Method for preparing silicon-based and aluminum-based materials from fly ash and coupling carbon emission reduction

Abstract

The invention discloses a method for preparing a silicon-based and aluminum-based material from fly ash and coupling carbon emission reduction, which realizes selective extraction of active silicon in fly ash through synergistic effect improvement of physical activation and microwave enhanced alkali dissolution; a CO2 acid leaching technology is introduced to remove sodium, calcium, magnesium and other impurities in the desilicication residues, so that the treated fly ash reaches the quality standard of low-grade bauxite; and preparing high value-added white carbon black from the desilicication liquid by adopting a carbon separation method, and recovering the carbonized mother liquid into sodium carbonate through low-temperature flash evaporation crystallization, so as to construct a byproduct resource closed-loop circulation system. According to the method, CO2 resources in the desulfurized flue gas of the power plant are fully coupled and utilized, a water-gas-solid multi-source synergistic green recycling system is constructed, the whole process has the characteristics of carbon capture, carbon fixation and resource utilization while realizing high-valued application of the fly ash, and the energy consumption is reduced while realizing high-valued utilization of the fly ash. Carbon emission and environmental load are effectively reduced, and the method has good industrial application prospect and industrial popularization value.

Description

Technical Field

[0001] This invention relates to the field of fly ash utilization technology, and to a method for preparing silicon-based and aluminum-based materials from fly ash and coupling them with carbon emission reduction, and more particularly to a method for desiliconizing fly ash to prepare bauxite and silica. Background Technology

[0002] With the continuous development of the coal-fired power industry, fly ash production has been increasing year by year, reaching approximately 899 million tons in my country in 2023. As a typical bulk industrial solid waste, its long-term and large-scale stockpiling not only occupies land resources but also may cause environmental pollution. Existing fly ash utilization technologies are mostly concentrated in the low-value-added building materials sector, resulting in problems such as low resource utilization, poor extraction efficiency, and low product added value. Meanwhile, affected by the downturn in the real estate industry, the demand in the traditional building materials market has shrunk, leading to difficulties in selling fly ash from grassroots power plants. Therefore, solving the problems of low fly ash utilization, low product yield, and difficulty in sales has become a pressing technical bottleneck and practical challenge.

[0003] China is the world's largest producer and consumer of aluminum, but its bauxite resources are scarce and of generally poor quality. The country imports large quantities of bauxite annually, leading to a growing problem of aluminum resource depletion. Fly ash is rich in silicon and aluminum, especially high-alumina fly ash, which has an alumina content exceeding 40%. Therefore, high-alumina fly ash can be considered a non-traditional reserve alumina resource for my country.

[0004] Currently, researchers have conducted studies on the high-value utilization technology of high-alumina fly ash. For example, patent CN117568652A proposes a method for preparing aluminum-based alloys using fly ash. The core of this method involves acid leaching to remove impurities, component adjustment, and high-temperature reduction, followed by aluminum electrolysis and refining processes to obtain aluminum alloy products that meet quality requirements, aiming to achieve high-value utilization of low-grade aluminum resources. This method broadens the application fields of fly ash and has resource utilization, emission reduction, and potential economic benefits. However, this process is lengthy, energy-intensive, and requires stringent equipment. It also involves high-temperature smelting and atmospheric control of hydrogen and methane, posing certain safety risks and difficulties for industrial implementation. The feasibility of its large-scale application still needs further verification. Patent CN 103342375A proposes a method for recovering alumina, silica, and other metallic components from fly ash. This method involves first desiliconizing the fly ash, then roasting it with ammonium sulfate to obtain clinker. Metal components are then dissolved using a leaching agent, followed by crystallization of aluminum ammonium alum, which is then calcined to produce alumina. The mother liquor from the leaching process can be recycled. This method achieves multi-metal cascade recovery with high product purity. However, the process requires a large amount of ammonium sulfate (6 to 15 times the mass of the fly ash), resulting in high costs. Furthermore, impurities such as iron and calcium in the leaching slurry require multiple separations and purifications, making the overall process complex.

[0005] Therefore, extracting high-value components and developing large-scale utilization technologies are of great significance in addressing the existing problems in the resource utilization of fly ash and changing the current predicament of fly ash utilization. Summary of the Invention

[0006] In view of the above-mentioned shortcomings, the technical problem to be solved by this invention is to overcome the problems of low utilization rate, difficult sales channels, and low yield of resource-based products in the existing high-alumina fly ash resource utilization. From the perspective of power plants, this invention makes full use of existing systems in power plants to construct a synergistic process path for fly ash: "high-efficiency desilication—precipitated silica preparation—aluminum resource enrichment and utilization—by-product resource utilization." Combining core technologies such as alkali-soluble desilication, acid leaching for impurity removal, precipitated silica synthesis, and by-product resource utilization, a green, efficient, and low-cost multi-component synergistic conversion process system is constructed. Ultimately, this achieves the tiered high-value utilization of elements such as silicon and aluminum in fly ash, enabling large-scale and widespread utilization. In addition, CO2 from power plant desulfurization flue gas is introduced into the process as a carbon source for precipitated silica preparation, which not only achieves carbon capture and fixation but also synergistically reduces alkali consumption and energy consumption, effectively reducing carbon emissions. The overall technical solution has the dual benefits of resource utilization and emission reduction, providing a feasible engineering path for the large-scale, high-value, and low-carbon utilization of fly ash, and promoting its development towards high quality and sustainability.

[0007] To achieve the above-mentioned objectives of the present invention, the present invention employs the following technical means:

[0008] This invention first discloses a method for preparing silicon-based and aluminum-based materials from fly ash and coupling them with carbon emission reduction, comprising:

[0009] (1) High-alumina fly ash is pretreated by ball milling to obtain pretreated fly ash;

[0010] (2) The pretreated fly ash was mixed with NaOH solution and placed in a microwave reactor for desiliconization reaction. After the reaction was completed, the mixture was filtered to obtain desiliconized fly ash and first filtrate. The main component of the first filtrate was Na2SiO3.

[0011] (3) Introduce CO2 from the desulfurization flue gas of the power plant into the first filtrate to carry out a carbonization reaction, and filter after the reaction; obtain white carbon black precipitate and second filtrate;

[0012] (4) Wash and dry the precipitated silica to obtain the silica product; the second filtrate is concentrated by low-temperature flash evaporation and crystallized to obtain Na2CO3; Na2CO3 can be used as a water treatment agent, and the water vapor generated during the flash evaporation concentration process can be condensed to obtain flash condensate.

[0013] (5) Mix desiliconized fly ash with flash condensate to make slurry, and introduce CO2 gas to acidify the system to further remove impurities such as sodium, calcium and magnesium. After the reaction is completed, use vacuum filtration to separate solid and liquid to obtain fly ash with high Al2O3 content and third filtrate.

[0014] (6) The third filtrate is combined with the second filtrate and fed into the low-temperature flash evaporation system; the flash condensate generated in step (4) is mixed with NaOH to prepare a NaOH solution for recycling. This step allows the wastewater to be recycled within the system, ultimately achieving zero discharge and recycling of wastewater, significantly improving resource utilization efficiency, reducing production costs, and minimizing environmental impact.

[0015] Furthermore, the pretreated fly ash particle size in step (1) is <5μm.

[0016] Further, the NaOH solution in step (2) has a mass concentration of 15% to 30%; the liquid-solid ratio of the NaOH solution to the fly ash is 1.5:1 to 3:1 (mL / g).

[0017] Further, the conditions for the desiliconization reaction in step (2) are: microwave frequency 2450MHz, output power 700W; reaction temperature 100℃~130℃, reaction time 1~3h.

[0018] Further, the CO2 ventilation rate in step (3) is 20-30 mL / min; the carbonization reaction temperature is 80℃-90℃; and the reaction endpoint is pH=9.

[0019] Further, the drying conditions in step (4) are: drying at a constant temperature of 105℃~120℃ for 4~6 hours.

[0020] Furthermore, the low-temperature flash concentration conditions in step (4) are: temperature 80℃~100℃, and total steam pressure stable above 0.5MPa.

[0021] Further, in step (5), the liquid-to-solid ratio of the desiliconized fly ash to the flash condensate is 5:1 to 10:1 (mL / g); the CO2 gas flow rate is 30 to 50 mL / min; the reaction temperature is 40℃ to 70℃; and the reaction time is 2 to 4 h.

[0022] Furthermore, the standard for fly ash with high Al2O3 content mentioned in step (5) is: Al2O3 content > 40% and Al / Si ratio > 1.8. According to the "Mineral Geological Exploration Specification for Bauxite" (DZ / T 0202-2020), the cut-off grade of bauxite usually requires an Al / Si ratio between 1.8 and 2.6, while the content of alumina (Al2O3) should not be less than 40%. Therefore, this fly ash product meets the application standards for medium and low grade bauxite, and power plants can directly sell it as bauxite resource. While realizing the high-value utilization of resources, it innovatively solves the problem of limited sales channels for high-alumina fly ash and expands its application path in the aluminum industry.

[0023] The beneficial effects of this invention are reflected in:

[0024] (1) Expanding the resource utilization pathways for silicon-based and aluminum-based products from fly ash, creating a new model for transforming by-product solid waste into strategic resources. This invention, for the first time, treats the high-alumina residue obtained from fly ash after directional desilication treatment as a metallurgically usable resource with characteristics of medium- and low-grade bauxite. This breaks through the low-end utilization mode of fly ash as a traditional cement admixture or building filler, realizing a leap from fly ash to a metallurgical-grade functional raw material. This innovative approach solves the sales problem of fly ash from power plants, provides the market with new product options, and creates economic value.

[0025] (2) Constructing an integrated process of "alkali leaching desilication—acid leaching impurity removal—high-value conversion" to achieve systematic integration and low-cost, high-efficiency utilization of fly ash resources. This invention innovatively constructs an integrated technical system with "microwave-enhanced alkali leaching desilication + precipitated silica preparation" as its core, systematically connecting the entire process of efficient separation of Si and Al in fly ash, deep removal of impurities, and high-value conversion of products, promoting the transformation from "coarse waste treatment" to "precise extraction of resource elements." Microwave-enhanced leaching technology is introduced, combined with the traditional alkali leaching process to efficiently extract Si and convert it into high-value-added precipitated silica. At the same time, acidic water generated from CO2 in power plant flue gas is introduced to purify the desilication residue, removing impurities such as Ca and Fe and increasing the Al2O3 content. The final residue can be used as a substitute raw material for bauxite, expanding its application path in the aluminum industry. This process realizes the synergistic conversion from by-product solid waste to functional materials and metallurgical raw materials, with advantages such as compact process, controllable cost, and strong industrial adaptability, providing a systematic solution for the high-value utilization of fly ash.

[0026] (3) In the process of fly ash resource utilization, this invention innovatively couples the power plant flue gas system, making full use of the CO2 resources rich in the flue gas after power plant desulfurization. The CO2 in the flue gas is used as a carbon source for the preparation of silica and the purification of residues. This not only effectively captures and fixes CO2 in the flue gas, significantly reducing carbon emissions and achieving carbon reduction targets, but also reduces the use of chemical reagents and greatly lowers treatment costs, achieving the dual benefits of carbon reduction and resource utilization. The process achieves zero wastewater discharge, making the overall process green and environmentally friendly, with good prospects for industrial application and promotional value. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer as a result. However, these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but all such modifications and substitutions fall within the protection scope of the present invention.

[0029] The high-alumina fly ash was obtained from a power plant, and its composition is shown in Table 1. It can be seen that the total content of Al2O3 and SiO2 in the fly ash reaches over 90%, making it an ideal raw material for preparing silicon-aluminum based materials.

[0030] Table 1 Main Components of High-Alumina Fly Ash Raw Material

[0031]

[0032] Example 1:

[0033] The process flow for preparing silicon-based and aluminum-based materials from fly ash is as follows: Figure 1 .

[0034] (1) Weigh 100g of high-alumina fly ash and place it in a ball mill. Grind it continuously for 8 hours at a speed of 400rpm to make the fly ash particle size less than 5μm after ball milling.

[0035] (2) 100g of ball-milled fly ash was mixed with 150ml of 25% NaOH solution (liquid-solid ratio 1.5:1), stirred thoroughly, and then placed in a microwave reactor. The microwave frequency was 2450MHz and the output power was 700W. The heating program was set to raise the temperature to 120℃ and the reaction was maintained at that temperature for 2 hours. After the reaction was completed, the mixture was removed, filtered, and the resulting filter cake was washed twice with 300mL of hot water (70℃~80℃) to remove residual alkali and soluble silicon components. After filtration, the filter cake was placed in a constant temperature drying oven and dried at 105℃ for 12 hours until constant weight. The concentration of silicon in the first filtrate was measured by the silicomolybdenum blue spectrophotometric method in the standard "General Method for Determination of Silicates in Chemical Reagents" (GB / T9742-2008). The desiliconization rate was calculated to be approximately 44.98%. The main components of the fly ash after alkali-dissolved desiliconization are shown in Table 2.

[0036] Table 2 Main Components of Fly Ash After Alkali Dissolution

[0037]

[0038]

[0039] (3) Transfer the first filtrate from step (2) to a water bath and heat the water bath to 90°C. Simultaneously, stir at a speed of 300 r / min and introduce CO2 gas at a flow rate of 25 mL / min under constant temperature stirring conditions. Monitor the pH value of the solution in real time. Stop the reaction when the pH value of the solution is 9. After the reaction, vacuum filter the mixture to separate the solid and liquid. Place the obtained silica precipitate in a constant temperature drying oven and dry it at 120°C for 6 hours to finally obtain the silica product and the second filtrate.

[0040] (4) The second filtrate obtained from the filtration in step (3) enters a low-temperature flash evaporation system for concentration. The temperature of the low-temperature flash evaporator is controlled at 90℃, and the total steam pressure is stabilized above 0.5MPa. The concentrated liquid obtained after flash evaporation is about 10% to 30% of the original liquid. After evaporation and crystallization, the concentrated liquid yields Na2CO3. The water vapor generated during the flash concentration process can be condensed to obtain flash condensate.

[0041] (5) The desiliconized fly ash obtained after desiliconization in step (2) and the flash condensate generated in step (4) are mixed at a liquid-to-solid ratio of 8:1 to form a slurry. The slurry is placed in a water bath and heated to 40°C while being stirred at a speed of 300 r / min. CO2 gas is introduced at a flow rate of 40 mL / min under constant temperature stirring conditions for 2 hours. This process acidifies the slurry with CO2, thereby further removing residual alkali and impurities such as Ca, Fe, and Mg from the fly ash. After the reaction, the mixture is vacuum filtered to separate the solid and liquid. The filter cake is placed in a constant temperature drying oven and dried at 120°C for 12 hours until constant weight. Finally, fly ash with a high Al2O3 content and the third filtrate are obtained. The main components of the fly ash at this time are shown in Table 3.

[0042] Table 3 Main Components of Fly Ash After Acid Leaching

[0043]

[0044] (6) The third filtrate obtained in step (5) and the second filtrate obtained in step (3) are combined and fed into the low-temperature flash evaporation system.

[0045] (7) The flash condensate produced in step (4) can also be mixed with NaOH to prepare NaOH solution for recycling.

[0046] The fly ash processed in this embodiment (see Table 3) has an Al2O3 content of 55.706% and an aluminum-silicon ratio (A / S) of 1.91. According to the "Mineral Geological Exploration Specification for Bauxite" (DZ-T 0202-2020), the cut-off grade for bauxite typically requires an Al / Si ratio between 1.8 and 2.6, while the alumina (Al2O3) content should not be less than 40%. Therefore, this fly ash product meets the application standards for medium- and low-grade bauxite, and power plants can directly sell it as bauxite resources. This innovatively solves the problem of limited sales channels for high-alumina fly ash while achieving high-value utilization of resources, thus expanding its application path in the aluminum industry.

[0047] Example 2:

[0048] (1) Weigh 100g of high-alumina fly ash and place it in a ball mill. Grind it continuously for 8 hours at a speed of 400rpm to make the fly ash particle size less than 5μm after ball milling.

[0049] (2) 100g of ball-milled fly ash was mixed with 200ml of 20% NaOH solution (liquid-solid ratio 2:1), stirred thoroughly, and then placed in a microwave reactor. The microwave frequency was 2450MHz and the output power was 700W. The heating program was set to raise the temperature to 110℃ and the reaction was maintained at this temperature for 2 hours. After the reaction was completed, the mixture was removed, filtered, and the resulting filter cake was washed twice with 300mL of hot water (70℃~80℃) to remove residual alkali and soluble silicon components. After filtration, the filter cake was placed in a constant temperature drying oven and dried at 105℃ for 12 hours until constant weight. The concentration of silicon in the first filtrate was measured by the silicomolybdenum blue spectrophotometric method in the standard "General Method for Determination of Silicates in Chemical Reagents" (GB / T9742-2008). The desiliconization rate was calculated to be 43.35%. The main components of the fly ash after alkali-dissolved desiliconization are shown in Table 4.

[0050] Table 4. Main components of fly ash after alkali dissolution

[0051]

[0052] (3) Transfer the first filtrate from step (2) to a water bath and heat the water bath to 80°C. Simultaneously, stir at a speed of 300 r / min and introduce CO2 gas at a flow rate of 30 mL / min under constant temperature stirring conditions. Monitor the pH value of the solution in real time. Stop the reaction when the pH value of the solution is 9. After the reaction, vacuum filter the mixture to separate the solid and liquid. Place the obtained silica precipitate in a constant temperature drying oven and dry it at 120°C for 6 hours to finally obtain the silica product and the second filtrate.

[0053] (4) The second filtrate obtained from the filtration in step (3) enters a low-temperature flash evaporation system for concentration. The temperature of the low-temperature flash evaporator is controlled at 90℃, and the total steam pressure is stabilized above 0.5MPa. The concentrated liquid obtained after flash evaporation is about 10% to 30% of the original liquid. After evaporation and crystallization, the concentrated liquid yields Na2CO3. The water vapor generated during the flash concentration process can be condensed to obtain flash condensate.

[0054] (5) The desiliconized fly ash obtained after desiliconization in step (2) and the flash condensate generated in step (4) are mixed at a liquid-to-solid ratio of 10:1 to form a slurry. The slurry is placed in a water bath and heated to 60°C while being stirred at a speed of 300 r / min. CO2 gas is introduced at a flow rate of 30 mL / min under constant temperature stirring conditions for 3 hours. This process acidifies the slurry with CO2, thereby further removing residual alkali and impurities such as Ca, Fe, and Mg from the fly ash. After the reaction, the mixture is vacuum filtered to separate the solid and liquid. The filter cake is placed in a constant temperature drying oven and dried at 120°C for 12 hours until constant weight. Finally, fly ash with a high Al2O3 content and the third filtrate are obtained. The main components of the fly ash at this time are shown in Table 5.

[0055] Table 5. Main components of fly ash after acid leaching

[0056]

[0057] (6) The third filtrate obtained in step (5) and the second filtrate obtained in step (3) are combined and fed into the low-temperature flash evaporation system.

[0058] (7) The flash condensate produced in step (4) can also be mixed with NaOH to prepare NaOH solution for recycling.

[0059] The treated fly ash (see Table 5) contained 54.916% Al2O3 and an A / S ratio of 1.85. According to the "Mineral Geological Exploration Specification for Bauxite" (DZ / T 0202-2020), the cut-off grade for bauxite typically requires an Al / Si ratio between 1.8 and 2.6, while the alumina (Al2O3) content should not be less than 40%. Therefore, this fly ash product meets the application standards for medium- and low-grade bauxite, and power plants can directly sell it as bauxite resource. This not only achieves high-value utilization of resources but also innovatively solves the problem of limited sales channels for high-alumina fly ash, expanding its application path in the aluminum industry.

[0060] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing silicon-based and aluminum-based materials from fly ash and coupling them with carbon emission reduction, comprising: (1) High-alumina fly ash is pretreated by ball milling to obtain pretreated fly ash; (2) The pretreated fly ash was mixed with NaOH solution and placed in a microwave reactor for desilication reaction. After the reaction was completed, the mixture was filtered to obtain desilication fly ash and the first filtrate. (3) Introduce CO2 from the desulfurization flue gas of the power plant into the first filtrate to carry out a carbonization reaction, and filter after the reaction; obtain white carbon black precipitate and second filtrate; (4) Wash and dry the precipitated silica to obtain the precipitated silica product; concentrate the second filtrate by low-temperature flash evaporation and crystallize it to obtain Na2CO3 and flash condensate; (5) Mix desiliconized fly ash with flash condensate to make slurry, and introduce CO2 gas to acidify the system. After the reaction is completed, use vacuum filtration to separate solid and liquid, and obtain fly ash with high Al2O3 content and third filtrate. (6) The third filtrate and the second filtrate are combined and fed into the low-temperature flash evaporation system; the flash condensate generated in step (4) is mixed with NaOH to prepare a NaOH solution for recycling.

2. The method according to claim 1, wherein: The pretreated fly ash particle size in step (1) is <5μm.

3. The method according to claim 1, wherein: The NaOH solution in step (2) has a mass concentration of 15% to 30%. The liquid-to-solid ratio of NaOH solution to fly ash is 1.5:1 to 3:1 (mL / g).

4. The method according to claim 1, wherein: The conditions for the desilication reaction in step (2) are as follows: Microwave frequency 2450MHz, output power 700W; reaction temperature 100℃~130℃, reaction time 1~3h.

5. The method according to claim 1, wherein: The CO2 ventilation rate in step (3) is 20-30 mL / min; The carbonization reaction temperature is 80℃~90℃, and the reaction endpoint is pH=9.

6. The method according to claim 1, wherein: The drying conditions described in step (4) are: drying at a constant temperature of 105℃~120℃ for 4~6 hours.

7. The method according to claim 1, wherein: The low-temperature flash concentration conditions described in step (4) are: temperature 80℃~100℃, and total steam pressure stable above 0.5MPa.

8. The method according to claim 1, wherein: The liquid-to-solid ratio of the desiliconized fly ash to the flash condensate in step (5) is 5:1 to 10:1 (mL / g); The CO2 gas flow rate is 30–50 mL / min, the reaction temperature is 40℃–70℃, and the reaction time is 2–4 h.

9. The method according to claim 1, wherein: The standard for fly ash with high Al2O3 content mentioned in step (5) is: Al2O3 content > 40%, aluminum-silicon ratio > 1.8.

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