JP2002320954A - Heavy metal elution inhibitor of heavy metal contaminated soil and method for inhibiting elution of heavy metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for achieving a standard elution value 11 at which at least a contaminated soil can be disposed of at a controlled disposal site by insolubilizing heavy metals in a soil contaminated with at least one kind or plural kinds of heavy metals of hexavalent chromium, arsenic, selenium, cadmium, total mercury and lead whose elution characteristics are individually different from each other to inhibit the elution of the heavy metals. SOLUTION: A heavy metal elution inhibitor is the one, which inhibits the elution of heavy metals in the soil contaminated with at least one kind or plural kinds of heavy metals of hexavalent chromium, arsenic, selenium, cadmium, total mercury and lead and is the heavy metal elution inhibitor of the heavy metal contaminated soil which comprises alkali materials (L) containing fine powder of a blast furnace slag (S), gypsum (G) and calcium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the elution of heavy metals from soils contaminated with heavy metals, especially soils contaminated with at least one or more heavy metals of hexavalent chromium, arsenic, selenium, cadmium, total mercury and lead. TECHNICAL FIELD The present invention relates to a heavy metal elution inhibitor used for suppressing leaching and a method for suppressing heavy metal elution from soil contaminated with heavy metals.

[0002]

2. Description of the Related Art Regarding surveys and countermeasures for contaminated soil, the Environment Agency published "Guidelines for Surveys and Countermeasures for Soil and Groundwater Pollution" in January 1999. According to the report, soil in which harmful substances exceeding soil environmental standards were detected is considered to be contaminated soil, and it is desirable that countermeasures be formulated based on this guideline.

[0003] Among the harmful substances indicated by these guidelines, there are heavy metals. As a permanent measure against heavy metals, there is a purification treatment for removing the target substance from contaminated soil. The mainstream of the purification treatment is a mechanical treatment such as classification or washing. In the purification treatment, contaminated soil and contaminated water separated and concentrated are generated as by-products, and it is necessary to further dispose of the contaminated soil and contaminated water.

The above guidelines prescribe containment as another measure against contaminated soil. This at least isolates the contaminated soil from the general environment. Containment: If the elution value of harmful substances is high, bring the contaminated soil to a concrete barrier type disposal site, enclose it with a barrier type structure of concrete walls, treat heavy metals with chemicals and bring it to a management type disposal site And treating heavy metals with chemicals and surrounding the contaminated soil with a high-density polyethylene sheet or the like in a water-blocking structure.

[0005] However, the above-mentioned containment and the use of a concrete structure increase the cost, and in practice, it is carried out by pre-treatment and brought to a controlled disposal site. There are many sites where containment is performed. As described above, as a countermeasure against heavy metal contaminated soil, pretreatment of heavy metals is usually necessary prior to containment so as to achieve the standard elution value II that can be disposed of in a controlled repository, and this pretreatment is extremely important. Processing was done.

Until now, in the process of insolubilizing heavy metals contaminated with soil, it has been necessary to select an insolubilizing agent according to the properties of each heavy metal because the insolubilization characteristics differ for each heavy metal. That is, sodium sulfide was used for insolubilizing cadmium, lead and total mercury, ferrous sulfate was used for insolubilizing hexavalent chromium, and ferric chloride was used for insolubilizing arsenic.

However, these insolubilizing agents are all expensive and may require generation of a large amount of harmful gas when mixed with soil, so that it is necessary to exercise caution when using them.

On the other hand, it has been practiced to use inexpensive cement and to suppress the elution of heavy metals by solidifying the cement.
This was suitable for suppressing the elution of arsenic and cadmium. However, cement does not have a sufficient function to suppress the elution of hexavalent chromium and lead.To suppress the elution of heavy metals from soils contaminated with heavy metals containing hexavalent chromium or lead, ferrous sulfate or ferrous sulfate must be added to the cement. It was necessary to use sodium sulfide in combination.

However, in recent years, a phenomenon that hexavalent chromium is contained in cement has appeared, and it has become necessary to pay attention to hexavalent chromium eluted from cement used as a solidifying agent. .

[0010]

The present invention provides a method for insolubilizing heavy metals in soil contaminated with at least one or more heavy metals of hexavalent chromium, arsenic, selenium, cadmium, total mercury and lead, each having a different elution characteristic. The purpose of the present invention is to suppress the elution of heavy metals and thereby achieve the standard elution value II at which contaminated soil can be disposed at least in a controlled repository.

[0011]

SUMMARY OF THE INVENTION The present invention relates to an inhibitor for suppressing the elution of heavy metals from soil contaminated with at least one or more heavy metals of hexavalent chromium, arsenic, selenium, cadmium, total mercury and lead. A heavy metal elution inhibitor for heavy metal contaminated soil comprising a blast furnace slag differential powder (S), gypsum (G) and an alkaline material (L) containing calcium (Claim 1). The ratio (G / S) of the blast furnace slag fine powder (S) is 2.0 or less, and the ratio (L / S) of the calcium-containing alkaline material (L) and the blast furnace slag fine powder (S) is 0.02. 2. The heavy metal elution inhibitor for heavy metal contaminated soil according to claim 1 (claim 2), which is contaminated with at least one or more heavy metals of hexavalent chromium, arsenic, selenium, cadmium, total mercury and lead. Heavy gold from the soil A method of inhibiting elution,
Blast furnace slag per contaminated soil 1m ³ (S) 35
a method for suppressing elution of heavy metals from soil contaminated with heavy metals, characterized by mixing at least 1 kg of gypsum (G) and 1 to 65 kg of calcium-containing alkali material (L) (claim 3); 4. A powder obtained by mixing blast furnace slag fine powder (S), gypsum (G) and an alkaline material (L) containing calcium, or water is added to this mixed powder to be mixed with soil as a slurry.
(4) A method for suppressing elution of heavy metals from soil contaminated with heavy metals according to (4).

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION
Hexavalent chromium, arsenic, selenium, cadmium, total mercury and lead. Looking at the mechanism of insolubilization of these heavy metals by conventional cement, hexavalent chromium and arsenic
Etrin Guide (3CaO), a hydration product of cement
・ Al ₂ O ₃ .3CaSO ₄ .32H ₂ O). It is generally known that cadmium, total mercury, and lead react with sulfide ions to form hardly soluble sulfides, and their elution is suppressed. But,
The ability of cement to solubilize heavy metal contaminated soil was excellent for arsenic, selenium, cadmium and total mercury, but insufficient for hexavalent chromium and lead.

Therefore, the present inventors added aluminum and sulfate ions so that a large amount of ettringite was generated for hexavalent chromium, and hexavalent chromium was further incorporated therein. The idea is to add sulfide ions so that sulfides are generated in large amounts and elution can be suppressed, and this is intended to improve the insolubilizing ability of hexavalent chromium and lead.

As a result, for the production of ettringite, blast furnace slag fine powder containing more aluminum and sulfide ions than cement was selected, and gypsum was selected as containing more sulfate ions. Further, it is necessary to activate the blast furnace slag fine powder at an early stage, and for this purpose, it is considered that an alkali material containing calcium is required. In the end, the blast furnace slag fine powder (S), gypsum (G), and calcium-containing alkaline material (L) are used as heavy metal elution inhibitors, so that only arsenic, selenium, cadmium and total mercury can be used. In addition, the present inventors have found that hexavalent chromium and lead, which were insufficient with conventional cement, can also be satisfactorily insolubilized at the same time.

[0015] Neither of the heavy metals can be insolubilized by mixing both gypsum and an alkaline material containing calcium into the contaminated soil. In addition, when blast furnace slag fine powder and gypsum are mixed into contaminated soil, solidification is slow and
Elution of hexavalent chromium, arsenic and selenium cannot be suppressed. Further, when the blast furnace slag fine powder and the calcium-containing alkaline material are mixed into the contaminated soil, the selenium elution is not sufficiently suppressed even when the slag is solidified.

However, when the blast furnace slag fine powder (S), gypsum (G), and calcium-containing alkaline material (L) are mixed into the contaminated soil as in the present invention, the calcium-containing alkaline material and the soil are mixed. The slag is activated by the water and the kneading water therein, and further, the aluminum ions and sulfide ions of the slag are dissolved, and the dissolved gypsum and ettringite are quickly generated. At the same time, lead is insolubilized by sulfide ions.

Blast furnace slag fine powder (S) used in the present invention
Is a crushed blast furnace slag with a specific surface area of 4000 to 500
It is preferable to use a cement of about 0 cm ² / g (Brain value) which is usually mixed with cement. This blast furnace slag is
It contains aluminum necessary for producing ettrine guides produced in the step of insolubilizing heavy metals and sulfide ions required for producing sulfides.

As the gypsum (G), any of anhydrous gypsum, hemihydrate gypsum and dihydrate gypsum can be used. As the calcium-containing alkaline material, either slaked lime or quick lime can be used.

The preferred mixing ratio of these three is, by weight ratio, the ratio of the gypsum (G) to the blast furnace slag fine powder (S) (G /
S) is 2.0 or less. By setting this ratio to 2 or less, a large amount of ettrine guide is generated, and the elution of hexavalent chromium can be suppressed. The ratio (L / S) of the calcium-containing alkaline material (L) to the blast furnace slag fine powder (S) is 0.1% by weight.
02 to 1.0. If the ratio is less than 0.02, the solidification is slow and the elution of hexavalent chromium cannot be suppressed. When L / S exceeds 1.0, the pH is so high that the elution of lead cannot be suppressed.
A more preferable range of L / S is 0.03 to 0.09. With such a material ratio, generation of ettrine guide and reaction of sulfide are promoted. Further, the pH of the soil after mixing the heavy metal elution inhibitor is in a range suitable for insolubilizing lead.

The heavy metal elution inhibitor of the present invention comprises
blast furnace slag per m ³ (S) 35kg or more,
It is preferable to mix and mix 2 kg or more of gypsum (G) and 1 to 65 kg of an alkaline material (L) containing calcium. Depending on the contamination degree of the soil, the ground granulated blast furnace slag (S) is less than the contaminated soil 1 m ³ per 35 kg, is insufficient dissolution inhibiting hexavalent chromium. Gypsum (G) is 2
If it is less than kg, the elution of selenium becomes insufficient. If the content of the calcium-containing alkaline material (L) is less than 1 kg, the elution suppression of hexavalent chromium is insufficient. Further, when the content of the alkali material (L) exceeds 65 kg, the elution of lead is insufficiently suppressed. It is necessary to appropriately adjust these mixing amounts and mixing ratios in the case of special soil such as Kanto loam according to the adsorption and elution characteristics of the soil.

The heavy metal elution inhibitor of the present invention is mixed with water as a powder or mixed with water into a contaminated soil depending on the on-site conditions. That is, in a soil with a relatively high water content, the powder can be mixed as it is, but in a soil with a low water content, it is suspended in water and mixed into the soil with a slurry. If the shallow layer is insolubilized, it can be treated by mixing with a backhoe or by a plant after excavation. Can be processed.

By mixing the dissolution inhibitor of the present invention as described above, soil contaminated with heavy metals can achieve at least a dissolution value II that can be transported to a controlled disposal site for disposal. Can now be improved to the soil environmental standard value, which is a value for judging healthy soil.
Since both blast furnace slag fine powder and gypsum used in the present invention can utilize industrial by-products, they are also advantageous in terms of economy, resources, environment and the like.

[0023]

EXAMPLES (Examples 1 to 5, Comparative Example 1) Potassium dichromate (K ₂ Cr ₂ O ₇ ) was used as a single heavy metal reagent, and water and No. 8 silica sand were added to a predetermined amount of the reagent and mixed to simulate contamination. The soil was created. The water content was 15%. The chromium elution value of this contaminated soil (original soil) was 13 ppm.

A predetermined amount of the test simulated contaminated soil and the heavy metal elution inhibitor of the present invention shown in Table 1 are added to a hobard mixer, and water is added so that the weight ratio becomes 1: 1 and mixed for 10 minutes. Put in a mold with a diameter of 5cm and a length of 10cm,
Cured for a predetermined period in a constant temperature room at 20 ° C. Thereafter, a dissolution test according to the Environment Agency Notification No. 46 was conducted. Table 1 shows the results.
It was shown to.

[0025]

[Table 1]

As is clear from Table 1, by mixing the heavy metal elution inhibitor of the present invention into soil contaminated with hexavalent chromium, the elution value that can be transported to a controlled disposal site at 7 days of age for disposal. II was satisfied, and all were not detected at 28 days of age. In contrast, in Comparative Example 1, the dissolution value II could not be achieved even at a material age of 28 days.

(Examples 6 to 15 and Comparative Examples 2 to 5) In order to avoid the influence of coprecipitation between heavy metals, an anionic heavy metal of hexavalent chromium, arsenic and selenium which dissolves in water and exhibits anionic properties is used. , Cadmium exhibiting cationic properties,
In the present example, a test for suppressing the dissolution of anionic heavy metals was performed by dividing the total heavy mercury and lead into cationic heavy metals.

K ₂ Cr ₂ O ₇ , NaAsO ₂ and Na ₂ SeO ₃ were used as heavy metal reagents, and water and No. 8 silica sand were added to a predetermined amount thereof and mixed to prepare a simulated contaminated soil. The water content was 19%. The elution value of heavy metals in the contaminated soil (original soil) was 16 ppm for hexavalent chromium and 0.1 ppm for arsenic.
A predetermined amount of the test simulated contaminated soil and the heavy metal elution inhibitor of the present invention shown in Table 2 were added to a hobard mixer having 52 ppm and selenium of 1.5 ppm, and water was further added so as to have a weight ratio of 1: 1. After mixing for 10 minutes, the mixture was placed in a mold having a diameter of 5 cm and a length of 10 cm, and cured in a constant temperature room at 20 ° C. for a predetermined period. Thereafter, a dissolution test according to the Environment Agency Notification No. 46 was conducted. The results are shown in Table 2.

[0029]

[Table 2]

As is clear from Table 2, the heavy metal elution inhibitor of the present invention was mixed into the soil contaminated with hexavalent chromium, arsenic and selenium, and was conveyed to a controlled disposal site at the age of 7 days. Satisfies the dissolution value II that can be disposed, and
In Nos. 1, 14, and 15, none of the heavy metals was detected. Further, Example 12 satisfies the environmental standard value. On the other hand, in Comparative Examples 2 to 5, none of the elution values II could be satisfied.

(Examples 16 to 24, Comparative Examples 6 to 9) In this example, the same contaminated soil as in Examples 6 to 15 was used. Blast furnace slag fine powder (S), gypsum (G),
The amount of slaked lime (L) was added as shown in Table 3, and a dissolution test was conducted in the same manner as in Examples 6 to 15 in accordance with the notification of the Environment Agency, No. 46. Table 3 shows the results.

[0032]

[Table 3]

As is clear from Table 3, by mixing the heavy metal elution inhibitor of the present invention into soil contaminated with hexavalent chromium or the like, elution can be carried to a controlled disposal site at 7 days of age to be disposed. Satisfying the value II, Examples 18, 19, 20, 21
No heavy metal was detected. In contrast,
In Comparative Examples 6, 7, 8, and 9, the elution value II could not be achieved.

In Comparative Example 8, 100 kg / kg of blast furnace type B cement was used.
although that m ³ is added, in this case, the elution of hexavalent chromium is greater than the dissolution values II. In contrast, in the case of Example 23 using the heavy metal inhibitor of the present invention, the same 100
With the addition of kg / m ³ , all elution of hexavalent chromium, arsenic, and selenium can be suppressed. Similarly,
Comparative Example 9 was obtained by adding 50 kg / m ³ of blast furnace Class B cement. In this case, the elution of hexavalent chromium was the elution value II.
Is greatly exceeded. On the other hand, in the case of Example 24 using the heavy metal inhibitor of the present invention, the same 50 kg / m ^{3 was used.}
It is possible to suppress all elution of hexavalent chromium, arsenic, and selenium by the addition.

(Examples 25 to 34, Comparative Examples 10 to 11)
As in the above-described example, in order to avoid the influence of co-precipitation between heavy metals, in this example, a test for suppressing elution was performed for cation heavy metals such as cadmium, total mercury, and lead.

CdCl ₂ , HgCl ₂ and PbN
The O ₃ as a heavy metal reagent to prepare a simulated contaminated soil were mixed with water and No. 8 silica sand to the predetermined amount. 19% moisture content
And The elution value of heavy metals in this contaminated soil (original soil) is C
A predetermined amount of the test simulated contaminated soil and the heavy metal elution inhibitor of the present invention shown in Table 4 were added to a Hobart mixer having d of 5.9 ppm, T-Hg of 1.2 ppm, and Pb of 1.7 ppm. Water was added at a weight ratio of 1: 1 and mixed for 10 minutes, then placed in a mold having a diameter of 5 cm and a length of 10 cm, and cured in a constant temperature room at 20 ° C. for a predetermined period. Thereafter, a dissolution test according to the Environment Agency Notification No. 46 was conducted. Table 4 shows the results.

[0037]

[Table 4]

As is clear from Table 4, the heavy metal elution inhibitor of the present invention is mixed into cadmium, total mercury and lead contaminated soil, and conveyed to a controlled disposal site at the age of 7 days for disposal. Satisfies the possible elution value II. In Example 31, none of the heavy metals was detected. Example 3
0, 32, 33, and 34 satisfy the environmental standard values. On the other hand, in Comparative Examples 10 and 11, the elution value II could not be achieved.

(Examples 35 to 43, Comparative Example 12) In this example, the same contaminated soil as in Examples 25 to 34 was used. Blast furnace slag fine powder (S), gypsum (G),
The amount of slaked lime (L) was added as shown in Table 5, and a dissolution test was conducted in the same manner as in the above Examples according to the Environment Agency Notification No. 46. The results are shown in Table 5.

[0040]

[Table 5]

As is clear from Table 5, the heavy metal elution inhibitor of the present invention is mixed with soil contaminated with cadmium, total mercury, and lead, and conveyed to a controlled disposal site at the age of 7 days for disposal. Satisfies the possible elution value II. On the other hand, in Comparative Example 12, the elution value II could not be achieved. Comparative Example 12 contained no gypsum and could not suppress the elution of lead to the elution value II.

(Example 44, Comparative Example 13) To clarify the influence of the reaction between metals, a contaminated soil was prepared using a heavy metal reagent, distilled water and No. 8 silica sand, and insolubilized with various materials. . An anionic heavy metal of hexavalent chromium, arsenic and selenium exhibiting anionic properties when dissolved in water was mixed with a cationic heavy metal of cadmium, total mercury and lead exhibiting cationic properties.

The content and water content of various heavy metals were determined in Examples 6 to
15 and Examples 25 to 34, K ₂ Cr ₂ O ₇ and NaAsO are used as anionic heavy metals.
Heavy metal reagent ₂ and _Na 2 SeO ₃ was dissolved in distilled water. CdCl ₂ ,
HgCl ₂ and PbNO ₃ heavy metal reagents were dissolved in distilled water. Further, when both were mixed, a yellow-white suspension was obtained. This suspension material is considered lead chromate.
This suspension was mixed with No. 8 silica sand to obtain a simulated contaminated soil.

A predetermined amount of the test contaminated soil was put in a Hobart mixer, and a slurry having a water ratio of 1: 1 was mixed for 10 minutes. Then, the mixture was put into a mold having a diameter of 5 cm and L 10 cm and cured in a constant temperature room at 20 ° C. A dissolution test was conducted according to Agency Notification No. 46. The results are shown in Table 6.

[0045]

[Table 6]

From the elution values of heavy metals in the original soil shown in Table 6, it can be seen that hexavalent chromium, arsenic, selenium, and lead were partially insolubilized by the reaction between anionic heavy metals and cationic heavy metals.

When blast furnace type B cement was mixed with this soil, hexavalent chromium and lead eluted more than the original soil (Comparative Example 13). On the other hand, when the inhibitor of the present invention was mixed, all heavy metals could be suppressed below the environmental standard value (Example 44). This is because although lead chromate in the original soil was re-eluted due to the increase in pH in the comparative example when mixed with blast furnace type B cement, the dissolution suppression was insufficient because the formation of ettrine guide was slow. On the other hand, in the examples, it is considered that the re-eluted chromium ions were quickly taken into the ettrine guide, and the elution of hexavalent chromium and lead could be suppressed.

The compounding ratio of the heavy metal elution inhibitor of the present invention is appropriately adjusted according to the ratio of the heavy metals contained in the contaminated soil. In addition, it is necessary to change the mixing ratio of the heavy metal elution inhibitor to the soil according to the degree of contamination of the soil.

[0049]

As described above, according to the present invention, one kind of heavy metal elution inhibitor comprising three components of blast furnace slag fine powder (S), gypsum (G) and calcium-containing alkali material (L) is used. One or more of hexavalent chromium, arsenic, selenium, cadmium, total mercury, and lead, and furthermore, the elution of all heavy metals can be suppressed. Moreover, the inhibitory effect is the elution value
In addition to satisfying II, in some cases, it will be possible to achieve even stricter environmental standard values.

In the past, since the insolubilizing properties differed for each heavy metal, it was necessary to select an insolubilizing agent in accordance with the properties of each heavy metal. However, according to the present invention, such a trouble is not required at all. It is also beneficial for cost reduction.

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Claims (4)

[Claims] 1. An inhibitor for suppressing the elution of heavy metals from soil contaminated with at least one or more heavy metals of hexavalent chromium, arsenic, selenium, cadmium, total mercury and lead, comprising a blast furnace slag differential powder ( A heavy metal elution inhibitor for heavy metal contaminated soil comprising S), gypsum (G) and an alkaline material (L) containing calcium. 2. The weight ratio of gypsum (G) to blast-furnace slag fine powder (S) is not more than 2.0, and calcium-containing alkali material (L) and blast-furnace slag fine powder. The heavy metal elution inhibitor according to claim 1, wherein the ratio (L / S) of (S) is 0.02 to 1.0. 3. A hexavalent chromium, arsenic, selenium, cadmium, from the total mercury and at least one or more heavy metal-contaminated soil of lead provides a method of inhibiting elution of heavy metals, per contaminated soil 1 m ³ Mixing blast furnace slag fine powder (S) 35 kg or more, gypsum (G) 2 kg or more, and calcium-containing alkali material (L) 1-65 kg. Suppress heavy metal elution from soil contaminated with heavy metal. Method. 4. Blast furnace slag fine powder (S), gypsum (G)
4. Elution of heavy metals from soil contaminated with heavy metals according to claim 3, wherein the mixture is mixed with soil as powder mixed with an alkali material (L) containing calcium and calcium, or as a slurry by adding water to the mixed powder. how to.