JP2002161263A - Iron power for decomposing organic halogen compound, method for producing the same and method for making contaminated soil and/or contaminated underground water harmless - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide inexpensive iron powder for decomposing organic halogen compounds which can start the decomposition of the organic halogen compounds without needing a transition time when used. SOLUTION: This iron powder has at least one metal selected from the group consisting of nickel copper, cobalt and molybdenum on the surface and the surface portions except the metal portions are covered with oxidized iron coating films, wherein the content of the metal is 0.01 to 10 mass % based on the total amount of the iron powder and the thickness of the oxidized iron coating film is >=30 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to iron powder for decomposing organic halogen compounds, a method for producing the same, contaminated soil and / or
More specifically, the present invention relates to a method for detoxifying contaminated groundwater, more particularly, an inexpensive iron powder for decomposing an organic halogen compound which starts decomposing an organic halogen compound without a transition time during use, a method for producing the same, a method for producing contaminated soil and / Or, it relates to a method for detoxifying contaminated groundwater.

[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. Furthermore, as a method of decomposing and detoxifying pollutants in groundwater or soil,
A purification method by a bioremediation method using a microorganism is known.

[0003] However, methods such as a vacuum extraction method and a pumping aeration method use activated carbon or decomposition 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.

[0004] 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 an organic halogen compound is reacted with iron to reductively dehalogenate it and render it harmless. However, the problem with pure iron is that the reaction rate is slow. Therefore, various proposals have been made to interpose a catalyst on the surface of iron in order to improve the reaction rate.
For example, in U.S. Pat. No. 4,382,865,
A technique for plating or alloying iron with at least one metal catalyst selected from copper, silver, cobalt or nickel is described. Also, WO 97/048
No. 68 pamphlet describes a method of replacing and depositing at least one metal selected from copper, cobalt, nickel, molybdenum, bismuth, tin, lead, silver, chromium, palladium, platinum and gold with iron powder. . Furthermore,
U.S. Pat. No. 5,611,936 describes a method for substituting and depositing palladium on iron powder. Further, JP-A-2000-5740 describes the use of copper-containing iron powder.

[0005]

However, in the method using palladium, since palladium is extremely expensive,
It is cost-effective and lacks practicality. Also,
When using the above metals other than palladium, from the start of use to accelerate the decomposition of organic halogen compounds,
There is a problem that a certain amount of time is required. For example, FIG. 1 shows an iron powder 5 in which nickel is deposited at 1 mass%.
g is a graph showing the time-dependent change of the TCE concentration when the TCE aqueous solution (50 mL / TCE concentration: 5 mg / L) is sealed in a 100-mL vial bottle and shaken.
It can be seen that the time does not decrease the TCE concentration at all.
In this way, the time during which the TCE concentration does not change at the beginning of shaking is defined as a transition time. Incidentally, C _i of the vertical axis in FIG. 1 TC
E initial concentration, C _t denotes the TCE concentration at each elapsed time.
After the elapse of the transition time, the decomposition reaction of the organohalogen compound starts, but the length of the transition time varies depending on the usage environment of the iron powder and cannot be controlled artificially. Has a problem. The experiment in FIG. 1 is performed in a system in which the reaction is promoted more than the reaction between iron powder and an organic halogen compound in groundwater or soil. Therefore, when actually treating groundwater or soil, the time during which the decrease in the concentration of the organic halogen compound such as TCE is small (transition time) is considered to be much longer than 50 hours.

Accordingly, it is an object of the present invention to provide an inexpensive iron powder for decomposing an organic halogen compound which starts to decompose an organic halogen compound without a transition time when used.

[0007]

That is, the present invention has at least one metal selected from the group consisting of nickel, copper, cobalt and molybdenum on the surface, and a portion other than the metal on the surface is an iron oxide film. An organic halogen compound for decomposing an organic halogen compound, wherein the content of the metal is 0.01 to 10 mass% with respect to the entire iron powder, and the thickness of the iron oxide film is 30 nm or more. Provide an iron powder for compound decomposition.

[0008] Further, the present invention provides a method for removing nickel, which is performed by any of a displacement deposition method, an electroless plating method, and a partial alloying method.
After providing at least one metal selected from the group consisting of copper, cobalt and molybdenum on the surface of the iron powder, by corroding the iron powder in the air or in degassed water to form an oxide film on the surface. A method for producing an organic halogen compound-decomposing iron powder, in which an iron oxide film is provided on a portion of the iron powder surface other than the metal to obtain an organic halogen compound-decomposing iron powder,
In the partial alloying method, after providing at least one metal selected from the group consisting of nickel, copper, cobalt and molybdenum on the surface of the iron powder, by cooling the iron powder in water other than the metal other than the metal on the surface of the iron powder. A method for producing iron powder for decomposing an organic halogen compound, wherein an iron oxide film is provided on a portion to obtain iron powder for decomposing an organic halogen compound.

Further, the present invention relates to a contaminated soil characterized by decomposing an organic halogen compound by bringing the above-mentioned iron powder for decomposing an organic halogen compound into contact with soil contaminated with an organic halogen compound and / or groundwater. And / or a method for detoxifying contaminated groundwater.

[0010]

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 used as the base iron powder of the iron powder for decomposing the organic halogen compound of the present invention is not particularly limited, and is obtained by subjecting a sponge iron powder obtained by reducing a mill scale with coke to a finish reduction treatment in a hydrogen stream. Iron powder obtained by atomizing powder or molten steel with water is preferably used. The BET specific surface area of the base iron powder is not particularly limited, and for example, one having a BET specific surface area of 0.03 to 0.9 m ² / g can be used.

The iron powder for decomposing an organic halogen compound according to the present invention has on its surface at least one metal selected from the group consisting of nickel, copper, cobalt and molybdenum.
These metals are practical because they are less expensive than noble metals such as palladium. The specific metal may be a simple metal or an alloy. For example, in the case of Ni, it may be Ni alone or an alloy such as a Ni-P alloy. In the iron powder for decomposing an organic halogen compound of the present invention, the specific metal may be present only on the surface, and may be present only on the surface or both on the surface and inside.

[0012] In the iron powder for decomposing an organic halogen compound of the present invention, the content of the specific metal is 0.01 to 10 mass% with respect to the whole iron powder, preferably 0.1 to 10 mass%.
It is 5 mass%. When the content of the specific metal is 0.01 to 10 mass% with respect to the entire iron powder, the ratio of the area occupied by the specific metal to the surface and the area occupied by the iron oxide film described below on the surface is: It is preferable because it becomes appropriate in terms of the decomposition rate of the organic halogen compound.

In the iron powder for decomposing an organic halogen compound of the present invention, a portion of the surface other than the specific metal is coated with an iron oxide film. The iron oxide film has a thickness of 30 nm or more, preferably 30 to 300 nm, more preferably 50 to 300 nm, and particularly preferably 50 to 100 nm.
nm. When the thickness of the iron oxide film is 30 nm or more, the surface of the iron powder can be uniformly coated with the iron oxide film, so that the decomposition of the organic halogen compound can be started without a transition time. It is preferable that the thickness of the iron oxide film be 300 nm or less, since the release of Fe ²⁺ from the base iron described later through the iron oxide film becomes easy.

In the present invention, the iron oxide film is
Using the Auger electron spectroscopy on the surface of the iron powder, the A was sputtered in the depth direction at a sputtering rate of 11 nm / min.
when sputtered with r, the ratio of O peak intensity (I _o) and Fe peak intensity (I _i) (I _o /
_Ii ) refers to a portion where 0.05 or more. Therefore,
The thickness of the iron oxide film of the present invention is ( _Io / I
_i ) is a distance in terms of Fe up to a depth at which 0.05 is obtained. FIG. 2 shows the result of Auger electron spectroscopy of the iron powder for decomposing an organic halogen compound of the present invention. The measurement conditions were as follows: sputtering time: 15 minutes, sputtering speed: 11 n
m / min (in terms of Fe). In FIG. 2, I _o is decreased with the lapse of sputtering time, it can be seen that I _i is increased. (I _o / I _i ) is 0.05 from the iron powder surface
The thickness of the iron oxide film can be calculated by converting the sputtering time up to the depth to the thickness into the thickness.

[0015] Magnetite (Fe
_The presence of ₃ O ₄ ) is preferred because of its excellent conductivity, and the presence of hematite (Fe ₂ O ₃ ) is also preferred because it becomes porous.

The iron powder for decomposing an organic halogen compound of the present invention starts decomposition of an organic halogen compound without a transition time when used. The reason will be described below. FIG. 3 shows the decomposition mechanism of organic halogen compounds such as TCE by iron powder estimated by the present inventors. As shown in FIG. 3, the decomposition of an organic halogen compound such as TCE by iron powder is carried out by (1) mass transfer (movement of organic halogen compound 1) and (2) adsorption (adsorption of organic halogen compound 1 on iron powder surface 2). Adsorption on site 3), (3) surface diffusion (diffusion of organic halogen compound 1 on iron powder surface 2 to cathode active site 4), (4) reduction reaction (reduction of organic halogen compound 1 on cathode active site 4) Reaction) and (5) desorption (desorption of compound 5 generated by the reduction reaction from cathode active site 4).

In ordinary pure iron powder, the number of cathode active sites 4 existing on the iron powder surface 2 is small. On the contrary,
The iron powder for decomposing an organic halogen compound of the present invention has the specific metal on its surface, and the surface on which this specific metal is present is more noble than iron. Therefore, it has many cathode active sites 4. Accordingly, the iron powder for decomposing an organic halogen compound of the present invention is more excellent in the decomposition rate of the organic halogen compound 1 than ordinary pure iron powder in that the reduction reaction of the above (4) is performed at many cathode active sites 4. .

Further, since the reaction rate of the reduction reaction of the above (4) is much higher than the rate at which the organic halogen compound 1 is supplied to the cathode active site, the decomposition rate of the organic halogen compound 1 is Depends on the feed rate of Here, the route through which the organohalogen compound 1 is supplied includes the adsorption sites 3 on the iron powder surface 2 in (2) above.
A path through which the organic halogen compound 1 adsorbed on the cathode active site 4 is diffused by the surface diffusion of the above (3);
There is a route in which the organic halogen compound 1 existing in the bulk liquid phase or gas phase moves directly to the cathode active site 4. However, the probability of direct transfer from the bulk liquid or gas phase to the cathode active site 4 is low, while the above (3)
Since the diffusion speed of the surface diffusion is high, the supply speed of the organic halogen compound 1 and the decomposition speed of the organic halogen compound 1 ultimately depend on the number of the adsorption sites 3.

FIG. 4 shows (A) the prior art (US Pat.
382,865, WO 97/04868.
Pamphlet, JP-A-2000-5740, etc.) and the surface of iron powder (iron powder having a metal catalyst interposed on the surface);
(B) It is the top view which showed typically the difference with the surface of the iron powder for organic halogen compound decomposition | disassembly of this invention. As shown in FIG. 4, the number of adsorption sites 3 is small in various iron powders in which a metal catalyst is interposed on the conventional surface (see FIG. 4).
(A)). On the other hand, in the iron powder for decomposing an organic halogen compound of the present invention, a portion other than the specific metal on the surface is coated with an iron oxide film, that is, a specific metal serving as the cathode active site 4 exists. Since the periphery of the surface is surrounded by the iron oxide film serving as the adsorption site 3, the number of the adsorption sites 3 for supplying the organic halogen compound 1 to the cathode active site 4 is large, and the supply speed is high (FIG. 4).
(B)). Here, the reason that the iron oxide film becomes the adsorption site 3, that is, the reason that the iron oxide film adsorbs the organic halogen compound is presumed to be that iron oxide has higher affinity for the organic halogen compound than pure iron. . Therefore, in the iron powder for decomposing an organic halogen compound of the present invention, the adsorption of the above (2) is performed at many adsorption sites 3, and the organic halogen compound is supplied to the cathode active site 4 by the surface diffusion of the above (3). In this respect, the organic halogen compound 1 is more excellent in the decomposition rate than various types of iron powder in which a metal catalyst is interposed on the conventional surface.

As described above, various iron powders in which a metal catalyst is interposed on the conventional surface have a small number of adsorption sites and a low decomposition rate of the organic halogen compound at an early stage after use. It is estimated that the reason why the decomposition rate is increased after the transition time is that the iron powder surface is oxidized with time and an iron oxide film is gradually formed. On the other hand, the iron powder for decomposing an organic halogen compound of the present invention is, as described above, an iron powder in which a portion of the surface other than the specific metal is coated with an iron oxide film, so The decomposition of the halogen compound starts.

Regarding the action of the iron powder for decomposing an organic halogen compound of the present invention, TC which is a typical example of an organic halogen compound is used.
A case where E is decomposed will be described as an example. FIG. 5 is a schematic sectional view of the vicinity of the surface of the iron powder for decomposing an organic halogen compound of the present invention. The iron powder for decomposing an organic halogen compound of the present invention has the above-mentioned specific metal (cathode active site 4) on the surface, and a portion other than the metal on the surface is an iron oxide film (adsorption site 3) having a thickness of 30 nm or more. Coated. At the anode portion, the base iron 6 is oxidized to release electrons, and the iron (I
I) It becomes an ion. On the other hand, in the cathode portion, after the TCE molecule 1a is adsorbed on the iron oxide film which is the adsorption site 3,
It moves to the specific metal portion which is the cathode active site 4 by surface diffusion, and is supplied with the electrons and decomposed,
It produces chloroacetylene molecules 5a and chloride ions (β-elimination). Since the generated chloroacetylene molecule 5a is unstable, it is further reduced and decomposed, and the organic halogen compound disappears. For example, it combines with hydrogen ions in water to produce acetylene (not shown). In this way, decomposition of TCE is achieved.

The decomposition (β-elimination) of TCE on the surface of the iron powder for decomposing an organic halogen compound according to the present invention is a local battery reaction, and its reaction formula is represented by the following formula. Anode reaction: Fe → Fe ²⁺ + 2e ⁻ (1) Cathode reaction: ClHC = CCl ₂ + 2e ⁻ → HC≡CCl + 2Cl ⁻ (2)

As described above, the thickness of the iron oxide film is 30
When the thickness is less than 0 nm, Fe generated by the above equation (1)
^It is easy to release ^{2+ out} of the system. When the thickness of the iron oxide film is too large, the release of Fe ²⁺ is inhibited, and the progress of the local battery reaction tends to be slow.

The method for producing the iron powder for decomposing an organic halogen compound of the present invention is not particularly limited. For example, first, the above-mentioned specific metal is provided on the surface of the iron powder, and then a portion other than the specific metal on the surface of the iron powder is provided. A method of providing an iron oxide film on the substrate. Specifically, after providing at least one metal selected from the group consisting of nickel, copper, cobalt and molybdenum on the surface of the iron powder by any one of the displacement precipitation method, the electroless plating method, and the partial alloying method. In an atmosphere or in degassed water, the iron powder is corroded to form an oxide film on the surface, thereby providing an iron oxide film on the surface of the iron powder other than the metal to form an iron powder for decomposing organic halogen compounds. And a method of producing iron powder for decomposing an organic halogen compound, wherein at least one metal selected from the group consisting of nickel, copper, cobalt and molybdenum is provided on the surface of the iron powder by a partial alloying method. A method for producing iron powder for decomposing organic halogen compounds, in which an iron oxide film is provided on a portion other than the metal on the surface of the iron powder by cooling the iron powder in water to obtain iron powder for decomposing organic halogen compounds. . Examples of a method for providing the specific metal on the surface of the iron powder include (A1) a method by substitution precipitation (substitution plating), and (A2) electroless plating (for example,
(A3) a method of mixing the above-mentioned specific metal and / or an oxide of the above-mentioned specific metal with iron powder and subjecting to a partial alloying by heat treatment in a reducing atmosphere (: Partial alloying method) is preferably mentioned.

As the method (A1), a conventionally known method can be used. For example, there is a method in which the base iron powder is immersed in an aqueous solution containing ions of the above-mentioned specific metal, and the metal is precipitated on the surface of the iron powder by a difference in ionization tendency.

As the method (A2), a conventionally known method can be used. For example, in the case of electroless nickel plating, the main components are nickel ions and hypophosphite,
Furthermore, there is a method in which a base iron powder is immersed in a plating solution containing auxiliary components such as a complexing agent, a pH buffer, and a reaction accelerator to obtain a Ni-P alloy film.

As the method (A3), powder of the above-mentioned specific metal and / or oxide of the above-mentioned specific metal is added to iron powder (base iron powder / metal and metal oxide) = 10 to 100.
00 (mass ratio), and a partial alloying by heat treatment at 600 to 900 ° C. in a reducing atmosphere such as a hydrogen stream.

In these methods, by appropriately selecting the treatment conditions, in the finally obtained iron powder for decomposing an organic halogen compound of the present invention, the content of the above-mentioned specific metal is set to 0.1 to the entire iron powder. It can be set to 01 to 10 mass%.

As a method of providing an iron oxide film on a portion other than the above-mentioned specific metal on the surface of the iron powder, for example, (B1) iron powder provided with the above-mentioned specific metal in the atmosphere or degassed water is used. There are a method of forming an oxide film on the surface by stirring to slightly corrode the iron powder, and a method of rapidly cooling in water (B2) when the method (A3) is performed.

As the method (B1), for example, NaO
A method in which iron powder is added while nitrogen gas is blown into the H aqueous solution and the mixture is stirred is used.

The method (B2) can be used when the above method (A3) is used as a method for providing the specific metal on the surface of the iron powder. As the method of (B2), for example, iron powder after heat treatment in a hydrogen stream at 600 to 900 ° C. is replaced with N ₂ gas, cooled to 200 ° C., taken out of the furnace, and placed in distilled water under air. There is a method of charging.

In these methods, the thickness of the iron oxide film in the finally obtained iron powder for decomposing an organic halogen compound is adjusted to 3 by appropriately selecting the treatment conditions.
It can be 0 nm or more.

The iron powder for decomposing an organic halogen compound obtained by the above-mentioned production method is obtained by providing the above-mentioned specific metal on the surface of the iron powder and then providing an iron oxide film on a portion other than the specific metal on the surface of the iron powder. It becomes. A conventional iron powder having only a metal on its surface may slightly oxidize its surface by the air during storage, but does not sufficiently adsorb the organic halogen compound in the decomposition of the organic halogen compound. On the other hand, the iron powder for decomposing an organic halogen compound obtained by the above production method is provided with an iron oxide film, and the iron oxide film is sufficient to adsorb the organic halogen compound in the decomposition of the organic halogen compound. Thick and uniform iron oxide film. Accordingly, the iron powder for decomposing an organic halogen compound obtained by the above production method is a preferred embodiment of the present invention.

The present invention is applicable to organic halogen compounds, and particularly, 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 And the like.

The use and method of use of the iron powder for decomposing an organic halogen compound of the present invention are not particularly limited, and the iron powder of the present invention can be suitably used by bringing groundwater or soil containing an organic halogen compound into contact with the iron powder of the present invention. . For example, groundwater and soil can be taken out and treated with the iron powder for decomposing an organic halogen compound of the present invention, and the groundwater and soil can be taken out by placing the iron powder for decomposing an organic halogen compound of the present invention underground. Alternatively, it can be processed at that location.

[0036]

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) A sponge iron powder obtained by reducing a mill scale with coke as a base iron powder in a hydrogen stream for 700 hours.
Iron powder (BET specific surface area: 0.05 m ² / g) subjected to finish reduction treatment at 1 ° C. for 1 hour was used. NiCl ₂ was added to 1 L of distilled water in a plastic beaker, and the NiCl ₂ concentration was 5
2,000 mg / L, dissolve and add NiCl
_Two aqueous solutions were prepared. Then, after adding 50 g of the base iron powder, the mixture was stirred for 5 minutes to cause Ni to be substituted and deposited on the surface of the iron powder. In 1 L of 1 mol / L NaOH aqueous solution,
At a flow rate of 0.5 L / min, while blowing nitrogen gas, iron powder obtained by substituting and depositing Ni was added to the surface, and 500 r using a Teflon (registered trademark) propeller under air.
After stirring at pm for 1 hour, the mixture was washed with water and dried to obtain an iron powder for decomposing an organic halogen compound of the present invention.

Example 2 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 concentration of the NiCl ₂ aqueous solution was 20,000 mg / L.

Example 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 concentration of the aqueous NiCl ₂ solution was 25 mg / L.

Example 4 The same base iron powder as used in Example 1 was used. A solution (NiCl ₂ · 6H
5 mL of ₂ O: 24 g / L, NaF: 10 g / L and liquid B (NiH ₂ PO ₂ .H ₂ O: 34 g / L, H ₃ BO ₃ :
30 g / L) 45 mL and 50 g of iron powder in a polyvin
Mixing was performed for 0 minutes to precipitate a Ni-P alloy on the surface of the iron powder.
After washing with water, it was dried in a vacuum desiccator. CaCO ₃ and Na ₂ SO in 1 L of distilled water in a plastic beaker
₃ was added so as to have a CaCO ₃ concentration of 40 mg / L and a Na ₂ SO ₃ concentration of 80 mg / L, and dissolved to prepare an aqueous solution. Next, 50 g of iron powder whose surface was Ni-P alloy plated was added, and the mixture was stirred at 500 rpm for 1 hour using a Teflon propeller in the atmosphere, washed with water, and dried to obtain the iron for decomposition of an organic halogen compound of the present invention. Powder was obtained.

Example 5 An iron powder for decomposing an organic halogen compound of the present invention was obtained in the same manner as in Example 4, except that the composition of the electroless plating solution was 25 mL of Solution A and 25 mL of Solution B.

(Example 6) As a base iron powder, molten steel was
Atomized iron powder (BET specific surface area 0.05m ^Two/
g) was used. Nickel oxide on 100g of the base iron powder
(NiO) 6.36 g was added, and 700
The heat treatment was performed at 1 ° C. for 1 hour. After heat treatment, heat treatment
The inside of the furnace used for the above was replaced with nitrogen gas and cooled to 200 ° C.
After that, remove the iron powder from the furnace and insert it into distilled water.
Quenching and oxidation treatment, the organic halogen compound of the present invention
An iron powder for decomposition was obtained.

Example 7 An iron powder for decomposing an organic halogen compound of the present invention was obtained in the same manner as in Example 6, except that the amount of NiO added was 8.9 g and the heat treatment temperature was 900 ° C. .

Example 8 An iron powder for decomposing an organic halogen compound of the present invention was obtained in the same manner as in Example 6, except that the amount of NiO added was 1.3 g and the heat treatment temperature was 600 ° C. .

Example 9 The same base iron powder as that used in Example 6 was used. 100g of the above base iron powder
The added Ni4g, the Cu1.5g and MoO ₃ 0.6 g, in a hydrogen stream, 880 ° C., subjected to heat treatment under conditions of 1 hour to obtain Ni, Cu and Mo to the partially alloyed alloy steel powder. After the heat treatment, the inside of the furnace used for the heat treatment was replaced with nitrogen gas, and cooled to 200 ° C., and then the iron powder was taken out of the furnace, inserted into distilled water, quenched, and oxidized,
An iron powder for decomposing an organic halogen compound of the present invention was obtained.

Example 10 Example 6 as a base iron powder
The same one used for the above was used. The above base iron powder 100
g, Ni4g, Cu1g, Co0.5g and MoO
_Three0.3 g, and added at 880 ° C. for 1 hour in a hydrogen stream.
Heat treatment under the conditions, Ni, Cu, Co and Mo
A partially alloyed alloy steel powder was obtained. After heat treatment, used for heat treatment
The inside of the furnace was replaced with nitrogen gas and cooled to 200 ° C.
After that, remove the iron powder from the furnace, insert it into distilled water and quench it.
At the same time as oxidation.
An iron powder for material decomposition was obtained.

Comparative Example 1 The same base iron powder as that used in Example 6 was used. The base iron powder is subjected to a finish reduction treatment at 800 ° C. for 1 hour in a hydrogen stream,
The iron powder of Comparative Example 1 was obtained.

Comparative Example 2 The same iron powder as that used in Example 6 was used as the base iron powder, and heat treatment was performed under the same conditions as in Example 6, to obtain an iron powder of Comparative Example 2.

2. Properties of Iron Powder (1) Content of Specific Metal The content of nickel, copper, cobalt, and molybdenum in each iron powder was measured by a method based on JIS G1257 "Iron and steel-atomic absorption spectrometry".

(2) Thickness of Iron Oxide Film The thickness of the iron oxide film of each iron powder was measured by Auger electron spectroscopy.

3. Organic Halogen Compound Decomposition Test Each iron powder obtained above was used as an organic halogen compound by TC
E was subjected to an organic halogen compound decomposition test using E. (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 iron powder 5
g, 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., 180 ° in the vertical axis direction of the vial.
Shake at rpm. 6 hours, 24 hours, 48 hours, 96 hours and 168 hours after the start of shaking,
The TCE concentration in the gas in the head space inside the vial was measured using a gas detector tube, and was converted to the TCE concentration in the aqueous solution according to Henry's law. 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.

DC / dt = −K _obs · C = − (K _sa · a / V) · C (1) C: TCE concentration in solution t: reaction time (h) K _obs : apparent reaction rate constant ( 1 / h) K _sa : intrinsic reaction rate constant (L / (m ² · h)) a: total surface area of iron powder (m ² ) V: amount of solution (L)

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

The logarithm of the analytical value (C _t ) of the TCE concentration in the aqueous solution divided by the initial concentration (C _i ) (C _t / C _i ) is plotted on the vertical axis, and the reaction time t is plotted on the horizontal axis. TC at the beginning of the reaction
The transition time was calculated from the time when the E concentration did not decrease. Further, K _obs of the above equation (1) was obtained from the slope. 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 this example, K _sa was obtained from each of the above formulas (1) and (2) for each iron powder, and was used as an index of the decomposition rate of TCE.

Table 1 shows the properties of the iron powder and the results of the organic halogen compound decomposition test. It can be seen that the iron powder for decomposing organohalogen compounds of the present invention obtained in Examples 1 to 10 starts decomposition of TCE without a transition time and is excellent in decomposition rate. In contrast, the iron powder of Comparative Example 1 having no specific metal on the surface requires a transition time and is inferior in decomposition rate. The iron powder of Comparative Example 2 having a specific metal on the surface but a thin iron oxide film has a high decomposition rate, but requires a long transition time.

[0056]

[Table 1]

[0057]

The iron powder for decomposing an organic halogen compound of the present invention can start decomposition of an organic halogen compound without a transition time at the time of use and is inexpensive. Therefore, it is suitably used for treating groundwater and soil containing an organic halogen compound. The method for producing iron powder for decomposing organic halogen compounds of the present invention is useful as a method for producing the iron powder for decomposing organic halogen compounds of the present invention. The iron powder for decomposing organic halogen compounds produced by the above production method is a preferred embodiment of the present invention.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in TCE concentration caused by a conventional iron powder having nickel deposited on its surface.

FIG. 2 is a graph showing the results of Auger electron spectroscopy for calculating the thickness of the iron oxide film of the iron powder for decomposing an organic halogen compound of the present invention.

FIG. 3 is a schematic diagram showing a decomposition mechanism of an organic halogen compound such as TCE by iron powder.

FIG. 4 is a plan view schematically showing a difference between a state of a conventional iron powder surface and a state of an organic halogen compound decomposing iron powder of the present invention.

FIG. 5 is a schematic sectional view of the vicinity of the surface of the iron powder for decomposing an organic halogen compound of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Organic halogen compound 1a Trichloroethylene (TCE) molecule 2 Iron powder surface 3 Adsorption site 4 Cathode active site 5 Compound generated by reduction reaction 5a Chloroacetylene molecule 6 Base iron 7 Iron (II) ion

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C07B 35/06 B09B 3/00 304K // C07D 319/24 (72) Inventor Yoshihide Kato Chiba, Chiba 1 Kawasaki-cho, Ward F-term in Kawasaki Steel Research Institute (reference) 2E191 BA11 BA13 BA15 BB01 BC01 BD11 4D004 AA41 AB06 AB07 CA37 CC11 DA03 DA10 DA20 4D050 AA02 AB19 BA01 BA02 4H006 AC13 BA05 BA14 BA19 BA20 BA21 BA30 BA81

Claims (4)

[Claims] Claims: 1. An iron for decomposing an organic halogen compound, which has at least one metal selected from the group consisting of nickel, copper, cobalt and molybdenum on its surface, and a portion other than the metal on the surface is coated with an iron oxide film. Powder, wherein the content of the metal is 0.01 to 10 ma with respect to the entire iron powder.
An iron powder for decomposing an organic halogen compound, wherein the iron oxide film has a thickness of 30 nm or more. 2. A method in which at least one metal selected from the group consisting of nickel, copper, cobalt and molybdenum is provided on the surface of iron powder by any of a displacement precipitation method, an electroless plating method and a partial alloying method. In an atmosphere or in degassed water, the iron powder is corroded to form an oxide film on the surface, thereby providing an iron oxide film on the surface of the iron powder other than the metal to form an iron powder for decomposing organic halogen compounds. Method for producing iron powder for decomposing organic halogen compounds to obtain 3. The method of claim 1, wherein at least one metal selected from the group consisting of nickel, copper, cobalt and molybdenum is provided on the surface of the iron powder by a partial alloying method, and the iron powder is cooled in water to obtain a surface of the iron powder. The method for producing iron powder for decomposing organic halogen compounds by providing an iron oxide film on a portion other than the metal to obtain iron powder for decomposing organic halogen compounds. 4. A contaminated soil, wherein the iron powder for decomposing an organic halogen compound according to claim 1 is brought into contact with soil contaminated with the organic halogen compound and / or groundwater to decompose the organic halogen compound. And / or a method for detoxifying contaminated groundwater.