JP2002200478A - Original position reduction method for soluble and insoluble heavy metal and organic halogen compound by pneumatic fracturing accompanied by iron powder injection for cleaning contaminated soil and groundwater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and durable novel cleaning treatment method which is capable of simultaneously detoxicating the heavy metals and organic halogen compounds in contaminated groundwater on site. SOLUTION: A boring hole 1 is dug down into a contaminated soil land and compressed air is blown into the ground by sealing the ground surface to generate fractures 2 in the weak segments of the ground. Iron powder is blown by the compressed air from the ground surface simultaneously with or after such an operation to form iron powder dispersion layers 4 in the fractures 2. Contaminated permeate 5 passes the iron powder dispersion layers 4 and comes into contact with the iron powder, by which the permeate is detoxicated. The permeated groundwater 6 is accepted in a pit section at the bottom of the boring hole 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying contaminated soil and groundwater, and more particularly to purifying heavy metals and organic halogen compounds contained in contaminated soil and groundwater by the action of iron powder. With the goal.

[0002]

2. Description of the Related Art Conventionally, as a method of treating an underground pollution source contaminated with heavy metals or organic halogen compounds, a solidification stabilization method of solidifying or insolubilizing contaminated soil itself and reclaiming the soil, and a method of treating an underground pollution by heat treatment. Generally, a heat treatment method of detoxifying a substance by vaporizing the substance and removing generated gas is generally performed.

[0003] Other special treatment methods include a washing and classification method for classifying contaminated soil and washing fine particles containing a large amount of heavy metals with water or the like, and a biological method for treating contaminants using bacteria that inhabit the soil. Processing methods are also known.

As described above, there are various treatment methods depending on the type of pollutant to be treated and the geological conditions, and each of these methods has advantages and disadvantages.

[0005] The above-mentioned fixed stabilization method is intended for inorganic pollutants, but if landfill is performed for a long period of time, it will be difficult to maintain it due to the leaching action of rainwater. Although suitable for application, it is particularly unsuitable for treating contaminated soil with alkali salts, and is applicable only to limited types of inorganic heavy metals such as mercury.

[0006] Further, the washing and classification method can also deal with non-volatile substances and the like, but when pollutants extend to deep layers, mining costs are required for excavating the soil, which is unsuitable.
The biological treatment method using bacteria has a long reaction time and has a limited effect on carbohydrates having a simple structure.
Almost no application was possible for inorganic substances.

Further, as disclosed in Japanese Patent Application No. Hei 7-93138, a method of forming an iron powder layer at the bottom of a pit excavated to a depth reaching the groundwater level of contaminated groundwater and purifying the contaminated groundwater through the iron powder layer is also possible. is there. This is an effective method that can remove heavy metals and organochlorine compounds in groundwater at once using inexpensive iron powder.However, since the applicable range is limited to the place where the groundwater channel is located, it can be used in a wide range of contaminated areas. It is not suitable when the underground waterway is complicatedly branched.

[0008] In addition, the contaminants in the soil are mixed into the groundwater vein by rainwater or the like with the passage of time and harm water resources such as well water. There is known a method of removing contaminants and a method of extracting pollutants while aerating pumped ground water. However, these methods have a problem that costs such as power cost and extraction cost at the time of pumping are required, and that processing facilities and buildings must be installed on the ground.

[0009]

As described above, the method of excavating contaminated soil and purifying it on the ground is a method that can be treated at low cost if the source of the contamination is narrow, but it can be contaminated in a wide range over a long period of time. This is an inconvenient method.

[0010] Accordingly, an object of the present invention is to provide a novel treatment method capable of inexpensively and permanently purifying heavy metals and organic halogen compounds in situ by treating contaminated soil and groundwater.

[0011]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above problems, and found that inexpensive iron powder can be used for purifying heavy metals and organic halogen compounds contained in groundwater. Thus, the method of the present invention could be provided.

That is, according to the method of the present invention, after drilling into the contaminated soil, the fracture 2 into which the iron powder is injected along the borehole 1 by simultaneously or separately blowing compressed air and iron powder into the borehole 1. And forming the iron powder dispersion layer 4 and bringing the iron powder dispersion layer 4 into contact with the groundwater flowing in the contaminated soil, whereby heavy metals such as chromium, copper, nickel, cadmium, lead, etc. And at least one of organic halogen compounds such as tetrachloroethylene can be made into a harmless form.

[0013]

According to the present invention, the iron powder dispersed layer 4 is formed by the fracture 2 into which the iron powder generated inside the underground is injected,
When the contaminated groundwater permeates and passes through the iron powder dispersion layer 4,
Pollutants (mainly organic halogen compounds and inorganic heavy metals) are rendered harmless by reactions such as reduction, adsorption, and substitution in the iron powder dispersion layer 4.

The present invention belongs to the scope of the patent of US Pat. No. 5,032,042 and is licensed to Accutech Remidal Systems, Inc. of Keyport, NJ, U.S.A., as well as iron powder technology of Dowa Mining Co., Ltd. It is a technology developed by combining

US Pat. No. 5,032,042 describes an apparatus and method for injecting compressed air underground to create a fracture in a contaminated soil layer and evaporate or convert harmful liquid pollutants to harmless liquid components by biodegradation. Have been.
On the other hand, in the method of the present invention, since the contaminant component is brought into contact with and reacts with the iron powder as described above, it is possible to detoxify heavy metals that could not be dealt with by heat treatment or biodegradation. The above prior art using iron powder (Japanese Patent Application No. 7-9313)
In 8), as described above, there was a problem that the applicable range was limited to the case where there is a groundwater channel, but in the method of the present invention, an iron powder dispersion layer was formed at an arbitrary place by pneumatic fracturing. Therefore, it can sufficiently deal with the case where the contaminated area is wide. Thus, the method of the present invention makes it possible to purify contaminated soil that could not be handled by the above prior art.

In the method of the present invention, a fracture in which iron powder is injected into a mobile or non-mobile pollutant of a heavy metal and an organic halogen compound is generated to form an iron powder dispersed layer,
The iron powder dispersion layer is brought into contact with the groundwater flowing in the contaminated soil. Iron powder, in the presence of moisture, comes into direct contact with soluble mobile heavy metals and organohalogens, which are nobler than iron, and to similar immobile heavy metals and organohalogens through soil compositions as electron mediators. When contacted, the following desired reduction reaction occurs, and a typical heavy metal ion (C
r ⁶⁺ , Cu ²⁺ , Ni ²⁺ , Cd ²⁺ , Pb ²⁺ ) and electrons for reducing the organohalogen compound trichloroethylene (C ₂ HCl ₃ ).

Fe ⁰ → oxidation → Fe ²⁺ + 2e (1) Fe ²⁺ → oxidation → Fe ³⁺ + e (2) 2H ₂ O + Fe ⁰ → H ₂ + 2OH ⁻ + Fe ²⁺ (3) Cr ⁶⁺ + 3Fe ^{2 +} → Cr ³⁺ + 3Fe ³⁺ (4) Cu ²⁺ + Fe ⁰ → Cu ⁰ + Fe ²⁺ (5) Ni ²⁺ + Fe ⁰ → Ni ⁰ + Fe ²⁺ (6) Cd ²⁺ + Fe ⁰ → Cd ⁰ + Fe ²⁺ (7) Pb ²⁺ + Fe ⁰ → Pb ⁰ + Fe ²⁺ (8) C ₂ HCl ₃ + 3H ⁺ + 3Fe ⁰ → C ₂ H ₄ + 3Cl ⁻ + 3Fe ²⁺ (9) Reduction of the heavy metal cation to a state of zero valence These heavy metals then become harmless, insoluble and immobile. Chromium and organohalogen compounds are reduced to considerably less toxic products. For example, according to U.S. regulations, soil contaminated with 7.8% Cr3 ⁺ is considered harmless, while soil containing ^{15ppm Cr6 +} requires purification.

In the pneumatic fracturing technique, a compressed gas is used to create a fracture. This fracture extends outwardly from the borehole along an essentially horizontal plane and enters a contaminated zone containing soluble and insoluble phases of heavy metals and organohalogen compounds.
FIG. 3 shows a schematic sectional view of the pneumatic fracturing method. The number of boreholes and fractures required depends on the volume and depth of these contaminated zones.

The fracture serves as a passage for injecting iron powder having a predetermined particle size range and bulk density at a pressure or a water pressure using a compressed gas or a slurry. The method chosen to deliver the iron powder depends on the amount and distance of spraying required to reach, directly or indirectly, known amounts of soluble and insoluble heavy metals and organohalogen compounds.

The minimum amount of iron powder required to reduce 1 kg of typical heavy metals and organohalogen compounds in the soluble and insoluble phases can be estimated by conventional stoichiometric calculations from equations (4) to (9). . Assuming that the reactants are 100% oxidized and reduced, the minimum required amount of iron powder is as shown in Table 1.

However, the amount of iron powder that is actually required for purifying the pollutant must be determined for each site. Characterizing the site about the type, amount, distribution and location of heavy metals and organohalogen compounds present, soil type, permeability and permeability provides the necessary information.

[0022]

[Table 1]

Generally, the moving speed of groundwater is 1 to 1.5.
m / day, and it is determined that the contaminated groundwater to be treated according to the present invention also moves at a similar speed.
m / Hr, and the construction site had a structure in which the fracture 2 was filled with iron powder as shown in FIG. 1 and contaminated groundwater permeated therein.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

[0025]

Example 1 As shown in FIG. 2, a boring was performed on a soil contaminated with A and a boring hole 1 was dug down. Next, the ground surface 7 was sealed and compressed air was blown into the underground to generate the fracture 2 in the weak part of the ground.

Next, as shown in the partially enlarged view of FIG. 1, compressed air is blown together with the iron powder from the iron powder blowing port that seals the ground surface 7, and these iron powders are blown into the fracture 2 obtained earlier. The iron powder dispersion layer 4 was formed, and the underground water 6 permeating the iron powder dispersion layer 4 was received by the pit 3 at the bottom of the boring hole 1.

When the permeated water 5 of the A-contaminated soil was analyzed at the time of drilling the boring hole 1, the pH was 4.9, the content of each heavy metal was Cr ⁶⁺ 0.76 mg / l,
1.2 mg / l and Ni 8.5 mg / l.

The contaminated permeated water 5 was permeated into the iron powder dispersion layer 4 in the fracture 2 at a rate of 6 cm / Hr, and the permeated groundwater 6 received at the pit 3 at the bottom of the borehole 1 was analyzed. , PH is 6.0, and the content of each heavy metal is Cr ⁶⁺ tr. , Total Cr tr. , Ni
0.1 mg / l, and the effect of the heavy metal treatment was satisfactory.

[0029]

Example 2 A boring hole 1 was dug down in a soil contaminated with B by means similar to that shown in Example 1, fractures 2 were generated, and the permeated water 5 was analyzed. As a result, it was found that trichlorethylene and tetrachloroethylene, which are organic halogen compounds, were contained. The amounts were all 5 mg / l.

After that, the fracture 2 is filled with iron powder to form an iron powder dispersion layer 4.
Permeation at the rate of Hr and analysis of the groundwater 6 after permeation revealed that the contents of trichlorethylene and tetrachloroethylene were all 0.1 mg / l or less.
Thus, it was confirmed that the method of the present invention can be applied to the treatment of an organic halogen compound.

[0031]

The method of the present invention is a treatment method capable of purifying heavy metal components and organic halogen compounds in contaminated groundwater using inexpensive iron powder as described above, and replacing the iron powder after a certain period of time. This will permanently purify the contaminated groundwater. In addition, the method of the present invention does not require facilities or buildings for treating contaminants on the ground, the time required for treatment is short, and the influence of geological conditions (air permeability, permeability coefficient, density, etc.) is small. There are advantages.

[Brief description of the drawings]

FIG. 1 is a partially enlarged cross-sectional view of a fracture site around a construction site according to the method of the present invention.

FIG. 2 is a schematic sectional view of a construction site according to the method of the present invention.

FIG. 3 is a cross-sectional view schematically showing a pneumatic fracturing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Boring hole 2 Fracture 3 Pit part 4 Iron powder dispersion layer 5 Infiltration water 6 Groundwater 7 Ground surface

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/62 C02F 1/62 Z 1/70 A B Z 1/70 C09K 3/00 S B09B 3/00 304K ZAB C09K 3/00 (71) Applicant 596137645 Cass Street at Highway 35, Keyport, New Jersey 07735, U.S.A. S. A. (72) Inventor Toshimune Kimura 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Jun Ogata 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor John Jay Riskowitz United States 07735 Keyport Cass Street at Highway 35, New Jersey 35 Accutech Limited Systems Inc. F-term (reference) 2E191 BA02 BA15 BB01 BC01 BD11 4D004 AA41 AB03 AB06 AC07 CA01 CA37 CA50 CC11 4D038 AA02 AB14 AB65 AB67 AB68 AB71 AB78 BA01 BB15 4D050 AA02 AB19 AB54 AB56 AB57 AB60 AB64 BA02 BD03

Claims (8)

[Claims] 1. After boring holes are drilled in soil contaminated with an organic halogen compound, a fracture is generated underground by blowing compressed air and iron powder into the boring holes. Forming a plurality of iron powder dispersion layers extending outward from the holes along a basically horizontal plane, and contacting the iron powder dispersion layer with groundwater flowing in the contaminated soil to remove the compounds in soil and groundwater. A soil and groundwater purification method characterized by detoxification. 2. After drilling a borehole in soil contaminated with an organic halogen compound, a fracture is generated underground by blowing compressed air into the borehole, and then the obtained fracture is subjected to iron powder by compressed air. To form a plurality of iron powder dispersion layers containing the iron powder and extending outward from the boring hole along a basically horizontal plane, and forming the iron powder dispersion layer with groundwater flowing through the contaminated soil. A method for purifying soil and groundwater, comprising detoxifying the above-mentioned compound in soil and groundwater by contact. 3. After boring a hole in soil contaminated with a heavy metal and an organic halogen compound, a fracture is generated underground by blowing compressed air and iron powder into the boring hole to contain the iron powder. Forming an iron powder dispersion layer and contacting the iron powder dispersion layer with groundwater flowing in the contaminated soil to detoxify the heavy metals and the compounds in the soil and groundwater, thereby purifying the soil and groundwater. Method. 4. After drilling a borehole in soil contaminated with heavy metals and organic halogen compounds, a fracture is generated underground by blowing compressed air into the borehole, and then the obtained fracture is compressed with compressed air. Forming an iron powder dispersion layer by injecting iron powder and detoxifying the heavy metals and the compounds in soil and groundwater by contacting the iron powder dispersion layer with groundwater flowing in the contaminated soil. Soil and groundwater purification methods. 5. The purification of soil and groundwater according to claim 3, wherein the iron powder dispersion layer is a plurality of layers containing the iron powder and extending outward from the boring hole along a basically horizontal plane. Method. 6. The method for purifying soil and groundwater according to claim 3, wherein the heavy metal is a heavy metal which is nobler than iron. 7. The at least one heavy metal selected from the group consisting of chromium, copper, nickel, cadmium and lead.
The method for purifying soil and groundwater according to claim 6, which is a seed. 8. The soil and groundwater according to claim 1, wherein said organic halogen compound is at least one chlorinated hydrocarbon selected from the group consisting of trichloroethylene, tetrachloroethylene, dichloroethylene, carbon tetrachloride and dichloromethane. Purification method.