JP3381764B2 - How to clean contaminated soil - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to cadmium, lead,
The present invention relates to a method for purifying the soil by removing these pollutants from a polluted soil containing ionic pollutants such as copper, zinc, nickel, chromium, arsenic, selenium, and cyan.

[0002]

2. Description of the Related Art Soil contaminated by factory wastewater, factory waste, mining wastewater, etc., may contain pollutants such as cadmium, lead, copper, zinc, nickel, chromium, arsenic and selenium. If such soil is left as it is, there is a risk that pollutants contained in the soil will diffuse into the environment through groundwater or biological cycles.

Therefore, the contaminated soil is excavated and removed, subjected to a predetermined treatment, and then disposed of at a management-type or blocking-type disposal site, while normal soil is excavated in the excavated hole. It is common to return to the original state after returning to the soil.

However, with such a method, there is a problem that the contaminated soil is disturbed during excavation to cause secondary pollution, a problem that a large amount of the contaminated soil must be carried out and transported, or a nearby part of an existing building. There is a problem that the excavation and removal itself becomes difficult directly below.

In order to solve such a problem, while supplying water to the contaminated soil, by applying a DC voltage between a pair of electrodes buried in the soil, ionic pollutants in the contaminated soil are directed toward the electrodes. Attention has been paid to the electric current collection method of moving the wastewater to and recovering it, and it is greatly expected as a technique for cleaning the contaminated soil in situ without excavating the contaminated soil.

[0006]

In order to prevent the ground surface from being flooded near the water supply point and preventing pollution from spreading to the surroundings, it is necessary to lower the water level in the water supply pipe from the ground surface to some extent. However, because of that, water supply is not performed near the ground surface, resulting in the problem that pollutants remain near the ground surface.

Such a problem becomes more serious on the drainage side where the water level is lowered by pumping up, and thus only the area near the ground surface cannot be purified by energization, and removal work by excavation is inevitable.

The present invention has been made in consideration of the above-mentioned circumstances, and provides a method for purifying contaminated soil in which a pollutant can be collected by energization without remaining in the ground surface area. To aim.

[0009]

In order to achieve the above object, the method for purifying contaminated soil according to the present invention, as described in claim 1, supplies water to the contaminated soil containing ionic pollutants. In a method for purifying contaminated soil in which the ionic contaminants are transferred to the electrodes and recovered by applying a DC voltage between a pair of electrodes arranged in the contaminated soil, an impermeable sheet is provided on the upper surface of the contaminated soil. Is laid to prevent the impermeable sheet from being lifted from the upper surface, and the water is supplied to a region below the impermeable sheet.

Further, the method for purifying contaminated soil according to the present invention comprises covering the above-mentioned impermeable sheet with soil.

Further, in the method for purifying contaminated soil according to the present invention, in the water pipe buried in the contaminated soil, the upper surface of the contaminated soil is set to a non-water supply range, and the water level in the water supply pipe is contaminated in such a state. The water level in the drainage pipe buried in the contaminated soil is maintained near the top surface of the contaminated soil while maintaining the position above the upper surface of the soil.

In the method for purifying contaminated soil according to the present invention, the upper surface of the contaminated soil is covered with a water impermeable sheet, and water is supplied below the water impermeable sheet while preventing the floating of the soil impermeable sheet. By doing this, it is possible to apply a water pressure on the water supply side that is such that the water level on the drainage side is as high as the upper surface of the contaminated soil, so sufficient water is also supplied near the upper surface of the contaminated soil. .

Any method can be used to prevent lifting.
For example, a method in which an anchor is driven into contaminated soil and a water impermeable sheet is fixed to the anchor is conceivable. However, when the water impermeable sheet is covered with, for example, good quality soil, the load of the good quality soil Since the water-impermeable sheet is loaded on the impermeable sheet, the impermeable sheet is prevented from rising due to water pressure.

The water supplied into the contaminated soil is blocked by the impermeable sheet and does not flow out to the soil cover portion. Therefore, the diffusion of the pollutants contained in the contaminated soil to the soil-covered portion is prevented in advance, and it becomes possible to reuse the high-quality soil for a desired purpose after the completion of the energization work.

The method of supplying water is arbitrary. For example, the water may be jetted at a predetermined water pressure from a nozzle embedded in the contaminated soil. Is a non-water supply range, and in such a state the water level in the water supply pipe is maintained above the upper surface of the contaminated soil, and the water level in the drainage pipe buried in the contaminated soil is maintained near the upper surface of the contaminated soil. In such a case, by monitoring the water levels in the water supply pipe and the drainage pipe, it becomes possible to reliably supply water to the vicinity of the upper surface of the contaminated soil.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a method for purifying contaminated soil according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a conceptual diagram explaining a case where the method for purifying contaminated soil according to the present invention is applied to the removal of anionic pollutants. As can be seen in the figure, in the method for purifying contaminated soil according to the present embodiment, first, the permeation pipe 2a as a drainage pipe and the water supply pipe are provided in the contaminated soil 1 containing anionic pollutants as ionic pollutants. The water permeable pipe 2b is embedded, and the electrode 3a is inserted inside the water permeable pipe 2a and the electrode 3b is inserted inside the water permeable pipe 2b.
These electrodes 3a and 3b are connected to the positive side and the negative side of the DC power supply 4 so that the electrode 3a serves as an anode and the electrode 3b serves as a cathode. If necessary, a water impervious wall is constructed so as to surround the purification area in the contaminated soil 1.

Since the reduction reaction occurs at the electrode 3b, the electrode 3b may be made of, for example, a reinforcing rod, but the electrode 3a may be made of an inactive conductor, for example, a carbon rod, since an oxidation reaction occurs.

Here, the anion means chromium, arsenic, selenium, cyan, etc., which are CrO ₄ ²⁻ , Cr ₂ O ₇ ²⁻ , A, respectively.
It is contained in the contaminated soil 1 in the form of sO ₄ ³⁻ , AsO ₃ ³⁻ , SeO ₄ ²⁻ , SeO ₃ ²⁻ , CN ^−, etc.

The water permeable pipes 2a and 2b are strainer pipes having a large number of holes. These water permeable pipes 2a, 2b
Are preferably embedded in a large number in a predetermined contaminant removal range, and are preferably arranged in a grid pattern at intervals of 1.5 to 2 m, for example.

A water supply pipe 5 is inserted in the water permeable pipe 2b, water is supplied to the water permeable pipe 2b through the water supply pipe at any time, and a drain pipe 8 is inserted in the water permeable pipe 2a. The water can be drained from the water permeable pipe 2a through the drain pipe at any time.

Next, a water-impermeable sheet 11 is laid on the upper surface of the contaminated soil 1, and the good-quality soil 1 is further laid on the water-impermeable sheet.
Cover 2 with soil. With such a configuration, the water impermeable sheet 11
It is possible to prevent the impermeable sheet from floating above the upper surface of the contaminated soil 1 due to the water pressure acting on the back surface of the. The impermeable sheet 11 may be made of, for example, a vinyl sheet.

Here, the area above the upper surface of the contaminated soil 1 of the water permeable pipe 2b is not supplied with water without providing a hole for water supply. In addition, at the location where the water-permeable pipes 2a, 2b and the water-impermeable sheet 11 interfere with each other, the water-impermeable sheet 11 should be placed as shown in FIG. Stand up around the water permeable pipes 2a, 2b.

When the preparation is completed in this way, the water level in the water permeable pipe 2b is maintained above the upper surface of the contaminated soil 1 and the water level in the water permeable pipe 2a is maintained near the upper surface of the contaminated soil 1. As described above, the amount and timing of water supply and drainage are adjusted, and the DC power supply 4 is operated in such a state so that the electrodes 3a,
Energize between b. The DC power source 4 is preferably adjusted to an optimum voltage, for example, about 60V while monitoring the current value, the ground temperature, and the like.

Then, in the contaminated soil 1, sufficient water is also supplied to the region near the upper surface thereof, and the anionic contaminants migrate to the anode 3a by electrophoresis, so that they are collected in the water permeable pipe 2a. Drain with clean water. The drained water is passed through an ion exchange resin or the like to separate and remove anionic contaminants, then subjected to pH treatment and discharged into sewage, or is recycled as it is for water supply.

As described above, in the conventional case, as shown in FIG.
Even if the water level on the water supply side is set near the upper surface of the contaminated soil 1 as shown in (a), the water level on the drainage side will be lower than the water supply side by Δh due to the decrease in the water level due to pumping. In the area near the ground surface above the water level line shown in the figure, it was not possible to remove the pollutants by energization, but according to the method for cleaning contaminated soil according to the present embodiment, it is shown in FIG. As described above, the upper surface of the contaminated soil 1 is covered with the impermeable sheet 11, and water is supplied below the impermeable sheet while preventing the floating of the impermeable sheet 11. Therefore, the water level on the drain side is equal to that of the contaminated soil 1. It is possible to set the water level on the water supply side as high as Δh so that the height is the same as the upper surface.

As a result, sufficient water can be supplied also to the area near the upper surface of the contaminated soil 1, thus making it possible to remove pollutants by energizing this area as well, and to perform removal work by excavation as in the past. It becomes unnecessary.

Further, the water supplied into the contaminated soil 1 tries to push up the impermeable sheet 11 in the direction of the arrow in the figure by the water pressure, but according to this embodiment, the impermeable sheet 11 Since the good quality soil 12 is covered therewith, it is possible to prevent the impermeable sheet 11 from being lifted up by a relatively simple construction method.

Further, according to this embodiment, since the water-permeable side water-permeable pipe 2b is not supplied with water in the region above the upper surface of the contaminated soil 1, there is no possibility that the ground surface will be flooded and the workability will be impaired. There is no need to pay special attention to wiring work for energization.

Further, according to this embodiment, the water supplied into the contaminated soil 1 is blocked by the impermeable sheet 11 and does not flow out to the good quality soil 12. Therefore, the diffusion of the pollutants contained in the contaminated soil 1 into the good quality soil is prevented in advance, and after the energization work is completed, the good quality soil 12 can be reused for a desired purpose.

Further, according to this embodiment, the water-permeable pipe 2b is not supplied with water in the region above the upper surface of the contaminated soil 1, and the water level in the water-permeable pipe 2b is located above the upper surface of the contaminated soil 1. And the water level in the water permeable pipe 2a is maintained near the upper surface of the contaminated soil 1.
Only by monitoring the water levels in a and 2b, it is possible to reliably supply water near the upper surface of the contaminated soil.

In this embodiment, the impermeable sheet 11 is prevented from being lifted up by using the load of the covering soil. Instead, for example, an anchor is driven into the contaminated soil and the impermeable sheet is attached to the anchor. May be fixed.

In this embodiment, the electrodes 3a and 3b are separate from the water permeable pipes 2a and 2b.
May be formed of a conductive material to serve also as an electrode. Further, although the water permeable pipes 2a and 2b are configured by strainer pipes, instead of this, for example, they may be configured by a net-shaped resin pipe.

Further, in the present embodiment, the anionic pollutants are targeted, but instead of this, cation pollutants such as lead, cadmium and copper may be targeted. In such a case, the connection of the DC power supply 4 is reversed, that is, the electrode 3a
Is connected to the minus side and the electrode 3b is connected to the plus side, the cation contaminant can be moved to the electrode 3a side and can be collected together with the water accumulated in the water permeation pipe 2a.

In recovering the cation contaminant, as it migrates to the electrode 3a side by electrophoresis, hydroxide easily precipitates in an alkaline environment. Therefore, an acidic solution is supplied around the electrode 3a. To prevent precipitation.

[0036]

As described above, according to the method for purifying contaminated soil according to the first aspect of the present invention, sufficient water can be supplied even to the area near the upper surface of the contaminated soil. In addition, it is possible to remove pollutants by energization and eliminate the conventional removal work by excavation.

Further, according to the method for purifying contaminated soil of the present invention according to the second aspect, it is possible to prevent the impermeable sheet from being lifted up by a relatively simple construction method.

According to the method for purifying contaminated soil according to the third aspect of the present invention, water can be reliably supplied to the vicinity of the upper surface of the contaminated soil simply by monitoring the water levels in the water-permeable and drain-side permeable pipes. There is also an effect that can be.

[0039]

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method for purifying contaminated soil according to the present embodiment.

2A and 2B are cross-sectional views for explaining the action of the method for cleaning contaminated soil, wherein FIG. 2A is a water level line in the conventional energization method, and FIG. 2B is a water level line in the energization method of the present embodiment.

[Explanation of symbols]

1 contaminated soil 2a Water permeable pipe (drain pipe) 2b Water permeable pipe (water supply pipe) 3 electrodes 11 Impermeable sheet 12 good quality soil

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) B09C 1/00-1/10 A62D 3/00

Claims (3)

(57) [Claims] 1. The ionic pollutant is moved to the electrode by supplying a direct current voltage between a pair of electrodes arranged in the contaminated soil while supplying water into the contaminated soil containing the ionic pollutant. In the method of purifying contaminated soil to be collected by laying a water impermeable sheet on the upper surface of the contaminated soil, while preventing the impermeable sheet from floating from the upper surface,
A method for purifying contaminated soil, characterized in that the water is supplied to a region below it. 2. The method for purifying contaminated soil according to claim 1, wherein soil is covered on the impermeable sheet. 3. The water pipe buried in the contaminated soil has a non-water supply range from the upper surface to the upper surface of the contaminated soil, and in such a state the water level in the water supply pipe is maintained above the upper surface of the contaminated soil. The method for purifying contaminated soil according to claim 1, wherein the water level in the drainage pipe buried in the contaminated soil is maintained near the upper surface of the contaminated soil.