JPH11197643A - Method for washing contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently separate and remove a contaminant fixed firmly to a surface of a contaminated particle by a method wherein an acid is added to a contaminated soil and simultaneously or after addition, and intensive attrition treatment is applied thereto. SOLUTION: In soil contamination due to a heavy metal or the like, a secondary mineral layer fixed to a surface of a contaminated particle is allowed to react with an acid while the fine particle containing contaminant in a high concentration is enfolded, and an intensive attrition treatment is executed while dissolving or embrittlement is executed, and a soil particle which can not be purified individually by an ordinary attrition treatment and an acid dissolving treatment, is recovered as a clean soil. That is, dissolving or change in quality advances from a mineral easy to react with the acid of a carbonate or the like in the secondary minerals, and layer thinning and embrittlement are generated in the whole secondary mineral layer. When intensive attrition treatment is applied herein, a contaminant layer together with the secondary mineral which is thinned and embrittled is stripped off, and an inside non-contaminated particle can be obtained. Thereby, a clean soil can be taken out efficiently with a small acid charge amount and a short treating time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning soil contaminated with heavy metals such as cadmium and lead to remove contaminants.

[0002]

2. Description of the Related Art In recent years, the number of cases in which soil contamination at factory sites and the like has been revealed through surveys associated with redevelopment of urban areas has been increasing. Generally, a treatment method for shielding contaminated soil from the surrounding environment such as water works and earth covering works is common. However, this method leaves the contaminants themselves on site and has limited land use even after treatment.

[0003] Recently, measures have been taken to discard highly contaminated soil and replace the soil at the site of contamination. However, it is clear that the final disposal site for industrial waste will be insufficient in the near future. The introduction of the "soil cleaning method" that has been put into practical use in Europe and the United States is beginning to be considered.

[0004] The "soil washing method" is a method of physically and chemically extracting and separating contaminants from soil using water or a suitable solvent to remove contaminants. It is an object of the present invention to reduce the volume of contaminants as waste by removing particles containing a high concentration of contaminant components and using the resulting clean product for backfilling of a contaminated site. Therefore, the higher the ratio of the obtained amount of the clean substance to the amount of the supplied contaminant, the more effective the purification method.

Conventionally proposed methods for cleaning such contaminated soil include separation and removal of high-concentration contaminant particles by classification (hereinafter referred to as classification), attrition, specific gravity separation, flotation, and acid separation. There is leaching treatment of contaminated components with a solvent such as a solution or a chelating agent solution.

[0006] The classification treatment is carried out for the purpose of separating and removing fine particles having a high ability to adsorb contaminating elements, and to take out particles having a particle size range that is not contaminated as clean products. However, as the weathering of the soil progresses and the resulting secondary minerals entrain the contaminated fine particles and become attached to the surface of the non-contaminated particles, very little cleanup is obtained by the classification process. Problem.

[0007] The attrition treatment method is a method in which when contaminants adhere to the surface of non-contaminated particles, the particles are abraded by rubbing the particles together, and is generally performed before classification. However, in the current attrition treatment method, when the contaminant is fixed on the surface of the non-contaminated particles together with the secondary mineral, the contaminant cannot be completely removed even if the treatment is performed for a long time.

Further, the specific gravity selection method cannot cope with the case where a contaminant adheres to the surface of non-contaminated particles. In addition, if fine grinding is performed until the contaminated fine particles and non-contaminating particles inside are separated, the flotation method can be used, but the collected recovered material is too fine and it is backfilled for land reuse. Is difficult to use.

According to the leaching treatment method in which the contaminant is leached with an extremely high acid concentration, the contaminant can be dissolved together with the secondary mineral, but the amount of reagent used for this is enormous. However, the processing requires a long time. If the amount of reagent used is large as described above, implementation becomes difficult in terms of cost and wastewater treatment, and if the treatment time is long, equipment must be enlarged to secure the amount of treated soil. It is a problem from above.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for cleaning contaminated soil capable of efficiently separating and removing contaminants firmly adhered to the surface of non-contaminated particles. It is intended for.

[0011]

Means for Solving the Problems As a result of intensive studies, the present inventors have conducted a strong attrition treatment simultaneously with or after the addition of an acid to soil particles having contaminants adhered to the surface. It has been found that contaminants firmly adhered to the particle surface can be efficiently separated and removed by adding the compound, and the present invention has been completed.

[0012] Therefore, in order to achieve the above object, the present invention relates to a method for cleaning soil contaminated with heavy metals and the like, wherein a contaminated soil is subjected to a strong attrition treatment simultaneously with or after the addition of an acid to the contaminated soil. Is characterized by the following cleaning method.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, in the case of soil contamination by heavy metals, etc., a secondary mineral layer adhered to the surface of non-contaminated particles is dissolved or embrittled by reacting with an acid while involving fine particles containing the contamination at high concentration. However, strong attrition treatment is performed, and soil particles that cannot be purified by ordinary attrition treatment or acid dissolution treatment alone are collected as clean soil.

That is, in the present invention, the secondary minerals are dissolved or deteriorated by the action of an acid such as nitric acid, hydrochloric acid, sulfuric acid or the like from the secondary minerals which easily react with an acid such as a carbonate. Cause embrittlement and embrittlement. If a strong attrition treatment is applied here, the contaminants can be stripped off together with the thinned and embrittled secondary minerals, and internal non-contaminated particles can be obtained. Therefore, since it is not necessary to dissolve the entire secondary mineral layer, it is possible to obtain a clean product from soil that cannot be dealt with by ordinary attrition treatment alone, with a smaller amount of acid input and treatment time compared to a simple dissolution treatment. is there.

In the present invention, the strong attrition treatment is performed by using a device such as a drum type scrubber, a drum washer, and an attrition machine used for mineral processing of raw materials for ceramics at a rotation speed of 30 to 100 times / min. Minutes, so that strong attrition can be more efficiently added to the contaminated soil. However, when the attrition process is performed by a drum type scrubber or a drum washer, if the liquid is added at a solid-liquid ratio of 6: 4 or more, the attrition efficiency is greatly reduced. is there. This strong attrition treatment can be carried out simultaneously with the addition of the acid, or can be carried out after the addition of the acid and after the action of the acid has progressed.

[0016]

Next, examples of the present invention will be described together with comparative examples. Particle size 75 ~ contaminated with cadmium sulfide and lead sulfide
Table 1 summarizes the results of the four treatments of Example 1 and Comparative Examples 1 to 3 performed on 2000 μm sand. 19
The standards for soil contamination as of 1997 include the Environmental Agency's “Guidelines for Measures against Soil Pollution Related to Heavy Metals, etc.”, where 9 mg / kg for Cd and 600 mg for Pb.
Content reference values of mg / kg are shown.

Example 1 2 kg of sand to be tested was put into a 10-liter drum type scrubber together with 480 ml of water and 20 ml of 14N nitric acid, and subjected to a strong acid addition treatment at 50 revolutions / minute for 15 minutes. And wet classification with a sieve having a mesh size of 75 μm to collect particles having a particle size of 75 μm or more.

Comparative Example 1 2 kg of sand to be tested was put into a 10-liter drum type scrubber together with 500 ml of water, and the number of rotations was 5
After performing attrition treatment 0 times / minute for 1 hour, wet classification was performed with a sieve having openings of 75 μm, and particles having a particle size of 75 μm or more were collected.

COMPARATIVE EXAMPLE 2 2 kg of sand to be tested was weighed in 20 liters of water and 200 N of 14N nitric acid.
Milliliter and into a water tank with stirring blades, and after performing an acid dissolution treatment at a blade rotation speed of 700 times / minute for 1 hour,
Wet classification was performed with a sieve having an opening of 75 μm, and particles having a particle size of 75 μm or more were collected.

Comparative Example 3 2 kg of sand to be tested was put into a 10-liter drum type scrubber together with 1980 ml of water and 20 ml of 14N nitric acid, and an acid addition treatment of 50 revolutions / minute was performed for 15 minutes. Wet classification was performed with a sieve having an opening of 75 μm, and particles having a particle size of 75 μm or more were collected.

[0021]

[Table 1]

[0022]

As described above, according to the present invention, an acid-added strong attrition treatment for separating and removing contaminants adhered to the surface of non-contaminated particles is incorporated. It is possible to efficiently remove clean soil from soil in which contaminants that cannot be purified by dissolution treatment are firmly adhered to the surface of non-contaminated particles, and the required time is shorter than the conventional treatment method, and the amount of reagent required is reduced. There is an effect that can be saved.

Claims (1)

[Claims] 1. A method for cleaning soil contaminated with heavy metals or the like, wherein a strong attrition treatment is performed simultaneously with or after the acid is added to the contaminated soil.