Method suitable for ion type rare earth mine area groundwater pollution remediation

Abstract

The invention belongs to the field of water pollution treatment, and particularly relates to a method suitable for ion type rare earth mine area groundwater pollution remediation. An in-situ chemical reduction area and an in-situ microbial enhanced purification area are sequentially arranged in the water flow direction, the in-situ chemical reduction area comprises a primary treatment area, a metal ion capture area and an adsorption reduction area, and a metal ion capture agent with a graphene-loaded nanoscale zero-valent iron composite material and lignin active powder loaded on a porous carrier is designed; the in-situ microbial enhanced purification area comprises a nitrification area and a denitrification area; according to the remediation method, chemical reduction, physical adsorption and microbial remediation are coupled, deep treatment of the ionic rare earth mine underground water polluted by heavy metal and polluted by rare earth ions, ammonia nitrogen and nitrate is achieved through mutually independent, synergistic and multi-stage treatment, the removal rate of the ammonia nitrogen can reach 99% or above, and the removal rate of the heavy metal and the rare earth ions can reach 100%.

Description

Technical Field

[0001] This invention belongs to the field of water pollution treatment, and particularly relates to the field of groundwater pollution remediation technology, specifically a method for remediating groundwater pollution in ion-adsorption rare earth mining areas. Background Technology

[0002] Ion-adsorption rare earth (IBA) deposits are important strategic mineral resources. These deposits primarily form in weathered granite deposits in the hot and humid climates of southern China, typically with a thickness of 5–30 meters and generally low permeability. The main mining process involves injecting electrolyte leaching agents such as ammonium sulfate into the ore body in situ to exchange and recover rare earth ions. This method requires injecting 6–8 tons of ammonium sulfate per ton of rare earth, resulting in 30–60% of the leachate remaining in the ore body, creating a large and long-term source of pollution. This leads to a sharp increase in ammonia nitrogen and sulfate concentrations in groundwater; simultaneously, rare earth ions (La)... 3+ Ce 3+ 、Nd 3+ (etc.) could not be fully recovered, and there were no existing heavy metal ions (Pb) in the formation. 2+ Cd 2+ Cu 2+ These pollutants, along with other elements, enter the groundwater, forming a complex pollution system of rare earth ions, sulfate ions, ammonia nitrogen, and heavy metals. Furthermore, some mining areas employ open-pit mining methods, leading to the destruction of surface vegetation and soil erosion, further exacerbating groundwater pollution. Therefore, groundwater pollution in ion-rich mining areas suffers from severe acidification, a high concentration of coexisting ions, and complex pollution conditions.

[0003] For groundwater pollution in ion-adsorption rare earth mining areas, ex-situ remediation using a pump-and-treatment method is commonly employed. This technology is simple to implement, convenient to construct, and yields rapid initial results. However, it also suffers from drawbacks such as significant interference, high energy consumption, and poor remediation effectiveness for low-permeability groundwater. Permeable reactive barriers (PRBs) are passive in-situ groundwater treatment technologies filled with a reactive material. These PRBs are installed across the cross-section of the contaminated groundwater flow path. Through contact between the reactive material within the PRB and the groundwater, the contaminants in the water are degraded and retained, thus remediating the contaminated groundwater. Compared to ex-situ remediation, in-situ groundwater remediation technologies offer longer-lasting effects and are more suitable as a remediation method for groundwater in ion-adsorption rare earth mining areas.

[0004] Chinese patent CN111622269B discloses a method for controlling shallow groundwater pollution in ion-adsorption rare earth mines. Addressing the common geological characteristics of shallowly buried and fractured bedrock in my country's ion-adsorption rare earth mines, the method employs the following measures: constructing a horizontal seepage barrier in the deep bedrock fracture zone of the mining area, and a vertical seepage barrier in the shallow bedrock fracture zone at the edge of the mining area to prevent the migration and diffusion of leachate; installing self-controlled extraction wells in the water-rich area within the seepage barrier to control the shallow groundwater level and prevent cross-flow pollution; setting up water quality monitoring wells outside the seepage barrier to monitor the groundwater leachate concentration and guide the control of the shallow groundwater level in the mining area; and cleaning with clean water and a low-concentration calcium hydroxide solution at the end of mining. However, this method is only applicable to the control of shallow groundwater pollution in ion-adsorption rare earth mines with shallowly buried and fractured bedrock, and does not offer a solution for the remediation of polluted groundwater.

[0005] The patent application CN114804346B describes a permeable reactive barrier system for remediating groundwater contaminated with heavy metals, ammonia nitrogen, and nitrates. This system comprises a ferrous ore permeable reactive barrier, an anaerobic ammonia oxidation permeable reactive barrier, and a deep treatment permeable reactive barrier, arranged sequentially along the seepage direction of the groundwater plume. The ferrous ore permeable reactive barrier is filled with one or both of siderite and pyrite particles. The anaerobic ammonia oxidation permeable reactive barrier is structured as either an anaerobic ammonia oxidation permeable reactive barrier wall or multiple anaerobic ammonia oxidation permeable reactive barrier units coupled with a ferrous ore layer. The permeable reactive barrier wall or individual units are filled with polypropylene ring packing. The deep treatment permeable reactive barrier contains a modified zeolite and volcanic rock composite filter media. The permeable reactive barrier has an internal steel reinforcement support, which is externally covered with permeable geotextile. The permeability coefficient of the wall is controlled to be more than twice the permeability coefficient of the aquifer, and remains equal or gradually increases along the seepage direction of the groundwater plume. This system can remediate heavy metal, ammonia nitrogen, and nitrate pollution, but its applicability to groundwater environments in ion-adsorption rare earth mines is insufficient. This is mainly due to the following: the anaerobic ammonia oxidation reaction requires highly precise control, which is difficult to achieve in groundwater environments; the pyrite and siderite filling the reaction wall often contain metallic impurities such as Mg, Mn, Ni, and Cu, which are easily dissolved and generate SO4 under the acidic groundwater conditions of ion-adsorption rare earth mining areas. 2- And other issues such as metal pollution.

[0006] Currently, in-situ remediation technology is a hot research topic in groundwater pollution control. It not only offers relatively low treatment costs but also reduces the need for surface treatment facilities, minimizing pollutant exposure and environmental disturbance, making it a promising groundwater pollution control technology. However, existing in-situ remediation technologies mostly target single pollutants, lacking synergistic treatment schemes for complex pollution of "rare earth ions-sulfate-ammonia nitrogen-heavy metals" in ion-adsorption rare earth mining areas. Furthermore, the lack of effective in-situ monitoring and control methods during the remediation process makes it difficult to adjust remediation strategies in real time according to changes in pollutant concentrations, leading to unstable remediation effects and a tendency for rebound. Therefore, developing an in-situ remediation method for ion-adsorption rare earth mining areas that can synergistically remove complex pollutants, achieve high remediation efficiency, low cost, no secondary pollution, and long-term stable effects has significant theoretical and engineering application value. Summary of the Invention

[0007] To address the shortcomings of existing groundwater pollution remediation technologies in ion-adsorption rare earth mining areas, this invention aims to provide a method suitable for groundwater pollution remediation in such areas. This method utilizes a combined and synergistic process of "in-situ chemical reduction technology and in-situ microbial enhanced purification technology" to achieve highly efficient removal of complex pollutants from groundwater. This solves the problems of poor remediation effect, high cost, high risk of secondary pollution, and unstable water quality after remediation in existing technologies, providing a practical and feasible technical solution for groundwater pollution control in ion-adsorption rare earth mining areas.

[0008] A method for remediating groundwater pollution in ion-adsorption rare earth mining areas comprises an in-situ chemical reduction zone and an in-situ microbial enhanced purification zone sequentially arranged along the water flow direction. The in-situ chemical reduction zone includes a primary treatment zone, a metal ion capture zone, and an adsorption-reduction zone. The primary treatment zone is filled with gravel and zeolite for primary adsorption and purification of pollutants. The adsorption-reduction zone is filled with graphene-supported nano-zero-valent iron composite material. The metal ion capture zone is filled with a metal ion capture agent consisting of lignin active powder loaded on a porous carrier.

[0009] A transition zone is provided between the in-situ chemical reduction zone and the in-situ microbial enhanced purification zone; the in-situ microbial enhanced purification zone includes a nitrification zone and a denitrification zone.

[0010] The transition zone filler includes bentonite and activated carbon. The mass ratio of bentonite to activated carbon is 10:2 to 3; the mass ratio of gravel to zeolite in the primary treatment zone is 10:1. The gravel can be quartz, feldspar, or rock chips with a particle size of 10-30 mm, used to disperse the active filler in each functional zone and increase the permeability coefficient of each reaction zone; The zeolite has a particle size of 5-10 mm; the metal ion scavenger has a particle size of 1-5 mm; and the graphene-supported nano-zero-valent iron composite material has a particle size of 100-150 μm.

[0011] The packing material of the nitrification zone includes nitrifying bacteria, alkali, slow-release oxidant, and gravel; the mass ratio of nitrifying bacteria, alkali, slow-release oxidant, and gravel is 1-2:0.2-0.3:1.5-2.8:10-15. The packing material of the denitrification zone includes denitrifying bacteria, solid carbon source, alkali agent and gravel; the mass ratio of denitrifying bacteria, solid carbon source, alkali agent and gravel is 1-2:0.1-0.2:2-3:10-15.

[0012] Alkali agents in the nitrification and denitrification zones are used to adjust the pH of the groundwater, keeping it at 7-8 and neutralizing the hydrogen ions produced by the nitrification reaction. The gravel in the nitrification and denitrification zones is used to disperse the aforementioned active filler and increase the permeability coefficient; In the nitrification zone, the aerobic nitrification of nitrifying bacteria further converts ammonia nitrogen in the pollutant plume into nitrate nitrogen. The slow-release oxidant maintains the dissolved oxygen concentration in groundwater at around 2 mg / L, providing sufficient oxygen for aerobic nitrification. In the denitrification zone, the anaerobic denitrification of denitrifying bacteria is used to further convert the nitrate nitrogen generated in the nitrification zone into nitrogen gas. The solid carbon source can sustainably and slowly release organic carbon, promoting denitrification, and is not easily washed away by the water flow. The transition zone is mainly used to filter clay and other mineral particles in the groundwater, preventing blockage in each reaction zone, while separating each reaction zone to maintain relatively independent internal reaction conditions and avoid mutual interference.

[0013] The slow-release oxidant comprises an active oxygen-releasing agent and a binder coating the active oxygen-releasing agent, wherein the weight ratio of the active oxygen-releasing agent to the binder is 1:0.2-0.3; the active oxygen-releasing agent is calcium peroxide or persulfate, and the binder is sodium alginate or silica; the alkali comprises a mixed alkali of NaHCO3 and NaOH in a weight ratio of 1:0.05; the solid carbon source comprises straw, coconut shell charcoal, and biomass charcoal in a weight ratio of 1:2:6-8. The nitrifying bacteria agent is composed of nitrite-oxidizing bacteria and nitrite-oxidizing bacteria, preferably nitrite-oxidizing cocci and nitrifying bacilli; the effective bacterial strain content is ≥10. 8 CFU / g.

[0014] The denitrifying bacteria agent is Pseudomonas, Bacillus, or Alcaligenes, etc., with an effective bacterial strain content ≥10. 8CFU / g can convert nitrate nitrogen in pollutant plumes into nitrogen gas through denitrification.

[0015] The adsorption-reduction zone is filled with graphene-supported nano-zero-valent iron composite material. When the filler is unmodified nano-zero-valent iron particles, its high reduction potential, large specific surface area, high reaction efficiency, small particle size, and high permeability make it suitable for remediation of environments polluted by nitrates and nitrites. However, due to the small nanoscale size and high surface potential of nano-zero-valent iron particles, coupled with the influence of gravity and interparticle magnetic forces, these particles tend to agglomerate, weakening their dispersibility, reducing active sites, and causing loss of mobility and transmissibility. Furthermore, the surface properties of nano-zero-valent iron are highly reactive, readily reacting with surrounding media (water, air, etc.) to form metal hydroxide or carbonate passivation layers, further hindering direct contact and reaction with pollutants. Therefore, to overcome the problems of reduced active sites and easy passivation and deactivation caused by the agglomeration of nano-zero-valent iron, a special method is needed.

[0016] We introduce graphene, which effectively promotes electron transfer between nano-zero-valent iron and pollutants, increases porosity, and improves removal efficiency. Simultaneously, it enhances the mechanical strength of the adsorbent material, reduces its breakage rate during the decontamination process, and minimizes secondary pollution. The preparation method of the graphene-supported nano-zero-valent iron composite material is as follows: To achieve a higher graphene loading rate, the graphene was first modified, specifically as follows: S1. Graphite is added to a mixture of H2SO4 and H3PO4 (volume ratio of H2SO4 to H3PO4 is 2:1), and stirred in an ice-water bath for 10–30 minutes. Potassium permanganate is slowly added, with a mass ratio of potassium permanganate to graphite of 3:1–6:1, while maintaining the system temperature below 15 °C. After the reaction is complete, the mixture is removed from the ice-water bath and stirred for another 60–80 minutes. The temperature is raised to 40 °C, and stirred for another 60 minutes. The temperature is then raised to 90 °C and stirred for 100 minutes. A mixture of deionized water and H2O2 is slowly added dropwise to the reaction mixture to obtain a graphene oxide mixture. The graphene oxide mixture is centrifuged and washed 2–3 times, and then dialyzed with deionized water. After vacuum freeze-drying, sponge-like graphene oxide is obtained. The sponge-like graphene oxide obtained by this method has a larger interlayer distance and more wrinkles, making it easier to improve the loading rate. Furthermore, the sponge-like graphene oxide can be modified to carry more active groups on its surface, providing more loading sites.

[0017] S2, sponge-like graphene oxide was added to N-methylpyrrolidone and stirred at room temperature for 100 minutes to dissolve it completely. Then, aminopropyltriethoxysilane was slowly added dropwise. After heating to 60-80℃ and reacting at a constant temperature for 3-5 hours, it was cooled to 50℃ and then hyperbranched polyamide-amine was added. Then, 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride was added and stirred at 60-80℃ for 20-24 hours to obtain graphene oxide grafted with diamine groups. It was then centrifuged, washed with water, and dried. The mass ratio of aminopropyltriethoxysilane to graphene oxide is 1:5; the mass ratio of 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, hyperbranched polyamide-amine, and graphene oxide is 2-3:3-5:8-10. Finally, a graphene-supported nano-zero-valent iron composite material was prepared: S3. The obtained graphene oxide grafted with diamine groups was placed in deionized water and ultrasonically dispersed. FeSO4·7H2O was added, stirred, and argon gas was introduced to ensure an oxygen-free environment. Then, KBH4 solution was added dropwise at a rate of 1-2 drops / second, with a volume ratio of KBH4 solution to FeSO4·7H2O solution of 1-2:1 and a concentration ratio of 5-10:1. Argon gas was introduced during the reaction to maintain an oxygen-free environment. After 1-2 hours of reaction, the mixture was washed with deionized water and anhydrous ethanol, centrifuged, and vacuum dried to obtain the graphene-supported nano-zero-valent iron composite material, wherein the mass ratio of zero-valent iron to graphene oxide was 3-4:1-2. The composite material of graphene supported on nano-zero valent iron significantly improves dispersion stability. This is because the hyperbranched polyamide-amine surface is rich in hydrophilic groups such as amino and hydroxyl groups, which enhance the dispersibility of graphene oxide in water, reduce agglomeration, and provide more loading sites for nano-zero valent iron. Pretreatment with aminopropyltriethoxysilane introduces more amino groups, followed by double grafting with hyperbranched polyamide-amine, resulting in more active sites on the graphene oxide surface. Furthermore, the functional groups of the hyperbranched polyamide-amine can interact with Fe²⁺. + Coordination occurs, guiding the uniform deposition of nano-zero-valent iron, enhancing the loading and stability of zero-valent iron, while inhibiting its oxidative aggregation and extending the material's lifespan. Furthermore, the steric hindrance effect of the hyperbranched structure reduces excessive stacking of nano-zero-valent iron and graphene sheets, improving the adsorption-reduction activity of the composite material for target pollutants. Moreover, thermal reduction treatment can revert the oxidized nano-zero-valent iron particles after use, thereby improving the composite material's reactivity and regeneration capabilities.

[0018] The metal ion capturing region is filled with a metal ion capturing agent consisting of lignin active powder loaded on a porous carrier. The specific preparation method of the metal ion scavenger is as follows: lignin active powder is added to an 8% citric acid aqueous solution to activate the active sites on the lignin active powder, and then a porous carrier is added. The reaction is carried out at 50-60 °C for 2-3 hours to allow the lignin active powder and the porous carrier to react and crosslink. After filtration and low-temperature drying, the metal ion scavenger is obtained. The mass ratio of lignin active powder to porous carrier is 1:3-5.

[0019] The porous carrier mentioned above is a porous carrier obtained by compositing silica onto bentonite, specifically: S01, add bentonite to deionized water, disperse thoroughly, heat to 40 ℃, add octadecyltrimethylammonium chloride, stir thoroughly, react for 1-2 hours, take out the suspension and centrifuge at 3500 rpm, wash with deionized water 2-3 times, centrifuge again, take out the solid mixture at the bottom, dry and grind at 60 ℃ to obtain modified bentonite; the mass ratio of octadecyltrimethylammonium chloride to bentonite is 1:8. S02, tetraethyl orthosilicate, ethanol and deionized water are mixed in a molar ratio of 1:4:4 at 40-50 °C, and dilute hydrochloric acid is added dropwise to adjust the pH to 4-5. The mixture is stirred to form a transparent sol. Modified bentonite is slowly added, and the mixture is stirred for 2-3 hours. The temperature is raised to 60 °C, and the mixture is allowed to stand for 12 hours. Then it is cooled to room temperature and allowed to stand for 24 hours. After centrifugation and filtration, gel microspheres are obtained. The microspheres are washed with water 2-3 times, dried at 60 °C, and then heated to 400-500 °C at a rate of 2 °C / min and kept at this temperature for 3 hours to obtain a porous carrier. The mass ratio of transparent sol to modified bentonite is 1:4.

[0020] The preparation method of the lignin active powder is as follows: S001, chitosan and 0.5% citric acid solution are stirred and heated at 100℃ for 80-120 minutes until completely dissolved to obtain chitosan aqueous solution; The mass concentration of the chitosan aqueous solution is 4-6%; S002, sodium hydroxide and deionized water are dissolved and added evenly, then lignin is added and stirred for 30-50 minutes until the lignin is completely dissolved; chitosan aqueous solution is added and stirred evenly, and reacted at 50-60℃ for 2-3 hours to allow the lignin and chitosan to undergo a cross-linking reaction, obtaining a solution containing lignin grafted with amino groups; the mass concentration of the sodium hydroxide aqueous solution is 25%; S003: Dissolve monochloroacetic acid in deionized water, add the monochloroacetic acid solution dropwise to the lignin solution finally obtained in S002, heat to 80-90℃ and react for 4-5 hours. After the reaction is complete, cool, pour off the reaction solution, adjust the pH of the solution to 5.0±0.1 with 2mol / L hydrochloric acid, filter the reaction product through a 0.5μm microporous membrane to remove impurities, then dialyze through a 1000da dialysis bag in deionized water for 24 hours, and freeze-dry for 72 hours to obtain lignin active powder; wherein, the mass concentration of the monochloroacetic acid solution is 60%, and the mass ratio of monochloroacetic acid to lignin is 3:25-30.

[0021] The amino groups of chitosan can bind heavy metal and rare earth ions through coordination. The carboxyl groups introduced by carboxylation can also capture heavy metal and rare earth ions. Carboxyl groups are among the most effective metal ion-capturing functional groups in nature, strongly adsorbing positively charged heavy metal and rare earth ions through ion exchange and electrostatic adsorption. Furthermore, this synergistic effect of amino and carboxyl groups allows different functional groups to function under different pH conditions. The introduction of carboxyl groups can also improve the hydrophilicity of the material and regulate its dispersibility in aqueous solutions. Therefore, modifying lignin by introducing these active groups can increase its adsorption performance and enhance its selective capture ability for specific heavy metal and rare earth ions. Moreover, lignin itself has a three-dimensional network structure, and the metal ion scavenger formed after cross-linking modification has a high specific surface area, which can accommodate more adsorption sites, further improving the adsorption capacity for heavy metal and rare earth ions. On the other hand, the prepared metal ion scavenger, as a green and sustainable remediation material, has excellent heavy metal and rare earth ion capture performance and can remove heavy metal and rare earth ions from water through adsorption, ion exchange, and precipitation.

[0022] In response to the groundwater pollution characteristics of ion-adsorption rare earth mining areas, in-situ chemical reduction zones and in-situ microbial enhanced purification zones were sequentially stacked along the water flow direction. The thickness of the primary treatment zone in the in-situ chemical reduction zone was 0.5–0.8 m, the thickness of the metal ion capture zone was 0.3–0.5 m, and the thickness of the adsorption reduction zone transition zone was 0.2–0.3 m; the thickness of the transition zone was 1.0–1.5 m; the thickness of the nitrification zone and the denitrification zone in the in-situ microbial enhanced purification zone was 2–3 m.

[0023] The active packing material in the in-situ chemical reduction zone underwent scientific and rational research and design. The scientific design of the active packing material and layered structure ensures synergistic effects among the various active packing materials, with each functional zone progressively treating pollutants. The combination of graphene-supported nano-zero-valent iron composite materials, metal ion scavengers, and highly active microorganisms, coupled with physical adsorption, chemical reduction, and microbial remediation technologies, effectively remediated groundwater acidification and NH4+ pollution in ion-adsorption rare earth mining areas. + -N, NO3 -The invention effectively addresses pollution issues related to nitrogen (N), heavy metals, and rare earth ions, demonstrating stable remediation results. Furthermore, the prepared graphene-supported nano-zero-valent iron composite material can be repeatedly reused after reduction and regeneration, with remediation effects largely consistent with the initial results. Compared to existing technologies, the advantages of this invention are: 1) The present invention provides a method for the remediation of groundwater pollution in ion-adsorption rare earth mining areas. Through the combined and synergistic process of "in-situ chemical reduction technology and in-situ microbial enhanced purification technology", it achieves efficient removal of complex pollutants in groundwater, solves the problems of poor remediation effect, high cost, high risk of secondary pollution and unstable water quality after remediation in the existing technology, and provides a practical and feasible technical solution for the treatment of groundwater pollution in ion-adsorption rare earth mining areas. This combined synergistic process is an organic whole. The in-situ chemical reduction zone promotes the bioremediation effect of the in-situ microbial enhanced purification zone, which in turn further enhances the purification and remediation effect of the entire system. The process employs in-situ chemical reduction and in-situ microbial enhanced purification zones stacked sequentially along the water flow direction, combining graphene-supported nano-zero-valent iron composite materials, metal ion capture agents, and highly active microorganisms, thus integrating physical adsorption, chemical reduction, and microbial remediation technologies. Furthermore, the active packing materials in the primary treatment zone, metal ion capture zone, and adsorption-reduction zone of the in-situ chemical reduction zone are scientifically and rationally designed. The scientific design of the active packing materials and layered structure ensures synergistic effects among the active packing materials, with each functional zone treating pollutants progressively. This effectively remediates groundwater acidification and NH4+ in ion-adsorption rare earth mining areas. + -N, NO3 - It addresses the pollution issues of nitrogen, rare earth ions, and heavy metals, providing stable remediation results and enabling rapid, efficient, and timely treatment of pollution. It exhibits good technical and economic applicability for ion-adsorption rare earth mines with severe groundwater pollution of ammonia nitrogen and nitrate nitrogen.

[0024] 2) This invention also provides a graphene-supported composite material of nano-zero-valent iron, which significantly improves dispersion stability, overcomes the problem of reduced active sites caused by the aggregation of nano-zero-valent iron, and the easy passivation and deactivation; it can effectively promote electron transfer between nano-zero-valent iron and pollutants, increase porosity, and improve removal efficiency; at the same time, it enhances the mechanical strength of the adsorption material, reduces its breakage rate during the decontamination process, and reduces secondary pollution. The functional groups of the grafted amine can interact with Fe²⁺. +The formation of coordination interactions guides the uniform deposition of nano-zero-valent iron, enhancing the loading and stability of zero-valent iron while inhibiting its oxidative aggregation and extending the material's lifespan. Furthermore, the steric hindrance effect of the hyperbranched structure reduces excessive stacking of nano-zero-valent iron and graphene sheets, improving the adsorption-reduction activity of the composite material for target pollutants and enhancing its treatment efficiency. Moreover, the graphene-loaded nano-zero-valent iron composite material can be thermally reduced to restore oxidized nano-zero-valent iron particles after use, thereby improving the composite material's reactivity and regeneration capacity. After reduction and regeneration, it can be reused repeatedly, with a repair effect not significantly different from the initial effect.

[0025] 3) This invention also provides a metal ion scavenger that loads lignin active powder onto a porous carrier. After cross-linking modification, the resulting metal ion scavenger has a high specific surface area, enabling it to accommodate more adsorption sites and further enhancing the adsorption capacity for heavy metals and rare earth ions. Furthermore, the prepared metal ion scavenger, as a green and sustainable remediation material, exhibits excellent heavy metal and rare earth ion capture performance, and can remove heavy metals and rare earth ions from water through adsorption, ion exchange, and precipitation.

[0026] 4) Through reasonable zoning, a synergistic treatment scheme for the complex water pollution of "rare earth ions-sulfate-ammonia nitrogen-heavy metals" in groundwater of ion-adsorption rare earth mining areas was implemented. This significantly reduced the impact between pollutants and improved the synergistic treatment efficiency of each pollutant. The prepared graphene-supported nano-zero-valent iron composite material and metal ion capture agent worked together in a multi-stage treatment process to achieve deep treatment of heavy metal pollution and rare earth ion, ammonia nitrogen, and nitrate pollution in ion-adsorption rare earth mining areas. Attached Figure Description

[0027] Figure 1 A three-dimensional structural diagram of the combined technology for groundwater pollution remediation in ion-adsorption rare earth mining areas; Figure 2 A schematic diagram of the three-dimensional partitioned structure of the in-situ chemical reduction zone; Figure 3 Electron micrograph of graphene oxide grafted with diamine groups; Figure 4 Regional distribution map of groundwater pollution concentration in the mining area; Figure 5 A graph showing the relationship between the dosage of graphene-supported nano-zero-valent iron composite material and the ammonia nitrogen removal rate. Figure 6 The image shows the removal effect of metal ion scavengers on heavy metals and rare earth ions. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the description of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0029] Example 1 A method for remediating groundwater pollution in ion-adsorption rare earth mining areas first involves preparing a graphene-supported nano-zero-valent iron composite material, specifically: Ten parts of graphite were added to a mixture of 100 parts of H2SO4 and H3PO4 and stirred in an ice-water bath for 20 minutes. 50 parts of potassium permanganate were slowly added, maintaining the system temperature below 15°C. After the reaction was complete, the mixture was removed from the ice-water bath and stirred for another 60 minutes. The temperature was raised to 40°C and stirred for another 60 minutes. The temperature was then raised to 90°C and stirred for 100 minutes. A mixture of 100 parts of deionized water and 15 parts of H2O2 was slowly added dropwise to the reaction mixture to obtain a graphene oxide mixture. The graphene oxide mixture was centrifuged and washed 2-3 times, dialyzed with deionized water, and then freeze-dried under vacuum to obtain sponge-like flocculent graphene oxide. Five parts of the sponge-like flocculent graphene oxide were added to 50 parts of N-methylpyrrolidone, ultrasonically dispersed, and stirred at room temperature for 100 minutes to ensure complete dissolution. One part of aminopropyltriethoxysilane was then slowly added dropwise. The mixture was heated to 80°C and reacted at a constant temperature for 4 hours, then cooled to 50°C. After reaching ℃, add 2 parts of hyperbranched polyamide-amine and 1.5 parts of 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride. Stir and react at 70℃ for 20 hours to obtain graphene oxide grafted with diamine groups. Centrifuge, wash with water and dry. Ten parts of graphene oxide grafted with diamine groups were placed in 100 parts of deionized water and ultrasonically dispersed. 20 parts of FeSO4·7H2O were added, stirred, and argon gas was introduced to ensure an oxygen-free environment. Then, 100 parts of 80mM KBH4 solution were added dropwise at a rate of 1-2 drops / second. Argon gas was introduced during the reaction to maintain an oxygen-free environment. After 2 hours of reaction, the mixture was washed with deionized water and anhydrous ethanol, centrifuged, and vacuum dried to obtain the graphene-supported nano-zero-valent iron composite material.

[0030] Furthermore, a porous support is prepared, specifically as follows: Eight parts of bentonite were added to 100 parts of deionized water and dispersed thoroughly. The mixture was heated to 40 °C, and one part of octadecyltrimethylammonium chloride was added. The mixture was stirred thoroughly and reacted for 2 hours. The suspension was removed and centrifuged at 3500 rpm. The mixture was washed 2-3 times with deionized water and centrifuged again. The solid mixture at the bottom was removed, dried at 60 °C, and ground to obtain modified bentonite. Tetraethyl orthosilicate, ethanol, and deionized water were mixed at 50 °C in a molar ratio of 1:4:4. The pH was adjusted to 4.2 by adding dilute hydrochloric acid. The mixture was stirred to form 10 parts of transparent sol. Forty parts of modified bentonite were slowly added and stirred for 2 hours. The mixture was heated to 60 °C and allowed to stand for 12 hours. Then, it was cooled to room temperature and allowed to stand for 24 hours. After centrifugation and filtration, gel microspheres were obtained. The microspheres were washed 2-3 times with water, dried at 60 °C, and then heated to 400 °C at a rate of 2 °C / min and kept at that temperature for 3 hours to obtain a porous carrier.

[0031] The preparation of lignin active powder is as follows: Chitosan is stirred and heated at 100 °C for 80 minutes with a 0.5% citric acid solution until completely dissolved, yielding a 5% chitosan aqueous solution; 50 parts of a 25% sodium hydroxide aqueous solution are dissolved in sodium hydroxide and deionized water, and 50 parts of lignin are added and stirred for 50 minutes until the lignin is completely dissolved; 50 parts of the chitosan aqueous solution are added and stirred evenly, and the mixture is reacted at 60 °C for 3 hours to allow the lignin and chitosan to undergo a cross-linking reaction, yielding a solution containing amino-grafted lignin; 6 parts of monochloroacetic acid are dissolved in 10 parts of deionized water, and the monochloroacetic acid solution is added dropwise to the amino-grafted lignin solution, while the temperature is raised to 90 °C. The reaction was carried out at ℃ for 4 hours. After the reaction was completed, the mixture was cooled and the reaction solution was poured out. The pH of the solution was adjusted to 5.0±0.1 with 2 mol / L hydrochloric acid. The reaction product was filtered through a 0.5 μm microporous membrane to remove impurities. Then, it was dialyzed in deionized water for 24 hours using a 1000 Da dialysis bag. Finally, it was freeze-dried for 72 hours to obtain lignin active powder.

[0032] To further prepare the metal ion scavenger, specifically: 5 parts of lignin active powder were added to 10 parts of citric acid aqueous solution with a mass concentration of 8%, and then 15 parts of porous support were added. The mixture was reacted at 60 °C for 3 hours to allow the lignin active powder and porous support to react and crosslink. After filtration and low-temperature drying, the metal ion scavenger was obtained.

[0033] The in-situ chemical reduction zone, transition zone, and in-situ microbial enhanced purification zone are sequentially arranged along the water flow direction. See details below. Figure 1 The in-situ chemical reduction zone is sequentially divided into a primary treatment zone, an adsorption-reduction zone, and a transition zone. See [link to details] for specific configuration. Figure 2The primary treatment zone is filled with a 10:1 mixture of gravel and zeolite, 0.8 m thick; the metal ion capture zone is filled with a metal ion capture agent, 0.4 m thick; the adsorption-reduction zone is filled with graphene-supported nano-zero-valent iron composite material, 0.3 m thick; the transition zone is filled with a 10:2 mixture of bentonite and activated carbon, 1.0 m thick; the in-situ microbial enhanced purification zone includes a nitrification zone and a denitrification zone, with the nitrification zone being 3 m thick and filled with nitrifying bacteria, alkali, slow-release oxidant, and gravel in a 1:0.2:2:10 ratio. The slow-release oxidant is a combination of calcium peroxide and sodium alginate; the alkali is a 1:0.05 mixture of NaHCO3 and NaOH; the nitrifying bacteria are Nitrostrophosporidium and Nitrobacterium; the effective bacterial content is 10. 8 CFU / g. The denitrification zone is 2m thick and filled with denitrifying bacteria, solid carbon source, alkali, and gravel in a 1:0.2:2:10 ratio. The alkali is a 1:0.05 mixture of NaHCO3 and NaOH. The solid carbon source comprises a mixture of straw, coconut shell charcoal, and biochar-based materials in a weight ratio of 1:2:6. The denitrifying bacteria are Pseudomonas and Bacillus, with an effective bacterial count ≥10. 8 CFU / g.

[0034] Several monitoring wells are set up in each functional area along the direction of the water flow cross section; after the system is put into operation, the changes in the groundwater quality in the area are observed.

[0035] Example 2 A method for remediating groundwater pollution in ion-adsorption rare earth mining areas first involves preparing a graphene-supported nano-zero-valent iron composite material, specifically: Ten parts of graphite were added to a mixture of 100 parts of H2SO4 and H3PO4 and stirred in an ice-water bath for 30 minutes. Then, 30 parts of potassium permanganate were slowly added, with a mass ratio of potassium permanganate to graphite of 3:1 to 6:1, while maintaining the system temperature below 15 °C. After the reaction was complete, the mixture was removed from the ice-water bath and stirred for another 70 minutes. The temperature was then raised to 40 °C and stirred for another 60 minutes. Finally, the temperature was raised to 90 °C and stirred for 100 minutes. A mixture of 100 parts of deionized water and 15 parts of H2O2 was slowly added dropwise to the reaction mixture to obtain a graphene oxide mixture. The graphene oxide mixture was centrifuged and washed 2-3 times, dialyzed with deionized water, and then freeze-dried under vacuum to obtain sponge-like flocculent graphene oxide. Five parts of sponge-like graphene oxide were added to 50 parts of N-methylpyrrolidone. After ultrasonic dispersion, the mixture was stirred at room temperature for 100 minutes to ensure complete dissolution. Then, one part of aminopropyltriethoxysilane was slowly added dropwise. The mixture was heated to 70 °C and reacted at a constant temperature for 4 hours. After cooling to 50 °C, 1.5 parts of hyperbranched polyamide-amine and 1 part of 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride were added. The mixture was stirred at 70 °C for 24 hours to obtain graphene oxide grafted with diamine groups. The graphene oxide was then centrifuged, washed with water, and dried. Ten parts of graphene oxide grafted with diamine groups were placed in 100 parts of deionized water and ultrasonically dispersed. 30 parts of FeSO4·7H2O were added, stirred, and argon gas was introduced to ensure an oxygen-free environment. Then, 100 parts of 80mM KBH4 solution were added dropwise at a rate of 1-2 drops / second. Argon gas was introduced during the reaction to maintain the reaction in an oxygen-free environment. After 2 hours of reaction, the mixture was washed with deionized water and anhydrous ethanol, centrifuged, and vacuum dried to obtain the graphene-supported nano-zero-valent iron composite material.

[0036] Furthermore, a porous support is prepared, specifically as follows: Eight parts of bentonite were added to 100 parts of deionized water and dispersed thoroughly. The mixture was heated to 40 °C, and one part of octadecyltrimethylammonium chloride was added. The mixture was stirred thoroughly and reacted for 2 hours. The suspension was removed and centrifuged at 3500 rpm. The mixture was washed 2-3 times with deionized water and centrifuged again. The solid mixture at the bottom was removed, dried and ground at 60 °C to obtain modified bentonite. The mass ratio of octadecyltrimethylammonium chloride to bentonite was 1:8. Tetraethyl orthosilicate, ethanol and deionized water were mixed at 50 °C in a molar ratio of 1:4:4. The pH was adjusted to 4.5 by adding dilute hydrochloric acid. The mixture was stirred to form 10 parts of transparent sol. 40 parts of modified bentonite were slowly added and stirred for 2-3 hours. The mixture was heated to 60 °C and allowed to stand for 12 hours. Then it was cooled to room temperature and allowed to stand for 24 hours. After centrifugation and filtration, gel microspheres were obtained. The microspheres were washed 2-3 times with water, dried at 60 °C, and then heated to 450 °C at a rate of 2 °C / min and kept at that temperature for 3 hours to obtain a porous carrier.

[0037] The preparation of lignin active powder is as follows: Chitosan is stirred and heated with a 0.5% citric acid solution at 100 °C for 120 minutes until completely dissolved, yielding a 6% chitosan aqueous solution; 50 parts of a 25% sodium hydroxide aqueous solution are dissolved uniformly in sodium hydroxide and deionized water, and 60 parts of lignin are added, stirred for 30 minutes until the lignin is completely dissolved; 50 parts of the chitosan aqueous solution are added, stirred uniformly, and reacted at 60 °C for 3 hours to allow the lignin and chitosan to undergo a cross-linking reaction, yielding a solution containing amino-grafted lignin; 6 parts of monochloroacetic acid are dissolved in 10 parts of deionized water, and the monochloroacetic acid solution is added dropwise to the amino-grafted lignin solution, while the temperature is raised to 90 °C. The reaction was carried out at ℃ for 4-5 hours. After the reaction was completed, the mixture was cooled and the reaction solution was poured out. The pH of the solution was adjusted to 5.0±0.1 with 2 mol / L hydrochloric acid. The reaction product was filtered through a 0.5 μm microporous membrane to remove impurities. Then, it was dialyzed in deionized water for 24 hours using a 1000 Da dialysis bag. The product was then freeze-dried for 72 hours to obtain lignin active powder. The mass concentration of the monochloroacetic acid solution was 60%, and the mass ratio of monochloroacetic acid to lignin was 3:25-30.

[0038] To further prepare the metal ion scavenger, specifically: 5 parts of lignin active powder were added to 10 parts of citric acid aqueous solution with a mass concentration of 8% to activate the active sites on the lignin active powder. Then, 15 parts of porous support were added, and the mixture was reacted at 60 °C for 3 hours to allow the lignin active powder and porous support to react and crosslink. After filtration and low-temperature drying, the metal ion scavenger was obtained.

[0039] Along the water flow direction, an in-situ chemical reduction zone, a transition zone, and an in-situ microbial enhanced purification zone are sequentially set up. Within the in-situ chemical reduction zone, a primary treatment zone, a metal ion capture zone, and a transition zone are sequentially set up. The primary treatment zone is filled with a 10:1 mixture of gravel and zeolite, 0.5 m thick; the metal ion capture zone is filled with a metal ion capture agent, 0.5 m thick; the adsorption reduction zone is filled with graphene-supported nano-zero-valent iron composite material, 0.3 m thick; the transition zone is filled with a 10:3 mixture of bentonite and activated carbon, 1.5 m thick; and the nitrification zone of the in-situ microbial enhanced purification zone is 2 m thick, filled with nitrifying bacteria, alkali, slow-release oxidant, and gravel in a 1:0.3:1.5:15 ratio. The slow-release oxidant is a combination of calcium peroxide and sodium alginate; the alkali is a 1:0.05 mixture of NaHCO3 and NaOH; the nitrifying bacteria are Nitrifying Cocci and Nitrifying Bacilli; and the effective bacterial content is 10... 8 CFU / g. The denitrification zone is 2m thick and filled with denitrifying bacteria, solid carbon source, alkali, and gravel in a 2:0.2:2:15 ratio. The alkali is a 1:0.05 mixture of NaHCO3 and NaOH. The solid carbon source comprises a mixture of straw, coconut shell charcoal, and biochar-based materials in a weight ratio of 1:2:8. The denitrifying bacteria are Pseudomonas and Bacillus, with an effective bacterial count ≥10. 8 CFU / g.

[0040] Several monitoring wells are set up in each functional area along the direction of the water flow cross section; after the system is put into operation, the changes in the groundwater quality in the area are observed.

[0041] Example 3 A method for remediating groundwater pollution in ion-adsorption rare earth mining areas first involves preparing a graphene-supported nano-zero-valent iron composite material, specifically: Ten parts of graphite were added to a mixture of 100 parts of H2SO4 and H3PO4 and stirred in an ice-water bath for 20 minutes. 40 parts of potassium permanganate were slowly added, maintaining the system temperature below 15°C. After the reaction was complete, the mixture was removed from the ice-water bath and stirred for another 60 minutes. The temperature was raised to 40°C and stirred for another 60 minutes, then raised to 90°C and stirred for 100 minutes. A mixture of 100 parts of deionized water and 15 parts of H2O2 was slowly added dropwise to the reaction mixture to obtain a graphene oxide mixture. The graphene oxide mixture was centrifuged and washed 2-3 times, dialyzed with deionized water, and then freeze-dried under vacuum to obtain sponge-like flocculent graphene oxide. Ten parts of the sponge-like flocculent graphene oxide were added to 100 parts of N-methylpyrrolidone, ultrasonically dispersed, and stirred at room temperature for 100 minutes to ensure complete dissolution. Two parts of aminopropyltriethoxysilane were slowly added dropwise, and the mixture was heated to 70°C and reacted at a constant temperature for 5 hours, then cooled to 50°C. After reaching ℃, add 5 parts of hyperbranched polyamide-amine and 2 parts of 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride. Stir and react at 70 ℃ for 24 hours to obtain graphene oxide grafted with diamine groups. Centrifuge, wash with water and dry. Ten parts of graphene oxide grafted with diamine groups were placed in 100 parts of deionized water and ultrasonically dispersed. 20 parts of FeSO4·7H2O were added, stirred, and argon gas was introduced to ensure an oxygen-free environment. Then, 100 parts of 80 mM KBH4 solution were added dropwise at a rate of 1-2 drops / second. Argon gas was introduced during the reaction to maintain an oxygen-free environment. After reacting for 1-2 hours, the mixture was washed with deionized water and anhydrous ethanol, centrifuged, and vacuum dried to obtain graphene-supported nano-zero-valent iron composite material, wherein the mass ratio of zero-valent iron to graphene oxide was 3-4:1-2.

[0042] Furthermore, a porous support is prepared, specifically as follows: Eight parts of bentonite were added to 100 parts of deionized water and dispersed thoroughly. The mixture was heated to 40 °C, and one part of octadecyltrimethylammonium chloride was added. The mixture was stirred thoroughly and reacted for 2 hours. The suspension was removed and centrifuged at 3500 rpm. The mixture was washed 2-3 times with deionized water and centrifuged again. The solid mixture at the bottom was removed, dried at 60 °C, and ground to obtain modified bentonite. Tetraethyl orthosilicate, ethanol, and deionized water were mixed at 40-50 °C in a molar ratio of 1:4:4. The pH was adjusted to 5 by adding dilute hydrochloric acid dropwise and stirring to form 10 parts of transparent sol. 40 parts of modified bentonite were slowly added and stirred for 3 hours. The mixture was heated to 60 °C and allowed to stand for 12 hours. Then it was cooled to room temperature and allowed to stand for 24 hours. After centrifugation and filtration, gel microspheres were obtained. The microspheres were washed 2-3 times with water, dried at 60 °C, and then heated to 500 °C at a rate of 2 °C / min and kept at that temperature for 3 hours to obtain a porous carrier.

[0043] The preparation of lignin active powder is as follows: Chitosan is stirred and heated with a 0.5% citric acid solution at 100 °C for 100 minutes until completely dissolved, yielding a 4% chitosan aqueous solution; sodium hydroxide and deionized water are dissolved evenly to obtain 50 parts of a 25% sodium hydroxide aqueous solution, and 50 parts of lignin are added and stirred for 50 minutes until the lignin is completely dissolved; 50 parts of the chitosan aqueous solution are added and stirred evenly, and the mixture is reacted at 60 °C for 2 hours to allow the lignin and chitosan to undergo a cross-linking reaction, yielding a solution containing amino-grafted lignin; 6 parts of monochloroacetic acid are dissolved in 10 parts of deionized water, and the monochloroacetic acid solution is added dropwise to the amino-grafted lignin solution, the temperature is raised to 90 °C and the reaction is carried out for 5 hours. After the reaction is completed, the mixture is cooled, the reaction solution is poured off, and 2 The pH of the solution was adjusted to 5.0 ± 0.1 with mol / L hydrochloric acid. The reaction product was filtered through a 0.5 μm microporous membrane to remove impurities. Then, it was dialyzed in deionized water for 24 hours using a 1000 Da dialysis bag. Finally, it was freeze-dried for 72 hours to obtain lignin active powder.

[0044] To further prepare the metal ion scavenger, specifically: 5 parts of lignin active powder were added to 10 parts of citric acid aqueous solution with a mass concentration of 8% to activate the active sites on the lignin active powder. Then, 15 parts of porous support were added, and the mixture was reacted at 60 °C for 3 hours to allow the lignin active powder and porous support to react and crosslink. After filtration and low-temperature drying, the metal ion scavenger was obtained.

[0045] Along the water flow direction, an in-situ chemical reduction zone, a transition zone, and an in-situ microbial enhanced purification zone are sequentially set up. The in-situ chemical reduction zone includes a primary treatment zone, a metal ion capture zone, and a transition zone. The primary treatment zone is filled with a 10:1 mixture of gravel and zeolite, 0.7m thick; the metal ion capture zone is filled with a metal ion capture agent, 0.4m thick; the adsorption reduction zone is filled with graphene-supported nano-zero-valent iron composite material, 0.3m thick; the transition zone is filled with a 5:1 mixture of bentonite and activated carbon, 1.2m thick; and the nitrification zone of the in-situ microbial enhanced purification zone is 2m thick, filled with nitrifying bacteria, alkali, slow-release oxidant, and gravel in a 2:0.2:2.8:15 ratio. The slow-release oxidant is a combination of calcium peroxide and sodium alginate; the alkali is a 1:0.05 mixture of NaHCO3 and NaOH; the nitrifying bacteria are Nitrifying Cocci and Nitrifying Bacilli; and the effective bacterial content is 10. 8 CFU / g. The denitrification zone is 2m thick and filled with denitrifying bacteria, solid carbon source, alkali, and gravel in a 1:0.1:2:15 ratio. The alkali is a 1:0.05 mixture of NaHCO3 and NaOH. The solid carbon source comprises a mixture of straw, coconut shell charcoal, and biochar-based materials in a weight ratio of 1:2:7. The denitrifying bacteria are Pseudomonas and Bacillus, with an effective bacterial count ≥10. 8 CFU / g.

[0046] Several monitoring wells are set up in each functional area along the direction of the water flow cross section; after the system is put into operation, the changes in the groundwater quality in the area are observed.

[0047] Comparative Example 1: No metal trapping zone or adsorption-reduction zone was set up; zero-valent nano-iron was directly added in equal amounts to the nitration zone and denitration zone, respectively; other aspects were the same as in Example 1. Comparative Example 2: The adsorption-reduction zone was directly filled with a mixture of bentonite and an equal amount of zero-valent nano-iron, and other aspects were the same as in Example 1. Comparative Example 3: The adsorption-reduction zone was filled with an equal amount of a mixture of graphene oxide loaded with zero-valent nano-iron. No modification was made to the graphene oxide. Otherwise, it was the same as in Example 1. Comparative Example 4: No metal trapping zone was set up. The adsorption-reduction zone was filled with a mixture of graphene oxide loaded with zero-valent nano-iron. No modification was made to the graphene oxide. Everything else was the same as in Example 1.

[0048] Experimental data and results analysis 1. Electron micrograph of graphene oxide grafted with diamine groups. Using a field emission scanning electron microscope (SEM) with an accelerating voltage of 20.0 kV, the diamine-grafted graphene oxide prepared in Example 1 was adhered to the sample stage. The sample was then sputter-coated with gold and observed under a scanning electron microscope at 1500x magnification. Figure 3 ,from Figure 3 As can be seen, the microstructure of graphene oxide grafted with diamine groups is more porous and thinner, as transparent as gauze, with an undulating and wrinkled surface. Due to oxidation, the original C=C sp2 planar structure of the graphene oxide surface is disrupted, causing the thin-layer graphene oxide to exhibit a certain wrinkled shape. For thin-layer graphene oxide, this wrinkled shape effectively reduces surface energy, improves stability, disperses more active sites of highly reactive groups on its surface, and increases its surface roughness, significantly improving its loading rate and stability within the graphene oxide layer.

[0049] 2. Groundwater quality assessment According to the "Groundwater Quality Standard" (GB / T 14848-2017), groundwater quality was evaluated using single-index evaluation and comprehensive evaluation methods. The evaluation covered 16 groundwater environmental monitoring points (ZK1~ZK16) in the mining area, with 18 monitoring indicators including water temperature, redox potential, dissolved oxygen, pH, oxygen consumption, total phosphorus, total nitrogen, ammonia nitrogen, nitrate nitrogen, nitrite nitrogen, mercury, cadmium, hexavalent chromium, lead, arsenic, nickel, lanthanum, and neodymium; and 3 groundwater environmental monitoring points (G8~G10), with 10 monitoring indicators including pH, ammonia nitrogen, nitrate nitrogen, nitrite nitrogen, mercury, cadmium, hexavalent chromium, lead, arsenic, and nickel. The monitoring indicators at the three soil environmental monitoring sites (ZK4, ZK7, and ZK14) include six items: pH, cation exchange capacity, total nitrogen, ammonium nitrogen, nitrite nitrogen, and nitrate nitrogen. The monitoring indicators at the three soil environmental monitoring sites (G8–G10) include ten items: pH, ammonium nitrogen, nitrite nitrogen, nitrate nitrogen, copper, mercury, arsenic, cadmium, lead, and nickel. See Tables 1-2 for details. Figure 4 A regional distribution map of groundwater pollution concentration in mining areas.

[0050] Table 1 Summary of Groundwater Environmental Monitoring Results in the Mining Area

[0051] Table 1 (Continued) - Summary of Groundwater Environmental Monitoring Results in the Mining Area

[0052] Table 1 shows that of the 18 indicators at the 19 groundwater environmental monitoring points (ZK1~ZK16, G8~G10), 11 are covered by the "Groundwater Quality Standard" (GB / T 14848-2017). According to the single indicator evaluation results, the indicators that reach Class V are pH, ammonia nitrogen, nitrate nitrogen, lead, and arsenic; the indicators that reach Class IV are oxygen consumption and nickel; the indicators that reach Class III are nitrite nitrogen and mercury; and the indicators that reach Class II are cadmium and hexavalent chromium, which both belong to Class I.

[0053] Table 2 Summary of Soil Environmental Monitoring Results in the Mining Area

[0054] Continued from Table 2: Summary of Soil Environmental Monitoring Results in the Mining Area

[0055] The comprehensive evaluation results are as follows: the ammonia nitrogen concentration at monitoring point ZK16 on the upstream boundary of the mining area was 31.60 mg / L, which is classified as Class V water quality. Of the 18 groundwater monitoring points within the mining area, 16 were Class V, 1 was Class IV, and 1 was Class III. Compared with the Class III standard, a total of 7 indicators exceeded the standards at all monitoring points, with exceedance rates of pH (88.89%), oxygen consumption (26.67%), ammonia nitrogen (94.44%), nitrate nitrogen (44.44%), nickel (27.78%), lead (38.89%), arsenic (33.33%), lanthanum (41.25%), and neodymium (48.29%).

[0056] 3. The effect of graphene-supported zero-valent iron nanocomposite material on ammonia nitrogen removal In the remediation system operated in Example 1, different dosages of graphene-supported nano-zero-valent iron composite materials showed varying effects on ammonia nitrogen removal. After 60 days of operation, the ammonia nitrogen removal rates were 33.7%, 51.4%, 82.9%, and 94.7% when the composite material dosage was 0 g / L, 5 g / L, 10 g / L, and 15 g / L, respectively. At lower dosages, the composite material did not significantly promote nitrification. However, with increasing zero-valent iron dosage, the nitrification rate gradually increased, and the ammonia nitrogen removal rate significantly improved when the dosage was 10 g / L. This is because with increasing dosage, the corrosion of zero-valent iron in water accelerates, the electron transfer rate increases, and more iron ions are released, promoting bacterial nitrification and thus improving ammonia nitrogen removal efficiency. Comparative examples of the graphene-supported zero-valent iron nanoparticle composite material prepared in Example 1, the graphene oxide prepared by directly adding zero-valent iron in Comparative Example 1, and the graphene oxide prepared by comparative example 3 with zero-valent iron nanoparticles are shown in the graphs after 60 days of system operation, illustrating their ammonia nitrogen removal effects. Figure 5 ,Depend on Figure 5 It can be seen that the removal effect of Example 1 is significantly improved compared with Comparative Example 3. This is because the functional groups of the amines grafted onto the modified graphene oxide can interact with Fe. 2+The formation of coordination interactions guides the uniform deposition of nano-zero-valent iron, enhancing the loading and stability of zero-valent iron. This overcomes the problems of reduced active sites caused by the aggregation of nano-zero-valent iron and its easy passivation and deactivation. It can effectively promote electron transfer between nano-zero-valent iron and pollutants, improving removal efficiency. Furthermore, the steric hindrance effect of the hyperbranched structure can reduce the excessive stacking of nano-zero-valent iron and graphene sheets, enhancing the adsorption-reduction activity of the composite material for the target pollutants. In contrast, the entire system in Comparative Example 1 had a very low ammonia nitrogen removal conversion rate. This is because Comparative Example 1 did not have a metal capture zone and an adsorption-reduction zone. The various links in the entire system affected each other, directly resulting in a very low remediation effect. Rare earth ions severely affected the microbial activity in the in-situ microbial enhanced purification zone, making the microbial remediation effect worse. The direct addition of nano-zero-valent iron, due to the reduced activity caused by its aggregation and easy passivation and deactivation, significantly reduced the ammonia nitrogen removal effect.

[0057] 4. Metal scavenging effect of metal ion scavengers The removal efficiency of lignin-based active powder loaded on a porous support for heavy metal and rare earth ions was investigated. After 30 days of system operation, bar charts showing the removal efficiency of heavy metal and rare earth ions in Comparative Example 4 and Examples 1-2 are shown below. Figure 6 ,Depend on Figure 6 It can be seen that Comparative Example 4, which did not have a metal ion capture zone, had a significantly reduced removal effect on heavy metals and rare earth ions. Consequently, the overall remediation effect of the system was also reduced due to the restriction of microbial activity by heavy metals and rare earth ions.

[0058] 5. Ammonia nitrogen removal effect after regeneration of graphene-supported zero-valent iron nanocomposite material The graphene-supported nano-zero-valent iron composite material used in Example 1 was subjected to thermal reduction treatment to restore the oxidized nano-zero-valent iron particles. After reduction and regeneration treatment, it can be reused repeatedly. Table 3 shows the ammonia nitrogen removal effect after 60 days of operation following 5 regenerations. As can be seen from Table 3, the repair effect after reduction and regeneration treatment is not much different from the initial effect.

[0059] Table 3. Ammonia nitrogen removal efficiency after regeneration of graphene-supported zero-valent iron nanocomposite material.

[0060] 6. Remediation Effect of Combined Technology for Groundwater Pollution Remediation in Ion-Adsorption Rare Earth Mining Areas To examine the effectiveness of the remediation methods in Examples 1-2 and Comparative Examples 1 and 4, a small-scale simulation of the pollution level of groundwater in a mining area was conducted, and the remediation effect of the system after 60 days of operation was simulated (see Table 4). Table 4 shows that Examples 1-2 exhibited significantly improved remediation effects compared to the comparative examples. Comparative Examples 1 and 4 lacked independent metal capture zones, resulting in poor remediation capabilities for rare earth ions. Rare earth ions significantly impact the microbial activity of the entire system, thereby affecting the overall remediation effect of the system on groundwater pollution.

[0061] Table 4 Comparison of Small-Scale Remediation Effects of Simulated Groundwater Pollutants

[0062] The remediation method described in Example 1 was applied to the most severely polluted area of ​​the mining district. After operation, the groundwater quality in the area gradually improved. With the growth of microorganisms and the enhancement of their nitrification and denitrification processes, the overall system's remediation effect on groundwater pollution in ion-adsorption rare earth mining areas gradually improved. The goal was to achieve a maximum ammonia nitrogen removal rate of 99.1% in the downstream groundwater of the mining area, and for nitrate nitrogen concentrations to meet the Class III standard of the "Groundwater Quality Standard" (GB / T 14848-2017). Specific results are shown in Table 5.

[0063] Table 5 Record of Groundwater Pollution Remediation Effects in Ion-Adsorption Rare Earth Mining Areas

[0064] Depend on Figure 5 It can be seen that after 10 months of operation, the groundwater downstream of the remediation system has been significantly improved, with ammonia nitrogen removal rate reaching over 99% and heavy metal and rare earth ion removal rate reaching 100%. The system has excellent remediation effect and has played a very significant role in the remediation of groundwater in the entire mining area.

[0065] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. Equal modifications and variations made by those skilled in the art to the technical solution of the present invention, as long as they do not depart from the overall concept of the present invention, shall still fall within the scope of the present invention.

Claims

1. A method for remediating groundwater pollution in ion-adsorption rare earth mining areas, characterized in that, The method for remediating groundwater pollution in ion-adsorption rare earth mining areas comprises an in-situ chemical reduction zone and an in-situ microbial enhanced purification zone arranged sequentially along the water flow direction. The in-situ chemical reduction zone includes a primary treatment zone, a metal ion capture zone, and an adsorption reduction zone. The primary treatment zone is filled with gravel and zeolite. The adsorption reduction zone is filled with graphene-supported nano-zero-valent iron composite material. The metal ion capture zone is filled with a metal ion capture agent in which lignin active powder is loaded onto a porous carrier. A transition zone is provided between the in-situ chemical reduction zone and the in-situ microbial enhanced purification zone; the transition zone is filled with bentonite and activated carbon. The in-situ microbial enhanced purification zone includes a nitrification zone and a denitrification zone; The packing material of the nitrification zone includes nitrifying bacteria, alkali, slow-release oxidant, and gravel; the mass ratio of nitrifying bacteria, alkali, slow-release oxidant, and gravel is 1-2:0.2-0.3:1.5-2.8:10-15. The packing material of the denitrification zone includes denitrifying bacteria, solid carbon source, alkali agent and gravel; the mass ratio of denitrifying bacteria, solid carbon source, alkali agent and gravel is 1-2:0.1-0.2:2-3:10-15.

2. The method for remediation of groundwater pollution in ion-adsorption rare earth mining areas according to claim 1, characterized in that, The preparation method of the graphene-supported nano-zero-valent iron composite material is as follows: S1. Add graphite to a mixture of H2SO4 and H3PO4 and stir in an ice-water bath for 10–30 minutes. Slowly add potassium permanganate, with a mass ratio of potassium permanganate to graphite of 3:1–6:1, and keep the system temperature below 15 °C. After the reaction is complete, remove from the ice-water bath and continue stirring for 60–80 minutes. Raise the temperature to 40 °C and stir for another 60 minutes. Raise the temperature to 90 °C and stir for 100 minutes. Slowly add a mixture of deionized water and H2O2 dropwise to the reaction mixture to obtain a graphene oxide mixture. Centrifuge and wash the graphene oxide mixture 2–3 times and dialyze it with deionized water. After vacuum freeze-drying, obtain sponge-like flocculent graphene oxide. S2, sponge-like graphene oxide was added to N-methylpyrrolidone and stirred at room temperature for 100 minutes to dissolve it completely. Then, aminopropyltriethoxysilane was slowly added dropwise. After heating to 60-80 °C and reacting at a constant temperature for 3-5 hours, the mixture was cooled to 50 °C. Then, hyperbranched polyamide-amine was added, followed by 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride. The mixture was stirred at 60-80 °C for 20-24 hours to obtain graphene oxide grafted with diamine groups. The graphene oxide was then centrifuged, washed with water, and dried. The mass ratio of aminopropyltriethoxysilane to graphene oxide is 1:5; the mass ratio of 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, hyperbranched polyamide-amine, and graphene oxide is 2-3:3-5:8-10. S3. The obtained graphene oxide grafted with diamine groups was placed in deionized water and ultrasonically dispersed. FeSO4·7H2O was added, stirred, and argon gas was introduced to make it anaerobic. Then, KBH4 solution was added dropwise at a rate of 1-2 drops / second. Argon gas was introduced during the reaction to keep the reaction in an anaerobic state. After reacting for 1-2 hours, the mixture was washed with deionized water and anhydrous ethanol, centrifuged, and vacuum dried to obtain the graphene-supported nano-zero-valent iron composite material.

3. The method for remediation of groundwater pollution in ion-adsorption rare earth mining areas according to claim 1, characterized in that, The specific preparation method of the metal ion scavenger is as follows: lignin active powder is added to an 8% citric acid aqueous solution to activate the active sites on the lignin active powder, and then a porous support is added. The reaction is carried out at 50-60℃ for 2-3 hours to allow the lignin active powder and the porous support to react and crosslink. After filtration and low-temperature drying, the metal ion scavenger is obtained. The mass ratio of lignin active powder to porous support is 1:3-5.

4. The method for remediation of groundwater pollution in ion-adsorption rare earth mining areas according to claim 3, characterized in that, The porous carrier mentioned above is a porous carrier obtained by compositing silica onto bentonite, specifically: S01, add bentonite to deionized water, disperse thoroughly, heat to 40℃, add octadecyltrimethylammonium chloride, stir thoroughly, react for 1-2 hours, remove the suspension and centrifuge at 3500 rpm, wash with deionized water 2-3 times, centrifuge again, remove the solid mixture at the bottom, dry and grind at 60℃ to obtain modified bentonite; the mass ratio of octadecyltrimethylammonium chloride to bentonite is 1:

8. S02, tetraethyl orthosilicate, ethanol and deionized water are mixed in a molar ratio of 1:4:4 at 40-50 °C, and dilute hydrochloric acid is added dropwise to adjust the pH to 4-5. The mixture is stirred to form a transparent sol. Modified bentonite is slowly added, and the mixture is stirred for 2-3 hours. The temperature is raised to 60 °C, and the mixture is allowed to stand for 12 hours. Then it is cooled to room temperature and allowed to stand for 24 hours. After centrifugation and filtration, gel microspheres are obtained. The microspheres are washed with water 2-3 times, dried at 60 °C, and then heated to 400-500 °C at a rate of 2 °C / min and kept at this temperature for 3 hours to obtain a porous carrier. The mass ratio of transparent sol to modified bentonite is 1:

4.

5. The method for remediation of groundwater pollution in ion-adsorption rare earth mining areas according to claim 3, characterized in that, The preparation method of the lignin active powder is as follows: S001, chitosan and 0.5% citric acid solution are stirred and heated at 100 °C for 80-120 minutes until completely dissolved to obtain chitosan aqueous solution; The mass concentration of the chitosan aqueous solution is 4-6%; S002, sodium hydroxide and deionized water are dissolved and added evenly, then lignin is added and stirred for 30-50 minutes until the lignin is completely dissolved; chitosan aqueous solution is added and stirred evenly, and reacted at 50-60℃ for 2-3 hours to allow the lignin and chitosan to undergo a cross-linking reaction, obtaining a solution containing lignin grafted with amino groups; the mass concentration of the sodium hydroxide aqueous solution is 25%; S003: Dissolve monochloroacetic acid in deionized water and add the monochloroacetic acid solution dropwise to the lignin solution finally obtained in S002. Heat to 80-90℃ and react for 4-5 hours. After the reaction is complete, cool and pour off the reaction solution. Adjust the pH of the solution to 5.0±0.1 with 2mol / L hydrochloric acid. Filter the reaction product through a 0.5μm microporous membrane to remove impurities. Then dialyze the product in deionized water for 24 hours using a 1000da dialysis bag. Freeze-dry for 72 hours to obtain lignin active powder. The mass concentration of the monochloroacetic acid solution is 60%, and the mass ratio of monochloroacetic acid to lignin is 3:25-30.

6. The method for remediation of groundwater pollution in ion-adsorption rare earth mining areas according to claim 1, characterized in that, The gravel can be quartz, feldspar, or rock chips with a particle size of 10-30 mm, used to disperse the active filler in each functional zone and increase the permeability coefficient of each reaction zone; The zeolite has a particle size of 5-10 mm; the metal ion scavenger has a particle size of 1-5 mm; and the graphene-supported nano-zero-valent iron composite material has a particle size of 100-150 μm.

7. The method for remediation of groundwater pollution in ion-adsorption rare earth mining areas according to claim 1, characterized in that, The slow-release oxidant comprises an active oxygen-releasing agent and a binder coating the active oxygen-releasing agent, wherein the weight ratio of the active oxygen-releasing agent to the binder is 1:0.2-0.3; the active oxygen-releasing agent is calcium peroxide or persulfate, and the binder is sodium alginate or silicon dioxide; the alkali comprises a mixed alkali of NaHCO3 and NaOH in a weight ratio of 1:0.05; the solid carbon source comprises straw, coconut shell charcoal, and biomass charcoal in a weight ratio of 1:2:6-8.

8. The method for remediation of groundwater pollution in ion-adsorption rare earth mining areas according to claim 1, characterized in that, The nitrifying bacteria agent is composed of nitrite-oxidizing bacteria and nitrite-oxidizing bacteria, preferably nitrite-oxidizing cocci and nitrifying bacilli; the effective bacterial strain content is ≥10. 8 CFU / g; the denitrifying bacteria agent is Pseudomonas, Bacillus, or Alcaligenes, etc., with an effective bacterial strain content ≥10. 8 CFU / g.

9. The method for remediation of groundwater pollution in ion-adsorption rare earth mining areas according to claim 1, characterized in that, The thickness of the primary treatment zone in the in-situ chemical reduction zone is 0.5–0.8 m, the thickness of the metal ion capture zone is 0.3–0.5 m, and the thickness of the adsorption reduction zone is 0.2–0.3 m; the thickness of the transition zone is 1.0–1.5 m; the thickness of the nitrification zone in the in-situ microbial enhanced purification zone is 2–3 m, and the thickness of the denitrification zone is 2–3 m.

10. The method for remediation of groundwater pollution in ion-adsorption rare earth mining areas according to any one of claims 1-9, characterized in that, The prepared graphene-supported nano-zero-valent iron composite material and metal ion capture agent are used for the deep treatment of groundwater in ion-type rare earth mining areas contaminated with heavy metals, rare earth ions, ammonia nitrogen, and nitrates.

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