A recycling process for waste lithium iron phosphate batteries

Abstract

This invention provides a recycling process for waste lithium iron phosphate batteries, relating to the field of battery recycling technology. The process includes the following steps: pretreating waste lithium iron phosphate batteries to obtain battery powder; mixing the battery powder with a lithium source, subjecting it to aerobic roasting at 400–600°C, and then water leaching to obtain a first lithium-containing solution and modified battery powder; adding 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 to the modified battery powder for flotation to obtain graphite products and lithium iron phosphate battery powder. This process can effectively improve the recovery rate and purity of graphite and lithium iron phosphate materials in the battery powder and is suitable for large-scale industrial recycling.

Description

Technical Field

[0001] This application relates to the field of battery recycling technology, specifically to a recycling process for waste lithium iron phosphate batteries. Background Technology

[0002] In recent years, with the rapid development of my country's new energy industry, lithium-ion batteries, due to their advantages such as high energy density, high voltage, good cycle performance, long service life, low self-discharge rate, and environmental friendliness, have become one of the important driving forces for the development of new energy and are widely used in important fields such as electric vehicles, energy storage systems, and smart grids. Currently, lithium-ion batteries can be classified according to their cathode materials into ternary lithium batteries, lithium iron phosphate batteries, lithium cobalt oxide batteries, and lithium manganese oxide batteries. Among them, lithium iron phosphate batteries, with their excellent cycle stability and safety performance, have seen a continuous increase in market share and are gradually becoming 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 daily. These used batteries still contain a large amount of valuable recyclable resources, while electrolyte residues pose a potential threat to the environment. Therefore, from both environmental protection and resource reuse perspectives, recycling is necessary. Current mainstream recycling processes typically employ a multi-stage crushing and multi-stage roasting method to dismantle battery cells and obtain recyclable battery powder. However, existing recycling methods struggle to achieve efficient separation of graphite and lithium iron phosphate materials from the battery powder during subsequent processing, thus affecting resource recovery rates 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 requirements for the high-value utilization of waste battery resources. Summary of the Invention

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

[0006] The waste lithium iron phosphate battery recycling process according to the first aspect of the present invention includes the following steps:

[0007] Waste lithium iron phosphate batteries are pretreated to obtain battery powder;

[0008] The battery powder is mixed with a lithium source and calcined in an oxygen environment at 400-600°C, followed by water immersion to obtain a first lithium-containing solution and modified battery powder.

[0009] Add 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 to the modified battery powder and carry out flotation to obtain graphite products and lithium iron phosphate battery powder.

[0010] The waste lithium iron phosphate battery recycling process according to the first aspect 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-rich atmosphere at a temperature below 600°C, organic impurities such as binders can be effectively removed, the hydrophilicity of lithium iron phosphate particles can be improved, and the interfacial property difference between them and graphite can be enhanced, thus facilitating efficient separation of the two in subsequent flotation processes. Simultaneously, the graphite structure remains stable under these temperature conditions, ensuring efficient recycling of graphite.

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

[0013] In the flotation separation stage, by optimizing the flotation reagent system, sodium hexametaphosphate is used as a dispersant, sulfuric acid as a modifier, kerosene as a collector, and No. 2 oil as a frother, and the dosage of each reagent is controlled within a reasonable range, the separation efficiency of graphite and lithium iron phosphate materials is significantly improved. This 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, showing significant potential for promotion and industrialization value.

[0015] According to some embodiments of the present invention, the pretreatment includes the following steps: placing the waste lithium iron phosphate battery under an inert atmosphere for a single roasting to separate the battery cells, crushing and sieving to obtain battery powder and copper-aluminum material.

[0016] Compared to existing technologies that combine multi-stage crushing and multi-stage calcination to disassemble battery cells, this pretreatment process has the following significant advantages:

[0017] By directly calcining the lithium iron phosphate battery cells, the structural characteristics of the cells being encased in a shell are utilized to create a localized high-pressure environment (similar to an autoclave) at the calcination temperature. This makes it easier to decompose the binder between the copper-aluminum current collector and the electrode materials. In subsequent processes, only a lower intensity of crushing force is needed to remove the battery powder from the surface of the current collector, avoiding excessive crushing of copper and aluminum. This significantly reduces 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 eliminates the discharge and separator air separation steps found in traditional recycling methods. The electrolyte in the battery cells is directly dried during the roasting process, and the separator is essentially pulverized during pyrolysis, effectively simplifying the pretreatment process. Furthermore, this process only uses nitrogen protection during the roasting stage, significantly reducing nitrogen consumption compared to traditional multi-stage roasting methods with nitrogen protection throughout. This lowers the requirements for equipment airtightness and reduces operating costs. It also solves the problems of dust collector bag clogging and material blockage at the discharge port caused by electrolyte residue in traditional methods, improving system operational stability.

[0019] In addition, the carbon coating layer formed by the carbonization of organic matter such as binders in the electrode material is easy to remove during 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 temperature of the first calcination is 350–600°C. When the calcination temperature is too low, electrolyte residue may remain, leading to an increase in the residual F element content in the battery powder. Consequently, more lithium source needs to be added to react with the residual F element in the subsequent aerobic calcination stage. When the calcination temperature is too high, energy consumption will be significantly increased, raising the overall processing cost.

[0021] This invention does not impose a limiting requirement on the roasting time for a single roasting. A suitable time range can be selected based on experience, for example, the roasting time can be more than 0.5 hours, specifically 0.5 to 2 hours.

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

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

[0024] According to some embodiments of the present invention, after the casing is crushed, it is mixed with the copper-aluminum material and sorted to obtain copper and aluminum products. The casing of lithium batteries is typically aluminum; sorting it together with the copper-aluminum material simplifies the processing flow and improves resource utilization.

[0025] According to some embodiments of the present invention, the lithium source is one or a combination of two of Li3PO4 and LiOH. The above-mentioned lithium source does not introduce other impurities during the roasting process. Furthermore, Li3PO4 is a neutral salt, which is more conducive to the recovery of iron phosphate through acid leaching compared to alkaline lithium sources, thus reducing the amount of acid used.

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

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

[0028] According to some embodiments of the present invention, the aerobic roasting time is 0.5 hours or more, specifically 0.5 to 2 hours.

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

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

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

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

[0033] (a) The lithium iron phosphate battery powder is mixed with iron powder and acid-leached to obtain a phosphorus iron leaching solution;

[0034] (b) The graphite product is mixed with a carbon source and calcined again 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 includes: mixing the lithium iron phosphate battery powder, iron powder and water, adjusting the pH and leaching, wherein the total mass of the lithium iron phosphate battery powder and iron powder to the mass-volume ratio of the water is 0.1 to 0.35 kg: 1 L;

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

[0039] (a4) The acid leaching temperature is 75-95℃ and the acid leaching time is 1-3h.

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

[0041] According to some embodiments of the present invention, the method further includes the steps of: solid-liquid separation after acid leaching to obtain slag and the ferrophosphate leachate, and electrolysis of the ferrophosphate leachate to obtain crude ferrophosphate and a second lithium-containing solution.

[0042] Electrolysis can be used to achieve rapid deposition of iron phosphate and efficient separation of iron and lithium ions. This invention does not impose particular limitations on the electrolysis system; the electrolyte can be an acidic solution (e.g., sulfuric acid solution with pH 1-3); the anode can be a platinum or graphite sheet, and the cathode can be an aluminum, copper, or graphite sheet. A DC power supply can be used during electrolysis, with a voltage range of 1-4V, and the electrolysis time can be more than 1 hour, for example, 1-4 hours.

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

[0044] (c) The crude ferric phosphate product is calcined to obtain anhydrous ferric phosphate;

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

[0046] This invention does not specifically limit the calcination process parameters. Calcination is mainly used to remove water of crystallization, and 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 (e.g., air). Using an air atmosphere is less costly; using an inert atmosphere can achieve faster crystal transformation and improve crystal quality. The calcination temperature can be above 400℃, for example, 400–600℃, and the calcination time can be controlled to be above 2 hours. Appropriately increasing the calcination temperature helps to shorten the calcination time, reduce crystal defects, and improve product quality.

[0047] Lithium precipitation is performed using known methods, such as adding carbonates to a lithium-containing solution to induce a precipitation reaction. The amount of carbonate added is measured in stoichiometric amounts (equivalent or slightly excess) of lithium ions to ensure complete precipitation.

[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 carbon source added is 5% to 10% of the mass of the graphite product;

[0051] (b3) The temperature of the secondary calcination is 2000–2800℃;

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

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

[0054] In this document, the term "flotation" includes the step of mixing modified battery powder with water to prepare a slurry, the solid content of which may be 5% to 20%. The amount of flotation reagents (sodium hexametaphosphate, sulfuric acid, kerosene, No. 2 oil) added is calculated based on the dry basis mass 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 atmospheric environment consisting of commonly used inert gases such as nitrogen and argon.

[0057] The term "multiple" means two or more kinds.

[0058] The terms “above” and “below” both include the numerical value itself.

[0059] In this article, the numerical ranges mentioned all include the endpoint values ​​and cover any subranges within that range, such as the ranges obtained by arbitrarily combining the specifically listed numerical values. Attached Figure Description

[0060] Figure 1 This is a process flow diagram of waste lithium iron phosphate battery recycling in Example 1. Detailed Implementation

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

[0062] By mass percentage, the lithium iron phosphate battery cell contains 43.28 wt% C, 1.81% Li, 13.26% Fe, 8.38% P, 13.90% Cu, and 4.10% Al. The remaining components are mainly electrolyte and separator.

[0063] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0064] Example 1

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

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

[0067] (2) Cut the shell of the lithium iron phosphate battery cell after baking in step (1) to obtain aluminum shell and battery cell;

[0068] (3) Use a hammer crusher to crush the battery cells obtained in step (2) for 20 seconds. Use a vibrating screen to screen the crushed material with a screen size of 80 mesh to obtain battery powder and copper-aluminum material.

[0069] (4) The aluminum shell obtained in step (2) is subjected to biaxial crushing and fed together with the copper and aluminum material in step (3) into a photoelectric sorting machine for sorting 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 evenly, and then feed it into a muffle furnace for aerobic calcination. The calcination temperature is 500℃, the calcination atmosphere is air, and the calcination time is 1h to obtain calcined battery powder.

[0071] (6) The calcined battery powder from step (5) is mixed with pure water at a mass-volume ratio of 1 kg: 10 L for 30 min, filtered, and Li solution (A) and modified battery powder are obtained.

[0072] (7) The modified battery powder from step (6) is fed into a flotation machine (solid content of 12%), with sodium hexametaphosphate as dispersant (dosage of reagent is 100g / t), sulfuric acid as modifier (500g / t), kerosene as collector (450g / t), and No. 2 oil as frother (dosage of reagent is 150g / t). The mixture is sorted, filtered, and dried to obtain flotation concentrate (mainly graphite products) and flotation tailings (lithium iron phosphate battery powder).

[0073] (8) Add 6% by mass of pitch to the flotation concentrate obtained in step (7), mix evenly, and then perform secondary roasting treatment (coating carbonization) under nitrogen atmosphere. The roasting temperature is 2800℃ and the roasting time is 2h to obtain battery-grade graphite products.

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

[0075] (10) The ferric phosphate leaching solution from step (9) is fed into an electrolytic cell for electrochemical precipitation. The pH value of the electrolytic cell is controlled at 2, the voltage at 1.4V, and the electrolysis time at 3h. 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 hours to remove the water of crystallization and complete the crystal transformation, so as to obtain anhydrous iron phosphate product.

[0077] (12) Combine the Li solutions (A and B) from steps (6) and (10), add Na2CO3 in equal stoichiometric amounts, and filter to obtain the Li2CO3 product and the NaF-containing solution.

[0078] Example 2

[0079] The difference from Example 1 is that the calcination temperature in step (1) is 350°C and the amount of Li3PO4 added in step (5) is 1% (based on the mass of battery powder).

[0080] Example 3

[0081] The difference from Example 1 is that the 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 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 flotation tailings).

[0088] Example 7

[0089] The difference from Example 1 is that Fe powder was not added in step (9).

[0090] Example 8

[0091] A waste lithium iron phosphate battery recycling process differs from Example 1 in that: Steps (1) to (3) of Example 8 are different from those of Example 1. In Example 8, the battery cells are crushed using a dual-shaft crusher and subjected to two-stage roasting. The specific steps are as follows:

[0092] (1) The lithium iron phosphate battery cells were fully discharged, and the discharged cells were crushed using a dual-shaft crusher. The crushed samples were placed in a nitrogen atmosphere for a first-stage roasting and drying process. The drying temperature was 180℃ and the drying time was 1h. The dried material was then dispersed using a dispersing machine.

[0093] (2) The dried material is screened using a 60-mesh sieve. The product on the sieve is air-separated using a Z-type separator to obtain the diaphragm and copper-aluminum material. The product under the sieve is calcined in a nitrogen atmosphere for two stages at a temperature of 450°C and a time of 1 hour to obtain battery powder.

[0094] (3) Feed the copper and aluminum materials from step (2) into a photoelectric sorting machine for sorting to obtain copper products and aluminum products;

[0095] The subsequent processing method for 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 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 hexametaphosphate and sulfuric acid were not added in step (7). 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 was 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, and the results are shown in Tables 1 to 3. The mass of recovered Li was measured to calculate the Li recovery rate. In each embodiment, the Li recovery rate was >96%, and the purity of recovered lithium carbonate was >99.6%. The recovery rate of each element was calculated as the percentage of the mass of that element in the recovered product relative to the mass of the corresponding element in the lithium iron phosphate battery cell before recovery. The C recovery rate of the graphite product was 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 a relatively small impact on the carbon content, this carbon content can be considered as the carbon content of the graphite product after flotation. The FePO4 recovery rate was calculated based on the P element recovery rate.

[0107] The electrochemical performance testing method for graphite products is as follows: The battery-grade graphite products obtained in the examples and comparative examples were slurried, coated, assembled with LiCoO2 positive electrode sheets, and pressed into coin cells. The cells were 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 / aluminum products in each example and comparative example.

[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), except for Example 8, whose 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 (or before) calcination” is generally calculated based on the battery powder obtained after aerobic calcination in step (5), except for Comparative Example 5, which is calculated based on the battery powder before calcination (i.e., the battery powder obtained in steps (1) to (3)) because step (5) is missing.

[0111] Table 2 shows the purity, recovery rate, and electrochemical performance of the graphite products in each example and comparative example.

[0112]

[0113]

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

[0115] 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 a complete cycle consisting of one feeding and one discharging operation, without considering material reuse or recycling steps. That is, "single cycle P recovery rate" is calculated based on the product (anhydrous ferric phosphate) directly obtained after processing according to the steps described in the examples or comparative examples.

[0117] As can be seen from Examples 1 to 3, when the first oxygen-free calcination temperature is too low, the electrolyte is not completely removed, and the residual electrolyte in the battery powder entering the subsequent oxygen-free calcination stage increases, which requires the addition of more Li3PO4 to remove the residual F element; while excessively high calcination temperature 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. Excessive crushing time leads to over-crushing of copper and aluminum materials, making them difficult to recover from in battery powder, while insufficient crushing time results in reduced battery powder yield. Therefore, it is necessary to reasonably control the crushing time to balance battery powder yield and copper and aluminum resource recovery rate.

[0119] Comparing the results of Examples 1 and 5 to 7, it can be seen that adding Fe powder can improve the dissolution rate of lithium iron phosphate battery powder during acid leaching. When the amount of Fe powder added is insufficient, the dissolution reaction rate is slow, which affects the subsequent recovery of phosphorus and iron; while excessive Fe powder does not affect the dissolution rate, it will cause excess iron powder to enter the circulation system, increasing the load.

[0120] Comparing Examples 1 and 8, the Cu and Al recovery rates in Example 1 are significantly higher than those in Example 8, resulting in a higher battery powder yield, better crushing effect, and no need for pre-discharge of individual battery cells, thus 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 recycling performance, and the graphite recovery rate is higher than that in Example 8. This is mainly because the battery powder recovery rate in Example 8 is lower, and the content of mixed Cu and Al impurities is higher, leading to a higher residual amount of metal impurities in the flotation graphite, which affects the electrical performance of the graphite product.

[0121] The comparison of Examples 1 and Comparative Examples 1 to 3 shows that the type and dosage of flotation reagents have a significant impact on the recovery effect of graphite. Example 1, based on optimized flotation reagent ratios, resulted in a significantly higher purity (99.88%) and recovery rate (98.88%) of the recovered graphite product. In Comparative Example 1, the dosages of collector (kerosene) and frother (No. 2 oil) were too low, leading to a decrease in graphite recovery rate to 91.23%. In Comparative Example 2, the dosages of collector and frother were too high, causing a decrease in flotation selectivity and consequently a decrease in recovery rate. These results indicate that rationally optimizing the type and dosage of flotation reagents is a key factor in improving graphite recovery rate and purity. Comparative Example 3, lacking dispersant (sodium hexametaphosphate) and modifier (sulfuric acid), showed a significant decrease in both the flotation separation recovery rate and purity of graphite.

[0122] Comparing Example 1 and 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 enhance the electrochemical performance of the recovered graphite material.

[0123] As can be seen from the comparison between Example 1 and Comparative Example 5, if the secondary roasting treatment is not performed, the carbon coating layer on the surface of the lithium iron phosphate material cannot be removed, and both graphite and 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 stage, which increases 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. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A recycling process for waste lithium iron phosphate batteries, characterized in that, Includes the following steps: Waste lithium iron phosphate batteries are pretreated to obtain battery powder; The battery powder is mixed with a lithium source and calcined in an oxygen environment at 400~600℃, followed by water immersion to obtain a first lithium-containing solution and modified battery powder. Add 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 pine oil to the modified battery powder and carry out flotation to obtain graphite products and lithium iron phosphate battery powder. The pretreatment includes the following steps: placing the waste lithium iron phosphate batteries under an inert atmosphere for a first roasting to separate the cells, crushing and sieving to obtain battery powder and copper-aluminum material; the temperature of the first roasting is 350~600℃; The lithium source is one or a combination of two of Li3PO4 and LiOH, and the amount of lithium source added is 0.3% to 1% of the mass of the battery powder.

2. The waste lithium iron phosphate battery recycling process according to claim 1, characterized in that, The roasting time for each roasting cycle is ≥0.5 hours; And / or, the sieve size for the screening is 60~100 mesh; And / or, the battery cell is obtained by cutting off the casing of a calcined waste lithium iron phosphate battery; optionally, the casing is crushed and mixed with the copper and aluminum materials, and then sorted to obtain copper and aluminum products.

3. The waste lithium iron phosphate battery recycling process according to claim 1, characterized in that, During the flotation process, the amount of kerosene added is 450~600g / t.

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

5. The waste lithium iron phosphate battery recycling process according to claim 1, characterized in that, It also includes at least one of the following steps: (a) The lithium iron phosphate battery powder is mixed with iron powder and acid-leached to obtain a phosphorus iron leaching solution; (b) The graphite product is mixed with a carbon source and calcined again under an inert atmosphere to obtain battery-grade graphite.

6. The waste lithium iron phosphate battery recycling process according to claim 5, characterized in that, 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 includes: mixing the lithium iron phosphate battery powder, iron powder and water, adjusting the pH and leaching, wherein the total mass of the lithium iron phosphate battery powder and iron powder to the mass-volume ratio of the water is 0.1~0.35kg:1L; (a3) The pH of the acid leaching is 1~2; (a4) The acid leaching temperature is 75~95℃ and the acid leaching time is 1~3h.

7. The waste lithium iron phosphate battery recycling process according to claim 5 or 6, characterized in that, The method also includes the following steps: after acid leaching, solid-liquid separation is performed to obtain slag and the ferrophosphate leachate, and the ferrophosphate leachate is electrolyzed to obtain crude ferrophosphate and a second lithium-containing solution.

8. The waste lithium iron phosphate battery recycling process according to claim 7, characterized in that, It also includes at least one of the following steps: (c) The crude ferric phosphate is calcined to obtain anhydrous ferric phosphate; (d) Combine the second lithium-containing solution and the first lithium-containing solution to precipitate lithium, and obtain lithium carbonate product and fluorine-containing solution.

9. The waste lithium iron phosphate battery recycling process according to claim 5, characterized in that, 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 carbon source added is 5% to 10% of the mass of the graphite product; (b3) The temperature of the secondary roasting is 2000~2800℃; (b4) The time for the secondary roasting is ≥1h.

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