Coal gangue backfill functional material, preparation method and application thereof in solidification of heavy metals in soil

Abstract

The application belongs to the technical field of coal gangue recycling, and particularly relates to a coal gangue backfill functional material, a preparation method and application of the coal gangue backfill functional material in heavy metal solidification of soil. The application discloses a coal gangue backfill functional material, which comprises, in terms of weight fraction, 5-15 parts of backfill raw materials and 5-10 parts of heavy metal solidification agents. The coal gangue backfill functional material can be prepared and applied to coal gangue backfill treatment, so that the coal gangue can be solidified and heavy metal ions in the coal gangue can be prevented from exosmosis.

Description

Technical Field

[0001] This invention belongs to the field of coal gangue recycling technology, specifically, it relates to a coal gangue backfill functional material, its preparation method and its application in soil heavy metal solidification. Background Technology

[0002] Coal gangue is a solid waste generated and discharged during coal mining and beneficiation, accounting for 10-15% of raw coal production. Currently, my country's coal gangue stockpile exceeds 7 billion tons, ranking first among my country's major industrial solid waste emissions.

[0003] According to data released by the Ministry of Ecology and Environment of China in the "2020 Annual Report on the Prevention and Control of Solid Waste Pollution in Large and Medium-sized Cities Nationwide," the comprehensive utilization rate of coal gangue resources in my country is relatively low compared to other bulk industrial solid wastes, at only 58.9%. The various heavy metal elements present in coal gangue, under the influence of external environmental factors such as weathering, erosion, and rainwater leaching, will inevitably migrate. These heavy metal elements, along with harmful gases, enter the atmosphere, worsening the air quality and affecting human health.

[0004] Domestic and international research and engineering practice have shown that underground green backfilling and reclamation of coal mining subsidence areas will become effective ways to utilize bulk coal-based solid waste resources. However, for the reclamation of coal mining subsidence areas, while utilizing coal-based solid waste resources, how to solidify heavy metals in coal gangue and reduce the impact and harm of heavy metals in coal gangue on the surrounding environment will become the core issue of ecological reclamation and backfilling using coal gangue. The control of heavy metals in coal gangue is a key component of the successful implementation of various ecological integrated disposal methods. All integrated disposal methods involve environmental risks from heavy metal elements in coal gangue. The "Management Measures for Comprehensive Utilization of Coal Gangue" issued by the state requires that the leaching concentration of heavy metal elements in coal gangue meet the concentration limits set by "GB18599-2020 Pollution Control Standard for General Industrial Solid Waste Storage and Disposal Sites" and its provisions 3.6 and 3.7 in "GB8978 Integrated Wastewater Discharge Standard". Currently, various heavy metal treatment technologies have emerged, such as precipitation, ion exchange, membrane separation, biological methods, solidification and stabilization, oxidation-reduction, and adsorption. Among these methods, solidification and stabilization are favored in the field of heavy metal disposal due to their advantages of low material cost, high efficiency, environmental friendliness, and recyclability. Heavy metal solidification and stabilization of coal gangue involves fixing characteristic heavy metal elements in coal gangue using effective physical, chemical, or biological methods, or converting them into a state with lower chemical activity, preventing their migration, transformation, and diffusion from the coal gangue into the surrounding environment, thereby reducing the environmental hazards posed by heavy metal elements.

[0005] Therefore, under the conditions of "reduction, resource utilization, and harmlessness", the preparation of functional materials for coal gangue backfill with high heavy metal solidification / stabilization performance is a hot issue in solving the practical application of coal gangue backfilling and reclamation. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems existing in the prior art and provide a functional material for coal gangue backfilling, its preparation method, and its application in the solidification of heavy metals in soil. This invention, by preparing a functional backfilling material and applying it to coal gangue treatment, can solidify the coal gangue and prevent the leakage of heavy metal ions from the coal gangue.

[0007] The objective of this invention and the technical problem it solves are achieved by the following technical solutions.

[0008] One aspect of the present invention provides a functional material for coal gangue backfilling, comprising, by weight fraction: 5-15 parts of backfilling raw material and 5-10 parts of heavy metal curing agent.

[0009] In a preferred embodiment of the present invention, the backfill material comprises the following components by weight fraction: 70-80 parts of silt, 1-10 parts of cement, and 10-20 parts of fly ash.

[0010] In a preferred embodiment of the present invention, the heavy metal curing agent is modified polyacrylamide.

[0011] In a preferred embodiment of the present invention, the modified polyacrylamide is obtained by modifying polyacrylamide through the Mannich reaction:

[0012] Formaldehyde and amine organic compounds were mixed and reacted under acidic conditions to obtain methyleneamine carbocations, and then polyacrylamide was added to react and give product I.

[0013] Product I was added to an alkaline solution of mercaptoacetic acid to react and obtain modified polyacrylamide.

[0014] In a preferred embodiment of the present invention, the coal gangue backfilling functional material further includes 1 to 5 parts of an synergistic agent.

[0015] In a preferred embodiment of the present invention, the synergist is a modified silica sol-coated three-dimensional ordered macroporous nanomaterial composite.

[0016] Another aspect of the present invention provides a method for preparing a functional material for coal gangue backfilling, the method comprising the following steps:

[0017] (1) Preparation of backfill material: According to the weight fraction, 70-80 parts of silt, 1-10 parts of cement and 10-20 parts of fly ash are mixed evenly to obtain backfill material;

[0018] (2) Preparation of modified polyacrylamide: Formaldehyde and amine organic compounds are mixed evenly to obtain a mixed solution. The pH of the solution is adjusted to 2-5 with acid. The mixture is stirred at room temperature for 1-3 hours to obtain an intermediate. Then, 1-5% by mass of polyacrylamide aqueous solution is added to the obtained intermediate and stirred for 2-4 hours to obtain product I.

[0019] Take a 40–60% mercaptoacetic acid solution, adjust the pH of the system to 8–12 using an alkali, then add product I to react and obtain modified polyacrylamide; and / or

[0020] (3) Preparation of synergistic agent: Add three-dimensional ordered macroporous metal-organic framework material to silica sol and stir continuously until uniform. After stirring, microwave the product for 5 to 15 minutes at a power of 600 to 800W to obtain modified silica sol.

[0021] Polylactic acid polyol was added to the obtained modified silica sol and stirred evenly. The system was then heated to 40-60°C and silane coupling agent was added dropwise while stirring. After the addition was completed, stirring was continued for 2-4 hours. After the reaction was completed, a modified silica sol-coated three-dimensional ordered macroporous nanomaterial composite was obtained, which is the synergistic agent.

[0022] In a preferred embodiment of the present invention, the preparation method further includes:

[0023] According to the weight fraction, 5-15 parts of backfill material, 5-10 parts of heavy metal curing agent and / or 1-5 parts of synergistic agent are mixed and stirred at 50-70℃ for 100-140 minutes to obtain coal gangue backfill functional material.

[0024] In a preferred embodiment of the present invention, in step (2), the amine organic compound is selected from any one of methylamine, dimethylamine, ethylamine, diethylamine, n-propylamine, and ethylenediamine.

[0025] In a preferred embodiment of the present invention, in step (2), the formaldehyde and amine organic compounds are added in a molar ratio of 1 to 2:1.

[0026] In a preferred embodiment of the present invention, in step (2), the amount of the polyacrylamide aqueous solution added is 3 to 5 times the volume of the intermediate.

[0027] In a preferred embodiment of the present invention, in step (2), product I is added in an amount with a volume ratio of 1:1 to 5 with the mercaptoacetic acid solution.

[0028] In a preferred embodiment of the present invention, in step (3), the three-dimensional ordered macroporous metal-organic framework material is added at a mass-volume ratio of 1g to 5-10mL with the silica sol.

[0029] In a preferred embodiment of the present invention, in step (3), the polylactic acid polyol is added at a mass-to-volume ratio of 1g to 3-7mL with the modified silica sol.

[0030] In a preferred embodiment of the present invention, in step (3), the silane coupling agent is selected from any one of isobutyltriethoxysilane, methacryloxysilane, vinyltriethoxysilane, and vinyltrimethoxysilane.

[0031] In a preferred embodiment of the present invention, the amount of the silane coupling agent added is 0.01 to 0.05 times the volume of the modified silica sol.

[0032] By employing the above technical solution, the present invention has at least the following advantages:

[0033] 1. This invention uses cement, fly ash, and silt as backfill materials. The aluminosilicate structure formed by the hydration of cement, fly ash, and silt can continuously physically encapsulate heavy metal ions, effectively solidifying them by sealing them within the aluminosilicate crystal lattice. Furthermore, the ion exchange between cations during aluminosilicate formation can form heavy metal cationic aluminosilicates with anionic aluminosilicates, effectively inhibiting the leaching of heavy metal ions and thus achieving heavy metal solidification.

[0034] 2. This invention uses modified polyacrylamide as a heavy metal curing agent. Modified polyacrylamide can form chemical bonds and coordination bonds with heavy metals to complete chemical bonding. In addition, the multiple coordination sites of modified polyacrylamide provide more lone pair electrons and the formed aluminosilicate anions can be electrostatically attracted to fix heavy metal ions.

[0035] 3. This invention adds synergistic agents to the original composition. By adding a three-dimensional ordered macroporous metal-organic framework (MOF) material to the silica sol, the MOF material is uniformly dispersed within the silica sol. Subsequently, it is treated under high-energy microwaves to obtain a modified silica sol. The mutual agglomeration force between the MOF material and the microwave-treated silica sol molecules is reduced, thereby improving compatibility with organic polymers. Therefore, this invention forms a homogeneous modified silica sol-coated three-dimensional ordered macroporous nanomaterial composite with polylactic acid polyol under the action of a silane coupling agent. The addition of the three-dimensional ordered macroporous MOF material also improves the compressive strength of the entire synergistic agent, thus endowing the synergistic agent with good hydrophilicity, adhesion, and compressive strength.

[0036] 4. This invention prepares a backfill functional material by mixing backfill raw materials and metal curing agents. It can solidify heavy metal ions in coal gangue and prevent the outward leakage of heavy metal ions in coal gangue. On this basis, adding synergistic additives can further improve the solidification effect and durability of the material on heavy metal ions.

[0037] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below. Attached Figure Description

[0038] Figure 1 Photos of the waste disposal site and sampling area;

[0039] Figure 2 This is a diagram of the original coal gangue.

[0040] Figure 3 Images of coal gangue samples and scanning electron microscope (SEM) images. Detailed Implementation

[0041] To make the technical means, creative features, achieved objectives, and effects of this invention readily understandable, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0042] The aluminosilicate structure formed by the hydration of cement, fly ash, and silt can continuously physically encapsulate heavy metal ions, effectively solidifying them by sealing them within the aluminosilicate crystal lattice. Furthermore, during the formation of aluminosilicates, the ion exchange between cations can form heavy metal cationic aluminosilicates with anionic aluminosilicates, effectively inhibiting the leaching of heavy metal ions and thus playing a role in solidifying heavy metals.

[0043] Polyacrylamide is a chemically reactive linear water-soluble polymer. The nitrogen atom in the amide group (-CONH2) of its molecular chain possesses a lone pair of electrons, giving it electron-donating ability. It can form hydrogen bonds with water and also complex with heavy metal cations to form coordination compounds, thus solidifying heavy metal ions into a stable state. However, polyacrylamide exhibits instability under different acidic and alkaline conditions, which can lead to its deactivation during the heavy metal solidification process in coal gangue, thus affecting the heavy metal solidification performance.

[0044] Polyacrylamide is easily deactivated under acidic or heated conditions, transforming into polyacrylic acid (PAA) and ammonium ions (NH4+).+ Polyacrylamide under acidic conditions H + The oxygen atom of the carbonyl group combines with the lone pair electrons to form a positively charged protonated amide oxygen atom, enhancing the positive charge of the carbonyl carbocation. This, in turn, attracts the lone pair electrons of the oxygen in the water molecule to attack and form a dihydroxyl intermediate, while the other part of H3O... + Due to its extremely strong positive charge, it readily reacts with the nitrogen atom on the amino group to form an NH3 molecule, which then leaves to re-form a protonated amide oxygen atom. In an acidic environment, the NH3 molecule further abstracts a hydrogen atom from the protonated amide oxygen atom. + Formation, NH4 + The ion, while the dihydroxy intermediate in the original side chain loses H + This leads to the formation of polyacrylic acid, which deactivates the polyacrylamide.

[0045] Polyacrylamide readily transforms into polyacrylic acid anions (PAA-A) and hydrated ammonia (NH3·H2O) under alkaline conditions. This transformation is due to the OH- ions in polyacrylamide under alkaline conditions. - Strong nucleophilicity, OH - Direct attack on the carbonyl carbon forms a negatively charged carbonyl intermediate, then -NH2, as a relatively easily leaving group, is eliminated by the intermediate to form PAA and amino anions (NH2). - However, in an alkaline environment, NH2... - Easy to steal H in PAA + This leads to the formation of PAA-A and NH3. In aqueous solution, NH3 easily combines with water to form NH3·H2O, which also deactivates PAM.

[0046] This invention utilizes the Mannich reaction to modify polyacrylamide. Under acid catalysis, the aldehyde and amine undergo a nucleophilic addition reaction, losing one molecule of water to generate an active electrophilic reagent, methyleneamine carbocation, which further attacks the nitrogen atom on the side chain of polyacrylamide, forming a positively charged nitrogen-ionized intermediate on the side chain. This improves the water solubility of polyacrylamide and increases the number of nitrogen atoms, providing more lone pairs of electrons for the heavy metal curing reaction. In addition, the higher positive charge is also beneficial for the next step of binding with mercaptoacetic acid (TGA) to form -SH and the curing site of heavy metal Cd.

[0047] Silica sol is a dispersion of nano-sized silica particles in water or other solvents. The silica particles contain a large number of hydroxyl groups on their surface, resulting in a large specific surface area and excellent properties such as high dispersibility, adsorption, and fire resistance and heat insulation. Due to the abundance of hydroxyl groups, silica sol exhibits good hydrophilicity, making it an important raw material for superhydrophilic anti-fog coatings. However, silica sol has poor compatibility with organic polymers. During the in-situ preparation of silica-polymer composites, silica sol tends to agglomerate, failing to form uniform inorganic / organic composite materials, which greatly limits its applications.

[0048] Based on the above, this invention first adds a three-dimensional ordered macroporous metal-organic framework (MOF) material to silica sol, ensuring the MOF material is uniformly dispersed within the silica sol. Subsequently, it is treated under high-energy microwaves to obtain a modified silica sol. The mutual agglomeration force between the MOF material and the microwave-treated silica sol molecules is reduced, thereby improving compatibility with organic polymers. Therefore, this invention combines the modified silica sol with polylactic acid polyol under the action of a silane coupling agent to form a homogeneous modified silica sol-coated three-dimensional ordered macroporous nanomaterial composite. This composite not only possesses good hydrophilicity and adhesion but also exhibits certain compressive strength and other properties. When used in coal gangue solidification, it can improve the solidification effect on heavy metal ions in coal gangue and enhance the durability of the solidification process.

[0049] Unless otherwise specified, the coal gangue used in the following examples includes coal gangue from the Bulian Tower waste disposal site, the Bulian Tower coal preparation plant, and the Wulanmulun coal preparation plant in the Shendong mining area, labeled as CG1, CG2, and CG3 respectively. Photos of the on-site sampling sites are shown below. Figure 1 As shown. Figure 2 Images (a) through (c) show the original samples of coal gangue CG1, CG2, and CG3, respectively. The three types of coal gangue were crushed and ground to a fineness below 200 mesh (0.075 mm). Figure 3 Images (a) to (c) show the samples of the three types of coal gangue after crushing, grinding, and sieving. Images (d) to (f) are scanning electron microscope (SEM) images of the coal gangue at corresponding magnifications. At low magnification, the gangue appears as irregular blocky solid particles. At high magnification, the blocky coal gangue structure is relatively compact, with some small pores. Some quartz-like glassy solids are attached to the surface of the blocky structure, and a small number of plate-like aluminosilicate structures have residual fragments remaining on the surface of the blocky structure during the crushing process, exhibiting an irregular crystal structure and a layered microstructure. This is related to the special silicon-oxygen tetrahedral and aluminum-oxygen octahedral unit cell configuration of aluminosilicates. Chemical composition analysis using X-ray fluorescence spectrometry (XRF) showed that the chemical composition of the three types of coal gangue was mainly composed of Si, Al, and C elements. CG1 had a Si content of 42.17% and an Al content of 16.90%. CG2 has a Si content of 39.15% and an Al content of 15.30%, with a Si-to-Al ratio of approximately 2.55. CG3 has a Si content of 37.41% and an Al content of 16.24%. The Si-to-Al ratios of CG1, CG2, and CG3 are approximately 2.50, 2.55, and 2.30, respectively. Based on the comprehensive mineral Si-to-Al ratio classification, these three types of gangue rocks belong to the rock-based Si-aluminum-polysilicon-oxygen polymer category. The main phase components of coal gangue are SiO2, Al2Si2O5(OH)4, and KCa2AlSi7O. 17The composition of (OH)2·6H2O and other components indicates that the various phases in coal gangue are composed of silica-based polymers, kaolinite-based polymers, and calcium-based (Ca, K) aluminosilicate multi-component copolymers.

[0050] Unless otherwise specified, the fly ash used in the following examples was taken from the Shangwan Thermal Power Plant in the Shendong Mining Area for characterization and analysis. The fly ash was ground to below 200 mesh (0.075 mm). Chemical composition analysis using X-ray fluorescence spectrometry (XRF) revealed that its main chemical components were Si, Al, Ca, and S elements. The Si content of FA was 20.72%, and the Al content was 10.01%. The Si-to-alumina ratio was approximately 2.07, roughly equal to 2, and the Ca content was 26.63%, with a S content of 9.12%, classifying it as a high-proportion calcium-based (Ca, K) aluminosilicate compound. XRD patterns of the fly ash showed that its surface morphology consisted of a mixture of spherical, blocky, and elongated shapes, with the main corresponding phases being quartz, hematite, and anhydrite. Anhydrite, upon hydration, easily forms an ettringite structure. Particle size analysis revealed that the intermediate particle size of fly ash was concentrated around 18.7 μm, accounting for 5.4%, while the boundary particle size ranged from 1.1 to 73.5 μm. The cumulative curves showed D10 = 8.1 μm, D50 = 15.1 μm, and D90 = 50.8 μm.

[0051] Unless otherwise specified, the silt used in the following examples was taken from the Shendong mining area reclamation demonstration site for characterization and analysis. The silt was ground to below 200 mesh (0.075 mm), and its chemical composition was tested using X-ray fluorescence spectrometry (XRF). Its main chemical components were Si, Al, Ca, and S elements, with a Si content of 20.72% and an Al content of 10.01%. The Si-Al ratio was approximately 2.55, classifying it as a rock-based silica-alumina-polysilicon polymer. XRD analysis of the silt revealed that its surface morphology consisted of polygonal, irregular blocks, with quartz and calcite as the main corresponding phases. Particle size analysis showed that the middle particle size of the silt distribution curve was concentrated at approximately 28.7 μm, accounting for 5.6%, while the boundary particle size ranged from 1.4 to 131.7 μm. In the cumulative curve, D10 = 24.1 μm, D50 = 47.1 μm, and D90 = 102.9 μm.

[0052] Unless otherwise specified, the PO 42.5 ordinary Portland cement used in the following examples was obtained from China National Building Materials Group Co., Ltd. For characterization analysis of the experimental materials, the cement was ground to below 200 mesh (0.075 mm), and its chemical composition was tested using X-ray fluorescence spectrometry (XRF). Its main chemical components were Si, Al, Ca, and S elements, with a Si content of 20.72% and an Al content of 10.01%. The Si / Al ratio was approximately 4, classifying it as a polysilicon-aluminosilicate compound. XRD analysis revealed that the cement surface morphology consisted of irregular granular phases, primarily dicalcium silicate and tricalcium silicate, which, upon hydration, could form hydrated calcium silicate and other hydration cementitious products. Particle size analysis showed that the intermediate particle size of the standard cement was concentrated around 17.8 μm, accounting for 9.1%, while the boundary particle size ranged from 3.5 to 64.5 μm. In the cumulative curve for cement, D10 = 8.9 μm, D50 = 17.8 μm, and D90 = 31.7 μm.

[0053] Unless otherwise specified, the preparation method of the three-dimensional ordered macroporous metal-organic framework material used in the following examples is as follows: A polystyrene emulsion was centrifuged at 6000 r / h for 5 h, and the supernatant was removed to obtain a bottom precipitate. After drying at 90℃ overnight, an ordered polystyrene template was obtained. This template was immersed in a 0.03 g / mL zinc nitrate / methanol dispersion for 4 hours, and then removed and dried overnight. The polystyrene template immersed in the zinc nitrate / methanol solution was then immersed in a 0.1 g / mL 2-methylimidazole / methanol solution and allowed to stand for 48 hours to obtain a polystyrene / organic framework composite material. The polystyrene / organic framework composite material was immersed in N,N-dimethylformamide and stirred for 24 hours to remove the polystyrene, yielding the three-dimensional ordered macroporous metal-organic framework material.

[0054] Unless otherwise specified, the polylactic acid polyol used in the following examples is prepared by mixing lactide and butanediol, and heating the mixture at 0.4 MPa and 110°C for 2 hours under the action of stannous chloride to obtain polylactic acid polyol.

[0055] Unless otherwise specified, the polyacrylamide used in the following examples is cationic with a molecular weight of 3 million. All other materials and reagents used are commercially available.

[0056] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0057] Example 1:

[0058] (1) Preparation of backfill material: According to the weight fraction, 78.9 parts of silt, 6 parts of cement and 15.1 parts of fly ash are mixed evenly to obtain backfill material;

[0059] (2) Preparation of modified polyacrylamide: Formaldehyde and ethylenediamine were mixed evenly at a molar ratio of 1.5:1 to obtain a mixed solution. The pH of the solution was adjusted to 3.5 with acid, and the mixture was stirred at room temperature for 2 hours to obtain an intermediate. Then, a 2.5% (w / w) aqueous solution of polyacrylamide (the amount added was 4 times the volume of the intermediate) was added to the intermediate and stirred for another 3 hours to obtain product I. A 45% (w / w) solution of mercaptoacetic acid was taken, and the pH of the system was adjusted to 10 with alkali. Then, product I (added at a volume ratio of 1:3 with mercaptoacetic acid solution) was added to react and obtain modified polyacrylamide.

[0060] (3) According to the weight fraction, 10 parts of backfill material and 7.5 parts of modified polyacrylamide are mixed and stirred at 60°C for 120 min to obtain the functional material for coal gangue backfill.

[0061] Example 2:

[0062] (1) Preparation of backfill material: According to the weight fraction, 75 parts of silt, 5 parts of cement and 20 parts of fly ash are mixed evenly to obtain backfill material;

[0063] (2) Preparation of modified polyacrylamide: Formaldehyde and ethylamine were mixed evenly in a molar ratio of 1:1 to obtain a mixed solution. The pH of the solution was adjusted to 5 with acid and stirred at room temperature for 1 h to obtain an intermediate. Then, a 5% (w / w) aqueous solution of polyacrylamide was added to the intermediate (the amount added was 3 times the volume of the intermediate), and stirring was continued for 2 h to obtain product I. A 60% (w / w) solution of mercaptoacetic acid was taken, and the pH of the system was adjusted to 8 with alkali. Then, product I was added (in a volume ratio of 1:5 with mercaptoacetic acid solution) to react and obtain modified polyacrylamide.

[0064] (3) According to the weight fraction, 5 parts of backfill material and 10 parts of modified polyacrylamide are mixed and stirred at 70°C for 100 min to obtain coal gangue backfill functional material.

[0065] Example 3:

[0066] (1) Preparation of backfill material: According to the weight fraction, 70 parts of silt, 10 parts of cement and 20 parts of fly ash are mixed evenly to obtain backfill material;

[0067] (2) Preparation of modified polyacrylamide: Formaldehyde and diethylamine were mixed evenly at a molar ratio of 2:1 to obtain a mixed solution. The pH of the solution was adjusted to 2 with acid, and the mixture was stirred at room temperature for 3 hours to obtain an intermediate. Then, a 1% (w / w) aqueous solution of polyacrylamide was added to the intermediate (the amount added was 5 times the volume of the intermediate), and the mixture was stirred for another 4 hours to obtain product I. A 40% (w / w) solution of mercaptoacetic acid was taken, and the pH of the system was adjusted to 12 with alkali. Then, product I was added (in a volume ratio of 1:1 with the mercaptoacetic acid solution) to react and obtain modified polyacrylamide.

[0068] (3) According to the weight fraction, 15 parts of backfill material and 5 parts of modified polyacrylamide are mixed and stirred at 50°C for 140 min to obtain the functional material for coal gangue backfill.

[0069] Example 4:

[0070] (1) Preparation of backfill material: According to the weight fraction, 78.9 parts of silt, 6 parts of cement and 15.1 parts of fly ash are mixed evenly to obtain backfill material;

[0071] (2) Preparation of modified polyacrylamide: Formaldehyde and ethylenediamine were mixed evenly at a molar ratio of 1.5:1 to obtain a mixed solution. The pH of the solution was adjusted to 3.5 with acid, and the mixture was stirred at room temperature for 2 hours to obtain an intermediate. Then, a 2.5% (w / w) aqueous solution of polyacrylamide (the amount added was 4 times the volume of the intermediate) was added to the intermediate and stirred for another 3 hours to obtain product I. A 45% (w / w) solution of mercaptoacetic acid was taken, and the pH of the system was adjusted to 10 with alkali. Then, product I (added at a volume ratio of 1:3 with mercaptoacetic acid solution) was added to react and obtain modified polyacrylamide.

[0072] (3) Preparation of synergistic agent: Three-dimensional ordered macroporous metal-organic framework material (added at a mass-volume ratio of 1g:7.5mL to silica sol) was added to silica sol and stirred continuously until homogeneous. After stirring, the product was microwaved for 10 minutes at a power of 700W to obtain modified silica sol. Polylactic acid polyol (added at a mass-volume ratio of 1g:5mL to modified silica sol) was added to the obtained modified silica sol and stirred until homogeneous. Then, the system was heated to 50℃ and methacryloyloxysilane (added at a volume of 0.03 times that of modified silica sol) was added dropwise while stirring. After the addition was completed, stirring was continued for 3 hours. After the reaction was completed, a modified silica sol-coated three-dimensional ordered macroporous nanomaterial composite was obtained, which is the synergistic agent.

[0073] (4) According to the weight fraction, 10 parts of backfill material, 7.5 parts of modified polyacrylamide and 3 parts of synergist are mixed and stirred at 60°C for 120 minutes to obtain coal gangue backfill functional material.

[0074] Example 5:

[0075] (1) Preparation of backfill material: According to the weight fraction, 75 parts of silt, 5 parts of cement and 20 parts of fly ash are mixed evenly to obtain backfill material;

[0076] (2) Preparation of modified polyacrylamide: Formaldehyde and ethylamine were mixed evenly in a molar ratio of 1:1 to obtain a mixed solution. The pH of the solution was adjusted to 5 with acid and stirred at room temperature for 1 h to obtain an intermediate. Then, a 5% (w / w) aqueous solution of polyacrylamide was added to the intermediate (the amount added was 3 times the volume of the intermediate), and stirring was continued for 2 h to obtain product I. A 60% (w / w) solution of mercaptoacetic acid was taken, and the pH of the system was adjusted to 8 with alkali. Then, product I was added (in a volume ratio of 1:5 with mercaptoacetic acid solution) to react and obtain modified polyacrylamide.

[0077] (3) Preparation of synergistic agent: Three-dimensional ordered macroporous metal-organic framework material (added at a mass-volume ratio of 1g:5mL to silica sol) was added to silica sol and stirred continuously until homogeneous. After stirring, the product was microwaved for 5 minutes at a power of 800W to obtain modified silica sol. Polylactic acid polyol (added at a mass-volume ratio of 1g:3mL to modified silica sol) was added to the obtained modified silica sol and stirred until homogeneous. Then, the system was heated to 60℃ and vinyltriethoxysilane (added at a volume of 0.01 times that of modified silica sol) was added dropwise while stirring. After the addition was completed, stirring was continued for 4 hours. After the reaction was completed, a modified silica sol-coated three-dimensional ordered macroporous nanomaterial composite was obtained, which is the synergistic agent.

[0078] (4) According to the weight fraction, mix 5 parts of backfill material, 10 parts of modified polyacrylamide and 5 parts of synergist and stir at 70°C for 100 min to obtain coal gangue backfill functional material.

[0079] Example 6:

[0080] (1) Preparation of backfill material: According to the weight fraction, 70 parts of silt, 10 parts of cement and 20 parts of fly ash are mixed evenly to obtain backfill material;

[0081] (2) Preparation of modified polyacrylamide: Formaldehyde and diethylamine were mixed evenly at a molar ratio of 2:1 to obtain a mixed solution. The pH of the solution was adjusted to 2 with acid, and the mixture was stirred at room temperature for 3 hours to obtain an intermediate. Then, a 1% (w / w) aqueous solution of polyacrylamide was added to the intermediate (the amount added was 5 times the volume of the intermediate), and the mixture was stirred for another 4 hours to obtain product I. A 40% (w / w) solution of mercaptoacetic acid was taken, and the pH of the system was adjusted to 12 with alkali. Then, product I was added (in a volume ratio of 1:1 with the mercaptoacetic acid solution) to react and obtain modified polyacrylamide.

[0082] (3) Preparation of synergistic agent: Three-dimensional ordered macroporous metal-organic framework material (added at a mass-volume ratio of 1g:10mL to modified silica sol) was added to silica sol and stirred continuously until homogeneous. After stirring, the product was microwaved for 15min at a power of 600W to obtain modified silica sol. Polylactic acid polyol (added at a mass-volume ratio of 1g:7mL to modified silica sol) was added to the obtained modified silica sol and stirred until homogeneous. Then, the system was heated to 40℃ and isobutyltriethoxysilane (added at a volume of 0.05 times that of modified silica sol) was added dropwise while stirring. After the addition was completed, stirring was continued for 2h. After the reaction was completed, a modified silica sol-coated three-dimensional ordered macroporous nanomaterial composite was obtained, which is the synergistic agent.

[0083] (4) According to the weight fraction, mix 15 parts of backfill material, 5 parts of modified polyacrylamide and 1 part of synergist and stir at 50°C for 140 min to obtain coal gangue backfill functional material.

[0084] Comparative Example 1:

[0085] (1) Preparation of backfill material: According to the weight fraction, 78.9 parts of silt, 6 parts of cement and 15.1 parts of fly ash are mixed evenly to obtain backfill material;

[0086] (2) Preparation of modified polyacrylamide: Formaldehyde and ethylenediamine were mixed evenly at a molar ratio of 1.5:1 to obtain a mixed solution. The pH of the solution was adjusted to 3.5 with acid, and the mixture was stirred at room temperature for 2 hours to obtain an intermediate. Then, a 2.5% (w / w) aqueous solution of polyacrylamide (the amount added was 4 times the volume of the intermediate) was added to the intermediate and stirred for another 3 hours to obtain product I. A 45% (w / w) solution of mercaptoacetic acid was taken, and the pH of the system was adjusted to 10 with alkali. Then, product I (added at a volume ratio of 1:3 with mercaptoacetic acid solution) was added to react and obtain modified polyacrylamide.

[0087] (3) Preparation of synergistic agent: Polylactic acid polyol (added at a mass-volume ratio of 1g:5mL to silica sol) was added to silica sol and stirred evenly. Then, the system was heated to 50°C and methacryloyloxysilane (added at a volume of 0.03 times that of silica sol) was added dropwise while stirring. After the addition was completed, stirring was continued for 3 hours. After the reaction was completed, the synergistic agent was obtained.

[0088] (4) According to the weight fraction, 10 parts of backfill material, 7.5 parts of modified polyacrylamide and 3 parts of synergist are mixed and stirred at 60°C for 120 minutes to obtain coal gangue backfill functional material.

[0089] Comparative Example 2:

[0090] (1) Preparation of backfill material: According to the weight fraction, 78.9 parts of silt, 6 parts of cement and 15.1 parts of fly ash are mixed evenly to obtain backfill material;

[0091] (2) According to the weight fraction, 10 parts of backfill material and 7.5 parts of polyacrylamide are mixed and stirred at 60°C for 120 minutes to obtain the functional material for coal gangue backfill.

[0092] Comparative Example 3:

[0093] (1) Preparation of backfill material: According to the weight fraction, 78.9 parts of silt, 6 parts of cement and 15.1 parts of fly ash are mixed evenly to obtain backfill material;

[0094] (2) According to the weight fraction, 10 parts of the backfill material are mixed and stirred at 60°C for 120 minutes to obtain the coal gangue backfill functional material.

[0095] Comparative Example 4:

[0096] (1) Preparation of modified polyacrylamide: Formaldehyde and ethylenediamine were mixed evenly at a molar ratio of 1.5:1 to obtain a mixed solution. The pH of the solution was adjusted to 3.5 with acid and stirred at room temperature for 2 hours to obtain an intermediate. Then, a 2.5% polyacrylamide aqueous solution (4 times the volume of the intermediate) was added to the intermediate and stirred for another 3 hours to obtain product I. A 45% mercaptoacetic acid solution was taken, and the pH of the system was adjusted to 10 with alkali. Then, product I (added at a volume ratio of 1:3 with mercaptoacetic acid solution) was added to react and modified polyacrylamide was obtained.

[0097] (2) The modified polyacrylamide was stirred at 60°C for 120 min to obtain the coal gangue backfill material.

[0098] Experimental Example 1: Evaluation of the solidification effect of different functional materials for coal gangue backfill on heavy metal ions in coal gangue

[0099] First, the backfilling functional materials prepared in Examples 1-6 and Comparative Examples 1-4 were mixed with the three types of coal gangue (CG1, CG2, and CG3) and water at a mass ratio of 1:1:5, and then allowed to stand and weather for 6 hours to obtain backfilled coal gangue. Using a pH=2 mixed nitric acid-sulfuric acid solution as the leaching solution, the backfilled coal gangue was immersed in a bucket containing 1L of leaching solution at a fixed solid-liquid ratio of 1:10, and the bucket was sealed. Sampling times were set at 1 day, 7 days, 14 days, 28 days, 56 days, and 112 days. Approximately 5mL of leaching solution was taken each time using a syringe and filtered through a 0.45μm filter membrane into a 10mL centrifuge tube to obtain the leaching solution to be tested.

[0100] The metal content in the leachate was determined according to the industry standard "HJ 766-2015 Determination of Metallic Elements in Solid Waste by Inductively Coupled Plasma Mass Spectrometry". For the same variable, the test was performed three times to calibrate the experimental error. After sampling, the leachate was replenished to a constant volume of 1 L. The results are shown in Tables 1-3.

[0101] By testing the total heavy metal content of three coal gangue samples (CG1, CG2, and CG3), only Cd exceeded the pollution risk screening value among the eight key heavy metals in coal gangue. Therefore, this embodiment focuses on the changes in the content of the heavy metal Cd.

[0102] Table 1 shows the effect of Cd ion content in coal gangue CG1.

[0103]

[0104] Table 2 shows the effect of Cd ion content in coal gangue CG2.

[0105]

[0106]

[0107] Table 3 shows the effect of Cd ion content in coal gangue CG3.

[0108]

[0109]

[0110] The results in Tables 1-3 show that different backfill materials exhibit significantly different effects on the solidification of Cd in different coal gangues. Furthermore, within a certain timeframe, the Cd content in the leachate shows an increasing trend over time. Compared to Comparative Examples 1-4, the Cd content increased over time after the backfill materials in Examples 1-6 coated and solidified the coal gangue, but the increase was slow and the concentration was low. Compared to Examples 1-3, the backfill materials in Examples 4-6 showed better solidification effects on coal gangue because the addition of synergistic agents to the backfill materials significantly improved their solidification effect.

[0111] Experimental Example 2: The effect of different coal gangue backfill functional materials on the solidification of heavy metal ions in simulated leachate

[0112] A simulated coal gangue leachate was prepared, wherein the heavy metal ion content of the coal gangue leachate was: Hg 8.3 mg / L, As 40 mg / L, Pb 250 mg / L, Ni 300 mg / L, Cu 200 mg / L, and Cr 400 mg / L.

[0113] The backfilling functional materials of Examples 1, 4, and Comparative Examples 1-4 were immersed in 1L of simulated leachate at a fixed solid-liquid ratio of 1:100 in buckets, and the buckets were sealed. The backfilling functional materials of Examples 1, 4, and Comparative Examples 1-4 were then added to their corresponding simulated coal gangue leachate and allowed to stand for 90 days. Afterward, approximately 5mL of leachate was taken using a syringe and filtered through a 0.45μm filter membrane into a 10mL centrifuge tube to obtain the test solution. The content of each metal in the test solution was detected, and the results are shown in Table 4.

[0114] Table 4. The curing effect of different backfill functional materials on heavy metal ions.

[0115]

[0116]

[0117] As can be seen from the results in Table 4, different backfill functional materials have a certain curing effect on heavy metals in leachate. Among them, compared with the backfill functional materials of Comparative Examples 1A to 4A, the backfill functional materials of Examples 1A and 4A have a more obvious heavy metal curing effect: when the initial concentrations all exceeded the standard, after curing treatment with the backfill functional materials of the present invention, the content of each heavy metal was significantly reduced and all were within the risk range.

[0118] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the methods and techniques disclosed above without departing from the scope of the present invention to create equivalent embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A functional material for coal gangue backfilling, characterized in that, By weight fraction, it includes: 5-15 parts of backfill material and 5-10 parts of heavy metal curing agent; The backfill material comprises the following components: 70-80 parts silt, 1-10 parts cement, and 10-20 parts fly ash; The heavy metal curing agent is modified polyacrylamide; The modified polyacrylamide is obtained by modifying polyacrylamide through the Mannich reaction: Formaldehyde and amine organic compounds were mixed and reacted under acidic conditions to obtain methyleneamine carbocations, which were then added to polyacrylamide to obtain product I. Product I was added to an alkaline solution of mercaptoacetic acid to obtain modified polyacrylamide. The coal gangue backfill functional material also includes 1 to 5 parts of an synergistic agent; the synergistic agent is a modified silica sol-coated three-dimensional ordered macroporous nanomaterial composite.

2. A method for preparing a functional material for coal gangue backfilling according to claim 1, characterized in that, The method includes the following steps: (1) Preparation of backfill material: According to the weight fraction, mix 70-80 parts of silt, 1-10 parts of cement and 10-20 parts of fly ash evenly to obtain backfill material; (2) Preparation of modified polyacrylamide: formaldehyde and amine organic compounds are mixed evenly to obtain a mixed solution. The pH of the solution is adjusted to 2-5 with acid. The mixture is stirred at room temperature for 1-3 hours to obtain an intermediate. Then, 1-5% by mass of polyacrylamide aqueous solution is added to the obtained intermediate and stirred for 2-4 hours to obtain product I. Take a 40-60% mercaptoacetic acid solution, adjust the pH of the system to 8-12 with alkali, and then add product I to react to obtain modified polyacrylamide; (3) Preparation of synergistic agent: Add three-dimensional ordered macroporous metal-organic framework material to silica sol and stir continuously until uniform. After stirring, microwave the product for 5 to 15 minutes at a power of 600 to 800W to obtain modified silica sol. Polylactic acid polyol was added to the obtained modified silica sol and stirred evenly. Then the system was heated to 40~60℃ and silane coupling agent was added dropwise while stirring. After the addition was completed, stirring was continued for 2h~4h. After the reaction was completed, a modified silica sol-coated three-dimensional ordered macroporous nanomaterial composite was obtained, which is the synergistic agent. According to the weight fraction, 5-15 parts of backfill material, 5-10 parts of heavy metal curing agent and 1-5 parts of synergistic agent are mixed and stirred at 50-70℃ for 100-140 minutes to obtain coal gangue backfill functional material.

3. The preparation method according to claim 2, characterized in that, In step (2), the amine organic compound is selected from any one of methylamine, dimethylamine, ethylamine, diethylamine, n-propylamine, and ethylenediamine.

4. The preparation method according to claim 2, characterized in that, In step (3), the three-dimensional ordered macroporous metal-organic framework material is added at a mass-volume ratio of 1g to 5~10mL with the silica sol.

5. The preparation method according to claim 2, characterized in that, In step (3), the polylactic acid polyol is added at a mass-volume ratio of 1g to 3~7mL with the modified silica sol; The silane coupling agent is selected from any one of isobutyltriethoxysilane, methacryloxysilane, vinyltriethoxysilane, and vinyltrimethoxysilane; The amount of the silane coupling agent added is 0.01 to 0.05 times the volume of the modified silica sol.

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