Method for mineralizing carbon dioxide with fly ash

Abstract

The application relates to the technical field of carbon dioxide, and provides a method for mineralizing carbon dioxide by using fly ash, which comprises the following steps: mixing fly ash, a salt solution and an alkali activator to prepare a mixed solution with a pH value of 9.5-11.5, introducing carbon dioxide into the mixed solution to perform a mineralization reaction, and preparing a mineralization product; wherein the fly ash contains silicate and alkaline oxides; the salt solution contains at least one of sodium ions, magnesium ions and calcium ions, and contains sulfate ions and chloride ions, and the mass concentration of the chloride ions in the salt solution is less than 0.5 g / L. According to the application, the salt solution and the fly ash are used to realize efficient mineralization of carbon dioxide, and the leaching of heavy metals in the fly ash is effectively reduced. Further, the salt solution can be obtained by performing a dechlorination treatment on seawater, the influence of high-concentration chloride ions on the mineralization reaction of the fly ash and the long-term stability of the mineralization product is reduced, and the seawater resource utilization and the carbon dioxide mineralization and storage are simultaneously performed.

Description

Technical Field

[0001] This application relates to the field of carbon dioxide technology, and in particular to a method for mineralizing carbon dioxide from fly ash. Background Technology

[0002] Carbon dioxide (CO2) sequestration is a process that mimics the natural weathering and CO2 absorption of rocks. It utilizes the reaction between CO2 gas and mineralized raw materials to form stable solid carbonates, thus achieving CO2 sequestration. Naturally occurring calcium magnesium silicate minerals (such as olivine and serpentine) can typically be used as raw materials for sequestration. While natural minerals are widely available and abundant, their mining areas are usually fixed, resulting in high transportation costs. Furthermore, pretreatment such as cutting and crushing of natural minerals before sequestration often increases sequestration costs and energy consumption.

[0003] As the coal-fired power generation industry moves towards greater energy efficiency, low carbon emissions, and green production, the resulting fly ash faces significant challenges in its disposal. Fly ash contains highly reactive alkaline metal oxides such as CaO and MgO, exhibiting substantial CO2 mineralization potential. Compared to natural minerals, fly ash is readily available and requires no costly or energy-intensive processing or pretreatment before mineralization, giving it a competitive advantage in mineralization raw material selection. However, fly ash contains heavy metals such as Pb and Cd, which are easily leached out after mineralization, affecting the usability of the resulting materials. Summary of the Invention

[0004] Therefore, it is necessary to provide a method for mineralizing carbon dioxide from fly ash, which can solve the problem of heavy metal leaching from fly ash while mineralizing carbon dioxide.

[0005] This application provides a method for mineralizing carbon dioxide from fly ash, comprising the following steps:

[0006] Fly ash, salt solution, and alkaline activator are mixed to prepare a mixed solution with a pH of 9.5-11.5. Carbon dioxide is then introduced into the mixed solution to carry out a mineralization reaction and prepare mineralized products.

[0007] Fly ash contains aluminosilicates and alkaline oxides;

[0008] The salt solution contains at least one of sodium, magnesium, and calcium ions, as well as sulfate and chloride ions, and the mass concentration of chloride ions in the salt solution is <0.5 g / L.

[0009] In some implementations, the method satisfies at least one of the following conditions:

[0010] (1) The pH of the mixture is controlled by the amount of alkali activator added, which is 1% to 5% of the mass of fly ash;

[0011] (2) The alkaline activator includes at least one of sodium silicate, sodium hydroxide and potassium hydroxide;

[0012] (3) Additives are also added to the mixture, including styrene-acrylic emulsion.

[0013] In some implementations, the method satisfies at least one of the following conditions:

[0014] (1) The mass concentration of magnesium ions in the salt solution is 1.0 g / L to 1.5 g / L;

[0015] (2) The mass concentration of calcium ions in the salt solution is 0.3 g / L to 0.5 g / L;

[0016] (3) The mass concentration of sulfate ions in the salt solution is 2.5 g / L to 3.0 g / L;

[0017] (4) The mass concentration of sodium ions in the salt solution is 8 g / L to 11 g / L.

[0018] In some embodiments, the basic oxide satisfies at least one of the following conditions:

[0019] (1) Alkaline oxides include calcium oxide, and the mass percentage of calcium oxide in fly ash is 5% to 25%;

[0020] (2) Alkaline oxides include magnesium oxide, and the mass percentage of magnesium oxide in fly ash is 1% to 8%;

[0021] (3) Alkaline oxides include iron oxide, and the mass percentage of iron oxide in fly ash is 3% to 10%;

[0022] (4) The total mass percentage of calcium oxide and magnesium oxide in fly ash is ≥8%.

[0023] In some embodiments, the molecular formula of the aluminosilicate is xAl2O3·ySiO2, where y:x = 1.8~6.5.

[0024] In some implementations, the method satisfies at least one of the following conditions:

[0025] (1) The mass ratio of fly ash to salt solution is 1:(2~5);

[0026] (2) The amount of carbon dioxide added is 1.1 to 1.3 times the theoretical mineralization amount;

[0027] (3) The temperature for mineralization treatment is 30℃~50℃, the pressure is 0.1MPa~0.4MPa, and the time is 2h~6h;

[0028] (4) The mineralized products contain calcium carbonate, magnesium carbonate, hydrated calcium silicate and hydrated aluminosilicate gel.

[0029] In some embodiments, after the mineralization reaction, the method further includes: sequentially filtering, washing and drying the mixture to obtain the mineralized product.

[0030] In some embodiments, the method for preparing the salt solution includes: mixing seawater and a tertiary amine dechlorinating agent, and then performing a dechlorination treatment to obtain the salt solution.

[0031] In some implementations, the dechlorination treatment satisfies at least one of the following conditions:

[0032] (1) Tertiary amine dechlorinating agents include at least one of tripropylamine, tributylamine, triethylamine and trioctylamine;

[0033] (2) The molar ratio of tertiary amine dechlorinating agent to chloride ions in seawater is (1.0~1.5):1.

[0034] In some implementations, a diluent is added to the seawater during the dechlorination process.

[0035] Optionally, the diluent includes at least one of n-butanol, isooctyl alcohol, and kerosene.

[0036] Optionally, the ratio of the amount of tertiary amine dechlorinating agent added to the amount of diluent added is (1~4):1.

[0037] Compared with traditional technologies, this application has at least the following beneficial effects:

[0038] This application utilizes a salt solution containing sodium, magnesium, calcium, sulfate, and chloride ions, mixed with fly ash and an alkaline activator. The alkaline activator acts on the covalent bonds in the aluminosilicates of fly ash, dissociating the surface glassy structure and promoting the dissolution of alkaline oxides such as CaO and MgO. The salt solution not only acts as a solvent to dissolve the fly ash but also provides calcium and magnesium ions to participate in the mineralization reaction. Furthermore, the sodium ions can regulate the ionic strength of the mineralization system, effectively promoting carbon dioxide absorption and the mineralization reaction. In addition, the salt content in the salt solution inhibits the leaching of heavy metals from the fly ash, and the small amount of chloride ions in the salt solution can form complexes with heavy metals that are more easily captured by the solid phase, synergistically reducing the leaching rate of heavy metals and promoting the mineralization reaction with carbon dioxide. Therefore, the mineralized product formed in this application contains a dense carbonate coating layer, which has improved volume stability compared to fly ash and can be directly used in roadbed materials or concrete aggregates, effectively avoiding the strength degradation problem caused by water absorption and expansion in traditional building materials. Attached Figure Description

[0039] Figure 1 This is a flowchart of a method for mineralizing carbon dioxide from fly ash according to one embodiment of this application.

[0040] Figure 2 This is a flowchart of another method for mineralizing carbon dioxide from fly ash provided in one embodiment of this application.

[0041] Figure 3 This is a SEM image of the mineralized product obtained in Example 1 of this application.

[0042] Figure 4 This is another SEM image of the mineralized product obtained in Example 1 of this application. Detailed Implementation

[0043] The present application will be further described in detail below with reference to the embodiments and examples. These embodiments and examples are only for illustrating the present application and are not intended to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the disclosure of the present application more thorough and comprehensive. It should also be understood that the present application can be implemented in many different forms and is not limited to the embodiments and examples described herein. Those skilled in the art can make various modifications or alterations without departing from the spirit of the present application, and the equivalent forms obtained also fall within the protection scope of the present application. In addition, numerous specific details are set forth in the following description to provide a fuller understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0044] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0045] In this application, when numerical intervals (i.e., numerical ranges) are involved, unless otherwise specified, the distribution of selectable values ​​within the numerical interval is considered continuous, and includes the two endpoints of the numerical interval (i.e., the minimum and maximum values), as well as every value between these two endpoints. Unless otherwise specified, when the numerical interval only refers to the integers within the numerical interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged.

[0046] Traditional techniques involve dissolving calcium magnesium silicate minerals and other mineralization and sequestration raw materials in fresh water, then mixing them with carbon dioxide for further mineralization to form materials such as calcium carbonate, magnesium carbonate, and silica-alumina gel for sequestration. However, fly ash contains some heavy metals (such as Pb and Cd), which are easily leached out after mineralization, affecting the usability of the materials. Therefore, this application utilizes salt solutions and alkaline activators to dissolve fly ash, promoting the mineralization of fly ash with carbon dioxide while inhibiting the leaching of heavy metals, resulting in mineralized products with good volume stability and excellent mechanical strength. Furthermore, fly ash mineralization for carbon dioxide sequestration integrates the main source of fly ash with the carbon dioxide emission source (thermal power plants), significantly reducing transportation and management costs.

[0047] This application provides a method for mineralizing carbon dioxide from fly ash, such as... Figure 1 As shown, it includes the following steps:

[0048] Fly ash, salt solution, and alkaline activator are mixed to prepare a mixture with a pH of 9.5-11.5. Carbon dioxide is then introduced into the mixture to carry out a mineralization reaction and prepare a mineralized product.

[0049] The fly ash contains aluminosilicates and basic oxides; the salt solution contains at least one of sodium ions, magnesium ions and calcium ions, as well as sulfate ions and chloride ions, and the mass concentration of chloride ions in the salt solution is <0.5 g / L.

[0050] This application utilizes a salt solution containing sodium, magnesium, calcium, sulfate, and chloride ions, mixed with fly ash and an alkaline activator. The alkaline activator acts on the covalent bonds in the aluminosilicates of fly ash, dissociating the surface glassy structure and promoting the dissolution of alkaline oxides such as CaO and MgO. Simultaneously, the salt content in the salt solution inhibits the leaching of heavy metals from the fly ash, and the small amount of chloride ions in the salt solution can form complexes with heavy metals that are more easily captured by the solid phase. This synergistic effect effectively reduces the leaching rate of heavy metals and promotes mineralization reactions with carbon dioxide. The mineralized product formed by this application contains a dense carbonate coating layer, exhibiting improved volume stability compared to fly ash. It can be directly used in roadbed materials or concrete aggregates, effectively avoiding the strength degradation problem caused by water absorption and expansion in traditional building materials.

[0051] The salt solution of this application contains magnesium and calcium ions, which can synergistically cooperate with the calcium and magnesium ions dissolved in fly ash to promote the mineralization reaction with carbon dioxide, forming a dense carbonate-coated mineralized product. Simultaneously, the ions in the salt solution can also inhibit the leaching of heavy metals from fly ash, effectively reducing the migration of heavy metals in the mineralized product after mineralization. Furthermore, the salt solution of this application contains a small amount of chloride ions, which can combine with heavy metals to form complexes that are easily captured by the solid phase, further reducing the leaching of heavy metals. If the chloride ion content is relatively high, it may inhibit the mineralization reaction, preventing the formation of mineralized products with excellent mechanical properties. In addition, although sodium ions do not directly participate in the formation of mineralized products, they can regulate the ionic strength of the solution and the stability of the reaction system, effectively promoting the mineralization reaction.

[0052] In some embodiments, the mixing method of fly ash, salt solution, and alkali activator includes: mixing fly ash and salt solution, and then adding alkali activator. This application first mixes fly ash and salt solution evenly, and then adds alkali activator to adjust the pH of the mixture. This utilizes the alkaline oxides in fly ash to neutralize the acidity of the salt solution, reducing the loss of alkali activator.

[0053] In some embodiments, the pH of the mixture may be, for example, 9.5, 9.7, 9.9, 10.1, 10.3, 10.5, 10.7, 10.9, 11.1, 11.3, or 11.5. The pH of the mixture can be controlled by the amount of alkali activator added, which is 1% to 5% of the mass of fly ash, for example, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, or 5.0%.

[0054] It should be noted that alkali activators are mainly used to disrupt the stable structure of fly ash, promote the depolymerization of active components (such as calcium oxide and magnesium oxide) and the formation of cementitious products, thereby utilizing the mineralization and sequestration of carbon dioxide.

[0055] In some embodiments, the alkali activator includes at least one selected from sodium silicate, styrene-acrylic emulsion, sodium hydroxide, and potassium hydroxide. In some embodiments, an auxiliary agent is also added to the mixture. Optionally, the auxiliary agent includes styrene-acrylic emulsion. It is understood that the styrene-acrylic emulsion contains a copolymer formed by the emulsion copolymerization reaction of styrene and acrylate monomers, which may also be referred to as a styrene-acrylate copolymer. The mass concentration of the styrene-acrylate copolymer in the styrene-acrylic emulsion is 30% to 50%, for example, 30%, 35%, 40%, 45%, or 50%. The number average molecular weight of the styrene-acrylate copolymer is 5000 to 50000, for example, 5000, 10000, 20000, 30000, 40000, or 50000.

[0056] In some embodiments, the alkali activator is sodium silicate, and the auxiliary agent is styrene-acrylic emulsion. The styrene-acrylic emulsion and the alkali activator are mixed and then added together to the mixture. Optionally, the mass ratio of sodium silicate to styrene-acrylic emulsion is (2~5):1.

[0057] Sodium silicate and styrene-acrylic emulsion are used in combination for mineralization. Sodium silicate can promote the dissolution of silica and aluminum components in fly ash and participate in the mineralization reaction. Styrene-acrylic emulsion acts as a dispersant and film-forming agent, improving the dispersion uniformity of fly ash and the structural compactness of mineralization products. The synergistic effect improves the alkali activation efficiency and the strength of mineralization products.

[0058] In some embodiments, the salt solution contains magnesium ions at a mass concentration of 1.0 g / L to 1.5 g / L, for example, 1.0 g / L, 1.1 g / L, 1.2 g / L, 1.3 g / L, 1.4 g / L, or 1.5 g / L. The calcium ion mass concentration is 0.3 g / L to 0.5 g / L, for example, 0.30 g / L, 0.35 g / L, 0.40 g / L, 0.45 g / L, or 0.50 g / L. The sulfate ion mass concentration is 2.5 g / L to 3.0 g / L, for example, 2.5 g / L, 2.6 g / L, 2.7 g / L, 2.8 g / L, 2.9 g / L, or 3.0 g / L. The sodium ion concentration is 8 g / L to 11 g / L, for example, 8.0 g / L, 8.5 g / L, 9.0 g / L, 9.5 g / L, 10.0 g / L, 10.5 g / L, or 11.0 g / L. This application controls the ion concentration in the salt solution as described above, thereby effectively inhibiting the leaching of heavy metals from fly ash and promoting the mineralization reaction between fly ash and carbon dioxide. Calcium and magnesium ions can react with carbon dioxide to form carbonate precipitates, co-precipitating and encapsulating heavy metals. Sulfate ions can form low-solubility sulfates with heavy metal ions, effectively inhibiting heavy metal migration. Sodium ions can adjust the ionic strength of the solution, reducing the leaching rate of heavy metals. Furthermore, in a low chloride ion concentration environment, the formation of chloride complexes of heavy metals can be effectively avoided, thereby inhibiting the activation of heavy metals.

[0059] In some embodiments, the alkaline oxide includes at least one of calcium oxide, magnesium oxide, and iron oxide.

[0060] Optionally, the fly ash contains 5% to 25% calcium oxide by mass, for example, 5%, 10%, 15%, 20%, 25%, or 25%. Magnesium oxide contains 1% to 8% by mass, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%. Iron oxide contains 3% to 10% by mass, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. Iron oxide can serve as an auxiliary component in the mineralization reaction, providing nucleation sites and improving the compactness of the product structure.

[0061] Among them, the total mass percentage of calcium oxide and magnesium oxide in fly ash is ≥8%. Calcium oxide and magnesium oxide are the main active mineralizing components and the main source of reactants for carbon dioxide mineralization reaction.

[0062] In some embodiments, the molecular formula of the aluminosilicate is xAl2O3·ySiO2, where y:x = 1.8~6.5, for example, it can be 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0 or 6.5.

[0063] Optionally, the mass percentage of Al2O3 in the aluminosilicate of fly ash is 15% to 30%, for example, 15%, 20%, 25%, or 30%. The mass percentage of SiO2 in the aluminosilicate of fly ash is 35% to 55%, for example, 35%, 40%, 45%, 50%, or 55%.

[0064] It is understandable that fly ash may also contain impurities that do not participate in the mineralization reaction, and the mass percentage of impurities in fly ash is less than 5%. Among these impurities, at least one of sodium oxide and potassium oxide can be present.

[0065] In some embodiments, the mass ratio of fly ash to salt solution is 1:(2~5), for example, it can be 1:2.0, 1:2.5, 1:3.0, 1:3.5, 1:40, 1:4.5, or 1:5.0. The above-mentioned selection of the amount of fly ash and salt solution added ensures the dissolution of fly ash and promotes the mineralization reaction.

[0066] In some embodiments, the amount of carbon dioxide added is 1.1 to 1.3 times the theoretical mineralization amount, for example, it can be 1.10, 1.15, 1.20, 1.25, or 1.30 times. The theoretical mineralization amount refers to the amount of carbon dioxide required for mineralization into magnesium carbonate and calcium carbonate, calculated based on the calcium oxide and magnesium oxide content in the fly ash. For example, if the mass percentage of calcium oxide in the fly ash is 'a' and the mass percentage of magnesium oxide is 'b', then the theoretical mineralization amount is a × (44 / 56) + b × (44 / 40). This application selects the amount of carbon dioxide added as described above to ensure that the calcium and magnesium ions in the mixture fully react with the carbon dioxide for mineralization.

[0067] In some embodiments, the temperature for mineralization is 30°C to 50°C, for example, 30°C, 32°C, 34°C, 36°C, 38°C, 40°C, 42°C, 44°C, 46°C, 48°C or 50°C.

[0068] In some embodiments, the pressure for mineralization is 0.1 MPa to 0.4 MPa, for example, 0.10 MPa, 0.15 MPa, 0.20 MPa, 0.22 MPa, 0.24 MPa, 0.26 MPa, 0.28 MPa, 0.30 MPa, 0.32 MPa, 0.34 MPa, 0.36 MPa, 0.38 MPa, or 0.40 MPa. Optionally, the carbon dioxide addition rate can be controlled according to the reactor volume and pressure, for example, 3 L / min to 7 L / min. The solid-liquid ratio during mineralization is 1:(2~4), for example, 1:2.0, 1:2.5, 1:3.0, 1:3.5, or 1:4.0.

[0069] This application selects the temperature, pressure, and solid-liquid ratio for mineralization treatment as described above to regulate the carbonate formation rate during mineralization, thereby forming a dense carbonate coating layer and improving the mechanical strength of the material. If the temperature is relatively low, the carbon dioxide mass transfer rate may decrease, reducing mineralization efficiency. If the temperature is relatively high or the pressure is relatively low, the solubility of carbon dioxide may decrease, affecting the mineralization reaction.

[0070] In some embodiments, the mineralization treatment time is 2h to 6h, for example, it can be 2.0h, 2.5h, 3.0h, 3.5h, 4.0h, 4.5h, 5.0h, 5.5h or 6.0h.

[0071] Alternatively, a reaction vessel with a fluidized bed function can be used for mineralization treatment.

[0072] In some embodiments, the mineralization product contains calcium carbonate, magnesium carbonate, hydrated calcium silicate, and hydrated aluminosilicate gel. The formed mineralization product encapsulates and solidifies fly ash particles, and the gel phase fills the pores, thereby improving the material's mechanical strength, inhibiting heavy metal migration, exhibiting good volume stability, and effectively improving engineering application performance.

[0073] In some embodiments, the method for preparing the salt solution includes: mixing seawater and a tertiary amine dechlorinating agent, and then performing a dechlorination treatment to obtain the salt solution. It is understood that the tertiary amine dechlorinating agent can remove chloride ions from seawater through extraction, and after the dechlorination treatment is completed, the dechlorinated seawater can be separated from the tertiary amine dechlorinating agent.

[0074] This application utilizes a dechlorination process to obtain a salt solution from seawater. Seawater is rich in sodium, magnesium, and calcium ions, which can form a complex reaction pathway with active components such as calcium oxide and magnesium oxide in fly ash. For example, magnesium ions in seawater react with carbon dioxide to form more stable magnesium carbonate hydrate, while free calcium oxide in fly ash can generate calcite (CaCO3) through a gas-liquid-solid three-phase reaction. This dual reaction pathway significantly increases the carbon dioxide sequestration capacity per unit of fly ash. Furthermore, the alkaline components in fly ash can neutralize seawater acidification. Therefore, this application achieves carbon dioxide mineralization through the combined use of seawater and fly ash, simultaneously solving the problems of fly ash accumulation, seawater desalination, and carbon dioxide mineralization in coastal coal-fired power plants, thus realizing "waste treatment with waste."

[0075] Optionally, the tertiary amine dechlorinating agent includes at least one of tripropylamine, tributylamine, triethylamine, and trioctylamine. Optionally, the molar ratio of the tertiary amine dechlorinating agent to chloride ions in seawater is (1.0~1.5):1, for example, it can be 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, or 1.5:1.

[0076] In some embodiments, a diluent is added to the seawater during the dechlorination process. The addition of a diluent during seawater dechlorination in this application reduces the viscosity of the organic phase, improves mass transfer efficiency and phase separation performance, effectively enhances the dispersion stability of tertiary amine dechlorinating agents, and effectively improves the dechlorination efficiency of seawater.

[0077] Optionally, the diluent includes n-butanol. Optionally, the ratio of the amount of tertiary amine dechlorinating agent added to the amount of diluent added is (1~4):1, for example, it can be 1:1, 2:1, 3:1 or 4:1.

[0078] Exemplarily, a method for mineralizing carbon dioxide from fly ash as described above is provided, such as... Figure 2 As shown, it includes the following steps:

[0079] Seawater, tertiary amine dechlorinating agent, and diluent are mixed evenly and then subjected to dechlorination treatment. The dechlorinated seawater is then separated into a salt solution. The amount of tertiary amine dechlorinating agent added is in the molar ratio of chloride ions in the seawater (1.0~1.5):1, and the mass ratio of tertiary amine dechlorinating agent to diluent is (1~4):1.

[0080] The above-mentioned salt solution, alkali activator, and fly ash are mixed to obtain a mixed solution with a pH of 9.5-11.5. The mass ratio of fly ash to salt solution is 1:(2-5), and the amount of alkali activator added is 1%-5% of the mass of fly ash.

[0081] Carbon dioxide was introduced into the above mixture and mineralized at 30℃~50℃ and 0.1MPa~0.4MPa for 2h~6h to obtain mineralized products. The total amount of carbon dioxide added was 1.1 to 1.3 times the theoretical mineralization amount.

[0082] Optionally, the mineralized products are used after being filtered, washed and dried in sequence.

[0083] The embodiments of this application will be described in detail below with reference to examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this application, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0084] In the following examples and comparative examples, the fly ash composition by mass percentage is as follows: calcium oxide, 18%; magnesium oxide, 5%; silicon oxide, 45%; aluminum oxide, 20%; iron oxide, 6%; and impurities <5%. The theoretical mineralization of this fly ash is 0.195 kg CO2 / kg fly ash.

[0085] The mass concentrations of various ions in seawater are as follows: chloride ion, 18 g / L; sodium ion, 11 g / L; magnesium ion, 1.3 g / L; calcium ion, 0.4 g / L; sulfate ion, 2.7 g / L.

[0086] Example 1

[0087] 33.8 kg of tributylamine and 13.5 kg of n-butanol were added to 300 L of seawater. After thorough mixing, the seawater was stirred and extracted for 30 min to separate chloride ions. After settling and separation, the dechlorinated seawater was obtained as a salt solution. The salt solution contained chloride ions at a concentration of 0.4 g / L, sodium ions at 11 g / L, magnesium ions at 1.3 g / L, calcium ions at 0.4 g / L, and sulfate ions at 2.7 g / L.

[0088] After mixing the above 300L salt solution and 100kg fly ash evenly, add 3kg of sodium silicate solution with a mass concentration of 40% to obtain a mixed solution with a pH of 10.5.

[0089] Carbon dioxide was introduced into the above mixture and mineralized at 40°C and 0.3 MPa for 4 hours. After filtration, washing, and drying, the mineralized product was obtained. The total amount of carbon dioxide added was 1.2 times the theoretical mineralization amount, and the introduction rate was 5 L / min. Figure 3 and Figure 4As shown, the mineralized product forms a relatively dense mineralized structure with obvious interparticle cementation, reduced porosity, and the formation of more carbonate crystals, which is beneficial for reducing the leaching rate of heavy metals and improving the compressive strength of the mineralized product.

[0090] Example 2

[0091] The method of Example 1 is used to mineralize carbon dioxide using fly ash, except that the alkaline activator is replaced with sodium hydroxide.

[0092] Comparative Example 1

[0093] The method of Example 1 was used to mineralize carbon dioxide using fly ash, except that the salt solution was replaced with fresh water, and the concentration of sodium ions in the fresh water was 0.04 g / L, the concentration of calcium ions was 0.03 g / L, the concentration of magnesium ions was 0.01 g / L, and the concentration of sulfate ions was 0.04 g / L.

[0094] Comparative Example 2

[0095] The method of Example 1 is used to mineralize carbon dioxide using fly ash, the difference being that seawater that has not undergone dechlorination treatment is directly used as the salt solution.

[0096] The performance of the mineralized products formed in the above embodiments and comparative examples was tested, and the test methods included:

[0097] CO2 fixation rate: The content of carbonates (magnesium carbonate and calcium carbonate) in the mineralized products was determined by thermogravimetric analysis (TG), and the mass of carbon dioxide fixed in the mineralized products was calculated. The CO2 fixation rate was calculated according to the following formula: mass of carbon dioxide fixed in the mineralized products / (amount of fly ash added × theoretical mineralization amount).

[0098] Heavy metal leaching rate: The mass of heavy metals (such as Pb, Cd, and Cr) in the leachate after leaching mineralized products was determined using the acetic acid buffer solution method (HJ / T 300) for leaching toxicity of solid waste. Similarly, the mass of heavy metals in fly ash was tested using the same method. Heavy metal leaching rate = mass of heavy metals in the leachate / total mass of heavy metals in the fly ash. ICP-OES or ICP-MS can be used to assist in the determination of heavy metal content.

[0099] Compressive strength: The compressive strength of the mineralized products was tested according to GB / T 17671 Cement Mortar Strength Test Method.

[0100] The test results are shown in Table 1.

[0101] Table 1

[0102]

[0103] As can be seen from the table above:

[0104] The CO2 fixation rate of the mineralized product in Example 1 of this application is significantly higher than that in Comparative Example 1 and Comparative Example 2. Meanwhile, the heavy metal leaching rate is reduced by more than 50% compared to Comparative Example 2. Furthermore, it can be seen that the compressive strength of the mineralized product formed in Example 1 is significantly improved, meeting the requirements for engineering applications.

[0105] In summary, this application utilizes a salt solution containing sodium, magnesium, calcium, sulfate, and chloride ions, mixed with fly ash and an alkaline activator. The alkaline activator acts on the covalent bonds in the aluminosilicates of fly ash, dissociating the surface glassy structure and promoting the dissolution of alkaline oxides such as CaO and MgO. Simultaneously, the salt content in the salt solution inhibits the leaching of heavy metals from the fly ash, and the small amount of chloride ions in the salt solution can form complexes with heavy metals that are more easily captured by the solid phase. This synergistic effect effectively reduces the leaching rate of heavy metals and promotes mineralization reactions with carbon dioxide. The mineralized product formed in this application contains a dense carbonate coating layer, exhibiting improved volume stability compared to fly ash. It can be directly used in roadbed materials or concrete aggregates, effectively avoiding the strength degradation problem caused by water absorption and expansion in traditional building materials.

[0106] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0107] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A method for mineralizing carbon dioxide from fly ash, characterized in that, Includes the following steps: Fly ash, salt solution, and alkaline activator are mixed to prepare a mixture with a pH of 9.5-11.

5. Carbon dioxide is then introduced into the mixture to carry out a mineralization reaction and prepare a mineralized product. The fly ash contains aluminosilicates and alkaline oxides; The salt solution contains at least one of sodium ions, magnesium ions, and calcium ions, and also contains sulfate ions and chloride ions, wherein the mass concentration of chloride ions in the salt solution is <0.5 g / L.

2. The method for mineralizing carbon dioxide from fly ash as described in claim 1, characterized in that, The method satisfies at least one of the following conditions: (1) The pH of the mixture is controlled by the amount of alkaline activator added, wherein the amount of alkaline activator added is 1% to 5% of the mass of the fly ash; (2) The alkaline activator includes at least one of sodium silicate, sodium hydroxide, and potassium hydroxide; (3) An auxiliary agent is also added to the mixture, including styrene-acrylic emulsion.

3. The method for mineralizing carbon dioxide from fly ash as described in claim 1, characterized in that, The method satisfies at least one of the following conditions: (1) The salt solution contains magnesium ions at a mass concentration of 1.0 g / L to 1.5 g / L; (2) The salt solution contains calcium ions at a mass concentration of 0.3 g / L to 0.5 g / L; (3) The salt solution contains sulfate ions at a mass concentration of 2.5 g / L to 3.0 g / L. (4) The mass concentration of sodium ions in the salt solution is 8 g / L to 11 g / L.

4. The method for mineralizing carbon dioxide from fly ash as described in claim 1, characterized in that, The basic oxide satisfies at least one of the following conditions: (1) The alkaline oxide includes calcium oxide, and the fly ash contains 5% to 25% calcium oxide by mass. (2) The alkaline oxide includes magnesium oxide, and the fly ash contains magnesium oxide at a mass ratio of 1% to 8%; (3) The alkaline oxide includes iron oxide, and the fly ash contains 3% to 10% of the iron oxide by mass. (4) The total mass percentage of calcium oxide and magnesium oxide in the fly ash is ≥8%.

5. The method for mineralizing carbon dioxide from fly ash as described in claim 1, characterized in that, The molecular formula of the aluminosilicate is xAl2O3·ySiO2, where y:x = 1.8~6.

5.

6. The method for mineralizing carbon dioxide from fly ash as described in claim 1, characterized in that, The method satisfies at least one of the following conditions: (1) The mass ratio of the fly ash to the salt solution is 1:(2~5); (2) The amount of carbon dioxide added is 1.1 to 1.3 times the theoretical mineralization amount; (3) The temperature for carrying out the mineralization reaction is 30℃~50℃, the pressure is 0.1MPa~0.4MPa, and the time is 2h~6h; (4) The mineralized products contain calcium carbonate, magnesium carbonate, hydrated calcium silicate and hydrated aluminosilicate gel.

7. The method for mineralizing carbon dioxide from fly ash as described in claim 1, characterized in that, Following the mineralization reaction, the method further includes: sequentially filtering, washing, and drying the mixture to obtain the mineralized product.

8. The method for mineralizing carbon dioxide from fly ash as described in any one of claims 1-7, characterized in that, The method for preparing the salt solution includes: mixing seawater and a tertiary amine dechlorinating agent, and then performing dechlorination treatment to obtain the salt solution.

9. The method for mineralizing carbon dioxide from fly ash as described in claim 8, characterized in that, The tertiary amine dechlorinating agent satisfies at least one of the following conditions: (1) The tertiary amine dechlorinating agent includes at least one of tripropylamine, tributylamine, triethylamine and trioctylamine; (2) The molar ratio of the tertiary amine dechlorinating agent to the chloride ions in the seawater is (1.0~1.5):

1.

10. The method for mineralizing carbon dioxide from fly ash as described in claim 8, characterized in that, During the dechlorination process, a diluent is also added to the seawater; Optionally, the diluent includes at least one of n-butanol, isooctanol, and kerosene; Optionally, the ratio of the amount of the tertiary amine dechlorinating agent added to the amount of the diluent added is (1~4):1.

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