A system and method for in-situ mineralization of heavy metals in soil

Abstract

The present application belongs to the technical field of heavy metal pollutant treatment, and relates to a soil heavy metal in-situ mineralization extraction system, which comprises a dosing purification system, a spraying pipe network, a leaching liquid collecting pool, a heavy metal mineralization extraction device, an anti-seepage system and a product recovery device; the dosing system is provided with leaching liquid, which is pumped to the spraying pipe network by the dosing system; the anti-seepage system comprises an anti-seepage baffle and a drainage slope, a drainage ditch is pre-dug in the drainage slope, the drainage ditch is connected with a drainage pipeline, and the drainage pipeline is connected with the leaching liquid collecting pool; the leaching liquid collecting pool is connected with the heavy metal mineralization extraction device, and the heavy metal mineralization extraction device is connected with the purification system and the product recovery device. Through in-situ leaching of soil, heavy metal ions in the soil are dissolved and separated out, and then the leaching liquid containing the heavy metal ions is introduced into the heavy metal mineralization extraction device to co-precipitate the heavy metal ions with added metal ions to form LDH-like, which can not only save cost, but also make resources be reasonably utilized.

Description

Technical Field

[0001] This invention belongs to the field of heavy metal pollutant treatment technology, specifically relating to a soil heavy metal in-situ mineralization extraction system and method. Background Technology

[0002] The influx of heavy metal pollutants has led to a severe deterioration of farmland soil environmental quality and posed a significant threat to the quality and safety of agricultural products. The main pollutants in arable land are cadmium, nickel, copper, arsenic, mercury, lead, DDT, and polycyclic aromatic hydrocarbons. Currently, heavy metal pollution in farmland soil shows a trend of spreading from specific points to broader areas and from the peripheries of large and medium-sized cities to remote rural areas. In many regions, heavy metal pollution in farmland soil exhibits regional and watershed-level pollution development trends.

[0003] Although heavy metals are a type of hazardous substance, they are also a valuable resource. Soil in-situ leaching technology ultimately requires injecting the leachate containing heavy metals into groundwater or extracting it for off-site treatment. These processes may lead to an expansion of the contaminated area or increase treatment costs. Summary of the Invention

[0004] The purpose of this invention is to provide a soil heavy metal in-situ mineralization extraction system and method, which solves the problem of expanding the pollution area caused by soil in-situ leaching.

[0005] This invention is achieved through the following technical solution:

[0006] A soil heavy metal in-situ mineralization extraction system includes a dosing and purification system, a spray pipe network, a leachate collection tank, a heavy metal mineralization extraction device, a seepage prevention system, and a product recovery device.

[0007] The sprinkler network is installed above the contaminated soil; the leachate collection tank is installed below the sprinkler network.

[0008] The chemical dosing and purification system includes a chemical dosing system and a purification system, and the purification system and the chemical dosing system are connected.

[0009] The dosing system contains a rinsing solution, which is pumped to the spray network by the dosing system.

[0010] The seepage prevention system includes a seepage prevention baffle installed below the shallow soil and a drainage slope formed by the shallow soil. A drainage ditch is pre-excavated in the drainage slope, and the drainage ditch is connected to a drainage pipe, which is connected to a leachate collection tank.

[0011] The leachate collection tank is connected to the heavy metal ore extraction device, which is equipped with a liquid outlet and a product outlet. The liquid outlet is connected to the purification system, and the product outlet is connected to the product recovery device.

[0012] Furthermore, the spray network includes a main water supply pipe for the rinsing liquid and multiple rows of branch water supply pipes for the rinsing liquid. Each row of branch water supply pipes for the rinsing liquid is evenly equipped with multiple spray nozzles, and the spray nozzles on adjacent branch water supply pipes for the rinsing liquid are staggered.

[0013] One end of the main water supply pipe for the rinsing solution is connected to the dosing system, and the other end is connected to the branch water supply pipe for the rinsing solution.

[0014] Furthermore, the dosing system includes a rinsing solution storage tank, a rinsing solution dissolving tank, an alkali solution storage tank, and an alkali solution dissolving tank, with the rinsing solution storage tank and the rinsing solution dissolving tank connected together, and the alkali solution storage tank and the alkali solution dissolving tank connected together;

[0015] The rinsing solution in the rinsing solution storage tank is pumped into the rinsing solution dissolving tank by a metering pump, and the rinsing solution dissolving tank is connected to the spray pipeline network.

[0016] The alkali solution in the alkali storage tank is pumped into the alkali dissolving tank by a metering pump, and the alkali dissolving tank is connected to the heavy metal ore extraction device.

[0017] Furthermore, the purification system includes an interconnected leaching solution purification tank and a leaching solution collection tank. The leaching solution collection tank is connected to the heavy metal ore extraction device, and the leaching solution purification tank is connected to the leaching solution dissolving tank. The purified leaching solution flows back into the leaching solution dissolving tank.

[0018] Furthermore, multiple sets of rinsing solution purification tanks and rinsing solution collection tanks are provided.

[0019] Furthermore, aluminum salt solution is added to the heavy metal ore extraction device, where aluminum ions can co-precipitate with heavy metal ions to form hydrotalcite-like secondary minerals.

[0020] Furthermore, the product recovery device includes a horizontal spiral dehydration centrifuge and an intermittent drum dryer.

[0021] Furthermore, the heavy metal mineral extraction device includes a box, in the middle of which two cation-passing membrane baffles are provided to form a co-precipitation reaction zone;

[0022] Multiple filtration baffles are installed in the area outside the coprecipitation reaction zone;

[0023] The coprecipitation reaction zone is equipped with a sludge scraper and multiple monitoring points, which are connected to an online pH meter to monitor the pH within the coprecipitation reaction zone.

[0024] Furthermore, each partition is divided into two sections: the lower section is a solid baffle, and the upper section is a filter layer.

[0025] This invention also discloses an extraction method for the aforementioned soil heavy metal in-situ mineralization extraction system, comprising the following steps:

[0026] First, lay the seepage prevention system: excavate the shallow soil of the contaminated soil, lay the seepage prevention barrier, and then backfill the excavated shallow soil onto the seepage prevention barrier. During backfilling, make the soil form multiple drainage slopes with intervals, and dig diversion ditches in advance in the drainage slopes. The diversion ditches are connected to the drainage pipes.

[0027] The leachate from the dosing system is delivered to the contaminated soil via a spray network;

[0028] After the heavy metal ions in the soil are dissolved, they flow into the leachate collection tank, and then enter the heavy metal mineralization extraction device to extract the heavy metal ions. After solid-liquid separation, the solid product is recovered to the product recovery device.

[0029] The liquid is then purified by a purification system into a reusable rinsing solution, and finally enters a chemical dosing system to add rinsing aids to become a new rinsing solution for recycling.

[0030] Compared with the prior art, the present invention has the following beneficial technical effects:

[0031] This invention discloses an in-situ heavy metal mineralization extraction system for soil. Designed around the core technology of induced mineralization, it employs a main process of in-situ leaching remediation equipment for contaminated soil combined with leaching solution induced mineralization extraction and collection treatment equipment. A suitable leaching agent is determined, and a suitable dosing device is used to stably output the leaching agent. Heavy metal ions in the soil are dissolved and separated through in-situ soil leaching technology. The leaching solution containing heavy metal ions is then introduced into the heavy metal mineralization extraction device. Subsequently, by adjusting the pH of the leaching solution and adding aluminum ions, the heavy metal ions and the added metal ions are co-precipitated to form a hydrotalcite-like secondary mineral (LDH). Heavy metal ions in the soil are removed and the LDH material is collected through LDH synthesis. During the remediation process, the recycled leaching solution saves on the addition of leaching reagents. The final solution saves costs, allows the soil remediation system to be used multiple times, and also makes rational use of resources.

[0032] Simultaneously, a seepage prevention system was designed, with seepage-proof baffles laid beneath the soil. The soil itself forms drainage slopes and diversion ditches, through which the leachate containing heavy metals is diverted to drainage pipes and collected in a collection tank. The leachate will not seep into groundwater, thus preventing groundwater pollution. Instead of extraction, it is collected and then treated.

[0033] Furthermore, the spray network primarily utilizes the soil's permeability and solvents that promote the dissolution or migration of pollutants in the soil environment. Through hydraulic pressure, it sprays the pollutant-containing liquid into the contaminated soil layer, extracting it for separation and wastewater treatment. The treated water can then be reused for circulating spraying. Spray nozzles on adjacent pipes are staggered to achieve efficient spraying and avoid waste of the scrubbing solution.

[0034] Furthermore, the heavy metal mineralization extraction device includes a box-shaped structure with two cation-passing membrane baffles in the middle to form a co-precipitation reaction zone. Multiple baffles are installed outside the co-precipitation reaction zone to filter and precipitate the collected leachate before it enters the co-precipitation reaction zone. By adding aluminum salt solution to the soil leachate in the co-precipitation reaction zone and then adding alkali solution to adjust the pH of the reaction, heavy metal ions and aluminum ions co-precipitate. The heavy metal ions enter the LDH structure, thus detaching from the water and forming a solid precipitate that is removed. A scraper periodically collects the precipitate, yielding a hydrotalcite-like secondary mineral containing soil heavy metal ions.

[0035] Furthermore, each partition is divided into upper and lower sections: the lower section is a solid baffle, and the upper section is a filter layer. This allows large sediments to settle on their own first, while the rest pass through the filter layer before entering the next partition, resulting in high filtration efficiency. Attached Figure Description

[0036] Figure 1 This is an overall connection diagram of a soil heavy metal in-situ mineralization extraction system according to the present invention;

[0037] Figure 2 This is a schematic diagram of the layout structure of the sprinkler network;

[0038] Figure 3 This is a layout diagram of the seepage prevention system;

[0039] Figure 4 This is a schematic diagram of the chemical dosing and purification system;

[0040] Figure 5 This is a schematic diagram of the product recovery device.

[0041] Figure 6a This is a top view of a heavy metal ore extraction device;

[0042] Figure 6b This is a front view of a heavy metal ore extraction device.

[0043] Figure 7 Zn at room temperature and pressure 2+ / Co 2+ / Ni 2+ with Fe 3+ / A1 3+XRD diffraction pattern of the effect;

[0044] Figure 8 These are the Zn removal kinetic curves for different systems. LDH-Zn refers to the adsorption system of Zn by MgAl-LDH; Zn-Al represents the homogeneous coprecipitation system of zinc and aluminum ions; and LDH-Zn-Al represents the coprecipitation system of zinc and aluminum in the presence of MgAl-LDH (i.e., the LDH seed-induced system).

[0045] The components include: 1. Main water supply pipeline for leachate; 2. Chemical dosing and purification system; 3. Staircase; 4. Anti-seepage system; 5. Heavy metal ore extraction device; 6. Leachate collection pipeline; 7. Product collection pipeline; 8. Product recovery device; 9. Leachate collection tank; 10. Spray network; 11. Spray nozzle; 12. Leachate distribution water supply pipeline.

[0046] 41. Impermeable partition; 42. Drainage slope; 43. Drainage ditch;

[0047] 21. Dosing system; 211. Eluent storage tank; 212. Eluent dissolving tank; 213. Alkali storage tank; 214. Alkali dissolving tank; 215. Metering pump;

[0048] 22. Purification system; 221. Rinse solution collection tank; 222. Rinse solution purification tank;

[0049] 81. Horizontal spiral centrifuge; 82. Intermittent drum dryer;

[0050] 51. Cations pass through the membrane baffle; 52. Solid baffle; 53. Filter layer; 54. Collection trench; 55. Monitoring point; 56. Online pH meter; 57. Sludge scraper. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0052] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0053] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus.

[0054] like Figure 1 As shown, the present invention consists of a dosing and purification system 2, a spray pipe network 10, a leachate collection tank 9, a heavy metal mineralization extraction device 5, and a product recovery device 8. The leachate is pumped from the dosing system 21 to the spray pipe network 10 above the contaminated soil. After dissolving the heavy metal ions in the soil, it flows by gravity through the diversion ditch 43 to the leachate collection tank 9, and then enters the heavy metal mineralization extraction device 5 to extract the heavy metal ions. It is then purified by the purification system 22 into a reusable leachate, and finally enters the dosing system 21 to add leaching aids to become a new leachate.

[0055] The main function of the spraying solution is to leach heavy metals from paddy field soil. The spraying network 10 device uses a pipe network spraying structure. For example... Figure 2 As shown, the spray network 10 includes a main water supply pipe 1 for the eluent and multiple rows of branch water supply pipes 12 for the eluent. One end of the main water supply pipe 1 is connected to the dosing system 21, and the other end is connected to the branch water supply pipes 12. Each row of branch water supply pipes 12 is evenly equipped with multiple spray nozzles 11. The spray nozzles 11 on adjacent pipes are staggered to ensure efficient spraying and avoid waste of the eluent.

[0056] The sprinkler system uses general chemical pipes that are resistant to acid and alkali corrosion, and the sprinkler nozzles 11 are made of 4-point ABS material that are resistant to acid and alkali corrosion.

[0057] In the spray network 10, the soil's permeability and the use of solvents that promote the dissolution or migration of pollutants in the soil environment are utilized to spray the polluted soil layer through hydraulic pressure head. The liquid containing pollutants is extracted from the soil layer, separated, and treated to remove pollutants from the water. The treated water can then be used for circulating spraying.

[0058] like Figure 3 As shown, the shallow layer of contaminated soil is excavated, and an impermeable barrier 41 is laid. The excavated shallow layer of soil is then backfilled onto the impermeable barrier 41. During backfilling, the soil forms multiple drainage slopes 42 at intervals, and a drainage ditch 43 is pre-excavated in the drainage slope 42. The drainage ditch 43 is connected to a drainage pipe. The leachate flows through the drainage ditch 43 and the drainage pipe and is collected in the leachate collection tank 9, which is equipped with an FSB type plastic alloy pump.

[0059] The seepage prevention system 4 is a seepage prevention barrier 41 laid under the shallow contaminated soil. The seepage prevention barrier 41 is covered with a seepage prevention membrane to prevent the expansion of the contamination range and avoid contaminating the groundwater. At the same time, it can better collect the leachate and prevent the leachate from seeping down.

[0060] Specialized welding machines are used for welding the waterproof geomembrane. The joints are treated with thermal welding; the surfaces of the PE membranes to be joined are heated to melt, and then fused together under pressure. When laying the HDPE geomembrane, the number of welds should be minimized. Before welding, the two PE membrane strips at the joint should be adjusted to ensure a certain overlap width. The overlap width between membranes should not be less than 0.1m, and the welds should be arranged parallel to the maximum slope, i.e., along the slope direction.

[0061] Considering the repair cycle and site factors, the chemical dosing and purification system 2 adopts an integrated dosing device. For example... Figure 4 As shown, the dosing and purification system 2 of the present invention is divided into a dosing system 21 and a purification system 22. The steel structure platform is designed with two layers, and a steel structure staircase 3 for passage is provided on the side. The dosing system 21 is located on the upper layer and mainly includes a rinsing solution storage tank 211, a rinsing solution dissolving tank 212, an alkali solution storage tank 213, and an alkali solution dissolving tank 214. The rinsing solution storage tank 211 and the rinsing solution dissolving tank 212 are connected, and the alkali solution storage tank 213 and the alkali solution dissolving tank 214 are connected. The rinsing solution in the rinsing solution storage tank 211 is pumped into the rinsing solution dissolving tank 212 by a metering pump 215, and the rinsing solution in the rinsing solution dissolving tank 212 then enters the spray pipe network 10 through the rinsing solution supply pipe.

[0062] The alkali solution in the alkali storage tank 213 is pumped into the alkali dissolving tank 214 by the metering pump 215. After dissolving, it flows into the heavy metal mineral extraction device 5 through the alkali water supply pipeline.

[0063] The purification system 22 is located in the lower layer. The purification system 22 mainly includes a leachate purification tank 222 and a leachate collection tank 221 that are connected to each other. The leachate collection tank 221 is connected to the heavy metal ore extraction device 5. The leachate purification tank 222 is connected to the leachate dissolving tank 212 through a pipeline. The purified leachate flows back into the leachate dissolving tank 212 and can be recycled.

[0064] More preferably, multiple sets of leaching liquid purification tank 222 and leaching liquid collection tank 221 are provided, which can efficiently purify the liquid discharged from the heavy metal ore extraction device 5.

[0065] like Figure 5 As shown, the product recovery device 8 includes a horizontal spiral dehydration centrifuge 81 and an intermittent drum dryer 82. After extraction by the metal ore extraction device, solid and liquid are separated, and the solid product enters the product recovery device 8 through the product collection pipe 7.

[0066] like Figure 6a and Figure 6b As shown, the heavy metal ore extraction device 5 includes a box body. Two cation-passing membrane baffles 51 are provided in the middle of the box body to form a co-precipitation reaction zone. Multiple baffles are provided in the area outside the co-precipitation reaction zone. Each baffle is divided into upper and lower sections. The lower section is a solid baffle 52 and the upper section is a filter layer 53. Through the obstruction of the solid baffle 52, large precipitates can be allowed to settle on their own first, and the rest can be filtered through the filter layer 53 and enter the next baffle. This design has high filtration efficiency and can also buffer water flow and filter sand and dust.

[0067] More preferably, the bottom of the middle area is a collection trough 54, which is cone-shaped to facilitate the collection of sediment.

[0068] Coprecipitation reaction zone: The center of the heavy metal ore extraction device 5 is a coprecipitation reaction zone where heavy metal ions and added cations are separated by a membrane baffle 51. It contains a built-in unidirectional continuous scraper 57 and multiple monitoring points 55. Monitoring points 55 are connected to an online pH meter 56 for monitoring the pH within the coprecipitation reaction zone. Multiple stirrers are also installed within the coprecipitation reaction zone to agitate the solution within this area.

[0069] The heavy metal ore extraction device 5 has a liquid outlet and a product outlet on its casing. The liquid outlet is connected to the purification system 22, and the product outlet is connected to the product recovery device 8.

[0070] The leachate from the leachate collection tank 9 enters the heavy metal mineralization extraction device 5 through the leachate collection pipe 6. Aluminum salt solution is added to the soil leachate in the co-precipitation reaction zone, followed by the addition of alkali to adjust the pH of the reaction. This causes heavy metal ions to co-precipitate with aluminum ions, allowing the heavy metal ions to enter the LDH structure and thus detach from the water to form a solid precipitate that is removed. A scraper periodically collects the formed precipitate, yielding a hydrotalcite-like secondary mineral containing soil heavy metal ions.

[0071] like Figure 1 As shown, the dosing system 21 is simultaneously connected to the heavy metal ore-forming extraction device 5, the spray pipe network 10, and the purification system 22. It provides leaching solution to the spray pipe network 10, receives the leaching solution treated by the purification system 22, adds leaching aids, and stirs thoroughly. The prepared leaching solution then enters the leaching solution tank to achieve recycling of the leaching solution. Simultaneously, it provides the appropriate proportion of reagents for the formation of hydrotalcite-like secondary minerals in the heavy metal ore-forming extraction device 5.

[0072] The invention will be further illustrated below with specific implementation examples:

[0073] An application scheme for in-situ mineralization extraction of heavy metals from soil is described, specifically for the in-situ mineralization extraction of heavy metals from paddy field soils. The scheme includes the following steps:

[0074] The length of the contaminated paddy field site is 32m, with a substrate deformation and membrane stretch allowance of 1.5%, and the seepage prevention flanks at both ends of the site are ≥0.5m, for a total membrane length of 33.48m; the width of the site is 24m, with a substrate deformation and membrane stretch allowance of 1.50%, and the seepage prevention flanks at both ends of the site are ≥0.5m, the welded joint width is 0.1m, for a total membrane width of 25.76m.

[0075] Specifically, HDPE geomembrane is used as the impermeable layer material, simply referred to as "HDPE geomembrane". It features a high impermeability coefficient; excellent chemical stability; aging resistance; resistance to plant roots; and high mechanical strength. The impermeable system 4 uses GH-2S type environmentally friendly smooth high-density polyethylene geomembrane, ensuring low adhesion of the leachate while using environmentally friendly materials. Figure 3 As shown, when laying the geomembrane, the membrane fabric is arranged longitudinally from south to north in the geomembrane layer below the paddy soil. Each roll of membrane fabric has at least 1.50% extra width to allow for local subsidence and stretching.

[0076] The membrane fabric is hot-welded together using a hot wedge type double-track geomembrane automatic welding machine.

[0077] The sprinkler system uses general-purpose chemical pipes resistant to acid and alkali corrosion, and the sprinkler nozzles 11 are made of 4-point ABS material, also resistant to acid and alkali corrosion. A staggered arrangement of the sprinkler nozzles 11 on adjacent pipes is employed. Sprinkler nozzle 11 parameters are as follows: Sprinkler radius: 0–4m; Sprinkler flow rate: 0.6–1m³ / h. 3 / h; Inner diameter: Ф=13.2mm; Outer diameter: Ф=20mm; Number of sprinkler nozzles 11: 31. While ensuring complete soil coverage, the number of sprinkler nozzles 11 is reduced, thereby decreasing the material cost of the sprinkler network 10. Sprinkler pipe parameters: Main water supply pipe: Material: PPH chemical anti-corrosion pipe; Size: DN50, Ф=63mm. Branch water supply pipe: Material: PPH chemical anti-corrosion pipe; Size: DN32, Ф=40mm. Vertical water supply pipe for sprinkler nozzles 11: Material: PPH chemical anti-corrosion pipe; Size: DN20, Ф=25mm.

[0078] A 0.01 mol / L HCl-0.4 mol / L FeCl3 composite leaching agent was used to continuously leach paddy soil contaminated with heavy metals. The leaching solution was pumped from the dosing system 21 to the spray pipe network 10 above the contaminated soil. After dissolving the heavy metal ions in the soil, the solution flowed by gravity through the diversion ditch 43 to the leaching solution collection pipe 6. The solution then entered the leaching solution collection tank 9 and then entered the heavy metal mineralization extraction device 5 to extract the heavy metal ions. The solution was then purified by the purification system 22 into a reusable leaching solution and finally entered the dosing system 21 to add leaching aids to become a new leaching solution.

[0079] The LDH precipitate obtained from the heavy metal ore extraction unit 5 will be transported by a centrifugal pump to the product recovery unit 8 for dehydration and drying. The product recovery unit 8 uses a fully automatic horizontal spiral centrifugal dewatering machine and an intermittent drum dryer 82 to dry the co-precipitated LDH into granules, thus facilitating its transport.

[0080] The heavy metal ore extraction device 5 adds alkali solution dropwise to a mixed salt solution containing leached heavy metal ions, causing ion hydrolysis and co-precipitation to form LDH, while simultaneously removing heavy metal ions. A leachate containing heavy metal ions is obtained through in-situ leaching. An aluminum ion salt solution is added to the leachate for mixing, and the pH value of the reaction is adjusted using sodium hydroxide solution. After a period of time, the resulting solid precipitate is collected from the bottom collection device, washed, and dried to obtain a solid hydrotalcite-like compound.

[0081] like Figure 7 As shown, Zn at room temperature and pressure 2+ / Co 2+ / Ni 2+ with Fe 3+ / A1 3+ The results of the action show that Zn 2+ / Co 2+ / Ni 2+ With A1 3+ When it reacts, it can form LDH; with Fe 3+ When it acts, under the influence of coexisting ions on the fate of heavy metals, heavy metal ions, anions, and trivalent metal ions interact to form LDH.

[0082] Figure 8 The figures show the Zn removal kinetics curves for different systems. The results indicate that the LDH-Zn-Al system exhibits the highest Zn removal rate, while the LDH-Zn system shows the lowest. Among all systems, only the LDH-Zn system does not contain added aluminum ions; therefore, the addition of aluminum ions can significantly improve the Zn removal rate and efficiency. The removal rate of the LDH-Zn-Al system is significantly higher than the sum of the removal rates of the LDH-Zn and Zn-Al systems, indicating that the combination of LDH and Al has a strong synergistic effect. The addition of LDH can significantly induce the reaction of Zn and Al ions to form a hydrotalcite-like substance.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A system for in-situ mineralization extraction of heavy metals from soil, characterized in that, The system comprises a dosing and purifying system (2), a spray pipe network (10), a leaching liquid collecting pool (9), a heavy metal mineral extraction device (5), an anti-seepage system (4) and a product recovery device (8); The spray pipe network (10) is arranged above the contaminated soil, and the leaching liquid collecting pool (9) is arranged below the spray pipe network (10); The dosing and purifying system (2) comprises a dosing system (21) and a purifying system (22), and the purifying system (22) is connected with the dosing system (21); The leaching liquid is added in the dosing system (21) and pumped to the spray pipe network (10) by the dosing system (21); the leaching liquid adopts 0.01 mol / L HCl-0.4 mol / L FeCl3 composite leaching agent; The anti-seepage system (4) comprises an anti-seepage baffle (41) arranged below the shallow soil and a drainage slope (42) formed by the shallow soil, a drainage ditch (43) is pre-dug in the drainage slope (42), the drainage ditch (43) is connected with a drainage pipeline, and the drainage pipeline is connected with the leaching liquid collecting pool (9); The leaching liquid collecting pool (9) is connected with the heavy metal mineral extraction device (5), the heavy metal mineral extraction device (5) is provided with a liquid outlet and a product outlet, the liquid outlet is connected with the purifying system (22), and the product outlet is connected with the product recovery device (8); The dosing system (21) comprises a leaching liquid storage tank (211), a leaching liquid dissolving tank (212), an alkali storage tank (213) and an alkali dissolving tank (214), the leaching liquid storage tank (211) is connected with the leaching liquid dissolving tank (212), and the alkali storage tank (213) is connected with the alkali dissolving tank (214); The leaching liquid in the leaching liquid storage tank (211) is pumped into the leaching liquid dissolving tank (212) through a metering pump (215), and the leaching liquid dissolving tank (212) is connected with the spray pipe network (10); The alkali in the alkali storage tank (213) is pumped into the alkali dissolving tank (214) through a metering pump (215), and the alkali dissolving tank (214) is connected with the heavy metal mineral extraction device (5); The purifying system (22) comprises a leaching liquid purifying tank (222) and a leaching liquid collecting tank (221) connected with each other, the leaching liquid collecting tank (221) is connected with the heavy metal mineral extraction device (5), the leaching liquid purifying tank (222) is connected with the leaching liquid dissolving tank (212), and the leaching liquid after purification flows into the leaching liquid dissolving tank (212) again; The heavy metal mineral extraction device (5) comprises a box body, two cation passing membrane baffles (51) are arranged in the middle of the box body, and a co-precipitation reaction zone is formed; A plurality of filtering baffles are arranged in regions outside the co-precipitation reaction zone; A mud scraping plate (57) and a plurality of monitoring points (55) are arranged in the co-precipitation reaction zone, the monitoring points (55) are connected with pH online detectors (56) for monitoring the pH in the co-precipitation reaction zone; Aluminum salt solution is added in the heavy metal mineral extraction device (5), and aluminum ions can co-precipitate with heavy metal ions to form a hydrotalcite-like secondary mineral.

2. The system for in-situ mineralization and extraction of heavy metals from soil according to claim 1, wherein, The spray pipe network (10) comprises a total spray liquid feed pipe (1) and multiple rows of spray liquid branch feed pipes (12), each of which is uniformly provided with multiple spray openings (11), and the spray openings (11) on adjacent spray liquid branch feed pipes (12) are staggered with each other. The total spray liquid feed pipe (1) is connected with the dosing system (21) at one end and connected with the spray liquid branch feed pipes (12) at the other end.

3. The system for in-situ mineralization and extraction of heavy metals from soil according to claim 1, wherein, The spray liquid purification tank (222) and the spray liquid collection tank (221) are each provided with multiple groups.

4. The system for in-situ mineralization and extraction of heavy metals from soil according to claim 1, wherein, The product recovery device (8) comprises a horizontal spiral dehydration centrifuge (81) and an intermittent drum dryer (82).

5. The system for in-situ mineralization and extraction of heavy metals from soil according to claim 1, wherein, Each partition is divided into two sections, a lower section being a solid baffle (52) and an upper section being a filter layer (53).

6. The extraction method of the system for in-situ mineralization extraction of heavy metals from soil according to any one of claims 1-5, characterized in that, The method comprises the following processes: First, lay the impermeable system (4): dig away the shallow soil of the contaminated soil, lay the impermeable baffle (41), and then backfill the dug shallow soil onto the impermeable baffle (41), when backfilling, form multiple spaced drainage slopes (42) in the soil, and pre-dig drainage ditches (43) in the drainage slopes (42), the drainage ditches (43) being connected to the drainage pipe; The spray liquid in the dosing system (21) is delivered to the top of the contaminated soil through the spray pipe network (10); After the heavy metal ions in the soil are dissolved, they flow to the spray liquid collection tank (9), and then enter the heavy metal ore extraction device (5) to extract the heavy metal ions, after solid-liquid separation, the solid product is recovered into the product recovery device (8); The liquid is purified into reusable spray liquid by the purification system (22), and finally added into the dosing system (21) as new spray liquid after adding spray liquid additives, for recycling.

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