Numerical simulation method for forming process of acidic pit water in tailings pond stacking area

Abstract

The invention discloses a numerical simulation method for a forming process of acidic pit water in a tailing pond stacking area, which is characterized in that a chemical reaction system for sulfide mineral oxidation and secondary mineral dissolution / precipitation is constructed based on a reactive solute migration mechanism in the forming process of the acidic pit water in a tailing pond; further, a reaction migration model suitable for the formation process of the acid mine wastewater is established, a reactive solute migration model of unsaturated-saturated two-phase flow is constructed by adopting a PFLOTRAN program, and water-gas two-phase flow and water chemical evolution characteristics in the formation process of the acid mine wastewater in a tailing pile are finely simulated; the influence of mineral dissolution / precipitation on pore water chemical conditions is analyzed. According to the invention, the formation and migration process of acidic water in the mine environment can be simulated and predicted, and support is provided for acidic mine wastewater pollution control and restoration strategy formulation.

Description

Technical Field

[0001] This invention belongs to the field of simulation and prediction technology of mine environmental pollution processes, and relates to a numerical simulation method for the formation process of acidic mine water in tailings dam dumping areas. Specifically, it relates to a reaction transport numerical simulation method based on water-gas two-phase flow for the formation process of acidic mine water in tailings dam dumping areas. Background Technology

[0002] Acidic mine water is one of the most serious water environment problems caused by mining activities. Its formation involves water-air two-phase flow, sulfide mineral oxidation, secondary mineral precipitation, and microbial activity, making it a prominent water environment problem resulting from the coupling of multiple fields of water, rock, and microorganisms. Pyrite is the most common sulfide mineral. Under the combined action of oxygen, water, and microorganisms (such as *Thiobacillus ferrooxidans*), it undergoes a series of geochemical reactions, ultimately generating acidic mine water characterized by low pH, high sulfate content, and various heavy metal ions, causing serious and long-term pollution to surrounding soil, groundwater, and ecosystems. Therefore, the key to solving water environment problems caused by mining activities lies in simulating the acid-producing process of sulfide minerals in tailings heaps.

[0003] Multiphase and multicomponent reactive solute transport simulation is a core numerical method for studying and predicting the migration and transformation of pollutants in underground environments. Compared to traditional models, this method can simultaneously characterize the flow of multiphase fluids, the migration of multiple chemical components, and the dynamic coupling processes of complex biogeochemical reactions. However, when simulating actual site pollution processes, the water-rock-microbe interactions, reaction kinetic parameters, and multi-process coupling mechanisms involved are difficult to directly observe and accurately quantify using field monitoring techniques. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a numerical simulation method that can accurately simulate and predict the formation process of acidic mine water in tailings dam dumping areas.

[0005] Technical solution: The present invention provides a numerical simulation method for the formation process of acidic mine water in tailings dam dumping areas, comprising:

[0006] (1) Collect basic data on the tailings dam dumping area and construct a conceptual model for the formation of acidic mine water in tailings dumps under water-gas two-phase flow conditions;

[0007] (2) Based on the basic data collected in step (1), combined with the mineral composition and structural characteristics of the tailings pile, and based on the law of conservation of mass and energy and Darcy's law of multiphase flow, establish a water-gas two-phase flow model for the tailings pile;

[0008] (3) Determine the initial conditions, boundary conditions, hydrogeological conditions and model parameters, source and sink terms of the tailings heap water-gas two-phase flow model, and carry out spatial grid division and temporal discretization of the simulation area;

[0009] (4) Solve the tailings pile water-gas two-phase flow model to simulate the groundwater flow field, saturation and velocity distribution under steady flow conditions, and the gas and water phase saturation distribution, oxygen partial pressure, pH value and concentration field in the tailings pile under atmospheric precipitation infiltration conditions.

[0010] (5) Based on the water-gas two-phase flow simulation in step (4), based on the convection-dispersion migration mechanism and hydrogeochemical reaction process of the oxidative dissolution products of sulfide minerals, mainly pyrite, in the tailings pore medium, a reaction transport model for the formation process of acidic mine water in the tailings dam stacking area is constructed.

[0011] (6) Determine the chemical reaction network of the formation process of acidic mine water, including the geochemical reactions of pyrite and secondary minerals, and the kinetically controlled oxidation process of pyrite, which includes... Thermodynamic and kinetic processes of oxidation;

[0012] (7) Based on the basic data collected in step (1), determine the reaction kinetics and thermodynamic parameters of the acid mine water formation process, the initial conditions, boundary conditions, dispersion and source-sink terms of the water-gas two-phase flow model, as well as the initial and boundary concentrations of the simulated components, the initial volume fractions and chemical equilibrium constants of the main minerals and secondary minerals, and the kinetic rate equations and reaction constants of different oxidation pathways of pyrite in the reaction transport model of the acid mine water formation process in the tailings dam stacking area.

[0013] (8) Solve the reaction and transport model of the formation process of acidic mine water in the tailings dam stacking area, obtain the spatial distribution of water and gas phase saturation, pH change, dissolved oxygen, dissolved iron, sulfate concentration field and secondary mineral volume fraction on the vertical profile of the tailings pile during the simulation period, analyze the concentration changes of the main components under different oxidation paths, and realize the reaction and transport simulation of the formation process of acidic mine water in the tailings dam stacking area.

[0014] Furthermore, in step (1), the basic data includes site geometry and spatial discrete data, aquifer thickness, phreatic depth, top infiltration recharge flow rate, initial and boundary water chemical composition and concentration conditions, and top and bottom boundary conditions.

[0015] Furthermore, in step (2), the mineral composition and structural characteristics of the tailings pile include the initial mineral composition and content, the initial volume fraction of key reactive minerals and the medium structure model, pore structure parameters and the division of unsaturated and saturated zones.

[0016] Furthermore, in step (3), the initial conditions include the initial head distribution, initial saturation and initial solute concentration; the boundary conditions include the head and flow rate of the simulated region boundary; the hydrogeological parameters include porosity, permeability and density; and the model parameters include the relative permeability model, the capillary pressure function model and the diffusion coefficients of the water phase and the gas phase.

[0017] Furthermore, in step (4), the unsaturated-saturated two-phase flow multi-component reactive solute transport simulation program PFLOTRAN is used to solve the tailings pile water-gas two-phase flow model.

[0018] Furthermore, in step (5), the reaction transport model for the formation of acidic mine water uses a mass balance equation to describe the migration process of multi-component reactive solutes:

[0019] (1)

[0020] in, Indicates time; Indicates the water phase saturation, [ ]; Indicates porosity; It is divergence; It is the gradient; Indicates gas phase saturation, [ ]; Indicates components The total concentration in the aqueous phase, [ ]; Indicates components The total concentration in the gas phase, [ ]; Indicates flux; It is the dispersion coefficient tensor of the aqueous phase component, [ ]; It is the dispersion coefficient tensor of the gas phase component, [ Source and sink items This indicates the effects of aqueous phase reactions and precipitation / dissolution reactions on... . contributions.

[0021] Further, step (6) includes: determining the kinetic and equilibrium reaction processes of the reaction transport model for the formation of acidic mine water, including:

[0022] (6-1) Determine the chemical reaction formulas of the major and secondary minerals.

[0023] (2)

[0024] (3)

[0025] (4)

[0026] (5)

[0027] (6)

[0028] (7)

[0029] (8)

[0030] (9)

[0031] (10)

[0032] (11)

[0033] (6-2) Determine the chemical reaction formulas for different oxidation reactions of pyrite.

[0034] (12)

[0035] (13)

[0036] (14)

[0037] (6-3) Establish a thermodynamic database for precipitation / dissolution equilibrium reactions

[0038] Based on the main mineral and gas composition, the precipitation / dissolution reaction process of simulated components and minerals during the formation of acidic mine water is determined. Based on the geochemical reaction database, the corresponding equilibrium reaction constants are obtained, and a thermodynamic database of the formation process of acidic mine water is constructed to calculate the migration process of reactive solutes involved in the simulated component forms and precipitation / dissolution.

[0039] (6-4) Establish the rate equation for the kinetic reaction.

[0040] Based on the pyrite reaction kinetic equation and the mineral kinetic process based on transition state theory, the different oxidation processes in which pyrite participates and the rate equations for the precipitation / dissolution reactions of secondary minerals are determined.

[0041] Furthermore, the established kinetic reaction rate expression includes:

[0042] Pyrite oxidation kinetics: Select the corresponding reaction kinetic rate equations based on different oxidation and dissolution pathways of pyrite.

[0043] The kinetic rate expression for the oxidation of pyrite by dissolved oxygen is as follows:

[0044] (15)

[0045] in, It is the reaction constant, [ ];

[0046] The kinetic rate expression for the oxidation of ferrous ions is as follows:

[0047] (16)

[0048] in, It is the reaction constant, [ ];

[0049] The kinetic rate expression for the oxidation of pyrite by ferric ions is as follows:

[0050] (17)

[0051] in, It is the reaction constant, [ ].

[0052] Furthermore, in step (8), the reaction transport model of the formation process of acidic mine water in the tailings dam stacking area is solved. The finite volume method in the saturated-unsaturated multi-component reactive solute migration simulation program PFLOTRAN is used for spatial discretization, and the Newton iteration method is used to solve the discretized nonlinear equation system. At the same time, the reaction transport model describing the formation process of acidic mine water is embedded into the PFLOTRAN program to realize the numerical simulation of multiphase multi-component reactive solute transport.

[0053] This invention is based on the numerical simulation program PFLOTRAN and the constructed water-gas two-phase flow reaction transport model. It comprehensively considers the dynamic buffering of pH by multiple oxidation pathways with pyrite as the main mineral and the precipitation / dissolution reactions of secondary minerals (such as chalcopyrite, ferrihydrite, and calcite). It achieves accurate simulation and quantitative analysis of the entire process of formation, evolution, and natural decay potential of acidic mine water in tailings heaps.

[0054] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The present invention explores the spatiotemporal variation characteristics of dissolved oxygen, pH and sulfate during the formation of acidic mine water in tailings heaps based on numerical models. By constructing a model that couples water-gas two-phase flow with reaction transport, it can analyze the acid production mechanism and biogeochemical reaction process of tailings heaps, providing scientific basis and technical support for the analysis of the formation and migration of acidic mine water under actual site conditions. Attached Figure Description

[0055] Figure 1 This is a flowchart of a numerical simulation method for the formation process of acidic mine water in a tailings dam dumping area, provided by an embodiment of the present invention.

[0056] Figure 2This is a conceptual model diagram of a vertical one-dimensional acidic mine water in an embodiment of the present invention;

[0057] Figure 3 These are the vertical concentration profiles of the main components in different oxidation processes of pyrite in the embodiments of the present invention, wherein (a) is the vertical concentration profile of the main components in the oxidation process of pyrite by dissolved oxygen, and (b) is the vertical concentration profile of the main components in all oxidation processes of pyrite.

[0058] Figure 4 This is a vertical one-dimensional concentration profile of the main reaction and product components during the dissolution-precipitation reaction of pyrite with calcite and secondary minerals in the embodiments of the present invention, wherein (a) is a water phase and gas phase saturation diagram, (b) is an oxygen partial pressure diagram, (c) is a pH change diagram, (d) is a sulfate concentration change diagram, (e) is a dissolved iron concentration change diagram, and (f) is a volume fraction diagram of reaction components and secondary minerals.

[0059] Figure 5 This is a conceptual model diagram of a two-dimensional cross-section of acidic mine water in an embodiment of the present invention;

[0060] Figure 6 These are two-dimensional cross-sectional diagrams of groundwater flow field, saturation, and velocity distribution in this embodiment of the invention, wherein (a) is a groundwater flow field distribution diagram, (b) is a saturation distribution diagram, and (c) is a velocity distribution diagram;

[0061] Figure 7 This is a diagram showing the migration process of pH over 0.2, 5, and 10 years in a two-dimensional profile according to an embodiment of the present invention.

[0062] Figure 8 This is a two-dimensional cross-section in the embodiment of the present invention. Migration process diagrams for 0.2, 5, and 10 years;

[0063] Figure 9 This is a two-dimensional cross-section in the embodiment of the present invention. Migration process diagrams for 0.2, 5, and 10 years;

[0064] Figure 10 The figures are graphs showing the changes in dissolved oxygen consumption and sulfate generation during tailings heap leaching in this embodiment of the invention, where (a) is a graph showing the changes in dissolved oxygen consumption and (b) is a graph showing the changes in sulfate generation. Detailed Implementation

[0065] The invention will now be further described with reference to the accompanying drawings.

[0066] like Figure 1 As shown in the figure, this invention provides a numerical simulation method for the formation process of acidic mine water in tailings dam dumping areas, comprising the following steps:

[0067] (1) Collect basic data of the tailings dam dump area and construct a conceptual model of the formation of acidic mine water in the tailings dam under water-air two-phase flow conditions. The basic data include site geometry and spatial discrete data, aquifer thickness, phreatic water depth, top infiltration recharge flow rate, initial and boundary water chemical composition and concentration conditions, and top and bottom boundary conditions.

[0068] (2) Based on the basic data collected in step (1), and combined with the mineral composition and structural characteristics of the tailings pile, a water-gas two-phase flow model of the tailings pile is established based on the law of conservation of mass and energy and Darcy's law for multiphase flow. The mineral composition and structural characteristics of the tailings pile include the initial mineral composition and content, the initial volume fraction of key reactive minerals and the medium structure model, pore structure parameters and the division of unsaturated and saturated zones.

[0069] (3) Determine the initial conditions, boundary conditions, hydrogeological parameters, and source-sink terms of the tailings heap water-gas two-phase flow model, and carry out spatial grid division and temporal discretization of the simulation area. The initial conditions include the initial head distribution, initial saturation, and initial solute concentration; the boundary conditions include the head and flow rate at the boundary of the simulation area; the hydrogeological parameters include porosity, permeability, and density; the model parameters include the relative permeability model, the capillary pressure function model, and the diffusion coefficients of the water and gas phases.

[0070] (4) The unsaturated-saturated two-phase flow multi-component reactive solute transport simulation program PFLOTRAN was used to solve the tailings pile water-gas two-phase flow model to simulate the groundwater flow field, saturation and velocity distribution under steady flow conditions, and the gas and water phase saturation distribution, oxygen partial pressure, pH value and concentration field in the tailings pile under atmospheric precipitation infiltration conditions.

[0071] (5) Based on the water-air two-phase flow simulation in step (4), a reaction transport model for the formation process of acidic mine water in the tailings dam stacking area is constructed based on the convection-dispersion migration mechanism and hydrogeochemical reaction process of the oxidative dissolution products of sulfide minerals, mainly pyrite, in the pore medium of tailings.

[0072] A reactive transport model for the formation of acidic mine water is proposed, using a mass balance equation to describe the migration of multi-component reactive solutes.

[0073] (1)

[0074] in, Indicates time; Indicates the water phase saturation, [ ]; Porosity is the ratio of pore volume to total volume in a porous medium. It is a dimensionless parameter and typically takes a value between 0 and 1. It is the divergence, which acts on the vector field and represents the net outflow. It is the gradient, acting on a scalar field, representing the rate of change in space; Indicates gas phase saturation, [ ]; Indicates components The total concentration in the aqueous phase, [ ]; Indicates components The total concentration in the gas phase, [ ]; Indicates flux; It is the dispersion coefficient tensor of the aqueous phase component, [ ]; It is the dispersion coefficient tensor of the gas phase component, [ Source and sink items This indicates the effects of aqueous phase reactions and precipitation / dissolution reactions on... . contributions.

[0075] (6) Determine the chemical reaction network of the formation process of acidic mine water, including the geochemical reactions of pyrite and secondary minerals, and the kinetically controlled oxidation process of pyrite, which includes... Thermodynamic and kinetic reaction processes such as oxidation.

[0076] The kinetics and equilibrium reaction processes of the reaction transport model for the formation of acidic mine water were determined, including:

[0077] (6-1) Determine the chemical reaction formulas of the major and secondary minerals.

[0078] (2)

[0079] (3)

[0080] (4)

[0081] (5)

[0082] (6)

[0083] (7)

[0084] (8)

[0085] (9)

[0086] (10)

[0087] (11)

[0088] (6-2) Determine the chemical reaction formulas for different oxidation reactions of pyrite.

[0089] (12)

[0090] (13)

[0091] (14)

[0092] (6-3) Establish a thermodynamic database for precipitation / dissolution equilibrium reactions

[0093] Based on the main mineral and gas composition, the precipitation / dissolution reaction process of simulated components and minerals during the formation of acidic mine water is determined. Based on the geochemical reaction database, the corresponding equilibrium reaction constants are obtained, and a thermodynamic database of the formation process of acidic mine water is constructed to calculate the migration process of reactive solutes involved in the simulated component forms and precipitation / dissolution.

[0094] (6-4) Establish the rate equation for the kinetic reaction.

[0095] Based on the pyrite reaction kinetic equation and the mineral kinetic process based on transition state theory, the different oxidation processes in which pyrite participates and the rate equations for the precipitation / dissolution reactions of secondary minerals are determined.

[0096] Specifically, the established kinetic reaction rate expression includes:

[0097] Pyrite oxidation kinetics: Select the corresponding reaction kinetic rate equations based on different oxidation and dissolution pathways of pyrite.

[0098] The kinetic rate expression for the oxidation of pyrite by dissolved oxygen is as follows:

[0099] (15)

[0100] in, It is the reaction constant, [ ]; here Value ;

[0101] The kinetic rate expression for the oxidation of ferrous ions is as follows:

[0102] (16)

[0103] in, It is the reaction constant, [ ]; here Value ;

[0104] The kinetic rate expression for the oxidation of pyrite by ferric ions is as follows:

[0105] (17)

[0106] in, It is the reaction constant, [ ]; here Value .

[0107] (7) Based on the basic data collected in step (1), determine the reaction kinetics and thermodynamic parameters of the acid mine water formation process, the initial conditions, boundary conditions, dispersion and source-sink terms of the water-gas two-phase flow model, as well as the initial and boundary concentrations of the simulated components, the initial volume fractions and chemical equilibrium constants of the main minerals and secondary minerals, and the kinetic rate equations and reaction constants of different oxidation pathways of pyrite.

[0108] (8) Solve the reaction and transport model of the formation process of acidic mine water in the tailings dam stacking area, obtain the spatial distribution of water and gas phase saturation, pH change, dissolved oxygen, dissolved iron, sulfate concentration field and secondary mineral volume fraction on the vertical profile of the tailings pile during the simulation period, analyze the concentration changes of the main components under different oxidation paths, and realize the reaction and transport simulation of the formation process of acidic mine water in the tailings dam stacking area.

[0109] A reaction transport model for the formation process of acidic mine water in tailings dam dumping areas was developed. The finite volume method in the saturated-unsaturated multi-component reactive solute migration simulation program PFLOTRAN was used for spatial discretization, and the Newton-Raphson iteration method was used to solve the discretized nonlinear equations. At the same time, the reaction transport model describing the formation process of acidic mine water was embedded into the PFLOTRAN program to achieve numerical simulation of multiphase and multi-component reactive solute transport.

[0110] The numerical simulation method provided in this invention, based on the reactive solute migration mechanism in the formation of acidic mine water, constructs a multi-pathway redox reaction system with pyrite as the main mineral and a secondary mineral dissolution / precipitation reaction system, thereby establishing a kinetic reaction model suitable for simulating the formation process of acidic mine water. This kinetic reaction model is then embedded into the PFLOTRAN program, a simulation program for water-gas two-phase flow and multi-component reactive transport, to refine the simulation of the water-gas two-phase flow and hydrochemical evolution characteristics during the formation of acidic mine water in tailings heaps. The buffering effect of the mineral dissolution-precipitation sequence on pH is analyzed, allowing for a deeper evaluation of the acid production contribution and natural decay potential of different oxidation pathways. Therefore, this invention can simulate and predict the long-term evolution of acidic mine water formation and migration in tailings heaps, providing technical support for the formulation of source control and remediation strategies for acidic mine wastewater pollution, and has broad application prospects.

[0111] Here is a specific example.

[0112] This example simulates the formation process of acidic mine water in tailings piles at the site scale. It implements a refined simulation that comprehensively considers processes such as water-gas two-phase flow, pyrite oxidation, and secondary mineral precipitation. It mainly includes two parts: 1) defining the kinetic reaction model for the formation of acidic mine water; 2) simulating the water-gas two-phase flow and solute migration in the formation process of acidic mine water in tailings piles.

[0113] 1) Define the kinetic reaction model for the formation of acidic mine water.

[0114] First, regarding the core reaction of pyrite oxidation, three different oxidation pathways are considered. The three oxidation pathways of pyrite are shown in Table 1, mainly including the parallel reaction pathways of pyrite oxidation by dissolved oxygen, ferrous ions oxidation to ferric ions, and pyrite oxidation by ferric ions, as well as the formation of acidic mine water and the migration and transformation of major components.

[0115] Table 1. Three oxidation pathways of pyrite

[0116]

[0117] The reaction rates of different oxidation pathways are described using reaction kinetic formulas. Pyrite is... The rate of oxidation and The concentration to the power of 0.5 and The concentration is proportional to the -0.11th power; the rate of ferrous ion oxidation is... and The concentration of pyrite is directly proportional to its concentration; pyrite is The rate of oxidation and Concentration to the power of 0.93 and The concentration is proportional to the -0.4 power. The main reaction kinetic parameters and reaction constants are shown in Table 2.

[0118] Table 2. Main reaction kinetic parameters and reaction constants

[0119]

[0120] The study comprehensively considered the potential precipitation of secondary minerals under acidic water conditions, including jaundice, ferruginous iron oxide, gibbsite, and calcite. The precipitation / dissolution reactions of the minerals were primarily simulated using the local equilibrium assumption. Reaction rate calculations employed mineral kinetic equations based on transition state theory, and the equilibrium constants were derived from standard thermodynamic databases. Detailed mineral chemical reaction equations and their equilibrium constants are shown in Table 3.

[0121] Table 3 Chemical reaction formulas and equilibrium constants of major and secondary minerals

[0122]

[0123] 2) Simulation of water-gas two-phase flow and solute migration during the formation process of acidic mine water in tailings heaps

[0124] Based on the aforementioned kinetic reaction model, one-dimensional vertical and two-dimensional cross-sectional conceptual models were constructed to simulate the formation and migration of acidic water in tailings piles. The one-dimensional vertical example simulates a homogeneous isotropic medium with a two-dimensional xz cross-section. The aquifer thickness is set to 10m, divided into 100 grids, with a groundwater depth of 4m. This is generalized as a porous medium water-gas two-phase flow model with infiltration recharge at the top. The top boundary is a fixed atmospheric pressure boundary. Pa, the fixed pressure at the bottom boundary is Pa. Rainfall infiltrates uniformly, with an infiltration rate of [value missing]. m / s. A conceptual model of vertical one-dimensional acidic mine water is as follows: Figure 2 As shown in the figure, the model does not consider temperature changes and is set to a constant temperature of 25℃. The concentrations of groundwater chemical components at the initial and infiltration boundaries are shown in Table 4.

[0125] Table 4. Concentration of groundwater chemical components at the initial and infiltration boundaries

[0126]

[0127] One-dimensional vertical case: The one-dimensional case considers the geochemical reactions of pyrite as the main mineral, calcite, and other secondary minerals. To compare the impact of different oxidation pathways on the formation of acidic mine water, simulations were first performed considering only the pyrite oxidation pathway by dissolved oxygen and the pathway considering all pyrite oxidation pathways, without considering the buffering reactions of other minerals. For example... Figure 3 As shown, the simulation predicted the vertical concentration changes of the main components under different reaction pathways in years 1, 3, and 5. It shows that considering the three oxidation reaction pathways, the formation process of acidic mine water tends to produce lower pH values ​​and higher sulfate and dissolved iron concentrations. In actual acid production, microbial-mediated oxidation significantly increases the kinetic reaction rate of the chain reaction pathway. This example also considers the dissolution / precipitation reaction processes of pyrite with typical minerals such as calcite and secondary minerals, such as... Figure 4 As shown, the vertical one-dimensional concentration changes of the main reactions and product components during the formation of acidic water reveal that a series of mineral dissolution / precipitation reactions create a step-like pH buffer zone. In the pH range below 2, secondary precipitation of jaundice and ferrous sulfate is the main component, while at around pH 5, the main component is... Precipitation in the form of gibbsite; The concentration profile variation of dissolved Fe is mainly controlled by the oxidation and dissolution of pyrite and its dissolution / precipitation reactions with secondary minerals, in the unsaturated zone. The concentration rose rapidly, near the diving level The concentration gradient slows down. The migration of [the substance] is mainly controlled by its reaction with calcite, and it readily reacts with soluble [substances]. Secondary minerals are formed.

[0128] Two-dimensional profile case: Based on the parameters and reaction networks in Tables 2 and 3, a two-dimensional profile is constructed to show how oxygen-laden precipitation infiltrates into the waste rock pile during rainfall infiltration, subsequently reacting with pyrite in acidic water, forming a reactive solute migration process in acidic groundwater. For example... Figure 5 The diagram shown is a conceptual model of a two-dimensional cross-section of acidic mine water. The aquifer is a phreatic aquifer, 100m long and 20m thick, vertically recharged by rainfall infiltration at a rate of 300mm / year. Lateral runoff flows from left to right, with the left side being the impermeable boundary, the right side being the given head boundary at 15m, and the bottom boundary being the impermeable boundary. Figure 6 This paper presents groundwater flow field, saturation, and velocity distribution under steady-flow conditions obtained from a two-dimensional model. Based on the groundwater flow field, the reactive migration process of acidic water was simulated and predicted over a 10-year period. The predicted pH, dissolved oxygen, and sulfate concentration profiles for years 0.2, 5, and 10 are shown. Figure 7 The diagram shows the pH migration process in a two-dimensional profile. Figure 8 Showing two-dimensional cross-section A diagram illustrating the migration process; Figure 9 Showing two-dimensional cross-section The migration process diagram. Figure 10 This study demonstrates the cumulative consumption of dissolved oxygen and the cumulative formation of sulfate during tailings leaching. As dissolved oxygen consumption gradually increases, the mass of sulfate produced by the rapid oxidation of pyrite increases synchronously. Building upon the aforementioned one-dimensional example, this model constructs a simulation model of acidic water formation during atmospheric precipitation infiltration into tailings pond waste rock piles under a two-dimensional profile. It analyzes the spatiotemporal evolution mechanisms of dissolved oxygen, pH, and sulfate, providing a quantifiable numerical simulation model for analyzing the acidic water formation process in tailings ponds under site conditions.

[0129] In summary, pyrite oxidation is the core geochemical process in the formation of acidic mine water, continuously generating high concentrations of sulfate, iron ions, and highly acidic water in tailings heaps, causing long-term pollution to downstream water and soil environments. However, neutral minerals such as calcite, present under natural conditions, can buffer acidic water through dissolution-precipitation reactions, forming a stepped pH buffer zone, thus slowing the spread of acidification to some extent. Simultaneously, bacterial sulfate reduction in anaerobic environments can consume some sulfate ions and produce sulfides, possessing certain potential for natural remediation. The occurrence of these processes strongly depends on various environmental factors, including oxygen transport, mineral composition, and microbial activity. The catalytic oxidation cycle of pyrite is a key mechanism for controlling acid production intensity, significantly enhancing acidification and pollutant release flux. If tailings lack sufficient acid buffering minerals, or if the oxidation rate far exceeds neutralization capacity, acidic water will rapidly form and continuously migrate downstream. Furthermore, the precipitation of secondary minerals (such as jaundice and ferrihydrite) alters the structural properties of the porous medium, potentially affecting the transport pathways and rates of water and solutes. Aquifer heterogeneity, infiltration recharge conditions, and initial mineral spatial distribution are important factors influencing the rate of acidic water formation, the spatial distribution of pollution plumes, and their natural decay potential. Therefore, accurately characterizing the reactive solute migration behavior of the water-gas-rock-microbe multi-process coupled system is crucial for predicting long-term environmental risks in mining areas and developing precise prevention and control strategies.

Claims

1. A numerical simulation method for the formation process of acidic mine water in tailings dam dumping areas, characterized in that, include: (1) Collect basic data on the tailings dam dumping area and construct a conceptual model for the formation of acidic mine water in tailings dumps under water-gas two-phase flow conditions; (2) Based on the basic data collected in step (1), combined with the mineral composition and structural characteristics of the tailings pile, and based on the law of conservation of mass and energy and Darcy's law of multiphase flow, establish a water-gas two-phase flow model for the tailings pile; (3) Determine the initial conditions, boundary conditions, hydrogeological conditions and model parameters, source and sink terms of the tailings heap water-gas two-phase flow model, and carry out spatial grid division and temporal discretization of the simulation area; (4) Solve the tailings pile water-gas two-phase flow model to simulate the groundwater flow field, saturation and velocity distribution under steady flow conditions, and the gas and water phase saturation distribution, oxygen partial pressure, pH value and concentration field in the tailings pile under atmospheric precipitation infiltration conditions. (5) Based on the water-gas two-phase flow simulation in step (4), based on the convection-dispersion migration mechanism and hydrogeochemical reaction process of the oxidative dissolution products of sulfide minerals, mainly pyrite, in the tailings pore medium, a reaction transport model for the formation process of acidic mine water in the tailings dam stacking area is constructed. (6) Determine the chemical reaction network of the formation process of acidic mine water, including the geochemical reactions of pyrite and secondary minerals, and the kinetically controlled oxidation process of pyrite, which includes... Thermodynamic and kinetic processes of oxidation; (7) Based on the basic data collected in step (1), determine the reaction kinetics and thermodynamic parameters of the acid mine water formation process, the initial conditions, boundary conditions, dispersion and source-sink terms of the water-gas two-phase flow model, as well as the initial and boundary concentrations of the simulated components, the initial volume fractions and chemical equilibrium constants of the main minerals and secondary minerals, and the kinetic rate equations and reaction constants of different oxidation pathways of pyrite in the reaction transport model of the acid mine water formation process in the tailings dam stacking area. (8) Solve the reaction and transport model of the formation process of acidic mine water in the tailings dam stacking area, obtain the spatial distribution of water and gas phase saturation, pH change, dissolved oxygen, dissolved iron, sulfate concentration field and secondary mineral volume fraction on the vertical profile of the tailings pile during the simulation period, analyze the concentration changes of the main components under different oxidation paths, and realize the reaction and transport simulation of the formation process of acidic mine water in the tailings dam stacking area.

2. The numerical simulation method for the formation process of acidic mine water in tailings dam dumping areas according to claim 1, characterized in that, In step (1), the basic data includes site geometry and spatial discrete data, aquifer thickness, phreatic depth, top infiltration recharge flow rate, initial and boundary water chemical composition and concentration conditions, and top and bottom boundary conditions.

3. The numerical simulation method for the formation process of acidic mine water in tailings dam dumping areas according to claim 1, characterized in that, In step (2), the mineral composition and structural characteristics of the tailings pile include the initial mineral composition and content, the initial volume fraction of key reactive minerals and the medium structure model, pore structure parameters and the division of unsaturated and saturated zones.

4. The numerical simulation method for the formation process of acidic mine water in tailings dam dumping areas according to claim 1, characterized in that, In step (3), the initial conditions include the initial head distribution, initial saturation and initial solute concentration; the boundary conditions include the head and flow rate of the simulated region boundary; the hydrogeological parameters include porosity, permeability and density; the model parameters include the relative permeability model, the capillary pressure function model and the diffusion coefficients of the water phase and the gas phase.

5. The numerical simulation method for the formation process of acidic mine water in tailings dam dumping areas according to claim 1, characterized in that, In step (4), the PFLOTRAN simulation program for multi-component reactive solute transport in unsaturated-saturated two-phase flow is used to solve the tailings pile water-gas two-phase flow model.

6. The numerical simulation method for the formation process of acidic mine water in tailings dam dumping areas according to claim 1, characterized in that, In step (5), the reaction transport model for the formation of acidic mine water uses a mass balance equation to describe the migration process of multi-component reactive solutes: (1) in, Indicates time; Indicates the water phase saturation, [ ]; Indicates porosity; It is divergence; It is the gradient; Indicates gas phase saturation, [ ]; Indicates components The total concentration in the aqueous phase, [ ]; Indicates components The total concentration in the gas phase, [ ]; Indicates flux; It is the dispersion coefficient tensor of the aqueous phase component, [ ]; It is the dispersion coefficient tensor of the gas phase components, [ Source and sink items This indicates the effects of aqueous phase reactions and precipitation / dissolution reactions on... . contributions.

7. The numerical simulation method for the formation process of acidic mine water in tailings dam dumping areas according to claim 1, characterized in that, Step (6) includes: determining the kinetic and equilibrium reaction processes of the reaction transport model for the formation of acidic mine water, including: (6-1) Determine the chemical reaction formulas of the major and secondary minerals. (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (6-2) Determine the chemical reaction formulas for different oxidation reactions of pyrite. (12) (13) (14) (6-3) Establish a thermodynamic database for precipitation / dissolution equilibrium reactions Based on the main mineral and gas composition, the precipitation / dissolution reaction process of simulated components and minerals during the formation of acidic mine water is determined. Based on the geochemical reaction database, the corresponding equilibrium reaction constants are obtained, and a thermodynamic database of the formation process of acidic mine water is constructed to calculate the migration process of reactive solutes involved in the simulated component forms and precipitation / dissolution. (6-4) Establish the rate equation for the kinetic reaction. Based on the pyrite reaction kinetic equation and the mineral kinetic process based on transition state theory, the different oxidation processes in which pyrite participates and the rate equations for the precipitation / dissolution reactions of secondary minerals are determined.

8. The numerical simulation method for the formation process of acidic mine water in tailings dam dumping areas according to claim 7, characterized in that, The established kinetic reaction rate expressions include: Pyrite oxidation kinetics: Select the corresponding reaction kinetic rate equations based on different oxidation and dissolution pathways of pyrite. The kinetic rate expression for the oxidation of pyrite by dissolved oxygen is as follows: (15) in, It is the reaction constant, [ ]; The kinetic rate expression for the oxidation of ferrous ions is as follows: (16) in, It is the reaction constant, [ ]; The kinetic rate expression for the oxidation of pyrite by ferric ions is as follows: (17) in, It is the reaction constant, [ ].

9. The numerical simulation method for the formation process of acidic mine water in the tailings dam dumping area according to claim 1, characterized in that, In step (8), the reaction transport model of the formation process of acidic mine water in the tailings dam stacking area is solved. The finite volume method in the saturated-unsaturated multi-component reactive solute migration simulation program PFLOTRAN is used for spatial discretization, and the Newton iteration method is used to solve the nonlinear equations after discretization. At the same time, the reaction transport model describing the formation process of acidic mine water is embedded into the PFLOTRAN program to realize the numerical simulation of multiphase multi-component reactive solute transport.

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