Coal gangue-bauxite-based tubular ceramic support body and preparation method thereof

Abstract

The application belongs to the technical field of solid waste resource utilization, and discloses a coal gangue-bauxite-based tubular ceramic support body and a preparation method. The tubular ceramic support body is prepared by adding methyl cellulose, sodium sulfate, sodium chloride, aluminum fluoride, boron oxide and water into a mud after crushing, ball milling, sieving and pre-calcining of coal gangue and bauxite as main inorganic raw materials, and then by pugging, extrusion molding, segmented drying and sintering in a half-closed condition of a covered crucible. The method attempts to utilize the joint action of the gas phase reaction participated by aluminum fluoride and the sodium sulfate-sodium chloride molten salt process, so as to consider the porosity and mechanical strength of the support body at a lower temperature and realize the resource utilization of coal gangue. The compressive strength of the ceramic support body is 12.14-20.27 MPa, and the porosity is 43%-61%, which indicates that the process has certain low-temperature preparation feasibility.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization technology, specifically relating to a coal gangue-bauxite based tubular ceramic support and its preparation method. Background Technology

[0002] Coal gangue is a low-carbon black rock that is associated with coal during coal formation and becomes industrial solid waste during coal mining and washing. Large-scale accumulation of coal gangue not only occupies land, causing soil erosion, landslides, and other disasters, but also easily leads to a series of environmental problems due to heavy metal leaching, sulfide release, and spontaneous combustion of carbon and sulfur, polluting surrounding groundwater, air, and soil. In recent years, the comprehensive utilization of coal gangue has mainly focused on low-value applications such as roadbed backfilling, land reclamation, and co-firing for power generation. However, high-value-added products made from coal gangue are attracting increasing attention due to its ability to generate economic benefits while consuming solid waste. Coal gangue is mainly composed of inorganic components such as SiO2, Al2O3, CaO, MgO, Fe2O3, and some rare metals, and can be used as a low-cost raw material for silicon-aluminum ceramics.

[0003] In the preparation of ceramic membrane supports, mechanical strength and porosity are two key indicators determining their performance and application value. Insufficient mechanical strength can lead to cracking, breakage, or deformation of the support during molding, handling, membrane loading, and use, making it difficult to stably support the separation layer. Porosity directly affects the permeability, pore structure characteristics, and the subsequent construction effect of the separation layer. Meanwhile, sintering temperature is a crucial process factor that must be carefully considered during preparation, significantly influencing particle bonding, crystal phase changes, pore structure formation, and preparation costs. Too low a sintering temperature can result in insufficient structural bonding and decreased strength; too high a temperature can cause pore shrinkage, reduced porosity, and increased energy consumption. Therefore, how to achieve both high porosity and sufficient mechanical strength under relatively low cost conditions through reasonable control of the sintering process remains a technical problem that needs to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to solve the problem that it is difficult to balance porosity and mechanical strength in the existing coal gangue-bauxite system at a relatively low sintering temperature, and to provide a coal gangue-bauxite based tubular ceramic support and its preparation method.

[0005] The present invention proposes a method for preparing a coal gangue-bauxite-based tubular ceramic support, comprising the following steps: After kneading the mud containing coal gangue and bauxite, the mud is then refurbished under vacuum conditions to obtain refurbished mud. The prepared clay is plastically shaped to produce a multi-channel tubular ceramic support blank. A multi-channel tubular ceramic support preform was dried in stages by gradient heating to obtain a dried and shaped ceramic support preform. The dried ceramic support blank was placed in a semi-enclosed sintering environment for sintering. After sintering, it was cooled to room temperature to obtain a coal gangue-bauxite based tubular ceramic support.

[0006] Preferably, the mud material comprises, by mass percentage of dry material: 45.1%–60.0% coal gangue, 22.7%–32.2% bauxite, 2.9%–3.0% methylcellulose, 1.3%–1.4% sodium sulfate, 1.3%–1.4% sodium chloride, 9.0%–14.2% aluminum fluoride, and 2.7%–2.8% boron oxide.

[0007] Preferably, aluminum fluoride is used to participate in the gas phase sintering process, and sodium sulfate and sodium chloride are used to participate in the molten salt process; Before preparing the mud, the coal gangue and bauxite are mechanically crushed, ball-milled, and sieved separately, and then calcined and activated separately to obtain the coal gangue and bauxite. The ball milling speed is 200 r / min~230 r / min, the ball milling time is 8h~12h, and the sieve is 180-220 mesh. Coal gangue powder is calcined at 750℃~850℃ for 3h~5h, and bauxite powder is placed in a tube furnace and calcined at 550℃~650℃ for 3h~5h.

[0008] Preferably, a pore-forming agent is also added to the powder used to prepare the mud, wherein the pore-forming agent is at least one of starch, charcoal powder, and calcium carbonate.

[0009] Preferably, in the raw materials used for the mud, the molar amount of all aluminum elements converted to aluminum oxide and the molar amount of all silicon elements converted to silicon dioxide, the molar ratio of aluminum oxide to silicon dioxide is 31:34 to 3:2.

[0010] Preferably, the kneading pretreatment involves repeatedly pounding and kneading the clay, with a pretreatment time of 45 to 90 minutes. The prepared clay material is extruded under a pressure of 10MPa to 15MPa to obtain a multi-channel tubular ceramic support blank.

[0011] Preferably, the step of using a gradient heating and segmented drying process to obtain a dried and shaped ceramic support blank for the multi-channel tubular ceramic support blank specifically involves: First, dry the ceramic support body at 35℃~40℃ for 6h~9h, then dry it at 58℃~60℃ for 6h~9h, turning the green body intermittently during the drying process, and finally dry it at 95℃~100℃ for 6h~9h.

[0012] Preferably, the dried ceramic support blank is sintered in a semi-enclosed sintering environment, and then cooled to room temperature after sintering to obtain a coal gangue-bauxite based tubular ceramic support, specifically as follows: The sintering temperature is 900℃~1100℃, and the temperature is held for 1h~3h. The heating process is divided into two stages: slow first and fast, with 800℃ as the turning point. Under semi-enclosed sintering conditions, aluminum fluoride participates in the gas phase sintering process, while sodium sulfate and sodium chloride participate in the molten salt process, working together to sinter the embryo.

[0013] Preferably, the heating rate in the first stage of the heating process is 1℃ / min to 3℃ / min, and the heating rate in the second stage is 2℃ / min to 5℃ / min.

[0014] The present invention proposes a coal gangue-bauxite based tubular ceramic support, which is prepared by the aforementioned preparation method.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: This invention proposes a method for preparing a coal gangue-bauxite-based tubular ceramic support. First, a clay material containing coal gangue and bauxite is kneaded and vacuum-refined to ensure uniform mixing of the clay components, complete removal of internal air bubbles, and consistent overall plasticity. This avoids internal stress and microcracks during subsequent molding, drying, and sintering, laying a solid foundation for a uniform microstructure and fundamental mechanical properties of the support. Next, the refined clay material is plastically molded into a multi-channel tubular green body, ensuring a regular morphology and uniform structure, avoiding localized strength deficiencies and porosity imbalances caused by molding defects. Finally, a gradient heating and segmented drying method is employed. The green body is processed to remove internal moisture steadily and in stages, avoiding cracking and pore collapse caused by rapid drying. This effectively preserves the original interconnected pore structure of the green body, ensuring a high porosity in the finished product. Finally, the dried and shaped green body is sintered in a semi-enclosed sintering environment. Relying on the stable local sintering atmosphere, effective bonding between coal gangue and bauxite particles can be achieved without high-temperature sintering. This improves the mechanical strength of the support under low-temperature conditions while avoiding pore shrinkage and closure caused by high-temperature sintering. The entire process works together to effectively solve the technical challenge of simultaneously achieving porosity and mechanical strength in the coal gangue-bauxite system at lower sintering temperatures. Preparing tubular ceramic supports using coal gangue and bauxite as the main raw materials is beneficial for reducing raw material costs and expanding the resource utilization pathways of solid waste.

[0016] Furthermore, mechanical crushing and ball milling of coal gangue and bauxite can pulverize the raw materials into fine powder with uniform texture, followed by screening to ensure consistent particle size and avoid problems such as uneven mud composition, molding defects, and insufficient strength after sintering caused by coarse particles. Calcination of coal gangue can effectively remove impurities such as organic matter and carbonates, while activating the activity of silicon and aluminum components in the coal gangue. Calcination of bauxite can remove its internal water of crystallization, promote mineral phase transformation, and enhance the sintering activity of bauxite. After overall pretreatment, the activity of the raw materials is significantly improved, which can reduce the subsequent sintering temperature, alleviate the problem of insufficient particle bonding during low-temperature sintering, and reduce the adverse effects of impurities on the pore structure and mechanical strength of the support.

[0017] Furthermore, coal gangue and bauxite are used as core raw materials, making full use of their silicon and aluminum components to achieve high added value utilization of solid waste. At the same time, the combination of the two can optimize the silicon and aluminum ratio of the support, providing a material basis for the subsequent formation of a stable crystalline phase and balancing porosity and strength.

[0018] Furthermore, the binder methylcellulose significantly improves the plasticity and adhesion of the clay, preventing cracking and deformation of the green body during molding and ensuring the molding quality of the multi-channel tubular green body. The combination of sodium sulfate, sodium chloride, and aluminum fluoride catalyst is key to achieving gas-phase-molten salt coupled sintering, providing core support for subsequent low-temperature sintering; boron oxide can further reduce the sintering temperature, promote particle interface bonding, and help improve the mechanical strength of the support; the addition of an appropriate amount of water can adjust the consistency of the clay, ensuring that the components are fully mixed and that the clay has good molding and refining properties.

[0019] Furthermore, the roles of aluminum fluoride, sodium sulfate, and sodium chloride are differentiated. Under subsequent semi-closed sintering conditions, the two can work synergistically to sinter the green body. Aluminum fluoride participates in gas phase sintering, and molten salt components participate in the molten salt process, jointly promoting particle bonding at low temperatures. This not only improves the mechanical strength of the support but also avoids excessive sintering that leads to a decrease in porosity. This provides key process support for solving the problem of difficulty in balancing porosity and strength in low-temperature sintering. Attached Figure Description

[0020] Figure 1 This is a photograph of a tubular ceramic membrane support. Figure 2 This is a scanning electron microscope image of the internal cross-section of a tubular ceramic membrane support. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0022] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0023] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0024] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0025] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0026] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0027] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0028] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0029] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0030] In existing technologies, vapor phase sintering and molten salt methods are used separately to control the sintering and forming process of ceramic materials and the preparation process of mullite whiskers, respectively. However, the application of these two methods in the low-temperature preparation of coal gangue-bauxite-based tubular ceramic supports still needs further improvement. Using vapor phase sintering and molten salt methods in the preparation of coal gangue-bauxite-based tubular ceramic supports will produce a certain synergistic effect. The molten salt medium is beneficial for promoting the migration of Si and Al components and the formation of the mullite phase at lower temperatures, while the vapor phase reaction process containing volatile intermediates may affect the crystal growth mode and its morphological evolution. The resulting special structure helps improve the pore structure and permeability of the ceramic, and maintains good mechanical properties under certain conditions. Therefore, coupling the two methods in the low-temperature preparation process may provide a new technical approach to balance the porosity and mechanical strength of ceramic membrane supports. Based on this, this invention proposes a method for preparing a coal gangue-bauxite-based tubular ceramic support, including the following steps: Step 1: After kneading the clay, knead the clay under vacuum conditions to obtain kneaded clay. The clay, by mass percentage of dry materials, comprises: 45.1%–60.0% coal gangue, 22.7%–32.2% bauxite, 2.9%–3.0% methylcellulose, 1.3%–1.4% sodium sulfate, 1.3%–1.4% sodium chloride, 9.0%–14.2% aluminum fluoride, and 2.7%–2.8% boron oxide, with the remainder being water. Aluminum fluoride is used in the gas-phase sintering process, while sodium sulfate and sodium chloride are used in the molten salt process. Before preparing the mud, the coal gangue and bauxite are mechanically crushed, ball-milled, and sieved separately, and then calcined and activated separately to obtain the coal gangue and bauxite. The ball milling speed is 200 r / min ~ 230 r / min, the ball milling time is 8h ~ 12h, and the sieve is 180-220 mesh. The coal gangue powder is calcined at 750℃ ~ 850℃ for 3h ~ 5h, and the bauxite powder is placed in a tube furnace and calcined at 550℃ ~ 650℃ for 3h ~ 5h.

[0031] A pore-forming agent is also added to the powder used to prepare the mud. The pore-forming agent is at least one of starch, carbon powder, and calcium carbonate, which can further improve the porosity of the support.

[0032] In the raw materials used for the mud, the total amount of aluminum as aluminum oxide and the total amount of silicon as silicon dioxide are expressed in molar amounts, with a molar ratio of aluminum oxide to silicon dioxide of 31:34 to 3:2.

[0033] The kneading pretreatment involves repeatedly pounding and kneading the clay for 45 to 90 minutes; then, it is kneaded under vacuum for 2 to 3 times to fully remove air from the clay and make it uniform throughout.

[0034] Step 2: The prepared clay is plastically shaped to produce a multi-channel tubular ceramic support blank; The prepared clay material is extruded under a pressure of 10MPa to 15MPa to obtain an extruded multi-channel tubular ceramic support blank.

[0035] Step 3: The multi-channel tubular ceramic support blank is dried in stages by gradient heating to obtain a dried and shaped ceramic support blank. The process of using a gradient heating and segmented drying method to obtain a dried and shaped ceramic support blank is as follows: First, dry the ceramic support body at 35℃~40℃ for 6h~9h, then dry it at 58℃~60℃ for 6h~9h, turning the green body intermittently during the drying process, and finally dry it at 95℃~100℃ for 6h~9h.

[0036] Step 4: Place the dried ceramic support blank in a semi-enclosed sintering environment for sintering. After sintering, cool to room temperature to obtain a coal gangue-bauxite based tubular ceramic support.

[0037] The dried ceramic support blank is placed in a semi-enclosed sintering environment for sintering. After sintering, it is cooled to room temperature to obtain a coal gangue-bauxite based tubular ceramic support. Specifically: The ceramic support preform was placed in a covered crucible, covered with raw material powder, and then placed in a muffle furnace for sintering. The sintering temperature was 900℃~1100℃, and the temperature was held for 1h~3h. Finally, the furnace was cooled to room temperature to obtain a tubular ceramic support. The heating process was divided into two stages, with 800℃ as the turning point: a slow initial heating followed by a rapid heating. Under semi-enclosed sintering conditions, aluminum fluoride participates in the gas phase sintering process, while sodium sulfate and sodium chloride participate in the molten salt process, working together to sinter the embryo.

[0038] The heating rate in the first stage of the heating process is 1℃ / min to 3℃ / min, and the heating rate in the second stage is 2℃ / min to 5℃ / min.

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0040] Example 1 After the coal gangue and bauxite were mechanically crushed separately, they were ball-milled in a planetary ball mill at a speed of 200 r / min for 8 h. The fine powder with uniform texture obtained by ball milling was passed through a 190-mesh sieve. The coal gangue powder was placed in a muffle furnace and calcined at 750℃ for 3 h, and the bauxite powder was placed in a tube furnace and calcined at 550℃ for 5 h.

[0041] The mud was prepared by mixing coal gangue (60.0%), bauxite (22.7%), methylcellulose (3.0%), sodium sulfate (1.3%), sodium chloride (1.3%), aluminum fluoride (9.0%), and boron oxide (2.7%) evenly with water.

[0042] The obtained clay is repeatedly pounded and kneaded for 45 minutes. Then, the clay is placed in a vacuum clay mixer and kneaded twice to fully remove air from the clay and make it uniform throughout.

[0043] The prepared clay is placed in an extruder and subjected to a pressure of 10 MPa to obtain an extruded multi-channel tubular ceramic support preform.

[0044] The tubular ceramic support green body was dried in a constant humidity drying oven at 40 degrees Celsius for 6 hours, then dried in an electric heating blast drying oven at 58 degrees Celsius for 8 hours, turning it over every 15 minutes, and finally dried in a blast drying oven at 100 degrees Celsius for 6 hours.

[0045] The ceramic support preform was placed in a covered crucible, covered with raw material powder, and then sintered in a muffle furnace. The sintering temperature was 900℃. The preform was held at the sintering temperature for 1 hour, and then cooled to room temperature in the furnace to obtain a tubular ceramic support. Under the covered crucible sintering conditions, aluminum fluoride participated in the gas-phase sintering process, while sodium sulfate and sodium chloride participated in the molten salt process, working together to sinter the preform. The heating rate in the first stage of the sintering curve was 1℃ / min, and the heating rate in the second stage was 2℃ / min.

[0046] Aluminum is calculated as aluminum oxide, and silicon is calculated as silicon dioxide. The molar ratio of aluminum to silicon is 31:34.

[0047] Example 2 After the coal gangue and bauxite were mechanically crushed separately, they were ball-milled in a planetary ball mill at a speed of 230 r / min for 9 h. The fine powder with uniform texture obtained by ball milling was passed through a 180-mesh sieve. The coal gangue powder was placed in a muffle furnace and calcined at 800℃ for 4 h, and the bauxite powder was placed in a tube furnace and calcined at 650℃ for 3 h.

[0048] The mud was prepared by mixing coal gangue (56.3%), bauxite (25.3%), methylcellulose (3.0%), sodium sulfate (1.3%), sodium chloride (1.3%), aluminum fluoride (10.0%), and boron oxide (2.8%) evenly with water.

[0049] The obtained clay is repeatedly pounded and kneaded for 50 minutes. Then, the clay is placed in a vacuum clay mixer and kneaded twice to fully remove air from the clay and make it uniform throughout.

[0050] The prepared clay is placed in an extruder and subjected to a pressure of 13 MPa to obtain an extruded multi-channel tubular ceramic support preform.

[0051] The tubular ceramic support green body was dried in a constant humidity drying oven at 38 degrees Celsius for 8 hours, then dried in an electric heating blast drying oven at 60 degrees Celsius for 7 hours, turning it over every 15 minutes, and finally dried in a blast drying oven at 95 degrees Celsius for 8 hours.

[0052] The ceramic support preform was placed in a covered crucible, covered with raw material powder, and then sintered in a muffle furnace. The sintering temperature was 950℃. The preform was held at the sintering temperature for 1.5 hours, and then cooled to room temperature in the furnace to obtain a tubular ceramic support. Under the covered crucible sintering conditions, aluminum fluoride participated in the gas-phase sintering process, while sodium sulfate and sodium chloride participated in the molten salt process, working together to sinter the preform. The heating rate in the first stage of the sintering curve was 1.5℃ / min, and the heating rate in the second stage was 2.5℃ / min.

[0053] Aluminum is calculated as aluminum oxide, and silicon is calculated as silicon dioxide. The molar ratio of aluminum to silicon is 35:34.

[0054] Example 3 After the coal gangue and bauxite were mechanically crushed separately, they were ball-milled in a planetary ball mill at a speed of 215 r / min for 10 h. The fine powder with uniform texture obtained by ball milling was passed through a 200-mesh sieve. The coal gangue powder was placed in a muffle furnace and calcined at 850℃ for 4 h, and the bauxite powder was placed in a tube furnace and calcined at 550℃ for 4 h.

[0055] The mud was prepared by mixing coal gangue (53.0%), bauxite (27.5%), methylcellulose (3.0%), sodium sulfate (1.3%), sodium chloride (1.3%), aluminum fluoride (11.1%), and boron oxide (2.8%) evenly with water.

[0056] The obtained clay is repeatedly pounded and kneaded for 45 minutes. Then, the clay is placed in a vacuum clay mixer and kneaded three times to fully remove air from the clay and make it uniform throughout.

[0057] The prepared clay is placed in an extruder and subjected to a pressure of 15 MPa to obtain an extruded multi-channel tubular ceramic support preform.

[0058] The tubular ceramic support green body was dried in a constant humidity drying oven at 37 degrees Celsius for 7 hours, then dried in an electric heating drying oven at 59 degrees Celsius for 8 hours, turning it over every 15 minutes, and finally dried in a forced air drying oven at 98 degrees Celsius for 8 hours.

[0059] The ceramic support preform was placed in a covered crucible, covered with raw material powder, and then sintered in a muffle furnace. The sintering temperature was 1000℃. The preform was held at the sintering temperature for 2 hours, and then cooled to room temperature in the furnace to obtain a tubular ceramic support. Under the covered crucible sintering conditions, aluminum fluoride participated in the gas-phase sintering process, while sodium sulfate and sodium chloride participated in the molten salt process, working together to sinter the preform. The heating rate in the first stage of the sintering curve was 2℃ / min, and the heating rate in the second stage was 3℃ / min.

[0060] Aluminum is calculated as aluminum oxide, and silicon is calculated as silicon dioxide. The molar ratio of aluminum to silicon is 39:34.

[0061] Example 4 After the coal gangue and bauxite were mechanically crushed separately, they were ball-milled in a planetary ball mill at a speed of 220 r / min for 11 h. The fine powder with uniform texture obtained by ball milling was passed through a 200-mesh sieve. The coal gangue powder was placed in a muffle furnace and calcined at 800℃ for 3 h, and the bauxite powder was placed in a tube furnace and calcined at 600℃ for 4 h.

[0062] The mud was prepared by mixing coal gangue (50.1%), bauxite (29.3%), methylcellulose (3.0%), sodium sulfate (1.4%), sodium chloride (1.4%), aluminum fluoride (12.1%), and boron oxide (2.7%) evenly with water.

[0063] The obtained clay is repeatedly pounded and kneaded for 60 minutes. Then, the clay is placed in a vacuum clay mixer and kneaded three times to fully remove air from the clay and make it uniform throughout.

[0064] The prepared clay is placed in an extruder and subjected to a pressure of 13 MPa to obtain an extruded multi-channel tubular ceramic support preform.

[0065] The tubular ceramic support green body was dried in a constant humidity drying oven at 35 degrees Celsius for 9 hours, then dried in an electric heating blast drying oven at 60 degrees Celsius for 6 hours, turning it over every 15 minutes, and finally dried in a blast drying oven at 95 degrees Celsius for 9 hours.

[0066] The ceramic support preform was placed in a covered crucible, covered with raw material powder, and then sintered in a muffle furnace. The sintering temperature was 1050℃. The preform was held at this temperature for 2.5 hours, and then cooled to room temperature in the furnace to obtain a tubular ceramic support. Under the covered crucible sintering conditions, aluminum fluoride participated in the gas-phase sintering process, while sodium sulfate and sodium chloride participated in the molten salt process, working together to sinter the preform. The heating rate in the first stage of the sintering curve was 2.5℃ / min, and the heating rate in the second stage was 3.5℃ / min.

[0067] Aluminum is calculated as aluminum oxide, and silicon is calculated as silicon dioxide. The molar ratio of aluminum to silicon is 43:34.

[0068] Example 5 After the coal gangue and bauxite were mechanically crushed separately, they were ball-milled in a planetary ball mill at a speed of 230 r / min for 12 h. The fine powder with uniform texture obtained by ball milling was passed through a 200-mesh sieve. The coal gangue powder was placed in a muffle furnace and calcined at 750℃ for 3 h, and the bauxite powder was placed in a tube furnace and calcined at 600℃ for 4 h.

[0069] The mud was prepared by mixing coal gangue (47.5%), bauxite (30.9%), methylcellulose (3.0%), sodium sulfate (1.3%), sodium chloride (1.3%), aluminum fluoride (13.2%), and boron oxide (2.8%) evenly with water.

[0070] The obtained clay is repeatedly pounded and kneaded for 90 minutes. Then, the clay is placed in a vacuum clay mixer twice to fully remove air from the clay and make it uniform throughout.

[0071] The prepared clay is placed in an extruder and subjected to a pressure of 12 MPa to obtain an extruded multi-channel tubular ceramic support preform.

[0072] The tubular ceramic support green body was dried in a constant humidity drying oven at 40 degrees Celsius for 6 hours, then dried in an electric heating blast drying oven at 58 degrees Celsius for 9 hours, turning it over every 15 minutes, and finally dried in a blast drying oven at 95 degrees Celsius for 9 hours.

[0073] The ceramic support preform was placed in a covered crucible, covered with raw material powder, and then sintered in a muffle furnace. The sintering temperature was 1100℃. The preform was held at this temperature for 3 hours, and then cooled to room temperature in the furnace to obtain a tubular ceramic support. Under the covered crucible sintering conditions, aluminum fluoride participated in the gas-phase sintering process, while sodium sulfate and sodium chloride participated in the molten salt process, working together to sinter the preform. The heating rate in the first stage of the sintering curve was 3.0℃ / min, and the heating rate in the second stage was 4.0℃ / min.

[0074] Aluminum is calculated as aluminum oxide, and silicon is calculated as silicon dioxide. The molar ratio of aluminum to silicon is 47:34.

[0075] Example 6 After mechanically crushing the coal gangue, it was ball-milled in a planetary ball mill at a speed of 225 r / min for 12 h. The fine powder with uniform texture obtained by ball milling was passed through a 220-mesh sieve. The coal gangue powder was placed in a muffle furnace and calcined at 800℃ for 5 h, while the bauxite powder was placed in a tube furnace and calcined at 550℃ for 4 h.

[0076] The mud was prepared by mixing 45.1% coal gangue, 32.2% bauxite, 2.9% methylcellulose, 1.4% sodium sulfate, 1.4% sodium chloride, 14.2% aluminum fluoride, and 2.8% boron oxide evenly with water.

[0077] The obtained clay is repeatedly pounded and kneaded for 80 minutes. Then, the clay is placed in a vacuum clay mixer and kneaded twice to fully remove air from the clay and make it uniform throughout.

[0078] The prepared clay is placed in an extruder and subjected to a pressure of 11 MPa to obtain an extruded multi-channel tubular ceramic support preform.

[0079] The tubular ceramic support green body was dried in a constant humidity drying oven at 39 degrees Celsius for 7 hours, then dried in an electric heating drying oven at 60 degrees Celsius for 7 hours, turning it over every 15 minutes, and finally dried in a forced air drying oven at 100 degrees Celsius for 8 hours.

[0080] The ceramic support preform was placed in a covered crucible, covered with raw material powder, and then sintered in a muffle furnace. The sintering temperature was 1050℃. The preform was held at the sintering temperature for 2.5 hours, and then cooled to room temperature in the furnace to obtain a tubular ceramic support. Under the covered crucible sintering conditions, aluminum fluoride participated in the gas-phase sintering process, while sodium sulfate and sodium chloride participated in the molten salt process, working together to sinter the preform. The heating rate in the first stage of the sintering curve was 1.5℃ / min, and the heating rate in the second stage was 5.0℃ / min.

[0081] Aluminum is calculated as aluminum oxide, and silicon is calculated as silicon dioxide. The molar ratio of aluminum to silicon is 3:2.

[0082] Comparative Example 1 After the coal gangue and bauxite were mechanically crushed separately, they were ball-milled in a planetary ball mill at a speed of 225 r / min for 12 h. The fine powder with uniform texture obtained by ball milling was passed through a 200-mesh sieve. The coal gangue powder was placed in a muffle furnace and calcined at 800℃ for 4 h, and the bauxite powder was placed in a tube furnace and calcined at 600℃ for 3 h.

[0083] The mud was prepared by mixing 40.9% coal gangue, 50.0% bauxite, 3.0% methylcellulose, 1.5% sodium sulfate, 1.5% sodium chloride, and 3.1% boron oxide evenly with water.

[0084] The obtained clay is repeatedly pounded and kneaded for 30 minutes. Then, the clay is placed in a vacuum clay mixer and kneaded twice to fully remove air from the clay and make it uniform throughout.

[0085] The prepared clay is placed in an extruder and subjected to a pressure of 15 MPa to obtain an extruded multi-channel tubular ceramic support preform.

[0086] The tubular ceramic support green body was dried in a constant humidity drying oven at 40 degrees Celsius for 9 hours, then dried in an electric heating drying oven at 60 degrees Celsius for 7 hours, turning it over every 15 minutes, and finally dried in a forced air drying oven at 100 degrees Celsius for 8 hours.

[0087] The ceramic support blank was placed in a covered crucible, covered with raw material powder, and then placed in a muffle furnace for sintering. The sintering temperature was 900℃.

[0088] The ceramic support was held at the sintering temperature for 1.0 h and then cooled to room temperature in the furnace to obtain a tubular ceramic support. Under the sintering conditions of the covered crucible, sodium sulfate participated in the molten salt process, and the two acted together on the sintering of the green body. The heating rate in the first stage of the sintering curve was 1.0 °C / min, and the heating rate in the second stage was 3.0 °C / min.

[0089] Aluminum is expressed as aluminum oxide, and silicon as silicon dioxide. The molar ratio of aluminum to silicon is approximately 15:8.

[0090] Comparative Example 2 After the coal gangue and bauxite were mechanically crushed separately, they were ball-milled in a planetary ball mill at a speed of 225 r / min for 12 h. The fine powder with uniform texture obtained by ball milling was passed through a 200-mesh sieve. The coal gangue powder was placed in a muffle furnace and calcined at 800℃ for 4 h, and the bauxite powder was placed in a tube furnace and calcined at 600℃ for 3 h.

[0091] The mud was prepared by mixing 38.0% coal gangue, 46.4% bauxite, 3.0% methylcellulose, 9.7% aluminum fluoride and 2.9% boron oxide evenly with water.

[0092] The obtained clay is repeatedly pounded and kneaded for 30 minutes. Then, the clay is placed in a vacuum clay mixer and kneaded twice to fully remove air from the clay and make it uniform throughout.

[0093] The prepared clay is placed in an extruder and subjected to a pressure of 15 MPa to obtain an extruded multi-channel tubular ceramic support preform.

[0094] The tubular ceramic support green body was dried in a constant humidity drying oven at 40 degrees Celsius for 9 hours, then dried in an electric heating drying oven at 60 degrees Celsius for 7 hours, turning it over every 15 minutes, and finally dried in a forced air drying oven at 100 degrees Celsius for 8 hours.

[0095] The ceramic support blank was placed in a covered crucible, covered with raw material powder, and then placed in a muffle furnace for sintering. The sintering temperature was 900℃.

[0096] The material was held at the sintering temperature for 1.5 hours and then cooled to room temperature in the furnace to obtain a tubular ceramic support. Under the sintering conditions of the covered crucible, aluminum fluoride participated in the gas-phase sintering process. The heating rate in the first stage of the sintering curve was 1.5 °C / min, and the heating rate in the second stage was 3.5 °C / min.

[0097] Aluminum is expressed as aluminum oxide, and silicon as silicon dioxide. The molar ratio of aluminum to silicon is approximately 40:19.

[0098] Comparative Example 3 After the coal gangue and bauxite were mechanically crushed separately, they were ball-milled in a planetary ball mill at a speed of 225 r / min for 12 h. The fine powder with uniform texture obtained by ball milling was passed through a 200-mesh sieve. The coal gangue powder was placed in a muffle furnace and calcined at 800℃ for 4 h, and the bauxite powder was placed in a tube furnace and calcined at 600℃ for 3 h.

[0099] The mud was prepared by mixing 38.0% coal gangue, 46.5% bauxite, 3.0% methylcellulose, 1.4% sodium sulfate, 1.4% sodium chloride, and 9.7% aluminum fluoride evenly with water.

[0100] The obtained clay is repeatedly pounded and kneaded for 30 minutes. Then, the clay is placed in a vacuum clay mixer and kneaded twice to fully remove air from the clay and make it uniform throughout.

[0101] The prepared clay is placed in an extruder and subjected to a pressure of 15 MPa to obtain an extruded multi-channel tubular ceramic support preform.

[0102] The tubular ceramic support green body was dried in a constant humidity drying oven at 40 degrees Celsius for 9 hours, then dried in an electric heating drying oven at 60 degrees Celsius for 7 hours, turning it over every 15 minutes, and finally dried in a forced air drying oven at 100 degrees Celsius for 8 hours.

[0103] The ceramic support blank was placed in a covered crucible, covered with raw material powder, and then placed in a muffle furnace for sintering. The sintering temperature was 900℃.

[0104] The ceramic support was held at the sintering temperature for 2.5 hours and then cooled to room temperature in the furnace to obtain a tubular ceramic support. Under the sintering conditions of the covered crucible, aluminum fluoride participated in the gas-phase sintering process, and sodium sulfate participated in the molten salt process; both acted together on the sintering of the green body. The heating rate in the first stage of the sintering curve was 2.0 °C / min, and the heating rate in the second stage was 4.0 °C / min.

[0105] Aluminum is calculated as aluminum oxide, and silicon is calculated as silicon dioxide. The molar ratio of aluminum to silicon is approximately 19:9.

[0106] Comparative Example 4 After the coal gangue and bauxite were mechanically crushed separately, they were ball-milled in a planetary ball mill at a speed of 225 r / min for 12 h. The fine powder with uniform texture obtained by ball milling was passed through a 200-mesh sieve. The coal gangue powder was placed in a muffle furnace and calcined at 800℃ for 4 h, and the bauxite powder was placed in a tube furnace and calcined at 600℃ for 3 h.

[0107] The mud was prepared by mixing 43.7% coal gangue, 53.3% bauxite, and 3.0% methylcellulose evenly with water.

[0108] The obtained clay is repeatedly pounded and kneaded for 30 minutes. Then, the clay is placed in a vacuum clay mixer and kneaded twice to fully remove air from the clay and make it uniform throughout.

[0109] The prepared clay is placed in an extruder and subjected to a pressure of 15 MPa to obtain an extruded multi-channel tubular ceramic support preform.

[0110] The tubular ceramic support green body was dried in a constant humidity drying oven at 40 degrees Celsius for 9 hours, then dried in an electric heating drying oven at 60 degrees Celsius for 7 hours, turning it over every 15 minutes, and finally dried in a forced air drying oven at 100 degrees Celsius for 8 hours.

[0111] The ceramic support blank was placed in a covered crucible, covered with raw material powder, and then placed in a muffle furnace for sintering. The sintering temperature was 900℃.

[0112] The material was held at the sintering temperature for 2.5 hours and then cooled to room temperature in the furnace to obtain a tubular ceramic support. The heating rate in the first stage of the sintering curve was 2.5 °C / min, and the heating rate in the second stage was 5.0 °C / min.

[0113] Aluminum is expressed as aluminum oxide, and silicon as silicon dioxide. The molar ratio of aluminum to silicon is approximately 28:15.

[0114] Table 1 Implementation Results

[0115] Table 1 shows the performance test results of the coal gangue-bauxite-based tubular ceramic membrane support of the present invention. All indicators were tested according to national standard methods, and the data are reliable. The present invention, through a gas-phase-molten salt coupled low-temperature sintering process, can achieve on-demand control of the compressive strength (12.14MPa~20.27MPa) and porosity (43%~61%) of the support within the range of 900℃-1100℃. Under the same low-temperature condition of 900℃, the compressive strength of the sample of the present invention is significantly higher than that of the comparative examples, proving that the process can achieve good sintering densification at low temperature, effectively solving the contradiction of difficulty in balancing strength and porosity in conventional low-temperature sintering, and greatly improving the mechanical stability and industrial application adaptability of the support.

[0116] Figure 1This is a photograph of the coal gangue-bauxite-based multi-channel tubular ceramic membrane support prepared according to the present invention. The support has a cylindrical structure with seven uniformly distributed through-flow channels across its cross-section, suitable for the industrial installation and fluid distribution requirements of tubular membrane modules. Its overall appearance is a uniform brownish-red, with a dense surface free of obvious defects, cracks, or deformation, indicating that the slurry preparation, molding, and sintering processes of the present invention can stably produce supports with regular dimensions and satisfactory appearance. The overall morphology and flow channel structure of the support provide a stable physical carrier foundation for subsequent loading of functional membrane layers and the realization of membrane separation processes. Figure 2 This is a scanning electron microscope (SEM) image of the internal cross-section of the coal gangue-bauxite-based tubular ceramic membrane support prepared according to the present invention (magnification scale bar is 100 μm). As can be seen from the image, the support has a uniform porous structure with interconnected three-dimensional pore networks between particles. The pore size distribution is uniform, with no obvious closed pores or local densification defects. This is a direct manifestation of the control of pore structure by the gas-phase-molten salt coupled low-temperature sintering process. At the same time, the particles are firmly bonded and the skeleton is intact, indicating that the process can achieve good sintering neck formation under low-temperature conditions, taking into account both the high porosity and mechanical strength of the support, effectively reducing fluid transport resistance, and meeting the mechanical requirements of industrial applications.

[0117] The ceramic support preform undergoes sintering densification and pore structure evolution under semi-closed sintering conditions in a covered crucible with an additive system containing aluminum fluoride and sodium sulfate. By adjusting the additive content and sintering temperature, the coupled sintering environment involving both gas-phase sintering and molten salt processes can be altered, which is beneficial for controlling the porosity, mechanical strength, and pore size distribution of the support. The beneficial effects of this invention are: 1) This invention combines the gas-phase sintering process involving aluminum fluoride with the sodium sulfate-sodium chloride molten salt process, constructing a coupled sintering environment under semi-closed conditions. Boron oxide and metal oxides in coal gangue are used to assist sintering for the low-temperature preparation of coal gangue-bauxite-based tubular ceramic supports. The conventional support sintering temperature is reduced from 1200–1600℃ to below 1100℃. A porosity of 43%–61% and mechanical properties of 12.14–20.27 MPa are obtained at 900–1100℃. This method significantly reduces sintering energy consumption, aligns with the principles of energy conservation, emission reduction, and green development, and offers significant economic, environmental, and social benefits. The product possesses strong market competitiveness. 2) The above method can produce tubular ceramic supports with good porosity and excellent compressive strength, facilitating a balance between structural and mechanical properties. The porosity is greater than 30%, and the compressive strength is greater than 3.5 MPa, meeting the "General Technical Conditions for Porous Ceramic Products," and exhibiting good resistance to brittleness. 3) This method uses coal gangue and bauxite as the main inorganic raw materials, which is beneficial for the resource utilization of industrial solid waste and the preparation of low-cost supports.

[0118] In summary, this invention proposes a method for the low-temperature preparation of coal gangue-bauxite-based tubular ceramic supports using a coupled gas-phase sintering-molten salt process. Under semi-enclosed conditions, this method couples an aluminum fluoride-involved gas-phase sintering process with a sodium sulfate molten salt process to prepare high-strength coal gangue-bauxite-based tubular ceramic supports at low temperatures. Specifically, coal gangue and bauxite are used as the main inorganic raw materials. After crushing, ball milling, sieving, and pre-calcining, methylcellulose, sodium sulfate, sodium chloride, aluminum fluoride, boron oxide, and water are added to prepare a slurry. After slurry preparation, extrusion molding, and segmented drying, the slurry is sintered at 900–1100℃ under semi-enclosed conditions in a covered crucible to obtain the tubular ceramic support. This method attempts to utilize the combined effect of the aluminum fluoride-involved gas-phase reaction and the sodium sulfate-sodium chloride molten salt process to balance the porosity and mechanical strength of the support at a relatively low temperature, while also realizing the resource utilization of coal gangue. Examples show that the compressive strength of the obtained samples is 12.14–20.27 MPa and the porosity is 43%–61%, indicating that the process has certain feasibility for low-temperature preparation.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a coal gangue-bauxite-based tubular ceramic support, characterized in that, Includes the following steps: After kneading the mud containing coal gangue and bauxite, the mud is then refurbished under vacuum conditions to obtain refurbished mud. The prepared clay is plastically shaped to produce a multi-channel tubular ceramic support blank. A multi-channel tubular ceramic support preform was dried in stages by gradient heating to obtain a dried and shaped ceramic support preform. The dried ceramic support blank was placed in a semi-enclosed sintering environment for sintering. After sintering, it was cooled to room temperature to obtain a coal gangue-bauxite based tubular ceramic support.

2. The method for preparing the coal gangue-bauxite-based tubular ceramic support according to claim 1, characterized in that, The mud material comprises, by mass percentage of dry material: 45.1%–60.0% coal gangue, 22.7%–32.2% bauxite, 2.9%–3.0% methylcellulose, 1.3%–1.4% sodium sulfate, 1.3%–1.4% sodium chloride, 9.0%–14.2% aluminum fluoride, and 2.7%–2.8% boron oxide.

3. The method for preparing the coal gangue-bauxite-based tubular ceramic support according to claim 2, characterized in that, Aluminum fluoride is used in the gas phase sintering process, while sodium sulfate and sodium chloride are used in the molten salt process. Before preparing the mud, the coal gangue and bauxite are mechanically crushed, ball-milled, and sieved separately, and then calcined and activated separately to obtain the coal gangue and bauxite. The ball milling speed is 200 r / min~230 r / min, the ball milling time is 8h~12h, and the sieve is 180-220 mesh. Coal gangue powder is calcined at 750℃~850℃ for 3h~5h, and bauxite powder is placed in a tube furnace and calcined at 550℃~650℃ for 3h~5h.

4. The method for preparing the coal gangue-bauxite-based tubular ceramic support according to claim 2, characterized in that, A pore-forming agent is also added to the powder used to prepare the mud, and the pore-forming agent is at least one of starch, charcoal powder, and calcium carbonate.

5. The method for preparing the coal gangue-bauxite-based tubular ceramic support according to claim 2, characterized in that, In the raw materials used for the mud, the total amount of aluminum as aluminum oxide and the total amount of silicon as silicon dioxide are expressed in molar amounts, with a molar ratio of aluminum oxide to silicon dioxide of 31:34 to 3:

2.

6. The method for preparing the coal gangue-bauxite-based tubular ceramic support according to claim 1, characterized in that, The kneading pretreatment involves repeatedly pounding and kneading the clay, with a pretreatment time of 45 to 90 minutes. The prepared clay material is extruded under a pressure of 10MPa to 15MPa to obtain a multi-channel tubular ceramic support blank.

7. The method for preparing the coal gangue-bauxite-based tubular ceramic support according to claim 1, characterized in that, The process of using a gradient heating and segmented drying method to obtain a dried and shaped ceramic support blank is as follows: First, dry the ceramic support body at 35℃~40℃ for 6h~9h, then dry it at 58℃~60℃ for 6h~9h, turning the green body intermittently during the drying process, and finally dry it at 95℃~100℃ for 6h~9h.

8. The method for preparing the coal gangue-bauxite-based tubular ceramic support according to claim 1, characterized in that, The dried ceramic support blank is placed in a semi-enclosed sintering environment for sintering. After sintering, it is cooled to room temperature to obtain a coal gangue-bauxite based tubular ceramic support. Specifically: The sintering temperature is 900℃~1100℃, and the temperature is held for 1h~3h. The heating process is divided into two stages: slow first and fast, with 800℃ as the turning point. Under semi-enclosed sintering conditions, aluminum fluoride participates in the gas phase sintering process, while sodium sulfate and sodium chloride participate in the molten salt process, working together to sinter the embryo.

9. The method for preparing the coal gangue-bauxite-based tubular ceramic support according to claim 8, characterized in that, The heating rate in the first stage of the heating process is 1℃ / min to 3℃ / min, and the heating rate in the second stage is 2℃ / min to 5℃ / min.

10. A coal gangue-bauxite based tubular ceramic support, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 9.

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