WO2019244856A1

WO2019244856A1 - Heavy metal-insolubilized solidification material and technique for improving contaminated soil

Info

Publication number: WO2019244856A1
Application number: PCT/JP2019/023984
Authority: WO
Inventors: 智彦金沢; 奈那西川
Original assignee: 日鉄セメント株式会社
Priority date: 2018-06-22
Filing date: 2019-06-18
Publication date: 2019-12-26
Also published as: JP7422071B2; JPWO2019244856A1

Abstract

Provided are: a heavy metal-insolubilized solidification material which can improve the strength of loose soil contaminated by a heavy metal and can also reduce the elution amounts of arsenic and lead; and a technique for improving loose soil or sludge. A heavy metal-insolubilized solidification material which can solidify loose soil or sludge containing a heavy metal to produce improved soil and which can prevent the elution of arsenic and lead from the improved soil, the heavy metal-insolubilized solidification material being characterized by comprising a cement-based solidification material that comprises cement, a blast-furnace slag and gypsum and lime hydrate or light-burnt dolomite, wherein the amount of lime hydrate or light-burnt dolomite added is 10 to 55% by mass relative to the total amount of the cement-based solidification material and lime hydrate or light-burnt dolomite; and a technique for improving loose soil or sludge using the heavy metal-insolubilized solidification material.

Description

Improvement method of heavy metal insolubilized solidified material and contaminated soils

The present invention can suppress the elution of heavy metals contained in soft soil such as construction sludge and dredged soil, and can improve the heavy metal insolubilized solidifying material that can be improved to soil of appropriate strength, particularly the amount of heavy metal elution from soft soil containing arsenic and lead. The present invention relates to an insolubilized solidified material capable of reducing the solidification.

In field construction, it has been reported that soft soil such as construction sludge and dredged soil contains heavy metal harmful substances such as arsenic and lead. Heavy metals such as arsenic and lead are pollutants regulated by environmental standards and may affect the human body if taken directly or ingested eluted water. It is necessary to take measures such as insolubilization, adsorption, and shielding.
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 by a solidification treatment in order to reuse the soil.

As a method of insolubilizing soil contaminated with arsenic or lead, for example, a method of adding a Ca / Mg-based basic substance and then adding a sulfate / hydrochloride of iron (Patent Document 1), calcined gypsum and an Al compound It has been proposed to insolubilize and solidify in a neutral region by a method of using and mixing a Ca / Mg-containing compound with a compound (Patent Document 2).
However, the methods described in Patent Literatures 1 and 2 can suppress the elution of arsenic and lead from soil, but have low strength expression of improved soil after insolubilization, and recycle soft soil. Is not enough.
With respect to the treatment of arsenic-containing sludge, a three-step treatment method (Patent Document 3) comprising an insolubilization treatment step using an insolubilizing agent, a solidification treatment step using a solidifying material, and a drying treatment step using a desiccant has been proposed. It is not suitable for on-site construction. In addition, a treatment method in which arsenic-contaminated soil is heated at 200 to 700 ° C. and then a Ca compound and water are added (Patent Document 4), but such a high-temperature heating treatment is not suitable for construction on site. .

On the other hand, cement is widely used as a cement-based solidifying material for soft soil, and is also effective in insolubilizing heavy metals. However, for soils with high clay content and heavy metal content, conventional cement-based solidification materials are not sufficient for insolubilizing arsenic and lead. When the addition amount of the solidifying agent is increased, the strength of the improved soil becomes excessive, and there is a concern that the recycling of the soft soil is hindered.

Patent Documents 5 to 9 disclose various cement-based solidifying materials or insolubilizing materials. That is, Patent Literature 5 discloses a contaminated soil insolubilizing material including a main material obtained by mixing gypsum, quicklime or cement, and blast furnace slag fine powder, and a pH adjuster for suppressing strong alkalinization of the soil by the main material. Disclose. Patent Literature 6 discloses an additive for a cement-based solidification material obtained by mixing slaked lime and lightly burned dolomite in a predetermined ratio with a cement-based solidification material for a soil, and a volcanic ash soil improvement method. Patent Document 7 discloses that, in a soil solidifying material containing cement clinker, gypsum and slaked lime, slaked lime containing 5 to 40% by volume of particles having a particle diameter of 30 μm or more is used as slaked lime. Patent Document 8 discloses a cement-based treatment material for heavy metal-contaminated soil containing Portland cement, blast furnace slag, and gypsum at a predetermined ratio, and a method for solidifying and insolubilizing heavy metal-contaminated soil. Patent Literature 9 discloses a ground improvement method using a cement-based solidified material mixed with a cement raw material powder (preheater raw material) extracted from a cement firing furnace preheater. The preheater raw material contains a lot of quicklime produced by thermal decomposition of limestone in the cement raw material.

JP 2006-205169 A JP 2010-207659 A JP 2005-103429 A JP 2006-167617 A JP 2012-055819 A JP 2011-256324 A JP 2010-159347 A JP 2007-222694A JP 2000-120059 A

The present invention provides a heavy metal insolubilized solidified material capable of suppressing the arsenic and lead elution amount of softly contaminated soil containing arsenic and lead and exhibiting appropriate strength development as an improved soil, and an improved method for contaminated soils. The purpose is to do.

The present inventor has found that in order to solve the above problems, the above problems can be solved by combining slaked lime with a specific cement-based solidifying material.

That is, the present invention is a heavy metal-insolubilized solidified material that solidifies soft soil or sludge containing arsenic and lead as heavy metals to improve soil and suppresses elution of arsenic and lead from the improved soil, including cement, blast furnace It contains a cement-based solidification material consisting of slag and gypsum, and slaked lime or lightly burnt dolomite. The blended amount of slaked lime is 10 to 55% by mass based on the total of the cement-based solidification material and slaked lime or lightly burnt dolomite. Heavy metal insolubilized solidified material.

As the slaked lime, those having an average particle diameter of 20 μm or less and containing CaO of 72.5% by mass or more are suitable. The lightly fired dolomite contains 93.0% by mass or more of CaO.MgO and has a fineness of 5,000 cm ² / g to 7000 cm ² / g. As the cement-based solidifying material, those 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 are suitable.

The heavy metal-insolubilized solidified material contains 2 to 20 parts by mass of an alkali metal and / or alkaline earth metal chloride and / or sulfate based on 100 parts by mass of the cement solidified material and slaked lime or lightly burnt dolomite in total. can do.

The heavy metal-insolubilized solidified material is used to convert soft soil or sludge into an improved soil having an unconfined compressive strength of 100 to 3000 kN / m ² , in which the arsenic and lead elution amounts are each 0.01 mg / L or less. It is preferably used for

Further, the present invention is an improved method for improving soft soil or sludge containing arsenic and lead, improving the strength of the soil and suppressing the elution of the heavy metal while increasing the strength. Alternatively, it is a method for improving soft soil or sludge characterized by mixing with sludge.
Suitable when soft soil or sludge is used as an improved soil with a uniaxial compressive strength of 100 to 3000 kN / m ² or an 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. It is a simple construction method.

According to the heavy metal insolubilized solidified material of the present invention, soft soil or sludge containing arsenic and lead can be easily solidified into an improved soil of appropriate strength, and the elution amount of arsenic and lead is below the environmental specification standard. Can be suppressed.

The heavy metal insolubilized solidified 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) to obtain improved soil, and arsenic from the improved soil. And a heavy metal insolubilized solidified material that suppresses the elution of lead and lead. The heavy metal insolubilized solidified material contains, as main components, a cement solidified material and slaked lime or lightly burnt dolomite (hereinafter also referred to as slaked limes).

配合 The compounding ratio of the cement-based solidifying material and the slaked lime is such that the compounding amount of the slaked lime is 10 to 55% by mass, and preferably 20 to 50% by mass, based on the total of both. When the amount of slaked lime is less than 10% by mass, the strength of the improved soil becomes excessive, and the insolubilization of arsenic and lead tends to be insufficient, which may hinder the recycling. If the amount of slaked lime exceeds 55% by mass, not only the strength of the improved soil becomes insufficient, but also the elution amount of lead increases because the pH increases.

The cement-based solidifying material is a solidifying material containing cement as a base material and is obtained by adding blast furnace slag or gypsum as an active ingredient to cement in order to stabilize soft soils efficiently. More preferably, the cement-based solidification material contains 100% by mass of cement, 25 to 90% by mass of cement, 5 to 50% by mass of blast furnace slag, and 5 to 25% by mass of gypsum.
As the cement, JIS standard products (JIS R 5210 to 5214) or clinker, which is an intermediate material for producing Portland cement, can be used. That is, portland cement, blast furnace cement, silica cement, fly ash cement, eco-cement and mixed cement are exemplified, but portland cement and blast furnace cement are preferred.
Examples of the blast furnace slag include gradually cooled slag and granulated slag, and granulated slag having latent hydraulic property is suitable.
As gypsum, anhydrous gypsum is suitable.
Although blast furnace slag and gypsum exist in cement such as blast furnace cement, it is understood that blast furnace slag and gypsum to be added to cement as a cement-based solidifying material of the present invention are amounts added separately from this. You.
In the production of the cement-based solidification material, either of the powders can be mixed or mixed and pulverized. Regarding the particle size of the cement-based solidification material, the Blaine specific surface area is 4000 cm ² / g or more, preferably 5000 cm ² / g or more.
The particle diameter of the heavy metal insolubilized solidified material obtained by mixing slaked lime or lightly burned dolomite with a cement-based solidified material has a specific surface area of 7000 cm ² / g or more, preferably 8000 cm ² / g or more when slaked lime is mixed. When blending the light burned dolomite, Blaine specific surface area of 5000 cm ² / g or more, preferably 6000 cm ² / g or more. The upper limit is not particularly limited, but is about 12000 cm ² / g from the viewpoint of the pulverization limit.

The mixing ratio of slaked lime or lightly burnt dolomite is preferably in the range of 10 to 55% by mass in the heavy metal insolubilized solidified material.
As slaked lime, JIS standard products (JIS R 9001) can be used. It is preferably a special name, and those containing 72.5% by mass or more of CaO are suitable. Also, slaked lime contains a compound that can become slaked lime when mixed with soil. Preferably, it is quicklime.
The average particle size (d50) of slaked lime is preferably 20 μm or less, more preferably 10 μm or less.
JIS standard products (JIS R 9001) can be used as lightly fired dolomite. It is preferably a special name, and those containing 93.0% by mass or more of CaO.MgO and 30.0% by mass of MgO are suitable.
The fineness (specific surface area) is preferably 5000 to 7000 cm ² / g. Here, the fineness is a value obtained by mixing and pulverizing lightly burned dolomite with a cement solidifying material or the like.

The heavy metal-insolubilized solidification material of the present invention further comprises, in addition to the cement-based solidification material and slaked lime, chlorides and / or sulfates of alkali metals and / or alkaline earth metals in order to suppress the leaching of arsenic and lead. Should be blended.
Chloride is preferably calcium chloride or sodium chloride, and sulfate is preferably magnesium sulfate, sodium sulfate or calcium sulfate, and these can be used alone or in combination of two or more. .
The chloride and / or sulfate is preferably used in an amount of 2 to 20 parts by mass, and more preferably 7 to 15 parts by mass, based on 100 parts by mass of the cement-based solidifying material and slaked lime.

重 The heavy metal insolubilized solidified material of the present invention may optionally contain other components such as a concrete admixture and inorganic powder. In addition, the heavy metal insolubilized solidified material may be mixed in advance with the compounding component or may be mixed at the construction site at the same time, but if mixed in advance, the quality stability of the product is excellent.

The heavy metal insolubilized solidified material of the present invention is used for treating soft soil or sludge to obtain improved soil.
The soft soil, commonly referred to as mud, there is a state exhibiting fluidity of the soil caused by the construction or dredging such as the strength, or less than the cone index 200 kN / m ^2, or uniaxial compression Some soils have a strength of about 50 kN / m ² or less.
There are sludges deposited in aquariums, rivers, ponds, lakes, marshes, sea floors, etc., but these have a large amount of water and a large fluidity. It is advisable to mix and pre-treat to adjust the water content.

As the state of the soil, the soil having a water content of 10 to 200% by mass, preferably 20 to 50% by mass is good. In order for the heavy metal insolubilized solidified material to solidify and exhibit strength, appropriate moisture is required, but if it is excessive, the effect of improving strength is poor.
It is suitable for soil having a wet density of 1 to 3 g / cm ³ , preferably 1.5 to 2.50 g / cm ³ .
In addition, soft soils containing arsenic and lead as heavy metals are also targeted. The contents of arsenic and lead are not particularly limited, but may be 1.0 mg or more, preferably 10.0 mg or more, per kg of soil. There is no upper limit, but if it is about 200 mg or less, it can be reduced to the release standard value (0.01 or less) in the improved soil after solidification.
In particular, in a soft soil containing a lot of clay, the solidified material and the improved method of the present invention are effective. Soil is usually composed of clay and sand, but soil with a lot of clay is called cohesive soil, and soil with a lot of sand is called sandy soil. INDUSTRIAL APPLICABILITY The present invention is effective for treating clayey soil containing 50% by mass or more of clay with respect to the total amount of clay and sand, or sandy soil containing 30% by mass or more of clay.

In the case of using the heavy metal insolubilized solidification material of the present invention to insolubilize and solidify soft soils, the heavy metal insolubilized solidification material is 10 to 300 kg, preferably 30 to 200 kg, particularly preferably 1 m ³ of the soft soil to be treated. It is preferable to use 50 to 150 kg. Further, the addition amount of slaked lime metals contained in the heavy metal insolubilization solidifying material, to soft soils such 1 m ^3, preferably in the range of 5 ~ 55 kg. More preferably, it is in the range of 10 to 55 kg.

The heavy metal insolubilized solidified material of the present invention enables soft soils to be improved soils having a uniaxial compressive strength of 100 to 3000 kN / m ² . In particular, it becomes possible to obtain an improved soil having a uniaxial compressive strength of 300 to 2,000 kN / m ² , and further an improved soil having an 800 to 1800 kN / m ² .
The heavy metal insolubilized solidified material of the present invention can solidify soft soils to a predetermined strength as described above, and can reduce the leaching of arsenic and lead. Preferably, at least one of the elution amounts of arsenic or lead can be set to an environmental standard value (0.01 mg / L or less). The measurement of the elution amount is in accordance with the conditions of the examples.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the following Examples. Unless otherwise specified, parts are parts by mass, and% is mass%.

The materials used for the heavy metal insolubilized solidified material are shown below.
Ordinary Portland Cement (OPC) Nippon Cement Co., Ltd., Blaine specific surface area 3340 cm ² / g
Blast furnace slag Manufactured by Nippon Steel Co., Ltd. Anhydrite gypsum from Thailand Slaked lime specialty specialty Made by Hokkaido Calcium Co., Ltd. (CaO: 73.5%, average particle size: 4.8 μm)
Light-baked dolomite manufactured by Kurosaki Harima (CaO / MgO: 97.0%, MgO: 39.5%, fineness: 6140 cm ² / g)

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

The following soil materials and heavy metal compounds (reagents) were used, and a soil obtained by dissolving heavy metal reagents in distilled water and distilled water at a temperature of 50 ° C. for 2 days was mixed for 3 minutes with a soil mixer to obtain a water content ratio, Simulated contaminated soil was prepared in which the amount of heavy metals was adjusted (Soils AE).
Satoshi Arakida Akagi Horticulture Crushed sand Shiraoi No. 8 silica sand Tohoku silica sand disodium hydrogen arsenate heptahydrate (special grade) Kanto Chemical Co., Ltd. Lead nitrate (II) Kanto Chemical Co., Ltd.

Table 1 shows the composition, soil quality, water content, density, and heavy metal content of the soils A to E.
In Table 1, the unit of wet density is (g / cm ³ ), the unit of arsenic and lead content (upper) is (mg / kg), and the unit of arsenic and lead elution amount (lower) is (mg / L). The amounts are parts.
In addition, the measurement of the elution amount prepared the test solution based on the notification of Ministry of the Environment No. 46, and measured it by ICP emission spectroscopy.

Reference Examples 1-4
The soil-based cement (II) was mixed with the soils A to D at a concentration of 100 kg / m ^3, and the arsenic elution amount and the uniaxial compressive strength after 7 days and 28 days were measured. Table 2 shows the results.

From Table 2, it can be seen that the arsenic elution amount decreases as the amount of sand in the soil increases, and in the soil D of Reference Example 4, arsenic can be insolubilized to below the environmental standard value even in the cement-based solidified material. . However, as the amount of clay (Arakita soil) increases, the amount of arsenic eluted increases, indicating that it is difficult to insolubilize the cement-based solidified material.

Examples 1 to 8, Comparative Examples 1 to 5
The soil E was mixed with a heavy metal insolubilized solidified material obtained by mixing a cement solidified material (II) and slaked lime, and the elution amount and uniaxial compressive strength after 7 days were measured. Table 3 shows the results. Table 3 also shows the Blaine specific surface area of the heavy metal insolubilized solidified material.

から From Table 3, it can be seen that when slaked lime is not blended, insolubilization of arsenic becomes insufficient, the amount of slaked lime increases, and the elution amount of arsenic decreases, but the elution amount of lead increases. In addition, when the cement-based solidifying material (I) of OPC alone is used in place of the cement-based solidifying material (II), the insolubilization of lead or arsenic becomes insufficient. This indicates that the blast furnace slag contained in the cement-based solidification material (II) is effective in suppressing the amount of elution. In other words, by using OPC, blast furnace slag, gypsum and slaked lime (10 to 55% by mass), the elution amount of arsenic and lead can be made equal to or less than the environmental standard value.

Examples 9 to 14
The simulated soil E was mixed with a heavy metal insolubilized solidified material obtained by mixing chloride in addition to the cement-based solidifying material (II) and slaked lime, and the elution amount and uniaxial compressive strength after 7 days were measured. Table 4 shows the results. In addition, Table 4 also shows the Blaine specific surface area of the heavy metal insolubilized solidified material.

Examples 15 to 20
The simulated soil E was mixed with a heavy metal insolubilized solidified material obtained by mixing a sulfate in addition to the cement solidified material (II) and slaked lime, and the elution amount and uniaxial compressive strength after 7 days were measured. Table 5 shows the results. In addition, Table 5 also shows the Blaine specific surface area of the heavy metal insolubilized solidified material.

From Tables 4 and 5, it can be seen that the use of a heavy metal insolubilized solidified material obtained by mixing chloride or sulfate in addition to the cement-based solidifying material (II) and slaked lime can further suppress the amount of lead eluted.

Examples 21 to 27
The above-mentioned soil E (soil under the same conditions as in Table 3) was subjected to a mixing treatment with a heavy metal insolubilized solidified material obtained by mixing cement-based solidified material (II) and lightly burned dolomite, and the elution amount and uniaxial compressive strength after 7 days Was measured. Table 6 shows the results. Table 6 also shows the Blaine specific surface area of the heavy metal insolubilized solidified material.

から Table 6 shows that lightly burnt dolomite also has an insolubilizing effect on arsenic and lead, similar to slaked lime, 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 an improved soil having an appropriate strength, and the elution amounts of arsenic and lead can be suppressed below the environmental specification standard. Therefore, it is very useful as a heavy metal insolubilized solidified material capable of improving the strength of soft soil contaminated with heavy metals and suppressing the elution amount of arsenic and lead, and a method for improving soft soil or sludge.

Claims

A heavy metal-insolubilized solidified material that solidifies soft soil or sludge containing arsenic and lead as heavy metals to improve soil and suppresses elution of arsenic and lead from the improved soil, and comprises cement, blast furnace slag, and gypsum A heavy metal comprising a cemented solidified material and slaked lime or lightly burned dolomite, wherein the blended amount of slaked lime or lightly burned dolomite is 10 to 55% by mass based on the total of the cemented solidified material and slaked lime or lightly burned dolomite. Insolubilized solidified material.
The heavy metal insolubilized solidified 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 insolubilized solidified material according to claim 1, wherein the lightly fired dolomite contains 93.0% by mass or more of CaO.MgO and has a fineness of 5,000 to 7,000 cm 2 / g.
The heavy metal insolubilized solidified material according to claim 1 or 2, wherein the cement-based solidified 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.
2. The method according to claim 1, wherein 2 to 20 parts by mass of a chloride and / or a sulfate of an alkali metal and / or an alkaline earth metal is blended with respect to a total of 100 parts by mass of the cement-based solidifying material and slaked lime or lightly burnt dolomite. Heavy metal insolubilized solidified material.
The soft soil or sludge, heavy metal insolubilization solidifying material according to claim 1, which is used to improve soil uniaxial compressive strength 100 ~ 3000kN / m 2.
The heavy metal insolubilized solidified material according to claim 1, which is used to convert soft soil or sludge into an improved soil having 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 which improves arsenic and lead-containing soft soil or sludge by increasing strength and suppressing elution of the heavy metal, wherein the heavy metal insolubilized solidified material according to claim 1 is used for soil or sludge. A method for improving soft soil or sludge, characterized by mixing with soil.
9. The improvement of soft soil or sludge according to claim 8, wherein the heavy metal insolubilized solidified material is mixed into the soil or sludge so that slaked lime or lightly burnt dolomite is added to the soft soil or sludge in an amount of 5 to 55 kg / m 3. Construction method.
9. The method for improving soft soil or sludge according to claim 8, wherein the soft soil or sludge is converted into an improved soil having a uniaxial compressive strength of 100 to 3000 kN / m 2 .
(10) The method for improving soft soil or sludge according to claim 8, wherein the soft soil or sludge is made into an improved soil having an arsenic elution amount of 0.01 mg / l or less or a lead elution amount of 0.01 mg / l or less.