Method for biological in-situ soilization improvement of a phosphogypsum stockpile

Abstract

The application discloses a method for biological in-situ soilization improvement of a phosphogypsum stockyard, and specifically comprises the following steps: S1, screening of acid-tolerant functional microorganisms in the phosphogypsum stockyard or the surrounding area and preparation of a composite microbial inoculum; S2, screening of typical indigenous plants in the phosphogypsum stockyard or the surrounding area; S3, land leveling of the phosphogypsum stockyard and pipeline laying; S4, spraying of the acid-tolerant functional microorganism composite microbial inoculum and planting of the indigenous plants; and S5, introduction of soil animals to complete the biological in-situ soilization improvement of the phosphogypsum stockyard. The method realizes the biological in-situ soilization improvement of the phosphogypsum stockyard through the synergistic effect of microorganisms, plants and animals, has good effects, is simple in process, does not need to cover the topsoil of the phosphogypsum stockyard or to migrate the phosphogypsum in the stockyard, has small engineering quantity, low cost, is green and environmentally friendly, is harmless to the phosphogypsum, and has great practical significance for ecological protection and harmlessness treatment of the phosphogypsum.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and ecological restoration technology, specifically to a method for in-situ biological soil improvement of phosphogypsum stockpiles. Background Technology

[0002] Phosphogypsum is an acidic industrial solid waste produced by the wet-process phosphoric acid production process. Its main component is CaSO4·2H2O, and it contains small amounts of undecomposed phosphoric acid, phosphorus, fluorine, and heavy metals. Approximately 5 tons of phosphogypsum are generated for every ton of phosphoric acid produced. Currently, the global stockpile of phosphogypsum is as high as 6 billion tons, and it is increasing at a rate of 100-280 million tons per year. As a major producer of phosphogypsum, my country has a stockpile of 800 million tons and an annual increase in phosphogypsum production of approximately 80 million tons. However, its comprehensive utilization rate is only 40%, which is significantly lower than that of developed countries such as Germany, Belgium, and Japan.

[0003] The large-scale stockpiling of phosphogypsum not only occupies vast areas of land but also poses environmental problems such as dust, groundwater, and soil pollution, as well as risks of landslides and dam collapses. It has become a major bottleneck hindering the healthy and sustainable development of the phosphate chemical industry, making the resource utilization of phosphogypsum an urgent priority. Traditional physical, chemical, and biological treatments for phosphogypsum resource utilization suffer from high costs, complex processes, susceptibility to secondary pollution, and inability to operate on a large scale. In contrast, microbial-plant co-processing technology is widely used in the field of ecological restoration.

[0004] The sulfur, calcium, iron, zinc, phosphorus, and silicon contained in phosphogypsum are all essential elements for plant growth and promote plant growth. The physiological activities of plant roots can improve the physical structure of the soil. During the growth process, plants can absorb and accumulate fluorine through different parts of their bodies, such as roots and leaves. Phosphorus-solubilizing microorganisms are also widely present in nature. They convert insoluble phosphorus into soluble phosphorus through the production of acids (such as citric acid and oxalic acid), which can be absorbed and utilized by plants. At the same time, many microorganisms can effectively promote nitrogen fixation in plants, improve plant growth activity and disease resistance, and help drive the retention of organic matter in the soil, promote the formation of water-stable aggregates, and enhance mineral nutrients. Summary of the Invention

[0005] Based on this, this invention proposes a method for in-situ biological soil remediation of phosphogypsum stockpiles. This ecological restoration model utilizes microbial-enhanced plant colonization technology to improve the pH, moisture content, soil enzyme activity, and pore size of the phosphogypsum in the waste stockpile, making it suitable for plant cultivation. This not only promotes vegetation restoration at phosphogypsum stockpiles and sustainable ecological reconstruction of mining areas but also contributes to the construction of green mines and alleviates the challenge of large-scale phosphogypsum disposal and utilization in my country.

[0006] This invention addresses the environmental problems and resource utilization challenges caused by the large-scale stockpiling of phosphogypsum. Starting with research on soil improvement of phosphogypsum, it first screens indigenous acid-tolerant microorganisms and typical indigenous plants capable of efficiently dissolving phosphorus, fixing nitrogen, and solubilizing potassium from or around the phosphogypsum stockpile. Then, the phosphogypsum stockpile is leveled along its fractured surface, pipes are laid, and plants are planted. A functional microbial compound inoculant is sprayed onto the plant roots through these pipes. Finally, soil animals are introduced to establish themselves. Through the synergistic effect of microorganisms and animals, the reconstruction of the rhizosphere microecology is promoted, comprehensively improving the biological functions of phosphogypsum. This achieves in-situ biological soil improvement of phosphogypsum stockpiles with minimal time investment.

[0007] The technical solution of the present invention:

[0008] A method for in-situ biological soil remediation of phosphogypsum stockpiles, the method comprising the following steps:

[0009] S1: Screen for acid-resistant native microorganisms in or around phosphogypsum stockpiles and prepare compound microbial agents;

[0010] S2: Screen for typical native plants in or around phosphogypsum stockpiles;

[0011] S3: Leveling of the land at the phosphogypsum stockpile and laying of pipelines;

[0012] S4: Spray with native acid-resistant functional microbial compound inoculant to plant native plants;

[0013] S5: Introduce soil animals to complete the biological in-situ soil improvement of the phosphogypsum stockpile.

[0014] Preferably, the indigenous acid-resistant functional microorganisms isolated and screened in step S1 include phosphate-solubilizing bacteria, free-living nitrogen-fixing bacteria, and potassium-solubilizing bacteria;

[0015] Phospholysin-solubilizing bacteria are Pseudomonas, free-living nitrogen-fixing bacteria are Azotobacter chrysodontii, and potassium-solubilizing bacteria are Bacillus mucilaginosus.

[0016] Preferably, the method for preparing the compound microbial agent in step S1 is as follows: the phosphate-solubilizing bacteria, free-living nitrogen-fixing bacteria and potassium-solubilizing bacteria obtained by isolation and screening in step S1 are cultured by shaking at 25-30℃ and 150-180r / min for 3-7 days to obtain an expanded culture solution. Then, the expanded culture solution is mixed evenly in a volume ratio of (1-3):(1-3):(1-3) to obtain the compound microbial agent.

[0017] More preferably, the process for isolating and screening phosphate-solubilizing bacteria used in the preparation of the compound microbial agent is as follows: Rhizosphere soil samples are collected from or near phosphogypsum stockpiles, mixed with sterile water at a ratio of 5-10 g: 100 mL, and diluted to a concentration gradient of 10. -1 ~10 -9Soil suspensions were collected, and 10 mL of each soil suspension from each concentration gradient was inoculated into 50 mL of phosphate-solubilizing liquid medium (Pikovskaya, PKO). The medium was shaken for 2-3 days at 25-30℃ and 150-180 rpm. An appropriate amount of supernatant from the PKO liquid medium was evenly spread onto PKO solid plates and incubated at 25-30℃ for 3-5 days. The colony morphology on the plates was observed, and colonies with a clear transparent phosphate-solubilizing zone around them were identified as phosphate-solubilizing bacteria. The isolated phosphate-solubilizing bacteria were streaked onto the plates and purified by incubation at 28-30℃ for 3-5 days to obtain purified phosphate-solubilizing bacteria strains. The purified phosphate-solubilizing bacteria strains were inoculated into modified PKO selection medium and incubated by shaking at 28-30℃ and 150-180 rpm for 7 days. The soluble phosphorus content in the culture medium was compared, and the strain with the highest soluble phosphorus content was selected as the highly efficient phosphate-solubilizing bacteria.

[0018] The PKO liquid culture medium formulation is as follows: 8-10 g / L glucose, 0.5 g / L yeast extract, 0.1-0.2 g / L (NH4)2SO4, 0.1-0.3 g / L KCl, 0.1-0.3 g / L MgCl2·7H2O, 0.8-1 g / L CaCl2, 0.03-0.05 g / L FeSO4·7H2O, 5-6 g Ca3(PO4)2, with sterile water as the solvent. The PKO solid culture medium formula is as follows: 8-10 g / L glucose, 0.5 g / L yeast extract, 0.1-0.2 g / L (NH4)2SO4, 0.1-0.3 g / L KCl, 0.1-0.3 g / L MgCl2·7H2O, 0.8-1 g / L CaCl2, 0.03-0.05 g / L FeSO4·7H2O, 5-6 g Ca3(PO4)2, 15-18 g / L agar, and sterile water as the solvent. The PKO screening medium formulation is as follows: 8-10 g / L glucose, 0.5 g / L yeast extract, 0.1-0.2 g / L (NH4)2SO4, 0.1-0.3 g / L KCl, 0.1-0.3 g / L MgCl2·7H2O, 0.8-1 g / L CaCl2, 0.03-0.05 g / L FeSO4·7H2O, 5-10 g / L phosphogypsum, and sterile water as the solvent.

[0019] More preferably, the isolation and screening process of the free-living nitrogen-fixing bacteria used in the compound microbial agent is as follows: collect rhizosphere soil samples from phosphogypsum stockpiles or nearby areas, mix them with sterile water at a ratio of 5-10g:100mL, and dilute to a concentration gradient of 10. -1 ~10 -9Soil suspensions were collected, and 10 mL of each soil suspension from each concentration gradient was inoculated into 50 mL of nitrogen-fixing liquid medium (Ashby nitrogen-free medium). The medium was shaken for 3-5 days at 25-30℃ and 150-180 rpm. An appropriate amount of supernatant from the Ashby liquid medium was evenly spread onto Ashby solid plates and incubated at 25-30℃ for 4-7 days. Colony morphology was observed; large, viscous, translucent colonies with white, brown, or dark brown colors were identified as free-living nitrogen-fixing bacteria. After streaking the isolated nitrogen-fixing bacteria onto plates, they were purified and cultured at 28-30℃ for 4-7 days to obtain purified nitrogen-fixing bacterial strains. The purified nitrogen-fixing bacterial strains were inoculated into modified Ashby selection medium and cultured at 28-30℃ and 150-180 r / min for 7 days. The ammonia nitrogen content in the culture medium was compared, and the strain with the highest ammonia nitrogen content was selected as the highly efficient free-living nitrogen-fixing bacteria.

[0020] The Ashby liquid culture medium is formulated as follows: 8-10 g / L mannitol, 0.1-0.3 g / L KH₂PO₄, 0.1-0.3 g / L NaCl, 0.1-0.3 g / L MgSO₄·7H₂O, 0.1-0.3 g / L CaSO₄·2H₂O, 4-6 g CaCO₃, with sterile water as the solvent. The Ashby solid culture medium is formulated as follows: 8-10 g / L mannitol, 0.1-0.3 g / L KH₂PO₄, 0.1-0.3 g / L NaCl, 0.1-0.3 g / L MgSO₄·7H₂O, 0.1-0.3 g / L CaSO₄·2H₂O, 4-6 g CaCO₃, 15-18 g / L agar, with sterile water as the solvent. The Ashby screening medium formulation is as follows: 8-10 g / L mannitol, 5-10 g / L phosphogypsum, 0.1-0.3 g / L KH2PO4, 0.1-0.3 g / L NaCl, 0.1-0.3 g / L MgSO4·7H2O, 0.1-0.3 g / L CaSO4·2H2O, 4-6 g CaCO3, and sterile water as the solvent.

[0021] More preferably, the isolation and screening process of potassium-solubilizing bacteria used in the preparation of the compound microbial agent is as follows: Rhizosphere soil samples are collected from or near phosphogypsum stockpiles, mixed with sterile water at a ratio of 5-10 g: 100 mL, and diluted to a concentration gradient of 10. -1 ~10 -9Soil suspensions were collected, and 10 mL of each concentration gradient was inoculated into 50 mL of silicate bacterial culture medium (SBM). The medium was shaken for 3-5 days at 25-30℃ and 150-180 rpm. A suitable amount of supernatant from the SBM liquid medium was evenly spread onto SBM solid plates and incubated at 25-30℃ for 4-7 days. Colony morphology was observed; colonies that were gelatinous, colorless, raised, and appeared as transparent oil droplets were identified as potassium-solubilizing strains. The isolated potassium-solubilizing bacteria were streaked onto plates and purified at 28-30℃ for 4-7 days to obtain purified potassium-solubilizing strains. These purified strains were then inoculated into a modified SBM selection medium and incubated at 28-30℃ and 150-180 rpm for 7 days. The available potassium content in the culture medium was compared, and the strain with the highest available potassium content was selected as the highly efficient potassium-solubilizing bacterium.

[0022] The SBM liquid culture medium formula is as follows: 5-6 g / L sucrose, 0.4-0.6 g / L MgSO4·7H2O, 0.1-0.3 g CaCO3, 1-3 g Na2HPO4, 0.004-0.006 g FeCl3, 1-2 g potassium feldspar powder, and sterile water as the solvent. The SBM solid culture medium formula is as follows: 5-6 g / L sucrose, 0.4-0.6 g / L MgSO4·7H2O, 0.1-0.3 g CaCO3, 1-3 g Na2HPO4, 0.004-0.006 g FeCl3, 1-2 g potassium feldspar powder, 15-18 g / L agar, and sterile water as the solvent. The SBM screening medium formulation is as follows: 5-6 g / L sucrose, 5-10 g / L phosphogypsum, 0.4-0.6 g / L MgSO4·7H2O, 0.1-0.3 g CaCO3, 1-3 g Na2HPO4, 0.004-0.006 g FeCl3, 1-2 g potassium feldspar powder, and sterile water as the solvent. More preferably, in step S2, the indigenous plants include: white clover or tall fescue as herbaceous plants, multiflora magnolia as shrubs, and black locust as trees, using a combination of shrubs, trees, and grasses to ecologically improve the phosphogypsum soil.

[0023] More preferably, in step S3, the phosphogypsum stockpile is leveled, branch pipes of 0.5m are laid perpendicularly along the ground slope, a sprinkler head is installed at each intersection, and drainage ditches are cleared in low-lying areas and collection tanks are set up.

[0024] More preferably, in step S4, each plant is near a sprinkler head, and the spray solution is transported to branch pipes on the ground of the storage area through the main infusion pipe. The sprinkler heads, evenly distributed on the branch pipes, can periodically spray the inoculant onto the plant roots; the spraying rate of the compound inoculant is 6-15 L / (h·m). 2The spraying method is intermittent, spraying for 1-3 hours every 3-5 days.

[0025] More preferably, in step S4, the plant planting is carried out by seedling transplanting. First, the plant seeds are germinated and raised in normal soil. Then, seedlings with the same growth are selected and transplanted to the phosphogypsum dump. The transplanting density is: 16-25 herbaceous plants / square meter, 3-9 shrubs / square meter, and 1 tree / square meter. The planting cycle is one year.

[0026] More preferably, in step S5, six months after plant establishment, soil animals, including earthworms, snails, beetles, or others, are introduced into the phosphogypsum at a rate of 20 animals per square meter. This accelerates the phosphogypsum soil conversion process. During plant growth, the biomass, average plant height, and other growth parameters are recorded. One year later, the physicochemical properties (pH, organic matter content, fluorine, phosphorus content, etc.) and physical structure (porosity, soil bulk density, aggregate structure, etc.) of the phosphogypsum are tested to evaluate the soil improvement effect.

[0027] The present invention has the following beneficial effects:

[0028] After being colonized by microorganisms, plants, and animals, the pH value of phosphogypsum increases, the content of harmful pollutants such as fluorine and phosphorus decreases significantly, and the organic matter and nutrients are greatly enhanced. Other physical and chemical properties are comparable to normal soil. It can be piled up like normal soil or used for landscaping or planting cash crops.

[0029] This invention achieves in-situ biological improvement of phosphogypsum landfills through the synergistic action of microorganisms, plants, and animals. While utilizing phosphogypsum ecologically, it also indirectly achieves its harmless treatment. This method is green and ecological, with a simple process and low cost. It has significant theoretical and practical implications for promoting ecological restoration and management models and solutions for abandoned phosphogypsum landfills nationwide. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of liquid distribution at the stockpile.

[0031] Figure 2 This is a top view of the branch piping system.

[0032] Specific implementation methods

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. 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.

[0034] The test results of the plants six months after planting in the examples and comparative examples are as follows:

[0035] In the examples and comparative examples, six months after the plants were planted, earthworms and beetles were introduced into the phosphogypsum, with 20 of each animal per square meter. During the plant growth process, the biomass, average plant height, and other growth conditions of the plants were recorded. One year later, the physicochemical properties (pH, organic matter content, fluorine, phosphorus content, etc.) and physical structure (porosity, soil bulk density, aggregate structure, etc.) of the phosphogypsum were tested to evaluate the improvement effect.

[0036] The sampling method is as follows:

[0037] Surface layer (0-10cm): One year later, 10 samples were taken from different locations in the waste phosphogypsum dump at a depth of 0-10cm from the surface. The samples were then mixed evenly and the above-mentioned physicochemical properties and physical structure were tested.

[0038] Deep layer (15-20cm): Two years later, 10 samples were taken from different locations within the phosphogypsum waste dump, from the surface to a depth of 15-20cm. These samples were then mixed thoroughly before undergoing the aforementioned physicochemical and physical structure tests. The screening method for the composite microbial agent used in the examples is as follows:

[0039] The process for isolating and screening phosphate-solubilizing bacteria is as follows: Rhizosphere soil samples were collected from phosphogypsum stockpiles or nearby areas, mixed with sterile water at a ratio of 8g:100mL, and diluted to a concentration gradient of 10. -1 ~10 -9 Soil suspensions were collected, and 10 mL of each soil suspension from each concentration gradient was inoculated into 50 mL of phosphate-solubilizing liquid medium (Pikovskaya, PKO). The medium was shaken for 2 days at 28℃ and 160 rpm. An appropriate amount of supernatant from the PKO liquid medium was evenly spread onto PKO solid plates and incubated at 28℃ for 4 days. The colony morphology on the plates was observed, and colonies with a clear transparent phosphate-solubilizing zone around them were identified as phosphate-solubilizing bacteria. The isolated phosphate-solubilizing bacteria were streaked onto the plates and purified by incubation at 28-30℃ for 3-5 days to obtain purified phosphate-solubilizing bacteria strains. The purified phosphate-solubilizing bacteria strains were inoculated into modified PKO selection medium and incubated by shaking at 30℃ and 160 rpm for 7 days. The soluble phosphorus content in the culture medium was compared, and the strain with the highest soluble phosphorus content was selected as the highly efficient phosphate-solubilizing bacteria.

[0040] The PKO liquid culture medium is formulated as follows: 8 g / L glucose, 0.5 g / L yeast extract, 0.1 g / L (NH4)2SO4, 0.2 g / L KCl, 0.2 g / L MgCl2·7H2O, 0.9 g / L CaCl2, 0.04 g / L FeSO4·7H2O, 6 g Ca3(PO4)2, with sterile water as the solvent. The PKO solid culture medium is formulated as follows: 9 g / L glucose, 0.5 g / L yeast extract, 0.2 g / L (NH4)2SO4, 0.2 g / L KCl, 0.2 g / L MgCl2·7H2O, 0.8 g / L CaCl2, 0.04 g / L FeSO4·7H2O, 5-6 g Ca3(PO4)2, 16 g / L agar, with sterile water as the solvent. The PKO screening medium formulation is as follows: 9 g / L glucose, 0.5 g / L yeast extract, 0.1 g / L (NH4)2SO4, 0.2 g / L KCl, 0.2 g / L MgCl2·7H2O, 0.9 g / L CaCl2, 0.04 g / L FeSO4·7H2O, 9 g / L phosphogypsum, and sterile water as the solvent.

[0041] The isolation and screening process for autotrophic nitrogen-fixing bacteria is as follows: Rhizosphere soil samples were collected from phosphogypsum stockpiles or nearby areas, mixed with sterile water at a ratio of 8g:100mL, and diluted to a concentration gradient of 10. -1 ~10 -9 Soil suspensions were collected, and 10 mL of each concentration gradient was inoculated into 50 mL of nitrogen-fixing liquid medium (Ashby nitrogen-free medium) and shaken at 28°C and 160 rpm for 4 days. A suitable amount of supernatant from the Ashby liquid medium was evenly spread onto Ashby solid plates and incubated at 28°C for 6 days. Colony morphology was observed; large, viscous, translucent colonies with white, brown, or dark brown colors were identified as free-living nitrogen-fixing bacteria. The isolated nitrogen-fixing bacteria were streaked onto plates and purified at 28°C for 6 days to obtain purified nitrogen-fixing bacterial strains. These purified strains were inoculated into modified Ashby selection medium and incubated at 28°C and 150-180 rpm for 7 days. The ammonia nitrogen content in the culture medium was compared, and the strain with the highest ammonia nitrogen content was selected as the highly efficient free-living nitrogen-fixing bacterium.

[0042] The Ashby liquid culture medium has the following formulation: 9 g / L mannitol, 0.2 g / L KH₂PO₄, 0.2 g / L NaCl, 0.2 g / L MgSO₄·7H₂O, 0.2 g / L CaSO₄·2H₂O, 5 g CaCO₃, and sterile water as the solvent. The Ashby solid culture medium has the following formulation: 9 g / L mannitol, 0.2 g / L KH₂PO₄, 0.2 g / L NaCl, 0.2 g / L MgSO₄·7H₂O, 0.2 g / L CaSO₄·2H₂O, 5 g CaCO₃, 16 g / L agar, and sterile water as the solvent. The Ashby screening medium formulation is as follows: 9 g / L mannitol, 9 g / L phosphogypsum, 0.2 g / L KH2PO4, 0.2 g / L NaCl, 0.2 g / L MgSO4·7H2O, 0.2 g / L CaSO4·2H2O, 5 g CaCO3, and sterile water as the solvent.

[0043] The process for isolating and screening potassium-solubilizing bacteria is as follows: Rhizosphere soil samples were collected from phosphogypsum stockpiles or nearby areas, mixed with sterile water at a ratio of 8g:100mL, and diluted to a concentration gradient of 10. -1 ~10 -9 Soil suspensions were collected, and 10 mL of each concentration gradient was inoculated into 50 mL of silicate bacterial culture medium (SBM). The medium was shaken for 4 days at 28℃ and 160 rpm. A suitable amount of supernatant from the SBM liquid medium was evenly spread onto SBM solid plates and incubated at 28℃ for 4 days. Colony morphology was observed; colonies that were gelatinous, colorless, raised, and appeared as transparent oil droplets were identified as potassium-solubilizing strains. The isolated potassium-solubilizing bacteria were streaked onto plates and purified at 28℃ for 6 days to obtain purified potassium-solubilizing strains. These purified strains were then inoculated into a modified SBM selection medium and incubated at 28℃ and 160 rpm for 7 days. The available potassium content in the culture medium was compared, and the strain with the highest content was identified as a highly efficient potassium-solubilizing bacterium.

[0044] The SBM liquid culture medium formula is: 7 g / L sucrose, 0.5 g / L MgSO4·7H2O, 0.2 g CaCO3, 2 g Na2HPO4, 0.005 g FeCl3, 1.5 g potassium feldspar powder, with sterile water as the solvent. The SBM solid culture medium formula is: 6 g / L sucrose, 0.5 g / L MgSO4·7H2O, 0.2 g CaCO3, 2 g Na2HPO4, 0.005 g FeCl3, 1.5 g potassium feldspar powder, 16 g / L agar, with sterile water as the solvent. The SBM screening culture medium formula is: 5.5 g / L sucrose, 6 g / L phosphogypsum, 0.5 g / L MgSO4·7H2O, 0.2 g CaCO3, 2 g Na2HPO4, 0.005 g FeCl3, 1.5 g potassium feldspar powder, with sterile water as the solvent.

[0045] Example 1

[0046] Taking the phosphogypsum waste dump in Yichang City, Hubei Province as an example, the following method was used to carry out in-situ biological soil improvement of the phosphogypsum dump.

[0047] (1) Screening native acid-resistant functional microorganisms in or around phosphogypsum stockpiles and preparing compound microbial agents;

[0048] Furthermore, indigenous acid-resistant functional microorganisms in or around the phosphogypsum stockpile were screened. The isolated and screened Pseudomonas, Azotobacter chrysophagus, and Bacillus mucilaginosus were cultured at 30℃ and 165r / min for 5 days to obtain amplified culture medium. Then, the amplified culture medium was mixed evenly with Pseudomonas:Azotobacter chrysophagus:Bacillus mucilaginosus in a volume ratio of 1:1:1 to obtain a compound microbial agent.

[0049] (2) Screening for typical native plants in or around phosphogypsum stockpiles;

[0050] Furthermore, the selected herbaceous plant was white clover, the selected shrub species was Magnolia multiflora, and the selected tree species was Robinia pseudoacacia. The combination of trees, shrubs, and grasses was used to carry out ecological soil improvement with phosphogypsum.

[0051] (3) Leveling of the land at the phosphogypsum stockpile and laying of pipelines;

[0052] Furthermore, the phosphogypsum stockpile was leveled, and branch pipes of 0.5m were laid perpendicularly along the ground slope. A sprinkler head was installed at each intersection, and drainage ditches were cleared and collection tanks were set up in low-lying areas.

[0053] (4) Spray with native acid-resistant functional microbial compound inoculant and plant native plants;

[0054] Furthermore, each plant is equipped with a sprinkler head. The spray solution is transported via a main infusion pipe to branch pipes on the ground of the storage area. The sprinkler heads, evenly distributed along these branch pipes, periodically spray the microbial agent onto the plant roots. The spraying rate of the compound microbial agent is 6 L / (h·m). 2 The spraying method is intermittent, with 1 hour of spraying every 3 days.

[0055] Furthermore, the plant cultivation method involves transplanting seedlings. First, the plant seeds are germinated and raised in normal soil. Then, seedlings with similar growth are selected and transplanted to the phosphogypsum composting area. The transplanting density is: 25 white clover plants / square meter, 3 magnolia plants / square meter, and 1 black locust plant / square meter. The planting cycle is one year.

[0056] (5) Introduce soil animals to complete the biological in-situ soil improvement of the phosphogypsum dump.

[0057] Furthermore, six months after planting, earthworms and beetles, soil animals, were introduced into the phosphogypsum at a rate of 20 of each species per square meter. During the plant growth process, the biomass, average plant height, and other growth characteristics of the plants were recorded. One year later, the physicochemical properties (pH, organic matter content, fluorine, phosphorus content, etc.) and physical structure (porosity, soil bulk density, aggregate structure, etc.) of the phosphogypsum were tested to evaluate the improvement effect.

[0058] Table 1 shows the physicochemical properties of the phosphogypsum soil matrix before and after improvement in this embodiment.

[0059]

[0060] One year after the microbial-plant-animal colonization, the herbaceous plants on the phosphogypsum site rapidly spread across the entire hillside, thriving. Besides the introduced earthworms and beetles, the population and number of invasive soil animals significantly increased. According to the data in Table 1, the improved surface phosphogypsum exhibited significantly increased organic matter content, total nitrogen, total potassium, and other nutrient components, as well as improved soil porosity; the pH value returned to neutral, and the content of harmful impurities such as soluble fluorine and phosphorus was significantly reduced; the soil bulk density was significantly decreased, and all indicators met the standards for general garden planting soil. This demonstrates that the present invention can effectively improve the physicochemical properties of phosphogypsum and soil structure, with excellent improvement effects. Furthermore, soil microbial community identification showed a significant increase in the variety of soil microorganisms.

[0061] Example 2

[0062] Taking the phosphogypsum waste dump in Yichang City, Hubei Province as an example, the following method was used to carry out in-situ biological soil improvement of the phosphogypsum dump.

[0063] (1) Screening native acid-resistant functional microorganisms in or around phosphogypsum stockpiles and preparing compound microbial agents;

[0064] Furthermore, indigenous acid-resistant functional microorganisms in or around the phosphogypsum stockpile were screened. The isolated and screened Pseudomonas, Azotobacter chrysophagus, and Bacillus mucilaginosus were cultured at 30℃ and 165r / min for 5 days to obtain amplified culture medium. Then, the amplified culture medium was mixed evenly with Pseudomonas:Azotobacter chrysophagus:Bacillus mucilaginosus in a volume ratio of 1:2:3 to obtain a compound microbial agent.

[0065] (2) Screening for typical native plants in or around phosphogypsum stockpiles;

[0066] Furthermore, the selected herbaceous plants were tall fescue, the selected shrub species were Magnolia multiflora, and the selected tree species were Robinia pseudoacacia. A combination of trees, shrubs, and grasses was used to improve the phosphogypsum soil in an ecological way.

[0067] (3) Leveling of the land at the phosphogypsum stockpile and laying of pipelines;

[0068] Furthermore, the phosphogypsum stockpile was leveled, and branch pipes of 0.5m were laid perpendicularly along the ground slope. A sprinkler head was installed at each intersection, and drainage ditches were cleared and collection tanks were set up in low-lying areas.

[0069] (4) Spray with native acid-resistant functional microbial compound inoculant and plant native plants;

[0070] Furthermore, each plant is equipped with a sprinkler head. The spray solution is transported through a main pipeline to branch pipes on the ground of the storage area. The sprinkler heads, evenly distributed along these branch pipes, periodically spray the microbial agent onto the plant roots. The spraying rate of the compound microbial agent is 10 L / (h·m). 2 The spraying method is intermittent, with 2 hours of spraying every 5 days.

[0071] Furthermore, the plant cultivation method involves transplanting seedlings. First, the plant seeds are germinated in normal soil to cultivate seedlings. Then, seedlings of similar growth are selected and transplanted to a phosphogypsum composting area. The transplanting density is: 16 tall fescue plants / square meter, 9 Magnolia multiflora plants / square meter, and 1 black locust plant / square meter. The planting cycle is one year.

[0072] (5) Introduce soil animals to complete the biological in-situ soil improvement of the phosphogypsum dump.

[0073] Furthermore, six months after the plants were planted, earthworms and snails were introduced into the phosphogypsum, with 20 of each animal per square meter. During the plant growth process, the biomass, average plant height, and other growth conditions of the plants were recorded. One year later, the physicochemical properties (pH, organic matter content, fluorine, phosphorus content, etc.) and physical structure (porosity, soil bulk density, aggregate structure, etc.) of the phosphogypsum were tested to evaluate the improvement effect.

[0074] Table 2 shows the physicochemical properties of the phosphogypsum soil matrix before and after improvement in this embodiment.

[0075]

[0076]

[0077] After a year-long soil improvement process involving microorganisms, plants, and animals, the phosphogypsum compost dump has been largely covered by vegetation. Data from Table 2 shows that the improved surface phosphogypsum exhibits significantly increased nutrient content and soil porosity, while soil bulk density has decreased substantially, indicating a transformation from a compacted to a loose and porous soil structure. The pH value is close to neutral, and the content of harmful impurities has significantly decreased. Overall, the improvement effect is excellent. The physicochemical properties of the improved phosphogypsum are comparable to those of normal soil, allowing it to be used for landscaping or planting cash crops, just like normal soil.

[0078] Example 3

[0079] Taking the phosphogypsum waste dump in Yichang City, Hubei Province as an example, the following method was used to carry out in-situ biological soil improvement of the phosphogypsum dump.

[0080] (1) Screening native acid-resistant functional microorganisms in or around phosphogypsum stockpiles and preparing compound microbial agents;

[0081] Furthermore, indigenous acid-resistant functional microorganisms in or around the phosphogypsum stockpile were screened. The isolated and screened Pseudomonas, Azotobacter chrysophagus, and Bacillus mucilaginosus were cultured at 30℃ and 165r / min for 5 days to obtain amplified culture medium. Then, the amplified culture medium was mixed evenly with Pseudomonas:Azotobacter chrysophagus:Bacillus mucilaginosus in a volume ratio of 2:3:1 to obtain a compound microbial agent.

[0082] (2) Screening for typical native plants in or around phosphogypsum stockpiles;

[0083] Furthermore, the selected herbaceous plants were tall fescue, the selected shrub species were Magnolia multiflora, and the selected tree species were Robinia pseudoacacia. A combination of trees, shrubs, and grasses was used to improve the phosphogypsum soil in an ecological way.

[0084] (3) Leveling of the land at the phosphogypsum stockpile and laying of pipelines;

[0085] Furthermore, the phosphogypsum stockpile was leveled, and branch pipes of 0.5m were laid perpendicularly along the ground slope. A sprinkler head was installed at each intersection, and drainage ditches were cleared and collection tanks were set up in low-lying areas.

[0086] (4) Spray with native acid-resistant functional microbial compound inoculant and plant native plants;

[0087] Furthermore, each plant is equipped with a sprinkler head. The spray solution is transported via a main infusion pipe to branch pipes on the ground of the storage area. The sprinkler heads, evenly distributed along these branch pipes, periodically spray the microbial agent onto the plant roots. The spraying rate of the compound microbial agent is 8 L / (h·m). 2 The spraying method is intermittent, with 1 hour of spraying every 3 days.

[0088] Furthermore, the plant cultivation method involves transplanting seedlings. First, the plant seeds are germinated and cultivated in normal soil. Then, seedlings with similar growth are selected and transplanted to the phosphogypsum composting area. The transplanting density is: 20 tall fescue plants / square meter, 6 magnolia plants / square meter, and 1 locust plant / square meter. The planting cycle is one year.

[0089] (5) Introduce soil animals to complete the biological in-situ soil improvement of the phosphogypsum dump.

[0090] Furthermore, six months after planting, soil animals earthworms, snails, and beetles were introduced into the phosphogypsum, with 20 of each animal per square meter. During the plant growth process, the biomass, average plant height, and other growth conditions were recorded. One year later, the physicochemical properties (pH, organic matter content, fluorine, phosphorus content, etc.) and physical structure (porosity, soil bulk density, aggregate structure, etc.) of the phosphogypsum were tested to evaluate the improvement effect.

[0091] Table 3 shows the physicochemical properties of the phosphogypsum soil matrix before and after improvement in this embodiment.

[0092]

[0093] After a year-long soil improvement program involving the colonization of microorganisms, plants, and animals, the phosphogypsum stockpile has been transformed into a green mine. The populations and numbers of soil microorganisms and animals have significantly increased, and exotic vegetation has also established itself. According to the data in Table 3, the physicochemical properties and physical structure of both the surface and deep layers of phosphogypsum have improved after soil improvement. The surface layer of phosphogypsum showed the most significant improvement, with a substantial increase in nutrient content and soil porosity, a significant decrease in harmful impurities, and other physicochemical properties comparable to normal soil, indicating a good improvement effect. The improvement in the deep layer of phosphogypsum was less pronounced than in the surface layer, but it still showed improvement compared to the data before improvement. This suggests that the colonization of microorganisms and plants and animals also has a certain improvement effect on the deep layer of phosphogypsum, and that the soil improvement process is gradual, progressing from the surface to the interior. As plant roots extend and develop, microorganisms and animals gradually settle in the deeper soil, deeply improving the phosphogypsum and ultimately achieving complete soil transformation of the phosphogypsum stockpile.

[0094] Example 4

[0095] Based on Example 3, in this example, the type of plant is changed in step (2), otherwise it is the same as in Example 3.

[0096] Furthermore, typical native plants in or around the phosphogypsum stockpile were selected. The selected herbaceous plant was alfalfa, the selected shrub species was honeysuckle, and the selected tree species was Amorpha fruticosa. A combination of trees, shrubs, and grasses was used to carry out soil ecological improvement of phosphogypsum.

[0097] Table 4 shows the physicochemical properties of the phosphogypsum soil matrix before and after improvement in this embodiment.

[0098]

[0099] After a year-long soil improvement program involving microorganisms, plants, and animals, some vegetation recovered at the phosphogypsum stockpile, but the vegetation cover was sparse. Data from Table 4 shows that while the nutrient content of the surface phosphogypsum improved after soil improvement, the reduction in harmful impurity fluorine was significantly lower than in other examples. Soil porosity only increased by 47%, and the improvement in soil bulk density was also less pronounced than in other examples. Furthermore, the soil pH was 5.5, indicating a slightly acidic environment, and the physicochemical properties of the deeper phosphogypsum layers showed minimal change. In summary, the soil improvement effect was less effective than in other examples, suggesting that microorganisms need to be combined with specific plants to synergistically promote the soil transformation of phosphogypsum.

[0100] Example 5

[0101] Based on Example 3, in this example, the type of the conforming strain is changed in step (1), and the rest is the same as in Example 3.

[0102] Furthermore, indigenous acid-resistant functional microorganisms from the phosphogypsum stockpile or its surrounding area were screened. The isolated and screened phosphate-solubilizing bacteria (Pseudomonas) and potassium-solubilizing bacteria (Bacillus mucilaginosus) were cultured separately at 30℃ and 165r / min for 5 days with shaking to obtain an expanded culture solution. Then, the expanded culture solution was mixed evenly with Pseudomonas:Bacillus mucilaginosus at a volume ratio of 2:3 to prepare a compound microbial agent for spraying in step (4).

[0103] Table 5 shows the physicochemical properties of the phosphogypsum soil matrix before and after improvement in this embodiment.

[0104]

[0105]

[0106] After a year-long soil improvement program involving microorganisms, plants, and animals, some vegetation recovered at the phosphogypsum stockpile, but the vegetation cover was sparse. Data from Table 5 shows that after soil improvement, the increase in various nutrients in the surface phosphogypsum was significantly lower than in other examples, the reduction in harmful impurity fluorine was not significant, soil porosity increased by only 5%, soil bulk density improved only slightly, and the soil pH was 5.0, indicating a slightly acidic environment. The improvement in the physicochemical properties of the deep phosphogypsum was not significant. Overall, the improvement in the soil's physicochemical properties and physical structure was poor for both the surface and deep phosphogypsum layers. In summary, the soil improvement effect was poor, indicating that the type of microorganism has a significant impact on plant colonization and the soil transformation process of phosphogypsum.

[0107] Example 6

[0108] Based on Example 3, in this example, the formulation of the screening culture medium for each functional microorganism is changed in step (1), and the other methods and steps are the same as in Example 3.

[0109] Furthermore, the indigenous functional microorganisms in the phosphogypsum stockpile or surrounding area were screened. The isolated and screened Pseudomonas, Azotobacter chrysophagus and Bacillus mucilaginosus were cultured at 30℃ and 165r / min for 5 days to obtain an expanded culture solution. Then, the expanded culture solution was mixed evenly with Pseudomonas:Azotobacter chrysophagus:Bacillus mucilaginosus in a volume ratio of 2:3:1 to prepare a compound microbial agent for spraying in step (4).

[0110] Furthermore, the PKO screening medium used for screening phosphate-solubilizing bacteria was formulated as follows: 9 g / L glucose, 0.5 g / L yeast extract, 0.1 g / L (NH4)2SO4, 0.2 g / L KCl, 0.2 g / L MgCl2·7H2O, 0.9 g / L CaCl2, 0.04 g / L FeSO4·7H2O, with sterile water as the solvent.

[0111] The Ashby screening medium used for screening nitrogen-fixing bacteria consisted of 9 g / L mannitol, 0.2 g / L KH2PO4, 0.2 g / L NaCl, 0.2 g / L MgSO4·7H2O, 0.2 g / L CaSO4·2H2O, and 5 g CaCO3, with sterile water as the solvent.

[0112] The SBM screening medium used for screening potassium-solubilizing bacteria was formulated as follows: 5.5 g / L sucrose, 0.5 g / L MgSO4·7H2O, 0.2 g CaCO3, 2 g Na2HPO4, 0.005 g FeCl3, 1.5 g potassium feldspar powder, and sterile water as the solvent.

[0113] Table 6 shows the physicochemical properties of the phosphogypsum soil matrix before and after improvement in this embodiment.

[0114]

[0115] After a year-long soil improvement program involving microorganisms, plants, and animals, the phosphogypsum dump had very little vegetation cover. Analysis of the data in Table 6 shows that after soil improvement, the physicochemical properties of the surface phosphogypsum changed slightly, with soil porosity increasing by only 4% and the soil pH reaching 4.5, indicating acidity. The physicochemical properties of the deeper phosphogypsum layers remained almost unchanged, indicating that the soil improvement effect was not significant. This is likely because the phosphate-solubilizing, nitrogen-fixing, and potassium-solubilizing bacteria selected after changing the screening medium formula were not acclimatized to phosphogypsum and could not grow and reproduce under the strongly acidic conditions of phosphogypsum. Consequently, they could not perform their specific functions and roles in promoting plant growth and development within the phosphogypsum environment, resulting in a poor soil improvement effect.

[0116] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The embodiments and features described in these embodiments can be arbitrarily combined without conflict. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for in-situ biological soil improvement of phosphogypsum stockpiles, characterized in that: The method includes the following steps: S1: Screen for acid-resistant native microorganisms in or around phosphogypsum stockpiles and prepare compound microbial agents; S2: Screen for typical native plants in or around phosphogypsum stockpiles; S3: Leveling of the land at the phosphogypsum stockpile and laying of pipelines; S4: Spray with native acid-resistant functional microbial compound inoculant to plant native plants; S5: Introduce soil animals to complete the biological in-situ soil improvement of the phosphogypsum dump; The compound microbial agent includes phosphate-solubilizing bacteria, free-living nitrogen-fixing bacteria, or potassium-solubilizing bacteria; In step S1, the process for isolating and screening phosphate-solubilizing bacteria used in the preparation of the compound bacterial agent is as follows: S1.1.1 Collect rhizosphere soil samples from or near phosphogypsum stockpiles, mix them with sterile water at a ratio of 5-10 g: 100 mL, and dilute to a concentration gradient of 10. -1 ~10 -9 Soil suspensions were collected, and 10 mL of soil suspension from each concentration gradient was inoculated into 50 mL of phosphorus-solubilizing liquid culture medium (PKO). The suspensions were shaken for 2-3 days at 25-30℃ and 150-180 r / min. S1.1.2 Take an appropriate amount of supernatant from PKO liquid medium and spread it evenly on PKO solid plates. Incubate at 25-30℃ for 3-5 days. Observe the colony morphology on the plates. Colonies with obvious transparent phosphate-solubilizing zones around them are phosphate-solubilizing bacteria. S1.1.3 After streaking the isolated phosphate-solubilizing bacteria onto plates, purify and culture them at 28-30℃ for 3-5 days to obtain purified phosphate-solubilizing bacteria strains. Inoculate the purified phosphate-solubilizing bacteria strains into modified PKO selection medium and culture them at 28-30℃ and 150-180 r / min for 7 days. Compare the soluble phosphorus content in the culture medium and select the strain with the highest index to determine the highly efficient phosphate-solubilizing bacteria. The PKO liquid culture medium formulation is as follows: 8-10 g / L glucose, 0.5 g / L yeast extract, 0.1-0.2 g / L (NH4)2SO4, 0.1-0.3 g / L KCl, 0.1-0.3 g / L MgCl2·7H2O, 0.8-1 g / L CaCl2, 0.03-0.05 g / L FeSO4·7H2O, 5-6 g Ca3(PO4)2, with sterile water as the solvent; The PKO solid culture medium formula is as follows: 8-10 g / L glucose, 0.5 g / L yeast extract, 0.1-0.2 g / L (NH4)2SO4, 0.1-0.3 g / L KCl, 0.1-0.3 g / L MgCl2·7H2O, 0.8-1 g / L CaCl2, 0.03-0.05 g / L FeSO4·7H2O, 5-6 g Ca3(PO4)2, 15-18 g / L agar, and sterile water as the solvent; The PKO screening medium formulation is as follows: 8-10 g / L glucose, 0.5 g / L yeast extract, 0.1-0.2 g / L (NH4)2SO4, 0.1-0.3 g / L KCl, 0.1-0.3 g / L MgCl2·7H2O, 0.8-1 g / L CaCl2, 0.03-0.05 g / L FeSO4·7H2O, 5-10 g / L phosphogypsum, with sterile water as the solvent; The isolation and screening process of the free-living nitrogen-fixing bacteria used in the compound bacterial agent is as follows: S1.2.1 Collect rhizosphere soil samples from or near phosphogypsum stockpiles, mix them with sterile water at a ratio of 5-10 g: 100 mL, and dilute to a concentration gradient of 10. -1 ~10 -9 Soil suspensions were collected, and 10 mL of soil suspension from each concentration gradient was inoculated into 50 mL of nitrogen-fixing liquid culture medium and shaken for 3-5 days at 25-30℃ and 150-180 r / min. S1.2.2 Take an appropriate amount of supernatant from Ashby liquid medium and spread it evenly on Ashby solid plates. Incubate at 25-30℃ for 4-7 days. Observe the colony morphology on the plates. Large, viscous, semi-transparent colonies with white, brown or dark brown color are free-living nitrogen-fixing bacteria. S1.2.3 After streaking the isolated nitrogen-fixing bacteria onto plates, purify and culture them at 28-30℃ for 4-7 days to obtain purified nitrogen-fixing bacterial strains. Inoculate the purified nitrogen-fixing bacterial strains into modified Ashby selection medium and culture them at 28-30℃ and 150-180 r / min for 7 days. Compare the ammonia nitrogen content in the culture medium and select the strain with the highest ammonia nitrogen content as the highly efficient free-living nitrogen-fixing bacteria. The nitrogen-fixing liquid culture medium is formulated as follows: 8-10 g / L mannitol, 0.1-0.3 g / L KH2PO4, 0.1-0.3 g / L NaCl, 0.1-0.3 g / L MgSO4·7H2O, 0.1-0.3 g / L CaSO4·2H2O, 4-6 g CaCO3, with sterile water as the solvent; The Ashby solid medium formula is: 8-10 g / L mannitol, 0.1-0.3 g / L KH2PO4, 0.1-0.3 g / L NaCl, 0.1-0.3 g / L MgSO4·7H2O, 0.1-0.3 g / L CaSO4·2H2O, 4-6 g CaCO3, 15-18 g / L agar, with sterile water as the solvent; The Ashby screening medium formulation is as follows: 8-10 g / L mannitol, 5-10 g / L phosphogypsum, 0.1-0.3 g / L KH2PO4, 0.1-0.3 g / L NaCl, 0.1-0.3 g / L MgSO4·7H2O, 0.1-0.3 g / L CaSO4·2H2O, 4-6 g CaCO3, with sterile water as the solvent; The isolation and screening process of potassium-solubilizing bacteria used in the preparation of the compound microbial agent is as follows: S1.3.1 Collect rhizosphere soil samples from or near phosphogypsum stockpiles, mix them with sterile water at a ratio of 5-10 g: 100 mL, and dilute to a concentration gradient of 10. -1 ~10 -9 Soil suspensions were collected, and 10 mL of soil suspensions from each concentration gradient were inoculated into 50 mL of silicate bacteria medium (SBM liquid medium) and shaken at 25-30℃ and 150-180 r / min for 3-5 days. S1.3.2 Take an appropriate amount of supernatant from SBM liquid medium and spread it evenly on SBM solid plate. Incubate at 25-30℃ for 4-7 days. Observe the colony morphology on the plate. Colonies that are gelatinous, colorless, raised, and transparent oil droplets are potassium-solubilizing strains. S1.3.3 After streaking the isolated potassium-solubilizing bacteria onto plates, purify and culture them at 28-30℃ for 4-7 days to obtain purified potassium-solubilizing bacterial strains. Inoculate the purified potassium-solubilizing bacterial strains into modified SBM selection medium and culture them at 28-30℃ and 150-180 r / min for 7 days. Compare the available potassium content in the culture medium and select the strain with the highest value for this index to be identified as a highly efficient potassium-solubilizing bacterium. The SBM liquid culture medium formula is as follows: 5-6 g / L sucrose, 0.4-0.6 g / L MgSO4·7H2O, 0.1-0.3 g CaCO3, 1-3 g Na2HPO4, 0.004-0.006 g FeCl3, 1-2 g potassium feldspar powder, and sterile water as the solvent; The SBM solid medium formula is: 5-6 g / L sucrose, 0.4-0.6 g / L MgSO4·7H2O, 0.1-0.3 g CaCO3, 1-3 g Na2HPO4, 0.004-0.006 g FeCl3, 1-2 g potassium feldspar powder, 15-18 g / L agar, and sterile water as the solvent; The SBM screening medium formula is as follows: 5-6 g / L sucrose, 5-10 g / L phosphogypsum, 0.4-0.6 g / L MgSO4·7H2O, 0.1-0.3 g CaCO3, 1-3 g Na2HPO4, 0.004-0.006 g FeCl3, 1-2 g potassium feldspar powder, and sterile water as the solvent.

2. The method for in-situ biological soil improvement of phosphogypsum stockpiles according to claim 1, characterized in that: The indigenous acid-resistant functional microorganisms isolated and screened in step S1 include phosphate-solubilizing bacteria, free-living nitrogen-fixing bacteria, and potassium-solubilizing bacteria; the phosphate-solubilizing bacteria are Pseudomonas, the free-living nitrogen-fixing bacteria are Azotobacter chrysophagus, and the potassium-solubilizing bacteria are Bacillus mucilaginosus.

3. The method for in-situ biological soil improvement of phosphogypsum stockpiles according to claim 1, characterized in that: The method for preparing the compound microbial agent in step S1 is as follows: The phosphate-solubilizing bacteria, free-living nitrogen-fixing bacteria and potassium-solubilizing bacteria obtained in step S1 are cultured by shaking at 25-30℃ and 150-180r / min for 3-7 days to obtain an expanded culture solution. Then, the expanded culture solutions of phosphate-solubilizing bacteria, free-living nitrogen-fixing bacteria and potassium-solubilizing bacteria are mixed evenly in a volume ratio of (1-3):(1-3):(1-3) to obtain the compound microbial agent.

4. The method for in-situ biological soil improvement of phosphogypsum stockpiles according to claim 1, characterized in that: In step S2, the native plants include: herbaceous plants such as white clover or tall fescue, shrubs such as Magnolia multiflora, and trees such as Robinia pseudoacacia. The combination of shrubs, trees, and grasses is used to improve the phosphogypsum soil in an ecological way.

5. The method for in-situ biological soil improvement of phosphogypsum stockpiles according to claim 1, characterized in that: In step S3, the phosphogypsum stockpile is leveled, and branch pipes of 0.5m are laid perpendicularly along the ground slope. A sprinkler head is installed at each intersection, and drainage ditches are cleared in low-lying areas, and collection tanks are set up. In step S5, six months after the plants are planted, soil animals, including earthworms, snails, and beetles, are introduced into the phosphogypsum, with 20 of each animal per square meter.

6. The method for in-situ biological soil improvement of phosphogypsum stockpiles according to claim 1, characterized in that: In step S4, each plant is near a sprinkler head. The spray solution is transported to branch pipes on the ground of the storage area through the main infusion pipe. The sprinkler heads, evenly distributed on the branch pipes, can periodically spray the inoculant onto the plant roots. The spraying rate of the compound inoculant is 6-15 L / (h·m). 2 The spraying method is intermittent, spraying for 1-3 hours every 3-5 days.

7. The method for in-situ biological soil improvement of phosphogypsum stockpiles according to claim 1, characterized in that: In step S4, the plant planting method is seedling transplantation. First, the plant seeds are germinated and cultivated in normal soil. Then, seedlings with the same growth are selected and transplanted to the phosphogypsum dump. The transplanting density is: 16-25 herbaceous plants / square meter, 3-9 shrubs / square meter, and 1 tree / square meter. The planting cycle is one year.

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