Coal mine goaf multi-source waste synergistic mineralization filling and gas-liquid waste self-purification method

Abstract

The invention discloses a coal mine goaf multi-source waste synergistic mineralization filling and gas-liquid waste self-purification method. The method comprises the following steps of goaf exploration and comprehensive evaluation; treating and transforming the goaf; preparing an artificial multifunctional argillaceous slurry; artificial multifunctional argillaceous slurry is injected into the goaf, an artificial argillaceous sediment filter element is formed in the goaf, and initial diagenesis is conducted in the gelling reaction process; a waste modified culture medium containing functional microorganism liquid is injected into the goaf, and gas waste is injected into the goaf; stable supporting of the goaf is achieved through artificial mudstone, and goaf filling is completed. According to the method, resource utilization of the coal-based waste and efficient and green support of the coal mine goaf are achieved, formation of a mode of coal development-conversion utilization-returning of the waste to underground artificial mudstone-goaf support waste-free development and utilization is assisted, and a new thought is provided for coal-based waste disposal and coal mine goaf filling; and a support is provided for a near-zero-carbon energy development and utilization technology system in the coal field.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling and CCUS technology, specifically involving a method for the synergistic mineralization and backfilling of multi-source waste in coal mine goaf and the self-purification of gas and liquid waste. Background Technology

[0002] Against the backdrop of global climate governance and my country's energy structure transformation, coal, as the mainstay of my country's energy supply, urgently needs innovative development and utilization methods to adapt to the requirements of the "dual carbon" goals. Despite the rapid development of clean energy, considering my country's resource characteristics of being "rich in coal, poor in oil, and scarce in gas," coal will remain the "ballast" and "stabilizer" of my country's energy supply for a considerable period. However, carbon emissions from the coal sector account for more than 60% of the country's total carbon emissions. Therefore, developing new coal production capacity through technological innovation and achieving carbon neutrality in the coal sector is key to achieving my country's "dual carbon" goals.

[0003] Coal has supported the progress of human civilization, but its development and utilization are still in the initial stage of "coal mining - conversion and utilization - waste retention on the surface - passive management of mining subsidence areas." This model exacerbates the dual constraints on resources and the environment. In the past decade, people have gradually paid attention to the low-carbon and clean utilization of coal-based energy. Chinese scholars have successively proposed new models for the clean utilization of coal, such as "deep in-situ fluidized coal mining," "underground coal gasification combined cycle power generation," and "underground coal gasification." Research on these new technologies, which convert coal underground into clean energy and achieve energy extraction without producing pollutants, points the way for the clean utilization of coal after future technological development reaches a certain level. In 2024, Academician Wang Shuangming and others proposed a new approach to green and low-carbon development in the coal industry: "treating waste with waste" and "returning to where it came from." In 2025, Academician Chai Liyuan and others proposed a circular green production model of "global macro-cycle" for bulk, difficult-to-dispose-of solid waste. These have pointed the way for the construction of a coal development and utilization model of "coal mining - conversion and utilization - filling of goaf areas with coal-based gas, solid and liquid wastes - green and efficient support for goaf areas" and provided solutions for the disposal of coal-based wastes remaining on the surface. However, it is urgent to build a practical and feasible carbon neutrality and technology path in the coal sector.

[0004] In view of the development requirements of "new quality productivity" under the "dual carbon" background and the current status of coal development and utilization, this invention proposes a technical solution for artificial mudstone backfilling of coal mine goaf areas with multi-source waste and self-purification of gaseous and liquid waste. It aims to mimic the deposition and diagenesis process of mudstone, the most widely distributed material in nature. Using coal-based solid, gaseous, and liquid wastes as the main source materials in coal mine goaf areas, it employs physical, chemical, and microbiological methods to create high-quality artificial mudstone filter elements in a short period. This achieves resource-based treatment of coal-based solid wastes such as fly ash, deep purification of gaseous waste, long-term storage of coal-based gaseous wastes such as carbon dioxide, adsorption and purification of coal-based liquid wastes such as coal washing wastewater, and stable support for coal mine goaf areas. This project provides new ideas for gaseous waste purification, coal-based waste disposal, and coal mine goaf backfilling, and supports a closed-loop coal green utilization energy technology system of "coal mining - conversion and utilization - coal-based solid, gaseous, and liquid waste backfilling of goaf areas - green and efficient support for goaf areas." Summary of the Invention

[0005] In order to solve the above-mentioned technical problems in the prior art, the present invention provides a method for synergistic mineralization backfilling of multi-source waste in coal mine goaf and self-purification of gaseous and liquid waste. This method not only realizes the resource reuse of multi-source solid waste (such as coal-based waste, carbide slag, red mud, steel slag, etc.), but also realizes the backfilling of coal mine goaf, purification of multi-source liquid waste (coal washing and mining wastewater, kitchen wastewater, etc.) and gaseous waste.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for synergistic mineralization backfilling of multi-source waste in coal mine goaf and self-purification of gaseous and liquid waste, comprising the following steps: S1. Conduct geological surveys and comprehensive evaluations of the goaf areas; S2. To manage and transform the goaf area; S3. Preparation of artificial multifunctional mud slurry; S4. Inject artificial multifunctional mud slurry into the goaf to form an artificial mud sediment filter element. S5. Inject a modified microbial culture medium containing functional microorganisms into the goaf area. The functional microorganisms purify the liquid waste in the goaf area. S6. Inject waste gas into the goaf to achieve multiphase storage; S7. Repeat steps S5 and S6, and dynamically adjust the number of cycles and the amount of cycles, so that a large amount of mineralized cementitious material is formed in the artificial mudstone sediment in the goaf, the porosity is reduced and the compressive strength is increased, and artificial mudstone that meets the requirements of goaf filling is gradually formed. S8 artificial mudstone provides stable support for the goaf, and the goaf filling is completed.

[0007] Furthermore, the exploration in step S1 includes the following two stages: (i) General survey – to ascertain the spatial development characteristics and hydrogeological conditions of the mining subsidence area; (ii) Detailed investigation—Based on the general survey, determine the upper three zones (collapse zone, fracture zone and bending subsidence zone) and the development of mining-induced cracks in the floor of the goaf; Based on the geological data of the goaf obtained from the general survey, if the feasibility of goaf renovation is too poor, then there is no need to conduct a detailed survey. Based on the results of the goaf exploration and economic benefit analysis, step S1 involves a comprehensive evaluation of the goaf, classifying it into the following three categories: Category I: Highly modifiable goaf areas – Expected benefits are more than 1.5 times the costs; Category II: Mined-out areas with weak modifiability – Expected benefits are 1 to 1.5 times the cost; Category III: Non-retrofitable goaf areas – Expected benefits are less than costs; Based on the evaluation results of goaf areas, Class I goaf areas will be given priority for treatment and renovation.

[0008] Furthermore, the methods for treating and modifying the goaf in step S2 include: (I) Bottom plate sealing and seepage prevention - Grouting and sealing treatment is carried out on the bottom plate of the goaf that connects to the aquifer or connects to the lower aquifer; (II) Overburden delamination filling - Delamination grouting is carried out to seal the goaf in the top three zones to prevent flue gas from escaping upward; Numerical simulations are conducted based on the spatial distribution of the goaf to determine the location and quantity of multi-functional wells and ancillary facilities. The multi-functional well and its ancillary facilities include: 1) Injection wells and intelligent mobile filling stations: These are set up at higher elevations within the goaf (i.e., "replenishment areas"). Through injection wells, artificial mud sediment slurry, subsequent functional microbial modified liquid waste and gas waste can be injected into the goaf of the coal mine. 2) Drainage well and intelligent monitoring and post-processing station: It is set in the lower part of the terrain in the goaf (i.e., the "drainage area"), and the bottom of the drainage well is equipped with a filter screen. The drainage well can provide a pressure difference from the "replenishment area" to the "drainage area", so that liquid waste / flue gas flows from the injection well to the drainage well. The flow rate can be controlled by controlling the extraction rate of the drainage well. During actual construction, due to uneven bonding of the cementing material, more cement is formed near the injection well and relatively less near the discharge well. The positions of the injection well and the discharge well need to be interchanged to fill the entire goaf more quickly.

[0009] Furthermore, step S3, the preparation of the artificial multifunctional mud slurry, specifically includes the following sub-steps: (I) Select coal-based solid waste and external functional solid waste and pretreat them; among which, coal-based solid waste includes coal gangue, fly ash, etc., and external functional solid waste includes cementitious material functional solid waste, flue gas purification functional solid waste (these two are mainly calcium-magnesium based solid waste, such as carbide slag, steel slag, etc.) and activator functional solid waste (red mud, etc.); these solid wastes are pretreated to obtain aggregates, cementitious materials, flue gas purification materials and activator materials respectively; (II) Pre-treat coal-based liquid waste (mine water and coal washing wastewater) and external functional liquid waste (organic wastewater, such as kitchen wastewater) to remove substances that are harmful to microorganisms and have a negative effect on flue gas purification and preparation of cementitious materials, add trace elements required for microbial growth, and modify it into a functional microbial culture medium suitable for carbon fixation, desulfurization and denitrification microorganisms in goaf areas. (III) Based on the regional differences in the composition of solid and liquid waste, the characteristics of flue gas composition, and economic benefits, the proportions of each solid and liquid material in (I) and (II) above were calculated and verified by experiments; (IV) After experimental verification, prepare multifunctional artificial mud slurry according to the formula ratio in (III); (V) During the preparation of multifunctional artificial mud slurry in step (IV), flue gas is introduced, which initially forms a large number of fine crystal nuclei in the multifunctional artificial mud slurry, enabling rapid diagenesis in the subsequent "depositional diagenesis" process of artificial mud sediments.

[0010] Furthermore, the specific process of step S4 is as follows: The artificial multifunctional mud slurry obtained through the injection well is injected into the goaf. At the same time, the pressure difference provided by the drainage well provides supplementary power for the artificial multifunctional mud slurry to move from the "replenishment zone" to the "drainage zone". This allows the artificial multifunctional mud slurry to gradually deposit from the "replenishment zone" to the "drainage zone". The flow rate and velocity of the liquid in the injection well and drainage well are controlled so that the artificial multifunctional mud slurry fills the entire goaf. Within the goaf, as dehydration and hydration occur, artificial mudstone sediments gradually form a large amount of cementitious material, which fills the pores of the artificial mudstone sediments. This increases the cementation degree, reduces the porosity, and enhances the compressive strength of the artificial mudstone sediments, gradually leading to initial diagenesis.

[0011] Furthermore, step S5 specifically includes the following sub-steps: (I) Based on the environmental conditions (temperature, pressure) in the goaf, functional microorganisms (carbon fixation, desulfurization and denitrification microorganisms) are oriented to domesticate. The domesticated functional microorganisms are added to the liquid waste modified microbial culture medium obtained in step (II) of step S3 for expansion culture so that the microorganisms have a certain abundance. (II) The microbial culture medium containing functional microorganisms is injected into the goaf through the injection well. During the process of flowing from the injection well to the discharge well in the goaf, the physical, chemical and biochemical purification of the liquid waste is achieved through solid-liquid-bacteria interaction. (III) The composition of the extracted liquid is detected by the intelligent monitoring and post-treatment station near the discharge well. If the composition meets the discharge standard, the liquid is discharged. If the discharge standard is not met, the discharged waste liquid is post-treated and discharged after meeting the standard. At the same time, by changing the rate of the injection well and the discharge well, the retention reaction time of the liquid waste in the artificial mud sediment filter in the goaf is extended so that the extracted liquid meets the discharge standard.

[0012] Furthermore, step S6 specifically includes the following sub-steps: (I) First, the waste gas is used for waste heat utilization (i.e., pretreatment process). This waste heat can be used to maintain the temperature of the culture tank for the expansion culture of functional microorganisms or for the preparation process of artificial multifunctional mud slurry. (II) The waste gas after the waste heat is utilized is injected into the goaf through the injection well and extracted through the discharge well, so that it flows from the injection well to the discharge well. In this process, under the coupling effect of gas-solid-liquid-bacteria, the physical, chemical and biochemical purification of sulfur oxides, nitrogen oxides, carbon oxides, dust and other substances in the waste gas is achieved. (III) The composition of the extracted gas is detected by the intelligent monitoring and post-treatment station near the discharge well. If the gas meets the emission standards, it is discharged. If the emission standards are not met, the discharged gas is post-treated and discharged after meeting the standards. At the same time, by changing the rates of the injection well and the discharge well, the retention reaction time of the gas in the artificial mud sediment filter in the goaf is extended so that the extracted gas meets the emission standards.

[0013] Furthermore, step S7 specifically includes the following sub-steps: Steps S5 and S6 are implemented in a cyclical manner. After a stable artificial mud-like sediment filter element is initially formed in the goaf, gaseous waste and liquid waste are sequentially injected and extracted. Modified liquid waste culture medium containing functional microorganisms and gaseous waste treated by waste heat utilization are alternately or simultaneously injected into the goaf through injection wells, so that a stable runoff is formed between the injection well and the discharge well. During the circulation process, the composition changes of gas and liquid in the discharge well are detected in real time through an intelligent monitoring and post-treatment system. The number of circulations, injection volume and flow rate are dynamically adjusted according to the monitoring results to optimize the reaction conditions and ensure the activity of functional microorganisms and the gas-liquid purification effect. Under repeated cycles, a multiphase coupling reaction of gas, liquid, solid, and bacteria occurs inside the goaf. Carbon oxides, nitrogen oxides, and sulfur oxides in the flue gas are adsorbed, mineralized, or fixed by microorganisms. Organic pollutants and inorganic ions in the liquid waste are decomposed, adsorbed, or precipitated and transformed, while a large amount of mineralized cementitious materials such as carbonates and silicates are generated. These mineralized products gradually fill the pores of the artificial mud sediment, causing its porosity to continuously decrease, its permeability to weaken, and its compressive strength to significantly increase. The artificial mud sediment gradually evolves from an initial loose state into a dense, natural-like rock mass structure. As the number of cycles increases, the mechanical properties inside the goaf tend to stabilize, the gas-liquid flow rate decreases, and the gas-liquid components extracted from the drainage well reach a stable equilibrium, indicating that the main physical, chemical, and biological reactions in the system tend to be sufficient; at this point, the injection of new gas-liquid waste stops, and the final filling and consolidation stage of step S8 begins.

[0014] Furthermore, step S8 specifically includes the following sub-steps: After completing the cycle steps S5 and S6, the gas and liquid flow rates, pressures, and gas-liquid composition changes of the injection and drainage wells are monitored in real time. When the pollutant concentrations in the gas and liquid extracted from the drainage well are consistently lower than the relevant national emission standards, and the pressure difference between the injection and drainage wells tends to stabilize and the flow rate decreases to the set threshold, it indicates that the porosity inside the goaf has significantly decreased, the densification degree of the filling material has increased, and the goaf filling is basically completed. At this time, by adjusting the extraction rate of the drainage well, the internal fluid disturbance of the system is gradually reduced, allowing the mineralization and cementation reaction in the artificial mudstone sediment to continue and eventually stabilize, forming an artificial mudstone mass with good integrity and high mechanical strength. After the filling is completed, a comprehensive test is conducted on the goaf, including mechanical strength testing, permeability coefficient testing, sonic logging, and downhole ground-penetrating radar detection, to verify the compactness and integrity of the artificial mudstone mass. If the test results show that the compressive strength, impermeability, and support capacity all meet the design requirements, the injection well and drainage well are closed, well sealing measures are implemented, and a long-term monitoring system is deployed in the overlying strata of the goaf to continuously track the stability of the filling area and the secondary migration of gas, liquid, and waste. Ultimately, an artificial mudstone stabilizer is formed inside the goaf, enabling underground reuse and long-term storage of multi-source waste. The goaf receives reliable support and ecological restoration, completing the entire process of synergistic resource utilization and pollutant purification of coal-based solid waste, liquid waste, and gaseous waste.

[0015] Adopting the above technical solution, the present invention is a method for filling coal mine goafs with artificial shale made from multi-source waste and realizing the purification of gas and liquid waste, which is briefly summarized as follows: First, geophysical means are used to查明 the development characteristics of coal mine goafs, including the spatial distribution characteristics of goafs, mining-induced fractures, the upper three zones (caving zone, fissure zone, and bending subsidence zone), the development characteristics of aquifers (confined aquifers), etc. Based on the exploration results, combined with the treatment cost and expected benefits, a comprehensive evaluation of the construction feasibility of the goaf is carried out. The goafs are divided into three types: Type I (highly reconstructable goafs), with an expected benefit more than 1.5 times the cost; Type II (weakly reconstructable goafs), with an expected benefit of 1 to 1.5 times the cost; Type III (non-reconstructable goafs), with an expected benefit less than the cost. According to the evaluation results of the goafs, Type I goafs are preferentially treated, followed by Type II goafs, and Type III goafs are not considered for treatment and development for the time. For the selected coal mine goafs to be treated, multifunctional wells (injection wells, drainage wells) and intelligent auxiliary facilities (intelligent mobile filling stations supporting injection wells, intelligent monitoring and post-treatment workstations supporting drainage wells) are set according to the numerical simulation results. A grouting material with specific functions is prepared to carry out grouting plugging and waterproof treatment for the mining-induced fractures in the floor and gas isolation treatment such as separated layer grouting for the upper three zones. At the same time, coal-based solid wastes (such as fly ash and coal gangue, etc.) and exogenous functional solid wastes (with cementitious material function, flue gas purification function, and activator function, the former two are mainly calcium and magnesium-based solid wastes, such as carbide slag, steel slag, etc., and the latter is mainly red mud, etc.) are preferably selected and pretreated, and then aggregate, cementitious material, flue gas purification material, and activator material are respectively prepared. The coal-based liquid wastes (such as mine water and coal washing wastewater, etc.) and exogenous functional liquid wastes (rich in organic matter wastewater, such as kitchen waste wastewater, etc.) are pretreated by removing the substances harmful to microorganisms and having a negative effect on flue gas purification and cementitious material preparation, adding trace elements required for microbial growth, etc., and modifying them into culture media suitable for carbon sequestration, desulfurization, and denitrification microorganisms in the goaf. According to the flue gas composition characteristics and economic benefit analysis, the optimal ratios of aggregate, cementitious material, flue gas purification material, activator material, and liquid waste modified microbial culture media are calculated to achieve the best purification effect, and grouting additives (such as water reducing agents, retarders, etc.) are added. After the effect is verified by experiments, a multifunctional grouting filling material is prepared with this formula. Subsequently, the goaf is grouted and filled through the injection well, and an artificial muddy sediment with a certain porosity and water saturation is formed in the goaf. At the same time, extraction is carried out through the drainage well. As the extraction process progresses, the water saturation of the artificial muddy sediment decreases, the cementitious substances are initially formed on a large scale, as the cementitious substances continue to accumulate, the compressive strength of the artificial muddy sediment also increases, and its pH value changes from strongly alkaline to weakly alkaline, and even tends to be neutral. At the same time, functional microorganisms for carbon sequestration, desulfurization, and denitrification are directionally screened, and the microorganisms are directionally domesticated according to the environmental conditions of the goaf.After domestication, the microorganisms were cultured in a modified liquid waste medium to achieve a certain abundance before being injected into the coal mine goaf. Simultaneously, the extraction rate of the discharge well was controlled to ensure that the liquid waste flowed from the injection well to the discharge well within the goaf. During this flow, physical, chemical, and biochemical purification occurred through interaction with artificial mud sediments. By controlling the extraction rate of the discharge well (i.e., controlling the liquid waste flow rate), the liquid waste, after being filtered through the artificial mud sediments, reached the discharge wells with water quality meeting discharge standards. Controlling the water saturation of the artificial mud sediments through the discharge wells ensured that the functional microorganisms operated in an environment conducive to their efficient function. Flue gas is injected into the goaf through the injection well at a certain rate. During the flow of flue gas from the injection well to the discharge well, a gas-solid-liquid-bacterial coupling effect occurs, achieving physical, chemical, and biochemical purification of the flue gas. By controlling the extraction rate of the discharge well, the nitrogen content in the flue gas reaches over 99% after filtration through the artificial mud sediment, and the purified flue gas meets emission standards. The purification process for liquid and gaseous wastewater is repeated. During the purification process, as the mineralization and sealing of flue gas and wastewater continue, the amount of cementing material in the artificial mud sediment increases, the porosity of the artificial mud sediment continuously decreases, and the degree of consolidation increases, thus forming artificial mudstone. Simultaneously, the compressive and flexural strength of the artificial mudstone further increases, and the supporting effect is further improved, forming stable support for the goaf. During the filling process, due to uneven cementing, more cementing material forms near the injection well and relatively less near the discharge well. Later, it will be necessary to exchange the injection well and the drainage well to achieve uniform cementation and uniform and stable support for the goaf.

[0016] In summary, this invention utilizes above-ground development and utilization to return multi-source waste underground, constructing a transitional stage in coal development and utilization. This method uses geophysical exploration to determine the basic geological conditions of coal mine goaf areas and conducts a feasibility evaluation for modification based on the exploration results and economic benefit analysis. Integrating achievements from multiple disciplines such as geological engineering, materials science, and environmental microbiology, it aims to achieve efficient treatment and resource utilization of coal-based solid waste, liquid waste, and flue gas, while providing innovative solutions for the stable backfilling and ecological reconstruction of coal mine goaf areas. This method not only reduces surface pollution but also effectively utilizes goaf space, laying the foundation for future transitions to advanced stages. This invention provides new ideas for coal-based waste disposal and coal mine goaf backfilling, supporting a closed-loop green coal utilization energy technology system encompassing coal mining, energy extraction, and coal-based waste backfilling. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the technical principle of the present invention; Figure 2 This is a process flow diagram of the present invention; Figure 3The graph shows the relationship between the curing days and compressive strength of five groups of geopolymers. Figure 4 A graph showing the relationship between curing pressure, carbon fixation, and compressive strength. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] like Figure 1 and Figure 2 As shown, the method for synergistic mineralization and backfilling of multi-source waste in coal mine goaf and self-purification of gaseous and liquid waste of the present invention includes the following steps: S1. Conduct geological surveys and comprehensive evaluations of the goaf areas; S2. To manage and transform the goaf area; S3. Preparation of artificial multifunctional mud slurry; S4. Inject artificial multifunctional mud slurry into the goaf to form an artificial mud sediment filter element. S5. Inject a modified microbial culture medium containing functional microorganisms into the goaf area. The functional microorganisms purify the liquid waste in the goaf area. S6. Inject waste gas into the goaf to achieve multiphase storage; S7. Repeat steps S5 and S6, and dynamically adjust the number of cycles and the amount of cycles, so that a large amount of mineralized cementitious material is formed in the artificial mudstone sediment in the goaf, the porosity is reduced and the compressive strength is increased, and artificial mudstone that meets the requirements of goaf filling is gradually formed. S8 artificial mudstone provides stable support for the goaf, and the goaf filling is completed.

[0020] Furthermore, the exploration in step S1 includes the following two stages: (i) General survey – to ascertain the spatial development characteristics and hydrogeological conditions of the mining subsidence area; (ii) Detailed investigation—Based on the general survey, determine the upper three zones (collapse zone, fracture zone and bending subsidence zone) and the development of mining-induced cracks in the floor of the goaf; Based on the geological data of the goaf obtained from the general survey, if the feasibility of goaf renovation is too poor, then there is no need to conduct a detailed survey. Based on the results of the goaf exploration and economic benefit analysis, step S1 involves a comprehensive evaluation of the goaf, classifying it into the following three categories: Category I: Highly modifiable goaf areas – Expected benefits are more than 1.5 times the costs; Category II: Mined-out areas with weak modifiability – Expected benefits are 1 to 1.5 times the cost; Category III: Non-retrofitable goaf areas – Expected benefits are less than costs; Based on the evaluation results of goaf areas, Class I goaf areas will be given priority for treatment and renovation.

[0021] Furthermore, the methods for treating and modifying the goaf in step S2 include: (I) Bottom plate sealing and seepage prevention - Grouting and sealing treatment is carried out on the bottom plate of the goaf that connects to the aquifer or connects to the lower aquifer; (II) Overburden delamination filling - Delamination grouting is carried out to seal the goaf in the top three zones to prevent flue gas from escaping upward; Numerical simulations are conducted based on the spatial distribution of the goaf to determine the location and quantity of multi-functional wells and ancillary facilities. The multi-functional well and its ancillary facilities include: 1) Injection wells and intelligent mobile filling stations: These are set up at higher elevations within the goaf (i.e., "replenishment areas"). Through injection wells, artificial mud sediment slurry, subsequent functional microbial modified liquid waste and gas waste can be injected into the goaf of the coal mine. 2) Drainage well and intelligent monitoring and post-processing station: It is set in the lower part of the terrain in the goaf (i.e., the "drainage area"), and the bottom of the drainage well is equipped with a filter screen. The drainage well can provide a pressure difference from the "replenishment area" to the "drainage area", so that liquid waste / flue gas flows from the injection well to the drainage well. The flow rate can be controlled by controlling the extraction rate of the drainage well. During actual construction, due to uneven bonding of the cementing material, more cement is formed near the injection well and relatively less near the discharge well. The positions of the injection well and the discharge well need to be interchanged to fill the entire goaf more quickly.

[0022] Furthermore, step S3, the preparation of the artificial multifunctional mud slurry, specifically includes the following sub-steps: (I) Select coal-based solid waste and external functional solid waste and pretreat them; among which, coal-based solid waste includes coal gangue, fly ash, etc., and external functional solid waste includes cementitious material functional solid waste, flue gas purification functional solid waste (these two are mainly calcium-magnesium based solid waste, such as carbide slag, steel slag, etc.) and activator functional solid waste (red mud, etc.); these solid wastes are pretreated to obtain aggregates, cementitious materials, flue gas purification materials and activator materials respectively; (II) Pre-treat coal-based liquid waste (mine water and coal washing wastewater) and external functional liquid waste (organic wastewater, such as kitchen wastewater) to remove substances that are harmful to microorganisms and have a negative effect on flue gas purification and preparation of cementitious materials, add trace elements required for microbial growth, and modify it into a functional microbial culture medium suitable for carbon fixation, desulfurization and denitrification microorganisms in goaf areas. (III) Based on the regional differences in the composition of solid and liquid waste, the characteristics of flue gas composition, and economic benefits, the proportions of each solid and liquid material in (I) and (II) above were calculated and verified by experiments; (IV) After experimental verification, prepare multifunctional artificial mud slurry according to the formula ratio in (III); (V) During the preparation of multifunctional artificial mud slurry in step (IV), flue gas is introduced, which initially forms a large number of fine crystal nuclei in the multifunctional artificial mud slurry, enabling rapid diagenesis in the subsequent "depositional diagenesis" process of artificial mud sediments.

[0023] Taking Jiaozuo area in Henan Province as an example, its solid and liquid waste resources have the following characteristics: Coal-based solid waste mainly consists of fly ash and coal gangue. Fly ash is rich in SiO2 and Al2O3, exhibiting high pozzolanic activity. Among exogenous solid waste, carbide slag (calcium-magnesium based solid waste) is rich in CaO and can be used as a cementing material and flue gas purification material. Red mud is rich in Fe2O3, Al2O3, and alkaline components, possessing activator properties. Regarding liquid waste, mine water and coal washing wastewater have high mineralization and require pretreatment to remove heavy metals and suspended solids. Kitchen wastewater is rich in organic matter and, after modification, can be used as a culture medium for functional microorganisms.

[0024] Table 1 Chemical composition (mass percentage) of red mud, carbide slag and fly ash / % Therefore, the following solid wastes were selected for the preparation of multifunctional artificial mud slurry: The fly ash was taken from a local power plant and ground to a particle size of ≤ 0.16mm to improve its reactivity; The red mud comes from a local aluminum plant and is naturally dried before being ground to a maximum particle size of 0.16 mm to reduce alkalinity fluctuations. The calcium carbide slag came from a local chlor-alkali chemical enterprise and was used in wet form. After standing and separating into layers, the upper clear liquid was used as a solvent (pH = 12.7-12.8, OH⁻ concentration 0.052 mol / L). The NaOH solution concentration was prepared to 5 mol / L, and the mass ratio of NaOH to Na₂SiO₃ was maintained at 2.5. The lower slurry (moisture content 50%-60%, effective CaO > 80%) was used as a calcium source. An orthogonal experimental design was used, with fly ash, red mud, and carbide slag as variables, to set multiple mix proportions (see Table 2), with a fixed sand-to-binder ratio of 3:1 and a liquid-to-solid ratio (L / S) of 0.7. For each group, 40mm × 40mm × 160mm specimens were prepared and tested for compressive and flexural strength after standard curing (20±2°C) for 7, 14, and 28 days. Figure 3 As shown.

[0025] Table 2. Geopolymer Formulation and Mechanical Properties (Unit: %)

[0026] Experimental results show that group D2 (fly ash: red mud: carbide slag = 4:3:3) achieved a compressive strength of 26.3 MPa and a flexural strength of 2.27 MPa after 28 days of curing, representing the optimal ratio. Microscopic analysis revealed that this ratio generated a large amount of CASH and CSH gels, exhibiting a dense structure and good strength development.

[0027] Therefore, 40 mm × 40 mm × 40 mm specimens were prepared using the D2 formulation (cured for 7 days). These specimens were then placed in a sealed container and carbonized by introducing CO2 gas at pressures of 0.3, 0.6, 0.9, 1.2, 1.5, and 1.8 MPa for 1 day at a temperature of (20 ± 2) ℃. The carbon fixation amount was then calculated. m seq The calculation formula is as follows: m seq =m2-m1 In the formula, represents the mass after carbonization curing, and represents the mass before carbonization curing. Simultaneously, the compressive strength of the specimen after mineralization curing was tested. The experimental results are as follows: Table 3 Carbon fixation rate under different pressures during carbonization curing Maintenance pressure (MPa) 0.3 0.6 0.9 1.2 1.5 1.8 Carbon sequestration (g) 7.82 8.20 8.71 9.01 9.16 9.34 Compressive strength (MPa) 16.02 16.58 16.84 16.92 17.15 17.34 Experimental results show that when the curing pressure is greater than 1 MPa, the increase in carbon fixation rate and compressive strength gradually decreases, indicating that the suitable carbonization curing pressure is 1 MPa. Figure 4 As shown.

[0028] Furthermore, the specific process of step S4 is as follows: The artificial multifunctional mud slurry obtained through the injection well is injected into the goaf. At the same time, the pressure difference provided by the drainage well provides supplementary power for the artificial multifunctional mud slurry to move from the "replenishment zone" to the "drainage zone". This allows the artificial multifunctional mud slurry to gradually deposit from the "replenishment zone" to the "drainage zone". The flow rate and velocity of the liquid in the injection well and drainage well are controlled so that the artificial multifunctional mud slurry fills the entire goaf. Within the goaf, as dehydration and hydration occur, artificial mudstone sediments gradually form a large amount of cementitious material, which fills the pores of the artificial mudstone sediments. This increases the cementation degree, reduces the porosity, and enhances the compressive strength of the artificial mudstone sediments, gradually leading to initial diagenesis.

[0029] Furthermore, step S5 specifically includes the following sub-steps: (I) Based on the environmental conditions (temperature, pressure) in the goaf, functional microorganisms (carbon fixation, desulfurization and denitrification microorganisms) are oriented to domesticate. The domesticated functional microorganisms are added to the liquid waste modified microbial culture medium obtained in step (II) of step S3 for expansion culture so that the microorganisms have a certain abundance. (II) The microbial culture medium containing functional microorganisms is injected into the goaf through the injection well. During the process of flowing from the injection well to the discharge well in the goaf, the physical, chemical and biochemical purification of the liquid waste is achieved through solid-liquid-bacteria interaction. (III) The composition of the extracted liquid is detected by the intelligent monitoring and post-treatment station near the discharge well. If the composition meets the discharge standard, the liquid is discharged. If the discharge standard is not met, the discharged waste liquid is post-treated and discharged after meeting the standard. At the same time, by changing the rate of the injection well and the discharge well, the retention reaction time of the liquid waste in the artificial mud sediment filter in the goaf is extended so that the extracted liquid meets the discharge standard.

[0030] Furthermore, step S6 specifically includes the following sub-steps: (I) First, the waste gas is used for waste heat utilization (i.e., pretreatment process). This waste heat can be used to maintain the temperature of the culture tank for the expansion culture of functional microorganisms or for the preparation process of artificial multifunctional mud slurry. (II) The waste gas after the waste heat is utilized is injected into the goaf through the injection well and extracted through the discharge well, so that it flows from the injection well to the discharge well. In this process, under the coupling effect of gas-solid-liquid-bacteria, the physical, chemical and biochemical purification of sulfur oxides, nitrogen oxides, carbon oxides, dust and other substances in the waste gas is achieved. (III) The composition of the extracted gas is detected by the intelligent monitoring and post-treatment station near the discharge well. If the gas meets the emission standards, it is discharged. If the emission standards are not met, the discharged gas is post-treated and discharged after meeting the standards. At the same time, by changing the rates of the injection well and the discharge well, the retention reaction time of the gas in the artificial mud sediment filter in the goaf is extended so that the extracted gas meets the emission standards.

[0031] Furthermore, step S7 specifically includes the following sub-steps: Steps S5 and S6 are implemented in a cyclical manner. After a stable artificial mud-like sediment filter element is initially formed in the goaf, gaseous waste and liquid waste are sequentially injected and extracted. Modified liquid waste culture medium containing functional microorganisms and gaseous waste treated by waste heat utilization are alternately or simultaneously injected into the goaf through injection wells, so that a stable runoff is formed between the injection well and the discharge well. During the circulation process, the composition changes of gas and liquid in the discharge well are detected in real time through an intelligent monitoring and post-treatment system. The number of circulations, injection volume and flow rate are dynamically adjusted according to the monitoring results to optimize the reaction conditions and ensure the activity of functional microorganisms and the gas-liquid purification effect. Under repeated cycles, a multiphase coupling reaction of gas, liquid, solid, and bacteria occurs inside the goaf. Carbon oxides, nitrogen oxides, and sulfur oxides in the flue gas are adsorbed, mineralized, or fixed by microorganisms. Organic pollutants and inorganic ions in the liquid waste are decomposed, adsorbed, or precipitated and transformed, while a large amount of mineralized cementitious materials such as carbonates and silicates are generated. These mineralized products gradually fill the pores of the artificial mud sediment, causing its porosity to continuously decrease, its permeability to weaken, and its compressive strength to significantly increase. The artificial mud sediment gradually evolves from an initial loose state into a dense, natural-like rock mass structure. As the number of cycles increases, the mechanical properties inside the goaf tend to stabilize, the gas-liquid flow rate decreases, and the gas-liquid components extracted from the drainage well reach a stable equilibrium, indicating that the main physical, chemical, and biological reactions in the system tend to be sufficient; at this point, the injection of new gas-liquid waste stops, and the final filling and consolidation stage of step S8 begins.

[0032] Furthermore, step S8 specifically includes the following sub-steps: After completing the cycle steps S5 and S6, the gas and liquid flow rates, pressures, and gas-liquid composition changes of the injection and drainage wells are monitored in real time. When the pollutant concentrations in the gas and liquid extracted from the drainage well are consistently lower than the relevant national emission standards, and the pressure difference between the injection and drainage wells tends to stabilize and the flow rate decreases to the set threshold, it indicates that the porosity inside the goaf has significantly decreased, the densification degree of the filling material has increased, and the goaf filling is basically completed. At this time, by adjusting the extraction rate of the drainage well, the internal fluid disturbance of the system is gradually reduced, allowing the mineralization and cementation reaction in the artificial mudstone sediment to continue and eventually stabilize, forming an artificial mudstone mass with good integrity and high mechanical strength. After the filling is completed, a comprehensive test is conducted on the goaf, including mechanical strength testing, permeability coefficient testing, sonic logging, and downhole ground-penetrating radar detection, to verify the compactness and integrity of the artificial mudstone mass. If the test results show that the compressive strength, impermeability, and support capacity all meet the design requirements, the injection well and drainage well are closed, well sealing measures are implemented, and a long-term monitoring system is deployed in the overlying strata of the goaf to continuously track the stability of the filling area and the secondary migration of gas, liquid, and waste. Ultimately, an artificial mudstone stabilizer is formed inside the goaf, enabling underground reuse and long-term storage of multi-source waste. The goaf receives reliable support and ecological restoration, completing the entire process of synergistic resource utilization and pollutant purification of coal-based solid waste, liquid waste, and gaseous waste.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. 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 still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for synergistic mineralization and backfilling of multi-source waste in coal mine goaf and self-purification of gaseous and liquid waste, characterized in that: Includes the following steps: S1. Conduct geological surveys and comprehensive evaluations of the goaf areas; S2. To manage and transform the goaf area; S3. Preparation of artificial multifunctional mud slurry; S4. Inject artificial multifunctional mud slurry into the goaf to form an artificial mud sediment filter element. S5. Inject a modified microbial culture medium containing functional microorganisms into the goaf area. The functional microorganisms purify the liquid waste in the goaf area. S6. Inject waste gas into the goaf to achieve multiphase storage; S7. Repeat steps S5 and S6, and dynamically adjust the number of cycles and the amount of cycles, so that a large amount of mineralized cementitious material is formed in the artificial mudstone sediment in the goaf, the porosity is reduced and the compressive strength is increased, and artificial mudstone that meets the requirements of goaf filling is gradually formed. S8 artificial mudstone provides stable support for the goaf, and the goaf filling is completed.

2. The method for synergistic mineralization and backfilling of multi-source waste in coal mine goaf and self-purification of gaseous and liquid waste according to claim 1, characterized in that: The exploration in step S1 includes the following two stages: (i) General survey – to ascertain the spatial development characteristics and hydrogeological conditions of the mining subsidence area; (ii) Detailed investigation—Based on the general survey, determine the upper three zones (collapse zone, fracture zone and bending subsidence zone) and the development of mining-induced cracks in the floor of the goaf; Based on the geological data of the goaf obtained from the general survey, if the feasibility of goaf renovation is too poor, then there is no need to conduct a detailed survey. Based on the results of the goaf exploration and economic benefit analysis, step S1 involves a comprehensive evaluation of the goaf, classifying it into the following three categories: Category I: Highly modifiable goaf areas – Expected benefits are more than 1.5 times the costs; Category II: Mined-out areas with weak modifiability – Expected benefits are 1 to 1.5 times the cost; Category III: Non-retrofitable goaf areas – Expected benefits are less than costs; Based on the evaluation results of goaf areas, Class I goaf areas will be given priority for treatment and renovation.

3. The method for synergistic mineralization and backfilling of multi-source waste in coal mine goaf and self-purification of gaseous and liquid waste according to claim 1, characterized in that: The methods for treating and modifying the goaf in step S2 include: (I) Bottom plate sealing and seepage prevention - Grouting and sealing treatment is carried out on the bottom plate of the goaf that connects to the aquifer or connects to the lower aquifer; (II) Overburden delamination filling - Delamination grouting is carried out to seal the goaf in the top three zones to prevent flue gas from escaping upward; Numerical simulations are conducted based on the spatial distribution of the goaf to determine the location and quantity of multi-functional wells and ancillary facilities. The multi-functional well and its ancillary facilities include: 1) Injection wells and intelligent mobile filling stations: These are set up at higher elevations within the goaf (i.e., "replenishment areas"). Through injection wells, artificial mud sediment slurry, subsequent functional microbial modified liquid waste and gas waste can be injected into the goaf of the coal mine. 2) Drainage well and intelligent monitoring and post-processing station: It is set in the lower part of the terrain in the goaf (i.e. "drainage area"), and the bottom of the drainage well is equipped with a filter screen. The drainage well can provide a pressure difference from the "replenishment area" to the "drainage area", so that liquid waste / flue gas flows from the injection well to the drainage well. The flow rate can be controlled by controlling the extraction rate of the drainage well. During actual construction, due to uneven bonding of the cementing material, more cement is formed near the injection well and relatively less near the discharge well. The positions of the injection well and the discharge well need to be interchanged to fill the entire goaf more quickly.

4. The method for synergistic mineralization and backfilling of multi-source waste in coal mine goaf and self-purification of gaseous and liquid waste according to claim 3, characterized in that: Step S3, the preparation of the artificial multifunctional mud slurry, specifically includes the following sub-steps: (I) Select coal-based solid waste and external functional solid waste and pretreat them; among which, coal-based solid waste includes coal gangue, fly ash, etc., and external functional solid waste includes cementitious material functional solid waste, flue gas purification functional solid waste (these two are mainly calcium-magnesium based solid waste, such as carbide slag, steel slag, etc.) and activator functional solid waste (red mud, etc.); these solid wastes are pretreated to obtain aggregates, cementitious materials, flue gas purification materials and activator materials respectively; (II) Pre-treat coal-based liquid waste (mine water and coal washing wastewater) and external functional liquid waste (organic wastewater, such as kitchen wastewater) to remove substances that are harmful to microorganisms and have a negative effect on flue gas purification and preparation of cementitious materials, add trace elements required for microbial growth, and modify it into a functional microbial culture medium suitable for carbon fixation, desulfurization and denitrification microorganisms in goaf areas. (III) Based on the regional differences in the composition of solid and liquid waste, the characteristics of flue gas composition, and economic benefits, the proportions of each solid and liquid material in (I) and (II) above were calculated and verified by experiments; (IV) After experimental verification, prepare multifunctional artificial mud slurry according to the formula ratio in (III); (V) During the preparation of the multifunctional artificial mud slurry in step (IV), flue gas is introduced, which initially forms a large number of fine crystal nuclei in the multifunctional artificial mud slurry, enabling rapid diagenesis in the subsequent "depositional diagenesis" process of the artificial mud sediment.

5. The method for synergistic mineralization and backfilling of multi-source waste in coal mine goaf and self-purification of gaseous and liquid waste according to claim 4, characterized in that: The specific process of step S4 is as follows: The artificial multifunctional mud slurry obtained through the injection well is injected into the goaf. At the same time, the pressure difference provided by the drainage well provides supplementary power for the artificial multifunctional mud slurry from the "replenishment zone" to the "drainage zone". This allows the artificial multifunctional mud slurry to gradually deposit from the "replenishment zone" to the "drainage zone". The flow rate and velocity of the liquid in the injection well and the drainage well are controlled so that the artificial multifunctional mud slurry fills the entire goaf. Within the goaf, as dehydration and hydration occur, artificial mudstone sediments gradually form a large amount of cementitious material, which fills the pores of the artificial mudstone sediments. This increases the cementation degree, reduces the porosity, and enhances the compressive strength of the artificial mudstone sediments, gradually leading to initial diagenesis.

6. The method for synergistic mineralization and backfilling of multi-source waste in coal mine goaf and self-purification of gaseous and liquid waste according to claim 5, characterized in that: Step S5 specifically includes the following sub-steps: (I) Based on the environmental conditions (temperature, pressure) in the goaf, functional microorganisms (carbon fixation, desulfurization and denitrification microorganisms) are oriented to domesticate. The domesticated functional microorganisms are added to the liquid waste modified microbial culture medium obtained in step (II) of step S3 for expansion culture so that the microorganisms have a certain abundance. (II) The microbial culture medium containing functional microorganisms is injected into the goaf through the injection well. During the process of flowing from the injection well to the discharge well in the goaf, the physical, chemical and biochemical purification of the liquid waste is achieved through solid-liquid-bacteria interaction. (III) The composition of the extracted liquid is detected by the intelligent monitoring and post-treatment station near the discharge well. If the composition meets the discharge standard, the liquid is discharged. If the discharge standard is not met, the discharged waste liquid is post-treated and discharged after meeting the standard. At the same time, by changing the rate of the injection well and the discharge well, the retention reaction time of the liquid waste in the artificial mud sediment filter in the goaf is extended so that the extracted liquid meets the discharge standard.

7. The method for synergistic mineralization and backfilling of multi-source waste in coal mine goaf and self-purification of gaseous and liquid waste according to claim 6, characterized in that: Step S6 specifically includes the following sub-steps: (I) First, the waste gas is used for waste heat utilization (i.e., pretreatment process). This waste heat can be used to maintain the temperature of the culture tank for the expansion culture of functional microorganisms or for the preparation process of artificial multifunctional mud slurry. (II) The waste gas after the waste heat is utilized is injected into the goaf through the injection well and extracted through the discharge well, so that it flows from the injection well to the discharge well. In this process, under the coupling effect of gas-solid-liquid-bacteria, the physical, chemical and biochemical purification of sulfur oxides, nitrogen oxides, carbon oxides, dust and other substances in the waste gas is achieved. (III) The composition of the extracted gas is detected by the intelligent monitoring and post-treatment station near the discharge well. If the gas meets the emission standards, it is discharged. If the emission standards are not met, the discharged gas is post-treated and discharged after meeting the standards. At the same time, by changing the rates of the injection well and the discharge well, the retention reaction time of the gas in the artificial mud sediment filter in the goaf is extended so that the extracted gas meets the emission standards.

8. The method for filling multi-source waste coal mine goaf with artificial mudstone and self-purifying gaseous and liquid waste according to claim 1, characterized in that: Step S7 specifically includes the following sub-steps: Steps S5 and S6 are implemented in a cyclical manner. After a stable artificial mud-like sediment filter element is initially formed in the goaf, gaseous waste and liquid waste are sequentially injected and extracted. Modified liquid waste culture medium containing functional microorganisms and gaseous waste treated by waste heat utilization are alternately or simultaneously injected into the goaf through injection wells, so that a stable runoff is formed between the injection well and the discharge well. During the circulation process, the composition changes of gas and liquid in the discharge well are detected in real time through an intelligent monitoring and post-treatment system. The number of circulations, injection volume and flow rate are dynamically adjusted according to the monitoring results to optimize the reaction conditions and ensure the activity of functional microorganisms and the gas-liquid purification effect. Under repeated cycles, a multiphase coupling reaction of gas, liquid, solid, and bacteria occurs inside the goaf. Carbon oxides, nitrogen oxides, and sulfur oxides in the flue gas are adsorbed, mineralized, or fixed by microorganisms. Organic pollutants and inorganic ions in the liquid waste are decomposed, adsorbed, or precipitated and transformed, while a large amount of mineralized cementitious materials such as carbonates and silicates are generated. These mineralized products gradually fill the pores of the artificial mud sediment, causing its porosity to continuously decrease, its permeability to weaken, and its compressive strength to significantly increase. The artificial mud sediment gradually evolves from an initial loose state into a dense, natural-like rock mass structure. As the number of cycles increases, the mechanical properties inside the goaf tend to stabilize, the gas-liquid flow rate decreases, and the gas-liquid components extracted from the drainage well reach a stable equilibrium, indicating that the main physical, chemical, and biological reactions in the system tend to be sufficient; at this point, the injection of new gas-liquid waste stops, and the final filling and consolidation stage of step S8 begins.

9. The method for filling multi-source waste coal mine goaf with artificial mudstone and self-purifying gaseous and liquid waste according to claim 1, characterized in that: Step S8 specifically includes the following sub-steps: After completing the cycle steps S5 and S6, the gas and liquid flow rates, pressures, and gas-liquid composition changes of the injection and drainage wells are monitored in real time. When the pollutant concentrations in the gas and liquid extracted from the drainage well are consistently lower than the relevant national emission standards, and the pressure difference between the injection and drainage wells tends to stabilize and the flow rate decreases to the set threshold, it indicates that the porosity inside the goaf has significantly decreased, the densification degree of the filling material has increased, and the goaf filling is basically completed. At this time, by adjusting the extraction rate of the drainage well, the internal fluid disturbance of the system is gradually reduced, allowing the mineralization and cementation reaction in the artificial mudstone sediment to continue and eventually stabilize, forming an artificial mudstone mass with good integrity and high mechanical strength. After the filling is completed, a comprehensive test is conducted on the goaf, including mechanical strength testing, permeability coefficient testing, acoustic wave transmission and downhole ground radar detection, to verify the compactness and integrity of the artificial mudstone mass; If the test results show that the compressive strength, impermeability and support capacity all meet the design requirements, the injection well and the discharge well will be closed, well sealing measures will be implemented, and a long-term monitoring system will be set up in the overlying strata of the goaf to continuously track the stability of the filling area and the secondary migration of gas, liquid and waste. Ultimately, an artificial mudstone stabilizer is formed inside the goaf, enabling underground reuse and long-term storage of multi-source waste. The goaf receives reliable support and ecological restoration, completing the entire process of synergistic resource utilization and pollutant purification of coal-based solid waste, liquid waste, and gaseous waste.

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