to its high power, reversibility, low toxicity, excellent thermal safety, and low cost. With the rapid consumption and growing demand for LiFePO4 batteries, an increasing number of retired LiFePO4 batteries are expected to enter the market over the next three to five years. Spent LiFePO4 batteries contain toxic electrolytes, heavy metals, organic chemicals, and plastics, which, if not properly disposed of, can lead to serious environmental problems.

[0005] Currently, most methods for recovering valuable metals from spent LiFePO4 battery active materials focus on lithium ion recovery, while relatively few methods target the recovery of less valuable elements like phosphorus and iron. This is primarily due to the difficulty in acid-dissolving the ferrophosphorus slag after lithium extraction from spent lithium iron phosphate, as well as the difficulty in removing the large amounts of impurities such as aluminum and copper contained in the ferrophosphorus slag.

[0006] A large number of studies and reports on the full-component recovery of lithium iron phosphate mostly use materials with relatively few impurities for recycling, but there is no effective method for the industrial recovery of high-impurity materials after industrial mass crushing. At the same time, many studies on the removal of impurities in ferrophosphorus slag are achieved by adding other impurity metal chelating agents or precipitants such as aluminum and copper to the ferrophosphorus-containing leachate, which will introduce organic matter or other metal impurities, which will have a certain impact on the subsequent synthesis of ferrophosphate, and will also make the recycling process more cumbersome and economically inefficient. With the increasing number of retired lithium-ion batteries and the improvement of domestic environmental protection requirements, the existing recycling methods are difficult to effectively respond to the demand for industrial recycling of battery black powder containing high impurities, and there are problems such as low economic benefits, long recycling process, and the generation of large amounts of impure waste slag. Therefore, it is urgent to develop a method for the efficient recovery and deep purification of high-impurity lithium iron phosphate black powder to achieve the purpose of short-process full-component recovery of waste lithium iron phosphate. Summary of the Invention

[0007] The purpose of this application is to overcome the problems existing in the prior art and provide a method for recycling waste lithium iron phosphate batteries, which is particularly suitable for the efficient recovery of all components of waste lithium iron phosphate batteries with high impurity content.

[0008] This application separates lithium and ferrophosphorus materials through a selective leaching step, and optimizes the leaching conditions to prevent the problem of ferrophosphorus crystal transformation causing difficulty in leaching ferrophosphorus and the inability to dissolve impurities. The resulting ferrophosphorus graphite slag is further purified and removed (deep purification) by dilute strong acid and alkali solution as the raw material for synthesizing ferrophosphate, reducing the tedious process of liquid phase impurity removal of the subsequent ferrophosphorus leachate. Finally, the purified ferrophosphorus graphite slag is acid-leached to obtain a high-purity filtrate containing phosphorus and iron for direct synthesis of battery-grade ferrophosphate. The entire process uses less acid, can process battery materials containing high impurities, has high impurity element removal efficiency, a short process flow, and high economic benefits.

[0009] In order to achieve the above objectives, the present application provides a method for recycling waste lithium iron phosphate batteries, wherein the method comprises the following steps:

[0010] (1) Selective leaching: The waste lithium iron phosphate battery material is selectively leached using a leaching agent at 20-65°C to obtain a leachate and phosphorus iron graphite slag;

[0011] (2) Deep purification: placing the ferrophosphorus graphite slag obtained in step (1) in a dilute strong acid solution at 30-65° C. for a first reaction, and adding alkaline solution dropwise to the first reaction product for a second reaction to obtain deeply purified ferrophosphorus graphite slag and an impurity-containing filtrate;

[0012] (3) Preparation of battery-grade iron phosphate: The deeply purified ferrophosphorus graphite slag obtained in step (2) is used to prepare battery-grade iron phosphate.

[0013] Through the above technical solution, the beneficial technical effects achieved by this application are as follows:

[0014] (1) The present application separates ferrophosphorus graphite slag from lithium and impurity elements by selectively leaching lithium and impurity elements, and controls the leaching conditions to prevent the ferrophosphorus graphite slag from crystallization.

[0015] (2) The present application controls the concentration of dilute acid and utilizes a combination of dilute strong acid and alkaline solution to deeply purify the phosphorus-iron graphite slag and reduce the loss of iron and phosphorus in the impurity removal process. It is capable of processing battery black powder materials with high impurities and has the characteristics of high impurity removal efficiency and good economic benefits.

[0016] (3) In this application, by strictly controlling the reaction conditions of each step, the problems of low ferrophosphorus leaching efficiency, difficult dissolution of impurities and large acid dosage caused by the crystal transformation of ferrophosphorus graphite slag are prevented, which provides favorable conditions for the recovery of ferrophosphate.

[0017] (4) The ferric phosphate regenerated in this application has high purity, high recovery rate and short process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG1 is a process flow chart of the method for efficiently recycling waste lithium iron phosphate batteries described in the present application;

[0019] FIG2 is an XRD pattern of ferrophosphorus graphite slag of Example 1 of the present application;

[0020] FIG3 is an XRD pattern of ferrophosphorus graphite slag of Example 2 of the present application;

[0021] FIG4 is an XRD pattern of ferrophosphorus graphite slag of Example 3 of the present application;

[0022] FIG5 is an XRD pattern of ferrophosphorus graphite slag of Example 4 of the present application;

[0023] FIG6 is an XRD diagram of ferrophosphorus graphite slag of Comparative Example 1 of the present application;

[0024] FIG7 is an XRD diagram of the ferrophosphorus graphite slag of Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0026] A first aspect of the present application provides a method for recycling waste lithium iron phosphate batteries, wherein the method comprises the following steps:

[0027] (1) Selective leaching: The waste lithium iron phosphate battery material is selectively leached using a leaching agent at 20-65°C to obtain a leachate and phosphorus iron graphite slag;

[0028] (2) Deep purification: placing the ferrophosphorus graphite slag obtained in step (1) in a dilute strong acid solution at 30-65° C. for a first reaction, and adding alkaline solution dropwise to the first reaction product for a second reaction to obtain deeply purified ferrophosphorus graphite slag and an impurity-containing filtrate;

[0029] (3) Preparation of battery-grade iron phosphate: The deeply purified ferrophosphorus graphite slag obtained in step (2) is used to prepare battery-grade iron phosphate.

[0030] In the present application, the leachate obtained in step (1) contains lithium and impurity elements; in step (2), the impurity metals and a small amount of iron-phosphorus elements in the ferrophosphorus graphite slag are dissolved by a first reaction, and an alkaline solution is added dropwise to the first reaction product without solid-liquid separation. After the reaction, the deeply purified ferrophosphorus graphite slag and the impurity-containing filtrate are obtained by separation.

[0031] The method provided by this application can preferentially extract lithium and a portion of other impurity elements from waste lithium iron phosphate battery materials, and the resulting leached slag has a ferrophosphite-type structure that is conducive to subsequent acid leaching and purification; then, the impurity-containing ferrophosphide graphite slag is deeply purified by a combination of dilute strong acid and alkali solution. This part uses a strong acid to produce a weak acid to create a mixed system of strong acid and phosphoric acid, and the phosphoric acid system effectively inhibits the dissolution of ferrophosphide, while the strong acid system promotes the dissolution of impurity elements, thereby solving the problem of difficult removal of impurities such as aluminum and copper in ferrophosphide slag; finally, the impurity-removed ferrophosphide graphite slag is used as a raw material for leaching and precipitation to synthesize battery-grade ferrophosphate. The entire process has mild conditions, high impurity element removal efficiency, high purity of regenerated ferrophosphate, high recovery rate, short process flow, and good economic benefits.

[0032] In addition, ferrophosphorus slag does not undergo crystallization. Under the same leaching conditions, ferrophosphorus slag that does not undergo crystallization has a good leaching effect and does not require a lot of acid to dissolve. However, ferrophosphorus slag that undergoes crystallization has a poor leaching effect and requires more acid to dissolve to achieve the same leaching efficiency. Therefore, the method of the present application also has the effect of reducing the amount of acid used.

[0033] In some embodiments of the present application, the waste lithium iron phosphate battery material described in step (1) is the mixed positive and negative electrode black powder obtained from the industrial large-scale disassembly and crushing of waste lithium iron phosphate batteries. The battery black powder obtained from the large-scale / large-scale disassembly and crushing of waste lithium iron phosphate batteries has a high impurity content and is consistent with the actual materials encountered in industrial production processes. Because this battery black powder contains a large amount of impurities, it is more difficult to handle than the battery black powder obtained by traditional manual disassembly.

[0034] In some embodiments of the present application, the copper content in the waste lithium iron phosphate battery material is 1-5%, preferably 1.5%, and the aluminum content is 1-3%, preferably 2.7%.

[0035] Currently, it is difficult to recycle battery black powder containing more than 1% Al impurities in the market. The process required is complex, and industrially produced battery black powder contains impurities introduced from the environment, such as Al, Cu, Ca, Mg, Ni, Co, Zn, Na, etc. For details, please see Table 1.

[0036] Existing technologies typically process lithium iron phosphate (LFP) cathode powder or black powder from spent LFP batteries obtained through small-scale laboratory disassembly. These materials, which have low impurity content (e.g., Al, Cu, etc.), are easy to process and easily yield high-purity and high-recovery LFP. However, recycling LFP battery materials with high impurity content often presents difficulties in removing these impurities, making it impossible to obtain battery-grade LFP. Therefore, finding suitable industrially viable recycling technologies is crucial for the recovery of spent LFP batteries.

[0037] In some embodiments of the present application, the leaching agent includes at least one of hydrogen peroxide, oxygen, sodium persulfate and ammonium persulfate and at least one of sulfuric acid, hydrochloric acid and nitric acid, preferably hydrogen peroxide and sulfuric acid.

[0038] In some embodiments of the present application, the mass volume ratio (ie, solid-liquid ratio) of the waste lithium iron phosphate battery material to the leaching agent is 100-500 g / L, preferably 200 g / L.

[0039] In some embodiments of the present application, the amount of sulfuric acid used is 100-130 wt % of the theoretical amount of lithium and impurity elements in the waste lithium iron phosphate battery material. The "sulfuric acid" in the present application is concentrated sulfuric acid with a mass fraction of 98%.

[0040] The theoretical amount of lithium and impurity elements in the waste lithium iron phosphate battery material refers to the amount of sulfuric acid theoretically required for the lithium and impurity element ions to form soluble metal sulfates with sulfate ions.

[0041] In some embodiments of the present application, the mass percentage of the hydrogen peroxide is 25-30%, preferably 30%.

[0042] In some embodiments of the present application, the amount of hydrogen peroxide is 0.2-0.6 mL / g, preferably 0.45 mL / g. In the present application, the amount is the amount relative to the mass of the waste lithium iron phosphate battery material.

[0043] In some embodiments of the present application, the selective leaching is carried out under stirring conditions, and the stirring speed is 0-600 rpm, preferably 300 rpm.

[0044] In some embodiments of the present application, the temperature of the selective leaching is 50-60°C.

[0045] In some embodiments of the present application, the selective leaching time is 1-5 hours, preferably 3 hours.

[0046] In some embodiments of the present application, the selective leaching is performed at a pH of 1.2-1.4. The pH may be 1.2, 1.3, 1.4, or any value within a range consisting of any two of the above values.

[0047] In this application, step (1) involves the selective leaching of lithium and impurity elements and the control of the crystal form of the leached slag, which is specifically described as follows:

[0048] The waste lithium iron phosphate battery powder is selectively leached using a three-necked flask as the leaching reaction vessel, which is then placed in a water bath with magnetic heating for the leaching reaction. Condensation reflux is also used to prevent water loss during the high-temperature leaching process. During the leaching process, sulfuric acid and hydrogen peroxide destroy the material's olivine structure, dissolving lithium ions from the material's crystal lattice. Simultaneously, divalent iron ions are oxidized by hydrogen peroxide to trivalent iron ions, which combine with phosphate to form iron phosphate. Battery black powder often contains difficult-to-remove impurities such as aluminum and copper. During this process, the impure metals mixed in the black powder further dissolve with the sulfuric acid and enter the solution in ionic form, thereby achieving the goal of selectively leaching lithium and impurity elements from the waste lithium iron phosphate battery black powder. The reactions that may be involved in this process are shown in equations (1)(2)(3)(4): 2LiFePO4+H2SO4+H2O2=Li2SO4+2FePO4+2H2O (1) Al2O3+3H2SO4=Al2(SO4)3+3H2O (2) 2Al+3H2SO4=Al2(SO4)3+3H2↑ (3) H2SO4+H2O2+Cu=CuSO4+2H2O (4)

[0049] During the selective leaching reaction, the leaching system undergoes an oxidation-reduction reaction, and the olivine-type LiFePO4 has a strong structural stability. After chemical in-situ oxidation, selective lithium removal can be achieved to obtain orthorhombic ferromagnetite-type FePO4, which is beneficial for subsequent phosphorus and iron leaching and recovery. This crystal system belongs to a metastable structure and is prone to crystal transformation in an acidic system to generate a monoclinic or orthorhombic stable structure. This structure is difficult to dissolve in acid, which affects the subsequent impurity removal and secondary leaching of ferrophosphorus slag. The present application avoids the occurrence of crystal transformation by controlling the temperature of selective leaching.

[0050] In some embodiments of the present application, the dilute strong acid in step (2) is selected from at least one of dilute sulfuric acid, dilute hydrochloric acid and dilute nitric acid.

[0051] In some embodiments of the present application, the concentration of the dilute strong acid solution is 0.2-0.8 mol / L, preferably 0.35-0.4 mol / L.

[0052] In some embodiments of the present application, the temperature of the deep purification in step (2) is 50-60°C.

[0053] In some embodiments of the present application, the deep purification is performed at a pH of 0.2-0.5. The pH can be 0.2, 0.3, 0.4, 0.5, or any value within a range consisting of any two of the above values.

[0054] In some embodiments of the present application, the first reaction time is 1-5 hours, preferably 1-2 hours.

[0055] In some embodiments of the present application, the first reaction is carried out under stirring conditions, and the stirring speed is 100-600 rpm, preferably 300 rpm.

[0056] In some embodiments of the present application, the alkali solution is selected from at least one of aqueous ammonia, sodium hydroxide solution and sodium carbonate solution.

[0057] In some embodiments of the present application, the concentration of the alkali solution is 1-6 mol / L, preferably 3-4 mol / L.

[0058] In some embodiments of the present application, alkaline solution is added dropwise to the first reaction product until the pH value reaches 1.4-2.5, preferably 1.8-2.

[0059] In some embodiments of the present application, the second reaction time is 20-60 min, preferably 20-40 min.

[0060] The filtrate containing impurities is removed and then evaporated and crystallized to obtain ammonium sulfate product.

[0061] In this application, step (2) involves deep purification of ferrophosphorus graphite slag, which is described in detail as follows:

[0062] The impure ferrophosphorus graphite slag obtained by filtration after leaching is deeply purified to remove residual impurities such as aluminum and copper in the ferrophosphorus graphite slag. A sulfuric acid and ammonia water impurity removal system is used. The ferrophosphorus graphite slag is first placed in a dilute sulfuric acid solution. At this time, a large amount of impurities such as aluminum and copper will dissolve into the acidic solution. Without solid-liquid separation, alkali solution is continuously added to the leaching slurry to adjust the pH value of the leaching system. According to the different solubility products of different metal ions combined with phosphate, some of the phosphorus and iron that enter the solution are precipitated as iron phosphate, while impurities such as aluminum and copper are retained in the leachate to achieve deep purification of the ferrophosphorus graphite slag. After the reaction is completed, the ferrophosphorus graphite slag and the impurity-containing filtrate with high purity are obtained by filtration. The ferrophosphorus graphite slag is used as a raw material to recover iron phosphate. To prevent the iron phosphate with a ferrophosphorus-type structure obtained in the leaching stage from re-crystallizing in this part, it is necessary to control the impurity removal conditions.

[0063] In some embodiments of the present application, the leachate obtained in step (1) is concentrated, impurity-removed, and precipitated to obtain lithium carbonate, and the supernatant is evaporated and crystallized to obtain sodium sulfate.

[0064] In some embodiments of the present application, the operation of step (3) is:

[0065] The deeply purified ferrophosphorus graphite slag obtained in step (2) is acid-leached to obtain ferrophosphorus liquid and graphite slag; after adjusting the molar ratio of phosphorus to iron in the ferrophosphorus liquid to 1:1, the pH is adjusted to synthesize ferric phosphate dihydrate; and the ferric phosphate dihydrate is subjected to high-temperature heat treatment (e.g., calcination) to remove crystal water to obtain battery-grade ferric phosphate.

[0066] In some embodiments of the present application, the acid leaching temperature is 30-80° C. and the time is 1-5 h.

[0067] In some embodiments of the present application, the acid leaching is carried out under stirring conditions with a stirring speed of 100-600 rpm.

[0068] In some embodiments of the present application, aqueous ammonia is added to adjust the pH to 1.4-2.5.

[0069] In some embodiments of the present application, the temperature of the high-temperature heat treatment is 500-700°C.

[0070] According to a particularly preferred embodiment of the present application, as shown in FIG1 , a method for recycling waste lithium iron phosphate batteries comprises the following steps:

[0071] (1) Selective leaching: waste lithium iron phosphate battery materials, 30% hydrogen peroxide and sulfuric acid are mixed and stirred at a stirring speed of 0-600 rpm, a solid-liquid ratio of 100-500 g / L, an amount of hydrogen peroxide of 0.2-0.6 mL / g, a pH of 1.2-1.4, and selective leaching is performed at 20-65° C. for 1-5 hours to obtain a leachate and phosphorus-iron graphite slag; the leachate is concentrated, impurity-removed, and precipitated to obtain lithium carbonate, and the supernatant is evaporated and crystallized to obtain sodium sulfate; the amount of sulfuric acid used is 100-130 wt% of the theoretical amount of lithium and impurity elements in the waste lithium iron phosphate battery materials;

[0072] (2) Deep purification: placing the phosphorus-iron graphite slag obtained in step (1) in a dilute sulfuric acid solution with a concentration of 0.2-0.8 mol / L and stirring at a stirring speed of 100-600 rpm at 30-65° C. for 1-5 hours, and the pH value is 0.2-0.5. Ammonia water with a concentration of 1-6 mol / L is added dropwise to the first reaction slurry until the pH value is 1.4-2.5, and a second reaction is carried out for 20-60 minutes to obtain deeply purified phosphorus-iron graphite slag and impurity-containing filtrate;

[0073] (3) preparing battery-grade iron phosphate: under stirring conditions, the deeply purified ferrophosphorus graphite slag obtained in step (2) is acid-leached with sulfuric acid at 30-80° C. for 1-5 h, the amount of sulfuric acid used is 0.2-1 mL / g, and the stirring speed is 100-600 rpm to obtain ferrophosphorus liquid and graphite slag; after adjusting the molar ratio of phosphorus to iron in the ferrophosphorus liquid to 1:1, ammonia water is added to adjust the pH to 1.4-2.5 to synthesize ferric phosphate dihydrate; the ferric phosphate dihydrate is subjected to high-temperature heat treatment at 600-700° C. to remove crystal water to obtain battery-grade iron phosphate.

[0074] This application primarily relates to a method for the green recycling of waste lithium iron phosphate batteries with high impurity content. By controlling leaching conditions to prevent the crystallization of ferrophosphorus graphite slag and remove most impurity elements, the residue is then purified using dilute strong acid and alkali to obtain high-purity ferrophosphorus graphite slag. The resulting high-purity ferrophosphorus graphite slag is used to prepare battery-grade iron phosphate, eliminating the need for subsequent cumbersome processes such as liquid-phase impurity removal of the ferrophosphorus leachate. This method not only solves the difficulty of acid leaching ferrophosphorus slag after lithium extraction from lithium iron phosphate materials, but also solves the problem of impurity removal from the ferrophosphorus slag.

[0075] The present application will be described in detail below through examples.

[0076] In the following examples and comparative examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents and instruments used, if no manufacturer is specified, are commercially available conventional products.

[0077] The waste lithium iron phosphate battery materials used in the following examples and comparative examples were obtained by the following method: the waste lithium iron phosphate batteries were discharged by a machine, then mechanically disassembled, crushed, dried, and sieved to obtain a mixed positive and negative electrode black powder. The composition of the powder is shown in Table 1.

[0078] Table 1

[0079] Example 1

[0080] A method for recycling waste lithium iron phosphate batteries comprises the following steps:

[0081] (1) Selective leaching of lithium and impurity elements and control of leaching residue crystal form

[0082] The waste lithium iron phosphate battery material is leached at a solid-liquid ratio of 200 g / L, the amount of sulfuric acid is 110 wt% of the theoretical amount of lithium and impurity elements in the waste lithium iron phosphate battery material, the amount of 30% hydrogen peroxide is 0.45 mL / g, the stirring speed is 300 rpm, and the leaching temperature is 60 ° C., the pH is 1.3. After leaching for 3 hours, the lithium leaching rate is 99%, the aluminum leaching rate is 75%, the copper leaching rate is 95%, the iron leaching rate is 3%, and the phosphorus leaching rate is 3.4%. After the reaction is completed, the solid-liquid separation is performed to obtain ferrophosphorus graphite slag containing isophosphorus manganese ore type iron phosphate, and its XRD pattern is shown in Figure 2; it can be seen from the XRD pattern that its peak is sharp and there is no impurity peak, which means that the material has a high crystallinity after delithiation; the highest peak represents the structural peak of the negative electrode graphite, and the other peaks correspond one to one with the standard peak of isophosphorus manganese ore type iron phosphate, which indicates that the iron phosphate after lithium extraction under this condition is isophosphorus manganese ore type iron phosphate;

[0083] (2) Deep purification of ferrophosphorus graphite slag

[0084] The ferrophosphorus graphite slag was placed in a dilute sulfuric acid solution, and the reaction was carried out for 1 hour under the conditions of controlling the concentration of the dilute sulfuric acid at 0.4 mol / L, stirring speed at 300 rpm, temperature at 50°C, and pH at 0.5. Then, 4 mol / L ammonia water was slowly added to the leached slurry, and the pH value was adjusted to 1.8 and the reaction was carried out for 20 minutes. After the reaction was completed, the ferrophosphorus graphite slag with high purity was obtained by filtration, with an impurity removal rate of 95% and a ferrophosphorus loss rate of less than 2%.

[0085] (3) Recovery of phosphorus and iron to prepare battery-grade iron phosphate

[0086] The deeply purified ferrophosphorus graphite slag obtained in step (2) is acid-leached at 50° C. for 3 hours to obtain ferrophosphorus liquid and graphite slag; after adjusting the molar ratio of phosphorus to iron in the ferrophosphorus liquid to 1:1, ammonia water is added to adjust the pH to 2 to synthesize dihydrated ferric phosphate; and the dihydrated ferric phosphate is subjected to high-temperature heat treatment at 600° C. to remove crystal water to obtain battery-grade ferric phosphate.

[0087] The impurity removal rate of the entire process is 98%, the iron phosphate recovery rate is 94%, and the iron phosphate purity is 99%.

[0088] Example 2

[0089] A method for recycling waste lithium iron phosphate batteries comprises the following steps:

[0090] (1) Selective leaching of lithium and impurity elements and control of leaching residue crystal form

[0091] The waste lithium iron phosphate battery material is leached at a solid-liquid ratio of 200 g / L, the amount of sulfuric acid is 110 wt% of the theoretical amount of lithium and impurity elements in the waste lithium iron phosphate battery material, the amount of 30% hydrogen peroxide is 0.45 mL / g, the stirring speed is 300 rpm, and the leaching temperature is 50 ° C., the pH is 1.4. After leaching for 3 hours, the lithium leaching rate is 99%, the aluminum leaching rate is 72%, the copper leaching rate is 91%, the iron leaching rate is 2.6%, and the phosphorus leaching rate is 2.9%. After the reaction is completed, the solid-liquid separation is performed to obtain ferrophosphorus graphite slag containing isophosphorus manganese ore type iron phosphate, and its XRD pattern is shown in Figure 3; it can be seen from the XRD pattern that its peak is sharp and there is no impurity peak, which means that the material has a high crystallinity after delithiation; the highest peak represents the structural peak of the negative electrode graphite, and the other peaks correspond one to one with the standard peak of isophosphorus manganese ore type iron phosphate, which indicates that the iron phosphate after lithium extraction under this condition is isophosphorus manganese ore type iron phosphate;

[0092] (2) Deep purification of ferrophosphorus graphite slag

[0093] The ferrophosphorus graphite slag was placed in a dilute sulfuric acid solution, and the reaction was carried out for 2 hours under the conditions of controlling the concentration of the dilute sulfuric acid at 0.35 mol / L, stirring speed at 300 rpm, temperature at 60°C, and pH at 0.4. Then, 3 mol / L ammonia water was slowly added to the leached slurry, and the pH value was adjusted to 2.0 and the reaction was carried out for 40 minutes. After the reaction was completed, the ferrophosphorus graphite slag with high purity was obtained by filtration, with an impurity removal rate of 96% and a ferrophosphorus loss rate of less than 1.3%.

[0094] (3) Recovery of phosphorus and iron to prepare battery-grade iron phosphate

[0095] The deeply purified ferrophosphorus graphite slag obtained in step (2) is acid-leached at 60° C. for 4 hours to obtain ferrophosphorus liquid and graphite slag; after adjusting the molar ratio of phosphorus to iron in the ferrophosphorus liquid to 1:1, ammonia water is added to adjust the pH to 2.5 to synthesize dihydrated ferric phosphate; and the dihydrated ferric phosphate is subjected to high-temperature heat treatment at 700° C. to remove crystal water to obtain battery-grade ferric phosphate.

[0096] The impurity removal rate of the entire process is greater than 98.5%, the iron phosphate recovery rate is greater than 95%, and the purity of iron phosphate is 99%.

[0097] Example 3

[0098] A method for recycling waste lithium iron phosphate batteries comprises the following steps:

[0099] (1) Selective leaching of lithium and impurity elements and control of leaching residue crystal form

[0100] The waste lithium iron phosphate battery material was leached at a solid-liquid ratio of 100 g / L, the amount of sulfuric acid was 100 wt% of the theoretical amount of lithium and impurity elements in the waste lithium iron phosphate battery material, and the amount of 30% hydrogen peroxide was 0.2 mL / g. After leaching for 5 hours at a leaching temperature of 20° C. and a pH of 1.4, the lithium leaching rate was 98.3%, the aluminum leaching rate was 72.6%, the copper leaching rate was 90.5%, the iron leaching rate was 1.4%, and the phosphorus leaching rate was 1.6%. After the reaction was completed, the solid-liquid separation was performed to obtain ferrophosphorus graphite slag containing isophosphite-type iron phosphate, and its XRD pattern is shown in Figure 4;

[0101] (2) Deep purification of ferrophosphorus graphite slag

[0102] The ferrophosphorus graphite slag was placed in a dilute sulfuric acid solution, and the reaction was carried out for 5 hours under the conditions of controlling the concentration of the dilute sulfuric acid at 0.2 mol / L, stirring speed at 100 rpm, temperature at 30°C, and pH at 0.5. Then, 1 mol / L ammonia water was slowly added to the leached slurry, and the pH value was adjusted to 1.4 and the reaction was carried out for 20 minutes. After the reaction was completed, the ferrophosphorus graphite slag with high purity was obtained by filtration, with an impurity removal rate of 93% and a ferrophosphorus loss rate of less than 2.7%.

[0103] (3) Recovery of phosphorus and iron to prepare battery-grade iron phosphate

[0104] The deeply purified ferrophosphorus graphite slag obtained in step (2) is acid-leached at 30° C. for 5 hours to obtain ferrophosphorus liquid and graphite slag; after adjusting the molar ratio of phosphorus to iron in the ferrophosphorus liquid to 1:1, ammonia water is added to adjust the pH to 1.4 to synthesize dihydrated ferric phosphate; and the dihydrated ferric phosphate is subjected to high-temperature heat treatment at 620° C. to remove crystal water to obtain battery-grade ferric phosphate.

[0105] The impurity removal rate of the entire process is greater than 97.4%, the iron phosphate recovery rate is greater than 92%, and the purity of iron phosphate is 99%.

[0106] Example 4

[0107] A method for recycling waste lithium iron phosphate batteries comprises the following steps:

[0108] (1) Selective leaching of lithium and impurity elements and control of leaching residue crystal form

[0109] The waste lithium iron phosphate battery material was leached at a solid-liquid ratio of 500 g / L, an amount of sulfuric acid of 130 wt% of the theoretical amount of lithium and impurity elements in the waste lithium iron phosphate battery material, and 0.65 mL / g of 30% hydrogen peroxide. The stirring speed was 600 rpm. After leaching for 1 hour at a leaching temperature of 65° C. and a pH of 1.2, the lithium leaching rate was 99%, the aluminum leaching rate was 80%, the copper leaching rate was 98%, the iron leaching rate was 2.7%, and the phosphorus leaching rate was 2.9%. After the reaction was completed, the solid-liquid separation was performed to obtain ferrophosphorus graphite slag containing isophosphite-type iron phosphate, the XRD pattern of which is shown in FIG5 .

[0110] (2) Deep purification of ferrophosphorus graphite slag

[0111] The ferrophosphorus graphite slag was placed in a dilute sulfuric acid solution, and the reaction was carried out for 1 hour under the conditions of controlling the concentration of the dilute sulfuric acid at 0.8 mol / L, stirring speed at 600 rpm, temperature at 65°C, and pH at 0.2. Then, 3 mol / L ammonia water was slowly added to the leached slurry, and the pH value was adjusted to 2.5 and the reaction was carried out for 60 minutes. After the reaction was completed, the ferrophosphorus graphite slag with high purity was obtained by filtration, with an impurity removal rate of 97% and a ferrophosphorus loss rate of less than 0.4%.

[0112] (3) Recovery of phosphorus and iron to prepare battery-grade iron phosphate

[0113] The deeply purified ferrophosphorus graphite slag obtained in step (2) is acid-leached at 80° C. for 1 hour to obtain ferrophosphorus liquid and graphite slag; after adjusting the molar ratio of phosphorus to iron in the ferrophosphorus liquid to 1:1, ammonia water is added to adjust the pH to 2.2 to synthesize dihydrated ferric phosphate; and the dihydrated ferric phosphate is subjected to high-temperature heat treatment at 680° C. to remove crystal water to obtain battery-grade ferric phosphate.

[0114] The impurity removal rate of the entire process is greater than 98%, the iron phosphate recovery rate is greater than 95.3%, and the purity of iron phosphate is 99%.

[0115] Comparative Example 1

[0116] (1) Selective leaching of lithium and impurity elements and control of leaching residue crystal form

[0117] Except for adjusting the leaching temperature to 80°C, other conditions were the same as in Example 1. The resulting lithium leaching rates were 99%, aluminum leaching rates were 72%, copper leaching rates were 96%, iron leaching rates were 2.7%, and phosphorus leaching rates were 2.9%. After the reaction, solid-liquid separation was performed to obtain monoclinic iron phosphate, the XRD pattern of which is shown in Figure 6.

[0118] (2) Deep purification of ferrophosphorus graphite slag

[0119] Other conditions are the same as those in Example 1. Since the ferrophosphate in the ferrophosphorus graphite slag is monoclinic and has a stable structure, impurity elements are wrapped in it, so the impurity removal rate is low, the impurity removal rate is 20%, and the ferrophosphorus loss rate is 2.3%.

[0120] (3) Recovery of phosphorus and iron to prepare battery-grade iron phosphate

[0121] The conditions are the same as in Example 1.

[0122] The impurity removal rate of the entire process is greater than 79%, and the iron phosphate recovery rate is greater than 25%.

[0123] Comparative Example 2

[0124] (1) Selective leaching of lithium and impurity elements and control of leaching residue crystal form

[0125] Same as Example 2.

[0126] (2) Deep purification of ferrophosphorus graphite slag

[0127] Except that the temperature was adjusted to 90° C., other conditions were the same as those in Example 2. After the reaction, filtration was performed to obtain a mixed slag of monoclinic iron phosphate and graphite, the XRD pattern of which is shown in FIG7 . The impurity removal rate reached 54%.

[0128] (3) Recovery of phosphorus and iron to prepare battery-grade iron phosphate

[0129] The conditions are the same as in Example 2.

[0130] The impurity removal rate of the entire process is greater than 87%, and the iron phosphate recovery rate is greater than 50%.

[0131] Comparative Example 3

[0132] Waste lithium iron phosphate batteries are recycled according to the method of Example 1, except that step (2) is omitted.

[0133] The impurity removal rate of the entire process is greater than 75%. If the impurity content exceeds the standard, battery-grade iron phosphate cannot be synthesized.

[0134] The above results indicate that during the selective lithium leaching process, parameters such as reaction temperature can affect the crystal structure of the ferrophosphate slag. Exceeding this temperature range can cause the ferrophosphate to transform from the isophosphite-type to the monoclinic type, making subsequent ferrophosphate slag leaching difficult and reducing ferrophosphate recovery efficiency. Furthermore, the transformed ferrophosphate slag can trap impurities within it, hindering further impurity removal.

[0135] The deep purification in the second step can better achieve the purification and impurity removal effect of ferrophosphorus graphite slag based on the leaching of lithium and impurities in the first step. By controlling parameters such as temperature and pH, the ferrophosphorus slag is prevented from crystallizing and losing ferrophosphorus at this stage, thereby making the ferrophosphorus slag in the next step purer, making it easier to leach ferrophosphorus liquid, and improving the recovery rate of ferrophosphorus.

[0136] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solution of the present application, including combining the various technical features in any other appropriate manner. These simple modifications and combinations should also be regarded as the contents disclosed in the present application and fall within the scope of protection of the present application. Industrial Applicability

[0137] The present application provides a method for recycling waste lithium iron phosphate batteries. The method includes selective leaching, deep purification and preparation of battery-grade iron phosphate. The present application separates lithium and ferrophosphorus materials in one step through selective leaching, and optimizes the leaching conditions to prevent the problem of difficulty in leaching ferrophosphorus due to ferrophosphorus crystal transformation and the inability to dissolve impurities; the obtained ferrophosphorus graphite slag is used as a raw material for synthesizing iron phosphate and is further purified and impurized (deep purification) by dilute strong acid and alkali solution. Finally, the purified ferrophosphorus graphite slag is acid-leached to obtain a high-purity filtrate containing phosphorus and iron for direct synthesis of battery-grade iron phosphate. The whole process uses less acid, can process battery materials containing high impurities, has high efficiency in removing impurity elements, has a short process, and has high economic benefits.

Claims

1. A method for recycling waste lithium iron phosphate batteries, characterized in that: The method comprises the following steps: (1) Selective leaching: The waste lithium iron phosphate battery material is selectively leached using a leaching agent at 20-65° C. to obtain a leachate and phosphorus iron graphite slag; (2) Deep purification: placing the ferrophosphorus graphite slag obtained in step (1) in a dilute strong acid solution at 30-65° C. for a first reaction, and adding an alkali solution dropwise to the first reaction product for a second reaction to obtain deeply purified ferrophosphorus graphite slag and an impurity-containing filtrate; (3) Preparation of battery-grade iron phosphate: The deeply purified ferrophosphorus graphite slag obtained in step (2) is used to prepare battery-grade iron phosphate.

2. The method according to claim 1, wherein: The waste lithium iron phosphate battery material in step (1) is the positive and negative electrode mixed black powder obtained by industrially dismantling and crushing waste lithium iron phosphate batteries in large quantities; Preferably, the copper content in the waste lithium iron phosphate battery material is 1-5%, and the aluminum content is 1-3%.

3. The method according to claim 1 or 2, wherein: The leaching agent includes at least one of hydrogen peroxide, oxygen, sodium persulfate and ammonium persulfate and at least one of sulfuric acid, hydrochloric acid and nitric acid, preferably hydrogen peroxide and sulfuric acid; Preferably, the mass volume ratio of the waste lithium iron phosphate battery material to the leaching agent is 100-500 g / L, preferably 200 g / L; Preferably, the amount of sulfuric acid used is 100-130wt% of the theoretical amount of lithium and impurity elements in the waste lithium iron phosphate battery material; Preferably, the mass percentage of the hydrogen peroxide is 25-30%, preferably 30%; Preferably, the amount of hydrogen peroxide used is 0.2-0.6 mL / g, preferably 0.45 mL / g.

4. The method according to any one of claims 1 to 3, wherein: The selective leaching is carried out under stirring conditions, with a stirring speed of 0-600 rpm, preferably 300 rpm; Preferably, the temperature of the selective leaching is 50-60°C; Preferably, the selective leaching time is 1-5h, preferably 3h; Preferably, the selective leaching is carried out at a pH of 1.2-1.

4.

5. The method according to any one of claims 1 to 4, wherein: The dilute strong acid in step (2) is selected from at least one of dilute sulfuric acid, dilute hydrochloric acid and dilute nitric acid; Preferably, the concentration of the dilute strong acid solution is 0.2-0.8 mol / L, preferably 0.35-0.4 mol / L; Preferably, the temperature of the deep purification in step (2) is 50-60°C; Preferably, the deep purification is carried out at a pH of 0.2-0.5; Preferably, the first reaction time is 1-5h, preferably 1-2h; Preferably, the first reaction is carried out under stirring conditions, with a stirring speed of 100-600 rpm, preferably 300 rpm.

6. The method according to any one of claims 1 to 5, wherein: The alkali solution is selected from at least one of aqueous ammonia, sodium hydroxide solution and sodium carbonate solution; Preferably, the concentration of the alkali solution is 1-6 mol / L, preferably 3-4 mol / L; Preferably, an alkali solution is added dropwise to the first reaction product until the pH value is 1.4-2.5, preferably 1.8-2; Preferably, the second reaction time is 20-60 min, preferably 20-40 min.

7. The method according to any one of claims 1 to 6, wherein: The leaching solution obtained in step (1) is concentrated, impurity-removed and precipitated to obtain lithium carbonate, and the supernatant is evaporated and crystallized to obtain sodium sulfate.

8. The method according to any one of claims 1 to 7, wherein: The operation of step (3) is: The deeply purified ferrophosphide graphite slag obtained in step (2) is subjected to acid leaching to obtain ferrophosphide liquid and graphite slag; after adjusting the molar ratio of phosphorus to iron in the ferrophosphide liquid to 1:1, the pH is adjusted to synthesize dihydrated ferric phosphate; and the dihydrated ferric phosphate is subjected to high-temperature heat treatment to remove crystal water to obtain battery-grade ferric phosphate.

9. The method according to claim 8, wherein: The acid leaching temperature is 30-80°C and the time is 1-5h; Preferably, the acid leaching is carried out under stirring conditions at a stirring speed of 100-600 rpm.

10. The method according to claim 8 or 9, wherein: Add ammonia to adjust the pH to 1.4-2.5; Preferably, the temperature of the high temperature heat treatment is 500-700°C.

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