JP4776064B2

JP4776064B2 - Waste stabilization treatment agent and treatment method

Info

Publication number: JP4776064B2
Application number: JP2000265392A
Authority: JP
Inventors: 博司長澤
Original assignee: Okutama Kogyo Co Ltd
Current assignee: Okutama Kogyo Co Ltd
Priority date: 2000-09-01
Filing date: 2000-09-01
Publication date: 2011-09-21
Anticipated expiration: 2020-09-01
Also published as: JP2002066497A

Description

【０００１】
【発明が属する技術分野】
本発明は、廃棄物、その焼却残渣、或いは焼却残渣等を溶融処理する際に発生する溶融飛灰の処理方法に関し、特に重金属を含有する酸性廃棄物の安定化処理方法に関する。
【０００２】
【従来の技術】
都市ごみ、産業廃棄物、汚泥等の焼却残渣を減容化し、無害化するために、一般に溶融処理が行われている。この溶融処理において、溶融スラグのほかに、鉛、亜鉛、カドミウム等の重金属を多量に含む溶融飛灰が発生する。このような溶融飛灰は、そのまま環境に放出された場合、重金属が雨水などに溶解して溶出し環境汚染源となるため、飛灰中の重金属を固定処理する方法が種々提案されている。
【０００３】
重金属を固定処理する方法としては、主に、キレート剤或いは安定化剤を用いて重金属を不溶化する方法と塩化第一鉄等の２価鉄を用いたフェライト化によって不溶化する方法が知られている。前者として、例えば、溶融飛灰に水及びキレート剤を加えて混練する方法（特開平５−８７３２４号公報）、溶融飛灰に消石灰を加えてｐＨ値を８．５以上にした後、多硫化カルシウムを加え、さらに鉱酸を加えてｐＨ値を所定範囲に調整した後、水を加えて混練する方法（特開平８−１９７０３４号公報）等が提案されている。また後者として、溶融飛灰に鉄塩の存在下でアルカリ成分を添加してｐＨ値を所定範囲に保ち混合する方法（特開平６−２３８２５９号公報）等が提案されている。
【０００４】
【発明が解決しようとする課題】
しかしながら、キレート剤を用いて固定化する方法では、キレート剤としてジチオカルバミン酸等のイオウ化合物を用いるため、固定化処理の際に二硫化炭素等の有毒ガスが発生するという問題がある。またキレート剤は一般に高価であり廃棄物の処理剤としては経済的でない。一方、フェライト化による方法では、フェライト反応を進行させるための適性ｐＨ値があるため、固定化処理においてｐＨの管理が必要となる。
【０００５】
さらに鉛や亜鉛等の両性金属は、適性ｐＨ値で固定化した場合でも、長期にわたって酸性の環境、例えば酸性雨等にさらされた場合、水溶性に変化し、溶出するという問題がある。
そこで本発明は、極めて簡便な方法で長期にわたって重金属の溶出を防止することができる廃棄物の安定化処理剤およびそれを用いた処理方法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
即ち本発明の廃棄物の安定化処理剤は、初期ｐＨ値調整剤（以下、単にｐＨ調整剤という）をｐＨ値安定剤とメカノケミカルに反応させることによって、初期ｐＨ値調整剤をｐＨ値安定剤の表面に付着させた複合体から成る。本発明の安定化処理剤は、重金属を含有する廃棄物、特に酸性の重金属含有廃棄物を対象とし、廃棄物に含有される重金属を所定のｐＨ値に調整することによって不溶性の重金属水酸化物にする。つまり、廃棄物中の重金属を不溶化処理させる処理剤である。
【０００７】
この際、まずｐＨ値調整剤によって、廃棄物の中に含まれる重金属が不溶化するｐＨ値に調整し、ついでｐＨ値安定剤によって調整されたｐＨ値に維持する。これにより酸性雨等により処理化後の廃棄物が酸性環境にさらされた場合でも、容易に重金属が溶出するのを防止できる。また単にｐＨ値安定剤を用いる場合に比べ、少量で速やかに目的とするｐＨ値、即ち重金属の塩が水に不溶性となるｐＨに調整することができる。
【０００８】
ｐＨ値調整剤としては、アルカリ金属またはアルカリ土類金属の水酸化物または酸化物であって、水溶液としたときのｐＨ値が１１以上となる強アルカリを用いることができる。このような強アルカリのうち、特に実用的なものとして水酸化カルシウム、酸化カルシウム、水酸化ナトリウム、水酸化カリウムが挙げられ、これらは1種または2種以上を混合して用いることができる。
【０００９】
これらｐＨ値調整剤は純粋な物質である必要はなく、例えば酸化カルシウムの場合、石灰石や貝がらを焼成した生石灰を、また水酸化カルシウムの場合はこのような生石灰を水と反応させて得られる消石灰を使用することができる。
【００１０】
ｐＨ値安定剤は、上述したようにｐＨ値調整剤によって調整した後のｐＨ値を一定に保ち、ｐＨ値の変動による重金属の再溶出を防止するためのものであり、水酸化マグネシウム及び／又は酸化マグネシウムが用いられる。水酸化マグネシウムはその添加量にかかわりなく一定のｐＨ値（10.3程度）を示すため、廃棄物のｐＨ値を両性金属が溶解しないｐＨ値に保つことができる。なお、酸化マグネシウムは、水酸化マグネシウムに比べ高価であり廃棄物の処理剤としての実用性は低いが、水との反応によって水酸化マグネシウムを生じ同様の効果が得られる。
【００１１】
水酸化マグネシウム及び／又は酸化マグネシウムを、単独で安定化処理剤として用いた場合でも、廃棄物のｐＨ値を調整し且つ安定に保つことは可能であるが、上述したｐＨ値調整剤と組み合わせたことにより、ｐＨ値安定剤の添加量が少量でも速やかに所望のｐＨ値に調整することができる。
【００１２】
本発明の安定化処理剤は、上述したｐＨ値調整剤とｐＨ値安定剤とを所定の割合で混合したものであり、１）両者を所望の割合で混合したもの、２）ｐＨ値安定剤の表面にｐＨ値調整剤を付着させた複合体のいずれでもよい。またｐＨ値調整剤をｐＨ値安定剤と混合する場合の形態は、特に限定されず、粒状、粉末、懸濁液、水溶液のいずれでもよい。但し、ｐＨ値調整剤は、廃棄物と混合したときに速やかにｐＨ値を調整するのに消費され、残留量がないことが好ましく、このような観点から粉末状或いは懸濁液として混合することが好ましい。特に表面積の大きい粉末であることが好ましい。
【００１３】
またｐＨ値安定剤は、上記のようにｐＨ値調整剤によって調整したｐＨ値を長期に亘って一定に保つものであるので、雨水等によって流れやすい形態（例えば粉末）よりも粒状であることが好ましい。
両者の混合物は、例えば粉末と粉末を単に混合することにより調製できる。また複合体としては、例えばｐＨ値安定剤の粉末および/または粒にｐＨ値調製剤の液体（水溶液または懸濁液）を噴霧して、表面を覆ったものや、ｐＨ値安定剤の粒にｐＨ値調整剤の粉末を添加し、メカノケミカルに反応させたものが用いられる。
【００１４】
ｐＨ値調整剤とｐＨ値安定剤との割合は、目的とする廃棄物のｐＨや含有される重金属の種類によっても異なるが、重量比で0.5：9.5〜9.5：0.5、好適には１：9〜9：1の範囲とする。
【００１５】
次に上記安定化処理剤を用いた本発明の廃棄物の安定化処理方法について説明する。本発明の廃棄物の安定化処理方法が対象とする廃棄物は、廃棄物焼却灰の溶融処理において集塵機等から回収された溶融飛灰のみならず、重金属を含む一般廃棄物、例えば電炉ダスト、汚泥、廃酸等の産業廃棄物や、その焼却灰をも含む。特にｐＨ値が７未満の酸性廃棄物に適用される。これら廃棄物は、必要に応じて焼却処理や脱水処理したものを用いる。
【００１６】
本発明の安定化処理方法では、このような酸性廃棄物に上述した安定化処理剤を添加し、水の存在下で混練処理する。水が存在することにより、重金属とｐＨ値調整剤（およびｐＨ値安定剤）の反応が進行し、不溶性の重金属の水酸化物が生成する。
ここで「水の存在下」とは、混練時に水が存在している状態であることを意味し、このような水は、混練に先立って或いは混練中に添加された水も、また廃棄物自体が水を含む場合や安定化処理剤がその添加形態によって水を含む場合には、そのような予め含有される水も含む意味である。
【００１７】
安定化処理剤の添加形態は、粒、粉末又は懸濁液を処理状況に応じて用いる。例えば飛灰のように殆ど水分を含まない廃棄物については、懸濁液として添加することにより均一に混合、処理することができる。廃棄物自体の水分含有量が多い場合には粒状又は粉末として添加することが好ましい。
また安定化処理剤は、ｐＨ調整剤とｐＨ安定剤とを予め混合して一体化することなく、それぞれ廃棄物に添加して混合してもよい。本発明の安定化処理剤は、このような形態で添加される場合も含む。
【００１８】
添加量は、廃棄物の種類によっても異なるが、水の存在下で混練した後においてｐＨ値が７.５〜１１、好適には９.５〜１０.５となるように添加する。ｐＨ値が７.５より低い場合には、長期に環境にさらされたときに酸性雨や酸性のガス等によって両性金属酸化物が溶出する可能性がある。ｐＨ値が１１を超える場合にも両性金属が溶出する。
【００１９】
混練工程は、開放系、密閉系のいずれでも行うことができるが、好適には密閉系で加温しながら行う。密閉系とすることにより水の散逸を防止し、確実に反応させることができる。また加温することにより反応を促進し、短時間で安定化処理を行うことができる。温度は、反応促進の点からは高い方がよいが、高すぎると密閉系で反応させた場合に圧力が上がり、圧力容器が必要となる。従って実用的には、圧力容器を必要としない圧力、具体的には２気圧未満の圧力となるまで加温しながら反応させることが好適である。密閉系であって加温しても２気圧に達しないような温度は、廃棄物や安定化処理剤の添加量によっても異なるが、具体的には１２０℃未満に維持することが好適である。
【００２０】
上述のように２気圧未満の圧力となるまで加温した場合には、安定化処理剤と廃棄物中に含まれる成分との鉱物反応によって生成する生成物中に重金属が取り込まれ、重金属がより強固に固定されると考えられる。反応時間は特に限定されないが、このように加温処理する場合も含め、通常数分〜２時間程度とする。
このように混練処理した後の処理物は、通常の無害化産業廃棄物と同様に埋立等により最終処分される。その場合、上述したように重金属類が安定に固定処理されているので、酸性雨等にさらされても重金属類の溶出による土壌や地下水の汚染を確実に防止することができる。
【００２１】
【実施例】
以下、本発明の廃棄物の安定化処理方法の実施例を説明するが、本発明はこれら実施例に限定されるものではない。
【００２２】
［参考例１］
酸性飛灰（ｐＨ＝６．３）１００ｇに水酸化マグネシウム（粉末）７ｇと水酸化カルシウム（粉末）３ｇを加えてよく混合し、水４０ｇを加えて約１時間混練した。混練後の試料１００ｇについて環境庁告示１３号に基づく溶出試験を行った。共試した酸性飛灰中には、鉛が６４００ｍｇ／ｋｇ、カドミウムが５１０ｍｇ／ｋｇ、水銀が３ｍｇ／ｋｇ、砒素が８ｍｇ／ｋｇ、クロムが３９ｍｇ／ｋｇ含有されていた。溶出試験の結果、鉛、水銀、砒素および６価クロムは検出されず、カドミウムの溶出量は０．０９ｍｇ／Ｌであり法定基準値以下であった。また、溶出水のｐＨ値は９．０であった。
【００２３】
［参考例２］
水酸化マグネシウム（１〜３ｍｍ粒）６ｇと水酸化カルシウム（粉末）４ｇとを混合した混合物を、実施例１で共試した飛灰１００ｇに加えよく混合し、さらに水４０ｇを加えて混練した。その後環境庁告示１３号に基づく溶出試験を行った。溶出試験の結果、鉛、水銀、砒素、６価クロムおよびカドミウムは検出されなかった。また、溶出水のｐＨ値は９．２であった。
【００２４】
［参考例３］
参考例１で共試した飛灰１００ｇに水酸化マグネシウム（１〜３ｍｍ粒）５ｇと水酸化カルシウム（粉末）５ｇを加えてよく混合し、水４０ｇを加えて混練した。その後環境庁告示１３号に基づく溶出試験を行った。溶出試験の結果、鉛、水銀、砒素、６価クロムおよびカドミウムは検出されなかった。また、溶出水のｐＨ値は１０．１であった。
【００２５】
［参考例４］
水酸化マグネシウム（粉末）９ｇと水酸化カルシウム１ｇを含む懸濁液２０ｇを加えてよく混合したものを、酸性飛灰（ｐＨ＝６．４）１００ｇに加えて混練した。その後環境庁告示１３号に基づく溶出試験を行った。共試した酸性飛灰中には、鉛が１２０００ｍｇ／ｋｇ、カドミウムが２８０ｍｇ／ｋｇ、水銀が３ｍｇ／ｋｇ、砒素が６ｍｇ／ｋｇ、クロムが２８ｍｇ／ｋｇ含有されていた。溶出試験の結果、鉛、水銀、砒素、６価クロムおよびカドミウムは検出されなかった。また、溶出水のｐＨ値は７．７であった。
【００２６】
［参考例５］
参考例４で共試した飛灰１００ｇに、水酸化マグネシウム（１〜３ｍｍ粒）８ｇと水酸化カルシウム２ｇ（粉末）を加えてよく混合し、水２０ｇを加えて混練した。その後環境庁告示１３号に基づく溶出試験を行った。溶出試験の結果、鉛、水銀、砒素、６価クロムおよびカドミウムは検出されなかった。また、溶出水のｐＨ値は１０．１であった。
【００２７】
［参考例６］
水酸化カルシウム２．５ｇを水２０ｇに懸濁させた懸濁液と、水酸化マグネシウム（１〜３ｍｍ粒）７．５ｇとを、参考例４で共試した飛灰１００ｇに加えてよく混合し、混練した。その後環境庁告示１３号に基づく溶出試験を行った。溶出試験の結果、鉛、水銀、砒素、６価クロムおよびカドミウムは検出されなかった。また、溶出水のｐＨ値は１０．８であった。
【００２８】
［参考例７］
参考例１で共試した飛灰１００ｇに、水酸化マグネシウム（粉末）７ｇと水酸化カルシウム（粉末）３ｇを加えてよく混合した後、密閉容器に移し、これに水４０ｇを加えて約１０分間混練し、さらに１１６℃で約１時間加温した。密閉容器内の圧力は１時間加温後で約１．８気圧（ａｔｍ）であった。この混練加温処理後の試料１００ｇについて、環境庁告示１３号に基づく溶出試験を行った結果、鉛、水銀、砒素、６価クロムおよびカドミウムは検出されなかった。また、溶出水のｐＨ値は９．５であった。
【００２９】
［参考例８］
参考例１で共試した飛灰２００ｇに、水酸化マグネシウム（粉末）１０ｇと水酸化カルシウム（粉末）１０ｇを加えてよく混合した後、水８０ｇを加えて約１時間混練した。混練後の試料について酸性水溶液に対する安定性を試験するために、試料２００ｇをカラムに詰め、１ｃｍ^３／ｍｉｎの速度でｐＨ値を４に調整した希硝酸水溶液３００ｃｍ^３を流し、１００ｃｍ^３毎の重金属の溶出量およびｐＨ値を測定した。その結果、３００ｃｍ^３迄の溶出液から鉛、水銀、砒素、６価クロムおよびカドミウムなどの重金属は検出されなかった。また何れの溶出液もｐＨ値は１０．１であった。
【００３０】
尚、試料200ｇに対する上記希硝酸水溶液量300 cm^３は埋立飛灰に対する1年間の降水量にほぼ対応するものとして計算されたものである。即ち、年平均降水量を1600mm、飛灰の比重を0.5、埋立時の層厚を2mとすると、飛灰埋立面積1cm^２（体積200cm^３、重量100ｇ）に対し1年の降水量は160ｇとなる。従って、飛灰200ｇについては降水量320ｇ（ほぼ300ｇ）となる。
次に、希硝酸水溶液を流した後の試料100ｇについて環境庁告示１３号に基づく溶出試験を行った結果、鉛、水銀、砒素、６価クロムおよびカドミウムは検出されなかった。また、溶出水のｐＨ値は10.1であった。
【００３１】
［参考例９］
水酸化カルシウム４ｇを水に懸濁させた懸濁液５０ｇと、水酸化マグネシウム（１〜３ｍｍ粒）６ｇとを参考例１で共試した飛灰１００ｇに加えて混練した。その後環境庁告示１３号に基づく溶出試験を行った。溶出試験の結果、鉛、水銀、砒素、６価クロムおよびカドミウムは検出されなかった。また、溶出水のｐＨ値は９．２であった。
【００３２】
［実施例１］
１〜３ｍｍの粒状の水酸化マグネシウムと粉末状水酸化カルシウムとをメカノケミカルに反応させて、水酸化マグネシウムの表面に水酸化カルシウムが付着した複合体｛Ｍｇ（ＯＨ）_２：Ｃａ（ＯＨ）_２＝６：４（重量比）｝を作成した。この安定化処理剤を参考例１で共試した飛灰１００ｇに加えてよく混合し、さらに水４０ｇを加えて混練した。その後環境庁告示１３号に基づく溶出試験を行った。溶出試験の結果、鉛、水銀、砒素、６価クロムおよびカドミウムは検出されなかった。また、溶出水のｐＨ値は９．２であった。
【００３３】
［参考例１０］
参考例１で共試した飛灰１００ｇに酸化マグネシウム（粉末）６ｇと水酸化カルシウム（粉末）４ｇを加えてよく混合し、水４０ｇを加えて混練した。その後環境庁告示１３号に基づく溶出試験を行った。溶出試験の結果、鉛、水銀、砒素、６価クロムおよびカドミウムは検出されなかった。また、溶出水のｐＨ値は９．２であった。
【００３４】
［実施例２］
１〜３ｍｍの粒状の酸化マグネシウムと粉末状水酸化カルシウムとをメカノケミカルに反応させて、酸化マグネシウムの表面に水酸化カルシウムが付着した複合体｛ＭｇＯ：Ｃａ（ＯＨ）_２＝６：４（重量比）｝を作成した。この安定化処理剤剤を参考例１で共試した飛灰１００ｇに加えてよく混合し、さらに水４０ｇを加えて混練した。その後環境庁告示１３号に基づく溶出試験を行った。溶出試験の結果、鉛、水銀、砒素、６価クロムおよびカドミウムは検出されなかった。また、溶出水のｐＨ値は９．２であった。
【００３５】
［参考例１１］
参考例１で共試した飛灰１００ｇに、酸化マグネシウム（粉末）６ｇと、水酸化ナトリウム４ｇを含む水溶液４０ｇとを加えて混練した。その後環境庁告示１３号に基づく溶出試験を行った。溶出試験の結果、鉛、水銀、砒素、６価クロムおよびカドミウムは検出されなかった。また、溶出水のｐＨ値は９．５であった。
【００３６】
［参考例１２］
粒状の酸化マグネシウムに水酸化ナトリウム水溶液を噴霧して、酸化マグネシウムの表面に水酸化ナトリウムが付着した複合体｛ＭｇＯ：ＮａＯＨ＝６：４（重量比）｝を作製した。この安定化処理剤１０ｇを参考例１で共試した飛灰１００ｇに加えてよく混合し、さらに水４０ｇを加えて混練した。その後環境庁告示１３号に基づく溶出試験を行った。溶出試験の結果、鉛、水銀、砒素、６価クロムおよびカドミウムは検出されなかった。また、溶出水のｐＨ値は９．５であった。
【００３７】
［比較例１］
参考例１で共試した飛灰１００ｇに水３０ｇを加えて混練した。その後、環境庁告示１３号に基づく溶出試験を行った。溶出試験の結果、水銀、砒素、６価クロムは検出されなかったが、鉛の溶出量は１１ｍｇ／Ｌ、カドミウムの溶出量は６．３ｍｇ／Ｌであった。また、溶出水のｐＨ値は６．３であった。
【００３８】
［比較例２］
参考例４で共試した飛灰１００ｇに水３０ｇを加えて混練した。その後、環境庁告示１３号に基づく溶出試験を行った。溶出試験の結果、水銀、砒素、６価クロムは検出されなかったが、鉛の溶出量は７ｍｇ／Ｌ、カドミウムの溶出量は１４ｍｇ／Ｌであった。また、溶出水のｐＨ値は６．４であった。
【００３９】
［比較例３］
参考例４で共試した飛灰１００ｇに水酸化マグネシウム（粉末）５ｇと水酸化カルシウム（粉末）５ｇを加えてよく混合し、水４０ｇを加えて混練した。その後環境庁告示１３号に基づく溶出試験を行った。溶出試験の結果、水銀、砒素、６価クロムおよびカドミウムは検出されなかったが鉛の溶出量は１７ｍｇ／Ｌであった。また、溶出水のｐＨ値は１２．２であった。
【００４０】
［比較例４］
参考例１で共試した飛灰２００ｇに水酸化カルシウム（粉末）１０ｇを加えてよく混合した後、水８０ｇを加えて約１時間混練することにより、ｐＨ値を１０．１に調整した。混練後の試料について酸性水溶液に対する安定性を試験するために、試料２００ｇをカラムに詰め、１ｃｍ^３／ｍｉｎの速度でｐＨ値を４に調整した希硝酸水溶液３００ｃｍ^３を流し、１００ｃｍ^３毎の重金属の溶出量およびｐＨ値を測定した。その結果、重金属の検出量は０〜１００ｃｍ^３で鉛が１２ｍｇ／Ｌ、カドミウムが１４ｍｇ／Ｌであり、水銀、砒素および６価クロムは検出されなかった。１０１〜２００ｃｍ^３で鉛が３６ｍｇ／Ｌ、カドミウムが３８ｍｇ／Ｌであり、水銀、砒素、６価クロムは検出されなかった。２０１〜３００ｃｍ^３で鉛が７２ｍｇ／Ｌ、カドミウムが８６ｍｇ／Ｌ、６価クロムが０．０２ｍｇ／Ｌであり水銀、砒素は検出されなかった。酸性水によって短期間で鉛の溶出が始まることが確認された。また、溶出液のｐＨ値は０〜１００ｃｍ^３では５．２、１０１〜２００ｃｍ^３が４．５、２０１〜３００ｃｍ^３が４．０であった。
【００４１】
さらに希硝酸水を流した後の試料100ｇについて環境庁告示13号に基づく溶出試験を行った。溶出試験の結果、重金属の検出量は鉛が122mg/L、６価クロムが0.03 mg/Lであり水銀、砒素は検出されなかった。また、溶出水のｐＨ値は4.0であった。
【００４２】
【表１】

【００４３】
【表２】

【００４４】
参考例、実施例および比較例で用いた安定化処理剤の量および形態を表１に示すとともに、これらの結果を表２に示す。表２からも明らかなように、本発明の安定化処理剤を用いた安定化処理方法により、高濃度の鉛含有飛灰であっても効果的に鉛の溶出量を抑えることができた。但し、本発明の安定化処理剤を用いた場合でも、ｐＨ調整後のｐＨ値が１１を超える場合には（比較例３）、鉛の溶出が見られ、十分な重金属固定がなされないことがわかった。
【００４５】
また参考例８及び比較例４の結果から明らかなように、水酸化カルシウムのようなアルカリで両性金属（鉛）を固定化するｐＨ値に調整した場合には、長期に酸性の雰囲気にさられたときに安定してそのｐＨ値を維持することができず、経時的に鉛の溶出量が増加したのに対し、参考例８の方法によって処理した飛灰は、長期にわたる酸性雨にさらされた後でも鉛の溶出量が低く、鉛が安定して固定されていた。
【００４６】
【発明の効果】
本発明によれば、重金属を含有する廃棄物と混練するだけで、効果的に重金属の固定処理を行うことができる安定化処理剤が提供される。この安定化処理剤を用いることにより、廃棄物を速やかに所望のｐＨ値に調整すると共に維持することができ、これによって高いｐＨ領域では水溶性となる両性金属について安定して不溶化を維持することができる。また本発明によれば、混練の加温条件を調整することにより、特別な圧力容器等を必要とせずに簡便且つ迅速に固定化処理を行うことができる。[0001]
[Technical field to which the invention belongs]
The present invention relates to a method for treating molten fly ash generated when melting waste, its incineration residue, or incineration residue, and more particularly to a method for stabilizing acidic waste containing heavy metals.
[0002]
[Prior art]
Generally, melting treatment is performed in order to reduce the volume of incineration residues such as municipal waste, industrial waste, and sludge and make them harmless. In this melting process, in addition to molten slag, molten fly ash containing a large amount of heavy metals such as lead, zinc and cadmium is generated. When such molten fly ash is released into the environment as it is, heavy metals are dissolved and eluted in rainwater and become an environmental pollution source, so various methods for fixing heavy metals in fly ash have been proposed.
[0003]
As a method for fixing heavy metals, there are mainly known a method of insolubilizing heavy metals using a chelating agent or a stabilizer and a method of insolubilizing by ferritization using divalent iron such as ferrous chloride. . As the former, for example, a method of adding water and a chelating agent to molten fly ash and kneading (Japanese Patent Laid-Open No. 5-87324), adding slaked lime to molten fly ash to make the pH value 8.5 or more, and then polysulfiding A method of adding calcium and further adding a mineral acid to adjust the pH value to a predetermined range and then adding water and kneading (Japanese Patent Laid-Open No. Hei 8-97034) has been proposed. As the latter, a method of adding an alkali component to molten fly ash in the presence of an iron salt and mixing it while keeping the pH value within a predetermined range (JP-A-6-238259) has been proposed.
[0004]
[Problems to be solved by the invention]
However, in the method of immobilizing using a chelating agent, a sulfur compound such as dithiocarbamic acid is used as the chelating agent, so that there is a problem that toxic gases such as carbon disulfide are generated during the immobilizing treatment. Chelating agents are generally expensive and are not economical as waste treatment agents. On the other hand, in the method using ferritization, since there is an appropriate pH value for advancing the ferrite reaction, it is necessary to manage the pH in the immobilization treatment.
[0005]
Furthermore, even when the amphoteric metals such as lead and zinc are fixed at an appropriate pH value, there is a problem that when they are exposed to an acidic environment for a long period of time, for example, acid rain, they become water-soluble and are eluted.
Therefore, an object of the present invention is to provide a waste stabilization treatment agent capable of preventing elution of heavy metals over a long period of time by a very simple method and a treatment method using the same.
[0006]
[Means for Solving the Problems]
That is, the waste stabilization treatment agent of the present invention reacts with an initial pH value adjusting agent (hereinafter simply referred to as a pH adjusting agent) with a pH value stabilizer and a mechanochemical, thereby stabilizing the initial pH value adjusting agent. It consists of a complex attached to the surface of the agent. The stabilizing treatment agent of the present invention is intended for waste containing heavy metals, particularly acidic heavy metal-containing waste, and adjusting the pH of the heavy metals contained in the waste to an insoluble heavy metal hydroxide. To. That is, it is a treatment agent that insolubilizes heavy metals in waste.
[0007]
At this time, first, the pH value is adjusted to a pH value at which heavy metals contained in the waste are insolubilized by the pH value adjusting agent, and then maintained at the pH value adjusted by the pH value stabilizer. Thereby, even when the waste after treatment is exposed to an acidic environment due to acidic rain or the like, it is possible to prevent the heavy metal from being easily eluted. In addition, compared with a case where a pH value stabilizer is simply used, the target pH value can be quickly adjusted to a pH at which a heavy metal salt becomes insoluble in water, in a small amount.
[0008]
As the pH value adjusting agent, alkali metals or alkaline earth metal hydroxides or oxides, and strong alkalis having a pH value of 11 or more when used as an aqueous solution can be used. Among such strong alkalis, calcium hydroxide, calcium oxide, sodium hydroxide, and potassium hydroxide are particularly practical, and these can be used alone or in combination of two or more.
[0009]
These pH value adjusting agents do not need to be pure substances. For example, calcium oxide is calcined lime obtained by baking limestone or shells, and calcium hydroxide is obtained by reacting such calcined lime with water. Can be used.
[0010]
The pH value stabilizer is for maintaining the pH value after being adjusted with the pH value adjusting agent as described above, and preventing re-elution of heavy metals due to fluctuations in the pH value, and magnesium hydroxide and / or Magnesium oxide is used. Magnesium hydroxide exhibits a constant pH value (about 10.3) regardless of the amount of addition thereof, so that the pH value of waste can be kept at a pH value at which amphoteric metals do not dissolve. Magnesium oxide is more expensive than magnesium hydroxide, and its practicality as a waste treatment agent is low. However, magnesium hydroxide is produced by reaction with water, and similar effects can be obtained.
[0011]
Even when magnesium hydroxide and / or magnesium oxide is used alone as a stabilizing agent, it is possible to adjust the pH value of the waste and keep it stable, but in combination with the pH value adjusting agent described above. Thus, even if the addition amount of the pH value stabilizer is small, it can be quickly adjusted to a desired pH value.
[0012]
The stabilizing agent of the present invention is a mixture of the above-described pH value adjusting agent and pH value stabilizer in a predetermined ratio, 1) a mixture of both in a desired ratio, and 2) a pH value stabilizer. Any of the composites in which a pH value adjusting agent is attached to the surface may be used. Moreover, the form in the case of mixing a pH value adjuster with a pH value stabilizer is not specifically limited, Any of a granular form, powder, suspension , and aqueous solution may be sufficient. However, the pH value adjusting agent is consumed to quickly adjust the pH value when mixed with waste and preferably has no residual amount. From this point of view, it is mixed as a powder or a suspension. Is preferred. A powder having a large surface area is particularly preferable.
[0013]
Further, the pH value stabilizer keeps the pH value adjusted by the pH value adjusting agent as described above constant over a long period of time, and therefore it is more granular than a form (for example, powder) that easily flows by rainwater or the like. preferable.
A mixture of both can be prepared, for example, by simply mixing the powder. In addition, as a complex, for example, a pH value stabilizer liquid (aqueous solution or suspension) is sprayed on a powder and / or granule of a pH value stabilizer to cover the surface, or to a pH value stabilizer particle. What added the powder of pH value adjuster and made it react with mechanochemical is used.
[0014]
The ratio between the pH value adjusting agent and the pH value stabilizer varies depending on the pH of the target waste and the type of heavy metal contained, but is 0.5: 9.5 to 9.5: 0.5, preferably 1: 9 in weight ratio. The range is ~ 9: 1.
[0015]
Next, the waste stabilization method of the present invention using the above-described stabilization treatment agent will be described. Waste targeted by the method for stabilizing waste of the present invention is not only molten fly ash recovered from a dust collector or the like in the melting treatment of waste incineration ash, but also general waste containing heavy metals, such as electric furnace dust, This includes industrial waste such as sludge and waste acid, and incinerated ash. In particular, it is applied to acidic waste having a pH value of less than 7. These wastes are incinerated or dehydrated as necessary.
[0016]
In the stabilization treatment method of the present invention, the above-described stabilization treatment agent is added to such acidic waste, and kneading is performed in the presence of water. Due to the presence of water, the reaction between the heavy metal and the pH value adjusting agent (and the pH value stabilizer) proceeds, and an insoluble heavy metal hydroxide is generated.
Here, “in the presence of water” means that water is present at the time of kneading, and such water is also added to the waste material prior to or during kneading. When itself contains water, or when the stabilizing agent contains water depending on its addition form, it means that it also contains such pre-containing water.
[0017]
As the addition form of the stabilizing treatment agent, grains, powder or suspension is used depending on the treatment situation. For example, waste containing almost no water such as fly ash can be uniformly mixed and treated by adding it as a suspension. If the waste itself has a high water content, it is preferably added as a granular or powder.
Further, the stabilizing agent may be added to the waste and mixed without mixing the pH adjusting agent and the pH stabilizer in advance and integrating them. The stabilization processing agent of this invention includes the case where it adds with such a form.
[0018]
The addition amount varies depending on the type of waste, but is added so that the pH value becomes 7.5 to 11, preferably 9.5 to 10.5 after kneading in the presence of water. When the pH value is lower than 7.5, amphoteric metal oxides may be eluted by acid rain or acidic gas when exposed to the environment for a long time. Amphoteric metals are also eluted when the pH value exceeds 11.
[0019]
The kneading step can be performed in either an open system or a closed system, but is preferably performed while heating in a closed system. By using a closed system, it is possible to prevent the dissipation of water and to react reliably. Further, the reaction can be promoted by heating, and the stabilization treatment can be performed in a short time. The temperature is preferably higher from the viewpoint of promoting the reaction, but if it is too high, the pressure rises when the reaction is carried out in a closed system, and a pressure vessel is required. Therefore, practically, it is preferable to carry out the reaction while heating until a pressure that does not require a pressure vessel, specifically, a pressure of less than 2 atm. Although the temperature is a closed system and does not reach 2 atm even when heated, it varies depending on the amount of waste and the amount of the stabilizing treatment agent added. .
[0020]
When heated to a pressure of less than 2 atm as described above, heavy metal is taken into the product produced by the mineral reaction between the stabilizing agent and the component contained in the waste, and the heavy metal is more It is thought that it is firmly fixed. Although reaction time is not specifically limited, Including the case where it heats in this way, it is normally made into several minutes-about 2 hours.
The processed material after the kneading treatment is finally disposed of by landfill or the like in the same manner as ordinary detoxified industrial waste. In that case, since the heavy metals are stably fixed as described above, soil and groundwater contamination due to elution of heavy metals can be reliably prevented even when exposed to acid rain or the like.
[0021]
【Example】
Examples of the waste stabilization method of the present invention will be described below, but the present invention is not limited to these examples.
[0022]
[ Reference Example 1]
To 100 g of acidic fly ash (pH = 6.3), 7 g of magnesium hydroxide (powder) and 3 g of calcium hydroxide (powder) were added and mixed well, and 40 g of water was added and kneaded for about 1 hour. An elution test based on Environmental Agency Notification No. 13 was conducted on 100 g of the kneaded sample. The co-tested acidic fly ash contained 6400 mg / kg of lead, 510 mg / kg of cadmium, 3 mg / kg of mercury, 8 mg / kg of arsenic, and 39 mg / kg of chromium. As a result of the elution test, lead, mercury, arsenic and hexavalent chromium were not detected, and the cadmium elution amount was 0.09 mg / L, which was below the legal reference value. The pH value of the elution water was 9.0.
[0023]
[ Reference Example 2]
A mixture obtained by mixing 6 g of magnesium hydroxide (1 to 3 mm grains) and 4 g of calcium hydroxide (powder) was added to and mixed well with 100 g of fly ash co-tested in Example 1, and 40 g of water was further added and kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. As a result of the dissolution test, lead, mercury, arsenic, hexavalent chromium and cadmium were not detected. Moreover, the pH value of the elution water was 9.2.
[0024]
[ Reference Example 3]
To 100 g of fly ash co-tested in Reference Example 1, 5 g of magnesium hydroxide (1 to 3 mm granules) and 5 g of calcium hydroxide (powder) were added and mixed well, and 40 g of water was added and kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. As a result of the dissolution test, lead, mercury, arsenic, hexavalent chromium and cadmium were not detected. Moreover, the pH value of the elution water was 10.1.
[0025]
[ Reference Example 4]
A suspension obtained by adding 9 g of magnesium hydroxide (powder) and 20 g of a suspension containing 1 g of calcium hydroxide and mixing them well was added to 100 g of acidic fly ash (pH = 6.4) and kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. The co-tested acidic fly ash contained 12000 mg / kg of lead, 280 mg / kg of cadmium, 3 mg / kg of mercury, 6 mg / kg of arsenic, and 28 mg / kg of chromium. As a result of the dissolution test, lead, mercury, arsenic, hexavalent chromium and cadmium were not detected. The pH value of the elution water was 7.7.
[0026]
[ Reference Example 5]
To 100 g of fly ash co-tested in Reference Example 4, 8 g of magnesium hydroxide (1 to 3 mm granules) and 2 g of calcium hydroxide (powder) were added and mixed well, and 20 g of water was added and kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. As a result of the dissolution test, lead, mercury, arsenic, hexavalent chromium and cadmium were not detected. Moreover, the pH value of the elution water was 10.1.
[0027]
[ Reference Example 6]
A suspension obtained by suspending 2.5 g of calcium hydroxide in 20 g of water and 7.5 g of magnesium hydroxide (1 to 3 mm granules) are added to 100 g of fly ash co-tested in Reference Example 4 and mixed well. Kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. As a result of the dissolution test, lead, mercury, arsenic, hexavalent chromium and cadmium were not detected. Moreover, the pH value of the elution water was 10.8.
[0028]
[ Reference Example 7]
To 100 g of fly ash co-tested in Reference Example 1, 7 g of magnesium hydroxide (powder) and 3 g of calcium hydroxide (powder) were added and mixed well, then transferred to a sealed container, and 40 g of water was added thereto for about 10 minutes. The mixture was kneaded and further heated at 116 ° C. for about 1 hour. The pressure in the sealed container was about 1.8 atmospheres (atm) after heating for 1 hour. As a result of conducting an elution test based on Environment Agency Notification No. 13 on 100 g of the sample after the kneading and heating treatment, lead, mercury, arsenic, hexavalent chromium and cadmium were not detected. The pH value of the elution water was 9.5.
[0029]
[ Reference Example 8]
After adding 200 g of magnesium hydroxide (powder) and 10 g of calcium hydroxide (powder) to 200 g of fly ash co-tested in Reference Example 1, 80 g of water was added and kneaded for about 1 hour. To test the stability to acidic aqueous solution for the sample after kneading, packed sample 200g in the ^column, 1 cm 3 / min rate flowing dilute nitric acid aqueous solution 300 cm ³ of the pH value was adjusted to 4 with a, 100 cm ³ each of heavy metals The elution amount and pH value of were measured. As a result, heavy metals such as lead, mercury, arsenic, hexavalent chromium and cadmium were not detected from the eluate up to 300 cm ³ . Moreover, pH value of all the eluates was 10.1.
[0030]
Incidentally, the above-mentioned amount of dilute nitric acid aqueous solution of 300 cm ³ for 200 g of sample was calculated as almost corresponding to the annual precipitation for landfill fly ash. That is, if the average annual precipitation is 1600mm, the specific gravity of fly ash is 0.5, and the layer thickness at the time of landfill is 2m, the annual precipitation is 160g for 1cm ^{2 of} fly ash landfill area (volume 200cm ³ , weight 100g). Become. Therefore, about 200 g of fly ash, the precipitation amount is 320 g (approximately 300 g).
Next, as a result of conducting an elution test based on Environmental Agency Notification No. 13 on 100 g of the sample after flowing the dilute nitric acid aqueous solution, lead, mercury, arsenic, hexavalent chromium and cadmium were not detected. The pH value of the elution water was 10.1.
[0031]
[ Reference Example 9]
50 g of a suspension obtained by suspending 4 g of calcium hydroxide in water and 6 g of magnesium hydroxide (1 to 3 mm grains) were added to 100 g of fly ash co-tested in Reference Example 1 and kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. As a result of the dissolution test, lead, mercury, arsenic, hexavalent chromium and cadmium were not detected. Moreover, the pH value of the elution water was 9.2.
[0032]
[Example 1 ]
A complex {Mg (OH) ₂ : Ca (OH) _{2 in which} 1 to 3 mm of granular magnesium hydroxide and powdered calcium hydroxide are reacted with mechanochemicals and calcium hydroxide is adhered to the surface of magnesium hydroxide. = 6: 4 (weight ratio)}. This stabilizing agent was added to and mixed well with 100 g of fly ash co-tested in Reference Example 1, and further 40 g of water was added and kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. As a result of the dissolution test, lead, mercury, arsenic, hexavalent chromium and cadmium were not detected. Moreover, the pH value of the elution water was 9.2.
[0033]
[ Reference Example 10 ]
To 100 g of fly ash co-tested in Reference Example 1, 6 g of magnesium oxide (powder) and 4 g of calcium hydroxide (powder) were added and mixed well, and 40 g of water was added and kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. As a result of the dissolution test, lead, mercury, arsenic, hexavalent chromium and cadmium were not detected. Moreover, the pH value of the elution water was 9.2.
[0034]
[Example 2 ]
A complex {MgO: Ca (OH) ₂ = 6: 4 (weight) obtained by reacting 1 to 3 mm of granular magnesium oxide with powdered calcium hydroxide in a mechanochemical manner and adhering calcium hydroxide to the surface of magnesium oxide Ratio)}. This stabilizing agent was added to 100 g of fly ash co-tested in Reference Example 1 and mixed well, and 40 g of water was further added and kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. As a result of the dissolution test, lead, mercury, arsenic, hexavalent chromium and cadmium were not detected. Moreover, the pH value of the elution water was 9.2.
[0035]
[ Reference Example 11 ]
To 100 g of fly ash co-tested in Reference Example 1, 6 g of magnesium oxide (powder) and 40 g of an aqueous solution containing 4 g of sodium hydroxide were added and kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. As a result of the dissolution test, lead, mercury, arsenic, hexavalent chromium and cadmium were not detected. The pH value of the elution water was 9.5.
[0036]
[ Reference Example 12 ]
Sodium hydroxide aqueous solution was sprayed on granular magnesium oxide to produce a composite {MgO: NaOH = 6: 4 (weight ratio)} in which sodium hydroxide was adhered to the surface of magnesium oxide. 10 g of this stabilizing treatment agent was added to 100 g of fly ash co-tested in Reference Example 1 and mixed well, and 40 g of water was further added and kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. As a result of the dissolution test, lead, mercury, arsenic, hexavalent chromium and cadmium were not detected. The pH value of the elution water was 9.5.
[0037]
[Comparative Example 1]
30 g of water was added to 100 g of fly ash co-tested in Reference Example 1 and kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. As a result of the elution test, mercury, arsenic and hexavalent chromium were not detected, but the elution amount of lead was 11 mg / L and the elution amount of cadmium was 6.3 mg / L. Moreover, the pH value of the elution water was 6.3.
[0038]
[Comparative Example 2]
30 g of water was added to 100 g of fly ash co-tested in Reference Example 4 and kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. As a result of the dissolution test, mercury, arsenic and hexavalent chromium were not detected. However, the dissolution amount of lead was 7 mg / L, and the dissolution amount of cadmium was 14 mg / L. Moreover, the pH value of the elution water was 6.4.
[0039]
[Comparative Example 3]
Magnesium hydroxide (powder) 5 g and calcium hydroxide (powder) 5 g were added to 100 g of fly ash co-tested in Reference Example 4 and mixed well, and 40 g of water was added and kneaded. Thereafter, a dissolution test based on Notification No. 13 of the Environment Agency was conducted. As a result of the elution test, mercury, arsenic, hexavalent chromium and cadmium were not detected, but the elution amount of lead was 17 mg / L. Moreover, the pH value of the elution water was 12.2.
[0040]
[Comparative Example 4]
After adding 10 g of calcium hydroxide (powder) to 200 g of fly ash co-tested in Reference Example 1 and mixing well, 80 g of water was added and kneaded for about 1 hour to adjust the pH value to 10.1. To test the stability to acidic aqueous solution for the sample after kneading, packed sample 200g in the ^column, 1 cm 3 / min rate flowing dilute nitric acid aqueous solution 300 cm ³ of the pH value was adjusted to 4 with a, 100 cm ³ each of heavy metals The elution amount and pH value of were measured. As a result, the detected amount of heavy metal was 0 to 100 cm ³ , lead was 12 mg / L, cadmium was 14 mg / L, and mercury, arsenic and hexavalent chromium were not detected. The lead was 36 mg / L and cadmium was 38 mg / L at 101 to 200 cm ³ , and mercury, arsenic and hexavalent chromium were not detected. Lead in 201～300Cm ³ is 72 mg / L, cadmium is 86 mg / L, 6-valent chromium was not detected is mercury, arsenic and 0.02 mg / L. It was confirmed that the elution of lead started in a short time with acidic water. Further, pH value of the eluate is 0～100Cm ³ in 5.2,101～200Cm ³ is 4.5,201～300Cm ³ was 4.0.
[0041]
Furthermore, an elution test was conducted on 100 g of the sample after flowing dilute nitric acid based on Notification No. 13 of the Environment Agency. As a result of the dissolution test, the amount of heavy metal detected was 122 mg / L for lead and 0.03 mg / L for hexavalent chromium, and mercury and arsenic were not detected. Moreover, the pH value of the elution water was 4.0.
[0042]
[Table 1]

[0043]
[Table 2]

[0044]
The amounts and forms of the stabilizing treatment agents used in Reference Examples, Examples and Comparative Examples are shown in Table 1, and the results are shown in Table 2. As is apparent from Table 2, the amount of lead elution could be effectively suppressed by the stabilization treatment method using the stabilization treatment agent of the present invention, even with high-concentration lead-containing fly ash. However, even when the stabilizing agent of the present invention is used, when the pH value after pH adjustment exceeds 11 (Comparative Example 3), lead elution is observed and sufficient heavy metal fixation may not be performed. all right.
[0045]
As is clear from the results of Reference Example 8 and Comparative Example 4, when the pH value is adjusted to fix the amphoteric metal (lead) with an alkali such as calcium hydroxide, the atmosphere is kept acidic for a long time. stable can not be maintained the pH value, while the elution amount over time of lead has increased, the fly ash treated by way of reference example 8, further the long-term acid rain when the Even after this, the amount of elution of lead was low, and lead was stably fixed.
[0046]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the stabilization processing agent which can perform the fixing process of heavy metal effectively only by knead | mixing with the waste containing a heavy metal is provided. By using this stabilizing agent, it is possible to quickly adjust and maintain the waste to a desired pH value, thereby stably maintaining the insolubilization of the amphoteric metal that becomes water-soluble in a high pH range. Can do. Further, according to the present invention, by adjusting the heating conditions for kneading, the immobilization treatment can be performed easily and quickly without the need for a special pressure vessel or the like.

Claims

In the stabilizing agent for insolubilizing heavy metals in waste,
By reacting the initial pH value adjusting agent pH value stabilizer and a mechanochemical, stabilization treatment agent of waste consisting of composite was deposited an initial pH value adjustment agent to the surface of the pH value stabilizers.

The initial pH value adjusting agent is at least one selected from calcium hydroxide, calcium oxide, sodium hydroxide and potassium hydroxide, and the pH value stabilizer is at least selected from magnesium hydroxide and magnesium oxide. The waste stabilization treatment agent according to claim 1, which is one kind.

Initial pH value adjustment agent is powder powder,
The waste stabilization treatment agent according to claim 1 or 2, wherein the pH value stabilizer is a granular material.

A stabilizing treatment agent according to any one of claims 1 to 3 is added to a heavy metal-containing waste having a pH value of less than 7, and kneaded in the presence of water. Stabilization method.

The stabilization treatment agent according to any one of claims 1 to 3 is added to a heavy metal-containing waste having a pH value of less than 7, and kneaded in the presence of water to adjust the pH value to 7.5 to 11. A method for stabilizing heavy metal-containing waste.

The stabilization agent according to any one of claims 1 to 3 is added to a heavy metal-containing waste having a pH value of less than 7, and after kneading in the presence of water, the mixture is heated to less than 120 ° C for a predetermined time. A method for stabilizing heavy metal-containing waste, characterized by carrying out heat treatment.

The stabilizing agent according to any one of claims 1 to 3 is added to a heavy metal-containing waste having a pH value of less than 7, kneaded in the presence of water, heated to less than 120 ° C, and a predetermined time. A stabilization method for heavy metal-containing waste, characterized in that the pH value of the waste is adjusted to 7.5 to 11 by heat treatment.