1. A preparation method of an ultralight fibrous xonotlite type heat-insulating material based on extraction of amorphous silicon in fly ash is characterized by comprising the following steps:

1) extracting amorphous silicon in the fly ash by a high-temperature high-pressure alkali dissolution method to obtain fly ash silicon extraction liquid;

2) taking the fly ash silicon extraction liquid obtained in the step 1) as a main siliceous raw material, taking lime milk as a main calcareous raw material, adding a crystal growth promoter, and preparing the ultralight fibrous xonotlite heat-insulating material by adopting a dynamic hydrothermal synthesis process.

2. The preparation method according to claim 1, wherein the specific steps of the step 1) are as follows:

11) preparing a fly ash silicon extracting solution: preparing 10-30 wt% sodium hydroxide solution, and mixing SiO₂Uniformly mixing pulverized coal furnace coal ash with the content of more than 30% and a sodium hydroxide solution according to the solid-to-liquid ratio of 1: 4-1: 2, placing the mixture into a high-pressure reaction kettle or a high-pressure sleeve heating container, and preserving heat for 0.5-3 h at the temperature of 100-150 ℃;

12) then carrying out solid-liquid separation on the reaction materials to obtain filtrate, adding clear water to the solid filtrate to enable the solid-liquid ratio to reach 1: 1.4-1: 1.7, carrying out countercurrent washing for 1-2 times, mixing the filtrate and the washing liquid, and heating and evaporating to enable Na in the mixed liquid₂The concentration of O is 20-70 g/L, SiO₂The concentration is 25-80 g/L, and the fly ash silicon extracting solution is obtained.

3. The preparation method according to claim 1, wherein the step 2) comprises the following specific steps:

21) synthesis of fibrous xonotlite: adding lime milk into the fly ash silicon extraction liquid obtained in the step 1) to ensure that the molar ratio of Ca/Si is 0.90-1.15, simultaneously adding a small amount of crystal growth promoter, adding water to adjust the mixture to be slurry with the solid-to-liquid ratio of 1: 10-1: 40, placing the slurry into a high-temperature high-pressure reaction kettle, firstly heating to 180-200 ℃ at the heating rate of 5-20 ℃/min, and keeping the temperature for 2-4 h at the stirring speed of 300-400 rpm; heating to 220-280 ℃ at a heating rate of 1-3 ℃/min, and keeping the temperature for 0.5-3 h under the condition of a stirring speed of 60-260 rpm to prepare fibrous xonotlite slurry;

22) recycling alkali liquor: step 21) cooling the fibrous xonotlite slurry prepared in the step to be below 80 ℃, discharging the fibrous xonotlite slurry from the kettle, dehydrating the fibrous xonotlite slurry in a filter pressing dehydration mode, and washing the fibrous xonotlite slurry with water at the temperature of 50-95 ℃ in a reverse direction for 2-5 times to finally obtain Na₂Fibrous xonotlite having an O content of 1 to 6 wt%;

evaporating and concentrating the filter liquor after filter pressing and dehydration, then adding lime milk for causticization, adding a small amount of NaOH to enable the NaOH concentration of the filter liquor to reach 10-30 wt%, and circularly using the filter liquor in the step 1) for preparing the fly ash silicon extracting solution;

23) preparation of the heat insulating material: adding water into the washed fibrous xonotlite obtained in the step 22) to adjust the solid-to-liquid ratio to 1: 5-1: 20, adding 1.5-5% of fiber and about 0-3% of water glass with the modulus of 2-3.2, fully and uniformly stirring, injecting into a suction filtration dehydration press molding machine, and carrying under the pressure of 2-8 MPa for 0.5-3 min; and (3) standing the formed xonotlite type heat insulation product at 20-30 ℃ for more than 8 hours, then placing the product in a tunnel kiln at 50-150 ℃, and drying for 16-24 hours to control the water content to be less than 5%.

4. The preparation method of claim 3, wherein the effective calcium content of the lime milk in the steps 21) and 22) is more than 80%, the activity index is more than 350ml, and the 120-mesh residue of the lime milk is less than 5%.

5. The method according to claim 3, wherein the crystal growth promoter of step 21) comprises ZrOCl₂·8H₂O and AlCl₃Adding 20-40 g of ZrOCl into each cubic slurry₂·8H₂O and 50-100 g of AlCl₃。

6. The method of claim 3, wherein the fiber of step 23) is one or more of a glass fiber, a pulp fiber, a carbon fiber, an aramid fiber, an ultra-high molecular weight polyethylene, and a recycled fiber.

7. An ultra-light fibrous xonotlite-type insulation material based on extraction of amorphous silicon from fly ash, prepared by the method of any one of claims 1 to 6.

Background

The energy structure of rich coal, less gas and poor oil in China results in that about 6.5 million tons of fly ash are discharged every year in China. And because coal resources and population distribution in China are uneven, economic development is east-west and south-north unbalanced, the utilization rate of the fly ash in developed regions of the south China and the east China coastal regions is more than 95%, while the utilization rate of the fly ash in regions of the northwest China and the north China, such as inner Mongolia, Shanxi, Shaanxi, Ningxia and Xinjiang, is only about 20%, and the fly ash is massively stockpiled, so that the local ecological environment is seriously damaged.

As a substance with pozzolanic activity, the traditional utilization mode mainly focuses on cement and concrete, and the added value is low although the utilization amount is high. Therefore, the high-value utilization of the fly ash is an important measure for realizing the development strategy of 'carbon peak reaching' and 'carbon neutralization'. The main phase of the fly ash is amorphous SiO₂Mullite, and small amount of quartz and corundum, amorphous SiO₂As a substance with high reaction activity, the compound has good solubility in alkaline environment, so the compound can be extracted by an alkaline dissolution method and is used with high value.

Xonotlite (6 CaO.6SiO)₂·H₂O) is a monoclinic system, and is a good heat insulation material because the microstructure of the monoclinic system is prism-shaped crystals or fibrous aggregates and has better high temperature resistance. The traditional xonotlite type heat-insulating material is prepared by taking siliceous raw materials (quartz sand powder and diatomite), calcareous raw materials (lime and slaked lime) and reinforcing fibers (such as wood fibers, asbestos, glass fibers and the like) as main raw materials, dynamically hydrothermally synthesizing xonotlite in a high-temperature high-pressure reaction kettle, and carrying out processes such as compression molding, drying and the like. By adopting the method, the raw materials need to be pulverizedGrinding and processing of quartz type SiO₂The activity is low, the dynamic hydrothermal synthesis process not only needs high liquid-solid ratio and long reaction time, so that the material consumption and the energy consumption are high, but also the generated xonotlite mineral fiber is short, and a large amount of unreacted quartz remains, so that the prepared heat-insulating material has high density and poor heat-insulating property.

Disclosure of Invention

The invention aims to realize high-value utilization of the fly ash, fully utilize amorphous silicon in the fly ash and prepare the ultra-light heat-insulating material.

In order to solve the technical problems, the invention provides a preparation method of an ultralight fibrous xonotlite type heat-insulating material based on extraction of amorphous silicon in fly ash, which comprises the following steps:

1) extracting amorphous silicon in the fly ash by a high-temperature high-pressure alkali dissolution method to obtain fly ash silicon extraction liquid;

2) taking the fly ash silicon extraction liquid obtained in the step 1) as a main siliceous raw material, taking lime milk as a main calcareous raw material, adding a crystal growth promoter, and preparing the ultralight fibrous xonotlite heat-insulating material by adopting a dynamic hydrothermal synthesis process.

Further, the specific steps of step 1) are as follows:

11) preparing a fly ash silicon extracting solution: preparing 10-30 wt% sodium hydroxide solution, and mixing SiO₂Uniformly mixing pulverized coal furnace coal ash with the content of more than 30% and a sodium hydroxide solution according to the solid-to-liquid ratio of 1: 4-1: 2, placing the mixture into a high-pressure reaction kettle or a high-pressure sleeve heating container, and preserving heat for 0.5-3 h at the temperature of 100-150 ℃;

12) then carrying out solid-liquid separation on the reaction materials to obtain filtrate, adding clear water to the solid filtrate to enable the solid-liquid ratio to reach 1: 1.4-1: 1.7, carrying out countercurrent washing for 1-2 times, mixing the filtrate and the washing liquid, and heating and evaporating to enable Na in the mixed liquid₂The concentration of O is 20-70 g/L, SiO₂The concentration is 25-80 g/L, and the fly ash silicon extracting solution is obtained.

Further, the specific steps of step 2) are as follows:

21) synthesis of fibrous xonotlite: adding lime milk into the fly ash silicon extraction liquid obtained in the step 1) to ensure that the molar ratio of Ca/Si is 0.90-1.15, simultaneously adding a small amount of crystal growth promoter, adding water to adjust the mixture to be slurry with the solid-to-liquid ratio of 1: 10-1: 40, placing the slurry into a high-temperature high-pressure reaction kettle, firstly heating to 180-200 ℃ at the heating rate of 5-20 ℃/min, and keeping the temperature for 2-4 h at the stirring speed of 300-400 rpm; heating to 220-280 ℃ at a heating rate of 1-3 ℃/min, and keeping the temperature for 0.5-3 h under the condition of a stirring speed of 60-260 rpm to prepare fibrous xonotlite slurry;

22) recycling alkali liquor: step 21) cooling the fibrous xonotlite slurry prepared in the step to be below 80 ℃, discharging the fibrous xonotlite slurry from the kettle, dehydrating the fibrous xonotlite slurry in a filter pressing dehydration mode, and washing the fibrous xonotlite slurry with water at the temperature of 50-95 ℃ in a reverse direction for 2-5 times to finally obtain Na₂Fibrous xonotlite having an O content of 1 to 6 wt%;

evaporating and concentrating the filter liquor after filter pressing and dehydration, then adding lime milk for causticization, adding a small amount of NaOH to enable the NaOH concentration of the filter liquor to reach 10-30 wt%, and circularly using the filter liquor in the step 1) for preparing the fly ash silicon extracting solution;

23) preparation of the heat insulating material: adding water into the washed fibrous xonotlite obtained in the step 22) to adjust the solid-to-liquid ratio to 1: 5-1: 20, adding 1.5-5% of fiber and about 0-3% of water glass with the modulus of 2-3.2, fully and uniformly stirring, injecting into a suction filtration dehydration press molding machine, and carrying under the pressure of 2-8 MPa for 0.5-3 min; and (3) standing the formed xonotlite type heat insulation product at 20-30 ℃ for more than 8 hours, then placing the product in a tunnel kiln at 50-150 ℃, and drying for 16-24 hours to control the water content to be less than 5%.

Further, the effective calcium content of the lime milk in the steps 21) and 22) is more than 80%, the activity index is more than 350ml, and the 120-mesh residue of the lime milk is less than 5%.

Further, the crystal growth promoter in the step 21) is ZrOCl₂·8H₂O and AlCl₃Adding 20-40 g of ZrOCl into each cubic slurry₂·8H₂O and 50-100 g of AlCl₃。

Further, the fiber in the step 23) is one or more of glass fiber, pulp fiber, carbon fiber, aramid fiber, ultra-high molecular weight polyethylene and recycled fiber.

The ultralight fibrous xonotlite type heat-insulating material based on the extraction of amorphous silicon in the fly ash is prepared according to the method.

Advantageous effects

The method for preparing the calcium silicate heat-insulating material by using the fly ash desiliconized material has the advantages of short reaction time, low energy consumption, cyclic utilization of alkali liquor and good product performance, and provides a new high-quality utilization way for the fly ash. Therefore, the invention has obvious social, economic and environmental benefits.

Drawings

FIG. 1 is a process flow diagram of the method for preparing the ultralight fibrous xonotlite-type thermal insulation material of the present invention.

Detailed Description

The present invention will be described in further detail with reference to specific examples.

The process flow of the invention is shown in figure 1. The invention takes fly ash silicon extracting liquid as main siliceous raw material, Si in the silicon extracting liquid is free [ H₂SiO]^4-Dissolving the form of anionic group in sodium hydroxide solution; lime milk as main calcium material, Ca is Ca (H)₂O)₅(OH)⁺The form of (A) is slightly soluble in water to form a suspension, and has the characteristic similar to colloid, so that the reaction of siliceous raw material and calcareous raw material is similar to liquid-liquid reaction, and the added crystal form promoter ZrOCl₂·8H₂O or AlCl₃Can effectively promote the growth of the fibrous xonotlite and can generate the fibrous xonotlite crystal form with high length-diameter ratio. Compared with the traditional process, the technology reduces the equipment investment and ball milling energy consumption required by quartz sand powder milling, slightly reduces the hydrothermal synthesis temperature in the aspect of synthesis process, ensures that the synthesis reaction is more sufficient, greatly shortens the reaction time in the synthesis process from 6-12 h to 2.0-8 h, reduces the equipment investment of unit productivity, reduces the solid-liquid ratio required in the synthesis process from 1: 30-1: 50 to 1: 10-1: 40, obviously reduces the energy consumption, and prepares the xonotlite heat-insulating materialAll performance indexes are obviously improved, and particularly, the density of the product is reduced by more than 50 percent compared with the traditional process and is only 100kg/m³And about, the ultra-light level is achieved.

The first embodiment is as follows:

to SiO₂Adding 32 wt% of fly ash into 15 wt% of sodium hydroxide solution to prepare slurry with a solid-to-liquid ratio of 1:4, placing the slurry in a high-pressure reaction kettle, carrying out silicon extraction reaction for 1.5h at the temperature of 120 ℃, carrying out solid-liquid separation on reaction products, adding clear water into solid filtrate to enable the solid-to-liquid ratio to reach 1:1.4, carrying out 2 times of countercurrent washing, mixing filtrate and washing liquid, heating and evaporating to prepare silicon extraction liquid, wherein Na in the silicon extraction liquid₂O concentration of 62g/L, SiO₂The concentration was 60 g/L. Adding lime milk (the content of available calcium is 86%, the activity index is 370ml, and the residue of a 120-mesh sieve is 3.2%) into the fly ash silicon extraction liquid to ensure that the Ca/Si (molar ratio) is 1.05, and simultaneously adding 23g of ZrOCl into each cubic of slurry₂·8H₂O and 70g of AlCl₃Adding water to adjust the slurry to be a slurry with a solid-to-liquid ratio of 1:25, adding the slurry into a high-temperature high-pressure reaction kettle, heating to 190 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 2.5h at a stirring speed of 300rpm, heating to 240 ℃ at a heating rate of 2 ℃/min, and keeping the temperature for 1.4h at a stirring speed of 130 rpm. After the heat preservation is finished, after the slurry in the kettle is cooled to be below 80 ℃, the slurry in the kettle is discharged, after the slurry is dehydrated by filter pressing, the filter cake is washed by water with the temperature of 70 ℃ for 3 times in a countercurrent way, and the length-diameter ratio of the filter cake is about 130, Na₂Fibrous xonotlite with the O content of 3 wt%, and causticizing, concentrating and recycling after mixing the filtrate and the washing liquor. Adding water into fibrous xonotlite to adjust solid-liquid ratio to 1:12, adding 3.5% fiber (glass fiber: polyethylene: 7:3) and about 0.5% water glass with modulus of 2.0, stirring well, injecting into a suction filtration dehydration press molding machine, and holding under 4.3Mpa for 2.3 min. And (3) standing the molded heat-insulating product at 25 ℃ for 8h, then placing the heat-insulating product in a tunnel kiln at 120 ℃, and drying for 16h to obtain a heat-insulating material finished product. The density of the obtained fibrous xonotlite-type heat-insulating material was measured to be 123kg/m³0.043W/(m.K) of heat conductivity coefficient at 100 ℃, 0.95MPa of compressive strength, 0.60MPa of flexural strength, 0.8 percent of linear shrinkage and 3.3 percent of water content,the maximum service temperature is 1000 ℃, and the fire resistance is grade A1, so that the requirements of III type products in GB/T10699-2015 calcium silicate heat insulation product standards are met.

Example two:

to SiO₂Adding 35 wt% of fly ash into 20 wt% of sodium hydroxide solution to prepare slurry with a solid-to-liquid ratio of 1:3, placing the slurry in a high-pressure reaction kettle, carrying out silicon extraction reaction for 1.7h at the temperature of 135 ℃, carrying out solid-liquid separation on reaction products, adding clear water into solid filtrate to enable the solid-to-liquid ratio to reach 1:1.5, carrying out 2 times of countercurrent washing, mixing filtrate and washing liquid, heating and evaporating to prepare silicon extraction liquid, wherein Na in the silicon extraction liquid₂O concentration of 63g/L, SiO₂The concentration was 64 g/L. Adding lime milk (effective calcium content 84%, activity index 363ml, 120-mesh residue 2.7%) into fly ash silicon extraction liquid to make Ca/Si (molar ratio) 0.98, and simultaneously adding 30g ZrOCl into every cubic slurry₂·8H₂O and 65g of AlCl₃Adding water to adjust the slurry to be a slurry with a solid-to-liquid ratio of 1:30, adding the slurry into a high-temperature high-pressure reaction kettle, heating to 200 ℃ at a heating rate of 7 ℃/min, keeping the temperature for 3.0h at a stirring speed of 280rpm, heating to 240 ℃ at a heating rate of 2 ℃/min, and keeping the temperature for 1.5h at a stirring speed of 110 rpm. After the heat preservation is finished, after the slurry in the kettle is cooled to be below 80 ℃, the slurry in the kettle is discharged, after the slurry is dehydrated by filter pressing, the filter cake is washed by water with the temperature of 75 ℃ for 3 times in a countercurrent way, and the length-diameter ratio of the filter cake is about 140, Na₂Fibrous xonotlite with an O content of 2.8 wt%, and causticizing, concentrating and recycling after mixing the filtrate and the washing liquor. Adding water into fibrous xonotlite to adjust solid-liquid ratio to 1:15, adding 5% fiber (glass fiber: pulp fiber: polyethylene: 5:2:3) and about 0.4% water glass with modulus of 2.3, stirring well, injecting into suction filtration dehydration press molding machine, and holding under 2.6Mpa for 2.0 min. And (3) standing the molded heat-insulating product at 25 ℃ for 8h, then placing the heat-insulating product in a tunnel kiln at 135 ℃, and drying for 20h to obtain a heat-insulating material finished product. The density of the obtained fibrous xonotlite-type heat-insulating material is 118kg/m³The heat conductivity coefficient at 100 ℃ is 0.041W/(m.K), the compressive strength is 0.83MPa, the breaking strength is 0.47MPa, the linear shrinkage rate is 1.1 percent, the water content is 2.8 percent, and the highest rate isThe service temperature is 1000 ℃, and the fireproof performance is grade A1, so that the requirements of III type products in GB/T10699-2015 calcium silicate heat insulation product standards are met.

Example three:

to SiO₂Adding fly ash with the content of 37 wt% into 22 wt% of sodium hydroxide solution to prepare slurry with the solid-to-liquid ratio of 1:4, placing the slurry in a high-pressure reaction kettle to perform silicon extraction reaction for 2.1 hours at the temperature of 150 ℃, performing solid-liquid separation on a reaction product, adding clear water into a solid filtrate to enable the solid-to-liquid ratio to reach 1:1.5, performing countercurrent washing for 2 times, mixing the filtrate and the washing solution, heating and evaporating to prepare silicon extraction liquid, and adding Na in the silicon extraction liquid₂O concentration of 75g/L, SiO₂The concentration was 62 g/L. Adding lime milk (the content of effective calcium is 87%, the activity index is 376ml, and the residue of a 120-mesh sieve is 3.4%) into the fly ash silicon extraction liquid to ensure that the Ca/Si (molar ratio) is 1.0, and simultaneously adding 35g of ZrOCl into each cubic of slurry₂·8H₂O and 85g of AlCl₃Adding water to adjust the slurry to be a slurry with a solid-to-liquid ratio of 1:30, adding the slurry into a high-temperature high-pressure reaction kettle, heating to 200 ℃ at a heating rate of 6 ℃/min, keeping the temperature for 3.5h at a stirring speed of 260rpm, heating to 260 ℃ at a heating rate of 2 ℃/min, and keeping the temperature for 2.0h at a stirring speed of 110 rpm. After the heat preservation is finished, after the slurry in the kettle is cooled to be below 80 ℃, the slurry in the kettle is discharged, after the slurry is dehydrated by filter pressing, the filter cake is washed by water with the temperature of 70 ℃ for 3 times in a countercurrent way, and the length-diameter ratio of the filter cake is about 150, Na₂Fibrous xonotlite with an O content of 3.2 wt%, and causticizing, concentrating and recycling after mixing the filtrate and the washing liquor. Adding water into fibrous xonotlite to adjust solid-liquid ratio to 1:20, adding 5% fiber (glass fiber: pulp fiber: polyethylene: 6:2:2) and about 0.4% water glass with modulus of 2.3, stirring well, injecting into a suction filtration dehydration press molding machine, and holding under 2.4Mpa for 1.7 min. And (3) standing the molded heat-insulating product at 25 ℃ for 8h, then placing the heat-insulating product in a tunnel kiln at 135 ℃, and drying for 22h to obtain a heat-insulating material finished product. The density of the fibrous xonotlite-type heat-insulating material prepared by detection is 97kg/m³The heat conductivity coefficient at 100 ℃ is 0.038W/(m.K), the compressive strength is 0.78MPa, the breaking strength is 0.43MPa, the linear shrinkage rate is 1.5 percent, the water content is 2.6 percent, and the highest use temperature isThe temperature is 1000 ℃, and the fireproof performance is grade A1, which meets the requirements of III type products in GB/T10699-2015 calcium silicate heat insulation product standard.