JP6587114B1 - Heavy metal pollution control material and heavy metal pollution control method using the pollution control material - Google Patents

Abstract

It is possible to insolubilize heavy metals and the like in acid soils and soils that are acidified in the long term, solidify the soil and improve the strength, and maintain the pH of the improved soil in a neutral region Provide a pollution control material for heavy metals and the like, and a pollution control method for heavy metals using the countermeasure materials. SOLUTION: A pollution control material such as heavy metals is a pollution control material that solidifies and insolubilizes heavy metals in acidic soil and soil that is acidified over the long term, and contains dolomite compounds, acidic sulfates and polymer materials as essential. In the total amount of the dolomite compound and the acidic sulfate as an ingredient, the acidic sulfate is contained in a proportion of 1 to 20% by mass, and the polymer material is divided by the total amount of the total amount of the dolomite compound and the acidic sulfate. And contained in an amount of 0.1 to 10% by mass, and 6 to 12% by mass of MgO in a pollution control material such as heavy metal. [Selection figure] None

Description

  The present invention relates to a pollution control material for heavy metals and the like, and a pollution control method for heavy metals using the pollution control material. The present invention relates to a pollution control material for heavy metals and the like having a soil reforming performance, which can improve the strength of the soil and keep the soil pH near neutral, and a pollution control method for heavy metals and the like using the pollution control material.

Conventionally, insolubilizing materials such as heavy metals in soil include iron powder-based insolubilizing materials such as ferric chloride and ferrous sulfate, cement-based insolubilizing materials, magnesium oxide (MgO) -based insolubilizing materials, quicklime and gypsum systems, blast furnaces Soil solidifying materials such as slag materials are known.
Iron powder-based insolubilizing materials such as ferric chloride and ferrous sulfate are limited to heavy metals that can be insolubilized, such as arsenic, and the insolubilizing effect may not be sufficient. There is a problem that it is difficult to do.

Further, as solidification materials, cement solidification materials, MgO solidification materials, or soil solidification materials using quick lime or blast furnace slag materials have been proposed.
However, these conventional soil-solidifying materials are affected by cement, quicklime, etc., so that the pH of the soil after modification becomes 10 or more and the alkalinity becomes strong, and the pH of the insolubilized soil remains high for a long time. Strongly alkaline groundwater flows out to the surrounding environment due to rainfall, etc., which may affect vegetation.
Moreover, since the heavy metal insolubilization ability is low, there is a problem that heavy metals that have not been eluted in the neutral region are eluted.

As a magnesium oxide (MgO) -based solidifying material, a solidified and insolubilized material obtained by adding an organic polymer flocculant and a plurality of insolubilizing aids to improve soil strength is proposed in Japanese Patent Application Laid-Open No. 2003-225640 (Patent Document 1). Has been.
Although such materials have excellent solidification / insolubilization properties, the pH is likely to be more alkaline than untreated soil, and as with cement-based solidification materials, there is a possibility of affecting the surrounding environment. There is a problem that it is restricted by the application range of soil.

In order to prevent soil pH from becoming alkaline, JP 2014-185300 A (Patent Document 2) is based on gypsum and blast furnace slag, and is added with magnesium oxide or aluminum sulfate so that the pH becomes neutral. A soil-solidifying material adjusted to the above has been proposed.
However, although the pH is maintained neutral, the use index of the improved soil is limited because the cone index of the improved soil is as low as about 200 to 400 kN / m ² . Further, in order to improve the corn index to 200 to 400 kN / m ^2, it is necessary to add 100 kg or more of solidifying material per 1 m ³ of soil, which is not appropriate in terms of increase in the amount of solidifying material and cost. In addition, the insolubilization performance of heavy metals is not described, and the gypsum solidified material is water-soluble dihydrate gypsum, which is a hydrated product. There is a problem that the index decreases.

  In the past, when modifying soil strength, such as improving the strength of heavy metal contaminated soil, an insolubilizing material and a solidifying material were added separately, but a material capable of expressing the solidifying performance and insolubilizing performance with a single material is expected. In addition, there is a growing need for materials in which the pH of the improved soil is in a neutral region in order to suppress the influence on the surrounding environment.

As a pH-neutral solidified insolubilizing material, Japanese Patent No. 5748015 (Patent Document 3) proposes a pH-neutral solidifying insolubilized material combining light-burned MgO, aluminum sulfate, and ferrous sulfate. No. 5315096 (Patent Document 4) proposes a pH neutral solidified insolubilized material containing calcined gypsum (hemihydrate gypsum), an aluminum compound, a calcium component and / or a magnesium component.
However, the solidified and insolubilized material disclosed in Patent Document 3 is not described regarding the reforming performance and long-term insolubilizing performance for soil other than neutral. Further, the solidified and insolubilized material shown in Patent Document 4 is based on gypsum as in the case of the pH neutral solidified material, and therefore the cone index of the improved soil is lowered to about 200 kN / m ² even if the addition amount is increased. There are drawbacks.
As described above, the conventional solidified and insolubilized material has a problem that the application range of the improved soil is restricted.

Japanese Patent Application Laid-Open No. 2017-179341 (Patent Document 5) has insolubilized heavy metals in the soil to improve the strength of the treated soil to have a solidification performance and a re-mudging suppression function. An anti-contamination material such as heavy metal capable of maintaining the performance to maintain the property is disclosed.
However, the anti-pollution material such as heavy metal of Patent Document 5 focuses on suppressing the soil that has been solidified from the treated soil and improved in strength from being re-mudged by external moisture. There is no description about pH neutral solidification and insolubilization performance for acidified soil.

In recent years, there is an increasing need for pH neutral solidified and insolubilized materials that can be applied to acidified soil and soil that gradually acidifies over time (soil that acidifies in the long term). A solidified and insolubilized material capable of exhibiting sufficient solidification and insolubilization performance for soil and retaining the soil in the vicinity of neutralization has not been disclosed so far.
For example, in soil containing sulfides such as pyrite, the pH is neutral to weakly alkaline immediately after excavation, but when placed outdoors in the long term, the pyrite gradually oxidizes due to contact with the atmosphere. As a result, the soil is acidified, and the pH property changes greatly compared to immediately after excavation.
Therefore, even if the soil immediately after excavation has been neutralized and insolubilized by maintaining the pH neutral, there are problems such as re-elution of heavy metals if the soil has been acidified for a long time.

In addition, when such soil is used for embankment or the like, the surface soil in contact with the atmosphere is acidified, but the inside is not acidified and is considered to be neutral to weakly alkaline.
Accordingly, there is a demand for a material capable of solidifying and insolubilizing soil that has a risk of being acidified in the long term and maintaining the pH in the vicinity of neutrality in the long term, regardless of the degree of acidification.
Although oxidation of pyrite in soil may proceed in units of several months, in Patent Documents 1 to 5, long-term pH state for long-term acidified soil, long-term solidification insolubilization performance, and pH state for acidic soil No solidification / insolubilization performance is described.

JP 2003-225640 A JP 2014-185300 A Japanese Patent No. 5748015 Japanese Patent No. 5315096 JP 2017-179341 A

  The object of the present invention is to solve the above-mentioned problems, and can insolubilize heavy metals contained in soil, particularly acid soil and soil that is acidified in the long term, in the long term, thereby improving the strength of the treated soil. An object of the present invention is to provide a pollution control material such as heavy metal, which can maintain the performance of maintaining the pH of the improved soil in the vicinity of neutrality for a long time, together with the solidification performance to be modified.

  Another object of the present invention is to apply the anti-pollution material for heavy metals of the present invention to soil contaminated with heavy metals, especially for acidic soils and soils that are acidified over the long term, to insolubilize heavy metals. At the same time, it is to provide a pollution control method for heavy metals and the like using a pollution control material such as heavy metals, which exhibits the soil improvement performance of improving the strength by solidifying the treated soil.

  This invention discovered that the said subject can be solved by including the specific material as an essential content material by a specific compounding ratio, etc., and came to this invention.

(1) The pollution control material such as heavy metals of the present invention is a pollution control material that solidifies and insolubilizes heavy metals in acidic soil and soil that is acidified over the long term, and contains dolomite compounds, acidic sulfates and polymer materials. As an essential component, acidic sulfate is ferrous sulfate, and in the total amount of dolomite compound and ferrous sulfate , ferrous sulfate is contained in a proportion of 1 to 20% by mass, and the polymer material is It is contained in a proportion of 0.1 to 10% by mass with respect to the total amount of the dolomite compound and ferrous sulfate , and 6 to 12% by mass of MgO in the pollution control material such as heavy metal , semi-calcined dolomite Is a pollution control material such as heavy metal, characterized by containing 30.6 to 53.4% by mass .

(2) In the pollution control material such as heavy metal of (1) above, the dolomite compound includes CaMg (CO ₃ ) ₂ , MgO, and CaCO ₃ .

(3) In the pollution control material for heavy metals or the like described in (1) or (2) above, the pollution control material for heavy metals or the like is in an equilibrium state with a pH of the slurry obtained by mixing the pollution control material for heavy metals and water and 8 to 10 It is what becomes.

(4) The heavy metal pollution control method according to the present invention is a heavy metal pollution control method characterized by using any of the above-mentioned (1) to (3) heavy metal pollution control materials mixed with acidic soil. .

(5) In the above (4) heavy metal pollution control method, the pH of the treated soil obtained by mixing the heavy metal pollution control material and the acidic soil becomes 5.8 to 8.6 after 180 days of age. It is characterized by that.

The anti-contamination material for heavy metals and the like and the construction method for anti-contamination of heavy metals using the countermeasure material of the present invention are effective and long-term insolubilization of heavy metals in soil, especially for acidic soil and soil that is acidified over the long term. The soil can be improved in strength by solidification of the treated soil, and the pH of the treated soil treated with the anti-contamination material such as heavy metal according to the present invention can be maintained near neutrality.
In the present invention, near neutral means that the pH is in the range of 5.8 to 8.6.

  Conventionally, neutralized solidified and insolubilized soil is acidified for a long time, and strong acid groundwater containing heavy metals flows out to the surrounding environment due to rainfall, etc. Although there was a concern about performance degradation, according to the pollution control material such as heavy metal of the present invention, it is possible to maintain the pH of the treated soil in the neutral vicinity from the initial stage for a long time. It is possible to cope with a site where a conventional solidified and insolubilized material could not be applied, and it is possible to expand the application range of soil treatment contaminated with heavy metals.

The present invention is illustrated by the following preferred examples, but is not limited thereto.
The pollution control material of the present invention, such as heavy metals, is a pollution control material that solidifies and insolubilizes heavy metals in acidic soil and soil that is acidified over the long term, and contains dolomite compounds, acidic sulfates and polymer materials as essential components In addition, in the total amount of the dolomite compound and the acidic sulfate, the acidic sulfate is contained in a ratio of 1 to 20% by mass, and the polymer material is divided by an extra amount with respect to the total amount of the dolomite compound and the acidic sulfate. It is contained in a proportion of 0.1 to 10% by mass, and contains 6 to 12% by mass of MgO in the antifouling material such as heavy metal.

The anti-contamination material such as heavy metal of the present invention is preferably in powder form. The powder form facilitates handling and workability at the construction site, and can react quickly with the moisture in the soil when mixed with the soil, effectively adsorbing heavy metals etc. Can be insolubilized.
Furthermore, by making the anti-contamination material such as heavy metals of the present invention containing dolomite compounds, acidic sulfates and polymer materials as essential components at a specific blending ratio into a powder form, it comes into contact with moisture in the soil and is hydrated. It is possible to improve the strength of the soil by precipitating things and making it easier to aggregate the soil, and it is possible to efficiently modify the soil.

  Here, heavy metals and the like mean heavy metals and halogens, and heavy metals include, for example, one or more of manganese, chromium, copper, cadmium, mercury, selenium, lead, arsenic, cadmium and the like, Moreover, a heavy metal simple substance and a compound thereof can be exemplified, and as a halogen, a simple substance such as fluorine and chlorine and a compound thereof can be exemplified. Furthermore, in addition to these, boron simple substance and its compound contained in the second kind specific harmful substance prescribed in the Soil Contamination Countermeasures Law can be exemplified, but it is not limited to these heavy metals and halogens.

The soil to which the anti-contamination material such as heavy metal of the present invention is applied is acid soil or soil that is acidified over the long term.
By applying the anti-contamination material such as heavy metal of the present invention to such soil, the above-mentioned effects such as being able to maintain the pH in the vicinity of neutrality for a long period from the initial stage are obtained.

  In the present invention, as an essential content material in pollution control materials such as heavy metals, dolomite compounds, acidic sulfates and polymer materials are contained, and by setting these contents to amounts within the above range, heavy metals, etc. Can be effectively insolubilized, and the soil can be modified by improving the strength of the treated soil (improvement of solidification performance) for acid soil or soil that will be acidified in the long term. It is possible to simultaneously achieve the above effects that are maintained near neutrality.

Preferably, the dolomite compound used for the pollution control material such as heavy metal of the present invention contains MgO, CaMg (CO ₃ ) ₂ and CaCO ₃ as essential components.
Examples of the dolomite compound containing the component include semi-baked dolomite mainly containing MgO, CaCO ₃ , CaMg (CO ₃ ) ₂ , dolomite mainly containing CaMg (CO ₃ ) ₂ , and CaCO ₃ . Examples thereof include calcium carbonate as a main component, and these may be used alone or in combination. In particular, those containing semi-baked dolomite, dolomite and calcium carbonate are preferably used, and particularly preferably, baked dolomite, dolomite and calcium carbonate are used as the dolomite compound.
As the dolomite, any commercially available dolomite can be used, and the production area is not limited.
In addition, any half-baked dolomite that can be obtained in the market and semi-baked dolomite obtained by firing any dolomite available in the market can be used. It doesn't matter. Semi-baked dolomite is not obtained by baking dolomite until the decomposition reaction is completely completed, but contains MgO, CaMg (CO ₃ ) ₂ and CaCO ₃ as essential components.

Dolomite has a double salt structure in which the molar ratio of limestone CaCO ₃ and magnesite MgCO ₃ is 1: 1, and Ca ²⁺ ions and Mg ²⁺ ions are alternately layered across the CO ₃ ^2- group. In general, the MgCO ₃ ratio is 10 to 45% by mass. Dolomite is present in large amounts in Japan, and adsorbents such as heavy metals using dolomite are advantageous from the viewpoint of cost and environmental burden.

  Dolomite reacts with water in the soil and calcium and magnesium are eluted as ions. The eluted calcium reacts with the aluminum component in the soil to precipitate an ettringite-like hydrate, thereby binding the soil particles to promote aggregation and increasing the strength of the soil. Also, dihydrate gypsum precipitates when the eluted calcium reacts with sulfate ions eluted from acidic sulfates such as ferrous sulfate, so that the soil strength improvement performance is improved by reducing the moisture content in the soil. . Similarly, magnesium sulfate hexahydrate precipitates when the eluted magnesium reacts with sulfate ions eluted from acidic sulfates such as ferrous sulfate, thereby reducing the moisture content in the soil and reducing the soil strength. Improvement performance can be enhanced.

CaCO ₃ and CaMg (CO ₃ ) ₂ contained in the dolomite compound are carbonates, and have a pH buffering effect by a carbonic acid-bicarbonate buffering action.
When the pollution control material such as heavy metal of the present invention is added to acidified soil, it is neutralized by carbonates contained in MgO and dolomite compounds, and the pH shifts to near neutrality. For soils that are acidified over the long term, acidic sulfates such as ferrous sulfate, which have the highest solubility among heavy metal and other pollution control materials, dissolve in the water in the soil when the initial pH is weakly alkaline. Thus, the soil can be neutralized and the pH can be lowered to the vicinity of neutrality. After that, when acidification proceeds, the acid buffer effect of the carbonate contained in the dolomite compound has excellent performance that can suppress the pH drop and maintain the soil pH neutral in the long term It is.

As the above-mentioned semi-baked dolomite, the content x of residual CaMg (CO ₃ ) ₂ phase in the dolomite fired product analyzed using the Rietveld method by powder X-ray diffraction is 0.4 ≦ x ≦ 35.4 (mass) %) Can be suitably used.
The amount of CaMg (CO ₃ ) ₂ phase contained in the semi-fired dolomite is quantified, and the amount of CaMg (CO ₃ ) ₂ phase remaining in the above-mentioned range is suitably used to produce the dolomite ore as the raw material. Regardless of the difference in composition due to the above, and the setting of firing conditions such as the firing temperature, dolomite can have the most excellent adsorption performance of heavy metals and the like.

Dolomite shows a decomposition reaction represented by CaMg (CO ₃ ) ₂ → MgO + CaCO ₃ + CO ₂ by firing. Further, it is considered that pores are formed by the above thermal decomposition due to dolomite firing and exhibit insolubilizing ability such as heavy metals. In the present invention, the residual amount of the dolomite phase (CaMg (CO ₃ ) ₂ phase) in the semi-fired dolomite obtained by firing dolomite is analyzed by the Rietveld method using powder X-ray diffraction, and the residual CaMg (CO ₃ ) ₂ phase is analyzed. Content x of 0.4 ≦ x ≦ 35.4 (mass%), preferably 1.8 ≦ x ≦ 17.4 (mass%), particularly preferably heavy metals, etc. It is possible to achieve insolubilization.

For example, such a suitable semi-fired dolomite has a residual CaMg (CO ₃ ) ₂ phase content x in the fired dolomite product analyzed by the Rietveld method by powder X-ray diffraction, preferably 0.4 ≦ x ≦ It can manufacture by baking so that it may become 35.4 (mass%), More preferably, 1.8 <= x <= 17.4 (mass%).
The temperature at which dolomite is calcined is not particularly limited, and can be usually calcined at a temperature at which dolomite is calcined to produce semi-calcined dolomite, for example, 650-1000 ° C. If the residual CaMg (CO ₃ ) ₂ phase content is 0.4 ≦ x ≦ 35.4 (mass%), the baking time is not limited.

  Semi-baked dolomite contributes to the insolubilization performance of heavy metals by the effect of MgO contained, and has a lower MgO content and a weak alkaline pH of 9 to 10 compared to MgO alone or lightly burned dolomite. Therefore, it can be suitably used in the present invention.

The MgO content in the anti-contamination material such as heavy metals of the present invention is 6 to 12% by mass, preferably 6 to 9% by mass, as analyzed by the Rietveld method using powder X-ray diffraction.
MgO in the pollution control material such as heavy metals is derived from the contained dolomite compound, specifically, is derived from semi-baked dolomite obtained by baking dolomite, and more preferably half It is derived from calcined dolomite.
If the MgO content is less than 6% by mass, the insolubilizing ability for lead and fluorine and the neutralizing ability for acidic soils are reduced. If the MgO content exceeds 12% by mass, the MgO pH is alkaline, resulting in anti-contamination materials such as heavy metals. The pH of the soil is 10 or more, and it becomes difficult to make the soil pH neutral.
In addition, when the amount of acidic sulfate is increased in order to adjust the pH of such soil, the essential material mixing ratio of the dolomite compound contained in the anti-pollution material such as heavy metal of the present invention is reduced, and improved There is a risk of suppressing improvement in soil solidification performance.

The dolomite compound contained in the pollution control material such as heavy metal of the present invention is optionally mixed with one and / or two or more materials so that the essential components MgO, CaMg (CO ₃ ) ₂ and CaCO ₃ are included. be able to.
As an example, when semi-baked dolomite containing 21% by mass of MgO is used, the mixing ratio of semi-baked dolomite in the anti-polluting material for heavy metals and the like is 29 to 57% by mass, so that the anti-pollution measures for heavy metals of the present invention Although content of MgO in a material can be 6-12 mass%, according to the dolomite-type material to be used, the said mixture ratio is not restricted.

Further, the anti-contamination material such as heavy metal of the present invention contains acidic sulfate as an essential material.
The acid sulfate, for example, ferrous sulfate, can be exemplified aluminum sulfate or the like, Ru ferrous der sulfate in the present invention.
By containing acidic sulfate, it can be more effectively insolubilized with heavy metals such as arsenic and hexavalent chromium due to its high reducing action like ferrous sulfate, and is acidic, By adjusting the blending ratio of the other essential materials, it is possible to keep the soil treated with the pollution control material such as heavy metal of the present invention near neutrality.
In addition, acid sulfate is presumed to have an effect as an inorganic flocculant, and is included in the pollution control material such as heavy metals of the present invention in order to easily agglomerate by finely agglomerating fine particles in the soil. It is also conceivable to have an effect of making it easier to compact the soil.

Moreover, the acidic sulfate contained in the pollution control material such as heavy metal of the present invention is 1% to 20% by mass, preferably 5 to 15% by mass of the acidic sulfate in the total amount of the dolomite compound and the acidic sulfate. % Inclusive.
At such a ratio, the effect of the present invention can be achieved by including a dolomite compound and an acidic sulfate in the anti-pollution material such as heavy metal, and further including a polymer material.

The anti-contamination material such as heavy metal of the present invention further contains a polymer material as an essential material, and the polymer material is preferably in a powder form because it needs to react with moisture in the soil.
The properties of the polymer material used in the present invention include that it is easily dissolved in cold water, the pH of the aqueous solution is in a neutral region, and the effective pH region covers a range of weak acid to weak alkalinity to cope with various soils. In addition, it is desirable to use a material that has a viscosity increase when dissolved in water.

  Polymer materials include polymer flocculants that have the effect of agglomerating fine particles by reacting with moisture in the soil and making it easier to compact the soil, and particles by reacting with moisture in the soil to increase the viscosity. A thickener to be bonded can be suitably used. As the kind of the organic polymer flocculant, at least one selected from the group consisting of an anionic polymer flocculant, a nonionic polymer flocculant, and a cationic polymer flocculant can be used. It is an anionic polymer flocculant having a neutral solution pH and a high viscosity. As the organic polymer flocculant, at least one selected from the group consisting of polyacrylamide, polyacrylate, polyamidine, sodium polyacrylate, polyethylene oxide, and sodium acrylate-acrylamide copolymer can be used. Particularly preferred is a polyacrylamide type, which has a high aqueous solution viscosity when dissolved in the same amount of water.

  Further, as the thickener, at least one selected from the group consisting of cellulose derivatives, polyamide derivatives, polyvinyl alcohol derivatives, guar gum, starch, xanthan gum and propylene glycol can be used, and particularly preferred is cellulose. The derivatives are hydroxyethyl methylcellulose (HEMC), hydroxypropylmethylcellulose (HPMC), and methylcellulose (MC).

Further, the polymer material has a neutral pH, and can further contribute to strength improvement by solidifying the soil by binding fine particles in the soil to become aggregated particles.
The content is 0.1 to 10% by mass, preferably 1 to 5% by mass, based on the total amount of the dolomite compound and acidic sulfate.
If it is less than 0.1% by mass, sufficient reforming performance cannot be obtained. When it exceeds 10 mass%, cost will become high and it is not economical. Moreover, there exists a risk that the improvement property of soil will become high by excessive addition, and workability will fall. Furthermore, addition of a large amount of organic matter to the soil is not environmentally preferable.

The anti-pollution material such as heavy metals of the present invention, when blended with the above-mentioned proportions of the dolomite-based compound, acidic sulfate and polymer material essential ingredients, when mixed with acidic soil and soil to be acidified in the long term The pH of the test solution prepared by the method based on the Environmental Agency Notification No. 46 (promulgated on August 23, 1991) is near neutral (the uniform drainage standard of the Ministry of the Environment (5.8 to 8.6)) Therefore, for example, the pH of the treated soil after 180 days of age can be maintained near neutrality (5.8 to 8.6).
Moreover, in the range which does not affect the solidification insolubilization performance of the pollution control material such as heavy metal of the present invention, in addition to the above-mentioned essential content materials, any material for pH adjustment such as slaked lime, and soil modification such as slag Any auxiliary material may be added.

The antipollution material such as heavy metal of the present invention can be prepared by mixing using any method as long as the dolomite compound, acidic sulfate and polymer material can be mixed uniformly.
In the pollution control material for heavy metals and the like of the present invention, the pH of the slurry obtained by mixing the pollution control material for heavy metals and water with water finally becomes 8 to 10, preferably 9 to 10, more preferably, for example, after 28 days. Is 8 to 10, preferably 9 to 10. Furthermore, desirably, the pH of the initial slurry obtained by mixing the anti-contamination material such as heavy metal and water is 6-8.
When added to acid soil and soil that is acidified in the long term, the anti-pollution material such as heavy metal of the present invention can maintain the soil pH in a neutral region for a long time immediately after the addition, and insolubilization performance of heavy metals, etc. It is possible to suppress a decrease in the solidification performance of the soil.

  In addition, the pollution control method such as heavy metal of the present invention is a method of mixing a pollution control material such as heavy metal and acid soil and contaminated soil that is acidified in the long term, but the mixing method is not particularly limited, for example, It is possible to apply a soil mixing facility similar to conventional powder insolubilizing materials, such as an improvement by heavy machinery having surface modification performance, or a facility for mixing with soil, by spraying pollution control materials such as heavy metals on the soil surface layer. By constructing the pollution control method for heavy metals and the like of the present invention, the pH of the soil can be made near neutral (5.8 to 8.6).

  In addition, heavy metal and other pollution control materials are preferably used in the form of powder, and as a mixing device with contaminated soil, it can be mixed using a backhoe, a deep mixing machine, a stationary mixer, a power blender, etc. And the compounding quantity of the pollution control processing material, such as a heavy metal, with respect to the treated soil varies depending on the moisture content of the soil, the required solidification strength of the treated soil, etc., and can be arbitrarily designed.

In this way, by bringing pollution control materials such as heavy metals into contact with acid-contaminated soil from which heavy metals, fluorine, etc. are eluted, insolubilizes heavy metals that are eluted from the contaminated soil and improve the solidification performance of the soil and treat it. It becomes possible to maintain the pH of the soil in the vicinity of neutrality for a long time.
For example, the amount of elution of heavy metals, etc., in the soil is all within the standards for soil elution, measured according to the Soil Contamination Countermeasures Law, and conforms to the Environmental Agency Notification No. 46 (promulgated on August 23, 1991) The pH of the test solution prepared by the method is, for example, in the range of 5.8 to 8.6 defined by the Ministry of the Environment's uniform drainage standard after 180 days of age. It can be set to 400 kN / m ² or more, which is prescribed for the third type construction generated soil of the soil classification standard in “Regarding the soil use standard”, and it can be designed to surely satisfy the environmental standard.
In particular, if the amount of lead, arsenic, and fluorine that are abundant in naturally derived contaminated soils is a low concentration contamination level that slightly exceeds the soil elution amount standard, insolubilization and expression of neutral soil modification performance can be achieved with a small addition amount Demonstrate the effect.

The invention is illustrated by the following examples and comparative examples.
(Test soil)
The test soil was arsenic eluting and acidified for a long time. Table 1 shows the moisture content, wet density, arsenic elution amount, and eluate pH of the test soil.
The arsenic elution amount was prepared by a method in accordance with the Environmental Agency Notification No. 46 (promulgated on August 23, 1991). The arsenic concentration in the test solution was JIS K 0102 “Factory Wastewater Test Method”. Measured according to the above.

(Raw materials used)
The following materials were used in preparing pollution control materials such as heavy metals.
・ Semi-baked dolomite (powder): baked dolomite produced in Tochigi Prefecture Kuzu ・ Dolomite (powder): Tochigi Prefecture Kuzu production ・ Calcium carbonate (powder): Tochigi Prefecture Kuzu production ・ Acidic sulfate: Ferrous sulfate monohydrate Powder / polymer materials: Anionic polymer flocculants

About the said semi-baked dolomite (powder), the said dolomite (powder), and the said calcium carbonate (powder), content of each component was measured using the Rietveld method by powder X-ray diffraction.
The results are shown in Table 2.

(Heavy metal pollution control materials)
The above-mentioned raw materials used were mixed at a blending ratio shown in Table 3 below to prepare anti-contamination materials such as heavy metals.
In addition, although the mixing order in particular of each raw material is not restrict | limited, each raw material was mixed simultaneously and each pollution control material, such as each heavy metal, was prepared.
In Table 3, semi-calcined dolomite, ferrous sulfate and dolomite indicate the blending ratio (mass%) in the internal ratio in the total amount of semi-calcined dolomite, ferrous sulfate and dolomite, and polymer flocculant Indicates the proportion (% by mass) of the dolomite compound and ferrous sulfate in an external ratio.
For each heavy metal pollution control material, the measurement result of the content of MgO in the heavy metal pollution control material measured using the Rietveld method by powder X-ray diffraction, and 5 g of each heavy metal pollution control material and ion-exchanged water. Table 3 below shows the results of measuring the pH of the ages 1 day, 7 days, and 28 days for each slurry obtained by mixing and stirring 50 g.

(Test example)
(Test Example 1: Insolubilization test for heavy metals)
To the test soil 1 m ³ of Table 1, the addition of the heavy metals pollution abatement material 50kg shown in Table 3, after kneading at low speed 2.5 min at soil mixer, attached to the container and paddle soil mixer The soil thus obtained was scraped off and kneaded again at a low speed for 2.5 minutes to prepare an insolubilized test soil.
After preparing each insolubilized soil, a test solution is prepared for each soil on the 7th, 28th, 91st, and 180th ages by a method in accordance with Environmental Agency Notification No. 46 (promulgated on August 23, 1991). Based on JIS K 0102 “Factory drainage test method”, the arsenic elution amount was measured for the test solution pH and the concentration of heavy metals and the like in the test solution.

As Comparative Example 1, the pH of the test solution and the amount of arsenic elution were measured in the same manner with respect to the soil in Table 1 where no anti-pollution material such as heavy metals was mixed.
The results are shown in Table 4.

(Test Example 2: Solidification test of soil)
After adding 50 kg of various anti-pollution materials such as heavy metals shown in Table 3 to 1 m ^{3 of the} soil to be acidified in the long term shown in Table 1 above, kneading at a low speed for 2.5 minutes with a soil mixer, The soil adhering to the container and the paddle was scraped off and kneaded again at a low speed for 2.5 minutes to prepare an insolubilized test soil.
After preparing each insolubilized test soil, each soil is filled in 10 cm mold defined in JIS A 1210: 2009 “Soil compaction test method by tamping” in three layers, and the material age at 20 ° C. After sealing and curing up to 7 days, the corn index at 7 days of age was measured according to JIS A 1228 “Testing method for cone index of compacted soil”.
The results are shown in Table 4 below.

In addition, the elution amount of arsenic was determined to be acceptable if the soil elution amount standard was 0.01 mg / L or less based on the Soil Contamination Countermeasures Law.
Moreover, the eluate test solution pH was determined to be acceptable if it falls within the range of 5.8 to 8.6 defined by the uniform drainage standards of the Ministry of the Environment.
The corn index passed 400 kN / m ² or more, which is stipulated for the type 3 construction generated soil in the soil classification standard of “Regarding the generated soil use standard” of the Ministry of Land, Infrastructure, Transport and Tourism.

From the said Table 4, in the Example using pollution control materials, such as a heavy metal of this invention containing all dolomite type compounds, ferrous sulfate, and a polymeric material, about the soil acidified in the long term, the material age is 7 days. The arsenic elution amount in the 180-day test soil is all within the soil elution amount standard, the test solution pH is within the uniform drainage standard range, and the corn index at age 7 is 400 kN / m ² or more. It has been clarified that the above-described effects of the invention can be effectively expressed.

For the pollution control material C1 such as heavy metal that does not contain the polymer material of Comparative Example 2, the corn index slightly increased compared to the test soil itself of Comparative Example 1, but it is less than 400 kN / m ² and the effect is insufficient. there were.
This is because the corn index is slightly improved as compared with Comparative Example 1 because ettringite and hydrate are precipitated by calcium ions and magnesium ions eluted from dolomite compounds and sulfate ions eluted from ferrous sulfate. However, it is considered that the solidification performance did not reach a satisfactory level because it did not have the effect of agglomerating fine particles in the soil by not containing the polymer material.

  About anti-contamination material C2 such as heavy metals shown in Comparative Example 3, the effect of insolubilization to arsenic was reduced because the content of MgO was small.

  The anti-pollution material C3 such as heavy metal shown in Comparative Example 4 is excellent in the arsenic insolubilization effect because the MgO content is as high as 12.2% by mass, but since the C3 is alkaline, the soil eluate pH is all ages. It became alkaline.

  About the pollution control material C4, such as a heavy metal which does not contain ferrous sulfate shown in the comparative example 5, soil elution pH became alkaline at all ages. The amount of arsenic elution exceeded the soil elution amount standard.

  About pollution control material C5, such as a heavy metal shown in the comparative example 6, since there were many compounding quantities of ferrous sulfate, pH of C5 became neutral. Therefore, the pH acidified as the acidification of the soil progressed, and the soil eluate pH became acidic after the age of 91 days.

  The anti-contamination material C6 such as heavy metal shown in Comparative Example 7 contains 60% by mass of hemihydrate gypsum with a small amount of dolomite compound and no pH buffering ability. Therefore, the pH acidified as the acidification of the soil progressed, and the soil eluate pH became acidic after the age of 91 days, and the arsenic elution amount increased accordingly.

The anti-contamination material for heavy metals and the like, and the anti-contamination method for heavy metals using the countermeasure material of the present invention can efficiently insolubilize heavy metals and halogens contained in acid soil and soil that is acidified over the long term, Since the soil can be solidified and improved in strength while being kept near neutral for a long time from the beginning, it can be effectively used for soil modification where heavy metals and halogens elute, such as tunnels and dams. It can be effectively applied to the treatment of contaminated soil from which heavy metals generated in large quantities due to excavation work or construction work are eluted.

Claims (5)

It is a pollution control material that solidifies and insolubilizes heavy metals in acidic soil and long-term acidified soil, and contains dolomite compounds, acidic sulfates and polymer materials as essential components, and acidic sulfates are ferrous sulfate In the total amount of dolomite compound and ferrous sulfate , ferrous sulfate is contained in a proportion of 1 to 20% by mass, and the polymer material is based on the total amount of dolomite compound and ferrous sulfate. In addition, it is contained at a rate of 0.1 to 10% by mass, and contains 6 to 12% by mass of MgO and 30.6 to 53.4% by mass of semi-baked dolomite in a pollution control material such as heavy metals. Features anti-contamination materials such as heavy metals. 2. The heavy metal pollution control material according to claim 1, wherein the dolomite compound contains CaMg (CO ₃ ) ₂ , MgO, CaCO ₃ .   3. The pollution control material for heavy metals and the like according to claim 1 or 2, wherein the pollution control material for heavy metals or the like is in an equilibrium state when the pH of the slurry obtained by mixing the pollution control material for heavy metals and water is 8 to 10. Features anti-contamination materials such as heavy metals.   A heavy metal pollution control method, comprising mixing the heavy metal pollution control material according to any one of claims 1 to 3 with acidic soil. The heavy metal pollution control method according to claim 4, wherein the pH of the treated soil obtained by mixing the heavy metal pollution control material and the acidic soil is 5.8 to 8.6 after 180 days of age. Heavy metal pollution control method.