JP2014021062A - Classification method of contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a classification method of contaminated soil capable of classifying and collecting fine particles having a harmful substance easily adhering thereto from the contaminated soil to achieve volume reduction of the contaminated soil.SOLUTION: A classification method of contaminated soil comprises: cleaning slurry adjusted by adding water to contaminated soil S so as to be concentration of 10 wt.% or less by a cavitation water jet; stirring the slurry by a flow rate variable water jet allowing a flow rate to be changed; precipitating and separating sand grains in a coarse particle classification tank 2; centrifuging the sand grains into silt particles and clay particles by a centrifugal separator 4; precipitating and separating the silt particles in a fine particle precipitator 5 to classify the clay particles; precipitating and depositing the clay particles in a fine particle precipitator 6; and classifying and collecting the clay particles from the contaminated soil.

Description

  The present invention relates to a method for classifying contaminated soil containing a radioactive substance, and in particular, by selectively classifying and removing particles having a small particle size and a large specific surface area, the radioactive substance tends to be adsorbed on the fine particles. It is related with the classification method of contaminated soil which removes from contaminated soil and realizes volume reduction of contaminated soil.

  Contaminated soil contaminated with radioactive materials must be temporarily stored in the intermediate storage facility until final disposal, and the storage space becomes so large that the amount of contaminated soil becomes large. Therefore, in order to compress the storage space, it is desired to reduce the volume of the contaminated soil, that is, to reduce the volume of the contaminated soil.

  In general, it is known that contaminants are adsorbed on particles having a small particle size, particularly clay. As a method of reducing the volume of contaminated soil using these characteristics of the pollutants, the soil particles of the contaminated soil are classified according to the size of the particles, and the soil particles adsorbed with the pollutants are removed. Methods for classifying contaminated soil are known.

  And classification of such contaminated soil is performed using the classification system of the following structures. That is, a sieve that removes foreign matter such as gravel and vegetation having a particle diameter of 5 mm or more from the contaminated soil and a contaminated soil that has been hydrated into a slurry state by rotating the stirring blade and stirring the gravel component having a particle diameter of 2 mm or more A separation tank that sediments and separates sand having a particle diameter smaller than 2 mm, a cleaning tank that stores and agitates the slurry and ultrasonically cleans it while stirring, and performs ultrasonic cleaning while circulating the washed slurry. The finishing washing tube is configured to be classified into a cyclone classifier that classifies the finish-washed slurry and takes out soil particles of 30 μm or more as washing soil (see, for example, Patent Document 1).

JP 2005-81247 A

  In the prior art described in Patent Document 1, when the sandy contaminated soil mainly composed of coarse particles is classified, the gravel and sand not adsorbing radioactive substances are classified from the contaminated soil to contaminate the soil. However, when categorizing clay-contaminated soil consisting mainly of fine particles such as wetlands, the classification is based on a relatively large particle size, so the diameter is smaller than the gravel and larger than the clay content. The contaminated soil was stored while containing a large amount of silt of the diameter, and the contaminated soil still tended to increase.

  In addition, when the clay is attached to the gravel, the clay is mixed in the gravel that is settled and separated to the bottom of the tank in the separation tank and discharged to the outside of the tank. There was a risk that the radioactive material diffused to the outside.

Therefore, among the contaminated soil that contains radioactive substances and needs to be isolated and stored for a long period of time, the fine particles that are likely to adhere to harmful substances are efficiently recovered, the volume of the contaminated soil is reduced, and the storage space is reduced. Furthermore, there is a technical problem to be solved in order to prevent fine particles from being mixed and collected in coarse particles and fine particles having a high sedimentation speed, and the present invention solves this problem. Objective.

  The present invention has been proposed in order to achieve the above object, and the invention according to claim 1 is a method for classifying contaminated soil containing a radioactive substance. A stirring step of stirring in the inside, and coarse particles having a diameter larger than the first particle size are settled and separated in the coarse particle classification tank, and fine particles and fine particles smaller than the first classified particle size are separated by rising water flow. A primary classification step for overflowing, a foreign matter removal step for removing foreign matters contained in the contaminated soil, and sludge that has undergone the primary classification step settles fine particles larger than the second particle size in a fine particle classification tank. Provided is a method for classifying contaminated soil which comprises a secondary classification step of separating and collecting fine particles having a diameter smaller than the second particle size.

  According to this configuration, coarse particles, fine particles, and fine particles contained in the contaminated soil are classified in two stages, and fine particles that are easily adsorbed by radioactive substances are efficiently removed by a predetermined amount from the smaller particle size. Can do. That is, first, the contaminated soil is hydrated and suspended so that coarse particles having a diameter larger than the first classified particle size are settled and separated at the bottom of the coarse particle classification tank, and the inside of the coarse particle tank is equal to or smaller than the first classified particle size. The fine particles and fine particles float on the upper part of the coarse particle classification tank by the rising water flow rising at a predetermined flow rate set so that the fine particles and fine particles rise without settling. Subsequently, the fine particles and the muddy water containing the fine particles are sent to the fine particle classification tank, where fine particles larger in diameter than the second classified particle size settle to the bottom of the fine particle classification tank. In addition to the separation, fine particles having a particle size equal to or smaller than the second classified particle size are suspended in the upper part of the fine particle classification tank and classified. Thereby, it is possible to reliably classify and collect only fine particles that are small in diameter and large in specific surface area (surface area per 1 g of particles) and easily adhere to harmful substances as compared with coarse particles and fine particles.

  In addition, even when coarse particles, fine particles, and fine particles adhere to each other in the muddy water, the fine particles can be separated by separating the particles by stirring the muddy water in the coarse particle classification tank. It is possible to avoid classification while adhering to fine particles.

  According to a second aspect of the present invention, in the first aspect of the invention, the contaminated soil is agitated by spraying the mud water with cavitation jet water including cavitation and flow rate variable jet water that maintains the flow rate of the rising water flow. Provide a method for classifying contaminated soil.

  According to this configuration, even when the coarse particles, fine particles, and fine particles in the muddy water stored in the coarse particle classification tank adhere to each other, vibrations caused by cavitation contained in the cavitation jet water. Cleaning particles, that is, separating particles and releasing adhesion between particles, and continuously raising particles smaller than the first classified particle size to the upper part of the coarse particle classification tank with a rising water flow at a constant flow rate Thus, it can be avoided that fine particles and fine particles are mixed in the coarse particles that settle and deposit at the bottom of the coarse particle classification tank.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the fine particles and the fine particles are separated by a centrifuge between the primary classification step and the secondary classification step. Provided is a method for classifying contaminated soil including a centrifugation step.

  According to this configuration, among the fine particles contained in the muddy water that has undergone the primary classification process, in the centrifugal separation process, fine particles that float independently without being attached to the fine particles in the muddy water are classified and collected by the centrifuge. By doing so, the concentration of fine particles in the fine particle classification tank is reduced, and classification in the secondary classification step can be performed efficiently.

  According to a fourth aspect of the present invention, in the first aspect of the first to third aspects, the second classified particle size is arbitrarily set according to the residual concentration of the radioactive substance allowed in the fine particles. Provide a possible method for classifying contaminated soil.

  According to this configuration, the fine particle is set in the fine particle classification tank by setting the particle size of the fine particle adhering to the residual concentration of the radioactive material allowed in the reused soil to the second classified particle size. The time required for sedimentation can be reduced.

  According to a fifth aspect of the present invention, there is provided a method for classifying contaminated soil in which the muddy water is hydrated to a concentration of 10 wt% or less in the coarse particle classification tank according to the first aspect of the present invention. I will provide a.

  According to this configuration, by setting the concentration of the mud water to 10 wt% or less, the difference in the sedimentation speed between the coarse particles and the fine particles before and after the first classified particle size is increased, and the coarse particles are converted into the coarse particle classification tank. It is possible to shorten the time required for sedimentation and separation in the inside.

  Since the invention described in claim 1 can reliably and efficiently recover fine particles mainly containing harmful substances from contaminated soil that contains radioactive substances and needs to be kept isolated for a long period of time, In addition to the classification of sandy soil that contains a lot of coarse particles, such as clay soil that contains a lot of fine particles, fine particles adhering to radioactive substances are classified and removed to remove contaminated soil. The volume can be reduced, the storage space can be reduced, and the efficiency of the decontamination work can be increased to greatly reduce the disposal cost. In addition, since the mud is agitated and the particles adhering to each other are separated, the fine particles are prevented from settling into the coarse particles and fine particles that have a high settling speed, and the coarse particles and fine particles are radioactive. It can avoid that the fine particle containing a substance mixes in.

  The invention described in claim 2 is a case where the coarse particles, fine particles, and fine particles in the muddy water stored in the coarse particle classification tank are adhered to each other in addition to the effect of the invention described in claim 1. However, in order to prevent fine particles and fine particles from being mixed into the coarse particles accumulated in the coarse particle classification tank, there is no radioactive substance in the coarse particles recovered from the coarse particle classification tank and reused. It is possible to avoid being mixed and spread outside.

  In addition to the effects of the invention described in claim 1 or 2, the invention described in claim 3 further classifies and collects fine particles floating independently in the muddy water in the centrifugal separation process, and performs the secondary classification process. In order to perform classification efficiently, fine particles can be classified in a short time from the muddy water that has undergone the primary classification process.

  In the invention according to claim 4, in addition to the effect of the invention according to claim 1 to claim 3, the second classified particle size can be set according to the concentration of the radioactive substance allowed in the fine particles. Therefore, the time required for the secondary classification process can be shortened according to the soil quality of the contaminated soil and the desired decontamination rate by avoiding an unnecessarily slow classification flow rate.

  In addition to the effects of the invention described in claim 1 to claim 4, the invention described in claim 5 further reduces the concentration of mud water in the coarse particle classification tank to the settling rate of fine particles. On the other hand, by setting it to be sufficiently large, it is possible to reliably classify the coarse particles and fine particles and reduce the time required for the coarse particles to settle and deposit on the bottom of the tank.

The figure shows a method for classifying contaminated soil according to an embodiment of the present invention.
The figure which shows the relationship between the particle size of a particle, a mass currency rate, and a surface area removal rate. The figure which shows the relationship between the particle size of particle | grains, and a sedimentation speed. The figure which shows the outline | summary of a classification system.

  The present invention efficiently collects fine particles, which contain radioactive substances and need to be isolated and stored for a long period of time, and to which harmful substances tend to adhere, and reduces the storage space by reducing the volume of contaminated soil. In addition, in order to prevent the fine particles from being collected and collected in the coarse particles and fine particles having a high sedimentation rate, mud water formed by hydrating contaminated soil is contained in the coarse particle classification tank. Stirring step for stirring, and primary particles in which coarse particles larger than the first classified particle size are settled and separated in the coarse particle classification tank, and fine particles and fine particles smaller than the first classified particle size are overflowed by the rising water flow. In the fine particle classification tank, the fine particles larger than the second classified particle size are settled and separated in the fine particle classification tank from the classification step, the foreign matter removal step for removing foreign matters contained in the contaminated soil, and the primary classification step. Fine particle size less than or equal to It was realized by the secondary classification step to recover the particles.

  Hereinafter, a method for classifying contaminated soil according to an embodiment of the present invention will be described with reference to FIGS.

  First, the classification mechanism of contaminated soil will be described. The contaminated soil in the present embodiment is soil containing soil particles that have adsorbed radioactive substances. The radioactive substance hardly adsorbs to coarse particles having a large particle size, and strongly adsorbs to fine particles, particularly fine particles. This is because fine particles have a large surface area (specific surface area) per gram, and the amount of contaminants that can be adsorbed accordingly is large. For this reason, generally, fine particles (so-called clay particles) contain a larger amount of radioactive material than coarse particles (so-called gravel particles, sand particles), and clay particles can be classified and recovered from contaminated soil. It is effective in reducing the volume of contaminated soil.

  The specific surface area is determined by the size and shape of the particles, and representative particle sizes of sand particles, silt particles, and clay particles constituting the soil particles are: sand particles: silt particles: clay particles = 1: 0.01: 0. .001 (mm), when the particles are spherical, the specific surface area of sand particles is 1, and the specific surface area ratio of sand: silt: clay is 1: 100: 1000. . Thus, for example, in a clay soil having a classification ratio of soil particles of 2% sand particles, 42% silt particles, and 56% clay particles, as shown in FIG. The particles are 0.01%, the silt particles are 1.99%, and the clay particles are 98.0%. Therefore, in such a soil, by removing the clay particles, the radioactive material adsorbed on the clay particles among the radioactive materials contained in the contaminated soil, that is, the radioactive materials adhering to the surface area of 98.0% is removed. be able to. Furthermore, in the soil mass, as shown in FIG. 1, since the removal amount of clay particles is 68% of the total mass, the volume is reduced by 32%.

  Therefore, in order to classify and recover clay particles from clay contaminated soil, clay particles are classified in two stages using the difference in sedimentation speed according to the particle size when the soil particles settle in the fluid. Is selectively recovered. The speed at which the particles settle in the fluid is related to the specific gravity of the particles, the viscosity coefficient depending on the temperature of the fluid, the size and shape of the particles, and the like.

  The equation representing the settling velocity v is known as Stokes' law under ideal conditions (for example, assuming that the particle is a sphere), and the resistance force F received when one soil particle sinks in the fluid is , As shown in Equation 1.

  The buoyancy Fb acting on the soil particles is as shown in Formula 2.

And the gravity Fg which moves to the soil particle is as shown in Formula 3.

  Therefore, since F + Fb = Fb holds at the terminal velocity Vs at which the soil particles settle in the fluid, the terminal velocity Vs is as shown in Equation 4.

  If the soil particles are in a rising water flow field having a flow velocity Vup larger than the terminal velocity Vs in the coarse particle classification tank, there are soil particles that do not settle or move upward.

  Next, the concentration of muddy water when the contaminated soil is hydrated in the coarse particle classification tank will be described. For example, as shown in FIG. 2, when the muddy water concentration is 15 wt%, if the particle size of 75 μm is set as the first classified particle size, the particle size of 75 μm and the particle size of 60 μm slightly smaller than this particle size are set. There is no significant difference in the depth of settling between the particles in 10 minutes. On the other hand, when the muddy water concentration is 10 wt% or less, a difference of 30 cm or more occurs in the sedimentation depth between the two. Therefore, by setting the mud concentration to 10 wt% or less, particles having a predetermined particle diameter or more can be settled and separated in a relatively short time.

  Next, the rising water flow that flows in the coarse particle classification tank and overflows the fine particles and the fine particles will be described. As shown in Table 1, for example, when particles having a particle diameter of 60 μm or less in a muddy water adjusted to a muddy water concentration of 8 wt% are suspended and particles having a particle diameter of 75 μm or less are settled and separated, 0,13828 cm / s to 0 A flow rate between 21607 cm / s, for example, a flow rate of 0.20 cm / s may be set. When the flow rate is set to 0.20 cm / s, particles with a particle size of 60 μm rise by 70 cm or more in 20 minutes. Therefore, if the height of the coarse particle classification tank is set to 70 cm, the particle size is 60 μm or less. The particles overflow from the upper part of the tank and can classify coarse particles and fine particles.

  Next, a system for classifying contaminated soil will be described. In this method, any clay particles contained in the contaminated soil are suspended in water, and sand particles and silt particles having a larger particle size than the clay particles are settled and separated in two stages. Even things can be applied.

  As shown in FIG. 3, the classification system includes a belt conveyor 1 for conveying the contaminated soil S, gravel particles and sand particles as coarse particles by introducing the contaminated soil S, and silt particles as fine particles smaller than these. And a coarse particle classification tank 2 for classifying into clay particles as fine particles, a suspended matter collection tank 3 for collecting foreign matter floating in the muddy water that has passed through the coarse particle classification tank 2, and a cyclone for classifying silt particles and clay particles. Type centrifugal separator 4, fine particle settling tank 5 as a fine particle classification tank for classifying clay particles mixed in centrifugally separated silt particles from silt particles, and sedimentation separation of clay particles from muddy water containing clay particles A fine particle settling tank 6, a water treatment system 7 for solid-liquid separation of clay particles, and a filter press 8 for dehydrating and collecting clay particles are provided.

  The belt conveyor 1 drops the contaminated soil S from the sedimentation field into the coarse particle classification tank 2. An oscillating sieve 9 that allows the contaminated soil S to pass is provided upstream of the belt conveyor 1. The vibration sieve 9 removes relatively large foreign matters having a particle size of, for example, 30 mm or more. The particle size of the foreign matter removed by the vibrating sieve 9 may be set as appropriate according to the type of the contaminated soil S.

  The coarse particle classification tank 2 is connected to a water storage tank 12 for storing fresh water via a cavitation jet pump 10 and a variable flow rate jet pump 11. The fresh water in the water storage tank 12 is supplied to adjust the contaminated soil S introduced into the coarse particle classification tank 2 to a concentration of 10 wt% or less. As a result, the concentration of the muddy water in the coarse particle classification tank 2 is set so that the settling speed of the sand particles is sufficiently larger than the settling speed of the silt particles, and the sand particles and clay particles are surely overflowed to sand. While classifying from the particles and gravel particles, the time required for the sand particles and gravel particles to settle and deposit at the bottom of the tank can be shortened. In addition, when the classification by the coarse particle classification tank 2 is performed by batch processing, the muddy water concentration in the coarse particle classification tank 2 is reduced by the amount of overflow of the silt particles or clay particles, and the pump flow rate needs to be controlled. In this embodiment, the contaminated soil S is continuously dropped from the belt conveyor 1 to the coarse particle classification tank 2 at 25 ton / hr. Thereby, continuous classification can be simply performed without maintaining the mud concentration in the coarse particle classification tank 2 and controlling the pump flow rate.

The cavitation jet pump 10 discharges cavitation jet water including cavitation generated by a cavitation nozzle (not shown). This cavitation

By spraying Giotto water on the muddy water, even if the particles adhere to each other in the muddy water, the particles are peeled apart and the clay particles are settled and deposited while adhering to the gravel particles and silt particles. Can be prevented.

  The variable flow rate jet pump 11 discharges variable flow rate jet water whose flow rate can be changed by an inverter (not shown). As a result, the flow rate of the ascending water flowing in the coarse particle classification tank 2 can be kept constant, and the mud concentration in the coarse particle classification tank 2 where the contaminated soil S is continuously dropped can be kept constant. it can. The ascending water flow supplied from the variable flow rate Giotto pump 11 into the coarse particle classification tank 2 is set to a flow velocity corresponding to the first classification particle size of 75 μm, and silt particles and clay particles having a diameter smaller than 75 μm. Is continued to overflow from the upper part of the tank, and gravel particles and sand particles having a diameter of 75 μm or more are settled and separated at the bottom of the tank. Thereby, gravel particles and sand particles can be classified from silt particles and clay particles. The rising water flow is freely set according to the muddy water concentration of the contaminated soil and the first classified particle size, which can be freely changed. For example, when the muddy water concentration is 8 wt% and the first classified particle size is set to 75 μm, the ascending flow rate is set to 0.20 cm / s.

  The coarse particle classification tank 2 is provided with a screw conveyor 13 for carrying out sand particles and gravel particles settled and deposited on the bottom of the tank. The sand particles and gravel particles carried out by the screw conveyor 13 are transported to the collection bag 15 by the belt conveyor 14 and dehydrated in a bag. These sand particles and gravel particles can be reused because they have a large particle size and do not adsorb radioactive substances.

  In the belt conveyor 14, an ultrasonic transmission device 16 that transmits ultrasonic waves irradiated from the upper side of the conveyance path for conveying the sand particles and gravel particles deposited on the bottom of the coarse particle classification tank 2 toward the conveyance path is arranged. It is installed. Thus, even if the silt particles and the clay particles are mixed in the sand particles and gravel particles, the silt particles and the clay particles adhered again by the ultrasonic vibration generated from the ultrasonic transmission device 16 are removed from the sand particles and gravel particles. Pull away and wash away. These silt particles and clay particles are sent to the suspended matter collection tank 3.

  The suspended matter recovery tank 3 includes muddy water containing silt particles and clay particles overflowed from the upper part of the coarse particle classification tank 2, and silt particles and clay particles separated from sand particles and gravel particles by the ultrasonic transmission device 16. It has a suspended matter collection basket 17 through which muddy water passes. In this embodiment, the mesh of the suspended matter collection basket 17 is set to 0.5 mm, and foreign matters such as fallen leaves and branches contained in the muddy water are removed.

  Centrifugal separator 4 uses a top liquid L1 containing clay particles having a particle size of 5 μm or less, which is a second classified particle size, and muddy water in suspended matter collection tank 3 sent via a pressure pump 18 and a particle size of 5 μm. Centrifuge into bottom liquid L2 containing large diameter silt particles. In this embodiment, the centrifuge 4 is interposed in order to achieve early classification of the bottom liquid L2 in the fine particle sedimentation tank 5 described later, but the soil quality of the contaminated soil S, that is, the fine particle content. Depending on the ratio, the fine particle sedimentation tank 5 may be directly connected to the suspended matter collection tank 3 without the centrifuge 4 interposed.

  The fine particle settling tank 5 collects a few clay particles mixed in the silt particles in the bottom liquid L2. Specifically, first, an appropriate amount of the bottom liquid L2 is introduced from the centrifuge 4 into the fine particle precipitation tank 5, and then jet water obtained by pressurizing dilution water in a dilution water tank (not shown) is added to the bottom of the fine particle precipitation tank 5. The bottom liquid L2 is stirred and the silt particles and the clay particles are floated on the water surface. Then, the silt particles floating on the water surface and the clay particles use the difference in the sedimentation speed due to the difference in particle size between the silt particles larger than the second classified particle size of 5 μm and the clay particles having a particle size of 5 μm or less. Then, after elapse of a predetermined standing time, it is separated into silt particles deposited on the tank bottom and supernatant L3 containing clay particles. In the classification in the fine particle sedimentation tank 5, since the sedimentation separation of the silt particles and the clay particles is carried out by batch processing, the concentration of the muddy water in the supernatant liquid L3 decreases as the particles settle. Therefore, for example, when the 40 wt% bottom liquid L2 discharged from the centrifuge 5 is diluted to 6 wt% with jet water, the particles have a 6 wt% settling depth as shown in Table 2 at the beginning of settling. However, as time passes, it can sink to the settling depth in fresh water as shown in Table 3. Therefore, when the standing time is 10 hours, the clay particles having a particle size of 5 μm or less are suspended from 40 cm to 80 cm from the water surface, and the supernatant L3 above this depth is pumped to the fine particle sedimentation tank 6. The clay particles floating in the upper part of the fine particle settling tank 5 can be classified and recovered by sending. The silt particles deposited on the bottom of the tank are dehydrated by being packed in a collection bag 19 outside the tank. The silt particle may be dehydrated through a filter press after being subjected to water treatment and solid-liquid separation. Further, the concentration of the radioactive substance adhering to the dehydrated fine particles is less than the allowable value, and can be reused.

  In the fine particle settling tank 5, the second classification particle size, that is, the lower limit of the particle size of the silt particles to be deposited can be adjusted by adjusting the time until the silt particles are settled and separated. And can be changed according to the residual concentration of radioactive material allowed in the silt particles. Thereby, it can avoid that the sedimentation speed | rate of silt particle | grains becomes slow unnecessarily, and the time required for the classification in the fine particle sedimentation tank 5 can be shortened according to the soil quality of the contaminated soil S and the required decontamination rate. .

  The fine particle sedimentation tank 6 settles and separates the clay particles contained in the top liquid L1 sent from the centrifuge 4 and the supernatant liquid L3 sent from the fine particle sedimentation tank 5 according to the particle size. Is further classified. The top liquid L1 and the supernatant liquid L3 in the fine particle sedimentation tank 6 are a deposit M containing clay particles having a relatively large particle size deposited on the tank bottom of the fine particle sedimentation tank 6 after a predetermined time has elapsed. The residual mud water L4 containing clay particles having a relatively small particle size deposited above the deposit M and the supernatant L5 containing no clay particles are separated by sedimentation. Since this supernatant L5 does not contain contaminants, it is sent to the water storage tank 12 by the pump 20 and reused for hydration of the contaminated soil S.

  The water treatment system 7 solid-liquid separates the residual mud water L4 that is sent from the fine particle sedimentation tank 6 to the muddy water concentration adjusting tank 22 before water treatment via the pump 21 and adjusted with the diluted water in the diluted water tank 23. The water treatment system 7 may include a settling accelerator that adsorbs radioactive substances in the liquid. Thereby, the radioactive substance in a liquid is removed and it becomes reusable for hydration adjustment of the residual mud water L4 as dilution water.

  The filter press 8 is used for diluting water in the diluting water tank 23 to the clay particles solid-liquid separated from the residual mud water L4 by the water treatment system 7 and the deposit M carried out from the tank bottom of the fine particle settling tank 6 by the pressure pump 24. The muddy water sent from the pre-dehydrating muddy water concentration adjusting tank 25 for adding water through the pressure pump 26 is dehydrated to recover the clay particles. Thereby, the clay particles which adsorb | suck a harmful substance firmly among the contaminated soil S can be isolate | separated and collect | recovered, and the contaminated soil S can be reduced in volume.

  As mentioned above, since contaminated soil S that contains radioactive substances and needs to be kept in isolation for a long period of time, clay particles to which mainly harmful substances adhere can be efficiently recovered, so decontamination of radioactive substances The volume of soil that requires treatment can be reduced, the storage space can be reduced, and the efficiency of the decontamination work can be increased to significantly reduce the disposal cost. Also, since the clay particles are peeled off from the sand particles, gravel particles, and silt particles, the clay particles are prevented from being mixed into the sand particles and settling, and the clay particles containing radioactive substances are mixed into the sand particles. It can be avoided. Therefore, not only conventional sandy soil classification, but also clay soil, it is possible to classify and remove clay particles to which radioactive substances adhere to achieve volume reduction of contaminated soil. .

  Further, even if gravel particles, sand particles, silt particles, and clay particles are adhered to each other in the coarse particle classification tank 2, the sand particles that are accumulated in the coarse particle classification tank 2 are collected. In order to prevent contamination with gravel particles, radioactive materials can be avoided from being inadvertently mixed with sand particles and gravel particles collected from the coarse particle classification tank 2 and reused. .

  Furthermore, since the second classified particle size can be set according to the residual concentration of radioactive material allowed in the recovered silt particles, the fine particle settling tank 5 can be set according to the soil quality of the contaminated soil S and the required decontamination rate. The time required for classification can be shortened.

  Then, by setting the concentration of the mud water in the coarse particle classification tank 2 so that the sedimentation speed of the sand particles and gravel particles is sufficiently larger than the sedimentation speed of the silt particles and clay particles, the sand particles, the silt particles, and While classifying clay particles with certainty, the time required for the sand particles to settle and deposit on the bottom of the tank can be shortened.

  It should be noted that the present invention can be variously modified without departing from the spirit of the present invention, and the present invention naturally extends to the modified ones.

  Sand that is essential to reduce the volume of contaminated soil by selectively removing particles with a small particle size and large specific surface area, and removing contaminants that tend to adsorb on these fine particles from the contaminated soil It can also be applied to classification of quality soil.

DESCRIPTION OF SYMBOLS 1 ... Belt conveyor 2 ... Coarse particle classification tank 3 ... Floating matter collection tank 4 ... Centrifugal separator 5 ... Fine particle precipitation tank 6 ... Fine particle precipitation tank 7 ... Water Treatment system 8 ・ ・ ・ Filter press 9 ・ ・ ・ Vibrating sieve 10 ・ ・ ・ Cavitation jet pump 11 ・ ・ ・ Variable flow jet pump 12 ・ ・ ・ Water storage tank 13 ・ ・ ・ Screw conveyor 14 ・ ・ ・ Belt conveyor 15 ・ ・・ Recovery bag 16 ... Ultrasonic transmission device 17 ... Floating substance recovery basket 18 ... Pressure feed pump 19 ... Recovery bag 20 ... Pump 21 ... Pump 22 ... Concentration of muddy water before water treatment Adjustment tank 23 ... Dilution water tank 24 ... Pressure feed pump 25 ... Pre-dehydration mud concentration control tank 26 ... Pressure feed pump

The present invention has been proposed in order to achieve the above object, and the invention according to claim 1 is a method for classifying contaminated soil containing a radioactive substance. A stirring step of stirring in the inside, and coarse particles having a diameter larger than the first particle size are settled and separated in the coarse particle classification tank, and fine particles and fine particles smaller than the first classified particle size are separated by rising water flow. A primary classification step for overflowing, a foreign matter removal step for removing foreign particles contained in fine particles and fine particles having a particle size equal to or smaller than the first classified particle size, and a muddy water that has undergone the primary classification step in a fine particle classification tank Provided is a method for classifying contaminated soil comprising a secondary classification step in which fine particles having a diameter larger than the particle size are settled and separated, and fine particles having a diameter smaller than the second particle size are collected.

The present invention efficiently collects fine particles, which contain radioactive substances and need to be isolated and stored for a long period of time, and to which harmful substances tend to adhere, and reduces the storage space by reducing the volume of contaminated soil. In addition, in order to prevent the fine particles from being collected and collected in the coarse particles and fine particles having a high sedimentation rate, mud water formed by hydrating contaminated soil is contained in the coarse particle classification tank. Stirring step for stirring, and primary particles in which coarse particles larger than the first classified particle size are settled and separated in the coarse particle classification tank, and fine particles and fine particles smaller than the first classified particle size are overflowed by the rising water flow. The fine particle having the first classification particle size or less and the foreign material removal step for removing foreign substances contained in the fine particle, and the muddy water that has undergone the primary classification step are larger than the second classification particle size in the fine particle classification tank. Sediment separation of fine particles Both were achieved in the secondary classification step of recovering the second classifying particle diameter or less of a fine particle.

Therefore, in the terminal velocity Vs of the soil particles settle in the fluid, since the F + Fb = F g is satisfied, terminal velocity Vs is shown in Equation 4.

The fine particle settling tank 5 collects a few clay particles mixed in the silt particles in the bottom liquid L2. Specifically, first, an appropriate amount of the bottom liquid L2 is introduced from the centrifuge 4 into the fine particle precipitation tank 5, and then jet water obtained by pressurizing dilution water in a dilution water tank (not shown) is added to the bottom of the fine particle precipitation tank 5. The bottom liquid L2 is stirred and the silt particles and the clay particles are floated on the water surface. Then, the silt particles floating on the water surface and the clay particles use the difference in the sedimentation speed due to the difference in particle size between the silt particles larger than the second classified particle size of 5 μm and the clay particles having a particle size of 5 μm or less. Then, after elapse of a predetermined standing time, it is separated into silt particles deposited on the tank bottom and supernatant L3 containing clay particles. In the classification in the fine particle sedimentation tank 5, since the sedimentation separation of the silt particles and the clay particles is carried out by batch processing, the concentration of the muddy water in the supernatant liquid L3 decreases as the particles settle. Therefore, for example, when the 40 wt% bottom liquid L2 discharged from the centrifuge 4 is diluted to 6 wt% with jet water, the particles have a settling depth of 6 wt% as shown in Table 2 at the beginning of settling. However, as time passes, it can sink to the settling depth in fresh water as shown in Table 3. Therefore, when the standing time is 10 hours, the clay particles having a particle size of 5 μm or less are suspended from 40 cm to 80 cm from the water surface, and the supernatant L3 above this depth is pumped to the fine particle sedimentation tank 6. The clay particles floating in the upper part of the fine particle settling tank 5 can be classified and recovered by sending. The silt particles deposited on the bottom of the tank are dehydrated by being packed in a collection bag 19 outside the tank. The silt particle may be dehydrated through a filter press after being subjected to water treatment and solid-liquid separation. Further, the concentration of the radioactive substance adhering to the dehydrated fine particles is less than the allowable value, and can be reused.

Claims (5)

In the classification method for contaminated soil containing radioactive substances,
An agitation step of agitating mud water obtained by hydrating the contaminated soil in a coarse particle classification tank;
A primary classification step of precipitating and separating coarse particles having a diameter larger than the first classified particle size in the coarse particle classification tank and overflowing fine particles and fine particles having a particle size equal to or smaller than the first classified particle size with an ascending water flow;
A foreign matter removing step of removing foreign matter contained in the contaminated soil;
A secondary classification step of separating and separating fine particles having a diameter larger than the second classified particle size in the fine particle classification tank from the muddy water that has undergone the primary classification step, and collecting fine particles having a particle size equal to or smaller than the second classified particle size; A method for classifying contaminated soil, characterized by comprising:   2. The contaminated soil classification according to claim 1, wherein the agitation of the contaminated soil is performed by spraying the mud water with cavitation jet water including cavitation and a flow rate variable jet water that maintains a flow rate of the rising water flow. Construction method.   The centrifugal separation process of separating the fine particles and the fine particles with a centrifugal separator between the primary classification process and the secondary classification process, according to claim 1 or 2. Classification method for contaminated soil.   4. The contaminated soil according to claim 1, wherein the second classified particle size can be arbitrarily set in accordance with a residual concentration of a radioactive substance allowed in the fine particles. 5. Classification method.   5. The method for classifying contaminated soil according to claim 1, wherein the muddy water is hydrated to a concentration of 10 wt% or less in the coarse particle classification tank.