JP2002326080A - Method for purifying material contaminated by chemical substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and reliably purify material contaminated by a chemical substance, in particular, soil, bottom material and sludge, etc., contaminated by an organic chlorine compound in a short period. SOLUTION: The contaminated soil 2 is dug and is transferred to a two-shaft mixer 4. Subsequently, iron powder 6 is added to the contaminated soil in the two-shaft mixer and the contaminated soil and the iron powder are uniformly stirred and mixed by the two-shaft mixer. Further, a mixed solution 8 of hydrogen peroxide water and sulfuric acid is added to the contaminated soil which is added with the iron powder and the contaminated soil and the mixed solution are uniformly stirred and mixed by the double shaft mixer. Then, after performing the stirring for a fixed period, the contaminated soil is purified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for physicochemically purifying contaminants contaminated by a chemical substance (chemical substance contaminants). The method for purifying chemical contaminants according to the present invention is suitably used, for example, for purifying soil, sediment, sludge and the like contaminated with organic chlorine compounds.

[0002]

2. Description of the Related Art Trichlorethylene (TCE), cis-
Organochlorine compounds such as 1,2-dichloroethylene (c-DCE) are suspected to be carcinogens, and in recent years, contamination of soil, groundwater, and the like by the organochlorine compounds has become a major social problem.

[0003] Conventionally, as a method for treating soil contaminated with an organic chlorine compound, a process for containing the contaminated soil, a process for excavating and containing the contaminated soil, and the like are mainly performed. In addition, as a method of treating groundwater contaminated with organochlorine compounds, a pump and a pump that combines pumping aeration and activated carbon treatment is used.
The treatment method is mainly used.

[0004] In recent years, a method for reductive decomposition of pollutant chemicals using iron powder and a method for reductive decomposition of pollutant chemicals using iron powder and anaerobic microorganisms have been studied.

[0005]

However, the above-described methods for contaminating contaminated soil, excavating and contaminating contaminated soil, and pumping and treating contaminated groundwater are described above.
There have been problems in that it is not a technology for actively decomposing polluting chemical substances to make it harmless, that it requires enormous cost, energy and labor, and that the purification period is as long as 10 to 20 years.

In recent years, a technique for decomposing contaminated chemical substances by excavating contaminated soil, adding a purifying agent such as iron powder and oxidizing agent to the contaminated soil and stirring the contaminated soil has been developed. . However, when the above technology is applied to actual contaminated soil, particularly when applied to cohesive soil such as cohesive soil, silty soil, and organic soil, a single-shaft kneader or backhoe (shovel car) conventionally used for stirring is used. In this method, since the contaminated soil and the purifying agent cannot be uniformly mixed, there has been a problem that the purification efficiency of the contaminated soil is extremely poor as compared with the results obtained in the laboratory. That is, in the above prior art,
Purification efficiency in full-scale processing (on-site processing)
The purification efficiency was very poor compared with the purification efficiency in the laboratory-scale processing (experimental processing).

The present invention has been made in view of the above-mentioned circumstances, and in full-scale treatment, contaminants contaminated by chemical substances, in particular, soil, sediment, and sludge contaminated by organic chlorine compounds are removed. It is an object of the present invention to provide a method that can efficiently and reliably purify in a short period of time.

[0008]

Means for Solving the Problems To achieve the above object, the present inventors have proposed trichloroethylene, cis-1,2-bis.
A treatment method to purify soil contaminated with organic chlorine compounds such as dichloroethylene was studied. As a result, when decomposing organic chlorine compounds by adding iron powder, a purifying agent such as an oxidizing agent and the like to the contaminated soil and stirring the contaminated soil,
When the contaminants and the purifying agent are agitated using a kneading mixer having two or more axes, or when the contaminants and the purifying agent are agitated at the original position of the contaminants using a ground improvement machine, the contaminated soil may be viscous or silty soil , Even on clayey soils such as organic soils,
The present inventors have found that contaminated soil and a purifying agent are uniformly mixed, and that contaminated soil can be efficiently and reliably purified in a short period of time in a full-scale treatment.

Further, the inventor of the present invention added a metal catalyst to the contaminated material and uniformly stirred and mixed the mixture with a kneading mixer or a ground improvement machine having two or more shafts, and then added hydrogen peroxide to the contaminated material to which the metal catalyst was added. When water is added and uniformly stirred and mixed with a kneading mixer or a ground improvement machine having two or more axes, hydroxyl radicals generated by contact of the metal-based catalyst with hydrogen peroxide cause, for example, a short period of about several days to reduce organic chlorine. It has been found that the compound can be decomposed.

[0010] The present invention has been made based on the above findings, and provides the following first to fourth inventions. (1st invention) A method for purifying chemical contaminants, wherein the contaminants and the purifying agent are agitated using a kneading mixer having two or more axes in purifying the contaminants contaminated by the chemical substance. (Second invention) In purifying contaminants contaminated by chemical substances and existing in the ground, the contaminants and the purifying agent are agitated in situ of the contaminants using a ground improvement machine. How to purify things. (Third invention) In purifying contaminants contaminated by a chemical substance, a metal-based catalyst is added to the contaminants, and the mixture is stirred using a kneading mixer having two or more axes. A method for purifying chemical contaminants, comprising adding and stirring using a kneading mixer having two or more axes. (4th invention) In purifying contaminants present in the ground contaminated by chemical substances, a metal-based catalyst is added to the contaminants in situ, and the mixture is stirred using a ground improvement machine. A method for purifying chemical contaminants, comprising adding a hydrogen peroxide solution at a position and stirring the mixture using a ground improvement machine.

Hereinafter, the present invention will be described in more detail. The kneading mixer having two or more shafts used in the first and third inventions has two or more rotating shafts arranged in parallel inside a stirring tank and a plurality of stirring blades extending radially outward on each rotating shaft. This is a kneading mixer in which two or more rotating shafts are rotated in opposite directions so that the rotating range of the stirring blade provided on one rotating shaft extends near the other rotating shaft. The kneading mixer having two or more axes has no dead space inside the mixer, and has strong stirring power and can sufficiently mix the viscous soil and the purifying agent.
According to the present invention, it is possible to obtain purification efficiency equivalent to that of a laboratory-scale treatment.

[0012] The soil improvement machine used in the second and fourth inventions is to add a modifier such as a cement-based soil conditioner (solidifying agent) to the soft ground and to stir the soft ground to make the solid ground stronger. It is a machine to improve on. In the second and fourth inventions, the contaminant and the purifying agent are agitated at the original position of the contaminant by the ground improvement machine, so that the contaminant and the purifying agent are sufficiently uniformly mixed. Purification efficiency can be obtained. As a ground improvement machine, for example,
A mixing machine in which a powder injection stirrer is installed in a base machine, a mixing machine in which a trencher type stabilizer is installed in a base machine, or a mixing machine in which a single-shaft or two-shaft vertical stirrer is installed in a mud wheel are preferably used. be able to.

In the first and second inventions, at least an oxidizing agent (potassium permanganate, hydrogen peroxide,
Persulfate) or a metal-based catalyst. In the third and fourth aspects of the present invention, a metal-based catalyst that generates hydroxyl radicals by contacting hydrogen peroxide is used. As the metal-based catalyst, specifically, one selected from iron powder, iron sulfate, and iron chloride can be suitably used.

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 preferable that the iron powder be small and uniform in particle size. The amount of the iron powder added is suitably 0.01 to 1% by weight, particularly 0.05 to 0.5% by weight of the chemical contaminants.

When iron sulfate or iron chloride is used as a metal-based catalyst, it is appropriate to add these solutions to chemical contaminants. Further, the addition amount of iron sulfate and iron chloride is 0.01 to 1% by weight of the chemical contaminants, particularly 0.05 to 1% by weight.
It is preferably 0.5% by weight.

In the third and fourth aspects of the present invention, when adding aqueous hydrogen peroxide to contaminants to which a metal-based catalyst has been added, the amount of the added hydrogen peroxide water is 100% hydrogen peroxide, and the amount of the chemical contaminants is one. It is suitable that the content is 0.0% by weight or less, particularly 0.1 to 0.5% by weight. The amount of hydrogen peroxide added is 1
1.0% by weight of chemical contaminants as 00% hydrogen peroxide
Beyond this, the effect of decomposing polluting chemicals is not further improved and the cost of purification can be high.

In the third and fourth aspects of the present invention, the metal catalyst is added to the contaminant and stirred before the hydrogen peroxide is added to the contaminant. At the time when the oxidative decomposition reaction of the chemical substance is started, the metal-based catalyst is already uniformly present in the contaminant. Therefore, in the third and fourth inventions, it is suppressed that hydrogen peroxide is decomposed into oxygen and water and is wasted, and hydroxyl radicals are effectively generated, thereby improving the decomposition efficiency of pollutant chemicals. Guessed. Further, it is presumed that the stirring efficiency of the contaminants after the addition of hydrogen peroxide further improved the decomposition efficiency of the contaminant chemicals.

In the third and fourth aspects of the present invention, it is more appropriate to add a mixed solution of aqueous hydrogen peroxide and sulfuric acid to the contaminants and stir the mixture under acidic conditions, preferably at pH 3 to 5. is there. This makes it possible to more efficiently oxidatively decompose contaminant chemicals. In this case, it is appropriate to use sulfuric acid in order to obtain acidic conditions. Hydrochloric acid has high volatility and is not preferred in terms of safety and workability. The use of nitric acid is not preferred because the nitrogen component increases. Use of an organic acid is not preferred because it unnecessarily increases the amount of organic substances to be oxidized and increases the cost.

The first to fourth inventions are suitably used for purifying soil, sediment, sludge, groundwater, etc., which are contaminated with an organic chlorine compound, but are not limited thereto. That is,
The first to fourth inventions relate to organic chlorine compounds (TCE, PCE,
The present invention is applicable not only to purification of contaminants by dioxins and PCBs, but also to purification of contaminants by other organic substances such as oil, benzene, toluene, xylene and the like. In particular, in the third and fourth inventions, various organic substances can be decomposed efficiently because organic substances are oxidatively decomposed by hydroxyl radicals having strong oxidizing power generated by contact between the metal-based catalyst and aqueous hydrogen peroxide. .

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing one embodiment of the first and third inventions. In the present embodiment, first,
(A) As shown in the figure, contaminated soil 2 is excavated and transferred to a biaxial kneading mixer 4. Next, as shown in FIG. 2B, the iron powder 6 is added to the contaminated soil 2 in the twin-screw kneading mixer 4, and the contaminated soil 2 and the iron powder 6 are uniformly stirred and mixed by the twin-screw kneading mixer 4. Further, as shown in FIG. 3C, a mixed solution 8 of a hydrogen peroxide solution and sulfuric acid is added to the contaminated soil 2 to which the iron powder 6 has been added, and the contaminated soil 2 and the mixed solution 8 are mixed by the twin-screw kneading mixer 4.
And stir and mix uniformly. If 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 polluting chemical substance proceeds even after the stirring is completed. Thereafter, the purified soil 10 is discharged from the twin-screw kneading mixer 4 as shown in (d), and the purified soil 10 is discharged as shown in (e).
Back in place. After backfilling, the purified soil 10 is covered with a vinyl sheet or the like so that rainwater etc. will not enter.
Soil is sampled over time to monitor the status of purification of pollutant chemicals.

The biaxial kneading mixer 4 used in the present embodiment is the same as that shown in FIG.
Referring to the schematic front view of (a) and the schematic side view of FIG.
Two rotating shafts 22a, 22b are arranged horizontally and in parallel inside the stirring tank 20, and each rotating shaft 22a, 22b
A plurality of stirring blades 24a and 24b extending radially outward are provided on the rotation shaft 22b, and two rotations are provided so that the rotation range of the stirring blade 24a provided on one rotation shaft 22a extends near the other rotation shaft 22b. This is a kneading mixer in which the shafts 22a and 22b are rotated in opposite directions.

FIG. 3 is a diagram showing one embodiment of the second and fourth inventions. In the present embodiment, first, as shown in FIG. 7A, a mixing machine (ground improvement machine) in which a contaminated soil 30 is covered with an appropriate amount of iron powder 32 and then a powder injection stirring blade 36 is mounted on a base machine 34. 38, the contaminated soil 30 and the iron powder 32 are uniformly stirred and mixed in situ. Next, as shown in FIG. 3 (b), a hydrogen peroxide solution is added to the contaminated soil 30 to which the iron powder 32 has been added, and the mixing machine 38 uniformly mixes the contaminated soil 30 and the hydrogen peroxide solution with stirring. For a certain time (usually 2
When the stirring is performed, the contaminated soil 30 is purified. However, the oxidative decomposition reaction of the polluting chemical substance proceeds even after the stirring is completed. Then, the purified soil is covered with a vinyl sheet or the like so that rainwater or the like is not mixed in, and the soil is sampled over time to monitor the purification status of pollutant chemicals.

The mixing machine 38 used in the present embodiment is a ground improvement machine based on a powder injection stirring method, and the powder injection stirring method supplies an improving material of powder and granular material to soft ground. This method involves forcibly mixing and improving the soil and the improver to chemically react the soil with the improver, thereby stabilizing the soil properties and increasing the strength. In the powder injection stirring method, referring to the schematic view of the powder injection stirring blade 36 shown in FIG. 4, the purifying agent is conveyed by an air flow and discharged from the root of the stirring blade to a gap created by rotation of the blade. You. The discharged purifying agent is evenly spread over the entire rotation trajectory with the rotation of the stirring blade, and is stirred and mixed with the soil at the original position. The air separated from the purifying agent is discharged to the ground surface along the stirring shaft from the gap between the shaft and the soil.

As the ground improvement machine, for example, the one shown in FIG. 5 or FIG. 6 can be used in addition to the above-described mixing machine in which the powder injection stirring blade is mounted on the base machine. The ground improvement machine 50 of FIG. 5 is a mixing machine in which a trencher-type stabilizer 54 is mounted on a base machine 52. The ground improvement machine 60 of FIG. 6 is a mixing machine in which a one-axis or two-axis vertical stirring processor 64 is mounted on a mud wheel 62.

[0025]

Example 1 150 g of real contaminated clay was placed in a 200 mL vial bin, iron powder, hydrogen peroxide, etc. were added to the soil under the following conditions, and the vial bin was sealed to start a processing experiment. did. Then, soil was collected from each vial bin with time, and the concentration of eluted trichloroethylene (TCE) was measured by gas chromatography to evaluate the treatment effect. Among the following conditions 1 and 2, an example in which the contaminated clay and the purifying agent were sufficiently uniformly stirred, and an example in which the contaminated clay and the purifying agent were not sufficiently uniformly stirred.

(Experimental conditions) Blank test 45 mL of water was added to the soil and stirred. Iron powder reduction method (stirring for 5 minutes) 45 mL of water and 5 g of reduced iron powder were added to the soil and stirred for 5 minutes. Iron powder reduction method (0.5 minute stirring) 45 mL of water and 5 g of reduced iron powder were added to the soil and stirred for 0.5 minute. Iron powder + hydrogen peroxide solution (pH 4) (stir for 5 minutes) After adding 45 mL of water and 5 g of iron powder to the soil and stirring for 5 minutes, add 1000 mg / kg of hydrogen peroxide solution and sulfuric acid and stir for 5 minutes. did. Iron powder + aqueous hydrogen peroxide (pH 4) (0.5 minutes stirring) After adding 45 mL of water and 5 g of iron powder to the soil and stirring for 0.5 minutes, 1000 mg / kg of hydrogen peroxide aqueous solution and sulfuric acid were added. And stirred for 0.5 minutes.

(Processing Result) FIG. 7 shows the processing result. From the comparison between and, it was clarified that the stirring time was significantly shortened by stirring the contaminated clay and the cleaning agent sufficiently uniformly by stirring for 5 minutes. In addition, it was confirmed that the oxidation treatment method using iron powder and hydrogen peroxide had a shorter treatment time than the iron powder reduction method, and accumulation of dichloroethylene and vinyl chloride as intermediate products occurred in the iron powder reduction method. Was.

Example 2 20 kg of iron powder, 0.5 w / v% of hydrogen peroxide and sulfuric acid were added to 1 m ³ of soil contaminated with trichloroethylene.
H4 was added, and the mixture was stirred for 5 minutes using a two-shaft kneading mixer and a tank truck as shown in FIGS. 1 and 2, respectively. The soil was collected over time, and the eluted TCE concentration was measured by gas chromatography to evaluate the treatment effect.

(Processing Result) FIG. 8 shows the processing result. It was confirmed that TCE was decomposed in both treatments,
It was clarified that when the two-shaft kneading mixer was used, the purification processing performance was higher than when a tank lorry was used, and performance equivalent to a lab test was obtained.

[0030]

As described above, according to the present invention, in a full-scale treatment, contaminants contaminated by chemical substances, in particular, soil, sediment, and sludge contaminated by an organic chlorine compound can be removed in a short period of time. Thus, purification can be performed efficiently and reliably. The third and fourth inventions, in particular, utilize a radical reaction that can efficiently decompose various hardly decomposable chemical substances, and are therefore effective for purifying high-concentration complex contaminants. Is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the first and third inventions.

FIG. 2 is a schematic side view of a twin-screw kneading mixer used in the embodiment of FIG.

FIG. 3 is a diagram showing one embodiment of the second and fourth inventions.

FIG. 4 is a schematic view of a powder injection stirring blade of the mixing machine used in the embodiment of FIG.

FIG. 5 is a schematic view showing an example of a mixing machine in which a trencher type stabilizer is mounted on a base machine.

FIG. 6 is a schematic view showing an example of a mixing machine in which a one-shaft or two-shaft vertical stirring processor is mounted on a mud carrier.

FIG. 7 is a graph showing the relationship between the number of days elapsed in the purification process of Example 1 and the concentration of eluted TCE.

FIG. 8 is a graph showing the relationship between the number of days elapsed in the purification process of Example 2 and the concentration of eluted TCE.

[Explanation of symbols]

 2 Contaminated soil 4 Two-axis kneading mixer 6 Iron powder 8 Mixed solution of hydrogen peroxide and sulfuric acid 10 Purified soil 20 Stirrer tank 22 Rotating shaft 24 Stirrer blade 30 Contaminated soil 32 Iron powder 34 Base machine 36 Powder injection stirrer blade 38 Ground Improvement machine 50 Soil improvement machine 52 Base machine 54 Trencher type stabilizer 60 Soil improvement machine 62 Mud car 64 Single-axis or two-axis vertical stirring processor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 11/06 F term (Reference) 2E191 BA11 BA12 BA13 BA15 BB01 BC01 BD13 4D004 AA41 AB05 AB06 AB07 AC04 AC07 CA15 CA35 CA36 CB21 CB27 CC09 CC11 CC12 DA20 4D059 AA09 BC02 BF12 BJ07 DA22 DA23 DA24 DA33 DA44 EA05 EB05 4G078 AA02 AB20 BA01 BA07 CA01 CA05 CA12 CA17 DA30 EA20

Claims (8)

[Claims] 1. A method for purifying a chemical contaminant comprising purifying a contaminant contaminated by a chemical substance using a kneading mixer having two or more axes. 2. Purification of a contaminant contaminated by a chemical substance and existing in the ground, wherein the contaminant and the purifying agent are agitated in situ of the contaminant using a ground improvement machine. How to purify things. 3. As a ground improvement machine, a mixing machine in which a powder injection stirring blade is mounted on a base machine, a mixing machine in which a trencher type stabilizer is mounted on a base machine, or a one-axis or two-axis vertical stirring process on a mud carrier. The method according to claim 2, wherein a mixing machine equipped with a mixing machine is used. 4. The method for purifying a chemical contaminant according to claim 1, wherein at least an oxidizing agent or a metal catalyst is used as the purifying agent. 5. In purifying contaminants contaminated by a chemical substance, a metal-based catalyst is added to the contaminants and the mixture is stirred using a kneading mixer having two or more axes. A method for purifying chemical contaminants, comprising adding and stirring using a kneading mixer having two or more axes. 6. In purifying contaminants present in the ground contaminated by a chemical substance, a metal-based catalyst is added to the contaminants in situ, and the mixture is stirred using a ground improvement machine. A method for purifying chemical contaminants, comprising adding a hydrogen peroxide solution at a position and stirring the mixture using a ground improvement machine. 7. As a ground improvement machine, a mixing machine in which a powder injection stirring blade is mounted on a base machine, a mixing machine in which a trencher type stabilizer is mounted on a base machine, or a one-axis or two-axis vertical stirring process on a mud carrier. 7. The method according to claim 6, wherein a mixing machine equipped with a mixing machine is used. 8. The method according to claim 5, wherein a metal catalyst selected from iron powder, iron sulfate and iron chloride is used.