JP2019174393A - Contaminated soil decontamination method - Google Patents

Abstract

To provide a contaminated soil decontamination method for preventing air pollution, carbon dioxide emission and secondary pollution due to transportation of contaminated soil, by quickly clarifying, dehydrating, and reducing the volume of contaminated soil with simple equipment at a collection site, a temporary storage yard, or intermediate storage facilities that do not involve the movement of the contaminated soil.SOLUTION: There is provided the contaminated soil decontamination method for collecting harmful contaminant from contaminated soil contaminated with radioactive material and heavy metal and the like. In the method, a water-permeable flexible container bag 2 is filled with contaminated soil D including moisture and suspended, and the positive and negative electrode rods 4 and 5 are inserted into the contaminated soil D with a space between them, and a voltage is applied between the electrode rods 4 and 5. The contaminant is ionized by electrolysis by the electric field between the electrode rods 4 and 5 and eluted on the particle surface of the contaminated soil D, and soil moisture D1 including the contaminant in the contaminated soil D is subjected to electrophoresis and electroosmosis, thereby concentrated to the periphery of electrode rod 5 (4), and is exuded under the flexible container bag 2 and dehydrated, and contaminant is removed from the contaminated soil D.SELECTED DRAWING: Figure 1

Description

  The present invention separates or removes salt from soil that contains a lot of moisture and is contaminated with radioactive substances, heavy metals and other harmful substances, and soil that has been damaged by tsunami (hereinafter referred to as “contaminated soil”). The present invention also relates to a decontamination method for contaminated soil that promotes dehydration.

Usually, in order to decontaminate soil contaminated with toxic substances such as heavy metals, scrape the contaminated soil from the soil, add drying accelerators such as quick lime and treatment agents such as insolubilizing agents, and treat at the final disposal site. Is done. In addition, the soil contaminated with radioactive material is stripped of the surface soil, stored in a flexible container bag, and processed at the final disposal site.
Conventionally, as a method of decontaminating soil contaminated with harmful substances, an electrode rod is inserted into the contaminated area, this electrode rod is connected to the anode of a DC power source, a well is excavated outside the contaminated area, and this well There is a method of connecting a conductor installed in the cathode to the cathode of a DC power source and installing a submersible pump in the well (see Patent Document 1). In this method, when a DC power supply is driven, forced drainage by electroosmosis occurs from the electrode rod side serving as the anode to the well side where the conductor serving as the cathode exists in the viscous ground, and the pollutants present in the pollution source and the contaminated area. Is discharged into the well together with the groundwater, pumped up to the ground with a submersible pump, and purified.
In addition, it contains radioactive cesium that contains particulate zeolite adsorbent inside a flexible container bag that has been laminated on the side of the flexible container bag to lose water permeability and mesh fabric is used on the bottom to increase the water permeability. There is a method in which radioactive cesium is adsorbed and separated from water by contact with wastewater to be disposed of, and the flexible containers containing these are landfilled (see Patent Document 2).
Furthermore, as a device for dehydrating the object to be treated, an electrode part is projected from the outer spacer to the inner spacer between the screens facing each other with an interval between the filter chambers, and a DC voltage is applied between the electrode part and the screen. There is a rotary pressure dehydrator that performs electroosmotic dehydration by applying (see Patent Document 3).

Japanese Patent Laid-Open No. 10-309562 JP 2013-186012 JP JP 2017-023944

The former method in the above-mentioned conventional method relating to the decontamination of pollutants is a method of treating contaminated soil on site. However, it requires a space for excavating a well, and the cost for excavating the well increases.
The latter is a landfill method at a waste disposal site or decontamination work site, but a huge amount of contaminated soil is stored in a temporary storage site for a long time due to the scattering of radioactive materials caused by the nuclear power plant accident in the Great East Japan Earthquake. In such a situation, it is necessary to transfer and store these untreated contaminated soils in an intermediate storage facility, and it is necessary to establish means for performing safe transfer before landfilling safely. In addition, if a large amount of untreated contaminated soil is transported from a storage location to a final disposal site, there are concerns about air pollution, carbon dioxide release, and secondary diffusion of radioactive materials due to the arrival of a considerable amount of large transport vehicles.
Furthermore, the rotary pressure dehydrator using electroosmosis related to the dehydration process increases the size and cost of the apparatus according to the processing capacity, has a limited processing amount, and has a huge amount as described above. Application to contaminated soil is not realistic.
Therefore, the present invention quickly purifies, dehydrates, and reduces the volume of contaminated soil while suppressing installation space and installation costs with simple equipment at a collection site, temporary storage, or intermediate storage facility that does not involve the movement of contaminated soil. Provide decontamination methods for contaminated soil to prevent air pollution, carbon dioxide emission and secondary pollution associated with transportation of contaminated soil.

  In this invention, the decontamination method of the contaminated soil which isolate | separates a harmful pollutant from the contaminated soil D, or removes salt content is employ | adopted. A water-permeable container such as the flexible container bag 2 containing the contaminated soil D containing moisture is suspended, and a voltage is applied to the positive and negative electrode rods 4 and 5 inserted into the contaminated soil D at intervals. Contaminants are ionized by electrolysis by the electric field between the electrode rods 4 and 5 to be eluted on the particle surface of the contaminated soil D, and the soil moisture D1 containing the contaminants in the contaminated soil D is electrophoresed and electroosmotically electrophoresed. Concentrate around 5 (4) to remove contaminants and exude moisture in the soil below the permeable container.

  In the present invention, the contaminated soil can be purified, dehydrated, and reduced in volume at a site where the contaminated soil is collected or stored, and the installation space and the installation cost can be reduced by simple equipment. This has the effect of preventing the air pollution, the release of carbon dioxide and the spread of secondary pollution caused by transportation vehicles.

It is the schematic of the decontamination equipment used for the decontamination method which concerns on 1st Example of this invention. It is the schematic of the decontamination equipment used for the decontamination method concerning 2nd Example of this invention. It is sectional drawing of the electrode rod of the decontamination equipment of FIG. It is the front view which notched some electrode bars of the decontamination equipment of FIG. It is the schematic of the decontamination equipment used for the decontamination method concerning 3rd Example of this invention. It is an expanded view of the mesh electrode of the decontamination equipment of FIG. It is the schematic of the modification of the decontamination equipment of FIG.

Embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, the decontamination equipment used for the decontamination method of the contaminated soil which concerns on 1st Example of this invention is the flexible container bag 2 which accommodates the contaminated soil suspended by the mount frame 1, the direct current | flow type power supply 3, and The positive and negative electrode rods 4 and 5 connected to the power source 3 and the filtrate receiving tank 6 are provided.
As the flexible container bag 2, as long as it is a container made of a water-permeable material having a strength and flexibility that does not easily break, another known bag may be applied.
The power source 3 is for applying a DC voltage to the electrode rods 4 and 5, and the applied voltage is about several V to 100 V. The power source 3 may be one that boosts the storage battery such as an automobile battery by a single or a plurality of stages connected in series, in addition to the AC-DC conversion using the primary side of the series regulator as an AC power source. The application direction of the voltage may be the same from the start to the end of the construction, or may be switched intermittently in consideration of the difference in the degree of diffusion of the ion movement region due to the polarity described later.
The electrode rods 4 and 5 are inserted in the longitudinal direction with a plurality of pairs arranged substantially parallel to each other at a distance from the contaminated soil in the flexible container 2. The electrode rods 4 and 5 are hollow or solid and have a long rod shape, and various electrode materials such as metals such as SUS, titanium and iron, and carbon can be used. The electrode rods 4 and 5 are attached or impregnated with adsorbents that adsorb pollutants such as activated carbon, zeolite, layered clay minerals, charcoal, and metal powder for fixing the pollutants on the side surfaces, or It may be formed by mixing these and a conductive material. The tip portions of the electrode rods 4 and 5 are covered with a protective cover 7 made of a flexible material such as rubber for preventing the bag from penetrating during insertion.
The filtrate receiving tank 6 is a thin water tank such as a vessel for storing and collecting the filtrate that has oozed out of the flexible container bag 2. In the filtrate receiving tank 6, an adsorbent 8 such as zeolite, layered clay mineral, ion exchange resin, chelate resin, shellfish powder, etc. may be introduced to adsorb harmful substances, or other coagulation precipitation methods, etc. It is good also as purifying using the muddy water processing apparatus using.

A decontamination method using the decontamination apparatus of this example will be described below.
The contaminated soil D excavated from the contaminated soil or stored in the temporary storage facility or intermediate storage facility is packed in the filtration flexible container bag 2, the flexible container bag 2 is suspended on the gantry 1, and a protective cover 7 is attached to the tip. The electrode bars 4 and 5 are inserted into the contaminated soil D in the flexible container bag 2 to the vicinity of the bottom of the flexible container bag 2, and a voltage is applied to the electrode bars 4 and 5 by the power source 3. Electrokinetic phenomena of electrolysis, electrophoresis and electroosmosis occur between the positive and negative electrode rods 4 and 5. At this time, hydrogen ions generated by electrolyzing soil moisture D1 of the contaminated soil D by the electric field between the electrode rods 4 and 5 move from the positive electrode rod 4 to the negative electrode rod 5 in the contaminated soil D. As a result, contaminants such as heavy metals having a higher ionization tendency than hydrogen are ionized and eluted on the surfaces of the particles of the contaminated soil D. The pollutant is attracted to the negative electrode rod 5 by the electric field between the electrode rods 4 and 5, causing migration, and concentrates around the electrode rod 5. On the other hand, the hydroxide ions generated by the electrolysis of the soil moisture D1 of the contaminated soil D move from the negative electrode rod 5 to the positive electrode rod 4 in the contaminated soil D to insolubilize contaminants such as heavy metals. And precipitate. Hydroxide ions are much heavier than hydrogen ions, and the migration speed of hydrogen ions associated with electrokinetic phenomena such as electrophoresis is much higher. Accordingly, the migration region of hydrogen ions is easily diffused, the periphery of the negative electrode rod 5 is easily alkalinized, and contaminants such as heavy metals are easily insolubilized, which makes collection difficult. In order to avoid this, it is effective to periodically change the polarities of the electrode rods 4 and 5. Moreover, the fine space between the particles of the contaminated soil D forms a water passage gap, and the particle surface of the contaminated soil D around the water passage gap is negatively charged. As a result, the surface of the water gap (the contact surface between the gap and the contaminated soil D) is also charged negatively. Positively charged particles such as cations contained in the moisture D1 in the soil moving through the water passage gap adhere to the surface of the water passage gap, and these move from the positive electrode to the negative electrode due to the electric field generated between the electrodes. As the cation moves, the soil moisture D1 in the water passage also flows, thereby generating an electroosmotic flow. In this way, contaminants are ionized by the influence of electrolysis due to the electric field between the electrode rods 4 and 5 and are eluted on the particle surface of the contaminated soil D, and are concentrated around the negative electrode rod 5 by electrophoresis and electroosmosis. At the same time, the flow of water due to the electroosmotic flow is generated, thereby facilitating drainage and improving the dewatering efficiency.
The protective cover 7 may be provided with a drain hole in order to prevent accumulation of moisture concentrated on the electrode rod 5 in the protective cover 7.

A second embodiment according to the present invention will be described with reference to FIG. In the following description, the same components as those of the previous embodiment are denoted by the same reference numerals and description thereof is omitted.
Strainer electrodes 14 and 15 are inserted into the contaminated soil D packed in the flexible container bag 2. As shown in FIG. 3, a hose 10 is connected to the upper ends of the strainer electrodes 14 and 15, and a suction pump 9 is connected via a branch manifold 11, and a discharge pipe of the suction pump 9 is connected to the filtrate receiving tank 6. Come on. As shown in FIG. 4, the strainer electrodes 14 and 15 are each formed of a pipe material provided with a large number of slits 14 a (15 a) and small holes on the side surface in order to easily collect the moisture D <b> 1 in the soil. An adsorption filter 14b (15b) that accumulates and reduces the harmful substances of contaminated water during suction is inserted into the upper ends of the strainer electrodes 14 and 15. The adsorption filter 14b (15b) is composed of a fiber assembly such as a water-permeable nonwoven fabric mixed with an adsorbent such as zeolite or clay mineral. The protective cover 7 includes a small hole 7a.
When a voltage is applied between the strainer electrodes 14 and 15, the soil moisture D1 of the contaminated soil D is taken into the periphery of the strainer electrode 15 through the slit 15a by electrophoresis and electroosmosis in the same manner as before, and sucked by the suction pump 9, The filtrate is discharged into the filtrate receiving tank 6. The soil moisture D1 is reduced in volume by adsorbing contaminants through the adsorption filter 14b (15b) and performing dehydration as well as purification.
In the present embodiment, since the suction process by the suction pump 9 is performed, the polarity of the strainer electrodes 14 and 15 is not periodically changed.

A third embodiment according to the present invention will be described with reference to FIG.
A flexible mesh electrode 12 is fixed to the flexible container bag 2 so as to surround the outer sliding surface. As shown in FIG. 6, the mesh electrode 12 is made of a conductive metal plate 12a such as SUS or titanium, and is formed in a mesh shape or a porous shape that can pass through the moisture D1 in the soil exuding from the flexible container bag 2. The portion is covered with a protective material 12b made of plastic, rubber or the like, and includes connecting members 12c and 12d that can be coupled to each other at both ends in the longitudinal direction, and is connected to the negative electrode side of the power source 3 and the ground wire 12e.
Similar to the electrode rod 5 for the electrode rod 4, the mesh electrode 12 forms an electric field between the electrode rod 4 and concentrates moisture D1 in the soil also on the side of the flexible container bag 2 by electrophoresis and electroosmosis. , Promote the adsorption of pollutants and purification by draining water.
Further, as shown in FIG. 7, the mesh electrode 12 may be a plurality of narrow mesh electrodes 12 arranged vertically on the outer periphery of the flexible container bag 2.

In this embodiment, when the electrical contact resistance between the mesh electrode 12 and the flexible container bag 2 is large, the voltage drop here becomes large, and a sufficient applied voltage cannot be applied to the contaminated soil to be purified. The flexible container bag 2 facing 12 may be partially processed to include carbon particles, metal particles, etc. in a non-woven fabric to improve the conductivity.
The mesh electrode 12 may be a commercially available mesh pallet.
The filtrate receiving tank 6 may be configured to be covered with a vessel or the like in order to prevent diffusion according to the pollutant in the contaminated soil. In this case, the contact between the mesh pallet and the vessel is electrically insulated.
When there are many pollutant components in the filtrate, a flocculant may be added to perform a simple coagulation precipitation treatment.
In addition, it cannot be overemphasized that the mesh electrode 12 in this embodiment is applicable also in 2nd Embodiment which provided the strainer electrodes 14 and 15 mentioned above.

  In order to promote the electrokinetic phenomenon of the contaminated soil D, a conductive additive may be added to the contaminated soil D as a pretreatment. As the conductive auxiliary agent, a conductive auxiliary agent made of sodium chloride or potassium salt that lowers the contact resistance with the electrode and the electric resistance in the contaminated soil D may be added. In particular, when the pollutant is radioactive cesium, elution of cesium from the particle surface of the contaminated soil D is promoted by the substitution action of potassium and cesium. When the pollutant is a heavy metal, the use of an acid such as acetic acid or oxalic acid as the conductive auxiliary promotes the elution of the heavy metal pollutant. In the case where the pollutant is an amphoteric element or an amphoteric oxide that reacts with both an acid such as lead and an alkali, it is effective to add an alkaline agent as a conductive aid.

DESCRIPTION OF SYMBOLS 1 Stand 2 Flexible container 3 Power supply 4 Electrode rod 5 Electrode rod 6 Filtrate receiving tank 7 Protective cover 8 Adsorbent 9 Suction pump 10 Hose 11 Manifold 12 Mesh electrode 12a Conductive metal plate 12b Protective material 12c Connection member 12d Connection member 12e Ground wire 14 Strainer electrode 14a Slit 14b Suction filter 15 Strainer electrode 15a Slit 15b Suction filter 17 Protective cover 17a Small hole D Contaminated soil D1 Soil moisture L Filtrate

Claims (5)

A decontamination method for contaminated soil that separates and collects harmful contaminants and salt from contaminated soil such as radioactive materials and heavy metals, and soil damaged by tsunami, etc.
In a state where a water-permeable container containing moisture is suspended, a voltage is applied to the positive and negative electrode rods inserted into the contaminated soil at intervals, and the contaminant is ionized by electrolysis. It elutes on the surface of the contaminated soil particles, removes the contaminants by concentrating the soil moisture containing the contaminants in the soil around the electrode rod by electrophoresis and electroosmosis, and in the soil below the permeable container A method for decontamination of contaminated soil, which exudes moisture and dehydrates it.   The method for decontamination of contaminated soil according to claim 1, wherein the water-permeable container is a flexible container bag. The electrode rod is a pipe-shaped strainer electrode having a water passage hole on a side surface,
3. The method for decontamination of contaminated soil according to claim 1, wherein moisture in the soil concentrated around the strainer electrode is sucked and discharged by a pump through a hose connected to the strainer electrode.   The decontamination method for contaminated soil according to claim 3, wherein contaminants are adsorbed from moisture in the soil by a filter inserted in the strainer electrode.   Applying a voltage between the mesh electrode fixed to the side surface of the water permeable container and the electrode rod to concentrate water in the soil containing contaminants in the soil around the side surface of the water permeable container. 5. The method for decontaminating contaminated soil according to any one of claims 1 to 4, wherein the soil is squeezed out and discharged.

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