A system for treating ammonia-nitrogen pollution and recycling rare earth in abandoned rare earth mine and application thereof

Abstract

The application discloses a kind of abandoned rare earth mine ammonia nitrogen pollution treatment and rare earth recovery system and application thereof, belong to mine restoration technical field.The system includes abandoned rare earth mine, intelligent power supply, electrode, high-level pool, liquid preparation pool, rare earth recovery pool, regulating pool and tidal biological filter.After injection into ore body, adsorbed ammonia nitrogen and rare earth ions in ore body exchange release and directional migration under the action of electric field, collect through liquid collecting hole and then enter rare earth recovery pool to recover rare earth, then enter tidal biological filter, build alternating aerobic-anoxic environment by periodic flooding and dry running, realize deep denitrification of leaching solution, and effluent is used for exchange liquid preparation or discharge in accordance with standard.The application solves the problems of long cycle, high cost, difficult to operate stably and unable to reduce ammonia nitrogen and recover rare earth simultaneously in prior art, realizes rapid treatment of ammonia nitrogen pollution and recovery of residual rare earth in abandoned rare earth mine by electric driving of ammonia nitrogen-rare earth migration and synergistic effect of tidal biological filter.

Description

Technical Field

[0001] This invention relates to a method for pollution control and rare earth recovery in abandoned rare earth mines, specifically to a system for ammonia nitrogen pollution control and rare earth recovery in abandoned rare earth mines and its application. Background Technology

[0002] Ion adsorption rare earth deposits are rich in valuable medium and heavy rare earth elements. In-situ ammonium salt leaching is widely used in the mining of these deposits. However, while this process reduces damage to the surface and mountains, it also leaves a large amount of ammonium salt residue in the ore body, which seeps into groundwater and surface water with rainfall, causing ammonia nitrogen pollution. Because ammonia nitrogen slowly desorbs from the ore body, the concentration of ammonia nitrogen in surface water exceeds the standard. This type of pollution is characterized by large quantities, large concentration fluctuations, low carbon-to-nitrogen ratios, and high remediation costs. In addition to environmental risks, the ammonium salt in-situ leaching process also has significant shortcomings in resource recovery. Due to the complex structure of the ore body, insufficient contact between the leaching agent and the ore body, and secondary adsorption, some rare earth elements cannot be recovered. At the same time, the phenomenon of mining easy-to-find and abandoning difficult-to-find elements is serious, resulting in a rare earth resource recovery rate of less than 50%.

[0003] For the treatment of ammonia nitrogen pollution, existing literature 1 (Chinese invention patent application with publication number CN110563252A) discloses a mixed treatment system for acidic mining wastewater and livestock wastewater. This system introduces exogenous nutrients and functional microorganisms to create a biodegradation environment within a specific reactor configuration, which can enhance the removal of pollutants such as heavy metal ions and sulfate ions from acidic wastewater under certain conditions, thereby improving the overall treatment efficiency to some extent. However, in practical engineering applications, this method usually relies heavily on the continuous addition of exogenous microbial agents or the precise control of specific biochemical reaction conditions, resulting in a long system start-up cycle and significant time consumption in the microbial acclimatization and biofilm formation processes. At the same time, its operational stability is easily affected by external factors such as ambient temperature, pH fluctuations, and changes in influent load, and its resistance to shock loads is relatively weak. In addition, the processes involved in the operation, such as agent replenishment, nutrient regulation, and equipment maintenance, make the overall operation and maintenance management complex and the comprehensive operating cost high, resulting in significant limitations in terms of economics.

[0004] Reference 2 (Chinese invention patent application with publication number CN111747511A) discloses a method and system for simultaneously removing ammonia nitrogen and rare earth ion pollution from rare earth mining areas. It employs a nitrification-denitrification coupled biofilm process to treat ammonia nitrogen-containing wastewater and improves microbial attachment conditions through composite packing materials, achieving process integration and simplification. This process utilizes porous ceramic particles and other packing materials to construct a biofilm reaction system, completing the nitrification and denitrification of ammonia nitrogen within a single reactor. Compared to the traditional activated sludge method, it has technical advantages such as high biomass concentration, low sludge yield, and simple operation and management, demonstrating process optimization and reengineering of biological nitrogen removal technology. However, a deeper analysis of its technical essence and application scenarios reveals that this technical solution is mainly for end-of-pipe treatment of polluted water or tailwater from rare earth mines that has already been discharged, belonging to a typical end-of-pipe treatment technology paradigm. Its treatment process requires a certain hydraulic retention time to ensure nitrogen removal efficiency, and stable system operation involves continuous operational steps such as aeration energy consumption control, regular maintenance and replacement of packing materials, and biofilm aging and renewal, requiring a high level of operational management. More importantly, because this technology targets polluted water bodies that have migrated from the ore body into the external environment, its technical means do not involve reducing residual ammonia nitrogen within the ore body, thus failing to prevent the leaching and migration of ammonia nitrogen at its source. Furthermore, the process design focuses on the harmless removal of pollutants rather than the resource recovery of rare earth elements from the water body, lacking a systematic consideration of rare earth resource recovery and recycling, and is therefore insufficient for current rare earth mines. Consequently, existing technologies cannot simultaneously achieve rapid reduction of ammonia nitrogen pollution and effective recovery of residual rare earth elements from abandoned rare earth mines, and still have shortcomings in terms of treatment cycle, operating costs, and system stability. Summary of the Invention

[0005] The purpose of this invention is to provide a system for the treatment of ammonia nitrogen pollution and the recovery of rare earths in abandoned rare earth mines and its application. This system solves the problems of long cycle, high cost, difficulty in stable operation and inability to reduce ammonia nitrogen at the source and recover rare earths simultaneously in existing technologies. Through the synergistic effect of electrically driven ammonia nitrogen-rare earth migration and tidal biological filter, the system achieves rapid treatment of ammonia nitrogen pollution in abandoned rare earth mines and recovery of residual rare earths.

[0006] To achieve the above objectives, this invention provides an electric field-driven exchange-tidal biological combined module collaborative system for ammonia nitrogen pollution control and rare earth recovery in abandoned rare earth mines, comprising: an abandoned rare earth mine with an injection port and a collection port inside; an electrode disposed within the injection port and connected to a smart power supply via a cable; a high-level tank connected to the injection port via an injection pipe for supplying exchange liquid into the abandoned rare earth mine; a preparation tank connected to the high-level tank for preparing and storing the exchange liquid; and a rare earth recovery tank connected to the collection port for recovering rare earths from the leachate collected in the collection port. The system includes: a regulating tank connected to the rare earth recovery tank; and a tidal biological filter connected to the regulating tank. The tidal biological filter comprises, from top to bottom, a tidal layer, an organic carbon source addition layer, a saturated flooded layer, and a drainage layer. The drainage layer is equipped with a water collection pipe. One end of the water collection pipe is connected to the solution preparation tank via a reuse pipe to form an exchange solution circulation loop, and the other end is discharged through the drainage pipe. The intelligent power supply supplies power to the electrodes, forming an electric field within the abandoned rare earth mine to promote the migration of ammonia nitrogen and rare earth ions in the ore body. The resulting leachate is treated sequentially through the liquid collection hole, the rare earth recovery tank, and the tidal biological filter.

[0007] Preferably, the system further includes an inoculation tank and a reagent tank; the inoculation tank is connected to an adjustment tank and is used to store an inoculation solution containing denitrifying microorganisms; the reagent tank is connected to a rare earth recovery tank and is used to add a pH adjuster to the rare earth recovery tank to achieve the precipitation and recovery of rare earth ions in the leachate.

[0008] Preferably, the intelligent power supply is a controllable DC power supply, including a main power supply and several independent control modules. Each module is connected to a corresponding electrode to achieve independent power supply or collaborative power supply.

[0009] Preferably, the electrode is made of a corrosion-resistant conductive material and is disposed in the injection hole corresponding to the contaminated layer of the ore body.

[0010] Preferably, the exchange liquid comprises water and / or a salt exchanger, the salt exchanger being used to promote the exchange and release of adsorbed ammonia nitrogen and rare earth ions in the ore body.

[0011] More preferably, when the concentration of residual leaching agent or exchange ions in the ore body is high, the exchange solution is water; when the concentration of residual leaching agent or exchange ions in the ore body is low, a salt exchange agent is added to the exchange solution.

[0012] More preferably, the salt exchanger is one or more of aluminum sulfate, magnesium sulfate, and calcium chloride.

[0013] Preferably, the diameter of the injection hole is 0.05~0.12 m, the hole spacing is 1.5~30.0 m, and the depth is determined according to the distribution characteristics of ammonia nitrogen pollution in the soil of the ore body.

[0014] Preferably, the tidal layer is filled with filler material that has adsorption, bioattachment and carbon supply functions; the saturated flooded layer is filled with filler material that has bioattachment and denitrification functions.

[0015] More preferably, the filler material of the tidal layer includes one or more of zeolite, vermiculite, gravel, and corn cobs; the filler material of the saturated flooded layer includes one or more of gravel and corn cobs.

[0016] This invention utilizes an electric field-driven exchange process to promote the migration and enrichment of residual ammonia nitrogen and rare earth ions in abandoned rare earth mines. Rare earth resources are recovered through a rare earth recovery pond, and the leachate is denitrified and purified using a tidal biological filter. The treated effluent can be reused for the preparation of exchange solutions, thereby achieving a synergistic unity of ammonia nitrogen pollution control, rare earth resource recovery, and exchange solution recycling.

[0017] This invention provides an application of the system in the treatment of ammonia nitrogen pollution and rare earth recovery in abandoned rare earth mines.

[0018] Preferably, the application includes the following steps: S1. Install injection holes, collection holes and electrodes in abandoned rare earth mines; S2. Inject exchange liquid into the injection hole in the abandoned rare earth mine and supply power to the electrodes through the intelligent power supply, so that ammonia nitrogen and rare earth ions in the abandoned rare earth mine migrate into the leachate; arrange electrodes in the injection hole, and connect the electrodes to the intelligent power supply through cables. Electrodes in the same row are connected in parallel to the corresponding power supply module, and each power supply module is independently controlled, thereby forming a multi-electrode array electric field.

[0019] S3. Collect the leachate and recover rare earth elements; by intermittently energizing or polling the power supply, a directional electric field is formed in the ore body, causing the adsorbed ammonia nitrogen in the ore body to exchange with rare earth ions and enter the liquid phase. Under the action of the electric field, they undergo directional migration, collect with the leachate to the collection hole, and enter the rare earth recovery tank; in the rare earth recovery tank, the pH is adjusted to 6.5~7.0 to cause rare earth ions to form carbonate or basic carbonate precipitates for recovery.

[0020] S4. The leachate after rare earth recovery is fed into the tidal biological filter for denitrification treatment. After the leachate after rare earth recovery is conditioned and enhanced in water quality through the inoculation tank and carbon source tank, it enters the tidal biological filter through the water distribution pipe and goes through the cycle of water intake, flooding, drainage and drying in sequence, achieving denitrification in the tidal layer and saturated flooded layer.

[0021] S5. The treated effluent is reused for the preparation of exchange solution or discharged in compliance with standards, thereby achieving the treatment of ammonia nitrogen pollution in abandoned rare earth mines and the recovery of rare earth resources. When the discharge requirements are not met, the effluent is returned to the preparation tank for the preparation of exchange solution and circulated for further treatment.

[0022] Preferably, during operation, when the rare earth concentration in the leachate drops below a set threshold, the electric field effect and rare earth recovery process can be stopped, and the water quality of the system can be adjusted by alkaline agents; when the ammonia nitrogen concentration in the leachate drops below a set threshold, the injection of exchange liquid can be stopped, and only the natural seepage liquid of the ore body can be treated by tidal biological treatment until the effluent stabilizes and meets the standards.

[0023] In the electro-driven ammonia nitrogen-rare earth migration process, after the exchange liquid is injected into the ore body, it undergoes ion exchange with the adsorbed ammonia nitrogen and rare earth, allowing the ammonia nitrogen and rare earth to enter the liquid phase system. Under the action of an applied electric field, the target ions undergo directional migration and accumulate at the collection end, thereby achieving enhanced migration and centralized collection of pollutants. Subsequently, rare earth resources are recovered through a rare earth recovery unit to obtain a low-load leachate suitable for biological treatment. The leachate after rare earth recovery enters a tidal biological filter for deep denitrification treatment. The tidal biological filter operates through periodic flooding and drying, creating an alternating aerobic and anoxic environment within the system: during the flooding stage, the tidal layer is in an anoxic state, the packing material adsorbs ammonia nitrogen, and utilizes the organic carbon source in the wastewater to provide electron donors for denitrification; during the drying stage, air enters the pores of the packing material to create an aerobic environment, promoting nitrification and providing substrate for the next cycle of denitrification. The saturated flooded layer, operating under anoxic conditions, is ideal for denitrification and allows for deep denitrification pathways coupled with short-cut denitrification and anaerobic ammonia oxidation, thus achieving cascaded removal of nitrogen pollutants. Electric field-driven exchange not only enables the simultaneous migration and resource recovery of ammonia nitrogen and rare earth elements in the ore body but also transforms the originally dispersed ammonia nitrogen pollutants into a centrally collected leachate, providing a stable and controllable treatment target for the tidal biological filter. The tidal biological filter then performs deep denitrification treatment on the centrally collected leachate, and the treated effluent can be reused for exchange solution preparation, forming a recycling system. The two systems are effectively integrated in terms of treatment targets, processes, and functional positioning, achieving synergistic governance through ore body pollution source reduction, rare earth resource recovery, deep leachate purification, and exchange solution recycling. Therefore, this invention achieves continuous coupling of pollutant migration and enrichment, resource recovery and deep denitrification through the synergistic effect of electric field-driven exchange and tidal biological treatment. It organically combines source migration, resource recovery, end-of-pipe purification and exchange liquid recycling, forming an integrated technical system for the treatment of ammonia nitrogen pollution in abandoned rare earth mines and the recovery of rare earth resources.

[0024] This invention discloses a system for treating ammonia nitrogen pollution in abandoned rare earth mines and for recovering rare earths, and its application. This system solves the problems of existing technologies, such as long cycles, high costs, difficulty in stable operation, and inability to reduce ammonia nitrogen at the source and simultaneously recover rare earths. Compared with existing technologies, it has the following beneficial effects: 1. This invention organically couples electric field-driven exchange with a tidal biological filter to construct a synergistic treatment system for ammonia nitrogen pollution source migration and enrichment in abandoned rare earth mines, residual rare earth resource recovery, and biological denitrification of leachate. Electric field-driven exchange promotes the directional migration of adsorbed ammonia nitrogen and rare earth ions in the ore body, achieving source reduction of pollutants and recovery of rare earth resources; the tidal biological filter performs deep denitrification treatment on the centrally collected leachate and enables the recycling of the treated effluent. The two systems work together to transform pollutants from dispersed occurrence in the ore body to centralized treatment, forming an integrated treatment model of "source migration—resource recovery—deep purification—recycling," effectively improving overall treatment efficiency and reducing treatment costs and environmental risks.

[0025] 2. This invention utilizes the synergistic effect of the exchange agent and the applied electric field to promote the synchronous exchange, release, and directional migration of adsorbed ammonia nitrogen and residual rare earth elements in the ore body. While reducing the ammonia nitrogen pollution load of the ore body, it achieves efficient recovery of residual rare earth resources, thus combining environmental remediation and comprehensive resource utilization functions.

[0026] 3. This invention uses a tidal biological filter to treat the centrally collected leachate. By periodically flooding and drying, an alternating aerobic-anoxic environment is created. Combined with the anoxic environment created by the bottom saturated flooded layer, synergistic nitrogen removal through multiple pathways such as nitrification-denitrification and anaerobic ammonia oxidation is achieved. At the same time, external organic wastewater is used as inoculum and carbon source to improve the system start-up speed and nitrogen removal efficiency, and reduce operating costs.

[0027] 4. This invention adopts a centralized leachate treatment mode, which only needs to treat a small amount of high-concentration leachate after electric migration and enrichment, avoiding long-term treatment of large-scale polluted surface water, significantly shortening the treatment cycle and reducing project investment; at the same time, the intelligent power supply, electrodes and treatment equipment in the system can be reused, further reducing operating costs and improving the value of engineering applications. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of the combined system of the present invention.

[0029] Figure 2 This is a comparison chart of the total wastewater treatment volume between Examples 1-2 and Comparative Example 2 of the present invention.

[0030] Figure 3 This is a comparison chart of the processing cycles of Embodiments 1-2 and Comparative Example 2 of the present invention.

[0031] Notes: 1. Abandoned rare earth mine; 2. Intelligent power supply; 3. Electrode; 4. Cable; 5. Liquid preparation tank; 6. High-level tank; 7. Injection pipe; 8. Injection hole; 9. Collection hole; 10. Electric rare earth migration module; 11. Submersible pump one; 12. Rare earth recovery tank; 13. Chemical tank; 14. Adjustment tank; 15. Drainage pipe; 16. Submersible pump two; 17. Reuse pipe; 18. Inoculation tank; 19. Carbon source tank; 20. Tidal biological module; 21. Water distribution pipe; 22. Tidal layer; 23. Organic carbon source addition layer; 24. Saturated flooded layer; 25. Drainage layer; 26. Collection pipe; 27. Solenoid valve; 28. Tidal biological filter. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0033] The sources of the reagents involved in the following examples are as follows: The inoculum source is used to provide active microorganisms to the system, specifically including activated sludge, anaerobic digestion sludge, or microbial communities in various high organic load wastewater systems (such as microorganisms in pig farm wastewater). All of the above-mentioned inoculum sources can achieve the microbial inoculation effect required by this invention.

[0034] External carbon sources are used to increase the COD / TN ratio of the system to promote denitrification. They can be selected from organic wastewater rich in biodegradable organic matter and with relatively low nitrogen content, or conventional carbon sources, including fruit juice wastewater, sugar factory wastewater, alcohol wastewater, starch processing wastewater, food processing wastewater, as well as sodium acetate, glucose and methanol, all of which can achieve the effect of promoting denitrification.

[0035] The pig farm wastewater was collected from typical large-scale pig farms around the experimental area, mainly including pigsty flushing water and mixed manure and urine wastewater. This type of wastewater usually has a high concentration of organic matter and ammonia nitrogen, and contains a rich microbial community, which can be used as a substrate and source of microorganisms for system operation.

[0036] The fruit juice wastewater was taken from organic wastewater (such as orange juice processing wastewater) generated during the production process of fruit juice processing enterprises around the experimental area. Its typical characteristics are high content of biodegradable organic matter and low nitrogen content, making it suitable as an external carbon source for the denitrification process.

[0037] Example 1: A system for the treatment of ammonia nitrogen pollution and rare earth recovery from abandoned rare earth mines using an electric field-driven exchange-tidal biological combined module, such as... Figure 1The diagram shows the overall structure of the combined system of the present invention. The system is divided into an electrically driven rare earth migration module (left) and a tidal biological module (right), the former used for remediation of pollution sources and rare earth recovery, and the latter for deep treatment of pollutants. The electrically driven rare earth migration module 10 includes an abandoned rare earth mine 1, a smart power supply 2, electrodes 3, cables 4, a liquid preparation tank 5, a high-level tank 6, an injection pipe 7, an injection hole 8, a collection hole 9, a submersible pump 11, a rare earth recovery tank 12, and a reagent tank 13. This module directly acts on the abandoned rare earth mine 1, aiming to simultaneously recover rare earth from the source and release adsorbed ammonia nitrogen. The abandoned rare earth mine 1 is the starting point and the leftmost main body of the entire system, with electrodes 3 embedded inside, an injection pipe 7 connected above, and a collection hole 9 at the bottom. It serves as the object to be remediated and the main reaction field, where residual ammonium ions (ammonia nitrogen) and rare earth ions migrate under the influence of an electric field. The intelligent power supply 2 is a DC power supply, consisting of a main power supply and several modules. Each module has two terminals for electrical connection to the electrodes 3 via cables 4, enabling independent or coordinated power supply to different electrodes. The intelligent power supply 2 provides stable voltage / current output and supports intermittent power supply or polarity switching operation modes, providing stable and controllable DC power, and is the core power source for the electrodynamic remediation process. The electrodes 3 are sheet-like or tubular, made of corrosion-resistant, highly conductive, and high-strength materials, and are arranged inside the injection hole 8, with their tops located in the upper region of the ammonia nitrogen contamination layer. They are electrically connected to the intelligent power supply 2 via cables 4, forming a DC electric field after being energized, driving the directional migration of ammonium and rare earth ions in the abandoned rare earth mine 1. After use, the electrodes 3 can be removed from the injection hole 8 without damage and reused to reduce engineering costs. The solution preparation tank 5 is located at the front end of the left module and is used to prepare the exchange solution for injection into the abandoned rare earth mine 1. The exchange medium is prepared from an exchange resin, which is one or more of aluminum sulfate, magnesium sulfate, and calcium chloride, with a total concentration of 0.005~0.1 mol·L⁻¹. -1The pH of the exchange solution is controlled within the range of 4.8 to 5.2 to ensure the stable existence of polyvalent cations and maintain the efficient migration capacity of ammonia nitrogen and rare earth elements. A submersible pump 11 is installed in or on the pipeline downstream of the mixing tank 5, pumping the exchange solution from the mixing tank 5 into the elevated tank 6 for temporary storage, providing the power for liquid transport. The elevated tank 6 is located downstream of the mixing tank 5, at a relatively high position (utilizing gravity), and is connected to the injection pipe 7 via a pipe at its bottom, allowing the exchange solution to flow by gravity into the injection hole 8. The injection flow rate is regulated by a valve installed on the injection pipe 7. The injection pipe 7 extends from the elevated tank 6 and is inserted into the abandoned rare earth mine 1. One end of the pipe connects to the elevated tank 6, and the other end communicates with the interior of the abandoned rare earth mine 1 through the injection hole 8, transporting and evenly distributing the exchange solution within the abandoned rare earth mine 1. Injection holes 8 are located in the abandoned rare earth mine 1. Their depth is determined by the distribution characteristics of ammonia nitrogen pollution in the soil of the ore body. The hole diameter is 0.05–0.12 m, and the spacing is 1.5–3.0 m. Injection holes 8 are used to arrange electrodes 3 and uniformly inject the exchange solution into the ore body, promoting the directional migration of rare earth and ammonium ions under the action of an electric field. Collection holes 9 are located at the bottom of the abandoned rare earth mine 1 and are used to discharge the collected leachate into the rare earth recovery tank 12. A reagent tank 13 is connected to the rare earth recovery tank 12 and is used to store sodium bicarbonate. Sodium bicarbonate is used to adjust the pH of the leachate in the rare earth recovery tank 12 to 6.5–7.0, causing rare earth ions to precipitate out as carbonates or basic carbonates, thereby achieving the recovery of residual rare earth and providing suitable pH conditions for subsequent biological denitrification treatment. After water quality adjustment, the solution enters the subsequent biological denitrification treatment unit for advanced treatment of various nitrogen-containing pollutants.

[0038] The leachate after rare earth recovery mainly includes various nitrogen-containing pollutants and leaching agent ions, which are introduced into the tidal biological composite module 20 for subsequent treatment. The tidal biological composite module 20 is located on one side of the rare earth recovery tank 12 and consists of lightweight, modular equipment, specifically including an equalization tank 14, a drainage pipe 15, a submersible pump 16, a reuse pipe 17, an inoculation tank 18, a carbon source tank 19, a tidal biological filter 28, a water collection pipe 26, and a solenoid valve 27. This module performs efficient biological denitrification treatment on the wastewater from the rare earth recovery tank and is easy to transport, install, and reuse in different waste rare earth mine remediation scenarios. The equalization tank 14 is located after the rare earth recovery tank 12, with influent from the rare earth recovery tank 12 and effluent flowing to the tidal biological filter 28. It is used to store the leachate after rare earth recovery to regulate water quality and quantity, ensuring stable operation of subsequent biological treatment.

[0039] The tidal biological filter 28 is the core treatment structure of the system, consisting of, from top to bottom, a water distribution pipe 21, a tidal layer 22, an organic carbon source addition layer 23, a saturated flooded layer 24, and a drainage layer 25. This unit efficiently removes nitrogenous pollutants from the water through tidal operation (alternating flooding and drainage) and a special layered structure. The water distribution pipe 21 is used to evenly distribute the influent. The tidal layer 22 operates in an alternating flooding and drying mode. During the drying stage, aerobic conditions are created for nitrification, converting ammonia nitrogen into nitrate nitrogen; during the flooding stage, an anoxic environment is created for denitrification. Its packing material is a mixture of zeolite, vermiculite, crushed stone, and corn cob, with a volume ratio of 1~2:0.1~2:0.5~1:1~2 and a particle size of 5~15 mm. Zeolite and vermiculite are used to adsorb ammonia nitrogen, corn cob provides a slow-release organic carbon source to promote denitrification, and crushed stone forms a stable structural framework. The organic carbon source addition layer 23 is used to add carbon sources, providing electron donors for denitrification. The carbon source comes from the carbon source tank 19. The saturated flooded layer 24 is continuously flooded to create an oxygen-deficient environment, where denitrification and anaerobic ammonia oxidation mainly occur, further removing residual nitrate nitrogen and ammonia nitrogen after the upper layer treatment. Its packing material is a mixture of crushed stone and corn cobs in a volume ratio of 1:(1~3), with a particle size of 7~20 mm. The drainage layer 25 supports the packing material and collects the treated water. Its packing material is crushed stone with a particle size of 20~40 mm. A water collection pipe 26 is installed in the drainage layer 25 to discharge the treated wastewater from the system. The carbon source tank 19 is connected to the organic carbon source addition layer 23 and the equalization tank 14, respectively, and is used to store high organic carbon and low total nitrogen wastewater such as fruit juice wastewater. This high organic carbon wastewater is used to adjust the COD / TN ratio of the leachate and the wastewater after treatment in the tidal layer 22 to 2~4, making it more suitable for denitrification. The inoculation tank 18 is connected to the equalization tank 14 and is used to store pig farm wastewater or septic tank wastewater. This wastewater is used to adjust the biodegradability of the leachate and to provide inoculated microorganisms for the tidal biofilter 28 system. The collection pipe 26 is located in the bottom drainage layer 25 of the tidal biofilter 28 and is used to collect the final effluent from the filter and divert it to the reuse pipe 17 or the drainage pipe 15. A solenoid valve 27 is installed on the branch pipe after the collection pipe 26 and switches the water flow direction under the command of the control system, automatically controlling the treated effluent to enter the reuse system or the discharge system. A submersible pump 16 is installed on the distribution pipe 21 and is used to input the wastewater from the equalization tank 14 into the tidal biofilter 28. The reuse pipe 17 branches off from the collection pipe 26 and connects to the distribution tank 5, used to return a portion of the treated water that meets the standards to the front end of the system for reuse, realizing water resource recycling. Drainage pipe 15 branches off from collection pipe 26 and leads to outside the system or a natural water body, for discharging the final qualified wastewater into the environment.

[0040] The above system is used for the treatment of ammonia nitrogen pollution and rare earth recovery in abandoned rare earth mines. The pollution source remediation route is as follows: Liquid preparation tank 5 → Submersible pump 11 → High-level tank 6 → Injection pipe 7 → Abandoned rare earth mine 1 (electrode 3 is simultaneously energized) → Collection hole 9 → Rare earth recovery tank 12. The deep biological treatment route is as follows: Adjustment tank 14 → Submersible pump 26 → Tidal biological filter 28 (carbon source is added from carbon source tank 19 simultaneously) → Water collection pipe 26 → Controlled by solenoid valve 27, part of the treated water is reused through reuse pipe 17, and the remainder is discharged through drainage pipe 15. Inoculation tank 18 and reagent tank 13 are used to add microbial inoculum and reagents as needed to achieve full-process control from "in-situ remediation of abandoned rare earth mine 1" to "centralized treatment of leachate." This method specifically includes: (1) Determine the distribution range of ammonia nitrogen and rare earth elements, and arrange the collection hole 9 and injection hole 8: In a test area measuring 33.6 meters long and 7.2 meters wide, two rows of exploration holes were arranged along each of the left and right edges, and one row of exploration holes was arranged along each of the top and bottom edges. The spacing between the exploration holes on the sides was 1.5 meters, and the spacing between the top and bottom rows was 7 meters, for a total of 8 exploration holes. The exploration holes were placed to a depth of 20 meters, and a mixed weathering crust sample was taken from each meter. The ammonia nitrogen content in the samples was determined according to the standard "Determination of Ammonia Nitrogen, Nitrite Nitrogen and Nitrate Nitrogen in Soil - Potassium Chloride Solution Extraction-Spectrophotometry" (HJ634-2012), and the rare earth content in the samples was determined according to the standard "Determination of 12 Metallic Elements in Soil and Sediments - Aqua Regulator Extraction-Inductively Coupled Plasma Mass Spectrometry" (HJ 803-2016). Test results show that the ammonia nitrogen content in the soil of the remediation area ranges from 60 to 460 mg / kg, with pollution mainly concentrated in the range of 3 to 18 m below the surface, averaging about 240 mg / kg; the rare earth content in the soil ranges from 0.01 to 0.04 wt%, with an average of about 0.025 wt%. Based on the spatial distribution characteristics of the above ammonia nitrogen and rare earth contents, the remediation and rare earth recovery area of ​​the abandoned rare earth mine 1 is determined to be an area 30.6 meters long and 7.2 meters wide, with a depth of 3 to 18 meters. The layout scheme of injection holes 8 (if the spacing is consistent with the actual injection hole spacing, the above exploration holes can be used as injection holes 8 laterally) is as follows: 5 rows and 18 columns, totaling 90 holes, with a horizontal and vertical spacing of 1.8 meters, a hole diameter of 0.1 meters, and a hole depth of 18 meters. The layout scheme of the liquid collection holes 9 is as follows: two liquid collection holes 9 are opened from the bottom of the selected area toward the abandoned rare earth mine 1, with a spacing of 2.4 meters and an average distribution on the 7.2-meter short side. The diameter of the holes is 0.1 meters and the depth is 32 meters. The height of the liquid collection holes 9 in the vertical direction is 1.5 meters lower than the bottom of the injection holes 8.

[0041] (2) Electrode arrangement: Insert 15-meter-long electrodes 3 into each of the 90 injection holes 8. The top of the electrode 3 is 3 meters away from the top of the injection hole 8. After connecting 5 electrodes 3 in the same row in parallel, they are connected to the corresponding modules of the smart power supply 2.

[0042] (3) Injection of exchange solution: Inject a 0.01 mol / L aluminum sulfate solution into injection hole 8. Determine the concentration of Al3 based on the charge equivalent relationship of ion exchange. + The dosage, specifically, is the amount of NH4 added within the remediation area. + One-third of the total amount is used to achieve the adsorption of NH4. + Effective replacement.

[0043] (4) Electro-driven ammonia nitrogen-rare earth migration: A 4-cycle polling energizing method was adopted, with each cycle lasting 50 min and a DC electric field strength of 25 V / m. Under the action of the electric field, NH4+... + Rare earth ions and leachate migrate under the influence of an electric field.

[0044] (5) Collecting the leachate and recovering rare earth elements: Under the action of an electric field, the rare earth elements are reacted with Al. 3+ Displaced NH4 + The rare earth ions migrate in a directional manner and are eventually discharged from the mountain with the leachate in the collection hole 9, flowing into the rare earth recovery pool 12. Approximately 50 tons of leachate are collected every day. Then, sodium bicarbonate in the reagent pool 13 is added to the rare earth recovery pool 12 to adjust the pH value of the leachate to 6.8. After stirring evenly, it is allowed to stand for 2 hours, and then the supernatant is transferred to the adjustment pool 14.

[0045] (6) The leachate was treated using a combined tidal biological filter system: ① Design parameters of the tidal biological filter: length, width and height are 8 meters, 3 meters and 3 meters respectively; tidal layer 22 is 1.5 meters thick and is composed of zeolite, vermiculite, crushed stone and corn cob. The volume ratio of zeolite, vermiculite, crushed stone and corn cob is 1:1:0.5:1 and the particle size is 5~12 mm; organic carbon source addition layer 23 is 0.1 meters thick and the filler is composed of crushed stone with a particle size of about 25 mm; saturated flooded layer 24 is 1.0 meter thick and is composed of crushed stone and corn cob. The volume ratio of crushed stone and corn cob is 1:2 and the particle size is 10 mm; drainage layer 25 is 0.2 meters thick and is composed of crushed stone with a particle size of about 25 mm.

[0046] ② Adjusting the leachate water quality: On average, 0.5 tons of pig farm wastewater (ammonia nitrogen and COD concentrations of 500 mg / L and 6000 mg / L, respectively) are added to 50 tons of leachate per day. After dilution, the introduced ammonia nitrogen and COD are approximately 5 mg / L and 60 mg / L, respectively. In addition, based on the influent ammonia nitrogen concentration, fruit juice wastewater is added to adjust the COD:TN ratio of the leachate to 3:1. The final pH value of the adjusted leachate is approximately 7.

[0047] ③ Operating parameters of the tidal biological filter 28: It operates for 8 cycles per day, with each cycle lasting 3 hours; the influent is obtained by spraying, with each influent volume being 1 / 8 of the total daily treatment volume; each cycle includes an influent-flooding stage and a drainage-drying stage, each lasting 1.5 hours. During the influent-flooding stage, the solenoid valve 27 is closed, keeping the tidal layer 22 in a flooded state; during the drainage-drying stage, the solenoid valve 27 is opened, emptying the water in the tidal layer 22 and restoring it to an aerated state; during the drainage process, fruit juice wastewater is introduced into the organic carbon source addition layer 23 to adjust the carbon-nitrogen ratio of the effluent from the tidal layer 22 to approximately 3, and then flows into the saturated flooded layer 24 for further deep denitrification.

[0048] ④ Leachate Treatment and Reuse: The tidal biological filter 28 operates according to the above parameters, treating approximately 50 tons of leachate per day. The system effluent is preferentially used for preparing the exchange medium and circulated into the injection port to continuously drive the electro-driven ammonia nitrogen-rare earth migration. When the system effluent exceeds the required amount of exchange medium, the amount of water used for preparation is reduced, and the remaining treated effluent is directly discharged through the drain pipe to ensure a relatively stable system treatment volume during the treatment period.

[0049] (7) End of Electro-driven Ammonia Nitrogen Treatment-Rare Earth Recovery: After 145 days of electro-repair operation, the rare earth concentration in the leachate collected by collection hole 9 drops below 50 mg / L, and the ammonia nitrogen concentration is below 20 mg / L. At this point, the injection of exchange solution into the injection hole is stopped and the electro-repair operation is terminated, ending the electro-driven ammonia nitrogen-rare earth migration process. Subsequently, the tidal biological filter 28 continues to treat the collected leachate. After 7 days of continuous operation, the ammonia nitrogen concentration in the leachate discharged from collection hole 9 drops below 1 mg / L, ending the repair and rare earth recovery process.

[0050] During the electrostatic treatment and rare earth recovery process, the system collects an average of approximately 50 m³ of leachate per day. 3 After 5 months of continuous operation, a total of approximately 7500 m³ of leachate was collected. 3 The collected leachate contained NH4+. + The nitrogen (N) content gradually decreased from approximately 260 mg / L at the beginning of operation to approximately 0.8 mg / L at the end, with an average content of approximately 150 mg / L during operation. The rare earth content fluctuated from approximately 300 mg / L at the beginning to approximately 20 mg / L at the end, with an average content of approximately 120 mg / L during operation. A total of approximately 0.9 tons of rare earth elements were recovered.

[0051] Example 2: An electric field-driven exchange-tidal biological combined module collaborative system for the treatment of ammonia nitrogen pollution in abandoned rare earth mines and rare earth recycling system is exactly the same as that in Example 1.

[0052] The above system uses magnesium sulfate as an exchanger to treat ammonia nitrogen pollution from abandoned rare earth mines and recover rare earths. The method is basically the same as in Example 1, except that: (1) Preparation of exchange medium Magnesium sulfate exchange solution is prepared in solution preparation tank 5 with a concentration of 0.02 mol / L and a pH controlled at around 5.0.

[0053] (2) Dosage of exchanger Based on NH4 in the ore body + Calculation of Mg -N content 2+ The dosage, its molar dosage is NH4 in the ore body + The amount of -N is 1 to 1.5 times the total amount, in order to achieve adsorption of NH4 on the mineral surface. + -N is an effective permutation.

[0054] (3) Scale of governance The investigation results showed that the ammonia nitrogen content in the soil of the remediation area ranged from 20 to 500 mg / kg, with the pollution mainly concentrated at a depth of 5 to 15 m below the surface, averaging approximately 260 mg / kg. The rare earth element content in the soil ranged from 0.006 to 0.06 wt%, with an average of approximately 0.032 wt%. Based on the above spatial distribution characteristics of the pollutants, the remediation area was determined to be 40 m × 10 m, with a remediation depth ranging from 5 to 15 m. A total of 126 injection holes were installed in the remediation area using a 2 m × 2 m grid. Three collection holes were installed at the bottom of the remediation area for leachate collection.

[0055] (4) Parameters of tidal biological filter Tidal biological filter 28 is 10 m long, 4 m wide and 3 m high, with a designed treatment capacity of approximately 90 m³. 3 / d. The filter bed consists of, from top to bottom, a tidal layer 22, an organic carbon source addition layer 23, a saturated flooded layer 24, and a drainage layer 25.

[0056] The tidal layer 22 is 1.6 m thick and consists of zeolite, vermiculite, gravel, and corn cobs in a volume ratio of 1.5:0.5:0.8:1 with a particle size of 7-10 mm. The organic carbon source addition layer 23 is 0.15 m thick and is filled with gravel with a particle size of 20-30 mm. The saturated flooding layer 24 is 0.9 m thick and consists of gravel and corn cobs in a volume ratio of 1:2 with a particle size of 10-20 mm. The drainage layer 25 is 0.20 m thick and consists of gravel with a particle size of 25-40 mm.

[0057] The tidal biological filter operates for 8 cycles per day, with each cycle lasting 3 hours, and each cycle processes approximately 11.25 m³ of water. 3During operation, the COD / TN ratio of the influent is adjusted to approximately 3 by adding fruit juice wastewater to ensure the smooth progress of the denitrification reaction.

[0058] (5) Power supply operating conditions The DC electric field strength is 20 V / m, and the polling energizing cycle is 60 min.

[0059] (6) Operational effect During the electrostatic treatment and rare earth recovery process, the system collects an average of approximately 90 m³ of leachate per day. 3 After 6 months of continuous operation, a total of approximately 16,200 m³ of leachate was collected. 3 . NH4 in the leachate + The -N concentration gradually decreased from approximately 190 mg / L at the beginning of operation to approximately 0.8 mg / L at the end, with an average concentration of approximately 100 mg / L during operation. The rare earth content fluctuated from approximately 280 mg / L at the beginning to approximately 20 mg / L at the end, with an average concentration of approximately 110 mg / L during operation. A total of approximately 1.78 tons of rare earth elements were recovered.

[0060] Comparative Example 1: This comparative example provides a natural attenuation method for ammonia nitrogen pollution in abandoned rare earth mines without any engineering remediation measures.

[0061] The scale, pollution range, and pollution degree of the abandoned rare earth mine involved in this comparative example are basically the same as those in Example 1. That is, the area of ​​the remediation area is about 30 m × 7 m, the pollution depth ranges from 3 to 18 m, and the distribution of ammonia nitrogen and rare earth content in the ore body is basically the same as that in Example 1.

[0062] In this comparative example, no artificial intervention measures such as electric migration system and tidal biological filter were set up. The ammonia nitrogen in the ore body gradually migrated outward under the leaching effect of natural rainfall and entered the surrounding surface water bodies, and then diffused and diluted with the stream.

[0063] According to on-site monitoring, the stream flow in this area is approximately 100 m³ / h. 3 / d, NH4 + The average concentration of -N is approximately 15 mg / L. Based on this, the stream outputs approximately 100 × 15 mg / L = 1.5 kg / d of ammonia nitrogen per day.

[0064] If the goal is to reduce the same total amount of ammonia nitrogen as in Example 1 (approximately 1.1 t), the required time would be approximately 1100 ÷ 1.5 ≈ 730 days, or approximately 2 years.

[0065] Therefore, under natural decay conditions, the pollutant removal cycle is relatively long. Furthermore, during this process, the polluted water continues to be transported downstream, potentially leading to excessive ammonia nitrogen concentrations in downstream water bodies and posing a significant risk of water pollution. In addition, rare earth elements in the ore body are lost through leachate migration during this process, making resource recovery impossible.

[0066] Comparative Example 2: This comparative example provides an end-of-pipe treatment method for ammonia nitrogen pollution in surface water caused by traditional abandoned rare earth mines. The scale, pollution range, and pollution degree of the abandoned rare earth mine involved in this comparative example are basically the same as those in Example 1, that is, the remediation area is approximately 30 m × 7 m, the pollution depth ranges from 3 m to 18 m, and the distribution of ammonia nitrogen and rare earth content in the ore body is basically the same as that in Example 1.

[0067] In this comparative example, no in-situ remediation was carried out on the ore body. The ammonia-nitrogen-containing leachate from the original collection wells and surrounding areas of the abandoned rare earth mine entered a nearby stream under the leaching effect of rainfall, thus polluting the surface water. Subsequently, only the polluted stream water was centrally treated to reduce the ammonia nitrogen concentration in the surface water.

[0068] Monitoring showed that the average flow rate of the stream was approximately 100 m³ / s. 3 / d, NH4 + The average concentration of ammonia nitrogen (-N) is approximately 15 mg / L. Therefore, the amount of ammonia nitrogen carried by the stream each day is approximately: 100 × 15 mg / L = 1.5 kg / d.

[0069] This comparative example treats polluted water bodies using a combination of conventional surface water treatment processes (such as aeration, biological treatment, and constructed wetlands). If the goal is to reduce the same total ammonia nitrogen level as in Example 1 (approximately 1.1 t), the required time is approximately 1100 ÷ 1.5 ≈ 730 days, or about 2 years. During this process, the volume of stream water requiring continuous treatment is approximately 100 m³. 3 / d ×730 d≈7.3×10 4 m 3 .

[0070] The total wastewater treatment volume refers to the cumulative volume of polluted surface water that needs to be collected and treated during the treatment process.

[0071] like Figure 2 The figure shows a comparison of the total wastewater treatment capacity between Examples 1-2 and Comparative Example 2 of the present invention.

[0072] like Figure 3 The figure shows a comparison of the processing cycles of Embodiments 1-2 and Comparative Example 2.

[0073] Depend on Figure 2 and Figure 3It can be seen that the total wastewater treatment capacity of Examples 1 and 2 of the present invention and Comparative Example 2 is 7500m³. 3 16200 m 3 and 73000 m 3 The treatment cycles were 5 months, 6 months, and 24 months, respectively. Comparative Example 2 represents an end-of-pipe treatment method after pollution occurs. Not only is the treatment cycle long, but during the treatment process, rare earth resources in the ore body enter surface water bodies with leachate and are gradually lost, making effective recovery and utilization of rare earth resources difficult, resulting in a significant increase in the equivalent amount of wastewater requiring treatment. Compared to Comparative Example 2, Examples 1 and 2 significantly shorten the treatment cycle and significantly reduce the total amount of wastewater requiring treatment while achieving pollution control. Therefore, the embodiments of the present invention, through electro-driven migration and directional collection, concentrate pollutants within a smaller area for centralized treatment, thereby significantly reducing wastewater generation.

[0074] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A system for the coordinated treatment of ammonia nitrogen pollution and rare earth recovery from abandoned rare earth mines using an electric field-driven exchange-tidal biological combined module, characterized in that, include: An abandoned rare earth mine (1) is provided with an injection hole (8) and a collection hole (9) inside. Electrode (3) is disposed in the injection hole (8) and connected to the smart power supply (2) via cable (4); The high-level pool (6) is connected to the injection hole (8) through the injection pipe (7) and is used to deliver exchange liquid into the abandoned rare earth mine (1); The solution preparation tank (5) is connected to the high-level tank (6) and is used for preparing and storing the exchange solution; Rare earth recovery pool (12), which is connected to the collection hole (9), is used to recover rare earth from the leachate collected by the collection hole (9); The regulating tank (14) is connected to the rare earth recovery tank (12); The tidal biological filter (28) is connected to the regulating tank (14). The tidal biological filter (28) includes, from top to bottom, a tidal layer (22), an organic carbon source addition layer (23), a saturated flooded layer (24), and a drainage layer (25). The drainage layer (25) is provided with a water collection pipe (26). Among them, one end of the water collection pipe (26) is connected to the liquid preparation tank (5) through the reuse pipe (17) to form an exchange liquid circulation loop, and the other end is discharged through the drain pipe (15); The exchange liquid is delivered into the abandoned rare earth mine (1) through the injection hole (8). The intelligent power supply (2) supplies power to the electrode (3) to form an electric field in the abandoned rare earth mine (1) to promote the migration of ammonia nitrogen and rare earth ions in the abandoned rare earth mine (1). The resulting leachate is then processed through the collection hole (9), the rare earth recovery pool (12), and the tidal biological filter (28).

2. The system according to claim 1, characterized in that, The system also includes an inoculation tank (18) and a reagent tank (13); the inoculation tank (18) is connected to the conditioning tank (14) and is used to store the inoculation solution containing denitrifying microorganisms; the reagent tank (13) is connected to the rare earth recovery tank (12) and is used to add pH adjuster to the rare earth recovery tank (12) to achieve rare earth ion precipitation and recovery in the leachate.

3. The system according to claim 1, characterized in that, The intelligent power supply (2) is a controllable DC power supply, including a main power supply and several independent control modules. Each module is connected to the corresponding electrode (3) to achieve independent power supply or collaborative power supply.

4. The system according to claim 1, characterized in that, The electrode (3) is made of corrosion-resistant conductive material and is placed in the injection hole (8) corresponding to the contaminated layer of the ore body.

5. The system according to claim 1, characterized in that, The exchange liquid includes water and / or a salt exchange agent, which is used to promote the exchange and release of adsorbed ammonia nitrogen and rare earth ions in the ore body.

6. The system according to claim 5, characterized in that, The salt exchanger is one or more of aluminum sulfate, magnesium sulfate, and calcium chloride.

7. The system according to claim 1, characterized in that, The diameter of the injection hole (8) is 0.05~0.12 m, the spacing between holes is 1.5~30.0 m, and the depth is determined according to the distribution characteristics of ammonia nitrogen pollution in the soil of the ore body.

8. The system according to claim 1, characterized in that, The tidal layer (22) is filled with filler material that has adsorption, bioattachment and carbon supply functions; the saturated flooded layer (24) is filled with filler material that has bioattachment and denitrification functions.

9. The system according to claim 8, characterized in that, The filler material of the tidal layer (22) includes one or more of zeolite, vermiculite, gravel and corn cob; the filler material of the saturated flooded layer (24) includes one or more of gravel and corn cob.

10. The application of the system according to any one of claims 1 to 9 in the treatment of ammonia nitrogen pollution and rare earth recovery in abandoned rare earth mines.

11. The application according to claim 10, characterized in that, Includes the following steps: S1. Install injection holes (8), collection holes (9) and electrodes (3) in the abandoned rare earth mine (1). S2. Inject exchange liquid into the injection hole (8) in the abandoned rare earth mine (1) and supply power to the electrode (3) through the intelligent power supply (2) so that ammonia nitrogen and rare earth ions in the abandoned rare earth mine (1) migrate into the leaching solution. S3. Collect the leachate and recover rare earth elements; S4. The leachate after rare earth recovery is fed into the tidal biological filter (28) for denitrification treatment; S5. The treated effluent is reused for the preparation of exchange solutions or discharged in compliance with standards, thereby achieving the treatment of ammonia nitrogen pollution in abandoned rare earth mines and the recovery of rare earth resources.

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