Modified biochar and method for preparing same, carbon sequestering cementitious material

Abstract

The application relates to the technical field of new materials, in particular to modified biochar and a preparation method thereof and a carbon fixation cement material. The preparation method comprises the following steps: adding a salt solution to solid waste for extraction treatment to obtain an extraction liquid; adding a soluble sulfide to the extraction liquid for precipitation treatment to obtain heavy metal precipitates and a modified solution; and modifying the biochar with the modified solution to obtain modified biochar. The modified solution is rich in various active ions, which can be combined with or react with functional groups rich in the biochar, enrich the active sites on the surface of the biochar and improve the pore structure, so that the prepared modified biochar can further improve the performance of capturing and fixing CO2, further improve the interaction with the cement material, enhance the compactness and the bending and compressive properties, and improve the durability and service life. The preparation method is simple in process, low in cost and difficult to cause secondary pollution. The cement material and the modified biochar can also be used to prepare a carbon fixation cement material.

Description

Technical Field

[0001] This application relates to the field of new carbon fixation materials technology, and in particular to modified biochar and its preparation method, and carbon fixation cement materials. Background Technology

[0002] Cement is a widely used basic material in construction engineering, and its production process involves large amounts of CO2 emissions, posing a significant challenge to global climate change and environmental protection. To reduce the carbon footprint of cement and improve its environmental friendliness, researchers have explored the addition of biochar. Biochar, due to its high specific surface area and abundant pore structure, shows great potential for application in environmental remediation, soil improvement, and carbon sequestration. However, unmodified biochar has limitations in adsorption capacity and stability, necessitating modification to improve its physicochemical properties and enhance its application effectiveness.

[0003] Existing biochar modification methods mainly rely on the treatment of various chemical reagents. Although these methods can improve the adsorption performance of biochar to some extent, the modification effect is not ideal. Moreover, these methods have problems such as high cost, complex process and large amount of chemical reagents used, which can easily cause secondary pollution and are not conducive to large-scale promotion and application.

[0004] At the same time, a large amount of solid waste is generated in industrial production and daily life. In addition to various mineral salts, industrial solid waste often contains a variety of heavy metal ions, such as lead, mercury, cobalt, and cadmium. If not treated, it will pollute the environment or harm the human body. Existing technologies often lack effective treatment methods and make it difficult to recycle and utilize these industrial solid wastes. Summary of the Invention

[0005] The purpose of this application is to provide modified biochar and its preparation method, aiming to solve the problems of high cost, complex process and easy pollution caused by the use of multiple chemical reagents in the existing technology for biochar modification.

[0006] Another objective of this application is to provide carbon-fixing cement materials, aiming to solve the problem that the mechanical properties and carbon fixation properties of existing carbon-fixing cement materials are still not ideal.

[0007] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0008] In a first aspect, this application provides a method for preparing modified biochar, comprising the following steps:

[0009] A salt solution was added to the solid waste for extraction to obtain an extract.

[0010] A soluble sulfide was added to the extract for precipitation treatment, resulting in a heavy metal precipitate and a modified solution.

[0011] The modified biochar was obtained by modifying the biochar with the modified solution.

[0012] The salt solution includes at least one of ammonium chloride solution, potassium chloride solution, and sodium nitrate solution.

[0013] The preparation method described in this application first treats solid waste with a specific salt solution and soluble sulfides. The resulting modified solution is rich in various active ions, which combine or react with the functional groups abundant in biochar. This enriches the active sites on the biochar surface and improves the pore structure, enabling the modified biochar to further enhance its CO2 capture and fixation performance. Simultaneously, it further enhances the interaction with cement materials, increasing density, flexural strength, compressive strength, durability, and service life. The preparation method only requires common solid waste, salt solutions, and soluble sulfides for treatment, eliminating the need for large quantities of expensive chemical reagents. The process is simplified, cost-effective, and less prone to secondary pollution.

[0014] Secondly, this application provides a modified biochar, which is the modified biochar prepared by the method described in the above application.

[0015] The modified biochar of this application is prepared by the method described above. Compared with ordinary biochar, the modified biochar has an improved pore structure and a richer number of active sites on its surface. Therefore, the modified biochar of this application not only improves the performance of capturing CO2, but also enhances its interaction with cement materials, thereby increasing density, flexural strength, compressive strength, durability, and service life.

[0016] Thirdly, this application provides a carbon-fixing cement material, including cement material, and also includes modified biochar prepared by the preparation method described above or modified biochar described above.

[0017] The modified biochar in this carbon-fixing cement material improves the pore structure and enriches the active sites, thus endowing the material with carbon-fixing properties, promoting green carbon reduction, and enhancing its interaction with cement materials. This improves density, flexural strength, compressive strength, durability, and service life. Therefore, this carbon-fixing cement material combines green carbon fixation with high strength, offering significant environmental, economic, and social benefits. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating the preparation method of modified biochar according to embodiments of this application and its application in cement-based materials;

[0020] Figure 2 This is a schematic diagram of the 7-day compressive strength test results of cement components prepared by biochar in Example A9 and Comparative Example A1 of this application, as well as the blank control group.

[0021] Figure 3 This is a schematic diagram of the 28-day compressive strength test results of cement components prepared by biochar in Example A9 and Comparative Example A1 of this application, as well as the blank control group.

[0022] Figure 4 This is a schematic diagram of the 7-day flexural strength test results of cement parts prepared by biochar in Example A9 and Comparative Example A1 of this application, as well as the blank control group.

[0023] Figure 5 This is a schematic diagram of the 28-day flexural strength test results of cement parts prepared by biochar in Example A9 and Comparative Example A1 of this application, as well as the blank control group.

[0024] Figure 6 This is a schematic diagram showing the thermogravimetric analysis results of cement parts prepared from biochar in Example A9 and Comparative Example A1 of this application, as well as the blank control group. Detailed Implementation

[0025] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0026] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0027] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0028] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0029] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0030] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as μg, mg, g, or kg.

[0031] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0032] Unless otherwise specified, all solid-liquid ratios in this application refer to solid-liquid mass ratios.

[0033] The first aspect of this application provides a method for preparing modified biochar, comprising the following steps S10 to S30:

[0034] S10. Add salt solution to solid waste for extraction treatment to obtain extract;

[0035] S20. Add soluble sulfide to the extract for precipitation treatment to obtain heavy metal precipitate and modified solution;

[0036] S30. Modify the biochar with the modified solution to obtain modified biochar;

[0037] The salt solution includes at least one of ammonium chloride solution, potassium chloride solution, and sodium nitrate solution.

[0038] The preparation method of this application first treats solid waste with a specific salt solution and soluble sulfides, resulting in a modified solution rich in various active ions. When biochar is modified using this modified solution, these active ions combine or react with the functional groups abundant in the biochar, enriching the active sites on the biochar surface and improving the pore structure. This allows the modified biochar to further enhance its CO2 capture and fixation performance, while also improving its interaction with cement materials, increasing density, flexural strength, compressive strength, durability, and service life. In summary, compared to existing biochar modification methods, the modified biochar prepared by the method of this application further improves carbon fixation performance and mechanical strength when compounded with cement materials. Moreover, the preparation method only requires common solid waste, salt solutions, and soluble sulfides for treatment, eliminating the need for large quantities of expensive chemical reagents, simplifying the process, reducing costs, and minimizing secondary pollution. The preparation method is controllable, and the resulting modified biochar is stable.

[0039] As an embodiment of this application, such as Figure 1 As shown:

[0040]

Step S10

[0041] Step S10 involves first extracting solid waste with a salt solution to obtain an extract. The solid waste can be industrial or domestic. Industrial solid waste, in particular, often contains various heavy metal ions, such as lead, mercury, cobalt, and cadmium, in addition to multiple mineral salts. If left untreated, these heavy metal ions can pollute the environment or harm human health. Existing technologies often lack effective treatment methods, making it difficult to recycle and utilize this industrial solid waste. Therefore, first extracting with a salt solution can dissolve these heavy metal ions and some mineral components in the solid waste into the extract. Subsequently, these heavy metal ions can be removed to obtain the desired modified solution, thus not only removing heavy metal ions but also fully utilizing the solid waste.

[0042] In some embodiments, the solid waste includes at least one of phosphogypsum (industrial waste from the production of phosphate fertilizer and phosphoric acid), blast furnace slag, recycled concrete, fly ash, and tailings, with phosphogypsum being an optional component. These solid wastes have high levels of heavy metal ions, making them difficult to utilize effectively as waste, and they also contain abundant silicate minerals, which can be dissolved and extracted using salt solutions.

[0043] In this embodiment, the solid waste can be pre-treated before extraction and processing. It undergoes physical sieving and washing to remove large particles and impurities, facilitating subsequent processing. Specifically, a sieve can be used to remove large particles from the solid waste, ensuring uniform particle size. Then, the sieved solid waste is washed to remove surface dust and soluble impurities, ensuring cleanliness. During washing, the water flow is kept uniform to prevent solid waste accumulation from affecting the washing effect.

[0044] In some embodiments, the salt solution may be ammonium chloride solution, potassium chloride solution, or sodium nitrate solution. Through ion exchange dissolution, active ions and heavy metal ions in the solid waste are released. In some embodiments, the concentration of the salt solution is 0.5 mol / L to 3 mol / L, and may include, but is not limited to, any concentration or a range between two of 0.5 mol / L, 1 mol / L, 2 mol / L, and 3 mol / L. When these types and concentrations of salt solutions are used to extract and treat the aforementioned solid waste, the salt solution can dissolve the silicate and other mineral salt components in the solid waste, extracting heavy metal ions and desired active ions such as calcium ions, silicate ions, and sulfate ions into the extractant. Furthermore, the treatment process is environmentally friendly.

[0045] In some embodiments, during the extraction process, the solid-liquid mass ratio of solid waste to salt solution can be 1:(2-5), including but not limited to any ratio of 1:2, 1:3, 1:4, 1:5 or any two of these ratios, to ensure the extraction effect and facilitate the full dissolution and extraction of heavy metal ions and desired active ions from the solid waste.

[0046] The extraction process may include the following steps: first, the solid waste and salt solution are mixed and heated to 30–90°C, followed by solid-liquid separation to obtain the extract. The first mixing process can be performed by stirring for 1 hour, combined with the aforementioned heating temperature, to ensure sufficient contact and reaction between the solid waste and the salt solution, facilitating the complete dissolution and extraction of heavy metal ions and desired active ions from the solid waste. The solid-liquid separation can be performed using a centrifuge at 3000–5000 rpm for 20–30 minutes. After centrifugation, the supernatant is collected to obtain the extract. The heavy metal ion content in the centrifuged solid residue is extremely low, allowing for further processing or harmless disposal, such as use as aggregate in concrete, road filler, or soil conditioner. Therefore, the preparation method described in this application not only produces modified biochar but also transforms difficult-to-utilize solid waste, especially industrial solid waste, into valuable resources through biochar modification, thus achieving significant environmental, economic, and social benefits.

[0047] The extract contains heavy metal ions, as well as various extracted active ions, such as calcium ions, silicate ions, and sulfate ions. The cations can include calcium ions, magnesium ions, aluminum ions, and iron ions, while the anions can include silicate ions, sulfate ions, phosphate ions, sulfide ions, and carbonate ions. Specifically, the extracts from the above-mentioned solid wastes, in addition to heavy metal ions and ions introduced by the salt solution, contain calcium ions, sulfate ions, and small amounts of magnesium ions and phosphate ions in the phosphogypsum extract; calcium ions, magnesium ions, aluminum ions, silicate ions, and sulfate ions in the blast furnace slag extract; calcium ions, carbonate ions, and small amounts of silicate ions and aluminum ions in the recycled concrete extract; calcium ions, aluminum ions, silicate ions, and small amounts of magnesium ions and iron ions in the fly ash extract; and calcium ions, iron ions, sulfate ions, and small amounts of silicate ions and aluminum ions in the tailings extract.

[0048]

Step S20

[0049] Step S20 is the step of removing heavy metal ions from the extract to obtain a modified solution. The extract obtained in step S10 still contains heavy metal ions such as lead, mercury, cobalt, and cadmium. Therefore, soluble sulfides are added to the extract for precipitation treatment to remove the heavy metal ions as precipitates. In some embodiments, the soluble sulfides include at least one of sodium sulfide and potassium sulfide. After these soluble sulfides are added to the extract, their sulfide ions react with the heavy metal ions to form insoluble heavy metal sulfides, which then precipitate. For example, lead ions react with sulfide ions to form insoluble lead sulfide precipitate.

[0050] In the precipitation process, soluble sulfides can be gradually added to the extract to avoid excessively high local sulfide ion concentrations. Alternatively, the soluble sulfide can be prepared into a solution with a concentration of 0.1 mol / L to 0.5 mol / L and then gradually added to the extract. pH control is also necessary during the process. In some embodiments, the pH of the mixed solution formed by the extract and soluble sulfides during precipitation is 7–9, including but not limited to any value or any two of 7, 7.5, 8, 8.5, and 9. Real-time monitoring of the pH is required during precipitation to prevent it from becoming too high or too low, ensuring that sulfide ions and heavy metal ions precipitate together, removing as many heavy metal ions as possible, and minimizing the formation of precipitates between sulfide ions and desired active ions, thus reducing the loss of active ions.

[0051] After precipitation, solid-liquid separation is performed. This can be done by filtration using filter paper or filter cloth to remove the precipitate, which can then be used in fields such as heavy metal recovery. The supernatant obtained after filtration is the modified solution, whose heavy metal content meets environmental standards and is also rich in various active ions. Figure 1As shown, if the heavy metal content still does not meet the requirements after testing, the above precipitation treatment can be repeated. In some embodiments, the modified solution contains at least one cation selected from calcium, magnesium, aluminum, and iron ions, with the first three cations being the most prevalent. In some embodiments, the modified solution contains at least one anion selected from silicate, sulfate, phosphate, sulfide, and carbonate ions, with the first three anions being the most prevalent. These active ions are beneficial for subsequent modification of biochar, improving the pore structure of biochar, increasing surface active sites, and enhancing the modification effect.

[0052]

Step S30

[0053] Step S30 is a modification process for biochar. Biochar can be prepared from biomass raw materials via pyrolysis. Biomass raw materials can include crop straw, fruit shells, etc. First, the biomass raw materials are crushed and dried to reduce moisture content and remove impurities. Then, they are pyrolyzed and carbonized under anaerobic conditions at a temperature controlled between 400 and 600°C for 2 to 4 hours to obtain biochar. Biochar has a porous structure and contains various functional groups, especially on its surface. In some embodiments, the biochar contains at least one of the following groups: carboxyl, carbonyl, hydroxyl, and amino groups. These functional groups in the biochar will undergo a series of reactions with the active ions in the modification solution, improving the pore structure of the biochar and increasing the surface active sites.

[0054] In some embodiments, the modification treatment includes a second mixing and reaction of biochar and a modification solution at a temperature of 25–60°C. The temperature can be, but is not limited to, any value or a range between two of 25°C, 40°C, 50°C, and 60°C, to promote the reaction. The second mixing treatment may involve immersing the biochar in the modification solution for up to 12 hours to allow the active ions in the modification solution to fully react with the biochar, resulting in modified biochar. The amount of biochar used can be at a mass ratio of 1:1 to the solid waste in step S10. The solid-liquid mass ratio of biochar to the modification solution can be 1:2.

[0055] Specifically, the carboxyl and carbonyl groups in biochar can form coordination bonds with cations such as calcium, magnesium, and aluminum ions in the modification solution, thereby enhancing the adsorption capacity of the biochar. The hydroxyl and amino groups in biochar can react with active ions through hydrogen bonds or ionic bonds, increasing the specific surface activity of the biochar. Silicate and sulfate ions in the modification solution can react with the hydroxyl or carboxyl groups on the biochar surface to form stable silicon-oxygen bonds or sulfur-oxygen bonds, increasing the surface area and active sites of the biochar.

[0056] After modification, the solid components are collected by solid-liquid separation and vacuum dried at a temperature of 60–80°C for 24–48 hours to remove moisture and stabilize the modification effect, thus obtaining modified biochar.

[0057] Therefore, the modified biochar prepared by the method in this application improves the pore structure, enriches the surface active sites, and enhances the carbon fixation performance for CO2 adsorption and the mechanical properties of its interaction with cement materials. The preparation method also fully recycles and utilizes solid waste resources while removing heavy metal ions, possessing high economic and environmental value. Furthermore, the preparation method only requires common solid waste, salt solutions, and soluble sulfides for treatment, eliminating the need for large quantities of expensive chemical reagents, simplifying the process, reducing costs, and minimizing secondary pollution. The preparation process is controllable, and the resulting modified biochar is stable.

[0058] The second aspect of this application provides a modified biochar, which is the modified biochar prepared by the preparation method described in the above-described application embodiments.

[0059] The modified biochar in this application embodiment is prepared by the method described in the previous embodiment. Compared with ordinary biochar, the modified biochar has an improved pore structure and a richer number of active sites on its surface. Therefore, the modified biochar in this application embodiment not only improves the performance of capturing CO2, but also enhances the interaction with cement materials, thereby increasing density, flexural strength, compressive strength, durability, and service life.

[0060] Testing revealed that in some embodiments, the specific surface area of ​​the modified biochar was 240–320 m². 2 / g; pore volume is 0.025~0.065cm³ 3 / g; average pore size is 13.5–18.5 nm.

[0061] The third aspect of this application provides a carbon-fixing cement material, including cement material, and also includes modified biochar prepared by the preparation method of the above-described application embodiments or modified biochar as described in the above-described application embodiments.

[0062] The modified biochar in the carbon-fixing cement material of this application improves the pore structure and enriches the active sites, thus endowing the carbon-fixing cement material with carbon-fixing properties, achieving green carbon reduction, and enhancing its interaction with cement materials, thereby increasing density, flexural strength, compressive strength, durability, and service life. Therefore, the carbon-fixing cement material of this application combines green carbon fixation with high strength, exhibiting significant environmental, economic, and social benefits.

[0063] In some embodiments, the mass ratio of cementitious material to modified biochar is (25–100):1, which may include, but is not limited to, any ratio or any two of 25:1, 50:1, 75:1, and 100:1. Furthermore, the carbon-fixing cementitious material may also include aggregates, auxiliary cementitious materials, water-reducing agents, etc., mixed in a reasonable proportion, with a water-cement ratio of (0.3–0.5):1, cast into shape, and cured in a standard curing room for 28 days to ensure its strength and stability.

[0064] The following description is based on specific embodiments.

[0065] Example A1

[0066] This embodiment provides modified biochar and its preparation method, the preparation method including the following steps:

[0067] S1. Perform extraction processing:

[0068] The phosphogypsum was sieved through a 50-mesh (0.3 mm) sieve. The fine phosphogypsum that passed through the sieve was washed with water to remove surface dust and soluble impurities, thus obtaining pretreated phosphogypsum.

[0069] Prepare a 0.5 mol / L ammonium chloride solution. Mix the pretreated phosphogypsum and ammonium chloride solution at a solid-liquid ratio of 1:2 and heat to 30°C. Maintain this temperature and stir for 1 hour. Centrifuge the mixture at 3000 rpm for 20 minutes. Collect the supernatant after centrifugation to obtain the extract. The solid residue can be used as aggregate.

[0070] S2. Perform precipitation treatment:

[0071] Prepare a 0.3 mol / L sodium sulfide solution and gradually add it to the extract. Monitor the pH of the mixed solution throughout the process to ensure that the pH is between 7 and 9, so that the heavy metal ions form insoluble sulfide precipitates. Stop adding the solution when the final pH is 7. Then filter the solution with filter paper to remove the precipitate and keep the supernatant as the modification solution.

[0072] S3. Perform modification treatment:

[0073] After the straw is crushed and dried, it is pyrolyzed and carbonized at 500℃ under anaerobic conditions for 3 hours. After cooling, biochar is obtained.

[0074] Biochar was soaked in a modified solution with a solid-liquid mass ratio of 1:2. The solution temperature was maintained at 30°C during the process. After soaking for 24 hours, the solution was filtered, and the filter residue was collected and vacuum dried at 60°C for 12 hours to obtain modified biochar.

[0075] Example A2

[0076] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the solid-liquid ratio in step S1 is changed from 1:2 to 1:3, and the temperature is changed from 30℃ to 50℃. All other aspects are the same.

[0077] Example A3

[0078] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the solid-liquid ratio in step S1 is changed from 1:2 to 1:4, and the temperature is changed from 30℃ to 70℃. All other aspects are the same.

[0079] Example A4

[0080] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the solid-liquid ratio in step S1 is changed from 1:2 to 1:5, and the temperature is changed from 30℃ to 90℃. All other aspects are the same.

[0081] Example A5

[0082] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the concentration of ammonium chloride solution is changed from 0.5 mol / L to 1 mol / L, and the heating temperature is changed from 30℃ to 50℃. All other aspects are the same.

[0083] Example A6

[0084] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the concentration of ammonium chloride solution in step S1 is changed from 0.5 mol / L to 1 mol / L, the solid-liquid ratio is changed from 1:2 to 1:3, and the heating temperature is changed from 30℃ to 70℃. All other aspects are the same.

[0085] Example A7

[0086] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the concentration of ammonium chloride solution in step S1 is changed from 0.5 mol / L to 1 mol / L, the solid-liquid ratio is changed from 1:2 to 1:4, and the heating temperature is changed from 30℃ to 90℃. All other aspects are the same.

[0087] Example A8

[0088] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the concentration of ammonium chloride solution in step S1 is changed from 0.5 mol / L to 1 mol / L, and the solid-liquid ratio is changed from 1:2 to 1:5. All other aspects are the same.

[0089] Example A9

[0090] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the concentration of ammonium chloride solution in step S1 is changed from 0.5 mol / L to 2 mol / L, and the heating temperature is changed from 30℃ to 70℃. All other aspects are the same.

[0091] Example A10

[0092] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the concentration of ammonium chloride solution in step S1 is changed from 0.5 mol / L to 2 mol / L, the solid-liquid ratio is changed from 1:2 to 1:3, and the heating temperature is changed from 30℃ to 90℃. All other aspects are the same.

[0093] Example A11

[0094] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the concentration of ammonium chloride solution in step S1 is changed from 0.5 mol / L to 2 mol / L, and the solid-liquid ratio is changed from 1:2 to 1:4. All other aspects are the same.

[0095] Example A12

[0096] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the concentration of ammonium chloride solution in step S1 is changed from 0.5 mol / L to 2 mol / L, the solid-liquid ratio is changed from 1:2 to 1:5, and the heating temperature is changed from 30℃ to 50℃. All other aspects are the same.

[0097] Example A13

[0098] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the concentration of ammonium chloride solution in step S1 is changed from 0.5 mol / L to 3 mol / L, and the heating temperature is changed from 30℃ to 90℃. All other aspects are the same.

[0099] Example A14

[0100] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the concentration of ammonium chloride solution in step S1 is changed from 0.5 mol / L to 3 mol / L, and the solid-liquid ratio is changed from 1:2 to 1:3. All other aspects are the same.

[0101] Example A15

[0102] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the concentration of ammonium chloride solution in step S1 is changed from 0.5 mol / L to 3 mol / L, the solid-liquid ratio is changed from 1:2 to 1:4, and the heating temperature is changed from 30℃ to 50℃. All other aspects are the same.

[0103] Example A16

[0104] This embodiment provides modified biochar and its preparation method. The only difference from Example A1 is that the concentration of ammonium chloride solution in step S1 is changed from 0.5 mol / L to 3 mol / L, the solid-liquid ratio is changed from 1:2 to 1:5, and the heating temperature is changed from 30℃ to 70℃. All other aspects are the same.

[0105] Example A17

[0106] This embodiment provides modified biochar and its preparation method. The only difference from Example A9 is that the ammonium chloride solution in step S1 is replaced with potassium chloride solution. All other aspects are the same.

[0107] Example A18

[0108] This embodiment provides modified biochar and its preparation method. The only difference from Example A9 is that the ammonium chloride solution in step S1 is replaced with sodium nitrate solution. All other aspects are the same.

[0109] Comparative Example A1

[0110] This comparative example provides biochar, and the preparation method includes: using the biochar obtained in step S3 of Example A1 as the biochar of this comparative example, that is, conventional biochar.

[0111] Comparative Example A2

[0112] This comparative example provides modified biochar, the preparation method of which includes: skipping steps S1 and S2 of Example A9, and directly using the ammonium chloride solution in step S1 as the modification solution in step S3, directly soaking the biochar in the ammonium chloride solution, and the rest being the same as step S3 of Example A1, to obtain modified biochar.

[0113] Comparative Example A3

[0114] This comparative example provides modified biochar, prepared by means of: replacing the modified solution in step S3 of Example A1 with a calcium nitrate solution at a concentration of 2 mol / L, while maintaining the same procedure as step S3 of Example A1, to obtain calcium nitrate modified biochar. The differences between the above examples are shown in Table 1 below:

[0115] Table 1

[0116] Case <![CDATA[Concentration of NH4Cl solution (mol / L)]]> solid-liquid ratio Stirring temperature (°C) Example A1 0.5 1：2 30 Example A2 0.5 1：3 50 Example A3 0.5 1：4 70 Example A4 0.5 1：5 90 Example A5 1 1：2 50 Example A6 1 1：3 70 Example A7 1 1：4 90 Example A8 1 1：5 30 Example A9 2 1：2 70 Example A10 2 1：3 90 Example A11 2 1：4 30 Example A12 2 1：5 50 Example A13 3 1：2 90 Example A14 3 1：3 30 Example A15 3 1：4 50 Example A16 3 1：5 70 Example A17 2(KCL) 1：2 70 Example A18 <![CDATA[2(NaNO3)]]> 1：2 70 Comparative Example A1 Untreated biochar Comparative Example A2 <![CDATA[2 (Biochar treated directly with NH4Cl)]]> 1：2 70 Comparative Example A3 <![CDATA[2 (Direct treatment of biochar with Ca(NO3)2)]]> 1：2 30

[0117] Biochar performance comparison

[0118] 1.1 Morphological Analysis

[0119] The samples from Examples A1 to A18 and Comparative Examples A1 to A3 were analyzed by scanning electron microscopy to obtain SEM images. Compared with the biochar of the comparative examples, the modified solution obtained after extraction and further modification of the biochar had a rougher surface, which is beneficial to increase the specific surface area and pore volume, enrich the pore structure, and improve the active sites.

[0120] 1.2. Specific surface area, pore volume, and pore diameter testing

[0121] Ten g of samples from Examples A1 to A16 (extracted with ammonium chloride solution and further prepared into biochar) and Comparative Examples A1 to A3 were taken and subjected to BET testing using an ASAP 2460 multi-station fully automated specific surface area and pore size analyzer. The specific surface area and other data were measured and recorded in Table 2 below. Table 2 shows that the biochar modified by this method has increased specific surface area and pore volume compared to unmodified biochar, and the average pore size is also improved, resulting in a richer pore structure.

[0122] Table 2

[0123] Case <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Average pore size (nm) Example A1 248.9367 0.027625 18.2135 Example A2 262.8647 0.036398 17.0156 Example A3 271.2543 0.036399 16.8919 Example A4 259.8764 0.032169 17.3926 Example A5 272.6573 0.038158 16.7012 Example A6 287.5671 0.050271 15.8923 Example A7 274.6918 0.043225 16.4293 Example A8 261.3512 0.033624 17.8589 Example A9 314.8561 0.064983 13.9051 Example A10 310.6475 0.058581 14.3157 Example A11 289.3238 0.054392 14.9672 Example A12 309.3266 0.061821 14.2534 Example A13 291.6354 0.053643 15.0347 Example A14 283.3242 0.050302 14.6249 Example A15 297.5319 0.057527 13.7228 Example A16 301.6482 0.061268 13.5682 Comparative Example A1 227.3126 0.025898 20.4154 Comparative Example A2 263.3156 0.03764 16.8391 Comparative Example A3 271.0489 0.04286 15.9652

[0124] 1.3 Heavy metal ion content in the solution before and after step S2 treatment

[0125] ICP-MS was used to determine the heavy metal content in the extract and modified solution before and after the S2 treatment in Example A9. This method allows for a rapid and effective assessment of the potential risks of heavy metals in the modified solution, providing a basis for its application in cement-based materials. Standard values ​​are referenced to standard (GB30760-2014).

[0126] Table 3

[0127]

[0128]

[0129] Examples of carbon-fixing cement materials:

[0130] The samples provided in Examples A1 to A18 and Comparative Examples A1 to A3 were respectively mixed with cement to prepare carbon-fixing cement materials, and other components were added and mixed in the following mass ratios:

[0131] 100 parts of PO52.5 cement;

[0132] 1-4 parts of modified biochar;

[0133] 40 parts water;

[0134] Then, the concrete is poured into shape, cured in a standard curing room for 1 day, and then demolded. It is then placed in a carbonization curing box with a CO2 concentration of 20%, a temperature of 20°C, and a humidity of 70% for 7 or 28 days to obtain cement components.

[0135] In this case, the modified biochar of Example A1 was used to prepare the cement component of Example B1, the modified biochar of Example A2 was used to prepare the cement component of Example B2, and so on, until the modified biochar of Comparative Example A3 was used to prepare the cement component of Comparative Example B3.

[0136] Relevant performance tests and results analysis

[0137] Performance tests were conducted on cement specimens from Examples B1 to B18 and Comparative Examples B1 to B3. The cement specimens were 40cm×40cm×40cm compressive strength test blocks and 40cm×40cm×160cm flexural strength test blocks.

[0138] To further investigate the effect of biochar content on performance, four test samples were provided for each example or comparative example, with biochar content of 1, 2, 3, and 4 parts respectively, and the test results of the examples or comparative examples were tested respectively. Among them, the modified biochar content of 1 to 4 parts obtained in Example A9 was used to prepare cement parts of Examples C1-C4, and the biochar content of 1 to 4 parts obtained in Comparative Example A1 was used to prepare cement parts of Comparative Examples D1-D4, respectively. The cement part E1 obtained without adding biochar was used as a blank group.

[0139] 1. Carbon fixation performance test

[0140] Fragments of cement test blocks that had been carbonized and cured for 7 days were ground into powder. The powder was then soaked in isopropanol for 15 minutes to prevent further hydration. The powder sample was then filtered through a 300-mesh sieve and dried in a vacuum oven for 24 hours. Next, a thermogravimetric analyzer was used to heat the sample to 1000 degrees Celsius under nitrogen atmosphere at a heating rate of 10 degrees Celsius per minute. The heat loss of different substances in the sample was measured. The thermogravimetric analysis results are shown in the figure below. Figure 6 As shown. The test method yielded test results, which are recorded in Table 4 below. The carbon fixation performance, based on the DTG curve obtained from thermogravimetric analysis, indicates that calcium carbonate decomposes between 430°C and 830°C. Therefore, the carbon fixation performance = (M... 430 -M 830 )÷M 1000 ×100%.

[0141] M 430 M 830 M represents the percentage of sample mass at its respective heating temperature. 1000 This represents the percentage of the remaining sample mass after heating to 1000°C.

[0142] 2. Compressive strength and flexural strength tests

[0143] The compression testing machine was controlled by a microcomputer. The test conditions were as follows: compression test block 40cm×40cm×40cm, loading rate 2.4kN / s; flexural test block 40cm×40cm×160cm, loading rate 50N / s. The test results were obtained and recorded in Table 4 below.

[0144] Among them, the 7-day compressive strength test results are as follows: Figure 2 As shown, the 28-day compressive strength test results are as follows: Figure 3 As shown, the 7-day flexural strength test is as follows: Figure 4 As shown, the 28-day flexural strength test is as follows: Figure 5 As shown in the figure, the modified biochar is the modified biochar of Example A9, the ordinary biochar is the biochar of Comparative Example A1, and 0% is the control group of Comparative Example E1 without biochar. Figures 2 to 5 The percentages 0%, 1%, 2%, 3%, and 4% represent the mass percentage of biochar or modified biochar in the cement.

[0145] Table 4

[0146]

[0147]

[0148] As can be seen from Table 4, the modified biochar prepared according to the method of this application can significantly improve the compressive strength, flexural strength and carbon fixation performance of cement components when used in cement-based materials. At the same time, it also realizes the resource utilization and green treatment of solid waste, and has good economic and environmental benefits.

[0149] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A carbon-fixing cement material, characterized in that, This includes modified biochar, and the preparation method of the modified biochar includes the following steps: A salt solution was added to the solid waste for extraction to obtain an extract. A soluble sulfide was added to the extract for precipitation treatment to obtain a heavy metal precipitate and a modified solution; The modified solution is used to modify the biochar to obtain the modified biochar. Wherein, the solid waste is phosphogypsum; the salt solution includes at least one of ammonium chloride solution, potassium chloride solution, and sodium nitrate solution; in the precipitation treatment, the pH value of the mixed solution formed by the extract and the soluble sulfide is 7-9; The preparation method of the carbon-fixed cement material includes the following steps: The modified biochar, cementitious materials, aggregates, auxiliary cementitious materials, and water-reducing agents are mixed in a reasonable proportion.

2. The carbon-fixing cement material according to claim 1, characterized in that: In the extraction process, the solid-liquid mass ratio of the solid waste to the salt solution is 1:(2-5). And / or, the concentration of the salt solution is 0.5 mol / L to 3 mol / L.

3. The carbon-fixing cement material according to claim 1 or 2, characterized in that, The extraction process includes the following steps: The solid waste and the salt solution are first mixed at 30–90°C, followed by solid-liquid separation to obtain the extract.

4. The carbon-fixing cement material according to claim 1 or 2, characterized in that: The soluble sulfide includes at least one of sodium sulfide and potassium sulfide.

5. The carbon-fixing cement material according to claim 1 or 2, characterized in that: The modified solution contains at least one cation selected from calcium ions, magnesium ions, aluminum ions, and iron ions; And / or, the modified solution contains at least one anion selected from silicate ions, sulfate ions, phosphate ions, sulfide ions, and carbonate ions; And / or, the biochar contains at least one group selected from carboxyl, carbonyl, hydroxyl, and amino groups.

6. The carbon-fixing cement material according to claim 1 or 2, characterized in that, The modification process includes the following steps: The biochar and the modified solution are subjected to a second mixing treatment and reaction at 25–60°C.

7. The carbon-fixing cement material according to claim 1, characterized in that, The modified biochar includes at least one of the following characteristics (1) to (3): (1) Specific surface area is 240–320 m² 2 / g; (2) The pore volume is 0.025–0.065 cm³. 3 / g; (3) The average pore size is 13.5–18.5 nm.

8. The carbon-fixing cement material according to claim 1, characterized in that: The mass ratio of the cement material to the modified biochar is (25-100):1.

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