JP2001300508A - Method for removing anion contaminant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently recovering anion contaminants from the inside of soil. SOLUTION: This method for removing the anion contaminant consists in embedding an anode and cathode into the soil containing the anion contaminants (step 101), than properly feeding water to this soil, energizing the anode and the cathode by impressing DC voltage across both, draining the anode side of the water fed thereto and not-draining the cathode side, thereby blocking the movement of the water to the cathode by electric percolation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to CrO ₄ ^2- , Cr
^{_{2 O 7 2-, AsO 4 3-}} , AsO 3 3-, SeO 4 2-, SeO 3 2-, CN -, PbO 2 2-
And other methods for removing anionic contaminants from soil.

[0002]

2. Description of the Related Art Soil contaminated by factory wastewater, factory waste, mine wastewater, and the like may contain contaminants such as cadmium, lead, copper, zinc, arsenic, selenium, nickel, and chromium. However, if such soil is left as it is, there is a risk that such substances will diffuse into the environment via groundwater and biological cycles.

For this reason, the contaminated soil is excavated and removed and subjected to a predetermined treatment. Thereafter, the contaminated soil is disposed of in a management type or cut-off type disposal site. It is common to return to the original state on the land.

However, in such a method, there is a possibility that the contaminated soil is disturbed during excavation and secondary contamination may occur. In addition, a large amount of contaminated soil must be carried out and transported. The problem that excavation removal itself becomes difficult directly underneath occurs. Therefore, recently, in-situ purification technology has begun to be studied, and as one of the methods, a method of recovering contaminants by energization has been disclosed in Japanese Patent Laid-Open No. 5-59716.
No. 6,086,045.

[0005] In the method, first, a water blocking wall is constructed in a ground area to be treated, and then an anode and a cathode each formed of a hollow tube having a large number of water passage holes are inserted into the ground area, A DC voltage is applied between the electrodes after water is appropriately sprayed on the ground area, and then water collected on the cathode side by an electroosmosis phenomenon is drained and collected through a hollow tube.

According to such a method, the predetermined contaminants are:
The contaminants can be removed by collecting the waste water by flowing into the cathode side by riding on the flow of water caused by the electroosmosis phenomenon.

[0007]

On the other hand, chromium, arsenic,
Selenium, cyanide, lead, etc. are CrO ₄ ^2- , Cr
^{_{2 O 7 2-, AsO 4 3-}} , AsO 3 3-, SeO 4 2-, SeO 3 2-, CN -, PbO 2 2-
(Under alkaline) in the soil in the form of anions. And when these anion contaminants are energized,
An experiment conducted by the applicant has revealed that since a force is applied in the anode direction by electrophoresis while opposing the flow of water moving to the cathode, almost no recovery is possible on the cathode side. Therefore, the only way to collect anion contaminants is to remove what has collected near the anode together with the soil.
A series of operations, such as transportation and soil, are required, and the removal efficiency is extremely poor.

The present invention has been made in view of the above circumstances, and has as its object to provide a method for removing anionic contaminants that can efficiently collect anionic contaminants from soil.

[0009]

In order to achieve the above object, a method for removing anionic contaminants according to the present invention comprises burying an anode and a cathode in soil containing anionic contaminants. Then, while appropriately supplying water to the soil and applying a DC voltage between the anode and the cathode to conduct electricity, the supplied water is drained only from the anode side, and the cathode side is not drained. By doing so, the movement of water to the cathode by electroosmosis is prevented.

[0010] In the method for removing anionic contaminants according to the present invention, the movement of water to the cathode due to electroosmosis is prevented by keeping the cathode side undrained, and water in the soil is removed from the anode in such a state. Drain from the side.

[0011] Then, the anionic contaminants naturally collect on the anode by electrophoresis and are collected together with the water without opposing the movement of water to the cathode by electroosmosis.
In addition, the closer to the anode, the higher the acidity and the higher the solubility of the anion contaminants, so that they can be more efficiently collected.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for removing anionic contaminants according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a flowchart showing a procedure of a method for removing anionic contaminants according to the present embodiment. In the removal method of this embodiment, first, as shown in FIG. 2A, CrO ₄ ²⁻ , Cr ₂ O ₇ ²⁻ , AsO ₄ ³⁻ , AsO ₃ ³⁻ , SeO ₄ ²⁻ , and SeO ₄ ²⁻
_The anode 2 and the cathode 3 are buried in the soil 1 containing anionic contaminants such as ₃ ²⁻ , CN ⁻ , and PbO ₂ ²⁻ (FIG. 1, step 10).
1).

Here, the anode 2 is made of, for example, a carbon rod.
The cathode 3 is preferably made of a reinforcing rod. In addition, the anode 2
It is disposed in a strainer pipe 4 having a number of holes formed in a hollow pipe, and a hose (not shown) is inserted between the strainer pipe 4 and the strainer pipe 4 so that water can be supplied or drained by pumping up. Has become.

Next, as shown in FIG. 2B, water is supplied into the soil 1 through the anode 2 side, for example, through a strainer tube 4, and a DC voltage is applied between the anode 2 and the cathode 3. Electricity is supplied, and the supplied water is drained from the anode 2 side to collect anion contaminants. In draining, only the anode 2 side is drained, and the cathode 3 side is not drained. The movement of water to the cathode 3 due to permeation is prevented (step 102). The water level near the anode 2 is appropriately adjusted so that the water level on the cathode 3 does not reach the ground surface.

Next, the water recovered from the anode is subjected to a water treatment using an ion exchange resin or the like in an acidic environment to separate and remove anionic contaminants in the water (step 103). Next, the treated water from which the anionic contaminants have been removed is recycled for water supply (step 104).

The water recovered on the anode side has a high acidity. Therefore, rather than making this an alkali and performing general water treatment, if the anionic environment is used as it is to separate and treat the anion contaminants, and the treated water after treatment is recycled for water supply, Water that easily dissolves anionic contaminants can be supplied to the soil.

The waste water from which the anionic contaminants have been separated and removed is subjected to a pH treatment after the completion of the construction and discharged to sewage.

In the method for removing anion contaminants according to the present embodiment, the movement of water to the cathode 3 due to electroosmosis is prevented by keeping the cathode 3 undrained. That is,
The water in the soil tends to move to the cathode 3 by electroosmosis, but if the water is not drained on the cathode side, the force to move to the cathode 3 and the pressure due to the rise in the water level near the cathode balance the water. Stops moving.

If electricity is supplied in such a state, the anionic contaminants will naturally collect on the anode 2 by electrophoresis without opposing the movement of water to the cathode 3 by electroosmosis as in the prior art. Moreover, the closer to the anode 2, the higher the acidity and the higher the solubility of the anion contaminants, so that more efficient recovery is possible.

As described above, according to the method for removing anionic contaminants according to the present embodiment, the cathode side is not drained and only the anode side is drained, so that CrO ₄ ²⁻ and Cr ₂ O ² are removed.
^{_{7 2-, AsO 4 3-, AsO}} 3 3-, SeO 4 2-, SeO 3 2-, CN -, PbO 2 2- anion contaminants, such as, being obstructed by the flow of water by electroosmosis Instead, the particles smoothly reach the anode by electrophoresis, and thus, it becomes possible to efficiently collect and collect anion contaminants on the anode.

Further, the solubility of the anionic contaminants increases as the distance from the anode increases, so that a wide range of soil between the cathode and the anode can be decontaminated.

In addition, since the cathode is not drained, the movement of water due to electroosmosis is eliminated, and accordingly, the flow of water in the soil can be controlled by the amount and position of water supply and drainage.

[0024] Further, the separation and removal of anionic contaminants in the wastewater is performed in an acidic state, and the treated water is recycled for water supply, so that the anionic contaminants in the soil are easily dissolved. This makes it possible to more efficiently collect and remove anionic contaminants in the soil than to return to alkali once and separate and remove it, and then recycle it for water supply.

In this embodiment, the anode made of a carbon rod is provided in the strainer tube, but the strainer tube itself may be used as the anode.

In this embodiment, the water supply is performed from the anode side. However, the water supply position is not particularly limited. In addition to or instead of the anode side, the water supply is performed at a desired position between the electrodes. Water may be sprinkled from the surface to replenish the loss due to electrolysis, for example.

In the present embodiment, a method using an ion exchange resin is employed as a method for performing water treatment in an acidic environment. Instead of such a method, for example, arsenic or selenium is adsorbed on an iron compound. A removal method may be employed.

Further, in this embodiment, the drained water is treated in an acidic environment. However, it is not always necessary to treat the drained water in an acidic environment. Water treatment may be performed, and in such a case, the treated water need not be recycled for water supply.

[0029]

As described above, according to the method for removing anionic contaminants according to the present invention, anionic contaminants can be efficiently recovered from soil.

[0030]

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure of a method for removing anionic contaminants according to an embodiment.

FIGS. 2A and 2B are diagrams illustrating the operation of the method for removing anionic contaminants according to the embodiment, in which FIG. 2A illustrates a state before energization and FIG. 2B illustrates a state during energization.

[Explanation of symbols]

 1 Contaminated soil 2 Anode 3 Cathode 4 Strainer tube

Claims (1)

[Claims] 1. An anode and a cathode are buried in soil containing anionic contaminants, and then water is supplied to the soil as appropriate, and a DC voltage is applied between the anode and the cathode to conduct electricity. A method for removing anionic contaminants, comprising draining water from only the anode side and keeping the cathode side undrained to prevent water from moving to the cathode by electroosmosis.