Recycling Method for Waste Lithium Iron Phosphate Batteries

Abstract

The present invention relates to the technical field of green recycling of waste lithium-ion batteries, and discloses a method for recycling waste lithium iron phosphate batteries. The method of the present invention includes selective leaching, deep impurity removal, and preparation of battery-grade iron phosphate. The present invention separates lithium and phosphorus-iron materials in one step through selective leaching, and optimizes the leaching conditions to prevent the problem of difficult leaching of phosphorus-iron due to the transformation of phosphorus-iron crystal form and the inability to dissolve impurities; the obtained phosphorus-iron graphite slag is used as a raw material for synthesizing iron phosphate and is further purified and decontaminated (deep impurity removal) through dilute strong acid and lye. Finally, the purified phosphorus-iron graphite slag is acid-leached to obtain a high-purity filtrate containing phosphorus and iron for directly synthesizing battery-grade iron phosphate. The whole process has the advantages of less acid consumption, the ability to process battery materials with high impurities, high impurity element removal efficiency, short process, and high economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of green recycling of waste lithium-ion batteries, and particularly relates to a method for recycling waste lithium iron phosphate batteries. Background Art

[0002] At present, most of the methods for recovering valuable metals from the active materials of waste LiFePO4 batteries are still recycling and regeneration aiming at recovering lithium ions, while the recovery of phosphorus and iron elements with low metal value is relatively less. This is mainly due to the difficult acid dissolution of the phosphorus-iron slag after lithium extraction from waste lithium iron phosphate, and the difficult removal of a large number of impurity elements such as aluminum and copper in the phosphorus-iron slag.

[0003] A large number of studies and reports on the full-component recovery of lithium iron phosphate mostly use materials with relatively few impurity components for recovery and treatment, but there is no effective method for industrial recovery of high-impurity materials after industrial large-scale crushing. At the same time, many studies remove impurities in the phosphorus-iron slag by adding other aluminum and copper metal complexing agents, which will introduce organic substances or other metal impurities, which will have a certain impact on the subsequent synthesis of iron phosphate. With the increasing number of retired lithium-ion batteries and the improvement of domestic environmental protection requirements, the existing recovery methods are difficult to effectively meet the industrial recovery requirements of battery black powder with high impurities, and there are problems such as low economic efficiency, long recovery process, and a large amount of miscellaneous waste residues. Therefore, it is urgent to develop a method for efficient recovery and deep impurity removal of high-impurity lithium iron phosphate black powder to achieve the purpose of full-component recovery of waste lithium iron phosphate. Summary of the Invention

[0004] The purpose of the present invention 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 full-component recovery of waste lithium iron phosphate batteries with high impurities.

[0005] The present invention separates lithium and phosphorus-iron materials in one step by selective leaching, and optimizes the leaching conditions to prevent the problem of difficult leaching of phosphorus-iron due to the transformation of phosphorus-iron crystal form and the inability to dissolve impurities; the obtained phosphorus-iron graphite slag is used as a raw material for synthesizing iron phosphate and is further purified and decontaminated (deep impurity removal) by dilute strong acid and alkali solution, and finally the purified phosphorus-iron graphite slag is acid-leached to obtain a high-purity filtrate containing phosphorus and iron for directly synthesizing battery-grade iron phosphate. The whole process has less acid consumption, can process battery materials with high impurities, has high impurity element removal efficiency, short process, and high economic efficiency.

[0006] To achieve the above purpose, the present invention provides a method for recycling waste lithium iron phosphate batteries, wherein the method comprises the following steps:

[0007] (1) Selective leaching: Selectively leach the waste lithium iron phosphate battery materials at 20-65 °C using a leaching agent to obtain a leaching solution and phosphorus-iron graphite slag;

[0008] (2) Deep impurity removal: At 30 - 65 °C, the phosphorus-iron graphite slag obtained in step (1) is placed in a dilute strong acid solution for the first reaction, and an alkali solution is added dropwise to the first reaction product for the second reaction to obtain the phosphorus-iron graphite slag after deep impurity removal and an impurity-containing filtrate.

[0009] (3) Preparation of battery-grade iron phosphate: The phosphorus-iron graphite slag after deep impurity removal obtained in step (2) is used to prepare battery-grade iron phosphate.

[0010] Through the above technical solutions, the beneficial technical effects achieved by the present invention are as follows:

[0011] (1) By selectively leaching lithium and impurity elements, the present invention realizes the separation of the phosphorus-iron graphite slag from lithium and impurity elements, and controls the leaching conditions to prevent the transformation of the phosphorus-iron graphite slag.

[0012] (2) Based on the principle of strong acid making weak acid, the present invention uses a combination of dilute strong acid and alkali solution for deep impurity removal of the phosphorus-iron graphite slag, which can treat battery black powder materials with high impurities, and has the characteristics of high impurity removal efficiency and good economic benefits.

[0013] (3) By strictly controlling the reaction conditions of each step in the present invention, problems such as low leaching efficiency of iron phosphate, difficult dissolution of impurities, and large acid consumption caused by the transformation of the phosphorus-iron graphite slag are prevented, providing favorable conditions for the recovery of iron phosphate.

[0014] (4) The regenerated iron phosphate in the present invention has high purity and high recovery rate. Brief Description of the Drawings

[0015] Figure 1 is the process flow chart of the method for efficiently recycling waste lithium iron phosphate batteries of the present invention;

[0016] Figure 2 is the XRD pattern of the phosphorus-iron graphite slag in Example 1 of the present invention;

[0017] Figure 3 is the XRD pattern of the phosphorus-iron graphite slag in Example 2 of the present invention;

[0018] Figure 4 is the XRD pattern of the phosphorus-iron graphite slag in Example 3 of the present invention;

[0019] Figure 5 is the XRD pattern of the phosphorus-iron graphite slag in Example 4 of the present invention;

[0020] Figure 6 is the XRD pattern of the phosphorus-iron graphite slag in Comparative Example 1 of the present invention;

[0021] Figure 7 is the XRD pattern of the phosphorus-iron graphite slag in Comparative Example 2 of the present invention. Detailed Embodiments

[0022] The endpoints and any values disclosed herein in ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0023] The first aspect of the present invention provides a method for recycling waste lithium iron phosphate batteries. Among them, the method includes the following steps:

[0024] (1) Selective leaching: The waste lithium iron phosphate battery materials are selectively leached with a leaching agent at 20 - 65 °C to obtain a leachate and a phosphorus-iron-graphite residue;

[0025] (2) Deep impurity removal: At 30 - 65 °C, the phosphorus-iron-graphite residue obtained in step (1) is placed in a dilute strong acid solution for a first reaction, and an alkali solution is added dropwise to the first reaction product for a second reaction to obtain a phosphorus-iron-graphite residue after deep impurity removal and an impurity-containing filtrate;

[0026] (3) Preparation of battery-grade iron phosphate: The phosphorus-iron-graphite residue after deep impurity removal obtained in step (2) is used to prepare battery-grade iron phosphate.

[0027] The method provided by the present invention can preferentially extract lithium and some other impurity elements from waste lithium iron phosphate battery materials, and the produced leaching residue has an isophosphoromanganoite structure, which is beneficial to subsequent acid leaching and purification; then, a dilute strong acid and an alkali solution are combined to deeply remove impurities from the phosphorus-iron-graphite residue containing impurities. In this part, a mixed system of strong acid and phosphoric acid is created by the method of strong acid making weak acid. The phosphoric acid system effectively inhibits the dissolution of phosphorus-iron, and the strong acid system promotes the dissolution of impurity elements, so as to solve the problem that it is difficult to remove impurities such as aluminum and copper in the phosphorus-iron slag; finally, the phosphorus-iron-graphite residue after impurity removal is used as a raw material for leaching and precipitation to synthesize battery-grade iron phosphate. The whole process has mild conditions, high efficiency in removing impurity elements, high purity of recycled iron phosphate, high recovery rate, and good economic benefits.

[0028] In addition, the phosphorus-iron slag does not undergo crystal transformation. Under the same leaching conditions, the phosphorus-iron without crystal transformation has good leaching effect and does not require a lot of acid to dissolve, while the phosphorus-iron slag with crystal transformation has poor leaching effect. To achieve the same leaching efficiency, more acid is required for dissolution. Therefore, the method of the present invention also has the effect of less acid consumption.

[0029] In some embodiments of the present invention, the waste lithium iron phosphate battery material in step (1) is a mixed black powder of positive and negative electrodes obtained after mass disassembly and crushing of waste lithium iron phosphate batteries in industry. The battery black powder obtained after mass / large-scale disassembly and crushing of waste lithium iron phosphate batteries has a high impurity content and conforms to the actual materials faced in the industrial production process. Since this battery black powder contains a large amount of impurities, it is more difficult to process than the battery black powder obtained by traditional manual disassembly.

[0030] In some embodiments of the present invention, the content of copper in the waste lithium iron phosphate battery material is 1-5%, preferably 1.5%, and the content of aluminum is 1-3%, preferably 2.7%.

[0031] Currently in the market, it is difficult to recycle battery black powder containing more than 1% of Al impurities, and there are impurities such as Al, Cu, Ca, Mg, Ni, Co, Zn, Na, etc. brought in from the environment in the battery black powder produced industrially. For details, see Table 1.

[0032] The prior art usually takes lithium iron phosphate cathode powder or waste lithium iron phosphate battery black powder obtained by small-scale manual disassembly in the laboratory as the treatment object, which has a low impurity content (such as Al, Cu, etc.), is easy to process, and it is easy to obtain iron phosphate with high purity and recovery rate. However, for waste lithium iron phosphate battery materials with high impurity content, it is often difficult to remove impurities during the recycling process, and it is impossible to obtain battery-grade iron phosphate. Therefore, it is crucial to find a suitable industrial recycling technology for the recycling of waste lithium iron phosphate batteries.

[0033] In some embodiments of the present invention, 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.

[0034] In some embodiments of the present invention, the mass-volume ratio (i.e., solid-liquid ratio) of the waste lithium iron phosphate battery material to the leaching agent is 100-500 g / L, preferably 200 g / L.

[0035] In some embodiments of the present invention, the dosage of sulfuric acid is 100-130 wt% of the theoretical required amount of lithium and impurity elements in the waste lithium iron phosphate battery material. The "sulfuric acid" in the present invention uses concentrated sulfuric acid chemical with a mass fraction of 98%.

[0036] The theoretical required amount of lithium and impurity elements in the waste lithium iron phosphate battery material refers to the amount of sulfuric acid required for lithium and impurity element ions to form soluble metal sulfates with sulfate ions theoretically.

[0037] In some embodiments of the present invention, the mass percentage of hydrogen peroxide is 25-30%, preferably 30%.

[0038] In some embodiments of the present invention, the dosage of hydrogen peroxide is 0.2 - 0.6 mL / g, preferably 0.45 mL / g. In the present invention, the dosage is based on the mass of the waste lithium iron phosphate battery material.

[0039] In some embodiments of the present invention, the selective leaching is carried out under stirring conditions, and the stirring speed is 0 - 600 rpm, preferably 300 rpm.

[0040] In some embodiments of the present invention, the temperature of the selective leaching is 50 - 60 °C.

[0041] In some embodiments of the present invention, the time of the selective leaching is 1 - 5 h, preferably 3 h.

[0042] In the present invention, step (1) involves the selective leaching of lithium and impurity elements and the regulation of the crystal form of the leaching residue, which is specifically described as follows:

[0043] The waste lithium iron phosphate battery powder is subjected to selective leaching. A three-necked flask is used as the leaching reaction vessel, and then it is placed in a water bath with magnetic heating function for the leaching reaction. At the same time, the way of condensation reflux is adopted to prevent the loss of water during the high-temperature leaching process. During the leaching process, sulfuric acid and hydrogen peroxide destroy the olivine-type structure of the material, and lithium ions dissolve out from the material lattice. At the same time, ferrous ions are oxidized by hydrogen peroxide to ferric ions and combine with phosphate radicals to form iron phosphate. And there are usually impurities such as aluminum and copper that are difficult to remove in the battery black powder. During this process, the impurity metals mixed in the black powder will further react with sulfuric acid to dissolve and enter the solution in the form of ions, so as to achieve the purpose of selective leaching of lithium and impurity elements in the waste lithium iron phosphate battery black powder. The possible reactions involved in this process are shown in equations (1), (2), (3), and (4):

[0044] 2LiFePO4 + H2SO4 + H2O2 = Li2SO4 + 2FePO4 + 2H2O (1)

[0045] Al2O3 + 3H2SO4 = Al2(SO4)3 + 3H2O (2)

[0046] 2Al + 3H2SO4 = Al2(SO4)3 + 3H2↑ (3)

[0047] H2SO4 + H2O2 + Cu = CuSO4 + 2H2O (4)

[0048] During the selective leaching reaction, a redox reaction occurs in the leaching system. Olivine-type LiFePO4 has strong structural stability and can achieve selective de-lithiation through chemical in-situ oxidation to obtain orthorhombic heterophosphomanganite-type FePO4, which is beneficial to the subsequent leaching and recovery of phosphorus and iron. This crystal system belongs to a metastable structure and is prone to crystal form transformation to generate monoclinic or orthorhombic stable structures in an acidic system. The acid dissolution of this structure is difficult, which affects the impurity removal and secondary leaching of the subsequent phosphorus-iron slag. In this application, the occurrence of crystal transformation is avoided by controlling the temperature of selective leaching.

[0049] In some embodiments of the present invention, the dilute strong acid described in step (2) is selected from at least one of dilute sulfuric acid, dilute hydrochloric acid, and dilute nitric acid.

[0050] In some embodiments of the present invention, the concentration of the dilute strong acid solution is 0.2 - 0.8 mol / L, preferably 0.35 - 0.4 mol / L.

[0051] In some embodiments of the present invention, the temperature of the deep impurity removal in step (2) is 50 - 60 °C.

[0052] In some embodiments of the present invention, the first reaction time is 1 - 5 h, preferably 1 - 2 h.

[0053] In some embodiments of the present invention, the first reaction is carried out under stirring conditions, and the stirring speed is 100 - 600 rpm, preferably 300 rpm.

[0054] In some embodiments of the present invention, the alkali solution is selected from at least one of ammonia water, sodium hydroxide solution, and sodium carbonate solution.

[0055] In some embodiments of the present invention, the concentration of the alkali solution is 1 - 6 mol / L, preferably 3 - 4 mol / L.

[0056] In some embodiments of the present invention, the alkali solution is added dropwise to the first reaction product until the pH value is 1.4 - 2.5, preferably 1.8 - 2.

[0057] In some embodiments of the present invention, the time of the second reaction is 20 - 60 min, preferably 20 - 40 min.

[0058] The impurity-containing filtrate can obtain ammonium sulfate products after impurity removal and evaporation crystallization.

[0059] In the present invention, step (2) involves the deep impurity removal of phosphorus-iron graphite slag, which is specifically described as follows:

[0060] The phosphorus-iron-graphite slag containing impurities obtained by filtration after leaching is deeply purified to remove residual impurity elements such as aluminum and copper in the slag. A purification system of sulfuric acid and ammonia water is adopted. First, the phosphorus-iron-graphite slag is placed in a dilute sulfuric acid solution. According to the principle of strong acid making weak acid, the solution is a mixed system of sulfuric acid and phosphoric acid at this time. The phosphoric acid environment in the solution will inhibit the leaching of phosphorus-iron, while a large amount of impurity elements such as aluminum and copper will dissolve into the acidic solution. Then, an alkaline solution is added dropwise to the leaching slurry to adjust the pH value of the leaching system. According to the different solubility products of different metal elements, a small part of the phosphorus and iron entering the solution will precipitate in the form of iron phosphate, and impurity elements such as aluminum and copper are retained in the leaching solution to achieve deep purification of the phosphorus-iron-graphite slag. After the reaction, a phosphorus-iron-graphite slag with higher purity and an impurity-containing filtrate are obtained by filtration. The phosphorus-iron-graphite slag is used as a raw material to recover iron phosphate. To prevent the transformation of the iron phosphate with the heterophosphomanganite structure obtained in the leaching stage from occurring again in this part, the purification conditions need to be well controlled.

[0061] In some embodiments of the present invention, the leaching solution obtained in step (1) is concentrated, purified, and precipitated to obtain lithium carbonate, and sodium sulfate is obtained after evaporation and crystallization of the supernatant.

[0062] In some embodiments of the present invention, the operation of step (3) is as follows:

[0063] The phosphorus-iron-graphite slag after deep purification obtained in step (2) is acid-leached to obtain a phosphorus-iron solution and graphite slag; after adjusting the molar ratio of phosphorus to iron in the phosphorus-iron solution to 1:1, the pH is adjusted to synthesize iron phosphate dihydrate; the iron phosphate dihydrate is calcined at a high temperature (such as calcination) to remove the crystal water and obtain battery-grade iron phosphate.

[0064] In some embodiments of the present invention, the temperature of the acid leaching is 30-80 °C; the time is 1-5 h.

[0065] In some embodiments of the present invention, the acid leaching is carried out under stirring conditions, and the stirring speed is 100-600 rpm.

[0066] In some embodiments of the present invention, ammonia water is added to adjust the pH to 1.4-2.5.

[0067] In some embodiments of the present invention, the temperature of the high-temperature heat treatment is 500-700 °C.

[0068] According to a particularly preferred embodiment of the present invention, as Figure 1 shown, a method for recycling waste lithium iron phosphate batteries, the method comprising the following steps:

[0069] (1) Selective leaching: Mix waste lithium iron phosphate battery materials, hydrogen peroxide with a concentration of 30%, and sulfuric acid, and stir at a stirring speed of 0 - 600 rpm, with a solid-liquid ratio of 100 - 500 g / L. The dosage of hydrogen peroxide is 0.2 - 0.6 mL / g. Perform selective leaching at 20 - 65 °C for 1 - 5 h to obtain a leaching solution and phosphorus-iron-graphite slag; the leaching solution is concentrated, purified, and precipitated to obtain lithium carbonate, and sodium sulfate is obtained after evaporation and crystallization of the supernatant; the dosage of the sulfuric acid is 100 - 130 wt% of the theoretical required amount of lithium and impurity elements in the waste lithium iron phosphate battery materials;

[0070] (2) Deep purification: At 30 - 65 °C, place 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 stir at a stirring speed of 100 - 600 rpm for the first reaction for 1 - 5 h. Add ammonia water with a concentration of 1 - 6 mol / L to the first reaction product until the pH value is 1.4 - 2.5, and perform the second reaction for 20 - 60 min to obtain the phosphorus-iron-graphite slag after deep purification and an impurity-containing filtrate;

[0071] (3) Preparation of battery-grade iron phosphate: Under stirring conditions, acid-leach the phosphorus-iron-graphite slag after deep purification obtained in step (2) with sulfuric acid at 30 - 80 °C for 1 - 5 h. The dosage of sulfuric acid is 0.2 - 1 mL / g, and the stirring speed is 100 - 600 rpm to obtain a phosphorus-iron solution and graphite slag; after adjusting the molar ratio of phosphorus to iron in the phosphorus-iron solution to 1:1, add ammonia water to adjust the pH to 1.4 - 2.5 to synthesize iron phosphate dihydrate; the iron phosphate dihydrate is heat-treated at 600 - 700 °C to remove the crystal water to obtain battery-grade iron phosphate.

[0072] The present invention mainly relates to a method for green recycling of waste lithium iron phosphate batteries with high impurities. By controlling the leaching conditions, it prevents the transformation of phosphorus-iron-graphite slag and removes most of the impurity elements. Then, by the way of strong acid making weak acid, dilute strong acid and alkali solution are used to purify the filter residue to obtain high-purity phosphorus-iron-graphite slag, and the obtained phosphorus-iron-graphite slag with higher purity is used to prepare battery-grade iron phosphate. This method not only solves the problem of difficult acid leaching of phosphorus-iron slag after lithium extraction from lithium iron phosphate materials, but also solves the problem of difficult impurity removal of phosphorus-iron slag.

[0073] The present invention will be described in detail below through examples.

[0074] For those not specifying specific conditions in the following examples and comparative examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial channels.

[0075] The waste lithium iron phosphate battery materials in the following examples and comparative examples were obtained by the following method: After the waste lithium iron phosphate batteries were discharged by a machine, they were mechanically disassembled, crushed, dried, and screened to obtain a mixture of positive and negative black powders. Its composition is shown in Table 1.

[0076] Table 1

[0077] Element type Li Fe P Al Cu Mn Ni Co Mg Zn Ca K Content, % 2.7 19.5 11.4 2.7 1.5 1.0 0.5 0.4 0.06 0.02 0.29 0.17

[0078] Example 1

[0079] A method for recycling waste lithium iron phosphate batteries includes the following steps:

[0080] (1) Selective leaching of lithium and impurity elements and regulation of the crystal form of the leaching residue

[0081] The waste lithium iron phosphate battery materials were leached for 3 h at a leaching temperature of 60 °C according to a solid-liquid ratio of 200 g / L, a sulfuric acid dosage of 110 wt% of the theoretical amount required for lithium and impurity elements in the waste lithium iron phosphate battery materials, a 30% hydrogen peroxide dosage of 0.45 mL / g, and a stirring speed of 300 rpm. After that, the lithium leaching rate was 99%, the aluminum leaching rate was 75%, the copper leaching rate was 95%, the iron leaching rate was 3%, and the phosphorus leaching rate was 3.4%. After the reaction ended, solid-liquid separation was carried out to obtain a phosphorus-iron graphite residue containing heterophosphomanganite-type iron phosphate. Its XRD pattern is as Figure 2 shown; it can be seen from the XRD pattern that its peak shape is sharp and there are no impurity peaks, indicating that the material after lithium deintercalation has a high crystallinity; the highest peak represents the structural peak of negative electrode graphite, and other peak shapes correspond one by one to the standard peak shape of heterophosphomanganite-type iron phosphate, which shows that the iron phosphate after lithium extraction under this condition is heterophosphomanganite-type iron phosphate;

[0082] (2) Deep impurity removal of the phosphorus-iron graphite residue

[0083] The phosphorus-iron graphite residue was placed in a dilute sulfuric acid solution, and the concentration of the dilute sulfuric acid was controlled at 0.4 mol / L, and the reaction was carried out at a stirring speed of 300 rpm and a temperature of 50 °C for 1 h. Then, 4 mol / L ammonia water was slowly added to the leaching slurry liquid, and the pH value was adjusted to 1.8 and reacted for 20 min. After the reaction ended, filtration was carried out to obtain a phosphorus-iron graphite residue with higher purity, and the impurity removal rate reached 95%, and the phosphorus-iron loss rate was lower than 2%;

[0084] (3) Recovery of phosphorus and iron to prepare battery-grade iron phosphate

[0085] The phosphorus-iron graphite residue after deep impurity removal obtained in step (2) was acid-leached at 50 °C for 3 h to obtain a phosphorus-iron solution and a graphite residue; after adjusting the molar ratio of phosphorus and iron in the phosphorus-iron solution to 1:1, ammonia water was added to adjust the pH to 2 to synthesize iron phosphate dihydrate; the iron phosphate dihydrate was heat-treated at 600 °C at high temperature to remove the crystal water and obtain battery-grade iron phosphate.

[0086] The impurity removal rate of the whole process is 98%, the recovery rate of iron phosphate is 94%, and the purity of iron phosphate is 99%.

[0087] Example 2

[0088] A method for recycling waste lithium iron phosphate batteries, comprising the following steps:

[0089] (1) Selective leaching of lithium and impurity elements and regulation of the crystal form of the leaching residue

[0090] After leaching the waste lithium iron phosphate battery materials at a solid-liquid ratio of 200 g / L, with the sulfuric acid dosage being 110 wt% of the theoretical requirement of lithium and impurity elements in the waste lithium iron phosphate battery materials, 30% hydrogen peroxide dosage of 0.45 mL / g, stirring speed of 300 rpm, and leaching temperature of 50 °C for 3 h, the leaching rate of lithium is 99%, the leaching rate of aluminum is 72%, the leaching rate of copper is 91%, the leaching rate of iron is 2.6%, and the leaching rate of phosphorus is 2.9%. After the reaction ends, solid-liquid separation is carried out to obtain a phosphorus-iron graphite slag containing heterophosphomanganite-type iron phosphate, and its XRD pattern is as Figure 3 shown; it can be seen from the XRD pattern that its peak shape is sharp and there are no impurity peaks, indicating that the crystallinity of the material after lithium deintercalation is relatively high; the highest peak represents the structural peak of the negative electrode graphite, and other peak shapes correspond one by one to the standard peak shape of heterophosphomanganite-type iron phosphate, which shows that the iron phosphate after lithium extraction under this condition is heterophosphomanganite-type iron phosphate;

[0091] (2) Deep impurity removal of the phosphorus-iron graphite slag

[0092] The phosphorus-iron graphite slag is placed in a dilute sulfuric acid solution, and the concentration of the dilute sulfuric acid is controlled at 0.35 mol / L, the stirring speed is 300 rpm, and the reaction is carried out at a temperature of 60 °C for 2 h. Then, 3 mol / L ammonia water is slowly added to the leaching slurry liquid to adjust the pH value to 2.0 and react for 40 min. After the reaction ends, filtration is carried out to obtain a phosphorus-iron graphite slag with relatively high purity, the impurity removal rate reaches 96%, and the phosphorus-iron loss rate is less than 1.3%;

[0093] (3) Recovery of phosphorus and iron to prepare battery-grade iron phosphate

[0094] The phosphorus-iron graphite slag after deep impurity removal obtained in step (2) is acid-leached at 60 °C for 4 h to obtain a phosphorus-iron solution and graphite slag; after adjusting the molar ratio of phosphorus and iron in the phosphorus-iron solution to 1:1, ammonia water is added to adjust the pH to 2.5 to synthesize iron phosphate dihydrate; the iron phosphate dihydrate is heat-treated at 700 °C at high temperature to remove the crystal water and obtain battery-grade iron phosphate.

[0095] The impurity removal rate of the whole process is greater than 98.5%, the recovery rate of iron phosphate is greater than 95%, and the purity of iron phosphate is 99%.

[0096] Example 3

[0097] A method for recycling waste lithium iron phosphate batteries, comprising the following steps:

[0098] (1) Selective leaching of lithium and impurity elements and regulation of the crystal form of the leaching residue

[0099] The waste lithium iron phosphate battery materials are leached at a solid-liquid ratio of 100 g / L, with the sulfuric acid dosage being 100 wt% of the theoretical requirement of lithium and impurity elements in the waste lithium iron phosphate battery materials, and the dosage of 30% hydrogen peroxide being 0.2 mL / g. After leaching for 5 h at a leaching temperature of 20 °C, the leaching rate of lithium is 98.3%, the leaching rate of aluminum is 72.6%, the leaching rate of copper is 90.5%, the leaching rate of iron is 1.4%, and the leaching rate of phosphorus is 1.6%. After the reaction ends, solid-liquid separation is carried out to obtain a phosphorus-iron graphite slag containing heterophosphomanganite-type iron phosphate, and its XRD pattern is as Figure 4 shown;

[0100] (2) Deep impurity removal of the phosphorus-iron graphite slag

[0101] The phosphorus-iron graphite slag is placed in a dilute sulfuric acid solution, and the concentration of the dilute sulfuric acid is controlled at 0.2 mol / L, the stirring speed is 100 rpm, and the reaction is carried out at a temperature of 30 °C for 5 h. Then, 1 mol / L ammonia water is slowly added to the leaching slurry liquid, and the pH value is adjusted to 1.4 and reacted for 20 min. After the reaction ends, filtration is carried out to obtain a phosphorus-iron graphite slag with higher purity, the impurity removal rate reaches 93%, and the phosphorus-iron loss rate is lower than 2.7%;

[0102] (3) Recovery of phosphorus and iron to prepare battery-grade iron phosphate

[0103] The phosphorus-iron graphite slag after deep impurity removal obtained in step (2) is acid-leached at 30 °C for 5 h to obtain a phosphorus-iron solution and a graphite slag; after adjusting the molar ratio of phosphorus and iron in the phosphorus-iron solution to 1:1, ammonia water is added to adjust the pH to 1.4 to synthesize iron phosphate dihydrate; the iron phosphate dihydrate is heat-treated at 620 °C to remove crystal water, and battery-grade iron phosphate is obtained.

[0104] The impurity removal rate of the whole process is greater than 97.4%, the recovery rate of iron phosphate is greater than 92%, and the purity of iron phosphate is 99%.

[0105] Example 4

[0106] A method for recycling waste lithium iron phosphate batteries, comprising the following steps:

[0107] (1) Selective leaching of lithium and impurity elements and regulation of the crystal form of the leaching residue

[0108] The waste lithium iron phosphate battery materials are leached at a solid-liquid ratio of 500 g / L, with the sulfuric acid dosage being 130 wt% of the theoretical required amount of lithium and impurity elements in the waste lithium iron phosphate battery materials, the dosage of 30% hydrogen peroxide being 0.65 mL / g, the stirring speed being 600 rpm, and the leaching temperature being 65 °C for 1 h. After that, the leaching rate of lithium is 99%, the leaching rate of aluminum is 80%, the leaching rate of copper is 98%, the leaching rate of iron is 2.7%, and the leaching rate of phosphorus is 2.9%. After the reaction ends, solid-liquid separation is carried out to obtain phosphorus-iron graphite slag containing heterophosphomanganite-type iron phosphate, and its XRD pattern is as shown in Figure 5 shown;

[0109] (2)Deep impurity removal of phosphorus-iron graphite slag

[0110] The phosphorus-iron graphite slag is placed in a dilute sulfuric acid solution, with the concentration of the dilute sulfuric acid controlled at 0.8 mol / L, the stirring speed being 600 rpm, and the reaction being carried out at 65 °C for 1 h. Then, 3 mol / L ammonia water is slowly added to the leaching slurry, and the pH value is adjusted to 2.5 for reaction for 60 min. After the reaction ends, filtration is carried out to obtain phosphorus-iron graphite slag with higher purity, and the impurity removal rate reaches 97%, and the phosphorus-iron loss rate is lower than 0.4%;

[0111] (3)Recovery of phosphorus and iron to prepare battery-grade iron phosphate

[0112] The phosphorus-iron graphite slag after deep impurity removal obtained in step (2) is acid-leached at 80 °C for 1 h to obtain a phosphorus-iron solution and graphite slag; after adjusting the molar ratio of phosphorus to iron in the phosphorus-iron solution to 1:1, ammonia water is added to adjust the pH to 2.2 to synthesize iron phosphate dihydrate; the iron phosphate dihydrate is heat-treated at 680 °C at high temperature to remove the crystal water and obtain battery-grade iron phosphate.

[0113] The impurity removal rate of the whole process is greater than 98%, the recovery rate of iron phosphate is greater than 95.3%, and the purity of iron phosphate is 99%.

[0114] Comparative Example 1

[0115] (1)Selective leaching of lithium and impurity elements and control of crystal form of leaching residue

[0116] Except that the leaching temperature is adjusted to 80 °C, other conditions are the same as those in Example 1. The leaching rate of lithium is 99%, the leaching rate of aluminum is 72%, the leaching rate of copper is 96%, the leaching rate of iron is 2.7%, and the leaching rate of phosphorus is 2.9%. After the reaction ends, solid-liquid separation is carried out to obtain monoclinic iron phosphate, and its XRD pattern is as shown in Figure 6 shown.

[0117] (2)Deep impurity removal of phosphorus-iron graphite slag

[0118] Other conditions are the same as in Example 1. Since the iron phosphate in the ferrophosphorus graphite slag is monoclinic and its structure is stable, the impurity elements are wrapped by it, so the impurity removal rate is low. The impurity removal rate is 20%, and the loss rate of ferrophosphorus is 2.3%.

[0119] (3)Recovery of phosphorus and iron to prepare battery-grade iron phosphate

[0120] The conditions are the same as in Example 1.

[0121] The overall process impurity removal rate is greater than 79%, and the recovery rate of iron phosphate is greater than 25%.

[0122] Comparative Example 2

[0123] (1)Selective leaching of lithium and impurity elements and control of the crystal form of the leaching residue

[0124] It is the same as in Example 2.

[0125] (2)Deep impurity removal of ferrophosphorus graphite slag

[0126] Except that the temperature is adjusted to 90 °C, other conditions are the same as in Example 2. After the reaction, a mixture of monoclinic iron phosphate and graphite slag is obtained by filtration. Its XRD pattern is as Figure 7 shown, and the impurity removal rate reaches 54%.

[0127] (3)Recovery of phosphorus and iron to prepare battery-grade iron phosphate

[0128] The conditions are the same as in Example 2.

[0129] The overall process impurity removal rate is greater than 87%, and the recovery rate of iron phosphate is greater than 50%.

[0130] Comparative Example 3

[0131] Recover the waste lithium iron phosphate battery according to the method of Example 1, the difference is that step (2) is omitted.

[0132] The overall process impurity removal rate is greater than 75%, the impurity content exceeds the standard, and battery-grade iron phosphate cannot be synthesized.

[0133] From the above results, it can be seen that during the selective leaching process for lithium extraction, parameters such as the reaction temperature will affect the crystal structure of the ferrophosphorus slag. When the temperature exceeds the range, the iron phosphate will change from the isophosphorite type to the monoclinic type, which leads to difficult leaching of the subsequent ferrophosphorus slag and reduces the recovery efficiency of ferrophosphorus. At the same time, the ferrophosphorus slag after crystal transformation will wrap the impurity elements inside it, hindering further impurity removal effect.

[0134] The deep impurity removal in the second step can better achieve the purification and impurity removal effect of the phosphorus-iron graphite slag on the basis of leaching lithium and impurities in the first step. By controlling parameters such as temperature, the transformation of the phosphorus-iron slag into crystals is prevented in this stage, making it easier to leach the phosphorus-iron liquid from the phosphorus-iron slag in the next step and improving the recovery rate of phosphorus-iron.

[0135] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for recycling waste lithium iron phosphate batteries, characterized in that, The waste lithium iron phosphate battery material is the mixed black powder of the positive and negative electrodes obtained after the large-scale disassembly and crushing of waste lithium iron phosphate batteries in industry; the method consists of the following steps: (1) Selective leaching: Mix and stir the waste lithium iron phosphate battery material, 30% hydrogen peroxide and sulfuric acid, with a stirring speed of 600 rpm, a solid-liquid ratio of 500 g / L, and the dosage of hydrogen peroxide being 0.65 mL / g. Carry out selective leaching at 65 °C for 1 h to obtain a leaching solution and phosphorus-iron-graphite slag; the leaching solution is concentrated, purified, and precipitated to obtain lithium carbonate, and sodium sulfate is obtained after evaporation and crystallization of the supernatant; the dosage of the sulfuric acid is 130 wt% of the theoretical required amount of lithium and impurity elements in the waste lithium iron phosphate battery material; The waste lithium iron phosphate battery material is obtained by the following method: After the waste lithium iron phosphate battery is discharged by a machine, it is mechanically disassembled, crushed, dried, and screened to obtain the mixed black powder of the positive and negative electrodes; its composition includes: 2.7% Li, 19.5% Fe, 11.4% P, 2.7% Al, 1.5% Cu, 1.0% Mn, 0.5% Ni, 0.4% Co, 0.06% Mg, 0.02% Zn, 0.29% Ca, and 0.17% K; (2) Deep purification: At 65 °C, place the phosphorus-iron-graphite slag obtained in step (1) in a dilute sulfuric acid solution and stir, control the concentration of the dilute sulfuric acid at 0.8 mol / L, and the stirring speed at 600 rpm. Carry out the first reaction for 1 h, and add ammonia water with a concentration of 3 mol / L to the first reaction product until the pH value is 2.5, and carry out the second reaction for 60 min to obtain the phosphorus-iron-graphite slag after deep purification and the filtrate containing impurities; (3) Preparation of battery-grade iron phosphate: Under stirring conditions, acid-leach the phosphorus-iron-graphite slag obtained in step (2) with sulfuric acid at 80 °C for 1 h to obtain a phosphorus-iron solution and graphite slag; after adjusting the molar ratio of phosphorus to iron in the phosphorus-iron solution to 1:1, add ammonia water to adjust the pH to 2.2 to synthesize iron phosphate dihydrate; the iron phosphate dihydrate is heat-treated at 680 °C at high temperature to remove the crystal water and obtain battery-grade iron phosphate.

2. The method according to claim 1, wherein, The acid leaching in step (3) is carried out under stirring conditions, and the stirring speed is 100 - 600 rpm.

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