A mineralized CO2 sequestration microbial cemented backfill material for mining, its preparation method and application

Abstract

This invention discloses a high-strength microbial cemented backfill material for mining with high efficiency in CO2 sequestration and its preparation method. The material uses a composite carbonic anhydrase-producing microorganism composed of *Bacillus mucilaginosus* and *Bacillus halophilus* as its core, in conjunction with soluble calcium salts, porous hydroxyapatite, industrial solid waste aggregates, and an organic acid-nanoparticle composite inducer, to achieve efficient CO2 mineralization and high-strength cementation under extreme high-salt and medium-high temperature environments in mines. Experiments show that the material achieves a 7-day compressive strength of 16.3–20.2 MPa, a CO2 sequestration capacity of 82.6–101.3 g / kg, and a microbial survival rate exceeding 80%, achieving a synergistic improvement in strength and carbon sequestration efficiency. This material has a simple process, is environmentally friendly, and is suitable for mining engineering such as goaf backfilling and roadway support, providing a new path for the integration of green mining and carbon sequestration.

Description

Technical Field

[0001] This invention relates to a mineralized microbial cemented backfill material for CO2 sequestration and its preparation method, and particularly to a novel mine backfill material that utilizes microbial induced calcium carbonate precipitation (MICP) technology to achieve efficient CO2 sequestration and synergistic improvement of material mechanical properties. Background Technology

[0002] In the mining industry, cemented backfill technology is an important technical means for the scientific mining of coal. However, traditional cemented backfill materials have several technical shortcomings: First, the extensive use of cement-based materials leads to significant high carbon emissions, with approximately 0.9 tons of CO2 emitted for every ton of cement clinker produced. Second, existing carbon sequestration technologies are inefficient; for example, the carbon sequestration rate of steel slag is only 8%-12%, and fly ash only reaches 8.4 g / kg in wet processes. Although basalt can achieve a CO2 mineralization rate of over 95%, the reaction depends on high temperature and pressure conditions, resulting in high energy consumption and costs. Furthermore, materials generally experience a decrease in strength after carbon sequestration; for example, the compressive strength of steel slag-based materials decreases by 73.48%, and long-term stability is insufficient. At the process level, existing carbonization technologies often require high pressure or chemical solvents, which are demanding conditions. Microbial induced mineralization (MICP) and other technologies pose environmental risks, such as the release of ammonia and the potential for heavy metal leaching. In addition, microbial strains have poor adaptability to the harsh environment of mines, the natural mineralization process is slow, and artificial acceleration is easily affected by nutrient limitations and byproduct interference. Overall, existing methods and processes are complex, and there is a lack of simple, efficient, and environmentally friendly solutions suitable for large-scale mining projects.

[0003] However, deep mines generally present extreme environments characterized by high salinity (5%–20% mineralization), high pressure (3–10 MPa), and medium to high temperatures (40–60°C). Conventional microorganisms used in microbial cementation (MICP) are easily inactivated under these conditions, leading to a sharp decline in carbonic anhydrase activity, resulting in insufficient cementation strength and low CO2 sequestration efficiency. Furthermore, existing microbial filling materials lack specifically designed CO2 sequestration pathways, making it difficult to achieve efficient CO2 mineralization and fixation. Therefore, screening for carbonic anhydrase-producing microorganisms tolerant to extreme environments and developing microbial cemented filling materials adapted to mine conditions is of great significance for promoting the integration of green mining and carbon sequestration technologies.

[0004] To address the aforementioned technical problems, this invention proposes an innovative technical solution. By screening highly efficient carbonic anhydrase-producing microorganisms, optimizing material formulation design, and improving preparation process parameters, it achieves a dual improvement in CO2 sequestration efficiency and filling strength, opening up a new technical path for the green and low-carbon development of mine backfilling. Summary of the Invention

[0005] The purpose of this invention is to overcome the technical shortcomings of existing microbial filling materials, such as weak resistance to extreme environments, insufficient CO2 sequestration, decreased mechanical properties, complex processes, and high environmental risks. This invention provides a mineralized CO2-sequestering microbial cemented filling material for mining and its preparation method. By screening high-salt, medium- and high-temperature tolerant composite microbial strains and optimizing the material formulation and preparation process, this material achieves efficient CO2 mineralization and sequestration under extreme mining environments, while synergistically improving the mechanical properties of the filling body. It also possesses advantages such as environmental friendliness, simple process, and controllable cost, making it suitable for large-scale mining engineering applications.

[0006] This invention provides a mineralized microbial cementitious backfill material for CO2 mineralization and storage. The raw materials, by weight, include: 8-20 parts of compound carbonic anhydrase-producing microorganisms, 20-60 parts of soluble calcium salt, 5-10 parts of porous hydroxyapatite, 90-120 parts of aggregate, 5-10 parts of compound inducer, 0-5 parts of additives, and water as the balance.

[0007] Preferably, the composite carbonic anhydrase-producing microorganisms consist of *Bacillus mucilaginosus* and *Bacillus halophilus*, with a mass ratio of (1-3):1, and the viable count of *Bacillus mucilaginosus* and *Bacillus halophilus* is 1.0 × 10⁻⁶. 8 -1.0×10 10 CFU / g.

[0008] Preferably, the porous hydroxyapatite has an average particle size of 10-80 μm. Its abundant pore structure not only serves as a carrier for microorganisms, adsorbing and enriching carbonic anhydrase-producing microorganisms and extracellular enzymes to form locally highly active carbonation reaction zones, but also acts as an adsorption site for CO2 and a slow-release calcium source. Under the weakly acidic environment produced by microbial metabolism, hydroxyapatite can continuously and controllably release Ca. 2+ This allows it to react with CO3 produced by microbial catalysis. 2- Better matching avoids rapid and disordered precipitation caused by local ion supersaturation; while significantly improving CO2 sequestration efficiency and mineralization product uniformity, it also effectively improves the overall strength and long-term durability of the material by enhancing the interfacial bonding force of the filler.

[0009] Preferably, the soluble calcium salt is one or more selected from calcium chloride, calcium acetate, calcium formate, and calcium nitrate. Soluble calcium salts have high solubility and can rapidly release Ca. 2+ With CO3 2- The reaction produces calcium carbonate precipitate, thus achieving CO2 mineralization and fixation.

[0010] Preferably, the aggregate is one or more of fly ash, blast furnace slag, coal gangue, or carbide slag, with a particle size of 100-300 μm. The aggregates used are all mining or industrial solid waste, widely available and inexpensive, achieving resource utilization of solid waste while their own active components can participate in the cementing reaction, improving the strength of the filling body.

[0011] Preferably, the composite inducer comprises organic acid and inorganic nanoparticles in a mass ratio of 5-10:1.

[0012] Preferably, the organic acid is at least one selected from citric acid, oxalic acid, tartaric acid, gluconic acid, and ethylenediaminetetraacetic acid.

[0013] Preferably, the inorganic nanoparticles are at least one of nano-silica, nano-zinc oxide, and nano-alumina. Preferably, the average particle size of the inorganic nanoparticles is 20-100 nm.

[0014] Preferably, the additive includes at least one of an emulsifier, a water-reducing agent, or a thickener. The emulsifier improves the dispersibility of the slurry, the water-reducing agent lowers the water-to-solid ratio, and the thickener improves the flowability and stability of the slurry; these additives are selectively added according to engineering requirements. The emulsifier is at least one of sodium stearate, sodium oleate, sodium dodecyl sulfonate, and fatty alcohol polyoxyethylene ether phosphate; the water-reducing agent is at least one of polycarboxylate superplasticizer and naphthalene-based superplasticizer; and the thickener is at least one of sodium polyacrylate, polyacrylamide, and hydroxypropyl methylcellulose.

[0015] This invention also provides a method for preparing a mineralized microbial cemented backfill material for CO2 sequestration, comprising the following steps: S1. Inoculate Bacillus mucilaginosus and Bacillus halophilus into the culture medium separately and incubate at 25-40℃ for 12-36h to obtain a single-strain bacterial solution. Mix the two bacterial solutions at a mass ratio of (1-3):1 to obtain a bacterial solution of compound carbonic anhydrase-producing microorganisms. S2. Weigh out the soluble calcium salt, porous hydroxyapatite, aggregate, composite inducer, and additives by weight, add an appropriate amount of water, stir and mix to prepare a uniform slurry with a solid content of 40%-70%. S3. Introduce CO2 gas or add dry ice into the bacterial solution from step S1 and stir for 10-30 minutes; then mix with the slurry from step S2 to obtain a mineralized microbial cemented backfill material for sealing CO2.

[0016] Preferably, the culture medium in step S1 comprises: glucose 10-20 g / L, peptone 5-10 g / L, yeast extract 3-5 g / L, sodium chloride 50-200 g / L, sodium bicarbonate 5-15 g / L, and the pH value is adjusted to 7.0-8.5.

[0017] The mixing in step S2 is carried out at 20-35℃ for 15-60 minutes.

[0018] Preferably, the CO2 ventilation rate in step S3 is 0.3-1.5 L / min.

[0019] This invention also provides an application of a mineralized CO2-sealing microbial cemented backfill material for mining in goaf filling, roadway support, soil solidification, and slope reinforcement. Specifically, the prepared microbial cemented backfill material is transported to the area to be reinforced via a high-pressure pipeline and naturally cured for 7-28 days to complete solidification and CO2 sequestration.

[0020] This invention relates to a compound bacterial agent of *Bacillus mucilaginosus* and *Bacillus halophilus*. In the typical extreme environments of mines—high salinity, medium-high temperature, and high pressure—the two bacteria complement each other to achieve synergistic effects, resulting in efficient, stable, and high-intensity CO2 mineralization and sequestration. *Bacillus mucilaginosus* exhibits comprehensive tolerance, especially under medium-high temperature conditions of 40-60℃, where it can still directly catalyze the hydration of CO2 to carbonate ions by producing carbonic anhydrase, providing a stable carbon source for mineralization. *Bacillus halophilus*, on the other hand, demonstrates excellent tolerance to high salinity (growing normally at 5-25% NaCl concentrations) and alkaline environments, but its high-temperature tolerance is relatively weak. It also exhibits the ability to produce carbonic anhydrase under high salinity and high alkalinity conditions. When the two are combined, the extracellular polysaccharides secreted by Bacillus mucilaginosus can construct a protective biofilm microenvironment, significantly improving the survival rate of Bacillus halophilus under combined stress. This not only fully utilizes the metabolic advantages of each under extreme conditions, but also makes the adaptability and stability of the entire microbial community system far exceed that of a single species, effectively avoiding the failure of the microbial community due to environmental fluctuations, thereby ensuring the continuous and efficient operation of the CO2 mineralization and sequestration process.

[0021] The organic acids of this invention influence the CO2 mineralization process through chelation and pH regulation mechanisms. On one hand, the organic acid molecules contain multiple carboxyl and hydroxyl functional groups, enabling them to react with Ca... 2+ Formation of stable chelates, regulating the free Ca in the system 2+ The concentration of CO3, and thus the concentration of CO3 2- / Ca 2+ The ratio and supersaturation of the system. On the other hand, the dissolution conditions of CO2 are optimized by adjusting the pH value of the system. Generally speaking, weakly acidic conditions are conducive to the dissolution of CO2 and the formation of carbonic acid; the Ca2+ ratio is controlled by chelation. 2+ The release rate is controlled to avoid rapid precipitation caused by excessive local supersaturation; by forming soluble complexes with metal ions, the concentration of ions available for reaction in the system is increased. During the calcium carbonate nucleation stage, organic acid molecules can be adsorbed on the crystal surface, affecting the crystal's growth habit and morphology, while providing additional nucleation sites, which is beneficial for calcium carbonate nucleation and improves carbon fixation efficiency.

[0022] The nanomaterials of this invention primarily function as structural reinforcing agents and nucleation promoters. Their extremely high specific surface area, abundant surface defects, and high surface energy make them excellent heterogeneous nucleation substrates, significantly reducing the interfacial free energy barrier for calcium carbonate crystal nucleation and synergistically inducing and accelerating crystal nucleation with organic acids. Furthermore, the nanoparticles can tightly bind with aggregates (such as fly ash) to form a "fly ash-nanoparticle" composite cementitious phase, thereby significantly improving the macroscopic mechanical properties of the final filling material or mineralized product.

[0023] The advantages or beneficial effects of the mineralized CO2 sequestration microbial cemented backfill material for mines of the present invention include at least the following: 1. For the first time, Bacillus mucilaginosus and Bacillus halophilus were combined to synergistically and efficiently express carbonic anhydrase. The enzyme maintained high activity and stability even in extreme mining environments such as high salt and medium-high temperature, significantly improving the CO2 hydration reaction rate and mineralization efficiency.

[0024] 2. Porous hydroxyapatite serves as a microbial carrier, CO2 adsorption site, and slow-release calcium source, promoting microbial attachment and colonization while providing the necessary Ca for continuous mineralization reactions. 2+ This enhances local CO2 enrichment and improves storage efficiency.

[0025] 3. Organic acid-nanoparticle composite inducers regulate the crystal form and crystallization process of calcium carbonate, guiding the formation of a dense, high-strength calcite phase, effectively improving the mechanical properties and durability of the filling material.

[0026] 4. Using industrial solid wastes such as fly ash and coal gangue as aggregates, we can achieve the resource utilization of all components of solid waste through "waste treatment", reduce material costs, and conform to the concepts of green mining and circular economy.

[0027] 5. While achieving a 7-day compressive strength of 16.3-20.2 MPa, the CO2 sequestration capacity is as high as 82.6-101.3 g / kg. Compared with traditional cement-based materials, it reduces carbon emissions and reduces solid waste pollution, breaking through the bottleneck of traditional filling materials that cannot balance strength and environmental protection. Detailed Implementation

[0028] To more clearly illustrate the purpose, technical solution, and advantages of this invention, the technical solution of this invention will be described in detail below through specific embodiments. It should be noted that these embodiments are only for illustrating this invention and not for limiting its scope of protection; the actual scope of protection of this invention should be determined by the claims.

[0029] Unless otherwise specified, the materials and reagents used in the following examples and comparative examples are commercially available. Unless otherwise specified, the amount of each component in the following examples is 1 g per part by weight.

[0030] Raw materials used in the following embodiments 1. Microbial strains: Bacillus mucilaginosus (strain number CICC 23575) was purchased from the China Industrial Microbial Culture Collection Center; Bacillus halodurans (strain number CICC 10447) was also purchased from the China Industrial Microbial Culture Collection Center. The viable counts of both strains were adjusted to 5.0 × 10⁻⁶. 9 CFU / g.

[0031] 2. Porous hydroxyapatite: average particle size 40μm, Xi'an Tianzhilu Biotechnology Co., Ltd. 3. Aggregates: fly ash (particle size 150-250μm, taken from a steel plant in Tangshan) and coal gangue (particle size 100-200μm, taken from a coal mine in Shanxi), both dried to a moisture content ≤2%.

[0032] 4. Additives: Polycarboxylate superplasticizer, polyacrylamide, sodium dodecyl sulfonate, commercially available.

[0033] 5. Soluble calcium salts, organic acids, nano-oxides, etc., are all commercially available.

[0034] I. Experimental examples and comparative examples of preparing mineralized CO2-sealing microbial cemented backfill materials for mining.

[0035] Example 1 The mine-use microbial cementitious backfill material of this embodiment has the following raw material composition by weight: 8 parts of composite carbonic anhydrase-producing microorganisms (Bacillus mucilaginosus: Bacillus halophilus = 1:1), 20 parts of calcium chloride, 5 parts of porous hydroxyapatite, 90 parts of fly ash, 5 parts of composite inducing agent (citric acid: nano silica = 8:1), 1 part of polycarboxylate superplasticizer, and 120 parts of water. The preparation method is as follows: S1: Prepare culture medium (15g / L glucose, 7g / L peptone, 4g / L yeast extract, 100g / L sodium chloride, 10g / L sodium bicarbonate, pH adjusted to 7.5), inoculate Bacillus mucilaginosus and Bacillus halophilus into the culture medium separately, and incubate at 30℃ for 24h to obtain single-strain bacterial suspensions, mix them at a 1:1 mass ratio to obtain compound microbial bacterial suspensions; S2: Weigh the above-mentioned parts by weight of calcium chloride, porous hydroxyapatite, fly ash, composite inducing agent, and polycarboxylate superplasticizer, add 120 parts of water, stir at 25°C for 30 minutes, and prepare a uniform slurry with a solid content of 50%. S3: Introduce CO2 gas into the composite bacterial solution from step S1 at a rate of 0.8 L / min and stir for 20 min; then mix with the slurry from step S2 to obtain the filling material.

[0036] Example 2 The mine-use microbial cementitious backfill material of this embodiment is composed of the following raw materials by weight: 12 parts of composite carbonic anhydrase-producing microorganisms (Bacillus mucilaginosus: Bacillus halophilus = 2:1), 40 parts of calcium acetate, 7 parts of porous hydroxyapatite, 60 parts of fly ash, 30 parts of coal gangue, 7 parts of composite inducing agent (citric acid: tartaric acid: nano silica = 5:3:1), 0.5 parts of polyacrylamide, and 130 parts of water. The preparation method is as follows: S1: Prepare culture medium (18 g / L glucose, 8 g / L peptone, 4 g / L yeast extract, 150 g / L sodium chloride, 12 g / L sodium bicarbonate, pH adjusted to 8.0), inoculate Bacillus mucilaginosus and Bacillus halophilus into the culture medium separately, and incubate at 35℃ for 20 h to obtain single-strain bacterial suspensions, mix them at a mass ratio of 2:1 to obtain compound microbial bacterial suspensions. S2: Weigh the above-mentioned parts by weight of calcium acetate, porous hydroxyapatite, fly ash, coal gangue, composite inducing agent, and polyacrylamide, add 130 parts of water, stir at 30°C for 45 minutes, and prepare a uniform slurry with a solid content of 55%. S3: Introduce CO2 gas into the composite bacterial solution from step S1 at a rate of 1.2 L / min and stir for 15 min; then mix it with the slurry from step S2 to obtain the filling material.

[0037] Example 3 The mine-use microbial cemented backfill material of this embodiment has the following raw material composition by weight: 16 parts of composite carbonic anhydrase-producing microorganisms (Bacillus mucilaginosus: Bacillus halophilus = 3:1), 40 parts of calcium nitrate, 9 parts of porous hydroxyapatite, 110 parts of blast furnace slag, 9 parts of composite inducing agent (gluconic acid: nano zinc oxide = 9:1), 2 parts of sodium oleate, 1 part of polycarboxylate superplasticizer, and 140 parts of water. The preparation method is as follows: S1: Prepare culture medium (20g / L glucose, 10g / L peptone, 5g / L yeast extract, 200g / L sodium chloride, 15g / L sodium bicarbonate, pH adjusted to 8.5), inoculate Bacillus mucilaginosus and Bacillus halophilus into the culture medium separately, and incubate at 40℃ for 18h to obtain single-strain bacterial suspensions, mix them at a mass ratio of 3:1 to obtain compound microbial bacterial suspensions. S2: Weigh the above-mentioned parts by weight of calcium nitrate, porous hydroxyapatite, blast furnace slag, composite inducer, and additives, add 140 parts of water, stir at 35°C for 60 minutes, and prepare a uniform slurry with a solid content of 60%.

[0038] S3: Introduce CO2 gas into the composite bacterial solution from step S1 at a rate of 1.5 L / min and stir for 18 min; then mix with the slurry from step S2 to obtain the filling material.

[0039] Example 4 The mine-use microbial cementitious backfill material of this embodiment has the following raw material composition by weight: 20 parts of composite carbonic anhydrase-producing microorganisms (Bacillus mucilaginosus: Bacillus halophilus = 2:1), 30 parts of calcium chloride + 30 parts of calcium formate, 10 parts of porous hydroxyapatite, 120 parts of carbide slag, 10 parts of composite inducing agent (ethylenediaminetetraacetic acid: nano alumina = 10:1), 3 parts of sodium polyacrylate, and 150 parts of water. The preparation method is as follows: S1: Prepare culture medium (12g / L glucose, 6g / L peptone, 3g / L yeast extract, 80g / L sodium chloride, 8g / L sodium bicarbonate, pH adjusted to 7.0), inoculate Bacillus mucilaginosus and Bacillus halophilus into the culture medium separately, and incubate at 25℃ for 36h to obtain single-strain bacterial suspensions, mix them at a mass ratio of 2:1 to obtain compound microbial bacterial suspensions. S2: Weigh the above-mentioned mixed calcium salt, porous hydroxyapatite, carbide slag, composite inducer, and sodium polyacrylate, add 150 parts of water, stir at 20°C for 15 minutes, and prepare a uniform slurry with a solid content of 65%. S3: Add dry ice (CO2 equivalent to bacterial solution mass ratio 1:5) to the composite bacterial solution from step S1 and stir for 30 minutes; then mix with the slurry from step S2 to obtain the filling material.

[0040] Example 5 The mine-use microbial cementitious backfill material of this embodiment has the following raw material composition by weight: 10 parts of composite carbonic anhydrase-producing microorganisms (Bacillus mucilaginosus: Bacillus halophilus = 2:1), 25 parts of calcium acetate, 25 parts of calcium nitrate, 6 parts of porous hydroxyapatite, 50 parts of fly ash, 50 parts of blast furnace slag, 6 parts of composite inducing agent (oxalic acid: nano silica = 6:1), and 125 parts of water. The preparation method is as follows: S1: Prepare culture medium (16g / L glucose, 7g / L peptone, 4g / L yeast extract, 120g / L sodium chloride, 11g / L sodium bicarbonate, pH adjusted to 7.8), inoculate Bacillus mucilaginosus and Bacillus halophilus into the culture medium separately, and incubate at 32℃ for 22h to obtain single-strain bacterial suspensions, mix them at a mass ratio of 2:1 to obtain compound microbial bacterial suspensions. S2: Weigh the above-mentioned mixed calcium salt, porous hydroxyapatite, fly ash, blast furnace slag, and composite inducer, add 125 parts of water, stir at 28°C for 40 minutes, and prepare a uniform slurry with a solid content of 52%. S3: Introduce CO2 gas into the composite bacterial solution from step S1 at a rate of 0.5 L / min and stir for 20 min; then mix it with the slurry from step S2 to obtain the filling material.

[0041] Comparative Example 1 The difference from Example 1 is that an equal amount of Bacillus mucilaginosus is used instead of Bacillus halophilus, while other conditions are the same as in Example 1.

[0042] Comparative Example 2 The difference from Example 1 is that an equal amount of halophilic Bacillus was used instead of mucilaginous Bacillus, while other conditions were the same as in Example 1.

[0043] Comparative Example 3 The difference from Example 1 is that an equal amount of fly ash is used instead of porous hydroxyapatite, while other conditions are the same as in Example 1.

[0044] Comparative Example 4 The difference from Example 1 is that an equal amount of fly ash is used instead of the composite inducing agent, while other conditions are the same as in Example 1.

[0045] Comparative Example 5 The difference from Example 1 is that only citric acid is used as the composite inducer, that is, an equal amount of citric acid is used instead of nano-silica, and other conditions are the same as in Example 1.

[0046] Comparative Example 6 The difference from Example 1 is that the composite inducer uses only nano-silica, that is, an equal amount of nano-silica is used instead of citric acid, and other conditions are the same as in Example 1.

[0047] II. Performance Testing 1. Perform compressive strength testing according to GB / T 17671-2020 standard, test three parallel specimens, and take the average value.

[0048] 2. Carbon dioxide sequestration capacity The carbon sequestration amount was determined by TG / DTG analysis. Test conditions: temperature range 40-1000℃, N2 atmosphere, heating rate: 15℃ / min. At 600℃~800℃, the CaCO3 produced by carbonization decomposes into CaO and CO2, and the carbon dioxide sequestration amount is obtained by weight loss.

[0049] 3. Microbial survival rate: The prepared microbial inoculum was placed in a simulated mine environment (temperature 50℃, NaCl concentration 10%) for 7 days. The number of viable bacteria of the compound strain was determined by plate counting method, and the survival rate was calculated (survival rate = number of viable bacteria after curing / initial number of viable bacteria × 100%).

[0050] Table 1 shows the performance of the examples and comparative examples.

[0051] According to the test results in Table 1, the high-strength mining microbial cemented backfill materials prepared in Examples 1–5 exhibit excellent comprehensive performance, with a 1-day compressive strength of 5.2–6.8 MPa and a 7-day strength further improved to 16.3–20.2 MPa. This can quickly meet the early support needs of mines and ensure long-term load-bearing capacity. At the same time, they have excellent CO2 sequestration capacity, with a sequestration amount of 82.6–101.3 g / kg, which is significantly better than traditional carbon sequestration materials. Under the harsh environment of simulated high salt (10% NaCl) and medium-high temperature (50℃) mines, the survival rate of the mixed agent of Bacillus mucilaginosus and Bacillus halophilus remains stable at 80.1%–86.7%, ensuring that the mineralization reaction continues to proceed efficiently. This performance advantage stems from a multi-component synergistic mechanism: a composite microbial system resistant to extreme environments provides stable enzyme activity and content; porous hydroxyapatite functions as both a microbial carrier and a slow-release calcium source; a composite inducer composed of organic acids and nanoparticles optimizes the crystallization quality of calcium carbonate; and industrial solid waste aggregates enhance interfacial bonding and reduce costs, achieving a balance between high strength, high carbon sequestration, and high environmental adaptability.

[0052] Comparative Example 1 used an equal amount of *Bacillus mucilaginosus* instead of *Bacillus halophilus*, replacing the composite microorganism with a single species. Its 1-day compressive strength was only 2.3 MPa, a decrease of 55.8% compared to Example 1; the 7-day compressive strength was 8.6 MPa, a decrease of 47.2%, the CO2 sequestration was 53.5 g / kg, and the microbial survival rate was 45.2%. The core reason is that although *Bacillus mucilaginosus* is heat-resistant, its high-salt tolerance is weak. The single species lacks a synergistic protection mechanism and cannot construct a biofilm to protect *Bacillus halophilus* through the extracellular polysaccharides secreted by *Bacillus mucilaginosus*, as the composite bacteria in the example did. This leads to the bacterial community being easily inactivated in a high-salt environment, a sharp decrease in carbonic anhydrase activity, insufficient CO2 catalytic conversion efficiency, and low and unevenly distributed calcium carbonate precipitation, ultimately resulting in a significant decrease in bonding strength and carbon fixation efficiency.

[0053] Comparative Example 2 used an equal amount of *Bacillus halophilus* instead of *Bacillus mucilaginosus*, replacing the composite microorganisms with a single species. Its 1-day compressive strength was 2.1 MPa, a decrease of 59.6% compared to Example 1; its 7-day compressive strength was 7.8 MPa, CO2 sequestration was 61.8 g / kg, and the microbial survival rate was 41.7%, significantly lower than Example 1. This may be because the single *Bacillus halophilus* species cannot adapt to the medium-high temperature environment of mines (40-60℃), resulting in low carbonic anhydrase activity, leading to stagnant mineralization reactions, weak cementation of the filling material, and significant deterioration of mechanical properties and carbon fixation effect.

[0054] Comparative Example 3, which used an equal amount of fly ash instead of porous hydroxyapatite, exhibited a 1-day compressive strength of 3.0 MPa, a 7-day compressive strength of 10.3 MPa, a CO2 sequestration capacity of 68.6 g / kg, and a microbial survival rate of 79.8%. Both the compressive strength and CO2 sequestration capacity were significantly lower than in Example 1. The core reason is that the porous structure of hydroxyapatite functions as a microbial carrier, CO2 adsorption site, and slow-release calcium source, allowing it to accumulate microorganisms and extracellular enzymes to form a highly active reaction zone, continuously releasing calcium. 2+ With CO3 2- Precise matching enhances the uniformity of mineralized products and interfacial bonding, while fly ash lacks this unique structure, making microbial enrichment and Ca enrichment impossible. 2+ Controlled release leads to a decrease in CO2 mineralization efficiency, a scattered distribution of calcium carbonate precipitates, a loose internal structure of the filling material, and a significant reduction in mechanical properties.

[0055] Comparative Example 4, using an equal amount of fly ash instead of the composite inducing agent, exhibited a 1-day compressive strength of 2.8 MPa, a 7-day compressive strength of 9.5 MPa, and a CO2 sequestration of 66.3 g / kg, both lower than those of Example 1. This demonstrates that the organic acid in the composite inducing agent of Example 1 can regulate the Ca2+ content through chelation. 2+ Concentration and optimized pH promote CO2 dissolution and provide nucleation sites. Inorganic nanoparticles can lower the nucleation energy barrier of calcium carbonate and strengthen the cementation structure. The two work together to improve mineralization efficiency and mechanical properties. However, fly ash does not have the above functions and cannot regulate the ion balance and CO2 dissolution conditions of the system. Calcium carbonate has a slow nucleation rate, loose crystal structure, and lacks the structural strengthening effect of nanoparticles, resulting in insufficient cementation strength of the filling body and a significant decrease in carbon fixation efficiency. The fact that the survival rate of microorganisms was not affected indicates that the difference stems from the mineralization reaction conditions rather than the adaptability of the microbial community.

[0056] Comparative Example 5 contained only organic acids, and Comparative Example 6 contained only nanoparticles, resulting in significantly lower mineralization efficiency and mechanical properties compared to Example 1. Although Comparative Example 5 could adjust pH and chelate Ca through organic acids... 2+However, lacking the heterogeneous nucleation sites and interfacial reinforcement provided by nanoparticles, calcium carbonate exhibits slow crystallization rate, non-dense structure, and significantly reduced 7-day strength and CO2 sequestration capacity. Comparative Example 6, while possessing the nucleation-promoting ability of nanoparticles, suffers from a lack of organic acid regulation of the system's pH and Ca2+. 2+ Release resulted in limited CO2 dissolution, localized supersaturation leading to disordered precipitation, and a decrease in both strength and sequestration capacity. Both of these factors indicate that the synergistic effect of organic acids and nanoparticles achieves a unified approach to optimizing mineralization reaction kinetics, controlling crystal morphology, and densifying the cemented structure. Furthermore, a single component cannot replace the multiple functions performed by the composite inducer in Example 1.

[0057] It should be clarified that the above embodiments are merely illustrative of specific implementations of the present invention and do not constitute a limitation on the scope of protection of the present invention. Based on the technical content disclosed in this invention, those skilled in the art can make various modifications, adjustments, or equivalent substitutions within its basic principles and design concepts. These modifications and improvements need not be listed exhaustively, but should all be considered to fall within the scope of protection of this invention.

Claims

1. A mineral-based microbial cementitious backfill material for CO2 mineralization and sequestration, characterized in that, The raw materials, by weight, include: 8-20 parts of compound carbonic anhydrase-producing microorganisms, 20-60 parts of soluble calcium salts, 5-10 parts of porous hydroxyapatite, 90-120 parts of aggregates, 5-10 parts of compound inducers, 0-5 parts of additives, and water as the balance. The composite carbonic anhydrase-producing microorganisms consist of Bacillus mucilaginosus and Bacillus halophilus, with a mass ratio of (1-3):

1. The composite inducer comprises an organic acid and inorganic nanoparticles in a mass ratio of 5-10:1; the organic acid is at least one of citric acid, oxalic acid, tartaric acid, gluconic acid, and ethylenediaminetetraacetic acid; and the inorganic nanoparticles are at least one of nano-silica, nano-zinc oxide, and nano-alumina.

2. The mineralized microbial cemented backing material for CO2 sequestration as described in claim 1, characterized in that, The viable counts of both *Bacillus mucilaginosus* and *Bacillus halophilus* were 1.0 × 10⁻⁶. 8 -1.0×10 10 CFU / g.

3. The mineralized microbial cemented backing material for CO2 mineralization and sequestration as described in claim 1, characterized in that, The average particle size of the porous hydroxyapatite is 10-80 μm.

4. The mineralized microbial cemented backfill material for CO2 mineralization and sequestration as described in claim 1, characterized in that, The soluble calcium salt is one or more of calcium chloride, calcium acetate, calcium formate, and calcium nitrate.

5. The mineralized microbial cemented backing material for CO2 mineralization and sequestration as described in claim 1, characterized in that, The aggregate is one or more of fly ash, blast furnace slag, coal gangue or carbide slag, with a particle size of 100-300μm.

6. The mineralized microbial cemented backing material for CO2 mineralization and sequestration as described in claim 1, characterized in that, The inorganic nanoparticles have an average particle size of 20-100 nm.

7. The mineralized microbial cemented backing material for CO2 mineralization and sequestration as described in claim 1, characterized in that, The additive includes at least one of emulsifier, water-reducing agent, or thickener; the emulsifier is at least one of sodium stearate, sodium oleate, sodium dodecyl sulfonate, or fatty alcohol polyoxyethylene ether phosphate; the water-reducing agent is at least one of polycarboxylate water-reducing agent or naphthalene-based water-reducing agent; and the thickener is at least one of sodium polyacrylate, polyacrylamide, or hydroxypropyl methylcellulose.

8. A method for preparing a mineralized CO2-sealing microbial cemented backfill material for mining as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Inoculate Bacillus mucilaginosus and Bacillus halophilus into the culture medium separately and incubate at 25-40℃ for 12-36h to obtain a single-strain bacterial solution. Mix the two bacterial solutions at a mass ratio of (1-3):1 to obtain a bacterial solution of compound carbonic anhydrase-producing microorganisms. S2. Weigh out the soluble calcium salt, porous hydroxyapatite, aggregate, composite inducer, and additives by weight, add an appropriate amount of water, stir and mix to prepare a uniform slurry with a solid content of 40%-70%. S3. Introduce CO2 gas or add dry ice into the bacterial solution from step S1 and stir for 10-30 minutes; then mix with the slurry from step S2 to obtain a mineralized microbial cemented backfill material for sealing CO2.

9. The preparation method of the mineralized CO2 sequestration microbial cemented backfill material for mining as described in claim 8, characterized in that, The culture medium in step S1 comprises: glucose 10-20 g / L, peptone 5-10 g / L, yeast extract 3-5 g / L, sodium chloride 50-200 g / L, sodium bicarbonate 5-15 g / L, and pH adjusted to 7.0-8.5; and / or, the mixing in step S2 is carried out at 20-35°C for 15-60 min; and / or, the CO2 aeration rate in step S3 is 0.3-1.5 L / min.

10. The application of a mineralized CO2-sealing microbial cemented backfill material for mining in goaf filling, roadway support, soil solidification, and slope reinforcement, specifically comprising transporting the mineralized microbial cemented backfill material according to any one of claims 1-7 to the area to be reinforced through a high-pressure pipeline, and naturally curing it for 7-28 days to complete solidification and CO2 sequestration.

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