Smoldering method for treating organic-heavy metal combined polluted soil

Abstract

The invention discloses a smoldering method for treating organic-heavy metal compound contaminated soil, which comprises the following steps: S1, respectively drying and crushing wood biomass and organic-heavy metal contaminated soil, and mixing 95-97 wt% of wood biomass and 96.2-98.2 wt% of organic-heavy metal contaminated soil to obtain a mixed material; s2, 3-5 wt% of dried and crushed wood biomass is poured into a reactor and flatly laid, then the mixed material is poured into the reactor and flatly laid, finally 1.8-3.8 wt% of organic-heavy metal contaminated soil is poured into the reactor, and hot air is introduced into the reactor to start a smoldering reaction; s3, after the reaction is completed and the temperature is cooled to be lower than 80 DEG C, cyclodextrin and polylactic acid are added and mixed, and the materials are poured out of the reactor and returned to the farmland; the smoldering method provided by the invention can effectively reduce the harm of organic pollutants and heavy metals in the soil.

Description

Technical Field

[0001] The invention belongs to the technical field of soil pollution control, and in particular relates to a smoldering method for controlling organic-heavy metal composite polluted soil. Background Art

[0002] Soil is composed of minerals formed by weathering of rocks, organic matter produced by decomposition of animal, plant and microbial residues, soil organisms (solid phase matter), water (liquid phase matter), air (gas phase matter), oxidized humus, etc. Solid matter includes soil minerals, organic matter and nutrients obtained by microorganisms after light inhibition and sterilization. Liquid matter mainly refers to soil moisture. Gas is the air existing in the pores of the soil. These three types of substances in the soil constitute a contradictory unity. They are interconnected and mutually restricted, providing the necessary living conditions for crops and are the material basis of soil fertility.

[0003] In the prior art, chemical leaching technology or thermal desorption technology is usually used to repair soils with organic-heavy metal complex pollution. However, for chemical leaching technology, the leaching liquid has a single effect, and there are limitations in eluting heavy metals and organic matter at the same time. It is difficult to remove heavy metals and organic pollutants at the same time. The elution rate of organic pollutants is low, and the waste liquid after leaching also contains pollutants, which need further treatment. Although thermal desorption technology can effectively remove volatile and semi-volatile organic pollutants and some volatile mercury and arsenic, most heavy metals cannot be removed.

[0004] In order to overcome the shortcomings of chemical leaching technology and thermal desorption technology, there is an existing technology that uses the method of smoldering wood biomass to treat heavy metal contaminated soil, but the effect is not significant and usually requires the addition of a large amount of wood biomass. Summary of the invention

[0005] In view of the deficiencies in the above-mentioned prior art, a smoldering method for the treatment of organic-heavy metal complex contaminated soil is provided. The present invention promotes the adsorption and fixation effects of biochar and the effect of changing the physical and chemical properties of soil by adding cyclodextrin and polylactic acid to the material after the smoldering reaction of wood biomass and organic-heavy metal contaminated soil, thereby effectively reducing the hazards of organic pollutants and heavy metals in the soil.

[0006] The object of the present invention is to provide a smoldering method for treating organic-heavy metal composite contaminated soil, comprising the following steps: S1. The wood biomass and the organic-heavy metal contaminated soil were dried and crushed separately, and 95-97 wt% of the wood biomass and 96.2-98.2 wt% of the organic-heavy metal contaminated soil were mixed to obtain a mixed material; S2. Pour 3~5wt% of the dried and crushed wood biomass into the reactor, spread it flat, then pour the mixed material, spread it flat, and finally pour 1.8~3.8wt% of the organic-heavy metal contaminated soil, and pass hot air into the reactor to start the smoldering reaction; S3. After the reaction is completed and cooled to a temperature below 80°C, cyclodextrin and polylactic acid are added and mixed, and the material is poured out of the reactor and returned to the farmland.

[0007] In some embodiments of the present invention, in S1, the wood biomass is dried to a moisture content of less than 15%, and the organic-heavy metal contaminated soil is dried to a moisture content of less than 10%.

[0008] In some embodiments of the present invention, in S1, the wood biomass is crushed to 10-50 mesh, and the organic-heavy metal contaminated soil is crushed to 10-50 mesh.

[0009] In some embodiments of the present invention, in S2, the temperature of the hot air is 200-400°C.

[0010] In some embodiments of the present invention, in S2, the reaction time is 5 to 10 hours.

[0011] In some embodiments of the present invention, the heavy metal in the organic-heavy metal composite contaminated soil is at least one of Cr, Pb, Cd, Hg, As, and Ni.

[0012] In some embodiments of the present invention, the organic pollutant in the organic-heavy metal complex contaminated soil is at least one of phenol and benzanthracene.

[0013] In some embodiments of the present invention, the mass ratio of the wood biomass, the organic-heavy metal contaminated soil, the cyclodextrin and the polylactic acid is 1:5~10:0.2~0.5:0.1~0.3.

[0014] In some embodiments of the present invention, in S3, the cyclodextrin is selected from at least one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin; and the relative molecular weight of the polylactic acid is 5000-10000.

[0015] In some embodiments of the present invention, in S3, the mixing time is not less than 30 minutes.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention pyrolyzes organic-heavy metal contaminated soil under smoldering combustion mode, and at high temperature, some volatile heavy metals and organic pollutants in the soil are volatilized into volatile gases and volatilized, thereby achieving the purpose of removing some heavy metals and organic pollutants.

[0017] (2) The present invention pyrolyzes wood biomass and organic-heavy metal contaminated soil under a smoldering combustion mode. The wood biomass generates a reducing atmosphere during pyrolysis. The reducing atmosphere converts weakly acid-extractable heavy metals and reducible heavy metals in the soil into oxidizable heavy metals or residual heavy metals, thereby reducing the environmental risk of heavy metals in the soil.

[0018] (3) The present invention adds cyclodextrin and polylactic acid to the material after the smoldering reaction of wood biomass and organic-heavy metal contaminated soil. The cyclodextrin and polylactic acid synergistically promote the adsorption and fixation of oxidizable heavy metals or residual heavy metals in biochar, and synergistically promote the effect of biochar on changing the physical and chemical properties of soil. The possible reason is that the molecular structure of cyclodextrin and polylactic acid contains hydroxyl or carboxyl groups, and there is a hydrogen bonding force between cyclodextrin and polylactic acid and biochar, which synergistically promotes the adsorption and fixation of biochar and the effect of changing the physical and chemical properties of soil, thereby reducing the content of weakly acid extractable and reducible heavy metals in the soil, and effectively reducing the hazards of organic pollutants and heavy metals in the soil; and cyclodextrin and polylactic acid are biodegradable, and after biodegradation, they can also play a nutrient role in the soil and are harmless to the soil. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0020] All raw materials of the present invention are conventionally commercially available.

[0021] Example 1 This embodiment provides a smoldering method for treating organic-heavy metal composite contaminated soil, which specifically includes the following steps: S1. 100 parts by mass of wood biomass and 500 parts by mass of organic-heavy metal contaminated soil were dried and crushed separately, the heavy metals in the organic-heavy metal contaminated soil were Cd and Hg, and the organic pollutant was phenol. The wood biomass was dried to a moisture content of less than 15%, and the organic-heavy metal contaminated soil was dried to a moisture content of less than 10%. The wood biomass was crushed to 10-50 mesh, and the organic-heavy metal contaminated soil was crushed to 10-50 mesh. 95wt% of the wood biomass and 98.2wt% of the organic-heavy metal contaminated soil were mixed to obtain a mixed material; S2. Pour 5wt% of the sun-dried and crushed wood biomass into the reactor, spread it flat, then pour the mixed material, spread it flat, and finally pour 1.8wt% of the organic-heavy metal contaminated soil, pass hot air at 200°C into the reactor to start the smoldering reaction for 2 hours, and then raise the temperature to 400°C for 3 hours; S3. After the reaction is completed and cooled to a temperature below 80°C, 50 parts by mass of β-cyclodextrin and 30 parts by mass of polylactic acid with a relative molecular weight of 5000 are added and mixed for 1 hour. After the temperature is naturally cooled to room temperature, the material is poured out of the reactor and returned to the farmland.

[0022] Example 2 This embodiment provides a smoldering method for treating organic-heavy metal composite contaminated soil, which specifically includes the following steps: S1. 100 parts by mass of wood biomass and 1000 parts by mass of organic-heavy metal contaminated soil were dried and crushed respectively, the heavy metals in the organic-heavy metal contaminated soil were Cd and Hg, and the organic pollutant was phenol. The wood biomass was dried to a moisture content of less than 15%, and the organic-heavy metal contaminated soil was dried to a moisture content of less than 10%. The wood biomass was crushed to 10-50 mesh, and the organic-heavy metal contaminated soil was crushed to 10-50 mesh. 97wt% of the wood biomass and 96.2wt% of the organic-heavy metal contaminated soil were mixed to obtain a mixed material; S2. Pour 3wt% of the sun-dried and crushed wood biomass into the reactor, spread it flat, then pour the mixed material, spread it flat, and finally pour 3.8wt% of the organic-heavy metal contaminated soil, pass hot air at 200°C into the reactor to start the smoldering reaction for 9 hours, and then heat it to 400°C for 1 hour; S3. After the reaction is completed and cooled to a temperature below 80°C, 20 parts by mass of β-cyclodextrin and 10 parts by mass of polylactic acid with a relative molecular weight of 10,000 are added and mixed for 30 minutes. After the temperature is naturally cooled to room temperature, the material is poured out of the reactor and returned to the farmland.

[0023] Example 3 This embodiment provides a smoldering method for treating organic-heavy metal composite contaminated soil, which specifically includes the following steps: S1. 100 parts by mass of wood biomass and 800 parts by mass of organic-heavy metal contaminated soil were dried and crushed separately, the heavy metals in the organic-heavy metal contaminated soil were Cd and Hg, and the organic pollutant was phenol. The wood biomass was dried to a moisture content of less than 15%, and the organic-heavy metal contaminated soil was dried to a moisture content of less than 10%. The wood biomass was crushed to 10-50 mesh, and the organic-heavy metal contaminated soil was crushed to 10-50 mesh. 96wt% of the wood biomass and 97wt% of the organic-heavy metal contaminated soil were mixed to obtain a mixed material; S2. Pour 4wt% of the sun-dried and crushed wood biomass into the reactor, spread it flat, then pour the mixed material, spread it flat, and finally pour 3wt% of the organic-heavy metal contaminated soil, pass hot air at 200°C into the reactor to start the smoldering reaction for 8 hours, and then heat it to 400°C for 2 hours; S3. After the reaction is completed and cooled to a temperature below 80°C, 30 parts by mass of β-cyclodextrin and 20 parts by mass of polylactic acid with a relative molecular weight of 5000 are added and mixed for 1 hour. After the temperature is naturally cooled to room temperature, the material is poured out of the reactor and returned to the farmland.

[0024] Comparative Example 1 This comparative example provides a smoldering method for treating organic-heavy metal composite contaminated soil, which specifically comprises the following steps: S1. 100 parts by mass of wood biomass and 800 parts by mass of organic-heavy metal contaminated soil were dried and crushed separately, the heavy metals in the organic-heavy metal contaminated soil were Cd and Hg, and the organic pollutant was phenol. The wood biomass was dried to a moisture content of less than 15%, and the organic-heavy metal contaminated soil was dried to a moisture content of less than 10%. The wood biomass was crushed to 10-50 mesh, and the organic-heavy metal contaminated soil was crushed to 10-50 mesh. 96wt% of the wood biomass and 97wt% of the organic-heavy metal contaminated soil were mixed to obtain a mixed material; S2. Pour 4wt% of the sun-dried and crushed wood biomass into the reactor, spread it flat, then pour the mixed material, spread it flat, and finally pour 3wt% of the organic-heavy metal contaminated soil, pass hot air at 200°C into the reactor to start the smoldering reaction for 8 hours, and then heat it to 400°C for 2 hours; S3. After the reaction is completed and cooled to a temperature below 80°C, 50 parts by mass of β-cyclodextrin is added and mixed for 1 hour. After the temperature is naturally cooled to room temperature, the material is poured out of the reactor and returned to the farmland.

[0025] Comparative Example 2 This comparative example provides a smoldering method for treating organic-heavy metal composite contaminated soil, which specifically comprises the following steps: S1. 100 parts by mass of wood biomass and 800 parts by mass of organic-heavy metal contaminated soil were dried and crushed separately, the heavy metals in the organic-heavy metal contaminated soil were Cd and Hg, and the organic pollutant was phenol. The wood biomass was dried to a moisture content of less than 15%, and the organic-heavy metal contaminated soil was dried to a moisture content of less than 10%. The wood biomass was crushed to 10-50 mesh, and the organic-heavy metal contaminated soil was crushed to 10-50 mesh. 96wt% of the wood biomass and 97wt% of the organic-heavy metal contaminated soil were mixed to obtain a mixed material; S2. Pour 4wt% of the sun-dried and crushed wood biomass into the reactor, spread it flat, then pour the mixed material, spread it flat, and finally pour 3wt% of the organic-heavy metal contaminated soil, pass hot air at 200°C into the reactor to start the smoldering reaction for 8 hours, and then heat it to 400°C for 2 hours; S3. After the reaction is completed and cooled to a temperature below 80°C, 50 parts by weight of polylactic acid with a relative molecular weight of 5000 is added and mixed for 1 hour. After the temperature is naturally cooled to room temperature, the material is poured out of the reactor and returned to the farmland.

[0026] The weakly acid extractable, reducible, oxidizable and residual states of heavy metals were determined according to the BCR method, and the removal rate of organic pollutants in the soil was determined. The results are shown in Table 1.

[0027] Table 1. Treatment effect of organic-heavy metal complex contaminated soil.

[0028]

[0029] Compared with Example 3, Comparative Examples 1 and 2 only added cyclodextrin or polylactic acid, which could not effectively reduce Cd and Hg in the contaminated soil, indicating that the compounding of cyclodextrin and polylactic acid synergistically promoted the adsorption and fixation of biochar and changed the physical and chemical properties of the soil, thereby reducing the content of weakly acid extractable and reducible heavy metals in the soil, and effectively reducing the hazards of organic pollutants and heavy metals in the soil.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that after reading the specification of this application, the technicians can still modify or replace the specific implementation mode of the present invention with equivalents, but these modifications or changes do not deviate from the scope of protection of the pending claims of the present application.

Claims

1. A smoldering method for treating organic-heavy metal composite contaminated soil, characterized in that: The steps include: S1. The wood biomass and the organic-heavy metal contaminated soil were dried and crushed separately, and 95-97 wt% of the wood biomass and 96.2-98.2 wt% of the organic-heavy metal contaminated soil were mixed to obtain a mixed material; S2. Pour 3~5wt% of the dried and crushed wood biomass into the reactor, spread it flat, then pour the mixed material, spread it flat, and finally pour 1.8~3.8wt% of the organic-heavy metal contaminated soil, and pass hot air into the reactor to start the smoldering reaction; S3. After the reaction is completed and cooled to a temperature below 80°C, cyclodextrin and polylactic acid are added and mixed, and the material is poured out of the reactor and returned to the farmland.

2. The smoldering method for treating organic-heavy metal composite contaminated soil according to claim 1, characterized in that: In S1, the wood biomass is dried to a moisture content of less than 15%, and the organic-heavy metal contaminated soil is dried to a moisture content of less than 10%.

3. The smoldering method for treating organic-heavy metal composite contaminated soil according to claim 1, characterized in that: In S1, the wood biomass is crushed to 10-50 mesh, and the organic-heavy metal contaminated soil is crushed to 10-50 mesh.

4. The smoldering method for treating organic-heavy metal composite contaminated soil according to claim 1, characterized in that: In S2, the temperature of the hot air is 200-400°C.

5. The smoldering method for treating organic-heavy metal composite contaminated soil according to claim 1, characterized in that: In S2, the reaction time is 5 to 10 hours.

6. The smoldering method for treating organic-heavy metal composite contaminated soil according to claim 1, characterized in that: The heavy metal in the organic-heavy metal composite contaminated soil is at least one of Cr, Pb, Cd, Hg, As and Ni.

7. The smoldering method for treating organic-heavy metal composite contaminated soil according to claim 1, characterized in that: The organic pollutant in the organic-heavy metal composite polluted soil is at least one of phenol and benzanthracene.

8. The smoldering method for treating organic-heavy metal composite contaminated soil according to claim 1, characterized in that: The mass ratio of the wood biomass, the organic-heavy metal contaminated soil, the cyclodextrin and the polylactic acid is 1:10-15:0.2-0.5:0.1-0.

3.

9. The smoldering method for treating organic-heavy metal composite contaminated soil according to claim 1, characterized in that: In S3, the cyclodextrin is selected from at least one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin; and the relative molecular weight of the polylactic acid is 5000-10000.

10. The smoldering method for treating organic-heavy metal composite contaminated soil according to claim 9, characterized in that: In S3, the mixing time is not less than 30 minutes.

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