Soil Treatment Method

Abstract

Provided is a soil treatment method that can easily remove radioactive materials from soil. [Solution] The soil treatment method is a method for treating soil containing mineral particles having radioactive substances adsorbed thereto, and includes injecting pressurized liquid into a slurry prepared by mixing soil with liquid, thereby generating cavitation by creating a flow velocity difference at the interface between the pressurized liquid and the slurry, and the mineral particles are separated from other particles by the impact force generated when bubbles generated by cavitation collapse.

Description

[Technical field]

[0001] The present invention relates to a method for treating soil containing radioactive material. [Background technology]

[0002] Classification processing technology is known as one of the volume reduction technologies for removing radioactive materials from soil containing radioactive materials and reducing the volume of soil with high radioactive concentrations.

[0003] In classification processing technology, soil containing radioactive materials is classified into a group of soil particles with small particle size, such as clay and silt (hereinafter referred to as "fine particle fraction"), and a group of soil particles with larger particle size than the fine particle fraction, such as gravel and sand (hereinafter referred to as "coarse particle fraction"). Radioactive materials such as radioactive cesium tend to adhere to relatively small particles (for example, mineral particles such as mica), so they are contained in large amounts in the fine particle fraction after classification. Therefore, the concentration of radioactive materials can be reduced by separating and removing the fine particle fraction from the soil. The coarse particle fraction after the fine particle fraction has been removed can be reused for construction purposes, etc.

[0004] Patent Document 1 proposes washing the coarse fraction after the above classification in order to further remove radioactive materials contained in the coarse fraction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-140021 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, there is room for improvement in conventional classification techniques in terms of more reliably removing radioactive materials from soil.

[0007] An object of the present invention is to solve the above problems and to provide a soil treatment method that can easily remove radioactive materials from soil. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, a soil treatment method according to one embodiment of the present invention is a method for treating soil containing mineral particles having radioactive substances adsorbed thereto, which includes injecting a pressurized liquid into a slurry obtained by mixing the soil with a liquid, and generating cavitation by creating a flow velocity difference at the interface between the pressurized liquid and the slurry, and the mineral particles are separated from other particles by the impact force generated when bubbles generated by the cavitation collapse. Effect of the Invention

[0009] According to the soil treatment method of the present invention, radioactive materials can be easily removed from soil. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic side view of a soil treatment apparatus according to a first embodiment. [Figure 2A] 2 is a schematic enlarged cross-sectional view of a region A shown in FIG. [Figure 2B] FIG. 2B is a schematic cross-sectional view taken along line IIB-IIB in FIG. 2A. [Figure 3A] FIG. 1 is a schematic diagram illustrating a soil treatment method I according to a first embodiment. [Figure 3B] FIG. 2 is a schematic diagram illustrating another soil treatment method II according to the first embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view showing a soil treatment apparatus according to a second embodiment. [Figure 5A] FIG. 4 is a schematic enlarged cross-sectional view showing a part of a flow path of a processing section. [Figure 5B] 5B is a schematic enlarged cross-sectional view taken along line VB-VB shown in FIG. 5A. [Figure 5C]5B is a schematic enlarged cross-sectional view taken along the line VC-VC shown in FIG. 5A. [Figure 6] FIG. 2 is a schematic top view of the fringe used in the experiment. [Figure 7A] FIG. 4 is a schematic top perspective view showing the positional relationship between a conveying device and a hopper. [Figure 7B] FIG. 7B is a schematic cross-sectional view taken along line VIIB-VIIB shown in FIG. 7A. [Figure 8A] 13 is a schematic perspective view showing a modified example of the liquid supply unit and the hopper. FIG. [Figure 8B] FIG. 8B is a top view of the liquid supply and hopper shown in FIG. 8A. [Figure 9] FIG. 11 is a schematic cross-sectional view showing a modified example of a flow channel. [Figure 10] FIG. 11 is a schematic side view showing an apparatus of a comparative example. [Figure 11A] 1 is a photograph showing a measurement sample after a crushing treatment in an example. [Figure 11B] 1 is a photograph showing a measurement sample of a comparative example. [Figure 11C] FIG. 2 is a graph showing particle size accumulation curves of measurement samples of Examples and Comparative Examples. [Figure 12] FIG. 2 is a schematic diagram showing a soil treatment method according to a reference example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (Findings on which the present invention is based) The present inventors conducted extensive research into ways to facilitate the removal of radioactive materials from soil, and as a result, reached the following findings.

[0012] Conventional classification processing technologies have the following problems (1) and (2).

[0013] (1) It is known that radioactive substances such as radioactive cesium are easily adsorbed to particles of layered clay minerals. Examples of layered clay minerals include mica minerals (hereinafter simply referred to as "mica") such as weathered biotite and its weathered product vermiculite. Particles of minerals such as mica may be attached to or included in large sand particles or gravel particles. If mineral particles are attached to (or included in) sand particles, even if classification is performed, the mineral particles with adsorbed radioactive substances will be included in the coarse fraction after classification. In addition, if the particle diameter of the mineral particles with adsorbed radioactive substances is large, the mineral particles will be separated into the coarse fraction. For this reason, it is difficult to remove radioactive substances more reliably by classification. In response to this, it has been proposed to perform advanced classification, washing, and other processes on the coarse fraction after classification to reduce the radioactive concentration (for example, Patent Document 1). However, it is considered difficult to more reliably peel off mineral particles that are fixed to or included in sand particles with the method described in Patent Document 1. More details will be provided below.

[0014] In addition, recent research has reported that radioactive materials such as radioactive cesium are adsorbed to layered clay mineral particles and further trapped (fixed) inside them. In layered clay mineral particles, the surface located between the layers is negatively charged, so radioactive materials are easily adsorbed to this surface. When a radioactive material is adsorbed between two layers that make up a layered clay mineral particle, the two layers sandwiching the radioactive material close over time. In this way, the radioactive material is trapped inside the layered clay mineral particle. When a radioactive material is fixed to a layered clay mineral particle, it becomes difficult for the radioactive material to be released or eluted from the particle. In particular, when a radioactive material is trapped in a part of a mica particle that has been altered by weathering, it becomes even more difficult to remove the radioactive material using conventional classification processing techniques.

[0015] Therefore, it may be difficult to reduce the concentration of radioactive materials in the coarse particles and increase the decontamination rate.

[0016] (2) To more reliably remove radioactive materials from soil by classification, it is necessary to separate and remove soil particles in a particle size range that includes mineral particles as fine particles with high concentrations of radioactive materials. As mentioned above, if radioactive materials are trapped in mineral particles and are difficult to dissolve or desorb, it may be difficult to reduce the fine particles and increase the volume reduction rate. "Volume reduction" refers to reducing the volume of soil that has a radioactive concentration higher than a specified value (e.g. 8000 Bq / kg) and cannot be reused as is.

[0017] Therefore, the inventors of the present application have conducted extensive research and found a method for generating cavitation by ejecting a pressurized liquid into a slurry containing soil and creating a flow velocity difference at the interface between the pressurized liquid and the slurry. With this method, mineral particles to which radioactive substances are adsorbed can be separated from other particles by the impact force generated when bubbles generated by cavitation collapse. This makes it easier to remove the radioactive substances from the soil. "Mineral particles to which radioactive substances are adsorbed" includes particles to which radioactive substances are adsorbed (trapped between layers) in addition to particles to which radioactive substances are adsorbed on the surface.

[0018] According to the above method, the impact force generated when the bubbles collapse can separate mineral particles attached to large soil particles such as sand particles from the soil particles. Alternatively, the impact force generated when the bubbles collapse can crush the mineral particles to which radioactive substances are adsorbed into smaller particles. As a result, the concentration of radioactive substances in the coarse particles after classification can be reduced. Furthermore, by reducing the particle size of the particles to which radioactive substances are attached, the volume of soil (fine particles) with a high concentration of radioactive substances can be reduced. Based on this new finding, the inventor of the present application arrived at the present invention.

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to this embodiment. For the purpose of illustration, the dimensions of each element in the drawings may be exaggerated and are not necessarily drawn to scale. In addition, the same reference numerals are used to refer to substantially the same components in the drawings.

[0020] In the following, for convenience of explanation, terms indicating directions such as "upper", "lower", "side", "left", and "right" are used assuming a state during normal use, but are not meant to limit the state of use of the device according to the present invention. For reference, the drawings show an X-axis, a Y-axis, and a Z-axis that are perpendicular to each other. The Z-axis is, for example, a vertical direction. In the following explanation, when the X-direction, the Y-direction, or the Z-direction is simply described, it refers to the respective axial directions, and includes two opposite directions (for example, the -X direction and the +X direction).

[0021] First Embodiment A soil treatment apparatus and a soil treatment method according to a first embodiment will be described.

[0022] [Soil treatment device] 1, 2A, and 2B are schematic diagrams for explaining the general structure and principle of the soil treatment device according to the first embodiment. Fig. 1 is a schematic side view of the soil treatment device. Fig. 2A is a schematic enlarged cross-sectional view of region A shown in Fig. 1, and Fig. 2B is a schematic cross-sectional view taken along line IIB-IIB in Fig. 2A.

[0023] The soil treatment device 1 is a device for treating soil containing mineral particles to which radioactive substances are adsorbed. In this embodiment, the soil to be treated contains mineral particles to which radioactive substances are adsorbed and soil particles having a particle size larger than that of the mineral particles. The soil to be treated by the soil treatment device 1 may be soil that has not been subjected to classification treatment, and may be soil having a wide particle size distribution including, for example, gravel particles (particle size: for example, 2 mm or more), sand particles (particle size: for example, 74 μm or more and less than 2 mm), silt particles (particle size: for example, 5 μm or more and less than 74 μm), and clay particles (particle size: for example, less than 5 μm).

[0024] As shown in FIG. 1, the soil treatment apparatus 1 includes a treatment section 3, an ejection section 2 that ejects pressurized liquid 20 to the treatment section 3, and a slurry supply section 4 that supplies a slurry 40 containing soil to the treatment section 3.

[0025] The processing section 3 includes a flow path 30. The flow path 30 is, for example, configured by a pipe having a circular cross section. The flow path 30 extends, for example, in a horizontal direction perpendicular to the vertical direction. For ease of understanding, in FIG. 1, the vertical upward direction is shown as the +Z direction, and the direction from the upstream side to the downstream side of the flow path 30 is shown as the +X direction. The flow path 30 may include an outlet 37 at the downstream end for discharging a mixture 70 including the treated slurry 40 and the pressurized liquid 20 from the processing section 3.

[0026] The ejection unit 2 is disposed so as to eject the pressurized liquid 20 in a direction (+X direction) from the upstream side to the downstream side of the flow path 30. The ejection unit 2 ejects the pressurized liquid 20 toward the slurry 40 in the flow path 30. The ejection unit 2 is, for example, a high-pressure ejector that ejects high-pressure water.

[0027] The slurry supplying unit 4 supplies a slurry 40, which is obtained by mixing soil with a liquid (e.g., water), to the flow path 30. The slurry supplying unit 4 is connected to the flow path 30 downstream of the ejection unit 2. In the flow path 30, the slurry supplying unit 4 supplies the slurry 40 toward the pressurized liquid 20 ejected by the ejection unit 2 in a direction intersecting the ejection direction of the pressurized liquid 20. In the example shown in FIG. 1, the slurry supplying unit 4 is configured to supply the slurry 40 in a direction (-Z direction) perpendicular to the ejection direction. The pressure of the liquid contained in the slurry 40 when supplied is, for example, approximately 1 atmosphere.

[0028] 2A and 2B, in this embodiment, the ejection unit 2 and the slurry supply unit 4 are configured to generate cavitation by generating a flow velocity difference at the interface 20s between the pressurized liquid 20 and the slurry 40. The mechanism by which cavitation is generated will be described below.

[0029] As shown in FIG. 2A and FIG. 2B, the pressurized liquid 20 ejected from the ejection unit 2 is a high-speed fluid (for example, pressure: 4 MPa, speed: about 50 m / s) that moves at high speed in the +X direction in the flow path 30. In the flow path 30, the pressurized liquid 20 collides with the slurry 40, and moves at high speed through the approximate center of the slurry 40 as shown in FIG. 2B. The slurry 40 is pulled by the flow of the pressurized liquid 20 to form a multiphase flow that flows around the pressurized liquid 20 in the same direction as the pressurized liquid 20. The multiphase flow here is a flow that includes at least the soil (solid phase) and liquid (liquid phase) contained in the slurry 40. A space 80 may exist above the slurry 40. Since the slurry 40 flows at a slower speed than the pressurized liquid 20, a flow velocity difference occurs at the interface 20s between the slurry 40 and the pressurized liquid 20. This causes cavitation. Specifically, as shown in Fig. 2A, a shear force caused by the difference in flow speed between the pressurized liquid 20 and the slurry 40 generates a vortex 82 in the slurry 40. The center of the vortex 82 is locally at low pressure, causing the liquid in the slurry 40 to evaporate and generate air bubbles 81. The slurry 40 flows downstream while entraining the air bubbles 81. As the slurry 40 flows downstream, the air bubbles 81 are compressed by the surrounding liquid and collapse.

[0030] When the bubbles 81 generated by cavitation collapse, a large impact force is generated. This impact force separates the mineral particles contained in the slurry 40 from other particles. In this specification, "separating the mineral particles from other particles" includes not only separating mineral particles attached to or contained within soil particles such as sand particles from the soil particles (hereinafter referred to as "disintegration"), but also crushing the mineral particles and dividing them into a plurality of smaller particles (hereinafter referred to as "crushing"). In this embodiment, the impact force generated when the bubbles 81 collapse causes disintegration, crushing, or both of the mineral particles.

[0031] The bubbles 81 caused by cavitation are generated one after another in the slurry 40 while the slurry 40 flows in contact with the pressurized liquid 20, and then collapse. Therefore, the impact force caused by the collapse of the bubbles 81 can be applied to the particles in the slurry 40 throughout the time the slurry 40 flows.

[0032] As shown in FIG. 1, in the flow path 30, the region Rc configured to generate cavitation by the above mechanism is called the "cavitation generation region." The cavitation generation region Rc is located downstream of a position (hereinafter, "slurry supply position") P where the slurry 40 is supplied from the slurry supply unit 4. In the cavitation generation region Rc, the slurry 40 flows around the pressurized liquid 20, as shown in FIGS. 2A and 2B. The decomposition of mineral particles in the slurry 40 mainly occurs in the cavitation generation region Rc. Downstream of the cavitation generation region Rc, the slurry 40 and the pressurized liquid 20 are mixed to form a mixture 70. The mixture 70 is discharged from the discharge port 37 and sent to, for example, a classification device.

[0033] In the example shown in Fig. 1, no air inlet is provided upstream of the slurry supply position P in the flow path 30 to allow air to flow in from the outside. In this embodiment, the air bubbles generated by cavitation are vaporized liquid in the slurry 40. Since cavitation is not caused by air flowing in from the outside, it is not necessary to provide an air inlet in the flow path 30. Note that an air inlet may be provided in the flow path 30 as long as it does not hinder the generation of cavitation due to a flow velocity difference.

[0034] In this embodiment, the cavitation generated by the above-mentioned mechanism is utilized, so that separation (for example, sludge pulverization and crushing) of mineral particles can be performed more efficiently and more reliably.

[0035] Incidentally, Patent Document 1 describes washing of sediment using cavitation generated by a method different from that of the present invention. In Patent Document 1, pressurized fluid is ejected from a jetting part to generate bubbles, and sediment is supplied to an area in the vicinity of the jetting part where the bubbles exist. However, the inventors of the present application have found that with such a configuration, it is difficult to reliably supply sediment to the limited area where the bubbles exist. In addition, the sediment can only receive the impact force in a limited area (area where the bubbles exist) in the vicinity of the jetting part. For this reason, it is difficult to efficiently apply an impact force to the sediment sufficient to sufficiently separate radioactive materials from the sediment or to crush mineral particles.

[0036] In contrast, in this embodiment, cavitation is generated at the interface 20s between the flow of the slurry 40 containing soil and the flow of the pressurized liquid 20, so that bubbles can be generated not only in the region close to the outlet of the pressurized liquid 20 but also along the length of the flow path 30. In addition, since the slurry 40 flows while entraining air bubbles, the impact force caused by the collapse of the air bubbles can be more reliably applied to the slurry 40. Furthermore, since the generation and collapse of air bubbles are repeated while the slurry 40 and the pressurized liquid 20 flow in contact with each other, high impact forces are repeatedly applied to the particles in the slurry 40. Therefore, the separation of mineral particles can be further promoted toward the downstream side of the flow path 30.

[0037] Furthermore, in the device of Patent Document 1, the area in which the bubbles exist is limited, and particles with relatively small diameters may not be easily affected by the cavitation effect. In contrast, in the soil treatment device 1 of this embodiment, the slurry 40 moves forward while entraining air bubbles, so the effect of cavitation is likely to reach even the small particles contained in the slurry 40. In addition, in the soil treatment device 1 of this embodiment, by reducing the amount of liquid relative to the soil in the slurry 40, the impact force of the collapse of the air bubbles 81 can be applied more efficiently to the mineral particles.

[0038] [Soil treatment method] The soil treatment method of this embodiment includes a step of generating cavitation by the mechanism described above with reference to Figs. 2A and 2B (hereinafter, "cavitation generating step"). In the cavitation generating step, pressurized liquid is ejected toward a slurry in which soil is mixed with liquid, and a flow rate difference is generated at the interface between the pressurized liquid and the slurry, thereby generating cavitation (see Figs. 2A and 2B). The cavitation generating step can be performed, for example, using a soil treatment device 1 shown in Fig. 1. Note that the device used in this step is not limited to the device shown in Fig. 1, as long as it is configured to generate cavitation by utilizing the flow rate difference between the slurry and the pressurized liquid.

[0039] 3A and 3B are schematic diagrams illustrating soil treatment methods I and II according to the first embodiment, respectively. As a reference example, FIG. 12 shows a schematic diagram of a treatment method in which only classification treatment is performed.

[0040] 3A, 3B, and FIG. 12 of the reference example show an example in which soil 10, which is the object to be treated, includes gravel particles (particle size: for example, 2 mm or more) 11, sand particles (particle size: for example, 74 μm or more and less than 2 mm) 12, and silt and clay particles (particle size of silt particles: for example, 5 μm or more and less than 74 μm, and particle size of clay particles: for example, less than 5 μm) 13. These particles include mineral particles (hereinafter referred to as "radioactive substance-containing mineral particles") 15 to which radioactive substances such as radioactive cesium are adsorbed. The particle size of the radioactive substance-containing mineral particles 15 is not particularly limited. Here, radioactive substance-containing mineral particles 15 of various particle sizes, from relatively small ones to ones of 2 mm or more, are shown as examples. Some of the radioactive substance-containing mineral particles 15 may be attached to or included in soil particles (for example, gravel particles 11, sand particles 12, etc.) larger in particle size than the particle.

[0041] For ease of understanding, the method of the reference example shown in FIG. 12 will be described first. In the reference example, the above soil 10 is classified into a coarse fraction having a particle size of 75 μm or more and a fine fraction having a particle size of less than 75 μm. In this case, the radioactive substance-containing mineral particles 15 having a particle size of 75 μm or more are classified into the coarse fraction. On the other hand, the radioactive substance-containing mineral particles 15 having a particle size of less than 75 μm can be classified into the fine fraction. However, as shown in the figure, some of the radioactive substance-containing mineral particles 15 having a particle size of less than 75 μm may be classified into the coarse fraction together with the sand particles 12 and gravel particles 11 in a state of being attached to or contained within these particles 11, 12. As a result, it is difficult to sufficiently lower the concentration of radioactive substances in the coarse fraction after classification.

[0042] In contrast, in the soil treatment methods I and II of the present embodiment, a cavitation generation step is performed before classification, which allows the amount of radioactive material contained in the coarse fraction after classification to be reduced compared to the method of the reference example shown in FIG.

[0043] <Soil treatment method I> As shown in Fig. 3A, in the cavitation generation step in soil treatment method I, radioactive substance-containing mineral particles 15 are separated from other particles by the impact force generated when the bubbles collapse. As a result, the radioactive substance-containing mineral particles 15 attached to soil particles such as sand particles 12 and gravel particles 11 are separated from the soil particles (disintegration). In addition, the radioactive substance-containing mineral particles 15 and particles of other minerals are crushed into smaller particles 14 (crushing). After crushing the radioactive substance-containing mineral particles 15, the radioactive substances may be in a state of being adsorbed to the particles 14 or in a state of being desorbed from the particles 14.

[0044] In the cavitation generation process, as shown in the figure, it is sufficient that at least the part of the radioactive substance-containing mineral particle 15 to which the radioactive substance is adsorbed is crushed. For example, when the radioactive substance-containing mineral particle 15 is mica, the radioactive substance is mainly adsorbed or fixed to the part of the mica particle that has been altered by weathering (weathered part), so it is sufficient that at least the weathered part is crushed. The weathered part is located, for example, near the surface of the mica particle. The unweathered part is harder than the weathered part and is therefore less likely to be crushed, and can be discharged from the flow path while maintaining a certain degree of size. Similarly, soil particles that are harder than the weathered part of mica are also less likely to be crushed, so they are not crushed as small as the weathered part, and can be discharged from the flow path while maintaining a certain degree of size.

[0045] After the cavitation generation step, the mixture of the treated slurry and the pressurized liquid is classified into a large particle group and a small particle group having a particle size smaller than that of the large particle group. In this processing method, the particle size of the large particle group is, for example, a particle group having a particle size equal to or larger than that of a radioactive substance-containing mineral particle. The small particle group is, for example, a particle group having a particle size smaller than that of a radioactive substance-containing mineral particle. The small particle group includes particles 14 obtained after the radioactive substance-containing mineral particle 15 is crushed. The radioactive substance is in a state of being adsorbed to the particle 14 or desorbed from the particle 14, and is therefore included in the small particle group. Classification may be performed based on the particle size of the radioactive substance-containing mineral particle 15 having a relatively small particle size (for example, the particle size of silt or clay), thereby making it possible to make the particle size at the classification point smaller. The particle size at the classification point may be less than 75 μm, for example, 20 μm or less.

[0046] According to the soil treatment method I, the radioactive material-containing mineral particles 15 are separated from the larger soil particles by the cavitation generation process. The larger radioactive material-containing mineral particles 15 are also crushed to become smaller particles 14. Therefore, the radioactive material can be more reliably separated into small particle groups by the subsequent classification. Therefore, the concentration of the radioactive material in the large particle group can be further reduced (i.e., the decontamination rate can be increased) than in the method of the reference example (FIG. 12). As an example, it is possible to reduce the radioactive concentration of soil with a radioactivity concentration of over 8000 Bq to a concentration (for example, 1000 Bq / kg or less) that is significantly below the reusable concentration of 8000 Bq / kg. In addition, since there is no need to perform advanced classification, washing, or other processes after this treatment, the equipment, cost, number of processes, and amount of water used for soil treatment can be reduced.

[0047] Furthermore, according to soil treatment method I, the radioactive substance-containing mineral particles 15 are crushed by the cavitation generation process, so that in the subsequent classification process, the particle size at the classification point can be made smaller, and the volume of soil with a high concentration of radioactive substances (small particle group) can be made smaller (i.e., the volume reduction rate can be increased).

[0048] <Soil treatment method II> In the soil treatment method II, at least the sludge treatment is carried out by the cavitation generation step. As shown in Fig. 3B, in the cavitation generation step, the impact force generated when the bubbles collapse separates the radioactive material-containing mineral particles 15 that were attached to (or contained within) the soil particles such as sand particles 12 and gravel particles 11 from the soil particles (sludge treatment).

[0049] Next, a classification step is performed in which the mixture of the slurry and the pressurized liquid is classified into a large particle group and a small particle group, as in the soil treatment method I. The large particle group is, for example, a particle group including soil particles (sand particles 12 or gravel particles 11 in this example) to which radioactive substance-containing mineral particles 15 were attached before thawing. The small particle group is, for example, a particle group including radioactive substance-containing mineral particles 15. The small particle group includes radioactive substance-containing mineral particles 15 separated from the soil particles. The particle size at the classification point is, for example, 75 μm.

[0050] According to the soil treatment method II, the radioactive material-containing mineral particles 15 are separated from the larger soil particles by the cavitation generation process, so that the radioactive material can be more reliably separated into small particle groups by the subsequent classification. Therefore, the concentration of radioactive material in the large particle group can be further reduced (i.e., the decontamination rate can be increased) than in the method of the reference example (FIG. 12).

[0051] (effect) As shown in Fig. 1 to Fig. 2B, the soil treatment device 1 of this embodiment is configured such that the ejection unit 2 and the slurry supply unit 4 generate a flow rate difference at the interface 20s between the pressurized liquid 20 and the slurry 40 in the flow path 30 of the treatment unit 3 to generate cavitation. With this configuration, it is possible to perform processes such as sludge disintegration and crushing, which separate mineral particles from other particles, by the impact force generated when bubbles caused by cavitation collapse. As a result, it is possible to easily remove radioactive materials.

[0052] 2A and 2B, the above-mentioned configuration allows the impact force caused by the collapse of bubbles to be applied to mineral particles more efficiently than in a conventional device (such as the device described in Patent Document 1). Therefore, the mineral particles can be separated from other particles more reliably.

[0053] Furthermore, with the above configuration, the decomposition of mineral particles can be promoted while the soil-containing slurry 40 and the pressurized liquid 20 are flowing in the same direction, which allows for continuous treatment and allows for a large amount of soil to be treated per hour (for example, 12 t / hour or more).

[0054] The emission section 2 and the slurry supply section 4 may be configured to perform a sludge deflocculation process in which radioactive material-containing mineral particles 15 attached to (or encapsulated within) soil particles such as sand particles 12 are separated from the soil particles by the impact force generated when bubbles generated by cavitation collapse, as shown in Fig. 3B. With this configuration, the amount of radioactive material contained in the large particle group after classification can be reduced in the subsequent classification process.

[0055] The emission section 2 and the slurry supply section 4 may be configured to perform a crushing process in which the radioactive substance-containing mineral particles 15 are crushed into particles 14 having a particle size smaller than that of the radioactive substance-containing mineral particles 15 by the impact force generated when the bubbles generated by cavitation collapse, as shown in FIG. 3A. The soil treatment device 1 can repeatedly apply a strong impact force to the mineral particles, and therefore can have a high crushing ability. With this configuration, the radioactive substance contained in the large particle group after classification can be further reduced in the subsequent classification process. In addition, even if the particle size at the classification point is made small (for example, less than the particle size of the radioactive substance-containing mineral particles 15), it becomes possible to remove the radioactive substance. Therefore, the volume of the small particle group having a high concentration of radioactive substance can be reduced.

[0056] The ejection section 2 and the slurry supply section 4 may be configured to separate the radioactive material-containing mineral particles from the soil particles by the impact force generated when the bubbles generated by cavitation collapse, and then crush the separated radioactive material-containing mineral particles. With this configuration, the sludge deflocculation process and the crushing process can be carried out simultaneously while the slurry 40 flows in contact with the pressurized liquid 20. Therefore, there is no need to prepare separate devices for sludge deflocculation and crushing, and therefore the cost, number of steps, time, etc. required for the process can be further reduced.

[0057] According to this embodiment, a soil treatment method including a cavitation generation step is provided. In the cavitation generation step, a pressurized liquid is ejected into a slurry obtained by mixing soil with a liquid, and a flow rate difference is generated at the interface between the pressurized liquid and the slurry, thereby generating cavitation. As shown in FIG. 3A and FIG. 3B, the impact force generated when bubbles generated by cavitation collapse separates mineral particles 15 to which radioactive substances are adsorbed from other particles. For example, the impact force performs sludge disintegration, crushing, or both. This makes it easier to remove radioactive substances, thereby making it possible to increase the decontamination rate and / or volume reduction rate.

[0058] The radioactive material adsorbed to the mineral particles may be, for example, radioactive cesium, and the mineral particles to which the radioactive cesium is adsorbed may be, for example, mica particles. It has been reported that most of the radioactive cesium is adsorbed or fixed to mica. Therefore, by crushing and disintegrating the mica particles to which the radioactive cesium is adsorbed, the radioactive cesium can be more effectively removed from the soil. As an example, it is possible to increase the decontamination rate, which was about 70% in the conventional classification process, to 80% or more, preferably to about 90%.

[0059] In the soil treatment method of this embodiment, the ratio of the weight of the liquid used to the weight of the soil to be treated (hereinafter referred to as the "total solid-liquid ratio") is, for example, 5 or more and 15 or less, preferably 10 or less. "Weight of soil" refers to the dry weight of the soil. "Weight of liquid used" refers to the total weight of liquid used in treatment, and includes the weight of liquid contained in slurry 40 (Figure 1) and the weight of pressurized liquid 20 (Figure 1). By keeping the total solid-liquid ratio to 15 or less, the costs associated with soil treatment and disposal of the liquid used can be reduced, and practicality can be increased.

[0060] The weight ratio of the pressurized liquid 20 (FIG. 1) to the soil is not more than 10, and preferably not more than 6. The weight ratio of the liquid contained in the slurry 40 to the soil (slurry solid-liquid ratio) is not more than 5, and preferably not more than 3. By keeping the amount of liquid contained in the slurry 40 small, the impact force caused by the collapse of bubbles is more easily applied to the particles in the slurry 40, and the separation of the mineral particles can be efficiently promoted.

[0061] In a conventional treatment method, for example, after normal classification using a trommel or the like, advanced classification may be performed by applying mechanical impact force to the coarse particles. In such a method, the amount of liquid used increases, and the total solid-liquid ratio exceeds, for example, 20. Since the liquid (water) used in the treatment contains radioactive materials, the storage and treatment of the liquid will be even more costly. In contrast, in this embodiment, before classification, a cavitation generation process for thawing and crushing is performed on the entire soil. In the classification process performed after that, the soil after thawing is classified, so there is no need to perform advanced classification as in the conventional method. Therefore, the total solid-liquid ratio can be made smaller than in the conventional method.

[0062] 3A and 3B show an example of a method for treating soil 10 containing clay, silt, sand, and gravel, but the soil treatment method of this embodiment can also be applied to treatment of only coarse particles (sand, gravel, etc.) or only fine particles (clay, silt) after normal classification. The soil treatment method of this embodiment can also be applied to soil that has been previously subjected to sludge thawing to break down mineral particles.

[0063] In the cavitation generation process shown in Figures 3A and 3B, it is shown that the mineral particles are thawed and crushed, but due to the impact force caused by the collapse of the bubbles, not only the mineral particles are thawed, but also lumps such as clay lumps in the slurry may be loosened. In addition, particles other than mineral particles may be crushed, and large particles such as gravel particles may be rounded off and polished. The changes that have occurred in the mineral particles and other particles can be confirmed, for example, by observing the soil before and after the cavitation generation process and comparing the particle size distribution.

[0064] Second Embodiment 4 is a schematic cross-sectional view showing a soil treatment device according to a second embodiment of the present invention. In the following, differences from the soil treatment device according to the first embodiment will be mainly described, and overlapping descriptions will be omitted as appropriate.

[0065] The soil treatment apparatus 1a shown in Fig. 4 comprises a treatment section 3 having a flow path 30, an ejection section 2 that ejects pressurized liquid 20, a slurry supply section (sometimes referred to as a "slurry supply device") 4 that supplies slurry 40, a classification section 7, and a control section 8. The slurry supply section 4 comprises a liquid supply section 5, a soil supply section 6, and a mixing section. The mixing section is configured to mix the liquid 50 supplied from the liquid supply section 5 with the soil 10 supplied from the soil supply section 6. In this example, a hopper 41 functions as the mixing section.

[0066] In the soil treatment device 1a, the soil 10, which is the object to be treated, is supplied to a hopper 41 by a soil supply unit 6. A liquid (here, water) 50 to be mixed with the soil 10 is supplied to the hopper 41 by a liquid supply unit 5. The soil 10 and the liquid 50 separately supplied to the hopper 41 are mixed on the inner wall of the hopper 41 to become a slurry 40, which is supplied to a flow path 30 of a treatment unit 3. In the flow path 30 of the treatment unit 3, a pressurized liquid 20 is ejected from an ejection unit 2 onto the slurry 40. In the flow path 30, a process is performed in which mineral particles in the slurry 40 are separated from other particles by using cavitation, as in the above-mentioned embodiment. The treated slurry 40 and the pressurized liquid 20 are discharged from an outlet 37 of the flow path 30 and sent to a classification unit 7.

[0067] The specific configuration of each component of the soil treatment device 1a will be described below. In the following description, the treatment conditions, size, capacity, etc. of each component when treating soil 10 at 1 kg / min may be exemplified. Note that the treatment conditions, size, capacity, etc. of each component may be appropriately selected depending on the type of soil, the amount of soil to be treated, etc., and are not limited to the exemplified values.

[0068] (Output part) The ejection unit 2 includes a high-pressure ejector equipped with a nozzle 22 having an ejection port at its tip, a triple-plunger type high-speed jet pump (capacity: for example, 6.3 L / m×5.5 MPa×0.83 kW×100 V) 23, and a pipe 24 located upstream of the nozzle 22 and fluidly connecting the high-speed jet pump 23 and the nozzle 22. The nozzle 22 is configured so that its cross-sectional area increases from the ejection port toward the pipe 24.

[0069] The high-pressure ejector is set, for example, to move at high speed along a portion of the flow path 30 extending in the X direction. In this embodiment, the high-pressure ejector ejects the pressurized liquid (here, pressurized water) 20 of 4 MPa along the X direction at a flow rate of 0.1 liters / second. The speed of the pressurized water is, for example, 50 meters per second.

[0070] (Processing section) The flow path 30 of the processing section 3 has a plurality of portions 31 to 34 having different cross-sectional areas. The cross-sectional area of ​​the flow path 30 refers to the cross-sectional area perpendicular to the extending direction of the flow path 30. In the example shown in Fig. 4, a plurality of pipes having different diameters are connected to form the flow path 30, but these may be formed integrally.

[0071] In this embodiment, the flow path 30 has an expansion section 36 that expands the cross-sectional area of ​​the flow path 30. The expansion section 36 is disposed downstream of the slurry supply position P to which the slurry supply section 4 is connected in the flow path 30. The slurry 40 is at a lower pressure downstream of the expansion section 36 than upstream of the expansion section 36, and the flow rate difference between the slurry 40 and the pressurized liquid 20 is larger, so that the amount of bubbles generated by cavitation can be increased. Therefore, by providing the expansion section 36, the cavitation generation region Rc in the flow path 30 can be made longer.

[0072] 4, the flow path 30 includes a first portion 31, a second portion 32 located downstream (+X side) of the first portion 31 and having a smaller cross-sectional area than the first portion 31, and a third portion 33 located downstream of the second portion 32 and having a larger cross-sectional area than the second portion 32. A slurry supply unit 4 is connected to the first portion 31. The downstream end of the second portion 32 and the upstream end of the third portion 33 form an enlarged portion 36 that enlarges the cross-sectional area of ​​the flow path 30.

[0073] 5A to 5C, the function of each portion of the flow channel 30 will be specifically described. Fig. 5A is a schematic enlarged cross-sectional view showing a portion of the flow channel 30. Figs. 5B and 5C are enlarged cross-sectional views taken along lines VB-VB and VC-VC shown in Fig. 5A, respectively.

[0074] In the illustrated example, the cross-section of the flow path 30 is, for example, circular. In this case, the diameter D1 of the first portion 31 and the diameter D3 of the third portion 33 are larger than the diameter D2 of the second portion 32 (D2 < D1, D3). From the slurry supply position P of the first portion 31 to at least a part of the third portion 33, it extends in the ejection direction (X direction) of the pressurized liquid 20. In FIG. 4, the diameters of each of the first portion 31 to the third portion 33 are substantially constant, but the diameter of each portion may be set so as to have a function as described below, and does not have to be substantially constant.

[0075] In the present embodiment, the cavitation generation region Rc includes a region that extends in the X direction from the slurry supply position P of the flow path 30 to at least a part of the third portion 33. In the illustrated example, from the slurry supply position P to the position where the pressurized liquid 20 collides with the inner wall of the pipe of the third portion 33 is the cavitation generation region Rc.

[0076] <First portion> The first portion 31 includes a region where the pressurized liquid 20 from the ejection portion 2 first collides with the slurry 40 at atmospheric pressure. After the collision, the pressurized liquid 20 travels downstream through the slurry 40 (see FIG. 2B). In the first portion 31, since the flow velocity difference between the slurry 40 and the pressurized liquid 20 is large, a vortex 82 is easily formed due to the flow velocity difference, and the generation amount of bubbles 81 is large.

[0077] The first portion 31 has a sufficient cross-sectional area so that the pressurized liquid 20 can flow downstream through the slurry 40. As shown in FIG. 5A, the first portion 31 may be configured to have a space 80 above the slurry 40 such that the slurry 40 collided by the pressurized liquid 20 can escape. In this example, the diameter (inner diameter) D1 of the first portion 31 is, for example, 27.0 mm.

[0078] The length L1 along the X direction from the slurry supply position P to the tapered portion 34 in the first part 31 may be smaller than each of the lengths L2 and L3 along the X direction of the second part 32 and the third part 33 (L1 < L2, L3). In the first part 31, since the slurry 40 can easily escape into the upper space 80, the contact area between the slurry 40 and the pressurized liquid 20 tends to be small. By keeping the length L1 of the first part 31 smaller than that of the second part 32 and the third part 33, the contact area (the area of the interface 20s) for generating cavitation can be increased more quickly.

[0079] <Second part> As shown in FIG. 5B, the second part 32 is configured such that the slurry 40 flows so as to generally fill the periphery of the pressurized liquid 20. The space 80 above the slurry 40 becomes narrower than that of the first part 31. Since the space 80 becomes narrower, it becomes difficult for the slurry 40 to escape from the impact force at the time of the collapse of the bubbles 81, and the impact force easily acts on the particles in the slurry 40. In addition, the slurry 40 can be more surely brought into contact with the peripheral surface of the pressurized liquid 20. As a result, the area of the interface 20s where the bubbles 81 are generated by cavitation can be increased. Further, since the radial thickness t of the slurry 40 is suppressed to be smaller than that of the first part 31, the impact force at the time of the collapse of the bubbles 81 is easily transmitted to the entire thickness t of the slurry 40.

[0080] The cross-sectional area of the second part 32 may be set such that the flow of the slurry 40 is formed around the flow (jet flow) of the pressurized liquid 20. As shown in FIG. 5, the diameter D2 of the second part 32 is set to be at least larger than the diameter Dj of the pressurized liquid 20 (jet flow). On the other hand, if the diameter D2 becomes too small, the flow rate of the slurry 40 may decrease or the slurry 40 may be clogged. To suppress this, the diameter (inner diameter) D2 may be 1 / 2 or more of the diameter D1. In this example, the diameter D2 of the second part 32 is, for example, 21.6 mm.

[0081] The cross-sectional area of ​​the second portion 32 may be set to be larger than the cross-sectional area of ​​the pipe 24 (FIG. 4) of the ejection unit 2. This makes it possible to more reliably make the cross-sectional area of ​​the second portion 32 larger than the cross-sectional area of ​​the pressurized liquid 20. Therefore, as shown in FIG. 5B, a flow of the slurry 40 is easily formed around the pressurized liquid 20.

[0082] When the flow rate of the slurry 40 is substantially constant, the cross-sectional area of ​​the slurry 40 becomes smaller in the second portion 32, and therefore the slurry 40 accelerates. As a result, the difference in flow rate between the slurry 40 and the pressurized liquid 20 gradually decreases, and cavitation becomes less likely to occur.

[0083] By providing the second portion 32, the pressure of the slurry 40 is released in the following third portion 33, so that it is possible to promote the generation of bubbles by cavitation. The length L2 of the second portion 32 may be smaller than the length L3 of the third portion 33, for example. This allows the slurry 40 to move more quickly to the third portion 33 where the amount of bubbles generated increases.

[0084] <3rd part> In the third portion 33, the cross-sectional area of ​​the flow path 30 increases, so that the pressure of the slurry 40 is suddenly released, generating air bubbles 81. In addition, the flow rate of the slurry 40 decreases, so that the flow rate difference between the slurry 40 and the pressurized liquid 20 increases again, making it easier for vortexes 82 to form, and increasing the number of air bubbles 81. In this way, in the third portion 33, the amount of air bubbles 81 generated increases, so that the impact force generated when the air bubbles 81 collapse can further promote sludge thawing and crushing of the soil in the slurry 40.

[0085] In the third section 33, since the flow rates of the pressurized liquid 20 and the slurry 40 are decreasing, they are more susceptible to the influence of the Coriolis force. As shown in FIG. 5C, in the Northern Hemisphere, the flow of the pressurized liquid 20 is affected by the Coriolis force and bends to the right with respect to the traveling direction (+X direction). Also, as shown in the enlarged view in FIG. 5C, among the particles in the slurry 40, the relatively heavy particles p1 are more susceptible to the influence of the Coriolis force and thus tend to gather on the right side of the traveling direction. In this way, the relatively light particles p2 in the slurry 40 can flow separately from the relatively heavy particles p1, so that the impact force at the time of the collapse of the bubbles 81 also easily acts on the light particles p1. Therefore, mineral particles such as relatively light mica can be crushed more efficiently. The mica that has been deslimed or crushed in the first section 31 and the second section 32 can be further crushed in the third section 33. Or, mica that was not sufficiently crushed due to the cavitation effect being difficult to reach in the first section 31 and the second section 32 can be crushed in the third section 33.

[0086] The diameter D3 of the third section 33 may be, for example, not more than twice the diameter D2 of the second section 32 (D2 < D3 ≤ 2×D2). Thereby, clogging is less likely to occur at the downstream end of the second section 32. The diameter (inner diameter) D3 of the third section 33 is, for example, 41.6 mm.

[0087] A tapered portion whose diameter increases toward the third section 33 may be provided between the second section 32 and the third section 33. In this case, the diameter D3 of the third section 33 can be made even larger.

[0088] The length L3 of the third portion 33 may be greater than each of the length L1 of the first portion 31 and the length L2 of the second portion 32. The length L3 may be greater than the length L4 from the slurry supply position P to the upstream end of the third portion 33 in the flow path 30. By increasing the length L3 of the third portion 33, it is possible to further promote sludge disintegration and crushing (particularly crushing) by cavitation. In particular, it is possible to perform efficient crushing using the Coriolis force. Furthermore, even if the soil contains relatively large (e.g., particle size: 2 mm or more) mineral particles, the weathered parts of the particles can be sufficiently crushed.

[0089] In the third portion 33, a portion located downstream of the cavitation generation region Rc extends, for example, in the -Z direction and is connected to the classifier 7. In the example shown in FIG. 4, the pipe constituting the third portion 33 is a bent pipe that extends in the X direction and then bends downward. Alternatively, the bent pipe constituting the third portion 33 may be bent in the horizontal direction and extend to the classifier 7. Alternatively, the third portion 33 may be formed using a straight pipe extending in the X direction. In this case, a discharge port, for example, facing vertically downward, may be provided on the side surface of the third portion 33.

[0090] It is also possible to provide a wall surface to block the flow path of the third portion, and collide the pressurized liquid and slurry against the wall surface to disintegrate and crush the mineral particles. However, according to the results of the study by the inventors of the present application, since the mineral particles are dispersed in the liquid, the impact force due to the collision is unlikely to be applied to the mineral particles themselves. For this reason, it is difficult to obtain a sufficient effect (especially a sufficient crushing ability). Rather, as described above, by making the length L3 of the third portion 33 larger than the other portions and utilizing the Coriolis force together with the cavitation effect, the crushing ability of the mineral particles can be more effectively improved.

[0091] The inventor of the present application conducted a confirmation experiment to confirm the above-mentioned effect of the third portion 33. In the confirmation experiment, a fringe was installed at the position R shown in FIG. 5C, a treatment was performed by the soil treatment device 1a, and the surface condition of the fringe after treatment was observed. FIG. 6 is a schematic top view of the fringe used in the experiment, showing the surface located on the flow path side. As a result of the observation, it was confirmed that the central portion 35c of the surface of the fringe 35 was worn. This is considered to be due to the impact of the high-pressure water. In addition, in the central portion 35c, rust was observed in the right-side portion 352 located on the right side of the traveling direction of the pressurized liquid, but rust was not observed in the left-side portion 351 located on the left side. This is considered to be because the right-side portion 352 was formed with unevenness due to the collision of relatively heavy particles. From this result, it was confirmed that in the third portion of the flow path, the slurry flows while being separated into heavy particles and light particles by the Coriolis force.

[0092] <Tapered section> As shown in FIGS. 4 and 5A, the flow path 30 may further have a tapered portion 34 between the first portion 31 and the second portion 32, the cross-sectional area of ​​which decreases from the first portion 31 toward the second portion 32.

[0093] Inside the tapered portion 34, a large vortex 82 like that in the first portion 31 is unlikely to occur. Therefore, the slurry 40 can flow more smoothly into the second portion 32 having a smaller diameter. By providing the tapered portion 34, the slurry 40 or the soil in the slurry 40 is unlikely to clog the downstream end of the first portion 31. Therefore, even when the soil contains small particles (particles such as clay and silt) or the soil has a wide particle size distribution, it is possible to suppress a decrease in the treatment speed due to clogging. The inclination angle α of the inner surface of the tapered portion 34 is not particularly limited, but may be, for example, 45° or less. This makes it possible to more effectively suppress clogging.

[0094] (Slurry supply section) As shown in FIG. 4, the slurry supplying unit 4 includes a hopper 41, a liquid supplying unit 5, and a soil supplying unit 6.

[0095] <Hopper> The hopper 41 has an upper opening 411 and a lower opening 412. The hopper 41 has a tapered shape in which the inner diameter decreases from the upper opening 411 toward the lower opening 412. The upper opening 411 is, for example, an opening facing vertically upward. The lower opening 412 is fluidly connected to the first portion 31 of the flow path 30 of the processing unit 3. In this embodiment, the hopper 41 is in the shape of a truncated cone, but may be in the shape of a truncated polygonal pyramid.

[0096] The hopper 41 is configured to mix the liquid 50 and the soil 10 supplied separately from the upper opening 411 on the inner wall of the hopper 41 to form a slurry 40, and to cause the slurry 40 to flow out from the lower opening 412. The slurry 40 flowing out from the lower opening 412 is supplied to the flow path 30 of the treatment section 3.

[0097] <Liquid supply section> The liquid supply unit 5 supplies liquid 50 from the upper opening 411 toward the inner wall of the hopper 41. The liquid 50 is, for example, water. The liquid supply unit 5 includes a centrifugal type submersible pump (capacity: for example, 40 L / m×4.2 m×0.1 kW×100 V) 53 and a liquid line 51 connected to the submersible pump 53. The liquid line 51 is provided with a liquid supply port that supplies the liquid to the hopper 41. The liquid supply unit 5 is set to supply water to the hopper 41 at a flow rate of, for example, 0.05 liters / second.

[0098] The liquid line 51 has a portion that extends along at least a part of the periphery of the upper opening 411 of the hopper 41. In the example shown in FIG. 4, the liquid line 51 has an annular portion 511 that extends in an annular shape along the periphery of the upper opening 411. The annular portion 511 is provided with a plurality of liquid supply ports that supply the liquid 50 toward the inner wall of the hopper 41. The "annular" is not limited to a circular annular shape, but also includes a polygonal annular shape such as a rectangular annular shape. The periphery of the upper opening 411 may be circular, and the annular portion 511 may be a rectangular annular shape. In this example, the portion of the liquid line 51 that extends along the periphery of the upper opening 411 is annular, but may be arc-shaped, linear, or the like.

[0099] When the soil treatment apparatus 1a is in operation, the liquid supply rate (here, the water supply rate) from the liquid line 51 to the hopper 41 is, for example, 0.05 liters / second. The supply rate is not particularly limited and is set appropriately depending on the soil supply rate, the flow rate of the pressurized liquid, etc. It is also possible to change the liquid supply rate through the control unit 8 during operation depending on the operating state of the soil treatment apparatus, etc.

[0100] <Soil Supply Division> The soil supplying unit 6 supplies soil 10 from the upper opening 411 toward the inner wall 41s of the hopper 41. In the example shown in FIG. 4, the soil supplying unit 6 includes a soil storage tank 61 that stores the soil 10, and a conveying device 62 that conveys the soil 10 supplied from the soil storage tank 61. The conveying device 62 is, for example, a belt conveyor. The soil 10 supplied to the conveying device 62 is conveyed to a predetermined input position Q above the hopper 41, and is supplied from the input position Q to the hopper 41. The supply rate of the soil is, for example, 1 kg / min.

[0101] Fig. 7A is a schematic top perspective view of the conveying device and the hopper, and Fig. 7B is a schematic cross-sectional view taken along line VIIB-VIIB shown in Fig. 7A.

[0102] 7A and 7B, the conveying device 62 includes a belt 621 that conveys the soil 10 above the hopper 41 to a loading position Q. The loading position Q is located inside the upper opening 411 of the hopper 41 in a plan view. The belt 621 is configured to proceed in one direction (here, the -X direction) to the loading position Q, and then make a downward U-turn at the loading position Q and proceed in the opposite direction (here, the +X direction). As a result, the soil 10 on the belt 621 is supplied from the loading position Q toward the inner wall 41s of the hopper 41.

[0103] The position and conveying speed of the conveying device 62 are set so that the soil 10 is supplied, for example, to a region 410 near the upper end of the inner wall 41s of the hopper 41. The height of the region 410 in the Z direction from the lower opening 412 of the hopper 41 is, for example, ½ or more of the height H of the hopper 41. This makes it possible to lengthen the distance over which the soil 10 flows on the inner wall 41s together with the liquid 50, and therefore the soil 10 and the liquid 50 can be mixed sufficiently.

[0104] In this embodiment, as shown in FIG. 7B, heavy and light particles of the soil 10 can be dropped to different positions on the inner wall 41s by utilizing the inertial force caused by the transport. For example, when the soil 10 contains gravel particles 11, sand particles 12, and mineral particles 13 in descending order of weight, the heavier particles fall toward the upstream side (+X side) in the transport direction. In this way, when the soil 10 is introduced, the lumps of the soil 10 can be loosened to facilitate mixing with the liquid 50. Therefore, a more uniform slurry 40 can be formed. In addition, it is possible to more effectively prevent the soil from being supplied to the treatment unit 3 with lumps of soil remaining.

[0105] 7A, the input position Q is a position offset from the center C of the lower opening 412 in a plan view. By offsetting the input position Q from the center C of the lower opening 412, the soil 10 can be more reliably supplied to the inner wall 41s of the hopper 41. Therefore, it is possible to prevent the input soil 10 particles from being sent directly from the lower opening 412 to the treatment section 3 without being mixed with the liquid 50.

[0106] The input position Q may be located downstream of the center C of the lower opening 412 in the conveying direction of the conveying device 62 (-X direction in Figs. 7A and 7B) in a plan view. With this configuration, the particles in the soil 10 tend to fly out from the input position Q toward the opposing part of the inner wall 41s due to inertial force and fall onto the inner wall 41s. This makes it possible to prevent the particles from falling into the lower opening 412 without contacting the inner wall 41s. Furthermore, even relatively heavy particles tend to fall into the region 410 near the upper end of the inner wall 41s, so that the particles can be sufficiently mixed with the liquid 50.

[0107] The conveying device 62 may further include an adjustment member 622 for adjusting the height of the soil 10, located upstream of the input position Q on the belt. The adjustment member 622 extends across the width of the belt 621 in a plan view. The lower end of the adjustment member 622 is disposed at a predetermined distance t in the Z direction from the upper surface of the belt 621. By providing the adjustment member 622, the height of the soil 10 on the belt 621 can be kept below the distance t. This makes it possible to prevent clogging of the treatment section 3 due to an increase in the amount of soil 10 supplied. In addition, the amount of soil 10 supplied to the hopper 41 per unit time can be kept approximately constant.

[0108] <Classification Department> As shown in FIG. 4, a mixture 70 obtained by mixing the pressurized liquid 20 and the slurry 40 is sent to the classification section 7 from the outlet 37 of the processing section 3. The classification section 7 classifies the mixture 70 into a large particle group having a particle size equal to or larger than a predetermined classification point, and a small particle group having a particle size less than the classification point and having a higher radioactive concentration than the large particle group. In this embodiment, classification is performed using a vibrating sieve, but this is not limited to a vibrating sieve, and various known classification devices can be used. Classification may be performed in multiple stages.

[0109] In the example shown in FIG. 4, the classification unit 7 includes a sieve 72 with a mesh size of 2 mm and a sieve 73 with a mesh size of 75 μm arranged downstream of the sieve 72. As a result, gravel particles 11 are removed by the sieve 72, and sand particles 12 are removed by the sieve 73. The mixture 70 that has passed through the sieve 72 is muddy water containing particles with a particle size of less than 75 μm, such as clay and silt, which contain mineral particles 13. Most of the radioactive material is contained in the muddy water. The muddy water may be further classified, for example, by a high mesh separator.

[0110] When a sludge deflocculation process is performed in the cavitation generation region Rc to separate mineral particles having adsorbed radioactive substances from soil particles, the classification section 7 may be configured to classify the mixture 70 into a large particle group including soil particles (e.g., particle size 75 μm or more) and a small particle group including mineral particles (e.g., particle size less than 75 μm) (see Figure 3B).

[0111] Alternatively, when sludge thawing and mineral particle crushing are performed in the cavitation generation region Rc, the classification section 7 may be configured to classify the mixture 70 into a large particle group having a particle size equal to or larger than the particle size of the mineral particles (e.g., 20 μm) and a small particle group having a particle size smaller than the mineral particles (see Figure 3A).

[0112] (Control unit) The control unit 8 is configured to control the operations of, for example, the ejection unit 2, the liquid supply unit 5, the soil supply unit 6, etc. This makes it possible to adjust the mixture ratio of the soil 10 and the liquid 50 contained in the slurry 40, the flow rate of the pressurized liquid 20, etc., as appropriate depending on, for example, the type and state of the soil 10 to be treated, the operating state of the soil treatment device 1a, etc.

[0113] (effect) In the soil treatment apparatus 1a of this embodiment, as illustrated in Figures 4 to 5C, the flow path 30 of the treatment unit 3 has an enlarged section 36 that enlarges the cross-sectional area downstream of the slurry supply position P. The slurry supply unit 4 and the outlet unit 2 are configured so that the difference in flow velocity between the slurry 40 and the pressurized liquid 20 is greater downstream of the enlarged section 36 than upstream of the enlarged section 36, and the amount of bubbles 81 generated by cavitation increases.

[0114] According to this configuration, the pressure of the slurry 40 drops sharply downstream of the expansion section 36. In addition, the flow rate of the slurry 40 drops, so the flow rate ratio between the slurry 40 and the pressurized liquid 20 increases. Therefore, the amount of bubbles 81 generated by cavitation can be increased downstream of the expansion section 36 compared to the upstream of the expansion section 36. As a result, the separation of mineral particles in the slurry 40 can be further promoted. In addition, the flow rate of the slurry 40 drops downstream of the expansion section 36, so that the effect of the Coriolis force increases. Therefore, the particles in the slurry 40 flow while being separated according to their weight, so that the impact force at the time of bubble collapse can be applied more efficiently to relatively light particles such as mineral particles.

[0115] Furthermore, with the above configuration, it is possible to lengthen the cavitation generation region Rc in the flow path 30. Since it is possible to continue generating cavitation in the flow path 30, it is possible to lengthen the processing time for disintegrating and crushing the mineral particles in the slurry 40 without increasing the amount of water used.

[0116] In the soil treatment apparatus 1a of this embodiment, the slurry supplying section 4 includes a hopper 41, a soil supplying section 6 that supplies soil 10 toward the inner wall 41s of the hopper 41, and a liquid supplying section 5 that supplies liquid 50 toward the inner wall 41s of the hopper 41. The soil supplying section 6 and the liquid supplying section 5 are configured so that the liquid 50 and the soil 10 are mixed on the inner wall 41s of the hopper 41 to become slurry 40, which is then supplied to the flow path 30 of the treatment section 3 from the lower opening 412 of the hopper 41.

[0117] According to such a configuration, it is possible to more reliably mix the soil 10 with the liquid 50 while keeping the amount of the liquid 50 small. Therefore, it is possible to reduce the overall solid-liquid ratio.

[0118] Moreover, with the above configuration, the slurry 40 having a substantially constant mixture ratio (mixture ratio of the soil 10 and the liquid 50) can be continuously supplied to the treatment section 3 at a substantially constant speed. Furthermore, the mixture ratio of the liquid 50 and the soil 10 can be easily adjusted. For example, the mixture ratio can be adjusted by the control section 8 during operation.

[0119] Furthermore, with the above configuration, even if the soil 10 contains relatively small particles such as clay, the particles are unlikely to adhere to the inner wall 41s of the hopper 41 because they come into contact with the liquid 50 on the inner wall 41s. This reduces the frequency of maintenance.

[0120] Furthermore, according to the above configuration, compared to the case where a previously prepared slurry is transported and supplied to the processing section, stirring operations, large mixing equipment, and a slurry transport device are not required, and it is possible to reduce the cost required for forming the slurry 40. Also, since there is no need to transport the slurry, there is no need to increase the amount of liquid to make it easier to transport the slurry.

[0121] Furthermore, with the above-mentioned configuration, the liquid 50 can be mixed with the amount of soil 10 flowing down the hopper 41 without stirring, etc. This is advantageous when the soil 10 contains radioactive materials, because dust containing the radioactive materials is less likely to fly up.

[0122] In the soil treatment device 1a of this embodiment, the liquid supply unit 5 includes a liquid line 51 that extends along at least a part of the periphery of the upper opening 411 of the hopper 41 and conveys the liquid 50, and a plurality of liquid supply ports that are arranged at intervals on the liquid line 51 and discharge the liquid 50. With this configuration, it is easy to supply the liquid 50 near the upper end of the inner wall 41s of the hopper 41. In addition, since the liquid 50 tends to flow in the circumferential direction on the inner wall 41s due to inertial force, the path along which the liquid 50 flows can be lengthened. Therefore, the liquid 50 and the soil 10 can be mixed more reliably. Furthermore, by providing a plurality of liquid supply ports, the liquid 50 can be flowed over a wider range of the inner wall 41s of the hopper 41. Therefore, adhesion of soil particles to the inner wall 41s can be suppressed.

[0123] Furthermore, according to this embodiment, in the soil treatment method including the cavitation generating step, as shown in Fig. 5A, it is possible to control the flow rate difference between the pressurized liquid 20 and the slurry 40 so that the amount of bubbles generated by cavitation decreases and then increases again while the pressurized liquid 20 flows together with the slurry 40 in the ejection direction. In this method, in the cavitation generating step, the mineral particles in the slurry 40 can be sludged or crushed not only immediately after the pressurized liquid 20 collides with the slurry 40, but also after the amount of bubbles generated increases again. Therefore, sludged or crushed can be more efficiently performed while suppressing the amount of liquid used.

[0124] (Variation 1: Slurry Supply Unit) The slurry supplying section 4 may be configured so that the liquid 50 and the soil 10 flow downward while swirling on the inner wall 41s of the hopper 41, and are mixed during this process to become the slurry 40. With this configuration, the soil 10 and the liquid 50 can be mixed more reliably and more uniformly.

[0125] Fig. 8A is a schematic perspective view showing a modified example of a liquid supply unit and a hopper, and Fig. 8B is a top view of the modified example shown in Fig. 8A.

[0126] In the example shown in FIGS. 8A and 8B, the liquid line 51 includes an annular portion 511 extending in an annular shape along the periphery of the upper opening 411 of the hopper 41. A plurality of liquid supply ports 512 are arranged at intervals in the annular portion 511. A nozzle 52 extending downward is connected to each liquid supply port 512. As shown in FIG. 8B, in a plan view along the height direction (Z direction) of the hopper 41, the extension direction of the nozzle 52 is inclined at an angle θ (0°<θ<90°) to the flow direction of the liquid 50 flowing through the annular portion 511 with respect to a direction d from the liquid supply port 512 toward the center C of the lower opening 412. The angle θ is, for example, 20° or more.

[0127] With this configuration, the liquid 50 from the nozzle 52 tends to flow in the circumferential direction due to inertial force, so that the liquid 50 tends to flow downward together with the soil 10 while swirling on the inner wall 41s of the hopper 41. Therefore, the path for mixing the liquid 50 and the soil 10 is longer, so that the liquid 50 and the soil 10 can be mixed more reliably and more uniformly.

[0128] 8A and 8B, all of the nozzles 52 are inclined at the same angle θ with respect to the direction d, but the angles θ may be different from one another. Furthermore, if the nozzle 52 provided in at least one liquid supply port 512 is inclined with respect to the direction d, the effect of swirling and flowing the liquid 50 can be obtained.

[0129] (Modification 2: Flow path of processing section) FIG. 9 is a schematic cross-sectional view showing a modified example of the flow path. The flow path 30 shown in FIG. 9 has a plurality of enlarged portions 36 downstream of the slurry supply position P. The plurality of enlarged portions 36 are arranged at a distance from each other. In this example, a fourth portion 320 having a smaller cross-sectional area than the third portion 33 is connected downstream of the third portion 33, and a fifth portion 330 having a larger cross-sectional area than the fourth portion 320 is connected downstream of the fourth portion 320 in this order. The fourth portion 320 and the fifth portion 330 form an enlarged portion 36 that promotes the generation of cavitation. The cross-sectional area of ​​the fourth portion 320 may be the same as or different from that of the second portion 32. Similarly, the cross-sectional area of ​​the fifth portion 330 may be the same as or different from that of the third portion 33. The flow path 30 may include the fourth portion 320 and the fifth portion 330 alternately downstream of the third portion 33, thereby having more enlarged portions 36.

[0130] According to this configuration, by providing a plurality of enlarged portions 36 in the flow passage 30, the cavitation generation region Rc can be made even longer.

[0131] (Example) In order to confirm the effect of this embodiment, a mica crushing experiment was carried out using the soil treatment device 1a shown in Fig. 4, and the method and results are described below. Here, instead of actual soil, commercially available vermiculite, which is mainly composed of only dried mica, was used as the material to be treated, and the particle size distribution after treatment was measured.

[0132] <Method of crushing experiment> In the embodiment, 1 kg of vermiculite was supplied together with liquid (water) 50 to the slurry supply section 4 of the soil treatment device 1a shown in Fig. 4, and passed through the flow path 30 of the treatment section to carry out a disintegration treatment using cavitation. Treatment conditions such as the supply speed of the material to be treated (vermiculite), the flow rate of water to be mixed with the vermiculite, and the ejection conditions of the pressurized liquid (pressurized water) were set to be the same as the conditions exemplified with reference to Fig. 4.

[0133] Next, the mixture (a mixture of the treated vermiculite-containing slurry and pressurized water) 70 discharged from the flow path 30 was collected in a storage container and thoroughly stirred. After that, a certain amount of the mixture was collected from the bottom and the top of the container, mixed, and used as a measurement sample.

[0134] <Comparative Example> As a comparative example, 1 kg of vermiculite was passed through a comparative apparatus not equipped with a pressurized water outlet, together with water, and the particle size distribution of the vermiculite was then measured. The comparative apparatus was an apparatus for producing a slurry under the same conditions as in the examples and measuring the particle size distribution.

[0135] Fig. 10 is a schematic side view of an apparatus of a comparative example. The apparatus 101 of the comparative example differs from the soil treatment apparatus 1a shown in Fig. 4 in that it does not include a high-pressure ejector that ejects pressurized water, and in that the cross-sectional area of ​​the flow path 30 is approximately constant. The flow path 30 of the apparatus 101 is inclined downward (in the -Z direction) with respect to the horizontal direction.

[0136] In the comparative example, 1 kg of vermiculite was supplied to the slurry supply section together with water and passed through the flow path 30. The supply rate of the material to be treated (vermiculite) and the flow rate of water mixed with the vermiculite were the same as in the example. Then, a measurement sample was taken from the mixture 70 discharged from the flow path 30 in the same manner as in the example.

[0137] In the comparative example, the vermiculite is not subjected to impact forces due to the collision of pressurized water or cavitation. Therefore, the particle size distribution of the measurement sample obtained in the comparative example is approximately the same as the particle size distribution of the vermiculite supplied to the device of the comparative example. Therefore, the particle size distribution measured in the comparative example can be considered to be approximately the same as the particle size distribution of the vermiculite before the crushing experiment in the embodiment.

[0138] <Comparison of particle size distribution> 11A and 11B are photographs showing the measurement samples of the Example and Comparative Example, respectively. These photographs confirm that the particle size of the vermiculite after the crushing experiment of the Example is clearly smaller than the particle size of the vermiculite of the Comparative Example.

[0139] Next, in order to compare particle size distributions in the small particle size range that is difficult to confirm visually, the particle size distributions of the measurement samples of the examples and comparative examples were measured. Here, the measurement samples of the examples and comparative examples were classified to remove particle groups with particle sizes of 0.212 mm or more, and the particle size distributions of the remaining particle groups were measured by a laser diffraction method.

[0140] Fig. 11C is a diagram showing particle size accumulation curves obtained by a laser diffraction method in the examples and comparative examples. In the results shown in Fig. 11C, the ratio of particles having a particle size of 0.02 mm to 0.04 mm is higher in the examples than in the comparative examples. From this, it is considered that in the examples, a part of the vermiculite particles (e.g., particles having a particle size of 0.2 mm or more) is disintegrated to a particle size of, for example, about 0.02 mm.

[0141] 11A to 11C, it is confirmed that the soil treatment device 1a of this embodiment has sufficient crushing ability for mineral particles such as vermiculite. Note that, although vermiculite was used as the object to be treated here, it is considered that a certain level of crushing ability is exhibited even when soil in which vermiculite is mixed with other soil particles is used.

[0142] (Other variations) The soil treatment device and soil treatment method of the present invention are not limited to the device and method exemplified in FIGS.

[0143] In Fig. 1, Fig. 4, Fig. 8A and Fig. 8B, the slurry supplying unit 4 includes a hopper 41, but may not include a hopper. For example, a premixed slurry may be transported by a pipe, and the pipe may be connected to a flow path of the processing unit. In the example shown in Fig. 4, the soil and the liquid are separately supplied to the hopper, but a premixed slurry may be supplied to the hopper.

[0144] It is also possible to treat soil using a plurality of the soil treatment devices of the first and second embodiments. In this case, the mixture discharged from the plurality of soil treatment devices may be sent to a common classifying section or a common classifying device. For example, the flow paths of the plurality of soil treatment devices may be joined together and sent to a common classifying section.

[0145] The apparatus and method having the configurations illustrated in Figs. 1 to 9 can be widely applied to soil containing radioactive materials. For example, they can be applied to soil containing organic components. They can also be applied to the purification of soil containing impurities such as oil, and to the sterilization of soil, not limited to soil containing radioactive materials. Furthermore, various powders and granules can be used as the object to be treated, not limited to soil. By applying the present apparatus or method, it is possible to efficiently separate particles contained in a slurry, disperse particles, separate particles from impurities, and crush particles by utilizing cavitation.

[0146] The slurry supplying device (slurry supplying section) described above with reference to FIG. 4, FIG. 8A, and FIG. 8B can be applied to various treatment devices. The above-mentioned slurry supplying device can be widely applied to devices for separating soil particles (including mineral particles) contained in soil from other particles and deposits by utilizing cavitation (see FIG. 2A and FIG. 2B) generated by the flow rate difference between the slurry and the pressurized liquid. By applying the above-mentioned slurry supplying device, the solid-liquid ratio in the slurry can be reduced, so that the separation of the soil particles can be performed more efficiently. In addition, the amount of liquid contained in the slurry can be reduced, so that the cost of purifying the liquid after treatment can be reduced. Furthermore, since operations such as stirring are not required when making the slurry, there is an advantage that radioactive materials are less likely to scatter. The above-mentioned slurry supplying device can also be applied to devices for separating soil particles from radioactive materials by methods other than those described in the above embodiment.

[0147] The above-mentioned slurry supplying device can be applied to a purification device for separating soil particles from impurities such as oil, a device for sterilizing soil particles, etc. Furthermore, it can be applied to a device for dispersing, mixing, crushing, polishing, etc., powder and granular materials other than soil. This can obtain the same effects as the above-mentioned embodiment, such as reducing the amount of liquid to be mixed with soil or powder and granular materials.

[0148] The present disclosure is not limited to the above-described embodiments, and design modifications are possible without departing from the scope of the present disclosure. In addition, by appropriately combining the configurations of any of the various embodiments (including modified examples) illustrated, it is possible to achieve the effects of each of the embodiments.

[0149] This specification discloses a soil treatment method as described in the following items. [Item 1] 1. A method for treating soil containing mineral particles having radioactive material adsorbed thereon, comprising the steps of: The method includes injecting a pressurized liquid into a slurry obtained by mixing the soil with a liquid, and generating a flow velocity difference at an interface between the pressurized liquid and the slurry, thereby generating cavitation; The method of treating soil, wherein the mineral particles are separated from other particles by the impact force generated when the bubbles generated by the cavitation collapse. [Item 2] The soil further includes soil particles having a particle size larger than that of the mineral particles, 2. The soil treatment method according to item 1, wherein the impact force separates the mineral particles attached to or encapsulated in the soil particles from the soil particles. [Item 3] 3. The soil treatment method according to item 2, wherein the impact force crushes the mineral particles separated from the soil particles into particles having a smaller particle size than the mineral particles. [Item 4] 2. The soil treatment method according to item 1, wherein the impact force causes the particles to have a particle size smaller than that of the mineral particles. [Item 5] 5. The soil treatment method according to any one of items 1 to 4, wherein the radioactive substance is radioactive cesium and the mineral is mica. [Item 6] 6. The soil treatment method according to any one of items 1 to 5, wherein the ratio of the weight of the liquid used, including the liquid and the pressurized liquid, to the dry weight of the soil to be treated is 5 or more and 15 or less. [Item 7] 4. The soil treatment method according to item 2 or 3, wherein the soil particles have a particle size of 0.075 mm or more, and the mineral particles have a particle size of less than 0.075 mm. [Item 8] 4. The soil treatment method according to item 2 or 3, further comprising classifying the mixture of the slurry and the pressurized liquid after generating the cavitation into a large particle group containing the soil particles and a small particle group containing the mineral particles. [Item 9] 5. The soil treatment method according to item 4, further comprising classifying the mixture of the slurry and the pressurized liquid after generating the cavitation into a particle group having a particle size equal to or larger than the particle size of the mineral particles and a particle group having a particle size smaller than the mineral particles. [Item 10] 10. The soil treatment method according to any one of items 1 to 9, wherein generating the cavitation includes controlling the flow velocity difference so that an amount of generated bubbles decreases and then increases while the pressurized liquid flows together with the slurry in the ejection direction.

[0150] This specification discloses a soil treatment apparatus described in the following items. [Item 1] A soil treatment device that performs a process for separating mineral particles having radioactive substances adsorbed thereto from other particles, the process comprising: A processing section having a flow path; an ejection section that ejects pressurized liquid from an upstream side to a downstream side of the flow path; A supply unit is connected to the downstream side of the flow path from the outlet unit and supplies a slurry obtained by mixing the soil with a liquid toward the pressurized liquid discharged by the outlet unit. The soil treatment device, wherein the ejection section and the supply section are configured to generate a flow velocity difference at the interface between the pressurized liquid and the slurry, thereby generating cavitation. [Item 2] The soil is a mixture of particles of the mineral and soil particles having a particle size larger than that of the mineral particles, 2. The soil treatment device according to item 1, wherein the emission unit and the supply unit are configured to separate the mineral particles attached to or contained within the soil particles from the soil particles by an impact force generated when the bubbles generated by the cavitation collapse. [Item 3] 3. The soil treatment device according to item 2, wherein the ejection unit and the supply unit are configured to crush the mineral particles separated from the soil particles by the impact force into particles having a smaller particle size than the mineral particles. [Item 4] The soil treatment device according to item 1, wherein the emission unit and the supply unit include a process of crushing the mineral particles into particles having a smaller particle size than the mineral particles by an impact force generated when the bubbles generated by the cavitation collapse. [Item 5] the flow path includes an expansion portion that expands a cross-sectional area perpendicular to an extension direction of the flow path, the expansion portion being located downstream of a position to which the supply portion is connected; 5. The soil treatment device according to any one of items 1 to 4, wherein the outlet section and the supply section are configured such that the flow rate difference is greater downstream of the expansion section than upstream of the expansion section, and an amount of bubbles generated by the cavitation is increased. [Item 6] The supply unit includes: A hopper having a tapered shape in which the inner diameter decreases from an upper opening toward a lower opening; a soil supplying unit that supplies the soil from the upper opening toward an inner wall of the hopper; a liquid supply unit that supplies the liquid from the upper opening toward the inner wall of the hopper, The soil supply unit and the liquid supply unit are configured so that the liquid and the soil are mixed on the inner wall of the hopper to form the slurry, and the slurry is supplied to the flow path from the lower opening. [Item 7] 4. The soil treatment device according to item 2 or 3, further comprising a classification unit that is fluidly connected to a downstream side of the flow path and classifies the mixture of the pressurized liquid and the slurry into a large particle group including the soil particles and a small particle group including the mineral particles. [Item 8] 5. The soil treatment device according to item 4, further comprising a classification unit that is fluidly connected to the downstream side of the flow path and classifies the mixture of the pressurized liquid and the slurry into a particle group having a particle size equal to or larger than the mineral particles and a particle group having a particle size smaller than the mineral particles. [Item 9] 9. The soil treatment device according to any one of items 1 to 8, wherein the radioactive material is radioactive cesium and the mineral is mica.

[0151] This specification also discloses a soil treatment apparatus as described in the following items. [Item 1] A soil treatment device that performs a process for separating mineral particles having radioactive substances adsorbed thereto from other particles, the process comprising: A processing section having a flow path; an ejection unit that ejects pressurized liquid from the upstream side toward the downstream side of the flow path, The ejection unit is configured to eject the pressurized liquid into a slurry obtained by mixing the soil with a liquid in the flow path, and to generate a flow velocity difference at an interface between the pressurized liquid and the slurry to generate cavitation, The flow path is A first part; a second portion located downstream of the first portion and having a cross-sectional area perpendicular to an extension direction of the flow path smaller than that of the first portion; a third portion located downstream of the second portion, the cross-sectional area of ​​the third portion being larger than that of the second portion. [Item 2] 2. The soil treatment device according to item 1, wherein the flow path is configured so that an amount of bubbles generated by the cavitation is greater in the third portion than in the second portion. [Item 3] A supply portion connected to the first portion and supplying the slurry, 3. The soil treatment device according to item 1 or 2, wherein the length of the third portion is greater than the length of the flow path from a position where the supply unit is connected to an upstream end of the third portion. [Item 4] The ejection unit includes a nozzle unit having an ejection port for ejecting the pressurized liquid, and a pipe located upstream of the nozzle unit and connected to the nozzle unit, and the nozzle unit is configured such that a cross-sectional area of ​​the nozzle unit increases from the ejection port toward the pipe, 4. The soil treatment device according to any one of items 1 to 3, wherein the cross-sectional area of ​​the second portion is larger than a cross-sectional area of ​​a pipe of the outlet portion. [Item 5] The flow path is a fourth portion located on the third portion side and having a cross-sectional area smaller than that of the third portion; 3. The soil treatment device according to item 1 or 2, further comprising a fifth portion located downstream of the fourth portion and having a cross-sectional area larger than that of the fourth portion. [Item 6] 6. The soil treatment device according to any one of items 1 to 5, wherein the flow path further includes a tapered section between the first portion and the second portion, the cross-sectional area of ​​which decreases from the first portion toward the second portion.

[0152] This specification discloses a slurry supplying device described in the following items. [Item 1] A slurry supplying device that supplies a slurry mixed with a liquid to soil, A hopper having a tapered shape in which the inner diameter decreases from an upper opening toward a lower opening; a soil supplying unit that supplies the soil from the upper opening toward an inner wall of the hopper; a liquid supply unit that supplies the liquid from the upper opening toward the inner wall, The soil supply unit and the liquid supply unit are configured so that the liquid and the soil are mixed on the inner wall to form the slurry, which then flows out from the lower opening. [Item 2] 2. The slurry supplying apparatus according to claim 1, wherein the soil supplying section and the liquid supplying section are configured such that the liquid and the soil are mixed to form the slurry while flowing downward on the inner wall in a swirling manner. [Item 3] The liquid supply unit includes: a liquid line extending along at least a portion of a periphery of the upper opening and conveying the liquid; 3. The slurry supplying apparatus according to claim 1 or 2, further comprising: a plurality of liquid supply ports spaced apart from one another in the liquid line, the liquid supply ports supplying the liquid to the hopper. [Item 4] the plurality of liquid supply ports include a first liquid supply port, the first liquid supply port is provided with a nozzle extending downward from the first liquid supply port, 4. The slurry supplying apparatus according to item 3, wherein, in a plan view along a height direction of the hopper, an extension direction of the nozzle is inclined with respect to a direction from the first liquid supply port toward a center of the lower opening. [Item 5] 5. The slurry supplying device according to any one of items 1 to 4, wherein the soil supplying unit is configured to supply the soil toward the inner wall from a supplying position that is offset from the center of the lower opening in a plan view along the height direction of the hopper. [Item 6] 6. The soil supplying device according to item 5, wherein the soil supplying unit is provided with a conveying device that, in the plan view, conveys the soil from outside the upper opening to the input position and drops the soil into the upper opening at the input position. [Item 7] 7. The slurry supplying device according to item 6, wherein the input position is located downstream of a center of the lower opening in a conveying direction of the conveying device in the plan view. [Item 8] 8. The slurry supplying apparatus according to any one of items 1 to 7, wherein the soil is soil containing a radioactive material. [Item 9] A soil treatment device for separating soil particles contained in soil from other particles or attached matter, A supply section including a slurry supply device according to any one of items 1 to 8; A flow path through which the slurry containing the soil is supplied from the supply unit; an ejection unit that ejects pressurized liquid from the upstream side to the downstream side of the flow path, The soil treatment device, wherein the ejection section and the supply section are configured to generate a flow velocity difference at the interface between the pressurized liquid and the slurry, thereby generating cavitation. [Industrial Applicability]

[0153] INDUSTRIAL APPLICABILITY The soil treatment method according to the present invention can facilitate the removal of radioactive materials from soil, and is therefore useful for decontaminating and reducing the volume of contaminated soil. [Explanation of symbols]

[0154] 1, 1a Soil treatment device 2. Output section 3 Processing section 4. Slurry supply section 5 Liquid supply section 6. Soil Supply Division 7 Classification Department 8. Control Unit 10. Soil 11 Gravel particles 12 sand particles 13 Mineral particles 15 Mineral particles containing radioactive materials 20 Pressurized Liquids 20s interface 22 Nozzle 23 High-speed jet pump 24 Piping 30 Flow Path 31 Part 1 32 Part 2 33 Part 3 34 Tapered section 35 Fringe 35c central part 36 Enlarged section 37 Outlet 40 Slurry 41 Hopper 41s interior wall 50 liquid 51 Liquid Line 52 Nozzle 53 Submersible Pump 61 Soil storage tank 62 Transport Equipment 70 mixture 72, 73 sieve 80 space 81 Bubbles 82 Vortex 320 Part 4 330 Part 5 351 Left side part 352 Right side part 411 Upper opening 412 Lower opening 511 Circular section 512 Liquid supply port 621 Belt 622 Adjustment parts C center d direction P Slurry supply position Q input position Rc Cavitation region

Claims

1. 1. A method for treating soil containing mineral particles having radioactive material adsorbed thereon, comprising the steps of: The method includes ejecting a pressurized liquid from an upstream side to a downstream side of a flow path for treating the soil, supplying a slurry in which the soil is mixed with a liquid and to which no dispersant that reduces a zeta potential has been added toward the ejected pressurized liquid within the flow path, and generating a flow velocity difference at an interface between the pressurized liquid and the slurry to generate cavitation. The method of treating soil, wherein the mineral particles are separated from other particles by the impact force generated when the bubbles generated by the cavitation collapse.

2. The soil further includes soil particles having a particle size larger than that of the mineral particles, 2. The soil treatment method according to claim 1, wherein the impact force separates the mineral particles attached to or encapsulated in the soil particles from the soil particles.

3. 3. The soil treatment method according to claim 2, wherein the impact force crushes the mineral particles separated from the soil particles into particles having a smaller diameter than the mineral particles.

4. 2. The soil treatment method according to claim 1, wherein the impact force breaks the mineral particles into particles having a smaller diameter than the mineral particles.

5. 3. The soil treatment method according to claim 1, wherein the radioactive substance is radioactive cesium and the mineral is mica.

6. 3. The soil treatment method according to claim 1, wherein the ratio of the weight of the liquid used, including the liquid and the pressurized liquid, to the dry weight of the soil to be treated is 5 or more and 15 or less.

7. 4. The soil treatment method according to claim 2, wherein the soil particles have a particle size of 0.075 mm or more, and the mineral particles have a particle size of less than 0.075 mm.

8. 4. The soil treatment method according to claim 2 or 3, further comprising: after generating the cavitation, transferring the mixture of the slurry and the pressurized liquid from the downstream side of the flow path to a classification section, and classifying the mixture in the classification section into a large particle group containing the soil particles and a small particle group containing the mineral particles.

9. 5. The soil treatment method according to claim 4, further comprising: after generating the cavitation, transferring the mixture of the slurry and the pressurized liquid from the downstream side of the flow path to a classification section, and classifying the mixture in the classification section into a particle group having a particle size equal to or larger than the particle size of the mineral particles and a particle group having a particle size smaller than the mineral particles.

10. The soil treatment method according to claim 1 or 2, wherein generating the cavitation includes controlling the flow velocity difference so that the amount of bubbles generated decreases and then increases while the pressurized liquid flows together with the slurry in the ejection direction.

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