Micro-expansion material and method for sealing roof-contacted cavity of filled goaf

Abstract

The invention discloses a micro-expansion material and method for sealing a roof-contacted cavity of a filled goaf, and the micro-expansion material is prepared by mixing the following components and an alkali activator, and the components comprise 12-16 parts by mass of slag, 8-12 parts by mass of carbide slag, 20-25 parts by mass of water and 50-55 parts by mass of high-silicon nickel smelting slag, naOH is adopted as the alkali activating agent, and the adding amount of the alkali activating agent is 4%-8% of the total amount of the slag, the carbide slag and the high-silicon-nickel smelting slag. In a static pressure self-flow grouting mode, micro-expansion material slurry which is stirred and mixed in a ground stirring site flows into a main pipeline (7) through an earth surface input pipeline, the area of a non-headspace cavity (6) is filled with the micro-expansion material slurry through the laid main pipeline (7) and a spiral pipeline (8), and when the flow monitored by a flow monitor is continuously zero or lower than a set threshold value, grouting filling is stopped; therefore, long-acting sealing with the high roof contact rate is achieved, and the roof contact rate of the roof contact cavity after the micro-expansion material is filled reaches up to 99% or above.

Description

Technical Field

[0001] This invention belongs to the technical field of underground mine filling materials, specifically relating to a filling material and method for sealing the roof cavity of a filled goaf. Background Technology

[0002] Backfilling mining technology utilizes waste to fill mined-out areas, reducing waste emissions and environmental impact. By filling these areas, it can reduce the occurrence of geological disasters such as surface subsidence and earthquakes, thus improving the mining environment. In summary, the application of backfilling mining technology in underground mines not only improves mining efficiency and reduces environmental impact but also enhances mine safety. By filling mined-out areas with waste, backfilling mining technology can maximize ore recovery rates and extend the utilization life of ore resources, effectively alleviating mineral resource shortages and providing crucial technical support for the sustainable utilization of mineral resources.

[0003] When using the backfilling method for underground mining, incompletely sealed areas (i.e., "roof cavities") can easily form between the backfill and the surrounding roof rock due to factors such as the solidification and shrinkage of the backfill material, the complex shape of the stope roof, and low roof contact rates caused by unreasonable backfilling processes. These cavities result in a lack of effective support for the roof strata, making them prone to continuous deformation and even failure under mining stress. In severe cases, this can induce roof collapse or large-scale instability in the goaf, posing a serious threat to underground safety. At the same time, the cavity and fracture system provide channels for groundwater migration, accelerating the leaching of harmful components (such as sulfides) from ore and solid waste, easily forming high-concentration acid mine drainage (AMD), polluting the mining area and surrounding environment. The treatment of AMD is both difficult and costly.

[0004] Currently, existing roof jointing technologies such as high-pressure grouting and paste filling have certain limitations: improper control of high-pressure grouting pressure can easily cause splitting damage to fragile roof slabs, and the equipment is complex; traditional paste or slurry materials shrink after curing, resulting in loose roof joints and failing to achieve effective long-term sealing of cavities, affecting the roof jointing effect; some processes are costly and have limited adaptability.

[0005] The article "Research on Backfilling and Roofing Technology in Underground Mines" published in the fifth issue of the Chinese journal "Mining Technology" in 2017 analyzed the main reasons why backfilling in underground mine goaf areas cannot be connected to the roof: (1) The shrinkage and fluidity (leveling) of the backfill slurry cause excess water to seep out on the surface of the backfill, thus forming a gap between the backfill and the roof of the goaf; (2) Inadequate drainage measures lead to a large amount of water accumulating on the surface of the backfill, making it impossible for the backfill to be connected to the roof; (3) Irregular shape of the goaf makes it difficult to fill some goaf areas, resulting in a void roof; (4) Unreasonable layout of the backfilling pipeline network. The article also gave a variety of roofing technologies, such as manual roofing, mechanical roofing, forced caving roofing, slurry pressurization roofing, slurry gravity roofing, and slurry expansion roofing, but these technologies are all principle-based and directional, without specific and feasible technical solutions.

[0006] Therefore, the industry urgently needs a new type of material and method for sealing the roof cavity of a filled goaf, which can overcome the above-mentioned defects and achieve safe and efficient sealing of the cavity in the filled goaf. Summary of the Invention

[0007] The purpose of this invention is to address the technical challenge of difficult roof connection when filling goaf areas in underground mines, and to provide a micro-expansion material based on the principle of micro-expansion for sealing the roof cavity of filled goaf areas. By developing and using a filling material with micro-expansion characteristics during the curing period, the volume loss caused by chemical shrinkage, water evaporation, etc. is compensated, and the filling body is made to fit tightly with the roof rock surface.

[0008] Another objective of this invention is to provide a method for sealing the roof cavity of a filled goaf. The method employs static pressure grouting, relying on the grout's own weight and fluidity for penetration and sealing, avoiding the adverse effects of high pressure on the stability of the goaf roof, and achieving full filling and sealing of the roof cavity and micro-crack system, thus laying the technological foundation for effective "sealing".

[0009] To achieve the above-mentioned objectives of this invention, a micro-expansion material for sealing the roof cavity of a filled goaf is provided. This material is composed of the following components mixed with an added alkali activator. The components, in a total mass of 100 parts, are: 12-16 parts slag, 8-12 parts calcium carbide slag, 20-25 parts water, and 50-55 parts high-silicon nickel smelting slag. The alkali activator is NaOH, and its addition amount is 4%-8% of the total mass of the slag, calcium carbide slag, and high-silicon nickel smelting slag.

[0010] Preferably, the chemical composition of the high-silicon nickel smelting slag, by mass percentage, is as follows: SiO2 45%~50%, MgO 16%~18%, Al2O3 10%~12%, CaO 0.5%~1%; its particle size distribution is as follows: D 10 =14~16 μm, D 50=110~120 μm, D90 =320~330 μm, specific surface area is 0.2~0.3 m² 2 / g.

[0011] Preferably, the slag is S95 grade slag powder, and the content of each component in its chemical composition by mass percentage is: CaO 44%~50%, SiO2 25%~30%, Al2O3 12%~15%, MgO 8%~10%.

[0012] Preferably, the CaO content in the carbide slag is greater than 59% by mass; the alkali activator is NaOH flake granules.

[0013] Preferably, the performance parameters of the micro-expansion material slurry prepared by mixing slag, carbide slag, water, high silicon nickel smelting slag, and alkali activator are: 28-day uniaxial compressive strength of 3~5 MPa, slump of 220~250 mm, and initial setting time of 240~300 min.

[0014] In practical applications, NaOH particles are mixed with water to prepare an alkali-activated solution; the pH of the water is 7-9. Slag, nickel smelting slag, and carbide slag are dry-powdered and mixed to obtain a solid mixture of micro-expanded materials. This solid mixture of micro-expanded materials is then mixed with the alkali-activated solution to obtain the micro-expanded material.

[0015] The present invention discloses a method for sealing the roof cavity of a filled goaf. The filling system includes a main pipeline, a spiral pipeline, and a flow monitor. The main pipeline is located on the upper part of the rear-end sealed retaining wall during the goaf backfilling process. The inlet of the main pipeline is connected to the surface input pipeline, and the outlet of the main pipeline is connected to the inlet of the spiral pipeline. The spiral pipeline extends into the roof cavity between the solidified filling body and the upper roof of the goaf. The spiral pipeline has openings on its walls along its length to ensure the output of micro-expansion material slurry. The flow monitor is installed on the main pipeline.

[0016] Using static pressure gravity grouting, the micro-expansion material slurry, which is mixed and prepared at the ground mixing site, flows into the main pipeline through the surface input pipeline. It is then filled into the unconnected cavity area through the laid main pipeline and spiral pipeline. Grouting and filling will stop when the flow rate monitored by the flow monitor is continuously zero or lower than the set threshold.

[0017] Furthermore, the diameter of the discharge hole at the front end of the spiral pipe is larger than that at the rear end to prevent the rear end of the spiral pipe from being filled too early and causing blockage, thus affecting the filling effect.

[0018] Furthermore, the micro-expansion material slurry undergoes volume expansion during the curing process, with a volume expansion coefficient of 1% to 2% after 28 days.

[0019] This invention achieves the dual effect of sealing the roof cavity by combining the preparation and filling methods of the micro-expansion material slurry: firstly, it provides effective support for the roof rock layer, controls ground pressure manifestation, and reduces safety risks (achieving structural support); secondly, it effectively blocks the main seepage channels of groundwater, inhibiting the generation and diffusion of acid mine wastewater (AMD) from the source (achieving seepage channel isolation).

[0020] The method for sealing the roof cavity of a filled goaf according to the present invention has relatively simple requirements for the filling system equipment, convenient process operation, can adapt to the complex environment of goaf with different shapes and sizes, and is easy to promote and apply in the mine site.

[0021] The micro-expansion material and method for sealing the roof cavity of a filled goaf, as described in this invention, have the following positive effects after adopting the above technical solution:

[0022] (1) The micro-expansion material is mainly composed of high silicon nickel smelting slag, ore slag, carbide slag, NaOH and water. The volume expansion coefficient is 1%~2%. It can actively compensate for solidification shrinkage and generate chemical prestress, so that the filling body and the top plate are continuously and tightly attached. It fundamentally solves the problem of secondary cavity caused by the shrinkage of traditional materials and achieves long-term sealing with high top contact rate.

[0023] (2) The high-silicon nickel smelting slag, mineral slag and carbide slag used in the micro-expansion material are all general industrial solid wastes. While obtaining micro-expansion characteristics, the material maintains good support strength (3-5 MPa), realizes the resource utilization of waste, is low in cost, and conforms to the concept of green mining.

[0024] (3) The micro-expansion material process has high reliability and strong adaptability. The slurry setting time of the micro-expansion material is controllable (initial setting 240-300 min), with a wide operating window, effectively preventing pipeline blockage. The technology requires simple equipment, does not require complex high-pressure equipment, can safely adapt to various complex goaf environments, has a high success rate and reproducibility, and is easy to promote.

[0025] (4) Both construction safety and filling uniformity are achieved: The static pressure self-flowing grouting process (slump 220-250mm) relies on the grout's own weight to flow, completely avoiding the risk of damage to the roof slab caused by high-pressure grouting. Combined with the unique spiral pipe layout design (large output at the front end), it can orderly expel air, ensuring that complex cavities and micro-cracks are uniformly and fully filled without blind spots.

[0026] (5) Synergistic effect of safety and environmental protection: The dual sealing effect of "structural support" and "seepage channel isolation" is ultimately achieved simultaneously: significantly enhancing the stability of the goaf and reducing safety risks; and inhibiting the generation and spread of acid mine wastewater (AMD) from the source, resulting in outstanding environmental benefits. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a goaf structure according to an embodiment of the method for sealing the roof cavity of a filled goaf according to the present invention.

[0028] Figure 2 This is a pipeline layout diagram of the roof cavity in an embodiment of the method for sealing the roof cavity of a filled goaf according to the present invention.

[0029] Figure 3 This is a schematic diagram of the spiral pipe opening used in an embodiment of the method for sealing the roof cavity of a filled goaf according to the present invention.

[0030] Attached reference numerals: 1-Upper roof of the goaf; 2-Lower floor of the goaf; 3-Front-end sealed retaining wall; 4-Rear-end sealed retaining wall; 5-Cureable filling material; 6-Cavity connecting to the roof; 7-Main pipeline; 8-Spiral pipeline. Detailed Implementation

[0031] To further describe the present invention, a micro-expansion material and method for sealing the roof cavity of a filled goaf are described in further detail below with reference to the accompanying drawings. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Specific conditions and parameters not specified in the embodiments are performed under conventional conditions or conditions recommended by on-site operators. Reagents and instruments used, unless otherwise specified, are all commercially available products.

[0032] In this embodiment, a micro-expansion material for sealing the roof cavity of a filled goaf is composed of the following components mixed with an alkali activator. The components, in a total mass fraction of 100 parts, are: 12-16 parts slag, 8-12 parts calcium carbide slag, 20-25 parts water, and 50-55 parts high-silicon nickel smelting slag. The alkali activator is NaOH, added at 4%-8% of the total mass of the slag, calcium carbide slag, and high-silicon nickel smelting slag. The performance parameters of the micro-expansion material slurry prepared by mixing slag, calcium carbide slag, water, high-silicon nickel smelting slag, and alkali activator are: 28-day uniaxial compressive strength of 3-5 MPa, slump of 220-250 mm, and initial setting time of 240-300 min.

[0033] The high-silicon nickel smelting slag is a waste residue from the smelting of silicate gangue minerals. Its main components are quartz, mica, forsterite, polysilicon lepidolite, and enstatite, etc. The chemical composition, by mass percentage, is as follows: SiO2 45%~50%, MgO 16%~18%, Al2O3 10%~12%, CaO 0.5%~1%; its particle size distribution is: D 10 =14~16 μm, D 50=110~120 μm, D90 =320~330 μm, specific surface area is 0.2~0.3 m² 2 / g. The slag is S95 grade slag powder, and its chemical composition by mass percentage is as follows: CaO 44%~50%, SiO2 25%~30%, Al2O3 12%~15%, MgO 8%~10%. The mass content of CaO in the carbide slag is greater than 59%.

[0034] The high-silicon nickel smelting slag used in this embodiment is a uniform, fine-particle high-silicon nickel smelting slag with a high SiO2 content. As a key aggregate framework and hydration reaction raw material, the high-silicon nickel smelting slag significantly enhances the hydration reaction of the micro-expansion material, thereby promoting the improvement of uniaxial compressive strength. The micro-expansion material prepared using high-silicon nickel smelting slag not only helps solve the problem of low utilization rate of bulk solid waste, but also significantly reduces costs in applications involving the roof cavity 6 of large-scale mining goaf areas, exhibiting good economic and environmental performance.

[0035] The aforementioned slag is a solid waste product generated from iron and steel smelting. The total content of CaO, SiO2, and Al2O3 in the slag exceeds 90%, with a Ca content lower than that of cement. It possesses high silica and aluminum content, resulting in good cementitious properties. Under alkali activation, it can form geopolymers with a micro-expansion effect. Furthermore, its micro-bead lubrication effect can effectively improve the fluidity of the slurry.

[0036] The aforementioned calcium carbide slag is a waste residue mainly composed of CaO, produced after the hydrolysis of calcium carbide to obtain acetylene gas. It possesses high alkalinity and calcium content, and can effectively fill fine pores. Its high calcium and alkalinity accelerate the hydration reaction and effectively regulate the setting time. Furthermore, the calcium carbide slag can neutralize the acidic wastewater already formed in the top cavity 6, increasing the alkalinity of the hydration reaction of the micro-expansion material.

[0037] The aforementioned alkali activator uses NaOH particles. In micro-expansion materials, it primarily functions as an alkali activator, helping the material dissolve rapidly and participate in the hydration reaction to form a stable three-dimensional network structure. This helps improve the density of the micro-expansion material and reduce water penetration.

[0038] The water mentioned above is an indispensable medium and solvent for the hydration reaction in micro-expansion materials. During the mixing process, water can dissolve solid mixtures to form a homogeneous slurry, providing fluidity. It also acts as an ion transport medium, promoting the reaction of each component and aiding in the curing and strength formation of the micro-expansion material.

[0039] In summary, these materials work together on the micro-expansion material. The calcium carbide slag primarily neutralizes the acidic wastewater in the top cavity 6 and provides the CaO needed for the hydration reaction; NaOH increases the OH- content in the liquid phase. -The concentration of these materials ensures the alkali-activated gelation hydration reaction within the system. High-silicon nickel smelting slag not only provides SiO2 for the hydration reaction, but its particles also act as micro-aggregate fillers, optimizing the slurry's skeletal structure. The slag provides SiO2 and Al2O3 for the hydration process, serving as the main donor for geopolymers. Water acts as the solvent and reaction medium for the solid mixture. Through the synergistic effect of these materials, a filling material with a micro-expansion effect is formed, effectively filling the solidified filling body 5 and the cavity 6 between the upper roof 1 of the goaf.

[0040] The aforementioned materials, through synergistic hydration effects, particularly their complementary physicochemical properties, help and enhance the macroscopic performance and microstructural density of the micro-expansion material. While ensuring the hydration reaction proceeds, they improve the erosion condition of the acidic wastewater in the top cavity and achieve stable compressive strength. This ensures the micro-expansion material maintains high efficiency, stability, and durability during use.

[0041] Depend on Figure 1 The diagram shown is a schematic representation of a goaf structure according to an embodiment of the present invention for sealing the roof cavity of a filled goaf, and is combined with... Figure 2 , Figure 3 It can be seen that a solidified filling body 5 has been formed between the upper roof 1 and the lower floor 2 of the goaf through tailings cementation and filling. There is a roof cavity 6 between the solidified filling body 5 and the upper roof 1 of the goaf. The front and rear ends of the solidified filling body 5 are respectively equipped with a front sealed retaining wall 3 and a rear sealed retaining wall 4. The filling system includes a main pipe 7, a spiral pipe 8, and a flow monitor. The main pipe 7 is located on the upper part of the rear sealed retaining wall 4 during the backfilling process of the goaf. The inlet of the main pipe 7 is connected to the surface input pipe, and the outlet of the main pipe 7 is connected to the inlet of the spiral pipe 8. The spiral pipe 8 extends into the cavity 6 between the solidified filling body 5 and the upper roof slab 1 of the goaf. The spiral pipe 8 has openings on its walls along its length to ensure the output of micro-expansion material slurry. The diameter of the discharge hole at the front end of the spiral pipe 8 is larger than the diameter of the discharge hole at the rear end, or the density of the openings is greater. The flow monitor is installed on the main pipe 7.

[0042] In some embodiments, the weight parts of each component in the micro-expansion material are as follows:

[0043] Slag, 12 to 16 parts; for example, it can be 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, etc.

[0044] Carbide slag, 8 to 12 parts; for example, it can be 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, etc.

[0045] Water, 20 to 25 parts; for example, 20 parts, 21 parts, 22 parts, 23 parts, 24 parts, 25 parts, etc.

[0046] High-silicon nickel smelting slag, 50 to 55 parts; for example, it can be 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, etc.

[0047] NaOH, 4% to 8% of the total solid mass; for example, it can account for 4%, 5%, 6%, 7%, 8% of the total solid mass, etc.

[0048] The present invention discloses a method for sealing the roof cavity in a filled goaf, which is implemented by the following steps:

[0049] S1 Micro-expansion Material Preparation

[0050] NaOH particles are mixed with water to prepare an alkali-activated solution; slag, nickel smelting slag and carbide slag are dry-mixed to obtain a solid mixture of micro-expansion materials; the solid mixture of micro-expansion materials and the alkali-activated solution are then mixed to obtain a micro-expansion material slurry.

[0051] S2 Filling the top cavity

[0052] Using static pressure gravity grouting, the micro-expansion material slurry, which is mixed and prepared at the ground mixing site, flows into the main pipe 7 through the surface input pipe. It is then filled into the unconnected cavity 6 area through the laid main pipe 7 and spiral pipe 8. Grouting is stopped when the flow rate monitored by the flow monitor is continuously zero or lower than the set threshold.

[0053] The present invention will be further illustrated below with specific embodiments, but it should be understood that the embodiments are merely preferred technical solutions and should not be construed as limiting the present invention in any way.

[0054] The composition of the selected materials is shown in Table 1:

[0055] Table 1 Raw material composition

[0056]

[0057] Table 2. Dosage of each component in the micro-expansion material of the examples

[0058]

[0059] The specific surface area of ​​the selected nickel smelting slag is 0.208 m². 2 / g,D 10 =14.793 μm, D 50 =119.312 μm, D 90 =329.323 μm.

[0060] The micro-expansion material was prepared in step 1) above, and its flow properties were tested. The setting time was measured using a Vicat apparatus. The underground goaf was filled according to the construction method in step 2). After 24 hours, borehole samples (Φ50 mm × h100 mm cylindrical samples) were drilled and their volume data recorded. The samples were then placed in the goaf for curing, and the volume data was measured again after 28 days. Borehole samples (Φ50 mm × h100 mm cylindrical samples) were also drilled after 28 days to obtain the 28-day compressive strength test data. Specific data are as follows.

[0061] Table 3 Performance test results of the examples

[0062]

[0063] Examples of experiments show that the three micro-expansion materials prepared using this invention with different proportions all meet the 28-day compressive strength requirements of 3 MPa to 5 MPa, with a maximum of 5.5 MPa, demonstrating good filling performance. The volume expansion coefficients are all between 1% and 2%. In terms of fluidity, all meet the slump limit of 220 mm to 250 mm. Furthermore, the initial setting time is between 240 min and 300 min, indicating good workability. Leachate testing of the filling body according to HJ 557-2010 standard shows that the heavy metal concentration in the leachate meets the Class III surface water quality standard. In addition, the method for sealing the roof cavity of a filled goaf based on micro-expansion materials provided by this invention can increase the roof connection rate of the filled goaf to over 99% after filling, up from 95%.

[0064] The micro-expansion material prepared by this invention for sealing the roof cavity of a filled goaf has been applied in the cemented backfilling project of tailings in a goaf of an underground iron mine using the backfilling method. The application results show that the backfilling rate is as high as 99.1%, achieving unexpected technical effects.

[0065] It should be noted that the terms "upper", "lower", "left", "right", "inner", "outer", "longitudinal", "lateral", "front end", "rear end", etc., used in this invention to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the parts or elements referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this invention.

[0066] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A micro-expansion material for sealing the roof cavity of a filled goaf, characterized in that... It is composed of the following components plus an alkali activator, and the proportions of each component are as follows based on a total mass of 100 parts: 12-16 parts slag, 8-12 parts calcium carbide slag, 20-25 parts water, and 50-55 parts high-silicon nickel smelting slag; the alkali activator is NaOH, and the amount added is 4%-8% of the total amount of slag, calcium carbide slag, and high-silicon nickel smelting slag.

2. The micro-expansion material for sealing the roof cavity of a filled goaf as described in claim 1, characterized in that: The chemical composition of the high-silicon nickel smelting slag, by mass percentage, is as follows: SiO2 45%~50%, MgO 16%~18%, Al2O3 10%~12%, CaO 0.5%~1%; its particle size distribution is as follows: D 10 =14~16 μm, D 50 =110~120μm, D90 =320~330 μm, specific surface area is 0.2~0.3 m² 2 / g.

3. The micro-expansion material for sealing the roof cavity of a filled goaf as described in claim 1, characterized in that: The slag is S95 grade slag powder, and its chemical composition by mass percentage is as follows: CaO 44%~50%, SiO2 25%~30%, Al2O3 12%~15%, MgO 8%~10%.

4. The micro-expansion material for sealing the roof cavity of a filled goaf as described in claim 1, characterized in that: The mass content of CaO in the carbide slag is greater than 59%.

5. The micro-expansion material for sealing the roof cavity of a filled goaf as described in claim 1, characterized in that: The performance parameters of the slurry prepared by mixing slag, carbide slag, water, high silicon nickel smelting slag, and alkali activator are: 28-day uniaxial compressive strength of 3~5 MPa, slump of 220~250 mm, and initial setting time of 240~300 min.

6. The micro-expansion material for sealing the roof cavity of a filled goaf as described in claim 2, characterized in that: The slag is S95 grade slag powder, and its chemical composition by mass percentage is as follows: CaO 44%~50%, SiO2 25%~30%, Al2O3 12%~15%, MgO 8%~10%; the CaO content in the carbide slag is greater than 59% by mass; the performance parameters of the micro-expansion material slurry prepared by mixing the slag, carbide slag, water, high silicon nickel smelting slag, and alkali activator are: 28-day uniaxial compressive strength 3~5 MPa, slump 220~250 mm, and initial setting time 240~300 min.

7. A method for sealing the roof cavity of a filled goaf, characterized in that... The micro-expansion material used is composed of the following components plus an alkali activator, with the following component fractions per 100 parts by mass: 12-16 parts slag, 8-12 parts calcium carbide slag, 20-25 parts water, and 50-55 parts high-silicon nickel smelting slag; the alkali activator is NaOH, and the addition amount is 4%-8% of the total amount of slag, calcium carbide slag, and high-silicon nickel smelting slag. The chemical composition of the high-silicon nickel smelting slag, by mass percentage, is as follows: SiO2 45%~50%, MgO 16%~18%, Al2O3 10%~12%, CaO 0.5%~1%; its particle size distribution is as follows: D 10 =14~16 μm, D 50 =110~120μm, D90 =320~330 μm, specific surface area is 0.2~0.3 m² 2 / g; The slag is S95 grade slag powder, and its chemical composition by mass percentage is: CaO 44%~50%, SiO2 25%~30%, Al2O3 12%~15%, MgO 8%~10%; The mass content of CaO in the carbide slag is greater than 59%; The performance parameters of the slurry prepared by mixing the slag, carbide slag, water, high silicon nickel smelting slag, and alkali activator are: 28-day uniaxial compressive strength 3~5 MPa, slump 220~250 mm, and initial setting time 240~300 min; The filling system includes a main pipe (7), a spiral pipe (8), and a flow monitor. The main pipe (7) is located on the upper part of the rear sealed retaining wall (4) during the backfilling process of the goaf. The inlet of the main pipe (7) is connected to the surface input pipe, and the outlet of the main pipe (7) is connected to the inlet of the spiral pipe (8). The spiral pipe (8) extends into the cavity (6) between the solidified filling body (5) and the upper roof plate (1) of the goaf. The spiral pipe (8) has openings on its walls along its length to ensure the output of the micro-expansion material slurry. The flow monitor is installed on the main pipe (7). By using static pressure self-flowing grouting, the micro-expansion material slurry, which is mixed and prepared at the ground mixing site, flows into the main pipeline (7) through the surface input pipeline. It is then filled into the unconnected cavity (6) area through the laid main pipeline (7) and spiral pipeline (8). When the flow rate monitored by the flow monitor is continuously zero or lower than the set threshold, the grouting and filling will stop.

8. A method for sealing the roof cavity of a filled goaf as described in claim 7, characterized in that: The diameter of the discharge hole at the front end of the spiral pipe (8) is larger than the diameter of the discharge hole at the rear end.

9. A method for sealing the roof cavity of a filled goaf as described in claim 8, characterized in that: The micro-expansion material slurry undergoes volume expansion during the curing process, with a volume expansion coefficient of 1% to 2% after 28 days.

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