A method for preparing electrode paste using recycled carbon materials

Abstract

This invention belongs to the field of electrode paste preparation technology, specifically relating to a method for preparing electrode paste using recycled carbon materials. Using recycled carbon materials as aggregate, modified diatomaceous earth is used to deeply adsorb residual molecular-level impurity ions. Its micro-nano particles can simultaneously fill the aggregate pores to improve the compactness of the preform. Furthermore, the saturated modified diatomaceous earth can be thermally regenerated and recycled, realizing the resource utilization of the adsorbent. KH-550 supported on silica is used as an interface modifier. High-speed shearing causes KH-550 to be uniformly dispersed on the silica surface. Thermal activation hydrolyzes KH-550 to generate silanol groups, which condense with the surface active functional groups of the aggregate and modified diatomaceous earth to form a Si-O-C covalent bond network. This strengthens the interfacial bonding between the aggregate and the binder, improving the mechanical properties and high-temperature stability of the electrode paste, achieving high-value resource utilization of recycled carbon materials, and balancing environmental protection and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of electrode paste preparation technology, and in particular to a method for preparing electrode paste using recycled carbon materials. Background Technology

[0002] In high-energy-consuming electrothermal smelting industries such as metallurgy and industrial silicon, electrode paste is a core material for self-baking electrodes. Its quality directly determines the electrode's electrical conductivity, thermal conductivity, mechanical strength, and thermal shock resistance under the high-temperature environment of an electric arc furnace, significantly impacting the stability of the production process, energy consumption, and production costs. Traditional electrode paste mainly relies on high-quality primary carbon materials such as petroleum coke and pitch coke. However, with resource scarcity and price fluctuations, raw material costs continue to rise. Meanwhile, a large amount of recycled carbon materials generated during production (such as waste electrodes, graphite fragments, and calcined fragments) often contain impurities and have damaged structures, typically requiring downgraded use or stockpiling for disposal. This not only wastes resources but also creates environmental pressure. Existing recycling technologies for carbon recycled materials mainly rely on physical crushing and screening combined with conventional acid and alkali washing pretreatment, after which the recycled materials are directly mixed into new raw materials in a certain proportion as aggregates to prepare medium and low grade electrode pastes or carbon blocks. However, there are still problems such as impurities being difficult to completely remove and weak interfacial bonding between carbon aggregates and binders. At the same time, the large-scale use of virgin carbon raw materials also leads to high production costs for electrode pastes, which restricts the high-value resource utilization of carbon recycled materials and the green and low-carbon development of the electrode paste industry. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing electrode paste using recycled carbon materials. The recycled carbon materials serve as aggregates, and modified diatomaceous earth is used to deeply adsorb residual molecular-level impurity ions. The micro-nano particles of modified diatomaceous earth simultaneously fill the pores of the aggregates to improve the density of the preform. Furthermore, the saturated modified diatomaceous earth can be thermally regenerated and recycled, achieving resource utilization of the adsorbent. KH-550 supported on silica is used as an interface modifier. High-speed shearing causes KH-550 to be uniformly dispersed on the silica surface. Thermal activation hydrolyzes KH-550 to generate silanol groups, which condense with the surface active functional groups of the aggregates and modified diatomaceous earth to form a Si-OC covalent network. This strengthens the interfacial bonding between the aggregates and the binder, improving the mechanical properties and high-temperature stability of the electrode paste. This method achieves high-value resource utilization of recycled carbon materials, balancing environmental protection and economic benefits.

[0004] To achieve the above objectives, the present invention employs the following technical solution:

[0005] This invention provides a method for preparing electrode paste using recycled carbon materials, comprising the following steps:

[0006] S1. The carbon return material is crushed and subjected to strong magnetic separation to remove metal blocks, and then subjected to alkaline washing, weak magnetic separation, acid washing and drying to obtain pretreated carbon return material;

[0007] S2. The modified diatomaceous earth is dry-mixed with the pretreated carbon return material, deionized water is added, and the mixture is stirred and filtered to obtain the impurity-removed carbon return material and the adsorption-saturated modified diatomaceous earth filter residue. The adsorption-saturated modified diatomaceous earth filter residue is dried and thermally regenerated to obtain the recycled material. The modified diatomaceous earth and the recycled material are mixed and the process is repeated for subsequent impurity removal.

[0008] S3. The silica, KH-550 and the first deionized water are dry-mixed for the first time, and the impurity-removed carbon return material and the second deionized water are added. After the second dry mixing and hot air activation, the activated carbon return material is obtained.

[0009] S4. Heat the coal tar pitch to the first set temperature, introduce air for oxidation, and allow it to cool naturally to the second set temperature to obtain medium-temperature modified asphalt. Mix the medium-temperature modified asphalt, thermosetting phenolic resin, C9 petroleum resin, and dibutyl phthalate to obtain a composite binder. After classifying the activated carbon recycled material, dry mix it, add the composite binder and PEG-400, knead, and then vibrate to form an electrode paste.

[0010] Further, in S1, the carbon return material comprises, by mass percentage: 50% residual electrode, 25% graphite fragments and 25% calcined fragments; the residual electrode is the waste residual electrode replaced by the aluminum electrolytic cell; the graphite fragments are the scraps and scraps generated during the graphite electrode processing; and the calcined fragments are the cracked waste fragments generated during the carbon calcination process.

[0011] The residual electrodes in the carbon recycled material, as waste generated by the electrolytic aluminum industry, have a high fixed carbon content and a stable carbon skeleton structure, which can provide basic mechanical support and carbon source supply for electrode paste, and are the core component of aggregate. Graphite fragments, with their excellent electrical and thermal conductivity and high purity, can effectively make up for the shortcomings of residual electrodes and calcined fragments in electrical conductivity. At the same time, their layered structure can improve the overall thermal uniformity of aggregate. After high-temperature calcination, the calcined fragments have a dense structure and outstanding mechanical strength, which can enhance the impact resistance and structural stability of aggregate. The combination of the three in proportion forms a synergistic effect of carbon skeleton support, electrical conductivity optimization and structural strength enhancement, while balancing the differences in particle morphology of each component, laying a preliminary foundation for the compact packing after subsequent crushing and grading.

[0012] Further, in step S1, the particle size of the carbon return material after crushing is ≤20mm; the magnetic field strength of the strong magnetic separation is 11000-13000Gs; the alkaline washing step is as follows: add a KOH solution with a mass fraction of 3wt%-5wt%, the mass ratio of KOH solution to carbon return material is (2.8-3.2):1, stir at 75-85℃ for 50-70min, and wash with water until the pH of the filtrate is 6.5-7.5; the magnetic field strength of the weak magnetic separation is 5500-6500Gs; the acid washing step is as follows: add a hydrochloric acid solution with a mass fraction of 4wt%-6wt%, the mass ratio of hydrochloric acid solution to carbon return material is (1.8-2.2):1, soak at 60-70℃ for 35-45min, and wash with water until the pH of the filtrate is 6.5-7.5; the drying temperature is 110-130℃, and the drying time is 15-25min.

[0013] Mechanical force disrupts the original structure of recycled carbon materials, increasing the specific surface area and exposing impurities hidden within the material to the surface. This creates conditions for sufficient contact between impurities and treatment agents in subsequent impurity removal processes. Utilizing the magnetic properties of metals and ferromagnetic impurities in strong magnetic separation, the magnetic field force efficiently separates blocky metals and large-particle magnetic impurities mixed in the raw material, preventing these impurities from forming hard spots or weak areas after electrode paste formation. Weak magnetic separation further targets fine-particle ferromagnetic impurities for deep capture, compensating for the insufficient adsorption of fine-particle impurities by strong magnetic separation. The alkaline environment of the alkali washing process reacts chemically with soluble electrolyte impurities in the raw material, converting them into water-soluble compounds for separation and removal via water washing. The acid washing process utilizes an acidic medium to dissolve residual metal oxides and insoluble salt impurities, thoroughly removing stubborn impurities that alkali washing cannot remove. Finally, drying is used to remove the moisture adsorbed on the surface and inside of the material, preventing moisture from affecting the adsorption activity of the adsorbent during subsequent deep impurity removal processes, or causing structural defects such as bubbles and pores during interface modification and bonding. This provides a pure, dry and well-dispersed aggregate base for subsequent processes, ensuring the treatment effect of each subsequent process.

[0014] Further, in step S2, the modified diatomaceous earth is hydroxylated industrial-grade diatomaceous earth with a specific surface area ≥200m² / g and a particle size of 1-5μm; the amount of modified diatomaceous earth used is 1.2%-1.6% of the mass of the pretreated carbon return material; the dry mixing speed is 140-160r / min, and the dry mixing time is 9-11min; the mass ratio of deionized water to the total mass of modified diatomaceous earth and pretreated carbon return material is 3:1.

[0015] Modified diatomaceous earth possesses a unique porous structure and extremely high specific surface area. Its abundant internal pores form a huge adsorption interface, which, through physical adsorption, can accurately capture residual molecular-level impurity ions such as sodium and iron after preliminary impurity removal, achieving deep purification of the aggregate and reducing the adverse effects of impurities on the mechanical and electrical properties of the electrode paste from the source. Simultaneously, the micro-nano-scale particles of modified diatomaceous earth can naturally fill the gaps between carbon return particles and the pores within the aggregate itself during mixing, acting as a physical filler. This effectively reduces the number of voids within the green body, increases the material bulk density and green body density, and provides structural support for the formation of the electrode paste's superior performance.

[0016] Further, in step S2, the stirring temperature is 60-70℃, the stirring rate is 120-150 r / min, and the stirring time is 35-45 min; the drying temperature is 105-115℃, and the drying time is 8-12 min; the thermal regeneration temperature is 480-520℃, and the thermal regeneration time is 25-35 min; the mass ratio of modified diatomaceous earth to recycled material is (3.8-4.2):1.

[0017] After adsorption saturation, modified diatomaceous earth undergoes a thermal regeneration process. Under high temperature, impurity molecules adsorbed within its pores are desorbed due to intensified thermal motion, restoring the modified diatomaceous earth's porous adsorption structure and adsorption activity. The regenerated modified diatomaceous earth can be mixed with new modified diatomaceous earth in a specific ratio for recycling. This avoids the resource waste and environmental pressure caused by single-use of adsorbents, significantly reduces raw material consumption costs, and forms a closed-loop process of deep impurity removal, adsorbent regeneration, and recycling. This ensures high aggregate purity while balancing the economic and environmental benefits of the process.

[0018] Further, in step S3, the specific surface area of ​​the silica is ≥150m² / g, and the particle size is 5-10μm; the mass ratio of silica, KH-550, and the first deionized water is 1:(3.5-3.8):(0.025-0.035); the rotation speed of the first dry mixing is 2800-3200r / min, and the time of the first dry mixing is 5-7min.

[0019] As an inorganic carrier with a high specific surface area, silica has a large number of hydroxyl groups on its surface, which can interact with KH-550 molecules, providing sufficient loading sites for KH-550. Through the shear force generated by high-speed mixing, KH-550 molecules can be uniformly dispersed and firmly fixed on the silica surface, forming a stable solid dispersion system. This completely solves the problem that KH-550 is prone to agglomeration due to strong intermolecular forces when added directly, which prevents its effective components from fully exerting their effects. When this solid dispersion system is mixed with deeply purified carbon recycled material, the silica not only acts as a dispersion carrier, but its unique nanoscale porous structure and surface chemical properties also create a unique and stable microenvironment for KH-550: On the one hand, the porous structure of silica confines KH-550 molecules inside the pores or on the surface, forming a physical barrier and reducing the direct contact between KH-550 and free moisture in the external environment, thereby significantly delaying the hydrolysis of KH-550; on the other hand, the hydrogen bonding between the hydroxyl groups on the surface of silica and KH-550 molecules can further stabilize the chemical structure of KH-550, inhibit its own self-polymerization reaction and ineffective hydrolysis, and ensure that KH-550 maintains high reactivity after being mixed with carbon recycled material and before thermal activation.

[0020] Further, in step S3, the amount of the second deionized water is 1.2%-1.8% of the mass of the purified carbon return material; the rotation speed of the second dry mixing is 180-220 r / min, and the time of the second dry mixing is 7-9 min; the temperature of the hot air activation is 160-180℃, and the time of the hot air activation is 30-40 min.

[0021] During thermal activation, heat provides the driving force for the hydrolysis reaction of KH-550, promoting its gradual hydrolysis to generate a large number of silanol groups. These silanol groups have extremely high reactivity and can undergo dehydration condensation reactions with active functional groups such as hydroxyl and carboxyl groups on the surface of recycled carbon materials and modified diatomaceous earth to form a stable and strong Si-OC covalent bond network. This covalent bond network can effectively cross the interface between aggregate and binder, tightly connecting the two into a whole, significantly enhancing the interfacial bonding force. This completely solves the industry pain point of traditional processes, which is characterized by the strong inertness of the recycled carbon material surface and poor compatibility with the binder, resulting in weak interfacial bonding and easy peeling failure at high temperatures. This provides a core guarantee for the excellent mechanical properties and high-temperature stability of the electrode paste.

[0022] Further, in step S4, the softening point of the coal tar pitch is 45-65℃, and the ash content is ≤0.5%; the first set temperature is 280-300℃; the air introduction rate is 0.8-1.2L / (kg·h); the oxidation time is 2-3h; the second set temperature is 140-160℃; the softening point of the medium-temperature modified pitch is 85-105℃, the coking value is ≥48%, and the ash content is ≤0.3%; the softening point of the thermosetting phenolic resin is 70-90℃, the free phenol content is ≤3%, and the moisture content is ≤1.5%; the softening point of the C9 petroleum resin is 100-120℃, and the ash content is ≤0.1%.

[0023] After oxidative modification, coal tar pitch undergoes cross-linking and reconstruction of its molecular chains, increasing its molecular weight and significantly improving its bonding performance, coking rate, and high-temperature stability. This results in medium-temperature modified pitch, which becomes the core component of the composite binder, providing basic adhesion and high-temperature carbon skeleton support for the electrode paste. Thermosetting phenolic resin, as an auxiliary binder, undergoes a cross-linking reaction during processing to form a network structure, enhancing the structural stability and mechanical strength of the binder system and compensating for the insufficient bonding strength of coal tar pitch at low temperatures. C9 petroleum resin exhibits good compatibility and solubility, improving the interfacial compatibility between coal tar pitch and phenolic resin, reducing system viscosity, and promoting uniform mixing of the binder components. Dibutyl phthalate, as a plasticizer, can insert between binder molecular chains, weakening intermolecular forces, further reducing the viscosity of the binder system, and improving the binder's fluidity and its ability to wet and coat aggregate surfaces, ensuring uniform coverage of aggregate particles.

[0024] Further, in step S4, the mass ratio of the medium-temperature modified asphalt, thermosetting phenolic resin, C9 petroleum resin, and dibutyl phthalate is 90:(9-11):(0.4-0.6):(0.4-0.6); the grading process is as follows: the activated carbon return material is fed into a three-layer vibrating screen with apertures of 20mm, 10mm, and 4mm, respectively, and the proportion of coarse aggregate (10-20mm) is controlled to be 28%-32%, the proportion of medium aggregate (4-10mm) to be 38%-42%, and the proportion of fine powder (below 4mm) to be 28%-32%.

[0025] The aggregate grading process separates activated carbon return material into particles of different sizes using vibrating screens with different apertures, so that coarse aggregate, medium aggregate and fine powder form a reasonable particle size distribution. Fine powder fills the gaps between medium aggregate, and medium aggregate fills the gaps between coarse aggregate, so as to achieve close packing of aggregate, minimize the voids generated during the packing process and improve the density of the green body.

[0026] Further, in step S4, the amount of the composite binder is 10%-12% of the mass of the activated carbon recycled material; the amount of PEG-400 is 0.3%-0.5% of the mass of the activated carbon recycled material; the dry mixing temperature is 140-160℃, the dry mixing speed is 60-100 r / min, and the dry mixing time is 4-6 min; the kneading temperature is 160-180℃, the kneading speed is 45-55 r / min, and the kneading time is 30-40 min; the vibration molding step is: under the conditions of vibration frequency 28-32Hz, amplitude 1.3-1.7mm, and molding pressure 32-38MPa, the pressure is held for 5-7 min.

[0027] The high-temperature kneading process promotes the full melting and flow of the composite binder, achieving comprehensive and close contact and coating with the aggregate particles. The combination of vibration molding and pressure molding effectively removes air from the paste, further promoting the tight bonding between particles, eliminating internal pores and structural defects, and ultimately forming an electrode paste preform with uniform structure, high density, and strong interfacial bonding. This ensures that the product has sufficient mechanical strength at room temperature and maintains stable structure and performance at high temperatures, meeting the needs of industrial applications.

[0028] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0029] This solution utilizes recycled carbon material as aggregate, modified diatomaceous earth as adsorbent, and KH-550 supported by silica as an interface modifier to obtain a high-performance, low-cost electrode paste, improving its mechanical properties and high-temperature stability. First, the recycled carbon material undergoes preliminary impurity removal through traditional alkaline washing, magnetic separation, and acid washing. Then, the highly porous structure of modified diatomaceous earth is used to deeply adsorb residual molecular-level sodium, iron, and other impurity ions. Simultaneously, its micro-nano particles effectively fill the aggregate pores, increasing the compactness of the green body. Furthermore, the adsorbed modified diatomaceous earth can be recycled through a thermal regeneration process, realizing the resource utilization of the adsorbent and reducing raw material costs. Silica, acting as a carrier, allows KH-550 to form a uniform solid dispersion on its surface through high-speed shearing, fundamentally preventing KH-550 agglomeration. This process creates a stable microenvironment for the full hydrolysis of KH-550. During the thermal activation stage, the silanol groups generated by the hydrolysis of KH-550 can undergo condensation reactions with the active functional groups on the surface of aggregates and modified diatomaceous earth to form a Si-OC covalent bond network. This strengthens the interfacial bonding between aggregates and binders, solving the problem that in traditional processes, the electrode paste prepared from recycled carbon materials is generally weak in interfacial bonding and prone to peeling failure at high temperatures due to the difficulty in completely removing impurities and the strong surface inertness. This provides a solution for the high-value resource utilization of recycled carbon materials, taking into account both environmental and economic benefits. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a method for preparing electrode paste using recycled carbon materials according to the present invention. Detailed Implementation

[0031] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the application will be further described in detail below with reference to embodiments. However, this should not be construed as limiting the scope of this application to the following examples. All other embodiments obtained by those skilled in the art without creative effort without departing from the above-described methodological spirit of this application are within the scope of protection of this application.

[0032] The singular forms “for,” “or,” “a,” “any,” and “described” used in this application are intended to include the plural forms unless the context clearly indicates otherwise. Furthermore, the terms “first” and “second” are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] Example 1

[0034] like Figure 1 As shown, a method for preparing electrode paste using recycled carbon materials includes the following steps:

[0035] S1. Select carbon recycled material with a mass percentage of 50% residual electrodes, 25% graphite fragments, and 25% calcined fragments. The residual electrodes are waste electrodes replaced in aluminum electrolysis cells; the graphite fragments are scraps and waste materials from the graphite electrode processing; and the calcined fragments are cracked waste materials generated during the carbon calcination process. First, the material is coarsely crushed to a particle size ≤50mm by a jaw crusher, then medium crushed to ≤20mm by an impact crusher, and subsequently passed through a high-intensity magnetic separator with a magnetic field strength of 12000Gs to remove more than 95% of the metal blocks. Then, it is fed into a reaction tank, where a 4wt% KOH solution is added. The KOH solution and carbon return material were mixed at a mass ratio of 3:1. The mixture was stirred at 80℃ for 60 min to remove electrolyte impurities such as NaF and AlF3. The mixture was then washed with water until the pH of the filtrate was 7.0. Subsequently, the mixture was further treated by a weak magnetic separator with a magnetic field strength of 6000 Gs to remove iron impurities. The mixture was then sent to an acid washing tank and a 5 wt% hydrochloric acid solution was added. The mass ratio of hydrochloric acid solution to carbon return material was 2:1. The mixture was soaked at 65℃ for 40 min and washed with water until the pH of the filtrate was 7.0. Finally, the mixture was dried at 120℃ for 20 min to obtain the pretreated carbon return material.

[0036] S2. Modified diatomaceous earth is added to the pretreated carbon return material. The modified diatomaceous earth is hydroxylated industrial-grade diatomaceous earth with a specific surface area ≥200 m² / g and a particle size of 3 μm. The dosage is 1.4% of the mass of the pretreated carbon return material. The mixture is dry-mixed for 10 min in a twin-shaft mixer at 150 r / min. Then, deionized water is added, with a deionized water mass ratio of 3:1 to the total mass of the modified diatomaceous earth and the pretreated carbon return material. The twin-shaft mixer speed is maintained at 140 r / min, and the temperature is increased to [temperature missing]. Impurity adsorption was completed by stirring at 65℃ for 40 minutes. The mixture was then filtered through a plate and frame filter press to separate the purified carbon return material and the adsorption-saturated modified diatomaceous earth filter residue. The adsorption-saturated modified diatomaceous earth filter residue was dried at 110℃ for 10 minutes and then fed into a rotary kiln utilizing the waste heat of the calcination furnace. It was then held at 500℃ for 30 minutes to desorb impurities and achieve regeneration. After cooling, the regenerated material was obtained. Subsequent impurity removal involved mixing the modified diatomaceous earth and the regenerated material at a mass ratio of 4:1, and then repeating the above compounding, dry mixing, adsorption, and filtration process.

[0037] S3. Mix silica, KH-550 and deionized water at a mass ratio of 1:3.65:0.03, wherein the silica has a specific surface area of ​​≥150m² / g and a particle size of 7μm. Dry mix at 3000r / min for 6min to form a uniform solid dispersion system. Add the purified carbon return material and 1.5% of the mass of the purified carbon return material with deionized water. Dry mix in a plow-type mixer at 200r / min for 8min. Send the mixed return material into a hot air circulating activation furnace and keep it at 170℃ for 35min to obtain activated carbon return material.

[0038] S4. Coal tar pitch with a softening point of 50℃ and ash content ≤0.5% is placed in a reactor and heated to 290℃. Air is introduced at a rate of 1.0 L / (kg·h) for oxidation. The mixture is kept at this temperature for 2.5 h and then naturally cooled to 150℃ to obtain medium-temperature modified asphalt with a softening point of 95℃, coking value ≥48%, and ash content ≤0.3%. Medium-temperature modified asphalt, thermosetting phenolic resin with a softening point of 80℃, free phenol content ≤3%, and moisture content ≤1.5%, C9 petroleum resin with a softening point of 110℃ and ash content ≤0.1%, and dibutyl phthalate (DBP) are mixed at a mass ratio of 90:10:0.5:0.5 and stirred at 120℃ for 20 min to obtain a composite binder. Activated carbon return material is fed into pores with apertures of 20 mm and 10 mm. A three-layer vibrating screen with a diameter of 4mm is used to control the proportion of coarse aggregate (10-20mm) at 30%, medium aggregate (4-10mm) at 40%, and fine powder (below 4mm) at 30%. The graded aggregate is fed into a kneader and dry-mixed at 80r / min for 5 minutes at 150℃. Then, a composite binder and PEG-400 are added. The amount of composite binder is 11% of the mass of the activated carbon recycled material, and the amount of PEG-400 is 0.4% of the mass of the activated carbon recycled material. The temperature is raised to 170℃ and kneaded at 50r / min for 35 minutes. The kneaded paste is then fed into a vibration molding machine with a vibration frequency of 30Hz, an amplitude of 1.5mm, and a molding pressure of 35MPa. After holding the pressure for 6 minutes, the paste is removed to obtain the electrode paste blank.

[0039] Example 2

[0040] like Figure 1 As shown, a method for preparing electrode paste using recycled carbon materials includes the following steps:

[0041] S1. Select carbon recycled material with a mass percentage of 50% residual electrodes, 25% graphite fragments, and 25% calcined fragments. The residual electrodes are waste electrodes replaced in aluminum electrolysis cells; the graphite fragments are scraps and waste materials from the graphite electrode processing; and the calcined fragments are cracked waste materials generated during the carbon calcination process. First, the material is coarsely crushed to a particle size ≤50mm by a jaw crusher, then medium crushed to ≤20mm by an impact crusher, and subsequently passed through a high-intensity magnetic separator with a magnetic field strength of 11000Gs to remove more than 95% of the metal blocks. Then, it is fed into a reaction tank, where a 3wt% KOH solution is added. The mass ratio of KOH solution to recycled carbon material was 2.8:1. The mixture was stirred at 75℃ for 50 min to remove electrolyte impurities such as NaF and AlF3. The mixture was then washed with water until the pH of the filtrate was 6.5. Subsequently, iron impurities were further removed by a weak magnetic separator with a magnetic field strength of 5500 Gs. The mixture was then sent to an acid washing tank, where a 4 wt% hydrochloric acid solution was added. The mass ratio of hydrochloric acid solution to recycled carbon material was 1.8:1. The mixture was soaked at 60℃ for 35 min. The mixture was then washed with water until the pH of the filtrate was 6.5. Finally, the mixture was dried at 110℃ for 15 min to obtain the pretreated recycled carbon material.

[0042] S2. Modified diatomaceous earth is added to the pretreated carbon return material. The modified diatomaceous earth is industrial-grade diatomaceous earth that has undergone hydroxylation modification, with a specific surface area ≥200 m² / g and a particle size of 1 μm. The amount added is 1.2% of the mass of the pretreated carbon return material. The mixture is dry-mixed for 9 min in a twin-shaft mixer at a speed of 140 r / min. Then, deionized water is added, with the mass ratio of deionized water to the total mass of modified diatomaceous earth and pretreated carbon return material being 3:1. The twin-shaft mixer is kept at a speed of 120 r / min, and the temperature is raised to 60°C. Impurity adsorption was completed by stirring at 0℃ for 35 minutes. The mixture was then filtered through a plate and frame filter press to separate the purified carbon return material and the adsorption-saturated modified diatomaceous earth filter residue. The adsorption-saturated modified diatomaceous earth filter residue was dried at 105℃ for 8 minutes and then fed into a rotary kiln utilizing the waste heat of the calcination furnace. It was then held at 480℃ for 25 minutes to desorb impurities and achieve regeneration. After cooling, the regenerated material was obtained. Subsequent impurity removal involved mixing the modified diatomaceous earth and the regenerated material at a mass ratio of 3.8:1, and then repeating the above compounding, dry mixing, adsorption, and filtration process.

[0043] S3. Mix silica, KH-550 and deionized water at a mass ratio of 1:3.5:0.025, wherein the silica has a specific surface area of ​​≥150m² / g and a particle size of 5μm. Dry mix at 2800r / min for 5min to form a uniform solid dispersion system. Add the purified carbon return material and 1.2% of the mass of the purified carbon return material with deionized water. Dry mix in a plow-type mixer at 180r / min for 7min. Send the mixed return material into a hot air circulating activation furnace and keep it at 160℃ for 30min to obtain activated carbon return material.

[0044] S4. Coal tar pitch with a softening point of 45℃ and ash content ≤0.5% is placed in a reactor and heated to 280℃. Air is introduced at a rate of 0.8 L / (kg・h) for oxidation. The mixture is kept at this temperature for 2 hours and then naturally cooled to 140℃ to obtain medium-temperature modified asphalt with a softening point of 85℃, coking value ≥48%, and ash content ≤0.3%. Medium-temperature modified asphalt, thermosetting phenolic resin with a softening point of 70℃, free phenol content ≤3%, and moisture content ≤1.5%, C9 petroleum resin with a softening point of 100℃ and ash content ≤0.1%, and dibutyl phthalate (DBP) are mixed at a mass ratio of 90:9:0.4:0.4 and stirred at 120℃ for 20 minutes to obtain a composite binder. Activated carbon return material is fed into a vibrating screen with apertures of 20 mm and 10 mm. A three-layer vibrating screen with diameters of 4 mm and 10-20 mm was used to control the proportion of coarse aggregate (10-20 mm) at 28%, medium aggregate (4-10 mm) at 42%, and fine powder (less than 4 mm) at 28%. The graded aggregates were fed into a kneader and dry-mixed at 140℃ and 60 r / min for 4 minutes. Then, a composite binder and PEG-400 were added. The amount of composite binder was 10% of the mass of the activated carbon recycled material, and the amount of PEG-400 was 0.3% of the mass of the activated carbon recycled material. The temperature was raised to 160℃ and kneaded at 45 r / min for 30 minutes. The kneaded paste was then fed into a vibration molding machine with a vibration frequency of 28 Hz, an amplitude of 1.3 mm, and a molding pressure of 32 MPa. After holding the pressure for 5 minutes, the paste was removed to obtain the electrode paste blank.

[0045] Example 3

[0046] like Figure 1 As shown, a method for preparing electrode paste using recycled carbon materials includes the following steps:

[0047] S1. Select carbon recycled material with a mass percentage of 50% residual electrodes, 25% graphite fragments, and 25% calcined fragments. The residual electrodes are waste electrodes replaced in aluminum electrolysis cells; the graphite fragments are scraps and waste materials from the graphite electrode processing; and the calcined fragments are cracked waste materials generated during the carbon calcination process. First, the material is coarsely crushed to a particle size ≤50mm by a jaw crusher, then medium crushed to ≤20mm by an impact crusher, and subsequently passed through a high-intensity magnetic separator with a magnetic field strength of 13000Gs to remove more than 95% of the metal blocks. Then, it is fed into a reaction tank, where a 5wt% KOH solution is added. The mass ratio of KOH solution to recycled carbon material was 3.2:1. The mixture was stirred at 85℃ for 70 min to remove electrolyte impurities such as NaF and AlF3. The mixture was then washed with water until the pH of the filtrate was 7.5. Subsequently, iron impurities were further removed by a weak magnetic separator with a magnetic field strength of 6500 Gs. The mixture was then sent to an acid washing tank, where a 6 wt% hydrochloric acid solution was added. The mass ratio of hydrochloric acid solution to recycled carbon material was 2.2:1. The mixture was soaked at 70℃ for 45 min. The mixture was then washed with water until the pH of the filtrate was 7.5. Finally, the mixture was dried at 130℃ for 25 min to obtain the pretreated recycled carbon material.

[0048] S2. Modified diatomaceous earth is added to the pretreated carbon return material. The modified diatomaceous earth is industrial-grade diatomaceous earth that has undergone hydroxylation modification, with a specific surface area ≥200 m² / g and a particle size of 5 μm. The amount added is 1.6% of the mass of the pretreated carbon return material. The mixture is dry-mixed for 11 min in a twin-shaft mixer at a speed of 160 r / min. Then, deionized water is added, with the mass ratio of deionized water to the total mass of modified diatomaceous earth and pretreated carbon return material being 3:1. The twin-shaft mixer is kept at a speed of 150 r / min, and the temperature is raised to 7°C. Impurity adsorption was completed by stirring at 0℃ for 45 minutes. The mixture was then filtered through a plate and frame filter press to separate the purified carbon return material and the saturated modified diatomaceous earth filter residue. The saturated modified diatomaceous earth filter residue was dried at 115℃ for 12 minutes and then fed into a rotary kiln utilizing the waste heat of the calcination furnace. It was then held at 520℃ for 35 minutes to desorb impurities and achieve regeneration. After cooling, the regenerated material was obtained. Subsequent impurity removal involved mixing the modified diatomaceous earth and the regenerated material at a mass ratio of 4.2:1, and then repeating the above compounding, dry mixing, adsorption, and filtration process.

[0049] S3. Mix silica, KH-550 and deionized water at a mass ratio of 1:3.8:0.035, wherein the silica has a specific surface area of ​​≥150m² / g and a particle size of 10μm. Dry mix at 3200r / min for 7min to form a uniform solid dispersion system. Add the purified carbon return material and 1.8% of the mass of the purified carbon return material with deionized water. Dry mix in a plow-type mixer at 220r / min for 9min. Send the mixed return material into a hot air circulating activation furnace and keep it at 180℃ for 40min to obtain activated carbon return material.

[0050] S4. Coal tar pitch with a softening point of 65℃ and ash content ≤0.5% is placed in a reactor and heated to 300℃. Air is introduced at a rate of 1.2L / (kg・h) for oxidation. The mixture is kept at this temperature for 3 hours and then naturally cooled to 160℃ to obtain medium-temperature modified asphalt with a softening point of 105℃, coking value ≥48%, and ash content ≤0.3%. Medium-temperature modified asphalt, thermosetting phenolic resin with a softening point of 90℃, free phenol content ≤3%, and moisture content ≤1.5%, C9 petroleum resin with a softening point of 120℃ and ash content ≤0.1%, and dibutyl phthalate (DBP) are mixed at a mass ratio of 90:11:0.6:0.6 and stirred at 120℃ for 20 minutes to obtain a composite binder. Activated carbon return material is fed into a vibrating screen with apertures of 20mm and 10mm. A three-layer vibrating screen with diameters of 1 mm and 4 mm is used to control the proportion of coarse aggregate (10-20 mm) at 32%, medium aggregate (4-10 mm) at 38%, and fine powder (less than 4 mm) at 32%. The graded aggregate is fed into a kneader and dry-mixed at 100 r / min for 6 minutes at 160℃. Then, a composite binder and PEG-400 are added, with the amount of composite binder being 12% of the mass of the activated carbon recycled material and the amount of PEG-400 being 0.5% of the mass of the activated carbon recycled material. The temperature is raised to 170℃ and kneaded at 55 r / min for 40 minutes. The kneaded paste is then fed into a vibration molding machine with a vibration frequency of 32 Hz, an amplitude of 1.7 mm, and a molding pressure of 38 MPa. After holding the pressure for 7 minutes, the paste is removed to obtain the electrode paste blank.

[0051] Comparative Example 1

[0052] A method for preparing electrode paste using recycled carbon materials differs from Example 1 in that modified diatomaceous earth is not used for impurity removal, while the remaining steps and parameters are the same.

[0053] Comparative Example 2

[0054] A method for preparing electrode paste using recycled carbon materials differs from Example 1 in that KH-550 is not supported by silica, but is directly added; the remaining steps and parameters are the same.

[0055] Comparative Example 3

[0056] A method for preparing electrode paste using recycled carbon materials differs from Example 1 in that the composite binder is a single medium-temperature modified asphalt, while the other steps and parameters are the same.

[0057] Performance testing:

[0058] Verification of impurity removal effect: Sodium and iron content were simultaneously determined by inductively coupled plasma optical emission spectrometry (ICP-OES). Five g samples of the electrode paste preforms prepared in Examples 1-3 and Comparative Examples 1-3 were pulverized to a particle size ≤0.15 mm and placed in a platinum crucible. The crucible was heated to 815 °C at a rate of 10 °C / min in a muffle furnace and held at that temperature for 2 h until constant weight was obtained, yielding ash residue. 10 mL of nitric acid and 5 mL of hydrofluoric acid were added to the residue. The platinum crucible was placed in a microwave digester, and the power was set to 800 W. The temperature was raised to 180 °C and held for 20 min for digestion. After the digestion solution was cooled to room temperature, it was transferred to a 50 mL volumetric flask, diluted to the mark with deionized water, and shaken well. The diluted solution was injected into an ICP-OES instrument. The characteristic spectral line of sodium (589.592 nm) and the characteristic spectral line of iron (259.940 nm) were selected, and the concentrations of sodium and iron were calculated using the standard curve method. The sodium and iron contents in the sample were then calculated. Three parallel tests were performed on each sample, and the average value was taken. The results are shown in Table 1.

[0059] Room temperature compressive strength test: Electrode paste blanks prepared in Examples 1-3 and Comparative Examples 1-3 were processed into 50mm×50mm×50mm cube specimens. The specimen surface was ensured to be flat and free of cracks. The specimens were placed between the upper and lower pressure plates of the electronic universal testing machine. The position of the specimens was adjusted so that the center was aligned with the center of the pressure plates. Pressure was applied to the specimens at a uniform loading rate of 2mm / min until the specimens fractured. The maximum pressure value at the moment of fracture was recorded in real time. The room temperature compressive strength was calculated according to the formula σ=F / S (where σ is the room temperature compressive strength, F is the maximum pressure at fracture, and S is the force-bearing area of ​​the specimen). Five sets of parallel tests were conducted for each sample, and the average value was taken. The results are shown in Table 1.

[0060] High-temperature compressive strength test: Electrode paste blanks prepared in Examples 1-3 and Comparative Examples 1-3 were processed into 50mm×50mm×50mm cube samples and placed in a high-temperature furnace. The temperature was slowly increased to 1000℃ at a rate of 5℃ / min and held for 30min to eliminate internal thermal stress. Then, the samples were quickly transferred to the testing station of the high-temperature compressive strength testing machine while maintaining the center of the sample aligned with the center of the pressure plate. Pressure was applied uniformly at a loading rate of 1mm / min until the sample broke. The maximum pressure value at the time of breakage was recorded and the high-temperature compressive strength was calculated using the formula σ=F / S. Three sets of parallel tests were conducted for each sample, and the average value was taken. The results are shown in Table 1.

[0061] Resistivity Testing: The electrode paste blanks prepared in Examples 1-3 and Comparative Examples 1-3 were processed into 100mm×20mm×20mm standard cuboid samples, ensuring smooth surfaces and uniform dimensions. A four-probe method was used for testing. Four probes were pressed vertically and evenly onto the sample surface, with a probe spacing of 20mm. A constant current I was applied to the two outer probes using a DC regulated power supply. The voltage V between the two middle probes was measured using a high-precision voltmeter. The resistivity was calculated using the formula ρ=πdV / (ln2×I) (where ρ is the resistivity, d is the sample thickness, V is the measured voltage value, and I is the applied constant current). Each sample was tested three times at different locations, and the average value was taken as the final result. The unit is expressed in μΩ·m. The results are shown in Table 1.

[0062] Ash content test: Take 5g of the electrode paste prepared in Examples 1-3 and Comparative Examples 1-3 respectively, crush it to a particle size ≤0.15mm, and place it in a porcelain crucible that has been constant-weighted at 815℃. Put the porcelain crucible into a muffle furnace and heat it to 815℃ at a rate of 10℃ / min. Hold it at this temperature for 2h to allow the sample to burn completely. Then turn off the muffle furnace and let the furnace temperature cool naturally to below 200℃. Transfer the porcelain crucible to a desiccator to cool to room temperature. Weigh the total mass of the crucible and the residue, calculate the mass of the residue m2, and calculate the ash content using the formula A=(m2 / m1)×100% (where A is the ash content and m1 is the initial mass of the sample). Test each sample in parallel for 2 groups and take the average value. The results are shown in Table 1.

[0063] Table 1. Electrode paste performance test results for each embodiment and comparative example.

[0064]

[0065] As shown in Table 1, the room temperature compressive strength and high temperature compressive strength of the electrode pastes prepared in Examples 1-3 are higher than those of Comparative Examples 1-3. Furthermore, the sodium and iron content, resistivity, and ash content of the electrode pastes prepared in Examples 1-3 are all lower than those of Comparative Examples 1-3. This indicates that the mechanical properties, high temperature stability, and electrical conductivity of the electrode pastes prepared in Examples 1-3 are all superior to those of Comparative Examples 1-3.

[0066] Comparative Example 1 did not employ a modified diatomaceous earth deep impurity removal process, relying solely on traditional impurity removal methods such as alkali washing, acid washing, and magnetic separation. This method was insufficient to remove molecularly dispersed impurity ions such as sodium and iron. These residual inorganic impurities would form numerous structural defects within the electrode paste, disrupting the continuity of the carbon network and creating an isolation layer at the aggregate-binder interface, weakening the interfacial bonding. Simultaneously, insulating impurities would increase electron transport resistance, ultimately resulting in poor impurity removal performance and a simultaneous decline in mechanical and electrical properties. This performance shortcoming directly demonstrates that modified diatomaceous earth deep impurity removal is a fundamental prerequisite for ensuring product purity and core performance.

[0067] Comparative Example 2 did not use the method of immobilizing KH-550 with silica, but instead directly added KH-550. This caused the directly added KH-550 to easily agglomerate due to intermolecular forces, failing to form a uniform solid dispersion system. This not only lost the stable hydrolytic microenvironment provided by the silica carrier, but also made it difficult to fully contact the active functional groups on the surface of aggregates and modified diatomaceous earth. As a result, the Si-OC covalent bond network could not be effectively formed, and the interfacial bonding force relied solely on physical coating. Consequently, the mechanical and electrical properties decreased significantly, highlighting the key role of silica immobilization in the interfacial modification effect.

[0068] Comparative Example 3 replaced the composite binder with a single medium-temperature modified asphalt, thus losing the low-temperature crosslinking strengthening effect of phenolic resin, the compatibility improvement effect of C9 petroleum resin, and the plasticizing effect of DBP. This resulted in insufficient uniformity of the binder system coating the aggregate, low crosslinking density, difficulty in forming a stable initial structure at room temperature, and poor stability of the carbon skeleton formed by coking at high temperature. Ultimately, this led to a decrease in mechanical and electrical properties, demonstrating the important value of the synergistic effect of the components of the composite binder in compensating for the defects of a single binder and improving the overall performance.

[0069] Comparative Examples 1-3 lacked key technical features such as the modified diatomaceous earth impurity removal process, the interface modification design of KH-550 solidified silica, and the synergistic system of composite binders. This resulted in poor impurity removal effect, weak interface bonding, and insufficient bonding effect. Consequently, a chain reaction occurred, with increased sodium and iron impurity content and ash content, decreased compressive strength at room temperature and high temperature, and increased resistivity. All of these factors combined to make the mechanical properties, high-temperature stability, and conductivity of the electrode paste inferior to those of the Examples.

[0070] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0071] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for preparing electrode paste using recycled carbon materials, characterized in that, Includes the following steps: S1. The carbon return material is crushed and subjected to strong magnetic separation to remove metal blocks, and then subjected to alkaline washing, weak magnetic separation, acid washing and drying to obtain pretreated carbon return material; S2. The modified diatomaceous earth is dry-mixed with the pretreated carbon return material, deionized water is added, and after stirring and filtration, impurity-removed carbon return material and adsorption-saturated modified diatomaceous earth filter residue are obtained. The modified diatomaceous earth filter residue that is saturated with adsorption is dried and thermally regenerated to obtain recycled material. The modified diatomaceous earth is then mixed with the recycled material and the process is repeated for subsequent impurity removal. S3. The silica, KH-550 and the first deionized water are dry-mixed for the first time, and the impurity-removed carbon return material and the second deionized water are added. After the second dry mixing and hot air activation, the activated carbon return material is obtained. S4. Heat the coal tar pitch to the first set temperature, introduce air for oxidation, and then let it cool naturally to the second set temperature to obtain medium-temperature modified asphalt. A composite binder is obtained by mixing medium-temperature modified asphalt, thermosetting phenolic resin, C9 petroleum resin and dibutyl phthalate; activated carbon recycled material is graded and then dry-mixed, the composite binder and PEG-400 are added, kneaded and then vibrated to form electrode paste.

2. The method for preparing electrode paste using recycled carbon material according to claim 1, characterized in that, In step S1, the carbon return material comprises, by mass percentage: 50% residual electrodes, 25% graphite fragments, and 25% calcined fragments; the residual electrodes are waste electrodes replaced by aluminum electrolytic cells; the graphite fragments are scraps and scraps from the graphite electrode processing; the calcined fragments are cracked waste fragments generated during the carbon calcination process; the carbon return material has a particle size ≤20mm after crushing; and the magnetic field strength of the strong magnetic separation is 11000-13000Gs.

3. The method for preparing electrode paste using recycled carbon materials according to claim 1, characterized in that, In step S1, the alkaline washing step is as follows: adding a KOH solution with a mass fraction of 3wt%-5wt%, the mass ratio of KOH solution to carbon return material is (2.8-3.2):1, stirring at 75-85℃ for 50-70 minutes, and washing with water until the pH of the filtrate is 6.5-7.5; the magnetic field strength of the weak magnetic separation is 5500-6500Gs; the acid washing step is as follows: adding a hydrochloric acid solution with a mass fraction of 4wt%-6wt%, the mass ratio of hydrochloric acid solution to carbon return material is (1.8-2.2):1, soaking at 60-70℃ for 35-45 minutes, and washing with water until the pH of the filtrate is 6.5-7.5; the drying temperature is 110-130℃, and the drying time is 15-25 minutes.

4. The method for preparing electrode paste using recycled carbon material according to claim 1, characterized in that, In step S2, the modified diatomaceous earth is industrial-grade diatomaceous earth modified by hydroxylation, with a specific surface area ≥200m² / g and a particle size of 1-5μm; the amount of modified diatomaceous earth used is 1.2%-1.6% of the mass of the pretreated carbon return material; the dry mixing speed is 140-160r / min, and the dry mixing time is 9-11min; the mass ratio of deionized water to the total mass of modified diatomaceous earth and pretreated carbon return material is 3:

1.

5. The method for preparing electrode paste using recycled carbon material according to claim 1, characterized in that, In step S2, the stirring temperature is 60-70℃, the stirring rate is 120-150 r / min, and the stirring time is 35-45 min; the drying temperature is 105-115℃, and the drying time is 8-12 min; the thermal regeneration temperature is 480-520℃, and the thermal regeneration time is 25-35 min; the mass ratio of modified diatomaceous earth to recycled material is (3.8-4.2):

1.

6. The method for preparing electrode paste using recycled carbon material according to claim 1, characterized in that, In step S3, the specific surface area of ​​the silica is ≥150 m² / g, and the particle size is 5-10 μm; the mass ratio of silica, KH-550 and the first deionized water is 1:(3.5-3.8):(0.025-0.035); the rotation speed of the first dry mixing is 2800-3200 r / min, and the time of the first dry mixing is 5-7 min.

7. The method for preparing electrode paste using recycled carbon material according to claim 1, characterized in that, In step S3, the amount of the second deionized water is 1.2%-1.8% of the mass of the purified carbon return material; the rotation speed of the second dry mixing is 180-220 r / min, and the time of the second dry mixing is 7-9 min; the temperature of the hot air activation is 160-180℃, and the time of the hot air activation is 30-40 min.

8. The method for preparing electrode paste using recycled carbon material according to claim 1, characterized in that, In step S4, the softening point of the coal tar pitch is 45-65℃, and the ash content is ≤0.5%; the first set temperature is 280-300℃; the air introduction rate is 0.8-1.2 L / (kg·h); the oxidation time is 2-3 h; the second set temperature is 140-160℃; the softening point of the medium-temperature modified pitch is 85-105℃, the coking value is ≥48%, and the ash content is ≤0.3%; the softening point of the thermosetting phenolic resin is 70-90℃, the free phenol content is ≤3%, and the moisture content is ≤1.5%; the softening point of the C9 petroleum resin is 100-120℃, and the ash content is ≤0.1%.

9. The method for preparing electrode paste using recycled carbon material according to claim 1, characterized in that, In step S4, the mass ratio of the medium-temperature modified asphalt, thermosetting phenolic resin, C9 petroleum resin, and dibutyl phthalate is 90:(9-11):(0.4-0.6):(0.4-0.6); the grading process is as follows: the activated carbon return material is fed into a three-layer vibrating screen with apertures of 20mm, 10mm, and 4mm, and the proportion of coarse aggregate (10-20mm) is controlled to be 28%-32%, the proportion of medium aggregate (4-10mm) to be 38%-42%, and the proportion of fine powder (below 4mm) to be 28%-32%.

10. A method for preparing electrode paste using recycled carbon materials according to claim 1, characterized in that, In step S4, the amount of the composite binder is 10%-12% of the mass of the activated carbon recycled material; the amount of PEG-400 is 0.3%-0.5% of the mass of the activated carbon recycled material; the dry mixing temperature is 140-160℃, the dry mixing speed is 60-100 r / min, and the dry mixing time is 4-6 min; the kneading temperature is 160-180℃, the kneading speed is 45-55 r / min, and the kneading time is 30-40 min; the vibration molding step is as follows: under the conditions of vibration frequency of 28-32 Hz, amplitude of 1.3-1.7 mm, and molding pressure of 32-38 MPa, the pressure is held for 5-7 min.

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