JP4219066B2 - Removal of arsenic in exhaust gas for remediation of contaminated soil - Google Patents
Removal of arsenic in exhaust gas for remediation of contaminated soil Download PDFInfo
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- JP4219066B2 JP4219066B2 JP29480099A JP29480099A JP4219066B2 JP 4219066 B2 JP4219066 B2 JP 4219066B2 JP 29480099 A JP29480099 A JP 29480099A JP 29480099 A JP29480099 A JP 29480099A JP 4219066 B2 JP4219066 B2 JP 4219066B2
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- Prior art keywords
- exhaust gas
- arsenic
- contaminated soil
- compound
- remediation
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Description
【０００１】
【発明の属する技術分野】
工場跡地や軍事施設の跡地においてヒ素化合物による汚染が問題となっている。これらを浄化する方法として土壌の加熱がある。加熱方式は、土壌中のヒ素化合物を脱離気化させる方式であり、ヒ素化合物を含む排ガスが必ず発生する。本発明は、このような排ガス中のヒ素化合物を除去する方法に関する。
【０００２】
【従来の技術】
加熱方式による土壌浄化方式は新しい技術であり、土壌浄化過程で発生する排ガス中のヒ素化合物の回収技術は、特にない。
【０００３】
ごみ焼却炉等の排ガス処理の場合、ＨＣｌ等の酸性成分の中和の目的で１７０℃〜２５０℃で排ガスの煙道中に消石灰を吹き込み、酸性成分の中和除去を行い、結果的に排ガス中のヒ素が除去できているという報告がある。
【０００４】
【発明が解決しようとする課題】
ごみ焼却炉等の排ガス処理工程では、後流側のバグフィルターのろ布の耐熱性能により排ガスを２００℃前後まで冷却する必要があり、排ガスを水噴霧等で冷却している。しかし、排ガス量が変動したりノズルが異常な水噴霧を行った場合、冷却水は完全には蒸発せず冷却塔やバグフィルターダクト内で結露し、ここに有害なヒ素化合物が付着することになり、ヒ素化合物の完全除去ができない。またヒ素化合物が消石灰と反応し、ヒ酸カルシウムに変化し易い温度は５００〜 ６００℃であるとされており、２００℃程度では該反応が効率的に進みにくい。排ガス中に酸化鉄を吹き込んでヒ素化合物をヒ酸鉄にする場合も同様である。
【０００５】
本発明の目的は、上記の点に鑑み、汚染土壌浄化における排ガス中のヒ素化合物を高効率で除去することができる、ヒ素化合物除去法を提供することにある。
【０００６】
【課題を解決するための手段】
本発明は、加熱処理による汚染土壌浄化プロセスで発生する排ガス中に４５０〜６００℃の高温にて、アルカリ土類金属または鉄の水酸化物を吹き込み、排ガス中のヒ酸またはその化合物をアルカリ土類金属または鉄のヒ酸塩に変換し、耐熱性材料で構成された集塵器を用いて、高温でこの塩を捕集することを特徴とする、汚染土壌浄化における排ガス中のヒ素除去法である。
【０００７】
アルカリ土類金属としてはカルシウム、マグネシウム等が挙げられ、消石灰（Ｃａ（ＯＨ）2 ）が好適に用いられる。この場合、排ガス中のヒ酸またはその化合物はヒ酸カルシウム（Ｃａ3 （ＡｓＯ4 ）2 ）に変換される。また、酸化鉄を吹き込むことによりヒ酸鉄（ＦｅＡｓＯ4 ）が生じる。好ましいヒ酸塩は、固体であり、水に難溶性である。
【０００８】
上記アルカリ土類金属または鉄化合物の吹き込みは、高温、例えば４５０〜６００℃の温度で行うのが好ましい。これにより、ダイオキシンの生成を防止することができる上に、ヒ素化合物が結露等により冷却塔、ダクト、集塵器に付着するのを避けることができる。生じたアルカリ土類金属または鉄のヒ酸塩の捕集は、セラミックなどの耐熱性材料で構成された集塵器を用いて行うのが好ましい。これにより、ヒ素化合物を高効率で除去でき、猛毒である亜ヒ酸（Ａｓ4 Ｏ6 ）の形での回収を避けることができる。
【０００９】
【発明の実施の形態】
図１において、汚染土壌をまずスクリーン(1) に掛けた後、間接加熱ロータリーキルン(2) に投入する。ここで、土壌を高温加熱し、土壌中のヒ素化合物を土壌から脱離気化させる。ここで発生したヒ素化合物含有排ガスを、次いで二次燃焼炉(3) へ送り、バ−ナもしくは電気ヒータで排ガスを８５０℃前後に加熱する。この高温排ガスを次いで排ガス冷却器(4) へ送り、ここで排ガスに水および／または空気を混入して排ガスを５００℃前後に冷却する。この排ガスに消石灰を吹き込み、その後、排ガスをセラミック製の耐熱集塵器(5) で集塵処理し、処理排ガスを煙突(6) から系外へ排出する。排ガス冷却器(4) および耐熱集塵器(5) から出たダストは搬出コンベヤ(7) および移送コンベヤ(8) において回収される。
【００１０】
土壌から脱離した固形状のヒ素化合物は耐熱集塵器(5) で捕集される。しかし、排ガス中に存在しているガス状のヒ素化合物は１３０℃以下に冷却しないと捕集できない。
【００１１】
そこで、本発明方法では、耐熱集塵器(5) の前流にて排ガスにＣａ化合物もしくはＦｅ化合物を吹き込むことにより、５００℃前後の排ガス温度でもヒ素化合物をヒ酸カルシウム（Ｃａ3 （ＡｓＯ4 ）2 ）、ヒ酸鉄（ＦｅＡｓＯ4 ）の形で捕集できるようにした。
【００１２】
Ｃａ化合物の場合の反応式は
Ａｓ2 Ｏ5 ＋３ＣａＯ＝Ｃａ3 （ＡｓＯ4 ）2
であると考えられ、この反応の熱力学的平衡定数は、
３００℃ −
４００℃ ２．０×１０36
５００℃ ３．１×１０31
６００℃ ５．３×１０27
７００℃ ４．７×１０24
であるため、６００℃以下の温度域では、排ガス中のヒ素化合物がＣａ化合物と反応した形で捕集できる。
【００１３】
【００１４】
またＳ．ＭＡＨＵＬＩらの報告ではＣａ（ＯＨ）2 は６００℃以上になると焼結し、ヒ素との結合、接解効率が悪くなり、ヒ酸カルシウムへの変化がしにくくなるとされている。
【００１５】
【発明の効果】
本発明によれば、汚染土壌浄化における排ガス中のヒ素化合物を高効率で除去することができ、猛毒である亜ヒ酸の形での回収を避けることができる。
【図面の簡単な説明】
【図１】 本発明の実施例を示すフローシートである。
【符号の説明】
１：スクリーン
２：間接加熱ロータリーキルン
３：二次燃焼炉
４：排ガス冷却器
５：耐熱集塵器
６：煙突
７：搬出コンベヤ
８：移送コンベヤ[0001]
BACKGROUND OF THE INVENTION
Contamination with arsenic compounds has become a problem at the sites of industrial sites and military facilities. There is heating of soil as a method of purifying these. The heating method is a method of desorbing and vaporizing arsenic compounds in the soil, and exhaust gas containing arsenic compounds is always generated. The present invention relates to a method for removing such an arsenic compound in exhaust gas.
[0002]
[Prior art]
The soil purification method using the heating method is a new technology, and there is no particular technology for recovering arsenic compounds in the exhaust gas generated during the soil purification process.
[0003]
In the case of exhaust gas treatment such as waste incinerator, slaked lime is blown into the flue of the exhaust gas at 170 to 250 ° C for the purpose of neutralizing acidic components such as HCl, neutralizing and removing the acidic components, resulting in the exhaust gas There is a report that arsenic has been removed.
[0004]
[Problems to be solved by the invention]
In an exhaust gas treatment process such as a garbage incinerator, it is necessary to cool the exhaust gas to around 200 ° C. due to the heat resistance performance of the filter cloth of the back filter, and the exhaust gas is cooled by water spray or the like. However, if the amount of exhaust gas fluctuates or the nozzle sprays with abnormal water, the cooling water does not evaporate completely, and condensation occurs in the cooling tower or bag filter duct, causing harmful arsenic compounds to adhere to it. Therefore, the arsenic compound cannot be completely removed. The temperature at which the arsenic compound reacts with slaked lime and easily changes to calcium arsenate is said to be 500 to 600 ° C., and at about 200 ° C., the reaction hardly proceeds efficiently. The same applies when iron oxide is blown into the exhaust gas to convert the arsenic compound to iron arsenate.
[0005]
In view of the above points, an object of the present invention is to provide an arsenic compound removal method capable of removing an arsenic compound in exhaust gas in the purification of contaminated soil with high efficiency.
[0006]
[Means for Solving the Problems]
The present invention is, at a high temperature of 450 to 600 ° C. Exhaust gas generated in the contaminated soil remediation process by heat treatment, blowing alkaline earth metal or water oxides of iron, alkaline-earth and arsenate or compounds thereof in the exhaust gas A method for removing arsenic in exhaust gas in the purification of contaminated soil, which is characterized by collecting the salt at a high temperature using a dust collector made of a heat-resistant material after converting it to a metal or iron arsenate It is.
[0007]
Examples of the alkaline earth metal include calcium and magnesium, and slaked lime (Ca (OH) 2 ) is preferably used. In this case, arsenic acid or its compound in the exhaust gas is converted to calcium arsenate (Ca 3 (AsO 4 ) 2 ). In addition, iron arsenate (FeAsO 4 ) is produced by blowing iron oxide. Preferred arsenates are solid and poorly soluble in water.
[0008]
The alkaline earth metal or iron compound is preferably blown at a high temperature, for example, 450 to 600 ° C. As a result, generation of dioxins can be prevented, and the arsenic compound can be prevented from adhering to the cooling tower, duct, and dust collector due to condensation. The resulting alkaline earth metal or iron arsenate is preferably collected using a dust collector made of a heat-resistant material such as ceramic. Thereby, the arsenic compound can be removed with high efficiency, and recovery in the form of highly toxic arsenous acid (As 4 O 6 ) can be avoided.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, the contaminated soil is first put on a screen (1) and then put into an indirect heating rotary kiln (2). Here, the soil is heated to a high temperature, and the arsenic compound in the soil is desorbed and vaporized from the soil. The arsenic compound-containing exhaust gas generated here is then sent to the secondary combustion furnace (3), and the exhaust gas is heated to about 850 ° C. with a burner or an electric heater. This high temperature exhaust gas is then sent to an exhaust gas cooler (4) where water and / or air is mixed into the exhaust gas to cool the exhaust gas to around 500 ° C. Slaked lime is blown into the exhaust gas, and then the exhaust gas is collected by a heat-resistant dust collector (5) made of ceramic, and the treated exhaust gas is discharged out of the system from the chimney (6). Dust from the exhaust gas cooler (4) and the heat-resistant dust collector (5) is collected in the carry-out conveyor (7) and the transfer conveyor (8).
[0010]
Solid arsenic compounds released from the soil are collected by a heat-resistant dust collector (5). However, the gaseous arsenic compound present in the exhaust gas cannot be collected unless cooled to 130 ° C. or lower.
[0011]
Therefore, in the method of the present invention, the arsenic compound is converted to calcium arsenate (Ca 3 (AsO 4 ) even at an exhaust gas temperature of around 500 ° C. by blowing Ca compound or Fe compound into the exhaust gas upstream of the heat-resistant dust collector (5). 2 ) It was made possible to collect in the form of iron arsenate (FeAsO 4 ).
[0012]
In the case of a Ca compound, the reaction formula is As 2 O 5 + 3CaO = Ca 3 (AsO 4 ) 2
The thermodynamic equilibrium constant of this reaction is
300 ° C-
400 ° C 2.0 × 10 36
500 ° C. 3.1 × 10 31
600 ° C 5.3 × 10 27
700 ° C. 4.7 × 10 24
Therefore, in the temperature range of 600 ° C. or lower, the arsenic compound in the exhaust gas can be collected in a form reacted with the Ca compound.
[0013]
[0014]
S. According to a report by MAHULI et al., Ca (OH) 2 is sintered at 600 ° C. or higher, and the bonding and contact efficiency with arsenic deteriorates, and it is difficult to change to calcium arsenate.
[0015]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the arsenic compound in the waste gas in the purification of contaminated soil can be removed with high efficiency, and recovery in the form of highly toxic arsenous acid can be avoided.
[Brief description of the drawings]
FIG. 1 is a flow sheet showing an embodiment of the present invention.
[Explanation of symbols]
1: Screen 2: Indirect heating rotary kiln 3: Secondary combustion furnace 4: Exhaust gas cooler 5: Heat-resistant dust collector 6: Chimney 7: Unloading conveyor 8: Transfer conveyor
Claims (1)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29480099A JP4219066B2 (en) | 1999-10-18 | 1999-10-18 | Removal of arsenic in exhaust gas for remediation of contaminated soil |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29480099A JP4219066B2 (en) | 1999-10-18 | 1999-10-18 | Removal of arsenic in exhaust gas for remediation of contaminated soil |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2001113122A JP2001113122A (en) | 2001-04-24 |
| JP4219066B2 true JP4219066B2 (en) | 2009-02-04 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP29480099A Expired - Fee Related JP4219066B2 (en) | 1999-10-18 | 1999-10-18 | Removal of arsenic in exhaust gas for remediation of contaminated soil |
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| JP (1) | JP4219066B2 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3886970B2 (en) * | 2004-01-13 | 2007-02-28 | 三菱重工業株式会社 | Recycling method of wood |
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1999
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| Publication number | Publication date |
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| JP2001113122A (en) | 2001-04-24 |
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