Insolubilization method for heavy metal

Abstract

To provide an insolubilization method capable of efficiently insolubilizing heavy metals in contaminated soil for purification of contaminated soil containing heavy metals such as arsenic and with less influence on soil properties.SOLUTION: An insolubilization method for heavy metals in contaminated soil includes bringing contaminated soil containing heavy metals into contact with an insolubilization agent containing a laminar complex oxide, wherein the laminar complex oxide has a composition represented by the following formula (1), and the average pore diameter of the laminar complex oxide is 2-10 nm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to a method for remediating contaminated soil containing heavy metals, and more particularly to a method for insolubilizing heavy metals in contaminated soil. [Background technology]

[0002] Soil contamination by heavy metals such as arsenic and lead has long been recognized as a problem. Arsenic, in particular, is a carcinogenic and harmful substance that affects human health, and is therefore subject to regulation under the Soil Contamination Countermeasures Act. Therefore, various methods for purifying soil contaminated by heavy metals, including arsenic, are being considered.

[0003] One known method for remediating contaminated soil is to insolubilize contaminants such as heavy metals. Insolubilization methods use an insolubilizer that adsorbs contaminants such as heavy metals or solidifies them together with the soil, preventing the contaminants from leaching out of the contaminated soil due to rainwater or other factors. When insolubilization methods are applied to remediate contaminated soil, the insolubilized contaminants, such as heavy metals, remain in the soil, and insufficient insolubilization can lead to recontamination. Therefore, there is a need for the development of an insolubilizer that can sufficiently insolubilize contaminants. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-119950 Summary of the Invention [Problem to be solved by the invention]

[0005] Typical insolubilizers used in the above-mentioned insolubilization methods include those containing lime, gypsum, iron salts, magnesium, cement, etc. (see, for example, Patent Document 1). However, when conventional insolubilizers are used, soil properties such as pH and soil water content can change drastically. Such drastic changes in soil properties are undesirable from the perspective of soil reuse, and post-treatment using a neutralizing agent, for example, to adjust the pH, may be necessary. Furthermore, taking into account the characteristics of the contaminants, multiple components may be blended together as insolubilizers, and the blending ratio of these components may need to be adjusted.

[0006] As described above, conventional insolubilization methods using insolubilizers have problems in terms of handling the insolubilizer, maintaining soil properties after insolubilization, etc. For these reasons, there is a need for a simple insolubilization method for remediating contaminated soil that has a high insolubilization effect, does not require blending adjustments of multiple components, has little effect on soil properties after treatment, and does not require post-treatment steps.

[0007] Therefore, in view of the above circumstances, an embodiment of the present invention provides a simple insolubilization method for purifying contaminated soil, which is highly effective in insolubilizing heavy metals in contaminated soil, has little effect on soil properties, and is easy to use. [Means for solving the problem]

[0008] The present inventors have conducted extensive research into the immobilization of heavy metals in contaminated soil and have found that a specific layered double oxide has excellent adsorption properties for heavy metals, has little effect on soil properties, and is therefore useful as an insolubilizer, leading to the completion of the present invention. That is, the present invention relates to the embodiments described below. However, the present invention is not limited to the embodiments described below and includes various embodiments.

[0009] <1> A method for insolubilizing heavy metals in contaminated soil, comprising contacting contaminated soil containing heavy metals with an insolubilizing agent containing a layered double oxide, wherein the layered double oxide has a composition represented by the following formula (1) and an average pore diameter of the layered double oxide is 2 to 10 nm:

[0010] [ka] (In the formula, M 2+ is Cu 2+ , Mn 2+ , Mg 2+ , Fe 2+ , Ca 2+ , Ni 2+ , Zn 2+ , Co 2+ and Cd 2+ M is one or more divalent metal ions selected from the group consisting of 3+ Al 3+ , Cr 3+ , Fe 3+ , Co 3+ , In 3+ , Mn 3+ and V 3+ and x is 0.20 to 0.33.)

[0011] <2> The insolubilizing agent comprises at least one selected from the group consisting of MgAl layered double oxide and MgFeAl layered double oxide. <1> 1. A method for insolubilizing heavy metals in contaminated soil according to claim 1.

[0012] <3> The insolubilizer contains an MgFeAl layered double oxide. <2> 1. A method for insolubilizing heavy metals in contaminated soil according to claim 1.

[0013] <4> The specific surface area of ​​the MgAl layered double oxide is 340 to 380 m 2 / g, and the specific surface area of ​​the MgFeAl layered double oxide is 220 to 250 m 2 / g, <2> 1. A method for insolubilizing heavy metals in contaminated soil according to claim 1.

[0014] <5> The heavy metal includes at least one selected from the group consisting of arsenic, lead, cadmium, copper, hexavalent chromium, selenium, and antimony. <1> ~ <4> 1. A method for insolubilizing heavy metals in contaminated soil according to any one of claims 1 to 9.

[0015] <6> The heavy metals include arsenic. <5> 1. A method for insolubilizing heavy metals in contaminated soil according to claim 1.

[0016] <7> The amount of the insolubilizing agent used is 0.5 to 10% by mass relative to the total mass of the contaminated soil containing the heavy metals. <1> ~ <6> 10. A method for insolubilizing heavy metals in contaminated soil according to any one of the preceding claims. [Effects of the Invention]

[0017] According to an embodiment of the present invention, it is possible to provide an insolubilization method that can efficiently insolubilize heavy metals such as arsenic in contaminated soil and that has little effect on soil properties. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the embodiments described below and includes various embodiments.

[0019] <Insolubilization method> One embodiment of the present invention relates to a method for insolubilizing heavy metals in contaminated soil, which comprises contacting the contaminated soil containing the heavy metals with an insolubilizing agent containing a layered double oxide, wherein the layered double oxide has a composition represented by the following formula (1) and an average pore diameter of the layered double oxide is 2 to 10 nm:

[0020] [ka]

[0021] In the formula, M 2+ is Cu 2+ , Mn 2+ , Mg 2+ , Fe 2+ , Ca 2+ , Ni 2+ , Zn 2+ , Co 2+ and Cd 2+ M is one or more divalent metal ions selected from the group consisting of 3+ Al 3+ , Cr 3+ , Fe3+ , Co 3+ , In 3+ , Mn 3+ and V 3+ The metal ions are one or more trivalent metal ions selected from the group consisting of: x is 0.20 to 0.33. In one embodiment, the combination of divalent and trivalent metal ions comprises at least Mg 2+ and Al 3+ and preferably further contains Fe. 2+ or Fe 3+ Such layered double oxides will be referred to hereinafter as MgAl layered double oxides and MgFeAl layered double oxides.

[0022] Layered double oxides (hereinafter also referred to as "LDO") can generally be obtained as a calcined product of layered double hydroxides (hereinafter also referred to as "LDH"). LDO having the composition represented by the above formula (1) can be produced, for example, via LDH having the composition represented by the following formula (2).

[0023] [ka]

[0024] In the formula, M 2+ is Cu 2+ , Mn 2+ , Mg 2+ , Fe 2+ , Ca 2+ , Ni 2+ , Zn 2+ , Co 2+ and Cd 2+ M is one or more divalent metal ions selected from the group consisting of 3+ Al 3+ , Cr 3+ , Fe 3+ , Co 3+ , In 3+ , Mn 3+ and V 3+A is one or more trivalent metal ions selected from the group consisting of n- is CO3 2- , SO4 2- , Cl - , O.H. - , SiO4 4- , SO4 2- , NO3 - , and C2H5O - The anion is an n-valent anion selected from the group consisting of: where x is 0.20 to 0.33, n is 1 to 3, and y is 1 to 12.

[0025] The LDH having the composition represented by the above formula (2) is, more specifically, 2+ Part of M 3+ The LDH is composed of a host layer of octahedral layers that are positively charged by substitution with , and a guest layer consisting of anions and interlayer water that compensate for the positive charge of the host layer, and has excellent adsorption ability. By calcining the LDH, anion species (A n- ) and interlayer water are released to form LDO.

[0026] Although LDH and LDO are generally produced by the coprecipitation method because the production process is simple, the insolubilization method of this embodiment can suitably use LDO obtained by a specific sol-gel method described below. Studies by the present inventors have confirmed that LDO obtained by the specific sol-gel method has a smaller average pore size and a larger specific surface area than LDO obtained by the coprecipitation method (hereinafter also referred to as co-precipitated LDO).

[0027] Specifically, the average pore size of LDH obtained by the coprecipitation method is typically 11 nm or more, and the specific surface area is 160 (m 2 On the other hand, the average pore size of LDO obtained by a specific sol-gel method is 10 nm or less, and the specific surface area is 180 (m 2 / g or more. Generally, as the average pore diameter and pore volume increase, the porosity improves, and the specific surface area also tends to increase. However, LDO obtained by a specific sol-gel method has a smaller average pore diameter and pore volume, but an increased specific surface area. In one embodiment of the present invention, it is preferable to distinguish LDO from LDO obtained by a conventional coprecipitation method in terms of the average pore diameter, pore volume, and specific surface area.

[0028] The average pore diameter of the LDO used in this embodiment may be 2 to 10 nm, preferably 2 to 8 nm, more preferably 2 to 6 nm, and even more preferably 2 to 4 nm. The specific surface area of ​​the LDO used in this embodiment varies depending on the components of the LDO, but is generally 180 to 400 (m 2 / g). Such LDO can be easily obtained by a specific sol-gel method described below. In one embodiment, the insolubilizer preferably consists essentially of LDO, and may also contain LDH remaining from the LDO production process. In another embodiment, the insolubilizer may further contain LDH and / or LDO having an average pore size of 10 nm or more.

[0029] The mass % of the LDO having an average pore size of 2 to 10 nm, based on the total mass of the insolubilizer, may be preferably 70 mass % or more, more preferably 80 mass % or more, and even more preferably 90 mass % or more. In one embodiment, the mass % of the LDO having an average pore size of 2 to 10 nm, based on the total mass of the insolubilizer, may be 100 mass %.

[0030] In one embodiment, the insolubilizer preferably contains at least one selected from the group consisting of MgAl-LDO and MgFeAl-LDO. From the viewpoint of heavy metal adsorption, the insolubilizer more preferably contains at least MgFeAl-LDO. Without being bound by theory, it is speculated that, compared to MgAl-LDO, MgFeAl-LDO exhibits new adsorption sites due to the intercalation of Fe, contributing to improved adsorption.

[0031] In the insolubilization method of the above embodiment, contact of the contaminated soil containing heavy metals with the insolubilizer can be carried out according to a known method. For example, a method of mixing the contaminated soil with the insolubilizer, a method of providing a layer of the insolubilizer below the contaminated soil, etc. are included. From the viewpoint of facilitating reuse of the soil after insolubilization treatment, contact by mixing is preferred.

[0032] For example, mixing can be performed by shaking or stirring the contaminated soil and insolubilizer using an agitator mixer such as a mixer. Since soil typically contains moisture, the above-described mixing can be performed without adding water, although water may be added during mixing as needed. The amount of water used is not particularly limited and may be adjusted depending on the mixing method, but it is preferable to use a water amount within a range that does not significantly change the moisture content of the soil. While this varies depending on the type of soil, the collection location, and the weather, the moisture content of soil is typically 5 to 80% by mass. From this perspective, in one embodiment, the moisture content is preferably 5 to 80% by mass, based on the total mass of the contaminated soil and the insolubilizer.

[0033] The soil after the heavy metals have been insolubilized by the above-mentioned mixing (hereinafter referred to as insolubilized soil) can be reused for various purposes such as backfill soil and embankment soil for banks.

[0034] In the insolubilization method, the heavy metals in the contaminated soil may be hazardous substances as defined in the Enforcement Regulations of the Soil Contamination Countermeasures Act. In one embodiment, the heavy metals may include at least one selected from the group consisting of arsenic, lead, cadmium, copper, hexavalent chromium, selenium, and antimony. In one embodiment, the insolubilization method is suitable for use with contaminated soil containing arsenic.

[0035] In one embodiment, the contaminated soil used in the insolubilization method may be soil containing elements, compounds, or ions of heavy metal elements such as arsenic. Here, the soil may be any soil collected from mountain forests, urban areas, agricultural land, former factory sites, etc. The soil contains silica as a main component and contains natural or artificial heavy metals such as arsenic and lead. In another embodiment, the contaminated soil may be excavation debris generated by excavation in construction work such as tunnels and dams. Excavation debris often contains naturally occurring heavy metals such as arsenic and lead. Therefore, the insolubilization method of the above embodiment can also be suitably applied to excavation debris.

[0036] In one embodiment, a process of crushing and classifying the contaminated soil may be carried out prior to mixing the contaminated soil with the insolubilizer. Soil contains a mixture of soil particles of different particle sizes, such as gravel, sand, silt, and clay. In many cases, the soil particles adhere to each other to form clods. Therefore, crushing the clods into smaller pieces and then classifying them to adjust the size of the soil particles facilitates the remediation process. In one embodiment, the contaminated soil used in the remediation process is preferably in the form of soil particles.

[0037] The particle size of the soil particles may be 10 mm or less. From the viewpoint of easily obtaining the effect of the insolubilizer, the particle size may be preferably 5 mm or less, more preferably 3 mm or less, and even more preferably 2 mm or less. In particular, when the particle size of the soil particles is 2 mm or less, a more excellent insolubilization effect can be easily obtained. In one embodiment, the contaminated soil to be mixed with the insolubilizer is preferably soil particles whose particle size has been adjusted to 75 μm to 2 mm by classification. When the particle size of the soil particles is adjusted to 75 μm to 2 mm, it tends to be easier for the insolubilizer to adsorb heavy metals such as arsenic.

[0038] In the above-described purification method, the amount of the insolubilizer used is not limited. In one embodiment, the amount of the insolubilizer used may be 0.5 to 10% by mass relative to the total mass of the contaminated soil containing heavy metals. The amount used may be more preferably 0.5 to 5% by weight, and even more preferably 1 to 3% by weight.

[0039] <Method of manufacturing the insolubilizer> One embodiment of the present invention relates to a method for producing an insolubilizing agent suitable for use in the method for insolubilizing heavy metals in contaminated soil of the above embodiment. The method for producing an insolubilizing agent includes producing LDO having a composition represented by the above formula (1) and an average pore diameter of 2 to 10 nm. From the viewpoint of adsorption properties, the insolubilizing agent preferably contains at least one of MgAl-LDO and MgFeAl-LDO.

[0040] The production of the LDO includes step 1 of producing an LDH by a sol-gel method and step 2 of producing an LDO by baking the LDH. More specifically, step 1 of producing an LDH by the sol-gel method can be carried out by mixing an alkoxide metal salt in a mixed solvent of an organic solvent and water. For example, MgAl-LDH can be obtained by mixing magnesium methoxide, aluminum isopropoxide, ethanol, ultrapure water, and 60 wt% nitric acid and drying the solid content, while MgFeAl-LDH can be obtained by adding an organic acid iron salt such as iron (II) acetate to the above components, mixing the mixture, and drying the solid content.

[0041] In one embodiment, in step 1 of producing LDH by the sol-gel method, an amine having a linear alkyl group with 12 or more carbon atoms (higher linear aliphatic amine) such as hexadecylamine (HDA) may be added to the reaction solution. The higher linear aliphatic amine is preferably a primary amine. The linear alkyl group in the higher linear aliphatic amine may have 12 to 20 carbon atoms. The use of a higher aliphatic amine such as HDA tends to facilitate an increase in the specific surface area of ​​the LDH obtained after calcination. Although not particularly limited, in one embodiment, the amount of higher aliphatic amine used is preferably adjusted to a range of 0.25 to 1 molar equivalent relative to aluminum isopropoxide.

[0042] In step 2, in which LDH is calcined to produce LDO, the calcination temperature is not particularly limited and can be adjusted depending on the form of the compound. In one embodiment, the calcination temperature may be 400 to 800°C. The calcination time is not particularly limited, but may be 1 to 10 hours. LDO can be identified by measuring X-ray diffraction (XRD) and detecting peaks specific to LDO. [Example]

[0043] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples and includes various embodiments.

[0044] <1-1> Manufacturing example of insolubilizer

[0045] (Production Example 1) To 200 mL of ethanol, 25.0 mmol of aluminum tripropoxide, 50 mmol of magnesium methoxide, 1.5 g of hexadecylamine (HAD), 1.03 mL of additional ultrapure water, and 0.130 mL of 60% nitric acid were added. The solution was stirred at 1500 rpm using a magnetic stirrer at room temperature for 5 hours. The resulting mixture was then subjected to solid-liquid separation, and the solid was recovered. The solid was dried under reduced pressure at 40 °C to obtain MgAl-LDH. The MgAl-LDH prepared as above was placed in an oven and baked at 450° C. for 2 hours to obtain MgAl-LDO.

[0046] When the above MgAl-LDO was subjected to elemental analysis by ICP-AES (ICP atomic emission spectroscopy), it was confirmed that it had a composition represented by the following formula (1A). [ka]

[0047] (Production Example 2) To 200 mL of ethanol, 25.0 mmol of aluminum tripropoxide, 50 mmol of magnesium methoxide, 25.0 mmol of iron(II) acetate, 1.5 g of hexadecylamine (HAD), 1.03 mL of ultrapure water, and 0.130 mL of 60% nitric acid were added. The solution was stirred at 1500 rpm using a magnetic stirrer at room temperature for 5 hours. The resulting mixture was then subjected to solid-liquid separation, and the solid was recovered. The solid was dried under reduced pressure at 40 °C to obtain MgFeAl-LDH. The MgFeAl-LDH was placed in an oven and calcined at 450 °C for 2 hours to obtain MgFeAl-LDO.

[0048] When the above MgFeAl-LDO was subjected to elemental analysis by ICP-AES, it was confirmed that it had a composition represented by the following formula (1B). [ka]

[0049] <1-2> Physical properties of insolubilizers The physical properties of each of the insolubilizers obtained in Production Examples 1 and 2 were measured as follows. The measurement results are shown in Table 1. (specific surface area) The specific surface area of ​​each insolubilizer was measured by the BET (Brunauer-Emmett-Teller) method.

[0050] (Average pore diameter) For each insolubilizer, the pore size was measured multiple times by the BJH (Barrett-Joyner-Halenda) method, and the average value was calculated to obtain the average pore size.

[0051] (pore volume) The pore volume of each insolubilizer was measured by the BJH (Barrett-Joyner-Halenda) method.

[0052] [Table 1]

[0053] <2> Immobilization of heavy metals in contaminated soil Examples 1 and 2 Methods for insolubilizing heavy metals in contaminated soil were investigated using the insolubilizers obtained in Production Examples 1 and 2. More specifically, with the aim of suppressing the amount of arsenic leaching from contaminated soil containing arsenic, the insolubilizers obtained in Production Examples 1 and 2 were used to investigate their effectiveness as arsenic insolubilizers, as described below.

[0054] First, 50 g of soil with an arsenic elution rate of 0.017 mg / L was adjusted to a particle size of 70 μm to 2 mm. To this soil, the insolubilizers obtained in Production Examples 1 and 2 were added and mixed. The amount of insolubilizer added was 1 mass % relative to the mass of the soil. The amount of arsenic elution (1) of the soil after mixing with the insolubilizer (immobilized soil) was measured in accordance with the test method based on the Soil Contamination Countermeasures Act (Environmental Notification No. 46 of 1991 and Environmental Notification No. 19 of 2003). As a result, the amount of arsenic elution (1) when the insolubilizer obtained in Production Example 1 was used was 0.006 mg / L, and the amount of arsenic elution (1) when the insolubilizer obtained in Production Example 2 was used was less than 0.002 mg / L. It was confirmed that both insolubilizers met the requirement of 0.01 mg / L or less, which is the standard value for arsenic elution in soil elution tests.

[0055] Next, the amount of arsenic adsorption (A-1) was calculated from the difference between the amount of arsenic eluted (A) (0.017 mg / L) from the soil (untreated soil) before insolubilization treatment with the insolubilizing agent and the amount of arsenic eluted (1). Furthermore, the insolubilization rate (%) was calculated from the ratio of the amount of arsenic adsorption (A-1) to the amount of arsenic eluted (A). The pH value of the soil after insolubilization was also measured using the glass electrode method. These results are shown in Table 2.

[0056] For comparison, the insolubilization rates and pH values ​​calculated based on data measured using the same method as above for representative conventional insolubilizers are shown in Table 2 as Reference Examples 1 to 6. The values ​​shown in Reference Examples 1 to 6 were calculated based on the figures shown in Figures 1 and 3 reported in Obayashi Corporation Technical Research Report No. 74, 2010, in a demonstration experiment of the arsenic insolubilizer "Hisoguard (registered trademark)."

[0057] In Table 2, cases where the requirement of arsenic leaching of 0.01 mg / L or less, which is the standard value in the soil leaching test, is met are indicated by "○", and cases where it is not met are indicated by "×".

[0058] The evaluation criteria for the properties of the soil after insolubilization shown in Table 2 are as follows: A: The increase or decrease in the pH value of the soil after insolubilization is within 1.2, based on the pH value of the untreated soil. B: The increase or decrease in the pH value of the soil after insolubilization is 1.3 or more and 2.9 or less, based on the pH value of the untreated soil. C: The increase or decrease in pH value of the soil after insolubilization is 3.0 or more based on the pH value of the untreated soil.

[0059] [Table 2]

[0060] As can be seen from Table 2, the embodiments of the present invention (Examples 1 and 2) provide an insolubilization method that not only achieves excellent insolubilization effects but also has little effect on soil properties such as pH. On the other hand, when the insolubilizers shown in Reference Examples 1 to 5 are used, the insolubilization effect is poor or the pH changes significantly, significantly affecting soil properties. The insolubilizer in Reference Example 6 (Hisoguard (registered trademark)) is a composite agent containing silicate, iron salt, and gypsum, and the mixing ratio of each component must be adjusted to adjust the pH.

[0061] Next, the stability of the insolubilizers obtained in Production Examples 1 and 2 was examined by repeatedly passing water through them as follows. (Consideration 2) The same soil as used in Study 1 above was prepared, and 500 mL of pure water and 1% by mass of insolubilizer relative to the soil mass were added. The mixture was stirred at room temperature using a magnetic stirrer at 1000 rpm for 2 hours. After stirring, the mixture was washed five times with 500 mL of pure water using suction filtration using filter paper. The solid matter was then separated, and the amount of arsenic leaching (2) was measured for the immobilized soil recovered as solid matter. Similar to Study 1, the measurement was performed in accordance with the test methods stipulated in the Soil Contamination Countermeasures Act (Environmental Notification No. 46 of 1991 and Environmental Notification No. 19 of 2003). The results are shown in Table 3.

[0062] [Table 3]

[0063] As shown in Table 3, according to the embodiments of the present invention (Examples 1 and 2), it was confirmed that the arsenic elution amount (2) after five water passes all met the requirement of 0.01 mg / L or less, which is the standard value for arsenic elution in the soil elution test. Furthermore, since this is equivalent to or not significantly different from the arsenic elution amount (1) previously examined, it can be seen that the insolubilizing effect of the insolubilizing agent can be stably maintained even after repeated water passes. From the above, it can be seen that layered double oxides such as MgAl-LDO and MgFeAl-LDO are useful as insolubilizers for heavy metals, and that their use can provide a simple and effective insolubilization method with little impact on soil properties for the remediation of contaminated soil containing heavy metals.

Claims

1. The method comprises contacting contaminated soil containing heavy metals with an insolubilizing agent containing a layered double oxide, The method for insolubilizing heavy metals in contaminated soil, wherein the layered double oxide has a composition represented by the following formula (1), and the layered double oxide has an average pore size of 2 to 10 nm: 【Chemical 1】 (In the formula, M ２＋ is Cu ２＋ , Mn ２＋ , Mg ２＋ , Fe ２＋ , Ca ２＋ , Ni ２＋ , Zn ２＋ , Co ２＋ and Cd ２＋ M is one or more divalent metal ions selected from the group consisting of ３＋ is Al ３＋ , Cr ３＋ , Fe ３＋ , Co ３＋ , In ３＋ , Mn ３＋ and V ３＋ and x is 0.20 to 0.

33.

2. 2. The method for insolubilizing heavy metals in contaminated soil according to claim 1, wherein the insolubilizing agent comprises at least one selected from the group consisting of MgAl layered double oxides and MgFeAl layered double oxides.

3. 3. The method for insolubilizing heavy metals in contaminated soil according to claim 2, wherein the insolubilizing agent comprises an MgFeAl layered double oxide.

4. The specific surface area of ​​the MgAl layered double oxide is 340 to 380 m ２ / g, and the specific surface area of ​​the MgFeAl layered double oxide is 220 to 250 m ２ 3. The method for insolubilizing heavy metals in contaminated soil according to claim 2, wherein the concentration of heavy metals in the contaminated soil is 1 / g.

5. The method for insolubilizing heavy metals in contaminated soil according to any one of claims 1 to 4, wherein the heavy metals include at least one selected from the group consisting of arsenic, lead, cadmium, copper, hexavalent chromium, selenium, and antimony.

6. 6. The method for insolubilizing heavy metals in contaminated soil according to claim 5, wherein the heavy metals include arsenic.

7. 2. The method for insolubilizing heavy metals in contaminated soil according to claim 1, wherein the amount of the insolubilizing agent used is 0.5 to 10 mass % based on the total mass of the contaminated soil containing the heavy metals.

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