CN110899323A

CN110899323A - Method for restoring farmland heavy metal contaminated soil by combining chemical leaching and phytoremediation

Info

Publication number: CN110899323A
Application number: CN201911374254.9A
Authority: CN
Inventors: 毕德; 王青玲; 刘原彬
Original assignee: Nanjing Civil Engineering Suzhou Environmental Rehabilitation Technology Co Ltd
Current assignee: Nanjing Civil Engineering Suzhou Environmental Rehabilitation Technology Co Ltd
Priority date: 2019-12-27
Filing date: 2019-12-27
Publication date: 2020-03-24

Abstract

The invention discloses a method for restoring farmland heavy metal polluted soil by combining chemical leaching and phytoremediation, which comprises the following steps: mixing the heavy metal contaminated farmland soil with the leacheate, and uniformly stirring; and adding a modifier into the heavy metal contaminated soil obtained after stirring, mixing, and treating, wherein after the modification is finished, super-accumulator plants are planted to finish the restoration of the heavy metal contaminated soil of the farmland. The method of the invention combines the soil leaching and phytoremediation technologies, which can effectively reduce the content of heavy metals in the soil and the biological effectiveness of the residual heavy metals and leacheate in the soil, thereby effectively controlling the harm of the residual leacheate and the heavy metals in the soil. The method has the advantages of simple process, low repair cost, high practicability, good repair effect and the like.

Description

Method for restoring farmland heavy metal contaminated soil by combining chemical leaching and phytoremediation

Technical Field

The invention belongs to the technical field of heavy metal contaminated soil remediation, and relates to a method for remediating farmland heavy metal contaminated soil by combining chemical leaching and phytoremediation.

Background

The soil is a material foundation for human survival and development and is a root for social and economic development. With the rapid development of global economy, the heavy metal pollution problem of soil is increasingly highlighted by industrial production and human activities, and the heavy metal pollution problem becomes one of the restriction problems of agricultural sustainable development in China. According to the survey of national soil pollution conditions conducted by the ministry of environmental protection and the ministry of national soil resources, the total point standard exceeding rate of national soil is 16.1%, wherein the number of the inorganic pollutant point standard exceeding bits accounts for 82.8% of all the point standard exceeding rates, the inorganic pollutants are mainly heavy metal pollutants, and the national soil environment conditions are very severe. The heavy metal pollution of the soil not only destroys the ecological environment and reduces the crop yield, but also seriously harms the health of human body.

The chemical repair method mainly comprises two methods, namely, an immobilization stabilization method and a leaching method. The fixation and stabilization are realized by adding a stabilizer into the polluted soil, increasing the organic matter, cation exchange capacity, clay content and the like of the soil, or changing the physicochemical properties of the soil, such as oxidation-reduction potential, conductivity and the like, so that the effects of oxidation, reduction, precipitation, adsorption and the like of heavy metals in the soil are realized, and the aim of reducing the biological effectiveness of the heavy metals in the soil is fulfilled. The leaching method is to add chemical leaching agent to the heavy metal contaminated soil to react with the heavy metal, so that the heavy metal adsorbed and fixed on the soil surface particles and the leaching agent form soluble ions or metal-reagent complexes to achieve the purpose of removing the heavy metal. The key point of the leaching method is the selection of the leaching agent, the commonly used chemical leaching agent comprises a metal chelating agent, inorganic salts, a surfactant, an organic acid and the like, and compared with a fixed stable method, the leaching method is more thorough and safer and is a permanent heavy metal restoration measure. In addition, the leaching method has high efficiency of removing heavy metals, quick effect, large treatment capacity and low cost, and is suitable for treating the highly polluted soil in large-area heavy metals. However, this method is liable to cause destruction of soil properties and loss of soil nutrients while removing heavy metals, and may cause pollution of groundwater. The addition of the soil conditioner and the subsequent utilization of the phytoremediation technology can quickly realize the application of efficiently removing the heavy metal in the soil and quickly recovering the farmland soil, and can provide wide application prospect for quickly repairing the heavy metal contaminated soil. Therefore, the soil remediation method which combines the soil leaching technology and the plant remediation technology together and can effectively reduce the content of heavy metals in the soil and recover the production function of farmland soil has important significance for realizing effective treatment and recycling of the heavy metal contaminated soil.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides the method for repairing the heavy metal polluted soil of the farmland by combining the chemical leaching and phytoremediation technologies, which has the advantages of simple process, low repairing cost, high practicability and good repairing effect.

In order to solve the technical problems, the invention adopts the technical scheme that:

a method for restoring farmland heavy metal contaminated soil by combining chemical leaching and phytoremediation comprises the following steps:

s1, leaching: mixing the heavy metal contaminated soil with the leacheate, and uniformly stirring;

s2, improvement: mixing the heavy metal contaminated soil obtained after the washing in the step S1 with a modifier for improvement and fertilization;

s3, phytoremediation: and (5) planting the super accumulator plants on the improved soil in the step S2 to finish the restoration of the soil polluted by the heavy metal.

In the method, the mass-volume ratio of the heavy metal contaminated soil to the leacheate is 1g to 2 mL.

In the above method, the leacheate is FeCl₃A solution; the FeCl₃The concentration of the solution was 10 m mol/L.

In the method, the passivation repairing agent comprises sepiolite and organic fertilizer.

In the method, the ratio of the sepiolite and the organic fertilizer in the modifying agent to the farmland heavy metal polluted soil obtained by washing in the step S1 is further improved to be 1: 3: 100.

In the above method, in a further improvement, in step S1, the heavy metals in the heavy metal contaminated soil include cadmium and lead.

In the above method, in step S1, the stirring time is 1 to 6 hours.

Compared with the prior art, the invention has the advantages that:

(1) the invention provides a method for restoring farmland heavy metal contaminated soil by combining chemical leaching and phytoremediation, which adopts a method combining soil leaching and phytoremediation technologies, can effectively reduce the heavy metal content in the soil, and has important significance for realizing effective treatment and recycling of the heavy metal contaminated soil by restoring the production function of the farmland soil. The method has the advantages of simple process, low repair cost, high practicability, good repair effect and the like.

(2) In the method of the invention, FeCl is used₃The solution is a leacheate which has less secondary pollution to soil, and FeCl is firstly added₃The solution (leacheate) is uniformly mixed with the heavy metal contaminated soil of the farmland, and heavy metal ions in the soil are promoted to enter the leacheate. On the basis, the conditioner is added into the washed heavy metal contaminated soil for improvement treatment, wherein the addition of the conditioner can improve the pH value of the soil, reduce the content of effective heavy metals, supplement the original fertility of the soil lost due to washing, increase the types, the number and the activity of microorganisms in the soil, be beneficial to further restoring the washed soil and improve the utilization value of the restored soil. After improvement, super accumulator plants are planted again for phytoremediation, and the remediation efficiency of heavy metals is further improved.

Detailed Description

The invention is further described below with reference to specific preferred embodiments, without thereby limiting the scope of protection of the invention.

Example 1:

(1) leaching: FeCl with the concentration of 10 m mol/L₃Mixing the solution (leacheate) and the heavy metal contaminated soil according to the liquid-solid ratio of 2mL to 1g, stirring for 1h at the rotating speed of 200r/min, centrifuging, and discarding the leacheate obtained by centrifuging to obtain the leached heavy metal contaminated soil.

(2) And (2) air-drying the heavy metal contaminated soil leached in the step (1) (the air-drying treatment is more beneficial to uniformly mixing the soil and the modifying agent), and mixing the soil with sepiolite and organic fertilizer (the sepiolite and the organic fertilizer are sold in the market, and the organic fertilizer is sieved by a 2mm sieve), wherein the mass ratio of the sepiolite to the organic fertilizer to the air-dried heavy metal contaminated soil is 1: 3: 100, and the moisture content of the uniformly mixed moisture-retaining soil is 50% for improvement treatment.

(3) Naturally balancing the soil improved in the step (2) for one week, and directly cutting the hyperaccumulator plant Sedum plumbizincicola for phytoremediation.

The total content and the effective state content of the heavy metals in the heavy metal contaminated soil after the leaching and the heavy metal contaminated soil after the phytoremediation in the embodiment 1 are detected, and the results show that:

the absorption amount of Cd from the overground part of the Sedum plumbizincicola in the unamended soil after washing is 0.38 mg kg^-1Adding sepiolite and organic fertilizer to improve Cd uptake to 0.58 mg kg^-1Soil CaCl in chemical leaching process₂0.89 mg kg of original soil with the concentration of Cd in an extracted state^-1Down to 0.33 mg kg^-1The concentration of Cd in the effective state of the improved fertilization is further reduced to 0.14 mg kg under the treatment of sepiolite and organic fertilizer^-1. After planting the Sedum plumbizincicola, the concentration of Cd in an effective state is further reduced, and soil CaCl₂The concentration of the extracted Cd is reduced to 0.04 mg kg^-1. The data result shows that the removal rate of single-purification chemical leaching Cd is 45.2%, the removal rate of pure plant absorption to Cd is 35.3%, and the removal rate of Cd in soil is improved to 63.8% through chemical leaching, improved fertilization and plant absorption treatment. Therefore, the leaching can generate certain destructive effects on the soil structure, the soil fertility and the like, and the addition of the modifier and the absorption and restoration of the Sedum plumbizincicola can not only increase the community structure of soil microorganisms and contribute to the restoration of the soil property, but also obviously improve the removal efficiency of pollutants in the soil. Therefore, the method for restoring the farmland heavy metal contaminated soil by combining chemical leaching and phytoremediation can remove most heavy metals in the soil, can reduce the damage of residual chemical leaching agent and residual heavy metals after leaching to the soil property, relieves the influence on the soil fertility, and simultaneously improves the restoring effect on the heavy metal contaminated soil. Hair brushThe method has the advantages of simple process, low restoration cost, high practicability, good restoration effect and the like, and is a method capable of effectively restoring the heavy metal polluted soil.

The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-described embodiments.

Claims

1. A method for restoring farmland heavy metal contaminated soil by combining chemical leaching and phytoremediation is characterized by comprising the following steps:

2. The method according to claim 1, wherein the mass-to-volume ratio of the heavy metal contaminated soil to the leacheate is 1 g: 2 mL.

3. The method of claim 2, wherein the leacheate is FeCl₃A solution; the FeCl₃The concentration of the solution was 10 m mol/L.

4. The method of claim 1, wherein the modifying agent comprises sepiolite and organic fertilizer.

5. The method of claim 4, wherein the mass ratio of the sepiolite and the organic fertilizer in the modifying agent to the farmland heavy metal contaminated soil obtained after the leaching in the step S1 is 1: 3: 100.

6. The method according to claim 1, wherein in step S1, the heavy metals in the heavy metal contaminated soil comprise cadmium and lead.

7. The method according to claim 1, wherein in step S1, the stirring time is 1-6 h.