JPH09215971A - 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, next, water is supplied to soil (Step 102) and, subsequently, DC voltage is applied across the anode and the cathode to supply a current (Step 103) and the concn. of the anion contaminant gathered to the anode is measured (Step 104) and it is judged whether the measured concn. exceeds a reference value (Step 105) and, when the measured concn. exceeds the reference value, water on the side of the anode is drained (Step 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 with industrial wastewater, industrial 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, a large amount of 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-
(Under alkaline) It is contained in 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, then water is supplied to the soil, then a direct current voltage is applied between the anode and the cathode to conduct electricity, and then the concentration of the anionic contaminants collected on the anode side is measured. Then, it is determined whether or not the measured concentration exceeds the reference value, and when the measured concentration exceeds the reference value, the water on the anode side is drained.

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 buried in soil containing anionic contaminants, and then water is supplied to the soil,
Next, a direct current voltage is applied between the anode and the cathode to conduct electricity, and then the concentration of the anion contaminants collected on the anode side is measured. When the measured concentration exceeds a reference value, the anode side is measured. The water is sucked up, but it is not drained on the cathode side from beginning to beginning during energization to prevent water from moving to the cathode by electroosmosis.

[0012] Then, the anionic contaminants naturally collect on the anode by electrophoresis, without countering the migration of water to the cathode by electroosmosis. When the anion contaminant near the anode reaches a certain concentration, it is sucked up with water and collected. 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.

If the separation and removal treatment of anionic contaminants contained in the drained water is carried out in an acidic environment and the treated water is recycled to the soil, the solubility of the anionic contaminants in the soil is increased. However, the removal efficiency is improved.

[0014]

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 according to the present embodiment, first, as shown in FIG. 2, CrO ₄ ²⁻ , Cr ₂ O ₇ ²⁻ , As
Anode 2 and cathode 3 are buried in soil 1 containing anionic contaminants such as O ₄ ³⁻ , AsO ₃ ³⁻ , SeO ₄ ²⁻ , SeO ₃ ²⁻ , CN ⁻ , PbO ₂ ²⁻ (Fig. 1 , Step 101).

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. A water supply / drainage pipe 5 for supplying water or draining water by pumping up is provided in the anode 2, and the water supply / drainage pipe 5 is connected to a water supply / drainage pump 6 installed on the ground.

On the other hand, a concentration sensor 7 for measuring the concentration of anionic contaminants is installed at the bottom of the anode 2, and the measurement data is transferred to a computer 8 installed on the ground at any time. Then, the computer 8 switches and controls water supply, drainage, and stop of the water supply / drainage pump 6 according to the size of the data.

Next, as shown in FIG. 3 (a), the computer 8 is operated to drive the water supply / drainage pump 6 to the water supply side to supply water to the contaminated soil 1 via the water supply / drainage pipe 5 and the anode 2 ( (Step 102), and subsequently, a DC voltage is applied between the anode 2 and the cathode 3 to energize (Step 1).
03). The energization time varies depending on the soil properties, the type and concentration of the anion contaminant, and the like, but it is preferable to continue the application for several days.

Here, 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.
Also, on the cathode 3 side, it is not drained all the time, including during energization,
The movement of water to the cathode 3 due to electroosmosis is prevented.

Then, the water in the soil 1 tries to move to the cathode 3 by electroosmosis, but it is not drained on the side of the cathode 3, so that 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 naturally collect on the anode 2 by electrophoresis without countering the movement of water to the cathode 3 due to electroosmosis. 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.

Next, the concentration of anionic contaminants gathering on the side of the anode 2 is measured by the concentration sensor 7 in real time,
The data is transferred to the computer 8 as needed (step 104).

Next, the computer 8 judges whether or not the measured concentration of the anionic contaminant exceeds the reference value (step 105). Here, the reference concentration of anionic contaminants is preferably 500 to 1000 ppm in consideration of the limit that the effect of electrophoresis decreases.

When the measured concentration is lower than the reference value, energization is continued, and when it exceeds the reference value, the computer 8 is operated to operate the water supply / drainage pump 6 as shown in FIG. 3 (b). Drive the water to the drain side and supply the water in the anode 2 to the drainage pipe 5
It is sucked up to the ground via the to collect anionic contaminants (step 106).

Next, the water recovered from the anode 2 is treated with an ion exchange resin or the like in an acidic environment to separate and remove anionic contaminants in the water (step 107).
Next, the treated water from which the anionic contaminants have been removed is recycled for water supply (step 108). For recycling, as in the case of FIG. 3 (a), the water supply / drainage pump 6 may be driven to the water supply side to feed water into the anode 2 via the water supply / drainage pipe 5.

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.

This procedure is repeated until the soil is washed, 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, the cathode side is not drained and only the anode side is drained. Therefore, 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.

Further, 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 depending on the amount and position of water supply and drainage.

Further, since the separation and removal treatment of the anion contaminants in the waste water is carried out in an acidic state and the treated water is recycled for water supply, the anion 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 concentration of anionic contaminants collected on the anode is measured and the water supply and drainage are switched depending on the size, automatic control over a long period of time becomes possible.

In the present embodiment, the anode made of carbon rods also serves as the strainer tube, but the anode and the strainer tube may be separate bodies.

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.

Further, in the present 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.

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

[0037]

As described above, the concentration control method for removing anionic contaminants of the present invention is to embed an anode and a cathode in soil containing anionic contaminants, and then supply water to the soil. Next, a direct current voltage is applied between the anode and the cathode to conduct electricity, and then the concentration of the anionic contaminants collected on the anode side is measured, and then whether the measured concentration exceeds a reference value. When the measured concentration exceeds the reference value, the water on the anode side is drained, so that the anion contaminants can be efficiently collected from the soil.

[0038]

[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.

FIG. 2 is a conceptual diagram showing a concentration management method for removing anionic contaminants according to the present embodiment.

FIG. 3 is a diagram for explaining the action of the concentration control method in removing anionic contaminants according to the present embodiment, where (a) is a state of supplying water and conducting electricity, and (b) is performing drainage. A diagram showing the situation.

[Explanation of symbols]

 1 Contaminated soil 2 Anode (strainer tube) 3 Cathode

Claims (2)

[Claims] 1. An anode and a cathode are buried in a soil containing an anion contaminant, and then water is supplied to the soil, and then 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, then it is determined whether the measured concentration exceeds a reference value, and when the measured concentration exceeds the reference value, the water on the anode side is removed. A method for controlling concentration in removing anionic pollutants, characterized by draining. 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.