Method for preparing self-gelling material through carbon sequestration and heavy metal solidification of coal-based tailings and fly ash

Abstract

The invention discloses a method for preparing a self-gel material from coal-based tailings and coal ash through carbon sequestration and heavy metal solidification, and belongs to the technical field of solid waste treatment and gel material preparation. The method comprises the following steps: S1, crushing the coal-based tailings, washing with water, and airing; grinding the fly ash, washing with water, and airing; s2, detecting the content of SiO2, Al2O3 and CaO in the coal-based tailings and the fly ash, and regulating and controlling the mixing mass ratio of the coal-based tailings to the fly ash to enable the mass ratio of SiO2 to Al2O3 to CaO to be (1-4): (0.5-1.5): (0.5-1.5); s3, adding an alkaline activator into the mixture obtained in the step S2, placing the mixture in a reaction kettle, carrying out carbonation reaction, and ending the reaction until the pH value of the mixture is less than 8; s4, a sodium silicate solution accounting for 10%-20% of the total mass and nano SiO2 accounting for 3%-8% of the total mass are added into a product in the step S3, curing is conducted for 12-24 h at the temperature of 60-90 DEG C, and the self-gel material is prepared. According to the method, carbon sequestration and heavy metal solidification are synchronously realized, the self-cementing material is prepared, and the method has remarkable environmental benefits and engineering application value.

Description

Technical Field

[0001] This invention relates to the technical field of solid waste treatment and gel material preparation, and particularly to a method for preparing self-gel materials by carbonizing and solidifying heavy metals from coal-based tailings and fly ash. Background Technology

[0002] With the acceleration of global industrialization, coal, as an important traditional energy source, occupies a pivotal position in the energy structure. While the entire coal industry chain, from mining to combustion, provides a continuous source of power for society, it also brings a series of serious environmental problems, among which the large-scale generation of coal-based tailings and fly ash is a prominent challenge.

[0003] Coal-based tailings mainly originate from the washing and beneficiation stages of coal mining. During coal washing, impurities are removed from the raw coal using physical or chemical methods to improve coal quality and utilization. These separated impurities primarily include gangue, peat, clay minerals, and small amounts of metallic minerals, collectively referred to as coal-based tailings. Coal-based tailings often contain certain amounts of heavy metals, such as mercury (Hg), lead (Pb), cadmium (Cd), and chromium (Cr). Under the influence of factors such as rainfall and surface runoff, these heavy metals migrate along with water-soluble substances in the tailings into the surrounding soil and water bodies, gradually accumulating and eventually entering the food chain, posing a potential threat to the ecological environment and human health.

[0004] Fly ash is one of the main solid wastes generated during coal-fired power generation. During coal combustion, the mineral components in the coal melt, volatilize, and condense at high temperatures, ultimately forming fly ash. On the one hand, large quantities of fly ash require specialized storage sites, which often occupy vast areas. Furthermore, without strict protective measures during site selection, construction, and operation, potential environmental risks exist. On the other hand, fly ash also contains heavy metals such as arsenic (As) and selenium (Se), which are toxic. If fly ash is exposed to the natural environment for extended periods, these heavy metals can migrate into the environment under natural conditions, posing a threat to ecosystems and human health.

[0005] In addition, the storage of coal-based tailings and fly ash poses other environmental and safety hazards. For example, under the influence of heavy rain, tailings ponds and fly ash storage sites may experience dam failures, landslides, and other accidents. This could lead to large amounts of tailings and fly ash flowing into surrounding areas, burying farmland, roads, and other infrastructure, causing severe soil erosion and pollution, and even posing a direct threat to the lives and property of nearby residents. Furthermore, acidic or alkaline substances in tailings and fly ash can leach out under certain conditions, altering the pH balance of surrounding soil and water bodies, affecting the living environment of soil microorganisms and the normal growth and reproduction of aquatic organisms, further disrupting the ecological balance.

[0006] Currently, the main methods for treating coal-based tailings and fly ash are as follows: (1) Stockpiling: Coal-based tailings and fly ash are directly stockpiled in designated tailings ponds or storage yards. However, this method not only occupies a large amount of land, but also poses many environmental risks and safety hazards. It is a simple but unsustainable disposal method. With increasingly stringent environmental protection requirements, the simple stockpiling method has become increasingly restricted.

[0007] (2) Backfilling: Coal-based tailings and fly ash are used for backfilling of mining goaf areas to reduce surface subsidence and prevent ground subsidence. However, improper handling during the backfilling process may trigger new geological disasters. At the same time, the solidification treatment of heavy metals in tailings and fly ash is not ideal, and there is still a risk of secondary pollution from heavy metals.

[0008] (3) Recycling: For example, fly ash can be used as road base material or filler material, or some valuable metals in coal tailings can be recovered and extracted. However, the application scope of these recycling methods is limited, and they cannot fundamentally solve the pollution problem for the large amount of coal tailings and fly ash produced. In the process of utilization, there are also many shortcomings in terms of the stability of heavy metals and the improvement of material performance.

[0009] Meanwhile, global climate change is becoming increasingly severe, with carbon dioxide emissions being one of the main causes. How to effectively utilize carbon dioxide to achieve carbon sequestration and emission reduction has become a focus of attention for countries worldwide. Among numerous carbon sequestration technologies, carbon dioxide carbonation is a promising method. The principle of carbon dioxide carbonation is to utilize the reaction between carbon dioxide and metal cations in certain minerals to generate stable carbonate minerals, thereby fixing carbon dioxide in solid minerals. This not only achieves carbon dioxide emission reduction but also, to some extent, alters the properties of solid waste, improving its stability and usability.

[0010] Furthermore, during the carbonation reaction, the microstructure and chemical composition of coal-based tailings and fly ash change along with the formation of carbonate minerals. These changes may endow them with new cementing properties, giving them a certain degree of self-cementing ability. Self-cementing materials refer to materials that, under appropriate conditions, can generate hydration products with adhesiveness and strength through chemical reactions within a certain time, thereby eliminating or reducing the need for external cementing materials (such as cement), achieving self-curing and forming with certain mechanical properties. If coal-based tailings and fly ash can be prepared into high-performance self-cementing materials through carbonation reactions, it can not only solve the problems of solid waste disposal and heavy metal pollution, but also transform them into building materials with practical application value, realizing resource recycling and generating significant economic and environmental benefits. Summary of the Invention

[0011] The main objective of this invention is to provide a method for preparing self-gelling materials by carbon fixation and solidification of heavy metals from coal-based tailings and fly ash, thereby solving the problem of heavy metal pollution in coal-based tailings and fly ash and improving their utilization. This invention utilizes a three-stage carbon fixation-solidification reaction to improve carbon dioxide utilization and reaction efficiency, ensuring that the metal cations in coal-based tailings and fly ash fully react with carbon dioxide to generate a sufficient amount of carbonate minerals, thus achieving excellent heavy metal solidification and improved self-gelling properties.

[0012] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing self-gel materials by carbon fixation and solidification of heavy metals from coal-based tailings and fly ash, comprising the following steps: S1. Crush the coal-based tailings, wash them with water, and air dry them; grind the fly ash, wash it with water, and air dry it. S2. Detect the content of SiO2, Al2O3 and CaO in coal-based tailings and fly ash, and adjust the mixing mass ratio of coal-based tailings and fly ash so that the mass ratio of SiO2, Al2O3 and CaO is 1~4:0.5~1.5:0.5~1.5; S3. Add an alkaline activator to step S2, place it in a reaction vessel, and carry out a carbonation reaction until the pH value of the mixture is less than 8, then end the reaction. S4. Add 10%~20% sodium silicate solution and 3%~8% nano-SiO2 by mass to the product of step S3, and cure at 60~90 ℃ for 12~24 h to obtain self-gel material.

[0013] In the preferred embodiment, in step S1, the particle size of the coal-based tailings is 0.1~1 mm, and the particle size of the fly ash is 0.05~0.15 mm. Smaller particle size can increase the specific surface area of ​​the raw materials, improve the reactivity, facilitate the full contact and reaction between carbon dioxide and the metal cations in the raw materials, promote the formation of carbonate minerals, and also help improve the microstructure and properties of self-cementing materials.

[0014] In the preferred embodiment, the specific steps of water washing in step S1 are as follows: The coal-based tailings or fly ash are soaked in a 10wt%~20wt% dilute acid solution for 1~3 hours at a solid-liquid ratio of 1:2~5 g / mL; then washed with water until the pH of the washing solution is 6.5~7. The dilute acid soaking serves two purposes: first, to remove grease and dust from the surface of the coal-based tailings or fly ash; and second, to break down the oxide layer on the surface of the coal-based tailings or fly ash, thereby increasing its activity.

[0015] In the preferred embodiment, in step S2, the fly ash is fly ash that has undergone activation pretreatment. The activation pretreatment includes the following steps: placing the fly ash in a microwave field with a power of 600~1000 W and a frequency of 2.45 GHz for 10~15 min; immediately after the treatment, adding 3%~5% K2CO3 by mass of the fly ash and mixing thoroughly. Microwave-induced lattice distortion breaks the Al-O-Si bonds in the glassy structure of the fly ash, thereby increasing the activity of SiO2 and Al2O3 in the fly ash.

[0016] In the preferred embodiment, in step S2, the mass ratio of SiO2, Al2O3, and CaO in the mixture of coal-based tailings and fly ash is adjusted by adding limestone powder, silica fume, or metakaolin.

[0017] In the preferred embodiment, in step S2, the mass ratio of SiO2, Al2O3 and CaO is 2~3:1:1.

[0018] This formulation helps promote the carbonation reaction and improves the strength and durability of self-gelling materials, while also helping to solidify heavy metals.

[0019] CaO is a key substance in the reaction with carbon dioxide to form calcium carbonate. Maintaining a certain CaO content ensures sufficient reaction with the introduced carbon dioxide, reduces other side reactions, improves carbon dioxide utilization, and directs the reaction towards the formation of carbonate minerals. Furthermore, the presence of SiO2 and Al2O3 can regulate the pH and chemical environment of the reaction system, helping to increase the rate and extent of the carbonation reaction, resulting in more complete calcium carbonate formation. In addition, under the action of an alkaline activator, SiO2 and Al2O3 can undergo hydration reactions to produce cementing products such as hydrated calcium silicate and hydrated calcium aluminate. An appropriate amount of CaO can interact with these hydration products, further enhancing their cementing properties. Moreover, the formation of calcium carbonate minerals can fill the spaces between coal tailings and fly ash particles, providing skeletal support. Simultaneously, the hydration products bind the particles together, forming a tight network structure, thereby improving the strength and durability of the self-cementing material. Meanwhile, the carbonate minerals and hydration products generated under this ratio can change the surface properties and chemical environment of coal-based tailings and fly ash. Calcium carbonate minerals have a layered or needle-like structure, which can encapsulate heavy metal ions in coal-based tailings and fly ash, preventing heavy metals from contacting the external environment and reducing their migration and diffusion in the environment. The hydration products of SiO2 and Al2O3 have certain adsorption and chemical stability, and can undergo adsorption, precipitation or complexation reactions with heavy metal ions to further fix heavy metals, reduce the chemical activity of heavy metals, and make them difficult to be oxidized, reduced or dissolved, thereby reducing the harm of heavy metals to the environment.

[0020] In the preferred embodiment, in step S3, the alkaline activator is composed of NaOH and Na2CO3 in a mass ratio of 1 to 3:1.

[0021] In a preferred embodiment, in step S3, the amount of alkaline activator added is 5% to 15% of the total mass of the mixture.

[0022] In the preferred embodiment, in step S3, the reaction vessel is purged with nitrogen before the carbonation reaction to remove all air from the vessel and prevent oxygen and other gases from interfering with the carbonation reaction.

[0023] In the preferred embodiment, during step S3, the CO2 pressure is 0.5~2.0 MPa, the temperature is 40~80 ℃, and the stirring speed is 100~300 r / min.

[0024] In the preferred embodiment, in step S3, the carbonation reaction is a three-stage reaction process. In the initial stage of the reaction, the pressure of CO2 is 1.5~2.0 MPa and the temperature is 40~60 ℃; when the pH value of the mixture decreases to 10~9, the pressure of CO2 is 0.8~1.5 MPa and the temperature is 60~80 ℃; when the pH value of the mixture decreases to 9~8, the pressure decreases to 0.5~0.8 MPa and the temperature is 60~80 ℃.

[0025] In the initial stage of the reaction, high pressure promotes the dissolution reaction. High pressure allows carbon dioxide to dissolve more quickly and completely in the reaction system, increasing the contact area between carbon dioxide and metal cations in coal tailings and fly ash, thus accelerating the initiation of the carbonation reaction. Lower temperatures ensure a faster reaction without causing excessive carbon dioxide volatilization. The main purpose of this stage is to enable the carbon dioxide to react rapidly with the alkaline components in the reaction system, consuming hydroxide ions and creating conditions for the subsequent carbonation reaction. Simultaneously, it initially forms carbonate minerals, laying the foundation for the entire reaction.

[0026] When the pH of the mixture drops to 10-9, reducing the carbon dioxide pressure can prevent excessive pressure from causing an overly vigorous reaction, which would hinder precise control of the reaction. Simultaneously, increasing the temperature accelerates the reaction rate, allowing the carbonation reaction to proceed more thoroughly and promoting the reaction of more metal cations with carbon dioxide to form carbonate minerals. The goal of this stage is to maximize the formation of carbonate minerals while ensuring the reaction remains controllable, further reducing the pH of the mixture and driving the reaction to a deeper level.

[0027] When the pH of the mixture drops to 9-8, the lower pressure also helps to release excess gas that may be generated during the reaction, which is conducive to the reaction system reaching equilibrium. This allows the metals and cations that have not yet fully reacted to have enough time to fully contact and react with carbon dioxide, ensuring that the carbonation reaction is as complete as possible and providing high-quality raw materials for the subsequent preparation of self-gelling materials.

[0028] In the preferred embodiment, in step S4, the molar ratio of silicon dioxide to sodium oxide in the sodium silicate solution is 2-3:1. If the molar ratio is too low, the sodium oxide content will be high, resulting in a stronger alkalinity. Although this can improve the reactivity, it will affect the strength of the self-gelling material.

[0029] In the preferred embodiment, in step S4, the nano-SiO2 particles have a particle size of 20~50 nm and a specific surface area ≥300 m². 2The introduction of nano-SiO2 not only promotes the formation of hydration products (CSH gel) but also enhances the network structure through physical filling and chemical bridging. Nano-silica possesses extremely high specific surface area and activity, providing numerous nucleation sites for the formation of hydration products and carbonate minerals, accelerating the hydration and carbonation reactions, resulting in more complete reactions and finer, more uniform mineral crystals. Furthermore, nano-silica can form a tight bond with hydration products and carbonate minerals, creating a three-dimensional network structure, thereby improving the early and later strength of the material.

[0030] In the preferred embodiment, in step S4, before curing, 0.1%~0.5% sodium alginate and 0.5%~1.5% amino-modified sericin are added by mass. The network structure formed by sodium alginate can effectively disperse the internal stress of the material, reducing the generation and propagation of cracks caused by stress concentration; the amino functional groups in the amino-modified sericin can undergo coordination reactions with silicate ions and metal ions to form a stable three-dimensional network structure, enhancing the internal bonding force of the material.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention is the first to propose coupling the carbonation fixation of coal-based tailings with the pozzolanic reaction of fly ash. By controlling CO2 pressure and alkaline activation conditions, efficient carbon fixation and heavy metal solidification are achieved simultaneously, resulting in the preparation of high-performance cementitious materials. This invention shortens production time, improves production efficiency, prevents the migration and diffusion of heavy metals in the environment, reduces the risk of pollution to soil, water, and other environmental media, and simultaneously achieves the mineralization and utilization of carbon dioxide, helping to reduce carbon emissions and mitigate the greenhouse effect. It has significant environmental benefits and engineering application value.

[0032] 2. This invention transforms two types of industrial solid waste, coal-based tailings and fly ash, into valuable building materials, realizing the recycling of resources, reducing the exploitation of natural resources, and lowering the land occupation and environmental pressure caused by waste stockpiling.

[0033] 3. This invention employs a process that simultaneously performs carbonation and self-gelling material preparation, simplifying the production process, reducing production costs, and improving production efficiency. Furthermore, by adjusting the composition and using additives, the material's performance can be precisely controlled to meet the needs of various engineering applications.

[0034] 4. The self-gelling material prepared by this invention has high compressive strength, flexural strength, and impermeability, making it suitable for various building material applications, such as road base materials and mine filling materials. Simultaneously, the material possesses excellent durability, including freeze-thaw resistance and chemical corrosion resistance, enabling it to remain stable under complex environmental conditions for extended periods, thus prolonging its service life.

[0035] 5. The production process of this invention is relatively clean, with no emissions of toxic or harmful substances, which meets environmental protection requirements and helps to promote the green and sustainable development of industrial solid waste treatment and disposal. Detailed Implementation

[0036] The technical solution of the present invention will be further described and illustrated below through examples. All raw materials used in the examples are commercially available or prepared using conventional methods.

[0037] Example 1 A method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash includes the following steps: S1. After crushing the coal-based tailings to a particle size of 0.1~1 mm, soak them in a 15wt% dilute hydrochloric acid solution with a solid-liquid ratio of 1:3 g / mL for 2 hours. Wash them with water until the pH of the washing solution is 7, and then air dry them. Grind the fly ash to a particle size of 0.05~0.15 mm, soak and wash it in the same way, and then air dry it. S2. Place the dried fly ash from step S1 in a microwave field with a power of 800 W and a frequency of 2.45 GHz for 15 min. Immediately after the treatment, add 3% K2CO3 by mass of fly ash and mix well. S3. Detect the content of SiO2, Al2O3 and CaO in coal-based tailings and fly ash. By adding limestone powder, adjust the mixing mass ratio of coal-based tailings and fly ash so that the mass ratio of SiO2, Al2O3 and CaO is 2:1:1. S4. Add 10% (by mass) of alkaline activator (NaOH to Na2CO3 mass ratio of 1:1) to the reaction vessel, place it in the reaction vessel, purge the air with nitrogen to remove air, and then carry out the carbonation reaction. Set an online pH detector and a stirring speed of 300 r / min. In the initial stage of the reaction, the pH of the mixture is 11.2, the CO2 pressure is set to 2.0 MPa, and the temperature is 60 ℃. When the pH of the mixture decreases to 10, the CO2 pressure is set to 1.5 MPa and the temperature is set to 80 ℃. When the pH of the mixture decreases to 9, the pressure is reduced to 0.8 MPa and the temperature is set to 80 ℃. The reaction ends when the pH of the mixture is less than 8. S5. Add 15% sodium silicate solution (molar ratio of silicon dioxide to sodium oxide is 2:1) and 5% particles with a diameter of 20~50 nm and a specific surface area ≥300 m² to the product of step S4. 2 Self-gel material was prepared by curing nano-SiO2 at 80 °C for 18 h with / g of nano-SiO2.

[0038] Example 2 A method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash includes the following steps: S1. After crushing the coal-based tailings to a particle size of 0.1~1 mm, soak them in a 10wt% dilute nitric acid solution with a solid-liquid ratio of 1:2 g / mL for 1 hour, wash them with water until the pH of the washing solution is 6.8, and then air dry them; after grinding the fly ash to a particle size of 0.05~0.15 mm, soak and wash it in the same way, and then air dry it. S2. Place the dried fly ash from step S1 in a microwave field with a power of 800 W and a frequency of 2.45 GHz for 15 min. Immediately after the treatment, add 3% K2CO3 by mass of fly ash and mix well. S3. Detect the content of SiO2, Al2O3 and CaO in coal-based tailings and fly ash. By adding silica fume, adjust the mixing mass ratio of coal-based tailings and fly ash to make the mass ratio of SiO2, Al2O3 and CaO 3:1:1. S4. Add 10% (by mass) of alkaline activator (NaOH to Na2CO3 mass ratio of 3:1) to the reaction vessel, place it in the reaction vessel, purge the air with nitrogen, and then carry out the carbonation reaction. Set an online pH detector and a stirring speed of 200 r / min. In the initial stage of the reaction, the pH of the mixture is 10.8, the CO2 pressure is set to 1.5 MPa, and the temperature is 40 ℃. When the pH of the mixture decreases to 10, the CO2 pressure is set to 0.8 MPa and the temperature is 70 ℃. When the pH of the mixture decreases to 9, the pressure is reduced to 0.5 MPa and the temperature is set to 60 ℃. The reaction ends when the pH of the mixture is less than 8. S5. Add 20% sodium silicate solution (molar ratio of silicon dioxide to sodium oxide is 3:1) and 8% of particles with a diameter of 20~50 nm and a specific surface area ≥300 m² to the product of step S4. 2 Self-gelling material was prepared by curing nano-SiO2 at 60 °C for 24 h with / g of nano-SiO2.

[0039] Example 3 A method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash includes the following steps: S1. After crushing the coal-based tailings to a particle size of 0.1~1 mm, soak them in a 12wt% dilute nitric acid solution with a solid-liquid ratio of 1:5 g / mL for 1 hour, wash them with water until the pH of the washing solution is 6.8, and then air dry them; after grinding the fly ash to a particle size of 0.05~0.15 mm, soak and wash it in the same way, and then air dry it. S2. Detect the content of SiO2, Al2O3 and CaO in coal-based tailings and fly ash. By adding metakaolin, adjust the mixing mass ratio of coal-based tailings and fly ash to make the mass ratio of SiO2:1:1. S3. Add 5% (by mass) of alkaline activator (NaOH to Na2CO3 mass ratio of 2:1) to the reaction vessel, place it in the reaction vessel, purge the air with nitrogen to remove air, and then carry out the carbonation reaction. Set an online pH detector and a stirring speed of 100 r / min. In the initial stage of the reaction, the pH of the mixture is 10.9, the CO2 pressure is set to 1.5 MPa, and the temperature is 40 ℃. When the pH of the mixture decreases to 9.5, the CO2 pressure is set to 0.8 MPa and the temperature to 60 ℃. When the pH of the mixture decreases to 9, the pressure is reduced to 0.5 MPa and the temperature is set to 60 ℃. The reaction ends when the pH of the mixture is less than 8. S4. Add 10% sodium silicate solution (molar ratio of silicon dioxide to sodium oxide is 2.5:1) to the product of step S3, and add 3% of the product containing particles with a diameter of 20~50 nm and a specific surface area ≥300 m². 2 A self-gel material was prepared by curing nano-SiO2 (g), sodium alginate (0.3% of total mass), and amino-modified sericin (1% of total mass) at 90 °C for 12 h.

[0040] Example 4 A method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash includes the following steps: S1. After crushing the coal-based tailings to a particle size of 0.1~1 mm, soak them in a 10wt% dilute hydrochloric acid solution with a solid-liquid ratio of 1:2 g / mL for 1 hour, wash them with water until the pH of the washing solution is 6.8, and then air dry them; after grinding the fly ash to a particle size of 0.05~0.15 mm, soak and wash it in the same way, and then air dry it. S2. Place the dried fly ash from step S1 in a microwave field with a power of 800 W and a frequency of 2.45 GHz for 10 min. Immediately after the treatment, add 5% K2CO3 by mass of fly ash and mix well. S3. Detect the content of SiO2, Al2O3 and CaO in coal-based tailings and fly ash, and adjust the mixing mass ratio of coal-based tailings and fly ash to make the mass ratio of SiO2, Al2O3 and CaO 3:1.2:1.5; S4. Add 12% (by mass) of alkaline activator (NaOH to Na2CO3 in a mass ratio of 2:1) to the reaction vessel, place it in the reaction vessel, purge the air with nitrogen, and then carry out the carbonation reaction. Set an online pH detector and a stirring speed of 300 r / min. In the initial stage of the reaction, the pH of the mixture is 11.7, the CO2 pressure is set to 2 MPa, and the temperature is set to 50 ℃. When the pH of the mixture decreases to 10, the CO2 pressure is set to 1 MPa and the temperature is set to 80 ℃. When the pH of the mixture decreases to 9, the pressure is reduced to 0.8 MPa and the temperature is set to 60 ℃. The reaction ends when the pH of the mixture is less than 8. S5. Add 18% sodium silicate solution (molar ratio of silicon dioxide to sodium oxide is 3:1) and 6% of particles with a diameter of 20-50 nm and a specific surface area ≥300 m² to the product of step S4. 2 Self-gelling material was prepared by curing nano-SiO2 at 75 °C for 15 h with / g of nano-SiO2.

[0041] Testing and Analysis Heavy metal solidification rate: Leaching tests were conducted according to GB / T 30760-2024 "Technical Specification for Co-processing Solid Waste in Cement Kilns" to determine the concentration of heavy metals in the leachate. The heavy metal solidification rate was calculated as follows: heavy metal solidification rate = (leaching concentration before carbonation reaction - leaching concentration before carbonation reaction) / leaching concentration before carbonation reaction.

[0042] Carbon sequestration: Tested in accordance with GB / T 32150-2015 "General Rules for Accounting and Reporting of Greenhouse Gas Emissions of Industrial Enterprises", and calculated as follows: Carbon sequestration = (mass after carbonation reaction - mass before carbonation reaction) * relative molecular mass of carbon dioxide / relative molecular mass of carbonate ion.

[0043] Compressive strength: Tested in accordance with GB / T 17671-2021 "Test method for strength of cement mortar (ISO method)".

[0044] Flexural strength: Tested in accordance with GB / T 17671-2021 "Test method for strength of cement mortar (ISO method)".

[0045] Durability: The test was conducted in accordance with GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete", and the mass loss rate was tested after 300 freeze-thaw cycles.

[0046] Freeze-thaw resistance: The test was conducted in accordance with GB / T 50082-2024 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete", and the strength loss rate was tested after 300 freeze-thaw cycles.

[0047] Impermeability: Tested in accordance with GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete".

[0048] The test results of Examples 1 to 4 are shown in the table.

[0049] Table 1 Performance data of Examples 1-4

[0050] As shown in Table 1, Example 4 exhibited the highest heavy metal solidification rate, while Example 2 showed a relatively lower solidification rate. This may be due to factors such as the shorter microwave treatment time of the fly ash and the lower proportion of alkaline activator, resulting in a slightly weaker heavy metal fixation effect. Example 3 did not involve microwave treatment of the fly ash or the addition of K2CO3, which may have led to relatively lower activity in the reaction, resulting in a relatively lower carbon fixation amount. Example 3 also added sodium alginate and amino-modified sericin, which may have improved the microstructure and properties of the material, giving it the best performance in terms of strength and durability.

[0051] It should be understood that the above embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash, characterized in that, Includes the following steps: S1. Crush the coal-based tailings, wash them with water, and air dry them; grind the fly ash, wash it with water, and air dry it. S2. Detect the content of SiO2, Al2O3 and CaO in coal-based tailings and fly ash, and adjust the mixing mass ratio of coal-based tailings and fly ash so that the mass ratio of SiO2, Al2O3 and CaO is 1~4:0.5~1.5:0.5~1.5; S3. Add an alkaline activator to step S2, place it in a reaction vessel, and carry out a carbonation reaction until the pH value of the mixture is less than 8, then end the reaction. S4. Add 10%~20% sodium silicate solution and 3%~8% nano-SiO2 by mass to the product of step S3, and cure at 60~90 ℃ for 12~24 h to obtain self-gel material.

2. The method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash according to claim 1, characterized in that, In step S1, the particle size of the coal-based tailings is 0.1~1 mm, and the particle size of the fly ash is 0.05~0.15 mm.

3. The method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash according to claim 1, characterized in that, In step S1, the specific steps of water washing are as follows: soak the coal-based tailings or fly ash in a 10wt%~20wt% dilute acid solution for 1~3 h at a solid-liquid ratio of 1:2~5 g / mL; then wash with water until the pH value of the washing solution is 6.5~7.

4. The method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash according to claim 1, characterized in that, In step S2, the fly ash is fly ash that has undergone activation pretreatment. The activation pretreatment includes the following steps: placing the fly ash in a microwave field with a power of 600~1000 W and a frequency of 2.45 GHz for 10~15 min, and immediately adding 3%~5% of K2CO3 by mass of the fly ash after the treatment and mixing it evenly.

5. The method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash according to claim 1, characterized in that, In step S2, the mass ratio of SiO2, Al2O3 and CaO in the mixture of coal-based tailings and fly ash is adjusted by adding limestone powder, silica fume or metakaolin; in step S2, the mass ratio of SiO2, Al2O3 and CaO is 2~3:1:

1.

6. The method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash according to claim 1, characterized in that, In step S3, the alkaline activator is composed of NaOH and Na2CO3 in a mass ratio of 1 to 3:1; in step S3, the amount of alkaline activator added is 5% to 15% of the total mass of the mixture.

7. The method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash according to claim 1, characterized in that, In step S3, the reaction vessel is purged with nitrogen before the carbonation reaction to remove all air from the vessel and prevent oxygen and other gases from interfering with the carbonation reaction. In step S3, the CO2 pressure is 0.5~2.0 MPa, the temperature is 40~80 ℃, and the stirring speed is 100~300 r / min.

8. The method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash according to claim 7, characterized in that, In step S3, the carbonation reaction is a three-stage reaction process. In the initial stage of the reaction, the pressure of CO2 is 1.5~2.0 MPa and the temperature is 40~60 ℃. When the pH value of the mixture decreases to 10~9, the pressure of CO2 is 0.8~1.5 MPa and the temperature is 60~80 ℃. When the pH value of the mixture decreases to 9~8, the pressure drops to 0.5~0.8 MPa and the temperature is 60~80 ℃.

9. The method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash according to claim 1, characterized in that, In step S4, the molar ratio of silicon dioxide to sodium oxide in the sodium silicate solution is 2~3:1; in step S4, the nano-SiO2 particles have a particle size of 20~50 nm and a specific surface area ≥300 m². 2 / g.

10. The method for preparing self-gel materials by carbon fixation and heavy metal solidification from coal-based tailings and fly ash according to claim 1, characterized in that, In step S4, before curing, sodium alginate (0.1% to 0.5% by weight) and amino-modified sericin (0.5% to 1.5% by weight) are added.

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