Apparatus and method for real-time online characterisation of the effect of carbon dioxide on cement dissolution behaviour

Abstract

The application relates to the technical field of material testing, in particular to a device and method for real-time online characterization of the influence of carbon dioxide on the dissolution behavior of cement. The device comprises a gas mixing subsystem, a constant-temperature bubbling reaction container and a real-time online monitoring subsystem; wherein the gas mixing subsystem is used for providing the constant-temperature bubbling reaction container with mixed gas of carbon dioxide and nitrogen gas with a set concentration; the constant-temperature bubbling reaction container is connected to the gas mixing subsystem and is configured to provide a constant-temperature dissolution environment for cement minerals to be detected and make the mixed gas enter the bottom of a reaction liquid in a bubbling form; and the real-time online monitoring subsystem is connected to the constant-temperature bubbling reaction container and is used for collecting electrochemical parameters of the reaction liquid in real time. The application can realize accurate control of the full range of carbon dioxide concentration, effectively separate dissolution and precipitation reactions, capture the transient behavior of cement mineral dissolution in real time and provide scientific data support for material durability evaluation.

Description

Technical Field

[0001] This invention relates to the field of materials testing technology, and more specifically, to an apparatus and method for real-time online characterization of the dissolution behavior of cement minerals in environments with different carbon dioxide concentrations. Background Technology

[0002] The long-term durability of cement-based materials in carbon dioxide-containing environments (such as atmospheric environments and carbon capture and storage scenarios) is a key factor determining the lifespan of building structures and the efficiency of carbon dioxide geological sequestration. Cement minerals, as a class of hydraulically active solid minerals, undergo a complex dissolution process driven by both thermodynamics and kinetics. This process is not only the starting point of cement hydration but also the rate-limiting step in subsequent carbonization reactions. Therefore, the dissolution rate of cement minerals has become a core indicator characterizing their reactivity. In-depth research on the dynamic dissolution behavior of cement minerals under different concentrations of carbon dioxide is of significant academic and engineering value for elucidating the durability mechanism of cement concrete and evaluating carbon dioxide sequestration efficiency.

[0003] Currently, conventional methods for studying the carbonation behavior of cement minerals mainly focus on accelerated carbonation experiments using solid hardened specimens in a constant high-concentration carbon dioxide environment, or inferring the reaction process by characterizing the phase composition of the reaction endpoint products. However, these methods have significant limitations in practical applications. First, traditional methods struggle to simulate the gradient changes in carbon dioxide concentration in the real atmosphere, and cannot accurately reproduce the specific carbon dioxide partial pressure environment at different depths or stages in geological repositories. Second, existing tests typically involve sampling and analysis after the reaction, representing static characterization, which fails to capture the instantaneous dynamic process of the dissolution reaction. This makes it difficult to obtain key parameters such as dissolution rate and reaction kinetics, and lacks the ability for real-time online monitoring. Furthermore, during the carbonation process of solid specimens, the diffusion of carbon dioxide and ions is often restricted, and the hydration product coating generated by the reaction inhibits the continued dissolution of the mineral surface. This results in test results mixed with multiple parallel reactions, making it difficult to clearly separate and quantify the initial dissolution step. Simultaneously, due to insufficient contact between carbon dioxide and the solution, the gas mass transfer efficiency is low, and the mass transfer process often becomes a bottleneck in the reaction, failing to accurately reflect the sensitivity of mineral dissolution itself to carbon dioxide concentration. Summary of the Invention

[0004] The purpose of this application is to provide a device for real-time online characterization of the effect of carbon dioxide on cement dissolution behavior.

[0005] The present invention adopts the following solution:

[0006] A device for real-time online characterization of the effect of carbon dioxide on cement dissolution behavior includes a gas mixing subsystem, a constant-temperature bubbling reaction vessel, and a real-time online monitoring subsystem; wherein,

[0007] The gas mixing subsystem includes a first gas system and a second gas system, which are respectively used to supply the isothermal bubbling reaction vessel with a set concentration of mixed gas of carbon dioxide and nitrogen.

[0008] The constant-temperature bubbling reaction vessel is connected to the gas mixing subsystem. It is configured to provide a constant-temperature dissolution environment for the cement minerals to be tested and to introduce the mixed gas into the bottom of the reaction liquid in a bubbling form, so that the concentration of gaseous carbon dioxide can be quickly converted into the concentration of liquid carbon dioxide, and the dissolution reaction on the surface of the minerals is not limited by the mass transfer of carbon dioxide. The constant-temperature bubbling reaction vessel includes a multi-port container set in a constant-temperature reaction tank with magnetic stirring function. A magnetic stir bar is set at the bottom of the multi-port container. The constant-temperature reaction tank maintains the reaction liquid in the multi-port container at a set temperature through a circulating temperature control medium.

[0009] The real-time online monitoring subsystem is connected to the constant-temperature bubbling reaction vessel and is used to collect the electrochemical parameters of the reaction solution in real time to capture the kinetic information of the entire process of dissolution reaction initiation, progress, and reaching equilibrium. The real-time online monitoring subsystem includes a multi-channel tester, a computer storage unit, and a detection end connected to the multi-channel tester. The detection end includes a conductivity electrode and a pH electrode suitable for insertion into the multi-port container. The multi-channel tester is used to record the changes in conductivity and pH value of the reaction solution in real time during the dissolution process and transmit the data to the computer storage unit.

[0010] Furthermore, the gas mixing subsystem includes a carbon dioxide gas source, a nitrogen gas source, and carbon dioxide gas passages and nitrogen gas passages for respectively delivering carbon dioxide and nitrogen to the gas mixing three-way pipe; wherein, the carbon dioxide gas passage and the nitrogen gas passage are respectively connected to high-precision pressure reducing valves; and float flow meters with different ranges are respectively installed in the carbon dioxide gas passage and the nitrogen gas passage for independently controlling the volumetric flow rate of carbon dioxide and nitrogen entering the gas mixing three-way pipe.

[0011] Furthermore, the multi-port container is provided with an air inlet, an electrode insertion port, a feeding port, and a sampling port; wherein, the air inlet is connected to the outlet of the mixing tee pipe through a pipeline, and the end of the pipeline extends to the bottom of the reaction liquid inside the multi-port container; the electrode insertion port is used to connect to the detection end of the real-time online monitoring subsystem, and the sensing end of the detection end is immersed in the reaction liquid; the feeding port is used to input the cement mineral to be tested; and the sampling port is used to connect to a peristaltic pump quantitative liquid sampling device to sample and test the test liquid.

[0012] This invention also provides a method for characterizing the dissolution behavior of cement minerals in environments with different carbon dioxide concentrations, comprising the following steps:

[0013] S1. Experimental Design: Environmental Pre-stabilization: Set up multiple experimental groups, including at least one control group with pure nitrogen gas introduced, and multiple experimental groups with mixed gases of different carbon dioxide concentrations and nitrogen gas introduced.

[0014] S2. In each experimental group, the multi-port container is placed in the constant temperature reaction tank, the gas mixing subsystem is turned on, and the mixed gas is introduced into the multi-port container through the gas inlet to pre-ventilate the multi-port container and pipeline.

[0015] S3. Prepare deionized water and mixed gas: Add deionized water to the multi-port container and stabilize for a preset time; then introduce the mixed gas into the multi-port container and bubble it, turn on the magnetic stirrer and stabilize for a preset time to improve the dissolution mass transfer rate of carbon dioxide in water, ensure that the concentration of gaseous carbon dioxide can be quickly converted into the concentration of liquid carbon dioxide, so that the dissolution reaction on the mineral surface is not limited by the mass transfer of carbon dioxide, so as to truly reflect the chemical dissolution kinetics.

[0016] S4. Real-time online monitoring experiment: The cement mineral powder is added to the multi-port container, and the real-time online monitoring subsystem is activated to record the changes in solution conductivity and pH value, so as to capture the kinetic information of the entire process of dissolution reaction initiation, progress and reaching equilibrium; wherein, the water-cement ratio of the added deionized water and cement mineral powder is not less than 10000 to prepare an extremely dilute suspension, thereby inhibiting the process of dissolved ions precipitating due to supersaturation to form hydration products or carbonates, forcing the reaction system to be in a state dominated by mineral dissolution for a long time, and removing the interference of subsequent precipitation reaction on the mineral surface coverage;

[0017] S5. Data Processing and Kinetic Characterization: The conductivity-time curves and pH-time curves obtained in step S4 at different carbon dioxide concentrations are used to characterize the following dissolution behavior of the minerals:

[0018] a. By comparing the differences in the initial slopes of different curves, the accelerating or inhibiting effects of different carbon dioxide concentrations on the initial dissolution rate of minerals can be quantitatively assessed;

[0019] b. Analyze the influence of carbon dioxide concentration on the dissolution equilibrium state by analyzing the time and value of the plateau phase in the curve; extract the raw data through the computer storage unit to generate conductivity-time curves and pH-time curves, and perform kinetic analysis.

[0020] Furthermore, the pre-ventilation time is controlled between 3 and 10 minutes to ensure that the gas phase space in the multi-port container and the dissolved gas in the reaction liquid reach the set concentration.

[0021] Further, in steps S3 and S4, 2000 grams of deionized water are weighed and added to a multi-mouth container according to the water-cement ratio, and 0.2 grams of cement mineral powder are weighed; the cement mineral powder includes tricalcium silicate and / or tricalcium aluminate.

[0022] Furthermore, in step S4, a mixture of carbon dioxide and nitrogen is continuously introduced into the bottom of the reaction liquid at a constant total flow rate of 0.5 liters / minute to 1.5 liters / minute; the multi-channel tester continuously records data at a resolution of seconds, and the experiment lasts for 5 to 60 minutes.

[0023] Further, in step S5, the kinetic analysis includes: extracting the linear portion of the conductivity-time curve at the beginning of the reaction and calculating the initial slope; analyzing the rate of decrease of the pH-time curve and the pH value at the final equilibrium; and comparing the time required for the curve to reach the plateau phase under different carbon dioxide concentrations.

[0024] Beneficial effects:

[0025] First, it achieves precise control of carbon dioxide concentration across the entire range. Through the high-precision pressure-reducing valve and float flowmeter in the gas mixing subsystem, this technical solution can stably maintain the carbon dioxide concentration at any set value between 0% and 100%. This dynamic gas mixing technology overcomes the limitation of traditional experimental devices that can only operate at fixed concentrations, enabling researchers to simulate a variety of complex engineering scenarios, from ordinary atmospheric environments to high-concentration carbon dioxide storage environments, significantly improving the coverage and applicability of experiments.

[0026] Secondly, this invention successfully achieved the independent separation and quantification of the dissolution kinetics process. In the carbonation study of cement minerals, dissolution and precipitation often occur in tandem. Precipitation products covering the mineral surface form an obstructive layer, causing the measured dissolution rate to be inconsistent with the true chemical kinetic rate. This invention creates an extremely dilute reaction environment by introducing an ultra-high water-cement ratio of no less than 10,000, ensuring that the concentration of ions released during dissolution remains below the saturation threshold for precipitation. This technique effectively suppresses secondary precipitation reactions, ensuring that changes in conductivity and pH are entirely dominated by the mineral dissolution process, thus obtaining true, undisturbed dissolution kinetic parameters.

[0027] Third, it possesses high temporal resolution and real-time dynamic monitoring capabilities. It employs an integrated online recording system for both conductivity and pH parameters. The multi-channel instrument can capture minute fluctuations in the chemical properties of the solution on a second-by-second basis, which is particularly important for substances like cement minerals that undergo extremely rapid dissolution reactions. Through complete dynamic curves, not only can the endpoint of the reaction be observed, but also the transient behavior during the initial stage, providing rich data support for elucidating the dissolution mechanism.

[0028] Fourth, the gas-liquid mass transfer efficiency was significantly optimized. By installing a bubbling device at the bottom of the multi-port container and combining it with magnetic stirring, the contact area between gaseous carbon dioxide and liquid deionized water was greatly increased. This forced mass transfer method ensures that the concentration of dissolved carbon dioxide in the solution can quickly reach equilibrium with the partial pressure of the gas phase. This makes the experimentally measured reaction rate truly depend on the chemical reaction rate between cement minerals and carbonic acid, rather than being limited by the rate of carbon dioxide diffusion from the gas phase to the liquid phase, thus improving the accuracy and scientific validity of the test results.

[0029] Fifth, it possesses a high degree of standardization and universality. The device involved in this invention has a simple structure and standardized operation process, and all core parameters, such as water-cement ratio, gas flow rate, and temperature, have clear quantitative standards. This makes the method applicable not only to silicate clinker minerals but also to various cement-based material components such as aluminates and aluminoferrites. It can even be extended to the carbonation kinetics research of other easily soluble minerals, demonstrating strong engineering application prospects and academic promotion value.

[0030] Sixth, by using both pH and conductivity as characterization methods, multi-dimensional monitoring of the system's chemical evolution process was achieved. Changes in conductivity directly correspond to the increase or decrease in the total ionic strength of the solution, serving as a direct physical quantity for evaluating the amount of minerals dissolved. Changes in pH reflect the consumption and generation of protons in the reaction. The synergistic monitoring of these two methods allows researchers to examine dissolution behavior from both ion migration and acid-base balance dimensions, thereby revealing a more comprehensive mechanism by which carbon dioxide concentration affects the dissolution process of cement minerals. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of an apparatus for real-time online characterization of the effect of carbon dioxide on cement dissolution behavior according to an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of a multi-port container of an embodiment of the present invention for a device for real-time online characterization of the effect of carbon dioxide on cement dissolution behavior;

[0033] Figure 3 This is a schematic diagram of an experimental test showing the change in conductivity over time caused by the dissolution of tricalcium silicate and tricalcium aluminate under different carbon dioxide concentrations.

[0034] Figure 4 This is a schematic diagram of an experimental test showing the pH change over time caused by the dissolution of tricalcium silicate and tricalcium aluminate at different carbon dioxide concentrations.

[0035] Figure label:

[0036] 1. Carbon dioxide gas source; 2. Nitrogen gas source; 3. High-precision pressure reducing valve; 4. Float flow meter; 5. Mixing gas tee; 6. Multi-port container; 7. Electrode insertion port; 8. Magnetic stir bar; 9. Gas inlet; 10. Conductivity electrode; 11. pH electrode; 12. Feed port; 13. Sampling port; 14. Constant temperature reaction tank. Detailed Implementation

[0037] Example 1

[0038] Combination Figure 1 As shown, this embodiment provides a device for real-time online characterization of the effect of carbon dioxide on cement dissolution behavior, including a gas mixing subsystem, a constant-temperature bubbling reaction vessel, and a real-time online monitoring subsystem. The gas mixing subsystem includes a first gas system and a second gas system, respectively used to provide a mixture of carbon dioxide and nitrogen at a set concentration to the constant-temperature bubbling reaction vessel. The constant-temperature bubbling reaction vessel, connected to the gas mixing subsystem, is configured to provide a constant-temperature dissolution environment for the cement mineral to be tested and to introduce the mixed gas into the bottom of the reaction liquid in a bubbling manner, so that the concentration of gaseous carbon dioxide can be rapidly converted into the concentration of liquid-phase carbonic acid, thus ensuring that the dissolution reaction on the mineral surface is not limited by the mass transfer of carbon dioxide. The real-time online monitoring subsystem is connected to the constant-temperature bubbling reaction vessel and is used to collect the electrochemical parameters of the reaction liquid in real time to capture the kinetic information of the entire process of dissolution reaction initiation, progress, and reaching equilibrium.

[0039] Specifically, in the apparatus of this embodiment, the gas mixing subsystem serves as the source of the entire experimental environment, responsible for providing simulated gases with precisely adjustable concentrations. This subsystem includes a carbon dioxide source 1 and a nitrogen source 2, which respectively store high-purity carbon dioxide gas and nitrogen gas as a dilution gas. High-precision pressure reducing valves 3 are threadedly connected to the outlets of both the carbon dioxide source 1 and the nitrogen source 2. The high-precision pressure reducing valves 3 can stably adjust the high-pressure gas output from the gas source to the low-pressure range required for the experiment, typically 0.1 MPa to 0.2 MPa, thereby ensuring the stability of subsequent flow control. In the depressurized gas paths, float flowmeters 4 with different ranges are installed in the carbon dioxide and nitrogen gas paths, respectively. The selection of the float flowmeter 4 depends on the concentration range set in the experiment. For example, when preparing low-concentration carbon dioxide gas, a float flowmeter with a smaller range is selected for the carbon dioxide gas path, while a float flowmeter with a larger range is selected for the nitrogen gas path, thus achieving independent control of the volumetric flow rate of the two gases. The two gas paths ultimately converge at the mixing tee 5. The mixing tee 5 has a specific mixing chamber inside, allowing for thorough turbulent mixing of carbon dioxide and nitrogen before they enter the reaction vessel. By adjusting the volumetric flow rate ratio of the two gases, this device can regulate the carbon dioxide concentration in the mixed gas across the full range from 0% to 100%, maintaining a control accuracy within ±2%. This configuration can simulate various operating conditions, from natural atmospheric conditions (approximately 0.04% carbon dioxide) to industrial waste gas environments (approximately 10% to 15% carbon dioxide) and even high-pressure geological storage environments (high concentrations of carbon dioxide).

[0040] refer to Figure 2The mixed gas is transported to a constant-temperature bubbling reaction vessel via a connecting pipeline. For example, this reaction vessel can be a multi-necked container 6, specifically a 5-liter multi-necked flask in the experiment. To ensure the reaction proceeds at a constant temperature, the multi-necked container 6 is placed inside a constant-temperature reaction bath 14 with magnetic stirring. The constant-temperature reaction bath 14 is filled with a circulating temperature-controlled medium, such as deionized water or silicone oil, and the temperature fluctuation of the reaction liquid is controlled within ±0.1 degrees Celsius through a built-in heating and cooling unit. The center port and side ports of the multi-necked container 6 have clearly defined functions. The gas inlet 9 is connected to the outlet of the mixing tee 5 via a Teflon pipe, with the end of the pipe extending to the bottom of the multi-necked container 6 below the reaction liquid. Preferably, the end of the gas inlet 9 can be equipped with a porous sand core bubbling head to cut the incoming gas flow into tiny bubbles, thereby greatly increasing the gas-liquid contact area. A conductivity electrode 10 and a pH electrode 11 are sealed and installed at the electrode insertion port 7 of the multi-necked container 6. The sensing ends of these two electrodes are completely immersed in the reaction solution to detect instantaneous changes in the chemical properties of the solution. In addition, the multi-port container 6 is equipped with a feed port 12, which remains sealed when not in use and is used to add cement mineral powder at the start of the reaction. The sampling port 13 is used to extract a small amount of suspension for offline analysis using a peristaltic pump for quantitative liquid sampling when necessary. To eliminate concentration gradients and enhance mass transfer, a magnetic stir bar 8 is placed at the bottom of the multi-port container 6. Driven by the magnetic force at the bottom of the constant-temperature reaction tank 14, the magnetic stir bar 8 rotates at a constant speed, creating forced convection in the reaction solution.

[0041] The real-time online monitoring subsystem consists of a multi-channel tester and a computer storage unit. The multi-channel tester is electrically connected to the conductivity electrode 10 and pH electrode 11 via shielded cables. The multi-channel tester has a high-frequency sampling function, capable of recording data at a rate of once per second or even higher. The computer storage unit runs accompanying data acquisition software, responsible for displaying and storing the changes in conductivity and pH over time in real time, and ultimately automatically generating conductivity-time curves and pH-time curves.

[0042] Based on the above-described apparatus, this invention also discloses a method for characterizing the dissolution behavior of cement minerals, which mainly includes the following steps:

[0043] System Setup and Environmental Pre-stabilization. First, connect all components and ensure there are no gas leaks. Before the experiment, calculate the required carbon dioxide and nitrogen flow rates based on the target carbon dioxide concentration. For example, if the target concentration is 10% (i.e., the volume ratio of carbon dioxide to nitrogen is 10:90), and the total flow rate is set to 1 L / min, then adjust the carbon dioxide flow rate to 100 mL / min and the nitrogen flow rate to 900 mL / min. After starting the gas mixing subsystem, the mixed gas enters the multi-port container 6 containing deionized water through inlet 9. Before adding solid minerals, perform a pre-aeration operation for 3 to 10 minutes. The physical significance of this step is to allow the dissolved gas in the solution to reach thermodynamic equilibrium with the partial pressure of the gas phase, preventing the gas dissolution process after the experiment begins from interfering with the signal generated by mineral dissolution.

[0044] Preparation of a simulated solution with an ultra-high water-cement ratio. A measured amount of cement mineral powder and deionized water were weighed out according to a water-cement ratio of not less than 10000. The cement mineral powder can be selected from one or more of tricalcium silicate, dicalcium silicate, tricalcium aluminate, or tetracalcium aluminoferrite. Under ultra-high water-cement ratio conditions, calcium ions, silicate ions, or aluminate ions generated from mineral dissolution diffuse rapidly in the extremely dilute solution. Due to the large total volume of the solution, the ion concentration is unlikely to reach the supersaturation required for carbonate precipitation or hydration product precipitation within the experimental observation time. This ensures that the surface of the mineral particles is not covered by reaction products, allowing the experimentally measured data to reflect the intrinsic dissolution kinetics of the cement minerals.

[0045] Real-time online monitoring of the experiment. After the temperature of the constant-temperature reaction tank 14 stabilizes at 20 degrees Celsius and the magnetic stirrer 8 rotates steadily at 500 rpm, 0.2 grams of cement mineral powder are rapidly added in one go through the feed port 12. The computer storage unit is activated simultaneously the moment the powder enters the water. The multi-channel analyzer begins acquiring data at a resolution of seconds. The mixed gas is continuously bubbled at a total flow rate of 1 liter / minute to ensure a constant carbonate concentration in the reaction solution. The experiment typically lasts from 5 to 60 minutes, observing the conductivity and pH curves until they reach a plateau with a slope close to zero.

[0046] Data processing and kinetic characterization. This is a crucial step in transforming experimental curves into research parameters. Software in the computer's storage unit is used to extract the data recorded in the previous steps. The initial slope is calculated by linearly fitting the first 30 to 60 seconds of the conductivity-time curve. This slope represents the rate of increase in solution ionic strength per unit time, directly corresponding to the initial dissolution rate of the mineral. By comparing the slope values ​​at different carbon dioxide concentrations, the acceleration or inhibition factor of carbon dioxide on the dissolution of a specific mineral can be quantitatively assessed. Simultaneously, analyzing the rate of decrease in the pH-time curve reveals the neutralization kinetics between protons generated from carbon dioxide dissolving in water and hydroxide ions generated from mineral dissolution.

[0047] The scientific principle behind this invention lies in the synergistic effect of bubbling and magnetic stirring, which eliminates gas-liquid mass transfer resistance, ensuring that the carbonic acid concentration in the liquid phase remains in equilibrium with the partial pressure of the gas phase. The ultra-high water-cement ratio eliminates precipitation resistance at the solid-liquid interface, transforming the experimental system into an ideal, chemically controlled kinetic model. This method has extremely high value in practical applications. For example, when evaluating the durability of cement sealing materials in deep salt layer carbon dioxide sequestration projects, this device can be used to simulate the partial pressure of carbon dioxide in different formations, quickly screening out the mineral composition with the best resistance to dissolution. In the field of building materials research and development, this method can be used to assess the early chemical stability of novel low-carbon cements (such as high-sulfur aluminate cement or calcined clay cement) during natural carbonization.

[0048] Furthermore, the real-time monitoring feature of this invention enables researchers to discover transient phenomena that are unobservable in traditional offline experiments. For example, some minerals may experience a very short induction period in the early stages of dissolution, or there may be abrupt changes in the dissolution rate at specific carbon dioxide concentrations. This information is crucial for establishing accurate cement carbonation kinetic models.

[0049] In summary, this invention provides an experimental system that achieves precise control of carbon dioxide concentration, high mass transfer efficiency, real-time data acquisition, and effective suppression of interfering reactions through the organic integration of a gas mixing subsystem, a constant-temperature bubbling reaction vessel, and a real-time online monitoring subsystem. This device and method not only fill the technological gap in online characterization of cement mineral dissolution kinetics but also provide standardized and high-precision testing methods for scientific research on civil engineering materials. Its application scope covers the entire industry chain, from basic theoretical research to engineering application evaluation, and has profound significance for promoting the green and low-carbon transformation of my country's building materials industry and the long-term safe operation of major infrastructure. By continuously tracking the dual parameters of conductivity and pH, this invention achieves comprehensive monitoring of the reaction process, ensuring that the acquisition of each kinetic parameter has solid experimental basis.

[0050] To further verify the effectiveness of this method, the following specific embodiments are provided:

[0051] Example 2

[0052] In the following embodiments, the specific steps of device setup, sample preparation, and experimental process are as follows:

[0053] (1) Apparatus setup: The system was set up. The reaction vessel was a 5-liter four-necked flask, which was placed in a constant temperature water bath at 20±1 degrees Celsius; online monitoring was performed using a Mettler Toledo Seven Excellence multichannel analyzer.

[0054] (2) Sample preparation: Weigh 0.2 g of cement minerals and 2000 g of deionized water according to the set water-cement ratio W / C=10000 to prepare the suspension. Place the reaction vessel in a constant temperature reaction bath. Different experimental groups were set up: control group (pure nitrogen gas) and groups with different concentrations of carbon dioxide.

[0055] (3) Experimental procedure:

[0056] (a) Taking the 1% carbon dioxide group as an example: set the total gas flow rate to 1 liter / minute, then the carbon dioxide flow rate is 10 milliliters / minute, the nitrogen flow rate is 990 milliliters / minute, and adjust the float flow meter of the corresponding range to the set value.

[0057] (b) Stabilize the system with pre-ventilation for 5 minutes.

[0058] (c) Place the flask in a constant temperature reaction bath, add the weighed deionized water to the flask, and allow it to stabilize for a period of time; introduce the mixed gas into the solution to start bubbling, and simultaneously turn on the magnetic stirrer (at a constant speed), and allow it to stabilize for a period of time. Immerse the pre-calibrated conductivity electrode and pH electrode below the liquid surface.

[0059] (d) Add cement minerals and start the test. Start data recording before the reaction begins. The mass ratio of deionized water to cement minerals should be no less than 10000:1.

[0060] (e) After the reaction is complete, take 0.5 g of the suspension sample, filter it quickly, freeze dry it, and keep it for XRD analysis.

[0061] (f) Repeat the above steps to complete the experiments for the remaining control and experimental groups. Each experiment was repeated twice.

[0062] Reference example

[0063] Add 2000 g of deionized water to the reaction vessel, bubble with pure nitrogen gas at a flow rate of 1000 mL / min, and keep the carbon dioxide concentration at 0%. Weigh 0.2 g of tricalcium silicate and add it to the reaction vessel to begin the reaction.

[0064] Example 3

[0065] Add 2000 g of deionized water to the reaction vessel, and bubble a 1% concentration carbon dioxide mixture at a flow rate of 10 mL / min and a nitrogen flow rate of 990 mL / min. Weigh 0.2 g of tricalcium silicate and add it to the reaction vessel to begin the reaction according to steps (a) to (f) in Exercise 2.

[0066] Example 4

[0067] Add 2000 g of deionized water to the reaction vessel, and bubble a mixture of 10% carbon dioxide gas at a flow rate of 100 mL / min and a nitrogen flow rate of 900 mL / min. Weigh 0.2 g of tricalcium silicate and add it to the reaction vessel to begin the reaction according to steps (a) to (f) in Exercise 2.

[0068] Example 5

[0069] Add 2000 g of deionized water to the reaction vessel, and bubble a mixture of 50% carbon dioxide gas at a flow rate of 500 mL / min and a flow rate of 500 mL / min. Weigh 0.2 g of tricalcium silicate and add it to the reaction vessel to begin the reaction according to steps (a) to (f) in Exercise 2.

[0070] Example 6

[0071] Add 2000 g of deionized water to the reaction vessel, and bubble a mixture of 50% carbon dioxide gas at a flow rate of 500 mL / min and a flow rate of 500 mL / min. Weigh 0.2 g of tricalcium aluminate and add it to the reaction vessel to begin the reaction according to steps (a) to (f) in Exercise 2.

[0072] Results analysis:

[0073] like Figure 3 As shown in the conductivity curves, the conductivity of all groups increased immediately after the gas was introduced, indicating that tricalcium silicate began to dissolve. The pure nitrogen group showed the fastest increase; the higher the carbon dioxide concentration, the smaller the initial slope of the conductivity increase, indicating that dissolution was significantly inhibited.

[0074] like Figure 4 As shown in the pH curve, the pH value of the pure nitrogen group increases slowly and continuously (due to the dissolution of tricalcium silicate to neutralize alkalinity). In contrast, the group with introduced carbon dioxide experiences a brief, slight increase or remains essentially unchanged before a significant decrease in pH. Furthermore, the higher the carbon dioxide concentration, the earlier the pH decrease begins, the faster the rate of decrease, and the lower the final equilibrium pH. This clearly reflects the neutralizing effect of carbonic acid formed by the dissolution of carbon dioxide on the alkalinity of the solution.

[0075] Combining the data on increased conductivity (dissolution inhibition) and decreased pH (carbonic acid neutralization), it can be clearly characterized that carbon dioxide not only lowers the solution pH but also inhibits the dissolution of tricalcium silicate. This accelerating effect increases with increasing carbon dioxide concentration.

[0076] It should be understood that the above are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of the present invention are within the scope of protection of the present invention.

[0077] The accompanying drawings used in the above description of the embodiments only illustrate certain embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

Claims

1. A device for real-time online characterization of the effect of carbon dioxide on cement dissolution behavior, characterized in that, It includes a gas mixing subsystem, a constant-temperature bubbling reaction vessel, and a real-time online monitoring subsystem; among which, The gas mixing subsystem includes a first gas system and a second gas system, which are respectively used to supply the isothermal bubbling reaction vessel with a set concentration of mixed gas of carbon dioxide and nitrogen. The constant-temperature bubbling reaction vessel, connected to the gas mixing subsystem, is configured to provide a constant-temperature dissolution environment for the cement minerals to be tested and to introduce the mixed gas into the bottom of the reaction liquid in a bubbling manner, so that the concentration of gaseous carbon dioxide can be quickly converted into the concentration of liquid carbon dioxide, and the dissolution reaction on the surface of the minerals is not limited by the mass transfer of carbon dioxide; the constant-temperature bubbling reaction vessel includes a multi-port container set in a constant-temperature reaction tank with magnetic stirring function, and a magnetic stir bar is set at the bottom of the multi-port container. The constant-temperature reaction tank maintains the reaction liquid in the multi-port container at a set temperature through a circulating temperature control medium. The real-time online monitoring subsystem is connected to the constant-temperature bubbling reaction vessel and is used to collect the electrochemical parameters of the reaction solution in real time to capture the kinetic information of the entire process of dissolution reaction initiation, progress, and reaching equilibrium. The real-time online monitoring subsystem includes a multi-channel tester, a computer storage unit, and a detection end connected to the multi-channel tester. The detection end includes a conductivity electrode and a pH electrode suitable for insertion into the multi-port container. The multi-channel tester is used to record the changes in conductivity and pH value of the reaction solution in real time during the dissolution process and transmit the data to the computer storage unit.

2. The device for real-time online characterization of the effect of carbon dioxide on cement dissolution behavior according to claim 1, characterized in that, The gas mixing subsystem includes a carbon dioxide gas source, a nitrogen gas source, and carbon dioxide gas passages and nitrogen gas passages for respectively delivering carbon dioxide and nitrogen to the gas mixing tee pipe; wherein, the carbon dioxide gas passage and the nitrogen gas passage are respectively connected to high-precision pressure reducing valves; and float flow meters with different ranges are respectively installed in the carbon dioxide gas passage and the nitrogen gas passage to independently control the volumetric flow rate of carbon dioxide and nitrogen entering the gas mixing tee pipe.

3. The apparatus for real-time online characterization of the effect of carbon dioxide on cement dissolution behavior according to claim 2, characterized in that, The multi-port container is equipped with an air inlet, an electrode insertion port, a feeding port, and a sampling port. The air inlet is connected to the outlet of the mixing tee pipe via a pipeline, and the end of the pipeline extends to the bottom of the reaction liquid inside the multi-port container. The electrode insertion port is used to connect to the detection end of the real-time online monitoring subsystem, and the sensing end of the detection end is immersed in the reaction liquid. The feeding port is used to input the cement mineral to be tested. The sampling port is used to connect to a peristaltic pump quantitative liquid sampling device to sample and test the test liquid.

4. A method for characterizing the dissolution behavior of cement minerals in different carbon dioxide concentration environments using the apparatus for real-time online characterization of the effect of carbon dioxide on cement dissolution behavior as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Experimental Design: Environmental Pre-stabilization: Set up multiple experimental groups, including at least one control group with pure nitrogen gas introduced, and multiple experimental groups with mixed gases of different carbon dioxide concentrations and nitrogen gas introduced. S2. In each experimental group, the multi-port container is placed in the constant temperature reaction tank, the gas mixing subsystem is turned on, and the mixed gas is introduced into the multi-port container through the gas inlet to pre-ventilate the multi-port container and pipeline. S3. Prepare deionized water and mixed gas: Add deionized water to the multi-port container and stabilize for a preset time; then introduce the mixed gas into the multi-port container and bubble it, turn on the magnetic stirrer and stabilize for a preset time to improve the dissolution mass transfer rate of carbon dioxide in water, ensure that the concentration of gaseous carbon dioxide can be quickly converted into the concentration of liquid carbon dioxide, so that the dissolution reaction on the mineral surface is not limited by the mass transfer of carbon dioxide, so as to truly reflect the chemical dissolution kinetics. S4. Real-time online monitoring experiment: Cement mineral powder is added to the multi-port container, and the real-time online monitoring subsystem is activated to record the changes in solution conductivity and pH value to capture the kinetic information of the entire process of dissolution reaction initiation, progress, and reaching equilibrium. The water-cement ratio of the added deionized water and cement mineral powder is not less than 10000 to prepare an extremely dilute suspension, thereby inhibiting the precipitation of dissolved ions due to supersaturation to form hydration products or carbonates, forcing the reaction system to remain in a state dominated by mineral dissolution for a long time, so as to remove the interference of subsequent precipitation reaction on the mineral surface. S5. Data Processing and Kinetic Characterization: The conductivity-time curves and pH-time curves obtained in step S4 at different carbon dioxide concentrations are used to characterize the following dissolution behaviors of the minerals: a. By comparing the differences in the initial slopes of different curves, the accelerating or inhibiting effects of different carbon dioxide concentrations on the initial dissolution rate of minerals can be quantitatively assessed; b. Analyze the influence of carbon dioxide concentration on the dissolution equilibrium state by analyzing the time and value of the plateau phase in the curve; extract the raw data through the computer storage unit to generate conductivity-time curves and pH-time curves, and perform kinetic analysis.

5. The method as described in claim 4, characterized in that, In step S2, the pre-ventilation time is controlled between 3 and 10 minutes to ensure that the gas phase space in the multi-port container and the dissolved gas in the reaction liquid reach the set concentration.

6. The method as described in claim 4, characterized in that, In steps S3 and S4, 2000 grams of deionized water are weighed and added to a multi-mouth container according to the water-cement ratio, and 0.2 grams of cement mineral powder is weighed; the cement mineral powder includes tricalcium silicate and / or tricalcium aluminate.

7. The method as described in claim 4, characterized in that, In step S4, a mixture of carbon dioxide and nitrogen is continuously introduced into the bottom of the reaction liquid at a constant total flow rate of 0.5 liters / minute to 1.5 liters / minute; a multi-channel tester continuously records data at a resolution of seconds, and the experiment lasts for 5 to 60 minutes.

8. The method as described in claim 4, characterized in that, In step S5, the kinetic analysis includes: extracting the linear portion of the conductivity-time curve at the beginning of the reaction and calculating the initial slope; analyzing the rate of decrease of the pH-time curve and the pH value at the final equilibrium; and comparing the time required for the curve to reach the plateau phase under different carbon dioxide concentrations.

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