Preparation method of multi-variety magnesium oxide and fluidized roasting device

Abstract

The invention belongs to the technical field of inorganic material preparation, and particularly relates to a preparation method of multi-variety magnesium oxide and a fluidized roasting device. The preparation method of the multi-variety magnesium oxide provided by the invention comprises the following steps: mixing magnesite particles and a return ash material, and carrying out fluidized roasting to obtain magnesium oxide, the mass of the magnesite particles is m1, the mass of the ash returning material is m2, and the adding proportion R of the ash returning material is equal to m2 / (m1 + m2) * 100%; when the magnesium oxide is building material powder, the adding proportion R of the ash returning material is controlled to be 10-30%; and when the magnesium oxide is chemical powder, the adding proportion R of the ash return material is controlled to be 0-9%. The method can be used for preparing magnesium oxide of building material powder and chemical powder, the roasting time is shortened, and the production efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of inorganic material preparation technology, specifically relating to a method for preparing various types of magnesium oxide and a fluidized bed roasting apparatus. Background Technology

[0002] Magnesium oxide, as an important inorganic chemical raw material, has wide applications in various fields such as building materials and chemicals. In the building materials industry, magnesium oxide is mainly used to produce magnesium-based building materials, such as magnesia cement and fireproof boards. Magnesium oxide is required to have moderate activity, good dispersibility, and a certain particle size distribution to ensure the strength, water resistance, and other properties of the building materials. In the chemical industry, magnesium oxide is used to manufacture catalysts, rubber reinforcing agents, and electronic materials, requiring high standards for purity, particle size uniformity, and specific surface area.

[0003] Traditional methods for preparing magnesium oxide (MgO) often employ fixed-bed calcination, which suffers from problems such as uneven heat transfer, difficulty in temperature control, and low production efficiency. Furthermore, traditional methods typically use single process conditions, producing only one type of MgO product with specific properties, failing to meet the diverse needs of different fields. Producing MgO products with different properties requires different preparation processes and equipment, increasing production costs and wasting resources. In addition, a certain amount of recycled ash is generated during MgO production; this material is usually treated as waste, further increasing production costs and environmental pressure.

[0004] Fluidized bed roasting technology has advantages such as high heat and mass transfer efficiency, uniform temperature, and easy control, enabling materials to fully contact the gas in a fluidized state and achieve a rapid and uniform roasting reaction. However, in the preparation of magnesium oxide, existing fluidized bed roasting technologies often require long roasting times (1.5~2.5 hours or more) to ensure product quality, which limits the improvement of production efficiency. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for preparing magnesium oxide of various varieties and a fluidized bed roasting apparatus. The preparation method provided by this invention can prepare magnesium oxide of building material powder and chemical powder, shorten the roasting time, and improve production efficiency.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing various types of magnesium oxide, comprising the following steps: Magnesia particles and recycled ash are mixed and then subjected to fluidized bed roasting to obtain magnesium oxide; the recycled ash is the recycled ash generated during the magnesium oxide production process. Let the mass of the magnesite particles be m1, the mass of the returned ash material be m2, and the addition ratio of the returned ash material R = m2 / (m1+m2)×100%; When magnesium oxide is used as building material powder, the proportion of returned ash material added, R, is controlled at 10-30%; when magnesium oxide is used as chemical powder, the proportion of returned ash material added, R, is controlled at 0-9%.

[0007] Preferably, when magnesium oxide is a building material powder, the fluidized bed calcination temperature is 650~750℃ and the holding time is 0.5~0.8h.

[0008] Preferably, when magnesium oxide is a chemical powder, the fluidized bed calcination temperature is 800~900℃ and the holding time is 0.3~0.6h.

[0009] Preferably, during the fluidized bed roasting process, high-temperature air is introduced as the fluidizing gas, and the fluidization number is controlled at 3 to 5; the fluidization number is the ratio of the actual operating gas velocity to the critical fluidizing gas velocity; the temperature of the high-temperature air is 300 to 400°C.

[0010] Preferably, before the fluidized bed roasting, the process further includes preheating the equipment used for the fluidized bed roasting to 250~350°C.

[0011] Preferably, the magnesite particles have a particle size of 30-100 mesh.

[0012] Preferably, the purity of the magnesite particles is not less than 90%.

[0013] The present invention also provides a fluidized bed roasting apparatus for the preparation method described in the above technical solution, comprising a fluidized bed roasting furnace 1, a control instrument 2, a gas distribution plate 3, a heating device 4, and a gas circulation system 7; The fluidized bed roasting furnace 1 is installed inside the heating device 4; the gas distribution plate 3 is installed inside the fluidized bed roasting furnace 1; the control instrument 2 is connected to the heating device 4; and the gas circulation system 7 is connected to the discharge port 5 of the fluidized bed roasting furnace 1.

[0014] Preferably, the gas distribution plate 3 is a quartz sintered permeable plate with a three-layer structure; the three-layer structure includes a protective layer, a filter layer and a reinforcing layer stacked in sequence.

[0015] Preferably, the protective layer is made of quartz sand with a thickness of 2-5 mm; the filter layer is made of fine quartz powder with a thickness of 5-10 mm, a porosity of 30-45%, and a pore size of 5-50 μm; and the reinforcing layer is made of coarse quartz sand with a thickness of 10-20 mm.

[0016] This invention provides a method for preparing various types of magnesium oxide, comprising the following steps: Magnesia particles and recycled ash are mixed and then subjected to fluidized bed roasting to obtain magnesium oxide; the recycled ash is the recycled ash generated during the magnesium oxide production process. Let the mass of the magnesite particles be m1, the mass of the returned ash material be m2, and the addition ratio of the returned ash material R = m2 / (m1+m2)×100%; When magnesium oxide is used as building material powder, the proportion of returned ash material added, R, is controlled at 10-30%; when magnesium oxide is used as chemical powder, the proportion of returned ash material added, R, is controlled at 0-9%.

[0017] Beneficial effects: 1. Shorten roasting time: By optimizing the fluidization state of fluidized bed roasting, the heat and mass transfer between materials and gas is made more efficient. At the same time, by reasonably controlling the roasting temperature, the roasting time is significantly shortened and the production efficiency is improved while ensuring product quality.

[0018] 2. Product diversification: By adjusting the temperature, fluidization state, and proportion of ash-returning materials added during fluidized bed calcination, this invention can flexibly produce magnesium oxide products that meet the different needs of the building materials and chemical industries, thus achieving product diversification of magnesium oxide.

[0019] 3. High resource utilization rate: By using the ash material from the magnesium oxide production process as one of the raw materials, waste emissions are reduced, resource utilization rate is improved, and production costs are lowered.

[0020] 4. Flexible process: The method of the present invention is flexible and can adjust the product type at any time according to market demand without changing large-scale production equipment and processes, thus improving the adaptability and flexibility of production.

[0021] 5. Stable product quality: By precisely controlling each process parameter, the quality of the prepared magnesium oxide products can be guaranteed to be stable, meeting the stringent requirements of different fields for magnesium oxide performance. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a fluidized bed roasting apparatus, where 1-fluidized bed roasting furnace, 2-control instrument, 3-gas distribution plate, 4-heating device, 5-discharge port, 6-flow meter, and 7-gas circulation system. Detailed Implementation

[0023] This invention provides a method for preparing various types of magnesium oxide, comprising the following steps: Magnesia particles and recycled ash are mixed and then subjected to fluidized bed roasting to obtain magnesium oxide; the recycled ash is the recycled ash generated during the magnesium oxide production process. Let the mass of the magnesite particles be m1, the mass of the returned ash material be m2, and the addition ratio of the returned ash material R = m2 / (m1+m2)×100%; When magnesium oxide is used as building material powder, the proportion of returned ash material added, R, is controlled at 10-30%; when magnesium oxide is used as chemical powder, the proportion of returned ash material added, R, is controlled at 0-9%.

[0024] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0025] This invention involves mixing magnesite particles and recycled materials, followed by fluidized bed roasting to obtain magnesium oxide.

[0026] As one implementation method, let the mass of magnesite particles be m1, the mass of the returned ash material be m2, and the addition ratio of the returned ash material R = m2 / (m1+m2)×100%; when the magnesium oxide is building material powder, the addition ratio R of the returned ash material is controlled at 10~30%, and in a specific embodiment it is 16.7% or 23.1%; when the magnesium oxide is chemical powder, the addition ratio R of the returned ash material is controlled at 0~9%, and in a specific embodiment it is 4.8%.

[0027] In one embodiment, the magnesite particles have a particle size of 30-100 mesh, specifically 50 mesh or 80 mesh in this embodiment; the purity of the magnesite particles is not less than 90%, specifically 92% or 93% in this embodiment; the magnesite particles are prepared by sequentially crushing and screening the magnesite to obtain the particles. This invention does not specifically limit the crushing and screening process; processes well-known in the art can be used. The magnesite particles within the above-mentioned particle size range used in this invention are beneficial for achieving a good fluidization state during fluidized bed roasting, thereby improving heat and mass transfer efficiency.

[0028] In one implementation method, the returned ash material is a collected return material generated during the industrial production of magnesium oxide. The main component of the returned ash material is magnesium oxide, and it also contains a small amount of impurities, such as magnesium carbonate and magnesium hydroxide. The returned ash material is a ground material; the particle size of the returned ash material is 30-100 mesh, and in a specific embodiment, it is 50 mesh or 80 mesh; the particle size of the returned ash material is similar to that of magnesite particles.

[0029] In one implementation, before the fluidized bed roasting, the process further includes: preheating the equipment used for fluidized bed roasting to 250-350°C, specifically 300°C or 320°C in this embodiment; the preheating involves introducing high-temperature air into the equipment used for fluidized bed roasting; the temperature of the high-temperature air is 300-400°C, specifically 350°C or 380°C in this embodiment. The high-temperature air allows the furnace temperature to reach 250-350°C in a short time, removing any moisture and impurities that may be present in the furnace, while simultaneously creating favorable conditions for the subsequent roasting reaction.

[0030] In one implementation, high-temperature air is introduced as a fluidizing gas during the fluidized bed roasting process, and the fluidization number is controlled at 3 to 5, specifically 3.5, 4, or 4.5 in this embodiment; the fluidization number is the ratio of the actual operating gas velocity to the critical fluidizing gas velocity; the temperature of the high-temperature air is 300 to 400°C, specifically 350°C or 380°C in this embodiment.

[0031] This invention involves uniformly adding the mixed raw materials into a preheated fluidized bed roasting furnace through the feed inlet, while simultaneously continuing to introduce high-temperature air as the fluidizing gas. The air flow rate is controlled to maintain the material in a highly fluidized state within the furnace, with the fluidization number (the ratio of the actual gas velocity to the initial fluidizing gas velocity) controlled between 3 and 5. This highly fluidized state enhances heat and mass transfer between the material and the gas, resulting in a more rapid reaction.

[0032] In one implementation method, when magnesium oxide is a building material powder, the fluidized bed calcination temperature is 650~750℃, specifically 680℃ or 700℃ in this embodiment, and the holding time is 0.5~0.8h, specifically 0.6h or 0.7h in this embodiment; when magnesium oxide is a chemical powder, the fluidized bed calcination temperature is 800~900℃, specifically 820℃ or 850℃ in this embodiment, and the holding time is 0.3~0.6h, specifically 0.4h or 0.5h in this embodiment.

[0033] Fluidized bed roasting refers to a process in which mineral particles come into contact with gas within a device, and their motion is adjusted by the gas velocity, creating a fluidized state with vigorous up-and-down movement. This state is characterized by good gas-solid dispersion and a large contact area, which improves mineral activity while drastically shortening roasting time. Comparative experiments between fluidized bed tubular roasters and traditional roasting methods show that roasting time is reduced from "hours" to "minutes." During fluidized bed roasting, components such as magnesium carbonate in magnesite and return ash rapidly decompose to generate magnesium oxide, while some magnesium oxide undergoes a certain degree of sintering, giving the product a certain level of activity.

[0034] When magnesium oxide is used as a building material powder, according to GB / T 19281-2014 "Method for Determination of Magnesium Oxide Activity", the citric acid activity (1 min) of the obtained magnesium oxide product is 280~300 mL / 4g-MgO, which meets the activity requirements of building material grade magnesium oxide (industry general index: ≥250 mL / 4g-MgO) and has good dispersibility. Using a Malvern Mastersizer 3000 laser particle size analyzer, the particle size distribution variation coefficient CV is 12~14%. 90 / D 10=2.5, with dispersion superior to commonly used indicators in the building materials industry: CV≤15%, D90 / D10≤3, meeting the requirements of the building materials industry. During the roasting process, part of the exhaust gas is recycled through a gas circulation system to improve heat utilization efficiency.

[0035] When magnesium oxide is used as a chemical powder, the calcination temperature is controlled at 800~900℃, and the calcination time is 0.3~0.6h. The higher temperature and optimized fluidization state allow magnesium oxide crystals to grow rapidly in a short time, forming a more complete crystal structure and improving the purity of the magnesium oxide product. ICP-MS (Inductively Coupled Plasma Mass Spectrometry) analysis shows that the purity of magnesium oxide is ≥99.0%, and the total impurity content (Fe2O3+Al2O3+SiO2) is ≤0.5%, meeting the purity requirements for chemical-grade magnesium oxide (≥98.5%). This also improves the particle size uniformity of magnesium oxide; laser particle size analysis shows that D... 50 =10±2μm, coefficient of variation (CV)=10%, which is better than the general index in the chemical industry: CV≤12%, while maintaining a high specific surface area. Measured by the Micromeritics TriStar II BET analyzer, the specific surface area is 22~25m². 2 / g (higher than the commonly used value in the chemical industry: ≥15m) 2 (g)), which meets the requirements of the chemical industry for magnesium oxide.

[0036] In one implementation method, after fluidized bed roasting, the process further includes: stopping the flow of high-temperature air, allowing the product to cool to room temperature, and then removing the product from the outlet; when the magnesium oxide is a building material powder, the product is directly pulverized and sieved to obtain building material powder with a particle size meeting the requirements; the particle size of the building material powder is 40-80 mesh; when the magnesium oxide is a chemical powder, the product is acid-washed, washed until neutral, and then dried, pulverized, and sieved sequentially; the reagent used for acid washing is hydrochloric acid solution; the concentration of the hydrochloric acid solution is 0.1-1.0 mol / L, specifically 0.5 mol / L in this embodiment; the acid washing temperature is from room temperature to 60°C, specifically 25°C in this embodiment, and the time is 10-60 min, specifically 30 min in this embodiment; the particle size of the building material powder is 20-60 mesh. This invention first uses dilute hydrochloric acid for acid washing to remove any possible impurities, then washes with deionized water until neutral, and then dries, pulverizes, and sieves to obtain high-purity chemical powder.

[0037] This invention uses magnesite as the main raw material, combined with some recycled ash, and employs fluidized bed roasting technology. By precisely controlling the roasting temperature, optimizing the fluidization state, and rationally controlling the proportion of recycled ash added, it achieves diversified production of magnesium oxide products while shortening the roasting time. It can produce building material powders that meet the needs of the building materials industry, as well as chemical powders that meet the standards of the chemical industry. This method is flexible, has high heat and mass transfer efficiency, effectively improves resource utilization, reduces production costs, and has significant economic and environmental benefits.

[0038] The present invention also provides a fluidized bed roasting apparatus for the preparation method described in the above technical solution, comprising a fluidized bed roasting furnace 1, a control instrument 2, a gas distribution plate 3, a heating device 4, and a gas circulation system 7; The fluidized bed roasting furnace 1 is installed inside the heating device 4; the gas distribution plate 3 is installed inside the fluidized bed roasting furnace 1; the control instrument 2 is connected to the heating device 4; and the gas circulation system 7 is connected to the discharge port 5 of the fluidized bed roasting furnace 1.

[0039] In one embodiment, the fluidized bed roasting apparatus further includes a flow meter 6 disposed at the outlet of the gas circulation system 7.

[0040] The control instrument 2 regulates the state of fluidization, i.e. the fluidization number, by controlling the gas volume, and thus adjusts the calcination temperature.

[0041] In one embodiment, the gas distribution plate 3 is a quartz sintered permeable plate with a three-layer structure; the three-layer structure includes a protective layer, a filter layer, and a reinforcing layer stacked sequentially; the protective layer is made of quartz sand with a thickness of 2-5 mm, specifically 2 mm in this embodiment; the quartz sand has a particle size of 0.5-1.5 mm, specifically 1 mm in this embodiment; the filter layer is made of fine quartz powder with a thickness of 5-10 mm, specifically 6 mm in this embodiment, a porosity of 30-45%, specifically 30% in this embodiment, and a pore size of 5-50 μm, specifically 20 μm in this embodiment; the fine quartz powder has a particle size of 50-150 μm, specifically 100 μm in this embodiment; the reinforcing layer is made of coarse quartz sand with a thickness of 10-20 mm, specifically 20 mm in this embodiment; the coarse quartz sand has a particle size of 2-5 mm, specifically 3 mm in this embodiment. In this embodiment of the invention, the quartz sintered breathable plate with a three-layer structure was purchased from Jinzhou Jintai Quartz Co., Ltd., and the model number is SQP-3-80.

[0042] The gas distribution plate is specially designed to ensure uniform gas distribution, guaranteeing good fluidization of materials in the furnace and reducing dead zones and channeling.

[0043] This invention employs optimized fluidized bed roasting technology and a specially designed gas distribution plate, which allows the material to fully contact the gas in a fluidized state, significantly improving heat and mass transfer efficiency, resulting in more uniform temperature and ensuring that the roasting reaction proceeds rapidly and evenly.

[0044] Quartz sintered permeable plates are filter materials with a special three-layer structure. This three-layer design gives them excellent filtration and permeability performance, typically including a protective layer, a filter layer, and a reinforcing layer. The protective layer is the outermost layer of the sintered plate, mainly serving to protect the inner filter and reinforcing layers. The filter layer is the core of the sintered plate, responsible for the actual filtration. The filter layer is usually porous, and the size and distribution of these pores determine the filtration efficiency and precision. The reinforcing layer is located below the filter layer, mainly serving to enhance the overall structural strength of the sintered plate. The design of the reinforcing layer gives the sintered plate high mechanical strength and overall rigidity, enabling it to withstand certain mechanical impact forces, making the sintered plate more stable and less prone to damage during use. The special three-layer structure of quartz sintered permeable plates not only ensures good filtration performance but also improves the product's service life and stability. Through special sintering processes and material selection, quartz sintered permeable plates perform excellently in various industrial applications, especially in situations requiring high-precision filtration and long-term stable operation.

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0046] Example 1: Preparation of building material powder 1. Raw material preparation: Select magnesite with a purity of 92%, crush and screen it to obtain magnesite particles of 50 mesh; collect the returned ash material and grind it to about 50 mesh; 2. Raw material mixing: Weigh 100kg of magnesite particles and 20kg of recycled ash material, mix them evenly, and at this time the proportion of recycled ash material added is R=20 / (100+20)×100%≈16.7%; 3. Construction and pretreatment of fluidized bed roasting equipment: Construct the fluidized bed roasting furnace (e.g., Figure 1 As shown), a specially designed gas distribution plate is used, which has a three-layer structure of quartz sintered permeable plate (purchased from Jinzhou Jintai Quartz Co., Ltd., model SQP-3-80). It includes a protective layer, a filter layer and a reinforcing layer stacked in sequence. The protective layer is made of quartz sand with a particle size of 1mm and a thickness of 2mm. The filter layer is made of fine quartz powder with a particle size of 100μm, a thickness of 6mm, a porosity of 30% and a pore size of 20μm. The reinforcing layer is made of coarse quartz sand with a particle size of 3mm and a thickness of 20mm. High-temperature air at a temperature of 350℃ is introduced into the furnace and preheated to 300℃. 4. Fluidized bed roasting: Add the mixed raw materials into the roasting furnace, introduce high-temperature air to make the material reach a highly fluidized state, control the fluidization number at 4, adjust the heating device to make the roasting temperature reach 700℃, and the roasting time is 0.6h; 5. Subsequent processing: After calcination, wait for the furnace temperature to drop to room temperature, remove the product, crush and sieve it to obtain building material powder with a particle size of 40-80 mesh.

[0047] Testing revealed that the building material powder exhibits moderate activity and good dispersibility. Laser particle size analysis showed CV=11%, D90=70μm, and D10=35μm, meeting the requirements for uniform mixing of building material powder and satisfying the application requirements in the building materials field. Furthermore, the calcination time is significantly reduced compared to traditional methods. The traditional static calcination method requires 1.5 hours to prepare building material powder, while this method only requires 0.6 hours, reducing the calcination time by 60%.

[0048] Example 2: Preparation of building material powder (different ash return ratios) 1. Raw material preparation: Same as in Example 1; 2. Raw material mixing: Weigh 100kg of magnesite particles and 30kg of recycled ash material, mix them evenly, and the proportion of recycled ash material added is R=30 / (100+30)×100%≈23.1%; 3. Construction and pretreatment of the fluidized bed roasting apparatus: Same as in Example 1; 4. Fluidized bed roasting: Add the mixed raw materials into the roasting furnace, introduce high-temperature air for fluidization, control the fluidization number at 4.5, adjust the heating device to make the roasting temperature reach 680℃, and the roasting time is 0.7h; 5. Subsequent processing: Same as in Example 1.

[0049] Testing revealed that the prepared building material powder met the building materials industry standards and the "building material grade" requirements of GB / T 18110-2019 "Light Magnesium Oxide": purity ≥90%, citric acid activity ≥250ml / 4g-MgO, and particle size 40-80 mesh (the test values ​​of this product all meet and exceed the standards). Compared with the product of Example 1, this example shows a certain improvement in strength. According to GB / T 17671-1999 "Test Method for Strength of Cement Mortar (ISO Method)," the 7-day compressive strength of the building material powder in this example is 35MPa, an increase of 16.7% compared to Example 1 (30MPa); the 28-day compressive strength is 42MPa, an increase of 14.3%. At the same time, the calcination time is further shortened. Traditional static calcination requires 1.5h, while this example requires 0.7h, a reduction of 53.3%; compared with Example 1 (0.6h), although the time is slightly longer, the strength improvement is significant.

[0050] Example 3: Preparation of chemical powder 1. Raw material preparation: Select magnesite with a purity of 93%, crush and screen it to obtain magnesite particles of 80 mesh; collect the returned ash material and grind it to about 80 mesh; 2. Raw material mixing: Weigh 100kg of magnesite particles and 5kg of returned ash material, mix them evenly, and the proportion of returned ash material added is R=5 / (100+5)×100%≈4.8%; 3. Construction and pretreatment of fluidized bed roasting equipment: Construct the fluidized bed roasting furnace (e.g., Figure 1 As shown), a specially designed gas distribution plate is used, which is a three-layer sintered permeable quartz plate (purchased from Jinzhou Jintai Quartz Co., Ltd., model SQP-3-80). It includes a protective layer, a filter layer and a reinforcing layer stacked in sequence. The protective layer is made of quartz sand with a particle size of 1mm and a thickness of 2mm. The filter layer is made of fine quartz powder with a particle size of 100μm, a thickness of 6mm, a porosity of 30% and a pore size of 20μm. The reinforcing layer is made of coarse quartz sand with a particle size of 3mm and a thickness of 20mm. High-temperature air at a temperature of 380℃ is introduced into the furnace and preheated to 320℃. 4. Fluidized bed roasting: Add the mixed raw materials into the roasting furnace, introduce high-temperature air to make the material reach a highly fluidized state, control the fluidization number at 3.5, adjust the heating device to make the roasting temperature reach 850℃, and the roasting time is 0.4h; 5. Subsequent processing: After roasting, wait for the furnace temperature to drop to room temperature, take out the product, and acid wash it with 0.5 mol / L dilute hydrochloric acid at 25℃ for 30 min. Then wash it with deionized water until neutral, and finally dry it at 105℃ for 2 h. After crushing and sieving, high-purity chemical powder with a particle size of 20-60 mesh is obtained.

[0051] Testing revealed that the chemical powder had a purity of over 99.5% and a large specific surface area, measured by a BET analyzer to be 25 m². 2 / g (Common specific surface area range for chemical grade magnesium oxide: 15~30m²) 2 / g, this product is at a relatively high level), meeting the requirements of the chemical industry, and the calcination time is significantly shortened (the traditional static calcination method for chemical powder requires 1.0h, while this method only requires 0.4h, shortening the calcination time by 60%).

[0052] Example 4: Preparation of chemical powder (under different calcination conditions) 1. Raw material preparation: Same as in Example 3; 2. Raw material mixing: Same as in Example 3; 3. Construction and pretreatment of the fluidized bed roasting apparatus: Same as in Example 3; 4. Fluidized bed roasting: Add the mixed raw materials to the roasting furnace, introduce high-temperature air for fluidization, control the fluidization number at 4, adjust the heating device to make the roasting temperature reach 820℃, and the roasting time is 0.5h; 5. Subsequent processing: Same as in Example 3.

[0053] Testing revealed that the prepared chemical powder exhibited better particle size uniformity (laser particle size analysis results: D50=8±1μm, coefficient of variation CV=8%, which is superior to Example 3 (CV=10%) (the more uniform the particle size, the higher the chemical reaction efficiency), and the purity was also maintained at a high level (ICP-MS analysis showed that the magnesium oxide purity was 99.2%, and the impurity content was ≤0.4%, meeting the requirements of "high-purity magnesium oxide" (≥99.0%) in the chemical industry), thus meeting the demand of the chemical industry for multiple varieties of magnesium oxide. Furthermore, the calcination time was further optimized, requiring 1.0 h in the traditional method, while this example requires only 0.5 h, a reduction of 50%; compared with Example 3 (0.4 h), the calcination temperature was reduced by 30℃ (from 850℃ to 820℃).

[0054] Comparative Example 1 The ash return ratio R=35% (outside the scope of this invention): the citric acid activity of the product decreased to 245mL / 4g-MgO (a decrease of 12.5% ​​compared to this invention), and the 7d compressive strength decreased to 30MPa (a decrease of 14.3%), verifying the optimization range of R=10%~20%. Magnesite particle size D 50 =120μm (outside the scope of this invention): Magnesium oxide purity decreased to 97.5% (a decrease of 1.5% compared to this invention), and specific surface area decreased to 18m². 2 / g (a decrease of 18.2%), verifying the importance of particle size control.

[0055] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing multi-variety magnesium oxide, characterized in that, Includes the following steps: Magnesia particles and recycled ash are mixed and then subjected to fluidized bed roasting to obtain magnesium oxide; the recycled ash is the recycled ash generated during the magnesium oxide production process. Let the mass of the magnesite particles be m1, the mass of the returned ash material be m2, and the addition ratio of the returned ash material R = m2 / (m1+m2)×100%; When magnesium oxide is used as building material powder, the proportion of returned ash material added, R, is controlled at 10-30%; when magnesium oxide is used as chemical powder, the proportion of returned ash material added, R, is controlled at 0-9%.

2. The preparation method according to claim 1, characterized in that, When magnesium oxide is used as building material powder, the fluidized bed calcination temperature is 650~750℃ and the holding time is 0.5~0.8h.

3. The preparation method according to claim 1, characterized in that, When magnesium oxide is a chemical powder, the fluidized bed calcination temperature is 800~900℃ and the holding time is 0.3~0.6h.

4. The preparation method according to claim 1, characterized in that, During the fluidized bed roasting process, high-temperature air is introduced as the fluidizing gas, and the fluidization number is controlled at 3 to 5; the fluidization number is the ratio of the actual operating gas velocity to the critical fluidizing gas velocity; the temperature of the high-temperature air is 300 to 400°C.

5. The preparation method according to claim 1, characterized in that, Before the fluidized bed roasting, the process further includes preheating the equipment used for the fluidized bed roasting to 250~350℃.

6. The preparation method according to claim 1, characterized in that, The magnesite particles have a particle size of 30-100 mesh.

7. The preparation method according to claim 1, characterized in that, The purity of the magnesite particles is not less than 90%.

8. A fluidized bed roasting apparatus for the preparation method according to any one of claims 1 to 7, characterized in that, It includes a fluidized bed roasting furnace (1), control instruments (2), gas distribution plate (3), heating device (4) and gas circulation system (7); The fluidized bed roasting furnace (1) is located inside the heating device (4); the gas distribution plate (3) is located inside the fluidized bed roasting furnace (1); the control instrument (2) is connected to the heating device (4); and the gas circulation system (7) is connected to the outlet (5) of the fluidized bed roasting furnace (1).

9. The fluidized bed roasting apparatus according to claim 8, characterized in that, The gas distribution plate (3) is a quartz sintered permeable plate with a three-layer structure; the three-layer structure includes a protective layer, a filter layer and a reinforcing layer stacked in sequence.

10. The fluidized bed roasting apparatus according to claim 9, characterized in that, The protective layer is made of quartz sand with a thickness of 2-5 mm; the filter layer is made of fine quartz powder with a thickness of 5-10 mm, a porosity of 30-45%, and a pore size of 5-50 μm; the reinforcing layer is made of coarse quartz sand with a thickness of 10-20 mm.

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