Harmless ardealite ecological backfilling method for preventing and controlling polluted underground water

Abstract

The invention discloses a harmless ardealite ecological backfilling method for preventing and controlling polluted underground water, and belongs to the technical field of ecological backfilling of solid waste strip mine pits. According to the backfilling method, a base layer, a lower leakage detecting layer, an impermeable layer, a flow guide layer, a backfilling layer, an upper leakage detecting layer, a blocking layer and a repairing layer are arranged from bottom to top. The upper leakage detection layer can discharge evaporated water in the backfill pile body, external rainwater can be discharged through the upper leakage detection layer after the barrier layer is damaged, the increment of percolate is controlled, the damage condition of the barrier layer can be reflected in time, and it is guaranteed that the water content in the pile body is low, the percolate amount is reduced, and the pollution source intensity is reduced. A solid tracer is doped in the lower leakage detection layer, so that the integrity of the impermeable layer can be indicated, and the impermeable layer can be repaired in time; quicklime is doped in the base layer, so that fluoride and phosphate in the percolate can be adsorbed or neutralized, time is bought for repairing the impermeable layer, and the effect of preventing and controlling underground water pollution is achieved. All functional layers have a synergistic effect, so that the percolate is effectively prevented from infiltrating to pollute underground water.

Description

Technical Field

[0001] The present invention belongs to the technical field of ecological backfilling of solid waste open-pit mines, and in particular relates to a harmless phosphogypsum ecological backfilling method for preventing and controlling groundwater pollution. Background Art

[0002] Phosphogypsum, a solid waste generated by the phosphate fertilizer industry, has seen increasing utilization rates in recent years. However, historically large stockpiles pose significant environmental risks. Currently, phosphogypsum utilization is primarily focused on building materials, but sustaining large quantities is difficult. Large-scale efforts are underway to reclaim and reclaim harmless open-pit phosphogypsum. This not only addresses the issue of balancing production and sales of phosphogypsum, but also promotes ecological restoration of open-pit mines and contributes to high-quality economic and social development. However, leachate from this reclaimed phosphogypsum can easily contaminate groundwater.

[0003] Existing ecological backfills for harmless phosphogypsum open-pit mines are protected by HDPE membranes at the top and bottom. However, aging and damage to the top membrane can allow rainwater to enter the harmless phosphogypsum pile, increasing leachate and making it difficult to detect. Damage to the bottom membrane can also cause leachate to seep down and contaminate groundwater, making it impossible to ensure the long-term environmental safety of the ecological backfill. Therefore, it is necessary to develop a harmless phosphogypsum ecological backfill method that can effectively prevent and control groundwater contamination. Summary of the Invention

[0004] In response to the above-mentioned existing technologies, the present invention discloses a harmless phosphogypsum ecological backfilling method for preventing and controlling groundwater pollution, so as to solve the technical problem that the existing phosphogypsum landfilling technology cannot ensure environmental safety.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is to provide a harmless phosphogypsum ecological backfill method for preventing and controlling groundwater pollution, which comprises the following steps: S1: Level the pit bottom and grout the strongly weathered and broken zone with cement slurry. Then spread the clay mixed with quicklime to the bottom of the pit. After compacting the clay, a 10 cm thick layer with a permeability coefficient of less than 1×10 -7 cm / s base layer; S2: Clay mixed with chloride solid tracer is laid on the surface of the base, and compacted to form a 5cm thick soil with a permeability coefficient of less than 1×10 -5 cm / s, and then lay clay on the surface of the lower leak detection layer, and compact it to form a layer with a thickness of ≥0.7m and a permeability coefficient of <1×10 -5 cm / s impermeable layer; S3: Set up several trapezoidal ditches with a spacing of 20m on the surface of the anti-seepage layer, and fill the trapezoidal ditches with 5-20mm graded pebbles to form a diversion layer; S4: backfilling the pretreated harmless phosphogypsum in layers onto the diversion layer to form a backfill layer with a stepped structure; S5: Clean sharp objects from the backfill layer surface. Install trapezoidal leak detection trenches at 5m intervals along the slope edge from the top of the backfill layer toward the slope foot. Connect the trapezoidal leak detection trenches at the slope foot to the trapezoidal trenches in the diversion layer. Fill the trapezoidal leak detection trenches with 5-10mm graded pebbles to form an upper leak detection layer. Lay HDPE film on the surface of the upper leak detection layer to form a barrier layer. Install trapezoidal leak detection trenches at welds where the HDPE film is prone to damage, at slope foot wrinkles, and below stress concentration areas. S6: laying eco-bags filled with cultivated soil on the surface of the barrier layer 7, laying pre-treated cultivated soil on top of the eco-bags and spreading grass seeds to form a repair layer.

[0006] On the basis of the above technical solution, the present invention can also be improved as follows.

[0007] Furthermore, the pH of the clay after adding quicklime in step S1 is 9-11.

[0008] Furthermore, the slope ratio on both sides of the base layer, the lower leak detection layer and the anti-seepage layer is 2%.

[0009] Furthermore, in step S3, the depth of the trapezoidal ditch is 200 mm, the width of the upper side is 250 mm, and the width of the lower side is 200 mm.

[0010] Furthermore, in step S4, each layer has a height of 3 to 5 m, a slope of less than 40%, and a 2 to 3 m wide platform is provided between layers.

[0011] Furthermore, in step S5, the thickness of the HDPE film is 1.5 mm.

[0012] Furthermore, in step S6, the thickness of the eco-bag filled with rooting soil is 100 mm; the pretreatment method of the cultivated soil is to remove plants and seeds with developed rhizomes; the thickness of the cultivated soil laid on the eco-bag is 200 mm, and the density of the grass seeds is 2-3 g / m 2 .

[0013] The beneficial effects of the present invention are: 1. After harmless pretreatment, phosphogypsum produces very little leachate. By setting an upper leak detection layer below the barrier layer and above the backfill layer, the evaporated water in the backfill pile can be discharged. At the same time, if the barrier layer is damaged, external rainwater can be discharged from the pile through the layer, effectively controlling the increase in leachate. The damage of the barrier layer can be reflected by the change in water volume and repaired in time, which can ensure that the moisture content in the pile is low, the amount of leachate is reduced, and the intensity of the pollution source is reduced.

[0014] 2. A lower leak detection layer mixed with chloride solid tracer is set on the base layer, and the permeability coefficient of the base layer is guaranteed to be greater than that of the lower leak detection layer. When the anti-seepage layer is penetrated by leachate, the dissolved chloride tracer seeps out of the pile through the junction of the two layers. The integrity of the anti-seepage layer is indicated by regularly testing the chloride concentration of the seepage liquid, so that timely repairs can be made to prevent groundwater pollution.

[0015] 3. By adding quicklime powder to the base layer to form clay with a pH of about 10, it can ensure that after the anti-seepage layer is penetrated by the leachate, it can adsorb or neutralize the fluoride and phosphate in the leachate, thereby buying time for the repair of the anti-seepage layer and playing a role in preventing and controlling groundwater pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a cross-sectional diagram of each functional layer in the ecological backfill method; Among them, 1. base layer; 2. lower leak detection layer; 3. anti-seepage layer; 4. diversion layer; 5. backfill layer; 6. upper leak detection layer; 7. barrier layer; 8. repair layer. DETAILED DESCRIPTION

[0017] The cross-sectional schematic diagram of each functional layer in the ecological backfill method of the present invention is as follows Figure 1 As shown, it includes a base layer 1, a lower leak detection layer 2, an anti-seepage layer 3, a guide layer 4, a backfill layer 5, an upper leak detection layer 6, a barrier layer 7 and a repair layer 8.

[0018] The specific implementation methods of the present invention are described in detail below with reference to the embodiments.

[0019] Example 1 A harmless phosphogypsum ecological backfill method for preventing and controlling groundwater pollution, the method comprising the following steps: S1: Level the bottom and slope of the open pit, and grout the strongly weathered and broken zone with cement slurry; add quicklime to the neutral clay, mix well, and adjust the clay pH to 10. Then spread the clay mixed with quicklime to the bottom and slope of the pit, and compact it to form a 10cm thick and permeability coefficient <1×10 -7 cm / s base 1; S2: Sodium chloride-added clay is laid on the surface of base 1 and compacted to form a 5 cm thick clay with a permeability coefficient of <1×10 - 5 cm / s lower leak detection layer 2 (the permeability coefficient of the base layer 1 is greater than that of the lower leak detection layer 2), and then clay is laid on the surface of the lower leak detection layer 2 to form a layer with a thickness of 1m and a permeability coefficient of less than 1×10 -5 cm / s anti-seepage layer 3; the slope ratio of the base layer 1, the lower leak detection layer 2 and the anti-seepage layer 3 is 2%; S3: excavate a trapezoidal ditch every 20m on the surface of the anti-seepage layer 3 (the trapezoidal ditch is 200mm deep, 250mm wide at the top, 200mm wide at the bottom, and has a 3% horizontal and vertical slope). Then fill the trapezoidal ditch with 5-20mm graded pebbles, with the pebble size increasing from bottom to top, to form the diversion layer 4. S4: The phosphogypsum is subjected to harmless treatment (selecting a combination of processes such as washing, flotation, solidification, and roasting) so that the pH, ammonia nitrogen, fluoride, phosphate, chemical oxygen demand, total lead, total cadmium, total arsenic, total mercury, and total chromium in the leachate prepared in accordance with HJ557-2010 "Solid Waste Leaching Toxicity Leaching Method - Horizontal Oscillation Method" meet the requirements of HJ1415 "Technical Specifications for Pollution Control of Phosphogypsum Utilization and Harmless Storage" and meet the requirements of Class I solid waste. The harmless phosphogypsum is then backfilled in layers above the diversion layer 4 to form a stepped backfill layer 5, with each layer 3-5m high and a slope of less than 40%. A 2-3m wide platform is set between layers. The harmless phosphogypsum between layers is compacted using a double steel wheel roller with a permeability coefficient of less than 1×10 -5 cm / s; S5: Level the surface of the backfill layer 5 and clean any sharp objects from it. Continuously excavate trapezoidal leak detection trenches at 5m intervals along the slope edge from the top of the backfill layer 5 toward the slope foot. The slope should be flush with the phosphogypsum surface of the backfill layer 5. The trapezoidal leak detection trench at the slope foot should be connected to the trapezoidal trench of the diversion layer 4. Fill the trapezoidal leak detection trench with 5-10mm graded pebbles, with the pebble particle size increasing from bottom to top, to form an upper leak detection layer 6. Lay a 1.5mm thick HDPE film on the surface of the upper leak detection layer 6. When laying the HDPE film, ensure that trapezoidal leak detection trenches are provided at welds where the HDPE film is easily damaged, at wrinkles at the slope foot, and below stress concentration areas. Weld the HDPE film into a whole to form a barrier layer 7. S6: Lay 100mm thick eco-bags (filled with cultivated soil) on the surface of the barrier layer 7 to compact and protect the soil. Then remove the shrubs, trees and other plants with developed roots and seeds in the cultivated soil and lay them on the eco-bags to a thickness of 200mm. Then, apply 2~3g / m 2 Grass seeds are densely spread and water is sprinkled to replenish moisture; rainwater collection ditches are dug on the interlayer platform to drain the rainwater from the top to form a repair layer 8.

[0020] Although the specific embodiments of the present invention have been described in detail in conjunction with the embodiments, this should not be construed as limiting the scope of protection of this patent. Within the scope described by the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A harmless phosphogypsum ecological backfill method for preventing and controlling groundwater pollution, characterized in that: The following steps are involved: S1: Level the pit bottom and grout the strongly weathered and broken zone with cement slurry. Then spread the clay mixed with quicklime to the bottom of the pit. After compacting the clay, a 10 cm thick layer with a permeability coefficient of less than 1×10 -7 cm / s base layer (1); S2: Clay doped with chloride solid tracer is laid on the surface of base (1) and compacted to form a 5 cm thick soil with a permeability coefficient of <1×10 -5 cm / s, and then clay is laid on the surface of the lower leak detection layer (2) to form a layer with a thickness of ≥0.7m and a permeability coefficient of <1×10 -5 cm / s impermeability layer (3); S3: setting a number of trapezoidal ditches with a spacing of 20m on the surface of the anti-seepage layer (3), and filling the trapezoidal ditches with 5-20mm graded pebbles to form a diversion layer (4); S4: backfilling the pre-treated harmless phosphogypsum in layers onto the diversion layer (4) to form a backfill layer (5) with a stepped structure; S5: clean the sharp objects on the surface of the backfill layer (5), and continuously set trapezoidal leak detection trenches from the top of the backfill layer (5) to the slope foot along the slope edge at intervals of 5 m. The trapezoidal leak detection trenches at the slope foot are connected to the trapezoidal trenches of the diversion layer (4), and the trapezoidal leak detection trenches are filled with 5-10 mm graded pebbles to form an upper leak detection layer (6); and then HDPE film is laid on the surface of the upper leak detection layer (6) to form a barrier layer (7); S6: laying an eco-bag filled with cultivated soil on the surface of the barrier layer (7), laying pre-treated cultivated soil on top of the eco-bag and spreading grass seeds to form a repair layer (8).

2. The method for ecological backfilling of harmless phosphogypsum for preventing and controlling groundwater pollution according to claim 1, characterized in that: The pH of the clay after adding quicklime in step S1 is 9-11.

3. The method for ecological backfilling of harmless phosphogypsum for preventing and controlling groundwater pollution according to claim 1, characterized in that: The slope ratio of both sides of the base layer (1), the lower leak detection layer (2) and the anti-seepage layer (3) is 2%.

4. The method for ecological backfilling of harmless phosphogypsum for preventing and controlling groundwater pollution according to claim 1, characterized in that: The trapezoidal ditch in step S3 has a depth of 200 mm, a width of 250 mm at the top and a width of 200 mm at the bottom.

5. The method for ecological backfilling of harmless phosphogypsum for preventing and controlling groundwater pollution according to claim 1, characterized in that: In step S4, each layer is 3-5 m high, with a slope of less than 40%, and a 2-3 m wide platform is provided between layers.

6. The method for ecological backfilling of harmless phosphogypsum for preventing and controlling groundwater pollution according to claim 1, characterized in that: The thickness of the HDPE film in step S5 is 1.5 mm.

7. The method for ecological backfilling of harmless phosphogypsum for preventing and controlling groundwater pollution according to claim 1, characterized in that: The thickness of the eco-bag in step S6 is 100mm; the pretreatment method of the cultivated soil is to remove plants with developed rhizomes and seeds; the thickness of the cultivated soil laid on the eco-bag is 200mm, and the density of the grass seeds is 2-3g / m 2 .

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