Modified biochar, preparation method thereof and carbon sequestration cement material

Abstract

The invention relates to the technical field of new materials, in particular to modified biochar, a preparation method thereof and a carbon sequestration cement material. The preparation method comprises the following steps: adding a salt solution into solid waste for extraction treatment to obtain an extracting solution; adding soluble sulfide into the extracting solution for precipitation treatment to obtain a heavy metal precipitate and a modified solution; and performing modification treatment on the biochar by using the modified solution to obtain the 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, so that active sites on the surface of the biochar are enriched, the pore structure is improved, the prepared modified biochar can further improve the performance of capturing and fixing CO2, and meanwhile, the interaction with a cement material is further improved; the compactness, the fracture resistance and the compression resistance are enhanced, the durability is improved, and the service life is prolonged. The preparation method is simple in process, low in cost and not prone to secondary pollution. The cement material and the modified charcoal can also be used for preparing a carbon-sequestration cement material.

Description

Technical Field

[0001] The present application relates to the technical field of new carbon fixation materials, and in particular to modified biochar and a preparation method thereof, and carbon fixation cement materials. Background Art

[0002] Cement is a basic material widely used in construction projects. Its production process is accompanied by a large amount of CO 2 Emissions have brought huge challenges to global climate change and environmental protection. In order to reduce the carbon footprint of cement materials and improve their environmental friendliness, researchers have tried to add biochar. Due to its high specific surface area and rich pore structure, biochar shows great application potential in environmental governance, soil improvement and carbon fixation. However, unmodified biochar has certain limitations in adsorption capacity and stability, and its physical and chemical properties need to be improved through modification to enhance its application effect.

[0003] Existing biochar modification methods mainly rely on treatment with a variety of chemical reagents. Although they can improve the adsorption performance of biochar to a certain extent, the biochar modification effect is not ideal. Moreover, these methods have the problems of high cost, complex process and large amount of chemical reagents used, which are prone to 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. These solid wastes, especially industrial solid wastes, often contain a variety of heavy metal ions such as lead, mercury, cobalt, cadmium, etc. in addition to a variety of mineral salts. If not treated, they will pollute the environment or harm the human body. Existing technologies often lack effective treatment methods and it is difficult to recycle these industrial solid wastes. Summary of the invention

[0005] The purpose of this application is to provide modified biochar and a preparation method thereof, aiming to solve the problems in the prior art that biochar modification requires the use of multiple chemical reagents, is costly, has a complex process, and is prone to pollution.

[0006] Another purpose of the present application is to provide a carbon-fixing cement material, aiming to solve the problem that the mechanical properties and carbon-fixing properties of carbon-fixing cement materials in the prior art are still not ideal.

[0007] In order to achieve the above application purpose, the technical solution adopted in this application is as follows:

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

[0009] Adding a salt solution to the solid waste for extraction treatment to obtain an extract;

[0010] adding soluble sulfide to the extract for precipitation treatment to obtain heavy metal precipitate and modified solution;

[0011] The modified solution is used to modify the biochar to obtain modified biochar;

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

[0013] The preparation method of the present application first treats the solid waste with a specific salt solution and soluble sulfide, and the obtained modified solution is rich in a variety of active ions, which will combine or react with the functional groups rich in biochar, enrich the active sites on the surface of biochar and improve the pore structure, so that the prepared modified biochar can further improve the capture and fixation of CO 2 The performance of the cementitious material is improved, and the interaction with the cement material is further improved, the density and the bending and compression resistance are enhanced, and the durability and service life are improved. The preparation method only needs to process common solid waste, salt solution and soluble sulfide, without a large amount of expensive chemical reagents, and the process is streamlined, the cost is reduced, and it is not easy to cause secondary pollution.

[0014] In a second aspect, the present application provides a modified biochar, which is the modified biochar prepared by the preparation method of the above text application.

[0015] The modified biochar of the present application is prepared by the preparation method of the above-mentioned application. Compared with ordinary biochar, the pore structure of the modified biochar is improved and the active sites on the surface are more abundant. Therefore, the modified biochar of the present application not only improves the capture and 2 It not only improves the performance of cement, but also improves the interaction with cement materials, enhances density and flexural and compressive properties, and improves durability and service life.

[0016] In a third aspect, the present application provides a carbon-fixing cement material, including a cement material, and also including modified biochar prepared by the preparation method of the above application or modified biochar as described in the above application.

[0017] The modified biochar in the carbon-fixing cement material of the present application improves the pore structure and enriches the active sites, thereby giving the carbon-fixing cement material carbon-fixing properties, green carbon reduction, and enhancing the interaction with the cement material, enhancing the density and flexural and compressive properties, and improving durability and service life. Therefore, the carbon-fixing cement material of the present application has both green carbon-fixing and high-strength properties, and has significant environmental, economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 It is a flow chart of the preparation method of modified biochar in the embodiment of the present application and its use in cement-based materials;

[0020] Figure 2 It is a schematic diagram of the 7-day compressive strength test results of the cement products made from biochar of Example A9 and Comparative Example A1 of the present application and the blank control group;

[0021] Figure 3 It is a schematic diagram of the 28-day compressive strength test results of the cement products made from biochar of Example A9 and Comparative Example A1 of the present application and the blank control group;

[0022] Figure 4 It is a schematic diagram of the 7-day flexural strength test results of the cement products made from biochar in Example A9 and Comparative Example A1 of the present application and the blank control group;

[0023] Figure 5 It is a schematic diagram of the 28-day flexural strength test results of the cement products made from biochar in Example A9 and Comparative Example A1 of the present application and the blank control group;

[0024] Figure 6 It is a schematic diagram of the thermogravimetric analysis test results of cement products made from biochar in Example A9 and Comparative Example A1 of the present application and a blank control group. DETAILED DESCRIPTION

[0025] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0026] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

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

[0028] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and 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 the present application.

[0029] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0030] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass in the embodiment description of the present application can be μg, mg, g, kg and other mass units known in the chemical industry.

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

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

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

[0034] S10. Adding a salt solution to the solid waste for extraction treatment to obtain an extract;

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

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

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

[0038] The preparation method of the embodiment of the present application first treats the solid waste with a specific salt solution and a soluble sulfide, and the obtained modified solution is rich in a variety of active ions. When the biochar is modified by the modified solution, these active ions will combine or react with the functional groups rich in the biochar, enriching the active sites on the surface of the biochar and improving the pore structure, so that the prepared modified biochar can further improve the capture and fixation of CO 2 performance, while further improving the interaction with cement materials, enhancing density and flexural and compressive properties, and improving durability and service life. In summary, compared with existing biochar modification methods, the modified biochar prepared by the preparation method of the embodiment of the present application further improves the carbon fixation performance and the mechanical strength of the compound with cement materials; and the preparation method only requires common solid waste, salt solution and soluble sulfide for treatment, without the need for a large amount of expensive multiple chemical reagents, the process is streamlined, the cost is reduced, and it is not easy to cause secondary pollution. The preparation method is controllable, and the modified biochar obtained has stable properties.

[0039] As an embodiment of the present application, Figure 1 As shown:

[0040] [Step S10]

[0041] Step S10 is a step of first extracting solid waste with a salt solution to obtain an extract. The solid waste can be industrial solid waste or domestic solid waste. These solid wastes, especially industrial solid wastes, often contain a variety of heavy metal ions in addition to a variety of mineral salts, such as lead, mercury, cobalt, cadmium, etc. If not treated, they will pollute the environment or harm the human body. The existing technology often lacks effective treatment methods and it is difficult to recycle these industrial solid wastes. Therefore, adding a salt solution for extraction treatment first can dissolve these heavy metal ions and some mineral components in the solid waste into the extract, and these heavy metal ions can be removed later to obtain the desired modified solution, so that not only can the heavy metal ions be removed, but also these solid wastes can be fully utilized.

[0042] In some embodiments, the solid waste includes at least one of phosphogypsum (industrial waste discharged from the production of phosphate fertilizer and phosphoric acid), blast furnace slag, recycled concrete, fly ash, and tailings, and phosphogypsum is optional. These solid wastes have high content of heavy metal ions and are often difficult to be effectively utilized as waste. They also contain rich minerals such as silicates, which can be dissolved and extracted by salt solutions.

[0043] In the embodiment, these solid wastes can be pre-treated before extraction, and first undergo physical screening and washing treatment to remove large particles and impurities, so as to facilitate the smooth progress of subsequent treatment. Specifically, a screen can be used to screen out large particles in the solid waste to ensure uniform particle size of the raw materials; then the screened solid waste is washed to remove dust and soluble impurities on the surface to ensure cleanliness, and the water flow is ensured to be uniform during washing to prevent solid waste accumulation from affecting the cleaning effect.

[0044] In some embodiments, the salt solution may be selected from ammonium chloride solution, potassium chloride solution, and sodium nitrate solution, and the active ions and heavy metal ions in the solid waste are released by ion replacement dissolution. In some embodiments, the concentration of the salt solution is 0.5mol / L to 3mol / L, and may include but is not limited to any concentration of 0.5mol / L, 1mol / L, 2mol / L, 3mol / L, or a range between any two concentrations. When these types and concentrations of salt solutions are used to extract and treat the above-mentioned solid waste, the salt solution can dissolve mineral salt components such as silicates in the solid waste, and extract the heavy metal ions in the solid waste and the required active ions such as calcium ions, silicates, sulfates, etc. into the extract, and 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), and can include but is not limited to any ratio of 1:2, 1:3, 1:4, 1:5 or a range between any two ratios to ensure the extraction effect, which is beneficial to dissolve and extract the heavy metal ions and required active ions in the solid waste as fully as possible.

[0046] The extraction process may include the following steps: firstly, the solid waste is mixed with the salt solution for a first treatment, and heated to 30-90°C, and then the solid-liquid separation process is carried out to obtain an extract. The first mixing process may be carried out by mixing and stirring, and the mixing may be carried out for 1h, assisted by the above-mentioned heating temperature, so that the solid waste and the salt solution are fully contacted and reacted, so as to facilitate the full dissolution of heavy metal ions and required active ions in the solid waste, and to fully extract them. The solid-liquid separation process may be separated by a centrifugal device, and the speed is set to 3000-5000 rpm for 20-30 minutes. After centrifugation, the supernatant is collected to obtain an extract, and the heavy metal ion content in the solid residue after centrifugation is extremely low, which can be further treated or harmlessly disposed of, for example, it can be used as aggregate in concrete, for road fillers, soil conditioners, etc. Therefore, the preparation method of the embodiment of the present application can not only produce modified biochar, but also turn solid waste that is difficult to effectively utilize, especially industrial solid waste, into treasure, for biochar modification, and give the beneficial effect of recycling solid waste resources, with significant environmental protection, economic and social benefits.

[0047] The extract contains heavy metal ions and a variety of active ions extracted, such as calcium ions, silicate, sulfate, etc. Among them, the cations can be calcium ions, magnesium ions, aluminum ions, iron ions, etc., and the anions can be silicate, sulfate, phosphate, sulfur ions, carbonate, etc. Specifically, in addition to the heavy metal ions and ions introduced by the salt solution, the extract of the above-mentioned solid waste after extraction treatment contains calcium ions, sulfate ions, and a small amount of magnesium ions and phosphate ions in the phosphogypsum extract; the blast furnace slag extract contains calcium ions, magnesium ions, aluminum ions, silicate ions and sulfate ions; the recycled concrete extract contains calcium ions, carbonate ions, and a small amount of silicate ions and aluminum ions; the fly ash extract contains calcium ions, aluminum ions, silicate ions and a small amount of magnesium ions and iron ions; the tailings extract contains calcium ions, iron ions, sulfate ions, a small amount of silicate ions and aluminum ions.

[0048] [Step S20]

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

[0050] During the precipitation treatment, it is optional to gradually add soluble sulfide to the extract to avoid excessive local sulfide ion concentration. Alternatively, the soluble sulfide is prepared into a solution with a concentration of 0.1 mol / L to 0.5 mol / L, and then gradually added to the extract. The pH value also needs to be controlled during the process. In some embodiments, during the precipitation treatment, the pH value of the mixed solution formed by the extract and the soluble sulfide is 7 to 9, which may include but is not limited to any value of 7, 7.5, 8, 8.5, 9 or a range between any two values. During the precipitation treatment, the pH value needs to be monitored in real time to prevent the pH value from being too high or too low, to ensure that the sulfide ions and heavy metal ions form a precipitate, to remove heavy metal ions as much as possible, and to reduce the precipitation of sulfide ions and required active ions, thereby reducing the loss of active ions.

[0051] After precipitation treatment, solid-liquid separation treatment is carried out. The precipitate can be removed by filtering with filter paper or filter cloth. The precipitate can be used in heavy metal recovery and other fields. The supernatant obtained by filtration is the modified solution, in which the heavy metal content meets environmental protection standards and is rich in a variety of active ions. Figure 1 As shown, after testing, if the heavy metal still does not meet the requirements, the above precipitation treatment can be performed again. In some embodiments, the modified solution contains at least one cation of calcium ion, magnesium ion, aluminum ion, and iron ion, wherein the first three cations are mainly present. In some embodiments, the modified solution contains at least one anion of silicate ion, sulfate ion, phosphate ion, sulfide ion, and carbonate ion, wherein the first three anions are mainly present. These active ions are beneficial to the subsequent modification of biochar, improve the pore structure of biochar, increase surface active sites, and improve the modification effect.

[0052] [Step S30]

[0053] Step S30 is a step of modifying the biochar. Biochar can be prepared from biomass raw materials by pyrolysis. The biomass raw materials may include crop straw, fruit shells, etc. The biomass raw materials are first crushed and dried to reduce the moisture content and remove impurities, and then pyrolyzed and carbonized under anaerobic conditions, with the temperature controlled at 400 to 600°C for 2 to 4 hours to obtain biochar. Biochar has a porous structure and contains a variety of groups in the biochar, especially on the surface. In some embodiments, the biochar contains at least one of carboxyl, carbonyl, hydroxyl, and amine groups. These groups in the biochar will undergo a series of reactions with the active ions in the modified solution to improve the pore structure of the biochar and increase the surface active sites.

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

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

[0056] After the modification treatment is completed, the solid components are collected by solid-liquid separation and vacuum dried. The drying temperature is controlled at 60-80°C for 24-48 hours to remove moisture and stabilize the modification effect to obtain modified biochar.

[0057] Therefore, the modified biochar prepared by the preparation method of the embodiment of the present application improves the pore structure, enriches the surface active sites, and increases the adsorption capacity of CO 2 The carbon fixation performance and mechanical properties of the cement material are good; the preparation method also fully recycles solid waste resources and removes heavy metal ions, which has high economic and environmental value; and the preparation method only needs to process common solid waste, salt solution and soluble sulfide, without a large amount of expensive chemical reagents, the process is streamlined, the cost is reduced, and it is not easy to cause secondary pollution. The preparation method is controllable and the modified biochar obtained has stable properties.

[0058] A second aspect of the embodiments of the present application provides a modified biochar, which is the modified biochar prepared by the preparation method of the embodiments of the present application.

[0059] The modified biochar in the embodiment of the present application is prepared by the preparation method of the embodiment of the present application. Compared with ordinary biochar, the pore structure of the modified biochar is improved and the active sites on the surface are more abundant. Therefore, the modified biochar in the embodiment of the present application not only improves the capture and 2 It not only improves the performance of cement, but also improves the interaction with cement materials, enhances density and flexural and compressive properties, and improves durability and service life.

[0060] According to the test, in some embodiments, the specific surface area of ​​the modified biochar is 240-320 m 2 / g; pore volume is 0.025~0.065cm 3 / g; the average pore diameter is 13.5~18.5nm.

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

[0062] The modified biochar in the carbon-fixing cement material of the embodiment of the present application improves the pore structure and enriches the active sites, thereby giving the carbon-fixing cement material carbon-fixing performance, green carbon reduction, and enhancing the interaction with the cement material, enhancing the density and flexural and compressive properties, and improving the durability and service life. Therefore, the carbon-fixing cement material of the embodiment of the present application has both green carbon fixation and high-strength performance, and has significant environmental, economic and social benefits.

[0063] In some embodiments, the mass ratio of cement material to modified biochar is (25-100):1, which may include but is not limited to any ratio of 25:1, 50:1, 75:1, 100:1 or any range between two ratios. In addition, the carbon-fixing cement material may also include aggregate, auxiliary cementitious material, water reducing agent and other ingredients, which are mixed in a reasonable ratio, and cast in a water-cement ratio of (0.3-0.5):1, and cured in a standard curing room for 28 days to ensure its strength and stability.

[0064] The following describes the invention in conjunction with specific embodiments.

[0065] Example A1

[0066] This embodiment provides modified biochar and a preparation method thereof, the preparation method comprising the following steps:

[0067] S1. Extraction process:

[0068] The phosphogypsum is sieved with a 50-mesh (0.3 mm) sieve, and the fine phosphogypsum under the sieve is washed with water to remove dust and soluble impurities on the surface to obtain pretreated phosphogypsum.

[0069] Prepare an ammonium chloride solution with a concentration of 0.5 mol / L, mix the pretreated phosphogypsum and the ammonium chloride solution in a solid-liquid ratio of 1:2, and heat to 30°C. Keep stirring at this temperature for 1 hour, centrifuge the mixture at a speed of 3000 rpm for 20 minutes, collect the supernatant after centrifugation to obtain the extract, and the solid residue can be used as aggregate.

[0070] S2. Precipitation treatment:

[0071] Prepare a sodium sulfide solution with a concentration of 0.3 mol / L, gradually add the sodium sulfide solution to the extract, monitor the pH value of the mixed solution throughout the process, ensure that the pH value is between 7 and 9, so that the heavy metal ions form insoluble sulfide precipitates, stop adding when the final pH value is 7, then filter with filter paper to remove the precipitate, and retain the supernatant as the modified solution.

[0072] S3. Modification treatment:

[0073] After the straw is crushed and dried, the temperature is controlled at 500°C under anaerobic conditions for pyrolysis and carbonization for 3 hours, and biochar is obtained after cooling.

[0074] The biochar was soaked in the 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 a preparation method thereof, which differs from Embodiment A1 only in that the solid-liquid ratio in step S1 is changed from 1:2 to 1:3, and the temperature is changed from 30° C. to 50° C., and the rest are the same.

[0077] Example A3

[0078] This embodiment provides modified biochar and a preparation method thereof, which is different from Embodiment A1 only in that the solid-liquid ratio in step S1 is changed from 1:2 to 1:4, and the temperature is changed from 30° C. to 70° C., and the rest are the same.

[0079] Example A4

[0080] This embodiment provides modified biochar and a preparation method thereof, which differs from Embodiment A1 only in that the solid-liquid ratio in step S1 is changed from 1:2 to 1:5, and the temperature is changed from 30° C. to 90° C., and the rest are the same.

[0081] Example A5

[0082] This embodiment provides modified biochar and a preparation method thereof, which is different from Embodiment A1 only in that the concentration of the ammonium chloride solution is changed from 0.5 mol / L to 1 mol / L, and the heating temperature is changed from 30° C. to 50° C., and the rest are the same.

[0083] Example A6

[0084] This embodiment provides modified biochar and a preparation method thereof, which differs from Embodiment A1 only in that the concentration of the 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°C to 70°C, and the rest are the same.

[0085] Example A7

[0086] This embodiment provides modified biochar and a preparation method thereof, which differs from Embodiment A1 only in that the concentration of the 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°C to 90°C, and the rest are the same.

[0087] Example A8

[0088] This embodiment provides modified biochar and a preparation method thereof, which differs from Embodiment A1 only in that the concentration of the 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, and the rest are the same.

[0089] Embodiment A9

[0090] This embodiment provides modified biochar and a preparation method thereof, which differs from Embodiment A1 only in that the concentration of the 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° C. to 70° C., and the rest are the same.

[0091] Embodiment A10

[0092] This embodiment provides modified biochar and a preparation method thereof, which differs from Embodiment A1 only in that the concentration of the 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°C to 90°C, and the rest are the same.

[0093] Embodiment A11

[0094] This embodiment provides modified biochar and a preparation method thereof, which differs from Embodiment A1 only in that the concentration of the 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, and the rest are the same.

[0095] Example A12

[0096] This embodiment provides modified biochar and a preparation method thereof, which differs from Embodiment A1 only in that the concentration of the 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°C to 50°C, and the rest are the same.

[0097] Embodiment A13

[0098] This embodiment provides modified biochar and a preparation method thereof, which differs from Embodiment A1 only in that the concentration of the 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° C. to 90° C., and the rest are the same.

[0099] Embodiment A14

[0100] This embodiment provides modified biochar and a preparation method thereof, which differs from Embodiment A1 only in that the concentration of the 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, and the rest are the same.

[0101] Embodiment A15

[0102] This embodiment provides modified biochar and a preparation method thereof, which differs from Embodiment A1 only in that the concentration of the 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°C to 50°C, and the rest are the same.

[0103] Embodiment A16

[0104] This embodiment provides modified biochar and a preparation method thereof, which differs from Embodiment A1 only in that the concentration of the 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°C to 70°C, and the rest are the same.

[0105] Embodiment A17

[0106] This embodiment provides modified biochar and a preparation method thereof, which is different from Embodiment A9 only in that the ammonium chloride solution in step S1 is replaced with a potassium chloride solution, and the rest is the same.

[0107] Embodiment A18

[0108] This embodiment provides modified biochar and a preparation method thereof, which is different from Embodiment A9 only in that the ammonium chloride solution in step S1 is replaced with a sodium nitrate solution, and the rest is the same.

[0109] Comparative Example A1

[0110] This comparative example provides biochar, and the preparation method includes: using the biochar prepared 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, and the preparation method includes: according to Example A9, steps S1 and S2 are not performed, and the ammonium chloride solution in step S1 is directly used as the modification solution of step S3, and the biochar is directly soaked with the ammonium chloride solution. The rest is the same as step S3 of Example A1, so as to obtain modified biochar.

[0113] Comparative Example A3

[0114] This comparative example provides modified biochar, and the preparation method includes: according to the modified solution in step S3 of Example A1, the modified solution is changed to a calcium nitrate solution, the solution concentration is 2 mol / L, and the other steps are the same as step S3 of Example A1, to obtain calcium nitrate modified biochar. The differences between the above cases are shown in Table 1 below:

[0115] Table 1

[0116] Case <![CDATA[NH 4 Concentration of Cl solution (mol / L)]]> Solid-liquid ratio Stirring temperature (℃) 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 Embodiment A9 2 1：2 70 Embodiment A10 2 1：3 90 Embodiment A11 2 1：4 30 Example A12 2 1：5 50 Embodiment A13 3 1：2 90 Embodiment A14 3 1：3 30 Embodiment A15 3 1：4 50 Embodiment A16 3 1：5 70 Embodiment A17 2(KCL) 1：2 70 Embodiment A18 <![CDATA[2(NaNO 3 )]]> 1：2 70 Comparative Example A1 Untreated biochar Comparative Example A2 <![CDATA[2(NH 4 Cl Direct Treatment of Biochar)]]> 1：2 70 Comparative Example A3 <![CDATA[2(Ca(NO 3 ) 2 Directly processed biochar)]]> 1：2 30

[0117] Biochar performance comparison

[0118] 1.1 Morphology analysis

[0119] The samples of 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 example, the surface of the biochar modified by the modified solution obtained by extraction treatment was rougher, which is beneficial to increase the specific surface area and pore volume, enrich the void structure, and increase the active sites.

[0120] 1.2. Specific surface area, pore volume and pore size test

[0121] 10 g of each of the samples of Examples A1 to A16 and Comparative Examples A1 to A3 extracted with ammonium chloride solution and further prepared as biochar were taken and BET tested using an ASAP 2460 multi-station fully automatic specific surface and pore size analyzer to measure specific surface area and other data, and the results are recorded in the following Table 2. It can be seen from Table 2 that the specific surface area and pore volume of the biochar modified by the method are improved compared with the unmodified biochar, and the average pore size is also improved, and the pore structure becomes richer.

[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 Embodiment A9 314.8561 0.064983 13.9051 Embodiment A10 310.6475 0.058581 14.3157 Embodiment A11 289.3238 0.054392 14.9672 Example A12 309.3266 0.061821 14.2534 Embodiment A13 291.6354 0.053643 15.0347 Embodiment A14 283.3242 0.050302 14.6249 Embodiment A15 297.5319 0.057527 13.7228 Embodiment 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 treatment in step S2 of Example A9. This method can quickly and effectively evaluate the potential risk of heavy metals in the modified solution, providing a basis for its application in cement-based materials. The standard value refers to the standard (GB30760-2014).

[0126] Table 3

[0127]

[0128]

[0129] Carbon-fixing cement material embodiment:

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

[0131] PO52.5 cement 100 parts;

[0132] 1 to 4 parts of modified biochar;

[0133] 40 parts water;

[0134] Then pour into shape, cure in a standard curing room for 1 day, remove the mold, and place in CO 2 The cement is cured in a carbonization curing box at a concentration of 20%, a temperature of 20°C and a humidity of 70% for 7 days or 28 days to obtain a cement product.

[0135] Among them, Example A1 modified biochar to produce Example B1 cement product, Example A2 modified biochar to produce Example B2 cement product, and so on, until Comparative Example A3 modified biochar to produce Comparative Example B3 cement product.

[0136] Related performance tests and result analysis

[0137] The performance tests were conducted on the cement products of the above-mentioned Examples B1 to B18 and Comparative Examples B1 to B3. The cement products were compression test blocks of 40 cm×40 cm×40 cm and flexural test blocks of 40 cm×40 cm×160 cm.

[0138] In order to further explore the effect of biochar content on performance, each example or comparative example provides 4 test block samples, which are 1 part, 2 parts, 3 parts, and 4 parts of biochar content, and the test results of the examples or comparative examples are tested respectively. Among them, the modified biochar content of 1 to 4 parts obtained in Example A9 is used to prepare Example C1-C4 cement products respectively, and the biochar content of 1 to 4 parts obtained in Comparative Example A1 is used to prepare Comparative Example D1-D4 cement products respectively, and the E1 cement product prepared without adding biochar is used as a blank group.

[0139] 1. Carbon fixation performance test

[0140] Take the broken pieces of cement test block that has been carbonized and cured for 7 days, grind them into powder, soak them in isopropanol for 15 minutes to prevent the cement from further hydration, and then filter the powder sample with a 300-mesh sieve, and dry the powder sample in a vacuum drying oven for 24 hours. Then use a thermogravimetric analyzer to heat the sample to 1000 degrees Celsius at a heating rate of 10 degrees Celsius per minute in a nitrogen environment, and detect the heat loss of different substances in the sample. The thermogravimetric analysis diagram is shown below: Figure 6 The test results are recorded in Table 4. The carbon fixation performance is shown in Table 4. The DTG curve obtained by thermogravimetric analysis shows that calcium carbonate decomposes between 430 degrees Celsius and 830 degrees Celsius, so the carbon fixation performance = (M 430 -M 830 )÷M 1000 ×100%.

[0141] M 430 、M 830 represents the mass percentage of the sample at each heating temperature, M 1000 is the mass percentage of the remaining sample after heating to 1000°C.

[0142] 2. Compressive strength and flexural strength test

[0143] The compression testing machine was controlled by a microcomputer. The test conditions were: 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, the modified biochar in the figure 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 adding biochar. Figures 2 to 5The 0%, 1%, 2%, 3% and 4% represent the mass ratio of biochar or modified biochar to cement.

[0145] Table 4

[0146]

[0147]

[0148] It can be seen from Table 4 that the modified biochar prepared according to the preparation method of the present application can be used in cement-based materials to significantly improve the compressive strength, flexural strength and carbon fixation performance of cement parts, while also achieving resource utilization and green treatment of solid waste, with good economic and environmental benefits.

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

Claims

1. A method for preparing modified biochar, characterized in that: The steps include: Adding a salt solution to the solid waste for extraction treatment to obtain an extract; adding soluble sulfide to the extract for precipitation treatment to obtain a heavy metal precipitate and a modified solution; Modifying the biochar with the modified solution to obtain modified biochar; Wherein, the salt solution includes at least one of ammonium chloride solution, potassium chloride solution and sodium nitrate solution.

2. The method for preparing modified biochar 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; And / or, the solid waste includes at least one of phosphogypsum, blast furnace slag, recycled concrete, fly ash, and tailings.

3. The method for preparing modified biochar according to claim 1 or 2, characterized in that: The extraction process comprises the following steps: The solid waste and the salt solution are first mixed at 30-90° C., and then solid-liquid separation is performed to obtain the extract.

4. The method for preparing modified biochar according to claim 1 or 2, characterized in that: In the precipitation treatment, the pH value of the mixed solution formed by the extract and the soluble sulfide is 7 to 9; And / or, the soluble sulfide includes at least one of sodium sulfide and potassium sulfide.

5. The method for preparing modified biochar according to claim 1 or 2, characterized in that: The modified solution contains at least one cation selected from the group consisting of calcium ions, magnesium ions, aluminum ions, and iron ions; and / or, the modified solution contains at least one anion selected from the group consisting of silicate ions, sulfate ions, phosphate ions, sulfide ions, and carbonate ions; And / or, the biochar contains at least one group selected from the group consisting of carboxyl, carbonyl, hydroxyl and amine.

6. The method for preparing modified biochar according to claim 1 or 2, characterized in that: The modification process comprises the following steps: The biochar and the modified solution are subjected to a second mixing treatment and reacted at 25-60°C.

7. A modified biochar, characterized in that: The modified biochar is the modified biochar prepared by the preparation method according to any one of claims 1 to 6.

8. The modified biochar according to claim 7, characterized in that The modified biochar comprises at least one of the following characteristics (1) to (3): (1) Specific surface area is 240 to 320 m 2 / g; (2) Pore volume is 0.025 to 0.065 cm 3 / g; (3) The average pore diameter is 13.5 to 18.5 nm.

9. A carbon-fixing cement material, characterized in that: It comprises cement material and also comprises the modified biochar prepared by the preparation method according to any one of claims 1 to 6 or the modified biochar according to claim 7 or 8.

10. The carbon-fixing cement material according to claim 9, characterized in that: The mass ratio of the cement material to the modified biochar is (25-100):1.

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