Method for preparing aluminum oxide ceramic membrane from industrial solid waste red mud and aluminum ash

Abstract

The invention aims to provide a method for preparing an aluminum oxide ceramic membrane by using industrial solid waste red mud and aluminum ash. The method comprises the following steps: S1, mixing the red mud, the aluminum ash, CTBA, urea and water according to a mass ratio of 1: (1-5): (0.5-3): (0.8-2.5): 20; s2, citric acid with the concentration being 0.5-2 mol / L and a nitric acid peptide agent with the concentration being 1-5 mol / L are sequentially added, sol is obtained after stirring and standing, and a mixed solution of PVA and ammonium nitrate with the volume ratio being 1: (0.2-2) is added into the sol to obtain film coating liquid; s3, adding a pore-forming agent into an Al2O3 porous ceramic support synthesized from aluminum ash, cane sugar, calcium carbide and other raw materials by using the film coating liquid, and carrying out film coating treatment; s4, performing shaping, drying, pre-pore-forming and sintering to obtain an aluminum oxide ceramic membrane; the alumina ceramic membrane has the characteristics of low raw material cost and good adsorption and interception effects. The retention rate of the membrane for 20 mg.L <-1 > Congo red dye can still reach more than 98.5% after the membrane is circulated for 4 times.

Description

Technical Field

[0001] The invention relates to a method for preparing a ceramic membrane, and in particular to a method for preparing an alumina ceramic membrane by utilizing industrial solid waste red mud and aluminum ash. Background Art

[0002] Red mud is an industrial solid waste discharged when the aluminum industry extracts alumina. It is called red mud because it contains a large amount of iron oxide and looks similar to red soil. Due to the differences in ore grade, production methods and technical levels, about 1.0 to 1.8 tons of red mud are discharged for every ton of alumina produced.

[0003] A variety of by-products are produced during the aluminum smelting and forming process. As the main by-product of the aluminum industry, aluminum ash is produced in all aluminum melting processes, and the aluminum content in it accounts for about 1-12% of the total loss during aluminum production and use. In the past, people regarded aluminum slag as waste and dumped it, which not only caused a waste of aluminum resources but also brought environmental problems.

[0004] In recent years, ceramic membranes have been widely used due to their unique properties such as high mechanical strength, good permeability, strong thermal stability, acid and alkali corrosion resistance, and long service life. Alumina ultrafiltration membranes are usually prepared by the traditional alcohol aluminum method, which has the disadvantages of high raw material cost, long reaction time, and long production cycle, which is not conducive to the low-cost, rapid and large-scale preparation of alumina ultrafiltration membranes.

[0005] With the rapid development of my country's economy and the continuous growth of industrialization, solid waste pollution and sewage pollution are still affecting our lives and environment, and ecological civilization construction is still an important task in the future. Therefore, it is of practical significance to develop ceramic membranes with lower raw material costs and better adsorption and retention effects. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a method for preparing an alumina ceramic membrane using industrial solid waste red mud and aluminum ash. The alumina ceramic membrane obtained by this method has the characteristics of low raw material cost, convenient preparation industry, and good adsorption and retention effect.

[0007] In order to achieve the above object, the present invention provides the following technical solutions: A method for preparing an alumina ceramic membrane using industrial solid waste red mud and aluminum ash comprises the following steps: S1: Mix industrial solid waste red mud, aluminum ash, CTBA, urea and water in a certain proportion to prepare a solution, and stir at 80°C to make them uniformly mixed. The mass ratio of red mud, aluminum ash, CTBA, urea and water in the solution is 1: (1-5): (0.5-3): (0.8-2.5): 20, and the stirring time is 1-5h; S2: first add 0.5-2 mol / L citric acid to the solution obtained after stirring in step S1, stir thoroughly for 30-120 min, then add 1-5 mol / L nitrate peptide agent, adjust the yield stress, flow viscosity and pH of the solution, and obtain a sol after standing for 24 hours, wherein the volume ratio of citric acid to nitrate peptide agent is 1:(0.5-3); S3: taking an appropriate amount of the sol obtained in step S2, adding a mixed solution of PVA and ammonium nitrate to the sol, and heating in an ultrasonic water bath at 70°C for 1-3h to obtain a coating solution, wherein the volume ratio of PVA to ammonium nitrate is 1:(0.2-2); S4: preparing an Al2O3 porous ceramic support by mixing aluminum ash, sucrose, calcium carbide and a macroporous pore-forming agent in a certain ratio, wherein the average pore size of the support is 100-500 nm, and the ratio of the aluminum ash, sucrose, calcium carbide and the pore-forming agent is 1: (0.2-1): (0.5-2): (0.2-5); S5: using the coating liquid and the small pore forming agent obtained in step S3, coating the Al2O3 porous ceramic support obtained in step S4 in a certain ratio, wherein the ratio of the coating liquid, the small pore forming agent and the Al2O3 ceramic support is 1: (0.2-3): (0.5-2); S6: The sample obtained in step S5 is processed according to the planned "forming - drying - pre-pore making - sintering" procedure, and finally a double-layer alumina ceramic membrane with large pores on the outside and small pores on the inside is obtained. The drying temperature is 60°C for 1-5h, and the sintering temperature is 600-800°C.

[0008] Preferably, the step S1 specifically comprises mixing industrial solid waste red mud, aluminum ash, CTBA, urea and water in a certain proportion to prepare a solution, and stirring at 80° C. to make them uniformly mixed, wherein the mass ratio of red mud, aluminum ash, CTBA, urea and water in the solution is 1: (1-3): (0.5-2): (0.8-2): 20, and the stirring time is 3 hours; Preferably, the step S2 specifically comprises first adding 1 mol / L citric acid to the solution obtained after stirring in step S1, stirring for 60 minutes, then adding 1-5 mol / L nitrate peptide agent, adjusting the yield stress, flow viscosity and pH of the solution, and obtaining a sol after standing for 24 hours, wherein the volume ratio of citric acid to nitrate peptide agent is 1:(0.5-3); Preferably, the step S2 specifically comprises first adding 1 mol / L citric acid to the solution obtained after stirring in step S1, stirring for 60 minutes, then adding 4 mol / L nitrate peptide agent, adjusting the yield stress, flow viscosity and pH of the solution, and leaving it to stand for 24 hours to obtain a sol, wherein the volume ratio of citric acid to nitrate peptide agent is 1:(0.5-2); Preferably, the step S3 specifically comprises taking an appropriate amount of the sol obtained in step S2, adding a mixed solution of PVA and ammonium nitrate to the sol, heating in an ultrasonic water bath at 70° C. for 2 hours, and defoaming for 60 minutes to obtain a coating solution, wherein the volume ratio of PVA to ammonium nitrate is 1:(0.2-1.5); Preferably, the step S4 is specifically, aluminum ash, sucrose, calcium carbide, macroporous pore forming agent according to a certain ratio to prepare Al2O3 porous ceramic support, the average pore size of the support is 300nm, the aluminum ash, sucrose, calcium carbide, pore forming agent ratio of 1: (0.2-0.8): (0.5-1.5): (0.2-3); Preferably, the step S5 is specifically to use the coating liquid and the small pore forming agent obtained in step S3 to coat the Al2O3 porous ceramic support obtained in step S4 in a certain ratio, wherein the ratio of the coating liquid, the small pore forming agent and the Al2O3 ceramic support is 1: (0.2-2): (0.5-1.5); Preferably, the step 6) is specifically to carry out the sample obtained in step S5 according to the planned "forming - drying - pre-pore making - sintering" procedure, and finally obtain a double-layer alumina ceramic membrane with large pores on the outside and alumina ceramic support body on the inside, and small pores on the inside. The drying temperature is 60°C for 3 hours, and the sintering temperature is 650°C.

[0009] Beneficial effects: The present invention discloses a method for preparing an alumina ceramic membrane using industrial solid waste red mud and aluminum ash, wherein the industrial solid waste red mud, aluminum ash, CTBA and water are mixed in a certain proportion, citric acid and nitrocellulose solution are added, and a sol is obtained after standing, and a mixed solution of PVA and ammonium nitrate is continuously added thereto to obtain a coating liquid, and then the coating liquid is used to coat an Al2O3 porous ceramic support synthesized using raw materials such as aluminum ash using a small pore forming agent, and an alumina ceramic membrane is obtained after "setting-drying-pre-pore-forming-sintering". The ceramic membrane has the characteristics of low raw material cost and good adsorption and interception effect. After the membrane is circulated 4 times for 20 mg·L-1 Congo red dye, the interception rate can still reach more than 98.5%. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0011] Example 1 S1: Mix industrial solid waste red mud, aluminum ash, CTBA, urea and water in a certain proportion to prepare a solution, and stir at 80°C to make them evenly mixed. The mass ratio of red mud, aluminum ash, CTBA, urea and water in the solution is 1:2.5:0.5:1:20, and the stirring time is 3 hours; S2: first add citric acid with a concentration of 2 mol / L to the solution obtained after stirring in step S1, stir thoroughly for 30 minutes, then add nitropeptide agent with a concentration of 4 mol / L, adjust the yield stress, flow viscosity and pH of the solution, and obtain a sol after standing for 24 hours, wherein the volume ratio of citric acid to nitropeptide agent is 1:2.5; S3: taking an appropriate amount of the sol obtained in step S2, adding a mixed solution of PVA and ammonium nitrate to the sol, and heating in an ultrasonic water bath at 70° C. for 1.5 h to obtain a coating solution, wherein the volume ratio of PVA to ammonium nitrate is 1:0.2; S4: preparing an Al2O3 porous ceramic support by mixing aluminum ash, sucrose, calcium carbide and a macroporous pore-forming agent in a certain ratio, wherein the average pore size of the support is 200 nm, and the ratio of the aluminum ash, sucrose, calcium carbide and the pore-forming agent is 1:0.2:0.5:0.8; S5: using the coating liquid and the small pore forming agent obtained in step S3, the Al2O3 porous ceramic support obtained in step S4 is subjected to coating treatment in a certain ratio, wherein the ratio of the coating liquid, the small pore forming agent and the Al2O3 ceramic support is 1:1:1; S6: The sample obtained in step S5 is processed according to the planned "forming - drying - pre-pore making - sintering" procedure, and finally a double-layer alumina ceramic membrane with large pores on the outside and alumina ceramic support body on the inside is obtained. The drying temperature is 60°C for 3 hours, and the sintering temperature is 650°C.

[0012] Example 2 A method for preparing an alumina ceramic membrane using industrial solid waste red mud and aluminum ash comprises the following steps: S1: industrial solid waste red mud, aluminum ash, CTBA, urea and water are mixed in a certain proportion to prepare a solution, and stirred at 80°C to make them uniformly mixed. The mass ratio of red mud, aluminum ash, CTBA, urea and water in the solution is 1:2:0.8:0.5:20, and the stirring time is 3h; S2: first add citric acid with a concentration of 2 mol / L to the solution obtained after stirring in step S1, stir thoroughly for 30 minutes, then add nitropeptide agent with a concentration of 4 mol / L, adjust the yield stress, flow viscosity and pH of the solution, and obtain a sol after standing for 24 hours, wherein the volume ratio of citric acid to nitropeptide agent is 1:2; S3: taking an appropriate amount of the sol obtained in step S2, adding a mixed solution of PVA and ammonium nitrate to the sol, and heating in an ultrasonic water bath at 70° C. for 1.5 h to obtain a coating solution, wherein the volume ratio of PVA to ammonium nitrate is 1:2; S4: preparing an Al2O3 porous ceramic support by mixing aluminum ash, sucrose, calcium carbide and a macroporous pore-forming agent in a certain ratio, wherein the average pore size of the support is 200 nm, and the ratio of the aluminum ash, sucrose, calcium carbide and the pore-forming agent is 1:0.2:0.5:0.8; S5: using the coating liquid and the small pore forming agent obtained in step S3, the Al2O3 porous ceramic support obtained in step S4 is subjected to coating treatment in a certain ratio, wherein the ratio of the coating liquid, the small pore forming agent and the Al2O3 ceramic support is 1:1:1; S6: The sample obtained in step S5 is processed according to the planned "forming - drying - pre-pore making - sintering" procedure, and finally a double-layer alumina ceramic membrane with large pores on the outside and alumina ceramic support body on the inside is obtained. The drying temperature is 60°C for 3 hours, and the sintering temperature is 650°C.

[0013] Example 3 A method for preparing an alumina ceramic membrane using industrial solid waste red mud and aluminum ash comprises the following steps: S1: industrial solid waste red mud, aluminum ash, CTBA, urea and water are mixed in a certain proportion to prepare a solution, and stirred at 80°C to make them uniformly mixed. The mass ratio of red mud, aluminum ash, CTBA, urea and water in the solution is 1:1:0.5:0.5:20, and the stirring time is 2.5h; S2: first add citric acid with a concentration of 2 mol / L to the solution obtained after stirring in step S1, stir thoroughly for 30 minutes, then add nitropeptide agent with a concentration of 4 mol / L, adjust the yield stress, flow viscosity and pH of the solution, and obtain a sol after standing for 24 hours, wherein the volume ratio of citric acid to nitropeptide agent is 1:2.5; S3: taking an appropriate amount of the sol obtained in step S2, adding a mixed solution of PVA and ammonium nitrate to the sol, and heating in an ultrasonic water bath at 70° C. for 2 h to obtain a coating solution, wherein the volume ratio of PVA to ammonium nitrate is 1:1.5; S4: preparing an Al2O3 porous ceramic support by mixing aluminum ash, sucrose, calcium carbide and a macroporous pore-forming agent in a certain ratio, wherein the average pore size of the support is 200 nm, and the ratio of the aluminum ash, sucrose, calcium carbide and the pore-forming agent is 1:0.2:0.5:0.5; S5: using the coating liquid and the small pore forming agent obtained in step S3, coating the Al2O3 porous ceramic support obtained in step S4 in a certain ratio, wherein the ratio of the coating liquid, the small pore forming agent and the Al2O3 ceramic support is 1:0.8:1; S6: The sample obtained in step S5 is processed according to the planned "forming - drying - pre-making holes - sintering" procedure, and finally a double-layer alumina ceramic membrane with large pores on the outside and alumina ceramic support body on the inside is obtained. The drying temperature is 60°C for 2 hours, and the sintering temperature is 650°C.

[0014] Example 4 A method for preparing an alumina ceramic membrane using industrial solid waste red mud and aluminum ash comprises the following steps: S1: Mix industrial solid waste red mud, aluminum ash, CTBA, urea and water in a certain proportion to prepare a solution, and stir at 80°C to make them evenly mixed. The mass ratio of red mud, aluminum ash, CTBA, urea and water in the solution is 1:3:1:1.5:20, and the stirring time is 2h; S2: first add citric acid with a concentration of 2 mol / L to the solution obtained after stirring in step S1, stir thoroughly for 30 minutes, then add nitropeptide agent with a concentration of 4 mol / L, adjust the yield stress, flow viscosity and pH of the solution, and obtain a sol after standing for 24 hours, wherein the volume ratio of citric acid to nitropeptide agent is 1:2.5; S3: taking an appropriate amount of the sol obtained in step S2, adding a mixed solution of PVA and ammonium nitrate to the sol, and heating in an ultrasonic water bath at 70° C. for 1.5 h to obtain a coating solution, wherein the volume ratio of PVA to ammonium nitrate is 1:1; S4: preparing an Al2O3 porous ceramic support by mixing aluminum ash, sucrose, calcium carbide and a macroporous pore-forming agent in a certain ratio, wherein the average pore size of the support is 200 nm, and the ratio of the aluminum ash, sucrose, calcium carbide and the pore-forming agent is 1:0.2:0.8:1; S5: using the coating liquid and the small pore forming agent obtained in step S3, the Al2O3 porous ceramic support obtained in step S4 is subjected to coating treatment in a certain ratio, wherein the ratio of the coating liquid, the small pore forming agent and the Al2O3 ceramic support is 1:0.5:1; S6: The sample obtained in step S5 is processed according to the planned "forming - drying - pre-pore making - sintering" procedure, and finally a double-layer alumina ceramic membrane with large pores on the outside and alumina ceramic support body on the inside is obtained. The drying temperature is 60°C for 2 hours, and the sintering temperature is 750°C.

[0015] Example 5 A method for preparing an alumina ceramic membrane using industrial solid waste red mud and aluminum ash comprises the following steps: S1: industrial solid waste red mud, aluminum ash, CTBA, urea and water are mixed in a certain proportion to prepare a solution, and stirred at 80°C to make them uniformly mixed. The mass ratio of red mud, aluminum ash, CTBA, urea and water in the solution is 1:4:0.5:1.5:20, and the stirring time is 4 hours; S2: first add citric acid with a concentration of 2 mol / L to the solution obtained after stirring in step S1, stir thoroughly for 30 minutes, then add nitropeptide agent with a concentration of 4 mol / L, adjust the yield stress, flow viscosity and pH of the solution, and obtain a sol after standing for 24 hours, wherein the volume ratio of citric acid to nitropeptide agent is 1:2.5; S3: taking an appropriate amount of the sol obtained in step S2, adding a mixed solution of PVA and ammonium nitrate to the sol, and heating in an ultrasonic water bath at 70° C. for 1.5 h to obtain a coating solution, wherein the volume ratio of PVA to ammonium nitrate is 1:0.5; S4: preparing an Al2O3 porous ceramic support by mixing aluminum ash, sucrose, calcium carbide and a macroporous pore-forming agent in a certain ratio, wherein the average pore size of the support is 200 nm, and the ratio of the aluminum ash, sucrose, calcium carbide and the pore-forming agent is 1:0.2:0.5:0.5; S5: using the coating liquid and the small pore forming agent obtained in step S3, the Al2O3 porous ceramic support obtained in step S4 is subjected to coating treatment in a certain ratio, wherein the ratio of the coating liquid, the small pore forming agent and the Al2O3 ceramic support is 1:0.7:0.6; S6: The sample obtained in step S5 is processed according to the planned "forming - drying - pre-pore making - sintering" procedure, and finally a double-layer alumina ceramic membrane with large pores on the outside and a ceramic membrane on the inside is obtained. The drying temperature is 60°C for 2 hours, and the sintering temperature is 700°C.

[0016] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that the mass ratio of red mud, aluminum ash, CTBA, urea and water in the solution is 1:1:0.5:0.5:20, and the other preparation methods and conditions are consistent with those of Example 1.

[0017] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that the mass ratio of red mud, aluminum ash, CTBA, urea and water in the solution is 1:3:0.8:0.8:20, and the other preparation methods and conditions are the same as those in Example 1.

[0018] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the volume ratio of citric acid to nitropeptide agent is 1:1, and the other preparation methods and conditions are the same as those of Example 1.

[0019] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the volume ratio of citric acid to nitropeptide agent is 1:2, and the other preparation methods and conditions are the same as those of Example 1.

[0020] For Examples 1-5 and Comparative Examples 1-4, the pore size distribution was tested using the BJH nitrogen adsorption-desorption method to determine the specific surface area and pore volume. The measurement results are shown in Appendix 1.

[0021] Table 1 Specific surface area (m2 / g) Pore ​​volume (cm3 / g) Example 1 215.56 0.356 Example 2 190.78 0.305 Example 3 210.45 0.379 Example 4 195.34 0.324 Example 5 210.67 0.367 Comparative Example 1 189.45 0.312 Comparative Example 2 205.36 0.378 Comparative Example 3 200.87 0.342 Comparative Example 4 209.45 0.320 From the specific surface area and pore volume data of Examples 1-5, it can be found that the product obtained by the method of preparing alumina ceramic membrane using industrial solid waste red mud and aluminum ash of the present invention has a higher specific surface area and pore volume, that is, the alumina ceramic membrane can be successfully synthesized, and the raw material cost is low and the production process is simple. From the comparison of Comparative Examples 1-4 with Example 1, it can be seen that in the method of the present invention, the mass ratio of industrial solid waste red mud, aluminum ash, CTBA, urea and water and the volume ratio of citric acid and nitropeptide directly affect the pore volume and specific surface area of ​​the alumina ceramic membrane. The mass ratio of red mud, aluminum ash, CTBA, urea and water is 1: (1-5): (0.5-3): (0.8-2.5): 20 and the volume ratio of citric acid and nitropeptide is 1: (0.5-3) to synthesize an alumina ceramic membrane with a larger specific surface area and pore volume.

[0022] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an alumina ceramic membrane using industrial solid waste red mud and aluminum ash, characterized in that: The method comprises the following steps: S1: Mix industrial solid waste red mud, aluminum ash, CTBA, urea and water in a certain proportion to prepare a solution, and stir at 80°C to make them uniformly mixed. The mass ratio of red mud, aluminum ash, CTBA, urea and water in the solution is 1: (1-5): (0.5-3): (0.8-2.5): 20, and the stirring time is 1-5h; S2: first add 0.5-2 mol / L citric acid to the solution obtained after stirring in step S1, stir thoroughly for 30-120 min, then add 1-5 mol / L nitrate peptide agent, adjust the yield stress, flow viscosity and pH of the solution, and obtain a sol after standing for 24 hours, wherein the volume ratio of citric acid to nitrate peptide agent is 1:(0.5-3); S3: taking an appropriate amount of the sol obtained in step S2, adding a mixed solution of PVA and ammonium nitrate to the sol, and heating in an ultrasonic water bath at 70°C for 1-3h to obtain a coating solution, wherein the volume ratio of PVA to ammonium nitrate is 1:(0.2-2); S4: preparing an Al2O3 porous ceramic support by mixing aluminum ash, sucrose, calcium carbide and a macroporous pore-forming agent in a certain ratio, wherein the average pore size of the support is 100-500 nm, and the ratio of the aluminum ash, sucrose, calcium carbide and the pore-forming agent is 1: (0.2-1): (0.5-2): (0.2-5); S5: using the coating liquid and the small pore forming agent obtained in step S3, coating the Al2O3 porous ceramic support obtained in step S4 in a certain ratio, wherein the ratio of the coating liquid, the small pore forming agent and the Al2O3 ceramic support is 1: (0.2-3): (0.5-2); S6: The sample obtained in step S5 is processed according to the planned "forming - drying - pre-pore making - sintering" procedure, and finally a double-layer alumina ceramic membrane with large pores on the outside and small pores on the inside is obtained. The drying temperature is 60°C for 1-5h, and the sintering temperature is 600-800°C.

2. The method according to claim 1, characterized in that Specifically, step S1 comprises mixing industrial solid waste red mud, aluminum ash, CTBA, urea and water in a certain proportion to prepare a solution, and stirring at 80° C. to make them uniformly mixed. The mass ratio of red mud, aluminum ash, CTBA, urea and water in the solution is 1: (1-3): (0.5-2): (0.8-2): 20, and the stirring time is 3 hours.

3. The method according to claim 1, characterized in that Specifically, step S2 includes first adding 1 mol / L citric acid to the solution obtained after stirring in step S1, stirring for 60 minutes, then adding 1-5 mol / L nitrate peptide agent, adjusting the yield stress, flow viscosity and pH of the solution, and obtaining a sol after standing for 24 hours. The volume ratio of citric acid to nitrate peptide agent is 1:(0.5-3).

4. The method according to claim 1, characterized in that: Specifically, step S2 includes first adding 1 mol / L citric acid to the solution obtained after stirring in step S1, stirring for 60 minutes, then adding 4 mol / L nitrate peptide agent, adjusting the yield stress, flow viscosity and pH of the solution, and obtaining a sol after standing for 24 hours. The volume ratio of citric acid to nitrate peptide agent is 1:(0.5-2).

5. The method according to claim 1, characterized in that The step S3 specifically comprises taking an appropriate amount of the sol obtained in step S2, adding a mixed solution of PVA and ammonium nitrate to the sol, heating in an ultrasonic water bath at 70° C. for 2 hours, and defoaming for 60 minutes to obtain a coating solution, wherein the volume ratio of PVA to ammonium nitrate is 1:(0.2-1).

6. The method according to claim 1, characterized in that The step S4 is specifically to prepare an Al2O3 porous ceramic support body by mixing aluminum ash, sucrose, calcium carbide and a macroporous pore-forming agent in a certain ratio, wherein the average pore size of the support body is 300 nm, and the ratio of the aluminum ash, sucrose, calcium carbide and the pore-forming agent is 1: (0.2-0.8): (0.5-1.5): (0.2-3).

7. The method according to claim 1, characterized in that Specifically, the step S5 is to use the coating liquid and small pore forming agent obtained in step S3 to coat the Al2O3 porous ceramic support obtained in step S4 in a certain ratio, and the ratio of the coating liquid, small pore forming agent and Al2O3 ceramic support is 1: (0.2-2): (0.5-1.5).

8. The method according to claim 1, characterized in that Specifically, the sample obtained in step S5 is subjected to the planned "forming-drying-pre-pore-sintering" procedure, and finally a double-layer alumina ceramic membrane with large pores on the outside and small pores on the inside is obtained. The drying temperature is 60°C for 3 hours, and the sintering temperature is 650°C.