JP7422071B2 - Heavy metal insolubilization solidification material and method for improving contaminated soil - Google Patents

Description

The present invention provides a heavy metal insolubilization solidification material that can suppress the elution of heavy metals contained in soft soil such as construction sludge and dredged soil, and can improve the soil to an appropriate strength, especially the amount of heavy metal leached from soft soil containing arsenic and lead. The present invention relates to an insolubilized solidifying material that can reduce

It has been reported that during construction sites, soft soil such as construction sludge and dredged soil contains toxic heavy metals such as arsenic and lead. Heavy metals such as arsenic and lead are pollutants regulated by environmental standards, and can affect the human body if ingested directly or in the water they elute. It is necessary to take measures such as insolubilization treatment, adsorption methods, and shielding treatment.
In addition, in the case of soft soil such as construction sludge or dredged soil, it is necessary to improve the soil to a predetermined strength through solidification treatment in order to reuse it.

As an insolubilization treatment method for soil contaminated with arsenic or lead, for example, a method of adding a Ca/Mg-based basic substance and then adding iron sulfate/hydrochloride (Patent Document 1), a method of adding iron sulfate/hydrochloride, a method of adding calcined gypsum and an Al compound, etc. It has been proposed to insolubilize and solidify in the neutral region by a method (Patent Document 2) in which Ca/Mg-containing compounds are mixed and used.
However, although the methods described in Patent Documents 1 and 2 can suppress the elution of arsenic and lead from soil, the strength development of improved soil after insolubilization is low, and it is difficult to recycle soft soil. is insufficient.
Regarding the treatment of arsenic-containing sludge, a three-step treatment method has been proposed (Patent Document 3) consisting of an insolubilization treatment process using an insolubilizing agent, a solidification treatment process using a solidification agent, and a drying treatment process using a desiccant agent, but the process is complicated. Therefore, it is not suitable for on-site construction. Additionally, a treatment method has been proposed in which arsenic-contaminated soil is heat-treated at 200 to 700°C and then Ca compounds and water are added (Patent Document 4), but such high-temperature heat treatment is also not suitable for on-site construction. .

On the other hand, cement is widely used as a cementitious solidifying agent for soft soil, and is also effective in insolubilizing heavy metals. However, for soils with a high clay content or heavy metal content, conventional cement-based solidifying agents are not sufficient to insolubilize arsenic and lead, and in order to meet the environmental standards for heavy metal elution, cement If the amount of solidification agent added is increased, there is a concern that the strength of the improved soil will become excessive, which will impede the recycling of soft soil.

Patent Documents 5 to 9 disclose various cement-based solidifying materials or insolubilizing materials. That is, Patent Document 5 discloses a contaminated soil insolubilizing material consisting of a main material mixed with gypsum, quicklime or cement, and pulverized blast furnace slag, and a pH adjuster that suppresses strong alkalization of the soil by the main material. Disclose. Patent Document 6 discloses an additive for a cement-based solidifying material and a method for improving volcanic ash soil, which is made by blending slaked lime and lightly calcined dolomite in a predetermined ratio with a cement-based soil solidifying material. Patent Document 7 discloses the use of slaked lime containing 5 to 40% by volume of particles with a particle size of 30 μm or more as the slaked lime in a soil solidification material containing cement clinker, gypsum, and slaked lime. Patent Document 8 discloses a cement-based treatment material for heavy metal-contaminated soil containing Portland cement, blast furnace slag, and gypsum in a predetermined ratio, and a method for solidifying and insolubilizing heavy metal-contaminated soil. Patent Document 9 discloses a ground improvement method in which cement raw material powder (preheater raw material) extracted from a cement kiln preheater is mixed with a cement-based solidifying material. The preheater raw material contains a large amount of quicklime produced by thermal decomposition of limestone in the cement raw material.

Japanese Patent Application Publication No. 2006-205169 Japanese Patent Application Publication No. 2010-207659 Japanese Patent Application Publication No. 2005-103429 Japanese Patent Application Publication No. 2006-167617 Japanese Patent Application Publication No. 2012-055819 JP2011-256324A Japanese Patent Application Publication No. 2010-159347 Japanese Patent Application Publication No. 2007-222694 Japanese Patent Application Publication No. 2000-120059

The present invention provides a heavy metal insolubilization solidification material that can suppress the elution amount of arsenic and lead from soft contaminated soil containing arsenic and lead and exhibit appropriate strength development properties as improved soil, and a method for improving contaminated soil. The purpose is to

In order to solve the above-mentioned problem, the present inventor found that the above-mentioned problem could be solved by combining slaked lime with a specific cement-based solidifying material.

That is, the present invention is a heavy metal insolubilization solidification material that solidifies soft soil or sludge containing arsenic and lead as heavy metals to make improved soil, and suppresses the elution of arsenic and lead from the improved soil. It is characterized by containing a cementitious solidifying material consisting of slag and gypsum, and slaked lime or lightly calcined dolomite, and the blending amount of slaked lime is 10 to 55% by mass based on the total of the cementitious solidifying material and slaked lime or lightly calcined dolomite. It is a heavy metal insolubilization solidification material.

As the above-mentioned slaked lime, one having an average particle size of 20 μm or less and containing 72.5% by mass or more of CaO is suitable. The above-mentioned light calcined dolomite contains 93.0% by mass or more of CaO/MgO, and suitably has a fineness of 5000 cm ² /g to 7000 cm ² /g. Further, as the above-mentioned cementitious solidifying material, one containing 25 to 90% by mass of cement, 5 to 50% by mass of blast furnace slag, and 5 to 25% by mass of gypsum is suitable.

The above-mentioned heavy metal insolubilization solidification material contains 2 to 20 parts by mass of chlorides and/or sulfates of alkali metals and/or alkaline earth metals to a total of 100 parts by mass of the cement-based solidification material and slaked lime or lightly calcined dolomite. can do.

The above-mentioned heavy metal insolubilization solidification material improves soft soil or sludge into improved soil with an unconfined compressive strength of 100 to 3000 kN/ ^m2 , and improves the elution amount of arsenic and lead to 0.01 mg/L or less each. It is suitably used for this purpose.

The present invention also provides a method for improving soft soil or sludge containing arsenic and lead to increase its strength and suppress the elution of the heavy metals, wherein the heavy metal insolubilization solidification material is applied to the soil. Or, it is a method for improving soft soil or sludge, which is characterized by mixing it with sludge.
Suitable for converting soft soil or sludge into improved soil with unconfined compressive strength of 100 to 3000 kN/ ^m2 , improved soil with arsenic elution of 0.01 mg/l or less, or lead elution of 0.01 mg/l or less. It is a construction method.

According to the heavy metal insolubilization solidification material of the present invention, soft soil or sludge containing arsenic and lead can be easily solidified into improved soil of appropriate strength, and the amount of arsenic and lead eluted can be reduced to below designated environmental standards. It can be suppressed.

The heavy metal insolubilization solidification material of the present invention solidifies soft soil or sludge containing arsenic and lead as heavy metals (hereinafter, both are also referred to as soft soils or soil) into improved soil, and also removes arsenic from the improved soil. It is a heavy metal insolubilization solidification material that suppresses lead elution. This heavy metal insolubilization solidification material contains a cement solidification material and slaked lime or light calcined dolomite (hereinafter also referred to as slaked lime) as main components.

The blending ratio of the cement-based solidifying agent and slaked lime is such that the blended amount of slaked lime is 10 to 55% by mass, preferably 20 to 50% by mass, based on the total of both. If the content of slaked lime is less than 10% by mass, the strength of the improved soil will be excessive, and the insolubilization of arsenic and lead will likely be insufficient, which may impede recycling. If the amount of slaked lime added exceeds 55% by mass, not only will the strength of the improved soil be insufficient, but also the pH will increase, leading to an increase in the amount of lead leached.

Cement-based solidifying materials are solidifying materials that use cement as a base material, and are made by adding blast furnace slag or gypsum to cement as active ingredients in order to efficiently stabilize soft soils. It is more preferable to contain 25 to 90 mass % of cement, 5 to 50 mass % of blast furnace slag, and 5 to 25 mass % of gypsum in 100 mass % of cement-based solidifying material.
As the cement, JIS standard products (JIS R 5210 to 5214) or clinker, which is an intermediate raw material when manufacturing Portland cement, can be used. That is, examples include Portland cement, blast furnace cement, silica cement, fly ash cement, ecocement, and mixed cement, with Portland cement and blast furnace cement being preferred.
Examples of blast furnace slag include slowly cooled slag and granulated slag, and granulated slag with latent hydraulic properties is suitable.
As the plaster, anhydrite is suitable.
Although there are cements such as blast furnace cement that contain blast furnace slag and gypsum, it is understood that the amount of blast furnace slag and gypsum that is mixed into cement as a cementitious solidifying agent of the present invention is added separately from this. Ru.
The cementitious solidifying material can be produced by mixing the respective powders or by pulverizing them. The particle size of the cement solidifying material has a Blaine specific surface area of 4000 cm ² /g or more, preferably 5000 cm ² /g or more.
The particle size of the heavy metal insolubilized solidifying material, which is a cement-based solidifying material blended with slaked lime or light calcined dolomite, has a Blaine specific surface area of 7000 cm ² /g or more, preferably 8000 cm ² /g or more when slaked lime is blended. When light calcined dolomite is blended, the Blaine specific surface area is 5000 cm ² /g or more, preferably 6000 cm ² /g or more. The upper limit is not particularly limited, but from the viewpoint of pulverization limit, it is about 12000 cm ² /g.

The blending ratio of slaked lime or lightly calcined dolomite is preferably in the range of 10 to 55% by mass in the heavy metal insolubilization solidification material.
As the slaked lime, a JIS standard product (JIS R 9001) can be used. Preferably, it is a special issue, and one containing 72.5% by mass or more of CaO is suitable. Slaked lime also contains compounds that can become slaked lime when mixed with soil. Preferably it is quicklime.
Moreover, the average particle diameter (d50) of slaked lime is preferably 20 μm or less, more preferably 10 μm or less.
As the light calcined dolomite, JIS standard products (JIS R 9001) can be used. Preferably, it is a special issue, and one containing 93.0% by mass or more of CaO/MgO and 30.0% by mass or more of MgO is suitable.
The fineness (specific surface area) is preferably 5000 to 7000 cm ² /g. Here, the fineness is a value obtained after mixing lightly calcined dolomite with a cement solidifying material and the like and pulverizing it.

In order to suppress the elution amount of arsenic and lead, the heavy metal insolubilizing solidifying material of the present invention contains, in addition to the above cementitious solidifying material and slaked lime, chlorides and/or sulfates of alkali metals and/or alkaline earth metals. It is recommended to mix.
The chloride preferably includes calcium chloride or sodium chloride, and the sulfate preferably includes magnesium sulfate, sodium sulfate, or calcium sulfate, and these can be used alone or in a mixture of two or more. .
The chloride and/or sulfate is preferably blended in an amount of 2 to 20 parts by mass, preferably 7 to 15 parts by mass, based on a total of 100 parts by mass of the cement solidifying agent and slaked lime.

The heavy metal insolubilization solidification material of the present invention may contain other components such as concrete admixtures and inorganic powders, if necessary. In addition, the components of the heavy metal insolubilization solidification material may be mixed in advance or simultaneously at the construction site, but if they are mixed in advance, the quality stability of the product will be excellent.

The heavy metal insolubilization solidification material of the present invention is used to treat soft soil or sludge to improve soil.
Soft soil is generally referred to as muddy soil, which is soil that is generated during construction or dredging and exhibits fluidity, and has a strength of less than 200 kN/ ^m2 in terms of Cone index, or uniaxial compression. There is soil with a strength of approximately 50kN/ ^m2 or less.
Sludge can be deposited in aquariums, rivers, ponds, lakes, ocean beds, etc., but since it has a high moisture content and is highly fluid, it must be left on land to dry out to some extent, or it can be removed from soil with low moisture content. It is advisable to mix and pre-treat to adjust the moisture content.

The soil preferably has a water content of 10 to 200% by mass, preferably 20 to 50% by mass. An appropriate amount of moisture is necessary for the heavy metal insolubilized solidification material to solidify and develop strength, but if it is in excess, the strength improvement effect will be poor.
Further, it is suitable for soil with a wet density of 1 to 3 g/cm ³ , preferably 1.5 to 2.50 g/cm ³ .
In addition, soft soils containing heavy metals such as arsenic and lead are targeted. The contents of arsenic and lead are not particularly limited, but each kg of soil preferably contains 1.0 mg or more, preferably 10.0 mg or more. There is no upper limit, but if it is about 200 mg or less, the elution amount can be reduced to the emission standard value (0.01 or less) in improved soil after solidification.
The solidification material and improved construction method of the present invention are particularly effective in soft soil containing a large amount of clay. Soil is usually composed of clay and sand, and soil with a lot of clay is called clayey soil, and conversely, soil with a lot of sand is called sandy soil. The present invention is effective in treating clay soil containing 50% by mass or more of clay or sandy soil containing 30% by mass or more of clay based on the total amount of clay and sand.

When insolubilizing and solidifying soft soil using the heavy metal insolubilizing solidifying material of the present invention, the heavy metal insolubilizing solidifying material is applied in an amount of 10 to 300 kg, preferably 30 to 200 kg, particularly preferably 1 m ³ of soft soil to be treated. It is recommended to use 50 to 150 kg. Further, the amount of slaked lime contained in the heavy metal insolubilization solidification material is preferably in the range of 5 to 55 kg per 1 m ³ of soft soil. More preferably, it is in the range of 10 to 55 kg.

The heavy metal insolubilization and solidification material of the present invention makes it possible to transform soft soil into improved soil with an unconfined compressive strength of 100 to 3000 kN/m ² . In particular, it becomes possible to make improved soil with an unconfined compressive strength of 300 to 2000 kN/m ² , and further to 800 to 1800 kN/m ² .
The heavy metal insolubilization solidification material of the present invention can solidify soft soil to a predetermined strength as described above, and can reduce the amount of arsenic and lead eluted. Preferably, it is also possible to reduce the elution amount of arsenic or lead to an environmental standard value (0.01 mg/L or less). Note that the measurement of the elution amount follows the conditions of the example.

EXAMPLES Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to the following Examples. In addition, unless otherwise specified, parts are parts by mass, and % is mass %.

The materials used for the heavy metal insolubilization solidification material are shown below.
Ordinary Portland Cement (OPC) Manufactured by Nippon Steel Cement Co., Ltd. Blaine specific surface area 3340 cm ² /g
Blast furnace slag Made by Nippon Steel Anhydrous gypsum Made in Thailand Specially selected slaked lime Made by Hokkaido Lime Kako Co., Ltd. (CaO: 73.5%, average particle size: 4.8 μm)
Light calcined dolomite manufactured by Kurosaki Harima Co., Ltd. (CaO/MgO: 97.0%, MgO: 39.5%, fineness: 6140 cm ² /g)

The above OPC alone was used as a cement solidifying material (I). Also called cement (I).
57.0 parts by mass of the above OPC, 34.7 parts of blast furnace slag, and 8.3 parts of gypsum were mixed and crushed to obtain a cement-based solidifying material (II) having a Blaine specific surface area of 6310 cm ² /g. Also called cement (II).

Using the following soil materials and heavy metal compounds (reagents), mix soil that has been dried at a temperature of 50 degrees for 2 days and heavy metal reagents dissolved in distilled water for 3 minutes with a soil mixer to determine the water content ratio, Simulated contaminated soils with adjusted amounts of heavy metals were created (soils A to E).
Arakida Soil, Akagi Gardening, Crushed Sand, Shiraoi Product
No. 8 silica sand, Tohoku Silica Sand Co., Ltd. Disodium hydrogen arsenate heptahydrate (special grade), Kanto Kagaku Co., Ltd. Lead nitrate (II), Kanto Kagaku Co., Ltd.

Table 1 shows the composition, soil quality, water content, density, and heavy metal content of soils A to E.
In Table 1, the unit of wet density is (g/cm ³ ), the unit of arsenic and lead content (upper row) is (mg/kg), and the unit of arsenic and lead elution amount (lower row) is (mg/L). The amount is in parts.
The elution amount was measured by preparing a test solution in accordance with Ministry of the Environment Notification No. 46 and using ICP emission spectrometry.

Reference examples 1 to 4
Cement solidification agent (II) was mixed into soils A to D at a concentration of 100 kg/m ³ , and the arsenic elution amount and unconfined compressive strength were measured after 7 and 28 days. The results are shown in Table 2.

From Table 2, it can be seen that as the amount of sand in the soil increases, the amount of arsenic eluted decreases, and in soil D of Reference Example 4, it is possible to insolubilize arsenic to below the environmental standard value even in cement-based solidification materials. . However, as the amount of clay (Arakita soil) increases, the amount of arsenic eluted increases, and it is clear that it is difficult to insolubilize it with cement-based solidifying agents.

Examples 1 to 8, Comparative Examples 1 to 5
The above soil E was mixed with a heavy metal insolubilizing solidifying material made by blending cement-based solidifying material (II) and slaked lime, and the elution amount and unconfined compressive strength were measured after 7 days. The results are shown in Table 3. Note that Table 3 also shows the Blaine specific surface area of the heavy metal insolubilization solidification material.

Table 3 shows that if slaked lime is not added, insolubilization of arsenic is insufficient, and as the amount of slaked lime increases, the amount of arsenic eluted decreases, but the amount of lead eluted increases. Furthermore, it can be seen that when the cement-based solidifying material (I) containing OPC alone is used instead of the cement-based solidifying material (II), the insolubilization of lead or arsenic becomes insufficient. This shows that the blast furnace slag contained in the cement solidifying agent (II) is effective in suppressing the amount of elution. That is, by using OPC, blast furnace slag, gypsum, and slaked lime (10 to 55% by mass), the elution amount of arsenic and lead can be kept below the environmental standard value.

Examples 9-14
The simulated soil E was mixed with a cement-based solidifying agent (II) and a heavy metal insolubilizing solidifying agent containing chloride in addition to slaked lime, and the elution amount and unconfined compressive strength were measured after 7 days. The results are shown in Table 4. Table 4 also shows the Blaine specific surface area of the heavy metal insolubilization solidification material.

Examples 15-20
The simulated soil E was mixed with a cement-based solidifying agent (II) and a heavy metal insolubilizing solidifying agent containing sulfate in addition to slaked lime, and the elution amount and unconfined compressive strength were measured after 7 days. The results are shown in Table 5. Note that Table 5 also shows the Blaine specific surface area of the heavy metal insolubilization solidification material.

From Tables 4 and 5, it can be seen that the amount of lead elution can be further suppressed by using a heavy metal insolubilization solidification material which is a mixture of cement-based solidification material (II) and slaked lime with chloride or sulfate.

Examples 21-27
The above soil E (soil under the same conditions as in Table 3) was mixed with a heavy metal insolubilization solidification material made by blending cement-based solidification material (II) and lightly calcined dolomite, and the elution amount and uniaxial compressive strength were measured after 7 days. We measured the The results are shown in Table 6. Note that Table 6 also shows the Blaine specific surface area of the heavy metal insolubilization solidification material.

From Table 6, similarly to slaked lime, light calcined dolomite has the effect of insolubilizing arsenic and lead, and the amount of arsenic and lead eluted can be suppressed.

According to the present invention, soft soil or sludge containing arsenic and lead can be easily solidified into improved soil of appropriate strength, and the amount of arsenic and lead elution can be suppressed to below designated environmental standards. Therefore, it is very useful as a heavy metal insolubilization solidification material that can improve the strength of soft soils contaminated with heavy metals and suppress the amount of arsenic and lead elution, and as a method for improving soft soil or sludge.

Claims (10)

A heavy metal insolubilization solidification material that solidifies soft soil or sludge containing arsenic and lead as heavy metals to make improved soil and suppresses the elution of arsenic and lead from the improved soil, and is made of cement, blast furnace slag, and gypsum. A heavy metal containing a cement-based solidifying agent and slaked lime (but not containing an alum stone component or aluminum sulfate ), the amount of slaked lime being 10 to 55% by mass based on the total of the cement-based solidifying agent and slaked lime. Insolubilization solidification material. The heavy metal insolubilization solidification material according to claim 1, wherein the slaked lime has an average particle size of 20 μm or less and contains 72.5% by mass or more of CaO. The heavy metal insolubilization solidification material according to claim 1 , wherein the cementitious solidification material contains 25 to 90% by mass of cement, 5 to 50% by mass of blast furnace slag, and 5 to 25% by mass of gypsum. The heavy metal insolubilization solidification according to claim 1, wherein 2 to 20 parts by mass of chlorides and/or sulfates of alkali metals and/or alkaline earth metals are mixed with a total of 100 parts by mass of the cement solidifying agent and slaked lime. Material. The heavy metal insolubilization solidification material according to claim 1, which is used for converting soft soil or sludge into improved soil having an unconfined compressive strength of 100 to 3000 kN/m ² . The heavy metal insolubilization and solidification material according to claim 1, which is used to transform soft soil or sludge into improved soil with an arsenic elution amount of 0.01 mg/l or less or a lead elution amount of 0.01 mg/l or less. A method for improving soft soil or sludge that improves soft soil or sludge containing arsenic and lead to increase its strength and suppress the elution of the heavy metals, wherein the heavy metal insolubilization solidification material according to claim 1 is applied to the soil or sludge. A method for improving soft soil or sludge, which is characterized by mixing it with sludge. The method for improving soft soil or sludge according to claim 7 , wherein the heavy metal insolubilization solidification agent is mixed with the soil or sludge so that the amount of slaked lime added to the soft soil or sludge is 5 to 55 kg/m ³ . The method for improving soft soil or sludge according to claim 7 , wherein the soft soil or sludge is made into improved soil with an unconfined compressive strength of 100 to 3000 kN/m ² . The method for improving soft soil or sludge according to claim 7 , wherein the soft soil or sludge is improved to have an arsenic elution amount of 0.01 mg/l or less, or a lead elution amount of 0.01 mg/l or less.