JP4482678B2 - Detoxification method of soil - Google Patents

Description

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

  Organochlorine compounds such as trichlorethylene, which have been used in large amounts as a degreasing solvent in semiconductor factories and metal processing factories from the past, and discharged or dumped after use, accumulate in a contaminated state of soil or groundwater. There are obstacles to use and land development in the surrounding area, and contamination of groundwater by accumulated organochlorine compounds has become a major social problem, such as the obstacle to the use of groundwater.

  About the method of treating contaminated water with such an organic chlorine-based compound with an iron-based metal reducing agent and decomposing and detoxifying the pollutants, for example, Japanese Patent Publication No. 2-49158, Japanese Patent Publication No. 2-49798, This is disclosed in Japanese Patent No. 2636171, Japanese Patent Application Laid-Open No. 5-501520, and Japanese Patent Application Laid-Open No. 6-506631.

  The method of Japanese Examined Patent Publication No. 2-49158 is a method in which the water to be treated, that is, the water containing hardly decomposable halogenated hydrocarbon is adjusted to pH 6.5 to 9.5 and then reduced with a base metal reducing agent such as iron, In the method of Japanese Patent Publication No. 2-49798, the water to be treated having an organic compound is detoxified with a metal reducing agent, the water to be treated is adjusted to pH 6.5 or more in advance, and the redox potential is lowered with a reducing substance. The method disclosed in Japanese Patent No. 2636171 is a method in which 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. In this method, the reduction treatment is performed by contacting with an equivalent carrier substance.

  In addition, the method disclosed in Japanese Patent Application Laid-Open No. 5-501520 is a method for purifying contaminated groundwater with halogen organic pollutants in a permeable ground made of metal such as iron particles in an environment where oxygen is blocked. It is a method of allowing the pollutant to decompose through the middle layer, and the method disclosed in Japanese Patent Publication No. Hei 6-506631 is an adsorbent such as activated carbon in which contaminated groundwater is formed in the ground as a similar method for purifying contaminated groundwater. In this method, the contaminants are adsorbed and decomposed by passing through a permeable layer made of a mixture of metal particles such as iron scrap and metal particles.

In addition, for contaminated groundwater, there are vacuum extraction methods and pumped water aeration methods that extract the contaminated groundwater out of the soil and render it harmless, and for soil, heat that is excavated and detoxified by heat treatment A desorption method and a thermal decomposition method are known, and a purification method using a bioremediation method using microorganisms is known as a method for decomposing and detoxifying contaminants in soil or groundwater.
Japanese Examined Patent Publication No. 2-49158 Japanese Patent Publication No. 2-49798 Japanese Patent No. 2636171 Japanese Patent Publication No. 5-501520 JP-T 6-506631 Publication

  However, the invention methods disclosed in Japanese Patent Publication No. 2-49158, Japanese Patent Publication No. 2-49798, and Japanese Patent No. 2636171 all deal with irrigation water or factory effluent, which is troublesome for the treatment of contaminated groundwater. It is premised on the drainage work of contaminated water, and it is necessary to remove dissolved oxygen by adjusting the pH of the contaminated water and supplying other reducing substances and hydrogen gas. Is difficult to apply, and has many disadvantages in terms of cost, such as using an iron reducing agent supported on activated carbon or the like.

In addition, the method of the invention of Tokuhei Hei 5-501520 and Tokuhei Hei 6-506631 is also an in-situ treatment method for groundwater, but mainly prevents the diffusion of contamination to the downstream area by the groundwater flow through the contaminated area. It is not intended to detoxify the contaminated area itself. In addition, a metal reducing agent is used in combination with an adsorbent made of activated carbon, and the iron layer is clogged with iron carbonate (FeCO ₃ ) produced by reaction with carbonate ions in groundwater, and therefore requires periodic replacement. There are many disadvantages in terms of cost. That is, in the case of the conventional technology, there has been the following problem with respect to the detoxification treatment of soil contaminated with organochlorine compounds and contaminated water in the soil.

  (1) Extracting and pumping soil gas and groundwater containing pollutants from the ground by vacuum extraction and pumping, etc., use activated carbon and a decomposing agent to remove and decompose pollutants in soil gas and extracted water. In addition, high-cost separate processing is required, such as installing facilities on the ground and detoxifying the pollutants generated by extraction and pumping. Moreover, since it does not purify the soil itself, the purpose of removing the obstacles in land development as described above cannot be achieved, and it cannot be said that it is a sufficient detoxification method.

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

  (3) The method of thermally decomposing excavated soil at a high temperature requires large-scale equipment for heat-treating the soil, and the soil particles themselves are altered by heat, for example, supporting structures and inhabiting living organisms. Since the function of the soil is significantly impaired, it becomes difficult to reuse the treated soil.

  (4) The bioremediation method is not adaptable to all soils due to the characteristics of each soil, and even if possible, the reaction is slow due to microbial action 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 in the unsaturated zone above the groundwater level or soil in general after excavation. It is an object of the present invention to provide a soil detoxification method that can decompose pollutants at room temperature in a short period of time by using a reductant containing only a relatively inexpensive iron material for contaminated soil.

In order to achieve this object, the present invention provides an iron powder for soil located deeper than groundwater level, soil located shallower than groundwater level, or excavated soil and contaminated with organochlorine compounds. The method of detoxifying the soil to purify the soil by decomposing the organochlorine compound by adding and mixing, and the iron powder is 0.1 wt% or more, preferably 0.2 wt% or more desirable and 500 cm ² / g or more include a carbon has a particle size of more than 50% by weight passes through a sieve of 150μm and having a higher specific surface area 2,000cm ² / g, 0.1~10 to the soil A method for detoxifying soil that is added within the range of% by weight, and a method for detoxifying soil in which the iron powder is spongy iron powder are also provided.

  According to the present invention, soil contaminated with organochlorine compounds, which has not been treated by the conventional method, includes not only saturated zone soil below groundwater level but also unsaturated zone soil and ground excavated soil above groundwater level. The target is to control the carbon component, shape, and dimensions of iron powder, and only by controlling the amount added to the soil. By the simple room temperature treatment method, it is possible to obtain an effect that the pollutants can be decomposed and rendered harmless in a short period of time without causing an environmental impact. Furthermore, the said effect can be acquired easily by utilizing spongy iron powder as iron powder.

  The present invention includes 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 organochlorine compounds such as 1,3-dichloropropene and organochlorine compounds such as PCBs and dioxins is subject to purification, and these organochlorine compounds are dechlorinated or dechlorinated. It is characterized by decomposing and detoxifying by the action of hydrogen.

  The iron powder used for the purification of 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 pollutant becomes slow, which is not practical. The particle size of the iron powder is adjusted so that 50% by weight or more of the whole 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 is added, which is economically disadvantageous.

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

  In order to add and mix iron powder into the soil, in the case of in-situ treatment, use a high-pressure medium such as air or water, or use a civil engineering machine used in ground improvement work. A method of excavating and mixing is taken. In the case of excavation processing, a mixing device such as a kneader, a mixer or a blender can be used.

  Since iron powder is gradually passivated due to oxidation of its surface and its reaction power decreases, in order to aid the decomposition action of pollutants by iron powder, it is newly added to the soil after mixing iron powder. Care must be taken not to supply oxygen or oxidizing substances. That is, it is desirable to prevent the soil surface from coming into direct contact with fresh outside air during in-situ processing or post-digging processing.

  By performing soil treatment as described above, environmental standards related to soil contamination in 2 to 3 months (August 23, 1991 notification, amendment, Heisei 5 notice 19, Heisei 6 notice 5, ring It is possible to detoxify the soil up to Notification 25, 1995 Notification 19).

  Samples prepared in Examples 1 to 4 were prepared by mixing soil contaminated with trichlorethylene and iron powder in a predetermined ratio into a container made of vinyl chloride that does not transmit light with an inner diameter of 100 mm and a height of 500 mm. Was enclosed. Further, distilled water was added up to 150 mm from the bottom of the vessel to reproduce a saturated zone corresponding to soil below the groundwater level, and an upper 350 mm reproduced an unsaturated zone corresponding to soil above the groundwater level.

Samples were prepared by preparing containers as many as the number of samples planned in advance, and were allowed to stand at room temperature for a predetermined period, and then sampled 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 contains both saturated and unsaturated soil.
The iron powder used was Dowa Iron Powder Industry Co., Ltd., spongy ore reduced iron powder (E-200), which had been adjusted to predetermined physical property values by operations of reduction purification, sintering, pulverization, and sieving.

  As for the analysis method of trichlorethylene, this time, it is not a method that complies with the environmental standards in order to grasp the situation where the iron powder is decomposing organochlorine compounds. (This method is based on the method described in “Environment and Measurement Technology” Vol. 16, No. 15, 1989, 31-34, published by the Japan Environmental Measurement and Analysis Association).

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

[Example 1]
The decomposition state of trichlorethylene in soil was investigated by changing the particle size of iron powder.
The iron powder, 0.2 wt% carbon content, using a specific surface area of 2,000 cm ² / g, the addition amount relative to the soil was 0.2 wt%, if no added iron powder to the soil And when the iron powder having a particle size of 50% by weight or more passing through a 300 μm sieve is added to the soil and the iron powder having a particle size of 50% by weight or more passing through a 150 μm sieve is added to the soil. The decomposition situation was investigated. 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 this result, it can be seen that it is desirable that the iron powder has a particle size of 50% by weight or more passing through a 150 μm sieve.

[Example 2]
The decomposition state of trichlorethylene was investigated by changing the ratio of iron powder added to the 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 passing through a 150 μm sieve. The decomposition state of trichlorethylene was investigated for the case where the iron powder was not added to the iron and for the case where the iron powder was added at a ratio of 0.03 wt%, 0.1 wt% and 1.0 wt%.
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 this result, 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 investigated by changing the carbon content of iron powder.
The iron powder has a specific surface area of 2,000 cm ² / g, the addition ratio to the soil is 0.2 wt%, and the particle size is 50 wt% or more that passes through a 150 μm sieve. The iron powder having a content of 0.005% by weight, 0.05% by weight, 0.1% by weight and 0.2% by weight was examined for the decomposition state of trichlorethylene.
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 this result, it is understood that the iron powder preferably has a carbon content of 0.1% by weight or more.

[Example 4]
The decomposition state of trichlorethylene was investigated about the iron powder from which the surface area per unit weight, ie, a specific surface area, differs.
The iron powder has 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. 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２，０００ｃｍ²／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 this result, 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, the iron powder necessary for the decomposition of the organic chlorine compound has a particle size distribution in which the carbon content in the 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.

[Example 5]
Degradation of trichlorethylene due to differences in soil moisture content (%) A test was conducted to reproduce unsaturated zone soils with different dry conditions.
In a 100 ml glass vial bottle, dry soil: 40 g, trichlorethylene 4 g, iron powder E-200: 1 g, and water were added after changing the addition amount, and the mixture was allowed to stand, and 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 even in a system without a saturated zone, if the water content in the soil is 5% or more, the decomposition of trichlorethylene by the method proceeds effectively.

Claims (6)

Wet iron powder containing 0.1% by weight or more of carbon in soil that is shallower than the groundwater level and has a water content of 5 to 10% and is contaminated with organochlorine compounds. A method for detoxifying soil, comprising decomposing the organic chlorine compound contaminating the soil to purify the soil by adding and mixing in a range of 0.1 to 10% by weight . The soil position to the water content in the shallow than groundwater level is contaminated by and organochlorine compounds comprising 5-10% of soil, the unrealized specific surface area of carbon than 0.1 wt% of at least 2000 cm ² / g of iron powder is added within a range of 0.1 to 10% by weight with respect to the wet weight of the soil and mixed to decompose the organochlorine compound that contaminated the soil, thereby purifying the soil. A soil detoxification method characterized by the above. Soil that is shallower than the groundwater level and has a water content of 5 to 10% and contaminated with organochlorine compounds should contain 0.1 wt% or more of carbon so that it does not come into direct contact with fresh outside air. By adding and mixing iron powder containing 0.1 to 10% by weight with respect to the wet weight of the soil, the organochlorine compound that contaminated the soil is decomposed and the soil is purified in situ. A method for detoxifying soil, characterized by comprising: Soil that is shallower than the groundwater level and has a water content of 5 to 10% and contaminated with organochlorine compounds should contain 0.1 wt% or more of carbon so that it does not come into direct contact with fresh outside air. by unrealized specific surface area to mix the iron powder of at least 2000 cm ² / g was added in an amount of 0.1 to 10% by weight relative to the wet weight of the soil, the organic chlorine compound contaminated the soil A soil detoxification method comprising decomposing and purifying the soil in situ. Wet iron powder containing 0.1% by weight or more of carbon in soil that is shallower than the groundwater level and has a water content of 5 to 10% and is contaminated with organochlorine compounds. It is characterized by decomposing organochlorine compounds contaminating the soil and purifying the soil in situ by adding 0.1 to 10% by weight and mechanically excavating and mixing. Soil detoxification treatment method. The soil position to the water content in the shallow than groundwater level is contaminated by and organochlorine compounds comprising 5-10% of soil, the unrealized specific surface area of carbon than 0.1 wt% of at least 2000 cm ² / g of iron powder is added in the range of 0.1 to 10% by weight with respect to the wet weight of the soil and mechanically excavated and mixed to decompose the organochlorine compound that contaminated the soil and A method for detoxifying soil, wherein the soil is purified by