JP2002241735A - Detoxifying treatment agent for object to-be-treated contaminated with organohalogen compound and detoxifying treatment method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a detoxifying treatment agent capable of decomposing organohalogen compound(s) in a short time and enabling the compound(s) to be detoxifyingly treated without forming toxic byproducts, and to provide a detoxifying treatment method using the above agent. SOLUTION: The detoxifying treatment agent for object(s) to-be-treated contaminated with organohalogen compound(s) is such that the carbon content of iron powder composed of iron (Fe) and carbon (C) is 1.0-60 wt.% determined by the high-frequency induction heating oven combustion-infrared-absorbing analysis method in accordance with JIS G 1211 and the cementite (Fe3C) content of the above iron powder is >=15 wt.% determined by X-ray microanalyzer method. The detoxifying treatment method using the above agent is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detoxifying agent for an object to be treated, such as soil, industrial waste, sludge, sludge, wastewater, and groundwater, and a method for detoxifying the same using the same. It is about.

[0002]

2. Description of the Related Art In recent years, trichloroethylene,
Environmental pollution problems due to organic halogen compounds such as tetrachloroethylene, dichloromethane, PCB (polychlorinated biphenyl), and dioxins have become apparent and have become a serious problem.

[0003] In order to solve these problems, in particular, treatment agents for detoxifying soil, drainage water, groundwater, and the like contaminated with an organic halogen compound and a treatment method thereof have been studied, and several technical reports and patent applications have been filed.

[0004] 1) In the case of contaminated wastewater and groundwater, vacuum extraction
Although the adsorption method and the pumping aeration method are known, a lifting device to the ground, a suction device for the contaminants further raised,
Regeneration or disposal of the activated carbon adsorbent is required. In addition, it does not detoxify contaminated wastewater, groundwater and nearby soil itself, and cannot be said to be an essential detoxification method. In recent years, treatment methods have been reported in which pollutants are decomposed and made harmless simply by mixing and spraying a base metal catalyst. As a method of detoxifying with an iron-based catalyst, for example, Japanese Patent Publication No. 2636171, Japanese Patent Publication No. 2-49158, Japanese Patent Publication No. 2-497
No. 98 discloses a method of adjusting the pH of wastewater contaminated by an organochlorine compound, further supplying hydrogen gas or a reducing agent, etc., and then performing a deoxygenation treatment. is there. In addition, Tokuhyo Hei 5-501520
JP-A-6-506661, JP-A-8-2
No. 57570 discloses a method in which iron or a permeable wall carrying iron is installed in a groundwater area and detoxified by in situ treatment. However, these techniques require the pH adjustment of contaminated wastewater and groundwater, the treatment of dissolved oxygen, and the conditions for addition of iron powder are unknown, which is difficult as a practical method. In addition, those in which an iron-based catalyst is supported on activated carbon are costly and remain economically problematic.

[0005] 2) As a method for treating contaminated soil, sludge, sludge, etc., a thermal desorption method and a thermal decomposition method in which a heating electrode is inserted into excavated soil or directly into soil to perform heat treatment are known. In this method, the vicinity of the electrode is thermally decomposed, but others are only volatilized on the ground mainly with volatile organic chlorine compounds and are not a fundamental treatment method. Although there is a bioremediation method in which detoxification is performed using a reducing substance via microorganisms, it is considered that detoxification requires a long time, and cannot be applied to all soils, so that complete detoxification is impossible. JP-A-11-235577 discloses a technique for decomposing and treating pollutants by adding an iron-based decomposition catalyst to contaminated soil.
Since it is not decomposed in a short time, higher performance is required.

[0006]

As described above, the method of treating an object contaminated with an organic halogen compound has a problem that the treatment time is long, the cost is high, and the treatment method is complicated and is not practical. I have. In particular, as a technology to add iron-based decomposition catalysts to make them harmless, it is necessary to adjust the pH of contaminated wastewater and groundwater, and to dissolve dissolved oxygen. Is required.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to solve these problems, and as a result, have completed the present invention. The present invention provides a detoxifying treatment agent and a treatment method using the same, whereby legally regulated values of contaminated organic halogen compounds can be cleared. That is, according to the present invention, the content of carbon (C) in iron powder composed of iron (Fe) and carbon (C) is 1.0 to 60 weight as measured by a high-frequency induction heating furnace combustion-infrared absorption method of JIS G 1211. %, And wherein the content of cementite (Fe ₃ C) in the iron powder is 15% by weight or more as measured by an X-ray microanalyzer method, for an object to be treated contaminated with an organic halogen compound. It is a detoxifying agent.

Hereinafter, the present invention will be described in more detail.

The object to be treated by the detoxifying agent of the present invention is one which is contaminated with an organic halogen compound. Here, the organic halogen compound is not particularly limited as long as it is a compound described in the soil environmental standard item. For example, dichloromethane, carbon tetrachloride, 1,2-dichloroethane, 1,1-dichloroethylene, cis −
Examples thereof include 1,2-dichloroethylene, 1,1,1-trichloroethane, 1,1,2-trichloroethane, TCE (trichloroethylene), tetrachloroethylene, and 1,3-dichloropropene.

The detoxifying agent of the present invention contains iron powder composed of iron (Fe) and carbon (C), and has a composition containing cementite (Fe ₃ C) in the iron powder. It is.

Here, cementite (Fe ₃ C) is
A metastable phase of iron carbide, for example, spheroidite (pearlite tempered), sorbite (fine layered
Light), tolstite (solpite or Fe)
₂ C), martensite, Fe ₂ C (martensite tempering), and the like.

When the organic halogen compound is made harmless by the detoxifying agent of the present invention, 1) the iron portion in the iron powder dissolves iron as an oxidation reaction site and emits electrons, and 2) the carbon portion in the iron powder emits electrons. The organic halogen compound is dechlorinated and decomposed as a reduction reaction field.

In order to increase the oxidation-reduction reaction rate, it is conceivable to increase the reaction field by dispersing and arranging iron and carbon in a microscopic manner. In particular, it is considered that a compound of iron and carbon including cementite or the like becomes a redox reaction field.

The detoxifying agent of the present invention has a carbon content in iron powder of a high-frequency induction heating furnace according to JIS G1211.
It is 1.0 to 60% by weight as measured by an infrared absorption method.
In the high-frequency induction heating furnace combustion-infrared absorption method of JIS G 1211, carbon is carried out in a carbon dioxide gas and / or carbon monoxide gas in an oxygen stream, and the infrared absorption amount thereof is measured.

The carbon content in the iron powder is 1.0 to 60% by weight.
It is necessary to be. The carbon content in the iron powder is 1.0
If the amount is less than 10% by weight, the decomposition reaction field in the iron powder becomes insufficient, so that the decomposition rate of the organic halogen compound is remarkably slow, and the treatment takes a long time. In addition, even if the amount of iron powder added to the material to be treated is increased, the performance does not remarkably appear and it is economically disadvantageous, and the legally regulated value cannot be cleared.

On the other hand, even if the carbon content in the iron powder exceeds 60% by weight, cementite (Fe ₃ C) is decomposed and the decomposition reaction field in the iron powder becomes insufficient, so that the decomposition reaction rate of the organic halogen compound is reduced. Gradually decreases. In addition, such a method for producing high-carbon iron powder is very special, which is economically disadvantageous.

The decomposition can be completed in a short time without generating an organic halogen compound corresponding to the soil environmental standard items, and the processing cost is economical. The carbon content is 3 to 25% by weight. Is more preferable, and the carbon content is more preferably 3 to 10% by weight in consideration of the production method, cost and the like.

Further, in the detoxifying agent of the present invention, the content of cementite (Fe ₃ C) in the iron powder is 15% by weight or more as measured by an X-ray microanalyzer method. This X
The X-ray microanalyzer method is a method for quantitatively analyzing the composition of an alloy, in which a characteristic X-ray wavelength generated from an incident electron beam is measured, and the composition of a minute portion is analyzed.

The content of cementite (Fe ₃ C) needs to be 15% by weight or more. Cementite (Fe
_{If the} 3C) content is less than 15% by weight, the decomposition reaction field in the iron powder becomes insufficient.

The iron powder of the detoxifying agent of the present invention has a specific surface area of 0.05 m ² / g or more and 200 μm or more.
By using iron powder having a particle size that passes through a m sieve,
It is more preferable because the decomposition reaction rate and the contact probability can be improved, and harmful organic halogen compounds described in the soil environment standard items such as cis-1,2DCE can be decomposed in a shorter time.

The shape of the iron powder in the present invention is not particularly limited, and includes a spherical shape, a spherical shape, a dendritic shape, a flake shape, a needle shape, a square shape, a laminated shape, a spongy shape and the like.

The detoxifying agent of the present invention contains iron powder as described above, but may contain additives to such an extent that its effect is not impaired. The additives are not particularly limited, and include, for example, antioxidants, reaction accelerators, dispersants and the like. In the case where the object to be treated is a fluid such as groundwater, it is preferable that the object contains only iron powder other than inevitable impurities.

In the detoxification treatment method of the present invention, the above-mentioned detoxification treatment agent is added to an object to be treated contaminated with an organic halogen compound, followed by treatment.

The amount of the detoxifying agent is not particularly limited. However, the probability of contact with the organic halogen compound in the object to be treated is increased to increase the decomposition rate, which is economically advantageous. It is preferably in the range of 0.1 to 10% by weight based on body soil, groundwater and the like.

Examples of the method of adding and mixing the detoxifying agent are as follows: 1) Continuous and uniform mixing of excavated soil or pumped ground water using a mixer, kneader or the like;
Alternatively, batch mixing using a mixing pit or the like, and 2) as an in-situ processing method, uniform mixing can be performed by injecting a detoxifying agent into soil, groundwater, or the like with air or water.

In addition, there is no need to adjust the pH or deoxygenate the object contaminated with the organic halogen compound,
Detoxification can be achieved by adding and mixing only the detoxifying agent.

In the detoxification treatment method of the present invention, an electrolyte, a dispersant and the like may be added in addition to the detoxification treatment agent to such an extent that the effect is not impaired. Here, examples of the electrolyte include sodium chloride and sodium sulfate, and examples of the dispersant include activated carbon, alumina, zeolite, silica gel, and silica-alumina.

[0028]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Examples 1 to 3 and Comparative Examples 1 to 6 A 125 ml vial was charged with a 100 ppm aqueous TCE solution, benzene in methanol, and iron powder, and sealed. This aqueous solution was not subjected to a dissolved oxygen treatment, and was adjusted to pH 6 to 7 with hydrochloric acid or sodium hydroxide.
Was adjusted. The reaction conditions were 30 ° C. and 200 rpm immersion.

The iron powder is a high frequency induction according to JIS G 1211.
Induction furnace combustion-carbon content measured by infrared absorption method
0.004 to 75% by weight, X-ray microanalyzer method
0.06 to 62.9 cementite content measured by
Wt%, specific surface area 0.2-1.2m^Two/ G, 75 μm
A particle size product passed through a sieve was used (Examples 1 to 3,
Comparative Examples 1 to 5). Comparative Example 5 has a carbon content of 0.004% by weight.
Iron powder under vacuum (10 ^-3Torr) for carbon coating
Comparative Example 6 crushed graphite plate
And using a product having a particle size of 75 μm or less to 100% by weight of carbon.
Was used. The amount of iron powder added was 1 g (1 per aqueous solution).
% By weight).

As a method of analyzing the TCE concentration, JIS
The TCE concentration was quantitatively analyzed over time using a head space method based on K 0125 (test method for volatile organic compounds in water and wastewater). The oxidation-reduction potential (ORP) after the test was also measured. The results of these measurements are shown in Table 1 and FIG.

[0032]

[Table 1] In Examples 1 to 3, the TCE concentration after 5 to 10 days was 0.03 ppm or less as the soil environmental standard. It was confirmed that although the decomposition product was mainly composed of ethylene, other organic halogen compounds listed in the soil environmental standard were not generated. In addition, the ORP value of the TCE solution alone is 250 to
It shows a potential well below 300 mV, suggesting that the TCE solution tends to undergo reductive decomposition.

In Comparative Examples 1 to 5, even after 10 days, the TCE concentration was not lower than 0.03 ppm in the soil environment standard and the ORP value was high. On the 10th day, the product with 100% carbon of Comparative Example 6 showed a decrease in TCE peak and seemed to be decomposed at first glance, but no internal benzene was observed at all, and it was judged that it was due to a mere adsorption action. Was.

Therefore, it was found that the ability to decompose organic halogen compounds was remarkable when the detoxifying agent of the present invention was used.

Examples 4 to 6 and Comparative Examples 7 to 12 The ability of the present invention to decompose TCE-contaminated model soil was examined.

Diatomaceous earth (Wako Pure Chemical, # 2)
5 to 30) and 0.5 g of iron powder (1.6% by weight based on soil) were mixed for 5 minutes.

A model soil mixed with iron powder in a 125 ml vial bottle, 10 ml of pure oxygen-free water (33% by weight based on soil), 10 ppm TCE and benzene in methanol dissolved therein were added and sealed. The reaction conditions were 30 vials.
C., 200 rpm immersion was maintained.

The iron powder has a carbon content of 0.004 to 75% by weight measured by a high frequency induction heating furnace combustion-infrared absorption method of JIS G 1211 and a cementite content of 0.06 to 62% measured by an X-ray microanalyzer method. .9
% By weight, specific surface area: 0.2 to 1.2 m ² / g, 75 μm
(Examples 4 to 6 and Comparative Examples 7 to 11) were used. Comparative Example 11 used iron powder having a carbon content of 0.004% by weight which was subjected to carbon coating under vacuum (10 ^-3 Torr). Comparative Example 12 was obtained by pulverizing a graphite plate to a particle size of 75 μm or less. 100% carbon by weight
Was used.

As a method of analyzing the TCE concentration, the TCE concentration was quantitatively analyzed with time using the head space method.
The measurement results are shown in Table 2 and FIG.

[0040]

[Table 2] Examples 4 to 6 use iron powder having a carbon content of 0.88 to 4.2% by weight, and the TCE concentration in the soil is from 0.03 mg / L or less to the soil environmental standard after 10 days to at least 30 days later. Thus, it was confirmed that the detoxifying agent of the present invention exhibited high resolution even in soil. In addition, it was confirmed that the decomposition by-product was mainly ethylene, and no other organic chlorine compounds listed in the soil environmental standard were produced.

In Comparative Examples 7 to 11, 0.1 mg /
It was found that the carbon content in the iron powder, that is, the amount of cementite (Fe ₃ C) was insufficient, without being lower than L. In addition, in the carbon 100% product of Comparative Example 12, the TCE peak decreased with time and seemed to be decomposed at first sight.
The internal standard benzene was not found at all, and it was judged to be due to a mere adsorption action.

Therefore, it was found that the ability to decompose organic halogen compounds was remarkable even in contaminated soil by using the detoxifying agent of the present invention.

Examples 7 to 10 and Comparative Examples 13 to 14 The effects of the specific surface area and the particle size of the detoxifying agent of the present invention on the TCE-containing solution were examined.

A 125-mL vial was charged with a 100 ppm aqueous TCE solution, benzene in methanol dissolved therein, and iron powder, and sealed. This aqueous solution was not subjected to the treatment of dissolved oxygen, but was adjusted to pH 6 to 7 with hydrochloric acid or sodium hydroxide. The reaction conditions are 30 ° C., 200
The rpm soak was maintained.

The iron powder has a cementite content of 3.0 to 61.5% by weight measured by an X-ray microanalyzer method, and a carbon content of 0.2 measured by a high frequency induction heating furnace combustion-infrared absorption method of JIS G 1211. % By weight (Comparative Examples 13 and 14), 3.9% by weight (Examples 7 and 8) and 4.1% by weight (Examples 9 and 10), and the specific surface area was 0.0
Iron passing through a sieve of 1 to 1.2 m ² / g with a particle size of 75 μm (Example 7, Example 9, Comparative Example 14), 200 μm (Example 8), 400 μm (Example 10, Comparative Example 13). Powder was used. The amount of iron powder added was all 1 g (1% by weight of aqueous solution).

As a method of analyzing the TCE concentration, the TCE concentration was quantitatively analyzed with time using a head space method.
Table 3 shows the measurement results.

[0047]

[Table 3] Examples 7 to 10 have a carbon content of 3.9% by weight and 4.1%.
% Iron powder, and even after changing the specific surface area and particle size, the TCE concentration was 0.03 pp in the soil environment standard after 10 days.
m or less. It was confirmed that although the decomposition product was mainly composed of ethylene, no other organic chlorine compounds listed in the soil environmental standard items were generated.

In Comparative Examples 13 and 14, the carbon content was less than 1.0% by weight, and TCE remained after 10 days. Further, the decomposition product is cis-1,2DCE in addition to ethylene.
Other organochlorine compounds listed in the soil environmental standard items were detected, and it was confirmed that complete detoxification was not possible.

Therefore, it was found that the use of the detoxifying agent of the present invention has a remarkable decomposition ability of the organic halogen compound and can be made harmless.

[0050]

As is clear from the above description, according to the detoxifying agent and the detoxifying method of the present invention, an organic halogen compound is decomposed in a short time, and no harmful by-products are generated, thereby making the detoxification possible. It has an effect that can be processed.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the carbon content in iron powder and the TCE concentration in a TCE-containing aqueous solution.

FIG. 2 is a graph showing the relationship between the carbon content in iron powder and the TCE concentration in a TCE-containing soil.

Claims (4)

[Claims] 1. An iron powder composed of iron (Fe) and carbon (C) has a carbon (C) content of 1.0 to 60 as measured by a high-frequency induction heating furnace combustion-infrared absorption method according to JIS G 1211.
% By weight and the cementite (Fe ₃
C) A detoxifying agent for an object to be treated contaminated with an organic halogen compound, wherein the content is 15% by weight or more as measured by an X-ray microanalyzer method. 2. The detoxifying treatment for an object to be treated according to claim 1, wherein the iron powder has a specific surface area of 0.05 m ² / g or more and a particle size passing through a 200 μm sieve. Agent. 3. A treatment object contaminated with an organic halogen compound, wherein the treatment object contaminated with an organic halogen compound is added, mixed and treated with the detoxifying agent according to claim 1 or 2. Detoxification method of goods. 4. The detoxification of an object to be treated contaminated with an organic halogen compound according to claim 3, wherein the amount of the detoxifying agent added is 0.1 to 10% by weight based on the object to be processed. Processing method.