A solidified soil slurry flame-retardant coal gangue composite material, a preparation method and application thereof

Abstract

This invention relates to a solidified soil slurry flame-retardant coal gangue composite material, its preparation method, and its application. Specifically, it relates to a solidified soil slurry flame-retardant coal gangue composite material, the components of which include coal gangue and solidified soil slurry; the mass ratio of coal gangue to solidified soil slurry is (1-4):1; the solidified soil slurry includes solids and water, the solids including silt, a curing agent, polyacrylamide, and a water-reducing agent; the mass ratio of the total mass of the solids to the mass of water is 1:(0.5-0.8). The mass of the silt is more than 90% of the total mass of the solids, the amount of the curing agent is 3%-8% of the mass of the silt, the amount of the polyacrylamide is 0.1‰-1‰ of the mass of the silt, the amount of the water-reducing agent is 0.1%-0.8% of the mass of the silt in the solidified soil slurry, and the amount of the water-reducing agent is 0.3%-0.5% of the mass of the medium silt. This invention significantly reduces oxygen diffusion and inhibits spontaneous combustion of coal gangue by filling the pores of coal gangue with solidified soil slurry.

Description

Technical Field

[0001] This invention relates to the field of flame retardant materials, specifically to a solidified soil slurry flame retardant coal gangue composite material, its preparation method, and its application. Background Technology

[0002] Coal gangue is a major solid waste generated during coal mining and washing. Long-term open-air storage not only occupies land, but the residual coal, pyrite, and other combustibles it contains are prone to oxidation and heat accumulation under oxygen, potentially leading to spontaneous combustion and the release of large amounts of harmful gases such as SO2 and CO, causing serious air pollution and ecological risks. Traditional treatment methods, such as loess covering and surface compaction, have limited flame-retardant effects, poor durability, and high costs. In recent years, the method of filling the gaps in gangue with grouting materials to isolate oxygen has attracted attention. However, existing grouting materials often suffer from difficulties in synergistically optimizing fluidity, curing strength, and long-term flame-retardant performance, especially lacking systematic research on the intrinsic correlation mechanism between "material-structure-flame-retardant performance." Therefore, developing a new type of solidified soil slurry flame-retardant material that can effectively seal pores and inhibit oxidation, while also possessing good workability and environmental adaptability, is an urgent technical requirement for the large-scale safe disposal and ecological restoration of coal gangue. Summary of the Invention

[0003] Based on the aforementioned technical deficiencies, this invention provides a coal gangue disposal method that combines high-efficiency flame retardancy, construction feasibility, and long-term stability. This overcomes the limitations of traditional treatment methods (such as loess covering), which suffer from limited flame retardant effects, poor durability, and the inability to synergistically optimize material flowability, curing strength, and flame retardant performance. Traditional physical covering methods cannot effectively seal the complex pores inside the gangue pile, leading to a persistent risk of spontaneous combustion due to oxygen infiltration. This invention actively fills and seals macroscopic pores with injectable solidified soil slurry, fundamentally isolating oxygen channels and solving the problem of flame retardant failure. Existing materials struggle to balance the good flowability required for construction with the dense structure and thermal stability needed after curing. This invention achieves a unified performance of "injectable" and "strong flame retardancy" through optimized material ratios and processes. It not only requires initial flame retardancy but also stability during long-term storage. The "solidified soil slurry-gangue" composite structure formed by this technology has a low thermal conductivity and high thermal stability, and can delay temperature rise by retaining bound water, providing long-lasting flame retardant protection.

[0004] This invention provides a solidified soil slurry flame-retardant coal gangue composite material, the components of which include coal gangue and solidified soil slurry; the mass ratio of coal gangue and solidified soil slurry is (1-4):1; the solidified soil slurry includes solid body and water, the solid body includes silt, curing agent, polyacrylamide, and water-reducing agent; the mass ratio of the total mass of the solid body to the mass of the water is 1:(0.5-0.8).

[0005] Furthermore, the mass of the silt is more than 90% of the total mass of the solid body, the amount of the solidifying agent is 3%-8% of the mass of the silt, the amount of the polyacrylamide is 0.1‰-1‰ of the mass of the silt, and the amount of the water-reducing agent is 0.1%-0.8% of the mass of the silt.

[0006] Furthermore, the curing agent is composed of cement, fly ash, and desulfurized gypsum, with a mass ratio of 10:(6-8):(1.5-2.5).

[0007] Furthermore, the polyacrylamide is an anionic type with a molecular weight of 15 million.

[0008] Furthermore, the water-reducing agent is a polycarboxylate water-reducing agent or a modified polycarboxylate high-efficiency water-reducing agent.

[0009] Furthermore, the preparation method of the modified polycarboxylate superplasticizer includes the following steps: (1) First, weigh out the methyl allyl polyoxyethylene ether macromonomer and put it into a four-necked flask with a mechanical stirrer and a feeding system. Then weigh out a certain amount of deionized water and add it to the flask for stirring and pre-dissolving. After the methyl allyl polyoxyethylene ether in the base material is completely dissolved, the preparation of the base material is completed. (2) Weigh out acrylic acid and deionized water to prepare material A; then weigh out hydroxypropionic acid, ascorbic acid and an appropriate amount of water to prepare material B; (3) After heating the water bath to the set temperature, turn on the peristaltic pump to add A and B materials at a uniform rate. After A and B materials have been completely added, keep the water bath warm.

[0010] (4) After the reaction is complete, add sodium hydroxide solution (mass fraction of 25-35%) to adjust the pH of the solution. After cooling to room temperature, add water. When the solid content of the solution is 35-45%, the modified polycarboxylate superplasticizer is obtained.

[0011] Furthermore, the particle size of the coal gangue is 1-6 mm.

[0012] The present invention also provides a method for preparing the solidified soil slurry flame-retardant coal gangue composite material described in the above-mentioned item, comprising the following steps: S1: Mix silt, solidifying agent, polyacrylamide, water-reducing agent and water in a certain proportion to prepare solidified soil slurry; S2: Mix the coal gangue with the solidified soil slurry prepared in step S1 according to the mass ratio, stir evenly, and obtain a mixture; S3: Vibrate the mixture prepared in step S2 for 20-50 seconds at a frequency of 0.5-2Hz to remove air bubbles and shape it into a soil column; S4: After curing the soil column formed in step S3 at 25℃ for 28 days, it is naturally cured for 150 days to obtain the solidified soil slurry flame-retardant coal gangue composite material.

[0013] The present invention also provides an application of the above-described solidified soil slurry flame-retardant coal gangue composite material in flame retardancy of coal mine gangue stockpiles.

[0014] Furthermore, the composite material is filled into the gaps in the gangue pile by grouting, and the thickness of the reconstructed soil layer is not less than 50 mm.

[0015] Beneficial effects This invention significantly reduces oxygen diffusion and inhibits spontaneous combustion of coal gangue by filling the pores of coal gangue with a solidified soil slurry. The optimized mix design achieves moderate porosity, forming a dense structure dominated by isolated pores, thus improving long-term stability. The composite material exhibits slow heating, and its heat resistance is significantly improved when the thickness is ≥50 mm, effectively delaying thermal decomposition. Utilizing industrial solid waste (coal gangue, fly ash, etc.) enables resource utilization and reduces storage risks. The slurry has good fluidity, making it suitable for grouting processes and facilitating large-scale gangue disposal. This invention combines flame retardancy, structural reinforcement, and environmental protection, providing a reliable technical approach for the ecological disposal of coal mine gangue. Attached Figure Description

[0016] Figure 1 Comparison of SEM morphology of Experiment Example 1 and gangue sample; Figure 2 Comparison of heat flux density changes between Experiment Example 1 and gangue sample; Figure 3 Pore ​​distribution of "solidified soil slurry-gangue" column: (a) different gangue particle size distribution; (b) different solidified soil slurry dosage; (c) CT simulation pore distribution map (solidification time: 150 days); Figure 4 Thermal infrared imaging of surface temperature of different soil column samples; Figure 5 Comparison of heating rates of "solidified soil slurry-gangue" samples with different thicknesses of solidified soil slurry dosage; Figure 6 TG-DTG characteristic curves of "solidified soil slurry-gangue" with different amounts of solidified soil slurry; Figure 7 Schematic diagrams of different soil column preparation methods, thermal stability testing platform, and CT testing. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, a more detailed description is provided below. However, it should be understood that the description herein is merely for explaining this application and is not intended to limit its scope.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. All reagents and instruments used herein are commercially available, and the characterization methods involved can be found in relevant descriptions in the prior art, and will not be repeated here.

[0019] To further understand this application, the following detailed description is provided in conjunction with the preferred embodiments.

[0020] Example 1 This invention provides a solidified soil slurry flame-retardant coal gangue composite material, the components of which include coal gangue and solidified soil slurry; the mass ratio of coal gangue and solidified soil slurry is (1-4):1; the solidified soil slurry includes solid body and water, the solid body includes silt, curing agent, polyacrylamide, and water-reducing agent; the mass ratio of the total mass of the solid body to the mass of the water is 1:(0.5-0.8).

[0021] like Figure 1 As shown, the encapsulation and filling effect of the solidified soil slurry on the gangue in Experiment Example 1 can be clearly seen. In the interfacial encapsulation layer on the gangue surface, due to the combined skeleton effect of the solidifying agent hydration products and polyacrylamide (PAM), the solidified soil slurry adheres more effectively to the gangue surface and effectively fills the macroscopic pores between the gangue. Figure 2 The TG-DSC results with a heating rate of 10℃ / min are presented, and differences in the DTG characteristic curves and heat flux density curves of the gangue and the sample from Experimental Example 1 are observed: In the reconstructed soil sample containing solidified soil slurry, the DTG rate during the endothermic phase is slower, while the heat flux density curve dHF reflects a longer endothermic temperature phase (reaching 530.7℃ at t2), indicating that the solidified soil slurry significantly improves the heat storage capacity of the reconstructed soil sample. The thermal conductivity of the soil column was tested using the transient planar heat source method, and the value for Experimental Example 1 was 1.268 W·m⁻¹. 1 ·K -1 Compared to 1.594 W·m of pure gangue -1 ·K -1The thermal conductivity of the "solidified soil slurry-gangue" reconstructed layer is reduced by 20%, resulting in poorer thermal conductivity and better flame retardant properties for gangue columns with the same particle size distribution. Simultaneously, the solidified soil slurry's superior water retention increases the proportion of bound and free water on the gangue surface. When encountering potential heat sources or internal heat storage and temperature rise, the solidified soil slurry effectively prolongs the water evaporation stage of the reconstructed soil sample, reduces the oxidative adsorption capacity of the gangue, increases the difficulty of diffusion when oxygen molecules contact active sites on the gangue surface, and hinders the activity of oxygen-containing functional groups. This aligns with the soil column thermal stability experiment, where the thicker the soil column, the lower the stable temperature of the "solidified soil slurry-gangue" soil column is in the later stages of heating compared to pure gangue.

[0022] As a further preferred embodiment, the silt accounts for more than 90% of the total solid mass; the amount of the curing agent is 3%-8% of the silt mass, the amount of the polyacrylamide is 0.1‰-1‰ of the silt mass, and the amount of the water-reducing agent is 0.1%-0.8% of the silt mass.

[0023] In the solidified soil slurry, silt is the main component, and the addition of other components is based on silt. The content of other components is relatively small, so the mass of silt accounts for more than 90% of the total solid mass of the solidified soil slurry, or is close to the total solid mass of the solidified soil slurry.

[0024] As a further preferred embodiment, the curing agent is composed of cement, fly ash, and desulfurized gypsum, with a mass ratio of 10:(6-8):(1.5-2.5).

[0025] As a further preferred embodiment, the polyacrylamide is an anionic type with a molecular weight of 15 million.

[0026] The polyacrylamide organic polymer (PAM) used in this invention is anionic with a molecular weight of 15 million, and is manufactured by Henan Dongshun Environmental Protection Materials Co., Ltd. The PAM has a pH range of 6.0-6.5 and a particle density of approximately 0.75 g·cm³. Because it is produced through a bulk polymerization reaction and then crushed into individual particles and sieved, all PAM particles have a relatively regular cubic or blocky structure.

[0027] As a further preferred embodiment, the water-reducing agent is a polycarboxylate water-reducing agent or a modified polycarboxylate high-efficiency water-reducing agent.

[0028] As a further preferred embodiment, the preparation method of the modified polycarboxylate superplasticizer includes the following steps: (1) First, weigh a certain amount of methyl allyl polyoxyethylene ether (HPEG) macromonomer and put it into a four-necked flask equipped with a mechanical stirrer and a feeding system. Then weigh a certain amount of deionized water and add it to the flask for stirring and pre-dissolving. After the methyl allyl polyoxyethylene ether (HPEG) in the base material is completely dissolved, the preparation of the base material is completed. (2) Weigh a certain amount of acrylic acid (AA) and deionized water to prepare material A; then weigh a certain amount of hydroxypropionic acid (3-MPA), ascorbic acid (VC) and an appropriate amount of water to prepare material B; (3) After heating the water bath to the set temperature, turn on the peristaltic pump and add A and B materials at a uniform rate (the addition coefficient is determined according to each prepared solution, and the time is controlled within 1 minute), so that the addition time of A and B materials is 150 minutes and 120 minutes respectively. After A and B materials are completely added, keep warm for 1 hour.

[0029] (4) After the reaction is complete, add sodium hydroxide solution (mass fraction of 25-35%) to adjust the pH of the solution. After cooling to room temperature, add water. When the solid content of the solution is 35-45%, the modified polycarboxylate superplasticizer H-PCE is obtained.

[0030] Preferably, the optimal preparation process for H-PCE is as follows: the acid-to-ether ratio n(AA):n(HPEG) is 4.0:1, the amount of transfer agent is 0.36%, and the synthesis temperature is 45℃. Under this synthesis process, H-PCE polycarboxylate superplasticizer exhibits excellent dispersion flowability and dispersion flow retention ability.

[0031] As a further preferred embodiment, the coal gangue has a particle size of 1-6 mm.

[0032] Preferably, the particle size of the coal gangue can be 1-3mm, 2-4mm, 3-5mm, 4-6mm, 3-6mm or any value within any two of these ranges.

[0033] When the coal gangue particle size is 1-6 mm, the porosity distribution in all "solidified soil slurry-gangue" soil columns is relatively uniform, with pore morphology mainly consisting of isolated pores, and the standard deviation is less than 1.5%. The overall porosity of the samples increases, and their Euler number and fractal dimension are also at their maximum, indicating that increasing the amount of solidified soil slurry increases the complexity of the pore structure and reduces the overall structural connectivity, which is beneficial for the flame retardancy of the gangue. It is evident that the number of pores in the "solidified soil slurry-gangue" soil column is mainly contributed by the solidified soil slurry itself.

[0034] Example 2 This embodiment provides a method for preparing the solidified soil slurry flame-retardant coal gangue composite material described in Embodiment 1 (e.g., Figure 7 (As shown) includes the following steps: S1: Mix silt, solidifying agent, polyacrylamide, water-reducing agent and water in a certain proportion to prepare solidified soil slurry; S2: Mix the coal gangue with the solidified soil slurry prepared in step S1 according to the mass ratio, stir evenly, and obtain a mixture; S3: Vibrate the mixture prepared in step S2 for 20-50 seconds at a frequency of 0.5-2Hz to remove air bubbles and shape it into a soil column; S4: After curing the soil column formed in step S3 at 25℃ for 28 days, it is naturally cured for 150 days to obtain the solidified soil slurry flame-retardant coal gangue composite material.

[0035] Example 3 This embodiment provides an application of the solidified soil slurry flame-retardant coal gangue composite material according to Embodiment 1 in flame retardancy of coal mine gangue stockpiles.

[0036] Preferably, the composite material is filled into the gaps of the gangue pile by grouting, and the thickness of the reconstructed soil layer is not less than 50 mm.

[0037] Example 4 Preparation of No. 1 solidified soil slurry: 1000g of silt was taken, and the solidifying agent was 6% of the silt (made of cement, fly ash and desulfurized gypsum in a mass ratio of 12:8:3), which was actually 60g. The PAM content was 0.5‰ (based on the mass of silt), which was 0.5g. The PCE content was 0.4% (based on the mass of silt), which was 4g. The water to solid mass ratio was 0.6. 1703g of solidified soil slurry No. 1 was prepared.

[0038] Preparation of No. 2 solidified soil slurry: Take 1000g of silt, add 6% (60g of solidifying agent by weight of silt), add 0.5g of PAM (0.5‰ by weight of silt), add 4g of modified polycarboxylate superplasticizer (0.4% by weight of silt), and the water-soil mass ratio is 0.6 to prepare 1703g of solidified soil slurry No. 2.

[0039] The preparation method of modified polycarboxylate superplasticizer includes the following steps: (1) First, weigh 30 g of methyl allyl polyoxyethylene ether (HPEG) macromonomer and put it into a four-necked flask equipped with a mechanical stirrer and a feeding system. Then weigh 20 mL of water and add it to the flask for stirring and pre-dissolving. After the methyl allyl polyoxyethylene ether (HPEG) in the base material is completely dissolved, the preparation of the base material is completed. (2) Weigh 10 g of acrylic acid (AA) and 50 mL of water to prepare material A; then weigh 5 g of hydroxypropionic acid (3-MPA), 2.5 g of ascorbic acid (VC) and 75 mL of water to prepare material B; (3) After heating the water bath to the set temperature, turn on the peristaltic pump and add A and B materials at a uniform rate (the addition coefficient is determined according to each prepared solution, and the time is controlled within 1 minute), so that the addition time of A and B materials is 150 minutes and 120 minutes respectively. After A and B materials are completely added, keep warm for 1 hour.

[0040] (4) After the reaction is complete, add sodium hydroxide solution (mass fraction of 30%) to adjust the pH of the solution. After cooling to room temperature, add water. When the solid content of the solution is 40%, the modified polycarboxylate superplasticizer H-PCE is obtained.

[0041] Example 5 Experimental Example 1 A flame-retardant coal gangue composite material with solidified soil slurry, comprising: 700g of coal gangue (particle size 1-3mm); and 300g of solidified soil slurry No. 1 prepared in Example 4 (mass ratio of coal gangue to solidified soil slurry 7:3). Preparation method: S1: Take 300g of the solidified soil slurry No. 1 prepared in Example 4 for later use; S2: Mix 700g of coal gangue (particle size 1-3mm) with the solidified soil slurry prepared in step S1 according to the mass ratio, stir evenly to obtain a mixture; S3: Vibrate the mixture prepared in step S2 for 30 seconds at a frequency of 1 Hz to remove air bubbles and shape it into a soil column of Φ5 cm × 10 cm. S4: After curing the soil column formed in step S3 at 25℃ for 28 days, it is naturally cured for 150 days to obtain the solidified soil slurry flame-retardant coal gangue composite material.

[0042] Experimental Example 2 Except for the use of coal gangue with a particle size of 3-6mm, all other conditions (raw materials, coal gangue to solidified soil slurry mass ratio of 7:3, additive dosage, preparation, curing, and testing) were exactly the same as in Experiment 1.

[0043] Experimental Example 3 A solidified soil slurry flame-retardant coal gangue composite material, comprising: 600g of coal gangue (particle size 1-3mm); and 400g of solidified soil slurry No. 2 prepared in Example 4 (mass ratio of coal gangue to solidified soil slurry 6:4).

[0044] The preparation method of solidified soil slurry flame-retardant coal gangue composite material is the same as that in Experimental Example 1.

[0045] Comparative Example 1: Pure Coal Gangue Only coal gangue (particle size 1-3 mm) is used, without adding any solidified soil slurry or additives.

[0046] Preparation method: Coal gangue was loaded into the mold in the same way as in Experiment 1, and gently vibrated to simulate the natural stacking state.

[0047] Comparative Example 2 Except for the mass ratio of coal gangue to solidified soil slurry being 8:2, all other conditions (raw materials, particle size 1-3 mm, additive dosage, preparation, curing, and testing) were exactly the same as in Experiment 1.

[0048] Comparative Example 3 Except for the coal gangue particle size being <1 mm, all other conditions (raw materials, coal gangue to solidified soil slurry mass ratio 7:3, additive dosage, preparation, curing, and testing) were exactly the same as in Experiment 1.

[0049] Comparative Example 4 Except for the use of coal gangue with a particle size of 6-13mm, all other conditions (raw materials, mass ratio of coal gangue to solidified soil slurry 7:3, additive dosage, preparation, curing, and testing) were exactly the same as in Experiment 1.

[0050] Example 6 Large-scale homogeneous solidified soil slurry-gangue composite material blocks were prepared using the solidified soil slurry flame-retardant coal gangue composite materials prepared in Experimental Examples 1-3 and Comparative Examples 2-4.

[0051] Tests: ① Industrial CT scan analysis of pore structure; ② Cutting into test blocks with thicknesses of 10, 30, 50, and 70 mm, heating on an 80℃ heating plate for 120 min, and recording the temperature rise curves by infrared thermal imaging; ③ TG-DSC analysis of thermogravimetric behavior.

[0052] Experimental results: 1. Industrial CT scanning analysis of pore structure, such as Figure 3 As shown in Table 1.

[0053] Table 1. Pore parameters of soil columns with different particle size grades of coal gangue and different amounts of solidified soil slurry.

[0054] The composite material of this invention (especially Example 1 with optimal proportions) can form a dense microstructure dominated by isolated pores and with low connectivity, which is key to achieving physical oxygen barrier. The Euler number of the sample in Example 1 is 1.09 × 10⁻⁶. 4The porosity was the lowest in the experimental group, significantly lower than that of pure solidified soil slurry, other "gangue-solidified soil slurry" ratios (Example 3, Comparative Example 2), and other gangue particle size distribution samples (Example 2, Comparative Example 4). This indicates that the composite material prepared with a 7:3 (coal gangue:solidified soil slurry) ratio and using 1-3mm gangue has the least interconnected internal pore network, making oxygen diffusion the most difficult. The fractal dimension of Example 1 (2.20) is moderate, indicating that its pore structure is neither too simple (unfavorable for filling) nor too complex (potentially affecting strength), forming an effective "encapsulation-filling" structure. The total porosity (5.28%) and isolated porosity (5.27%) of Example 1 are very close, and the standard deviation (1.11%) and coefficient of variation (20.94%) are low. This indicates that its pore distribution is uniform, and most pores are isolated pores rather than interconnected channels. This perfectly aligns with the invention mechanism of "solidified soil slurry effectively filling macroscopic pores to form isolated pores." Experimental Example 1 possesses the largest equivalent pore diameter and area, but combined with its lowest Euler number, this indicates that it formed a relatively small number of pores (1.20 × 10⁻⁶). 4 Isolated pores (of medium size) but relatively large in size and effectively separated by the solidified soil slurry are beneficial for blocking oxygen pathways rather than providing them. As the proportion of solidified soil slurry increases (Comparative Example 2 > Experimental Example 1 > Experimental Example 3), the porosity change is not monotonic, but the connectivity (Euler number) first decreases significantly and then increases. Experimental Example 1 (7:3) reaches the lowest point of connectivity, indicating that this ratio is the key point for optimizing filling and structure formation. At the 7:3 ratio, the 1-3 mm particle size (Experimental Example 1) has the lowest Euler number and the worst connectivity. Particle sizes that are too small (<1 mm, Comparative Example 3) or too large (3-6 mm, Experimental Example 2; 6-13 mm, Comparative Example 4) will lead to poor connectivity or excessively high porosity, both of which are not conducive to forming the optimal barrier structure.

[0055] 2. The infrared thermal imaging and recording temperature rise curves are shown below. Figure 4 , Figure 5 As shown.

[0056] For all samples, the thickness of the test block was the most significant factor affecting the final surface temperature. When the thickness increased from 10 mm to 70 mm, the final temperature of all samples (including pure gangue) decreased significantly. This clearly demonstrates that increasing the thickness of the capping layer can effectively block external heat sources.

[0057] At a thickness of 10 mm: the temperature of all samples rose rapidly, with relatively significant differences between formulations, but all were above ambient temperature. At this point, the physical barrier effect was limited.

[0058] Thickness of 30 mm and above: The advantages of the formulation (7:3) in Experimental Example 1 began to emerge.

[0059] 50mm thickness: The final temperature of Test Example 1 was 31.6℃, which was lower than that of pure solidified soil slurry (32.5℃) and pure coal gangue (31.4℃) of the same thickness, demonstrating the synergistic heat insulation effect of the composite material.

[0060] 70mm thickness: The final temperature of Test Example 1 was only 27.4℃, one of the lowest among all samples, and the heating process was the most gradual. This demonstrates that after reaching a certain thickness (≥50mm), the composite material with the optimal ratio of the present invention can form an extremely effective thermal barrier, reducing the influence of an external 80℃ heat source to a level close to ambient temperature.

[0061] 3. TG-DTG curve as shown Figure 6 As shown in Table 2.

[0062] Table 2 Combustion characteristic parameters of different samples

[0063] The composite material of the present invention significantly alters the thermal decomposition process of coal gangue, delays the main combustion stage, and reduces the total weight loss, demonstrating its flame-retardant effectiveness from the perspective of chemical reaction kinetics.

[0064] Stage I: The initial moisture content of the gangue is low, with the highest DTG value at the start of heating, which then gradually decreases, resulting in a slow rate of thermal weight loss. The absence of a T1 temperature at which the DTG is at its maximum indicates that the gangue enters a heat storage phase from the beginning of heating, and the rate of thermal weight loss only stabilizes when the sample temperature T2 reaches 225.8℃. In this stage, the thermal weight loss rate of the gangue is only 0.87%, while that of the solidified soil slurry is the highest at 7.56%. This is because the difference in water content retained by the ISA hydration products CSH and PAM in the solidified soil slurry leads to a relatively high free water content. As the temperature rises, the water evaporates rapidly, and the sample exhibits the maximum rate of thermal weight loss in the first stage at a T1 temperature of 103.2℃, stabilizing at 225.7℃. It can be seen that the T2 temperature of the solidified soil slurry is close to that of the gangue. The thermal weight loss rates of Experimental Example 3, Experimental Example 1, and Comparative Example 2 in this stage were 3.01%, 1.93%, and 2.44%, respectively, falling between those of pure gangue and solidified soil slurry. The lowest thermal weight loss rate was observed when the ratio of gangue to solidified soil slurry was 7:3. As the amount of gangue increased, T1 decreased from 91.9℃ to 85.3℃. This indicates that the less solidified soil slurry used and the higher the proportion of gangue, the faster the water and air desorption rate in the reconstructed soil layer, the greater the oxygen absorption rate, and the higher the risk of heat storage and spontaneous combustion.

[0065] Stage II: The T3 for gangue is 508.3℃, where the combustible combustion rate is highest, corresponding to the cracking of alkyl chain structures in the organic matter of gangue. In contrast, the T3 for solidified soil slurry is 480.4℃, significantly shifted to the left, corresponding to the cracking of PAM chain structures. The DTG rate in this stage is significantly lower for solidified soil slurry than for gangue, indicating that once the cracking of organic matter and macromolecular structures in gangue begins, its heating and combustion rate is more intense, and the temperature is higher. For "solidified soil slurry-gangue" samples with different component ratios, the T3 and T4 show a trend of higher temperature and greater thermal weight loss with less solidified soil slurry. The rate of thermal weight loss in this stage is also the highest among the three stages.

[0066] Phase III: When the experimental temperature exceeds T4, the thermal weight loss rate of the gangue tends to stabilize, but the peak value of the DTG curve of the solidified soil slurry is at this stage, corresponding to the decomposition of carbonates. Comparison shows that the T5 temperatures for pure gangue, Experiment 3, Experiment 1, Comparative Example 2, and solidified soil slurry are 700.8℃, 732.8℃, 735.7℃, 742.0℃, and 768.2℃, respectively, with thermal weight loss rates of 1.87%, 3.08%, 3.76%, 4.20%, and 8.28%. The addition of solidified soil slurry enhances the heat resistance of the components. The main reason is that when the gangue exceeds 550℃, the stable hydroxyl groups and active groups in its structure are destroyed, while the addition of solidified soil slurry increases the proportion of bound water in the components. Although the rate of thermal decomposition is relatively increased, macroscopically, the decomposition temperature of the gangue in the stable thermal weight loss stage is increased.

[0067] In summary, the use of solidified soil slurry altered the microstructure of pure gangue components, slowed down the thermal decomposition rate of gangue in stage I, and increased the total weight loss of the sample. The moisture and CSH products contained in the solidified soil slurry effectively buffered the decomposition rate of gangue during the heating stage, resulting in a good flame-retardant effect.

[0068] TG-DTG data show that the flame-retardant mechanism of this invention is not only physical insulation, but also chemically slows down and reduces the rate and total amount of coal gangue oxidation and decomposition by inhibiting oxygen contact. This is completely consistent with the mechanisms of "inhibiting oxidation and heat storage" mentioned in the background art and "impeding oxygen molecule diffusion" in the invention.

[0069] Example 6 Large-scale homogeneous "solidified soil slurry-gangue" composite material blocks were prepared together with pure gangue and solidified soil slurry samples using the solidified soil slurry flame-retardant coal gangue composite material prepared in Experimental Example 1, Experimental Example 2 and Comparative Example 2.

[0070] Standard test blocks of four different thicknesses—10 mm, 30 mm, 50 mm, and 70 mm—were cut from the sample.

[0071] Infrared thermal imaging experiments were conducted under uniform conditions (80℃ heating plate, 120 min), and the heating curve and final surface temperature distribution were recorded. The results are shown in Table 3.

[0072] Table 3. Temperature (°C) of the surface of "solidified soil slurry-gangue" samples with different amounts of solidified soil slurry over time.

[0073] Conclusion: In practical applications of flame retardant treatment in gangue dumps, when using this composite material for grouting reconstruction, the thickness of the reconstructed soil layer should not be less than 50 mm. This thickness ensures that the internal temperature is effectively suppressed under the influence of external heat sources with temperatures similar to the critical auto-ignition temperature (80℃), thereby achieving a safe and flame-retardant engineering effect.

[0074] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A flame resistant coal refuse composite material of a solidified soil slurry, characterized by, Its components include coal gangue and solidified soil slurry; the mass ratio of the coal gangue and solidified soil slurry is (1-4):1; the solidified soil slurry includes solids and water, the solids include silt, solidifying agent, polyacrylamide, and water-reducing agent; the mass ratio of the total mass of the solids to the mass of the water is 1:(0.5-0.8).

2. The composite material of claim 1, wherein, The mass of the silt is more than 90% of the total mass of the solid body, the amount of the solidifying agent is 3%-8% of the mass of the silt, the amount of the polyacrylamide is 0.1‰-1‰ of the mass of the silt, and the amount of the water-reducing agent is 0.1%-0.8% of the mass of the silt.

3. The composite material of claim 1, wherein, The curing agent is composed of cement, fly ash, and desulfurized gypsum, with a mass ratio of 10:(6-8):(1.5-2.5).

4. The composite material according to claim 1, characterized in that, The polyacrylamide is an anionic type with a molecular weight of 15 million.

5. The composite material according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate water-reducing agent or a modified polycarboxylate high-efficiency water-reducing agent.

6. The composite material according to claim 5, characterized in that, The preparation method of the modified polycarboxylate superplasticizer includes the following steps: (1) First, weigh out the methyl allyl polyoxyethylene ether macromonomer and put it into a four-necked flask with a mechanical stirrer and a feeding system. Then weigh out a certain amount of deionized water and add it to the flask for stirring and pre-dissolving. After the methyl allyl polyoxyethylene ether in the base material is completely dissolved, the preparation of the base material is completed. (2) Weigh out acrylic acid and deionized water to prepare material A; then weigh out hydroxypropionic acid, ascorbic acid and an appropriate amount of water to prepare material B; (3) After heating the water bath to the set temperature, turn on the peristaltic pump to add A and B materials at a uniform rate. After A and B materials have been completely added, keep the water bath warm. (4) After the reaction is complete, add sodium hydroxide solution with a mass fraction of 25-35% to adjust the pH of the solution. After cooling to room temperature, add water. When the solid content of the solution is 35-45%, the modified polycarboxylate superplasticizer is obtained.

7. The composite material according to claim 1, characterized in that, The particle size of the coal gangue is 1-6 mm.

8. A method for preparing a solidified soil slurry flame-retardant coal gangue composite material according to any one of claims 1-7, characterized in that, Includes the following steps: S1: Mix silt, solidifying agent, polyacrylamide, water-reducing agent and water in a certain proportion to prepare solidified soil slurry; S2: Mix the coal gangue with the solidified soil slurry prepared in step S1 according to the mass ratio, stir evenly, and obtain a mixture; S3: Vibrate the mixture prepared in step S2 for 20-50 seconds at a frequency of 0.5-2Hz to remove air bubbles and shape it into a soil column; S4: After curing the soil column formed in step S3 at 25℃ for 28 days, it is naturally cured for 150 days to obtain the solidified soil slurry flame-retardant coal gangue composite material.

9. The application of a solidified soil slurry flame-retardant coal gangue composite material according to any one of claims 1-7 in flame retardancy of coal mine gangue stockpiles.

10. The application according to claim 9, characterized in that, The composite material is filled into the gaps in the gangue pile by grouting, and the thickness of the reconstructed soil layer is not less than 50 mm.

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