A method for preparing low-carbon waste incineration fly ash (MSWIFA) cement-based materials by modified nano-solution carbonization and its application.

Abstract

This invention discloses a method for preparing low-carbon waste incineration fly ash (MSWIFA) cement-based materials by modified nano-solution carbonization and its application. The method disperses nano-silica in a VTES (vinyltriethoxysilane) ethanol solution as a medium for MSWIFA carbonization modification, while simultaneously utilizing an ethanolamine solution to enhance the degree of MSWIFA carbonization. The carbonized and modified MSWIFA is incorporated into cement-based materials as a supplementary cementitious material, not only improving the compressive strength of the cement-based materials but also consolidating heavy metal ions in the MSWIFA. Most importantly, the carbonization method described in this invention is superior to traditional carbonization methods. The carbonization modification process eliminates the need for steps such as filtration and drying, retaining finer particles, reducing energy consumption, saving time, and improving carbonization efficiency. Building materials produced using modified MSWIFA reduce environmental pollution and possess excellent thermal insulation properties, achieving the goals of green environmental protection, energy conservation, and emission reduction.

Description

Technical Field

[0001] This invention relates to the preparation of cement-based materials, and more specifically to a method for preparing low-carbon waste incineration fly ash (MSWIFA) cement-based materials by modified nano-solution carbonization and its application. Background Technology

[0002] my country currently generates hundreds of millions of tons of municipal solid waste annually. MSWIFA, produced after incineration, is rich in heavy metals such as Pb, Cu, Zn, and Cr, requiring further treatment before landfilling or utilization. Currently, solidifying MSWIFA with cementitious materials is a common method for the harmless disposal of fly ash. MSWIFA contains raw materials such as calcium oxide, silica, alumina, and calcium sulfate, which can undergo hydration reactions with cement to generate stable structures like CSH and ettringite, which can solidify and stabilize the heavy metals in MSWIFA and produce cement components with a certain strength. However, using silicate cement to solidify MSWIFA also has many drawbacks: the cement production process is energy-intensive and produces large amounts of greenhouse gases; the solidified body has low strength; and the solidification effect on heavy metals is poor. The ultra-large specific surface area of ​​nanomaterials can serve as nucleation sites for cement hydration products, promoting the generation and growth of CSH gel and accelerating the hydration reaction process. Furthermore, nanomaterials can fill pores, refine the cement pore structure, and promote the formation of denser cement hydration products. Adding nanomaterials to silicate cement can be expected to improve the stabilization effect of solidified heavy metals to some extent. However, nanomaterials tend to agglomerate in mortar environments, resulting in poor diffusion.

[0003] MSWIFA is a typical calcium-rich alkaline waste. Accelerated carbonation can facilitate fly ash reuse. Heavy metal ions in fly ash react with CO2 to form insoluble carbonates. These heavy metal ions are stabilized internally through chemical precipitation and physical encapsulation, thus reducing their leaching toxicity. Carbonation enhances the pozzolanic activity of MSWIFA, and the carbonated MSWIFA plays a positive role in cement hydration. Carbonated MSWIFA can be incorporated into cementitious materials as a supplementary cementitious material, not only improving the compressive strength of the cementitious materials but also consolidating the heavy metal ions within the MSWIFA. This carbonated MSWIFA can effectively reduce cement usage, offering advantages such as low carbon footprint, environmental friendliness, and low economic cost.

[0004] Existing MSWIFA modification technologies typically require steps such as filtration and drying, resulting in high energy consumption. Therefore, a new low-carbon and environmentally friendly MSWIFA treatment method is urgently needed. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a method for preparing low-carbon waste incineration fly ash (MSWIFA) cement-based materials by modified nano-solution carbonization and its application. Nano-silica is dispersed in a silane coupling agent vinyltriethoxysilane (VTES) ethanol solution as a medium for MSWIFA carbonization modification. Ethanolamine solution is used to improve the degree of MSWIFA carbonization. Gas containing carbon dioxide (purity > 99%) is introduced into the reaction vessel. The carbon dioxide reacts with MSWIFA to undergo a carbonization reaction. The carbonized and modified MSWIFA can be incorporated into cement-based materials as a supplementary cementitious material, which can not only improve the compressive strength of cement-based materials, but also solidify heavy metal ions in MSWIFA.

[0006] The carbonization method described in this invention is superior to traditional carbonization methods. After carbonization modification, steps such as filtration and drying are unnecessary, reducing energy consumption and saving time, while improving carbonization efficiency. The carbonized MSWIFA can be incorporated into cement-based materials as a supplementary cementitious material, not only improving the compressive strength of the cement-based materials but also solidifying heavy metal ions in the MSWIFA. Utilizing modified MSWIFA to produce building materials is an effective way to reduce carbon emissions, offering green environmental protection, energy conservation, and emission reduction effects.

[0007] Specifically, the present invention provides a method for preparing low-carbon waste incineration fly ash (MSWIFA) cement-based materials by modified nano-solution carbonization, comprising the following raw materials: MSWIFA, vinyltriethoxysilane (VTES), nano-silica, ethanolamine, water, and carbon dioxide gas; wherein, VTES, nano-silica, ethanolamine, and carbon dioxide gas are used sequentially to carbonize and modify MSWIFA.

[0008] Preferably, the chemical composition of the MSWIFA is 30-40% CaO, 3%-8% SiO2, and 1%-4% MgO; the particle size of the MSWIFA is D50 = 20-30 μm, and the particle size range is 10-50 μm.

[0009] Preferably, the liquid-to-solid ratio of VTES to nano-silica is 5:1-6:1 mL / g, and the ratio of VTES to water is 1:2-1:3.

[0010] Preferably, hydrophilic amorphous free-flowing nano-silica powder with an average particle size range of 20-30 nm is added to anhydrous ethanol and mixed and stirred. Then, a mixed solution of VTES and water is added, stirred, and the suspension is ultrasonically dispersed to obtain a VTES-modified nano-silica solution.

[0011] Preferably, the ethanolamine is prepared as a 1-2 wt% ethanolamine solution to participate in the modification of MSWIFA.

[0012] Preferably, the carbon dioxide gas is introduced at a rate of 2-3 L / min, the reaction pressure is 0.5-1 MPa, the reaction time is 1-3 h, the reaction temperature is 20-30 °C, and the humidity is 50-80%; the carbon dioxide gas is a high-purity gas with a mass fraction of 99-99.9%.

[0013] Preferably, the carbonized MSWIFA and ordinary silicate cement are mixed and stirred to improve the compressive strength of the cement base.

[0014] The detailed steps of the method described in this invention are as follows:

[0015] Step 1: Collect MSWIFA. The incineration fly ash is sieved through a 0.075mm square hole sieve. The fly ash with a particle size of less than 0.075mm is collected for subsequent use.

[0016] Step 2: Mix distilled water and incineration fly ash at a liquid-to-solid ratio of L / S = 5-20:1, and magnetically stir at a speed of 300-500 r / min for 15-30 min;

[0017] Step 3: Use a vacuum filter to separate the distilled water from the mixed solution of distilled water and waste incineration fly ash to obtain solid fly ash from waste incineration. The filter membrane used for vacuum filtration is a 0.45μm filter membrane. Then dry it at 40-60℃ for 24-48h. After drying until the mass is constant, take it out, cool it to room temperature, and sieve it to obtain homogeneous powder with a particle size range of 10-50μm.

[0018] Step 4: Mix and stir nano-silica and anhydrous ethanol to disperse the nano-silica in the anhydrous ethanol. Mix and stir the silane coupling agent vinyltriethoxysilane (VTES) and water to hydrolyze the VTES, obtaining a VTES solution. Pour the VTES solution into the anhydrous ethanol solution of nano-silica and stir to mix, obtaining a VTES-modified nano-silica solution. By using VTES to modify the nano-silica, the nano-silica is uniformly dispersed in the material.

[0019] Step 5: Mix MSWIFA with VTES-modified nano-silica solution to obtain a mixed slurry;

[0020] Step 6: Place the mixed slurry in a water bath device, put it into a microwave reactor, react for 30-40 minutes, react at 60-70℃, microwave power 300-400W, and start the microwave reactor water bath heating.

[0021] Step 7: Prepare a 1-2 wt% ethanolamine solution, perform ultrasonic vibration at a frequency of 40-50 kHz and a power of 25-35 W, vibrate for 2 seconds and rest for 3 seconds, and cool after every 15-20 minutes of vibration, repeat 4-6 times.

[0022] Step 8: Place the mixed slurry and the prepared ethanolamine solution in a reaction vessel, heat and stir in a water bath, and introduce carbon dioxide gas into the reaction vessel. Adjust the pressure and reaction time of the reaction vessel to carry out the carbonization reaction.

[0023] Step 9: The carbonized slurry is mixed with ordinary silicate cement to obtain a slurry mixture. The slurry mixture is a mixture of waste incineration fly ash and ordinary silicate cement mortar, wherein the waste incineration fly ash content is 30%. The slurry mixture is placed in a mold, vibrated, and cured under standard curing conditions for 24 hours before demolding. After demolding, the specimens are transferred to a high-temperature steam curing chamber at a temperature of 90°C and a humidity of 100% for 48 hours. After curing, the specimens are transferred to a standard curing room for curing at 7 days and 28 days to obtain test blocks.

[0024] The magnetic stirring in step 2 is preferably performed at a speed of 400 r / min for 20 min.

[0025] In step 3, the preferred drying temperature is 48°C and the drying time is 36 hours.

[0026] In step 4, the preferred liquid-to-solid ratio of VTES to nano-silica is 5:1-6:1 mL / g, and the ratio of VTES to water is 1:2-1:3.

[0027] In step 4, the preferred nano-silica suspension is made by adding hydrophilic amorphous free-flowing nano-silica powder with an average particle size range of 20-30 nm to anhydrous ethanol, mixing and stirring, then adding a mixed solution of VTES and water and magnetically stirring at a speed of 200-300 r / min for 10-20 min. The suspension is then ultrasonically dispersed for 30-40 min at a frequency of 40-50 kHz to obtain a VTES-modified nano-silica solution.

[0028] In step 6, the preferred microwave reaction time is 35 min, the reaction temperature is 65℃, and the microwave power is 350 W.

[0029] Preferably, in step 7, a 1.5% wt% ethanolamine solution is used, the preferred ultrasonic oscillation frequency is 45 kHz, the oscillation power is 30 W, the oscillation is 2 seconds followed by a 3-second rest, and cooling is performed after every 15-20 minutes of oscillation, and this process is repeated 4-6 times.

[0030] In step 8, the preferred carbon dioxide gas introduction rate is 2-3 L / min, the reaction pressure is 0.5-1 MPa, the reaction time is 1-3 h, the reaction temperature is 20-30℃, the humidity is 50-80%, and the stirring speed is 200-300 r / min.

[0031] The beneficial effects of this invention are:

[0032] 1. This invention modifies waste incineration fly ash (MSWIFA) without requiring steps such as filtration and drying, retaining finer particles, reducing energy consumption, and saving time.

[0033] 2. This invention can effectively stabilize heavy metals in MSWIFA, reduce the leaching of heavy metal ions, and reduce environmental pollution. After carbon dioxide is introduced, the heavy metal ions in the solution react with it to form insoluble heavy metal carbonate precipitates. The heavy metal ions are stabilized inside due to chemical precipitation and physical encapsulation.

[0034] 3. The nano-silica suspension added in this invention serves as a carbonization medium. Its high specific surface area can adsorb and solidify heavy metals, and act as a nucleation site to promote cement hydration, generating more hydrated calcium silicate gel products, thereby further improving mechanical properties.

[0035] 4. The ethanolamine solution added in this invention serves as a CO2 carrier, which increases the solubility of CO2 in the liquid phase, promotes the carbonization reaction rate on the MSWIFA surface, and its alkaline environment promotes the formation of hydroxide or carbonate precipitates of heavy metal ions in MSWIFA.

[0036] 5. This invention enables the incorporation of MSWIFA as a supplementary cementitious material into cement-based materials. The solidified body has high strength, and the heavy metal leaching concentration is far below the national solid waste leaching toxicity identification standard. Under the premise of ensuring strength, the use of MSWIFA to replace part of the cement as a building material reduces environmental pollution and lowers carbon emissions. Attached Figure Description

[0037] Figure 1 Schematic diagram of the process for modifying fly ash from waste incineration Detailed Implementation

[0038] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0039] Example 1

[0040] The waste incineration fly ash (MSWIFA) treatment process in this embodiment specifically includes the following steps:

[0041] (1) Collect MSWIFA, and screen the fly ash from the waste incineration through a 0.075mm square hole sieve. Take the fly ash from the waste incineration with a particle size of less than 0.075mm that is screened out for subsequent use.

[0042] (2) Distilled water and waste incineration fly ash were mixed at a liquid-to-solid ratio of L / S = 10:1 and magnetically stirred at a speed of 400 r / min for 20 min. The mixture of distilled water and waste incineration fly ash was separated into solid waste incineration fly ash by a vacuum filter. The filter membrane used for vacuum filtration was 0.45 μm. The mixture was then dried at 48 °C for 36 h. After drying until the mass was constant, the mixture was taken out, cooled to room temperature, and the product was passed through a 625 mesh sieve to obtain waste incineration fly ash with a particle size of 0.020 mm.

[0043] (3) Mix 1% of the mass fraction of MSWIFA hydrophilic amorphous free-flowing powder nano-silica and anhydrous ethanol, then add a mixed solution of silane coupling agent VTES and water. The liquid-solid ratio of silane coupling agent VTES to nano-silica is 5:1 mL / g, and the ratio of silane coupling agent VTES to water is 1:2. Stir magnetically at 200 r / min for 10 min to obtain a suspension. Then take the suspension and ultrasonically disperse it for 30 min at a frequency of 40 kHz to obtain a nano-silica suspension. Weigh MSWIFA and put it into a microwave reactor together with the nano-silica suspension. The reaction time is 35 min, the reaction temperature is 65℃, and the microwave power is 350 W.

[0044] (4) Prepare a 1% ethanolamine solution and perform ultrasonic vibration at a frequency of 45KHz and a power of 30W. Vibrate for 2 seconds and rest for 3 seconds, and cool after every 20 minutes of vibration. Repeat this process 6 times.

[0045] (5) Add the mixed solution obtained in (3) and the ethanolamine solution obtained in (4) into the reaction vessel, stir magnetically, and introduce CO2 gas into the reaction vessel at a rate of 2L / min, and continue the reaction for 2h.

[0046] (6) Mix the mixed slurry obtained after carbonation in (5) with ordinary silicate cement, and then stir it in a cement mixer at a speed of 300 r / min for 5 minutes to obtain a slurry mixture;

[0047] (7) The slurry mixture was placed in a mold, vibrated, and placed in a constant temperature and humidity chamber at 25°C and 100% humidity for 24 hours. After curing, the specimen was demolded and transferred to a high temperature steam curing chamber at 90°C and 100% humidity for 48 hours. After curing, the specimen was transferred to a standard curing room for curing until 28 days to obtain a test block.

[0048] (8) The compressive strength of the specimen obtained by using a pressure testing machine is 45.2 MPa;

[0049] (9) The test block prepared in (7) is crushed until it passes through a sieve with a hole of 3 mm, and then placed in a drying oven at 60°C for 24 h.

[0050] (10) Using deionized water as the leaching agent, the liquid-to-solid ratio was 10:1 (L / kg), the amplitude was 40 mm, 2 g of solid sample was mixed into 20 mL of deionized water, then the mixture was horizontally vibrated at 110 ± 10 times / min for 8 h, left to stand for 16 h, and finally filtered through a 0.45 μm membrane. The concentration of heavy metals in the leachate was detected by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0051] Table 1. Mixing ratio of Example 1

[0052]

[0053] Table 2. Heavy metal leaching concentrations in fly ash from raw waste incineration and the final product of Example 1.

[0054] heavy metal elements Cr μg / L Cuμg / L Znμg / L Cdμg / L Pbμg / L raw fly ash 232.60 174.30 6.45 26.85 20.36 Example 1 14.56 12.22 0.98 2.11 1.85

[0055] Example 2

[0056] The MSWIFA processing procedure in this embodiment specifically includes the following steps:

[0057] (1) Collect MSWIFA, and screen the fly ash from the waste incineration through a 0.075mm square hole sieve. Take the fly ash from the waste incineration with a particle size of less than 0.075mm that is screened out for subsequent use.

[0058] (2) Distilled water and waste incineration fly ash were mixed at a liquid-to-solid ratio of L / S = 10:1 and magnetically stirred at a speed of 400 r / min for 20 min. The mixture of distilled water and waste incineration fly ash was separated into solid waste incineration fly ash by a vacuum filter. The filter membrane used for vacuum filtration was 0.45 μm. The mixture was then dried at 48 °C for 36 h. After drying until the mass was constant, the mixture was taken out, cooled to room temperature, and the product was passed through a 625 mesh sieve to obtain waste incineration fly ash with a particle size of 0.020 mm.

[0059] (3) Mix 2% of the mass fraction of MSWIFA hydrophilic amorphous free-flowing powder nano-silica and anhydrous ethanol, then add a mixed solution of silane coupling agent VTES and water. The liquid-solid ratio of silane coupling agent VTES to nano-silica is 5:1 mL / g, and the ratio of silane coupling agent VTES to water is 1:2. Stir magnetically at 200 r / min for 10 min to obtain a suspension. Then take the suspension and ultrasonically disperse it for 30 min at a frequency of 40 kHz to obtain a nano-silica suspension. Weigh MSWIFA and put it into a microwave reactor together with the nano-silica suspension. The reaction time is 35 min, the reaction temperature is 65℃, and the microwave power is 350 W.

[0060] (4) Prepare a 1% ethanolamine solution and perform ultrasonic vibration at a frequency of 45KHz and a power of 30W. Vibrate for 2 seconds and rest for 3 seconds, and cool after every 20 minutes of vibration. Repeat this process 6 times.

[0061] (5) Add the mixed solution obtained in (3) and the ethanolamine solution obtained in (4) into the reaction vessel, stir magnetically, and introduce CO2 gas into the reaction vessel at a rate of 2L / min, and continue the reaction for 2h.

[0062] (6) Mix the mixed slurry obtained after carbonation in (5) with ordinary silicate cement, and then stir it in a cement mixer at a speed of 300 r / min for 5 minutes to obtain a slurry mixture;

[0063] (7) The slurry mixture was placed in a mold, vibrated, and placed in a constant temperature and humidity chamber at 25°C and 100% humidity for 24 hours. After curing, the specimen was demolded and transferred to a high temperature steam curing chamber at 90°C and 100% humidity for 48 hours. After curing, the specimen was transferred to a standard curing room for curing until 28 days to obtain a test block.

[0064] (8) The compressive strength of the specimen obtained by using a pressure testing machine is 48.2 MPa;

[0065] (9) The test block prepared in (7) is crushed until it passes through a sieve with a hole of 3 mm, and then placed in a drying oven at 60°C for 24 h.

[0066] (10) Using deionized water as the leaching agent, the liquid-to-solid ratio was 10:1 (L / kg), the amplitude was 40 mm, 2 g of solid sample was mixed into 20 mL of deionized water, then the mixture was horizontally vibrated at 110 ± 10 times / min for 8 h, left to stand for 16 h, and finally filtered through a 0.45 μm membrane. The concentration of heavy metals in the leachate was detected by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0067] Table 3. Mixing ratio of Example 2

[0068]

[0069] Table 4. Heavy metal leaching concentrations in fly ash from original waste incineration and the final product of Example 2.

[0070] heavy metal elements Cr μg / L Cuμg / L Znμg / L Cdμg / L Pbμg / L raw fly ash 232.60 174.30 6.45 26.85 20.36 Example 2 11.72 10.01 0.87 2.04 1.67

[0071] Example 3

[0072] The waste incineration fly ash treatment process in this embodiment specifically includes the following steps:

[0073] (1) Collect MSWIFA, and screen the fly ash from the waste incineration through a 0.075mm square hole sieve. Take the fly ash from the waste incineration with a particle size of less than 0.075mm that is screened out for subsequent use.

[0074] (2) Distilled water and waste incineration fly ash were mixed at a liquid-to-solid ratio of L / S = 10:1 and magnetically stirred at a speed of 400 r / min for 20 min. The mixture of distilled water and waste incineration fly ash was separated into solid waste incineration fly ash by a vacuum filter. The filter membrane used for vacuum filtration was 0.45 μm. The mixture was then dried at 48 °C for 36 h. After drying until the mass was constant, the mixture was taken out, cooled to room temperature, and the product was passed through a 625 mesh sieve to obtain waste incineration fly ash with a particle size of 0.020 mm.

[0075] (3) Mix 3% of the mass fraction of MSWIFA hydrophilic amorphous free-flowing powder nano-silica and anhydrous ethanol, then add a mixed solution of silane coupling agent VTES and water. The liquid-solid ratio of silane coupling agent VTES to nano-silica is 5:1 mL / g, and the ratio of silane coupling agent VTES to water is 1:2. Stir magnetically at 200 r / min for 10 min to obtain a suspension. Then take the suspension and ultrasonically disperse it for 30 min at a frequency of 40 kHz to obtain a nano-silica suspension. Weigh MSWIFA and put it into a microwave reactor together with the nano-silica suspension. The reaction time is 35 min, the reaction temperature is 65℃, and the microwave power is 350 W.

[0076] (4) Prepare a 1% ethanolamine solution and perform ultrasonic vibration at a frequency of 45KHz and a power of 30W. Vibrate for 2 seconds and rest for 3 seconds, and cool after every 20 minutes of vibration. Repeat this process 6 times.

[0077] (5) Add the mixed solution obtained in (3) and the ethanolamine solution obtained in (4) into the reaction vessel, stir magnetically, and introduce CO2 gas into the reaction vessel at a rate of 2L / min, and continue the reaction for 2h.

[0078] (6) Mix the mixed slurry obtained after carbonation in (5) with ordinary silicate cement, and then stir it in a cement mixer at a speed of 300 r / min for 5 minutes to obtain a slurry mixture;

[0079] (7) The slurry mixture was placed in a mold, vibrated, and placed in a constant temperature and humidity chamber at 25°C and 100% humidity for 24 hours. After curing, the specimen was demolded and transferred to a high temperature steam curing chamber at 90°C and 100% humidity for 48 hours. After curing, the specimen was transferred to a standard curing room for curing until 28 days to obtain a test block.

[0080] (8) The compressive strength of the specimen obtained by using a pressure testing machine is 43.4 MPa;

[0081] (9) The test block prepared in (7) is crushed until it passes through a sieve with a hole of 3 mm, and then placed in a drying oven at 60°C for 24 h.

[0082] (10) Using deionized water as the leaching agent, the liquid-to-solid ratio was 10:1 (L / kg), the amplitude was 40 mm, 2 g of solid sample was mixed into 20 mL of deionized water, then the mixture was horizontally vibrated at 110 ± 10 times / min for 8 h, left to stand for 16 h, and finally filtered through a 0.45 μm membrane. The concentration of heavy metals in the leachate was detected by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0083] Table 5. Mixing ratio of Example 3

[0084]

[0085] Table 6. Heavy metal leaching concentrations of fly ash from original waste incineration and the final product of Example 3.

[0086] heavy metal elements Cr μg / L Cuμg / L Znμg / L Cdμg / L Pbμg / L raw fly ash 232.60 174.30 6.45 26.85 20.36 Example 3 16.72 13.34 1.41 2.52 2.36

[0087] Example 4

[0088] The waste incineration fly ash treatment process in this embodiment specifically includes the following steps:

[0089] (1) Collect MSWIFA, and screen the fly ash from the waste incineration through a 0.075mm square hole sieve. Take the fly ash from the waste incineration with a particle size of less than 0.075mm that is screened out for subsequent use.

[0090] (2) Distilled water and waste incineration fly ash were mixed at a liquid-to-solid ratio of L / S = 10:1 and magnetically stirred at a speed of 400 r / min for 20 min. The mixture of distilled water and waste incineration fly ash was separated into solid waste incineration fly ash by a vacuum filter. The filter membrane used for vacuum filtration was 0.45 μm. The mixture was then dried at 48 °C for 36 h. After drying until the mass was constant, the mixture was taken out, cooled to room temperature, and the product was passed through a 625 mesh sieve to obtain waste incineration fly ash with a particle size of 0.020 mm.

[0091] (3) Mix 2% of the mass fraction of MSWIFA hydrophilic amorphous free-flowing powder nano-silica with water and stir. Then, ultrasonically disperse the nano-silica for 30 min at a frequency of 40 kHz to obtain a nano-silica suspension. Weigh MSWIFA and put it into a microwave reactor together with the nano-silica solution. The reaction time is 35 min, the reaction temperature is 65 ℃, and the microwave power is 350 W.

[0092] (4) Prepare a 1% ethanolamine solution and perform ultrasonic vibration at a frequency of 45KHz and a power of 30W. Vibrate for 2 seconds and rest for 3 seconds, and cool after every 20 minutes of vibration. Repeat this process 6 times.

[0093] (5) Add the mixed solution obtained in (3) and the ethanolamine solution obtained in (4) into the reaction vessel, stir magnetically, and introduce CO2 gas into the reaction vessel at a rate of 2L / min, and continue the reaction for 2h.

[0094] (6) Mix the mixed slurry obtained after carbonation in (5) with ordinary silicate cement, and then stir it in a cement mixer at a speed of 300 r / min for 5 minutes to obtain a slurry mixture;

[0095] (7) The slurry mixture was placed in a mold, vibrated, and placed in a constant temperature and humidity chamber at 25°C and 100% humidity for 24 hours. After curing, the specimen was demolded and transferred to a high temperature steam curing chamber at 90°C and 100% humidity for 48 hours. After curing, the specimen was transferred to a standard curing room for curing until 28 days to obtain a test block.

[0096] (8) The compressive strength of the specimen obtained by using a pressure testing machine is 45.3 MPa;

[0097] (9) The test block prepared in (7) is crushed until it passes through a sieve with a hole of 3 mm, and then placed in a drying oven at 60°C for 24 h.

[0098] (10) Using deionized water as the leaching agent, the liquid-to-solid ratio was 10:1 (L / kg), the amplitude was 40 mm, 2 g of solid sample was mixed into 20 mL of deionized water, then the mixture was horizontally vibrated at 110 ± 10 times / min for 8 h, left to stand for 16 h, and finally filtered through a 0.45 μm membrane. The concentration of heavy metals in the leachate was detected by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0099] Table 7. Mixing ratio of Example 4

[0100]

[0101] Table 8. Heavy metal leaching concentrations in fly ash from primary waste incineration and the final product of Example 4.

[0102] heavy metal elements Cr μg / L Cuμg / L Znμg / L Cdμg / L Pbμg / L raw fly ash 232.60 174.30 6.45 26.85 20.36 Example 4 15.73 12.91 1.39 2.31 2.27

[0103] Comparative Example 1

[0104] (1) Collect MSWIFA, and screen the fly ash from the waste incineration through a 0.075mm square hole sieve. Take the fly ash from the waste incineration with a particle size of less than 0.075mm that is screened out for subsequent use.

[0105] (2) Distilled water and waste incineration fly ash were mixed at a liquid-to-solid ratio of L / S = 10:1 and magnetically stirred at a speed of 400 r / min for 20 min. The mixture of distilled water and waste incineration fly ash was separated into solid waste incineration fly ash by a vacuum filter. The filter membrane used for vacuum filtration was 0.45 μm. The mixture was then dried at 48 °C for 36 h. After drying until the mass was constant, the mixture was taken out, cooled to room temperature, and the product was passed through a 625 mesh sieve to obtain waste incineration fly ash with a particle size of 0.020 mm.

[0106] (3) Mix 2% of the mass fraction of MSWIFA hydrophilic amorphous free-flowing powder nano-silica and anhydrous ethanol, then add a mixed solution of silane coupling agent VTES and water. The liquid-solid ratio of silane coupling agent VTES to nano-silica is 5:1 mL / g, and the ratio of silane coupling agent VTES to water is 1:2. Stir magnetically at 200 r / min for 10 min to obtain a suspension. Then take the suspension and ultrasonically disperse it for 30 min at a frequency of 40 kHz to obtain a nano-silica suspension. Weigh MSWIFA and put it into a microwave reactor together with the nano-silica suspension. The reaction time is 35 min, the reaction temperature is 65℃, and the microwave power is 350 W.

[0107] (4) Add the mixed solution obtained in (3) into the reaction vessel, stir magnetically, and introduce CO2 gas into the reaction vessel at a rate of 2L / min, and continue the reaction for 2h.

[0108] (5) Mix the mixed solution obtained after carbonization in (4) with ordinary silicate cement, and then stir it in a cement mixer at a speed of 300 rpm for 5 minutes to obtain a slurry mixture;

[0109] (6) The slurry mixture was placed in a mold, vibrated, and placed in a constant temperature and humidity chamber at 25°C and 100% humidity for 24 hours. After curing, the specimen was demolded and transferred to a high temperature steam curing chamber at 90°C and 100% humidity for 48 hours. After curing, the specimen was transferred to a standard curing room for curing until 28 days to obtain a test block.

[0110] (7) The compressive strength of the specimen obtained by using a pressure testing machine was 44.8 MPa;

[0111] (8) The test block prepared in (5) was crushed until it passed through a sieve with a hole size of 3 mm, and then placed in a drying oven and dried at 60°C for 24 h.

[0112] (9) Using deionized water as the leaching agent, the liquid-to-solid ratio was 10:1 (L / kg), the amplitude was 40 mm, 2 g of solid sample was mixed into 20 mL of deionized water, then the mixture was horizontally vibrated at 110 ± 10 times / min for 8 h, left to stand for 16 h, and finally filtered through a 0.45 μm membrane. The concentration of heavy metals in the leachate was detected by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0113] Table 9. Mixing ratio of Comparative Example 1

[0114]

[0115] Table 10 Heavy metal leaching concentrations in fly ash from raw waste incineration and final products of Comparative Example 1

[0116] heavy metal elements Cr μg / L Cuμg / L Znμg / L Cdμg / L Pbμg / L raw fly ash 232.60 174.30 6.45 26.85 20.36 Comparative Example 1 15.31 13.12 1.18 2.22 2.31

[0117] Comparative Example 2

[0118] (1) Collect MSWIFA, and screen the fly ash from the waste incineration through a 0.075mm square hole sieve. Take the fly ash from the waste incineration with a particle size of less than 0.075mm that is screened out for subsequent use.

[0119] (2) Distilled water and waste incineration fly ash were mixed at a liquid-to-solid ratio of L / S = 10:1 and magnetically stirred at a speed of 400 r / min for 20 min. The mixture of distilled water and waste incineration fly ash was separated into solid waste incineration fly ash by a vacuum filter. The filter membrane used for vacuum filtration was 0.45 μm. The mixture was then dried at 48 °C for 36 h. After drying until the mass was constant, the mixture was taken out, cooled to room temperature, and the product was passed through a 625 mesh sieve to obtain waste incineration fly ash with a particle size of 0.020 mm.

[0120] (3) Weigh out ordinary silicate cement, waste incineration fly ash and distilled water, mix them, and then mix them in a cement mixer at a speed of 300 r / min for 5 minutes to obtain a slurry mixture;

[0121] (4) The slurry mixture is placed in a mold, vibrated, and placed in a constant temperature and humidity chamber at 25°C and 100% humidity for 24 hours. After curing, the specimen is demolded and transferred to a high temperature steam curing chamber at 90°C and 100% humidity for 48 hours. After curing, the specimen is transferred to a standard curing room for curing until 28 days to obtain a test block.

[0122] (5) The compressive strength of the specimen obtained by using a pressure testing machine is 37.8 MPa;

[0123] (6) The test block prepared in (4) is crushed until it passes through a sieve with a 3 mm hole, and then placed in a drying oven at 60°C for 24 h.

[0124] (7) Using deionized water as the leaching agent, the liquid-to-solid ratio was 10:1 (L / kg), the amplitude was 40 mm, 2 g of solid sample was mixed into 20 mL of deionized water, then the mixture was horizontally vibrated at 110 ± 10 times / min for 8 h, left to stand for 16 h, and finally filtered through a 0.45 μm membrane. The concentration of heavy metals in the leachate was detected by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0125] Table 11. Mixing ratio of Comparative Example 2

[0126] Table 12 Heavy metal leaching concentrations in fly ash from raw waste incineration and final products of Comparative Example 2

[0127] heavy metal elements Cr μg / L Cuμg / L Znμg / L Cdμg / L Pbμg / L raw fly ash 232.60 174.30 6.45 26.85 20.36 Comparative Example 2 99.24 88.14 4.29 13.04 11.32

[0128] Comparative Example 3

[0129] (1) Weigh ordinary Portland cement and distilled water and mix them. Then, mix them in a cement mixer at a speed of 400 r / min for 5 minutes to obtain a slurry mixture.

[0130] (2) The slurry mixture was placed in a mold, vibrated, and placed in a constant temperature and humidity chamber at 25°C and 100% humidity for 24 hours. After curing, the specimen was demolded and transferred to a high temperature steam curing chamber at 90°C and 100% humidity for 48 hours. After curing, the specimen was transferred to a standard curing room for curing until 28 days to obtain a test block.

[0131] (3) The compressive strength of the specimen obtained by using a pressure testing machine is 42.6 MPa.

[0132] Table 13. Mixing ratio of Comparative Example 3

[0133]

[0134] Comparative Example 4

[0135] (1) Collect MSWIFA, and screen the fly ash from the waste incineration through a 0.075mm square hole sieve. Take the fly ash from the waste incineration with a particle size of less than 0.075mm that is screened out for subsequent use.

[0136] (2) Distilled water and waste incineration fly ash were mixed at a liquid-to-solid ratio of L / S = 10:1 and magnetically stirred at a speed of 400 r / min for 20 min. The mixture of distilled water and waste incineration fly ash was separated into solid waste incineration fly ash by a vacuum filter. The filter membrane used for vacuum filtration was 0.45 μm. The mixture was then dried at 48 °C for 36 h. After drying until the mass was constant, the mixture was taken out, cooled to room temperature, and the product was passed through a 625 mesh sieve to obtain waste incineration fly ash with a particle size of 0.020 mm.

[0137] (3) Prepare a 1% ethanolamine solution and perform ultrasonic vibration at a frequency of 45KHz and a power of 30W. Vibrate for 2 seconds and rest for 3 seconds, and cool after every 20 minutes of vibration. Repeat this process 6 times.

[0138] (4) Weigh the ethanolamine solution obtained in (3), the fly ash from the waste incineration plant and the distilled water, mix them together in proportion and add them to the reaction vessel. Stir magnetically and introduce CO2 gas into the reaction vessel at a rate of 2L / min. Continue the reaction for 2 hours.

[0139] (5) The mixed slurry obtained in (4), the fly ash from waste incineration and ordinary silicate cement are mixed according to the following conditions, and then the mixture is stirred in a cement mixer at a speed of 300 r / min for 5 minutes to obtain a slurry mixture;

[0140] (6) The slurry mixture was placed in a mold, vibrated, and placed in a constant temperature and humidity chamber at 25°C and 100% humidity for 24 hours. After curing, the specimen was demolded and transferred to a high temperature steam curing chamber at 90°C and 100% humidity for 48 hours. After curing, the specimen was transferred to a standard curing room for curing until 28 days to obtain a test block.

[0141] (7) The compressive strength of the specimen obtained by using a pressure testing machine is 43.5 MPa;

[0142] (8) The solidified body prepared in (5) is crushed until it passes through a sieve with a pore size of 3 mm, and then placed in a drying oven and dried at 60°C for 24 h.

[0143] (9) Using deionized water as the leaching agent, the liquid-to-solid ratio was 10:1 (L / kg), the amplitude was 40 mm, 2 g of solid sample was mixed into 20 mL of deionized water, then the mixture was horizontally vibrated at 110 ± 10 times / min for 8 h, left to stand for 16 h, and finally filtered through a 0.45 μm membrane. The concentration of heavy metals in the leachate was detected by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0144] Table 14. Mixing ratio of Comparative Example 4

[0145]

[0146] Table 15 Heavy metal leaching concentrations in fly ash from raw waste incineration and final products of Comparative Example 4.

[0147] heavy metal elements Cr μg / L Cuμg / L Znμg / L Cdμg / L Pbμg / L raw fly ash 232.60 174.30 6.45 26.85 20.36 Comparative Example 4 16.11 13.41 1.28 2.21 2.04

[0148] The analysis and test results of the various examples and comparative examples show that the solidified specimens prepared by carbonizing MSWIFA with VTES, nano-silica, ethanolamine, and carbon dioxide gas exhibit good compressive strength and relatively stable heavy metal content. Compared with Examples 1-3, the results show that the compressive strength of cement first increases and then decreases with the increase of nano-silica content, indicating that there is an optimal range for nano-silica. Compared with Comparative Example 2, Examples 1-3 show that carbonization significantly improves the mechanical properties of MSWIFA-containing cement paste, indicating that the carbonization process enhances the pozzolanic activity of MSWIFA. The carbonized MSWIFA plays a positive role in the cement hydration reaction. The calcium carbonate particles produced after the carbonization reaction of carbon dioxide with hydrated calcium silicate and calcium hydroxide can fill pores and microcracks, thereby improving its mechanical properties. At the same time, heavy metal ions in the solution react with carbon dioxide to form insoluble carbonates. The heavy metal ions are stabilized internally due to chemical precipitation and physical encapsulation, making the heavy metals in fly ash relatively stable. Compared with Comparative Example 4, Example 2 shows that the MSWIFA cement-based material incorporating nano-silica has a stronger ability to consolidate heavy metals and its strength is improved. This is because the higher specific surface area of ​​nano-silica can adsorb and consolidate heavy metals, and as a nucleation site, it promotes cement hydration, generating more hydrated calcium silicate gel products. It can also fill the micropores and cracks in the hardened paste, making the matrix more compact. Compared with Example 4, Example 2 shows that after modifying nano-silica with VTES, nano-silica can better fill pores, generate more hydrated calcium silicate gel products, and the matrix is ​​more compact and stronger, thus more effectively encapsulating heavy metal ions. Compared with Comparative Example 1, Example 2 shows that ethanolamine solution accelerates the carbonation reaction rate on the surface of fly ash particles. Its alkaline environment not only promotes the hydration of calcium oxide to form calcium hydroxide, which then reacts with carbon dioxide to form calcium carbonate, but also promotes the formation of hydroxide or carbonate precipitates of heavy metal ions in fly ash.

Claims

1. A method for preparing low-carbon waste incineration fly ash (MSWIFA) cement-based materials by modified nano-solution carbonization, characterized in that, Includes the following steps: S1. The fly ash from waste incineration is screened through a 0.075mm square hole sieve, and the fly ash with a particle size of less than 0.075mm is collected for subsequent use. S2. Mix distilled water and fly ash from waste incineration at a liquid-to-solid ratio of L / S = 5-20:1, and magnetically stir at a speed of 300-500 r / min for 15-30 min. S3. The distilled water in the mixed solution of distilled water and waste incineration fly ash is separated by a vacuum filter to obtain solid fly ash from waste incineration. The filter membrane used for vacuum filtration is a 0.45μm filter membrane. Then, it is dried at 40-60℃ for 24-48h. After drying until the mass is constant, it is taken out, cooled to room temperature, and sieved to obtain homogeneous powder with a particle size range of 10-50μm. S4. Mix and stir nano-silica and anhydrous ethanol to disperse the nano-silica in the anhydrous ethanol. Mix and stir the silane coupling agent vinyltriethoxysilane (VTES) and water to hydrolyze the VTES and obtain a VTES solution. Pour the VTES solution into the anhydrous ethanol solution of nano-silica and stir to mix it to obtain a VTES-modified nano-silica solution. By using VTES to modify nano-silica, the nano-silica is uniformly dispersed in the material. S5. Mix MSWIFA with VTES-modified nano-silica solution to obtain a mixed slurry; S6. Place the mixed slurry in a water bath device, put it into a microwave reactor, react for 30-40 minutes, react at 60-70°C, microwave power 300-400W, and start the microwave reactor water bath heating. S7. Prepare a 1-2 wt% ethanolamine solution and perform ultrasonic vibration at a frequency of 40-50 kHz and a power of 25-35 W. Vibrate for 2 seconds and rest for 3 seconds, and cool after every 15-20 minutes of vibration. Repeat this process 4-6 times. S8. Place the mixed slurry and the prepared ethanolamine solution in a reaction vessel, heat and stir in a water bath, and introduce carbon dioxide gas into the reaction vessel. Adjust the pressure and reaction time of the reaction vessel to carry out the carbonization reaction. S9. The carbonized slurry is mixed with ordinary silicate cement and stirred to obtain a slurry mixture. The slurry mixture is a mixture of waste incineration fly ash and ordinary silicate cement mortar, wherein the waste incineration fly ash content is 30%. The slurry mixture is placed in a mold, vibrated, and cured under standard curing conditions for 24 hours before demolding. After demolding, the specimen is transferred to a high-temperature steam curing chamber at a temperature of 90°C and a humidity of 100% for 48 hours. After curing, the specimen is transferred to a standard curing room for curing until 28 days to obtain a test block.

2. The method according to claim 1, characterized in that, The MSWIFA has a chemical composition of 30-40% CaO, 3%-8% SiO2, and 1%-4% MgO; the MSWIFA particles have a particle size of D50 = 20-30 μm and a particle size range of 10-50 μm.

3. The method according to claim 1, characterized in that, The liquid-solid ratio of VTES to nano-silica is 5:1-6:1 mL / g, and the ratio of VTES to water is 1:2-1:

3.

4. The method according to claim 3, characterized in that, Hydrophilic amorphous free-flowing nano-silica powder with an average particle size range of 20-30 nm was added to anhydrous ethanol and mixed. Then, a mixed solution of VTES and water was added, stirred, and the suspension was ultrasonically dispersed to obtain a VTES-modified nano-silica solution.

5. The method according to claim 1, characterized in that, The ethanolamine was prepared as a 1-2 wt% ethanolamine solution to participate in the modification of MSWIFA.

6. The method according to claim 1, characterized in that, The carbon dioxide gas is introduced at a rate of 2-3 L / min, the reaction pressure is 0.5-1 MPa, the reaction time is 1-3 h, the reaction temperature is 20-30°C, and the humidity is 50-80%; the carbon dioxide gas is a high-purity gas with a mass fraction of 99-99.9%.

7. The method according to claim 1, characterized in that, Carbonated MSWIFA is mixed with ordinary Portland cement to improve the compressive strength of the cement base.

8. The application of the method according to any one of claims 1-7 in improving the compressive strength of cement-based materials and / or in the recycling of MSWIFA.

Images