A process for preparing paste-filling materials based on CO2 mineralization and sequestration

Abstract

This invention discloses a process for preparing a paste-based backfill material based on CO2 mineralization and sequestration, relating to the field of mining backfilling technology. The process includes mixing carbide slag with water to form a suspension, obtaining a pre-carbonized carbide slag slurry; obtaining a CO2-saturated paste; preparing a stress-responsive bacterial strain carrier; forming a backfill body after initial setting; the CO2 dissolved in the paste reacts with calcium ions to generate calcium carbonate precipitate; and the bacterial strain utilizes the CO2 and calcium ions dissolved in the paste's pore liquid to deposit calcite on the fracture surface. This invention achieves saturated dissolution and stable transport of CO2 in the paste, enabling crack self-healing and a second-stage CO2 supplementary sequestration. It directly sequesters CO2 while reducing carbon emissions from cement production, achieving a dual carbon reduction effect. While ensuring the 28-day compressive strength of the backfill body meets the requirements for backfilling mining, it also endows it with long-term crack self-healing capabilities, providing a low-carbon, low-cost, and highly stable green technology solution for coal mine backfilling mining.

Description

Technical Field

[0001] This invention relates to the field of mine backfilling technology, and in particular to a process for preparing paste backfill materials based on CO2 mineralization and sequestration. Background Technology

[0002] Backfilling mining, as an important technical means for green coal mining, can not only effectively control surface subsidence and improve the coal resource recovery rate, but also dispose of coal-based solid wastes such as coal gangue and fly ash on a large scale. It has shown unique technical advantages in disaster reduction and solid waste disposal. With the in-depth advancement of my country's strategic goal of "carbon peaking and carbon neutrality", backfilling mining technology has been given a new mission - to realize the resource utilization of solid waste and build a technical path for permanent CO2 mineralization and storage, so as to promote the development of coal mining towards high quality, low environmental damage, and green and low-carbon development. At present, the research on combining CO2 mineralization and storage technology with paste backfilling process has become a hot topic in the industry. Existing technologies mainly revolve around two technical routes: one is the direct mineralization method, which directly introduces CO2 into the paste backfilling material and uses the alkaline components in the paste (such as cement hydration product Ca(OH)2) to react with CO2 to generate calcium carbonate precipitate; the other is the indirect method. The mineralization method, which involves first dissolving calcium and magnesium ions from solid waste using chemical reagents and then reacting them with CO2 to form carbonates, still faces many technical bottlenecks in practical applications. Direct mineralization faces the dilemma of "difficulty in balancing mineralization efficiency and filling performance." After CO2 is introduced into the paste, the mineralization reaction mainly concentrates on the surface of the material, with a low degree of reaction inside, resulting in uneven carbon fixation. The rapid escape of CO2 reduces the fluidity and pumpability of the paste, and the mineralization reaction competes with the cement hydration reaction, affecting the early strength development of the filling body. Although indirect mineralization can increase the reaction rate, it requires a large amount of chemical reagents, resulting in high waste liquid treatment costs and poor adaptability to large-scale mining projects. Existing mineralized filling materials face long-term stability challenges during service: the filling body is prone to microcracks under the pressure of overburden, which not only leads to the decline of mechanical properties but may also destroy the stability of the sealed CO2, creating a potential risk of carbon leakage.

[0003] However, current common solutions have many drawbacks, including: existing direct mineralization methods cannot balance CO2 mineralization efficiency and the mechanical properties of the backfill; the mineralization reaction is concentrated on the surface of the material and interferes with cement hydration; severe CO2 escape leads to low carbon sequestration efficiency; the backfill is prone to microcracks under mining stress, and existing self-healing technologies rely on external carbon sources and the triggering mechanism is difficult to respond accurately to crack propagation, making it impossible to achieve long-term stability maintenance throughout the entire life cycle; when alkaline calcium-rich solid wastes such as carbide slag directly replace cementitious materials, the strength decreases significantly due to the consumption of mixing water, interference with hydration reaction, and poor interfacial adhesion; existing pre-carbonization technology is not integrated with the paste backfilling process system, and its nano-CaCO3 nucleation and filling effects are not fully utilized; the dissolution and transport of CO2 in the paste lack effective control methods, traditional stirring has low gas-liquid contact efficiency, and pressure fluctuations during transport can easily lead to premature CO2 escape. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the preparation process of paste filling materials based on CO2 mineralization and storage, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to provide a paste filling material preparation process based on CO2 mineralization and storage. This process addresses the challenges of existing direct mineralization methods, which struggle to balance CO2 mineralization efficiency with the mechanical properties of the filling material. Specifically, the mineralization reaction is concentrated on the material surface and interferes with cement hydration, leading to severe CO2 escape and low carbon sequestration efficiency. Furthermore, the filling material is prone to microcracks under mining stress, and existing self-healing technologies rely on external carbon sources with inaccurate triggering mechanisms, failing to achieve long-term stability maintenance throughout its entire lifecycle. When alkaline calcium-rich solid wastes such as carbide slag directly replace cementitious materials, their strength significantly decreases due to water consumption, interference with hydration reactions, and poor interfacial adhesion. Existing pre-carbonization technologies are not integrated with the paste filling process system, and their nucleation and filling effects of nano-CaCO3 are not fully utilized. Finally, the dissolution and transport of CO2 in the paste lack effective control methods, traditional stirring methods have low gas-liquid contact efficiency, and pressure fluctuations during transport can easily lead to premature CO2 escape.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0008] In a first aspect, embodiments of the present invention provide a process for preparing a paste-like filling material based on CO2 mineralization and sequestration, comprising: mixing carbide slag with water to form a suspension; introducing CO2 into the suspension for pre-carbonization treatment to obtain a pre-carbonized carbide slag slurry; mixing a cementing material, water, and a porous carrier loaded with CO2 mineralizing bacterial spores to form a matrix slurry; mixing the matrix slurry with the pre-carbonized carbide slag slurry and feeding it into a gas-slurry countercurrent contact device to obtain a CO2-saturated paste; loading the CO2 mineralizing bacterial spores and nutrient substrate into the pores of the porous carrier, and coating the surface of the carrier with a layer that can be mechanically absorbed. A stress-responsive bacterial strain carrier was prepared by exposing the brittle shell layer to mechanical stress. The CO2-saturated paste was mixed with the stress-responsive bacterial strain carrier and pumped into the goaf area, where it initially solidified to form a filling body. During the initial solidification of the filling body, the CO2 dissolved in the paste reacted with calcium ions to form calcium carbonate precipitate, achieving the first stage of CO2 sequestration. When the filling body developed microcracks due to stress, the shear force generated by the crack propagation destroyed the brittle shell layer, activating CO2 mineralization bacterial spores. The strain used the CO2 and calcium ions dissolved in the paste pore liquid to deposit calcite on the crack surface, achieving crack self-repair and the second stage of CO2 sequestration.

[0009] As a preferred embodiment of the preparation process of paste filling material based on CO2 mineralization and storage described in this invention, in the pre-carbonization process, the mixing mass ratio of carbide slag and water is 1:4, the pre-carbonization time is configured to be 15~45 minutes, so that the Ca(OH)2 conversion rate reaches 43%~91.4%, and the average particle size of the generated CaCO3 particles is reduced to 9.8~68.15μm.

[0010] As a preferred embodiment of the paste filling material preparation process based on CO2 mineralization and storage described in this invention, the gas-slurry countercurrent contact device is provided with multiple layers of hydrophilic filler. CO2 gas is injected from the bottom of the device, and a mixed slurry of matrix slurry and pre-carbonized carbide slag slurry is sprayed from the top of the device. The gas and liquid phases are in countercurrent contact in the filler layer. A gas phase pressure maintenance unit is provided at the top of the device to maintain the gas phase pressure in the device to prevent CO2 from escaping prematurely.

[0011] As a preferred embodiment of the preparation process of the paste filling material based on CO2 mineralization and sealing described in this invention, the porous carrier is selected from at least one of modified biochar, nanoporous silica or zeolite, and its pore size is configured to accommodate and protect the CO2 mineralized bacterial spores and nutrient substrate.

[0012] As a preferred embodiment of the preparation process of paste filling material based on CO2 mineralization and storage described in this invention, the brittle shell is made of nano-calcium carbonate or brittle polymer material, and the thickness of the brittle shell is configured such that it will fracture under the shear force generated by the propagation of microcracks, and the fracture threshold is lower than the stress level of the filling body under normal service conditions.

[0013] As a preferred embodiment of the preparation process of paste filling material based on CO2 mineralization and preservation according to the present invention, wherein: the CO2 mineralized bacterial spores are Bacillus pasteurellii spores, the nutrient medium contains urea and calcium source, the stress-responsive strain carrier maintains the spores in a dormant state under no stress, and the spores are activated after the brittle shell breaks and comes into contact with moisture and nutrient medium.

[0014] As a preferred embodiment of the preparation process of paste backfill material based on CO2 mineralization and storage described in this invention, the pre-carbonized carbide slag replaces part of the cementitious material, with a replacement rate of 10% to 40%. When the replacement rate is 30% and the pre-carbonization time is 45 minutes, the 28-day compressive strength of the backfill body meets the requirements for backfill mining strength.

[0015] As a preferred embodiment of the preparation process of paste filling material based on CO2 mineralization and storage described in this invention, the nano-CaCO3 particles generated in the pre-carbonized carbide slag have both nucleation and filling effects. On the one hand, they provide heterogeneous nucleation sites for hydrated calcium silicate gel to promote cement hydration, and on the other hand, they fill the pores of the paste to refine the pore structure and improve the density.

[0016] As a preferred embodiment of the preparation process of paste filling material based on CO2 mineralization and storage described in this invention, wherein: the CO2 dissolved in the CO2 saturated paste is stored in the paste pore liquid in the form of bicarbonate ions, providing an in-situ carbon source for the strains in the second stage of CO2 storage, so that the crack self-healing process does not require external CO2 supplementation.

[0017] As a preferred embodiment of the CO2 mineralization sequestration-based paste filling material preparation process described in this invention, wherein: the first stage of CO2 sequestration is chemical mineralization sequestration, which mainly occurs during the initial setting stage of the filling material, and is achieved by reacting dissolved CO2 in the paste with calcium ions to generate calcium carbonate; the second stage of CO2 sequestration is biomineralization sequestration, which mainly occurs when microcracks appear during the service life of the filling material, and is achieved by inducing calcium carbonate deposition through activated CO2 mineralization bacterial spores.

[0018] The beneficial effects of this invention are as follows: The pre-carbonization treatment efficiently converts Ca(OH)2 in carbide slag into nano-CaCO3, transforming it from a "performance weakener" into a "performance enhancer" with both nucleation and filling effects, effectively solving the strength degradation problem caused by directly replacing cement with carbide slag; the gas-slurry countercurrent contact device, through multi-layer packing countercurrent contact and gas phase pressure maintenance, achieves saturated dissolution and stable transport of CO2 in the paste, providing sufficient carbon source for chemical mineralization; during the initial setting stage of the filling body, CO2 is rapidly sealed and strength support is formed through chemical mineralization; during service, when microcracks occur, the stress-responsive bacterial carrier precisely ruptures under shear force and activates mineralizing bacterial spores, utilizing the pore liquid in the paste... The stored bicarbonate in-situ carbon source deposits calcite on the fracture surface, achieving self-repair of the fracture and secondary CO2 sequestration, forming a two-stage full life cycle carbon sequestration mechanism of "initial chemical mineralization + long-term biomineralization". This process also realizes the synergistic resource utilization of multiple sources of industrial solid waste such as carbide slag, coal gangue, and fly ash. By replacing 10% to 40% of cement with pre-carbonized carbide slag, it directly sequesters CO2 and reduces carbon emissions from cement production, achieving a dual carbon reduction effect. While ensuring that the 28-day compressive strength of the backfill body meets the requirements for backfilling and mining, it endows it with long-term fracture self-repair capability, effectively preventing carbon leakage risks, and providing a low-carbon, low-cost, and highly stable green technology solution for coal mine backfilling mining. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0020] Figure 1 This is a flowchart illustrating the implementation of the present invention in Example 1. Detailed Implementation

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0022] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0023] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0024] Example 1

[0025] Reference Figure 1 This is the first embodiment of the present invention, which provides a process for preparing a paste-filling material based on CO2 mineralization and sequestration, including the following steps:

[0026] S1: Mix carbide slag with water to form a suspension, and introduce CO2 into the suspension for pre-carbonization treatment to obtain pre-carbonized carbide slag slurry.

[0027] Preferably, during the pre-carbonization process, the mass ratio of carbide slag to water is 1:4, and the pre-carbonization time is configured to be 15~45 minutes, so that the Ca(OH)2 conversion rate reaches 43%~91.4%, and the average particle size of the generated CaCO3 particles is reduced to 9.8~68.15μm.

[0028] Furthermore, during the pre-carbonization process, carbide slag and water are placed in a mixing container in a certain proportion and stirred at a speed of 300-500 rpm to fully disperse the carbide slag. CO2 is continuously introduced into the suspension through a bubble diffuser at a rate of 5-10 liters per minute. The pH and temperature of the suspension are monitored in real time during the reaction. When the pH value gradually decreases from the initial value of about 12.5 to about 6.7 and remains stable, the pre-carbonization reaction is considered complete.

[0029] Specifically, during the pre-carbonization process, the pH of the suspension changes through three stages: a stable stage, a rapid decrease stage, and a re-stabilization stage. The temperature first rises and then falls as the reaction exothermics. When the temperature of the suspension reaches its peak, it indicates that the neutralization reaction between Ca(OH)2 and CO2 is basically completed.

[0030] Preferably, by mixing carbide slag and water at a mass ratio of 1:4 to form a suspension, CO2 is introduced for pre-carbonization treatment for 15-45 minutes. The reaction process is precisely controlled by real-time monitoring of pH and temperature, so that the Ca(OH)2 conversion rate reaches 43%-91.4%, and the average particle size of the generated CaCO3 particles is refined from 68.15μm to 9.8μm. This pre-carbonization process achieves efficient mineralization and sequestration of approximately 0.33 tons of CO2 per ton of carbide slag. On the other hand, it transforms carbide slag from a "performance weakener" to a "performance enhancer": the nano-CaCO3 particles have both nucleation and filling effects. They can act as heterogeneous nucleation sites for hydrated calcium silicate gel to promote cement hydration, and they can also fill the pores of the paste to refine the pore structure and improve density. Thus, under the condition of replacing 10%-40% of cement, the 28-day compressive strength of the filling body is increased by 15.4% compared with the uncarbonized group, effectively solving the technical problem of strength deterioration caused by direct replacement of traditional carbide slag.

[0031] For example, using carbide slag produced by a chemical plant as raw material, its main component is Ca(OH)2 with a content of approximately 85%, take 400 kg of carbide slag and 1600 Add kg of water at a mass ratio of 1:4 to a volume of 2.5. In a stirred reactor with a volume of m³, the carbide slag was stirred at 400 rpm for 10 minutes to fully disperse it into a uniform suspension. Industrial-grade CO2 gas was continuously introduced into the suspension through a bubble diffuser at a rate of 8 L / min. The pH and temperature of the suspension were monitored in real time during the reaction. The initial pH was 12.5. As CO2 was introduced, the temperature of the suspension gradually increased to 65°C. The pH stabilized at around 11.8 within 36 minutes, then dropped rapidly to 6.8 within 8 minutes and remained stable thereafter. After 45 minutes of reaction, the gas supply was stopped, resulting in a pre-carbonized carbide slag slurry. XRD and TGA analysis showed that the Ca(OH)2 conversion rate in the pre-carbonized product reached 91.4%, and the average particle size of CaCO3 was 9.8 μm, achieving efficient carbonization conversion and particle size refinement of the carbide slag.

[0032] S2: The cementitious material, water and porous carrier loaded with CO2 mineralizing bacteria spores are mixed to form a matrix slurry. The matrix slurry is then mixed with pre-carbonized carbide slag slurry and sent into a gas-slurry countercurrent contact device to obtain CO2 saturated paste.

[0033] Preferably, the gas-slurry countercurrent contact device is equipped with a multi-layer hydrophilic packing layer. CO2 gas is injected from the bottom of the device, and a mixture of matrix slurry and pre-carbonized carbide slag slurry is sprayed from the top of the device. The gas and liquid phases are in countercurrent contact in the packing layer. A gas phase pressure maintenance unit is provided at the top of the device to maintain the gas phase pressure inside the device to prevent CO2 from escaping prematurely.

[0034] Specifically, the porous carrier is selected from at least one of modified biochar, nanoporous silica, or zeolite, and its pore size is configured to accommodate and protect CO2-mineralized bacterial spores and nutrient substrate.

[0035] Furthermore, the CO2 mineralizing bacteria spores are Pasteurella spores, and the nutrient medium contains urea and calcium sources. The stress-responsive strain carrier maintains the spores in a dormant state under no stress, and the spores are activated after the brittle shell breaks and comes into contact with water and the nutrient medium.

[0036] Specifically, pre-carbonized carbide slag can replace part of the cementitious materials, with a replacement rate of 10% to 40%. When the replacement rate is 30% and the pre-carbonization time is 45 minutes, the 28-day compressive strength of the backfill meets the requirements for backfill mining strength.

[0037] Specifically, the nano-CaCO3 particles generated in pre-carbonized carbide slag have both nucleation and filling effects. On the one hand, they provide heterogeneous nucleation sites for hydrated calcium silicate gel to promote cement hydration, and on the other hand, they fill the pores of the paste to refine the pore structure and improve the density.

[0038] Furthermore, the cementing materials include ordinary silicate cement and fly ash, with the fly ash being Class II fly ash and particles smaller than 45μm accounting for more than 80%; when the matrix slurry is mixed with the pre-carbonized carbide slag slurry, the amount of water added is calculated based on the water content in the pre-carbonized carbide slag slurry and deducted, so that the total mass concentration of the paste is controlled between 75% and 80%.

[0039] Preferably, the matrix slurry is mixed with the pre-carbonized carbide slag slurry and then fed into a gas-slurry countercurrent contact device. Through a multi-layer hydrophilic filler layer, CO2 gas is injected from the bottom and slurry is sprayed from the top, achieving countercurrent contact, which greatly increases the gas-liquid mass transfer area and efficiency. The gas phase pressure maintenance unit at the top of the device effectively prevents CO2 from escaping prematurely before transportation, ensuring that the paste reaches a CO2 saturation state. On the one hand, it provides sufficient dissolved CO2 for the first stage of chemical mineralization in the initial setting stage of the filling body. On the other hand, it stores CO2 in the form of bicarbonate in the pore liquid of the paste, reserving an "in-situ carbon source" for the subsequent second stage of biomineralization. This allows the crack self-healing process to be carried out without the need for external CO2 supplementation, realizing a closed-loop design for carbon source supply. At the same time, by controlling the total mass concentration of the paste between 75% and 80%, the pumpability of the filling slurry is ensured.

[0040] For example, take 119 kg of ordinary silicate cement, 150 kg of Grade II fly ash (85% of which are particles smaller than 45 μm), and 5 kg of modified biochar porous carrier loaded with Bacillus pasteurellii spores, and mix them with an appropriate amount of water to form a matrix slurry. Mix the above matrix slurry with the pre-carbonized carbide slag slurry (containing 51 kg of carbide slag) obtained in step S1. Calculate and deduct the amount of additional water added based on the water content in the pre-carbonized slurry to control the total mass concentration of the paste at 77%. Send the mixed slurry into the air-slurry countercurrent contact device. The device is equipped with three layers of hydrophilic polypropylene packing. CO2 gas is injected from the bottom of the device at a rate of 10 liters / minute, and the mixed slurry is evenly distributed from the top of the device in the form of spray. The gas and liquid phases are in countercurrent contact in the packing layer. The gas phase pressure maintenance unit at the top of the device controls the pressure at 0.4 MPa, so that CO2 is fully dissolved in the slurry. After treatment, the CO2 in the paste reaches a saturated state, resulting in a CO2-saturated paste. The CO2 dissolved in the pore liquid of this paste is stored in the form of bicarbonate ions, providing an in-situ carbon source for subsequent mineralization reactions.

[0041] S3: CO2-mineralized bacterial spores and nutrient medium are loaded into the pores of a porous carrier, and a brittle shell layer that can be destroyed by mechanical stress is coated on the surface of the carrier to obtain a stress-responsive bacterial strain carrier.

[0042] Preferably, the brittle shell is made of nano-calcium carbonate or a brittle polymer material, and the thickness of the brittle shell is configured such that it fractures under the shear force generated by the propagation of microcracks, and the fracture threshold is lower than the stress level of the filling body under normal service conditions.

[0043] Furthermore, the method for loading CO2 mineralized bacterial spores and nutrient substrate is as follows: a porous carrier is placed in a mixed solution containing Bacillus pasteurellii spores, urea and calcium source, and soaked at room temperature for 24 to 48 hours to allow the bacterial spores and nutrient substrate to be adsorbed into the pores of the carrier. Then it is taken out and dried to obtain a porous carrier loaded with bacterial spores.

[0044] Specifically, the coating method for the brittle shell is as follows: a porous carrier loaded with bacterial spores is dispersed in a nano-calcium carbonate suspension or a brittle polymer solution, and a uniform shell with a thickness of 10~50μm is formed on the surface of the carrier by spray drying or fluidized bed coating process.

[0045] Furthermore, in the stress-responsive strain vector, the spore loading was 10 spores per gram of vector. 8 ~10 10 Each spore contains urea at a concentration of 10-20 g / L and calcium source at a concentration of 5-15 g / L in the nutrient medium.

[0046] Specifically, the calcium source is at least one of calcium chloride, calcium nitrate, or calcium acetate.

[0047] Furthermore, the fracture threshold of the brittle shell is controlled by adjusting the shell thickness and material composition, so that it remains intact under the stress level (0.5~2.0MPa) of the filling body under normal service conditions, and only fractures under the shear stress (≥2.5MPa) generated by the propagation of microcracks.

[0048] Preferably, CO2-mineralized bacterial spores and a nutrient substrate are loaded into the pores of a porous carrier, and a brittle shell layer that can be broken by mechanical stress is coated on the surface to obtain a stress-responsive bacterial strain carrier. The shear force generated by the propagation of microcracks serves as a trigger signal. The brittle shell fracture threshold is precisely controlled above 2.5 MPa by adjusting the shell thickness and material composition, ensuring the carrier remains intact under the normal service stress (0.5~2.0 MPa) of the filling material. Release is triggered only when cracks occur, achieving "on-demand precise activation" of the self-healing function. The bacterial spores can survive for a long time in a dormant state, with each gram of carrier loading 10... 8 ~10 10 When the brittle shell breaks, the spores are activated by contact with water and nutrients. They utilize urease produced by urea hydrolysis to catalyze the formation of carbonate ions, which combine with calcium ions to deposit calcite. The carrier is evenly distributed in the paste, giving the filling material a multi-round self-healing ability. When new cracks appear in different areas, the carrier in the corresponding area is triggered in sequence, realizing dynamic maintenance throughout the entire life cycle.

[0049] For example, *Sporosarcina* A pasteurii spore suspension was mixed with a nutrient solution containing 15 g / L urea and 10 g / L calcium chloride. A nanoporous silica porous carrier (pore size 50-150 nm) was placed in the mixture and soaked at room temperature for 36 hours to allow the spores and nutrient solution to be fully adsorbed into the carrier pores. Each gram of carrier was loaded with approximately 5 × 10⁻⁵ spores. 9 The spores were extracted and vacuum dried at 40°C for 12 hours to obtain a porous carrier loaded with spores. The carrier was dispersed in a nano-calcium carbonate suspension (15% solid content). A uniform brittle shell layer with a thickness of about 30 μm was formed on the surface of the carrier through a fluidized bed coating process. The coating temperature was controlled at 50°C and the air velocity was adjusted to keep the carrier in a fluidized state. The coated carrier is a stress-responsive strain carrier. Its brittle shell fracture threshold is controlled at about 3.0 MPa by the shell thickness to ensure that it remains intact under the normal service stress level of the filling body (≤2.0 MPa) and only fractures under the shear stress generated by the propagation of microcracks.

[0050] S4: After mixing CO2-saturated paste with stress-responsive bacterial strain carrier, it is pumped into the goaf area and forms a filling body after initial solidification.

[0051] Preferably, the CO2-saturated paste and the stress-responsive bacterial strain carrier are mixed online using a pipeline static mixer. After mixing, the paste is immediately pumped into the goaf via a filling pump. The time interval between mixing and pumping is controlled within 10 minutes to prevent the paste from initially coagulating or CO2 from escaping during transport.

[0052] Specifically, the amount of stress-responsive strain carrier in CO2-saturated paste is 1% to 5% of the dry mass of the cementitious material. The carrier is uniformly dispersed in the paste to ensure that the carrier is distributed throughout the microcrack propagation area.

[0053] Preferably, the CO2-saturated paste and stress-responsive bacterial strain carrier are mixed online via a pipeline static mixer and immediately pumped into the goaf. The time interval between mixing and pumping is controlled within 10 minutes. The pipeline static mixer ensures uniform dispersion of the carrier in the paste, guaranteeing that the carrier is distributed throughout the microcrack propagation area and ensuring the integrity of the self-healing function. Strictly controlling the time interval between mixing and pumping effectively prevents the paste from initially setting or premature CO2 escape during transportation, ensuring the continuity and stability of the filling process. The dosage of the stress-responsive bacterial strain carrier is controlled at 1% to 5% of the dry mass of the cementitious material, ensuring both self-healing effect and material cost economy, making the technical solution feasible for large-scale application.

[0054] For example, the CO2-saturated paste obtained in step S2 and the stress-responsive bacterial strain carrier obtained in step S3 are mixed online using a DN150 pipeline static mixer at a dosage of 3% of the dry mass of the gelling material. The static mixer is equipped with staggered spiral blades to ensure uniform dispersion of the carrier in the paste. After mixing, the mixture is immediately pumped through a filling pump at 80m³ / h. 3 The paste is pumped into the goaf at a flow rate of / h, and the time interval between mixing and pumping is controlled within 8 minutes. This effectively prevents the paste from coagulating prematurely or CO2 from escaping prematurely during transportation. The carrier is evenly distributed in the paste. Sampling tests show that the distribution deviation of the carrier in the paste is less than 5%, ensuring that the carrier is distributed in all areas of the filling material in the goaf.

[0055] S5: During the initial setting of the filling material, the CO2 dissolved in the paste reacts with calcium ions to form calcium carbonate precipitate, achieving the first stage of CO2 sequestration.

[0056] Specifically, the first stage of CO2 sequestration is chemical mineralization sequestration, which mainly occurs during the initial setting stage of the filling body. It is achieved by reacting dissolved CO2 in the paste with calcium ions to generate calcium carbonate. The second stage of CO2 sequestration is biomineralization sequestration, which mainly occurs when microcracks appear during the service life of the filling body. It is achieved by inducing calcium carbonate deposition through activated CO2 mineralizing bacterial spores.

[0057] Furthermore, during the first stage of CO2 sequestration, the CO2 dissolved in the pore liquid of the paste is in the form of bicarbonate ions (HCO3-). - It exists in the form of free Ca. 2+ The reaction produces calcium carbonate precipitate, and this reaction continues for 24 to 72 hours after the initial setting of the filling material. The sealed CO2 accounts for 40% to 60% of the total carbon sequestration.

[0058] Preferably, during the initial setting of the filling material, the CO2 dissolved in the paste reacts with calcium ions to form calcium carbonate precipitate, achieving the first stage of CO2 sequestration. This stage occurs within 24 to 72 hours of the initial setting of the filling material. Taking advantage of the high reactivity of the paste in its fresh state, CO2 is rapidly sequestered, with the sequestered amount accounting for 40% to 60% of the total carbon fixation. The generated calcium carbonate precipitate directly contributes to the early strength of the filling material as a rigid supporting framework. On the other hand, it works synergistically with the cement hydration reaction—the hydration reaction consumes water and generates an alkaline environment that provides favorable conditions for mineralization. The nano-calcium carbonate generated by mineralization acts as a crystal nucleus to promote the formation of hydration products. The two promote each other and jointly drive the formation and development of the early strength of the filling material.

[0059] For example, after the filling material is pumped into the goaf, it is left to cure under conditions of 35°C and ≥95% humidity in the well. During the initial setting of the filling material, the CO2 dissolved in the CO2-saturated paste prepared in step S2 is converted into bicarbonate ions (HCO3-). - It exists in the form of free Ca in the paste. 2+ The reaction produces calcium carbonate precipitate, which continues for 48 hours during the initial setting of the filling material. According to TGA quantitative analysis, the CO2 sealed in this stage accounts for about 52% of the total carbon fixation. The generated calcium carbonate precipitate contributes to the early strength of the filling material as a rigid support skeleton, and also promotes cement hydration as a crystal nucleus, enabling the filling material to reach a 3-day compressive strength of 1.8 MPa, laying the foundation for subsequent strength development.

[0060] S6: When the filling material develops microcracks due to stress, the shear force generated by the crack propagation destroys the brittle shell and activates CO2 mineralizing bacterial spores. The strain uses CO2 and calcium ions dissolved in the paste pore liquid to deposit calcite on the crack surface, realizing crack self-repair and second-stage CO2 sequestration.

[0061] Specifically, the CO2 dissolved in the CO2-saturated paste is stored in the paste pore liquid in the form of bicarbonate ions, providing an in-situ carbon source for the strains in the second stage of CO2 sealing, so that the crack self-healing process does not require external CO2 supplementation.

[0062] Furthermore, during the second stage of CO2 sequestration, activated Bacillus pasteurellii spores utilize urea in the nutrient medium to hydrolyze and produce urease. Urease catalyzes the hydrolysis of urea to generate carbonate ions (CO3).2- carbonate ions and Ca in pore fluid 2+ By depositing calcite crystals on the surface of the crack, the calcite crystals gradually fill the crack and achieve complete sealing of the crack.

[0063] Specifically, the self-healing process of the crack includes the following stages: the expansion of microcracks triggers the rupture of the brittle shell and releases bacterial spores and nutrients; the bacterial spores are activated and multiply under the action of moisture and nutrients; urease produced by the bacterial strain catalyzes the hydrolysis of urea, increasing the local carbonate concentration; carbonate and calcium ions nucleate and grow on the crack surface to form a calcite layer; the calcite layer gradually thickens until it completely fills the crack, realizing the self-healing of the crack and the secondary sequestration of CO2.

[0064] Furthermore, the self-healing process of cracks can be repeated during the service life of the filling body. When new microcracks are generated in the filling body, the brittle shell of the carrier in the crack propagation area breaks again and releases bacterial spores, achieving multiple rounds of self-healing.

[0065] Preferably, when the infill material develops microcracks due to stress, the shear force generated by the crack propagation breaks down the brittle shell, activating CO2-mineralizing bacterial spores. The strains utilize CO2 and calcium ions dissolved in the paste pore fluid to deposit calcite on the crack surface, achieving self-repair of the cracks and second-stage CO2 sequestration. The self-repair function is triggered synchronously with the crack formation process, achieving precise spatiotemporal positioning and avoiding ineffective strain consumption. The activated Bacillus pasteurellii utilizes urea hydrolysis to produce urease, catalyzing the formation of carbonate ions from urea. These carbonate ions combine with calcium ions in the pore fluid to form a dense calcite layer on the crack surface, gradually filling until the cracks are completely sealed. This process does not require external CO2 supplementation; it directly utilizes the bicarbonate ions stored in the pore fluid in step S2 as an in-situ carbon source, achieving a closed-loop cycle of carbon source supply. The repair process simultaneously completes secondary CO2 sequestration, further increasing the total amount of carbon sequestration. When new cracks occur in different areas of the infill material, the corresponding carriers are triggered sequentially, achieving multiple rounds of self-repair, providing long-term protection for the structural integrity and carbon sequestration stability of the infill material throughout its entire service life.

[0066] For example, after 6 months of service, the infill material developed microcracks with a width of about 0.5 mm in a local area due to overburden pressure. The shear stress generated by the crack propagation (measured at about 3.2 MPa) exceeded the brittle shell fracture threshold, causing the brittle shell of the stress-responsive bacterial carrier in the crack propagation area to fracture, releasing the Bacillus pasteurellii spores and nutrient substrate inside. The spores were rapidly activated and multiplied under the action of water and nutrient substrate that seeped into the crack. Urease produced by the bacterial metabolism catalyzed the hydrolysis of urea to generate carbonate ions, which, together with bicarbonate and calcium ions stored in the paste pore liquid, deposited dense calcite crystals on the crack surface. After 14 days of repair, the crack was completely filled with calcite, and the impermeability of the repaired area was restored to 92% of the level of the intact infill material. This repair process also completed the secondary sequestration of CO2. It was calculated that about 0.25 kg of CO2 was sequestered per meter of crack repair. When new cracks appeared in other areas of the infill material, the carrier in the corresponding area was triggered in sequence, realizing multiple rounds of self-repair.

[0067] In summary, the pre-carbonization treatment of this invention efficiently converts Ca(OH)2 in carbide slag into nano-CaCO3, transforming it from a "performance weakener" into a "performance enhancer" with both nucleation and filling effects, effectively solving the strength degradation problem caused by directly replacing cement with carbide slag. The gas-slurry countercurrent contact device achieves saturated dissolution and stable transport of CO2 in the paste through multi-layer packing countercurrent contact and gas phase pressure maintenance, providing sufficient carbon source for chemical mineralization. During the initial setting stage of the filling body, CO2 is rapidly sealed and strength support is formed through chemical mineralization. During service, when microcracks occur, the stress-responsive bacterial carrier precisely breaks under shear force and activates mineralized bacterial spores, utilizing the carbon stored in the pore liquid of the paste. In-situ carbon sources of bicarbonate deposit calcite on the surface of cracks, achieving self-repair of cracks and secondary CO2 sequestration, forming a two-stage, full-life-cycle carbon sequestration mechanism of "initial chemical mineralization + long-term biomineralization". This process also realizes the synergistic resource utilization of multiple sources of industrial solid waste such as carbide slag, coal gangue, and fly ash. By replacing 10% to 40% of cement with pre-carbonized carbide slag, it directly sequesters CO2 and reduces carbon emissions from cement production, achieving a dual carbon reduction effect. While ensuring that the 28-day compressive strength of the backfill meets the requirements for backfill mining, it endows the backfill with long-term crack self-repair capability, effectively preventing carbon leakage risks, and providing a low-carbon, low-cost, and highly stable green technology solution for coal mine backfill mining.

[0068] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A process for preparing paste-like filling materials based on CO2 mineralization and sequestration, characterized in that: include: Carbide slag is mixed with water to form a suspension, and CO2 is introduced into the suspension for pre-carbonization treatment to obtain pre-carbonized carbide slag slurry. A matrix slurry is formed by mixing cementitious materials, water, and a porous carrier loaded with CO2 mineralizing bacterial spores. The matrix slurry is then mixed with the pre-carbonized carbide slag slurry and fed into a gas-slurry countercurrent contact device to obtain a CO2 saturated paste. The CO2-mineralized bacterial spores and nutrient medium were loaded into the pores of a porous carrier, and a brittle shell layer that could be destroyed by mechanical stress was coated on the surface of the carrier to obtain a stress-responsive bacterial strain carrier. The CO2 saturated paste was mixed with the stress-responsive bacterial strain carrier and then pumped into the goaf area, where it initially solidified to form a filling body. During the initial setting of the filling material, the CO2 dissolved in the paste reacts with calcium ions to form calcium carbonate precipitate, thus achieving the first stage of CO2 sequestration. When the filling material develops microcracks due to stress, the shear force generated by the crack propagation destroys the brittle shell layer, activates CO2 mineralizing bacterial spores, and the strain uses CO2 and calcium ions dissolved in the paste pore liquid to deposit calcite on the crack surface, realizing crack self-repair and second-stage CO2 sequestration.

2. The preparation process of a paste filling material based on CO2 mineralization and sequestration as described in claim 1, characterized in that: During the pre-carbonization process, the mass ratio of carbide slag to water is 1:4, and the pre-carbonization time is configured to be 15-45 minutes, so that the Ca(OH)2 conversion rate reaches 43%-91.4%, and the average particle size of the generated CaCO3 particles is reduced to 9.8-68.15 μm.

3. The preparation process of a paste-filling material based on CO2 mineralization and sequestration as described in claim 1, characterized in that: The gas-slurry countercurrent contact device is equipped with multiple layers of hydrophilic packing. CO2 gas is injected from the bottom of the device, and a mixture of matrix slurry and pre-carbonized carbide slag slurry is sprayed from the top of the device. The gas and liquid phases are in countercurrent contact in the packing layer. A gas phase pressure maintenance unit is provided at the top of the device to maintain the gas phase pressure inside the device to prevent CO2 from escaping prematurely.

4. The preparation process of a paste filling material based on CO2 mineralization and sequestration as described in claim 1, characterized in that: The porous carrier is selected from at least one of modified biochar, nanoporous silica, or zeolite, and its pore size is configured to accommodate and protect the CO2 mineralized bacterial spores and nutrient substrate.

5. The preparation process of a paste filling material based on CO2 mineralization and sequestration as described in claim 4, characterized in that: The brittle shell is made of nano-calcium carbonate or a brittle polymer material. The thickness of the brittle shell is configured such that it fractures under the shear force generated by the propagation of microcracks, and the fracture threshold is lower than the stress level of the filling body under normal service conditions.

6. The preparation process of a paste filling material based on CO2 mineralization and sequestration as described in claim 5, characterized in that: The CO2-mineralized bacterial spores are Bacillus pasteurellii spores, the nutrient medium contains urea and a calcium source, and the stress-responsive strain carrier maintains the spores in a dormant state when not under stress. After the brittle shell breaks, the spores are activated upon contact with moisture and the nutrient medium.

7. The preparation process of a paste filling material based on CO2 mineralization and sequestration as described in claim 1, characterized in that: The pre-carbonized carbide slag is used to replace part of the cementitious material, with a replacement rate of 10% to 40%. When the replacement rate is 30% and the pre-carbonization time is 45 minutes, the 28-day compressive strength of the backfill body meets the backfill mining strength requirements.

8. The preparation process of a paste filling material based on CO2 mineralization and sequestration as described in claim 7, characterized in that: The nano-CaCO3 particles generated in the pre-carbonized carbide slag have both nucleation and filling effects. On the one hand, they provide heterogeneous nucleation sites for hydrated calcium silicate gel to promote cement hydration; on the other hand, they fill the pores of the paste to refine the pore structure and improve the density.

9. The preparation process of a paste filling material based on CO2 mineralization and sequestration as described in claim 1, characterized in that: The CO2 dissolved in the CO2-saturated paste is stored in the paste pore liquid in the form of bicarbonate ions, providing an in-situ carbon source for the strains in the second stage of CO2 sealing, so that the crack self-healing process does not require external CO2 supplementation.

10. The preparation process of a paste filling material based on CO2 mineralization and sequestration as described in claim 1, characterized in that: The first stage of CO2 sequestration is chemical mineralization sequestration, which mainly occurs during the initial setting stage of the filling body. It is achieved by reacting dissolved CO2 in the paste with calcium ions to generate calcium carbonate. The second stage of CO2 sequestration is biomineralization sequestration, which mainly occurs when microcracks appear during the service of the filling body. It is achieved by inducing calcium carbonate deposition through activated CO2 mineralizing bacterial spores.

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