Preparation method of high-purity graphite powder

Abstract

A method for preparing high-purity graphite powder, specifically relating to the field of high-purity graphite powder preparation technology. The method mainly includes the following steps: pretreating graphite powder raw materials with a mixed leaching bacterial solution, culture medium, and surfactant; centrifuging to obtain a solid, washing, grinding, and drying to obtain a pre-purified powder; and using the supernatant to prepare a bio-electrolysis composite electrolyte. A functionalized graphite composite anode is prepared using the pre-purified powder, and it is used as the reaction electrode along with a platinum mesh cathode. Argon gas is continuously introduced in a pulse mode for 2 hours to obtain a graphite powder mixture, which is then centrifuged and dried to obtain the high-purity graphite powder product. This invention achieves efficient and deep removal of difficult-to-remove impurities such as boron and vanadium through the synergistic effect of biological pretreatment and pulse electrolysis. The product has a fixed carbon content ≥99.99%, and the entire process is green and environmentally friendly, with low energy consumption and stable operation, making it suitable for high-end fields such as semiconductors.

Description

Technical Field

[0001] This invention relates to the field of high-purity graphite powder preparation technology, and particularly to a method for preparing high-purity graphite powder. Background Technology

[0002] High-purity graphite powder refers to micro-powdered graphite material made from natural flake graphite through a series of physical and chemical purification processes, resulting in extremely high fixed carbon content and extremely low impurity content. Ordinary natural graphite contains various impurities, such as silicon, aluminum, iron, calcium, magnesium, sodium, and potassium, mainly existing in the form of silicates and oxides. These trace impurities can have fatal negative effects in high-end materials.

[0003] Traditional technologies, primarily represented by the hydrofluoric acid method, involve the mixed acid method using low-concentration HF with H2SO4 and HCl, and high-temperature purification. While these methods offer good purification results and relatively low costs, hydrofluoric acid is highly toxic and corrosive, posing significant hazards to the environment and operators. Furthermore, waste acid treatment is difficult and costly. Therefore, developing non-toxic, pollution-free, and green purification processes is currently a key research focus.

[0004] Removing impurities such as boron (B) and vanadium (V) economically and effectively is a key technical challenge in the industry. Boron (B) content is typically between 5-50 ppm, while some associated boron-containing minerals can have B content as high as 30-50 ppm in their graphite raw materials, existing as fine encapsulated boride particles within the graphite flakes. Vanadium (V) content is generally between 2-25 ppm. Vanadium in graphite mainly exists as V₂O₃, V₂O₅, vanadates, or complex oxides formed with iron and aluminum, often adhering to the surface of graphite flakes or filling interlayer gaps. Conventional physical or simple chemical methods are insufficient for its separation. Improving purity while reducing overall production costs, especially energy and environmental costs, is crucial for industrial application. Simultaneously, precise control over the particle size, morphology, and surface properties of graphite powder is essential to meet the personalized needs of different applications.

[0005] Patent 201910491637.8 describes the addition of a small amount of organic acid to traditional inorganic mixed acid salts, nitric acid, and hydrofluoric acid. The organic acid can form complexes with metallic impurities in graphite and regenerate through ion exchange, thus acting as a catalyst and significantly improving the purification effect of inorganic acids. The entire purification process is completed at room temperature through impregnation, avoiding the heating and stirring steps required in traditional methods and significantly reducing energy consumption. This process relies on the use of hydrofluoric acid, which, although an effective reagent for removing silicate impurities, is highly toxic and corrosive, posing extremely high safety and equipment requirements for operators. Furthermore, the resulting fluoride-containing wastewater is costly and difficult to treat.

[0006] Patent 201810208716.9 discloses a method for preparing graphite powder and the graphite powder prepared therefrom. Graphite waste is used as raw material, and resource recovery is achieved through a carbonization-graphitization stage heating process. It is suitable for medium purity scenarios that are sensitive to cost. However, the heating process takes a very long time, with carbonization taking 10-16 hours and graphitization taking 8-16 hours. The production efficiency is low, and the upper limit of product purity is only 99.99%, which cannot meet the requirements of semiconductor grade.

[0007] Patent 202011288810.3 discloses a high-purity graphite powder preparation process that combines gas thermal purification with high-temperature treatment. It uses argon protection and purification gases such as CCl4 and CHClF2 to accurately remove impurities such as B, Al, and V that form high-melting-point carbides, which can meet the needs of high-end fields such as semiconductors and nuclear industries. Although it achieves ultra-high purity, it uses highly corrosive gases such as Cl2 and CCl4, which can easily cause equipment corrosion and increase the cost of waste gas treatment. The energy consumption in the high-temperature stage of 2600~3000℃ accounts for more than 60%, and the intermittent production mode limits the efficiency of industrial mass production.

[0008] Based on the background and existing technologies, the most commonly used methods for preparing ultrapure graphite powder are traditional acid methods, represented by the hydrofluoric acid method. These methods rely on highly toxic and corrosive HF or mixed acids, posing a significant safety threat to operators. Furthermore, the waste acid contains difficult-to-treat components such as fluoride ions. While conventional neutralization and precipitation methods can remove some acidic substances and metal ions, the removal efficiency of fluoride ions is limited, and a large amount of fluoride-containing waste residue is generated, resulting in "secondary pollution." Deep defluorination technology not only requires high equipment investment but also has problems such as high waste acid treatment costs.

[0009] Therefore, this invention proposes a method for preparing high-purity graphite powder to solve the above problems. Summary of the Invention

[0010] The main objective of this invention is to provide a method for preparing high-purity graphite powder, which can effectively solve the problems of high energy consumption, deep removal of difficult-to-remove impurities such as boron (B) and vanadium (V), single product performance, and insufficient process stability.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing high-purity graphite powder, comprising the following steps: S1: Take 100 portions of natural flake graphite powder with a diameter of 0.03mm~0.2mm and a carbon content of 95~98% and place it in a bioreactor. Add mixed leaching bacterial solution, culture medium and 50~150mg / L rhamnolipid surfactant. The volume ratio of mixed leaching bacterial solution to culture medium is 1:1. Under sterile conditions, control the temperature at 30℃ and react for 3~5 days. Maintain the pH at 2.0~2.5 with dilute H2SO4 to obtain a graphite mixture. S2: The graphite mixture obtained in S1 is centrifuged at high speed to separate the supernatant and solids. The supernatant is used to prepare a bio-electrolysis composite electrolyte. The solids are washed with deionized water 1-3 times, and then vacuum dried and ground to obtain pre-purified graphite powder. S3: Take 5 parts of the pre-purified graphite powder obtained in S2, mix and grind it with 5% PVDF binder, fill it into a mold and press it into a sheet at 10MPa, then dry it in a vacuum at 120℃ for 12h to obtain a functionalized graphite composite anode. S4: Take 20 parts of the pre-purified graphite powder obtained in S2 as cathode material, pour it into the reactor cavity, fix the platinum mesh cathode and the functionalized graphite composite anode prepared in S3 to the reactor cover, add the bio-electrolysis composite electrolyte prepared in S2, seal the reactor and purge with argon gas for 15 minutes. S5: Take 75 portions of pre-purified graphite powder, use the pulse mode of "on for 10s and off for 20s" to control the system temperature at 70~80℃, apply a constant voltage of 12V between the anode and cathode, and continuously introduce argon gas at 20~50mL / min. React for 2h, centrifuge the graphite powder mixture at 3000rpm for 10~20min, wash with deionized water until the pH is 7.0 to obtain wet graphite powder, centrifuge and dry again to obtain high-purity graphite powder.

[0012] Preferably, the centrifugal drying operation in step S2 is as follows: the prepurified graphite powder is centrifuged at 3000 rpm for 10 min in a high-speed centrifuge and then dried in a vacuum drying oven at 70°C for 2 hours.

[0013] Preferably, the mixed leaching bacterial solution in step S1 is a mixture of *Thiobacillus acidophilus* and *Thiobacillus acidophilus* in a volume ratio of 1:1.

[0014] Preferably, the diameter of the natural flake graphite powder is 30μm~200μm.

[0015] Preferably, the bio-electrolysis composite electrolyte in step S2 is prepared by: filtering the supernatant after centrifugation in S2 through a 0.45 μm filter membrane to obtain a metabolically active liquid; taking 20% ​​of the metabolically active liquid and mixing it with 0.1 mol H2SO4 at a volume ratio of 1:4 to prepare the bio-electrolysis composite electrolyte.

[0016] More preferably, the metabolically active liquid is refrigerated at 4°C.

[0017] Preferably, the preparation process of the culture medium in step S1 is as follows: Weigh 3.0g (NH4)2SO4, 0.1g KCl, 0.5g K2HPO4, 0.5g MgSO4·7H2O, and 0.01g Ca(NO3)2 and dissolve them in 1L of deionized water. Add 10.0g sulfur powder, adjust the pH value to 4.0 with 10% H2SO4 solution, and autoclave at 115~125℃ for 20min.

[0018] More preferably, the sulfur powder is an energy substance.

[0019] Preferably, the grinding process in step S3 involves adding a metabolically active liquid to the solid before grinding, with the amount added being 5% of the graphite mass. The grinding process is carried out by grinding for 30 minutes, letting it stand for 10 minutes, and then grinding for another 30 minutes. During the standing stage, the temperature is maintained at 45°C. After grinding, the solid is rinsed with deionized water until the pH of the filtrate is 4.0.

[0020] Preferably, the platinum mesh in step S4 is prepared by ultrasonically cleaning an 80-100 mesh platinum mesh for 15 minutes each with acetone, ethanol, dilute acid, and ultrapure water.

[0021] Preferably, the supernatant in step S2 contains low-molecular-weight organic acids, active enzymes, and rhamnolipids.

[0022] Preferably, the drying operation in step S5 is as follows: the wet graphite powder slurry washed with water to a pH of 7.0 is transferred to a petri dish and placed in a vacuum drying oven. The drying temperature is set to 70°C, and the slurry is dried under vacuum for 5 hours until it is in a loose state. After drying, the slurry is cooled to room temperature under vacuum protection.

[0023] More preferably, the step between steps S2 and S3 further includes the following step: S2-1: Add hydroxylation solution prepared by mixing refrigerated active liquid and deionized water at a ratio of 1:3, with a solid-liquid ratio of 1:10. React in a shaker at 55℃ and 150rpm for 1 hour. Then rinse with deionized water until the solution pH is 5.0. Place in a vacuum chamber and dry at 75℃ for 1.5 hours to enhance the hydroxylation of the graphite surface.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1. Addressing the challenge of removing difficult-to-remove impurities such as boron and vanadium from graphite powder, this invention focuses on the synergistic effect of "biological pretreatment and pulsed electrolysis." In the biological pretreatment stage, the metabolites of leaching bacteria can pre-bind with the structures of high-melting-point impurities, weakening the binding force between the impurities and the graphite matrix, while simultaneously altering the chemical morphology of the impurities. Subsequent pulsed electrolysis can further transform these impurities into soluble forms. Through the synergistic effect of these two processes, the purity of the graphite powder is significantly improved, exceeding the core threshold of high-purity graphite powder and meeting the demands of high-end fields such as semiconductors and the nuclear industry.

[0025] 2. Compared to traditional processes that use highly toxic hydrofluoric acid and strongly corrosive mixed acids, this invention innovatively employs bioleaching technology. The reaction only requires adjusting the pH value with dilute sulfuric acid, and it does not produce difficult-to-treat pollutants such as fluoride ions and highly corrosive gases. Furthermore, the preparation of a bio-electrolysis composite electrolytic solution using the bacterial solution generated from the biological pretreatment not only solves the environmental pollution problems of traditional processes but also significantly reduces treatment costs. It also avoids operator exposure to highly toxic reagents and other risk sources, and the equipment requires no special anti-corrosion modifications, reducing production cost investment.

[0026] 3. The medium-temperature pulsed electrolysis mode designed in this invention does not require the extreme temperature conditions of traditional high-temperature purification processes. The pulsed power supply method saves more energy than continuous electrolysis. The process time for biological pretreatment and electrolysis reaction is short, far less than the long processing time of existing carbonization-graphitization processes. Simultaneously, the raw materials used in the process, such as culture media and binders, are inexpensive, eliminating the need for expensive reagents. Overall energy consumption and production costs are significantly reduced, and production efficiency is significantly improved, solving the problem of high energy consumption and high cost inherent in the purification of ultra-high purity graphite powder.

[0027] 4. The differentiated electrode system in this invention, comprising a functionalized graphite composite anode and a platinum mesh-graphite powder composite cathode, effectively avoids problems such as electrode corrosion and powder shedding, ensuring stable reaction. Furthermore, it reduces the introduction of external impurities, resulting in high-quality graphite powder products. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the process of the present invention; Figure 2 Electron micrograph of high-purity graphite powder; Detailed Implementation

[0029] To more clearly illustrate the technical solutions of the embodiments in this specification, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this specification. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0030] The following are the specific implementation steps of the method for preparing high-purity graphite powder proposed in this invention, and the experimental flowchart is shown below. Figure 1 As shown: 1. Graphite powder pretreatment Take 100 portions of natural flake graphite powder with a diameter of 0.03mm to 0.2mm and a carbon content of 95% to 98%, and place them in a bioreactor. Add a mixed leaching solution of *Thiobacillus ferrooxidans* and *Thiobacillus thiooxidans* at a volume ratio of 1:1, culture medium, and 50 to 150 mg / L rhamnolipid surfactant. The ratio of the mixed leaching solution to the culture medium is 1:1. Under sterile conditions, control the temperature at 30°C and react for 3 to 5 days. Maintain the pH at 2.0 to 2.5 with dilute H2SO4 to obtain a graphite mixture.

[0031] The acidophilic ferrous thiobacillus in the added mixed leaching solution can oxidize ferrous ions in graphite powder to ferric ions. When ferric ions react with metal sulfides, elemental sulfur is usually produced and covers the surface of graphite powder, hindering the reaction. However, the acidophilic ferrous thiobacillus can oxidize this elemental sulfur to sulfuric acid, maintaining the strong acidic environment required by the system. Under strong acidic conditions, boron and vanadium oxides or silicates will exist in the form of boric acid, borate ions, or vanadium oxide ions.

[0032] 2. Graphite mixture treatment The graphite mixture obtained in S1 was centrifuged at 3000 rpm for 10-20 min to separate the supernatant and solids. The supernatant was used to prepare a bio-electrolysis composite electrolyte. The solids were washed with deionized water 1-3 times and dried in a vacuum drying oven at 70℃ for 2 h. Metabolic active liquid was added to the dried solids at 5% of the graphite mass. The mixture was ground for 30 min, allowed to stand for 10 min, and then ground for another 30 min. The temperature was maintained at 45℃ during the standing stage. After grinding, the mixture was washed with deionized water until the pH of the filtrate was 4.0. The resulting pre-purified graphite powder was obtained.

[0033] The bio-electrolysis composite electrolyte was prepared by filtering the supernatant after centrifugation through a 0.45μm filter membrane to obtain a metabolically active liquid. 20% of the metabolically active liquid was mixed with 0.1M H2SO4 at a volume ratio of 1:4 to obtain the bio-electrolysis composite electrolyte. The remaining 80% of the active liquid was refrigerated at 4℃ for later use.

[0034] A hydroxylation solution prepared by mixing refrigerated active liquid and deionized water at a ratio of 1:3 (solid-liquid ratio 1:10) was added to pre-purified graphite powder. The mixture was reacted in a shaker at 55℃ and 150 rpm for 1 hour. The solution was then rinsed with deionized water until the pH reached 5.0, and finally dried in a vacuum chamber at 75℃ for 1.5 hours to enhance the hydroxylation of the graphite powder surface. The hydroxylation of the graphite powder surface provides more active sites for subsequent electrolytic reactions. While natural graphite powder is hydrophobic, the increased number of hydroxyl groups significantly enhances its hydrophilicity, making it easier to wet and resulting in a more complete reaction.

[0035] 3. Preparation of Functionalized Graphite Composite Anodes Five parts of the pre-purified graphite powder were accurately weighed, mixed with 5% PVDF binder, and the metabolic active liquid was added. The amount added was 5% of the graphite mass. The mixture was ground for 30 min, allowed to stand for 10 min, and then ground for another 30 min. During the standing stage, the temperature was maintained at 45℃. After grinding, the mixture was rinsed with deionized water until the pH of the filtrate was 4.0 to form a slurry. The slurry was then filled into a mold and pressed into a sheet at 10 MPa. The sheet was then dried in a vacuum at 120℃ for 12 h to obtain the functionalized graphite composite anode.

[0036] The anode material made of high-purity graphite powder greatly reduces the introduction of external impurities. The functionalized anode prepared by using pre-purified graphite powder with surface hydroxylation can serve as a superior catalyst to more efficiently catalyze the generation of hydroxyl radicals and carry out more efficient electrolysis reactions.

[0037] 4. Positive and negative electrode assembly Accurately weigh 20 parts of pre-purified graphite powder as cathode material and pour it into the cavity of the reactor. Fix the above-mentioned functionalized graphite composite anode and platinum mesh cathode on the reactor cover. The platinum mesh contacts the pre-purified graphite powder. The platinum mesh cathode is a clean and stable cathode conductive component made by ultrasonically cleaning an 80-100 mesh platinum mesh for 15 minutes each with acetone, ethanol, dilute acid, and ultrapure water.

[0038] A standalone platinum mesh, as a cathode material, has a limited surface area and very few reaction sites for electron conduction, making it inefficient at triggering the conversion reactions of impurities such as boron (B) and volatile organic compounds (V). By stacking 20g of pre-purified graphite powder beneath the platinum mesh to form a loose cathode layer, the powder's morphology provides a significantly larger specific surface area. Electrons conducted by the platinum mesh can then rapidly diffuse through this cathode layer to the entire cathode region, allowing impurity ions in the electrolyte to fully contact the reaction sites and significantly improving electrolytic purification efficiency.

[0039] 5. Electrolytic pulse reaction Rinse and dry the sealed polytetrafluoroethylene cylindrical reactor. Take 20 parts of the pre-purified graphite powder cathode material prepared by S2 and spread it evenly on the bottom PTFE support mesh with a thickness of 1~1.5cm. Keep the powder loose to leave space for electrolyte penetration and argon gas flow, and avoid compaction which is not conducive to electron conduction.

[0040] The prepared 80-100 mesh platinum mesh is fixed inside the reactor cover, ensuring that the bottom of the platinum mesh is in contact with the surface of the cathode material at a depth of 0.5-1 cm. The edge of the platinum mesh is bound with titanium wire, and one end of the titanium wire passes through the cover interface and is connected to the negative terminal of a 12V DC power supply.

[0041] The functionalized graphite composite anode prepared by S3 is fixed to the inside of the reactor cover using a reactor clamp, ensuring a distance of 3-5 cm between the anode and cathode material layers. The anode wire passes through the cover interface and is connected to the positive terminal of a 12V DC power supply.

[0042] Slowly pour in 200-300 parts of the bio-electrolysis composite electrolyte prepared by S4, ensuring the liquid level completely submerges the anode, platinum mesh, and cathode material layer, with the liquid level 1-2 cm above the top layer. Tightly seal the reactor lid. Connect the argon exhaust pipe to a tail gas absorption bottle containing 5% NaOH solution to absorb trace amounts of acidic gas. Open the argon valve and purge at a flow rate of 50 mL / min for 15 minutes to expel air from the chamber.

[0043] The reactor employs a pulsed mode of "10s on, 20s off." Since the rate of biological and chemical reactions is slower than that of pure electron transfer, the reactor is turned on for 10s to initiate the electrochemical reaction, followed by a 20s off to allow the enzymes and organic acids in the electrolyte to fully react and prepare for the next cycle. The system temperature is controlled at 70-80℃, while a constant voltage of 12V is applied between the anode and cathode, and argon gas is continuously introduced at a rate of 20-50 mL / min. The reaction is carried out for 2 hours. The graphite powder mixture is then centrifuged at 3000 rpm for 10 minutes, washed with deionized water until the pH reaches 7.0, and the neutralized wet graphite powder slurry is transferred to a petri dish and placed in a vacuum drying oven. The drying temperature is set to 70℃, and the mixture is dried under vacuum for 5 hours until it reaches a loose state. After drying, the mixture is cooled to room temperature under vacuum protection to obtain high-purity graphite powder. Scanning electron microscopy (SEM) experiments were performed on the obtained high-purity graphite powder, and the microstructure of the high-purity graphite powder is shown below. Figure 2 As shown.

[0044] The purpose of introducing argon gas is to isolate oxygen, provide an anaerobic inert environment for the electrolytic pulse reaction, prevent the deactivation of components in the metabolic active liquid, and at the same time, the argon gas bubbles can also act as a stirrer to keep the pre-purified graphite powder suspended in the electrolyte, maximize the solid-liquid contact area, and ensure that the powder can fully accept the electrolysis. The continuously introduced argon gas can also carry byproduct gases such as H2 out of the reactor, maintain the stability of the system pressure, and ensure the safe progress of the reaction.

[0045] The present invention will be further described below with reference to Examples 1-5 and Comparative Examples 1-4: Example 1 The preparation method of high-purity graphite powder is based on the above operations and includes the following steps: S1: Take 100 portions of natural flake graphite powder with a diameter of 0.03 mm and a carbon content of 95% and place them in a bioreactor. Add mixed leaching bacterial solution, culture medium and 50 mg / L rhamnolipid surfactant. Control the temperature at 30℃ under sterile conditions and react for 3 days. Maintain the pH at 2.0 with dilute H2SO4 to obtain a graphite mixture. S2: The graphite mixture obtained in S1 is centrifuged at high speed to separate the supernatant and solids. The supernatant is used to prepare a bio-electrolysis composite electrolyte. The solids are washed once with deionized water, and then vacuum dried and ground to obtain pre-purified graphite powder. S3: Take 5 parts of the pre-purified graphite powder obtained in S2, mix and grind it with 5% PVDF binder. The graphite composite anode was prepared by pressing the anode into a mold at 10 MPa and then drying it in a vacuum at 120°C for 12 hours. S4: Take 20 parts of the pre-purified graphite powder obtained in S2 as cathode material, pour it into the reactor cavity, fix the platinum mesh cathode and the functionalized graphite composite anode prepared in S3 to the reactor cover, add the bio-electrolysis composite electrolyte prepared in S2, seal the reactor and purge with argon gas for 15 minutes. S5: Take 75 portions of pre-purified graphite powder, use the pulse mode of "on for 10s and off for 20s" to control the system temperature at 70℃, apply a constant voltage of 12V between the anode and cathode, and continuously introduce argon gas at 20mL / min. React for 2 hours, centrifuge the graphite powder mixture at 3000rpm for 10min, wash with deionized water until the pH is 7.0 to obtain wet graphite powder, centrifuge and dry again to obtain high-purity graphite powder.

[0046] Example 2 The preparation method of high-purity graphite powder is based on the above operations and includes the following steps: S1: Take 100 portions of natural flake graphite powder with a diameter of 0.05 mm and a carbon content of 96% and place them in a bioreactor. Add mixed leaching bacterial solution, culture medium and 150 mg / L rhamnolipid surfactant. Control the temperature at 30℃ under sterile conditions and react for 5 days. Maintain the pH at 2.5 with dilute H2SO4 to obtain a graphite mixture. S2: The graphite mixture obtained in S1 is centrifuged at high speed to separate the supernatant and solids. The supernatant is used to prepare a bio-electrolysis composite electrolyte. The solids are washed twice with deionized water, vacuum dried and ground to obtain pre-purified graphite powder. S3: Take 5 parts of the pre-purified graphite powder obtained in S2, mix and grind it with 5% PVDF binder, fill it into a mold and press it into a sheet at 10MPa, then dry it in a vacuum at 120℃ for 12h to obtain a functionalized graphite composite anode. S4: Take 20 parts of the pre-purified graphite powder obtained in S2 as cathode material, pour it into the reactor cavity, fix the platinum mesh cathode and the functionalized graphite composite anode prepared in S3 to the reactor cover, add the bio-electrolysis composite electrolyte prepared in S2, seal the reactor and purge with argon gas for 15 minutes. S5: Take 75 portions of pre-purified graphite powder, use the pulse mode of "10s on, 20s off" to control the system temperature at 80℃, apply a constant voltage of 12V between the anode and cathode, and continuously introduce argon gas at 50mL / min. React for 2 hours, centrifuge the graphite powder mixture at 3000rpm for 11min, wash with deionized water until the pH is 7.0 to obtain wet graphite powder, centrifuge and dry again to obtain high-purity graphite powder.

[0047] Example 3 The preparation method of high-purity graphite powder is based on the above operations and includes the following steps: S1: Take 100 portions of natural flake graphite powder with a diameter of 1 mm and a carbon content of 96% and place them in a bioreactor. Add mixed leaching bacterial solution, culture medium and 100 mg / L rhamnolipid surfactant. Control the temperature at 30℃ under sterile conditions and react for 4 days. Maintain the pH at 2.2 with dilute H2SO4 to obtain a graphite mixture. S2: The graphite mixture obtained in S1 is centrifuged at high speed to separate the supernatant and solids. The supernatant is used to prepare a bio-electrolysis composite electrolyte. The solids are washed twice with deionized water, vacuum dried and ground to obtain pre-purified graphite powder. S3: Take 5 parts of the pre-purified graphite powder obtained in S2, mix and grind it with 5% PVDF binder, fill it into a mold and press it into a sheet at 10MPa, then dry it in a vacuum at 120℃ for 12h to obtain a functionalized graphite composite anode. S4: Take 20 parts of the pre-purified graphite powder obtained in S2 as cathode material, pour it into the reactor cavity, fix the platinum mesh cathode and the functionalized graphite composite anode prepared in S3 to the reactor cover, add the bio-electrolysis composite electrolyte prepared in S2, seal the reactor and purge with argon gas for 15 minutes. S5: Take 75 portions of pre-purified graphite powder, use the pulse mode of "10s on, 20s off" to control the system temperature at 75℃, apply a constant voltage of 12V between the anode and cathode, and continuously introduce argon gas at 35mL / min. Centrifuge the graphite powder mixture at 3000rpm for 15min, wash with deionized water until the pH is 7.0 to obtain wet graphite powder, and centrifuge and dry again to obtain high-purity graphite powder.

[0048] Example 4 The preparation method of high-purity graphite powder is based on the above operations and includes the following steps: S1: Take 100 portions of natural flake graphite powder with a diameter of 0.18 mm and a carbon content of 97% and place them in a bioreactor. Add mixed leaching bacterial solution, culture medium and 60 mg / L rhamnolipid surfactant. Control the temperature at 30℃ under sterile conditions and react for 3.5 days. Maintain the pH at 2.1 with dilute H2SO4 to obtain a graphite mixture. S2: The graphite mixture obtained in S1 is centrifuged at high speed to separate the supernatant and solids. The supernatant is used to prepare a bio-electrolysis composite electrolyte. The solids are washed three times with deionized water, and then vacuum dried and ground to obtain pre-purified graphite powder. S3: Take 5 parts of the pre-purified graphite powder obtained in S2, mix and grind it with 5% PVDF binder, fill it into a mold and press it into a sheet at 10MPa, then dry it in a vacuum at 120℃ for 12h to obtain a functionalized graphite composite anode. S4: Take 20 parts of the pre-purified graphite powder obtained in S2 as cathode material, pour it into the reactor cavity, fix the platinum mesh cathode and the functionalized graphite composite anode prepared in S3 to the reactor cover, add the bio-electrolysis composite electrolyte prepared in S2, seal the reactor and purge with argon gas for 15 minutes. S5: Take 75 portions of pre-purified graphite powder, use the pulse mode of "on for 10s and off for 20s" to control the system temperature at 72℃, apply a constant voltage of 12V between the anode and cathode, and continuously introduce argon gas at 25mL / min. Centrifuge the graphite powder mixture at 3000rpm for 18min, wash with deionized water until the pH is 7.0 to obtain wet graphite powder, and centrifuge and dry again to obtain high-purity graphite powder.

[0049] Example 5 The preparation method of high-purity graphite powder is based on the above operations and includes the following steps: S1: Take 100 portions of natural flake graphite powder with a diameter of 0.2 mm and a carbon content of 98% and place it in a bioreactor. Add mixed leaching bacterial solution, culture medium and 145 mg / L rhamnolipid surfactant. Control the temperature at 30℃ under sterile conditions and react for 4.5 days. Maintain the pH at 2.4 with dilute H2SO4 to obtain a graphite mixture. S2: The graphite mixture obtained in S1 is centrifuged at high speed to separate the supernatant and solids. The supernatant is used to prepare a bio-electrolysis composite electrolyte. The solids are washed three times with deionized water, and then vacuum dried and ground to obtain pre-purified graphite powder. S3: Take 5 parts of the pre-purified graphite powder obtained in S2, mix and grind it with 5% PVDF binder, fill it into a mold and press it into a sheet at 10MPa, then dry it in a vacuum at 120℃ for 12h to obtain a functionalized graphite composite anode. S4: Take 20 parts of the pre-purified graphite powder obtained in S2 as cathode material, pour it into the reactor cavity, fix the platinum mesh cathode and the functionalized graphite composite anode prepared in S3 to the reactor cover, add the bio-electrolysis composite electrolyte prepared in S2, seal the reactor and purge with argon gas for 15 minutes. S5: Take 75 portions of pre-purified graphite powder, use the pulse mode of "on for 10s to off for 20s" to control the system temperature at 78℃, apply a constant voltage of 12V between the anode and cathode, and continuously introduce argon gas at 45mL / min. Centrifuge the graphite powder mixture at 3000rpm for 20min, wash with deionized water until the pH is 7.0 to obtain wet graphite powder, and centrifuge and dry again to obtain high-purity graphite powder.

[0050] Comparative Example 1 In step S1, a 5% HF + 10% H2SO4 mixed acid was used instead of the mixed leaching bacterial solution to pretreat the natural flake graphite powder, resulting in a graphite mixture. The remaining steps were the same as in Example 1.

[0051] Comparative Example 2 In step S2, only 0.1 mol H2SO4 was used to replace 20% of the metabolic active liquid in S2 to prepare the electrolytic composite electrolyte. The rest is the same as in Example 1.

[0052] Comparative Example 3 The functionalized graphite composite anode prepared in step S3 is replaced with ordinary graphite sheets; the rest is the same as in Example 1.

[0053] Comparative Example 4 The pre-purified graphite powder used as cathode material in step S4 is stacked into the reactor cavity, and the remaining steps are the same as in Example 1.

[0054] Samples from Examples 1-5 and Comparative Examples 1-4 were subjected to the following product performance tests: 1. Determination of fixed carbon content: Refer to GB / T3521-2008 "Methods for Chemical Analysis of Graphite" Moisture content determination: Weigh 1g of sample (accurate to 0.0001g) into a weighing bottle that has been dried to constant weight at 105~110℃. Open the bottle cap and place it in a drying oven at 105~110℃ for 2 hours. Remove the bottle, close the cap, and place it in a desiccator to cool to room temperature, then weigh it. Repeat the drying, cooling, and weighing steps until the difference between two weighings does not exceed 0.001g.

[0055] Moisture content = [(Weight before drying - Weight after drying) / Sample weight] × 100% Ash content determination: Weigh 1g of sample (accurate to 0.0001g) and place it in an ash dish or porcelain crucible that has been ignited to constant weight at 800±25℃. Place the ash dish in a high-temperature furnace, gradually increasing the temperature from a low temperature to 800±25℃, and ignite at this temperature for at least 2 hours until the carbon is completely burned off and no black spots remain. Remove the sample, allow it to cool slightly, and then place it in a desiccator to cool to room temperature. Weigh the sample. Repeat the ignition, cooling, and weighing steps until the difference between two weighings does not exceed 0.001g.

[0056] Ash content = [(weight of residue after ignition) / weight of sample] × 100% Volatile matter determination: Weigh 1g of sample (accurate to 0.0001g) and place it in a covered ceramic crucible for volatile matter determination. Quickly place the crucible into a high-temperature furnace preheated to 950±25℃ and ignite for 7 minutes. Remove and cool in air for 5 minutes, then transfer to a desiccator to cool to room temperature and weigh.

[0057] Volatile content = [(weight before ignition - weight after ignition) / sample weight] × 100% - moisture.

[0058] Fixed carbon (%) = 100% - Moisture % - Ash % - Volatile matter % 2. Determination of B and V impurity element content: Refer to GB / T24533-2019 "Graphite Anode Materials for Lithium-ion Batteries" Weigh approximately 0.1 g (accurate to 0.0001 g) of graphite sample and place it in a polytetrafluoroethylene (PTFE) digestion vessel. Wet the vessel with a small amount of ultrapure water, and add 5–10 mL of high-purity nitric acid and 3–5 mL of high-purity hydrofluoric acid. Cover the vessel and place it in a microwave digester. Digest according to the set temperature and pressure program. After digestion, cool the vessel and transfer the digest to a plastic volumetric flask. Rinse the digestion vessel several times with ultrapure water and bring the volume to 50 mL.

[0059] Prepare separate standard solutions for B and V, dilute them with 2% nitric acid solution, and prepare a series of standard working curve solutions of different concentrations.

[0060] Turn on the ICP-MS instrument, first measure the standard curve solution, then measure the digested and diluted sample solution. Based on the signal intensity of the sample, calculate the concentration of each element in the sample solution by referring to the standard curve.

[0061] Element content (ppm) = [Instrument-measured concentration (μg / L) × Dose-rate volume (L)] / Sample weight (g) 3. Ash content determination: Refer to GB / T3521-2008 "Chemical Analysis Methods for Graphite" Weigh 1g of graphite powder sample (accurate to 0.0001g) into an ashing dish. Place the dish in a high-temperature furnace and gradually increase the temperature from a low temperature to 800±25℃. Calcinate at this temperature for at least 2 hours until the carbon is completely burned and no black spots remain. Remove the dish, allow it to cool slightly, and then place it in a desiccator to cool to room temperature. Weigh the dish. Repeat the calcination, cooling, and weighing process until the difference between two weighings does not exceed 0.001g.

[0062] Ash content = [(weight of residue after ignition) / weight of sample] × 100% The test results of samples from Examples 1-5 and Comparative Examples 1-3 are shown in Table 1 below: Table 1: Performance Test Table of Fixed Carbon and B / V Impurities in Examples 1-5 and Comparative Examples 1-3 In the test data, Examples 1-5 and Comparative Examples 1-4 have complete process flows. From the core indicators, the fixed carbon content of Examples 1-5 all exceeded 99.99%, ranging from 99.991% to 99.996%, and the ash content was only 0.001% to 0.002%. Even the boron and vanadium impurities, which have always been difficult to remove in the industry, were controlled in the low ppm range of 0.8-2.0ppm and 1.2-3.0ppm, respectively, meeting the high-end needs of semiconductor and other fields.

[0063] The fixed carbon content ranged from 99.991% to 99.996%, exceeding the 99.99% threshold for high-purity graphite powder. The ash content was as low as 0.001% to 0.002%, and B and V impurities were controlled within the low ppm range of 0.8–2.0 ppm and 1.2–3.0 ppm, respectively. In contrast, the comparative examples, lacking core processes, did not reach 99.99% fixed carbon content, had ash content 3–25 times higher than the examples, and B and V impurities were 2–15 times higher.

[0064] The performance differences in Examples 1-5 stem from adjustments to key process parameters. Example 3, employing a combination of "100 mg / L rhamnolipin + 4 days of reaction + 35 mL / min argon gas," achieved optimal performance with 99.996% carbon fixation and B / V impurities of 0.8 / 1.2 ppm. Example 1 suffered from insufficient graphite dispersion and inadequate pretreatment, resulting in lower carbon fixation. Example 5, achieving 99.994% carbon fixation, demonstrated superior performance due to sufficient pretreatment.

[0065] Comparative Example 1 used a mixed acid instead of bioleaching. Although the acid could corrode away some impurities, it couldn't precisely bind impurities like boron and vanadium as effectively as biological pretreatment. The final fixed carbon rate was better than Comparative Example 2, but still didn't reach high purity standards. Comparative Example 3 replaced the functionalized graphite composite anode with ordinary graphite sheets, which immediately destroyed the electrode's catalytic and stabilizing effects on the electrolysis reaction. Ordinary graphite sheets lacked sufficient conductivity and corrosion resistance, causing a sharp drop in efficiency during electrolysis. Impurities couldn't be fully converted, resulting in a final fixed carbon level of 99.973%, ash content of 0.018%, and a B / V impurity ratio of 9.0 / 11.0 ppm.

[0066] Comparative Example 2 and Comparative Example 1 mainly modified the core link of "bio-electrolysis synergy". Comparative Example 2 directly replaced the composite electrolyte containing the metabolic active liquid with pure 0.1 mol H2SO4, which is equivalent to removing the low molecular weight organic acids and active enzymes produced by the leaching bacteria, which are key substances that can react with impurities. It became the worst performing of the comparative examples, which also proves that the bioactive liquid plays a core role in the synergistic process.

[0067] In Comparative Example 4, the "loose laying of 1~1.5cm" of pre-purified graphite powder in step S4 was changed to "stacking". Stacking will compact the powder, preventing the electrolyte from penetrating into the inner layer and the argon gas from flowing smoothly. The graphite powder in the inner layer cannot fully participate in the reaction, and impurities cannot be completely removed. In the end, the fixed carbon, ash content of 0.017%, and B / V impurity content are all relatively high, which also illustrates the necessity of loose laying.

[0068] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-purity graphite powder, characterized in that, Includes the following steps: S1: Take 100 portions of natural flake graphite powder with a diameter of 0.03mm~0.2mm and a carbon content of 95~98% and place it in a bioreactor. Add mixed leaching bacterial solution, culture medium and 50~150mg / L rhamnolipid surfactant. The volume ratio of mixed leaching bacterial solution to culture medium is 1:

1. Under sterile conditions, control the temperature at 30℃ and react for 3~5 days. Maintain the pH at 2.0~2.5 with dilute H2SO4 to obtain a graphite mixture. S2: The graphite mixture obtained in S1 is centrifuged at high speed to separate the supernatant and solids. The supernatant is used to prepare a bio-electrolysis composite electrolyte. The solids are washed with deionized water 1-3 times, and then vacuum dried and ground to obtain pre-purified graphite powder. S3: Take 5 parts of the pre-purified graphite powder obtained in S2, mix and grind it with 5% PVDF binder, fill it into a mold and press it into a sheet at 10MPa, then dry it in a vacuum at 120℃ for 12h to obtain a functionalized graphite composite anode. S4: Take 20 parts of the pre-purified graphite powder obtained in S2 as cathode material, pour it into the reactor cavity, fix the platinum mesh cathode and the functionalized graphite composite anode prepared in S3 to the reactor cover, add the bio-electrolysis composite electrolyte prepared in S2, seal the reactor and purge with argon gas for 15 minutes. S5: Take 75 portions of pre-purified graphite powder, use the pulse mode of "10s on, 20s off" to control the system temperature at 70~80℃, apply a constant voltage of 12V between the anode and cathode, and continuously introduce argon gas at 20~50mL / min. React for 2h, centrifuge the graphite powder mixture at 3000rpm for 10~20min, wash with deionized water until pH is 7.0 to obtain wet graphite powder, centrifuge and dry again to obtain high-purity graphite powder.

2. The method for preparing high-purity graphite powder according to claim 1, characterized in that, The centrifugal drying operation in step S2 is as follows: the pre-purified graphite powder is centrifuged at 3000 rpm in a high-speed centrifuge for 10-20 min, and then dried in a vacuum drying oven at 70℃ for 1.5-2.5 hours.

3. The method for preparing high-purity graphite powder according to claim 1, characterized in that, The mixed leaching bacterial solution in step S1 is a mixture of *Thiobacillus acidophilus* and *Thiobacillus acidophilus* at a volume ratio of 1:

1.

4. The method for preparing high-purity graphite powder according to claim 1, characterized in that, The bio-electrolysis composite electrolyte in step S2 is prepared by filtering the supernatant after centrifugation in S2 through a 0.45 μm filter membrane to obtain a metabolically active liquid. 20% of the metabolically active liquid is mixed with 0.1 mol H2SO4 at a volume ratio of 1:4 to prepare the bio-electrolysis composite electrolyte.

5. The method for preparing high-purity graphite powder according to claim 1, characterized in that, The preparation process of the culture medium in step S1 is as follows: Weigh 3.0g (NH4)2SO4, 0.1g KCl, 0.5g K2HPO4, 0.5g MgSO4·7H2O, and 0.01g Ca(NO3)2 and dissolve them in 1L of deionized water. Add 10.0g sulfur powder and adjust the pH value to 4.0 with 10% H2SO4 solution. Autoclave at 115~125℃ for 20min.

6. The method for preparing high-purity graphite powder according to claim 4, characterized in that, In step S3, the grinding process involves adding a metabolically active liquid to the solid before grinding, with the amount added being 5% of the graphite mass. The process is then followed by grinding for 30 minutes, standing for 10 minutes, and grinding for another 30 minutes. The grinding process is carried out at a constant temperature of 45°C. After grinding, the solid is rinsed with deionized water until the pH of the filtrate is 4.

0.

7. The method for preparing high-purity graphite powder according to claim 1, characterized in that, The platinum mesh cathode in step S4 is an 80-100 mesh platinum mesh, which is prepared by ultrasonic cleaning with acetone, ethanol, dilute acid, and ultrapure water for 15 minutes.

8. The method for preparing high-purity graphite powder according to claim 1, characterized in that, The supernatant in step S2 contains low molecular weight organic acids, active enzymes, and rhamnolipids.

9. The method for preparing high-purity graphite powder according to claim 1, characterized in that, The drying operation in step S5 is as follows: the wet graphite powder washed with water to a pH of 7.0 is transferred to a petri dish and placed in a vacuum drying oven. It is dried under vacuum conditions at 70°C for 5 hours. After drying, it is cooled to room temperature under vacuum protection.

Images