JP2002316050A - Iron powder for decomposing organic chlorine compound and method for purifying soil, water and gas stained with the same compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for purifying soil, water such as underground water and gas at a low cost by raising reductive decomposition rate with iron of organic chlorine compounds in the soil, the water such as underground water and the gas stained with the organic chlorine compounds of decomposability and strong staining property such as cis-1,2-dichloroethylene and to provide iron powder suitable for the purifying method. SOLUTION: In the method for purifying the soil, the water and the gas stained with the organic chlorine compounds by bringing the organic chlorine compounds contained at least in one among the soil, the water and the gas with the iron powder to decompose the organic chlorine compounds, iron powder of high purity containing <0.1 mass% C, <0.25 mass% Si, <0.60 mass% Mn, <0.03 mass% P, <0.03 mass% S and <0.5 mass% O is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to iron powder for decomposing organochlorine compounds, soil contaminated with the organochlorine compounds,
Regarding water and gas purification methods, more specifically, cis-1,1 in contaminated soil, water and gas using high-purity iron powder.
The present invention relates to a method for decomposing and rendering harmless organic chlorine compounds such as 2-dichloroethylene.

[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, has been discharged and discarded after use, has been used.
Contamination of soil and groundwater by organochlorine compounds such as CE) has become a major social problem. Conventionally, as a method of treating these contaminants, for the contaminated groundwater, a vacuum extraction method, a pumping aeration method, and the like, in which the contaminated groundwater is extracted outside the soil and detoxified and buried, are known. As for the contaminated soil, a thermal desorption method and a thermal decomposition method of excavating the contaminated soil and heat-treating the soil to make it harmless are known. As a method of decomposing contaminants in soil or groundwater to make them harmless, a purification method by a bioremediation method using microorganisms is known.

[0003] However, after extracting and pumping soil, groundwater and soil gas containing pollutants from the ground, methods such as vacuum extraction, pumping aeration and the like for removing or decomposing pollutants are used to remove pollutants. In order to use activated carbon and decomposing agents for decomposition, high-cost separate treatment is required, such as installing equipment on the ground, extracting and pumping water, and then detoxifying the pollutants. 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 transformed by heat,
For example, the original functions of the soil, such as supporting structures and inhabiting living organisms, are significantly impaired, so that it is difficult to reuse the soil after the treatment. In the bioremediation method,
Due to the difference in properties of each soil, it cannot be applied to all soils, and even when applied, the reaction is slow due to the action of microorganisms, requiring a long treatment period, and is not practical.

In order to overcome the above-mentioned problems of the conventional countermeasures against soil and groundwater pollution, there are various methods for reacting a halogen-containing organic substance as a cause of pollution with iron to reductively dehalogenate and detoxify the substance. It has been proposed and is attracting attention.
For example, Japanese Unexamined Patent Publication No. Hei 5-501520 discloses a method of digging a groove in a flow path of groundwater, filling it with iron in the form of granules, sections, fibers, etc., and bringing it into contact with a halogen-containing organic substance that causes pollution. And a method for reductive dehalogenation and detoxification. The iron used here does not need to be specially adjusted, and is waste generated in the metal cutting process and low-purity iron powder generated in the iron casting process. Japanese Patent Application Laid-Open No. 6-506631 discloses that, in principle, Japanese Patent Application Publication No.
No. 01520, but a method using a mixture of metallic iron and activated carbon is described. All of the above are methods of detoxifying pollutants in groundwater.

Further, Japanese Patent Application Laid-Open No. 11-235577 proposes a method of detoxifying an organic chlorine compound contained in soil above the groundwater surface or in excavated soil by reduction with iron powder. In this method, the C content is 0.1.
1% or more, specific surface area 0.05m ² / g or more, 50% by weight
It is necessary to use iron powder having a particle size that passes through a 150 μm sieve, and spongy iron ore reduced iron powder is recommended. Japanese Patent Application Laid-Open No. 2000-5740 discloses a method for decomposing an organic chlorine compound and quickly purifying soil and groundwater by adding and mixing Cu-containing iron powder to soil or groundwater contaminated with the organic chlorine compound. Has been described.

[0006]

Any of the above-mentioned methods of reacting an organic chlorine compound, which is a contaminant, with iron to reductively dechlorinate and detoxify it is excellent in cost. This is a departure from measures against contaminated soil and contaminated groundwater. However, since the iron used in the above method is not necessarily optimized for its purpose and application, for example, a hardly decomposable organic chlorine compound such as cis-1,2-dichloroethylene is used. There was a problem that the decomposition could not always be performed at a sufficient speed. Also,
In the case of the method described in JP-A-2000-5740, Cu itself of the Cu-containing iron powder used is a harmful element, and there is a risk of causing secondary contamination, and the environment and use conditions are limited. There was something.

Numerous studies have been made on the mechanism of decomposition of organochlorine compounds by iron powder. For example, when tetrachloroethylene (PCE) is used as a starting material,
Decomposition proceeds according to the reaction route shown in FIG.
Proposed by J. et al. According to it, first P
Pathway (a) beginning with reductive degradation by β-elimination of CE;
Although there is a possibility of competition of the route (b) starting from reductive cracking by PCE hydrocracking, in practice, the route (a)
Is believed to take precedence. When the route (b) is followed, as shown in FIG.
Dichloroethylene (DCE) such as 2-dichloroethylene, trans-1,2-dichloroethylene, and 1,1-dichloroethylene is produced.

The decomposition rate of DCE by iron is as follows:
It is reported by, for example, Sivavec ™ that the rate of decomposition of PCE or trichlorethylene (TCE) by iron is slower. For this reason, if the decomposition according to the route (b) occurs, unreacted DCE at least temporarily accumulates and remains. Among them, cis-1,2
-Dichloroethylene is more polluting than PCE and TCE and has a much lower decomposition rate, so if it accumulates and remains in soil or groundwater, the pollution will worsen before the PCE begins to decompose by iron. There are cases. However, in practice, as described above, since route (a) takes precedence, there is no contamination with cis-1,2-dichloroethylene.
It has been believed that using iron is no problem.

However, recently, T
It has been pointed out that CE and the like are dechlorinated and decomposed due to the involvement of microorganisms in the soil, transformed into more contaminating and hardly decomposed DCE, and accumulated and remained in the soil. Then, even if low-purity iron powder conventionally proposed for decomposing organochlorine compounds is used for soil and groundwater in which hardly decomposable cis-1,2-dichloroethylene is accumulated and remains, the It has been found that not only is it difficult to decompose -1,2-dichloroethylene, but also causes deep problems such as accumulation and persistence of new pollutants, and removal of DCE, especially cis-1,2-dichloroethylene, which is hardly decomposable. Decomposition is a new pollution problem.

Accordingly, the present invention is particularly directed to cis-1,2
-Increases the rate of reductive decomposition of organochlorine compounds in soil, water such as groundwater, and gas, which are hardly decomposable and highly contaminated by organic chlorine compounds such as dichloroethylene, by iron powder,
It is an object of the present invention to provide a method for purifying water and gas such as soil and groundwater at low cost and an iron powder suitable for reductive decomposition in the purification method.

[0011]

Means for Solving the Problems The present invention provides a method for producing C,
An iron powder for decomposing organochlorine compounds, wherein Si, Mn, P, S and O are in the following range. C: less than 0.1% by mass, Si: less than 0.25% by mass, Mn: less than 0.60% by mass, P: less than 0.03% by mass, S: less than 0.03% by mass, O: 0.5 Less than mass%.

[0012] The present invention also provides an organic chlorine compound contained in at least one of soil, water and gas, which is brought into contact with iron powder to decompose the organic chlorine compound and contaminate it with the organic chlorine compound. Soil, a method of purifying water and gas, wherein the content of C, Si, Mn, P, S and O in the iron powder is contaminated soil characterized by using iron powder in the following range: It is a method of purifying water and gas. C: less than 0.1% by mass, Si: less than 0.25% by mass, Mn: less than 0.60% by mass, P: less than 0.03% by mass, S: less than 0.03% by mass, O: 0.5 Less than mass%.

The present invention is effective for the above-mentioned organic chlorine compounds obtained by substituting hydrogen atoms of hydrocarbons, particularly aliphatic hydrocarbons with chlorine atoms, and specifically, dichloromethane, chloroform, carbon tetrachloride, 1-dichloroethane, methyl chloroform, 1,1,2-trichloroethane,
1,1,1,2-tetrachloroethane, 1,1,2,2
From tetrachloroethane, 1,1-dichloroethylene, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, trichloroethylene (TCE), tetrachloroethylene (PCE), 1,3-dichloropropane and 1,3-dichloropropene It is effective with at least one organic chlorine compound selected from the group consisting of cis-1,2-dichloroethylene.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the iron powder for decomposing organochlorine compounds of the present invention will be described in detail. The iron powder used in the present invention is characterized in that it has higher purity and a purity close to pure iron powder as compared with iron powder conventionally proposed for decomposing organic chlorine compounds. Since the high-purity iron powder of the present invention has excellent compressibility and moldability, and has little variation in quality, conventionally, powder metallurgy mainly for automobiles, warmers, welding rods, oxygen absorbers, etc., have higher performance and higher performance. It can be used for high-grade applications and products that require long-term stability and the like, and its use as a decomposer for organic chlorine compounds is not known.

One reason is that even when high-purity iron powder is added to soil or groundwater contaminated with a hardly decomposable organic chlorine compound, decomposition of the compound does not proceed immediately after the addition. Guessed.

However, after adding high-purity iron powder to the contaminated soil and the groundwater, the inventor of the present invention has a certain period of time.
After the elapse of day), it was found that the decomposition of the hardly decomposable organic chlorine compound was started, and the present invention was reached.
Although the reason is not clear, the inventor first found that active dissolution of high-purity iron powder occurred, followed by the formation of corrosion products on the iron powder surface, which decomposed the hardly decomposable organic chlorine compound. Presumed to start and promote.

The high-purity iron powder of the present invention has a content of C, Si, Mn, P, S and O other than iron in the following range. C: less than 0.1% by mass, Si: less than 0.25% by mass, Mn: less than 0.60% by mass, P: less than 0.03% by mass, S: less than 0.03% by mass, O: 0.5 Less than mass%.

Preferred are components other than iron, such as C, Si,
The contents of Mn, P, S and O are in the following ranges. C: less than 0.02 mass%, Si: less than 0.15 mass%, Mn: less than 0.40 mass%, P: less than 0.02 mass%, S: less than 0.020 mass%, O: 0.20 Less than mass%.

More preferably, C and S components other than iron are used.
The content of i, Mn, P, S and O is in the following range. C: less than 0.01% by mass, Si: less than 0.02% by mass, Mn: less than 0.10% by mass, P: less than 0.015% by mass, S: less than 0.01% by mass, O: 0.18% Less than mass%.

When the purity of the high-purity iron powder of the present invention deviates from the above range, the decomposition of the organochlorine compound does not start even after a certain period of time, so that the use of the high-purity iron powder in the above range is extremely important. The particle size and particle size distribution of the high-purity iron powder of the present invention are not particularly limited, but can be appropriately determined according to the condition of soil or groundwater to which the iron powder is added. When added to soil, for example, 60% by mass or more
It is preferable that the particles have a particle size enough to pass through a sieve. Also,
When it is necessary to ensure a certain permeability coefficient by adding to groundwater, for example, a particle having a particle size such that 80% by mass or more does not pass through a 250 μm sieve is preferable.

The high-purity iron powder of the present invention is obtained, for example, by milling reduced iron powder obtained by roughly reducing mill scale or iron ore with coke to adjust the particle size, and further subjecting the reduced iron powder to finish reduction in a stream of hydrogen. It is preferable to use a method of producing the powder by adjusting the purity to a predetermined purity, or a method of producing and reducing the iron powder produced by the water atomization method in a hydrogen stream. Oxide reduction method,
Iron powder produced by a water atomization method, a carbonyl method, or the like, which has been adjusted to the above purity, can also be used. In addition, iron dust or the like that has been adjusted to the above purity by pickling or reducing it in a hydrogen stream can also be used. The high-purity iron powder of the present invention preferably has a substantially spherical shape in view of ease of mixing with soil or the like, but is not limited to a spherical shape. As the high-purity iron powder of the present invention, commercially available pure iron powder for powder metallurgy can be used without surface treatment.

The method of bringing the high-purity iron powder of the present invention into contact with an organic chlorine compound contained in water, gas or the like containing soil or groundwater containing the organic chlorine compound is not particularly limited, and has been conventionally proposed. The method may be selected according to the situation. Locations where the concentration of organochlorine compounds is high, for example, water or gas, such as soil or groundwater, which are leaking and contaminated with organochlorine compounds, or water such as soil or groundwater in which organochlorine compounds are accumulated or retained. , Gas and the like are efficient.

Specifically, the following (a) to (e) can be exemplified. (A) In groundwater veins contaminated with organochlorine compounds,
A method of depositing high-purity iron powder, (b) a method of pumping groundwater contaminated with organochlorine compounds and bringing it into contact with high-purity iron powder, and (c) a method of depositing high-purity iron in soil contaminated with organochlorine compounds. (D) excavating soil contaminated with an organochlorine compound, and mixing the excavated soil with high-purity iron powder. (E) A method of contacting a gas obtained by suction from soil and / or groundwater contaminated with an organochlorine compound with high-purity iron powder.

The environment to which the high-purity iron powder of the present invention is applied is as follows:
In the case of soil, the water content is preferably 5% by mass or more, and the atmosphere may be either aerobic or anaerobic. The pH of the soil may be 1 to 10. Even in the case of groundwater, it can be applied in a wide range regardless of the concentration of dissolved oxygen.

The organic chlorine compound is reduced by high-purity iron powder, and is converted into a non-polluting compound such as a non-chlorine compound and hydrogen halide through the routes (a) and (b) shown in FIG. . Therefore, the purified soil, water and gas can be reused, left alone, or discarded.

[0026]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. (Inventive Examples 1-4, Comparative Examples 1-2) [1] Preparation of Iron Powder Preparation Methods 1-3 Preparation Method 1: A sponge iron powder is produced by roughly reducing a mill scale with coke, and then pulverized. , In a stream of hydrogen (dew point 3
0 °) Finish reduction at 850 ° C. for 1 hour to obtain high-purity iron powder having a trace component content shown in Table 1. At this time, the sintered iron powder is pulverized again and sieved to a predetermined particle size (60%).
(% By mass passed through a 75 μm sieve). (Invention Examples 1 and 4)

Preparation method 2: adjusted to predetermined components 17
Atomized raw powder is produced from a molten steel at 00 ° C. by a water atomizing method, and then produced in a hydrogen stream (dew point 30 °) 85.
Finish reduction was performed at 0 ° C. for 1 hour to obtain a high-purity iron powder having a trace component content shown in Table 1. At this time, the sintered iron powder is crushed again, and a predetermined particle size (50% by mass is 7
5 μm). (Invention Examples 2 and 3)

Preparation method 3: In the preparation of high-purity iron powder 2, except that the finish reduction was omitted, an iron powder having the content of trace components shown in Table 1 was obtained in the same manner as the preparation method. The particle size is such that 50% by weight passes through a 75 μm sieve.
(Comparative Examples 1 and 2)

Table 1 shows the content of trace components in each iron powder. The content of trace components in iron powder was measured as follows. C: JIS G1211, Si: JIS G1258, Mn: JIS G1257, P: JIS G1258, S: JIS G1215, O: JIS Z2613.

[2] Decomposition test of cis-1,2-dichloroethylene in soil A sandy soil having an average particle size of 176 μm, which was previously dried in an oven at 40 ° C. for 2 days and dried to an absolute dry state, was mixed with iron powder. Then, a sample having a total mass of 40 g and a mixing ratio of iron powder of 1 mass% was prepared. This sample was placed in a glass vial having a capacity of 100 mL, and a butyl rubber stopper with a fluororesin liner was closed with an aluminum cap and sealed.

Cis-1,2-dichloroethylene (manufactured by Kanto Kagaku Co., Ltd .; reagent special grade) was dissolved in distilled water to give a concentration of 0.1.
A 1 molar aqueous solution was prepared. Using a microsyringe, 4.5 mL of this was added to the vial containing the sample, and the water content of the sample was adjusted to 10% by mass. The cis-1,2-dichloroethylene concentration in the sample was 43.6 mg /
40 g. The obtained sample was placed in a constant temperature chamber at 25 ° C., and a gas in the head space was collected at predetermined intervals by 50 μL using a gas tight syringe, and the concentration of cis-1,2-dichloroethylene was determined using a GC / FID device. Analyze,
FIG. 2 shows the change in density.

[3] Decomposition test of cis-1,2-dichloroethylene in groundwater CaCO ₃ (manufactured by Kanto Chemical Co., Ltd .: reagent grade) was dissolved in deionized water to prepare an aqueous solution having a concentration of 0.4 mmol.
This was used as simulated groundwater. Simulated groundwater with a capacity of 50 mL
Into a glass vial, blow nitrogen gas in the glove box, completely remove the gas, add 5 g of iron powder, tighten a butyl rubber stopper with a fluororesin liner with an aluminum cap, and remove the head space. It was sealed without any. The total liquid volume at this time is
Each bottle has been investigated.

Next, cis-1,2-dichloroethylene standard stock solution for water quality analysis (1 mg / mL-methanol; manufactured by Kanto Chemical Co., Ltd.) was added to the bottle by a suitable amount using a microsyringe. A dichloroethylene concentration of 5
mg / L. The obtained sample was shaken at 60 rpm using a rotary shaker in a constant temperature room at 23 ° C.
Sampling was performed after 2, 4, 8 days.

Separately, in a bias bottle having a capacity of 25 mL for GC / MS analysis, 300 g /
Prepare by adding 9.8 mL of L sodium chloride aqueous solution.
The sample, which had been shaken for a certain period of time, was
00 μL was collected and added to the aqueous sodium chloride solution,
The total volume was adjusted to 10 mL, and immediately sealed with a septum with a fluororesin liner. The obtained sample was subjected to JIS K
In accordance with the method for testing volatile organic compounds in water and wastewater of No. 0125, cis-
The concentration of 1,2-dichloroethylene was analyzed.

The horizontal axis of FIG. 2 showing one example of the results of the above soil test is the reaction time of cis-1,2-dichloroethylene with iron powder, and the vertical axis is the ratio of the concentration after the passage of time to the initial concentration. It is the logarithm of the dimensionless value. From FIG. 2, in Comparative Example 1 using iron powder not subjected to finish reduction, cis-
While the concentration of 1,2-dichloroethylene did not decrease at all, in the case of Invention Example 1 using the high-purity iron powder of the present invention, the concentration of cis-1,2-dichloroethylene was increased after about 3 days. It starts to decrease rapidly. In addition, a pseudo-first-order reaction rate constant can be obtained from the linear portion of Example 1 of the present invention in FIG. The results are shown in Table 1. Since a similar tendency was observed in Invention Examples 2 and 3, a pseudo-first-order reaction rate constant was determined from the linear portion.

From the comparison between Inventive Example 4 using the simulated groundwater and Comparative Example 2, almost the same phenomenon and tendency were observed in the simulated groundwater. Similarly, a pseudo-first-order reaction rate constant was determined from the linear portion.

[0037]

[Table 1]

[0038]

When the high-purity iron powder of the present invention is used,
Since the decomposition rate of the hardly decomposable organochlorine compound is high, the soil containing the contaminated organochlorine compound, water such as groundwater,
Detoxification of gas, especially accumulation of persistent organic chlorine compounds,
It is suitable for purifying water and gas such as residual soil and groundwater. Moreover, the high-purity iron powder of the present invention is easily available,
Since the conventional detoxification method can be applied as it is, it is extremely practical.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a decomposition route of tetrachloroethylene. (EnVironmental Toxicology and Chemistry
Transcribed from Vol.16, No.4, p.625-630. )

FIG. 2 is a graph showing a decomposition rate as a result of a decomposition test of cis-1,2-dichloroethylene.

[Explanation of symbols]

(A) ... a route that starts reductive decomposition by β-elimination of PCE (b) ... a route that starts reductive decomposition by hydrogenolysis of PCE (c) ... a reduction route from alkyne to alkene ( d) Reduction route from alkyne to alkane

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/58 B01D 53/36 G 4G069 1/70 B01J 23/74 301A (72) Inventor Yoshihide Kato Chiba 1 Kawasaki-cho, Chuo-ku, Chiba-shi Kawasaki Steel Engineering Co., Ltd. (72) Inventor Kuniaki Ogura 2-3-2 Uchisaiwaicho, Chiyoda-ku, Tokyo F-term (reference) 2E191 BA15 BC01 BD11 4D004 AA41 AB06 CA50 CC11 DA03 DA10 4D038 AA02 AA08 AB14 AB90 4D048 AA11 AB03 BA05Y BA06Y BA28Y BA36X BA44Y BA46Y BB01 4D050 AA12 AB19 BA02 4G069 AA02 AA08 BA08A BB02 BC62CABCA01 BD08

Claims (3)

[Claims] 1. C, Si, Mn, P, S and O in iron powder
Is in the following range: iron powder for decomposing organochlorine compounds. C: less than 0.1% by mass, Si: less than 0.25% by mass, Mn: less than 0.60% by mass, P: less than 0.03% by mass, S: less than 0.03% by mass, O: 0.5 Less than mass%. 2. An organic chlorine compound contained in at least one of soil, water, and gas is brought into contact with iron powder to decompose the organic chlorine compound and contaminate the soil and water contaminated with the organic chlorine compound. And a method for purifying gas, wherein the content of C, Si, Mn, P, S and O in the iron powder is contaminated soil characterized by using an iron powder in the following range:
Water and gas purification methods. C: less than 0.1% by mass, Si: less than 0.25% by mass, Mn: less than 0.60% by mass, P: less than 0.03% by mass, S: less than 0.03% by mass, O: 0.5 Less than mass%. 3. The method for purifying contaminated soil, water and gas according to claim 2, wherein said organochlorine compound is cis-1,2-dichloroethylene.