Heavy metal immobilizing agent and heavy metal immobilizing method

Abstract

The present invention provides a heavy metal immobilizing agent and a heavy metal immobilizing method that can suppress the elution of heavy metals (e.g., hexavalent chromium) and increase the strength of the target object after immobilization treatment. [Solution] A heavy metal immobilizer containing blast furnace slag fine powder and a sodium thiosulfate-containing substance, wherein the heavy metal immobilizer has a Fe2O3 content of 0.19 to 1.00 mass% and a Cl content of 0.01 to 0.06 mass%. The mass ratio of blast furnace slag fine powder to sodium thiosulfate (blast furnace slag fine powder / sodium thiosulfate) contained in the heavy metal immobilizer is preferably 3.0 to 99.0.

Description

[Technical Field]

[0001] The present invention relates to a heavy metal immobilizing agent and a method for immobilizing heavy metals using the heavy metal immobilizing agent. [Background technology]

[0002] In recent years, numerous cases have been reported of soil contamination by heavy metals such as hexavalent chromium in former factory and business sites. When the concentration of heavy metals in the soil of a plot of land exceeds environmental standards and the area is designated as a "requiring remediation area," the land cannot be used as is. To make effective use of the land, one possible method is to excavate and remove the soil contaminated with heavy metals (hereinafter also referred to as "contaminated soil") and then use uncontaminated soil for backfilling. However, the handling of the removed contaminated soil becomes an issue, and this method does not provide a final solution. Furthermore, at waste disposal sites, there is the problem of heavy metals contained in waste leaching out due to rainfall, etc. If these leached heavy metals spread into the surrounding soil and groundwater, they can eventually accumulate in grains and the human body, potentially causing adverse effects.

[0003] Furthermore, when cement-based solidification materials, which use cement containing heavy metals such as cement clinker, are used on soil for the purpose of solidification, the amount of heavy metals such as hexavalent chromium leaching from the solidified soil may increase depending on the type of soil, the mixing conditions, and the properties and type of cement-based solidification material. For this reason, care must be taken when handling soil that has been solidified with cement-based solidification materials (for example, construction waste). Therefore, various technologies have been proposed to insolubilize heavy metals contained in contaminated soil and suppress their leaching from the soil.

[0004] For example, Patent Document 1 describes a cement-based treatment material for heavy metal-contaminated soil containing Portland cement, blast furnace slag, and gypsum, wherein the material contains 30 to 70% by mass of blast furnace slag and 2 to 8% by mass of gypsum based on SO3, with the remainder being Portland cement, relative to the total amount of Portland cement, blast furnace slag, and gypsum. Furthermore, Patent Document 2 describes a method for treating contaminated soil contaminated with harmful heavy metals, which involves adding and mixing magnesium oxide and calcium sulfide and / or sodium sulfide as sulfides in a total amount of 30 to 300 kg / m3 to contaminated soil, characterized in that 95 to 50% by mass of magnesium oxide is added and mixed to the contaminated soil based on 100% by mass of the total amount of magnesium oxide and sulfides, and then 5 to 50% by mass of sulfides is added and mixed based on 100% by mass of the total amount of magnesium oxide and sulfides, thereby setting the pH value to 8.0 or higher and less than 11.0. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2007-222694 [Patent Document 2] Patent No. 4712483 [Overview of the project] [Problems that the invention aims to solve]

[0006] When a heavy metal immobilizer is added to soil containing heavy metals and mixed with it for the purpose of immobilizing heavy metals, the strength of the soil may decrease after immobilization treatment, depending on the type of soil. The object of the present invention is to provide a heavy metal immobilizing agent and a heavy metal immobilizing method that can suppress the elution of heavy metals (e.g., hexavalent chromium) and increase the strength of the target object after immobilization treatment.

[0007] As a result of diligent research to solve the above problems, the inventors of the present invention have found that the above objective can be achieved by using a heavy metal immobilizer containing blast furnace slag fine powder and a sodium thiosulfate-containing substance, with an Fe2O3 content of 0.19 to 1.00 mass% and a Cl content of 0.01 to 0.06 mass%. In other words, the present invention provides the following [1] to [6]. [1] A heavy metal immobilizer comprising blast furnace slag fine powder and a sodium thiosulfate-containing substance, characterized in that the heavy metal immobilizer contains 0.19 to 1.00% by mass of Fe2O3 and 0.01 to 0.06% by mass of Cl. [2] The heavy metal immobilizer described in [1] above, wherein the mass ratio of blast furnace slag fine powder to sodium thiosulfate (blast furnace slag fine powder / sodium thiosulfate) contained in the heavy metal immobilizer is 3.0 to 99.0. [3] The heavy metal immobilizer according to [1] or [2], wherein the blast furnace slag fine powder contains 0.005 to 0.035% by mass of P2O5, and the sodium thiosulfate-containing substance contains 0.05% by mass or less of water-soluble phosphoric acid.

[0008] [4] A heavy metal immobilizer according to any one of [1] to [3] above, comprising at least one alkaline powder selected from magnesium oxide, light-calcined magnesia, quicklime, slaked lime, dolomite, light-calcined dolomite, semi-calcined dolomite, and calcium carbonate, wherein the proportion of the alkaline powder in the heavy metal immobilizer is 70% by mass or less. [5] The heavy metal immobilizer described in any of [1] to [4] above is applied to the object to be immobilized, 1 m 3 A method for immobilizing heavy metals by mixing them in quantities of 30 to 150 kg per unit. [6] The heavy metal immobilization method according to [5], wherein the substance to be immobilized is a hexavalent chromium-containing substance. [Effects of the Invention]

[0009] The heavy metal immobilizing agent of the present invention can suppress the elution of heavy metals (e.g., hexavalent chromium) from the object to be immobilized, and can also increase the strength of the object after immobilization treatment. [Modes for carrying out the invention]

[0010] The heavy metal immobilizer of the present invention is a heavy metal immobilizer containing blast furnace slag fine powder and a sodium thiosulfate-containing substance, wherein the Fe2O3 content in the heavy metal immobilizer is 0.19 to 1.00% by mass, and the Cl content is 0.01 to 0.06% by mass. Here, heavy metals refer to any of the following: cadmium and its compounds, hexavalent chromium compounds (hereinafter also simply referred to as "hexavalent chromium"), cyanide, mercury and its compounds, selenium and its compounds, lead and its compounds, arsenic and its compounds, fluorine and its compounds, and boron and its compounds (those listed as Class II specified hazardous substances under the Soil Contamination Countermeasures Act (2003)). Although cyanide, arsenic, selenium, fluorine, and boron are not heavy metals, they are included in the category of heavy metals.

[0011] Examples of blast furnace slag fine powder include water-granulated slag, which is obtained by rapidly cooling molten slag, a by-product of pig iron production in a blast furnace, with water and then crushing it, and slowly cooled slag, which is obtained by slowly cooling and then crushing it. The content of P2O5 contained as a trace component in blast furnace slag fine powder is preferably 0.005 to 0.035% by mass, more preferably 0.008 to 0.032% by mass, and particularly preferably 0.01 to 0.030% by mass. If the above content is within the above numerical range, the elution of heavy metals (especially hexavalent chromium) can be further suppressed. The Blaine specific surface area of ​​blast furnace slag fine powder is preferably 3,000 to 10,000 cm². 2 / g, more preferably 3,500~5,000cm 2 The specific surface area of ​​the Braine is 3,000 cm². 2When it is / g or more, the elution of heavy metals can be further suppressed, and the strength development of the target object after insolubilization treatment (for example, improved soil) can be further improved. The Blaine specific surface area is 10,000 cm 2 / g or less, it is easily available and improves workability. The content of sulfide sulfur in ground granulated blast furnace slag, measured in accordance with the quantification method for sulfide sulfur content specified in "JIS R 5202:2015 Methods for Chemical Analysis of Portland Cement", is preferably 0.3 to 1.8% by mass, particularly preferably 0.5 to 1.6% by mass. When the content is 0.3% by mass or more, the elution of heavy metals can be further suppressed, and the strength development of the target object after insolubilization treatment (for example, improved soil) can be further improved. When the content is 1.8% by mass or less, the risk that the amount of hydrogen sulfide generated from the target object after insolubilization treatment (for example, improved soil) becomes excessive can be suppressed.

[0012] The content of ground granulated blast furnace slag in the heavy metal insolubilizing material is preferably 20 to 98% by mass, more preferably 30 to 95% by mass, still more preferably 40 to 92% by mass, and particularly preferably 50 to 88% by mass. When the content is within the above numerical range, heavy metals can be more effectively insolubilized. Further, when the content is 20% by mass or more, the strength development of the target object after insolubilization treatment (for example, improved soil) can be further improved.

[0013] The sodium thiosulfate-containing substance used in the present invention is a substance containing sodium thiosulfate as a main component. From the viewpoint of further suppressing the elution of heavy metals (particularly hexavalent chromium), the content of sodium thiosulfate in the sodium thiosulfate-containing substance, calculated as anhydride, is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 65% by mass or more. From the viewpoint of further suppressing the elution of heavy metals (particularly hexavalent chromium), the content of water-soluble phosphoric acid contained as a minor component in the sodium thiosulfate-containing substance, converted in terms of P2O5, is preferably 0.05% by mass or less, more preferably 0.02% by mass or less. Further, from the viewpoint of suppressing the generation of hydrogen sulfide from the target substance, the pH of a test solution prepared from a sodium thiosulfate-containing substance in accordance with "Test Methods for Fertilizers, etc. (2024)" supervised by the Food and Agricultural Materials Inspection Center (FAMIC), an Incorporated Administrative Agency of Japan, is preferably 6 or higher, and more preferably 7 or higher. Further, the content of sodium thiosulfate (sodium thiosulfate contained in the sodium thiosulfate-containing substance that is a raw material of the heavy metal insolubilizing material) in the heavy metal insolubilizing material, calculated on an anhydride basis, is preferably 1.0 to 20.0% by mass, more preferably 1.5 to 18.0% by mass, still more preferably 2.0 to 15.0% by mass, and particularly preferably 2.5 to 12.0% by mass. When the content falls within the above numerical range, heavy metals can be more sufficiently insolubilized.

[0014] The heavy metal insolubilizing material of the present invention may contain alkaline powder within a range that does not impair the effects of the present invention. When the heavy metal insolubilizing material contains alkaline powder, it is possible to prevent the target substance after insolubilization treatment (for example, improved soil) from becoming acidic, and suppress the generation of hydrogen sulfide from the target substance. Examples of the alkaline powder include magnesium oxide, lightly burned magnesia, partial hydrates of lightly burned magnesia, quicklime, slaked lime, dolomite, lightly burned dolomite, partial hydrates of lightly burned dolomite, half-burned dolomite, and calcium carbonate. Among these, from the viewpoints of easy availability and not exerting adverse effects on the insolubilization of heavy metals, magnesium oxide, lightly burned magnesia, quicklime, slaked lime, dolomite, lightly burned dolomite, half-burned dolomite, and calcium carbonate are preferable. From the viewpoints of further suppressing the elution of heavy metals and suppressing the generation of hydrogen sulfide, the proportion of the alkaline powder in the heavy metal insolubilizing material is preferably 70% by mass or less, more preferably 2 to 50% by mass, and particularly preferably 8 to 35% by mass.

[0015] The mass ratio (blast furnace slag fine powder / sodium thiosulfate) of blast furnace slag fine powder contained in the heavy metal immobilizer to sodium thiosulfate (sodium thiosulfate contained in the sodium thiosulfate-containing substance which is a material of the heavy metal immobilizer) is preferably 3.0 to 99.0, more preferably 5.0 to 50.0, even more preferably 7.5 to 25.0, and particularly preferably 8.0 to 18.0. If the above mass ratio is within the above numerical range, the elution of heavy metals (especially hexavalent chromium) can be further suppressed.

[0016] The Fe2O3 content in the heavy metal immobilizer is 0.19 to 1.00% by mass, preferably 0.30 to 0.94% by mass, and more preferably 0.50 to 0.90% by mass. If the above content is within the above numerical range, the elution of heavy metals (especially hexavalent chromium) can be further suppressed. The Cl content in the heavy metal immobilizer is 0.01 to 0.06% by mass, preferably 0.015 to 0.055% by mass, and more preferably 0.02 to 0.05% by mass. If the above content is within the above numerical range, the elution of heavy metals (especially hexavalent chromium) can be further suppressed.

[0017] By adding and mixing the heavy metal immobilizing agent of the present invention with the object to be immobilized, the elution of heavy metals from the object can be suppressed. The heavy metal insolubilizing agent of the present invention is suitable for suppressing the elution of heavy metals, particularly cadmium and its compounds, hexavalent chromium compounds, mercury and its compounds, selenium and its compounds, lead and its compounds, arsenic and its compounds, and fluorine and its compounds, and is especially suitable for suppressing the elution of hexavalent chromium. The materials subject to immobilization treatment (objects to be immobilized) are those containing heavy metals (for example, materials containing hexavalent chromium). Specific examples of materials containing heavy metals include (i) soil and (ii) cement-based solidifying agents, for example, at 50 kg / m³. 3 Examples include improved soil obtained by adding and mixing the above, (iii) incineration ash such as coal ash, municipal solid waste incineration ash, paper sludge incineration ash, furnace cleaning waste, coke ash, and heavy oil combustion ash, and (iv) molten slag. In addition, the substance to be insolubilized usually does not satisfy the environmental standard values for heavy metals specified in Notification No. 46 of the Environment Agency. Specifically, examples include substances to be insolubilized that contain hexavalent chromium, and the elution amount of hexavalent chromium measured in accordance with Notification No. 46 of the Environment Agency exceeds the environmental standard value of 0.05 mg / L. When the substance to be insolubilized satisfies the environmental standard values for heavy metals specified in Notification No. 46 of the Environment Agency, the necessity of using the heavy metal insolubilizing material of the present invention becomes low.

[0018] For 1 m 3 of the substance to be insolubilized, the addition amount of the heavy metal insolubilizing material varies depending on the substance to be insolubilized, but is preferably 30 to 150 kg, more preferably 40 to 140 kg, and particularly preferably 45 to 135 kg. When the amount is 30 kg or more, the elution amount of heavy metals can be further reduced. When the amount is 150 kg or less, an increase in cost for the heavy metal insolubilizing material can be prevented. Examples of the method for adding and mixing the heavy metal insolubilizing material include dry addition, in which the heavy metal insolubilizing material is added as a powder to the substance to be insolubilized and mixed, and wet addition, in which water is added to the heavy metal insolubilizing material to form a slurry, and the slurry is added to the substance to be insolubilized and mixed. In the case of wet addition, the mass ratio of water to the heavy metal insolubilizing material is preferably 0.5 to 2.0, more preferably 0.6 to 1.5.

Examples

[0019] Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The materials used are as shown below. (1) Ground granulated blast furnace slag A; produced in Japan, Blaine specific surface area: 4,170 cm 2 / g, P2O5 content: 0.01% by mass, sulfide sulfur content: 0.72% by mass (2) Ground granulated blast furnace slag B; produced in Japan, Blaine specific surface area: 3,980 cm 2 / g, P2O5 content: 0.02% by mass, sulfide sulfur content: 1.08% by mass (3) Ground granulated blast furnace slag C; produced in Indonesia, Blaine specific surface area: 4,080 cm2 / g, P2O5 content: 0.04 mass%, sulfur content: 0.68 mass% (4) Blast furnace slag fine powder D; from Vietnam, Blaine specific surface area: 3,780 cm² 2 / g, P2O5 content: 0.003 mass%, sulfur content: 0.82 mass% (5) Sodium thiosulfate-containing substance A; Japanese origin, anhydrous sodium thiosulfate (content of anhydrous sodium thiosulfate in the sodium thiosulfate-containing substance: 99% by mass), content of water-soluble phosphoric acid (P2O5 equivalent): less than 0.01% by mass, pH (pH of the test solution prepared in accordance with the "Test Methods for Fertilizers, etc. (2024)" supervised by the Food and Agricultural Materials Inspection Center (FAMIC), the same applies below): 7.1 (6) Sodium thiosulfate-containing substance B; from China, sodium thiosulfate pentahydrate (content of sodium thiosulfate pentahydrate in sodium thiosulfate-containing substance: 97% by mass), content of water-soluble phosphoric acid (calculated as P2O5): 0.02% by mass, pH: 7.3 (7) Sodium thiosulfate-containing substance C; from China, anhydrous sodium thiosulfate (content of anhydrous sodium thiosulfate in sodium thiosulfate-containing substance: 97% by mass), content of water-soluble phosphoric acid (calculated as P2O5): 0.06% by mass, pH: 7.2 (8) Alkaline powder A; Magnesium oxide-containing substance, manufactured by Taiheiyo Cement Co., Ltd., light-calcined magnesia (magnesium oxide content: 88% by mass or more) (9) Alkaline powder B; from Indonesia, lightly calcined dolomite (10) Alkaline powder C; Japanese origin, slaked lime (11) Alkaline powder D; Made in Japan, quicklime (12) Alkaline powder E; calcium carbonate, manufactured by Okutama Kogyo Co., Ltd. (13) Alkaline powder F; from Indonesia, dolomite (14) Cement-based solidifying agent; Japanese-made, general-purpose solidifying agent for soft soils (15) Molten slag; water content: 12.5%, hexavalent chromium elution amount measured in accordance with Environmental Agency Notification No. 46: 0.22 mg / liter, pH of test solution prepared in accordance with Environmental Agency Notification No. 46: 6.8) (16) Soil; Red volcanic ash, wet density: 1.31 g / cm³ 3 Natural water content: 102.2%, Hexavalent chromium elution amount measured in accordance with Environmental Agency Notification No. 46: less than 0.02 mg / liter, pH of test solution prepared in accordance with Environmental Agency Notification No. 46: 6.3)

[0020] [Examples 1-6, Comparative Examples 1-4] A heavy metal immobilizer was prepared by mixing blast furnace slag fine powder of the types and proportions shown in Table 1 (referred to as "blast furnace slag" in Tables 1 and 3), a sodium thiosulfate-containing substance, and an optionally added alkaline powder. Table 1 shows the mass ratio of blast furnace slag fine powder to sodium thiosulfate, the Fe2O3 content, and the Cl content in the heavy metal immobilizer. The prepared powdered heavy metal immobilizer was added to the molten slag, 1 m³ of molten slag. 3 An immobilized material was prepared by adding and mixing heavy metal immobilizers in the amounts shown in Table 1. The immobilized material was sealed and stored in a polyethylene bag. At 3 days of age, the amount of hexavalent chromium leached from the immobilized material was measured by obtaining a test solution in accordance with Environmental Agency Notification No. 46, and then measuring the amount of hexavalent chromium leached from the test solution in accordance with "JIS K 0102:2019 (Industrial wastewater testing methods)". The environmental standard value for hexavalent chromium is 0.05 mg / liter or less. The results are shown in Table 1.

[0021] [Table 1]

[0022] Table 1 shows that the amount of hexavalent chromium leached in Examples 1 to 6 met the environmental standard (0.05 mg / liter or less), whereas the amount of hexavalent chromium leached in Comparative Examples 1 to 4 did not meet the environmental standard.

[0023] [Examples 7-10, Comparative Examples 6-7] A heavy metal immobilizer was prepared by mixing blast furnace slag fine powder of the types and proportions shown in Table 2, a sodium thiosulfate-containing substance, and an optionally added alkaline powder. Table 2 shows the mass ratio of blast furnace slag fine powder to sodium thiosulfate, the Fe2O3 content, and the Cl content in the heavy metal immobilizer. A slurry was prepared by mixing water with a heavy metal immobilizer, resulting in a water / heavy metal immobilizer mass ratio of 0.7. For soil, 1 m 3 A cement-based solidifying agent in an amount equivalent to 300 kg, and soil 1 m 3 Slurries containing heavy metal immobilizers (calculated on a solid content basis) were added and mixed to prepare improved soil. The amount of hexavalent chromium leached from the improved soil at 3 days of age was measured in the same manner as in Example 1. Furthermore, the unconfined compressive strength of the improved soil was measured in accordance with "JIS A 1216:2020 (Unconfined Compression Test Method for Soil)". The unconfined compressive strength is 1,400 kN / m 3 The above were set as target values. [Comparative Example 5] For soil, 1 m 3 To this extent, 300 kg of cement-based solidifying agent was added and mixed to prepare improved soil. The amount of hexavalent chromium leached from the improved soil at 3 days of age was measured in the same manner as in Example 1. Furthermore, the unconfined compressive strength of the improved soil was measured in accordance with "JIS A 1216:2020 (Unconfined Compression Test Method for Soil)". The results are shown in Table 3.

[0024] [Table 2]

[0025] [Table 3]

[0026] Table 3 shows the uniaxial compressive strength (1,421-1,485 kNm) of Examples 7-10. 2 ) is the uniaxial compressive strength (736-1395 kN / m²) of Comparative Examples 5-7. 2 It is greater than the target value (1,400 kN / m 2 It can be seen that the condition is met. Furthermore, it can be seen that the amount of hexavalent chromium leached in Examples 7 to 10 meets the environmental standard, while the amount of hexavalent chromium leached in Comparative Examples 5 to 7 does not meet the environmental standard.

Claims

1. A heavy metal insolubilizer containing blast furnace slag fine powder and a sodium thiosulfate-containing substance, Among the above heavy metal immobilizing agents, Fe ２ O ３ A heavy metal immobilizer characterized by having a content of 0.19 to 1.00 mass% of and a Cl content of 0.01 to 0.06 mass%.

2. The heavy metal immobilizing agent according to claim 1, wherein the mass ratio of blast furnace slag fine powder to sodium thiosulfate (blast furnace slag fine powder / sodium thiosulfate) contained in the heavy metal immobilizing agent is 3.0 to 99.

0.

3. In the above blast furnace slag fine powder, P ２ O ５ The content is 0.005 to 0.035% by mass, In the above sodium thiosulfate-containing substance, the content of water-soluble phosphoric acid (P ２ O ５ The heavy metal immobilizer according to claim 1, wherein the equivalent amount is 0.05% by mass or less.

4. It contains at least one alkaline powder selected from magnesium oxide, light-calcined magnesia, quicklime, slaked lime, dolomite, light-calcined dolomite, semi-calcined dolomite, and calcium carbonate. The heavy metal immobilizer according to claim 1, wherein the proportion of the alkaline powder in the heavy metal immobilizer is 70% by mass or less.

5. The heavy metal immobilizing agent according to any one of claims 1 to 4 is applied to the object to be immobilized, to a depth of 1 m ３ A method for immobilizing heavy metals by mixing them in quantities of 30 to 150 kg per unit.

6. The method for immobilizing heavy metals according to claim 5, wherein the substance to be immobilized is a hexavalent chromium-containing substance.

Images