Ultrahigh-temperature reducing atmosphere intermediate frequency roasting furnace, graphite material and preparation method thereof

Abstract

The application provides an ultrahigh-temperature reducing atmosphere medium-frequency roasting furnace, a graphite material and a preparation method thereof, and relates to the technical field of graphite materials. The ultrahigh-temperature reducing atmosphere medium-frequency roasting furnace comprises, from top to bottom, a first furnace front bin, a second furnace front bin, a preheating section, a high-temperature section, a cooling section, a water cooling section and a discharger which are sequentially connected. The outer surface of the high-temperature section is further provided with a furnace body coil connected with a medium-frequency cabinet. The medium-frequency cabinet is used for providing a medium-frequency power source to perform medium-frequency heating on the furnace body coil. The preparation method of the graphite material comprises the following steps: feeding waste cathode material into the ultrahigh-temperature reducing atmosphere medium-frequency roasting furnace, performing high-temperature roasting under a reducing atmosphere, and obtaining a graphite crude product; and then performing purification and magnetic separation to obtain the graphite material. Through the treatment of the waste cathode material in the ultrahigh-temperature reducing atmosphere medium-frequency roasting furnace, sodium salt and iron salt are reduced in situ as catalysts in a reducing atmosphere, and the graphite material with a graphene crystal structure is obtained.

Description

Technical Field

[0001] This application relates to the field of graphite materials technology, and in particular to an ultra-high temperature reducing atmosphere medium-frequency calcining furnace, graphite materials and their preparation methods. Background Technology

[0002] Graphene is a type of carbon atom arranged in sp... 2 Two-dimensional carbon nanomaterials with a hexagonal honeycomb lattice composed of hybrid orbitals possess excellent optical, electrical, and mechanical properties, and hold significant application potential in materials science, micro / nano fabrication, energy, biomedicine, and drug delivery, thus being considered a revolutionary material for the future. Reported methods for preparing graphene materials include mechanical exfoliation, chemical oxidation, crystal epitaxial growth, chemical vapor deposition, organic synthesis, and carbon nanotube exfoliation. Graphene products include two main categories: powdered graphene and thin-film graphene. However, research on preparing macroscopically granular graphene with a microscopically crystalline graphene structure is still scarce.

[0003] my country has ranked first in the world in electrolytic aluminum production for 21 consecutive years, with an output of approximately 38.53 million tons in 2021. While my country's aluminum industry has developed rapidly, it has also generated a large amount of hazardous waste, including waste overhaul tanks (overhaul slag), anode carbon slag, secondary aluminum ash, and secondary aluminum ash from aluminum processing. Waste cathodes from electrolytic aluminum are an important component of overhaul slag. During the long-term aluminum electrolysis process, due to thermal, chemical, mechanical erosion, electrical effects, and the penetration of sodium and electrolytes, molten salt reactions and chemical reactions occur, resulting in the permeation of NaF, AlF3, Al2O3, metallic sodium, Na2CO3, NaCN, etc., into the cathodes. When the cathode develops large cracks, its conductivity changes significantly, potentially damaging the electrolytic cell, and it needs to be removed, becoming a waste cathode. Based on the calculation that each ton of primary aluminum produces 15-20 kg of aluminum electrolysis cell overhaul slag, and that this slag contains approximately 55% waste cathodes, my country's aluminum electrolysis waste cathode production in 2021 was between 318,000 and 424,000 tons. Waste cathode carbon blocks are mainly composed of carbon and fluorides, with a small amount of cyanide. The carbon content is approximately 65%, the fluoride content is approximately 35%, and the cyanide content is approximately 100 ppm. Due to prolonged exposure to high temperatures, the carbon in the waste aluminum electrolysis cathodes has become highly graphitized, possessing high recycling value. Research has found that during the formation of aluminum electrolysis waste cathodes, intercalation compounds CxNa are generated between graphite layers, leading to a larger interlayer spacing and weakening the van der Waals forces between the graphite layers. This means that the carbon blocks from the waste cathodes, after certain processing, can be used as precursors for graphene production, offering higher production efficiency and benefits compared to the currently commonly used natural graphite and expanded graphite in graphene material production. Therefore, while waste cathodes are defined as hazardous waste, they also possess significant resource value.

[0004] Currently, there are very few industrial-scale technologies for the harmless and resource-based disposal of waste cathodes. Most companies dispose of them through landfill or storage, but substances such as sodium fluoride, aluminum fluoride, and cryolite, when exposed to rain, seep into the soil, seriously harming the environment and causing fluoride pollution. Some companies use incineration, but the secondary pollution caused by fluorides fails to meet environmental protection requirements. Under the current environmental situation, electrolytic aluminum companies urgently need suitable waste cathode harmless disposal equipment and resource utilization technologies to achieve the recycling of waste cathodes. Summary of the Invention

[0005] The purpose of this application is to provide an ultra-high temperature reducing atmosphere medium-frequency calcining furnace, graphite materials, and a method for preparing the same. By using this calcining furnace and employing a high-temperature reducing calcination process, sodium and iron salts from the waste cathode are utilized in situ to be reduced to metals in a reducing atmosphere and used as a catalyst to prepare graphite materials with a graphene crystal structure.

[0006] To achieve the above objectives, the technical solution of this application is as follows:

[0007] In one aspect, this application provides an ultra-high temperature reducing atmosphere medium frequency roasting furnace, which includes, from top to bottom, a first furnace front chamber, a second furnace front chamber, a preheating section, a high temperature section, a cooling section, a water cooling section, and a unloader connected in sequence.

[0008] The first furnace front silo is connected to the second furnace front silo via a discharge valve, and the second furnace front silo is connected to the preheating section via a feed valve;

[0009] The outer surface of the high-temperature section is also provided with a furnace body coil, which is connected to an intermediate frequency cabinet. The intermediate frequency cabinet is used to provide intermediate frequency power to heat the furnace body coil.

[0010] In conjunction with the first aspect, in some alternative embodiments, the medium-frequency calcining furnace satisfies at least one of the following conditions:

[0011] a. The second furnace front compartment is also provided with an air inlet and an air outlet, the air inlet being used to introduce inert gas and the air outlet being used to discharge air from the second furnace front compartment;

[0012] b. The inert gas includes at least one of nitrogen, argon, and helium;

[0013] c. The preheating section has a structure that is thicker in the middle and thinner at the top and bottom;

[0014] d. At least one chimney is provided in the middle of the preheating section for discharging the flue gas volatilized in the high-temperature section;

[0015] e. The outer surface of the water-cooled section is also provided with a cooling water pipe for cooling the material in the water-cooled section;

[0016] f. The lining material inside the preheating section, the high-temperature section, the cooling section and the water-cooling section includes carbon blocks and / or graphite crucibles;

[0017] g. The carbon content of the carbon block and / or the graphite crucible is ≥97%, and the ash content is ≤1%.

[0018] Secondly, this application provides a method for preparing a graphite material, comprising:

[0019] Waste cathode material is fed into the ultra-high temperature reducing atmosphere medium frequency roasting furnace described in the first aspect above, and high temperature roasting is carried out under reducing atmosphere to obtain crude graphite.

[0020] The crude graphite is purified and magnetically separated to obtain the graphite material.

[0021] In conjunction with the second aspect, in some alternative embodiments, the waste cathode material satisfies at least one of the following conditions:

[0022] A. The waste cathode material includes graphite cathodes;

[0023] B. The waste cathode material includes waste cathodes removed from aluminum electrolytic cells built using graphitized cathodes;

[0024] C. The service life of the aluminum electrolytic cell is 3 to 10 years.

[0025] In some alternative embodiments, prior to the high-temperature reduction roasting, the waste cathode material is further crushed to 1mm-100mm.

[0026] In some alternative embodiments, the process of feeding the material into the ultra-high temperature reducing atmosphere intermediate frequency calcining furnace and performing high-temperature calcination under a reducing atmosphere includes:

[0027] The waste cathode material is first fed into the first furnace front silo, and then fed into the second furnace front silo through the discharge valve;

[0028] After the air in the second furnace front chamber is discharged, the waste cathode material is fed into the preheating section through the feed valve and then into the high-temperature section. After high-temperature roasting, graphite fragments are obtained.

[0029] The graphite fragments are passed sequentially through the cooling section and the water cooling section, and then discharged from the medium-frequency roasting furnace through the unloader to obtain the crude graphite product.

[0030] The preheating section, the high-temperature section, the cooling section, and the water-cooling section are all within a reducing atmosphere, and the gas in the reducing atmosphere includes at least one of hydrogen and carbon monoxide.

[0031] In some preferred embodiments, at least one of the following conditions is met:

[0032] D. When the second furnace front compartment is provided with an air inlet and an air outlet, the air discharged from the second furnace front compartment includes:

[0033] Close the feed valve and the discharge valve, introduce inert gas through the air inlet, and discharge the air in the second furnace front chamber through the air outlet;

[0034] E. The inert gas flow rate is 0.5 L / kg to 1.0 L / kg;

[0035] F. The temperature in the high-temperature section is 2400℃-2800℃;

[0036] G. The total time from the time the material is fed into the first furnace front silo until it is discharged from the unloader is 4-6 hours.

[0037] H. When at least one chimney is provided in the middle of the preheating section, the gas pressure discharged from the chimney is 20Pa-100Pa.

[0038] In some alternative embodiments, the preparation method further satisfies at least one of the following conditions:

[0039] I. The purification process includes: grinding and crushing the crude graphite, and then immersing it in a mixed acid solution for purification;

[0040] J. The particle size of the crude graphite after grinding and crushing is ≤0.15mm;

[0041] K. The mixed acid solution includes hydrofluoric acid and hydrochloric acid;

[0042] L. The liquid-solid mass ratio of the mixed acid solution to the crude graphite is 1:(1-4);

[0043] M. The immersion time is 0.5h-1.5h;

[0044] N. The mass concentration of the hydrofluoric acid is 40%-47%, the mass concentration of the hydrochloric acid is 30%-38%, and the volume ratio of the hydrofluoric acid to the hydrochloric acid is 1:(1-3).

[0045] In some alternative embodiments, the magnetic separation includes: performing dry magnetic separation using a magnetic separator;

[0046] The surface magnetic field strength of the magnetic separator is 600KA / m-1600KA / m.

[0047] Thirdly, this application provides a graphite material prepared using the preparation method described in the second aspect above.

[0048] The beneficial effects of this application are:

[0049] The ultra-high temperature reducing atmosphere medium-frequency roasting furnace of this application has a simple structure. By setting up a preheating section, a high temperature section, a cooling section and a water cooling section, the roasting furnace can be used continuously without interruption, which greatly improves the production and recovery efficiency.

[0050] The preparation method of this application makes full use of the microcrystalline graphite with high graphitization degree in the waste cathode material, uses an ultra-high temperature reducing atmosphere medium frequency roasting furnace, adopts an ultra-high temperature roasting process, and synergistically utilizes the sodium salt and iron salt in the waste cathode material. After being reduced to metal in situ in a reducing atmosphere, the metal material is used as a catalyst to accelerate the graphitization process of carbon and form a perfect graphene structure, thereby obtaining graphite material with graphene crystal structure, realizing the harmless disposal and resource utilization of waste cathode carbon blocks.

[0051] The graphite material of this application has a carbon content of over 99.99%, high purity, and a graphene crystal structure, making it a high-quality precursor for graphene production and capable of being directly processed into graphene material. Attached Figure Description

[0052] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope of the present invention.

[0053] Figure 1 This is a schematic diagram of the structure of an ultra-high temperature reducing atmosphere medium-frequency roasting furnace.

[0054] Component descriptions in the attached diagram:

[0055] 1-Waste cathode material; 2-First furnace front chamber; 3-Gas outlet; 4-Second furnace front chamber; 5-Feed valve; 6-Discharge valve; 7-Gas inlet; 8-Chimney; 9-High temperature section; 10-Furnace coil; 11-Cooling section; 12-Cooling water pipe; 13-Preheating section; 14-Medium frequency cabinet; 15-Water cooling section; 16-Unloader; 17-Graphite crude product. Detailed Implementation

[0056] As used in this article:

[0057] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0058] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0059] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0060] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0061] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiplier). It is important to understand that, unlike the number of parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0062] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0063] like Figure 1 The present application provides an ultra-high temperature reducing atmosphere medium frequency roasting furnace, which includes, from top to bottom, a first furnace front chamber 2, a second furnace front chamber 4, a preheating section 13, a high temperature section 9, a cooling section 11, a water cooling section 15, and a unloader 16 connected in sequence.

[0064] The first furnace front chamber 2 is connected to the second furnace front chamber 4 via a discharge valve 6, and the second furnace front chamber 4 is connected to the preheating section 13 via a feed valve 5. A furnace body coil 10 is also provided on the outer surface of the high-temperature section 9. The furnace body coil 10 is connected to a medium-frequency cabinet 14, which provides medium-frequency power to heat the furnace body coil 10, thereby ensuring that medium-frequency heating is used in the high-temperature section to achieve a high-temperature effect.

[0065] It should be noted that the ultra-high temperature in the ultra-high temperature reducing atmosphere medium-frequency roasting furnace of this application mainly refers to a high temperature of 2400℃-2800℃, and the reducing atmosphere means that at least in the preheating section and the high temperature section, reducing gases such as hydrogen and carbon monoxide are provided to protect the materials inside the furnace.

[0066] The preheating section 13 has a structure that is coarse in the middle and thin at the top and bottom. It receives the material supplied by the second furnace front chamber 4 from the top and then discharges it from the bottom into the high-temperature section 9. This structure, which is thin at the top and bottom and coarse in the middle, can ensure that the material is tightly packed in the high-temperature section.

[0067] The preheating section 13 is also provided with at least one chimney 8, more preferably two chimneys, for quickly discharging the volatile flue gas in the high-temperature section.

[0068] The second furnace front chamber 4 is also provided with an air inlet 7 and an air outlet 3, wherein the air inlet 7 is used to introduce inert gas, and the air outlet 3 is used to discharge the air inside the second furnace front chamber 4.

[0069] Furthermore, the inert gas includes at least one of nitrogen, argon, and helium;

[0070] Cooling water pipes 12 are also provided on the outer surface of the water-cooled section 15 to cool the material in the water-cooled section 15 so as to ensure that the material can be discharged from the unloader at room temperature.

[0071] In a preferred embodiment of this application, in order to use the medium-frequency calcining furnace for preparing graphite materials, carbon blocks and / or graphite crucibles are used as lining materials inside the preheating section 13, the high-temperature section 9, the cooling section 11, and the water-cooling section 15 to prevent unnecessary contamination of the graphite. The carbon blocks and / or graphite crucibles contain ≥97% carbon and ≤1% ash.

[0072] This application also provides a method for preparing graphite materials, using the ultra-high temperature reducing atmosphere medium-frequency calcining furnace described in this application, specifically including the following steps:

[0073] (1) Provide waste cathode material. The waste cathode material is preferably graphite cathode material, and more preferably waste cathode material after the aluminum electrolytic cell built with graphitized cathode is dismantled. Generally, the service life of aluminum electrolytic cells is 3-10 years.

[0074] (2) The waste cathode material is crushed to 1mm-100mm, more preferably 20mm-70mm.

[0075] (3) The crushed waste cathode material 1 is fed into the first furnace front chamber 2 of the ultra-high temperature reducing atmosphere medium frequency roasting furnace, and then into the second furnace front chamber 4. The feed valve 5 and the discharge valve 6 are closed. Then, inert gas nitrogen or argon is introduced through the gas inlet 7 to expel the air in the second furnace front chamber 4. Then, the gas inlet 7 and the gas outlet 3 are closed. More preferably, nitrogen is introduced through the gas inlet 7, and the amount of nitrogen used is 0.5L / kg to 1.0L / kg.

[0076] (4) Open the feed valve 5 and feed the waste cathode material into the preheating section 13 of the ultra-high temperature reducing atmosphere medium frequency roasting furnace.

[0077] (5) Feed material intermittently from the upper part of the preheating section 13 and discharge material continuously from the lower part; the preheating section 13 has a structure that is coarse in the middle and thin at the top and bottom, which ensures that the waste cathode material is tightly packed in the high temperature section 9. Then the chimney 8 is set in the middle of the preheating section 13 to ensure that the flue gas volatilized at high temperature is discharged as soon as possible.

[0078] (6) After the waste cathode material passes through the preheating section 13 and enters the high-temperature section 9, it is heated to 2400℃-2800℃ in the high-temperature section 9. For example, it can be any value between 2400℃, 2500℃, 2600℃, 2700℃, 2800℃, or 2400℃-2800℃, maintaining a reducing atmosphere in the furnace. Then, some fluoride salts and other substances in the material are discharged from the furnace body through the chimney 8 along with the reducing gas. The flue gas pressure at the chimney outlet is positive, between 20-100 Pa. Furthermore, the high-temperature section 9 uses medium-frequency heating, and the furnace body coil 10 is heated through the medium-frequency cabinet 14.

[0079] (7) After roasting at the high-temperature section 9, the material is sent to the cooling section 11, then to the water cooling section 15, and finally discharged from the furnace body through the unloader 16 to obtain crude graphite 17. The total time required from feeding into the first furnace front chamber 2 to discharging from the unloader 16 is 4-6 hours. The material obtained after roasting at the high-temperature section 9 still contains some impurities, so the material discharged from the unloader 16 is crude graphite.

[0080] (8) After grinding and crushing the crude graphite to ≤0.15mm, a mixture of hydrofluoric acid and hydrochloric acid is added for purification. Preferably, hydrofluoric acid with a mass concentration of 40%-47% and hydrochloric acid with a mass concentration of 30%-38% are mixed, and the volume ratio of the two can be any value between 1:1, 1:2, 1:3 or 1:(1-3), more preferably 1:2; then the liquid-solid mass ratio of the mixed acid to the crude graphite is 1:(1-4), for example, it can be any value between 1:1, 1:2, 1:3, 1:4 or 1:(1-4), more preferably 1:3; the acid leaching time is 0.5h-1.5h, more preferably 1h.

[0081] (9) After the acid-washed material is washed with water and dried, it may still contain some magnetic metal impurities such as iron. Therefore, magnetic separation is used to remove trace amounts of magnetic iron. The surface magnetic field strength of the magnetic separator is 600-1600 KA / m, more preferably 1200-1600 KA / m. The final non-magnetic product is a high-purity graphite material with a graphene crystal structure.

[0082] It should be noted that the reducing atmosphere in the medium-frequency roasting furnace mainly consists of at least one of hydrogen and carbon monoxide. The carbon monoxide can be supplied externally or naturally generated within the furnace due to low oxygen levels. During the roasting process, the basic principle is that the high-temperature hydrogen or carbon monoxide gas reacts with the metal oxides in the waste cathode material to form elemental metals. These elemental metals act as catalysts, accelerating the graphitization process of carbon in the cathode and forming a complete graphene structure.

[0083] More preferably, the roasting furnace operates under positive pressure, which prevents large amounts of air from entering the furnace. The small amount of oxygen in the air reacts with the carbon in the furnace to form carbon monoxide, maintaining a strong reducing atmosphere inside the high-temperature roasting furnace. Alternatively, hydrogen gas can be introduced to maintain the positive pressure and reducing atmosphere within the furnace, with the mass of hydrogen gas being 1%-3% of the mass of the waste cathode material.

[0084] The advantages of the technical solution in this application are:

[0085] 1. The waste cathode material used contains a large amount of fine crystalline graphite. This graphite is formed in the aluminum electrolysis cell at low temperature (about 960°C) and long time (about 4 to 10 years). It has an imperfect graphene crystal structure. This invention makes full use of the above characteristics of waste cathode.

[0086] 2. It adopts ultra-high temperature roasting process and acid leaching and magnetic separation purification process, which has a short process and is easier to industrialize;

[0087] 3. The reducing atmosphere used can synergistically utilize graphite and metal compound impurities in the waste cathode at ultra-high temperature. After the metal compounds are reduced to metals at high temperature, the graphitization process of carbon is accelerated and a perfect graphene structure is formed, thus realizing the high-quality utilization of waste cathodes.

[0088] 4. By using acid leaching, magnetic separation and other methods to further improve the purity of graphite materials, high-purity graphite materials with a carbon content of over 99.99% can be obtained, which have a graphene crystal structure and are high-quality precursors for the production of graphene, and may be directly processed into graphene materials.

[0089] The embodiments of the present invention will be described in detail below with reference to specific 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 the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0090] The carbon block composition in the aluminum electrolysis waste cathode raw materials used in the following embodiments is the same, specifically C: 63.34%, O: 2.52%, F: 12.31%, Na: 14.21%, Al: 3.25%, Si: 2.12%, S: 0.12%, Ca: 1.20%, Fe: 0.54%. Furthermore, the following embodiments all use... Figure 1 The ultra-high temperature reducing atmosphere medium-frequency roasting furnace described in the article.

[0091] Example 1

[0092] This embodiment provides a graphite material, the specific preparation method of which includes:

[0093] 1) The raw materials used are waste aluminum electrolysis cathodes that have been dismantled after 4 to 6 years of use;

[0094] 2) Crush the above-mentioned waste cathode carbon blocks from electrolytic aluminum to 20-50mm;

[0095] 3) Feed the crushed waste cathode material into the first furnace front chamber 2 of the ultra-high temperature reducing atmosphere medium frequency roasting furnace, and then feed it into the second furnace front chamber 4. Close the feed valve 5 and the discharge valve 6. Then introduce nitrogen gas from the gas inlet 7 at a rate of 1L / kg to drive out the air in the furnace front chamber. Then close the gas inlet 7 and the gas outlet 3.

[0096] 4) Open the feed valve 5 and feed the waste cathode material into the preheating section 13 of the ultra-high temperature reducing atmosphere medium frequency roasting furnace;

[0097] 5) After passing through the preheating section 13 and the high-temperature section 9, the waste cathode material is discharged from the furnace body through the chimney 8 at high temperature, along with substances such as fluoride salts.

[0098] 6) The waste cathode is heated to 2400℃~2500℃ in an ultra-high temperature reducing atmosphere medium frequency roasting furnace. The residence time of the waste cathode in the high temperature furnace (from the time of feeding from the first furnace front chamber 2 to the time of discharge from the unloader 16) is 5h.

[0099] 7) The flue gas pressure at the chimney outlet of the ultra-high temperature reducing atmosphere medium frequency roasting furnace is positive pressure, with a pressure of 50 Pa, to maintain the reducing atmosphere inside the high temperature furnace.

[0100] 8) The crude graphite is crushed and ground to ≤0.15mm, and then purified again with a mixture of hydrofluoric acid and hydrochloric acid. The mass concentration of hydrofluoric acid is 40%, the mass concentration of hydrochloric acid is 37%, the volume ratio of hydrofluoric acid to hydrochloric acid is 1:2, the liquid-solid mass ratio of the mixed acid to the crude graphite is 3, and the acid leaching time is 1h.

[0101] 9) The purified graphite powder was subjected to magnetic separation to remove trace amounts of magnetic iron. The magnetic field strength of the magnetic separator was 1000KA / m, resulting in high-purity graphite material with a graphene crystal structure and a fixed carbon content of 99.992%.

[0102] Example 2

[0103] This embodiment provides a graphite material, the specific preparation method of which includes:

[0104] 1) The raw materials used are waste aluminum electrolysis cathodes that have been dismantled after 4 to 6 years of use;

[0105] 2) Crush the above-mentioned waste cathode carbon blocks from electrolytic aluminum to 20-50mm;

[0106] 3) Feed the crushed waste cathode material into the first furnace front chamber 2 of the ultra-high temperature reducing atmosphere medium frequency roasting furnace, and then feed it into the second furnace front chamber 4. Close the feed valve 5 and the discharge valve 6. Then introduce nitrogen gas from the gas inlet 7 at a rate of 1L / kg to drive out the air in the furnace front chamber. Then close the gas inlet 7 and the gas outlet 3.

[0107] 4) Open the feed valve 5 and feed the waste cathode material into the preheating section 13 of the ultra-high temperature reducing atmosphere medium frequency roasting furnace;

[0108] 5) After passing through the preheating section 13 and the high-temperature section 9, the waste cathode material is discharged from the furnace body through the chimney 8 at high temperature, along with substances such as fluoride salts.

[0109] 6) The waste cathode material is heated to 2550℃~2600℃ in an ultra-high temperature reducing atmosphere medium frequency roasting furnace. The residence time of the waste cathode in the high temperature furnace (from the time of feeding from the first furnace front chamber 2 to the time of discharge from the unloader 16) is 6h.

[0110] 7) The flue gas pressure at the outlet of the chimney in the ultra-high temperature reducing atmosphere medium frequency roasting furnace is positive pressure, with a pressure of 50 Pa, to maintain the reducing atmosphere in the high temperature furnace.

[0111] 8) The crude graphite is crushed and ground to ≤0.15mm, and then purified again with a mixture of hydrofluoric acid and hydrochloric acid. The mass concentration of hydrofluoric acid is 40%, the mass concentration of hydrochloric acid is 37%, the volume ratio of hydrofluoric acid to hydrochloric acid is 1:2, the liquid-solid mass ratio of the mixed acid to the crude graphite is 3, and the acid leaching time is 1h.

[0112] 9) The graphite powder that has been purified again is subjected to magnetic separation to remove trace amounts of magnetic iron. The magnetic field strength of the magnetic separator is 1000KA / m, resulting in high-purity graphite material with a graphene crystal structure and a fixed carbon content of 99.994%.

[0113] Example 3

[0114] This embodiment provides a graphite material, the specific preparation method of which includes:

[0115] 1) The raw materials used are waste aluminum electrolysis cathodes that have been dismantled after 4 to 6 years of use;

[0116] 2) Crush the above-mentioned waste aluminum cathode carbon blocks to 10-40mm;

[0117] 3) Feed the crushed waste cathode material into the first furnace front chamber 2 of the ultra-high temperature reducing atmosphere medium frequency roasting furnace, and then feed it into the second furnace front chamber 4. Close the feed valve 5 and the discharge valve 6. Then introduce nitrogen gas from the gas inlet 7 at a rate of 1L / kg to drive out the air in the furnace front chamber. Then close the gas inlet 7 and the gas outlet 3.

[0118] 4) Open the feed valve 5 and feed the waste cathode material into the preheating section 13 of the ultra-high temperature reducing atmosphere medium frequency roasting furnace;

[0119] 5) After passing through the preheating section 13 and the high-temperature section 9, the waste cathode material is discharged from the furnace body through the chimney 8 at high temperature, along with substances such as fluoride salts.

[0120] 6) The waste cathode material is heated to 2600℃~2650℃ in an ultra-high temperature reducing atmosphere medium frequency roasting furnace. The residence time of the waste cathode in the high temperature furnace (from the time of feeding from the first furnace front chamber 2 to the time of discharge from the unloader 16) is 8h.

[0121] 7) The flue gas pressure at the outlet of the chimney in the ultra-high temperature reducing atmosphere medium frequency roasting furnace is positive pressure, with a pressure of 50 Pa, to maintain the reducing atmosphere in the high temperature furnace.

[0122] 8) The crude graphite is crushed and ground to ≤0.15mm, and then purified again with a mixture of hydrofluoric acid and hydrochloric acid. The mass concentration of hydrofluoric acid is 40%, the mass concentration of hydrochloric acid is 37%, the volume ratio of hydrofluoric acid to hydrochloric acid is 1:2, the liquid-solid mass ratio of the mixed acid to the crude graphite is 3, and the acid leaching time is 1h.

[0123] 9) The purified graphite powder is then subjected to magnetic separation to remove trace amounts of magnetic iron. The magnetic field strength of the magnetic separator is 1000KA / m, resulting in high-purity graphite material with a graphene crystal structure and a fixed carbon content of 99.995%.

[0124] Example 4

[0125] This embodiment provides a graphite material, the specific preparation method of which includes:

[0126] 1) The raw materials used are waste aluminum electrolysis cathodes that have been dismantled after 4 to 6 years of use;

[0127] 2) Crush the above-mentioned waste aluminum cathode carbon blocks to 10-40mm;

[0128] 3) Feed the crushed waste cathode material into the first furnace front chamber 2 of the ultra-high temperature reducing atmosphere medium frequency roasting furnace, and then feed it into the second furnace front chamber 4. Close the feed valve 5 and the discharge valve 6. Then introduce nitrogen gas from the gas inlet 7 at a rate of 1.5 L / kg to drive out the air in the furnace front chamber. Then close the gas inlet 7 and the gas outlet 3.

[0129] 4) Open the feed valve 5 and feed the waste cathode material into the preheating section 13 of the ultra-high temperature reducing atmosphere medium frequency roasting furnace;

[0130] 5) After passing through the preheating section 13 and the high-temperature section 9, the waste cathode material is discharged from the furnace body through the chimney 8 at high temperature, along with substances such as fluoride salts.

[0131] 6) The waste cathode material is heated to 2550℃~2600℃ in an ultra-high temperature reducing atmosphere medium frequency roasting furnace. The residence time of the waste cathode in the high temperature furnace (from the time of feeding from the first furnace front chamber 2 to the time of discharge from the unloader 16) is 8h.

[0132] 7) The flue gas pressure at the outlet of the chimney in the ultra-high temperature reducing atmosphere medium frequency roasting furnace is positive pressure, with a pressure of 20Pa, to maintain the reducing atmosphere in the high temperature furnace;

[0133] 8) The crude graphite is crushed and ground to ≤0.15mm, and then purified again with a mixture of hydrofluoric acid and hydrochloric acid. The mass concentration of hydrofluoric acid is 40%, the mass concentration of hydrochloric acid is 37%, the volume ratio of hydrofluoric acid to hydrochloric acid is 1:3, the liquid-solid mass ratio of the mixed acid to the crude graphite is 3, and the acid leaching time is 1.5h.

[0134] 9) The purified graphite powder was subjected to magnetic separation to remove trace amounts of magnetic iron. The magnetic field strength of the magnetic separator was 1000KA / m, resulting in high-purity graphite material with a graphene crystal structure and a fixed carbon content of 99.996%.

[0135] Comparative Example 1

[0136] This comparative example provides a graphite material, the specific preparation method of which includes:

[0137] 1) The raw materials used are waste aluminum electrolysis cathodes that have been dismantled after 4 to 6 years of use;

[0138] 2) Crush the above-mentioned waste aluminum cathode carbon blocks to 10-40mm;

[0139] 3) The crushed waste cathode material is directly put into an ultra-high temperature heating furnace at 2550℃~2600℃. There is a certain amount of air in the high temperature furnace. After heating for a period of time, the sample is taken out.

[0140] 4) Similar to the acid washing and magnetic separation steps in Example 4, the sample was also subjected to acid washing and magnetic separation to obtain graphite material. Compared with Example 4, this graphite material had a 10% reduction in mass, and lacked a distinct graphene crystal structure, with a fixed carbon content of 99.9%.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0142] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of the invention and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing a graphite material with a graphene crystal structure, characterized in that, Waste cathode material is fed into an ultra-high temperature reducing atmosphere medium-frequency roasting furnace and roasted at high temperature under a reducing atmosphere to obtain crude graphite. The crude graphite is purified and magnetically separated to obtain the graphite material with a graphene crystal structure. The waste cathode material includes graphite cathodes; The waste cathode material includes waste cathodes removed from aluminum electrolytic cells that were built using graphitized cathodes. The service life of the aluminum electrolytic cell is 3 to 10 years. The medium-frequency roasting furnace includes, from top to bottom, a first furnace front chamber, a second furnace front chamber, a preheating section, a high-temperature section, a cooling section, a water-cooling section, and a discharger, connected in sequence. The first furnace front silo is connected to the second furnace front silo via a discharge valve, and the second furnace front silo is connected to the preheating section via a feed valve; The outer surface of the high-temperature section is also provided with a furnace body coil, which is connected to a medium-frequency cabinet. The medium-frequency cabinet is used to provide medium-frequency power to heat the furnace body coil in medium frequency. The process of feeding the material into the ultra-high temperature reducing atmosphere intermediate frequency roasting furnace and performing high-temperature roasting under a reducing atmosphere includes: The waste cathode material is first fed into the first furnace front silo, and then fed into the second furnace front silo through the discharge valve; After the air in the second furnace front chamber is discharged, the waste cathode material is fed into the preheating section through the feed valve and then into the high-temperature section. After high-temperature roasting, graphite fragments are obtained. The graphite fragments are passed sequentially through the cooling section and the water cooling section, and then discharged from the medium-frequency roasting furnace through the unloader to obtain the crude graphite product. The preheating section, the high-temperature section, the cooling section, and the water-cooling section are all within a reducing atmosphere. The gas in the reducing atmosphere includes at least one of hydrogen and carbon monoxide. The reducing gas reacts with the metal oxides in the waste cathode material to form elemental metals. The elemental metals act as a catalyst to accelerate the graphitization process of carbon in the cathode and form a complete graphene structure. The purification process includes: grinding and crushing the crude graphite, and then immersing it in a mixed acid solution for purification; the particle size of the crude graphite after grinding and crushing is ≤0.15mm; The mixed acid solution includes hydrofluoric acid and hydrochloric acid; The liquid-solid mass ratio of the mixed acid solution to the crude graphite is 1:(1-4). The immersion time is 0.5h-1.5h; The hydrofluoric acid has a mass concentration of 40%-47%, the hydrochloric acid has a mass concentration of 30%-38%, and the volume ratio of the hydrofluoric acid to the hydrochloric acid is 1:(1-3).

2. The preparation method according to claim 1, characterized in that, At least one of the following conditions must be met: a. The second furnace front compartment is also provided with an air inlet and an air outlet, the air inlet being used to introduce inert gas and the air outlet being used to discharge air from the second furnace front compartment; b. The inert gas includes at least one of nitrogen, argon, and helium; c. The preheating section has a structure that is thicker in the middle and thinner at the top and bottom; d. At least one chimney is provided in the middle of the preheating section for discharging the flue gas volatilized in the high-temperature section; e. The outer surface of the water-cooled section is also provided with a cooling water pipe for cooling the material in the water-cooled section; f. The lining material inside the preheating section, the high-temperature section, the cooling section and the water-cooling section includes carbon blocks and / or graphite crucibles; g. The carbon content of the carbon block and / or the graphite crucible is ≥97%, and the ash content is ≤1%.

3. The preparation method according to claim 1, characterized in that, Before the high-temperature reduction roasting, the process also includes: crushing the waste cathode material to 1mm-100mm.

4. The preparation method according to claim 1, characterized in that, At least one of the following conditions must be met: D. When the second furnace front compartment is provided with an air inlet and an air outlet, the air discharged from the second furnace front compartment includes: Close the feed valve and the discharge valve, introduce inert gas through the air inlet, and discharge the air in the second furnace front chamber through the air outlet; E. The inert gas flow rate is 0.5 L / kg to 1.0 L / kg; F. The temperature in the high-temperature section is 2400℃-2800℃; G. The total time from the time the material is fed into the first furnace front silo until it is discharged from the unloader is 4h-8h; H. When at least one chimney is provided in the middle of the preheating section, the gas pressure discharged from the chimney is 20Pa-100Pa.

5. The preparation method according to any one of claims 1-4, characterized in that, The magnetic separation includes: dry magnetic separation using a magnetic separator; The surface magnetic field strength of the magnetic separator is 600KA / m-1600KA / m.

6. A graphite material having a graphene crystal structure, characterized in that, It was prepared using the preparation method described in any one of claims 1-5.

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