Foundation injection material

Abstract

To provide an economical and efficient grouting material that can effectively penetrate the soil contaminated with one or more heavy metals or the like, and can insolubilize the leaching levels of one or more heavy metals or the like to below the soil environment standards.SOLUTION: A grouting material contains (A) calcium aluminate, (B) aluminum sulfate, (C) alkali metal phosphate, (D) a reduction component and (E) hydrated lime. The maximum particle size of the overall mixture is 10.5 μm or less, and particles with a size of 2.2 μm or less account for at most 50 vol.%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a ground grouting material and grouting method for insolubilizing and improving soil and ground contaminated with one or more heavy metals and the like. [Background technology]

[0002] Ground contamination can be caused by natural factors or by man-made causes that are discovered through soil contamination surveys of former factory sites. In either case, there is the potential for adverse effects on human health and the surrounding environment, and further spread of contamination and damage to human health must be avoided.

[0003] For this reason, the Soil Contamination Countermeasures Act was enacted in 2013 with the aim of protecting the health of the public by understanding the state of soil contamination and implementing soil contamination countermeasures to prevent damage to human health caused by soil contamination. Therefore, if it is confirmed that the leaching amount of heavy metals or other contaminants from the soil exceeds the standard or that the content exceeds the limit, and if there is a threat to health risks such as ingestion via groundwater or direct ingestion through the mouth, the contaminated soil in question must be contained in situ using water-blocking works, barriers or embankments, insolubilized with cement or chemicals, or excavated and removed, or replaced with good quality soil.

[0004] In many cases, landowners and users wish to remove the source of contamination itself as a countermeasure. If contaminated soil is excavated and removed, it must be replaced with good quality soil. Therefore, the cost of countermeasures, such as modifying and properly treating the excavated contaminated soil and securing good quality soil, can be enormous.

[0005] For this reason, the number of cases in which contaminated soil insolubilization treatments are being adopted, using cement-based solidification materials and various chemicals to neutralize or immobilize harmful heavy metals contained in contaminated soil, is increasing year by year. Meanwhile, in cases where contaminated soil with contaminated groundwater is located directly below existing structures, excavation and removal of the contaminated soil is not possible, leading to a growing need for contaminated soil insolubilization by injecting highly permeable chemical solutions or ground injection materials into the gaps between soil particles. While water glass-based injection materials are well known for their low durability due to silica leaching, they cannot be expected to provide an insolubilization effect. In recent years, ground injection into contaminated soil has been investigated, and examples include a heavy metal insolubilizer for hexavalent chromium-contaminated soil, consisting of colloidal silica and at least one chelating agent selected from tannic acid, amines, and diphenols (Patent Document 1), and a method for preventing arsenic diffusion and injection solutions for arsenic-contaminated soil (Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-249466 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-228685 Summary of the Invention [Problem to be solved by the invention]

[0007] However, these ground injection technologies are targeted at soil contaminated with a single type of heavy metal that has been specified in advance, and have the drawback of not being able to insolubilize soil contaminated with one or more types of heavy metals. In addition, powder-based ground injection materials are mixed with water to form ground injection material slurry, which is then injected into contaminated soil, but there is also the issue that the material often does not penetrate sufficiently into the gaps between the contaminated soil and ground, and the expected insolubilization effect is not achieved. Therefore, the object of the present invention is to provide an economical and efficient ground injection material that has good permeability into soil contaminated with one or more heavy metals, etc., and can insolubilize the amount of leaching of one or more heavy metals, etc. to below the soil environmental standards. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors have found that, in order to insolubilize ground from which the leaching amounts of one or more elements selected from boron, fluorine, arsenic, selenium, and hexavalent chromium exceed the soil environmental standards, the leaching amounts of these heavy metals and the like can be reduced to or below the soil environmental standards by injecting into the ground to be insolubilized a slurry of ground grouting material containing calcium aluminate, aluminum sulfate, alkali metal phosphate, a reducing component, and hydrated lime, where the maximum particle size of the mixture is 10.5 μm or less and the particle size distribution is controlled so that particles of 2.2 μm or less account for 50% or less by volume, and thus have completed the present invention.

[0009] That is, the present invention relates to the following [1] to [5]. [1] A ground grouting material containing (A) calcium aluminate, (B) aluminum sulfate, (C) alkali metal phosphate, (D) a reducing component, and (E) slaked lime, in which the maximum particle size of the entire mixture is 10.5 μm or less, and the particles with a particle size of 2.2 μm or less constitute 50% or less by volume. [2] The ground grouting material according to [1], wherein the calcium aluminate is crystalline calcium aluminate having a molar ratio of CaO to Al2O3 of CaO / Al2O3=0.9 to 1.4 and / or amorphous calcium aluminate having a molar ratio of CaO to Al2O3 of CaO / Al2O3=1.6 to 2.6. [3] A ground grouting material slurry containing the ground grouting material (M) according to [1] or [2] and water (W), wherein the weight ratio (W / M) of the ground grouting material (M) to water (W) is 2 to 10. [4] The ground grouting material slurry according to [3], further comprising a dispersant. [5] A ground injection method characterized by injecting the ground injection material slurry described in [3] or [4] into ground where the amount of leaching of one or more contaminants selected from boron, fluorine, arsenic, selenium, and hexavalent chromium exceeds the soil environmental standard. [Effects of the Invention]

[0010] By carrying out a ground grouting method using the grouting material of the present invention, it is possible to reduce the amount of leaching of one or more contaminants selected from boron, fluorine, arsenic, selenium, and hexavalent chromium from contaminated soil to below the soil environmental standard value with an economical and effective method. Therefore, the present invention is an extremely useful technology as an example of soil contamination countermeasure technology. DETAILED DESCRIPTION OF THE INVENTION

[0011] The calcium aluminate (A) used in the grouting agent of the present invention is essentially a substance obtained by heat-treating raw CaO and Al2O3 materials. The calcium aluminate may be a crystalline or vitrified hydrated active substance consisting of CaO and Al2O3 as chemical components, or may be a compound, solid solution, glassy substance, or mixture thereof containing other chemical components in addition to CaO and Al2O3. Examples of the former (crystalline) include 12CaO·7Al2O3, CaO·Al2O3, 3CaO·Al2O3, CaO·2Al2O3, and CaO·6Al2O3. Examples of the latter (glassy) include 4CaO·3Al2O3·SO3, 12CaO·7Al2O3, 11CaO·7Al2O3·CaF2, and Na2O·8CaO·3Al2O3.

[0012] Furthermore, the calcium aluminate used in the present invention is preferably crystalline calcium aluminate or amorphous calcium aluminate, and a combination of both is also preferred. To achieve a sufficient insolubilization effect on the contaminated components in contaminated soil, crystalline calcium aluminate with a CaO to Al2O3 molar ratio of CaO / Al2O3 = 0.9 to 1.4 and amorphous calcium aluminate with a CaO to Al2O3 molar ratio of CaO / Al2O3 = 1.6 to 2.6 are more preferred. Furthermore, when using only amorphous calcium aluminate, it is preferable to use one mainly composed of 12CaO·7Al2O3 with a CaO to Al2O3 molar ratio of CaO / Al2O3 = 1.7.

[0013] Crystalline calcium aluminate having a CaO / Al2O3 molar ratio of 0.9 to 1.4 can be obtained by heating a mixture of a CaO source and an Al2O3 source, calculated as CaO and Al2O3, to a molar ratio within the range, for example, at 1600°C, followed by slow cooling. While natural cooling within a heating device is generally employed for slow cooling, if the structure of the heating device causes a rapid temperature drop, it is preferable to adjust the heating so that the temperature drop rate is approximately 10°C / min or less. The CaO source is not particularly limited, but suitable examples include limestone powder, slaked lime, and quicklime powder. Suitable Al2O3 sources include bauxite powder, aluminum hydroxide, aluminum carbonate, aluminum ash, and alumina powder. The Blaine specific surface area of ​​the crystalline calcium aluminate can be adjusted to 3000 to 10,000 cm3 by adjusting the particle size through appropriate procedures such as pulverization, classification, and sieving. 2 / g is preferable as a preliminary step for final adjustment to the optimum particle size distribution of the ground grouting material. At the same time, it is preferable that the Blaine specific surface area of ​​the amorphous calcium aluminate is also approximately the same.

[0014] Amorphous calcium aluminate having a CaO / Al2O3 molar ratio of 1.6 to 2.6 can be obtained by mixing a CaO source and an Al2O3 source in CaO and Al2O3 equivalents within the molar ratio range, for example, by heating and melting the mixture at 1400 to 1900°C, and then quenching the mixture. The quenching can be performed by known quenching techniques, such as removing the molten material from the heating temperature, quenching in water, or spraying with a cooling gas. The particle size of the amorphous calcium aluminate can be adjusted by appropriate procedures such as pulverization, classification, sieving, etc., and the resulting product can have a Blaine specific surface area of ​​3000 to 10000 cm, similar to the crystalline calcium aluminate. 2 It is preferable to use one having a CaO content of 1 / g. The CaO source and Al2O3 source can be the same as those used in the case of the crystalline calcium aluminate.

[0015] The calcium aluminate used in the present invention may be either the crystalline calcium aluminate having a CaO / Al2O3 molar ratio of 0.9 to 1.4 or the amorphous calcium aluminate having a CaO / Al2O3 molar ratio of 1.6 to 2.6, either used alone or as a calcium aluminate mixture of any ratio, which can effectively insolubilize the contaminants in contaminated soil. Furthermore, the calcium aluminate used in the present invention is preferably either a crystalline calcium aluminate primarily composed of CaO·Al2O3 or an amorphous calcium aluminate primarily composed of 12CaO·7Al2O3, which can be used alone, particularly in combination with a reducing component and / or slaked lime, to achieve an excellent insolubilization effect on the contaminated soil.

[0016] The aluminum sulfate (B) used in the present invention may be either a hydrate represented by the chemical formula Al2(SO4)3·nH2O or an anhydrous salt represented by Al2(SO4)3. Preferably, a hydrate with n of 14 to 18 is used, as this has an excellent effect of insolubilizing the contaminants in the contaminated soil. The Blaine specific surface area of ​​the aluminum sulfate can be adjusted to 3,000 to 10,000 cm by adjusting the particle size through appropriate processes such as pulverization, classification, and sieving.2 / g is preferable as a preliminary step for final adjustment to the optimum particle size distribution of the ground grouting material.

[0017] Examples of the alkali metal phosphate (C) used in the present invention include readily soluble salts such as sodium phosphate and potassium phosphate. In the present invention, by incorporating an alkali metal phosphate, a good insolubilization effect of the contaminated components in the contaminated soil can be obtained. As the alkali metal phosphate, potassium phosphate represented by the following formulas (1) to (3) is preferred, and potassium dihydrogen phosphate represented by the following formula (2) is more preferred because of its excellent insolubilization effect. The Blaine specific surface area of ​​potassium phosphate can be adjusted to 3,000 to 10,000 cm by adjusting the particle size by appropriate procedures such as pulverization, classification, and sieving. 2 / g is preferable as a preliminary step for final adjustment to the optimum particle size distribution of the ground grouting material.

[0018] K2HPO4(1) KH2PO4(2) K3PO4(3)

[0019] The reducing component (D) used in the present invention may be any reducing component that does not contain harmful heavy metals, and examples thereof include ferrous sulfate, sodium thiosulfate, formic acid, and oxalic acid. Ferrous sulfate is preferably used because it is easy to handle and relatively inexpensive. Ferrous sulfate includes ferrous sulfate heptahydrate, which has seven crystal waters, and ferrous sulfate monohydrate, which has one crystal water. However, it is preferable to use ferrous sulfate monohydrate, which has high storage stability. The Blaine specific surface area of ​​ferrous sulfate monohydrate can be adjusted to 3,000 to 10,000 cm by adjusting the particle size through appropriate processes such as pulverization, classification, and sieving. 2 / g is preferable as a preliminary step for final adjustment to the optimum particle size distribution of the ground grouting material.

[0020] The (E) slaked lime used in the present invention can be suitably used as long as it is mainly composed of calcium hydroxide represented by the chemical formula Ca(OH). In order to effectively insolubilize the contaminated components in the contaminated soil, the Blaine specific surface area of ​​the slaked lime should be adjusted to 3,000 to 10,000 cm by appropriately performing pulverization, classification, sieving, etc.2 / g is preferable as a preliminary step for final adjustment to the optimum particle size distribution of the ground grouting material.

[0021] In the grouting material of the present invention, the ratios of aluminum sulfate, alkali metal phosphate, reducing component, and slaked lime to 100 parts by weight of calcium aluminate are preferably 5 to 50 parts by weight of aluminum sulfate, 0.5 to 10 parts by weight of alkali metal phosphate, 20 to 200 parts by weight of reducing component, and 100 to 1,000 parts by weight of slaked lime, because this provides a good insolubilization effect for the contaminated components in contaminated soil.More preferably, the ratios of the components to 100 parts by weight of calcium aluminate are 5 to 50 parts by weight of aluminum sulfate, 0.5 to 10 parts by weight of alkali metal phosphate, 20 to 100 parts by weight of reducing component, and 500 to 1,000 parts by weight of slaked lime.

[0022] The ground grouting material of the present invention may be blended with a solidifying agent such as cement, a bulking agent such as calcium carbonate powder, a setting adjuster such as citric acid, etc., as long as this does not impair the permeability into the ground and the insolubilizing effect.

[0023] The grouting material of the present invention has a maximum particle size of 10.5 μm or less for the entire mixture of the above components, and particles of 2.2 μm or less account for 50% by volume or less. By adjusting the particle size distribution in this way, the grouting material of the present invention can be used as a slurry to inject into the target ground (contaminated soil), thereby achieving good permeability into the ground and a good insolubilization effect for the above contaminated components in the contaminated soil. Such particle size distribution can be adjusted by a conventional powder classification method, for example, by mixing the above-mentioned components and then centrifuging them with a classifier or the like.

[0024] The grouting material of the present invention can be used by injecting it into the target ground by a conventional grouting method. Specifically, the grouting method is carried out by mixing the grouting material of the present invention with water to form a grouting material slurry and injecting it into the target ground. Here, the ratio of the ground grouting material (M) to water (W) when preparing the ground grouting material slurry depends on the soil properties and permeability coefficient of the contaminated soil / ground to be injected, but a weight ratio (W / M) of 2 to 10 is preferable in terms of permeability into the target ground.

[0025] When preparing the ground grouting material slurry, it is preferable to add a dispersant in addition to the ground grouting material in order to improve the penetration of the ground grouting material into the ground. The dispersant used is not particularly limited, and may be a water-reducing agent, a high-performance water-reducing agent, a high-performance air-entraining water-reducing agent, or a superplasticizer used in mortar or concrete. Specific examples include melamine sulfonic acid-based water-reducing agents, naphthalene sulfonic acid-based water-reducing agents, and polycarboxylic acid-based water-reducing agents. Of these, it is more preferable to use a naphthalene sulfonic acid-based water-reducing agent. The amount of dispersant added to the grouting material is preferably 0.5 to 2.0 parts by mass per 100 parts by mass of the grouting material, and more preferably 1.0 to 1.5 parts by mass from the viewpoints of both penetration into the ground and economy. When a dispersant is used, the ground grouting material of the present invention is added to a predetermined amount of water to which a dispersant has been added, to prepare a ground grouting material slurry, which is then injected into the target ground.

[0026] The method for mixing the grouting material of the present invention with water is not particularly limited, and a grouting material slurry can be prepared using a general grout mixer used in ground injection work, and the slurry can be injected into the gap between the contaminated soil and the ground to perform the insolubilization treatment. When a dispersant is used, the dispersant can be mixed in addition to the grouting material and water.

[0027] The ground to which the grouting material of the present invention is injected is naturally contaminated with one or more heavy metals, or contaminated soil or ground from former factory sites, etc. Specifically, it is preferable that the ground is one in which the amount of elution of one or more contaminants selected from boron, fluorine, arsenic, selenium, and hexavalent chromium exceeds the soil environmental standard. By injecting the ground grouting material slurry of the present invention into ground where the amount of leaching of one or more contaminants selected from boron, fluorine, arsenic, selenium, and hexavalent chromium exceeds the soil environmental standard, the amount of leaching of one or more contaminants selected from boron, fluorine, arsenic, selenium, and hexavalent chromium in the contaminated soil can be reduced to below the soil environmental standard value. [Example]

[0028] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0029] Coarsely crushed particles (particle size approximately 1 mm or less) of limestone (CaO content: 56% by mass) as the CaO source and alumina shale (AlO content: 88% by mass) as the AlO source were used to prepare calcium aluminate powders, designated A1 and A2 below. The CaO and AlO sources were mixed in a predetermined molar ratio and heated to 1800°C (±50°C) in an electric furnace. After 60 minutes of heating, the mixture was cooled naturally in the furnace (A1). Similarly, the mixture was heated to 1800°C (±50°C) and held there for 60 minutes. The mixture was then removed from the electric furnace at 1800°C to room temperature, and immediately quenched by blowing nitrogen gas onto the surface at a flow rate of approximately 100 cc / s (A2). The cooled mixture was pulverized in a ball mill to obtain a powder with a Blaine specific surface area of ​​7000±500 cm. 2 The fineness was adjusted by changing the grinding time so that the powder density was 1 / g. A1: Crystalline calcium aluminate with a CaO / Al2O3 molar ratio of 1.0 A2: Amorphous calcium aluminate with a CaO / Al2O3 molar ratio of 1.7

[0030] A1-A2 calcium aluminate and a material selected from B-E shown below are used to prepare a material having a Blaine specific surface area of ​​7000±500cm 2 The powder size was adjusted to be / g, and the mixture was dry mixed for 3 minutes using a Henschel mixer in the proportions shown in Table 1. The mixture was then centrifuged using a classifier to adjust the particle size distribution to the desired level, producing a ground grouting material. B: Aluminum sulfate 14-18 hydrate: Reagent manufactured by Kanto Chemical Co., Ltd. C: Potassium dihydrogen phosphate: Reagent manufactured by Kanto Chemical Co., Ltd. D: Ferrous sulfate monohydrate: Fuji Titanium Industry Co., Ltd. E: Slaked lime: Reagent manufactured by Kanto Chemical Co., Ltd. F: Dispersant (naphthalene sulfonic acid-based water-reducing agent): MC Helper (manufactured by Pacific Materials Co., Ltd.) G: Ordinary Portland cement (manufactured by Taiheiyo Cement Corporation) W: Water (tap water)

[0031] [Table 1]

[0032] [Permeability evaluation test] The permeability was evaluated by placing Toyoura sand (soil particle density ρ; 2.63 g / cm ) in an acrylic mold with an inner diameter of 50 mm to a height of 100 mm. 3 ) was filled with a porosity of 45% to prepare a simulated ground. A ground grouting material slurry (200 mL) prepared to a predetermined slurry concentration using the ground grouting material of the present invention, a dispersant, and tap water was poured into this simulated ground from the top, and the discharge of the ground grouting material slurry suspension from the bottom was confirmed. The soil was visually judged and evaluated as follows: Good permeability was evaluated as ○, permeation stopped midway through the simulated ground as △, and no permeation at all into the sand layer of the simulated ground as ×. Table 2 shows the results of the permeability evaluation test of the ground grouting material of the present invention.

[0033] [Table 2]

[0034] [Insolubilization performance confirmation test] Table 3 shows a list of simulated contaminated pore water with the concentrations of each heavy metal, etc. set. The insolubilization performance confirmation test was carried out by adjusting the simulated contaminated pore water to the ground grouting material of the present invention and a predetermined ground grouting material slurry concentration (ratio of simulated contaminated infected water to ground grouting material), and using Toyoura sand (soil particle density ρ; 2.63 g / cm) with a porosity of 40%. 3) and cured in a thermostatic chamber at 20°C for 7 days, after which an elution test (Environment Agency Notification No. 46) was conducted. Table 4 shows the results of the insolubilization performance confirmation test. When the injectable soil grouting material of the present invention was used, all of the values ​​were below the soil environmental standard values, confirming that the insolubilization performance was demonstrated. It was also found that the material can be used to insolubilize soil contaminated with one or more heavy metals selected from boron, fluorine, arsenic, selenium, and hexavalent chromium.

[0035] [Table 3]

[0036] [Table 4]

Claims

1. A ground grouting material containing (A) calcium aluminate, (B) aluminum sulfate, (C) alkali metal phosphate, (D) a reducing component, and (E) slaked lime, wherein the maximum particle size of the entire mixture is 10.5 μm or less, and particles having a particle size of 2.2 μm or less account for 50% by volume or less.

2. The calcium aluminate is a mixture of CaO and Al 2 O 3 The molar ratio of CaO / Al 2 O 3 = 0.9 to 1.4 crystalline calcium aluminate and / or CaO and Al 2 O 3 The molar ratio of CaO / Al 2 O 3 2. The ground grouting material according to claim 1, which is amorphous calcium aluminate having a viscosity of 1.6 to 2.

6.

3. A ground grouting material slurry comprising the ground grouting material (M) according to claim 1 or 2 and water (W), wherein the weight ratio of the ground grouting material (M) to water (W) is 2 to 10.

4. The grouting slurry according to claim 3, further comprising a dispersant.

5. A ground grouting method, characterized by injecting the ground grouting material slurry according to claim 3 or 4 into ground from which the amount of leaching of one or more pollutants selected from boron, fluorine, arsenic, selenium and hexavalent chromium exceeds the soil environmental standard.

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