Coal-based solid waste cementing material for coal mine filling engineering, preparation method and application

Abstract

The application provides a coal-based solid waste cementing material for coal mine filling engineering, a preparation method and application. The preparation method comprises the following steps: mixing and grinding coal-based solid waste including fly ash 30-60 parts, furnace bottom ash 20-40 parts and gasification slag 20-30 parts under the action of a grinding aid to obtain a mixture A; wherein the mass of the grinding aid is 0.1%-0.5% of the coal-based solid waste; preparing a solid waste solution with a mass concentration of 20%-40% from the mixture A by using a solvent, and introducing carbonization gas into the solid waste solution to obtain an acidified solution; mixing and grinding desulfurization gypsum 30-60 parts, lime 30-50 parts and cement clinker 10-20 parts to obtain a mixture B, and adding the mixture B into the acidified solution to obtain the coal-based solid waste cementing material. The coal-based solid waste cementing material has a wider application scene, and can effectively reduce the cost of goaf filling and improve the coal-based solid waste consumption efficiency.

Description

Technical Field

[0001] This application relates to the fields of resource utilization of bulk coal-based solid waste and coal mine backfilling engineering technology, and in particular to a coal-based solid waste cementing material, preparation method and application for coal mine backfilling engineering. Background Technology

[0002] Currently, the disposal approach for bulk coal-based solid wastes such as fly ash, coal gangue, gasification slag, and bottom ash is to prepare them into filling materials to prevent spontaneous combustion of residual coal in goaf areas and further compaction and subsidence. However, the current approach faces the following problems: ① Using bulk coal-based solid wastes as a base material results in large fluctuations in raw material composition, particularly the unstable CaO content, leading to unstable performance and poor stability of the filling product. Furthermore, ② the process of preparing polymer cementitious materials from bulk coal-based solid wastes often uses strong alkaline activators such as sodium silicate and sodium hydroxide, which is costly, dangerous, and has poor on-site applicability. Summary of the Invention

[0003] This application aims to at least partially address one of the technical problems in related technologies. This application proposes a coal-based solid waste cementitious material for coal mine backfilling projects, its preparation method, and its application. It fully utilizes the large quantities of coal-based solid waste surrounding coal mines to prepare the material through physical grinding activation, carbon dioxide acidification, chemical activation, and other methods. It also proposes a suitable application process, making it more feasible for construction, applicable to a wider range of scenarios, and effectively reducing backfilling costs while improving the efficiency of coal-based solid waste disposal.

[0004] According to an embodiment of the first aspect of this application, a method for preparing a coal-based solid waste cementitious material for coal mine backfilling projects is provided, comprising the following steps:

[0005] The coal-based solid waste comprises 30-60 parts by weight of fly ash, 20-40 parts by weight of bottom ash and 20-30 parts by weight of gasification slag, which are mixed and ground under the action of a grinding aid to obtain mixture A; wherein the mass of the grinding aid is 0.1%-0.5% of the coal-based solid waste.

[0006] The mixture A is prepared into a solid waste solution with a mass concentration of 20%-40% using a solvent, and carbonization gas is introduced into the solid waste solution to obtain an acidified solution;

[0007] By weight, 30-60 parts of desulfurized gypsum, 30-50 parts of lime, and 10-20 parts of cement clinker are mixed and ground to obtain mixture B. Mixture B is then added to the acidification solution and stirred until homogeneous to obtain coal-based solid waste cementitious material. The mass of mixture B is 10%-20% of that of mixture A.

[0008] In some embodiments, the specific surface area of ​​mixture A is 300 m².2 / kg-400m 2 / kg;

[0009] And / or, the molar ratio of Si to Al in the coal-based solid waste is 1.5-3:1;

[0010] And / or, the grinding aid comprises 0.02-2 parts of triisopropanolamine, 0.015-1.5 parts of octadecyltrimethylammonium chloride, 0.01-1 parts of phosphate methacrylate, 0.005-0.5 parts of sodium allyl sulfonate and 0.02-1.5 parts of water;

[0011] And / or, the mass ratio of isopropanolamine, octadecyltrimethylammonium chloride, phosphate methacrylate, sodium allyl sulfonate, and water in the grinding aid is 4:3:2:1:3.

[0012] In some embodiments, the solvent includes water or contains SO4. 2- Cl - Na + The brine; the brine contains SO4 2- Concentration of 100-200 mg / L; Cl - Concentration of 100-600 mg / L; Na + The concentration is 100-1000 mg / L;

[0013] And / or, the carbonized gas contains a certain concentration of CO2 gas and / or SO2 gas; the flow rate of the carbonized gas is 3-10 L / min;

[0014] And / or, the pH of the acidified solution is 7-8.

[0015] In some embodiments, the specific surface area of ​​the mixture B is 300 m². 2 / kg-400m 2 / kg.

[0016] In some embodiments, the mass ratio of the fly ash, the bottom ash, and the gasification slag is (3-6):(2-4):(2-3);

[0017] And / or, the mass ratio of the desulfurized gypsum, the lime and the cement clinker is (3-6):(3-5):(1-2).

[0018] In some embodiments, the coal-based solid waste cementitious material contains at least 90% coal-based solids by mass.

[0019] According to an embodiment of the second aspect of this application, a coal-based solid waste cementitious material for coal mine backfilling projects is provided, which is obtained using the preparation method described in any of the above embodiments.

[0020] According to the embodiments of the third aspect of this application, the application of the coal-based solid waste cementitious material described in any of the above embodiments in goaf filling is proposed.

[0021] In some embodiments, goaf filling includes the following steps: preparing the coal-based solid waste cementitious material into a cementitious material solution with a water-ash ratio of 1-1.4:1;

[0022] The coal gangue aggregate is crushed to a particle size not exceeding 30mm;

[0023] The cementitious material solution is mixed with the coal gangue aggregate at a mass ratio of 1:2-4, and then sprayed into the branch roadway to be filled through a spraying device and connected to the roof through a reserved pipe.

[0024] In some embodiments, the cementitious material solution and the coal gangue aggregate are transported separately to the mine, and the cementitious material solution and the coal gangue aggregate are mixed in the backfilling branch roadway.

[0025] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0026] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 This is a flowchart of a method for preparing coal-based solid waste cementitious materials according to one embodiment of this application;

[0028] Figure 2 This is a SEM image of fly ash before grinding, provided in one embodiment of this application;

[0029] Figure 3 This is a SEM image of the ground fly ash provided in one embodiment of this application;

[0030] Figure 4 This is a 1000x SEM magnification image of the coal-based solid waste cementitious material after 7 days of curing, provided in one embodiment of this application.

[0031] Figure 5 This is a 10,000x SEM magnification image of a coal-based solid waste cementitious material after 7 days of curing, provided in one embodiment of this application.

[0032] Figure 6 This is a 1000x SEM magnification image of the coal-based solid waste cementitious material after 28 days of curing, provided in one embodiment of this application.

[0033] Figure 7 This is a 10,000x SEM magnification image of a coal-based solid waste cementitious material after 28 days of curing, provided in one embodiment of this application.

[0034] Figure 8 This is an application scenario diagram of coal-based solid waste cementitious materials provided in one embodiment of this application;

[0035] Figure 9 This is an application scenario diagram of coal-based solid waste cementitious materials from another perspective, provided in one embodiment of this application. Detailed Implementation

[0036] Embodiments of this application are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. Rather, this application includes all variations, modifications, and equivalents falling within the spirit and scope of the appended claims.

[0037] This application is an improvement based on the following deficiencies in related technologies. Currently, an important direction for the disposal of bulk coal-based solid wastes such as fly ash, coal gangue, gasification slag, and bottom ash is to prepare them into filling materials to prevent hazards such as spontaneous combustion of residual coal in goaf areas and further compaction and subsidence of goaf areas.

[0038] However, the preparation of filler materials from bulk coal-based solid waste currently faces the following problems: First, the composition of raw materials using bulk coal-based solid waste fluctuates greatly, especially the CaO content, which is unstable, resulting in unstable performance and poor stability of the filler product. Second, the process of preparing cemented filler materials from bulk coal-based solid waste often uses strong alkaline activators such as sodium silicate and sodium hydroxide, which is costly, dangerous, and has poor on-site applicability.

[0039] Related technologies propose a geopolymer cementitious material for coal mine solid waste base and its preparation method, which uses sodium hydroxide (caustic soda) as an activator. However, in practical applications, the cost is difficult to control, and sodium hydroxide is a highly corrosive chemical, posing a certain danger to workers operating it at the filling site. For example, related technologies propose a cementitious agent suitable for full tailings filling and an ecological cementitious material and its preparation method, which mainly uses slag powder (40%-70%), specifically water-quenched iron slag powder, which is commonly available from steel mills near iron mines, but difficult to obtain around coal mines. Long-distance transportation increases the material preparation cost, and the raw materials are targeted at non-coal mines, making it irrelevant to those skilled in the art. Another example is a geopolymer concrete and its preparation method, which uses sodium silicate and sodium hydroxide to prepare a composite activator, producing high-strength concrete (28-day strength greater than 50 MPa). However, its high preparation cost and strength do not meet the requirements of coal mine filling projects.

[0040] Based on this, the technical solution of this application provides a coal-based solid waste cementitious material, its preparation method, and its application for coal mine backfilling projects. Taking the practical application of coal mine backfilling projects as a starting point, and considering the characteristics of solid waste output from coal mines and nearby coal chemical and coal-fired power plants, it utilizes bottom ash and fly ash from coal-fired power plants and gasification slag from coal chemical plants as base materials. Through physical grinding activation, carbon dioxide acidification, and chemical activation, a low-cost and easy-to-use coal-based solid waste cementitious material is prepared. Furthermore, this application also proposes an application process adapted to the coal-based solid waste cementitious material, making it more feasible for construction, expanding its application scenarios, and effectively reducing backfilling costs while improving the efficiency of coal-based solid waste disposal.

[0041] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0043] To achieve the above objectives, according to an embodiment of the first aspect of this application, a method for preparing coal-based solid waste cementitious materials for coal mine backfilling projects is proposed, such as... Figure 1 As shown, it includes the following steps:

[0044] S1: Coal-based solid waste, by weight, includes 30-60 parts fly ash, 20-40 parts bottom ash, and 20-30 parts gasification slag, which are mixed and ground under the action of a grinding aid to obtain mixture A; wherein the mass of the grinding aid is 0.1%-0.5% of the coal-based solid waste.

[0045] S2: Prepare a solid waste solution with a mass concentration of 20%-40% by using a solvent for mixture A, and pass carbonization gas into the solid waste solution to obtain an acidified solution;

[0046] S3: Mix and grind 30-60 parts of desulfurized gypsum, 30-50 parts of lime and 10-20 parts of cement clinker by weight to obtain mixture B. Add mixture B to the acidification solution and stir to obtain coal-based solid waste cementitious material; wherein the mass of mixture B is 10%-20% of mixture A.

[0047] S1 contains coal-based solid waste including fly ash, bottom ash, and gasification slag. In this embodiment, fly ash is the fine ash particles produced after coal combustion in a coal-fired power plant boiler. These particles are discharged with the flue gas and collected by dust removal equipment (such as electrostatic precipitators and bag filters). The main components of fly ash include silicon dioxide, alumina, and iron oxide, and it also contains small amounts of oxides such as carbon, calcium, and magnesium. Bottom ash is solid waste formed by the deposition of unburned coal slag and ash at the bottom of the boiler during the combustion process. The composition of bottom ash is similar to that of fly ash, but it usually contains more unburned carbon, so its calorific value is relatively high. Gasification slag is the solid residue produced after the gasification reaction in the gasifier. The gasification process involves partially oxidizing coal at high temperatures to generate syngas (mainly composed of hydrogen and carbon monoxide), while simultaneously producing solid slag. The main components of gasification slag include silicon dioxide, aluminum oxide, calcium oxide, etc., and may also contain small amounts of heavy metals and unreacted carbon.

[0048] In this process, 30-60 parts by weight of fly ash, 20-40 parts by weight of bottom ash, and 20-30 parts by weight of gasification slag are mixed, and a grinding aid is added for grinding to obtain mixture A. The fly ash weight parts in the example mixture A are 30, 33, 34, 35, 36, 38, 40, 41, 42, 45, 46, 47, 48, 49, 50, 51, 52, 55, 56, 59, and 60 parts, etc., and the SEM images of the fly ash before and after grinding are shown below. Figure 2 As shown. The weight parts of the bottom ash are 20, 22, 24, 25, 26, 28, 29, 30, 33, 34, 35, 36, 38, 40, etc.; the weight parts of the gasification slag are 20, 21, 22, 25, 26, 27, 28, 29, 30, etc. In some embodiments, the mass ratio of fly ash, bottom ash and gasification slag can be (3-6):(2-4):(2-3); for example, the mass ratio of fly ash, bottom ash and gasification slag can be (3, 4, 5, 6):(2, 3, 4):(2 or 3), etc.

[0049] Fly ash, gasification slag, and bottom ash are all high-temperature, rapid-cooling silicate-rich wastes. These wastes contain abundant Si-O and Al-O bonds, which are activated during the mixing and grinding process of fly ash, gasification slag, and bottom ash. Further processing of mixture A then produces Si(OH)4 and Al(OH)4. - Monomers, which form a network gel structure through polymerization reactions.

[0050] In some embodiments, the molar ratio of Si to Al in the coal-based solid waste is adjusted to 1.5-3:1. The compressive strength of the gel is adjusted by modifying the proportions of fly ash, gasification slag, and bottom ash, as well as the proportions and content of the activator. For example, the molar ratio of Si to Al in the coal-based solid waste is (1.5, 2, 2.5, or 3):1. When the molar ratio of Si to Al in the coal-based solid waste is too large, such as greater than 3, the resulting hydrated product CSH gel network is loose, with low strength and high porosity. When the molar ratio of Si to Al in the coal-based solid waste is too small, such as less than 1.5, excessive Al3+ generates expansive ettringite (AFt), increasing the risk of expansion and resulting in poor durability.

[0051] In some embodiments, the mass of the grinding aid is 0.1%-0.5% of the coal-based solid waste. In other words, based on the coal-based solid waste, the mass percentage of the grinding aid is 0.1%-0.5%. As can be seen from the above, the addition of the grinding aid is used to activate the potential activity of the coal-based solid waste through grinding. For example, based on the coal-based solid waste, the mass percentage of the grinding aid is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc. When the mass percentage of the grinding aid is too large, such as greater than 0.5%, the excessive grinding aid will cause the particle surface to become oversaturated, which will lead to the re-agglomeration of the particles in mixture A, resulting in a decrease in the actual specific surface area and a surge in process costs. When the mass percentage of the grinding aid is too small, such as less than 0.1%, the grinding efficiency will be low and the performance of mixture A will be uneven.

[0052] In this embodiment, the grinding aid includes 0.02-2 parts of triisopropanolamine, 0.015-1.5 parts of octadecyltrimethylammonium chloride, 0.01-1 parts of phosphate methacrylate, 0.005-0.5 parts of sodium allyl sulfonate, and 0.02-1.5 parts of water. The main function of triisopropanolamine is to reduce surface energy by adsorbing onto the material surface, thereby reducing particle agglomeration and improving grinding efficiency. Examples of triisopropanolamine weight parts are 0.02 parts, 0.05 parts, 0.6 parts, 0.7 parts, 0.8 parts, 1 part, 1.2 parts, and 2 parts, etc. The main function of octadecyltrimethylammonium chloride is to reduce interfacial tension and grinding resistance by adsorbing onto the particle surface through hydrophobic long chains. Examples of octadecyltrimethylammonium chloride weight parts are 0.015 parts, 0.02 parts, 0.08 parts, 0.1 parts, 1 part, and 1.5 parts, etc. The main function of phosphate methacrylate is that the phosphate groups can react with metal ions (such as Ca) on the mineral surface. 2+ Al 3+The grinding aid is combined with phosphate methacrylate in weight parts of 0.01, 0.1, 0.15, and 1 parts to enhance dispersibility. Sodium allyl sulfonate is used in examples where the sulfonic acid groups enhance the hydrophilicity of the system and improve the compatibility of the grinding aid with high-silicon-aluminum solid waste. Sodium allyl sulfonate is used in weight parts of 0.005, 0.01, 0.1, 0.3, and 0.5 parts. Water is used as a solvent in examples where the water content is 0.02, 0.1, 0.2, 1, and 1.5 parts. In some embodiments, the mass ratio of isopropanolamine, octadecyltrimethylammonium chloride, phosphate methacrylate, sodium allyl sulfonate, and water in the grinding aid is 4:3:2:1:3.

[0053] In this embodiment, coal-based solid waste is mixed and ground under the action of a grinding aid to obtain mixture A, wherein the SEM morphology image of the ground fly ash is as follows. Figure 3 As shown, the surface of fly ash particles is smooth before grinding, but the inert layer is destroyed after grinding, and the reactivity is improved. The specific surface area of ​​mixture A is 300 m². 2 / kg-400m 2 / kg; the specific surface area of ​​the example mixture A is 300m². 2 / kg, 320m 2 / kg, 350m 2 / kg, 360m 2 / kg, 390m 2 / kg, 400m 2 / kg, etc., when the specific surface area of ​​mixture A is too large, such as greater than 400m² 2 When the specific surface area of ​​mixture A is low, it is composed of ultrafine particles (particle size <10μm). Van der Waals forces exacerbate agglomeration, thus reducing actual activity. The high specific surface area of ​​mixture A leads to an increase in the molecular weight of water adsorbed on the particle surface, requiring a water-cement ratio of 1.5-1.8 (normally 1.0-1.4). This results in poor flowability and increased porosity of the filling slurry formed when using coal-based solid waste cementitious materials. Conversely, if the specific surface area of ​​mixture A is too small, such as less than 300m², it will negatively impact the material's overall performance. 2 When the concentration is / kg, the proportion of coarse particles (particle size >45μm) in mixture A exceeds 30%, the dissociation degree of aluminosilicate glass is insufficient, and the release of active SiO2 / Al2O3 is reduced by 40-50%.

[0054] In S2, mixture A is prepared into a solid waste solution with a mass concentration of 20%-40% using a solvent, wherein the solvent includes water or contains SO4. 2- Cl - Na + The brine; it needs to be explained that the brine is waste brine discharged from coal mines, which contains SO4. 2- Cl -Na + Plasma increases the consumption of waste brine discharged from coal mines, and the SO4 in it... 2- Cl - Na + Plasma facilitates the dissolution and activation of coal-based solid waste; SO4 in brine... 2- Concentration of 100-200 mg / L; Cl - Concentration of 100-600 mg / L; Na + The concentration is 100-1000 mg / L.

[0055] For example, the mass concentration of the solid waste solution is 20%-40%, meaning it can be 20%, 22%, 24%, 25%, 28%, 30%, 37%, 39%, or 40%, etc. A carbonizing gas with a flow rate of 3-10 L / min is introduced into the solid waste solution to obtain an acidified solution with a pH of 7-8. This carbonizing gas contains a certain concentration of CO2 and / or SO2. The carbonizing gas can be boiler flue gas, which includes CO2 and / or SO2. By introducing CO2 and / or SO2 into the solid waste solution, the CaO and MgO in the solution can be depleted, eliminating the performance fluctuations of the resulting coal-based solid waste cementitious material caused by differences in CaO content in the solid waste, thus promoting the stability of the material's properties. Furthermore, introducing carbonizing gas into the solid waste solution can produce calcium carbonate microcrystals, which is beneficial for the later strength development of the filling body formed during the application of the coal-based solid waste cementitious material.

[0056] In step S3, 30-60 parts by weight of desulfurized gypsum, 30-50 parts by weight of lime, and 10-30 parts by weight of cement clinker are mixed and ground to obtain mixture B. The desulfurized gypsum is a byproduct of flue gas desulfurization in coal-fired power plants. Through wet flue gas desulfurization, limestone or lime reacts with sulfur dioxide to produce calcium sulfate, i.e., desulfurized gypsum; its main component is calcium sulfate dihydrate, and it may also contain small amounts of unreacted limestone, calcium sulfite, heavy metals, and other impurities. Cement clinker is the main raw material for cement production. It is a semi-finished product formed by mixing limestone, clay, iron ore, and other raw materials in a certain proportion and then calcining them at high temperature (usually around 1450℃) in a cement rotary kiln. Its main components include tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite. Lime is obtained by decomposing limestone (whose main component is calcium carbonate) by calcining it at high temperature (usually 900℃-1200℃). During calcination, calcium carbonate decomposes into calcium oxide and carbon dioxide. The main component is calcium oxide, but it may also contain small amounts of impurities such as silicon dioxide and magnesium oxide.

[0057] The main role of desulfurization gypsum in this process is to provide key SO4. 2-Ions react with aluminum phases (such as Al2O3) in coal-based solid waste to form ettringite (AFt, 3CaO·Al2O3·3CaSO4·32H2O), forming a needle-like crystal structure, which significantly improves early strength. Examples of desulfurization gypsum weight parts are 30 parts, 34 parts, 37 parts, 40 parts, 41 parts, 45 parts, 48 ​​parts, 50 parts, 53 parts, 55 parts, 59 parts, 60 parts, etc.

[0058] The main functions of lime include: firstly, its reaction with water to generate Ca(OH)2, raising the pH of the system to 12-13, and disrupting the Si-O-Al glassy structure in coal-based solid waste (fly ash, gasification slag), releasing active SiO2 and Al2O3. Secondly, it can supplement calcium, providing Ca... 2+ It participates in the formation of CSH gel (CaO-SiO2-H2O) and ettringite, enhancing the density of the cementitious network. The weight parts of lime can be 30, 34, 37, 39, 40, 41, 44, 45, 48, 50, etc.

[0059] The main functions of cement clinker include: First, it acts as a nucleation inducing agent, providing C3S (tricalcium silicate) and C2S (dicalcium silicate) as nuclei for hydration reactions, accelerating the nucleation and growth of the gel phase, and shortening the setting time. Second, cement clinker contributes to early strength by generating CSH gel and Ca(OH)2 through its own hydration. Third, cement clinker maintains an alkaline environment, i.e., Ca(OH)2 continuously releases OH-, synergistically maintaining a high pH in the system with lime, promoting secondary hydration of solid waste. In this embodiment, the weight percentages of cement clinker can be 10 parts, 11 parts, 12 parts, 15 parts, 16 parts, 17 parts, 20 parts, etc.

[0060] In some embodiments, the mass ratio of desulfurized gypsum, lime, and cement clinker is (3-6):(3-5):(1-2), for example, (3, 4, 5, or 6):(3, 4, or 5):(1 or 2). The desulfurized gypsum, lime, and cement clinker respectively perform sulfate activation, alkaline activation, and crystal nucleation induction functions in the system, achieving efficient gelation of coal-based solid waste through precise proportioning.

[0061] The specific surface area of ​​mixture B obtained in this process is 300 m². 2 / kg-400m 2 / kg. The specific surface area of ​​mixture B is 300m². 2 / kg-400m 2 / kg; the specific surface area of ​​the example mixture B is 300m². 2 / kg, 320m 2 / kg, 350m 2 / kg, 360m 2 / kg, 390m 2 / kg, 400m 2 / kg, etc., when the specific surface area of ​​mixture B is too large, such as greater than 400m² 2 When the specific surface area of ​​mixture B is low, the ultrafine particles (particle size <10μm) will agglomerate due to van der Waals forces, thus reducing the actual activity. The high specific surface area of ​​mixture B leads to an increase in the molecular weight of water adsorbed on the particle surface, requiring a water-cement ratio of 1.5-1.8 (normally 1.0-1.4). This results in poor flowability and increased porosity of the filling slurry formed when using coal-based solid waste cementitious materials. Conversely, if the specific surface area of ​​mixture B is too small, such as less than 300m², it will also cause problems. 2 When the concentration is / kg, the homogeneity of mixture B is poor, which triggers the unreacted free CaO in the components to react with water to generate Ca(OH)2, with a volume expansion rate >0.1%, causing cracking of the filling slurry formed when coal-based solid waste cementitious materials are applied.

[0062] Based on mixture A, the mass of mixture B is 10%-20% of that of mixture A. For example, the mass of mixture B is 10%, 11%, 12%, 14%, 16%, 17%, 19%, and 20% of that of mixture A. Mixture B is added to the acidification solution and stirred until homogeneous to obtain coal-based solid waste cementitious material, wherein the mass percentage of coal-based solids in the coal-based solid waste cementitious material is at least 90%.

[0063] Therefore, the coal-based solid waste in this application is a silicate-aluminate-rich waste. Its potential activity is activated by grinding with the addition of grinding aids to obtain mixture A. Mixture A is then prepared into a solid waste solution with a mass concentration of 20%-40%. Carbonization gas is introduced into the solid waste solution to purify its components, removing components such as CaO that significantly affect product performance fluctuations, resulting in an acidification solution. A mixture B, composed of desulfurized gypsum, lime, and cement clinker, is then added to the acidification solution for composite activation. Under the mechanical forces such as stirring and the alkaline environment provided by the clinker and lime, the inert structures such as the glassy body inside the acidification solution undergo Si-O and Al-O bond breakdown, producing Si(OH)4 and Al(OH)4. - Monomers, through polymerization reactions, form a network gelling structure, exhibiting macroscopically stable performance in coal-based solid waste gelling materials, which possess gelling properties.

[0064] In summary, based on the different characteristics and performance differences of solid waste generated by coal mines, coal-fired power plants and coal chemical plants around the filling project, the basic materials for preparing solid waste cementitious materials can be replaced. The basic purpose is to select silicate mineral solid wastes such as fly ash with pozzolanic activity, and use desulfurization gypsum and cement clinker as activators to prepare cementitious materials.

[0065] According to an embodiment of the second aspect of this application, a coal-based solid waste cementitious material for coal mine backfilling projects is provided, which is obtained using the preparation method in any of the above embodiments.

[0066] According to the embodiments of the third aspect of this application, the application of coal-based solid waste cementitious materials in any of the above embodiments in goaf filling is proposed.

[0067] The goaf filling process includes the following steps: preparing a cementitious material solution with a water-ash ratio of 1-1.4:1 using coal-based solid waste cementitious material; crushing coal gangue aggregate to a particle size not exceeding 30mm; mixing the cementitious material solution and coal gangue aggregate at a mass ratio of 1:2-4, and then spraying the mixture into the branch roadway to be filled, with grouting applied to the roof through a pre-reserved pipe. It should be noted that the cementitious material solution and coal gangue aggregate are transported to the mine separately, and the cementitious material solution and coal gangue aggregate are mixed in the filling branch roadway, such as... Figures 8-9 .

[0068] Therefore, this application utilizes various coal-based solid wastes with pozzolanic activity potential, such as fly ash, gasification slag, and bottom ash, as the main base materials for synergistic application. This allows the raw materials to complement each other, achieving a better cementing effect. The prepared coal-based solid waste cementitious material has a solid waste content of over 90%, reducing backfilling costs while improving the efficiency of bulk solid waste disposal and resource utilization. Furthermore, this application proposes a backfilling construction process to complement the coal-based solid waste cementitious material, transporting the cementitious material and gangue aggregate separately. This avoids the problems of short transport distances and pipe blockages encountered in conventional high-concentration slurry (paste, paste-like, etc.) pipeline transport backfilling due to fluctuations in the properties of solid waste raw materials.

[0069] In summary, the filling material prepared in this application has a low preparation cost compared to silicate cement bonding. Under the same strength conditions, the preparation cost of the filling material mainly made from coal-based solid waste is reduced by about 30%, and it greatly improves the disposal efficiency of bulk solid wastes such as gasification slag and fly ash. In addition, compared with high-concentration slurry (paste or paste-like) filling processes, the filling process of this application has low investment and maintenance costs, high safety, can be applied to various geological and mining conditions, and has strong scalability and replicability.

[0070] To facilitate a further understanding of this application, the solutions described below are further described in conjunction with embodiments. Those skilled in the art will understand that the examples described in this application are only a portion of the examples, and any other suitable specific examples are within the scope of this application.

[0071] Example 1

[0072] This embodiment provides a coal-based solid waste cementitious material for coal mine backfilling projects. The preparation method and specific operating parameters are as follows: The coal-based solid waste comprises 60 parts by weight of fly ash, 20 parts of bottom ash, and 20 parts of gasification slag. These are mixed and ground under the action of a grinding aid to obtain mixture A, wherein the specific surface area of ​​mixture A is 300 m². 2 / kg. The grinding aid consists of triisopropanolamine, octadecyltrimethylammonium chloride, phosphate methacrylate, sodium allyl sulfonate, and water in a mass ratio of 4:3:2:1:3, and the mass of the grinding aid is 0.2% of the coal-based solid waste.

[0073] Mixture A was prepared into a 40% (w / w) solid waste solution using water, and carbon dioxide gas was introduced into the solid waste solution to obtain an acidification solution (pH 7). Mixture B was obtained by mixing and grinding 9 parts by weight of desulfurization gypsum, 4.5 parts by weight of lime, and 1.5 parts by weight of cement clinker. The specific surface area of ​​mixture B was 400 m². 2 / kg, then add mixture B to the acidification solution and stir to obtain coal-based solid waste cementitious material.

[0074] Example 2

[0075] This embodiment differs from Embodiment 1 in the following ways: the specific surface area of ​​mixture A is 400 m². 2 / kg. The grinding aid constitutes 0.5% of the coal-based solid waste.

[0076] Example 3

[0077] This embodiment differs from Embodiment 1 in the following ways: The coal-based solid waste comprises, by weight, 30 parts fly ash, 40 parts bottom ash, and 30 parts gasification slag, wherein the specific surface area of ​​mixture A is 400 m². 2 / kg. The grinding aid constitutes 0.3% of the coal-based solid waste by mass.

[0078] By weight, 6 parts of desulfurized gypsum, 10 parts of lime, and 4 parts of cement clinker were mixed and ground to obtain a specific surface area of ​​400 m². 2 Mixture B is added to the acidification solution and stirred until homogeneous to obtain coal-based solid waste cementitious material.

[0079] Example 4

[0080] This embodiment differs from Embodiment 1 in the following ways: The coal-based solid waste comprises, by weight, 30 parts fly ash, 40 parts bottom ash, and 30 parts gasification slag, wherein the specific surface area of ​​mixture A is 350 m². 2 / kg. The grinding aid comprises 0.4% of the coal-based solid waste by mass.

[0081] Mixture A is prepared into a solid waste solution with a mass concentration of 40% using water, and carbon dioxide gas is introduced into the solid waste solution to obtain an acidified solution (pH 8).

[0082] By weight, 8 parts of desulfurized gypsum, 8 parts of lime, and 4 parts of cement clinker were mixed and ground to obtain a specific surface area of ​​350 m². 2 Mixture B is added to the acidification solution and stirred until homogeneous to obtain coal-based solid waste cementitious material.

[0083] Example 5

[0084] This embodiment differs from Embodiment 1 in the following ways: The coal-based solid waste comprises, by weight, 40 parts fly ash, 30 parts bottom ash, and 30 parts gasification slag, wherein the specific surface area of ​​mixture A is 350 m². 2 / kg. The grinding aid constitutes 0.5% of the coal-based solid waste by mass.

[0085] Mixture A is prepared into a solid waste solution with a mass concentration of 40% using water, and carbon dioxide gas is introduced into the solid waste solution to obtain an acidified solution (pH 8).

[0086] By weight, 4 parts desulfurized gypsum, 4 parts lime, and 2 parts cement clinker were mixed and ground to obtain a specific surface area of ​​300 m². 2 Mixture B is added to the acidification solution and stirred until homogeneous to obtain coal-based solid waste cementitious material.

[0087] Example 6

[0088] This embodiment differs from Embodiment 1 in the following ways: Mixture A is prepared into a solid waste solution with a mass concentration of 40% using "mine concentrated brine".

[0089] Comparative Example 1

[0090] This comparative example differs from Example 1 in that mixture B is replaced with the conventional activator sodium hydroxide (10%).

[0091] Comparative Example 2

[0092] This comparative example differs from Example 1 in the following ways: CO2 gas is not introduced into the A solution for acidification.

[0093] Comparative Example 3

[0094] This comparative example differs from Example 1 in the following ways: Material A is subjected to ultrafine grinding, with a specific surface area of ​​500m². 2 / kg.

[0095] Comparative Example 4

[0096] This comparative example differs from Example 1 in the following ways: the ratio of fly ash to bottom ash to gasification slag in mixture A is 1:2:7, the Al content in mixture A is increased, and the Si / Al molar ratio is <1.5.

[0097] Comparative Example 5

[0098] This comparative example differs from Example 1 in the following ways: the amount of component B is adjusted to 30%.

[0099] Test case

[0100] Samples of the coal-based solid waste cementitious materials from Examples 1-4 were taken at 7-day and 28-day curing periods and observed using a scanning electron microscope. The results are as follows: Figures 4-7 As shown, where Figure 4 This is a 1000x SEM magnification image of coal-based solid waste cementitious materials after 7 days of curing. Figure 5 This is a 10,000x SEM magnification image of coal-based solid waste cementitious materials after 7 days of curing. Figure 5 In this context, A represents acicular ettringite, and B represents a reticulated cementitious product; among which... Figure 6 This is a 1000x SEM magnification image of coal-based solid waste cementitious materials after 28 days of curing. Figure 7 This is a 10,000x SEM magnification image of coal-based solid waste cementitious materials after 28 days of curing. Figure 7 In this context, A represents acicular ettringite, and C represents the cross-linking of various network-like hydration cementitious products. Figures 4-7 It can be known that coal-based solid waste cementitious materials produce a large number of needle-like ettringite and network gel structures during the 7-day curing period. During the 28-day curing period, the network structure and some amorphous gel structures generated by the coal-based solid waste cementitious materials are intertwined and connected, making their structure compact. That is, the activity of solid waste materials such as fly ash is effectively activated in the later stage of curing.

[0101] The coal-based solid waste cementitious materials in the above embodiments and comparative examples were prepared into a cementitious material solution with a water-ash ratio of 1:1, and the coal gangue aggregate was crushed to a particle size of no more than 30 mm. The cementitious material solution and the coal gangue aggregate were mixed at a mass ratio of 1:3 to prepare 100 mm × 100 mm × 100 mm filling slurry test blocks. The 28-day compressive strength of the test blocks was tested in accordance with GB / T50081-2019, as shown in Table 1.

[0102] Table 1. Configuration parameters and application testing parameters of coal-based solid waste cementitious materials in each embodiment and comparative example.

[0103]

[0104] As shown in Table 1, in Example 1, the mass ratio of fly ash, bottom ash, and gasification slag is 6:2:2. Coal-based solid waste provides highly active SiO2, promoting CSH gel formation, but Al2O3 is relatively insufficient, limiting ettringite formation, resulting in a strength of 6.7 MPa. In Example 2, increasing the amount of grinding aid increases the specific surface area of ​​mixture A, leading to higher strength of the resulting coal-based solid waste cementitious material. In Example 3, the mass ratio of fly ash, bottom ash, and gasification slag is 3:4:3. Increased Al content in the coal-based solid waste, combined with increased grinding aid, increases the specific surface area of ​​mixture A, resulting in higher strength of the obtained coal-based solid waste cementitious material. In Example 4, when the mass ratio of desulfurized gypsum:lime:cement clinker is 4:4:2, mixture B achieves sulfate-alkaline activation equilibrium, resulting in the densest structure and highest strength. In Example 5, the amount of mixture B is 10% of mixture A, and the specific surface area of ​​mixture B is relatively low at 300 m². 2 / kg, Mixture B has low utilization rate as an activator, with a strength of only 7.1 MPa. In Example 6, Mixture A was prepared into a solid waste solution with a mass concentration of 40% using "mine brine", that is, the solvent "water" was replaced with coal mine "brine", which makes full use of SO4 in the mine brine. 2- The intensity was increased to 7.5 MPa by the excitation effect of Cl- and other ions.

[0105] In Comparative Example 1, although the traditional alkaline activator (NaOH) could activate the solid waste, it resulted in a strongly alkaline pH in the generated coal-based solid waste cementitious material, which easily corroded the transport pipelines during transportation and increased the cost per ton by 30%. In Comparative Example 2, no carbonation gas was introduced for solid waste solution acidification. Free CaO in the solid waste solution reacted with water to form Ca(OH)2, and the volume expansion caused cracking of the filling slurry. In Comparative Example 3, the ultrafine mixture A resulted in a 1.5-fold increase in water requirement to achieve the same fluidity in the cementitious material. In Comparative Example 4, the increased content of gasification slag resulted in a lower Si / Al ratio in the coal-based solid waste, leading to Al... 3+ Excessive concentration of ettringite during its later stages significantly reduces the structural strength of the filling grout. In Comparative Example 5, the filling cost increased by 35%, while the strength increased by only 5.9%, resulting in a cost-benefit imbalance.

[0106] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0107] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing a coal-based solid waste cementitious material for coal mine backfilling projects, characterized in that, Includes the following steps: The coal-based solid waste comprises 30-60 parts by weight of fly ash, 20-40 parts by weight of bottom ash, and 20-30 parts by weight of gasification slag. These are mixed and ground under the action of a grinding aid to obtain mixture A. The molar ratio of Si to Al in the coal-based solid waste is (1.5-3):

1. The mass of the grinding aid is 0.1%-0.5% of the coal-based solid waste. The grinding aid comprises 0.02-2 parts of triisopropanolamine, 0.015-1.5 parts of octadecyltrimethylammonium chloride, 0.01-1 parts of phosphate methacrylate, 0.005-0.5 parts of sodium allyl sulfonate, and 0.02-1.5 parts of water. The mixture A is prepared into a solid waste solution with a mass concentration of 20%-40% using a solvent, and a carbonizing gas is introduced into the solid waste solution to obtain an acidified solution with a pH of 7-8; the carbonizing gas contains CO2 gas and SO2 gas, and the flow rate of the carbonizing gas is 3-10 L / min; the solvent includes water or contains SO4. 2- Cl - Na + The brine; the brine contains SO4 2- Concentration of 100-200 mg / L; Cl - Concentration of 100-600 mg / L; Na + The concentration is 100-1000 mg / L; Mix and grind 30-60 parts of desulfurized gypsum, 30-50 parts of lime and 10-20 parts of cement clinker by weight to obtain mixture B. Add mixture B to the acidification solution and stir to obtain coal-based solid waste cementitious material; wherein the mass of mixture B is 10%-20% of mixture A.

2. The preparation method according to claim 1, characterized in that, The specific surface area of ​​the mixture A is 300 m². 2 / kg-400m 2 / kg; And / or, the mass ratio of isopropanolamine, octadecyltrimethylammonium chloride, phosphate methacrylate, sodium allyl sulfonate, and water in the grinding aid is 4:3:2:1:

3.

3. The preparation method according to claim 1, characterized in that, The specific surface area of ​​the mixture B is 300 m². 2 / kg-400m 2 / kg.

4. The preparation method according to any one of claims 1-3, characterized in that, The mass ratio of the fly ash, the bottom ash and the gasification slag is (3-6):(2-4):(2-3); And / or, the mass ratio of the desulfurized gypsum, the lime and the cement clinker is (3-6):(3-5):(1-2).

5. The preparation method according to claim 4, characterized in that, The coal-based solid waste cementitious material contains at least 90% coal-based solids by mass.

6. A coal-based solid waste cementitious material for coal mine backfilling projects, characterized in that, It is obtained using any of the preparation methods described in claims 1-5.

7. The application of the coal-based solid waste cementitious material as described in claim 6 in goaf backfilling.

8. The application according to claim 7, characterized in that, The backfilling of the goaf includes the following steps: preparing the coal-based solid waste cementitious material into a cementitious material solution with a water-ash ratio of 1-1.4:1; The coal gangue aggregate is crushed to a particle size not exceeding 30mm; The cementitious material solution is mixed with the coal gangue aggregate at a mass ratio of 1:2-4, and then sprayed into the branch roadway to be filled through a spraying device and connected to the roof through a reserved pipe.

9. The application according to claim 8, characterized in that, The cementitious material solution and the coal gangue aggregate are transported separately to the mine, and the cementitious material solution and the coal gangue aggregate are mixed in the backfilling branch roadway.

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