JP2004154778A - Soil detoxification treatment method - Google Patents

Abstract

[PROBLEMS] For a soil contaminated with an organochlorine compound, relatively inexpensive and a small amount of iron material in comparison with the conventional one in a short period of time, not only for a saturated zone below the groundwater level but also for excavated soil, And a method capable of detoxifying at room temperature.
A method of adding and mixing iron powder as a reducing agent by means of spraying underground together with a high-pressure medium on soil or mechanically mixing using a civil engineering machine or the like. Preferably, the iron powder contains 0.1% by weight or more of carbon, 50% by weight or more has a particle size passing through a 150 μm sieve, and has a specific surface area of 500 cm ² / g or more, It is a method of being added in the range of 0.1 to 10% by weight based on the soil. The purpose can be efficiently achieved by using spongy iron powder as the iron powder.
[Selection diagram] None

Description

  The present invention relates to a technique for purifying soil contaminated with an organochlorine compound.

  Organochlorine compounds such as trichloroethylene, which have been used in larger quantities as degreasing solvents in semiconductor factories and metal processing factories than ever before and have been discharged or discarded after use, accumulate in soil or groundwater contaminated areas and rebuild the factory site. The use and land development in the surrounding area are hindered, and the contamination of groundwater by the accumulated organochlorine compounds is a major social problem such as an obstacle to the use of the groundwater.

  For the method of treating contaminated water with such an organic chlorine-based compound with an iron-based metal reducing agent to decompose and detoxify contaminants, for example, Japanese Patent Publication No. 2-49158 and Japanese Patent Publication No. 2-49798, It is disclosed in Japanese Patent Publication No. 2636171, Japanese Patent Publication No. 5-501520 and Japanese Patent Publication No. 6-506661.

  The method disclosed in Japanese Patent Publication No. 49158/1990 is a method in which water to be treated, that is, water containing hardly decomposable halogenated hydrocarbons is adjusted to pH 6.5 to 9.5 and then reduced with a base metal-based reducing agent such as iron. In the method disclosed in Japanese Patent Publication No. 49798/1990, when water to be treated having an organic compound is rendered harmless by a metal-based reducing agent, the water to be treated is adjusted to pH 6.5 or higher in advance, and the oxidation-reduction potential is reduced by a reducing substance. In the method disclosed in Japanese Patent No. 2636171, hydrogen is supplied to contaminated water containing an organic halogen compound to remove dissolved oxygen, and then activated carbon carrying a metal such as iron. This is a method in which a reduction treatment is carried out by contacting a carrier substance.

  The method disclosed in Japanese Patent Application Laid-Open No. 5-501520 discloses a method for purifying contaminated groundwater with halogen organic pollutants in an environment in which oxygen is cut off. This is a method of decomposing pollutants through a middle layer, and the method of Japanese Patent Publication No. Hei 6-506631 discloses a method for purifying contaminated groundwater, which is a method for adsorbing activated carbon such as activated carbon formed in the ground. This is a method in which a contaminant is adsorbed and decomposed by passing through a permeable layer made of a mixture of metal particles such as iron filings and dust.

In addition, for contaminated groundwater, there are a vacuum extraction method and a pumping aeration method in which this contaminated groundwater is extracted outside the soil to make it harmless, and the soil is excavated and heat-treated to make it harmless by heat treatment. A desorption method and a thermal decomposition method are known, and a purification method by a bioremediation method using microorganisms is known as a method for decomposing and contaminating pollutants in soil or groundwater.
Japanese Patent Publication No. 2-49158 Japanese Patent Publication No. 49798/1990 Japanese Patent No. 2636171 JP-T5-501520 Japanese Unexamined Patent Publication No. Hei 6-506631

  However, the invention methods disclosed in Japanese Patent Publication No. 2-49158, Japanese Patent Publication No. 2-49798 and Japanese Patent No. 2636171 target water or industrial wastewater, and are troublesome for treating contaminated groundwater. It is premised on the drainage of contaminated water, and it is necessary to adjust the pH of contaminated water and remove dissolved oxygen by supplying other reducing substances and hydrogen gas, etc., so that in-situ treatment of contaminated soil or groundwater is required. Is difficult to apply, and there are many disadvantages in terms of cost such as using an iron reducing agent carried on activated carbon or the like.

The methods of the inventions of Japanese Patent Application Laid-Open Nos. 5-501520 and 6-506661 are also in-situ treatment methods for groundwater, but mainly for preventing the diffusion of pollution to downstream areas by groundwater flow flowing through the contaminated area. It is not intended to detoxify the contaminated area itself. Furthermore, a metal reducing agent is used in combination with an adsorbent made of activated carbon, and an iron layer is clogged with iron carbonate (FeCO ₃ ) generated by reacting with carbonate ions in groundwater, and therefore requires periodic replacement. There are many disadvantages in terms of equal cost. That is, regarding the detoxification treatment of soil contaminated with the organochlorine compound and contaminated water in the soil, the conventional technique has the following problems.

  (1) In the method of extracting and pumping soil gas and groundwater containing pollutants from the ground by vacuum extraction and pumping, etc., use activated carbon or a decomposer to remove and decompose pollutants in soil gas and extracted water. Therefore, high-cost separate treatment is required, such as installing facilities on the ground and detoxifying pollutants generated by extraction and pumping. In addition, since the method does not purify the soil itself, it is not possible to achieve the object of eliminating the above-mentioned obstacles in land development and the like, and it cannot be said that this is a sufficient detoxification method.

(2) The groundwater purification method using a metal-based reducing agent such as iron is intended for groundwater to the utmost and does not purify the soil itself even if it can prevent the diffusion of contaminated groundwater. Since it cannot be applied to the purification of the unsaturated zone or soil after excavation, it cannot be said to be a sufficient detoxification method as in the above method.
The method also uses large-grain iron to improve groundwater permeability and to avoid the blockage problem described above. For this reason, the reactivity is poor and the amount of use is large, which is disadvantageous in terms of cost.

  (3) The method of pyrolyzing excavated soil at a high temperature requires large-scale equipment for heat-treating the soil, and the soil particles themselves are altered by heat, such as supporting structures and inhabiting living organisms. Significant loss of soil function makes it difficult to reuse the soil after treatment.

  (4) The bioremediation method cannot be applied to all soils due to the characteristics of each soil, and even if possible, the reaction is slow due to the action of microorganisms and requires a long treatment period. .

  Therefore, the present invention can treat not only soil in the saturated zone below the groundwater level but also soil including excavated soil and the like, and relatively inexpensive iron material for soil contaminated with organochlorine compounds. An object of the present invention is to provide a method for detoxifying soil, which can decompose pollutants in a short period of time and at room temperature using only a reducing agent.

In order to achieve this object, the present invention provides a method for adding and mixing iron powder to soil located deeper than the groundwater level or excavated soil and contaminated with an organochlorine compound. A method for detoxifying a soil, wherein the soil is purified by decomposing a chlorine compound, and wherein the iron powder contains 0.1% by weight or more, preferably 0.2% by weight or more of carbon. the method, or the iron powder, is desirable and 500 cm ² / g or more include preferably at least 0.2 wt% carbon 0.1% by weight or more and has a higher specific surface area 2,000 cm ² / g 50 A method for detoxifying a soil, wherein at least about 10% by weight of the iron powder has a particle size passing through a sieve of 150 μm and added in a range of 0.1 to 10% by weight to the soil; Is spongy iron powder To provide a detoxification method of soil of a certain place.

  According to the present invention, in the conventional method, the soil contaminated with the organochlorine compound which has been excluded from the treatment, not only the soil in the saturated zone below the groundwater level but also the excavated soil, the carbon component of the iron powder, It is relatively inexpensive only by controlling the shape and dimensions and the amount added to the soil. Thus, the effect that the pollutant can be decomposed and made harmless to a state where there is no influence on the environment can be obtained. Further, by using spongy iron powder as the iron powder, the above effect can be easily obtained.

  The present invention relates to dichloromethane, carbon tetrachloride, 1,2-dichloroethane, 1,1-dichloroethylene, cis-1,2-dichloroethylene, 1,1,1-trichloroethane, 1,1,2-trichloroethane, trichloroethylene, tetrachloroethylene, Soil contaminated with volatile organic chlorinated compounds such as 1,3-dichloropropene and organic chlorinated compounds such as PCBs and dioxins is the object of purification, and these organic chlorinated compounds are dechlorinated or dechlorinated. It is characterized by being decomposed and rendered harmless by the action of hydrogen.

  The iron powder used for the purification of the contaminated soil has a carbon content of 0.1% by weight or more, and includes most ordinary steel components and ordinary cast iron components. If the amount of carbon is lower than 0.1% by weight, the decomposition rate of the pollutants becomes slow, which is not practical. The particle size of the iron powder is adjusted so that 50% by weight or more of the iron powder passes through a sieve having an opening of 150 μm. If iron powder having a coarser particle size is used, the decomposition rate of pollutants is reduced, the utilization efficiency of iron powder is reduced, and a larger amount of iron powder must be added, which is economically disadvantageous.

As the shape of the iron powder to be added to the soil, a powder having a specific surface area of 500 cm ² / g or more is used from the viewpoint of increasing the contact area with the pollutant and increasing the reaction efficiency. It can be easily obtained by sponge iron (sponge iron). At the same time, the iron powder desirably has a low crystal growth degree and has a pearlite structure as a crystal structure in order to enhance the reactivity with contaminants.
The amount of iron powder added to the soil is in the range of 0.1 to 10% by weight based on the wet weight of the soil. When the amount added is less than 0.1% by weight, the decomposition rate is remarkably reduced, and when the amount added is 10% by weight or more, it is economically disadvantageous.

  To add iron powder to the soil and mix it, in the case of in-situ treatment, use a high-pressure medium such as air or water to spray it into the ground, or use a civil engineering machine used in ground improvement work The method of excavation and mixing is adopted. In the case of excavation processing, it is also possible to use a mixing device such as a kneader, a mixer or a blender.

  Since the surface of the iron powder is gradually passivated as the surface is oxidized and its reaction force is reduced, in order to assist the decomposition of pollutants by the iron powder, the soil after the mixing of the iron powder is newly added to the soil. Care must be taken not to supply any oxygen or oxidizing substances. That is, it is desirable that the soil surface does not come into direct contact with fresh air in the in-situ processing or the post-digging processing.

  By performing the above-mentioned soil treatment, the environmental standards for soil pollution can be achieved in two to three months (Announcement on August 23, 1991, amendment, Hei 5 Announcement 19, Hei 6 Announcement 5 Soil can be rendered harmless up to the following levels:

  The samples prepared in Examples 1 to 4 were prepared by mixing soil contaminated with trichlorethylene and a predetermined ratio of iron powder in a light-impermeable container made of vinyl chloride having an inner diameter of 100 mm and a height of 500 mm. Was enclosed. Distilled water was further added from the bottom of the vessel to 150 mm to reproduce a saturated zone corresponding to soil below the groundwater level.

Samples were prepared by preparing containers in a number equal to the number of samples expected in advance, and after being left at room temperature for a predetermined period, sampling was performed for each container. Since the sample was collected in a rod shape from the top to the bottom of the container using a cylindrical sampler, the sample contained both saturated zone soil and unsaturated zone soil.
As the iron powder, a sponge ore-reduced iron powder (E-200) manufactured by Dowa Iron Powder Co., Ltd. was used as a raw material and adjusted to predetermined physical properties by reduction, sintering, pulverization, and sieving operations.

  Regarding the analysis method of trichlorethylene, this time it is not a method that complies with environmental standards in order to more fully grasp the situation in which the iron powder is decomposing organic chlorine compounds, but the moisture content in soil is measured and the soil dryness is measured. (This method is based on the method described in "Environment and Measurement Technology" Vol. 16, No. 15, 1989, 31-34, published by the Japan Society for Environmental Measurement and Analysis).

  In addition, the soil environmental standard is indicated by an elution value (mg / l) of 10 times the soil weight in water. Therefore, if the content value (mg / kg) is 10 times or less the soil environment standard value (mg / l), it can be determined that the soil environment standard is satisfied.

Example 1 The state of decomposition of trichlorethylene in soil was examined by changing the particle size of iron powder.
Iron powder having a carbon content of 0.2% by weight and a specific surface area of 2,000 cm ² / g was used, and the amount added to the soil was 0.2% by weight, and iron powder was not added to the soil. And the case where 50% by weight or more of iron powder having a particle size passing through a sieve of 300 μm is added to the soil, and the case where 50% by weight or more of iron powder having a particle size passing through a sieve of 150 μm is added to the soil. The decomposition situation was examined.
The results are shown in Table 1.

この結果から、鉄粉の粒度は５０重量％以上が１５０μｍのふるいを通過する微粒側の粒子であることが望ましいことがわかる。

From these results, it is understood that it is desirable that 50% by weight or more of the iron powder is fine particles passing through a 150 μm sieve.

[Example 2] Decomposition of trichlorethylene was examined by changing the addition ratio of iron powder to soil.
The iron powder has a carbon content of 0.2% by weight, a specific surface area of 2,000 cm ² / g, and a particle size of 50% by weight or more passes through a 150 μm sieve. The decomposition state of trichlorethylene was examined when no iron powder was added and when iron powder was added at a ratio of 0.03% by weight, 0.1% by weight and 1.0% by weight.
The results are shown in Table 2.

この結果から、鉄粉の土壌への添加割合としては少なくとも０．１重量％の場合が望ましいことがわかる。

From these results, it can be seen that the addition ratio of iron powder to the soil is preferably at least 0.1% by weight.

Example 3 The decomposition state of trichlorethylene was examined by changing the carbon content of iron powder.
Iron powder having a specific surface area of 2,000 cm ² / g is used. The proportion of the iron powder added to the soil is 0.2% by weight. The particle size of 50% by weight or more passes through a 150 μm sieve. The decomposition state of trichlorethylene was examined for iron powders having contents of 0.005% by weight, 0.05% by weight, 0.1% by weight and 0.2% by weight.
The results are shown in Table 3.

この結果から、鉄粉としては炭素含有量が０．１重量％以上のものが望ましいことがわかる。

From these results, it is understood that iron powder having a carbon content of 0.1% by weight or more is desirable.

[Example 4] The decomposition state of trichlorethylene was examined for iron powders having different surface areas per unit weight, that is, different specific surface areas.
Iron powder having a carbon content of 0.2% by weight and a particle size distribution of 50% by weight or more passing through a 150 μm sieve with a particle size of 0.2% by weight is used as the iron powder. the specific surface area of 300 cm ² / g of iron powder, was examined degradation status of trichlorethylene in the case of a 500 cm ² / g and 2,000 cm ² / g.
The results are shown in Table 4.

この結果から、鉄粉の比表面積は少なくとも２，０００ｃｍ^２／ｇのものにおいて顕著な効果が得られることがわかる。

From these results, it can be seen that a remarkable effect is obtained when the specific surface area of the iron powder is at least 2,000 cm ² / g.

As described above, iron powder necessary for decomposing organochlorine compounds has a particle size distribution in which the carbon content of iron powder is 0.1% by weight or more and 50% by weight or more passes through a 150 μm sieve, in a specific surface area 500 cm ² / g or more and particularly 2,000 cm ² / g or more and not found in the prior art by the addition in a proportion of 0.1 wt% to 10 wt% of the soil with respect to the soil A remarkable effect was obtained.

[Reference Example] Decomposition state of trichlorethylene due to difference in moisture content (%) of soil A test was conducted in which unsaturated zone soils with different dry conditions were reproduced.
In a 100 ml glass vial, dry soil: 40 g, trichlorethylene 4 g, iron powder E-200: 1 g, water was added in varying amounts and mixed, and the mixture was allowed to stand. The change in TCE concentration in the headspace was measured.

上記試験結果より、飽和帯の存在しない系でも土壌中の水分量が５％以上あれば当該方法によるトリクロロエチレンの分解が効果的に進行することが判明した。

From the above test results, it was found that the decomposition of trichlorethylene by the method effectively proceeds when the water content in the soil is 5% or more even in a system having no saturated zone.

  With regard to soil contaminated with organochlorine compounds, which has not been treated in the conventional method, not only soil in the saturated zone below the groundwater level but also excavated soil can be used to decompose pollutants and render them harmless.

Claims (4)

  By adding and mixing iron powder to soil located deeper than groundwater level or excavated soil and contaminated with organochlorine compounds, the organochlorine compounds are decomposed to purify the soil. A method for detoxifying soil, comprising:   The soil detoxification method according to claim 1, wherein the iron powder contains 0.1% by weight or more of carbon. The iron powder contains not less than 0.1% by weight of carbon, has a specific surface area of not less than 500 cm ² / g, and has a particle size of not less than 50% by weight passing through a 150 μm sieve. The soil detoxification method according to claim 1, wherein the soil is added within a range of 1 to 10% by weight. The method for detoxifying soil according to any one of claims 1 to 3, wherein the iron powder is spongy iron powder.