JP4660958B2 - Purification of soil, water and gas contaminated with organochlorine compounds - Google Patents

Description

【００３８】
【発明の効果】
本発明の高純度鉄粉を用いた場合には、難分解性の有機塩素化合物の分解速度が速いので、汚染された有機塩素化合物を含有する土壌、地下水等の水、ガスの無害化、特に難分解性の有機塩素化合物が蓄積、残留する土壌、地下水等の水、ガスの浄化に好適である。しかも、本発明の高純度鉄粉は入手が容易であり、従来の無害化方法がそのまま適用することができるので、極めて実用性が高い。
【図面の簡単な説明】
【図１】 テトラクロロエチレンの分解経路を示す説明図である。（EnVironmental Toxicology and Chemistry Vol.16, No.4, p.625-630から転記。）
【図２】 シス−１，２−ジクロロエチレンの分解試験の結果の分解速度を示すグラフである。
【符号の説明】
（ａ）・・・ＰＣＥのβ脱離による還元的分解に始まる経路
（ｂ）・・・ＰＣＥの水素化分解による還元的分解に始まる経路
（ｃ）・・・アルキンからアルケンへの還元経路
（ｄ）・・・アルキンからアルカンへの還元経路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an iron powder for decomposing organochlorine compounds and a method for purifying soil, water, and gas contaminated with the organochlorine compounds, and more specifically, contaminated soil, water, The present invention relates to a method for decomposing and detoxifying a hardly decomposable organochlorine compound such as cis-1,2-dichloroethylene in a gas.
[0002]
[Prior art]
In recent years, contamination of soil and groundwater by organic chlorine compounds such as trichlorethylene (TCE), which has been used in large quantities as a degreasing solvent for a long time in semiconductor factories, metal processing factories, etc. It has become a social problem.
Conventionally, as a method for treating such contamination, a vacuum extraction method, a pumping water aeration method, or the like is known for contaminated groundwater, in which the contaminated groundwater is extracted outside the soil and detoxified. As for the contaminated soil, a thermal desorption method or a thermal decomposition method in which the contaminated soil is excavated and heat-treated to make it harmless is known. In addition, as a method for decomposing and detoxifying contaminants in soil or groundwater, a purification method using 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, etc. that remove or decompose pollutants, remove pollutants and decompose them. For this reason, when using activated carbon or a decomposing agent, it is necessary to carry out high-cost separate processing such as providing facilities on the ground, extracting and pumping, and then detoxifying the pollutants.
In addition, the method of thermally decomposing excavated soil at a high temperature requires a large facility for heat-treating the soil, and the soil particles themselves are altered by heat, for example, supporting structures and inhabiting living organisms. Since the original function of the soil is significantly impaired, it is difficult to reuse the treated soil.
The bioremediation method is not applicable to all soils due to the differences in the properties of each soil. Even when applied, the reaction is slow due to the action of microorganisms, requiring a long treatment period, and practical use. Poor nature.
[0004]
In order to overcome the problems of conventional soil and groundwater contamination countermeasures as described above, various methods have been proposed for reacting halogen-containing organic substances that cause contamination with iron to dehalogenate and render them harmless. It is getting attention.
For example, in Japanese Patent Publication No. 5-501520, a groove is dug in a groundwater channel, filled with iron in a granular shape, a section shape, a fiber shape, etc., and brought into contact with a halogen-containing organic substance causing contamination. A method of dehalogenating reductively and detoxifying is described. The iron used here does not need to be adjusted specifically, and is waste generated in the metal cutting process or low-purity iron powder that appears in the iron casting process.
Japanese Patent Laid-Open No. 6-506631 discloses the same method as that of Japanese Patent Laid-Open No. 5-501520 in principle, but describes a method using a mixture of metallic iron and activated carbon.
All of the above are methods for detoxifying contaminants in groundwater.
[0005]
Japanese Patent Application Laid-Open No. 11-235577 proposes a method for detoxifying organochlorine compounds contained in soil above the groundwater surface and soil after excavation by reduction with iron powder. In this method, it is necessary to use iron powder having a C content of 0.1% or more, a specific surface area of 0.05 m ² / g or more, and 50% by weight or more passing through a 150 μm sieve, Iron ore reduced iron powder is recommended.
Japanese Patent Laid-Open No. 2000-5740 discloses a method for decomposing organic chlorine compounds and quickly purifying the soil and groundwater by adding and mixing Cu-containing iron powder to soil and groundwater contaminated with organic chlorine compounds. Are listed.
[0006]
[Problems to be solved by the invention]
Any of the above-mentioned methods of reacting organochlorine compounds, which are pollutants, with iron, dechlorinating them reductively and detoxifying them is excellent in terms of cost. It sets a line. However, since the iron used in the above method is not necessarily optimized for its purpose and use, for example, a hardly decomposable organochlorine compound such as cis-1,2-dichloroethylene is used. There was a problem that it could not be decomposed at a sufficient rate.
In addition, in the case of the method described in Japanese Patent Application Laid-Open No. 2000-5740, Cu itself of the Cu-containing iron powder to be 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 to be done.
[0007]
Numerous studies have been conducted on the mechanism of decomposition of organochlorine compounds by iron powder. For example, when the starting material is tetrachloroethylene (PCE), decomposition proceeds in the reaction route shown in FIG. Proposed. According to this, there is a possibility of competition between the path (a) starting from the reductive decomposition by β-elimination of PCE and the path (b) starting from the reductive decomposition by hydrogenolysis of PCE. Route (a) is considered to have priority. In addition, when the route (b) is followed, as shown in FIG. 1, dichloroethylene (DCE) such as cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, 1,1-dichloroethylene is intermediately provided. Produces.
[0008]
By the way, it has been reported by, for example, Sivavec ™ that the decomposition rate of DCE by iron is slower than the decomposition rate of PCE or trichlorethylene (TCE) by iron. For this reason, if the decomposition according to the route (b) occurs, unreacted DCE accumulates and remains at least temporarily. Above all, cis-1,2-dichloroethylene is more pollutant than PCE and TCE, and its decomposition rate is extremely slow, so if it accumulates and remains in soil or groundwater, it will be more than before decomposition of PCE by iron begins. Rather, the contamination may worsen.
However, in fact, as described above, since the route (a) is prioritized, there is no contamination with cis-1,2-dichloroethylene, so there is no problem even if iron is used as a countermeasure against contamination by PCE or TCE. It has been believed.
[0009]
However, recently, TCE discharged from factories, etc. is transformed into DCE, which is dechlorinated and decomposed due to the involvement of microorganisms in the soil, and is more pollutant and difficult to decompose, and accumulates and remains in the soil. Has been pointed out. Even if the low-purity iron powder conventionally proposed for the decomposition of organochlorine compounds is used for soil and groundwater in which persistent cis-1,2-dichloroethylene accumulates and remains, cis -1,2-dichloroethylene is not only difficult to decompose, but it has also been found to cause a deep problem of accumulation and residue of new pollutants, and removal of DCE, especially persistent cis-1,2-dichloroethylene Decomposition has become a new pollution problem.
[0010]
Therefore, the present invention reduces the organic chlorine compounds in the soil, groundwater, etc., contaminated with organic chlorine compounds that are difficult to decompose, especially cis-1,2-dichloroethylene, etc. It is an object to provide a method for purifying water and gas such as soil and groundwater at low cost, and iron powder suitable for reductive decomposition in the purification method.
[0011]
[Means for Solving the Problems]
The present invention is an iron powder for decomposing organochlorine compounds, wherein C, Si, Mn, P, S and O in the iron powder are in the following ranges.
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 mass%,
S: less than 0.03 mass%,
O: Less than 0.5% by mass.
[0012]
Further, the present invention is a method of contacting an organic chlorine compound and iron powder contained in at least one of soil, water and gas, decomposing the organic chlorine compound, and soil contaminated with the organic chlorine compound, In a method for purifying water and gas, contaminated soil, water and gas, wherein the iron powder has a content of C, Si, Mn, P, S and O in the following range in the iron powder. It is a purification method.
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 mass%,
S: less than 0.03 mass%,
O: Less than 0.5% by mass.
[0013]
The present invention is effective when the organic chlorine compound is a hydrocarbon, in particular, a hydrogen atom of an aliphatic hydrocarbon substituted with a chlorine atom, specifically, dichloromethane, chloroform, carbon tetrachloride, 1,1-dichloroethane. Methyl chloroform, 1,1,2-trichloroethane, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, 1,1-dichloroethylene, cis-1,2-dichloroethylene, trans- Effective with at least one organochlorine compound selected from the group consisting of 1,2-dichloroethylene, trichloroethylene (TCE), tetrachloroethylene (PCE), 1,3-dichloropropane and 1,3-dichloropropene, It is particularly effective for 2-dichloroethylene.
[0014]
DETAILED DESCRIPTION OF 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 by high purity and purity close to that of pure iron powder as compared with iron powder conventionally proposed for decomposing organochlorine compounds. The high-purity iron powder of the present invention is excellent in compressibility and moldability, and has little variation in quality. Conventionally, powder metallurgy mainly composed of automobiles, warmers, welding rods, oxygen scavengers, etc. It can be used for high-grade applications and products that require long-term stability, and its use as a decomposition agent for organochlorine compounds is not known.
[0015]
It is presumed that, even if high-purity iron powder is added to soil and groundwater contaminated with persistent organic chlorine compounds, this compound does not progress in decomposition immediately after the addition. .
[0016]
However, when the present inventor adds high-purity iron powder to the contaminated soil and the groundwater, a certain period of time (approximately 3 days in Invention Example 1 to be described later, although it varies depending on the iron powder use conditions) elapses. The present inventors have found that the decomposition of a hardly decomposable organochlorine compound has started, and have reached the present invention.
The reason for this is not clear, but the present inventor firstly activated the high-purity iron powder, followed by the formation of corrosion products on the iron powder surface, which decomposed the hardly-decomposable organochlorine compounds. Estimated to start and promote.
[0017]
The high-purity iron powder of the present invention has contents of C, Si, Mn, P, S, and O other than iron in the following ranges.
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 mass%, O: Less than 0.5 mass%.
[0018]
Preference is given to the content of C, Si, Mn, P, S and O other than iron in the following range.
C: less than 0.02% by mass, Si: less than 0.15% by mass,
Mn: less than 0.40 mass%, P: less than 0.02 mass%,
S: Less than 0.020 mass%, O: Less than 0.20 mass%.
[0019]
More preferably, the contents of C, Si, Mn, P, S and O of components other than iron are within 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: Less than 0.18% by mass.
[0020]
If 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 lapse of a certain period.
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 state of the soil or groundwater to which the iron powder is added. When added to soil, for example, it is preferable that the particle size is such that 60% by mass or more passes through a 106 μm sieve mesh. Moreover, when it is necessary to ensure a certain water permeability coefficient by adding to groundwater, for example, a material having a particle size of 80% by mass or more that does not pass through a 250 μm sieve is preferable.
[0021]
The high-purity iron powder of the present invention is, for example, pulverized reduced iron powder obtained by roughly reducing mill scale or iron ore with coke to adjust the particle size, and further reducing this in a hydrogen stream, A method of manufacturing by adjusting to a predetermined purity or a method of manufacturing iron powder manufactured by a water atomizing method by finishing reduction in a hydrogen stream is preferable. Iron powder produced by the oxide reduction method, water atomization method, carbonyl method, etc., adjusted to the above purity can also be used. Moreover, what adjusted the said purity by pickling iron dust etc. or reducing in a hydrogen stream can also be used.
The high-purity iron powder of the present invention preferably has a substantially spherical shape in terms of ease of mixing with soil or the like, but is not limited to a spherical shape.
In addition, as pure iron powder of this invention, it can use, without surface-treating commercially available pure iron powder for powder metallurgy.
[0022]
The method of bringing the high-purity iron powder of the present invention into contact with the organic chlorine compound contained in the soil containing the organic chlorine compound, water such as groundwater, gas, etc. is not particularly limited, and the conventional method has been proposed. You may select according to. Places where the concentration of organochlorine compounds is high, for example, soil, groundwater, or other water that is highly contaminated due to leakage of organochlorine compounds, gas, etc., or soil, groundwater, or other water that accumulates or retains organochlorine compounds It is efficient to select gas or the like.
[0023]
Specifically, the following (a) to (e) can be exemplified.
(A) a method of placing high-purity iron powder in a groundwater vein contaminated with an organic chlorine compound;
(B) A method of drawing up groundwater contaminated with an organic chlorine compound and bringing it into contact with high-purity iron powder,
(C) A method of adding high-purity iron powder to soil contaminated with organochlorine compounds,
(D) A method of excavating soil contaminated with an organic chlorine compound and mixing the excavated soil and high-purity iron powder.
(E) A method of contacting a gas obtained by suction from soil and / or groundwater contaminated with an organic chlorine compound and high-purity iron powder.
[0024]
In the case of soil, the environment to which the high purity iron powder of the present invention is applied preferably has a moisture content of 5% by mass or more, and the atmosphere can be either aerobic or anaerobic. The pH of the soil may be 1-10. In the case of groundwater, it can be applied in a wide range regardless of the concentration of dissolved oxygen.
[0025]
The organic chlorine compound is reduced by the high-purity iron powder, and is converted into a non-polluting compound such as a non-chlorine compound and hydrogen halide through the paths (a) and (b) shown in FIG. Therefore, the purified soil, water and gas can be reused, left or discarded.
[0026]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
(Invention Examples 1-4, Comparative Examples 1-2)
[1] Preparation method 1 of iron powder preparation method 1-3 Preparation of sponge iron powder by rough reduction of mill scale with coke, pulverization, and then 1 at 850 ° C in a hydrogen stream (dew point 30 °) The fine reduction of time was performed and the high purity iron powder of the content of the trace component shown in Table 1 was obtained. At this time, the sintered iron powder was reground and adjusted to a predetermined particle size (60% by mass passed through a 75 μm sieve mesh) by sieve classification. (Invention Examples 1 and 4)
[0027]
Preparation method 2: From 1700 ° C molten steel adjusted to a predetermined component, atomized raw powder is produced by a water atomization method, and then subjected to a finish reduction for 1 hour at 850 ° C in a hydrogen stream (dew point 30 °). A high-purity iron powder having a trace component content shown in 1 was obtained. At this time, the sintered iron powder was reground and adjusted to a predetermined particle size (50% by mass passed through a 75 μm sieve) by sieve classification. (Invention Examples 2 and 3)
[0028]
Preparation method 3: In the preparation of the high-purity iron powder 2, an iron powder having a trace component content shown in Table 1 was obtained in the same manner as the preparation method except that the finish reduction was omitted. The particle size is such that 50% by mass passes through a 75 μm sieve. (Comparative Examples 1 and 2)
[0029]
Table 1 shows the contents of trace components of each iron powder. The content of trace components of iron powder was measured as follows.
C: JIS G1211, Si: JIS G1258,
Mn: JIS G1257, P: JIS G1258,
S: JIS G1215, O: JIS Z2613.
[0030]
[2] Decomposition test of cis-1,2-dichloroethylene in soil Sandy soil with an average particle size of 176 μm, which had been dried in an oven at 40 ° C. in advance for 2 days and then completely dried, was mixed with iron powder, A sample having a mass of 40 g and an iron powder mixing ratio of 1 mass% was prepared.
This sample was put in a glass vial with a capacity of 100 mL, and a butyl rubber stopper with a fluororesin liner was fastened with an aluminum cap and sealed.
[0031]
Cis-1,2-dichloroethylene (manufactured by Kanto Chemical Co., Inc .; reagent special grade) was dissolved in distilled water to prepare an aqueous solution having a concentration of 0.1 mol. Using a microsyringe, 4.5 mL of this was added to a vial containing the sample, and the moisture content of the sample was adjusted to 10% by mass. The cis-1,2-dichloroethylene concentration in the sample is 43.6 mg / 40 g.
The obtained sample is put in a constant temperature room at 25 ° C., and 50 μL of the gas in the head space is sampled with a gas tight syringe every predetermined time, and the concentration of cis-1,2-dichloroethylene is measured with a GC / FID device. Analysis was made and the change in concentration is shown in FIG.
[0032]
[3] Decomposition test of cis-1,2-dichloroethylene in groundwater Dissolve CaCO ₃ (manufactured by Kanto Chemical Co., Inc .: reagent grade) in deionized water to prepare an aqueous solution with a concentration of 0.4 mmol, and simulate this Groundwater was used. Add simulated groundwater to the mouth of a glass vial with a capacity of 50 mL, blow nitrogen gas in the glove box, completely deaerate it, add 5 g of iron powder, and cover the butyl rubber stopper with fluororesin liner with an aluminum cap Tightened with, and sealed without head space. In addition, the total liquid amount at this time has been investigated for each bottle in advance.
[0033]
Next, a cis-1,2-dichloroethylene standard stock solution for water quality analysis (1 mg / mL-methanol; manufactured by Kanto Chemical Co., Inc.) is added to the bottle in an appropriate amount with a microsyringe, and cis-1,2-dichloroethylene concentration is determined. Was adjusted to 5 mg / L. The obtained sample was shaken at 60 rpm in a thermostatic chamber at 23 ° C. using a rotary shaker, and sampled after 1, 2, 4, and 8 days.
[0034]
Separately, 9.8 mL of 300 g / L sodium chloride aqueous solution prepared using deionized water is prepared in a 25 mL capacity bias bottle for GC / MS analysis.
200 μL of the sample shaken for a certain period was collected using a microsyringe, added to the sodium chloride aqueous solution to make a total volume of 10 mL, and immediately sealed with a septum with a fluororesin liner. The obtained sample was analyzed for the concentration of cis-1,2-dichloroethylene by the headspace GC / MS method in accordance with the test method for volatile organic compounds in water and wastewater according to JIS K0125.
[0035]
The horizontal axis of FIG. 2 showing an example of the result of the soil test is the reaction time of cis-1,2-dichloroethylene and 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 the iron powder not subjected to finish reduction, the concentration of cis-1,2-dichloroethylene was not decreased at all, whereas the invention example using the high-purity iron powder of the present invention was used. In the case of 1, the concentration of cis-1,2-dichloroethylene starts to decrease rapidly after about 3 days.
Further, a pseudo-first-order reaction rate constant can be obtained from the straight line portion of Invention Example 1 in FIG. The results are shown in Table 1. Since the same tendency was recognized also about the invention examples 2 and 3, the pseudo primary reaction rate constant was calculated | required from the linear part.
[0036]
From the comparison between Invention Example 4 and Comparative Example 2 using simulated groundwater, almost the same phenomenon and tendency were also observed in the case of simulated groundwater. Similarly, a pseudo first-order reaction rate constant was determined from the straight line portion.
[0037]
[Table 1]

[0038]
【The invention's effect】
When the high-purity iron powder of the present invention is used, the decomposition rate of the hardly-decomposable organochlorine compound is fast, so soil containing soiled organic chlorine compound, water such as groundwater, gas harmless, especially It is suitable for purification of water and gas such as soil, groundwater, etc. in which persistent organic chlorine compounds accumulate and remain. Moreover, the high-purity iron powder of the present invention is easily available, and the conventional detoxification method can be applied as it is, so that it is extremely practical.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory view showing a decomposition path of tetrachlorethylene. (Translated from EnVironmental Toxicology and Chemistry Vol.16, No.4, p.625-630.)
FIG. 2 is a graph showing the decomposition rate as a result of the decomposition test of cis-1,2-dichloroethylene.
[Explanation of symbols]
(A) ... Path starting from reductive decomposition by β-elimination of PCE (b) ... Path starting from reductive decomposition by hydrogenolysis of PCE (c) ... Reduction path from alkyne to alkene ( d) ... Reduction route from alkyne to alkane

Claims (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, thereby purifying the soil, water, and gas contaminated with the organic chlorine compound. A method for purifying contaminated soil, water, and gas, wherein the method uses iron powder in which the content of C, Si, Mn, P, S and O in the iron powder is 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%. 2. The method for purifying contaminated soil, water and gas according to claim 1 , wherein the organochlorine compound is cis-1,2-dichloroethylene.

Images