Red mud-based ceramic flat sheet membrane and preparation method thereof

Abstract

The invention relates to the field of new materials, and discloses a red mud-based ceramic flat sheet membrane and a preparation method thereof. The red mud-based ceramic flat sheet membrane comprises a substrate and a separation layer integrally attached to the surface of the substrate, the matrix is prepared from the following raw materials in parts by weight: 2000 to 4000 parts of Al2O3 powder with the average particle size of 5000nm, 200 to 350 parts of corn starch, 300 to 500 parts of red mud, 400 to 600 parts of kaolin and 2 to 8 parts of polyvinyl alcohol; the separation layer is prepared from the following raw materials in parts by weight: 4-10 parts of Al2O3 powder with the average particle size of 5000nm, 1-3 parts of a dispersing agent, 0.1-0.3 part of a defoaming agent and 1-3 parts of polyvinyl alcohol. The red-mud-based ceramic flat sheet membrane has good physical properties, the preparation method is scientific and reasonable, and the red-mud-based ceramic flat sheet membrane has the characteristics of short production period, low raw material and sintering cost and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of new material ceramic membranes, and more specifically, to a red mud-based ceramic flat membrane and a preparation method thereof. Background Art

[0002] Amidst global water shortages and escalating industrial separation demands, ceramic membranes, thanks to their high-temperature resistance, corrosion resistance, and mechanical strength, have become a core material in separation technology. Compared to polymer membranes, ceramic membranes' stability under extreme operating conditions (such as tolerance to pH 0-14 and temperatures exceeding 500°C) makes them irreplaceable in the energy and chemical industries.

[0003] The high cost of ceramic membranes is attributed to expensive raw materials, high sintering costs and low recovery rates. The preparation of ceramic membranes involves multiple "sintering-coating-sintering" processes, which require high sintering temperatures and long cycle times, thereby increasing the overall cost. Studies have shown that the total cost of membrane manufacturing includes three main components: material cost, sintering cost and manufacturing process cost, which account for 20%, 60% and 20% of the total cost respectively. The raw material and energy costs associated with the sintering process are the main factors for the high price of ceramic membranes. Therefore, reducing sintering costs and raw material costs can effectively reduce the overall cost of ceramic membranes. Secondly, how to further improve the performance of ceramic membranes, specifically, improving permeability and selectivity by controlling pore size and designing new structures remains the main goal of recent research.

[0004] Red mud, as a by-product of the aluminum industry, has high alkalinity and complex chemical composition (including Fe2O3, Al2O3, SiO2, etc.). Long-term storage of red mud causes serious environmental problems. Its resource utilization has become a research hotspot in the field of environmental materials. Summary of the Invention

[0005] The present invention provides a red mud-based ceramic flat membrane and its preparation method. Red mud is used as a functional additive in ceramic membrane preparation, which not only realizes solid waste resource utilization but also optimizes membrane material performance by utilizing its metal oxide components. Furthermore, the preparation method of the present invention is scientific and rational, with a short production cycle and low raw material and firing costs.

[0006] The technical solutions of the present invention are as follows: The red mud-based ceramic flat membrane comprises a substrate and a separation layer integrally attached to the surface of the substrate; The matrix is made of the following raw materials in parts by weight: 2000-4000 parts of Al2O3 powder with an average particle size of 5000 nm, 200-350 parts of corn starch, 300-500 parts of red mud, 400-600 parts of kaolin, and 2-8 parts of polyvinyl alcohol; The separation layer is made of the following raw materials in parts by weight: 4-10 parts of Al2O3 powder with an average particle size of 5000nm, 1-3 parts of a dispersant, 0.1-0.3 parts of a defoaming agent, and 1-3 parts of polyvinyl alcohol.

[0007] The pore size of the matrix is 81-1100 nm.

[0008] The pore size of the separation layer is 170-220 nm.

[0009] The dispersant is an olefinic acid with 3 to 6 carbon atoms; and the defoaming agent is organic silicone oil.

[0010] The average particle size of the Al2O3 powder is 5000nm.

[0011] The matrix preparation method comprises the following steps: A. Mix polyvinyl alcohol with ultrapure water to prepare a 2-6 wt% polyvinyl alcohol solution for later use; B. Mix Al2O3 powder, corn starch, red mud, and kaolin, then slowly add the polyvinyl alcohol solution and water obtained in step A, stir and mix evenly, then transfer to a kneader and knead for 1.5-2.5h, then seal in a kneader and age for 36-60h to obtain an aged material; C. Transfer the aged material to a high-pressure vacuum extruder, perform secondary kneading for 2-3 hours under a vacuum degree of ≤0.10 MPa, and extrude to obtain a vacuum extruded material; then, select a special mold for flat film, load the vacuum extruded material into a screw extruder, and extrude continuously at a constant rate to obtain a flat film blank; D. After mechanical cutting and trimming of the flat membrane body, it is dried at 50-70° C. and the final moisture content is controlled below 1.50% to obtain a dry green body; E. Place the dried green compact in a high-temperature sintering container for high-temperature sintering. The specific sintering process is controlled as follows: Raise the temperature to 280-320°C at a heating rate of 1.5-2.5°C / min, and keep warm for 0.3-0.8h; then raise the temperature to 420-480°C at a heating rate of 1.5-2.5°C / min, and keep warm for 0.3-0.8h; then raise the temperature to 1080-1120°C at a heating rate of 4-6°C / min, and keep warm for 1-3h; then raise the temperature to 1180-1220°C at a heating rate of 4-6°C / min, and keep warm for 1-3h; raise the temperature to 1240-1260°C at a heating rate of 4-6°C / min, and keep warm for 1-3h; raise the temperature to 1280-1320°C at a heating rate of 4-6°C / min, and keep warm for 1-3h, and then naturally cool to room temperature.

[0012] In the step C, the extrusion conditions of the screw extruder are: extrusion speed 0.40-0.60 mm / s, extrusion pressure 12-18 MPa, and the temperature of the flat film blank is controlled at 25±2°C.

[0013] The spraying process of the separation layer comprises the following steps: a. ultrasonically cleaning the substrate, and then drying it at 105° C. for more than 2 h to obtain a pretreated substrate; b. Mix polyvinyl alcohol with ultrapure water to prepare a 4-7 wt% polyvinyl alcohol solution for later use; c. Disperse Al2O3 powder evenly in 8-12 times ultrapure water, then add dispersant and defoamer in sequence, and ball mill for 20-50 minutes to obtain Al2O3 suspension. d. Evenly mix the Al2O3 suspension with the polyvinyl alcohol solution prepared in step B, let it stand to eliminate bubbles, and obtain a homogeneous separation layer slurry; e. Use a high-pressure spray gun to evenly spray the homogeneous separation layer slurry on the pretreated substrate surface, and then dry the sprayed sample at a relative humidity of 30-50% and a temperature of 50-70°C for 3-5 hours to preliminarily solidify the coating to obtain a prefabricated flat membrane; f. Place the prefabricated flat membrane in a high-temperature sintering container for high-temperature sintering. The specific sintering process is controlled as follows: heat to 1050-1150°C at a heating rate of 0.8-1.2°C / min, and then keep the temperature for 1-3 hours to obtain a sintered flat membrane; g. Bond the fired flat membrane and membrane end-sealing assembly together to obtain the product.

[0014] In the step e, the nozzle diameter of the high-pressure spray gun is 0.50 mm, the spraying pressure is 0.27-0.32 MPa, the spraying distance is controlled at 18-23 cm; the number of spraying times is 2-4 times, and the interval between each spraying is 8-20 minutes.

[0015] In the step g, the fired flat membrane and the membrane end-sealing assembly are bonded together using AB glue, and then allowed to stand for more than 24 hours to allow the adhesive layer to completely solidify.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: The red mud-based ceramic flat membrane prepared by the present invention has both mechanical strength and permeability, and is suitable for industrial wastewater treatment. Long-term operation experiments have shown that the amount of metal ions dissolved in the flat membrane is far below the safety threshold. Combined with ozone treatment technology, it can construct an efficient and low-cost ceramic membrane-ozone coupled wastewater treatment system, which is particularly suitable for the deep treatment of printing and dyeing wastewater.

[0017] The present invention uses red mud as a sintering aid and forms a low-melting liquid phase at high temperature through the Fe2O3-SiO2-Al2O3 system, significantly reducing the densification temperature of the alumina-based ceramic membrane to 1250°C. Compared with the traditional pure Al2O3 that requires a temperature greater than 1600°C, this has achieved great progress and greatly saved energy consumption.

[0018] The preparation method of the present invention is scientific and rational, eliminating the need for a transition layer and shortening the production cycle of flat ceramic membranes. Furthermore, the use of red mud as raw material significantly reduces raw material costs. Furthermore, the spraying method used to prepare the separation layer reduces firing costs and energy consumption compared to existing multiple-coating and multiple-firing processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the particle size distribution diagram of the sample prepared in Example 3; Figure 2 The chemical composition diagram of the sample prepared in Example 3; Figure 3 The comparison chart of the porosity of the base ceramic membrane after sintering at different temperatures; Figure 4 The comparison chart of gas flux after sintering the base ceramic membrane at different temperatures; Figure 5 This is the pore size distribution diagram of the substrate calcined at 1250°C based on the method of Example 3; Figure 6 FTIR graph of the substrate calcined at 1250°C based on the method of Example 3; Figure 7 is the XRD pattern of the substrate calcined at 1250°C based on the method of Example 3; Figure 8 The SEM images of the substrate surface calcined at different temperatures; Figure 9 This is the EDS image of the substrate surface calcined at 1250°C based on the method of Example 3; Figure 10 This is the pore size distribution diagram of the surface ceramic flat membrane prepared in Example 3; Figure 11 This is a graph showing the mass loss of the ceramic flat membrane prepared in Example 3 under extreme acid and alkaline environments; Figure 12 This is a comparison chart of the permeation flux of the ceramic flat membrane prepared in Example 3 and the substrate calcined at different temperatures; Figure 13 This is the surface EDS image of the ceramic flat membrane prepared in Example 3; Figure 14 This is a graph showing the metal ion leaching concentration of the ceramic flat membrane prepared in Example 3 after continuous operation for 60 days. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The raw materials used in the following examples and comparative examples are all commercially available. Example 1

[0021] A red mud-based ceramic flat membrane comprises a substrate and a separation layer integrally attached to the surface of the substrate; The matrix was made of the following raw materials: 2000 g of Al2O3 powder with an average particle size of 5000 nm, 200 g of corn starch, 300 g of red mud, 400 g of kaolin, and 2 g of polyvinyl alcohol; The matrix preparation method comprises the following steps: A. Mix polyvinyl alcohol with ultrapure water to prepare a 2 wt% polyvinyl alcohol solution for later use; B. Mix Al2O3 powder, corn starch, red mud and kaolin, then slowly add the polyvinyl alcohol solution and water prepared in step A, stir and mix evenly, then transfer to a kneader and knead for 1.5 hours, then seal in the kneader and age for 36 hours to obtain an aged material; C. Transfer the aged material to a high-pressure vacuum extruder, perform secondary kneading for 2 hours under a vacuum degree of ≤0.10 MPa, and extrude to obtain a vacuum extrusion material; then select a special mold for flat film, load the vacuum extrusion material into a screw extruder, and extrude continuously at a constant rate to obtain a flat film blank; D. After mechanically cutting and trimming the flat membrane body, it is dried at 50° C. and the final moisture content is controlled below 1.50% to obtain a dry green body; E. Place the dried green compact in a high-temperature sintering container for high-temperature sintering. The specific sintering process is controlled as follows: Raise the temperature to 280°C at a heating rate of 1.5°C / min, and keep warm for 0.3h; then raise the temperature to 420°C at a heating rate of 1.5°C / min, and keep warm for 0.3h; then raise the temperature to 1080°C at a heating rate of 4°C / min, and keep warm for 1h; then raise the temperature to 1180°C at a heating rate of 4°C / min, and keep warm for 1h; raise the temperature to 1240°C at a heating rate of 4°C / min, and keep warm for 1h; raise the temperature to 1280°C at a heating rate of 4°C / min, and keep warm for 1h, and then naturally cool to room temperature.

[0022] In the step C, the extrusion conditions of the screw extruder are: extrusion speed 0.40 mm / s, extrusion pressure 12 MPa, and the temperature of the flat film blank is controlled at 25±2°C.

[0023] The separation layer is made from the following materials: 4g of Al2O3 powder with an average particle size of 5000nm, 1g of a dispersant, 0.1g of a defoamer, and 1g of polyvinyl alcohol. The dispersant is acrylic acid, and the defoamer is silicone oil.

[0024] The spraying process of the separation layer comprises the following steps: a. ultrasonically cleaning the substrate, and then drying it at 105° C. for more than 2 h to obtain a pretreated substrate; b. Mix polyvinyl alcohol with ultrapure water to prepare a 4 wt% polyvinyl alcohol solution for later use; c. Disperse Al2O3 powder evenly in 8 times ultrapure water, then add dispersant and defoamer in sequence, and ball mill for 20 minutes to obtain Al2O3 suspension. d. Evenly mix the Al2O3 suspension with the polyvinyl alcohol solution prepared in step B, let it stand to eliminate bubbles, and obtain a homogeneous separation layer slurry; e. Use a high-pressure spray gun to evenly spray the homogeneous separation layer slurry on the pretreated substrate surface, and then dry the sprayed sample at a relative humidity of 30% and a temperature of 50°C for 3 hours to preliminarily solidify the coating to obtain a prefabricated flat membrane; Among them, the nozzle diameter of the high-pressure spray gun is 0.50mm, the spraying pressure is 0.27Mpa, and the spraying distance is controlled at 18cm; the number of spraying times is 2 times, and the interval between each spraying is 8min.

[0025] f. Place the prefabricated flat membrane in a high-temperature sintering container for high-temperature sintering. The specific sintering process is controlled as follows: heat to 1050°C at a heating rate of 0.8°C / min, and then keep the temperature for 1 hour to obtain a sintered flat membrane; g. Bond the fired flat membrane and membrane end-sealing assembly with AB glue, and let it stand for more than 24 hours to allow the adhesive layer to completely solidify.

[0026] Use airtightness testing equipment to test the airtightness of the assembled ceramic diaphragm at a test pressure of 0.20MPa. If a leak is found, repair it with local glue filling and retest until the airtightness meets the standard, ensuring a leakage rate of ≤0.10%. Example 2

[0027] A red mud-based ceramic flat membrane comprises a substrate and a separation layer integrally attached to the surface of the substrate; The matrix was made of the following raw materials: 4000 g of Al2O3 powder with an average particle size of 5000 nm, 350 g of corn starch, 500 g of red mud, 600 g of kaolin, and 8 g of polyvinyl alcohol; The matrix preparation method comprises the following steps: A. Mix polyvinyl alcohol with ultrapure water to prepare a 6 wt% polyvinyl alcohol solution for later use; B. Mix Al2O3 powder, corn starch, red mud and kaolin, then slowly add the polyvinyl alcohol solution and water prepared in step A, stir and mix evenly, then transfer to a kneader and knead for 2.5 hours, then seal in a kneader and age for 60 hours to obtain an aged material; C. Transfer the aged material to a high-pressure vacuum extruder, perform secondary kneading for 3 hours under a vacuum degree of ≤0.10 MPa, and extrude to obtain a vacuum extrusion material; then select a special mold for flat film, load the vacuum extrusion material into a screw extruder, and extrude continuously at a constant rate to obtain a flat film blank; The extrusion conditions of the screw extruder are: extrusion speed 0.60 mm / s, extrusion pressure 18 MPa, and the temperature of the flat film blank is controlled at 25±2°C.

[0028] D. After mechanically cutting and trimming the flat membrane body, it is dried at 70° C. and the final moisture content is controlled below 1.50% to obtain a dry green body; E. Place the dried green compact in a high-temperature sintering container for high-temperature sintering. The specific sintering process is controlled as follows: Raise the temperature to 320°C at a heating rate of 2.5°C / min, and keep it warm for 0.8h; then raise the temperature to 480°C at a heating rate of 2.5°C / min, and keep it warm for 0.8h; then raise the temperature to 1120°C at a heating rate of 6°C / min, and keep it warm for 3h; then raise the temperature to 1220°C at a heating rate of 6°C / min, and keep it warm for 3h; raise the temperature to 1260°C at a heating rate of 6°C / min, and keep it warm for 3h; raise the temperature to 1320°C at a heating rate of 6°C / min, and keep it warm for 3h, and then naturally cool to room temperature.

[0029] The separation layer is made from the following raw materials: 10g of Al2O3 powder with an average particle size of 5000nm, 3g of a dispersant, 0.3g of a defoamer, and 3g of polyvinyl alcohol. The dispersant is hexenoic acid, and the defoamer is silicone oil.

[0030] The spraying process of the separation layer comprises the following steps: a. ultrasonically cleaning the substrate, and then drying it at 105° C. for more than 2 h to obtain a pretreated substrate; b. Mix polyvinyl alcohol with ultrapure water to prepare a 7 wt% polyvinyl alcohol solution for later use; c. Disperse Al2O3 powder evenly in 12 times ultrapure water, then add dispersant and defoamer in sequence, and mill with a ball mill for 50 minutes to obtain Al2O3 suspension. d. Evenly mix the Al2O3 suspension with the polyvinyl alcohol solution prepared in step B, let it stand to eliminate bubbles, and obtain a homogeneous separation layer slurry; e. Use a high-pressure spray gun to evenly spray the homogeneous separation layer slurry on the pretreated substrate surface, and then dry the sprayed sample at a relative humidity of 50% and a temperature of 70°C for 5 hours to preliminarily solidify the coating to obtain a prefabricated flat membrane; Among them, the nozzle diameter of the high-pressure spray gun is 0.50mm, the spraying pressure is 0.32Mpa, and the spraying distance is controlled at 23cm; the number of spraying times is 4 times, and the interval between each spraying is 20min.

[0031] f. Place the prefabricated flat membrane in a high-temperature sintering container for high-temperature sintering. The specific sintering process is controlled as follows: heat to 1150°C at a heating rate of 1.2°C / min, and then keep the temperature for 3 hours to obtain a sintered flat membrane; g. Bond the fired flat membrane and membrane end-sealing assembly with AB glue, and let it stand for more than 24 hours to allow the adhesive layer to completely solidify.

[0032] Use airtightness testing equipment to test the airtightness of the assembled ceramic diaphragm at a test pressure of 0.20MPa. If a leak is found, repair it with local glue filling and retest until the airtightness meets the standard, ensuring a leakage rate of ≤0.10%. Example 3

[0033] A red mud-based ceramic flat membrane comprises a substrate and a separation layer integrally attached to the surface of the substrate; The matrix was made of the following raw materials: 3000 g of Al2O3 powder with an average particle size of 5000 nm, 270 g of corn starch, 400 g of red mud, 420 g of kaolin, and 4 g of polyvinyl alcohol; The matrix preparation method comprises the following steps: A. Mix polyvinyl alcohol with ultrapure water to prepare a 4 wt% polyvinyl alcohol solution for later use; B. Mix Al2O3 powder, corn starch, red mud, and kaolin, then slowly add the polyvinyl alcohol solution and water obtained in step A, stir and mix evenly, then transfer to a kneader and knead for 2 hours, then seal in the kneader and age for 48 hours to obtain an aged material; C. Transfer the aged material to a high-pressure vacuum extruder, perform secondary kneading for 2.5 hours under a vacuum degree of ≤0.10 MPa, and extrude to obtain a vacuum extrusion material; then, select a special mold for flat film, load the vacuum extrusion material into a screw extruder, and extrude continuously at a constant rate to obtain a flat film blank; The extrusion conditions of the screw extruder are: extrusion speed 0.50 mm / s, extrusion pressure 15 MPa, and the temperature of the flat film blank is controlled at 25±2°C.

[0034] D. After mechanical cutting and trimming of the flat membrane body, it is dried at 60° C. and the final moisture content is controlled below 1.50% to obtain a dry green body; E. Place the dried green compact in a high-temperature sintering container for high-temperature sintering. The specific sintering process is controlled as follows: Raise the temperature to 300°C at a heating rate of 2°C / min, and keep it warm for 0.5h; then raise the temperature to 450°C at a heating rate of 2°C / min, and keep it warm for 0.5h; then raise the temperature to 1100°C at a heating rate of 5°C / min, and keep it warm for 2h; then raise the temperature to 1200°C at a heating rate of 5°C / min, and keep it warm for 2h; raise the temperature to 1250°C at a heating rate of 5°C / min, and keep it warm for 2h; raise the temperature to 1300°C at a heating rate of 5°C / min, and keep it warm for 2h, and then naturally cool to room temperature.

[0035] The separation layer is made from the following raw materials: 6g of Al2O3 powder with an average particle size of 5000nm, 2g of a dispersant, 0.2g of a defoamer, and 2g of polyvinyl alcohol. The dispersant is crotonic acid, and the defoamer is silicone oil.

[0036] The spraying process of the separation layer comprises the following steps: a. ultrasonically cleaning the substrate, and then drying it at 105° C. for more than 2 h to obtain a pretreated substrate; b. Mix polyvinyl alcohol with ultrapure water to prepare a 5.5 wt% polyvinyl alcohol solution for later use; c. Disperse Al2O3 powder evenly in 10 times ultrapure water, then add dispersant and defoamer in sequence, and ball mill for 30 minutes to obtain Al2O3 suspension. d. Evenly mix the Al2O3 suspension with the polyvinyl alcohol solution prepared in step B, let it stand to eliminate bubbles, and obtain a homogeneous separation layer slurry; e. Use a high-pressure spray gun to evenly spray the homogeneous separation layer slurry on the pretreated substrate surface, and then dry the sprayed sample at a relative humidity of 40% and a temperature of 60°C for 4 hours to preliminarily solidify the coating to obtain a prefabricated flat membrane; Among them, the nozzle diameter of the high-pressure spray gun is 0.50mm, the spraying pressure is 0.30Mpa, and the spraying distance is controlled at 20cm; the number of spraying times is 3 times, and the interval between each spraying is 10min.

[0037] f. Place the prefabricated flat membrane in a high-temperature sintering container for high-temperature sintering. The specific sintering process is controlled as follows: heat to 1100°C at a heating rate of 1°C / min, and then keep the temperature for 2 hours to obtain a sintered flat membrane; g. Bond the fired flat membrane and membrane end-sealing assembly with AB glue, and let it stand for more than 24 hours to allow the adhesive layer to completely solidify.

[0038] Use airtightness testing equipment to test the airtightness of the assembled ceramic diaphragm at a test pressure of 0.20MPa. If a leak is found, repair it with local glue filling and retest until the airtightness meets the standard, ensuring a leakage rate of ≤0.10%. Example 4

[0039] A red mud-based ceramic flat membrane comprises a substrate and a separation layer integrally attached to the surface of the substrate; The matrix was made of the following raw materials: 3500 g of Al2O3 powder with an average particle size of 5000 nm, 250 g of corn starch, 360 g of red mud, 540 g of kaolin, and 6 g of polyvinyl alcohol; The matrix preparation method comprises the following steps: A. Mix polyvinyl alcohol with ultrapure water to prepare a 5 wt% polyvinyl alcohol solution for later use; B. Mix Al2O3 powder, corn starch, red mud and kaolin, then slowly add the polyvinyl alcohol solution and water prepared in step A, stir and mix evenly, then transfer to a kneader and knead for 1.8 hours, then seal in a kneader and age for 40 hours to obtain an aged material; C. Transfer the aged material to a high-pressure vacuum extruder, perform secondary kneading for 2.3 hours under a vacuum degree of ≤0.10 MPa, and extrude to obtain a vacuum extrusion material; then, select a special mold for flat film, load the vacuum extrusion material into a screw extruder, and extrude continuously at a constant rate to obtain a flat film blank; The extrusion conditions of the screw extruder are: extrusion speed 0.46 mm / s, extrusion pressure 14 MPa, and the temperature of the flat film blank is controlled at 25±2°C.

[0040] D. After mechanically cutting and trimming the flat membrane body, it is dried at 62° C. and the final moisture content is controlled below 1.50% to obtain a dry green body; E. Place the dried green compact in a high-temperature sintering container for high-temperature sintering. The specific sintering process is controlled as follows: Raise the temperature to 290°C at a heating rate of 1.7°C / min and keep it warm for 0.4h; then raise the temperature to 430°C at a heating rate of 2.2°C / min and keep it warm for 0.6h; then raise the temperature to 1110°C at a heating rate of 5°C / min and keep it warm for 2.5h; then raise the temperature to 1190°C at a heating rate of 4°C / min and keep it warm for 1.6h; raise the temperature to 1245°C at a heating rate of 4.5°C / min and keep it warm for 1.8h; raise the temperature to 1310°C at a heating rate of 5°C / min and keep it warm for 2h, then naturally cool to room temperature.

[0041] The separation layer is made from the following raw materials: 8g of Al2O3 powder with an average particle size of 5000nm, 2g of a dispersant, 0.16g of a defoamer, and 3g of polyvinyl alcohol. The dispersant is pentenoic acid, and the defoamer is silicone oil.

[0042] The spraying process of the separation layer comprises the following steps: a. ultrasonically cleaning the substrate, and then drying it at 105° C. for more than 2 h to obtain a pretreated substrate; b. Mix polyvinyl alcohol with ultrapure water to prepare a 4.5 wt% polyvinyl alcohol solution for later use; c. Disperse Al2O3 powder evenly in 11 times ultrapure water, then add dispersant and defoamer in sequence, and ball mill for 40 minutes to obtain Al2O3 suspension. d. Evenly mix the Al2O3 suspension with the polyvinyl alcohol solution prepared in step B, let it stand to eliminate bubbles, and obtain a homogeneous separation layer slurry; e. Use a high-pressure spray gun to evenly spray the homogeneous separation layer slurry on the pretreated substrate surface, and then dry the sprayed sample at a relative humidity of 35% and a temperature of 62°C for 4 hours to preliminarily solidify the coating to obtain a prefabricated flat membrane; Among them, the nozzle diameter of the high-pressure spray gun is 0.50mm, the spraying pressure is 0.28Mpa, and the spraying distance is controlled at 21cm; the number of spraying times is 3 times, and the interval between each spraying is 15min.

[0043] f. placing the prefabricated flat membrane in a high-temperature sintering container for high-temperature sintering. The specific sintering process is controlled as follows: heating to 1090°C at a heating rate of 1.1°C / min, and then keeping the temperature for 2 hours to obtain a sintered flat membrane; g. Bond the fired flat membrane and membrane end-sealing assembly with AB glue, and let it stand for more than 24 hours to allow the adhesive layer to completely solidify.

[0044] Use airtightness testing equipment to test the airtightness of the assembled ceramic diaphragm at a test pressure of 0.20MPa. If a leak is found, repair it with local glue filling and retest until the airtightness meets the standard, ensuring a leakage rate of ≤0.10%. Example 5

[0045] 1. Physical properties test of the red mud-based ceramic flat membrane prepared in Example 3: The particle size and composition of the red mud-based ceramic flat membrane prepared in Example 3 are as follows: Figure 1 As shown in Figure 2, the red mud particle size shows a multimodal distribution (main peaks at 1080 nm and 11570 nm). Figure 2 As shown in the figure, its chemical components are mainly Fe2O3 (32.85%), Al2O3 (23.67%) and SiO2 (14.37%).

[0046] Such as Figure 2-7 As shown in the figure, based on the method of Example 3, the comprehensive performance comparison results of the matrix samples with different sintering temperatures show that the sample sintered at 1250 ° C has the best comprehensive performance, with a flexural strength of 35.95 kg / cm² (30% higher than the national standard), a porosity of 41.20%, and an air flux of 0.86 L·m⁻²·h⁻¹·bar⁻¹. The pore size is concentrated in the range of 80-540 nm, accounting for 62.30%, and has both mechanical strength and permeability. Figure 8 and 9 As shown, Figure 8 Middle: a is the matrix sintered at 1100 ℃, b is the matrix sintered at 1200 ℃, c is the matrix sintered at 1250 ℃, and d is the matrix sintered at 1300 ℃; its microscopic characterization shows that red mud promotes the formation of α-Al2O3 crystal phase and multi-level pore structure, uniformly distributes Fe elements, and significantly improves the surface chemical stability.

[0047] 2. Performance testing of red mud-based ceramic flat membrane The red mud-based ceramic flat membranes prepared using the method of Example 3 and substrates prepared at different sintering temperatures were tested for their pore size distribution, acid and alkali resistance, permeation flux, and surface properties. The results are as follows: like Figure 10 As shown, Figure 5 In contrast, the substrate prepared by the method of Example 3 at a sintering temperature of 1250°C was sprayed with a separation layer by the spraying process. Compared with the substrate, the pore size uniformity of the membrane layer was optimized, and the molecular sieving ability was significantly improved. like Figure 11 As shown, the mass loss test results of the red mud-based ceramic flat membrane prepared by the method of Example 3 and the substrates prepared at different sintering temperatures under extreme acid and alkaline environments; Figure 11Middle: (a) is 0.10 mol / L hydrochloric acid solution, (b) is 6 mol / L hydrochloric acid solution, (c) is 0.10 mol / L sodium hydroxide solution, and (d) is 6 mol / L sodium hydroxide solution; the results show that the acid and alkali resistance of the substrate prepared at a sintering temperature of 1250°C is significantly improved after the separation layer is sprayed via the spraying process.

[0048] like Figure 12 As shown in the figure, the permeation flux test of the red mud-based ceramic flat membrane prepared in Example 3 and the matrix membranes prepared at different sintering temperatures showed that the pure water flux reached a peak value of 3043.04 L·m⁻²·h⁻¹ at 1250 ℃, and the densification and pore control achieved improved permeation stability.

[0049] like Figure 13 As shown, Figure 13 Middle: a is the surface magnified 100 times, b is the surface magnified 250 times, c is the surface magnified 1500 times, and d is the cross-section magnified 130 times; SEM shows that the film layer is dense and well bonded to the substrate; like Figure 14 As shown, the metal ion leaching concentration of the red mud-based ceramic flat membrane prepared in Example 3 was continuously operated for 60 days, indicating that the metal ion dissolution amount of the red mud-based ceramic flat membrane of the present invention during long-term operation is far below the safety threshold, verifying the environmental safety of the material.

[0050] 3. The red mud-based ceramic flat membrane prepared in Example 3 was tested. A catalyst, titanium dioxide, was attached to the red mud-based ceramic flat membrane and then calcined. The resulting catalyst-attached red mud-based ceramic flat membrane was installed in a membrane reactor for wastewater treatment experiments. The specific experimental results are as follows: Experiments on the degradation of rhodamine B (RhB) using a coupled ozone system showed that hydraulic retention time (HRT) and ozone flow rate were the primary controlling factors. The membrane reactor parameters for the treatment were as follows: HRT = 4 h, ozone flow rate 840 mg / min, catalyst 0.25 g / L, and catalyst calcined at 600°C.

[0051] The test found that the removal rates of COD and RhB reached 66.70% and 99.71% respectively. The free radical quenching experiment confirmed that hydroxyl radical (·OH) was the dominant active species (contribution rate > 48.17%), superoxide radical (·O2 - ) assisted degradation. Intermediate product analysis revealed the degradation pathway of RhB: N-deethylation → chromophore cleavage → ring opening → mineralization to CO2 and H2O.

[0052] In the initial stage of stable operation (1-5 days), the total COD removal rate was > 95.00%, but it dropped to 43.70% after 30 days, mainly due to catalyst deactivation (reduction of anatase phase and organic matter coverage). Example 6

[0053] The red mud-based ceramic flat membrane prepared in Example 3 was compared with the prior art ceramic membrane. The results are shown in Table 1 below: Table 1 Comparison of the excellence of ceramic membranes Performance parameters Traditional ceramic membrane Red mud-based ceramic flat membrane Production costs $82 / m² $34 / m² Sintering temperature >1600 ℃ 1250 ℃ Flexural strength 27.7 kg / cm² (national standard) 35.95 kg / cm² Pure water flux 2000 L·m⁻²·h⁻¹ 3043 L·m⁻²·h⁻¹ COD removal rate 70% (traditional ozonation) 92.7% (coupling process) Acid resistance (6M HCl) 0.95 0.99 As can be seen from Table 1, the red mud-based ceramic flat membrane prepared in Example 3 of the present invention is much better than the traditional ceramic membrane in terms of both cost and various performances.

Claims

1. A red mud-based ceramic flat membrane, characterized in that: The invention comprises a substrate, and a separation layer integrally attached to the surface of the substrate; The matrix is made of the following raw materials in parts by weight: 2000-4000 parts of Al2O3 powder, 200-350 parts of corn starch, 300-500 parts of red mud, 400-600 parts of kaolin, and 2-8 parts of polyvinyl alcohol; The separation layer is made of the following raw materials in parts by weight: 4-10 parts of Al2O3 powder, 1-3 parts of a dispersant, 0.1-0.3 parts of a defoaming agent, and 1-3 parts of polyvinyl alcohol.

2. The red mud-based ceramic flat membrane according to claim 1, characterized in that: The pore size of the matrix is 81-1100 nm.

3. The red mud-based ceramic flat membrane according to claim 1, characterized in that: The pore size of the separation layer is 170-220 nm.

4. The red mud-based ceramic flat membrane according to claim 1, characterized in that: The dispersant is an olefinic acid with 3 to 6 carbon atoms; and the defoaming agent is organic silicone oil.

5. The red mud-based ceramic flat membrane according to claim 1, characterized in that: The average particle size of the Al2O3 powder is 5000nm.

6. The red mud-based ceramic flat membrane according to claim 1, characterized in that: The matrix preparation method comprises the following steps: A. Mix polyvinyl alcohol with ultrapure water to prepare a 2-6 wt% polyvinyl alcohol solution for later use; B. Mix Al2O3 powder, corn starch, red mud, and kaolin, then slowly add the polyvinyl alcohol solution and water obtained in step A, stir and mix evenly, then transfer to a kneader and knead for 1.5-2.5h, then seal in a kneader and age for 36-60h to obtain an aged material; C. Transfer the aged material to a high-pressure vacuum extruder, perform secondary kneading for 2-3 hours under a vacuum degree of ≤0.10 MPa, and extrude to obtain a vacuum extruded material; then, select a special mold for flat film, load the vacuum extruded material into a screw extruder, and extrude continuously at a constant rate to obtain a flat film blank; D. After mechanical cutting and trimming of the flat membrane body, it is dried at 50-70° C. and the final moisture content is controlled below 1.50% to obtain a dry green body; E. Place the dried green compact in a high-temperature sintering container for high-temperature sintering. The specific sintering process is controlled as follows: Raise the temperature to 280-320°C at a heating rate of 1.5-2.5°C / min, and keep warm for 0.3-0.8h; then raise the temperature to 420-480°C at a heating rate of 1.5-2.5°C / min, and keep warm for 0.3-0.8h; then raise the temperature to 1080-1120°C at a heating rate of 4-6°C / min, and keep warm for 1-3h; then raise the temperature to 1180-1220°C at a heating rate of 4-6°C / min, and keep warm for 1-3h; raise the temperature to 1240-1260°C at a heating rate of 4-6°C / min, and keep warm for 1-3h; raise the temperature to 1280-1320°C at a heating rate of 4-6°C / min, and keep warm for 1-3h, and then naturally cool to room temperature.

7. The red mud-based ceramic flat membrane according to claim 6, characterized in that: In the step C, the extrusion conditions of the screw extruder are: extrusion speed 0.40-0.60 mm / s, extrusion pressure 12-18 MPa, and the temperature of the flat film blank is controlled at 25±2°C.

8. The red mud-based ceramic flat membrane according to claim 1 or 6, characterized in that: The preparation and spraying process of the separation layer includes the following steps: a. ultrasonically cleaning the substrate, and then drying it at 105° C. for more than 2 h to obtain a pretreated substrate; b. Mix polyvinyl alcohol with ultrapure water to prepare a 4-7 wt% polyvinyl alcohol solution for later use; c. Disperse Al2O3 powder evenly in 8-12 times ultrapure water, then add dispersant and defoamer in sequence, and ball mill for 20-50 minutes to obtain Al2O3 suspension. d. Evenly mix the Al2O3 suspension with the polyvinyl alcohol solution prepared in step B, let it stand to eliminate bubbles, and obtain a homogeneous separation layer slurry; e. Use a high-pressure spray gun to evenly spray the homogeneous separation layer slurry on the pretreated substrate surface, and then dry the sprayed sample at a relative humidity of 30-50% and a temperature of 50-70°C for 3-5 hours to preliminarily solidify the coating to obtain a prefabricated flat membrane; f. Place the prefabricated flat membrane in a high-temperature sintering container for high-temperature sintering. The specific sintering process is controlled as follows: heat to 1050-1150°C at a heating rate of 0.8-1.2°C / min, and then keep the temperature for 1-3 hours to obtain a sintered flat membrane; g. Bond the fired flat membrane and membrane end-sealing assembly together to obtain the product.

9. The red mud-based ceramic flat membrane according to claim 8, characterized in that: In the step e, the nozzle diameter of the high-pressure spray gun is 0.50 mm, the spraying pressure is 0.27-0.32 MPa, the spraying distance is controlled at 18-23 cm; the number of spraying times is 2-4 times, and the interval between each spraying is 8-20 minutes.

10. The red mud-based ceramic flat membrane according to claim 8, characterized in that: In the step g, the fired flat membrane and the membrane end-sealing assembly are bonded together using AB glue, and then allowed to stand for more than 24 hours to allow the adhesive layer to completely solidify.

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