Microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites

Abstract

This invention relates to the field of soil pollution control technology, specifically to a microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites. It includes a supporting base layer, on which a leachate collection layer, a heavy metal passivation and isolation layer, a microbial reinforcement layer, and a plant growth layer are sequentially arranged. This invention organically integrates multi-layered structural units to form a spatially ordered structure of leachate drainage—heavy metal passivation—microbial loading—plant growth. It employs immobilized functional microbial agents and embeds multi-parameter sensing devices to establish a monitoring-feedback-control closed-loop system. Simultaneously, hyperaccumulating plants are planted and inoculated with arbuscular mycorrhizal fungi, achieving a shift from an open-loop passive mode to a closed-loop active collaborative mode, avoiding problems such as delayed remediation response, poor synergy, and insufficient long-term stability.

Description

Technical Field

[0001] This invention relates to the field of soil pollution control technology, and more specifically, to a microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites. Background Technology

[0002] In the remediation of heavy metal-contaminated soil in abandoned mining sites, on-site construction workers typically face complex conditions such as multi-metal complex pollution, the impact of acidic mine drainage, and difficulties in vegetation restoration. Taking an abandoned lead-zinc mine area as an example, the content of heavy metals such as lead, zinc, and cadmium in the soil often exceeds the soil environmental quality standards by several to dozens of times. Moreover, due to long-term weathering and leaching, the heavy metals are mainly in exchangeable and carbonate-bound forms, with high bioavailability, and are extremely easy to migrate and spread through surface runoff or infiltration.

[0003] For such sites, existing remediation technologies mainly include physicochemical remediation, phytoremediation, and microbial remediation. While physicochemical remediation is fast-acting, it involves large-scale engineering and is costly, and passivating materials are difficult to achieve long-term stabilization of heavy metals. Phytoremediation has the advantages of being environmentally friendly and cost-effective, but hyperaccumulating plants grow slowly, have small biomass, and have limited tolerance to high concentrations of heavy metal stress, resulting in remediation cycles that can take several to several decades. Microbial remediation (such as sulfate-reducing bacteria and iron-reducing bacteria) can reduce the activity of heavy metals through bioreduction precipitation or bioadsorption, but functional microorganisms are easily inactivated under acidic mine drainage conditions, lack immobilized carrier support, and the bacteria are severely lost with leachate, making it difficult to sustain the remediation effect. More importantly, in the existing construction technology system, the above-mentioned remediation methods are often implemented in a fragmented and step-by-step manner: construction workers usually first level the site, then directly till and apply passivating agents or inoculate microbial solutions, and then plant remediation plants. In this process, there is a lack of spatial order and functional synergy between heavy metal passivation materials, microbial agents, and plant roots. The passivation layer cannot effectively prevent the downward migration of heavy metals, the microorganisms have low survival rates due to the lack of a suitable carrier microenvironment, and the plant roots also find it difficult to form a stable symbiotic relationship with the microorganisms. At the same time, the entire remediation process lacks in-situ monitoring and feedback control methods. Construction workers can only rely on periodic sampling and testing to evaluate the remediation effect, and cannot obtain real-time information on the dynamic changes in soil pH, redox potential, heavy metal ion concentration, and microbial activity. Furthermore, it is impossible to adjust the amount of microbial agent supplementation, irrigation strategy, or nutrient solution ratio in a timely manner when abnormal conditions occur. This open-loop construction method leads to low remediation efficiency and repeated effects. Many remediation projects still fail to achieve the expected goals after several years of operation. In view of this, this invention proposes a microbial-plant co-remediation method for heavy metal contaminated soil in mining waste sites. Summary of the Invention

[0004] The purpose of this invention is to provide a microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites, in order to solve the problems mentioned in the background art, such as the fragmentation of existing remediation technologies, lack of spatial coordination and real-time feedback, resulting in low efficiency and repeated effects.

[0005] To address the above issues, a microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites is provided, comprising the following steps: S1: Conduct site investigation and base treatment for heavy metal contaminated areas in mine waste sites, remove surface debris, level and compact to form a supporting base surface; S2: On the supporting foundation surface, leachate drainage material, heavy metal passivation material, microbial loading material and plant growth substrate are laid sequentially from bottom to top to form a multi-layered repair structural unit; S3: Inject immobilized functional microbial agents into the microbial load material and embed in-situ monitoring and sensing devices between each layer of material to establish a closed-loop system of "monitoring-feedback-control". S4: Plant heavy metal hyperaccumulators in the plant growth substrate and inoculate them with arbuscular mycorrhizal fungi. Maintain water and fertilizer conditions through an intelligent regulation subsystem. Harvest the above-ground parts after the plants have grown to the maximum biomass stage. Repeat planting until the soil heavy metal content drops below the safe threshold. The repaired structure includes the following: a support base layer, on the upper side of which are arranged a leachate collection layer, a heavy metal passivation isolation layer, a microbial reinforcement layer, and a plant growth layer.

[0006] As a further improvement to this technical solution, immobilized microbial carrier particles are uniformly distributed within the microbial enhancement layer; Soil pH, redox potential, heavy metal ion concentration and microbial activity sensors are buried between each layer. The sensors are connected to a remote monitoring platform via a wireless transmission module.

[0007] As a further improvement to this technical solution, in step S3, the immobilized functional microbial agent is made by loading functional microbial communities onto a composite microbial carrier; The functional microbial community includes sulfate-reducing bacteria, iron-reducing bacteria, and plant growth-promoting bacteria, combined in a 2:1:1 ratio, with a bacterial concentration of 10. 8 CFU / mL; The composite microbial carrier is prepared by cross-linking mine tailings sand, biochar, sodium alginate and modified cellulose in a mass ratio of 3:4:2:1.

[0008] As a further improvement to this technical solution, in step S2, the heavy metal passivation isolation layer is made by mixing and pressing modified phosphate rock powder, limestone powder, iron-manganese oxide composite material and clay minerals in a mass ratio of 3:2:2:3, with a thickness of 10-20cm, and is used to adsorb, precipitate or convert heavy metal ions. The bottom of the leachate collection layer is equipped with a drainage pipe. The collected leachate is treated by an integrated sedimentation-adsorption-microbial degradation treatment device and then reused in the irrigation system.

[0009] As a further improvement to this technical solution, in step S4, the hyperaccumulating plants include at least one of the following: centipede grass, southeastern sedum, mineral-bearing sedum, and sea elm. Arbuscular mycorrhizal fungi are *Gymnospermum moses* or *Rhizospora endophyta*. The inoculation method involves uniformly mixing the mycorrhizalized seedling substrate into the plant growth layer, with an inoculation amount of 5%-10% of the plant growth layer volume.

[0010] As a further improvement to this technical solution, in step S3, the in-situ monitoring sensing device includes a soil pH electrode, a redox potential electrode, a heavy metal ion selective electrode, and a microbial activity electrode. Each sensor is arranged with a monitoring node in a 10m×10m grid, and the data acquisition frequency is once every 30 minutes. When the concentration of heavy metal ions is detected to be higher than the set threshold or the microbial activity decreases, the system automatically replenishes microbial agents or activates the electrochemical auxiliary remediation module through the intelligent control subsystem.

[0011] As a further improvement to this technical solution, the method also includes the use of a mobile operating platform, which integrates a soil crushing and screening device, a microbial agent atomizing spraying device, a plant seed strip sowing and covering device, a drip irrigation and nutrient solution replenishment device, and a GPS positioning and path planning system. The mobile operating platform sequentially completes the base surface treatment, fungicide spraying, plant sowing, and maintenance operations in steps S1 to S4.

[0012] As a further improvement to this technical solution, while maintaining the activity of the microbial community in the enhanced microbial layer, an intermittent sprinkler irrigation method is used to supplement the nutrient solution. The nutrient solution formula is: glucose 0.5g / L, ammonium sulfate 0.2g / L, potassium dihydrogen phosphate 0.1g / L, and trace element stock solution 1mL / L. During irrigation, the drip irrigation tape is used to evenly apply the solution to the plant growth layer.

[0013] As a further improvement to this technical solution, the thickness of the microbial reinforcement layer is 20-30 cm, the particle size of the immobilized microbial carrier particles is 2-5 mm, and the internal porosity of the carrier is 40%-60%. The permeability coefficient of the heavy metal passivation isolation layer is less than 1×10-6 cm / s, and the leachate collection layer is filled with gravel or ceramsite with a thickness of 10-15 cm.

[0014] As a further improvement to this technical solution, the method is particularly suitable for multi-metal composite pollution, acid mine drainage impact areas and mine wastelands where vegetation restoration is difficult. The resulting microbial-plant joint remediation structure has a synergistic effect mechanism during the remediation process. The method integrates the following innovative technologies: preparation technology of biological carrier materials based on mine tailings sand, microbial-plant-mineral synergistic remediation technology, in-situ monitoring and intelligent control technology integrating multi-source sensing devices, and modular and assembleable remediation structural unit design. The method, upon completion of construction, forms a composite restoration body consisting of a supporting foundation layer, a leachate collection layer, a heavy metal passivation and isolation layer, a microbial reinforcement layer, a plant growth layer, and an intelligent monitoring and control system.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In the microbial-phytoremediation method for heavy metal contaminated soil in the abandoned mine site, the shortcomings of existing remediation methods, such as fragmentation and lack of in-situ monitoring and closed-loop control, are addressed by organically integrating multi-level structural units to form a spatially ordered structure of leachate drainage, heavy metal passivation, microbial loading, and plant growth. Immobilized functional microbial agents are used and multi-parameter sensing devices are buried to establish a monitoring-feedback-control closed-loop system. Hyperaccumulating plants are planted simultaneously and arbuscular mycorrhizal fungi are inoculated, realizing the transformation from an open-loop passive mode to a closed-loop active collaborative mode, avoiding the problems of delayed remediation response, poor synergy, and insufficient long-term stability.

[0016] 2. In the microbial-phytoremediation method for heavy metal contaminated soil in the mine wasteland, the activity of the microbial community is maintained by intermittent sprinkler irrigation with nutrient solution, the carbon source is slowly released by the tailings sand-based carrier to prolong the action period of the microbial agent, the plant root exudates provide carbon source for the microorganisms, and the microbial metabolites promote plant growth, forming a positive feedback cycle. The leachate is treated and then reinjected to realize the recycling of water resources. This mechanism enables the remediation system to remain stable and efficient under harsh conditions such as acidic mine drainage. The ecological function of the mine wasteland is gradually restored through multiple planting-harvesting cycles. Attached Figure Description

[0017] Figure 1 This is a flowchart of the present invention; Figure 2 This is a schematic diagram of the overall structure of the present invention.

[0018] The meanings of the labels in the diagram are as follows: 1. Supporting base layer; 2. Leachate collection layer; 3. Heavy metal passivation and isolation layer; 4. Microbial reinforcement layer; 5. Plant growth layer; 6. Immobilized microbial carrier particles; 7. Sensor. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0021] Example 1 First, please refer to Figures 1-2 The purpose of this embodiment is to provide a microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites, including the following steps: S1: Conduct site investigation and surface treatment for heavy metal contaminated areas in mine wastelands, remove surface debris, level and compact to form a supporting foundation surface, specifically: A grid-based sampling survey was conducted in the mining area to identify the type and extent of heavy metal pollution. Subsequently, large pieces of waste rock and debris were removed from the surface, and the surface was leveled and compacted to form a support base with a suitable slope and no water accumulation, ensuring the stability and uniformity of subsequent structural layers. S2: On the supporting foundation surface, leachate drainage material, heavy metal passivation material, microbial loading material and plant growth substrate are laid sequentially from bottom to top to form a multi-layered repair structure unit. Each layer is laid continuously and the boundaries are tightly overlapped to form a spatially ordered multi-layered repair structure. S3: Inject immobilized functional microbial agents into the microbial load material and embed in-situ monitoring and sensing devices between each layer of material to establish a closed-loop system of "monitoring-feedback-control". Specifically: Inject the pre-prepared immobilized functional microbial agents evenly into the microbial load material, and then embed in-situ monitoring and sensing devices between each layer to collect soil environmental parameters in real time and upload them to a remote platform to establish a closed-loop system of automatic early warning and control. S4: Plant heavy metal hyperaccumulators in the plant growth substrate and inoculate them with arbuscular mycorrhizal fungi. Maintain water and fertilizer conditions through an intelligent control subsystem. Harvest the above-ground parts after the plants have grown to the maximum biomass stage. Repeat planting until the soil heavy metal content drops below the safe threshold. Maintain suitable soil moisture through a drip irrigation system and supplement nutrient solution as needed to promote plant and microbial growth. The repaired structure includes the following components: a support base layer 1, on which a leachate collection layer 2, a heavy metal passivation and isolation layer 3, a microbial reinforcement layer 4, and a plant growth layer 5 are sequentially arranged. This solves the core problems of disordered functional layers, open-loop repair process, and disconnection between plants and microorganisms in existing technologies. It achieves a chain-like synergistic repair process of heavy metal physical barrier control, chemical stabilization, biotransformation, and plant absorption, thereby improving repair efficiency and long-term effectiveness.

[0022] For further details, please refer to Figure 2 Immobilized microbial carrier particles 6 are evenly distributed within the microbial enhancement layer 4, utilizing the plant-microbe symbiotic relationship to achieve continuous absorption and removal of heavy metals. Soil pH, redox potential, heavy metal ion concentration and microbial activity sensors 7 are embedded between each layer. The sensors 7 are connected to the remote monitoring platform via a wireless transmission module, introducing in-situ multi-parameter sensing devices and intelligent feedback, enabling the remediation process to shift from experience-driven to data-driven.

[0023] And, please see Figure 1 In step S3, the immobilized functional microbial agent is made by loading functional microbial communities onto a composite microbial carrier. The functional microbial communities include sulfate-reducing bacteria, iron-reducing bacteria, and plant growth-promoting bacteria, which are compounded in a 2:1:1 ratio. Mine tailings sand is used as the carrier skeleton, biochar provides adsorption sites and carbon source, and sodium alginate and modified cellulose form a three-dimensional network structure to embed the microbial cells. Three bacterial communities work synergistically: sulfate-reducing bacteria produce sulfides to precipitate heavy metals; iron-reducing bacteria reduce iron and manganese oxides, releasing adsorbed heavy metals and promoting reduction conversion; and plant growth-promoting bacteria secrete substances such as indoleacetic acid to stimulate plant root growth. The bacterial solution concentration is 10. 8 The CFU / mL composite microbial carrier is prepared by cross-linking mine tailings sand, biochar, sodium alginate and modified cellulose in a mass ratio of 3:4:2:1. The carrier protects the microbial community from the impact of acidic mine drainage, while slowly releasing carbon source to maintain the metabolism of the microbial community.

[0024] For further details, please refer to Figures 1-2In step S2, the heavy metal passivation isolation layer 3 is made by mixing and pressing modified phosphate rock powder, limestone powder, iron-manganese oxide composite material and clay minerals in a mass ratio of 3:2:2:3, with a thickness of 10-20cm. It is used to adsorb, precipitate or convert heavy metal ions. The passivation isolation layer uses a combination of multiple minerals: phosphate rock powder forms phosphate precipitate with heavy metals, limestone powder neutralizes acidity and precipitates some metals, iron-manganese oxide fixes heavy metals through adsorption and co-precipitation, and clay minerals provide ion exchange and physical retention. This layer has an extremely low permeability coefficient, which effectively blocks the downward migration of heavy metals. The bottom of the leachate collection layer 2 is equipped with a drainage pipe. The collected leachate is treated by an integrated sedimentation-adsorption-microbial degradation treatment device and then reused in the irrigation system. The leachate treatment device integrates sedimentation, adsorption, and microbial degradation modules to realize water resource recycling, reduce the environmental risk of external discharge, and save water resources and reduce secondary pollution by re-injecting leachate, thereby improving the sustainability of the remediation project.

[0025] For further details, please refer to Figures 1-2 In step S4, the hyperaccumulating plants include at least one of the following: Sedum morganianum, Sedum spp., Sedum spp. var. spp., and Elsholtzia ciliata. The arbuscular mycorrhizal fungi are Gyrodactylus moses or Rhizospora moses. The inoculation method is to uniformly mix the mycorrhizal seedling substrate into the plant growth layer 5, with an inoculation amount of 5%-10% of the volume of the plant growth layer 5. The selected plants are all species with heavy metal hyperaccumulation or strong tolerance. Among them, Sedum morganianum has a significant enrichment capacity for arsenic, Sedum spp. for zinc / cadmium, Sedum spp. for cadmium / zinc, and Elsholtzia ciliata for copper. Arbuscular mycorrhizal fungi can form a symbiotic relationship with plant roots, and the mycelial network expands the root absorption range and secretes substances such as gyromycin to improve soil structure.

[0026] Secondly, please refer to Figures 1-2 In step S3, the in-situ monitoring sensing device includes a soil pH electrode, a redox potential electrode, a heavy metal ion selective electrode, and a microbial activity electrode. Each sensor 7 is arranged with a monitoring node in a 10m×10m grid. The data acquisition frequency is once every 30 minutes. When the concentration of heavy metal ions is detected to be higher than the set threshold or the microbial activity decreases, the system automatically replenishes microbial agents or activates the electrochemical auxiliary remediation module through the intelligent control subsystem. The microbial activity electrode can reflect the metabolic intensity of the microbial community in real time by measuring the redox current or impedance changes. The electrochemical auxiliary remediation module adopts a low-voltage DC electric field, which can promote the directional migration of heavy metal ions to the electrode and stimulate the metabolic activity of microorganisms. All data is wirelessly transmitted to the remote platform to realize unattended automatic control.

[0027] For further details, please refer to Figure 1The method also includes the use of a mobile work platform, which integrates a soil crushing and screening device, a microbial agent atomizing spraying device, a plant seed row sowing and covering device, a drip irrigation and nutrient solution replenishment device, and a GPS positioning and path planning system. This platform realizes the mechanization and automation of the entire construction process. The crushing and screening device can handle large rocks and debris in the mine wasteland, the atomizing spraying ensures that the microbial agent is evenly distributed in the microbial reinforcement layer 4, the row sowing device precisely controls the sowing amount and row spacing, the drip irrigation system provides zoned control, and the GPS path planning avoids repetition or omission. All devices are integrated on the same chassis, completing multiple processes at once. In steps S1 to S4, the mobile work platform sequentially completes the base treatment, microbial agent spraying, plant sowing, and maintenance operations.

[0028] For further details, please refer to Figure 2 While maintaining the activity of the microbial community in the microbial enhancement layer 4, nutrient solution was supplemented by intermittent sprinkler irrigation. The nutrient solution formula was: glucose 0.5g / L, ammonium sulfate 0.2g / L, potassium dihydrogen phosphate 0.1g / L, and trace element stock solution 1mL / L. During irrigation, the nutrient solution was evenly applied to the plant growth layer 5 through the drip irrigation tape. The nutrient solution provided exogenous carbon, nitrogen, and phosphorus sources for the functional microorganisms, maintaining the metabolic activity of the microbial community. The intermittent sprinkler irrigation simulated the natural rainfall rhythm, avoiding the anaerobic environment or microbial loss caused by continuous irrigation. The drip irrigation tape mainly applied the nutrient solution to the plant growth layer 5, which not only met the needs of the plants, but also indirectly supplied the microorganisms through root exudates, reducing the direct erosion of the microbial enhancement layer 4. Furthermore, the thickness of the microbial reinforcement layer 4 is 20-30 cm, the particle size of the immobilized microbial carrier particles 6 is 2-5 mm, the internal porosity of the carrier is 40%-60%, and the permeability coefficient of the heavy metal passivation isolation layer 3 is less than 1×10⁻⁶. -6 The leachate collection layer 2 is filled with gravel or ceramic particles with a thickness of 10-15 cm / s. The thickness of the microbial reinforcement layer 4 and the design of the carrier particle size / porosity ensure that the microbial community has sufficient growth space and is not easily blocked. The passivation isolation layer has an extremely low permeability coefficient, which ensures its effectiveness as a physical barrier. The gravel or ceramic particles in the leachate collection layer form large pore drainage channels to prevent water accumulation.

[0029] For example, please see Figure 1In practical applications, the Dabao Mountain Xinshan area mine ecological restoration and governance project was selected as one of the second batch of typical cases of the national integrated protection and restoration project of mountains, rivers, forests, fields, lakes, grasslands and deserts. The project adopted a restoration strategy of source control, process interruption and end treatment. It pioneered the use of in-situ matrix improvement + direct vegetation technology to increase the vegetation coverage of the mine governance area from basically bare to more than 95%, enriching the plant species to 32. The content of heavy metal elements such as lead, zinc, copper, cadmium and arsenic in the external drainage was reduced by more than 90%, solving the problems of soil erosion and soil pollution from the source. The technical route of the project is consistent with the idea of ​​constructing S2 multi-level restoration structural units and forming a new composite structural layer by planting S4 plants.

[0030] For further details, please refer to Figures 1-2 This method is particularly suitable for multi-metal complex pollution, acid mine drainage affected areas and mine wastelands where vegetation restoration is difficult. The resulting microbial-plant co-remediation structure has a synergistic effect mechanism during the remediation process. In acid mine drainage affected areas, the pH is often as low as 2-4, making it difficult for ordinary microorganisms and plants to survive. However, this invention creates a microenvironment for microbial communities and roots through the neutralization ability of immobilized carriers and passivation isolation layers. This method integrates the following innovative technologies: preparation technology of biological carrier materials based on mine tailings sand, microbial-plant-mineral synergistic remediation technology, in-situ monitoring and intelligent control technology integrating multi-source sensing devices, and modular and assembleable remediation structural unit design. This method, upon completion, forms a composite remediation structure consisting of a supporting foundation layer 1, a leachate collection layer 2, a heavy metal passivation and isolation layer 3, a microbial reinforcement layer 4, a plant growth layer 5, and an intelligent monitoring and control system. The modular, assembleable design allows for flexible adjustments to layer thickness, material ratios, and sensor density 7 based on site contamination levels and terrain conditions. Its long-term self-sustaining capability is reflected in: continuous energy supply from microbial slow-release carbon sources; self-growth of plants; leachate recharge forming a water cycle; and intelligent control reducing the frequency of human intervention.

[0031] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites, characterized in that, Includes the following steps: S1: Conduct site investigation and base treatment for heavy metal contaminated areas in mine waste sites, remove surface debris, level and compact to form a supporting base surface; S2: On the supporting foundation surface, leachate drainage material, heavy metal passivation material, microbial loading material and plant growth substrate are laid sequentially from bottom to top to form a multi-layered repair structural unit; S3: Inject immobilized functional microbial agents into the microbial load material, and embed in-situ monitoring and sensing devices between each layer of material to establish a closed-loop system of "monitoring-feedback-control"; S4: Plant heavy metal hyperaccumulators in the plant growth substrate and inoculate them with arbuscular mycorrhizal fungi. Maintain water and fertilizer conditions through an intelligent regulation subsystem. Harvest the above-ground parts after the plants have grown to the maximum biomass stage. Repeat planting until the soil heavy metal content drops below the safe threshold. The repaired structure includes the following: a support base layer (1), on which a leachate collection layer (2), a heavy metal passivation isolation layer (3), a microbial reinforcement layer (4) and a plant growth layer (5) are sequentially arranged.

2. The microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites according to claim 1, characterized in that: Immobilized microbial carrier particles (6) are uniformly distributed within the microbial enhancement layer (4). Soil pH, redox potential, heavy metal ion concentration and microbial activity sensors (7) are buried between each layer. The sensors (7) are connected to the remote monitoring platform through a wireless transmission module.

3. The microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites according to claim 1, characterized in that: In step S3, the immobilized functional microbial agent is made by loading functional microbial communities onto a composite microbial carrier. The functional microbial community includes sulfate-reducing bacteria, iron-reducing bacteria, and plant growth-promoting bacteria, combined in a 2:1:1 ratio, with a bacterial concentration of 10. 8 CFU / mL; The composite microbial carrier is prepared by cross-linking mine tailings sand, biochar, sodium alginate and modified cellulose in a mass ratio of 3:4:2:

1.

4. The microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites according to claim 1, characterized in that: In step S2, the heavy metal passivation isolation layer (3) is made by mixing and pressing modified phosphate rock powder, limestone powder, iron manganese oxide composite material and clay mineral in a mass ratio of 3:2:2:3, with a thickness of 10-20cm, and is used to adsorb, precipitate or convert heavy metal ions. The bottom of the leachate collection layer (2) is provided with a drainage pipe. The collected leachate is treated by an integrated treatment device of sedimentation-adsorption-microbial degradation and then reused in the irrigation system.

5. The microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites according to claim 1, characterized in that: In step S4, the hyperaccumulating plants include at least one of the following: centipede grass, southeastern sedum, mineral-bearing sedum, and sea elm. Arbuscular mycorrhizal fungi are *Gymnospermum mossae* or *Rhizospermum radiata*. The inoculation method is to uniformly mix the mycorrhizal seedling substrate into the plant growth layer (5), and the inoculation amount is 5%-10% of the volume of the plant growth layer (5).

6. The microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites according to claim 2, characterized in that: In step S3, the in-situ monitoring sensing device includes a soil pH electrode, a redox potential electrode, a heavy metal ion selective electrode, and a microbial activity electrode. Each sensor (7) is arranged with a monitoring node in a 10m×10m grid. The data acquisition frequency is once every 30 minutes. When the concentration of heavy metal ions is detected to be higher than the set threshold or the microbial activity decreases, the system automatically replenishes microbial agents or starts the electrochemical auxiliary repair module through the intelligent control subsystem.

7. The microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites according to claim 1, characterized in that: The method also includes the use of a mobile operating platform, which integrates a soil crushing and screening device, a microbial agent atomizing spraying device, a plant seed strip sowing and covering device, a drip irrigation and nutrient solution replenishment device, and a GPS positioning and path planning system. The mobile operating platform sequentially completes the base surface treatment, fungicide spraying, plant sowing, and maintenance operations in steps S1 to S4.

8. The microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites according to claim 1, characterized in that: While maintaining the activity of the microbial community in the microbial reinforcement layer (4), the nutrient solution is supplemented by intermittent sprinkler irrigation. The nutrient solution formula is: glucose 0.5g / L, ammonium sulfate 0.2g / L, potassium dihydrogen phosphate 0.1g / L, and trace element mother liquor 1mL / L. During irrigation, the drip irrigation tape is used to evenly apply the irrigation to the plant growth layer (5).

9. The microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites according to claim 2, characterized in that: The thickness of the microbial reinforcement layer (4) is 20-30 cm, the particle size of the immobilized microbial carrier particles (6) is 2-5 mm, and the internal porosity of the carrier is 40%-60%. The permeability coefficient of the heavy metal passivation isolation layer (3) is less than 1×10-6cm / s, and the leachate collection layer (2) is filled with gravel or ceramsite with a thickness of 10-15cm.

10. The microbial-phytoremediation method for heavy metal contaminated soil in mining waste sites according to claim 1, characterized in that: The method is particularly suitable for polymetallic complex pollution, acid mine drainage impact areas, and mine wastelands where vegetation restoration is difficult. The resulting microbial-plant co-remediation structure has a synergistic effect mechanism during the remediation process. The method integrates the following innovative technologies: preparation technology of biological carrier materials based on mine tailings sand, microbial-plant-mineral synergistic remediation technology, in-situ monitoring and intelligent control technology integrating multi-source sensing devices, and modular and assembleable remediation structural unit design. After construction, the method forms a composite restoration body consisting of a supporting foundation layer (1), a leachate collection layer (2), a heavy metal passivation and isolation layer (3), a microbial reinforcement layer (4), a plant growth layer (5), and an intelligent monitoring and control system.

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