Method for filling mine pit by effectively utilizing coal gangue

Abstract

The invention discloses a pit filling method capable of effectively utilizing coal gangue. The pit filling method comprises the following steps that (1) an impermeable layer is laid at the bottom of a leveled pit; (2) laying a coal gangue layer on the impermeable layer, and sequentially injecting a grouting base solution 1 and a water-based crosslinking solution 1 to form at least one coal gangue solidified layer; (3) injecting a grouting base solution 2 on the coal gangue curing layer, and adding a water-based crosslinking solution 2 and an alkali solution containing fly ash in stages to form a water-blocking gel layer; (4) a supporting layer is arranged on the water-blocking gel layer, and a soil layer is laid on the supporting layer; and carrying out vegetation recovery. The material capable of solidifying the coal gangue is poured into gaps of the coal gangue, gel is formed in situ between the coal gangue, the coal gangue is coated and bonded, air can be prevented from entering a coal gangue layer, the spontaneous combustion risk is reduced, the water content of the gel is rich, and the spontaneous combustion risk of the coal gangue layer is greatly reduced.

Description

Technical Field

[0001] The present application belongs to the technical field of mine filling and relates to a mine filling method that effectively utilizes coal gangue. Background Art

[0002] Minerals are natural energy sources primarily derived from minerals. However, during the mining process, some land is damaged, polluted, or unreclaimed, resulting in areas that cannot be reused. These areas include open pits, coal mines, subsidence areas, spoil dumps, and gangue heaps. These areas often suffer severe ecological damage and present numerous social and ecological challenges. Therefore, the management of abandoned mine sites has become an urgent ecological task. Within the broader context of ecological restoration, the ecological restoration and renovation of abandoned mines is crucial for future economic and social development. Therefore, we must prioritize the management and restoration of abandoned mines.

[0003] Gangue, a byproduct with high density and strong bearing capacity, can be used as backfill material to complete mine filling. This practice reduces the land area occupied by gangue storage and ensures its local utilization. However, using gangue directly for backfilling also has some problems. For example, its high porosity allows air to enter, increasing the risk of spontaneous combustion. In addition, heavy metals in the gangue may pollute the environment through leaching. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention discloses a method for effectively utilizing coal gangue for mine filling. The present invention can solidify the material in the coal gangue by pouring it into the gaps in the coal gangue, forming a gel in situ between the coal gangue, coating and bonding the coal gangue, and preventing air from entering the coal gangue layer, thereby reducing the risk of spontaneous combustion. The gel of the present invention itself has a rich water content, which also greatly reduces the risk of spontaneous combustion of the coal gangue layer. In addition, the grouting base liquid of the present invention can react quickly with water to form a gel material that can tightly wrap the coal gangue layer, and the gel material has the function of blocking and stopping water; therefore, the coal gangue layer wrapped in the gel material of the present invention is not easy to leak metal ions, thereby reducing environmental pollution.

[0005] To achieve the above objectives, the present invention adopts the following solutions:

[0006] A first aspect of the present invention is to provide a method for effectively utilizing coal gangue in a mine filling process, comprising the following steps:

[0007] (1) Laying an anti-seepage layer on the leveled bottom of the mine;

[0008] (2) laying a coal gangue layer on the anti-seepage layer, and injecting a grouting base liquid 1 and an aqueous cross-linking liquid 1 in sequence to form at least one coal gangue solidified layer;

[0009] (3) injecting grouting base liquid 2 onto the coal gangue solidified layer, and adding aqueous cross-linking liquid 2 and alkali solution containing fly ash in stages to form a water-blocking gel layer;

[0010] The staged injection means first adding a portion of the volume of aqueous cross-linking liquid to the grouting base liquid for reaction, then adding an alkaline solution containing fly ash for reaction, and finally adding the remaining aqueous cross-linking liquid to obtain a water-blocking gel layer.

[0011] (4) A support layer is set above the water-blocking gel layer, and a soil layer is laid on the support layer; during vegetation restoration, the water-blocking gel layer will absorb water and swell, so when a support layer is laid 10-20 cm above the water-blocking gel layer, a certain expansion space must be left for the water-blocking gel layer.

[0012] In addition, the present invention further provides a water-blocking gel layer on the above-mentioned coal gangue solidification layer. The gel layer can further block water and isolate oxygen, thereby further reducing environmental pollution and other problems caused by using coal gangue for mine filling.

[0013] As a preferred embodiment, in step (1), the anti-seepage layer is composed of a clay layer, a bentonite layer and a polyethylene LDPE film layer from bottom to top; wherein the clay layer has a thickness of 30-40 cm, the bentonite layer has a thickness of 20-30 cm, and the polyethylene LDPE film layer has a thickness of 1.0-1.5 mm.

[0014] As a preferred embodiment, in step (2), the thickness of each gangue layer is 10-20 cm, the grouting base liquid 1 is injected to a position 3-5 cm from the top of the gangue layer and then the aqueous cross-linking liquid 2 is added for reaction and solidification.

[0015] As a preferred embodiment, it is characterized in that:

[0016] In step (3), the formation of the medium-resistance hydrogel layer includes:

[0017] S1: Inject grouting base liquid 2 on the gangue solidification layer to a thickness of 5-10cm.

[0018] S2: adding aqueous crosslinking liquid 2 in two steps. First, add 75%-90% volume of aqueous crosslinking liquid 2 and react for 1-3 minutes. Then, add alkali solution containing fly ash and react for 1-2 hours. Finally, add the remaining aqueous crosslinking liquid 2.

[0019] As a preferred embodiment, it is characterized in that:

[0020] The grouting base liquid is prepared by mixing a hydrophilic polyurethane prepolymer and a modified coal-based solid waste suspension in a mass ratio of 1:(0.1-0.3);

[0021] The aqueous cross-linking liquid comprises sodium alginate and water, and the mass ratio of sodium alginate to water is 1:(100-150).

[0022] As a preferred embodiment, it is characterized in that:

[0023] In step (2), the mass ratio of the hydrophilic polyurethane prepolymer in the grouting base liquid 1 to the aqueous cross-linking liquid 1 is 1:(15-25);

[0024] In step (3), the mass ratio of the hydrophilic polyurethane prepolymer in the grouting base liquid 2 to the aqueous cross-linking liquid 2 is 1:(10-20).

[0025] As a preferred embodiment,

[0026] The preparation method of the hydrophilic polyurethane prepolymer comprises the following steps:

[0027] In a protective atmosphere, polyether polyol and isocyanate are mixed and then heated to react to obtain the hydrophilic polyurethane prepolymer;

[0028] Preferably, the polyether polyol is dehydrated at 110-120° C. for 1.5-2.5 hours before use;

[0029] The molar ratio of -NCO of the isocyanate to -OH of the polyether polyol is 5-8:1;

[0030] The temperature of the temperature-raising reaction is 75-82°C, and the reaction time is 2.5h-3h;

[0031] The polyether polyol is selected from polyether polyols having a functionality of 3 and a molecular weight of about 4000-10000; preferably BD3-9000A;

[0032] The isocyanate is selected from diphenylmethane diisocyanate (MDI).

[0033] As a preferred embodiment,

[0034] The modified coal-based solid waste suspension comprises a mixture of modified fly ash, modified coal gangue and an organic solvent;

[0035] Preferably,

[0036] Modified fly ash Modified fly ash is fly ash modified with silane coupling agent;

[0037] The modified coal gangue is coal gangue modified by a silane coupling agent;

[0038] The organic solvent is ethyl acetate or methyl acetate;

[0039] The mass ratio of fly ash before modification to coal gangue before modification is 1:1.2-1.5;

[0040] The mass ratio of modified fly ash to organic solvent is 1-2:100.

[0041] As a preferred embodiment,

[0042] The preparation method of modified coal gangue comprises the following steps:

[0043] The coal gangue is added to a water-alcohol mixed solution, and then a silane coupling agent is added. After the hydrolysis reaction, the mixture is vacuum dried and ground, and the coal gangue modified with the silane coupling agent having a particle size of 2-4 mm is selected;

[0044] The preparation method of modified fly ash comprises the following steps:

[0045] The fly ash is added into a water-alcohol mixed solution, and then a silane coupling agent is added, and after a hydrolysis reaction, the fly ash is vacuum dried and ground to obtain fly ash modified with the silane coupling agent;

[0046] Preferably,

[0047] The silane coupling agent is KH-550 or KH-560;

[0048] The hydroalcohol mixed solution is a mixed solution of water and ethanol, and the volume ratio of the two is 1:8-9;

[0049] The mass ratio of the coal gangue to the water-alcohol mixed solution is 1:10-15;

[0050] The mass ratio of the fly ash to the water-alcohol mixed solution is 1:10-15;

[0051] The mass ratio of the silane coupling agent to the water-alcohol mixed solution is 1:40-50;

[0052] The hydrolysis reaction time is 50-60 min.

[0053] The modified fly ash, modified coal gangue and organic solvent are evenly mixed to obtain a modified coal-based solid waste suspension.

[0054] As a preferred embodiment,

[0055] The aqueous cross-linking liquid in step (2) or step (3) comprises sodium alginate and water, and the mass ratio of sodium alginate to water is 1:100-150;

[0056] Step (2), the mass ratio of the hydrophilic polyurethane prepolymer to the aqueous cross-linking liquid is 1:15-25;

[0057] In step (3), the mass ratio of the hydrophilic polyurethane prepolymer to the aqueous cross-linking liquid is 1:10-20.

[0058] As a preferred embodiment, it is characterized in that:

[0059] In step (3), the fly ash-containing alkali solution comprises fly ash, alkali and ethanol; wherein the fly ash and alkali are dissolved in ethanol with a concentration of 2-4 mol / L in a mass ratio of 1:(4-8); the alkali is sodium hydroxide or potassium hydroxide;

[0060] The mass ratio of the hydrophilic polyurethane prepolymer to the fly ash-containing alkali solution in the grouting base liquid 2 is 1:0.5-1.

[0061] As a preferred embodiment, it is characterized in that the support layer in step (4) is formed by mixing and solidifying fly ash, lime, cement in a mass ratio of (45-70): (18-30): (15-20) with water glass (4-7% of the cement mass) and water, and has a thickness of 10-20 cm.

[0062] As a preferred embodiment, it is characterized in that:

[0063] In step (4), the thickness of the soil layer is 100-150 cm.

[0064] As a preferred embodiment, it is characterized in that the limiting oxygen index of the water-blocking gel layer is ≥70%, the water absorption rate of the solidified body is greater than the shrinkage rate, and the metal ion solidification rate is ≥99%.

[0065] In the present invention, the material that can solidify the coal gangue is poured into the gaps of the coal gangue, forming a gel in situ between the coal gangue to coat and bond the coal gangue. The specific process is as follows:

[0066] The present invention injects a grouting base liquid into the gangue layer and stops injecting the grouting base liquid when the distance from the uppermost part of the gangue layer is 3-5 cm. This is because the grouting base liquid will foam due to the reaction after the subsequent addition of the aqueous cross-linking liquid, so it is not advisable to add too much volume into the gangue layer. When the aqueous cross-linking liquid is added to the gangue layer for reaction, the isocyanate groups in the hydrophilic polyurethane prepolymer react with water to cross-link and solidify into a water-insoluble gel, and the coal-based solid waste and the sodium alginate in the aqueous cross-linking liquid are fixedly dispersed in the gel. During the formation of the initial gel, CO2 gas is also released. The generated gas The gel will push the slurry to continue to diffuse deep into the cracks, which is beneficial to increasing the coverage of the coal gangue layer; in addition, the above-mentioned gel contains water, which slowly reacts with the coal-based solid waste fixed in the primary gel (that is, the coal-based solid waste introduced into the primary gel from the modified coal-based solid waste suspension) to form high-strength ettringite and CSH gel filled in the gel, and some calcium ions will also be dissolved. These calcium ions can form a coordination effect with the sodium alginate molecular chain, so that the sodium alginate is further cross-linked in the gel after the polyurethane prepolymer reacts with water, thereby increasing the stability of the above-mentioned gel in the coverage of the coal gangue layer.

[0067] The water-blocking gel layer of the present invention comprises at least four types of gels: the first type is a gel formed by the reaction of a polyurethane prepolymer with water; the second type is a gel formed by a hydration reaction of coal-based solid waste with water or with water under the action of an alkali, embedded in the gel formed by the reaction of the polyurethane prepolymer with water; the third type is a hydrate and gel formed by a hydration reaction of fly ash with an alkali and water, which enters the pores of the gel formed by the reaction of the polyurethane prepolymer with water; and the fourth type is sodium alginate distributed in the aqueous crosslinking liquid in the gel formed by the reaction of the polyurethane prepolymer with water, which can react with calcium ions overflowing from the coal gangue or fly ash to further crosslink and form a gel. The specific reaction process is as follows:

[0068] The present invention adds a modified coal-based solid waste suspension to a hydrophilic polyurethane prepolymer. The modified coal-based solid waste suspension can reduce the viscosity of the hydrophilic polyurethane prepolymer on the one hand, preventing the viscosity from being too high and making grouting difficult; on the other hand, it can introduce coal-based solid waste into the hydrophilic polyurethane prepolymer. After the grouting base liquid of the hydrophilic polyurethane prepolymer and the modified coal-based solid waste suspension is injected into the matrix to be grouted, a partial volume of aqueous cross-linking liquid is first added to react, wherein the isocyanate groups in the hydrophilic polyurethane prepolymer react with water to cross-link and solidify into a water-insoluble primary gel, and the coal-based solid waste and the sodium alginate in the aqueous cross-linking liquid are fixed and dispersed in the above-mentioned primary gel. During the formation of the above-mentioned primary gel, CO2 gas is also released at the same time. The generated gas will push the slurry to continue to diffuse deep into the cracks. At the same time, the released CO2 gas will leave pores in the above-mentioned primary gel due to diffusion, part of which overflows the primary gel and part remains in the primary gel; after the primary gel is formed, an alkali solution containing fly ash is added. The alkali solution containing fly ash does not contain water, and it basically does not react with the hydrophilic polyurethane prepolymer, but can enter the pores of the primary gel and further react with fly ash in the above-mentioned pores. hydration reaction with alkali solution; finally, the remaining aqueous cross-linking liquid is added to continue reacting with the hydrophilic polyurethane prepolymer, further increasing the gel degree of the hydrophilic polyurethane prepolymer gel, and further wrapping the alkali solution into the above-mentioned primary gel; since the alkali in the alkali solution is in excess relative to the fly ash, it can react with the fly ash to generate high-strength ettringite and CSH gel, etc. to fill the pores of the primary gel, and can further diffuse in the above-mentioned gel, and slowly hydrate with the coal-based solid waste fixed in the primary gel (that is, the coal-based solid waste introduced into the primary gel from the modified coal-based solid waste suspension), and also react with the hydrophilic polyurethane prepolymer to generate high-strength ettringite and CSH gel, etc. to fill the primary gel, thereby enhancing the compressive strength of the gel after the polyurethane prepolymer reacts with water, and reducing the shrinkage of the gel after the polyurethane prepolymer reacts with water. In addition, when the fly ash or coal gangue of the present invention reacts with water or with water under the action of alkali solution, some calcium ions will also be dissolved. These calcium ions can form a coordination effect with the sodium alginate molecular chain, thereby further cross-linking the sodium alginate in the gel formed by the reaction of the polyurethane prepolymer and water. It can also enhance the compressive strength of the gel formed by the reaction of the polyurethane prepolymer and water, and reduce the shrinkage of the gel formed by the reaction of the polyurethane prepolymer and water.

[0069] It can be seen that the water-blocking gel layer of the present invention has at least four types of gels in the coal gangue: the first is the gel formed by the reaction of polyurethane prepolymer and water, the second is the gel formed by the hydration reaction of coal-based solid waste with water or with water under the action of alkali embedded in the gel formed by the reaction of polyurethane prepolymer and water; the third is the hydrate and gel formed by the hydration reaction of fly ash with alkali and water that enters the pores of the gel formed by the reaction of polyurethane prepolymer and water; the fourth is the sodium alginate distributed in the aqueous cross-linking liquid in the gel formed by the reaction of polyurethane prepolymer and water, which can react with calcium ions overflowing from the coal gangue or fly ash to further cross-link to form a gel.

[0070] The present invention also adds a support layer on the water-blocking gel layer, which can prevent the pressure of the soil layer from damaging the water-blocking gel layer, thereby maintaining the stable performance of the water-blocking gel layer.

[0071] Beneficial effects

[0072] The present invention can solidify the material in the gangue by pouring it into the gaps within the gangue, forming an in-situ gel between the gangue, coating and bonding the gangue. This prevents air from entering the gangue layer, reducing the risk of spontaneous combustion. Furthermore, the gel of the present invention is rich in water, significantly reducing the risk of spontaneous combustion within the gangue layer. Furthermore, the grouting base fluid of the present invention can react rapidly with water to form a gel material that can tightly wrap the gangue layer. This gel material also acts as a water-blocking and water-stopping agent. Therefore, the gangue layer coated with the gel material of the present invention is less susceptible to metal ion leakage, thereby reducing environmental pollution. DETAILED DESCRIPTION

[0073] Example 1

[0074] Raw material preparation:

[0075] A: The preparation method of the hydrophilic polyurethane prepolymer comprises the following steps:

[0076] In a protective atmosphere (nitrogen), a polyether polyol and an isocyanate are mixed and then heated to react to obtain the hydrophilic polyurethane prepolymer. The polyether polyol is dehydrated at 120°C for 2 hours before use. The molar ratio of -NCO (isocyanate group (-NCO)) of the isocyanate to -OH of the polyether polyol is 5:1. The temperature of the heated reaction is 82°C and the reaction time is 2.5 hours. The polyether polyol is selected from BD3-9000A (purchased from Jiangsu Bader Polyurethane Co., Ltd.) with a functionality of 3 and a molecular weight of approximately 9000. The isocyanate is selected from diphenylmethane diisocyanate (MDI).

[0077] B: The preparation method of modified coal gangue includes the following steps:

[0078] The coal gangue was added to a water-alcohol mixed solution (wherein the volume ratio of water to ethanol was 1:9), and then the silane coupling agent KH-550 was added, and the mass ratio of the silane coupling agent to the water-alcohol mixed solution was 1:50. After 50 minutes of hydrolysis reaction, the mixture was vacuum dried at 60°C for 12 hours and ground for 3 hours. The coal gangue modified with the silane coupling agent with a particle size of 2 mm was selected.

[0079] C: The preparation method of modified fly ash comprises the following steps:

[0080] The fly ash was added to a water-alcohol mixed solution (wherein the volume ratio of water to ethanol was 1:8), and then a silane coupling agent KH-550 was added, and the mass ratio of the silane coupling agent to the water-alcohol mixed solution was 1:50. After the hydrolysis reaction was carried out for 50 minutes, the fly ash was vacuum dried at 60°C for 12 hours and ground for 1 hour to obtain fly ash modified with the silane coupling agent.

[0081] D: The modified fly ash, modified coal gangue and organic solvent (ethyl acetate) are mixed evenly to obtain a modified coal-based solid waste suspension.

[0082] The hydrophilic polyurethane prepolymer and the modified coal-based solid waste suspension are evenly mixed to obtain a grouting base liquid.

[0083] E: Aqueous crosslinking liquid: Sodium alginate and water are evenly mixed to obtain an aqueous crosslinking liquid, wherein the mass ratio of sodium alginate to water is 1:100.

[0084] F: Alkali solution containing fly ash: fly ash, alkali and ethanol are uniformly mixed to obtain an alkali solution containing fly ash; wherein the mass ratio of fly ash to alkali is 1:8; the concentration of alkali in ethanol is 4 mol / L; and the alkali is potassium hydroxide.

[0085] Example 2

[0086] Raw material preparation:

[0087] A: The preparation method of the hydrophilic polyurethane prepolymer comprises the following steps:

[0088] In a protective atmosphere (nitrogen), a polyether polyol and an isocyanate are mixed and then heated to react to obtain the hydrophilic polyurethane prepolymer. The polyether polyol is dehydrated at 120°C for 2 hours before use. The molar ratio of -NCO (isocyanate group (-NCO)) of the isocyanate to -OH of the polyether polyol is 8:1. The temperature of the heated reaction is 75°C and the reaction time is 3 hours. The polyether polyol is selected from BD3-9000A (purchased from Jiangsu Bader Polyurethane Co., Ltd.) with a functionality of 3 and a molecular weight of approximately 9000. The isocyanate is selected from diphenylmethane diisocyanate (MDI).

[0089] B: The preparation method of modified coal gangue includes the following steps:

[0090] The coal gangue was added to a water-alcohol mixed solution (wherein the volume ratio of water to ethanol was 1:8), and then the silane coupling agent KH-560 was added, and the mass ratio of the silane coupling agent to the water-alcohol mixed solution was 1:40. After 60 minutes of hydrolysis reaction, the mixture was vacuum dried at 60°C for 12 hours and ground for 2 hours. The coal gangue modified with the silane coupling agent with a particle size of 4 mm was selected.

[0091] C: The preparation method of modified fly ash comprises the following steps:

[0092] The fly ash was added to a water-alcohol mixed solution (wherein the volume ratio of water to ethanol was 1:8), and then a silane coupling agent KH-560 was added, and the mass ratio of the silane coupling agent to the water-alcohol mixed solution was 1:40. After the hydrolysis reaction was carried out for 60 minutes, the fly ash was vacuum dried at 60°C for 12 hours and ground for 0.5 hours to obtain fly ash modified with the silane coupling agent.

[0093] D: The modified fly ash, modified coal gangue and organic solvent (methyl acetate) are mixed evenly to obtain a modified coal-based solid waste suspension.

[0094] The hydrophilic polyurethane prepolymer and the modified coal-based solid waste suspension are evenly mixed to obtain a grouting base liquid.

[0095] E: Aqueous crosslinking liquid: Sodium alginate and water are mixed evenly to obtain an aqueous crosslinking liquid, wherein the mass ratio of sodium alginate to water is 1:150.

[0096] F: Alkali solution containing fly ash: fly ash, alkali and ethanol are uniformly mixed to obtain an alkali solution containing fly ash; wherein the mass ratio of fly ash to alkali is 1:4; the concentration of alkali in ethanol is 2 mol / L; and the alkali is sodium hydroxide.

[0097] Example 3

[0098] Experimental Example 1

[0099] (1) Leveling the bottom of the mine pit and laying an anti-seepage layer on the leveled bottom of the mine pit; wherein the anti-seepage layer is composed of a 35 cm clay layer, a 30 cm bentonite layer and a 1.0 mm polyethylene LDPE film layer from bottom to top.

[0100] (2) laying a gangue layer on the anti-seepage layer, the height of the gangue layer being 20 cm, then injecting a grouting base liquid into the gangue layer, and stopping the injection of the grouting base liquid when the distance from the uppermost part of the gangue layer is 4 cm, then adding all the aqueous cross-linking liquid into the gangue layer for reaction to obtain a first gangue solidified layer; repeating the above steps to obtain a fourth gangue solidified layer; the raw materials prepared in Preparation Example 1 are used; wherein the mass ratio of the hydrophilic polyurethane prepolymer to the modified coal-based solid waste suspension is 1:0.2; and the mass ratio of the hydrophilic polyurethane prepolymer to the aqueous cross-linking liquid is 1:20;

[0101] (3) Preparation of water-blocking gel layer: The water-blocking gel layer is prepared by reacting the following raw materials: a hydrophilic polyurethane prepolymer, a modified coal-based solid waste suspension, an aqueous cross-linking liquid, and an alkaline solution containing fly ash, and the raw materials prepared in Preparation Example 1 are used; wherein the mass ratio of the hydrophilic polyurethane prepolymer to the modified coal-based solid waste suspension is 1:0.2; the mass ratio of the aqueous cross-linking liquid to the hydrophilic polyurethane prepolymer is 1:18; and the mass ratio of the hydrophilic polyurethane prepolymer to the alkaline solution containing fly ash is 1:0.8.

[0102] The grouting base liquid is injected into the 4th coal gangue solidification layer, and then an aqueous cross-linking liquid accounting for 90% of the total volume of the aqueous cross-linking liquid is added. After the aqueous cross-linking liquid is added to react for 1 minute, an alkali solution containing fly ash is added to react for 2 hours, and then the remaining aqueous cross-linking liquid is added to obtain a water-blocking gel layer.

[0103] (4) A support layer is laid 15 cm above the water-blocking gel layer. The support layer is obtained by solidifying a slurry prepared by mixing fly ash, lime, cement, water glass and water; the mass ratio of fly ash, lime and cement is 60:22:20; the amount of water glass added is 6% of the cement mass; the liquid-solid ratio of the slurry is 0.75; the thickness of each support layer is 20 cm; then a soil layer is laid on the support layer; plants are planted in the soil layer to complete the filling of the mine.

[0104] Experimental Example 2

[0105] (1) Leveling the bottom of the mine pit and laying an anti-seepage layer on the leveled bottom of the mine pit; wherein the anti-seepage layer is composed of a 35 cm clay layer, a 30 cm bentonite layer and a 1.0 mm polyethylene LDPE film layer from bottom to top.

[0106] (2) laying a gangue layer on the anti-seepage layer, the height of the gangue layer is 16 cm, and then injecting a grouting base liquid into the gangue layer, and stopping the injection of the grouting base liquid when the distance from the uppermost part of the gangue layer is 3 cm, and then adding all the aqueous cross-linking liquid to the gangue layer for reaction to obtain a first gangue solidified layer; repeating the above steps to obtain a fourth gangue solidified layer; the raw materials prepared in Preparation Example 1 are used; wherein the mass ratio of the hydrophilic polyurethane prepolymer to the modified coal-based solid waste suspension is 1:0.3; the mass ratio of the hydrophilic polyurethane prepolymer to the aqueous cross-linking liquid is 1:15;

[0107] (3) Preparation of water-blocking gel layer: The water-blocking gel layer is prepared by reacting the following raw materials: a hydrophilic polyurethane prepolymer, a modified coal-based solid waste suspension, an aqueous cross-linking liquid, and an alkaline solution containing fly ash, wherein the raw materials prepared in Preparation Example 1 are used; wherein the mass ratio of the hydrophilic polyurethane prepolymer to the modified coal-based solid waste suspension is 1:0.3; the mass ratio of the aqueous cross-linking liquid to the hydrophilic polyurethane prepolymer is 1:12; and the mass ratio of the hydrophilic polyurethane prepolymer to the alkaline solution containing fly ash is 1:0.5.

[0108] The grouting base liquid is injected into the 4th coal gangue solidification layer, and then an aqueous cross-linking liquid accounting for 85% of the total volume of the aqueous cross-linking liquid is added. After the aqueous cross-linking liquid is added and reacted for 2 minutes, an alkali solution containing fly ash is added and reacted for 1.5 hours, and then the remaining aqueous cross-linking liquid is added to obtain a water-blocking gel layer.

[0109] (4) A support layer is laid 18 cm above the water-blocking gel layer. The support layer is obtained by solidifying a slurry prepared by mixing fly ash, lime, cement, water glass and water; the mass ratio of fly ash, lime and cement is 60:22:20; the amount of water glass added is 6% of the cement mass; the liquid-solid ratio of the slurry is 0.75; the thickness of each support layer is 20 cm; then a soil layer is laid on the support layer; plants are planted in the soil layer to complete the filling of the mine.

[0110] Experimental Example 3

[0111] (1) Leveling the bottom of the mine pit and laying an anti-seepage layer on the leveled bottom of the mine pit; wherein the anti-seepage layer is composed of a 35 cm clay layer, a 30 cm bentonite layer and a 1.0 mm polyethylene LDPE film layer from bottom to top.

[0112] (2) laying a gangue layer on the anti-seepage layer, the height of the gangue layer being 20 cm, then injecting a grouting base liquid into the gangue layer, and stopping the injection of the grouting base liquid when the distance from the uppermost part of the gangue layer is 5 cm, then adding all the aqueous cross-linking liquid into the gangue layer for reaction to obtain a first gangue solidified layer; repeating the above steps to obtain a fourth gangue solidified layer; the raw materials prepared in Preparation Example 2 are used; the mass ratio of the hydrophilic polyurethane prepolymer to the aqueous cross-linking liquid is 1:25;

[0113] (3) Preparation of water-blocking gel layer: The water-blocking gel layer is prepared by reacting the following raw materials: a hydrophilic polyurethane prepolymer, a modified coal-based solid waste suspension, an aqueous cross-linking liquid, and an alkaline solution containing fly ash, and the raw materials prepared in Preparation Example 2 are used; wherein the mass ratio of the hydrophilic polyurethane prepolymer to the modified coal-based solid waste suspension is 1:0.25; the mass ratio of the aqueous cross-linking liquid to the hydrophilic polyurethane prepolymer is 1:10; and the mass ratio of the hydrophilic polyurethane prepolymer to the alkaline solution containing fly ash is 1:1.

[0114] The grouting base liquid is injected into the 4th coal gangue solidification layer, and then an aqueous cross-linking liquid accounting for 90% of the total volume of the aqueous cross-linking liquid is added. After the aqueous cross-linking liquid is added and reacted for 3 minutes, an alkali solution containing fly ash is added and reacted for 1.5 hours, and then the remaining aqueous cross-linking liquid is added to obtain a water-blocking gel layer.

[0115] (4) A support layer is laid 10 cm above the water-blocking gel layer. The support layer is obtained by solidifying a slurry prepared by mixing fly ash, lime, cement, water glass and water; the mass ratio of fly ash, lime and cement is 60:22:20; the amount of water glass added is 6% of the cement mass; the liquid-solid ratio of the slurry is 0.75; the thickness of each support layer is 20 cm; then a soil layer is laid on the support layer; plants are planted in the soil layer to complete the filling of the mine.

[0116] Experimental Example 4

[0117] (1) Leveling the bottom of the mine pit and laying an anti-seepage layer on the leveled bottom of the mine pit; wherein the anti-seepage layer is composed of a 35 cm clay layer, a 30 cm bentonite layer and a 1.0 mm polyethylene LDPE film layer from bottom to top.

[0118] (2) laying a gangue layer on the anti-seepage layer, the height of the gangue layer being 18 cm, then injecting a grouting base liquid into the gangue layer, and stopping the injection of the grouting base liquid when the distance from the uppermost part of the gangue layer is 4 cm, then adding all the aqueous cross-linking liquid into the gangue layer for reaction to obtain a first gangue solidified layer; repeating the above steps to obtain a fifth gangue solidified layer; the raw materials prepared in Preparation Example 2 are used; the mass ratio of the hydrophilic polyurethane prepolymer to the aqueous cross-linking liquid is 1:18;

[0119] (3) Preparation of water-blocking gel layer: The water-blocking gel layer is prepared by reacting the following raw materials: a hydrophilic polyurethane prepolymer, a modified coal-based solid waste suspension, an aqueous cross-linking liquid, and an alkaline solution containing fly ash, and the raw materials prepared in Preparation Example 2 are used; wherein the mass ratio of the hydrophilic polyurethane prepolymer to the modified coal-based solid waste suspension is 1:0.1; the mass ratio of the aqueous cross-linking liquid to the hydrophilic polyurethane prepolymer is 1:15; and the mass ratio of the hydrophilic polyurethane prepolymer to the alkaline solution containing fly ash is 1:0.6.

[0120] The grouting base liquid is injected into the 5th coal gangue solidification layer, and then an aqueous cross-linking liquid accounting for 75% of the total volume of the aqueous cross-linking liquid is added. After the aqueous cross-linking liquid is added to react for 2 minutes, an alkali solution containing fly ash is added to react for 1 hour, and then the remaining aqueous cross-linking liquid is added to obtain a water-blocking gel layer.

[0121] (4) A support layer is laid 20 cm above the water-blocking gel layer. The support layer is obtained by solidifying a slurry prepared by mixing fly ash, lime, cement, water glass and water; the mass ratio of fly ash, lime and cement is 60:22:20; the amount of water glass added is 6% of the cement mass; the liquid-solid ratio of the slurry is 0.75; the thickness of each support layer is 20 cm; then a soil layer is laid on the support layer; plants are planted in the soil layer to complete the filling of the mine.

[0122] The gangue layer prepared in the above experimental example was tested for the solidification rate of metal ions. The test method was as follows:

[0123] The gangue solidified layer of the above experimental example was rinsed with an equal amount of water, and the solidification rate of metal ions in the middle gangue solidified layer of the above experimental example was measured. The specific data are shown in Table 1 below:

[0124] The solidification rate is calculated from the leaching toxicity value of heavy metals before and after solidification:

[0125] Q=C0-C1 / C0

[0126] Where: Q is the solidification rate (%); C0 is the initial leaching concentration of heavy metals in the coal gangue without any solidification material (mg / L); C1 is the leaching concentration of heavy metals in the coal gangue after adding solidification material (mg / L).

[0127] Among them, LA-ICP-MS was used to determine the Cr, Cd, Cu, and Pb ion contents in the heavy metal release solution of coal gangue.

[0128] Table 1

[0129]

[0130]

[0131] In step (2), the present invention utilizes the gel of the present invention to completely encapsulate the gangue through a reasonable raw material ratio, and the gel encapsulating the gangue has a water-blocking and water-stopping effect. That is, when testing, the water initially poured will be absorbed by the gangue gel of the present invention (the gangue solidified layer). As the adsorption limit of the gangue gel is reached, it no longer absorbs water, but it also no longer allows water to enter the interior of the gel. Therefore, almost no water flows out of the gel encapsulating the gangue, so the measured metal ion solidification rate is certainly good. Therefore, the gangue solidified layer of the present invention can effectively solidify the metal ions in the gangue, resulting in a gangue solidified layer with little metal ion overflow.

[0132] Comparative Example 1

[0133] The preparation method is basically the same as that of Experimental Example 1, with the only difference being that, in the preparation of the water-blocking gel layer, sodium alginate is not added to the aqueous cross-linking liquid, and an equal mass of pure water is used instead of sodium alginate.

[0134] Comparative Example 2

[0135] The preparation method is basically the same as that of Experimental Example 1, with the only difference being that, in the preparation of the water-blocking gel layer, alkali and fly ash are not added to the fly ash-containing alkali solution, and ethanol of equal mass is used instead of alkali and fly ash.

[0136] Comparative Example 3

[0137] The preparation method is basically the same as that of Experimental Example 1, with the only difference being that, in the preparation of the water-blocking gel layer, fly ash is not added to the alkali solution containing fly ash, and an equal mass of ethanol is used instead of the fly ash.

[0138] Comparative Example 4

[0139] It adopts basically the same preparation method as Experimental Example 1, with the only difference being that, in the preparation of the water-blocking gel layer, modified fly ash and modified coal gangue are not added to the modified coal-based solid waste suspension, and an equal mass of ethyl acetate is used instead of the modified fly ash and modified coal gangue.

[0140] Effect Example 1

[0141] Test method:

[0142] Compressive strength test: According to GB / T 2567-2008, the composite gel materials prepared in Experimental Examples 1-4 and the water-blocking gel layer materials prepared in Experimental Examples 1-4 were subjected to a compressive strength test after being sealed and placed at room temperature for 7 days.

[0143] Limiting oxygen index (LOI) test: According to GB / T 2406.2-2009, the limiting oxygen index (LOI) of the water-blocking gel layer materials prepared in Experimental Examples 1-4 was tested using a critical oxygen index instrument;

[0144] Solidification shrinkage test: Cut the solidification body (i.e. the water-blocking gel layer material prepared above) into a size of 20.0 mm × 20.0 mm × 20.0 mm and weigh its mass m a , put it into 80℃ electric heating blast drying, take it out and weigh its mass every 1 hour, wait until it is constant weight, take it out and test its mass m b The formula for calculating the shrinkage rate of the solid body is as follows: R1=(m a -m b ) / m a .

[0145] Solidified body water absorption test: Cut the solidified body sample (i.e., the water-blocking gel layer material prepared above) into a volume of 20.0 mm × 20.0 mm × 20.0 mm. Dry it in an oven to constant weight, and record its mass m1. Maintain the temperature at 20°C and immerse it in distilled water for 8 hours. Remove it every hour to drain the surface moisture and weigh it. When the weight remains constant, weigh it again and record its weight m2. The formula for calculating the solidified body water absorption is as follows: R2 = (m2 - m1) / m1.

[0146] The test results of the water-blocking gel layers prepared in the above experimental examples and comparative examples are shown in Table 2.

[0147] Table 2

[0148]

[0149] From the comparison of the compressive strength of the composite gel material prepared in the experimental example and the composite gel material after being sealed and placed at room temperature for 7 days, it can be seen that since the composite gel material prepared in the present invention contains water and alkali, a hydration reaction of fly ash, coal gangue and water will further occur during the subsequent standing process, thereby further increasing the compressive strength of the composite gel material.

[0150] From the limiting oxygen index of the water-blocking gel layer prepared in the experimental example, it can be seen that the composite gel material of the present invention has a good flame retardant effect.

[0151] The sealing principle of polyurethane gel material is mainly that NCO in the system reacts with water, and quickly solidifies to form a large amount of gel solidified body. Since the generated solidified body contains a large amount of water, it is inevitable that drying and shrinkage will occur during use. If the shrinkage rate of the solidified body is large, repeated leakage may occur. The standard for testing repeated leakage is "solidified body water absorption rate > solidified body shrinkage rate". The water absorption rate of the composite gel of coal-based solid waste and polyurethane prepared in the experimental example of the present invention is greater than the solidified body shrinkage rate, indicating that the composite gel of coal-based solid waste and polyurethane prepared in the experimental example of the present invention will not experience repeated leakage when used, and the composite gel of coal-based solid waste and polyurethane of the present invention has a lower solidified body shrinkage rate than the control example. The smaller solidified body shrinkage rate helps to reduce the distance between the solidified body shrinkage and the bonding matrix, thereby improving the overall performance and durability of the material.

[0152] It can be seen from the results of Experimental Example 1 and Comparative Examples 1-4 that only under the joint action of the four gels in the water-blocking gel layer of the present invention can a gel layer with good water-blocking effect be obtained. The gel layer can fully absorb water from the support layer or elsewhere. Even if it cannot absorb water, due to its water-blocking and water-stopping properties, it can also prevent excessive water from entering the coal gangue layer, thereby avoiding the large-scale leakage of metal ions from the coal gangue layer due to water penetration and polluting the environment.

[0153] In addition, the water-blocking gel layer has good compressive strength and is not easy to be damaged, and has a good flame retardant effect. Applying it above the gangue layer can provide secondary protection for reducing the combustion of the gangue layer and reducing the pollution of the gangue layer.

[0154] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be understood by those skilled in the art that various modifications or variations made by those skilled in the art based on the technical solution of the present invention without creative effort are still within the scope of protection of the present invention.

Claims

1. A method for effectively utilizing coal gangue to fill a mine, characterized in that: The following steps are involved: (1) Laying an anti-seepage layer on the leveled bottom of the mine; (2) laying a coal gangue layer on the anti-seepage layer, and injecting a grouting base liquid 1 and an aqueous cross-linking liquid 1 in sequence to form at least one coal gangue solidified layer; (3) injecting grouting base liquid 2 onto the coal gangue solidified layer, and adding aqueous cross-linking liquid 2 and alkali solution containing fly ash in stages to form a water-blocking gel layer; (4) A support layer is provided above the water-blocking gel layer, and a soil layer is laid on the support layer; and vegetation restoration is performed.

2. The method for effectively utilizing coal gangue to fill a mine according to claim 1, characterized in that: In step (1), the anti-seepage layer is composed of a clay layer, a bentonite layer and a polyethylene LDPE film layer from bottom to top; wherein the clay layer has a thickness of 30-40 cm, the bentonite layer has a thickness of 20-30 cm, and the polyethylene LDPE film layer has a thickness of 1.0-1.5 mm.

3. The method for effectively utilizing coal gangue to fill a mine according to claim 1, characterized in that: In step (2), the thickness of each gangue layer is 10-20 cm, the grouting base liquid 1 is injected to a position 3-5 cm from the top of the gangue layer and then the aqueous cross-linking liquid 2 is added to react and solidify.

4. The method for effectively utilizing coal gangue to fill a mine according to claim 1, characterized in that: In step (3), the formation of the medium-resistance hydrogel layer includes: S1: Inject grouting base liquid 2 on the gangue solidification layer to a thickness of 5-10cm. S2: adding aqueous crosslinking liquid 2 in two steps. First, add 75%-90% volume of aqueous crosslinking liquid 2 and react for 1-3 minutes. Then, add alkali solution containing fly ash and react for 1-2 hours. Finally, add the remaining aqueous crosslinking liquid 2.

5. The method for effectively utilizing coal gangue to fill a mine according to claim 1, characterized in that: The grouting base liquid is prepared by mixing a hydrophilic polyurethane prepolymer and a modified coal-based solid waste suspension in a mass ratio of 1:(0.1-0.3); The aqueous cross-linking liquid comprises sodium alginate and water, and the mass ratio of sodium alginate to water is 1:(100-150).

6. The method for effectively utilizing coal gangue to fill a mine according to claim 1, characterized in that: In step (2), the mass ratio of the hydrophilic polyurethane prepolymer in the grouting base liquid 1 to the aqueous cross-linking liquid 1 is 1:(15-25); In step (3), the mass ratio of the hydrophilic polyurethane prepolymer in the grouting base liquid 2 to the aqueous cross-linking liquid 2 is 1:(10-20).

7. The method for effectively utilizing coal gangue to fill a mine according to claim 1, characterized in that: In step (3), the fly ash-containing alkali solution comprises fly ash, alkali and ethanol; wherein the fly ash and alkali are dissolved in ethanol with a concentration of 2-4 mol / L in a mass ratio of 1:(4-8); the alkali is sodium hydroxide or potassium hydroxide; The mass ratio of the hydrophilic polyurethane prepolymer to the fly ash-containing alkali solution in the grouting base liquid 2 is 1:0.5-1.

8. The method for effectively utilizing coal gangue to fill a mine according to claim 1, characterized in that: The support layer in step (4) is solidified by mixing fly ash, lime, cement in a mass ratio of (45-70): (18-30): (15-20) with water glass (4-7% of the cement mass) and water, and has a thickness of 10-20 cm.

9. The method for effectively utilizing coal gangue to fill a mine according to claim 1, characterized in that: In step (4), the thickness of the soil layer is 100-150 cm.

10. The method for effectively utilizing coal gangue to fill a mine according to claim 1, characterized in that: The limiting oxygen index of the water-blocking gel layer is ≥70%, the water absorption rate of the solidified body is greater than the shrinkage rate, and the metal ion solidification rate is ≥99%.

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