A method for preparing magnesium-aluminum spinel-carbon refractory material based on primary aluminum dross

Abstract

This invention relates to a method for preparing magnesium-aluminate spinel-carbon refractory materials based on primary aluminum ash, belonging to the field of refractory materials and solid waste resource utilization technology. The method includes: ball milling, washing, vacuum filtration, and drying primary aluminum ash to obtain pretreated aluminum ash powder; mixing the pretreated aluminum ash powder, magnesium raw materials, magnesium-aluminate spinel, carbon, and a binder to obtain a refractory material mixture; pressing and curing the mixture to obtain the finished magnesium-aluminate spinel-carbon refractory material. The pretreated aluminum ash powder obtained by this invention can directly replace expensive industrial alumina and metallic aluminum powder, significantly reducing raw material costs and significantly improving the density and oxidation resistance of the material. The preparation process is fully compatible with existing magnesium-aluminate spinel-carbon refractory material production systems, has wide application scenarios, and is easy to promote, possessing strong industrial practicality and market competitiveness.

Description

Technical Field

[0001] This invention relates to a method for preparing magnesium aluminum spinel-carbon refractory materials based on primary aluminum ash, belonging to the field of refractory materials and solid waste resource utilization technology. Background Technology

[0002] Primary aluminum ash (also known as white aluminum ash or virgin aluminum slag) is the main solid waste generated during the electrolytic aluminum production process. It primarily originates from processes such as aluminum tapping from electrolytic cells, anode replacement, ingot casting, and major overhauls of electrolytic cells. Each ton of primary aluminum production generates 15-40 kg of primary aluminum ash. As the second largest metal materials industry in the modern industrial system after the steel industry, the aluminum industry's applications in aerospace, automobile manufacturing, power equipment, and building materials continue to expand. In 2024, global aluminum production capacity was approximately 80 million tons, with China accounting for about 56% (approximately 44 million tons). This has led to a surge in aluminum ash emissions year by year. Because aluminum ash is listed as metallurgical solid waste in the "National Hazardous Waste List," its harmless disposal and resource utilization have become a key bottleneck restricting the green development of the aluminum industry, possessing both significant theoretical research value and urgent industrial application needs.

[0003] The chemical composition of primary aluminum ash is complex and fluctuates considerably. Its core valuable components are metallic aluminum (Al) and alumina (Al₂O₃), with metallic aluminum typically ranging from 20% to 75% and alumina from 20% to 85%. It also contains impurities such as aluminum nitride, chloride salts, Fe₂O₃, SiO₂, MgO, and small amounts of fluorides. Its environmental hazards are mainly manifested in two aspects: first, AlN readily hydrolyzes in water to generate NH₃, causing air pollution; second, soluble impurities such as chlorides and fluorides easily seep into soil and groundwater, leading to soil salinization and water pollution. Furthermore, directly stockpiling unrecovered valuable components from aluminum ash will result in a serious waste of resources.

[0004] Currently, primary aluminum ash treatment technologies mainly focus on the recovery of metallic aluminum, including pressing recovery, ash-frying recovery, rotary kiln processing, MRM method, plasma rapid melting method, and ALUEC method. These technologies utilize the difference in melting points between metallic aluminum and other components to achieve the separation of metallic aluminum through high-temperature melting. Although existing technologies have made some progress in metallic aluminum recovery, they still face multiple bottlenecks. The pressing recovery method involves applying static or dynamic pressure to hot aluminum slag to extrude molten aluminum, but its aluminum recovery rate is low, energy consumption is high, and its adaptability in domestic industrial applications is poor, failing to meet expectations. The ash-frying recovery method utilizes the difference in wettability between molten aluminum and other components, adding solvents and stirring at high temperatures to separate molten aluminum, but it generates a large amount of smoke and dust, and the solvent reacts with moisture in the air to generate HCl, causing secondary pollution. Solvent residues also reduce the quality of the recovered aluminum. The rotary kiln treatment method uses mechanical stirring with an inclined cylinder to allow the molten aluminum at high temperatures to aggregate and separate under gravity, but the residue still requires secondary aluminum extraction, focusing only on aluminum recovery, leaving 20%–85% of alumina unutilized, resulting in low resource utilization. The improved MRM method treats hot aluminum slag under inert gas protection, which can reduce the aluminum burn-off rate, but the residue still requires secondary recycling, failing to solve the problem of high-value utilization of alumina and other components. The plasma rapid melting method melts aluminum slag with high-temperature plasma, adding calcium oxide slag-forming agents to separate metallic aluminum and calcium aluminate, achieving high aluminum recovery rate and excellent production efficiency, but... The equipment and technology requirements are extremely high, making industrial promotion difficult. It also has high energy consumption and operating costs, and only recovers metallic aluminum without utilizing the alumina in the slag. The ALUEC method uses a rotary melting furnace with pure oxygen for combustion and heating, and operates under negative pressure to separate metallic aluminum. It has a high degree of mechanization and a friendly operating environment, but requires potassium chloride / sodium chloride as a covering agent, increasing raw material costs. Poor furnace sealing makes it prone to drawing in cold air, affecting efficiency, and residual aluminum ash still requires further harmless treatment. The electric heating recovery method remelts aluminum ash using high-power electric heating equipment, using melting point differences to separate metallic aluminum. Although it has a high purification rate, its energy consumption and production costs are extremely high, making it unsuitable for large-scale promotion. Furthermore, it only extracts metallic aluminum and does not involve the recovery of valuable components such as alumina and aluminum nitride. The method of directly returning the aluminum ash to the electrolytic cell is problematic because the α-Al2O3 in the primary aluminum ash has extremely low activity and is difficult to dissociate by cryolite molten salt, thus failing to participate in the electrolytic reaction. This also leads to increased energy consumption, higher cell voltage, and more sediment at the furnace bottom, affecting current efficiency and cell lifespan, thus preventing large-scale application. These methods generally suffer from common defects: they all focus only on the recovery of metallic aluminum, and valuable components such as alumina are not utilized in a high-value manner, resulting in resource waste; thermal methods often have high energy consumption problems, and some processes are accompanied by secondary pollution; most methods do not form a closed loop of "harmlessness + full component utilization", and the residue needs further treatment; some methods have high equipment requirements and poor adaptability, making it difficult to promote on a large scale.

[0005] In general, existing primary aluminum ash treatment technologies mainly face problems such as low resource utilization, limited environmental benefits, large equipment investment, and high energy consumption. Crucially, the secondary aluminum ash generated after these methods not only significantly increases the difficulty of recycling but also still suffers from increased harmful components and impurity accumulation. These technologies fail to fundamentally address the core bottleneck of solid waste resource utilization and cannot achieve the goal of high-value recovery of all components of aluminum ash.

[0006] With increasingly stringent environmental policies and the advancement of "dual carbon" targets, the electrolytic aluminum industry has placed higher demands on the harmless and resource-oriented treatment of primary aluminum ash. This requires not only the deep removal of harmful substances but also the promotion of high-value utilization of valuable components such as alumina, while reducing processing costs. Against this backdrop, developing a primary aluminum ash treatment and high-value utilization technology that combines high efficiency, harmlessness, economic efficiency, and environmental friendliness has become a key technical challenge that the industry urgently needs to address. Summary of the Invention

[0007] To address the aforementioned shortcomings of existing technologies, this invention provides a method for preparing magnesium aluminum spinel-carbon refractory materials based on primary aluminum ash.

[0008] First, this invention innovatively adopts a combined process of ball milling, multi-stage water washing, vacuum filtration, and drying to deeply remove harmful impurities such as chlorides, fluorides, and aluminum nitrides from primary aluminum ash to a content of ≤1%, while enriching valuable components such as metallic aluminum and alumina to a total content of ≥80%. This breaks through the limitation of traditional thermal methods that only recover metallic aluminum, and realizes the full-component resource utilization of aluminum ash from hazardous waste to functional components of refractory materials.

[0009] Secondly, this invention utilizes the in-situ generation of magnesium aluminum spinel phase from aluminum oxide and magnesium raw materials in aluminum ash to precisely compensate for the gaps in brick joints; as a natural antioxidant, metallic aluminum preferentially oxidizes to form a protective film or reduces carbon oxidation products, synergistically inhibiting carbon matrix burn-off, solving the pain point of easy hydration and cracking when adding metallic aluminum powder in the traditional way, and simultaneously improving the material's thermal shock resistance and slag erosion resistance.

[0010] The pretreated aluminum ash powder obtained by this invention can directly replace expensive industrial alumina and metallic aluminum powder, significantly reducing raw material costs. The preparation process is fully compatible with the existing magnesium aluminum spinel-carbon refractory material production system, requiring no additional special equipment, and can be directly adapted to large-scale production, taking into account both environmental benefits and industrial practicality.

[0011] To achieve the above objectives, the technical solution of the present invention is as follows:

[0012] A method for preparing magnesium aluminum spinel-carbon refractory based on primary aluminum ash includes the following steps: (1) The primary aluminum ash is ball-milled, washed with water, vacuum filtered and dried to obtain pretreated aluminum ash powder; (2) The pretreated aluminum ash powder, magnesium raw materials, magnesium aluminum spinel, carbon and binder are mixed to obtain refractory material mixture; (3) The refractory material mixture is pressed into shape to obtain a refractory green blank; (4) The refractory green body is cured to obtain the finished magnesium aluminum spinel-carbon refractory.

[0013] In the above technical solution, in step (1), the ball milling time is 1~10 h and the ball milling speed is 100~500 r / min; the ball milled aluminum ash is mixed with deionized water at a solid-liquid mass ratio of 1:3~6, and stirred and washed at 300~600 r / min for 1~3 h at 30~80℃, followed by vacuum filtration. The stirring, washing and vacuum filtration are repeated 2~5 times; the filter residue obtained by vacuum filtration is dried at 70~110℃ to constant weight to obtain pretreated aluminum ash powder.

[0014] In the above technical solution, in step (1), the total content of Al2O3, Al(OH)3 and Al in the pretreated aluminum ash powder is ≥80%, and the total content of chloride and fluoride is ≤1%.

[0015] In the above technical solution, in step (2), by mass fraction, the pretreated aluminum ash powder is 1%~30%, magnesium raw material is 0.4%~12%, carbon is 3%~20%, binder is 3%~6%, and magnesium aluminum spinel is 32%~92.6%.

[0016] Furthermore, in step (2), the molar ratio of alumina to magnesium raw material in the pretreated aluminum ash powder is 1~1.5:1.

[0017] In the above technical solution, in step (2), the magnesium raw material is active magnesium oxide with a purity of ≥96% and a particle size of ≤0.075 mm.

[0018] Furthermore, the active magnesium oxide can be obtained by purchasing or by extracting it from one or more of magnesite, brucite, dolomite, or salt lake water using conventional techniques.

[0019] In the above technical solution, in step (2), the carbon is one or more of flake graphite or carbon black, with a purity ≥99% and a particle size ≤0.18 mm.

[0020] In the above technical solution, in step (2), the binder is a thermosetting phenolic resin with a carbonization rate of 30%~50%.

[0021] In the above technical solution, in step (2), the magnesium aluminum spinel includes three particle sizes, wherein the particle size of 1~3 mm accounts for 30%~50% of the magnesium aluminum spinel, the particle size of 0~1 mm accounts for 20%~40% of the magnesium aluminum spinel, and the particle size of ≤0.075 mm accounts for 10%~30% of the magnesium aluminum spinel.

[0022] Preferably, in step (2), magnesium aluminum spinel with a particle size of 1~3 mm is first mixed evenly with a binder, and then carbon, magnesium aluminum spinel with a particle size of 0~1 mm, magnesium aluminum spinel with a particle size ≤0.075 mm, pretreated aluminum ash powder, and magnesium raw materials are added in sequence.

[0023] In the above technical solution, in step (3), the pressing and molding conditions are carried out under a pressure of 100~300 MPa and a holding time of 10 s~10 min.

[0024] In the above technical solution, in step (4), the curing conditions are to keep warm at 150~220℃ for 12~36h and then cool to room temperature.

[0025] Magnesium-aluminum spinel-carbon (MgAl2O4-C) refractories, as a high-performance composite refractory material, have been applied to key parts of the steelmaking industry, such as the sidewalls, bottom linings, and slag lines of ladles, due to their excellent resistance to molten steel / slag erosion, high-temperature mechanical strength, good thermal shock stability, and anti-spading properties. This significantly extends the service life of ladles and reduces refractory material consumption and production costs. In the preparation and service of these MgAl2O4-C refractories, the in-situ formation process of the MgAl2O4 phase is the core factor determining the final performance of the material. Its in-situ synthesis reaction (MgO + Al2O3 → MgAl2O4) is accompanied by a slight volume expansion of approximately 8%-10%. This expansion effect is continuous and uniform, accurately compensating for the gaps in the brick joints caused by thermal expansion and contraction during high-temperature thermal cycling and cooling stages. This effectively blocks the channels through which molten steel and slag penetrate into the lining, thereby significantly improving the overall erosion resistance and structural integrity of the material and preventing lining spalling failure caused by brick joint erosion. Based on the aforementioned in-situ synthesis mechanism, and considering that the main chemical components of primary aluminum ash are alumina, metallic aluminum, and small amounts of silicon and iron oxides, its compositional characteristics are highly compatible with the preparation requirements of magnesium-aluminum spinel-carbon refractories. On the one hand, primary aluminum ash can be directly used as an alumina source, replacing traditional industrial alumina raw materials. During the high-temperature sintering process of refractory materials, it reacts in situ with magnesia components (such as fused magnesia and lightly calcined magnesia powder) to generate the magnesium-aluminum spinel phase, which simplifies the preparation process and realizes the resource utilization of industrial solid waste. On the other hand, the metallic aluminum contained in the aluminum ash has strong reducing properties at high temperatures and can act as an antioxidant. It can preferentially oxidize to form an alumina protective film or react with carbon oxidation products (such as CO) (2Al + 3CO → Al2O3 + 3C), inhibiting the oxidation and burn-off of the carbon matrix, reducing the increase in internal porosity of the material, and further ensuring the structural stability and service performance of magnesium-aluminum spinel-carbon refractories.

[0026] The beneficial effects of this invention are: 1. This invention addresses the environmental pollution problem of aluminum ash as hazardous waste at its source. Simultaneously, it transforms all valuable components such as metallic aluminum and alumina in aluminum ash into functional components for refractory materials, significantly improving resource utilization and reducing energy consumption compared to traditional thermal recovery methods. This aligns perfectly with the "dual carbon" goals and the policy direction of solid waste resource utilization.

[0027] 2. In the pretreated aluminum ash powder obtained by the present invention, metallic aluminum preferentially reacts with oxygen to form a dense alumina protective layer, which effectively delays graphite oxidation. The alumina and fused magnesium aluminum spinel form a stable solid solution, which synergistically improves the material density and oxidation resistance.

[0028] 3. The pretreated aluminum ash powder obtained by this invention can directly replace expensive industrial-grade alumina and metallic aluminum powder, significantly reducing the raw material cost of refractory materials. Its preparation process is fully compatible with the existing magnesium-aluminate spinel-carbon refractory material production system, requiring no additional specialized equipment. It can be directly adapted to the large-scale production of various high-temperature metallurgical equipment such as continuous casting stopper rods and ladle liners, with wide application scenarios and low promotion difficulty, possessing strong industrial practicality and market competitiveness. Attached Figure Description

[0029] Figure 1 The image shows a cross-sectional view of the refractory material after oxidation at 1400℃ for 2 hours. In this image, a represents the refractory material obtained in Comparative Example 1, and b represents the refractory material obtained in Example 1. Detailed Implementation

[0030] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0031] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0032] Example 1 A method for preparing magnesium aluminum spinel-carbon refractory based on primary aluminum ash includes the following steps: (1) Take aluminum ash once and ball mill it for 1 hour at a speed of 100 r / min. Then mix the aluminum ash obtained after ball milling with deionized water at a solid-liquid mass ratio of 1:3. Stir and wash for 1 hour at 30°C and 300 r / min. Vacuum filter. Repeat the stirring and washing-vacuum filtration operation twice. Place the filter residue in a drying oven at 70°C and dry it to constant weight to obtain pretreated aluminum ash powder (total content of Al2O3+Al(OH)3+Al 82%, total content of chloride+fluoride 0.8%). (2) Weigh the raw materials according to the following mass fractions: 1% pretreated aluminum ash powder, 0.4% active magnesium oxide (96% purity, particle size ≤0.075mm), 3% flake graphite (99% purity, particle size ≤0.18mm), 3% thermosetting phenolic resin (30% carbonization rate), and the remainder is 92.6% magnesium aluminum spinel (including three particle sizes: 30% for 1~3 mm particle size, 40% for 0~1 mm particle size, and 30% for ≤0.075mm particle size). The molar ratio of alumina to active magnesium oxide in the aluminum ash powder is 1:1. Then, first mix the 1~3 mm magnesium aluminum spinel with the thermosetting phenolic resin evenly, and then add flake graphite, 0~1 mm magnesium aluminum spinel, and ≤0.075mm particle size in sequence. mm magnesium aluminum spinel, pretreated aluminum ash powder, and active magnesium oxide are dry-mixed until homogeneous to obtain a refractory material compound. (3) The refractory material mixture obtained above is pressed and molded under a pressure of 100 MPa for 10 s to obtain a refractory green body; (4) The refractory green obtained above is kept at 150°C for 12 h and then naturally cooled to room temperature to obtain magnesium aluminum spinel-carbon refractory.

[0033] Example 2 (1) Take aluminum ash once and ball mill it for 10 h at a speed of 500 r / min. Then mix the ball-milled aluminum ash with deionized water at a solid-liquid mass ratio of 1:6. Stir and wash for 3 h at 80℃ and 600 r / min. Vacuum filter. Repeat the stirring-washing-vacuum filtration operation 5 times. Place the filter residue in a drying oven at 110℃ and dry it to constant weight to obtain pretreated aluminum ash powder (total content of Al2O3+Al(OH)3+Al 91%, total content of chloride+fluoride 0.5%). (2) Weigh the raw materials according to the following mass fractions: 30% pretreated aluminum ash powder, 12% active magnesium oxide (98% purity, particle size ≤0.075mm), 20% carbon black (99% purity, particle size ≤0.18mm), 6% thermosetting phenolic resin (50% carbonization rate), and the remainder is 32% magnesium aluminum spinel (including three particle sizes: 1~3 mm particle size accounts for 50% of magnesium aluminum spinel, 0~1 mm particle size accounts for 20% of magnesium aluminum spinel, and ≤0.075mm particle size accounts for 10% of magnesium aluminum spinel). The molar ratio of alumina to active magnesium oxide in the aluminum ash powder is 1.5:1. Then, first mix the 1~3 mm magnesium aluminum spinel with the thermosetting phenolic resin evenly, and then add carbon, 0~1 mm magnesium aluminum spinel, and ≤0.075mm particle size in sequence. mm magnesium aluminum spinel, pretreated aluminum ash powder, and active magnesium oxide are dry-mixed until homogeneous to obtain a refractory material compound. (3) Press the above-obtained refractory material mixture under a pressure of 300 MPa for 10 min to obtain a refractory green body; (4) The refractory green obtained above is kept at 220°C for 36 h and then naturally cooled to room temperature to obtain magnesium aluminum spinel-carbon refractory.

[0034] Example 3 (1) Take aluminum ash once and ball mill it for 5 h at a speed of 300 r / min. Then mix the ball-milled aluminum ash with deionized water at a solid-liquid mass ratio of 1:4. Stir and wash for 2 h at 65℃ and 450 r / min. Vacuum filter. Repeat the stirring-washing-vacuum filtration operation 3 times. Place the filter residue in a 90℃ drying oven and dry it to constant weight to obtain pretreated aluminum ash powder (total content of Al2O3+Al(OH)3+Al 88%, total content of chloride+fluoride 0.5%). (2) Weigh the raw materials according to the following mass fractions: 15% pretreated aluminum ash powder, 6% active magnesium oxide (purity 97%, particle size ≤0.075mm), 12% a mixture of flake graphite and carbon black in a mass ratio of 1:1 (purity 99%, particle size ≤0.18mm), 4.5% thermosetting phenolic resin (carbonization rate 40%), and the remainder is 62.5% magnesium aluminum spinel (including three particle sizes: 40% for 1~3 mm, 30% for 0~1 mm, and 20% for ≤0.075mm). The molar ratio of alumina to active magnesium oxide in the aluminum ash powder is 1.2:1. Then, first mix the 1~3 mm magnesium aluminum spinel with the thermosetting phenolic resin evenly, and then add carbon, 0~1 mm magnesium aluminum spinel, and ≤0.075mm in sequence. mm magnesium aluminum spinel, pretreated aluminum ash powder, and active magnesium oxide are dry-mixed until homogeneous to obtain a refractory material compound. (3) Press the above-obtained refractory material mixture under a pressure of 200 MPa for 5 min to obtain a refractory green body; (4) The refractory green obtained above is kept at 180°C for 24 h and then naturally cooled to room temperature to obtain magnesium aluminum spinel-carbon refractory.

[0035] Example 4 (1) Take aluminum ash once and ball mill it for 8 hours at a speed of 400 r / min. Then mix the ball-milled aluminum ash with deionized water at a solid-liquid mass ratio of 1:5. Stir and wash for 2.5 hours at 70℃ and 500 r / min. Vacuum filter. Repeat the stirring-washing-vacuum filtration operation 4 times. Place the filter residue in a 100℃ drying oven and dry it to constant weight to obtain pretreated aluminum ash powder (total content of Al2O3+Al(OH)3+Al 85%, total content of chloride+fluoride 0.6%). (2) Weigh the raw materials according to the following mass fractions: 25% pretreated aluminum ash powder, 10% active magnesium oxide (purity 96.5%, particle size ≤0.075mm), 18% flake graphite (purity 99%, particle size ≤0.18mm), 5% thermosetting phenolic resin (carbonization rate 35%), and the remainder is 42% magnesium aluminum spinel (including three particle sizes: 1~3 mm particle size accounts for 35% of magnesium aluminum spinel, 0~1 mm particle size accounts for 35% of magnesium aluminum spinel, and ≤0.075mm particle size accounts for 30% of magnesium aluminum spinel). The molar ratio of alumina to active magnesium oxide in the aluminum ash powder is 1.4:1. Then, first mix the 1~3 mm magnesium aluminum spinel with the thermosetting phenolic resin evenly, and then add carbon, 0~1 mm magnesium aluminum spinel, and ≤0.075mm particle size in sequence. mm magnesium aluminum spinel, pretreated aluminum ash powder, and active magnesium oxide are dry-mixed until homogeneous to obtain a refractory material compound. (3) Press the above-obtained refractory material mixture under a pressure of 250 MPa for 8 min to obtain a refractory green body; (4) The refractory green obtained above is kept at 200℃ for 30 h and then naturally cooled to room temperature to obtain magnesium aluminum spinel-carbon refractory.

[0036] Comparative Example 1 The difference between this comparative example and Example 1 is that no pre-treated aluminum ash powder was added in step (2), while the rest of the operations were the same as in Example 1.

[0037] The magnesium-aluminate spinel-carbon refractory materials obtained in Example 1 and Comparative Example 1 were subjected to oxidation tests after being treated at 1400℃ for 2 h. The results are shown in the figure. Figure 1 It can be seen that the oxide layer thickness of the refractory material obtained in Example 1 is smaller than that of Comparative Example 1, indicating that treating primary aluminum ash with the method described in this invention can significantly improve the oxidation resistance of existing magnesium aluminum spinel-carbon refractory materials, and further realize the resource utilization of industrial solid waste.

Claims

1. A method for preparing magnesium aluminum spinel-carbon refractory materials based on primary aluminum ash, characterized in that: Includes the following steps: (1) The primary aluminum ash is ball-milled, washed with water, vacuum filtered and dried to obtain pretreated aluminum ash powder; (2) The pretreated aluminum ash powder, magnesium raw materials, magnesium aluminum spinel, carbon and binder are mixed to obtain refractory material mixture; (3) The refractory material mixture is pressed into shape to obtain a refractory green body; (4) The refractory green body is cured to obtain the finished magnesium aluminum spinel-carbon refractory.

2. The method according to claim 1, characterized in that: In step (1), the ball milling time is 1~10 h and the ball milling speed is 100~500 r / min; the ball milled aluminum ash is mixed with deionized water at a solid-liquid mass ratio of 1:3~6, and stirred and washed at 300~600 r / min at 30~80℃ for 1~3 h, followed by vacuum filtration. The stirring, washing and vacuum filtration are repeated 2~5 times; the filter residue obtained by vacuum filtration is dried at 70~110℃ to constant weight to obtain pretreated aluminum ash powder.

3. The method according to claim 1, characterized in that: In step (1), the total content of Al2O3, Al(OH)3 and Al in the pretreated aluminum ash powder is ≥80%, and the total content of chloride and fluoride is ≤1%.

4. The method according to claim 1, characterized in that: In step (2), by mass fraction, the pretreated aluminum ash powder is 1%~30%, magnesium raw material is 0.4%~12%, carbon is 3%~20%, binder is 3%~6%, and magnesium aluminum spinel is 32%~92.6%.

5. The method according to claim 1, characterized in that: In step (2), the magnesium raw material is active magnesium oxide with a purity of ≥96% and a particle size of ≤0.075 mm.

6. The method according to claim 1, characterized in that: In step (2), the carbon is one or more of flake graphite or carbon black, with a purity ≥99% and a particle size ≤0.18 mm.

7. The method according to claim 1, characterized in that: In step (2), the binder is a thermosetting phenolic resin with a carbonization rate of 30% to 50%.

8. The method according to claim 1, characterized in that: In step (2), the magnesium aluminum spinel includes three particle sizes, wherein a particle size of 1~3 mm accounts for 30%~50% of the magnesium aluminum spinel, a particle size of 0~1 mm accounts for 20%~40% of the magnesium aluminum spinel, and a particle size ≤0.075 mm accounts for 10%~30% of the magnesium aluminum spinel.

9. The method according to claim 1, characterized in that: In step (3), the pressing is carried out under a pressure of 100~300 MPa and a holding time of 10 s~10 min.

10. The method according to claim 1, characterized in that: In step (4), the curing conditions are to keep the temperature at 150~220℃ for 12~36 h and then cool it to room temperature.

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