Method for preparing silicon dioxide aerogel powder from building solid waste micro powder and silicon dioxide aerogel powder

Abstract

The invention discloses a method for preparing silicon dioxide aerogel powder from building solid waste micro-powder and silicon dioxide aerogel powder.The method comprises the steps that calcium removal and aluminum removal pretreatment is conducted on the building solid waste micro-powder, and a pretreatment filter cake is obtained; the content of SiO2 in the pretreated filter cake is more than 85%, the content of CaO is less than 1.5%, and the content of Al2O3 is less than 3% by mass; mixing the pretreated filter cake with alkali liquor, and carrying out hydrothermal synthesis reaction to obtain first sol; sequentially carrying out flash evaporation concentration and modulus adjustment on the first sol to obtain modulus-adjusted water glass; mixing the water glass with ethanol and methyltrimethoxysilane, adding a catalyst, carrying out dispersion treatment to obtain second sol, carrying out injection molding gelation on the second sol, and carrying out aging treatment to obtain aged gel; and carrying out hydrophobic modification, crushing, multi-stage gradient drying and screening on the aged gel to obtain the silicon dioxide aerogel powder. The problem of difficulty in resource utilization of the solid waste micro powder is solved.

Description

Technical Field

[0001] This invention belongs to the field of solid waste material resource utilization technology, and particularly relates to a method for preparing silica aerogel powder using construction solid waste micro powder and the silica aerogel powder. Background Technology

[0002] According to estimates by the China Urban Environmental Sanitation Association, the annual amount of construction waste generated in large and medium-sized cities in my country has exceeded 2 billion tons in recent years, of which the resource utilization rate is less than 20%. In the traditional disposal methods for construction solid waste concrete, recycled coarse aggregate (particle size ≥ 4.75mm) can be used in the preparation of lower-grade concrete as a partial or complete replacement of coarse aggregate, and there are already relatively mature application cases. However, there is a lack of high-value resource utilization pathways for recycled fine aggregate and recycled micro powder with a particle size ≤ 4.75mm. In fact, construction solid waste mainly consists of concrete, glass, and bricks, containing a large amount of SiO2. After treatment and impurity removal, it can be used as an inorganic silicon source for high-value utilization.

[0003] The main components of building micro powder are SiO2 (40-75%), CaO (8-25%), and Al2O3 (5-15%), with active silicon accounting for approximately 50%. However, due to its diverse sources, the composition is complex and unstable, and it may contain impurities such as aluminum (Al), iron (Fe), calcium (Ca), and magnesium (Mg). These impurities can have adverse effects on the preparation of water glass and the formation of aerogel.

[0004] Currently, the most mature water glass extraction technology is the alkali fusion purification method, which mainly relies on high temperatures above 1100℃ and a large amount of strongly alkaline solution (such as NaOH). This method is energy-intensive and generates a large amount of alkaline waste liquid. Furthermore, the modulus of the prepared water glass is between 1.5 and 2.5, which is significantly different from the 3.0 modulus required for the preparation of aerogels. In addition, the ion exchange membranes used in the impurity removal process need to be replaced frequently due to aluminum ion poisoning, further increasing the cost burden of solid waste treatment.

[0005] In aerogel preparation, supercritical drying equipment has a high initial investment cost, while high-temperature and high-pressure equipment poses safety hazards and consumes a lot of energy, making it unsuitable for large-scale industrial application. In recent years, atmospheric pressure drying technology, which has gradually matured, still lags behind supercritical drying in terms of aerogel powder quality; although the equipment and process costs are lower, the product quality is inconsistent.

[0006] Therefore, a comprehensive solution is needed to purify high-modulus (≥3.0) water glass from construction solid waste while developing aerogel formulations and drying processes suitable for this type of water glass, thereby forming aerogel products with superior performance and stable quality. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing silica aerogel powder using construction solid waste micropowder, as well as the silica aerogel powder itself, thus solving the problem of difficult resource utilization of solid waste micropowder.

[0008] The technical solution provided by this invention is as follows:

[0009] This invention provides a method for preparing silica aerogel powder using construction solid waste micronized powder, comprising the following steps: Pretreatment of construction solid waste powder for calcium and aluminum removal yields a pretreated filter cake. The pretreated filter cake contains SiO2 > 85% by mass percentage, CaO < 1.5% by mass, and Al2O3 < 3%. The pretreated filter cake was mixed with alkaline solution and subjected to a hydrothermal synthesis reaction to obtain the first sol. The first sol was subjected to flash evaporation concentration and modulus adjustment in sequence to obtain water glass with modulus adjustment; The water glass was mixed with ethanol and methyltrimethoxysilane, a catalyst was added, and the mixture was dispersed to obtain a second sol. The second sol was then gelled by molding and aged to obtain an aged gel. The aged gel was subjected to hydrophobic modification, crushing, multi-stage gradient drying and sieving to obtain silica aerogel powder.

[0010] Furthermore, the calcium removal operation includes: mixing construction solid waste powder with a particle size ≤4mm and a moisture content of 5~10% with a 0.3~0.8mol / L oxalic acid solution at a solid-liquid ratio of 1:2~3, stirring and reacting at 50~70℃ for 1~4h, and monitoring the calcium content in real time. 2+ Concentration, when Ca in the leachate 2+ The reaction was terminated when the concentration was below 500 ppm; after the reaction was completed, the filter cake was obtained by pressure filtration.

[0011] Furthermore, the aluminum removal process includes: mixing the calcium-removed filter cake with a 0.1~0.3mol / L phosphate solution at a solid-liquid ratio of 1:2~3, stirring and reacting at 70~90℃ and pH=7.5~8.0 for 1~2 hours, and then filtering by pressure after the reaction is completed to obtain the pretreated filter cake; the phosphate is sodium phosphate or sodium pyrophosphate.

[0012] Furthermore, the conditions for the hydrothermal synthesis reaction are as follows: the pretreated filter cake is mixed with 4~6 mol / L alkaline solution at a solid-liquid ratio of 1:2~4, and reacted at 180±5℃ and a pressure of 2.8~3.2MPa for 2~4 hours to obtain a first sol with a viscosity of 2000~3000 cP; the alkaline solution is NaOH solution.

[0013] Furthermore, the conditions for flash concentration are as follows: the first sol is sprayed into the flash tower, the inlet temperature of the flash tower is 160~190℃, the pressure is 0.1~0.3MPa, the vacuum degree inside the flash tower is -90~-100kPa, the top temperature of the tower is 110~130℃, and the solid content after concentration exceeds 35%.

[0014] Furthermore, the modulus adjustment involves adding silica sol micropowder with a particle size of 0.1 μm to adjust the water glass modulus to 3.1 ± 0.1.

[0015] Furthermore, the molar ratio of water glass to anhydrous ethanol and methyltrimethoxysilane is 1:(3~5):(0.2~0.5); the catalyst is NH4F, and the amount of NH4F added is 0.5wt%; the dispersion conditions are: stirring and dispersing at 500~2500 rpm for 10~40 min at 20~40℃; the injection molding gelation conditions are: injecting the second sol into the mold and letting it stand at 20~40℃ for 30~60 min; the aging treatment conditions are: after demolding the second sol of the injection molding gel, placing it in a mixed solution of ethanol and water with a volume ratio of 9:1 and aging at 50~70℃ for 20~30 h.

[0016] Furthermore, the hydrophobic modification operation is as follows: a mixed solution of hexamethyldisilazane and ethanol with a volume ratio of 1:10 is added to the aged gel and refluxed at 70~90℃ for 2~4h. The solid-liquid ratio of the aged gel to the mixed solution is (1~2):(4~6).

[0017] Furthermore, the multi-stage gradient drying operation is as follows: the broken hydrophobically modified gel is first dried at 40~50℃ and hot air flow rate of 1~4m / s for 4~6h, then dried at 70~80℃ and hot air flow rate of 4~6m / s for 1~3h, and finally dried at 110~120℃ and hot air flow rate of 0.2~1.0m / s for 0.5~1h; the particle size of the broken hydrophobically modified gel is 2~5mm.

[0018] The present invention also provides a silica aerogel powder, which is prepared according to the preparation method described above.

[0019] Beneficial effects

[0020] The greatest advantage of this technology lies in achieving a dual disruptive breakthrough: "high-value utilization of solid waste" and "low-cost manufacturing of high-end materials." Through a unique gradient acid washing process (oxalic acid calcium removal rate >90% combined with phosphate aluminum removal rate >85%) and hydrothermal flash evaporation concentration, construction solid waste concrete powder (below 4mm) is transformed into high-modulus water glass, significantly increasing the resource utilization value of solid waste. Combined with MTMS hydrophobic modification and multi-stage gradient drying technology, high-performance aerogel powder is successfully prepared by atmospheric pressure drying, with a thermal conductivity below 0.025 W / (m·K). The overall cost is reduced to ¥50 / kg (less than 40% of the market average). Producing 1 ton of aerogel powder can dispose of 3.2 tons of solid waste powder, simultaneously saving landfill costs and reducing the carbon footprint by 62%, completely transforming the "environmental burden" of construction waste into a "profit source," thus overcoming the two major industry bottlenecks of poor economic viability of solid waste resource utilization and high aerogel application costs. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments. The following embodiments are not intended to limit the present invention, but only to illustrate the present invention. Unless otherwise specified, the experimental methods used in the following embodiments are generally performed under conventional conditions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0022] This invention provides a method for preparing silica aerogel powder using construction solid waste micronized powder, comprising the following steps: Pretreatment of construction solid waste powder for calcium and aluminum removal yields a pretreated filter cake. The pretreated filter cake contains SiO2 > 85% by mass percentage, CaO < 1.5% by mass, and Al2O3 < 3%. The pretreated filter cake was mixed with alkaline solution and subjected to a hydrothermal synthesis reaction to obtain the first sol. The first sol was subjected to flash evaporation concentration and modulus adjustment in sequence to obtain water glass with modulus adjustment; The water glass was mixed with ethanol and methyltrimethoxysilane, a catalyst was added, and the mixture was dispersed to obtain a second sol. The second sol was then gelled by molding and aged to obtain an aged gel. The aged gel was subjected to hydrophobic modification, crushing, multi-stage gradient drying and sieving to obtain silica aerogel powder.

[0023] In this embodiment, the calcium removal operation includes: mixing construction solid waste powder with a particle size ≤4mm and a moisture content of 5~10% with a 0.3~0.8mol / L oxalic acid solution at a solid-liquid ratio of 1:2~3, stirring and reacting at 50~70℃ for 1~4h, and monitoring the calcium content in real time. 2+ Concentration, when Ca in the leachate 2+The reaction was terminated when the concentration was below 500 ppm; after the reaction was completed, the filter cake was obtained by pressure filtration.

[0024] In this embodiment, the aluminum removal operation includes: mixing the calcium-removed filter cake with a 0.1~0.3mol / L phosphate solution at a solid-liquid ratio of 1:2~3, stirring and reacting at 70~90℃ and pH=7.5~8.0 for 1~2 hours, and then filtering by pressure after the reaction is completed to obtain the pretreated filter cake; the phosphate is sodium phosphate or sodium pyrophosphate.

[0025] In this embodiment, the conditions for the hydrothermal synthesis reaction are as follows: the pretreated filter cake is mixed with 4~6 mol / L alkaline solution at a solid-liquid ratio of 1:2~4, and reacted at 180±5℃ and a pressure of 2.8~3.2MPa for 2~4 hours to obtain a first sol with a viscosity of 2000~3000 cP; the alkaline solution is NaOH solution.

[0026] In this embodiment, the conditions for flash concentration are as follows: the first sol is sprayed into the flash tower, the inlet temperature of the flash tower is 160~190℃, the pressure is 0.1~0.3MPa, the vacuum degree inside the flash tower is -90~-100kPa, the top temperature of the tower is 110~130℃, and the solid content after concentration exceeds 35%.

[0027] In this embodiment, the modulus adjustment is achieved by adding silica sol micropowder with a particle size of 0.1 μm to adjust the modulus of the water glass to 3.1 ± 0.1.

[0028] In this embodiment, the molar ratio of water glass to anhydrous ethanol and methyltrimethoxysilane is 1:(3~5):(0.2~0.5); the catalyst is NH4F, and the amount of NH4F added is 0.5wt%; the dispersion conditions are: stirring and dispersing at 500~2500 rpm for 10~40 min at 20~40℃; the injection molding gelation conditions are: injecting the second sol into the mold and letting it stand at 20~40℃ for 30~60 min; the aging treatment conditions are: after demolding the second sol of the injection molding gel, placing it in a mixed solution of ethanol and water with a volume ratio of 9:1 and aging at 50~70℃ for 20~30 h.

[0029] In this embodiment, the hydrophobic modification operation is as follows: a mixed solution of hexamethyldisilazane and ethanol with a volume ratio of 1:10 is added to the aged gel and refluxed at 70~90℃ for 2~4h. The solid-liquid ratio of the aged gel to the mixed solution is (1~2):(4~6).

[0030] In this embodiment, the multi-stage gradient drying operation is as follows: the broken hydrophobically modified gel is first dried at 40~50℃ and hot air flow rate of 1~4m / s for 4~6h, then dried at 70~80℃ and hot air flow rate of 4~6m / s for 1~3h, and finally dried at 110~120℃ and hot air flow rate of 0.2~1.0m / s for 0.5~1h; the particle size of the broken hydrophobically modified gel is 2~5mm.

[0031] This invention also provides a silica aerogel powder, prepared according to the preparation method described above.

[0032] The following detailed description of a solid-phase repair method for waste lithium iron phosphate cathode materials provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0033] Example 1

[0034] (1) Raw material pretreatment:

[0035] Construction solid waste powder (particle size ≤ 4 mm) with a moisture content of 5% was added to an oxalic acid tank, along with a 0.5 mol / L oxalic acid solution (solid-liquid ratio of construction solid waste powder to oxalic acid solution of 1:3). The steam jacket in the oxalic acid tank was turned on to raise the temperature to 60±2℃, and the anchor stirrer was run at 30 rpm for 2 hours. During this period, the Ca²⁺ concentration was monitored in real time. When the Ca²⁺ concentration in the leachate was < 500 ppm, the reaction was terminated, and the calcium ion concentration was reduced to below 0.5%, with a calcium removal rate of over 90%. After calcium removal, the material was introduced into a high-pressure plate and frame filter press and filtered for 20 minutes at a pressure of 0.6 MPa to obtain the calcium-removed filter cake. The filtrate (containing calcium oxalate) was recovered into the oxalic acid tank.

[0036] The decalcified filter cake was transferred to a phosphate complexing tank, and a 0.2 mol / L sodium phosphate solution was added (the solid-liquid ratio of the decalcified filter cake to the sodium phosphate solution was 1:2). The temperature was raised to 80±2℃, and the turbine stirrer was run at 40 rpm for 1 hour. The pH was controlled at 7.5~8.0 (adjusted by the automatic acid addition system) to complete the aluminum removal process. The aluminum ion concentration was lower than 0.1%, and the aluminum removal rate exceeded 85%. After aluminum removal, the filter cake was filtered again in a high-pressure plate and frame filter press to obtain the pretreated filter cake. By mass percentage, the pretreated filter cake contained 92.4% SiO2, 1.12% CaO, and 1.95% alumina.

[0037] (2) Synthesis of water glass: The pretreated filter cake was first mixed with 4 mol / L NaOH solution at a solid-liquid ratio of 1:3 and pumped into a high-pressure reactor. The reactor was then heated to 180±5℃ (heating rate 3℃ / min) under sealed conditions and stirred for 3 hours (pressure 2.8~3.2MPa) to obtain a first sol with a viscosity of 2000~3000 cP. The first sol was then sprayed into a flash evaporator (inlet temperature 180℃, pressure 0.1MPa) through a pressure reducing valve. The evaporator was kept under a vacuum of -95 kPa and the top temperature was 120℃. During the concentration process, the atomized droplets evaporated water in the middle section of the evaporator, and the concentrate fell to the bottom (at which point the solid content exceeded 35%). The steam collected at the top of the evaporator was then sent to a cyclone separator to remove silica particles. The clean steam was condensed to recover ethanol, and the wastewater was sent to the treatment system. The concentrate was pumped into a mixing tank, where silica sol powder (particle size 0.1μm) was added to increase the modulus from 2.5 to 3.05.

[0038] (3) Aerogel preparation:

[0039] Water glass, anhydrous ethanol, and methyltrimethoxysilane (MTMS) were mixed in a mixing tank at a molar ratio of 1:4:0.3, and 0.5 wt% NH4F catalyst was added. The mixture was dispersed at 2000 rpm for 30 min at 40 °C using a stirrer to obtain a second sol. The second sol was injected into a mold and allowed to stand at 25 °C for 45 min. Then, it was demolded and placed in an ethanol aging solution (ethanol:water = 9:1) and aged at 60 °C for 24 h. The aged gel was transferred to a hydrophobic modification vessel, and 10 vol% HMDS / ethanol solution was added (the solid-liquid ratio of the aged gel to the HMDS / ethanol solution was 1:5). The mixture was heated to 80 °C and refluxed for 3 h to obtain a modified gel with a hydrophobic angle >150°. The modified gel was crushed into particles (2-5 mm in diameter) and laid on the mesh belt of a drying kiln. Zone 1 (40℃): hot air flow rate 3 m / s, drying for 5 h (skeletal reinforcement); Zone 2 (70℃): hot air flow rate 5 m / s, drying for 2 h; Zone 3 (120℃): hot air flow rate 0.5 m / s, drying for 1 h (removal of bound water). The material at the outlet was classified by a vibrating screen (20~100 mesh) to obtain aerogel powder.

[0040] Aerogel performance testing:

[0041] Referring to ISO 22007-2-2008 "Determination of thermal conductivity and thermal diffusivity of plastics", the properties of aerogel powder were tested. The thermal conductivity of the aerogel powder was found to be 0.021 W / m·K.

[0042] Referring to GB / T 21354-2008 "General Method for Determination of Tap Density of Powder Products", the tap density of aerogel powder was tested. The test results showed that the tap density of aerogel in Example 1 was 65 g / L.

[0043] Example 2

[0044] (1) Raw material pretreatment:

[0045] Construction solid waste powder (particle size ≤ 4 mm) with a moisture content of 5% was added to an oxalic acid tank, along with a 0.7 mol / L oxalic acid solution (solid-liquid ratio of construction solid waste powder to oxalic acid solution was 1:2). The steam jacket in the oxalic acid tank was turned on to raise the temperature to 60±2℃, and the anchor stirrer was run at 30 rpm for 2 hours. During this time, the Ca²⁺ concentration was monitored in real time. The reaction was terminated when the Ca²⁺ concentration in the leachate was < 500 ppm, completing the calcium removal process. The calcium ion concentration was reduced to below 0.5%, and the calcium removal rate exceeded 90%. After calcium removal, the material was introduced into a high-pressure plate and frame filter press and filtered for 20 minutes at 0.6 MPa to obtain the calcium-removed filter cake. The filtrate (containing calcium oxalate) was recovered back into the oxalic acid tank.

[0046] The decalcified filter cake was transferred to a phosphate complexing tank, and 0.3 mol / L sodium phosphate solution was added (the solid-liquid ratio of the decalcified filter cake to the sodium phosphate solution was 1:2). The temperature was raised to 80±2℃, and a turbine stirrer was run at 40 rpm for 1 hour, controlling the pH to 7.5~8.0 (adjusted by an automatic acid addition system). Aluminum removal was completed, with the aluminum ion concentration below 0.1% and an aluminum removal rate exceeding 85%. After aluminum removal, the filter cake was subjected to further filtration in a high-pressure plate and frame filter press to obtain the pretreated filter cake. By mass percentage, the pretreated filter cake contained 92% SiO2, 1.30% CaO, and 2.8% Al2O3.

[0047] (2) Synthesis of water glass:

[0048] The pretreated filter cake was first mixed with 4 mol / L NaOH solution at a solid-liquid ratio of 1:2 and pumped into a high-pressure reactor. The reactor was then heated to 180±5℃ (heating rate 3℃ / min) under sealed conditions and stirred for 3 hours (pressure 2.8~3.2MPa) to obtain a first sol with a viscosity of 2000~3000 cP. The first sol was then sprayed into a flash evaporator (inlet temperature 180℃, pressure 0.1MPa) through a pressure reducing valve. The evaporator was kept under a vacuum of -95 kPa and the top temperature was 120℃. During the concentration process, the atomized droplets evaporated water in the middle section of the evaporator, and the concentrate fell to the bottom (at which point the solid content exceeded 35%). The steam collected at the top of the evaporator was then sent to a cyclone separator to remove silica particles. The clean steam was condensed to recover ethanol, and the wastewater was sent to the treatment system. The concentrate was pumped into a mixing tank, where silica sol powder (particle size 0.1μm) was added to increase the modulus from 2.7 to 3.1.

[0049] (3) Aerogel preparation:

[0050] Water glass, anhydrous ethanol, and methyltrimethoxysilane (MTMS) were mixed in a mixing tank at a molar ratio of 1:3:0.5, and 0.5 wt% NH4F catalyst was added. The mixture was dispersed at 2000 rpm for 30 min at 40 °C using a stirrer to obtain a second sol. The second sol was injected into a mold and allowed to stand at 25 °C for 45 min. Then, it was demolded and placed in an ethanol aging solution (ethanol:water = 9:1) and aged at 60 °C for 24 h. The aged gel was transferred to a hydrophobic modification vessel, and 10 vol% HMDS / ethanol solution was added (the solid-liquid ratio of the aged gel to the HMDS / ethanol solution was 1:5). The mixture was heated to 80 °C and refluxed for 3 h to obtain a modified gel with a hydrophobic angle >150°. The modified gel was crushed into particles (2-5 mm in diameter) and laid on the mesh belt of a drying kiln. Drying was carried out in three zones: Zone 1 (40℃): hot air velocity 3 m / s, 5 h (skeletal reinforcement); Zone 2 (80℃): hot air velocity 5 m / s, 2.5 h; Zone 3 (120℃): hot air velocity 0.5 m / s, 1 h (removal of bound water). The outlet material was classified by a vibrating screen (20-100 mesh) to obtain aerogel powder.

[0051] Aerogel performance testing:

[0052] Referring to ISO 22007-2-2008 "Determination of thermal conductivity and thermal diffusivity of plastics", the properties of aerogel powder were tested. The thermal conductivity of the aerogel powder was found to be 0.023 W / m·K.

[0053] Referring to GB / T 21354-2008 "General Method for Determination of Tap Density of Powder Products", the tap density of aerogel powder was tested. The test results showed that the tap density of aerogel in Example 1 was 55 g / L.

[0054] The specific embodiments of the present invention have been described in detail above, but the scope of the present invention is not limited to the above embodiments. For those skilled in the art, various adjustments, modifications, or substitutions can be made to the embodiments without departing from the core principles and spirit of the present invention, but these modifications still fall within the protection scope of the present invention.

Claims

1. A method for preparing a silica aerogel powder using building solid waste micro powder, characterized by, The method comprises the following steps: The calcium and aluminum in the building solid waste micro powder are removed to obtain a pretreated filter cake; the content of SiO2 in the pretreated filter cake is > 85%, the content of CaO is < 1.5%, and the content of Al2O3 is < 3% by mass percentage; The pretreated filter cake is mixed with an alkali solution to perform a hydrothermal synthesis reaction to obtain a first sol; The first sol is sequentially subjected to flash concentration and modulus adjustment to obtain a modulus-adjusted water glass; The water glass is mixed with ethanol and methyltrimethoxysilane, and a catalyst is added to perform dispersion treatment to obtain a second sol, and then the second sol is injected into a mold for gelation, and then the gelation is subjected to aging treatment to obtain an aged gel; The aged gel is subjected to hydrophobic modification, crushing, multi-stage gradient drying and screening to obtain a silica aerogel powder. 2.The method for preparing silica aerogel powder using building solid waste micro powder according to claim 1, characterized in that, The calcium removal operation comprises: mixing the building solid waste micro-powder with a particle size of ≤4 mm and a water content of 5-10% with a 0.3-0.8 mol / L oxalic acid solution at a solid-liquid ratio of 1:2-3, stirring and reacting at 50-70 ℃ for 1-4 h, and monitoring the Ca 2+ concentration in the leaching solution in real time, and terminating the reaction when the Ca 2+ concentration in the leaching solution is lower than 500 ppm; and after the reaction is completed, pressure filtration is performed to obtain a filter cake after calcium removal. 3.The method of claim 2, wherein the method further comprises: drying the silica aerogel powder. The operation of removing aluminum comprises the following steps: the filter cake after calcium removal is mixed with a 0.1-0.3 mol / L phosphate solution at a solid-liquid ratio of 1:2-3, and is stirred and reacted at 70-90 DEG C and pH = 7.5-8.0 for 1-2 h, and then is pressed and filtered to obtain the pretreated filter cake; the phosphate is sodium phosphate or sodium pyrophosphate. 4.The method for preparing a silica aerogel powder at normal pressure using building solid waste micro powder according to claim 1, characterized in that, The hydrothermal synthesis reaction is performed under the following conditions: the pretreated filter cake is mixed with a 4-6 mol / L alkali solution at a solid-liquid ratio of 1:2-4, and is reacted at 180±5 DEG C and a pressure of 2.8-3.2 MPa for 2-4 h to obtain a first sol with a viscosity of 2000-3000 cP; the alkali solution is a NaOH solution. 5.The method for preparing silica aerogel powder using building solid waste micro powder according to claim 1, characterized in that, The flash concentration is performed under the following conditions: the first sol is sprayed into a flash tower, the inlet temperature of the flash tower is 160-190 DEG C, the pressure is 0.1-0.3 MPa, the vacuum degree in the tower is -90--100 kPa, and the overhead temperature is 110-130 DEG C, and the solid content after concentration is more than 35%. 6.The method for preparing a silica aerogel powder using building solid waste micro powder according to claim 1, characterized in that, The modulus adjustment is to add silica sol micro powder with a particle size of 0.1 μm to adjust the modulus of the water glass to 3.1±0.

1. 7.The method of claim 1, wherein the building solid waste micro powder is used as a raw material for preparing the silica aerogel powder. The molar ratio of the water glass to anhydrous ethanol and methyltrimethoxysilane is 1:(3-5):(0.2-0.5); the catalyst is NH4F, the addition amount of the NH4F is 0.5 wt%, the dispersion is performed at a stirring speed of 500-2500 rpm for 10-40 min at 20-40 DEG C, the gelation is performed by injecting the second sol into a mold and standing for 30-60 min at 20-40 DEG C, and the aging treatment is performed by placing the second sol after demolding in a mixed solution of ethanol and water at a volume ratio of 9:1 and aging for 20-30 h at 50-70 DEG C. 8.The method of claim 1, wherein the building solid waste micro powder is used to prepare the silica aerogel powder. The operation of hydrophobic modification comprises the following steps: a mixed solution of hexamethyldisilazane and ethanol at a volume ratio of 1:10 is added to the aged gel, and the mixture is refluxed and reacted at 70-90 DEG C for 2-4 h, and the solid-liquid ratio of the aged gel to the mixed solution is (1-2):(4-6). 9.The method of claim 1, wherein the method further comprises a step of drying the silica aerogel powder. The operation of the multistage gradient drying is: the broken hydrophobically modified gel is dried at 40-50 DEG C, hot air flow rate of 1-4 m / s for 4-6 h, then dried at 70-80 DEG C, hot air flow rate of 4-6 m / s for 1-3 h, and finally dried at 110-120 DEG C, hot air flow rate of 0.2-1.0 m / s for 0.5-1 h; the particle size of the broken hydrophobically modified gel is 2-5 mm.

10. A silica aerogel powder, characterized by, Prepared according to the preparation method of any one of claims 1-9.