Method and device for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag

Abstract

The present invention discloses a method and device for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag. The method comprises the following steps: (1) mixing carbide slag with water, sealing and allowing the mixture to stand to obtain a carbide slag suspension; (2) introducing carbon-fixing gas containing carbon dioxide into the carbide slag suspension while stirring the mixture in a sealed state to carry out a carbon-fixing reaction, and obtaining a pre-carbonized carbide slag slurry after the carbon-fixing reaction is completed; (3) mixing and stirring the pre-carbonized carbide slag slurry with cement slurry dry material to obtain a carbide slag clean slurry; (4) injecting the carbide slag clean slurry into a mold for molding, and obtaining a carbide slag cement blank after demoulding; and (5) placing the carbide slag cement blank in a carbon curing box for carbon curing, and obtaining a finished cement-based building material after the carbon curing is completed. The present invention can solve the technical problem that the existing carbide slag carbonization cannot directly utilize the low-concentration carbon dioxide flue gas recovered industrially.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon dioxide sequestration, in particular to a method and device for preparing cement-based building materials by utilizing carbon dioxide pre-carbonized carbide slag. Background Art

[0002] With the increasing emission of the greenhouse gas CO2, carbon reduction strategies have become increasingly important. Most researchers are using carbon curing of building materials to achieve this goal. Carbon curing involves the incorporation of CO2 into cementitious materials, where carbon is stored through a carbon-solidification reaction. In recent years, the direct mixing of CO2 with cementitious materials has become a highly sought-after internal carbon sequestration technology. Its core technology involves injecting CO2 captured from industrial sources into the mixture during the mixing process of concrete, mortar, and other materials. This allows the CO2 to react with Portland cement clinker minerals and their hydration products to form a carbon mineralization reaction, thereby improving product performance and reducing its carbon footprint. However, the use of carbon curing and direct mixing of CO2 with cementitious materials alone does not achieve significant carbon sequestration results. Combining these two methods can improve carbon sequestration rates to a certain extent. Therefore, the synergistic use of direct mixing of CO2 with cementitious materials and carbon curing is more beneficial for carbon sequestration. In the early stages, internal carbon fixation is achieved by mixing cement-based materials with CO2. In this initial stage, CO2 reacts with the hydration product Ca(OH)2 within the cement-based materials to form CaCO3. The presence of fine CaCO3 particles acts as seed crystals, promoting the carbon solidification reaction during the subsequent carbon curing process. Therefore, developing a new carbon fixation method for mixing cement-based materials with CO2 is of great significance.

[0003] Calcium carbide slag is a type of industrial waste residue and a by-product of the hydrolysis of calcium carbide (CaC2) to produce acetylene. Its main component is Ca(OH)2 (content >80%), and it has great potential for mineralization and fixation of CO2. my country is a major emitter of calcium carbide slag solid waste. Therefore, harmless treatment of calcium carbide slag and efficient resource utilization are the only way to solve the environmental pollution problem in the calcium carbide industry.

[0004] Patent CN115215586A discloses a method for preparing autoclaved aerated concrete bricks by wet-grinding carbonization with carbide slag. This method involves adding water to the carbide slag and wet-ball milling it. Carbon dioxide is introduced during the milling process to fix the carbon. After carbonization, the resulting carbon-fixed slurry is mixed with cement, gypsum, lime, and fine aggregate (tailings), stirred, and then water and aluminum powder are added to form a mixed mortar. Finally, the mixed mortar is formed and carbon-cured to produce concrete bricks. While industrial solid waste carbide slag can be utilized, this method requires the introduction of carbon dioxide during the wet ball milling process for carbonization, resulting in low carbonization efficiency, high mechanical energy consumption, and the need for a relatively high concentration of carbon dioxide (40% to 60%) to achieve effective carbonization. However, the carbon dioxide concentration in flue gas emitted during industrial production is only 20%, making it unsuitable for direct use in this method. Therefore, further improvements are needed to reduce the energy consumption and improve the efficiency of carbonization with carbide slag, allowing low-concentration carbon dioxide to be directly used for carbonization. Summary of the Invention

[0005] To this end, the technical problem to be solved by the present invention is to provide a method and apparatus for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag, so as to solve the technical problem that the existing carbide slag carbon fixation cannot directly utilize the low-concentration carbon dioxide flue gas recovered industrially. The present invention uses carbide slag for early pre-carbonization and later carbonization not only solves the problem of carbon emission reduction, but also effectively utilizes industrial solid waste carbide slag. If it is applied on a large scale in practice, it will produce good economic benefits.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A method for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag comprises the following steps:

[0008] Step (1), mixing carbide slag with water and sealing and letting it stand to obtain a carbide slag suspension;

[0009] Step (2), in a sealed state, introducing a carbon-fixing gas containing carbon dioxide into the carbide slag suspension while stirring to carry out a carbon-fixing reaction, and after the carbon-fixing reaction is completed, obtaining a pre-carbonized carbide slag slurry;

[0010] Step (3), mixing the pre-carbonized carbide slag slurry with the cement slurry dry material to obtain carbide slag cement slurry;

[0011] Step (4), injecting carbide slag cement slurry into a mold to form it, and then demoulding to obtain a carbide slag cement blank;

[0012] Step (5): placing the carbide slag cement blank in a carbon curing box for carbon curing. After the carbon curing is completed, a finished cement-based building material is obtained.

[0013] The present invention utilizes a method for preparing cement-based building materials from carbon dioxide pre-carbonized carbide slag. In the pre-mixed carbide slag process, carbon dioxide is introduced into the pre-carbonized carbide slag slurry to prepare the pre-carbonized carbide slag slurry, thereby avoiding the problem of incompatibility between the pre-carbonized carbide slag and cement caused by directly adding the carbide slag. The prepared pre-carbonized carbide slag slurry is then mixed with cement paste to prepare carbide slag cement blank. Finally, the carbide slag cement blank is subjected to carbon curing to obtain a finished cement-based building material. The CaCO generated in the pre-mixed carbide slag process promotes the carbon curing reaction in the carbon curing process as a crystal seed. Throughout the entire process, the green concept of solid waste carbon fixation is realized through the utilization of carbide slag waste and two technical means of internal and external carbon fixation, making significant contributions to protecting the environment, improving economic efficiency, enhancing mechanical properties, and alleviating the greenhouse effect.

[0014] In the method for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag, in step (1), the carbide slag has a particle size range of 5 to 75 μm; the mass ratio of carbide slag to water is 1:(1.5-5); and the sealed and standing time is 10 to 20 minutes. Carbide slag of this particle size range can be mixed with water at a mass ratio of 1:(1.5-5) to form a carbide slag suspension of moderate concentration. After 10 to 20 minutes of sealed and standing, as much calcium hydroxide (CH) in the carbide slag as possible can be dissolved and dispersed in the water, which is conducive to the subsequent carbonization reaction.

[0015] If the particle size of carbide slag is too large, the calcium hydroxide in the form of "lime milk" in the carbide slag suspension cannot be replenished and dissolved in water in time to participate in the carbon fixation reaction during the carbon fixation process, thereby affecting the carbon fixation effect. If the particle size of carbide slag is too small, the generated calcium carbonate particles will wrap the calcium hydroxide and affect its participation in the carbon fixation reaction.

[0016] If the ratio of carbide slag to water in the carbide slag suspension exceeds the above range, for example, if the amount of carbide slag is too large, the "lime milk" in the formed carbide slag suspension will be denser, and during the carbon fixation reaction, the calcium hydroxide in the "lime milk" will not be easily released quickly, thereby affecting the efficiency of the carbon fixation reaction; and, excessive carbide slag will also affect the strength of the cement-based building materials finally formed; but if the amount of carbide slag is too small, the introduced carbon dioxide gas will find it difficult to capture sufficient calcium hydroxide and will not react fully, thereby affecting the utilization rate of carbon dioxide in the carbon fixation gas.

[0017] The present invention controls the ratio of carbide slag in a specific particle size range to water in the carbide slag suspension within the above-mentioned range, so that a part of the calcium hydroxide in the carbide slag can be fully dissolved in the water, and the other part can be combined with water to temporarily form "lime milk" with moderate density. During the carbon fixation reaction, the calcium hydroxide in the "lime milk" can be continuously and rapidly released into the water to participate in carbon fixation as the calcium hydroxide in the water is consumed. This can not only significantly improve the carbon fixation efficiency of the carbide slag, but also provide the introduced carbon fixation gas with sufficient carbon fixation reaction opportunities, so that the carbon dioxide in the carbon fixation gas with low carbon dioxide concentration can also be fully utilized, and the flue gas recovered from the cement plant or steel plant can be directly utilized to avoid the use of high-concentration carbon dioxide.

[0018] In the above-mentioned method for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag, in step (1), the particle size range of the carbide slag is 10 to 40 μm; the mass ratio of the carbide slag to water is 1:2.5; and the sealed static time is 10 minutes. The purpose of the sealed static time is to dissolve as much calcium hydroxide in the carbide slag as possible, thereby increasing the pH of the carbide slag suspension. At this time, the introduction of carbon dioxide is more likely to cause a reaction, which is beneficial to improving the carbon fixation efficiency and the utilization rate of carbon dioxide in the carbon fixation gas. If the static sealing is not performed and the carbon fixation gas containing CO2 is immediately introduced for carbon fixation reaction, the CO2 in the carbon fixation gas will be more soluble in water than calcium hydroxide, thereby rapidly reducing the pH value of the carbide slag suspension. The acidic environment thus formed is more unfavorable for the carbonization reaction, thereby being unfavorable for the full utilization of the low-concentration carbon dioxide carbon fixation gas.

[0019] In the above-mentioned method for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag, in step (2), during the carbon fixation reaction: the stirring rate is 600-800 rpm; the flow rate of the carbon fixation gas is 1.5-2.5 L / min; the carbon fixation reaction is carried out at room temperature; the carbon fixation reaction time is 10-30 minutes; and the volume concentration of carbon dioxide in the carbon fixation gas is greater than or equal to 20%.

[0020] During the carbon fixation reaction, if the stirring rate is too low, the CO2 gas will not be evenly distributed in the carbide slag suspension, affecting the contact effect between the carbide slag and CO2, resulting in insufficient CaCO3 production, which not only affects the carbon fixation efficiency, but also affects the strength and hardening properties of the cement slurry. If the stirring rate is too high, the CO2 bubbles will burst too quickly, thereby reducing the dissolution efficiency of CO2 and affecting the uniformity of the reaction. If the flow rate of the carbon fixation gas is too large, the excess CO2 will be directly discharged before it has time to react, greatly reducing the utilization rate of CO2. If the flow rate of the carbon fixation gas is too small, the pre-carbonization effect will be reduced, and the purpose of carbon fixation and improving compatibility with cement will not be achieved. If the pre-carbonization reaction time is too short, the carbonization reaction will be incomplete, insufficient CaCO3 will be generated, the pH value of the carbide slag suspension will remain high, the carbon fixation will be low, and the compatibility with cement will not be improved. If the pre-carbonization time is too long, the generated CaCO3 particles will accumulate. When there are too many CaCO3 particles, since the CaCO3 particles mainly play a filling role and do not participate in the hydration reaction like Ca(OH)2, too many CaCO3 particles will cause the pore structure of the cement slurry to be less dense, which will ultimately affect the strength and density of the cement. The present invention can effectively improve the utilization rate and carbon fixation efficiency of carbon dioxide by controlling the carbon fixation gas flow rate, stirring rate and carbon fixation time during the carbon fixation reaction within the above ranges, so that the carbon dioxide in the carbon fixation gas with low concentration of carbon dioxide is fully utilized, and at the same time provide a basis for subsequently obtaining cement-based building materials with better mechanical properties.

[0021] In the above-mentioned method for preparing cement-based building materials using carbon dioxide pre-carbonized calcium carbide slag, in step (2), during the carbon fixation reaction: the stirring rate is 600 rpm; the flow rate of carbon dioxide gas is 2.0 L / min; the carbon fixation reaction time is 20 min; the carbon fixation gas is carbon dioxide gas with a purity of 99.99% by volume that has been liquefied and purified; or, the carbon fixation gas is a mixture of carbon dioxide gas with a purity of 99.99% by volume that has been liquefied and purified and air; or, the carbon fixation gas is flue gas recovered from a cement plant and / or steel plant.

[0022] Compared with the wet ball milling carbon fixation method in the background technology patent CN115215586A, the present invention has the following advantages: (1) faster reaction rate: when CO2 is introduced into the carbide slag suspension, the reaction is faster. During the carbon fixation process, stirring at a stirring rate of 600 rpm will make the carbide slag suspension in a flowing state, which is conducive to the rapid reaction of CO2 and calcium hydroxide. In addition, due to the rapid reaction, the reaction releases heat more quickly, the temperature rises rapidly, and the reaction is further promoted. (2) higher economic benefits: carbide slag of a specific particle size range is mixed with water in a specific mass ratio, and then sealed and allowed to stand for a certain period of time to form a carbide slag suspension, and a specific stirring rate and solidification rate are used. The carbon gas flow rate is used to introduce carbon-fixing gas into the carbide slag suspension, which can fully utilize low-concentration carbon dioxide gas (the volume concentration of carbon dioxide is greater than or equal to 20%). Therefore, this process is more conducive to docking with industrialization. For example, the flue gas recovered from cement plants or steel plants has a CO2 volume concentration of about 20%, which can be directly used for carbide slag carbon fixation without treatment, and does not require complex mechanical equipment, so the cost is low; (3) Low energy consumption: the carbon fixation method of introducing CO2 into the carbide slag suspension is more energy-saving and does not require high mechanical energy input; (4) The operation steps are simple: it is only necessary to mix water with carbide slag to prepare carbide slag suspension, and then mix the carbide slag suspension with cement slurry dry material, which is easy to operate.

[0023] In addition, when preparing carbide slag cement slurry, the present invention only needs to mix the pre-carbonized carbide slag slurry obtained after carbon fixation with the cement slurry dry material. In this process, there is no need to add water for the second time to prepare the pure slurry. Therefore, there are fewer bubbles and denser pores. The resulting cement-based building materials have higher strength and a wider range of applications.

[0024] In the above-mentioned method for preparing cement-based building materials using carbon dioxide precarbonized carbide slag, in step (3), the mass ratio of the precarbonized carbide slag slurry to the cement slurry dry material is 1:(0.8-1.5); the mixing and stirring time is 3-10 minutes; the cement slurry dry material is a composite material with cement as a gelling material; and the preparation method of the cement slurry dry material is: mixing and stirring the raw material components of the cement slurry dry material according to the designed proportion for 3-5 minutes. The present invention controls the amount ratio of the precarbonized carbide slag slurry to the cement slurry dry material so that the water-cement ratio of the finally prepared carbide slag cement slurry is within an appropriate range, thereby making the carbide slag cement slurry have relatively ideal fluidity, avoiding segregation during the preparation of cement-based building materials, affecting the uniformity of the carbide slag cement slurry, and causing stratification and uneven hardening effects, while also ensuring that the cement is fully hydrated, so that the finally prepared cement-based building materials have ideal mechanical properties.

[0025] In the above-mentioned method for preparing cement-based building materials using carbon dioxide precarbonized carbide slag, in step (3), the mass ratio of precarbonized carbide slag slurry to cement slurry is 1:1.14; the mixing time is 3 minutes; the cement slurry dry material is cement, cement mortar dry material (mixed by cement and sand in a mass ratio of 1:3 to 6) or concrete dry material (mixed by cement, sand and gravel in a mass ratio of 1:2 to 3:3 to 6); the mixing time when preparing the cement slurry dry material is 3 minutes; and the cement is ordinary Portland cement with a strength grade of 42.5.

[0026] In the above-mentioned method for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag, in step (4), the carbide slag cement slurry molding conditions are: standing at room temperature and pressure for 24 hours before demolding; in step (5), the carbon curing conditions are: carbon dioxide volume concentration of 20±3%, relative humidity of 70±5%, temperature of 20±3°C; and carbon curing time is 7 to 28 days. During the carbon-oxygen curing process: if the carbon dioxide concentration is too high, the carbonization reaction of the specimen surface will be too fast, affecting the carbonization reaction of the inner layer of the specimen, thereby affecting the strength of the specimen; if the carbon dioxide concentration is too low, Ca(OH)2 cannot be fully converted into CaCO3, lacking sufficient filling effect and seed effect, and thus cannot effectively improve the microstructure and strength of the specimen; if the relative humidity is too high, there will be too much moisture on the surface of the specimen, which will cause the hydration reaction to proceed rapidly. The exothermic expansion of the hydration reaction will cause the pores to increase, affecting the density of the specimen; if the humidity is too low, it will affect the hydration process of the cement, resulting in incomplete hardening of the cement, thereby reducing the ultimate strength of the specimen; if the temperature is too high, it will accelerate the hydration reaction of the cement, causing the cement slurry to generate too much heat, resulting in cracks on the cement surface, affecting its ultimate strength and durability; when the temperature is too low, the cement hydration reaction rate will be significantly reduced, resulting in a delay in the cement hardening process, affecting the strength development of the specimen. Under the above-mentioned carbon curing conditions of the present invention, the purpose of "making full use of the pre-carbonized calcium carbonate as a seed for carbon fixation reaction in a relatively low concentration of carbon dioxide environment, and further improving the mechanical properties of cement-based building materials" can be achieved.

[0027] In the above method for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag, in step (1), the particle size of the carbide slag is in the range of 10 to 40 μm; the mass ratio of the carbide slag to water is 1:2.5; and the sealed standing time is 10 minutes;

[0028] In step (2), during the carbon fixation reaction, the stirring rate is 600 rpm; the flow rate of the carbon fixation gas is 2.0 L / min; the carbon fixation reaction is carried out at room temperature; the carbon fixation reaction time is 20 min; the carbon fixation gas is flue gas recovered from a cement plant and / or a steel plant, and the volume concentration of carbon dioxide in the flue gas is 20%;

[0029] In step (3), the mass ratio of the pre-carbonized carbide slag slurry to the cement slurry is 1:1.14; the mixing time is 3 minutes; the cement slurry is ordinary Portland cement with a strength grade of 42.5;

[0030] In step (4), the carbide slag cement slurry molding conditions are: standing at room temperature and pressure for 24 hours and then demoulding;

[0031] In step (5), the carbon curing conditions are: a volume concentration of carbon dioxide of 20%, a relative humidity of 70%, and a temperature of 20° C.; and the carbon curing time is 28 days.

[0032] A device for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag comprises a carbon dioxide storage container, a primary mixing container, an exhaust gas absorption tank, a secondary mixing container, a building material forming mold, and a carbon curing box; the gas outlet end of the carbon dioxide storage container is fluidly connected to the gas inlet end of the primary mixing container, the gas outlet end of the primary mixing container is fluidly connected to the gas inlet end of the exhaust gas absorption tank; the slurry outlet end of the primary mixing container is fluidly connected to the slurry inlet end of the secondary mixing container; the slurry outlet end of the secondary mixing container is fluidly connected to the slurry inlet end of the building material forming mold; after demolding the building material forming mold, the carbide slag cement blank is transferred to the carbon curing box for carbon curing;

[0033] Carbide slag and water are added to a primary mixing container, mixed, sealed and allowed to stand to obtain a carbide slag suspension; in a sealed state, carbon-fixing gas containing carbon dioxide is introduced into the carbide slag suspension using a carbon dioxide storage container while stirring to carry out a carbon fixation reaction, and after the carbon fixation reaction is completed, pre-carbonized carbide slag slurry is obtained; the waste gas discharged from the primary mixing container is introduced into a waste gas absorption tank; the pre-carbonized carbide slag slurry and cement slurry dry material are added to a secondary mixing container, mixed and stirred to obtain carbide slag cement slurry; the carbide slag cement slurry is injected into a building material forming mold for forming, and a carbide slag cement blank is obtained after demolding; the carbide slag cement blank is placed in a carbon curing box for carbon curing, and after the carbon curing is completed, a finished cement-based building material is obtained.

[0034] The technical solution of the present invention achieves the following beneficial technical effects:

[0035] 1. The present invention adopts a method of coordinating CO2 premixed carbide slag and carbon curing to prepare cement-based building materials. CO2 is absorbed and fixed during the CO2 mineralization premixed carbide slag process, and the CO2 can be effectively captured. The generated CaCO3 product can continue to play a role as a seed in the carbon curing process. During the carbon curing process, CO2 further undergoes a carbon solidification reaction with the hydration products in the cement and the incompletely reacted carbide slag. Through the combined action of the two carbon fixation methods, the carbon fixation rate can be maximized, and a green and environmentally friendly carbon fixation effect can be achieved.

[0036] 2. The present invention adopts carbide slag as an enhanced carbon-fixing material to improve the carbon-fixing efficiency of CO2 directly mixed with cement-based materials, which can avoid the problem of incompatibility with cement caused by directly adding carbide slag to cement, as well as the low solubility of CO2 during pre-carbonization and the low diffusion rate in cement particles. The principle is that Ca(OH)2 in carbide slag first reacts with CO2 to generate CaCO3. The generated CaCO3 greatly improves the mechanical properties of building materials products, which not only achieves carbon emission reduction of greenhouse gases (industrial waste gas containing low concentration of carbon dioxide is directly utilized), but also effectively utilizes industrial solid waste, realizes the green concept of carbon fixation of solid waste and waste gas, and has great economic and social benefits.

[0037] 3. The present invention adopts the concept of synergistic preparation of low-carbon cement-based materials and resource utilization of carbide slag to solve the difficult problems of low carbon fixation efficiency of CO2 on cement-based materials and resource utilization of carbide slag. Carbide slag is first used to pre-mix CO2, and then the test pieces made by mixing the pre-mixed carbide slag with cement slurry are carbon-cured. This "pre-carbonization-re-carbonization" two-stage carbon fixation technology not only solves the problem of carbon emission reduction, but also effectively utilizes industrial solid waste and industrial waste gas (flue gas containing a lower concentration of carbon dioxide). The carbide slag cement-based environmentally friendly material in the present invention can not only promote the absorption and fixation of CO2, but also the CaCO3 generated in the CO2 pre-mixing process and the carbon curing process increases the density of the building material, thereby improving the mechanical properties of the building material product. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the carbide slag pre-carbonization reaction in an embodiment of the present invention;

[0039] Figure 2 The device for preparing pre-carbonized carbide slag cement slurry in the embodiment of the present invention;

[0040] Figure 3 A technical roadmap for preparing carbide slag cement-based building materials according to an embodiment of the present invention;

[0041] Figure 4 Relationship diagram between carbon curing time and carbon fixation rate under different pre-carbonization times in the embodiment of the present invention (10% carbide slag content);

[0042] Figure 5 Relationship diagram between carbon curing time and carbon fixation rate under different pre-carbonization times in the embodiment of the present invention (with 20% carbide slag content);

[0043] Figure 6 Relationship diagram between carbon curing time and carbon fixation rate under different pre-carbonization times in the embodiment of the present invention (30% carbide slag content);

[0044] Figure 7 Relationship diagram between carbide slag dosage and compressive strength under different curing methods in the embodiment of the present invention.

[0045] The reference numerals in the figure are as follows: 1-carbon dioxide storage container; 2-flow controller; 3-magnetic stirrer; 4-rotor; 5-glass tube; 6-rubber hose; 7-temperature measuring rod; 8-wax seal; 9-CaCO3 precipitate; 10-NaOH solution; 11-carbide slag suspension. DETAILED DESCRIPTION

[0046] The method of preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag in this embodiment includes the following steps:

[0047] Step 1: Mix carbide slag with water in a specific proportion, seal, and allow to stand for 10 minutes to obtain a carbide slag suspension. Step 2: After sealing and standing, the carbide slag suspension was stirred at 600 rpm. Simultaneously, carbon-fixing gas (flue gas recovered from a cement plant, with a carbon dioxide concentration of 20%) was diffused into the solution through a glass tube at a rate of 2 L / min, allowing the solution to absorb and fix carbon dioxide while stirring. The carbon dioxide gas was introduced for three different times: 10 minutes, 20 minutes, or 30 minutes. Furthermore, during the carbon dioxide precarbonization process, the pH and conductivity of the precarbonized carbide slag suspension were continuously measured every 2 minutes using a REX PHS-3C pH meter and a DDS-11 conductivity meter. The carbonized product was collected every 5 minutes, vacuum filtered, washed three times with ethanol, dried at 105°C, and then subjected to XRD analysis to analyze the changes in the mineral composition of the carbonized product over the precarbonization time.

[0048] Step 3: Add the carbide slag suspension that has been pre-carbonized for 10 minutes, 20 minutes, or 30 minutes to a slurry mixer, add cement according to the amount in Table 1, and stir for another 3 minutes to prepare carbide slag cement slurry. The mix proportions of the pre-carbonized carbide slag cement slurry are shown in Table 1.

[0049] Table 1 Ratio of pre-carbonized carbide slag cement slurry

[0050]

[0051] In Table 1, the particle size of carbide slag ranges from 10 to 40 μm; the cement is ordinary Portland cement with a strength grade of 42.5.

[0052] Step 4: Inject carbide slag cement slurry into 100×100×100mm 3 The samples were placed in a mold and removed after 24 hours for standard curing and carbonization curing, yielding standard-cured and carbonization-cured specimens, respectively. The standard curing time was 28 days; the carbonization-cured specimens were placed in a TH-B concrete carbonation test chamber under conditions of 70% relative humidity, 20°C, and 20% CO2 concentration for 7, 14, and 28 days.

[0053] Step 5: Compressive strength tests were conducted on standard-cured and carbonized-cured specimens at a loading rate of 2.4 kN / m. Specific procedures were performed in accordance with the "Test Methods for Basic Properties of Building Mortar" (JGJ / T 70-2009). A muffle furnace test was performed on the carbonized-cured specimens. First, the cured sample was sliced ​​into approximately 30g pieces, then dried at 65°C for 3 days. Finally, the sample was heated in a muffle furnace to 520°C and 950°C. The sample mass was measured, and the carbon fixation rate was calculated as follows:

[0054] (1);

[0055] (2);

[0056] Where a is the carbon fixation rate, m 520℃ It is 520 ℃ Sample quality, m 950℃ It is 950 ℃ Sample quality, m c and m ccs is the mass of cement (g) and carbide slag (g) in the sample, M max is the theoretical maximum carbon fixation rate, CaO, SO3, M g O, Na2O, and K2O represent the proportions of each mineral in cement and carbide slag (CCS), respectively. Table 2 shows the proportions of mineral compositions of cement and carbide slag.

[0057] Table 2 Mineral composition ratio of cement and carbide slag

[0058]

[0059] The device for preparing cement-based building materials by using carbon dioxide pre-carbonized carbide slag in this embodiment includes a carbon dioxide storage container, a primary mixing container, a waste gas absorption tank, a secondary mixing container, a building material forming mold and a carbon curing box, wherein the primary mixing container is a closed container; the gas outlet end of the carbon dioxide storage container is fluidly connected to the gas inlet end of the primary mixing container, the gas outlet end of the primary mixing container is fluidly connected to the gas inlet end of the waste gas absorption tank; the slurry outlet end of the primary mixing container is fluidly connected to the slurry inlet end of the secondary mixing container; the slurry outlet end of the secondary mixing container is fluidly connected to the slurry inlet end of the building material forming mold; the carbide slag cement blank after demoulding the building material forming mold is transferred to the carbon curing box for carbon curing protection; adding carbide slag and water into a primary mixing container, mixing and sealing and standing to obtain carbide slag suspension; in a sealed state, using a carbon dioxide storage container to introduce carbon-fixing gas containing carbon dioxide into the carbide slag suspension while stirring to carry out carbon fixation reaction, and after the carbon fixation reaction is completed, obtaining pre-carbonized carbide slag slurry; the waste gas discharged from the primary mixing container is introduced into the waste gas absorption tank; the pre-carbonized carbide slag slurry and cement slurry dry material are added to a secondary mixing container, mixed and stirred to obtain carbide slag cement slurry; the carbide slag cement slurry is injected into a building material forming mold for forming, and after demoulding, a carbide slag cement blank is obtained; the carbide slag cement blank is placed in a carbon curing box for carbon curing, and after the carbon curing is completed, a cement-based building material finished product is obtained.

[0060] For the above-mentioned steps 1 to 3, the preparation method is as follows: Figure 2 The preparation device shown in the figure includes a carbon dioxide storage container 1 and a flow control unit. The gas outlet of the carbon dioxide storage container 1 is connected by a pipeline, and a flow control meter 2 is provided on the pipeline. The device also includes a primary mixing container (a magnetic stirrer 3, a rotor 4 and a beaker with a rubber stopper); the carbon dioxide that has not yet reacted is discharged from the glass tube 5, and a rubber hose 6 is used to connect the glass tube. The conical flask serves as a waste gas absorption tank and contains NaOH solution 10, which is used to absorb the carbon dioxide that has not yet reacted, thereby achieving an environmental protection effect. The calcium carbide slag suspension 11 generated by pre-carbonization and the CaCO3 precipitate 9. It should be noted that the test must be carried out in a sealed state, so a wax seal 8 must be performed. During the test, a temperature measuring rod 7 can be used to detect the temperature.

[0061] In step 1 to step 5, the technical roadmap of the two-stage carbonization of carbide slag cement-based materials is as follows: Figure 3 As shown, in this embodiment, the secondary mixing container is a pure pulp mixer, the carbon curing box is a TH-B type carbonization box; the building material forming mold is 100×100×100mm 3 box.

[0062] Figures 4 to 6 The relationship between different carbide slag dosage, pre-carbonization time, carbon curing time and carbon fixation rate. Figures 4 to 6It can be obtained that: when the dosage is constant, the carbon fixation rate gradually increases with the increase of carbon curing time and tends to be stable in the later period; the carbon fixation rate increases with the increase of pre-carbonization time; in addition, when the carbide slag dosage increases from 10% to 20% and 20% to 30%, the carbon fixation rate increases by 1.26 times and 1.21 times respectively. It can be found that with the increase of carbide slag dosage, the carbon fixation rate gradually increases, realizing the high-value utilization of bulk solid waste.

[0063] from Figures 4 to 6 It can also be seen that when the amount of carbide slag and the pre-carbonization time are constant, the carbon fixation rate increases with the increase of carbonization curing time. That is to say, the carbon fixation rate is the highest when the carbonization curing time is 28 days. Therefore, in this embodiment, the compressive strength of the test pieces prepared with different amounts of carbide slag and different pre-carbonization times was measured after 28 days of carbonization curing. The test results are shown in Figure 2. Figure 7 As shown. Figure 7 It can be seen from the data that with the increase of carbide slag content, the compressive strength of the specimens prepared under various conditions tends to decrease; and the strength during the two-stage carbon fixation of pre-carbonization and carbon curing is higher than that of standard curing, indicating that the synergistic effect of CO2 premixed carbide slag and carbon curing can make up for the insufficient strength caused by the addition of carbide slag. The strength of premixing for 10, 20, and 30 minutes plus carbon curing for 28 days is 2.67 times, 2.90 times, and 1.30 times higher than that under standard curing conditions, respectively. Therefore, the synergistic effect of CO2 premixed carbide slag and carbon curing can significantly improve the compressive strength of the specimens.

[0064] In addition, when the pre-carbonization and carbon fixation reaction is carried out in step 2 of this embodiment, the carbon fixation conditions of carbon-fixing gases with carbon dioxide concentrations of 40% and 60% are also compared. The test results show that as the carbon dioxide concentration in the carbon-fixing gas increases, the carbon fixation rate also increases, but the increasing trend is not obvious (so this part of the test content will not be repeated here). This also shows that under the process conditions of this embodiment, the use of low-concentration carbon dioxide as the carbon-fixing gas for carbide slag carbon fixation to prepare cement-based building materials can achieve an ideal carbon fixation effect.

[0065] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the claims of this patent application.

Claims

1. A method for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag, characterized in that: The steps include: Step (1), mixing carbide slag with water and sealing and standing to obtain a carbide slag suspension; the particle size range of the carbide slag is 5 to 75 μm; the mass ratio of the carbide slag to water is 1: (1.5 to 5); the sealing and standing time is 10 to 20 minutes; Step (2), in a sealed state, introducing a carbon-fixing gas containing carbon dioxide into the carbide slag suspension while stirring to carry out a carbon-fixing reaction, and obtaining a pre-carbonized carbide slag slurry after the carbon-fixing reaction is completed; during the carbon-fixing reaction: the stirring rate is 600-800 rpm; the flow rate of the carbon-fixing gas is 1.5-2.5 L / min; the carbon-fixing reaction is carried out at room temperature; the carbon-fixing reaction time is 10-30 min; the volume concentration of carbon dioxide in the carbon-fixing gas is greater than or equal to 20%; Step (3), mixing the pre-carbonized carbide slag slurry with the cement slurry dry material to obtain carbide slag cement slurry; Step (4), injecting the carbide slag cement slurry into a mold for molding, and demolding to obtain a carbide slag cement blank; Step (5), placing the carbide slag cement blank in a carbon curing box for carbon curing, and obtaining a finished cement-based building material after the carbon curing is completed; In step (5), the carbon curing conditions are: the volume concentration of carbon dioxide is 20±3%, the relative humidity is 70±5%, and the temperature is 20±3°C; and the carbon curing time is 7 to 28 days.

2. The method for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag according to claim 1, wherein: In step (1), the particle size range of carbide slag is 10 to 40 μm; the mass ratio of carbide slag to water is 1:2.5; and the sealed standing time is 10 minutes.

3. The method for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag according to claim 1, characterized in that: In step (2), during the carbon fixation reaction, the stirring rate is 600 rpm; the flow rate of the carbon fixation gas is 2.0 L / min; the carbon fixation reaction time is 20 min; the carbon fixation gas is liquefied and purified carbon dioxide gas with a purity of 99.99% by volume; or, the carbon fixation gas is a mixture of liquefied and purified carbon dioxide gas with a purity of 99.99% by volume and air; or, the carbon fixation gas is flue gas recovered from a cement plant and / or steel plant.

4. The method for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag according to claim 1, characterized in that: In step (3), the mass ratio of the pre-carbonized carbide slag slurry to the cement slurry dry material is 1: (0.8-1.5); the mixing time is 3-10 minutes; the cement slurry dry material is a composite material with cement as a gelling material; the preparation method of the cement slurry dry material is: mixing and stirring the raw material components of the cement slurry dry material according to the designed ratio for 3-5 minutes.

5. The method for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag according to claim 4, characterized in that: In step (3), the mass ratio of the pre-carbonized carbide slag slurry to the cement slurry dry material is 1:1.14; the mixing time is 3 minutes; the cement slurry dry material is cement, cement mortar dry material or concrete dry material; the mixing time when preparing the cement slurry dry material is 3 minutes; The cement is ordinary Portland cement with a strength grade of 42.

5.

6. The method for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag according to claim 1, characterized in that: In step (4), the carbide slag cement slurry molding conditions are: standing at room temperature and pressure for 24 hours and then demoulding.

7. The method for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag according to any one of claims 1 to 6, characterized in that: In step (1), the particle size of the carbide slag is in the range of 10 to 40 μm; the mass ratio of the carbide slag to water is 1:2.5; and the sealed standing time is 10 minutes; In step (2), during the carbon fixation reaction, the stirring rate is 600 rpm; the flow rate of the carbon fixation gas is 2.0 L / min; the carbon fixation reaction is carried out at room temperature; the carbon fixation reaction time is 20 min; the carbon fixation gas is flue gas recovered from a cement plant and / or a steel plant, and the volume concentration of carbon dioxide in the flue gas is 20%; In step (3), the mass ratio of the pre-carbonized carbide slag slurry to the cement slurry dry material is 1:1.14; the mixing time is 3 minutes; the cement slurry dry material is ordinary Portland cement with a strength grade of 42.5; In step (4), the carbide slag cement slurry molding conditions are: standing at room temperature and pressure for 24 hours and then demoulding; In step (5), the carbon curing conditions are: a volume concentration of carbon dioxide of 20%, a relative humidity of 70%, and a temperature of 20° C.; and the carbon curing time is 28 days.

8. A device for preparing cement-based building materials using carbon dioxide pre-carbonized carbide slag, characterized in that: It includes a carbon dioxide storage container, a primary mixing container, an exhaust gas absorption tank, a secondary mixing container, a building material forming mold and a carbon curing box, wherein the primary mixing container is a sealed container; the gas outlet end of the carbon dioxide storage container is fluidly connected to the gas inlet end of the primary mixing container, and the gas outlet end of the primary mixing container is fluidly connected to the gas inlet end of the exhaust gas absorption tank; the slurry outlet end of the primary mixing container is fluidly connected to the slurry inlet end of the secondary mixing container; the slurry outlet end of the secondary mixing container is fluidly connected to the slurry inlet end of the building material forming mold; after demolding the building material forming mold, the carbide slag cement blank is transferred to the carbon curing box for carbon curing; Carbide slag and water are added to a primary mixing container, mixed, sealed and allowed to stand to obtain a carbide slag suspension; in a sealed state, carbon-fixing gas containing carbon dioxide is introduced into the carbide slag suspension using a carbon dioxide storage container while stirring to carry out a carbon fixation reaction, and after the carbon fixation reaction is completed, pre-carbonized carbide slag slurry is obtained; the waste gas discharged from the primary mixing container is introduced into a waste gas absorption tank; the pre-carbonized carbide slag slurry and cement slurry dry material are added to a secondary mixing container, mixed and stirred to obtain carbide slag cement slurry; the carbide slag cement slurry is injected into a building material forming mold for forming, and a carbide slag cement blank is obtained after demolding; the carbide slag cement blank is placed in a carbon curing box for carbon curing, and after the carbon curing is completed, a finished cement-based building material is obtained.

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