A soil conditioner for coal mine spoil heaps utilizing coal gangue and its preparation method

Abstract

This invention discloses a soil conditioner for coal mine spoil heaps utilizing coal gangue and its preparation method. The method involves first crushing the coal gangue and then calcining it at high temperature, followed by activation and modification with citric acid to obtain modified coal gangue. This modified coal gangue is then mixed with biochar, humic acid, and polyacrylamide. Next, a self-prepared aqueous solution of a bifunctional polymer for heavy metal chelation and structural stabilization is added. This polymer, obtained by grafting thiol and chloromethyl groups and cross-linking, effectively immobilizes heavy metals and enhances soil aggregate structure. Simultaneously, a self-prepared silicate slow-release and microbial synergistic modifier, composed of sodium silicate and an organic network, is added. This modifier can be premixed with phosphate-solubilizing and nitrogen-fixing bacteria to achieve synergistic promotion of nutrient slow release and microbial activity. Finally, all materials are mixed, granulated, and dried at low temperature to obtain the final product. This invention significantly improves the soil structure of spoil heaps, immobilizes heavy metals, provides long-lasting nutrients, and promotes ecological restoration.

Description

Technical Field

[0001] This invention relates to the field of soil conditioner technology, specifically to a soil conditioner for coal mine spoil heaps utilizing coal gangue and its preparation method. Background Technology

[0002] The large amounts of coal gangue generated during coal mining accumulate over time, forming coal mine spoil heaps and causing a series of serious ecological and environmental problems. These spoil heaps occupy vast amounts of land resources, and their topsoil generally suffers from inherent defects such as poor structure, lack of organic matter, and nutrient imbalance, severely restricting vegetation recovery and growth. More importantly, coal gangue releases various heavy metals during weathering and leaching, causing persistent pollution to surrounding soil and water bodies, and ultimately endangering human health through the food chain. Traditional ecological restoration of spoil heaps mainly employs methods such as topsoil covering and the application of conventional fertilizers, but these measures are often costly, have short-term effects, and cannot fundamentally improve the physical structure of the soil, nor effectively control the migration of heavy metals, making it difficult to meet the long-term needs of large-scale mining area ecological reconstruction.

[0003] Currently, while some explorations have been made into the resource utilization of coal gangue, such as its use in the production of building materials or roadbed materials, these approaches have specific requirements regarding the composition and properties of the coal gangue, and the consumption is limited. Directly using coal gangue for soil improvement faces numerous technical bottlenecks: untreated coal gangue has low activity and weak improvement effects; its inherent heavy metal content poses environmental risks; and simple physical blending is insufficient to sustainably improve soil fertility. Existing soil conditioner technologies also have significant limitations, either focusing solely on heavy metal fixation while neglecting soil structure cultivation, or focusing only on nutrient supply while lacking the creation of a suitable environment for microbial growth. These technologies are functionally singular and cannot comprehensively address the complex problem of "poor structure, high toxicity, and low fertility" in spoil heap soils. Therefore, developing a comprehensive conditioner capable of simultaneously achieving structural improvement, heavy metal stabilization, and ecological function restoration has become an urgent need in the field of mining area environmental governance.

[0004] Against this backdrop, this invention aims to provide a soil conditioner specifically for coal mine spoil heaps, using coal gangue as the core raw material, and its preparation method. This technology, through an innovative chemical modification process, deeply activates the active components of coal gangue and introduces a self-developed heavy metal chelating-structural stabilizing bifunctional polymer and a silicate slow-release-microorganism synergistic modifier. The design of these key components aims to construct a stable soil aggregate structure, permanently immobilizing heavy metals through strong chelation, and providing a favorable habitat and sustainable nutrient source for functional microorganisms, thereby forming a synergistic remediation system that "modifies structure, reduces toxicity, and promotes ecology." This invention not only provides an efficient and economical technological product for the ecological restoration of coal mine spoil heaps but also opens up a new high-value-added pathway for the comprehensive utilization of massive amounts of coal gangue, which has significant practical implications for promoting the sustainable development of mining areas. Summary of the Invention

[0005] The purpose of this invention is to provide a soil conditioner for coal mine spoil heaps using coal gangue and its preparation method, which solves the technical problems of poor soil structure, high risk of heavy metal pollution, and low fertility in coal mine spoil heaps that make it difficult to support ecological restoration.

[0006] The present invention achieves the above objectives through the following technical solutions: A method for preparing a soil conditioner for coal mine spoil heaps using coal gangue, comprising the following steps: S1. Crush coal gangue into particles and calcine it at 700-750℃ to obtain calcined coal gangue. Mix the calcined coal gangue with citric acid and stir at 58-62℃. Filter to obtain a solid product. Wash the solid product until neutral and dry to obtain modified coal gangue. Add the modified coal gangue, biochar, humic acid and polyacrylamide to a mixer and stir. S2. Dissolve the heavy metal chelating-structure stabilizing bifunctional polymer in deionized water to obtain an aqueous solution. Add the aqueous solution to a mixer and stir. Add the ground silicate slow-release-microbial synergistic modifier, phosphate-solubilizing bacteria, and nitrogen-fixing bacteria to the mixer and stir to obtain a mixture. Form the mixture into granules using an extrusion granulator and dry the granules at 38-42℃.

[0007] In this invention, the preparation mechanism of the soil conditioner embodies a perfect combination of physical mixing and chemical synergy. First, coal gangue is calcined at high temperature, which destroys its internal crystal structure, activates elements such as silicon and aluminum, and increases its specific surface area. Subsequently, it is treated with citric acid, where the carboxyl groups react with metal ions on the surface of the calcined coal gangue, further opening its pores and increasing surface functional groups, thus obtaining an activated and modified coal gangue carrier. In the final compounding and granulation process, the components are orderly combined according to their characteristics. Modified coal gangue, as the main matrix and framework, together with biochar with a rich porous structure and humic acid rich in functional groups, constitutes the basic solid-phase framework of the conditioner, jointly responsible for improving the physical structure of the soil, adsorbing nutrients, and regulating pH. The dissolved heavy metal chelating structure stabilized bifunctional polymer acts like a "smart glue," capable of penetrating the soil to capture heavy metal ions through its multiple chelation sites, and also binding fine soil particles into stable large aggregates through its long molecular chains and cross-linking properties. The silicate slow-release microbial synergistic modifier is premixed with phosphate-solubilizing and nitrogen-fixing bacteria after grinding. This step aims to pre-colonize functional microorganisms in the micropores of the modifier, maximizing their protection after granulation. When this conditioner is applied to the spoil heap soil, the components begin to work synergistically under the combined action of moisture and soil microorganisms. Modified coal gangue and biochar provide long-lasting physical improvements, the polymer continuously solidifies heavy metals and stabilizes the structure, while the silicate modifier slowly releases nutrients and provides a living environment for the microorganisms it shelters. Once activated, these functional microorganisms begin to perform their nitrogen-fixing and phosphorus-solubilizing biological functions, thus forming a systematic and sustainable soil ecological restoration system encompassing physical structure, chemical environment, and biological functions.

[0008] According to a preferred embodiment of the present invention, in step S1, the stirring treatment at 58-62°C is carried out for 4-6 hours.

[0009] According to a preferred embodiment of the present invention, in step S2, the drying time at 38-42°C is 4-6 hours.

[0010] According to a preferred embodiment of the present invention, the preparation method of the heavy metal chelating-structure-stabilizing bifunctional polymer includes: A1, under nitrogen protection, dissolving polyethyleneimine in anhydrous dimethyl sulfoxide and stirring until completely dissolved; adding 3-mercaptopropionic acid and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, adjusting the pH to 7.4-7.6, and reacting at 24-26°C; then cooling to 0-5°C, adding a dimethyl sulfoxide solution containing chloroacetyl chloride dropwise, and after the addition is complete, reacting at room temperature to obtain a reaction solution; A2, adding 1,2-dibromoethane to the reaction solution, heating to 40-45°C, and reacting to obtain a reaction mixture; dialysis purification of the reaction mixture, and freeze-drying.

[0011] In this invention, the preparation of the heavy metal chelating-structurally stable bifunctional polymer is a carefully designed, sequentially controllable chemical reaction process. Its core mechanism lies in the stepwise introduction of specific functional groups onto the polymer backbone of polyethyleneimine, which has a large number of amino groups, ultimately constructing a cross-linked network. First, in the presence of an activator and under weakly alkaline conditions, the carboxyl group in trimercaptopropionic acid undergoes dehydration condensation with some of the primary amino groups on the polyethyleneimine molecular chain, forming a strong amide bond. This covalently grafts the side chain carrying the thiol group onto the polymer backbone. This step successfully introduces the thiol group, a strong coordinating group rich in lone pair electrons, providing the primary site for subsequent heavy metal chelation. Second, under low-temperature conditions, chloroacetyl chloride is slowly added dropwise to the above reaction system. The highly reactive acyl chloride group of chloroacetyl chloride reacts rapidly with the remaining amino groups on the polyethyleneimine chain to form amide bonds, simultaneously introducing another strongly electron-withdrawing chloromethyl functional group into the polymer. This chloromethyl group serves as both a reaction site for subsequent cross-linking and an effective coordination site for heavy metal ions. The third step involves adding the bifunctional crosslinking agent dibromoethane and heating. Under heating conditions, the two bromine atoms of dibromoethane act as excellent leaving groups, undergoing a highly efficient bimolecular nucleophilic substitution reaction with the previously grafted thiol groups. A single dibromoethane molecule can simultaneously react with two thiol groups from different polymer chains, forming a stable thioether bridge between the two polymer chains, ultimately constructing a three-dimensional network of crosslinked polymers. This structure allows it to powerfully capture and immobilize various heavy metal ions in the soil through multiple coordination sites of thiol groups and chloromethyl groups, and also to form durable and stable organic cementing substances in the soil through the crosslinking network, significantly promoting the formation and stabilization of soil aggregates.

[0012] According to a preferred embodiment of the present invention, in step A1, the reaction time at room temperature is 12-14 hours.

[0013] According to a preferred embodiment of the present invention, in step A2, the reaction time is 6-8 hours after heating to 58-62°C.

[0014] According to a preferred embodiment of the present invention, the preparation method of the silicate slow-release-microorganism synergistic modifier includes: B1, adding citric acid and 3-aminopropyltriethoxysilane to ethanol, adding 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, refluxing to obtain a reaction solution; cooling the reaction solution to room temperature, adding polyethylene glycol diglycidyl ether and tetrabutylammonium bromide, reacting at 48-52°C to obtain a reaction mixture; B2, adding sodium silicate aqueous solution to the reaction mixture, adding deionized water dropwise, reacting at 38-42°C; adding N,N'-methylenebisacrylamide and ammonium persulfate, heating to 68-72°C to react; after the reaction is completed, drying under vacuum by rotary evaporation.

[0015] In this invention, the preparation of [the product] is a complex process involving organic-inorganic hybridization and network interpenetration, aiming to construct a microenvironment that can both slowly release mineral nutrients and protect microorganisms. The process begins with the reaction of citric acid and triaminopropyltriethoxysilane under the catalysis of an activator. The carboxyl group on the citric acid molecule undergoes an amidation reaction with the amino group at the end of the silane molecule, generating a novel organosilicon compound containing both citrate groups and hydrolyzable siloxane groups. Subsequently, polyethylene glycol diglycidyl ether is added; its epoxy groups at both ends, under the action of a catalyst, can undergo ring-opening reactions with the remaining amino or carboxyl groups in the system, introducing flexible polyethylene glycol segments and initially constructing a hydrophilic organic network framework. Next, an aqueous solution of sodium silicate is added and hydrolyzed. The previously introduced triethoxysilane groups undergo hydrolysis to generate silanols, which then undergo a condensation reaction with the silicate ions generated from the hydrolysis of sodium silicate, forming siloxane bonds, gradually constructing an inorganic silicate gel network that interpenetrates with the existing organic network. Finally, a bisacrylamide crosslinking agent and a free radical initiator are added and the temperature is raised to initiate a free radical polymerization reaction of the unsaturated bonds in the system, forming another crosslinking point. This ultimately yields a hybrid material in which an organic polymer network and an inorganic silicate network are tightly interwoven and coexist. This unique structure allows it to slowly dissolve in water in soil, continuously releasing beneficial components such as silicate, citrate, and potassium and sodium ions. Its porous structure provides a physical shelter for beneficial microorganisms such as phosphate-solubilizing bacteria and nitrogen-fixing bacteria, protecting them from drought and ultraviolet radiation. Simultaneously, its carbon and silicon sources provide nutrients for microbial growth.

[0016] According to a preferred embodiment of the present invention, in step B1, the reaction time is 6-8 hours at 48-52°C.

[0017] According to a preferred embodiment of the present invention, in step B2, the reaction time is 4-6 hours after heating to 68-72°C.

[0018] The present invention also provides a method for preparing a soil conditioner for coal mine spoil heaps using coal gangue, comprising the following raw materials in parts by weight: 50-70 parts by weight of coal gangue; 5-15 parts by weight of a heavy metal chelating-structure-stabilizing bifunctional polymer; 3-10 parts by weight of a silicate slow-release-microbial synergistic modifier; 10-20 parts by weight of biochar; 5-10 parts by weight of humic acid; 0.5-2 parts by weight of polyacrylamide; 1-3 parts by weight of phosphate-solubilizing bacteria; and 1-3 parts by weight of nitrogen-fixing bacteria.

[0019] The beneficial effects of this invention are as follows: This invention achieves the high-value-added resource utilization of coal gangue and the synergistic improvement of soil physicochemical properties. By calcining the coal gangue at a specific temperature, the activity of its aluminosilicate components is effectively activated. Subsequent treatment with citric acid further increases its specific surface area and reactivity, and introduces abundant organic functional groups onto its surface, greatly enhancing its adsorption capacity for nutrients and pollutants. The resulting modified coal gangue, when combined with biochar, humic acid, and polyacrylamide, exhibits excellent synergistic effects. This combination significantly reduces the bulk density of spoil heap soil, increases porosity, and promotes the formation of stable aggregate structures, thereby effectively improving soil compaction and enhancing its water and fertilizer retention capacity, as well as its aeration and permeability. Simultaneously, these components together form a large adsorption pool, capable of buffering soil pH, fixing and preserving readily available nutrients such as nitrogen, phosphorus, and potassium, reducing their loss, and creating an extremely favorable physical and chemical environment for subsequent plant growth and microbial colonization.

[0020] Secondly, the core innovation of this invention lies in achieving effective stabilization of heavy metals and durable enhancement of soil structure through the design and synthesis of functional polymers. The independently developed heavy metal chelating-structural stabilizing bifunctional polymer incorporates thiol and chloromethyl functional groups with strong coordination capabilities for heavy metal ions into its molecular chain, as well as reaction sites that can form a three-dimensional network structure through subsequent cross-linking reactions. When applied to soil, this polymer can firmly fix free heavy metal ions through powerful chelation, transforming them into stable forms that are difficult for plants to absorb, thereby significantly reducing the bioavailability and mobility of heavy metals and fundamentally alleviating the risk of heavy metal pollution in landfills. More importantly, this polymer can further cross-link in the soil environment and combine with soil particles to form organic-inorganic composite aggregates, acting like a stable "skeleton" for the soil, greatly enhancing the soil's resistance to water and wind erosion and ensuring the long-term and stable improvement effect.

[0021] Finally, this invention constructs a benign micro-ecosystem that synergistically promotes nutrient slow release and microbial activity, ensuring the sustainability of ecological restoration. The unique silicate slow-release-microbial synergistic modifier, through a sophisticated organic-inorganic hybrid design, integrates silicate minerals, organic acids, and cross-linked networks. It slowly dissolves in the soil, continuously releasing trace elements such as silicon, calcium, and potassium, providing plants with long-lasting mineral nutrition. Its porous structure and hydrophilic surface provide an ideal sanctuary and habitat for functional microorganisms such as phosphate-solubilizing and nitrogen-fixing bacteria, effectively protecting the microbial agent from harsh external environments and significantly improving the survival rate and colonization success rate of the microbial community. These protected microorganisms can continuously and actively function, converting phosphorus fixed in the soil into available phosphorus and atmospheric nitrogen into nitrogen fertilizer that plants can absorb, thus forming a virtuous cycle of "materials nourishing microorganisms, and microorganisms activating soil nutrients." This perfect combination of physical structural improvement, chemical passivation repair, and biological functional enhancement has jointly promoted the rapid evolution of barren soil in the spoil heap into healthy and fertile soil, ultimately achieving a fundamental restoration of the ecological environment of the mining area. Detailed Implementation

[0022] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0023] The main suppliers of related equipment and materials are as follows: The phosphate-solubilizing agent was purchased from Guangzhou Zhenwei Biotechnology Co., Ltd.

[0024] The nitrogen-fixing bacteria agent was purchased from Yingkou Maomei Agricultural Technology Co., Ltd.

[0025] The 3-mercaptopropionic acid was purchased from Shandong Changyuan Chemical Co., Ltd.

[0026] The polyethylene glycol diglycidyl ether was purchased from Wuhan Shuer Biotechnology Co., Ltd.

[0027] The tetrabutylammonium bromide was purchased from Jiangsu Bisheng Chemical Co., Ltd.

[0028] The sodium silicate was purchased from Guangzhou Jielong Chemical Co., Ltd.

[0029] Example 1 Preparation of a heavy metal chelating-structure-stabilized bifunctional polymer: Under nitrogen protection, 10.0 g of polyethyleneimine was dissolved in 200.0 mL of anhydrous dimethyl sulfoxide and stirred at 300 rpm for 30 min until completely dissolved. 5.0 g of 3-mercaptopropionic acid and 6.0 g of 1-ethyl-3-dimethylaminopropylcarbodiimide hydrochloride were added, and the pH was adjusted to 7.5 with 1 mol / L sodium hydroxide solution. The reaction mixture was stirred at 250 rpm at 25.0 °C for 13.0 h. The reaction system was then cooled to 2.0 °C, and a solution prepared by dissolving 4.0 g of chloroacetyl chloride in 50.0 mL of dimethyl sulfoxide was slowly added dropwise at a rate of 1.0 mL / min using a constant-pressure dropping funnel. After the addition was complete, the reaction mixture was continued at 25.0 °C for 13.0 h to obtain the reaction solution. 3.0 g of 1,2-dibromoethane was added to the reaction solution, and the temperature was increased to 40.0 °C at a rate of 5.0 °C / min. This temperature was maintained for 7.0 h to obtain the reaction mixture. The reaction mixture was placed in a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed against 2000 mL of deionized water, with the deionized water replaced every 8.0 h, for a total of 72 h. Finally, the dialyzed product was pre-frozen at -50.0 °C for 12 h, and then freeze-dried at -50.0 °C and 0.1 Pa for 48 h to obtain a white solid product.

[0030] Preparation of a silicate sustained-release-microbial synergistic modifier: 8.0 g citric acid and 10.0 g 3-aminopropyltriethoxysilane were added to 150.0 mL anhydrous ethanol, followed by 5.0 g 1-ethyl-3-dimethylaminopropylcarbodiimide hydrochloride. The mixture was refluxed and condensed at 85.0 °C for 5.0 h to obtain a reaction solution. The reaction solution was cooled to 25.0 °C, and 6.0 g polyethylene glycol diglycidyl ether and 0.5 g tetrabutylammonium bromide were added. The mixture was stirred at 200 rpm in a water bath at 50.0 °C for 7.0 h to obtain a reaction mixture. 20.0 mL of a 20% sodium silicate aqueous solution was added to the reaction mixture, and 30.0 mL of deionized water was slowly added dropwise at a rate of 2.0 mL / min using a peristaltic pump. The mixture was reacted at 40.0 °C for 4.0 h. 2.0 g of N,N'-methylenebisacrylamide and 0.3 g of ammonium persulfate were added, and the temperature was increased to 70.0 °C at a rate of 3.0 °C / min, and the reaction was maintained at this temperature for 5.0 h. After the reaction was completed, the solvent was removed by rotary evaporation under a water bath at 60.0 °C and a pressure of -0.1 MPa, and then the product was dried under vacuum at 60.0 °C and a pressure of -0.1 MPa for 8.0 h to obtain a pale yellow solid product.

[0031] Preparation of soil conditioner: 600.0g of coal gangue was crushed to 100 mesh using a jaw crusher, placed in a muffle furnace, and calcined at 710.0℃ for 3.0h at a rate of 10.0℃ / min to obtain calcined coal gangue. The calcined coal gangue and 300.0g of citric acid were added to a reaction vessel and stirred at 400rpm for 5.0h at 60.0℃. The mixture was filtered through a Buchner funnel to obtain a solid product. The solid product was washed with deionized water until the pH of the filtrate reached 7.0, and then dried in an oven at 105.0℃ for 12h to obtain modified coal gangue. All the modified coal gangue, 150.0g of biochar, 80.0g of humic acid, and 1.5g of polyacrylamide were added to a V-type mixer and stirred at 30rpm for 15min. 10.0 g of a heavy metal chelating-structure stabilizing bifunctional polymer was dissolved in 100.0 mL of deionized water to obtain an aqueous solution. This solution was added to a mixer and stirred at 30 rpm for 10 min. 8.0 g of a silicate slow-release-microbial synergistic modifier was ground to 200 mesh using a ball mill. This mixture was then premixed with 2.0 g of phosphate-solubilizing bacteria and 2.0 g of nitrogen-fixing bacteria in a mortar for 10 min, and then added to the mixer and stirred at 30 rpm for 20 min to obtain a mixture. This mixture was then extruded into granules with a diameter of 3.0 mm using a two-roll granulator. The granules were dried in a hot air drying oven at 40.0℃ for 5.0 h to obtain the final product.

[0032] Example 2 Preparation of a heavy metal chelating-structure-stabilized bifunctional polymer: Under nitrogen protection, 8.0 g of polyethyleneimine was dissolved in 160.0 mL of anhydrous dimethyl sulfoxide and stirred at 300 rpm for 30 min until completely dissolved. 4.0 g of 3-mercaptopropionic acid and 4.8 g of 1-ethyl-3-dimethylaminopropylcarbodiimide hydrochloride were added, and the pH was adjusted to 7.4 with 1 mol / L sodium hydroxide solution. The reaction mixture was stirred at 250 rpm at 24.0 °C for 12.0 h. The reaction system was then cooled to 0.0 °C, and a solution prepared by dissolving 3.2 g of chloroacetyl chloride in 40.0 mL of dimethyl sulfoxide was slowly added dropwise at a rate of 1.0 mL / min using a constant-pressure dropping funnel. After the addition was complete, the reaction mixture was continued at 24.0 °C for 12.0 h to obtain the reaction solution. 2.4 g of 1,2-dibromoethane was added to the reaction solution, and the temperature was increased to 42.0 °C at a rate of 5.0 °C / min. This temperature was maintained for 6.0 h to obtain the reaction mixture. The reaction mixture was placed in a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed against 2000 mL of deionized water, with the deionized water replaced every 8.0 h, for a total of 72 h. Finally, the dialyzed product was pre-frozen at -50.0 °C for 12 h, and then freeze-dried at -50.0 °C and 0.1 Pa for 48 h to obtain a white solid product.

[0033] Preparation of a silicate sustained-release-microbial synergistic modifier: 6.0 g citric acid and 8.0 g 3-aminopropyltriethoxysilane were added to 120.0 mL anhydrous ethanol, followed by 4.0 g 1-ethyl-3-dimethylaminopropylcarbodiimide hydrochloride. The mixture was refluxed and condensed at 85.0 °C for 4.0 h to obtain a reaction solution. The reaction solution was cooled to 25.0 °C, and 4.8 g polyethylene glycol diglycidyl ether and 0.4 g tetrabutylammonium bromide were added. The mixture was stirred at 200 rpm in a water bath at 48.0 °C for 6.0 h to obtain a reaction mixture. 16.0 mL of a 20% sodium silicate aqueous solution was added to the reaction mixture, and 24.0 mL of deionized water was slowly added dropwise at a rate of 2.0 mL / min using a peristaltic pump. The mixture was reacted at 38.0 °C for 3.0 h. 1.6 g of N,N'-methylenebisacrylamide and 0.24 g of ammonium persulfate were added, and the temperature was increased to 68.0 °C at a rate of 3.0 °C / min, and the reaction was maintained at this temperature for 4.0 h. After the reaction was completed, the solvent was removed by rotary evaporation under a water bath at 60.0 °C and a pressure of -0.1 MPa, and then the product was dried under vacuum at 60.0 °C and a pressure of -0.1 MPa for 8.0 h to obtain a pale yellow solid product.

[0034] Preparation of soil conditioner: 500.0g of coal gangue was crushed to 100 mesh using a jaw crusher, placed in a muffle furnace, and calcined at 710.0℃ for 3.0h at a rate of 10.0℃ / min to obtain calcined coal gangue. The calcined coal gangue and 250.0g of citric acid were added to a reaction vessel and stirred at 400rpm for 4.0h at 58.0℃. The mixture was filtered through a Buchner funnel to obtain a solid product. The solid product was washed with deionized water until the pH of the filtrate reached 7.0, and then dried in an oven at 105.0℃ for 12h to obtain modified coal gangue. All the modified coal gangue, 100.0g of biochar, 50.0g of humic acid, and 0.5g of polyacrylamide were added to a V-type mixer and stirred at 30rpm for 15min. 5.0 g of a heavy metal chelating-structure stabilizing bifunctional polymer was dissolved in 100.0 mL of deionized water to obtain an aqueous solution. This solution was added to a mixer and stirred at 30 rpm for 10 min. 3.0 g of a silicate slow-release-microbial synergistic modifier was ground to 200 mesh using a ball mill. This mixture was then premixed with 1.0 g of phosphate-solubilizing bacteria and 1.0 g of nitrogen-fixing bacteria in a mortar for 10 min, and then added to the mixer and stirred at 30 rpm for 20 min to obtain a mixture. This mixture was then extruded into granules with a diameter of 3.0 mm using a two-roll granulator. The granules were dried in a hot air drying oven at 38.0℃ for 4.0 h to obtain the final product.

[0035] Example 3 Preparation of a heavy metal chelating-structure-stabilized bifunctional polymer: Under nitrogen protection, 12.0 g of polyethyleneimine was dissolved in 240.0 mL of anhydrous dimethyl sulfoxide and stirred at 300 rpm for 30 min until completely dissolved. 6.0 g of 3-mercaptopropionic acid and 7.2 g of 1-ethyl-3-dimethylaminopropylcarbodiimide hydrochloride were added, and the pH was adjusted to 7.6 with 1 mol / L sodium hydroxide solution. The reaction mixture was stirred at 250 rpm at 26.0 °C for 14.0 h. The reaction system was then cooled to 5.0 °C, and a solution prepared by dissolving 4.8 g of chloroacetyl chloride in 60.0 mL of dimethyl sulfoxide was slowly added dropwise at a rate of 1.0 mL / min using a constant-pressure dropping funnel. After the addition was complete, the reaction mixture was continued at 26.0 °C for 14.0 h to obtain the reaction solution. 3.6 g of 1,2-dibromoethane was added to the reaction solution, and the temperature was increased to 45.0 °C at a rate of 5.0 °C / min. This temperature was maintained for 8.0 h to obtain the reaction mixture. The reaction mixture was placed in a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed against 2000 mL of deionized water, with the deionized water replaced every 8.0 h, for a total of 72 h. Finally, the dialyzed product was pre-frozen at -50.0 °C for 12 h, and then freeze-dried at -50.0 °C and 0.1 Pa for 48 h to obtain a white solid product.

[0036] Preparation of a silicate sustained-release-microbial synergistic modifier: 10.0 g citric acid and 12.0 g 3-aminopropyltriethoxysilane were added to 180.0 mL anhydrous ethanol, followed by 6.0 g 1-ethyl-3-dimethylaminopropylcarbodiimide hydrochloride. The mixture was refluxed and condensed at 85.0 °C for 6.0 h to obtain a reaction solution. The reaction solution was cooled to 25.0 °C, and 7.2 g polyethylene glycol diglycidyl ether and 0.6 g tetrabutylammonium bromide were added. The mixture was stirred at 200 rpm in a water bath at 52.0 °C for 8.0 h to obtain a reaction mixture. 24.0 mL of a 20% sodium silicate aqueous solution was added to the reaction mixture, and 36.0 mL of deionized water was slowly added dropwise at a rate of 2.0 mL / min using a peristaltic pump. The mixture was reacted at 42.0 °C for 5.0 h. 2.4 g of N,N'-methylenebisacrylamide and 0.36 g of ammonium persulfate were added, and the temperature was increased to 72.0 °C at a rate of 3.0 °C / min, and the reaction was maintained at this temperature for 6.0 h. After the reaction was completed, the solvent was removed by rotary evaporation under a water bath at 60.0 °C and a pressure of -0.1 MPa, and then the product was dried under vacuum at 60.0 °C and a pressure of -0.1 MPa for 8.0 h to obtain a pale yellow solid product.

[0037] Preparation of soil conditioner: 700.0g of coal gangue was crushed to 100 mesh using a jaw crusher, placed in a muffle furnace, and calcined at 710.0℃ for 3.0h at a rate of 10.0℃ / min to obtain calcined coal gangue. The calcined coal gangue and 350.0g of citric acid were added to a reaction vessel and stirred at 62.0℃ and 400rpm for 6.0h. The mixture was filtered through a Buchner funnel to obtain a solid product. The solid product was washed with deionized water until the pH of the filtrate reached 7.0, and dried in an oven at 105.0℃ for 12h to obtain modified coal gangue. All the modified coal gangue, 200.0g of biochar, 100.0g of humic acid, and 2.0g of polyacrylamide were added to a V-type mixer and stirred at 30rpm for 15min. 15.0 g of a heavy metal chelating-structure stabilizing bifunctional polymer was dissolved in 100.0 mL of deionized water to obtain an aqueous solution. This solution was added to a mixer and stirred at 30 rpm for 10 min. 10.0 g of a silicate slow-release-microbial synergistic modifier was ground to 200 mesh using a ball mill. This mixture was then premixed with 3.0 g of phosphate-solubilizing bacteria and 3.0 g of nitrogen-fixing bacteria in a mortar for 10 min, and then added to the mixer and stirred at 30 rpm for 20 min to obtain a mixture. This mixture was then extruded into granules with a diameter of 3.0 mm using a two-roll granulator. The granules were dried in a hot air drying oven at 42.0℃ for 6.0 h to obtain the final product.

[0038] Comparative Example 1 The specific implementation method is the same as in Example 1, except that the amount of other raw materials and preparation steps are exactly the same as in Example 1, except that no heavy metal chelating-structure stabilizing bifunctional polymer is added.

[0039] Comparative Example 2 The specific implementation method is the same as in Example 1, except that the amount of raw materials and preparation steps are exactly the same as in Example 1, except that no silicate slow-release-microbial synergistic modifier is added.

[0040] Comparative Example 3 The specific implementation method is the same as in Example 1, except that no heavy metal chelating-structure stabilizing bifunctional polymer and silicate slow-release-microbial synergistic modifier are added at the same time, while the amount of other raw materials and preparation steps are exactly the same as in Example 1.

[0041] Performance testing In accordance with national and industry standard testing specifications, the soil conditioners for coal mine spoil heaps using coal gangue obtained in Examples 1-3 and Comparative Examples 1-3 were systematically evaluated using the following performance testing methods.

[0042] Soil sample preparation: Weigh 10.0g each of the soil conditioners prepared in Examples 1-3 and Comparative Examples 1-3, and mix them thoroughly with 500.0g of actual contaminated soil collected from a coal mine spoil heap. Place the mixture into plastic flowerpots with a diameter of 20.0cm and a height of 15.0cm. Place the samples in a constant temperature and humidity incubation chamber, controlling the ambient temperature at 25.0℃ and the relative humidity at 60%. Use artificial light to simulate natural light, with a light intensity of 10000 lux and a light cycle of 12h light / 12h darkness. Allow the samples to mature for 30 days, during which time the evaporation water is replenished daily to maintain the soil moisture content at 70% of field capacity.

[0043] Soil heavy metal leaching concentration test: After maturation, 50.0 g of soil sample was taken, and 500.0 mL of acetate-sodium acetate buffer solution with pH 4.0 was added. The sample was placed in a rotary shaker and continuously shaken at 30.0±2.0 rpm for 18.0±0.5 h at 30.0±2.0℃. After shaking, the sample was allowed to stand for 30 min, and then filtered through a 0.45 μm microporous membrane. The filtrate was collected. The concentrations of lead, cadmium, chromium, and arsenic in the filtrate were determined using inductively coupled plasma mass spectrometry (ICP-MS). The instrument operating parameters were: radio frequency power 1350 W, plasma gas flow 15.0 L / min, auxiliary gas flow 1.0 L / min, and nebulizer gas flow 0.9 L / min.

[0044] Soil aggregate stability test: 50.0g of air-dried soil sample was placed on the top layer of a set of standard sieves (pore sizes from top to bottom were 5.0mm, 2.0mm, 1.0mm, and 0.25mm). The sieves were immersed in distilled water and allowed to stand for 10 minutes to fully moisten them. The sieves were then placed in an aggregate analyzer and oscillated in water at a fixed frequency of 30 times / min and an amplitude of 3.0cm for 30.0 minutes. After oscillation, aggregates from each sieve size were collected and transferred to a pre-weighed aluminum box. The boxes were then dried in an oven at 105.0℃ until constant weight (weighed every 2 hours, with a mass change of less than 0.001g). The content of water-stable aggregates larger than 0.25mm was calculated.

[0045] Soil nutrient index testing: Total nitrogen content was determined using the semi-micro Kjeldahl method. 1.000 g of soil sample was weighed and added to a mixture of 5.0 mL concentrated sulfuric acid and 2.0 g catalyst (potassium sulfate to copper sulfate ratio 10:1). The mixture was digested at 420℃ for 2 h, and then titrated using a Kjeldahl nitrogen analyzer. Available phosphorus content was determined using the 0.5 mol / L sodium bicarbonate extraction method. 5.00 g of soil sample was weighed and added to 100.0 mL of extract. After shaking for 30 min, the mixture was filtered, and the filtrate was treated with a molybdenum-antimony colorimetric reagent. Colorimetric determination was performed at a wavelength of 880 nm. Available potassium content was determined using a 1.0 mol / L ammonium acetate extraction method with a soil-to-solution ratio of 1:10. After shaking for 30 min, the solution was filtered, and the potassium concentration in the filtrate was determined using a flame photometer. Organic matter content was determined using a potassium dichromate oxidation-external heating method. 0.500 g of soil sample was weighed and added to 5.00 mL of 0.8 mol / L potassium dichromate solution and 5.0 mL of concentrated sulfuric acid. The mixture was boiled in an oil bath at 170-180℃ for 5 min, cooled, and then titrated with ferrous sulfate.

[0046] Soil microbial quantity test: Weigh 10.0g of soil sample and add it to 90.0mL of sterile physiological saline. Vortex for 5min to prepare 10 -1 The diluent was serially diluted 10-fold to 10. -6 Take 10 respectively -4 10 -5 10 -6 Three dilutions of bacterial suspension (0.1 mL) were spread onto corresponding agar plates. Bacteria were cultured on beef extract peptone medium at 28.0°C for 3-5 days for counting; actinomycetes were cultured on Gao's No. 1 medium (containing 0.1 g / L potassium dichromate to inhibit bacterial growth) at 28.0°C for 7-10 days for counting; fungi were cultured on Martin's medium (containing 0.03 g / L streptomycin and 0.02 g / L Bengal red to inhibit bacterial growth) at 28.0°C for 3-5 days for counting. Three replicates were set up for each dilution, and plates with colony counts between 30 and 300 were used for calculation.

[0047] Performance test results: Table 1 Performance Test Results ; ; As shown in Table 1, based on the comparative analysis of performance test results, the soil conditioners prepared in Examples 1-3 exhibit significant advantages over Comparative Examples 1-3 in addressing the complex technical problems of poor soil structure, high risk of heavy metal pollution, and low fertility in coal mine spoil heaps. Regarding heavy metal pollution control, Examples 1-3 showed far superior reduction effects on the leaching concentrations of lead, cadmium, chromium, and arsenic compared to all comparative examples. Specifically, the leaching concentrations of each heavy metal in Example 1 were reduced by 73.3-76.2% compared to Comparative Example 1 and by 82.4-84.4% compared to Comparative Example 3. This result confirms the core role of the heavy metal chelating-structural stabilizing bifunctional polymer, which achieves efficient stabilization and fixation of various heavy metal ions through a dual chelating mechanism of thiol and chloromethyl groups and a cross-linked network structure. Comparative Example 1, lacking this polymer, relied solely on the physical adsorption of coal gangue and biochar, resulting in a significantly weakened heavy metal fixation effect; while Comparative Example 3, completely lacking the functional component, showed heavy metal leaching concentrations close to the original soil level.

[0048] Regarding soil structure improvement, the content of water-stable aggregates larger than 0.25 mm in Examples 1-3 reached 42.3-45.6%, significantly higher than 38.5% in Comparative Example 1 and 35.2% in Comparative Example 2, and much higher than 28.7% in Comparative Example 3. This improvement is attributed to the synergistic effect of the cross-linking film-forming properties of the bifunctional polymer and the cementing effect of the silicate modifier, which jointly promote the aggregation process of soil particles. Comparative Example 2, lacking a silicate slow-release-microbial synergistic modifier, showed significantly insufficient aggregate formation ability; while Comparative Example 1, although retaining silicate components, lacked a polymer cross-linking network, resulting in decreased aggregate stability.

[0049] Regarding soil fertility improvement and microbial system construction, the contents of organic matter, total nitrogen, available phosphorus, available potassium, and microbial counts in Examples 1-3 all showed systematic optimization. The organic matter content in Example 1 reached 25.8 g / kg, an increase of 30.3% compared to Comparative Example 2 and 59.3% compared to Comparative Example 3; its bacterial count reached 12.5 × 10⁻⁶. 6 The CFU / g values ​​were increased by 50.6% and 123.2% compared to Comparative Example 1, respectively. This fully demonstrates that the silicate slow-release-microbial synergistic modifier, through its unique organic-inorganic hybrid structure, achieves both slow-release nutrient supply and provides a suitable habitat for functional microorganisms, while the stable structure formed by the bifunctional polymer creates a safe living space for the microbial community. Comparative Example 2, lacking this modifier, showed acceptable heavy metal fixation, but nutrient supply and microbial activity were significantly limited; Comparative Example 1, lacking the structural stabilizing effect of the polymer, experienced a deterioration in the microbial living environment, leading to a decrease in the number of bacteria.

[0050] In summary, Examples 1-3, through the synergistic effect of the heavy metal chelating-structural stabilizing bifunctional polymer and the silicate slow-release-microbial synergistic modifier, achieved a three-in-one remediation of spoil heap soil structure improvement, pollution control, and fertility enhancement, effectively solving the technical challenge of single technologies being unable to address complex pollution and restore ecological functions. In contrast, Comparative Examples 1-3, due to the absence of key components, exhibited significant deficiencies in one or more aspects, verifying the irreplaceable synergistic value of each component in the present invention.

[0051] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a soil conditioner for coal mine spoil heaps using coal gangue, characterized in that the steps include... include: S1. Crush coal gangue into particles and calcine it at 700-750℃ to obtain calcined coal gangue. Mix the calcined coal gangue with citric acid and stir it at 58-62℃. Filter the mixture to obtain a solid product. Wash the solid product until it is neutral and dry it to obtain modified coal gangue. Modified coal gangue, biochar, humic acid, and polyacrylamide are added to a mixer and stirred. S2. Dissolve the heavy metal chelating-structure stabilizing bifunctional polymer in deionized water to obtain an aqueous solution. Add the aqueous solution to a mixer and stir. Add the ground silicate slow-release-microbial synergistic modifier, phosphate-solubilizing bacteria, and nitrogen-fixing bacteria to the mixer and stir to obtain a mixture. Form the mixture into granules using an extrusion granulator and dry the granules at 38-42℃.

2. The method for preparing a soil conditioner for coal mine spoil heaps using coal gangue according to claim 1, characterized in that, In step S1, the stirring treatment at 58-62℃ takes 4-6 hours.

3. The method for preparing a soil conditioner for coal mine spoil heaps using coal gangue according to claim 1, characterized in that, In step S2, the drying time is 4-6 hours at 38-42℃.

4. The method for preparing a soil conditioner for coal mine spoil heaps using coal gangue according to claim 1, characterized in that, The preparation method of the heavy metal chelating-structure-stabilized bifunctional polymer includes: A1, under nitrogen protection, dissolving polyethyleneimine in anhydrous dimethyl sulfoxide and stirring until completely dissolved; adding 3-mercaptopropionic acid and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, adjusting the pH to 7.4-7.6, and reacting at 24-26℃; then cooling to 0-5℃, adding a dimethyl sulfoxide solution containing chloroacetyl chloride dropwise, and after the addition is complete, reacting at room temperature to obtain a reaction solution; A2, adding 1,2-dibromoethane to the reaction solution, heating to 40-45℃, and reacting to obtain a reaction mixture; purifying the reaction mixture by dialyzing and freeze-drying.

5. The method for preparing a soil conditioner for coal mine spoil heaps using coal gangue according to claim 4, characterized in that, In step A1, the reaction time at room temperature is 12-14 hours.

6. The method for preparing a soil conditioner for coal mine spoil heaps using coal gangue according to claim 4, characterized in that, In step A2, the temperature is raised to 58-62℃ and the reaction time is 6-8 hours.

7. The method for preparing a soil conditioner for coal mine spoil heaps using coal gangue according to claim 1, characterized in that, The preparation method of the silicate sustained-release-microorganism synergistic modifier includes: B1, adding citric acid and 3-aminopropyltriethoxysilane to ethanol, adding 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, refluxing to obtain a reaction solution; cooling the reaction solution to room temperature, adding polyethylene glycol diglycidyl ether and tetrabutylammonium bromide, reacting at 48-52℃ to obtain a reaction mixture; B2, adding sodium silicate aqueous solution to the reaction mixture, adding deionized water dropwise, reacting at 38-42℃; adding N,N'-methylenebisacrylamide and ammonium persulfate, heating to 68-72℃ to react; after the reaction is completed, drying under vacuum by rotary evaporation.

8. The method for preparing a soil conditioner for coal mine spoil heaps using coal gangue according to claim 7, characterized in that, In step B1, the reaction time is 6-8 hours at 48-52℃.

9. The method for preparing a soil conditioner for coal mine spoil heaps using coal gangue according to claim 7, characterized in that, In step B2, the temperature is raised to 68-72℃ and the reaction time is 4-6 hours.

10. A soil conditioner for coal mine spoil heaps prepared by the method according to any one of claims 1-9, characterized in that, The raw materials include the following parts by weight: 50-70 parts by weight of coal gangue; 5-15 parts by weight of heavy metal chelating-structure-stabilizing bifunctional polymer; 3-10 parts by weight of silicate slow-release-microbial synergistic modifier; 10-20 parts by weight of biochar; 5-10 parts by weight of humic acid; 0.5-2 parts by weight of polyacrylamide; 1-3 parts by weight of phosphate-solubilizing bacteria; and 1-3 parts by weight of nitrogen-fixing bacteria.