JP2001009438A - Treatment of contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the time for uniformly mixing soil contaminated with organic compounds to a slurry form by adding and mixing sand, decomposing agents for organic compounds and water to the soil. SOLUTION: The sand of about 0.5 μm to 5 mm in grain size, the decomposing agents, such as hydrogen peroxide, permanganate and reduced iron, for the organic chlorine compounds and the water are added to the clay soil contaminated with the organic chlorine compounds, such as dichloroethylene, trichloroethylene and tetrachloroethylene, by which the slurry-like soil is obtained. As a result, the clayey soil and the water may be easily and uniformly mixed and, therefore, the efficient dispersion of the organic chlorine compounds under good work with a smaller amount of the water to be added is made possible. In addition, the treatment efficiency may be improved by shortening the time required for the mixing.

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]

By the way, organochlorine compounds tend to be accumulated in large amounts in poorly permeable clayey soil due to their properties.

However, when a decomposing agent and water are added to and contaminated with contaminated soil, if the soil to be treated is clayey, it is difficult to mix it uniformly with water. Was inferior in contact efficiency, and sufficient decomposition efficiency could not be obtained.

[0006] In this case, it is necessary to increase the amount of water to be added and to lengthen the time in order to uniformly mix the clay with the clayey soil. In addition, the soil content after the treatment is high, there is a problem in handling property and workability, and there is also a problem that a long time is required for the treatment and the treatment efficiency is poor.

[0007] The present invention solves the above-mentioned conventional problems. Even when the soil to be treated is clayey soil, it does not require a large amount of water and a long mixing time, so that the contaminated soil and the decomposing agent can be used. It is an object of the present invention to provide a method for treating contaminated soil in which mixing of soil is reliably performed, the contact efficiency between the soil and the decomposing agent is increased, and efficient treatment is performed at a high reaction rate.

[0008]

The method for treating contaminated soil according to the present invention comprises the steps of: treating soil contaminated with an organic compound with sand;
The organic compound decomposer and water are added and mixed.

In the present invention, sand is added to the soil when adding an aqueous solution of a decomposing agent to the soil contaminated with an organic compound, particularly clayey soil to decompose the organic compound and purify the soil. The time required for uniformly mixing the soil in a slurry state is reduced, and the required amount of added water is reduced.

In the present invention, the effect of adding sand is as follows. That is, the sand weakens the viscosity of the clayey soil, and the viscous soil is easily dispersed by adding water in this state. For this reason, the amount of water required for forming a slurry can be reduced, and the mixing time can be shortened.

[0011]

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), especially clayey soil.

In the present invention, first, contaminated soil is excavated, sand is added thereto, and mixed. In the present invention, “sand” refers to a particle having a particle size of 0.5 μm to 5 mm, particularly about 0.5 to 2 mm, and the amount added to the clay soil varies depending on the properties of the clay soil to be treated. In the normal case, the amount is preferably 100 to 1000 g, more preferably 300 to 500 g, per kg of clay soil.

The sand can be mixed with the clay soil at the same time as the decomposing agent and the water. However, in order to sufficiently obtain the above-mentioned effect of reducing the viscosity of the clay soil by adding sand, it is necessary to mix the clay with the clay. It is preferable that sand is previously added to the soil and mixed, and then a dispersant and water or an aqueous solution of the dispersant are added.

After the sand is added to and mixed with the clayey soil, an organic compound decomposer and water, preferably an aqueous solution of the decomposer are added to make the soil into a slurry and thoroughly mixed.

As the decomposing agent used here, hydrogen peroxide, permanganate, reduced iron and the like can be used. Particularly, permanganate is preferable. 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 a 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.

Such a decomposing agent aqueous solution is used in an amount of 200 to 1000 mL per 1 kg of soil (soil before mixing sand).
It is preferable to sufficiently mix the soil and the decomposer to increase the contact efficiency between the soil and the decomposer and to smoothly decompose the organic compound.

The mixing time of the clayey soil and the sand and the mixing time of the clayey soil mixed with the sand and the aqueous solution of the decomposing agent are not particularly limited, as long as a sufficiently uniform mixing state can be obtained.
Preferably, the mixing time of the clay soil and the sand is about 5 to 20 minutes, and the mixing time of the clay soil mixed with the sand and the decomposing agent aqueous solution is about 5 to 30 minutes.

[0020]

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

Examples 1 to 4 Small concrete mixer (main dimensions: 0.74 mφ ×
1.36 m of contaminated clayey soil (TCE concentration, cis-DCE concentration; about 15 mg / L, about 4 mg / L by water elution method) excavated into 1.36 m, capacity: 120 L,
7.5 kg of sand (filling a particle size of 0.5 to 2 mm) was added and mixed for 10 minutes. Thereafter, an aqueous solution of the decomposing agent shown in Table 1 was added in an amount shown in Table 1, and mixed for the time shown in Table 1. After mixing, the soil is sampled and the remaining T
CE and cis-DCE concentrations were measured by gas chromatography, and the results are shown in Table 1.

The method of measuring the concentrations of TCE and cis-DCE is as follows.

[Method of Measuring TCE, cis-DCE Concentration (Water Elution Method)] 50 g of soil is quickly weighed into a 500 mL Erlenmeyer flask, 500 mL of water (pH 5.8) is quickly added, the lid is covered, and a magnetic stirrer is used. Stir for 4 hours. Next, let it stand for 30 minutes, and quickly remove the supernatant to 10 mL.
Was transferred to a vial, covered with a butyl rubber septum and an aluminum sheet cap, and the head space was injected into a gas chromatograph (hydrogen flame ionization detector) and quantified. Regarding the measurement method described on pages 861 to 864).

Further, the mixed state of the sample after the treatment was observed, and the results are shown in Table 1.

In order to examine the variation in the processing results, each of the above processings was performed three times, and the results are shown in Table 1 for each batch.

Comparative Examples 1 and 4 TCE and cis-contaminated clay soils to which no sand and no decomposing agent aqueous solution were added were used in the same manner as in Examples 1 and 3.
The DCE concentration was measured and the results are shown in Table 1.

Comparative Examples 2, 3, 5 and 6 Examples 1 and 3 were the same as those in Examples 1 and 3 except that the decomposing agent aqueous solution shown in Table 1 was added in the amount shown in Table 1 without adding sand and mixed for the time shown in Table 1. Is performed in the same manner as described above, and TCE and cis-DCE
The concentration was measured, and the results are shown in Table 1.

In each of these comparative examples, the above processing was performed three times each in order to examine the variation in the results. The results are shown in Table 1 for each batch.

[0029]

[Table 1]

From Table 1, the following is clear.

That is, in Comparative Examples 2 and 5 in which the mixing time was 10 minutes without mixing the sand, the TCE, cis-DCE was determined for each batch even though the test conditions were the same.
The dispersion of the concentration is large, and the condition of the treated soil is not constant. This is because the mixing is insufficient and the decomposing agent is not sufficiently dispersed and mixed in the soil.
Due to large variations and insufficient processing, T
The CE, cis-DCE concentration is also relatively high.

In Comparative Examples 3 and 6, in which the mixing time was 30 minutes without mixing the sand, the mixing time was long, so that TCE, c
The variation in the is-DCE concentration is smaller than Comparative Examples 2 and 5, and the state of the treated soil is stable, but the mixing time is long and disadvantageous.

On the other hand, Examples 1 to 4 in which sand was mixed
In 10 minutes, the decomposing agent is sufficiently uniformly dispersed and mixed in the soil in a mixing time of 10 minutes, the concentration of TCE and cis-DCE is sufficiently reduced, the dispersion is small, and the condition of the treated soil is stable.

In particular, Examples 1 and 2 and Examples 3 and 4 show that even if the amount of added water is reduced, the treatment effects are the same, and that the present invention can reduce the amount of water used.

The untreated comparative examples 1 and 4 and the example 1
2. When Examples 3 and 4 are compared, TCE, cis-DC
It can be seen that permanganate is more effective in decomposing E than hydrogen peroxide.

[0036]

As described above in detail, according to the method for treating contaminated soil according to the present invention, an aqueous solution of a decomposing agent is added to and mixed with clay soil to decompose organic compounds in the clay soil. The homogeneous soil and the aqueous solution of the decomposing agent can be easily and uniformly mixed. Therefore, the organic compound can be efficiently decomposed with good workability with a small amount of water added and the amount of the decomposing agent used, and the time required for mixing can be shortened to improve the processing efficiency.

Claims (1)

[Claims] 1. A method for soil contaminated with organic compounds,
A method for treating contaminated soil, comprising adding sand, a decomposer for the organic compound and water, and mixing.