Method for recovery of valuable materials and simultaneous removal of pollutants from complex contaminated soil

Abstract

This application provides a method for the recovery of valuable substances and synergistic removal of pollutants from complex contaminated soil, belonging to the field of soil pollution remediation and resource utilization. The method involves pre-treating the complex contaminated soil to remove slag particles larger than 2 cm; then, after adjusting the pre-treated soil slurry, flotation is used to collect valuable substances. The flotation slurry is further separated to remove fine soil particles ≤20 μm in diameter; a leaching solution is added to the slurry after the fine particles are removed for cavitation stripping and sieving to obtain soil particles of different sizes and a leaching underflow; the leaching underflow is then pressure filtered to obtain filter residue and clarified liquid; a stabilizing agent is added to the filter residue for solidification and stabilization treatment; and the leached soil is discharged after passing quality tests. This application efficiently recovers valuable substances such as gold and silver from soil through flotation, achieving resource utilization. Subsequent removal, leaching, and solidification steps achieve the harmless removal of heavy metals, balancing environmental and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of soil pollution remediation and resource utilization technology, specifically to a method for recovering valuable substances and synergistically removing pollutants from complex polluted soil. Background Technology

[0002] Gold production often employs cyanide extraction, and gold ore frequently contains polymetallic minerals, resulting in soil pollution from the gold industry often exhibiting characteristics of mixed pollution containing valuable substances and heavy metals. Remediation of heavy metal-contaminated soil is mainly categorized into four types: physical remediation, chemical remediation, bioremediation, and combined remediation. Currently, commonly used methods include leaching, solidification / stabilization, and redox methods. However, existing remediation methods generally have several limitations: First, traditional processes focus solely on removing heavy metals and other pollutants, neglecting the recovery of valuable substances like gold and silver from the soil, leading to resource waste and a lack of resource utilization value. Second, during heavy metal removal, the treatment of fine-particle soil with high heavy metal content is not specifically addressed, resulting in large remediation volumes, low remediation efficiency, and high treatment costs. Furthermore, remediation methods such as chemical leaching are prone to secondary pollution and have poor compatibility with multiple heavy metals, making them unsuitable for treating mixed-contaminated soils. Additionally, the current remediation steps are not well-integrated, failing to form a unified process, resulting in poor overall treatment effectiveness.

[0003] In view of this, it is necessary to design a method for the recovery of valuable substances and the synergistic removal of pollutants in composite contaminated soil in order to solve the above problems. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a method for recovering valuable substances and synergistically removing pollutants from complex contaminated soil, aiming to solve the technical problems of low resource utilization rate, low remediation efficiency and high cost of existing remediation methods.

[0005] This application provides a method for the recovery of valuable substances and the synergistic removal of pollutants in soil with complex contamination, including the following steps: S1. Pre-treat the complex contaminated soil to remove slag particles larger than 2 cm in diameter; S2. Mix the pretreated soil with clean water to form a slurry, thus obtaining soil slurry; S3. Add flotation reagents to the soil slurry for flotation treatment and collect valuable substances; the valuable substances include gold and / or silver; S4. Separate the soil slurry after flotation to remove fine soil particles with a particle size ≤20μm; S5. Add leaching solution to the soil slurry after removing fine particles, perform cavitation stripping leaching, and after leaching, screen to obtain soil and leaching underflow of different particle sizes; S6. The scrubbing underflow is subjected to pressure filtration to obtain filter residue and clarified liquid; a stabilizing agent is added to the filter residue for solidification and stabilization treatment; S7. Test the leached soil for heavy metals. If the soil meets the standards, it will be discharged. If it does not meet the standards, return to step S5 and leach again.

[0006] As a further improvement of this application, in step S2, the mass ratio of soil to clean water is 1:(2~5), the stirring speed is 100~300r / min, and the stirring time is 10~30min.

[0007] As a further improvement of this application, in step S3, the flotation reagent is obtained by mixing xanthate reagent and black reagent at a mass ratio of (2~5):1; the amount of flotation reagent added is 0.01~0.05% of the mass of the pretreated soil, the flotation time is 10~20 min, and the flotation temperature is 20~35℃.

[0008] As a further improvement of this application, in step S4, a hydrocyclone centrifugal separation method is used to remove fine soil particles, with a feed concentration of 25-35%, a separation pressure of 0.6-1.2 MPa, and a separation time of 15-40 min.

[0009] As a further improvement of this application, in step S5, the leaching solution is an organic acid solution with a concentration of 0.05~0.2mol / L, and the amount added is 1~3 times the mass of the pretreated soil; the cavitation stripping leaching pressure is 1~20MPa, and the leaching time is 5~10min; the organic acid solution is one or more of citric acid, oxalic acid, tartaric acid, acetic acid, and humic acid.

[0010] As a further improvement of this application, in step S5, a double-layer vibrating screen is used for screening, with screen sizes of 2 mm and 0.15 mm respectively.

[0011] As a further improvement of this application, in step S6, the stabilizing agent is obtained by mixing alkaline substances, phosphate salts and iron salts in a mass ratio of (0.1~0.5):(1~2):(1~2), the amount of the stabilizing agent added is 1~10% of the mass of the filter press residue, and the solidification and stabilization treatment time is 24~36h.

[0012] As a further improvement of this application, the alkaline substance is one or more of quicklime, hydrated lime, and limestone; the phosphate salt is one or more of calcium dihydrogen phosphate, hydroxyapatite, and phosphate rock powder; and the iron salt is one or more of polyferric sulfate, ferric chloride, ferrous sulfate, ferrous citrate, nano-zero ferric iron, and iron-based biochar.

[0013] As a further improvement of this application, the clarified liquid obtained in step S6 is recycled for soil slurry preparation in step S2 after flocculation and sedimentation treatment.

[0014] As a further improvement of this application, the heavy metal pollutants in the composite contaminated soil are one or more of As, Pb, Cu, Zn, Cd, Cr, and Mn.

[0015] The beneficial effects of this application are as follows: This application provides a method for the recovery of valuable substances and synergistic removal of pollutants from complex contaminated soil. The method involves pretreating the complex contaminated soil to remove slag particles larger than 2 cm; mixing the pretreated soil with water to form a soil slurry; adding flotation reagents to the soil slurry for flotation treatment to collect valuable substances, including gold and / or silver; separating the flotation soil slurry to remove fine soil particles ≤20 μm; adding a leaching solution to the soil slurry after fine particle removal for cavitation stripping leaching; sieving after leaching to obtain soil particles of different sizes and leaching underflow; filtering the leaching underflow to obtain filter residue and clarified liquid; adding a stabilizing agent to the filter residue for solidification and stabilization treatment; and testing the leached soil for heavy metals, discharging if the standards are met, and returning if the standards are not met for re-leaching. This application utilizes flotation technology to efficiently recover valuable substances such as gold and silver from soil, achieving resource utilization. Simultaneously, through subsequent removal, rinsing, and solidification steps, it achieves the harmless removal of heavy metals, balancing environmental and economic benefits.

[0016] This application utilizes precise removal of fine soil particles, specifically targeting particles with high heavy metal content, significantly reducing subsequent remediation workload, shortening the remediation cycle, and lowering treatment costs. Through cavitation stripping and leaching, it efficiently removes pollutants adsorbed on the surface of soil particles using the energy of cavitation bubble collapse, saving leaching solution and significantly shortening leaching time. The leaching solution is recyclable, and the filter residue, after solidification and stabilization treatment, is disposed of via landfill without generating secondary pollution, meeting green environmental protection requirements. This method can treat soils contaminated with various heavy metals, showing good removal effects on different types and concentrations of heavy metals, and is suitable for various contaminated soil scenarios. The steps are seamlessly integrated, the technology is mature, and no complex equipment is required, facilitating industrial-scale application.

[0017] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0019] Figure 1 This is a flowchart illustrating the method for recovering valuable substances and synergistically removing pollutants from complex contaminated soil, as provided in the embodiments of this application. Detailed Implementation

[0020] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0024] Due to the cyanide gold extraction process and the presence of multiple metals in the soil, soils from the gold industry often exhibit characteristics of combined pollution of valuable substances and heavy metals. Existing physical, chemical, and biological remediation technologies have significant shortcomings: First, they focus only on heavy metal removal while neglecting the recovery of valuable substances such as gold and silver, lacking resource value; second, they do not specifically treat soils with high concentrations of fine particles, resulting in large remediation volumes, low efficiency, and high costs; third, some methods (such as chemical leaching) have poor compatibility with combined heavy metals and are prone to secondary pollution; fourth, the various treatment stages are isolated and disconnected, failing to form an integrated process, resulting in poor overall remediation effects.

[0025] To address the technical problems of low resource utilization, low remediation efficiency, and high cost in existing remediation methods, this application provides a method for the recovery of valuable substances and the synergistic removal of pollutants in composite contaminated soil. Through an integrated process of "recovery-removal-washing-solidification", the method achieves the dual goals of efficient recovery of valuable substances and harmless removal of heavy metals, while reducing the amount of remediation, improving remediation efficiency, avoiding secondary pollution, and balancing environmental and economic benefits.

[0026] Please refer to Figure 1 This application provides a method for recovering valuable substances and synergistically removing pollutants from complex contaminated soil, comprising the following steps: S1. Pre-treat the complex contaminated soil to remove slag particles larger than 2 cm in diameter; S2. Mix the pretreated soil with clean water to form a slurry, thus obtaining soil slurry; S3. Add flotation reagents to the soil slurry for flotation treatment and collect valuable substances; valuable substances include gold and / or silver; S4. Separate the soil slurry after flotation to remove fine soil particles with a particle size ≤20μm; S5. Add leaching solution to the soil slurry after removing fine particles, perform cavitation stripping leaching, and after leaching, screen to obtain soil and leaching underflow of different particle sizes; S6. The scrubbing underflow is subjected to pressure filtration to obtain filter residue and clarified liquid; a stabilizing agent is added to the filter residue for solidification and stabilization treatment; S7. Test the leached soil for heavy metals. If the soil meets the standards, it will be discharged. If it does not meet the standards, return to step S5 and leach again.

[0027] In the technical solution of this application embodiment, valuable substances such as gold and silver in the soil are first selectively enriched and recovered through slurry preparation and flotation to avoid resource waste. Then, hydrocyclone separation is used to precisely remove soil particles with high heavy metal content and ≤20μm fine particles, significantly reducing subsequent processing volume. Cavitation stripping and leaching are introduced into the remaining coarse-particle soil. The impact energy and local turbulence generated by the collapse of high-pressure cavitation bubbles accelerate the desorption and dissolution of adsorbed heavy metals on the particle surface by the organic acid leaching solution, achieving short-time and efficient removal. Finally, the leaching underflow is subjected to pressure filtration and solidification stabilization treatment to render the residue harmless, while the clarified liquid can be recycled. The overall process, through the coupling of multiple processes, simultaneously completes the recovery of valuable resources and the deep purification of multi-metal pollutants in the same system, featuring high treatment efficiency, controllable cost, and no secondary pollution.

[0028] Furthermore, in some embodiments, in step S2, the mass ratio of soil to water is 1:(2~5), the stirring speed is 100~300 r / min, and the stirring time is 10~30 min.

[0029] In the technical solution of this application embodiment, the viscosity of the slurry is reduced by sufficient water volume, which helps the soil particles to be fully dispersed and maintain good fluidity, avoiding agglomeration; the appropriate stirring speed can provide sufficient shear force to separate the adhered fine soil particles from the coarse particles, while avoiding excessive crushing of the soil and affecting the subsequent flotation and particle size classification effect; the appropriate stirring time helps the water and soil to mix evenly, so that heavy metal ions are initially dissolved and exposed on the particle surface, creating a stable slurry state for subsequent flotation recovery of gold and silver and precise removal of fine particles.

[0030] Furthermore, in some embodiments, in step S3, the flotation reagent is obtained by mixing xanthate reagent and black reagent at a mass ratio of (2~5):1; the amount of flotation reagent added is 0.01~0.05% of the mass of the pretreated soil, the flotation time is 10~20 min, and the flotation temperature is 20~35℃.

[0031] In the technical solution of this application embodiment, xanthate has a strong collecting ability for gold and silver sulfide minerals, while black powder has both collecting and foaming effects and can improve foam stability. The synergistic use of the two in proportion can improve the selective enrichment efficiency of gold and silver. Controlling the amount of reagent added helps to form a stable adsorption with sufficient reagent concentration, avoiding waste or inhibition of flotation due to excessive reagent. Appropriate flotation time and temperature allow the bubbles to fully contact the mineral particles, which is conducive to the adsorption reaction of reagent molecules on the mineral surface and maintains good fluidity of the slurry. Thus, valuable substances such as gold and silver can be efficiently recovered under mild conditions, reducing the burden on subsequent heavy metal removal. Specifically, the xanthate reagent can be one or more of ethyl xanthate, butyl xanthate, pentyl xanthate, and isopentyl xanthate; the black powder reagent can be one or more of butylammonium black powder, sodium butyl black powder, sodium isobutyl black powder, and aniline black powder.

[0032] Furthermore, in some embodiments, in step S4, a hydrocyclone centrifugal separation method is used to remove fine soil particles, with a feed concentration of 25-35%, a separation pressure of 0.6-1.2 MPa, and a separation time of 15-40 min.

[0033] In the technical solution of this application embodiment, a strong centrifugal force field generated inside the hydrocyclone is used to induce differentiated radial migration velocities for particles of different sizes in the soil slurry. Fine soil particles with a diameter ≤20μm, due to their small mass and weak centrifugal force, are discharged upwards from the overflow port with the internal vortex, thus achieving precise removal. The feed concentration ensures good fluidity and dispersibility of the slurry, avoiding excessive concentration that could cause particle interference and affect separation accuracy. Appropriate separation pressure and time provide sufficient centrifugal acceleration, resulting in clear particle size boundaries and ensuring thorough separation of fine particles from the underflow. Since heavy metal pollutants are mainly concentrated in fine particles ≤20μm, this step can remove approximately 20-25% of the pollution load in one step, significantly reducing the amount of subsequent cavitation leaching required, thereby improving overall remediation efficiency and saving reagent costs.

[0034] Furthermore, in some embodiments, in step S5, the leaching solution is an organic acid solution with a concentration of 0.05~0.2mol / L, and the amount added is 1~3 times the mass of the pretreated soil; the cavitation stripping leaching pressure is 1~20MPa, and the leaching time is 5~10min; the organic acid solution is one or more of citric acid, oxalic acid, tartaric acid, acetic acid, and humic acid.

[0035] In the technical solution of this application embodiment, organic acid molecules contain active groups such as carboxyl groups, which can undergo complexation / chelation reactions with heavy metal ions adsorbed on the surface of soil particles to form soluble complexes, thereby transferring heavy metals from the solid phase to the liquid phase. A suitable concentration can provide sufficient complexation sites, avoiding excessive concentration that could lead to waste of reagents or soil acidification. Under cavitation conditions, the high-pressure water flow rapidly depressurizes at the nozzle, generating a large number of cavitation bubbles. The bubbles collapse instantaneously near the surface of soil particles, releasing strong shock waves and microjets, which can effectively destroy the interfacial bonding force between heavy metals and particles, and flush away pollutants that are difficult to desorb from micropores. At the same time, it enhances the mass transfer and mixing efficiency between the liquid and solid phases. A suitable liquid-solid ratio ensures that the slurry has good fluidity. A suitable pressure range and time can stimulate a strong cavitation effect without excessive energy loss, completing efficient desorption in a very short time, which is significantly better than conventional rinsing processes.

[0036] Furthermore, in some embodiments, in step S5, a double-layer vibrating screen is used for screening, with screen sizes of 2 mm and 0.15 mm respectively.

[0037] In the technical solution of this application embodiment, two-stage classification is performed using screens with different aperture sizes. Based on particle size differences, the leached soil can be divided into two particle sizes: >2mm and 0.15~2mm, and the leaching underflow with a particle size <0.15mm. Coarse-grained soil has a small specific surface area and low heavy metal adsorption, and can usually achieve compliance levels through pre-leaching. Medium-grained soil is the main remediation target, facilitating compliance testing or return to leaching as needed. Fine-grained soil (leaching underflow) has a large specific surface area and high concentrations of heavy metals and residual leaching solution, requiring centralized pressure filtration and solidification stabilization treatment. This classification avoids all soil entering the subsequent pressure filtration unit, thus reducing the treatment load. It allows soil of different particle sizes to be treated according to their pollution characteristics, thereby reducing overall energy consumption and reagent usage. Simultaneously, it provides an operational basis for subsequent particle size detection and selective back-leaching.

[0038] Further, in some embodiments, in step S6, the stabilizing agent is obtained by mixing an alkaline substance, a phosphate salt, and an iron salt in a mass ratio of (0.1~0.5):(1~2):(1~2). The amount of stabilizing agent added is 1~10% of the mass of the filter press residue, and the solidification and stabilization treatment time is 24~36 hours. The alkaline substance is one or more of quicklime, hydrated lime, and limestone; the phosphate salt is one or more of calcium dihydrogen phosphate, hydroxyapatite, and phosphate rock powder; and the iron salt is one or more of polyferric sulfate, ferric chloride, ferrous sulfate, ferrous citrate, nano-zero ferric iron, and iron-based biochar.

[0039] In the technical solution of this application embodiment, alkaline substances provide an alkaline environment, promoting the conversion of heavy metal ions into hydroxide precipitates, while simultaneously adjusting the pH to facilitate phosphate salt reactions. Phosphate salts react with heavy metal ions to generate phosphate minerals with extremely low solubility, achieving chemical fixation of heavy metals. Iron salts, on the one hand, can encapsulate heavy metals through adsorption, co-precipitation, or the formation of ferrites; on the other hand, some iron salts possess reducing capabilities, reducing high-valence heavy metals to low-toxicity, low-valence states before precipitation. The synergistic effect of these three substances transforms the residual heavy metals in the filter press residue into mineral forms with low solubility and high environmental stability, meeting landfill or safe utilization standards.

[0040] Furthermore, in some embodiments, the clarified liquid obtained in step S6 is recycled for soil slurry preparation in step S2 after flocculation and sedimentation treatment.

[0041] In the technical solution of this application embodiment, the clarified liquid still contains a small amount of suspended fine soil particles and dissolved organic acid residues. By adding a flocculant, the suspended particles are agglomerated into large-diameter flocs and settle rapidly, effectively removing solid impurities that hinder reuse and ensuring that the supernatant water quality meets the requirements for slurry preparation. Recycling the purified clarified liquid can significantly reduce the amount of fresh water used, thereby reducing water consumption and wastewater discharge. Furthermore, the low concentration of organic acid remaining in the clarified liquid can assist in the initial dispersion and heavy metal pre-washing during the slurry preparation stage, helping to improve the efficiency of subsequent flotation and washing. Specifically, the flocculant can be a combination of polyacrylamide (PAM) and polyaluminum chloride (PAC) or polyferric sulfate (PFS).

[0042] Furthermore, in some embodiments, the heavy metal pollutants in the composite contaminated soil are one or more of As, Pb, Cu, Zn, Cd, Cr, and Mn.

[0043] In the technical solution of this application embodiment, this application has a universal synergistic removal effect on the above-mentioned typical heavy metal composite contaminated soil. These heavy metal ions all have strong particle affinity and are easily enriched on the surface or in the lattice of fine soil particles ≤20 μm. They can also form stable soluble complexes with organic acids, thereby being efficiently desorbed into the liquid phase during the cavitation stripping and leaching process. At the same time, these heavy metals can react with alkaline substances, phosphate salts and iron salts in the subsequent filter press residue to generate hydroxides, phosphate minerals or ferrites with low solubility products, thereby achieving simultaneous solidification and stabilization.

[0044] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0045] Example 1 This embodiment provides a method for the recovery of valuable substances and synergistic removal of pollutants from complex contaminated soil. A heavy metal-contaminated soil sample (containing copper, lead, arsenic, cadmium, and a certain amount of gold) from a gold smelting enterprise was selected as the sample for this implementation. Sampling and testing revealed the following content of heavy metals and valuable components in the soil: Table 1. Component content of the complex contaminated soil to be treated Specifically, the following steps are included: S1. Pre-treat the complex contaminated soil to remove slag particles larger than 2 cm in diameter; S2. Take 100kg of pretreated soil, add 300kg of clean water, and stir at 200r / min for 20min to obtain a uniform soil slurry; S3. Add 0.03 kg of flotation reagent (ethyl xanthate and butyl ammonium black compound, ratio 4:1) to the soil slurry, stir for 10 min, then float for 15 min at a flotation temperature of 25℃, and collect the flotation concentrate with a yield of 4.57%. S4. The soil slurry after flotation is centrifuged using a hydrocyclone to remove fine soil particles with a particle size ≤20μm; the feed concentration is 30%, the separation pressure is 1.0MPa, the separation time is 25min, and approximately 20kg of fine particles are removed. S5. Add 200 kg of leaching solution (0.1 mol / L citric acid solution) to the soil slurry after removing fine particles, and perform cavitation stripping leaching for 5 min at a cavitation leaching pressure of 20 MPa; after leaching, the soil is sieved through 0.15 mm and 2 mm vibrating screens to obtain soil with >2 mm, 0.15-2 mm and <0.15 mm leaching underflow; S6. The underflow from the leaching process was subjected to pressure filtration to obtain 25 kg of filter residue. 0.25 kg of stabilizing agent (a mixture of quicklime, calcium dihydrogen phosphate, and polyferric sulfate in a mass ratio of 0.5:1:1) was added, stirred evenly, and then solidified for 24 h. The heavy metal content in the leachate was tested and found to meet the Class IV standard in the "Groundwater Quality Standard" (GB / T 14848-2017) before being disposed of in a landfill. The clarified liquid was treated with flocculants PAM and PAC (mass ratio 1:60) for flocculation and sedimentation, and then recycled for the next slurry preparation. S7. Heavy metal testing was conducted on the leached soil. The contents of copper, lead, arsenic, and cadmium in the soil all met the environmental quality standards for soil used in construction land, and the soil was discharged as compliant.

[0046] Example 2 This embodiment provides a method for the recovery of valuable substances and the synergistic removal of pollutants from soil with complex contamination. A sample of soil from a gold smelting enterprise, contaminated with heavy metals (containing copper, lead, arsenic, cadmium, and trace amounts of gold), was selected. After sampling and testing, the contents of heavy metals and valuable components in the soil were as follows: Table 2. Component content of the complex polluted soil to be treated Specifically, the following steps are included: S1. Pre-treat the complex contaminated soil to remove slag particles larger than 2 cm in diameter; S2. Take 100kg of pretreated soil, add 500kg of clean water, and stir at 300r / min for 10min to obtain a uniform soil slurry; S3. Add 0.05 kg of flotation reagent (butyl xanthate and butyl ammonium black compound, ratio 2:1) to the soil slurry, stir for 10 min, then float for 20 min at a flotation temperature of 25℃, and collect the flotation concentrate with a yield of 5.84%. S4. The soil slurry after flotation is centrifuged using a hydrocyclone to remove fine soil particles with a particle size ≤20μm; the feed concentration is 30%, the separation pressure is 1.2MPa, the separation time is 15min, and approximately 24kg of fine particles are removed. S5. Add 210 kg of leaching solution (0.2 mol / L oxalic acid solution) to the soil slurry after removing fine particles, and perform cavitation stripping leaching for 10 min at a cavitation leaching pressure of 20 MPa; after leaching, the soil is sieved through 0.15 mm and 2 mm vibrating screens to obtain soil with >2 mm, 0.15-2 mm and <0.15 mm leaching underflow; S6. The leaching underflow was subjected to pressure filtration to obtain 50 kg of filter residue. 0.5 kg of stabilizing agent (a mixture of quicklime, hydroxyapatite, and ferrous sulfate in a mass ratio of 0.5:1:2) was added, stirred evenly, and then solidified for 36 h. The heavy metal content in the leachate was tested and found to meet the Class IV standard in the "Groundwater Quality Standard" (GB / T 14848-2017) before being disposed of in a landfill. The clarified liquid was treated with flocculants PAM and PFS (mass ratio 1:50) for flocculation and sedimentation, and then recycled for the next slurry preparation. S7. Perform heavy metal testing on the leached soil. If the arsenic content in the 0.15-2mm soil sample after the first leaching is below the standard, return the soil for a second leaching for 10 minutes. If the sample passes the test again, the soil is discharged.

[0047] Example 3 Example 3 provides a method for the recovery of valuable substances and synergistic removal of pollutants in soil with complex contamination. The same batch of heavy metal contaminated soil as in Example 1 is used for treatment. The method specifically includes the following steps: S1. Pre-treat the complex contaminated soil to remove slag particles larger than 2 cm in diameter; S2. Take 100kg of pretreated soil, add 200kg of clean water, and stir at 100r / min for 30min to obtain a uniform soil slurry; S3. Add 0.01 kg of flotation reagent (isoamyl xanthate and sodium butyrate xanthate compounded in a ratio of 5:1) to the soil slurry, stir for 10 min, then float for 10 min at a flotation temperature of 25℃, and collect the flotation concentrate with a yield of 4.57%. S4. The soil slurry after flotation is centrifuged using a hydrocyclone to remove fine soil particles with a particle size ≤20μm; the feed concentration is 30%, the separation pressure is 1.0MPa, the separation time is 25min, and approximately 22kg of fine particles are removed. S5. Add 200 kg of leaching solution (0.1 mol / L citric acid solution) to the soil slurry after removing fine particles, and perform cavitation stripping leaching for 5 min at a cavitation leaching pressure of 20 MPa; after leaching, the soil is sieved through 0.15 mm and 2 mm vibrating screens to obtain soil with >2 mm, 0.15-2 mm and <0.15 mm leaching underflow; S6. The underflow from the leaching process is subjected to pressure filtration to obtain 25 kg of filter residue. 0.25 kg of stabilizing agent (a mixture of quicklime, calcium dihydrogen phosphate, and polyferric sulfate in a mass ratio of 0.2:1:2) is added, and the mixture is stirred evenly and then solidified for 24 h. The heavy metal content in the leachate is tested and found to meet the Class IV standard in the "Groundwater Quality Standard" (GB / T 14848-2017) before being disposed of in a landfill. The clarified liquid is treated with flocculants PAM and PFS (mass ratio 1:40) for flocculation and sedimentation, and then recycled for the next slurry preparation. S7. Heavy metal testing was conducted on the leached soil. The contents of copper, lead, arsenic, and cadmium in the soil all met the environmental quality standards for soil used in construction land, and the soil was discharged as compliant.

[0048] Example 4 Example 4 provides a method for recovering valuable substances and synergistically removing pollutants from compound contaminated soil. The only difference from Example 1 is that in step S5, the leaching solution is a 0.05 mol / L citric acid solution. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here.

[0049] Example 5 Example 5 provides a method for recovering valuable substances and synergistically removing pollutants from compound contaminated soil. The only difference from Example 1 is that in step S6, the mass ratio of quicklime, calcium dihydrogen phosphate, and polyferric sulfate is 0.1:1:1. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here.

[0050] Example 6 Example 6 provides a method for recovering valuable substances and synergistically removing pollutants from compound contaminated soil. The only difference from Example 1 is that in step S6, the mass ratio of quicklime, calcium dihydrogen phosphate, and polyferric sulfate is 0.5:2:2. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here.

[0051] Comparative Example 1 Comparative Example 1 provides a method for the recovery of valuable substances and synergistic removal of pollutants from soil with complex contamination. It uses the same batch of heavy metal contaminated soil as Example 1 for treatment and specifically includes the following steps: S1. Pre-treat the complex contaminated soil to remove slag particles larger than 2 cm in diameter; S2. Take 100 kg of pretreated soil, add 500 kg of leaching solution (0.1 mol / L HCl), stir at 100 r / min for 30 min, and after leaching, the soil is sieved through 0.15 mm and 2 mm vibrating screens to obtain soil >2 mm, 0.15-2 mm and <0.15 mm leaching underflow.

[0052] Comparative Example 2 Comparative Example 2 provides a method for the recovery of valuable substances and synergistic removal of pollutants in soil with complex contamination. It uses the same batch of heavy metal contaminated soil as Example 1 for treatment and specifically includes the following steps: S1. Pre-treat the complex contaminated soil to remove slag particles larger than 2 cm in diameter; S2. Take 100 kg of pretreated soil, add 500 kg of leachate (0.1 mol / L H2SO4), stir at 100 r / min for 30 min, and after leaching, the soil is sieved through 0.15 mm and 2 mm vibrating screens to obtain soil >2 mm, 0.15-2 mm and <0.15 mm leachate underflow.

[0053] Comparative Example 3 Comparative Example 3 provides a method for recovering valuable substances and synergistically removing pollutants from complex polluted soil. The only difference from Example 1 is that flotation recovery is not performed. Instead, the soil slurry is directly subjected to fine particle removal and cavitation stripping and leaching. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0054] Comparative Example 4 Comparative Example 4 provides a method for recovering valuable substances and synergistically removing pollutants from composite contaminated soil. The only difference from Example 1 is that the fine soil particles are not removed, and the cavitation stripping and rinsing of the flotation slurry is performed directly. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0055] Comparative Example 5 Comparative Example 5 provides a method for recovering valuable substances and synergistically removing pollutants from compound contaminated soil. The only difference from Example 1 is that the stabilizing agent is only quicklime. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0056] Comparative Example 6 Comparative Example 6 provides a method for recovering valuable substances and synergistically removing pollutants from compound contaminated soil. The only difference from Example 1 is that the stabilizing agent is only calcium dihydrogen phosphate. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0057] Table 3. Results of processing in the examples and comparative examples Comparative experiments show that the method of this application is superior to existing technologies in terms of recovery of valuable substances, removal of heavy metals, remediation efficiency, and environmental friendliness in soils contaminated with multiple heavy metals. The remediation volume in Table 1 refers to the amount of soil leached. Comparative Examples 1 and 2 used conventional acid leaching, which removed some lead but could not recover gold and silver, had a low arsenic removal rate, required the treatment of all 100 kg of soil, and generated secondary pollution. Comparative Example 3, omitting flotation, achieved acceptable heavy metal removal but lost all valuable substance recovery value. Comparative Example 4, omitting fine particle removal, resulted in a sharp decrease in arsenic and lead removal rates and a significant increase in remediation volume, indicating that the fine particle removal step is a crucial pre-step for ensuring the high efficiency of cavitation leaching. Comparative Examples 5 and 6, using only a single stabilizing agent, showed significantly lower arsenic and lead removal rates than the examples, demonstrating that a combination of alkaline substances, phosphate salts, and iron salts is necessary to achieve efficient solidification and stabilization of heavy metals.

[0058] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for the recovery of valuable substances and synergistic removal of pollutants in complexly contaminated soil, characterized in that, Includes the following steps: S1. Pre-treat the complex contaminated soil to remove slag particles larger than 2 cm in diameter; S2. Mix the pretreated soil with clean water to form a slurry, thus obtaining soil slurry; S3. Add flotation reagents to the soil slurry for flotation treatment and collect valuable substances; the valuable substances include gold and / or silver; S4. Separate the soil slurry after flotation to remove fine soil particles with a particle size ≤20μm; S5. Add leaching solution to the soil slurry after removing fine particles, perform cavitation stripping leaching, and after leaching, screen to obtain soil and leaching underflow of different particle sizes; S6. The scrubbing underflow is subjected to pressure filtration to obtain filter residue and clarified liquid; a stabilizing agent is added to the filter residue for solidification and stabilization treatment; S7. Test the leached soil for heavy metals. If the soil meets the standards, it will be discharged. If it does not meet the standards, return to step S5 and leach again.

2. The method for recovering valuable substances and synergistically removing pollutants from compoundly contaminated soil according to claim 1, characterized in that, In step S2, the mass ratio of soil to water is 1:(2~5), the stirring speed is 100~300 r / min, and the stirring time is 10~30 min.

3. The method for recovering valuable substances and synergistically removing pollutants from compound contaminated soil according to claim 1, characterized in that, In step S3, the flotation reagent is obtained by mixing xanthate reagent and black reagent at a mass ratio of (2~5):1; the amount of flotation reagent added is 0.01~0.05% of the mass of the pretreated soil, the flotation time is 10~20 min, and the flotation temperature is 20~35℃.

4. The method for recovering valuable substances and synergistically removing pollutants from compound contaminated soil according to claim 1, characterized in that, In step S4, fine soil particles are removed by hydrocyclone centrifugation, with a feed concentration of 25-35%, a separation pressure of 0.6-1.2 MPa, and a separation time of 15-40 min.

5. The method for recovering valuable substances and synergistically removing pollutants from compound contaminated soil according to claim 1, characterized in that, In step S5, the leaching solution is an organic acid solution with a concentration of 0.05~0.2mol / L, and the amount added is 1~3 times the mass of the pretreated soil; the cavitation stripping leaching pressure is 1~20MPa, and the leaching time is 5~10min; the organic acid solution is one or more of citric acid, oxalic acid, tartaric acid, acetic acid, and humic acid.

6. The method for recovering valuable substances and synergistically removing pollutants from compound contaminated soil according to claim 1, characterized in that, In step S5, a double-layer vibrating screen is used for screening, with screen sizes of 2 mm and 0.15 mm respectively.

7. The method for recovering valuable substances and synergistically removing pollutants from compound contaminated soil according to claim 1, characterized in that, In step S6, the stabilizing agent is obtained by mixing alkaline substances, phosphate salts and iron salts in a mass ratio of (0.1~0.5):(1~2):(1~2). The amount of the stabilizing agent added is 1~10% of the mass of the filter press residue, and the solidification and stabilization treatment time is 24~36h.

8. The method for recovering valuable substances and synergistically removing pollutants from compound contaminated soil according to claim 7, characterized in that, The alkaline substance is one or more of quicklime, hydrated lime, and limestone; the phosphate salt is one or more of calcium dihydrogen phosphate, hydroxyapatite, and phosphate rock powder; and the iron salt is one or more of polyferric sulfate, ferric chloride, ferrous sulfate, ferrous citrate, nano-zero ferric iron, and iron-based biochar.

9. The method for recovering valuable substances and synergistically removing pollutants from compound contaminated soil according to claim 1, characterized in that, The clarified liquid obtained in step S6 is recycled for soil conditioning in step S2 after flocculation and sedimentation treatment.

10. The method for recovering valuable substances and synergistically removing pollutants from compoundly contaminated soil according to claim 1, characterized in that, The heavy metal pollutants in the composite contaminated soil are one or more of As, Pb, Cu, Zn, Cd, Cr, and Mn.

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