Coal mine filling material based on loess composite curing agent and preparation method thereof

Abstract

The invention discloses a coal mine filling material based on a loess composite curing agent and a preparation method thereof, and relates to the technical field of coal mine filling materials. The coal mine filling material is prepared from the following raw material components in parts by weight: 58 to 62 parts of loess composite curing agent and 100 parts of polyacrylate emulsion, the loess composite curing agent comprises the following raw material components in parts by weight: 25-28 parts of a loess composite material, 20-23 parts of fly ash and 10-12 parts of a cementing material. The loess composite material is prepared from conventional loess, calcium-increased loess and isocyanate modified loess in a mass ratio of (2-3): 1: 1. The cementing material is prepared from the following raw material components in parts by weight: 2 to 2.5 parts of sulphoaluminate cement, 0.5 to 1 part of ammonium dihydrogen phosphate, 1 to 1.5 parts of desulfurized gypsum, 0.5 to 1 part of quick lime, 1 to 2 parts of water glass and 4 to 5 parts of water-quenched slag. The coal mine filling material has excellent compressive strength.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mine filling materials, and specifically to a coal mine filling material based on loess composite curing agent and a preparation method thereof. Background Art

[0002] In recent years, with the development of coal mining technology, filling mining can not only effectively control surface subsidence, but also reduce the damage to underground water resources and ecological environment. It is a safe and green mining method and has been widely developed.

[0003] Traditional coal mine filling materials have a large demand for fly ash, resulting in high costs. Loess is a material with low cost and wide sources and can be widely used in coal mine filling materials. However, pure loess has the problem of wet collapse and has limitations in mechanical properties and durability. In existing coal mine filling materials, auxiliary materials are usually used to improve their defects, but the general performance improvement is limited. At the same time, in practical applications, the introduction amount of loess is limited, and a large amount of fly ash still needs to be introduced to ensure performance. The introduction of a high content of loess has the following problems: First, the coal mine filling material containing loess has poor fluidity, affecting the filling effect. Second, water seepage and shrinkage problems will occur during the curing process, resulting in pores inside the filling, affecting properties such as compressive strength and durability.

[0004] In summary, to solve the above problems, it is of great significance to prepare a coal mine filling material based on loess composite curing agent. Summary of the Invention

[0005] The purpose of the present invention is to provide a coal mine filling material based on loess composite curing agent and a preparation method thereof to solve the problems raised in the above background art.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: A coal mine filling material based on loess composite curing agent, the raw materials of the coal mine filling material include the following components: by weight, 58 - 62 parts of loess composite curing agent, 100 parts of polyacrylate emulsion; The raw materials of the loess composite curing agent include the following components: by weight, 25 - 28 parts of loess composite material, 20 - 23 parts of fly ash, 10 - 12 parts of binder; the solid content of the polyacrylate emulsion is 4 - 8 wt%.

[0007] More preferably, the raw materials of the binder include the following components: by weight, 2 - 2.5 parts of sulfoaluminate cement, 0.5 - 1 part of ammonium dihydrogen phosphate, 1 - 1.5 parts of desulfurized gypsum, 0.5 - 1 part of quicklime, 1 - 2 parts of water glass, 4 - 5 parts of water quenched slag.

[0008] Preferably, the loess composite material is composed of conventional loess, calcium-enriched loess, and isocyanate-modified loess with a mass ratio of 2 - 3:1:1.

[0009] Preferably, the preparation method of the isocyanate-modified loess is as follows: (1) Add conventional loess into an aqueous solution of sodium hexametaphosphate with a concentration of 3 - 5 wt%, stir evenly, dropwise add an aqueous hydrochloric acid solution, set the temperature at 95 - 98 °C, reflux for 4 - 6 hours, wash and dry to obtain pretreated loess; (2) Add the pretreated loess into an aqueous ethanol solution with a concentration of 85 - 90 wt%, add an amino-silane coupling agent, set the temperature at 80 - 85 °C, stir for 4 - 6 hours, wash and dry to obtain amino-modified loess; (3) Add the amino-modified loess, L-lysine diisocyanate, and an organotin catalyst into acetone in sequence and stir evenly; under a nitrogen atmosphere, set the temperature at 80 - 85 °C, stir for 10 - 12 hours, wash and dry to obtain isocyanate-modified loess.

[0010] Preferably, the mass ratio of the pretreated loess to the amino-silane coupling agent is 1:0.05; the mass ratio of the amino-modified loess to L-lysine diisocyanate is 5:(8 - 10).

[0011] Preferably, the preparation method of the polyacrylate emulsion is as follows: (1) Mix methyl methacrylate, butyl acrylate, and vinyl pyridine in proportion to obtain a monomer mixture; (2) Add vinyl silicone rubber and silica sol to the monomer mixture, disperse evenly by ultrasonic wave; add vinyl siloxane, emulsifier, initiator, and deionized water, adjust to neutral with a pH regulator, and shear for 10 - 30 minutes to obtain a pre-emulsion; (3) Heat part of the pre-emulsion to 75 - 85 °C, dropwise add a mixed solution of the remaining part of the pre-emulsion and an epoxy-silane coupling agent, with a dropping time of 1 - 2 hours, keep the temperature for reaction for 2 - 3 hours, discharge and filter, and dilute with deionized water to obtain a polyacrylate emulsion.

[0012] Preferably, the raw materials of the polyacrylate emulsion include the following components: by weight, 18 - 20 parts of methyl methacrylate, 10 - 12 parts of butyl acrylate, 6 - 8 parts of vinyl pyridine, 1 - 2 parts of vinyl silicone rubber, 10 - 15 parts of silica sol, 2 - 3 parts of vinyl siloxane, 1 - 2 parts of emulsifier, 0.1 - 0.3 parts of initiator, and 2 - 3 parts of epoxy-silane coupling agent.

[0013] Preferably, the silica sol is vinyl-modified nano-silica sol, with a concentration of 20 - 25 wt% and an average particle size of 10 - 30 nm.

[0014] A preparation method of a coal mine filling material based on a loess composite curing agent includes the following steps: Step 1: (1) Mix conventional loess, calcium-enriched loess, and isocyanate-modified loess evenly to obtain a loess composite; (2) Mix sulfoaluminate cement, ammonium dihydrogen phosphate, desulfurized gypsum, quicklime, water glass, and granulated blast furnace slag evenly to obtain a binder. Step 2: Mix the loess composite, fly ash, and binder to obtain a loess composite curing agent; add it to a polyacrylic acid solution and mix homogenously to obtain a coal mine filling material.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: In the solution, based on loess, a loess composite is formed to partially replace fly ash; at the same time, a binder with optimized components is compounded, and a polyacrylate emulsion is introduced to improve the disadvantages of the loess-based coal mine filling material, improve fluidity and solidification, and increase the compressive strength of the coal mine filling material.

[0016] Since the content of fly ash partially replaced by the loess composite is relatively high, in order to improve its applicability, a binder is needed to stimulate and assist its solidification and improve its strength and durability. In the solution, the binder includes sulfoaluminate cement, ammonium dihydrogen phosphate, desulfurized gypsum, quicklime, water glass, and granulated blast furnace slag. Among them, sulfoaluminate cement and quicklime are common binders; by increasing the introduction of other components and optimizing the formulation content, the performance of the coal mine filling material can be comprehensively promoted. Water glass can hydrolyze to produce SiO 3 2- which can combine with Ca 2+ to form a CSH gel; the introduction of desulfurized gypsum can promote the early hydration process and promote the formation of an alkaline environment, and synergistically promote gel formation with granulated blast furnace slag. At the same time, the introduction of granulated blast furnace slag can fill the curing pores of the coal mine filling material, improve the density and strength, and can reduce the erosion of the filling material and improve the durability. In addition, ammonium dihydrogen phosphate is also introduced, which can release phosphate ions, react with the carbonate of loess to produce a composite precipitate, and form a network structure inside to improve comprehensive properties such as compressive strength.

[0017] In the solution, polyacrylate emulsion is introduced. Since it contains polymers, it can increase the cementing effect between substances such as loess in coal mine filling materials, penetrate and crosslink between fine cracks, and strengthen the strength of coal mine filling materials. Among them, the polyacrylate emulsion is obtained by first copolymerizing monomers and then polycondensing with a silane coupling agent. The monomers contain vinylpyridine, and the pyridine group can interact with the surface active groups of loess through ion exchange and hydrogen bonding to improve the strength and stability after curing. Vinyl silicone rubber is introduced to promote crosslinking toughness; at the same time, the hydrophobicity is increased, excessive hydration will not occur, the fluidity is ensured, and the wet collapse of loess is reduced; silica sol is introduced to make it contain silicon dioxide, comprehensively improving the strength of the coal mine filling material after curing. It should be noted that the solid content of the polyacrylate emulsion should not be too much, which will affect the fluidity, resulting in insufficient cementing effect and affecting the performance.

[0018] In the solution, the loess composite includes conventional loess, calcium-enriched loess, and isocyanate-modified loess. Among them, due to the wet collapse of conventional loess, in order to ensure high compressive performance after introducing a high content of loess. Therefore, the pre-treated loess is compounded to optimize the complementary performance. Among them, calcium-enriched loess helps the cementitious system to generate more ettringite and promotes early strength. At the same time, although polymers are introduced in the solution, the polymers will complex with calcium ions and hinder the hydration process; while calcium-enriched loess can complement the disadvantages of polyacrylate emulsion. Isocyanate-modified loess can crosslink with polyacrylate under the condition of exothermic hydration, increase the curing density, and improve the mechanical strength. In this way, the strength of the coal mine filling material is comprehensively improved. Specific embodiments

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] It should be noted that the following parts are by weight, and there are no special restrictions on the purchase manufacturers of all raw materials involved in the present invention. Exemplarily, in the following embodiments, the relevant raw materials are all commercially available. Among them, the conventional loess is pre-screened through a 5 mm sieve and then dried for use. The fineness of fly ash is 2000 mesh; the density of desulfurized gypsum is 2.3 g / cm 2 ³, the particle size is 200 mesh; the fineness of quicklime is 325 mesh; the grade of water glass is industrial grade, and the grade of ammonium dihydrogen phosphate is industrial grade; the water quenched slag is nickel-iron slag from a smelter, mainly composed of silicon dioxide, magnesium oxide and iron oxide, and the average particle size is 30 μm.

[0021] The silica sol is a vinyl-modified nano-silica sol with an average particle size of 20 nm; it is purchased from Zhende Chemical Technology; before use, it is pretreated by removing part of ethanol until the solid content is 20 wt%.

[0022] The preparation method of calcium loess is prepared according to the existing method. The preparation process is as follows: conventional loess, dolomite and soda ash with a mass ratio of 2:0.5:0.5 are ground and mixed; transferred to a high-temperature furnace, calcined at 1100 °C for 1 hour, and cooled to obtain calcium-enriched loess.

[0023] Preparation of isocyanate-modified loess: (1) Conventional loess is put into an aqueous solution of 5 wt% sodium hexametaphosphate and stirred evenly. The solid-liquid ratio is 1:2. An aqueous solution of 6 mol / L hydrochloric acid is added dropwise until no bubbles are generated. The temperature is set at 98 °C and refluxed for 5 hours, washed and dried to obtain pretreated loess; (2) 10 parts of pretreated loess are added to an aqueous solution of 85 wt% ethanol, and 0.5 part of amino-silane coupling agent KH-620 is added. The temperature is set at 80 °C and stirred for 5 hours, washed and dried to obtain amino-modified loess; (3) 5 parts of amino-modified loess, 8.5 parts of L-lysine diisocyanate, and 0.01 part of organotin catalyst T-12 are successively added to 150 parts of acetone and stirred evenly; under a nitrogen atmosphere, the temperature is set at 80 °C and stirred for 12 hours, washed and dried to obtain isocyanate-modified loess.

[0024] Example 1: A preparation method of a coal mine filling material based on a loess composite curing agent, comprising the following steps: Pre-preparation: Preparation of polyacrylate emulsion: (1) 20 parts of methyl methacrylate, 10 parts of butyl acrylate, and 6 parts of vinyl pyridine are mixed evenly in proportion to obtain a monomer mixture; (2) 1.5 parts of vinyl silicone rubber and 12.5 parts of silica sol are added to the monomer mixture and ultrasonically dispersed evenly; 2.5 parts of vinyl siloxane KH-171, 1.5 parts of emulsifier SP-80, 0.2 part of potassium persulfate, and deionized water are added. Sodium bicarbonate is used as a pH regulator to adjust to neutral, and sheared for 10 minutes to obtain a pre-emulsion; (3) One-third of the pre-emulsion is heated to 80 °C, and a mixed solution of the remaining two-thirds of the pre-emulsion and 3 parts of epoxy-silane coupling agent KH-560 is added dropwise. The dropping time is 2 hours, and the reaction is kept warm for 2 hours. Ethanol is removed at low temperature, discharged and filtered, and diluted with deionized water to obtain a polyacrylate emulsion with a solid content of 5 wt%.

[0025] Step 1: (1) Conventional loess, calcium-enriched loess, and isocyanate-modified loess with a mass ratio of 2:1:1 are stirred evenly to obtain a loess composite; (2) 2.2 parts of sulfoaluminate cement, 0.8 part of ammonium dihydrogen phosphate, 1 part of desulfurized gypsum, 1 part of quicklime, 1 part of water glass, and 4 parts of water quenched slag are stirred evenly to obtain a binder; Step 2: Mix 28 parts of loess composite material, 22 parts of fly ash, and 10 parts of binder to obtain 60 parts of loess composite solidifying agent; add it to 100 parts of polyacrylic acid solution and mix homogenously to obtain coal mine filling material.

[0026] Example 2: A preparation method of a coal mine filling material based on loess composite solidifying agent, comprising the following steps: Pre-preparation: Preparation of polyacrylate emulsion: (1) Mix 20 parts of methyl methacrylate, 10 parts of butyl acrylate, and 6 parts of vinyl pyridine in proportion to obtain a monomer mixture; (2) Add 1.5 parts of vinyl silicone rubber and 12.5 parts of silica sol to the monomer mixture and disperse evenly by ultrasonic wave; add 2.5 parts of vinyl siloxane KH-171, 1.5 parts of emulsifier SP-80, 0.2 part of potassium persulfate, and deionized water, use sodium bicarbonate as a pH regulator, adjust to neutral, shear for 10 minutes to obtain a pre-emulsion; (3) Heat one-third of the pre-emulsion to 80 °C, dropwise add a mixed solution of the remaining two-thirds of the pre-emulsion and 3 parts of epoxy group silane coupling agent KH-560, the dropping time is 2 hours, keep the temperature for reaction for 2 hours, remove ethanol at low temperature, discharge and filter, and dilute with deionized water to obtain a polyacrylate emulsion with a solid content of 4 wt%.

[0027] Step 1: (1) Stir evenly the conventional loess, calcium-enriched loess, and isocyanate-modified loess with a mass ratio of 2:1:1 to obtain loess composite material; (2) Stir evenly 2.5 parts of sulfoaluminate cement, 1 part of ammonium dihydrogen phosphate, 1.5 parts of desulfurized gypsum, 1 part of quicklime, 2 parts of water glass, and 4 parts of water quenched slag to obtain binder; Step 2: Mix 25 parts of loess composite material, 23 parts of fly ash, and 12 parts of binder to obtain 60 parts of loess composite solidifying agent; add it to 100 parts of polyacrylic acid solution and mix homogenously to obtain coal mine filling material.

[0028] Example 3: A preparation method of a coal mine filling material based on loess composite solidifying agent, comprising the following steps: Pre - preparation: Preparation of polyacrylate emulsion: (1) Mix 20 parts of methyl methacrylate, 10 parts of butyl acrylate, and 6 parts of vinyl pyridine evenly to obtain a monomer mixture; (2) Add 1.5 parts of vinyl silicone rubber and 12.5 parts of silica sol to the monomer mixture and disperse evenly by ultrasonic treatment; then add 2.5 parts of vinyl siloxane KH - 171, 1.5 parts of emulsifier SP - 80, 0.2 parts of potassium persulfate, and deionized water. Use sodium bicarbonate as the pH regulator to adjust to neutral, and shear for 10 minutes to obtain a pre - emulsion; (3) Heat one - third of the pre - emulsion to 80 °C, and dropwise add a mixed solution of the remaining two - thirds of the pre - emulsion and 3 parts of epoxy - group silane coupling agent KH - 560 over 2 hours. Keep the temperature for reaction for 2 hours, remove ethanol at low temperature, discharge and filter, and dilute with deionized water to obtain a polyacrylate emulsion with a solid content of 8 wt%.

[0029] Step 1: (1) Stir evenly a conventional loess, calcium - enriched loess, and isocyanate - modified loess with a mass ratio of 3:1:1 to obtain a loess composite; (2) Stir evenly 2 parts of sulfoaluminate cement, 1 part of ammonium dihydrogen phosphate, 1 part of desulfurized gypsum, 1 part of quicklime, 2 parts of water glass, and 5 parts of water - quenched slag to obtain a binder. Step 2: Mix 28 parts of the loess composite, 20 parts of fly ash, and 12 parts of the binder to obtain 60 parts of a loess composite curing agent; add it to 100 parts of a polyacrylic acid solution and mix and homogenize to obtain a coal mine filling material.

[0030] Comparative Example 1: Use a single conventional loess to replace the loess composite, and the rest is the same as Example 1; the specific differences are as follows: Step 1: Stir evenly 2.2 parts of sulfoaluminate cement, 0.8 part of ammonium dihydrogen phosphate, 1 part of desulfurized gypsum, 1 part of quicklime, 1 part of water glass, and 4 parts of water - quenched slag to obtain a binder. Step 2: Mix 28 parts of conventional loess, 22 parts of fly ash, and 10 parts of the binder to obtain 60 parts of a loess composite curing agent; add it to 100 parts of a polyacrylic acid solution and mix and homogenize to obtain a coal mine filling material.

[0031] Comparative Example 2: Do not introduce isocyanate - modified loess into the loess composite, and the rest is the same as Example 1; the specific differences are as follows: Step 1: (1) Stir evenly a conventional loess and calcium - enriched loess with a mass ratio of 3:1 to obtain a loess composite; (2) Stir evenly 2.2 parts of sulfoaluminate cement, 0.8 part of ammonium dihydrogen phosphate, 1 part of desulfurized gypsum, 1 part of quicklime, 1 part of water glass, and 4 parts of water - quenched slag to obtain a binder. Step 2: Mix 28 parts of the loess composite, 22 parts of fly ash, and 10 parts of the binder to obtain 60 parts of a loess composite curing agent; add it to 100 parts of a polyacrylic acid solution and mix and homogenize to obtain a coal mine filling material.

[0032] Comparative Example 3: Ammonium dihydrogen phosphate was not introduced into the binder, and the rest was the same as in Example 1; the specific differences are as follows: Step 1: (1) Mix 2 parts of conventional loess, 1 part of calcium-enriched loess, and 1 part of isocyanate-modified loess by mass ratio evenly to obtain a loess composite; (2) Mix 3 parts of sulfoaluminate cement, 1 part of desulfurized gypsum, 1 part of quicklime, 1 part of water glass, and 4 parts of water quenched slag evenly to obtain a binder; Step 2: Mix 28 parts of the loess composite, 22 parts of fly ash, and 10 parts of the binder to obtain 60 parts of a loess composite curing agent; add it to 100 parts of polyacrylic acid solution and mix and homogenize to obtain a coal mine filling material.

[0033] Comparative Example 4: The solid content of the polyacrylate emulsion was increased, and the rest was the same as in Example 1; the specific differences are as follows: Preparation in advance: Preparation of polyacrylate emulsion: (1) Mix 20 parts of methyl methacrylate, 10 parts of butyl acrylate, and 6 parts of vinyl pyridine in proportion evenly to obtain a monomer mixture; (2) Add 1.5 parts of vinyl silicone rubber and 12.5 parts of silica sol to the monomer mixture and disperse evenly by ultrasonic; add 2.5 parts of vinyl siloxane KH-171, 1.5 parts of emulsifier SP-80, 0.2 part of potassium persulfate, and deionized water, use sodium bicarbonate as a pH regulator, adjust to neutral, shear for 10 minutes to obtain a pre-emulsion; (3) Heat one-third of the pre-emulsion to 80 °C, dropwise add the remaining two-thirds of the pre-emulsion and a mixed solution of 3 parts of epoxy group silane coupling agent KH-560, the dropping time is 2 hours, keep the temperature for reaction for 2 hours, remove ethanol at low temperature, discharge and filter, and dilute with deionized water to obtain a polyacrylate emulsion with a solid content of 12 wt%.

[0034] Step 1: (1) Mix 2 parts of conventional loess, 1 part of calcium-enriched loess, and 1 part of isocyanate-modified loess by mass ratio evenly to obtain a loess composite; (2) Mix 2.2 parts of sulfoaluminate cement, 0.8 part of ammonium dihydrogen phosphate, 1 part of desulfurized gypsum, 1 part of quicklime, 1 part of water glass, and 4 parts of water quenched slag evenly to obtain a binder; Step 2: Mix 28 parts of the loess composite, 22 parts of fly ash, and 10 parts of the binder to obtain 60 parts of a loess composite curing agent; add it to 100 parts of polyacrylic acid solution and mix and homogenize to obtain a coal mine filling material.

[0035] Comparative Example 5: Use a conventional polyacrylate emulsion (brand: Jibin, grade: 3527), dilute it to a solid content of 5 wt% for use, and the rest is the same as in Example 1.

[0036] Performance test: The coal mine filling materials prepared in the examples and comparative examples were made into 7×7×7 cm3 For the samples, after final setting, they were cured at a constant temperature of 25°C. An electronic universal testing machine was used to test the stone formation rate and uniaxial compressive strength, and the obtained data are shown in the following table:

[0037] Conclusion: The data of Example 1 indicate that a coal mine filling material with high compressive strength is prepared according to the present application. From the data of Comparative Examples 1 to 5, it can be seen that in Comparative Example 1, due to the single use of conventional loess, there is obvious wet collapse, the relevant interfacial action decreases, so the stone formation rate and compressive strength decrease; in Comparative Example 2, since isocyanate-modified loess is not introduced into the loess composite, the interfacial crosslinking with related substances such as polyacrylate decreases, resulting in a decrease in compressive strength; in Comparative Example 3, since ammonium dihydrogen phosphate is not introduced into the binder and stronger adhesive hydroxyapatite is not formed, the performance decreases; in Comparative Example 4, due to the increase in the solid content of the polyacrylate emulsion, the fluidity decreases, which hinders the relevant interfacial action and hydration reaction, resulting in a decrease in the stone formation rate and compressive strength; in Comparative Example 5, due to the use of a conventional polyacrylate emulsion without substances such as nano-silica, the compressive strength decreases.

[0038] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A coal mine filling material based on loess composite curing agent, characterized in that: The raw materials of the coal mine filling material include the following components: 58-62 parts by weight of loess composite curing agent and 100 parts of polyacrylate emulsion; The raw materials of the loess composite curing agent include the following components: by weight, 25-28 parts of loess composite material, 20-23 parts of fly ash, and 10-12 parts of binder; the solid content of the polyacrylate emulsion is 4-8wt%.

2. The coal mine filling material based on loess composite curing agent according to claim 1, characterized in that: The raw materials of the binder include the following components: by weight, 2 to 2.5 parts of sulphoaluminate cement, 0.5 to 1 part of diammonium phosphate, 1 to 1.5 parts of desulfurized gypsum, 0.5 to 1 part of quicklime, 1 to 2 parts of water glass, and 4 to 5 parts of water-quenched slag.

3. The coal mine filling material based on loess composite curing agent according to claim 1, characterized in that: The loess composite material consists of conventional loess, calcium-enhanced loess and isocyanate-modified loess in a mass ratio of 2-3:1:

1.

4. The coal mine filling material based on loess composite curing agent according to claim 3, characterized in that: The preparation method of the isocyanate-modified loess is as follows: (1) adding conventional loess to a 3-5 wt% sodium hexametaphosphate aqueous solution and stirring evenly, dripping a hydrochloric acid aqueous solution, setting the temperature to 95-98° C. and refluxing for 4-6 hours, washing, and drying to obtain pretreated loess; (2) adding the pretreated loess to an 85-90 wt% ethanol aqueous solution, adding an aminosilane coupling agent, stirring at 80-85°C for 4-6 hours, washing and drying to obtain amino-modified loess; (3) Add amino-modified loess, L-lysine diisocyanate, and an organic tin catalyst to acetone in sequence and stir evenly; under a nitrogen atmosphere, set the temperature to 80-85°C and stir for 10-12 hours, wash, and dry to obtain isocyanate-modified loess.

5. The coal mine filling material based on loess composite curing agent according to claim 4, characterized in that: The mass ratio of pretreated loess to aminosilane coupling agent is 1:0.05; the mass ratio of amino-modified loess to L-lysine diisocyanate is 5:(8~10).

6. The coal mine filling material based on loess composite curing agent according to claim 1, characterized in that: The preparation method of the polyacrylate emulsion is as follows: (1) methyl methacrylate, butyl acrylate and vinyl pyridine are mixed uniformly in proportion to obtain a monomer mixture; (2) vinyl silicone rubber and silica sol are added to the monomer mixture, and ultrasonic dispersion is performed uniformly; vinyl siloxane, emulsifier, initiator and deionized water are added, and the pH value is adjusted to neutral using a pH adjuster, and shearing is performed for 10 to 30 minutes to obtain a pre-emulsion; (3) a part of the pre-emulsion is heated to 75 to 85° C., and a mixed solution of the remaining part of the pre-emulsion and an epoxy silane coupling agent is added dropwise for 1 to 2 hours, and the mixture is kept warm for reaction for 2 to 3 hours, and the mixture is discharged, filtered and diluted with deionized water to obtain a polyacrylate emulsion.

7. The coal mine filling material based on loess composite curing agent according to claim 6, characterized in that: The raw materials of the polyacrylate emulsion include the following components: by weight, 18 to 20 parts of methyl methacrylate, 10 to 12 parts of butyl acrylate, 6 to 8 parts of vinyl pyridine, 1 to 2 parts of vinyl silicone rubber, 10 to 15 parts of silica sol, 2 to 3 parts of vinyl siloxane, 1 to 2 parts of emulsifier, 0.1 to 0.3 parts of initiator, and 2 to 3 parts of epoxy silane coupling agent.

8. The coal mine filling material based on loess composite curing agent according to claim 7, characterized in that: The silica sol vinyl modified nano silica sol has a concentration of 20-25wt% and an average particle size of 10-30nm.

9. The method for preparing a coal mine filling material based on a loess composite curing agent according to claim 1, characterized in that: The following steps are involved: Step 1: (1) conventional loess, calcium-enhanced loess, and isocyanate-modified loess are mixed evenly to obtain a loess composite; (2) sulphoaluminate cement, diammonium phosphate, desulfurized gypsum, quicklime, water glass, and water-quenched slag are mixed evenly to obtain a binder; Step 2: Mix the loess composite material, fly ash and binder to obtain a loess composite curing agent; add the loess composite curing agent into the polyacrylic acid solution, mix and homogenize, and obtain a coal mine filling material.

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