A red mud-based alumina ceramic membrane support, a preparation method and application thereof

Abstract

The application provides a red mud-based alumina ceramic membrane support and a preparation method and application thereof, and belongs to the technical field of ceramic separation membranes. The application introduces a coarse-fine bimodal particle system, a removable pore-forming agent and a red mud low-melting-point component, realizes the collaborative formation of a surface fine pore layer and an internal coarse pore layer in a one-time debinding sintering process, and constructs a longitudinal pore size gradient structure which continuously or stepwisely changes from small to large along the thickness direction. The support can significantly reduce fluid pressure drop, improve flux while maintaining high mechanical strength, and can realize high-proportion resource utilization of red mud.

Description

Technical Field

[0001] This invention belongs to the field of ceramic separation membrane technology, specifically relating to a red mud-based alumina ceramic membrane support, its preparation method, and its application. Background Technology

[0002] Red mud is a large amount of solid waste generated during the Bayer process for alumina production. It is mainly composed of metal oxides such as Al₂O₃, Fe₂O₃, SiO₂, and TiO₂. These components are not only important elements of high-performance alumina ceramics but also act as sintering aids to lower the sintering temperature. However, the long-term stockpiling of large quantities of red mud not only occupies land resources but also may cause environmental pollution problems such as alkaline leachate and heavy metal migration. Therefore, utilizing red mud resources for the preparation of ceramic membrane materials with controllable structures has significant environmental and economic implications.

[0003] Existing ceramic membrane supports typically employ a mixture of unimodal ceramic powder and a pore-forming agent, which is then pressed or extruded and sintered to obtain a nearly uniform pore structure. A microporous separation layer is then formed on the surface through multiple cycles of coating, drying, and sintering. This traditional process requires at least two sintering operations, is complex, energy-intensive, and during coating, fine particles easily penetrate the support pores, leading to reduced effective porosity and permeation flux. To simplify the process, some studies have proposed a co-sintering technique between the support and the membrane layer. However, this method requires strict matching of the sintering shrinkage behavior of both, demanding high control over raw material particle size, composition, and sintering parameters, making scale-up difficult.

[0004] In terms of pore structure design, existing porous ceramic supports mostly exhibit a single or statistically bimodal pore size distribution. This means the pore size is basically uniform across the entire cross-section or only shows two peaks in a statistical distribution, making it difficult to construct a continuous gradient structure from fine pores on the surface to coarse pores in the thickness direction. Literature reports that porous alumina ceramic membranes prepared using polymethyl methacrylate or starch as pore-forming agents, while exhibiting a bimodal pore size distribution, show a basically uniform pore size variation along the cross-section. In contrast, materials with a longitudinal gradient pore structure can provide a fine filtration interface on the surface and low-resistance channels in the interior, thus balancing mechanical strength and mass transfer performance. These materials have been validated in fields such as biomaterials, but their processing is challenging, especially in the field of ceramic membrane supports, where there is a lack of structurally stable, simplified, and scalable technical solutions.

[0005] Therefore, it is necessary to provide a red mud-based alumina ceramic film support and its preparation method to solve the above problems. Summary of the Invention

[0006] This invention provides a red mud-based alumina ceramic membrane support, its preparation method, and its applications. It aims to overcome problems in existing ceramic membrane support preparation processes, such as a single pore structure, the need for multiple coating and sintering processes, high pressure drop, and insufficient utilization of red mud resources. By introducing a coarse-fine bimodal particle system, a removable pore-forming agent, and low-melting-point components of red mud, the invention achieves the synergistic formation of a surface fine-pore layer and an internal coarse-pore layer during a single degreasing and sintering process, constructing a longitudinal pore size gradient structure that continuously or stepwise varies in size along the thickness direction. The support of this invention can significantly reduce fluid pressure drop and increase flux while maintaining high mechanical strength, and can achieve a high proportion of red mud resource utilization.

[0007] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0008] A method for preparing a red mud-based alumina ceramic film support includes the following steps:

[0009] Step S1, prepare the slurry, the solids of the slurry include the following components: 40-55wt% coarse alumina powder, 30-40wt% fine red mud-alumina composite powder, 8-12wt% removable pore-forming agent and 3-8wt% organic binder.

[0010] Step S2: The slurry is shaped to obtain a blank with an initial layered structure. The surface of the blank is enriched with fine-particle red mud-alumina composite powder, and the interior is enriched with coarse-particle skeleton and removable pore-forming agent.

[0011] Step S3 involves debinding and sintering the blank using a continuous heating process in a single debinding-sintering step to complete the preparation of the ceramic film support. This single debinding-sintering process includes three stages:

[0012] Stage I: Pre-dehydration stage, at 1-3℃·min -1 Heat to 200℃ and hold for 0.5-2 hours to remove free water and some bound water;

[0013] Stage II, Organic Matter Decomposition Stage: at 1-2℃·min -1 Heat to 350-600℃ and hold at 350-500℃ for 1-3 hours to allow the organic binder and removable pore-forming agent to decompose and burn gradually, forming a through-hole pre-placed channel inside the green body while retaining the skeleton structure composed of coarse particles.

[0014] Stage III, Main Sintering Stage: at 2-5℃·min -1The temperature is raised to 1250-1450℃ and kept in air or a micro-oxygen atmosphere for 1-3 hours. This allows the low-melting-point components of the red mud to form a low-melting-point liquid phase on the surface of the blank, accelerating the growth rate of the sintering neck on the surface, reducing the pore size of the surface, and forming a longitudinal pore size gradient structure that changes continuously or stepwise from fine pores on the surface to coarse pores inside.

[0015] As a preferred improvement, step S1 specifically includes the following process:

[0016] Step S11: Dry mix coarse alumina powder and fine red mud-alumina composite powder according to the slurry formula ratio for 30 minutes to obtain a uniform graded particle system.

[0017] Step S12: Add pre-dissolved organic binder and deionized water, and perform wet ball milling for 6 hours to fully disperse the fine particles and coat the surface of the coarse particles.

[0018] Step S13: Then add a removable pore-forming agent and stir at low speed for 30 minutes to disperse it evenly, so as to obtain a slurry with a solid content of 45-55 vol% by volume and 70-80 wt% by mass.

[0019] As a preferred improvement, the coarse alumina powder is selected as high-purity α-Al2O3 powder with an Al2O3 content of not less than 95% and a particle size range of 20-80μm; the fine red mud-alumina composite powder is composed of red mud and alumina, with a particle size range of 0.5-5μm, wherein the mass ratio of red mud to alumina is (20-80):(80-20), and the red mud is obtained from red mud waste in the Bayer process of alumina production after iron removal, drying, and calcination; the removable pore-forming agent is an organic particulate material that decomposes or burns in the temperature range of 300-500℃, with a particle size range of 30-150μm; the organic binder is a water-soluble or thermally decomposable polymer.

[0020] As a preferred improvement, the chemical composition of the fine-particle red mud-alumina composite powder includes: Al2O3 30-45wt%, Fe2O3 15-25wt%, SiO2 10-20wt%, TiO2 3-8wt%, and a total content of Na2O and CaO of 5-12wt%; the removable pore-forming agent is selected from one or more of starch, wood flour, cellulose-based particles, lignin, or their complexes; the organic binder is selected from one or more of polyvinyl alcohol, acrylate emulsions, hydroxymethyl cellulose, and ammonium polyacrylate.

[0021] As a preferred improvement, step S2 specifically includes:

[0022] The slurry is formed into tubular or flat blanks by means of vacuum extrusion, casting, or dry pressing; the tubular structure is a single-channel or multi-channel honeycomb structure, and the thickness of the flat structure is 2-6mm.

[0023] As a preferred improvement, the blank is dried at 40-80°C.

[0024] A red mud-based alumina ceramic membrane support is prepared using the above-described method for preparing a red mud-based alumina ceramic membrane support.

[0025] As a preferred improvement, the red mud-based alumina ceramic membrane support comprises a longitudinal pore size gradient structure that continuously or stepwise changes from surface fine pores to internal coarse pores, and the total open porosity of the ceramic membrane support is 30-50%, wherein:

[0026] A fine porous layer with modal pore sizes of 0.1-2.0 μm is formed in the surface region;

[0027] The internal region forms a coarse-porous layer with modal pore sizes of 3-20 μm.

[0028] As a preferred improvement, the modal aperture ratio of the surface region to the internal region is 1:(3-20).

[0029] An application of the red mud-based alumina ceramic membrane support as described above, used as a support layer for microfiltration, ultrafiltration or nanofiltration membranes.

[0030] The beneficial effects of this invention are as follows:

[0031] (1) A longitudinal pore size gradient structure is formed by one-time debinding and sintering, which simplifies the process and reduces costs.

[0032] By utilizing a bimodal particle system of coarse and fine particles, the differential distribution of removable pore-forming agents, and the differential sintering effect caused by red mud fluxing, a longitudinal pore size gradient structure with fine surface pores and coarse internal pores can be achieved in a single degreasing-sintering process, eliminating the need for post-separation coating and secondary sintering. This process significantly simplifies the workflow, shortens the production cycle, reduces energy consumption and costs, and avoids problems such as interfacial particle infiltration, interlayer microcracks, and delamination caused by multiple sintering processes, thereby improving the reliability of the preparation process.

[0033] (2) The gradient structure balances high strength and high flux, improving mass transfer performance.

[0034] The support adopts a three-dimensional structure of "coarse-particle skeleton - fine-particle filling": coarse-particle alumina forms a continuous skeleton, providing excellent bending and compressive strength; fine particles and red mud are enriched and preferentially densified on the surface, forming a fine-pore surface layer that facilitates load separation; the internal removable pore-forming agent retains large-pore channels after burn-off, giving the support a high open porosity and good connectivity. Under the same or similar porosity conditions, the gradient support of this invention has a continuous transition in pore size from small to large along the thickness direction, which weakens the local contraction-expansion effect during fluid flow, reducing pressure drop by about 20-40% and increasing flux by about 20-40% compared to non-gradient supports.

[0035] (3) High-value utilization of red mud resources and green manufacturing

[0036] By utilizing Bayer process red mud as the main inorganic component and sintering aid, this invention fully leverages its low-melting-point liquid-phase sintering characteristics, containing components such as Na₂O, CaO, and Fe₂O₃, to promote densification while lowering the sintering temperature. Compared to traditional pure alumina systems, this invention can achieve a red mud incorporation ratio of 10-30 wt%, reducing the pressure of red mud storage and realizing high-value-added utilization of industrial solid waste and environmentally friendly manufacturing, demonstrating outstanding resource recovery and energy conservation and emission reduction effects.

[0037] (4) It has high structural stability, flexible application forms, and good engineering prospects.

[0038] The gradient structure is obtained through a bulk self-organizing mechanism, and there are no layer interfaces inside the support, avoiding the interlayer desorption and microcrack problems commonly found in traditional multi-coating processes, resulting in high long-term operational stability. This technical solution is applicable to single-channel, multi-channel tubular and flat structures. By adjusting the molding method and sintering parameters, gradient hole characteristics can be stably replicated under different structural morphologies, demonstrating good process compatibility and engineering scale-up potential. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0040] Figure 1 This shows a SEM image of the pore structure of the flat porous ceramic membrane support obtained in Example 1.

[0041] Figure 2 The image shows the SEM image of the pore structure of the flat porous ceramic membrane support obtained in Comparative Example 1. Detailed Implementation

[0042] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] This embodiment provides a method for preparing a red mud-based alumina ceramic film support, including the following steps:

[0044] Step S1, prepare the slurry, the solids of the slurry include the following components: 40-55wt% coarse alumina powder, 30-40wt% fine red mud-alumina composite powder, 8-12wt% removable pore-forming agent and 3-8wt% organic binder.

[0045] Step S1 specifically includes the following process:

[0046] Step S11: Dry mix coarse alumina powder and fine red mud-alumina composite powder according to the slurry formula ratio for 30 minutes to obtain a uniform graded particle system.

[0047] Step S12: Add pre-dissolved organic binder and deionized water, and perform wet ball milling for 6 hours to fully disperse the fine particles and coat the surface of the coarse particles.

[0048] Step S13: Then add a removable pore-forming agent and stir at low speed for 30 minutes to disperse it evenly, so as to obtain a slurry with a solid content of 45-55 vol% by volume and 70-80 wt% by mass.

[0049] The slurry was subjected to a shear rate of 100 s at 25°C. -1 The apparent viscosity of the slurry is 80-300 mPa·s, exhibiting shear-thinning or slightly thixotropic properties, making it suitable for vacuum extrusion, casting, or multi-channel molding.

[0050] The coarse alumina powder has a particle size range of 20-80 μm. The coarse alumina powder is selected as high-purity α-Al₂O₃ powder, with an Al₂O₃ content ≥95 wt% and a median particle size D. 50 It is 35-60μm.

[0051] The coarse alumina powder forms a through skeleton during the molding and sintering process, which is used to construct the three-dimensional load-bearing skeleton and internal coarse pore channels of the support, providing the support with mechanical strength and fluid channels.

[0052] The fine-particle red mud-alumina composite powder is composed of red mud and alumina, with a mass ratio of red mud to alumina of (20-80):(80-20), preferably (30-70):(70-30). The red mud is obtained from red mud waste generated during the Bayer process of alumina production after iron removal, drying, and calcination.

[0053] The chemical composition of the fine-particle red mud-alumina composite powder includes: Al2O3 30-45wt%, Fe2O3 15-25wt%, SiO2 10-20wt%, TiO2 3-8wt%, Na2O+CaO 5-12wt%, with a particle size range of 0.5-5μm and a median particle size D. 50 The mass fraction of 1.0-2.0μm red mud in all inorganic solid raw materials (including coarse alumina powder and fine red mud-alumina composite powder) is 10-60wt%. The alkaline oxides such as Na2O and CaO in the red mud can generate a low-melting-point eutectic liquid phase during the sintering stage, which promotes preferential densification in the fine particle region.

[0054] The removable pore-forming agent is an organic particulate material that decomposes or burns within a temperature range of 300-500℃, selected from one or more of starch, wood flour, cellulose-based particles, lignin, or their complexes. After decomposition or combustion removal during the degreasing stage, the removable pore-forming agent can form a continuous macroporous structure inside the support. The particle size range of the removable pore-forming agent is 30-150 μm.

[0055] The organic binder is a water-soluble or thermally decomposable polymer used to provide the molding strength of the preform and the rheological stability of the slurry. It can be selected from one or more of polyvinyl alcohol (PVA), acrylate emulsions, carboxymethyl cellulose (HPMC), and ammonium polyacrylate (PAA). The above binder can be completely decomposed during the degreasing stage, leaving no harmful impurities in the ceramic support.

[0056] Step S2: The slurry is shaped to obtain a blank with an initial layered structure. The surface of the blank is enriched with fine-particle red mud-alumina composite powder, and the interior is enriched with coarse-particle skeleton and removable pore-forming agent.

[0057] The molding process employs conventional techniques in the field, and the resulting blanks also adopt conventional structural forms. For example, the slurry is molded into tubular or flat blanks using methods such as vacuum extrusion, casting, or dry pressing; the tubular structure can be a single-channel or multi-channel honeycomb structure, while the flat structure typically has a thickness of 2-6 mm.

[0058] During extrusion or casting processes, due to the high shear rate near the wall, fine-grained red mud-alumina composite powder with a particle size of 0.5-5 μm is more likely to migrate and accumulate towards the forming wall under the influence of the flow shear gradient and particle size difference. Meanwhile, coarse-grained alumina powder with a particle size of 20-80 μm and removable pore-forming agents with a particle size of 30-150 μm have lower migration rates in high-solids systems and are mainly distributed in the internal region of the green body. Therefore, an initial layered structure is formed in the formed green body: the surface layer (first region) is enriched with fine-grained red mud-alumina composite powder; the interior (second region) is enriched with a coarse-grained framework and removable pore-forming agents. This initial particle distribution provides the basis for the formation of a pore size gradient structure during subsequent sintering.

[0059] The blank needs to be dried at 40-80℃ to remove residual water and ensure the stability of the layered structure.

[0060] Step S3 involves debinding and sintering the blank using a continuous heating process in a single debinding-sintering step to complete the preparation of the ceramic film support. This single debinding-sintering process includes three stages:

[0061] Stage I: Pre-dehydration stage, at 1-3℃·min -1 Heat to 200℃ and hold for 0.5-2 hours to remove free water and some bound water;

[0062] Stage II, Organic Matter Decomposition Stage: at 1-2℃·min -1 Heat to 350-600℃ and hold at 350-500℃ for 1-3 hours to allow the organic binder and removable pore-forming agent to decompose and burn gradually, forming a through-hole pre-placed channel inside the green body while retaining the skeleton structure composed of coarse particles.

[0063] Stage III, Main Sintering Stage: at 2-5℃·min -1 The temperature is raised to 1250-1450℃ and kept in air or a micro-oxygen atmosphere for 1-3 hours. This allows the low-melting-point components of the red mud to form a low-melting-point liquid phase on the surface of the blank, accelerating the growth rate of the sintering neck on the surface, reducing the pore size of the surface, and forming a longitudinal pore size gradient structure that changes continuously or stepwise from fine pores on the surface to coarse pores inside.

[0064] Through the above-described single debinding-sintering process, a pore structure with a significant longitudinal gradient can be obtained:

[0065] Surface region: A fine porous layer with modal pore sizes of 0.1-2.0 μm is formed;

[0066] Internal region: A coarse-porous layer with modal pore sizes of 3-20 μm is formed;

[0067] Aperture gradient characteristics: The modal aperture ratio between the surface and internal regions is 1:(3-20), and the longitudinal aperture gradient structure varies continuously or stepwise along the thickness direction.

[0068] The ceramic membrane support can form a stable longitudinal pore size gradient structure in a single debinding-sintering process, mainly due to the synergistic effect of the following three structural evolution mechanisms:

[0069] (1) Migration and stratification of graded particles during molding: During extrusion or casting molding, due to shear gradient and wall filtration effect, fine red mud-alumina composite powder and red mud are easy to migrate and accumulate in the wall area, while coarse alumina particles and organic pore-forming agents with larger particle size are mainly distributed in the interior of the cross section due to their lower migration speed, so that the green body has a particle stratification structure of "fine particle area on the surface - coarse particle area inside".

[0070] (2) The removable pore-forming agent forms internal interconnected macropores during the degreasing stage: In the degreasing temperature range of 350-500℃, the organic binder and the removable pore-forming agent gradually decompose and burn from the outside to the inside, while retaining the coarse particle skeleton, forming an interconnected macropore network in the internal region, further enhancing the internal coarse pore structure.

[0071] (3) The low-melting-point components of red mud generate liquid phase, which promotes preferential densification of the surface layer: The alkaline oxides such as Na2O, CaO, and Fe2O3 in red mud form a small amount of low-melting-point liquid phase in the range of about 900-1100℃. The content of this liquid phase is higher in the surface area where fine particles are concentrated, which is conducive to the growth of sintering neck and the connection between grains, so that the surface area preferentially densifies and the pore size is reduced; while the liquid phase content in the internal area is lower, and the coarse particle skeleton and the large pore channels formed by degreasing are maintained, thus forming a longitudinal pore size gradient structure from the surface fine pores to the internal coarse pores.

[0072] Using the above method, without the need for secondary coating or secondary sintering, the synergistic formation of surface fine pores and internal coarse pores can be achieved in a single degreasing-sintering process. This results in a support with a longitudinal gradient structure of surface fine pores, internal coarse pores, and pore diameters that gradually increase from the outside to the inside. The overall structure is continuous and stable, and can be directly used as a high-flux, low-pressure-drop support layer for ceramic separation membranes.

[0073] This embodiment also provides a red mud-based alumina ceramic membrane support, prepared using the above-described preparation method. The total open porosity of the ceramic membrane support is 30-50%. The support forms two characteristic pore structure regions along its thickness direction: the first region (surface layer) has a modal pore size of 0.1-2.0 μm; the second region (interior) has a modal pore size of 3-20 μm; the ratio of the modal pore sizes of the two regions is 1:(3-20).

[0074] This embodiment also provides an application of a red mud-based alumina ceramic membrane support, which can be made into a tubular (including single-channel and multi-channel honeycomb structure) or flat plate structure, and can be used directly as a support layer for microfiltration, ultrafiltration or nanofiltration membranes.

[0075] The technical solution provided by the present invention will be described in detail below with reference to different embodiments. It should be noted that the mass fractions mentioned in the slurry formulations of each embodiment are relative to the mass fraction of solids in the slurry, excluding the mass of solvent (deionized).

[0076] Example 1: Flat red mud-based alumina gradient support

[0077] (1) Slurry formulation

[0078] Coarse alumina powder: 50 wt% by mass, particle size range 20-80 µm, D 50 ≈45µm;

[0079] Fine-grained red mud-alumina composite powder: 35 wt% red mud to alumina mass ratio of 60:40, particle size range 0.5-5 µm, D 50 ≈1.5µm;

[0080] Removable pore-forming agent: corn starch, 10 wt% by mass, particle size 30-80 µm;

[0081] Organic binder: Polyvinyl alcohol (PVA), 5 wt%;

[0082] Solvent: Deionized water, used to adjust the slurry volume fraction to 52 vol%. Based on the average solid density (approximately 3.1 g·cm³). -3 The density of water (1.0 g·cm³) -3 The slurry has a solid content of approximately 78 wt%.

[0083] (2) Slurry preparation and rheological control

[0084] Coarse alumina powder and fine red mud-alumina composite powder were dry-mixed for 30 minutes according to the slurry formulation to obtain a uniform, graded particle system. Pre-dissolved PVA aqueous solution and some deionized water were added, and the mixture was wet-milled for 6 hours to ensure thorough dispersion of the fine particles and coating of the coarse particles. Corn starch was then added and stirred at low speed for 30 minutes to ensure uniform dispersion in the slurry. Finally, the slurry volume fraction was adjusted to 52 vol%, and the mixture was stirred at 25°C and a shear rate of 100 s. -1The apparent viscosity is approximately 160 mPa·s, and the rheological behavior exhibits obvious shear-thinning characteristics. During extrusion molding, fine particles and red mud are more likely to migrate towards the die wall region under the action of the shear field, while the larger starch pore-forming agent particles are relatively concentrated in the internal region of the cross section.

[0085] (3) Flat blank forming

[0086] The film was formed using a casting process, with a thickness of approximately 2.5 mm. After drying, the sheet was cut into 100 mm × 50 mm flat samples. Due to the presence of the casting shear field, fine particles and red mud were enriched on the upper surface of the sheet, while coarse particles and pine wood powder pore-forming agent were concentrated in the lower middle part of the sheet, thus forming an initial layered structure of a surface fine particle layer and an inner coarse particle layer at the preform stage.

[0087] (4) One-time degreasing-sintering

[0088] Stage I (Pre-dehydration): Heating from room temperature to 200℃ at a rate of 1℃·min -1 Keep it at 200℃ for 1 hour to remove free water and some bound water;

[0089] Stage II (Decomposition of Organic Matter): Heating from 200℃ to 600℃ at a rate of 1.5℃·min -1 The PVA and corn starch are kept at 400℃ for 1.5 hours, which allows the PVA and corn starch to decompose and burn gradually from the outside to the inside, retaining the coarse particle skeleton and forming a through-pore channel in the internal area.

[0090] Stage III (Main Sintering): Heating from 600℃ to 1350℃ at a rate of 3℃·min -1 The mixture was kept at 1350℃ for 2 hours. During this stage, components such as Na2O, CaO, and Fe2O3 in the red mud generated a small amount of low-melting-point liquid phase, which was more abundant in the surface region where fine particles were concentrated. This promoted the preferential necking and densification of the fine particles on the surface, while the coarse particle region inside maintained a relatively large pore structure due to the smaller amount of liquid phase.

[0091] (5) Structure and performance

[0092] After sintering, a red mud-based alumina tubular ceramic membrane support was obtained, and its properties are shown in Table 1.

[0093] Example 2: Tubular red mud-based alumina gradient support

[0094] (1) Slurry formulation

[0095] Coarse alumina powder: 55 wt%, D 50 ≈60µm;

[0096] Fine-grained red mud-alumina composite powder: 30 wt% red mud to alumina mass ratio of 50:50, D50 ≈1.0µm;

[0097] Removable pore-forming agent: pine wood powder, 8 wt% by mass, particle size 50-150 µm;

[0098] Organic binder: acrylic emulsion, 7 wt%;

[0099] Solvent: Deionized water, adjusted to 50 vol in slurry volume.

[0100] (2) Slurry preparation and rheological control

[0101] Coarse alumina powder and fine red mud-alumina composite powder were added to a ball mill jar according to the slurry formulation ratio and dry-mixed for 30 min. Pre-prepared acrylic emulsion and deionized water were added, and the mixture was wet-milled for 6 h to obtain a uniformly dispersed slurry. Then, pine wood powder pore-forming agent was added, and the mixture was stirred at low speed for 30 min to ensure uniform distribution within the system. The slurry volume fraction was adjusted to 50 vol%, and the mixture was milled at 25 °C and a shear rate of 100 s. -1 The apparent viscosity is approximately 150 mPa·s, exhibiting shear-thinning behavior, which is suitable for subsequent casting. During the casting process, fine particles and red mud preferentially aggregate towards the upper surface of the mold cavity, while coarse particles and pore-forming agents are relatively concentrated in the lower part of the sheet, laying the foundation for the formation of a "fine pores on the upper surface - coarse pores inside" structure.

[0102] (3) Tubular embryo formation

[0103] Vacuum extrusion molding was used, with an outer diameter of 12 mm and an inner diameter of 8 mm. The extrusion pressure was 3-6 MPa and the vacuum degree was -0.08 MPa, resulting in a single-channel tubular preform. After molding, the preform was dried at 40-60℃ for 24 hours to obtain a dry preform with an initial layered structure of "fine particle enrichment on the surface and coarse particle and pore-forming agent enrichment inside".

[0104] (4) One-time degreasing-sintering

[0105] Stage I: Heating from room temperature to 200℃ at a rate of 1℃·min -1 Keep warm at 200℃ for 1 hour;

[0106] Stage II: Heating from 200℃ to 600℃ at a rate of 1.5℃·min -1 The mixture is kept at 400℃ for 1.5 hours to allow the organic binder and pine powder to fully decompose.

[0107] Stage III: Heating from 600℃ to 1300℃ at a rate of 3℃·min -1 The surface is kept at 1300℃ for 1.5 hours to form a fine pore structure on the surface and a coarse pore structure inside.

[0108] (5) Structure and performance

[0109] After sintering, a flat red mud-based alumina gradient support was obtained, and its properties are shown in Table 1.

[0110] Example 3: Multi-channel tubular red mud-based gradient support

[0111] (1) Slurry formulation

[0112] Coarse alumina powder: 40 wt%, D 50 ≈35µm;

[0113] Fine-grained red mud-alumina composite powder: mass fraction 40wt%, mass ratio of red mud to alumina is 70:30, D 50 ≈2µm;

[0114] Removable pore-forming agent: starch-lignin composite particles, mass fraction 12wt%, particle size 40-120µm;

[0115] Organic binder: PVA, 8 wt% (by mass);

[0116] Solvent: Deionized water, adjusted to a slurry volume fraction of 55 vol.

[0117] (2) Slurry preparation and rheological control

[0118] Coarse alumina powder and fine red mud-alumina composite powder were dry-mixed in a specific ratio for 30 min. PVA aqueous solution and deionized water were added, and the mixture was wet-milled in a ball mill for 6 h to ensure uniform dispersion of the graded particle system. Subsequently, a starch-lignin composite pore-forming agent was added, and the mixture was stirred at low speed for 30 min to ensure uniform distribution of the pore-forming agent within the system. The slurry volume fraction was adjusted to 55 vol%, at which point the slurry viscosity was approximately 210 mPa·s, exhibiting significant shear-thinning behavior, suitable for multi-channel extrusion molding.

[0119] (3) Multi-channel extrusion molding

[0120] A ten-hole honeycomb mold with an outer diameter of 25 mm and a single hole diameter of approximately 3 mm was used; the extrusion pressure was 5-8 MPa and the vacuum degree was -0.09 MPa. After molding, the material was dried at 50℃ for 24 hours to obtain a multi-channel tubular preform with a cross-sectional morphology exhibiting a layered characteristic of "fine particles on the surface of the channel wall - coarse particles and pore-forming agent inside".

[0121] (4) One-time degreasing-sintering

[0122] Stage I: Heating from room temperature to 200℃ at a rate of 1℃·min -1 Keep warm at 200℃ for 1 hour;

[0123] Stage II: Heating from 200℃ to 600℃ at a rate of 1.5℃·min -1 Keep at 400℃ for 2 hours to ensure that the starch-lignin composite pore-forming agent is fully decomposed;

[0124] Stage III: Heating from 600℃ to 1260℃ at a rate of 3℃·min -1 The liquid phase was kept at 1260℃ for 3 hours, and the amount of liquid phase was controlled to avoid excessive densification of the multichannel structure.

[0125] (5) Structure and performance

[0126] The sintering yielded a multi-channel gradient support, the properties of which are shown in Table 1.

[0127] Comparative Example 1: Single-peak particles, without "skeleton-filler" structure

[0128] (1) Slurry formulation

[0129] Single-peak alumina powder: 90wt% by mass, particle size 2-20µm, D 50 ≈5µm;

[0130] Removable pore-forming agent: starch, 5 wt%;

[0131] Organic binder: PVA, 5 wt% (w / w)

[0132] Solvent: Deionized water, adjusted to a slurry volume fraction of 48 vol.

[0133] The slurry formulation uses only unimodal alumina powder, does not contain red mud, and does not have a grading system of coarse skeleton powder and fine filler powder. Therefore, it does not have the "skeleton-filler" structural feature of the present invention.

[0134] (2) Slurry preparation and rheological control

[0135] Single-peak alumina powder and starch were dry-mixed in a specific ratio for 30 min. PVA aqueous solution and deionized water were added, and the mixture was wet-milled for 8 h to obtain a uniform slurry. The slurry volume fraction was adjusted to 48 vol%, and the slurry viscosity was approximately 110 mPa·s. After molding, there was virtually no obvious particle stratification in the cross-section.

[0136] (3) Forming and sintering

[0137] Using the same plate preform preparation process and one-time degreasing-sintering procedure as in Example 1, a porous alumina plate support with a single-peak structure was obtained.

[0138] (4) Structure and performance

[0139] The performance is shown in Table 1, which is used to compare and verify the effects of graded particles and red mud on gradient structure and performance.

[0140] Comparative Example 2: Non-removable pore-forming agent

[0141] (1) Slurry formulation

[0142] Coarse alumina powder: mass fraction 42.5 wt%, D 50 ≈45µm;

[0143] Fine-grained red mud-alumina composite powder: mass fraction 42.5 wt%, red mud to alumina mass ratio 60:40, D 50 ≈1.5µm;

[0144] Organic binder: PVA, 5 wt% (w / w)

[0145] Solvent: Deionized water, adjusted to a slurry volume fraction of 50% vol%.

[0146] The main difference between this comparative example and Example 1 is that no removable pore-forming agent is added; the liquid phase sintering effect is introduced only through coarse and fine graded particles and red mud, without relying on organic pore-forming agents to form an internal macroporous network.

[0147] (2) Slurry preparation and rheological control

[0148] Coarse alumina powder and fine red mud-alumina composite powder were dry-mixed for 30 minutes according to the slurry formulation. PVA aqueous solution and deionized water were added, and the mixture was wet-milled for 6 hours. The slurry volume fraction was adjusted to 50 vol%, and the slurry viscosity was approximately 140 mPa·s. Due to the lack of a pore-forming agent, the molded green body was generally dense, making it difficult to form interconnected large pore channels inside.

[0149] (3) Forming and sintering

[0150] The tubular extrusion molding, drying, and one-time sintering process are the same as in Example 2.

[0151] (4) Structure and performance

[0152] After sintering, a tubular support was obtained, and its properties are shown in Table 1. This table is used to compare and analyze the changes in gradient structure and permeability under the condition of no pore-forming agent.

[0153] Comparative Example 3: Flat alumina ceramic membrane support for separation layer prepared by spray coating process

[0154] In this comparative example, to verify the difference between the secondary coating-sintering process and the one-time molding gradient structure of the present invention, a nano-separation layer was prepared on the surface of the sintered coarse-porous support using a spraying process, as detailed below.

[0155] (1) Preparation of the separation layer slurry

[0156] γ-Al₂O₃ nanoparticles (100 nm in diameter) were added to deionized water at a mass percentage of 10 wt%, along with 0.5 wt% ammonium polyacrylate (PAA) dispersant and 0.5 wt% PVA (5 wt% solution). The mixture was dispersed by high-speed stirring for 10 min, followed by wet milling in a planetary ball mill for 4 h to ensure thorough dispersion of the nanoparticles. The resulting slurry had a solid content of 10 wt% and a viscosity of 10 mPa·s (25 °C), suitable for spray atomization deposition.

[0157] (2) Pretreatment of support structure

[0158] The coarse-pore support after one sintering was placed in a 60°C oven to dry for 2 hours. Then, its surface was blown with compressed air to remove dust, and it was preheated at 80°C for 10 minutes to improve the uniformity of the sprayed film.

[0159] (3) Spray coating film forming process

[0160] The coating is applied using a spray gun with a nozzle diameter of 0.3 mm, an atomization pressure of 0.20 MPa, and a liquid delivery pressure of 0.05 MPa. The distance between the spray gun and the support is 15 cm, and the spraying speed is approximately 50 mm / s. -1 The spraying angle is 90°. Each spraying time is 15 seconds. After spraying, allow it to stand for 5 minutes to evaporate naturally. Repeat the spraying 3 times to form a continuous precursor film. After spraying, place the sample in a 60℃ oven to dry for 1 hour.

[0161] (4) Separation layer sintering treatment

[0162] Secondary sintering is performed after spraying:

[0163] The temperature is raised from room temperature to 200°C at a rate of 1°C / min. -1 ;

[0164] Heating from 200℃ to 600℃ at a rate of 2℃·min -1 ;

[0165] Heating from 600℃ to 1300℃ at a rate of 3℃·min -1 The first dense structure of the γ-Al2O3 separation layer was formed by holding the temperature at 1300℃ for 2 hours.

[0166] After the first sintering, the spraying-drying steps were repeated, followed by a second sintering under the same conditions (1300℃ for 2 hours). The final separation layer thickness was approximately 10-15µm.

[0167] (5) Structure and performance

[0168] The tubular alumina ceramic film support was obtained, and its properties are shown in Table 1.

[0169] The performance testing process for Examples 1-3 and Comparative Examples 1-3 includes the following:

[0170] (1) Pore structure and morphology characterization

[0171] (i) Scanning electron microscope (SEM)

[0172] The surface and cross-sectional morphology of the samples were observed using field emission scanning electron microscopy. The samples were photographed after gold sputtering to analyze the differences in surface and internal pore structures and particle migration and stratification.

[0173] (ii) Pore size distribution and open porosity

[0174] The mercury intrusion porosimetry method was used to test the porosity and pore size distribution of porous ceramics according to GB / T32361-2015 "Test Method for Porosity and Pore Size Distribution of Porous Ceramics" to obtain the modal pore size and open porosity; some samples were verified by the bubble point method (GB / T24602-2009).

[0175] (2) Mechanical property testing

[0176] (i) Bending strength (tubular / flat sample)

[0177] The test was conducted according to GB / T1965-2023 "Test Method for Room Temperature Bending Strength of Porous Ceramics", using a three-point bending method with a span of 30 mm and a loading rate of 0.5 mm·min. -1 Five samples were tested in each group, and the average value was taken.

[0178] (ii) Axial compressive strength (tubular sample)

[0179] The compressive strength of porous ceramics was determined according to GB / T1964-2023 "Test Method for Room Temperature Compressive Strength of Porous Ceramics", with a loading rate of 0.5 mm·min. -1 Calculate the ratio of maximum load to cross-sectional area.

[0180] (3) Rheological properties of slurry

[0181] The shear viscosity of the slurry (shear rate 0.1-1000 s⁻¹) was determined using a rotational rheometer at 25°C. -1 Shear rate-viscosity curves were obtained. By comparing the rheological behavior of slurries with different volume fractions in the range of 45-55 vol%, the suitable shear thinning range and rheological window for molding were determined to ensure particle migration and molding stability during extrusion or casting.

[0182] (4) Filtration performance test and pressure drop calculation

[0183] (i) Pure water flux and permeability test

[0184] The pure water flux test for tubular samples was performed according to the test procedure in HY / T064-2002 "Test Method for Tubular Ceramic Microporous Filter Membranes"; the pure water flux test for plate-shaped samples was performed according to the relevant test procedures in GB / T39717-2020 "Ceramic Membrane Plates for Water Treatment". The volumetric flux was determined at 25℃ using deionized water as the medium, within the range of 0.02-0.12 MPa. (L·m) -2 ·h -1 ),Record Linear relationship. Volumetric flux is calculated using the following formula:

[0185] J = V / (A·t)

[0186] In the formula, V is the permeate volume (L) passing through the membrane support in time t, and A is the effective filtration area (m²). 2 ), where t is the filtering time (h).

[0187] Convert volumetric flux to SI units (J / s, m·s) -1 And calculate the permeability coefficient k according to Darcy's law:

[0188] J_s=k·ΔP / (μ·L)

[0189] In the formula, J_s is the volumetric flux (m·s). -1 ); ΔP is the pressure difference across the membrane (Pa); μ is the viscosity of the medium (μ≈1.0×10 when water is used as the medium). -3 Pa·s); L is the wall thickness or plate thickness of the support (m); k is the permeability coefficient of the support.

[0190] By linearly fitting the J_s-ΔP data, k / (μ·L) is obtained, and then the permeability coefficient k is calculated.

[0191] To compare the pressure drop characteristics of different supports, a standard flux of 1000 L·m was selected. -2 ·h -1 (approximately 2.78 × 10) -4 m·s -1 Based on the above relationship, the required pressure difference under this flux is calculated and recorded as the corresponding operating pressure drop.

[0192] (ii) Suspended particulate filtration test

[0193] Using 200 mg·L -1Simulated wastewater containing SiO2 suspended particles was used as feed, and the samples were filtered under constant pressure of 0.10 MPa at 25°C. The initial flux and steady-state flux at 60 min were recorded, the flux retention rate was calculated, and the pressure drop change was recorded to evaluate the impact of the gradient structure on fluid resistance and pollution suppression performance.

[0194] The cross-sectional morphology of the flat ceramic membrane support prepared in Example 1 is as follows: Figure 1 As shown. Figure 1 Region (a) in the figure represents the surface fine-pored layer, formed by the enrichment of fine-particle red mud-alumina composite powder, with a uniform pore size distribution and a modal pore size of 0.5 μm. Region (b) in the figure represents the internal coarse-pored layer, composed of a three-dimensional framework of coarse-particle alumina and interconnected macroporous channels formed after the removal of the removable pore-forming agent, with a modal pore size of 8 μm. The pore size between the two regions increases along the thickness direction. The cross-sectional morphology of the flat ceramic membrane support prepared in Comparative Example 1 is shown below. Figure 2 As shown, since this sample uses unimodal alumina powder as raw material, its pore size remains basically consistent along the thickness direction, and no obvious gradient structure of surface fine pores and internal coarse pores is formed.

[0195] The results of the remaining experiments are shown in Table 1:

[0196] Table 1. Performance Comparison of Examples 1-3 and Comparative Examples 1-3

[0197]

[0198] Note: (1) All tests were conducted at 25±1℃ in deionized water or medium containing 200 mg·L⁻¹ -1 SiO2 suspended particles simulate wastewater;

[0199] (2) The pure water flux and pressure drop shall be carried out in accordance with GB / T21601-2008, and the suspended particle filtration flux retention rate shall be calculated based on the steady-state flux at a constant pressure of 0.10 MPa and filtration time of 60 min.

[0200] (3) Comparative Example 3 is a monolithic membrane element. Its permeation behavior is mainly dominated by the separation layer and interfacial resistance. The permeability coefficient k of its support was not calculated separately. Performance verification and results analysis:

[0201] (1) Pore structure characteristics and formation mechanism

[0202] Mercury intrusion porosimetry and bubble point testing results show that the surface modal pore size of the gradient structure samples (Examples 1-3) of the present invention is mainly concentrated in 0.5-1.0 μm, while the internal modal pore size is 6-15 μm. The ratio of surface to internal modal pore size is approximately 1:8-1:15, forming a significant longitudinal pore size gradient.

[0203] In comparison, the unimodal alumina support obtained in Comparative Example 1 has a basically uniform pore size distribution throughout the entire cross-section, without showing a clear surface fine pore layer and an internal coarse pore layer; although Comparative Example 2 uses coarse and fine graded particles and red mud, due to the lack of a removable pore-forming agent, the internal through-pores are insufficient, the overall pore size distribution is biased towards medium pore size, and the gradient characteristics are weakened; Comparative Example 3 involves spraying a nano separation layer on the surface of a coarse pore support, and its overall cross-section presents a typical double-layer structure of "dense film layer + coarse pore support", lacking the bulk phase gradient from surface fine pores to internal coarse pores described in this invention.

[0204] It should be noted that, under the typical parameters shown in Examples 1-3, the surface modal pore size is 0.5-1.0 μm, and the internal modal pore size is 6-15 μm, corresponding to a modal pore size ratio of approximately 1:8-1:15. Those skilled in the art can achieve a wider range of pore size ratios by appropriately adjusting parameters such as sintering temperature, holding time, and the proportion of fine-particle red mud-alumina composite powder, without departing from the spirit of this invention.

[0205] (2) Synergistic balance between porosity and mechanical properties

[0206] The open porosity of Examples 1-3 is 36-45%, which is slightly lower than the 45-50% of the traditional single-peak structure support (Comparative Example 1), but still maintains high permeability.

[0207] Mechanical performance test results show that the three-point bending strength of the gradient support of the present invention is ≥50MPa, and the axial compressive strength can reach up to about 80MPa, which is about 30-60% higher than that of the non-gradient comparative sample. This indicates that the "coarse particle skeleton-fine particle filler" three-dimensional structure constructed by the present invention provides an enhanced three-dimensional load-bearing skeleton while maintaining high porosity, achieving synergistic optimization of porosity and mechanical strength, and is suitable for continuous operation and backwashing conditions.

[0208] (3) Permeability and pressure drop characteristics

[0209] At 0.10 MPa, the pure water flux in Examples 1-3 was between 850-1350 L·m. -2 ·h -1 The flux was increased by approximately 20-40% compared to the non-gradient supports of Comparative Examples 1 and 2. The permeability coefficient k calculated according to Darcy's law was significantly higher than that of the comparative samples.

[0210] When 1000 L·m -2 ·h -1When the flux is used as a baseline, the required operating pressure drop of the gradient support of the present invention is reduced by approximately 30-65% compared to the comparative sample. This indicates that the longitudinal pore size gradient structure can effectively reduce the local contraction-expansion effect of the fluid within the support, improve the transition process between the surface fine pores and the internal coarse pores, thereby significantly reducing the pressure drop and improving the permeability without sacrificing mechanical strength.

[0211] (4) Suspended particulate filtration and anti-fouling performance

[0212] Filter containing 200 mg·L -1 When the SiO2 suspension is used, the gradient support of the present invention can still maintain a flux retention rate of 92-93% after running at a constant pressure of 0.10 MPa for 60 minutes, and the steady-state pressure drop is maintained in the range of 0.08-0.11 MPa, indicating that it still has good flux stability and low operating resistance under particulate clogging conditions.

[0213] In contrast, the supports of Comparative Examples 1 and 2, under the same test conditions, exhibited a flux retention rate of only 65-75% and a pressure drop increase of 40-80%. This indicates that single-peak structures or structures without pore-forming agents are more prone to deep blockage and local pore shrinkage during particle retention, leading to rapid flux decay and a significant increase in pressure drop.

[0214] A comprehensive comparison shows that the gradient support of the present invention has both high throughput and excellent anti-fouling stability, and is suitable for continuous filtration and backwashing conditions containing suspended particles or easily contaminated media.

[0215] (5) Red mud fluxing and environmental benefits

[0216] The alkaline oxides (Na₂O, CaO, etc.) in red mud form a low-melting-point liquid phase at 1250-1350℃. This promotes the sintering and densification of the fine-particle region on the surface, improving the structural integrity and mechanical strength of the support surface. Furthermore, it lowers the overall sintering temperature by approximately 100-150℃, resulting in significant energy savings compared to pure alumina systems. Simultaneously, by introducing 10-30 wt% red mud into the inorganic solid raw materials, this invention effectively reduces red mud stockpiles, achieving both energy conservation and emission reduction, as well as high-value utilization of solid waste, thus demonstrating significant environmental and economic benefits.

[0217] (6) Overall Conclusion

[0218] Compared to traditional non-gradient supports (single-peak particle size or pore-forming agent-free systems) and monolithic membrane elements using a two-stage spray-sintering process to prepare the separation layer, this invention achieves a longitudinal pore size gradient structure through a single debinding-sintering process, while maintaining high mechanical strength: a flux increase of approximately 20-40%; and at the same flux (e.g., 1000 L·m⁻¹). -2 ·h -1The pressure drop during operation is reduced by approximately 30-65%; the flux retention rate is significantly improved during anti-pollution operation. The red mud-based gradient support described in this invention can stably replicate gradient pore characteristics in tubular, flat, and multi-channel structures, making it suitable as a support for microfiltration, ultrafiltration, and nanofiltration membranes. It can also be used in catalytic carriers, separation / reaction coupling, and other fields, showing promising prospects for engineering and industrial applications.

[0219] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other modifications under the guidance of the present invention without departing from the spirit of the present invention, and all of these modifications are within the protection scope of the present invention.

Claims

1. A method for preparing a red mud-based alumina ceramic film support, characterized in that, Includes the following steps: Step S1: Prepare a slurry. The solids of the slurry include the following components: 40-55 wt% coarse alumina powder, 30-40 wt% fine red mud-alumina composite powder, 8-12 wt% removable pore-forming agent, and 3-8 wt% organic binder. The particle size range of the coarse alumina powder is 20-80 μm. The particle size range of the fine red mud-alumina composite powder is 0.5-5 μm. The removable pore-forming agent is an organic particulate material that decomposes or burns within a temperature range of 300-500℃, with a particle size range of 30-150 μm. Step S2: The slurry is shaped to obtain a blank with an initial layered structure. The surface of the blank is enriched with fine-particle red mud-alumina composite powder, and the interior is enriched with coarse-particle skeleton and removable pore-forming agent. Step S3 involves debinding and sintering the blank using a continuous heating process in a single debinding-sintering step to complete the preparation of the ceramic film support. This single debinding-sintering process includes three stages: Stage I: Pre-dehydration stage, at 1-3℃·min -1 Heat to 200℃ and hold for 0.5-2 hours to remove free water and some bound water; Stage II, Organic Matter Decomposition Stage: at 1-2℃·min -1 Heat to 350-600℃ and hold at 350-500℃ for 1-3 hours to allow the organic binder and removable pore-forming agent to decompose and burn gradually, forming a through-hole pre-placed channel inside the green body while retaining the skeleton structure composed of coarse particles. Stage III, Main Sintering Stage: at 2-5℃·min -1 Heat to 1250-1450℃ and keep warm in air or micro-oxygen atmosphere for 1-3 hours to allow the low melting point components of red mud to form a low melting point liquid phase on the surface of the blank, accelerate the growth rate of the sintering neck on the surface, reduce the pore size on the surface, and form a longitudinal pore size gradient structure that is continuous or stepped from the fine pores on the surface to the coarse pores inside. The fine-particle red mud-alumina composite powder is composed of red mud and alumina, wherein the mass ratio of red mud to alumina is (20-80):(80-20). The red mud is obtained from red mud waste in the Bayer process of alumina production after iron removal, drying and calcination.

2. The method for preparing the red mud-based alumina ceramic film support according to claim 1, characterized in that, Step S1 specifically includes the following process: Step S11: Dry mix coarse alumina powder and fine red mud-alumina composite powder according to the slurry formula ratio for 30 minutes to obtain a uniform graded particle system. Step S12: Add pre-dissolved organic binder and deionized water, and perform wet ball milling for 6 hours to fully disperse the fine particles and coat the surface of the coarse particles. Step S13: Then add a removable pore-forming agent and stir at low speed for 30 minutes to disperse it evenly, so as to obtain a slurry with a solid content of 45-55 vol% by volume and 70-80 wt% by mass.

3. The method for preparing the red mud-based alumina ceramic film support according to claim 1, characterized in that, The coarse alumina powder is selected as high-purity α-Al2O3 powder with an Al2O3 content of not less than 95%; the organic binder is a water-soluble or thermally decomposable polymer.

4. The method for preparing the red mud-based alumina ceramic film support according to claim 3, characterized in that, The chemical composition of the fine-particle red mud-alumina composite powder includes: Al2O3 30-45wt%, Fe2O3 15-25wt%, SiO2 10-20wt%, TiO2 3-8wt%, and a total content of Na2O and CaO of 5-12wt%; the removable pore-forming agent is selected from one or more of starch, cellulose-based particles, lignin, or their complexes; the organic binder is selected from one or more of polyvinyl alcohol, acrylate emulsions, hydroxymethyl cellulose, and ammonium polyacrylate.

5. The method for preparing the red mud-based alumina ceramic film support according to claim 1, characterized in that, Step S2 is as follows: The slurry is formed into flat or tubular blanks by vacuum extrusion, casting, or dry pressing; the thickness of the flat structure is 2-6mm, and the tubular structure is a single-channel or multi-channel honeycomb structure.

6. The method for preparing the red mud-based alumina ceramic film support according to claim 1, characterized in that, The blank is dried at 40-80℃.

7. A red mud-based alumina ceramic membrane support, characterized in that, It is prepared by the preparation method of the red mud-based alumina ceramic film support according to any one of claims 1-6.

8. The red mud-based alumina ceramic film support according to claim 7, characterized in that, The red mud-based alumina ceramic membrane support comprises a longitudinal pore size gradient structure that changes continuously or stepwise from fine pores on the surface to coarse pores on the inside. The total open porosity of the ceramic membrane support is 30-50%, wherein: A fine porous layer with modal pore sizes of 0.1-2.0 μm is formed in the surface region; The internal region forms a coarse-porous layer with modal pore sizes of 3-20 μm.

9. The red mud-based alumina ceramic film support according to claim 8, characterized in that, The modal aperture ratio between the surface region and the internal region is 1:(3-20).

10. The application of a red mud-based alumina ceramic film support as described in any one of claims 7-8, characterized in that, Used as a support layer for microfiltration, ultrafiltration or nanofiltration membranes.

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