JP3610916B2 - How to remove anionic contaminants - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to anionic contaminants such as CrO ₄ ²⁻ , Cr ₂ O ₇ ²⁻ , AsO ₄ ³⁻ , AsO ₃ ³⁻ , SeO ₄ ²⁻ , SeO ₃ ²⁻ , CN ⁻ , and PbO ₂ ^2−. The present invention relates to a method for removing from the soil.
[0002]
[Prior art]
Soil contaminated by factory wastewater, factory waste, mine wastewater, etc. may contain contaminants such as cadmium, lead, copper, zinc, arsenic, selenium, nickel, chromium, etc. If left untreated, there is a risk that such substances will diffuse into the environment through groundwater or biological cycles.
[0003]
Therefore, the contaminated soil is excavated and removed and subjected to a predetermined treatment. After that, it is disposed of in a managed or shut-down disposal site, while ordinary soil is left in the excavated hole. It is common to return to the original state.
[0004]
However, in this method, the contaminated soil may be disturbed during excavation and there is a risk of secondary contamination, and there is a problem that a large amount of contaminated soil must be carried out and transported. There arises a problem that excavation and removal itself becomes difficult. Therefore, recently, a technique for purifying in-situ has begun to be studied, and as one of them, a method for recovering pollutants by energization is disclosed in JP-A-5-59716.
[0005]
In the method, first, a water blocking wall is constructed in the ground range to be treated, then an anode and a cathode made of a hollow tube having a large number of water passage holes are inserted into the ground range, and then the ground range Then, water is appropriately sprayed, a DC voltage is applied between the electrodes, and then water collected on the cathode side due to the electroosmosis phenomenon is recovered through a hollow tube.
[0006]
According to this method, the predetermined pollutant flows on the cathode side along the flow of water due to the electroosmosis phenomenon, and the pollutant can be removed by collecting the wastewater.
[0007]
[Problems to be solved by the invention]
On the other hand, chromium, arsenic, selenium, cyan, lead, etc. are CrO ₄ ²⁻ , Cr ₂ O ₇ ²⁻ , AsO ₄ ³⁻ , AsO ₃ ³⁻ , SeO ₄ ²⁻ , SeO ₃ ²⁻ , CN ⁻ , respectively. It is contained in the soil in the form of anions such as PbO ₂ ²⁻ (under alkaline). These anionic contaminants, when energized, are subjected to force in the anode direction by electrophoresis against the flow of water moving to the cathode. Turned out. For this reason, in order to recover the anionic contaminants, it is only possible to remove what is collected in the vicinity of the anode together with the soil, but 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-described circumstances, and an object of the present invention is to provide a method for removing anionic contaminants that can efficiently recover anionic contaminants from the soil.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the method for removing anionic contaminants of the present invention, as described in claim 1, an anode and a cathode are embedded in soil containing anionic contaminants, Supplying water and applying a DC voltage between the anode and the cathode to conduct electricity, draining the supplied water only from the anode side, and non-draining the cathode side to the cathode by electroosmosis This prevents water from moving.
Moreover, the removal method of the anion contaminant which concerns on this invention supplies water from the said anode side, and drains the supplied water from this anode side.
[0010]
In the method for removing anionic contaminants according to the present invention, water movement to the cathode due to electroosmosis is prevented by non-draining the cathode side, and water in the soil is drained from the anode side in such a state. To do.
[0011]
Then, the anionic contaminants naturally gather at the anode by electrophoresis without being countered by the movement of water to the cathode by electroosmosis, and are collected together with the water. In addition, the acidity increases as it approaches the anode, and the solubility of the anionic contaminants increases, so that it can be recovered more efficiently.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an anion contaminant removal method according to the present invention will be described below with reference to the accompanying drawings.
[0013]
FIG. 1 is a flowchart showing the procedure of the anion contaminant removal method according to the present embodiment. In the removal method 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} -, burying the anode 2 and cathode 3 in the soil 1 containing anionic contaminants _PbO ^{2 2-like} (Figure 1, step 101).
[0014]
Here, the anode 2 is preferably composed of a carbon rod, for example, and the cathode 3 is preferably composed of a reinforcing bar. The anode 2 is arranged in a strainer tube 4 having a hollow tube with a large number of holes. A hose (not shown) is inserted between the anode 2 and the strainer tube 4 to drain water by supplying water or pumping up. Can be done.
[0015]
Next, as shown in FIG. 2 (b), water is supplied into the soil 1 via the anode 2 side, for example, the strainer tube 4, and a DC voltage is applied between the anode 2 and the cathode 3 to energize. The supplied water is drained from the anode 2 side to recover the anionic contaminants. In draining, the cathode 2 is drained only from the anode 2 side, and the cathode 3 side is not drained so that the cathode is electroosmotic. The movement of water to 3 is blocked (step 102). The water level in the vicinity of the anode 2 is appropriately adjusted so that the water level on the cathode 3 side does not reach the ground surface.
[0016]
Next, the water collected from the anode is subjected to water treatment using an ion exchange resin or the like in an acidic environment to separate and remove the 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).
[0017]
The water collected on the anode side is highly acidic. Therefore, rather than performing general water treatment using this as an alkali, if the acidic environment is used as it is, the anionic contaminants are separated and the treated water is recycled for water supply. Water that easily dissolves anionic contaminants can be supplied to the soil.
[0018]
In addition, the wastewater from which the anionic contaminants are separated and removed is subjected to pH treatment and discharged into sewage after the completion of the construction.
[0019]
In the method for removing anionic contaminants according to the present embodiment, the cathode 3 side is not drained to prevent water from moving to the cathode 3 due to electroosmosis. That is, the water in the soil tries to move to the cathode 3 by electroosmosis, but if it 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 are balanced. The water stops moving.
[0020]
If energization is performed in such a state, the anionic contaminants naturally gather on the anode 2 by electrophoresis without daring to counter the movement of water to the cathode 3 by electroosmosis as in the prior art. In addition, 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.
[0021]
As described above, according to the method for removing anionic contaminants according to the present embodiment, the cathode side is not drained and drained only from the anode side, so CrO ₄ ²⁻ , Cr ₂ O ₇ ²⁻ , AsO ₄ ³⁻ , AsO ₃ ³⁻ , SeO ₄ ²⁻ , SeO ₃ ²⁻ , CN ⁻ , PbO ₂ ^2−, etc. The migration smoothly reaches the anode, and thus it becomes possible to efficiently collect and recover the anionic contaminants on the anode.
[0022]
Moreover, since the solubility of an anionic contaminant becomes high as it approaches the anode, a wide range of soil between the cathode and the anode can be decontaminated.
[0023]
In addition, the cathode non-drainage 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 the water supply / drainage.
[0024]
In addition, the separation and removal treatment of the anionic contaminants in the wastewater is carried out in an acidic state, and the treated water is recycled for water supply. It is possible to recover and remove the anionic contaminants in the soil more efficiently than by separating and removing the water and recycling it for water supply.
[0025]
In this embodiment, the anode composed of carbon rods is disposed in the strainer tube, but the strainer tube itself may be used as the anode.
[0026]
Further, in this embodiment, water supply is performed from the anode side, but the water supply position is not particularly limited, and water is sprayed from the ground surface at a desired position between the electrodes in addition to or instead of the anode side. For example, the loss due to electrolysis may be supplemented.
[0027]
In this embodiment, a method using an ion exchange resin is adopted as a method for performing water treatment in an acidic environment. However, instead of such a method, for example, arsenic or selenium is adsorbed on an iron compound to be removed. A method may be adopted.
[0028]
Further, in this embodiment, the drained water is treated with water in an acidic environment, but it is not always necessary to treat it with acidity, and once it is made alkaline, water treatment for separating and removing anionic contaminants is performed. You may make it perform, and in such a case, it is not necessary to recycle treated water for water supply.
[0029]
【The invention's effect】
As described above, according to the method for removing anionic contaminants according to the present invention, anionic contaminants can be efficiently recovered from the soil.
[0030]
[Brief description of the drawings]
FIG. 1 is a flowchart showing a procedure of a method for removing an anionic contaminant according to the present embodiment.
FIGS. 2A and 2B illustrate the operation of the anion contaminant removal method according to the present embodiment, and FIG. 2A shows a state before energization, and FIG. 2B shows a state during energization.
[Explanation of symbols]
1 Contaminated soil 2 Anode 3 Cathode 4 Strainer tube

Claims (2)

An anode and a cathode are embedded in the 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 energize the supplied water. A method for removing anionic contaminants, wherein water is drained only from the side and the cathode side is not drained to prevent water from moving to the cathode due to electroosmosis. The method for removing anionic contaminants according to claim 1, wherein water is supplied from the anode side and the supplied water is drained from the anode side.

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