JP2000135483A - Contaminated soil purification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To purify contaminants in the ground by diffusing iron powder together with water or muddy water into the contaminants in the ground. SOLUTION: A prescribed quantity of iron powder is mixed with water or muddy water to adjust drilling water. Next, from a nozzle 1 opened at the head of a bit 12, the drilling water is jetted to perform boring in the ground. On boring, iron powder contained in the drilling water is injected together with water or muddy water. Or, on boring, a rotary tool (reamer) is driven to agitate the water or muddy water and iron powder and to incorporate the iron powder into the stratum. In this way, contaminants in underground water or soil can be purified.

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 by in-situ iron powder injection, and more particularly, to an iron for effectively detoxifying soil containing contaminants such as trichloroethylene and tetrachloroethylene. The present invention relates to a method for purifying contaminated soil by injecting powder into the ground.

[0002]

2. Description of the Related Art Organochlorine compounds such as trichloroethylene and tetrachloroethylene have been widely used in the semiconductor industry, the cleaning industry, and the like because of their high degreasing properties. However, it has been reported that when these organochlorine compounds contaminate soil and groundwater, they are eventually ingested into the human body by material circulation and induce leukemia in children. Standards are set.

[0003] Factors that affect the spread of contaminants to soil and groundwater include the groundwater level, the amount of groundwater, the solubility, volatility, specific gravity, viscosity, surface tension of contaminants, the rate of adsorption to soil, There are various factors such as the permeability of water, and the situation of diffusion of pollution differs depending on the situation of these factors. In the case of a liquid contaminant, the upper surface of the water-impermeable layer often diffuses together with the groundwater, and the contamination often spreads deeper at the point where the water-impermeable layer is cut.

To remove contaminants from soil or groundwater that was contaminated by contaminants such as organochlorine compounds in situ, multiple vertical boreholes were constructed for contaminants above the groundwater level. Soil gas suction method that uses the volatility of contaminants to remove them from boreholes (in this method, air or steam is sent from one borehole to actively vaporize contaminants, (Including methods such as suction removal from the borehole)
Has been done.

[0005] Alternatively, for pollutants located below the groundwater level, a plurality of vertical boreholes are installed,
2. Description of the Related Art A pumping aeration method and the like for removing contaminants dissolved in groundwater by pumping groundwater to the ground and contacting the air with the air for aeration have been performed. Further, in order to decompose pollutants in soil or groundwater, a method using microbial decomposition, or Japanese Patent Application Laid-Open No. Hei 5-50152 and Japanese Patent Application Laid-Open No. Hei 6-506, is used.
No. 631 discloses a method using an underground reaction wall.

Further, a borehole is dug down in the contaminated soil, the ground surface is sealed, and compressed air is blown into the underground to generate a fracture in the ground. Simultaneously with or after this operation, iron powder is compressed from the ground surface with compressed air. A method of blowing iron, forming an iron powder dispersion layer in the fracture, and passing the permeated water contaminated into the iron powder dispersion layer into contact with the iron powder to detoxify heavy metals and organic halogen compounds in soil and groundwater is also disclosed in No. 10-71386.

[0007]

However, the conventional method of this kind has the following problems. In other words, the soil gas suction method and the pumping aeration method could only deal with either the upper or lower groundwater level. In addition, all of these are soil purification techniques that utilize the high volatility of the target pollutants, and are easily affected by soil permeability such as local water permeability and underground structures. In addition, since pollutants in the ground, especially organochlorine compounds such as trichloroethylene, have a higher specific gravity than water, they often penetrate deeper and diffuse in a plane along an impermeable layer. In the case of the vertical boring holes, the contact points with the contaminants were local, and a large number of vertical boring holes were required for suction and recovery of the contaminants. In addition, ground facilities used for the vertical boring need to be provided for each vertical boring hole in many cases, and it has been difficult to efficiently remove underground pollutants.

In addition, when there is a building or a structure on the contaminated soil, it is difficult to drill below the contaminated soil, and in many cases, purification cannot be performed. Further, there is a problem that an additional step of separately detoxifying the removed contaminants is required. In addition to these problems, the soil gas suction method and the groundwater aeration method have a drawback that it is difficult to completely remove soil pollutants in situ.

Furthermore, the above-mentioned method using microbial decomposition is not applicable to all soils due to the properties of the soil, and even if it is possible, a long time is required for purification due to the action of microorganisms. .

[0010] In the method using the underground reaction wall,
The target of purification is limited to groundwater and is not intended for soil purification. In addition, it is necessary to construct trenches and culverts, and deep trenches are required depending on the groundwater level. Furthermore, in the trench in which iron is diffused, a reaction occurs between iron and carbonate ions in the groundwater, and iron carbonate is generated, thereby blocking the permeable layer. Was.

Further, according to the method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 10-71383, an additional step is not required for detoxifying contaminants, and contaminants can be purified in situ. Although effective, compressed air and iron powder required ground equipment such as pressure vessels that require careful handling.

An object of the present invention is to solve such a conventional problem, and to efficiently inject, agitate, and diffuse iron powder particles into soil or groundwater together with water or muddy water. To provide a method for in situ purification of pollutants in soil and groundwater.

[0013]

According to the method for purifying contaminated soil of the present invention, a predetermined amount of iron powder is mixed into water or muddy water to adjust drilling water, and then the drilling water is injected from a nozzle at the tip of a bit. While performing horizontal and / or diagonal boring while purging pollutants present in the ground by injecting iron powder contained in the drilling water into the ground together with the water or mud during the boring. Features.

The boring is performed on the soil above and / or below the water table depending on the state of the pollutants. Furthermore, the nozzle can be implemented in a fixed state, but it is preferable to open the nozzle with a rotatable bit and propel it underground.

[0015] The iron powder used in the method of the present invention can be used when the main particle size of the soil to be purified is 2 mm to 0.15 mm.
Iron powder having a fine particle size of about 20 μm to 5 mm and being porous and having a large specific surface area is preferred. This is because if the particle size is too small, iron powder is a flammable solid and it is difficult to handle it.If the particle size is too large, it will not be uniformly slurried in a water tank before injection, and stable injection into the soil will not be possible. Because it becomes difficult. By the way, if 50% or more of iron powder having a particle size smaller than 53 μm is contained, it becomes a dangerous substance (a second-class dangerous substance-possible solid).

The amount of iron powder added to the soil varies depending on the condition of the target contaminated soil, but in many cases is 0.1% to 10% by weight based on the target soil and groundwater. It is preferable to inject and diffuse so as to have a ratio.
If the injection / diffusion amount is too small, the purification period becomes long, and if it is too large, it is disadvantageous in terms of cost. In addition, the elution pH of the soil to be purified is desirably pH 10 or less from the decomposition conditions of iron powder. This is because, when the soil is in a strong alkaline atmosphere, the activity of the surface of the iron powder is reduced, and the decomposition efficiency of the organochlorine compound is reduced. Also, in order to maintain and promote the activity of iron powder, it is preferable that the atmosphere of the target soil or groundwater is a reducing atmosphere. This is because iron powder decomposes organic chlorine compounds more efficiently in a reducing atmosphere.

Further, in the method for cleaning contaminated soil according to the present invention, a rotary tool is installed behind the bit in claim 2;
During the boring, the rotary tool is driven to stir the soil and the iron powder, so that the iron powder can be efficiently diffused into the soil.

The rotary tool has a main purpose of diffusing iron powder in a wide range by using water or muddy water, and includes an appropriate type such as a screw type or an impeller type. Among them, a reamer can be exemplified.

The organic chlorine compounds to be purified according to the present invention include volatile organic chlorine compounds such as trichloroethylene (TCE), tetrachloroethylene (PCE) and 1,1,1-trichloroethane (MC). Organic compounds (CVOC). When iron powder is used for soil purification, a weakly acidic reducing agent
For example, sodium hydrogen sulfite (NaHSO ₃ ) can be mixed to promote the decomposition of volatile organic chlorine compounds (CVOC) by iron powder. In the following, the use of the name "horizontal boring" includes boring in an oblique direction.

As is clear from the above description, in the purification procedure of the present invention, first, a predetermined amount of iron powder is mixed into water or muddy water to prepare drilling water. Then, the drilling water is bored in the horizontal and / or diagonal direction while the drilling water is injected at a high pressure from a nozzle at the tip of the bit. At this time, the iron powder contained in the drilling water is injected into the ground. Alternatively, a rotating tool is provided behind the bit, and the drilling tool is driven at the time of boring to stir the excavation water with the soil or the groundwater, thereby ensuring that the iron powder is diffused and mixed into the target soil and the groundwater. Is good.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the method for injecting iron powder into the ground according to the present invention will be described in more detail with reference to an embodiment shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto, unless otherwise specified. It is only an illustrative example.

FIG. 1 shows an embodiment of the method for injecting iron powder into the ground according to the present invention, and FIG. 2 shows a side view of a bit used in the embodiment. FIG. 3 shows a plane of soil into which iron powder has been injected, and FIG. 4 shows the same cross section. FIG. 5 shows a cross section of the soil showing the flow direction of groundwater, and FIG. 6 shows a plane of FIG.

An embodiment of the present invention will be described with reference to FIGS. On the ground surface 19 (GL), a storage tank 1 containing iron powder, a water tank (WT) 2 connected to the storage tank 1 through a passage 3, and further connected to the water tank 2 via a bribe 5. Pump unit (PU) 6 is installed. In addition,
The pump unit 6 has a built-in turbine pump that is driven to rotate by a motor (not shown). Further, a power unit track 13 and a rotary drive unit 14 are arranged in the vicinity thereof.

First, a predetermined amount of iron powder is sent from the storage tank 1 through the passage 3 to the water tank (WT) 2 to prepare slurry-form drilling water. The pump unit 6 pumps the slurry-form drilling water from the water tank 2, and pumps the drilling water from a joint (not shown) to a conduit 7 shown in FIG.
It is needless to say that a suitable unit such as a plunger pump or a piston pump can be used as the pump unit 6 in addition to the turbine pump.

The conduit 7 is inserted concentrically into the rod 10 as is apparent from FIG.
The bearing members 11 which enable relative rotation with each other between 0 and 0 are incorporated in some places. A bit 12 as shown in FIG.
The rear end is connected to a rotary drive device 14 arranged near the power unit track 13.

The power unit truck 13 has a driving device (not shown) such as a hydraulic motor or an electric motor.
Is incorporated. Due to such a structure, the rotation drive device 14 can be driven by the power unit truck 13 to rotate the rod 10, and can arbitrarily set an oblique boring driving angle into the ground.

The bit 12 has a substantially cylindrical shape and has an elliptical head 12a which is obliquely cut. Further, a nozzle 15 that opens on the acute angle side of the head 12a is provided. This nozzle 15 is connected to the aforementioned conduit 7 inside the bit 12.

According to the method for purifying contaminated soil, as described above, a predetermined amount of iron powder is sent from the storage tank 1 to the water tank (WT) 2 via the passage 3 to adjust the slurry-form drilling water. Next, the pump unit 6 is driven to suck up the slurry-like drilling water from the water tank 2, and the slurry is inserted into the rod 10 from the channel 8 by applying a high pressure to the drilling water (usually a water supply pressure of 10 kg / cm ² or more). Into the pipe 7
The jet water 16 for drilling is jetted from a nozzle 15 provided at the tip of the second. The bit 12 starts boring in an oblique direction while injecting drilling water 16 obliquely from a penetrating pit 17 formed in the soil.

In the above-described boring, the rotary drive unit 14 is driven by the power unit track 13 to move the rod 10 and the bit 12 around their respective central axes (CC) as shown by the arrow A in FIG. Rotate to. Nozzle 1
The drilling water 16 jetted at high pressure along with the rotation of the boring 2 bores the soil and drills the boring holes 2 as shown in FIGS.
5 is drilled in a diagonal direction to a predetermined depth (in the present embodiment, above the groundwater level WL, the unsaturated layer 22 without groundwater).

Then, in the direction of arrow B, that is, the ground surface (G
L) Drill substantially parallel to 19 and drill a boring hole 25 as shown in FIGS. The boring hole 25 is formed without discharging the excavated soil to the ground, and a well hole that needs to be maintained for a long time is not constructed. At the same time, a portion (iron powder diffusion portion) 26 where the iron powder is diffused is formed in the soil.

In this embodiment, the bit 12 is provided with a transmitter (not shown), and a radio signal 20 emitted from the transmitter is detected on the ground surface 19 by a flow indicator 21 as a detector. Then, the boring position of the bit 12 is checked, and if the boring position is off the predetermined course, the flow locator 21 is moved to the predetermined course while moving. Alternatively, detour is performed in an arbitrary direction by the flow locator 21 as shown in FIG. 3, or boring is performed to an arbitrary depth as shown in FIG.

As shown in FIG. 3, in order to change the boring direction and provide a portion 26 into which a plurality of iron powders are injected (iron powder diffusion portion), the rotation of the rod 10 is stopped and the rotation driving device 14 is rotated. After adjusting the oblique insertion angle and direction into the ground and pushing the bit 12 as it is, the bit 1
The second head 12a contacts the soil, and the inclined surface of the head 12a is bent in the direction of arrow D by earth pressure to perform boring. Such an operation is repeated a plurality of times. Also, as shown in FIG. 4, a similar operation is performed when forming a portion (iron powder diffusion portion) 26 into which iron powder is injected in the depth direction.

A portion into which the iron powder is injected (iron powder diffusion portion)
26, the substance to be purified is trichloroethylene (TC
E) In the case of tetrachloroethylene (PCE), the iron powder decomposes the substance to be purified by reducing and detoxifying it.
Further, the substance to be purified is 1,1,1-trichloroethane (M
C) 1,1,2-trichloroethane (1,1,2-TC
A) 1,1,2,2-tetrachloroethane (1,1,2,2
-TeCA), decomposition by iron powder is performed, but 1,1,2-trichloroethane (1,1,2-TC
A) 1,1,2,2-tetrachloroethane (1,1,2-T
With regard to eCA), in the early stage of the decomposition reaction, the iron powder acts not as a reducing agent but as a catalyst, and the dehydrochlorination reaction proceeds to detoxify the substance to be purified.

In the present embodiment, there is no need to drill a well hole to be maintained for a long time as in the prior art. Therefore, it is not necessary to use a bentonite to make the hole wall of the boring hole self-supporting. Construction work is possible only by injecting and diffusing iron powder, and the work efficiency is good, and the iron powder can be injected into the ground at extremely low cost. In particular, in the case of boring in the horizontal direction, a reaching pit as in the case of digging a conventional horizontal well hole is not required, and boring only needs to be started from a penetrating pit, and the work becomes easy. Moreover, when this embodiment is compared with the conventional vertical boring method, there is no generation of excavated soil, and there is no need to treat construction residual soil. There are also significant advantages such as no relocation of ground equipment.

In this embodiment, it is also possible to perform a horizontal boring along the aquifer 36 below the groundwater level WL as in the modified examples shown in FIGS.
As described above, iron powder can be injected even in soil below a place where a building 30 such as a factory or a tank is installed on the ground surface 19 (GL).

Further, according to the present embodiment, a portion where iron powder as iron powder is diffused and mixed in the ground (iron powder diffusion portion).
Reference numeral 26 denotes a barrier, which prevents the diffusion of the pollution from the polluted area 35 to the downstream area of the groundwater 36 in the direction of the arrow. In this case, it is possible to execute a barrier (iron powder diffusion portion) 26 for injecting contamination into a local area and preventing the diffusion from a single ground facility. 5 and 6
In the figure, the same reference numerals are given to parts equivalent to those in FIGS.

When the target organochlorine compound is hardly decomposable, a reducing substance exhibiting weak acidity is added to the water tank (WT) 2 in order to enhance the reactivity of the iron powder, thereby enhancing the effectiveness of the iron powder. The effect of purification is high when injected into soil.

Similarly, depending on the type of the organochlorine-based compound and the surrounding environment, iron powder or divalent iron salt is dispersed in advance in the contaminated area of the groundwater by the above method, and hydrogen peroxide is separated by another system. It is also possible to oxidatively decompose underground pollutants by injecting the Feton reaction. However, the Feton reaction is a reaction that proceeds instantaneously, and the purification method cannot be carried out by adding hydrogen peroxide to an iron slurry production tank on the ground. Therefore, the method of adding hydrogen peroxide is spraying from the ground surface of the target area, or making this boring equipment two systems, or providing two storage tanks on the ground, an iron slurry production tank and a hydrogen peroxide tank, It is necessary to perform pumping to the target area while periodically switching (or making the pipe structure two layers).

As effects of this embodiment, diffusion of iron powder and purification of organochlorine compounds when using iron powder were confirmed. In this test, iron powder was stirred and mixed by horizontal boring on soil actually contaminated with trichlorethylene, and soil samples were collected before and after the test. The iron powder used was E-200 manufactured by Dowa Iron Powder Industry Co., Ltd., and 1% or more of the iron powder was stirred and mixed with the soil. Samples were collected by performing vertical boring before and after the test. The sampling location was 2 m in length and 30 cm in width from the center of the horizontal boring, and a sample within 30 cm from the center where the iron powder was diffused and mixed by horizontal boring was sampled.

The iron concentration (mg / kg) of the soil before and after the treatment and the elution amount of soil trichlorethylene (mg / l) before and after the treatment were determined by sampling the sample soil as described above. The soil was as shown in Table 2. The soil after the treatment is a sample value collected 60 days after the treatment.

[0041]

[Table 1]

[0042]

[Table 2] It can be seen that the addition of iron powder into the ground by horizontal boring in the above example increased the iron concentration in the soil by an average of 11,400 mg / kg before the treatment, and the diffusion and mixing of iron powder into the ground It turned out that was done. In addition, the amount of trichlorethylene eluted in the soil detected before the treatment was hardly detected after the treatment, demonstrating that the method of the present invention is effective for organic chlorine compounds in the ground. .

[0043]

As described above, according to the method for injecting iron powder into the ground according to the present invention, horizontal and / or oblique directions can be obtained while digging water in which iron powder is mixed with water or muddy water is injected. The following effects are achieved by advancing the boring. a) The iron powder can be effectively injected, diffused and mixed together with water or muddy water at a predetermined place in the ground during excavation. b) By using a rotary tool during excavation, it is possible to stir iron powder in soil and muddy water or groundwater, to ensure that iron powder is injected into the ground, and to improve the purification effect of pollutants. Become. Moreover, after the iron powder has diffused into the soil, the purification effect can be maintained without any power. c) Unlike conventional soil gas suction method and pumping aeration method, iron powder can be diffused and mixed into both upper and lower groundwater levels where contamination is recognized. d) If the contaminants are spreading horizontally through the aquifer, iron powder can be injected, diffused and mixed efficiently along the area where the contaminants spread. e) It is possible not only to purify the contaminated area but also to prevent the diffusion of the contaminants from the contaminated area. f) A diffusion layer of iron powder is formed in the ground by horizontal boring, and the diffusion of the contaminants through the diffusion layer is prevented, so that the diffusion of the contamination outside the site is prevented. It is unnecessary to perform such operations as excavation of a trench, mixing of soil and iron powder on the ground, and burying of iron powder in the trench. g) Even if a building exists on the ground surface, it is possible to spray iron powder under the building. h) Since the well hole which needs to be maintained for a long time is not excavated, there is no need to make the hole wall of the boring hole self-supporting using bentonite as in the related art, and only water or drilling water mixed with muddy water and iron powder is used. It becomes a boring with water and can inject iron powder into the ground very efficiently. i) Since iron powder is fine particles, it becomes slurry with water,
It can be easily pumped by a pump. In addition, the purifying effect can be maintained for a long time. j) Since iron powder can be injected from one location to a plurality of desired locations, efficient work can be performed without relocating a tank for storing iron powder or other ground equipment. k) Since pollutants can be detoxified locally, there is no generation of secondary waste.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a method for injecting iron powder into the ground according to an embodiment of the present invention, showing a cut soil.

FIG. 2 is a side view of a bit used in the embodiment of FIG.

FIG. 3 is a plan view of soil into which iron powder has been injected.

FIG. 4 is a sectional view of FIG. 3;

FIG. 5 is a sectional view of soil showing a flow direction of groundwater.

FIG. 6 is a plan view of FIG. 5;

[Explanation of symbols]

 12 bits 15 Nozzle 16 Drilling water 14 Rotary drive

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) C09K 101: 00 (72) Inventor Jin Hitoshi Yamauchi 2nd Rokubancho, Chiyoda-ku, Tokyo Inside Kokusai Kogyo Co., Ltd. F term (reference) 2E191 BA12 BA15 BB01 BC01 BD11 4D004 AA41 AB06 AC07 CA15 CA35 CA37 CA50 CB21 CB42 CC03 CC11 DA01 DA02 DA20 4H026 AA01 AB04

Claims (2)

[Claims] A drilling water is prepared by mixing a predetermined amount of iron powder into water or muddy water, and then boring in a horizontal direction and / or an oblique direction while jetting the drilling water from a nozzle at a tip of a bit. A method for cleaning contaminated soil, comprising injecting iron powder contained in the drilling water into the ground together with the water or mud during the boring. 2. A rotary tool is installed behind the bit,
The contaminated soil purification method according to claim 1, wherein the rotating tool is driven during the boring to stir the soil and the iron powder to efficiently diffuse the soil / groundwater purification substance into the soil.