JPH09215970A - Concentration control method in removal of anion contaminant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently recover an anion contaminant from soil. SOLUTION: An anode and a cathode are embedded in soil containing an anion contaminant (Step 101) and DC voltage is applied across the anode and the cathode while the supply of water to soil and the drainage from the vicinity of the anode are continuously performed to supply a current (Step 102) and the concn. of the anion contaminant gathered toward the anode is measured and, when the measured concn. is not within a predetermined range, the supply and discharge amts. of water are adjusted (Steps 104-106).

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-
The present invention relates to a method for removing anionic pollutants such as the like from the soil.

[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, arsenic, selenium, nickel and chromium. If such soil is left as it is, there is a risk that such substances 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, in such a method, there is a possibility that the contaminated soil may be disturbed during excavation to cause secondary pollution, and a large amount of the contaminated soil must be carried out and transported, and the proximity of existing buildings. There is a problem that the excavation and removal itself becomes difficult directly below. Therefore, recently, in-situ purification technology has begun to be researched, and one of them is a method of collecting pollutants by energization.
No. 6,086,045.

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

According to such a method, the predetermined pollutant is
Since the water flows due to the electroosmosis phenomenon and flows into the cathode side, the pollutant can be removed by collecting the waste water.

[0007]

On the other hand, chromium, arsenic,
For selenium, cyanide, lead, etc., CrO ₄ ^2- and Cr, respectively
^{_{2 O 7 2-, AsO 4 3-}} , AsO 3 3-, SeO 4 2-, SeO 3 2-, CN -, PbO 2 2-
Contained in the soil in the form of anions such as. And, when these anionic contaminants are energized, they are subjected to a force in the direction of the anode by electrophoresis against the flow of water moving to the cathode, so that the cathode side can hardly recover them. Found out. Therefore, in order to collect the anion contaminants, the material collected in the vicinity of the anode must be removed together with the soil, but a series of operations such as soil excavation, transportation, and soil for the soil are required, and the removal efficiency is extremely poor.

The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a concentration control method for removing anionic contaminants that can efficiently recover the anionic contaminants from the soil. .

[0009]

In order to achieve the above object, the method for controlling concentration in removing anionic contaminants according to the present invention is, as described in claim 1, an anode and a soil in soil containing anionic contaminants. A cathode is buried, and then a DC voltage is applied between the anode and the cathode while continuously supplying water to the soil and draining from the vicinity of the anode to energize the cathode, and the shadow gathered on the anode side. The concentration of ion contaminants is measured, and when the measured concentration is not within a predetermined range, the amount of water supply and drainage is adjusted.

Further, the concentration control method for removing anionic contaminants according to the present invention is a method for separating and removing the anionic contaminants contained in drained water in an acidic environment and supplying the treated water for water supply. It is to be recycled.

In the concentration control method for removing anionic contaminants according to the present invention, an anode and a cathode are embedded in soil containing anionic contaminants, and then water is supplied to the soil and drainage from the vicinity of the anode is performed. DC voltage is applied between the positive electrode and the negative electrode while continuously conducting the current, but it is not drained on the negative electrode side at all times, including during the current is passed, and water migration to the negative electrode is prevented by electroosmosis. Keep it.

[0012] Then, the anionic contaminants naturally collect on the anode by electrophoresis, without countering the migration of water to the cathode by electroosmosis. It should be noted that the closer to the anode, the higher the acidity and the higher the solubility of the anionic contaminants, and thus the more efficient recovery.

On the other hand, the concentration of anionic contaminants collected on the anode side is measured and monitored, and if the measured concentration is not within a predetermined range, the amount of water supply and drainage is adjusted to keep the concentration of anionic contaminants near the anode constant. To maintain.

Here, if the separation and removal treatment of the anion contaminants contained in the drained water is performed in an acidic environment and the treated water is recycled to the soil, the solubility of the anion contaminants in the soil is increased. However, the removal efficiency is improved.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the concentration control method for removing anionic contaminants according to the present invention will be described below.
This will be described with reference to the accompanying drawings.

FIG. 1 is a flow chart showing the procedure of a concentration control method for removing anionic contaminants according to this embodiment. In the concentration control method in the removal of this 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 buried (step 101 in FIG. 1).

Here, the cathode 3 is preferably composed of, for example, a reinforcing rod. Further, the anode 2 is configured by providing a large number of holes in a conductive hollow tube such as a carbon rod, and serves as both an electrode and a strainer tube. Then, in the anode 2, there is a water supply pipe 5
Also, a drainage pipe 6 for draining water by pumping up is provided, and the water supply pipe 5 and the drainage pipe 6 are connected to a water supply / drainage pump 7 installed on the ground.

On the other hand, a concentration sensor 8 for measuring the concentration of anionic contaminants is installed inside the anode 2, and the measurement data is transferred to a computer 9 installed on the ground at any time. Then, the computer 9 switches and controls the operation and stop of the water supply / drainage pump 7 according to the size of the data.

Next, as shown in FIG.
Is operated to operate the water supply / drainage pump 7 to supply water to the contaminated soil 1 via the water supply pipe 5 and the anode 2 and to drain water from the anode 2 via the drainage pipe 6. Further, while supplying and draining these, a DC voltage is applied between the anode 2 and the cathode 3 to conduct electricity (step 102).

Here, the energization time varies depending on the soil properties, the type and concentration of the anion contaminants, etc., but it is preferable to continue for several days. The amount of water exchanged may also be set appropriately according to the amount of electricity and the properties of the soil.

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. On the cathode 3 side, water is not drained from beginning to beginning during energization to prevent water from moving to the cathode 3 due to electroosmosis.

Then, the water in the soil 1 tries to move to the cathode 3 by electroosmosis, but is not drained on the side of the cathode 3, so the force to move to the cathode 3 and a slight rise in the water level near the cathode 3 occur. Equilibrium with the pressure due to, the water does not move.

If the energization is continued in such a state, the anion contaminants will be absorbed by the cathode 3 by electroosmosis as shown in FIG. 2 (b).
The water naturally collects on the anode 2 by electrophoresis without countering the movement of water. Moreover, the closer to the anode 2, the higher the acidity and the higher the solubility of the anionic contaminants, so that more efficient recovery is possible.

The water recovered from the anode 2 is subjected to water treatment in an acidic environment using an ion exchange resin or the like to separate and remove anionic contaminants in the water, and at the same time, remove the anionic contaminants. After treatment, the treated water is recycled for water supply.

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 acidic environment is used as it is to separate the anion contaminants and the treated water after treatment is recycled for water supply, Water capable of dissolving anionic contaminants can be supplied to the soil.

On the other hand, the concentration of the anionic contaminant collected on the side of the anode 2 is measured by the concentration sensor 8 in real time and transferred to the computer 9 at any time (step 103). The computer 9 continuously monitors whether it is within a predetermined range (step 104). Here, the upper limit of the predetermined range is 500 to 1000 ppm in consideration of the limit that the effect of electrophoresis decreases.
It is good to do.

If the measured concentration is within the predetermined range, monitoring of the concentration of the anionic contaminant is continued as it is. If the measured concentration is not within the predetermined range, the concentration of the anionic contaminant is The computer 9 drives and controls the water supply / drainage pump 7 so as to be constant, and the amount of water supply / drainage is appropriately adjusted (step 105).

Such monitoring of water supply and drainage is repeated until the soil cleaning is completed, and after the construction is completed, the wastewater from which the anionic contaminants have been separated and removed is subjected to pH treatment and discharged into the sewage.

As described above, according to the concentration control method for removing anionic contaminants according to the present embodiment, since the cathode side is not drained and only the anode side is drained, 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 It becomes possible to collect this by collecting it at the anode.

Further, since the solubility of the anionic contaminant becomes higher as it gets closer to the anode, it is possible to decontaminate a wide range of soil between the cathode and the anode.

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.

Further, since the treatment for separating and removing the anionic contaminants in the waste water is carried out in an acidic state and the treated water is recycled for water supply, the anionic contaminants in the soil are easily dissolved. It becomes possible to recover and remove anionic contaminants in soil more efficiently than once returning to alkali to separate and remove it, and to recycle it for water supply.

Further, since the amount of water supply and drainage is adjusted as necessary so that the concentration of the anionic contaminants collected in the anode becomes constant, long-term automatic management becomes possible and the anion contaminants are collected from the anode. Also, the concentration of the anionic contaminants is always constant, and the post-process of separation and removal is extremely easy to perform.

In the present embodiment, the anode made of carbon rod is also used as the strainer tube, but the anode and the strainer tube may be separately provided.

Further, in the present embodiment, the water is supplied from the anode side, but the water supply position is not particularly limited, and in addition to or instead of the anode side, the ground is provided at a desired position between the electrodes. You may make it sprinkle water from the surface and supplement the loss by electrolysis, for example.

In this embodiment, a method using an ion exchange resin is adopted as a method for water treatment in an acidic environment. Instead of such a method, for example, arsenic or selenium is adsorbed on an iron compound. You may employ the method of removing.

Further, in the present embodiment, the drained water is treated in an acidic environment, but it is not always necessary to treat it in an acidic state, and once it is made alkaline, separation and removal of anionic contaminants are carried out. Water treatment may be performed, and in such a case, treated water may not be recycled for water supply.

[0038]

As described above, the concentration control method for removing anionic contaminants according to the present invention comprises burying an anode and a cathode in soil containing anionic contaminants, and then supplying water to the soil and While continuously discharging water from the vicinity of the anode, a direct current voltage is applied between the anode and the cathode to conduct electricity, and the concentration of the anionic contaminant collected on the anode side is measured to obtain the measured concentration. Since the amount of water supply and drainage is adjusted when it is not within the predetermined range, anion contaminants can be efficiently recovered from the soil.

[0039]

[Brief description of drawings]

FIG. 1 is a flowchart showing a procedure of a concentration management method in removing anionic contaminants according to the present embodiment.

2A and 2B are diagrams for explaining the operation of the concentration control method in removing anionic contaminants according to the present embodiment, FIG. 2A showing a state before energization and FIG. 2B showing a state during energization.

[Explanation of symbols]

 1 Contaminated soil 2 Anode (strainer pipe) 3 Cathode 5 Water supply pipe 6 Drain pipe 7 Water supply / drainage pump

Claims (2)

[Claims] 1. A direct current voltage is applied between the anode and the cathode while burying the anode and the cathode in the soil containing anion contaminants and then continuously supplying water to the soil and draining water from the vicinity of the anode. Is applied to conduct current, and the concentration of the anion contaminants collected on the anode side is measured, and when the measured concentration is not within a predetermined range, the amount of the water supply / drainage is adjusted. Concentration control method for contaminant removal. 2. The concentration for removing anionic contaminants according to claim 1, wherein the treatment for separating and removing the anionic contaminants contained in the drained water is performed in an acidic environment, and the treated water is recycled for water supply. Management method.