A method for backfilling a mine pit by squeezing dewatering of bauxite washing slurry water based on a tube bag

Abstract

The application discloses a method for filling a mine pit by extruding and dehydrating based on bauxite washing slurry engineering pipe bag, which comprises the following steps: carrying out site arrangement on the bottom of the mine pit, laying out matched drainage system facilities, layer by layer adding flocculation slurry filling to the engineering pipe bag, starting the drainage system to timely discharge clean water extruded from the slurry filling engineering pipe bag, and using straw rods and the like as filter-pressing drainage channels between the engineering pipe bags when the last six layers of engineering pipe bags at the top of the slurry landfill are operated, and completely overlapping the last two layers of engineering pipe bags at the top and reserving gaps between the two layers of engineering pipe bags as rainwater drainage ditches of the site. The application can solve the problems of poor drainage consolidation, slow gravity extrusion and dehydration speed and poor rainwater drainage when the slurry in a mine pit with a large area is filled.

Description

Technical Field

[0001] This invention belongs to the field of landscape and ecological restoration technology, specifically relating to a method for backfilling mine pits based on the extrusion dewatering of bauxite washing slurry in a water-manhole bag. Background Technology

[0002] Aluminum is the most produced non-ferrous metal, but bauxite mining and washing lead to numerous ecological and environmental problems, including large-scale stockpiling of bauxite slime, difficulties in dewatering and disposing of bauxite slime, insufficient soil sources for filling bauxite mining voids, and fragmentation of the ecological landscape. Bauxite slime is a solid waste product from bauxite washing, and its material composition originates from weathered colluvial deposits in the mining area. Bauxite slime has a similar chemical composition to the soil of surrounding slopes and farmland, but its physical properties, such as particle size, structure, and moisture content, are altered; other properties are basically similar to bauxite slime.

[0003] Geotextile tubes are containers used in geotechnical construction. They typically consist of tubes constructed from permeable geotextiles, with filling ports on the tubes for filling. After bottom mud, silt, and other materials are filled into the geotextile tubes, the water contained within is discharged through the geotextiles, achieving the purpose of dehydration.

[0004] Adhering to the natural principle of "returning to where it came from," the soil-based treatment of bauxite mining mud from mine pits has become the most effective disposal site for bulk solid waste from the alumina industry. This approach can also restore the landscape and ecology damaged by mining, and restore the original soil properties of the mud and, in some cases, the land resource attributes of the mine pits. However, traditional belt dewatering and plate-and-frame filter press dewatering facilities are insufficient to meet the large-scale production demands for mud treatment and disposal, and their high operating costs create a bottleneck in mud dewatering capacity.

[0005] In recent years, geotextile bags have been widely used for gravity dewatering of river and lake silt above the ground with good results. However, in the operation of mine pits with large depths and areas, there are obvious problems of poor drainage and slow dewatering speed, which restricts the application and promotion of this technology in the in-situ backfilling and reclamation of ore washing mud in the alumina industry.

[0006] Chinese patent CN116114571A discloses a method for dewatering and simultaneously fermenting dredged river and lake sediment into planting soil using geotextile bags. The method includes: S1, pumping a porous biopolymer solution into a sediment conveying pipeline, causing the sediment particles to aggregate and the sediment to separate into layers; adding a conditioner to the conveying pipeline; S2, filling the treated sediment into geotextile bags, where the sediment moisture is drained under internal pressure and gravity; the soil enters a micro-fermentation state under the action of local microorganisms; 3-5 days after filling the geotextile bags, the conditioner coating layer disintegrates under the action of moisture, and coconut coir and compound microbial agents are evenly dispersed into the sediment. The coconut coir promotes a decrease in the sediment moisture content, and the concentrated sediment officially enters the fermentation stage; periodically supplying air into the geotextile bags further reduces the sediment moisture content during fermentation; S3, after 30-45 days, the dredged sediment is fermented into planting soil. This method significantly reduces engineering costs and improves sediment treatment efficiency.

[0007] The aforementioned method of dewatering river and lake dredged sediment using geotextile bags faces challenges such as poor drainage, extremely slow dewatering speed, and difficulty in consolidating the sediment when used in deep and large-area mining pits. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a method for dewatering and backfilling mine pits based on bauxite washing mud in hydraulic pipe bags, which can improve the problems of poor drainage, extremely slow dewatering speed and difficulty in mud consolidation in the operation of deep and large goaf mine pits.

[0009] To solve the above technical problems, the present invention adopts the following technical solution:

[0010] A method for backfilling mine pits based on bauxite washing sludge through a water-manipulation pipe bag for dewatering is characterized by the following steps:

[0011] (1) Mix bauxite washing mud with coagulant aid and flocculant, and flocculate to obtain flocculated mud;

[0012] (2) The bottom of the mine pit is leveled, and the first layer of geotextile bags is laid on the leveled bottom of the mine pit. The laying method is to lay multiple geotextile bags side by side, with an overlap of 0.6~1.0m between two adjacent flat geotextile bags that have not been filled with mud, so as to ensure that after these side by side geotextile bags are filled with flocculated sludge, a gap of 0.08~0.12m is formed between two adjacent geotextile bags, which is conducive to drainage.

[0013] (3) Turn 90° and lay the second layer of geotextile bags vertically side by side on the first layer of geotextile bags; the laying method is the same as step (2); the subsequent layers of geotextile bags are laid vertically side by side on the next layer in the same way until the sixth layer at the top ends this method.

[0014] (4) At every intersection of four geotextile bags, a PVC vertical pipe with multiple openings around its walls is installed. The PVC vertical pipe is open at both the top and bottom ends, and two adjacent PVC vertical pipes are connected by a PE pipe; or, at every intersection of four geotextile bags, a hollow circular vertical pipe with a diameter of 200-400mm made of steel bars is installed, and the hollow circular vertical pipes are connected by a PE pipe; finally, these PVC vertical pipes or hollow circular vertical pipes are connected to the mine pit through a PE pipe, so that the geotextile bags collected in the mine pit are squeezed out and the clean water is continuously discharged to the mine pit.

[0015] (5) A multi-hole plastic pipe with a length of ≥5m, a diameter of 50mm, and a hole with a diameter of 5-6mm is laid in the gap between every two geotextile bags around the perforated PVC pipe or the hollow circular vertical pipe to collect the clear liquid discharged from the geotextile bags; the multi-hole plastic pipe is connected to the perforated PVC pipe or the hollow circular vertical pipe.

[0016] (6) After filling 5 to 10 layers of geotextile bags, repeat steps (4) to (5) and lay a layer of PE connecting pipes with PVC pipes or hollow circular vertical pipes.

[0017] (7) In a low-lying area near the mine pit with convenient drainage, a simple large-diameter well is constructed by using red bricks or cement bricks in the form of a flower wall, and a water pump and its water level sensor are installed to collect and discharge all the clear liquid discharged by gravity squeezing of the soil in the geotextile bag in the mine pit; the clear liquid is returned to the bauxite washing plant through the original pipeline or discharged into the nearby ditch.

[0018] (8) When the mine pit is backfilled to the last six layers, the perforated PVC pipe or hollow circular vertical pipe no longer uses PE connecting pipe, but instead the space between two adjacent geotextile bags in each layer is filled with bundled straw sticks or biodegradable material sticks.

[0019] (9) When the ore mud in the mine pit is backfilled to the last two layers, a gap of 0.3~0.5m is reserved between the two adjacent geotextile bags in each layer after they are filled with ore mud, as a drainage ditch for the site;

[0020] (10) Before laying the last layer of geotextile bags, spread a small amount of boiler bottom ash or fly ash fine particles from the thermal power plant on the penultimate layer of geotextile bags, and then lay the last layer of geotextile bags; at the same time, the laying direction of the last layer of geotextile bags is adjusted to overlap with the laying direction of the next layer of geotextile bags.

[0021] Preferably, in step (4), the diameter is set as follows: starting from the PVC vertical pipe furthest from the large well of the mine, every three PVC vertical pipes of the same diameter are spaced apart, and their diameters are gradually increased from 200 mm to 225 mm, 250 mm, 280 mm, 315 mm, 355 mm, and 400 mm.

[0022] Preferably, in step (4), the diameter of the PE connecting pipe connected to the PVC vertical pipe or the hollow circular vertical pipe also gradually increases from 40 mm to 50 mm, 63 mm, 75 mm, 90 mm and 110 mm.

[0023] Preferably, the opening diameter of the PE connecting pipe on the PVC vertical pipe is the same as the pipe diameter of the corresponding PE connecting pipe, and the opening spacing is the same as the spacing of the two layers of PE pipes to be installed, or corresponds to the cumulative thickness of the geotextile bag stacking design layer in the proposed steps.

[0024] Preferably, in step (5), the PE connecting pipe has a reserved length of 0.5~1m.

[0025] Preferably, in step (4), the height of the PVC vertical pipe is higher than the height of the water pipe bag after this layer is filled.

[0026] Preferably, in step (9), when working on the last two layers of geotextile bags, a temporary bridge needs to be erected between every two geotextile bags to facilitate the construction of workers and ensure their safety.

[0027] Preferably, in step (1), the solid content of the bauxite washing mud is 10-15%, and the amount of flocculant used is equivalent to 0.05-0.1‰ of the dry weight of the bauxite washing mud.

[0028] The present invention has the following advantages:

[0029] This invention involves overlapping two adjacent, unfilled geotextile bags by 0.6-1.0m between each other, vertically crisscrossing geotextile bags between each pair of upper and lower layers, and setting up a perforated circular vertical pipe (200-400mm in diameter) or a 200-400mm PVC vertical pipe (with openings based on the diameter of the connected PE pipe and its vertical position) approximately every 20m around the mine pit. A large-diameter well with a lift pump is installed in the low-lying area of ​​the backfilled mine pit to pump the filtered liquid from the backfilled mine pit to a drainage ditch outside the mine pit or into a pipe network for transport to the clean water pool in the mine's ore washing workshop. To ensure future agricultural reclamation, no non-environmentally friendly materials, except for geotextile bags, can be used in the final six layers of mine mud backfill. Bundled straw or biodegradable material rods are used as channels for the filtration liquid between two flat geotextile bags in each layer. To facilitate rainwater drainage from the mine mud backfill site, a 0.3-0.5m gap is left between two flat geotextile bags in the top two layers as drainage ditches at the end of the site. Water level sensors are installed in simple large-diameter wells built into brick walls. When the dewatered liquid in the wells exceeds the set level, the water pump automatically starts, squeezing the mud and discharging the liquid into ditches outside the mine pit or into the pipe network, returning it to the mine's washing pond for further washing. Through the technological transformation of the drainage system during the above-mentioned geotextile bag mud dewatering construction process, a method has been developed to improve the dewatering, drainage, and consolidation effects of gravity-compression mud dewatering in the mine pit. Detailed Implementation

[0030] To facilitate a better understanding of the present invention, the following examples are provided. These examples fall within the scope of protection of the present invention, but do not limit the scope of protection of the present invention. Example 1

[0031] Anionic polyacrylamide flocculant with a molecular weight of 18 million was prepared to a concentration of 0.05% in a dosing tank. Sludge with a solid content of 10% from the thickening tank of the bauxite washing plant was transported to the sludge disposal site next to the landfill pit through a pipeline transportation system. The above sludge and anionic polyacrylamide were metered into the pipeline mixer, and 50g of anionic polyacrylamide / (t dry weight sludge) was added to the pipeline mixer at one time and mixed with the sludge for 1 min. The sludge that was basically mixed in the pipeline mixer was then entered into the flocculation tank and stirred and flocculated at 80 r / h for 60 min.

[0032] (2) The bottom of the mine pit is leveled, and the first layer of geotextile bags is laid on the leveled bottom of the mine pit. The laying method is to lay multiple geotextile bags side by side, with an overlap of 0.8m between two adjacent flat geotextile bags that have not been filled with mud, so as to ensure that after these side by side geotextile bags are filled with flocculated sludge, a gap of 0.08m is formed between two adjacent geotextile bags, which is conducive to drainage.

[0033] (3) Turn 90° and lay the second layer of geotextile bags vertically side by side on the first layer of geotextile bags. The laying method is to lay multiple geotextile bags side by side. The geotextile bags in this layer are perpendicular to the first layer of geotextile bags. The two adjacent flat geotextile bags that have not been filled with mud overlap each other by 0.8m. Fill these geotextile bags with the flocculated bauxite washing mud and dewater them. At this time, the gap between two adjacent geotextile bags is 0.08m.

[0034] (4) At every intersection of four geotextile bags, a PVC vertical pipe with multiple openings around its perimeter is installed, with openings at both the top and bottom. The openings in the vertical pipe are determined according to the diameter of the connecting PE pipe and its vertical position to collect, receive, and transfer the clean water filtered out by the geotextile bags. Among them, the PVC vertical pipes farthest from the large well are DN200 pipes, and two adjacent PVC vertical pipes are connected by DN40 PE pipes to ensure that the clean liquid pressed by the gravity of the sludge in the geotextile bags is discharged in a timely manner after being pumped out by the large well water pump. The diameter setting method of the PVC vertical pipe is as follows: counting from the PVC vertical pipe farthest from the large well in the mine pit, after three consecutive DN200 PVC vertical pipes are used, its pipe diameter is changed to a DN2250 perforated vertical pipe; after three consecutive DN225 pipes are used, the perforated vertical pipe is replaced with a DN250 pipe; the diameter of the PE connecting pipe is also changed from 40 to DN250. Starting with mm, they are successively replaced with DN50, DN63, and DN75; finally, these PVC vertical pipes are connected to the large well of the mine pit through PE pipes, squeezing out the geotextile bags collected in the mine pit and continuously discharging the clean water into the large well.

[0035] (5) A multi-hole plastic pipe with a length of 5m and a diameter of 50mm is laid in the gap between every two geotextile bags around the perforated PVC pipe to collect the clear liquid discharged from the geotextile bags; the multi-hole plastic pipe is connected to the perforated PVC pipe.

[0036] (6) Repeat steps (4) to (5) after filling 6 layers of geotextile bags, and lay a layer of PE connecting pipes to connect PVC pipes;

[0037] (7) In a low-lying area near the mine pit with convenient drainage, a simple large-diameter well is constructed using red bricks in the form of a flower wall, and a water pump and its water level sensor are installed to collect and discharge all the clear liquid discharged by gravity squeezing of the soil in the geotextile bag in the mine pit; the clear liquid is returned to the bauxite washing plant through the original pipeline or discharged into the nearby ditch.

[0038] (8) When the mine pit is backfilled to the last six layers, no non-environmentally friendly materials such as PE pipes and porous plastic pipes will be used; between two adjacent flat geotextile bags in each layer, straw sticks with a diameter of 0.1m will be used as flow channels for pressure filtration and drainage.

[0039] (9) When the sludge in the mine pit is backfilled to the last two layers, a gap of 0.3 m shall be reserved between two adjacent geotextile bags in each layer as a rainwater drainage ditch for the site.

[0040] (10) When the sludge is backfilled to the last layer, the geotextile bags are arranged in the same direction and overlapped. A small amount of fly ash is sprinkled on the second to last layer of geotextile bags, and then the last layer of geotextile bags is laid. Example 2

[0041] (1) Prepare anionic polyacrylamide flocculant with a molecular weight of 18 million to a concentration of 0.05% in a dosing tank; transport sludge with a solid content of 13% from the thickening tank of the bauxite washing plant to the sludge disposal site next to the landfill pit through a pipeline transportation system; the above sludge and anionic polyacrylamide are metered into the pipeline mixer, and 60g of anionic polyacrylamide / (t dry weight sludge) is added to the pipeline mixer at one time and mixed with the sludge for 1.5 min; the sludge that has been basically mixed in the pipeline mixer enters the flocculation tank and is stirred and flocculated at 100 r / h for 50 min;

[0042] (2) The bottom of the mine pit is leveled, and the first layer of geotextile bags is laid on the leveled bottom of the mine pit. The laying method is to lay multiple geotextile bags side by side, with an overlap of 0.75m between two adjacent flat geotextile bags that have not been filled with mud, so as to ensure that after these side by side geotextile bags are filled with flocculated sludge, a gap of 0.05m is formed between two adjacent geotextile bags, which is conducive to drainage.

[0043] (3) Turn 90° and lay the second layer of geotextile bags vertically side by side on the first layer of geotextile bags; the laying method is the same as step (2); the subsequent layers of geotextile bags are laid vertically side by side on the next layer in the same way until the sixth layer at the top ends this method.

[0044] (4) At every intersection of four geotextile bags, a PVC vertical pipe with multiple openings around its perimeter is installed. The PVC vertical pipe is open at both ends, and the openings are determined according to the diameter of the connected PE pipe and its vertical position to collect, receive, and transfer the clean water filtered out by the geotextile bags. Among them, the PVC vertical pipes farthest from the large well are DN200 pipes, and two adjacent PVC vertical pipes are connected by DN40 PE pipes to ensure that the clean liquid pressed by the gravity of the sludge in the geotextile bags is discharged in time after being pumped out by the large well water pump. The diameter setting method of the PVC vertical pipe is as follows: counting from the PVC vertical pipe farthest from the large well in the mine pit, after three consecutive DN200 PVC vertical pipes are used, its pipe diameter is changed to DN225 perforated vertical pipe; after three consecutive DN225 pipes are used, the perforated vertical pipe is replaced with a DN250 pipe; the diameter of the PE connecting pipe is also changed from 40 to DN250. Starting with mm, they are successively replaced with DN50, DN63, and DN75; finally, these PVC vertical pipes are connected to the large well of the mine pit through PE pipes, squeezing out the geotextile bags collected in the mine pit and continuously discharging the clean water into the large well.

[0045] (5) A multi-hole plastic pipe with a length of 6m and a diameter of 50mm is laid in the gap between every two geotextile bags around the perforated PVC pipe to collect the clear liquid discharged from the geotextile bags; the multi-hole plastic pipe is connected to the perforated PVC pipe.

[0046] (6) Fill 8 layers of geotextile bags and repeat steps (3) to (4) to lay a layer of PE connecting pipes that connect to PVC pipes;

[0047] (7) In a low-lying area near the mine pit with convenient drainage, a simple large-diameter well is constructed using cement bricks in the form of a flower wall, and a water pump and its water level sensor are installed to collect and discharge all the clear liquid discharged by gravity squeezing of the sludge in the geotextile bag in the mine pit; the clear liquid is returned to the bauxite washing plant through the original pipeline.

[0048] (8) When the mine pit is backfilled to the last six layers, no non-environmentally friendly materials such as PE pipes and porous plastic pipes will be used; between two adjacent flat geotextile bags in each layer, biodegradable material rods with a diameter of 0.15 m will be used as the flow channel for pressure filtration and drainage.

[0049] (9) When the ore mud in the mine pit is backfilled to the last two layers, a gap of 0.4 m shall be reserved between two adjacent geotextile bags in each layer as a rainwater drainage ditch for the site.

[0050] (10) When the sludge is backfilled to the last layer, the geotextile bags are arranged in the same direction and overlapped. A small amount of fly ash is sprinkled on the second to last layer of geotextile bags, and then the last layer of geotextile bags is laid. Example 3

[0051] Anionic polyacrylamide flocculant with a molecular weight of 18 million was prepared to a concentration of 0.05% in a dosing tank. Sludge with a solid content of 15% from the thickening tank of the bauxite washing plant was transported to the sludge disposal site next to the landfill pit through a pipeline transportation system. The above sludge and anionic polyacrylamide were metered into the pipeline mixer, and 75g of anionic polyacrylamide / (t dry weight sludge) was added to the pipeline mixer at one time and mixed with the sludge for 1 min. The sludge that was basically mixed in the pipeline mixer was then introduced into the flocculation tank and stirred and flocculated at 120 r / h for 48 min.

[0052] (2) The bottom of the mine pit is leveled, and the first layer of geotextile bags is laid on the leveled bottom of the mine pit. The laying method is to lay multiple geotextile bags side by side, with an overlap of 0.9m between two adjacent flat geotextile bags that have not been filled with mud, so as to ensure that after these side by side geotextile bags are filled with flocculated sludge, a gap of 0.12m is formed between two adjacent geotextile bags, which is conducive to drainage.

[0053] (3) Turn 90° and lay the second layer of geotextile bags vertically side by side on the first layer of geotextile bags; the laying method is the same as step (2); the subsequent layers of geotextile bags are laid vertically side by side on the next layer in the same way until the sixth layer at the top ends this method.

[0054] (4) At every intersection of four geotextile bags, a hollow circular vertical pipe with a diameter of 200mm is installed, which is welded with steel bars. The hollow circular vertical pipes are connected to each other by PE pipes. Finally, these hollow circular vertical pipes are connected to the mine pit well through PE pipes, so that the geotextile bags collected in the mine pit are squeezed out and the clean water is continuously discharged to the well.

[0055] (5) A porous plastic pipe with a length of 7m, a diameter of 50mm, and a hole with a diameter of 5mm every 0.50m is laid in the gap between every two geotextile bags around each hollow circular vertical pipe to collect the clear liquid discharged from the geotextile bags; the porous plastic pipe is connected to the hollow circular vertical pipe.

[0056] (6) For every 10 layers of geotextile bags filled, repeat steps (4) to (5) and lay a layer of PE connecting pipes that connect the hollow circular vertical pipes;

[0057] (7) In a low-lying area near the mine pit with convenient drainage, a simple large-diameter well is constructed using cement bricks in the form of a flower wall, and a water pump and its water level sensor are installed to collect and discharge all the clear liquid discharged by gravity squeezing of the sludge in the geotextile bag in the mine pit; the clear liquid is returned to the bauxite washing plant through the original pipeline.

[0058] (8) When the mine pit is backfilled to the last six layers, no non-environmentally friendly materials such as PE pipes and porous plastic pipes will be used; between two adjacent flat geotextile bags in each layer, straw sticks with a diameter of 0.2 m will be used as flow channels for pressure filtration and drainage.

[0059] (9) When the ore mud in the mine pit is backfilled to the last two layers, a gap of 0.5m is reserved between the two adjacent geotextile bags in each layer after they are filled with ore mud, as a rainwater drainage ditch for the site.

[0060] (10) When the sludge is backfilled to the last layer, the geotextile bags are arranged in the same direction and overlapped. A small amount of fly ash is sprinkled on the second to last layer of geotextile bags, and then the last layer of geotextile bags is laid.

[0061] Dewatering was carried out in the No. 18 mine pit using the original operating conditions. The specific operation was as follows: flocculated sludge was poured into geotextile bags. Under the hydraulic squeezing action of the sludge conveying pump, most of the pore water in the sludge seeped out of the geotextile bags and automatically flowed into the mine pit to fill the low-lying areas on the surface of the geotextile bags or the depressions on the side of the mine pit, and was then pumped away.

[0062] The dewatering of sludge in geotextile bags in mines No. 8, No. 19, and No. 49 was systematically improved according to the methods in Examples 1 to 3.

[0063] The experimental results are shown in the table below.

[0064] As shown in the table above, due to the improved dewatering speed of the geotextile bag sludge dewatering process, the production process time for geotextile bag sludge dewatering has been reduced by more than 25% compared to the original operating conditions. Simultaneously, rainwater drainage from the mine pit surface has been greatly improved, and the dewatering and consolidation effects in the top three layers of geotextile bags have been significantly enhanced. Previously, it took five months or more to reduce the moisture content of the top two layers of geotextile bag sludge to 60%, while the method described in the three improved examples of this patent reduces the time required to reduce the moisture content of the top two layers of geotextile bag sludge to 60% to less than three months. Furthermore, during the summer and autumn months of July to November, the time to reduce the moisture content of the top 0.5m thick sludge to 40% or less is completed in two months or less, demonstrating a significant improvement in performance.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for backfilling a mine pit using a bauxite washing slurry pipe bag for extrusion dewatering, characterized in that... Includes the following steps: (1) Mix bauxite washing mud with coagulant aid and flocculant, and flocculate to obtain flocculated mud; (2) The bottom of the mine pit is leveled, and the first layer of geotextile bags is laid on the leveled bottom of the mine pit. The laying method is to lay multiple geotextile bags side by side, with an overlap of 0.6~1.0m between two adjacent flat geotextile bags that have not been filled with mud, so as to ensure that after these side by side geotextile bags are filled with flocculated sludge, a gap of 0.08~0.12m is formed between two adjacent geotextile bags, which is conducive to drainage. (3) Turn 90° and lay the second layer of geotextile bags vertically side by side on the first layer of geotextile bags; the laying method is the same as step (2); the subsequent layers of geotextile bags are laid vertically side by side on the next layer in the same way until the sixth layer at the top ends this method; fill these geotextile bags with the flocculated bauxite washing mud and dewater them. (4) At every intersection of four geotextile bags, a PVC vertical pipe with multiple openings around its walls is installed. The PVC vertical pipe is open at both the top and bottom ends, and two adjacent PVC vertical pipes are connected by a PE pipe; or, at every intersection of four geotextile bags, a hollow circular vertical pipe with a diameter of 200-400mm made of steel bars is installed, and the hollow circular vertical pipes are connected by a PE pipe; finally, these PVC vertical pipes or hollow circular vertical pipes are connected to the mine pit through a PE pipe, so that the geotextile bags collected in the mine pit are squeezed out and the clean water is continuously discharged to the mine pit. (5) A porous plastic pipe with a length of ≥5m, a diameter of 50mm, and a hole with a diameter of 5-6mm is laid in the gap between every two geotextile bags around the perforated PVC pipe or the hollow circular vertical pipe to collect the clear liquid discharged from the geotextile bags; the porous plastic pipe is connected to the perforated PVC pipe or the hollow circular vertical pipe. (6) Repeat steps (4) to (5) after filling 5 to 10 layers of geotextile bags, and lay a layer of PE pipe connecting PVC pipe or hollow circular vertical pipe; (7) In a low-lying area near the mine pit with convenient drainage, a simple large-diameter well is constructed by using red bricks or cement bricks in the form of a flower wall, and a water pump and its water level sensor are installed to collect and discharge all the clear liquid discharged by gravity squeezing of the soil in the geotextile bag in the mine pit; the clear liquid is returned to the bauxite washing plant through the original pipeline or discharged into the nearby ditch. (8) When the mine mud is backfilled to the last six layers, the perforated PVC pipe or hollow circular vertical pipe no longer uses PE connecting pipe, but instead the space between two adjacent geotextile bags in each layer is filled with bundled straw sticks or biodegradable material sticks. (9) When the ore mud in the mine pit is backfilled to the last two layers, a gap of 0.3~0.5m is reserved between the two adjacent geotextile bags in each layer after they are filled with ore mud, as a drainage ditch for the site; (10) Before laying the last layer of geotextile bags, spread a small amount of boiler bottom ash or fly ash fine particles from the thermal power plant on the penultimate layer of geotextile bags, and then lay the last layer of geotextile bags; at the same time, the laying direction of the last layer of geotextile bags is adjusted to overlap with the laying direction of the next layer of geotextile bags.

2. The method for backfilling a mine pit based on bauxite washing slurry water pipe extrusion dewatering according to claim 1, characterized in that: In step (4), the diameter of the PVC vertical pipe is set as follows: starting from the PVC vertical pipe furthest from the large well of the mine, every three PVC vertical pipes of the same diameter are spaced apart, and their diameters are gradually increased from 200 mm to 225 mm, 250 mm, 280 mm, 315 mm, 355 mm, and 400 mm.

3. The method for backfilling a mine pit based on bauxite washing slurry water pipe extrusion dewatering according to claim 1, characterized in that: In step (4), the diameter of the PE connecting pipe connected to the PVC vertical pipe or the hollow circular vertical pipe also increases gradually from 40 mm to 50 mm, 63 mm, 75 mm, 90 mm and 110 mm.

4. The method for backfilling a mine pit based on bauxite washing slurry water pipe extrusion dewatering according to claim 3, characterized in that: The opening diameter of the PE connecting pipe on the PVC vertical pipe is the same as the pipe diameter of the corresponding PE connecting pipe, and the opening spacing is the same as the spacing of the two layers of PE pipes to be installed, or corresponds to the cumulative thickness of the geotextile bag stacking design layer in the proposed steps.

5. The method for backfilling a mine pit based on bauxite washing slurry water pipe extrusion dewatering according to claim 1, characterized in that: In step (5), the PE connecting pipe is reserved with a spare length of 0.5~1m.

6. The method for backfilling a mine pit based on bauxite washing slurry using a pipe bag for extrusion dewatering, as described in claim 1, is characterized in that: In step (4), the height of the PVC vertical pipe is higher than the height of the water pipe bag after this layer is filled.

7. The method for backfilling a mine pit based on bauxite washing slurry using a pipe bag for extrusion dewatering, as described in claim 1, is characterized in that: In step (9), when working on the last two layers of geotextile bags, a temporary bridge needs to be erected between every two geotextile bags to facilitate the construction of workers and ensure their safety.

8. The method for backfilling a mine pit based on bauxite washing slurry using a pipe bag for extrusion dewatering, as described in claim 1, is characterized in that: In step (1), the solid content of the bauxite washing mud is 10-15%, and the amount of flocculant used is equivalent to 0.05-0.1‰ of the dry weight of the bauxite washing mud.