Method and apparatus for recycling contaminated soil

Abstract

Based on a classification method, even fine-grained soil (for example, less than 75 μm) is recovered in a reusable state with low contamination levels. [Solution] The method includes a step of stirring and washing the contaminated soil with washing water, a step of classifying the soil after stirring and washing and recovering coarse particles of a predetermined particle size (for example, 75 μm) or larger, and a step of recovering the fine particles from the washing water containing the remaining fine particles (for example, less than 75 μm). Between the stirring and washing step and the fine particle recovery step, a plasma arc discharge treatment is performed at least once on the washing water containing the soil to separate radioactive materials such as cesium attached to the fine particles of soil and transfer them to the washing water. In the fine particle recovery step, the fine particles of soil and radioactive materials are separated and recovered from the washing water.

Description

Technical Field

[0001] The present invention aims at the resource utilization of contaminated soil.

[0002] This technology relates to a method and apparatus for resource utilization of contaminated soil that generates reusable gravel, sand, silt, and clay from soil contaminated by radioactive substances.

Background Art

[0003] In Japan, the treatment of radioactive contaminated soil that has an adverse effect on the human body generated by the accident at the Fukushima Daiichi Nuclear Power Plant caused by the Great East Japan Earthquake has become a problem.

[0004] Therefore, radioactive contaminated soil is collected in intermediate storage facilities and stored in large quantities.

[0005] Generally, the "classification treatment method" is used to reduce the volume of radioactive contaminated soil.

[0006] In this "classification treatment method", since the fine particle fraction (silt and clay) of radioactive contaminated soil has the property that radioactive substances such as cesium easily adhere to it, the soil is classified into a coarse particle fraction (gravel) with a particle size of 4 mm or more and a particle fraction with a particle size of less than 4 mm (part of fine gravel, sand, silt, and clay), and the coarse particle fraction (gravel) to which radioactive substances hardly adhere is recovered as a recycled resource to reduce the volume of contaminants to be sent to final disposal.

[0007] In the present specification, the use of the names of "gravel", "sand", "silt", and "clay" for the particles contained in the soil is based on the particle size distribution shown in Table 1 below.

[0008]

Table 1

[0009] In addition to the "classification treatment method", "chemical treatment method" and "heat treatment method" have also been proposed as methods for reducing the volume of contaminated soil. <

[0010] One of these methods, the "chemical treatment method," uses strong acids or other solvents to elute cesium ions attached to the soil and adsorb them onto an adsorbent. The cesium adsorbed onto this adsorbent is then condensed and recovered as a pollutant, thereby reducing the volume of pollutants that need to be sent for final disposal.

[0011] Furthermore, the "heat treatment method" involves heating soil containing cesium to recover soil components as molten or calcined material, while simultaneously cooling exhaust gas containing vaporized cesium to condense the cesium. The condensed cesium is then collected and recovered using an exhaust gas filter and sent for final disposal, thereby reducing the volume of pollutants that need to be disposed of.

[0012] Furthermore, the above volume reduction methods may be used in combination. For example, after recovering coarse-grained material (gravel and sand) as a recycled resource using a classification method, the remaining fine-grained material (silt and clay) may be further reduced in volume by applying chemical or heat treatment methods.

[0013] Regarding the aforementioned "classification treatment method," Patent Document 1, listed below, describes that, as shown in Figure 4, the removed soil Sc is washed with water in a washing treatment device WM, then classified in a classification treatment device CM to recover soil components with a particle size of 75 μm or larger as regenerated soil Sp, and the washing water and remaining soil are introduced into a separation treatment device DM such as a thickener to precipitate and recover the soil components, and dewatering is performed using a dewatering treatment device DHM, thereby reducing the volume of contaminants by making the dewatered cake Sd of soil components with a particle size of less than 75 μm the target of reprocessing or final disposal (Patent Document 1,

[0058] -

[0061] , Figures 9 and 11).

[0014] Furthermore, Patent Document 2, cited below, acknowledges that the aforementioned classification method may not reliably reduce the cesium concentration in coarse-grained soil (particle size 75 μm or larger) recovered as a recyclable resource to below the target value. Therefore, it is proposed to extract cesium from the coarse-grained soil by washing it with an extractant consisting of an alkaline salt after classification (see Claim 1 and Figure 1 of Patent Document 2).

[0015] Although it does not target soil treatment, Patent Document 3, cited below, describes a water treatment method that targets conductive water containing impurities, solidifying inorganic substances such as heavy metals and radioactive materials dissolved in the water in an ionized state so that they can be extracted, as well as performing gasification, sterilization, washing, and activation through the decomposition of organic matter.

[0016] In this water treatment method, an operating gas such as air or carbon dioxide is injected into the water to be treated in a plasma treatment tank to generate a bubble jet, which is a two-phase gas-liquid flow composed of minute bubbles of the operating gas dispersed in the water to be treated and the water to be treated. By introducing this bubble jet to the tip of an electrode to which an AC voltage is applied, a plasma arc discharge is generated between the electrodes, directly generating highly active molecules and radicals in the bubbles. This solidifies inorganic substances such as heavy metals and radioactive materials that are ionized and dissolved in the water to be treated, without generating harmful secondary products, and simultaneously decomposes organic substances in the water to be treated. [Prior art documents] [Patent Documents]

[0017] [Patent Document 1] Japanese Patent Publication No. 2020-163265 [Patent Document 2] Japanese Patent Publication No. 2017-215269 [Patent Document 3] Patent No. 6208968 [Overview of the project] [Problems that the invention aims to solve]

[0018] In the methods described in Patent Document 1 and Patent Document 2 explained above, the contaminated soil is classified into a coarse fraction with a particle size of 75 μm or more to which radioactive substances hardly adhere and a fine fraction with a particle size of less than 75 μm to which radioactive substances easily adhere, and the volume reduction of the contaminated soil is enabled by a relatively simple method of recovering the coarse fraction with a particle size of 75 μm or more as a recycled resource. However, the treatment of the classified washing water has become a problem.

[0019] In particular, in the method described in Patent Document 2, by performing washing with an extractant composed of an alkali salt added to the classified coarse fraction (75 μm or more) to extract and remove cesium, it is excellent in that soil with a lower contamination level of the coarse fraction can be recovered as a recycled material. However, the treatment of the washing water to which an alkali salt is added has become a problem.

[0020] Moreover, in any of the above methods, the fine fraction (less than 75 μm) of the contaminated soil cannot be recovered as a recycled resource. Therefore, when the contaminated soil to be treated has a large content ratio of fine fractions such as silt and clay, even after recovering the coarse fraction of the soil, a large amount of the fine fraction of the soil remains as a pollutant, resulting in a significantly low volume reduction effect.

[0021] In addition, by classifying and recovering the coarse fraction with a relatively low contamination level from the contaminated soil, the contamination level of the remaining fine fraction of the soil will increase. Therefore, even if the fine fraction of the soil is recovered, it cannot be reused as it is.

[0022] Therefore, if all of the recovered fine fraction of the soil is sent for final disposal, the amount of pollutants to be subject to final disposal is still large, and the volume reduction effect is low, making it difficult to secure a final disposal site and the like.

[0023] In order to avoid such problems, it is also conceivable to perform further reprocessing and volume reduction on the soil of the fine fraction remaining as a pollutant by classification by the classification treatment method using other methods, for example, the chemical treatment method or the heat treatment method described above.

[0024] However, in this case, although the volume reduction effect is high, it is necessary to set up a separate reprocessing facility for the recovered fine-grained soil, in addition to the facility for classification, which increases the cost of volume reduction.

[0025] Furthermore, if the fine-grained soil can be recovered in its original state (for example, as silt or clay), it can be reused as construction material. However, with the chemical treatment method mentioned above, in order to reuse the soil after the radioactive material has been leached out with a solvent, it is necessary to neutralize the solvent adhering to the soil with alkali or rinse it off by washing, which is a complicated process, and the treatment of the treated water used is also extremely difficult.

[0026] Furthermore, with heat treatment methods, the soil is recovered in a dissolved or sintered state, making it unsuitable for reuse. Further processing is required for reuse, and the amount of unusable residue also increases.

[0027] Furthermore, if radioactive cesium in the exhaust gas generated during heating by the heat treatment method is to be adsorbed onto an exhaust gas filter and recovered, the level of radioactive contamination in the exhaust gas filter becomes so high that it becomes difficult for people to approach it.

[0028] Thus, conventional volume reduction methods based on classification treatment make it difficult to recover fine-grained soil with a particle size of less than 75 μm in a reusable state. Furthermore, applying chemical or heat treatment methods to the soil with a particle size of less than 75 μm recovered by classification treatment leads to increased treatment costs and also creates difficulties in disposing of treated water.

[0029] Therefore, it would be convenient if, while based on a classification method, even fine-grained soil could be recovered at a reusable contamination level by adding only minor modifications to the classification method.

[0030] In order to recover the fine-grained soil at a reduced level of contamination, it is essential to separate radioactive materials such as cesium attached to the fine-grained soil from the soil itself.

[0031] However, most of the radioactive materials attached to the fine-grained soil are strongly adsorbed to the soil, and there is no effective means to separate the radioactive materials from the fine-grained soil.

[0032] To elaborate further on this point, it is known that radioactive materials can adhere to fine-grained soil, particularly clay particles, in three forms: "water-soluble," "ion-exchanged," and "immobilized."

[0033] Of these, radioactive materials that are attached in a "water-soluble" state can be separated from the soil and leached into the washing water by relatively simple treatments such as washing with water.

[0034] However, radioactive materials that have attached in an "ion exchange state" will have their ions (e.g., Cs) transferred to particles in the soil (clay particles) that have cation adsorption capacity. + Because the ions are ionically bonded, they cannot be separated by washing with washing water alone. To separate cesium, treatment is required to exchange the ions of radioactive material attached to the soil with other cations.

[0035] Furthermore, in the "stationary state," radioactive materials are firmly fixed in the form of dehydrated ions between layers of minerals such as mica contained in the soil. As a result, there is almost no exchange with other cations, and separation cannot be achieved by washing with washing water, nor by exchange with cations. Therefore, there is no effective means to separate radioactive materials attached in the "stationary state" from fine-grained soil.

[0036] Furthermore, since over 90% of radioactive materials such as cesium adhere to soil in a "fixed state," less than 10% in an "ion-exchanged state," and only a very small amount in a "water-soluble state," developing a method to separate radioactive materials attached to the soil in a "fixed state" is essential in order to recover fine-grained soil that has had its contamination level reduced to a state where it can be reused as a resource.

[0037] Furthermore, Patent Document 3, mentioned above, describes a water treatment method that can remove inorganic substances such as heavy metals and radioactive materials that are dissolved in the water to be treated by solidifying them.

[0038] In the water treatment method described in Patent Document 3, a plasma arc discharge is generated in a jet containing bubbles of working gas generated in the water to be treated, thereby discharging OH radicals (OH) into the water to be treated. - By generating radicals such as ), heavy metal ions (e.g., Cd) dissolved in the treated water are removed. 2+ (etc.) and ions of radioactive materials (e.g., Cs) + (etc.) and OH radicals (OH - The bonding of these molecules generates hydroxides of heavy metals (e.g., Cd(OH)2) and hydroxides of radioactive materials (e.g., CsOH). These hydroxides are then aggregated, solidified, and precipitated in the treated water, allowing for the removal of heavy metals and radioactive materials from the treated water through subsequent recovery of the precipitate.

[0039] Therefore, based on the operation of the plasma arc discharge treatment described in Patent Document 3, it cannot be predicted that it has the function of separating radioactive materials such as cesium attached to fine-grained soil, especially radioactive materials attached in a "fixed state," from the fine-grained soil.

[0040] However, the inventors of the present invention have found that by performing a plasma arc discharge as described in Patent Document 3 on wash water containing contaminated soil, radioactive cesium attached to the soil is separated from the soil by high-frequency shock waves generated in the water, and if the soil also contains heavy metals such as cadmium (Cd), the heavy metals are also separated from the soil along with the radioactive cesium and transferred to the wash water.

[0041] Thus, the present invention is based on the fact that the aforementioned plasma arc discharge has the effect of separating radioactive cesium and heavy metals from soil, and also converts organic matter contained in contaminated soil into oxides (CO2). By adding a component to the classification treatment method, the present invention aims to provide a method and apparatus for resource recovery of contaminated soil that can recover not only coarse-grained soil (for example, gravel and sand) with a particle size of 75 μm or more in a low-contamination state, but also fine-grained particles (for example, less than 75 μm) (silt and clay, etc.) as reusable resources (silt, clay) with a low-contamination level.

[0042] Furthermore, the present invention makes it possible to separate radioactive cesium (and heavy metals along with radioactive cesium if the soil contains heavy metals) from the soil and transfer it to the washing water by applying the aforementioned plasma arc discharge treatment to washing water containing soil. Consequently, a process is needed to separate and recover the fine-grained soil (e.g., silt and clay) from the radioactive cesium and heavy metals in the washing water, which is a mixture of fine-grained soil, radioactive cesium, and heavy metals. Therefore, an object of the present invention also includes providing a method and apparatus for resource recovery of contaminated soil that includes a method and means for performing such a separation and recovery operation. [Means for solving the problem]

[0043] The means for solving the problem are described below, along with the reference numerals used in the embodiments for carrying out the invention. These reference numerals are intended to clarify the correspondence between the claims and the descriptions of the embodiments for carrying out the invention, and needless to say, they are not used restrictively to interpret the technical scope of the present invention.

[0044] To achieve the above objective, the method for resource recovery of contaminated soil according to the present invention is The process involves agitating and washing the contaminated soil together with washing water, for example, in an agitating and washing device (drum washer) 10. The soil after the stirring and washing step is classified in the presence of the washing water, and coarse-grained soil (e.g., gravel and sand) with a predetermined particle size (for example, 75 μm) or larger is recovered using, for example, a coarse-grain recovery device (high-mesh separator) 40, and the remaining fine-grained soil (e.g., soil with a particle size less than 75 μm) (e.g., silt and clay) and the washing water are supplied to the next step in a coarse-grain recovery step. A fine-grain recovery step is performed to recover the fine-grained soil (e.g., silt and clay) from the washing water containing the fine-grained soil (e.g., silt and clay) that remains after the recovery of the coarse-grained soil (e.g., gravel and sand), The process includes a plasma arc discharge treatment step in which a predetermined plasma arc discharge is performed at least once on the washing water containing soil after the stirring and washing step and before the fine particle recovery step, In the aforementioned plasma arc discharge process, In a plasma treatment tank 31 in which the tips of a plurality of electrodes 32 to which an AC voltage is applied are arranged at predetermined intervals, the cleaning water containing the soil is introduced so that at least the tip of each electrode 32 is immersed in the cleaning water, and working gas is injected into the cleaning water introduced between the tips of the electrodes to generate minute bubbles of the working gas dispersed in the cleaning water, thereby generating a plasma arc discharge between the electrodes 32 and separating the radioactive material attached to the soil from the soil. In the aforementioned fine particle recovery process, From the washing water containing the fine-grained soil, the fine-grained soil (e.g., silt and clay) and the radioactive material separated from the soil are separated and recovered. (Claim 1) characterized by the above.

[0045] In the aforementioned fine particle recovery process, By generating bubbles in the aforementioned washing water, the radioactive material is made to adhere to the bubbles, float to the surface, and be recovered. The fine-grained soil (e.g., silt and clay) can be recovered by settling in the washing water (Claim 2).

[0046] The above resource recovery method may further include, following the stirring and washing step, a coarse particle recovery step in which coarse particles of a predetermined particle size (for example, 4 mm) or larger (for example, some fine gravel, medium gravel, and coarse gravel) from the coarse particle content (for example, 75 μm or larger) of the soil (for example, gravel and sand) are recovered (Claim 3).

[0047] Furthermore, a washing water tank 70 for storing the washing water and a recovery channel 68 for introducing the washing water after the fine particle recovery process into the washing water tank are provided. The recovery channel 68 may also be provided with an auxiliary recovery step to recover the fine particles (e.g., silt and clay) that remain in the washing water and are not recovered in the fine particle recovery step (claims 4, 5).

[0048] Furthermore, the contaminated soil resource recovery device 1 of the present invention is A drum washer or similar agitation and washing device 10 for washing contaminated soil by agitating it with washing water, The soil, after being stirred and washed by the stirring and washing device 10, is classified in the presence of the washing water, and coarse-grained soil (e.g., gravel and sand) of a predetermined particle size (for example, 75 μm or larger) is recovered, and the remaining fine-grained soil (e.g., silt and clay) after the recovery of the coarse-grained soil (e.g., gravel and sand), along with the washing water, is supplied to the next process by a coarse-grain recovery device 40 such as a high-mesh separator. A fine particle recovery device 50 recovers the fine particles (e.g., silt and clay) from the washing water containing the fine soil (e.g., silt and clay) that remains after the recovery of the coarse soil (e.g., gravel and sand), The system includes at least one plasma arc discharge device 30 (30a, 30b) that performs a predetermined plasma arc discharge on the washing water containing soil at any point after the stirring and washing device 10 and before the fine particle recovery device 50, The plasma arc discharge processing apparatus 30 (30a, 30b) The plasma treatment tank 31 into which the washing water containing the soil is introduced, with the tips of the electrodes 32 arranged at a predetermined interval, and a gas introduction passage 36 into which an operating gas is injected into and / or into the washing water introduced into the plasma treatment tank 31 to generate minute bubbles of the operating gas dispersed in the washing water, and a voltage source (not shown) that applies an AC voltage to each of the electrodes 32 necessary to generate a plasma arc discharge between the tips of the electrodes 32 under the generation of the bubbles, thereby separating radioactive material attached to the soil from the soil by the plasma arc discharge, The aforementioned fine particle recovery device 50 A radioactive material recovery means 53 for recovering the radioactive material separated from the soil, Claim 6 is characterized by comprising a soil recovery means (not shown) for recovering the fine-grained soil.

[0049] The aforementioned fine particle recovery device 50 A bubble generator 52 that generates bubbles in the aforementioned washing water, A storage tank 51 for storing the washing water that has generated the bubbles, The radioactive material recovery means 53 recovers the radioactive material that has adhered to the bubble and floated to the surface in the storage tank 51, The storage tank 51 may be equipped with a soil recovery means (not shown) for recovering the fine-grained soil (e.g., silt and clay) that has settled in the storage tank (Claim 7).

[0050] The resource recovery apparatus 1 described above may further include a coarse particle recovery apparatus 20, such as a vibrating screen, which is arranged following the stirring and washing apparatus 10 and recovers coarse particles (for example, some of the fine gravel, medium gravel, and coarse gravel) of a predetermined particle size (for example, 4 mm) or larger from the coarse-grained soil (for example, gravel and sand) (Claim 8).

[0051] Furthermore, a washing water tank 70 for storing the washing water and a recovery channel 68 for introducing the washing water, after passing through the fine particle recovery device 50, into the washing water tank 70 are provided. An auxiliary recovery device 90 may be provided in the recovery channel 68 to recover the fine-grained soil (e.g., silt and clay) that remains in the washing water and is not recovered by the fine-grained soil recovery device 50 (claims 9, 10). [Effects of the Invention]

[0052] According to the contaminated soil resource recovery method and resource recovery apparatus of the present invention described above, by performing a predetermined plasma arc discharge treatment on the washing water containing the soil at least once during any of the steps from the stirring and washing step to the fine particle recovery step, it was possible to separate a high proportion of radioactive materials (and heavy metals along with radioactive materials if the soil contains heavy metals such as cadmium) attached to the soil (especially the fine particles) and transfer them to the washing water.

[0053] As a result, in the fine particle recovery process, fine particles (e.g., silt and clay) and radioactive materials mixed in the washing water, and heavy metals along with the radioactive materials if the soil contains heavy metals, can be easily and efficiently separated and recovered, for example by separate recovery using bubbles as described later, or by magnetic separation, which recovers the radioactive materials by magnetic attraction together with magnetic powder. This makes it possible to recover not only coarse particles (e.g., 75 μm or larger) but also fine particles (e.g., less than 75 μm) (e.g., silt and clay) as reusable resources with low levels of contamination.

[0054] Furthermore, in the method of the present invention, the washing water after the radioactive material has been recovered can be recycled and reused, or it can be discharged as is, thus eliminating any problems related to the treatment of the water used for washing.

[0055] By passing contaminated soil through plasma along with washing water, radioactive materials and heavy metals attached to the soil are separated from the soil by the high-frequency shock waves generated by the plasma and ionized and dissolved into the washing water. At the same time, working gases such as oxygen and carbon dioxide are injected into the washing water as it passes through the plasma, generating active substances such as O+ and O3+. These active substances undergo an oxidation reaction with the radioactive materials and heavy metals dissolved in the washing water within about 5 minutes after passing through the plasma, causing them to solidify.

[0056] As a result, when the aforementioned fine particle recovery process is performed in the washing water in which bubbles have been generated, radioactive materials and heavy metals that remain suspended as solids for a long time adhere to the bubbles generated in the washing water, making it possible to lift them out of the washing water.

[0057] Furthermore, it has been confirmed that the iron contained in the contaminated soil is ionized along with radioactive cesium when passed through arc plasma, dissolves in water, and then solidifies again over approximately 5 minutes.

[0058] As a result, instead of injecting bubbles, the iron content per ton of soil (approximately 30-40 kg / t), or by adding a small amount of iron to the washing water as needed, causes nearly a million times more iron particles to solidify and float around the radioactive material (non-magnetic) that has solidified in the water. When the solidified iron is adsorbed and removed by the magnetic filter, the iron particles also attract and adsorb radioactive cesium and heavy metal particles, which are then removed together by the magnetic filter (the amount of radioactive cesium recovered per ton of contaminated soil is up to about 32 mg).

[0059] Furthermore, in a configuration in which a coarse particle recovery step is provided between the stirring and washing step and the coarse particle recovery step, in which coarse particles of a predetermined particle size (for example, 4 mm) or larger are recovered from the soil after the stirring and washing step, the coarse particles that may become obstacles during transport, etc., are removed from the soil first, thereby preventing clogging of the flow channels in subsequent steps, and also making it easier for the plasma arc discharge treatment to affect the soil.

[0060] In a configuration in which an auxiliary recovery device 90 is provided in the recovery channel for introducing the washing water, after passing through the fine particle recovery device, into the washing water tank, to recover the fine particles of soil (e.g., silt and clay) that remain in the washing water and are not recovered by the fine particle recovery device 50, the fine particles of soil (e.g., silt and clay) can be recovered more reliably. [Brief explanation of the drawing]

[0061] [Figure 1] An explanatory diagram of the contaminated soil resource recovery apparatus of the present invention. [Figure 2] Diagram illustrating a plasma arc discharge treatment device. [Figure 3] Diagram illustrating the fine particle recovery device. [Figure 4] Diagram illustrating a conventional contaminated soil treatment method (classification method) (corresponding to Figure 9 in Patent Document 1). [Modes for carrying out the invention]

[0062] The contaminated soil resource recovery apparatus and the resource recovery method using this apparatus of the present invention will be described below with reference to the attached drawings.

[0063] [Overall configuration of the resource recovery equipment] Figure 1 shows the overall configuration of the contaminated soil resource recovery apparatus 1 of the present invention.

[0064] This contaminated soil resource recovery device 1 includes an agitation and washing device 10 that performs an agitation and washing process in which the contaminated soil is agitated and washed together with washing water; a coarse particle recovery device 40 that performs a coarse particle recovery process in which coarse particles of a predetermined particle size or larger (for example, 75 μm or larger) (e.g., gravel and sand) are classified and recovered from the soil after agitation and washing; and a fine particle recovery device 50 that performs a fine particle recovery process in which fine particles (for example, silt and clay) are recovered from the washing water containing fine particles (for example, less than 75 μm) (e.g., silt and clay) after the coarse particles (e.g., gravel and sand) have been recovered in the coarse particle recovery process. This configuration is common to that of a conventional volume reduction device using a classification process cited in Patent Document 1.

[0065] The resource recovery apparatus 1 of the present invention further includes a plasma arc discharge treatment apparatus 30 (30a, 30b) that performs a predetermined plasma arc discharge treatment at least once at any point between the completion of processing by the stirring and washing apparatus 10 and the fine particle recovery apparatus 50. Furthermore, the fine particle recovery apparatus 50 is capable of separating and recovering fine particles (e.g., silt and clay) from the washing water and radioactive materials separated from the soil (heavy metals separated together with the radioactive materials if the soil contains heavy metals such as cadmium), which is a significant difference from conventional volume reduction apparatuses based on classification methods.

[0066] In the embodiment shown in Figure 1, a configuration is adopted in which plasma arc discharge processing devices 30a and 30b are provided before and after the coarse particle recovery device 40, respectively. However, instead of this configuration, a configuration in which only one of the plasma arc discharge processing devices 30 (30a or 30b) is provided may be adopted, or three or more plasma arc discharge processing devices 30 may be provided.

[0067] Furthermore, in the illustrated embodiment, a coarse particle recovery device 20 is provided after the stirring and washing device 10, and a configuration is adopted in which coarse particles, for example, with a particle size of 4 mm or larger, are recovered from the soil after stirring and washing as a recyclable resource in the initial stage of processing.

[0068] The various devices that make up the contaminated soil resource recovery apparatus 1 are all connected via transport channels 61-67 for transporting wash water containing soil, and are configured so that the soil treated in each device can be transported to the next process together with the wash water.

[0069] In Figure 1, reference numeral 70 denotes a washing water tank for storing washing water. This washing water tank 70 is configured to supply washing water to each part via washing water supply channels 71-73. Furthermore, the washing water remaining after fine-grained soil (e.g., silt and clay) and radioactive materials (or radioactive materials and heavy metals if the contaminated soil to be treated contains heavy metals) have been removed in the aforementioned fine-grained material recovery device 50 is configured to be recoverable into the washing water tank 70 via the recovery channel 68. This allows the washing water to be circulated and reused within the resource recovery device 1 shown in Figure 1.

[0070] In the illustrated embodiment, stirring tanks 81 and 82 are provided in front of each plasma arc discharge treatment device 30a and 30b. By stirring the soil in these stirring tanks 81 and 82 to disperse it, the plasma arc discharge treatment is performed on the washed water, thereby ensuring uniformity of the plasma arc discharge treatment.

[0071] [Agitation and washing device] The stirring and washing device 10 performs a stirring and washing process in which it mixes and washes the contaminated soil that has been introduced via the hopper 11 and the washing water supplied from the washing water tank 70 together.

[0072] In the illustrated embodiment, the agitation and washing device 10 is a drum washer that washes contaminated soil while agitating it with washing water in a rotating drum. However, the agitation and washing device 10 is not limited to a drum washer; any known device that can agitate and wash soil and washing water may be used, such as a paddle mixer.

[0073] In this embodiment, the soil introduced into the drum washer 10 via the hopper 11 was agitated and washed by supplying approximately twice the weight of washing water from the washing water tank 70.

[0074] By agitating and washing the contaminated soil with washing water in this manner, clumps of soil and other materials contained within the soil are loosened, and smaller particles such as sand, silt, and clay attached to the surface of larger particles such as gravel are washed away, separating the particles according to their different particle sizes.

[0075] The soil, which has been agitated and washed in this manner, is then supplied along with the washing water to the coarse particle recovery device 20, which will be described later.

[0076] [Coarse particle recovery device] The soil, which has been agitated and washed by the agitation and washing device 10, is supplied to the coarse particle recovery device 20 along with the washing water. There, a coarse particle recovery process is performed in which particles of a predetermined size (4 mm in this embodiment) or larger are classified and recovered as recycled resources.

[0077] In this embodiment, as an example, particles with a diameter of 4 mm or more in the contaminated soil were recovered as "coarse particles." However, the lower limit of the particle size of the particles recovered as coarse particles can be appropriately set within a range of, for example, 1 to 10 mm, depending on the pipe diameter of the piping used in the resource recovery device 1 of the present invention, and is not limited to 4 mm as used in this embodiment.

[0078] In this embodiment, when introducing the coarse particles into the coarse particle recovery device 20, an additional amount of washing water, approximately twice the weight of the soil, is added to the washing water tank 70 and introduced, and the coarse particles are recovered in the presence of this washing water.

[0079] In this embodiment, a vibrating screen equipped with a screen with a mesh opening of 4 mm is used as the coarse particle recovery device 20. Soil is introduced onto the vibrating screen along with washing water, and particles with a particle size of 4 mm or larger remaining on the screen (in this embodiment, some fine gravel, medium gravel, and coarse gravel, etc.) are recovered as recycled resources. At the same time, soil with a particle size of less than 4 mm that has passed through the screen and the washing water are supplied together to the next process.

[0080] The radioactivity concentration of the soil recovered in the coarse-grain recovery process (in this embodiment, a portion of the fine gravel, as well as medium and coarse gravel, etc.) is at a level that allows it to be reused as construction material.

[0081] Furthermore, as the coarse particle recovery device 20, any device capable of classifying and recovering soil particles of a predetermined particle size (4 mm or larger in this embodiment) may be used instead of the aforementioned vibrating screen 20, such as a trommel or cyclone.

[0082] [Agitation tank] As described above, after the coarse particles (particle size of 4 mm or more in this embodiment) have been recovered by the coarse particle recovery device 20, the soil and washing water are introduced into the stirring tank 81 for stirring of the soil and washing water.

[0083] This stirring tank 81 is equipped with rotating stirring blades inside, and after the soil and washing water are thoroughly mixed in the stirring tank 81, they are supplied to the plasma arc discharge treatment device 30a, which will be described later, and subjected to plasma arc discharge treatment.

[0084] [Plasma arc discharge treatment device] The washing water containing soil, which has been agitated in the agitation tank 81, is then introduced into the plasma arc discharge treatment device 30a(30).

[0085] Figure 2 shows an example configuration of the plasma arc discharge processing apparatus 30a(30).

[0086] This plasma arc discharge processing apparatus 30a consists of a plasma processing tank 31 into which washing water containing soil (soil with a particle size of less than 4 mm) after the removal of coarse particles is introduced, an electrode supply device 33 for supplying electrodes 32 into the plasma processing tank 31, and an AC voltage source (not shown) for applying an AC voltage to the electrodes 32.

[0087] In the illustrated embodiment, the aforementioned plasma treatment tank 31 is composed of a cylindrical body with both ends closed. A water inlet 34 for introducing cleaning water containing soil is provided at one end of this cylindrical plasma treatment tank 31 (the lower side of the paper in Figure 2), and a drain outlet 35 for discharging the cleaning water that has passed through the plasma treatment tank 31 and been treated is provided at the other end of the plasma treatment tank 31 (the upper side of the paper in Figure 2).

[0088] At the end of the plasma processing tank 31 on the side where the water inlet 34 is located, a pair of gas introduction passages 36, 36 are provided at symmetrical positions with respect to the water inlet 34. By blowing air, carbon dioxide, or a mixture thereof as an operating gas into the cleaning water in the plasma processing tank 31 through these gas introduction passages 36, 36, a jet of operating gas bubbles can be formed in the cleaning water in the plasma processing tank 31.

[0089] In the illustrated embodiment, the gas introduction passages 36, 36 are opened inside the plasma processing tank 31, and the working gas is blown into the cleaning water after it has been introduced into the plasma processing tank 31. However, instead of this configuration, the ends of the gas introduction passages 36, 36 may be opened inside the introduction passage 63 connected to the plasma processing tank 31, and working gas such as air or carbon dioxide may be blown in, thereby generating bubbles of the working gas in the cleaning water before it is introduced into the plasma processing tank 31.

[0090] A gas flow disperser 37, made of a porous material such as a cylindrical mesh, is attached to the tip of the gas introduction passage 36. The gas injected into the washing water through the gas introduction passage 36 is pulverized into fine bubbles as it passes through the gas flow disperser 37 and dispersed in the washing water.

[0091] In the direction of gas injection through the gas introduction passage 36, an electrode insertion hole 38 is formed by penetrating the side wall of the plasma processing tank 31. By inserting the electrode 32 into this electrode insertion hole 38 from the outside to the inside of the plasma processing tank 31, the tip of the electrode 32 can be made to protrude into the space inside the plasma processing tank 31.

[0092] As an example, the electrode 32 is positioned at an angle of 30° to 90°, preferably 45° to 90°, with respect to the central axis of the plasma processing tank 31. In the illustrated embodiment, it is inserted with its tip facing upward at an angle of approximately 70° with respect to the central axis of the plasma processing tank 31.

[0093] The electrode insertion hole 38 is preferably located directly above the gas introduction passage in a plan view. Therefore, in the illustrated embodiment in which two electrode insertion holes 38 are provided at symmetrical positions, two gas introduction passages 36 are also provided, and the system is configured to generate two streams of bubble jets within the plasma processing tank 31.

[0094] In a configuration in which working gases such as air or carbon dioxide are mixed into the cleaning water in the introduction passage 63 before it is introduced into the plasma processing tank 31, the water inlet 34 connected to the introduction passage 63 may be provided to open toward the gap between electrodes 32, 32, or cleaning water mixed with working gas bubbles may be introduced from the location where the gas introduction passage 36 in Figure 2 is provided (two locations in the illustrated example).

[0095] The electrode 32 inserted into the electrode insertion hole 38 can be quantitatively supplied into the plasma processing tank 31 by the electrode supply device 33. In the illustrated example, the electrode 32 is represented as a rod of a predetermined length, but instead of this configuration, for example, a long wire-shaped electrode wound in a coil may be supplied into the plasma processing tank 31 while being pulled out by the electrode supply device 33.

[0096] In the plasma arc discharge processing apparatus 30 described above, a predetermined AC voltage is applied to each electrode 32, 32, and cleaning water containing soil is introduced into the plasma processing tank 31 via the water inlet 34. At the same time, by introducing working gas into the cleaning water in the plasma processing tank 31 via the gas introduction passage 36, or by introducing cleaning water mixed with working gas bubbles in the introduction passage 63, the gas content in the cleaning water is introduced to be 30-90% by volume, thereby creating a flow of cleaning water containing bubbles toward the tips of the electrodes. This creates the conditions necessary for dielectric breakdown, as the cleaning water comes into contact with the surface of the electrodes 32 and bubbles are present between the tips of the electrodes 32, thereby generating a plasma arc discharge between the electrodes 32, 32.

[0097] The high-frequency shock waves generated by this plasma arc discharge make it possible to separate radioactive materials such as cesium attached to the soil, and if heavy metals are attached to the soil, to the wash water along with the radioactive materials.

[0098] Radioactive materials and heavy metals separated from the soil and transferred to the washing water are ionized and dissolved into the washing water. At the same time, active substances such as O+ and O3+ generated by the injection of working gases such as oxygen and carbon dioxide into the washing water as it passes through the plasma oxidize with the radioactive materials and heavy metals dissolved in the washing water, causing them to solidify.

[0099] [Coarse particle recovery device] As described above, the washing water containing soil after plasma arc discharge treatment (in this embodiment, fine gravel, sand, silt, and clay, which are particles of 4 mm or less) is supplied to the coarse particle recovery device 40, where a coarse particle recovery process is performed in which coarse particles of a predetermined particle size (for example, 75 μm) or larger are classified and recovered from the washing water.

[0100] In this embodiment, the particle size of the particles recovered in the coarse particle recovery step is set to "75 μm or larger," but the particles recovered as coarse particles do not necessarily have to be 75 μm or larger; the lower limit of classification may be greater than or less than 75 μm.

[0101] Furthermore, in the coarse-grain recovery process, it is not necessary to recover all of the coarse-grained soil strictly. As long as the coarse-grained soil can be roughly separated and recovered, some of the coarse-grained soil may not be recovered and may be transported to the next process along with the fine-grained soil.

[0102] In this embodiment, when starting the coarse particle recovery process, approximately twice the weight of the soil at the time of input into the hopper 11 is supplied as washing water from the washing water tank 70 to the coarse particle recovery device 40.

[0103] In this embodiment, a high-mesh separator with a screen opening of 75 μm is used as the coarse particle recovery device 40 to classify and recover soil particles with a particle size of 75 μm or more and less than 4 mm from the washing water, and fine particles with a particle size of less than 75 μm (silt and clay in this embodiment) are introduced into the next process together with the washing water.

[0104] The concentration of radioactive materials in the coarse-grained soil (75 μm or larger, less than 4 mm) recovered in the coarse-grain recovery process is recovered in a way that allows it to be reused as construction material.

[0105] [Plasma arc discharge treatment device] As described above, after the coarse-grained soil (particle size 75 μm or larger) (in this embodiment, sand and some fine gravel) has been recovered, the washing water containing the fine-grained soil (particle size less than 75 μm) (in this embodiment, silt and clay) is first introduced into the stirring tank 82 and stirred before being introduced into the plasma arc discharge treatment device 30b.

[0106] This plasma arc discharge treatment apparatus 30b has the same configuration as the plasma arc discharge treatment apparatus 30a described above with reference to Figure 2. Here, the washing water containing fine-grained soil (silt and clay in this embodiment) is subjected to plasma arc discharge treatment again. If radioactive material (or radioactive material and heavy metals if heavy metals are present in the soil) is still attached to the soil, these are separated from the soil and dissolved into the washing water. The radioactive material and heavy metals dissolved in the washing water are then reacted with an activating substance (O+, O3+, etc.) to solidify.

[0107] [Fine particle recovery device] The washing water containing fine-grained soil (silt and clay in this embodiment), which has been treated in the aforementioned plasma arc discharge treatment device 30b, is introduced into the fine-grained recovery device 50, where the fine-grained soil (silt and clay in this embodiment) and the radioactive material (radioactive material and heavy metals if heavy metals are attached to the soil) that has been separated and solidified from the fine-grained soil (silt and clay in this embodiment) by the plasma arc discharge treatment are separated and recovered separately.

[0108] The fine particle recovery device 50 can be configured in various ways as long as it can separate and recover radioactive material (radioactive material and heavy metals if the washing water contains heavy metals) and fine-grained soil (silt and clay in this embodiment). In this embodiment, the fine particle recovery device 50 includes a storage tank 51 into which washing water after plasma arc discharge treatment is introduced, as shown in Figure 3; a bubble generator 52 that generates bubbles, which are, for example, a group of bubbles with a diameter of 100 μm or less, in the washing water; a radioactive material recovery means 53 that recovers radioactive material (radioactive material and heavy metals if the washing water contains heavy metals) that has adhered to the bubbles and floated to the surface in the storage tank 51; and a means (not shown) for recovering fine-grained soil (silt and clay in this embodiment) that has settled in the storage tank 51.

[0109] The washing water treated by the plasma arc discharge treatment device 30b is introduced into the aforementioned storage tank 51.

[0110] Soil such as silt and clay settle relatively quickly in the washing water, while solid radioactive materials and heavy metals generated by the plasma arc discharge treatment float in the washing water for a relatively long time. When bubbles are generated in the washing water by the bubble generator 52 installed at the bottom of the storage tank 51, the bubbles attach to the solidified radioactive materials and heavy metals, causing them to float and fall into the collection cup 54.

[0111] The radioactive materials and heavy metals attached to the bubbles, collected in the recovery cup 54, are circulated between the circulation tank 56 and the storage tank 51 for 5 minutes, then sent to the dewatering tank 57, where they are dewatered and placed in storage capsules.

[0112] In this manner, radioactive materials and heavy metals that float to the surface of the washing water are recovered by the radioactive material recovery means 53, and fine-grained soil (silt and clay in this embodiment) that settles at the bottom of the storage tank 51 is recovered by the soil recovery means (not shown). This configuration allows for the separation and recovery of radioactive materials and fine-grained soil (silt and clay in this embodiment) from the washing water.

[0113] In order to recover radioactive materials and heavy metals that have been brought to the surface by the bubbles, in this embodiment, the radioactive material recovery means 53 described above consists of a recovery cup 54 that is floated in the washing water by a floater so that its upper opening edge is at the same level as the liquid surface, and a suction hose 55a connected to the bottom of the recovery cup 54 that sends the materials to the circulation tank 56.

[0114] The washing water sent to the circulation tank 56 is returned to the storage tank 51 via the circulation hose 55b. After this circulation is performed for 5 minutes, the circulation via the suction hose 55a and circulation hose 55b is stopped, and the washing water in the circulation tank 56 is dropped into the dewatering tank 57 located at the bottom of the circulation tank 56 for dewatering and other treatments. The radioactive materials and heavy metals after dewatering and other treatments are stored in a radioactive material storage capsule.

[0115] The radioactive materials and heavy metals recovered in this way can be used, for example, as materials for radiation sources in industrial X-ray machines.

[0116] On the other hand, the fine-grained soil (with a particle size of less than 75 μm) that accumulates at the bottom of the storage tank 51 due to sedimentation (silt and clay in this embodiment) is recovered as a reusable recycled resource.

[0117] In this embodiment, the concentration of the recovered radioactive material was approximately 500,000 Bq / kg or less.

[0118] Furthermore, in this embodiment, the radioactivity concentration of the washing water after recovering the fine-grained soil and radioactive materials was 200 Bq / kg or less.

[0119] In this manner, after the fine-grained material recovery device 50 recovers radioactive materials, heavy metals, and fine-grained soil (silt and clay in this embodiment), the wash water is returned to the wash water tank 70 via a recovery channel 68.

[0120] In the illustrated embodiment, a configuration was adopted in which radioactive materials and heavy metals were separated and recovered from the washing water using bubbles, separating them from fine particles (silt and clay in this embodiment). However, instead of this configuration, radioactive materials and heavy metals could be selectively recovered from the washing water by means of magnetic separation, for example.

[0121] In this case, prior to magnetic separation, necessary treatments such as adding magnetic particles of iron or other materials to the washing water are performed.

[0122] As a result, magnetic particles float around the radioactive material suspended in the washing water, and these magnetic particles then attract the radioactive material, causing it to be adsorbed onto the magnetic filter.

[0123] [Auxiliary recovery device] An auxiliary recovery device 90 is provided in the recovery channel 68 that connects the fine particle recovery device 50 and the washing water tank 70 to recover fine particles (silt and clay in this embodiment) that could not be recovered from the washing water by the fine particle recovery device 50 (see enlarged view in Figure 1).

[0124] In this embodiment, a plurality of baffle plates 91 are erected at the 80% point of the total length of the recovery channel 68, in a direction perpendicular to the flow direction of the washing water and protruding upward from the bottom of the recovery channel 68, and are provided as an auxiliary recovery device 90. This configuration allows for the recovery of fine-grained soil (silt and clay in this embodiment) that has accumulated at the bottom of the recovery channel because it cannot overcome the aforementioned baffle plates 91, as a recyclable resource.

[0125] [Effect, etc.] As described above, in the resource recovery apparatus 1 of the present invention, by performing a predetermined plasma arc discharge treatment on the wash water containing soil using the plasma arc discharge treatment apparatus 30 (30a, 30b), radioactive materials can be separated from the fine-grained soil (for example, silt and clay less than 75 μm) and transferred to the wash water, and solidified. Furthermore, in the subsequent fine-grained material recovery process, the fine-grained soil (for example, silt and clay) can be recovered by separating it from the solidified radioactive materials and heavy metals, thereby recovering the fine-grained soil (for example, silt and clay) in a state where the radioactivity concentration has been reduced to a reusable level.

[0126] Furthermore, by using bubbles to recover radioactive materials and heavy metals, it was possible to easily and efficiently separate and recover radioactive materials, heavy metals, and fine-grained soil (such as silt and clay) that were mixed in the washing water.

[0127] The recovered radioactive materials and heavy metals may be sent for final disposal, but they can also be reused, for example, as materials for radiation sources in industrial X-ray machines. [Explanation of symbols]

[0128] 1. (Contaminated soil) resource recovery device 10. Agitation and cleaning device (drum washer) 11 Hoppa 20. Coarse particle recovery device (vibrating screen) 30 (30a, 30b) Plasma arc discharge treatment device 31 Plasma treatment tank 32 electrodes 33 Electrode feeding device 34 Water inlet 35 Drain 36 Gas Inlet 37. Gas flow disperser 38 electrode insertion holes 40. Coarse particle recovery device (high-mesh separator) 50. Fine particle recovery device 51 Storage tank 52 Bubble Generator 53. Means of recovering radioactive materials 54 Collection cups 55a Suction hose 55b Circulation hose 56 Circulation tank 57 Dehydration tank 61, 62, 63, 64, 65, 66, 67 Conveyor channel 68 Recovery channel 70 Washing water tank 71, 72, 73 Wash water supply channel 81,82 Agitation tank 90 Auxiliary recovery device 91 Obstacle board WM cleaning treatment device CM Classification Apparatus DM separation processing device DHM Dehydration Treatment System Sc-removed soil Sp purified soil, etc. Sd Dehydrated Cake

Claims

1. A stirring and washing process in which contaminated soil is washed by stirring it with washing water, The soil after the stirring and washing step is classified in the presence of the washing water to recover coarse-grained soil with a predetermined particle size or larger, and the remaining fine-grained soil after the recovery of the coarse-grained soil, along with the washing water, is supplied to the next step in a coarse-grain recovery step. A fine-grain recovery step is performed to recover the fine-grained soil from the washing water containing the fine-grained soil that remains after the recovery of the coarse-grained soil, After the stirring and washing step and before the fine particle recovery step, a plasma arc discharge treatment step is included in which a predetermined plasma arc discharge is performed at least once on the washing water containing soil. In the aforementioned plasma arc discharge process, In a plasma treatment tank in which the tips of a plurality of electrodes to which an AC voltage is applied are arranged with a predetermined interval between them, the cleaning water containing the soil is introduced so that at least the tip of each electrode is immersed in the cleaning water, and a working gas is injected into the cleaning water introduced between the tips of the electrodes to generate minute bubbles of the working gas dispersed in the cleaning water, thereby generating a plasma arc discharge between the electrodes and separating the radioactive material attached to the soil from the soil. In the aforementioned fine particle recovery process, From the washing water containing the fine-grained soil, the fine-grained soil and the radioactive material separated from the soil are separated and recovered. A method for recycling contaminated soil, characterized by the following features.

2. In the aforementioned fine particle recovery process, By generating bubbles in the washing water, the radioactive material is made to adhere to the bubbles, float to the surface, and be recovered. The method for resource recovery of contaminated soil according to claim 1, characterized in that the fine-grained soil is recovered by settling in the washing water.

3. The method for resource recovery of contaminated soil according to claim 1 or 2, further comprising a coarse particle recovery step of recovering coarse particles of a predetermined particle size or larger from the coarse-grained soil, following the stirring and washing step.

4. A washing water tank for storing the washing water and a recovery channel for introducing the washing water after the fine particle recovery process into the washing water tank are provided. The method for resource recovery of contaminated soil according to claim 1 or 2, characterized in that an auxiliary recovery step is provided in the recovery channel for recovering the fine-grained soil that remains in the washing water and is not recovered in the fine-grained soil recovery step.

5. A washing water tank for storing the washing water and a recovery channel for introducing the washing water after the fine particle recovery process into the washing water tank are provided. The method for resource recovery of contaminated soil according to claim 3, characterized in that an auxiliary recovery step is provided in the recovery channel for recovering the fine soil particles that remain in the washing water and are not recovered in the fine particle recovery step.

6. A stirring and washing device that washes contaminated soil by stirring it with washing water, A coarse particle recovery device that classifies the soil after it has been stirred and washed by the aforementioned stirring and washing device in the presence of the washing water, recovers the coarse particle portion of the soil with a predetermined particle size or larger, and supplies the remaining fine particle portion of the soil and the washing water to the next process, A fine-grain recovery device for recovering the fine-grained soil from the washing water containing the fine-grained soil remaining after the recovery of the coarse-grained soil, The system includes at least one plasma arc discharge apparatus that performs a predetermined plasma arc discharge on the washing water containing soil at any point after the stirring and washing apparatus and before the fine particle recovery apparatus, The plasma arc discharge processing apparatus, The plasma treatment tank is provided into which the cleaning water containing the soil is introduced, with the tips of the electrodes arranged at a predetermined interval between them; a gas introduction path is provided into which an operating gas is injected into and / or the cleaning water introduced into the plasma treatment tank to generate minute bubbles of the operating gas dispersed in the cleaning water; and a voltage source is provided to apply an AC voltage to each of the electrodes necessary to generate a plasma arc discharge between the tips of the electrodes under the generation of the bubbles, thereby separating radioactive material attached to the soil from the soil by the plasma arc discharge, The aforementioned fine particle recovery device A means for recovering the radioactive material separated from the soil, A contaminated soil resource recovery apparatus characterized by comprising a soil recovery means for recovering the fine-grained portion of the soil.

7. The aforementioned fine particle recovery device A bubble generating device that generates bubbles in the aforementioned washing water, A storage tank for storing the washing water that has generated the bubbles, The radioactive material recovery means recovers the radioactive material that has adhered to the bubble and floated to the surface in the storage tank, The contaminated soil resource recovery apparatus according to claim 6, further comprising the soil recovery means for recovering the fine-grained soil that has settled in the storage tank.

8. The contaminated soil volume reduction apparatus according to claim 6 or 7, further comprising a coarse particle recovery device arranged after the stirring and washing device for recovering coarse particles of a predetermined particle size or larger from the coarse-grained soil.

9. A washing water tank for storing the washing water and a recovery channel for introducing the washing water, after passing through the fine particle recovery device, into the washing water tank are provided. The contaminated soil resource recovery apparatus according to claim 6 or 7, characterized in that an auxiliary recovery device is provided in the recovery channel for recovering the fine soil particles that remain in the washing water and are not recovered by the fine particle recovery device.

10. A washing water tank for storing the washing water and a recovery channel for introducing the washing water, after passing through the fine particle recovery device, into the washing water tank are provided. The contaminated soil resource recovery apparatus according to claim 8, characterized in that an auxiliary recovery device is provided in the recovery channel for recovering the fine soil particles that remain in the washing water and are not recovered by the fine particle recovery device.

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