Method for recovering graphite material from waste power battery tailings

Abstract

The invention belongs to the technical field of graphite material recovery, and particularly relates to a method for recovering a graphite material from waste power battery tailings. The method comprises the following steps: adding the battery tailings into a culture solution containing a compound functional flora, fermenting for 5-8 days, and separating to obtain fermentation tailings; the fermentation tailings are subjected to microwave irradiation treatment under nitrogen protection, and heat treatment tailings are obtained; after the heat treatment tailings are crushed, flotation separation is conducted, and graphite slurry is obtained; carrying out spray drying on the graphite slurry to obtain graphite powder; and mixing the graphite powder with the biomass carbon precursor, and carrying out microwave heating treatment to obtain regenerated graphite. By optimizing the recovery process and adopting the mode of combining biological fermentation, microwave activation, flotation and microwave repair, the method is simple in process, low in energy consumption and environmentally friendly, and the obtained regenerated graphite is high in purity and excellent in electrochemical performance and can be directly used for production of the negative electrode material.

Description

Technical Field

[0001] The invention belongs to the technical field of graphite material recycling, and particularly relates to a method for recycling graphite material from waste power battery tailings. Background Art

[0002] With the advancement of technology, the installed capacity of lithium iron phosphate batteries has increased annually, and the scale of retired power batteries has also increased year by year. If not properly handled, they will lead to serious environmental and safety problems. Retired lithium iron phosphate batteries are rich in resources such as lithium, phosphorus, iron, and graphite, with content far higher than that of primary mineral resources. They are a high-quality urban mineral resource. Recycling them not only alleviates the environmental pressure caused by battery waste, but also has huge social and economic benefits, contributing to the green and sustainable development of the entire industry. Lithium iron phosphate power batteries are mainly composed of a casing, positive electrode materials, negative electrode materials, and a separator. Whether lithium iron phosphate battery materials are used safely and efficiently is mainly measured by whether the metal materials in the positive electrode can be used efficiently. Currently, most battery recycling companies only consider the utilization of the high-value lithium metal in the positive electrode material, but have not addressed the effective utilization of iron phosphate slag. The remaining components, over 95%, are treated as solid waste in the form of tailings.

[0003] Graphite is a common non-metallic mineral material with excellent properties such as high temperature resistance, high chemical stability, and thermal conductivity. However, its production and graphitization process requires enormous energy consumption. The graphite in the negative electrode material of lithium iron phosphate power batteries is a valuable resource, and its recycling can effectively alleviate the shortage of graphite resources and the high energy consumption of its production. Currently, there are five main methods for recovering graphite from waste power batteries: physical recovery, wet leaching recovery, thermal treatment recovery, and extraction. Physical recovery typically combines mechanical pulverization with vibration screening and airflow sorting to separate waste graphite based on the density properties of the negative electrode material. The graphite material collected by this method has low added value and limited economic benefits. Wet leaching processes primarily utilize a wet leaching method to extract and dissolve impurities in the negative electrode graphite by adding solvents such as trifluoroacetic acid, hydrochloric acid, and sulfuric acid to achieve graphite purification. This requires the use of concentrated acid, which produces large amounts of acidic wastewater, which can pollute the environment if not properly handled. The heat treatment recovery process mainly removes impurities such as adhesives and conductive agents from waste graphite through high-temperature treatment. This process has wide applicability and strong processing capacity, but it has high energy consumption and requires good tail gas treatment during the process. The extraction method uses subcritical carbon dioxide and acetonitrile to extract graphite, which can better protect the internal crystallinity of graphite and ensure good electrochemical properties, but this method is complex and has high production costs. The above-mentioned recovery methods have problems such as high energy consumption, complex procedures, low efficiency, and serious pollution, and the regenerated graphite often has a low initial efficiency, making it difficult to use directly in the manufacture of high-end batteries. Therefore, it is of great significance to develop a recovery method with simple process, environmental protection, and low cost. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention provides a method for recovering graphite materials from waste power battery tailings. The recovery method is relatively simple, does not require high-temperature heating treatment, has low energy consumption, does not require the use of concentrated acid treatment, and is green and environmentally friendly. The obtained regenerated graphite has high purity and excellent electrochemical properties and can be directly used in the production of negative electrode materials.

[0005] The object of the present invention is to provide a method for recovering graphite material from waste power battery tailings, the method comprising the following steps: (1) Adding battery tailings to a culture medium containing a composite functional bacterial community, mixing evenly, introducing air, and fermenting for 2-4 days. Stop introducing air, continue fermenting for 3-4 days, and separate to obtain fermentation tailings; specifically, battery tailings are graphite slag after recycling lithium iron phosphate battery materials and undergoing crushing and separation treatment. Its main impurities include organic matter such as binders, phosphates, iron oxides, nickel, cobalt, manganese and other oxides, copper, aluminum, lithium, etc.; (2) subjecting the fermentation residue obtained in step (1) to microwave irradiation treatment under nitrogen protection to obtain heat-treated residue; (3) crushing the heat-treated tailings obtained in step (2), adding water, an inhibitor, a collector, and a foaming agent, mixing them evenly in a stirring tank, and then entering a flotation column for flotation separation to obtain a graphite slurry; (4) spray drying the graphite slurry obtained in step (3) to obtain graphite powder; (5) The graphite powder obtained in step (4) is mixed with a biomass carbon precursor, subjected to microwave heating treatment under nitrogen protection, and cooled to obtain regenerated graphite.

[0006] The present invention combines "biological fermentation + microwave activation + flotation + microwave repair" and first adopts composite microbial pre-decontamination treatment, using organic acids (such as citric acid, oxalic acid, etc.) produced by composite microbial metabolism to selectively dissolve and strip metal impurities such as cobalt, nickel, manganese, lithium, etc. on the surface and between layers of graphite. At the same time, microorganisms have a certain biodegradation effect on organic binders, achieving the purpose of preliminary decontamination under mild conditions without the need for strong acid treatment, which is more environmentally friendly; then microwave heating treatment is adopted, utilizing the instantaneous heating characteristics of microwaves to further gasify and decompose residual organic binders and other organic matter, and quickly escape from the graphite layers, while also dissociating inorganic impurities into smaller particles , which is convenient for subsequent removal. This method does not require ultra-high temperature treatment and has low energy consumption. Graphite has excellent natural floatability, and the residual inorganic impurities can be separated from the graphite through a flotation process to further improve the purity of the graphite. The graphite enriched by flotation is then spray-dried to allow it to re-aggregate, and then treated with microwaves to decompose the trace collectors and frothers introduced by flotation, promote the rearrangement of the graphite structure, repair lattice defects, and form an amorphous carbon coating on the graphite surface. The resulting regenerated graphite has high purity and a relatively dense graphite structure. It is used as a negative electrode material for batteries with high initial efficiency. This recycling process organically combines biological, physical, and chemical processes, and the process is reasonable, economically feasible, environmentally friendly, and has low energy consumption.

[0007] Preferably, in step (1) of the above technical solution, the composite functional bacteria is a mixed bacteria of Thiobacillus ferrooxidans, Sulfolobus and Aspergillus niger in a volume ratio of 1.5-2.5:1:1, and the inoculation amount is 5-8% of the total culture solution; the solid-liquid ratio of the battery tailings to the culture solution is 1:5-8. The present invention uses commonly used Thiobacillus ferrooxidans, Sulfolobus and Aspergillus niger as composite functional bacterial communities, utilizes the metabolic effects and growth differences of Thiobacillus ferrooxidans and Sulfolobus acidophilus, oxidizes sulfur in the culture medium into sulfuric acid, and oxidizes ferrous ions into ferric ions, which can efficiently dissolve metal impurities such as cobalt, nickel, manganese, lithium, etc. in battery tailings; utilizes the characteristics of Aspergillus niger fungus metabolism to produce organic acids such as citric acid and oxalic acid, which can form stable water-soluble complexes with metal ions, promote the dissolution and separation of metals, and prevent the metals from being deposited on the graphite surface again, and can also degrade certain organic adhesives, thereby achieving preliminary impurity removal under mild conditions without damaging the graphite skeleton, replacing the problem of foreign strong acid treatment in the existing technology that not only consumes a large amount of chemicals but also makes subsequent waste liquid difficult to treat.

[0008] Preferably, in the above technical solution, the components of the culture solution include 2-4 g / L of ammonium sulfate, 0.3-0.5 g / L of potassium dihydrogen phosphate, 0.4-0.7 g / L of magnesium sulfate, 0.1-0.2 g / L of potassium chloride, 0.02-0.05 g / L of calcium chloride, 5-10 g / L of sodium thiosulfate, 10-30 g / L of ferrous sulfate, 8-20 g / L of sucrose, and the balance is distilled water; the air introduction rate is 0.5-1 vvm, and the fermentation temperature is 30-45°C.

[0009] Preferably, in step (2) of the above technical solution, the microwave irradiation treatment process is as follows: frequency of 900-2500 MHz, power of 500-800 W, temperature of 400-600°C, and time of 15-30 min. The present invention selects microwave heat treatment after preliminary impurity removal, which can further instantly gasify and crack organic impurities such as binders, thereby removing obstacles for subsequent flotation. At the same time, the graphite wrapped in organic matter and fine impurities adhered to the graphite are exposed, creating conditions for subsequent crushing and flotation separation. At the same time, the residual lithium between the graphite layers can be decomposed, laying the foundation for the subsequent repair of the graphite structure.

[0010] Preferably, in step (3) of the above technical solution, the Dv50 particle size of the heat-treated tailings after crushing is controlled to be 15-20 μm.

[0011] Preferably, in step (3) of the above technical solution, the inhibitor is lime or water glass, and the dosage is 300-600 g / t; the collector is kerosene or stearic acid, and the dosage is 200-500 g / t; and the foaming agent is No. 2 oil, and the dosage is 50-100 g / t.

[0012] Preferably, in step (3) of the above technical solution, the specific process of flotation is as follows: the heat-treated tailings are prepared into a slurry with a solid content of 30-40%, and after adjusting the pH to 1-2, an inhibitor is first added and stirred for 3-5 minutes, and then a collector is added and stirred for 8-15 minutes, and then a frother is added and stirred evenly, and the mixture is poured into a flotation column for ventilation, and foam is scraped to collect the foam concentrate.

[0013] Preferably, in step (4) of the above technical solution, the spray drying process is as follows: a feed rate of 300-400 mL / min, an inlet temperature of 150-200°C, and an outlet temperature of 50-100°C. The spray drying process used in this technical solution can cause the graphite powder to reaggregate. The gaps formed between the small particles after agglomeration form certain pores after subsequent high-temperature treatment, which is beneficial to improving the energy storage capacity of the battery.

[0014] Preferably, in step (5) of the above technical solution, the biomass carbon precursor is lignin sulfonate or cellulose derivative, and its usage amount is 2-4% of the graphite powder.

[0015] Preferably, in step (5) of the above technical solution, the microwave heating process is as follows: frequency of 900-2500 MHz, power of 1000-1200 W, temperature of 500-800°C, and time of 5-10 min. In this technical solution, by selecting a higher power microwave heating process, not only can a small amount of organic impurities introduced by the flotation process be removed, but the crystal structure of the graphite can also be further repaired, internal stress can be eliminated, and its electrochemical performance can be improved. At the same time, the introduced biomass carbon precursor forms a thin and dense coating on the graphite surface, connecting the graphite particles and improving the conductive properties.

[0016] Advantages compared to existing technologies: The present invention adopts a process that combines "biological fermentation + microwave activation + flotation + microwave repair". First, inorganic acids (such as sulfuric acid) and organic acids (such as citric acid and oxalic acid) produced by the metabolism of composite microorganisms are used to selectively dissolve and strip metal impurities such as cobalt, nickel, manganese, and lithium on the surface and between graphite layers. At the same time, the microorganisms have a certain biodegradation effect on the organic binder, achieving the purpose of preliminary impurity removal under mild conditions. Then, the instantaneous heating property of microwaves is used to further vaporize and decompose residual organic binders and other organic matter, and quickly escape from the graphite interlayers. At the same time, inorganic impurities can also be dissociated into smaller particles, facilitating subsequent impurity removal. The remaining inorganic impurities can be separated from the graphite through a flotation process, further improving the purity of the graphite. The graphite enriched by flotation is then spray-dried to re-aggregate. Finally, microwave treatment is used to decompose the trace impurities introduced by flotation, promote the rearrangement of the graphite structure, repair lattice defects, and form an amorphous carbon coating on the graphite surface. The resulting regenerated graphite has a smooth surface and a purity of over 99.5%.

[0017] The recycling process of the present invention organically combines biological, physical and chemical processes, and has a simple process, low energy consumption and is environmentally friendly. The obtained regenerated graphite has high purity, high initial efficiency and specific capacity, and excellent electrochemical properties, and can be directly used in the production of negative electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a process flow chart for recovering graphite materials from waste power battery tailings according to the present invention; Figure 2 The SEM images of the regenerated graphite obtained in Example 1 of the present invention and the graphite in battery tailings are shown in Figure 1, where a is the regenerated graphite obtained in Example 1 and b is the graphite in battery tailings. Figure 3 This is the XRD pattern of the regenerated graphite obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0019] The above-mentioned technical features of the present invention and the technical features specifically described below (such as embodiments) can be combined with each other to form new or preferred technical solutions, but the present invention is not limited to these embodiments, and these embodiments do not limit the present invention in any way.

[0020] The experimental methods in the following examples are conventional methods unless otherwise specified. The preparations involved in the following examples are common commercial products and can be purchased from the market unless otherwise specified.

[0021] The composite functional bacteria used in the present invention, including Thiobacillus ferrooxidans, Sulfolobus and Aspergillus niger, were purchased from the National Standard Product Network and cultured to OD 600 = 1.

[0022] The culture medium used was 3 g / L ammonium sulfate, 0.4 g / L potassium dihydrogen phosphate, 0.5 g / L magnesium sulfate, 0.1 g / L potassium chloride, 0.05 g / L calcium chloride, 8 g / L sodium thiosulfate, 25 g / L ferrous sulfate, 15 g / L sucrose, and the balance was distilled water. The pH was adjusted to 1.5-2.5 with sulfuric acid.

[0023] The present invention is described in further detail below in conjunction with the embodiments: Example 1 A method for recovering graphite material from waste power battery tailings comprises the following steps: (1) The battery tailings after crushing and separation of recycled lithium iron phosphate battery materials are added to a culture medium containing a composite functional bacterial community (Thiobacillus ferrooxidans, Sulfolobus and Aspergillus niger in a volume ratio of 1.5:1:1). After mixing evenly, air is introduced at a rate of 0.5 vvm. The mixture is first fermented at 30-35°C for 4 days, and then the air is stopped and fermented at 40-45°C for 3 days to separate the fermentation tailings; the fermentation filtrate can recover the corresponding metals according to the situation.

[0024] (2) The fermentation tailings obtained in step (1) were subjected to microwave irradiation treatment at a frequency of 2450 MHz, a power of 500 W, and a temperature of 400° C. under nitrogen protection for 30 min to obtain heat-treated tailings.

[0025] (3) The heat-treated tailings obtained in step (2) are crushed (Dv50 particle size is controlled at 15-20 μm), added to a stirring tank, and water is added to prepare a slurry with a solid content of 30%. After adjusting the pH to 1-2, 300 g / t of lime is added and stirred for 3 minutes, and then 300 g / t of kerosene is added and stirred for 8 minutes, and then 50 g / t of No. 2 oil is added and stirred evenly. The mixture is poured into a flotation column for ventilation, foam is scraped, and foam concentrate is collected to obtain graphite slurry.

[0026] (4) The graphite slurry obtained in step (3) was spray-dried at a feed rate of 300 mL / min, an inlet temperature of 150-200° C., and an outlet temperature of 50-100° C. to obtain graphite powder.

[0027] (5) The graphite powder obtained in step (4) was evenly mixed with 2% sulfonated lignin, and subjected to microwave heating treatment under nitrogen protection at a frequency of 2450 MHz, a power of 1000 W, a temperature of 600°C, and a time of 10 min, and then cooled to obtain regenerated graphite.

[0028] Example 2 A method for recovering graphite material from waste power battery tailings comprises the following steps: (1) The battery tailings after crushing and separation of recycled lithium iron phosphate battery materials are added to a culture medium containing a composite functional bacterial community (Thiobacillus ferrooxidans, Sulfolobus and Aspergillus niger in a volume ratio of 2:1:1). After mixing evenly, air is introduced at a rate of 0.8 vvm. The mixture is first fermented at 30-35°C for 3 days, and then the air is stopped and fermented at 40-45°C for 4 days to separate the fermentation tailings; the fermentation filtrate can recover the corresponding metals according to the situation.

[0029] (2) The fermentation residue obtained in step (1) was subjected to microwave irradiation treatment for 25 min at a frequency of 2450 MHz, a power of 600 W, and a temperature of 500° C. under nitrogen protection to obtain heat-treated residue.

[0030] (3) The heat-treated tailings obtained in step (2) are crushed (Dv50 particle size is controlled at 15-20 μm), added to a stirring tank, and water is added to prepare a slurry with a solid content of 35%. After adjusting the pH to 1-2, 400 g / t of lime is added and stirred for 4 minutes, and then 400 g / t of kerosene is added and stirred for 10 minutes. Then, 60 g / t of No. 2 oil is added and stirred evenly. The mixture is poured into a flotation column for ventilation, foam is scraped, and foam concentrate is collected to obtain graphite slurry.

[0031] (4) The graphite slurry obtained in step (3) was spray-dried at a feed rate of 350 mL / min, an inlet temperature of 150-200° C., and an outlet temperature of 50-100° C. to obtain graphite powder.

[0032] (5) The graphite powder obtained in step (4) was evenly mixed with 3% cellulose, and subjected to microwave heating treatment under nitrogen protection at a frequency of 2450 MHz, a power of 1100 W, a temperature of 700°C, and a time of 8 min, and then cooled to obtain regenerated graphite.

[0033] Example 3 A method for recovering graphite material from waste power battery tailings comprises the following steps: (1) The battery tailings after crushing and separation of recycled lithium iron phosphate battery materials are added to a culture medium containing a composite functional bacterial community (Thiobacillus ferrooxidans, Sulfolobus and Aspergillus niger in a volume ratio of 2.5:1:1). After mixing evenly, air is introduced at a rate of 1 vvm. The mixture is first fermented at 30-35°C for 2 days, and then the air is stopped and fermented at 40-45°C for 4 days to separate the fermentation tailings. The fermentation filtrate can be used to recover the corresponding metals according to the situation.

[0034] (2) The fermentation tailings obtained in step (1) were subjected to microwave irradiation treatment at a frequency of 2450 MHz, a power of 800 W, and a temperature of 600° C. under nitrogen protection for 15 min to obtain heat-treated tailings.

[0035] (3) The heat-treated tailings obtained in step (2) are crushed (the Dv50 particle size is controlled at 15-20 μm), added to a stirring tank, and water is added to prepare the heat-treated tailings into a slurry with a solid content of 40%. After adjusting the pH to 1-2, 600 g / t of lime is first added and stirred for 5 minutes, then 500 g / t of kerosene is added and continued to stir for 8-15 minutes, and then 100 g / t of No. 2 oil is added and stirred evenly. The mixture is poured into a flotation column for ventilation, foam is scraped, and the foam concentrate is collected to obtain a graphite slurry.

[0036] (4) The graphite slurry obtained in step (3) was spray-dried at a feed rate of 400 mL / min, an inlet temperature of 150-200° C., and an outlet temperature of 50-100° C. to obtain graphite powder.

[0037] (5) The graphite powder obtained in step (4) was evenly mixed with 4% sulfonated lignin, and subjected to microwave heating treatment under nitrogen protection at a frequency of 2450 MHz, a power of 1200 W, a temperature of 800°C, and a time of 5 min, and then cooled to obtain regenerated graphite.

[0038] Comparative Example 1 A method for recovering graphite material from waste power battery tailings, which differs from Example 1 in that, in step (1), the composite functional bacterial community is a mixture of Thiobacillus ferrooxidans and Aspergillus niger in a volume ratio of 1.5:1.

[0039] Comparative Example 2 A method for recovering graphite material from waste power battery tailings, which differs from Example 1 in that, in step (1), fermentation is carried out at a temperature of 30° C. for 7 days.

[0040] Comparative Example 3 A method for recovering graphite material from waste power battery tailings, which differs from Example 1 in that, in step (1), fermentation is carried out at a temperature of 45°C for 7 days.

[0041] Comparative Example 4 A method for recovering graphite material from waste power battery tailings, which differs from Example 1 in that step (1) is omitted and the battery tailings are directly subjected to microwave irradiation treatment.

[0042] Comparative Example 5 A method for recovering graphite material from waste power battery tailings, which differs from Example 1 in that step (2) is omitted and the fermentation tailings are directly subjected to flotation.

[0043] Comparative Example 6 A method for recovering graphite material from waste power battery tailings, which differs from Example 1 in that step (3) is omitted and the heat-treated tailings are directly rinsed twice with water.

[0044] Comparative Example 7 A method for recovering graphite material from waste power battery tailings, which differs from Example 1 in that step (4) is omitted, and the graphite slurry and sulfonated lignin are directly mixed uniformly and microwave-treated.

[0045] Comparative Example 8 A method for recovering graphite material from waste power battery tailings, which differs from Example 1 in that, in step (5), the graphite powder is directly subjected to microwave addition treatment.

[0046] Comparative Example 9 A method for recovering graphite material from waste power battery tailings, which differs from Example 1 in that step (5) is omitted and the graphite powder is the recovered graphite.

[0047] Test example 1. The impurity organic matter and elements in the regenerated graphite and the graphite slag in the battery tailings obtained in Example 1 were detected, and SEM and XRD tests were performed at the same time. The results are shown in Table 1 and Figures 2 to 3 shown.

[0048] Table 1 Comparison of impurity element content (wt.%)

[0049] From the results in Table 1, it can be seen that the impurity elements in the regenerated graphite obtained by the recovery method of the present invention are greatly reduced. It can also be seen from its XRD spectrum that its peak is mainly graphite and has high purity. In addition, it can be seen from its SEM image that after the graphite is purified and recovered, most of its surface impurities are removed, making it smoother and more pure, which is conducive to improving the electrochemical performance.

[0050] 2. The purity of the regenerated graphite obtained in Comparative Examples 1-3 and Comparative Examples 1-9 was tested, and its electrochemical properties were tested at the same time. The results are shown in Table 2. The electrochemical performance test method is as follows: the regenerated graphite material, conductive carbon black SP, CMC and SBR obtained in each embodiment and comparative example were weighed in a mass ratio of 95:2:1.5:1.5, respectively, and stirred evenly in water to form a slurry. The slurry was applied to both sides of the copper foil using an applicator, and the electrode coated on both sides was placed in a vacuum drying oven at a temperature of 110°C and dried for 2h, and then pressed into a negative electrode. The electrolyte composition is (volume ratio): EC:EMC:DNC=1:1:1, containing 1mol / L LiPF6, the counter electrode is metallic lithium, and a CR-2420 button cell is made. The charge and discharge test was carried out on a blue battery test cabinet with a voltage range of 0.005-1.0V and a charge and discharge rate of 0.1C to obtain the first discharge capacity and the first coulomb efficiency.

[0051] Table 2 Graphite purity and electrochemical performance results

[0052] As can be seen from the results in Table 2, the purity of the regenerated graphite obtained by the recovery method of the present invention in Examples 1-3 is relatively high, indicating that the recovery method of the present invention is feasible and can effectively remove impurities in battery tailings. After being directly used in lithium-ion batteries, its first discharge specific capacity is above 380 mAh / g, and the first coulombic efficiency reaches 94.4%, with excellent electrochemical performance. However, in Comparative Examples 1-9, due to changes in the recovery process conditions or process omissions, the purity and electrochemical properties of the recovered graphite are affected to a certain extent; this further illustrates the feasibility and advantages of the recovery method of the present invention, and each step and reaction condition is mutually coordinated and has a certain impact on the performance of the recovered product.

[0053] Finally, it should be emphasized that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for recovering graphite material from waste power battery tailings, characterized in that: The method comprises the following steps: (1) Add battery tailings to a culture medium containing a composite functional bacterial community, mix well, introduce air, and ferment for 2-4 days. Stop introducing air, continue fermenting for 3-4 days, and separate the fermentation tailings; (2) subjecting the fermentation residue obtained in step (1) to microwave irradiation treatment under nitrogen protection to obtain heat-treated residue; (3) crushing the heat-treated tailings obtained in step (2), adding water, an inhibitor, a collector, and a foaming agent, mixing them evenly in a stirring tank, and then entering a flotation column for flotation separation to obtain a graphite slurry; (4) spray drying the graphite slurry obtained in step (3) to obtain graphite powder; (5) The graphite powder obtained in step (4) is mixed with a biomass carbon precursor, subjected to microwave heating treatment under nitrogen protection, and cooled to obtain regenerated graphite.

2. The method for recovering graphite material from waste power battery tailings according to claim 1, characterized in that: In step (1), the composite functional bacterial community is a mixed bacteria of Thiobacillus ferrooxidans, Sulfolobus and Aspergillus niger in a volume ratio of 1.5-2.5:1:1, and the inoculation amount is 5-8% of the total culture solution; the solid-liquid ratio of the battery tailings to the culture solution is 1:5-8.

3. A method for recovering graphite material from waste power battery tailings according to claim 1 or 2, characterized in that: The culture solution comprises 2-4 g / L of ammonium sulfate, 0.3-0.5 g / L of potassium dihydrogen phosphate, 0.4-0.7 g / L of magnesium sulfate, 0.1-0.2 g / L of potassium chloride, 0.02-0.05 g / L of calcium chloride, 5-10 g / L of sodium thiosulfate, 10-30 g / L of ferrous sulfate, 8-20 g / L of sucrose, and the balance is distilled water; the air is introduced at a rate of 0.5-1 vvm, and the fermentation temperature is 30-45°C.

4. The method for recovering graphite material from waste power battery tailings according to claim 1, characterized in that: In step (2), the microwave irradiation treatment process is as follows: frequency of 900-2500 MHz, power of 500-800 W, temperature of 400-600° C., and time of 15-30 min.

5. The method for recovering graphite material from waste power battery tailings according to claim 1, characterized in that: In step (3), the Dv50 particle size of the heat-treated tailings after crushing is controlled to be 15-20 μm.

6. The method for recovering graphite material from waste power battery tailings according to claim 1, characterized in that: In step (3), the inhibitor is lime or water glass, and the dosage is 300-600 g / t; the collector is kerosene or stearic acid, and the dosage is 200-500 g / t; the foaming agent is No. 2 oil, and the dosage is 50-100 g / t.

7. The method for recovering graphite material from waste power battery tailings according to claim 1, characterized in that: In step (3), the specific process of flotation is as follows: the heat-treated tailings are prepared into a slurry with a solid content of 30-40%, and after adjusting the pH to 1-2, an inhibitor is first added and stirred for 3-5 minutes, and then a collector is added and stirred for 8-15 minutes, and then a frother is added and stirred evenly, and the mixture is poured into a flotation column for ventilation, and foam is scraped to collect the foam concentrate.

8. The method for recovering graphite material from waste power battery tailings according to claim 1, characterized in that: In step (4), the spray drying process is as follows: feed rate is 300-400 mL / min, inlet temperature is 150-200°C, and outlet temperature is 50-100°C.

9. The method for recovering graphite material from waste power battery tailings according to claim 1, characterized in that: In step (5), the biomass carbon precursor is lignin sulfonate or cellulose derivative, and its usage amount is 2-4% of the graphite powder.

10. The method for recovering graphite material from waste power battery tailings according to claim 1, characterized in that: In step (5), the microwave heating process is as follows: frequency of 900-2500 MHz, power of 1000-1200 W, temperature of 600-800° C., and time of 5-10 min.

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