JPH08243536A - Method of concentrating contaminant in soil - Google Patents

Abstract

PURPOSE: To cause an electroendosmosis phenomenon to effectively concentrate contaminant without injecting water in a moisture unsaturated zone above the level of the underground water by freezing soil from the periphery of a cathode and also giving potential difference between the cathode and an anode. CONSTITUTION: In a concentrator, first when a refrigerator 2 is operated to feed brine into a freezing pipe 1, soil is frozen from the part in contact with the outer peripheral surface of the freezing pipe 1 to concentrically grow frozen soil. Next, when a DC power source 4 is operated to give potential difference to between the freezing pipe 1 and an electrode bar 3, contaminant concentrated in nonfrozen water by freezing begins to move toward the freezing pipe 1 which is a cathode together with the nonfrozen water by an electroendosmosis phenomenon. That is, while the concentration of contaminant in soil is decreased to a desired value, contaminant is gradually accumulated on soil around the freezing pipe 1. Consecutively, soil contg. contaminant of high concentration is excavated and removed after removing the freezing pipe 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is directed to reducing the concentration of pollutants such as heavy metals, oils, and organic chlorine compounds existing in soil, so that these pollutants can be concentrated and concentrated at specific parts of the soil. The present invention relates to a method for concentrating pollutants, and more particularly to a method for concentrating pollutants in soil using an electroosmosis phenomenon.

[0002]

2. Description of the Related Art Soil pollution, which causes great damage to human bodies and agricultural products, has become a social problem in recent years. For such soil pollution, there is a method of replacing contaminated soil, that is, so-called soil, but it is difficult in many cases because enormous cost is required. Therefore, if the pollutants contained in the contaminated soil can be concentrated and concentrated in one place and the pollutant concentration can be reduced to the extent that the environmental standards are satisfied, the amount of soil to be removed will decrease and it will be necessary for excavation work and transportation. It is convenient because it can reduce costs.

As a method of concentrating such pollutants in the soil, there is known a method in which a potential difference is applied between a pair of electrodes inserted in the soil. By doing so, the water moves due to the reaction of the electrostatic force generated by the surface charge of the soil particles, so that a flow occurs in the underground water due to the so-called electroosmosis phenomenon, so that the pollutants contained in this underground water are moved. It becomes possible. Further, if the pollutant is an ion, it moves by electrostatic force according to the direction of the applied electric field, and the pollutant can be concentrated around the electrode. Moreover, when H ^{+ and} OH ⁻ generated by electrolysis move due to electrostatic force, the contaminants are dissolved in the liquid phase, so that the contaminants can be effectively concentrated.

[0004]

However, according to such a conventional method for concentrating pollutants, in the water unsaturated zone above the groundwater level, the soil water is used to connect the electrodes to connect the electrodes with each other. Since the gap is not filled, the electroosmosis phenomenon is unlikely to occur, and the contaminants cannot be efficiently accumulated on the electrodes. This is especially noticeable in sandy soils with low soil water. On the other hand, if water or an aqueous solution is injected into such a water unsaturated zone in order to facilitate the electroosmosis phenomenon, a large amount of injected water causes
There was a possibility of causing the following pollution.

The present invention has been devised in order to eliminate such disadvantages of the prior art, and its main purpose is to:
To provide a method for concentrating pollutants in soil, which can efficiently condense pollutants by generating an electroosmotic phenomenon without water injection or by a small amount of water injection in a water unsaturated zone above the groundwater level. is there. Another object of the present invention is to make the method for concentrating pollutants in a water saturated zone below the groundwater level more efficient.

[0006]

According to the present invention, such an object is to provide a potential difference between a cathode and an anode that are inserted in the soil at a predetermined distance from each other, thereby causing contamination contained in the soil. A method of concentrating a pollutant in soil for concentrating a substance around the cathode, the process of freezing the soil from the periphery of the cathode by a freezing means, and a potential difference between the cathode and the anode. And a method of concentrating pollutants in soil. Alternatively, it is a method of concentrating pollutants in soil by applying a potential difference between a cathode and an anode inserted at a predetermined distance in the soil to concentrate pollutants contained in the soil around the cathode. A step of freezing the soil in a water-saturated zone by a freezing means for freezing the soil from around the anode, and a step of applying a potential difference between the cathode and the anode. This is accomplished by providing a method for concentrating pollutants. In particular,
It is preferable to freeze the soil by the anode or the cathode provided with the freezing means.

[0007]

As described above, when the soil is frozen by the freezing means, that is, the water in the soil existing in the gaps between the soil particles is frozen, the water near the surface of the soil particles has a low chemical potential, as shown in FIG. Therefore, it does not freeze and remains on the soil particle surface as antifreeze water, and only free water relatively far from the soil particle surface freezes. At this time, while pure ice is produced, pollutants, which are solutes dissolved in soil water, are concentrated in antifreeze water.

On the other hand, when the frozen soil grows around the freezing means, that is, when the soil is frozen from one direction, the non-freezing water in the frozen soil becomes larger than that in the unfrozen soil. Due to the low chemical potential, underground water will move from the unfrozen soil side to the frozen soil side. Then, even in the unsaturated water zone above the groundwater level, the frozen soil gradually grows while attracting the surrounding soil water, and the fine gaps filled with antifreeze water fill the narrow gap between the ice and the soil particle surface. A large number of reticulated water veins are formed.

In this state, when a potential difference is applied between the anode and the cathode inserted in the frozen soil at a predetermined distance from each other, the water vein of the antifreezing water acts so as to connect the electrodes. ,
The electroosmotic flow described above is generated, and the antifreeze water in which the pollutants are concentrated moves toward the cathode. The antifreeze water collected around the cathode is deposited as pure ice one after another, and the pollutants are further concentrated. If the water content of the soil is low and the veins are not well formed, water or an aqueous solution is injected.

At this time, in the case of clay-like soil, the electroosmosis phenomenon effectively occurs, and therefore, the concentration property is particularly good. On the other hand, also in sandy soil, an electroosmosis phenomenon occurs due to the formation of water veins made of antifreeze water due to freezing, and improvement in concentration can be expected.

If the pollutant is in an ionic state, the pollutant tends to move according to the direction of the potential applied to the soil. In particular, metal ions (eg Pb ²⁺ , C
If a cation such as u ²⁺ , Zn ²⁺ , Cd ²⁺ ) moves toward the cathode, it coincides with the direction of the electroosmotic flow and promotes concentration.

By freezing the soil from the periphery of the cathode in this manner, an electroosmotic flow is effectively generated even in a moisture unsaturated zone where the electroosmosis phenomenon is unlikely to occur, and pollutants are efficiently generated around the cathode and the freezing means. It can be well concentrated. On the other hand, in the unsaturated water zone, as described above, by freezing the soil, in addition to the electroosmosis phenomenon, the movement phenomenon of soil water containing pollutants to the frozen surface and the soil water freeze Concentration of pollutants into antifreeze water is added, so that the concentration efficiency of pollutants is improved.

By the way, in the moisture unsaturated zone, the moving direction of the pollutant may differ depending on the characteristics of the pollutant, soil properties, freezing rate, and method of collecting the concentrated pollutant. That is, when the soil water freezes in the growing portion of the frozen soil, most of the pollutants dissolved therein may be concentrated in the soil water on the unfrozen soil side instead of the non-freezing water. When the pollutant acts on the unfrozen soil side in this manner, the pollutant gradually moves away from the freezing means as the frozen soil grows. Therefore,
In such a case, in order to prevent the migration direction of pollutants, that is, the growth direction of frozen soil, from being opposite to the migration direction due to the phenomenon of condensation of pollutants on the cathode due to the above-mentioned electroosmosis, etc. By freezing, contaminants can be efficiently concentrated around the cathode.

In particular, in the case of freezing from the soil around the cathode, if the cathode is equipped with a freezing means, the flow direction of the underground water toward the above-mentioned freezing surface and the flow direction to the cathode due to electroosmosis or the like are Are the same, the concentration property is further improved. Further, in the case of freezing from the soil around the anode, if this anode is equipped with a freezing means, the movement direction of the above-mentioned contaminants and the flow direction to the cathode due to electroosmosis etc. are the same, The concentration property is improved. Moreover, since the cathode or anode and the freezing means are integrated, the cost required for installation work can be reduced.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described in detail below with reference to specific embodiments shown in the accompanying drawings.

Example 1 FIG. 1 shows a first example of a concentrating apparatus to which the method for concentrating pollutants in soil according to the present invention is applied. This concentrator concentrates pollutants such as heavy metals such as lead, copper, chromium, cadmium, and zinc, oils, and organic chlorine compounds that extend into the soil to specific locations. Portion of the freezing pipe 1 inserted into the soil, a freezer 2 for supplying brine (antifreeze) as a refrigerant to the freezing pipe 1, a predetermined distance from the freezing pipe 1 and inserted into the soil And an electrode rod 3 and a DC power source 4 for applying a DC voltage so that the freezing tube 1 serves as a cathode and the electrode rod 3 serves as an anode.

The freezing tube 1 has a double structure consisting of an outer tube 1a and an inner inserting tube 1b, and the brine introduced from the refrigerator 2 to the upper part of the freezing tube 1 via the pipe P1 is the outer tube. 1a
The cold heat is released to the surrounding soil while flowing down through the gap between the inner peripheral surface of and the outer peripheral surface of the insertion tube 1b. The brine whose temperature has risen in this way is returned to the refrigerator 2 through the pipe P2 after rising inside the insertion pipe 1b.

The outer tube 1a of the freezing tube 1 is made of a conductive material and is connected to the wiring L1 from the DC power source 4. On the other hand, the wiring L2 from the DC power supply is also connected to the electrode rod 3 made of a conductive material.

The freezing tube 1 and the anode rod 3 are shown in FIG.
As shown in FIG. 4, an electrode rod row 5 in which four electrode rods 3 are arranged in a row at equal intervals, and a freeze tube in which four freezing tubes 1 are similarly arranged in a row at equal intervals to each other The rows 6 are alternately arranged at a predetermined interval such that the electrode tube rows 5 are located on both the left and right sides, and surround the entire contaminated part.

In such a concentrating device, when the refrigerator 2 and the DC power source 4 are operated, contaminants are concentrated in the soil around the freezing tube 1 which is the cathode. First, refrigerator 2
Is operated to supply brine to the freezing tube 1, the soil contacting the outer peripheral surface of the freezing tube 1 is cooled and the frozen soil grows concentrically. The frozen soil columns that have grown around the freezing tube 1 continue to grow after they are united, and continue until they expand to cover the entire contaminated part.

Simultaneously with such freezing work or after the freezing work is finished, the DC power source 4 is operated to apply a potential difference between the freezing tube 1 and the electrode rod 3. Then, as mentioned above,
The pollutants concentrated in the antifreeze water by freezing start moving toward the freezing tube 1 which is the cathode together with the antifreeze water by the electroosmosis phenomenon. In this way, the pollutant concentration in the soil is reduced to a desired value, while the pollutant is gradually accumulated in the soil around the freezing tube 1. The soil containing the pollutant at a high concentration is removed by excavating the freezing pipe 1 and then excavating.

As shown in FIG. 3, four perforated pipes 11 are inserted in the soil so as to surround the freezing pipe 1, and the inside of the perforated pipe 11 is decompressed by the vacuum pump 12 to contaminate it. Soil water in which the substance is concentrated may be sucked and collected.
The concentrated water flowing into the depressurized perforated tube 11 flows into the liquid receiving tank 13 through the pipe P3 inserted in the perforated tube 11. This recovery work can be carried out with the soil frozen or in a thawed state. This has an advantage that it is not necessary to excavate and remove the soil in the concentrated portion.

Embodiment 2 FIG. 5 shows a second embodiment of a concentrating device to which the method for concentrating pollutants in soil according to the present invention is applied. This concentrator concentrates pollutants existing in the water saturated zone below the groundwater level, and is used in Example 1 (see FIG. 1).
After replacing the freezing tube 1 and the electrode rod 3 shown in Fig. 1, the DC power source 4 is set so that the freezing tube 1 serves as an anode and the electrode rod 3 serves as a cathode.
Respectively connected to.

As described above, this concentrating device is designed so that the pollutant is gradually separated from the freezing means as the frozen soil grows, depending on the characteristics of the pollutant, the soil quality, the freezing rate, and the method for collecting the concentrated pollutant. The pollutants can be effectively concentrated when they move. That is, by operating the refrigerator 2 and the DC power source 4, the pollutant is concentrated in the soil around the electrode rod 3 that is the cathode. This concentrated pollutant was used for soil excavation, as in Example 1.
Alternatively, it is removed by suction and collection of concentrated soil water by the porous tube 11 (see FIG. 3). However, when the perforated tube 11 is used, the perforated tube 11 is installed around the electrode rod 3.

In each of the above-mentioned embodiments, the freezing means is the freezing tube 1 through which brine flows, but the present invention is not limited to this, and a known soil freezing device is appropriately applied and used. be able to. Furthermore, it is not always necessary to configure the freezing tube 1 and other soil freezing devices with a conductive material to integrate the freezing means and the electrodes. The separate freezing means and the electrodes may be arranged close to each other.

[0026]

As described above, according to the present invention, by freezing the soil, even in the unsaturated water zone above the groundwater level, it is possible to effectively perform electroosmosis without pouring water or by pouring a small amount of water. It is possible to cause a phenomenon, and there is a very remarkable effect in preventing the secondary contamination by the injected water. Moreover, when soil is frozen, in addition to this electroosmosis phenomenon, the phenomenon of migration of soil water containing pollutants to the frozen surface and the phenomenon of condensation of pollutants into antifreeze water when soil water is frozen are added. Even in the water saturation zone, the concentration efficiency of pollutants is significantly improved.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view schematically showing a first embodiment of a concentrating device to which a method for concentrating pollutants in soil according to the present invention is applied.

FIG. 2 is a plan view showing the arrangement of the concentrating device shown in FIG.

FIG. 3 is a vertical cross-sectional view showing a schematic configuration of an apparatus for sucking and collecting soil water in which pollutants are concentrated.

FIG. 4 is a conceptual diagram showing a situation in which antifreeze water in frozen soil moves by electroosmosis.

FIG. 5 is a vertical cross-sectional view schematically showing a second embodiment of the concentrating device to which the method for concentrating pollutants in soil according to the present invention is applied.

[Explanation of symbols]

 1 Frozen tube 1a Outer tube 1b Inner tube 2 Refrigerator 3 Electrode rod 4 DC power supply 5 Electrode rod row 6 Freezing tube row 11 Perforated tube 12 Vacuum pump 13 Liquid receiving tank P1 to P3 Piping L1 and L2 Wiring

Claims (3)

[Claims] 1. Concentration of pollutants in soil by concentrating pollutants contained in the soil in the vicinity of the cathode by applying a potential difference between a cathode and an anode inserted in the soil at a predetermined distance. The method is a pollutant in soil, comprising a step of freezing the soil by a freezing means for freezing the soil from the periphery of the cathode, and a step of applying a potential difference between the cathode and the anode. Concentration method. 2. Concentration of pollutants in soil by concentrating pollutants contained in the soil around the cathode by applying a potential difference between a cathode and an anode that are inserted in soil at a predetermined distance. The method is characterized by comprising a step of freezing the soil in a water saturated zone by a freezing means for freezing the soil from the periphery of the anode, and a step of applying a potential difference between the cathode and the anode. Concentration method of pollutants in soil. 3. The method for concentrating pollutants in soil according to claim 1 or 2, wherein the soil is frozen by the anode or the cathode provided with the freezing means.