JP3784654B2 - Purification method for chemical contaminants - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for physicochemically purifying contaminants (chemical contaminants) contaminated by chemical substances. The method for purifying chemical contaminants according to the present invention is suitably used for purification of soil, sediment, sludge and the like contaminated with organic chlorine compounds, for example.
[0002]
[Prior art]
Organochlorine compounds such as trichlorethylene and tetrachlorethylene are widely used as cleaning agents in various factories and cleaning shops, but these organochlorine compounds are suspected to be carcinogenic substances. Contamination of groundwater is a major social problem.
[0003]
Conventional methods for treating soil contaminated with organochlorine compounds include pumping and treating by combining contaminated soil containment, excavation and containment of contaminated soil, pumping aeration and vacuum extraction, and activated carbon adsorption treatment. Laws are mainly adopted.
[0004]
Also, in recent years, reductive decomposition of pollutant chemicals using iron powder, reductive decomposition of pollutant chemicals using iron powder and anaerobic microorganisms, oxidation of pollutant chemicals using hydrogen peroxide Decomposition methods have been studied.
[0005]
[Problems to be solved by the invention]
However, the contaminated soil containment process, excavation / containment process, and pump-and-treat method are not technologies that aggressively decompose and detoxify polluted chemicals, requiring enormous costs, energy, and labor. The problem is that the purification period is as long as 10 to 20 years.
[0006]
In addition, the reductive decomposition method using iron powder or iron powder and anaerobic microorganisms is an anaerobic dechlorination method for reductive decomposition, but the purification period is as long as six months to one year. In addition, when dechlorination is incomplete, dichloroethylene and vinyl chloride, which are harmful byproducts, are generated.
[0007]
Furthermore, the oxidative decomposition treatment method using hydrogen peroxide cannot selectively oxidize pollutant chemicals because the contaminated soil contains a large amount of organic matter to be oxidized, and as a result, There was a problem that the concentration of contaminated chemicals after treatment could not be reduced sufficiently. In addition, it is necessary to use an oxidizing agent (hydrogen peroxide) of about several percent by weight of the contaminated soil, and the amount of the oxidizing agent added to the contaminated soil is very large.
[0008]
The present invention has been made in view of the above-described circumstances, and it is possible to remove pollutants contaminated with chemical substances, particularly soil, sediment, sludge, etc. contaminated with organochlorine compounds in a short period of time at low cost and low cost. The object is to provide a method that can be purified with energy.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present inventor has intensively studied an oxidation treatment method for purifying soil contaminated with an organic chlorine compound such as trichlorethylene (TCE) or cis-1,2-dichloroethylene (c-DCE). went. As a result, were uniformly stirred and mixed by adding iron powder as metallic catalysts in the contaminated soil, uniformly stirred and mixed under acidic conditions by adding hydrogen peroxide to the contaminated soil by adding a metal-based catalyst In such a case, it has been found that a high concentration of an organic chlorine compound can be decomposed in a short period of time, for example, about one day by hydroxyl radicals generated by contact between the metal catalyst and hydrogen peroxide.
[0010]
The present invention has been made on the basis of the above-described knowledge. In purifying contaminants contaminated with chemical substances, after adding iron powder to the contaminants and stirring , the moisture content of the contaminants is 5 to 40. Provided is a method for purifying chemical contaminants, characterized in that a mixed solution of hydrogen peroxide and sulfuric acid is added to the contaminants so as to be in weight% and stirred under acidic conditions.
[0011]
Conventionally, an oxidation treatment method in which only hydrogen peroxide is added to contaminated soil, or hydrogen peroxide and an iron compound or iron ion are simultaneously added has been known. However, in these conventional methods, it is difficult to reduce the pollutant chemicals to the environmental standard value or less even if the pollutant chemicals can be oxidatively decomposed to some extent.
[0012]
On the other hand, in the present invention, since the metal catalyst is added to the contaminant before the hydrogen peroxide is added to the contaminant, the hydrogen peroxide is brought into contact with the metal catalyst and the pollutant When the oxidative decomposition reaction is started, the metal catalyst is already present uniformly in the contaminant. Therefore, in this invention, it is estimated that hydrogen peroxide is decomposed | disassembled into oxygen and water, and is consumed wastefully, a hydroxyl radical is produced | generated effectively and the decomposition | disassembly efficiency of a pollutant chemical substance improved. Further, it is presumed that the decomposition efficiency of the contaminating chemical substance is further improved by further stirring the contaminant after adding hydrogen peroxide.
[0013]
Hereinafter, the present invention will be described in more detail. In the present invention, first, a metal-based catalyst is added to a chemical contaminant and stirred uniformly. As the metal catalyst, a catalyst that generates hydroxyl radicals by contact with hydrogen peroxide is used. Specifically, iron powder is used as the metal catalyst.
[0014]
When iron powder is used as the metal-based catalyst, there is no particular limitation on the properties of the iron powder, but it is preferably a uniform iron powder having a small particle size. The amount of iron powder added is suitably 0.01 to 1% by weight, especially 0.05 to 0.5% by weight of the chemical contaminant.
[0016]
In the present invention, next, a mixed solution of hydrogen peroxide and sulfuric acid is added to the contaminated material to which the metal catalyst has been added, and stirred uniformly. The amount of hydrogen peroxide water added is 100% hydrogen peroxide, and it is appropriate that it is 1.0% by weight or less, particularly 0.1 to 0.5% by weight of the chemical contaminant. Even if the amount of hydrogen peroxide added exceeds 100% by weight as 100% hydrogen peroxide, the decomposition effect of the pollutant chemicals will not be improved any further, and the purification cost will increase. is there.
[0017]
Moreover, in this invention, the contaminant which added the liquid mixture of hydrogen peroxide solution and a sulfuric acid is stirred on acidic conditions, Preferably the conditions of pH 3-5 are stirred. This makes it possible to oxidize and decompose pollutant chemical substances more efficiently. An acid is added to adjust the pH to 3 to 5. In the present invention, sulfuric acid is used. Hydrochloric acid is highly volatile and is not preferable in terms of safety and workability. The use of nitric acid is not preferred because the nitrogen component increases. The use of an organic acid is not preferable because an organic matter to be oxidized is unnecessarily increased and the cost is increased.
[0018]
In the present invention, you of hydrogen peroxide and a mixture of sulfuric acid to contaminants as the water content I became 5 to 40 wt% of contaminants. This is because if the water content of the contaminant is less than 5% by weight, hydrogen peroxide is not uniformly mixed with the contaminant, and the oxidative decomposition efficiency of the contaminant chemical is deteriorated. A more preferable value of the moisture content of the contaminant is 10 to 40% by weight. If the moisture content of the pollutant exceeds 40% by weight, trouble may occur when the pollutant is backfilled in the ground . The water content of the upper Symbol contaminants can be adjusted by the proportion of water in the hydrogen peroxide solution to be added to the contaminant.
[0019]
In the present invention, it is preferable to further neutralize the obtained purified product. Thereby, it becomes easy to reuse the obtained purified material. Examples of the neutralization treatment method include means for adding an alkaline agent such as calcium hydroxide to the purified product.
[0020]
Further, in the present invention, a modifier can be added to the obtained purified product. Examples of the modifier include a cement-based soil improver (solidifying agent). By adding about 1 to 5% by weight of cement-based modifier to the purified soil, the soil that has become weak due to an increase in water content is returned to the state before purification (for example, with a soil strength of 50 kg / m ² ). Can be backfilled inside.
[0021]
The method for purifying chemical contaminants according to the present invention is preferably used for purification of soil, sediment, sludge and the like contaminated with organic chlorine compounds, but is not limited thereto. That is, in the purification method of the present invention, organic substances are oxidatively decomposed by hydroxyl radicals having strong oxidizing power generated by contact between the metal catalyst and hydrogen peroxide, so that various organic substances can be efficiently decomposed. Therefore, the purification method of the present invention is not limited to the purification of pollutants by organochlorine compounds (TCE, PCE, dioxins, PCBs, etc.), but also the contamination of other organic substances such as oil, benzene, toluene, xylene, etc. It can also be applied to purification.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram showing an embodiment of the present invention. In the present embodiment, first, the contaminated soil 2 is excavated as shown in FIG. Next, as shown in (b), iron powder 6 is added to the contaminated soil 2 in the kneader 4, and the contaminated soil 2 and the iron powder 6 are uniformly stirred and mixed by the kneader 4. Further, as shown in FIG. 5 (c), a mixed solution 8 of hydrogen peroxide and sulfuric acid is added to the contaminated soil 2 to which the iron powder 6 is added, and the contaminated soil 2 and the mixed solution 8 are uniformly made by the kneader 4. Stir and mix. When the stirring is performed for a certain time (usually about 2 to 60 minutes), the contaminated soil 2 is purified. However, the oxidative decomposition reaction of the contaminated chemical substance proceeds even after the stirring is completed. Thereafter, the purified soil 10 is discharged from the kneader 4 as shown in FIG. Further, as shown in (e), the cementitious soil conditioner 12 is added to the purified soil 10 and mixed, and (f) the purified soil 10 is refilled in the original location as shown in the figure. After the backfilling, the purified soil 10 is covered with a vinyl sheet or the like so that rainwater or the like is not mixed, and the soil is sampled over time to monitor the purification status of polluted chemical substances.
[0024]
【Example】
150 g of soil is put into a 100 mL vial, and iron powder, hydrogen peroxide, etc. are added to the soil under the conditions shown in (1) to (6) below, and trichlorethylene (TCE) is eluted with TCE (headspace of the vial) After injecting so that the concentration of trichlorethylene contained therein was 1 mg / L, the vial was sealed and a treatment experiment was started. Then, the treatment effect was evaluated by measuring the elution TCE concentration of each vial over time by gas chromatography. Of the following conditions (1) to (6) , (3) and (4) are examples of the present invention, and others are comparative examples. Condition (5) is an example in which the order of addition of iron powder and hydrogen peroxide is reversed in the present invention, and condition (6) is an example in which the moisture content of the soil is low.
[0025]
(Experimental conditions)
(1) Blank test 45 mL of water was added to the soil and stirred.
(2) Iron powder reduction method 45 mL of water and 5 g of reduced iron were added to the soil and stirred.
(3) Iron powder + hydrogen peroxide (pH 4)
After adding 45 mL of water and 5 g of iron powder to the soil and stirring, hydrogen peroxide 1000 mg / kg soil and sulfuric acid were added and stirred.
(4) Iron powder + hydrogen peroxide (pH 7)
After 45 mL of water and 5 g of iron powder were added to the soil and stirred, 1000 mg / kg soil of hydrogen peroxide was added and stirred.
(5) Hydrogen peroxide + iron powder (pH 4)
After 45 mL of water and 1000 mg / kg of hydrogen peroxide were added to the soil and stirred, 5 g of iron powder and sulfuric acid were added and stirred.
(6) Iron powder + hydrogen peroxide (pH 4)
To the soil, 4.5 mL of water and 5 g of iron powder were added and stirred, and then 1000 mg / kg of hydrogen peroxide and sulfuric acid and sulfuric acid were added and stirred.
[0026]
(Processing result)
FIG. 2 shows the processing result. In the iron powder reduction method (2) , TCE was gradually reduced and decomposed, but it took several months to purify, and it was confirmed that dichloroethylene and vinyl chloride accumulate as intermediate products. In the present inventions of (3) and (4) , it has become clear that TCE can be purified below the environmental standard value in a short time of 2 hours and 1 day, respectively. From the above treatment results, it became clear that the present invention is extremely effective for short-term purification of contaminated soil. It was also found that the degradation rate of pollutant chemicals is higher under acidic conditions. On the other hand, when the amount of the added drug was the same and hydrogen peroxide was added before the iron powder (5) , TCE was not purified to the environmental standard value. Moreover, when the moisture content of the soil was as low as 3.3% (6) , hydrogen peroxide did not reach the entire soil, and the entire soil could not be purified.
[0027]
【The invention's effect】
As described above, according to the present invention, contaminants contaminated with chemical substances, particularly soil, sediment, sludge, etc. contaminated with organochlorine compounds can be reduced in a short period of several hours to several months. It can be purified at low cost and low energy. In addition, since the present invention utilizes a radical reaction that can efficiently decompose various hardly decomposable chemical substances, it is also effective for purification of high-concentration complex contaminants, and its usefulness is extremely large.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of the present invention.
FIG. 2 is a graph showing the relationship between the elapsed processing days and the eluted TCE concentration in the purification process of the example.
[Explanation of symbols]
2 Contaminated soil 4 Kneading machine 6 Iron powder 8 Liquid mixture of hydrogen peroxide and sulfuric acid 10 Purified soil 12 Cement-based soil conditioner

Claims (5)

In purifying the pollutant contaminated with the chemical substance, after adding iron powder to the pollutant and stirring, the pollutant is charged with hydrogen peroxide so that the water content of the pollutant becomes 5 to 40% by weight. A method for purifying chemical contaminants, comprising adding a liquid mixture of sulfuric acid and sulfuric acid and stirring under acidic conditions. The mixed solution of hydrogen peroxide and sulfuric acid is added to the contaminant so that the moisture content of the contaminant is 10 to 40% by weight, and the mixture is stirred under acidic conditions . Purification method for chemical contaminants. The method for purifying chemical contaminants according to claim 1 or 2 , wherein the obtained purified product is further neutralized. The method for purifying chemical contaminants according to any one of claims 1 to 3 , wherein a modifier is added to the obtained purified product. The pollutant contaminated with a chemical substance is selected from soil, sediment and sludge contaminated with a chemical substance, The chemical substance contaminant purification method according to any one of claims 1 to 4, .

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