Solidified insolubilized neutral modifier and low-flow mud modification method using said modifier

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

[Technical field]

[0001] The present invention relates to a solidified insolubilizing neutral modifier and a low-fluidity mud improvement method using said modifier, in particular to a solidified insolubilizing neutral modifier for low-fluidity mud and a low-fluidity mud improvement method using said modifier, and relates to a solidified insolubilizing neutral modifier and a low-fluidity mud improvement method using said modifier, which have soil improvement performance that can reduce leaching by insolubilizing and adsorbing heavy metals such as arsenic, bring the soil pH into the neutral range, and improve the strength of the compacted soil, such as the cone index, by adding said modifier to mud such as high-water-content dredged soil or shield generated soil that has been made low-fluidity with an organic polymer emulsion-type mud modifier or an eruption prevention agent. [Background technology]

[0002] Conventionally, dredged soil, shield generated soil, and other muddy soils have a high water content and are highly fluid due to the effects of foaming agents, so unless they are temporarily stored and dehydrated and dried to a certain degree of strength, they are difficult to transport outside the site. Therefore, there were many cases where it took a long time to transport them. Furthermore, much of this mud contains naturally occurring low concentrations of heavy metals such as arsenic and lead that leach into the soil. To effectively use this soil for embankments and other purposes, it is necessary not only to modify the soil so that it has the required strength, but also to insolubilize the heavy metals so that they are below the leaching standard value, and to maintain the modified soil in a neutral range in order to reduce the impact on vegetation and aquatic life.

[0003] In order to improve the handling of high water content mud such as dredged soil and soil generated by shield tunneling in a short time and to reduce fluidity, mud-adding materials, the main component of which is an emulsion containing organic polymers, are generally added to the mud. Note that "mud-adding materials" are also called mud conditioners and eruption prevention agents (hereinafter referred to as "mud-adding materials"). It is possible to modify high water content mud soil by breaking it into aggregates and giving it a certain degree of strength using mud-adding materials, but adding large amounts can have an adverse effect on aquatic life. Furthermore, known mud-adding materials are poor at insolubilizing heavy metals and adjusting the pH, so in order to achieve the solidification performance required for strength development and the insolubilization of heavy metals, it is necessary to add further solidification or insolubilization materials to meet the required performance requirements.

[0004] Conventional solidification materials include cement-based solidification materials, MgO (magnesium oxide)-based solidification materials, and quicklime and blast furnace slag-based materials, but cement and quicklime have the effect of making the soil strongly alkaline, so that strong alkaline groundwater will flow into the surrounding environment due to rainfall, etc., and this is undesirable because it could have an impact on vegetation. In addition, because they have a low ability to immobilize heavy metals, there is a problem that heavy metals that do not dissolve in the neutral range will dissolve. There are also gypsum-based solidification materials that keep the modified soil neutral, but these tend to have inferior solidification performance compared to cement-based and magnesium oxide-based solidification materials.

[0005] Known conventional insolubilizing agents include MgO-based insolubilizing agents, semi-burnt dolomite-based insolubilizing agents, iron-based insolubilizing agents, and aluminum-based insolubilizing agents. However, after soil improvement using MgO-based insolubilizing materials, the soil becomes highly alkaline, with a pH of 10 or higher, and the pH of the insolubilized soil remains high for the long term, causing high-pH groundwater to flow into the surrounding environment, raising concerns about the impact on vegetation. Semi-burned dolomite has an alkaline pH of 9 to 10, iron-based insolubilizing materials are mainly in the form of iron salts and are acidic, and aluminum-based insolubilizing materials such as polyaluminum chloride and aluminum sulfate are also acidic.

[0006] Many proposals have been made to combine conventional solidification and insolubilization materials and use an MgO-based insolubilization material as a base material so that the modified soil becomes neutral. For example, Japanese Patent No. 6936003 (Patent Document 1) describes a soil modifier that contains (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 solidification insolubilization material consisting of magnesium oxide, quicklime, or hydrated lime, (C) 10 to 100 parts by mass of a thickening material, and (D) 500 to 600 parts by mass of an auxiliary material, wherein the thickening material (C) is one or more selected from guar gum, methyl cellulose, and polyacrylamide-sodium acrylate copolymer, and the auxiliary material (D) is one or more selected from hemihydrate gypsum, calcium carbonate, bentonite, and activated clay.

[0007] In addition, Japanese Patent No. 6021706 (Patent Document 2) discloses a soil solidification agent characterized by containing 21 to 39 weight% gypsum, 14 to 35 weight% magnesium oxide, 15 to 25 weight% aluminum sulfate, and 21 to 39 weight% blast furnace slag, while Japanese Patent Laid-Open No. 2021-134320 (Patent Document 3) discloses a neutral solidification material containing magnesium oxide, at least one sulfate salt selected from aluminum sulfate, ferrous sulfate, and gypsum, and a polymer flocculant having an acrylamide unit and a sodium acrylate unit, wherein the composition ratio of the acrylamide units constituting the polymer flocculant is 55 to 90 mol%.

[0008] Furthermore, Japanese Patent No. 6503812 (Patent Document 4) discloses a neutral solidification material that includes an inorganic powder composition consisting of 15 to 55 mass% light-burned magnesium oxide, 35 to 80 mass% aluminum sulfate, and 3 to 20 mass% ferrous sulfate, and a tile, and is characterized in that the tile is contained in an amount of 1 to 12 parts by mass per 100 parts by mass of the inorganic powder composition.

[0009] The above conventional materials use alkaline MgO-based materials to improve soil strength and insolubilization performance through soil solidification, and are combined with acidic materials such as ferrous sulfate or aluminum sulfate in a specified mixing ratio to insolubilize arsenic, etc., and further enhance the solidification performance with other contained ingredients and auxiliary materials, thereby attempting to exhibit solidification and insolubilization performance while neutralizing the soil pH.

[0010] However, these neutral solidification materials have the problem that they inhibit the strength development performance of soil that has been made low-fluidity by adding a mud-adding material whose main component is an emulsion containing organic polymers. The main component of these muddy soil materials is an emulsion of polyacrylamide, which is an organic polymer. In order to avoid the influence on aquatic toxicity, mainly negatively charged anionic materials are used. These organic polymers are adsorbed to the positively charged soil particles in the muddy soil, cross-linking progresses, and the muddy soil can be made less fluid by absorbing the pore water in the soil and forming aggregates. In this state, if a large amount of water-soluble materials such as iron or aluminum that dissolve acidic substances or polyvalent cations, especially trivalent cations, are added, the charge is neutralized by reaction with the polymer, the cross-linking structure of the organic polymer is cut and disturbed, the pore water held by the organic polymer flows out, the soil becomes muddy again, and the strength is reduced. In particular, neutral solidification materials that contain a lot of MgO to give strength development require the addition of a large amount of acidic ferrous sulfate or aluminum sulfate for neutralization, which causes the pore water held by the organic polymer in the muddy soil to flow out, weakening the strength development, and there is a problem of a long-term risk of strength reduction. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 6936003 [Patent Document 2] Patent No. 6021706 [Patent Document 3] JP 2021-134320 A [Patent Document 4] Patent No. 6503812 Summary of the Invention [Problem to be solved by the invention]

[0012] The object of the present invention is to solve the above problems and to provide a new solidifying, insolubilizing, neutral modifying material which can insolubilize heavy metals and the like eluted from the soil without re-fluidizing the mud, by mixing an organic polymer emulsion which is a mud-adding material with mud such as dredged soil or shield generated soil which has high fluidity due to high water content or the effects of foaming agents, and which has the solidifying ability to improve and modify the strength of the treated soil, as well as to modify the pH of construction generated soil to a neutral range.

[0013] Another object of the present invention is to provide a low-fluidity mud improvement method using the solidifying and insolubilizing neutral improver of the present invention, which can be used to insolubilize heavy metals, etc., and exhibit soil improvement performance such as improving the strength of the treated soil by solidifying it and neutralizing the pH, by applying the solidifying and insolubilizing neutral improver of the present invention to low-fluidity mud, which is obtained by mixing an organic polymer emulsion mud-adding material with dredged soil or shield generated soil, which has high fluidity due to high water content or the effects of foaming agents, to reduce the fluidity of the mud. [Means for solving the problem]

[0014] The present invention was made based on the discovery that the above-mentioned problems can be solved by including specific materials as essential ingredients in specific blending ratios.

[0015] (1) The solidifying, insolubilizing, neutral modifier of the present invention contains magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and / or porous volcanic ash soil, and a polymer flocculant as essential components, CaMg(CO 3 ) 2 Does not include Magnesium oxide 0.1 to 20 mass%, aluminum sulfate 3 mass% or more but less than 25 mass%, ferrous sulfate More than 0% by massThis is a solidified, insolubilized, neutral modifier characterized in that it contains 10% by mass or less of calcium carbonate, 50% by mass or more of calcium carbonate and / or porous volcanic ash soil, and 0.1 to 10% by mass of a polymer flocculant, 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.

[0016] (2) In the solidified, insolubilized neutral modifier of (1) above, the polymer flocculant is a solidified, insolubilized neutral modifier characterized in that it contains polyacrylamide as a main component and has a viscosity of 400 mPa s or more when made into a 0.25% aqueous solution.

[0017] (3) The solidified, insolubilized neutral modifier of (1) or (2) above is characterized in that it is in a powder form. (4) The solidified, insolubilized neutral modifier described in any one of items (1) to (3) above is a modifier used for low-fluidity mud containing a mud-adding agent having an organic polymer emulsion as its main component, characterized in that the organic polymer emulsion, which is the main component of the mud-adding agent, is a polyacrylamide-based emulsion.

[0018] (5) The low-fluidity mud improvement method of the present invention is a low-fluidity mud improvement method, characterized in that a solidified, insolubilized neutral improver described in any one of items (1) to (4) above is mixed with low-fluidity mud containing a mud-adding material mainly composed of an organic polymer emulsion.

[0019] (6) In the low-fluidity mud improvement method described in (5) above, the solidified insolubilized neutral improvement material is mixed with the mud to produce a treated soil having a pH of 5.8 to 8.6, an amount of arsenic elution of 0.01 mg / L or less, and a cone index of 200 kN / m 2 This is a low-fluidity mud improvement method characterized by the above.

[0020] In the present invention, the term "low-fluidity mud" refers to mud that has been reduced in fluidity by adding a known mud-adding material to the mud specified in the "Standards for the Use of Generated Soil" by the Ministry of Land, Infrastructure, Transport and Tourism. Specifically, for example, dredged soil with high water content or soil generated by shield tunneling is mixed with a known mud-adding material such as an organic polymer emulsion to reduce the fluidity of the mud. 2 This refers to soil that has reduced the fluidity of mud. Effect of the Invention

[0021] The solidifying and insolubilizing neutral improver of the present invention can be added to muddy soil or soft soil such as high-water-content dredged soil or soil generated by shield tunneling, and particularly to soil that has been treated to reduce fluidity with an organic polymer emulsion-type mud-adding material, without inhibiting the moisture fixation and fluidization performance of the mud-adding material (without re-mudification), and can reduce the leaching of heavy metals such as arsenic by insolubilizing and adsorbing them for the long term.It can also maintain the pH of the improved soil in the neutral range and improve the strength performance of the compacted soil, such as the cone index, thereby exhibiting excellent soil improvement properties. Furthermore, in the low-fluidity mud improvement method of the present invention, the solidified, insolubilized neutral improvement material of the present invention is mixed with mud or soft soil such as high-water content dredged soil or soil generated by shield tunneling, particularly soil that has been treated to reduce fluidity with an organic polymer emulsion-type mud-adding material, to thereby prevent the soil from being hindered in terms of the water fixation and low fluidity properties of the mud-adding material (without re-mudification), and to reduce the leaching of heavy metals such as arsenic by insolubilizing and adsorbing them for the long term. In addition, the pH of the soil after improvement can be maintained in the neutral range, and the strength properties of the compacted soil, such as the cone index, can be improved, making it possible to effectively improve mud such as high-water content dredged soil or soil generated by shield tunneling. In the present invention, the term "neutral range" refers to a neutral range of pH 5.8 to 8.6, which is defined by the uniform wastewater standards of the Ministry of the Environment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The present invention will be described below with reference to the preferred embodiments, but is not limited thereto. The solidified insolubilized neutral modifier of the present invention contains magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and / or porous volcanic ash soil, and a polymer flocculant as essential components, and contains 0.1 to 20 mass% magnesium oxide, 3 to less than 25 mass% aluminum sulfate, 10 mass% or less ferrous sulfate, 50 mass% or more calcium carbonate and / or porous volcanic ash soil, and 0.1 to 10 mass% polymer flocculant, with the content of ferrous sulfate being less than the content of aluminum sulfate, and the total amount of aluminum sulfate and ferrous sulfate being more than 3 mass% and 25 mass% or less.

[0023] The solidified, insolubilized neutral modifier of the present invention is preferably applied to low-fluidity mud, which has been produced by adding a mud-adding agent such as an organic polymer emulsion to high-water content mud, such as dredged soil or soil generated by shield drilling, to reduce fluidization. As the muddying material, a known muddying material can be used, and for example, a muddying material of organic polymer emulsion type, for example, a muddying material mainly composed of polyacrylamide-based emulsion, can be suitably used. Although it is possible to improve the strength of high water content mud to a certain degree by adding such mud-adding materials, the resulting low-fluidity mud is still not strong enough to run heavy machinery such as trucks on it, and the cone index is about 50 to about 400 kN / m. 2 The soil to which the solidifying, insolubilizing, neutral improver of the present invention is applied is preferably such low-fluidity mud. By applying the solidifying, insolubilizing, neutral modifier of the present invention to such soil, it is possible to achieve the above-mentioned effects without the moisture in the high-water-content mud flowing out of the interstitial water held as pore water in the polymers in the mud-adding material, and therefore without causing re-mudification.

[0024] The solidified insolubilized neutral modifier of the present invention is preferably in a powder form, which makes it easier to handle and work at the construction site, and when mixed with low-fluidity mud, it can efficiently adsorb and insolubilize heavy metals and the like dispersed in the soil. Furthermore, by making the solidified insolubilized neutral modifier of the present invention into a powder form, it can come into contact with moisture in the soil to produce hydrates, making it easier to aggregate the soil, thereby improving the strength of the soil and making it possible to efficiently modify the soil.

[0025] Here, heavy metals and the like refer to heavy metals and halogens. Examples of heavy metals include one or more of manganese, chromium, copper, cadmium, mercury, selenium, lead, arsenic, cadmium, etc., and include heavy metal elements and their compounds. Examples of halogens include elements such as fluorine and chlorine, and their compounds, but are not limited to these heavy metals and halogens. In addition to these, examples of boron elements and its compounds, which are included in the second type of specified hazardous substance specified in the Soil Contamination Countermeasures Act (Environmental Environment Agency No. 1703313), can be exemplified.

[0026] In the present invention, the essential ingredients of the solidification / insolubilization neutral modifier are magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and / or porous volcanic ash soil, as well as a polymer flocculant, and by setting the content of each of these within the above-mentioned ranges, heavy metals and the like can be effectively insolubilized, and the soil can be modified by improving the strength and solidification performance of the treated soil without allowing the pore water held in the low-fluidization mud to flow out, and the above-mentioned effects of maintaining the pH of the treated soil in the neutral range can be simultaneously achieved.

[0027] The magnesium oxide contained in the solidifying insolubilizing neutral modifier of the present invention mainly exhibits strength development performance and heavy metal insolubilization performance, and reacts with moisture in the low-fluidity mud to become magnesium hydroxide, which fixes the moisture and reduces the apparent moisture content.In addition, the magnesium hydroxide has an insolubilizing effect of adsorbing heavy metals such as arsenic and fluorine, and precipitating sparingly soluble compounds. Magnesium oxide can be contained in the solidified, insoluble neutral modifier of the present invention by using a magnesium oxide-containing substance, such as, but not limited to, semi-burnt dolomite (MgO·CaCO3).

[0028] The magnesium oxide is contained in the solidified insolubilized neutral modifier in an amount of 0.1 to 20 mass %, preferably 0.5 to 15 mass %, and more preferably 1 to 12 mass %. Within the above range, the solidification performance is particularly 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 is poor, strength development and heavy metal insolubilization performance are reduced, and if it exceeds 20% by mass, the soil pH tends to become strongly alkaline, and the amount of acidic substance blended for neutralization increases, which is undesirable as it may reduce the water fixing ability of the mud-adding material and lead to a decrease in strength.

[0029] In addition, the aluminum sulfate contained in the solidifying / insolubilizing neutral modifier of the present invention mainly exhibits strength and insolubilizing performance, and reacts with the moisture in the low-fluidization mud to precipitate aluminum hydrate, thereby fixing the moisture and reducing the apparent water content, and also has an insolubilizing effect by adsorbing heavy metals to the surface. Aluminum sulfate can be applied in both anhydrous and / or hydrated form.

[0030] The aluminum sulfate is contained in the solidified insolubilized neutral modifier in an amount of 3 mass % or more and less than 25 mass %, preferably 5 to 22 mass %, and more preferably 8 to 20 mass %. In the above range, the solidification performance is particularly excellent, strength development is good, and heavy metals can be effectively solidified and insolubilized. If it is less than 3% by mass, the solidification performance is poor, strength development and heavy metal insolubilization performance are reduced, and if it is 25% by mass or more, the water fixing ability of the mud material is inhibited, which may lead to a decrease in strength, which is undesirable.

[0031] Furthermore, the ferrous sulfate contained in the solidifying and insolubilizing neutral conditioner of the present invention has a high reducing action, which has an insolubilizing action against heavy metals such as arsenic and hexavalent chromium, by adsorbing arsenic to ferric hydroxide precipitated by hydration, and by precipitating poorly soluble ferric arsenate, etc., and because it is acidic, by adjusting the mixing ratio of other essential ingredients, it is possible to maintain soil treated with the solidifying and insolubilizing neutral conditioner of the present invention in the neutral range. In addition, ferrous sulfate is presumed to be effective as an inorganic coagulant, electrically coagulating fine particles in the soil to make them easier to form aggregates, and therefore it is thought that when included in the solidification, insolubilization, neutral modifier of the present invention, it also has the effect of making it easier to compact the soil.

[0032] The solidified insolubilized neutral modifier contains ferrous sulfate in an amount of more than 0 mass % and not more than 10 mass %, preferably 1 to 8 mass %, and more preferably 2 to 6 mass %. If the content exceeds the above range, the mud will react with the mud-adding material contained in the low-fluidity mud, causing the moisture held by the mud-adding material to be released and the mud will turn back into mud, which is undesirable as it may result in a decrease in strength.

[0033] The content of aluminum sulfate is greater than the content of ferrous sulfate, and the total content of both is greater than 3 mass % and is 25 mass % or less. By setting the total content at this level, the aluminum sulfate, which releases a large amount of acid and aluminum ions, can effectively exert the above-mentioned effects. Aluminum ions are converted into aluminum hydroxide in a short time by hydration, and unlike ferrous sulfate, there is a low risk of leaking pore water from the mud-adding material over the long term, so it is blended in larger amounts than ferrous sulfate.

[0034] Furthermore, the calcium carbonate and / or porous volcanic ash soil contained in the solidifying, insolubilizing, neutralizing modifier of the present invention mainly exhibit solidification performance and pH neutralization functions, and calcium carbonate in particular has a pH buffering effect due to its carbonate-bicarbonate buffering effect, making it possible to maintain the pH of the treated soil at neutral for a long period of time. Calcium carbonate also reacts with aluminum sulfate to precipitate gypsum dihydrate, which fixes moisture and can reduce the water content of the soil. The calcium carbonate and / or porous volcanic ash soil is contained in the solidified insolubilized neutral modifier in an amount of 50 mass % or more, preferably 60 to 85 mass %, and more preferably 70 to 80 mass %. If the content is less than 50% by mass, sufficient strength cannot be obtained, which is undesirable.

[0035] An example of porous volcanic ash soil is Kanuma soil. Kanuma soil is a porous volcanic ash soil that is naturally and abundantly produced mainly in Tochigi Prefecture. Since Kanuma soil itself is weakly acidic, it not only has a pH neutralizing function, but also reduces the interstitial water in the soil by fixing water in the pores, and can exhibit early soil improvement performance. A suitable one is a dry one with a moisture content of 20% or less and a maximum particle size of 3 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less. By using finer Kanuma soil, the mixing performance with other components is improved, and the above-mentioned effect can be more effectively achieved. In addition, by using such fine Kanuma soil that is not used as a commercially available product, it is possible to make effective use of Kanuma soil. Calcium carbonate and Kanuma soil may be used alone or in combination.

[0036] Furthermore, the polymer flocculant contained in the solidifying and insolubilizing neutral modifier of the present invention reacts with the moisture in the soil, flocculating fine particles in the soil and making it easier to compact the soil. In addition, because of its high viscosity, it is difficult for the viscosity to decrease even when it reacts with iron ions, which contributes to the development of soil strength. The properties of the polymer flocculant are preferably such that it is easily soluble in cold water, the pH of the aqueous solution is in the neutral range, the effective pH range covers the neutral range to accommodate various types of low-fluidity soil, and it becomes highly viscous when dissolved in water.

[0037] As the polymer flocculant, an organic polymer flocculant that reacts with moisture in the soil to flocculate fine particles and make the soil easier to compact can be preferably used, and as the type of organic polymer flocculant, at least one type 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 are anionic polymer flocculants that have a neutral solution pH, an effective pH range that includes the neutral range, and high viscosity.

[0038] The organic polymer flocculant may be at least one selected from the group consisting of polyacrylamide, polyacrylic ester, polyamidine, sodium polyacrylate, polyethylene oxide, and sodium acrylate-acrylamide copolymer. In particular, it is desirable to use one having a viscosity of 400 mPa·s or more in a 0.25% aqueous solution.

[0039] Regarding the particle size of the organic polymer flocculant contained, the finer it is, the faster it reacts with water in terms of strength development, and therefore the more immediate the effect. However, in order to prevent the water fixing ability from being affected by ferrous sulfate and the like, which would cause a decrease in the modification performance, the content is set as below so that the polymer flocculant dissolves in water with a delay after the reaction of the acid sulfate, and the particle size is desirably a maximum particle size of 2 mm or less, preferably 0.05 mm to 1 mm, and even more preferably 0.1 mm to 0.5 mm, in order to allow the reaction to occur with a time lag.

[0040] The content of the polymer flocculant in the solidified insolubilized neutral modifier is 0.1 to 10 mass %, preferably 1 to 8 mass %, and more preferably 3 to 6 mass %. If it is less than 0.1% by mass, sufficient strength cannot be obtained, whereas if it exceeds 10% by mass, the cost increases, which is uneconomical and undesirable.

[0041] The solidified, insoluble, neutral modifier of the present invention, by mixing the above-mentioned magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and / or porous volcanic ash soil, and the essential ingredients of the polymer flocculant in the above-mentioned ratio, can reduce the concentration of heavy metals such as arsenic in a test solution prepared according to the method in accordance with the Environment Agency Notification No. 46 (promulgated on August 23, 1991) to 0.01 mg / L or less when measured in accordance with JIS K 0102 "Factory Wastewater Test Method", and can bring the pH of the test solution into the neutral range (the Ministry of the Environment's uniform wastewater standard (5.8 to 8.6)) when measured in accordance with JIS Z8802:2011 "pH Measurement Method", and can also reduce the cone index to 200 kN / m, which is specified for Type 4 construction generated soil in the soil quality classification standard in the Ministry of Land, Infrastructure, Transport and Tourism's "Regarding the Utilization Standards for Generated Soil", without re-mudification. 2 More preferably, 400kN / m 2 More preferably, it is 800kN / m 2 It is possible to improve the above.

[0042] In addition to the above-mentioned materials, auxiliary additives can be added within a range that does not affect the above-mentioned effects of the solidifying, insolubilizing, neutral modifier of the present invention. Examples of auxiliary additives include calcium oxide, gypsum, zeolite, and bentonite, which are used to impart strength.

[0043] The solidified insolubilized neutral modifier of the present invention can be prepared by mixing the above-mentioned magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and / or porous volcanic ash soil, as well as the polymer flocculant and auxiliary additives contained as necessary, in any order and can be mixed all at once, or by mixing these materials using any method, as long as the materials can be mixed uniformly.

[0044] The solidifying, insolubilizing neutral modifier of the present invention prepared in this manner can be added and mixed with low-fluidity mud soil, particularly mud soil that has been treated with a mud-adding material, to effectively insolubilize heavy metals and other substances in the soil for the long term, and has the soil modifier ability of improving the strength of the treated soil by solidifying it without causing it to re-mud, while also being able to maintain the pH of the treated soil in the neutral range. Specifically, the solidified, insolubilized, neutral modifier of the present invention is applied to the low-fluidity mud at a rate of, for example, 10 to 200 kg / m 3 The soil pH is neutralized (5.8-8.6) after 1-7 days of mixing, heavy metals such as arsenic are insoluble below the elution amount standard value as mentioned above, and the cone index of the compacted soil is increased to 200 kN / m, which is the fourth type of construction waste soil specified in the waste soil utilization standard. 2 More preferably, 400kN / m 2 More preferably, it is 800kN / m 2 It is possible to improve the above.

[0045] The low-fluidity mud improvement method of the present invention is a method of mixing the solidified insolubilized neutral improver of the present invention with low-fluidity mud, but the mixing method is not particularly limited. For example, the solidified insolubilized neutral improver of the present invention can be spread on the surface of the low-fluidity mud, and the mud can be improved with heavy machinery having surface improvement mixing capabilities, or mixed with soil in a mixing facility, using a mixing method that applies soil mixing equipment similar to that of conventional powder insolubilizers. In this way, by applying the low-fluidity mud improvement method of the present invention to soil, the pH of the soil can be made neutral (5.8 to 8.6).

[0046] In particular, the solidified insolubilized neutral modifier of the present invention is preferably used in the form of a powder, and can be mixed with low-fluidized soil using a backhoe, deep layer mixer, stationary mixer, power blender, etc. The amount of solidified insolubilized neutral modifier mixed with the treated soil varies depending on the water content of the soil and the required solidification strength of the treated soil, and can be designed as desired. As a specific example, it is possible to add and mix the muddy material in a mud storage tank, then spread it and mix it with heavy machinery, or to mix it using conventional soil mixing equipment such as soil modifier equipment.

[0047] In this way, by bringing the solidifying and insolubilizing neutral modifier of the present invention into contact with low-fluidity mud (containing heavy metals, etc.) in which a mud-adding agent has been added to mud such as dredged soil or shield generated soil which has high fluidity due to its high water content or the effects of foaming agents, it is possible to insolubilize the heavy metals, etc. without the interstitial water captured by the mud-adding agent in the soil flowing out, improve the solidification performance of the soil, and maintain the pH of the treated soil in the neutral range. For example, the amount of elution of heavy metals in soil, as measured based on the Soil Contamination Countermeasures Law, was all within the soil elution amount standard, and the pH of the test solution prepared according to the Environment Agency Notification No. 46 (promulgated on August 23, 1991) after 7 days of use, for example, satisfied the environmental standard of 5.8 to 8.6 specified in the Ministry of the Environment's uniform wastewater standard. Furthermore, the cone index was 200 kN / m, which is specified for Type 4 construction waste soil in the soil quality classification standard in the Ministry of Land, Infrastructure, Transport and Tourism's "Regarding the Use of Generated Soil." 2 More preferably, 400kN / m 2 More preferably, it is 800kN / m 2 It is possible to modify the road surface as described above, and the road surface can be designed to enable heavy machinery such as trucks to run on. EXAMPLES

[0048] The present invention will now be described with reference to the following examples and comparative examples.

[0049] (Test soil) The muddy soil with the physical properties shown in Table 1 below, from which arsenic is eluted, was treated with a slurry containing polyacrylamide emulsion as the main component at a rate of 3 kg / m. 3 The soil was added in an amount of 100 ml, mixed at low speed in a soil mixer for 90 seconds, and then the soil adhering to the container and paddle of the soil mixer was scraped off, and the soil was mixed again at low speed for 90 seconds to prepare the test soil.

[0050] Table 1 shows the water content, wet density, fine particle fraction less than 75 μm in particle size, amount of arsenic leaching, and pH of the leaching solution of the mud, as well as the cone index of the mud (before the addition of mud additive) and the test soil (after the addition of mud additive). The amount of arsenic eluted and the Cohn Index were measured in accordance with the methods described in Test Examples 1 and 2 below.

[0051] [Table 1]

[0052] (Raw materials used) The following materials were used to prepare the solidified, insolubilized, neutral modifier. Magnesium oxide: fine powder (reagent, manufactured by Kanto Chemical Co., Ltd.) Aluminum sulfate: powder (reagent, 14-18 hydrate, Kanto Chemical Co., Ltd.) Calcium carbonate: Powder (produced in Kudzu, Tochigi Prefecture) Porous volcanic ash soil: Kanuma soil (produced in Tochigi Prefecture, dried at 105°C and classified to less than 1mm) 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)

[0053] (Solidifying, insolubilizing, neutral modifier) Examples 1 to 8, Comparative Examples 1 to 7 Using each of the raw materials described above, each raw material was mixed in the mixing ratio shown in Table 2 below to prepare each solidified, insolubilized, neutral modifier. The order in which the raw materials were mixed was not particularly limited, but each of the solidified, insolubilized, neutral modifiers was prepared by simultaneously mixing the raw materials.

[0054] [Table 2]

[0055] (Test Example) Test Example 1: Modification test (insolubilization test and neutralization confirmation test) Test soil 1m 3 50 kg of each solidified, insolubilized, neutral modifier shown in Table 2 was added to each sample, and the sample was mixed at low speed in a soil mixer for 90 seconds. After that, the soil adhering to the soil mixer's container and paddle was scraped off, and the sample was mixed again at low speed for 90 seconds to prepare each treated soil. After preparing each treated soil, it was sealed and cured at 20℃ for 7 days. Then, for each treated soil after 7 days, a test solution (eluate) was prepared according to the Environment Agency Notification No. 46 (issued on August 23, 1991). The pH of the eluate (test solution) and the arsenic concentration in the eluate (test solution) were measured in accordance with JIS K 0102 "Testing Methods for Factory Wastewater". The results are shown in Table 3 below.

[0056] Test example 2: Soil strength test Test soil 1m 3 50 kg of each solidification, insolubilization, and neutral amendment shown in Table 2 was added to the soil, which was then mixed at low speed in a soil mixer for 90 seconds. After that, the soil adhering to the soil mixer's container and paddle was scraped off, and the soil was mixed again at low speed for 90 seconds to prepare the treated soil. Each treated soil was prepared and sealed and cured at 20℃ for 7 days, after which each treated soil was divided into three layers and filled into a 10 cm mold as specified in JIS A 1210:2009 "Test method for soil compaction by tamping", and the cone index at 7 days was measured in accordance with JIS A 1228 "Test method for cone index of compacted soil". The results are shown in Table 3 below.

[0057] As a reference example, the test solution pH, arsenic elution amount, and Corn Index were measured in the same manner for test soil in which no solidified insolubilized neutral amendment was mixed with the soil in Table 1 above, and the results are shown in Table 3.

[0058] Exam passing criteria: The cone index is 400kN / m, which is the soil quality classification standard for Type 3 construction waste soil in the Ministry of Land, Infrastructure, Transport and Tourism's "Standards for the Use of Generated Soil." 2 Anything above that was deemed to have passed. The amount of arsenic leaching was deemed to have passed the soil leaching standard of 0.01 mg / L under the Soil Contamination Countermeasures Act. The pH of the eluate test solution was determined to be in the neutral range of 5.8 to 8.6, as specified by the uniform wastewater standards of the Ministry of the Environment.

[0059] [Table 3]

[0060] From Table 3 above, the solidified, insolubilized, neutral improvement materials of the Examples (E1 to E8) containing magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and / or porous volcanic ash soil, and polymer flocculant as essential components within the specific ranges of the present invention, showed that in soils treated with high water content fluidized mud and mud-adding materials to reduce fluidity, the amount of arsenic eluted from the treated soil at 7 days of age was all within the soil elution amount standard, the pH of the soil eluate was within the uniform drainage standard range, and the cone index at 7 days of age was 400 kN / m 2 From the above, it has become clear that the above-mentioned effects of the present invention can be effectively exhibited.

[0061] As for the solidified insoluble neutral modification material C1 in Comparative Example 1, which has an excessive magnesium oxide content and an insufficient calcium carbonate and / or porous volcanic ash soil content, the cone index and arsenic leaching standards are met, but the soil leachate pH is not in the neutral range, which poses environmental problems. In addition, the solidified insolubilized neutral modifier C2 in Comparative Example 2, which had an excessive aluminum sulfate content, met the arsenic elution standard, but the soil eluate pH was in the acidic range, and the cone index increased compared to the test soil, but the cone index was 400 kN / m 2 The solidification performance is insufficient.

[0062] In the case of the solidified insolubilized neutral amendment C3 containing no aluminum sulfate in Comparative Example 3, the pH of the soil eluate was in the neutral range, but the arsenic elution amount standard was exceeded and the cone index was increased compared to the test soil, but the cone index was 400 kN / m 2 The solidification performance is insufficient. In addition, in the case of the solidified insolubilized neutral modified material C4 in Comparative Example 4, which had an excessive ferrous sulfate content, the arsenic elution standard was met, the soil eluate pH was in the neutral region, and the cone index was increased compared to the test soil, but the cone index was 400 kN / m 2 The solidification performance is insufficient.

[0063] As for the solidified insolubilized neutral modifier C5 not containing ferrous sulfate in Comparative Example 5, although it satisfies the Cone Index and the soil eluate pH is in the neutral region, it does not meet the arsenic elution amount standard. In the case of the solidified insoluble neutral modification material C6 in Comparative Example 6, which contains an excessive amount of aluminum sulfate and ferrous sulfate in excess of 25% in total, the arsenic elution standard is met and the soil eluate pH is in the neutral region. However, the cone index was increased compared to the test soil, but the cone index was 400 kN / m 2 The solidification performance is insufficient.

[0064] For the solidified insolubilized neutral modified material C7 not containing a polymer flocculant in Comparative Example 7, the arsenic elution amount standard was met and the soil eluate pH was in the neutral region, but the cone index increased compared to the test soil, but the cone index was 400 kN / m 2 The solidification performance is insufficient. [Industrial Applicability]

[0065] The solidified insolubilized neutral modifier of the present invention and the low-fluidity mud modification method using said modifier can efficiently insolubilize the heavy metals and halogens contained in mud that has been treated to reduce fluidity using a mud-adding material, and can solidify the soil while maintaining the treated soil near the neutral region, thereby improving its strength. Therefore, the method can be effectively used for low-fluidity soil that contains a mud-adding material. For example, the method can be effectively applied to the treatment of heavy metals and other substances in highly water-containing fluid mud that is generated in large quantities during excavation and construction work for tunnels, dams, etc., and can make it easier to effectively use the modified soil.

Claims

1. A solidified, insoluble, neutral modifier comprising magnesium oxide, aluminum sulfate, ferrous sulfate, calcium carbonate and / or porous volcanic ash soil, and a polymer flocculant as essential components, not containing CaMg(CO3)2, and containing 0.1 to 20 mass% magnesium oxide, 3 mass% or more but less than 25 mass% aluminum sulfate, more than 0 mass% but less than 10 mass% ferrous sulfate, 50 mass% or more calcium carbonate and / or porous volcanic ash soil, and 0.1 to 10 mass% polymer flocculant, with the ferrous sulfate content being less than the aluminum sulfate content, and the total amount of aluminum sulfate and ferrous sulfate being more than 3 mass% but not more than 25 mass%.

2. The solidified, insolubilized neutral modifier according to claim 1, characterized in that the polymer flocculant has polyacrylamide as its main component and has a viscosity of 400 mPa·s or more when made into a 0.25% aqueous solution.

3. The solidified, insolubilized neutral modifier according to claim 1 or 2, characterized in that it is in a powder form.

4. The solidified, insolubilized neutral modifier according to any one of claims 1 to 3 is a modifier used for low-fluidity mud containing a mud-adding agent whose main component is an organic polymer emulsion, characterized in that the organic polymer emulsion, which is the main component of the mud-adding agent, is a polyacrylamide-based emulsion.

5. A method for improving low-fluidity mud, comprising mixing the solidified, insolubilized, neutral improver according to any one of claims 1 to 4 with low-fluidity mud containing a mud-adding material mainly composed of an organic polymer emulsion.

6. In the low-fluidity mud improvement method according to claim 5, the solidified insolubilized neutral improver is mixed with the mud to produce a treated soil having a pH of 5.8 to 8.6, an amount of arsenic elution of 0.01 mg / L or less, and a cone index of 200 kN / m ２ A low-fluidity mud modification method characterized by the above.

Images