Method for recycling graphite negative electrode, nitrogen-doped graphite filler and method for treating wastewater

Abstract

The application discloses a recycling method of graphite negative electrode, nitrogen-doped graphite filler and a wastewater treatment method, and belongs to the technical field of resource recycling. The recycling method of the graphite negative electrode comprises the following steps: grinding waste graphite negative electrode material, then soaking the waste graphite negative electrode material in an acid solution, stirring, filtering and cleaning; mixing the cleaned waste graphite negative electrode material with a nitrogen-doping solution and carrier particles, stirring and granulating to obtain graphite particles mixed with a nitrogen source; the nitrogen-doping solution contains calcium chloride and polyacrylamide; and performing anaerobic sintering on the graphite particles at a temperature of 900-1100 DEG C for 1-3 hours to obtain the nitrogen-doped graphite filler. Through the recycling method, the nitrogen-doped graphite filler with nitrogen-doping amount of 0.1-0.8%, porosity of 40-50% and nitrogen-containing functional groups such as amino nitrogen and graphite nitrogen can be obtained, and the nitrogen-doped graphite filler can be used in an anaerobic biological reactor to remove nickel ions in wastewater.

Description

Technical Field

[0001] This application relates to the field of resource recycling technology, and more specifically, to a method for recovering graphite anodes, nitrogen-doped graphite fillers, and a method for treating wastewater. Background Technology

[0002] Graphite materials possess advantages such as high crystallinity, good conductivity, low charge-discharge plateau, stable layered structure, and low cost, making them widely used in the lithium-ion battery industry. For discarded lithium-ion batteries, the recycling of valuable metals in the positive electrode and current collectors (such as lithium, nickel, cobalt, manganese, copper, and aluminum) has attracted significant attention due to its substantial economic benefits. However, the recycling of negative electrode materials has received relatively less attention due to its low added value.

[0003] Graphite recovered from lithium-ion battery anodes is typically used to re-fabricate anodes. However, the initial coulombic efficiency and capacity retention of recycled anode materials are usually lower than those of commercial graphite. Furthermore, recycled graphite exhibits a faster degradation rate, and the amount of graphite used in lithium-ion batteries is small, resulting in relatively low value. Alternatively, the waste graphite anode material can be directly burned as fuel. Currently, the utilization value of waste graphite anode materials is low. Summary of the Invention

[0004] In view of the above-mentioned shortcomings, this application provides a method for recycling graphite anodes, nitrogen-doped graphite fillers, and wastewater treatment, so as to partially or completely improve the problem of recycling graphite anodes in related technologies.

[0005] This application is implemented as follows:

[0006] In a first aspect, an example of this application provides a method for recycling a graphite anode, the method comprising:

[0007] S1. Grind the waste graphite negative electrode material, then soak it in an acidic solution, stir, filter, and wash it.

[0008] S2. The waste graphite anode material cleaned in S1 is mixed with nitrogen-doped solution and carrier particles, stirred, and granulated to obtain graphite particles mixed with nitrogen source; the nitrogen-doped solution contains calcium chloride and polyacrylamide.

[0009] S3. Graphite particles are sintered in an oxygen-free environment at 900-1100℃ for 1-3 hours to obtain nitrogen-doped graphite filler.

[0010] In the above process, the waste graphite anode material is ground and then acid-washed to remove residual heavy metals and other impurities. The cleaned waste graphite anode material, nitrogen-doped solution, and carrier particles are mixed, stirred evenly, and then granulated to obtain spherical graphite particles mixed with a nitrogen source. After oxygen-free sintering of the graphite particles, nitrogen-doped graphite loaded onto the carrier particles is obtained. Since the nitrogen-doping solution contains calcium chloride and polyacrylamide, polyacrylamide provides a nitrogen source and carbonyl and nitrogen-containing functional groups for the nitrogen-doped graphite filler obtained in the subsequent oxygen-free sintering process. Calcium chloride reduces the viscosity of polyacrylamide, facilitating uniform mixing of materials and increasing the specific surface area of ​​the graphite material during the subsequent oxygen-free sintering process. The nitrogen-doped graphite filler prepared by the above method, doped with nitrogen and containing carbonyl and nitrogen-containing functional groups, can serve as a biological filler, improving the adsorption effect on nickel ions and increasing the concentration of nickel ions on the filler surface. This allows microorganisms loaded on the filler to precipitate nickel ions, thereby removing them.

[0011] In conjunction with the first aspect, in one possible implementation, in step S1, the acidic solution includes phosphoric acid and hydrochloric acid.

[0012] Optionally, the mass concentration of phosphoric acid is 60-85%.

[0013] Optionally, the mass concentration of hydrochloric acid is 20-30%.

[0014] Optionally, in acidic solutions, the mass ratio of phosphoric acid to hydrochloric acid is 3-6:1.

[0015] Optionally, in step S1, the waste graphite anode material after ball milling is immersed in an acidic solution at 60-80℃ for 2-4 hours, and the stirring speed is 100-200 r / min.

[0016] In the above process, the ball-milled waste graphite anode material is immersed in an acidic solution at 60-80℃ for 2-4 hours. The acidic solution contains 60-85% phosphoric acid and 20-30% hydrochloric acid by mass concentration, and is stirred at a stirring speed of 100-200 r / min. This process can remove metallic impurities from the waste graphite anode material. Furthermore, the presence of phosphoric acid in the acidic solution can also modify the graphite.

[0017] In conjunction with the first aspect, in one possible implementation, the carrier particles are selected from aluminum hydroxide particles.

[0018] Optionally, the carrier particles are selected from aluminum hydroxide particles with a particle size of 100-200 nm.

[0019] In the above process, using aluminum hydroxide particles as carrier particles can improve the specific surface area and porosity of nitrogen-doped graphite fillers obtained by oxygen-free sintering. Aluminum hydroxide particles with a particle size of 100-200 nm can be transformed into porous spherical alumina particles of 5-10 mm after sintering.

[0020] In conjunction with the first aspect, in one possible implementation, in step S2, the nitrogen-doped solution further includes sucrose and urea.

[0021] Optionally, by mass percentage, the nitrogen-doped solution comprises: 5-10% calcium chloride, 2-3% sucrose, 0.5-1% urea, and 1.5-2.5% polyacrylamide, with the balance being water.

[0022] In the above process, a nitrogen-doped solution containing 5-10% calcium chloride, 2-3% sucrose, 0.5-1% urea and 1.5-2.5% polyacrylamide is mixed with acid-washed waste graphite anode material and carrier particles. After subsequent oxygen-free sintering, graphite filler with a high nitrogen doping content can be obtained, which has nitrogen-containing functional groups such as amino nitrogen and graphite nitrogen, and can improve the removal efficiency of nickel ions in wastewater.

[0023] In conjunction with the first aspect, in one possible implementation, in step S2, 0.4-1% of waste graphite anode material, 20-30% of carrier particles and 40-50% of nitrogen doping solution are mixed in the remainder water, by mass percentage.

[0024] Optionally, in step S2, the mixture is stirred at a temperature of 60-75°C for 20-30 minutes.

[0025] In conjunction with the first aspect, in one possible implementation, the graphite particles have a particle size of 1-5 mm.

[0026] In the above process, 0.4-1% of waste graphite anode material, 20-30% of carrier particles and 40-50% of nitrogen doping solution are mixed in the remaining water and stirred at 60-75℃ for 20-30 minutes to make the material evenly dispersed, so as to obtain nitrogen doped graphite filler after subsequent oxygen-free sintering, which can be used to remove nickel ions from wastewater.

[0027] In conjunction with the first aspect, in one possible implementation, in step S3, under an inert atmosphere, the graphite particles are heated to 400-500℃ and sintered for 1-2 hours, then heated to 900-1100℃ and sintered for 1-3 hours to obtain nitrogen-doped graphite filler.

[0028] In the above process, the graphite particles are first heated to 400-500℃ and sintered for 1-2 hours, and then heated to 900-1100℃ and sintered for 1-3 hours. This can reduce the probability of damage to nitrogen-containing groups such as amino nitrogen and graphitic nitrogen during the sintering process, so as to obtain nitrogen-doped graphite fillers containing nitrogen-containing groups such as amino nitrogen and graphitic nitrogen.

[0029] In a second aspect, an example of this application provides a nitrogen-doped graphite filler obtained according to the recycling method provided in the first aspect.

[0030] In conjunction with the second aspect, in one possible implementation, the nitrogen doping content of the nitrogen-doped graphite filler is 0.1-0.8%, the porosity of the nitrogen-doped graphite filler is 40-50%, and the nitrogen-doped graphite filler has nitrogen-containing functional groups such as amino nitrogen and graphite nitrogen.

[0031] In the above-mentioned implementation process, by using the recovery method provided in the first aspect, nitrogen-doped graphite fillers with a nitrogen doping content of 0.1-0.8%, a porosity of 40-50%, and nitrogen-containing functional groups such as amino nitrogen and graphitic nitrogen can be obtained, which can be used in bioreactors to remove nickel ions from wastewater.

[0032] In a third aspect, this application provides a method for treating wastewater containing sulfate and nickel ions; the treatment method includes:

[0033] Wastewater is fed into an anaerobic biological reactor, which contains a bioreactor to remove nickel ions from the wastewater. The bioreactor contains anaerobic activated sludge and nitrogen-doped graphite packing provided by the second party.

[0034] In the above-described process, the nitrogen-doped graphite packing material and activated sludge provided in this application are placed in a bioreactor, enabling the treatment of wastewater containing sulfate and nickel ions. The nitrogen-doped graphite packing material has a high specific surface area and porosity, providing loading sites for microorganisms. It contains a high content of nitrogen and nitrogen-containing functional groups such as amino nitrogen and graphite nitrogen, which can adsorb nickel ions, increasing the nickel ion concentration on the packing surface. Anaerobic microorganisms loaded on the packing material can utilize sulfate ions in the water to produce sulfides. These sulfides react with the high concentration of nickel ions on the packing surface to form nickel sulfide precipitates, thereby removing nickel ions from the wastewater. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0036] Figure 1 A schematic diagram of the recycling process for waste graphite negative electrodes provided as an example in this application;

[0037] Figure 2 This is a comparison chart of nickel ion content between Example 3 and Comparative Example 3 of this application. Detailed Implementation

[0038] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0039] Graphite materials are widely used in the lithium-ion battery industry. The recycling of valuable metals from the positive electrode and current collectors (such as lithium, nickel, cobalt, manganese, copper, and aluminum) from spent lithium-ion batteries has attracted significant attention due to its substantial economic benefits. However, the recycling of negative electrode materials has received relatively less attention due to its low added value.

[0040] Graphite recovered from lithium-ion battery anodes is typically used to re-process anodes. However, the initial coulombic efficiency and capacity retention of recycled anode materials are usually lower than those of commercial graphite. Furthermore, recycled graphite exhibits a faster degradation rate, and the amount of graphite used in lithium-ion batteries is small, resulting in relatively low value. Alternatively, the waste graphite anode material can be burned directly as fuel. However, the utilization value of waste graphite anode materials is currently low.

[0041] To improve the reuse pathways of graphite anode materials and increase the recycling of graphite anodes, this application provides a method for recycling waste graphite anodes, a method for treating nitrogen-doped graphite fillers, and a method for treating wastewater. To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0042] Please see Figure 1 The recycling method for waste graphite negative electrodes provided in this application includes:

[0043] S1. Grind the waste graphite anode material, then soak it in an acidic solution, stir, filter, and wash.

[0044] Dismantle used lithium batteries to extract the waste graphite anode material. Since graphite anode material contains some heavy metals and organic matter during the use of lithium batteries, when recycling waste graphite anode material, the dismantled waste graphite anode material can be soaked in an acidic solution for acid washing, and then filtered to obtain acid-washed waste graphite anode material.

[0045] This application does not limit the specific type of acidic solution. In one possible embodiment, the acidic solution may include phosphoric acid and hydrochloric acid.

[0046] Furthermore, the mass concentration of phosphoric acid can be 60-85%.

[0047] For example, the mass concentration of phosphoric acid can be one of 60%, 65%, 70%, 75%, 80%, or 85%, or any combination thereof.

[0048] Furthermore, the mass concentration of hydrochloric acid is 20-30%.

[0049] For example, the mass concentration of hydrochloric acid can be one of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%, or any combination thereof.

[0050] Furthermore, in acidic solutions, the mass ratio of phosphoric acid to hydrochloric acid can be 3-6:1.

[0051] For example, the mass ratio of phosphoric acid to hydrochloric acid can be one of 3:1, 4:1, 5:1 or 6:1 or any range between two of them.

[0052] To further improve pickling efficiency, in one possible embodiment, the waste graphite anode material can be immersed in an acidic solution at a temperature of 60-80°C for pickling.

[0053] For example, the temperature at which waste graphite anode materials are acid-washed using an acidic solution can be one of 60°C, 65°C, 70°C, 75°C or 80°C or any combination thereof.

[0054] Furthermore, during the pickling process, stirring can be carried out at a speed of 100-200 r / min.

[0055] For example, the stirring speed can be one of or between any two of 100 r / min, 110 r / min, 120 r / min, 130 r / min, 140 r / min, 150 r / min, 160 r / min, 170 r / min, 180 r / min, 190 r / min or 200 r / min.

[0056] Furthermore, in order to improve pickling efficiency, in one possible embodiment, the waste graphite anode material can be ground before pickling.

[0057] For example, waste graphite anode material can be placed in a grinding device and ground for 1-2 hours.

[0058] For example, the grinding equipment can be a ball mill or a sand mill, etc. Zirconia balls with a diameter of 0.2 to 1.0 mm can be used in the grinding equipment.

[0059] Furthermore, after pickling is completed, the pickled waste graphite anode material can be filtered, and then washed with distilled water or tap water until the pH of the washing water is greater than 6.0.

[0060] Please continue reading. Figure 1 The recycling method for waste graphite negative electrodes provided in this application also includes:

[0061] S2. The waste graphite anode material cleaned in S1 is mixed with nitrogen-doped solution and carrier particles, stirred, and granulated to obtain graphite particles mixed with nitrogen source; the nitrogen-doped solution contains calcium chloride and polyacrylamide.

[0062] The cleaned waste graphite anode material is mixed with a nitrogen-doped solution and carrier particles. Since the nitrogen-doped solution contains calcium chloride and polyacrylamide, calcium chloride reduces the viscosity of polyacrylamide, ensuring uniform dispersion of the raw materials. Polyacrylamide provides a nitrogen source and nitrogen-containing functional groups. After subsequent oxygen-free sintering, nitrogen-doped graphite filler with nitrogen-containing functional groups can be obtained. The carrier particles, acting as a support for graphite, have a high specific surface area. Calcium chloride further promotes the formation of a porous structure in the graphite during subsequent oxygen-free sintering, further increasing the porosity and specific surface area of ​​the filler, and enhancing its adsorption capacity.

[0063] To further increase the nitrogen doping content, in one possible embodiment, the nitrogen doping solution also includes sucrose and urea.

[0064] Furthermore, in one possible embodiment, the nitrogen-doped solution comprises, by mass percentage: 5-10% calcium chloride, 2-3% sucrose, 0.5-1% urea and 1.5-2.5% polyacrylamide, with the balance being water.

[0065] For example, the mass percentage of calcium chloride can be one of 5%, 6%, 7%, 8%, 9% or 10% or any combination thereof.

[0066] For example, the sucrose mass percentage can be one of 2%, 2.5%, or 3%, or any combination thereof.

[0067] For example, the mass percentage of urea can be one of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%, or any combination thereof.

[0068] For example, the mass percentage of polyacrylamide can be one of 1.5%, 2%, or 2.5%, or any combination thereof.

[0069] Carrier particles are used to support graphite materials. Carrier particles generally have a large specific surface area and porosity.

[0070] In one possible embodiment, the carrier particles can be aluminum hydroxide particles or bentonite particles.

[0071] Aluminum hydroxide particles can be converted into aluminum oxide after subsequent oxygen-free sintering.

[0072] Furthermore, in one possible implementation, 0.4-1% by mass of waste graphite anode material, 20-30% by mass of carrier particles, and 40-50% by mass of nitrogen-doped solution are mixed in the remainder of water.

[0073] For example, when the cleaned waste graphite anode material is mixed with the nitrogen-doped solution and the carrier particles, the mass percentage of the waste graphite anode material can be one of 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%, or any combination thereof.

[0074] For example, when the cleaned waste graphite anode material is mixed with a nitrogen-doped solution and carrier particles, the mass percentage of the carrier particles can be one of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%, or any combination thereof.

[0075] For example, when the cleaned waste graphite anode material is mixed with a nitrogen-doped solution and carrier particles, the mass percentage of the nitrogen-doped solution can be one of 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%, or any combination thereof.

[0076] Furthermore, the cleaned waste graphite anode material can be mixed and stirred with nitrogen-doped solution and carrier particles at a water temperature of 60-75℃ and a stirring speed of 20-30 minutes for 20-30 minutes.

[0077] Furthermore, before sintering, the mixed slurry can be granulated in a granulator to obtain graphite particles mixed with a nitrogen source, so as to obtain granular biological fillers after subsequent oxygen-free sintering.

[0078] Please continue reading. Figure 1 The recycling method for waste graphite negative electrodes provided in this application also includes:

[0079] S3. Graphite particles are sintered in an oxygen-free environment at 900-1100℃ for 1-3 hours to obtain nitrogen-doped graphite filler.

[0080] Nitrogen-doped graphite filler can be obtained by sintering the graphite particles obtained in step S2 at 900-1100℃ in an oxygen-free environment for 1-3 hours.

[0081] For example, the oxygen-free sintering temperature can be one of 900°C, 1000°C, or 1100°C, or any range between two of them.

[0082] Furthermore, in order to avoid damaging the functional groups during the oxygen-free sintering process, in one possible embodiment, in step S3, the graphite particles are heated to 400-500℃ and sintered for 1-2 hours under an inert atmosphere, and then heated to 900-1100℃ and sintered for 1-3 hours to obtain the nitrogen-doped graphite filler.

[0083] For example, the graphite particles are first heated to one of 400°C, 450°C, or 500°C, or any combination thereof, and sintered for 1-2 hours. Then the temperature is raised to 900°C, 1000°C, or 1100°C and sintered for 1-3 hours.

[0084] For example, the inert atmosphere can be a nitrogen atmosphere.

[0085] For example, the heating rate can be 5°C / min.

[0086] This application also provides a nitrogen-doped graphite filler obtained according to the above-described recycling method.

[0087] In nitrogen-doped graphite fillers, the nitrogen doping content is 0.1-0.8%, the porosity is 40-50%, and the nitrogen-doped graphite fillers have nitrogen-containing functional groups such as amino nitrogen and graphite nitrogen.

[0088] Further examples of this application also provide an application of nitrogen-doped filler for treating wastewater and removing nickel ions from the wastewater.

[0089] For example, a wastewater treatment method includes:

[0090] Wastewater is fed into an anaerobic biological reactor, which contains a bioreactor to remove nickel ions from the wastewater. The bioreactor contains anaerobic activated sludge and nitrogen-doped graphite packing.

[0091] Wastewater from battery manufacturing typically contains sulfate and nickel ions. When treating this wastewater using a bioreactor containing nitrogen-doped graphite packing and activated sludge, anaerobic microorganisms in the anaerobic bioreactor are loaded onto the nitrogen-doped graphite packing. Because the nitrogen-doped graphite packing has a nitrogen doping content of 0.1-0.8%, contains nitrogen-containing functional groups such as amino nitrogen and graphite nitrogen, and has a porosity of 40-50%, it can adsorb nickel ions from the wastewater, increasing the nickel ion concentration on the packing surface. The anaerobic microorganisms loaded onto the packing can react with sulfates in the wastewater to produce sulfides. These sulfides can then react with the high concentration of nickel ions to form nickel sulfide precipitates, thereby removing nickel ions from the wastewater.

[0092] If the nickel ion concentration on the surface of the filler is low, it will not be conducive to the reaction with sulfides to form nickel sulfide precipitate. Therefore, the nitrogen-doped graphite filler provided in this application can adsorb nickel ions, thereby increasing the nickel ion concentration on the surface of the filler and thus forming nickel sulfide precipitate.

[0093] Furthermore, during the wastewater treatment process, a certain amount of carbon source can be added to the anaerobic biological reactor to enhance the microorganisms.

[0094] For example, 50 mg / L of glucose can be added to the anaerobic bioreactor as a carbon source for microorganisms and pumped into the bioreactor using a peristaltic pump.

[0095] The following describes in further detail the recycling method of waste graphite anode material, the nitrogen-doped graphite filler, and the wastewater treatment method of this application, with reference to the embodiments.

[0096] Example 1

[0097] Example 1 provides a method for recycling waste graphite anode materials, including:

[0098] (1) The waste graphite anode material from lithium batteries after thermal recovery of electrolyte was placed in a ball mill and ground for 1.5 hours. Zirconia balls with a diameter of 0.5 mm were used in the ball mill. A mixed acidic solution was prepared by mixing 60% phosphoric acid and 20% hydrochloric acid at a ratio of 5:1. The waste graphite anode material was taken out of the ball mill and added to the mixed acidic solution so that the mixed acidic solution could completely wet the waste graphite anode material. A heated stirrer was used at a stirring speed of 100 r / min and a temperature of 70℃. After soaking and stirring for 3 hours, the mixture was filtered. The collected waste graphite anode material was then washed with tap water until the pH of the washing water was greater than 6.0.

[0099] (2) Prepare a nitrogen-doped solution by mixing calcium chloride (5%), sucrose (3%), urea (0.5%), polyacrylamide (2%), and water as the remainder. Mix the materials with a negative electrode graphite material content of 0.6%, aluminum hydroxide addition of 25%, and polyacrylamide solution of 45%, with the remainder being water. Control the temperature at 65℃ and stir at high speed for 30 minutes to form a uniform slurry.

[0100] (3) The slurry mixed in step (2) is pressed into particles with a diameter of 5 mm using a granulator, and then sintered in an oxygen-free furnace under nitrogen protection. The temperature is increased to 500℃ at a rate of 5℃ / min and sintered for 1 h, and then increased to 950℃ at a rate of 5℃ / min and sintered for 2 h. After cooling, nitrogen-doped graphite filler is obtained.

[0101] The porosity, nitrogen-containing functional groups such as amino nitrogen and graphite nitrogen, and nitrogen element content of the nitrogen-doped graphite filler obtained in Example 1 were tested, and the test results are shown in Table 1.

[0102] Example 2

[0103] The difference between Example 2 and Example 1 is as follows:

[0104] In step (3), the slurry mixed in step (2) is pressed into particles with a diameter of 5 mm using a granulator, and then sintered in an oxygen-free furnace under nitrogen protection. The temperature is increased to 950℃ at a rate of 5℃ / min and sintered for 2 hours. After cooling, nitrogen-doped graphite filler is obtained.

[0105] The porosity, nitrogen-containing functional groups such as amino nitrogen and graphite nitrogen, and nitrogen element content of the nitrogen-doped graphite filler obtained in Example 2 were tested, and the test results are shown in Table 1.

[0106] Example 3

[0107] Example 3 provides a wastewater treatment method, and the wastewater quality is shown in Table 2.

[0108] Recycling methods include:

[0109] The nitrogen-doped graphite packing material prepared in Example 1 was mixed with the acclimated anaerobic sludge and placed in an upflow anaerobic sludge bed bioreactor with a HRT of 6 h.

[0110] Table 2 Wastewater Quality Information

[0111]

[0112] The nickel ion content in the reactor effluent is statistically analyzed, such as... Figure 2 As shown.

[0113] Comparative Example 1

[0114] The difference between Comparative Example 1 and Example 1 is as follows:

[0115] In step (2), the nitrogen-doped solution comprises, by mass percentage: 5% calcium chloride, 3% sucrose, 2.5% urea, and the remainder is water. That is, the nitrogen-doped solution does not contain polyacrylamide.

[0116] The porosity, nitrogen-containing functional groups such as amino nitrogen and graphitic nitrogen, and nitrogen content of the nitrogen-doped graphite filler obtained in Comparative Example 1 were tested, and the test results are shown in Table 1.

[0117] Comparative Example 2

[0118] The difference between Comparative Example 2 and Example 1 is as follows:

[0119] In step (2), the nitrogen-doped solution, by mass percentage, comprises: 3% sucrose, 0.5% urea, 2% polyacrylamide, and the remainder is water. That is, the nitrogen-doped solution does not contain calcium chloride.

[0120] The porosity, nitrogen-containing functional groups such as amino nitrogen and graphitic nitrogen, and nitrogen content of the nitrogen-doped graphite filler obtained in Comparative Example 2 were tested, and the test results are shown in Table 1.

[0121] Table 1

[0122] Group Porosity (%) Functional groups (mmol / g) Nitrogen content (%) Example 1 48.1 0.35 0.4 Example 2 46.3 0.16 0.2 Comparative Example 1 47.6 0.07 0.09 Comparative Example 2 39.7 0.14 0.2

[0123] Comparative Example 3

[0124] The difference between Comparative Example 3 and Example 3 is that the ordinary polyurethane packing was mixed with the acclimated anaerobic sludge and then placed into an upflow anaerobic sludge bed bioreactor, with an HRT of 6h.

[0125] The nickel ion content in the reactor effluent is statistically analyzed, such as... Figure 2 As shown.

[0126] As can be seen from Table 1, in combination with Examples 1 and 2, Example 1 adopted segmented oxygen-free sintering, and the nitrogen-doped graphite filler obtained had a higher content of nitrogen-containing groups such as amino nitrogen and graphite nitrogen.

[0127] Combining Example 1 and Comparative Example 1, it can be seen that the nitrogen-doped graphite filler prepared in Example 1 contains more nitrogen-containing functional groups such as amino nitrogen and graphite nitrogen.

[0128] Combining Example 1 and Comparative Example 2, it can be seen that adding calcium chloride in Example 1 can improve the porosity of nitrogen-doped graphite filler. The nitrogen-doped graphite filler obtained in Example 1 has a high nitrogen doping content and a high content of nitrogen-containing functional groups such as amino nitrogen and graphite nitrogen.

[0129] Depend on Figure 2It can be seen that the nickel content in the effluent from the bioreactor using nitrogen-doped graphite packing is less than 0.2 mg / L, and the nickel ion content in the effluent meets the discharge requirements of the "Integrated Wastewater Discharge Standard" (GB 8978-1996). In contrast, the nickel content in the effluent from the bioreactor using ordinary polyurethane packing is 0.7-0.95 mg / L, which exceeds the 0.5 mg / L discharge requirement of the "Integrated Wastewater Discharge Standard" (GB8978-1996).

[0130] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for recovering graphite negative electrodes, characterized in that, The method includes: S1. Grind the waste graphite negative electrode material, then soak it in an acidic solution, stir, filter, and wash it. S2. The waste graphite anode material cleaned in S1 is mixed with nitrogen-doped solution and carrier particles, stirred, and granulated to obtain graphite particles mixed with nitrogen source; the nitrogen-doped solution contains calcium chloride and polyacrylamide. S3. The graphite particles are sintered in an oxygen-free environment at 900-1100℃ for 1-3 hours to obtain nitrogen-doped graphite filler, which is used to remove nickel ions from wastewater.

2. The recycling method according to claim 1, characterized in that, In step S1, the acidic solution includes phosphoric acid and hydrochloric acid.

3. The recycling method according to claim 2, characterized in that, The mass concentration of the phosphoric acid is 60-85%; And / or, the mass concentration of the hydrochloric acid is 20-30%.

4. The recycling method according to claim 2, characterized in that, In the acidic solution, the mass ratio of phosphoric acid to hydrochloric acid is 3-6:

1.

5. The recycling method according to claim 2, characterized in that, In step S1, the waste graphite anode material after ball milling is immersed in the acidic solution at 60-80℃ for 2-4 hours, and the stirring speed is 100-200 r / min.

6. The recycling method according to claim 1, characterized in that, The carrier particles are selected from aluminum hydroxide particles.

7. The recycling method according to claim 6, characterized in that, The carrier particles are selected from aluminum hydroxide particles with a particle size of 100-200 nm.

8. The recycling method according to claim 1, characterized in that, In step S2, the nitrogen-doped solution also includes sucrose and urea.

9. The recycling method according to claim 8, characterized in that, The nitrogen-doped solution comprises, by mass percentage: 5-10% calcium chloride, 2-3% sucrose, 0.5-1% urea, and 1.5-2.5% polyacrylamide, with the balance being water.

10. The recycling method according to claim 4, characterized in that, In step S2, 0.4-1% of the waste graphite anode material, 20-30% of the carrier particles and 40-50% of the nitrogen doping solution are mixed in the remaining water by mass percentage.

11. The recycling method according to claim 10, characterized in that, In step S2, stir at 60-75℃ for 20-30 minutes.

12. The recycling method according to claim 1, characterized in that, In step S2, the particle size of the graphite particles is 1-5 mm.

13. The method for recycling waste graphite anode materials according to any one of claims 1-12, characterized in that, In step S3, under an inert atmosphere, the graphite particles are heated to 400-500℃ and sintered for 1-2 hours, then heated to 900-1100℃ and sintered for 1-3 hours to obtain the nitrogen-doped graphite filler.

14. A nitrogen-doped graphite filler, characterized in that, Obtained by the recycling method according to any one of claims 1-12.

15. The nitrogen-doped graphite filler according to claim 14, characterized in that, The nitrogen-doped graphite filler has a nitrogen doping content of 0.1-0.8%, a porosity of 40-50%, and nitrogen-doped graphite filler has nitrogen-containing functional groups.

16. The nitrogen-doped graphite filler according to claim 15, characterized in that, The nitrogen-containing functional group includes at least one of amino nitrogen or graphitic nitrogen.

17. A method for treating wastewater, wherein the wastewater contains sulfate and nickel ions; characterized in that, The processing method includes: The wastewater is fed into an anaerobic biological reactor, which contains a bioreactor to remove nickel ions from the wastewater; the bioreactor contains anaerobic activated sludge and nitrogen-doped graphite packing material as described in any one of claims 14 to 16.

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