JP2002307050A - Method of treating and reutilizing soil containing heavy metals, and heavy metal ellution reducing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soil treatment method for reducing the elution amount of heavy metals from soil containing heavy metals, a soil reutilizing method for reutilizing treated soil and a heavy metal elution reducing material capable of reducing the elution amount of heavy metals. SOLUTION: The methods for treating and reutilizing soil are characterized in that a lime-based treatment material containing carbide slag containing calcium hydroxide, gypsum and a silica or alumina inorganic filler is added to soil containing heavy metals and effective for reducing the elution of heavy metals such as hexavalent chromium, lead or the like. The heavy metal ellution reducing material contains carbide slag containing calcium hydroxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating a soil containing heavy metals and a method for reusing the soil subjected to the treatment. More specifically, the present invention relates to a method for immobilizing heavy metals contained in soil and removing the same from soil. The present invention relates to a method for treating soil that reduces the amount of eluted heavy metals and a method for reusing soil after treatment. The present invention also relates to a heavy metal elution reducing material for treating a soil containing a heavy metal.

[0002]

2. Description of the Related Art In recent years, it has been often reported that soils at former sites such as factories / offices, industrial waste disposal sites, and shooting ranges are contaminated with heavy metals. Heavy metals reported as soil pollution sources include lead, hexavalent chromium, mercury, cadmium, selenium, etc. (September 2001)
Month, how the system of soil environmental conservation measures should be (interim summary), reference material). For example, lead is the most frequently reported heavy metal as a heavy metal contaminating soil, and it has been reported that lead is contained in soil at sites such as factories and offices. In addition, lead is a component of a bullet at a shooting range, and may be locally contained in a high concentration in soil at a shooting range. It has been reported that hexavalent chromium is contained in soil using cement or cement-based solidification material for soil improvement, as described later, in addition to the former sites of factories and offices. This is because the cement or the cement-based solidifying material itself contains hexavalent chromium. If the soil is contaminated with heavy metals, groundwater is also contaminated, affecting not only the health and safety issues that affect the human body. Hinders the effective use of In order to effectively utilize the site where the heavy metal is contained in the soil, a method of fixing the heavy metal contained in the soil and suppressing / preventing the elution of the heavy metal from the soil is desired.

[0003] Conventionally, in order to improve the ground such as soft ground, subgrade, embankment, construction foundation ground, etc., a lime-based stabilizing material, a construction method using cement or cement-based solidified material, and the like have been adopted. . What is the construction method using lime-based stabilizing material?
This is a method of modifying sludge and residual soil into high-quality soil using a lime-based treatment material containing lime as a main component. All the methods using cement or cement-based solidification material are implemented for the purpose of improving the ground strength of soft ground, subgrade, embankment, building foundation, etc. It has been pointed out that soil has a soil quality in which hexavalent chromium contained in a cement component is eluted at a concentration exceeding a soil environmental standard. For this reason, a hexavalent chromium leaching test was carried out on soil improved with cement and cement-based solidification material by a notice of the Minister of Construction, Technical Coordinator for Technology, No. 48 of the Ministry of Construction on March 24, 2000 by the Ministry of Construction. In addition, it was necessary to confirm that the elution amount was 0.05 mg / liter or less, and the improved soil that did not satisfy the soil environmental standard could not be used as the improved soil.

[0004] Under such circumstances, there has been proposed a cement-based solidifying material that generates and releases a relatively small amount of hexavalent chromium, and a method of modifying soil contaminated with heavy metals. For example, JP-A-9-85224, JP-A-9-852
No. 25 discloses a method for detoxifying a soil by adding water, a ferrous salt, an aluminum salt or the like to soil contaminated with heavy metals and fixing the heavy metals. Japanese Patent Application Laid-Open No. 2000-86322 discloses a material for reducing the dissolution of hexavalent chromium containing a reducing substance such as ferrous sulfate or sulfur as a main component and a ground improvement material using the same. However, research and development on a new cement-based solidifying material has been conducted, but studies have been conducted from the viewpoint of improving the contaminated soil by treating hexavalent chromium-containing soil treated with the conventional cement-based solidifying material. Is almost never done. For example, JP-A-9-
JP-A-85224 and JP-A-9-85225 disclose methods of detoxifying soil contaminated with heavy metals, but no studies have been made from the viewpoint of reusing soil after detoxification. .

[0005]

As described above, sites such as factories and business establishments that elute heavy metals exceeding the soil environmental standard value cannot be reused as soil for civil engineering as it is. In particular, soil and sludge generated when reconstructing the ground once modified with cement and cement-based solidifying material elute hexavalent chromium, which exceeds the soil environmental standard. Have been coming.

The present invention has been made in view of the above circumstances, and has been made in consideration of the above circumstances, and has been made in view of the above circumstances. It is intended to provide a reducing material.

[0007]

Means for Solving the Problems The present invention, which has solved the above-mentioned problems, comprises adding a lime-based treatment material containing calcium hydroxide and / or calcium oxide as an essential component to a soil containing heavy metals. It is a soil treatment method characterized by the following. According to the treatment method of the present invention, heavy metals contained in soil are immobilized in soil, and elution from soil is suppressed. Therefore, the present invention can be suitably applied to soil containing at least one heavy metal selected from the group consisting of hexavalent chromium, lead, cadmium, copper, mercury, selenium, manganese, nickel, thallium, rhodium, and antimony. Can be. Further, the present invention focuses on hexavalent chromium, which has a particularly harmful effect among heavy metals, and the elution amount is 0.06.
A lime-based treatment material containing calcium hydroxide and / or calcium oxide as an essential component is added to soil having a concentration of more than 5 mg / liter, and the dissolution amount of hexavalent chromium is 0.05 mg.
/ Liter or less, and is particularly useful as a soil treatment method characterized in that the amount of hexavalent chromium eluted exceeds 0.05 mg / liter by being modified with cement or cement-based solidifying material. It can be applied effectively to soil that has become.

Preferably, the lime-based treatment material is a carbide slag. This is because the use of the carbide residue produced as a by-product when producing acetylene from the carbide provides the benefit of two birds with one stone combined with the effective use of waste materials. The lime-based treatment material preferably further contains an inorganic filler, and the inorganic filler is desirably silica or alumina. This is because by incorporating these inorganic fillers, the strength of the soil after the treatment can be increased. The treated soil treated by the method for treating soil of the present invention has excellent strength and can be suitably reused as soil for civil engineering and construction.

[0009] The present invention further relates to calcium hydroxide and / or calcium hydroxide.
Alternatively, a material for reducing heavy metal elution from soil containing calcium oxide as an essential component is provided. This heavy metal elution reducing material is desirably a carbide residue. Preferably, the heavy metal elution reducing material further contains an inorganic filler, and the inorganic filler is desirably silica or alumina. The heavy metal elution reducing material of the present invention is used to reduce the elution of at least one heavy metal selected from the group consisting of hexavalent chromium, lead, cadmium, copper, mercury, selenium, manganese, nickel, thallium, rhodium and antimony. It can be suitably used.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present invention is characterized in that a lime-based treatment material containing calcium hydroxide and / or calcium oxide as an essential component is added to a soil containing heavy metals,
Thus, by immobilizing the heavy metal to the soil, it is possible to reduce the elution amount of the heavy metal from the soil. The soil containing heavy metals is not limited as long as it contains heavy metals. For example, hexavalent chromium, lead, cadmium,
Examples include soils containing at least one heavy metal selected from the group consisting of copper, mercury, selenium, manganese, nickel, thallium, rhodium, and antimony.
This is because these heavy metals are used in various industries. Among these, hexavalent chromium, lead, cadmium,
Copper, mercury, selenium and the like are often reported as harmful heavy metals contained in soil, so that the present invention can be applied effectively. Incidentally, in the present invention, the heavy metal is defined as having a density of 4 g / cm.
³ or more metals, in addition to the heavy metals exemplified above,
Examples include tin, iron, cobalt, bismuth, and zinc.
Arsenic is originally considered to be a nonmetallic element, but is treated as a heavy metal in the technical field related to soil contamination, and is therefore treated as a heavy metal in the present invention.

The soil containing a heavy metal to which the present invention is applied is as follows:
It is not limited as long as it contains heavy metals.For example, soil on former sites such as factories and offices, industrial waste disposal sites, garbage disposal sites, shooting ranges, soil improved by ground improvement, excavation work and construction work Soil, sludge, and sandy quality. Soil on the site of factories / offices, industrial waste disposal sites, and garbage disposal sites contains various heavy metals leaked from chemicals and industrial waste, etc. This is because lead is often contained. It goes without saying that the present invention can be applied not only to soil containing heavy metals due to artificial factors as described above, but also to soils where heavy metals exist naturally.

In addition, soil environmental standards (0.05 mg / L)
A lime-based treatment material containing calcium hydroxide and / or calcium oxide as an essential component is added to the soil that elutes hexavalent chromium in excess of 0.1 m2, and the amount of hexavalent chromium eluted is 0.05 m.
Suppression to g / L or less is a preferred embodiment of the present invention. This is because soil that does not satisfy the soil environmental standards cannot be used as improved soil. Examples of the soil in which the elution amount of hexavalent chromium exceeds 0.05 mg / L, which is the soil environmental standard, include a soil containing a cement or a cement-based solidifying material (treated with a cement or a cement-based solidifying material). Can be This is because hexavalent chromium contained in a cement-based solidifying material or the like causes elution of hexavalent chromium exceeding the soil environmental standard. The elution amount of the hexavalent chromium is 0.0
Soil exceeding 5 mg / L often occurs when redeveloping land whose soil has been improved with a cement-based solidifying material or the like.

The lime-based treatment material containing calcium hydroxide and / or calcium oxide as an essential component used in the present invention is not particularly limited as long as it contains calcium hydroxide and / or calcium oxide as a main component. However, a lime-based treatment material containing calcium hydroxide as a main component is more preferable. In the present invention, it is said that a lime-based treatment material containing calcium oxide as a main component can also be used, because calcium oxide reacts with water to generate calcium hydroxide. This is because the same effect as the contained lime-based treatment material is exhibited. However, it is particularly preferable to use a lime-based treatment material containing calcium hydroxide as an essential component, since it can be used without considering the reaction with water.

As the calcium hydroxide and calcium oxide, for example, those sold as slaked lime (calcium hydroxide) or quick lime (calcium oxide) can be used. Preferably, it is used.

Further, more preferred specific examples of the lime-based treatment material containing calcium hydroxide as an essential component include:
For example, a carbide (residue) residue, which is a residue generated by adding water to a carbide to generate acetylene gas, may be mentioned. The carbide (residual) residue includes a wet-type carbide residue obtained in a slurry state and a dry-type carbide residue obtained in an almost dry powder state. The wet and dry carbide slags contain about 80% by mass or more of calcium hydroxide, and also contain calcium carbonate, oxides of iron and Al, and the like. Carbide slag, especially dry carbide slag, is obtained as a by-product when producing acetylene gas and is inexpensive, so it is particularly desirable to use it as the lime-based treatment material.

Preferably, the lime-based treatment material further contains gypsum and an inorganic filler. This is because the strength of the soil after the treatment is improved by including an appropriate amount of the inorganic filler and the gypsum. The content of the inorganic filler and gypsum may be appropriately determined according to the type and quality of the soil, the required strength of the soil, etc., but the generally recommended content is 100 masses of the lime-based treatment material. Parts by weight, gypsum is 5 parts by mass or more, preferably 20 parts by mass or more, 30 parts by mass or less, preferably 25 parts by mass or less, and the inorganic filler is 5 parts by mass or more, preferably 10 parts by mass or more, 30 parts by mass or less. It is at most 15 parts by mass, preferably at most 15 parts by mass. The same applies when lime or carbide slag is used as the lime-based treatment material. Of course, the type and quality of the soil,
Depending on the required strength, the contents of gypsum and the inorganic filler may be outside the above-mentioned ranges.

Examples of the inorganic filler include silica, alumina, glass fiber, mica, zeolite, kaolin, clay, bentonite, talc, magnesium hydroxide, calcium carbonate and the like, and more preferred is silica (silicon dioxide). And alumina (aluminum oxide). Silica and alumina react with the lime component to produce lime silicate hydrate, lime aluminate hydrate, and the like, which serve as binders and contribute to improvement in soil strength.

In carrying out the soil treatment method of the present invention, an appropriate amount of the lime-based treatment material may be added to the soil containing heavy metals. For example, the lime-based treatment material is mixed into the surface layer of the ground to increase the strength. Surface mixing treatment method: There is a deep mixing treatment method for excavating a region from the ground surface to a considerable depth and forcibly mixing with a lime-based treatment material to form a solid improved ground.

The amount of the lime-based treatment material added to the soil is preferably set as appropriate depending on the type and quality of the soil, the amount of heavy metal eluted, the required soil strength, and the like. amount, 50k against soil 1m ³
g or more, preferably 100 kg or more and 300 k
g, preferably 250 kg or less. If the addition amount is less than 50 kg, it is difficult to obtain a satisfactory heavy metal elution prevention effect and a soil strengthening effect on the soil after the treatment, and it is easy to cause uneven mixing. In addition, if the added amount exceeds 300 kg, their soil modifying effect is saturated.

The mechanism by which the elution of heavy metals is suppressed by the soil treatment method of the present invention is not clear, but lime reacts with lime and alumina or silica forming clay minerals or colloids to form lime aluminate-based water. It is presumed that in the process of producing a hydrate or a hydrated silicate, a heavy metal is taken in as a stable compound and captured as a part of the metal species. In any case, from the soil treated according to the present invention, the elution of heavy metals is suppressed, and the strength as improved soil is also enhanced, so that the improved soil is used for roadbeds, embankments, civil engineering buildings such as building foundations, etc. It can be reused as soil without any problems, and is extremely useful from the viewpoint of environmental conservation and economics.

The treatment of the soil and the method of recycling the treated soil according to the present invention have been described above. However, calcium hydroxide and / or calcium oxide are contained as essential components to reduce the elution of heavy metals from the soil. The treated material itself is also novel as a heavy metal elution reducing material and is included in one embodiment of the present invention.

The heavy metal elution reducing material containing calcium hydroxide and / or calcium oxide may be any material containing calcium hydroxide and / or calcium oxide.
Although not particularly limited, preferred is the above-mentioned carbide residue, and more preferred is dry-type carbide residue. Preferably, the heavy metal elution reducing material further contains an inorganic filler such as gypsum, silica and alumina for the same reason as described above. Further, the heavy metal elution-reducing material of the present invention, as a heavy metal which can be immobilized in soil to reduce elution, includes hexavalent chromium, lead, cadmium, copper, mercury, selenium, manganese for the same reason as described above. , Nickel, thallium, rhodium, and antimony. As described above, the present invention can be applied to heavy metals other than those described above. And the heavy metal elution reducing material is
By applying to soils that elute heavy metals exceeding the soil environmental standards, not only can the amount of heavy metals eluted be reduced,
The soil after application exhibits excellent strength as an improved soil.

[0023]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and can be modified without departing from the scope of the present invention.
All of the embodiments are included in the scope of the present invention.

[Evaluation method] Analysis method for elution of heavy metals from soil Analysis method for elution of heavy metals and the like in soil (Soil environmental standards, a method listed in Notification No. 46 of the Environment Agency dated August 23, 1991)
, The following heavy metals were eluted from soil, and the amount of heavy metals eluted in the eluate was determined based on JIS K0102. Hexavalent chromium: Method specified in JIS K0102 65.2.1 Lead: Method specified in JIS K010 54.2 Uniaxial compressive strength A sample was prepared, and JSF T 511-19 was prepared using the sample.
A uniaxial compressive strength test was carried out in accordance with No. 90 (Japan Geotechnical Society JGS 0511-2000).

[Reference Example: Hexavalent chromium leaching test of soil treated with cement-based solidification material] Sampling was performed at three locations from soil whose soil had been improved using a commercially available cement-based solidification material, and hexavalent chromium was sampled. A dissolution test was performed. The results are shown in Table 1.

[0026]

[Table 1]

Cement-based solidifying material A: Denka Soil Pack SP-20 Cement-based solidifying material B: Ube-Mitsubishi Eustabila 10 From Table 1, all soil treated with the cement-based solidifying material have an environmental standard of 0. Hexavalent chromium exceeding 05 mg / L was detected. Even when blast furnace cement, which is said to have a small amount of hexavalent chromium eluted, was used, hexavalent chromium exceeding the environmental standard was detected from one place.

[Preparation of lime-based treatment material] Carbide slag, gypsum, silica, etc. were blended based on the blending recipe shown in Table 2,
Lime-based treatment materials 1 to 3 were produced.

[0029]

[Table 2]

Carbide slag: SC trade name: Spent carbide (containing 96% by mass of calcium hydroxide, 0.4% by mass of calcium carbonate, 0.8% by mass of iron and alumina-based oxide (average value))

(Example 1) First, 75 kg of cement-based solidifying material (Geoset made by Taiheiyo Cement) was added to 1 m ^{3 of} natural soil not containing hexavalent chromium and uniformly mixed to prepare an improved soil. . The hexavalent chromium elution amount of the obtained improved soil was 0.11 mg / L, which exceeded the soil environmental standard. For 1 m ^{3 of} this improved soil, 5
0 kg was added and mixed uniformly to prepare a treated soil. Thereafter, the treated soil was cured at a temperature of 20 ° C. ± 3 ° C. for 10 days, and then a hexavalent chromium elution test was performed. In addition, 2
After curing for 9 days at a temperature of 0 ° C. ± 3 ° C. and then immersing in water for 1 day, a uniaxial compressive strength test was performed. The test results are shown in Table 3. Table 3 also shows the uniaxial compressive strength of the improved soil using a commercially available cement-based solidifying material for comparison.

[0032]

[Table 3]

According to Table 3, the amount of hexavalent chromium eluted from the soil treated with the lime-based treatment material 1 of the present invention is less than the detection limit of 0.01 mg / L, which exceeds the soil environmental standard.
6 (0.11 mg / L)
It was revealed that the amount of chromium (II) elution could be reduced. Further, the uniaxial compressive strength of the soil treated with the lime-based treated material 1 of the present invention was 670 kN / m ² , which was close to the strength of 884 kN / m ² of the soil treated with the conventional cement-based solidified material. .

(Examples 2 and 3) Based on the composition shown in Table 4, the elution amount of hexavalent chromium exceeds the soil environmental standard.
The lime-based treatment materials 2 and 3 shown in Table 2 were added to the dehydrated cake of 18 mg / L to prepare a treated soil. This treated soil was cured at 20 ° C. ± 3 ° C. for 10 days, and a hexavalent chromium elution test was performed. In addition, the treated soil was cured at 20 ° C. ± 3 ° C. for 9 days, then immersed in water for 1 day, and then measured for uniaxial compressive strength.

[0035]

[Table 4]

As is clear from Table 4, the amount of hexavalent chromium eluted from the soil treated with the soil treatment method of the present invention was 0.01 mg / mg.
L (detection limit: 0.01 mg / L). Further, the strength of the treated soil is increased by increasing the amount of the lime-based treatment material, and it can be seen that the lime-based treatment materials 2 and 3 containing silica and alumina are effective in improving the strength of the treated soil.

Example 4 The soil from which the shots were removed from the soil at the shooting range was used as test soil. The lead elution amount of the test soil was 3.7 mg / L. This test soil 1m ³
Then, 100 kg of the lime-based treatment material 2 was added and uniformly mixed to prepare a treated soil. 20 ℃ ± 3 ℃
And a lead elution test was performed on the seventh day and one month after the start of the curing. The results are shown in Table 5.

[0038]

[Table 5]

As is clear from Table 5, the amount of lead eluted from the untreated test soil was 3.7 mg / L, but after treatment, the lead elution amount was 0.42 mg / L on the 7th day of curing. In the first month of curing, it was found to be 0.088 mg / L, which was significantly reduced over time. From these results, it can be confirmed that the soil treatment method and the heavy metal elution reducing material of the present invention are also effective in reducing lead elution. The lead elution amount in the first month of curing is higher than the environmental standard value of lead of 0.01 mg / L or less, but it is expected that the elution amount will be further reduced by extending the curing period.

[0040]

According to the method for treating soil of the present invention, the amount of heavy metal eluting from soil containing heavy metal can be reduced by immobilizing the heavy metal on the soil. The amount of hexavalent chromium eluted from soil that elutes hexavalent chromium exceeding 0.05 mg / L) can be reduced. Therefore, if the present invention is applied to soil at a site such as a factory / office where an elution amount of heavy metal exceeds an environmental standard value, an industrial waste disposal site, and a shooting range, the elution amount of heavy metal from the soil can be suppressed. As a result, the former site can be effectively used. Since the soil after the treatment of the present invention has higher strength, it can be reused as soil for civil engineering construction such as roadbed, embankment, and construction foundation.

The heavy metal elution reducing material of the present invention can be suitably used as a heavy metal elution reducing material contained in soil.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09K 17/02 C09K 17/12 17/06 103: 00 17/08 B09B 3/00 304K 17/12 ZAB / / C09K 103: 00 F term (reference) 2E191 BA02 BB01 BC01 4D004 AA41 AB03 BA02 CA34 CC06 CC11 CC13 DA03 DA10 4H026 CA02 CA06 CB05 CB06 CC06

Claims (13)

[Claims] 1. A method for treating a soil, comprising adding a lime-based treating agent containing calcium hydroxide and / or calcium oxide as an essential component to a soil containing a heavy metal. 2. The soil according to claim 1, wherein the soil contains at least one heavy metal selected from the group consisting of hexavalent chromium, lead, cadmium, copper, mercury, selenium, manganese, nickel, thallium, rhodium, and antimony. Item 4. The method for treating soil according to Item 1. 3. A lime-based treatment material containing calcium hydroxide and / or calcium oxide as an essential component is added to soil having a hexavalent chromium elution amount of more than 0.05 mg / liter, and the hexavalent chromium elution amount is determined. The method for treating soil, wherein the amount is controlled to 0.05 mg / liter or less. 4. The method for treating soil according to claim 3, wherein the soil contains cement or a cement-based solidifying material. 5. The soil treatment method according to claim 1, wherein the lime-based treatment material is a carbide slag. 6. The soil treatment method according to claim 1, wherein the lime-based treatment material further contains an inorganic filler. 7. The method for treating soil according to claim 6, wherein the inorganic filler is silica or alumina. 8. A method for reusing soil treated by the method according to claim 1 as soil for civil engineering and construction. 9. A material for reducing elution of heavy metals from soil, comprising calcium hydroxide and / or calcium oxide as an essential component. 10. The heavy metal elution reducing material according to claim 9, wherein the heavy metal elution reducing material is carbide residue. 11. The heavy metal elution reducing material according to claim 10, wherein the heavy metal elution reducing material further contains an inorganic filler. 12. The heavy metal elution reducing material according to claim 11, wherein the inorganic filler is silica or alumina. 13. The heavy metal is at least one heavy metal selected from the group consisting of hexavalent chromium, lead, cadmium, copper, mercury, selenium, manganese, nickel, thallium, rhodium, and antimony. The material for reducing elution of heavy metals according to any one of the above.