JP2001113261A - Method for detoxifying dioxin-contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for detoxifying dioxin-contaminated soil inexpensively and simply. SOLUTION: This method for detoxifying dioxin-contaminated soil comprises (i) a process in which contaminated soil ranging from the surface layer of the contaminated soil to a deep layer which is substantially uncontaminated is separated, (ii) a process in which the separated soil is agitated/dispersed in water, (iii) a process in which fine soil particles 100 μm or below in average particle size are classified from the soil dispersed in water, (iv) a process in which the classified soil particles are brought into contact with a hydrochloric acid aqueous solution containing a dioxin decomposition catalyst to be detoxified due to the decomposition of dioxins, (v) a process in which the classified larger soil particles are returned to a place from which the contaminated soil are taken out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for detoxifying dioxin-contaminated soil.

[0002]

BACKGROUND OF THE INVENTION Soil in areas close to incinerators can often show severe dioxin contamination. At present, a technology capable of detoxifying such dioxin-contaminated soil inexpensively and simply has not yet been developed.

[0003]

An object of the present invention is to provide a method for inexpensively and simply detoxifying soil in a dioxin-contaminated area.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, in the method for detoxifying dioxin-contaminated area soil, there is provided (i) dioxin existing from a surface layer of the dioxin-contaminated area soil to a soil portion at a depth substantially free of dioxin contamination. A step of separating contaminated soil, (ii) a step of stirring and dispersing the separated soil obtained in the soil separation step in water, (iii)
A step of classifying fine soil particles having an average particle diameter of 100 μm or less from the soil dispersed in water obtained in the stirring step;
(Iv) contacting the fine soil particles obtained in the classification step with an aqueous hydrochloric acid solution containing a dioxin decomposition reaction catalyst to decompose the dioxins, and (v)
Burying the coarse soil particles after classifying the fine soil particles from the soil in the classifying step into the traces obtained by separating the dioxin-contaminated area soil, and providing a method for detoxifying the dioxin-contaminated area soil. Is done.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for inexpensively and simply detoxifying soil (hereinafter referred to as dioxin-contaminated area soil) in an area contaminated with dioxins (hereinafter simply referred to as DXN). It is. The dioxin-contaminated area soil referred to in the present specification means soil on land in a region (area) contaminated with dioxins, and includes soil existing in fields and residential areas.

In the present invention, first, the DXN-contaminated soil portion is separated from the DXN-contaminated area soil. This separation of the soil may be performed by separating the soil existing from the surface of the land to a depth of 30 cm, preferably 15 cm. To select the specific depth to separate, from the surface of the soil (land), in the depth direction,
The soil is collected according to the depth (distance from the surface layer), and the DXN concentration of the collected soil is measured. Then, the depth of the DXN-contaminated soil can be known from the measured DXN concentration. The present inventors have analyzed the DXN in the DXN-contaminated area soil obtained as described above, and found that DXN is concentrated and present in fine soil particles having a particle size of 100 μm (0.1 mm) or less. And that the ratio of the fine soil particles to the total soil is relatively small, and by separating the fine soil particles from the coarse soil particles and detoxifying the soil, the soil in the DXN-contaminated area can be produced at low cost. It has been found that detoxification can be performed efficiently.

[0007] Further, the present inventors have studied that DX
The particle diameter of the soil in which N is concentrated varies depending on the type of the soil, but is represented by a soil called "cohesive soil".
In the case of soil existing in fields, residential lands, and the like, it has been found that DXN is concentrated and present in fine soil particles having an average particle size of 100 μm (0.1 mm) or less, particularly 30 μm or less.
Therefore, preferably classifying soil particles of 30 μm or less,
By performing the detoxification process, an inexpensive and efficient detoxification process can be achieved. It should be noted that clay soil is 3 to 6% clay, 10 to 30% silt, and 20 to 4 fine sands.
0%, 30 to 50% coarse sand.

In the present invention, the soil separated from the DXN-contaminated area is sent to a submerged stirring step, where the soil is converted into fine soil particles (primary particles) and dispersed in water. In this case, the proportion of water used as the dispersion medium is 300 to 5000 parts by weight, preferably 1000 to 2,000 parts by weight, per 100 parts by weight of soil particles (dry matter basis). A water tank having a stirrer can be used as the underwater stirrer for soil particles. In the underwater stirring step, a water slurry liquid containing fine soil particles is obtained, which is sent to the underwater classification step, where the fine soil particles containing DXN in a concentrated state and the coarse soil containing substantially no DXN are obtained. Classified into particles. As described above, the average particle size of the fine soil particles classified from the soil particles is usually 100 μm or less, but the specific particle size range is appropriately selected according to the type of the soil. The proportion of fine soil particles is relatively small, usually 10 to 50%, in particular 10 to 25%, based on the total soil particles. As the underwater classification device, a cyclone device is usually used.

The water slurry containing the fine soil particles classified in the underwater classification step is passed through a concentration step such as a sedimentation separation step or a solid-liquid separation step as it is or as necessary, and then a DXN detoxification step. Sent to It is sent to DXN detoxification process. On the other hand, the water slurry liquid containing the coarse soil particles after the fine soil particles have been classified is sent to the solid-liquid separation step.

In the solid-liquid separation step, coarse soil particles in the water slurry are separated. As the device, a conventional device such as a filtration device, a centrifugal separator, and a sedimentation separator is used. The separated coarse soil particles are substantially DX
It is non-toxic and non-toxic and is used to send the soil to a separate site and backfill it in the DXN contaminated area.

The water slurry containing the fine soil particles obtained in the underwater classification step is preferably subjected to a concentration treatment or a solid-liquid separation treatment. In this case, the concentration treatment can be performed using a sedimentation / separation device such as a thickener. In addition, the solid-liquid separation treatment can be performed using a filtration device, a centrifugal separation device, or the like. By subjecting the water slurry liquid containing the fine soil particles to such a concentration treatment or a solid-liquid separation treatment, the fine soil particles have a concentration of 70 to 100%, preferably 80 to 95%, more preferably 90 to 98%. A soil particle concentrate is obtained.

In the DXN detoxification step, DXN in the fine soil particles in the aqueous slurry is decomposed and made harmless.
In this case, the concentration of the fine soil particles in the water slurry liquid is 5
５０50%, preferably 15-40%. The dioxins referred to in this specification are 2,3,
7,8-tetrachlorodibenzo-p-dioxin (2,
3,7,8-TCDD) and its related compounds, and polychlorodibenzo-p-dioxins (PCDD) in which dibenzo-p-dioxin nucleus is substituted with 1 to 8 chlorine atoms.
s) and polychlorodibenzofurans (PCDFs) in which the dibenzofuran nucleus is substituted with 1 to 8 chlorine atoms.

Although dioxins include various chlorine compounds as described above, the degree of harm of each type of dioxin differs depending on the specific type thereof. In order to evaluate, a scale is needed to evaluate the harmfulness of different dioxins. Therefore, based on the short-term toxicity evaluation results of various dioxins, the amounts of various dioxins are reduced to 2,3,7,8-
Coefficient converted to TCDD amount (Toxicity equivalent coefficient (TE
F)) is calculated, and the sum of the actual amount of each dioxin multiplied by this toxic equivalent coefficient is called the toxicity equivalent conversion value (TEQ), and the amount of dioxin emissions And is used to represent concentration.

In the detoxification treatment of the fine soil particles according to the present invention, the soil particles are treated with a hydrochloric acid acidic aqueous solution containing a DXN decomposition reaction catalyst (hereinafter, also simply referred to as an aqueous solution or a reaction treating agent).
And is brought into contact with. In this case, contacting the fine soil particles with the aqueous solution means that the fine soil particles themselves are brought into contact with the aqueous solution, in other words, that the water component with which the fine soil particles are in contact is an aqueous solution. It is. In order to bring the fine soil particles into contact with the aqueous solution, the water in the water slurry liquid is added by adding hydrochloric acid and a reaction catalyst to the water slurry liquid containing the fine soil particles, or by adding hydrochloric acid containing the reaction catalyst. What is necessary is just to convert into a hydrochloric acid aqueous solution containing a reaction catalyst. Hydrochloric acid aqueous solution containing a reaction catalyst to decompose dioxins
In this case, the treatment temperature is lower than the boiling point of water (100 ° C.), preferably 80 ° C. or lower. The lower limit temperature is 2
It is about 0 ° C. This aqueous solution is used as a reaction treatment agent for decomposing and rendering DXN harmless.

Reaction catalysts for decomposing DXN to detoxification include Cu, Zn, Fe, Mn, Ni, Co, Mo, C
Compounds containing metals such as r, V, Sn, and Ag are used, and these metal compounds can be present in a dissolved and / or solid state in an aqueous hydrochloric acid solution brought into contact with soil particles. In the present invention, it is particularly preferable to use an iron compound and / or a copper compound as the reaction catalyst. In the present invention, it is preferable to use an aqueous hydrochloric acid solution containing an iron compound as a reaction treatment agent to be brought into contact with the fine soil particles. In this aqueous solution, the concentration of the iron compound is expressed in terms of metallic iron (Fe). The amount is at least 5 mmol, preferably at least 10 mmol, more preferably at least 20 mmol, per liter of water. Its upper limit is about 200 mmol. Its pH is between 2 and 6, preferably between 3 and 5. The aqueous solution can include other inorganic acids, such as sulfuric acid, in which case the Cl ⁻ ions and the SO
The molar ratio [Cl ⁻ ] / [SO ₄ ²⁻ ] to ₄ ²⁻ ions is adjusted to 5 or more, preferably 20 or more. In this case, the upper limit is not particularly limited. In this specification, the hydrochloric acid aqueous solution refers to an acidic aqueous solution containing chloride ions. Examples of the acid for maintaining the acidity include hydrochloric acid, sulfuric acid, and nitric acid, and the use of hydrochloric acid is preferred.
Decomposition of dioxins means that dioxins are converted into non-dioxins.

The preferred aqueous hydrochloric acid solution used in the present invention contains a reaction catalyst comprising a solid iron compound which promotes the decomposition of dioxins. The present inventors' research has revealed that, at a temperature lower than 100 ° C., the aqueous solution can be made harmless by contacting the aqueous solution with dioxins, but when using an aqueous solution not containing the reaction catalyst, Requires a considerable amount of time to detoxify dioxins,
Inclusion of the reaction catalyst in an aqueous solution is very important from an industrial or commercial point of view. According to the study of the present inventors, it has been found that an iron compound existing in a solid state in an aqueous hydrochloric acid solution exhibits a high DXN decomposition rate. To make iron compounds exist in a solid state in hydrochloric acid aqueous solution,
The pH of the aqueous hydrochloric acid solution of the iron compound containing the iron compound in a dissolved state may be adjusted to a range of pH 2.5 or more, which is a precipitation region of the iron compound, to precipitate the iron compound in the dissolved state. In this case, it is preferable that solid particles are present in the aqueous solution, the iron compound is precipitated on the solid fine particles, and the insoluble (solid state) iron compound is supported on the solid fine particles.

In the aqueous hydrochloric acid solution of the iron compound,
As the iron compound, a compound in which the valence of iron is lower than 3 is preferable, and a compound in which the valence of iron is divalent is more preferable. Specifically, ferrous chloride (FeCl
₂ ), ferrous sulfate (FeSO ₄ ), ferrous formate (Fe (C
OO) ₂ ), ferrous bromide (FeBr ₂ ), ferrous iodide (FeI ₂ ), ferrous phosphate (Fe ₃ (PO ₄ ) ₂ ), iron perchlorate (Fe (ClO ₄ )) ₂ ) and the like. The pH of the aqueous solution is 6 or less, preferably 3 or less, which is a region in which the iron compound dissolves, and the lower limit is not particularly limited. The chloride ion concentration in the aqueous solution is 10 mmol / L or more, preferably 100 mmol / L or more, and the upper limit is about 3000 mmol / L. The concentration of the iron compound in the aqueous solution is 5 mmol / L or more, preferably 10 mmol / L or more, more preferably 20 mmol / L or more, in terms of metallic iron (Fe), and the upper limit is not particularly limited. However, it is usually about 200 mmol / liter. In the case of the present invention, when the concentration of the iron compound is 20 mmol / L or more, the decomposition reaction of DXN is remarkably accelerated.

The pH at which the iron compound existing in a dissolved state in the aqueous hydrochloric acid solution is precipitated is 2.5 or more, preferably 3.0 or more, more preferably 3.5 or more, which is the pH of the precipitation region of the iron compound. The upper limit is not particularly limited, but is usually about 6.

To precipitate the iron compound in the aqueous hydrochloric acid solution, a pH adjuster is added to the aqueous solution. In this case, the pH adjuster may be an alkaline substance. Such materials include sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, calcium hydroxide, calcium carbonate, magnesium hydroxide, magnesium carbonate and the like.

In the case where solid fine particles are present in an aqueous hydrochloric acid solution when insolubilizing the iron compound, the solid fine particles may be those which are stably present in the form of fine solid particles in the aqueous solution. Such solid fine particles include various inorganic substances, for example, incinerated ash (fly ash, furnace ash), zeolite, alumina, silica, metals or metal oxides stable in aqueous hydrochloric acid. When fine particles having alkaline surfaces are used as the solid fine particles, the iron compound may be easily insolubilized, and such solid fine particles are preferably used. Examples of such solid fine particles include incinerated ash (fly ash, furnace ash) and the like. Generally, incineration ash (fly ash, furnace ash) is alkaline, and in the process of dissolving in an acidic aqueous solution, even if the bulk pH is acidic, the incineration ash (fly ash, furnace ash) At the interface between the ash) solid surface and the bulk acidic aqueous solution, the solid surface side is considered alkaline. Therefore, the iron compound supplied through the film on the particle surface is rapidly insolubilized on the particle surface. The average particle size of the solid fine particles is 50
It is 0 μm or less, preferably 200 μm or less, and the lower limit thereof is not particularly limited, but is usually about 10 μm. The concentration of the solid fine particles in the aqueous solution is 5 to 50%, preferably 10 to 30%. The ratio between the iron compound and the solid fine particles is 0.001 to 0.4, preferably 0.005 to 0.2 by weight ratio of metallic iron (Fe) to the solid fine particles.
It is.

The iron compound existing in the solid state in the aqueous hydrochloric acid solution is in the form of an insoluble iron compound, that is, iron hydroxide (F
e (OH) ₂ ) and iron hydroxide chloride Fe (ClOH).

The hydrochloric acid aqueous solution containing the insoluble iron compound is
It can also be prepared by dispersing a particulate insoluble iron compound in an aqueous hydrochloric acid solution. The average particle size of the insoluble iron compound is 10 μm or less, preferably 1 μm or less, and the lower limit is not particularly limited.
It is about. The concentration in the aqueous solution is expressed in terms of metallic iron,
It is about 0.002 to 1%, preferably about 0.005 to 0.5%. The insoluble iron compound may be one previously supported on solid fine particles, or an iron compound complexed with another metal, for example, potassium ferric sulfate (KFe (S
O ₄ ) ₂ ), iron manganate (FeMnO ₄ ), iron molybdate (FeMoO ₄ ), and the like. The concentration of the iron compound in the solid fine particles is 2 to 20%, preferably 5 to 15% in terms of metallic iron.

In the present invention, the pH of the aqueous hydrochloric acid solution containing the insoluble iron compound to be brought into contact with the fine soil particles is as follows:
2.0 to 6.0, preferably 3.5 to 5.0, and the concentration of the insoluble iron compound in the aqueous solution is 0.00
It is 3 to 3%, preferably 0.008 to 0.8%. The chlorine concentration in the aqueous solution is 10 to 3000 mmol / L, preferably 100 to 1000 mmol / L. It is also preferable that the copper compound exists in a dissolved state in this aqueous solution. In this case, the amount of the copper compound in the aqueous solution is 0.3 to 150 mmol / L, preferably 3 to 80 mmol / L in terms of metallic copper (Cu).

The insoluble iron compound (hereinafter, also referred to as an iron catalyst) used in the present invention is preferably a compound having a valence of iron lower than 3, more preferably a compound having a valence of iron in a divalent state. Generally, these iron compounds are provided in the form of metal oxides or salts, such as chlorides, oxides, carbonates, sulfates and the like. The hydrochloric acid aqueous solution as a reaction treating agent for detoxifying dioxins in soil particles used in the present invention contains these insoluble iron compounds in a solid state as a reaction catalyst, in which case the reaction catalyst contains dissolved components be able to. This dissolved component is usually in the process of shifting to a solid state. Such a reaction catalyst containing dissolved components in the process of transitioning to the solid state also works effectively. As the insoluble iron compound used in the present invention, incinerated ash such as fly ash and furnace ash and other iron components contained in other iron-containing waste can be used. Incinerated ash often contains iron that acts as a reaction catalyst as described above. In order to utilize the iron component contained in such incineration ash as a reaction catalyst, the incineration ash may be added to a hydrochloric acid aqueous solution under a pH condition at which the iron compound does not dissolve and stirred. And
The aqueous hydrochloric acid solution containing such an iron catalyst can be used as a reaction treating agent for dioxins in soil particles in the present invention.

The aqueous solution used as the reaction treating agent in the present invention may contain a substance (contact promoting agent) that promotes the contact between the aqueous solution and DXN in the fine soil particles. The contact promoter includes a surfactant and an alcohol. The type of surfactant in this case is not particularly limited, and anionic, cationic, nonionic and amphoteric surfactants can be used. The addition amount of the surfactant is 0.005 to 1%, preferably 0.01 to 0.5%. As the alcohols, lower alcohols are preferably used, and specific examples thereof include methanol, ethanol, and propanol. The added amount is 0.5
-10%, preferably 1-10%. In the present invention, it is preferable to irradiate the aqueous solution with ultrasonic waves in order to promote the contact between the aqueous solution and DXN. As the ultrasonic wave, an ultrasonic wave generally used for preparing an emulsion or the like is used. Furthermore, according to the present invention, if necessary, oxygen or an oxygen-containing gas can be brought into contact with the aqueous solution to increase the dissolved oxygen concentration in the aqueous solution. The presence of dissolved oxygen promotes the expression of the activity of the reaction catalyst and effectively promotes the decomposition of DXN. As a method of contacting the aqueous solution with oxygen or an oxygen-containing gas in this case, a method of blowing oxygen or an oxygen-containing gas into the aqueous solution,
A method in which oxygen or an oxygen-containing gas is brought into contact with fine droplets of an aqueous solution is exemplified. Examples of the oxygen-containing gas include air and oxygen-enriched air.

According to the present invention, DXN adhering to fine soil particles as described above can be detoxified.
In this case, the processing temperature is from room temperature to less than 100 ° C.,
Since the temperature is preferably 30 to 80 ° C. and lower than the boiling point of water, the energy consumption rate is very low and the apparatus cost is low. Processing time is 10
The specific treatment time varies depending on the state of the dioxins present in the fine soil particles as the raw material to be treated, the treatment conditions including the aqueous solution composition, the desired DXN decomposition rate, and the like. It is difficult to determine the target. In the case of the present invention, DX at the processing temperature
It is an essential requirement that the decomposition rate of N be 60% or more, preferably 80% or more, more preferably 90% or more. In other words, in the case of the present invention, the treatment conditions including the composition of the aqueous solution and the treatment time, the type of the reaction catalyst contained in the aqueous solution, the pretreatment for enhancing the reactivity of DXN, and the like are appropriately selected, so that the ratio is preferably 60% or more. Can achieve a decomposition rate of dioxins of 80% or more, more preferably 90% or more. In the DXN detoxification step, a water slurry liquid containing detoxified fine soil particles is obtained, which is subjected to a solid-liquid separation treatment in a solid-liquid separation step. In this case, as the solid-liquid separation device, a filtration device, a centrifugal separation device,
A conventional device such as a sedimentation separation device (thickener) is used. When a device having a solid-liquid separation function (for example, a sedimentation separation device) is used in the DXN detoxification process, the detoxified fine soil particles can be discharged from the DXN detoxification device. Since the detoxified fine soil particles contain insoluble metals (insoluble catalyst metals and the like), they can be reused after subjecting them to a removal treatment if necessary. Further, the aqueous solution after the detoxified fine soil particles are separated is a hydrochloric acid aqueous solution containing a water-soluble catalytic metal, which is subjected to a concentration treatment or a treatment for controlling the concentration of hydrochloric acid, and then supplied for replenishment in the DXN detoxification process. It can be reused as an aqueous hydrochloric acid solution.

Next, the present invention will be described in detail with reference to the drawings. FIG. 1 shows an example of a flow sheet when the method for detoxifying soil in a DXN-contaminated area according to the present invention is performed. In FIG. 1, 1 is a stirrer, 2 is a hydraulic classifier,
Reference numeral 3 denotes a sedimentation / separation device, and reference numeral 4 denotes a DXN detoxifying device.

To detoxify the soil in the DXN-contaminated area according to the flow sheet shown in FIG. 1, make-up water is supplied to the stirring device 1 in the stirring process through the line 11 and circulated through the lines 12 and 13. Water is supplied, and contaminated area soil is supplied through line 14, where the contaminated area soil is agitated and dispersed in water.
As the stirring device 1 used in the underwater stirring process of the contaminated area soil, any device can be used as long as it can disperse the massive soil into fine particles (primary particles) in water, and various conventionally known devices can be used. it can. Examples of such a device include a stirring tank, an in-line mixer, a jet stirrer, and the like.

From the stirring device 1, through a line 15,
A water slurry containing the micronized soil particles is discharged. This is passed through the pump 6 and classified in the hydraulic classification device 2 in the hydraulic classification step into soil particles having a fine particle diameter smaller than a predetermined particle diameter and soil particles having a larger average particle diameter and a coarse particle diameter having a larger average particle diameter. . As the hydraulic classifier 1, any device capable of separating fine particles and coarse particles in water may be used, and conventionally known various devices can be used. Examples of such an apparatus include a filter and a combination thereof in addition to a cyclone apparatus. From the hydraulic classifier 2, a water slurry liquid containing fine soil particles and a slurry liquid containing coarse soil particles are discharged. The water slurry liquid containing the fine soil particles is supplied to the sedimentation separation device 7 in the sedimentation separation step through the line 16. On the other hand, the water slurry liquid containing coarse soil particles is sent to the solid-liquid separation device 7 in the solid-liquid separation step through the line 17. In the solid-liquid separation device 7, coarse soil particles and water are separated. The separated coarse soil particles Y are discharged through the line 18. Since this is substantially free of DXN contamination, the DXN-contaminated area soil can be backfilled at the site where it was separated. As the solid-liquid separation device 7, a conventional device such as a filtration separation device, a centrifugal separation device, and a sedimentation separation device is used.

On the other hand, in the sedimentation / separation device 3, a sedimentation layer composed of fine soil particles is formed. This is supplied to the DXN detoxifying apparatus 4 in the DXN detoxifying step through a line 19 as a concentrated water slurry containing fine soil particles. As the sedimentation / separation device 3, a conventional one such as a thickener or a filter is used. The concentration of the fine soil particles in the concentrated water slurry discharged from the sedimentation separation device 3 is usually 10 to 50%, preferably 20 to 30% in the water slurry.

The DXN detoxifying device 4 is supplied with an aqueous hydrochloric acid solution through a line 21 in addition to the concentrated water slurry containing the fine soil particles,
An XN cracking catalyst is provided, where DX in fine soil particles is
N is decomposed and made harmless. The DXN detoxifying device 4 discharges the detoxified fine soil particles X through the line 23. Since it contains insoluble metals (such as catalytic metals), it is sent to the final disposal site and undergoes appropriate treatment. Also, from the DXN detoxifying device 4, through the line 24,
The separated water after separating the fine soil particles is discharged. Since this is an aqueous hydrochloric acid solution, it can be recycled to a DXN detoxifying device after being subjected to an appropriate treatment such as a concentration treatment or a hydrochloric acid concentration adjustment treatment.

[0032]

Next, the present invention will be described in more detail by reference examples and examples. The experiments shown in Reference Examples 1 to 4 were performed using the experimental device shown in FIG. The container shown in FIG. 2 is a glass flask having an internal capacity of 2000 ml. This flask has a structure in which a stirrer can be connected so as to be able to stir, and a structure in which a cooling pipe for preventing the liquid in the container from escaping due to evaporation can also be connected. Further, the container is provided with a tube for introducing hydrochloric acid and air, and a pH meter and a thermometer are inserted therein. In order to keep the reaction temperature constant, the vessel was fixed in a constant temperature warm bath.

Reference Example 1 A water slurry liquid containing the following soil containing DXN-contaminated fine soil particles was used as a raw material to be treated, and dioxins contained in the fine soil particles were detoxified as follows. . (Properties of water slurry liquid of fine soil particles) (i) Fine soil particle concentration: 20% (ii) Average particle size of fine soil particles: 42 μm (iii) Dioxin content: 0.12 ng-TEQ /
g

(Experimental method) Ferric chloride tetrahydrate (FeCl ₂ .4H ₂ O: special grade reagent) in 2 liters of pure water 21.3
g was dissolved. At this time, the pH of the aqueous solution was about 2.0. Here, 200 g of a dried product of fine soil particles (hereinafter referred to as soil particles) separated from the water slurry was added, hydrochloric acid was added while heating and stirring, and air was introduced into the solution at 800 Ncc / min. , 65 ° C, p
H3.5 was maintained for 24 hours. Cl in aqueous solution at this time
The concentration was 110 mmol / l. Further, the total Fe concentration in the slurry was 3,000 mg / liter, and after stirring for 24 hours, the slurry was subjected to suction filtration, and the dioxin contained in the soil particles after the treatment, the treatment solution, the exhaust gas, and the soil particles before the treatment Were analyzed. Further, iron precipitated on the soil particles after the treatment was quantified by atomic absorption spectrometry and X-ray fluorescence analysis. For quantitative analysis by atomic absorption spectrometry, use a model SAS 7500 atomic absorption spectrometer manufactured by Seiko Electronics Co., Ltd.
An X-ray fluorescence spectrometer of model PW1400 manufactured by IPS was used.

The concentrations of dioxins in the soil particles before and after the wet treatment are as shown in Table 1, and the concentration in the soil particles after the treatment is generally much lower than the concentration in the soil particles before the treatment. became. The abbreviations in Table 1 have the following meanings. T4CDDs: tetrachlorodibenzoparadioxin P5CDDs: pentachlorodibenzoparadioxin H6CDDs: hexachlorodibenzoparadioxin H7CDDs: heptachlorodibenzoparadioxin O8CDD: octachlorodibenzoparadioxin Total PCDDs: all polychlorodibenzoparadioxin T4CDFs: tetrachlorodibenzofuran Pentachlorodibenzofuran H6CDFs: Hexachlorodibenzofuran H7CDFs: Heptachlorodibenzofuran O8CDFs: Octachlorodibenzofuran Total PCDFs: Total polychlorodibenzofuran Total Total dioxins

[0036]

[Table 1]

Table 2 shows the removal rate (decomposition rate) of dioxins.
(%). This removal rate is calculated by the following equation (1).

(Equation 1)

[0038]

[Table 2]

Reference Example 2 Detoxification treatment of dioxins contained in soil particles shown in Reference Example 1 was performed as follows.

(Experimental method) Ferrous chloride tetrahydrate (FeCl ₂ .4H ₂ O: special grade reagent) in 2 liters of pure water 21.3
g, cupric chloride (CuCl: reagent grade) 31.3
Mmol / l was dissolved. At this time, the pH of the aqueous solution was about 2.0. Here, 200 g of the soil particles were added, hydrochloric acid was added while heating and stirring, and air was introduced into the solution at 800 Ncc / min.
H3.5 was maintained for 24 hours. Cl in aqueous solution at this time
The concentration was 140 mmol / l. The total Fe concentration in the slurry was 3,000 mg / liter, and the total Cu concentration was 2,000 mg / liter.
After stirring for 24 hours, the slurry was subjected to suction filtration, the dioxins contained in the treated soil particles were analyzed, and the dioxin decomposition rate was calculated by the formula (1) described in Reference Example 1. As a result, the decomposition was 96%. Rate was obtained. At this time, when dioxins in the aqueous solution after filtration were analyzed, the amount was sufficiently negligible. Furthermore, when iron and copper deposited on the soil particles after the treatment were quantified by atomic absorption spectrometry and X-ray fluorescence spectrometry, an iron salt corresponding to 79% of the added iron was precipitated. The amount of copper deposited was negligible. For quantitative analysis by atomic absorption spectrometry, use a model SAS 7500 atomic absorption spectrometer manufactured by Seiko Electronics Co., Ltd. For quantitative determination by fluorescent X-ray analysis, use PHILIP
An X-ray fluorescence spectrometer of model PW1400 manufactured by Company S was used.

Reference Example 3 Dioxins contained in soil particles shown in Reference Example 1
Was made as follows. (Experimental method) Sulfosuccine as a contact promoter in pure water
8 g of anionic surfactant and 4 g of nonionic surfactant
Ferrous chloride tetrahydrate (Fe
Cl _Two・ 4H_TwoO: reagent grade) 21.3 g together with the first salt
3.1 g of copper chloride (CuCl: reagent grade) was dissolved. this
The pH of the aqueous solution at that time was about 2.0. Here, before
Add 200 g of furnace ash and add hydrochloric acid while heating and stirring
And introduce air into the solution at 800 Ncc / min.
And maintained at 65 ° C. and pH 3.5 for 24 hours. At this time
The Cl concentration in the aqueous solution is 140 mmol / l.
Was. The total Fe concentration in the slurry was 3,000 mg.
/ Liter, and the total Cu concentration is 2,000 mg / liter.
Torr. After stirring for 24 hours, the slurry was filtered by suction.
Of dioxins in soil particles after treatment
The dioxin decomposition rate was described in Reference Example 1 (1).
As a result of calculation using the equation, a decomposition rate of 78% was obtained. This
At the time of analysis, dioxins in the aqueous solution after filtration were analyzed
However, the amount was sufficiently negligible.

Reference Example 4 An experiment was performed in the same manner as in Reference Example 3, except that the aqueous solution was irradiated with ultrasonic waves. In this case, a decomposition rate of 83% was obtained. In addition, the ultrasonic wave generated from the ultrasonic processing device UP-50H manufactured by Kubota Corporation was used as the ultrasonic wave.

Example 1 In accordance with the flow sheet shown in FIG. 1, detoxification treatment was performed on DXN-contaminated area soil. The main operating conditions in this case are shown in FIG.
It is shown below in relation to It should be noted that the data in this example is based on the results obtained in individual small-scale experiments. The type of DXN-contaminated area soil used as the raw material to be treated in this example is viscous soil and contains about 18% of particles having a particle size of 100 μm or less.

(1) Line 14 (DXN-contaminated area soil) (i) Water content: 10% (ii) Supply amount: 100 parts by weight / h (2) Line 15 (dispersed soil particle water slurry) (i) Soil particles Concentration: 14.6% (ii) Flow rate: 650 parts by weight / h (3) Line 16 (water slurry liquid of fine soil particles) (i) Average particle size of fine soil particles: 40 μm (ii) Concentration of fine soil particles: 5% (iii) Flow rate: 400 parts by weight / h (iv) DXN content in fine soil particles: 0.3-TEQ
/ G (4) Line 17 (water slurry liquid of coarse soil particles) (i) Average particle size of coarse soil particles: 1,500 μm (ii) Concentration of coarse soil particles: 30% (iii) Flow rate: 250 parts by weight / h (Iv) DXN content in coarse soil particles: 0.026-T
EQ / g or less (5) Line 19 (fine soil particle concentrated water slurry liquid) (i) Fine soil particle concentration: 20% (ii) Flow rate: 100 parts by weight / h (6) DXN detoxifying device 4 (i) Reaction temperature: 30 ° C. (ii) Reaction time: 24 hours (iii) Fine soil particle concentration: 15% (iv) Composition of aqueous solution Fe ion concentration: 3,200 mg / l Cu ion concentration: 2,500 mg / l Cl ion concentration: 150 mg / l pH: 3.5 (7) Line 23 (detoxified fine soil particle water slurry) (i) Coarse soil particle concentration: 40% (ii) Flow rate: 43 parts by weight / h (iii) In fine soil particles DXN content of 0.03-TE
Q / g or less (iv) DXN decomposition rate: 90%

[0045]

According to the present invention, soil on DXN-contaminated land can be detoxified efficiently at low cost.

[Brief description of the drawings]

FIG. 1 shows an example of a flow sheet for carrying out the method of the present invention.

FIG. 2 is an explanatory view of an experimental apparatus for detoxifying dioxin-containing fine soil particles.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 stirrer 2 hydraulic classifier 3 sedimentation and separation device 4 dioxin detoxification device 5 and 20 stirrer 6 pump 7 solid-liquid separation device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2E191 BA12 BB01 BD13 4D004 AA41 AB07 AC07 CA34 CC09 CC12

Claims (2)

[Claims] 1. A method for detoxifying dioxin-contaminated soil, comprising: (i) removing dioxin-contaminated soil existing from a surface layer of the dioxin-contaminated soil to a soil portion having a depth substantially free of dioxin contamination. Separating, (ii) stirring and dispersing the separated soil obtained in the soil separation step in water, and (iii) obtaining fine particles having an average particle size of 100 μm or less from the water dispersed in the water obtained in the stirring step. Classifying the soil particles, (iv) contacting the fine soil particles obtained in the classifying step with an aqueous hydrochloric acid solution containing a dioxin decomposition reaction catalyst to decompose the dioxins, and (v) Refilling the coarse soil particles after classifying the fine soil particles from the soil in the classification step into the traces of the dioxin-contaminated area soil. Detoxification method of the new pollution zone soil. 2. The method according to claim 1, wherein the dioxin-contaminated area soil is dioxin-contaminated field soil.