Preparation method of homologous nano boehmite sheet reinforced SiO2 aerogel

Abstract

The invention discloses a preparation method of homologous nano boehmite sheet reinforced SiO2 aerogel, and belongs to the technical field of solid waste resource utilization and aerogel new material low-cost preparation. The method comprises the following steps: S1, mixing and ball-milling nitric acid pressurized lithium salt solid waste and an alkaline activator, and then roasting and activating; s2, the activated product is subjected to water leaching, a sodium silicate solution and water leaching residues are obtained, and the sodium silicate solution is subjected to ion exchange; s3, the water leaching residues are subjected to acid leaching and solid-liquid separation, and acid leaching residues and an aluminum-rich solution are obtained; dropwise adding a precipitator into the aluminum-rich solution to obtain an aluminum hydroxide suspension, so as to obtain nano boehmite sheet powder; and S4, doping the nano boehmite sheet powder into a silicic acid solution to obtain the blocky composite aerogel. According to the method disclosed by the invention, silicon and aluminum resources with relatively high content in the lithium salt solid waste are pressurized by using nitric acid, and are respectively used for preparing the SiO2 aerogel precursor and the nano boehmite sheet through step-by-step extraction and directional conversion, so that high-valued and synergistic utilization of the resources is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste resource utilization and low-cost preparation of new aerogel materials, and in particular to a method for preparing a homologous nano-boehmite sheet reinforced SiO2 aerogel. Background Art

[0002] Aerogel is a new type of porous material with ultra-high specific surface area, ultra-low density and excellent thermal insulation properties. It is widely used in building insulation, aerospace thermal control, electronic packaging and other fields. Currently, the silicon sources commonly used to prepare aerogels on the market are mainly organosilicon precursors, such as tetramethoxysilane (TMOS) and tetraethoxysilane (TEOS). The preparation technology of this type of organosilicon source is mature and can relatively stably obtain SiO2 aerogels with complete bulk morphology. However, organosilicon sources are expensive and the preparation cost is high, which limits the promotion of aerogels in large-scale low-cost applications.

[0003] Replacing organic silicon with inorganic silicon sources (such as sodium silicate) to produce aerogels at low cost has become a hot topic in current research. Inorganic silicon sources are inexpensive and widely available, offering significant economic advantages. However, due to limitations in their reactivity and crosslinking density during hydrolysis and polycondensation, aerogels prepared from inorganic silicon sources often suffer from loose structures, cracking during drying, and difficulty forming intact blocks.

[0004] To overcome the above problems, researchers have proposed to introduce a reinforcing phase (such as fiber material) to construct a supporting skeleton to improve the structural integrity and mechanical properties of the aerogel during drying and molding. The current common method is to introduce large-sized reinforcing materials such as glass fiber, alumina fiber, and ceramic fiber into the aerogel system, and build a three-dimensional support network by physical doping to achieve toughening molding of the aerogel. However, these fibers are mostly micron-sized, and it is difficult to form a synergistic effect with the SiO2 network at the nanoscale. In addition, the reinforcing phase and the matrix are mainly physical interfaces, which have problems such as poor interfacial adhesion and poor structural stability.

[0005] In recent years, nanosheet materials, such as graphene and boron nitride nanosheets, have been widely used to modify and reinforce aerogels due to their excellent mechanical properties and high specific surface area. These nanosheets, as reinforcing materials, can be uniformly dispersed within the aerogel network at the nanoscale, significantly improving its mechanical and thermal properties. However, this comes at the cost of high costs.

[0006] Therefore, it is necessary to provide a preparation method of homologous nano-boehmite sheet reinforced SiO2 aerogel. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for preparing homologous nano-boehmite flake reinforced SiO2 aerogel to solve the problems of poor structural integrity, easy cracking, low mechanical properties and high cost of the reinforcement phase in the existing process of preparing aerogel using inorganic silicon sources.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for preparing a homologous nano-boehmite sheet reinforced SiO2 aerogel comprises the following steps:

[0010] S1, mixing nitric acid pressurized lithium salt solid waste and alkaline activator with ball milling and then calcining and activating to obtain an activated product;

[0011] S2, soaking the activated product with deionized water, and then performing solid-liquid separation to obtain a sodium silicate solution and a leached residue, and performing ion exchange on the sodium silicate solution using a cation exchange resin to obtain a silicic acid solution;

[0012] S3, acid leaching the water-leached residue and performing solid-liquid separation using nitric acid to obtain an acid leaching residue and an aluminum-rich solution; adding a precipitant to the aluminum-rich solution to adjust the pH to 2-4, allowing it to stand and filtering, and again adjusting the pH of the filtrate to 9.5-10.5 to obtain an aluminum hydroxide suspension; transferring the aluminum hydroxide suspension to a reactor for hydrothermal reaction to obtain a boehmite sol; centrifuging the boehmite sol, washing it, and drying it to obtain nano-boehmite flake powder;

[0013] S4, adding the nano-boehmite flake powder to the silicic acid solution, stirring evenly, adjusting the pH to 5.5-7.5, and allowing to stand to obtain a wet gel, and performing solvent replacement, hydrophobic modification, and normal pressure drying on the wet gel to obtain a block-shaped composite aerogel.

[0014] Furthermore, in step S1, the ball milling time is 20-180 min, and the product is sieved after ball milling.

[0015] Furthermore, in step S1, the mass ratio of the nitric acid pressurized lithium salt solid waste to the alkaline activator is 1:0.8-1.6.

[0016] Furthermore, in step S1, the calcination temperature is 700-900°C, and the sintering time is 1-4 hours.

[0017] Furthermore, in step S2, the solid-liquid ratio of the activated product to the deionized water is 1 g:5-25 mL, and the water immersion temperature is 25-95°C.

[0018] Furthermore, in step S3, the concentration of the nitric acid is 0.5-3.5 mol / L, the solid-liquid ratio of the water-leached residue to the nitric acid is 1 g:5-25 mL, and the temperature of the acid leaching is 25-95°C.

[0019] Furthermore, in step S3, the precipitant includes ammonia water and sodium hydroxide; the temperature of the hydrothermal reaction is 120° C.-200° C., and the reaction time of the hydrothermal reaction is 12 h-48 h.

[0020] Furthermore, in step S4, the modifiers used in the modification process include: anhydrous ethanol, n-hexane and trimethylchlorosilane.

[0021] Furthermore, in step S4, the drying is performed at normal pressure, and is performed in stages at 40°C, 80°C, and 120°C.

[0022] The present invention has the following beneficial effects:

[0023] 1. The present invention makes full use of the high content of silicon and aluminum resources in nitric acid pressurized lithium salt solid waste, and uses them to prepare SiO2 aerogel precursor and nano-boehmite flakes through step-by-step extraction and directional conversion, thereby achieving high value and coordinated utilization of resources and improving the level of solid waste resource utilization.

[0024] 2. The present invention significantly reduces the stockpile volume and environmental risks of pressurized lithium salt solid waste from nitric acid, effectively alleviates the migration and diffusion problems of heavy metals and high salt ions in solid waste, and is in line with the concept of green, low-carbon and ecological and environmental protection development.

[0025] 3. The present invention obtains a two-dimensional sheet-like boehmite nanomaterial by regulating the acid-base conditions and hydrothermal reaction parameters. The material has a high specific surface area and excellent dispersibility. It can effectively enhance the skeleton support in the aerogel matrix and improve the thermal insulation performance and crack resistance of the composite material.

[0026] 4. The process flow of the present invention is clear and the steps are closely connected. It not only realizes the effective separation and recovery of silicon and aluminum components, but also completes the preparation and compounding of functional materials. It has good process integration and industrial application potential.

[0027] 5. The nano-boehmite flake-reinforced SiO2 aerogel material prepared by the present invention has excellent thermal insulation, flame retardancy, lightness and stability, and can be widely used in multiple high-performance material application fields such as building insulation, aerospace thermal control, and electronic packaging, with both environmental benefits and economic value.

[0028] 6. The process flow of the present invention is simple and low-cost. The raw materials of nano-boehmite flakes and SiO2 aerogel are both derived from lithium salt solid waste, which synergistically realizes the high-value utilization of lithium salt solid waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A flow chart of the preparation method of the homologous nano-boehmite sheet reinforced SiO2 aerogel provided by the present invention;

[0030] Figure 2 This is a scanning electron microscope photograph of the nano-boehmite flakes obtained in Example 1 of the present invention;

[0031] Figure 3 This is a scanning electron microscope photograph of the nano-boehmite flakes obtained in Example 2 of the present invention;

[0032] Figure 4 This is a scanning electron microscope photograph of the nano-boehmite flakes obtained in Example 3 of the present invention. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0034] The present invention proposes a preparation method of homologous nano-boehmite flake reinforced SiO2 aerogel, which has the advantages of low cost, good interface bonding, and excellent performance, and promotes the resource utilization of lithium salt solid waste. It uses the solid waste generated in the process of nitric acid pressurized lithium salt smelting as raw material, adopts alkaline roasting-water leaching to obtain inorganic silicon source solution for the preparation of SiO2 aerogel, and simultaneously utilizes acid leaching of aluminum-rich solution to synthesize nano-scale boehmite flake materials by regulating pH and hydrothermal conditions. The nanosheet is introduced into the SiO2 aerogel system as a reinforcing phase, which can not only effectively construct a skeleton support network and improve the mechanical and thermal properties of the aerogel, but also synergistically realize the high-value resource utilization of lithium salt solid waste. Specifically comprising the following steps:

[0035] S1. Mix the nitric acid pressurized lithium salt solid waste and an alkaline activator (such as Na2CO3 or NaOH), ball-mill them, and then calcine and activate them to obtain an activated product. The ball-milling time is 20-180 minutes, and the product is sieved after ball-milling. The mass ratio of the nitric acid pressurized lithium salt solid waste to the alkaline activator is 1:0.8-1.6. The heating rate from room temperature to the calcination temperature is 3-8°C / min; the calcination temperature is 700-900°C, and the sintering time is 1-4 hours.

[0036] S2, the activated product is soaked in deionized water, and then the solid-liquid separation is carried out to obtain a sodium silicate solution and a water-leached residue, and the sodium silicate solution is ion exchanged with a cation exchange resin to remove Na + The activated product and deionized water have a solid-liquid ratio of 1 g:5-25 mL, and the immersion temperature is 25-95° C.

[0037] S3, firstly, using the solid waste generated in the process of nitric acid pressurized lithium salt smelting as the aluminum source, nano-boehmite flakes are prepared by the following steps: the lithium salt solid waste roasting product is treated with acid leaching, and insoluble impurities are removed by filtration to obtain Al-rich 3+The process involves slowly adding a precipitant (such as NaOH or aqueous ammonia) to the acid leaching solution, adjusting the pH to 2-4 to allow some impurities to precipitate, and then filtering and separating them. The precipitant is then added to the filtrate to adjust the pH to 9.5-10.5, generating an aluminum hydroxide suspension. The suspension is then transferred to a sealed reactor and subjected to a hydrothermal reaction at 120-180°C for 6-24 hours to generate a boehmite nanomaterial with a flaky structure. The boehmite nanomaterial is then centrifuged, washed, and dried to obtain a high-purity, uniformly sized nanoboehmite flake powder. These flakes have a nanometer-scale particle size distribution, a regular flake structure, and a large specific surface area, making them suitable for building a skeletal network and enhancing structural strength in subsequent composite aerogels.

[0038] S4, adding the nanoboehmite flake powder to the silicic acid solution, stirring evenly, adjusting the pH to 5.5-7.5, and allowing to stand to obtain a wet gel. The wet gel is then subjected to solvent replacement, hydrophobic modification, and drying at normal pressure and in stages at 40°C, 80°C, and 120°C to obtain a block-shaped composite aerogel. The modifiers used in the modification process include: anhydrous ethanol, n-hexane, trimethylchlorosilane, methyltrimethoxysilane, hexamethyldisilazane, etc. Specifically,

[0039] The present invention makes full use of the high content of silicon and aluminum resources in nitric acid pressurized lithium salt solid waste, and uses them to prepare SiO2 aerogel precursor and nano-boehmite flakes through step-by-step extraction and directional conversion, thereby achieving high value and coordinated utilization of resources and improving the level of solid waste resource utilization.

[0040] The present invention significantly reduces the stockpile volume and environmental risks of pressurized lithium salt solid waste from nitric acid, effectively alleviates the migration and diffusion problems of heavy metals and high salt ions in the solid waste, and is in line with the green, low-carbon and ecological and environmental protection development concepts.

[0041] The present invention obtains a two-dimensional flaky boehmite nanomaterial by regulating the acid-base conditions and hydrothermal reaction parameters. The material has a high specific surface area and excellent dispersibility. It can effectively enhance the skeleton support in the aerogel matrix and improve the thermal insulation performance and crack resistance of the composite material.

[0042] The process flow of the present invention is clear and the steps are closely connected. It not only realizes the effective separation and recovery of silicon and aluminum components, but also completes the preparation and compounding of functional materials. It has good process integration and industrial application potential.

[0043] The nano-boehmite flake reinforced SiO2 aerogel material prepared by the present invention has excellent thermal insulation, flame retardancy, lightness and stability, and can be widely used in multiple high-performance material application fields such as building insulation, aerospace thermal control, and electronic packaging, with both environmental benefits and economic value.

[0044] The process of the present invention is simple and low-cost. The raw materials of the nano-boehmite flakes and SiO2 aerogel are both derived from lithium salt solid waste, which synergistically realizes the high-value utilization of lithium salt solid waste.

[0045] Example 1

[0046] (1) Activation treatment: 10.2 g of lithium salt solid waste was mixed with 9.2 g of sodium carbonate (mass ratio 1:0.9), ball milled for 120 min, sieved after ball milling, and calcined the resulting mixture at 850 °C for 2 h at a heating rate of 5 °C / min to obtain a calcined product;

[0047] (2) Water leaching separation: The calcined product was added to deionized water at a solid-liquid ratio of 1 g:20 mL, stirred for 1.5 h, leached at 85°C, and filtered to obtain filtrate A and residue B. Filtrate A was treated with a cation exchange resin column to obtain silicic acid solution C.

[0048] (3) Aluminum extraction: leaching the filter residue B with 2 mol / L nitric acid at a liquid-to-solid ratio of 20 mL / g at 80°C for 3 h, and obtaining an aluminum-rich solution D after filtration;

[0049] (4) Aluminum salt precipitation: Ammonia water was added dropwise to the aluminum-rich solution D, and the pH was adjusted to 3.0 and 9.5 respectively. After standing and separation, aluminum hydroxide suspension E was obtained;

[0050] (5) Hydrothermal reaction: E was placed in a hydrothermal reactor and reacted at 180°C for 24 h to obtain boehmite sol F and prepare nanoboehmite flake powder;

[0051] (6) Aerogel compounding: Add 2.5 g of nanoboehmite flake powder to 80 mL of silicic acid solution C, adjust the pH to 6.5, and allow to stand for gel formation;

[0052] (7) Modification and drying: The gel was subjected to three solvent replacement treatments with anhydrous ethanol and n-hexane, then modified with trimethylchlorosilane, and finally dried at normal pressure in stages (40°C, 80°C, and 120°C for 6 h each) to obtain block aerogel.

[0053] The aerogel obtained in this example has a thermal conductivity of 0.021 W / (m·K), a hydrophobic angle of 142.5°, and a density of 0.14 g / cm 3 , the porosity is 92.6%.

[0054] Example 2

[0055] (1) Activation treatment: 10.0 g of lithium salt solid waste was mixed with 8.5 g of sodium hydroxide (mass ratio 1:0.85), ball milled for 60 min, sieved, and calcined at 750 °C for 3 h at a heating rate of 6 °C / min;

[0056] (2) Water leaching and silicon extraction: The activated product was added to water at a solid-liquid ratio of 1 g:15 mL, leached at 70 °C for 2 h, filtered, and the filtrate A was treated with an ion exchange column to obtain silicic acid solution C;

[0057] (3) Aluminum extraction and precipitation: The filter residue was treated with 3 mol / L nitric acid at a liquid-to-solid ratio of 25 mL / g at 90°C for 2 h, and sodium hydroxide solution was added dropwise to adjust the pH to 2.8 and precipitated in 10 steps to obtain suspension E;

[0058] (4) Hydrothermal reaction: E was hydrothermally treated at 200 °C for 36 h to obtain boehmite sol F, which was then prepared into nano-boehmite flake powder;

[0059] (5) Compounding and drying: 2.0 g of nano-boehmite flake powder was added to 90 mL of silicic acid solution C and the pH was adjusted to 6.8 to form a gel; then, the solution was subjected to three ethanol / n-hexane replacements, hexamethyldisilazane modification, and finally, drying in stages at normal pressure to obtain an aerogel.

[0060] The aerogel obtained in this example has a thermal conductivity of 0.019 W / (m·K), a hydrophobic angle of 144.3°, and a density of 0.13 g / cm 3 , the porosity is 94.0%.

[0061] Example 3

[0062] (1) Calcination: 10.3 g of lithium salt solid waste was mixed with 10.2 g of sodium carbonate (mass ratio of about 1:0.99), ball milled for 150 min and sieved, and then calcined at 900 °C for 1.5 h at a heating rate of 4 °C / min;

[0063] (2) Water leaching: The calcined product was leached in 95°C water at a solid-liquid ratio of 1 g:25 mL for 1 h. The filtrate A and the residue B were obtained by filtration. The filtrate A was treated with an ion exchange column to obtain a silicic acid solution C.

[0064] (3) Acid leaching: The filter residue was treated with 1 mol / L nitric acid at a liquid-to-solid ratio of 15 mL / g at room temperature for 4 h. After precipitation, the pH was adjusted to 3.2 and 10.5 to obtain aluminum hydroxide suspension E;

[0065] (4) Hydrothermal synthesis: E was subjected to hydrothermal reaction at 180 °C for 18 h to obtain boehmite sol F;

[0066] (5) Compounding and drying: 2.8 g of nano-boehmite flake powder was added to 70 mL of silicic acid solution, and the pH was adjusted to 6.2. After the gel was formed, it was replaced with anhydrous ethanol / n-hexane, and then modified with methyltrimethoxysilane. The aerogel was prepared by drying at 40 °C, 80 °C, and 120 °C in three stages.

[0067] The aerogel product obtained in this embodiment has a thermal conductivity of 0.020 W / (m·K), a hydrophobic angle of 141.0°, and a density of 0.13 g / cm 3 , the porosity is 92.5%.

[0068] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a homologous nano-boehmite sheet reinforced SiO2 aerogel, characterized in that: The following steps are involved: S1, mixing nitric acid pressurized lithium salt solid waste and alkaline activator with ball milling and then calcining and activating to obtain an activated product; S2, soaking the activated product with deionized water, and then performing solid-liquid separation to obtain a sodium silicate solution and a leached residue, and performing ion exchange on the sodium silicate solution using a cation exchange resin to obtain a silicic acid solution; S3, acid leaching the water-leached residue and performing solid-liquid separation using nitric acid to obtain an acid leaching residue and an aluminum-rich solution; adding a precipitant to the aluminum-rich solution to adjust the pH to 2-4, allowing it to stand and filtering, and again adjusting the pH of the filtrate to 9.5-10.5 to obtain an aluminum hydroxide suspension; transferring the aluminum hydroxide suspension to a reactor for hydrothermal reaction to obtain a boehmite sol; centrifuging the boehmite sol, washing it, and drying it to obtain nano-boehmite flake powder; S4, adding the nano-boehmite flake powder to the silicic acid solution, stirring evenly, adjusting the pH to 5.5-7.5, and allowing to stand to obtain a wet gel, and performing solvent replacement, hydrophobic modification, and normal pressure drying on the wet gel to obtain a block-shaped composite aerogel.

2. The method for preparing the homologous nano-boehmite flake reinforced SiO2 aerogel according to claim 1, characterized in that: In step S1, the ball milling time is 20-180 min, and the product is sieved after ball milling.

3. The method for preparing the homologous nano-boehmite flake reinforced SiO2 aerogel according to claim 1, characterized in that: In step S1, the mass ratio of the nitric acid pressurized lithium salt solid waste to the alkaline activator is 1:0.8-1.

6.

4. The method for preparing the homologous nano-boehmite flake reinforced SiO2 aerogel according to claim 1, characterized in that: In step S1, the calcination temperature is 700-900° C., and the sintering time is 1-4 hours.

5. The method for preparing the homologous nano-boehmite flake reinforced SiO2 aerogel according to claim 1, characterized in that: In step S2, the solid-liquid ratio of the activated product to the deionized water is 1 g:5-25 mL, and the water immersion temperature is 25-95°C.

6. The method for preparing the homologous nano-boehmite flake reinforced SiO2 aerogel according to claim 1, characterized in that: In step S3, the concentration of the nitric acid is 0.5-3.5 mol / L, the solid-liquid ratio of the water-leached residue to the nitric acid is 1 g:5-25 mL, and the temperature of the acid leaching is 25-95°C.

7. The method for preparing the homologous nano-boehmite flake reinforced SiO2 aerogel according to claim 1, characterized in that: In step S3, the precipitant includes ammonia water and sodium hydroxide; the temperature of the hydrothermal reaction is 120° C.-200° C., and the reaction time of the hydrothermal reaction is 12 h-48 h.

8. The method for preparing homologous nano-boehmite flake reinforced SiO2 aerogel according to claim 1, characterized in that: In step S4, the modifying agents used in the modification process include: anhydrous ethanol, n-hexane and trimethylchlorosilane.

9. The method for preparing homologous nano-boehmite flake reinforced SiO2 aerogel according to claim 1, characterized in that: In step S4, the drying is performed at normal pressure, and the drying is performed in stages at 40°C, 80°C, and 120°C.

Images