JP5308068B2 - Method for improving contaminated soil - Google Patents

Description

The present invention relates to a technique of soil improvement technology for contaminated soil, and more specifically, excavates soil containing pollutants such as heavy metals in the field, mixes the soil with a specific composition, and then backfills the soil. The present invention relates to a method for preventing the leakage of pollutants by promoting a solidifying action between the soil and improving the site to soil that can be used in the same manner as general soil.

In the present invention, pollutants refer to heavy metals, volatile organic compounds (VOC), chemicals including agricultural chemicals, and the treatment of soil containing such pollutants has become a serious environmental problem worldwide. In Japan, the number of land where soil contamination has been found has increased dramatically since 1996, and it is estimated that soil contamination has occurred in about 320,000 locations at present.

According to the “Summary of Survey Results on FY 2003 Soil Contamination Surveys / Countermeasures and Response Status” published by the Ministry of the Environment, the results of soil contamination surveys obtained by prefectures by March 31, 2004 showed that all cases 4 , Out of 812 cases, 1,458 cases, accounting for 30% of the total, revealing the current state of serious soil contamination in Japan. The breakdown of the causes of soil contamination was as follows: excess cases such as heavy metals were 60%, volatile organic compound (VOC) excess cases were 28%, and composite pollution excess cases were 12%. The rate of contamination is very high. Contaminants such as heavy metals are in the order of arsenic, lead, and hexavalent chromium. Against this background, the Soil Contamination Countermeasures Law was enforced in Japan in 2003, and measures focusing on avoiding risks from direct intake and groundwater intake were shown. Establishment of drastic countermeasure technology that can meet environmental standards is required.

In contrast, replacement methods, soil cleaning, shielding, and insolubilization treatment of harmful substances have been proposed as techniques for treating soil contaminated with harmful substances such as heavy metals. It is inevitable that the land value will be reduced by the treatment, and that it will be limited to a limited amount even if it is used.
For example, the replacement method and soil cleaning in housing, parking lots, tree planting, etc., require enormous costs to replace or clean the contaminated soil, and shielding must enclose the pollutant. Congested land is contaminated with limited use.

Among these techniques, in the insolubilization treatment of harmful substances, a cement-based insolubilizer is generally used. For example, a method using a cement and an insolubilizer (Patent Document 1) is known. However, in the above method, since the contaminant is insolubilized by supplying calcium ions, the object is limited to heavy metals that react with causium ions, and treatment of contaminants in a wide range is not possible. Is possible.
JP 2004-313817 A

The present invention has been made in view of the above circumstances, and after excavating soil containing pollutants on site, it is mixed with a specific composition and backfilled. It is intended to propose a method for improving the soil that can prevent leakage, prevent the land value from being reduced, and can be used in the same wide range as ordinary soil.

In order to achieve the above object, the method for improving contaminated soil according to claim 1 comprises 100 parts by weight of mountain sand having an average particle diameter of 10 mm or less, 5-15 parts by weight of charcoal having an average particle diameter of 5 mm or less, Portland cement 60 1 to 65 parts by weight, a composition mixture formed by mixing 4 to 10 parts by weight of pearlite and some nonionic surfactant, and soil containing at least one of dug heavy metals, chemicals, and VOCs. : Mixing and stirring at a ratio of 0.8 to 1.2, backfilling the mixture containing the composition mixture, soil containing the pollutant, and water as necessary, and backfilling, and surrounding the contaminated soil with the composition mixture It is characterized in that it is solidified.

The method for improving contaminated soil according to claim 2 is characterized in that an inorganic pigment is included in the composition mixture.

In the composition mixture used in the present invention, when soil containing pollutants is mixed therein, dispersed Portland cement and the like react with water, and Portland cement surrounds the soil containing pollutants. Since it is solidified as it is, it is possible to prevent leakage and diffusion of contaminants. At this time, chemicals such as heavy metals and agricultural chemicals are easily dissolved in the soil, and since the soil containing the heavy metals and agricultural chemicals is surrounded and solidified by Portland cement, leakage and diffusion from there are prevented, while VOC is Although it is difficult to dissolve in the soil, it is adsorbed by the porous portion of the mixed charcoal, and Portland cement surrounds the charcoal, so that leakage and diffusion are similarly suppressed.
The soil containing the above pollutants often contains a lot of excess water and becomes muddy. In this case, pearlite absorbs excess water and adjusts the minimum amount of water necessary for the solidification reaction. I can do it.
Portion cement is uniformly and satisfactorily dispersed by the nonionic surfactant contained in the above composition mixture, so that sand such as mountain sand and soil can be efficiently and as thin as possible, and after solidification reaction Forms a gap (hole) between each particle. As a result, the solidified soil can be made in a porous state, can maintain water permeability and air permeability, and can have excellent vegetation.
Mountain sand functions as a kind of aggregate, can give a certain strength to the solidified soil, and retains strength as a foundation for building a building or the like on the soil.
Furthermore, if an inorganic pigment is mix | blended with soil, the soil before a process and the soil after a process can be visually discriminate | determined with the color of an inorganic pigment.

Embodiments of the present invention will be described with reference to FIGS. 1 to 3 and Tables 1 to 3.
The present invention is intended for soil containing pollutants such as heavy metals, chemicals, and VOCs, and forms a composition mixture as an inorganic composition having water permeability, adsorbability of pollutants, and chemical reactivity. Uses mountain sand, charcoal, inorganic pigments and Portland cement, and a nonionic surfactant as an additive is mixed to form a composition mixture.
Hereinafter, characteristics of each constituent material of the contaminated soil and the composition mixture will be described.

Contaminated soil as a target in the present invention refers to soil containing factory polluted land, agricultural land, residential land, and the like and containing pollutants therein. Pollutants include heavy metals, chemicals such as agricultural chemicals, and VOCs (volatile organic compounds). Etc. Heavy metals are cadmium, cyanide, lead, hexavalent chromium, arsenic, mercury, selenium, fluorine, boron, etc. Agricultural chemicals include simazine, thiraum, thiopencalf, organophosphorus, PCB, and VOC is dichloromethane. , Carbon tetrachloride, dichloroethane, trichloroethylene, benzene and the like.
Soil has mineral particles or the like as a skeleton, and water, air, etc. are included in the gaps, and the particle size is mixed with particles having different diameters of about 10 mm or less in diameter. While chemicals such as agricultural chemicals are hardly soluble in water, they are easily adsorbed on the soil, while VOCs are easily dissolved in water and hardly adsorbed on the soil.

Mountain sand is soil made mainly from weathered granite and the like, and is sand that can be collected in the mountains, and is an aggregate excluding clay like volcanic ash. It also includes crushed stones that correspond to aggregates by crushing and sizing rocks. The particle size was 10 mm or less and mainly 2 mm or less was used.
The mountain sand has a porous structure after being hardened when mixed with the soil and functions as an aggregate.

Portland cement combines and solidifies the particles of contaminated soil and mountain sand in the presence of water, and substantially surrounds the surface of contaminated soil and mountain sand to form a number of voids. However, while Portland cement can maintain large joint strength between aggregates, it itself tends to form dumplings and lumps and can easily fill the space, so the amount used can be as small as possible and it can block contaminants. The amount of thickness.

Charcoal, which is the next composition of the composition mixture, has a porous property, can adsorb pollutants such as VOC in the porous portion, and has a large specific surface area, so it can adsorb a lot of VOC even in a small amount. In the composition mixture, a large amount of contaminants are carried.

Nonionic surfactants are used. Its properties increase the wettability of mountain sand and soil, and when Portland cement is evenly dispersed on the surface of the mountain sand and soil and is uniformly dispersed on the surface of the water, it reacts with moisture and exhibits an appropriate strength. However, if Portland cement is uneven on the surface of mountain sand and soil, it becomes unsuitable because it becomes dumplings or lumps, resulting in excessively strong parts and brittle parts. However, since the nonionic surfactant uniformly and well disperses the Portland cement, the sand such as mountain sand and soil can be efficiently and as thin as possible, and after the solidification reaction, A gap (hole) is formed between the particles.
As the nonionic surfactant, a nonylphenyl ether polymer having 6 to 7 carbon atoms can be used.

Perlite is a closed-cell foam made by crushing obsidian into sand and combusting it at 1000 ° C., and is an inorganic ultralight gravel aggregate. This porosity is a material that does not completely saturate even when sufficiently absorbed, and always contains a considerable amount of air.
The soil containing the above pollutants often contains a lot of moisture and becomes muddy. In this case, pearlite absorbs excess moisture and adjusts the minimum amount of moisture required for the solidification reaction. I can do it.

Based on the characteristic of each material described above, the improvement method of this invention contaminated soil is demonstrated.
First, Table 1 shows formulation examples of a composition mixture having water permeability, adsorptivity, and prevention of contaminant elution.

In order to obtain a composition mixture based on the above formulation, a certain amount of mountain sand and Portland cement are weighed, and a surfactant is added dropwise while stirring with a stirrer. Thereafter, charcoal, inorganic pigment, and pearlite are added to form a smooth composition mixture of mountain sand, Portland cement, charcoal, inorganic pigment, pearlite, and nonionic surfactant.

More specifically, 100 parts by weight of sand with an average particle diameter of 10 mm or less, 5-15 parts by weight of charcoal with an average particle diameter of 5 mm or less, 60-65 parts by weight of Portland cement, 5-6 parts by weight of an inorganic pigment, pearlite A composition mixture is formed by mixing 4 to 10 parts by weight and some nonionic surfactant.
Portland cement 60-65 parts by weight with respect to 100 parts by weight of sand is less than 60 parts, the strength after solidification is weak, can not sufficiently surround the sand and soil, solidification at 65 parts or more This is because the later voids are reduced.
The reason why 5 to 15 parts by weight of charcoal having an average particle diameter of 5 mm or less is used is that the amount of adsorption is small at 5 parts or less and the strength after solidification is weak at 15 parts or more.
The reason why the pearlite is 4 to 10 parts by weight is that the amount of water absorption is small at 4 parts or less, and the strength after solidification is weak at 10 parts or more as in the case of charcoal. This is because this is sufficient as the coloring amount.

Next, as shown in FIG. 2, in a site that may have soil containing contaminants, soil containing contaminants such as heavy metals, chemicals, and VOCs is dug up at the site. The digging and raising means is not limited, but a heavy machine such as a back-for is generally used.
Then, the excavated soil and the composition mixture are mixed and stirred with a large mixer or the like at a ratio of 1: 0.8 to 1.2. Here, the mixing ratio of the contaminated soil and the composition mixture was set to a ratio of 1: 0.8 to 1: 1.2 because, depending on the degree of contamination, when the contamination was heavy, the ratio of the soil was decreased. When the degree of contamination is light, the ratio of soil is increased to about 1: 1.2, and in the range of 1: 0.8 to 1: 1.2. If there is, a porous gap can be formed after solidification in relation to mountain sand and strength can be maintained.
At the time of the mixing, water is added as necessary, and then the mixture mixture, the contaminated soil and water mixed as necessary are stirred and mixed at the site or in the vicinity thereof before the solidification. Backfill while in state. In other words, by refilling the mixture at or near the excavated site while it is movable before solidification, it is possible to backfill in a shape suitable for the topography and form.
Thus, when it is backfilled, solidification starts in about 8 to 10 hours, and solidification is completed in a state in which the soil containing the pollutant is surrounded by the composition mixture in about 2 to 5 days.

After solidification is completed, it will be used for houses, parking lots, etc., and on top of it, trees will be planted and used for gardens, parks, etc.

Next, the effect which accompanies the improvement method of this invention contaminated soil is demonstrated below.
The present invention is, for example, a place where construction, use, etc. of a house, a parking lot, a tree planting, etc. are scheduled, and this includes pollutants such as heavy metals, chemicals, VOCs, etc. due to operations in factories, cleaning shops, coin laundry, etc. Applicable when the soil is a fear.
At the site, first, the soil with the possibility of contamination is dug up, and when it is mixed and stirred with the above composition mixture, the dispersed Portland cement etc. reacts with water, and the soil containing the pollutant is converted into the Portland cement. It is solidified in a state of being surrounded by the entire area, preventing leakage and diffusion of pollutants.
At this time, since chemicals such as heavy metals and agricultural chemicals are easily dissolved in the soil, the soil containing the heavy metals and agricultural chemicals is surrounded and solidified by Portland cement, thereby preventing leakage and diffusion therefrom. However, on the other hand, VOC has properties that are difficult to dissolve in the soil, and there is a risk of leakage or the like as it is, but due to the presence of mixed charcoal, it is adsorbed by the porous portion, and Portland cement surrounds the charcoal. Therefore, leakage and diffusion are similarly suppressed.
Moreover, the soil containing the pollutants in the field often contains excessive moisture and is in a muddy state. In such a case, pearlite acts, the pearlite absorbs excess moisture, and the soil and the composition mixture are in a mortar state suitable for backfilling and the minimum moisture necessary for the subsequent solidification reaction. The amount can be adjusted.
As described above, when the Portland cement is uniformly and satisfactorily dispersed by the nonionic surfactant, the sand such as mountain sand and soil can be efficiently and as thin as possible, and after the solidification reaction, A gap (hole) is formed between the particles. That is, Portland cement sufficiently dispersed with a nonionic surfactant can sufficiently surround mountain sand, soil, and the like and solidify the soil, thereby making the soil porous. As a result, water permeability and air permeability can be maintained. For example, when planting trees there, the soil can be made excellent in vegetation.
In addition, mountain sand functions as a kind of aggregate, so it can give a certain level of strength to the solidified soil. For example, when building houses or other buildings on the soil, Keep the strength of.
Moreover, if an inorganic pigment is blended in the soil, the soil before treatment and the soil after treatment can be visually discriminated by the color of the inorganic pigment, and the soil before treatment and the soil after treatment are confused. You can avoid the problems.

An example of the present invention was manufactured based on the above embodiment. The implementation status will be described below.
In producing the pollutant-adsorbing soil improving composition mixture based on the above form, the following formulation was carried out.
The composition mixture was prepared by mixing 600 kg of mountain sand, 40 kg of charcoal, 345 kg of Portland cement, 6 kg of inorganic pigment (Bengara), 20 kg of pearlite and 3 kg of nonionic surfactant (nonylphenyl ether polymer).
The granular mixture produced by the above blending is shown in FIG. 1 in a mixed state, and in FIG. 2 and FIG. 3 in cross section as a method for improving contaminated soil. FIG. 2 shows a state diagram in which the contaminated soil and the granular mixture are mixed, and the contaminated soil is excavated. In the second stage, the mixture was mixed with the composition mixture at a weight ratio of 1: 1 with a large mixer. The composition mixture mixed in the third stage was backfilled in the hole dug up by the pouring hose.

The sample of the present invention manufactured based on the above-mentioned example was mixed with contaminated soil and a composition mixture at a weight ratio of 1: 1, and an elution test was conducted based on Environmental Standard Environment Agency Notification No. 46. The measurement method and the results are described below.
After mixing the contaminated soil of Taiwan original soil and the composition mixture at a weight ratio of 1: 1, the mixture is packed in a 10 cm × 10 cm formwork, and after watering, the composition mixture and water are reacted to solidify. The mixture was crushed to 2 mm or less, soaked in pure water, vibrated for 6 hours, filtered, and an elution test was conducted by an elution test method based on Environment Agency Notification No. 46. The actual organization was inspected by the Tochigi Environmental Technology Association.

The above table shows the dissolution test results before treatment.

The above table shows the dissolution test results after treatment.

As shown in the table above, the elution of 0.53 m / l copper before treatment was reduced to 0.02 mg / l after treatment, and the elution of 0.04 mg / l zinc was reduced to 0.02 mg / l. It was confirmed to be effective.

INDUSTRIAL APPLICABILITY The present invention can be widely used for effective utilization of soil containing pollutants such as heavy metals in factory sites, houses, parking lots, and the like.

FIG. 1 is a schematic diagram illustrating a mixing state of an object to be mixed and the composition mixture. FIG. 2 is a schematic diagram showing the excavation status of contaminated soil. FIG. 3 is a schematic diagram showing the backfill of contaminated soil and the composition mixture.

Claims (2)

100 parts by weight of sand with an average particle diameter of 10 mm or less, 5-15 parts by weight of charcoal with an average particle diameter of 5 mm or less, 60-65 parts by weight of Portland cement, 4-10 parts by weight of pearlite, and a nonionic surfactant And a mixture containing at least one of the excavated heavy metal, pesticide and VOC at a ratio of 1: 0.8 to 1.2,
Backfilling at or near the site where the composition mixture and the soil containing the pollutant and water as needed are stirred and mixed while still in the mortar state by mixing before solidification,
A method for improving contaminated soil, comprising solidifying the backfilled contaminated soil surrounded by the composition mixture. The method for improving contaminated soil according to claim 1, wherein an inorganic pigment is contained in the composition mixture.