JP6503812B2 - Neutral solidifying material and solidifying method - Google Patents

Description

  The present invention relates to a neutralizing material and a solidifying method that can insolubilize arsenic-contaminated soil and the like, increase the solidification strength of the insolubilized treated soil in a short period, and make the pH of the treated soil neutral.

  In recent years, there have been cases where a large amount of soil containing lead, arsenic and fluorine is generated on roads and tunnels. Because it is difficult to excavate and remove all contaminated soil, it can be effectively used for road road embankments, river construction, etc. Attention is focused on neutral solidified materials that can prevent elution. Since insolubilization with a cement-based material or a magnesium oxide-based material tends to make the pH of the improved soil or ground water alkaline, a neutral solidification material having an insolubilizing function has been developed. For example, a neutralizing material has been proposed in which calcium carbonate and an acidic sulfate compound such as aluminum sulfate or ferrous sulfate are added to light-burned magnesia or light-burned magnesia partial hydrate (see Patent Document 1) ). In addition, pH says the range of 5.8-8.6 as said here.

Since the improved soil treated with the neutral solidification material may be used effectively as a filling, river construction, etc., the cone index (in-situ strength), which is an index of the improvement characteristics, is, for example, 400 kN / m ² or more (third It is desirable that it is a seed construction soil). As the (field / indoor) strength ratio decreases due to the dispersion of soil quality, the fluctuation of water content ratio, etc., a cone index (indoor strength) of about 500 kN / m ² or more may be required. The initial strength development property of the neutral solidification material may be relatively low, and as an auxiliary material for enhancing the strength of the neutral solidification material, porous materials perlite, zeolite, bentonite and the like are disclosed (patent document 2 to 5).

JP 2012-92180 A Unexamined-Japanese-Patent No. 2003-334526 Unexamined-Japanese-Patent No. 2003-342569 Unexamined-Japanese-Patent No. 2006-187773 Unexamined-Japanese-Patent No. 2000-109830

  However, the strength increase rate of the neutral solidification material to which the conventional strength enhancement material is added is low, and it may not be suitable as a strength enhancement material of the neutral solidification material.

  Therefore, the present invention can increase the initial strength of the soil contaminated with arsenic etc., insolubilize the arsenic-contaminated soil below the soil elution amount standard, and neutralize the pH of the surrounding environment of the treated soil such as groundwater. It is an object of the present invention to provide a solidifying material that can be used as the solidifying material and a solidifying method using the solidifying material.

  As a result of intensive studies to solve the above problems, the present inventors added a predetermined amount of a tile as a porous material to an inorganic powder composition composed of light-burned magnesium oxide, aluminum sulfate and ferrous sulfate. It has been found that the initial strength of the modified soil can be enhanced as compared with the neutralizing material to which the conventional porous material is added, and the present invention has been completed.

That is, the present invention is a neutral solidification material containing an inorganic powder composition comprising 15 to 55% by mass of light-burned magnesium oxide, 35 to 80% by mass of aluminum sulfate and 3 to 20% by mass of ferrous sulfate, and tiles. I will provide a. According to this neutral solidification material, the initial strength of the improved soil can be increased, and insolubilization of arsenic is possible.
Moreover, the neutral solidification material of this invention contains 1-12 mass parts of tiles with respect to 100 mass parts of inorganic powder compositions. By setting this range, the initial strength of the improved soil can be further enhanced, and insolubilization of arsenic is possible.
Moreover, as for the neutral solidification material of this invention, it is preferable that the BET specific surface area of the said tile is 0.3-3.0 m < ² > / g. By setting it in this range, the initial strength of the improved soil can be further enhanced, and insolubilization of arsenic is possible.
Also, neutral solidifying material of the present invention, SiO ₂ content of 60 to 70% by weight of the tile, _Al 2 _{O 3} content of 18 to 25 wt%, _Fe 2 _{O 3} content of 2-7 wt% The CaO content is preferably 0.1 to 3.0% by mass, and the boron content is preferably 0.1 to 60 mg / kg.
Further, the present invention, the neutral solidifying material, added and mixed 20 to 200 kg / ^{m 3} with respect to the soil 1 m ^3, to provide a solidification method. According to this solidification treatment method, the initial strength of the improved soil can be increased, and insolubilization of arsenic is possible.
Moreover, it is preferable that the solidification treatment method of this invention is arsenic contamination soil whose arsenic content of the said soil is 0.1-100 mg / kg.

  According to the present invention, the initial strength of soil contaminated with arsenic or the like can be enhanced, the arsenic-contaminated soil is insolubilized below the soil elution amount standard, and the pH of the surrounding environment of treated soil such as groundwater is neutral. It is possible to provide a neutral solidifying material that can be used as well as a solidifying method.

It is a figure which shows the X-ray-diffraction pattern of a waste tile.

  Hereinafter, preferred embodiments of the neutral solidification material and the solidification treatment method of the present invention will be described in detail.

<Neutralizing material>
The solidifying material of the present invention is an inorganic powder comprising 15 to 55% by mass of light-burned magnesium oxide, 35 to 80% by mass of aluminum sulfate (in terms of anhydride) and 3 to 20% by mass of ferrous sulfate (in terms of anhydride) It contains a composition and tiles.
Here, the term "burned magnesium oxide" means magnesium oxide obtained by firing magnesium hydroxide (Mg (OH) ₂ ) or magnesite ore (MgCO ₃ ) at a low temperature of 600 to 900 ° C.

The content of light-burned magnesium oxide is preferably 15 to 55% by mass, more preferably 16 to 54% by mass, still more preferably 17 to 53% by mass, and particularly preferably 18 to 52% by mass in terms of anhydride.
When the content of light-burned magnesium oxide is less than 15% by mass, the strength developing property is unfavorably reduced. In addition, when the content of the light-burned magnesium oxide exceeds 55% by mass, the pH of the treated soil exceeds 8.6 and the surrounding environment such as ground water becomes alkaline, which is not preferable.

  35-80 mass% is preferable in conversion of an anhydride, as for content of aluminum sulfate, 36-78 mass% is more preferable, 37-76 mass% is more preferable, 38-74 mass% is especially preferable. If the content of aluminum sulfate is less than 35% by mass, it is not preferable to secure the pH at neutrality (pH 8.6 or less), which is not preferable. Further, when the content of aluminum sulfate exceeds 80% by mass, it is difficult to secure the pH at neutrality (pH 5.8 or more), which is not preferable.

3-20 mass% is preferable, as for content of ferrous sulfate, 4-18 mass% is more preferable, 5-15 mass% is more preferable, 6-12 mass% is especially preferable.
If the content of ferrous sulfate is less than 3% by mass, it is not preferable because insolubilization of arsenic becomes difficult. Further, if the content of ferrous sulfate exceeds 20% by mass, the strength developing property is unfavorably lowered. The mineral powder composition may contain a small amount of gypsum, limestone powder, calcium carbonate and the like in addition to light-burned magnesium oxide, aluminum sulfate and ferrous sulfate.

  The content of the tile is preferably 1 to 12 parts by mass, more preferably 2 to 12 parts by mass, still more preferably 3 to 11 parts by mass, and particularly preferably 5 to 10 parts by mass with respect to 100 parts by mass of the inorganic powder composition. If the content of the tile is less than 1 part by mass, the strength developing effect is reduced, such being undesirable. Moreover, since the strength expression effect may fall when content of a tile exceeds 12 mass parts, it is unpreferable.

  Although the light-burned magnesium oxide can be sufficiently used if it is commercially available light-burned magnesium oxide, it is preferable that the magnesium oxide has high hydration activity. For example, light-burned magnesium oxide having a large brane specific surface area or BET specific surface area is more preferable.

Blaine specific surface area of the light burned magnesium oxide is preferably 6000~20000cm ² / g, more preferably 7000~20000cm ² / g, more preferably from 8000~20000cm ² / g. If the brane specific surface area is less than 6000 cm ² / g, the hydration activity of the light-burned magnesium oxide composition is low, and the insolubilizing effect and the solidification performance are insufficient. If the brane specific surface area exceeds 20000 m ² / g, the flowability of the powder or the slurry is lowered, and the dusting property and the workability of the neutralized solidifying material deteriorate, which is not preferable. BET specific surface area of the light burned magnesium oxide is preferably 5 to 30 m ² / g, more preferably 7~30m ² / g, more preferably from 8~30m ² / g. If the BET specific surface area is less than 5 m ² / g, the hydration activity of the light-burned magnesium oxide composition is low, and the insolubilizing effect and the solidification performance are insufficient. If the BET specific surface area exceeds 30 m ² / g, the flowability of the powder or the slurry is unfavorably reduced.

The MgO content of light-burned magnesium oxide is preferably 80% by mass or more, and the CaO content is preferably 3% by mass or less. The content of MgO is more preferably 85% by mass or more, further preferably 90% by mass or more, and particularly preferably 95% by mass or more. If the MgO content is less than 80% by mass, there is a risk that the pH buffering capacity of the surrounding environment (ground water and the like) of the treated soil may be reduced, and the insolubilization performance may be reduced, which is not preferable.
Moreover, 2 mass% or less is more preferable, and, as for a CaO content rate, 1 mass% or less is especially preferable. If the CaO content exceeds 3% by mass, the pH of the surrounding environment (ground water etc.) of the treated soil may become alkaline, or the insolubilization performance may be reduced, which is not preferable.

  The MgO content rate and the CaO content rate contained in light burned magnesium oxide can be measured with reference to JIS M 8853: 1998 “Chemical analysis method of aluminosilicate material for ceramics”.

  Aluminum sulfate can be used sufficiently as long as it is commercially available aluminum sulfate, and may be either powder or liquid, but preferably powder. Aluminum sulfate may be either anhydrate or hydrate.

  Ferrous sulfate can be used sufficiently as long as it is commercially available ferrous sulfate, and may be in the form of powder or liquid, preferably in the form of powder. Also, ferrous sulfate may be either anhydrate or hydrate.

Tiles include clay tiles and cement tiles, but the tiles used for the solidifying material of the present invention are preferably clay tiles. Clay tiles are roughly divided into glazed tiles, glazed tiles, and glazed tiles, but any of them can be used. Smoked tiles and glazed tiles are more preferable. In the case of smoked tiles and glazed tiles, it is preferable because the content of harmful substances such as boron is small. In addition, crushed tiles and waste tiles can be used. The grain size is preferably 5 mm under, more preferably 4 mm under, even more preferably 3 mm under, particularly preferably 2 mm under. When the grain size of the tile used for the neutral solidification material of the present invention is under 0.1 mm, the strength developing property is not sufficiently exhibited, which is not preferable.
BET specific surface area of the tile is preferably 0.3~3.0m ² / g, more preferably 0.4~2.5m ² / g, more preferably 0.5~2.0m ² / g, 0.6 -1.5 m < ² > / g is especially preferable. If it is less than 0.3 m ² / g, the strength developing effect is lowered, and if it exceeds 3.0 m ² / g, it is not preferable because cost increase and workability in a slurry are lowered.

SiO ₂ content of tiles is preferably 60 to 70 wt%, more preferably 62-68 wt%, more preferably 63 to 67 wt%. If it is 60 mass% or less, it is not preferable in terms of strength development or insolubilization of arsenic etc. If it exceeds 70 mass%, the quartz content becomes too large, which is not preferable in terms of strength development or insolubilization of arsenic etc.
Further, _Al 2 _{O 3} content is preferably 18 to 25 wt%, more preferably from 19 to 24 wt%, more preferably 20 to 23 wt%. If it is less than 18% by mass, it is not preferable in terms of strength development, and if it is more than 25% by mass, it is not preferable in terms of strength development or insolubilization such as arsenic.
Further, it is preferred 2-7 wt% _Fe 2 _{O 3} content is more preferably 3 to 6 wt%, more preferably 4-5 wt%. If it is 2% by mass or less, the purity of the tile is preferable in terms of strength expression and insolubilization such as arsenic, and if it exceeds 7% by mass, contamination with impurities and the like increases, and in terms of strength expression and insolubilization such as arsenic is preferable. Absent.

Moreover, 0.1-3.0 mass% is preferable, 0.1-2.0 mass% is more preferable, 0.1-1.0 mass% is more preferable. If the CaO content exceeds 3% by mass, the pH of the surrounding environment (ground water etc.) of the treated soil may become alkaline, or the insolubilization performance may be reduced, which is not preferable.
The boron content is preferably 0.1 to 60 mg / kg, more preferably 0.2 to 40 mg / kg, still more preferably 0.3 to 20 mg / kg, and particularly preferably 0.4 to 10 mg / kg. If it is less than 0.1 mg / mg, it is not preferable because it becomes difficult to obtain and cost increases. When it exceeds 60 mg / kg, it is not preferable because the elution amount of boron may exceed the soil elution amount standard.

  In the neutral solidification material of the present invention, limestone powder, silica stone powder, hydrotalcite, hydrocalumite, magnesium carbonate, according to the properties of the contaminated soil and in the range not impairing the performance of the original neutral solidification material It can be optionally mixed with various additives such as sepiolite, chelate, iron powder and the like. In addition, about mixing of various additives, it is preferable to determine based on the result of the previous chamber | room mixing | blending test, and / or the result of the mixing | blending test using a local mixer.

<Solidification method>
The soil to be ground-improved by the solidification treatment method of the present invention is preferably a contaminated soil having an elution amount of arsenic of 0.011 to 0.50 mg / L, more preferably 0.011 to 0.40 mg / L, and 0.011. -0.35 mg / L is further preferable, and 0.011-0.30 mg / L is particularly preferable.

The addition amount of the neutral solidification material used in the solidification treatment method of the present invention is selected according to the type and the degree of contamination of the contaminated soil to be treated, but addition of 20 to 200 kg / m ³ to the soil is sufficient insolubilization An effect is obtained. Preferably, it is added at 20 to 150 kg / m ³ , more preferably 20 to 100 kg / m ³ , particularly preferably 20 to 75 kg / m ³ . If the addition amount is less than 20 kg / m ³ , it is not preferable because mixing of the neutral solidification material and the soil may be insufficient. On the other hand, if the addition amount exceeds 200 kg / m ³ , the treatment cost becomes too high, which is economically unpreferable.
In addition, it is preferable to determine the addition amount of the neutral solidification material based on the result of the previous indoor mixing test and / or the result of the mixing test using the on-site mixer.

  Moreover, the addition of the neutral solidification material to the contaminated soil can be used either in the form of powder or in the form of slurry. Neutralization material and contaminated soil are mixed by backhoe, backhoe with mixing bucket, stabilizer, self-propelled soil conditioner, stationary mixer, trencher type mixer, deep layer mixer, power blender, plant mixing etc. A mixing method usually used may be used.

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

1. Materials used In the present invention, light-burned magnesium oxide manufactured by Ube Materials Co., Ltd. is used, aluminum sulfate is manufactured by Daimei Chemical Industries, Ltd. (trade name: aluminum sulfate, 14 hydrate), ferrous sulfate is used. Titanium Industry Co., Ltd. (trade name: ferrous sulfate, heptahydrate) was used. In addition, as porous material, waste tile (brand name: special chamotte 0.5 mm under goods, BET specific surface area 0.76 m ² / g) made by Aichi Prefectural ceramic tile industry association, zeolite (Ube Industries, Ltd.) Ube zeolite) and bentonite (Kunigel Fs) manufactured by Kunimine Industries were used.

[Chemical composition of burnt magnesium oxide]
The chemical composition of the light-burned magnesium oxide used is shown in Table 1. The chemical composition of the light-burned magnesium oxide was measured in accordance with JIS M 8853: 1998 "Chemical analysis method of aluminosilicate material for ceramics". The unit in the table is% by mass.

[酸化マグネシウムのブレーン比表面積]
使用した軽焼酸化マグネシウムのブレーン比表面積は、ＪＩＳ Ｒ ５２０１：１９９７「セメントの物理試験方法」に従い、ブレーン空気透過装置を用いて測定した。その結果を表２に示す。
[軽焼酸化マグネシウムのＢＥＴ比表面積]
前記軽焼酸化マグネシウムのＢＥＴ比表面積は、高精度ガス吸着装置（日本ベル社製、ＢＥＬＳＯＲＰ−ｍｉｎｉ）を用いて、定容量型ガス吸着法にて測定した。その結果を表２に示す。
[軽焼酸化マグネシウムの密度]
使用した軽焼酸化マグネシウムの密度は、ＪＩＳ Ｒ ５２０１：１９９７「セメントの物理試験方法」に従い、ルシャテリエフラスコを用いて測定した。その結果を表２に示す。

[Brain specific surface area of magnesium oxide]
The brane specific surface area of the light-burned magnesium oxide used was measured using a brane air permeation device according to JIS R 5201: 1997 "Physical test method for cement". The results are shown in Table 2.
[BET specific surface area of lightly burned magnesium oxide]
The BET specific surface area of the light-burned magnesium oxide was measured by a fixed volume gas adsorption method using a high-precision gas adsorption device (BELSORP-mini manufactured by Nippon Bell Co., Ltd.). The results are shown in Table 2.
[Density of burnt magnesium oxide]
The density of the light-burned magnesium oxide used was measured using a Le Chatelier flask according to JIS R 5201: 1997 "Physical test method for cement". The results are shown in Table 2.

[多孔質材料の化学組成]
使用した多孔質材料の化学組成を表３に示す。多孔質材料の化学組成は、ＪＩＳ Ｍ ８８５３：１９９８「セラミックス用アルミノけい酸塩質原料の化学分析方法」に準拠して測定した。なお、ほう素の含有量測定では、環境庁告示１９号に準拠して試料を調製し、測定はＪＩＳ Ｋ０１０２−４７．３に準拠して行った。

[Chemical composition of porous material]
The chemical composition of the used porous material is shown in Table 3. The chemical composition of the porous material was measured in accordance with JIS M 8853: 1998 "Chemical analysis method of aluminosilicate material for ceramics". In addition, in content measurement of boron, the sample was prepared based on Environment Agency notification No. 19, and the measurement was performed based on JIS K 0102-47.3.

[廃瓦に含まれる化合物の同定]
粉末Ｘ線回折（ＲＩＮＴ−２５００、リガク社製）を用いて廃瓦に含まれる化合物を同定した結果を図１に示す。図１に示すように、廃瓦に含まれる主な化合物としては石英とムライトであることが確認された。粘土原料にはカオリナイト、雲母鉱物、石英などから構成されるが、粘土瓦の製造において高温焼成したときにムライトが生成し、石英は融点が高いため残存していると推察できる。その高温焼成・冷却工程において、瓦内部に空隙が生じ、多孔質性を有するものと考えられる。

[Identification of compounds contained in waste tiles]
The result of having identified the compound contained in a waste tile using powder X-ray diffraction (RINT-2500, RIGAKU Co., Ltd. make) is shown in FIG. As shown in FIG. 1, it was confirmed that quartz and mullite were the main compounds contained in the waste tile. The clay raw material is composed of kaolinite, mica mineral, quartz and the like, but it can be inferred that mullite is formed when fired at high temperature in the manufacture of clay tile and quartz has a high melting point and thus remains. In the high temperature baking and cooling process, voids are generated inside the tile, and it is considered to be porous.

[Sample soil]
In the present invention, soil collected in Yamaguchi Prefecture is provided. The properties of the sample soil are shown in Table 4. The moisture content was measured in accordance with JIS A 1203 "Test method for moisture content of soil". The wet density was determined by filling a sample soil into a mold having a diameter of 5 cm and a height of 10 cm, and determining the mass of the loaded sample soil and the volume of the mold. Moreover, pH was measured using the test solution of Environment Agency notification No. 18 method, and the particle size was measured according to JIS A 1204 "Grade size test method of soil".

[Simulated contaminated soil]
After mixing in advance silica sand (63% by mass, Ube Sand Industry Co., Ltd.) and kaolinite (37% by mass, Kanaya Kosan Co., Ltd.), disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ · 7H ₂ O, Wako pure A predetermined amount of aqueous solution is added, and it is mixed with a soil mixer at low speed for 2.5 minutes, the soil adhering to the container or paddle is scraped off, and then mixed for another 2.5 minutes at low speed. The mock-contaminated soil was made by curing for 1 day in a bag-sealed state.
The properties of the produced simulated contaminated soil are shown in Table 5. The moisture content was measured in accordance with JIS A 1203 "Test method for moisture content of soil". The wet density was determined by filling a sample soil into a mold having a diameter of 5 cm and a height of 10 cm, and determining the mass of the loaded sample soil and the volume of the mold. Moreover, pH was measured using the test solution of Environment Agency notification No. 18 method, and the particle size was measured according to JIS A 1204 "Grade size test method of soil". The arsenic content and the elution amount were prepared in accordance with the Environment Agency Notification 19 Law and Environment Agency Notification 18 Law, and the measurement was performed in accordance with JIS K 0102 “Testing method for factory drainage”.

2. Test method
[Unaxial compression strength]
60 kg / m ^{3 of} various neutral solidification materials are added to the sample soil and mixed at a low speed with a soil mixer for 1.5 minutes, and then the soil adhering to the container or paddle is scraped off, and further 1.5 minutes at a low speed I mixed it. The treated soil obtained in this manner is divided into three layers in a φ5 × 10 cm mold to prepare a cylindrical specimen, sealed and cured at 20 ° C. until age 1 day, and then JIS A 1216 The uniaxial compression strength was measured in accordance with the "uniaxial compression test", and the cone index was determined from the relationship between the uniaxial compression strength and the cone index.

[PH of treated soil]
After crushing the test body after the uniaxial compression test, a test solution according to Environment Agency Notification No. 18 was prepared, and the pH of the test solution was measured with a glass electrode type pH meter (manufactured by Toa DKK).

[Insolubilization test]
After adding 30 kg / m ^{3 of} various neutral solidification materials to the above-mentioned simulated polluted soil and mixing with a soil mixer for 1.5 minutes at low speed, the soil adhering to the container or paddle is scraped off, and further 1.5 at low speed. I mixed it for a minute. The treated soil thus obtained was cured for 1 day at 20 ° C. in the state of being sealed with a polyethylene bag, and then a test solution was prepared according to the method disclosed in the Environment Agency Notification No. 18. The heavy metal concentration of the test solution was measured in accordance with JIS K 0102 “Testing method for factory drainage”.

3. Test results [Corn index of solidified soil]

  An inorganic powder composition comprising 32.5% by mass of light-burned magnesium oxide, 57.5% by mass of aluminum sulfate and 10% by mass of ferrous sulfate, and 3 to 10 of waste tile, zeolite and bentonite as porous materials Mass% (external division) was added to prepare a neutral solidification material (Formulation Nos. 2 to 10). Moreover, the neutral solidification material which did not add the porous material was also produced as a reference example (composition No. 1). The sample soil shown in Table 4 was used as the soil to be treated. The cone index (one-day old) of the treated soil modified with these neutralizing agents is shown in Table 6.

［砒素およびほう素の溶出試験結果］

[Dissolution test result of arsenic and boron]

  Formulation No. 1 described above. The amount of elution of arsenic and boron from the solidified treated soil treated with the neutral solidified materials of 1, 3 and 4 was measured. As the soil to be treated, the simulated contaminated soil shown in Table 5 was used. The results are shown in Table 7.

  As shown in Table 6, the neutral solidification materials (Examples 1 to 3) to which the waste tile of the present invention is added are compared to the cases (Zero example 1 and 3 and 4 and 5) when zeolite and bentonite are added. , It is understood that the strength increase rate (%) / addition rate (mass%) is large, and the strength increase effect is high.

  Moreover, as shown in Table 7, it was confirmed that the neutral solidified materials (Examples 4 and 5) to which the waste tile of the present invention was added did not adversely affect the elution amount of arsenic and boron.

  As described above, an inorganic powder composition composed of 15 to 55% by mass of lightly burned magnesium oxide, 35 to 80% by mass of aluminum sulfate, and 3 to 20% by mass of ferrous sulfate in the range of the present invention; It can be seen that, as compared with neutral solidified materials using zeolite and bentonite as porous materials, the neutral solidified materials containing B have higher initial strength of the improved soil and do not adversely affect the elution amount of arsenic and boron. .

Claims (5)

Light burned magnesium oxide 15 to 55 wt%, seen containing a mineral powder composition consisting of aluminum sulfate 35 to 80 wt% and ferrous 3-20 wt% sulfuric acid, and a tile,
The relative mineral powder 100 parts by mass of the composition, neutral solidifying material, wherein 1 to 12 parts by mass including Mukoto the tile. BET specific surface area of the tile is 0.3~3.0m ² / g, according to claim 1 Symbol placement neutral solidifying material. The SiO ₂ content of 60 to 70 wt% of the tiles, _Al 2 _{O 3} content of 18 to 25 wt%, _Fe 2 _{O 3} content of 2-7 wt%, CaO content is 0.1 to 3. The neutral solidification material according to claim 1 or 2 whose 0 mass% and boron content are 0.1 to 60 mg / kg. Solidification method characterized by the claims 1 to 3 neutral solidifying material according to any one of the described, it added and mixed 20 to 200 kg / ^{m 3} with respect to the soil 1 m ^3. 5. The method according to claim 4 , wherein the soil is arsenic-contaminated soil with an arsenic content of 0.1 to 100 mg / kg.

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