Method for preparing paste based on coal-electricity combined operation three wastes and filling mining method

Abstract

The invention provides a method for preparing paste based on coal-electricity joint operation'three wastes' and a filling mining method, and belongs to the technical field of industrial waste resource utilization. The method comprises the following steps: capturing and analyzing CO2 in flue gas in sequence to obtain high-concentration CO2 gas; fly ash and first purified mine water are subjected to first mixing, obtained fly ash slurry is subjected to second mixing with Na2CO3, NaHCO3, NaCl and an alcohol amine solution, obtained mixed slurry containing fly ash is atomized and then subjected to third mixing with the high-concentration CO2 gas, and mixed slurry containing carbonate is obtained through a neutralization reaction; the carbonate-containing mixed slurry, gangue particles and second purified mine water are subjected to fourth mixing, and paste is obtained. According to the method, solid, liquid and gas three wastes such as gangue, fly ash, mine water and flue gas generated by coal-electricity joint operation can be synchronously treated, the cost is low, and the prepared paste can be used for coal mine filling mining and is high in economic benefit.

Description

Technical Field

[0001] The present invention relates to the technical field of resource utilization of industrial wastes, and in particular to a method for preparing paste based on "three wastes" of coal-electricity joint ventures and a filling mining method. Background Art

[0002] Building a coal-fired power plant near a coal mine can directly use the coal produced by the coal mine to generate electricity, changing the external transmission of coal to the external transmission of electricity. Coal mining will inevitably produce a large amount of gangue, and mine drainage will also produce a large amount of wastewater; coal-fired power plants will inevitably produce fly ash and emit flue gas (including CO2) when generating electricity. The ground accumulation of gangue and fly ash and the emission of mine water and CO2 will cause pollution to ground vegetation, water bodies and air. At present, related technologies usually only treat one of the above-mentioned "three wastes" of solid, liquid and gas, which is costly. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preparing a paste based on the "three wastes" of coal-electricity joint ventures and a filling mining method. The method of the present invention can simultaneously treat the "three wastes" of solid, liquid and gas, such as gangue, fly ash, mine water and flue gas, with low cost, and the prepared paste can be used for coal mine filling mining, with high economic benefits.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a method for preparing a paste based on the "three wastes" of coal-electricity joint venture, comprising the following steps:

[0006] The CO2 in the flue gas is captured and analyzed in sequence to obtain a high-concentration CO2 gas, wherein the volume fraction of CO2 in the high-concentration CO2 gas is ≥96%;

[0007] The fly ash is first mixed with the first purified mine water, and the obtained fly ash slurry is second mixed with Na2CO3, NaHCO3, NaCl, and alcohol amine solution to obtain a fly ash-containing mixed slurry;

[0008] Atomizing the fly ash-containing mixed slurry and performing a third mixing with the high-concentration CO2 gas to obtain a carbonate-containing mixed slurry through a neutralization reaction;

[0009] The carbonate-containing mixed slurry, gangue particles and the second purified mine water are mixed for the fourth time to obtain the paste.

[0010] Preferably, the water-cement ratio of the fly ash slurry is 2 to 4:1; and the first mixing is carried out on the ground.

[0011] Preferably, the alcoholamine solution is prepared from alcoholamine and water, and the concentration of the alcoholamine solution is 10-30wt%; the mass ratio of the fly ash slurry, Na2CO3, NaHCO3, NaCl and the alcoholamine solution is 5-10:1-2:1-2:1-2:1-2; and the second mixing is carried out on the ground.

[0012] Preferably, the temperature of the fly ash-containing mixed slurry during atomization is 30-90°C; the mass ratio of the fly ash-containing mixed slurry to high-concentration CO2 gas is 50-100:1-3; and the atomization, the third mixing and the neutralization reaction are carried out on the ground.

[0013] Preferably, the maximum particle size of the gangue particles is less than 25 mm, and the mass of the gangue particles with a particle size of ≤5 mm accounts for more than 40% of the total mass of the gangue particles.

[0014] Preferably, the mass ratio of the fly ash to the gangue particles is 1:2-5; the mass ratio of the total mass of the fly ash and gangue particles to the second purified mine water is 0.5-2:1; and the fourth mixing is carried out underground or on the ground in a coal mine.

[0015] Preferably, the flue gas and fly ash are derived from a coal-fired power plant;

[0016] The first purified mine water and the second purified mine water are obtained by purifying the mine drainage collected in the underground water tank of the coal mine;

[0017] The preparation method of the gangue particles comprises the following steps: using the TDS method to sort the raw coal transported from the underground mining face of the coal mine, mixing the sorted gangue with the gangue transported from the underground mining face of the coal mine, and then crushing and screening them in sequence.

[0018] Preferably, the purification treatment and the sorting are carried out independently in a coal mine or on the ground.

[0019] Preferably, the method for preparing the paste based on the "three wastes" of coal-electricity joint venture comprises the following steps:

[0020] The CO2 in the flue gas generated by the coal-fired power plant is captured by the ethanolamine wet purification method, and then a high-concentration CO2 gas with a volume fraction of more than 96% is obtained by analysis;

[0021] The fly ash generated by the coal-fired power plant is first mixed with the first purified mine water on the ground, and the obtained fly ash slurry, Na2CO3, NaHCO3, NaCl and alcohol amine solution are second mixed to obtain a fly ash-containing mixed slurry;

[0022] The fly ash-containing mixed slurry is injected into the top of a spray tower, and the fly ash-containing mixed slurry is atomized by an ultrasonic vibration device, and at the same time, the high-concentration CO2 gas is introduced into the bottom of the spray tower to perform a third mixing with the atomized fly ash-containing mixed slurry, and a carbonate-containing mixed slurry is obtained through a neutralization reaction;

[0023] In the underground pit yard of the coal mine, the raw coal transported from the mining face is sorted by the TDS method, the sorted coal is transported to the surface, the sorted gangue is mixed with the gangue transported from the mining face, and the mixed gangue is crushed and screened in turn to obtain gangue particles;

[0024] The carbonate-containing mixed slurry, gangue particles and second purified mine water are mixed for the fourth time to obtain the paste;

[0025] The first purified mine water and the second purified mine water are obtained by purification treatment of mine drainage collected from underground water tanks in coal mines.

[0026] The present invention provides a backfill mining method, comprising the following steps:

[0027] The paste is prepared by the method described in the above technical solution;

[0028] The paste is pressurized by a concrete pump and transported to the use site of the underground mining working face of the coal mine through a pipeline, and is used for replacing coal in the continuous mining and filling working face, building walls along the goaf, or preventing and extinguishing fire in the goaf area.

[0029] Beneficial effects: The present invention sequentially captures and analyzes CO2 in flue gas to obtain high-concentration CO2 gas, wherein the volume fraction of CO2 in the high-concentration CO2 gas is ≥96%; the fly ash is first mixed with the first purified mine water, and the obtained fly ash slurry, Na2CO3, NaHCO3, NaCl and alcohol amine solution are second mixed to obtain a fly ash-containing mixed slurry; the fly ash-containing mixed slurry is atomized and then thirdly mixed with the high-concentration CO2 gas, and a carbonate-containing mixed slurry is obtained through a neutralization reaction; the carbonate-containing mixed slurry, gangue particles and the second purified mine water are fourthly mixed to obtain a paste. The method of the present invention can simultaneously treat the solid, liquid and gaseous "three wastes" such as gangue, fly ash, mine water and flue gas generated by coal-electricity joint ventures, with low cost, and the prepared paste can be used for coal mine filling mining, with high economic benefits. DETAILED DESCRIPTION

[0030] The present invention provides a method for preparing a paste based on the "three wastes" of coal-electricity joint venture, comprising the following steps:

[0031] The CO2 in the flue gas is captured and analyzed in sequence to obtain a high-concentration CO2 gas, wherein the volume fraction of CO2 in the high-concentration CO2 gas is ≥96%;

[0032] The fly ash is first mixed with the first purified mine water, and the obtained fly ash slurry is second mixed with Na2CO3, NaHCO3, NaCl, and alcohol amine solution to obtain a fly ash-containing mixed slurry;

[0033] Atomizing the fly ash-containing mixed slurry and performing a third mixing with the high-concentration CO2 gas to obtain a carbonate-containing mixed slurry through a neutralization reaction;

[0034] The carbonate-containing mixed slurry, gangue particles and the second purified mine water are mixed for the fourth time to obtain the paste.

[0035] Building a coal-fired power plant near a coal mine can directly use the coal produced by the coal mine to generate electricity, changing the external transmission of coal to the external transmission of electricity. This model is called the "coal-electricity joint venture" model. The "coal-electricity joint venture" model will produce solid, liquid and gas "three wastes", such as gangue, fly ash, mine water and flue gas. At present, the relevant technology usually only treats one of the above-mentioned solid, liquid and gas "three wastes". For example, for the disposal of gangue, the relevant technology is to separate gangue from coal by washing on the ground. The accumulation of gangue on the ground occupies a large amount of land resources and pollutes the environment. For the disposal of fly ash, the relevant technology usually uses fly ash as building materials, road construction and backfill, agricultural fertilizers and soil conditioners, and recovers industrial raw materials and environmental protection materials from fly ash. In addition, the direct discharge of CO2-containing flue gas generated by coal-fired power plants will cause environmental pollution, and it is impossible to fully recycle CO2. The present invention takes into account the overall "three wastes" generated by the "coal-electricity joint venture" model, systematically plans the disposal methods of solid, liquid and gaseous wastes, and realizes the local efficient and coordinated harmless treatment and resource utilization of coal mine and power plant wastes. The method of the present invention is described in detail below.

[0036] The present invention sequentially captures and analyzes CO2 in flue gas to obtain high-concentration CO2 gas, wherein the volume fraction of CO2 in the high-concentration CO2 gas is ≥96%. As an embodiment of the present invention, the flue gas may be derived from a coal-fired power plant, that is, the flue gas may be specifically flue gas generated during the production process of a coal-fired power plant. As an embodiment of the present invention, a wet purification method using ethanolamine (MEA) may be specifically used to capture CO2; the present invention has no special limitation on the analysis, and an analysis method familiar to those skilled in the art may be used. As an embodiment of the present invention, the capture and analysis may be performed on the ground.

[0037] The present invention first mixes fly ash with first purified mine water to obtain fly ash slurry. As an embodiment of the present invention, the fly ash may come from a coal-fired power plant, that is, the fly ash may specifically be fly ash produced in the production process of a coal-fired power plant (its mineral composition is specifically shown in Table 1 in Example 1, which will not be repeated here), and it may be stored in a closed manner before use. As an embodiment of the present invention, the water-to-ash ratio of the fly ash slurry may be 2 to 4:1, specifically 2:1, 3:1 or 4:1; in the embodiment of the present invention, the water-to-ash ratio of the fly ash slurry is set within the above range, which can improve the stability of the fly ash slurry and facilitate the transportation of the fly ash slurry.

[0038] As an embodiment of the present invention, the first purified mine water can be obtained by purifying the mine drainage collected by the underground water tank of the coal mine. Specifically, after the mine drainage collected by the underground water tank of the coal mine is purified, a part of it can be used as the first purified mine water to prepare fly ash slurry and as the second purified mine water to prepare paste, and the other part can be transported to the coal-fired power plant through a pipeline for use as power generation water; the purification treatment can be carried out in the coal mine or on the ground. As an embodiment of the present invention, the first mixing can be carried out on the ground.

[0039] After obtaining the fly ash slurry, the present invention performs a second mixing of the fly ash slurry, Na2CO3, NaHCO3, NaCl and an alcoholamine solution to obtain a fly ash-containing mixed slurry. As an embodiment of the present invention, the alcoholamine solution is prepared by alcoholamine and water, and the alcoholamine can be one or more of monoethanolamine, diethanolamine and diisopropanolamine, specifically monoethanolamine, diethanolamine or diisopropanolamine; the concentration of the alcoholamine solution can be 10-30wt%, specifically 10wt%, 15wt%, 20wt%, 25wt% or 30wt%; the mass ratio of the fly ash slurry, Na2CO3, NaHCO3, NaCl and the alcoholamine solution can be 5-10:1-2:1-2:1-2:1-2, further can be 8-10:1-1.5:1-1.5:1-1.5:1-1.5, specifically can be 10:1:1:1:1. As an embodiment of the present invention, the second mixing can be performed on the ground.

[0040] After obtaining the fly ash-containing mixed slurry, the present invention atomizes the fly ash-containing mixed slurry and then performs a third mixing with the high-concentration CO2 gas, and obtains a carbonate-containing mixed slurry through a neutralization reaction. As an embodiment of the present invention, the temperature of the fly ash-containing mixed slurry during atomization can be 30 to 90°C, specifically 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or 90°C; the mass ratio of the fly ash-containing mixed slurry to the high-concentration CO2 gas is 50 to 100:1 to 3, further 50 to 70:1 to 2, and further 50 to 60:1 to 1.5, specifically 50:1. In the embodiment of the present invention, the amount ratio of the fly ash-containing mixed slurry to the high-concentration CO2 gas is limited to the above range, which can ensure that the reaction is fully carried out and is conducive to the maximum treatment of CO2.

[0041] As an embodiment of the present invention, the atomization, the third mixing and the neutralization reaction can be carried out on the ground, specifically in a spray tower. For example, in an embodiment of the present invention, the fly ash-containing mixed slurry can be heated to 30-90°C and then injected into the top of a spray tower. The fly ash-containing mixed slurry is atomized by an ultrasonic vibration device, and at the same time, the high-concentration CO2 gas is introduced into the bottom of the spray tower and fully mixed with the atomized fly ash-containing mixed slurry. The CO2 reacts with the alkaline substances in the fly ash-containing mixed slurry to obtain a carbonate-containing mixed slurry.

[0042] After obtaining the carbonate-containing mixed slurry, the present invention performs a fourth mixing of the carbonate-containing mixed slurry, gangue particles and the second purified mine water to obtain the paste. As an embodiment of the present invention, the mass ratio of the fly ash to the gangue particles can be 1:2-5, specifically 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5; the mass ratio of the total mass of the fly ash and gangue particles to the second purified mine water can be 0.5-2:1, specifically 0.5:1, 1:1, 1.5:1 or 2:1. In the embodiment of the present invention, the amount of each component is limited to the above range, which can ensure good working performance of the paste and is conducive to improving its mechanical strength after solidification.

[0043] As an embodiment of the present invention, the mass of the gangue particles with a maximum particle size of <25mm and a particle size of ≤5mm accounts for more than 40% of the total mass of the gangue particles, for example, it can be 40-60%, specifically 40%, 45%, 50%, 55% or 60%. As an embodiment of the present invention, the preparation method of the gangue particles may include the following steps: using the TDS method to sort the raw coal transported from the underground mining face of the coal mine, mixing the sorted gangue with the gangue transported from the underground mining face of the coal mine, and then crushing and screening in sequence; the sorting can be carried out in the coal mine or on the ground.

[0044] As an embodiment of the present invention, the second purified mine water can be obtained by purifying the mine drainage collected by the underground water tank of the coal mine. Specifically, after the mine drainage collected by the underground water tank of the coal mine is purified, a part of it can be used as the first purified mine water to prepare fly ash slurry and as the second purified mine water to prepare paste, and the other part can be transported to the coal-fired power plant through a pipeline for use as power generation water; the purification treatment can be carried out in the coal mine or on the ground. As an embodiment of the present invention, the fourth mixing can be carried out in the coal mine or on the ground.

[0045] As an embodiment of the present invention, the strength of the paste after solidification can be between 1 and 5 MPa. If its strength needs to be further improved, the raw material for preparing the paste can also use cement to replace part of the fly ash. For example, when cement is used, the mass ratio of cement to fly ash can be 1 to 2:5 to 10.

[0046] As an embodiment of the present invention, the method for preparing paste based on the "three wastes" of coal-electricity joint venture may include the following steps:

[0047] The CO2 in the flue gas generated by the coal-fired power plant is captured by the ethanolamine wet purification method, and then a high-concentration CO2 gas with a volume fraction of more than 96% is obtained by analysis;

[0048] The fly ash generated by the coal-fired power plant is first mixed with the first purified mine water on the ground, and the obtained fly ash slurry, Na2CO3, NaHCO3, NaCl and alcohol amine solution are second mixed to obtain a fly ash-containing mixed slurry;

[0049] The fly ash-containing mixed slurry is injected into the top of a spray tower, and the fly ash-containing mixed slurry is atomized by an ultrasonic vibration device, and at the same time, the high-concentration CO2 gas is introduced into the bottom of the spray tower to perform a third mixing with the atomized fly ash-containing mixed slurry, and a carbonate-containing mixed slurry is obtained through a neutralization reaction;

[0050] In the underground pit yard of the coal mine, the raw coal transported from the mining face is sorted by the TDS method, the sorted coal is transported to the surface, the sorted gangue is mixed with the gangue transported from the mining face, and the mixed gangue is crushed and screened in turn to obtain gangue particles;

[0051] The carbonate-containing mixed slurry, gangue particles and second purified mine water are mixed for the fourth time to obtain the paste;

[0052] The first purified mine water and the second purified mine water are obtained by purification treatment of mine drainage collected from underground water tanks in coal mines.

[0053] The present invention provides a backfill mining method, comprising the following steps:

[0054] The paste is prepared by the method described in any one of the above technical solutions;

[0055] The paste is pressurized by a concrete pump and transported to the use site of the underground mining face of the coal mine through a pipeline, and is used for replacing coal in the continuous mining and filling working face, building walls along the goaf, or preventing and extinguishing fire in the goaf area.

[0056] The present invention systematically considers the harmless treatment and resource utilization of solid, liquid and gaseous wastes generated by the "coal-electricity joint venture" model. The gangue generated by the mine can be used as the aggregate of the paste, and the mixed slurry containing fly ash can be used as the bonding material of the paste after neutralization reaction with CO2. At the same time, the mine water is used and digested. Through a complete set of process, the comprehensive utilization of the "three wastes" is realized, and the pollution to the environment caused by the accumulation of gangue on the ground and the discharge of mine water is eliminated, and the emission of CO2 is reduced. Moreover, the main raw materials for preparing the paste of the present invention are all derived from the waste generated by the "coal-electricity joint venture" model, which reduces its preparation cost; at the same time, the gangue sorting and mine water purification treatment are carried out in the coal mine, which avoids the reverse transportation of gangue and mine water and reduces the production cost of the mine; in addition, the paste can replace the coal in the coal mine, improve the recovery rate of coal, and further create economic benefits.

[0057] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] Example 1

[0059] (1) The fly ash generated in the production process of the coal-fired power plant is stored in a closed manner, and samples are taken for determination of physical and chemical properties (the specific determination results are shown in Table 1); the CO2 in the flue gas generated in the production process of the coal-fired power plant is captured by a wet purification method using ethanolamine (MEA), and then a high-concentration CO2 gas with a volume fraction of more than 96% is obtained by analysis;

[0060] Table 1 Physical and chemical properties of fly ash

[0061] Mineral composition Silicon dioxide Aluminum oxide Calcium sulfate Calcium carbonate Calcium Oxide Quality content 27.0％ 11.9％ 42.0％ 8.0％ 10.9％

[0062] (2) Purifying the mine drainage collected in the underground water tank to obtain purified mine water, a portion of which is transported to the surface through a pipeline for use in power plant power generation water and the preparation of fly ash slurry, and another portion of which is used as first purified mine water for the subsequent step of preparing fly ash slurry and as second purified mine water for the subsequent step of preparing paste;

[0063] (3) mixing the fly ash with the first purified mine water at a water-to-ash ratio of 3:1 on the ground to prepare a fly ash slurry, and adding Na2CO3, NaHCO3, NaCl, and an alcohol amine solution (specifically prepared from monoethanolamine and water with a concentration of 30 wt%) to the obtained fly ash slurry according to the measured physical and chemical properties of the fly ash to obtain a fly ash mixed slurry; wherein the mass ratio of the fly ash slurry, Na2CO3, NaHCO3, NaCl, and the alcohol amine solution is The ratio of the mixed slurry containing fly ash to the mixed slurry is 10:1:1:1:1; the fly ash-containing mixed slurry is heated to 60°C and injected into the top of the spray tower, the fly ash-containing mixed slurry is atomized by an ultrasonic vibration device, and the high-concentration CO2 gas is introduced into the bottom of the spray tower to fully mix with the atomized fly ash-containing mixed slurry, so that CO2 and the alkaline substances in the fly ash-containing mixed slurry undergo a neutralization reaction to form a carbonate-containing mixed slurry; wherein the mass ratio of the fly ash-containing mixed slurry to the high-concentration CO2 gas is 50:1;

[0064] (4) In the underground pit yard of the coal mine, the raw coal transported from the mining face is sorted by the TDS method, the sorted coal is transported to the surface, the sorted gangue is mixed with the gangue transported from the mining face, the mixed gangue is crushed, pulverized and screened in sequence, and the gangue particles obtained after screening are used as aggregates for preparing the paste, wherein the maximum particle size of the gangue particles is less than 23 mm, and the mass of the gangue particles with a particle size of ≤5 mm accounts for 50% of the total mass of the gangue particles;

[0065] (5) transporting the carbonate-containing mixed slurry prepared on the ground to the underground, mixing it with the gangue particles, and adding the second purified mine water, wherein the mass ratio of the carbonate-containing mixed slurry, the gangue particles and the second purified mine water is 4:3:4, that is, the mass ratio of fly ash (dry weight) to the gangue particles is 1:3, and the mass ratio of solid waste (the sum of the mass of fly ash and gangue particles) to total water (including the first purified mine water used to prepare the fly ash slurry and the second purified mine water used to prepare the paste) is 4:7, and then stirring and mixing to obtain a paste;

[0066] (6) The paste is pressurized by a concrete pump and transported through a pipeline to the continuous mining and filling working face for filling and replacing coal. The average strength of the paste after solidification 28 days is tested to be 2 MPa, which meets the use requirements.

[0067] Example 2

[0068] The method of Example 1 was used, except that the concentration of the alcoholamine solution in step (2) was 10 wt %. The average strength of the paste obtained after solidification for 28 days was 1 MPa, which met the use requirements.

[0069] Comparative Example 1

[0070] The method of Example 1 was followed, except that the alcoholamine solution used in preparing the fly ash mixed slurry in step (2) was omitted. The average strength of the resulting paste after solidification for 28 days was 0.05 MPa, which did not meet the use requirements.

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a paste based on the "three wastes" of coal-electricity joint ventures, comprising the following steps: The CO2 in the flue gas is captured and analyzed in sequence to obtain a high-concentration CO2 gas, wherein the volume fraction of CO2 in the high-concentration CO2 gas is ≥96%; The fly ash is first mixed with the first purified mine water, and the obtained fly ash slurry is second mixed with Na2CO3, NaHCO3, NaCl, and alcohol amine solution to obtain a fly ash-containing mixed slurry; Atomizing the fly ash-containing mixed slurry and performing a third mixing with the high-concentration CO2 gas to obtain a carbonate-containing mixed slurry through a neutralization reaction; The carbonate-containing mixed slurry, gangue particles and the second purified mine water are mixed for the fourth time to obtain the paste.

2. The method according to claim 1, characterized in that The water-cement ratio of the fly ash slurry is 2-4:1; and the first mixing is carried out on the ground.

3. The method according to claim 2, characterized in that The alcoholamine solution is prepared from alcoholamine and water, and the concentration of the alcoholamine solution is 10-30wt%; the mass ratio of the fly ash slurry, Na2CO3, NaHCO3, NaCl and the alcoholamine solution is 5-10:1-2:1-2:1-2:1-2; the second mixing is carried out on the ground.

4. The method according to claim 1, characterized in that: The temperature of the fly ash-containing mixed slurry during atomization is 30-90°C; the mass ratio of the fly ash-containing mixed slurry to high-concentration CO2 gas is 50-100:1-3; the atomization, the third mixing and the neutralization reaction are carried out on the ground.

5. The method according to claim 1, characterized in that The maximum particle size of the gangue particles is less than 25 mm, and the mass of the gangue particles with a particle size of ≤5 mm accounts for more than 40% of the total mass of the gangue particles.

6. The method according to any one of claims 1 to 5, characterized in that: The mass ratio of the fly ash to the gangue particles is 1:2-5; the mass ratio of the total mass of the fly ash and gangue particles to the second purified mine water is 0.5-2:1; and the fourth mixing is carried out underground or on the ground in a coal mine.

7. The method according to claim 1, characterized in that The flue gas and fly ash are derived from a coal-fired power plant; The first purified mine water and the second purified mine water are obtained by purifying the mine drainage collected in the underground water tank of the coal mine; The preparation method of the gangue particles comprises the following steps: using the TDS method to sort the raw coal transported from the underground mining face of the coal mine, mixing the sorted gangue with the gangue transported from the underground mining face of the coal mine, and then crushing and screening them in sequence.

8. The method according to claim 7, characterized in that The purification process and the sorting are carried out independently in the coal mine or on the ground.

9. The method according to claim 1, characterized in that: The following steps are involved: The CO2 in the flue gas generated by the coal-fired power plant is captured by the ethanolamine wet purification method, and then a high-concentration CO2 gas with a volume fraction of more than 96% is obtained by analysis; The fly ash generated by the coal-fired power plant is first mixed with the first purified mine water on the ground, and the obtained fly ash slurry, Na2CO3, NaHCO3, NaCl and alcohol amine solution are second mixed to obtain a fly ash-containing mixed slurry; The fly ash-containing mixed slurry is injected into the top of a spray tower, and the fly ash-containing mixed slurry is atomized by an ultrasonic vibration device, and at the same time, the high-concentration CO2 gas is introduced into the bottom of the spray tower to perform a third mixing with the atomized fly ash-containing mixed slurry, and a carbonate-containing mixed slurry is obtained through a neutralization reaction; In the underground pit yard of the coal mine, the raw coal transported from the mining face is sorted by the TDS method, the sorted coal is transported to the surface, the sorted gangue is mixed with the gangue transported from the mining face, and the mixed gangue is crushed and screened in turn to obtain gangue particles; The carbonate-containing mixed slurry, gangue particles and second purified mine water are mixed for the fourth time to obtain the paste; The first purified mine water and the second purified mine water are obtained by purification treatment of mine drainage collected from underground water tanks in coal mines.

10. A backfill mining method, characterized in that: The following steps are involved: The paste is prepared by the method according to any one of claims 1 to 9; The paste is pressurized by a concrete pump and transported to the use site of the underground mining working face of the coal mine through a pipeline, and is used for replacing coal in the continuous mining and filling working face, building walls along the goaf, or preventing and extinguishing fire in the goaf area.