Step unit type drainage trench purification system for modified ardealite roadbed

Abstract

The invention provides a step unit type drainage groove purification system for a modified ardealite roadbed, and belongs to the technical field of road environmental protection, the step unit type drainage groove purification system is composed of a rain collection groove, a fluorine removal groove and a phosphorus removal groove which are sequentially connected in series, when the modified ardealite roadbed is subjected to damage emergency treatment, ardealite leachate can be safely and efficiently purified, and the service life of the ardealite leachate is prolonged. The device has the functions of collecting, guiding, discharging and purifying rainwater runoff, realizes comprehensive treatment of pollutants in the ardealite roadbed and rainwater, and has the advantages of local material utilization, convenience in construction, simplicity in maintenance, high regional adaptability and the like.

Description

Technical Field

[0001] This invention relates to the field of highway environmental protection technology, specifically to a tiered unit-type drainage ditch purification system for modified phosphogypsum roadbeds. Background Technology

[0002] Phosphogypsum is a major byproduct of sulfuric acid decomposition of phosphate rock for phosphoric acid extraction. Currently, the global stockpile of phosphogypsum is approximately 6 billion tons, and this figure continues to grow at a rate of about 200 million tons per year. my country's annual phosphogypsum production has exceeded 80 million tons, with a cumulative stockpile of approximately 800 million tons. This stockpiled phosphogypsum not only occupies and wastes a large amount of land resources, but also causes environmental pollution problems due to its high phosphate and fluoride content. For example, fluorides can pollute surrounding soil and water bodies through rainwater runoff or groundwater infiltration, and unreacted phosphates in the phosphogypsum can enter water bodies with rainwater, leading to explosive algal blooms and disrupting the aquatic ecological balance.

[0003] Existing technologies for the comprehensive utilization of phosphogypsum mainly include processing it into building materials, backfilling mine pits, ecological restoration, and road construction materials. With the continuous expansion of highway networks, roadbed filling has become a significant application scenario for the large-scale disposal of phosphogypsum. Modified phosphogypsum, used as roadbed filler, can be safely disposed of with proper external protective measures. When the road section is located near environmentally sensitive areas, in order to prepare for emergency response to damage to the roadbed protection structure caused by accidents, the environmental risk of modified phosphogypsum leaching out with rainwater under rainfall conditions should also be considered.

[0004] Currently, common methods for defluorinating and purifying phosphogypsum include chemical precipitation, ion exchange, electrochemical methods, bioadsorption, and membrane separation. Some composite technologies are also being explored; for example, CN118877919A proposes a phosphogypsum purification system based on electrocoagulation, CN118180125B invented a highly efficient defluorinating and phosphorus-removing purification device for phosphogypsum based on iron oxide packing adsorption, and CN210030077U discloses a multi-stage vacuum filter technology for phosphogypsum purification. These technologies involve complex processes, high investment costs, and require dedicated personnel for operation and management. Furthermore, they are suitable for treating long-term, stable phosphogypsum wastewater and are not applicable to scenarios such as highways with limited power supply, inconvenient supervision, or only temporary, intermittent operation.

[0005] Therefore, it is urgent to study the structure and application method of a stepped unit-type drainage ditch purification system for modified phosphogypsum roadbeds, based on the characteristics of highway transportation infrastructure construction and the problem of emergency treatment of modified phosphogypsum roadbed damage. This system should achieve safe and efficient purification of phosphogypsum leachate in the event of an accident, while also having the functions of rainwater runoff collection, drainage, and purification in normal circumstances. Summary of the Invention

[0006] To achieve the above objectives, this invention provides a tiered unit-type drainage ditch purification system for modified phosphogypsum roadbeds. It can be used in highway transportation infrastructure, particularly addressing the technical problems of phosphogypsum leachate purification and emergency treatment of damage to modified phosphogypsum roadbeds. It improves and optimizes the existing roadside ditch structure, facilitating construction. The main building materials are conventional natural materials and waste materials, making it easy to source materials locally and achieve resource recycling. It can rapidly and deeply remove fluoride and phosphorus, requiring no special maintenance in daily operation. When the roadbed protection structure is damaged and rainfall occurs, resulting in a high concentration of modified phosphogypsum leachate, the filler can be directly replaced without destroying or dismantling the system structure.

[0007] Specifically, the technical solutions include the following:

[0008] A stepped unit-type drainage ditch purification system for modified phosphogypsum roadbeds, the purification system comprising: a roadbed, a stepped unit-type drainage ditch purification system 1, and a leachate collection pipe 2; the stepped unit-type drainage ditch purification system 1 is connected to the roadbed via the leachate collection pipe 2; the middle of the roadbed is filled with modified phosphogypsum filler 8, the modified phosphogypsum filler 8 is provided with a first sealing layer 5 and a second sealing layer 4 above and below, respectively, and a first edge layer 6 and a second edge layer 7 on the left and right sides, respectively; the leachate collection pipe 2 is provided at the bottom of the second sealing layer 4, and the section of the leachate collection pipe 2 that contacts the second sealing layer has uniformly arranged liquid accumulation holes 3 on its surface.

[0009] Furthermore, the first sealing layer 5, the second sealing layer 4, the first edge layer 6, and the second edge layer 7 are all impermeable materials. Under normal circumstances, the modified phosphogypsum is sealed within the impermeable system and will not pollute the surrounding environment. However, when the subgrade structure develops cracks due to unexpected events or deformation during long-term use, coupled with rainfall, the modified phosphogypsum pollutants may be washed away, forming leachate.

[0010] Furthermore, water quality monitoring wells 9 are installed around the cascade unit-type drainage ditch purification system 1 to monitor changes in the surrounding groundwater quality. When the groundwater phosphorus and fluoride levels exceed the standards, the cause needs to be verified and emergency measures taken.

[0011] Furthermore, the inner cavity of the tiered unit-type drainage ditch purification system 1 is divided into three parts by setting a first baffle wall 13 and a second baffle wall 14. These are the rainwater collection tank 10, the fluoride removal tank 11, and the phosphorus removal tank 12, which are connected in series in the tiered unit-type drainage ditch purification system 1. Under normal circumstances, it serves to guide and discharge rainwater runoff from the drainage ditch and can purify suspended solids, organic matter, heavy metals, and other pollutants in the rainwater. In case of an accident, it can efficiently and directionally purify pollutants such as fluoride and phosphorus in the modified phosphogypsum leachate, ensuring the safety of the surrounding water quality.

[0012] Furthermore, the tiered unit-type drainage ditch purification system 1 is composed of a first side wall 28 and a second side wall 29 on the longitudinal sides of its perimeter, and a side wall 31 on the transverse sides. A base plate 30 is set at the bottom. The first side wall and the second side wall are at the same height, which is basically level with the road surface. The impermeable geotextile 15 is laid in the cavity formed by the first side wall, the second side wall, the side wall and the base plate.

[0013] Furthermore, the first retaining wall 13 is a brick structure, built from the bottom plate upwards. The top of the first retaining wall 13 is 10-20cm lower than the first side wall. The second retaining wall 14 is a brick structure, with the top being 10-20cm higher than the first side wall. The bottom is provided with water outlets 20-30cm high at intervals. A grid plate 16 is provided on the side near the phosphorus removal tank to intercept large particulate pollutants and debris, which needs to be cleaned regularly.

[0014] Furthermore, the rainwater collection trough 10 is located between the first side wall 28 and the first retaining wall 13, and its interior is an empty channel. The modified phosphogypsum leachate collected by the leachate collection pipe 2 flows into the rainwater collection trough 10. When natural rainfall also flows into the rainwater collection trough, the two mix and flow through the top of the first retaining wall 13. After being purified by the functional material filled in the defluorination tank 11, it flows into the dephosphorization tank 12 from the water outlet at the bottom of the second retaining wall 14. After the total phosphorus pollution is reduced in the dephosphorization tank, it enters the rainwater collection trough 10 of the next stage unit-type drainage ditch purification system, or is discharged into the subsequent highway drainage system. Rainwater runoff collected from the surrounding area of ​​the rainwater collection trough mixes with the modified phosphogypsum leachate and undergoes preliminary purification through sedimentation in the rainwater collection trough to reduce pollution such as suspended solids and organic matter in the rainfall.

[0015] Furthermore, the defluorination tank 11 is located between the first baffle wall 13 and the second baffle wall 14, and is provided with an aggregate layer 17, a purification layer 18, an activated carbon layer 19 and a composite layer 20 in sequence from bottom to top. A lightweight cover plate 21 is provided on the top to prevent the composite layer filler from being washed away.

[0016] Furthermore, the aggregate layer is 30-40cm high and filled with 5-8mm thick clinoptilolite, a natural porous mineral with a negatively charged aluminosilicate component that attracts positively charged fluoride ions. The purification layer is 20-30cm high and, depending on the surrounding mineral resources, is mainly filled with one or more combinations of apatite, illite, montmorillonite, and maifanite. The apatite, illite, and montmorillonite particles are 1-3mm in diameter, and the maifanite particles are 3-5mm in diameter. It primarily purifies fluoride pollution through ion exchange and physical adsorption. The activated carbon layer is 15-20cm high and filled with 4-6mm thick modified granular activated carbon. This carbon is modified by loading with metal oxides such as iron and aluminum or by introducing surface functional groups such as amino and thiol groups, thereby significantly improving the chemical adsorption effect of the modified activated carbon on fluorides. The composite layer is 15-20m high and consists of 5-10mm blast furnace slag and 0.5-2mm kaolin or fly ash. The volume ratio of blast furnace slag to kaolin or fly ash is 30-40:60-70. By compounding adsorbents of different particle sizes, the number of fluoride adsorption sites is increased.

[0017] Furthermore, the phosphorus removal tank 12 is located between the second retaining wall 14 and the second side wall 29, and is provided with a limestone layer 22, a steel slag layer 23, and a sand layer 24 from bottom to top. Green plants 25 are planted on top of the sand layer. The limestone layer is 50-60cm high and is filled with 8-12mm limestone particles and 10-20mm gravel. The volume ratio of limestone particles to gravel is 20-30:70-80. The gravel provides skeletal support, and the calcium ions gradually released by the limestone particles combine with phosphorus ions to achieve chemical phosphorus removal. The steel slag layer is 30-40cm high and is filled with 3-10mm steel slag and 10-20mm clinoptilolite. The volume ratio of steel slag to clinoptilolite is 30-40:60-70. Sulfates and iron salts in the water form ferric phosphate precipitate, further reducing the total phosphorus concentration. The sandy soil layer, 15-20cm high, consists of local soil and river sand in a volume ratio of 60-70:30-40, serving to loosen the soil, improve drainage, and anchor plants. The green plants can further absorb phosphorus from the water as fertilizer and also contribute to landscaping.

[0018] Furthermore, a sampling tube 26 is installed on the upper part of the second sidewall 29, with its specific height located at the top of the steel slag layer 23. An observation mirror 27 is installed on the outside of the sampling tube. During rainfall, the observation mirror can be removed to facilitate sampling and testing to determine whether the concentration of pollutants such as fluoride and phosphorus after purification by the stepped unit-type drainage ditch purification system meets local environmental protection standards. It can also be used to sample and test steel slag samples after long-term operation to determine whether the steel slag has become ineffective. Under normal circumstances without rainfall, the physical condition of the internal filler material of the steel slag layer can be directly observed through the observation mirror, and corresponding cleaning measures can be taken based on the observation.

[0019] The beneficial effects of this application are:

[0020] 1. This application adopts a protective structure that fully wraps the modified phosphogypsum subgrade on all four sides, and a leachate collection pipe is provided at the bottom of the second sealing layer. In the event of damage to the protective structure, the leachate from the modified phosphogypsum can be fully collected through the liquid accumulation hole and enter the tiered unit-type drainage ditch purification system for efficient defluorination and phosphorus removal, thus preventing pollution of the surrounding groundwater and soil.

[0021] 2. This application is the first to develop a tiered unit-type drainage ditch purification system, which consists of rainwater collection trough, defluorination trough and dephosphorization trough connected in sequence. The rainwater collection trough, defluorination trough and dephosphorization trough are interconnected and cooperate to give full play to their respective advantages, so as to realize the functions of directional and synchronous defluorination and dephosphorization and the purification functions of conventional road runoff such as suspended solids and organic matter, effectively ensuring the safety of surrounding water quality.

[0022] 3. The fillers inside the defluorination tank and the dephosphorization tank are mainly natural minerals such as zeolite, gravel, maifanite, limestone, kaolin, and river sand, as well as industrial solid wastes such as blast furnace slag, fly ash, and steel slag. This allows for the sourcing of materials locally, reduces costs, and enables the targeted and efficient removal of characteristic pollutants such as fluorine and phosphorus, reflecting the green development concept of resource recycling.

[0023] 4. The mixture of rainwater runoff and modified phosphogypsum leachate in the tiered unit-type drainage ditch purification system is subjected to two-stage vertical baffles to extend the residence time and increase the contact time between the mixture and the defluorination tank and dephosphorization tank, ensuring that the reaction occurs fully.

[0024] 5. The rainwater collection trough functions as a conventional roadside ditch for collecting and draining road runoff. Pre-sedimentation helps settle large particles of silt and suspended solids, allowing the supernatant to pass over the first retaining wall and enter the defluorination and dephosphorization tanks. This extends the service life of both tanks, requiring only periodic cleaning of the rainwater collection trough. The bottom of the second retaining wall is equipped with a water outlet and a grid plate to intercept large particles from entering the dephosphorization tank, ensuring its purification effect.

[0025] 6. The defluorination tank is equipped with an aggregate layer, a purification layer, an activated carbon layer, and a composite layer. The filling materials, such as clinoptilolite, kaolin, blast furnace slag, and fly ash, have a large specific surface area. Furthermore, the silicate, metal ion, and negatively charged properties of these materials enable them to directionally adsorb and filter fluorides through electrostatic interactions and van der Waals forces. Activated carbon, through metal oxide loading or surface functional group modification, enhances chemical adsorption, increasing defluorination efficiency by 30-50%. Natural minerals such as apatite, illite, montmorillonite, and maifanite are excellent fluoride adsorbents, achieving deep defluorination through ion exchange and physical adsorption.

[0026] 7. The phosphorus removal tank is structured with layers of limestone, steel slag, and sand, and filled with specialized fillers such as limestone, gravel, clinoptilolite, steel slag, river sand, and local soil. Gravel and clinoptilolite primarily serve as adsorption filters and provide structural support; the calcium and iron ions in the limestone and steel slag react chemically with phosphorus to form precipitates that remove phosphorus pollution; and the proportioned river sand and local soil help anchor vegetation and increase permeability, facilitating rapid rainwater infiltration.

[0027] 8. A sampling pipe is installed at the top of the steel slag layer at the end of the dephosphorization tank. Routine observation of the packing material morphology changes inside the tank can be performed using an observation lens attached to the sampling pipe. In the event of a modified phosphogypsum leak, a water sample can be taken through the observation lens to confirm whether the water quality treated by the cascade unit-type drainage ditch purification system meets local environmental standards. If the standards are exceeded, the corresponding emergency plan should be activated promptly to ensure water safety.

[0028] 9. The top of the defluorination tank is equipped with a lightweight cover to prevent the packing material from being washed away by heavy rain. Planting vegetation on top of the phosphorus removal tank allows the phosphorus to be absorbed as nutrients for plant growth, and also helps to stabilize the sand layer, thus enhancing the landscape.

[0029] 10. The tiered unit-type drainage ditch purification system has impermeable geotextiles laid on the first sidewall, second sidewall, side walls, and bottom slab to ensure that modified phosphogypsum leachate will not seep out. In the event of a hazardous chemical spill, the spilled hazardous materials can be stored in the filler material inside the defluorination and dephosphorization tanks, thereby controlling the water environment risk. After the accident, the filler material can be cleaned and replaced to restore functionality. Attached Figure Description

[0030] Figure 1 This application includes a cross-sectional structural diagram of the modified phosphogypsum roadbed.

[0031] Figure 2 Plan view of the cascade unit-type drainage ditch purification system in this application;

[0032] Figure 3 Cross-sectional view of the cascade unit-type drainage ditch purification system of this application;

[0033] Figure 4 This application includes a structural diagram of the defluorination tank;

[0034] Figure 5 This application includes a structural diagram of the dephosphorization tank.

[0035] 1: Tiered unit-type drainage ditch purification system; 2: Leachate collection pipe; 3: Liquid accumulation hole; 4: Second sealing layer; 5: First sealing layer; 6: First edging layer; 7: Second edging layer; 8: Modified phosphogypsum filler; 9: Water quality monitoring well; 10: Rainwater collection trough; 11: Defluoridation trough; 12: Dephosphorization trough; 13: First retaining wall; 14: Second retaining wall; 15: Impermeable geotextile; 16: Grating plate; 17: Aggregate layer; 18: Purification layer; 19: Activated carbon layer; 20: Composite layer; 21: Lightweight cover plate; 22: Limestone layer; 23: Steel slag layer; 24: Sand layer; 25: Green plants; 26: Sampling tube; 27: Observation mirror; 28: First side wall; 29: Second side wall; 30: Base plate; 31: Side wall. Detailed Implementation

[0036] 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.

[0037] Example 1

[0038] A stepped unit-type drainage ditch purification system for modified phosphogypsum roadbeds, the purification system comprising: a roadbed, a stepped unit-type drainage ditch purification system 1, and a leachate collection pipe 2; the stepped unit-type drainage ditch purification system 1 is connected to the roadbed via the leachate collection pipe 2; the middle of the roadbed is filled with modified phosphogypsum filler 8, the modified phosphogypsum filler 8 is provided with a first sealing layer 5 and a second sealing layer 4 above and below, respectively, and a first edge layer 6 and a second edge layer 7 on the left and right sides, respectively; the leachate collection pipe 2 is provided at the bottom of the second sealing layer 4, and the section of the leachate collection pipe 2 that contacts the second sealing layer has uniformly arranged liquid accumulation holes 3 on its surface; the first sealing layer 5, the second sealing layer 4, the first edge layer 6, and the second edge layer 7 are all impermeable materials. The inner cavity of the stepped unit-type drainage ditch purification system 1 is divided into three parts by setting a first retaining wall 13 and a second retaining wall 14, namely, the rainwater collection trough 10, the defluorination trough 11, and the phosphorus removal trough 12 connected in series in the stepped unit-type drainage ditch purification system 1; the longitudinal sides of the stepped unit-type drainage ditch purification system 1 are composed of a first side wall 28 and a second side wall 29 respectively, and the transverse sides are composed of side walls 31. A bottom plate 30 is set at the bottom. The first side wall and the second side wall are at the same height, basically level with the road surface. The inner cavity formed by the first side wall, the second side wall, the side walls and the bottom plate is all lined with impermeable geotextile 15. The first retaining wall 13 is a brick structure, built from the bottom slab upwards. The top of the first retaining wall 13 is lower than the first side wall. The second retaining wall 14 is a brick structure, with its top higher than the first side wall. Water outlets are spaced at the bottom. A grating plate 16, made of high-strength resin material, is installed on the side near the dephosphorization tank. The rainwater collection trough 10 is located between the first side wall 28 and the first retaining wall 13, and is an empty channel inside. The modified phosphogypsum leachate collected by the leachate collection pipe 2 flows into the rainwater collection trough 10. The defluorination tank 11 is located between the first retaining wall 13. Between the second retaining wall 14, from bottom to top, there are aggregate layer 17, purification layer 18, activated carbon layer 19 and composite layer 20, and a lightweight cover plate 21 is provided on top; the lightweight cover plate 21 is made of fiberglass, and a sampling tube 26 is provided on the upper part of the second side wall 29. The specific height of the sampling tube is located at the top of the steel slag layer 23, and an observation mirror 27 is provided on the outside of the sampling tube. Water quality monitoring wells 9 are set around the perimeter of the stepped unit drainage ditch purification system 1; the leachate collection pipe 2 and the sampling pipe 26 are made of PP pipe, and the observation mirror 27 is made of plexiglass.

[0039] Example 2

[0040] As shown in Example 1, a stepped unit-type drainage ditch purification system for modified phosphogypsum roadbed has the following specific design specifications: The defluorination tank consists of an aggregate layer, a purification layer, an activated carbon layer, and a composite layer from bottom to top, with a total height of 110cm. The aggregate layer is 40cm high and filled with 5-8mm clinoptilolite; the purification layer is 30cm high and filled with 1-3mm montmorillonite and 3-5mm maifanite, with a volume ratio of montmorillonite to maifanite of 30:70; the activated carbon layer is 20cm high and filled with amino-modified granular activated carbon with a particle size of 4-6mm; the composite layer is 20cm high and filled with 5-10mm blast furnace slag and 0.5-2mm fly ash, with a volume ratio of blast furnace slag to fly ash of 40:60. The dephosphorization tank consists of a limestone layer, a steel slag layer, and a sand layer from bottom to top, with a total filler layer height of 110cm. The second retaining wall and the second side wall have a total height of 120cm. The limestone layer is 50cm high, filled with 8-12mm limestone particles and 10-20mm gravel, with a volume ratio of limestone particles to gravel of 30:70; the steel slag layer is 40cm high, filled with 3-10mm steel slag and 10-20mm clinoptilolite, with a volume ratio of steel slag to clinoptilolite of 35:65; the sand layer is 20cm high, filled with yellow soil and river sand in a volume ratio of 60:40. Ryegrass and bermudagrass are planted on the sand layer.

[0041] Example 3

[0042] As shown in Example 1, a tiered unit-type drainage ditch purification system for modified phosphogypsum roadbed has the following specific design specifications: The first retaining wall is 100cm high, and the grating plate is 25cm high. The aggregate layer in the defluorination tank is 35cm high and filled with 5-8mm modified clinoptilolite. The purification layer is 25cm high and filled with 1-3mm apatite, 1-3mm illite, and 3-5mm maifanite, with a volume ratio of 30:30:40. The activated carbon layer is 20cm high and filled with 4-6mm alumina-modified granular activated carbon. The composite layer is 20cm high and filled with 5-10mm blast furnace slag and 0.5-2mm kaolin, with a volume ratio of 35:65. The limestone layer in the dephosphorization tank is 55cm high, filled with 8-12mm limestone particles and 10-15mm gravel, with a volume ratio of 30:70. The steel slag layer is 30cm high, filled with 3-10mm steel slag and 15-20mm clinoptilolite, with a volume ratio of 40:60. The sand layer is 15cm high, filled with red soil and river sand in a volume ratio of 70:30, and alfalfa is planted in the sand layer.

[0043] The specific working principle of this application is as follows: Modified phosphogypsum leachate collected through the leachate collection pipe flows into the rainwater collection tank for temporary storage. When highway drainage enters the rainwater collection tank, it is thoroughly mixed with the modified phosphogypsum leachate, and sedimentation occurs, resulting in pretreatment and purification. When the liquid level of the mixture is higher than the first retaining wall, the supernatant of the mixture enters from the top of the defluorination tank. It undergoes step-by-step defluorination and purification through adsorption filtration and chemical reactions in the composite layer, activated carbon layer, purification layer, and aggregate layer. After passing through the water outlet at the bottom of the second retaining wall and intercepting large suspended particles by the grid plate, it enters the dephosphorization tank. In the dephosphorization tank, chemical dephosphorization and adsorption filtration are carried out through the limestone layer, followed by solidification of iron phosphate through the steel slag layer. After the phosphorus is absorbed by the roots and stems of the green plants planted in the sandy soil layer, the mixed liquid, whose pollutants have met the standards, is discharged from the top of the dephosphorization tank into the rainwater collection tank of the next-stage unit-type drainage ditch purification system or a conventional highway ditch.

[0044] Experiment 1: A Comparative Experiment on the Purification Effect of Different Cascade Unit Drainage Ditch Layout Methods

[0045] Experimental Methods: This experiment employed an artificial simulation of high-concentration modified phosphogypsum leachate purification. The influent concentration was set, and a comparative purification experiment was conducted using a simulated drainage ditch with different tiers, based on the structure of Example 1 of this application. Artificial drainage was carried out for 3 hours, simulating pollutant runoff sequentially through a rainwater collection tank, a fluoride removal tank, and a phosphorus removal tank. The flow velocity of the polluted water was 2.0 m / s. The initial pollutant concentrations of the simulated high-concentration modified phosphogypsum leachate were SS 300.0 mg / L, COD 150.0 mg / L, total fluoride 20 mg / L, and total phosphorus 10 mg / L. After the simulated wastewater discharge, water samples were collected from the outlet of the phosphorus removal tank, with each sample repeated three times. The pollutant content in the water samples is shown in the table below. The percentage reduction of each pollutant is calculated as follows: (Initial pollutant concentration - Actual measured pollutant concentration after purification) / Initial pollutant concentration * 100%.

[0046] Experimental Example 1

[0047] Same as Example 2, except that the purification layer is replaced with montmorillonite with a particle size of 1-3 mm; and the composite layer is blast furnace slag with a particle size of 5-10 mm.

[0048] Experiment Example 2

[0049] Same as Example 2, except that the purification layer is replaced with maifanite with a particle size of 3-5mm; and the composite layer is fly ash with a particle size of 0.5-2mm.

[0050] Experimental Example 3

[0051] Same as Example 3, except that the purification layer is replaced with 1-3mm apatite and 1-3mm illite in a volume ratio of 3:3, and the composite layer is 0.5-2mm kaolin.

[0052] Experiment Example 4

[0053] Same as Example 3, except that the purification layer of the defluorination tank is omitted.

[0054] Experimental Example 5

[0055] Same as Example 3, except that the composite layer of the defluorination tank is omitted.

[0056] Experimental Example 6

[0057] Same as Example 2, except that the steel slag layer is 3-10mm thick.

[0058] Experimental Example 7

[0059] Same as Example 2, except that the steel slag layer is replaced with 10-20mm clinoptilolite.

[0060] Experimental Example 8

[0061] Same as Example 2, except that the limestone layer of the dephosphorization tank is omitted.

[0062] Experimental Example 9

[0063] Same as Example 2, except that the steel slag layer of the dephosphorization tank is omitted.

[0064] Table 1. Comparative experiment on purification of drainage ditches with different cascade unit layouts (unit: mg / L)

[0065] Pollutant concentration mg / L SS COD Total fluorine Total phosphorus Example 2 4.3 23.1 0.82 0.15 Example 3 3.0 22.8 0.71 0.11 Experimental Example 1 7.4 24.0 1.32 0.24 Experiment Example 2 8.7 24.9 1.48 0.25 Experimental Example 3 5.5 23.5 0.92 0.21 Experiment Example 4 18.1 48.5 3.71 0.28 Experimental Example 5 17.4 47.8 3.53 0.26 Experimental Example 6 5.4 27.1 0.88 0.31 Experimental Example 7 5.6 28.8 0.91 0.33 Experimental Example 8 7.6 50.8 1.90 0.99 Experimental Example 9 7.0 43.1 1.87 0.49

[0066] Experimental Results: The tiered unit drainage ditch layout described in Examples 2-3 of this application showed the best pollutant purification effect. This involved a rainwater collection trough, a fluoride removal trough, and a phosphorus removal trough, utilizing the layered purification structure of this application. The fluoride removal trough consisted of an aggregate layer, a purification layer, an activated carbon layer, and a composite layer from bottom to top; the phosphorus removal trough consisted of a limestone layer, a steel slag layer, and a sand layer from bottom to top. This effectively removed suspended solids (SS), carbon dioxide (COD), total fluoride, and total phosphorus from polluted water. This method was effective for both rainwater runoff and phosphogypsum roadbed infiltration. The multi-layered structure works together to achieve good removal effects. The simulated initial pollutant concentrations introduced were SS 300.0 mg / L, COD 150.0 mg / L, total fluoride 20 mg / L, and total phosphorus 10 mg / L. After the simulated purification was completed, water samples were collected and measured at the outlet of the phosphorus removal tank. The concentrations of each pollutant were reduced by 98.6%, 84.6%, 95.9%, 98.5% (Example 2), 99.0%, 84.8%, 96.5%, and 98.9% (Example 3), respectively. The purification layer and activated carbon layer of the defluorination tank are the core layers for defluorination. This application is the first to develop a combination of purification layer and composite layer, which mainly uses ion exchange and physical adsorption to deeply purify fluoride pollution. In particular, the layout of the purification layer is a key technology for defluorination in this system. Natural minerals such as apatite, illite, montmorillonite, and maifanite are good fluoride adsorbents. Through experiments, we selected a purification layer filled with 1-3 mm montmorillonite and 3-5 mm maifanite (3:7), and a composite layer filled with 5-10 mm blast furnace slag and 0.5-2 mm maifanite. The composition of the defluorination layer can be: 1-3 mm of fly ash (4:6); or 1-3 mm of apatite, 1-3 mm of illite, and 3-5 mm of maifanite (3:3:4) filling the purification layer, and 5-10 mm of blast furnace slag and 0.5-2 mm of kaolin (35:65) filling the composite layer. This multi-layer core defluorination layer combination achieves a superior defluorination effect. Comparative purification effects in Examples 4-5 (omitting one layer) show that the defluorination effect is not as good as that in Examples 2-3 of this application, especially in terms of the purification rates for SS, COD, and total fluorine, which are significantly lower than in Examples 2-3. Similarly, the dephosphorization tank has a structure including a limestone layer, a steel slag layer, and a sand layer, filled with specific fillers such as limestone, gravel, clinoptilolite, steel slag, river sand, and local soil. Gravel and clinoptilolite mainly serve as adsorption filters and skeletal support; calcium and iron ions in limestone and steel slag can react chemically with phosphorus to generate precipitates that remove phosphorus pollution. The limestone layer and steel slag layer are the core layers for phosphorus removal. Through experiments, we have screened and found that a combination of multiple core phosphorus removal layers can achieve better fluoride removal. Through comparative purification effects of omitting one layer in Experiment 8-9, it was found that the phosphorus removal effect was not as good as that of Examples 2-3 of this application, especially the purification rate of SS, COD and total phosphorus was significantly lower than that of Examples 2-3.Meanwhile, we obtained the component ratios of each layer through different formulation experiments. Through Experiments 1-3 and 6-7, we obtained the material ratios of the core layer for purification and defluorination and the core layer for purification and dephosphorization of this application. By using one or two of the purification materials alone to replace the combined materials, the simultaneous purification effect on SS, COD, total fluorine and total phosphorus was not as good as the purification effect after combination. In addition, the experiments showed that the purification structure of this application has a better effect on removing SS. Except for Experiments 4-5, the SS in other embodiments and examples is below 10 mg / L.

[0067] Experiment 2: Adsorption kinetics of fluoride on different defluorination tank material formulations

[0068] Experimental Methods: This experiment was conducted in the laboratory. The adsorption test was a simulated phosphogypsum permeate test. A sodium fluoride solution with an initial fluoride concentration of 20 mg / L was added to a 250 mL Erlenmeyer flask. Each treatment group's sample (3 g per layer) was added sequentially. The particle size of each treatment group was measured in mm, and the proportions were by volume. The pH of the mixed solution was maintained at approximately 7 using HCl or NaOH. The Erlenmeyer flask was then placed in a shaking device at 200 r / min at room temperature. Samples were taken and filtered after 24 h, with each sample repeated three times. Finally, the fluoride ion concentration of the filtrate was measured. The data after treatment are shown in Table 2.

[0069] Table 2. Adsorption kinetics of fluoride on different defluorination tank material formulations.

[0070] Material proportions Aggregate layer Purification layer Activated carbon layer Composite layer 24-hour fluoride concentration (mg / L) Experimental Example 10 5-8 clinoptilolite 1-3 apatite, 1-3 illite, 1-3 montmorillonite, 3-5 maifanite, 3:3:4 4-6 Amino Modified Granular Activated Carbon 5-10 blast furnace slag, 0.5-2 kaolin, 4:6 0.65 Experimental Example 11 5-8 clinoptilolite 1-3 Montmorillonite, 3-5 Maifanite, 3:7 4-6 Alumina Modified Granular Activated 5-10 blast furnace slag, 0.5-2 fly ash, 4:6 0.57 Experimental Example 12 5-8 clinoptilolite 1-3 apatite, 1-3 illite, 1-3 montmorillonite, 3-5 maifanite, 2:3:5 4-6 Amino Modified Granular Activated Carbon 5-10 blast furnace slag, 0.5-2 kaolin, 4:6 0.67 Experimental Example 13 5-8 clinoptilolite 1-3 apatite, 1-3 illite, 1-3 montmorillonite, 3-5 maifanite, 3:3:4 4-6 Amino Modified Granular Activated Carbon 5-10 blast furnace slag, 0.5-2 kaolin, 5:5 0.69 Experimental Example 14 5-8 clinoptilolite 1-3 Montmorillonite, 3-5 Maifanite, 5:5 4-6 Alumina Modified Granular Activated 5-10 blast furnace slag, 0.5-2 fly ash, 7:3 0.75 Experimental Example 15 5-8 clinoptilolite 1-3 Montmorillonite, 3-5 Maifanite, 3:7 4-6 Alumina Modified Granular Activated 2-4 Blast furnace slag, 3-5 Fly ash, 4:6 0.78 Experimental Example 16 5-8 clinoptilolite 1-3 apatite, 1-3 illite, 1-3 montmorillonite, 3-5 maifanite, 3:3:4 2-3 Activated Carbon 5-10 blast furnace slag, 0.5-2 kaolin, 4:6 0.90 Experimental Example 17 1-4 zeolite 1-3 Montmorillonite, 3-5 Maifanite, 3:7 4-6 Alumina Modified Granular Activated 5-10 blast furnace slag, 0.5-2 fly ash, 4:6 0.98 Experimental Example 18 5-8 clinoptilolite 5-10 blast furnace slag, 0.5-2 fly ash, 4:6 4-6 Alumina Modified Granular Activated 1-3 Montmorillonite, 3-5 Maifanite, 3:7 1.18 Experimental Example 19 5-8 clinoptilolite 1-3 apatite, 1-3 illite, 1-3 montmorillonite, 3-5 maifanite, 3:3:4 5-10 blast furnace slag, 0.5-2 kaolin, 4:6 4-6 Amino Modified Granular Activated Carbon 1.04

[0071] Experimental Results: The fluoride removal tank of this application, consisting of an aggregate layer, a purification layer, an activated carbon layer, and a composite layer, effectively adsorbs fluoride ions from the phosphogypsum permeation simulation solution. This application, through research on the fluoride removal mechanism of the phosphogypsum permeation solution, determined the purification sequence of the fluoride removal tank: passing through the composite layer, activated carbon layer, purification layer, and aggregate layer sequentially. First, materials with large specific surface areas, such as kaolin, blast furnace slag, and fly ash, directionally adsorb fluorides, enabling rapid physical adsorption through electrostatic interactions and van der Waals forces. Next, a modified activated carbon particle layer, with metal oxide loading and surface functional group modification, enhances the adsorption effect and effectively solidifies and stabilizes the adsorbed solids. Finally, a combination of excellent fluoride adsorbents, such as apatite, illite, montmorillonite, and maifanite, is used to achieve deep defluorination again through ion exchange. By simulating the tiered unit drainage ditch defluorination tank of this application using leachate, the defluorination and purification are carried out step by step through adsorption filtration and chemical reaction of composite layer, activated carbon layer, purification layer and aggregate layer. In Experimental Examples 10-11 of this application, the combination ratio of aggregate layer, purification layer, activated carbon layer and composite layer has the best defluorination effect. Experimental Examples 12-17, which changed the selection, particle size and ratio of purification and defluorination materials, did not have the same defluorination effect as Experimental Examples 10-11. The order of the purification structure of aggregate layer, purification layer, activated carbon layer and composite layer in the defluorination tank of this application has a significant impact on the defluorination effect. By adjusting the addition order of purification layer, activated carbon layer and composite layer purification materials in Experimental Examples 18-19, it was found that the purification effect was significantly lower than that of Experimental Examples 10-11 of this application, indicating that the addition order has a significant impact on the defluorination effect.

[0072] Experiment 3: Adsorption kinetics of phosphorus by different phosphorus removal tank material formulations

[0073] Experimental Methods: This experiment was conducted in the laboratory. The adsorption test was a simulated phosphogypsum permeation test. A potassium dihydrogen phosphate solution with an initial phosphorus concentration of 10 mg / L was placed in a 250 mL Erlenmeyer flask. Each treatment group's sample (3 g per layer) was added sequentially. The particle size of each treatment group was measured in mm, and the proportions were by volume. After mixing, the pH of the mixed solution was adjusted to approximately 7 using HCl or NaOH and maintained throughout the process. The Erlenmeyer flask was then placed in a shaking device at 200 r / min at room temperature. The supernatant of the sample was sampled and filtered after 24 h, with each sample repeated three times. Finally, the phosphate concentration of the filtrate was measured. The data after treatment are shown in Table 3 below.

[0074] Table 3. Adsorption kinetics of phosphorus for different phosphorus removal tank material formulations.

[0075] Material proportions limestone layer Steel slag layer Sandy soil layer 24-hour phosphate concentration (mg / L) Experimental Example 20 8-12 lime, 10-20 gravel, 3:7 3-10 steel slag, 10-20 clinoptilolite, 35:65 Yellow soil and river sand 6:4 0.12 Experimental Example 21 8-12 lime, 10-15 gravel, 3:7 3-10 steel slag, 15-20 clinoptilolite, 4:6 Red soil and river sand 7:3 0.11 Experiment Example 22 8-12 lime, 10-20 gravel, 5:5 3-10 steel slag, 10-20 clinoptilolite, 5:5 Yellow soil and river sand 6:4 0.17 Experimental Example 23 8-12 lime, 10-15 gravel, 7:3 3-10 steel slag, 15-20 clinoptilolite, 6:4 Red soil and river sand 7:3 0.20 Experimental Example 24 3-10 steel slag, 10-20 clinoptilolite, 35:65 8-12 lime, 10-20 gravel, 3:7 Yellow soil and river sand 6:4 0.45

[0076] Experimental Results: The phosphorus removal tank of this application, consisting of a limestone layer, a steel slag layer, and a sand layer, effectively adsorbs phosphorus ions from the phosphogypsum permeate solution. This application investigates the phosphorus removal mechanism of phosphogypsum permeate solution and establishes a purification sequence where the phosphorus removal tank passes through the limestone layer, steel slag layer, and sand layer sequentially. First, the limestone layer chemically removes phosphorus; calcium and iron ions react with phosphorus to form precipitates that remove phosphorus pollution. Then, the steel slag layer further adsorbs and solidifies the phosphorus, effectively solidifying and stabilizing the adsorbed solids. The gravel and steel slag in these two layers also provide support, improving the stability of the phosphorus removal tank and increasing the permeability coefficient. The river sand and local soil, prepared according to the specified ratio, can fix the greening plants while further discharging the purified permeate. In Experiment Examples 20-21 of this application, the combination ratio of limestone layer, steel slag layer and sand layer showed the best phosphorus removal effect. In Experiment Examples 22-23, changing the particle size and ratio of the purification and phosphorus removal materials did not achieve the same phosphorus removal effect as Experiment Examples 20-21. The purification structure sequence of this application has a significant impact on the phosphorus removal effect. By adjusting the addition order of limestone layer and steel slag layer materials in Experiment Example 24, it was found that its purification effect was significantly lower than that of Experiment Examples 20-21 of this application, indicating that the addition order has a significant impact on the phosphorus removal effect.

[0077] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A stepped cell drainage trench purification system for modifying a phosphogypsum roadbed, characterized by, The purification system comprises a roadbed, a gradient unit drainage ditch purification system (1), and a leachate collection pipe (2); the gradient unit drainage ditch purification system (1) is communicated with the roadbed through the leachate collection pipe (2); the middle part of the roadbed is filled with modified phosphogypsum fillers (8), the upper and lower parts of the modified phosphogypsum fillers (8) are respectively provided with a first seal layer (5) and a second seal layer (4), and the left and right sides of the modified phosphogypsum fillers (8) are respectively provided with a first edge layer (6) and a second edge layer (7); the bottom of the second seal layer (4) is provided with the leachate collection pipe (2), and the part of the leachate collection pipe (2) in contact with the second seal layer is uniformly provided with liquid accumulation holes (3) on the surface; the gradient unit drainage ditch purification system (1) is sequentially connected by a rain collecting groove (10), a defluorination groove (11) and a phosphorus removal groove (12).

2. The stepped cell gutter purification system of claim 1, wherein, The inner cavity of the gradient unit drainage ditch purification system (1) is divided into three parts, i.e. the rain collecting groove (10), the defluorination groove (11) and the phosphorus removal groove (12), by the first barrier wall (13) and the second barrier wall (14).

3. The stepped cell gutter purification system of claim 2, wherein, The outer periphery of the gradient unit drainage ditch purification system (1) is composed of the first side wall (28) and the second side wall (29) on the longitudinal sides, the side wall (31) on the transverse sides, and the bottom plate (30) at the bottom, the first side wall and the second side wall have the same height and are basically level with the road surface, and the inner cavity formed by the first side wall, the second side wall, the side wall and the bottom plate is paved with the impermeable geotextile (15).

4. The stepped cell gutter purification system of claim 3, wherein, The top of the first barrier wall (13) is lower than the first side wall (28), the top of the second barrier wall (14) is higher than the first side wall (28), and the bottom is provided with a water overflow port, and a grating plate (16) is arranged on the side close to the phosphorus removal groove.

5. The stepped cell gutter purification system of claim 4, wherein, The rain collecting groove (10) is between the first side wall (28) and the first barrier wall (13), and the inside is empty, and the modified phosphogypsum leachate collected by the leachate collection pipe (2) flows into the rain collecting groove (10).

6. The stepped cell gutter purification system of claim 5, wherein, The defluorination groove (11) is between the first barrier wall (13) and the second barrier wall (14), and is sequentially provided with an aggregate layer (17), a purification layer (18), an activated carbon layer (19) and a composite layer (20) from bottom to top, and is provided with a light cover plate (21) at the top; the aggregate layer is mainly filled with clinoptilolite; the purification layer is mainly filled with one or more combinations of apatite, illite, montmorillonite and medical stone; the activated carbon layer is mainly filled with modified granular activated carbon; and the composite layer is composed of blast furnace slag, kaolin or fly ash.

7. The stepped cell gutter purification system of claim 6, wherein, The phosphorus removal groove (12) is between the second barrier wall (14) and the second side wall (29), and is sequentially provided with a limestone layer (22), a steel slag layer (23) and a sandy soil layer (24) from bottom to top, and a green plant (25) is planted on the top of the sandy soil layer; the limestone layer is mainly filled with limestone and gravel; the steel slag layer is mainly filled with steel slag and clinoptilolite; and the sandy soil layer is composed of local soil and river sand.

8. The stepped cell gutter purification system of claim 7, wherein, The gradient unit drainage ditch purification system (1) is provided with a water quality monitoring well (9) around the periphery.

9. The stepped cell gutter purification system of claim 8, wherein, A sampling pipe (26) is arranged on the upper portion of the second side wall (29), and the sampling pipe is arranged at the top of the steel slag layer (23) in particular, and an observation mirror (27) is arranged outside the sampling pipe.

10. The step unit drainage ditch purification system according to claims 1-9 is applied in any one of the following aspects: (1) application in purifying leachate in emergency disposal of pollutants after damage of phosphogypsum subgrade; (2) application in collecting, guiding, draining and purifying highway rainwater runoff; (3) application in simultaneously removing fluorine ions, phosphorus ions, SS and COD in the drainage ditch of the phosphogypsum subgrade; (4) application in drainage safety guarantee in the construction and mine backfill industry.

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