Method for preparing brown aluminum oxide by smelting chromium-aluminum spinel
By using chromium aluminum spinel smelting and modified sodium citrate dispersion technology, the problems of raw material impurity fluctuations and high energy consumption in traditional brown fused alumina production have been solved, and high-purity brown fused alumina powder with narrow particle size distribution has been prepared, expanding its application range.
Patent Information
- Application Number
- CN202511084661.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-04
- Publication Date
- 2025-11-18
AI Technical Summary
Traditional brown fused alumina production processes suffer from large fluctuations in raw material impurities, high energy consumption, and unstable product performance, making it difficult to prepare high-purity brown fused alumina using bauxite as a raw material.
Brown fused alumina was prepared by carbon reduction smelting using chromium aluminum spinel as raw material. The density difference between high-carbon metallic chromium and brown fused alumina was used for separation. The brown fused alumina powder was refined by combining wet ball milling and ultrasonic dispersion technology, and the particle size distribution was optimized by using modified sodium citrate dispersant.
The preparation of high-purity brown fused alumina with concentrated particle size distribution has been achieved, reducing production costs, broadening the application range of brown fused alumina, and improving product quality and stability.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of brown fused alumina production technology, and more specifically, this invention relates to a method for preparing brown fused alumina by smelting chromium aluminum spinel. Background Technology
[0002] Brown fused alumina (BFA), also known as brown fused alumina sand or corundum, is a synthetic high-strength abrasive and refractory material. Its main component is alumina (Al₂O₃), requiring an alumina purity greater than 90%, while the national standard GB / T 2478-2017 requires a minimum of 92%. It contains small amounts of impurities (such as silicon dioxide, iron oxide, and titanium oxide), giving it a brownish-red color, hence its name. As an important abrasive and refractory material in the industrial field, brown fused alumina has long relied on bauxite as its main raw material, produced through high-temperature electric arc furnace smelting. However, traditional processes face problems such as large fluctuations in raw material impurities, high energy consumption, and limited product performance. Traditional processes use bauxite (Al₂O₃ content approximately 60-85%) as raw material, adding coke and iron filings as reducing agents, and smelting in an electric arc furnace at 2000-2200℃. The large fluctuations in the content of impurities such as SiO₂ and Fe₂O₃ in bauxite lead to unstable product composition. In recent years, novel smelting technologies using chromium-aluminum spinel as raw material or additive have gradually attracted attention. This technology aims to optimize the microstructure, mechanical properties, and high-temperature stability of brown fused alumina by introducing chromium-containing composite oxides. Spinel acts as a nucleating agent, promoting the uniform growth of α-Al₂O₃ microcrystals and improving the material's density. The introduction of chromium can endow brown fused alumina with higher hardness and wear resistance. Summary of the Invention
[0003] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.
[0004] To achieve these and other advantages according to the present invention, a method for preparing brown fused alumina by smelting chromium aluminum spinel is provided, comprising the following steps:
[0005] Step 1: Crush the chromium aluminum spinel into chromium aluminum spinel particles. The chromium aluminum spinel contains 75-85% aluminum oxide and 8-18% chromium oxide.
[0006] Step 2: Mix the chromium aluminum spinel particles with carbon particles to obtain a mixture;
[0007] Step 3: Place the mixture into the bottom of the electric arc furnace and compact it;
[0008] Step 4: Use three-phase graphite electrodes for smelting; after smelting, continuously circulate cooling water to the electric arc furnace for a period of time, and then allow it to cool naturally; dismantle the furnace, clean and separate the brown corundum and high-carbon metallic chromium, and pack them.
[0009] Preferably, in step one, the particle size of the chromium aluminum spinel particles is less than 8 mm.
[0010] Preferably, in step two, the mass ratio of chromium aluminum spinel to carbon particles is 80-120:1-5.
[0011] Preferably, in step four, the three-phase graphite electrodes are inserted into the mixture and arranged in a triangular symmetrical pattern, with the position of the three-phase graphite electrodes adjusted according to the smelting conditions of the material during smelting.
[0012] Preferably, in step four, the smelting current is greater than 3000A.
[0013] Preferably, in step four, the ratio of total smelting time to the type of mixture is 1-1.5 h:1 t.
[0014] Preferably, in step four, the continuous cooling water flow time is 12–36 hours, and the natural cooling time is 12–36 hours.
[0015] Preferably, the smelting temperature in step four is 2000–2200°C.
[0016] Preferably, in steps three and four, 4 to 6 tons of mixed material are first added, and then the mixed material is gradually added according to the smelting situation.
[0017] Preferably, in step four, the generated high-carbon metallic chromium has a higher density than brown fused alumina. The high-carbon metallic chromium is deposited at the bottom of the molten material, while most of the brown fused alumina is concentrated at the top of the molten material. The top of the molten material is crushed, precisely sorted, and refined, and then packaged to obtain the brown fused alumina product. After the high-carbon metallic chromium at the bottom of the molten material is separated, the brown fused alumina with high-carbon metallic chromium adhering to the middle of the molten material is used as the raw material for the next batch of smelting.
[0018] The specific methods for refining brown fused alumina include:
[0019] S1. Brown fused alumina particles with a particle size distribution of 20-50 mm, which are precisely sorted, are put into a ball mill jar. The mass ratio of brown fused alumina particles to stainless steel grinding balls is 1:2-4. Anhydrous ethanol is used as the ball milling medium. The amount of anhydrous ethanol is 0.8-1.2 times the mass of brown fused alumina particles. The ball milling is carried out at a speed of 500-800 rpm for 12-24 hours. After solid-liquid separation, the powder is washed and dried to obtain brown fused alumina powder.
[0020] S2. Brown fused alumina powder is added to deionized water, and modified sodium citrate dispersant is added. The temperature is raised to 60-80℃, and ultrasonic dispersion is carried out at 60-120kHz for 6-12 hours. Then, solid-liquid separation is performed, and the powder is washed and dried to obtain fine brown fused alumina powder. The mass ratio of brown fused alumina powder, deionized water, and modified sodium citrate dispersant is 6-12:250-500:0.05-1.
[0021] The preparation method of the modified sodium citrate dispersant used in S2 includes:
[0022] S21. Dissolve sodium citrate and polyethylene glycol-4000 in N,N-dimethylformamide to obtain a mixed solution for later use; wherein, the ratio of sodium citrate, polyethylene glycol-4000 and N,N-dimethylformamide is 5-8g:1-3g:25-100mL.
[0023] S22. Add concentrated H2SO4 to the mixture, reflux at 130-150℃ for 6-12 hours, cool to precipitate the product, wash with ethanol to remove unreacted polyethylene glycol-4000, and vacuum dry to obtain modified sodium citrate; the volume ratio of concentrated H2SO4 to N,N-dimethylformamide is 0.5-1:25-100.
[0024] The present invention has at least the following beneficial effects: The present invention uses chromium aluminum spinel containing chromium trioxide impurities as raw material (aluminum trioxide content 75-85%, chromium trioxide content 8-18%), and adopts a carbon reduction smelting method to reduce the chromium trioxide impurities in the chromium aluminum spinel to high-carbon metallic chromium. This not only removes most of the chromium trioxide impurities, making the generated aluminum-containing product meet the impurity requirements of brown fused alumina, but also takes advantage of the fact that the density of the generated high-carbon metallic chromium is greater than that of brown fused alumina, which facilitates the separation of high-carbon metallic chromium from brown fused alumina, greatly simplifying the process and saving production costs.
[0025] This invention refines smelted brown fused alumina using a wet ball milling combined with ultrasonic dispersion process. This process yields brown fused alumina powder with a concentrated particle size distribution and smaller particle size, reducing its SPAN value ((D90-D10) / D50) to below 1.8 and significantly narrowing the particle size distribution. Specifically, the ultrasonic dispersion uses modified citric acid as a dispersant. Polyethylene glycol-4000 (PEG-4000) segments are linked to sodium citrate via ester bonds, enhancing the steric hindrance and hydrophilicity of sodium citrate. Citrate ions (-COO-) are adsorbed onto the surface of brown fused alumina through electrostatic interactions. The long chains of PEG-4000 form a 5-10 nm thick hydration layer in water, rapidly spreading across the surface of the brown fused alumina particles. The modified sodium citrate, through the synergistic effects of enhanced steric hindrance, optimized anchoring adsorption, and controlled interfacial properties, significantly improves the dispersion effect of brown fused alumina, narrowing the particle size distribution to the submicron to micron level. Meanwhile, the refinement of brown fused alumina powder not only improves product quality and stability, but also greatly expands its application range, enabling brown fused alumina powder to be used in sapphire and silicon wafer polishing and sandblasting, preparation of wear-resistant coatings and ceramic / metal composite materials, and as a catalyst carrier.
[0026] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation
[0027] The present invention will now be described in further detail so that those skilled in the art can implement it based on the description.
[0028] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.
[0029] Example 1
[0030] This embodiment provides a method for preparing brown corundum by smelting chromium aluminum spinel, characterized by the following steps:
[0031] Step 1: Crush the chromium aluminum spinel into chromium aluminum spinel particles. The chromium aluminum spinel contains 82.03% aluminum oxide and 12.11% chromium oxide.
[0032] Step 2: Mix chromium aluminum spinel particles and carbon particles in a mass ratio of 25:1 to obtain a mixture.
[0033] Step 3: Place 6 tons of mixture into the bottom of the electric arc furnace and compact it;
[0034] Step 4: Electrolytic smelting is performed using three-phase graphite electrodes. The three-phase graphite electrodes are inserted into the mixture and arranged in a triangular symmetrical pattern. The position of the three-phase graphite electrodes is adjusted according to the melting situation of the material during smelting. The smelting current is 3500A, and the smelting temperature is 2000℃. Then, 4t of mixture is gradually added according to the smelting situation, and the smelting time is 10h. After smelting, cooling water is continuously circulated through the electric arc furnace for 24h, followed by natural cooling for 24h. The generated high-carbon metallic chromium has a higher density than brown fused alumina. The high-carbon metallic chromium is deposited at the bottom of the molten material, while most of the brown fused alumina is concentrated at the top. The upper part of the molten material is crushed, precisely sorted, and refined, and then packaged to obtain the brown fused alumina product. After separating the high-carbon metallic chromium at the bottom of the molten material, the brown fused alumina with high-carbon metallic chromium adhering to the middle part of the molten material is used as raw material for the next batch of smelting. The main component contents of the brown fused alumina obtained in this embodiment are shown in Table 1.
[0035] Table 1. Content of major components in brown fused alumina
[0036]
[0037] As can be seen from the table above, the Al2O3 content in the brown fused alumina prepared in this embodiment reached 96.37%, which meets the requirements of the national standard GB / T 2478-2017.
[0038] Example 2
[0039] The brown fused alumina obtained in Example 1 is refined in this example, and the specific methods include:
[0040] S1. 10 kg of precisely sorted brown fused alumina particles with a particle size distribution of 20-50 mm were put into a ball mill jar. 20 kg of stainless steel grinding balls and 8 kg of anhydrous ethanol were used as the ball milling medium. The mixture was ball milled at 600 rpm for 12 h. After solid-liquid separation, the powder was washed and dried to obtain brown fused alumina powder.
[0041] S2. Add 600g of brown fused alumina powder to 25000mL of deionized water, add 5g of modified sodium citrate dispersant, heat to 80℃, and ultrasonically disperse at 60kHz for 7h. Then, separate the solid and liquid, wash and dry to obtain fine brown fused alumina powder.
[0042] The preparation method of the modified sodium citrate dispersant used in S2 includes:
[0043] S21. Dissolve 80g sodium citrate and 20g polyethylene glycol-4000 in 250mL N,N-dimethylformamide to obtain a mixed solution for later use.
[0044] S22. Add 5 mL of concentrated H2SO4 to the mixture, reflux at 150 °C for 6 h, cool and precipitate the product, wash with ethanol to remove unreacted polyethylene glycol-4000, and vacuum dry at 0.5 Pa and 60 °C to obtain modified sodium citrate.
[0045] Example 3
[0046] The brown fused alumina obtained in Example 1 is refined in this example, and the specific methods include:
[0047] S1. 10 kg of finely sorted brown fused alumina particles with a particle size distribution of 20-50 mm were put into a ball mill jar. The amount of stainless steel grinding balls was 25 kg and the amount of anhydrous ethanol was 10 kg. The mixture was ball-milled at 800 rpm for 12 h. After solid-liquid separation, the powder was washed and dried to obtain brown fused alumina powder.
[0048] S2. Add 800g of brown fused alumina powder to 3000mL of deionized water, add 10g of modified sodium citrate, heat to 80℃, and ultrasonically disperse at 80kHz for 8h. Then, separate the solid and liquid, wash and dry to obtain fine brown fused alumina powder.
[0049] The preparation method of the modified sodium citrate used in S2 includes:
[0050] S21. Dissolve 50g sodium citrate and 10g polyethylene glycol-4000 in 250mL N,N-dimethylformamide to obtain a mixed solution for later use.
[0051] S22. Add 5 mL of concentrated H2SO4 to the mixture, reflux at 150 °C for 6 h, cool and precipitate the product, wash with ethanol to remove unreacted polyethylene glycol-4000, and vacuum dry at 0.5 Pa and 60 °C to obtain modified sodium citrate.
[0052] Comparative Example 1
[0053] The brown fused alumina obtained in Example 1 was further refined in this comparative example. The specific methods included:
[0054] S1. 10 kg of precisely sorted brown fused alumina particles with a particle size distribution of 20-50 mm were put into a ball mill jar. 20 kg of stainless steel grinding balls and 8 kg of anhydrous ethanol were used as the ball milling medium. The mixture was ball milled at 600 rpm for 12 h. After solid-liquid separation, the powder was washed and dried to obtain brown fused alumina powder.
[0055] S2. Add 600g of brown fused alumina powder to 25000mL of deionized water, add 5g of sodium citrate dispersant, heat to 80℃, and ultrasonically disperse at 60kHz for 7h. Then, separate the solid and liquid, wash and dry to obtain fine brown fused alumina powder.
[0056] Comparative Example 2
[0057] The brown fused alumina obtained in Example 1 was further refined in this comparative example. The specific methods included:
[0058] S1. 10 kg of precisely sorted brown fused alumina particles with a particle size distribution of 20-50 mm were put into a ball mill jar. 20 kg of stainless steel grinding balls and 8 kg of anhydrous ethanol were used as the ball milling medium. The mixture was ball milled at 600 rpm for 12 h. After solid-liquid separation, the powder was washed and dried to obtain brown fused alumina powder.
[0059] S2. Add 600g of brown fused alumina powder to 25000mL of deionized water, add 4g of sodium citrate and 1g of polyvinyl alcohol-4000, heat to 80℃, and ultrasonically disperse at 60kHz for 7h. Then, separate the solid and liquid, wash and dry to obtain fine brown fused alumina powder.
[0060] The particle size distribution of the refined brown fused alumina powders in Examples 2, 3, Comparative Example 1, and Comparative Example 2 was measured, and the results are shown in Table 2.
[0061] Table 2. Particle size distribution of brown fused alumina powder for each sample.
[0062]
[0063]
[0064] As can be seen from the table above, the brown fused alumina powder obtained in Examples 2 and 3 by wet ball milling followed by dispersion with modified sodium citrate has a more concentrated particle size distribution and a smaller particle size, significantly higher than the particle size data of the undispersed powder and Comparative Examples 1 and 2. In Comparative Examples 1 and 2, the unmodified sodium citrate relies solely on electrostatic repulsion and lacks the steric hindrance effect brought by PEG-4000 grafting, resulting in weaker anti-agglomeration ability. Therefore, although the particle size of the dispersed brown fused alumina powder is reduced to some extent, the particle size concentration is still relatively high.
[0065] The number of devices and processing scale described herein are for the purpose of simplifying the description of the invention. Applications, modifications, and variations of the invention will be readily apparent to those skilled in the art.
[0066] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.
Claims
1. A method for preparing brown fused alumina by smelting chromium aluminum spinel, characterized in that, Includes the following steps: Step 1: Crush chromium aluminum spinel into chromium aluminum spinel particles with an aluminum oxide content of 75-85% and a chromium oxide content of 8-18%. Step 2: Mix the chromium aluminum spinel particles with carbon particles to obtain a mixture; Step 3: Place the mixture into the bottom of the electric arc furnace and compact it; Step 4: Use three-phase graphite electrodes for smelting; after smelting, continuously circulate cooling water to the electric arc furnace for a period of time, and then allow it to cool naturally; dismantle the furnace, clean and separate the brown corundum and high-carbon metallic chromium, and pack them.
2. The method for preparing brown fused alumina by smelting chromium aluminum spinel as described in claim 1, characterized in that, In step one, the particle size of the chromium aluminum spinel particles is less than 8 mm.
3. The method for preparing brown fused alumina by smelting chromium aluminum spinel as described in claim 1, characterized in that, In step two, the mass ratio of chromium aluminum spinel to carbon particles is 80-120:1-5.
4. The method for preparing brown fused alumina by smelting chromium aluminum spinel as described in claim 1, characterized in that, In step four, the three-phase graphite electrodes are inserted into the mixture and arranged in a triangular symmetrical pattern. The position of the three-phase graphite electrodes is adjusted according to the smelting conditions of the material during the smelting process.
5. The method for preparing brown corundum by smelting chromium aluminum spinel as described in claim 1, characterized in that, In step four, the smelting current is greater than 3000A and the smelting temperature is 2000-2200℃.
6. The method for preparing brown corundum by smelting chromium aluminum spinel as described in claim 1, characterized in that, In step four, the ratio of total smelting time to the type of mixed material is 1-1.5 h: 1 t.
7. The method for preparing brown corundum by smelting chromium aluminum spinel as described in claim 1, characterized in that, In step four, the cooling water is continuously circulated for 12 to 36 hours, and the natural cooling time is 12 to 36 hours.
8. The method for preparing brown corundum by smelting chromium aluminum spinel as described in claim 1, characterized in that, In steps three and four, 4 to 6 tons of mixed material are first added, and then the mixed material is gradually added according to the smelting situation.
9. The method for preparing brown corundum by smelting chromium aluminum spinel as described in claim 1, characterized in that, Step four also includes refining the brown fused alumina. Specific methods for refining the brown fused alumina include: S1. Brown fused alumina particles with a particle size distribution of 20-50 mm, which are precisely sorted, are put into a ball mill jar. The mass ratio of brown fused alumina particles to stainless steel grinding balls is 1:2-4. Anhydrous ethanol is used as the ball milling medium. The amount of anhydrous ethanol is 0.8-1.2 times the mass of brown fused alumina particles. The ball milling is carried out at a speed of 500-800 rpm for 12-24 hours. After solid-liquid separation, the powder is washed and dried to obtain brown fused alumina powder. S2. Brown fused alumina powder is added to deionized water, and modified sodium citrate dispersant is added. The temperature is raised to 60-80℃, and ultrasonic dispersion is carried out at 60-120kHz for 6-12 hours. Then, solid-liquid separation is performed, and the powder is washed and dried to obtain fine brown fused alumina powder. The mass ratio of brown fused alumina powder, deionized water, and modified sodium citrate dispersant is 6-12:250-500:0.05-1. The preparation method of the modified sodium citrate dispersant used in S2 includes: S21. Dissolve sodium citrate and polyethylene glycol-4000 in N,N-dimethylformamide to obtain a mixed solution for later use; wherein, the ratio of sodium citrate, polyethylene glycol-4000 and N,N-dimethylformamide is 5-8g:1-3g:25-100mL. S22. Add concentrated H2SO4 to the mixture, reflux at 130-150℃ for 6-12 hours, cool to precipitate the product, wash with ethanol to remove unreacted polyethylene glycol-4000, and vacuum dry to obtain modified sodium citrate; the volume ratio of concentrated H2SO4 to N,N-dimethylformamide is 0.5-1:25-100.
10. The method for preparing brown corundum by smelting chromium aluminum spinel as described in claim 1, characterized in that, In step four, the generated high-carbon metallic chromium has a higher density than brown fused alumina. The high-carbon metallic chromium is deposited at the bottom of the molten material, while most of the brown fused alumina gathers at the top of the molten material. The top of the molten material is crushed, precisely sorted, and refined, and then packaged to obtain the brown fused alumina product. After the high-carbon metallic chromium at the bottom of the molten material is separated, the brown fused alumina with high-carbon metallic chromium adhering to the middle of the molten material is used as the raw material for the next batch of smelting.