JP2002177940A - Method of cleaning contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To separate and remove hardly decomposable hazardous materials, such as PCBs or PCDDs(polychlorinated-dibenzo-p-dioxins) and the like without impairing the characteristics of the soil contaminated by the hardly decomposable hazardous materials and to reuse the treated soil as the farming land. SOLUTION: The hardly decomposable hazardous materials are separated and removed by putting the contaminated soil into a distillation flask and adding water thereto, then subjecting the soil to steam distillation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying soil contaminated with organic harmful substances and the like.

[0002]

2. Description of the Related Art Conventionally, soil contaminated with harmful substances and the like is insolubilized with a solidifying agent such as cement and then buried in the ground, or after adding a chemical such as sodium bicarbonate. In general, a method in which volatile harmful substances are volatilized and desorbed by heat decomposition or heating, or a method in which incineration and decomposition treatment is performed in a baking furnace is common.

[0003]

In the conventional purification treatment method, the properties of the soil after the treatment significantly change, the chemicals used for the treatment remain, or the high-boiling-point hardly decomposable organic chlorine compound is desorbed. There were problems such as inability to do so. For this reason, the soil after the treatment could not be reused as green farmland soil. An object of the present invention is to purify contaminated soil and reuse purified soil for green farmland.

[0004]

SUMMARY OF THE INVENTION The present invention provides a high-boiling-point PCB, dioxins and a hard-to-decompose material by subjecting contaminated soil to steam distillation at a temperature of 100 ° C. without significantly impairing the properties of the soil. Organic compounds could be separated and removed from the contaminated soil.

[0005] The term "contaminated soil" as used in the present invention refers to lands or agricultural soils that are contaminated by toxic substances or the like when they are leaked or sprayed onto factory premises, general residential areas or public lands for some reason. It refers to ground, earth and sand, submarine sediment, sludge, etc. The harmful substances and the like in the present invention refer to hardly decomposable organic compounds such as PCB, coplanar PCB, dioxins, volatile organic compounds, residual agricultural chemicals, and environmental hormones.

The contaminated soil used in the present invention is a harbor,
Dredged soil and dredged from the bottom of lakes, rivers, canals, waterways, etc. is there. If necessary, these contaminated soils may be used after reducing the water content in advance using a physical means such as a dehydrator, or may be used after appropriately adding water in the case of fly ash or the like. In addition, make a slurry in advance,
Mechanical stirring or ultrasonic treatment is also effective for increasing the efficiency of the distillation separation. Further, depending on the target substance to be removed, the pH is adjusted with an acid or alkali before steam distillation.
Is effective because distillation separation can be easily performed.

The additives used here are not particularly limited.
It may be an industrial chemical and may contain some impurities.

[0008] In the distillation treatment, the amount of water to be added is preferably about 1 to 10 parts, more preferably about 3 to 5 parts per part by weight of the contaminated soil. If the ratio of the added water is higher than this, the distillation energy efficiency decreases, and if the ratio is lower, the mixing and stirring are not sufficient, and the efficiency of removing harmful substances decreases.

[0009] The distillation time required to separate harmful substances by distillation cannot be specified unconditionally under various conditions, but is about 5 to 60 minutes. About 60% or more of high-boiling compounds such as PCBs are removed by a distillation treatment for 10 minutes, but thereafter, only a small amount is distilled out gradually.

Most of the harmful organic compounds remaining in the contaminated soil are removed by the distillation treatment as described above. At the same time, malodorous components such as ammonia or hydrogen sulfide can be almost completely removed. As a result, the contaminated soil is purified and can be reused as agricultural soil or general residential soil.

[0011]

FIG. 1 shows an example of a steam distillation apparatus used in the experiment of the present invention.

Hereinafter, the present invention will be described by reference examples, examples and comparative examples. (Reference Example 1) Properties of contaminated soil Table 1 shows an example of seabed sediment (dredge soil) in a port where a certain amount of PCB and coplanar PCB remain.

[0013]

[Table-1] Table-1 Properties of the bottom of the port water

[0014] As shown in Table 1, the bottom of the harbor water bottom (dredge soil)
In the case of, the dioxins (dioxin and dibenzofuran) are 5% of the standard value of the residential soil (1000 pg / g).
1/10 or less, but coplanar PCB is 110pg-TEQ
/ kg dry soil remains. At the same time, about 5.1 mg /
kg of dry soil remains. In addition to ammonia nitrogen and total sulfide, zinc also exceeds the soil management standard (120 mg / kg dry soil). For this reason, it is not suitable for farmland soil.

(Embodiment 1) The bottom of the port water (dredged soil) of Reference Example-1 was passed through a 5 mm sieve in advance to remove rake and coarse dust, and then 20 g per dry soil was placed in an Erlenmeyer flask. 0.1 mol / l hydrochloric acid 100
The mixture is shaken at room temperature for 30 minutes, centrifuged (3000 rpm, 5 minutes), the supernatant is collected in a separate beaker, and the remaining soil is washed with 100 ml of water. After 50 ml of a 0.1 mol / l slaked lime solution was added to the washed residue, steam distillation was performed. The steam distillation rate was 5 g / min for 15 minutes. Residual soil after treatment, PC in distillate
The content of B etc. is as shown in Table-2.

[0016]

[Table-2] Table-2 Concentration of components after steam distillation of harbor water bottom sediment (dredge soil)

As a result of steam distillation of the bottom sediment (dredged soil) of the port water, dioxins were reduced by 72% from the sediment. Similarly, 83% of the coplanar PCB was removed and 90% of the PCB was removed. At the same time, the concentration of ammonia nitrogen and total sulfide content was removed by 90% or more. Zinc is also reduced to one-tenth or less before treatment.
The concentration became low.

[0018]

[Example 2] 1,3,6,8-TCDD (tetrachlorodioxin), one of dioxins, was added to three kinds of soils at a concentration of 5,000 pg / g (5 µg / g) per dry soil. After that, steam distillation treatment was performed for 10 minutes. The content of 1,3,6,8-TCDD in the residual soil was analyzed, and the dioxin removal rate was examined. The test soil used was volcanic Kuroboku soil, Neogene mudstone residual soil, and high-organic port water bottom sediment. Dioxin removal rate of 10 minutes distillation is 68.0% Kuroboku soil,
Mudstone residual soil = 65.2% and port bottom sediment = 53.8%.

[0019]

[Table-3] Table-3 Dioxin (1,3,3)
Example of dioxin removal from 6,8-TCDD) added soil (steam distillation for 10 minutes)

(Comparative Example 1) The seabed sediment used in Example 1 was placed in the same Erlenmeyer flask, and the flask was directly heated without blowing steam and boiled for 15 minutes.
As a result, 67% of the PCB was removed.

[0021]

[Table-4] Table-4 Change in PCB concentration by heating evaporation

[0022]

As described above, according to the present invention,
Since the soil can be purified without impairing the properties of underwater soil and soil or land on land contaminated by PCBs or dioxins, the treated soil can be reduced and reused on agricultural land. For this reason, it is intended to contribute to environmental purification and effective use of land use, and the actual profit is great.

[Brief description of the drawings]

FIG. 1 is an example of a steam distillation apparatus used in an experiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Water tank 6 Distilled water 2 Suction filtration device 7 Cooling pipe 3 Steam generator 8 Receiver 4 Distillation flask 9 PCB collected with distillate 5 Test sample

Claims (1)

[Claims] 1. A method for purifying contaminated soil, comprising blowing steam into soil contaminated with PCBs, dioxins or other organic harmful substances, and removing the harmful substances by a steam distillation method.