JP2002166171A - Iron powder for decomposing organic halogen compound and method for making contaminated soil, ground water, and gas harmless - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an iron powder for decomposing organic halogen compounds which is excellent in decomposition rate of organic halogen compounds and is highly safe. SOLUTION: At the surface of this iron powder for decomposing organic halogen compounds, there is graphite in a high concentration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to iron powder for decomposing organic halogen compounds and a method for detoxifying contaminated soil, groundwater and gas. High organic halogen compound decomposition iron powder and contaminated soil using the iron powder,
Detoxification of groundwater and gas.

[0002]

2. Description of the Related Art In recent years, trichlorethylene (T) which has been used in large quantities as a degreasing solvent in semiconductor factories and metal processing factories, and has been discharged and discarded after use, has been used.
Contamination of groundwater and soil by organic halogen compounds such as CE) is a major social problem. Conventionally, as a method of solving these pollutions, there are a vacuum extraction method, a pumping aeration method, and the like, in which contaminated groundwater is extracted outside the soil and detoxified and buried. As for soil, a thermal desorption method and a thermal decomposition method in which contaminated soil is excavated and made harmless by heat treatment are known. Further, as a method of decomposing and detoxifying contaminants in groundwater or soil, a purification method by a bioremediation method using microorganisms is known.

[0003] However, methods such as a vacuum extraction method and a pumping aeration method use a method in which activated carbon or decomposition gas is used to remove or decompose pollutants after pumping and extracting groundwater or soil gas containing pollutants from the ground. Use of the agent requires high-cost separate treatment, such as installing equipment on the ground and detoxifying and embedding generated contaminants. In addition, the method of pyrolyzing excavated soil at a high temperature requires a large-scale facility for heat-treating the soil, and the soil particles themselves are deteriorated by heat, and for example, the function of the soil to inhabit living organisms is significantly impaired. Therefore, it is difficult to reuse the soil after treatment. Furthermore, the bioremediation method cannot be applied to all soils due to differences in soil characteristics, and even when applicable, the reaction is slow due to the action of microorganisms and requires a long treatment period.

In order to overcome the above-mentioned problems of the conventional countermeasures against pollution of groundwater and soil, various methods have been proposed in which halogen-containing organic contaminants are reacted with iron to reductively dehalogenate and detoxify them. And is gaining attention. For example, Japanese Unexamined Patent Publication No. Hei 5-501520 discloses that a groove is formed in a flow path of groundwater, and iron having a granular shape, a piece shape, a fibrous shape, or the like is filled and brought into contact with a halogen-containing organic pollutant. It describes a method of dehalogenating and detoxifying it. Japanese Patent Publication No. 6-506631 describes a method which is similar in principle to the method disclosed in Japanese Patent Publication No. 5-501520 and uses a mixture of metallic iron and activated carbon. Further, Japanese Patent Application Laid-Open No. 11-235577 discloses that an organic halogen-based compound contained in an unsaturated zone soil at a groundwater level or higher or an excavated soil is reduced by iron powder containing 0.1% or more of C. The method of detoxifying the iron powder is described, and it is described that the crystal structure of the iron powder preferably has a pearlite structure. Further, Japanese Patent Application Laid-Open
JP-5740 discloses the use of copper-containing iron powder.

[0005]

SUMMARY OF THE INVENTION However, Japanese Patent Publication No.
All of the methods described in JP-A No. 01520, JP-A-6-506631 and JP-A-11-235577 have a problem that the decomposition rate of the organic halogen compound is low. Further, the method described in JP-A-2000-5740 has a problem that copper itself is a harmful element, which may cause secondary contamination.

Accordingly, the present invention provides a highly safe iron powder for decomposing organic halogen compounds, which has a high decomposition rate, and a method for detoxifying contaminated soil, groundwater and gas using the iron powder. The purpose is to provide.

[0007]

Means for Solving the Problems The present inventor has conducted intensive studies to solve the above-mentioned problems, and completed the present invention. That is,
The present invention provides an iron powder for decomposing an organic halogen compound in which graphite is concentrated on the surface.

[0008] Probability P _ad of the graphite on the surface
Is preferably from 0.001 to 0.9.

It is preferable that the reaction active site existence probability coefficient K _{p (reactive site)} represented by the following formula (1 ₎ is 0.05 or more. K _{p (reactive site)} = (0.04π × n × P _ad ) ^1/2 (1) where n is the surface 1 of the iron powder for decomposing the organic halogen compound.
Represents the number of graphite particles present per 00 μm ² ,
_ad represents the existence probability of graphite on the surface of the iron powder for decomposing an organic halogen compound.

In addition, the above-mentioned iron powder for decomposing an organic halogen compound is brought into contact with at least one of soil, groundwater and gas contaminated with the organic halogen compound to decompose the organic halogen compound. To provide detoxification methods for soil, groundwater and gas. Preferably, the above-mentioned contacting method includes the following (a), (b),
It is at least one of (c), (d) and (e). (A) A method of placing the iron powder for decomposing an organic halogen compound in groundwater contaminated with the organic halogen compound. (B) A method in which groundwater contaminated with an organic halogen compound is pumped and brought into contact with the iron powder for decomposing the organic halogen compound. (C) adding iron powder for decomposing the organic halogen compound to soil contaminated with the organic halogen compound. (D) excavating soil contaminated with organohalogen compounds,
A method of mixing the excavated soil with the iron powder for decomposing an organic halogen compound. (E) A method in which a gas obtained by suction from soil and / or groundwater contaminated with an organic halogen compound is brought into contact with the iron powder for decomposing the organic halogen compound.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the iron powder for decomposing an organic halogen compound of the present invention will be described in detail. The iron powder for decomposing an organic halogen compound of the present invention is characterized in that graphite is present on the surface in a concentrated state. That is, graphite is present in a larger amount on the surface of the iron powder than inside the iron powder. As described later, the organic halogen compound is easily adsorbed by graphite and is decomposed at the boundary between graphite and ground iron. The iron powder for decomposing an organic halogen compound of the present invention has a high probability that the organic halogen compound contacts and is adsorbed on the graphite because the graphite is concentrated on the surface, and as a result, the decomposition rate of the organic halogen compound is high. Become.

As a method of checking graphite on the surface, for example,
AES (Auger electron spectroscopy) analysis can be used. Hereinafter, a specific description will be given. Observing a BSE image (reflection electron image) of the iron powder surface with a SEM attached to the FE-AES analyzer (FIG. 1), and conducting a survey scan by focusing the beam on a portion presumed to be a precipitate from the contrast, Fe, C, O, etc. are detected in the iron part (FIG. 2), and in the graphite, O is slightly detected but Fe is not detected, and almost all is C (FIG. 3). In the above method, the presence of graphite was also confirmed by X-ray diffraction analysis performed on the same sample and cross-sectional observation performed on a sample obtained by embedding and polishing the same sample. It can be used as a method for confirming graphite.

Here, the X-ray diffraction analysis has a problem of the S / N ratio. Therefore, when the amount of graphite on the surface is extremely small,
Can not be used. Also, the method by cross-section observation is
This method cannot be said to be an easy method because a cross-section embedding polishing process is required. On the other hand, the method of confirming graphite on the surface using AES analysis can be used even when the amount of graphite on the surface is extremely small, and the measurement is easy. .

In the iron powder for decomposing an organic halogen compound of the present invention, the thickness of the graphite is preferably 0.01 to 5 μm, more preferably 0.1 to 3 μm. The thickness of the graphite can be measured by, for example, cross-sectional observation.

[0015] In the organic halogen compound-decomposing iron powder for the present invention, the presence probability P _ad on the surface of the graphite,
It is preferably 0.001 to 0.9. Within the above range, the decomposition rate of the organic halogen compound is increased. P _ad
Is more preferably 0.01 to 0.8, and 0.2
More preferably, it is 0.6. Here, the existence probability P _ad at the surface of the graphite, the ratio of the total area of the graphite relative to the total area of the iron powder surface (area ratio of graphite). The area ratio of graphite was measured at a magnification of 1000 by the AES analysis described above.
A BSE image of the surface of the iron powder is photographed at a magnification of 10000 to 10000, and the surface is 100 μm ² (for example, 10 μm per side) using commercially available image analysis software (for example, particle analysis software (version 1.0) manufactured by Sumitomo Metal Technology Co., Ltd.) Total area S _graphite per square area) (unit: μm)
Was measured, from P _ad = S _graphite / 100, obtains the P _ad. The measurement is performed at a plurality of locations, for example, 10
It is preferably performed at a point, in which case an average value is used as _Pad .

Further, in the iron powder for decomposing an organic halogen compound of the present invention, the reaction probability site existence probability coefficient K _{p (reactive site)} represented by the following formula (1 ₎ is 0.05 or more. Preferably, it is 0.05 to 3.0, more preferably 0.1 to 1.0. K _{p (reactive site)} = (0.04π × n × P _ad ) ^1/2 (1) where n is the surface 1 of the iron powder for decomposing the organic halogen compound.
Represents the number of graphite particles present per 00 μm ² ,
_ad represents the existence probability of graphite on the surface of the iron powder for decomposing an organic halogen compound. When _{Kp (reactive site)} is in the above range, graphite particles are dispersed on the surface, and many reaction active sites are present on the surface, so that the decomposition rate of the organic halogen compound is increased.

The _{Kp (reactive site)} will be described. FIG. 4 is a schematic diagram showing a part of the surface of the iron powder for decomposing an organic halogen compound of the present invention. A boundary portion 3 having a width W exists between the graphite 1 and the ground iron portion 2. The present inventor has estimated that in the decomposition of the organic halogen compound such as TCE by the iron powder for decomposing an organic halogen compound of the present invention, the boundary portion 3 becomes a reaction active site. The existence probability of the reaction active site on the iron powder surface is the ratio of the area of the reaction active site to the entire area of the iron powder surface (area ratio of the reaction active site). Here, considering the decomposition of the organic halogen compound in the solution, the boundary portion 3 assumed to be a reaction active site is considered.
Is a value that varies depending on the specific conductivity of the solution,
Since it is estimated to be on the order of at most 0.1 μm, the product of the sum of the perimeters of all graphite particles present per 100 μm ^{2 of} the surface (unit: μm) and W (unit: μm) is 100 μm ^2. Can be approximated. Further, assuming that all the graphite particles are circular and have the same size, the following equation (2) is derived. (Area ratio of reaction active site) = n × W × 2πr / 100 (2) where n is the surface 1 of the iron powder for decomposing an organic halogen compound.
Represents the number of graphite particles present per 00 μm ² , r
Is the radius of graphite assuming that the graphite is a circle (unit:
μm).

In the measurement of n, a BSE image of the iron powder surface is photographed at a magnification of 1,000 to 10,000 times by the above-mentioned AES analysis, and commercially available image analysis software (for example, particle analysis software manufactured by Sumitomo Metal Technology Co., Ltd. (version 1.
Using 0)) or visually, the number of graphite particles per 100 μm ² surface (for example, a square area of 10 μm on a side) is measured. The above measurement is performed at multiple locations by changing the field of view,
For example, it is preferably performed at 10 places, in which case n
Is used as the average value.

[0019] Here, from the above assumption, it is considered that _{P ad = n × π × r} 2/100, which is _{r = 10 × (P ad /} (n × π)) 1/2 (3). Therefore, from the above equations (2) and (3), (area ratio of reaction active site) = n × W × 2πr / 100
= (0.04π × n × P _ad ) ^1/2 × W.

Here, by defining (0.04π × n × P _ad ) ^1/2 = K _{p (reactive site)} (1), the surface 1 which is a condition unique to iron powder is defined.
It depends only on the number (n) of graphite particles present per 00 μm ² and the probability of presence (P _ad ) of graphite on the surface of the iron powder for decomposing organic halogen compounds, and the width of reaction active site (W ) Independent coefficient K
_{p (reactive site)} is required. The present inventor has found that when the presence probability coefficient K _{p (reactive site) of the} reaction active site is within a specific range, the decomposition rate of the organic halogen compound is high, and thus the present invention has been determined as preferable conditions of the present invention.

The iron powder for decomposing organic halogen compounds of the present invention preferably has an average particle size of 10 μm to 5 mm.
Further, the iron powder for decomposing an organic halogen compound of the present invention preferably has a substantially spherical shape in that it can be easily mixed with soil or the like.

The method for producing iron powder for decomposing organic halogen compounds of the present invention is not particularly limited as long as graphite can be concentrated and present on the surface of iron powder. As a method of causing graphite to be concentrated on the surface of iron powder, for example, a method of depositing graphite on the surface of iron powder can be mentioned. That is, one preferred embodiment of the present invention is an iron powder for decomposing an organic halogen compound which is present by enriching graphite on the surface of iron powder by depositing graphite on the surface. As a method for producing the iron powder for decomposing an organic halogen compound of the present invention by depositing graphite on the surface, for example, (1) molten iron having a pig iron or carbon content of 3% by mass or more (for example, molten steel component: 4% by mass C -0.025
Mass% Si-0.4 mass% Mn-0.17 mass% P) was rapidly solidified by a water atomization method to obtain iron powder, and then subjected to a finish reduction treatment in a hydrogen stream at 700 ° C. for 1 hour. A method of depositing supersaturated solid solution carbon as graphite on the surface by further applying a heat treatment at 100 to 600 ° C. in an inert gas; (2) a sponge iron powder obtained by coke-reducing a mill scale ( Graphite powder is added to the reduced iron powder) and heat-treated at 600 ° C. for 1 hour in an inert gas atmosphere to partially diffuse the graphite powder and precipitate graphite particles on the surface of the iron powder. Method. The above method (1) is preferable because the deposited graphite is finely dispersed, and as a result, _{Kp (reactive site)} tends to be in a desired range.

As described above, JP-A-6-506661
In Japanese Patent Application Publication No. 2000-205, a method is described in which water contaminated by an organic halogen compound is treated by passing the water through a permeable mixture consisting of activated carbon and iron file shavings. This is to increase the time for the substance to pass through the permeable mixture and not to adsorb on the iron surface. Therefore, in the permeable mixture, the activated carbon and the file of iron are simply mixed, and the contact portion between the activated carbon and iron, which is considered to function as a reaction active site, is extremely small. The decomposition rate is lower than that of the organic halogen compound decomposition iron powder of the present invention. Japanese Patent Application Laid-Open No. H11-235577 discloses that an organic halogen-based compound contained in soil in an unsaturated zone above groundwater level or excavated soil is reduced by iron powder containing 0.1% or more of C. The method of detoxifying the iron powder is described, and it is described that the crystal structure of the iron powder preferably has a pearlite structure. The pearlite structure is a structure in which the α-Fe phase and the Fe ₃ C phase are mixed. Therefore, the iron powder described in the above publication does not have graphite (graphite) on the surface, and the decomposition rate of the organic halogen compound is slower than that of the iron powder for decomposing an organic halogen compound of the present invention.

Conventionally, cast iron powder (Daliko) has been known as an iron powder having graphite. FIG. 5 is a schematic cross-sectional view of (a) cast iron powder and (b) iron powder for decomposing an organic halogen compound of the present invention. In the cast iron powder 20, the graphite 1 is present almost uniformly over the entire iron powder, and the amount of the graphite 1 exposed on the surface is very small. Although a small amount of graphite 1 is present, graphite 1 is concentrated on the surface. Therefore, when the cast iron powder 20 is used for decomposing the organic halogen compound, the graphite 1 exposed on the surface can be a reaction active site, but the graphite 1 is not concentrated on the surface. The ratio is smaller than the iron powder 10 for decomposing an organic halogen compound of the present invention, and therefore,
The decomposition rate of organic halogen compounds is also slow.

The iron powder for decomposing an organic halogen compound according to the present invention is contaminated by leaking a place where the concentration of the organic halogen compound is high, such as soil, groundwater or gas, for example, a solvent containing the organic halogen compound. Soil, groundwater,
Applicable to gas and the like. That is, the organic halogen compound-decomposing iron powder of the present invention is brought into contact with soil, groundwater, and gas to decompose the organic halogen compound, and the soil, groundwater,
Gas can be made harmless.

Specifically, the following (a), (b),
(C), (d) and (e) can be exemplified. (A) A method of placing the iron powder for decomposing an organic halogen compound in groundwater contaminated with the organic halogen compound. (B) A method in which groundwater contaminated with an organic halogen compound is pumped and brought into contact with the iron powder for decomposing the organic halogen compound. (C) adding iron powder for decomposing the organic halogen compound to soil contaminated with the organic halogen compound. (D) excavating soil contaminated with organohalogen compounds,
A method of mixing the excavated soil with the iron powder for decomposing an organic halogen compound. (E) A method in which a gas obtained by suction from soil and / or groundwater contaminated with an organic halogen compound is brought into contact with the iron powder for decomposing the organic halogen compound.

The organic halogen compound which causes contamination in the method of the present invention is not particularly limited as long as it is an organic compound having a halogen such as a chlorine atom. For example,
Trichloroethylene (TCE), tetrachloroethylene, 1,1-dichloroethylene, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, vinyl chloride, 1,1,1-trichloroethane, 1,
1,2-trichloroethane, dichloroethane, dichloromethane, carbon tetrachloride, polychlorinated biphenyl (PCB),
Dioxin.

The organic halogen compound is reduced by the iron powder and converted into a harmless compound such as a non-halogen compound and hydrogen halide. For example, TCE receives (reduced) electrons on the surface of iron powder, and is converted to a chlorine-free compound such as acetylene through β-elimination via an intermediate such as chloroacetylene, thereby rendering it harmless. Alternatively, the reduction may further proceed, but in any case, the reaction proceeds upon receiving (reducing) electrons on the surface of the iron powder, and as a result, the compound changes to a harmless compound.

[0029]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. 1. Preparation of Various Iron Powders (Example 1) Molten steel having a carbon content of 4.3% by mass (molten steel component: 4.3% by mass C-0.3% by mass Si-0.3% by mass)
Mn-0.12 mass% P) was quenched and solidified by a water atomizing method to obtain iron powder, which was then subjected to a finish reduction treatment in a hydrogen stream at 700 ° C. for 1 hour, and further treated in an inert gas at 5 ° C.
By applying a heat treatment at 00 ° C., carbon dissolved in supersaturation was precipitated as graphite on the surface, to obtain iron powder for decomposing organic halogen compounds of the present invention. The average particle size of the iron powder for decomposing organic halogen compounds was 60 μm.

(Examples 2, 3, 7, 8 and 10-1
3) An iron powder for decomposing an organic halogen compound of the present invention was obtained in the same manner as in Example 1 except that the contents of C, Si, and Mn in the molten steel used were changed. The average particle size of these iron powders for decomposing organic halogen compounds was 50 to 200 μm.

Example 4 Graphite powder was added to sponge iron powder obtained by coke reduction of a mill scale and heat-treated at 600 ° C. for 1 hour in an inert gas atmosphere to obtain graphite. The powder was partially diffused, and graphite was precipitated on the surface of the iron powder to obtain the iron powder for decomposing an organic halogen compound of the present invention. The average particle size of the iron powder for decomposing organic halogen compounds is
It was 2000 μm.

(Examples 5, 6 and 9) Iron powder for decomposing organic halogen compounds of the present invention was obtained in the same manner as in Example 4 except that the amount of the graphite powder used was changed. The average particle size of these iron powders for decomposing organic halogen compounds is 8
It was 0 to 2500 μm.

Comparative Example 1 Molten steel having a carbon content of 1% by mass (molten steel component: 1% by mass C-0.05% by mass Si-0.1)
5 mass% Mn-0.02 mass% P) was rapidly solidified by a water atomizing method to obtain an iron powder of Comparative Example 1. The average particle size of the iron powder was 80 μm.

(Comparative Example 2) A sponge iron powder (reduced iron powder) obtained by coke reduction of a mill scale was reduced to 70% in a hydrogen stream.
A finish reduction treatment was performed at 0 ° C. for 1 hour to obtain an iron powder of Comparative Example 2. The average particle size of the iron powder was 80 μm.

Comparative Example 3 Molten steel having a carbon content of 1% by mass (molten steel component: 1% by mass C-0.05% by mass Si-0.1)
5% by mass Mn-0.02% by mass P) was rapidly solidified by a water atomizing method, and then subjected to a finish reduction treatment in a hydrogen stream at 700 ° C. for 1 hour to obtain an iron powder of Comparative Example 3. .
The average particle size of the iron powder was 80 μm.

(Comparative Example 4) A graphite powder having an average particle size of 1 μm was used as Comparative Example 4.

2. Properties of iron powder The existence probability _Pad and the existence probability coefficient _{Kp (} reactive _site) of the reaction active site on the graphite surface were measured. For the iron powder and graphite powder obtained above, a BSE image of the surface was taken at a magnification of 10,000 by AES analysis, and commercially available image analysis software (particle analysis software (version 1.0) manufactured by Sumitomo Metal Technology Co., Ltd.) was used. Then, the total area S _graphite (unit: μm) per square area (100 μm ² ) of 10 μm on each side and the number n of graphite particles existing per square area were measured, and _Pad = S
_{Graphi te} / 100 and from the equation (1) to determine the P _ad and K _{p (reactive site).} The above measurement was carried out at 10 points by changing the field of view, the average value as the P _ad and K _{p (reactive site),} shows these in Table 1.

3. Organic halogen compound decomposition test Each of the iron powder and graphite powder obtained above was subjected to an organic halogen compound decomposition test using TCE as an organic halogen compound. (1) Experiment In a 100 mL glass vial, CaCO ₃ concentration was 40 mg / L, Na ₂ SO ₃ concentration was 80 mg / L, TC
50 mL of an aqueous solution having an E concentration of 5 mg / L and 5 g of iron powder or graphite powder were put therein, and sealed using a butyl rubber stopper with a Teflon seal and an aluminum cap. Then
In a constant temperature room controlled at 23 ± 2 ° C., the vial was shaken at 180 rpm in the vertical axis direction. Six hours, 24 hours, 48 hours, 96 hours, and 168 hours after the start of shaking, the TCE concentration in the gas in the headspace inside the vial was measured using a gas detector tube, and Henry's law was used. To TCE concentration in the aqueous solution. Note that a plurality of samples were prepared for the above measurement, and the measurement after each time elapsed was performed for different samples.

(2) Analysis of Experimental Results Since TCE in an aqueous solution is decomposed by reaction with iron powder, the TCE concentration in the aqueous solution decreases with time. The reaction rate equation for this reaction is generally considered to have a first-order reaction rate constant with respect to the TCE concentration in the solution, and is expressed by the following equation.

[0040] C: TCE concentration in solution t: Reaction time (h) K _obs : Apparent reaction rate constant (1 / h) K _sa : Specific reaction rate constant (L / (m ² · h)) a: Iron powder Total surface area (m ² ) V: amount of solution (L)

Where, a = S _a · W _p (5) S _a : specific surface area (m ² / kg) W _p : amount of iron powder used (kg)

[0042] on the vertical axis the logarithm of the analytical values of TCE concentration in the aqueous solution (C _t) and divided by the initial concentration (C _i) values (C _t / C _i), plotting the response time t on the horizontal axis, from the slope to determine the K _obs of the above formula (4). However, since the value of K _obs changes depending on various experimental conditions, it is generally performed to evaluate the characteristics of iron powder using K _sa which is a constant specific to iron powder regardless of the experimental conditions. I have. Therefore, also in the present embodiment, the above formula (4) is used for each iron powder and graphite powder.
K _sa was determined from (5) and used as an index of the decomposition rate of TCE.

Table 1 shows the properties of the iron powder and graphite powder and the results of the organic halogen compound decomposition test. Example 1
Organic halogen compound-decomposing iron powder for the present invention obtained in -13 was found to be graphite surface from the value of the cross-section observation and P _ad is those present in concentrated, and the value of K _sa large It can be seen that the decomposition rate of TCE was high. On the other hand, the iron powders of Comparative Examples 1 to 3 having no graphite on the surface had a K _sa
And the decomposition rate is slow. Further, the graphite powder of Comparative Example 4 does not decompose TCE.

[0044]

[Table 1]

[0045]

The iron powder for decomposing an organic halogen compound according to the present invention has a high safety because the decomposition rate of the organic halogen compound is high and a metal such as copper is not used. Therefore, it is suitably used for treating soil, groundwater and gas containing an organic halogen compound. In particular, the method for detoxifying contaminated soil, groundwater, and gas of the present invention is suitably used.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a surface of an example of iron powder for decomposing an organic halogen compound of the present invention, which is created based on a BSE image of about 10,000 times of the surface.

FIG. 2 is a graph showing the results of AES analysis of a ground iron portion on the surface of an example of the iron powder for decomposing an organic halogen compound of the present invention.

FIG. 3 is a graph showing the results of AES analysis of graphite on the surface of an example of the iron powder for decomposing an organic halogen compound of the present invention.

FIG. 4 is a schematic diagram showing a part of the surface of the iron powder for decomposing an organic halogen compound of the present invention.

FIG. 5 is a schematic sectional view of a cast iron powder and an iron powder for decomposing an organic halogen compound of the present invention. (A) is a cross-sectional schematic diagram of cast iron powder, and (b) is an iron powder for decomposing an organic halogen compound of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Graphite 2 Ground iron part 3 Boundary part 10 Iron powder for decomposition | disassembly of the organic halogen compound of this invention 20 Cast iron powder

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/70 B01D 53/36 G 4H006 C07B 35/06 B09B 3/00 304K C07C 19/05 (72) Invention Person Yoshihide Kato 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba F-term in the Technical Research Laboratory, Kawasaki Steel Co., Ltd. BA08A BA08B BB02A BB02B BC66A BC66B CA02 CA05 CA10 CA19 EA01X EA01Y EB18Y EC27 4H006 AA05 AC13 BA19 BA32

Claims (4)

[Claims] An iron powder for decomposing an organic halogen compound in which graphite is concentrated on the surface. 2. The existence probability _Pad of the graphite on the surface.
The iron powder for decomposing an organic halogen compound according to claim 1, wherein is 0.001 to 0.9. 3. The iron powder for decomposing an organic halogen compound according to claim 1, wherein the reaction active site existence probability coefficient K _{p (reactive site)} represented by the following formula (1) is 0.05 or more. . K _{p (reactive site)} = (0.04π × n × P _ad ) ^1/2 (1) where n is the surface 1 of the iron powder for decomposing the organic halogen compound.
Represents the number of graphite particles present per 00 μm ² ,
_ad represents the existence probability of graphite on the surface of the iron powder for decomposing an organic halogen compound. 4. The iron powder for decomposing an organic halogen compound according to any one of claims 1 to 3 is brought into contact with at least one of soil, groundwater and gas contaminated with the organic halogen compound to remove the organic halogen compound. A method for detoxifying contaminated soil, groundwater and gas, which is characterized by decomposing.