Hexavalent chromium elution inhibitor

Abstract

To provide a hexavalent chromium elution suppressing agent that contains a slag powder originating from metal manufacturing process, and in which the effect of suppressing elution of hexavalent chromium from contaminated soil containing hexavalent chromium is enhanced, and to provide a method for suppressing elution of hexavalent chromium.SOLUTION: Provided is a hexavalent chromium elution suppressing agent that comprises a slurry containing a slag powder originating from a metal manufacturing process, an alkaline-based material, and carbon dioxide-containing water. The carbon dioxide concentration of the carbon dioxide-containing water is preferably 1,000 mg / liter or more. The pH of the hexavalent chromium elution suppressing agent is preferably 11.0 to 13.0. A method for suppressing elution of hexavalent chromium, comprising adding and mixing a hexavalent chromium elution suppressing agent to soil containing hexavalent chromium.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an agent for inhibiting the elution of hexavalent chromium. [Background technology]

[0002] In recent years, it has been frequently reported that soil is contaminated with heavy metals such as hexavalent chromium at the sites of factories, business establishments, and industrial waste treatment plants. When soil is contaminated with heavy metals such as hexavalent chromium, the contamination spreads to groundwater, affecting the human body and even grains, creating a health and safety problem. In addition, if the contamination concentration of soil exceeds the environmental standard value, the site cannot be used as it is, and there is also the problem that the land cannot be used effectively. Therefore, various techniques have been proposed for insolubilizing heavy metals in contaminated soil and inhibiting the elution of these heavy metals from the soil. For example, Patent Document 1 describes an insolubilizing material for suppressing the elution of hexavalent chromium, which is characterized by containing blast furnace slag powder and sodium hydrogen sulfite. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-87190 A Summary of the Invention [Problem to be solved by the invention]

[0004] The blast furnace slag powder in the insolubilizing material described in Patent Document 1 is produced using slag, which is a by-product produced when producing pig iron in a blast furnace, as a raw material. However, due to the recent decline in domestic steel demand in Japan, it is not necessarily guaranteed that there will be a stable supply of blast furnace slag powder and other slag powder originating from metal manufacturing processes in the future. An object of the present invention is to provide a hexavalent chromium elution inhibitor containing slag powder originating from a metal manufacturing process, which has an enhanced effect of inhibiting the elution of hexavalent chromium from contaminated soil containing hexavalent chromium. [Means for solving the problem]

[0005] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned object can be achieved by using a hexavalent chromium elution inhibitor consisting of a slurry containing slag powder originating from a metal production process, an alkaline material, and water containing carbon dioxide, and have completed the present invention. The present invention provides the following [1] to [5]. [1] A hexavalent chromium elution inhibitor for suppressing the elution of hexavalent chromium from soil containing hexavalent chromium, comprising a slurry containing slag powder originating from a metal production process, an alkaline material, and water containing carbon dioxide. [2] The hexavalent chromium elution inhibitor according to [1] above, wherein the carbon dioxide concentration of the carbon dioxide-containing water is 1,000 mg / L or more. [3] The inhibitor for inhibiting elution of hexavalent chromium according to the above [1] or [2], wherein the pH of the inhibitor for inhibiting elution of hexavalent chromium is 11.0 to 13.0. [4] A method for suppressing elution of hexavalent chromium from soil containing hexavalent chromium, using the inhibitor for elution of hexavalent chromium according to any one of [1] to [3] above, comprising adding the inhibitor for elution of hexavalent chromium to the soil and mixing the same. [5] Unit volume of the above soil: 1 m 3 The method for suppressing elution of hexavalent chromium according to the above-mentioned [4], wherein the amount of the elution inhibitor of hexavalent chromium added per unit time is 100 kg or more. Effect of the Invention

[0006] According to the hexavalent chromium elution inhibitor of the present invention, the elution of hexavalent chromium from contaminated soil can be more effectively inhibited than in the case where ordinary water is used instead of the carbon dioxide-containing water. In addition, in the present invention, when the ratio of slag powder originating from the metal manufacturing process in the total amount of slag powder originating from the metal manufacturing process and alkaline materials is the same, water containing carbon dioxide gas is used as the mixing water instead of water not containing carbon dioxide gas, thereby suppressing the leaching of hexavalent chromium while suppressing the decrease in uniaxial compressive strength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The hexavalent chromium elution inhibitor of the present invention comprises a slurry containing slag powder originating from a metal manufacturing process, an alkaline material, and water containing carbon dioxide gas. Slag powder originating from metal manufacturing processes has the ability to inhibit the elution of hexavalent chromium from contaminated soil containing hexavalent chromium. Examples of raw materials for slag powder originating from metal manufacturing processes include blast furnace slag and steelmaking slag. Examples of blast furnace slag include granulated blast furnace slag and slowly cooled blast furnace slag. The steelmaking slag may be electric furnace slag, etc. The electric furnace slag may be oxidized slag or reduced slag. The slag powder originating from the metal manufacturing process can be obtained by grinding the various types of slag mentioned above. In particular, ground blast furnace slag is known as ground granulated blast furnace slag, which is a cement admixture. The ground granulated blast furnace slag is obtained by drying and pulverizing granulated blast furnace slag, which is obtained by quenching with water molten slag, a by-product of pig iron production in a blast furnace.

[0008] The Blaine specific surface area of ​​the slag powder originating from the metal manufacturing process is preferably 1,000 cm 2 / g or more, more preferably 2,500 to 10,000 cm 2 / g, and particularly preferably 3,000 to 8,000 cm 2 / g. Blaine specific surface area is 1,000cm 2 / g or more, the effect of suppressing the elution of hexavalent chromium from contaminated soil containing hexavalent chromium can be further improved. 2When the slag content is 100% or less, the labor required for pulverization can be reduced, and the efficiency of production of slag powder originating from a metal production process can be further improved.

[0009] The alkaline material used in the present invention is used to adjust the pH of the hexavalent chromium elution inhibitor (slurry) of the present invention. If the alkaline material is not used, the pH will be low and harmful hydrogen sulfide originating from slag powder originating from the metal manufacturing process may be generated from the hexavalent chromium elution inhibitor (slurry). Examples of alkaline materials include various types of cement (for example, Portland cement, ecocement, etc.), magnesium oxide-based materials, hydroxides of alkali metals, and hydroxides of alkaline earth metals. Examples of Portland cement include ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, and low-heat Portland cement. In the present invention, blast furnace cement (containing ground granulated blast furnace slag) may be used as a material containing both slag powder originating from a metal manufacturing process and an alkaline material.

[0010] Examples of magnesium oxide-based materials include powders of light-burned magnesia, partial hydrates of light-burned magnesia, light-burned dolomite, and partial hydrates of light-burned dolomite. Light-burned magnesia can be obtained by firing a raw material containing either or both of magnesium carbonate and magnesium hydroxide at a temperature of 600 to 1,300°C. Lightly burned dolomite includes, for example, one obtained by burning dolomite at a temperature of 650 to 1,100°C. Examples of partial hydrates of light-burned magnesia include those obtained by crushing light-burned magnesia, adding water to the resulting crushed material and stirring and mixing, or by storing the resulting crushed material in an atmosphere with a relative humidity of 80% or more for one week or more to partially hydrate the light-burned magnesia. The partial hydrate of light-burned dolomite may be obtained in the same manner as for obtaining the partial hydrate of light-burned magnesia described above, except that light-burned dolomite is used in place of light-burned magnesia.

[0011] Examples of the alkali metal hydroxide include sodium hydroxide and potassium hydroxide. Examples of the hydroxides of alkaline earth metals include calcium hydroxide. In the present invention, the alkaline material may be a combination of two or more of the above-mentioned examples (for example, light-burned magnesia powder and sodium hydroxide).

[0012] In the present invention, the amount of slag powder originating from the metal production process per 100 parts by mass of the total amount of slag powder originating from the metal production process and alkaline materials varies depending on the carbon dioxide concentration of the carbon dioxide-containing water, but is preferably 10 to 95 parts by mass, more preferably 20 to 90 parts by mass, and particularly preferably 30 to 85 parts by mass. When the amount is 10 parts by mass or more, the effect of suppressing the elution of hexavalent chromium is increased. When the amount is 95 parts by mass or less, the amount of the alkaline material is increased, so that it is easier to control the pH of the elution inhibitor (slurry) of the present invention within a numerical range in which hydrogen sulfide is not generated.

[0013] Carbon dioxide-containing water can usually be obtained by blowing carbon dioxide gas into water. The carbon dioxide concentration of the carbon dioxide-containing water varies depending on the mass ratio of the slag powder originating from the metal production process and the alkaline material, but is preferably 1,000 mg / liter or more, more preferably 1,500 to 7,500 mg / liter, and particularly preferably 2,000 to 6,000 mg / liter. When the concentration is 1,000 mg / L or more, the effect of suppressing the elution of hexavalent chromium is greater. In addition, since more carbon dioxide gas (carbon dioxide) can be used, for example, when exhaust gas generated in a cement manufacturing plant is used, the effect of reducing carbon dioxide emissions is greater. When the concentration is 7,500 mg / L or less, the effect of suppressing the elution of hexavalent chromium is greater.

[0014] The amount of carbon dioxide-containing water per 100 parts by mass of the total amount of slag powder originating from the metal production process and the alkaline material is preferably 50 to 150 parts by mass, more preferably 60 to 140 parts by mass, even more preferably 70 to 130 parts by mass, and particularly preferably 80 to 120 parts by mass. When the amount is 50 parts by mass or more, it becomes easier to mix powder such as slag powder originating from a metal manufacturing process with carbon dioxide-containing water. Also, the effect of inhibiting elution of hexavalent chromium becomes greater. When the amount is 150 parts by mass or less, when the hexavalent chromium elution inhibitor of the present invention, which is a slurry, is added to contaminated soil, the contaminated soil after addition can be prevented from becoming weak. Also, an increase in treatment costs due to an excessive amount of carbon dioxide-containing water can be avoided.

[0015] An example of a method for producing the hexavalent chromium elution inhibitor of the present invention includes a carbon dioxide-containing water preparation step of preparing carbon dioxide-containing water by blowing carbon dioxide into water, a powder mixture preparation step of mixing slag powder originating from a metal production process with an alkaline material to obtain a powder mixture, and a slurry preparation step of mixing the powder mixture with the carbon dioxide-containing water to prepare a hexavalent chromium elution inhibitor in the form of a slurry.

[0016] In the carbon dioxide-containing water preparation step, examples of the method for blowing carbon dioxide into water include a method for blowing a gas containing carbon dioxide into water using a carbon dioxide supply means (e.g., an exhaust pipe for supplying a gas containing carbon dioxide) installed in water. In order to increase the carbon dioxide concentration in the carbon dioxide-containing water or to improve the treatment efficiency, the blowing may be performed by pressurizing an atmosphere rich in water and carbon dioxide. Here, the ratio of carbon dioxide gas in the gas containing carbon dioxide gas is preferably 5% by volume or more, more preferably 10% by volume or more, even more preferably 15% by volume or more, even more preferably 20% by volume or more, even more preferably 40% by volume or more, even more preferably 60% by volume or more, and particularly preferably 80% by volume or more. If the ratio is 5% by volume or more, carbon dioxide gas-containing water can be obtained in a shorter time. The gas containing carbon dioxide may be a gas consisting of only carbon dioxide. Examples of gases containing carbon dioxide include exhaust gas (carbon dioxide concentration: about 20% by volume) generated in the cement manufacturing process, and gas separated and recovered from the exhaust gas (carbon dioxide concentration: about 100% by volume).

[0017] The pH of the hexavalent chromium elution inhibitor (slurry) of the present invention is preferably 11.0 to 13.0, more preferably 11.1 to 12.9, and particularly preferably 11.2 to 12.8. When the pH is 11.0 or more, the generation of hydrogen sulfide from the hexavalent chromium elution inhibitor (slurry) of the present invention can be more reliably suppressed, and when the pH is 13.0 or less, an increase in treatment cost due to excessive use of alkaline materials can be avoided.

[0018] The method for inhibiting elution of hexavalent chromium of the present invention involves adding the above-mentioned elution inhibitor of hexavalent chromium to soil containing hexavalent chromium and mixing the same to obtain treated soil (treated soil). Unit volume of soil containing hexavalent chromium (1 m 3 The amount of the hexavalent chromium elution inhibitor to be added per unit time varies depending on the concentration of hexavalent chromium in the soil, but from the viewpoint of obtaining a sufficient effect of inhibiting elution of hexavalent chromium, the amount is preferably 100 kg or more, more preferably 200 kg or more, and particularly preferably 300 kg or more. The upper limit of the amount added is not particularly limited, but from the viewpoint of avoiding an increase in processing costs, it is preferably 600 kg, more preferably 500 kg, and particularly preferably 400 kg. EXAMPLES

[0019] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. [Materials used] (1) Slag powder originating from metal manufacturing process (fine blast furnace slag powder; product name: Cerament; manufactured by DC Corporation; Blaine specific surface area: 4,000 cm) 2 / g;Meets the quality standards of "Blast Furnace Slag Powder 4000" specified in "JIS A 6206 (Blast Furnace Slag Powder for Concrete)" (2) Alkaline material (ordinary Portland cement; manufactured by Taiheiyo Cement Corporation; Blaine specific surface area: 3,300 cm) 2 / g) (3) Carbon dioxide-containing water (carbon dioxide concentration: 1,800 to 7,200 mg / liter; tap water into which gas with a carbon dioxide concentration of 99.9% by volume has been blown) (4) Water (for comparison; tap water) (5) Contaminated soil containing hexavalent chromium (Kanto loam, a type of volcanic ash clay soil)

[0020] [Example 1] 80 parts by mass of ground granulated blast furnace slag and 20 parts by mass of normal Portland cement were mixed to obtain a powder mixture. 100 parts by mass of this powder mixture and 100 parts by mass of carbon dioxide-containing water (carbon dioxide concentration: 2,000 mg / L) were mixed to obtain a slurry (hexavalent chromium elution inhibitor). The pH of this slurry was 11.5. The pH of the slurry was measured 1 minute after contact with water. Next, this slurry was applied to contaminated soil containing hexavalent chromium in an amount of 1 m 3 The soil was added in an amount of 300 kg per unit area and mixed to obtain treated soil (treated soil).

[0021] The following tests were conducted on the treated soil. (a) Uniaxial compressive strength In accordance with "JIS A1216:2020", the unconfined compressive strength of the treated soil (unit: kN / m 2 ) was measured. (b) Amount of hexavalent chromium leached A test solution was obtained in accordance with the method described in "Environmental Standards for Soil Contamination" (Environment Agency Notification No. 46 of 1991), and the amount of hexavalent chromium (unit: mg / liter) in this test solution was measured in accordance with the method described in "JIS K 0102:2019" (Testing method for industrial wastewater). The environmental standard for hexavalent chromium is 0.05 mg or less per liter of test solution.

[0022] [Examples 2 to 9, Comparative Examples 1 to 6] As shown in the "Powder" and "Water" columns of Table 1, the experiment was carried out in the same manner as in Example 1, except that the type and amount of powder and the carbon dioxide concentration in the water were changed. The above results are shown in Table 1. In Table 1, "cement" is ordinary Portland cement. "Parts" is parts by mass. "Hexavalent chromium (mg / L)" is the amount of hexavalent chromium eluted (unit: mg / liter). "Reduction rate of hexavalent chromium (%)" represents the reduction rate of hexavalent chromium (%) of the Examples compared to the Comparative Examples in a group (e.g., Examples 1-2, Comparative Example 1) in which the ratio of ground granulated blast furnace slag in the total amount of ground granulated blast furnace slag and cement is the same.

[0023] [Table 1]

[0024] Comparing Examples 1 and 2 (using water containing carbon dioxide gas) with Comparative Example 1 (using water not containing carbon dioxide gas) in Table 1, it can be seen that the amount of hexavalent chromium eluted in Examples 1 and 2 is less than that in Comparative Example 1. In Table 1, when comparing Examples 3 to 7 with Comparative Example 2, or Examples 8 to 9 with Comparative Example 3, it can be seen that the same tendency is observed. On the other hand, among Comparative Examples 4 to 6 in which no ground granulated blast furnace slag was used, no difference in the amount of hexavalent chromium eluted due to the presence or absence of carbon dioxide in the water was observed.

Claims

1. A hexavalent chromium elution inhibitor for suppressing the elution of hexavalent chromium from soil containing hexavalent chromium, the hexavalent chromium elution inhibitor being characterized in that it comprises a slurry containing slag powder originating from a metal production process, an alkaline material, and water containing carbon dioxide.

2. 2. The hexavalent chromium elution inhibitor according to claim 1, wherein the carbon dioxide gas-containing water has a carbon dioxide gas concentration of 1,000 mg / L or more.

3. The hexavalent chromium elution inhibitor according to claim 1 or 2, wherein the pH of the hexavalent chromium elution inhibitor is 11.0 to 13.

0.

4. A method for suppressing elution of hexavalent chromium from soil containing hexavalent chromium, using the elution inhibitor of hexavalent chromium according to any one of claims 1 to 3, A method for inhibiting elution of hexavalent chromium, comprising adding and mixing the elution inhibitor of hexavalent chromium to the soil.

5. Unit volume of the above soil is 1 m ３ 5. The method for suppressing elution of hexavalent chromium according to claim 4, wherein the amount of the elution inhibitor of hexavalent chromium added per unit time is 100 kg or more.

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