Waste lithium iron phosphate battery recovery process

Abstract

The invention provides a waste lithium iron phosphate battery recovery process, and relates to the technical field of battery recovery, the waste lithium iron phosphate battery recovery process comprises the following steps: pre-treating waste lithium iron phosphate batteries to obtain battery powder; mixing the battery powder with a lithium source, and carrying out aerobic roasting and water leaching at 400-600 DEG C to obtain a first lithium-containing solution and modified battery powder; 90-120 g / t of sodium hexametaphosphate, 400-1000 g / t of sulfuric acid, 400-600 g / t of kerosene and 100-200 g / t of 2 # oil are added into the modified battery powder for flotation, and a graphite product and lithium iron phosphate battery powder are obtained. The process can effectively improve the recovery rate and recovery purity of graphite and lithium iron phosphate materials in the battery powder, and is suitable for large-scale industrial recovery treatment.

Description

Technical Field

[0001] The present application relates to the field of battery recycling technology, and in particular to a process for recycling waste lithium iron phosphate batteries. Background Art

[0002] In recent years, with the rapid development of my country's new energy industry, lithium-ion batteries have become a key driving force for the development of new energy due to their advantages such as high energy density, high voltage, good cycle performance, long service life, low self-discharge rate, and environmental friendliness. They are widely used in important fields such as electric vehicles, energy storage systems, and smart grids. Currently, lithium-ion batteries can be divided into ternary lithium batteries, lithium iron phosphate batteries, lithium cobalt oxide batteries, and lithium manganese oxide batteries based on the cathode material. Among them, lithium iron phosphate batteries, due to their excellent cycle stability and safety performance, have continuously increased their market share and gradually become one of the main power sources for new energy vehicles.

[0003] As the market share of lithium iron phosphate batteries continues to grow, the number of retired batteries is also increasing. Used batteries still contain a large amount of valuable recyclable resources, and the residual electrolyte poses a potential threat to the environment. Therefore, from the perspectives of both environmental protection and resource reuse, they need to be recycled. The current mainstream recycling process usually uses a combination of multi-stage crushing and multi-stage roasting to disassemble battery cells to obtain recyclable battery powder. However, existing recycling methods have difficulty in achieving efficient separation of graphite and lithium iron phosphate materials in battery powder during subsequent processing, which in turn affects resource recovery rate and product quality.

[0004] Therefore, it is necessary to develop an efficient lithium iron phosphate battery recycling process to achieve full separation of graphite and lithium iron phosphate materials, improve the recovery rate and purity of resources, and thus better meet the technical needs of high-value utilization of waste battery resources. Summary of the Invention

[0005] The present application provides a waste lithium iron phosphate battery recycling process, which can effectively improve the recovery rate and recovery purity of graphite and lithium iron phosphate materials in battery powder.

[0006] The first embodiment of the present invention is a waste lithium iron phosphate battery recycling process, comprising the following steps:

[0007] Pre-treating waste lithium iron phosphate batteries to obtain battery powder;

[0008] The battery powder is mixed with a lithium source, and subjected to oxygen roasting at 400-600° C., and water soaking to obtain a first lithium-containing solution and modified battery powder;

[0009] 90-120 g / t of sodium hexametaphosphate, 400-1000 g / t of sulfuric acid, 400-600 g / t of kerosene and 100-200 g / t of No. 2 oil are added to the modified battery powder for flotation to obtain a graphite product and lithium iron phosphate battery powder.

[0010] The waste lithium iron phosphate battery recycling process according to the first embodiment of the present invention has at least the following beneficial effects:

[0011] By adding a lithium source to the battery powder and calcining it in an oxygen atmosphere at a temperature below 600°C, organic impurities such as binders can be effectively removed, the hydrophilicity of the lithium iron phosphate particles can be improved, and the difference in interfacial properties between the lithium iron phosphate particles and the graphite can be enhanced, thereby facilitating efficient separation of the two during the subsequent flotation process. Furthermore, the graphite structure remains stable under these temperature conditions, ensuring efficient recycling of the graphite.

[0012] During the roasting process, the lithium source can react with the residual fluorine element in the battery powder to generate soluble lithium fluoride (LiF), which enters the solution after subsequent water immersion treatment, significantly reducing the fluorine impurity content in graphite and lithium iron phosphate, improving the product purity, and realizing the efficient recycling of lithium resources.

[0013] In the flotation separation process, by optimizing the flotation reagent system, using sodium hexametaphosphate as a dispersant, sulfuric acid as a regulator, kerosene as a collector, and 2# oil as a foaming agent, and controlling the dosage of each reagent within a reasonable range, the separation efficiency of graphite and lithium iron phosphate materials has been significantly improved, which helps to obtain high-purity graphite products and lithium iron phosphate battery powder products, and effectively improves resource recovery rate and product quality.

[0014] The process is simple, easy to implement, and suitable for large-scale industrial recycling and treatment. It has significant promotion prospects and industrial value.

[0015] According to some embodiments of the present invention, the pretreatment includes the following steps: placing the waste lithium iron phosphate batteries in an inert atmosphere for a single roasting, separating the battery cells, crushing, and screening to obtain battery powder and copper and aluminum materials.

[0016] Compared with the existing technology of disassembling battery cells by combining multi-stage crushing and multi-stage roasting, this pretreatment process has the following significant advantages:

[0017] By directly calcining the lithium iron phosphate battery cells and utilizing the structural characteristics of the battery cells wrapped in the shell, a local high-pressure environment (similar to an autoclave) is formed at the calcination temperature, making it easier to decompose the binder between the copper and aluminum current collectors and the electrode materials. In the subsequent process, only a relatively low-intensity crushing force is required to make the battery powder fall off the surface of the current collector, avoiding excessive crushing of copper and aluminum, and significantly reducing the proportion of copper and aluminum impurities entering the battery powder during the screening process, thereby improving the sorting purity and overall recovery rate of the battery powder.

[0018] This process omits the discharge and diaphragm air separation steps found in traditional recycling methods. The electrolyte in the battery cells is directly dried during the roasting process, and the diaphragms are essentially pulverized during pyrolysis, effectively simplifying the pre-treatment process. Furthermore, this process only incorporates nitrogen protection during the roasting phase, significantly reducing nitrogen consumption compared to traditional multi-stage roasting methods that employ nitrogen protection throughout the entire process. This lowers equipment airtightness requirements and operating costs, and eliminates the issues of dust bag clogging and material obstruction at the discharge port caused by residual electrolyte in traditional methods, thereby improving system operational stability.

[0019] In addition, the carbon coating formed by the carbonization of organic matter such as binders in the electrode material can be easily removed in the subsequent aerobic roasting process, which can ensure the separation efficiency of graphite and lithium iron phosphate materials in the subsequent flotation process.

[0020] According to some embodiments of the present invention, the primary calcination temperature is 350-600°C. Low calcination temperatures may result in residual electrolyte, increasing the residual F content in the battery powder. This may necessitate the addition of more lithium source to react with the residual F during the subsequent aerobic calcination phase. High calcination temperatures significantly increase energy consumption and overall processing costs.

[0021] The present invention does not impose any restrictions on the time of a single roasting, and a suitable time range can be selected based on experience. For example, the roasting time is more than 0.5 hours, specifically 0.5 to 2 hours.

[0022] According to some embodiments of the present invention, the screen size of the screening is 60-100 mesh.

[0023] According to some embodiments of the present invention, the battery cell is obtained by cutting the shell of the calcined waste lithium iron phosphate battery and removing the shell.

[0024] According to some embodiments of the present invention, the housing is crushed and then mixed with the copper and aluminum materials, and then sorted to obtain copper and aluminum products. The housing of a lithium battery is typically an aluminum shell. Sorting it together with the copper and aluminum materials can simplify the processing process and improve resource utilization.

[0025] According to some embodiments of the present invention, the lithium source is one or a combination of Li3PO4 and LiOH. These lithium sources do not introduce other impurities during the roasting process. Furthermore, Li3PO4 is a neutral salt, which is more conducive to recovering iron phosphate by acid leaching than alkaline lithium sources, thereby reducing the amount of acid used.

[0026] According to some embodiments of the present invention, the amount of the lithium source added is 0.3% to 1% of the mass of the battery powder. When the F content in the battery powder is high, the amount of the lithium source added can be appropriately increased to promote its reaction with the F in the battery powder to form LiF.

[0027] According to some embodiments of the present invention, the atmosphere of the oxygen roasting is air.

[0028] According to some embodiments of the present invention, the oxygen roasting time is more than 0.5 h, for example, specifically 0.5 to 2 h.

[0029] According to some embodiments of the present invention, during the water immersion process, the mass volume ratio of the solid phase (i.e., the battery powder after calcination) to the liquid phase is 1 kg:8-12 L.

[0030] According to some embodiments of the present invention, the water immersion time is 0.5 to 1 hour.

[0031] According to some embodiments of the present invention, during the flotation process, the amount of kerosene added is 450-600 g / t.

[0032] According to some embodiments of the present invention, at least one of the following steps is further included:

[0033] (a) mixing the lithium iron phosphate battery powder with iron powder, and acid leaching to obtain a ferrophosphorus leachate;

[0034] (b) mixing the graphite product with a carbon source and performing secondary calcination under an inert atmosphere to obtain battery-grade graphite.

[0035] According to some embodiments of the present invention, step (a) satisfies at least one of the following conditions:

[0036] (a1) The amount of iron powder added is 5% to 20% of the mass of the lithium iron phosphate battery powder;

[0037] (a2) the acid leaching process comprises: mixing the lithium iron phosphate battery powder, iron powder and water, adjusting the pH, and leaching, wherein the mass-to-volume ratio of the total mass of the lithium iron phosphate battery powder and iron powder to the water is 0.1-0.35 kg:1 L;

[0038] (a3) the pH of the acid leaching is 1 to 2;

[0039] (a4) The acid leaching temperature is 75 to 95° C., and the acid leaching time is 1 to 3 hours.

[0040] Adding Fe powder during the acid leaching process can significantly increase the dissolution rate of lithium iron phosphate battery powder. If the amount of iron powder added is insufficient, the battery powder dissolution reaction rate will decrease, affecting the efficiency of subsequent processing. However, if the amount of iron powder added is too high, the dissolution rate will not be further improved, but the cyclic load of the system will increase.

[0041] According to some embodiments of the present invention, the further step is further included: solid-liquid separation after the acid leaching to obtain slag and the ferrophosphorus leachate, and electrolysis of the ferrophosphorus leachate to obtain crude ferric phosphate and a second lithium-containing solution.

[0042] Electrolysis allows for rapid deposition of ferric phosphate and efficient separation of iron and lithium ions. The present invention does not specifically limit the electrolysis system; the electrolyte employed can be an acid solution (e.g., a sulfuric acid solution with a pH of 1 to 3); the anode can be a platinum sheet or graphite sheet, and the cathode can be an aluminum sheet, copper sheet, or graphite sheet. A DC power supply can be used during the electrolysis process, with a voltage range of 1 to 4 V and an electrolysis time of at least 1 hour, for example, 1 to 4 hours.

[0043] According to some embodiments of the present invention, at least one of the following steps is further included:

[0044] (c) calcining the crude ferric phosphate to obtain anhydrous ferric phosphate;

[0045] (d) combining the second lithium-containing solution and the first lithium-containing solution to precipitate lithium to obtain a lithium carbonate product and a fluorine-containing solution.

[0046] Among them, the present invention does not specifically limit the process parameters of calcination. Calcination is mainly used to remove crystal water. The relevant parameters can be reasonably selected by those skilled in the art based on actual needs and experience. For example, the calcination atmosphere can be an inert atmosphere or an oxygen-containing atmosphere (such as air), among which the use of air atmosphere is less expensive; the use of an inert atmosphere can achieve faster crystal transformation and improve crystal quality. The calcination temperature can be above 400°C, for example, 400-600°C, and the calcination time can be controlled to be more than 2 hours. Appropriately increasing the calcination temperature helps to shorten the calcination time, reduce crystal defects, and improve product quality.

[0047] Lithium precipitation is carried out using known methods, such as adding carbonate to a lithium-containing solution to cause a precipitation reaction. The amount of carbonate added is measured according to the chemical equivalent of lithium ions (equivalent or appropriately excessive) to ensure complete precipitation of lithium ions.

[0048] According to some embodiments of the present invention, step (b) satisfies at least one of the following conditions:

[0049] (b1) the carbon source is at least one of asphalt and phenolic resin;

[0050] (b2) the amount of the carbon source added is 5% to 10% of the mass of the graphite product;

[0051] (b3) the secondary calcination temperature is 2000-2800° C.;

[0052] (b4) The secondary roasting time is ≥1h.

[0053] Graphitization treatment can improve the electrochemical properties of graphite. The present invention does not limit the time of secondary calcination (coating carbonization or graphitization treatment), for example, it can be 1 to 3 hours.

[0054] As used herein, the term "flotation" includes the step of mixing the modified battery powder with water to form a slurry. The slurry may have a solids content of 5% to 20%. The amount of flotation reagent (sodium hexametaphosphate, sulfuric acid, kerosene, and No. 2 oil) added is calculated based on the dry weight of the modified battery powder.

[0055] The term "2# oil" refers to No. 2 flotation oil (pine oil), which is a type of frother commonly used in flotation processes.

[0056] The term "inert atmosphere" refers to an atmosphere composed of commonly used inert gases such as nitrogen and argon.

[0057] The term "plurality" means two or more.

[0058] The terms "above" and "below" include the stated values ​​themselves.

[0059] Herein, the numerical ranges mentioned include the endpoint values ​​and encompass any sub-ranges within the range, such as the range obtained by any combination of the specifically listed numerical values. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 This is a process flow chart for recycling waste lithium iron phosphate batteries in Example 1. DETAILED DESCRIPTION

[0061] The following are specific embodiments of the present invention, and the technical solutions of the present invention are further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0062] Among them, by mass percentage, in the lithium iron phosphate battery monomer, the C content is 43.28wt%, the Li content is 1.81%, the Fe content is 13.26%, the P content is 8.38%, the Cu content is 13.90%, the Al content is 4.10%, and the remaining components are mainly electrolyte and diaphragm.

[0063] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents or instruments used, if the manufacturer is not specified, are commercially available conventional products.

[0064] Example 1

[0065] like Figure 1 As shown, a waste lithium iron phosphate battery recycling process includes the following steps:

[0066] (1) Pretreatment: Remove the safety valve on the upper cover of the lithium iron phosphate battery cell, and then bake it once in a nitrogen atmosphere at a temperature of 500°C for 1 hour;

[0067] (2) cutting the lithium iron phosphate battery cell after calcination in step (1) to obtain an aluminum shell and a battery cell;

[0068] (3) crushing the battery cell obtained in step (2) using a hammer crusher for 20 seconds, and sieving the crushed material using a vibrating screen with a screen size of 80 mesh to obtain battery powder and copper and aluminum materials;

[0069] (4) The aluminum shell obtained in step (2) is subjected to biaxial crushing and fed into a photoelectric separator together with the copper and aluminum materials obtained in step (3) for separation to obtain copper products and aluminum products;

[0070] (5) Add 0.7% by mass of Li3PO4 to the battery powder obtained in step (3), mix well, and then feed into a muffle furnace for aerobic roasting at a temperature of 500°C in an air atmosphere for 1 hour to obtain the roasted battery powder.

[0071] (6) stirring the calcined battery powder in step (5) with pure water at a mass volume ratio of 1 kg:10 L for 30 min, and filtering to obtain a Li solution (A) and a modified battery powder;

[0072] (7) feeding the modified battery powder in step (6) into a flotation machine (slurry solid content 12%), using sodium hexametaphosphate as a dispersant (agent dosage is 100 g / t), sulfuric acid as a regulator (500 g / t), kerosene as a collector (450 g / t), and No. 2 oil as a foaming agent (agent dosage is 150 g / t), sorting, filtering, and drying to obtain flotation concentrate (mainly graphite products) and flotation tailings (lithium iron phosphate battery powder);

[0073] (8) adding 6% by mass of asphalt to the flotation concentrate obtained in step (7), mixing well, and then performing a secondary roasting treatment (coating carbonization) under nitrogen atmosphere at a roasting temperature of 2800° C. for 2 h to obtain a battery-grade graphite product;

[0074] (9) Add 15% by mass of Fe powder to the flotation tailings obtained in step (7) and feed it into a stirring barrel, add pure water to adjust the mass volume ratio of the solid phase and the liquid phase to 1kg:5L, and add 6mol / L sulfuric acid to adjust the pH value to 1.5. The reaction time is 1h and the reaction temperature is 80°C. After the acid leaching is completed, filter and obtain the ferrophosphorus leaching solution (Li + PO4 2- 、Fe 2+ solution) and filter residue (unreacted battery powder and Fe powder), and the filter residue is reused in the acid leaching process.

[0075] (10) The ferrophosphorus leaching solution in step (9) is fed into an electrolytic cell for electrochemical precipitation, and the pH value of the electrolytic cell is controlled to be 2, the voltage is 1.4 V, and the electrolysis time is 3 h; after filtration, FePO4·2H2O product (crude ferric phosphate) and Li solution (B) are obtained.

[0076] (11) The FePO4·2H2O product in step (10) is calcined in a nitrogen atmosphere at a temperature of 550° C. for 2 h to remove crystal water and complete crystal transformation to obtain anhydrous ferric phosphate product.

[0077] (12) The Li solutions (A and B) from step (6) and step (10) are combined, and Na2CO3 is added in equal chemical equivalents. The mixture is filtered to obtain a Li2CO3 product and a NaF-containing solution.

[0078] Example 2

[0079] The difference from Example 1 is that the primary calcination temperature in step (1) is 350° C., and the amount of Li 3 PO 4 added in step (5) is 1% (based on the mass of the battery powder).

[0080] Example 3

[0081] The difference from Example 1 is that the primary calcination temperature in step (1) is 600°C.

[0082] Example 4

[0083] The difference from Example 1 is that the crushing time in step (3) is 40s.

[0084] Example 5

[0085] The difference from Example 1 is that the amount of Fe powder added in step (9) is 5% (based on the mass of the flotation tailings).

[0086] Example 6

[0087] The difference from Example 1 is that the amount of Fe powder added in step (9) is 20% (based on the mass of the flotation tailings).

[0088] Example 7

[0089] The difference from Example 1 is that no Fe powder is added in step (9).

[0090] Example 8

[0091] A waste lithium iron phosphate battery recycling process is different from Example 1 in that: Example 8 is different from Steps (1) to (3) of Example 1. Example 8 uses a double-shaft crusher to crush the battery cells and perform a two-stage roasting process. The specific steps are as follows:

[0092] (1) The lithium iron phosphate battery monomer is fully discharged, and the discharged monomer is crushed using a double-shaft crusher. The crushed sample is placed in a nitrogen atmosphere for a period of calcination and drying at a drying temperature of 180°C for 1 hour, and the dried material is dispersed using a disperser;

[0093] (2) The dried material was sieved using a 60-mesh sieve, and the product on the sieve was air-sorted using a Z-type separator to obtain a diaphragm and copper-aluminum materials. The product under the sieve was subjected to a second-stage roasting in a nitrogen atmosphere at a roasting temperature of 450°C and a roasting time of 1 hour to obtain battery powder;

[0094] (3) feeding the copper and aluminum materials from step (2) into a photoelectric separator for separation to obtain copper products and aluminum products;

[0095] The subsequent processing method of the battery powder is the same as steps (5) to (12) of Example 1.

[0096] Comparative Example 1

[0097] The difference from Example 1 is that the amount of kerosene used in step (7) is 200 g / t and the amount of No. 2 oil used is 50 g / t. In addition, the modified battery powder used in this comparative example is the one prepared in steps (1) to (6) of Example 1.

[0098] Comparative Example 2

[0099] The difference from Example 1 is that the amount of kerosene used in step (7) is 1000 g / t and the amount of No. 2 oil used is 400 g / t. In addition, the modified battery powder used in this comparative example is the one prepared in steps (1) to (6) of Example 1.

[0100] Comparative Example 3

[0101] The difference from Example 1 is that in step (7), hexametaphosphoric acid and sulfuric acid were not added. In addition, the modified battery powder used in this comparative example was prepared in steps (1) to (6) of Example 1.

[0102] Comparative Example 4

[0103] The difference from Example 1 is that Li3PO4 is not added in step (5).

[0104] Comparative Example 5

[0105] The difference from Example 1 is that step (5) is omitted.

[0106] The purity and recovery rate of Cu, Al, FePO4 and graphite products recovered in each embodiment and comparative example were measured respectively, and the results are shown in Tables 1 to 3. The mass of the recovered Li was measured to calculate the recovery rate of Li. In each embodiment, the Li recovery rate was greater than 96%, and the purity of the recovered lithium carbonate was greater than 99.6%. Among them, the recovery rate of each element was calculated as the percentage of the mass of the element in the recovered product to the mass of the corresponding element in the lithium iron phosphate battery cell before recovery. The C recovery rate of the graphite product is calculated based on the mass of the graphite product obtained after flotation, excluding the mass of asphalt added during the subsequent coating and carbonization process; the C content of the graphite product refers to the mass percentage of C in the graphite product after coating and carbonization. Since the coating and carbonization process has little effect on the carbon content, this carbon content can be regarded as the carbon content of the graphite product after flotation. The recovery rate of FePO4 is calculated based on the recovery rate of P element.

[0107] The electrochemical performance testing method of the graphite product is as follows: the battery-grade graphite products obtained in the embodiment and comparative example are pulped and coated, assembled with LiCoO2 positive electrode sheets, and pressed into button batteries. The batteries are tested under the conditions of charging voltage of 4.2V and current of 0.1C. The test results are shown in Table 2.

[0108] Table 1 Purity and recovery rate of battery powder and copper and aluminum products in various embodiments and comparative examples

[0109]

[0110] In Table 1, "battery powder yield" is generally calculated based on the mass of the battery powder prepared in steps (1) to (3), with the exception of Example 8, in which the battery powder yield is calculated based on the mass of the battery powder obtained in steps (1) to (2); "F content in battery powder after calcination (or before calcination)" is generally calculated based on the battery powder obtained after aerobic calcination in step (5), with the exception of Comparative Example 5, in which the F content is calculated based on the battery powder before calcination (i.e., the battery powder obtained in steps (1) to (3)) due to the lack of step (5).

[0111] Table 2 Purity, recovery rate and electrochemical properties of graphite products in various embodiments and comparative examples

[0112]

[0113]

[0114] Table 3 Purity of ferric phosphate products and single cycle P element recovery rate in each embodiment and comparative example

[0115] Test batch <![CDATA[FePO4 purity]]> Single cycle P recovery rate / % Example 1 99.9 97.14 Example 2 99.9 96.67 Example 3 99.9 96.11 Example 4 99.9 97.03 Example 5 99.9 76.31 Example 6 99.9 97.53 Example 7 99.9 40.34 Example 8 95.3 96.87 Comparative Example 1 99.9 97.00 Comparative Example 2 99.7 96.87 Comparative Example 3 99.5 96.25 Comparative Example 4 98.1 97.01 Comparative Example 5 99.9 92.55

[0116] In Table 3, "single cycle" refers to one feeding and one discharging as a complete cycle, without considering the material reuse or recycling steps, that is, the "single cycle P recovery rate" is calculated based on the product (anhydrous ferric phosphate) directly obtained after the treatment steps described in the examples or comparative examples.

[0117] It can be seen from Examples 1 to 3 that when the temperature of the first anaerobic calcination is too low, the electrolyte is not completely removed, and the residual electrolyte in the battery powder entering the subsequent aerobic calcination stage increases, resulting in the need to add more Li3PO4 to remove the residual F element; and if the calcination temperature is too high, it will significantly increase energy consumption and increase the overall processing cost.

[0118] A comparison of Examples 1 and 4 shows that crushing time has a certain impact on copper and aluminum recovery rates. Too long a crushing time can lead to excessive crushing of the copper and aluminum materials, making them difficult to recover in the battery powder. On the other hand, too short a crushing time can reduce the battery powder yield. Therefore, it is important to rationally control the crushing time to balance battery powder yield and copper and aluminum resource recovery rates.

[0119] Comparing the results of Examples 1 and 5 to 7, we can see that adding Fe powder can increase the dissolution rate of lithium iron phosphate battery powder during the acid leaching process. Insufficient Fe powder slows the dissolution reaction, affecting subsequent ferrophosphorus recovery. Excessive Fe powder, while not affecting the dissolution rate, can cause excess iron powder to enter the circulation system, increasing the load.

[0120] Comparing Example 1 and Example 8, Example 1 shows significantly higher Cu and Al recovery rates than Example 8, resulting in a higher battery powder yield and better crushing. Pre-discharging of the battery cells is also unnecessary, reducing nitrogen consumption, shortening the processing flow, and lowering overall production costs. As shown in Table 2, the graphite material recovered in Example 1 exhibits superior cycling performance and a higher graphite recovery rate than Example 8. This is primarily due to the lower battery powder recovery rate in Example 8 and the higher levels of Cu and Al impurities present, which resulted in higher levels of residual metal impurities in the flotation graphite, impacting the electrical properties of the graphite product.

[0121] From the comparison of Example 1 and Comparative Examples 1 to 3, it can be seen that the type and dosage of flotation reagents have a significant impact on the recovery effect of graphite. Example 1 is based on the optimization of the flotation reagent ratio, so that the recovered graphite product has a significantly higher purity (99.88%) and recovery rate (98.88%). The dosage of collector (kerosene) and foaming agent (2# oil) in Comparative Example 1 is too low, resulting in a decrease in the graphite recovery rate to 91.23%. The dosage of collector and foaming agent in Comparative Example 2 is too high, which in turn causes a decrease in flotation selectivity and a decrease in recovery rate. The above results show that the reasonable optimization of the type and dosage of flotation reagents is a key factor in improving the recovery rate and purity of graphite. Comparative Example 3 lacks a dispersant (sodium hexametaphosphate) and a regulator (sulfuric acid), and the flotation separation recovery rate and purity of graphite are significantly reduced.

[0122] By comparing Example 1 with Comparative Example 4, it can be seen that adding Li3PO4 can effectively reduce the F element content in the battery powder, significantly improve the purity of the FePO4 product, and improve the electrochemical properties of the recovered graphite material.

[0123] By comparing Example 1 with Comparative Example 5, it can be seen that if the secondary calcination treatment is not performed, the carbon coating on the surface of the lithium iron phosphate material cannot be removed, and both the graphite and the lithium iron phosphate powder remain hydrophobic, resulting in a decrease in separation efficiency during flotation, a decrease in graphite recovery rate, and a large amount of graphite entering the subsequent acid leaching step, increasing the acid leaching cycle load.

[0124] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Various changes can be made within the scope of knowledge possessed by ordinary technicians in the relevant technical field without departing from the spirit of the present invention.

Claims

1. A waste lithium iron phosphate battery recycling process, characterized in that: The steps include: Pre-treating waste lithium iron phosphate batteries to obtain battery powder; The battery powder is mixed with a lithium source, and subjected to oxygen roasting at 400-600° C., and water soaking to obtain a first lithium-containing solution and modified battery powder; 90-120 g / t of sodium hexametaphosphate, 400-1000 g / t of sulfuric acid, 400-600 g / t of kerosene and 100-200 g / t of No. 2 oil are added to the modified battery powder for flotation to obtain a graphite product and lithium iron phosphate battery powder.

2. The waste lithium iron phosphate battery recycling process according to claim 1, characterized in that: The pretreatment comprises the following steps: placing the waste lithium iron phosphate battery in an inert atmosphere for a first calcination, separating the battery core, crushing, and screening to obtain battery powder and copper and aluminum materials.

3. The waste lithium iron phosphate battery recycling process according to claim 2, characterized in that: The primary calcination temperature is 350-600°C; And / or, the time of the first roasting is ≥0.5h; and / or, the sieve size of the sieving is 60-100 mesh; And / or, the battery cell is obtained by cutting the shell of the calcined waste lithium iron phosphate battery and removing the shell; optionally, the shell is crushed and mixed with the copper and aluminum materials, and sorted to obtain copper products and aluminum products.

4. The waste lithium iron phosphate battery recycling process according to claim 1, characterized in that: The lithium source is one or a combination of Li3PO4 and LiOH; And / or, the amount of the lithium source added is 0.3% to 1% of the mass of the battery powder; And / or, during the flotation process, the amount of kerosene added is 450-600 g / t.

5. The waste lithium iron phosphate battery recycling process according to claim 1, characterized in that: The atmosphere of the aerobic roasting is air; and / or the time of the aerobic roasting is ≥0.5h; and / or, during the water immersion process, the mass volume ratio of the solid phase to the liquid phase is 1kg:8~12L; and / or, the water immersion time is 0.5~1h.

6. The waste lithium iron phosphate battery recycling process according to claim 1, characterized in that: Also includes at least one of the following steps: (a) mixing the lithium iron phosphate battery powder with iron powder, and acid leaching to obtain a ferrophosphorus leachate; (b) mixing the graphite product with a carbon source and performing secondary calcination under an inert atmosphere to obtain battery-grade graphite.

7. The waste lithium iron phosphate battery recycling process according to claim 6, characterized in that: The step (a) satisfies at least one of the following conditions: (a1) The amount of iron powder added is 5% to 20% of the mass of the lithium iron phosphate battery powder; (a2) the acid leaching process comprises: mixing the lithium iron phosphate battery powder, iron powder and water, adjusting the pH, and leaching, wherein the mass-to-volume ratio of the total mass of the lithium iron phosphate battery powder and iron powder to the water is 0.1-0.35 kg:1 L; (a3) the pH of the acid leaching is 1 to 2; (a4) The acid leaching temperature is 75 to 95° C., and the acid leaching time is 1 to 3 hours.

8. The waste lithium iron phosphate battery recycling process according to claim 6 or 7, characterized in that: The method also includes the following steps: solid-liquid separation after acid leaching to obtain slag and the ferrophosphorus leaching solution, and electrolysis of the ferrophosphorus leaching solution to obtain crude ferric phosphate and a second lithium-containing solution.

9. The waste lithium iron phosphate battery recycling process according to claim 8, characterized in that: Also includes at least one of the following steps: (c) calcining the crude ferric phosphate to obtain anhydrous ferric phosphate; (d) combining the second lithium-containing solution and the first lithium-containing solution to precipitate lithium to obtain a lithium carbonate product and a fluorine-containing solution.

10. The waste lithium iron phosphate battery recycling process according to claim 6, characterized in that: The step (b) satisfies at least one of the following conditions: (b1) the carbon source is at least one of asphalt and phenolic resin; (b2) the amount of the carbon source added is 5% to 10% of the mass of the graphite product; (b3) the secondary calcination temperature is 2000-2800° C.; (b4) The secondary roasting time is ≥1h.

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