A method for preparing alumina refractory castables based on aluminum ash

Abstract

This invention discloses a method for preparing alumina refractory castables based on aluminum ash, comprising the following steps: using demetallized aluminum ash as raw material, the raw material is sequentially sieved, washed and desalted, dried, ground, and hydrolyzed and calcined to obtain aluminum ash a; then, aluminum ash a is mixed with NaOH solution to react, causing the alumina in aluminum ash a to dissolve and generate sodium aluminate solution, obtaining solution b; solution b is sequentially subjected to coarse filtration and fine filtration to remove insoluble residues, obtaining solution c; then, CO2 is introduced into solution c to adjust the pH value, causing solution c to react and generate aluminum hydroxide precipitate, obtaining precipitate d; then, precipitate d is washed and dealkalized to remove residual NaOH on the surface of precipitate d, obtaining precipitate e; finally, precipitate e is calcined at low temperature to obtain the finished alumina. This invention can improve the purity, specific surface area, and activity of alumina after preparation.

Description

Technical Field

[0001] This invention relates to an alumina refractory castable, and more particularly to a method for preparing an alumina refractory castable based on aluminum ash. Background Technology

[0002] During use, refractory castables are susceptible to the combined effects of slag penetration and alkali metal corrosion, leading to thin-layer damage, performance degradation, and severely impacting their service life. Analysis of the corrosion mechanism of refractory castables reveals that under high-temperature conditions, alumina in the refractory reacts chemically with alkali metals such as sodium and potassium to form aluminates. This causes volume expansion of the refractory, resulting in internal stress accumulation and crack propagation, leading to alumina detachment from grain boundaries and a sharp drop in alumina content on the refractory surface. Simultaneously, CaO-SiO2 components in the slag penetrate to the refractory surface through 5–20 μm capillary channels, forming a SiO2-enriched reaction layer. While this layer initially hinders penetration, under a reducing atmosphere, it readily reacts with elements such as sodium and potassium, accelerating the formation of low-melting-point phases and ultimately destroying the refractory structure. Due to the aforementioned limitations, the surface corrosion layer of refractory castables after long-term use exhibits significant compositional differences compared to the internal removal layer. The alumina content in the corrosion layer is generally 30-50% lower than that in the removal layer, and the SiO2 content in the corrosion layer is twice as high as that in the removal layer, which seriously affects the structural stability and service reliability of the refractory.

[0003] Building upon the above, alumina, as a core component of refractory castables, directly affects the overall corrosion resistance and erosion resistance of the refractory material due to its purity, specific surface area, and activity. Increasing the purity of alumina effectively reduces the likelihood of impurities damaging the main crystalline phase of alumina after reacting with alkali metals, thus preventing surface corrosion. Increasing the specific surface area of ​​alumina optimizes the sintering and filling effect of the refractory, refines the matrix pore size, blocks continuous capillary penetration channels, inhibits the intrusion of slag liquid phase along micropores into the material, and reduces abnormal enrichment of SiO2 and the formation of low-melting-point phases on the surface. Furthermore, increasing the activity of alumina allows for tighter bonding with the refractory matrix, preventing slag penetration and erosion due to a loose structure, further reducing the possibility of surface corrosion. Therefore, improving the purity, specific surface area, and activity of alumina materials has become a key research focus in the industry.

[0004] On the other hand, existing alumina preparation processes require the use of a constant-temperature water bath to hydrolyze aluminum ash in a high-temperature water bath environment to remove aluminum nitride from the ash. However, conventional constant-temperature water baths struggle to achieve stable hydrolysis of aluminum ash powder. This is because existing constant-temperature water baths primarily use two heating methods for hydrolysis: direct heating with electric heating tubes and external cavity medium heating. Direct heating involves inserting the heating tubes directly into the mixing tank to heat the water; while external cavity medium heating uses the mixing tank as an inner chamber, exchanging heat with the water inside by injecting a heat-conducting medium into the outer cavity. As the particle size of aluminum ash powder decreases, its adsorption capacity increases. This means that if direct heating with electric heating tubes is used, the powder will adhere directly to the surface of the heating tubes during hydrolysis, causing overheating and sintering, thus affecting the heating effect and lifespan of the heating tubes. If external cavity heating is used, the powder will easily accumulate on the inner wall and harden when heated, thus reducing the hydrolysis effect of the powder and hindering the heat exchange between the inner and outer media, thereby reducing its temperature control effect.

[0005] Secondly, the existing constant-temperature water bath mixing tanks, which use stirring rods for agitation, exhibit significant variations depending on the particle size of the powder. This is because if the stirring rods do not contact the tank walls during agitation, powder tends to accumulate on the walls and in dead zones, preventing continuous circulation with the powder in the center. Conversely, if a scraper-equipped mixing structure is used to scrape the tank walls, the scraper can compress and break down the powder, further refining the inner layer and compacting it into a dense, agglomerated layer, thus hindering hydrolysis. These limitations force manufacturers to increase the alumina particle size to mitigate these defects during alumina hydrolysis, ultimately affecting the decomposition of aluminum nitride.

[0006] Therefore, there is a need for an alumina preparation method that can improve the purity, specific surface area, and activity of alumina. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing alumina refractory castables based on aluminum ash. This method can improve the purity, specific surface area, and activity of the prepared alumina.

[0008] The technical solution of this invention: A method for preparing an alumina refractory castable based on aluminum ash, comprising the following steps:

[0009] A. Using demetallized aluminum ash as raw material, the raw material is sequentially subjected to sieving, water washing and desalination, drying and grinding and hydrolysis and calcination treatment to obtain a aluminum ash;

[0010] B. Mix aluminum ash (a) with NaOH solution to react, causing the aluminum oxide in aluminum ash (a) to dissolve and form sodium aluminate solution, thus obtaining solution (b);

[0011] C. Perform coarse filtration and fine filtration on solution b in sequence to remove insoluble residues in solution b, and obtain solution c;

[0012] D. CO2 is bubbled into solution c to adjust the pH value, causing solution c to react and form aluminum hydroxide precipitate, resulting in precipitate d;

[0013] E. Wash and dealkalize precipitate d to remove residual NaOH from its surface, yielding precipitate e.

[0014] F. The precipitate e is calcined at low temperature to obtain the finished alumina.

[0015] In the aforementioned method for preparing an alumina refractory castable based on aluminum ash, step A specifically includes the following steps:

[0016] A1. Using demetallized aluminum ash as raw material, the raw material is sieved through a screen to obtain a1 aluminum ash;

[0017] A2. A1 aluminum ash is washed and stirred three times with water at a solid-liquid ratio of 1:7. The water washing and stirring temperature is 50-80℃, and the time for each water washing and stirring is 60 minutes to obtain A2 aluminum ash.

[0018] A3. Place the a2 aluminum ash in an environment of 100-140℃ and dry for 3-4 hours, then grind the dried aluminum ash to less than 100 mesh to obtain a3 aluminum ash;

[0019] A4. Hydrolyze a3 aluminum ash at a solid-liquid ratio of 1:7 in a water temperature environment of 95℃ for 3 hours, and then calcine the hydrolyzed a3 aluminum ash at an environment of 800℃ for 2 hours to obtain a aluminum ash.

[0020] In the aforementioned method for preparing an alumina refractory castable based on aluminum ash, the mass fraction of the NaOH solution in step B is 10-15%, the mixing reaction temperature is 100℃, and the reaction time is 4 hours.

[0021] In the aforementioned method for preparing an alumina refractory castable based on aluminum ash, in step D, CO2 is introduced into solution c to adjust the pH value of solution c to 9.2, so that solution c reacts to generate aluminum hydroxide precipitate, and the reaction time is 3 hours.

[0022] In the aforementioned method for preparing an alumina refractory castable based on aluminum ash, in step E, the d precipitate is washed and dealkalized in a water temperature environment of 40°C. The solid-liquid ratio during each wash is 1:4, and the washing time is 15-20 minutes. After repeating the washing 5 times, the e precipitate is obtained.

[0023] In the aforementioned method for preparing an alumina refractory castable based on aluminum ash, in step F, the precipitate e is calcined at a constant temperature of 500-700℃ for 3 hours to obtain the finished alumina.

[0024] In the aforementioned method for preparing an alumina refractory castable based on aluminum ash, the aluminum ash in step A4 (a3) ​​is hydrolyzed by a water bath stirring mechanism. The water bath stirring mechanism includes an inner liner and an outer liner arranged in a nested configuration. A hydrolysis chamber is formed inside the inner liner, and a heating chamber is formed between the inner and outer liner. A partition is formed at the upper end of the inner liner, and a screen is formed at the lower end of the inner liner. Both the inner and outer liners are filled with reaction water, and the surface of the reaction water extends above the screen. A stirring assembly is provided in the middle of the hydrolysis chamber, and an inner vent pipe is connected to the top of the hydrolysis chamber. An inlet pipe and an outlet pipe are connected to the top of the heating chamber, and one end of the outlet pipe is connected to the inner vent pipe. A pressure regulating valve is provided on the outlet pipe.

[0025] The air inlet pipe is used to fill the heating chamber with pressurized air to create a pressure difference between the heating chamber and the hydrolysis chamber.

[0026] The reaction water in the heating chamber is used to flow into the inner liner through the screen section under the action of air pressure difference;

[0027] The pressure regulating valve is used to release pressure in the heating chamber after it is opened.

[0028] In the aforementioned method for preparing an alumina refractory castable based on aluminum ash, a first one-way valve is provided on the outgoing air pipe; a speed regulating valve, an electric ball valve, and a second one-way valve are respectively provided on the inlet air pipe, and an air bag is connected to the outer end of the inlet air pipe.

[0029] In the aforementioned method for preparing an alumina refractory castable based on aluminum ash, a heating tube, a temperature sensor, and a liquid level sensor are respectively provided in the heating chamber, wherein the heating tube forms an annular structure in the middle and is sleeved on the radial outer side of the inner liner.

[0030] In the aforementioned method for preparing an alumina refractory castable based on aluminum ash, an installation opening is formed in the middle of the top surface of the outer liner, a connecting ring is provided on the radially outer side of the installation opening, and an installation groove is formed between the connecting ring and the outer liner. The inner liner is installed into the outer liner through the installation opening, and the top of the inner liner is fastened to the installation groove by a stepped plate. A pressure cap is provided above the stepped plate, and a connecting ring is threaded around the pressure cap. A sealing plate is provided at the connection between the pressure cap, the connecting ring, and the stepped plate.

[0031] In the aforementioned method for preparing an alumina refractory castable based on aluminum ash, the hydrolysis chamber forms an inner pressure chamber above the reaction water, and the heating chamber forms an outer pressure chamber above the reaction water. The air inlet pipe fills the outer pressure chamber with pressurized air each time it is pressurized, so that the pressure in the outer pressure chamber is 15-25 kPa higher than that in the inner pressure chamber. Each filling time is 10-30 seconds, and the interval between two fillings is 2-10 minutes.

[0032] Compared with the prior art, the present invention has the following characteristics:

[0033] (1) The present invention uses demetallized aluminum ash as raw material. By limiting the raw material preparation process and parameters, it is possible to remove impurities and purify alumina in demetallized aluminum ash during the preparation process, that is, to remove soluble salts and impurity components in aluminum ash raw material, thereby effectively improving the purity of alumina after preparation.

[0034] Meanwhile, by sequentially performing water washing and desalination processes and hydrolysis processes on the raw materials in step A, soluble alkali metals and chlorofluorine impurities in the aluminum ash can be removed, preventing impurities from sintering and coating the alumina grains at high temperatures, thus avoiding passivation and deactivation of the alumina, thereby improving the activity of the alumina after preparation. By grinding the aluminum ash to below 100 mesh before subsequent processing, the specific surface area of ​​the alumina during hydrolysis can be increased, allowing the aluminum nitride in the aluminum ash to be fully decomposed, further increasing the alumina content of the aluminum ash after hydrolysis, and consequently increasing the contact area of ​​the aluminum ash in subsequent reactions, thereby improving the treatment effect of subsequent processes on alumina.

[0035] (2) By calcining the hydrolyzed aluminum ash at 800℃, the residual bound water, crystal water and volatile impurities in the aluminum ash can be removed more thoroughly, avoiding agglomeration during subsequent processing. At the same time, the residual aluminum nitride, carbides and other impurities in the aluminum ash are decomposed, improving the purity of the finished alumina product.

[0036] By controlling the calcination temperature of the e precipitate at 500-700℃, recrystallization and pore closure caused by high-temperature calcination of alumina can be avoided, so that alumina can maintain a rich micropore and pore structure after crystallization, thereby improving its specific surface area and activity.

[0037] (3) Based on the process of hydrolyzing aluminum ash below 100 mesh, by limiting the structure of the water bath stirring mechanism, the aluminum ash powder can be periodically filled with pressurized air through the air inlet pipe during the hydrolysis process, and the reaction water in the heating chamber can flow through the screen section to the hydrolysis chamber under the action of air pressure. The flow of reaction water can impact the aluminum ash powder accumulated on the inner wall of the inner liner, so that the powder can be kept in a flowing state under this action, effectively avoiding the long-term accumulation of powder. After the pressurization is completed, the heating chamber and the hydrolysis chamber can be connected by the cooperation of the air outlet pipe and the pressure regulating valve, and the air in the two chambers can be discharged outward together through the inner air outlet pipe, thereby realizing the depressurization function of the heating chamber.

[0038] (4) By matching the structure of the inner and outer liner, the heating tube for heating the reaction water and the temperature sensor for detecting the water temperature can be set in the heating chamber. At the same time, the heat exchange function is achieved by the circulation of the reaction water in the heating chamber and the hydrolysis chamber and the stirring of the stirring component. Thus, while ensuring the temperature control effect of the reaction water in the hydrolysis chamber, it effectively prevents aluminum ash from contacting the temperature sensor and the heating tube to form adhesion and sintering, thereby improving the working stability of the present invention.

[0039] (5) The structure of the air bag, air inlet pipe and speed control valve limits the air bag to maintain the set air pressure value. After the electric ball valve is opened, the air pressure in the heating chamber is rapidly increased in a short time by quickly filling with pressurized air. This causes the reaction water to flow faster under the action of air pressure and flushes away the aluminum ash powder accumulated on the edge and dead corner of the inner liner, further reducing the possibility of powder agglomeration. When the air pressure in the heating chamber is increased to the same as that of the air bag, the heating chamber can switch from pressurization to pressure holding state, so that the reaction water in the heating chamber can be continuously injected into the hydrolysis chamber under the action of air pressure, preventing the aluminum ash powder from re-accumulating in a short time. On this basis, the operator can also adjust the air intake efficiency of the air bag through the speed control valve, so that the flow rate of the reaction water at the moment of air intake can drive the aluminum ash powder to flow inward to contact the stirring component, without causing overpressure damage to the equipment. With the above combination, the present invention can effectively improve the hydrolysis effect of aluminum ash powder, so that the aluminum nitride in the aluminum ash can be fully decomposed during the hydrolysis process, and improve the purity of alumina after preparation.

[0040] Therefore, the present invention can improve the purity, specific surface area and activity of alumina after preparation. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the structure of Example 3;

[0042] Figure 2 This is the system schematic diagram of Example 3;

[0043] Figure 3 This is an electronic image of the refractory material corresponding to sample 1 in Experiment Example 2;

[0044] Figure 4 This is an electronic image of the refractory material corresponding to sample 2 in Experiment Example 2.

[0045] The labels in the attached diagram are as follows: 1-Inner liner, 2-Outer liner, 3-Hydrolysis chamber, 4-Heating chamber, 5-Stirring assembly, 6-Inner air outlet pipe, 7-Air inlet pipe, 8-Outer air outlet pipe, 9-Pressure regulating valve, 10-First check valve, 11-Speed ​​regulating valve, 12-Electric ball valve, 13-Second check valve, 14-Air tank, 15-Heating tube, 16-Temperature sensor, 17-Liquid level sensor, 18-Connecting ring, 19-Step plate, 20-Pressure cap, 21-Sealing sheet, 22-Inner pressure chamber, 23-Outer pressure chamber, 101-Separation section, 102-Screen section. Detailed Implementation

[0046] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0047] Example 1. A method for preparing an alumina refractory castable based on aluminum ash, comprising the following steps:

[0048] A. Using demetallized aluminum ash as raw material, the raw material is sequentially subjected to sieving, water washing and desalination, drying and grinding and hydrolysis and calcination treatment to obtain a aluminum ash;

[0049] B. Mix aluminum ash (a) with NaOH solution to react, causing the aluminum oxide in aluminum ash (a) to dissolve and form sodium aluminate solution, thus obtaining solution (b);

[0050] C. Perform coarse filtration and fine filtration on solution b in sequence to remove insoluble residues in solution b, and obtain solution c;

[0051] D. CO2 is bubbled into solution c to adjust the pH value, causing solution c to react and form aluminum hydroxide precipitate, resulting in precipitate d;

[0052] E. Wash and dealkalize precipitate d to remove residual NaOH from its surface, yielding precipitate e.

[0053] F. The precipitate e is calcined at low temperature to obtain the finished alumina.

[0054] Step A specifically includes the following steps:

[0055] A1. Using demetallized aluminum ash as raw material, the raw material is sieved through a 40-mesh sieve to remove large impurities, thus obtaining a1 aluminum ash.

[0056] A2. Mix a1 aluminum ash and water at a mass ratio of 1:7 and then wash and stir with water at a temperature of 50-80℃. Each washing and stirring session lasts for 60 minutes and is repeated 3 times to remove soluble salt impurities from a1 aluminum ash and obtain a2 aluminum ash.

[0057] A3. Place the a2 aluminum ash in an environment of 100-140℃ and dry for 3-4 hours, then grind the dried aluminum ash to less than 100 mesh to obtain a3 aluminum ash;

[0058] A4. Hydrolyze a3 aluminum ash at a solid-liquid ratio of 1:7 in a water environment at 95℃ for 3 hours, and then calcine the hydrolyzed a3 aluminum ash at 800℃ for 2 hours, so that the aluminum nitride in a3 aluminum ash is completely decomposed and aluminum oxide is generated, thus obtaining a aluminum ash.

[0059] In step B, the mass fraction of the NaOH solution is 10-15%, the mixing reaction temperature is 100℃, and the reaction time is 4 hours.

[0060] In step D, CO2 is introduced into solution c to adjust the pH value of solution c to 9.2, so that solution c reacts to form aluminum hydroxide precipitate, and the reaction time is 3 hours.

[0061] In step E, the d precipitate is washed and dealkalized in a water temperature environment of 40℃. The mass solid-liquid ratio is 1:4 for each wash, and the washing time is 15-20 minutes. After washing 5 times, the e precipitate is obtained.

[0062] In step F, the precipitate e is calcined at a constant temperature of 500-700℃ for 3 hours to obtain the finished alumina.

[0063] This embodiment uses demetallized aluminum ash as a raw material. By limiting the preparation process and parameters, impurities such as aluminum nitride, water-soluble salts, and insoluble residues in the demetallized aluminum ash can be stably removed, thereby effectively improving the purity, specific surface area, and activity of the finished alumina. This further promotes the bonding effect between alumina and other refractory matrices when used as a filler in refractory castables, alleviates surface corrosion and grain boundary spalling during use, and improves the corrosion resistance and erosion resistance of the refractory castables.

[0064] Example 2. A method for preparing an alumina refractory castable based on aluminum ash, comprising the following steps:

[0065] A. Using demetallized aluminum ash as raw material, the raw material is sequentially subjected to sieving, water washing and desalination, drying and grinding and hydrolysis and calcination treatment to obtain a aluminum ash;

[0066] B. Mix aluminum ash (a) with NaOH solution to react, causing the aluminum oxide in aluminum ash (a) to dissolve and form sodium aluminate solution, thus obtaining solution (b);

[0067] C. Perform coarse filtration and fine filtration on solution b in sequence to remove insoluble residues in solution b, and obtain solution c;

[0068] D. CO2 is bubbled into solution c to adjust the pH value, causing solution c to react and form aluminum hydroxide precipitate, resulting in precipitate d;

[0069] E. Wash and dealkalize precipitate d to remove residual NaOH from its surface, yielding precipitate e.

[0070] F. The precipitate e is calcined at low temperature to obtain the finished alumina.

[0071] Step A specifically includes the following steps:

[0072] A1. Using demetallized aluminum ash as raw material, the raw material is sieved through a 40-mesh sieve to remove large impurities, thus obtaining a1 aluminum ash.

[0073] A2. Mix a1 aluminum ash and water at a mass ratio of 1:7 and then wash and stir with water at a temperature of 60℃ for 60 minutes each time to remove soluble salt impurities from a1 aluminum ash. After washing and stirring three times, a2 aluminum ash is obtained.

[0074] A3. Dry the a2 aluminum ash at 105℃ for 4 hours. The moisture content of the dried a2 aluminum ash is ≤0.4%. Then grind the aluminum ash to less than 100 mesh to obtain a3 aluminum ash.

[0075] A4. Hydrolyze a3 aluminum ash at a solid-liquid ratio of 1:7 in a water temperature environment of 95℃ for 3 hours. Then place the hydrolyzed a3 aluminum ash in a muffle furnace and calcine it at a temperature of 800℃ for 2 hours, so that the aluminum nitride in a3 aluminum ash is completely decomposed and aluminum oxide is generated, thus obtaining a aluminum ash.

[0076] In step B, the mass fraction of the NaOH solution is 12%, the solid-liquid ratio of aluminum ash to NaOH solution is 1:5, the mixing reaction temperature is 100℃, and the reaction time is 4 hours.

[0077] In step C, solution b is first coarsely filtered through a 200-mesh filter cloth using a plate and frame press, so that the suspended solids content of solution b after coarse filtration is below 120 mg / L. Then, solution b is finely filtered with a precision filter at a filtration accuracy of 5 μm, so that the suspended solids content of solution b after fine filtration is below 5 mg / L, thus obtaining solution c.

[0078] In step D, CO2 is introduced into solution c to adjust the pH value of solution c to 9.2, so that solution c reacts to form aluminum hydroxide precipitate, and the reaction time is 3 hours.

[0079] In step E, the precipitate d is washed and dealkalized in a water temperature environment of 40℃. The solid-liquid ratio is 1:4 for each wash, and the washing time is 20 minutes. After washing 5 times, precipitate e is obtained.

[0080] In step F, the precipitate e is calcined at a constant temperature of 600℃ for 3 hours in a muffle furnace with a heating rate of 5℃ / min to obtain the finished alumina.

[0081] Compared to Example 1, this example further specifies the preparation process and parameters, thereby improving the preparation effect and stability of alumina, and enhancing the purity, specific surface area, and activity of the finished alumina. This allows it to effectively improve the corrosion resistance and erosion resistance of refractory castables when used as fillers, thus preventing corrosion damage during use.

[0082] Example 3. Water bath stirring mechanism, configured as follows: Figure 1-2 As shown, the aluminum ash in Examples 1 and 2 is hydrolyzed by the water bath stirring mechanism; specifically, it includes an inner liner 1 and an outer liner 2 arranged in a nested configuration. A hydrolysis chamber 3 is formed inside the inner liner 1, and a heating chamber 4 is formed between the inner liner 1 and the outer liner 2. A partition 101 is formed at the upper end of the side wall of the inner liner 1, and a screen 102 is formed at the lower end of the side wall and the bottom surface of the inner liner 1. The mesh size of the screen 102 is greater than 150 mesh to prevent the aluminum ash in the hydrolysis chamber 3 from flowing into the heating chamber 4. Both the inner liner 1 and the outer liner 2 contain... The chamber is filled with reaction water, the surface of which extends above the screen section 102. A stirring assembly 5 is provided in the middle of the hydrolysis chamber 3. An internal vent pipe 6 is connected to the top of the hydrolysis chamber 3. The outer end of the internal vent pipe 6 is connected to a waste gas treatment device. An electric ball valve is connected to the internal vent pipe 6. An inlet pipe 7 and an outlet pipe 8 are connected to the top of the heating chamber 4. One end of the outlet pipe 8 is connected to the internal vent pipe 6. A pressure regulating valve 9 is provided on the outlet pipe 8. The pressure regulating valve 9 can be an electric ball valve or a speed regulating valve.

[0083] The air inlet pipe 7 is used to fill the heating chamber 4 with pressurized air to create a pressure difference between the heating chamber 4 and the hydrolysis chamber 3.

[0084] The reaction water in the heating chamber 4 is used to flow into the inner liner 1 through the screen section 102 under the action of air pressure difference;

[0085] The pressure regulating valve 9 is used to release pressure in the heating chamber 4 after it is opened, so that the heating chamber 4 returns to the normal pressure state.

[0086] The outgoing air pipe 8 is equipped with a first one-way valve 10; the inlet air pipe 7 is equipped with a speed regulating valve 11, an electric ball valve 12, and a second one-way valve 13. The outer end of the inlet air pipe 7 is connected to an air tank 14, and the air tank 14 is connected to an air pressure sensor and an air pump. The operator adjusts the flow rate of pressurized air entering the heating chamber 4 through the speed regulating valve 11, so that the heating chamber 4 is rapidly pressurized after air intake and drives the reaction water to impact the aluminum ash powder accumulated on the inner wall of the liner. This causes the aluminum ash powder to flow inward with the reaction water and contact the stirring component 5, thereby realizing the continuous stirring of aluminum ash powder in different areas by the stirring component 5.

[0087] The heating chamber 4 is equipped with a heating tube 15, a temperature sensor 16, and a liquid level sensor 17. The heating tube 15 forms a ring structure in the middle and is fitted on the radial outer side of the inner liner 1. The two ends of the heating tube 15 extend vertically upward to the top of the heating chamber 4 and are connected to the driving power supply. The heating tube 15 is used to heat the reaction water and keep it at 95°C. The temperature sensor 16 is used to detect the water temperature of the reaction water in the heating chamber 4.

[0088] After the heating tube 15 heats the reaction water at the bottom of the heating chamber 4, the reaction water will form convection in the heating chamber 4 along the height direction under the action of temperature difference; at the same time, the reaction water in the heating chamber 4 will flow into the hydrolysis chamber 3 under the action of air pressure, and form mixed flow heat exchange with the stirring component 5, thereby achieving the same water temperature in the hydrolysis chamber 3 and the heating chamber 4.

[0089] The liquid level sensor 17 is used to detect the liquid level in the heating chamber 4. When the liquid level of the reaction water under high pressure reaches the first threshold, the liquid level sensor 17 triggers the electric ball valve 12 to close and the pressure regulating valve 9 to open, thereby balancing the gas pressure in the heating chamber 4 and the hydrolysis chamber 3. When the liquid level of the reaction water under normal pressure reaches the second threshold, the liquid level sensor 17 triggers an alarm and the operator replenishes the water.

[0090] An installation opening is formed in the middle of the top surface of the outer liner 2. A connecting ring 18 is provided on the radially outer side of the installation opening. An installation groove is formed between the connecting ring 18 and the outer liner 2. The inner liner 1 is installed into the outer liner 2 through the installation opening. The top of the inner liner 1 is fastened to the installation groove by a step plate 19. A pressure cap 20 is provided above the step plate 19. The connecting ring 18 is bolted around the pressure cap 20. An annular sealing plate 21 is provided at the connection between the pressure cap 20, the connecting ring 18 and the step plate 19. The top surface of the sealing plate 21 is in contact with the pressure cap 20, and the bottom surface of the sealing plate 21 is in contact with the step plate 19 and the connecting ring 18 respectively. A pipe joint for connecting the inner air outlet pipe 6 is provided on the pressure cap 20.

[0091] Through the structural cooperation of the step plate 19, the pressure cap 20 and the sealing plate 21, on the one hand, the inner liner 1 can be detachably connected to the outer liner 2 and the function of quick installation and removal can be realized; on the other hand, after the pressure cap 20 is tightened, the sealing plate 21 can also be used to seal the connection between the connecting ring 18 and the step plate 19, thereby preventing the gas between the inner liner 1 and the outer liner 2 from leaking out from the gap and ensuring its sealing effect.

[0092] The stirring assembly 5 includes a stirring rod located in the hydrolysis chamber 3. The upper end of the stirring rod passes through the pressure cover 20 and is connected to a drive motor, which is fixed to the top of the pressure cover 20.

[0093] The hydrolysis chamber 3 forms an inner pressure chamber 22 above the reaction water, and the heating chamber 4 forms an outer pressure chamber 23 above the reaction water. The air inlet pipe 7 fills the outer pressure chamber 23 with pressurized air each time it is pressurized, so that the pressure in the outer pressure chamber is 20 kPa higher than that in the inner pressure chamber. Each inflation time is controlled at 20 seconds, and the interval between two inflations is set to 5 minutes.

[0094] In this embodiment, aluminum ash is placed inside the inner liner 1 and continuously stirred by the stirring assembly 5 to achieve the hydrolysis function. Simultaneously, the heating tube 15 and temperature sensor 16 work together to maintain a constant temperature for the reaction water in the heating chamber 4. Heat exchange between the heating chamber 4 and the reaction water in the hydrolysis chamber 3 keeps the reaction water in the hydrolysis chamber 3 at a constant temperature, thus ensuring heating effectiveness while preventing the aluminum ash powder from directly contacting the temperature sensor 16 and heating tube 15 and causing adhesion and clumping.

[0095] During the hydrolysis of aluminum ash, the air chamber 14 maintains a set air pressure value with the cooperation of the air pressure sensor and the air pump. The electric ball valve 12 is opened periodically to allow the pressurized gas in the air chamber 14 to enter the outer pressure chamber 23 through the air inlet pipe 7. This causes the reaction water in the heating chamber 4 to be rapidly injected into the hydrolysis chamber 3 through the screen part 102 under the action of air pressure. This impacts the aluminum ash powder accumulated on the side wall of the outer liner 2, causing the aluminum ash powder to flow inward with the water flow and contact the stirring component 5. This achieves the function of continuous stirring of aluminum ash powder in different areas of the inner liner 1 in this embodiment.

[0096] When the reaction water in the heating chamber 4 drops to the set liquid level, the liquid level sensor 17 detects and triggers the electric ball valve 12 to close. Simultaneously, the pressure regulating valve 9 opens, allowing the external pressure chamber 23 to connect with the internal pressure chamber 22 via the internal exhaust pipe 6 and the external exhaust pipe 8. Gases from both chambers are simultaneously discharged through the internal exhaust pipe 6, causing the external pressure chamber 23 to return to normal pressure. The liquid level in the heating chamber 4 then rises again, completing one inflation cycle. This combination ensures that the aluminum ash powder in the inner liner 1 remains fluid throughout the hydrolysis process, effectively preventing powder deposition, agglomeration, or adhesion / sintering problems, thus improving the hydrolysis effect of aluminum ash powder with a fineness below 100 mesh.

[0097] Example 1: This example combines the preparation method of Example 2 and the water bath stirring mechanism of Example 3 to prepare demetallized aluminum ash. The demetallized aluminum ash used is from Anda Auto Parts Co., Ltd., and has an aluminum content of 28.6%, an alumina content of 41.2%, an aluminum nitride content of 7.8%, a total water-soluble salt content of 5.3%, and a moisture content of 1.2%. Various data of the demetallized aluminum ash were monitored in real time during the preparation process. The test results are as follows:

[0098] A. Using demetallized aluminum ash as raw material, the raw material is sieved. The proportion of large impurities removed by sieving is 1.8%, and the proportion of qualified aluminum ash obtained by sieving is 98.2%, thus obtaining a1 aluminum ash.

[0099] A1 aluminum ash was washed and stirred three times to remove soluble salt impurities. The parameters of A1 aluminum ash after three washings and stirrings are shown in Table 1, and A2 aluminum ash was obtained.

[0100] Table 1. Test data of a1 aluminum ash after 3 water washing and stirring.

[0101]

[0102] A2 aluminum ash was dried and ground. After grinding, the moisture content of A2 aluminum ash was found to be less than 0.4%, and 99.2% of A2 aluminum ash particles were smaller than 100 mesh. A3 aluminum ash.

[0103] Hydrolyzing A3 aluminum ash revealed that the residual aluminum nitride content in the hydrolyzed A3 aluminum ash was less than 0.5%. The hydrolyzed A3 aluminum ash was then calcined, and the aluminum nitride in the A3 aluminum ash completely decomposed after calcination, while the aluminum oxide content in the A3 aluminum ash increased to 46.9%, thus obtaining A aluminum ash.

[0104] B. Aluminum ash a was mixed with NaOH solution and reacted to dissolve the aluminum oxide in aluminum ash a and generate sodium aluminate solution. The dissolution rate of aluminum oxide was found to be 87.5%, resulting in solution b.

[0105] C. Solution b is subjected to coarse filtration and fine filtration in sequence to remove insoluble residues in solution b. The content of alumina in the filter residue is detected to be 3%, thus obtaining solution c.

[0106] D. CO2 is bubbled into solution c to adjust the pH value, causing solution c to react and form aluminum hydroxide precipitate, resulting in precipitate d;

[0107] E. The d precipitate was washed and dealkalized 5 times to remove the residual NaOH on the surface of the d precipitate. The parameters of the d precipitate after each washing and dealkalization are shown in Table 2. After 5 washings, the water content of aluminum hydroxide was 30.23% and the purity of aluminum hydroxide was 99.1%, thus obtaining the e precipitate.

[0108] Table 2. Detection data of d precipitate after 5 washes and dealkali removals.

[0109]

[0110] F. The precipitate e was calcined at low temperature to obtain the finished alumina. The parameters of the finished alumina are shown in Table 3.

[0111] Table 3 Test data of finished alumina

[0112]

[0113] Experiments show that this application can effectively improve the hydrolysis effect of A3 aluminum ash by modifying the preparation process and water bath stirring mechanism, and the resulting alumina has a purity of over 99%, a specific surface area of ​​280 m² / g, and a bulk density of 0.82 g / cm³, which effectively improves the bonding effect of alumina with other refractory matrices.

[0114] Experimental Example 2: Using the finished alumina from Experimental Example 1 as Sample 1 and commercially available alumina as Sample 2, Sample 1 and Sample 2 were mixed with refractory aggregate and kaolin in the same proportion to prepare refractory materials. The specific preparation process is as follows:

[0115] S1. Mix refractory aggregate, alumina and kaolin in a mass ratio of 8:1:1, and dry mix for 15 minutes to obtain dry material;

[0116] S2. Add water to the dry materials at a rate of 5% of the total dry material mass, and mix the water and dry materials evenly by mechanical stirring to obtain a mixture;

[0117] S3. The mixture is molded under a molding pressure of 120 MPa and a holding time of 20 seconds to produce refractory blanks of standard size;

[0118] S4. Dry the refractory blank at 110 ℃ for 18 hours to obtain dry refractory material;

[0119] S5. Sinter the dry refractory material at a sintering temperature of 1500℃ and a heating rate of 4℃, hold for 4 hours, and allow it to cool naturally to room temperature after sintering to obtain the finished refractory material.

[0120] The refractory material spectrogram test results prepared from Sample 1 are shown in Table 4:

[0121] Table 4. Spectral detection data of the refractory material corresponding to Sample 1

[0122]

[0123] Then, after using both refractory materials on the same incineration line for 720 hours, scanning electron microscopy was performed. The scanning results are as follows: Figure 3 and Figure 4 As shown, where Figure 3 This is an electronic image of the refractory material corresponding to Sample 1. Figure 4 The image shows an electron image of the refractory material corresponding to Sample 2. The electron image reveals that the refractory material corresponding to Sample 1 exhibits an irregular blocky structure at the microscopic level, with a rough surface but no obvious cracks or pores, and relatively tight bonding between particles. This indicates that the refractory material achieved high density during preparation, which is beneficial for mechanical strength and thermal shock resistance. In contrast, the refractory material corresponding to Sample 2 shows discontinuous large particle agglomerations (…). Figure 4 Left), obvious crack ( Figure 4 (medium) and particle crushing ( Figure 4 (Right) These defects can significantly reduce the mechanical properties of materials. Cracks may originate from thermal stress or mechanical loads, while particle breakage indicates that the refractory castable has undergone phase transformation and corrosion during use.

[0124] From the surface morphology, the refractory material corresponding to Sample 1 has an uneven surface without sharp defects, which is due to the natural morphology of the raw material particles and sintering shrinkage. This structure provides some protection against erosion under high-temperature environments. In contrast, the refractory material corresponding to Sample 2 exhibits more pronounced crack propagation. The crack length and direction reflect the location of stress concentration, indicating that the material has been subjected to non-uniform thermal expansion or mechanical impact during service. Furthermore, the fine particles in this refractory material show a significant reduction in particle size (scale bar 1 μm), possibly due to structural pulverization caused by high-temperature oxidation, chemical corrosion, or phase transformation, accelerating material failure.

[0125] As can be seen from the above comparison, by limiting the alumina preparation method, this application enables the prepared alumina product to have better purity, specific surface area and activity. As a result, it can be tightly combined with other refractory matrices during the casting and sintering process of refractory materials to form a stable composite structure, effectively improving the interfacial bonding strength and reducing interfacial porosity and defects, thereby improving the corrosion resistance and erosion resistance of the refractory material after preparation.

Claims

1. A method for preparing an alumina refractory castable based on aluminum ash, characterized in that, Includes the following steps: A. Using demetallized aluminum ash as raw material, the raw material is sequentially subjected to sieving, water washing and desalination, drying and grinding and hydrolysis and calcination treatment to obtain a aluminum ash; B. Mix aluminum ash (a) with NaOH solution to react, causing the aluminum oxide in aluminum ash (a) to dissolve and form sodium aluminate solution, thus obtaining solution (b); C. Perform coarse filtration and fine filtration on solution b in sequence to remove insoluble residues in solution b, and obtain solution c; D. CO2 is bubbled into solution c to adjust the pH value, causing solution c to react and form aluminum hydroxide precipitate, resulting in precipitate d; E. Wash and dealkalize precipitate d to remove residual NaOH from its surface, yielding precipitate e. F. The precipitate e is calcined at low temperature to obtain the finished alumina.

2. The method for preparing an alumina refractory castable based on aluminum ash according to claim 1, characterized in that, Step A specifically includes the following steps: A1. Using demetallized aluminum ash as raw material, the raw material is sieved through a screen to obtain a1 aluminum ash; A2. A1 aluminum ash is washed and stirred three times with water at a solid-liquid ratio of 1:

7. The water washing and stirring temperature is 50-80℃, and the time for each water washing and stirring is 60 minutes to obtain A2 aluminum ash. A3. Place the a2 aluminum ash in an environment of 100-140℃ and dry for 3-4 hours, then grind the dried aluminum ash to less than 100 mesh to obtain a3 aluminum ash; A4. Hydrolyze a3 aluminum ash at a solid-liquid ratio of 1:7 in a water temperature environment of 95℃ for 3 hours, and then calcine the hydrolyzed a3 aluminum ash at an environment of 800℃ for 2 hours to obtain a aluminum ash.

3. The method for preparing an alumina refractory castable based on aluminum ash according to claim 1, characterized in that: In step B, the mass fraction of the NaOH solution is 10-15%, the mixing reaction temperature is 100℃, and the reaction time is 4 hours.

4. The method for preparing an alumina refractory castable based on aluminum ash according to claim 1, characterized in that: In step D, CO2 is introduced into solution c to adjust the pH value of solution c to 9.2, so that solution c reacts to form aluminum hydroxide precipitate, and the reaction time is 3 hours.

5. The method for preparing an alumina refractory castable based on aluminum ash according to claim 1, characterized in that: In step E, the precipitate d is washed and dealkalized in a water temperature environment of 40℃. The solid-liquid ratio is 1:4 for each wash, and the washing time is 15-20 minutes. After washing 5 times, the precipitate e is obtained.

6. The method for preparing an alumina refractory castable based on aluminum ash according to claim 1, characterized in that: In step F, the precipitate e is calcined at a constant temperature of 500-700℃ for 3 hours to obtain the finished alumina.

7. The method for preparing an alumina refractory castable based on aluminum ash according to claim 2, characterized in that: In step A4, the a3 aluminum ash is hydrolyzed by a water bath stirring mechanism. The water bath stirring mechanism includes an inner liner (1) and an outer liner (2) nested inside and outside. A hydrolysis chamber (3) is formed inside the inner liner (1), and a heating chamber (4) is formed between the inner liner (1) and the outer liner (2). A partition (101) is formed at the upper end of the inner liner (1), and a screen (102) is formed at the lower end of the inner liner (1). Both the inner liner (1) and the outer liner (2) are filled with reaction water, and the surface of the reaction water extends above the screen (102). A stirring assembly (5) is provided in the middle of the hydrolysis chamber (3), and an inner air outlet pipe (6) is connected to the top of the hydrolysis chamber (3). An air inlet pipe (7) and an air outlet pipe (8) are respectively connected to the top of the heating chamber (4). One end of the air outlet pipe (8) is connected to the inner air outlet pipe (6), and a pressure regulating valve (9) is provided on the air outlet pipe (8). The air inlet pipe (7) is used to fill the heating chamber (4) with pressurized air to create a pressure difference between the heating chamber (4) and the hydrolysis chamber (3); The reaction water in the heating chamber (4) is used to flow into the inner liner (1) through the screen section (102) under the action of air pressure difference. The pressure regulating valve (9) is used to release pressure in the heating chamber (4) after it is opened.

8. The method for preparing an alumina refractory castable based on aluminum ash according to claim 7, characterized in that: The outgoing air pipe (8) is provided with a first one-way valve (10); the inlet air pipe (7) is provided with a speed regulating valve (11), an electric ball valve (12), and a second one-way valve (13), and the outer end of the inlet air pipe (7) is connected to an air bag (14).

9. The method for preparing an alumina refractory castable based on aluminum ash according to claim 7, characterized in that: An installation opening is formed in the middle of the top surface of the outer liner (2). A connecting ring (18) is provided on the radial outer side of the installation opening. An installation groove is formed between the connecting ring (18) and the outer liner (2). The inner liner (1) is installed into the outer liner (2) through the installation opening. The top of the inner liner (1) is fastened to the installation groove by a step plate (19). A pressure cap (20) is provided above the step plate (19). The connecting ring (18) is bolted around the pressure cap (20). A sealing plate (21) is provided at the connection between the pressure cap (20), the connecting ring (18) and the step plate (19).

10. The method for preparing an alumina refractory castable based on aluminum ash according to claim 7, characterized in that: The hydrolysis chamber (3) forms an inner pressure chamber (22) above the reaction water, and the heating chamber (4) forms an outer pressure chamber (23) above the reaction water. The air inlet pipe (7) fills the outer pressure chamber (23) with pressurized air each time it is pressurized, so that the pressure of the outer pressure chamber (23) is 15-25 kPa higher than that of the inner pressure chamber (22). Each inflation time is 10-30 seconds, and the interval between two inflations is 2-10 minutes.

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