A method for preparing high-quality magnesium-aluminum refractory raw material by using aluminum thermal reduction magnesium smelting waste residue

Abstract

This invention discloses a method for preparing high-quality magnesium-aluminum refractory raw materials from aluminothermic reduction magnesium smelting waste, belonging to the field of high-value utilization technology of industrial solid waste. This application utilizes a unique "aerobic heat treatment" purification process to pre-eliminate the reactivity of aluminum, ensuring that metallic aluminum (Al) in the waste is completely oxidized to stable alumina (Al2O3). This effectively avoids and reduces bulging and cracking problems in subsequent products. Furthermore, by combining two directional transformation material design paths, the phase and properties of the final product are controlled, transforming hazardous waste into high-quality magnesium-aluminum refractory raw materials that can be directly used in mid-to-high-end refractory materials. This achieves the harmless treatment and efficient utilization of resources from aluminothermic reduction magnesium smelting waste.

Description

Technical Field

[0001] This invention relates to the field of high-value utilization technology of magnesium smelting waste, specifically a method for preparing high-quality magnesium-aluminum refractory raw materials by aluminothermic reduction of magnesium smelting waste. Background Technology

[0002] The aluminothermic reduction process involves the reduction reaction of aluminum and magnesium oxide at high temperatures to produce metallic magnesium and aluminum oxide. This method is one of the important processes for the industrial production of metallic magnesium.

[0003] The aluminothermic reduction process typically uses magnesite as raw material and excess aluminum powder as a reducing agent to produce metallic Mg through vacuum thermal reduction. During magnesia smelting, a large amount of magnesia slag rich in magnesium-aluminum spinel phase is generated. Effective recycling and utilization of this slag could not only solve the solid waste disposal problem but also achieve resource recycling. However, in practical applications, due to the residual metallic aluminum inside the magnesia slag, when it is used in refractory material construction (such as hydrated castables) or in high-temperature service environments, an internal reaction occurs (2Al + 6H₂O → 2Al(OH)₃ + 3H₂↑). This reaction produces gas, and under thermal shock conditions, the poor deformation capacity leads to volume stability problems such as bulging and cracking in the products, making it impossible to obtain refractory materials with good performance. This severely limits the industrial application of magnesia slag.

[0004] Therefore, developing an industrial technology that can eliminate the hazards of residual aluminum and stably transform magnesium smelting waste into high-performance refractory raw materials is of great significance for opening up a "green closed loop" in aluminothermic magnesium smelting and promoting cost reduction and efficiency improvement in the refractory materials industry. Summary of the Invention

[0005] Therefore, this invention provides a method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction of magnesium smelting waste slag. This method can eliminate residual metallic aluminum inside the magnesium smelting waste slag, effectively solve the problem of volume stability of the product, and obtain high-performance refractory raw materials.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesia slag includes the following steps:

[0008] S1. Crushing and grinding: The aluminothermic reduction magnesium smelting waste residue is crushed and ground to obtain waste residue powder;

[0009] S2. Aerobic heat treatment: The waste residue powder obtained in step S1 is subjected to aerobic heat treatment to obtain stabilized powder.

[0010] S3. Dual-path sintering conversion: The stabilized powder obtained in step S2 is mixed evenly with lime powder or spinel precursor powder and sintered at high temperature to obtain magnesium-aluminum refractory raw materials.

[0011] In the above technical solution, the aluminothermic reduction magnesium smelting waste slag is pulverized to increase its specific surface area, providing kinetic advantages for subsequent oxidation and sintering reactions; through a unique "aerobic heat treatment" purification process, the activity of aluminum is eliminated, and the metallic aluminum (Al) in the waste slag is completely oxidized into stable alumina (Al2O3), effectively avoiding and reducing bulging and cracking problems in subsequent products; combined with two directional conversion material design paths, the phase and properties of the final product are controlled, transforming hazardous waste slag into magnesium-aluminum raw materials that can be directly used in mid-to-high-end refractory materials.

[0012] Preferably, in step S3: the stabilized powder is mixed with lime powder, and after molding, high-temperature sintering and grinding, spinel-aluminate cement composite powder is obtained, wherein the lime powder is one or a mixture of quicklime and limestone.

[0013] In the above technical solution, the stabilized powder is mixed with the calcium source of lime powder (CaO or CaCO3 provides CaO), and then sintered at high temperature. The spinel-aluminate cement composite powder prepared by this route has a phase composition including magnesium aluminum spinel phase and calcium aluminate cement mineral phase (such as CA, CA2), and has hydration hardening ability, and can be used as a functional bonding material.

[0014] Preferably, in step S3: the stabilized powder and spinel precursor micro powder are mixed evenly, and after molding, high-temperature sintering and crushing, synthetic magnesium aluminum spinel clinker is obtained, wherein the spinel precursor micro powder is one or a mixture of two of industrial alumina powder and lightly calcined magnesium oxide powder.

[0015] In the above technical solution, industrial alumina is used as the aluminum source due to its high reactivity, while lightly calcined magnesia (active MgO) is used as the magnesium source, whose lattice activation effect is beneficial for low-temperature synthesis and densification. By mixing the stabilized powder with spinel precursor micro-powder (industrial Al2O3 micro-powder or industrial MgO micro-powder) and then sintering at high temperature, the synthetic magnesium-aluminum spinel clinker prepared by this route has a well-developed magnesium-aluminum spinel as its main crystalline phase and can be used as a high-performance refractory aggregate and matrix powder.

[0016] Preferably, the particle size of the waste residue powder is ≤0.088mm, and the D50 particle size of the lime powder is ≤5μm.

[0017] In the above technical solution, the ultrafine lime powder can form a large contact interface with the waste residue powder, ensuring that the calcium-aluminum reaction proceeds rapidly and effectively at the microscale. At the same time, the ultrafine lime powder can promote the formation of the liquid phase at high temperature, which can reduce the high-temperature sintering temperature required for synthesis and shorten the holding time, thereby achieving the purpose of energy saving and consumption reduction.

[0018] Preferably, in step S2: the aerobic heat treatment temperature is 800-1400℃, and the holding time is 1-4h.

[0019] In the above technical solution, precise control of heat treatment temperature and holding time can ensure that the aluminum metal is fully oxidized, while avoiding adverse phase transformation or sintering of other useful phases in the waste residue (such as the already formed magnesium aluminum spinel).

[0020] Preferably, the lime powder is a mixture of quicklime powder and limestone powder in a mass ratio of 2:1.

[0021] In the above technical solution, quicklime (CaO) is an active oxide obtained by high-temperature calcination. After micronization (D50≤5μm), it has a large specific surface area and chemical activity, making it a fast and efficient reactant in the system. During the high-temperature sintering stage, quicklime powder can quickly react with alumina (Al2O3) in the waste residue powder to generate calcium aluminate cement phases (such as CA, CA2), which is the key to giving the product hydraulic bonding ability. The main component of limestone powder is calcium carbonate (CaCO3), which is chemically stable at room temperature and does not easily hydrate. During the high-temperature sintering process, it can decompose to provide a secondary calcium source: CaCO3→CaO +CO2↑. The newly generated CaO in this process has high activity and can participate in the reaction as a supplementary calcium source. This "delayed" way of providing active calcium source helps to promote the reaction in a wider temperature range, reduce the formation of harmful low-melting phases at high temperatures, and improve the refractory performance and mechanical strength of the product. At the same time, the generated gas can obtain a uniform microporous structure, providing deformation space for the expansion and contraction of the material volume.

[0022] Preferably, after the stabilized powder and spinel precursor micro powder are mixed evenly, the molar ratio of MgO / Al2O3 in the material composition is 0.8-1.5:1.

[0023] In the above technical solution, by precisely controlling the molar ratio of MgO / Al2O3, the materials can react fully to obtain magnesium aluminum spinel clinker with high bulk density.

[0024] Preferably, after the stabilized powder and spinel precursor micro powder are mixed evenly, a mixed powder is obtained, and the mixed powder is coated with a polyvinyl alcohol solution.

[0025] In the above technical solution, although the powder has been pre-mixed, different components (such as waste residue powder, alumina, and magnesium oxide powder) have differences in density and particle size, which can easily lead to segregation in subsequent processing. The polyvinyl alcohol (PVA) coating layer is like forming a "gel coat" on the particle surface, which can more firmly "fix" the particles of different components together, maintain the uniformity of mixing, and ensure that the chemical reaction proceeds more uniformly at the microscale. At the same time, PVA is an organic polymer, which will be completely decomposed and burned off during the subsequent high-temperature sintering process (usually in the range of 500-700℃). After its decomposition, it leaves a microporous structure in the green body, which can improve the thermal shock resistance of the refractory material.

[0026] Preferably, the polyvinyl alcohol solution also includes sodium erythritol, the mass fraction of polyvinyl alcohol in the polyvinyl alcohol solution is 4-6%, and the mass ratio of sodium erythritol to polyvinyl alcohol is 0.8-1.2:5.

[0027] In the above technical solution, the addition of sodium erythritol significantly reduces the viscosity index of the polyvinyl alcohol solution, ensuring uniform wetting and coating of each powder particle, preventing clumping or uneven coating. Simultaneously, a key characteristic of sodium erythritol is its ability to crosslink or chelate with metal ions, rapidly forming a gel on the particle surface. This microscopically enhances the cohesive strength and toughness of the polyvinyl alcohol coating layer, creating an interpenetrating network between the stabilized powder and the spinel precursor microparticles, effectively improving the overall reactivity of the mixed powder and the thermal shock resistance of the refractory material. Therefore, the combined use of polyvinyl alcohol and sodium erythritol can yield refractory materials with both microporous structure and mechanical strength, achieving a synergistic effect of "1+1>2".

[0028] Preferably, the amount of polyvinyl alcohol solution added is 4-6% of the total mass of the mixed powder.

[0029] In the above technical solution, by precisely controlling the amount of PVA added and the concentration of the solution, it can achieve a suitable coating amount and coating uniformity, leaving a uniformly distributed microporous structure after sintering, thereby improving the deformation capacity and thermal shock resistance of the refractory material.

[0030] The technical solution of the present invention achieves the following beneficial technical effects:

[0031] 1. This invention completely solves the volume stability problem caused by residual metallic aluminum in aluminothermic reduction magnesium smelting waste slag through the "aerobic heat treatment" process, clearing a key obstacle for the high-value utilization of waste slag. On this basis, two directional conversion paths are innovatively designed, which not only realize the harmless treatment of magnesium smelting waste slag, but also transform it into magnesium-aluminum refractory raw materials with clear application scenarios and high added value, truly turning waste into treasure. This provides strong technical support for the green and sustainable development of the aluminothermic magnesium smelting industry, and also opens up a new source of low-cost, high-performance raw materials for the refractory materials industry.

[0032] 3. In the dual-path conversion, a spinel-aluminate cement composite powder with both magnesium aluminum spinel phase and calcium aluminate cement mineral phase is prepared by composite sintering with lime micro powder. This powder has excellent hydration and hardening ability and can be used as a high-performance binder in the field of refractory materials. By mixing and sintering with spinel precursor micro powder at a specific magnesium-aluminum molar ratio, a well-developed magnesium aluminum spinel clinker with high bulk density and good heat resistance is obtained. This clinker can be used as a high-quality aggregate and matrix powder for mid-to-high-end refractory materials. This conversion path meets the urgent needs of the metallurgical and refractory materials industry for low carbonization and circular economy under the "dual carbon" target. Attached Figure Description

[0033] Figure 1 XRD phase analysis diagram of the synthesized magnesium aluminum spinel clinker obtained in Example 1 of this invention;

[0034] Figure 2 XRD phase analysis diagram of the spinel-aluminate cement composite powder obtained in Example 2 of this invention. Detailed Implementation

[0035] Example 1

[0036] A method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesia slag includes the following steps:

[0037] S1. Crushing treatment: 10 kg of aluminothermic reduction magnesium smelting waste residue (XRD shows that the main phase is MgAl2O4) is crushed, ball-milled, and passed through a 200-mesh sieve (≤74μm) to obtain waste residue powder;

[0038] S2. Aerobic heat treatment: The waste residue powder obtained in step S1 is placed in an air atmosphere furnace, heated to 1200℃ at 5℃ / min and held for 2 hours to obtain stabilized powder.

[0039] S3. Sintering Conversion: The stabilized powder obtained in step S2 is mixed evenly with 1.5 kg of lightly calcined magnesium oxide powder to obtain a mixed powder. The molar ratio of MgO / Al2O3 in the mixed powder is 1.2:1. Then, 5% of the total mass of the mixed powder is added to a polyvinyl alcohol solution. The mass percentage of each component in the polyvinyl alcohol solution is as follows: 5% polyvinyl alcohol, 1% sodium erythritol, and the balance water. After the polyvinyl alcohol solution and the mixed powder are mixed evenly, they are pressed into shape under a pressure of 100 MPa to obtain a cylindrical blank with a diameter of 50×50 mm. The blank is placed in a high-temperature electric furnace and heated to 1700℃ at a rate of 5℃ / min. After sintering at this temperature for 3 hours, it is cooled to room temperature with the furnace. The sintered block is then crushed to obtain synthetic magnesium aluminum spinel clinker.

[0040] like Figure 1 XRD phase analysis showed that the phases of the obtained synthetic magnesium aluminum spinel clinker were magnesium aluminum spinel and a small amount of magnesium oxide.

[0041] Example 2

[0042] A method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesia slag includes the following steps:

[0043] S1. Crushing treatment: 10 kg of aluminothermic reduction magnesium smelting waste residue (XRD shows that the main phase is MgAl2O4) is crushed, ball-milled, and passed through a 200-mesh sieve (≤74μm) to obtain waste residue powder;

[0044] S2. Aerobic heat treatment: The waste residue powder obtained in step S1 is placed in an air atmosphere furnace, heated to 1200℃ at 5℃ / min and held for 2 hours to obtain stabilized powder.

[0045] S3. Sintering Conversion: The stabilized powder obtained in step S2 is mixed evenly with 0.9 kg of lime powder to obtain a mixed powder. The lime powder is a mixture of quicklime powder and limestone powder in a mass ratio of 2:1, and the D50 particle size of the lime powder is ≤5 μm. The mixed powder is then pressed into a cylindrical blank with a diameter of Φ50×50 mm under a pressure of 100 MPa. The blank is placed in a high-temperature electric furnace and heated to 1500℃ at a rate of 5℃ / min. After sintering at this temperature for 5 hours, the blank is cooled to room temperature with the furnace. The sintered block is then crushed and ground in a ball mill to a specific surface area ≥4000 cm². 2 / g, spinel-aluminate cement composite powder was obtained.

[0046] like Figure 2 XRD phase analysis showed that the phases of the obtained spinel-aluminate cement composite powder were magnesium aluminum spinel (MgAl2O4), magnesium oxide (MgO), calcium aluminate (CA) and dicalcium aluminate (CA2).

[0047] Example 3

[0048] The only difference between this embodiment and Embodiment 1 is that in step S3, the mixed powder is not coated with a polyvinyl alcohol solution; that is, the polyvinyl alcohol solution is replaced with water, as detailed below:

[0049] A method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesia slag includes the following steps:

[0050] S1. Crushing treatment: 10 kg of aluminothermic reduction magnesium smelting waste residue (XRD shows that the main phase is MgAl2O4) is crushed, ball-milled, and passed through a 200-mesh sieve (≤74μm) to obtain waste residue powder;

[0051] S2. Aerobic heat treatment: The waste residue powder obtained in step S1 is placed in an air atmosphere furnace, heated to 1200℃ at 5℃ / min and held for 2 hours to obtain stabilized powder.

[0052] S3, Sintering Conversion: The stabilized powder obtained in step S2 is mixed evenly with 1.5 kg of lightly calcined magnesium oxide powder to obtain a mixed powder. The molar ratio of MgO / Al2O3 in the mixed powder is 1.2:1. Then, 5% of the total mass of water is added to the mixed powder. After the water and mixed powder are mixed evenly, the mixture is pressed into a cylindrical blank with a diameter of 50×50 mm under a pressure of 100 MPa. The blank is placed in a high-temperature electric furnace and heated to 1700℃ at a rate of 5℃ / min. After sintering at this temperature for 3 hours, the blank is cooled to room temperature with the furnace. The sintered block is then crushed to obtain synthetic magnesium aluminum spinel clinker.

[0053] Example 4

[0054] The only difference between this embodiment and Embodiment 1 is that sodium erythritol was not added to the polyvinyl alcohol solution in step S3, as detailed below:

[0055] A method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesia slag includes the following steps:

[0056] S1. Crushing treatment: 10 kg of aluminothermic reduction magnesium smelting waste residue (XRD shows that the main phase is MgAl2O4) is crushed, ball-milled, and passed through a 200-mesh sieve (≤74μm) to obtain waste residue powder;

[0057] S2. Aerobic heat treatment: The waste residue powder obtained in step S1 is placed in an air atmosphere furnace, heated to 1200℃ at 5℃ / min and held for 2 hours to obtain stabilized powder.

[0058] S3. Sintering Conversion: The stabilized powder obtained in step S2 is mixed evenly with 1.5 kg of lightly calcined magnesium oxide powder to obtain a mixed powder. The molar ratio of MgO / Al2O3 in the mixed powder is 1.2:1. Then, 5% of the total mass of the mixed powder is added to a polyvinyl alcohol solution. The mass percentage of each component in the polyvinyl alcohol solution is as follows: 5% polyvinyl alcohol and the balance water. After the polyvinyl alcohol solution and the mixed powder are mixed evenly, they are pressed into a cylindrical blank with a pressure of 100 MPa to obtain a Φ50×50 mm cylindrical blank. The blank is placed in a high-temperature electric furnace and heated to 1700℃ at a rate of 5℃ / min. After holding at the temperature for 3 hours, it is cooled to room temperature with the furnace. The sintered block is crushed to obtain synthetic magnesium aluminum spinel clinker.

[0059] Example 5

[0060] The only difference between this embodiment and Embodiment 1 is that in step S3, the polyvinyl alcohol solution is replaced with sodium erythritol solution, as detailed below:

[0061] A method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesia slag includes the following steps:

[0062] S1. Crushing treatment: 10 kg of aluminothermic reduction magnesium smelting waste residue (XRD shows that the main phase is MgAl2O4) is crushed, ball-milled, and passed through a 200-mesh sieve (≤74μm) to obtain waste residue powder;

[0063] S2. Aerobic heat treatment: The waste residue powder obtained in step S1 is placed in an air atmosphere furnace, heated to 1200℃ at 5℃ / min and held for 2 hours to obtain stabilized powder.

[0064] S3. Sintering and Conversion: The stabilized powder obtained in step S2 is mixed evenly with 1.5 kg of lightly calcined magnesium oxide powder to obtain a mixed powder. The molar ratio of MgO / Al2O3 in the mixed powder is 1.2:1. Then, 5% of the total mass of the mixed powder sodium erythritol solution is added. The mass fraction of sodium erythritol in the sodium erythritol solution is 1%. After the sodium erythritol solution and the mixed powder are mixed evenly, they are pressed into shape under a pressure of 100 MPa to obtain a cylindrical blank with a diameter of 50×50 mm. The blank is placed in a high-temperature electric furnace and heated to 1700℃ at a rate of 5℃ / min. After holding at the temperature for 3 hours, it is cooled to room temperature with the furnace. The sintered block is crushed to obtain synthetic magnesium aluminum spinel clinker.

[0065] The synthetic magnesium-aluminate spinel clinker obtained in Examples 1 and 3-5 was used in refractory bricks, and the strength retention rate after three thermal shock cycles (1100℃) was tested. The specific test results are shown in Table 1.

[0066] Table 1

[0067]

[0068] As can be seen from Examples 1 and 3-5 and the data in Table 1, when the synthetic magnesium aluminum spinel clinker obtained in Examples 1 and 3-5 is used in refractory bricks, the strength retention rate of the refractory bricks after 3 thermal shocks is above 36.2%, indicating that the synthetic magnesium aluminum spinel clinker obtained in this invention has good thermal shock resistance.

[0069] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesia slag, characterized in that, Includes the following steps: S1. Crushing and grinding: The aluminothermic reduction magnesium smelting waste residue is crushed and ground to obtain waste residue powder; S2. Aerobic heat treatment: The waste residue powder obtained in step S1 is subjected to aerobic heat treatment to obtain stabilized powder. S3. Dual-path sintering conversion: The stabilized powder obtained in step S2 is mixed evenly with lime powder or spinel precursor powder and sintered at high temperature to obtain magnesium-aluminum refractory raw materials.

2. The method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesium smelting waste slag according to claim 1, characterized in that, In step S3: the stabilized powder is mixed with lime powder, and after molding, high-temperature sintering and grinding, spinel-aluminate cement composite powder is obtained. The lime powder is one or a mixture of quicklime and limestone.

3. The method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesium smelting waste slag according to claim 1, characterized in that, In step S3: the stabilized powder and spinel precursor micro powder are mixed evenly, and after molding, high-temperature sintering and crushing, synthetic magnesium aluminum spinel clinker is obtained. The spinel precursor micro powder is one or a mixture of two of industrial alumina powder and lightly calcined magnesium oxide powder.

4. The method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesium smelting waste slag according to claim 2, characterized in that, The particle size of the waste residue powder is ≤0.088mm, and the D50 particle size of the lime powder is ≤5μm.

5. The method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesium smelting waste slag according to claim 4, characterized in that, In step S2: the aerobic heat treatment temperature is 800-1400℃, and the holding time is 1-4h.

6. The method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesium smelting waste slag according to claim 4, characterized in that, Lime powder is a mixture of quicklime powder and limestone powder in a mass ratio of 2:

1.

7. The method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesium smelting waste slag according to claim 3, characterized in that, After the stabilized powder and spinel precursor micro powder are mixed evenly, the molar ratio of MgO / Al2O3 in the material composition is 0.8-1.5:

1.

8. The method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesium smelting waste slag according to claim 7, characterized in that, After the stabilized powder and spinel precursor micro powder are mixed evenly, a mixed powder is obtained, which is then coated with a polyvinyl alcohol solution.

9. The method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesium smelting waste slag according to claim 8, characterized in that, The polyvinyl alcohol solution also contains sodium erythritol, and the mass fraction of polyvinyl alcohol in the polyvinyl alcohol solution is 4-6%, with the mass ratio of sodium erythritol to polyvinyl alcohol being 0.8-1.2:

5.

10. The method for preparing high-quality magnesium-aluminum refractory raw materials using aluminothermic reduction magnesium smelting waste slag according to claim 9, characterized in that, The amount of polyvinyl alcohol solution added is 4-6% of the total mass of the mixed powder.

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