Method for preparing graphene from aluminum electrolysis cell overhaul waste cell lining and graphene

Abstract

The invention discloses a method for preparing graphene by using aluminum electrolysis overhaul slag, which comprises the following steps: grinding and screening the aluminum electrolysis overhaul slag to obtain fine particles, soaking the fine particles of the overhaul slag in 4-15mol / L of acid, fully stirring at 50-100 DEG C, removing harmful components to obtain purified carbon powder, and drying the purified carbon powder to obtain the graphene. And finally, preparing the graphene by using a chemical oxidation method or a mechanical stripping method. The invention also discloses the graphene prepared by the method. Compared with graphene prepared from traditional graphite, the method for preparing the graphene by purifying the overhaul slag of the aluminum electrolysis cell has the advantages that dangerous solid waste can be effectively and safely treated, the graphite electrolyzed for a long time has the characteristics of multiple pores and the like, the method is superior to commercial graphite, and the method is better in economical efficiency, higher in practicability and wider in application prospect.

Description

Technical Field

[0001] This invention relates to the field of resource utilization of solid waste from the aluminum electrolysis industry, specifically to a method and application for preparing graphene materials by purifying overhaul slag. Background Technology

[0002] Aluminum is widely distributed in nature, ranking third in abundance in the Earth's crust after oxygen and silicon, making it the most abundant metallic element in the Earth's crust. Aluminum's position in the periodic table, after sodium and magnesium, determines its relatively reactive chemical properties, thus existing in nature as oxides and silicates. Long ago, humans used clay containing aluminum compounds to make utensils for their use.

[0003] Aluminum is currently the most demanded non-ferrous metal in the world. It possesses excellent thermal and electrical conductivity, corrosion resistance, and is relatively lightweight, making it widely used in various fields such as transportation, electrical industries, and aerospace. With the improvement of my country's primary aluminum production level and further development of aluminum properties, the aluminum industry's development prospects will be even broader.

[0004] Currently, large-scale industrial production of aluminum almost exclusively employs the cryolite-alumina molten salt electrolysis method. The basic principle of this method is as follows: carbon materials are used as the anode of the aluminum electrolysis cell, metallurgical-grade alumina is used as the electrolytic raw material, and cryolite melt is used as the electrolyte solution. Electrolysis is carried out under direct current conditions. A reduction reaction occurs at the cathode to produce molten aluminum, while an oxidation reaction occurs at the anode to release carbon monoxide and carbon dioxide gases. The overall electrolysis reaction process is shown in the equation.

[0005] Al₂O₃ (molten) + 1.5C (s) → 2Al (l) + 1.5CO₂ (g)

[0006] The electrode reaction process is as follows:

[0007]

[0008] Cathode reaction:

[0009] Al 3+ (络合态) +3e - →Al(l)

[0010] Anode reaction:

[0011] O 2- (络合态) -2e - →O (原子)

[0012] 2O (原子) +C (原子) →CO2(g)

[0013] With the rapid development of my country's aluminum industry, the amount of solid waste generated during aluminum electrolysis is increasing, especially the amount of overhaul slag (also known as waste pot lining, abbreviated as SPL), which is growing rapidly every year, putting enormous environmental pressure on the aluminum electrolysis industry. Approximately 30 kg of overhaul slag is generated for every 1 ton of aluminum produced, of which waste cathodes account for about 50%-70%.

[0014] High concentrations of soluble fluorides and cyanides are found in the slag from major overhauls of aluminum electrolytic cells in China, including F. - and CN - The contents were approximately 2000 mg / L and 15 mg / L, respectively, of which F - The concentration of fluoride can reach as high as 6000 mg / L. The fluoride concentration exceeds the maximum limit of 100 mg / L for fluoride concentration in leachate specified in the "Standard for Identification of Hazardous Waste—Leaching Toxicity Identification" (GB5085.3-2007). Therefore, in June 2016, various wastes from the aluminum electrolysis process, including maintenance slag, were included in China's "National Hazardous Waste List," with waste code 321-023-48 and a hazardous characteristic of "T" (leaching toxicity). The state has issued relevant policies prohibiting the open-air storage, illegal discharge, and transfer of aluminum electrolysis maintenance slag.

[0015] The preparation of graphene materials has been a widely studied topic. Graphene (Gr) is a single-atom-thick layer of carbon atoms arranged in a hexagonal lattice, possessing strong σ bonds and exhibiting excellent mechanical, electrical, thermal, and physical properties. Graphene oxide (GO) is a derivative of graphene, composed of graphene sheets with oxygen-containing functional groups, including hydroxyl and epoxy groups. Internally, the edges of the graphene layers have numerous carbonyl and carboxyl groups. GO can be prepared by oxidation-exfoliation of graphite in solution with stirring. Compared to graphene (Gr), GO has a larger specific surface area, higher transparency, better electrical insulation, thermal conductivity, mechanical strength, barrier properties, and fracture toughness. It has a 2D crystal structure composed of carbon atoms arranged in a hexagonal pattern, with many functional oxygen groups on the surface. Due to its sp... 2Graphene oxide (GO), with its hybridization, π-π / or n-π orbital interactions, and multifunctional bioconjugated chemistry, is considered an effective material for enhancing biosensor applications. The functional groups present in GO allow for direct binding with a variety of biomolecules and biomaterials. Compared to pristine graphene, it is more hydrophilic and easier to disperse in solvents. Due to its excellent dispersibility and functionalization capabilities, GO is commonly used in applications such as membranes, sensors, and biomedical devices. Graphene / graphene oxide has extremely high application prospects and economic value, and is widely used in energy, environment, aerospace, electronics, and other fields. SPL has relatively high specific capacitance and stability. However, due to residual contaminants in graphite form, SPL limits its full potential in energy storage. Therefore, converting SPL into graphene oxide (GO) by leaching residual contaminants is a promising research direction. Furthermore, the cost of synthesizing graphene / graphene oxide from SPL is lower than that of other carbon solid wastes, meaning that preparing graphene / graphene oxide from SPL has greater economic appeal. Summary of the Invention

[0016] Therefore, the technical problem to be solved by the present invention is to provide a method for purifying and preparing graphene materials using waste residue from aluminum electrolysis cell overhaul. Another technical problem to be solved by the present invention is to provide graphene prepared by this method.

[0017] The technical solution of this invention is a method for preparing graphene using aluminum electrolysis overhaul slag, comprising the following steps:

[0018] First, the aluminum electrolysis overhaul slag is ground and sieved to obtain fine particles. Then, the fine particles of the overhaul slag are soaked in 4-15 mol / L acid. After being thoroughly stirred at 50-100℃, harmful components are removed to obtain purified carbon powder. Finally, graphene is prepared by chemical oxidation or mechanical exfoliation.

[0019] The overhaul slag originates from waste tank linings generated during the electrolytic aluminum production process. This invention provides a comprehensive treatment for overhaul waste slag generated in the aluminum electrolysis industry (including cathode carbon block waste slag, cathode paste waste slag, anti-seepage material waste slag, refractory brick waste slag, castable waste slag, and calcium silicate board waste slag), eliminating the need for additional sorting in practical engineering applications. In actual engineering applications, all waste materials are mixed together, with the main components being carbonaceous and aluminosilicate components, both of which are corroded by the electrolyte and contain fluorine. During the crushing and screening process, based on the difference in material hardness, carbonaceous materials are easily crushed, while aluminosilicate materials are not, so the fine particles obtained from screening are enriched with carbonaceous materials. Subsequent acid leaching to remove fluorine effectively ensures the purity of the carbon components.

[0020] The overhaul slag powder, after sieving, is enriched with carbon, but still contains certain amounts of fluorine, aluminum, and silicon, specifically in the form of sodium fluoride, sodium hexafluoroaluminate, calcium fluoride, aluminum oxide, and silicon oxide. Failure to remove these elements will affect the quality of the subsequent graphene production. Stirring with nitric acid solution, followed by filtration and drying, yields overhaul slag graphite powder with a higher carbon content, facilitating subsequent preparation.

[0021] The acid soaking described above is mainly to remove harmful fluorine components and aluminum and calcium elements from the overhaul residue. There are no specific requirements for the ratio of overhaul residue to acid solution; it can be determined based on the composition of the obtained overhaul residue, but immersion is generally preferred.

[0022] Graphene obtained through chemical oxidation is primarily graphene oxide, accounting for up to 90%, while graphene prepared by mechanical exfoliation is mainly ordinary graphene. Graphene oxide contains oxygen-containing functional groups, resulting in better water solubility and bioactivity, and is commonly used in membranes, sensors, and biomedical devices. Ordinary graphene is used in materials, electrode materials, and electronic devices. The carbon elements in overhaul slag undergo significant graphitization due to prolonged electrolysis; after four months of electrolysis, the carbon cathode block is transformed into graphite, with a graphitization degree comparable to that obtained through high-temperature treatment at 2500℃. Furthermore, the graphite from overhaul slag, after prolonged electrolysis, exhibits porous and expandable characteristics, offering advantages over commercially available soft carbon.

[0023] According to a method for preparing graphene using aluminum electrolysis overhaul slag of the present invention, preferably, the particle size of the fine particles is less than 0.25 mm. Preferably, the purified carbon powder has a purity reaching chemical purity.

[0024] According to a method for preparing graphene using aluminum electrolysis overhaul slag according to the present invention, preferably, the acid is selected from hydrochloric acid, sulfuric acid, nitric acid and perchloric acid.

[0025] Furthermore, the acid is selected from nitric acid. Nitric acid was chosen because it is more environmentally friendly and less expensive compared to other acids.

[0026] The reaction principle is as follows:

[0027] Na3AlF6+4HNO3→4HF↑+NaAl(NO3)4

[0028] Al₂O₃ + 6HNO₃ → 2Al(NO₃)₃ + 3H₂O

[0029] CaF₂ + 2HNO₃ → 2HF↑ + Ca(NO₃)₂

[0030] Acid leaching removes most of the fluorine, aluminum, and calcium elements, while enriching the carbon element. The generated HF gas can also be recycled and reused.

[0031] According to a method for preparing graphene using aluminum electrolysis overhaul slag according to the present invention, preferably, the thorough stirring is stirring for more than one hour.

[0032] According to a method for preparing graphene using aluminum electrolysis overhaul slag, preferably, in the chemical oxidation method, the treated carbon powder is added to a mixed solution of sulfuric acid and phosphoric acid, stirred thoroughly at room temperature, transferred to an ice bath, and then mixed with excess potassium permanganate. The mixture is stirred thoroughly to ensure a complete reaction, then transferred to a hot plate at 40-60°C and placed for 2-4 hours. Deionized water is then added to the reaction solution, and the mixture is cooled to room temperature. After cooling, centrifugation is performed, and the liquid on top is collected to obtain a brownish-yellow graphene oxide colloid.

[0033] Add 3%-35wt% hydrogen peroxide solution to the obtained graphene oxide colloid and let it stand for a while; add 0.5-4mol / L acid solution for acidification, and control the pH between 1 and 2 to allow all manganese to enter the liquid and for the graphene oxide to aggregate, thus achieving solid-liquid separation; finally, centrifuge at 4000-10000rpm to obtain the supernatant and solid precipitate; take the precipitate after centrifugation, which is the obtained graphene oxide sample.

[0034] In this chemical oxidation method, acidification, pH control, and centrifugation speed parameters are used, which result in better graphene quality.

[0035] This invention employs a modified Hummer chemical oxidation method, which reduces the use of nitrates compared to the traditional Hummer method. It utilizes concentrated phosphoric acid and concentrated sulfuric acid in a ratio of 1:8-10, making it more environmentally friendly, while maintaining the same graphite intercalation effect as the traditional method.

[0036] The main step in this process is to add potassium permanganate, which reacts with hydrogen peroxide, to convert it into divalent manganese ions. The concentration can vary, the key is complete removal, but excess hydrogen peroxide can affect the graphene structure, so the concentration must be controlled accordingly.

[0037] Preferably, the molar ratio of sulfuric acid to phosphoric acid is 8-10:1; the concentration of hydrogen peroxide solution is 10-30%; and the sufficient standing time is 20 hours or more.

[0038] Before adding potassium permanganate, SPL is treated with a mixture of sulfuric acid and phosphoric acid to break down the graphite layers in order to obtain layered graphene.

[0039] Furthermore, in the above chemical oxidation method, the 0.5-4 mol / L acid solution is a hydrochloric acid solution; the stirring is sufficient for more than one hour; the centrifugation speed is 4500-9000 rpm; and the centrifugation time is 15-25 minutes. Using hydrochloric acid is more effective, primarily for acidification without causing other reactions.

[0040] Furthermore, in the chemical oxidation method, the stirring is sufficient for more than one hour; the concentration of the hydrogen peroxide solution is 10-35%; and the settling is sufficient for more than 20 hours.

[0041] Preferably, the wet mechanical peeling technique in the mechanical peeling method is mainly selected from either ultrasonic peeling or ball milling peeling.

[0042] Ultrasonic exfoliation involves placing treated overhaul residue carbon powder and a solvent in an ultrasonic instrument. The shear force released by the rupture of microbubbles generated during ultrasonic wave propagation is used to exfoliate the graphite layers. The main steps of ultrasonic exfoliation are: mixing the treated overhaul residue carbon powder with a solution to prepare a graphite dispersion; then using ultrasound to exfoliate the graphene; and finally, centrifuging to purify and separate the unexfoliated graphite from single / few-layer graphene. Solvents used for ultrasonic exfoliation can include N-methylpyrrolidone (NMP), DMF-water mixtures, and water-TMU mixtures.

[0043] Ball milling exfoliation: Overhaul residue carbon powder, abrasive, and steel balls are placed together in a ball mill jar, and the graphene is exfoliated by transferring kinetic energy through the collision of the steel balls.

[0044] Graphene materials can be produced by mixing carbon powder from overhaul slag with a solvent and then using a high-speed rotating drill to generate shear force to break the interlayer van der Waals forces. Alternatively, graphene materials can be produced by mixing carbon powder from overhaul slag with water and a surfactant, injecting the mixture under pressure into microchannels, and then exfoliating the graphene using shear force, cavitation effect (micro-jets generated by bubble collapse), and stress wave exfoliation. These are mechanical exfoliation methods, distinct from ultrasonic and ball milling exfoliation.

[0045] Wet mechanical exfoliation is one method for preparing high-quality graphene through mechanical exfoliation. Its core principle is to break down the van der Waals forces between graphite layers using mechanical force to obtain monolayer graphene. The wet process primarily involves adding surfactants to improve yield. Wet mechanical exfoliation methods include ultrasonic exfoliation and ball milling exfoliation.

[0046] Microchannel injection is a novel form of wet exfoliation. It utilizes a precisely designed microfluidic system to achieve shear-strengthened exfoliation. The microchannels can be serpentine / spiral, with widths ranging from 50-200 μm, to generate high-intensity shear fields. The shear force is determined based on the interlayer van der Waals forces in graphite, with an exfoliation threshold of approximately 0.2 J / m. 2 The corresponding critical τ≥10 3 Pa, optimal range: 104 -10 5 Pa can balance peeling efficiency and defect control (ID / IG < 0.1), damage threshold: τ > 10 6 Pa causes fragmentation (particle size < 200 nm).

[0047] There are many choices of solvents and surfactants, such as NMP solvent, ethanol, and SDS (sodium dodecyl sulfate). The ratio of toner to solvent varies depending on the solvent; for example, 2-5 wt% graphite in an NMP system and 1-4% in an ethanol system. Surfactants are added, with an SDS concentration of 0.1-0.5 mM.

[0048] The present invention also provides graphene prepared by the above method. Preferably, the graphene prepared by the chemical oxidation method is graphene oxide, and the graphene prepared by the mechanical exfoliation method is graphene; the graphene or graphene oxide has a layered structure.

[0049] After a prolonged electrolysis process at high temperatures of 800℃ to 950℃, the graphitization degree of carbon in SPL was significantly improved. After four months of electrolysis, the carbon cathode block was transformed into graphite, with a graphitization degree comparable to that achieved at 2500℃. Semi-graphitized carbon cathode blocks (CCBs) are the mainstream type for most aluminum electrolytic cells, with apparent density, actual density, and porosity of 1.54-1.63 g / cm³. 3 1.94-2.0 g / cm³ 3 And 20-23%. SPL underwent a long-term graphitization and impregnation process with molten salt, resulting in an apparent density of SPL (2.19 g / cm³). 3 ) and actual density (2.22 g / cm³) 3 The porosity decreased significantly (1.52%), while the overall porosity increased significantly. The cost of synthesizing graphene / graphene oxide from overhaul slag is lower than that of other carbon solid wastes, meaning that the preparation of graphene / graphene oxide from overhaul slag is more economically attractive.

[0050] The graphene produced from the overhaul residue has properties comparable to those produced from commercially available graphite. The long-term electrolysis of carbon blocks reduces the need for graphitization of commercially available carbon powder, resulting in significant economic advantages. Furthermore, the electrolytic cell waste residue is hazardous waste, which can be treated and valued.

[0051] Utilizing the long-term electrolysis characteristics of graphite electrodes in aluminum electrolytic cells, the waste carbon cathodes generated during overhauls possess a porous structure, resulting in lower cost and better performance compared to commercial carbon for graphene preparation. The purification process not only achieves the harmless treatment of the overhaul slag but also further realizes the resource utilization of the waste residue.

[0052] The beneficial effects of this invention are as follows:

[0053] Compared with the preparation of graphene from aluminum electrolytic cell overhaul slag, the present invention can effectively and safely treat hazardous solid waste. Furthermore, the graphite prepared by long-term electrolysis has the characteristics of being porous, which is superior to commercial graphite. It is also more economical, more practical, and has a broader application prospect. Attached Figure Description

[0054] Figure 1 This is a flowchart of the chemical oxidation method for preparing graphene according to the present invention. Detailed Implementation

[0055] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0056] Example 1

[0057] A series of graphene products prepared from overhaul slag are produced through the following methods:

[0058] The initial blocky overhaul slag was crushed and ground, and fine powder with a particle size ≤0.25mm was obtained by passing it through a 60-mesh sieve. The powder was then soaked in 4 mol / L nitric acid and stirred at 50℃ for one hour to remove most of the fluorine components, yielding the treated SPL powder, denoted as T-SPL. Graphene / graphene oxide was subsequently prepared using a chemical oxidation method (Hummer process).

[0059] A mixture of concentrated H₂SO₄ and H₃PO₄ was prepared in a 9:1 ratio and vigorously stirred at room temperature. Treated SPL powder was added, and the mixture was then stirred in an ice bath maintained below 5°C. KMnO₄ was gradually added in a 1:6 ratio to initiate an exothermic reaction, raising the temperature to 25–35°C, which caused the solution to decompose due to the presence of MnO₄. - The solution darkened due to ions. The oxidation process was completed by heating the reaction mixture at 40°C for 3 hours, yielding a brown solution indicating successful graphite oxidation. The solution was cooled and diluted with ice-cold deionized water, then 2.5 ml of 30% H₂O₂ was added to remove excess permanganate. After complete reaction, an orange-yellow graphene oxide dispersion was obtained. This dispersion was centrifuged at 4000 rpm for 15 minutes to separate the gelled graphene oxide, which was then redispersed in water. The pH was adjusted to 1 with 4 mol / L HCl, and the mixture was stirred for one hour. Finally, it was centrifuged at 4000 rpm for 15 minutes, and the solid was filtered. The solid was washed with water until neutral. The solid was dried at 85°C to obtain the product. The resulting graphene oxide from overhaul slag underwent further characterization.

[0060] A schematic diagram illustrating the process of purifying and preparing graphene / graphene oxide using aluminum electrolytic cell overhaul slag as raw material according to this invention is shown below. Figure 1 As shown.

[0061] Result characterization:

[0062] 1. FTIR spectroscopy: revealed new vibrational bands in GO, proving the existence of the graphene oxide structure.

[0063] 2. Electron scanning spectroscopy (XPS): confirmed the increase in oxygen content and the presence of oxygen groups.

[0064] 3. X-ray diffraction (XRD): The presence of the 002 peak confirmed the formation of monolayer or few-layer graphene.

[0065] 4. Raman spectroscopy determination: It has D peak and G peak, and the intensity ratio ID / IG is 1.01, which shows the defect structure unique to graphene oxide.

[0066] Example 2

[0067] A series of graphene products prepared from overhaul slag are produced through the following methods:

[0068] The initial blocky overhaul slag was crushed and ground, and fine powder with a particle size ≤0.25mm was obtained by passing it through a 60-mesh sieve. The powder was then soaked in 4 mol / L nitric acid and stirred at 50℃ for one hour to remove most of the fluorine components, yielding treated SPL powder, denoted as T-SPL. Composition analysis using XRD, XRF, and ash combustion experiments revealed a 99.9% purity graphite powder from the overhaul slag. Subsequently, graphene was prepared by wet mechanical exfoliation using the graphite powder from the overhaul slag.

[0069] 5g of overhaul residue graphite powder was placed in 50ml of concentrated sulfuric acid / nitric acid (3:1) solution and sonicated for 30min to enhance the solvent wettability of the graphite powder. After completion, it was vacuum dried at 60℃ until the water content was <0.5wt%. The treated graphite powder was then added to water and surfactant SDS (sodium dodecyl sulfate), followed by ultrasonic exfoliation. The mixture was placed in an ice bath at 400W (20kHz) for 4 hours. After ultrasonication, gradient centrifugation was performed: centrifugation at 500rpm for 10min precipitated large graphite particles, centrifugation at 3000rpm for 20min precipitated multilayer graphene, and finally centrifugation at 9000rpm for 30min collected the supernatant, yielding the wet-exfoliated graphene product.

[0070] Result characterization:

[0071] 1. FTIR spectroscopy: revealed new vibrational bands, proving the existence of the graphene structure.

[0072] 2. X-ray diffraction (XRD): The 002 peak was observed, and the peak was prominent, indicating a clear graphene structure.

[0073] 3. Raman spectroscopy determination: It has D peak and G peak, and the intensity ratio ID / IG is 0.30. The G' peak is prominent, indicating that there is a large amount of monolayer graphene.

[0074] Example 3

[0075] A series of graphene products prepared from overhaul slag are produced through the following methods:

[0076] The initial blocky overhaul slag was crushed and ground, and fine powder with a particle size ≤0.25mm was obtained by passing it through a 60-mesh sieve. The powder was then soaked in 4 mol / L nitric acid and stirred at 50℃ for one hour to remove most of the fluorine components, yielding treated SPL powder, denoted as T-SPL. Composition analysis using XRD, XRF, and ash combustion experiments revealed a 99.9% purity graphite powder from the overhaul slag. Graphene was subsequently prepared by mechanical exfoliation using this graphite powder.

[0077] Zirconia balls with a particle size of 1.0 mm were selected as the grinding medium, and graphite powder from overhaul residue was added and placed in a ball mill for grinding. The speed was set to 400 rpm, and the milling time was 8 hours. After the grinding, the product was placed in water for separation and sedimentation. The supernatant was centrifuged at 8000 rpm for 15 minutes to separate the solid, which was the graphene product.

[0078] Result characterization:

[0079] 1. X-ray diffraction (XRD): The 002 peak was observed, and the peak was prominent, indicating a clear graphene structure.

[0080] 2. Raman spectroscopy determination: It has D peak and G peak, and the intensity ratio ID / IG is 0.20. The G' peak is prominent, indicating that there is a large amount of monolayer graphene.

[0081] 3. Atomic force microscopy (AFM) showed that the average thickness of graphene was 0.65 nm with a standard deviation of 0.059.

[0082] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing graphene using aluminum electrolysis overhaul slag, characterized in that: Includes the following steps: First, the aluminum electrolysis overhaul slag is ground and sieved to obtain fine particles. Then, the fine particles of the overhaul slag are soaked in 4-15 mol / L acid. After being thoroughly stirred at 50-100℃, harmful components are removed to obtain purified carbon powder. Finally, graphene is prepared by chemical oxidation or mechanical exfoliation.

2. The method for preparing graphene using aluminum electrolysis overhaul slag according to claim 1, characterized in that: The fine particles have a particle size of less than 0.25 mm; the purified carbon powder has a purity that meets chemical purity standards.

3. The method for preparing graphene using aluminum electrolysis overhaul slag according to claim 1, characterized in that: The acid is selected from hydrochloric acid, sulfuric acid, nitric acid, and perchloric acid.

4. The method for preparing graphene using aluminum electrolysis overhaul slag according to claim 3, characterized in that: The acid is selected from nitric acid.

5. The method for preparing graphene using aluminum electrolysis overhaul slag according to claim 1, characterized in that: The term "thorough stirring" refers to stirring for at least one hour.

6. The method for preparing graphene using aluminum electrolysis overhaul slag according to claim 1, characterized in that: In the chemical oxidation method, the treated carbon powder is added to a mixed solution of sulfuric acid and phosphoric acid, stirred thoroughly at room temperature, and then transferred to an ice bath. It is then mixed with excess potassium permanganate and stirred thoroughly to ensure a complete reaction. The mixture is then transferred and placed on a hot plate at 40-60°C for 2-4 hours. Deionized water is then added to the reaction solution, and the mixture is cooled to room temperature. After cooling, the mixture is centrifuged, and the liquid on top is collected to obtain a brownish-yellow graphene oxide colloid. Add 3%-35wt% hydrogen peroxide solution to the obtained graphene oxide colloid and let it stand for a while; add 0.5-4mol / L acid solution for acidification, and control the pH between 1 and 2 to allow all manganese to enter the liquid and for the graphene oxide to aggregate, thus achieving solid-liquid separation; finally, centrifuge at 4000-10000rpm to obtain the supernatant and solid precipitate; take the precipitate after centrifugation, which is the obtained graphene oxide sample.

7. The method for preparing graphene using aluminum electrolysis overhaul slag according to claim 6, characterized in that: The 0.5-4 mol / L acid solution is a hydrochloric acid solution; the stirring is sufficient for more than one hour; the centrifugation speed is 4500-9000 rpm; and the centrifugation time is 15-25 minutes.

8. A method for preparing graphene using aluminum electrolysis overhaul slag according to claim 6, characterized in that: The molar ratio of sulfuric acid to phosphoric acid is 8-10:1; the concentration of hydrogen peroxide solution is 10-30%; and the sufficient standing time is 20 hours or more.

9. The method for preparing graphene using aluminum electrolysis overhaul slag according to claim 1, characterized in that: The wet mechanical peeling technique in the mechanical peeling method is mainly selected from either ultrasonic peeling or ball milling peeling.

10. The graphene prepared by the method of claim 1, characterized in that: The chemical oxidation method produces graphene oxide, while the mechanical exfoliation method produces graphene; the graphene or graphene oxide has a layered structure.

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