JP2013178177A - Soil decontamination treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soil decontamination treatment method capable of decontaminating contaminated soil accumulating radioactive substances.SOLUTION: The soil decontamination treatment method for decontaminating contaminated soil accumulating radioactive cesium includes: a decontamination step of decontaminating the contaminated soil and separating it into a removed object and treated soil; and a plant removal step of separating the contaminated soil into plants mixed in the contaminated soil and plant removed soil from which the plants are removed. In this case, the decontamination step may include a primary decontamination step of performing decontamination by wet classification of a primary mixture generated by mixing and agitating the contaminated soil and water, and then separating the primary mixture into primary treated soil whose grain size is equal to or larger than a prescribed grain size and a primary removed object whose grain size is smaller than the prescribed grain size.

Description

  The present invention relates to a soil decontamination treatment method for decontaminating contaminated soil in which radioactive substances are accumulated.

  In recent years, there are concerns about the effects on the human body due to the intake of radioactive materials and exposure to radiation, and rapid development of a method for decontaminating contaminated soil in which radioactive materials have accumulated is desired.

  As a technique for decontaminating such contaminated soil, for example, a soil improvement method (for example, see Patent Document 1), a method for removing radioactive contamination factors (for example, see Patent Document 2), and heavy metals and radioactive contamination from a contamination process. A method for removing a factor (see, for example, Patent Document 3) has been proposed. Here, the conventional soil decontamination processing methods described in Patent Documents 1, 2, and 3 are decontamination methods for soil washing extract solutions containing heavy metals and the like generated by soil decontamination processing.

JP-A-6-51096 Japanese Patent Laid-Open No. 7-973 Japanese Unexamined Patent Publication No. 7-974

  Here, in order to decontaminate heavy metals and the like by the conventional soil decontamination methods described in Patent Documents 1, 2, and 3, it is assumed that the heavy metals are once eluted from the soil into the aqueous phase. However, unlike other heavy metals, radioactive materials such as radioactive cesium are difficult to elute into the water phase once adsorbed to the soil due to their properties, so it is difficult to apply these conventional decontamination methods in a unified manner. It can be said.

  In fact, radioactive materials such as radioactive cesium scattered from the sky fall mainly on the ground and accumulate. Therefore, in order to decontaminate such radioactive materials, it is necessary to remove the soil on the surface. However, the soil on the surface is often mixed with plants. In addition, radioactive materials that have fallen on the surface of the earth adhere to or are absorbed by the plants and accumulate in the plants at a high concentration. Therefore, when removing soil on the surface, the plants that accumulate radioactive materials are also removed at the same time. To be treated. However, in the conventional decontamination method, such plant decontamination was not considered at all.

  The present invention has been made in view of the above, and is a soil decontamination processing method that is capable of decontaminating contaminated soil in which radioactive substances are accumulated and contaminated with plants. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, the soil decontamination processing method according to claim 1 is a soil decontamination processing method for decontaminating contaminated soil in which radioactive substances are accumulated. A decontamination step of classifying the contaminated soil into a removed material and treated soil, and a plant removal step of separating the contaminated soil into a plant mixed with the contaminated soil and a plant-removed soil from which the plant has been removed. Including.

  Moreover, the soil decontamination processing method of Claim 2 is a primary mixture produced | generated by mixing and stirring the said contaminated soil and water in the soil decontamination processing method of Claim 1. Including a primary decontamination step of separating the primary mixture into a primary treated soil having a particle size equal to or greater than a predetermined particle size and a primary removal product having a particle size less than the predetermined particle size. .

  The soil decontamination method according to claim 3 is the soil decontamination method according to claim 1, wherein the decontamination step is a primary mixture generated by mixing and stirring the contaminated soil and water. Is a treated soil separated by wet classification, the primary treated soil having a particle size of a predetermined particle size or more, or the plant-removed soil, and a secondary mixture produced by grinding and stirring water, A secondary decontamination step of separating the secondary mixture into a secondary treated soil having a particle size equal to or larger than a predetermined particle size and a secondary removed material having a particle size smaller than the predetermined particle size by classification is included.

  Moreover, the soil decontamination processing method of Claim 4 is a soil decontamination processing method of Claim 1, By carrying out wet classification of the primary mixture produced | generated by mixing and stirring the said contaminated soil and water. Wet classification of the secondary mixture produced by mixing and stirring the primary treated soil having a particle size equal to or larger than a predetermined particle size or the plant-removed soil, water, and an adsorbent. The secondary decontamination process which isolate | separates the said secondary mixture into the secondary treatment soil whose particle size is more than predetermined particle size, and the secondary removal thing whose particle size is less than predetermined particle size is included.

  Moreover, the soil decontamination processing method of Claim 5 is a soil decontamination processing method of Claim 4, The particle size of the said adsorbent is less than the said predetermined particle size.

  Moreover, the soil decontamination processing method of Claim 6 is a soil decontamination processing method as described in any one of Claim 1 to 5. WHEREIN: The said plant removal process mixes the said contaminated soil and water. The step of separating the plant by specific gravity separation.

  Moreover, the soil decontamination processing method according to claim 7 is the soil decontamination processing method according to any one of claims 1 to 6, wherein a precipitant is added to the removed product, and treated water and radioactive Separated into concentrated sludge containing substances.

According to the soil decontamination processing method according to claim 1, a decontamination step of decontaminating the contaminated soil and separating it into a removed material and treated soil, a plant in which the contaminated soil is mixed with the contaminated soil, The plant removal step for separating the plant into the plant removal soil from which the plant has been removed includes the removal of the removed material in the decontamination step, the removal of the plant in the plant removal step, and accumulation of radioactive materials. It is possible to decontaminate contaminated soil that is contaminated with plants.
In addition, by providing the plant removal process as a separate process from the decontamination process, it is possible to perform decontamination that combines various processes.

  According to the soil decontamination processing method according to claim 2, the decontamination step performs classification decontamination by wet-classifying the primary mixture generated by mixing and stirring the contaminated soil and water, Since the primary mixture includes a primary decontamination step in which the primary particle is separated into a primary treated soil having a particle size equal to or larger than a predetermined particle size and a primary removed material having a particle size less than the predetermined particle size, the heavy metal is eluted from the soil into the aqueous phase. Thus, since it is not necessary to use an acid or alkali for adjusting the pH of the washing water or a strong acid or strong alkali as a washing liquid, decontamination can be performed easily and at low cost. Moreover, since heavy metals are not re-eluted from the soil as in the case of using acids or strong acids, it is not necessary to treat heavy metals, and decontamination can be performed more easily and at a lower cost. .

  According to the soil decontamination treatment method according to claim 3, the secondary mixture produced by grinding and stirring primary treated soil or plant-removed soil having a particle size equal to or larger than a predetermined particle size and water is wet. Classifying and decontaminating by classifying, and performing a secondary decontamination step of separating the secondary mixture into a secondary treated soil having a particle size equal to or larger than a predetermined particle size and a secondary removed material having a particle size smaller than the predetermined particle size. Therefore, it is possible to further reduce the accumulated amount of radioactive substances in the contaminated soil by further decontaminating the primary treated soil or the plant-removed soil.

  According to the soil decontamination treatment method according to claim 4, the secondary mixture produced by mixing and stirring the primary treated soil or the plant-removed soil having a predetermined particle diameter or more, water, and the adsorbent is wet-treated. Decontamination is performed by classification, and a secondary decontamination step is performed in which the secondary mixture is separated into a secondary treated soil having a particle size equal to or larger than a predetermined particle size and a secondary removed material having a particle size smaller than the predetermined particle size. Therefore, it is possible to prevent the radioactive material peeled from the contaminated soil from adsorbing again to the contaminated soil, and to improve the accuracy of the secondary decontamination process.

  According to the soil decontamination processing method according to claim 5, since the particle size of the adsorbent is less than a predetermined particle size, classification is performed so that the radioactive material and the adsorbed adsorbent do not remain in the treated soil. Is possible.

  According to the soil decontamination processing method according to claim 6, the plant removal step is a step of mixing contaminated soil and water and separating plants by specific gravity separation, and therefore, by a relatively simple method called specific gravity separation. It is possible to remove plants from contaminated soil.

  According to the soil decontamination processing method according to claim 7, it is possible to separate the removed matter generated by the soil decontamination processing method into reusable treated water and concentrated sludge containing a high concentration of radioactive substances. It becomes.

It is a block diagram which shows notionally the soil decontamination processing method concerning this Embodiment. It is a figure which shows the classification | category of a term. It is a figure which shows the result of Example 1. It is a figure which shows the result of Example 2. It is a block diagram which shows the modification of a soil decontamination processing method.

  Hereinafter, embodiments of a soil decontamination processing method according to the present invention will be described in detail with reference to the accompanying drawings. [I] First, the basic concept of the embodiment will be described, then [II] the specific contents of the embodiment will be described, and [III] Finally, modifications to the embodiment will be described. However, the present invention is not limited to the embodiments.

[I] Basic Concept of Embodiment First, the basic concept of the embodiment will be described. The soil decontamination processing method according to the present embodiment is a method for performing decontamination processing on collected contaminated soil. FIG. 1 is a block diagram conceptually showing a soil decontamination processing method according to the present embodiment, and FIG. 2 is a diagram showing classification of terms.

  As shown in FIGS. 1 and 2, the soil decontamination processing method according to the present embodiment includes a primary decontamination process, a plant removal process, a secondary decontamination process, and a muddy water treatment process. Here, the “primary decontamination process” is a process of decontaminating contaminated soil, and includes a primary mixing process and a primary classification process. The “plant removal step” is a step of removing plants from contaminated soil. The “secondary decontamination process” is a process of decontaminating contaminated soil, and includes a secondary mixing process and a secondary classification process. The “primary decontamination process” and the “secondary decontamination process” are collectively referred to as “decontamination process” as necessary.

  In addition, as shown in FIGS. 1 and 2, the treated soil of the contaminated soil is separated into removed materials by the soil decontamination processing method according to the present embodiment. Here, “contaminated soil” is a soil to which decontamination by the soil decontamination method is applied, and is a concept including primary treated soil, plant removed soil, and secondary treated soil. However, unless otherwise specified, it is simply referred to as “contaminated soil”. “Radioactive substance” is a general term for substances having radioactivity and is a concept including, for example, cesium, uranium, plutonium, thorium, etc. In this embodiment, the case where the radioactive substance is radioactive cesium will be described. . “Processed soil” is a concept including primary treated soil and secondary treated soil. “Primary treated soil” is soil generated by decontamination in the primary decontamination process. “Plant removal soil” is soil generated by removing plants in the plant removal step. “Secondary treated soil” is soil generated by decontamination in the secondary decontamination process. A “plant” is a plant (including branches, leaves, stems, roots, fruits, seeds, etc.) previously mixed in contaminated soil. The “removed product” is a substance containing a high concentration of radioactive material discharged in the primary decontamination process or the secondary decontamination process, and is a concept including the primary removal product and the secondary removal product. The “primary removal product” is a substance containing a high concentration of radioactive material discharged in the primary decontamination process. The “secondary removal product” is a substance containing a high concentration of radioactive material discharged in the secondary decontamination process. A “primary mixture” is a mixture produced by a primary mixing process. A “secondary mixture” is a mixture produced by a secondary mixing process.

[II] Specific Contents of Embodiment Next, specific contents of the embodiment according to the present invention will be described.

(Constitution)
Here, each process shown in FIG. 1 will be described, and finally the overall flow of the soil decontamination processing method will be described.

  First, the primary decontamination process will be described. A primary decontamination process is a process of decontaminating contaminated soil. As shown in FIG. 1, the primary decontamination process according to the present embodiment includes a primary mixing process and a primary classification process. Each process will be described below.

(Configuration-Primary decontamination process-Primary mixing process)
First, the primary mixing process in FIG. 1 will be described. The primary mixing process is a mixing process in which contaminated soil is mixed with water and stirred. The reason for performing such processing is as follows. That is, since radioactive cesium exists in the state adsorbed on the surface of soil particles, soil particles with a large specific surface area (that is, silt or clay with small particle size) contain a high concentration of radioactive cesium, Soil particles having a small specific surface area (that is, sand and gravel, which are soil particles having a large particle size) contain a low concentration of radioactive cesium. Here, in order to decontaminate contaminated soil, it is necessary to classify soil particles containing a high concentration of radioactive cesium and soil particles containing a low concentration of radioactive cesium according to the difference in particle size. There is. However, even if a process for classifying contaminated soil is performed, if soil particles with a small particle size have become agglomerates or adsorbed on soil particles with a large particle size, Soil particles with a small diameter are not normally classified. Therefore, in the previous stage of performing the classification treatment, the contaminated soil is mixed with water by the primary mixing treatment and stirred, thereby releasing the bond between the soil particles having a small particle size or the particle size. The soil particles having a small particle size adsorbed on the soil particles having a large particle size are exfoliated to increase the efficiency of the primary classification process described later.

(Configuration-primary decontamination step-primary mixing treatment-primary mixing device 1)
This primary mixing process is performed using the primary mixing apparatus 1. The primary mixing device 1 is a mixing means that mixes and contaminates contaminated soil with water. The primary mixing device 1 is a device having a substantially hollow cylindrical housing, and the housing is a drum-type device that can freely rotate along a circumferential direction around its axis.

  The contaminated soil and water are supplied to the inside of the casing of the primary mixing device 1, and the contaminated soil and water are agitated by rotating the casing to which these are supplied to make a slurry. A mixture (hereinafter referred to as a primary mixture) generated by mixing and stirring contaminated soil with water by the primary mixing device 1 is sent to a primary classification device 2 described later using a hopper or the like. The water supplied to the casing at this time is supplied to the casing for wet classification of radioactive cesium by the primary classifier 2 described later, and any washing water may be used. In addition, since this well-known mixing apparatus can be employ | adopted as this primary mixing apparatus 1, the detailed description is abbreviate | omitted.

(Configuration-Primary decontamination process-Primary classification process)
Next, the primary classification process in FIG. 1 will be described. A primary classification process is a classification process which classifies a primary mixture into a primary removal thing and primary treatment soil. More specifically, by this primary classification treatment, the primary mixture produced by the above-described primary mixing treatment is divided into a primary removal product that is a soil having a high radioactive cesium-containing concentration and a primary treatment that is a soil having a low radioactive cesium-containing concentration. Separated into soil. In this way, it is possible to decontaminate contaminated soil by excluding only soil with a high concentration of radioactive cesium from the contaminated soil.

(Configuration-primary decontamination step-primary classification treatment-primary classification device 2)
This primary classification process is performed using the primary classification device 2. The primary classifier 2 is a classifying means for classifying the primary mixture into a primary removed material and a primary treated soil. The primary classifying device 2 is a device having a substantially hollow cylindrical housing, and the housing is a drum-type device that can freely rotate along the circumferential direction around its axis. Further, the outer peripheral surface of the housing is formed in a mesh shape having a large number of classification holes having a predetermined particle diameter penetrating from the outer wall to the inner wall of the housing.

  As this “predetermined particle size”, an arbitrary value can be adopted, but at least a value at which soil particles (for example, clay and silt) adsorbed with a high concentration of radioactive cesium can pass through the classification hole To do. In the present embodiment, the predetermined particle size is described as “a particle size that allows only molecules less than 75 μm to pass through the mesh”. In fact, since a molecule having a particle size of 75 μm cannot pass through a classification hole having a particle size of 75 μm, in order to obtain a classification hole capable of passing a molecule having a size of 75 μm, the particle size of the classification hole is 75 μm. Will be a little bigger. Therefore, the mesh classification hole is not used as the standard for the predetermined particle size, such as “the particle size of 75 μm”, but the particle size is such that only molecules having a particle size of less than 75 μm can pass through the mesh. The particle diameter of molecules passing through the classification holes was used as a reference for the predetermined particle diameter. In the present embodiment, soil having a particle size of less than 5 μm is referred to as “clay”, soil having a particle size of 5 μm or more and less than 75 μm is “silt”, soil having a particle size of 75 μm or more and less than 2 mm is “sand”, and soil having a particle size of 2 mm or more is “gravel”. Called.

  Then, the classification process of the primary classification apparatus 2 is demonstrated. First, the primary mixture is supplied to the inside of the casing of the primary classifier 2, and the casing is rotated. As a result, a centrifugal force in a direction from the inside of the housing toward the outside of the housing is applied to the primary mixture, and the primary mixture is pressed against the inner wall of the housing. At that time, among the particles constituting the primary mixture, particles having a particle size smaller than the particle size of the mesh (radioactive cesium, clay, silt having a particle size of less than 75 μm in this embodiment) Since it passes through the mesh provided on the outer peripheral surface, it is discharged outside the housing. On the other hand, particles having a particle size larger than the particle size of the mesh (in this embodiment, the particle size is larger than 75 μm, sand, gravel) cannot pass through the mesh provided on the outer peripheral surface of the case, so the inside of the case To accumulate. In this way, it is possible to classify into primary removed substances (radioactive cesium, clay, silt) discharged to the outside of the casing and primary treated soil (sand, gravel) accumulated inside the casing. In addition, since this well-known classifier can be employ | adopted as this primary classifier 2, the detailed description is abbreviate | omitted.

  Actually, it is difficult to completely classify the primary treated soil and the primary removed matter only by the difference in particle diameter, and clay and silt with high radioactive cesium concentration will remain in the primary treated soil. The secondary decontamination step described later is preferably performed. Further, among the primary treated soil classified by the primary classifying device 2, further, a primary treated soil having a particle size equal to or larger than a second predetermined particle size (predetermined particle size set to be smaller than the predetermined particle size); It may be divided into primary treated soil having a particle size less than the second predetermined particle size. That is, since the primary treated soil having a particle size equal to or larger than the second predetermined particle size originally does not contain plants, for example, via a device similar to the primary classification device 2 and only the mesh diameter is changed, By performing such two-stage classification, it is possible to previously separate the primary treated soil that does not require the plant removal process described later.

(Configuration-plant removal process)
Next, a plant removal process is demonstrated. A plant removal process is a process of removing the plant contained in contaminated soil.

(Configuration-plant removal step-specific gravity separation device 3)
This plant removal step is performed using the specific gravity separator 3. The specific gravity separation device 3 is a plant removal means for separating the contaminated soil into a plant mixed in the contaminated soil and a plant removal soil from which the plant has been removed. The specific gravity separation device 3 is a device including a substantially hollow cylindrical casing, and is a sedimentation separation device including a plurality of bubble jets on the inner wall thereof.

  Contaminated soil and water are supplied to the inside of the casing of the specific gravity separator 3, bubbles are introduced into the liquid composed of the contaminated soil and water, and a plant that is a hydrophobic substance is attached to the surface of the bubbles to be floated and separated. This makes it possible to easily remove plants that have floated on the contaminated soil. In addition, since this well-known apparatus can be employ | adopted as this specific gravity separation apparatus 3, the detailed description is abbreviate | omitted.

  In the present embodiment, as the contaminated soil, the primary treated soil generated in the above-described primary decontamination process is supplied to the specific gravity separation device 3, but only the primary treated soil having a relatively small particle diameter is supplied. May be supplied to the specific gravity separator 3. This is because, as described above, the primary treated soil having a large particle size does not originally contain a plant, and therefore a treatment for removing the plant is not necessary.

(Configuration-secondary decontamination process)
Next, the secondary decontamination process of FIG. 1 will be described. A secondary decontamination process is a process of decontaminating contaminated soil, and is a process performed at least after a plant removal process. As shown in FIG. 2, the secondary decontamination process according to the present embodiment includes a secondary mixing process and a secondary classification process. Each process will be described below.

(Configuration-secondary decontamination process-secondary mixing process)
First, the secondary mixing process will be described. The secondary mixing process is a mixing process in which contaminated soil is mixed with water and stirred. Since the secondary mixing process is configured in the same manner as the primary mixing process unless otherwise specified, the description of the same points as the primary mixing process will be omitted, and only the differences from the primary mixing process will be described. The reason for performing this secondary mixing process is that, as in the case of the primary mixing process, it is possible to increase the efficiency of the secondary classification process described later.

(Configuration-secondary decontamination step-secondary mixing treatment-secondary mixing device 4)
This secondary mixing process is performed using the secondary mixing device 4. The secondary mixing device 4 is a mixing means for mixing and stirring the contaminated soil, and is a grinding means for separating the radioactive cesium still adsorbed on the surface of the contaminated soil from the contaminated soil even after the primary decontamination step. is there.

  The secondary mixing device 4 is a device that includes a substantially hollow cylindrical housing, and is a drum cleaning device that can freely rotate along the circumferential direction around the axis. Note that a plurality of grinding rods are mounted inside the housing, and this is different from the primary mixing device 1 in this respect.

  The grinding rod is, for example, a rod-like body and a spherical body formed as a metal substantially solid cylindrical shape having a predetermined strength, and the outer peripheral surface thereof has a surface area so that grinding can be performed efficiently. A large shape or the like is used.

  The contaminated soil and water are supplied into the casing of the secondary mixing device 4, and the casing to which these are supplied is rotated to bring the plurality of grinding rods inside the casing into contact with the contaminated soil, thereby contaminating the soil. And mix and stir the water. In this way, by grinding the contaminated soil with the grinding rod when the housing rotates, compared to the primary mixing device 1 that does not have the grinding rod, the soil particles having a small particle size are smaller than each other. It becomes possible to perform the release of the bonds and the separation of the soil particles having a small particle size adsorbed on the soil particles having a large particle size more efficiently. Thereby, it is possible to peel the radioactive cesium still adsorbed to the contaminated soil from the contaminated soil even after the primary decontamination step.

  A mixture (hereinafter, secondary mixture) generated by mixing and stirring the contaminated soil with water by the secondary mixing device 4 is sent to a secondary classification device 5 described later using a hopper or the like. In addition, since this well-known mixing apparatus can be employ | adopted as this secondary mixing apparatus 4, the detailed description is abbreviate | omitted.

  In addition, if the process which grinds such contaminated soil in the front | former stage of a plant removal process will be performed, since the plant contained in contaminated soil will be ground, the precision in a plant removal process will fall. Therefore, the secondary mixing treatment is preferably performed after the plant removal step.

  However, even if the secondary mixing process is performed by an apparatus not equipped with a grinding rod (for example, the same apparatus as the primary mixing apparatus 1), the radioactive cesium that is still adsorbed to the contaminated soil even after the primary decontamination process. It is possible to peel to some extent from contaminated soil.

(Configuration-secondary decontamination process-secondary classification process)
Next, the secondary classification process of FIG. 1 will be described. The secondary classification treatment is a classification step for classifying the secondary mixture into secondary removal products and secondary treatment soil. By this secondary classification treatment, the secondary mixture produced by the secondary mixing treatment described above is divided into a secondary removal product that is a soil having a high radioactive cesium-containing concentration and a secondary treated soil that is a soil having a low radioactive cesium-containing concentration. And can be separated. The secondary classification process is performed by the secondary classifier 5, but the secondary classifier 5 can adopt the same configuration as the primary classifier 2, and thus detailed description thereof is omitted.

(Configuration-muddy water treatment process)
Next, the muddy water treatment process of FIG. 1 will be described. The muddy water treatment process is a process of adding a precipitant to the removed product and separating it into treated water and concentrated sludge containing radioactive substances, and this muddy water treatment step collects reusable treated water from the removed product. It is possible. The process for separating the treated water and the concentrated sludge from the primary removed product and the process for separating the treated water and the concentrated sludge from the secondary removed product can be configured in the same manner. Only explained.

  The turbid water treatment step uses a known turbid water treatment means such as a centrifugal separator, an individual liquid separator, or a pressure filtration device (not shown), and administers the precipitating agent etc. as necessary to concentrate the removed product as sludge. And the process of separating into treated water. The concentrated sludge thus separated is dehydrated by a dehydrator, stored in a cake yard or the like, and then transported to a dedicated processing facility or the like for processing. On the other hand, since the treated water has been decontaminated to a state where radioactive cesium can hardly be detected, it can be reused or discharged into public sewers. In addition, since this muddy water treatment process can be performed using a well-known muddy water treatment means, the detailed description is abbreviate | omitted.

(Treatment-soil decontamination method)
Finally, based on each process mentioned above, the flow of the whole soil decontamination processing method is demonstrated later on.

  First, the collected contaminated soil is supplied to the primary mixing device 1 and water is supplied to the primary mixing device 1 at the same time. A primary mixing process is performed by the primary mixing apparatus 1 to generate a primary mixture. The primary mixture produced in this way is carried to the primary classifier 2 where the primary classification soil and the primary removal product are classified. This primary treated soil is separated into a plant and a plant-removed soil by the specific gravity separator 3. And this plant removal soil is supplied to the secondary mixing apparatus 4, and water is supplied to the secondary mixing apparatus 4 simultaneously. In addition, since the plant is not mixed in the primary treated soil having a large particle size as described above, it may be directly supplied to the secondary mixing device 4 without performing the plant removal step. And this secondary mixing apparatus 4 performs a secondary mixing process, and a secondary mixture is produced | generated. The secondary mixture thus produced is conveyed to the secondary classifier 5, where it is classified into secondary treated soil and secondary removed material. Thereby, secondary treated soil from which radioactive cesium has been decontaminated and from which plants have been removed can be obtained.

  Thus, according to Embodiment 1, it is possible to effectively decontaminate contaminated soil mixed with plants. Moreover, when decontaminating the contaminated soil, it is possible to decontaminate the contaminated soil without using an acid or alkali for adjusting the pH of the washing water or a strong acid or strong alkali as a washing liquid. Moreover, it is possible to further reduce the accumulated amount of radioactive cesium in the contaminated soil by further decontaminating the primary treated soil or the plant-removed soil. Moreover, it is possible to remove a plant from contaminated soil by a simple method. Moreover, it becomes possible to isolate | separate the removal thing produced by the soil decontamination processing method into the reusable treated water and the concentrated sludge which contains radioactive cesium in high concentration.

[Embodiment 2]
Next, a second embodiment will be described. The second embodiment is a soil decontamination method using an adsorbent in the secondary decontamination process. The configuration of the second embodiment is substantially the same as the configuration of the first embodiment except where otherwise specified, and the same configuration as that of the first embodiment is used in the first embodiment. The same reference numerals are attached as necessary, and the description thereof is omitted.

  The soil decontamination processing method according to the present embodiment includes a primary decontamination process, a plant removal process, and a secondary decontamination process. Of these, the primary decontamination process and the plant removal process can be configured in the same manner as in the first embodiment, and therefore only the secondary decontamination process will be described. In addition, the secondary decontamination process which concerns on this Embodiment contains a secondary mixing process and a secondary classification process similarly to the secondary decontamination process which concerns on Embodiment 1. FIG.

(Configuration-secondary decontamination process-secondary mixing process)
In the secondary mixing process, contaminated soil, water, and an adsorbent are supplied into the housing of the secondary mixing device 4 and then stirred. Thereby, the water-soluble radioactive cesium in contaminated soil is adsorbed by the adsorbent by this stirring treatment.

(Configuration-secondary decontamination process-secondary mixing treatment-adsorbent)
Here, the adsorbent is a classification promoting means that adsorbs water-soluble radioactive cesium in the contaminated soil and improves the accuracy of the classification process. The adsorbent has only to have a particle size that passes through the mesh of the secondary classifier 5 described later, and can easily absorb radioactive cesium, such as vermiculite, bentonite, zeolite, or mica powder, Any adsorbent can be used. The adsorbent is adsorbed with radioactive cesium contained in the contaminated soil by being stirred together with the contaminated soil and water in the casing of the secondary mixing device 4. The radioactive cesium adsorbed by the adsorbent becomes difficult to adsorb again with the soil particles of the contaminated soil, so it is possible to prevent the radioactive cesium from being re-adsorbed to the soil particles at the stage of secondary classification treatment, The accuracy of the secondary classification process can be improved.

(Configuration-secondary decontamination step-secondary classification treatment-secondary classification device 5)
An arbitrary value can be adopted as the predetermined particle diameter of the classification hole provided on the outer peripheral surface of the casing of the secondary classification device 5, but at least a value that allows the adsorbent to pass through the classification hole. Thus, particles having a particle size smaller than the particle size of the mesh (in this embodiment, the particle size is less than 75 μm, radioactive cesium, adsorbent adsorbed with radioactive cesium, clay, silt) are external to the casing. Discharged. On the other hand, particles having a particle size larger than the particle size of the mesh (in this embodiment, the particle size is greater than 75 μm, sand, gravel) accumulate in the housing. Secondary removal materials (radiocesium, adsorbents adsorbed with radioactive cesium, clay, silt) discharged outside the housing in this way, and secondary treated soil (sand, gravel) accumulated inside the housing ).

  Thus, according to Embodiment 2, it is possible to prevent the radioactive cesium peeled from the contaminated soil from being adsorbed again on the contaminated soil, and to improve the accuracy of the secondary decontamination step. Moreover, it is possible to classify so that the adsorbent adsorbed with radioactive cesium does not remain in the treated soil. Moreover, it becomes possible to prevent the adsorbent adsorbed with radioactive cesium from remaining in the soil of 75 μm to 250 μm or more obtained as the treated soil.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the technical scope of the present invention is not limited to these examples.

Example 1
In this example, the radioactive concentration of the contaminated soil when each step is performed in the order of the primary decontamination step, the plant removal step, and the secondary decontamination step on the contaminated soil containing radioactive cesium with a radioactive concentration of 15000 Bq / kg. Changes were measured. FIG. 3 is a diagram showing the results at that time.

  At this time, the radioactive concentration of two patterns of contaminated soil was measured when the plant removal step was performed as usual and when the plant removal step was omitted.

  In addition, in the secondary decontamination process, when adsorbent is added to the secondary mixing device 4 and when it is not added, when the grinding treatment is performed in the secondary mixing treatment (the grinding to the secondary mixing device 4). The radioactive concentration of the contaminated soil was measured when a total of four patterns were performed: when the rod was attached) and when the grinding treatment was not performed (when the grinding rod was not attached to the secondary mixing device 4).

  From the results of FIG. 3, it was revealed that the radioactive concentration of the contaminated soil can be reduced to 50% (15000 Bq / kg → 7500 Bq / kg) by performing the primary decontamination process. Moreover, it became clear that a radioactive density | concentration can further be reduced by performing a plant removal process with respect to the primary treated soil produced | generated by performing a primary decontamination process (7500Bq / kg-> 3000Bq / kg). Also, in the secondary decontamination process, by adding adsorbents and attaching grinding rods, compared to the case where these treatments are not performed, the radioactivity of the secondary treated soil generated by the secondary decontamination process It was revealed that the concentration was further reduced.

(Example 2)
In this example, each step is performed in the order of primary decontamination step, plant removal step, and secondary decontamination step (with adsorbent and grinding treatment) for contaminated soil containing radioactive cesium with a radioactive concentration of 15000 Bq / kg. It performed and the change of the radioactive density | concentration of the secondary treatment soil obtained when the particle size of the secondary classifier 5 was changed in the secondary decontamination process was measured. FIG. 4 is a diagram showing the results at that time.

  In addition, the measurement (FIG. 4 (a)) about the contaminated soil in which the soil particles having a particle diameter of 75 μm or more account for 70% of the entire contaminated soil, and the soil particles having a particle diameter of 75 μm or more are 98% of the entire contaminated soil. The measurement (FIG.4 (b)) about the contaminated soil which occupies was performed.

  Here, FIG. 4A will be described. In this measurement, the particle size of the secondary classifier 5 is “particle size through which only particles less than 500 μm can pass”, “particle size through which only particles less than 250 μm can pass”, and “particles through which only particles less than 125 μm can pass”. The radioactive cesium concentration of the secondary treated soil and the recovered amount of the secondary treated soil in the case of “diameter” or “particle size through which only particles less than 75 μm can pass” were measured.

  Next, FIG. 4B will be described. In this measurement, the particle size of the secondary classification device 5 when the particle size of the secondary classification device 5 is “particle size through which only particles less than 250 μm can pass” or “particle size through which only particles less than 75 μm can pass” is used. The concentration of radioactive cesium and the amount of secondary treated soil recovered were measured.

  From the results of FIG. 4, it is clear that the larger the particle size of the secondary classifier 5, the lower the concentration of radioactive cesium in the secondary treated soil that can be recovered, but the smaller the amount of secondary treated soil recovered. Moreover, it becomes possible to perform a more appropriate decontamination process by changing the setting of the particle size of the secondary classifier 5 according to the soil condition of the contaminated soil and the like and the target radioactive cesium concentration. In this way, the secondary classifier can arbitrarily set the lower limit of the particle size of the secondary treated soil that can be collected, but the lower limit of the particle size is the amount of the secondary treated soil recovered. Considering the balance of the radioactive cesium concentration of the recovered secondary treated soil, it is possible to perform a more efficient decontamination process especially by setting the thickness to 75 μm to 250 μm.

[III] Modifications to Each Embodiment While each embodiment according to the present invention has been described above, the specific configuration and means of the present invention are the same as the technical idea of each invention described in the claims. Modifications and improvements can be arbitrarily made within the range. Hereinafter, such a modification will be described.

(About problems to be solved and effects of the invention)
First, the problems to be solved by the invention and the effects of the invention are not limited to the above-described contents, and the present invention solves the problems not described above or has the effects not described above. There are also cases where only some of the described problems are solved or only some of the described effects are achieved. For example, when it is possible to decontaminate contaminated soil in which radioactive substances are accumulated by a method different from the conventional method, the problem of the present invention is solved.

(About each device)
In the present embodiment, each device has been described as a separate device, but each step is performed using a device that integrally includes the functions of any of these devices, and soil decontamination processing is performed. You may do the method.

(Treatment soil, plant removal soil)
When performing the primary decontamination process, plant removal process, and secondary decontamination process, water is added to the contaminated soil for wet classification or specific gravity separation. In the case of collecting as soil, it is necessary to dry each contaminated soil using a dehydrator (not shown) after completing each step. However, as described above, each process can be performed by the same apparatus. For example, when the primary decontamination process and the plant removal process are performed in the same apparatus, the primary treated soil is once collected as soil. When it is not necessary, it is not necessary to perform such a drying process, and it may be supplied to the specific gravity separator 3 as the primary treated soil containing a lot of moisture. Since the primary treated soil in such a case already contains a lot of water, it is not necessary to supply water when the primary treated soil is supplied to the specific gravity separator 3.

(About soil decontamination method)
Each process and each process included in the soil decontamination processing method are not limited to the forms shown in the present embodiment. That is, even if each process or each process is performed as shown in FIG. For example, in the present embodiment, as illustrated in FIG. 5A, it has been described that the respective steps are performed in the order of the primary decontamination step, the plant removal step, and the secondary decontamination step. The removal process may be reversed in order. That is, as shown in FIG.5 (b), it is good also as performing each process in order of a plant removal process, a primary decontamination process, and a secondary decontamination process. Further, as shown in FIGS. 5C and 5D, either one of the secondary decontamination process or the primary decontamination process may be omitted.

  Further, in the present embodiment, as illustrated in FIG. 5E, it has been described that each process is performed in the order of the primary mixing process and the primary classification process. However, the order of the primary mixing process and the primary classification process is reversed. Also good. That is, as shown in FIG. 5F, each process may be performed in the order of the primary classification process and the primary mixing process. Similarly, as shown in FIG. 5F, the order of the secondary mixing process and the secondary classification process may be reversed. Moreover, as shown in FIG.5 (g), you may perform a plant removal process between a primary mixing process and a primary classification process, or between a secondary mixing process and a secondary classification process.

  Moreover, as shown in FIG.5 (h), you may perform repeatedly each process of a primary decontamination process, a plant removal process, and a secondary decontamination process. Or you may perform repeatedly the soil decontamination processing method as shown to Fig.5 (a) from FIG.5 (h). This makes it possible to decontaminate radioactive cesium contained in contaminated soil with higher accuracy.

(About muddy water treatment process)
In the present embodiment, the muddy water treatment process related to the primary treated soil and the muddy water treatment process related to the secondary treated soil have been described as separate processes, but these may be combined into one process. That is, the same effect can be obtained by performing the muddy water treatment step on the treated soil obtained by mixing the primary treated soil and the secondary treated soil.

(About the primary classifier 2 and the secondary classifier 5)
In the present embodiment, the primary classifying device 2 and the secondary classifying device 5 have been described as drum-type devices having a large number of classification holes on the outer peripheral surface of the housing. However, these devices are limited to the form shown in the present embodiment. Absent. That is, any device capable of classifying contaminated soil may be used. For example, a mechanical vibration sieving device that performs solid-liquid separation by vibration of an electric motor, a specific gravity separation device that separates fine particles and coarse particles, and the like are used. Also good.

(About specific gravity separator 3)
In the present embodiment, the specific gravity separation device 3 used in the plant removal process has been described as a sedimentation separation device including a plurality of bubble jets on the inner wall, but this device is not limited to the form shown in the present embodiment. In other words, any device that can remove plants from contaminated soil may be used. For example, a device that does not include a bubble outlet and performs specific gravity separation by natural sedimentation may be used.

DESCRIPTION OF SYMBOLS 1 Primary mixing apparatus 2 Primary classification apparatus 3 Specific gravity separation apparatus 4 Secondary mixing apparatus 5 Secondary classification apparatus

Claims (7)

A soil decontamination method for decontaminating contaminated soil in which radioactive substances have accumulated,
A decontamination step of decontaminating the contaminated soil and separating it into a removed material and treated soil;
A plant removal step of separating the contaminated soil into a plant mixed in the contaminated soil and a plant-removed soil from which the plant has been removed;
A soil decontamination treatment method. The decontamination step performs decontamination by wet-classifying the primary mixture generated by mixing and stirring the contaminated soil and water, and the primary mixture is treated with primary treated soil having a particle size equal to or larger than a predetermined particle size. Including a primary decontamination step in which the particle size is separated into primary removal products less than the predetermined particle size,
The soil decontamination method according to claim 1. The decontamination step is a treated soil separated by wet classification of a primary mixture generated by mixing and stirring the contaminated soil and water, and the primary treated soil having a particle size of a predetermined particle size or more, or By subjecting the secondary mixture produced by grinding and stirring the plant-removed soil and water to wet classification, the secondary mixture is treated with a secondary-treated soil having a particle size equal to or larger than a predetermined particle size and a particle size. Including a secondary decontamination step of separating into secondary removal products having a particle size of less than a predetermined particle size,
The soil decontamination method according to claim 1. The decontamination step is a treated soil that is separated by wet classification of the primary mixture generated by mixing and stirring the contaminated soil and water, and the primary treated soil having a particle size of a predetermined particle size or more or The secondary mixture produced by mixing and stirring the plant-removed soil, water, and the adsorbent is subjected to wet classification, thereby converting the secondary mixture into a secondary treated soil and particles having a particle size equal to or larger than a predetermined particle size. Including a secondary decontamination step in which the diameter is separated into secondary removal products having a particle size less than a predetermined particle size,
The soil decontamination method according to claim 1. The adsorbent has a particle size less than the predetermined particle size,
The soil decontamination processing method according to claim 4. The plant removal step is a step of mixing the contaminated soil and water and separating the plant by specific gravity separation.
The soil decontamination processing method according to any one of claims 1 to 5. A muddy water treatment step of adding a precipitant to the removed product and separating it into treated water and concentrated sludge containing radioactive substances,
The soil decontamination processing method as described in any one of Claim 1 to 6 containing this.

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