JP2001009437A - Treatment of contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the need for a vast place for placing slurried soil by adding decomposing agents for organic compounds and water to the soil contaminated with the organic compounds to make the soil to a slurry form, then adding solidifying agents to the slurried soil. SOLUTION: The decomposing agents, such as hydrogen peroxide, permanganate and reduced iron, for the organic chlorine compounds, such as dichloroethylene, trichloroethylene and tetrachloroethylene, and the water are added to the soil, by which the slurried soil regulated in the moisture content of the soil to 15 to 50% is obtained. The solidifying agents prepared by using quicklime, cement, etc., are added and mixed to and with such slurried soil in such a manner that the weight ratio thereof to the slurried soil attained 10%. As a result, the need for the vast place and container of a large capacity for placing the slurried soil is eliminated and the amount of the contaminated soil which can be treated by one time of manipulation may be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for efficiently treating soil contaminated with an organic compound such as an organic chlorine compound.

[0002]

BACKGROUND OF THE INVENTION Organochlorine compounds have been used as excellent degreasing agents (solvents), but their release to the environment has been restricted in recent years. However, contamination by organic chlorine compounds has not been solved yet, and soil and groundwater contamination by organic chlorine compounds such as trichloroethylene and tetrachloroethylene has become a major social problem.

Hitherto, as a method for treating soil contaminated with an organic chlorine compound, a method has been proposed in which a decomposing agent such as hydrogen peroxide is directly injected into contaminated soil to decompose and remove an organic chlorine compound such as trichloroethylene. JP-A-7-7577
No. 2). In this case, in order to increase the reaction rate, water is added to the contaminated soil together with the decomposing agent, specifically, an aqueous solution of the decomposing agent is added to the excavated contaminated soil to treat the soil as a slurry. Is being done. In this way, by making the soil slurry, mixing of the contaminated soil with the decomposing agent is ensured, the contact efficiency between the soil and the decomposing agent is increased, and efficient treatment can be performed at a high reaction rate.

[0004]

As in the prior art, when an aqueous solution of a decomposing agent is injected into contaminated soil to form a slurry, the slurry is allowed to stand still during the reaction and after the treatment. Requires a large space or a large-capacity container surrounding all sides.

[0005] The present invention solves the above-mentioned conventional problems, and by adding an aqueous solution of a decomposing agent to contaminated soil to form a slurry, mixing of the contaminated soil and the decomposing agent is ensured. This is a method of performing efficient treatment at a high reaction rate by increasing the contact efficiency with a large space or a large capacity container for allowing the slurry soil to stand still during and after the reaction. It is an object of the present invention to provide a method for treating contaminated soil that is not required.

[0006]

The method for treating contaminated soil according to the present invention comprises adding a decomposing agent for the organic compound and water to the soil contaminated with the organic compound to form a slurry. It is characterized in that a solidifying agent is added to the slurry soil.

In the present invention, an aqueous solution of a decomposing agent is added to excavated soil, and the soil is slurried to surely mix the soil and the aqueous solution of the decomposing agent to sufficiently contact the decomposing agent with the soil. . Then, after adding a solidifying agent, the mixture is allowed to stand to completely decompose the organic compounds in the soil. By adding the solidifying agent to the slurry soil, the decomposition process of the organic compound by the decomposing agent proceeds smoothly even during the process of solidifying the soil and after the solidification. Efficient processing can be performed without requiring a place or a large-capacity container.

[0008]

Embodiments of the present invention will be described below in detail.

In the present invention, the contaminated soil to be treated is soil contaminated with an organic compound, particularly, dichloroethylene (DCE), trichloroethylene (T
CE), soil contaminated with organochlorine compounds such as tetrachloroethylene (PCE).

In the present invention, first, contaminated soil is excavated, and a decomposing agent for an organic compound and water, preferably an aqueous solution of a decomposing agent, are added to the excavated soil to form a slurry and sufficiently mixed.

As the decomposing agent used here, hydrogen peroxide, permanganate, reduced iron and the like can be used. Particularly, permanganate is preferable. When permanganate is used as the decomposing agent, Means DCE, EC in soil
By oxidizing aliphatic organic chlorine compounds such as E and PCE preferentially to organic matter in soil, these substances can be efficiently decomposed into carbon dioxide and chloride ions.

When permanganate is used as the decomposing agent, potassium permanganate,
Sodium permanganate or the like can be used. The permanganate is generally preferably used as an aqueous solution having a concentration of 0.01 to 10% by weight. The amount of permanganate to be added varies depending on the degree of contamination of the soil to be treated.
It is preferable to add so that it may become 0.1 weight%. When hydrogen peroxide is used as the decomposing agent, the hydrogen peroxide is preferably used as a hydrogen peroxide solution having a concentration of 0.1 to 30% by weight, and the amount of addition in this case also depends on the degree of contamination of the soil to be treated. Although different, hydrogen peroxide is added so that the ratio of hydrogen peroxide to soil is 0.0002 to 0.045% by weight.

The concentration of the decomposing agent aqueous solution and the amount of addition to the soil are determined by adding and mixing the decomposing agent aqueous solution to the water content of the soil which has been slurried (this water content is determined by the water content described in Examples below). Is adjusted to be 15 to 50% by sufficiently mixing the soil and the decomposer to increase the contact efficiency between the soil and the decomposer. It is preferable for smoothly decomposing the organic compound.

In the present invention, a solidifying agent is added to the soil which has been made into a slurry by the addition and mixing of the aqueous solution of the decomposing agent, and the mixture is sufficiently mixed to cause a dehydration reaction to solidify the soil. The mixing time of the aqueous solution of the decomposing agent and the soil varies depending on the amount of the soil to be treated, but generally about 5 to 60 minutes is sufficient.

As the solidifying agent to be added to the slurry soil, quick lime, cement and the like can be used.
It is preferable to use a cement-based solidifying agent. A solidifying agent such as a cement-based solidifying agent absorbs moisture in the slurry soil,
The moisture content is reduced, and piled up without the need for an enclosure or the like, or solidified to the extent that it can be easily transported and backfilled in the original place.

By leaving the soil in such a state,
The decomposition of the organochlorine compound further progressed, and about 2
After 4 hours, the concentration of the organic chlorine compound measured by the water elution method described below can be reduced to 0.01 mg / L or less.

The degree of solidification of the soil by the solidifying agent is as follows:
In consideration of the handleability, the cost of the solidifying agent, and the like, it is preferable that the moisture content of the soil be about 5 to 15%. In general, the amount of the solidifying agent used to obtain such a moisture content is as follows. Depending on the type of solidifying agent used and the water content of the slurry-like soil, 5 to 20
A weight percent is sufficient.

[0018]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1 and 2 Small concrete mixer (main dimensions: 0.74 mφ ×
Contaminated soil 60 excavated to 1.36m, capacity: 120L)
kg (TCE concentration; about 100 μg / L by a water elution method), 9 L of a decomposing agent aqueous solution shown in Table 1 was added, and mixed for 10 minutes to form a slurry. Next, a solidifying agent (cement) was added and mixed so that the weight ratio to the slurry soil was 10%, and the mixture was allowed to stand. The concentration of TCE remaining 24 hours after the addition of the solidifying agent was measured by gas chromatography. The water content of each sample was measured, and the results are shown in Table 1.

The method for measuring the TCE concentration and the method for measuring the water content are as follows.

[Method of Measuring TCE Concentration (Water Elution Method)] 50 g of soil was quickly weighed into a 500 mL Erlenmeyer flask, 500 mL of water (pH 5.8) was quickly added, and the mixture was closed and stirred with a magnetic stirrer for 4 hours. . next,
Let stand for 30 minutes, quickly transfer 10 mL of the supernatant to a vial, cover with a butyl rubber septum and an aluminum sheet cap, inject the head space into a gas chromatograph (hydrogen flame ionization detector) and quantify (Environmental 6 method; 1998 version) Of "Environmental Standards Related to Soil Pollution" 8
(Based on the measurement method described on pages 61 to 864).

[Water Content Measurement Method] The soil was weighed at 10 g wet weight, dried at 100 ° C. for 8 hours, and the dry weight was weighed. The amount of dry water was determined from the difference between the wet weight and dry weight of the soil, and the ratio of the amount of water to the wet weight of the soil was determined.

Comparative Example 1 The TCE concentration and the water content were measured in the same manner as in Example 1 for the contaminated soil to which the aqueous solution of the decomposing agent and the solidifying agent were not added, and the results are shown in Table 1.

Comparative Examples 2 and 4 The same treatment as in Examples 1 and 2 was carried out except that only the solidifying agent was added without adding the aqueous solution of the decomposing agent.
The CE concentration and the water content were measured, and the results are shown in Table 1.

Comparative Examples 3 and 5 The same treatment as in Examples 1 and 2 was carried out except that only the aqueous solution of the decomposing agent was added without adding the solidifying agent.
The CE concentration and the water content were measured, and the results are shown in Table 1.

[0026]

[Table 1]

From Table 1, the following is clear.

That is, comparing Example 1 with Comparative Example 3 and Example 2 with Comparative Example 5, there is no significant difference in the residual TCE concentration, and the addition of the solidifying agent does not impair the decomposition efficiency at all. I understand. Thus, in Examples 1 and 2, the moisture content was significantly reduced as compared with Comparative Examples 3 and 5, and soil having sufficient hardness was obtained, as in the case where the slurry-like soil was allowed to stand still. It can be seen that the soil can be piled up and left without requiring a vast place or a large capacity container.

Further, since the water content of Examples 1 and 2 is smaller than that of the untreated Comparative Example 1, it can be seen that the solidification by the solidifying agent has sufficiently proceeded.

Further, by comparing Comparative Examples 2 and 4 with Examples 1 and 2, respectively,
It is understood that there is almost no influence by the presence or absence of the decomposing agent aqueous solution.

When the untreated comparative example 1 is compared with the examples 1 and 2, the TCE is almost completely decomposed in the example 1, and the decomposition of TCE is more difficult than decomposition of hydrogen peroxide. It can be seen that manganate is more effective.

[0032]

As described above in detail, according to the method for treating contaminated soil of the present invention, organic compounds in contaminated soil can be efficiently decomposed, and during or after treatment,
No need for a large space or a large capacity container to keep the slurry-like soil stationary, it is possible to increase the amount of contaminated soil that can be treated in a single operation, and work efficiency is remarkable. improves.

Claims (1)

[Claims] 1. A method of adding a solidifying agent to a soil contaminated with an organic compound by adding a decomposing agent for the organic compound and water to the soil to form a slurry, and then adding a solidifying agent to the slurry-like soil. To treat contaminated soil.