A heavy filling material, its preparation method and application

Abstract

The present invention relates to a heavy filling material for coal mines and a preparation method thereof. The material includes components such as modified iron tailings, fly ash, wollastonite and fibers. By using a composite modification system of calcium activator and sodium activator, the activity of calcined iron tailings is effectively improved, promoting the formation of abundant C-S-H gel and C-A-S-H gel. The modified iron tailings with different particle sizes are mixed and used, optimizing the particle size combination of the filling material, and thus significantly improving the compressive strength, density and water resistance of the filling body. Combined with fly ash, wollastonite and fibers, the compactness, compressive strength and water resistance of the filling body are further improved. The synergistic effect of fibers, wollastonite and fly ash is beneficial to improving the comprehensive performance of the filling body, and is particularly suitable for applications in coal mine filling.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal mine safety production, and particularly relates to a heavy filling material, a preparation method thereof and an application thereof. Background Art

[0002] Underground coal mining often causes a series of serious problems, such as rock stratum rupture, surface subsidence, groundwater system damage and environmental pollution. These challenges make the scientific mining of coal extremely difficult. As an environmentally friendly mining technology, the filling mining technology plays an important role in the scientific mining of coal. Cemented filling, as a key branch of coal mine filling mining technology, fills the goaf with cementitious materials to support the surrounding rock strata, reduces the impact of mining activities on the overlying rock strata, improves the recovery rate of resources, and reduces the discharge of surface waste, thereby reducing environmental pollution. This technology has been widely applied in coal mines at home and abroad. The core of the cemented filling mining technology lies in the selection of filling materials, because the performance of the materials directly affects the implementation effect of the filling mining process and the effectiveness of rock stratum control. Generally, coal mine cemented filling materials are made by mixing solid wastes such as tailings slag and fly ash with cementitious materials and adding water for stirring. In typical cemented filling materials, the content of cementitious materials is about between 15% and 40%, and the mass concentration of the slurry is between 60% and 85%.

[0003] In the filling operation in the small coal mine damaged area, the high-water filling material is widely used because of its simple construction. However, the density of this material is usually 1.11 - 1.16 g / cm 3 , which is lower than the density of coal and gangue, 1.4 g / cm 3 . This density difference makes it difficult to effectively wash the area filled with high-water materials or the parts adjacent to it by the heavy medium coal preparation method, which in turn affects the coal quality and reduces the economic benefits of coal. Summary of the Invention

[0004] Aiming at the technical problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a heavy filling material, a preparation method thereof and an application thereof, so as to solve the problems of low density, poor fluidity and poor water resistance of the filling materials in the prior art. The filling material significantly improves the density, compressive strength and water resistance of the filling body by modifying iron tailings and cooperating with fly ash, wollastonite and fibers, and is particularly suitable for applications in coal mine filling.

[0005] A heavy filling material provided by the present invention, the filling material comprises the following components in parts by weight: 40 - 80 parts of modified iron tailings, 10 - 30 parts of fly ash, 10 - 20 parts of wollastonite, 5 - 10 parts of fibers, 1 - 8 parts of accelerating agent, 1 - 8 parts of suspending agent, 1 - 3 parts of water reducing agent, and 120 - 300 parts of water.

[0006] The preparation method of the modified iron tailings comprises the following steps:

[0007] S1. Crush 100 parts by weight of iron tailings and dry them, then mix them evenly with 10 - 15 parts by weight of an activator. The activator includes a sodium activator and a calcium activator. The sodium activator includes at least one of sodium chloride, sodium sulfate, and sodium hydroxide; the calcium activator includes at least one of calcium hydroxide, calcium oxide, calcium chloride, and gypsum. The mass ratio of the sodium activator to the calcium activator is 1 - 3:5 - 10;

[0008] S2. Convey the evenly mixed materials in step S1 to a rotary kiln for calcination, cooling, and grinding. Then, screen them through 10 - mm and 5 - mm sieves respectively to obtain fine particles with d1 < 5 mm and coarse particles with 5 ≤ d2 < 10 mm. Mix the fine particles and the coarse particles evenly according to the mass ratio of 1 - 3:5 - 8 to obtain the modified iron tailings.

[0009] The fiber includes at least one of glass fiber, polypropylene fiber, polyester fiber, and basalt fiber, and the length of the fiber is 2 - 10 mm; further preferably, the length of the fiber is 4 - 8 microns.

[0010] The water - reducing agent includes at least one of naphthalene - based water - reducing agent, melamine water - reducing agent, and polycarboxylate water - reducing agent.

[0011] The accelerating agent includes at least one of sodium metaaluminate, sodium sulfate, and sodium carbonate.

[0012] The suspending agent includes at least one of sodium carboxymethyl cellulose, water - soluble polyvinyl alcohol, and hydroxypropyl methylcellulose.

[0013] In step S2, the calcination temperature is 800 - 1400 °C and the calcination time is 2 - 5 h.

[0014] The present invention also provides a method for preparing a heavy filling material, which comprises the following steps:

[0015] 1) Accurately weigh 40 - 80 parts of modified iron tailings, 10 - 30 parts of fly ash, 10 - 20 parts of wollastonite, 5 - 10 parts of fiber, 1 - 8 parts of accelerating agent, 1 - 8 parts of suspending agent, and 120 - 300 parts of water;

[0016] 2) First, mix the modified iron tailings, fly ash, wollastonite, fiber, accelerating agent, and suspending agent evenly, and then mix them evenly with water to prepare the heavy filling material.

[0017] In step 2), there are no specific requirements for the mixing temperature and time, as long as the materials are mixed evenly. Further preferably, the mixing temperature is 20 - 40 °C and the mixing time is 20 - 60 min.

[0018] The present invention also relates to the application of a heavy filling material in coal mine filling, which is characterized in that after the filling materials are mixed, the filling materials are pumped to the use site.

[0019] The present invention adopts the combination of a sodium activator and a calcium activator, which can effectively improve the activity of calcined iron tailings, optimize its microstructure, and enhance the durability. The application of this composite activator can accelerate the dissolution process of silicate and aluminate in iron tailings, promote the formation of abundant hydration products, such as C-S-H gel and C-A-S-H gel, and thus significantly improve the strength of the material. In addition, the generated hydration products, especially C-S-H gel, further enhance the durability and density of the material due to its excellent compactness and anti-permeability performance.

[0020] The present invention uses modified iron tailings with different particle sizes in combination, optimizes the particle size composition of the filling material, effectively improves its rheological properties, and thus enhances the stability and fluidity of the filling body. In this method, the coarse-grained modified iron tailings construct a solid skeleton, providing the necessary support for the filling body; the fine-grained iron tailings penetrate and fill the voids between the coarse grains, further improving the compactness of the filling body. This scientific ratio of coarse and fine particle sizes promotes the uniform distribution of internal stress in the filling body, effectively avoids the problem of stress concentration, and enhances the overall stability of the filling body. At the same time, the filling effect of the fine-grained iron tailings also increases the density of the filling body, ensuring the long-term stability and safety of the project. Through this innovative particle size matching strategy, the present invention significantly improves the performance of the filling material, providing strong technical support for the sustainable development of coal mines.

[0021] The second concept of the present invention lies in that the combination of modified iron tailings and fibers can effectively improve the mechanical properties and stability of the filling body. The modified iron tailings play a cementing role in the filling body, forming hydration products such as calcium silicate hydrate (C-S-H) gel, enhancing the early strength of the filling body. The addition of fibers further strengthens the structure of the filling body. The fibers form a network structure in the filling body, improving its crack resistance and ductility. This strengthening effect of the structure reduces the internal defects of the filling body, optimizes the internal pore structure, and thus improves the compressive strength of the filling body. At the same time, the addition of fibers can also improve the rheological properties of the filling material, enhancing its fluidity and stability, which is of great significance for improving the filling efficiency and reducing the loss during the filling process.

[0022] Furthermore, appropriately increasing the fiber length can increase its contact area with the filling body matrix, enhance the cohesion and structural stability, and thus improve the strength and density of the filling body; however, if the fiber length is too long, it may reduce the fluidity of the slurry, increase the viscosity and yield stress, and affect the uniformity and compactness of the filling body. The fiber length is 2-10 mm; further preferably, the fiber length is 4-8 microns.

[0023] The present invention utilizes the high-density characteristic of wollastonite, whose density value ranges from 2.75 to 2.91 g / cm 3 , and this high-density characteristic helps to improve the stability and compactness of the filling body, thereby enhancing the density and compressive strength of the filling body.

[0024] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0025] 1) The present invention mainly uses iron tailings, fly ash, etc. to prepare filling materials, avoiding environmental pollution by solid waste and greatly reducing the cost of preparing filling materials; the combination of sodium activator and calcium activator can effectively improve the activity of calcined iron tailings and further enhance the strength and density of the filling body. The modified iron tailings with different particle sizes are mixed and used. The coarse-grained modified iron tailings construct a solid framework, providing necessary support for the filling body; the fine-grained iron tailings penetrate and fill the voids between the coarse grains, further improving the density, strength and water resistance of the filling body.

[0026] 2) By combining modified iron tailings with fibers, the present invention significantly improves the mechanical properties and stability of the filling body. The modified iron tailings play a cementing role in the filling body, enhancing the early strength of the filling body by forming hydration products such as calcium silicate hydrate (C-S-H) gel. At the same time, the fibers construct a network structure in the filling body, further improving the strength of the filling body. In addition, using wollastonite with a relatively large density as a filling material further enhances the density and compressive strength of the filling body. Due to its pozzolanic activity, fly ash can generate more hydration products such as C-S-H gel, thereby further improving the compactness, compressive strength and water resistance of the filling body. Generally speaking, the synergistic effect of modified iron tailings, fibers, wollastonite and fly ash jointly improves the comprehensive performance of the filling body.

[0027] 3) The raw materials such as iron tailings, fly ash and wollastonite used in the present invention are not only widely sourced but also low in cost. At the construction site, the required filling materials can be quickly prepared by simply mixing and stirring. This method greatly simplifies the on-site operation process, significantly reduces the production cost, and greatly improves the construction efficiency. Specific Embodiments

[0028] The technical solution of the present invention will be further described below in conjunction with and through specific embodiments. However, the following examples are merely simple examples of the present invention and do not represent or limit the scope of the patent protection of the present invention. The scope of protection of the present invention is subject to the claims.

[0029] Experimental Materials:

[0030] The iron tailings used in the present invention are derived from the tailings produced by iron ore dressing plants, and the main chemical components are silicon dioxide, iron oxide, aluminum oxide, magnesium oxide, calcium oxide, etc. The specific composition is as follows: SiO2 62.11%, CaO 3.11%, MgO 4.34%, Al2O3 13.81%, Fe2O3 11.26%, K2O 2.33%, Na2O 0.64%, and others 2.40%.

[0031] The average particle size of wollastonite is 30 - 50 μm, and the average particle size of fly ash is 20 - 40 μm. All other raw materials are commercially available.

[0032] Example 1

[0033] This example provides a heavy filling material with the following formula: 40 parts of modified iron tailings, 30 parts of fly ash, 20 parts of wollastonite, 8 parts of fiber, 4 parts of quick-setting agent, 5 parts of suspending agent, 2 parts of water reducing agent, and 150 parts of water.

[0034] The preparation method of the modified iron tailings includes the following steps:

[0035] S1. Crush and dry 100 parts by weight of iron tailings, and mix them evenly with 10 parts by weight of an activator. The activator includes a sodium activator and a calcium activator. The sodium activator includes sodium chloride, and the calcium activator includes calcium hydroxide. The mass ratio of the sodium activator to the calcium activator is 1:5;

[0036] S2. Transport the uniformly mixed materials in step S1 to a rotary kiln, calcine them at 800 °C for 5 h, cool, grind, and pass through 10 - mm and 5 - mm sieves respectively to obtain a fine particle size with d1 < 5 mm and a coarse particle size with 5 ≤ d2 < 10 mm. Mix the fine particle size and the coarse particle size evenly according to a mass ratio of 1:5 to obtain the modified iron tailings.

[0037] The fiber is glass fiber with a length of 6 mm.

[0038] The water reducing agent is a naphthalene - based water reducing agent.

[0039] The quick - setting agent is sodium metaaluminate.

[0040] The suspending agent is sodium carboxymethyl cellulose.

[0041] This example also provides a method for preparing a heavy filling material, including the following steps:

[0042] 1) Accurately weigh 40 parts of modified iron tailings, 30 parts of fly ash, 20 parts of wollastonite, 8 parts of fiber, 4 parts of quick - setting agent, 5 parts of suspending agent, 2 parts of water reducing agent, and 150 parts of water;

[0043] 2) First, uniformly mix the modified iron tailings, fly ash, wollastonite, fiber, accelerating agent, and suspending agent, and then uniformly mix with water to prepare a heavy filling material.

[0044] Example 2

[0045] This example provides a heavy filling material with the following formula: 60 parts of modified iron tailings, 15 parts of fly ash, 20 parts of wollastonite, 10 parts of fiber, 5 parts of accelerating agent, 4 parts of suspending agent, 3 parts of water reducing agent, and 200 parts of water.

[0046] Among them, the preparation method of the modified iron tailings includes the following steps:

[0047] S1. Crush and dry 100 parts by weight of iron tailings, and uniformly mix with 15 parts by weight of an activator. The activator includes a sodium activator and a calcium activator. The sodium activator includes sodium sulfate; the calcium activator includes gypsum, and the mass ratio of the sodium activator to the calcium activator is 2:7;

[0048] S2. Convey the uniformly mixed material in step S1 to a rotary kiln, calcine at 1000 °C for 3 h, cool, grind, and pass through 10 mm and 5 mm sieves respectively to obtain a fine particle size with d1 < 5 mm and a coarse particle size with 5 ≤ d2 < 10 mm. Mix the fine particle size and the coarse particle size evenly according to a mass ratio of 3:8 to obtain the modified iron tailings.

[0049] The fiber is basalt fiber with a length of 10 mm.

[0050] The water reducing agent is melamine water reducing agent.

[0051] The accelerating agent is sodium carbonate.

[0052] The suspending agent is water-soluble polyvinyl alcohol.

[0053] This example also provides a method for preparing a heavy filling material, including the following steps:

[0054] 1) Accurately weigh 60 parts of modified iron tailings, 15 parts of fly ash, 20 parts of wollastonite, 10 parts of fiber, 5 parts of accelerating agent, 4 parts of suspending agent, 3 parts of water reducing agent, and 200 parts of water;

[0055] 2) First, uniformly mix the modified iron tailings, fly ash, wollastonite, fiber, accelerating agent, and suspending agent, and then uniformly mix with water to prepare a heavy filling material.

[0056] Example 3

[0057] This example provides a heavy filling material with the following formula: 70 parts of modified iron tailings, 10 parts of fly ash, 10 parts of wollastonite, 10 parts of fiber, 2 parts of accelerating agent, 3 parts of suspending agent, 3 parts of water reducing agent, and 180 parts of water.

[0058] The preparation method of the modified iron tailings includes the following steps:

[0059] S1. Crush and dry 100 parts by weight of iron tailings, and mix them evenly with 12 parts by weight of an activator. The activator includes a sodium activator and a calcium activator. The sodium activator includes sodium chloride and sodium sulfate in a 1:1 combination; the calcium activator is calcium oxide, and the mass ratio of the sodium activator to the calcium activator is 3:10;

[0060] S2. Convey the materials evenly mixed in step S1 to a rotary kiln, calcine at 1100 °C for 3 h, cool, grind, and pass through 10 mm and 5 mm sieves respectively to obtain a fine particle size with d1 < 5 mm and a coarse particle size with 5 ≤ d2 < 10 mm. Mix the fine particle size and the coarse particle size evenly according to a mass ratio of 3:5 to obtain the modified iron tailings.

[0061] The fiber is polypropylene fiber, and the length of the fiber is 8 mm.

[0062] The water reducing agent is melamine water reducing agent.

[0063] The accelerating agent is sodium sulfate.

[0064] The suspending agent is hydroxypropyl methyl cellulose.

[0065] This embodiment also provides a method for a heavy filling material, including the following steps:

[0066] 1) Accurately weigh 70 parts of modified iron tailings, 10 parts of fly ash, 10 parts of wollastonite, 10 parts of fiber, 2 parts of accelerating agent, 3 parts of suspending agent, 3 parts of water reducing agent, and 180 parts of water;

[0067] 2) First, mix the modified iron tailings, fly ash, wollastonite, fiber, accelerating agent, and suspending agent evenly, and then mix them evenly with water to make a heavy filling material.

[0068] Example 4

[0069] This embodiment provides a heavy filling material, and the formula is: 80 parts of modified iron tailings, 15 parts of fly ash, 20 parts of wollastonite, 6 parts of fiber, 1 part of accelerating agent, 3 parts of suspending agent, 3 parts of water reducing agent, and 230 parts of water.

[0070] The preparation method of the modified iron tailings includes the following steps:

[0071] S1. Crush and dry 100 parts by weight of iron tailings, and mix them evenly with 10 parts by weight of an activator. The activator includes a sodium activator and a calcium activator. The sodium activator is a combination of sodium sulfate and sodium hydroxide in a 1:2 ratio; the calcium activator includes calcium chloride and gypsum in a 2:1 combination, and the mass ratio of the sodium activator to the calcium activator is 1:6;

[0072] S2. Transfer the uniformly mixed materials in step S1 to a rotary kiln, calcine at 1200 °C for 2.5 h, cool, grind, and pass through 10-mm and 5-mm sieves respectively to obtain fine particles with d1 < 5 mm and coarse particles with 5 ≤ d2 < 10 mm. Mix the fine particles and the coarse particles evenly according to a mass ratio of 2:7 to obtain modified iron tailings.

[0073] The fiber is glass fiber with a length of 10 mm.

[0074] The water reducing agent is a naphthalene-based water reducing agent.

[0075] The accelerating agent is sodium carbonate.

[0076] The suspending agent is hydroxypropyl methylcellulose.

[0077] This embodiment also provides a method for preparing a heavy filling material, including the following steps:

[0078] 1) Accurately weigh 80 parts of modified iron tailings, 15 parts of fly ash, 20 parts of wollastonite, 6 parts of fiber, 1 part of accelerating agent, 3 parts of suspending agent, 3 parts of water reducing agent, and 230 parts of water;

[0079] 2) First, mix the modified iron tailings, fly ash, wollastonite, fiber, accelerating agent, and suspending agent evenly, and then mix them evenly with water to prepare a heavy filling material.

[0080] Example 5

[0081] This embodiment provides a heavy filling material with a formula: 65 parts of modified iron tailings, 25 parts of fly ash, 20 parts of wollastonite, 7 parts of fiber, 3 parts of accelerating agent, 6 parts of suspending agent, 3 parts of water reducing agent, and 250 parts of water.

[0082] The preparation method of the modified iron tailings includes the following steps:

[0083] S1. Crush and dry 100 parts by weight of iron tailings, and mix them evenly with 15 parts by weight of an activator. The activator includes a sodium activator and a calcium activator. The sodium activator is sodium hydroxide; the calcium activator is calcium hydroxide, and the mass ratio of the sodium activator to the calcium activator is 2:5;

[0084] S2. Transfer the uniformly mixed materials in step S1 to a rotary kiln, calcine at 1300 °C for 3 h, cool, grind, and pass through 10-mm and 5-mm sieves respectively to obtain fine particles with d1 < 5 mm and coarse particles with 5 ≤ d2 < 10 mm. Mix the fine particles and the coarse particles evenly according to a mass ratio of 1:8 to obtain modified iron tailings.

[0085] The fiber is a 1:1 combination of polypropylene fiber and polyester fiber, and the length of both fibers is 2 mm.

[0086] The water reducing agent is a melamine water reducing agent.

[0087] The quick setting agent is sodium carbonate.

[0088] The suspending agent is sodium carboxymethyl cellulose.

[0089] This embodiment provides a method for preparing a heavy filling material, including the following steps:

[0090] 1) Accurately weigh 65 parts of modified iron tailings, 25 parts of fly ash, 20 parts of wollastonite, 7 parts of fiber, 3 parts of quick setting agent, 6 parts of suspending agent, 3 parts of water reducing agent, and 250 parts of water;

[0091] 2) First, mix the modified iron tailings, fly ash, wollastonite, fiber, quick setting agent, and suspending agent evenly, and then mix them evenly with water to prepare a heavy filling material.

[0092] Example 6

[0093] This embodiment provides a heavy filling material with the following formula: 75 parts of modified iron tailings, 25 parts of fly ash, 15 parts of wollastonite, 8 parts of fiber, 3 parts of quick setting agent, 3 parts of suspending agent, 2 parts of water reducing agent, and 280 parts of water.

[0094] The preparation method of the modified iron tailings includes the following steps:

[0095] S1. Crush and dry 100 parts by weight of iron tailings, and mix them evenly with 13 parts by weight of an activator. The activator includes a sodium activator and a calcium activator. The sodium activator is sodium sulfate; the calcium activator is calcium oxide, and the mass ratio of the sodium activator to the calcium activator is 1:8;

[0096] S2. Convey the materials evenly mixed in step S1 to a rotary kiln, calcine them at 1100 °C for 3 h, cool, grind, and pass through sieves with apertures of 10 mm and 5 mm respectively to obtain a fine particle size with d1 < 5 mm and a coarse particle size with 5 ≤ d2 < 10 mm. Mix the fine particle size and the coarse particle size evenly according to a mass ratio of 2:7 to obtain the modified iron tailings.

[0097] The fiber is a combination of polyester fiber and basalt fiber in a ratio of 1:3, and the length of both fibers is 4 mm.

[0098] The water reducing agent is a polycarboxylate water reducing agent.

[0099] The quick setting agent is sodium metaaluminate.

[0100] The suspending agent is water-soluble polyvinyl alcohol.

[0101] This embodiment also provides a method for preparing a heavy filling material, including the following steps:

[0102] 1) Weigh accurately 75 parts of modified iron tailings, 25 parts of fly ash, 15 parts of wollastonite, 8 parts of fiber, 3 parts of quick-setting agent, 3 parts of suspending agent, 2 parts of water-reducing agent, and 280 parts of water;

[0103] 2) First, mix the modified iron tailings, fly ash, wollastonite, fiber, quick-setting agent, and suspending agent evenly, and then mix them evenly with water to prepare a heavy filling material.

[0104] Example 7

[0105] The length of the glass fiber is 2 mm, and other conditions are the same as those in Example 1.

[0106] Example 8

[0107] The length of the glass fiber is 4 mm, and other conditions are the same as those in Example 1.

[0108] Example 9

[0109] The length of the glass fiber is 8 mm, and other conditions are the same as those in Example 1.

[0110] Example 10

[0111] The length of the glass fiber is 10 mm, and other conditions are the same as those in Example 1.

[0112] Comparative Example 1

[0113] The difference from Example 1 is that the preparation method of the modified iron tailings is as follows:

[0114] S1. Crush and dry 100 parts by weight of iron tailings;

[0115] S2. Convey the material dried in step S1 to a rotary kiln, calcine it at 800 °C for 5 h, cool it, grind it, and pass it through sieves with apertures of 10 mm and 5 mm respectively to obtain fine particles with d1 < 5 mm and coarse particles with 5 ≤ d2 < 10 mm. Mix the fine particles and coarse particles evenly according to a mass ratio of 1:5 to obtain the modified iron tailings.

[0116] Comparative Example 2

[0117] The difference from Example 1 is that during the preparation of the modified iron tailings, an equal amount of sodium chloride is used instead of calcium hydroxide, and the others are the same as those in Example 1.

[0118] Comparative Example 3

[0119] The difference from Example 1 is that during the preparation of the modified iron tailings, an equal amount of calcium hydroxide is used instead of sodium chloride, and the others are the same as those in Example 1.

[0120] Comparative Example 4

[0121] The difference from Example 1 is that the same amount of fine-sized modified iron tailings is used to replace the coarse-sized ones, that is, all fine-sized modified iron tailings are used, and the others are the same as in Example 1.

[0122] Comparative Example 5

[0123] The difference from Example 1 is that the same amount of coarse-sized modified iron tailings is used to replace the fine-sized ones, that is, all coarse-sized modified iron tailings are used, and the others are the same as in Example 1.

[0124] Comparative Example 6

[0125] The difference from Example 1 is that the weight ratio of the fine-sized (d1) to the coarse-sized (d2) is 1:10, and the others are the same as in Example 1.

[0126] Comparative Example 7

[0127] The difference from Example 1 is that the weight ratio of the fine-sized (d1) to the coarse-sized (d2) is 4:1, and the others are the same as in Example 1.

[0128] Comparative Example 8

[0129] The difference from Example 1 is that the same amount of modified iron tailings is used to replace fly ash.

[0130] Comparative Example 9

[0131] The difference from Example 1 is that the same amount of modified iron tailings is used to replace wollastonite.

[0132] Comparative Example 10

[0133] The difference from Example 1 is that the same amount of modified iron tailings is used to replace fibers.

[0134] Relevant tests were carried out on the main indexes such as the slump, bleeding rate, strength, density of the filling body, and the retention rate of water penetration resistance of the filling materials in the examples and comparative examples. The performance of the high-quality filling materials is shown in Table 1.

[0135] Retention rate of water penetration and compressive strength: Take the specimen at the age of 48d in the filling area of the coal mine underground to test the compressive strength, denoted as M1. Then soak the specimen in water for 2d, dry it, and test the compressive strength, denoted as M2. The retention rate of compressive strength = M2 / M1 * 100.

[0136] Samples of the filling body at the ages of 1d, 3d, and 7d in the filling area of the coal mine underground were taken, and the test blocks were processed into standard specimens of Ф50mm×100mm. The unilateral compressive strength test results are shown in Table 1. The specimen density is obtained by sampling and testing the filling body at the age of 7d.

[0137] The slump test was carried out using a CA mortar spread meter with dimensions of 50×150×100 mm, and the bleeding rate was mainly measured using a bleeding rate measuring bucket with dimensions of 185×200 mm.

[0138] Table 1 Performance of filling materials for different examples and control examples

[0139]

[0140] According to the performance tested in Table 1, the slump of the heavy filling material slurry prepared by the present invention is not less than 180 mm, and the bleeding rate is not more than 3.6%, ensuring good pipeline transportation performance during actual use. In addition, the 1-day uniaxial compressive strength of the filling material of the present invention can reach above 1.30 MPa, and the 7-day uniaxial compressive strength can reach above 3.50 MPa. At the same time, it has good water resistance, and this strength can meet the requirements of most coal mine gob filling mining for the strength of the filling material; moreover, the density of the filling body is not less than 1.69 g / cm 3 , which is greater than that of coal. The filling body can be washed by the heavy medium method, significantly improving the coal quality.

[0141] By comparing the test results of Example 1 with those of Examples 7-10, it can be seen that fibers of different lengths have a significant impact on the compressive strength, density, and water permeability resistance retention rate of the filling body. This may be due to the different fiber lengths, resulting in different dispersibility in the filling body, and then affecting the compressive strength of the filling body. Specifically, fibers with appropriate particle sizes can form effective lap joints with modified iron tailings, thereby enhancing the bonding force of the matrix and improving the compressive strength and water resistance of the filling body. However, when the fiber length exceeds a certain limit, continuing to increase its length will have limited effect on improving the compressive strength and water resistance. Therefore, choosing an appropriate fiber length is crucial for optimizing the performance of the filling body.

[0142] By comparing Example 1 with Comparative Examples 1-3, it was found that no activator was added in Comparative Example 1, while only a calcium activator or a sodium activator was added in Comparative Examples 2 and 3 respectively. The results showed that the filling bodies of Comparative Examples 1-3 were significantly lower than those of Example 1 in terms of compressive strength, density, and water resistance. This indicates that the combination of using a sodium activator and a calcium activator can significantly improve the activity of calcined iron tailings, accelerate the dissolution of aluminosilicates, and promote the formation of hydration products such as C-S-H gel and C-A-S-H gel. The formation of these hydration products significantly enhances the compressive strength of the material. At the same time, these hydration products, especially C-S-H gel, further enhance the water resistance and density of the material due to their excellent compactness and anti-permeability ability.

[0143] By comparing Example 1 with Comparative Examples 4-7, we found that in Comparative Examples 4-5, only fine particle size (d1 < 5 mm) or coarse particle size (5 ≤ d2 < 10 mm) was used, while in Comparative Examples 6-7, the mixing ratio of coarse particle size to fine particle size exceeded the range of 1-3:5-8. The filling bodies of these comparative examples were significantly lower than that of Example 1 in terms of compressive strength, density, and water resistance. This indicates that by mixing modified iron tailings with different particle sizes, the present invention optimized the particle size combination of the filling material, effectively improved its rheological properties, and enhanced the stability and fluidity of the filling body. In this method, the coarse-grained modified iron tailings constructed a solid framework, providing the necessary support for the filling body; the fine-grained iron tailings penetrated and filled the voids between the coarse grains, further improving the compactness of the filling body. This scientific ratio of coarse and fine particle sizes promoted the uniform distribution of internal stress in the filling body, effectively avoiding the problem of stress concentration, thereby enhancing the overall stability of the filling body.

[0144] From the results of comparing Example 1 with Comparative Examples 8-10, it can be seen that when any one of fiber, wollastonite, or fly ash was omitted, the filling bodies of Comparative Examples 8-10 were significantly lower than that of Example 1 in terms of compressive strength, density, and water resistance. The main manifestations are as follows: The modified iron tailings played a cementing role in the filling body, enhancing the early strength of the filling body by forming hydration products such as calcium silicate hydrate (C-S-H) gel. The addition of fiber formed a network structure in the filling body, further improving the compressive strength, density, and water resistance of the filling body. The high-density characteristic of wollastonite contributed to improving the stability and density of the filling body, thereby enhancing the density and compressive strength of the filling body. Due to its pozzolanic activity, fly ash could generate more hydration products such as C-S-H gel, further improving the density, compressive strength, and water resistance of the filling body. Therefore, the synergistic effect of fiber, wollastonite, and fly ash is crucial for improving the comprehensive performance of the filling body.

[0145] The filling material of the present invention, which uses iron tailings, fly ash, and wollastonite as the main raw materials and is applied to coal mine filling mining, can meet the normal production of coal mines. The slump of the filling material is not less than 180 mm, and the bleeding rate is not more than 3.6%, ensuring good pipeline transportation performance during actual use. In addition, the 1-day uniaxial compressive strength of the filling material of the present invention can reach more than 1.30 MPa, and the 7-day uniaxial compressive strength can reach more than 3.50 MPa. At the same time, it has good water resistance, and this strength can meet the requirements of most coal mine goaf filling mining for the strength of the filling material; moreover, the density of the filling body is not less than 1.69 g / cm 3 , which is greater than that of coal. The filling body can be washed by the heavy medium method, significantly improving the coal quality.

[0146] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. Moreover, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0147] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present application, "a plurality" means two or more unless otherwise specifically defined.

[0148] As described above, the above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of various changes or substitutions, and these should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A heavy filling material, characterized in that: The filling material comprises the following components in parts by weight: 40-80 parts of modified iron tailings, 10-30 parts of fly ash, 10-20 parts of wollastonite, 5-10 parts of fiber, 1-8 parts of accelerating setting agent, 1-8 parts of suspending agent, 1-3 parts of water reducing agent, and 120-300 parts of water; the length of the fiber is 2-10 mm; The preparation method of modified iron tailings comprises the following steps: S1, crushing and drying 100 parts by weight of iron tailings, and uniformly mixing with 10-15 parts by weight of an activator, wherein the activator comprises a sodium activator and a calcium activator, wherein the sodium activator comprises at least one of sodium chloride, sodium sulfate, and sodium hydroxide; the calcium activator comprises at least one of calcium hydroxide, calcium oxide, calcium chloride, and gypsum, and the mass ratio of the sodium activator to the calcium activator is 1-3:5-10; S2, conveying the uniformly mixed material in step S1 to a rotary kiln for calcination, cooling, grinding, and passing through 10 mm and 5 mm sieves respectively to obtain a fine particle size of d1 < 5 mm and a coarse particle size of 5 ≤ d2 < 10 mm, and uniformly mixing the fine particle size and the coarse particle size according to a mass ratio of 1-3:5-8 to obtain a modified iron tailings.

2. The heavy filling material according to claim 1, characterized in that: The fiber includes at least one of glass fiber, polypropylene fiber, polyester fiber and basalt fiber.

3. The heavy filling material according to any one of claims 1 to 2, characterized in that: The length of the fibers is 4-8 mm.

4. The heavy filling material according to claim 1, characterized in that: The water reducer includes at least one of a naphthalene-based water reducer, a melamine-based water reducer or a polycarboxylic acid-based water reducer.

5. The heavy filling material according to claim 1, characterized in that: The accelerating setting agent includes at least one of sodium aluminate, sodium sulfate or sodium carbonate.

6. The heavy filling material according to claim 1, characterized in that: The suspending agent includes at least one of sodium carboxymethylcellulose, water-soluble polyvinyl alcohol or hydroxypropyl methylcellulose.

7. The heavy filling material according to claim 1, characterized in that: In the step S2, the calcination temperature is 800-1400° C., and the calcination time is 2-5 hours.

8. A method for preparing the heavy filling material according to any one of claims 1 to 7, characterized in that: 1) Accurately weigh 40-80 parts of modified iron tailings, 10-30 parts of fly ash, 10-20 parts of wollastonite, 5-10 parts of fiber, 1-8 parts of accelerator, 1-8 parts of suspending agent, and 120-300 parts of water; 2) First, evenly mix the modified iron tailings, fly ash, wollastonite, fiber, accelerator, and suspending agent, and then evenly mix with water to make a heavy filling material.

9. A method for preparing a heavy filling material according to claim 8, characterized in that: In step 2), the mixing temperature is 20-40° C. and the mixing time is 20-60 min.

10. Use of the heavy filling material according to any one of claims 1 to 7 in coal mine filling, characterized in that: The method comprises mixing the filling materials and then pumping the filling materials to the use site.

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