阅读说明：本技术 一种热处理法修复土壤重金属污染的方法 (Method for remedying heavy metal pollution of soil by heat treatment method ) 是由 房彬 张建 李书锋 路明 马劲 刘建阔 王兆丰 于 2021-09-15 设计创作，主要内容包括：本发明属于土壤污染治理技术领域,尤其涉及一种热处理法修复土壤重金属污染的方法,包括以下步骤：将重金属污染土壤进行均质化处理；向土壤添加钝化剂,混合均匀,加水,所述钝化剂包括二氧化硅材料和石灰材料；将添加钝化剂的土壤在搅拌状态下进行热处理；对处理后的土壤进行浸出毒性检测,浸出毒性检测结果达到环境污染控制标准后可用于回填。本发明的优点在于处理后土壤重金属转化为稳定的残渣态,钝化效果彻底,稳定性强且不需要后续养护,避免了重金属再次活化,能有效避免重金属二次活化风险。本发明所述的方法可操作性强,对重金属污染处理效率高,可处理的重金属污染种类广,对于复合重金属污染可实现同步钝化。(The invention belongs to the technical field of soil pollution treatment, and particularly relates to a method for remedying heavy metal pollution in soil by using a heat treatment method, which comprises the following steps: homogenizing the heavy metal contaminated soil; adding a passivating agent into soil, uniformly mixing, and adding water, wherein the passivating agent comprises a silicon dioxide material and a lime material; carrying out heat treatment on the soil added with the passivator under a stirring state; and (4) carrying out leaching toxicity detection on the treated soil, wherein the leaching toxicity detection result can be used for backfilling after reaching the environmental pollution control standard. The method has the advantages that the heavy metal in the treated soil is converted into a stable residue state, the passivation effect is thorough, the stability is strong, the follow-up maintenance is not needed, the heavy metal is prevented from being activated again, and the risk of secondary activation of the heavy metal can be effectively avoided. The method has strong operability, high treatment efficiency on heavy metal pollution, wide range of treatable heavy metal pollution and synchronous passivation on the composite heavy metal pollution.)

1. The method for remedying the heavy metal pollution of the soil by the heat treatment method is characterized by comprising the following steps:

(1) homogenizing the heavy metal contaminated soil;

(2) adding a passivating agent into the homogenized soil, uniformly mixing, and adding water, wherein the passivating agent comprises a silicon dioxide material and a lime material;

(3) carrying out heat treatment on the soil added with the passivator under a stirring state;

(4) and (4) carrying out leaching toxicity detection on the treated soil, wherein the leaching toxicity detection result can be used for backfilling after reaching the environmental pollution control standard.

2. The method for remediating heavy metal pollution of soil by heat treatment as claimed in claim 1, wherein the homogenizing treatment in step (1) comprises crushing and screening the soil to a particle size of less than 5 mm.

3. The method for remediating heavy metal pollution of soil by using the heat treatment method as claimed in claim 1, wherein water is added in the step (2) until the water content of the soil is 20% -40%.

4. The method for remediating heavy metal pollution of soil by using heat treatment as claimed in claim 1, wherein the silica material in step (2) is amorphous SiO-rich₂The mineral material or the byproduct material of (c).

5. The method for remediating heavy metal pollution of soil by heat treatment according to claim 4, wherein the silica material is one or more of silica fume, pumice powder, or diatomaceous earth.

6. The method of claim 1, wherein the lime material in step (2) is one or both of quicklime or slaked lime.

7. The method for remediating heavy metal pollution of soil by heat treatment according to claim 1, wherein the ratio of the silica material to the lime material in step (2) is determined based on the available silicon content of the soil; the mass ratio of the total mass of the silicon dioxide material and the lime material to the soil is determined according to the heavy metal pollution degree of the soil.

8. The method for remediating heavy metal pollution of soil by heat treatment according to claim 7, wherein the ratio of the silica material to the lime material in step (2) is amorphous SiO₂The mol ratio of the CaO and the CaO is 1 (1-5).

9. The method for remediating heavy metal pollution of soil by heat treatment according to claim 7, wherein the mass ratio of the total mass of the silica material and the lime material to the mass of the soil in the step (2) is 2% to 10%.

10. The method for remediating heavy metal pollution of soil by using a heat treatment method as claimed in claim 1, wherein the process conditions of the heat treatment in the step (2) are as follows: the heating temperature is 400-600 ℃, and the heating time is 30-120 minutes.

Technical Field

The invention belongs to the technical field of soil pollution treatment, and particularly relates to a method for remedying heavy metal pollution of soil by a heat treatment method.

Background

The chemical passivation and restoration of heavy metals is a method for reducing the chemical activity of pollutants by taking the change of the occurrence form of the heavy metals as a way based on chemical measures so as to achieve the purpose of restoring the heavy metal contaminated soil. With the continuous and deep application research of different types of passivation materials, passivation repair becomes the most widely applied means for repairing heavy metal pollution at present.

Alkaline materials, phosphate materials, silicate materials and chelate organic materials are common soil heavy metal restoration stabilizing materials, and the action mechanisms comprise pH control, adsorption, precipitation, complexation, ion exchange and the like: the alkaline material increases the pH value of the soil, so that the heavy metal in the soil forms precipitates in the forms of hydroxide and carbonate. The mechanism of passivating heavy metals by phosphate materials includes various forms such as adsorption, precipitation, coprecipitation and the like, wherein the precipitation mechanism is the main form. The phosphate shows strong passivation effect on lead and cadmium under the dominance of a precipitation mechanism, and the passivation effect on copper and zinc is not obvious. The silicate material mainly reduces the mobility of heavy metals and the availability of plants by utilizing the characteristics of large specific surface area and high porosity of materials such as sepiolite, bentonite, zeolite and the like through adsorption or coordination. The chelate organic material utilizes organic functional groups and heavy metals to form a metal organic complex with a certain stability degree, and reduces water-soluble and exchangeable components of the heavy metals in soil, thereby reducing the bioavailability of the chelate organic material.

However, with the conventional passivation repair method in the prior art, there are still some non-negligible problems:

(1) the influence of physical and chemical properties such as soil pH and organic matters is remarkable: particularly, the passivation and repair effect of the alkaline material mainly depends on the change of the pH value of the soil and cannot adapt to the soil acidification reaction, when the environmental condition is changed, the temporarily passivated heavy metal can be reactivated into a form which can be utilized by organisms, and the influence is more obvious on the heavy metal with amphoteric characteristics such as lead, zinc and the like.

(2) There is a great application limit to complex heavy metal contamination: in the composite contaminated soil, competitive adsorption relations exist among different heavy metals and among the heavy metals and inherent alkali metals, magnesium and manganese in the soil, and even the situation that the migration of certain heavy metals is improved under the interaction occurs.

(3) The reaction rate and progress are influenced by the incubation time: the self granular structure of the soil influences the ion activity in the soil solution, the passivation reaction processes such as complexation, ion exchange or hydrolysis-precipitation are slow, and the maintenance of the repair effect depends on the excessive application of the passivation material and the supplement addition in the later period to a large extent.

(4) The long-term persistence of the passivation repair effect and possible environmental risks require later maintenance and supervision: such as the acidification of phosphate materials and the reactivation of organic-bound heavy metals caused by the degradation of chelating organic materials.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides the method for repairing the heavy metal pollution of the soil by the heat treatment method, the passivation efficiency on the heavy metal pollution is high, the stability is strong, the subsequent maintenance is not needed, and the risk of secondary activation of the heavy metal can be effectively avoided.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for remedying soil heavy metal pollution by a heat treatment method comprises the following steps:

(1) and (3) crushing and screening the heavy metal contaminated soil to homogenize until the granularity of the soil is less than 5 mm.

(2) Adding a silicon dioxide material and a lime material into quantitative soil in sequence, mixing uniformly, adding water, and keeping the water content at 20-40%.

(3) And (3) carrying out heat treatment on the soil added with the passivator under a stirring state.

(4) The leaching toxicity detection result can be used for backfilling after reaching the environmental pollution control standard.

Preferably, the silicon dioxide material in step 2 is amorphous-rich SiO₂The mineral material or byproduct material of (a); still more preferably, the silica material is silica fume, pumiceOne or more of flour or diatomaceous earth.

Preferably, the lime material in step 2 is one or both of quicklime or slaked lime.

Preferably, the ratio of the silica material to the lime material in step 2 is determined according to the available silicon content in the soil; still more preferably, the ratio of the silicon dioxide material and the lime material is amorphous SiO₂The mol ratio of the CaO and the CaO is 1 (1-5).

Preferably, the mass ratio of the total mass of the silicon dioxide material and the lime material to the soil in the step 2 is determined according to the heavy metal pollution degree of the soil; still preferably, the mass ratio of the silica material and the lime material to the soil is 2-10%.

Preferably, the heat treatment in step 3 is performed by using a rotary kiln or other heating device with a stirring device.

Preferably, the heating temperature in step 3 is set to 400-600 ℃ and the residence time is 30-120 minutes.

Advantageous effects

Compared with the conventional in-situ passivation and natural maintenance method, the method for repairing the heavy metal pollution of the soil by the heat treatment method utilizes natural or byproduct minerals and the silicon dioxide component of the soil to generate CaSiO by a simple process₃、Ca₂SiO₄、Ca₃SiO₅、Ca₃Fe₂(SiO₄)₃And (Ca)₃Al₂(SiO₄)(OH)₈) The polymer with the grid structure binds heavy metals in a stable crystal structure, the form is converted into a stable residue state, the leaching method of sulfuric acid and nitric acid or acetic acid solution or the drastic change of the pH value of the soil is difficult to dissolve out, the soil passivation effect is thorough after treatment, subsequent maintenance is not needed, and the secondary environmental risk can be effectively avoided. The invention has strong operability, high treatment efficiency and wide range of heavy metal pollution types, and can realize synchronous passivation on the composite heavy metal pollution.

Detailed Description

Hereinafter, the present invention will be described in detail. Before the description is made, it should be understood that the terms used in the present specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Accordingly, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the invention.

The following examples are given by way of illustration of embodiments of the invention and are not to be construed as limiting the invention, and it will be understood by those skilled in the art that modifications may be made without departing from the spirit and scope of the invention. Unless otherwise specified, reagents and equipment used in the following examples are commercially available products.

Examples

The repaired polluted soil comes from the ex-service plant area of a certain smelting plant.

The specific implementation method comprises the following steps:

(1) soil is collected to remove macroscopic impurities and grassroots, the crushed soil is sieved by a 2mm sieve, and a soil sample is subjected to toxicity leaching experiment detection by adopting a solid waste leaching toxicity leaching method acetic acid buffer solution method (HJ/T300-2007), so that the heavy metals of the polluted soil in the embodiment are mainly lead and cadmium (Table 1); and adopting a BCR three-step fractional extraction method to obtain the morphological distribution of lead, cadmium acid solution state, reducible state, oxidizable state and residue state in the sample (tables 2 and 3).

(2) And measuring the effective silicon content in the polluted soil, calculating the adding proportion of the silica fume and the hydrated lime to be 2.7 percent and 4.8 percent respectively, mixing the soil uniformly after the adding is finished, and supplementing water until the water content of the soil reaches 30 percent.

(3) And (3) placing the soil added with the passivator in a heating device provided with a stirrer, setting the temperature to be 600 ℃, stirring and heating for 1 hour, and taking out the soil after the soil is cooled.

(4) Determining the lead and cadmium leaching toxicity of the treated soilAnd form distribution: the lead leaching concentration is reduced to 0.05 mg.L^-1The cadmium leaching concentration is reduced to 0.003 mg.L^-1The quality of the water is lower than the IV-class water quality standard (Table 1) in the groundwater quality standard (GB/T14848-2017); while the percentage of lead residue increased from 12.4% to 85.6%, and the percentage of cadmium residue increased from 21.2% to 93.4% (Table 2, Table 3).

TABLE 1 leaching concentration of heavy metals lead and cadmium before and after passivation treatment

TABLE 2 lead morphology distribution before and after passivation treatment

TABLE 3 morphological distribution of cadmium before and after passivation

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions.