JP2003300058A - Soil treating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for extracting PCB efficiently from the soil contaminated with PCB or PCB-containing oils and decomposing the extracted PCB. <P>SOLUTION: In this method for treating the soil contaminated with PCB, PCB or PCB-containing oil are extracted from the contaminated soil by using lower alcohol. Then a high-boiling point hydrocarbon solvent is added to the PCB-containing lower alcohol, and the used lower alcohol is recovered by distillation so that PCB is transferred to the high-boiling point hydrocarbon solvent. Subsequently, the PCB-containing high-boiling point hydrocarbon solvent is taken out and PCB in the high-boiling point hydrocarbon solvent is detoxified by chemical extraction/decomposition. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a halogenated aromatic compound from a soil polluted with a harmful halogenated aromatic compound, in particular, a halogenated aromatic compound represented by PCB, at high efficiency under normal pressure. It belongs to the field of environmental protection technology in which a halogenated aromatic compound that is removed in a short time is further chemically decomposed.

[0002]

2. Description of the Related Art Conventionally, purification methods for various contaminated soils have been proposed and implemented. As a method of treating soil containing a halogenated aromatic compound, for example, incineration treatment, thermal desorption treatment, washing extraction treatment, etc. are performed. Among them, the washing and extraction treatment with an organic solvent, which is said to require a small amount of energy and is said to be low in cost, is the most excellent.
However, the conventional method of washing and extracting with an organic solvent requires a great amount of time for the extraction step because the contaminated soil and the washing solvent are brought into contact with each other under normal pressure to perform the extraction, and the phase separation is carried out by leaving them standing. Has been a problem, and there has been a need for a method for treating contaminated soil that allows rapid phase separation. Aromatic compounds such as toluene, benzene, and chlorobenzene are excellent in extractability as an extraction solvent, but they are not preferable because they have toxicity and odor problems and may remain in soil. Lower alcohols such as ethanol and 2-propanol have a slightly lower extraction power than aromatics, but have low toxicity and low odor, and even if they remain in soil, they are rapidly biodegradable and have an extremely low environmental load. small. In the case of using ethanol as the extraction solvent (Patent Document 1), it is reported that 95% of the halogenated aromatic compound can be extracted by washing and extracting at room temperature under reduced pressure for 15 minutes, but the extraction rate is not sufficient.

A problem in carrying out washing and extraction of soil is when the soil contains water. It is very often the case that the soil contains water due to precipitation, snowfall, etc. However, if the soil containing water is washed and extracted, the extraction efficiency may become very poor. Furthermore, water may be transferred to the extraction solvent phase during the extraction process, and with this,
When recycling the extraction solvent, an operation of separating water is indispensable, which is very complicated.

In the case of recovering only water from a water-containing contaminated soil, for example, a method of heating the water-containing contaminated soil with stirring to evaporate the water can be considered. The halogenated aromatic compound, which is a pollutant contained in, also migrates to the water side,
Very inconvenient. Therefore, it is desired to develop a method for recovering only water from such water-containing contaminated soil.

There are various methods for decomposing the extracted halogenated aromatic compound. Decomposition treatment with metallic sodium (Patent Document 2), decomposition treatment with electron beam irradiation (Patent Document 3, Patent Document 4 and Patent Document 5), mechanochemical treatment with a ball mill containing calcium oxide (Patent Document 6) and the like are disclosed. Has been done. However, in decomposition treatment with metallic sodium, there is a problem in safety because metallic sodium is dangerous to handle because it is ignitable, and in decomposition treatment by electron beam irradiation, the processing cost is high because the device is expensive. In the mechanochemical treatment, since an impact crushing device such as a ball mill is used in the mechanochemical treatment, the device is expensive and the safety remains a problem. None of these methods is necessarily a satisfactory decomposition treatment method. Therefore, it is considered that safety and cost are the issues in developing the treatment of contaminated soil with halogenated aromatic compounds. The way in which hazardous and hazardous substances are dealt with, and the way large-scale equipment and costs are required, is a hindrance to progress.

As another decomposition treatment method for halogenated aromatic compounds, there is a chemical extraction decomposition method. The chemical extraction decomposition method is provided by the present inventors as a method for treating PCB-containing insulating oil (Patent Document 7, Patent Document 8, Patent Document 9, and Patent Document 10). Specifically, it is a method of dehalogenating a halogenated aromatic compound using a strong alkaline substance in a heat-resistant alkaline polar solvent having excellent solubility.

Prior art document information relating to the invention of this application is as follows.

[0008]

[Patent Document 1] Japanese Unexamined Patent Publication No. 9-75908

[Patent Document 2] Japanese Patent Laid-Open No. 2000-246002

[Patent Document 3] Japanese Patent Laid-Open No. 2001-9408

[Patent Document 4] Japanese Patent Laid-Open No. 2000-9409

[Patent Document 5] Japanese Patent Laid-Open No. 2000-70913

[Patent Document 6] Japanese Patent Laid-Open No. 2001-47026

[Patent Document 7] JP-A-6-25691

[Patent Document 8] JP-A-7-8572

[Patent Document 9] Japanese Patent Laid-Open No. 7-289656

[Patent Document 10] JP-A-9-253602

[0009]

The object of the present invention is to extract the halogenated aromatic compound by washing and extracting the soil contaminated with the halogenated aromatic compound with a solvent with high efficiency and in a short time to separate the halogenated aromatic compound. Another object of the present invention is to provide a soil treatment method for decomposing using a simple chemical extraction decomposition method.

Another object of the present invention is to provide a method for recovering only water from soil containing water and contaminated with halogenated aromatic compounds. A further object of the present invention is to first preliminarily recover only water from a soil containing water and contaminated with a halogenated aromatic compound, and then washing and extracting the soil with a solvent in a highly efficient and short time. It is an object of the present invention to provide a soil treatment method in which a halogenated aromatic compound is separated and decomposed by a safe and simple chemical extraction decomposition method.

Another object of the present invention is to separate the halogenated aromatic compound by washing and extracting the soil polluted with the halogenated aromatic compound with a solvent with high efficiency and in a short time, and in some cases, halogenated aromatic compound. It is an object of the present invention to provide a method for recovering a halogenated aromatic compound from a soil contaminated with a halogenated aromatic compound, which may include a preliminary step of recovering water from the compound contaminated soil. The halogenated aromatic compound recovered by this method can be subjected to conventional decomposition treatment methods as well as chemical extraction decomposition methods.

[0012]

Means for Solving the Problems The present invention relates to extraction of contaminated soil, solid-liquid separation of an extraction suspension, concentration of an extraction solvent, decomposition treatment of a concentrated liquid of a halogenated aromatic compound, and extraction of soil. It consists of 5 steps of drying. That is, the present invention is a method for purifying soil contaminated with a halogenated aromatic compound, which comprises extracting a halogenated aromatic compound from a soil contaminated with a halogenated aromatic compound using a lower alcohol. Step, second step for solid-liquid separation of the lower alcohol phase after extraction from the soil, a high boiling hydrocarbon solvent is added to the halogenated aromatic compound-containing lower alcohol phase, and then the lower alcohol is distilled and recovered to obtain the halogenated aromatic Third step of transferring the compound to a high boiling hydrocarbon solvent, decomposition treatment of a halogenated aromatic compound-containing high boiling hydrocarbon solvent in a heat resistant alkaline polar organic solvent using a strong alkaline substance
There is provided a method for treating soil contaminated with a halogenated aromatic compound, which comprises a step and a fifth step of removing lower alcohol from the soil after extraction.

Further, the present invention may include a step of preliminarily recovering only water from the contaminated soil when the contaminated soil contains water.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for treating contaminated soil according to the present invention, the term "soil contaminated with a halogenated aromatic compound" means a halogenated aromatic compound or an oil containing the halogenated aromatic compound. Contaminated soil. The halogenated aromatic compound is a compound that is highly toxic to humans and animals and plants, such as polychlorinated biphenyl (PCB),
An aromatic compound having chlorine as a substituent, such as DDT or dioxin, and particularly polychlorinated biphenyl. Polychlorinated biphenyl is a general term for compounds in which several chlorine atoms are substituted in biphenyl, and isomers exist depending on the substitution position of chlorine atoms and the number of substitutions. Examples of oils containing a halogenated aromatic compound include insulating oils used in transformers, capacitors and the like.

The first to fifth steps and optional preliminary steps in the method for treating contaminated soil according to the present invention will be described in detail. (1) First Step In this step, as shown in FIG. 1, a halogenated aromatic compound is extracted from a soil contaminated with a halogenated aromatic compound using a lower alcohol (primary extraction solvent).

The lower alcohol used for washing the contaminated soil and extracting the halogenated aromatic compound used in the present invention is preferably one which has a high biodegradability even if it remains in the soil after extraction and has a small effect on the environment. For example, a linear or branched alcohol having 1 to 4 carbon atoms can be mentioned, and more preferably,
Examples include ethanol or 2-propanol. The amount of the lower alcohol used is usually preferably about 100 to 1500% by volume based on the total volume of the contaminated soil.

The extraction operation can be carried out under normal pressure using a mixing tank equipped with a usual stirring device. Preferably, a closed type mixing tank equipped with a low speed agitator and a high speed agitator can be used. The reason why it is preferable to use the low speed agitator and the high speed agitator is to increase the agitation efficiency to increase the dispersion of the contaminated soil in the lower alcohol and increase the extraction efficiency of the halogenated aromatic compound contained in the contaminated soil. Because you can. The reason why it is preferable to use the closed type mixing tank is that the lower alcohol which is a solvent can be prevented from volatilizing.

The mixing / stirring temperature in the mixing tank may be in the range of room temperature to the boiling point of the extract or lower. The mixing / stirring time varies depending on the volume of the reaction tank, the mixing / stirring speed, the amount of contaminated soil and lower alcohol, etc., but the halogenated aromatic compound contained in the contaminated soil dissolves in the lower alcohol and extraction processing is possible. It will be good if it is the time.

(2) Second Step In this step, as shown in FIG. 1, the lower alcohol phase after extraction and the soil are subjected to solid-liquid separation.

After the completion of the mixing and stirring in the first step, the extracted alcohol phase and the solid phase of the soil can be separated by a conventional method such as pressure filtration, suction filtration or centrifugation. . The separation operation may be performed either while the alcohol phase and the solid content phase of the soil remain suspended, or after being left to stand for a certain period of time.

For example, when the halogenated aromatic compound is PCB, it is possible to remove 98% or more of PCB from the contaminated soil by the first extraction and separation operation. Further, if this operation is performed 2 to 4 times, N. D. (Lower limit of quantification 0.1 ppm)
PCB can be removed up to.

A halogenated aromatic compound (for example,
PCB) content is measured by the "Bottom Sediment Survey Method"
No. 27. GC-ECD based on September 8, 1988)
(Electron capture detection type gas chromatograph).

(3) Third Step In this step, as shown in FIG. 1, after a high boiling hydrocarbon solvent (second extraction solvent) is added to the halogenated aromatic compound-containing lower alcohol phase (extraction solution), The lower alcohol is distilled and recovered to transfer the halogenated aromatic compound to the high boiling hydrocarbon solvent.

The high boiling hydrocarbon solvent to be added is preferably an aliphatic hydrocarbon solvent having a boiling point higher than the reaction temperature of the decomposition treatment in the fourth step, for example, a boiling point of 150 to 300 ° C.
Of the aliphatic hydrocarbon solvents are preferred. Specific examples include n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, and naphthenic solvents having a boiling point of 200 ° C or higher and lower than 250 ° C. . More preferably, the boiling point is 2
Examples include linear aliphatic hydrocarbon (n-paraffin) solvents having a temperature of about 40 to 270 ° C., for example, n-tridecane and n.
-Tetradecane, n-pentadecane and the like. The high-boiling point hydrocarbon solvent may be a mixture of one or more selected from the above-listed compounds.

The amount of the high boiling hydrocarbon solvent used may be, for example, about 1 to 20% by weight of the extract. The high boiling hydrocarbon solvent is added to the extraction liquid because the halogenated aromatic compound is easily dissolved in the high boiling hydrocarbon solvent and is difficult to azeotrope with the lower alcohol, so that high purity lower alcohol can be recovered by distillation. The reason is that stable and rapid decomposition treatment can be carried out in the fourth step, and further, a slight amount of halogenated aromatic compound is transferred to a small amount of a high-boiling point hydrocarbon solvent, which makes handling and temporary storage convenient.

Distillation of the lower alcohol from the extract containing the high-boiling point hydrocarbon solvent may be carried out by a conventional method. For example, the lower alcohol may be distilled off by heat distillation under normal pressure or reduced pressure. The distilled lower alcohol is recycled and used as the lower alcohol for washing and extracting in the first step and the second step. The halogenated aromatic compound is transferred to the high boiling hydrocarbon solvent by distilling off the lower alcohol.

(4) Fourth Step In this step, as shown in FIG. 1, a halogenated aromatic compound-containing high-boiling hydrocarbon solvent is decomposed by using a strongly alkaline substance in a heat-resistant alkaline polar solvent (chemical extraction). Decomposition method).

Examples of the heat-resistant alkaline polar solvent include 1,3-dimethyl-2-imidazolidinone (DM
I), sulfolane, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polyethylene glycol lower alkyl ether, trimethylene glycol, butylene glycol, and lower alkyl ethers thereof. In particular,
In order to enhance the effect of the main decomposition treatment, 1,3-dimethyl-2-imidazolidinone and sulfolane are preferable, and the other ones are preferably used supplementarily. The lower alkyl refers to a straight or branched chain alkyl having 1 to 6 carbon atoms.

Here, the heat-resistant alkaline polar solvent is added in order to enhance the reactivity between the PCB and the strongly alkaline substance due to the solvent effect and to enhance the efficiency of the decomposition treatment. The amount of the heat-resistant alkaline polar solvent used may be, for example, about 100 to 200% by weight based on the high boiling hydrocarbon solvent.

The strong alkaline substance is not particularly limited as long as it does not adversely affect the reaction, and examples thereof include sodium hydroxide, potassium hydroxide, sodium alkoxide, potassium alkoxide, calcium hydroxide and the like, and preferably , Sodium hydroxide, and potassium hydroxide. Further, at least one or a mixture of two or more selected from these can also be used as the strong alkaline substance.

The amount of the strongly alkaline substance used is, for example, DM when DMI is used as the heat resistant alkaline polar solvent.
It is preferably about 1 to 10 wt% with respect to I. The upper limit of the temperature of the main decomposition treatment is preferably less than the lowest temperature of the boiling points of the halogenated aromatic compound, the high boiling point hydrocarbon solvent and the heat resistant alkaline polar solvent. This is because when the temperature is too high, even a stable heat-resistant alkaline polar solvent is an organic substance, so that it is inevitable to gradually decompose. The lower limit may be at least 100 ° C. or higher in consideration of reactivity. More specifically, it can be appropriately selected from about 150 ° C to 250 ° C.

The time of this decomposition treatment depends on the type of halogenated aromatic compound, the volume of the decomposition treatment tank, the type and amount of solvent used,
It can be appropriately selected depending on the type and amount of the strongly alkaline substance, decomposition treatment temperature, and the like. For example, in the case of PCB, although it depends on other processing conditions, it can be decomposed to a quantitative detection limit (0.5 ppm) or less as stipulated by law in about several minutes to 6 hours.

In order to effectively carry out this decomposition treatment, a usual heating and stirring device can be used. The heating and stirring device may be any device provided with a decomposition treatment tank, a heater, a stirrer, a filling tower, a circulation device and the like. It is possible to enhance the decomposition effect by providing not only a mere packing but also an adsorption layer in the packed tower.

By this decomposition reaction, the halogenated aromatic compound is dechlorinated and rendered harmless. For example, the chlorine in the PCB becomes sodium chloride or potassium chloride by the dechlorination reaction, and the PCB is rendered harmless.

Further, the high boiling point hydrocarbon solvent (secondary extraction solvent) and the heat resistant alkaline polar solvent can be recovered from the reaction liquid after the main decomposition treatment. This is because, when the halogenated aromatic compound is continuously decomposed, it is economically advantageous to recover and reuse the high boiling point hydrocarbon solvent and the heat resistant alkaline polar solvent from the reaction liquid after the decomposition treatment.

The following methods may be mentioned as recovery methods.
For example, solid components such as residual strong alkaline substances and inorganic salts (eg, sodium chloride, potassium chloride) are separated from the reaction solution after the reaction by centrifugation or the like. The liquid phase part consisting of the heat-resistant alkaline polar solvent, the high boiling hydrocarbon solvent and the halogenated aromatic compound decomposition product is distilled, and the heat-resistant alkaline polar solvent is separated and reused. On the other hand, the high boiling hydrocarbon solvent containing the halogenated aromatic compound decomposition product is reused for other purposes such as fuel, and the residual strong alkaline substance and the inorganic salt are neutralized and then treated.

Other recovery methods include the following methods. When recovering by utilizing the low mutual solubility,
For example, a method of distilling a reaction solution containing a heat-resistant alkaline polar solvent and a high-boiling hydrocarbon solvent, cooling a distillate containing both to a temperature at which both layers are separated, and then recovering the separated solvent is adopted. . For the purpose of reusing the heat resistant alkaline polar solvent, it is preferable that the amount of the high boiling point hydrocarbon solvent contained in the recovered heat resistant alkaline polar solvent is as small as possible. When the recovered heat-resistant alkaline polar solvent is subjected to the chemical extraction decomposition method, the solubility of the high-boiling hydrocarbon solvent in the heat-resistant alkaline polar solvent at 25 ° C is in a range that does not inhibit the chemical extraction decomposition, that is, 5%.
It is desired to be less than. Similarly, when the purpose is to reuse the high-boiling point hydrocarbon solvent, it is preferable that the amount of the heat-resistant alkaline polar solvent contained in the recovered high-boiling point hydrocarbon solvent is as small as possible. When the recovered high-boiling point hydrocarbon solvent is used as the secondary extraction solvent (third step), 2 of the heat-resistant alkaline polar solvent for the high-boiling point hydrocarbon solvent is used.
It is desired that the solubility at 5 ° C is less than 5%.

(5) Fifth Step In this step, as shown in FIG. 1, lower alcohol is removed from the extracted soil.

The lower alcohol remaining in the soil after extraction generally has low toxicity, low odor and fast biodegradability,
It needs to be removed from the soil to give due consideration to the environment. As a method for removing lower alcohol from the soil after extraction, any method may be used as long as it is dried and the lower alcohol is distilled off, and examples thereof include a method of heating and stirring under reduced pressure, and a method of drying by blowing under normal pressure. Under reduced pressure means, for example, 5
About 0 to 200 Torr is preferable, and heating is preferably about 30 to 90 ° C., for example.

(6) Preliminary Step It is desirable that this step be preliminarily performed before the first step described above. That is, this preliminary step is a treatment method for recovering only water from the soil when the contaminated soil contains water. As mentioned above, lower alcohols, preferably ethanol or 2-propanol, are used in the first step of washing and extracting the soil. When ethanol, for example, is used as the cleaning solvent and the contaminated soil contains water, the water may migrate to the cleaning solvent phase, resulting in a very low extraction efficiency. As a result of diligent studies by the present inventors, if about 10% (based on the weight of the extraction solvent) of water is transferred into the extraction solvent,
It is known that the water can be extracted, but if more water is transferred, it is naturally possible that the efficiency will drop significantly. Further, it is desirable that the extraction solvent is recycled and used, from the viewpoints of cost, environmental consideration, etc.
If the water is transferred to the extraction solvent phase, the work of water separation becomes indispensable for each recycling, which is very complicated. Therefore, especially when the contaminated soil contains water, it is desirable to perform the treatment by the preliminary step described below before carrying out the method of the present invention.

In this preliminary step, first, to the soil containing water and contaminated with the halogenated aromatic compound, a solvent for dissolving the halogenated aromatic compound is added. The solvent that dissolves the halogenated aromatic compound is a solvent that can dissolve the halogenated aromatic compound,
It can be used with both inorganic and organic solvents,
Preferably, organic solvents, especially aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, etc. can be used. Especially n-tetradecane, n-undecane, n-dodecane,
Oils such as n-tridecane, n-pentadecane and n-hexadecane are preferably used. The solvent for dissolving the halogenated aromatic compound is added 0.1 to 2 times, preferably 0.2 to 1 times, more preferably 0.4 to 0.7 times the weight of the soil to be treated. can do. A solvent that dissolves such a halogenated aromatic compound is added to the contaminated soil and preferably stirred. In this way, the halogenated aromatic compound contained in the contaminated soil can be sufficiently dissolved in the solvent.

Next, the solvent-added contaminated soil is heated with stirring to separate water. Heating can be carried out in various reactors, vessels, etc., but it is preferable to use the closed type mixing tank described in the first step. By using such a mixing tank, it is possible to perform the treatment in the first step immediately after performing the preliminary step, which is highly desirable in that each step can be continuously performed. . In addition, heating of contaminated soil with addition of solvent requires the volume of the reaction tank,
Although it changes depending on the mixing / stirring speed, the amount of water, contaminated soil, the amount of solvent, etc., it may be carried out at a temperature at which water is azeotropic, for example, 9
It can be carried out in the range of 0 to 200 ° C, preferably 120 to 180 ° C, and more preferably 130 to 160 ° C.
By heating at such a temperature, the contained water, the added solvent, and the halogenated aromatic compound dissolved therein are azeotroped. By separating the water from the azeotrope, it is possible to recover only the water from the contaminated soil.

For separating water, a water separator, preferably a U-shaped tube or the like is connected to the mixing tank. As an apparatus capable of performing the treatment in the preliminary step, for example, an apparatus as shown in FIG. 2 can be mentioned, but as long as it is an apparatus capable of separating oil and water, for example, a general Dean-Stark water separator or the like is used. It is also possible to connect a conventional water separator. FIG. 2 shows a U-shaped pipe having a cooling pipe connected to the mixing tank. From the heated mixing tank, water, a solvent, and a halogenated aromatic compound dissolved therein are azeotropically distilled, cooled by a cooling pipe, and dropped to the bottom of the U-shaped pipe. At this time, since the solvent phase is the upper layer and the aqueous phase is the lower layer, water and the solvent can be separated. Since the halogenated aromatic compound which is a pollutant stays on the solvent phase side due to its affinity and does not transfer to the water phase, it becomes possible to recover only water from the water-containing contaminated soil.

In order to carry out oil-water separation more effectively, a small amount of water is preferably put in the connected U-tube. More preferably, a small amount of a solvent that dissolves the above-mentioned halogenated aromatic compound is floated on the water surface of the U-shaped tube on the side of the mixing tank. By doing so, the water, the solvent, and the halogenated aromatic compound contained therein are cooled by the cooling pipe, and U
When falling to the bottom of the tube, the solvent and the halogenated aromatic compound remain in the solvent floating on the water surface, and only water reaches the lower layer. Therefore, the possibility that the halogenated aromatic compound is transferred to the water phase is extremely low.

After the water is substantially completely recovered from the soil by the above treatment method, the treatment by the above-mentioned first step can be continued.

[0046]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited to these.

Preparation of test soil (No. 1 to 4) PCB 0.2 to 0.4 g (KC400 or KC100 )
(0: Kanegafuchi Chemical Industry Co., Ltd.) was dissolved in 300 g of n-hexane, and this was uniformly mixed with dry soil uncontaminated by chemicals and the like, and then n-hexane was volatilized to prepare 4 points of PCB-contaminated soil. The PCB content concentration of the contaminated soil is as shown in Table 1. The analysis is based on the “sediment survey method”
No. 7 (September 8, 1988) based on GC-ECD.

[0048]

[Table 1]

Examples 1 to 3 First step: 500 g of the contaminated soil prepared above and 4000 g of ethanol were placed in a closed mixing tank (equipped with one low-speed anchor type stirrer and two high-speed stirrers for dispersion), and the low-speed stirrer 50-
It was washed and extracted at 100 rpm and a high speed stirrer 3000 to 6000 rpm for 15 to 30 minutes. Second step: After washing and extraction, the suspension was suction filtered with a glass fiber filter paper.
(The first step and the second step were set as one cycle.) Next, the separated soil was again charged into the washing tank with 4000 g of fresh ethanol, and the same treatment was performed for several cycles.

The final solid-liquid separated soil was placed in a closed mixing tank, and the mixture was stirred at 10 to 20 rpm at a low speed, at 80 ° C. for 5
It was dried under reduced pressure at 0 Torr. PC in this dry soil
The B concentration was measured (the analysis was performed by GC-ECD), and the results are shown in Table 2.

[0051]

[Table 2]

Third step: Extraction liquid 3800 in the first cycle
g is a high boiling hydrocarbon solvent (boiling point 240 to 270 ° C. n
-Paraffin, the same applies hereinafter) 380 g was added, and ethanol was distilled and recovered using an evaporator. PCBs in recovered ethanol were analyzed. The results are shown in Table 3.

[0053]

[Table 3]

Example 4 Using the recovered ethanol obtained in the third step of Example 1 as the extraction solvent, the test soil 4 was washed and extracted (the first step) and the soil was separated (the second step) as in Examples 1 to 3. Table 2 shows the results of performing the steps.

Example 5 70 g of high boiling hydrocarbon solvent containing 230 ppm of PCB
Then, 140 g of DMI and 7 g of sodium hydroxide were added to the reaction vessel and treated at 210 ° C. for 6 hours to decompose the PCB. The PCB concentration in the high boiling hydrocarbon solvent after the reaction is determined by GC.
Analyzed by ECD. The results are shown in Table 4.

From this result, the extraction rate from soil with alcohol reached 99.9% or more, and the residual PCB in the soil was
Was ND (lower limit of quantification 0.1 ppm or less). Further, the PCB extracted in the high boiling hydrocarbon solvent could be reduced to the standard value or less (0.5 ppm or less) by the chemical extraction decomposition method.

[0057]

[Table 4]

Example 6 This example is intended to verify a preliminary step of recovering only water from a soil that is contaminated with halogenated aromatics when the soil contains water.

Contaminated soil was prepared in the same manner as in the above example.
The amount of PCB contained in the contaminated soil used in this example was 139.5 ppm. 400g of this contaminated soil
And 400g of tap water was charged into the closed type mixing tank (1 low speed anchor type stirrer and 2 high speed stirring stirrer for dispersion) used in the 1st step, stirred with 1 low speed anchor type stirrer, and contained water. A soil model was created. Next, a solvent (N-3033: industrial oil containing tetradecane as a main component,
200 g of Neos) was added and further stirred.

A water separator including a U-shaped pipe, a Claisen pipe, and a Dimroth cooling pipe as shown in FIG. 2 was connected to the closed type mixing tank, and 60 g of tap water was charged at the bottom of the U-shaped tube. 2 g of the solvent (N-3033 above) was floated on the water surface. In this state, the low-speed anchor type stirrer is rotated at 20 rpm, and the jacket circulating heat medium temperature of the closed type mixing tank is 140 ° C.
Raised to.

As the temperature rises, the water, solvent and halogenated aromatic compounds contained in the soil begin to azeotrope,
It was observed that it was cooled by the Dimroth cooling pipe and dropped to the bottom of the U-shaped pipe. In the U-shaped tube, the solvent containing the halogenated aromatic was in the upper layer and the water was in the lower layer, and oil-water separation proceeded.

After heating for about 4 hours, the amount of recovered water distilled from the inside of the U-shaped tube was measured and found to be 350 g. The amount of PCB contained in this water was measured, but no dissolution of PCB was observed.

[0063]

INDUSTRIAL APPLICABILITY In the method for purifying contaminated soil of the present invention, the halogenated aromatic compound can be washed and extracted from the contaminated soil in a short time and with high efficiency, even though the extraction with the lower alcohol is performed under normal pressure. I can. Further, by chemically extracting and decomposing the PCB extracted from the contaminated soil, it is possible to safely and easily reduce the generation of secondary waste to zero as much as possible.

Further, when the contaminated soil contains water, only the water can be first recovered from the soil. By performing this pretreatment, the lower alcohol used for extraction can be recycled for use without impairing the extraction efficiency with the lower alcohol, which is extremely advantageous from the viewpoint of cost and environment.

The halogenated aromatic compound recovered from the contaminated soil by the method of the present invention can be subjected to not only the chemical extraction decomposition method but also various conventional decomposition treatment methods.

[Brief description of drawings]

FIG. 1 shows the processing steps of the present invention.

FIG. 2 is a diagram showing an example of a water separator used in the preliminary step of the present invention.

[Explanation of symbols]

1 Soil contaminated with halogenated aromatic compounds 2 Lower alcohol (primary extraction solvent) 3 wash extraction tank 4 filter 5 extract 6 treated soil 7 High boiling hydrocarbon solvent (secondary extraction solvent) 8 still 9 Recovery primary extraction solvent 10 Secondary extraction solvent containing halogenated aromatic compound 11 Strongly alkaline substances 12 Heat-resistant alkaline polar solvent 13 Decomposition tank 14 Recovery heat resistant alkaline polar solvent 15 Recovery secondary extraction solvent 16 Claisen tube 17 U-shaped tube 18 Jimroth Cooling Tube 19 solvent 20 water

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C07B 35/06 C07C 25/18 37/06 B09B 3/00 304K C07C 25/18 (72) Inventor Domoto Takuya 4-1, Egasaki-cho, Tsurumi-ku, Yokohama-shi, Kanagawa, Tokyo, Japan Energy and Environmental Research Laboratory (72) Inventor Hideki Kubota 1-1, Oike-cho, Kosai-cho, Koga-gun, Shiga Prefecture Within Neos (72) ) Inventor Shin Takada 1-1, Oike-cho, Kosai-cho, Koga-gun, Shiga Prefecture Neos Co., Ltd. (72) Inventor, Hitoshi Matsumoto 2-6-15, Shiba Park, Minato-ku, Tokyo Kuroryushi Park Building 7F, Neos Co., Ltd. F term (reference) 2E191 BA12 BA13 BB01 BC01 BD11 4D004 AA41 AB01 AB06 AB07 CA34 CA40 CC04 4D056 AB17 AB18 AC02 AC06 BA04 CA01 CA06 CA14 CA17 CA20 CA26 CA28 CA31 CA39 4D076 AA05 AA1 2 AA22 BB01 FA02 FA04 FA12 FA16 HA03 JA01 JA03 4H006 AA05 AC13 AC26 BB23 BB24 BE10 EA22

Claims (9)

[Claims] 1. A method of purifying soil contaminated with a halogenated aromatic compound, the first step of extracting a halogenated aromatic compound from a soil contaminated with a halogenated aromatic compound using a lower alcohol. A second step of solid-liquid separating the lower alcohol phase after extraction from the soil, a high-boiling hydrocarbon solvent is added to the halogenated aromatic compound-containing lower alcohol phase, and then the lower alcohol is recovered by distillation to obtain a halogenated aromatic compound. To a high boiling hydrocarbon solvent, a third step, a fourth step of decomposing the halogenated aromatic compound-containing high boiling hydrocarbon solvent with a strong alkaline substance in a heat resistant alkaline polar solvent, and from the soil after extraction A method for treating soil contaminated with halogenated aromatic compounds, which comprises a fifth step of removing lower alcohols. 2. The treatment method according to claim 1, further comprising a preliminary step of optionally recovering water from the soil contaminated with the halogenated aromatic compound. 3. The method for treating soil according to claim 1, wherein the halogenated aromatic compound is dioxins or polychlorinated biphenyl (PCB). 4. The lower alcohol is ethanol or 2-
The method for treating soil according to any one of claims 1 to 3, which is propanol. 5. The high boiling hydrocarbon solvent has a boiling point of 150 to 3
The method for treating soil according to any one of claims 1 to 4, which is an aliphatic hydrocarbon at 00 ° C. 6. The method for treating soil according to claim 1, wherein the heat-resistant alkaline polar solvent is 1,3-dimethyl-2-imidazolidinone (DMI) or sulfolane. 7. The strong alkaline substance is at least one selected from sodium hydroxide, potassium hydroxide, sodium alkoxide and potassium alkoxide, or a mixture of two or more thereof, according to claim 1. Soil treatment method. 8. A method for recovering a halogenated aromatic compound from a soil contaminated with a halogenated aromatic compound, comprising the step of using a lower alcohol from the soil contaminated with a halogenated aromatic compound. In the first step, the second step of solid-liquid separating the lower alcohol phase after extraction from the soil, the high-boiling hydrocarbon solvent is added to the halogenated aromatic compound-containing lower alcohol phase, and then the lower alcohol is recovered by distillation. Halogenated fragrance, comprising a third step of transferring the halogenated aromatic compound to a high boiling hydrocarbon solvent, and optionally a preliminary step of recovering water from soil contaminated with the halogenated aromatic compound. Method for recovering halogenated aromatic compounds from soil contaminated with group compounds. 9. A method for recovering water from a soil containing water and contaminated with a halogenated aromatic compound, comprising dissolving the halogenated aromatic compound in a soil containing water and the halogenated aromatic compound. The method, comprising the step of adding a solvent and heating the soil to separate water.