Method and system for preparing geopolymer by using CO2

Abstract

The invention discloses a method and system for preparing a geopolymer by using CO2, and the method comprises the following steps: 100 parts by mass of a cementing material is weighed, and the cementing material comprises 30-55 parts by mass of carbide slag and 45-70 parts by mass of fly ash; adding 30-60 parts of water into the dry-mixed cementing material, and stirring for 2-5 minutes at the speed of 600-1000rpm, so as to activate the slurry; the stirring speed is reduced to 200-500 rpm, CO2 is introduced into the slurry, in the process, the introduction flow is dynamically adjusted based on the real-time pH value and viscosity of the slurry and the CO2 concentration, and introduction of CO2 is stopped until the pH value of the slurry reaches a preset target window; and pouring the homogeneous slurry into a mold, molding, and curing to a specified age under a standard curing condition to obtain the geopolymer building block. According to the method, the low-cost and low-carbon geopolymer with high CO2 solid stock and excellent mechanical property is synergistically prepared in the single reactor.

Description

Technical Field

[0001] This invention relates to the intersection of green and low-carbon building materials and carbon dioxide capture, utilization and storage (CCUS) technology, and particularly to a method and system for preparing geopolymers using CO2. Background Technology

[0002] Against the backdrop of global efforts to address climate change and achieve carbon peaking and carbon neutrality, energy conservation and emission reduction are crucial for the building materials industry. The traditional production process of silicate cement is a significant energy consumer and a major source of carbon dioxide (CO2) emissions. Therefore, developing green cementitious materials to replace cement has become a hot research topic in the industry. Geopolymers, also known as alkali-activated cementitious materials, are three-dimensional amorphous aluminosilicate network gel materials formed by activating silica-alumina-rich industrial solid wastes (such as fly ash and slag) with a strong alkaline activator. Because their production process does not require high-temperature calcination and can utilize large quantities of industrial solid waste, geopolymers are widely recognized as a highly promising low-carbon cement alternative. Meanwhile, calcium carbide slag, a byproduct of acetylene production via the calcium carbide process, is mainly composed of calcium hydroxide (Ca(OH)2), a highly alkaline industrial solid waste, and possesses the potential to serve as a component of geopolymer activators. Based on this background, to synergistically address the two major challenges of industrial solid waste disposal and greenhouse gas emission reduction, the following two main technical routes exist in this field: Technical Route 1: CO2 mineralization and capture technology based on alkaline solid waste. The core of this technology is to use CO2 as an acidic gas to chemically react with alkaline industrial solid waste such as carbide slag, converting gaseous CO2 into stable solid carbonates (mainly CaCO3), thus achieving permanent fixation. The technical goal of this route is to maximize CO2 capture efficiency, i.e., the amount of CO2 that can be mineralized per unit mass of solid waste. The research focuses on optimizing reaction conditions (such as temperature, pressure, liquid-to-solid ratio, and solid-waste ratio) to improve the rate and extent of carbonization. However, geopolymer formation depends on a highly alkaline environment (usually pH>11) to dissolve the active silica-alumina components in fly ash. This route, in pursuit of a high mineralization rate, continuously introduces CO2, inevitably leading to a large consumption of hydroxide ions in the system and a sharp drop in pH. This excessive carbonization severely inhibits or even completely terminates the gelation reaction of the geopolymer, fundamentally destroying the possibility of the material achieving strength. This technology uses a fixed-time "open-loop" control method, which cannot precisely control the reaction endpoint, essentially sacrificing material performance in exchange for carbon capture volume. Therefore, although this method fixes CO2, its final product is only a carbonized mixed powder, which does not have the cementing activity and mechanical strength required as a building material. These powders still need to be processed, and the solid waste is not truly transformed into valuable structural materials.

[0003] Technical Route Two: Preparation Technology of Porous CO2 Adsorbent Materials Based on Traditional Geopolymers. The core of this technology is to use the geopolymer itself as a porous carrier, utilizing its well-developed pore structure to physically adsorb CO2. A typical implementation method is disclosed in Chinese Patent CN119869447B, which first uses a traditional strong alkali activator mixed with fly ash to prepare a geopolymer slurry, which is then cast and hardened. To further improve its adsorption performance, porous materials such as zeolite may be added, or the hardened geopolymer may undergo post-treatment processes such as hydrothermal treatment. The technical goal of this route is to prepare functional materials with high CO2 physical adsorption capacity. The performance evaluation index of the final product is the CO2 adsorption capacity per unit mass of material. This method relies on traditional strong alkali activators such as industrially pure sodium hydroxide and sodium silicate. These activators are expensive, and their industrial production processes (such as the chlor-alkali industry) are themselves high-energy-consuming and high-carbon-emission processes. This largely offsets the low-carbon advantages of geopolymers as "green materials," limiting the economic viability of their large-scale application.

[0004] In summary, there is a fundamental technical contradiction in the existing technology: the process of pursuing CO2 chemical mineralization (technical route one) will destroy the necessary conditions for geopolymer gelation, while the traditional geopolymer preparation (technical route two) relies on high-cost, high-carbon-emission activators. To date, no solution has been provided in this field that can combine the advantages of both. Summary of the Invention

[0005] To address the shortcomings of existing technologies and overcome the inherent conflict between CO2 chemical mineralization (which consumes alkalinity) and efficient geopolymer polymerization (which requires alkalinity), this invention proposes a method and system for preparing geopolymers using CO2.

[0006] The specific technical solution is as follows: A method for preparing geopolymers using CO2 includes the following steps: S1: Weigh 100 parts of cementitious material by mass fraction, the cementitious material including 30-55 parts of carbide slag and 45-70 parts of fly ash; after dry mixing of the cementitious material, add 30-60 parts of water and stir at 600-1000 rpm for 2-5 minutes to activate the slurry; S2: Reduce the stirring speed to 200-500 rpm, and then introduce CO2 into the slurry through the aeration disc arranged at the bottom of the sealed stirred reactor; during the introduction of CO2, dynamically adjust the instantaneous flow rate of CO2 based on the detected real-time pH value and viscosity of the slurry and the concentration of CO2 in the introduced gas until the pH value of the slurry reaches the preset target window of 10.2-10.8, and then stop introducing CO2; S3: The homogeneous slurry is poured into a predetermined mold, and after molding, it is cured under standard curing conditions to a specified age to obtain geopolymer blocks.

[0007] Furthermore, the cementing material also includes blast furnace slag powder; 5-20 parts of the fly ash are replaced with an equal amount of blast furnace slag powder.

[0008] Furthermore, in step S2, the introduction of CO2 and the reduction of the stirring speed are both performed within 120 seconds after the slurry activation is completed.

[0009] Furthermore, in S2, during the process of dynamically adjusting the CO2 inlet flow rate, a control dead zone of ±0.1 pH is set so that the final pH overshoot is no greater than 0.15 pH.

[0010] Furthermore, in step S2, the instantaneous flow rate of CO2 is controlled by a mass flow controller, and the expression for the control signal input to the mass flow controller is: In the formula, e(t) is the pH deviation at time t, e(t) = SP - PV(t), where SP is the target endpoint pH value, and PV(t) is the measured pH value of the slurry at time t; K p K is the controller gain coefficient of the proportional element. i The controller gain coefficient for the integral element. The controller gain coefficient is the differential element; F represents the feedforward compensation function, and C... in Q represents the measured concentration of CO2 introduced. in The total flow rate of CO2 introduced is represented by μ(t), and the real-time viscosity of the slurry is represented by μ(t).

[0011] Furthermore, in S3, the standard maintenance conditions are a temperature of 20±2℃ and a relative humidity of ≥95%.

[0012] Furthermore, in step S3, the molded specimen is first heat-cured in an environment of 40-70℃ for 12-48 hours, and then cured under standard curing conditions to the specified age to obtain geopolymer blocks.

[0013] A system for preparing geopolymers using CO2, for implementing the method of preparing geopolymers using CO2, includes: a reactor vessel, a stirrer motor, stirrer blades, an integrated sensor, a sealed vessel cover, an aeration disc, a gas source, a gas analyzer, a mass flow controller, an inlet pipeline, and a PLC controller. The reactor vessel is used to place the reaction raw materials and provide a reaction site. A sealed vessel cover is arranged on the top of the vessel cover. An agitator motor is installed on the upper surface of the sealed vessel cover. The agitator blades are arranged inside the reactor vessel, and their rotation shaft passes through the sealed vessel cover and is coaxially and fixedly connected to the output shaft of the agitator motor. The PLC controller is electrically connected to the agitator motor and controls its rotation speed. The integrated sensors are arranged inside the reactor vessel and include: an online pH meter, an online viscometer, and a temperature sensor; An aeration disc is arranged at the bottom of the reactor body to provide CO2 input for the reaction; the gas source is connected to the aeration disc through an air inlet pipeline, and a gas analyzer is installed at the gas source outlet to measure the real-time CO2 concentration; a mass flow controller is installed on the air inlet pipeline to control the CO2 flow rate input to the aeration disc. The gas analyzer and integrated sensor are electrically connected to the PLC controller and transmit detection data to it. The PLC controller is electrically connected to the mass flow controller and sends instructions to it.

[0014] Furthermore, the aeration disc is provided with a plurality of microholes evenly distributed, or the aeration disc is provided with a plurality of aeration holes evenly distributed, and a Venturi tube is provided in the aeration hole.

[0015] Furthermore, during the reaction process, the micro-positive pressure inside the reactor vessel is within the safe reaction range of 0.1-0.3 MPa.

[0016] The beneficial effects of this invention are: (1) This invention employs a synergistic strategy of "post-ventilation timing" (i.e., reducing the rotation speed after activation before ventilating) and "closed-loop control of the pH target window," resolving the fundamental technical contradiction between CO2 mineralization (consuming alkalinity) and geopolymer polymerization (requiring alkalinity) in existing technologies. It achieves a fundamental transformation of the reaction properties, creatively transforming the introduction of CO2 from a recognized "inhibitor" of geopolymer reactions into a controllable "nanocrystalline nucleus generator" and "microstructure densifier," making it possible to achieve CO2 chemical fixation and the preparation of high-performance geopolymers within a single system. Simultaneously, it achieves optimal synergy between performance and carbon fixation: within the pH target window defined by this invention, a nonlinear synergistic gain between material mechanical strength and CO2 fixation rate can be obtained, realizing a leap from single technical objective to multi-objective synergistic optimization.

[0017] (2) This invention uses two industrial wastes, "carbide slag + CO2", as the core activation system, which solves the major drawback of traditional geopolymer technology that relies on expensive and high-carbon-emission strong alkaline activators (sodium hydroxide and sodium silicate). It significantly reduces raw material costs and its own carbon footprint, significantly enhances the market competitiveness of the product, and builds a more thorough low-carbon technology path from the source. Attached Figure Description

[0018] Figure 1 This is a system architecture diagram of preparing geopolymers using CO2 in an embodiment of the present invention.

[0019] Figure 2This is a process flow diagram of preparing geopolymers using CO2 in an embodiment of the present invention.

[0020] Figure 3 This is a flowchart of a PID feedback control system for preparing geopolymers using CO2, as described in an embodiment of the present invention.

[0021] In the figure, 1 is the reactor body, 2 is the agitator motor, 3 is the agitator blades, 4 is the integrated sensor, 5 is the sealed reactor lid, 6 is the aeration disc, 7 is the gas source, 8 is the gas analyzer, 9 is the mass flow controller (MFC), 10 is the air inlet pipeline, and 11 is the PLC controller. Detailed Implementation

[0022] The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The objectives and effects of the present invention will become clearer as a result. The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0023] like Figure 1 As shown, a system for preparing geopolymers using CO2 includes: a reactor vessel 1, a stirrer motor 2, stirrer blades 3, an integrated sensor 4, a sealed vessel cover 5, an aeration disc 6, a gas source 7, a gas analyzer 8, a mass flow controller 9, an air inlet pipeline 10, and a PLC controller 11.

[0024] The reactor vessel 1, stirrer motor 2, stirrer blades 3, and sealing lid 5 form a sealed stirred reactor. The reactor vessel 1 is used to hold the reactants and provide a reaction area. A sealing lid 5 with an exhaust port is located on the top of the reactor vessel 1. The stirrer motor 2 is installed at the center of the upper surface of the sealing lid 5. The stirrer blades 3 are arranged inside the reactor vessel 1, and their rotation shaft passes through the sealing lid 5 and is coaxially connected to the output shaft of the stirrer motor 2. A PLC controller 11 is electrically connected to the stirrer motor 2 and controls its rotation speed, thereby controlling the stirring speed.

[0025] An integrated sensor 4 is arranged inside the reactor vessel 1 and electrically connected to the PLC controller 11 for real-time transmission of the measured sensor data. The integrated sensor 4 includes an online pH meter, an online viscometer, and a temperature sensor; used to measure the pH value, viscosity, and temperature of the slurry inside the reactor vessel 1 in real time.

[0026] An aeration disc 6 is arranged at the bottom of the reactor vessel 1 to provide CO2 input for the reaction. Multiple micropores are evenly distributed on the aeration disc 6, or multiple aeration holes are evenly distributed on the aeration disc 6, with Venturi tubes installed in the aeration holes. A gas source 7 is used to supply CO2, and the gas source 7 is connected to the aeration disc 6 through an inlet pipeline 10. A gas analyzer 8 is installed at the outlet of the gas source 7 to measure the real-time CO2 concentration. The gas analyzer 8 is electrically connected to a PLC controller 11 to transmit the measured CO2 concentration in real time. A mass flow controller 9 is installed on the inlet pipeline 10 to control the valve opening, thereby controlling the CO2 flow rate into the aeration disc 6. The PLC controller 11 is electrically connected to the mass flow controller 9 and sends commands to it.

[0027] like Figure 2 and Figure 3 As shown, a method for preparing geopolymers using CO2 includes the following steps: S1: Raw material preparation and slurry activation. This step creates the necessary initial highly alkaline environment for subsequent synergistic reactions. This is achieved through the following sub-steps: (1.1) Raw material weighing and dry mixing: Weigh 100 parts of cementitious material according to the mass fraction, of which carbide slag accounts for 30-55 parts and fly ash accounts for 45-70 parts. Place the weighed dry powder raw material (i.e. cementitious material) in a sealed stirred reactor and dry mix at a speed of 300-1000 rpm for 1-2 minutes to ensure the macroscopic uniformity of the raw material and obtain aluminosilicate raw material.

[0028] Furthermore, if it is necessary to further improve the later performance of the material, 5-20 parts of fly ash in the cementitious material can be replaced with an equal amount of blast furnace slag powder (GGBS).

[0029] (1.2) Slurry preparation and activation: Add 30-60 parts of water to the dry-mixed aluminosilicate raw materials at once, and immediately start high-speed stirring (600-1000 rpm) for 2-5 minutes. During this process, the calcium hydroxide (Ca(OH)2) in the carbide slag dissolves rapidly, causing the pH value of the slurry system to rise to above 12.0 in a short time, forming a strongly alkaline environment and achieving activation. This strongly alkaline environment erodes the vitreous body on the surface of fly ash (and slag particles if GGBS is added), dissolving the active silicon (SiO2) and aluminum (Al2O3) components into the liquid phase in the form of silicate ions and aluminate ions.

[0030] S2: In-situ CO2 introduction and coordinated reaction based on closed-loop control algorithm. The PLC controller 11 sends instructions to the mass flow controller 9 according to the closed-loop control algorithm to control the valve opening, allowing CO2 from the gas source 7 to be introduced into the activated slurry through the aeration disc 6 for reaction; simultaneously, the PLC controller 11 sends instructions to the agitator motor 2 to control the agitation speed. This is specifically achieved through the following sub-steps: (2.1) Timing and Adjustment of Aeration: Within a 120-second time window after the slurry activation in S1, the PLC controller 11 controls the agitator motor 2 to reduce the speed of the agitator blades 3 to a low-to-medium speed uniform stirring state of 200-500 rpm to maintain the homogeneity of the slurry and facilitate the dispersion of bubbles. Subsequently, the PLC controller 11 sends a command to the mass flow controller 9 to control the valve opening and begin to introduce CO2-containing gas into the slurry (also within a 120-second time window).

[0031] The reason this step needs to be performed within a 120-second time window after the slurry activation in S1 is that calcium hydroxide (Ca(OH)2) dissolves rapidly, creating a highly alkaline environment with a pH value exceeding 12.0 in the slurry system. This highly alkaline environment rapidly dissolves the surface of siliceous and aluminous raw materials such as fly ash, releasing the active silicon and aluminum components into the liquid phase in the form of silicate and aluminate ions. This process places the slurry in a metastable state with high ion concentration and high reactivity. However, this highly active state is transient. If the waiting time after activation is too long (exceeding 120 seconds), the high concentration of silicate and aluminate ions in the solution will spontaneously undergo a condensation reaction in the highly alkaline environment, which is the traditional geopolymer gelation process. Once this disordered and uncontrolled polymerization occurs on a large scale, it will not only prematurely consume the active ions required for subsequent reactions, but also cause an abnormal increase in slurry viscosity and a decrease in fluidity. This will seriously interfere with the uniform dispersion and mass transfer of subsequent CO2 gas. Therefore, after the slurry activation in S1 is completed, this step must be carried out within a 120-second time window.

[0032] (2.2) Mass transfer enhancement: The introduced CO2 gas (which can be industrial flue gas with a CO2 volume fraction of 10-40%, or pure CO2 with a volume fraction ≥99%) is injected into the activated slurry via an aeration disc 6 installed at the bottom of the reactor vessel 1. This is intended to shear the gas flow into tiny bubbles, ensuring that the average diameter d of the bubbles formed in the slurry is... 32The diameter threshold is not greater than a certain value; in this embodiment, the diameter threshold is 1.5 mm. Simultaneously, the gauge pressure (i.e., slightly positive pressure) within the sealed stirred reactor must be maintained within a safe reaction range; in this embodiment, the safe reaction range is 0.1-0.3 MPa. The combination of microbubbles and slightly positive pressure significantly increases the contact surface area of ​​the gas-liquid-solid three phases, improves the solubility of CO2, significantly enhances the mass transfer rate and utilization efficiency of CO2 from the gas phase to the liquid phase, shortens the reaction time in the slurry stage, and reduces energy consumption.

[0033] (2.3) Intelligent endpoint control: The present invention adopts a closed-loop control algorithm based on predictive feedforward-feedback to dynamically adjust the CO2 introduction process until the preset reaction endpoint is reached.

[0034] The control objective of the closed-loop control algorithm is to determine the reaction endpoint based on the real-time pH value of the slurry. The control objective is to precisely stop the slurry pH value from the initial ≥12.0 within a preset pH target window. In this embodiment, the preset pH target window is 10.2–10.8. This target window is the range that achieves the optimal synergy between "CO2 fixation" and "geopolymer strength development" as discovered through numerous experiments. A preferred target endpoint (SP) pH value is 10.5.

[0035] Closed-loop control algorithm and implementation: This algorithm is pre-installed in the PLC controller 11. Its core is to dynamically calculate the control signal sent by the PLC controller 11 to the mass flow controller 9 through a comprehensive control equation, as shown in the following expression: The physical meanings of each parameter in the formula are as follows: Valve output (t) represents the control signal sent by the PLC controller 11 to the mass flow controller 9 at time t, which is used to control the degree of valve opening and closing and determines the instantaneous flow rate of CO2.

[0036] The first term of the expression (within square brackets) is the PID feedback control part, where e(t) is the pH deviation at time t, e(t) = SP - PV(t), SP is the target endpoint pH value, and PV(t) is the real-time pH value of the slurry measured by the online pH meter (belonging to integrated sensor 4) at time t; K p K is the controller gain coefficient of the proportional element. i The controller gain coefficient for the integral element. The controller gain coefficient of the differential element is used. All three are obtained through debugging and tuning of the specific system and are used to make basic adjustments to the CO2 flow rate based on the real-time pH deviation.

[0037] The second term of the expression This is the feedforward predictive control section, where F represents the feedforward compensation function. Its function is to predict the impact of measurable disturbance variables on the rate of pH decrease in the slurry in advance, and to compensate the control signal to overcome the system's time lag and suppress overshoot. If the introduced CO2 gas is industrial flue gas with a volume fraction of 10-40%, F takes a relatively high gain function (2.5-10), and is related to Q. in / C in The value is positively correlated, and the specific value depends on the model and size of the PCL control valve; if the introduced CO2 gas is pure CO2 with a volume fraction ≥99%, F is taken as 0. in The real-time CO2 concentration of the introduced gas is measured by gas analyzer 8. The higher the concentration, the faster the pH of the slurry decreases, and the valve opening needs to be reduced in advance. Q in The total flow rate of the introduced gas is represented (measured by the MFC). μ(t) represents the real-time viscosity of the slurry, measured by an online viscometer (part of integrated sensor 4). An increase in viscosity indicates that the geopolymer gel is being formed, thereby reducing the CO2 consumption rate (the CO2 required for the formation of the geopolymer is reduced, and the system needs to adjust accordingly to reduce the CO2 introduction rate). Its trend can be used to predict the transition of the reaction stage.

[0038] The control logic of the closed-loop control algorithm is as follows: After the PLC controller 11 starts introducing CO2-containing gas, it continuously adjusts the CO2 flow rate according to the control equation mentioned above. When the pH value is detected to enter the preset pH target window, it immediately sends a command to the mass flow controller 9 to lock the CO2 inlet valve and stop the gas supply. To ensure control accuracy, the PLC controller 11 needs to set a control dead zone of ±0.1pH to ensure that the final pH overshoot does not exceed 0.15pH.

[0039] This invention employs a closed-loop control algorithm based on "predictive feedforward-feedback," overcoming the shortcomings of existing technologies that use fixed-time open-loop control, such as poor process repeatability and inability to adapt to fluctuations in operating conditions. It significantly improves the accuracy and stability of the process: the algorithm can proactively compensate for disturbances such as raw material activity and gas concentration, ensuring that each production run accurately hits the preset pH target window, effectively suppressing overshoot, and guaranteeing high uniformity and repeatability of the final product quality, thus fulfilling the prerequisites for large-scale industrial production.

[0040] S3: Casting and curing.

[0041] After stopping the CO2 supply, immediately pour the homogeneous slurry from reactor vessel 1 into a predetermined mold, and use vibration to remove any trapped air bubbles. Subsequently, cure the molded specimens under standard curing conditions (temperature 20±2℃, relative humidity ≥95%) to the specified age (e.g., 3 days, 7 days, 28 days) to obtain geopolymer blocks.

[0042] Furthermore, to accelerate early strength development, heat curing can be carried out in an environment of 40-70℃ for 12-48 hours, followed by standard curing.

[0043] The present invention will be specifically described below through examples.

[0044] Example 1 This embodiment uses externally sourced calcium carbide slag and fly ash from a certain company as raw materials, and industrial flue gas with a CO2 volume fraction of 15%, to prepare carbon-fixed geopolymer blocks with a curing age of 28 days and a compressive strength not lower than the C40 grade requirement (40MPa) using the method of this invention. The specific steps are as follows: S1: Raw material preparation and slurry activation.

[0045] (1.1) Raw material weighing and dry mixing. First, prepare the raw materials: dry the collected carbide slag (moisture content of about 30%) and fly ash separately to constant weight, and then grind them together using a ball mill until the specific surface area is not less than 400 m². 2 / kg. Weigh out a total of 100kg of cementitious materials, including: 40kg of carbide slag and 60kg of fly ash. Prepare 38kg of clean industrial water.

[0046] Next, system preparation is performed: the reactor vessel 1 has a volume of 200L, with an aeration disc 6 installed at the bottom. Integrated sensors 4 are arranged inside the vessel, including a Mettler Toledo InPro 4260i online pH electrode, a temperature sensor, and an online viscometer. The gas source 7 contains pre-mixed simulated flue gas with a composition of 15% CO2 and 85% N2 by volume. The gas pipeline is connected to a mass flow controller 9 via a pressure reducing valve, which is controlled by a PLC controller 11. On the human-machine interface (HMI) of the PLC controller 11, the following control parameters are set: the target endpoint pH value is 10.5, K... p =1.2, K i =0.5, =0.2 (three gain coefficients were pre-tuned); flue gas CO2 concentration was set constant at C in =15%, and the pressure inside the vessel is set to 0.2 MPa.

[0047] Finally, 100 kg of cementitious material was added to reactor vessel 1, sealed, and stirred at a speed of 300 rpm to obtain a dry mixture (i.e., aluminum-silicon raw material).

[0048] (1.2) Slurry preparation and activation: 38 kg of water was rapidly injected into reactor vessel 1 through the feed port, and then high-speed stirring was started at 800 rpm for 3 minutes. During this period, the pH value of the slurry was monitored by integrated sensor 4, which showed that the pH value of the slurry rose rapidly from the initial value of about 11.0 and stabilized at 12.4, and the temperature rose slightly.

[0049] S2: In-situ CO2 introduction and synergistic reaction based on closed-loop control algorithm: After high-speed stirring, within 60 seconds, PLC controller 11 controls the stirrer motor 2 to reduce the stirring speed to 300 rpm. PLC controller 11 sends a command to mass flow controller 9 to start gas injection, and flue gas enters the slurry in the form of fine bubbles through aeration disc 6. During this period, the CO2 injection flow rate is dynamically adjusted through a closed-loop control algorithm.

[0050] After the reaction begins, the pH curve displayed on the HMI interface starts to slowly decrease. In the early stages of the reaction, the PLC controller 11 maintains a relatively high gas flow rate to improve efficiency. When the pH value drops to around 11.0, it can be observed that the PLC controller 11, according to the closed-loop control algorithm, begins to reduce the gas flow rate in advance and smoothly to prevent overshoot when approaching the set point.

[0051] After approximately 18 minutes of reaction, the online pH meter in integrated sensor 4 measured 10.5. The PLC immediately controlled the mass flow controller 9 to close the valve and stop the gas supply. At this point, a slight overshoot of pH was observed, which eventually stabilized at 10.4, falling entirely within the target window of 10.2-10.8. Throughout the entire reaction process, the gauge pressure inside the reactor remained stable at 0.2 MPa, meeting the requirements.

[0052] S3: Casting and curing.

[0053] After stopping the CO2 supply, immediately pour the homogeneous slurry from reactor vessel 1 into a predetermined mold, and use vibration to remove any trapped air bubbles. Then, cure the molded specimens under standard curing conditions for the specified 28-day period to obtain geopolymer blocks.

[0054] Unconfined compressive strength tests were conducted on samples taken at 3 days and 28 days of curing. The mechanical properties of the geopolymer blocks were as follows: the average compressive strength at 3 days reached 28.67 MPa, and the average compressive strength at 28 days reached 45.4 MPa, which exceeded the requirements of C40 grade at the specified curing time.

[0055] CO2 fixation test: By analyzing the difference between the total solid carbon content before and after the grout activation reaction and the total carbon content of the blocks before and after curing (thermogravimetric analysis, TGA), it was calculated that every 100 kg of cementitious material chemically fixes approximately 11.2 kg of CO2 throughout its entire life cycle (approximately 8.5 kg during the grouting stage and approximately 2.7 kg during the curing stage), with a CO2 fixation rate of 11.2%.

[0056] Table 1. Experimental results of the performance of the geopolymer at the target endpoint pH of 10.5. Table 1 shows the overall performance data obtained from three independent parallel repeated experiments (labeled GPC-1, GPC-2, and GPC-3) under optimal process parameters (final pH=10.5).

[0057] As shown in Table 1, the results of the three repeated experiments were highly consistent, demonstrating the process stability and control precision of the method of this invention. Its core intelligent control algorithm can precisely control the reaction endpoint within the target pH window of 10.2-10.8, resulting in a highly efficient and stable reaction process, fully meeting the conditions for industrial production.

[0058] Secondly, the final product exhibits an average compressive strength of 45.4 MPa after 28 days, exceeding the requirements of the C40 high-strength grade, making it suitable for use as a high-performance building material. Simultaneously, its extremely low water absorption rate indicates excellent density and durability, meeting stringent engineering application standards.

[0059] Finally, based on the measured data, it was calculated that every 100 kg of raw material can stably solidify more than 11 kg of CO2, and the utilization efficiency of input CO2 is as high as 91% or more. This indicates that the technology can not only dispose of industrial solid waste on a large scale, but also efficiently and permanently convert greenhouse gases into part of building materials. It is a negative carbon technology path with both economic and environmental benefits.

[0060] Example 2 The treatments for S1 and S3 are the same as in Example 1. When performing closed-loop control in S2, six experimental groups were set up with target endpoint pH values ​​of 11.5, 11.0, 10.5, 10.0, 9.5, and 9.0, respectively. Each group was subjected to three independent parallel replicate experiments to ensure the reliability of the data.

[0061] The experimental results are shown in Table 2 below: Table 2. Experimental results of geopolymer performance at different target endpoint pH values. The experimental results show that the overall effect on compressive strength and CO2 fixation is best when the target endpoint pH value is 10.5. Experimental results show that the target endpoint pH value of the carbonation reaction has a significant impact on various properties of the cementitious material: the amount of CO2 solidified increases continuously as the target endpoint pH value decreases, reaching a maximum of 115.7 g / kg at pH 9.0, but the material strength is the lowest under this condition; when the target endpoint pH value is 10.5, the mechanical properties of the material reach their best, under this condition, the compressive strength at 3 days and 28 days reaches its maximum value of 28.5 MPa and 45.3 MPa, respectively; when the pH value is higher or lower than 10.5, the compressive strength decreases, especially when the pH value is lower than 10.0, the strength decrease is very significant. In summary, to achieve high CO2 curing efficiency while ensuring excellent mechanical properties, the target endpoint pH of 10.5 is the optimal process parameter. At this point, the material achieves the highest compressive strength, while the CO2 curing amount also reaches a considerable 85.3 g / kg. The overall effect of compressive strength and CO2 fixation is relatively the best. This indicates that there is a balance between mechanical properties and carbon curing efficiency, and pH=10.5 is the optimal choice to achieve this balance.

[0062] This invention utilizes inexpensive carbide slag and CO2 as core reactants, achieving not only permanent chemical fixation of CO2 but also transforming the mineralization process into an effective activation process for siliceous aluminate solid wastes such as fly ash. This allows for the synergistic preparation of low-cost, low-carbon geopolymer building materials with both high CO2 retention and excellent mechanical properties within a single reactor. Through intelligent and predictive closed-loop control of the reaction sequence, mass transfer process, and reaction endpoint, this invention transforms the CO2 mineralization process from a potentially inhibiting step in geopolymer reactions into a controllable, synergistically promoting activation and enhancement step.

[0063] It will be understood by those skilled in the art that the above descriptions are merely preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for preparing geopolymers using CO2, characterized in that, Includes the following steps: S1: Weigh 100 parts of cementitious material by mass fraction, the cementitious material including 30-55 parts of carbide slag and 45-70 parts of fly ash; after dry mixing of the cementitious material, add 30-60 parts of water and stir at 600-1000 rpm for 2-5 minutes to activate the slurry; S2: Reduce the stirring speed to 200-500 rpm, and then introduce CO2 into the slurry through the aeration disc arranged at the bottom of the sealed stirred reactor; during the introduction of CO2, dynamically adjust the instantaneous flow rate of CO2 based on the detected real-time pH value and viscosity of the slurry and the concentration of CO2 in the introduced gas until the pH value of the slurry reaches the preset target window of 10.2-10.8, and then stop introducing CO2; S3: The homogeneous slurry is poured into a predetermined mold, and after molding, it is cured under standard curing conditions to a specified age to obtain geopolymer blocks.

2. The method for preparing geopolymers using CO2 according to claim 1, characterized in that, The cementing material also includes blast furnace slag powder; 5-20 parts of the fly ash are replaced with an equal amount of blast furnace slag powder.

3. The method for preparing geopolymers using CO2 according to claim 1, characterized in that, In step S2, the introduction of CO2 and the reduction of stirring speed are both performed within 120 seconds after the slurry activation is completed.

4. The method for preparing geopolymers using CO2 according to claim 1, characterized in that, In S2, during the process of dynamically adjusting the CO2 inlet flow rate, a control dead zone of ±0.1 pH is set so that the final pH overshoot is no greater than 0.15 pH.

5. The method for preparing geopolymers using CO2 according to claim 1, characterized in that, In step S2, the instantaneous flow rate of CO2 is controlled by a mass flow controller. The expression for the control signal input to the mass flow controller is: ； In the formula, e(t) is the pH deviation at time t, e(t) = SP - PV(t), where SP is the target endpoint pH value, and PV(t) is the measured pH value of the slurry at time t; K p K is the controller gain coefficient of the proportional element. i The controller gain coefficient for the integral element. The controller gain coefficient is the differential element; F represents the feedforward compensation function, and C... in Q represents the measured concentration of CO2 introduced. in The total flow rate of CO2 introduced is represented by μ(t), and the real-time viscosity of the slurry is represented by μ(t).

6. The method for preparing geopolymers using CO2 according to claim 1, characterized in that, In S3, the standard curing conditions are a temperature of 20±2℃ and a relative humidity of ≥95%.

7. The method for preparing geopolymers using CO2 according to claim 6, characterized in that, In step S3, the molded specimens are first heat-cured in an environment of 40-70℃ for 12-48 hours, and then cured under standard curing conditions to the specified age to obtain geopolymer blocks.

8. A system for preparing geopolymers using CO2, for implementing the method for preparing geopolymers using CO2 according to any one of claims 1-7, characterized in that, include: Reactor body, agitator motor, agitator blades, integrated sensor, sealed vessel cover, aeration disc, gas source, gas analyzer, mass flow controller, air inlet pipeline, PLC controller; The reactor vessel is used to place the reaction raw materials and provide a reaction site. A sealed vessel cover is arranged on its top, and a stirrer motor is installed on the upper surface of the sealed vessel cover. The stirrer blades are arranged inside the reactor vessel, and their rotation shaft passes through the sealed vessel cover and is coaxially and fixedly connected to the output shaft of the stirrer motor. The PLC controller is electrically connected to the stirrer motor and controls its speed. The integrated sensors are arranged inside the reactor vessel and include: an online pH meter, an online viscometer, and a temperature sensor; An aeration disc is arranged at the bottom of the reactor body to provide CO2 input for the reaction; the gas source is connected to the aeration disc through an air inlet pipeline, and a gas analyzer is installed at the gas source outlet to measure the real-time CO2 concentration; a mass flow controller is installed on the air inlet pipeline to control the CO2 flow rate input to the aeration disc. The gas analyzer and integrated sensor are electrically connected to the PLC controller and transmit detection data to it. The PLC controller is electrically connected to the mass flow controller and sends instructions to it.

9. The system for preparing geopolymers using CO2 according to claim 8, characterized in that, The aeration disc is provided with a plurality of micro-holes evenly distributed, or the aeration disc is provided with a plurality of aeration holes evenly distributed, and a Venturi tube is provided in the aeration hole.

10. The system for preparing geopolymers using CO2 according to claim 8, characterized in that, During the reaction, the micro-positive pressure inside the reactor vessel is within the safe reaction range of 0.1-0.3 MPa.

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