Method for repairing polluted soil through chemical leaching

Abstract

The invention discloses a method for repairing polluted soil through chemical leaching, and relates to the technical field of soil repairing, the method comprises the following steps: pretreating the polluted soil, preparing a composite leaching agent, mixing the pretreated soil and the composite leaching agent according to a solid-liquid mass volume ratio, carrying out synergistic physical field treatment on the mixed system, and after the treatment is completed, carrying out chemical leaching to repair the polluted soil. The method has the advantages that the potassium phosphate solution is adopted as the eluting agent, molybdate ions immobilized on the surfaces of soil particles are directionally released through the ion replacement effect, and the remedied soil can be directly used for agricultural production; the problems that soil fertility is reduced and reclamation cannot be achieved due to a traditional leaching technology are effectively solved, the contact efficiency of a leaching agent and soil particles can be remarkably enhanced through ultrasonic-assisted treatment, the remediation period is shortened, the operation convenience is improved through flexible selection of oscillation multiple times of leaching, and the remediation requirements of contaminated soil of different scales are met.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, specifically to a method for chemical leaching to remediate contaminated soil. Background Technology

[0002] Heavy metal pollution in soil is a major challenge for global environmental governance. Among them, molybdenum pollution has gradually attracted attention due to its hidden nature and cumulative effects. As an essential trace element for plants, animals and humans, molybdenum is crucial for the metabolism of organisms when present in appropriate amounts. However, excessive amounts can accumulate through the food chain and harm ecosystems and human health. With the intensification of molybdenum mining and smelting activities, the molybdenum content in farmland soils around mining areas often far exceeds the background value of molybdenum in my country's soils. In some areas, it is even as high as 2292 mg / kg, leading to reduced crop yields and decreased quality, directly threatening food safety and human health.

[0003] Existing technologies for remediating molybdenum-contaminated soil mainly include phytoremediation, chemical leaching, and passivation. Among these, chemical leaching has been widely studied due to its ability to rapidly and permanently remove pollutants. However, existing technologies still have significant drawbacks. For example, when using trisodium phosphate as a leaching agent, even after three consecutive shaking leaches, the molybdenum removal rates are only 12.93%, 11.12%, and 17.66%, respectively, which is inefficient and increases leaching costs. At the same time, traditional leaching agents easily damage the soil structure, leading to a decline in soil fertility after remediation and making it difficult to reclaim and reuse the soil. Therefore, developing efficient, low-cost, and soil-friendly molybdenum-contaminated remediation technologies has become an urgent research need. To this end, we propose a method for chemical leaching to remediate contaminated soil. Summary of the Invention

[0004] The purpose of this invention is to provide a method for chemical leaching to remediate contaminated soil.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for chemically leaching contaminated soil remediation, comprising a remediation method, wherein the remediation method includes the following steps:

[0006] The contaminated soil is pretreated by adding a pH adjuster and biochar to adjust the soil pH to 5.0-7.0 and mixing them evenly.

[0007] A composite rinsing agent is prepared, wherein the composite rinsing agent comprises potassium phosphate solution and biochar particles;

[0008] The pretreated soil and the composite leaching agent were mixed according to the solid-liquid mass-volume ratio to obtain a mixed system.

[0009] The mixed system is subjected to synergistic physical field treatment, which includes alternating mechanical stirring and intermittent ultrasonic treatment;

[0010] After treatment, the mixed system is subjected to solid-liquid separation to obtain the remediated soil and waste liquid;

[0011] The waste liquid is treated by rinsing agent recovery to obtain regenerated rinsing agent.

[0012] As a further aspect of the present invention: the pH adjuster is a citric acid solution, and the amount added is 0.1%-0.5% of the soil mass; the biochar is straw biochar, and the amount added is 2%-5% of the soil mass; the stirring speed during the pretreatment process is 150-200 r / min, and the pretreatment time is 30-60 minutes.

[0013] As a further aspect of the present invention: the concentration of potassium phosphate solution in the composite rinsing agent is 0.3-0.5 mol / L, the particle size of biochar particles is 0.1-0.5 mm, the addition ratio of biochar particles in the composite rinsing agent is 5-10 g / L, and the stirring time during the preparation of the composite rinsing agent is 20-30 minutes.

[0014] As a further aspect of the present invention: the solid-liquid mass-volume ratio is 1:3-1:5 g / mL, and during the mixing process, the mixture is stirred at 180-220 r / min for 10-15 minutes, and the temperature of the mixing system is controlled at 25-40℃.

[0015] As a further aspect of the present invention: the power of the mechanical stirring is 150-250W, the stirring time is 15-25 minutes, and the insertion depth of the stirring paddle is 1 / 2-2 / 3 of the height of the mixing system.

[0016] As a further aspect of the present invention: the power of the intermittent ultrasonic treatment is 300-500W, the ultrasonic frequency is 30-50KHz, the single ultrasonic working time is 10-15 minutes, the pause time is 5-8 minutes, and the total ultrasonic duration is 20-40 minutes.

[0017] As a further aspect of the present invention: the total time for the synergistic physical field treatment is 40-60 minutes, and the pH value of the mixed system is monitored every 10-15 minutes during the treatment to ensure that the pH is maintained within the range of 5.0-7.0.

[0018] As a further aspect of the present invention: the solid-liquid separation is carried out by centrifugation, with a centrifugation speed of 4000-6000 r / min and a centrifugation time of 8-12 minutes. After separation, the remediated soil is naturally air-dried to a moisture content of 15%-20%.

[0019] As a further aspect of the present invention: the rinsing agent recovery treatment includes adding 0.1 mol / L sodium chloride solution to the waste liquid, stirring for 30-40 minutes, allowing it to stand and precipitate, and separating to obtain regenerated rinsing agent, which can be recycled 2-3 times.

[0020] Compared with the prior art, the beneficial effects of the present invention by adopting the above technical solution are as follows:

[0021] 1. This invention achieves synergistic improvement in the efficient remediation and soil property protection of molybdenum-contaminated soil by optimizing the selection of leaching agents and auxiliary treatment methods. Potassium phosphate solution is used as the leaching agent, which releases molybdate ions fixed on the surface of soil particles through ion exchange, avoiding damage to the soil colloidal structure, organic matter and microbial community. The remediated soil can be directly used for agricultural production, effectively solving the problem of soil fertility decline and inability to be reclaimed caused by traditional leaching technology. At the same time, ultrasonic-assisted treatment can significantly enhance the contact efficiency between the leaching agent and soil particles and shorten the remediation cycle. The flexible selection of multiple oscillation leaching can adjust the treatment method according to the actual needs of the scenario, improve the convenience of operation and meet the remediation needs of contaminated soil of different scales.

[0022] 2. This invention achieves efficient remediation while also offering advantages in resource utilization and cost optimization. The potassium phosphate leaching agent not only eliminates the risk of secondary pollution, but its phosphorus and potassium elements can directly replenish soil nutrients and improve soil fertility, making it particularly suitable for the remediation of agriculturally polluted soils and reducing subsequent soil improvement inputs. Furthermore, by controlling the concentration of potassium phosphate solution, the solid-liquid ratio, and auxiliary treatment parameters, the amount of leaching agent can be reduced while ensuring the remediation effect. Combined with the substitution effect of multiple oscillating leaching for ultrasonic treatment, it reduces reliance on high-power equipment, lowers energy consumption and equipment investment costs, and forms an integrated technical solution of "remediation-fertilization-cost reduction," significantly improving the economic feasibility and promotion value of this method. Attached Figure Description

[0023] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0024] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that the description of these embodiments is for the purpose of helping to understand the present invention, but does not constitute a limitation of the present invention.

[0025] Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] Please see the appendix Figure 1 This invention discloses a method for chemically leaching to remediate contaminated soil, comprising the following steps:

[0027] The contaminated soil is pretreated by adding a pH adjuster and biochar to adjust the soil pH to 5.0-7.0 and mixing them thoroughly.

[0028] A composite rinsing agent was prepared, comprising potassium phosphate solution and biochar particles;

[0029] The pretreated soil and the composite leaching agent were mixed according to the solid-liquid mass-volume ratio to obtain a mixed system.

[0030] The mixed system is subjected to synergistic physical field treatment, which includes alternating mechanical stirring and intermittent ultrasonic treatment;

[0031] After treatment, the mixed system is subjected to solid-liquid separation to obtain the remediated soil and waste liquid;

[0032] The waste liquid is treated by rinsing agent recovery to obtain regenerated rinsing agent.

[0033] In one embodiment of the present invention: the pH adjuster is citric acid solution, and the amount added is 0.1%-0.5% of the soil mass; the biochar is straw biochar, and the amount added is 2%-5% of the soil mass; the stirring speed during the pretreatment process is 150-200 r / min; and the pretreatment time is 30-60 minutes.

[0034] In one embodiment of the present invention: the concentration of potassium phosphate solution in the composite rinsing agent is 0.3-0.5 mol / L, the particle size of biochar particles is 0.1-0.5 mm, the addition ratio of biochar particles in the composite rinsing agent is 5-10 g / L, and the stirring time during the preparation of the composite rinsing agent is 20-30 minutes.

[0035] In one embodiment of the present invention: the solid-liquid mass-volume ratio is 1:3-1:5 g / mL, and during the mixing process, the mixture is stirred at 180-220 r / min for 10-15 minutes, and the temperature of the mixing system is controlled at 25-40℃.

[0036] In one embodiment of the present invention: the power of the mechanical stirring is 150-250W, the stirring time is 15-25 minutes, and the insertion depth of the stirring paddle is 1 / 2-2 / 3 of the height of the mixing system.

[0037] In one embodiment of the present invention: the power of the intermittent ultrasonic treatment is 300-500W, the ultrasonic frequency is 30-50KHz, the single ultrasonic working time is 10-15 minutes, the pause time is 5-8 minutes, and the total ultrasonic duration is 20-40 minutes.

[0038] In one embodiment of the present invention: the total time for synergistic physical field treatment is 40-60 minutes, and the pH value of the mixed system is monitored every 10-15 minutes during the treatment to ensure that the pH is maintained within the range of 5.0-7.0.

[0039] In one embodiment of the present invention: solid-liquid separation is performed by centrifugation, with a centrifugation speed of 4000-6000 r / min and a centrifugation time of 8-12 minutes. After separation, the remediated soil is naturally air-dried to a moisture content of 15%-20%.

[0040] In one embodiment of the present invention: the rinsing agent recovery treatment includes adding 0.1 mol / L sodium chloride solution to the waste liquid, stirring for 30-40 minutes, allowing it to stand and precipitate, and separating to obtain regenerated rinsing agent, which can be recycled 2-3 times.

[0041] Example 1: Sound-assisted chemical leaching for the remediation of high-concentration molybdenum-contaminated clay soil

[0042] I. Soil Sample Preparation

[0043] Soil samples were collected from the topsoil (0-20cm) of farmland surrounding a molybdenum mining area. The molybdenum content was 2292 mg / kg, and the soil texture was clay loam (35% clay, 20% sand, and 2.8% organic matter). The soil was air-dried naturally (at room temperature of 25℃ and under ventilation for 7 days). After removing impurities such as stones and plant residues, the soil was ground in an agate mortar and pestle, passed through a 2.0mm nylon sieve (sieve aperture size 2.0mm, sieve material nylon 66), packed into polyethylene self-sealing bags (10cm×15cm), and stored in a desiccator (relative humidity 40%) for no more than 15 days.

[0044] II. Preparation of Compound Rinsing Agent

[0045] 1. Reagent preparation: Weigh 165.4g of analytical grade potassium phosphate (K3PO4, purity ≥99.0%), place it in a 500mL beaker, add 300mL of deionized water (conductivity ≤10μS / cm), and stir with a glass rod until completely dissolved (stirring speed 300r / min, stirring time 5min);

[0046] 2. Volume adjustment: Transfer the above solution to a 1000mL volumetric flask, rinse the beaker three times with deionized water (50mL each time), transfer the washings to the volumetric flask, add deionized water to the mark, shake well to obtain a 0.6mol / L potassium phosphate solution, seal and store in a brown reagent bottle (refrigerate at 4℃, storage time not exceeding 7 days).

[0047] III. Soil and Leaching Agent Mixing

[0048] 1. Weighing and adding solution: Weigh 5.00g of the pretreated soil sample using an electronic balance (accuracy 0.01g) and place it in a 100mL polytetrafluoroethylene centrifuge tube (100mL specification, with a sealing cap). According to the solid-liquid mass-volume ratio of 1:3g / mL, accurately transfer 15.0mL of 0.6mol / L potassium phosphate solution using a pipette (range 20mL, accuracy 0.1mL) and slowly add it to the centrifuge tube.

[0049] 2. Preliminary mixing: Place the centrifuge tube on a vortex mixer (model XW-80A), set the speed to 2500 r / min, and mix for 30 seconds to allow the soil and leaching agent to come into initial contact and form a uniform suspension system (without obvious soil clumping).

[0050] IV. Ultrasound-assisted treatment

[0051] 1. Equipment debugging: Select a CNC ultrasonic cleaner (model KQ-800DE, power adjustable range 0~800W, frequency 40KHz), add deionized water to the ultrasonic tank to the liquid level line (15cm from the bottom of the tank), set the ultrasonic temperature to room temperature (25℃, no additional heating), and preheat for 5 minutes.

[0052] 2. Ultrasonic treatment: Place the centrifuge tube containing the mixed system into the special support of the ultrasonic tank (ensure that the bottom of the centrifuge tube is 5cm away from the bottom of the ultrasonic tank), set the ultrasonic power to 800W, the ultrasonic time to 10min, start the ultrasonic instrument, and observe the status of the centrifuge tube every 2min during the treatment to ensure that the suspended system does not overflow or separate.

[0053] V. Solid-Liquid Separation and Soil Post-treatment

[0054] 1. Centrifugation: After ultrasonic treatment, immediately place the centrifuge tubes in a high-speed benchtop centrifuge (model TGL-16M), set the speed to 5000 r / min, centrifugation time to 10 min (centrifugal acceleration 3900×g), and after centrifugation, slowly pour off the supernatant with a pipette (avoid carrying out soil particles) and collect the lower layer of soil residue.

[0055] 2. Soil washing: Add 20 mL of deionized water to a centrifuge tube, mix at 2000 r / min for 1 min on a vortex mixer, repeat centrifugation (5000 r / min, 5 min), and discard the washing liquid. The purpose of this step is to remove residual leaching agent from the soil surface.

[0056] 3. Drying and storage: Transfer the washed soil to a ceramic evaporating dish (6cm in diameter), place it in a forced-air drying oven (model DHG-9070A), set the temperature to 40℃, and dry until constant weight (weigh once every 2 hours, with the difference between two weighings ≤0.02g) to obtain the remediated soil.

[0057] VI. Testing the Treatment Effect

[0058] 1. Molybdenum content detection: 0.5g of remediated soil was weighed and digested with nitric acid-perchloric acid (volume ratio 3:1) (digestion temperature 180℃, digestion time 2h). After cooling, the volume was adjusted to 50mL with deionized water and filtered through a 0.45μm microporous membrane (polyethersulfone). The molybdenum concentration was detected by inductively coupled plasma mass spectrometry (ICP-MS 7900). The results showed that the molybdenum content of the remediated soil decreased to 847mg / kg, with a removal rate of 63.0%.

[0059] 2. Soil property testing: The pH value of the remediated soil was measured to be 6.8 (original soil pH 6.7) using a pH meter (model PHS-3C), with a variation range of ≤0.2. Soil particle distribution was analyzed using a laser particle size analyzer (model Mastersizer 3000), with changes in clay and sand content of ≤2%. The organic matter content was determined to be 2.7% (original soil 2.8%) using the potassium dichromate oxidation-external heating method, with no significant loss. The soil structure remained intact, with no compaction.

[0060] Example 2: Oscillation-assisted multiple leaching remediation of medium-concentration molybdenum-contaminated sandy soil (2 consecutive treatments)

[0061] I. Soil Sample Preparation

[0062] Soil samples (0-20cm) from dry land surrounding a molybdenum smelter were collected. The molybdenum content was 856 mg / kg, and the soil texture was sandy loam (sand content 60%, clay content 15%, organic matter content 1.5%). The soil pretreatment was the same as in Example 1: natural air drying (room temperature 28℃, ventilated for 5 days) → grinding → passing through a 2.0mm nylon sieve → storage in a desiccator for later use.

[0063] II. Preparation of rinsing agent

[0064] Same as Example 1: Weigh 165.4g of potassium phosphate → dissolve in 300mL of deionized water → bring the volume up to 1000mL → obtain a 0.6mol / L potassium phosphate solution, and store at 4℃.

[0065] III. First Shaking Rinse

[0066] 1. Weighing and adding solution: Weigh 5.00g of pretreated soil into a 100mL centrifuge tube, add 15.0mL of 0.6mol / L potassium phosphate solution at a solid-liquid ratio of 1:3g / mL, and mix with a vortex mixer at 2500r / min for 30s to form a suspension system;

[0067] 2. Constant temperature shaking: Place the centrifuge tubes in a constant temperature shaker (model THZ-300, temperature control accuracy ±0.5℃, speed accuracy ±5r / min), set the shaking temperature to 40℃, the speed to 210r / min, and the shaking time to 60min (tilt the centrifuge tubes at 45° during shaking to ensure that the solution is fully mixed).

[0068] 3. Centrifugation: After shaking, immediately transfer to a centrifuge and centrifuge at 5000 r / min for 10 min. Discard the supernatant (record the volume of the supernatant as 14.5 mL, with no obvious soil loss), and retain the soil residue.

[0069] IV. Second Shaking Rinse

[0070] 1. Second addition of liquid: Add 15.0 mL of fresh 0.6 mol / L potassium phosphate solution (with the same concentration and volume as the first leaching agent) to the centrifuge tube, and mix with a vortex mixer at 2500 r / min for 30 s to allow the soil residue and the new leaching agent to re-form a suspension system;

[0071] 2. Repeated shaking and separation: Same as the first operation, shake in a constant temperature shaker at 40℃ and 210r / min for 60min → centrifuge at 5000r / min for 10min → decan the supernatant and collect the soil residue;

[0072] 3. Soil washing and drying: Add 20 mL of deionized water to wash the soil residue, vortex mix for 1 min → centrifuge at 5000 r / min for 5 min → desiccate the washing liquid → dry at 40℃ with forced air until constant weight, to obtain the soil after secondary rinsing.

[0073] V. Testing the Treatment Effect

[0074] 1. Molybdenum content detection: The soil was digested and tested according to the method in Example 1. After remediation, the molybdenum content in the soil was reduced to 380 mg / kg, and the cumulative removal rate after two treatments was 55.6%.

[0075] 2. Soil property testing: After remediation, the soil pH was 6.5 (original soil pH 6.4), sand content was 61% (original soil 60%), and organic matter content was 1.4% (original soil 1.5%), all showing no significant changes. The soil bulk density, measured using a soil compaction meter (model SC-900), was 1.3 g / cm³. 3 (Original soil 1.3g / cm³) 3 Porosity 45% (original soil 46%), permeability coefficient 1.2×10⁻⁶ -4 m / s (original soil 1.1×10 -4The measured m / s indicates that the soil physical structure is stable and meets the requirements for dryland crop cultivation. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make possible variations and modifications without departing from the spirit and scope of the invention. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solution of the present invention, fall within the protection scope defined by the claims of the present invention.

Claims

1. A method of remediating contaminated soil by chemical elution, comprising a remediation method, characterised in that: The repair method comprises the following steps: The contaminated soil is pretreated, and the pretreatment comprises adding a pH regulator and biochar into the soil, adjusting the pH of the soil to 5.0-7.0 and mixing uniformly; A composite leaching agent is prepared, and the composite leaching agent comprises a potassium phosphate solution and biochar particles; The pretreated soil and the composite leaching agent are mixed to obtain a mixed system according to a solid-liquid mass / volume ratio; The mixed system is subjected to a synergistic physical field treatment, and the synergistic physical field treatment comprises alternating mechanical stirring and intermittent ultrasonic treatment; After the treatment is completed, the mixed system is subjected to solid-liquid separation to obtain repaired soil and waste liquid; The waste liquid is subjected to leaching agent recovery treatment to obtain regenerated leaching agent.

2. A method of remediating contaminated soil by chemical elution according to claim 1, characterized in that: The pH regulator is a citric acid solution, and the addition amount is 0.1%-0.5% of the mass of the soil; the biochar is straw biochar, and the addition amount is 2%-5% of the mass of the soil; the stirring speed during the pretreatment process is 150-200 r / min, and the pretreatment time is 30-60 minutes.

3. A method of remediating contaminated soil by chemical elution according to claim 1, characterized in that: The concentration of the potassium phosphate solution in the composite leaching agent is 0.3-0.5 mol / L, the particle size of the biochar particles is 0.1-0.5 mm, the addition ratio of the biochar particles in the composite leaching agent is 5-10 g / L, and the stirring time during the preparation of the composite leaching agent is 20-30 minutes.

4. A method of remediating contaminated soil by chemical elution according to claim 1, characterized in that: The solid-liquid mass / volume ratio is 1:3-1:5 g / mL, and during the mixing process, stirring is first performed at 180-220 r / min for 10-15 minutes; and the temperature of the mixed system is controlled to be 25-40 DEG C.

5. A method of remediating contaminated soil by chemical elution according to claim 1, characterized in that: The power of the mechanical stirring is 150-250 W, the stirring time is 15-25 minutes, and the insertion depth of the stirring paddle is 1 / 2-2 / 3 of the height of the mixed system.

6. A method of remediating contaminated soil by chemical elution according to claim 1, characterized in that: The power of the intermittent ultrasonic treatment is 300-500 W, the ultrasonic frequency is 30-50 KHz, the single ultrasonic working time is 10-15 minutes, the pause time is 5-8 minutes, and the total ultrasonic time length is 20-40 minutes.

7. A method of remediating contaminated soil by chemical elution according to claim 1, characterized in that: The total time of the synergistic physical field treatment is 40-60 minutes, and during the treatment process, the pH value of the mixed system is monitored every 10-15 minutes to ensure that the pH is maintained in the range of 5.0-7.

0.

8. A method of remediating contaminated soil by chemical elution according to claim 1, characterized in that: The solid-liquid separation is performed in a centrifugal separation mode, the centrifugal speed is 4000-6000 r / min, and the centrifugal time is 8-12 minutes; after the separation, the repaired soil is naturally air-dried to a water content of 15%-20%.

9. A method of remediating contaminated soil by chemical elution according to claim 1, characterized in that: The leaching agent recovery treatment comprises adding a 0.1 mol / L sodium chloride solution into the waste liquid, stirring for 30-40 minutes and then standing for precipitation, so as to separate the regenerated leaching agent; and the regenerated leaching agent can be recycled for 2-3 times.

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