JP2023135692A - Solidification insolubilization neutral modifier and low fluidization mud modification method using the same - Google Patents

Abstract

To provide a novel solidification insolubilization neutral modifier and a low fluidization mud modification method, capable of preventing low fluidization mud which is subjected to low fluidization by blending dredge oil having high fluidization property by affection of high water content and a frother, or mud such as shield generation soil or the like, to a mud-added material being an organic polymer emulsion, from becoming in a mud state again, achieving insolubilization of a heavy metal eluted from soil, achieving solidification performance for improving intensity of treated soil and modifying the same, and modifying a pH of construction generation soil to a neutral region.SOLUTION: There is provided a solidification insolubilization neutral modifier comprising: as essential content components, magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and/or porous volcanic ash soil, and polymer coagulant. The solidification insolubilization neutral modifier includes, 0.1-20 mass%, 3 mass% or greater and less than 25 mass% of aluminum sulfate, 10 mass% or less of ferrous sulfate, 50 mass% or greater of calcium carbonate and/or porous volcanic ash soil, and 0.1-10 mass% of polymer coagulant. The ferrous sulfate is included by a smaller content than a content of the aluminum sulfate, and a total amount of the aluminum sulfate and the ferrous sulfate is greater than 3 mass% and equal to or less than 25 mass%.SELECTED DRAWING: None

Description

The present invention relates to a solidified, insolubilized, neutral modifier and a low-fluidization mud modification method using the modifier, and in particular, a solidified, insolubilized, neutral modifier for low-fluidization mud, and a method using the modifier. This relates to a low-fluidization mud reforming method, and is used for soils that have been made low fluidity by using organic polymer emulsion-type mud reforming materials, blowout prevention agents, etc., such as high water content dredged soil and shield-generated soil. By adding it, it can reduce elution by insolubilizing and adsorbing heavy metals such as arsenic, bring the soil pH to a neutral range, and improve the strength of compacted soil, such as the Cone index. The present invention relates to a solidified, insolubilized, neutral soil reforming material that has soil reforming performance, and a low-fluidization mud reforming method using the soil reforming material.

Conventionally, muddy soil such as dredged soil and shield generated soil has a high water content and is highly fluid due to the influence of foaming agents, so it has to be dehydrated and dried by temporary storage to maintain a specified strength. However, it was difficult to remove the product from the site. Therefore, there were many cases where it took a long time to carry out the shipment.
In addition, many of these muddy soils contain naturally occurring heavy metals such as arsenic and lead at low concentrations, and in order to effectively utilize these soils for embankments, etc., it is necessary to obtain a certain level of strength. In addition to reforming the soil, it is necessary to insolubilize heavy metals and other substances to below the standard value for elution, and to maintain the reformed soil in a neutral range to reduce the impact on vegetation and aquatic organisms.

In order to improve the handling of these highly hydrated muds such as dredged soil and shield generated soil in a short time and to reduce their fluidity, muddying materials mainly composed of emulsions containing organic polymers are generally used. May be added and processed. Note that the "mud material" is also referred to as a mud modifying material or a blowout prevention agent (hereinafter referred to as "mud material").
It is possible to agglomerate high water content mud and modify it to have a certain degree of strength using mud additives, but if added in large quantities, it may have an impact on aquatic organisms, and Additive materials have poor performance in insolubilizing heavy metals, etc., and in adjusting pH.For solidification performance to develop strength and insolubilization of heavy metals, etc., solidifying and insolubilizing materials are added to satisfy the specified performance. I had to.

Conventional solidifying agents include cement-based solidifying agents, MgO (magnesium oxide)-based solidifying agents, quicklime, and blast furnace slag-based materials, but cement, quicklime, etc. have the effect of making the pH of the soil strongly alkaline. Because of this, strongly alkaline groundwater flows into the surrounding environment due to rainfall, which is undesirable as it may affect vegetation. Furthermore, 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.
There are also gypsum-based solidification agents that keep the modified soil neutral, but they tend to have inferior solidification performance compared to cement-based solidification materials and magnesium oxide-based solidification materials.

Further, as conventional insolubilizing materials, MgO-based insolubilizing materials, semi-baked dolomite-based insolubilizing materials, iron-based insolubilizing materials, and aluminum-based insolubilizing materials are known.
However, with MgO-based insolubilizers, after soil reformation, the soil pH is 10 or more, which is highly alkaline, and the pH of the insolubilized soil remains high for a long time, causing high pH groundwater to flow into the surrounding environment, causing vegetation to grow. There are concerns about the impact on
Semi-calcined dolomite is alkaline with a pH of 9 to 10, iron-based insolubilizers are mainly in the form of iron salts and are acidic, and aluminum-based insolubilizers include polyaluminum chloride and aluminum sulfate, which are acidic. It is something.

Many proposals have been made that combine a conventional solidifying agent and an insolubilizing agent and use an MgO-based insolubilizing agent as a base material so that the amended soil becomes neutral. For example, Japanese Patent No. 6936003 (Patent No. Document 1) describes (A) 100 parts by mass of a metal salt consisting of either or both of a metal sulfate and a metal chloride, (B) 5 to 50 parts by mass of a solidified and insolubilized material consisting of magnesium oxide, quicklime or slaked lime, (C) 10 to 100 parts by mass of a thickening material; and (D) 500 to 600 parts by mass of an auxiliary material; A soil reforming material is described, which is one or more selected from polymers, and the auxiliary material (D) is one or more selected from gypsum hemihydrate, calcium carbonate, bentonite, and activated clay. has been done.

Furthermore, Patent No. 6021706 (Patent Document 2) states that gypsum is 21 to 39% by weight, magnesium oxide is 14 to 35% by weight, aluminum sulfate is 15 to 25% by weight, and blast furnace slag is 21 to 39% by weight. Japanese Patent Laid-Open No. 2021-134320 (Patent Document 3) describes a soil solidification agent characterized by containing magnesium oxide and at least one type of sulfuric acid among aluminum sulfate, ferrous sulfate, and gypsum. Disclosed is a neutral solidifying material comprising a salt and a polymer flocculant having an acrylamide unit and a sodium acrylate unit, the composition ratio of the acrylamide unit constituting the polymer flocculant being 55 to 90 mol%. There is.

Further, Patent No. 6503812 (Patent Document 4) discloses that an inorganic powder composition consisting of 15 to 55% by mass of lightly burnt magnesium oxide, 35 to 80% by mass of aluminum sulfate, and 3 to 20% by mass of ferrous sulfate; Disclosed is a neutral solidifying material characterized by containing 1 to 12 parts by mass of tiles per 100 parts by mass of the inorganic powder composition.

The above conventional materials improve strength and insolubilization performance through soil solidification using alkaline MgO-based materials, and insolubilize arsenic etc. by combining with acidic materials such as acidic ferrous sulfate and aluminum sulfate at a predetermined mixing ratio. However, by further enhancing the solidification performance with other contained components and auxiliary materials, it is intended to neutralize the pH of the soil while exhibiting solidification and insolubilization performance.

However, these neutral solidifying materials have a problem in that they inhibit the strength development performance of soil that has been rendered low fluid by adding a muddying material whose main component is an emulsion containing an organic polymer.
The main component of these muddying materials is an emulsion of polyacrylamide, which is an organic polymer, and in order to avoid affecting aquatic toxicity, materials that are predominantly negatively charged and anionic are used. The organic polymers adsorb to the positively charged soil particles contained in the mud, proceeding with cross-linking, and agglomerate while absorbing pore water in the soil, making it possible to make the mud less fluid. . In this state, when a large amount of water-soluble materials such as iron and aluminum from which acidic substances and polyvalent cations, especially trivalent cations, are eluted, they react with the polymer, neutralizing the charge and forming the organic polymer. The problem is that the crosslinked structure is cut and disturbed, the pore water contained in the organic polymer flows out, the soil becomes muddy again, and its strength decreases. In particular, neutral solidifying materials containing a large amount of MgO in order to impart strength development properties require the addition of a large amount of acidic ferrous sulfate or aluminum sulfate for neutralization, which will cause the organic polymer in the muddying material to There is a problem in that the retained pore water is allowed to flow out, weakening the strength development, and posing the risk of long-term strength reduction.

Patent No. 6936003 Patent No. 6021706 Japanese Patent Application Publication No. 2021-134320 Patent No. 6503812

The purpose of the present invention is to solve the above-mentioned problems, and to reduce the amount of mud by adding a muddying agent, which is an organic polymer emulsion, to muddy soil such as dredged soil or shielding soil, which has high fluidity due to the influence of high water content and foaming agents. The fluidized low-fluidization mud can insolubilize heavy metals etc. leached from the soil without re-sludge, and has solidification performance that improves and improves the strength of treated soil, as well as improving the pH of construction soil. An object of the present invention is to provide a novel solidified and insolubilized neutral modifying material that can be modified to a neutral region.

Another object of the present invention is to reduce fluidity by blending muddying material, which is an organic polymer emulsion, into muddy soil such as dredged soil and shield soil, which have high fluidity due to the influence of high water content and foaming agents. The solidified insolubilized neutral modifier of the present invention is applied to the low-fluidized mud to insolubilize heavy metals, etc., and improve the strength and neutralize the pH by solidifying the treated soil. It is an object of the present invention to provide a low fluidization mud reforming method using the solidified insolubilized neutral reforming material of the present invention, which can exhibit performance.

The present invention was achieved based on the discovery that the above-mentioned problems can be solved by including a specific material as an essential ingredient and including it in a specific blending ratio.

(1) The solidified and insolubilized neutral modifying material of the present invention contains magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and/or porous volcanic ash, and a polymer flocculant as essential components. 0.1 to 20% by mass, aluminum sulfate from 3% to less than 25% by mass, ferrous sulfate to 10% by mass or less, calcium carbonate and/or porous volcanic ash to 50% by mass or more, polymer flocculant It is contained in a proportion of 0.1 to 10% by mass, the content of ferrous sulfate is less than the content of aluminum sulfate, and the total amount of aluminum sulfate and ferrous sulfate is more than 3% by mass and 25% by mass or less. It is a solidified, insolubilized and neutral modified material.

(2) In the solidified and insolubilized neutral modifier of (1) above, the polymer flocculant is characterized by having polyacrylamide as its main component and having a viscosity of 400 mPa·s or more when made into a 0.25% aqueous solution. It is a solidified, insolubilized, neutral modifying material.

(3) The solidified insolubilized neutral modifier of (1) or (2) above is a solidified insolubilized neutral modifier characterized by being in powder form.
(4) The solidified and insolubilized neutral modifier described in any one of (1) to (3) above is a modifier used for low-fluidized mud containing a muddying material whose main component is an organic polymer emulsion. The organic polymer emulsion, which is the main component of the muddying material, is a solidified and insolubilized neutral modifier characterized by being a polyacrylamide emulsion.

(5) The low-fluidization mud reforming method of the present invention uses the solidified insolubilized neutral modifier described in any of the above (1) to (4) as a muddying material whose main component is an organic polymer emulsion. This is a low fluidity mud reforming method characterized by using it in combination with low fluidity mud containing.

(6) In the low fluidity mud reforming method described in (5) above, the amount of arsenic eluted when the pH of the treated soil obtained by mixing the solidified and insolubilized neutral modifier with the mud is 5.8 to 8.6. This is a low fluidization mud reforming method characterized by a cone index of 0.01 mg/L or less and a cone index of 200 kN/m ^{2 or} more.

In addition, in the present invention, "low fluidity mud" refers to mud that is defined in the Ministry of Land, Infrastructure, Transport and Tourism's "Standards for Use of Generated Soil" by adding and blending known muddying agents to reduce the fluidity of mud. Specifically, it refers to muddy soil such as highly water-containing dredged soil or shield-generated soil, which is mixed with known muddying agents such as organic polymer emulsions to give a cone index of 50 to about 50. This refers to soil with reduced mud fluidity of 400 kN/ ^m2 .

The solidified and insolubilized neutral modifier of the present invention is added to muddy soil and soft soil such as high water content dredged soil and shield generated soil, especially soil that has been treated to have low fluidity with an organic polymer emulsion type muddying agent. By doing so, it does not impede the water fixation and low fluidity performance of muddying materials (no re-sludge), and it also prevents the elution of heavy metals such as arsenic by insolubilizing and adsorbing them over a long period of time. It has soil reforming performance, such as being able to reduce the soil pH, maintain the pH of the soil after reformation in the neutral range, and improve the strength performance such as the Cone index of compacted soil. , can produce excellent effects.
In addition, the low-fluidization mud reforming method of the present invention uses the solidified insolubilized neutral modifying material of the present invention for muddy soil and soft soil such as high water content dredged soil and shield generated soil, especially organic polymer emulsion type muddying material. By mixing it with soil that has been treated to reduce fluidity with muddying materials, etc., it does not impede the water fixation and low fluidity properties of muddying materials (no re-sludge), and also removes heavy metals such as arsenic. Through long-term insolubilization and adsorption, it is possible to reduce the elution of heavy metals, etc., maintain the pH of soil after modification in the neutral range, and improve the strength performance such as the Cone index of compacted soil. Therefore, it becomes possible to effectively modify muddy soil such as high water content dredged soil and shield generated soil.
In the present invention, the term "neutral range" means a pH range of 5.8 to 8.6, which is the neutral range defined by the Uniform Effluent Standards of the Ministry of the Environment.

The present invention will be explained by the following preferred embodiments, but is not limited thereto.
The solidified and insolubilized neutral modifier of the present invention contains magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and/or porous volcanic ash, and a polymer flocculant as essential components, and contains 0.1% of magnesium oxide. ~20% by mass, aluminum sulfate 3% by mass or more and less than 25% by mass, ferrous sulfate 10% by mass or less, calcium carbonate and/or porous volcanic ash soil 50% by mass or more, polymer flocculant 0.1% by mass During solidification and insolubilization, the content of ferrous sulfate is less than that of aluminum sulfate, and the total amount of aluminum sulfate and ferrous sulfate is more than 3% by mass and less than 25% by mass. It is a sex modifying material.

The solidified and insolubilized neutral modifier of the present invention is preferably a low-fluidized mud that is obtained by adding a muddying agent such as an organic polymer emulsion to a highly water-containing mud such as dredged soil or shield generated soil to reduce fluidization. It is desirable to apply it to
As the mudding material, a known mudding material can be used, and for example, a mudding material mainly composed of an organic polymer emulsion type, such as a polyacrylamide emulsion, can be suitably used.
Although it is possible to improve the strength of highly water-containing mud to a certain degree by adding such muddying materials, the obtained low-fluidized mud is difficult to drive on such low-fluidized mud with heavy machinery such as trucks. is a low-fluidized mud with a cone index of about 50 to about 400 kN/ ^m2 , which is still not strong enough, and is a target to which the solidified insolubilized neutral modification material of the present invention is applied. The soil is preferably such a low fluidization mud.
By applying the solidified and insolubilized neutral modifier of the present invention to such soil, the water in the highly water-containing mud will not flow out of the pore water held in the polymers in the muddy material. Therefore, it is possible to have the above effects without re-silting.

The solidified and insolubilized neutral modifier of the present invention is preferably in powder form. Being in powder form makes it easier to handle and work at the construction site, and when mixed with low-fluidization mud, it can efficiently adsorb and insolubilize heavy metals dispersed in the soil. .
Furthermore, by making the solidified and insolubilized neutral modifying material of the present invention in powder form, it comes into contact with moisture in the soil to generate hydrates, making it easier to aggregate the soil, thereby improving the strength of the soil. This makes it possible to improve soil efficiently.

Here, heavy metals and the like mean heavy metals and halogens. Examples of heavy metals include one or more of manganese, chromium, copper, cadmium, mercury, selenium, lead, arsenic, and cadmium, as well as single heavy metals and their compounds. Examples of halogens include fluorine and other heavy metals. Examples include simple substances such as , chlorine, and compounds thereof, but are not limited to these heavy metals and halogens. Furthermore, in addition to these, simple boron and its compounds included in the Class 2 Specified Hazardous Substances specified in the Soil Contamination Countermeasures Law (Kansui Daido Hatsu No. 1703313: Ministry of the Environment) can be exemplified.

In the present invention, the solidified and insolubilized neutral modifier contains magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and/or porous volcanic ash, and a polymer flocculant as essential materials. By setting each content within the above range, heavy metals, etc. can be effectively insolubilized, and the strength of the treated soil can be improved without draining the pore water retained in low fluidity mud. By improving the solidification performance, the soil can be improved, and the above-mentioned effects such as maintaining the pH of the treated soil in the neutral range can be achieved at the same time.

Magnesium oxide contained in the solidified and insolubilized neutral modifier of the present invention mainly exhibits strength development performance and heavy metal insolubilization performance, and reacts with water in the low-fluidization mud to become magnesium hydroxide. It has an insolubilizing effect that adsorbs heavy metals, such as arsenic and fluorine, and precipitates poorly soluble compounds on magnesium hydroxide. .
Magnesium oxide can be contained in the solidified and insolubilized neutral modifier of the present invention using a magnesium oxide-containing substance, such as semi-calcined dolomite (MgO.CaCO ₃ ). It is not limited.

Magnesium oxide is contained in the solidified insolubilized neutral modifier in an amount of 0.1 to 20% by mass, preferably 0.5 to 15% by mass, and more preferably 1 to 12% by mass.
Within the above range, particularly, solidification performance is excellent, strength development is good, and heavy metals can be effectively solidified and insolubilized. If it is less than 0.1% by mass, the solidification performance will be poor, and strength development and heavy metal insolubilization performance will be reduced. If it exceeds 20% by mass, the pH of the soil will tend to become strongly alkaline, and acidic substances for neutralization will be used. An increase in the blending amount is undesirable because it may reduce the water fixing ability of the muddy material and cause a decrease in strength.

In addition, the aluminum sulfate contained in the solidified and insolubilized neutral modifier of the present invention mainly exhibits strength and insolubilization performance, and reacts with water in the low-fluidization mud to precipitate aluminum hydrate and fix water. It can lower the apparent water content by oxidation, and also has an insolubilizing effect that allows heavy metals to be adsorbed on the surface.
Aluminum sulfate can be applied both in anhydrous and/or hydrated form.

Aluminum sulfate is contained in the solidified and insolubilized neutral modifier in an amount of 3% by mass or more and less than 25% by mass, preferably 5 to 22% by mass, and more preferably 8 to 20% by mass.
Within the above range, particularly, solidification performance is excellent, strength development is good, and heavy metals can be effectively solidified and insolubilized. If it is less than 3% by mass, solidification performance will be poor and strength development and heavy metal insolubilization performance will be reduced, and if it is more than 25% by mass, it may inhibit the water fixing ability of the muddy material and cause a decrease in strength, so it is not desirable. do not have.

Furthermore, due to its high reducing action, ferrous sulfate contained in the solidified and insolubilized neutral modifier of the present invention has a strong reducing effect on heavy metals such as arsenic and hexavalent chromium, and on iron hydroxide precipitated by hydration. It has an insolubilizing effect through arsenic adsorption and precipitation of poorly soluble iron arsenate, etc., and is acidic, so by adjusting the blending ratio of other essential materials, the solidified insolubilized neutral modifier of the present invention can be used. This makes it possible to maintain treated soil in a neutral region.
In addition, ferrous sulfate is presumed to have an effect as an inorganic flocculant, and is used in the solidification insolubilization neutral modifier of the present invention to electrically flocculate fine particles in the soil and make it easier to aggregate. It is also thought that its inclusion has the effect of making it easier to compact the soil.

Ferrous sulfate is contained in the solidified and insolubilized neutral modifier in an amount of more than 0% by mass and less than 10% by mass, preferably 1 to 8% by mass, more preferably 2 to 6% by mass.
If the content exceeds the above content, the moisture contained in the muddy material will be released due to the reaction with the muddying material contained in the low fluidity mud, resulting in re-sludge formation, which may lead to a decrease in strength. Yes, undesirable.

Further, the content of aluminum sulfate is greater than the content of ferrous sulfate, and the total content of both is more than 3% by mass and not more than 25% by mass.
With such a total content, aluminum sulfate that releases a large amount of acid and aluminum ions can effectively exhibit the above effects. Aluminum ions are converted into aluminum hydroxide in a short time by hydration, so unlike ferrous sulfate, there is a lower risk of pore water flowing out of the muddying material over the long term, so it is added in a larger amount than ferrous sulfate.

Furthermore, the calcium carbonate and/or porous volcanic ash contained in the solidified and insolubilized neutral modifier of the present invention can mainly exhibit solidification performance and pH neutralization function. It has a pH buffering effect due to the bicarbonate buffering effect, making it possible to maintain the pH of the treated soil at a neutral level over a long period of time. Furthermore, calcium carbonate can lower the moisture content of soil by reacting with aluminum sulfate to precipitate dihydrate gypsum and fixing moisture.
Calcium carbonate and/or porous volcanic ash soil is contained in the solidified insolubilized neutral modifier in an amount of 50% by mass or more, preferably 60 to 85% by mass, more preferably 70 to 80% by mass.
If it is less than 50% by mass, sufficient strength development cannot be obtained, which is undesirable.

An example of the porous volcanic ash soil is Kanuma soil. Kanuma soil is a porous volcanic ash soil that is produced naturally and in large quantities mainly in Tochigi Prefecture.As it is weakly acidic, it not only has a pH neutralizing function, but also has the ability to fix moisture within its pores. Pore water in the soil can be reduced, and soil reforming performance can be developed at an early stage. A suitable particle is a dried one with a water content of 20% or less, and the maximum particle size is 3 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less. The mixing performance with the above-mentioned materials is improved, and the above-mentioned effects can be produced more effectively. Furthermore, by using fine Kanuma soil that is not used as a commercially available product, Kanuma soil can be used effectively.
Calcium carbonate and Kanuma soil may be used alone or in combination.

Furthermore, the polymer flocculant contained in the solidified and insolubilized neutral modifier of the present invention reacts with moisture in the soil, aggregates fine particles of the soil, and facilitates compaction of the soil. In addition, since it has a high viscosity, it is difficult to reduce its viscosity even when it reacts with iron ions, so it has the ability to develop the strength of soil.
The properties of the polymer flocculant include that it is easily soluble in cold water, that the pH of the aqueous solution is in the neutral range, and that the effective pH range covers the neutral range in order to correspond to various low fluidity soils. It is preferable that the viscosity increases when dissolved in water.

As the polymer flocculant, an organic polymer flocculant that has the effect of reacting with moisture in the soil and flocculating fine particles to facilitate soil compaction can be suitably used. As for the type, at least one selected from the group consisting of anionic polymer flocculants, nonionic polymer flocculants, cationic polymer flocculants, and amphoteric polymer flocculants can be preferably used, and particularly preferred. It is an anionic polymer flocculant that has a neutral solution pH, an effective pH range that includes the neutral range, and a high viscosity.

As the organic polymer flocculant, at least one selected from the group consisting of polyacrylamide, polyacrylic ester, polyamidine, sodium polyacrylate, polyethylene oxide, and sodium acrylate-acrylamide copolymer can be used. In particular, it is desirable that the viscosity of a 0.25% aqueous solution be 400 mPa·s or more.

Regarding the particle size of the organic polymer flocculant contained in it, in terms of strength development, the finer the particle size, the faster the reaction with water and the faster the effect, but the moisture fixing ability is affected by ferrous sulfate, etc. In order to ensure that the reforming performance does not deteriorate, the polymer flocculant will be dissolved in water with a delay after the reaction of the acidic sulfate in order to carry out the reaction with a time lag, and the content will be as follows, and the particle size will be 2 mm or less in maximum particle size. The thickness is preferably 0.05 mm to 1 mm, more preferably 0.1 mm to 0.5 mm.

The content of the polymer flocculant is 0.1 to 10% by mass, preferably 1 to 8% by mass, and more preferably 3 to 6% by mass in the solidified and insolubilized neutral modifier.
If it is less than 0.1% by mass, sufficient strength development cannot be obtained, and if it exceeds 10% by mass, the cost will increase, making it undesirable and uneconomical.

The solidified and insolubilized neutral modifier of the present invention contains the above-mentioned essential ingredients of magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and/or porous volcanic ash, and a polymer flocculant in the above-mentioned proportions. As a result, the concentration of heavy metals such as arsenic in the test solution prepared in accordance with the Environment Agency Notification No. 46 (promulgated on August 23, 1991) can be measured in accordance with JIS K 0102 "Industrial Wastewater Test Method". The pH of the test solution was measured in accordance with JIS Z8802: 2011 "pH measurement method" to be in the neutral range (the uniform wastewater standard of the Ministry of the Environment (5.8 to 8.0). 6)), and without re-silting, the cone index can be increased to 200 kN/m2 or ^more , which is specified for type 4 construction generated soil in the soil classification standards of the Ministry of Land, Infrastructure, Transport and Tourism's ``Standards for Generated Soil Utilization.'' It becomes possible to reform the soil to more preferably 400 kN/m ² or more, which is Type 3 construction generated soil, and even more preferably 800 kN/m ^{2 or} more, which is Type 2 construction generated soil.

Further, in addition to the above-mentioned materials, auxiliary additives can be blended within a range that does not affect the above-mentioned effects of the solidified and insolubilized neutral modifier of the present invention. Examples of auxiliary additives include calcium oxide, gypsum, zeolite, bentonite, and the like to impart strength.

The solidified and insolubilized neutral modifier of the present invention includes the above magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and/or porous volcanic ash, a polymer flocculant, and auxiliary additives contained as necessary. As long as they can be mixed uniformly, they can be mixed all at once regardless of the order of mixing, or they can be prepared by mixing these materials using any method.

The solidified and insolubilized neutral modifier of the present invention prepared in this manner can be added to and mixed with low fluidization mud treated with a muddying agent to effectively remove heavy metals, etc. in the soil. It can be insolubilized over a long period of time, has the ability to improve soil by solidifying the treated soil to improve its strength, and can maintain the pH of the treated soil in a neutral range without being re-sludged.
Specifically, the solidified and insolubilized neutral modifier of the present invention is added and mixed to the low-fluidization mud at a rate of, for example, 10 to 200 kg/m ³ and the soil pH is adjusted to neutral (5 .8 to 8.6), and heavy metals such as arsenic are insolubilized to below the elution standard value as mentioned above, and the Cone index of compacted soil is used as the soil strength according to the fourth standard for the use of generated soil. Modify the soil to 200 kN/ ^m2 or more, which is type 2 construction generated soil, more preferably 400 kN/m2 or ^more , which is type 3 construction generated soil, and even more preferably 800 kN/m2 or more, which is type ² construction generated soil. becomes possible.

The low fluidity mud reforming method of the present invention is a method of mixing the solidified insolubilized neutral modifier of the present invention with low fluidity mud, but the mixing method is not particularly limited. The solidified insolubilized neutral modifier of the present invention is spread on the surface layer of fluidized mud, and it can be improved using heavy machinery with surface modification mixing performance, or mixed with soil in mixing equipment, similar to conventional powdered insolubilized materials. A mixing method using soil mixing equipment can be used. As described above, by applying the low fluidity mud reforming method of the present invention to soil, the pH of the soil can be brought into the neutral range (5.8 to 8.6).

In particular, the solidified and insolubilized neutral modifier of the present invention is preferably used in powder form, and as a mixing device with low fluidization soil, a backhoe, deep mixing machine, stationary mixer, power blender, etc. The amount of solidified, insolubilized, and neutral modifier mixed into the treated soil varies depending on the water content ratio of the soil, the required solidification strength of the treated soil, etc., and can be designed as desired. can. As a specific example, it is possible to add and mix the muddy material in a mud storage tank and then spread it and mix it with heavy machinery, or to mix it using conventional soil mixing equipment such as soil reforming equipment.

In this way, the solidified and insolubilized neutral modifier of the present invention can be applied to low-fluidity mud, such as dredged soil and shield-generated soil, which have high fluidity due to the influence of high water content and foaming agents. (including heavy metals, etc.), the pore water captured by the muddying material in the soil will not flow out, the heavy metals, etc. will be insolubilized, the solidification performance of the soil will be improved, and the treated soil It becomes possible to maintain the pH in the neutral range.
For example, all elution amounts of heavy metals, etc. in the soil measured based on the Soil Contamination Countermeasures Act are within the soil elution amount standards, and are compliant with the Environment Agency Notification No. 46 (promulgated on August 23, 1991). For example, after 7 days of age, the pH of the test solution prepared by this method can satisfy the environmental standard of 5.8 to 8.6 stipulated by the Ministry of the Environment's Uniform Effluent Standards. 200 kN/m ² or more specified as type 4 construction generated soil in the soil classification standards of the Ministry of Land, Infrastructure, Transport and Tourism's "Generated soil usage standards", more preferably 400 kN/m ² or more as type 3 construction generated soil, and Preferably, it becomes possible to improve the soil to 800 kN/m ² or more, which is the second type of construction generated soil, and it can be designed to allow heavy machinery such as trucks to run on it.

The present invention will be illustrated by the following examples and comparative examples.

(Test soil)
A muddying material containing polyacrylamide emulsion as a main component was added in an amount of 3 kg/ ^m3 to muddy soil having the physical properties shown in Table 1 below from which arsenic is eluted, mixed at low speed for 90 seconds with a soil mixer, and then After scraping off the soil adhering to the soil mixer container and paddle, the mixture was mixed again at low speed for 90 seconds to prepare test soil.

Regarding the water content ratio, wet density, fine particles with a particle size of less than 75 μm, arsenic elution amount and eluate pH of mud soil, and the Cone index of mud soil (before addition of mud addition) and test soil (after addition of mud addition), It is shown in Table 1.
The arsenic elution amount and Cohn index were measured according to the methods described in Test Examples 1 and 2 below.

(Raw materials used)
In preparing the solidified and insolubilized neutral modifier, the following materials were used.
・Magnesium oxide: fine powder (reagent, manufactured by Kanto Kagaku Co., Ltd.)
・Aluminum sulfate: powder (reagent, 14-18 hydrate, manufactured by Kanto Kagaku Co., Ltd.)
・Calcium carbonate: Powder (Kudzu production in Tochigi Prefecture)
・Porous volcanic ash soil: Kanuma soil (produced in Tochigi Prefecture, classified to 1mm or less after drying at 105℃)
・Ferrous sulfate: Ferrous sulfate hydrate fine powder (manufactured by Sakai Chemical Industry Co., Ltd.)
・Polymer flocculant: Anionic polymer flocculant (manufactured by Sanyo Chemical Industries, Ltd.) (0.25% aqueous solution, viscosity 420 mPa/s, maximum particle size 1 mm)

(Solidified insolubilized neutral modifier)
Examples 1 to 8, Comparative Examples 1 to 7
Using each of the raw materials used above, each raw material was blended and mixed in the proportions shown in Table 2 below to prepare each solidified and insolubilized neutral modifier.
Although the mixing order of each raw material is not particularly limited, each raw material was mixed at the same time to prepare each solidified and insolubilized neutral modifier.

(Test example)
Test example 1: Modification test (insolubilization test and neutralization confirmation test)
50 kg of each of the solidified and insolubilized neutral modifiers shown in Table 2 was added to 1 m ³ of the test soil in Table 1 above, and after mixing at low speed in a soil mixer for 90 seconds, it adhered to the container and paddle of the soil mixer. The soil was scraped off and mixed again at low speed for 90 seconds to prepare each treated soil.
After each treated soil was prepared, it was sealed and cured at 20°C for 7 days, and then the 7-day treated soil was treated in accordance with the Environment Agency Notification No. 46 (promulgated on August 23, 1991). Prepare a test solution (eluate), and measure the pH of the eluate (test solution) and the concentration of arsenic in the eluate (test solution) as the arsenic elution amount in accordance with JIS K 0102 "Factory wastewater test method". was measured.
The results are shown in Table 3 below.

Test Example 2: Soil Strength Test 50 kg of each of the solidified and insolubilized neutral modifiers shown in Table 2 was added to 1 m ³ of the test soil in Table 1 above, and after mixing at low speed with a soil mixer for 90 seconds, The soil adhering to the container and paddle of the soil mixer was scraped off and mixed again at low speed for 90 seconds to prepare treated soil.
After preparing each treated soil and curing it in a hermetically sealed manner at 20°C for 7 days, the treated soil was placed in three layers in a 10 cm mold specified in JIS A 1210:2009 "Test method for soil compaction by compaction". The materials were filled separately and the cone index at 7 days of age was measured in accordance with JIS A 1228 "Cone index test method for compacted soil."
The results are shown in Table 3 below.

As a reference example, the pH of the test solution, the amount of arsenic elution, and the Cohn index were measured in the same manner for the test soil in which the solidified and insolubilized neutral modifier was not mixed with the soil in Table 1 above, and the results are shown in Table 3. show.

Exam passing criteria:
The cone index was passed if it was 400 kN/m ² or higher, which is specified for type 3 construction generated soil in the soil classification standards of the Ministry of Land, Infrastructure, Transport and Tourism's ``Standards for Generated Soil Use.''
The amount of arsenic eluted was judged to have passed if it was less than the standard 0.01 mg/L for leached arsenic based on the Soil Contamination Countermeasures Act.
Furthermore, the pH of the eluate test solution was considered to be in the neutral range and passed if it fell within the range of 5.8 to 8.6 specified by the uniform wastewater standards of the Ministry of the Environment.

From Table 3 above, examples (E1 ～E8) The solidified and insolubilized neutral modifier is used to reduce the amount of arsenic eluted in the treated soil after 7 days of age for soil made by adding a muddying agent to high water content fluidized mud. The amount of soil elution is within the standard, the pH of the soil eluate is uniformly within the wastewater standard range, and the cone index at 7 days of age is 400 kN/m2 or ^more , and the above effects of the present invention can be effectively expressed. One thing became clear.

Regarding the solidified and insolubilized neutral modifier C1 of Comparative Example 1, which has an excessive content of magnesium oxide and an insufficient content of calcium carbonate and/or porous volcanic ash, the Cohn index and the arsenic elution amount standards are satisfied. However, the pH of the soil eluate is not in the neutral range, which is an environmental problem.
In addition, the solidified insolubilized neutral modifying material C2 with an excessive aluminum sulfate content of Comparative Example 2 met the arsenic elution standard, but the pH of the soil eluate was in the acidic range, and compared to the test soil, the soil elution pH was in the acidic range. Although the index increased, the cone index was less than 400 kN/m ² and the solidification performance was not sufficient.

In Comparative Example 3, solidified insolubilized neutral modifier C3 that does not contain aluminum sulfate, the pH of the soil eluate was in the neutral range, but the arsenic elution amount exceeded the standard, and the Cohn index increased compared to the test soil. However, the cone index is less than 400 kN/ ^m2 , and the solidification performance is not sufficient.
In addition, regarding the solidified insolubilized neutral modifier C4 of Comparative Example 4, which has an excessive ferrous sulfate content, the arsenic elution amount standard is met and the soil eluate pH is in the neutral range, and compared to the test soil, the corn Although the index increased, the cone index was less than 400 kN/m ² and the solidification performance was not sufficient.

Regarding the solidified insolubilized neutral modifier C5 that does not contain ferrous sulfate of Comparative Example 5, it satisfies the Cohn index and the pH of the soil eluate is in the neutral range, but it does not meet the arsenic elution amount standard.
Regarding the solidified and insolubilized neutral modifier C6 of Comparative Example 6, which contains excessive amounts of aluminum sulfate and ferrous sulfate exceeding 25%, the arsenic elution amount standard is met and the soil eluate pH is also in the neutral range. However, although the cone index increased compared to the test soil, the cone index was less than 400 kN/m ² and the solidification performance was not sufficient.

Regarding the solidified and insolubilized neutral modifier C7 that does not contain a polymer flocculant in Comparative Example 7, the arsenic elution amount standard is met and the soil eluate pH is in the neutral range, but the Cohn index increases compared to the test soil. However, the cone index was less than 400 kN/m ² and the solidification performance was not sufficient.

The solidification and insolubilization neutral modifier of the present invention and the low fluidity mud modification method using the modifier effectively insolubilizes heavy metals and halogens contained in mud, especially in mud that has been treated to have low fluidity with a muddying agent. In addition, it is possible to solidify the soil and improve its strength while keeping the treated soil near the neutral region, so it can be effectively used for low fluidity soil containing muddying materials, for example. It can be effectively applied to the treatment of heavy metals, etc. in muddy soil with high water content and fluidity, which is generated in large quantities by excavation work and construction work of tunnels and dams, etc., and makes it easier to use modified soil effectively. becomes possible.

Claims (6)

Magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and/or porous volcanic ash, and a polymer flocculant are essential components, with 0.1 to 20% by mass of magnesium oxide and 3% by mass or more of aluminum sulfate. Contains less than 25% by mass, 10% by mass or less of ferrous sulfate, 50% by mass or more of calcium carbonate and/or porous volcanic ash, 0.1 to 10% by mass of a polymer flocculant, A solidified and insolubilized neutral modification material, characterized in that the content of iron is less than that of aluminum sulfate, and the total amount of aluminum sulfate and ferrous sulfate is more than 3% by mass and less than 25% by mass. The solidified and insolubilized neutral modifier according to claim 1, wherein the polymer flocculant is mainly composed of polyacrylamide and has a viscosity of 400 mPa·s or more when made into a 0.25% aqueous solution. Solidified and insolubilized neutral modification material. The solidified insolubilized neutral modifier according to claim 1 or 2, wherein the solidified insolubilized neutral modifier is in a powder form. The solidified and insolubilized neutral modifier according to any one of claims 1 to 3 is a modifier for use in low-fluidized mud containing a muddying material containing an organic polymer emulsion as a main component; The organic polymer emulsion, which is the main component of the mud material, is a solidified and insolubilized neutral modifier characterized by being a polyacrylamide emulsion. A low-fluidization mud, characterized in that the solidified and insolubilized neutral modifier according to any one of claims 1 to 4 is used in combination with a low-fluidization mud containing a muddying material whose main component is an organic polymer emulsion. Fluidized mud reforming method. In the low-fluidization mud reforming method according to claim 5, the treated soil obtained by mixing the solidified and insolubilized neutral modifier with the mud has a pH of 5.8 to 8.6 and an eluted amount of arsenic of 0.01 mg. /L or less, and the cone index is 200kN/ ^m2 or more.