JP2007098299A - Method for cleaning heavy metal contaminated soil using chelating agent as cleaning agent - Google Patents

Method for cleaning heavy metal contaminated soil using chelating agent as cleaning agent Download PDF

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JP2007098299A
JP2007098299A JP2005292292A JP2005292292A JP2007098299A JP 2007098299 A JP2007098299 A JP 2007098299A JP 2005292292 A JP2005292292 A JP 2005292292A JP 2005292292 A JP2005292292 A JP 2005292292A JP 2007098299 A JP2007098299 A JP 2007098299A
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chelating agent
cleaning
contaminated soil
heavy metal
soil
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Minoru Nakajima
Kozo Toida
実 中島
幸三 樋田
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Teijin Fibers Ltd
帝人ファイバー株式会社
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for inexpensively and efficiently cleaning heavy metal contaminated soil which maintains a cleaning capacity and realizes a high circulating efficiency by re-utilizing a recovered chelating agent for cleaning contaminated soil through highly effectively recovering the chelating agent by acid precipitation directly using hydrochloric acid without performing removal of heavy metals after the contaminated soil is cleaned by using the aqueous solution of the chelating agent and the heavy metals are extracted as complexes. <P>SOLUTION: The method for cleaning heavy metal contaminated soil comprises the following processes: (A) a process of obtaining an extracting solution containing the heavy metals as the complexes by cleaning the contaminated soil with the heavy metals by the chelating agent; (B) a process of recovering the chelating agent by solid-liquid separation and washing by water after precipitating the chelating agent as the complexes formed by acid precipitation using hydrochloric acid of 5-20 wt.% from the extracting solution containing the heavy metals as the complexes; and (C) a process of preparing a chelating agent aqueous solution for cleaning soil by using the recovered chelating agent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は重金属で汚染された土壌を、キレート剤を使用して浄化する方法の改良に関する。   The present invention relates to an improved method for purifying soil contaminated with heavy metals using a chelating agent.
近年、工場跡地などを中心に鉛やカドミウムなどの重金属による土壌汚染が各地で見出されており、また、土壌汚染対策法の制定、施工に伴い、重金属汚染土壌の浄化方法についての研究が積極的に進められるようになっている。
重金属は有機物のように分解することができないため、重金属汚染土壌を処理するには汚染土壌を掘削して処分場に搬入する、不溶性の重金属塩を生成させて不溶化する、汚染土壌にセメントなどの固形化剤を加えて固化する、土壌に通電して発熱させてガラス状に固化するなどの手法が取られる。しかしながら、これらの方法は何れも土壌中に重金属を残したままにするものであり、長期安定性の面で信頼性にかけるものであった。
In recent years, soil contamination due to heavy metals such as lead and cadmium has been found in various places mainly in factory sites, etc. Also, with the establishment and construction of the soil contamination countermeasure law, research on purification methods for heavy metal contaminated soil has been actively conducted. Can be advanced.
Since heavy metals cannot be decomposed like organic matter, in order to treat heavy metal contaminated soil, excavate the contaminated soil and carry it to the disposal site, generate insoluble heavy metal salts and insolubilize it, cement in the contaminated soil, etc. Methods such as adding a solidifying agent to solidify, or applying electricity to the soil to generate heat and solidifying into a glassy state are taken. However, all of these methods leave heavy metals in the soil, and depend on reliability in terms of long-term stability.
これに対し、キレート剤を用いて汚染土壌から重金属を除去する方法が提案されており(例えば非特許文献1参照。)、エチレンジアミン四酢酸塩(EDTA)、ニトリロ三酢酸塩(NTA)などの様々なキレート剤が検討されてきた。しかしながら、キレート剤を用いる方法は、効果は高いものの、洗浄にEDTAのようなキレート剤を5〜20重量%含有する液を使用する為、キレート剤の消費量が大きく、処理コストが高い問題があった。更に、洗浄により発生した錯体を含む廃液の処理の問題もある。   On the other hand, a method of removing heavy metals from contaminated soil using a chelating agent has been proposed (for example, see Non-Patent Document 1), and various methods such as ethylenediaminetetraacetate (EDTA) and nitrilotriacetate (NTA). Chelating agents have been investigated. However, although the method using a chelating agent is highly effective, since a solution containing 5 to 20% by weight of a chelating agent such as EDTA is used for washing, the consumption of the chelating agent is large and the processing cost is high. there were. In addition, there is a problem with the treatment of waste liquid containing complexes generated by washing.
一般的にキレート剤と形成した錯体の溶液から重金属を除去する方法としては、溶液のpHを調整し、イオン交換樹脂に通じることにより重金属をイオン効果樹脂に吸着させ、重金属を含まないキレート剤の水溶液を得る技術がある(例えば特許文献1参照。)。この方法は、処理に際して温度を調整する必要がある上、イオン交換により重金属が除去される代わりにナトリウム或いはカルシウムなどの金属イオンの濃度が上昇し、pHが著しく上昇するか、H型のイオン効果樹脂を使用することにより著しく低下する。キレート剤による重金属の抽出能力はpHにより大きく変化するため、キレート剤を再使用する場合にはイオン交換処理後に再度pH調整を行う必要がある。更に、イオン交換樹脂については定期的に交換、若しくは再生する必要があり再生時の排水の処理が必要となる。   In general, as a method of removing heavy metals from a complex solution formed with a chelating agent, the pH of the solution is adjusted, and the heavy metal is adsorbed on the ion effect resin by passing through the ion exchange resin. There is a technique for obtaining an aqueous solution (see, for example, Patent Document 1). In this method, it is necessary to adjust the temperature at the time of treatment, and instead of removing heavy metals by ion exchange, the concentration of metal ions such as sodium or calcium increases, the pH increases significantly, or the H-type ion effect This is significantly reduced by using resin. Since the extraction ability of heavy metals by the chelating agent varies greatly depending on the pH, it is necessary to adjust the pH again after the ion exchange treatment when the chelating agent is reused. Further, the ion exchange resin needs to be periodically replaced or regenerated, and wastewater treatment at the time of regeneration is necessary.
アルカリ性条件下でカルシウム或いは硫化物を加えて重金属を沈殿として除去し、その後塩酸や硫酸などの鉱酸を用いてEDTAを沈殿化して回収するする方法もあるが、重金属除去時にアルカリ性に調整し、重金属を沈殿化する際には再度pHを強酸性条件まで調整する必要がある上、キレート剤が高濃度に存在する状態のままでは完全に重金属を沈殿化することが困難であり、更に、回収したEDTAを使用して重金属を抽出する場合にもpHの調整が必要となる(例えば特許文献2参照。)。   There is a method in which calcium or sulfide is added under alkaline conditions to remove heavy metals as a precipitate, and then EDTA is precipitated and recovered using a mineral acid such as hydrochloric acid or sulfuric acid. When precipitating heavy metals, it is necessary to adjust the pH to a strongly acidic condition again, and it is difficult to completely precipitate heavy metals if the chelating agent is present at a high concentration. Even when heavy metals are extracted using the prepared EDTA, it is necessary to adjust the pH (see, for example, Patent Document 2).
また、重金属を含むEDTA水溶液に対してはpHを9以上に調整後、硫化ナトリウムなどの不溶化剤を用いて重金属を沈殿させ、得られる分離液を洗浄に再使用する方法も提案されている(例えば特許文献3参照。)。しかし、この方法では重金属沈殿形成前、また、重金属沈殿除去後にpHを所定のpHに維持しないと沈殿が形成されない上、沈殿物が非常に微粒子であり、完全に捕集することができない。更に、分離された液はpHが高くそのまま使用する場合には所望の重金属除去率が達成できず、洗浄能力が低下するため、結果的にpH調整が必要となるため、キレート剤水溶液の濃度を維持することが困難となるという問題がある。
キレート剤回収際し、先行して重金属を沈殿として除去する場合には、分離した沈殿物の含液率が高く成る傾向があり、沈殿物の含液中に含まれるEDTAは回収することができず高回収率を達成することが困難であるという問題もあった。
In addition, a method has also been proposed in which an aqueous EDTA solution containing heavy metals is adjusted to a pH of 9 or more, then heavy metals are precipitated using an insolubilizing agent such as sodium sulfide, and the resulting separated liquid is reused for washing ( For example, see Patent Document 3.) However, in this method, unless the pH is maintained at a predetermined pH before the heavy metal precipitate is formed or after the heavy metal precipitate is removed, a precipitate is not formed and the precipitate is very fine and cannot be completely collected. Furthermore, the separated liquid has a high pH, and when it is used as it is, the desired heavy metal removal rate cannot be achieved, and the cleaning ability is lowered. As a result, pH adjustment is necessary. There is a problem that it is difficult to maintain.
When recovering the chelating agent, if heavy metals are removed as precipitates in advance, the liquid content of the separated precipitate tends to be high, and EDTA contained in the liquid containing the precipitate can be recovered. There was also a problem that it was difficult to achieve a high recovery rate.
特開平1−11827号公報Japanese Unexamined Patent Publication No. 1-111827 特開昭51−10176号公報Japanese Patent Laid-Open No. 51-10176 特開平4−263874号公報JP-A-4-263874
本発明の目的は、このような技術の現状を一歩進め、キレート剤の水溶液を用いて汚染土壌を洗浄し、重金属を錯体として抽出した後、重金属を除去する操作を行わずに直接塩酸を用いた酸析によりキレート剤を高回収率で回収し、回収したキレート剤を汚染土壌の洗浄操作に再利用することによって高洗浄能力を維持すると同時に高い循環効率を達成し、かつ、低コストで効率よく重金属汚染土壌を洗浄する方法を提供することにある。   The purpose of the present invention is to advance the current state of such technology, wash contaminated soil with an aqueous solution of a chelating agent, extract heavy metals as a complex, and then use hydrochloric acid directly without removing heavy metals. By recovering the chelating agent at a high recovery rate by acid precipitation, the recovered chelating agent is reused for the washing operation of contaminated soil, maintaining high washing capacity and at the same time achieving high circulation efficiency and low cost. It is often to provide a method for cleaning heavy metal contaminated soil.
上記目的を達成する為に、本発明者らは鋭意検討を行った結果、本発明の重金属汚染土壌に対する洗浄方法は下記の工程からなる。
A)重金属で汚染された土壌を、キレート剤水溶液で洗浄し、重金属を錯体として含む抽出液を得る工程
B)重金属を錯体として含む抽出液から5〜20重量%の塩酸を用いた酸析操作により錯体を形成したキレート剤を沈殿させた後、固液分離、水洗浄操作によりキレート剤を回収する工程
及び
C)回収したキレート剤を用いて土壌洗浄用のキレート剤水溶液を調製する工程
酸析操作にて塩酸の濃度を調整すると同時に、沈殿形成開始から分離開始までの時間を0.5時間以上とすることにより沈殿物を熟成させ、固液分離物の含液率を低減させることにより、回収キレート剤に残留する金属濃度を低く、また、キレート剤の回収率を高く維持することができる。キレート剤そのものを回収することにより所望の土壌洗浄剤としての濃度に調製することが可能であり、重金属汚染土壌の洗浄効率も高く維持することができる。
In order to achieve the above object, the present inventors have conducted intensive studies. As a result, the cleaning method for heavy metal-contaminated soil of the present invention comprises the following steps.
A) Washing soil contaminated with heavy metals with a chelating agent aqueous solution to obtain an extract containing heavy metal as a complex B) Acidifying operation using 5 to 20% by weight hydrochloric acid from the extract containing heavy metal as a complex Step of precipitating the chelating agent that has formed a complex by the following steps: solid-liquid separation, recovering the chelating agent by washing with water, and C) preparing the aqueous chelating agent solution for soil washing using the recovered chelating agent At the same time as adjusting the concentration of hydrochloric acid by the operation, by aging the precipitate by setting the time from the start of the precipitation to the start of separation to 0.5 hours or more, by reducing the liquid content of the solid-liquid separation, The metal concentration remaining in the recovered chelating agent can be lowered, and the recovery rate of the chelating agent can be maintained high. By collecting the chelating agent itself, it can be adjusted to a desired concentration as a soil cleaning agent, and the cleaning efficiency of heavy metal-contaminated soil can be maintained high.
本発明により、キレート剤の水溶液を用いて汚染土壌を洗浄し、重金属を錯体として抽出した後、重金属を除去する操作を行わずに直接塩酸を用いた酸析により含有金属量の少ないキレート剤を高回収率で回収し、回収したキレート剤を汚染土壌の洗浄操作に再利用することによって高洗浄能力を維持すると同時に高い循環効率を達成可能となった。   According to the present invention, a contaminated soil is washed with an aqueous solution of a chelating agent, a heavy metal is extracted as a complex, and then a chelating agent containing a small amount of metal is obtained by acid precipitation directly using hydrochloric acid without performing an operation of removing the heavy metal. Recovering at a high recovery rate and reusing the recovered chelating agent for cleaning operations of contaminated soil has enabled the maintenance of high cleaning capacity and at the same time achieving high circulation efficiency.
本発明の浄化対象となる重金属汚染土壌としては市街地、山林、工業跡地、農業用地、沼地、更には排土などで重金属の元素単位、化合物又はイオンを含有する土壌が挙げられる。本発明のキレート剤水溶液で浄化可能な重金属元素としては鉛、カドミウム、水銀、砒素、セレンなど特に限定されるものではないが、鉛、水銀、カドミウムに対して極めて有効である。   Examples of the heavy metal-contaminated soil to be purified in the present invention include urban areas, mountain forests, industrial sites, agricultural land, marshes, and soil containing heavy metal element units, compounds, or ions such as waste soil. The heavy metal elements that can be purified with the aqueous chelating agent solution of the present invention are not particularly limited, such as lead, cadmium, mercury, arsenic, and selenium, but are extremely effective for lead, mercury, and cadmium.
また、本発明で用いるキレート剤水溶液において、洗浄剤成分として用いるキレート剤はアミノカルボン酸系キレート剤から選ばれる洗浄剤であり、重金属と共に錯体を形成する、たとえばグルタミン酸二酢酸4ソーダ、アスパラギン酸二酢酸4ソーダ(ASDA)、メチルグリシン二酢酸3ソーダ(MGDA)、N,N−エチレンジアミンコハク酸(EDDS4H)、N,N−エチレンジアミンコハク酸3ソーダ(EDDS3Na)、エチレンジアミン4酢酸塩(EDTA)が挙げられる。
これらキレート剤水溶液中のキレート剤濃度は0.01〜1M、特に0.01〜0.5Mであるのが薬剤コストの低減、重金属汚染土壌の洗浄回数の低減、洗浄廃液処理の負荷低減の点で好ましいが、土壌中の重金属濃度に応じて調整することが好ましい。
In the aqueous chelating agent solution used in the present invention, the chelating agent used as the cleaning agent component is a cleaning agent selected from aminocarboxylic acid-based chelating agents and forms a complex with heavy metals, such as glutamic acid diacetic acid 4 soda, aspartic acid 2 Examples include acetic acid 4 soda (ASDA), methylglycine diacetate 3 soda (MGDA), N, N-ethylenediamine succinic acid (EDDS4H), N, N-ethylenediamine succinic acid 3 soda (EDDS3Na), and ethylenediamine tetraacetate (EDTA). It is done.
The chelating agent concentration in these chelating agent aqueous solutions is 0.01 to 1M, particularly 0.01 to 0.5M, in order to reduce drug costs, reduce the frequency of washing heavy metal contaminated soil, and reduce the load of washing waste liquid treatment. However, it is preferable to adjust according to the heavy metal concentration in the soil.
これらのキレート剤水溶液のpHについては4〜6であることが好ましい。アミノカルボン酸系キレート剤の多くは錯体形成のための多数の酸型官能基を持つが、これらの官能基がアルカリと結合した場合にはpHが上昇する。アルカリとの結合が多く、pHが高い状態となると土壌中の重金属とアルカリ成分との交換が遅く、結果として重金属の抽出率が低下する。また、アルカリとの結合が全くない場合にはほとんどのキレート剤において水への溶解度が極めて低くなり、キレート剤濃度を上昇させることができず、洗浄効率が低下する。重金属汚染土壌を原位置で洗浄する場合には地下構造物への影響を考慮する必要があり、低pHでは地下構造物への影響が懸念される。重金属汚染土壌を洗浄する場合洗浄液が高pHの場合、一般的に重金属は高pH域で不溶状態となることが知られており、また、土壌中に含まれるイオン性の鉄、アルミ成分が不溶状態となる際に一緒に砒素、カドミウム、セレン、水銀などの重金属成分が共沈され浄化効率が低下するため好ましくない。更に、pHを4〜6にて使用することにより緩衝効果によりpH変化が少なく、安定した浄化能力を維持することができる。緩衝効果を確実にする為に既知の緩衝溶液を用いても良い。尚、本発明で用いるキレート剤の水溶液のpH調整は苛性ソーダなどの汎用アルカリで調整することができる。   The pH of these chelating agent aqueous solutions is preferably 4-6. Many of the aminocarboxylic acid-based chelating agents have a large number of acid-type functional groups for complex formation, but the pH increases when these functional groups are bonded to an alkali. When there are many bonds with alkalis and the pH is high, the exchange of heavy metals and alkaline components in the soil is slow, resulting in a decrease in the extraction rate of heavy metals. Further, when there is no bond with alkali, most of the chelating agents have extremely low solubility in water, the chelating agent concentration cannot be increased, and the cleaning efficiency is lowered. When heavy metal contaminated soil is washed in-situ, it is necessary to consider the effect on the underground structure. At low pH, there is a concern about the effect on the underground structure. When washing heavy metal contaminated soil When the pH of the washing solution is high, it is generally known that heavy metals become insoluble in the high pH range, and ionic iron and aluminum components contained in the soil are insoluble. When the state is reached, heavy metal components such as arsenic, cadmium, selenium, and mercury are co-precipitated and the purification efficiency is lowered. Furthermore, when the pH is used at 4 to 6, there is little pH change due to the buffer effect, and stable purification ability can be maintained. In order to ensure the buffering effect, a known buffer solution may be used. In addition, pH adjustment of the aqueous solution of the chelating agent used by this invention can be adjusted with general purpose alkalis, such as caustic soda.
このようなキレート剤の水溶液を用いて重金属汚染土壌を洗浄する形式は特に制限されず、原位置にて薬剤通水により洗浄する方法、土壌を掘削して洗浄した後、浄化土壌を埋め戻す方法などの何れでも良い。   The type of washing heavy metal contaminated soil using such an aqueous solution of a chelating agent is not particularly limited, and is a method of washing with chemical water in situ, a method of excavating and washing the soil, and then refilling the purified soil Any of these may be used.
また、本発明において水溶液で洗浄するとは土壌と水溶液を直接混合する以外に、土壌に洗浄剤と水を別々に加えて混合して洗浄する方法、水を含む土壌に洗浄剤を混合して洗浄する方法も含まれる。
このように処理することにより土壌中の重金属は水溶液中に溶出する。水溶液による洗浄は上記洗浄の方法により洗浄回数が変化するが、掘削して洗浄する場合少なくとも数回行われる。このような洗浄操作を行うことにより重金属とキレート剤が錯体を形成し、その錯体を含む水溶液(抽出液)を得る。
In addition, in the present invention, washing with an aqueous solution is not only mixing the soil and the aqueous solution directly, but also adding a cleaning agent and water separately to the soil and mixing and washing, and washing the soil containing water by mixing the cleaning agent The method of doing is also included.
By treating in this way, heavy metals in the soil are eluted in the aqueous solution. Cleaning with an aqueous solution varies depending on the cleaning method described above, but is performed at least several times when excavated and cleaned. By performing such a washing operation, a heavy metal and a chelating agent form a complex, and an aqueous solution (extract) containing the complex is obtained.
洗浄後土壌と分離された水溶液(抽出液)中にはキレート剤と共に抽出された重金属が存在しており、掘削洗浄法の場合には一般的に使用される遠心分離機、ろ過装置などの固液分離装置により土壌と抽出液を分離する。原位置にて薬剤通水により土壌浄化を行う場合には揚水口より抽出液がくみ出される。この重金属を含有する状態の抽出液に対し、酸を添加し、酸析操作によりキレート剤成分のみを沈殿化させる。この際に回収率を高くする為にはpHを2以下とすることが好ましい。回収率を高く維持するためにはpHを1以下することがより好ましい。   In the aqueous solution (extract) separated from the soil after washing, heavy metals extracted together with the chelating agent are present. In the case of excavation washing, solid materials such as commonly used centrifuges and filtration devices are used. The soil and the extract are separated using a liquid separator. When soil purification is performed in the original position by passing chemicals, the extract is drawn from the pumping outlet. An acid is added to the extract containing the heavy metal, and only the chelating agent component is precipitated by an acid precipitation operation. In this case, in order to increase the recovery rate, the pH is preferably set to 2 or less. In order to maintain a high recovery rate, the pH is more preferably 1 or less.
酸析操作で使用する酸は硫酸、硝酸などの鉱酸が使用可能である。しかし、高い回収率を維持すること、回収キレート剤中に重金属を残留させないことなどの点にて塩酸を用いることが必要である。極めて低い濃度ではあるが低pHの状態でも水に対しキレート剤は溶解するため、高回収率達成のためには液量の上昇を抑制することが重要ではあるが、35重量パーセントの塩酸水(濃塩酸)を直接使用すると理由は不明であるが、回収率は逆に低下する。また、同時に回収されるキレート剤成分に残留する金属も増加する傾向となる。回収率及び回収キレート剤中への金属成分残留を抑制するために、使用する塩酸濃度は5〜20重量パーセントであることが必要である。酸析の方式は特に限定されるものではなく、バッチ方式、連続方式、半連続方式いずれも適用可能である。塩酸添加開始から固液分離開始までの時間としては長いほど析出したキレート剤の結晶が十分熟成され、固液分離が容易となる上、分離キレート剤の含液率を低減できるため、回収キレート剤への残留金属量を低減できる傾向があるが、塩酸添加開始から固液分離開始までの所要時間としては0.5時間以上であれば十分である。   A mineral acid such as sulfuric acid or nitric acid can be used as the acid used in the acid precipitation operation. However, it is necessary to use hydrochloric acid in terms of maintaining a high recovery rate and preventing heavy metals from remaining in the recovered chelating agent. Although the chelating agent dissolves in water even at a very low concentration but at a low pH, it is important to suppress an increase in the liquid volume in order to achieve a high recovery rate, but 35 weight percent aqueous hydrochloric acid ( The reason for using concentrated hydrochloric acid directly is unknown, but the recovery rate decreases. Further, the metal remaining in the chelating agent component recovered at the same time tends to increase. In order to suppress the recovery rate and residual metal components in the recovered chelating agent, the concentration of hydrochloric acid used needs to be 5 to 20 weight percent. The acid precipitation method is not particularly limited, and any of a batch method, a continuous method, and a semi-continuous method can be applied. The longer the time from the start of the addition of hydrochloric acid to the start of solid-liquid separation, the precipitated chelating agent crystals are sufficiently aged, so that solid-liquid separation becomes easier and the liquid content of the separated chelating agent can be reduced. Although there is a tendency to reduce the amount of residual metal, the time required from the start of hydrochloric acid addition to the start of solid-liquid separation is sufficient if it is 0.5 hours or longer.
固液分離には一般的に使用される遠心分離機、ろ過装置などが使用でき、特に限定されないが、水洗浄機能を持つものが好ましい。この水洗浄操作により固体となって沈殿したEDTAと重金属の錯体からEDTAのみが固体として回収することができ、重金属は高濃度の水溶液として得ることができる。水洗浄機能がない場合には分離されたキレート剤の沈殿を水洗浄後、再度脱水する。水洗浄に使用する水量に限定はないが、水使用量増加に伴い、回収率が低下し、残留金属濃度は低下する傾向となる。一般的には回収されるキレート剤重量に対し1〜5倍重量の水にて洗浄することで回収キレート剤に残留する金属濃度を100ppm以下まで低減可能である。また、重金属汚染土壌洗浄時には洗浄作業進行と共に水使用量を増加させ残留金属濃度を低下させるなどの使用方法も適用可能である。上記方法でキレート剤を回収する場合、キレート剤濃度、塩酸濃度、pH、洗浄水量により回収率は若干変化するが、回収率95%以上を安定して達成することが可能である。   For solid-liquid separation, commonly used centrifuges, filtration devices and the like can be used, and although not particularly limited, those having a water washing function are preferred. Only EDTA can be recovered as a solid from the complex of EDTA and heavy metal precipitated as a solid by this water washing operation, and heavy metal can be obtained as a high-concentration aqueous solution. When there is no water washing function, the separated chelating agent precipitate is washed with water and dehydrated again. There is no limitation on the amount of water used for water washing, but the recovery rate decreases and the residual metal concentration tends to decrease as the amount of water used increases. Generally, the metal concentration remaining in the recovered chelating agent can be reduced to 100 ppm or less by washing with 1 to 5 times the weight of the recovered chelating agent. In addition, when washing heavy metal contaminated soil, a method of use such as increasing the amount of water used and reducing the residual metal concentration with the progress of the washing operation can be applied. When the chelating agent is recovered by the above method, the recovery rate slightly changes depending on the chelating agent concentration, hydrochloric acid concentration, pH, and amount of washing water, but it is possible to stably achieve a recovery rate of 95% or more.
回収されたキレート剤は乾燥することなく、再度重金属汚染土壌を洗浄するための洗浄剤を調製する工程に使用できる。キレート剤を分離・回収することにより、所望の濃度、pHに調製することが可能であり、pH調製には汎用アルカリである苛性ソーダなどが使用可能である。上記の方式でキレート剤を回収した場合、回収キレート剤のみでの土壌洗浄用の水溶液を調製、使用した場合でも洗浄能力は新品と同程度であり、重金属除去能力の低下はほとんど見られない。土壌洗浄に伴い、土壌への収着、分解により一般的には5〜20%の範囲でキレート剤そのものを損失する為、場合によっては損失分を補う必要があるが、上記調製工程にて回収品に新品をブレンドすることにより問題なく調製可能である。   The recovered chelating agent can be used in the step of preparing a cleaning agent for cleaning heavy metal contaminated soil again without drying. By separating and recovering the chelating agent, it can be adjusted to a desired concentration and pH, and caustic soda, which is a general-purpose alkali, can be used for pH adjustment. When the chelating agent is recovered by the above method, even when an aqueous solution for soil washing using only the recovered chelating agent is prepared and used, the cleaning ability is about the same as that of a new article, and there is almost no decrease in heavy metal removal ability. Along with soil washing, the chelating agent itself is generally lost in the range of 5 to 20% due to sorption and decomposition to the soil. In some cases, it is necessary to compensate for the loss, but it is recovered in the above preparation step. It can be prepared without problems by blending a new product with the product.
分離した重金属を含有する廃液はキレート剤を先行して除去していることにより、一般的な重金属排水処理方法で処理することが可能となり、特に水酸化カルシウム等のCa成分を使用することによりアルカリ沈殿法にて重金属を沈殿とし、固液分離により分離された水は直接下水として排出することが可能となる。   The waste liquid containing the separated heavy metal can be treated by a general heavy metal wastewater treatment method by removing the chelating agent in advance, and in particular, by using a Ca component such as calcium hydroxide, it becomes alkaline. The heavy metal is precipitated by the precipitation method, and the water separated by solid-liquid separation can be directly discharged as sewage.
以上のように本発明によれば重金属汚染土壌の浄化に要するキレート剤量を大幅に低減することが可能である他、排水処理も容易となり、処理コストおよび環境影響の低減した状態で重金属汚染土壌の洗浄が可能となる。   As described above, according to the present invention, the amount of chelating agent required for the purification of heavy metal-contaminated soil can be greatly reduced, and wastewater treatment is facilitated, and the heavy metal-contaminated soil is reduced in treatment costs and environmental impacts. Can be cleaned.
以下、本発明を実施例により更に詳細に説明するが、本発明はこれにより何等限定を受けるものではない。重金属定量分析はICP分析装置にて実施した。また抽出率は下記式にて算出した。
抽出率(%)=[抽出液中の金属濃度]×[抽出液量]/[含有量] ×100
含有量 = [汚染土壌含有量試験結果] × [使用した土壌量]
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention does not receive any limitation by this. Heavy metal quantitative analysis was carried out with an ICP analyzer. The extraction rate was calculated by the following formula.
Extraction rate (%) = [Metal concentration in the extract] × [Amount of extract] / [Content] × 100
Content = [Contaminated soil content test result] × [Amount of soil used]
[実施例1]
環境省告示46号の含有量試験に基づき試験した結果、鉛含有量1200mg/kg及び砒素含有量600mg/kgの汚染土壌に対しpHを4に調整した2重量%のEDTA水溶液二重量部を混合し、EDTA−重金属錯体を形成させた。その後、ろ過分離により得た抽出液の金属濃度を常法に従い確認した結果、鉛の抽出率は90%、砒素の抽出率は20%であった。この抽出液に10重量パーセントの塩酸水をpHが1となるまで添加し、0.5時間攪拌後、沈殿物をろ過、沈殿物の約2重量部に相当する水にて洗浄し、再度脱水を行った結果、EDTAの回収率は95%、回収EDTA中に含まれる金属は90mg/kg(90ppm)であった。また、この回収EDTAを苛性ソーダでpHを4に調整しながら再度2重量%の水溶液とし、上記と同じ汚染土壌に対し2重量部となるように混同しろ過分離した結果、鉛の抽出率が89%、砒素の抽出率は21%であった。
[Example 1]
As a result of testing based on the content test of Ministry of the Environment Notification No. 46, 2 parts by weight of 2% EDTA aqueous solution adjusted to pH 4 was mixed with contaminated soil with a lead content of 1200 mg / kg and an arsenic content of 600 mg / kg. Then, an EDTA-heavy metal complex was formed. Then, as a result of confirming the metal concentration of the extract obtained by filtration separation according to a conventional method, the lead extraction rate was 90% and the arsenic extraction rate was 20%. To this extract, 10 weight percent aqueous hydrochloric acid was added until the pH reached 1, and after stirring for 0.5 hour, the precipitate was filtered, washed with water corresponding to about 2 parts by weight of the precipitate, and dehydrated again. As a result, the recovery rate of EDTA was 95%, and the metal contained in the recovered EDTA was 90 mg / kg (90 ppm). Further, the recovered EDTA was adjusted to a pH of 4 with caustic soda and again into a 2% by weight aqueous solution, and mixed with 2 parts by weight with respect to the same contaminated soil as described above. %, And the extraction rate of arsenic was 21%.
[実施例2]
実施例1と同じ汚染土壌をカラム型装置内に充填し、下部よりpHを4に調整した2重量%のEDTA水溶液を通水し、カラム上部より排出する方式にて汚染土壌を洗浄した。カラムに充填した土壌に対し約10重量部のEDTA水溶液を通水した後、カラム内部の汚染土壌について重金属含有量評価試験を行った結果鉛含有量が100mg/kgとなった。排出されたEDTA水溶液に10重量パーセントの塩酸水をpHが1となるまで添加し、0.5時間攪拌後、沈殿物をろ過、沈殿物の約2倍の重量に相当する水にて洗浄し、再度脱水を行った結果、EDTAの回収率は96重量%、回収EDTA中に含まれる金属は75mg/kgであった。また、この回収EDTAを苛性ソーダでpHを4に調整しながら再度2重量%の水溶液とし、上記と同様、汚染土壌を充填したカラムの下部より通水しながら汚染土壌の洗浄を実施した。カラムに充填した土壌に対し約10重量部のEDTA水溶液を通水した後、カラム内部の汚染土壌について含有量試験を行った結果鉛含有量が110mg/kgとなった。
[Example 2]
The same contaminated soil as in Example 1 was filled in the column-type apparatus, and 2 wt% EDTA aqueous solution having a pH adjusted to 4 was passed from the lower part, and the contaminated soil was washed by discharging from the upper part of the column. About 10 parts by weight of an EDTA aqueous solution was passed through the soil packed in the column, and then a heavy metal content evaluation test was performed on the contaminated soil inside the column. As a result, the lead content was 100 mg / kg. To the discharged EDTA aqueous solution, 10% by weight of hydrochloric acid is added until the pH becomes 1, and after stirring for 0.5 hour, the precipitate is filtered and washed with water corresponding to about twice the weight of the precipitate. As a result of dehydration again, the recovery rate of EDTA was 96% by weight, and the metal contained in the recovered EDTA was 75 mg / kg. Further, the recovered EDTA was adjusted again to a 2 wt% aqueous solution while adjusting the pH to 4 with caustic soda, and the contaminated soil was washed while passing water from the bottom of the column filled with the contaminated soil in the same manner as described above. About 10 parts by weight of EDTA aqueous solution was passed through the soil packed in the column, and then a content test was performed on the contaminated soil inside the column. As a result, the lead content was 110 mg / kg.
[比較例1]
実施例1と同じ要領で実施し、EDTAの沈殿化操作を濃塩酸(35重量%)で実施した結果EDTAの回収率は85%、回収EDTA中の金属濃度は150mg/kgであった。
[Comparative Example 1]
The same procedure as in Example 1 was performed, and precipitation of EDTA was performed with concentrated hydrochloric acid (35% by weight). As a result, the recovery rate of EDTA was 85%, and the metal concentration in the recovered EDTA was 150 mg / kg.
[比較例2]
実施例1と同じ要領で実施し、EDTAの沈殿化操作を10重量%の塩酸水を添加後、10分で終了し固液分離を行った結果、EDTAの回収率は83%、回収EDTA中の金属濃度は180mg/kgであった。
[Comparative Example 2]
The same procedure as in Example 1 was performed, and the precipitation of EDTA was completed in 10 minutes after adding 10% by weight of hydrochloric acid, and solid-liquid separation was performed. As a result, the recovery rate of EDTA was 83% and the recovered EDTA The metal concentration of was 180 mg / kg.
本発明により、キレート剤の水溶液を用いて汚染土壌を洗浄し、重金属を錯体として抽出した後、重金属を除去する操作を行わずに直接塩酸を用いた酸析により含有金属量の少ないキレート剤を高回収率で回収し、回収したキレート剤を汚染土壌の洗浄操作に再利用することによって高洗浄能力を維持すると同時に高い循環効率を達成可能となった。また、キレート剤を高回収率で回収することにより残る、排水処理も容易となり、処理コストおよび環境影響の低減した状態で重金属汚染土壌の洗浄が可能となる。   According to the present invention, a contaminated soil is washed with an aqueous solution of a chelating agent, a heavy metal is extracted as a complex, and then a chelating agent containing a small amount of metal is obtained by acid precipitation directly using hydrochloric acid without performing an operation of removing the heavy metal. Recovering at a high recovery rate and reusing the recovered chelating agent for cleaning operations of contaminated soil has enabled the maintenance of high cleaning capacity and at the same time achieving high circulation efficiency. In addition, wastewater treatment that remains by recovering the chelating agent at a high recovery rate is facilitated, and heavy metal-contaminated soil can be washed with reduced processing costs and environmental impact.

Claims (7)

  1. 下記の工程から成る、キレート剤を洗浄剤とする重金属汚染土壌の洗浄方法。
    A)重金属で汚染された土壌を、キレート剤水溶液で洗浄し、重金属を錯体として含む抽出液を得る工程
    B)重金属を錯体として含む抽出液から5〜20重量%の塩酸を用いた酸析操作により錯体を形成したキレート剤を沈殿させた後、固液分離、水洗浄操作によりキレート剤を回収する工程
    及び
    C)回収したキレート剤を用いて土壌洗浄用のキレート剤水溶液を調製する工程
    A method for cleaning heavy metal contaminated soil using a chelating agent as a cleaning agent, comprising the following steps.
    A) Washing soil contaminated with heavy metals with a chelating agent aqueous solution to obtain an extract containing heavy metal as a complex B) Acidifying operation using 5 to 20% by weight hydrochloric acid from the extract containing heavy metal as a complex The step of precipitating the chelating agent that has formed a complex by the step of solid-liquid separation, recovering the chelating agent by water washing operation, and C) preparing the aqueous chelating agent solution for soil washing using the recovered chelating agent
  2. キレート剤がアミノカルボン酸系キレート剤であることを特徴とする請求項1記載の洗浄方法。   The cleaning method according to claim 1, wherein the chelating agent is an aminocarboxylic acid chelating agent.
  3. キレート剤がエチレンジアミン四酢酸塩である請求項2記載の洗浄方法。   The cleaning method according to claim 2, wherein the chelating agent is ethylenediaminetetraacetate.
  4. 洗浄に使用するキレート剤水溶液のpHが4〜6であることを特徴とする請求項1〜3いずれか1項記載の洗浄方法。   The pH of the chelating agent aqueous solution used for washing | cleaning is 4-6, The washing | cleaning method of any one of Claims 1-3 characterized by the above-mentioned.
  5. 酸析操作におけるpHを2以下とすることを特徴とする請求項1〜4いずれか1項記載の洗浄方法。   The cleaning method according to any one of claims 1 to 4, wherein the pH in the acid precipitation operation is 2 or less.
  6. 酸析操作にて塩酸の添加から固液分離開始までの所要時間を0.5時間以上とすることを特徴とする請求項1〜5いずれか1項記載の洗浄方法。   The cleaning method according to any one of claims 1 to 5, wherein the time required from the addition of hydrochloric acid to the start of solid-liquid separation in an acid precipitation operation is 0.5 hours or more.
  7. 回収されたキレート剤中に含まれるトータル金属濃度が100ppm以下であることを特徴とする請求項1〜6いずれか1項記載の洗浄方法。   The cleaning method according to claim 1, wherein the total metal concentration contained in the recovered chelating agent is 100 ppm or less.
JP2005292292A 2005-10-05 2005-10-05 Method for cleaning heavy metal contaminated soil using chelating agent as cleaning agent Pending JP2007098299A (en)

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103706627A (en) * 2013-12-17 2014-04-09 辽宁石油化工大学 Method for restoring chromium contaminated soil through EDTMPA (ethylenediamine tetra methylenephosphonic acid)
JP2016064354A (en) * 2014-09-24 2016-04-28 国立大学法人金沢大学 Contaminated soil treating method
JP6052943B1 (en) * 2016-10-20 2016-12-27 公信 山▲崎▼ Soil purification method in a soil purification facility using a chelating agent
JP6052944B1 (en) * 2016-10-20 2016-12-27 公信 山▲崎▼ Soil purification methods for soil purification facilities using chelating agents
JP6052942B1 (en) * 2016-10-19 2016-12-27 公信 山▲崎▼ Chelating agent recovery method using rainwater in soil remediation facilities
CN110484263A (en) * 2019-07-02 2019-11-22 广东省生态环境技术研究所 A kind of compound leaching agent and its application

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103706627A (en) * 2013-12-17 2014-04-09 辽宁石油化工大学 Method for restoring chromium contaminated soil through EDTMPA (ethylenediamine tetra methylenephosphonic acid)
JP2016064354A (en) * 2014-09-24 2016-04-28 国立大学法人金沢大学 Contaminated soil treating method
JP6052942B1 (en) * 2016-10-19 2016-12-27 公信 山▲崎▼ Chelating agent recovery method using rainwater in soil remediation facilities
JP6052943B1 (en) * 2016-10-20 2016-12-27 公信 山▲崎▼ Soil purification method in a soil purification facility using a chelating agent
JP6052944B1 (en) * 2016-10-20 2016-12-27 公信 山▲崎▼ Soil purification methods for soil purification facilities using chelating agents
CN110484263A (en) * 2019-07-02 2019-11-22 广东省生态环境技术研究所 A kind of compound leaching agent and its application

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