A special leaching agent for organic matter and heavy metal compound contaminated soil with synergistic reinforcement leaching and a preparation method thereof

Abstract

The application discloses a special leaching agent for organic matter and heavy metal compound contaminated soil and a preparation method thereof, relates to the technical field of leaching agents for compound contaminated soil and preparation thereof, and the preparation steps are as follows: first, carboxyl-modified fulvic acid is prepared, a mineral source fulvic acid is taken to prepare a suspension, high-purity nitrogen is introduced to remove oxygen, and then ammonium persulfate initiator is added; after water bath heating, acrylic acid monomer is uniformly and slowly added for reaction; after the reaction is completed, the system pH is adjusted; after dialysis and impurity removal, freeze-drying is carried out to obtain modified fulvic acid with an acrylic acid grafting rate of 15% to 30%; and the modified fulvic acid is taken to prepare a phosphate buffer suspension. The application improves the number of active functional groups of fulvic acid through acrylic acid grafting modification, greatly enhances the heavy metal chelation and polycyclic aromatic hydrocarbon solubilization capacity, and covalently crosslinks functional bacteria on the fulvic acid carrier, so that the functional bacteria can be adapted to different acid-base values of contaminated sites and are suitable for soil remediation of various compound contaminated sites.

Description

Technical Field

[0001] This invention relates to the field of leaching agents for composite contaminated soil and their preparation technology, specifically to a special leaching agent for composite contaminated soil containing organic matter and heavy metals that synergistically enhances leaching and its preparation method. Background Technology

[0002] Decommissioned industrial and mining sites in my country are commonly contaminated with a combination of heavy metals and polycyclic aromatic hydrocarbons (PAHs). This type of pollution is characterized by strong cumulative effects and high migration risks, making it a key area of ​​research in soil remediation. Leaching remediation technology, suitable for both in-situ and ex-situ scenarios, with a short treatment cycle and a wide range of applicable pollution concentrations, is currently one of the mainstream technologies for remediating soils with complex contamination. The core industry requirement is that the leaching agent must simultaneously possess the triple characteristics of high removal efficiency of complex pollutants, no secondary pollution, and no damage to the original soil ecosystem.

[0003] Currently, mainstream leaching agents are mainly divided into two categories. The first category is chemically synthesized leaching agents, which use ethylenediaminetetraacetic acid (EDTA) chelating agents combined with anionic chemical surfactants. The working principle is that the chelating agent binds heavy metal ions through coordination, while the surfactant reduces interfacial tension and solubilizes hydrophobic organic matter. It has been applied in several industrial contaminated site remediation projects, with advantages such as fast reaction rate, readily available raw materials, and low single-factor treatment cost. However, this type of leaching agent has significant drawbacks: the chelating agent is difficult to biodegrade, and its residue can cause secondary soil salinization; the chemical surfactant can easily remain in soil pores and damage the microbial community; and the leaching process can significantly reduce the soil organic matter content. In addition, the synergistic effect between the two components is weak, resulting in low efficiency in the simultaneous removal of complex pollutants. It can also easily cause large fluctuations in soil pH, making it unsuitable for the remediation of sensitive sites.

[0004] The second type is bio-based leaching agents, which mostly use unmodified fulvic acid, single rhamnolipids, and free functional bacteria. The working principle is that the weak complexation of fulvic acid binds heavy metals, biosurfactants solubilize organic matter, and functional bacteria degrade residual organic pollutants. The advantage is stronger environmental friendliness and less impact on the soil background. However, this type of leaching agent has significant drawbacks: the number of active functional groups in unmodified fulvic acid is small, and the efficiency of heavy metal complexation and organic matter solubilization is only about 40% of that of chemical leaching agents. The free functional bacteria have poor salt tolerance and are easily washed away by water during the leaching process, with an actual survival rate of less than 30%. Furthermore, the system lacks pH buffering capacity and is greatly affected by the background pH of the site, requiring repeated adjustments to the leaching agent ratio. The remediation cycle is long, and the overall cost is high, making it unsuitable for the remediation needs of large-scale, multi-contaminated sites. Summary of the Invention

[0005] To address the shortcomings of existing leaching agents for soils with complex contamination, such as low simultaneous removal efficiency, easy secondary pollution, low survival rate of functional bacteria, and poor compatibility, this invention provides a special leaching agent for soils with complex contamination of organic matter and heavy metals that synergistically enhances leaching, and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a special leaching agent for soil contaminated with organic matter and heavy metals in a synergistic and enhanced leaching process, which is composed of the following components by mass: 28-32 parts of thiol-amide double-grafted modified mineral fulvic acid, 14-16 parts of biodegradable chelating agent, 9-11 parts of rhamnolipin-sophorolipid compound biosurfactant, 4-6 parts of double-layer encapsulated salt-tolerant composite functional bacterial agent, 4.5-5.5 parts of citric acid-sodium citrate pH buffer regulator, and 29-40.5 parts of deionized water; The thiol-amide double-grafted modified mineral fulvic acid is obtained by grafting thiol and amide groups after hydrogen peroxide oxidation and γ-ray irradiation activation. The carboxyl content is ≥14mmol / g. The thiol groups target and complex heavy metals, and the amide groups solubilize organic pollutants. The double-layer encapsulated salt-tolerant composite functional bacterial agent is obtained by mixing Pseudomonas, Bacillus subtilis, and Aspergillus niger in a viable bacteria ratio of 2:2:1 and then encapsulating it in a sodium alginate-chitosan double-layer biodegradable wall material. The total viable bacteria count is ≥3×10^9 CFU / g. The wall material can be completely degraded in soil without residue in 45 days.

[0007] Preferably, the biodegradable chelating agent is a composition obtained by compounding polyaspartic acid and tetrasodium glutamate diacetate at a mass ratio of 1:1.2~1.5; the polyaspartic acid has a number-average molecular weight of 3000~5000 Da, the tetrasodium glutamate diacetate has a chelating capacity of 2.5~3.0 mmol / g, and the heavy metal chelation selectivity after compounding is increased by more than 30% compared with the single chelating agent, and the chelation stability is ≥95% in the pH range of 5.5~7.5.

[0008] Preferably, the rhamnolipin-sophorolipid compound biosurfactant is a composition obtained by compounding rhamnolipin and sophorolipid at a mass ratio of 1:0.8~1, with a critical micelle concentration of 22~28 mg / L. It can reduce the interfacial tension of soil pores to 28~32 mN / m, and the solubilization factor for polycyclic aromatic hydrocarbons is more than 1.5 times that of a single surfactant. The biodegradation rate after 28 days is ≥98%.

[0009] Preferably, the pH of the citric acid-sodium citrate pH buffering system is 6.0~6.5, the buffering capacity is 0.02~0.03mol / L, and the pH fluctuation range of the leachate during the leaching process does not exceed ±0.3. This not only matches the optimal pH range for heavy metal chelation and organic matter solubilization, but also avoids large fluctuations in soil pH that could damage the native microbial community.

[0010] Preferably, the number-average molecular weight of the thiol-amide double-grafted modified mineral fulvic acid is 1200~1800 Da, the thiol grafting rate is ≥8%, the complexation stability constant for cadmium and lead is ≥10^12, the amide grafting rate is ≥10%, the adsorption partition coefficient Kd for polycyclic aromatic hydrocarbons is ≥10^3 L / kg, the number of active sites after activation is increased by more than 60% compared with unmodified fulvic acid, and the residual fulvic acid can increase the soil cation exchange capacity by ≥15%; The double-layered salt-tolerant composite functional microbial agent has an encapsulation rate of ≥92%, an outer layer of chitosan with a degree of deacetylation of ≥90%, an inner layer of sodium alginate with a viscosity of 100~200 mPa·s, a strain salt tolerance concentration of ≥1.8wt%, a survival rate of ≥90% at a salt concentration of 1.8wt%, and a water erosion resistance during leaching that is more than 4 times higher than that of unencapsulated strains. It gradually releases active strains within 30 days after entering the soil. The leaching agent has a water-insoluble content of ≤0.08wt%, is diluted 300-400 times during application, has a solid-liquid ratio of 1:2-3, a leaching rate of 1.5-2.0mL / min, and can reach the remediation threshold after 2-3 consecutive leachings. It has a leaching rate of ≥72% for polycyclic aromatic hydrocarbons and an increase in bioavailability of ≥70%, a leaching rate of ≥78% for heavy metals such as cadmium, lead, and copper and a reduction in available content of ≥80%, and an increase in soil organic matter of ≥3g / kg after leaching. It is suitable for both ex-situ and in-situ leaching remediation scenarios.

[0011] Preferably, a method for preparing a special leaching agent for organic and heavy metal contaminated soil with synergistic enhanced leaching includes the following steps: S1. Disperse mineral fulvic acid into a suspension of 12-13 wt%, and after sequential oxidation with hydrogen peroxide and activation by γ-ray irradiation, add mercaptoacetic acid and acrylamide. Under nitrogen protection, carry out grafting reaction using an ascorbic acid-peroxide hydrogen oxidative reduction initiation system, and purify and dry to obtain double-grafted modified mineral fulvic acid. S2. Pseudomonas, Bacillus subtilis and Aspergillus niger after gradient salt tolerance acclimation were mixed according to the ratio of live bacteria, and double-layered encapsulation was carried out using sodium alginate-chitosan as the wall material by sharp-pore-coagulation bath method, and low-temperature vacuum drying was used to obtain salt-tolerant composite functional bacterial agent. S3. Add the pH buffer adjuster to deionized water and stir to dissolve. Then add the biodegradable chelating agent and compound biosurfactant in sequence. During stirring, filter the solution through a 0.22μm filter to remove insoluble impurities and obtain the basic mixture. S4. After dissolving the double-grafted modified mineral fulvic acid in the basic mixture, cool it down to 22~24℃ with circulating water, add salt-tolerant compound functional bacterial agent, fill with high-purity nitrogen and mix at low speed, then aseptically seal and fill to obtain the finished product. The dissolved oxygen content of the system is controlled to ≤0.5mg / L throughout the process to avoid bacterial inactivation.

[0012] Preferably, in step S1, the amount of hydrogen peroxide added is 3% of the mass of the suspension, the oxidation reaction time is 45 min, the gamma ray irradiation dose is 7-8 kGy, the irradiation time is 22 min, the amounts of mercaptoacetic acid and acrylamide added are 6-8% and 9-11% of the dry weight of mineral fulvic acid, respectively, the grafting reaction temperature is 40-45℃, the stirring speed is 180 r / min, the reaction time is 2 h, and after the reaction, unreacted monomers are removed by purification using a nanofiltration membrane with a molecular weight cutoff of 1000 Da, and the product purity is ≥95%.

[0013] Preferably, in S2, the strain is subjected to salt tolerance acclimatization using LB medium with a gradient concentration of sodium chloride, the salt concentration gradient being 0.4wt%, 0.8wt%, 1.2wt%, and 1.6wt% respectively. Each concentration gradient is passaged three times, with each passage lasting 24 hours. After acclimatization, the polycyclic aromatic hydrocarbon degradation efficiency of the strain is increased by more than 50% compared to the unacclimatized strain. The double-layer embedding coagulation bath is a 2wt% calcium chloride solution, and the solidification time is 30 minutes. The resulting microcapsule particle size of the bacterial agent is 200~300μm.

[0014] Preferably, in step S3, the stirring and dissolving temperature is 35~38℃, the stirring speed is 250r / min, and the stirring time is 25min. The pH value is checked every 10min during the dissolving process. If it deviates from the range of 6.0~6.5, it is adjusted with 1mol / L citric acid or sodium citrate solution. After stirring, the mixture is filtered through a 0.22μm precision filter, and the turbidity of the resulting basic mixture is ≤0.1NTU.

[0015] Preferably, in step S4, the circulating water cooling rate is 2℃ / min to avoid sudden temperature changes from damaging the stability of the components. The low-speed stirring speed is 80r / min and the stirring time is 12min. The nitrogen gas used for filling has a purity of ≥99.9%. The filling uses aseptic aluminum foil bags. After sealing, the residual oxygen content in the headspace of the bag is ≤0.1%. After the finished product is stored at room temperature for 6 months, the effective retention rate of each component is ≥90% and the viable bacteria retention rate is ≥88%.

[0016] The present invention has the following beneficial effects: This invention utilizes a technique of coupling modified humic acid with cross-linked supported functional bacteria and rhamnolipids to achieve a multi-effect synergistic effect of heavy metal chelation, polycyclic aromatic hydrocarbon solubilization, and degradation of residual organic pollutants. It effectively solves the defects of existing technologies, such as the high risk of secondary pollution from chemical leaching agents and the low efficiency of simultaneous removal of composite pollutants by bio-based leaching agents. The simultaneous removal capacity of heavy metals and polycyclic aromatic hydrocarbons is superior to the two existing types of leaching agents. Moreover, there are no exogenous recalcitrant components remaining in the soil after leaching, and the original physiological and chemical structure and microbial community background of the soil are not damaged.

[0017] This invention utilizes modified fulvic acid as a carrier to crosslink and immobilize functional bacteria, providing a microenvironmental protective layer for the functional bacteria. This avoids water erosion during the rinsing process and inhibits the toxicity of background pollutants in the site. It effectively solves the defects of low survival rate and rapid activity decay of free functional bacteria in existing bio-based rinsing agents, ensuring the stable degradation activity of functional bacteria throughout the rinsing process. It eliminates the need for repeated replenishment of bacterial agents and simplifies the remediation process.

[0018] This invention utilizes the modified carboxyl and phenolic hydroxyl buffer system of fulvic acid to adjust the pH of the rinsing agent. This allows it to adapt to contaminated sites with different background pH levels without the need for additional pH adjusters. It effectively solves the shortcomings of existing rinsing agents that are greatly limited by the pH of the site and require repeated adjustments to the mixing ratio. It is suitable for various rinsing scenarios, including in-situ and ex-situ rinsing, without the need for additional pretreatment steps, thus reducing the overall cost of engineering applications.

[0019] The raw materials for the leaching agent of this invention can be prepared entirely from components derived from renewable biomass. The raw materials are widely available and the production process is simple. It can be adapted to the remediation needs of complex contaminated soils with different pollution concentrations and site types. It has high application value in various application scenarios such as decommissioned industrial and mining sites and contaminated farmland soils. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the preparation method of the special leaching agent for organic and heavy metal composite contaminated soil with synergistic enhanced leaching proposed in this invention. Figure 2 This is a line graph comparing the simultaneous removal rates of polycyclic aromatic hydrocarbon-cadmium composite pollutants by different samples in this invention. Figure 3 This is a line graph showing the fluctuation of the total removal rate of composite pollutants by the rinsing agent under different background pH conditions according to the present invention. Detailed Implementation

[0021] The following will refer to the appendices in the embodiments of the present invention. Figure 1-3 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 This embodiment uses the lower limit of the parameter range defined in the claims to prepare the rinsing agent, which is specifically divided into 4 steps: S1. Preparation of carboxylated modified fulvic acid: Take 100g of commercially available mineral fulvic acid, add deionized water to prepare a suspension with a mass fraction of 10wt%, pass high-purity nitrogen gas to remove oxygen for 30min, add 0.5g of ammonium persulfate initiator, heat to 50℃ in a water bath, add 15g of acrylic acid monomer dropwise at a uniform rate, keep the reaction at the temperature for 2h, cool to room temperature after the reaction is completed, adjust the pH of the system to 7.0 with 0.1mol / L sodium hydroxide solution, transfer to a dialysis bag with a molecular weight cutoff of 1000Da, dialyze for 3d to remove unreacted monomers and small molecule impurities, freeze-dry to obtain carboxylated modified fulvic acid with an acrylic acid grafting rate of 15%.

[0023] S2. Activation of carboxyl groups on the surface of modified fulvic acid: Take 100g of the above carboxylated modified fulvic acid, add 0.1mol / L phosphate buffer solution with pH 7.2 to prepare a suspension with a mass fraction of 8wt%, add 2g of carbodiimide activator, stir and activate at room temperature for 1h to obtain the activated modified fulvic acid suspension.

[0024] S3. Covalently cross-linked functional bacteria: Pseudomonas bacterial suspension with a concentration of 1×10^10 CFU / mL was added to the activated modified fulvic acid suspension to control the final functional bacteria loading to 1×10^8 CFU / g modified fulvic acid. The mixture was stirred at room temperature for 3 hours, centrifuged at 4000 r / min for 10 min to collect the solid product, and washed three times with 0.1 mol / L phosphate buffer to remove unbound free bacteria, thus obtaining modified fulvic acid loaded with functional bacteria.

[0025] S4. Preparation of the finished rinsing agent by multi-component compounding: The modified humic acid, rhamnolipin and deionized water loaded with the above functional bacteria are mixed in a mass ratio of 82:5:13 and stirred at room temperature for 30 minutes until the system is uniform to obtain the rinsing agent of Example 1.

[0026] Once the leaching agent in this embodiment is prepared, it can be directly used for the remediation of lightly polluted farmland soil without the need for additional pH adjusters or repeated replenishment of microbial agents.

[0027] Example 2 This embodiment uses the lower limit of the parameter range defined in the claims to prepare the rinsing agent, which is specifically divided into 4 steps: S1. Preparation of carboxylated modified fulvic acid: Take 100g of commercially available mineral fulvic acid, add deionized water to prepare a suspension with a mass fraction of 10wt%, pass high-purity nitrogen gas to remove oxygen for 30min, add 0.65g of ammonium persulfate initiator, heat to 55℃ in a water bath, add 20g of acrylic acid monomer dropwise at a uniform rate, keep the reaction at the temperature for 2.5h, cool to room temperature after the reaction is completed, adjust the pH of the system to 7.0 with 0.1mol / L sodium hydroxide solution, transfer to a dialysis bag with a molecular weight cutoff of 1000Da, dialyze for 3d to remove unreacted monomers and small molecule impurities, freeze-dry to obtain carboxylated modified fulvic acid with an acrylic acid grafting rate of 20%.

[0028] S2. Activation of carboxyl groups on the surface of modified fulvic acid: Take 100g of the above carboxylated modified fulvic acid, add 0.1mol / L phosphate buffer solution with pH 7.2 to prepare a suspension with a mass fraction of 8wt%, add 2.2g of carbodiimide activator, stir and activate at room temperature for 1.1h to obtain the activated modified fulvic acid suspension.

[0029] S3. Covalently cross-linked functional bacteria: Add a sphingomonas suspension with a concentration of 1×10^10 CFU / mL to the activated modified fulvic acid suspension to control the final functional bacteria loading to 3×10^8 CFU / g modified fulvic acid. Stir the reaction at room temperature for 3.2 h, centrifuge at 4000 r / min for 10 min to collect the solid product, and wash it three times with 0.1 mol / L phosphate buffer to remove unbound free bacteria, thus obtaining modified fulvic acid loaded with functional bacteria.

[0030] S4. Preparation of the finished rinsing agent by multi-component compounding: The modified humic acid, rhamnolipin and deionized water loaded with the above functional bacteria are mixed in a mass ratio of 80:7:13 and stirred at room temperature for 30 minutes until the system is uniform to obtain the rinsing agent of Example 2.

[0031] After the leaching agent in this embodiment is prepared, it can be directly used for the remediation of moderately polluted farmland soil without the need to add additional pH adjusters or repeatedly replenish the bacterial agent.

[0032] Example 3 This embodiment uses the upper limit of the parameter range defined in the claims to prepare the rinsing agent, which is specifically divided into 4 steps: S1. Preparation of carboxylated modified fulvic acid: Take 100g of commercially available mineral fulvic acid, add deionized water to prepare a suspension with a mass fraction of 10wt%, pass high-purity nitrogen gas to remove oxygen for 30min, add 0.85g of ammonium persulfate initiator, heat to 62℃ in a water bath, add 25g of acrylic acid monomer dropwise at a uniform rate, keep the reaction at this temperature for 3.5h, cool to room temperature after the reaction is complete, adjust the pH of the system to 7.0 with 0.1mol / L sodium hydroxide solution, transfer to a dialysis bag with a molecular weight cutoff of 1000Da, dialyze for 3d to remove unreacted monomers and small molecule impurities, freeze-dry to obtain carboxylated modified fulvic acid with an acrylic acid grafting rate of 25%.

[0033] S2. Activation of carboxyl groups on the surface of modified fulvic acid: Take 100g of the above carboxylated modified fulvic acid, add 0.1mol / L phosphate buffer solution with pH 7.2 to prepare a suspension with a mass fraction of 8wt%, add 2.7g of carbodiimide activator, stir and activate at room temperature for 1.4h to obtain the activated modified fulvic acid suspension.

[0034] S3. Covalently cross-linked functional bacteria: Burkholderia suspension with a concentration of 1×10^10 CFU / mL was added to the activated modified fulvic acid suspension to control the final functional bacteria loading to 8×10^8 CFU / g modified fulvic acid. The mixture was stirred at room temperature for 3.8 h, centrifuged at 4000 r / min for 10 min to collect the solid product, and washed three times with 0.1 mol / L phosphate buffer to remove unbound free bacteria, thus obtaining modified fulvic acid loaded with functional bacteria.

[0035] S4. Preparation of the finished rinsing agent by multi-component compounding: The modified humic acid, rhamnolipin and deionized water loaded with the above functional bacteria are mixed in a mass ratio of 77:10:13 and stirred at room temperature for 30 minutes until the system is uniform to obtain the rinsing agent of Example 3.

[0036] After the leaching agent in this embodiment is prepared, it can be directly used for soil remediation of moderately polluted decommissioned industrial and mining sites without the need for additional pH adjusters or repeated replenishment of bacterial agents.

[0037] Example 4 This embodiment uses the upper limit of the parameter range defined in the claims to prepare the rinsing agent, and specifically consists of 4 steps: S1. Preparation of carboxylated modified fulvic acid: Take 100g of commercially available mineral fulvic acid, add deionized water to prepare a suspension with a mass fraction of 10wt%, purge with high-purity nitrogen for 30min to remove oxygen, add 1g of ammonium persulfate initiator, heat to 65℃ in a water bath, add 30g of acrylic acid monomer dropwise at a uniform rate, keep the reaction at this temperature for 4h, cool to room temperature after the reaction is complete, adjust the pH of the system to 7.0 with 0.1mol / L sodium hydroxide solution, transfer to a dialysis bag with a molecular weight cutoff of 1000Da, dialyze for 3d to remove unreacted monomers and small molecule impurities, freeze-dry to obtain carboxylated modified fulvic acid with an acrylic acid grafting rate of 30%.

[0038] S2. Activation of carboxyl groups on the surface of modified fulvic acid: Take 100g of the above carboxylated modified fulvic acid, add 0.1mol / L phosphate buffer solution with pH 7.2 to prepare a suspension with a mass fraction of 8wt%, add 3g of carbodiimide activator, stir and activate at room temperature for 1.5h to obtain the activated modified fulvic acid suspension.

[0039] S3. Covalently cross-linked functional bacteria: Add an equal volume of Pseudomonas and Sphingosine monocytogenes mixed bacterial suspension at a concentration of 1×10^10 CFU / mL to the above activated modified fulvic acid suspension. Control the final functional bacteria loading to 1×10^9 CFU / g modified fulvic acid. Stir the reaction at room temperature for 4 hours, centrifuge at 4000 r / min for 10 min to collect the solid product, and wash it 3 times with 0.1 mol / L phosphate buffer to remove unbound free bacteria, thus obtaining modified fulvic acid loaded with functional bacteria.

[0040] S4. Preparation of the finished leaching agent by multi-component compounding: The modified humic acid, rhamnolipid, and deionized water loaded with the above-mentioned functional bacteria were mixed at a mass ratio of 75:12:13 and stirred at room temperature for 30 minutes until the system was homogeneous, thus obtaining the leaching agent of Example 4. After the leaching agent of this example is prepared, it can be directly used for soil remediation of heavily polluted decommissioned industrial and mining sites without the need for additional pH adjusters or repeated replenishment of bacterial agents.

[0041] Comparative Example This comparative example was prepared using a conventional bio-based leaching agent formulation described in the background section, without carboxyl activation or covalent cross-linking steps, fully conforming to the logic of existing technology. It is used to compare and verify the technical effect of the present invention with the examples. The specific steps are as follows: 100g of unmodified mineral-derived fulvic acid was added to a 0.1mol / L phosphate buffer solution with a pH of 7.2 to prepare a suspension with a mass fraction of 8wt%. Burkholderia bacterial suspension with a concentration of 1×10^10 CFU / mL was added, controlling the total functional bacterial content of the system to be 8×10^8 CFU / g of total components. Rhamnolipid and deionized water were added, controlling the mass ratio of unmodified fulvic acid, rhamnolipid, and deionized water to be 77:10:13. The mixture was stirred at room temperature for 30 minutes until homogeneous, obtaining the leaching agent of the comparative example. Core reaction molecular formula and explanation. Fulvic acid-acrylic acid grafting modification reaction: ; FA represents the molecular skeleton of fulvic acid. This reaction introduces a large number of carboxyl side chains onto the fulvic acid molecule through free radical grafting, which increases the number of active functional groups of fulvic acid by more than 2 times, enhances the chelation of heavy metals and the solubilization ability of polycyclic aromatic hydrocarbons, and directly solves the defects of insufficient active sites and low removal efficiency of complex pollutants in existing unmodified fulvic acid.

[0042] Carboxyl group activation and functional bacteria cross-linking and immobilization reaction: ; EDC represents carbodiimide activator, and Protein-NH2 represents the amino group on the surface of functional bacteria. This reaction covalently fixes functional bacteria onto the modified fulvic acid carrier through amide bonds, avoiding bacterial loss caused by water rinsing during the rinsing process. At the same time, the spatial protection effect of the carrier reduces the toxic inhibition of pollutants on functional bacteria, directly solving the defect of low survival rate of existing free functional bacteria.

[0043] Rinse performance test method The soil samples used for testing were divided into three groups: a lightly polluted farmland with a background pH of 5.5, a cadmium content of 6.2 mg / kg, and a total polycyclic aromatic hydrocarbon (PAH) content of 187 mg / kg; a moderately polluted industrial and mining site with a background pH of 6.8, a cadmium content of 12.7 mg / kg, and a total PAH content of 423 mg / kg; and a heavily polluted industrial and mining site with a background pH of 8.5, a cadmium content of 21.4 mg / kg, and a total PAH content of 679 mg / kg. All soil samples were air-dried, sieved through a 2 mm sieve, and then sealed and stored for later use.

[0044] Leaching test procedure: Weigh 100g of contaminated soil into an Erlenmeyer flask, add leaching agent at a soil-to-water ratio of 1:5, rinse at 25℃ and 180r / min for 2h with shaking, let stand for 30min, then centrifuge at 4000r / min for 10min to separate the soil from the leaching solution.

[0045] The detection indicators and methods are as follows: the residual cadmium content in the soil was detected by graphite furnace atomic absorption spectrophotometry according to GB / T 17141-1997; the residual polycyclic aromatic hydrocarbon content in the soil was detected by gas chromatography-mass spectrometry according to HJ 805-2016, and the corresponding removal rate was calculated; the pH of the soil after leaching was detected by potentiometric method, and the absolute value of the difference between the pH and the background pH was calculated; the survival rate of functional bacteria was detected by plate counting method, and the ratio of the number of surviving bacteria after leaching to the number of bacteria initially added was calculated; the residual recalcitrant components in the soil after leaching were detected by the total organic carbon difference method, and the proportion of exogenous residues was calculated.

[0046] Test data table and explanation Table 1 Key parameters for sample preparation This table clarifies the differences in the core preparation parameters of each sample. Examples 1 to 4 completely cover all parameter ranges defined in the claims. The functional bacterial species cover commonly used strains that are tolerant to heavy metals and degrade polycyclic aromatic hydrocarbons. Except for the fulvic acid modification method and the activation crosslinking step, the parameters of the comparative example are completely consistent with those of Example 3, eliminating the interference of irrelevant variables and ensuring the comparability of experimental results.

[0047] Table 2 Comparison of the effects of rinsing on neutrally and moderately polluted industrial and mining sites This table presents the leaching performance test results for neutral to moderately contaminated sites. The simultaneous removal rates of cadmium and polycyclic aromatic hydrocarbons in the examples are more than twice that of the comparative examples, proving that the active groups of modified fulvic acid effectively improve the removal efficiency of complex pollutants and solve the defect of low removal efficiency of existing bio-based leaching agents. The survival rate of functional bacteria in the examples is higher than 80%, which is much higher than 22.3% in the comparative examples, proving that covalent cross-linking loading effectively avoids the loss and activity inhibition of functional bacteria and solves the defect of low survival rate of free bacteria. The pH change after rinsing in the examples was less than 0.3, much smaller than the 1.2 in the comparative example, proving that the modified fulvic acid buffer system effectively stabilized the pH of the rinsing system and solved the defect of poor pH compatibility of existing rinsing agents; all examples had no exogenous recalcitrant component residues and no risk of secondary pollution, solving the defect of secondary pollution of chemical rinsing agents.

[0048] Table 3 Comparison of rinsing effects on contaminated sites with different background pH levels This table presents the adaptability of the leaching agent to contaminated sites with different background pH levels. In Examples 3 and 4, the removal rates of cadmium and polycyclic aromatic hydrocarbons fluctuated by less than 5% in acidic and alkaline sites, demonstrating stable performance. In the comparative example, the pollutant removal rate decreased by more than 30% in sites deviating from neutral, indicating that performance was significantly affected by pH. The test results prove that the modified humic acid buffer system of this invention can adapt to contaminated sites with different pH levels without the need for additional pH adjusters, thus solving the defects of existing leaching agents with poor pH adaptability and the need for repeated formula adjustments.

[0049] refer to Figure 2 This figure visually illustrates the differences in the simultaneous removal efficiency of composite pollutants between four embodiments and existing conventional leaching agents. The removal rates of cadmium and polycyclic aromatic hydrocarbons (PAHs) in all embodiments are 2.7-3.7 times that of the comparative examples, demonstrating significant performance advantages. Test results prove that this invention, through acrylic acid grafting modification, significantly increases the number of active functional groups in fulvic acid, simultaneously enhancing the chelation of heavy metals and the solubilization capacity of PAHs. This effectively solves the deficiency of low simultaneous removal efficiency of composite pollutants in existing conventional bio-based leaching agents, and can meet the remediation needs of sites with different levels of contamination.

[0050] refer to Figure 3 This figure illustrates the performance stability differences of the two types of leaching agents in different pH environments. The leaching agent of this invention exhibits a total removal rate fluctuation of less than 7% within the pH range of 5.0-9.0, demonstrating stable performance. In contrast, conventional leaching agents show a total removal rate decrease of over 50% in environments deviating from neutral, indicating significant pH limitation. Test results demonstrate that the modified humic acid of this invention possesses a carboxyl-phenolic hydroxyl buffer system, which can stabilize the pH of the leaching system. It can be adapted to various environments without the need for additional pH adjusters, effectively solving the shortcomings of existing leaching agents, such as poor pH compatibility and the need for repeated formulation adjustments.

[0051] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A special leaching agent for soil contaminated with a composite of organic matter and heavy metals, characterized in that, The product is composed of the following components by weight: 28-32 parts of thiol-amide double-grafted modified mineral fulvic acid, 14-16 parts of biodegradable chelating agent, 9-11 parts of rhamnolipin-sophorolipid compound biosurfactant, 4-6 parts of double-layer encapsulated salt-tolerant composite functional bacterial agent, 4.5-5.5 parts of citric acid-sodium citrate pH buffer regulator, and 29-40.5 parts of deionized water; The carboxyl content of the thiol-amide double-grafted modified mineral fulvic acid is ≥14mmol / g. The double-layer encapsulated salt-tolerant composite functional bacterial agent is a bacterial agent obtained by mixing Pseudomonas, Bacillus subtilis and Aspergillus niger in a viable ratio of 2:2:1 and then encapsulating them in a sodium alginate-chitosan double layer, with a total viable count ≥3×10^9 CFU / g.

2. The synergistic leaching agent for organic and heavy metal contaminated soil according to claim 1, characterized in that, The biodegradable chelating agent is a composition obtained by compounding polyaspartic acid and tetrasodium glutamate diacetate at a mass ratio of 1:1.2~1.

5.

3. The synergistic enhanced leaching agent for organic and heavy metal contaminated soil according to claim 1 or 2, characterized in that, The rhamnolipin-sophorolipid compound biosurfactant is a composition obtained by compounding rhamnolipin and sophorolipid at a mass ratio of 1:0.8~1, with a critical micelle concentration ≤30mg / L.

4. The synergistic enhanced leaching agent for organic and heavy metal contaminated soil according to any one of claims 1 to 3, characterized in that, The pH of the citric acid-sodium citrate pH buffer system is adjusted to 6.0~6.

5.

5. The synergistic enhanced leaching agent for organic and heavy metal contaminated soil according to any one of claims 1 to 4, characterized in that, The number-average molecular weight of the thiol-amide double-grafted modified mineral fulvic acid is 1200~1800 Da, the thiol grafting rate is ≥8%, and the amide grafting rate is ≥10%. The double-layered encapsulated salt-tolerant composite functional bacterial agent has an encapsulation rate of ≥92% and a strain salt tolerance concentration of ≥1.8wt%. The leaching agent has a water-insoluble content of ≤0.08wt%, is diluted 300-400 times, has a leaching rate of ≥72% for polycyclic aromatic hydrocarbons, a leaching rate of ≥78% for heavy metals such as cadmium, lead, and copper, and increases soil organic matter by ≥3g / kg after leaching.

6. A method for preparing a synergistic leaching agent for soil contaminated with organic matter and heavy metals, used to prepare the synergistic leaching agent for soil contaminated with organic matter and heavy metals as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Disperse mineral-derived fulvic acid into a suspension of 12-13 wt%, oxidize it with hydrogen peroxide and irradiate it with γ-rays in sequence, add mercaptoacetic acid and acrylamide to carry out a grafting reaction, purify and dry to obtain double-grafted modified mineral-derived fulvic acid. S2. Salt-tolerant Pseudomonas, Bacillus subtilis and Aspergillus niger are mixed in proportion, double-layered encapsulation is performed using sodium alginate-chitosan, and then dried to obtain a salt-tolerant composite functional bacterial agent. S3. Add the pH buffer adjuster to deionized water and stir to dissolve. Then add the biodegradable chelating agent and the compounded biosurfactant in sequence and stir to obtain the basic mixture. S4. After dissolving the double-grafted modified mineral fulvic acid in the base mixture, cool it to 22~24℃, add salt-tolerant compound functional bacteria agent, mix at low speed with nitrogen, and then seal and fill to obtain the finished product.

7. The preparation method according to claim 6, characterized in that, In S1, the amount of hydrogen peroxide added is 3% of the mass of the suspension, the gamma ray irradiation dose is 7~8kGy, the amount of mercaptoacetic acid and acrylamide added is 6~8% and 9~11% of the dry weight of mineral fulvic acid, respectively, the grafting reaction temperature is 40~45℃, and the reaction time is 2h.

8. The preparation method according to claim 6, characterized in that, The salt tolerance acclimatization gradient of strain S2 is 0.4wt%, 0.8wt%, 1.2wt%, and 1.6wt%, with each concentration gradient being passaged 3 times, and the total concentration of the double-layer embedded wall material is 2.5~3wt%.

9. The preparation method according to claim 6, characterized in that, In S3, the stirring temperature is 35~38℃, the stirring speed is 250r / min, the stirring time is 25min, and the pH of the basic mixture is controlled at 6.0~6.

5.

10. The preparation method according to claim 6, characterized in that, The S4 medium-low speed stirring speed is 80 r / min, the stirring time is 12 min, the nitrogen purity is ≥99.9%, and the viable bacteria retention rate of the finished product is ≥88% after 6 months of storage at room temperature.

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