METHOD FOR DECONTAMINATING SOIL, AND INSTALLATION FOR IMPLEMENTING SAME

Abstract

The invention is intended for integrated decontamination of soils contaminated with mercury (amalgam) or/and radionuclides. Method for soil decontamination includes preparation of pulp by mixing soils with water at the soil sampling point with separation of fraction with fragments more than 100 mm in the pulp preparation module, disintegration of pulp and soil aggregates in the disintegration module with separation of plants residues and fraction with fragments more than 10 mm. Pulp thickening. In the hydroclassification module the pulp is separated into sand and fine particle fractions, the fine particle fraction goes to the dehydration module, designed as a concentrator, where it is thickened and dehydrated for further disposal. If mercury and amalgam are present in soils they are separated in the thickening module. Technical result—implementation of a low-waste nonchemical technology for decontamination of soil from mercury, its water-insoluble forms, amalgam or/and radionuclides in a single technological process without equipment resetting, separation of metal mercury or its amalgam.

Claims

1. The method for soil decontamination from contaminants, which includes preparation of pulp by mixing soils with water, separation of fraction with fragments more than 100 mm and fraction with fragments more than 10 mm, disintegration of soil aggregates, hydroclassification of pulp into sand and fine particle fractions with separation of the sand fraction, thickening and dehydration of the fine particle fraction with its further disposal and treatment of circulating water, is different in that the pulp is prepared by mixing of contaminated soils with water at the soils sampling point with separation of fraction with fragments more than 100 mm, after separation of fraction with fragments more than 10 mm during disintegration there is additional pulp thickening, also plants residues are separated at the stage of separation of fraction with fragments more than 10 mm, thickening and dehydration of the fine particle fraction is done in one stage by concentration.

2. Method according to claim 1, wherein additional pulp thickening provides separation of metal mercury and amalgam.

3. Method according to claim 1, wherein fine particle fraction, containing water-insoluble forms of mercury and/or radionuclides, is subject to disposal.

4. The facility for decontamination of soils from contaminants, comprising of modules integrated into a single technological process, includes disintegration, hydroclassification, dehydration of fine particle fraction, circulating water treatment, is different in that the facility contains an additional module for pulp preparation with a function to separate fraction with fragments more than 100 mm and the thickening module located before the hydroclassification module, the disintegration module is additionally equipped with a device to separate plants residues, and the module for dehydration of fine particle fraction is designed as a concentrator.

5. Facility according to claim 4, wherein thickening module is equipped with a device to separate metal mercury and amalgam.

6. Facility according to claim 4, wherein concentrator is equipped with a device to separate fine particle fraction containing water-insoluble forms of mercury and/or radionuclides.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The FIG. 1 shows the basic scheme of the soil decontamination facility for the case of mixed contamination, which includes

[0054] 1—pulp preparation module,

[0055] 2—disintegration module,

[0056] 3—thickening module,

[0057] 4—hydroclassification module,

[0058] 5—dehydration module,

[0059] 6—circulating water treatment module.

DETAILED DESCRIPTION

[0060] The facility consists of modules 1-6 connected according the technological process by pipelines with installed valves, and instrumentation, pumps (not given in the FIG. 1).

[0061] The facility operates as follows.

[0062] Mix contaminated soils with water and separate coarse fractions (>100 mm): construction debris, bricks, concrete etc. at the soil sampling point in pulp preparation module 1. Coarse fractions (>100 mm) remain at the soil sampling point.

[0063] Then the pulp goes to disintegration module 2, where, for example, using scrubbers happens separation of fractions more than 10 mm and plants residues. The separated fractions are sent for recycling. The module also provides pulp dispersion by its vigorous mixing.

[0064] Then the pulp goes to thickening module 3. For decontamination of soils containing mercury or mixed contamination (mercury and radionuclides) the module can be designed, for example, as a concentrator and equipped with a device to remove metal mercury (amalgam). Separated metal mercury and amalgam are collected into a leak-tight container and sent for reprocessing. For decontamination of radionuclide-contaminated soils module 3 provides pulp thickening.

[0065] The pulp from module 3 goes to hydroclassification module 4, where it is divided into sand and fine particle fraction enriched with water-insoluble forms of mercury or/and radionuclides. Hydroclassification module 4, for example, can be designed as a mechanical classifier (screw-type, centrifugal etc.). The sand fraction is sent for recycling, the fine particle fraction—to dehydration module 5, designed as a concentrator. Dehydrated fine particle fraction, contaminated with water-insoluble forms of mercury or/and radionuclides, is collected into leak-tight containers and sent for disposal, and clarified circulating water—to circulating water treatment module 6. Treated circulating water is then returned to the cycle.

EXAMPLE 1

According to the Prototype

[0066] Contaminated soils with moisture 12.5% and mercury concentration 300 mg/kg are collected and sent to the decontamination point.

[0067] Mercury-containing soils (1000 kg) are loaded into the disintegration module, mixed with water, and afterwards the pulp is subject to subsequent separation of fractions more than 100 mm and more than 10 mm. Mercury content in the extracted fractions does not exceed 2.1 mg/kg—MAC for soils. Then the pulp goes to the hydroclassificaiton module, where it is separated into the sand fraction (>0.04 mm) and the fine particle fraction (<0.04 mm). After dehydration the fine particle fraction with mercury concentration ˜450 mg/kg is collected into leak-tight containers for further disposal. The sand fraction with mercury concentration ˜360 mg/kg is sent for repeated decontamination.

[0068] Fractions separated during decontamination of mercury-containing soils:

TABLE-US-00001 coarse (>10 mm and >100 mm) 10.5% wt.   sand (>0.04 mm) 52% wt. fine particles (<0.04 mm) 25% wt.

[0069] Based on the results of soil decontamination according to the prototype diagram the sand fraction, having the maximum content, requires repeated decontamination due to high mercury content. It should be noted that the process of pulp separation does not allow to extract plants residues.

EXAMPLE 2

[0070] Mix contaminated soils (1000 kg), described in example 1, with water at the sampling point and separate fractions more than 100 mm in the pulp preparation module 1. After the pulp goes to disintegration module 2. Here happens separation of fraction, which is more than 10 mm. Mercury content in fractions with components more than 10 mm and 100 mm—does not exceed 2.1 mg/kg. Disintegration module 2 provides separation of plants residues with mercury concentration not more than 2.1 mg/kg. After disintegration module the pulp goes to thickening module 3, where it is thickened to extract metal mercury (amalgam). The amount of mercury extracted in this module equals to ˜220 g. Then in hydroclassification module 4 the thickened pulp is separated into the sand fraction with particles more than 0.04 mm and the fine particle fraction with particles less than 0.04 mm. Mercury concentration in the sand fraction, sent for recycling, does not exceed 2.1 mg/kg. The fine particle fraction with mercury content of 300 mg/kg is dehydrated in module 5, packed in leak-tight containers and sent for disposal. Water goes to circulating water treatment module 6 and returns to the cycle.

[0071] Fractions separated during decontamination of mercury-containing soils:

TABLE-US-00002 coarse (>10 mm and >100 mm)  9% wt. plants residues 1.5% wt.  sand (>0.04 mm) 52% wt. fine particles (<0.04 mm) 25% wt.

[0072] Mercury content in the facility circulating water does not exceed MAC values for water bodies of household water use (0.0005 mg/l).

EXAMPLE 3

[0073] Decontamination of soils (1000 kg) with specific activity of .sup.137Cs 8.0 kBq/kg, moisture—14%. Mix soils with water in pulp preparation module 1 and separate fraction more than 100 mm, which remains at the soils sampling point. The prepared pulp goes to disintegration module 2 to separate fraction more than 10 m, plants residues, dispersion. Then the pulp goes to thickening module 3. The thickened pulp is decontaminated similar to example 2.

[0074] Fractions separated during decontamination:

TABLE-US-00003 coarse (>10 mm and >100 mm)  7% wt. plants residues  1% wt. sand (>0.04 mm) 58% wt. fine particles (<0.04 mm) 20% wt.

[0075] Specific activity of coarse fractions equals to 0.12 kBq/kg, plants residues—0.1 kBq/kg, sand fraction—0.87 kBq/kg. Fine particle fraction with specific activity ˜37.4 kBq/kg is sent for disposal.

EXAMPLE 4

[0076] Decontamination of soils (1000 kg) contaminated with radionuclides and mercury (mixed contamination). Moisture of soils equals to 12.5%, mercury concentration—300 mg/kg, .sup.137Cs specific activity—3.0 kBq/kg. After pulp preparation and separation of fraction more than 100 mm the pulp goes to the disintegration module. The pulp is decontaminated similar to example 2.

[0077] Fractions separated during decontamination:

TABLE-US-00004 coarse (>10 mm and >100 mm)  9% wt. plants residues 1.5% wt.  sand (>0.04 mm) 52% wt. fine particles (<0.04 mm) 25% wt.

[0078] Mercury content in coarse, sand fractions, as well as plants residues does not exceed 2.1 mg/kg. Specific activity of coarse fractions—0.16 kBq/kg; plants residues—0.1 kBq/kg; sand fraction—0.3 kBq/kg. Mercury amount in the thickening module equals to ˜220 g. Mercury concentration in the clay fraction equals to 300 mg/kg, and specific activity ˜11.3 kBq/kg.

[0079] Content of mercury and radionuclides in the facility circulating water does not exceed standard values.

[0080] By specific sequence of procedures and binding of modules the announced invention provides separation of mercury (amalgam), or radionuclides, or mixed contamination (mercury and radionuclides) from soils without resetting the operating procedures. The invention provides separation of pure fractions (sand, coarse) and plants residues, which can be returned to the economic turnover. The most contaminated fine particle fraction is subject to disposal. Extraction of elemental mercury (amalgam) from soils with mercury and mixed contamination in the thickening module prevents metal from getting in sand fractions, and consequently to the environment.