Novel goaf filling material

Abstract

The invention discloses a novel goaf filling material, and belongs to the technical field of solid waste resource utilization. The novel goaf filling material comprises the following components in percentage by mass: 45-60% of sulphoaluminate cement, 15-25% of coal gangue, 10-25% of titanium gypsum, 3-8% of an activating agent, 0.5-1.5% of a thickening agent and 0.5-1% of a surfactant. The research and development of the novel goaf filling material aims at reducing the cost, improving the solid waste utilization rate and reducing carbon emission, and the goaf filling technology is promoted to develop in a more efficient and more environment-friendly direction. Research, development and popularization of the filling material not only have remarkable technical innovation value, but also play an important role in sustainable development of the mine industry.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization technology, and more specifically relates to a new type of goaf filling material. Background Technology

[0002] Numerous goaf areas formed during mining operations are a common legacy issue after mining. The existence of these goaf areas often triggers a series of environmental and safety hazards, including: surface subsidence and collapse, geological disasters, landslides, and surface fissures. These disasters not only damage the ecological environment surrounding the mining area but also threaten the lives and property of residents and the normal operation of mining facilities.

[0003] In order to effectively control the hazards caused by goaf, goaf backfilling technology has emerged. As a key component of backfilling technology, the performance of backfilling materials directly affects the backfilling effect. Currently, the materials commonly used for backfilling goaf can be divided into the following categories: cement-based backfilling materials, tailings-based backfilling materials, industrial by-product-based backfilling materials, and polymer-based backfilling materials. Although existing backfilling materials have been widely used in goaf management, their performance and applicability still have limitations: (1) The contradiction between material strength and cost: high-strength materials are often accompanied by high costs, while the strength of low-cost materials is difficult to meet the needs of deep-buried goaf. (2) Insufficient environmental friendliness: the carbon emissions and potential pollution problems of cement-based materials and polymer-based materials are inconsistent with the goal of green mine construction. (3) Low resource utilization rate: the utilization rate of tailings and industrial by-products is limited, and existing backfilling materials have not completely solved the resource utilization problem of mine solid waste.

[0004] In summary, given the problems and challenges of existing filling materials in treating goaf areas, this invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a new type of goaf filling material to solve the problems existing in the prior art. It can not only efficiently solve the stability problem of goaf, but also realize the resource utilization of solid waste, and promote the coordinated development of mining area governance technology and energy conservation and emission reduction goals.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] One of the technical solutions of this invention is to provide a novel goaf filling material, which, by mass percentage, comprises: 45-60% sulfoaluminate cement, 15-25% coal gangue, 10-25% titanium gypsum, 3-8% activator, 0.5-1.5% thickener, and 0.5-1% surfactant.

[0008] Preferably, the novel goaf filling material comprises, by mass percentage: 50% sulfoaluminate cement, 25% coal gangue, 20% titanium gypsum, 4% activator, 0.5% thickener, and 0.5% surfactant.

[0009] Preferably, the particle size of the coal gangue is 10-20 mm.

[0010] Preferably, the activator includes one or more of sodium silicate, sodium tripolyphosphate, and aluminate.

[0011] Preferably, the thickener includes one or more of sodium carboxymethyl cellulose, xanthan gum, and polyacrylamide.

[0012] Preferably, the surfactant comprises one or more of polyvinyl alcohol, fatty alcohol ether, and alkyl polyglycoside.

[0013] Preferably, the water content of the titanium gypsum is 0.7-1.5%.

[0014] Preferably, the moisture content of the novel goaf filling material is 1-2%.

[0015] The second technical solution of the present invention provides a method for preparing the above-mentioned novel goaf filling material, comprising the following steps:

[0016] The sulfoaluminate cement, coal gangue, titanium gypsum, activator, thickener, surfactant and water are mixed to obtain a mixture; the mixture is then subjected to low-temperature treatment under a nitrogen atmosphere to obtain the novel goaf filling material.

[0017] Preferably, the mixing step includes: mixing coal gangue and titanium gypsum at a stirring speed of 50-70 rpm, then adding sulfoaluminate cement and an activator and mixing at a stirring speed of 80-100 rpm for 5-10 minutes, then increasing the stirring speed to 200-300 rpm, adding a thickener and stirring for 3-5 minutes, then increasing the stirring speed to 400-500 rpm, adding a surfactant and stirring for 3-5 minutes to obtain a mixture.

[0018] By adding the raw materials in the above-described order, the present invention achieves the following effects:

[0019] (1) Preliminary mixing of coal gangue and titanium gypsum: When coal gangue and titanium gypsum are added to the mixing system as filler materials, their main purpose is to provide a stable skeletal structure for subsequent reactions. The goal of mixing these two materials is to ensure their homogeneity. The homogeneity of the mixture not only affects the bulk density and surface properties of the materials, but is also closely related to the performance of the final cured material. A lower stirring speed can avoid air entrainment during excessive stirring, ensuring uniform mixing. The stirring speed (50-70 rpm) during the mixing process is consistent with the particle properties of the materials in actual operation, avoiding excessive stirring that could lead to material breakage or uneven dispersion.

[0020] (2) Mixing of sulfoaluminate cement and activator: Sulfoaluminate cement is a key hydraulic material, and its effectiveness is closely related to the activation effect of the activator. The activator can accelerate the hydration reaction of cement, improving early strength and final strength. Setting the stirring speed at this stage (80-100 rpm) helps to ensure thorough mixing of sodium silicate and cement, guaranteeing reaction efficiency. If the stirring speed is too low, uneven mixing may occur, thus affecting the hydration efficiency of the cement and the final strength of the material.

[0021] (3) Adding a thickener: Thickeners improve the flowability and thixotropy of the mixture, making it more manageable during molding, transportation, and construction. Their solubility and dispersibility place high demands on the mixing process. Using a stirring speed of 200–300 rpm ensures uniform dispersion of the thickener without air entrainment, maintaining the high viscosity of the mixture. This stirring speed is appropriate, promoting rapid dissolution of the thickener in water-based systems and improving rheological properties.

[0022] (4) Adding surfactants: Surfactants can reduce the surface tension of cured materials and improve their adhesion and toughness, especially for high-water curing systems. The surfactants are added at this step to enhance the crack resistance and toughness of the material; therefore, they need to be added at a high stirring speed (400–500 rpm) to ensure complete dissolution and uniform distribution. High stirring speed helps avoid premature reaction or incomplete dissolution of polyvinyl alcohol with other materials, ensuring optimal results.

[0023] The purpose of determining the order of adding each raw material: The order of adding each raw material is not only based on its physical properties, but also takes into account the interaction between each raw material and other components. For example: Pre-mixing of coal gangue and titanium gypsum: These two mainly serve as fillers and skeleton materials. They do not undergo strong chemical reactions upon addition, requiring only a low stirring speed to maintain particle stability and prevent excessive air entrainment. Addition of sulfoaluminate cement and activator: The activator plays an activating role. Adding cement and activator first ensures that the cement hydration reaction is activated and effectively promotes the curing of the mixture. Addition of thickeners and surfactants: Thickeners and surfactants typically affect rheology, viscosity, and the surface properties of the final cured material. Therefore, these components should be added after other raw materials are mixed to ensure that they do not interfere with the reactions of other components.

[0024] The order in which raw materials are added cannot be arbitrarily changed. In practice, the order of addition and mixing conditions for each raw material have specific purposes, and changing the order of addition will affect the reaction efficiency, material properties, and final result. For example, if polyvinyl alcohol or thickener is added first, it will affect the cement hydration process or cause other components to react incompletely. Therefore, changing the order will lead to a decrease in performance or process problems.

[0025] The order of addition determined by this invention helps ensure that the effect of each ingredient is maximized while minimizing interference between them. Adjusting the order of addition of each ingredient will affect the flowability, stability, strength, and final curing properties of the mixture.

[0026] Preferably, the low-temperature treatment is performed at a temperature of 50–70°C for 2–3 hours.

[0027] The third technical solution of the present invention is to provide the application of the above-mentioned novel goaf filling material in goaf filling.

[0028] The fourth technical solution of the present invention provides a method for improving the treatment effect of goaf, comprising the following steps: filling the goaf with the novel goaf filling material prepared by the above preparation method.

[0029] The addition of coal gangue can significantly improve the strength of backfill materials. This invention controls the particle size of the added coal gangue to be 10-20 mm. Coal gangue provides reasonable skeletal structural support, improving compressive strength, crack resistance, and stability, while avoiding excessively rapid reaction caused by overly fine particles and excessively high porosity caused by overly large particles. Overly small coal gangue particles often have high reactivity, promoting excessively rapid cement hydration, generating a large amount of heat, leading to temperature rise, which may result in cracks and uneven curing. Coal gangue with a particle size of 10-20 mm maintains a relatively slow reaction rate during curing, avoiding problems caused by thermal expansion and excessively rapid hydration, ensuring greater material stability. Conversely, large particles lead to lower fluidity, making it difficult for the mixture to distribute evenly during mixing, resulting in material inhomogeneity. It may also cause crack formation, especially during curing, where its larger size may lead to uneven shrinkage, thus affecting the integrity and durability of the structure.

[0030] Despite the large amount of solid waste used, this invention still ensures that the resulting filling material has excellent performance. The reason is that this invention can guarantee the high performance of the final material through reasonable particle size control and optimized mixing process. The following are some key factors: (1) The role of particle size control at 10-20mm: As mentioned above, by controlling the particle size of coal gangue at 10-20mm, the filling and reinforcing effect of coal gangue can be maximized, without the reaction being too fast due to too small a particle size, or the mixing being uneven or the porosity being too high due to too large a particle size. Controlling the particle size of coal gangue helps to improve the stability of the material while ensuring that the hydration reaction of the cement-based material is not too fast or too slow, thereby ensuring the comprehensive performance of the mixture. (2) Reasonable cement to coal gangue ratio: Cement is the core component of the curing material, and its hydration reaction has a direct impact on the final performance. By reasonably controlling the ratio of cement to coal gangue, the hydration reaction of cement can be fully activated, while coal gangue acts as a reinforcing material to improve the mechanical properties of the curing material. In this invention, the appropriate addition of coal gangue can increase the volume of the mixture while maintaining good strength and durability. (3) Optimization of mixing process: The process of gradually increasing the mixing speed can ensure that coal gangue is mixed evenly with other components (such as cement, thickener, surfactant, etc.) and prevent coal gangue particles from accumulating or stratifying. This helps to avoid uneven particle distribution in the material and ensures the consistency of the final filler material in terms of mechanical properties. (4) Low temperature treatment and use of nitrogen atmosphere: The curing process under low temperature atmosphere helps to control the hydration rate of cement and reduce cracks or unevenness caused by temperature rise. At the same time, nitrogen atmosphere can avoid the influence of oxygen, reduce possible oxidation reactions, and help maintain the stability of the material with a high amount of coal gangue. Through the control of low temperature treatment and nitrogen atmosphere, the thermal expansion effect during cement hydration can be effectively reduced, and cracks can be avoided. The efficient mixing process and reasonable proportion ensure the water resistance, compressive strength, crack resistance and durability of the material during long-term use.

[0031] Before use, titanium gypsum undergoes heat treatment. The specific steps are as follows: After grinding and sieving the titanium gypsum, the undersize product is collected and heated at 100–150℃ for 50–70 minutes, resulting in a moisture content of 0.7–1.5%. The purpose of heat treatment is that titanium gypsum typically contains crystal water and free water in its natural state. This moisture can adversely affect the final properties of the material during the hydration reaction of cement. Heating at 100–150℃ for 50–70 minutes removes this moisture, thereby enhancing the reactivity of the titanium gypsum. Removing the moisture not only improves the reactivity of the titanium gypsum but also enhances the physical properties of the material, including compressive strength, density, durability, and workability.

[0032] Adding sodium silicate can enhance gelling properties, improve fluidity, increase durability and environmental friendliness.

[0033] Sodium carboxymethyl cellulose is a water-soluble polymer material with good water absorption, water retention, thickening, and stability, which improves the overall stability of materials, especially for paste filling materials and hydrogels.

[0034] Polyvinyl alcohol (PVA) exhibits good solubility in aqueous systems, effectively increasing the viscosity of the system and acting as a thickener. It can form a transparent, tough film in aqueous materials, enhancing the surface strength of the filler material, improving its water resistance, and simultaneously enhancing the material's mechanical properties.

[0035] This invention uses sulfoaluminate cement, coal gangue, titanium gypsum, sodium silicate, sodium carboxymethyl cellulose, and polyvinyl alcohol as raw materials, combined with low-temperature treatment under a nitrogen atmosphere, to achieve the following effects:

[0036] Synergistic effects and reactions among raw materials: (1) Sulfoaluminate cement: The calcium aluminate in sulfoaluminate cement, combined with the silicates in coal gangue, the calcium sulfate in titanium gypsum, and the activation effect of sodium silicate, can form beneficial products such as calcium silicate (CSH) during hydration, thereby enhancing the strength and durability of cement-based materials. In addition, the components of sulfoaluminate cement work together with other raw materials to improve the crack resistance and corrosion resistance of the material. (2) Coal gangue: Coal gangue is mainly composed of inorganic minerals such as silicates and aluminates. As a solid waste resource, it can be used as a reinforcing material or filler. Coal gangue mainly contains silicon, aluminum, etc., which can react with calcium and calcium sulfate in cement to generate compounds such as calcium silicate (CSH) and calcium aluminum sulfate, further improving the strength and crack resistance of cement-based materials. When coal gangue is used as aggregate, it can provide structural support and increase the compressive strength and durability of the material. (3) Titanium gypsum: Titanium gypsum (mainly calcium sulfate) reacts with the calcium in cement to form calcium aluminum sulfate, which enhances the strength, crack resistance and durability of cement. Titanium gypsum can play a role similar to gypsum in cement, delaying the setting time of cement and enhancing the stability of the material. (4) Activator: Activator can accelerate the hydration reaction in cement, promote the reaction of calcium and aluminum with components such as coal gangue and titanium gypsum, and generate calcium silicate and calcium aluminum sulfate. This can improve the strength and stability of the material. (5) Thickener: Thickener improves the fluidity and thixotropy of the slurry, avoids sedimentation and stratification, and improves workability. It can help the material maintain a uniform distribution and improve stability. (6) Surfactant: Surfactant can reduce the surface tension of cement slurry, increase the adhesion between cement and other components, improve the crack resistance and toughness of the material, and enhance the overall stability.

[0037] Synergistic effects: There are synergistic effects among the various raw materials (sulfoaluminate cement, coal gangue, titanium gypsum, activator, thickener, and surfactant). Calcium aluminate in the cement reacts with components in the coal gangue and titanium gypsum to produce calcium silicates and calcium aluminum sulfates, which enhance the strength and stability of cement-based materials. The addition of the activator accelerates the cement hydration process, further enhancing the strength and durability of the material.

[0038] Furthermore, this invention utilizes a low-temperature nitrogen atmosphere treatment, which allows the various raw materials in the filling material (sulfoaluminate cement, coal gangue, titanium gypsum, activator, thickener, and surfactant) to synergistically generate beneficial hydration products, significantly improving the compressive strength, crack resistance, durability, and workability of the filling material. The moderate reaction rate at low temperatures avoids side reactions caused by excessively high temperatures, ensuring the stability and long-term performance of the material.

[0039] The present invention discloses the following technical effects:

[0040] This invention relates to a novel goaf filling material that forms a filler with certain compressive strength and can solidify rapidly during application. This novel goaf filling material has low raw material costs and low subsequent maintenance costs, thereby improving mine utilization. It meets green mine construction standards, promotes the integration of ecological restoration and safety management in mining areas, and drives the sustainable development of the mining industry. This material has significant advantages in improving goaf safety, reducing environmental burden, and promoting the green transformation of the mining industry, demonstrating broad application prospects and economic and social value. Detailed Implementation

[0041] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0042] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0043] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0044] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0045] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0046] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0047] Unless otherwise specified, all other raw materials used in the following embodiments and comparative examples of this invention are commercially available products, and the source of these commercially available products does not affect the technical effect of this invention.

[0048] The filling materials prepared in the following embodiments and comparative examples of the present invention must meet the downhole filling requirements of "24h early strength > 1MPa and 28d compressive strength 3.0~8.0MPa".

[0049] Example 1

[0050] This embodiment provides a novel goaf filling material, which is composed of sulfoaluminate cement, coal gangue, titanium gypsum, sodium silicate powder, sodium carboxymethyl cellulose, and polyvinyl alcohol in a weight ratio of 6:2:1:0.8:0.15:0.05. The particle size requirements are as follows: sulfoaluminate cement 20 μm, coal gangue 10 mm, titanium gypsum 20 μm, and sodium silicate 50 μm.

[0051] The specific preparation steps are as follows:

[0052] (1) After grinding and sieving titanium gypsum, take the sieve product and heat it at 100℃ for 50 minutes. The moisture content after heating is 1.5%.

[0053] (2) Thoroughly mix coal gangue with cooled titanium gypsum, controlling the stirring speed at 50 rpm. Then mix with sulfoaluminate cement and sodium silicate, stirring at 80 rpm for 5 minutes. Then increase the speed to 200 rpm and slowly add sodium carboxymethyl cellulose to fully dissolve and disperse it evenly, controlling the stirring time at 3 minutes. Then increase the stirring speed to 400 rpm and add polyvinyl alcohol, maintaining continuous stirring for 3 minutes until a uniform slurry is formed.

[0054] (3) Place the well-mixed slurry in the reactor and heat it at 50°C by introducing nitrogen gas for 2 hours. During the heating process, nitrogen gas is continuously introduced to ensure that the nitrogen atmosphere concentration in the reactor is stable, and finally a filling material with a water content of 2% is obtained.

[0055] Water and the prepared filling material were mixed at a mass ratio of 1.6:1. The mixed material was allowed to stand and mature, and the compressive strength was measured at different maturation times. The results showed that the compressive strength was 0.4 MPa after 2 hours, 1.4 MPa after 24 hours, and 3.5 MPa after 28 days. This meets the downhole filling requirements.

[0056] Example 2

[0057] This embodiment provides a novel goaf filling material, which is composed of sulfoaluminate cement, coal gangue, titanium gypsum, sodium silicate powder, sodium carboxymethyl cellulose, and polyvinyl alcohol, with a weight ratio of sulfoaluminate cement:coal gangue:titanium gypsum:sodium silicate powder:sodium carboxymethyl cellulose:polyvinyl alcohol = 5:2.5:2:0.3:0.1:0.1. The particle size requirements are: sulfoaluminate cement 30μm, coal gangue 12mm, titanium gypsum 25μm, and sodium silicate 60μm.

[0058] The specific preparation steps are as follows:

[0059] (1) After grinding and sieving titanium gypsum, the undersize product is taken and heated at 110℃ for 55 minutes. The moisture content after heating is 1.2%.

[0060] (2) Thoroughly mix coal gangue with cooled titanium gypsum, controlling the stirring speed at 55 rpm. Then mix with sulfoaluminate cement and sodium silicate, stirring at 85 rpm for 5 minutes. Then increase the speed to 250 rpm and slowly add sodium carboxymethyl cellulose to fully dissolve and disperse it evenly, controlling the stirring time at 3 minutes. Then increase the stirring speed to 450 rpm and add polyvinyl alcohol, maintaining continuous stirring for 3 minutes until a uniform slurry is formed.

[0061] (3) Place the well-mixed slurry in the reactor and heat it at 55°C by introducing nitrogen gas for 2 hours. During the heating process, nitrogen gas is continuously introduced to ensure that the nitrogen atmosphere concentration in the reactor is stable, and finally a filling material with a water content of 1.8% is obtained.

[0062] Water and the prepared filling material were mixed at a mass ratio of 1.6:1. The mixed material was allowed to stand and mature, and the compressive strength was measured at different maturation times. The results showed that the compressive strength was 0.5 MPa after 2 hours, 1.6 MPa after 24 hours, and 3.8 MPa after 28 days. This meets the downhole filling requirements.

[0063] Example 3

[0064] This embodiment provides a novel goaf filling material, which is composed of sulfoaluminate cement, coal gangue, titanium gypsum, sodium silicate powder, sodium carboxymethyl cellulose, and polyvinyl alcohol, with a weight ratio of sulfoaluminate cement:coal gangue:titanium gypsum:sodium silicate powder:sodium carboxymethyl cellulose:polyvinyl alcohol = 5.5:2:1.7:0.6:0.15:0.05. The particle size requirements are: sulfoaluminate cement 40μm, coal gangue 15mm, titanium gypsum 25μm, and sodium silicate 70μm.

[0065] The specific preparation steps are as follows:

[0066] (1) After grinding and sieving titanium gypsum, the undersize product is taken and heated at 120℃ for 60 min. The moisture content after heating is 0.8%.

[0067] (2) Thoroughly mix coal gangue with cooled titanium gypsum, controlling the stirring speed at 60 rpm. Then mix with sulfoaluminate cement and sodium silicate, stirring at 90 rpm for 8 minutes. Then increase the speed to 200 rpm and slowly add sodium carboxymethyl cellulose to fully dissolve and disperse it evenly, controlling the stirring time at 5 minutes. Then increase the stirring speed to 450 rpm and add polyvinyl alcohol, maintaining continuous stirring for 5 minutes until a uniform slurry is formed.

[0068] (3) Place the uniformly mixed material in the reactor and heat it at 60°C by introducing nitrogen gas for 2 hours. During the heating process, nitrogen gas is continuously introduced to ensure that the nitrogen atmosphere concentration in the reactor is stable, and finally a filling material with a water content of 1.4% is obtained.

[0069] Water and the prepared filling material were mixed at a mass ratio of 1.6:1. The mixed material was allowed to stand and mature, and the compressive strength was measured at different maturation times. The results showed that the compressive strength was 0.7 MPa after 2 hours, 1.9 MPa after 24 hours, and 4 MPa after 28 days. This meets the downhole filling requirements.

[0070] Example 4

[0071] This embodiment provides a novel goaf filling material, which is composed of sulfoaluminate cement, coal gangue, titanium gypsum, sodium silicate powder, sodium carboxymethyl cellulose, and polyvinyl alcohol, with a weight ratio of sulfoaluminate cement:coal gangue:titanium gypsum:sodium silicate powder:sodium carboxymethyl cellulose:polyvinyl alcohol = 5:2.5:2:0.4:0.05:0.05. The particle size requirements are: sulfoaluminate cement 50μm, coal gangue 20mm, titanium gypsum 30μm, and sodium silicate 100μm.

[0072] The specific preparation steps are as follows:

[0073] (1) After grinding and sieving titanium gypsum, the undersize product is taken and heated at 150℃ for 70 min. The moisture content after heating is 0.7%.

[0074] (2) Thoroughly mix coal gangue with cooled titanium gypsum, controlling the stirring speed at 70 rpm. Then mix with sulfoaluminate cement and sodium silicate, stirring at 100 rpm for 10 min. Then increase the speed to 300 rpm and slowly add sodium carboxymethyl cellulose to fully dissolve and disperse it evenly, controlling the stirring time at 5 min. Then increase the stirring speed to 500 rpm and add polyvinyl alcohol, maintaining continuous stirring for 5 min until a uniform slurry is formed.

[0075] (3) Place the uniformly mixed material in the reactor and heat it at 70°C by introducing nitrogen gas for 3 hours. During the heating process, nitrogen gas is continuously introduced to ensure that the nitrogen atmosphere concentration in the reactor is stable, and finally a filling material with a water content of 1% is obtained.

[0076] Water and the prepared filling material were mixed at a mass ratio of 1.6:1. The mixed material was allowed to stand and mature, and the compressive strength was measured at different maturation times. The results showed that the compressive strength was 0.8 MPa after 2 hours, 2 MPa after 24 hours, and 4.3 MPa after 28 days. This meets the downhole filling requirements.

[0077] Comparative Example 1

[0078] The preparation method is the same as in Example 1, except that the mass ratio of sulfoaluminate cement, coal gangue, titanium gypsum, sodium silicate powder, sodium carboxymethyl cellulose, and polyvinyl alcohol is 7:1:1:0.9:0.05:0.05.

[0079] Testing revealed that the compressive strength was 0.1 MPa after 2 hours, 0.7 MPa after 24 hours, and 2.4 MPa after 28 days. This does not meet the requirements for downhole filling.

[0080] Comparative Example 2

[0081] The preparation method is the same as in Example 2, except that the mass ratio of sulfoaluminate cement, coal gangue, titanium gypsum, sodium silicate powder, sodium carboxymethyl cellulose, and polyvinyl alcohol is 4:3.5:1:1.3:0.15:0.05.

[0082] Testing revealed that the compressive strength was 0.09 MPa at 2 hours, 0.5 MPa at 24 hours, and 2.2 MPa at 28 days. This does not meet the requirements for downhole filling.

[0083] Comparative Example 3

[0084] The preparation method is the same as in Example 3, except that the mass ratio of sulfoaluminate cement, coal gangue, titanium gypsum, sodium silicate powder, sodium carboxymethyl cellulose, and polyvinyl alcohol is 6.5:1.7:1:0.5:0.3:0.1.

[0085] Testing revealed that the compressive strength was 0.07 MPa after 2 hours, 0.4 MPa after 24 hours, and 1.8 MPa after 28 days. This does not meet the requirements for downhole filling.

[0086] Comparative Example 4

[0087] The preparation method is the same as in Example 4, except that the mass ratio of sulfoaluminate cement, coal gangue, titanium gypsum, sodium silicate powder, sodium carboxymethyl cellulose, and polyvinyl alcohol is 4:4:1:0.4:0.4:0.1.

[0088] Testing revealed that the compressive strength was 0.02 MPa after 2 hours, 0.2 MPa after 24 hours, and 1.5 MPa after 28 days. This does not meet the requirements for downhole filling.

[0089] Comparative Example 5

[0090] The preparation method is the same as in Example 4, except that the "low-temperature heating by introducing nitrogen at 70°C" was not performed.

[0091] Testing revealed that the compressive strength was 0.05 MPa at 2 hours, 0.35 MPa at 24 hours, and 1.66 MPa at 28 days. This does not meet the requirements for downhole filling.

[0092] Comparative Example 6

[0093] The preparation method is the same as in Example 4, except that sodium silicate is omitted and the weight ratio of each raw material is adjusted to: sulfoaluminate cement: coal gangue: titanium gypsum: sodium carboxymethyl cellulose: polyvinyl alcohol = 5:2.5:2.4:0.05:0.05.

[0094] Testing revealed a compressive strength of 0.01 MPa after 2 hours and 0.15 MPa after 24 hours. This does not meet the early downhole filling requirements.

[0095] Comparative Example 7

[0096] The preparation method is the same as in Example 4, except that sodium silicate is adjusted to an equal amount of sodium tripolyphosphate. That is, the filling material is a mixture of sulfoaluminate cement, coal gangue, titanium gypsum, sodium tripolyphosphate, sodium carboxymethyl cellulose, and polyvinyl alcohol, with a weight ratio of sulfoaluminate cement: coal gangue: titanium gypsum: sodium tripolyphosphate: sodium carboxymethyl cellulose: polyvinyl alcohol = 5:2.5:2:0.4:0.05:0.05. The particle size requirements are: sulfoaluminate cement 50 μm, coal gangue 20 mm, titanium gypsum 30 μm, and sodium tripolyphosphate 100 μm.

[0097] The specific preparation steps are as follows:

[0098] (1) After grinding and sieving titanium gypsum, the undersize product is taken and heated at 150℃ for 70 min. The moisture content after heating is 0.7%.

[0099] (2) Thoroughly mix coal gangue with cooled titanium gypsum, controlling the stirring speed at 70 rpm. Then mix with sulfoaluminate cement and sodium tripolyphosphate, stirring at 100 rpm for 10 min. Then increase the speed to 300 rpm and slowly add sodium carboxymethyl cellulose to fully dissolve and disperse it evenly, controlling the stirring time at 5 min. Then increase the stirring speed to 500 rpm and add polyvinyl alcohol, and continue stirring for 5 min until a uniform slurry is formed.

[0100] (3) Place the uniformly mixed material in the reactor and heat it at 70°C by introducing nitrogen gas for 3 hours. During the heating process, nitrogen gas is continuously introduced to ensure that the nitrogen atmosphere concentration in the reactor is stable, and finally a filling material with a water content of 1% is obtained.

[0101] Water and the prepared filling material were mixed at a mass ratio of 1.6:1. The mixed material was allowed to stand and mature, and the compressive strength was measured at different maturation times. The results showed that the compressive strength was 0.35 MPa at 2 hours, 0.8 MPa at 24 hours, and 2.7 MPa at 28 days. This does not meet the downhole filling requirements.

[0102] Comparative Example 8

[0103] The preparation method is the same as in Example 4, except that sodium silicate is adjusted to an equal amount of aluminate. That is, the filling material is a mixture of sulfoaluminate cement, coal gangue, titanium gypsum, aluminate, sodium carboxymethyl cellulose, and polyvinyl alcohol, with a weight ratio of sulfoaluminate cement: coal gangue: titanium gypsum: aluminate: sodium carboxymethyl cellulose: polyvinyl alcohol = 5:2.5:2:0.4:0.05:0.05. The particle size requirements are: sulfoaluminate cement 50 μm, coal gangue 20 mm, titanium gypsum 30 μm, and aluminate 100 μm.

[0104] The specific preparation steps are as follows:

[0105] (1) After grinding and sieving titanium gypsum, the undersize product is taken and heated at 150℃ for 70 min. The moisture content after heating is 0.7%.

[0106] (2) Thoroughly mix coal gangue with cooled titanium gypsum, controlling the stirring speed at 70 rpm. Then mix with sulfoaluminate cement and aluminate, stirring at 100 rpm for 10 min. Then increase the speed to 300 rpm and slowly add sodium carboxymethyl cellulose to fully dissolve and disperse it evenly, controlling the stirring time at 5 min. Then increase the stirring speed to 500 rpm and add polyvinyl alcohol, maintaining continuous stirring for 5 min until a uniform slurry is formed.

[0107] (3) Place the uniformly mixed material in the reactor and heat it at 70°C by introducing nitrogen gas for 3 hours. During the heating process, nitrogen gas is continuously introduced to ensure that the nitrogen atmosphere concentration in the reactor is stable, and finally a filling material with a water content of 1% is obtained.

[0108] Water and the prepared filling material were mixed at a mass ratio of 1.6:1. The mixed material was allowed to stand and mature, and the compressive strength was measured at different maturation times. The results showed a compressive strength of 0.1 MPa after 2 hours and 0.5 MPa after 24 hours. This does not meet the requirements for early downhole filling.

[0109] Comparative Example 9

[0110] The preparation method is the same as in Example 4, except that sodium carboxymethyl cellulose is adjusted to an equal amount of xanthan gum. That is, the filling material is a mixture of sulfoaluminate cement, coal gangue, titanium gypsum, sodium silicate powder, xanthan gum, and polyvinyl alcohol, with a weight ratio of sulfoaluminate cement: coal gangue: titanium gypsum: sodium silicate powder: xanthan gum: polyvinyl alcohol = 5:2.5:2:0.4:0.05:0.05. The particle size requirements are: sulfoaluminate cement 50 μm, coal gangue 20 mm, titanium gypsum 30 μm, and sodium silicate 100 μm.

[0111] The specific preparation steps are as follows:

[0112] (1) After grinding and sieving titanium gypsum, the undersize product is taken and heated at 150℃ for 70 min. The moisture content after heating is 0.7%.

[0113] (2) Mix the coal gangue with the cooled titanium gypsum thoroughly, and control the stirring speed at 70 rpm. Then mix it with sulfoaluminate cement and sodium silicate, and stir at 100 rpm for 10 min. Then increase the speed to 300 rpm and slowly add xanthan gum to fully dissolve and disperse it evenly. Control the stirring time at 5 min. Then increase the stirring speed to 500 rpm and add polyvinyl alcohol, and continue stirring for 5 min until a uniform slurry is formed.

[0114] (3) Place the uniformly mixed material in the reactor and heat it at 70°C by introducing nitrogen gas for 3 hours. During the heating process, nitrogen gas is continuously introduced to ensure that the nitrogen atmosphere concentration in the reactor is stable, and finally a filling material with a water content of 1% is obtained.

[0115] Water and the prepared filling material were mixed at a mass ratio of 1.6:1. The mixed material was allowed to stand and mature, and the compressive strength was measured at different maturation times. The results showed a compressive strength of 0.33 MPa at 2 hours, 1.2 MPa at 24 hours, and 2.6 MPa at 28 days. This does not meet the requirements for subsequent downhole filling.

[0116] Comparative Example 10

[0117] The preparation method is the same as in Example 4, except that sodium carboxymethyl cellulose is replaced with an equal amount of polyacrylamide. That is, the filling material is a mixture of sulfoaluminate cement, coal gangue, titanium gypsum, sodium silicate powder, polyacrylamide, and polyvinyl alcohol, with a weight ratio of sulfoaluminate cement: coal gangue: titanium gypsum: sodium silicate powder: polyacrylamide: polyvinyl alcohol = 5:2.5:2:0.4:0.05:0.05. The particle size requirements are: sulfoaluminate cement 50 μm, coal gangue 20 mm, titanium gypsum 30 μm, and sodium silicate 100 μm.

[0118] The specific preparation steps are as follows:

[0119] (1) After grinding and sieving titanium gypsum, the undersize product is taken and heated at 150℃ for 70 min. The moisture content after heating is 0.7%.

[0120] (2) Mix the coal gangue with the cooled titanium gypsum thoroughly, and control the stirring speed at 70 rpm. Then mix it with sulfoaluminate cement and sodium silicate, and stir at 100 rpm for 10 min. Then increase the speed to 300 rpm and slowly add polyacrylamide to fully dissolve and disperse it evenly, and control the stirring time at 5 min. Then increase the stirring speed to 500 rpm and add polyvinyl alcohol, and continue stirring for 5 min until a uniform slurry is formed.

[0121] (3) Place the uniformly mixed material in the reactor and heat it at 70°C by introducing nitrogen gas for 3 hours. During the heating process, nitrogen gas is continuously introduced to ensure that the nitrogen atmosphere concentration in the reactor is stable, and finally a filling material with a water content of 1% is obtained.

[0122] Water and the prepared filling material were mixed at a mass ratio of 1.6:1. The mixed material was allowed to stand for curing, and the compressive strength was measured at different curing times. The results showed that the compressive strength was 0.25 MPa at 2 hours, 0.58 MPa at 24 hours, and 2.69 MPa at 28 days. This does not meet the downhole filling requirements.

[0123] Comparative Example 11

[0124] The preparation method is the same as in Example 4, except that the polyvinyl alcohol is adjusted to an equal amount of fatty alcohol ether. That is, the filling material is a mixture of sulfoaluminate cement, coal gangue, titanium gypsum, sodium silicate powder, sodium carboxymethyl cellulose, and fatty alcohol ether, with a weight ratio of sulfoaluminate cement: coal gangue: titanium gypsum: sodium silicate powder: sodium carboxymethyl cellulose: fatty alcohol ether = 5:2.5:2:0.4:0.05:0.05. The particle size requirements are: sulfoaluminate cement 50 μm, coal gangue 20 mm, titanium gypsum 30 μm, and sodium silicate 100 μm.

[0125] The specific preparation steps are as follows:

[0126] (1) After grinding and sieving titanium gypsum, the undersize product is taken and heated at 150℃ for 70 min. The moisture content after heating is 0.7%.

[0127] (2) Thoroughly mix coal gangue with cooled titanium gypsum, controlling the stirring speed at 70 rpm. Then mix with sulfoaluminate cement and sodium silicate, stirring at 100 rpm for 10 min. Then increase the speed to 300 rpm and slowly add sodium carboxymethyl cellulose to fully dissolve and disperse it evenly, controlling the stirring time at 5 min. Then increase the stirring speed to 500 rpm and add fatty alcohol ether, and continue stirring for 5 min until a uniform slurry is formed.

[0128] (3) Place the uniformly mixed material in the reactor and heat it at 70°C by introducing nitrogen gas for 3 hours. During the heating process, nitrogen gas is continuously introduced to ensure that the nitrogen atmosphere concentration in the reactor is stable, and finally a filling material with a water content of 1% is obtained.

[0129] Water and the prepared filling material were mixed at a mass ratio of 1.6:1. The mixed material was allowed to stand for curing, and the compressive strength was measured at different curing times. The results showed that the compressive strength was 0.28 MPa at 2 hours, 0.76 MPa at 24 hours, and 2.49 MPa at 28 days. This does not meet the downhole filling requirements.

[0130] Comparative Example 12

[0131] The preparation method is the same as in Example 4, except that the polyvinyl alcohol is adjusted to an equal amount of alkyl polyglycoside. That is, the filling material is a mixture of sulfoaluminate cement, coal gangue, titanium gypsum, sodium silicate powder, sodium carboxymethyl cellulose, and alkyl polyglycoside, with a weight ratio of: sulfoaluminate cement: coal gangue: titanium gypsum: sodium silicate powder: sodium carboxymethyl cellulose: alkyl polyglycoside = 5:2.5:2:0.4:0.05:0.05. The particle size requirements are: sulfoaluminate cement 50 μm, coal gangue 20 mm, titanium gypsum 30 μm, and sodium silicate 100 μm.

[0132] The specific preparation steps are as follows:

[0133] (1) After grinding and sieving titanium gypsum, the undersize product is taken and heated at 150℃ for 70 min. The moisture content after heating is 0.7%.

[0134] (2) Thoroughly mix coal gangue with cooled titanium gypsum, controlling the stirring speed at 70 rpm. Then mix with sulfoaluminate cement and sodium silicate, stirring at 100 rpm for 10 min. Then increase the speed to 300 rpm and slowly add sodium carboxymethyl cellulose to fully dissolve and disperse it evenly, controlling the stirring time at 5 min. Then increase the stirring speed to 500 rpm and add alkyl polyglycosides, maintaining continuous stirring for 5 min until a uniform slurry is formed.

[0135] (3) Place the uniformly mixed material in the reactor and heat it at 70°C by introducing nitrogen gas for 3 hours. During the heating process, nitrogen gas is continuously introduced to ensure that the nitrogen atmosphere concentration in the reactor is stable, and finally a filling material with a water content of 1% is obtained.

[0136] Water and the prepared filling material were mixed at a mass ratio of 1.6:1. The mixed material was allowed to stand and mature, and the compressive strength was measured at different maturation times. The results showed a compressive strength of 0.1 MPa after 2 hours and 0.37 MPa after 24 hours. This does not meet the requirements for early downhole filling.

[0137] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0138] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A novel goaf filling material, characterized in that, By weight percentage, it includes: 45-60% sulfoaluminate cement, 15-25% coal gangue, 10-25% titanium gypsum, 3-8% activator, 0.5-1.5% thickener, and 0.5-1% surfactant.

2. The novel goaf filling material according to claim 1, characterized in that, By weight percentage, it includes: 50% sulfoaluminate cement, 25% coal gangue, 20% titanium gypsum, 4% activator, 0.5% thickener and 0.5% surfactant.

3. The novel goaf filling material according to claim 1 or 2, characterized in that, The particle size of the coal gangue is 10-20 mm.

4. The novel goaf filling material according to claim 1 or 2, characterized in that, The activator includes one or more of sodium silicate, sodium tripolyphosphate, and aluminate; and / or the thickener includes one or more of sodium carboxymethyl cellulose, xanthan gum, and polyacrylamide; and / or the surfactant includes one or more of polyvinyl alcohol, fatty alcohol ether, and alkyl polyglycoside.

5. The novel goaf filling material according to claim 1 or 2, characterized in that, The water content of the titanium gypsum is 0.7-1.5%; and / or the water content of the novel goaf filling material is 1-2%.

6. The method for preparing the novel goaf filling material according to any one of claims 1 to 5, characterized in that, The steps include the following: The sulfoaluminate cement, coal gangue, titanium gypsum, activator, thickener, surfactant and water are mixed to obtain a mixture; the mixture is then subjected to low-temperature treatment under a nitrogen atmosphere to obtain the novel goaf filling material.

7. The preparation method according to claim 6, characterized in that, The mixing steps include: mixing coal gangue and titanium gypsum at a stirring speed of 50-70 rpm, then adding sulfoaluminate cement and an activator and mixing at a stirring speed of 80-100 rpm for 5-10 minutes, then increasing the stirring speed to 200-300 rpm, adding a thickener and stirring for 3-5 minutes, then increasing the stirring speed to 400-500 rpm, adding a surfactant and stirring for 3-5 minutes to obtain a mixture.

8. The preparation method according to claim 6, characterized in that, The low-temperature treatment is performed at a temperature of 50–70°C for 2–3 hours.

9. The application of the novel goaf filling material according to any one of claims 1 to 5 in goaf filling.

10. A method for improving the effectiveness of goaf treatment, characterized in that, The method includes the following steps: filling the goaf with the novel goaf filling material prepared by the preparation method according to any one of claims 6 to 8.