Preparation method of high-carbon-fixing high-strength lightweight building material

Abstract

This invention relates to a method for preparing lightweight building materials with high carbon sequestration and high strength, comprising the following steps: preparation and activation of biochar; mixing biochar with solid waste raw materials to obtain a mixture; preparing biochar-modified lightweight aggregate in a granulator; curing the obtained lightweight aggregate according to a process of pre-curing – carbonization curing – subsequent wet curing; and drying to obtain lightweight building materials. This invention uses activated biochar as a modifying material, uses fly ash, coal gangue, desulfurized gypsum, and other multi-element solid wastes instead of cement as raw materials, uses blast furnace slag instead of traditional silicone, vinyl acetate (VAM) emulsion, polyurethane, etc., as binders, and uses CO2 from flue gas emitted from steelmaking furnaces, cement kilns, and coal-fired power plants for carbonization curing. This achieves optimized control of the internal pore structure of the lightweight aggregate and accelerates the carbonization reaction rate between CO2 and the internal and external aggregate media, effectively improving the overall carbonization degree and CO2 adsorption performance of the lightweight aggregate.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide mineralization technology, and in particular to a method for preparing a lightweight building material with high carbon fixation content and high strength. Background Technology

[0002] Carbon sequestration and utilization (CSH) is a crucial pathway for my country to build a clean and low-carbon energy system, and CO2 mineralization technology is an important component of CSH. It simulates and accelerates the natural weathering process of silicate minerals. The most reactive compounds commonly used for CO2 mineralization are oxides of divalent metals Ca and Mg, i.e., CO2 reacts with calcium oxide (CaO) and magnesium oxide (MgO) to form carbonates. The carbonates produced during carbonation are chemically stable and can almost permanently store CO2. Furthermore, this reaction is spontaneous and exothermic, which is thermodynamically favorable. Currently, China is one of the world's largest producers of solid waste, facing immense pressure in the disposal of industrial solid waste. It is necessary to achieve resource utilization of industrial solid waste during the disposal of large quantities of solid waste. Most industrial solid waste is rich in CaO and MgO, exhibiting good mineralization activity. Moreover, because these wastes originate from industrial processes and are closer to CO2 emission sources, the potential for large-scale CO2 mineralization from industrial solid waste is enormous. Lightweight building materials have become one of the main carriers for the disposal of industrial solid waste. CO2 mineralization of solid waste building materials, as an emerging CO2 utilization technology, holds promise for large-scale CO2 sequestration and emission reduction, as well as solid waste treatment. Biochar, a negative carbon material produced by the thermochemical conversion of various biomass wastes such as straw in an oxygen-deficient environment, has a 12% global CO2 emission reduction capacity. Adding biochar to the CO2 mineralization of solid waste can achieve dual carbon emission reduction and effectively increase the CO2 diffusion rate, significantly improving the CO2 absorption rate and sequestration rate, and drastically shortening the carbonization and curing time. In existing methods for preparing lightweight building materials, during the CO2 mineralization and curing process, the formation of calcium carbonate increases, leading to a denser microstructure and hindering the diffusion of CO2 from the environment into the aggregates. This process ultimately slows down the later stages of carbonization, limiting the improvement of the carbonization degree of lightweight aggregates, especially the core aggregate portion. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a method for preparing lightweight building materials with high carbon content and high strength. The aim is to regulate the pore structure of the aggregate formed during the preparation process by using porous biochar, and to accelerate the carbonization reaction between CO2 and the calcium and magnesium mineral components inside and outside the aggregate by utilizing the CO2 adsorption performance of biochar, thereby improving its ability to absorb and mineralize CO2 and the degree of carbonization, ultimately improving the performance of the finished product.

[0004] The technical solution adopted in this invention is as follows:

[0005] Preparation method of lightweight building materials with high carbon sequestration and high strength: preparation of biochar: screen biomass raw materials to below 2mm, and obtain biochar by pyrolysis in a tubular furnace;

[0006] Activation treatment of biochar: The biochar is immersed in an activation solution at a certain ratio and stirred continuously for 11-13 hours. After standing at room temperature for 23-25 ​​hours, it is dried in an oven at 110-130℃. After cooling to room temperature, it is rinsed with hydrochloric acid and washed with deionized water until the pH is neutral. After vacuum filtration, it is dried in an oven at 100-110℃ to obtain modified porous biochar.

[0007] Biochar and solid waste raw material mixing: The activated biochar is mixed with crushed and ground solid waste raw material, binder and cement. The mixture is stirred at high speed in a concrete mixer for 1.5 to 2.5 minutes until uniformly mixed to obtain a mixture. The mixture is divided into two parts. The first part accounts for 60 to 80% by weight. The solid waste raw material includes fly ash, coal gangue and desulfurized gypsum. The binder is blast furnace slag.

[0008] Preparation of biochar-modified lightweight aggregate: The first part of the mixture is transferred into a disc granulator and sprayed with deionized water for 2 to 4 minutes at a speed of 35 to 40 rpm to form a granular mixture. Then, the second part of the mixture is added evenly without water spraying and is automatically formed to finally obtain spherical lightweight aggregate with a diameter of 4.75 to 16 mm.

[0009] Curing of lightweight aggregate: The lightweight aggregate is cured according to the process of pre-curing - carbonization curing - subsequent wet curing;

[0010] Drying of lightweight aggregate: After curing, the lightweight aggregate is placed in a drying oven to dry, thereby obtaining the lightweight building material.

[0011] Furthermore, a method for preparing lightweight building materials with high carbon sequestration and high strength.

[0012] In the activation treatment of the biochar: the mixture is continuously stirred with a magnetic stirrer for 12 hours, allowed to stand at room temperature for 24 hours, dried in an oven at 120°C for 48 hours, cooled to room temperature, rinsed with 1 mol / L hydrochloric acid (HCl) and washed with deionized water until the pH of the washing water is neutral, vacuum filtered and dried in an oven at 105°C for 12 hours.

[0013] In the step of mixing biochar and solid waste raw materials: after high-speed mixing for 2 minutes in a concrete mixer to obtain a uniform mixture;

[0014] In the step of preparing biochar-modified lightweight aggregate: spray deionized water for 2 minutes.

[0015] In the above-mentioned method for preparing lightweight building materials with high carbon sequestration and high strength, the activation solution is a KOH solution with a mass concentration of 35-45%, and the mixing ratio of biochar to the activation solution is 1:(4-6). Preferably, the activation solution is a KOH solution with a mass concentration of 40%, and the mixing ratio of biochar to the activation solution is 1:5.

[0016] In the above-mentioned method for preparing lightweight building materials with high carbon content and high strength, when pre-curing the lightweight aggregate before carbonization curing, the moisture content of the lightweight aggregate is controlled at 11-15%.

[0017] In the above-mentioned method for preparing high-carbon-content, high-strength lightweight building materials, the drying conditions for the lightweight aggregate are: temperature 60–70°C, drying time 11–13 hours. Preferably, the drying conditions for the lightweight aggregate are: temperature 65°C, drying time 12 hours.

[0018] In the above-mentioned method for preparing high-carbon-content, high-strength lightweight building materials, the lightweight aggregate has a 1-hour water absorption rate of 8.76–13.29% and a bulk density of 952.63–1143.94 kg·m³. 3 The cylinder compressive strength is 10.13–14.16 MPa, and the CO2 absorption rate is 9.36–13.15 wt%.

[0019] In the above-mentioned method for preparing lightweight building materials with high carbon sequestration and high strength, the biochar is one or a mixture of several of corn straw biochar, rice straw biochar, and wood chip biochar.

[0020] In the above-mentioned method for preparing lightweight building materials with high carbon sequestration and high strength, the ratio of solid waste raw materials to cement is (3-5):1.

[0021] The above-mentioned method for preparing high-carbon-content, high-strength lightweight building materials involves the following steps in the biochar preparation process: The biomass raw material is washed, dried to constant weight at 60–70°C, then pyrolyzed at 400–500°C for 2 hours, naturally cooled, crushed, and sieved to below 75 μm. The biomass raw material is one or a mixture of corn stalks, rice stalks, and waste wood chips. Corn stalks are preferred as the biomass raw material.

[0022] The preparation method of the above-mentioned high carbon content and high strength lightweight building materials requires the following pre-curing conditions: curing temperature 10-30℃, curing humidity 70% RH, and curing time 1-3 days.

[0023] The preparation method of the above-mentioned high carbon content and high strength lightweight building materials requires the following carbonization curing conditions: the carbonization curing atmosphere is one of the flue gas emitted from steelmaking furnaces, cement kilns and coal-fired power plants, the CO2 volume fraction is 15-20%, the pressure is 0.5 MPa, and the carbonization curing time is 2 hours.

[0024] The preparation method of the above-mentioned high carbon content and high strength lightweight building material requires the following conditions for subsequent wet curing: curing temperature 10-30℃, curing humidity 50% RH, and curing time 3 days.

[0025] The high-carbon-fixing, high-strength lightweight building material prepared by any of the above methods comprises the following components by weight: 20 parts cement: (40-60) parts fly ash: (10-20) parts coal gangue: (10-20) parts desulfurized gypsum. The weight proportion of blast furnace slag is 5-10 wt% of the sum of the solid waste raw materials and cement, and the weight proportion of activated biochar is 1-7 wt% of the sum of the solid waste raw materials and cement. Preferably, the solid waste powder has a particle size <200 μm, the ratio of solid waste powder to cement is 4:1, and the specific compounding ratio is cement / fly ash / coal gangue / desulfurized gypsum = 2:4:1:1. The blast furnace slag binder accounts for 5 wt% of the weight.

[0026] In the aforementioned high-carbon-content, high-strength lightweight building materials, the activated biochar accounts for 3 to 7 wt% of the sum of the weight of the solid waste raw materials and the cement.

[0027] The aforementioned high-carbon-content, high-strength lightweight building materials are used as lightweight aggregates in the preparation of concrete.

[0028] The beneficial effects of this invention are as follows:

[0029] This invention uses porous biochar as a modifying material and employs a pre-curing-carbonization curing-subsequent wet curing process. This allows for the regulation of the internal pore structure of lightweight aggregates based on multi-source solid waste, shortening the curing time and effectively improving the carbonization degree of the lightweight aggregates, thereby enhancing their carbonization efficiency and ultimately improving the overall quality of the finished lightweight building materials. Simultaneously, it optimizes and regulates the flue gas emitted from actual steelmaking furnaces, cement kilns, and coal-fired power plants for CO2 curing, achieving "waste treatment with waste." Specifically, it also includes the following advantages:

[0030] (1) This invention uses biochar as a modified material for lightweight aggregate, which solves the problem of secondary pollution caused by a large amount of waste biomass during incineration. Biochar has a high specific surface area and porous structure, and has a high affinity for non-polar compounds. It is a new type of CO2 adsorbent, which is nearly 10 times cheaper than various carbon dioxide adsorbents such as zeolite, mesoporous carbon and engineered carbon nanomaterials, providing a significant cost-effective advantage.

[0031] (2) This invention uses multi-source industrial solid waste such as fly ash, coal gangue, and desulfurized gypsum to replace most of the cement, and uses solid waste-type adhesive blast furnace slag to replace traditional adhesives such as silicone, vinyl acetate (VAM) emulsion, and polyurethane. This reduces CO2 emissions during cement production and the consumption of energy and economy. It also provides a new approach to effectively dispose of a large amount of industrial solid waste. At the same time, the granulation process uses one-time pelletizing and two-time slurry coating to make the lightweight aggregate have higher bulk density and compressive strength, and increases the success rate of lightweight aggregate preparation.

[0032] (3) This invention utilizes KOH solution to activate biochar, instead of other activators such as zinc chloride or phosphoric acid, because potassium hydroxide, compared to other activators, can give biochar more pores and a higher specific surface area. Furthermore, potassium hydroxide can provide hydroxide ions, increasing the alkaline groups on the surface of biochar, thereby providing more carbon dioxide adsorption sites. Ensuring that the biochar has a rich pore structure and a large specific surface area, and then using different types and proportions of activated biochar to prepare lightweight aggregates, can optimize and regulate the pore structure inside the aggregate medium, improving its mechanical properties while increasing the degree of carbonation. Because the activated biochar has obvious tubular and fibrous morphologies, these macroscopic pores can provide channels for CO2 transport during the carbonation process. In addition, biochar modified with KOH solution contains a large number of oxygen-containing functional groups and nano-sized or even smaller pores, which can form CO2 adsorption sites and interlock with the surrounding calcium carbonate generated by carbonation, greatly promoting the densification and refinement of the pore structure. Desulfurized gypsum contains a high amount of CaO, so it can provide more alkaline components to react with CO2 to generate CaCO3, thereby improving the performance of lightweight aggregates. Moreover, as a solid waste, desulfurized gypsum can be used in the preparation of lightweight aggregates, realizing the comprehensive utilization of solid waste.

[0033] (4) The present invention found that there is a certain correlation between the various properties of lightweight aggregates: the degree of increase in bulk density, the degree of decrease in water absorption rate, and the degree of increase in cylinder compressive strength are positively correlated. When the added biochar is corn straw biochar and the weight ratio is 3wt%, this positive correlation trend is the most obvious and the carbonization degree of lightweight aggregates is the greatest.

[0034] (5) This invention pre-cures lightweight aggregates before carbonization to control the moisture content at 11-15%, creating a suitable humidity environment inside the aggregates, thereby promoting subsequent mineralization reactions. In addition, the pre-curing temperature can meet the requirements of any weather environment, making it more applicable and economical than pre-curing aggregates that requires heating.

[0035] (6) In the mineralization curing (carbonization curing) process, the present invention uses CO2 from the flue gas emitted by steelmaking furnaces, cement kilns and coal-fired power plants for carbonization curing. Compared with high-purity CO2, using flue gas for curing is more practical and effective in reducing CO2 emissions, and can achieve the purpose of "using waste to produce waste".

[0036] (7) This invention performs subsequent wet curing after mineralization curing. By replenishing the aggregate with water, it promotes a more complete hydration reaction of the material, further effectively improving the porosity structure and mechanical strength of the building material. Research has shown that the calcite obtained from aggregate carbonization provides new nucleation sites for the growth of new CSH gels during subsequent hydration, thereby increasing the degree of hydration. The newly formed CSH gel begins to grow and fill the pores of the aggregate medium. Simultaneously, calcite crystals cross-bond with the newly generated CSH gel during the subsequent hydration process, forming a dense network structure, thus improving the density of the aggregate.

[0037] (8) The present invention sets reasonable drying conditions after subsequent wet curing to avoid the incomplete drying of moisture in aggregate due to excessively low temperature or short time, and excessively high temperature or long time, which leads to excessively high cost and changes in aggregate composition, thereby ensuring the excellent quality of the finished aggregate.

[0038] (9) This invention uses solid waste as the main raw material and biochar as the modified material. It adopts a mineralization curing process to prepare high-performance lightweight material. The biochar coupled with the CO2 mineralization of solid waste can achieve dual carbon emission reduction and effectively improve the CO2 diffusion rate, significantly improve the CO2 absorption rate and storage rate, and greatly shorten the carbonization curing time.

[0039] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0040] The following describes specific embodiments of the present invention.

[0041] The method for preparing the high carbon sequestration and high strength lightweight building material of this application includes:

[0042] Preparation of biochar: Biochar is obtained by sieving biomass raw materials to a size of less than 2 mm and then pyrolyzing them in a tubular furnace.

[0043] Activation treatment of biochar: The biochar is immersed in an activation solution at a certain ratio and stirred continuously with a magnetic stirrer for 11h, 12h, or 13h. After standing at room temperature for 23h, 24h, or 25h, it is dried in an oven at 110℃, 120℃, or 130℃ for 50h, 48h, or 46h. After cooling to room temperature, it is rinsed with hydrochloric acid (HCl) at a concentration of 0.5mol / L, 1mol / L, or 1.5mol / L, and then washed with deionized water until the pH is neutral. After vacuum filtration, it is dried in an oven at 100℃, 105℃, or 110℃ for 13h, 12h, or 11h to obtain activated porous biochar. The activation solution is a KOH solution with a mass concentration of 35%, 40%, or 45%, and the mixing ratio of biochar to activation solution is 1:4, 1:5, or 1:6.

[0044] Biochar and solid waste raw material mixing: The activated biochar is mixed with crushed and ground solid waste raw materials, binder and cement in a certain proportion. The mixture is stirred at high speed in a concrete mixer for 1.5 min, 2 min or 2.5 min until uniform, and the mixture is divided into two parts. The first part accounts for 60%, 70% or 80% by weight. The solid waste raw materials include fly ash, coal gangue and desulfurized gypsum. The binder is blast furnace slag.

[0045] Preparation of biochar-modified lightweight aggregate: The first part of the mixture is transferred into a disc granulator and sprayed with deionized water for 2 min, 3 min or 4 min at a speed of 35 rpm, 37 rpm or 40 rpm to form a granular mixture. Then the second part of the mixture is added evenly without water spraying and automatically formed to finally obtain spherical lightweight aggregate of 4.75 mm, 10 mm or 16 mm.

[0046] Curing of lightweight aggregate: The lightweight aggregate is cured according to the process of pre-curing - carbonation curing - subsequent wet curing; when pre-curing the lightweight aggregate, the moisture content of the lightweight aggregate is controlled at 11%, 13% or 15%.

[0047] Drying of lightweight aggregate: After curing, the lightweight aggregate is placed in a drying oven to dry, thereby obtaining the lightweight building material. The drying conditions for the lightweight aggregate are: temperature 60℃, 65℃ or 70℃, and drying time 13h, 12h or 11h.

[0048] The specific weight proportions of each component can be: 20 parts cement: 40 parts fly ash: 10 parts coal gangue: 10 parts desulfurized gypsum; or 20 parts cement: 50 parts fly ash: 15 parts coal gangue: 15 parts desulfurized gypsum; or 20 parts cement: 60 parts fly ash: 20 parts coal gangue: 20 parts desulfurized gypsum. The weight proportion of blast furnace slag can be 5 wt%, 7 wt%, or 10 wt% of the sum of the weight of solid waste raw materials and cement, and the weight proportion of activated biochar can be 1 wt%, 3 wt%, 5 wt%, or 7 wt% of the sum of the weight of solid waste raw materials and cement.

[0049] The method in this application uses porous biochar as a modifying material, which can regulate the pore structure inside the solid waste-based lightweight aggregate, effectively improve the carbonization degree of the lightweight aggregate, thereby increasing its carbonization efficiency and ultimately improving the overall quality of the finished lightweight building materials. At the same time, the method optimizes and regulates the flue gas emitted from actual steelmaking furnaces, cement kilns, and coal-fired power plants for CO2 curing, realizing "waste treatment with waste".

[0050] The method of this application is further illustrated below with specific embodiments.

[0051] The examples provided are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, specific conditions were applied in the examples. Reagents or instruments used, unless otherwise stated, are commercially available products.

[0052] In the following embodiments, the solid waste materials used include fly ash, coal gangue, desulfurized gypsum and blast furnace slag. The flue gas emitted from steelmaking furnaces, cement kilns and coal-fired power plants containing CO2 was obtained through laboratory simulation. The basic composition is shown in Table 1.

[0053] Table 1. Main chemical composition of raw materials (wt%)

[0054] Element <![CDATA[SiO2]]> <![CDATA[Al2O3]]> CaO <![CDATA[SO3]]> <![CDATA[Fe2O3]]> <![CDATA[Na2O]]> <![CDATA[TiO2]]> MgO other fly ash 35.44 32.16 1.63 1.03 2.70 0.312 1.42 0.429 24.849 Coal gangue 52.82 23.73 1.6 0.322 3.71 0.450 0.807 0.728 15.833 Desulfurized gypsum 1.67 0.62 39.02 - - - - - - Blast furnace slag 28.00 15.91 39.6 0.00 0.268 0.244 0.576 6.90 8.499 cement 22.54 7.83 50.81 4.67 3.48 0.393 0.454 3.60 6.223

[0055] Example 1

[0056] Methods for preparing lightweight building materials with high carbon sequestration and high strength include:

[0057] Preparation of biochar: Corn stalks were washed and dried to constant weight at 60-70℃, sieved to below 2mm, and then pyrolyzed in a tube furnace at 400℃ for 2h. After natural cooling, the stalks were crushed and sieved to below 75μm to obtain biochar.

[0058] Activation treatment of biochar: The biochar was immersed in a 40% KOH solution (solid-liquid ratio = 1:5) and stirred continuously for 12 h with a magnetic stirrer. After standing at room temperature for 24 h, it was dried in an oven at 120℃ for 48 h. After cooling to room temperature, it was rinsed with 1 mol / L hydrochloric acid (HCl) and washed with deionized water until the pH was neutral. After vacuum filtration, it was dried in an oven at 105℃ for 12 h to obtain activated porous biochar.

[0059] Biochar and solid waste raw material mixing: The activated biochar is mixed with crushed, ground, and sieved solid waste raw materials to below 200μm and cement in a certain proportion. After high-speed mixing for 2 minutes in a concrete mixer, the mixture is obtained. The ratio of solid waste powder to cement in the mixture is 4:1. The specific compounding ratio is cement / fly ash / coal gangue / desulfurized gypsum = 2:4:1:1. The activated biochar content is 1-7 wt%. Then the mixture is divided into two parts, with the first part accounting for 70% of the weight.

[0060] Preparation of biochar-modified lightweight aggregate: The first part of the mixture is transferred into a disc granulator and sprayed with deionized water for 2 minutes at a speed of 37 rpm to form a granular mixture. Then, the second part of the mixture is added evenly without water spraying and automatically formed to finally obtain spherical lightweight aggregate of 4.75-16 mm.

[0061] Curing of lightweight aggregate: The lightweight aggregate is first placed in a pre-curing box at 23℃ and 70%RH for 2 days, and then transferred to a carbonization curing reactor. CO2-containing flue gas is introduced for carbonization curing for 2 hours at a pressure of 0.5 MPa. Finally, the lightweight aggregate is subjected to subsequent wet curing.

[0062] Drying of lightweight aggregate: The lightweight aggregate is placed in a drying oven at 65°C and dried for 12 hours to obtain the lightweight building material.

[0063] Following the steps above, the weight ratio of biochar was adjusted, and the performance of the final product was tested. The results are shown in Table 2, and the degree of carbonization is shown in Table 3.

[0064] Table 2 Performance test results of lightweight building materials modified with different proportions of biochar

[0065]

[0066] Table 3. Test results of carbonization degree of lightweight building materials modified with different proportions of biochar.

[0067]

[0068]

[0069] Example 2

[0070] Methods for preparing lightweight building materials with high carbon sequestration and high strength include:

[0071] Preparation of biochar: Corn stalks, rice stalks and waste wood chips were washed and dried to constant weight at 60-70℃, sieved to below 2 mm, and then pyrolyzed in a tube furnace at 500℃ for 2 h. After natural cooling, the biochar was crushed and sieved to below 75 μm to obtain biochar.

[0072] Activation treatment of biochar: The biochar was immersed in a 40% KOH solution (solid-liquid ratio = 1:5) and stirred continuously for 12 h with a magnetic stirrer. After standing at room temperature for 24 h, it was dried in an oven at 120℃ for 48 h. After cooling to room temperature, it was rinsed with 1 mol / L hydrochloric acid (HCl) and washed with deionized water until the pH was neutral. After vacuum filtration, it was dried in an oven at 105℃ for 12 h to obtain activated porous biochar.

[0073] Biochar and solid waste raw material mixing: The activated biochar is mixed with crushed, ground, and sieved solid waste raw materials (screened to below 200μm), blast furnace slag binder, and cement in a certain proportion. The mixture is stirred at high speed in a concrete mixer for 2 minutes to obtain a uniform mixture. The activated biochar content in the mixture is 3 wt%, the ratio of solid waste powder to cement is 4:1, and the specific compounding ratio is cement / fly ash / coal gangue / desulfurized gypsum = 2:4:1:1. The blast furnace slag binder content is 5 wt%. The mixture is then divided into two parts, with the first part accounting for 70% of the weight.

[0074] Preparation of biochar-modified lightweight aggregate: The first part of the mixture is transferred into a disc granulator and sprayed with deionized water for 2 minutes at a speed of 37 rpm to form a granular mixture. Then, the second part of the mixture is added evenly without water spraying and automatically formed to finally obtain spherical lightweight aggregate of 4.75-16 mm.

[0075] Curing of lightweight aggregate: The lightweight aggregate is first placed in a pre-curing box at 23℃ and 70%RH for 2 days, and then transferred to a carbonization curing reactor. CO2-containing flue gas is introduced for carbonization curing for 2 hours at a pressure of 0.5 MPa. Finally, the lightweight aggregate is subjected to subsequent wet curing.

[0076] Drying of lightweight aggregate: The lightweight aggregate is placed in a drying oven at 65°C and dried for 12 hours to obtain the lightweight building material.

[0077] Following the steps above, the type of biochar was adjusted, and the performance of the final product was tested. The performance test results of the finished products with different types of biochar are shown in Table 4, and the degree of carbonization is shown in Table 5.

[0078] Table 4 Performance test results of different types of biochar-modified lightweight building materials

[0079]

[0080]

[0081] Table 5. Test results of carbonization degree of different types of biochar-modified lightweight building materials

[0082] Types of biochar Natural pH value Hydroxide alkalinity / % Carbonate alkalinity / % none 11.97 82.65 18.15 Corn stalk biochar 11.02 67.61 32.39 Rice straw biochar 11.28 68.91 31.09 Wood biochar 11.46 64.26 25.74

[0083] The carbon fixation test results of the samples from each embodiment show that the lightweight aggregates based on solid waste absorbed a certain amount of CO2 after carbonization curing. This is because the calcium oxides and hydroxides in the aggregate medium react with CO2 to form stable carbonate minerals (such as CaCO3). The addition of biochar further enhances the carbon fixation capacity of the lightweight aggregates. With the increase of biochar content, the CO2 absorption rate of the aggregate medium gradually increases, and different types of biochar have different degrees of improvement on the carbon fixation of lightweight aggregates. Among them, corn straw biochar has the greatest improvement. It can be concluded that biochar, as a modifier, can effectively improve carbonization efficiency. In addition, adding blast furnace slag as a binder to the addition of 3 wt% biochar can further improve carbonization efficiency and promote the absorption of CO2 by lightweight aggregates.

[0084] The degree of carbonation and alkalinity characteristics of lightweight aggregate samples were quantitatively analyzed using carbonate alkalinity. Total alkalinity is the amount of acid required to lower the sample's natural pH from the reagent water to the endpoint pH of 4.5 on the alkalinity curve. Simultaneously, hydroxide alkalinity is established by measuring the amount of acid required to lower the extraction pH to 8.3. Carbonate alkalinity is the difference between total alkalinity and hydroxide alkalinity. The carbonate alkalinity test results of the samples from various embodiments show that the lower the natural pH of the prepared lightweight aggregate, the higher the carbonate alkalinity, indicating a greater degree of carbonation. Furthermore, the degree of carbonation of the aggregate increases with the increase in the proportion of biochar incorporation. Among the three types of biochar incorporation, corn straw biochar showed significant superiority in improving the degree of carbonation of lightweight aggregate. In addition, the carbon fixation capacity of lightweight aggregate also showed a significant correlation with the degree of carbonation; the higher the carbon fixation capacity, the greater the degree of carbonation.

[0085] The performance test results of the samples from each embodiment show that the bulk density of the prepared solid waste-based aggregate is less than 1200 kg / m³. 3It meets the requirements of lightweight aggregates of various density grades. When the added biochar is corn straw biochar at a dosage of 3 wt%, the bulk density of the lightweight aggregate increases to the maximum, the water absorption rate decreases to the minimum, and the compressive strength of the cylinder reaches the maximum. Moreover, for lightweight aggregates made from the same raw materials, the degree of increase in bulk density, the degree of decrease in water absorption rate, and the degree of increase in compressive strength show a positive correlation.

[0086] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions or parameter settings of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing lightweight building materials with high carbon fixation content and high strength, characterized in that, Includes the following steps, Preparation of biochar: Biochar is obtained by screening biomass raw materials to a particle size of less than 2 mm and then pyrolyzing them in a tubular furnace. Activation treatment of biochar: The biochar is immersed in an activation solution at a certain ratio and stirred continuously for 11-13 h. After standing at room temperature for 23-25 ​​h, it is dried in an oven at 110-130℃. After cooling to room temperature, it is washed until the pH is neutral. After vacuum filtration, it is dried in an oven at 100-110℃ to obtain modified porous biochar. The activation solution is a KOH solution with a mass concentration of 35%-45%, and the mixing ratio of biochar to activation solution is 1:4-6. Biochar and solid waste raw material mixing: The activated biochar is mixed with crushed and ground solid waste raw materials, binder and cement. The mixture is stirred at high speed in a concrete mixer for 1.5-2.5 minutes to obtain a uniform mixture. The mixture is divided into two parts. The first part accounts for 60%-80% by weight. The solid waste raw materials include fly ash, coal gangue and desulfurized gypsum. The binder is blast furnace slag. Preparation of biochar-modified lightweight aggregate: The first part of the mixture is transferred into a granulator and sprayed with deionized water for 2-4 minutes at a speed of 35-40 rpm to form a granular mixture. Then, the second part of the mixture is added evenly. No water spraying is required. The mixture is automatically formed and finally spherical lightweight aggregate of 4.75-16 mm is obtained. Curing of lightweight aggregate: The lightweight aggregate is cured according to the process of pre-curing - carbonation curing - subsequent wet curing; when pre-curing the lightweight aggregate before carbonation curing, the moisture content of the lightweight aggregate is controlled at 11%-15%; Drying of lightweight aggregate: After curing, the lightweight aggregate is placed in a drying oven to dry, thereby obtaining the lightweight building material.

2. The method for preparing high-carbon-content, high-strength lightweight building materials according to claim 1, characterized in that, The drying conditions for the lightweight aggregate are: temperature 60-70℃, drying time 11-13h.

3. The method for preparing the high carbon content and high strength lightweight building material according to claim 1, characterized in that, The lightweight aggregate has a 1-hour water absorption rate of 8.76%-13.29% and a bulk density of 952.63-1143.94 kg / m³. 3 The cylinder compressive strength is 10.13-14.16 MPa, and the CO2 absorption rate is 9.36 wt%-13.15 wt%.

4. The method for preparing high-carbon-content, high-strength lightweight building materials according to claim 1, characterized in that, The biochar is one or a mixture of several of the following: corn stalk biochar, rice stalk biochar, and sawdust biochar.

5. The method for preparing high-carbon-content, high-strength lightweight building materials according to claim 1, characterized in that, The ratio of solid waste raw materials to cement is 3-5:

1.

6. The high-carbon-content, high-strength lightweight building material prepared by the preparation method according to any one of claims 1-5, characterized in that, The weight proportions of each component of the lightweight building material are as follows: 20 parts cement, 40-60 parts fly ash, 10-20 parts coal gangue, and 10-20 parts desulfurized gypsum. The weight proportion of blast furnace slag is 5 wt%-10 wt% of the sum of the weight of solid waste raw materials and cement. The weight proportion of activated biochar is 1 wt%-7 wt% of the sum of the weight of solid waste raw materials and cement.

7. The high carbon sequestration and high strength lightweight building material according to claim 6, characterized in that, The activated biochar is 3 wt%-7 wt% of the sum of the weight of the solid waste raw materials and cement.

8. The use of the high carbon sequestration and high strength lightweight building material according to claim 7, characterized in that, It is used as a lightweight aggregate in the preparation of concrete.

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