JP2007222694A - Cement based treatment material for heavy metal-contaminated soil and solidification/insolubilization treatment method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cement based treatment material suitable for solidifying/insolubilizing heavy metal-contaminated soil stipulated in a soil contamination counter measure regulation, and a solidification/insolubilization treatment method for heavy metal-contaminated soil using it. <P>SOLUTION: The cement based treatment material for the heavy metal-contaminated soil containing portland cement, a blast furnace slug and a plaster contains 30-70 mass% and relative to a total amount of portland cement, blast furnace slug and plaster and 2-8 mass% of plaster based on SO<SB>3</SB>and the residue is the portland cement. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to soil, sludge contaminated with harmful heavy metals such as hexavalent chromium, mercury, arsenic, lead, cadmium or selenium, or harmful metals such as fluorine and boron (hereinafter collectively referred to as “heavy metals”). The present invention relates to a cementitious treatment material that suppresses elution of heavy metals from wastes and bottom sediments (hereinafter referred to as “heavy metal contaminated soil”), particularly hexavalent chromium or mercury, and a solidification and insolubilization method using the same.

  In order to ensure human health and reduce the environmental burden on animals and plants, there are known treatment methods for solidification insolubilization and containment that suppress elution of heavy metals from harmful heavy metal contaminated soil. In addition to mercury, hexavalent chromium, arsenic, lead, cadmium, selenium, and the like as contaminated heavy metal species, regulations on fluorine and boron have been started in the environmental standards established in 2001.

  Furthermore, various treatment materials (agents) used in such solid metal insolubilized soil insolubilization or containment treatment methods have been developed and put to practical use. Of these, various cements are used as bases, reducing agents, pH adjusters, Treatment materials using a fixing agent (coprecipitation agent, sulfurizing agent), chelating agent (complex forming agent), ion adsorbent and the like are known. For example, Patent Document 1 includes a cement-based solidifying material including cement and gypsum, a processing material including slag and a sulfite compound, Patent Document 2 includes quick lime and / or slaked lime-based processing material, and Patent Document 3 includes A cement-based or lime-based treatment material is disclosed.

  Conventionally, it has been thought that the amount of heavy metal elution from heavy metal contaminated soil generally decreases with an increase in the amount of cementitious treatment material added. For example, Patent Document 1 discloses a treatment material in which a small amount of a sulfite compound, a thiosulfate compound, or a sulfide is added to cement. However, if the amount of the treatment material added to heavy metal-contaminated soil is small, uneven mixing tends to occur, and the treated soil. Therefore, it was difficult to homogenize the amount of elution from the material, and it was necessary to increase the amount of treatment material added. In addition, sulfur compounds are generally unstable in the atmosphere, and there is also a concern that the elution suppression performance decreases with time.

Generally, the state of elution of heavy metal after solidification insolubilization treatment of heavy metal contaminated soil varies depending on the heavy metal species to be treated, the concentration of the contamination, the degree of complex contamination, soil properties (solidification characteristics, heavy metal ion adsorption capacity), and the like. For this reason, there is no treatment material or drug having a so-called all-purpose effect, a coping treatment according to the contamination condition of heavy metal-contaminated soil is required, and individual prescriptions are required. In particular, in the soil contaminated with hexavalent chromium or mercury, if an excessive amount of cement-based treatment material is added, the elution amount of these heavy metals may increase again from the solidified soil, which is a problem.

On the other hand, the cement itself contains a small amount of hexavalent chromium or mercury derived from the raw fuel used, and in some cases the hexavalent chromium is eluted from the soil solidified with the cement-based solidifying material containing this cement. It was also necessary to consider secondary elution from the system treatment material.
JP 2001-79536 A JP 2005-238193 A JP 2005-162895 A

According to the Ordinance for Enforcement of the Soil Contamination Countermeasures Law (Ministry of the Environment Ordinance No. 29, December 26, 2002), heavy metals are classified as Type 2 Specified Hazardous Substances, and appropriate measures are taken according to the contaminated soil contamination level and insolubilization level. Is stipulated. Table 1 shows reference values related to the solidification and insolubilization treatment of heavy metals excluding the cyanide compound among the second type specific harmful substances. Table 2 shows the relationship between the amount of elution of heavy metals before and after treatment and the applicable measures. That is, the elution amount of heavy metals is less than the second elution amount standard in soil contaminated exceeding the second elution amount standard, and in the soil that is less than the second elution amount standard and exceeding the elution amount standard. It is necessary to suppress below the elution amount standard.

  Therefore, the present invention is intended to treat serious heavy metal contaminated soil exceeding the second elution amount standard or elution amount standard (soil environmental standard) specified in the Enforcement Regulations of the Soil Contamination Countermeasures Law, below the second elution amount standard, or the elution amount standard. An object of the present invention is to provide a cement-based treatment material suitable for solidifying and insolubilizing and a method for solidifying and insolubilizing heavy metal-contaminated soil using the same.

  In particular, a cement-based treatment material that efficiently contains elution from hexavalent chromium and mercury-contaminated soil, which has been difficult to solidify and insolubilize with conventional cement-based treatment materials, and a method for solidifying and insolubilizing heavy metal-contaminated soil using the same. The purpose is to provide.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that a cement containing a large amount of blast furnace slag, unlike conventional cement-based treatment materials containing a sulfurous acid compound, a thiosulfuric acid compound, or a sulfide. Knowing that the system treatment material can stably secure the elution suppression performance of heavy metals, the present inventors have completed a cement-based treatment material containing Portland cement-blast furnace slag-gypsum of the present invention. In addition, the cementitious treatment material of the present invention newly shows that it exhibits specific elution suppression performance for specific heavy metals such as hexavalent chromium and mercury, and that there is an upper limit for the appropriate amount added to contaminated soil. As a result, the solidified insolubilization method for heavy metal-contaminated soil of the present invention was completed.

That is, the cementitious treatment material for heavy metal-contaminated soil of the present invention includes Portland cement, blast furnace slag, and gypsum, and blast furnace slag is 30 to 70% by mass and gypsum is 2 on the basis of SO ₃ with respect to the total amount thereof. It is a cement-based treatment material containing ˜8% by mass and the remainder being Portland cement. More preferably, the blast furnace slag is 40 to 60% by mass, the gypsum is 4 to 6% by mass based on SO ₃ , and the balance is Portland cement.

The method for solidifying and insolubilizing heavy metal-contaminated soil according to the present invention includes Portland cement, blast furnace slag and gypsum, and blast furnace slag is 30 to 70% by mass and gypsum is 2 to 2 based on SO _{3 based on} the total amount thereof. A solidified and insolubilized treatment method in which 8% by mass and the rest of Portland cement is cement-based treatment material is added in a range of 50 kg or more per 1 m ^{3 of} hexavalent chromium or mercury-contaminated soil and not exceeding 250 kg, and mixed and stirred. is there. More preferably, a cementitious treatment material of 40 to 60% by mass of blast furnace slag and 4 to 6% by mass of gypsum based on SO ₃ is used, and the remainder is Portland cement.

Moreover, since the elution of hexavalent chromium or mercury from the solidified and insolubilized treated soil of hexavalent chromium or mercury-contaminated soil also changes in the soil particles constituting the soil, the appropriate amount of cementitious treatment material is also different. That is, the appropriate amount of cementitious treatment material per 1 m ^{3 of} hexavalent chromium or mercury-contaminated soil is in the range of 50 to 150 kg for sandy soil and 100 kg or more and 250 kg for viscous soil and volcanic ash clay.

In particular, in the soil contaminated with hexavalent chromium or mercury, when an excessive amount of cement-based treatment material is added, the amount of elution of these heavy metals from the solidified soil increases again. it is essential to be added in an amount not in excess of mercury contaminated soil 1 m ³ per 250 kg.

  The method for solidifying and insolubilizing heavy metal-contaminated soil of the present invention can also be suitably applied to lead, arsenic, fluorine, or boron.

  The cement-based treatment material for heavy metal-contaminated soil and the solidification and insolubilization treatment method of the present invention are based on the Ordinance for Enforcement of the Soil Contamination Countermeasures Law (Declaration of the Ministry of the Environment) No. 29) can be reduced below the second elution amount reference value or elution amount reference value, and hexavalent chromium or mercury contaminated soil can be effectively contained. For this reason, it can selectively be applied to in-situ (on-site) containment, impermeable containment, in-situ insolubilization, insolubilization backfill, and containment containment as measures for contaminated soil. Furthermore, the cement-based treatment material for heavy metal-contaminated soil of the present invention and the solidified insolubilization method using the same are effective for contaminated soil containing lead, arsenic, fluorine and boron in addition to hexavalent chromium and mercury. The amount of heavy metal leaching from contaminated soil can be reduced.

The cement-based treatment material for heavy metal-contaminated soil of the present invention is a cement-based treatment material for heavy metal-contaminated soil containing Portland cement, blast furnace slag, and gypsum, with respect to the total amount of Portland cement, blast furnace slag, and gypsum, It is a cementitious treatment material containing 30 to 70% by mass of blast furnace slag and 2 to 8% by mass of gypsum based on SO ₃ , with the remainder being Portland cement.

As the Portland cement, a cement specified in JIS R5210: 2003 “Portland cement” can be used, and particularly ordinary Portland cement and early-strength Portland cement can be preferably used.

As the blast furnace slag, any blast furnace slag having a quality defined in JIS R 5211: 2003 “Blast furnace cement” can be used. Basicity 1.80 or more, fineness is in Blaine specific surface area of 3500 cm ² / g or more, preferably blast furnace slag powder is preferably 4500cm ² / g or more. The blast furnace slag has a sulfur content of 0.5% by mass or more, more preferably 1.0% by mass or more based on sulfur, and preferably exhibits a “reduction potential”. The compounding quantity of the blast furnace slag in a cement-type processing material is 30-70 mass% with respect to the total amount of Portland cement, a blast furnace slag, and a gypsum. When the amount of blast furnace slag in the cement treatment material is 30% by mass or more, it is sufficient to reduce the elution amount of hexavalent chromium or mercury from contaminated soil and the elution amount of heavy metals such as hexavalent chromium contained in the cement itself. When the amount of blast furnace slag is 70% by mass or less, the solidification strength is increased and the elution suppression performance of heavy metal, which is the main purpose, can be ensured. Preferably, the compounding quantity of blast furnace slag is 40-60 mass%.

As the gypsum, any of dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum can be used, but the preferred crystal form is anhydrous gypsum. The blending amount of gypsum in the cement-based treatment material is 2 to 8% by mass, preferably 4 to 6% by mass on the basis of SO _{3 with} respect to the total amount of Portland cement, blast furnace slag and gypsum. When the blending amount of gypsum is 2% by mass or more based on SO ₃ , the effect of improving the solidification strength by adding gypsum can be obtained, or the heavy metal insolubilization performance does not deteriorate. When the blending amount of gypsum is 8% by mass or less on the basis of SO ₃ , the contaminated soil in the case of poor mixing of the contaminated soil and the cementitious treatment material partially causes excessive expansion. "Pure phenomenon" is suppressed, and as a result, the amount of elution of heavy metals can be reduced. The gypsum in the cement-based treatment material is an additional gypsum component other than gypsum originally contained in Portland cement.

In the solidified and insolubilized treatment method of the present invention, the above cement-based treatment material is added within a range of 50 kg or more per 1 m ^{3 of} hexavalent chromium or mercury-contaminated soil and not exceeding 250 kg, and mixed and stirred. Further, if hexavalent chromium or mercury contaminated soil is sandy soil, contaminated soil 1 m ³ per 50～150Kg, in the case of cohesive soil and volcanic ash quality cohesive soil, contaminated soil 1 m ³ per 100kg or more, it does not exceed 250kg range It is preferable to add and mix and stir.

  The mixing / stirring method of contaminated soil and cementitious treated soil is not particularly limited, and can be applied to in-situ (in situ) insolubilization measures, insolubilization backfill measures, in-situ containment measures, and impermeable containment measures. Things are the target.

  The solidification and insolubilization treatment of the present invention has the most excellent effect on hexavalent chromium or mercury contaminated soil. This is because hexavalent chromium and mercury are generally difficult to solidify and insolubilize with cement from the elution mechanism, and it is difficult to significantly reduce the elution amount of heavy metals from the treated soil. The solidification and insolubilization treatment method of the present invention can be suitably applied even if the heavy metal contamination heavy metal species is lead, arsenic, fluorine or boron.

As a standard, the contamination level of the contaminated soil subject to the solidification and insolubilization treatment of the present invention exceeds the second elution amount standard or elution amount standard stipulated in the Ordinance for Enforcement of the Soil Contamination Countermeasures Law (Ministry of the Environment Ordinance No. 29). It is done. However, for high-concentration contaminated soil that greatly exceeds the second elution amount standard, for example, the elution amount level of hexavalent chromium-contaminated soil exceeds several tens mg / L, only the cement-based treatment material and treatment method of the present invention are used. Since solidification and insolubilization by means of is not always sufficient, it is preferable to use other treatment methods in combination. In addition, the amount of heavy metal elution in the present invention is based on the Ministry of the Environment Notification No. 46.

In the solidification insolubilization treatment method of the present invention, the cement-based treatment material is used in a range not less than 50 kg and not exceeding 250 kg per 1 m ^{3 of} hexavalent chromium or mercury-contaminated soil. That is, it is characterized by not using an excessive amount of cementitious treatment material for hexavalent chromium or mercury contaminated soil. This is because there is an upper limit of the optimum amount of treatment material because excessive addition of cement-based treatment material to hexavalent chromium or mercury contaminated soil causes an increase in the elution amount of hexavalent chromium or mercury from the treated soil. Based on our new findings.

In this case, the optimum amount of cementitious treatment material per 1 m ^{3 of} hexavalent chromium or mercury contaminated soil varies depending on the soil quality of the contaminated soil. When the contaminated soil is sandy soil, the range is 50 to 150 kg. When the contaminated soil is viscous soil, the range is 100 kg or more and does not exceed 250 kg. Increasing the amount of the cementitious treatment material of the present invention to hexavalent chromium or mercury contaminated soil is useful for improving the solidification strength, but there is an upper limit to the amount of addition from the viewpoint of containment of heavy metals. Is as described above.

  For the heavy metal species that can be more effectively contained by the cement-based treatment material of the present invention, the treated soil (age 7 days) obtained by solidifying and insolubilizing the cement-based treatment material and heavy metal-contaminated soil by mixing and stirring. The relationship between the addition amount and the heavy metal elution amount is shown in FIGS. Here, the blending ratio (mass%) of the constituent material of the cement-based treatment material used in the test is early strong Portland cement: blast furnace slag: anhydrite = 50: 40: 10.

FIG. 1 is an example of mercury-contaminated soil (soil: sandy soil, mercury contamination: elution amount 0.12 mg / L). The amount of mercury elution from the solidified insolubilized soil can be significantly reduced by adding a relatively small amount of cementitious treatment material, but the amount of elution increases conversely when adding a larger amount. Hexavalent chromium also belongs to this category. If contaminated soil is sandy soil, the addition amount of a cement-based processing material heavy metal contaminated soil 1 m ³ per produces effects by the addition of more than 50 kg, elution is increased significantly from the addition mixing is treated soil exceeding 150kg Therefore, it is not preferable.

  The elution mechanism of mercury and hexavalent chromium by adding a large amount of such cement-based treatment material is the mechanism of hexavalent chromium or mercury ion cement hydrate (high crystalline hydrate or low crystalline colloid) into the structure. It is considered that ion substitution, adsorption on the surface of colloidal fine particles, hydroxide, sulfide, hydrosulfide or reduction reaction (detoxification by reduction of hexavalent chromium to trivalent chromium) are related. These are complex effects of the hydration reaction of the constituent materials of cementitious treatment materials, the speed and hydration rate of latent hydraulic reactions, or the environmental conditions (pH, ion adsorption amount, equilibrium state, etc.). And belongs to a unique phenomenon in which there is no correlation between the elution amount and the solidification strength as described above.

  FIG. 2 is an example of lead-contaminated soil (soil: viscous soil, lead contamination: elution amount 8.8 mg / L). If a predetermined amount of cement-based treatment material is added to lead-contaminated soil and mixed and stirred, even if it is contaminated soil that greatly exceeds the second leaching amount or leaching amount standard stipulated in the Soil Contamination Countermeasures Law, it is within the leaching amount standard (In FIG. 2, it can be reduced to less than the lower limit of quantification (0.002 mg / L)). Cadmium also belongs to this category.

  FIG. 3 is an example of boron-contaminated soil (soil: viscous soil, boron contamination: elution amount 45 mg / L). As the amount of cementitious treatment material increases, the amount of heavy metal elution from the treated soil decreases gradually. Fluorine also belongs to this category.

  Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to these examples.

Cement-based treatment material:
The cement-based processing material used was 42% by mass of blast furnace slag powder (sulfuric sulfur 1.32% by mass, Blaine specific surface area: 4320 cm ² / g), natural anhydrous gypsum (Blaine specific surface area: 3970 cm ² / g) is 4.7% by mass on the basis of SO ₃ , and the remainder is Hayashi Portland Cement (manufactured by Ube Industries). These compositions were mixed to prepare a cementitious treatment material. Hereinafter, the cementitious treatment material of this composition was used except for the experiment for confirming the influence of the blending amount of blast furnace slag.

Preparation of heavy metal contaminated soil:
As the sample soil, sandy soil, viscous soil, or Kanto loam (volcanic ash clay) was used which classified and removed soil particles having a particle size of 4.75 mm or more. After drying the sample soil to about half of the natural water content, add a predetermined amount of various heavy metal reagents dissolved in ion exchange water corresponding to the amount of evaporated water to the sample soil. And mixed and stored sealed for 24 hours. In accordance with the Ministry of the Environment Notification No. 46 (August 23, 1991), the amount of elution of heavy metals was measured and the pollution level was confirmed. Depending on the soil, there are cases where the amount of heavy metal added does not correspond to the amount of elution, and this confirmation operation is indispensable for setting the conditions.

[Sample soil]
The following three types were used. These soil properties are shown in Table 3.
Sandy soil from Ube City, Yamaguchi Pref. Viscous soil from Biei City, Yamaguchi Pref. Kanto Loam from Chiba Prefecture (volcanic ash clay)

[Heavy metal reagent]
The following seven heavy metal-containing reagents were used.
Mercury Mercury chloride: Hiroshima Wako Co., Ltd. Reagent grade 1 Hexavalent chromium Potassium dichromate: Hiroshima Wako Co., Ltd. reagent grade 1 Lead Nitrate: Hiroshima Wako Co., Ltd. Reagent grade 1 Cadmium Cadmium nitrate: Hiroshima Wako ( Reagent grade 1 arsenic Disodium hydrogen arsenate heptahydrate made by Hiroshima Wako Co., Ltd. Reagent grade 1 Fluorine Potassium fluoride dihydrate Boron Sodium metaborate tetrahydrate

Solidification and insolubilization treatment method:
A predetermined amount of cementitious treatment material was added to the contaminated soil. The mixing operation was performed by scraping with a soil mixer for 2 minutes at low speed for 2 minutes at low speed. The treated soil thus obtained can be obtained from the Japan Geotechnical Society standard JGS 0821-2000 “Method of preparing specimens without compacting the stabilized soil” or the Cement Association standard test method JCAS L-1: 2003 “Cement-based solidification In accordance with “Testing method for stabilized soil using materials”, a cylindrical specimen was prepared by dividing into 3 layers in a mold of φ5 × 10 cm and removing bubbles for each layer, and at 20 ° C. for 7 days Sealed and cured until. The uniaxial compressive strength of the cylindrical specimen cured for 7 days was measured according to JIS A 1216: 1998 “Soil uniaxial compression test method”.

Heavy metal dissolution test from treated soil:
Cylinder specimen subjected to uniaxial compressive strength test is crushed to 2mm or less, and the amount of elution of heavy metals from treated soil is measured according to the Ministry of the Environment Notification No. 46 (August 23, 1991) did.

  Table 4 shows the mercury elution amount after the solidification and insolubilization treatment of the mercury-contaminated soil with the cement-based treatment material. Here, the amount of mercury contamination is a numerical value of the portion to which no treatment material is added in Table 4, the upper numerical value indicates high-concentration contaminated soil, and the lower numerical value indicates low-concentration contaminated soil.

  As shown in FIG. 1 above, the relationship between the amount of cementitious treatment material added and the amount of mercury eluted from the treated soil has a range of the optimum amount of cementitious treatment material that can reduce the amount of mercury eluted most. I understand that.

Next, the influence of the blend amount of blast furnace slag was investigated. The cementitious treatment material contains 6% by mass (constant) hydrofluoric anhydride gypsum based on SO ₃ in the cementitious treatment material and blast furnace slag changed to 10 to 70% by mass, and the remainder is early-strength Portland cement. It is. The amount of treatment material added is 200 kg / m ³ (constant) with respect to mercury-contaminated soil. Table 5 shows the elution amount of mercury from the treated soil (cohesive soil) when the blend amount of the blast furnace slag is changed. The amount of mercury contamination in this experiment is the untreated portion (0.34 mg / L) in Table 5, and in order to clarify the effect of blast furnace slag, extremely high concentration mercury contaminated soil was tested. .

  As can be seen from Table 5, the elution amount of mercury from the treated soil after solidification and insolubilization varies depending on the blend amount of blast furnace slag in the cementitious treatment material, and the proper blend amount of blast furnace slag is 30 to 70% by mass, more preferably 40 to 40%. It turns out that it is 60 mass%.

  Next, Table 6 shows the elution amount of hexavalent chromium after solidification insolubilization treatment with a cement-based treatment material for hexavalent chromium contaminated soil. Here, the amount of hexavalent chromium contamination is the treatment material-free portion (0.835, 0.892, 0.723 mg / L) in Table 6.

  It can be seen that, in the hexavalent chromium contaminated soil, there is a range of the appropriate amount of cementitious treatment material that can reduce the amount of hexavalent chromium elution from the treated soil as much as the mercury contaminated soil.

It is a figure which shows the relationship between the mercury elution amount from a treated soil, and cement-type process material addition amount. It is a figure which shows the relationship between the amount of lead elution from a treated soil, and the amount of cementitious treatment material addition. It is a figure which shows the relationship between the boron elution amount from a treated soil, and cement-type process material addition amount.

Claims (7)

A cement-based treatment material for heavy metal-contaminated soil containing Portland cement, blast furnace slag, and gypsum, and 30 to 70 mass% of blast furnace slag and SO ₃ with respect to the total amount of Portland cement, blast furnace slag, and gypsum. A cement-based treatment material for heavy metal-contaminated soil, which contains 2 to 8% by mass on the basis and the remainder is Portland cement. The cementitious treatment material for heavy metal-contaminated soil according to claim 1, wherein the blast furnace slag is 40 to 60% by mass, the gypsum is 4 to 6% by mass based on SO ₃ , and the remainder is Portland cement. A method for solidifying and insolubilizing heavy metal-contaminated soil, comprising Portland cement, blast furnace slag and gypsum, 30 to 70% by mass of blast furnace slag and SO Add cement-based treatment material containing 2-8% by mass on the basis of ₃ standards and the remainder being Portland cement within a range of 50 kg or more per 1 m ^{3 of} hexavalent chromium or mercury-contaminated soil and not exceeding 250 kg, and mixing and stirring. Solidification and insolubilization treatment method for heavy metal contaminated soil. The method for solidifying and insolubilizing heavy metal-contaminated soil according to claim 3, wherein the cement-based treatment material contains 40 to 60% by mass of blast furnace slag and 4 to 6% by mass of gypsum based on SO ₃ , and the remainder is Portland cement. Soil heavy metal contaminated soil is sandy soil, the addition of cementitious treatment material in the range of hexavalent chromium or mercury contaminated soil 1 m ³ per 50～150Kg, solidification insolubilization of heavy metal contaminated soil according to claim 3 or 4, wherein Method. The soil of the heavy metal-contaminated soil is a viscous soil or a volcanic ash clay, and the cementitious treatment material is added in a range not less than 100 kg per 1 m ^{3 of} hexavalent chromium or mercury-contaminated soil and not exceeding 250 kg. Solidification and insolubilization treatment method for heavy metal contaminated soil.   The method for solidifying and insolubilizing heavy metal-contaminated soil according to any one of claims 3 to 6, wherein the contaminated heavy metal species of the heavy metal-contaminated soil is lead, cadmium, arsenic, fluorine or boron.

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