Method for preparing fiber-reinforced coal gangue-based composite functional aerogel

Abstract

The invention belongs to the field of coal gangue resource utilization, and particularly discloses a method for preparing fiber-reinforced coal gangue-based composite functional aerogel. After being activated, the coal gangue is put into an acid leaching solution to be leached, and an aluminum-rich solution is obtained; adding ammonia water into the aluminum-rich solution to adjust the pH to obtain hydroxide precipitate; adding a sodium hydroxide solution into the precipitate to react to obtain a sodium aluminate solution; neutralizing the sodium aluminate solution with hydrochloric acid to obtain an aluminum chloride solution, stirring to obtain aluminum sol, and adding ceramic fibers into the aluminum sol; violently stirring the sol, and adding epoxypropane to obtain wet gel; after aging the wet gel, carrying out surface modification to obtain hydrophobic coal gangue-based aluminum oxide and composite wet gel of the hydrophobic coal gangue-based aluminum oxide; and drying the modified wet gel at normal pressure to obtain the hydrophobic coal gangue-based aluminum oxide and the composite aerogel thereof. Ceramic fibers are introduced as a reinforcing phase, so that the compressive strength and toughness of the material are improved; the composite aerogel is subjected to surface modification, uniform modification is ensured, the contact angle is remarkably increased, the hygroscopicity is reduced, and the stability of the material is enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of aerogel preparation, and particularly relates to a method for preparing fiber-reinforced gangue-based composite functional aerogel. Background Art

[0002] The comprehensive utilization of coal gangue, a solid waste generated during coal mining and washing, is crucial for promoting the sustainable development of the coal industry. Gangue has a complex and diverse composition, primarily containing various valuable elements such as silica and alumina, making it an important secondary resource. However, the comprehensive utilization rate of gangue resources in my country remains low. Large accumulations not only severely deplete resources but also easily release large amounts of toxic and harmful gases, which seep into groundwater and soil, causing severe environmental damage over time.

[0003] Gangue is currently primarily used in building materials production, chemical raw material extraction, and agriculture. While it serves as an inexpensive source of valuable elements like silicon and aluminum, its high-value utilization still faces numerous challenges due to factors such as inefficient extraction technology and low added value.

[0004] Coal gangue is rich in silicon and aluminum and can be used as a cheap silicon and aluminum raw material. In the inventor's previous research, different types of silica and alumina products were successfully synthesized from coal gangue, but the extracted silica and alumina products were mostly in traditional forms (such as powder and granules).

[0005] Aerogels are novel materials with a three-dimensional amorphous structure and an open, cross-linked network. Their unique structure endows them with exceptional properties, including high surface area, high porosity, low thermal conductivity, and low dielectric constant. These properties offer aerogels promising applications in aerospace, ultra-thermal insulation, adsorption separation, catalysis, and other fields. Currently, various types of aerogels have been developed, including metal oxide aerogels, carbon aerogels, and organic aerogels. Alumina aerogels, a representative of metal oxide aerogels, have attracted considerable attention due to their unique high-temperature stability, large pore volume, and excellent chemical durability. Compared to traditional silica, monolithic alumina aerogels offer a wider operating temperature range and exhibit significant advantages in thermal insulation. However, similar to other aerogels, alumina aerogels exhibit a tendency to absorb moisture, exhibit significant brittleness, and exhibit poor mechanical strength. These characteristics limit their long-term use, particularly in thermal insulation applications where durability and structural integrity are crucial.

[0006] To address the mechanical limitations of alumina aerogels, efforts have been made to improve their mechanical properties. Fiber reinforcement is one of the most common and effective strategies for improving the mechanical properties of alumina aerogels. High-strength fibers are incorporated into the aerogel matrix to form fiber-reinforced composite aerogels. Among the various fibers used as reinforcements for aerogel composites, refractory fibers such as aluminum silicate fibers have attracted widespread attention due to their low density, high-temperature resistance, long-term stability, and excellent mechanical properties. Introducing these fibers into the aerogel structure is beneficial for enhancing its mechanical properties while maintaining excellent thermal properties. However, uniformly dispersing and effectively incorporating the fibers into the alumina aerogel matrix typically requires multiple, carefully controlled steps, including fiber pretreatment, sol-gel processing, and specialized drying methods (such as supercritical drying). These processes require high levels of equipment and operator skill, resulting in low production efficiency and high costs, which seriously hinder the large-scale industrial production and widespread application of this technology. Furthermore, achieving highly uniform dispersion of fibers in the gel network and optimizing the strong interfacial bonding between the fibers and the brittle aerogel matrix remain technical challenges, directly affecting the stability and efficiency of the reinforcement effect. At the same time, when introducing fiber-reinforced mechanical properties, how to maximize the maintenance of aerogel's inherent excellent properties such as ultra-low density, high porosity and extremely low thermal conductivity also requires delicate balance and regulation.

[0007] Common methods for preparing fiber aerogel composites include atmospheric pressure drying, vacuum freeze drying and supercritical fluid drying. Compared with the other two methods, ambient pressure drying offers the advantages of simplicity, economy and environmental protection. However, due to the inherent hydrophilic characteristics of the alumina aerogel material itself, which leads to environmental humidity sensitivity problems, it is usually necessary to perform surface modification before the drying process to construct a surface hydrophobic modification system to enhance the environmental stability of the material. Currently commonly used modifiers such as organosilanes can effectively reduce the hydrophilicity of the aerogel surface, but may introduce some organic components, affecting the high-temperature stability of the material, and the residual modifiers may cause the material to produce harmful gases at high temperatures or affect the optical properties of the material. Summary of the Invention

[0008] To address the shortcomings of the existing technology, the present invention aims to provide a ceramic fiber-reinforced alumina composite aerogel prepared using coal gangue, a solid waste generated during coal mining and washing, as raw material. This process utilizes a sol-gel method combined with atmospheric pressure drying, replacing the complex supercritical drying process. Furthermore, the hydrophilic alumina and composite aerogel surfaces are chemically modified using a methyltriethoxysilane / n-hexane mixed solution.

[0009] To achieve the above objectives, the technical solution of the present invention is: a method for preparing alumina and its fiber-reinforced composite functional aerogel using coal gangue as an aluminum source, the specific steps of which are as follows:

[0010] (1) Activation pretreatment of coal gangue: crush the coal gangue, ball-mill it to 100-200 mesh, and then calcine it at 500-900°C for 1-2h to obtain activated coal gangue powder;

[0011] The calcination activation temperature of coal gangue is preferably 600°C, and the time is preferably 2 hours;

[0012] (2) Preparation of aluminum precursor: prepare an acid leaching solution, then place the activated gangue powder obtained in step (1) into the acid leaching solution, leach at 70-100°C for 1-2.5 hours, and separate by centrifugation to obtain an acid leaching residue and an aluminum-rich solution. Add ammonia water to the aluminum-rich solution to adjust the pH to 11 to obtain a metal hydroxide precipitate. In order to obtain a high-purity aluminum precursor, add sodium hydroxide solution to the precipitate until the pH is 14, and NaOH reacts with the precipitate. Finally, filter to obtain a sodium aluminate solution, which is used as an aluminum precursor for the synthesis of alumina aerogel;

[0013] The acid leaching solution is a hydrochloric acid solution with a concentration of 3 to 6 mol / L, the sodium hydroxide solution has a concentration of 1 to 3 mol / L, and the reaction time with the precipitation is 0.5 to 2 hours;

[0014] (3) Preparation of aluminum sol and composite sol: neutralize the sodium aluminate solution obtained in step (2) with hydrochloric acid solution, adjust the pH to 2-3, and obtain a clear aluminum chloride solution. Measure the concentration of aluminum ions in the solution by ultraviolet spectrophotometer, add a certain amount of anhydrous ethanol and water, and stir to obtain aluminum sol. Add the pretreated ceramic fiber to the aluminum sol prepared above, and stir until the fiber is completely dispersed in the sol.

[0015] The concentration of the hydrochloric acid solution is 1 mol / L, and the mass ratio of aluminum chloride, anhydrous ethanol and water is 1:

[0016] (6-10): (10-15), the amount of ceramic fiber added is 1-15 wt% of the total mass of the wet gel system;

[0017] The present invention adopts ceramic fiber as reinforcing material. The pretreated fiber is prepared by cutting the ceramic fiber into small pieces and soaking them in a 2wt% NaOH solution for 2 hours to remove oil and impurities on the surface. The fiber is then washed with water several times, then soaked in a 2wt%-KH-550 solution for 4 hours and ultrasonically treated for 30 minutes. Finally, the treated fiber is rinsed with clean water to a pH value of 7 and dried at 80°C for 12 hours. The pretreated fiber is incorporated into the sol to directly form a composite gel. The process is simple, and the ceramic fiber is used as a skeleton reinforcement material to improve the skeleton strength of the gangue-based aerogel and enhance the performance stability of the aerogel.

[0018] (4) Preparation of aluminum gel and its composite gel: While vigorously stirring the sol obtained in step (3), a certain amount of propylene oxide is rapidly added, and stirring is continued until the solution becomes a milky white gel. Stirring is stopped and the solution is allowed to stand for 8-10 minutes to obtain a wet gel;

[0019] Wherein, the mass ratio of aluminum chloride to propylene oxide is 1:8-10.

[0020] (5) Aging of wet gel: After the wet gel obtained in step (4) was statically aged for 24 h at room temperature, the wet gel was transferred to an alcohol solution and aged in an oven at 30-60°C;

[0021] The alcohol solution is a 10% tetraethyl orthosilicate (TEOS) / ethanol solution, and the gel is washed with a solution 2-5 times the volume of the gel each time (washed 2-3 times), and replaced every 8-12 hours; the gel is washed with a n-hexane solution 2-5 times the volume of the gel each time (washed 2-3 times), and replaced every 10-12 hours;

[0022] (6) Surface modification of the wet gel: soaking the wet gel in a modified mixed solution of n-hexane and a modifier at 30-60° C. for 1-36 h to obtain a hydrophobic gangue-based alumina and a composite wet gel thereof;

[0023] Among them, the surface hydrophobic modification adopts 10% methyltriethoxysilane (MTES) / n-hexane mixed solution, and the volume ratio of the mixed solution to the gel is 2-4:1h;

[0024] (7) Drying of wet gel: The modified wet gel is dried at normal pressure gradient to obtain hydrophobic gangue-based alumina and its composite aerogel.

[0025] The normal pressure gradient drying is as follows: drying at 60°C for 6 hours, drying at 80°C for 6 hours, and drying at 100°C for 6 hours to obtain the integral aerogel.

[0026] Compared with the existing technology, the present invention has the following advantages:

[0027] (1) The present invention utilizes coal gangue solid waste as a resource. The aluminum element in the coal gangue is purified by acid leaching instead of the traditional alumina aerogel that relies on high-purity aluminum salts, thereby improving the resource utilization rate of coal gangue and solving the problems of land occupation and environmental pollution caused by coal gangue accumulation, which is in line with the green material concept of "treating waste with waste".

[0028] (2) This invention replaces expensive and complex supercritical drying with atmospheric pressure drying. The sol-gel method is combined with atmospheric pressure drying to reduce surface tension through solvent replacement and reduce the influence of capillary forces through surface hydrophobic modification. This significantly reduces production costs, improves process safety, and promotes large-scale production of aerogels.

[0029] (3) The present invention uses ceramic fibers to reinforce gangue-based alumina composite aerogels. Gangue-based aerogels are highly brittle and have poor mechanical properties. By introducing ceramic fibers as a reinforcing phase and forming a three-dimensional network structure through sol-gel impregnation or blending, the fibers and matrix work synergistically to improve the material's compressive strength and toughness, expanding its potential for application in thermal insulation, catalysis, and other fields.

[0030] (4) The present invention performs surface modification on the gangue-based composite aerogel, and uses methyltriethoxysilane (MTES) / n-hexane as a mixed modifier to perform surface hydrophobic modification. MTES is hydrolyzed to generate silanol (Si-OH), which condenses with the hydroxyl groups (Al-OH) on the surface of alumina to form Si-O-Al bonds, covering the hydrophobic methyl groups. N-hexane is used as a solvent to promote the diffusion of MTES in the pores of the aerogel, ensure uniform modification, significantly improve the contact angle, reduce hygroscopicity, and enhance the stability of the material in a humid environment.

[0031] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A roadmap for extracting silicon and aluminum components from coal gangue.

[0033] Figure 2 This is a diagram of the steps for preparing alumina and its composite aerogel using coal gangue as a precursor in Example 1.

[0034] Figure 3 (a) (b) (c) are scanning electron microscope images of the fiber-reinforced gangue-based alumina aerogel materials prepared in Comparative Example 1, Example 1, and Example 2, respectively.

[0035] Figure 4 These are N2 adsorption and desorption curves of the fiber-reinforced gangue-based alumina aerogel materials prepared in Comparative Example 1, Example 1, and Example 2.

[0036] Figure 5 These are contact angle pictures of the fiber-reinforced gangue-based alumina aerogel materials prepared in Comparative Example 1, Example 1, Example 2, and Example 3.

[0037] Figure 6 These are digital images of fiber-reinforced gangue-based alumina aerogel materials prepared in Comparative Example 1, Example 1, Example 2, and Example 3.

[0038] Figure 7 A graph showing the aluminum leaching rate at different calcination temperatures, acid leaching temperatures, and acid leaching times. DETAILED DESCRIPTION

[0039] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the specific implementation methods of the present invention are described in detail below with reference to embodiments.

[0040] Example 1

[0041] (1) Activation pretreatment of coal gangue: The coal gangue was crushed, ball-milled, and passed through a 100-mesh sieve. It was then placed in a muffle furnace and calcined at 600°C for 2 h, followed by natural cooling.

[0042] (2) Preparation of aluminum precursor: Weigh 5 g of activated gangue powder and leach it with 60 mL of 6 mol / L hydrochloric acid solution at 90°C for 2 h. Then, centrifuge and separate to obtain an aluminum-rich solution. Ammonia water is added to adjust the pH to 11, and metal hydroxide is precipitated. To obtain a high-purity aluminum precursor, 3 mol / L NaOH solution is added to the precipitate until the pH reaches 14. After reacting for 1 h, the solution is filtered to obtain sodium aluminate as an aluminum precursor for the synthesis of alumina aerogel.

[0043] (3) Preparation of aluminum sol and its composite sol: Sodium aluminate solution was neutralized with 1 mol / L hydrochloric acid solution and the pH was adjusted to 2-3 to obtain aluminum chloride solution. The aluminum ion concentration in the solution was measured by ultraviolet spectrophotometer. 10 mL of aluminum chloride solution (the mass of aluminum chloride calculated based on the aluminum ion concentration was 1.8 g), 6.35 mL of anhydrous ethanol and 3.68 mL of water were mixed and stirred to obtain aluminum sol. 2 g of pretreated ceramic fiber was added to the aluminum sol and stirred until the fiber was completely dispersed in the sol. The amount of ceramic fiber added was 10 wt%;

[0044] (4) Preparation of aluminum gel and its composite gel: 9.52 mL of propylene oxide (PO) was rapidly added to the aluminum sol while vigorously stirring it at a magnetic stirring speed of 300 rpm. The stirring was continued until the solution showed a milky white gel state. The stirring was stopped and the solution was allowed to stand for 10 min to obtain a wet gel.

[0045] (5) Aging of wet gel: The wet gel was dynamically aged at room temperature for 24 h and then transferred to a 10% tetraethyl orthosilicate (TEOS) / ethanol solution 3 times the gel volume to soak the wet gel. The solution was changed every 8 h and the soaking and washing were repeated 3 times. Subsequently, the gel was soaked in a n-hexane solution 3 times the gel volume. The n-hexane was changed every 12 h and the soaking and washing were repeated 2 times. During the aging solvent replacement process, the gel was sealed and stored in a 40°C oven.

[0046] (6) Surface modification of wet gel: The aged gel was subjected to surface hydrophobic modification. The surface modifier was a 10% methyltriethoxysilane (MTES) / n-hexane mixed solution. The volume of the surface modification mixed solution was 3 times the volume of the gel. The solution was replaced every 12 h, and the gel was soaked 3 times. The gel was sealed and placed in a 40°C oven for surface modification for 24 h.

[0047] (7) Drying of wet gel: The hydrophobically modified gel was dried at normal pressure in a stepwise manner at 60°C for 6 h, 80°C for 6 h, and 100°C for 6 h to obtain a monolithic aerogel. The actual sample is shown in Figure 6 .

[0048] The density of the gangue-based alumina aerogel prepared by the above process is 0.24 g / cm 3 , with a specific surface area of ​​121.9m 2 ·g -1 , the hydrophobic angle is 135.784°, the thermal conductivity is 0.049W / (m·K), and the N2 adsorption and desorption curve is shown in Figure 3 . Figure 2 This is a microscopic morphology of the gangue-based alumina aerogel material prepared in Example 1.

[0049] Comparative Example 1

[0050] The difference between this comparative example and Example 1 is that no fiber is added, and the rest of the preparation process is the same as that of Example 1. The density of the gangue-based alumina aerogel prepared by the above process is 0.108 g / cm 3 , with a specific surface area of ​​198.32m 2 ·g -1 , the hydrophobic angle is 91.74°, the thermal conductivity is 0.036W / (m·K), and the N2 adsorption and desorption curve is shown in Figure 3 . Figure 2 This is a microscopic morphology of the gangue-based alumina aerogel material prepared in Comparative Example 1.

[0051] Comparative Example 2

[0052] The difference between this comparative example and comparative example 1 is that the wet gel is dried directly at 100°C for 24 hours without gradient drying. The rest of the preparation process is the same as that of comparative example 1. Figure 6 The density of the gangue-based alumina aerogel prepared by the above process is 0.189 g / cm 3 , with a specific surface area of ​​126.72m 2 ·g -1 , thermal conductivity is 0.058W / (m·K).

[0053] Example 2

[0054] (1) Activation pretreatment of coal gangue: same as in Example 1;

[0055] (2) Preparation of aluminum precursor: Weigh 5g of activated gangue powder and leach it with 60mL of 6mol / L hydrochloric acid solution at 90℃ for 2h, then centrifuge and separate to obtain an aluminum-rich solution. Ammonia water is added to adjust the pH to 11 to obtain a metal hydroxide precipitate. To obtain a high-purity aluminum precursor, 2mol / L NaOH solution is added to the precipitate until the pH reaches 14. After reacting for 30min, the solution is filtered to obtain sodium aluminate as an aluminum precursor for the synthesis of alumina aerogel.

[0056] (3) Preparation of aluminum sol and its composite sol: Sodium aluminate solution was neutralized with 1 mol / L hydrochloric acid solution and the pH was adjusted to 2-3 to obtain aluminum chloride. The concentration of aluminum ions in the solution was measured by ultraviolet spectrophotometry. 10 mL of aluminum chloride solution (1.8 g of aluminum chloride), 4.76 mL of anhydrous ethanol, and 3.68 mL of water were mixed and stirred to obtain aluminum sol. 0.18 g of pretreated ceramic fiber was added to the aluminum sol and stirred until the fiber was completely dispersed in the sol. The fiber addition amount was 1 wt%;

[0057] (4) Preparation of aluminum gel and its composite gel: 9.52 mL of propylene oxide (PO) was rapidly added to the aluminum sol while stirring vigorously with a magnetic stirring speed of 500 rpm. The stirring was continued until the solution showed a milky white gel state. The stirring was stopped and the solution was allowed to stand for 10 min to obtain a wet gel.

[0058] (5) Aging of wet gel: The wet gel was dynamically aged at room temperature for 24 h and then transferred to a 10% tetraethyl orthosilicate (TEOS) / ethanol solution with a volume 4 times that of the gel to soak the wet gel. The solution was changed every 8 h and the soaking and washing was repeated 4 times. Subsequently, the gel was soaked in a n-hexane solution with a volume 4 times that of the gel to soak the wet gel. The n-hexane was changed every 12 h and the soaking and washing was repeated 3 times. During the aging solvent replacement process, the gel was sealed and stored in an oven at 40 °C.

[0059] (6) Surface modification of wet gel: The aged gel was subjected to surface hydrophobic modification. The surface modifier was a 10% methyltriethoxysilane (MTES) / n-hexane mixed solution. The volume of the surface modification mixed solution was 4 times the volume of the gel. The solution was replaced every 12 h, and the gel was soaked 4 times. The gel was sealed and placed in a 40°C oven for 48 h for surface modification.

[0060] (7) Drying of wet gel: The hydrophobically modified gel was dried at normal pressure in a stepwise manner at 60°C for 6 h, 80°C for 6 h, and 100°C for 6 h to obtain a monolithic aerogel. The actual sample is shown in Figure 6 .

[0061] The density of the gangue-based alumina aerogel prepared by the above process is 0.21 g / cm 3 , with a specific surface area of ​​146.6m 2 ·g -1, the hydrophobic angle is 117.448°, the thermal conductivity is 0.041W / (m·K), and the N2 adsorption and desorption curve is shown in Figure 3 . Figure 2 This is a microscopic morphology of the gangue-based alumina aerogel material prepared in Example 2.

[0062] Example 3

[0063] (1) Activation pretreatment of coal gangue: same as in Example 1;

[0064] (2) Preparation of aluminum precursor: Weigh 5 g of activated gangue powder and leach it with 60 mL of 5 mol / L hydrochloric acid solution at 90°C for 2 h, then centrifuge and separate to obtain an aluminum-rich solution. Ammonia water is added to adjust the pH to 11, and metal hydroxide is precipitated. To obtain a high-purity aluminum precursor, 3 mol / L NaOH solution is added to the precipitate until the pH reaches 14. After reacting for 30 min, the solution is filtered to obtain sodium aluminate as an aluminum precursor for the synthesis of alumina aerogel.

[0065] (3) Preparation of aluminum sol and its composite sol: Sodium aluminate solution was neutralized with 1 mol / L hydrochloric acid solution and the pH was adjusted to 2-3 to obtain aluminum chloride. The concentration of aluminum ions in the solution was measured by ultraviolet spectrophotometry. 10 mL of aluminum chloride solution (1.8 g of aluminum chloride), 6.35 mL of anhydrous ethanol, and 2.45 mL of water were mixed and stirred to obtain aluminum sol. 0.94 g of pretreated ceramic fiber was added to the aluminum sol and stirred until the fiber was completely dispersed in the sol. The fiber addition amount was 5 wt%;

[0066] (4) Preparation of aluminum gel and its composite gel: 9.52 mL of propylene oxide (PO) was rapidly added to the aluminum sol while vigorously stirring it at a magnetic stirring speed of 300 rpm. The stirring was continued until the solution showed a milky white gel state. The stirring was stopped and the solution was allowed to stand for 10 min to obtain a wet gel.

[0067] (5) Aging of wet gel: The wet gel was dynamically aged at room temperature for 24 h and then transferred to a 10% tetraethyl orthosilicate (TEOS) / ethanol solution 3 times the gel volume to soak the wet gel. The solution was changed every 8 h and the soaking and washing were repeated 3 times. Subsequently, the gel was soaked in a n-hexane solution 3 times the gel volume. The n-hexane was changed every 12 h and the soaking and washing were repeated 3 times. During the aging solvent replacement process, the gel was sealed and stored in a 40°C oven.

[0068] (6) Surface modification of wet gel: The aged gel was subjected to surface hydrophobic modification. The surface modifier was a 10% methyltriethoxysilane (MTES) / n-hexane mixed solution. The volume of the surface modification mixed solution was 3 times the volume of the gel. The solution was replaced every 12 h, and the gel was soaked 4 times. The gel was sealed and placed in a 40°C oven for 48 h for surface modification.

[0069] (7) Drying of wet gel: The hydrophobically modified gel was dried at normal pressure in a stepwise manner, at 60°C for 6 h, at 80°C for 6 h, and at 100°C for 6 h to obtain the overall aerogel. Figure 6 .

[0070] The density of the gangue-based alumina aerogel prepared by the above process is 0.22 g / cm 3 , with a specific surface area of ​​139.8m 2 ·g -1 , the hydrophobic angle is 121.845°, and the thermal conductivity is 0.047W / (m·K).

[0071] Example 4

[0072] (1) Activation pretreatment of coal gangue: same as in Example 1;

[0073] (2) Preparation of aluminum precursor: Weigh 5 g of activated gangue powder and leach it with 60 mL of 5 mol / L hydrochloric acid solution at 90°C for 2 h, then centrifuge and separate to obtain an aluminum-rich solution. Ammonia water is added to adjust the pH to 11, and metal hydroxide is precipitated. To obtain a high-purity aluminum precursor, 3 mol / L NaOH solution is added to the precipitate until the pH reaches 14. After reacting for 30 min, the solution is filtered to obtain sodium aluminate as an aluminum precursor for the synthesis of alumina aerogel.

[0074] (3) Preparation of aluminum sol and its composite sol: Sodium aluminate solution was neutralized with 1 mol / L hydrochloric acid solution and the pH was adjusted to 2-3 to obtain aluminum chloride solution. The concentration of aluminum ions in the solution was measured by ultraviolet spectrophotometer. 10 mL of aluminum chloride solution (1.8 g of aluminum chloride), 6.35 mL of anhydrous ethanol, and 2.45 mL of water were mixed and stirred to obtain aluminum sol. 1.5 g of pretreated ceramic fiber was added to the aluminum sol and stirred until the fiber was completely dispersed in the sol. The fiber addition amount was 7 wt%;

[0075] (4) Preparation of aluminum gel and its composite gel: 9.52 mL of propylene oxide (PO) was rapidly added to the aluminum sol while vigorously stirring it at a magnetic stirring speed of 300 rpm. The stirring was continued until the solution showed a milky white gel state. The stirring was stopped and the solution was allowed to stand for 10 min to obtain a wet gel.

[0076] (5) Aging of wet gel: The wet gel was dynamically aged at room temperature for 24 h and then transferred to a 10% tetraethyl orthosilicate (TEOS) / ethanol solution 3 times the gel volume to soak the wet gel. The solution was changed every 8 h and the soaking and washing were repeated 3 times. Subsequently, the gel was soaked in a n-hexane solution 3 times the gel volume. The n-hexane was changed every 12 h and the soaking and washing were repeated 3 times. During the aging solvent replacement process, the gel was sealed and stored in a 40°C oven.

[0077] (6) Surface modification of wet gel: The aged gel was subjected to surface hydrophobic modification. The surface modifier was a 10% methyltriethoxysilane (MTES) / n-hexane mixed solution. The volume of the surface modification mixed solution was 3 times the volume of the gel. The solution was replaced every 12 h, and the gel was soaked 4 times. The gel was sealed and placed in a 40°C oven for 48 h for surface modification.

[0078] (7) Drying of wet gel: The hydrophobically modified gel was dried at normal pressure in a stepwise manner, drying at 60°C for 6 h, 80°C for 6 h, and 100°C for 6 h to obtain a monolithic aerogel.

[0079] The density of the gangue-based alumina aerogel prepared by the above process is 0.23 g / cm 3 , with a specific surface area of ​​129.7m 2 ·g -1 , the hydrophobic angle is 129.625°, and the thermal conductivity is 0.045W / (m·K).

[0080] Example 5

[0081] The difference between this embodiment and embodiment 1 is that, when calcining and activating the coal gangue, the calcination and activation temperature is 500° C., and the rest of the leaching process and preparation process are the same as those in embodiment 1.

[0082] The density of the gangue-based alumina aerogel prepared by the above process is 0.44 g / cm 3 , with a specific surface area of ​​106.9m 2 ·g -1 , thermal conductivity is 0.068W / (m·K).

[0083] Example 6

[0084] The difference between this embodiment and embodiment 1 is that, when calcining and activating the coal gangue, the calcination and activation temperature is 800° C., and the rest of the leaching process and preparation process are the same as those in embodiment 1.

[0085] The density of the gangue-based alumina aerogel prepared by the above process is 0.26 g / cm 3 , with a specific surface area of ​​118.7m 2 ·g -1 , thermal conductivity is 0.051W / (m·K).

[0086] From Examples 5 and 6, it can be seen that the calcination temperature has a significant effect on the extraction of aluminum source from coal gangue, and thus affects the properties of the prepared coal gangue-based alumina aerogel material. Figure 7It can be seen that with the increase of activation temperature, the extraction rate of aluminum becomes higher. When the temperature is too low (500℃), the degree of activation of the mineral is insufficient, resulting in low leaching efficiency. When the temperature is too high (800℃), the leaching efficiency of aluminum remains almost unchanged, indicating that it has been basically activated. Considering energy saving, 600℃ is preferred.

[0087] Example 7

[0088] The difference between this embodiment and embodiment 1 is that the amount of fiber added is different, and the amount of ceramic fiber added is 1 wt %. The rest of the preparation process is the same as that of embodiment 1.

[0089] The density of the gangue-based alumina aerogel prepared by the above process is 0.25 g / cm 3 , with a specific surface area of ​​108.4m 2 ·g -1 , thermal conductivity is 0.068W / (m·K).

[0090] Example 8

[0091] The difference between this embodiment and embodiment 1 is that the amount of fiber added is different, and the amount of ceramic fiber added is 15 wt %. The rest of the preparation process is the same as that of embodiment 1.

[0092] The density of the gangue-based alumina aerogel prepared by the above process is 0.47 g / cm 3 , with a specific surface area of ​​101.2m 2 ·g -1 , thermal conductivity is 0.075W / (m·K).

[0093] It can be seen from Examples 7 and 8 that the addition of fibers plays an important role in aerogels. However, when the fiber content is too low (1 wt%), the fibers may not be evenly dispersed and aggregate to form local weak points, which aggravates the pore collapse caused by capillary force during the drying process and reduces the specific surface area. When the fiber content is too high (15 wt%), it is easy to agglomerate in the sol, hindering the uniform cross-linking of the sol-gel process, resulting in cracks or uneven density in the aerogel matrix. An addition of 10 wt% can achieve synergistic optimization of uniform fiber dispersion and pore structure.

[0094] Example 9

[0095] The difference between this embodiment and embodiment 1 is that in the aluminum gel process, the amount of propylene oxide added is different, the amount added is 8.57 mL, and it is necessary to stand for 30 minutes to obtain a wet gel. The rest of the preparation process is the same as that of embodiment 1. The density of the coal gangue-based alumina aerogel prepared by the above process is 0.24 g / cm 3 , with a specific surface area of ​​108.5m 2 ·g -1, thermal conductivity is 0.052W / (m·K).

[0096] Example 10

[0097] The difference between this embodiment and embodiment 1 is that, during the acid leaching process for extracting the aluminum source, the acid leaching temperature is different, that is, the acid leaching temperature is 70° C. The rest of the leaching process and preparation process are the same as those in embodiment 1.

[0098] The density of the gangue-based alumina aerogel prepared by the above process is 0.39 g / cm 3 , with a specific surface area of ​​96.2m 2 ·g -1 , thermal conductivity is 0.058W / (m·K).

[0099] Example 11

[0100] The difference between this embodiment and embodiment 1 is that, during the acid leaching process for extracting the aluminum source, the acid leaching temperature is different, and the acid leaching temperature is 100° C. The rest of the leaching process and preparation process are the same as those in embodiment 1.

[0101] The density of the gangue-based alumina aerogel prepared by the above process is 0.24 g / cm 3 , with a specific surface area of ​​124.7m 2 ·g -1 , thermal conductivity is 0.048W / (m·K).

[0102] From Examples 10 and 11, it can be seen that the acid leaching temperature has a significant effect on the extraction of aluminum source from coal gangue, and thus affects the properties of the prepared coal gangue-based alumina aerogel material. Figure 7 As the acid leaching temperature increases, the aluminum extraction rate increases, indicating that the acid leaching solution at high temperatures more fully activates the gangue, promoting aluminum leaching. The aerogel material prepared at 100°C has similar performance to that prepared at 90°C. Considering energy consumption, 90°C is preferred.

[0103] Example 12

[0104] The difference between this embodiment and embodiment 1 is that, during the acid leaching process for extracting the aluminum source, the acid leaching time is different, that is, the acid leaching time is 1 hour, and the rest of the leaching process and preparation process are the same as those in embodiment 1.

[0105] The density of the gangue-based alumina aerogel prepared by the above process is 0.38 g / cm 3 , with a specific surface area of ​​108.4m 2 ·g -1 , thermal conductivity is 0.056W / (m·K).

[0106] Example 13

[0107] The difference between this embodiment and embodiment 1 is that, during the acid leaching process for extracting the aluminum source, the acid leaching time is different, that is, the acid leaching time is 2.5 hours. The rest of the leaching process and preparation process are the same as those in embodiment 1.

[0108] The density of the gangue-based alumina aerogel prepared by the above process is 0.25 g / cm 3 , with a specific surface area of ​​135.7m 2 ·g -1 , thermal conductivity is 0.055W / (m·K).

[0109] From Examples 12 and 13, it can be seen that the acid leaching time has a significant effect on the extraction of aluminum source from coal gangue, and thus affects the properties of the prepared coal gangue-based alumina aerogel material. Figure 7 It can be seen that with the increase of acid leaching time, the leaching rate gradually tends to equilibrium, and the leaching reaction of the surface coal gangue powder reaches equilibrium. Therefore, considering the economic factors comprehensively, the optimal leaching time is 2h.

[0110] The present invention provides a method for preparing and applying a fiber-reinforced gangue-based composite functional aerogel material. There are many methods and approaches for implementing this technical solution. The above examples are only preferred embodiments of the present invention. It should be noted that the above examples are only intended to illustrate the technical methods of the present invention and are not intended to limit the present invention. Although experiments and analyses were conducted with reference to the specific conditions and operating steps in the above examples, the scope of the present invention is not limited to these examples. Those skilled in the art may, based on the principles and ideas of the present invention, make appropriate modifications and optimizations to the examples without departing from the spirit and scope of the present invention.

Claims

1. A method for preparing fiber-reinforced gangue-based composite functional aerogel, characterized in that: The method steps are as follows: (1) crushing and ball-milling the coal gangue and then calcining it to obtain activated coal gangue powder; (2) leaching the activated gangue powder into an acid leaching solution to obtain an aluminum-rich solution, adding ammonia water to the solution to adjust the pH to obtain a hydroxide precipitate; adding sodium hydroxide solution to the precipitate to react and obtain a sodium aluminate solution; (3) neutralizing the sodium aluminate solution with hydrochloric acid to obtain a clear aluminum chloride solution, adding anhydrous ethanol and water and stirring to obtain an aluminum sol, adding the pretreated ceramic fiber and stirring to completely disperse it; then adding propylene oxide under vigorous stirring, continuing to stir until the solution becomes a milky white gel, stopping stirring and letting it stand to obtain a wet gel; (4) After the wet gel is statically aged, it is transferred to an alcohol solution for aging, and then the wet gel washed with n-hexane is immersed in a modified mixed solution to obtain a hydrophobic gangue-based alumina and a composite wet gel thereof; (5) The modified wet gel is dried at normal pressure to obtain hydrophobic gangue-based alumina and its composite aerogel.

2. The method for preparing fiber-reinforced gangue-based composite functional aerogel according to claim 1, characterized in that: In step (1), the coal gangue is crushed and ground to 100-200 mesh, the calcination temperature is 500-900° C., and the calcination time is 1-2 hours.

3. The method for preparing fiber-reinforced gangue-based composite functional aerogel according to claim 1, characterized in that: In step (2), the acid leaching solution is a hydrochloric acid solution with a concentration of 3 to 6 mol / L, the leaching temperature is 70 to 100° C., and the leaching time is 1 to 2.5 hours; ammonia water is added to adjust the pH to 11; the concentration of the sodium hydroxide solution is 1 to 3 mol / L, and the reaction time with the precipitation is 0.5 to 2 hours.

4. The method for preparing fiber-reinforced gangue-based composite functional aerogel according to claim 1, characterized in that: In step (3), the concentration of the hydrochloric acid solution is 1 mol / L, and the sodium aluminate solution is neutralized with hydrochloric acid to adjust the pH to 2-3 to obtain an aluminum chloride solution; the mass ratio of aluminum chloride, anhydrous ethanol and water is 1:6-10:10-15.

5. The method for preparing fiber-reinforced gangue-based composite functional aerogel according to claim 1, characterized in that: In step (3), the pre-treated fibers are prepared by soaking the ceramic fibers in a 2 wt% NaOH solution for 2 h to remove surface oil and impurities; the fibers are then washed with water, subsequently soaked in a 2 wt% KH-550 solution for 4 h, and ultrasonically treated for 30 min; finally, the treated fibers are rinsed with clean water to a pH of 7, and dried at 80°C for 12 h. The amount of ceramic fibers added is 1 to 15 wt% of the total mass of the wet gel system.

6. The method for preparing fiber-reinforced gangue-based composite functional aerogel according to claim 1, characterized in that: In step (3), the mass ratio of aluminum chloride to propylene oxide is 1:8-10, and the mixture is allowed to stand for 8-10 minutes to obtain a wet gel.

7. The method for preparing fiber-reinforced gangue-based composite functional aerogel according to claim 1, characterized in that: In step (4), dynamic aging is performed by standing at room temperature for 24 hours; the aging temperature in the alcohol solution is 30-60°C, the alcohol solution is a 10% ethyl orthosilicate ethanol solution, and a solution 2-5 times the volume of the gel is used for washing each time, which is replaced every 8-12 hours, and the alcohol solution is washed 2-3 times; each time the gel is washed with a n-hexane solution 2-5 times the volume of the gel, which is replaced every 10-12 hours.

8. The method for preparing fiber-reinforced gangue-based composite functional aerogel according to claim 1, characterized in that: In step (4), the modified mixed solution is a 10% n-hexane solution of methyltriethoxysilane, the volume ratio of the mixed solution to the gel is 2-4:1, and the gel is immersed in the mixed solution at 30-60° C. for 1-36 hours.

9. The method for preparing fiber-reinforced gangue-based composite functional aerogel according to claim 1, characterized in that: In step (5), the atmospheric pressure drying method is gradient drying, drying at 60° C. for 6 h, drying at 80° C. for 6 h, and drying at 100° C. for 6 h to obtain the integral aerogel.

10. A fiber-reinforced gangue-based composite functional aerogel prepared according to the method according to any one of claims 1 to 9.

Images