Solidification material, solidified soil and solidification method

Abstract

To provide a solidifying material used for obtaining solidified soil suppressed in plant development and growth.SOLUTION: Provided is a solidifying material containing the elements selenium (Se), cadmium (Cd), and lead (Pb). The solidifying material has a selenium (Se) content of 3.5 ppm or more, a cadmium (Cd) content of 110 ppm or more, and a lead (Pb) content of 430 ppm or more. The solidifying material preferably includes rapid-hardening Portland cement, blast furnace slag, and gypsum.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a solidification material and solidified soil obtained by solidification treatment using the solidification material. The present invention also relates to a soil solidification treatment method using the solidification material. [Background technology]

[0002] Solidification materials are used to solidify and improve soil quality, such as preventing soil liquefaction and strengthening the solidification of soft ground. In the solidified soil obtained by soil solidification treatment, there are cases where it is required to suppress the emergence and growth of plants in order to prevent cracks, etc. One example of a technique for inhibiting plant emergence and growth is to sufficiently increase the strength of solidified treated soil to prevent seeds from germinating in the soil (see, for example, Patent Document 1). However, this technique has the drawback of being unable to be applied when medium-strength solidified treated soil is required.

[0003] As a soil solidification method that can overcome the above-mentioned drawbacks, a method of solidifying soil using a solidification material containing a heavy metal element can be mentioned. For example, Patent Document 2 proposes a cement composition containing 0.8 mg / kg to 15.0 mg / kg of selenium. Furthermore, Patent Document 3 proposes a cement-based solidification material containing zinc and lead in a total amount of 500 mg / kg or more and 1000 mg / kg or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-045226 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-053064 [Patent Document 3] Japanese Patent Publication No. 2020-083712 Summary of the Invention [Problem to be solved by the invention]

[0005] Although the techniques described in Patent Documents 2 and 3 can inhibit the emergence and growth of plants in solidified treated soil to a certain extent, there is a demand for more powerful inhibition of plant emergence and growth.

[0006] Therefore, an object of the present invention is to provide a solidification material that can be used to obtain solidification-treated soil in which the emergence and growth of plants is inhibited. [Means for solving the problem]

[0007] The present invention contains selenium (Se), cadmium (Cd), and lead (Pb), The selenium (Se) element content is 3.5 ppm or more, The cadmium (Cd) element content is 110 ppm or more, The present invention provides a solidification material having a lead (Pb) content of 430 ppm or more.

[0008] The present invention also provides a solidification material, The unconfined compressive strength of the solidified soil obtained by mixing the soil with the solidification material and solidifying the soil is 50 kN / m at 7 days old. 2 More than 350kN / m 2 The present invention provides a solidification material that is less than [Effects of the Invention]

[0009] According to the present invention, there is provided a solidification material used to obtain solidification-treated soil in which the emergence and growth of plants is inhibited. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below based on preferred embodiments thereof. The present invention relates to a solidification material capable of inhibiting the emergence and growth of plants. For this purpose, the solidification material of the present invention preferably contains predetermined amounts of predetermined types of heavy metal elements. Specifically, the solidification material of the present invention preferably contains 3.5 ppm or more of Se, 110 ppm or more of Cd, and 430 ppm or more of Pb. In this specification, "ppm" is based on mass.

[0011] By containing the elements Se, Cd, and Pb in the above-mentioned amounts, the solidification material of the present invention can effectively inhibit the emergence and growth of plants in solidified soil when the solidification material is used to treat soil to produce solidified soil. From this perspective, the content of Se in the solidification material of the present invention is preferably 3.5 ppm or more, more preferably 4.5 ppm or more, and even more preferably 5.5 ppm or more. From the same viewpoint, the content of Cd element in the solidifying material of the present invention is preferably 110 ppm or more, more preferably 120 ppm or more, and even more preferably 150 ppm or more. From the same viewpoint, the content of Pb element in the solidifying material of the present invention is preferably 430 ppm or more, and more preferably 500 ppm or more.

[0012] When the solidification material of the present invention contains all three of the above-mentioned heavy metal elements (i.e., Se, Cd, and Pb), plant emergence and growth are effectively inhibited, and the total content of heavy metal elements can be particularly reduced compared to when one or more of the three heavy metal elements are not contained. As a result, the amount of heavy metal elements contained in the solidification material of the present invention that elutes into soil can be reduced while sufficiently inhibiting plant emergence and growth.

[0013] In order to sufficiently suppress the leaching of heavy metal elements into the soil, the content of Se element in the solidification material of the present invention is preferably 20 ppm or less, more preferably 15 ppm or less, even more preferably 5.0 ppm or less, and particularly preferably 4.0 ppm or less. From the same viewpoint, the content of Cd element in the solidifying material of the present invention is preferably 200 ppm or less, more preferably 170 ppm or less. From the same viewpoint, the content of Pb element in the solidifying material of the present invention is preferably 1000 ppm or less, more preferably 800 ppm or less, even more preferably 700 ppm or less, and particularly preferably 500 ppm or less.

[0014] From the viewpoint of sufficiently suppressing the emergence and growth of plants while reducing the amount of heavy metal elements contained in the solidification material of the present invention that leach into the soil, the mass ratio Cd / Se of Cd element to Se element contained in the solidification material of the present invention is preferably 0.1 or more and 100 or less, more preferably 1.0 or more and 50 or less, and even more preferably 5.0 or more and 30 or less. From a similar viewpoint, the mass ratio Pb / Se of Pb element to Se element contained in the solidifying material of the present invention is preferably 1.0 or more and 1000 or less, more preferably 10 or more and 300 or less, and even more preferably 25 or more and 100 or less.

[0015] There are no particular limitations on the state of existence of the Se element, Cd element, and Pb element contained in the solidifying material of the present invention, but these elements are generally considered to exist in the form of oxides.

[0016] The solidifying material of the present invention may contain heavy metal elements other than Se, Cd and Pb, such as chromium, zinc, nickel, molybdenum and tin. From the viewpoint of reducing the amount of heavy metal elements leaching into the soil, the total content of heavy metal elements other than Se, Cd and Pb in the solidification material of the present invention is preferably 3000 ppm or less, and more preferably 2000 ppm or less.

[0017] The content of heavy metal elements contained in the solidifying material of the present invention can be measured by ICP-MS (inductively coupled plasma mass spectrometry) or the like.

[0018] Generally, the solidified soil obtained by solidifying soil with a solidification agent has an unconfined compressive strength of 350 kN / m 2 If the solidification rate exceeds this level, plant emergence and growth are inhibited. The inclusion of the above-mentioned heavy metal elements in the solidification material of the present invention has the advantage that plant emergence and growth are inhibited without the need to sufficiently increase the unconfined compressive strength of the solidified soil. From this perspective, the solidification material of the present invention is sufficient if it can solidify the soil to a moderate strength. The solidification material of the present invention can suppress plant emergence without the need to excessively increase the strength, thereby reducing the amount of solidification material used. Furthermore, since the strength of the solidified soil is not excessively increased, it has the advantage of being easy to re-excavate. Therefore, the solidification material of the present invention is particularly preferably used for soil that may require re-excavation in the future.

[0019] The solidification material of the present invention preferably contains high-early-strength Portland cement from the viewpoint of solidifying soil to a moderate degree and suppressing the elution of heavy metal elements. As the high-early-strength Portland cement, for example, one specified in JIS R5210:2019 can be used. High-early-strength Portland cement has a Blaine specific surface area of ​​3300 cm 2 / g or more is preferable. Although it is possible to use ordinary Portland cement as the cement component, this is uneconomical because it requires an increased amount of hardener to ensure early strength. In this respect, ordinary Portland cement is at a disadvantage compared to high-early-strength Portland cement.

[0020] High-early-strength Portland cement may contain at least one of Se, Cd, and Pb elements. When high-early-strength Portland cement contains at least one of these elements, the total amount is preferably 100 ppm to 600 ppm, more preferably 200 ppm to 600 ppm, and even more preferably 200 ppm to 400 ppm.

[0021] From the viewpoint of solidifying the soil to a moderate degree and suppressing the leaching of heavy metal elements, the content of high-early-strength Portland cement in the solidification material of the present invention is preferably 30% by mass or more and 60% by mass or less, more preferably 40% by mass or more and 60% by mass or less, and even more preferably 45% by mass or more and 60% by mass or less.

[0022] The solidification material of the present invention preferably contains blast furnace slag from the viewpoint of achieving moderate soil solidification and suppressing the elution of heavy metal elements. Blast furnace slag is a by-product of blast furnaces in steelworks and other facilities. Examples of blast furnace slag that can be used include commercially available granulated blast furnace slag and slag specified in JIS A6206:2013. Blast furnace slag contains a high alumina content, which contributes to increasing the amount of ettringite produced and improves the strength of the soil after solidification. Furthermore, blast furnace slag has latent hydraulic properties, which allow it to harden in response to the alkalis contained in cement. This allows it to improve the strength of the soil after solidification when it is solidified with water.

[0023] It is known that basicity is generally used as a measure of the reactivity of blast furnace slag when used in cement. The higher the basicity of blast furnace slag, the greater its reactivity. Basicity is calculated as (CaO + MgO + Al2O3) / SiO2 among the components of blast furnace slag. From the viewpoint of high reactivity, the blast furnace slag used in the present invention preferably has a basicity of 1.75 or more, more preferably 1.79 or more. The upper basicity limit is approximately 2.00. As will be described later, the basicity of blast furnace slag is not constant but varies depending on the lot and brand. Therefore, the basicity of blast furnace slag generated from a blast furnace is continuously measured, and if the basicity of the blast furnace slag is 1.75 or more, the blast furnace slag is sampled for use as a raw material for the solidification material of the present invention. The Blaine specific surface area of ​​the ground granulated blast furnace slag is preferably 3000 to 7000 cm 2 / g, more preferably 3500 to 6000 cm 2The Blaine specific surface area of ​​blast furnace slag can be measured in accordance with JIS R5201:2015 "Physical testing methods for cement." By using blast furnace slag with such basicity and Blaine specific surface area, it is possible to reduce the manufacturing costs of the solidification material and the costs required for the solidification treatment, while at the same time imparting high strength to the soil after the solidification treatment.

[0024] The blast furnace slag may contain at least one of Se, Cd, and Pb elements. When the blast furnace slag contains at least one of these elements, the total amount thereof is preferably 0.1 ppm or more and 300 ppm or less, more preferably 100 ppm or more and 300 ppm or less, and even more preferably 200 ppm or more and 250 ppm or less.

[0025] From the viewpoint of solidifying the soil to a moderate degree and suppressing the leaching of heavy metal elements, the content of blast furnace slag in the solidification material of the present invention is preferably 1% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 40% by mass or less, and even more preferably 10% by mass or more and 35% by mass or less.

[0026] The solidification material of the present invention preferably contains gypsum from the viewpoint of moderately solidifying the soil and suppressing the elution of heavy metal elements. Examples of gypsum that can be used include anhydrous gypsum, hemihydrate gypsum, and dihydrate gypsum.

[0027] The gypsum may contain at least one of Se, Cd, and Pb elements. When the gypsum contains at least one of these elements, the total amount thereof is preferably 0.1 ppm or more and 300 ppm or less, more preferably 100 ppm or more and 300 ppm or less, and even more preferably 200 ppm or more and 250 ppm or less.

[0028] From the viewpoint of solidifying the soil to a moderate degree and suppressing the leaching of heavy metal elements, the gypsum content in the solidification material of the present invention is preferably 1% by mass or more and 55% by mass or less, more preferably 3% by mass or more and 35% by mass or less, and even more preferably 5% by mass or more and 20% by mass or less.

[0029] The solidifying material of the present invention may contain components other than high-early-strength Portland cement, blast furnace slag, and gypsum. Examples of such components include clinker dust. Clinker dust is dust (granular or powdery material) that is generated and recovered when a portion of the chlorine-containing exhaust gas generated in the cement kiln of a cement plant facility is extracted through a chlorine bypass system when raw fuels with a high chlorine content are used in the cement manufacturing process, and the extracted exhaust gas is cooled. Clinker dust often contains Se, Cd, and Pb, and the use of clinker dust makes it possible to adjust the contents of these elements in the solidifying material of the present invention. The total content of Se, Cd and Pb elements in the clinker dust is preferably 100 ppm or more and 50,000 ppm or less, more preferably 1,000 ppm or more and 30,000 ppm or less, and even more preferably 5,000 ppm or more and 20,000 ppm or less.

[0030] From the viewpoint of appropriately adjusting the content of heavy metal elements in the solidifying material of the present invention, when the solidifying material contains clinker dust, the content of clinker dust in the solidifying material of the present invention is preferably 0.1 mass% or more and 10.0 mass% or less, more preferably 0.1 mass% or more and 8.0 mass% or less, and even more preferably 0.1 mass% or more and 5.0 mass% or less.

[0031] The solidifying material of the present invention can be produced, for example, by mixing the above-mentioned raw materials in a known mixer. There are no particular limitations on the type of mixer, and the solidifying material can be produced by mixing and grinding the materials using, for example, a ball mill.

[0032] The Se, Cd, and Pb elements contained in the solidifying material of the present invention may be contained in each of the raw materials of the solidifying material described above, or may be added separately from each of the raw materials of the solidifying material. From the viewpoint of reducing production costs, it is preferable that the Se, Cd, and Pb elements contained in the solidifying material of the present invention are contained in the various raw materials of the solidifying material described above.

[0033] The solidification-treated soil of the present invention can be obtained by mixing soil with the solidification material of the present invention and solidifying the soil. Examples of soil that can be solidified include clayey soil, Kanto loam, sandy soil, and black soil. The amount of solidification material to be added can be changed as appropriate depending on the type and properties of the soil to be solidified. Generally, the amount of solidification material to be added is determined based on the type and properties of the soil to be solidified. 3 The amount of solidification material added is preferably 50 kg to 1000 kg, more preferably 50 kg to 800 kg, and even more preferably 50 kg to 500 kg. By setting the amount of solidification material added as described above, it is possible to obtain solidified soil having the strength described below. In this way, the solidified treated soil of the present invention is specified by its manufacturing method, because it is not realistic to specify the components that make up the solidified treated soil of the present invention and their contents, and there are impossible circumstances that make it necessary to use such expressions.

[0034] There are no particular limitations on the means for mixing the solidification material with the soil to be solidified. For example, devices or methods commonly used in the technical field can be used, such as backhoes, backhoes with mixing buckets, stabilizers, self-propelled soil improvement machines, stationary mixers, Hobart mixers, trencher-type agitation mixers, deep mixers, power blenders, and plant mixers.

[0035] The solidification-treated soil produced using the solidification material of the present invention is only required to be moderately solidified. Specifically, the unconfined compressive strength at 7 days is 50 kN / m 2 More than 350kN / m 2 Preferably less than 100 kN / m2 More than 350kN / m 2 More preferably, it is 200 kN / m or less. 2 More than 350kN / m 2 In other words, it is preferable that the solidification material of the present invention is such that the unconfined compressive strength of the solidified soil obtained by mixing the solidification material with soil and solidifying the soil is within the above-mentioned range at 7 days. In the solidified soil produced using the solidification material of the present invention, the heavy metal elements effectively inhibit the development and growth of plants, making it difficult for plants to develop and grow even if the unconfined compressive strength of the solidified soil at 7 days is within the medium range described above. The unconfined compressive strength of the solidified soil at 7 days is 50kN / m 2 More than 350kN / m 2 In order to make the solidification amount less than this, for example, the contents of the various components contained in the solidification material of the present invention and the amount of the solidification material added to the soil may be appropriately adjusted. The unconfined compressive strength of solidified soil can be measured based on JIS A 1216:2020. [Example]

[0036] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0037] Examples 1 to 12 (1) Manufacturing of solidification materials High-early-strength Portland cement, anhydrous gypsum, and blast furnace slag were mixed in a mass ratio of 60.0:8.5:31.5 to obtain a raw material composition. This raw material composition was mixed with one of clinker dusts a to d shown in Table 1 in the mass ratio shown in Table 2 to obtain solidification materials A to D. The details of each material are as follows: High-early-strength Portland cement (manufactured by UBE Mitsubishi Cement Co., Ltd.) Anhydrous gypsum (manufactured by Kokusai Shoji Co., Ltd.) Blast furnace slag (manufactured by Kobe Steel K-ment Co., Ltd.) Clinker dust a (manufactured by UBE Mitsubishi Cement Co., Ltd.) Clinker dust b (UBE Mitsubishi Cement) Clinker dust c (manufactured by UBE Mitsubishi Cement Co., Ltd.) Clinker dust d (manufactured by UBE Mitsubishi Cement Co., Ltd.) The heavy metal element contents contained in the raw material composition and clinker dust are shown in Table 1. The heavy metal element contents contained in solidification materials A to D are shown in Table 2. These heavy metal element contents were measured by ICP-MS.

[0038] (2) Soil to be solidified Kuroboku soil (produced in Shibushi City, Kagoshima Prefecture, moisture content: 74.5%, wet density: 1.453 g / cm 3 , particle size composition: gravel 3.1%, sand 38.1%, fine grain 58.8%)

[0039] (3) Preparation of solidified soil The black soil was passed through a sieve with 2 mm openings, and then the solidification material was added in the proportions shown in Table 3. The two were mixed using a Hobart mixer in an environment of 20°C, and then left to stand at 20°C for 7 days.

[0040] (4) Evaluation The unconfined compressive strength of the solidified soil after 7 days, the degree of plant growth inhibition, and the amount of heavy metal elements eluted were measured using the following methods. The results are shown in Table 3.

[0041] [Uniaxial compressive strength] The unconfined compressive strength of the solidified soil at 7 days was measured in accordance with JIS A 1216:2020.

[0042] [Degree of plant growth inhibition] To investigate the extent of plant growth inhibition by solidified soil, a test was conducted using the following method. This test was conducted in accordance with the "Cultivation Test Methods and Commentary on Harm to Plants (Agricultural, Forestry, and Fisheries Consumer Safety Technology Center, 2022)." First, several cylindrical test containers (diameter: 113 mm, height: 63 mm) were prepared. The test containers were filled with solidified soil while compacting it in three layers using a 1.5 kg rammer. The amount of solidified soil filled in each test container was approximately 500 mL. Next, 20 holes, each 8 mm in diameter and 10 mm deep, were drilled in the third (top) layer of the compacted solidified soil. One komatsuna seed was placed in each hole and grown for 21 days at 25°C under 12 hours of 5000 lm LED light irradiation. The above-ground parts of the komatsuna were then cut off and their mass (harvested material) was measured. The smaller the harvested matter amount, the more suppressed the emergence of plants.

[0043] [Heavy metal element elution amount] The amount of heavy metal elements leached from the solidified soil was measured in accordance with JIS K 0058. For reference, Table 3 also shows the allowable leaching amounts of each heavy metal element in the soil environmental standards that are scheduled to be adopted in Japan in the future.

[0044] [Control Example] The Andosol was subjected to the evaluations described in "(4) Evaluation" above without any solidification treatment. The results are shown in Table 3.

[0045] [Table 1]

[0046] [Table 2]

[0047] [Table 3]

[0048] As is clear from Table 3, the solidified treated soils of each Example effectively inhibited plant growth. Furthermore, the amounts of heavy metal elements eluted from the solidified treated soils were all within the soil environmental standards.

Claims

1. Contains selenium (Se), cadmium (Cd), and lead (Pb), The content of selenium (Se) element is 3.5 ppm or more, The content of cadmium (Cd) element is 110 ppm or more, A solidification material having a lead (Pb) element content of 430 ppm or more.

2. The solidifying material according to claim 1, comprising high-early-strength Portland cement, blast furnace slag, and gypsum.

3. 1m of soil ３ A solidified soil obtained by mixing 50 kg or more of the solidification material according to claim 1 or 2 with the soil and solidifying the soil, Unconfined compressive strength at 7 days is 50 kN / m ２ 350kN / m or more ２ Solidified treated soil that is less than.

4. A solidification material, The unconfined compressive strength of the solidified soil obtained by mixing the soil with the solidification material and solidifying the soil is 50 kN / m at 7 days old. ２ 350kN / m or more ２ A solidification material that is designed to be less than

5. Contains selenium (Se), cadmium (Cd), and lead (Pb), The content of selenium (Se) element is 3.5 ppm or more, The content of cadmium (Cd) element is 110 ppm or more, 5. The solidifying material according to claim 4, wherein the content of lead (Pb) element is 430 ppm or more.

6. The solidifying material according to claim 4, comprising high-early-strength Portland cement, blast furnace slag, and gypsum.

7. A soil solidification method comprising mixing the solidification material according to any one of claims 1, 2, and 4 to 6 with soil to solidify the soil.

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