JP7658708B2 - Dioxin-contaminated soil cleaning treatment system and cleaning treatment method - Google Patents

Description

The present invention relates to a system and method for cleaning soil contaminated with dioxins.

Dioxins are stable, non-volatile organic chlorine compounds, and their effects on the human body are of concern. For this reason, there is a demand for a process to render contaminated soil contaminated with dioxins harmless. Known detoxification processes include treatment at incineration facilities capable of decomposition treatment such as high-temperature treatment, and transporting the contaminated soil to a specially managed waste disposal site. In addition, Patent Document 1 proposes a cleaning treatment system for dioxin-contaminated soil in which contaminated soil is immersed in an aqueous solution containing a cleaning agent for cleaning, classified into coarse soil and fine soil using a vibrating sieve classification device, and the fine soil is made into a suspended water solution and detoxified using a photocatalyst device.

The cleaning treatment system in Patent Document 1 reduces the concentration of dioxins in the classified coarse soil and the fine soil to below the environmental standard value, purifies the cleaning water used for cleaning, and makes it possible to reuse the coarse soil and cleaning water.

JP 2008-246273 A

However, the cleaning treatment system in Patent Document 1 did not provide a sufficient rate of dioxin removal.

Therefore, the present invention aims to provide a system and method for cleaning soil contaminated with dioxins that can increase the rate of removal of dioxins from soil contaminated with dioxins.

In order to solve the above problems, the present invention has the following aspects.
[1] A cleaning treatment system for dioxin-contaminated soil, comprising: a classification device for obtaining sand of a desired particle size range from dioxin-contaminated soil containing dioxins; a stripping and cleaning device for stripping the dioxins from the particle surfaces of the sand; and a removal device for generating bubbles in the presence of water containing a flotation agent, causing the stripped dioxins to adhere to the bubbles to form froth, and removing the froth.
[2] The cleaning treatment system for dioxin-contaminated soil described in [1], wherein the stripping and cleaning device is a scrubber equipped with an agitation tank and an agitation blade.

[3] A method for cleaning soil contaminated with dioxins, comprising: a classification step for obtaining sand of a desired particle size range from dioxin-containing contaminated soil; a stripping and cleaning step for stripping the dioxins from the particle surfaces of the sand; and a removal step for generating bubbles in the presence of water containing a flotation agent, causing the stripped dioxins to adhere to the bubbles to form froth, and removing the froth.
[4] The method for washing soil contaminated with dioxins according to [3], wherein the peeling and washing step includes an operation of stirring the sand particles and rubbing them against each other using a scrubber equipped with a stirring tank and stirring blades.
[5] The method for washing and treating dioxin-contaminated soil according to [3] or [4], wherein the flotation agent contains one or more collectors selected from fatty acid salts, alkyl sulfates, alkyl sulfonates, dialkyl dithiophosphates, xanthates, primary amine salts, light oils, kerosene, and coal tar.
[6] The method for washing and treating dioxin-contaminated soil described in [5], wherein the flotation agent further contains one or more stripping and dispersing agents selected from alcohol, anionic surfactants (excluding fatty acid salts, alkyl sulfates, and alkyl sulfonates), cationic surfactants (excluding primary amine salts), calcium chloride, sodium carbonate, sodium silicate, and lignin sulfonates.

The system and method for cleaning soil contaminated with dioxins of the present invention can further increase the rate of removal of dioxins from soil contaminated with dioxins.

1 is a schematic diagram showing an example of a cleaning treatment system for dioxin-contaminated soil according to the present invention.

<Dioxin-contaminated soil cleaning treatment system>
The dioxin-contaminated soil cleaning treatment system of the present invention (hereinafter also referred to simply as the cleaning treatment system) cleans the dioxin-contaminated soil by peeling and removing dioxins from the dioxin-contaminated soil containing dioxins.
The cleaning treatment system of the present invention includes a classification device, a peeling/cleaning device, and a removal device.
Hereinafter, an embodiment of a cleaning processing system of the present invention will be described with reference to FIG.

As shown in FIG. 1, the cleaning system 1 of this embodiment includes a classification device 10, a stripping/cleaning device 20, a removal device 30, a coagulation/sedimentation device 40, a first dehydration device 50, and a second dehydration device 52. The classification device 10 is composed of a first classification device 11 and a second classification device 12.

A second classifier 12 is provided on the secondary side of the first classifier 11 .
A stripping/cleaning device 20 and a coagulation/sedimentation device 40 are provided on the secondary side of the second classification device 12 .
A removal device 30 is provided on the secondary side of the peeling and cleaning device 20 .
A first dehydration device 50 is provided on the secondary side of the removal device 30 .
A second dewatering device 52 is provided on the secondary side of the coagulation sedimentation device 40 .

The first classification device 11 is a device for classifying dioxin-contaminated soil S0 containing dioxins (hereinafter simply referred to as contaminated soil) into a coarse particle fraction S2 having a particle size larger than a given particle size and soil S1 not containing the coarse particle fraction S2 (hereinafter simply referred to as soil S1). The particle size of the soil S1 is equal to or smaller than the particle size of the coarse particle fraction S2.
A known classification device can be used as the first classification device 11. Examples of the first classification device 11 include a circular vibration sieving machine equipped with a wire mesh sieve with a predetermined mesh size, and a wet vibration sieving machine equipped with a two-stage wet sieve. The two-stage wet sieve is a sieve equipped with two stages, an upper stage and a lower stage, of wire mesh sieves with predetermined mesh sizes. The predetermined mesh size of the upper stage sieve is, for example, 20 to 50 mm. The predetermined mesh size of the lower stage sieve is, for example, 1 to 4 mm.
The predetermined mesh size of the lower sieve is appropriately set according to the particle size of the coarse particles S2 to be removed.
In this specification, "particle size" refers to the representative particle size of soil particles that make up soil. The representative particle size D _M is the particle size of soil particles separated by sieves with sieve openings of _DL and _DU , and is calculated by the following formula (I). For example, the representative particle size D _M of soil particles passing through a sieve with a sieve opening of 38 μm is D M = 26.9 μm, since _DL = 0 _μm and _DU = 38 μm.

Dioxins are a general term for polychlorinated dibenzoparadioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (DL-PCBs). DL-PCBs are polychlorinated biphenyls (PCBs) that have toxicity specific to dioxins. The toxicity of dioxins is expressed using the toxicity equivalent (TEQ) based on the toxicity of 2,3,7,8-tetrachlorodibenzo-1,4-dioxin (TCDD).

The first classification device 11 can separate coarse particles S2 of any particle size from the contaminated soil S0.

The second classification device 12 is a device that classifies the soil S1 into a fine particle fraction S3 having a particle diameter smaller than a given particle diameter and a sand fraction S4 having a particle diameter equal to or larger than a given particle diameter.
A known classifier can be used as the second classifier 12. Examples of the second classifier 12 include a circular vibration sieving machine equipped with a wire mesh sieve with a predetermined mesh size, a wet vibration sieving machine equipped with a two-stage wet sieve, a classifier that utilizes the difference in sedimentation velocity of soil particles, and a classifier that utilizes centrifugal force. Examples of classifiers that utilize the difference in sedimentation velocity of soil particles include Akins and high mesh separators. Examples of classifiers that utilize centrifugal force include hydrocyclones.
The classification device using centrifugal force is a device that uses centrifugal force to classify a slurry obtained by mixing soil S1 and water W. An example of a classification device using centrifugal force is a device that has a circular tower bottom made of a container with a conical shape, and is equipped with an upper inlet for introducing the slurry, a lower outlet for taking out the underflow (hereinafter also referred to as UF), and an upper outlet for taking out the overflow (hereinafter also referred to as OF).
In this specification, the "classification size" refers to the particle size of soil particles that is the boundary between classification into OF and UF.
The arbitrary particle size is, for example, 30 to 250 μm.

The second classification device 12 can obtain sand S4 of any particle size range from the contaminated soil S0. The any particle size range can be, for example, 30 to 4000 μm.

The stripping/cleaning device 20 is a device for stripping dioxins from the particle surfaces of the sand S4.
Examples of the peeling and cleaning device 20 include a cleaning device equipped with a cleaning tank, an agitation device equipped with an agitator, and a scrubber equipped with an agitation tank and an agitation blade. In this specification, the term "scrubber" refers to a device equipped with an agitation tank and an agitation blade, which mechanically mixes and agitates soil particles in the presence of water using the agitation blade to rub the soil particles against each other. With a scrubber, the soil particles (sand fraction S4) are caused to collide with each other to scrub the surfaces of the soil particles, thereby peeling off dioxins adhering to the surfaces. For this reason, it is preferable to use a scrubber as the peeling and cleaning device 20.

The stripping and cleaning device 20 can strip dioxins from the particle surfaces of the sand S4.

The removal device 30 is a removal device that generates bubbles in the presence of water containing a flotation agent, causes the detached dioxins to adhere to the bubbles to form froth (foam) F, and removes the froth F.
The removal device 30 may be a flotation device equipped with a water tank and a scraper. The scraper scrapes off and removes froth (foam) F floating on the surface of a liquid containing sand S4 and water W in the water tank. The flotation device may be one that supplies water W and causes the froth F to overflow and be removed. The flotation device can efficiently remove dioxins peeled off by the peeling and cleaning device 20. For this reason, a flotation device is preferable as the removal device 30.

The flotation chemicals include collectors.
The collector is a chemical that adsorbs to the surface of the target contaminant particle to make the particle surface hydrophobic. Examples of the collector include fatty acid salts, alkyl sulfates, alkyl sulfonates, dialkyl dithiophosphates, xanthates, primary amine salts, light oil, kerosene, and coal tar. The collector may be used alone or in combination of two or more. In addition, fatty acid salts, alkyl sulfates, alkyl sulfonates (so-called anionic surfactants), primary amine salts (so-called cationic surfactants), light oil, and kerosene also function as stripping dispersants in the stripping and cleaning process described below. In addition, in this specification, the term "surfactant" refers to a compound having a hydrophilic group and a hydrophobic group, and is not used for the purpose of solubilizing dioxins in water.

Flotation chemicals may include foaming agents, stripping and dispersing agents, activators, inhibitors, and pH adjusters.
A foaming agent is a surfactant that has high surface activity and does not have specific adsorption properties. The foaming agent generates a large number of stable bubbles in water. Examples of foaming agents include 4-methyl-2-pentanol (MIBC), pine oil, and 2-ethyl-1-hexanol. One type of foaming agent may be used alone, or two or more types may be used in combination.
The peeling dispersant used in the flotation agent is an agent that peels off and disperses dioxins from the surface of contaminant particles. Examples of the peeling dispersant used in the flotation agent include alcohol, anionic surfactants (excluding fatty acid salts, alkyl sulfates, and alkyl sulfonates), cationic surfactants (excluding primary amine salts), calcium chloride, sodium carbonate, sodium silicate, and lignin sulfonates. Examples of the alcohol include monoalcohols such as ethanol. The peeling dispersant used in the flotation agent may be used alone or in combination of two or more.
Activators are chemicals that increase the buoyancy of target pollutant particles. When the affinity between the surface of a pollutant particle and the collector is low, the buoyancy of the pollutant particle is low. The activator acts on the surface of the pollutant particle to increase the affinity with the collector and increase the buoyancy of the pollutant particle. Examples of activators include copper sulfate, calcium chloride, and sodium sulfide. One type of activator may be used alone, or two or more types may be used in combination.
Depressants are chemicals that suppress the buoyancy of minerals. Examples of depressants include sodium sulfide, sodium carbonate, sodium hydroxide, sodium silicate, tannin, lignin, etc. Depressants may be used alone or in combination of two or more.
The pH adjuster is an agent that adjusts the pH of the liquid containing the sand S4 and the water W. Examples of the pH adjuster include sulfuric acid, sodium hydroxide, calcium hydroxide, carbon dioxide gas, etc. The pH adjuster may be used alone or in combination of two or more kinds.

The removal device 30 can remove the exfoliated dioxins as floss F.

The coagulation settling device 40 is a device that adds a coagulant to the suspended water, stirs it, and causes the fine particle fraction S3 in the suspended water and the fine contaminant particles attached to the froth F to settle as large precipitated sludge S7, thereby separating clear treated water TW. The suspended water contains the fine particle fraction S3 separated by the second classifier 12, the fine contaminant particles attached to the froth F removed by the remover 30, and the filtrate E removed by the first dewatering device 50.
The coagulation settling device 40 may be a vessel equipped with a water tank, a reaction tower, or the like.
The coagulation settling device 40 can separate the treated water TW from the settled sludge S7.

The first dewatering device 50 is a device that dewaters the washed sand S5 from which dioxins have been removed by the removal device 30, to obtain recovered sand S6.
The first dehydration device 50 may be a dehydration sieve, a dehydration cyclone, or the like.
The first dehydration device 50 obtains recovered sand S6 by removing moisture from the washed sand S5 from which dioxins have been removed.

The second dewatering device 52 is a device that dewaters the settled sludge S7 obtained in the coagulation settling device 40 to obtain a concentrated residue T.
The concentrated residue T contains a high concentration of dioxins. An example of the concentrated residue T is a dehydrated cake.
An example of the second dewatering device 52 is a pressure filtration device (filter press machine) equipped with a filter made of filter cloth or the like and a press machine.

<Method for cleaning and treating dioxin-contaminated soil>
The method for washing dioxin-contaminated soil of the present invention (hereinafter also referred to simply as the washing method) is a method for washing dioxin-contaminated soil by peeling and removing dioxins from the dioxin-contaminated soil containing dioxins.
The cleaning method of the present invention includes a classification step, a peeling/cleaning step, and a removal step.
An embodiment of the cleaning method of the present invention will be described below with reference to FIG.

(Classification process)
The classification step is a step of obtaining a sand fraction S4 having a given particle size range from the dioxin-contaminated soil S0 that contains dioxins. In this embodiment, the classification step includes a first classification step and a second classification step.
The first classification step is a step of separating the soil into soil S1 having a particle size equal to or smaller than a given particle size and coarse particle fraction S2 having a particle size larger than a given particle size.
The arbitrary particle size is appropriately set depending on the degree of contamination of the contaminated soil S0 and the allowable size of the second classification device 12. The arbitrary particle size is, for example, 1 to 4 mm, and 2 mm is particularly preferable.
Dioxins are not easily adsorbed to the coarse particle fraction S2 having a particle diameter larger than a predetermined value. Therefore, if the coarse particle fraction S2 is removed from the contaminated soil S0 in advance, the efficiency of washing the contaminated soil S0 is easily improved. Here, the predetermined particle diameter can be, for example, 1 to 4 mm, with 2 mm being particularly preferred. In addition, if the coarse particle fraction S2 is removed from the contaminated soil S0 in advance, the load on the second classification device 12 is easily reduced.
Therefore, the classification step preferably includes a first classification step and a second classification step.

In the first classification step, water W is added to the contaminated soil S0 placed in the first classification device 11 to form a slurry. Next, the contaminated soil S0 is sieved into soil S1 having a particle size equal to or smaller than a given particle size and coarse particle fraction S2 having a particle size larger than the given particle size.
In general, the dioxin concentration in the coarse particle fraction S2 is low and is equal to or lower than the soil environmental standard value (1000 pg-TEQ/g). The coarse particle fraction S2 exceeding the soil environmental standard value is treated by washing with a gravel washing device such as a log washer. In this way, the coarse particle fraction S2 can be reused.

In general, the smaller the particle size of soil, the higher the dioxin concentration. Therefore, soil S1 has a higher dioxin concentration than coarse particle fraction S2. Soil S1 is sent to the second classification device 12.

The second classification step is a step of separating the soil S1 into a fine particle fraction S3 having a particle size smaller than a given particle size and a sand fraction S4 having a particle size equal to or larger than a given particle size.
In general, the fine particle fraction S3 has a high dioxin concentration, while the sand fraction S4 has a low dioxin concentration. By separating the fine particle fraction S3, the dioxin concentration of the recovered sand fraction S4 is significantly reduced.
The arbitrary particle size is, for example, 30 to 250 μm.
In the second classification step, the fine particle fraction S3 is classified into OF and UF including sand fraction S4 by the second classification device 12. In the second classification step, water W may be supplied to the second classification device 12 from the outside.

When a hydrocyclone is used as the second classifier 12, the slurry soil S1 entering from the upper inlet is supplied at high speed in the circumferential direction of the cylindrical container, and is classified by the centrifugal action caused by the swirling motion. At this time, particles with a large particle size or a heavy specific gravity in the slurry are collected on the peripheral wall by centrifugal force, and gradually move toward the UF outlet (lower outlet) and are discharged. Particles with a small particle size or a light specific gravity rise in a vortex in the center of the cylindrical container, and are discharged from the OF outlet (upper outlet).
The desired particle size range can be adjusted by the flow rate of the slurry soil S1 when rotating the hydrocyclone, the supply pressure, the outlet size of the hydrocyclone, and the like.

The UF containing the sand fraction S4 is sent to the stripping and cleaning device 20. The OF containing the fine particle fraction S3 is sent to the coagulation and sedimentation device 40.

(Peeling and cleaning process)
The peeling and washing step is a step of peeling dioxins from the particle surfaces of the sand S4.
The sand S4 in the UF is surface-treated with a stripping/cleaning agent in the stripping/cleaning device 20. This surface treatment makes the surface of the sand S4 more susceptible to chemical stripping of dioxins.
Examples of the release dispersant include alcohol, anionic surfactants, cationic surfactants, light oil, kerosene, calcium chloride, sodium carbonate, sodium silicate, lignin sulfonate, etc. The release dispersant may be used alone or in combination of two or more kinds.
Next, dioxins are physically and chemically stripped from the surface of the sand S4 by scrubbing (rubbing and washing by stirring).
The peeling and washing step preferably includes an operation of stirring and rubbing the sand S4 against each other using a scrubber equipped with a stirring tank and stirring blades. By including the above operation in the peeling and washing step, dioxins can be more effectively peeled off from the surface of the sand S4.
The time required for the peeling and washing step is preferably 2 to 10 minutes, more preferably 4 to 6 minutes. When the time required for the peeling and washing step is equal to or more than the above-mentioned lower limit, dioxins can be easily peeled off sufficiently from the surface of the sand fraction S4. When the time required for the peeling and washing step is equal to or less than the above-mentioned upper limit, the working efficiency can be easily improved.
The type, amount, pH condition, etc. of the stripping/washing agent used in the stripping/washing step can be appropriately adjusted depending on the concentration, form, etc. of the dioxins adsorbed on the sand S4.

The slurry containing the sand S4 from which the dioxins have been removed is sent to the removal device 30.

(Removal process)
The removal step is a step in which air bubbles are generated in the presence of water containing a flotation agent, the exfoliated dioxins are caused to adhere to the air bubbles to form froth, and the froth is then removed.
In the removal process, the slurry containing the sand content S4 is supplied to the water tank (flotation cell) of the removal device 30. In the removal process, a foaming agent is added as a flotation agent and flotation is performed. Flotation involves introducing a desired amount of air into the water tank of the removal device 30. The introduced air is rapidly stirred by the stirring blades of the removal device 30, and bubbles of a desired size are generated in the process. The action of the flotation agent (collector) causes the dioxins removed in the stripping and cleaning process to adhere to the bubbles.
The conditions for forming a good froth F vary depending on the type of contaminant, the type of flotation agent, the rotation speed of the stirring blade, the amount of air introduced, etc. The rotation speed of the stirring blade is preferably adjusted so that the sand S4 does not settle to the bottom of the removal device 30 and does not rise to the liquid surface. The flow rate of the supplied air is preferably adjusted so that a froth F of a good size is formed.

The bubbles to which the dioxins are attached rise to the liquid surface as froth F, are collected by a scraper of the removal device 30, and are removed from the system of the removal device 30. In the removal step, water W may be supplied to the removal device 30 from the outside. The water W may be supplied to cause the froth F to overflow and be removed.
The time required for the removal step is preferably 5 to 20 minutes, more preferably 10 to 15 minutes. When the time required for the removal step is equal to or greater than the lower limit, the floss F can be easily removed sufficiently. When the time required for the removal step is equal to or less than the upper limit, the work efficiency can be easily improved.
The type, amount added, pH conditions, etc. of the flotation agent used in the removal step can be appropriately adjusted depending on the concentration of dioxins in the slurry containing sand S4, the slurry concentration, the slurry flow rate, the residence time of the slurry, etc.

In the removal process, contaminant particles that have adsorbed dioxins are selectively separated from soil particles that have not adsorbed dioxins by utilizing the difference in interfacial chemical properties, and rise to the liquid surface together with air bubbles, where they are removed as froth F.

The fine contaminant particles adhering to the froth F are sent to the coagulation settling device 40 together with the OF containing the fine particle fraction S3.
The washed sand S4 from which dioxins have been removed is sent to the first dewatering device 50 as washed sand S5.
The dioxin concentration in the washed sand S5 purified through the peeling/washing step and the removal step is further reduced compared to the dioxin concentration in the sand S4 after the classification step.

(Other processes)
The cleaning method of the present invention may include other steps in addition to the classification step, the peeling and cleaning step, and the removal step. Examples of the other steps include a first dehydration step, a second dehydration step, and a coagulation and sedimentation step.
The first dewatering step is a step of dewatering the washed sand S5. In the first dewatering step, the washed sand S5 is dewatered by a first dewatering device 50 and recovered as recovered sand S6. If the concentration of dioxins in the recovered sand S6 is equal to or lower than the soil environmental standard value, it can be reused, and if it is higher than the soil environmental standard value, it is transported to an incineration facility or a specially managed waste disposal site capable of decomposition treatment such as high-temperature treatment, and treated there.
The water removed by dehydration is sent as filtrate E to the flocculating sedimentation device 40 together with OF containing fine particle fraction S3 and fine contaminant particles adhering to the froth F.

The coagulation and sedimentation process is a process in which a coagulant is added to the suspended water, the water is stirred, and the fine particles S3 in the suspended water and the fine contaminant particles attached to the froth F are precipitated as large settled sludge S7, and clear treated water TW is separated.
The OF containing the fine particle fraction S3, the fine contaminant particles adhering to the froth F, and the suspended water containing the filtrate E are supplied to the coagulation settling device 40. In the coagulation settling step, a coagulant is added to the suspended water and stirred. By adding the coagulant and stirring, the fine particle fraction S3 and the fine contaminant particles in the suspended water can be precipitated as large precipitated sludge S7. By precipitating the precipitated sludge S7, the suspended water can be reused as clear treated water TW.
The flocculant is not particularly limited, and examples thereof include inorganic flocculants, organic polymer flocculants, pH adjusters, flocculation assistants, and the like.
The settled sludge S7 is sent to the second dewatering device 52.

The second dehydration process is a process for dehydrating the settled sludge S7. In the second dehydration process, the settled sludge S7 is dehydrated by the second dehydration device 52 to become concentrated residue T. The concentrated residue T is transported to an incineration facility or a specially managed waste disposal site capable of decomposition treatment such as high-temperature treatment, and then treated there.

The above describes the system and method for cleaning dioxin-contaminated soil of the present invention. However, the present invention is not limited to the above-described embodiments and can be modified as appropriate without departing from the spirit of the present invention.
For example, in the cleaning treatment system, the classification device 10 may be configured as a single classification device.
The peeling and cleaning device 20 and the removal device 30 may be combined into one device.
The treated water TW may be supplied as water W to the classification device 10 or the removal device 30 .

According to the dioxin-contaminated soil washing treatment system 1 of the present invention, the classifier 10 can separate the coarse particle fraction S2 having a low dioxin concentration from the contaminated soil S0.
The classification device 10 can obtain sand S4 of any particle size range from the contaminated soil S0.
The stripping and cleaning device 20 can strip dioxins from the particle surfaces of the sand S4.
The removed dioxins can be removed as floss F by the removal device 30.
The peeling and washing device 20 and the removal device 30 provide washed sand S5 from which dioxins have been removed.
The cleaning treatment system 1 of the present invention, having the above-mentioned configuration, can efficiently remove dioxins, and can further increase the removal rate of dioxins from dioxin-contaminated soil.
In addition, according to the cleaning treatment system 1 of the present invention, it is possible to achieve both a high removal rate of dioxins and a high recovery rate of washed sand, which was not possible with conventional classification cleaning (sieve + cyclone) or with contaminated soil that has undergone surface polishing after classification cleaning.
Furthermore, according to the cleaning treatment system 1 of the present invention, treatment of water containing dioxins becomes much easier than in the conventional technology of cleaning the contaminated soil S0 by solubilizing dioxins in water using detergent or the like.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[Examples 1 to 5]
In this example, a cleaning treatment test was performed using contaminated soil S0 with the particle size composition and dioxin concentration shown in Table 1. A circular vibration sieve (KGCR-500-2D, Kowa Kogyosho Co., Ltd.) was used as the first classification device. The contaminated soil S0 was classified into coarse particles S2 with a particle diameter of more than 2 mm and soil S1 with a particle diameter of 2 mm or less using a wet two-stage sieve with a sieve opening of 2 mm. The soil S1 with a particle diameter of 2 mm or less was supplied to the second classification device. A cyclone (classification diameter: 63 μm, supply pressure: 0.1 MPa) made by Mozley was used as the second classification device. The slurry containing the soil S1 was classified inside the cyclone, and OF (fine particles S3 with a particle diameter of less than 63 μm) flowed out from the top, and UF (sand particles S4 with a particle diameter of 63 μm or more and 2 mm or less) flowed out from the bottom. This UF sample was supplied to the peeling and cleaning device. A flotation tester manufactured by Denver was used as the stripping/cleaning device and removal device. This tester has both scrubber and flotation functions. The flotation chemicals were adjusted as appropriate. The UF sample was stripped and washed using the flotation tester to obtain washed sand S5. The washed sand S5 was dehydrated to obtain recovered sand S6, and the dioxin concentration of this recovered sand S6 was measured. The dioxin removal rate was calculated using the following formula.
Dioxin removal rate (%) = (dioxin concentration in contaminated soil S0 (pg-TEQ/g) - dioxin concentration in recovered sand S6 (pg-TEQ/g)) / dioxin concentration in contaminated soil S0 (pg-TEQ/g) x 100
The results are shown in Table 1.

As shown in Table 1, in Examples 1 to 5 in which the present invention was applied, an extremely high dioxin removal rate of 93.6 to 97.6% was obtained. It was found that by applying the present invention, it is possible to further increase the removal rate of dioxins from dioxin-contaminated soil.

The cleaning system and cleaning method of the present invention can be widely used to clean contaminated soil containing harmful substances such as dioxins.

1...Dioxin-contaminated soil cleaning treatment system, 10...Classification device, 11...First classification device, 12...Second classification device, 20...Stripping and cleaning device, 30...Removal device, 40...Coagulation and sedimentation device, 50...First dehydration device, 52...Second dehydration device, S0...Contaminated soil, S1...Soil, S2...Coarse particles, S3...Fine particles, S4...Sand, S5...Washed sand, S6...Recovered sand, S7...Settled sludge, W...Water, E...Filtrate, F...Froth (foam), T...Concentrated residue, TW...Treated water

Claims (11)

a classification device for obtaining sand having a particle size range of 30 to 4000 μm from dioxin-contaminated soil containing dioxins;
a stripping and cleaning device for stripping the dioxins from the surfaces of the sand particles;
a removal device for generating bubbles in the presence of water containing a flotation agent, causing the separated dioxins to adhere to the bubbles to form froth, and removing the froth;
the flotation agent comprises one or more collectors selected from the group consisting of fatty acid salts, alkyl sulfates, alkyl sulfonates, dialkyl dithiophosphates, xanthates, primary amine salts, light oil, kerosene, and coal tar, and one or more exfoliating dispersants selected from the group consisting of alcohols, anionic surfactants (excluding fatty acid salts, alkyl sulfates, and alkyl sulfonates), cationic surfactants (excluding primary amine salts), calcium chloride, sodium carbonate, sodium silicate, and lignin sulfonates;
The system for washing and treating soil contaminated with dioxins, wherein the collector contains at least a primary amine salt, and the stripping and dispersing agent contains at least one member selected from the group consisting of alcohol and calcium chloride. a classification device for obtaining sand having a particle size range of 30 to 4000 μm from dioxin-contaminated soil containing dioxins;
A device having both a scrubber function and a flotation function,
A cleaning treatment system for soil contaminated with dioxins, in which an apparatus having both the functions of a scrubber and a flotation device peels off the dioxins from the surfaces of the sand particles, generates air bubbles in the presence of water containing a flotation agent, causes the peeled dioxins to adhere to the air bubbles to form froth, and then removes the froth. a classification device for obtaining sand having a particle size range of 30 to 4000 μm from dioxin-contaminated soil containing dioxins;
a stripping and cleaning device for stripping the dioxins from the surfaces of the sand particles by surface treatment with a stripping dispersant;
a removal device for generating bubbles in the presence of water containing a flotation agent, causing the separated dioxins to adhere to the bubbles to form froth, and removing the froth;
The release dispersant is at least one selected from the group consisting of alcohol, anionic surfactants (excluding polyphosphate surfactants), cationic surfactants (excluding primary amine salts), calcium chloride, sodium carbonate, sodium silicate, and lignin sulfonate;
The system for cleaning and treating soil contaminated with dioxins, wherein the stripping and dispersing agent contains at least one member selected from the group consisting of alcohol and calcium chloride. a classification device for obtaining sand having a particle size range of 30 to 4000 μm from dioxin-contaminated soil containing dioxins;
a stripping and cleaning device for stripping the dioxins from the surfaces of the sand particles;
a removal device for generating bubbles in the presence of water containing a flotation agent, causing the separated dioxins to adhere to the bubbles to form froth, and removing the froth;
the flotation agent comprises one or more collectors selected from the group consisting of fatty acid salts, alkyl sulfates, alkyl sulfonates, dialkyl dithiophosphates, xanthates, primary amine salts, diesel, and coal tar;
A system for washing and treating soil contaminated with dioxins, wherein the collector contains at least a primary amine salt. a classification device for obtaining sand having a particle size range of 30 to 4000 μm from dioxin-contaminated soil containing dioxins;
a stripping and cleaning device for stripping the dioxins from the surfaces of the sand particles;
a removal device for generating bubbles in the presence of water containing a flotation agent, causing the separated dioxins to adhere to the bubbles to form froth, and removing the froth;
A cleaning treatment system for dioxin-contaminated soil that does not have a gravity separation device for separating metal contaminants. a classification step for obtaining sand having a particle size range of 30 to 4000 μm from dioxin-contaminated soil containing dioxins;
a peeling and washing step of peeling off the dioxins from the surfaces of the sand particles;
a removing step of generating bubbles in the presence of water containing a flotation agent, causing the detached dioxins to adhere to the bubbles to form froth, and removing the froth;
the flotation agent comprises one or more collectors selected from the group consisting of fatty acid salts, alkyl sulfates, alkyl sulfonates, dialkyl dithiophosphates, xanthates, primary amine salts, light oil, kerosene, and coal tar, and one or more exfoliating dispersants selected from the group consisting of alcohols, anionic surfactants (excluding fatty acid salts, alkyl sulfates, and alkyl sulfonates), cationic surfactants (excluding primary amine salts), calcium chloride, sodium carbonate, sodium silicate, and lignin sulfonates;
The method for washing and treating soil contaminated with dioxins, wherein the collector contains at least a primary amine salt, and the stripping and dispersing agent contains at least one member selected from the group consisting of alcohol and calcium chloride. A method for washing and treating soil contaminated with dioxins using the washing and treating system for soil contaminated with dioxins according to claim 2,
a classification step for obtaining sand having a particle size range of 30 to 4000 μm from dioxin-contaminated soil containing dioxins;
a peeling and washing step of peeling off the dioxins from the surfaces of the sand particles;
A method for cleaning and treating soil contaminated with dioxins, comprising a removal step of generating bubbles in the presence of water containing a flotation agent, causing the detached dioxins to adhere to the bubbles to form froth, and removing the froth. a classification step for obtaining sand having a particle size range of 30 to 4000 μm from dioxin-contaminated soil containing dioxins;
a stripping and washing step of stripping the dioxins from the surfaces of the sand particles by surface treatment with a stripping dispersant;
a removing step of generating bubbles in the presence of water containing a flotation agent, causing the detached dioxins to adhere to the bubbles to form froth, and removing the froth;
The release dispersant is at least one selected from the group consisting of alcohol, anionic surfactants (excluding polyphosphate surfactants), cationic surfactants (excluding primary amine salts), calcium chloride, sodium carbonate, sodium silicate, and lignin sulfonate;
The method for washing and treating soil contaminated with dioxins, wherein the stripping and dispersing agent contains at least one member selected from the group consisting of alcohol and calcium chloride. a classification step for obtaining sand having a particle size range of 30 to 4000 μm from dioxin-contaminated soil containing dioxins;
a peeling and washing step of peeling off the dioxins from the surfaces of the sand particles;
a removing step of generating bubbles in the presence of water containing a flotation agent, causing the detached dioxins to adhere to the bubbles to form froth, and removing the froth;
the flotation agent comprises one or more collectors selected from the group consisting of fatty acid salts, alkyl sulfates, alkyl sulfonates, dialkyl dithiophosphates, xanthates, primary amine salts, diesel, and coal tar;
The method for washing and treating soil contaminated with dioxins, wherein the collector contains at least a primary amine salt. a classification step for obtaining sand having a particle size range of 30 to 4000 μm from dioxin-contaminated soil containing dioxins;
a peeling and washing step of peeling off the dioxins from the surfaces of the sand particles;
a removing step of generating bubbles in the presence of water containing a flotation agent, causing the detached dioxins to adhere to the bubbles to form froth, and removing the froth;
A method for cleaning and treating dioxin-contaminated soil, which does not include a step of separating metal contaminants. 11. The method for washing soil contaminated with dioxins according to claim 6, wherein the peeling and washing step comprises an operation of stirring the sand fraction and rubbing the sand fraction against each other using a scrubber equipped with a stirring tank and stirring blades.

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