Ecological restoration method for acidic coal gangue dump

Abstract

The invention relates to the technical field of ecological restoration of coal gangue piles, and particularly discloses an ecological restoration method of an acid coal gangue pile. The ecological restoration method for the acid coal gangue mountain comprises the steps that coal gangue mountain information data are collected, and a combined model is built; key factors influencing the stability and spontaneous combustion of the coal gangue mountain slope are selected, a value combination is constructed to form a data set, after the model runs, the data set is input for simulation restoration, restoration results are screened, and an optimal restoration scheme is obtained; then carrying out mountain cutting and shaping, and carrying out crushing and deacidification treatment on the cut coal gangue; and according to the corresponding remediation parameters in the optimal remediation scheme, the coal gangue mountain is covered with the deacidified coal gangue and loess in proportion, and ecological remediation is carried out. According to the method, the problems of slope stability and internal spontaneous combustion of the acid coal gangue mountain are comprehensively considered, the slope model and the spontaneous combustion multi-field coupling model are cooperatively driven to simulate restoration, the restoration effect can be improved, the cost problem can be considered according to the actual situation, and great economic benefits are achieved.

Description

Technical Field

[0001] The present application relates to the technical field of ecological restoration of coal gangue heaps, and in particular to an ecological restoration method for acidic coal gangue heaps. Background Art

[0002] Gangue is a mineral rock discarded during coal mining and washing. It has a low carbon content, low calorific value, and is harder than coal. It accounts for approximately 10% to 15% of raw coal. Gangue accumulates and is stored around mining areas, compressing the soil, damaging the soil's natural ecosystem, and even triggering geological disasters with serious consequences. Due to the unique structure of gangue piles, a "chimney effect" is prone to occur within them. Acidic gangue piles, in particular, contain large amounts of pyrite (FeS2) and other combustible carbides. The pyrite reacts with water and oxygen that escape into the gangue pile, releasing heat that accumulates within the pile. When the heat reaches the ignition point of the combustibles, spontaneous combustion occurs. The pyrite also produces acidic substances during the reaction. Under low pH conditions, heavy metals in the gangue particles are released, forming highly acidic and toxic mine wastewater. A key method to prevent the spontaneous combustion of acidic gangue piles and the formation of acidic wastewater is to block the oxygen supply. However, gangue spontaneous combustion and slope instability are dynamically coupled, and a single oxygen-isolating measure alone cannot effectively address the problem. Furthermore, there is a lack of scientific methods to accurately quantify the parameters for covering and isolating acidic gangue heaps, leading to uncertainty in the effectiveness of the repairs.

[0003] The prior art discloses a method for resource-based sealing of gangue mines in gangue mountains. The main contents are as follows: after the gangue is made into fine powder, it is modified with a composite adhesive curing agent, and then a water-reducing agent and a water-retaining agent are added to make a cementitious material. Finally, the gangue cementitious material is mixed with the gangue aggregate in a certain proportion to prepare a sealing material, and the gangue pile is sealed to achieve the purpose of reducing the generation of acidic leachate and preventing the spontaneous combustion of gangue. However, in actual operation, this type of method is difficult to determine the amount of sealing material. Too much will introduce more external additives, and too little will lead to poor sealing effect. In addition, cracks will appear in the structure of the sealing material over time, resulting in failure of the sealing of the gangue pile, and the gangue pile will once again produce a series of pollution hazards. Summary of the Invention

[0004] In order to solve the above technical problems, the present application provides an ecological restoration method for acidic coal gangue heaps.

[0005] In response to the deficiencies of the prior art, the present application discloses a method for ecological restoration of acidic gangue mountains. The present application forms a combined model by combining a slope stability model with a natural coupling multi-field model to simulate the shaping and covering of acidic gangue mountains. It can not only determine the stability of the model slope by the change of the safety factor, but also judge the impact of the simulation results on the interior of the acidic gangue mountain by the temperature change inside the model. The simulation results are screened by setting limits, and the final results are obtained for the shaping and covering of the actual acidic gangue mountain, and subsequent ecological restoration of the mountain. The present application comprehensively considers the problems of slope stability and internal spontaneous combustion of acidic gangue mountains, and uses the slope model and the spontaneous combustion multi-field coupling model to synergistically drive the simulation restoration. It can not only improve the restoration effect of acidic gangue mountains, but also consider the cost issue according to the actual situation, which has great economic benefits.

[0006] This application provides an ecological restoration method for acidic coal gangue heaps, which specifically includes the following steps: S1: Collect information on the acidic gangue pile and determine the spontaneous combustion status of the acidic gangue pile. If the pile is in a spontaneous combustion state, inject grouting into the spontaneous combustion area to extinguish the fire and reduce the temperature. Then, collect the temperature field information after extinguishing the fire and replace the original temperature field information to build a gangue pile composite model in COMSOL software. If the gangue pile has not yet spontaneously combusted, directly use the collected data to build the gangue pile composite model. S2: Select key factors that affect the stability and spontaneous combustion of acidic gangue slopes. Based on the preset ranges of each key factor, construct a data set with value combinations. After the model is running, input the data set into a simulated remediation process. The remediation results are then screened to determine the optimal remediation solution. S3: According to the optimal restoration plan, the actual acidic coal gangue mountain is cut and shaped, and the cut coal gangue is then crushed and deacidified; S4: According to the corresponding restoration parameters in the optimal restoration plan, the deacidified coal gangue and loess will be re-covered in proportion on the coal gangue mountain after mountain cutting and shaping, and ecological restoration will be carried out.

[0007] Preferably, step S1 specifically includes the following steps: S1.1: Collect information on acidic gangue piles, including using drone oblique photography to obtain on-site topographic data of the acidic gangue piles, including slope height, slope aspect, and contour data of the acidic gangue piles; collect geological data of the acidic gangue piles, including historical collapse points, crack conditions, and historical landslide points; measure and collect geotechnical parameters of the gangue piles, including porosity, permeability, internal friction angle, effective cohesion, bulk density, pore air pressure, pore water pressure, thermal conductivity, specific heat capacity, density, and air diffusion coefficient; measure and collect meteorological and hydrological data of the gangue piles, including external ambient temperature of the mountain, wind speed, rainfall conditions, groundwater flow, internal temperature of the mountain, air specific heat capacity, air thermal conductivity, air density, and oxygen concentration; S1.2: Based on the on-site topography, meteorological and hydrological data of the gangue pile, determine whether the internal temperature has reached the critical point for spontaneous combustion of the gangue. If not, proceed directly to the next step of model construction. If so, grouting is performed in the spontaneous combustion area to extinguish the fire and cool it down. Then, data after extinguishing the fire and cooling the temperature are collected to proceed to the next step of model construction. The spontaneous combustion zone grouting fire extinguishing method includes dividing the spontaneous combustion coal gangue pile into the spontaneous combustion occurrence zone and the spontaneous combustion danger zone according to the collected temperature data, and injecting the corresponding amount of alkaline material into different zones to achieve the purpose of extinguishing the fire, reducing the temperature and neutralizing the acidity; S1.3: Based on the on-site topographic data and geological data, a geometric model of the acidic gangue pile is constructed using COMSOL software; based on the meteorological and hydrological data, an external environmental field model of the acidic gangue pile of the same scale is established based on the geometric data of the geometric model of the gangue pile; the geometric model and the environmental field model are superimposed at the same coordinate points, that is, the coordinate data of the edge of the geometric model and the internal edge of the environmental field model are completely overlapped to form a three-dimensional model of the gangue pile; at the same time, the overlapping coordinate portions are set to the same node, and a physical interface is added at the node to realize data interaction between the external environmental field and the geometric model of the gangue pile; the interactive external environmental field data includes air seepage and ambient temperature; S1.4: Input the collected geotechnical parameters into the geomechanics module of COMSOL software to calculate the slope safety factor of the acid coal gangue pile to determine whether the slope is stable; when the slope safety factor F S >1, the slope is in a stable state; when the slope safety factor F S ≤1, the slope is in an unstable state; the slope safety factor calculation formula is shown in formula (1), where F S is the slope safety factor; c ′ is the effective cohesion, kPa; σ is the total stress, kN / m 2 ;u a is the pore gas pressure, kPa; u w is the pore water pressure, kPa; is the net normal stress state variable (σ-u a ) related internal friction angle, °; is the matrix suction (u a -u w ) is the internal friction angle of the coal gangue slope, °; γ is the bulk density of the coal gangue slope, g / cm 3 ; z is the depth of the slope, m; β is the slope angle, °; S1.5: Utilize the collected temperature field information within the gangue pile and the constructed three-dimensional model to analyze the coupling relationship between air seepage, oxygen oxidation reaction, and temperature field within the gangue pile. Establish the corresponding air seepage velocity field balance equation, oxygen component migration field balance equation, and temperature field transmission balance equation in a custom COMSOL software module. Construct a multi-field coupling model of spontaneous combustion within the three-dimensional model of the gangue pile based on the air seepage velocity field balance equation, oxygen component migration field balance equation, and temperature field transmission balance equation. The air seepage velocity of the gangue pile is an important factor affecting spontaneous combustion. At the same time, considering that spontaneous combustion inside the gangue pile will generate thermal buoyancy, based on the porous media seepage theory, the momentum balance equation of the seepage velocity field of the gangue pile is shown in formula (2), where, is the Hamilton operator; v is the seepage velocity, m / s; μ is the air dynamic viscosity coefficient, kg / (m·s); k is the permeability in the gangue pile, m / s; P is the pressure, Pa; ρ g is the air density, kg / m 3 ; T0 is the atmospheric temperature, K; T is the internal temperature of the gangue pile, K; The main ways of oxygen supply inside the gangue pile are air infiltration and diffusion of oxygen molecules. According to the theory of heat and mass transfer in porous media, the mass balance equation of oxygen concentration is shown in formula (3), where ε is the porosity of the gangue, %; c is the oxygen concentration, mol / m 3 ; t is time, s; D is the air diffusion coefficient, m 2 / s; A is the pre-exponential factor, s -1 ; E is the activation energy, kJ / mol; R is the universal gas constant, its value is 8.314 J / (mol·K); The heat transfer modes inside coal gangue include heat conduction, heat convection and heat radiation. Since the object of the spontaneous combustion multi-field coupling model is the entire acidic coal gangue mountain, and the model focuses on the dynamic balance between heat generation and conduction, and heat radiation is not a core factor, it can be ignored here. According to the porous media heat transfer theory, the temperature field transmission balance equation is shown in formula (4), where ρ gIndicates the density of air, kg / m 3 ρ s Indicates the density of the solid, kg / m 3 ; C g Indicates the specific heat capacity of air, J / (kg·K); C s Indicates the specific heat capacity of the solid, J / (kg.K); λ g Indicates the thermal conductivity of air, W / (m·K); λ s represents the thermal conductivity of the solid, W / (m·K); ΔH is the heat released by coal gangue per mol of oxygen consumed under standard conditions, i.e., enthalpy change, J / mol; S1.6: Data Interaction Based on the mapping of the temperature field output in the spontaneous combustion multi-field coupling model to material parameters in the slope model and the situation that slope deformation will cause changes in the porosity of the coal gangue pile in the natural multi-field coupling model, a two-way data interaction interface is established between the slope model and the spontaneous combustion multi-field coupling model to achieve dynamic data interaction between the models; the parameter mapping includes the decrease in slope cohesion caused by the increase in internal temperature of the acidic coal gangue pile and the increase in internal porosity caused by the deformation of the acidic coal gangue pile slope; The formula for the effect of internal temperature of gangue pile on slope cohesion is shown in formula (5), where c′0 represents the original cohesion, kPa; c'=c′0×e -0.002(T-20) Formula (5); The formula for the change of porosity of coal gangue pile caused by slope deformation is shown in formula (6), where ε0 is the original porosity, %; S1.7: After the model is run, the results obtained from randomly selected sites are compared and verified with the measured coal gangue pile information to ensure the authenticity and reliability of the model.

[0008] Preferably, in step S2, the key factors affecting the slope stability and spontaneous combustion of the acidic coal gangue pile include the height of the coal gangue pile, the thickness of the coal gangue pile covering material (25 to 85 cm), the coal gangue particle size in the covering material (2 to 10 mm), and the mixing ratio of coal gangue to loess in the covering material (1:9 to 9:1); the data set includes a data set formed by constructing a value combination based on the preset range of each key factor.

[0009] Preferably, in step S2, the simulated repair and the repair result screening include preliminary screening and final screening; The preliminary screening includes inputting the data set into the model for simulation repair and setting constraints; the constraints include the slope safety factor F S>1, the maximum temperature inside the gangue pile T <80℃; Based on the model operation results, a data set suitable for the remediation of acidic gangue piles is obtained; The final screening includes setting an objective function on economic cost to obtain the most economically beneficial simulation results; the cost corresponding to each repair data can be obtained according to the unit cost and the implementation amount, and the repair plan with the lowest cost is selected from them; the objective function is shown in formula (7); where, F i is the cost of repairing the data of item i, RMB; C i is the unit cost of the material in the i-th item of restoration data, which includes the unit cost of cutting the mountain, the unit cost of the material cover layer, the unit cost of coal gangue crushing and the cost of loess, RMB; x i is the implementation amount of the i-th restoration data, which includes the cutting thickness, covering thickness, crushed gangue amount and mixed material ratio; F i =C i ×x i F min =(F1,F2,…,F i ,…,F n ) Formula (7).

[0010] Preferably, in step S3, the optimal restoration plan includes the height of the acidic gangue mountain, and the actual acidic gangue mountain is cut and shaped according to the corresponding heights of each point of the gangue mountain in the simulation results.

[0011] Preferably, in step S3, the crushing treatment includes transferring the shaved acidic coal gangue to a crusher and crushing it into deacidified coal gangue particles of the corresponding particle size in the optimal repair solution; the deacidification treatment includes soaking the crushed acidic coal gangue in a soaking tank for a certain period of time and then transferring it to a washing tank, washing it to neutrality and then collecting the deacidified coal gangue.

[0012] Preferably, in step S4, the repair parameters corresponding to the optimal repair scheme include the thickness of the covering material (25 to 85 cm), the particle size of the deacidified coal gangue (2 to 10 mm) and the mixing ratio of coal gangue to loess in the covering material (1:9 to 9:1); the shaped acidic coal gangue mountain is covered and oxygen-isolating repaired according to the repair parameters.

[0013] Preferably, in step S4, the ecological restoration includes planting shrubs on the covered acidic coal gangue mountain terrace surface and laying ecological vegetation bags on the slope surface. In order to enhance the stability of the coal gangue mountain slope and reduce rainwater erosion of the slope foot, it is necessary to install a protective anchor frame, a drainage trough and a gangue retaining wall.

[0014] Preferably, the ecological planting bag is made of degradable material, and the materials contained in the ecological planting bag are seeds, mixed matrix, organic fertilizer, water retaining agent, plant growth promoting agent, and composite microbial agent; An anchor frame is installed around the ecological vegetation bag and reinforced on the slope of the coal gangue mountain to prevent the vegetation belt from slipping; The drainage trough is installed at the angle between the slope surface of the coal gangue mountain and the step surface. At the same time, a drainage trough is set along the slope surface to connect the drainage troughs of each step surface; the retaining wall is placed at the foot of the coal gangue mountain, and the retaining wall is cast with cement around the foot of the coal gangue mountain.

[0015] Preferably, step S4 also includes intelligent maintenance, and the specific steps are to build an intelligent monitoring system, by burying distributed optical fiber sensors on the repaired coal gangue mountain and setting up multiple intelligent monitoring points to observe the status of the coal gangue mountain from the end of construction to the formation of the vegetation community, and carry out work including vegetation replanting, topdressing, watering and pest and disease control as appropriate, so as to promote the vegetation ecosystem to complete self-succession.

[0016] In summary, the technical solution of this application has the following effects: This application combines a slope stability model with a multi-field coupled spontaneous combustion model for the simulation of acidic gangue pile remediation. This eliminates the uncertainty associated with slope stability and internal temperature fluctuations in gangue piles, often caused by remediation methods such as covering or sealing. This improves the effectiveness of acidic gangue pile remediation. Furthermore, by screening different simulation results, the optimal remediation solution, which is both effective and economical, is identified. This effectively reduces remediation costs, achieves comprehensive optimization of the ecological restoration plan for acidic gangue piles, and provides a strong guarantee for the long-term stability and ecological restoration of gangue piles.

[0017] This application utilizes the removed coal gangue in situ, which not only reduces the potential risks brought by the addition of external materials, but also effectively improves the utilization rate of acidic coal gangue and reduces the ecological problems caused by the accumulation of acidic coal gangue. It is eco-friendly and environmentally friendly, and plays a demonstration role in improving the comprehensive utilization of acidic coal gangue. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of the ecological restoration method for acidic coal gangue heaps in this application.

[0019] Figure 2 This is the mountain cutting and soil covering treatment map of the acidic coal gangue mountain in this application.

[0020] Figure 3 This is the ecological management map of the acidic coal gangue mountain in this application.

[0021] In the figure, 1-acidic coal gangue mountain, 2-mixed matrix, 3-gangue retaining wall, 4-drainage trough, 5-drainage pipe, 6-ecological vegetation bag, 7-fixed frame, 8-shrub vegetation. DETAILED DESCRIPTION

[0022] The present application is further described in detail below in conjunction with examples, comparative examples and performance testing experiments. These examples should not be construed as limiting the scope of protection claimed in this application. Example

[0023] The embodiment provides an ecological restoration method for an acidic coal gangue mountain.

[0024] Figure 1 Shown is a flow chart of the ecological restoration method for acidic coal gangue heap in this application, and the specific process is as follows.

[0025] S1: Site survey and model building Collect information and data on the acidic coal gangue mountain to determine the spontaneous combustion situation inside the acidic coal gangue mountain. If it is in a spontaneous combustion state, grouting is performed in the spontaneous combustion area to extinguish the fire and cool it down. Then, the temperature field information after extinguishing the fire is collected to replace the original temperature field information and build a coal gangue combination model in COMSOL software. If the coal gangue mountain has not yet spontaneously combusted, the collected data is directly used to build the coal gangue combination model.

[0026] S1.1: Collecting information and data on acidic coal gangue hills includes using drone oblique photography to obtain on-site topographic data of the acidic coal gangue hills, and the on-site topographic data include the slope height, slope direction, and contour line data of the acidic coal gangue hills; collecting geological data of the acidic coal gangue hills, and the geological data include historical collapse points, crack conditions, and historical landslide points; measuring and collecting rock and soil parameters of the coal gangue hills, and the rock and soil parameters of the coal gangue hills include porosity, permeability, internal friction angle, effective cohesion, bulk density, pore air pressure, pore water pressure, thermal conductivity, specific heat capacity, density, and air diffusion coefficient; measuring and collecting meteorological and hydrological data of the coal gangue, and the meteorological and hydrological data include the external environmental temperature of the mountain, wind speed, rainfall conditions, groundwater flow, internal temperature of the mountain, air specific heat capacity, air thermal conductivity, air density, and oxygen concentration.

[0027] S1.2: Based on the on-site topography, meteorological and hydrological data of the gangue mountain, determine whether the internal temperature has reached the critical point for spontaneous combustion of the gangue. If not, proceed directly to the next step of model construction. If so, grouting is performed in the spontaneous combustion area to extinguish the fire and cool it down, and then the data after extinguishing the fire and cooling are collected to proceed to the next step of model construction.

[0028] The grouting fire extinguishing in the spontaneous combustion zone includes dividing the spontaneous combustion gangue mountain into the spontaneous combustion occurrence zone and the spontaneous combustion danger zone according to the collected temperature data, and selecting alkaline materials to inject corresponding amounts into different areas to achieve the purpose of extinguishing the fire, cooling the temperature and neutralizing the acidity; because the deacidified gangue will be reused to cover the surface of the acidic gangue mountain to form an oxygen barrier layer after subsequent simulation, it is sufficient to select suitable alkaline materials to extinguish the fire and cool the spontaneous combustion area for the spontaneous combustion area or the natural warning area. Specifically: according to the results of the on-site temperature field survey of the gangue mountain, the spontaneous combustion gangue mountain is divided into the spontaneous combustion occurrence zone and the spontaneous combustion warning zone, and suitable materials are selected to inject corresponding amounts into different areas to achieve the purpose of extinguishing the fire and cooling the temperature. At the same time, the selection of alkaline fire extinguishing materials can neutralize the acidic substances produced by the oxidation of the gangue.

[0029] S1.3: Based on the on-site topographic data and geological data, a geometric model of the acidic coal gangue mountain is constructed using COMSOL software; based on the meteorological and hydrological data, an external environmental field model of the acidic coal gangue mountain with the same scale is established according to the geometric data of the geometric model of the coal gangue mountain; the geometric model and the environmental field model are superimposed at the same coordinate points, that is, the edge of the geometric model and the internal edge coordinate data of the environmental field model are completely overlapped to form a three-dimensional model of the coal gangue mountain; at the same time, the overlapping coordinate parts are set to the same node, and a physical interface is added at the node to realize data interaction between the external environmental field and the geometric model of the coal gangue mountain; the interactive external environmental field data include air seepage and ambient temperature.

[0030] S1.4: Input the collected geotechnical parameters into the geomechanics module of COMSOL software to calculate the slope safety factor of the acid coal gangue pile to determine whether the slope is stable; when the slope safety factor F S >1, the slope is in a stable state; when the slope safety factor F S ≤1, the slope is in an unstable state; the slope safety factor calculation formula is shown in formula (1), where F S is the slope safety factor; c ′ is the effective cohesion, kPa; σ is the total stress, kN / m 2 ;u a is the pore gas pressure, kPa; u w is the pore water pressure, kPa; is the net normal stress state variable (σ-u a ) related internal friction angle, °; is the matrix suction (u a -u w ) is the internal friction angle of the coal gangue slope, °; γ is the bulk density of the coal gangue slope, g / cm 3 ; z is the depth of the slope, m; β is the slope angle, °;

[0031] S1.5: Utilize the collected temperature field information inside the gangue pile and combine it with the constructed three-dimensional model to analyze the coupling relationship between the air seepage, oxygen oxidation reaction and temperature field in the gangue pile, and establish the corresponding air seepage velocity field balance equation, oxygen component migration field balance equation and temperature field transmission balance equation in the custom module of COMSOL software; construct a multi-field coupling model of spontaneous combustion inside the three-dimensional model of the gangue pile based on the air seepage velocity field balance equation, oxygen component migration field balance equation and temperature field transmission balance equation.

[0032] The air seepage velocity of the gangue pile is an important factor affecting spontaneous combustion. At the same time, considering that spontaneous combustion inside the gangue pile will generate thermal buoyancy, based on the porous media seepage theory, the momentum balance equation of the seepage velocity field of the gangue pile is shown in formula (2), where, is the Hamilton operator; v is the seepage velocity, m / s; μ is the air dynamic viscosity coefficient, kg / (m·s); k is the permeability in the gangue pile, m / s; P is the pressure, Pa; ρ g is the air density, kg / m 3 ; T0 is the atmospheric temperature, K; T is the internal temperature of the gangue pile, K;

[0033] The main ways of oxygen supply inside the gangue pile are air infiltration and diffusion of oxygen molecules. According to the theory of heat and mass transfer in porous media, the mass balance equation of oxygen concentration is shown in formula (3), where ε is the porosity of the gangue, %; c is the oxygen concentration, mol / m 3 ; t is time, s; D is the air diffusion coefficient m 2 / s; A is the pre-exponential factor, s -1 ; E is the activation energy, kJ / mol; R is the universal gas constant, its value is 8.314 J / (mol·K);

[0034] The heat transfer modes inside coal gangue include heat conduction, heat convection and heat radiation. Since the object of the spontaneous combustion multi-field coupling model is the entire acidic coal gangue mountain, and the model focuses on the dynamic balance between heat generation and conduction, and heat radiation is not a core factor, it can be ignored here. According to the porous media heat transfer theory, the temperature field transmission balance equation is shown in formula (4), where ρ g Indicates the density of air, kg / m 3 ρ s Indicates the density of the solid, kg / m 3 ; C g Indicates the specific heat capacity of air, J / (kg·K); C s Indicates the specific heat capacity of the solid, J / (kg.K); λ gIndicates the thermal conductivity of air, W / (m·K); λ s represents the thermal conductivity of the solid, W / (m·K); ΔH is the heat released by coal gangue per mol of oxygen consumed under standard conditions, i.e., enthalpy change, J / mol;

[0035] S1.6: Data Interaction Based on the mapping of the temperature field output in the spontaneous combustion multi-field coupling model to the material parameters in the slope model and the situation that slope deformation will cause changes in the porosity of the coal gangue pile in the natural multi-field coupling model, a two-way data interaction interface between the slope model and the spontaneous combustion multi-field coupling model is established to realize dynamic data interaction between the models; the parameter mapping includes the increase in internal temperature of the acidic coal gangue pile leading to the attenuation of slope cohesion and the increase in internal porosity caused by the deformation of the acidic coal gangue pile slope.

[0036] The formula for the effect of internal temperature of gangue pile on slope cohesion is shown in formula (5), where c′0 represents the original cohesion, kPa; c'=c′0×e -0.002(T-20) Formula (5).

[0037] The formula for the change of porosity of coal gangue pile caused by slope deformation is shown in formula (6), where ε0 is the original porosity, %;

[0038] S1.7: After the model is run, the results obtained from randomly selected sites are compared and verified with the measured coal gangue pile information to ensure the authenticity and reliability of the model.

[0039] S2: Simulate repair and filter results Key factors affecting the stability and spontaneous combustion of acidic gangue slopes are selected, and a value combination is constructed based on the preset range of each key factor to form a data set. After the model is running, the data set is input for simulated repair, and then the repair results are screened.

[0040] The key factors affecting the slope stability and spontaneous combustion of acidic coal gangue piles include the height of the coal gangue pile, the thickness of the coal gangue pile cover material (25 to 85 cm), the coal gangue particle size in the cover material (2 to 10 mm), and the coal gangue to loess mixing ratio in the cover material (1:9 to 9:1). The data set includes a data set formed by constructing a value combination based on the preset range of each key factor.

[0041] Simulation restoration and restoration result screening include preliminary screening and final screening; The initial screening includes inputting the data set into the model for simulation repair and setting constraints; the constraints include the slope safety factor F S>1, the maximum temperature inside the gangue pile T < 80℃; Based on the model operation results, a remediation data set suitable for acidic gangue pile remediation is obtained; The final screening includes setting the objective function of economic cost to obtain the most economically beneficial simulation results; according to the unit cost and the implementation amount, the cost corresponding to each repair data can be obtained, and the repair plan with the lowest cost can be selected from them; the objective function is shown in formula (7); where, F i is the cost of repairing the data of item i, RMB; C i is the unit cost of the material in the i-th item of restoration data, which includes the unit cost of cutting the mountain, the unit cost of the material cover layer, the unit cost of coal gangue crushing and the cost of loess, RMB; x i is the implementation amount of the i-th restoration data, which includes the cutting thickness, covering thickness, crushed gangue amount and mixed material ratio; F i =C i ×x i F min =(F1,F2,…,F i ,…,F n ) Formula (7).

[0042] S3: Mountain cutting and shaping, gangue crushing and deacidification According to the best restoration plan, the actual acidic coal gangue mountain is cut and shaped, and then the cut coal gangue is crushed and deacidified.

[0043] The best restoration plan includes the height of the acidic coal gangue mountain. The actual acidic coal gangue mountain is cut and shaped according to the corresponding heights of each point of the coal gangue mountain in the simulation results.

[0044] The crushing treatment includes transferring the shaved acidic coal gangue to a crusher and crushing it into deacidified coal gangue particles corresponding to the optimal repair plan; the deacidification treatment includes soaking the crushed acidic coal gangue in a soaking tank for a certain period of time and then transferring it to a washing tank, washing it to neutrality and then collecting the deacidified coal gangue.

[0045] S4: Coal gangue covering and ecological restoration According to the corresponding restoration parameters in the optimal restoration plan, the deacidified coal gangue and loess will be re-covered in proportion on the coal gangue mountain after mountain cutting and shaping, and ecological restoration will be carried out.

[0046] S4.1: The corresponding restoration parameters in the optimal restoration scheme include the thickness of the covering material (25 to 85 cm), the particle size of the deacidified coal gangue (2 to 10 mm), and the mixing ratio of coal gangue to loess in the covering material (1:9 to 9:1); the shaped acidic coal gangue mountain is covered and oxygen-isolating based on the restoration parameters.

[0047] S4.2: Carry out ecological restoration, including planting cold-resistant and drought-resistant shrub vegetation 8 on the covered step surface of the acidic coal gangue mountain 1, laying ecological vegetation bags 6 on the slope surface, and installing protective anchor frames 7, drainage channels 4 and gangue retaining walls 5 to enhance the stability of the coal gangue mountain slope and reduce rainwater erosion of the slope foot; set up intelligent maintenance treatment after carrying out ecological restoration.

[0048] The ecological vegetation bag 6 is made of degradable materials. The materials contained in the ecological vegetation bag 6 are mixed seeds of cold-resistant and drought-resistant plants, mixed growth matrix, organic fertilizer, water-retaining agent, and plant growth promoter. The anchor frame 7 is installed around the ecological vegetation bag 6 and reinforced on the slope of the coal gangue mountain to prevent the vegetation bag 6 from slipping. The drainage trough 4 is installed at the angle between the slope of the coal gangue mountain and the step surface, with a width and depth of 25 to 35 cm respectively. At the same time, the drainage trough 4 is set along the slope to connect the drainage troughs 4 of each step surface. The retaining wall 3 is placed at the foot of the acidic coal gangue mountain 1. The retaining wall 3 is cast with cement and surrounds the foot of the acidic coal gangue mountain 1. The height is 0.5 to 1 m higher than the slope.

[0049] Ecological planting bags are made of degradable materials. The materials contained in the ecological planting bags are seeds, mixed matrix, organic fertilizer, water retaining agent, plant growth promoter, and compound microbial agent; Install the anchor frame around the ecological vegetation bag and reinforce it on the slope of the coal gangue mountain to prevent the vegetation belt from slipping; The drainage trough is installed at the angle between the slope surface of the coal gangue mountain and the step surface. At the same time, a drainage trough is set along the slope surface to connect the drainage troughs of each step surface; the retaining wall is placed at the foot of the coal gangue mountain, and the retaining wall is cast with cement around the foot of the coal gangue mountain.

[0050] S4.3: Intelligent maintenance. The specific steps are to build an intelligent monitoring system. By burying distributed fiber optic sensors on the repaired coal gangue mountain, multiple intelligent monitoring points are set up to observe the status of the coal gangue mountain from the end of construction to the formation of the vegetation community. Depending on the situation, work including vegetation replanting, topdressing, watering, and pest and disease control will be carried out to promote the self-succession of the vegetation ecosystem.

[0051] like Figure 2-3 As shown, one side of the unrepaired acidic gangue mountain 1 is a gentle slope with a slope of about 20°, and the other side has no buffer and a slope greater than 60°. Ecological restoration is carried out in this embodiment according to the model.

[0052] After importing the basic data of the embodiment into the combined model, the acidic coal gangue mountain was ecologically restored according to the optimal restoration plan screened after the model operation. Specifically, the original acidic coal gangue mountain 1 was cut and shaped, and the removed coal gangue was transferred to the sides of the mountain. According to the model results, it was shaped into a multi-step ladder-shaped mountain structure. After shaping, the slope of the mountain was 9m long, the slope was 20°, the step surface was 4m long, and the step surface was reversed at 2°. The remaining coal gangue was crushed into particles with a particle size of less than 5mm by a crusher, and deacidification was carried out by a coal gangue soaking and washing device. According to the optimal restoration plan, the surface of the shaped acidic coal gangue mountain 1 was first covered with a 37cm thick mixed matrix 2 with a ratio of deacidified coal gangue to loess of 1:9, and then covered with a 32cm thick mixed matrix 2 with a ratio of deacidified coal gangue to loess of 7:3, forming an exposed mountain. A planting layer is laid on the exposed mountain steps, with Amorpha fruticosa and Tamarix multibranchedis planted. Ecological vegetation bags 6 filled with mixed seeds of cold-resistant and drought-resistant plants, mixed growth medium, organic fertilizer, water-retaining agent, and plant growth promoter are laid on the slope. Ecological vegetation bags 6 are reinforced to the slope using anchor frames 7. Drainage troughs with a width and depth of 30 cm are installed at the angle between the slope of the coal gangue mountain and the step surface. At the same time, drainage troughs 4 of the same type are installed downward along the slope to connect the drainage troughs 4 on each step surface. A retaining wall 3 with a height of approximately 2.1 m and a width of 1 m is installed at the foot of the coal gangue mountain to prevent rainwater or other runoff from accumulating near the retaining wall 3 and eroding the slope. A drainage trough 4 with a width and depth of 30 cm is installed on the side of the retaining wall 3 close to the slope of the acidic coal gangue mountain 1, and a drainage pipe 5 is installed in the retaining wall 3 to drain the rainwater or runoff accumulated in the drainage trough 4.

[0053] The relevant data of the embodiment are shown in the table below; the relevant parameters of the model are shown in Table 1 below: Table 1 Basic data of acidic coal gangue pile Model validation: Three points in the acidic coal gangue heap were randomly selected to measure the temperature and calculate the corresponding safety factor. The data were compared with the data of the same points after the model was run. The comparison of the model validation data is shown in Table 2.

[0054] Table 2 Comparison of model validation data According to the data in the table, the maximum safety factor error rate is only 5.9%, and the maximum temperature error rate is 7.1%, which shows that the model used in this application is accurate and reliable.

[0055] Table 3 shows the comparison of data before and after the restoration of the acidic coal gangue mountain.

[0056] Table 3 Comparison of data before and after repair The cost of repairing an acidic coal gangue mountain of the scale of the embodiment using conventional repair measures is about RMB 40 million or more. This application reduces the repair cost by more than 22%.

[0057] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for ecological restoration of acidic coal gangue heaps, characterized in that: The specific steps include: S1: Collect information on the acidic gangue pile and determine the spontaneous combustion status of the acidic gangue pile. If the pile is in a spontaneous combustion state, inject grouting into the spontaneous combustion area to extinguish the fire and reduce the temperature. Then, collect the temperature field information after extinguishing the fire and replace the original temperature field information to build a gangue pile composite model in COMSOL software. If the gangue pile has not yet spontaneously combusted, directly use the collected data to build the gangue pile composite model. S2: Select key factors that affect the stability and spontaneous combustion of acidic gangue slopes. Based on the preset ranges of each key factor, construct a data set with value combinations. After the model is running, input the data set into a simulated remediation process. The remediation results are then screened to determine the optimal remediation solution. S3: According to the optimal restoration plan, the actual acidic coal gangue mountain is cut and shaped, and the cut coal gangue is then crushed and deacidified; S4: According to the corresponding restoration parameters in the optimal restoration plan, the deacidified coal gangue and loess will be re-covered in proportion on the coal gangue mountain after mountain cutting and shaping, and ecological restoration will be carried out.

2. The ecological restoration method for acidic coal gangue heap according to claim 1, characterized in that: Step S1 specifically includes the following steps: S1.1: Collect information on acidic gangue piles, including using drone oblique photography to obtain on-site topographic data of the acidic gangue piles, including slope height, slope aspect, and contour data of the acidic gangue piles; collect geological data of the acidic gangue piles, including historical collapse points, crack conditions, and historical landslide points; measure and collect geotechnical parameters of the gangue piles, including porosity, permeability, internal friction angle, effective cohesion, bulk density, pore air pressure, pore water pressure, thermal conductivity, specific heat capacity, density, and air diffusion coefficient; measure and collect meteorological and hydrological data of the gangue piles, including external ambient temperature of the mountain, wind speed, rainfall conditions, groundwater flow, internal temperature of the mountain, air specific heat capacity, air thermal conductivity, air density, and oxygen concentration; S1.2: Based on the on-site topography, meteorological and hydrological data of the gangue pile, determine whether the internal temperature has reached the critical point for spontaneous combustion of the gangue. If not, proceed directly to the next step of model construction. If so, grouting is performed in the spontaneous combustion area to extinguish the fire and cool it down. Then, data after extinguishing the fire and cooling the temperature are collected to proceed to the next step of model construction. The spontaneous combustion zone grouting fire extinguishing method includes dividing the spontaneous combustion coal gangue pile into the spontaneous combustion occurrence zone and the spontaneous combustion danger zone according to the collected temperature data, and injecting the corresponding amount of alkaline material into different zones to achieve the purpose of extinguishing the fire, reducing the temperature and neutralizing the acidity; S1.3: Based on the on-site topographic data and geological data, a geometric model of the acidic gangue pile is constructed using COMSOL software; based on the meteorological and hydrological data, an external environmental field model of the acidic gangue pile of the same scale is established based on the geometric data of the geometric model of the gangue pile; the geometric model and the environmental field model are superimposed at the same coordinate points, that is, the coordinate data of the edge of the geometric model and the internal edge of the environmental field model are completely overlapped to form a three-dimensional model of the gangue pile; at the same time, the overlapping coordinate portions are set to the same node, and a physical interface is added at the node to realize data interaction between the external environmental field and the geometric model of the gangue pile; the interactive external environmental field data includes air seepage and ambient temperature; S1.4: Input the collected geotechnical parameters into the geomechanics module of COMSOL software to calculate the slope safety factor of the acid coal gangue pile to determine whether the slope is stable; when the slope safety factor F S >1, the slope is in a stable state; when the slope safety factor F S ≤1, the slope is in an unstable state; the slope safety factor calculation formula is shown in formula (1), where F S is the slope safety factor; c ′ is the effective cohesion, kPa; σ is the total stress, kN / m 2 ;u a is the pore gas pressure, kPa; u w is the pore water pressure, kPa; is the net normal stress state variable (σ-u a ) related internal friction angle, °; is the matrix suction (u a -u w ) is the internal friction angle of the coal gangue slope, °; γ is the bulk density of the coal gangue slope, g / cm 3 ; z is the depth of the slope, m; β is the slope angle, °; S1.5: Utilize the collected temperature field information within the gangue pile and the constructed three-dimensional model to analyze the coupling relationship between air seepage, oxygen oxidation reaction, and temperature field within the gangue pile. Establish the corresponding air seepage velocity field balance equation, oxygen component migration field balance equation, and temperature field transmission balance equation in a custom COMSOL software module. Construct a multi-field coupling model of spontaneous combustion within the three-dimensional model of the gangue pile based on the air seepage velocity field balance equation, oxygen component migration field balance equation, and temperature field transmission balance equation. According to the porous media seepage theory, the momentum balance equation of the seepage velocity field of the gangue heap is shown in formula (2), where, is the Hamilton operator; v is the seepage velocity, m / s; μ is the air dynamic viscosity coefficient, kg / (m·s); k is the permeability in the gangue pile, m / s; P is the pressure, Pa; ρ g is the air density, kg / m 3 ; T0 is the atmospheric temperature, K; T is the internal temperature of the gangue pile, K; According to the theory of heat and mass transfer in porous media, the mass balance equation of oxygen concentration is shown in formula (3), where ε is the porosity of coal gangue, %; c is the oxygen concentration, mol / m 3 ; t is time, s; D is the air diffusion coefficient, m 2 / s; A is the pre-exponential factor, s -1 ; E is the activation energy, kJ / mol; R is the universal gas constant, its value is 8.314 J / (mol·K); According to the porous media heat transfer theory, the temperature field transmission balance equation is shown in formula (4), where ρ g Indicates the density of air, kg / m 3 ρ s Indicates the density of the solid, kg / m 3 ; C g Indicates the specific heat capacity of air, J / (kg·K); C s Indicates the specific heat capacity of the solid, J / (kg.K); λ g Indicates the thermal conductivity of air, W / (m·K); λ s represents the thermal conductivity of the solid, W / (m·K); ΔH is the heat released by coal gangue per mol of oxygen consumed under standard conditions, i.e., enthalpy change, J / mol; S1.6: Data Interaction Based on the mapping of the temperature field output in the spontaneous combustion multi-field coupling model to material parameters in the slope model and the situation that slope deformation will cause changes in the porosity of the coal gangue pile in the natural multi-field coupling model, a two-way data interaction interface is established between the slope model and the spontaneous combustion multi-field coupling model to achieve dynamic data interaction between the models; the parameter mapping includes the decrease in slope cohesion caused by the increase in internal temperature of the acidic coal gangue pile and the increase in internal porosity caused by the deformation of the acidic coal gangue pile slope; The formula for the effect of internal temperature of gangue pile on slope cohesion is shown in formula (5), where c′0 represents the original cohesion, kPa; c’=c′0×e -0.002(T-20) Formula (5); The formula for the change of porosity of coal gangue pile caused by slope deformation is shown in formula (6), where ε0 is the original porosity, %; S1.7: After the model is run, the results obtained from randomly selected sites are compared and verified with the measured coal gangue pile information to ensure the authenticity and reliability of the model.

3. The ecological restoration method for acidic coal gangue heap according to claim 1, characterized in that: In step S2, the key factors affecting the slope stability and spontaneous combustion of acidic coal gangue piles include the height of the coal gangue pile, the thickness of the coal gangue pile covering material, the coal gangue particle size in the covering material, and the mixing ratio of coal gangue to loess in the covering material; the data set includes a data set formed by constructing a value combination based on the preset range of each key factor.

4. The ecological restoration method for acidic coal gangue heap according to claim 1, characterized in that: In step S2, the simulated repair and the screening of the repair results include preliminary screening and final screening; The preliminary screening includes inputting the data set into the model for simulation repair and setting constraints; the constraints include the slope safety factor F S >1, the maximum temperature inside the gangue pile T <80℃; Based on the model operation results, a data set suitable for the remediation of acidic gangue piles is obtained; The final screening includes setting an objective function on economic cost in order to obtain the most economically beneficial simulation result; According to the unit cost and the amount of implementation, the cost corresponding to each repair data can be obtained, and the repair plan with the lowest cost can be selected from them; the objective function is shown in formula (7); where, F i is the cost corresponding to the i-th item of repair data, yuan; C i is the unit cost of the material in the i-th item of restoration data, which includes the unit cost of cutting the mountain, the unit cost of the material cover layer, the unit cost of coal gangue crushing and the cost of loess, RMB; x i is the implementation amount of the i-th restoration data, which includes the cutting thickness, covering thickness, crushed gangue amount and mixed material ratio; F i =C i ×x i F min =(F1,F2,…,F i ,…,F n ) Formula (7).

5. The ecological restoration method for acidic coal gangue heap according to claim 1, characterized in that: In step S3, the optimal restoration plan includes the height of the acidic gangue mountain, and the actual acidic gangue mountain is cut and shaped according to the corresponding heights of each point of the gangue mountain in the simulation results.

6. The ecological restoration method for acidic coal gangue heap according to claim 1, characterized in that: In step S3, the crushing treatment includes transferring the shaved acidic coal gangue to a crusher and crushing it into coal gangue particles of the corresponding particle size in the optimal repair solution; the deacidification treatment includes soaking the crushed acidic coal gangue in a soaking tank for a certain period of time and then transferring it to a washing tank, washing it to neutrality and collecting it to obtain deacidified coal gangue.

7. The ecological restoration method for acidic coal gangue heap according to claim 1, characterized in that: In step S4, the corresponding repair parameters in the optimal repair scheme include the thickness of the covering material, the particle size of the deacidified coal gangue, and the mixing ratio of coal gangue and loess in the covering material; the shaped acidic coal gangue mountain is covered and oxygen-isolating repaired according to the repair parameters.

8. The ecological restoration method for acidic coal gangue heap according to claim 1, characterized in that: In step S4, the ecological restoration includes planting shrubs on the covered acidic coal gangue mountain terrace surface and laying ecological vegetation bags on the slope surface. In order to enhance the stability of the coal gangue mountain slope and reduce rainwater erosion of the slope foot, it is necessary to install protective anchor frames, drainage troughs and gangue retaining walls.

9. The ecological restoration method for acidic coal gangue heap according to claim 8, characterized in that: The ecological planting bag is made of degradable material, and the materials contained in the ecological planting bag are seeds, mixed matrix, organic fertilizer, water retention agent, plant growth promoting agent, and composite microbial agent; An anchor frame is installed around the ecological vegetation bag and reinforced on the slope of the coal gangue mountain to prevent the vegetation belt from slipping; The drainage trough is installed at the angle between the slope surface of the coal gangue mountain and the step surface. At the same time, a drainage trough is set along the slope surface to connect the drainage troughs of each step surface; the retaining wall is placed at the foot of the coal gangue mountain, and the retaining wall is cast with cement around the foot of the coal gangue mountain.

10. The ecological restoration method for acidic coal gangue heap according to claim 1, characterized in that: Step S4 also includes intelligent maintenance. The specific steps are to build an intelligent monitoring system. By burying distributed fiber optic sensors on the repaired coal gangue mountain, multiple intelligent monitoring points are set up to observe the status of the coal gangue mountain from the end of construction to the formation of the vegetation community. Depending on the situation, work including vegetation replanting, topdressing, watering, and pest and disease control is carried out to promote the self-succession of the vegetation ecosystem.

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