JP2002001298A - Electrode arranging method for anionic pollutant removal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently recover anionic pollutants from soil. SOLUTION: In this anionic pollutant removing method, an anode and a cathode are embedded almost vertically in a soil containing the anionic pollutants (a step 101), and then, while water is supplied to the soil properly, a D.C. voltage is applied between the anode and the cathode to carry a current, and the supplied water is discharged only from the anode side (a step 102). When the electrodes are arranged, a number of the cathodes are installed around the anode.

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.

[0004] However, such a method has a problem that contaminated soil may be disturbed during excavation and secondary contamination may occur. In addition, a large amount of contaminated soil must be carried out and transported. Directly underneath, there is a problem that excavation and removal itself becomes difficult. Therefore, recently, in-situ purification technology has begun to be studied, and as one of the methods, a method of collecting contaminants by energizing is disclosed in Japanese Patent Application Laid-Open No. 5-59716.
No. 6,009,045.

[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 alkalinity) in the form of anions. The experiment conducted by the applicant that these anion contaminants could be hardly recovered on the cathode side because, when energized, they were subjected to a force in the anode direction by electrophoresis while opposing the flow of water moving to the cathode. It turned out.
Therefore, the only way to collect anion contaminants is to remove those collected near the anode together with the soil. However, a series of operations such as excavation, transportation, and soil of the soil are required, and the removal efficiency is extremely poor.

[0008] The present invention has been made in view of the above circumstances, and has as its object to provide an electrode arrangement method for removing anionic contaminants that can efficiently collect anionic contaminants from soil. .

[0009]

To achieve the above object, the present invention provides a method for arranging electrodes for removing anionic contaminants, as described in claim 1, wherein an anode and an anode are provided in soil containing anionic contaminants. The cathode is buried almost vertically, and then water is appropriately supplied to the soil and a DC voltage is applied between the anode and the cathode to conduct electricity. A method of draining supplied water only from the anode side while preventing the movement of water, wherein a large number of the cathodes are arranged around the anode.

Further, according to the electrode arrangement method for removing anionic contaminants according to the present invention, the anode and the cathode are buried almost vertically in the soil containing the anionic contaminants. Water is supplied while appropriately supplying water to the soil and applying a DC voltage between the anode and the cathode to conduct electricity, and preventing the movement of water to the cathode due to electroosmosis by making the cathode side non-drained. Draining water from only the anode side, wherein the anodes are arranged substantially linearly at predetermined intervals, and the cathodes are arranged substantially parallel to both sides of the anodes.

Further, in the method for arranging electrodes for removing anionic contaminants according to the present invention, the method comprises the steps of: forming a trench in the soil; arranging the anode in the trench; Are formed of steel sheet piles which are driven substantially parallel to both sides of the trench.

In the method for arranging electrodes in the removal of 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. Drain water from the anode side.

[0013] Then, the anion 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.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of an electrode arrangement method for removing anionic contaminants according to the present invention will be described.
This will be described with reference to the accompanying drawings.

(First Embodiment)

FIG. 1 is a flowchart showing a procedure of an electrode arrangement method in removing anionic contaminants according to the present embodiment. In the electrode arrangement method in the removal of the present embodiment, first, as shown in FIG. 2 (a), CrO ₄ ^2- , Cr ₂ O _{7
^{2-, AsO 4 3-, AsO 3}} 3-, SeO 4 2-, SeO 3 2-, CN -, anode within the soil 1 containing anionic contaminants PbO ₂ ^2-like 2 and cathode 3
Is embedded almost vertically (step 101 in FIG. 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.

FIGS. 3 and 4 show examples of the planar arrangement of the anode 2 and the cathode 3. FIG. First, FIG. 3 (a) shows a number of cathodes 3 arranged so as to surround the anode 2.
FIG. 3B shows a state in which the anodes 2 are arranged in a staggered manner and a large number of cathodes 3 are arranged around each anode 2. FIG. 4 shows that a trench 5 is formed in the contaminated soil 1, and the anode 2 and the strainer tube 4 are arranged substantially linearly at a predetermined interval in the trench, and the gap therebetween is filled with crushed stone 6. The cathode 3 formed of a steel sheet pile is driven in substantially parallel to both sides. In addition, you may use what replaced the steel sheet pile in the shape of a lattice, etc.

After arranging the electrodes in this manner, as shown in FIG. 2 (b), water is supplied into the soil 1 through the anode 2 side, for example, through a strainer tube 4, and between the anode 2 and the cathode 3 An electric current is applied by applying a DC voltage, and the supplied water is drained from the side of the anode 2 to collect anion contaminants (step 1).
02). The water level near the anode 2 is appropriately adjusted so that the water level on the cathode 3 side does not reach the ground surface.

Here, the cathode 3 side is not drained all the time, including during energization, to prevent the movement of water to the cathode 3 by electroosmosis. 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 for moving to the cathode 3 and the pressure due to the rise in the water level near the cathode are balanced. , The water stops moving.

If electricity is supplied in such a state, the anionic contaminants naturally collect on the anode 2 by electrophoresis without opposing the movement of water to the cathode 3 due to 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.

When the electrodes are arranged in a staggered pattern as shown in FIG. 3 (b), not all the electrodes are energized at the same time.
For example, energizing only the odd number for a certain number of days and then energizing the even number alternately, so that the anion contaminants located in the middle do not move to either side. I do.

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 wastewater from which the anion contaminants have been separated and removed is subjected to a pH treatment after the completion of the construction and discharged to sewage.

As described above, according to the electrode arrangement 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- , ^{_{cr 2 O 7 2-, AsO 4}} 3-, AsO 3 3-, SeO 4 2-, SeO 3
^2-, CN ^-, PbO ^{₂ 2-} anion contaminants, such as, without being disturbed by the flow of water by electroosmosis, smoothly reach the anode by electrophoresis, thus efficiently anion contaminants This can be collected at the anode and collected.

Further, the solubility of the anionic contaminants increases as the distance from the anode increases, so that the vicinity of the anode can be efficiently decontaminated. In particular, when a large number of cathodes are arranged around the anode, it is possible to decontaminate a wide area around the anode. Furthermore, if these are arranged in a staggered manner, decontamination can be performed over a wide range. If a trench is formed, an anode is arranged linearly in the trench, and cathodes are arranged on both sides of the trench, an effective electrode arrangement method can be provided when the contaminated region is spread in a strip shape.

In addition, the non-drainage of the cathode eliminates the movement of water due to electroosmosis, and accordingly the flow of water in the soil can be controlled by the amount and position of water supply and drainage.

Further, the separation and removal of the anion contaminants in the wastewater is performed in an acidic state, and the treated water is recycled for water supply, so that the anion 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, water is supplied from the anode side. However, the water supply position is not particularly limited. In addition to or instead of the anode side, water is supplied 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.

In this embodiment, the drained water is treated in an acidic environment. However, it is not always necessary to treat the discharged 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.

(Second Embodiment)

Next, a second embodiment will be described. Note that components that are substantially the same as those in the first embodiment are given the same reference numerals, and descriptions thereof are omitted.

FIG. 5 is a flowchart showing a procedure of an electrode arrangement method for removing anionic contaminants according to the second embodiment. The electrode arrangement method in the removal of the present embodiment is a method particularly suitable for decontaminating below the existing structure 11 as shown in FIG. 6, and firstly, of the contaminated soil 1 spreading below the existing structure 11. A working shaft 16 is dug to the side, and a cathode 12 and an anode 13 are
Are buried almost in parallel so as to be in the upper stage (FIG. 5, step 111).

Here, each of the cathode 12 and the anode 13 is formed by providing a large number of holes in a conductive hollow tube, and serves as both an electrode and a strainer tube. In addition, the cathode 12
A water supply pipe 14 is provided therein, and a drainage pipe 15 is provided in the anode 13. The water supply pipe 14 and the drainage pipe 15 are connected to a water supply / drainage pump (not shown).

After arranging the electrodes in this way, the water supply pipe 14
And water into the soil 1 via the cathode 12 and
A DC voltage is applied between the anode 13 and the cathode 12 to conduct electricity. Then, the supplied water is supplied to the anode 1 through the drain pipe 15.
Drain from side 3 to collect anionic contaminants (step 112).

At this time, the drain of the cathode 12 is not drained from the start to the end of the operation, and the movement of water to the cathode 12 by electroosmosis is prevented. That is, the water in the soil tends to move to the cathode 12 by electroosmosis, but if the water is not drained on the cathode side, the force to move to the cathode 12 at a position slightly higher than the surrounding groundwater level and the cathode The pressure due to the rise of the nearby water level is balanced, and the water does not move upward.

When electricity is supplied in such a state, the anion contaminants naturally collect on the anode 13 by electrophoresis and self-weight without opposing the movement of water to the cathode 12 by electroosmosis as in the conventional case. In addition, the closer to the anode 13, the higher the acidity and the higher the solubility of the anion contaminants, so that more efficient recovery is possible.

Thereafter, water treatment is carried out in the same manner as in the first embodiment to separate and remove anionic contaminants (step 113), and the treated water after separation and removal is recycled for water supply (step 114).

As described above, according to the electrode arrangement method for removing anionic contaminants according to the present embodiment, in addition to the same effects as those of the first embodiment, even in the region below the existing structure. There is an effect that this can be efficiently decontaminated.

[0043]

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

[0044]

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure of an electrode arrangement method in removing anionic contaminants according to a first embodiment.

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

FIG. 3 is a plan view showing an example of an electrode arrangement, wherein (a) shows an example in which a large number of cathodes are arranged around an anode, and (b) shows an example in which they are arranged in a staggered arrangement.

FIG. 4 is another plan view showing an example of an electrode arrangement.

FIG. 5 is a flowchart showing a procedure of an electrode arrangement method according to a second embodiment.

FIG. 6 is a sectional view showing an electrode arrangement state according to a second embodiment.

[Explanation of symbols]

 1 Contaminated soil 2,13 Anode 3,12 Cathode 4 Strainer tube

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Jun Mitsumoto 4-640 Shimoseito, Kiyose-shi, Tokyo F-term in Obayashi Corporation Technical Research Institute Co., Ltd. 4D004 AA41 AB03 AC07 CA44 CB50 CC03

Claims (3)

[Claims] 1. An anode and a cathode are buried substantially vertically in soil containing anionic contaminants. 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 of draining supplied water only from the anode side while preventing movement of water to the cathode by electroosmosis by making the cathode side non-draining, wherein a large number of the cathodes are provided around the anode. An electrode arrangement method for removing anionic contaminants, which is provided. 2. An anode and a cathode are buried substantially vertically in soil containing anion contaminants, and then water is appropriately supplied to the soil and a DC voltage is applied between the anode and the cathode to conduct electricity. A method of draining supplied water only from the anode side while preventing movement of water to the cathode by electroosmosis by making the cathode side non-draining, wherein the anode is substantially straight at predetermined intervals. And disposing the cathode substantially parallel to both sides of the anode. 3. A trench is formed in the soil, the anode is arranged in the trench, and a space therebetween is filled with crushed stone, and the cathode is formed of a steel sheet pile driven substantially parallel to both sides of the trench. 3. The method for arranging electrodes in removing anionic contaminants according to claim 2.