JP2005034676A

JP2005034676A - Method for stabilizing heavy metals contained in incineration residue

Info

Publication number: JP2005034676A
Application number: JP2003149280A
Authority: JP
Inventors: Takayuki Shimaoka; 隆行島岡; Shogo Sakida; 省吾崎田; Akiko Nakano; 彰子中野; Terufumi Motohata; 照文本幡; Seiichi Abe; 清一阿部; Toshihito Uchida; 敏仁内田; Hiroaki Kawabata; 博昭河端; Masayuki Futamatsu; 雅之二松; Masahide Nishigaki; 正秀西垣; Hiroichi Obata; 博一小畑
Original assignee: Takuma Co Ltd; Kubota Corp; Kurita Water Industries Ltd; Hitachi Zosen Corp; Mitsui Engineering and Shipbuilding Co Ltd; Kyushu TLO Co Ltd; Kobelco Eco Solutions Co Ltd
Current assignee: Takuma Co Ltd; Shinko Pantec Co Ltd; Kubota Corp; Kurita Water Industries Ltd; Hitachi Zosen Corp; Mitsui Engineering and Shipbuilding Co Ltd; Kyushu TLO Co Ltd
Priority date: 2003-05-27
Filing date: 2003-05-27
Publication date: 2005-02-10
Anticipated expiration: 2023-05-27
Also published as: JP4374402B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stabilizing heavy metals such as lead contained in an incineration residue comprising incineration main ashes and/or incineration fly ash discharged from, for example, a municipal waste incineration plant or an industrial waste treatment plant by insolubilizing them efficiently and easily by a simple method and to eminently decrease running costs by making conventional chemicals including a chelating agent, power rates, etc., unnecessary. <P>SOLUTION: In the method for stabilizing the heavy metals contained in the incineration residue, first, treatment for wetting the incineration residue containing the heavy metals such as lead and treatment for drying the incineration residue are repeated, second, the incineration residue is treated at high temperatures and high pressures, third, after the treatment for drying the incineration residue and the method for drying the incineration residue are repeated, the incineration residue is treated at high temperatures and high pressures. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、焼却残渣に含まれる重金属類の安定化処理方法に関し、例えば都市ごみ焼却プラント、産業廃棄物処理プラントなどから排出される焼却残渣に含まれる鉛等の重金属類の安定化処理に適用されるものである。ここで、焼却残渣とは、焼却主灰及び／又は焼却飛灰を意味する。
【０００２】
また、本発明は、ガス化溶融炉・灰溶融炉プラントなどから排出される焼却残渣、あるいはまた、下水処理・し尿処理などから排出される汚泥の焼却残渣の重金属類の安定化処理にも適用されるものである。
【０００３】
【従来の技術】
産業廃棄物および都市生活からの廃棄物等のうち、可燃物は回収後、焼却炉で焼却されて焼却灰（焼却主灰、以下、単に焼却灰ともいう）の形態として投棄されたり埋設処分に付されたりしている。
【０００４】
しかしながら、これら焼却灰（焼却主灰）は、鉛（Ｐｂ）、カドミウム（Ｃｄ）、クロム（Ｃｒ）、水銀（Ｈｇ）、ひ素（Ａｓ）などの有害な重金属類を含んでいるため、最近では規制が厳しくなり、各種溶出試験などにおいて一定のレベル以下でないと土壌中に投棄したりすることはできず、埋立て地の溶出基準値をクリアする必要があった。また、道路の路盤材として再利用する場合には、土壌環境基準値をクリアする必要があった。
【０００５】
その一方で、このような廃棄物を燃焼すると、各種成分中の低沸点物質が揮散し、いわゆる焼却飛灰（以下、単に飛灰ともいう）となるが、この飛灰は、上記焼却灰に比べて有害な重金属類などを非常に多く含むので、一般廃棄物のように埋め立てることができないばかりか、外部環境に拡散させないために消石灰を担持させたバグフィルターなどにこれを捕集している。このような飛灰は、環境衛生上厳重な管理が必要とされ、そのままでは投棄したり埋め立て資材として利用することはできない。
【０００６】
しかしながら、近年、産業廃棄物や一般家庭からの廃棄物の量は増加の一途であり、既存の処分場の飽和化と環境汚染の問題等から処分場用地の確保が困難となっており、焼却灰、飛灰などをコンクリート成形体として各種土木工事や建築工事の基礎としたり路盤材として再利用することが検討されている。
【０００７】
さらに、焼却炉からの焼却灰や飛灰を溶融処理することにより減容化やダイオキシン類の熱分解を図ることが行われているが、上記溶融処理においては蒸気圧の大きい鉛やカドミウム等の重金属は、炉内で揮発して排ガス中に入り、排ガスに入った重金属は排ガス処理設備内で凝縮し、再び飛灰となってしまうという問題があった。
【０００８】
従来、このような焼却残渣に含まれる鉛等の重金属類の安定化処理方法としては、つぎの５つの処理が実用化されている。
【０００９】
（１）溶融固化処理：溶融固化は、燃料の燃焼熱や電気から得られた熱エネルギーまたはその他のエネルギーにより、媒塵や焼却灰等を加熱し、１２００〜１４００℃の高温下で有機物を燃焼、ガス化させ、無機物を溶融して、ガラス質のスラグとして回収する処理方法である。
【００１０】
（２）セメント固化：セメント固化は、セメント中のケイ酸カルシウム等の組織鉱物が水と結合し、水和物結晶を生じて硬化する過程において、焼却残渣中の有害物質の吸着や固溶化を伴い、またセメントの強いアルカリ性によって有害物質の難溶性化合物を生成して、固化体中に沈着、固定する処理方法である。
【００１１】
ここで、このセメント固化による焼却残渣の安定化処理方法には、つぎのような先行特許文献がある。
【００１２】
【特許文献１】
「特開２００２−８６１００号公報」
この特許文献１記載の発明は、ｐＨの管理を行わず最適ｐＨ値の範囲に収まり、飛灰の重金属、特に鉛の溶出を簡便に安定して防止できる重金属溶出防止方法を提供することを目的としており、特許文献１記載の発明では、溶融飛灰及び／又は焼成飛灰に、該飛灰当たりセメントを１〜１００％添加して混合後、鉄塩を前記飛灰当たりＦｅ換算で０．１％以上添加し、水を加えて混練し湿潤状態、又は、造粒することとするか、又は、前記飛灰を含有する排ガスを、前段のバグフィルタに通して該飛灰を捕集し、捕集後の排ガスに消石灰を噴霧して後段のバグフィルタを通して排ガスを処理するに際し、前記前段のバグフィルタで捕集した飛灰に、該飛灰当たりセメントを１〜１００％と後段のバグフィルタによる捕集灰を添加して混合後、鉄塩を前記飛灰当たりＦｅ換算で０．１％以上添加し、水を加えて混練し湿潤状態、又は、造粒することとしている。
【００１３】
（３）薬剤処理：薬剤処理は、焼却残渣をキレート剤等の薬剤で処理し、薬剤との反応により安定化を図る処理方法である。
【００１４】
ここで、この薬剤処理による焼却残渣の安定化処理方法には、つぎのような先行特許文献がある。
【００１５】
【特許文献２】
「特開２００１−１３７８２３号公報」
この特許文献２記載の発明は、都市ごみ焼却飛灰、特に流動床炉飛灰処理物の体積膨張を抑制し、固化状態を良好にし、鉛の溶出を基準値以下に抑えて処理を行うことを目的としており、都市ごみ焼却飛灰に対し、液体キレート剤と、ポルトランドセメントと、ケイ酸アルカリ金属塩と、炭酸アルカリ金属塩とを併用配合し、水と共に混練するものである。
【００１６】
（４）酸・その他の溶媒による安定化処理：酸抽出・水酸化物法／酸抽出・硫化物法／酸抽出・重金属固定剤法／排ガス中和法による安定化処理。
【００１７】
ここで、この酸・その他の溶媒による安定化処理方法には、つぎのような先行特許文献がある。
【００１８】
【特許文献３】
「特開２００１−４９３６０号公報」
この特許文献３記載の発明は、低コストで飛灰中に含まれる鉛を除去することにより飛灰を安定化するとともに、除去した鉛を回収する飛灰中の鉛回収処理法を提供することを目的としており、焼却炉又は溶融炉から排出される鉛などの重金属類を含有する飛灰に、硫酸を加えて、鉛以外の重金属類を抽出したのち固液分離し、次いで、固液分離して得られた鉛を含む残渣にチオ硫酸アルカリ塩を加えて鉛を抽出したのち固液分離し、さらに固液分離して得られた濾液に硫化薬剤を加えて鉛を不溶化物としたのち固液分離するものである。
【００１９】
（５）焼成固化：焼却残渣単独またはこれに粘土等を添加し、粒状、レンガ状に成形した後、概ね１０００℃以上の高温で焼成することにより、固体粒子が加熱によって互いに融解固着し、さらに付随して起こる収縮、緻密化、再結晶等により固化安定させる処理方法である。
【００２０】
【発明が解決しようとする課題】
しかしながら、上記の従来の焼却残渣に含まれる鉛等の重金属類の安定化処理方法のうち、（１）溶融固化処理方法では、燃料の燃焼熱や電気によるエネルギー費用が非常に高くつくという問題があった。また、上記（２）セメント固化処理方法では、セメント費用を必要とするし、セメントの添加によって処理物量が増大するという問題があった。さらに、上記（３）薬剤処理方法では、液体キレート剤等の薬剤の費用が非常に高くつくという問題があった。また、上記（４）酸・その他の溶媒による安定化処理方法では、薬品（酸）と水処理設備が必要であるという問題があった。また、上記（５）焼成固化処理方法では、焼成固化での成形、高温処理のための設備を必要とし、設備費が高くつくという問題があった。
【００２１】
本発明の目的は、上記の従来技術の問題を解決し、焼却主灰及び／又は焼却飛灰よりなる焼却残渣に含まれる鉛等の重金属類を、簡易な方法で、しかも高効率で容易に不溶化して安定化することができて、従来のキレート剤等の薬剤、電気代等が不要で、ランニングコストを大幅に低減することができる、焼却残渣に含まれる重金属類の安定化処理方法を提供しようとするにある。
【００２２】
【課題を解決するための手段】
上記の点に鑑み、本発明者らは鋭意研究を重ねた結果、鉛等の重金属類を含む焼却残渣（焼却主灰及び／又は焼却飛灰）を湿潤状態で放置するより湿潤処理と乾燥処理を繰り返す方が、鉛等の不溶化が促進されることがわかった。一方、鉛等の重金属類を含む焼却残渣を高温・高圧で処理することにより、鉛等の不溶化が促進されることがわかった。さらに、本発明者らは、上記第１の方法と第２の方法とを組み合わせて、鉛等の重金属類を含む焼却残渣（焼却主灰及び／又は焼却飛灰）の湿潤処理と乾燥処理とを繰り返した後、焼却残渣を、高温・高圧で処理することにより、さらに鉛等の重金属類の不溶化が促進されることを見出し、本発明を完成した。
【００２３】
本発明の請求項１記載の焼却残渣に含まれる重金属類の安定化処理方法は、鉛等の重金属類を含む焼却残渣（焼却主灰及び／又は焼却飛灰）を湿潤する処理と、乾燥する処理とを繰り返すことを特徴としている。
【００２４】
上記請求項１記載の焼却残渣に含まれる重金属類の安定化処理方法においては、焼却残渣の湿潤処理が、焼却残渣を含水率５〜３５％に湿潤する処理であり、焼却残渣の乾燥処理が、湿潤状態の焼却残渣を５０℃以上１１５℃以下の温度で乾燥させる処理である。
【００２５】
また、本発明の請求項３記載の焼却残渣に含まれる重金属類の安定化処理方法は、鉛等の重金属類を含む焼却残渣（焼却主灰及び／又は焼却飛灰）を、高温・高圧で処理することを特徴としている。
【００２６】
上記請求項３記載の焼却残渣に含まれる重金属類の安定化処理方法においては、焼却残渣の高温・高圧処理を、温度１１５℃以上１５０℃以下、及び圧力２００ｋＰａ以上５００ｋＰａ以下の条件で行なうものである。
【００２７】
本発明の請求項５記載の焼却残渣に含まれる重金属類の安定化処理方法は、鉛等の重金属類を含む焼却残渣（焼却主灰及び／又は焼却飛灰）の湿潤処理と乾燥処理とを繰り返した後、焼却残渣を、高温・高圧で処理することを特徴としている。
【００２８】
上記請求項５記載の焼却残渣に含まれる重金属類の安定化処理方法においては、焼却残渣の湿潤処理が、焼却残渣を含水率５〜３５％に湿潤する処理であり、焼却残渣の乾燥処理が、湿潤状態の焼却残渣を５０℃以上１１５℃以下の温度で乾燥させる処理であり、焼却残渣の高温・高圧処理が、温度１１５℃以上１５０℃以下、及び圧力２００ｋＰａ以上５００ｋＰａ以下の条件で行なう処理である。
【００２９】
【発明の実施の形態】
つぎに、本発明の実施の形態を説明する。
【００３０】
一般廃棄物の焼却残渣（焼却主灰及び／又は焼却飛灰）を有効利用するためには、重金属等有害物質の溶出に対処することが不可欠である。その方法の一つとして、エージング（ａｇｉｎｇ）による重金属の不溶化現象を利用することが挙げられる。
【００３１】
例えば、日本の表層土の約４割が火山灰に由来することに注目すると、「人工の火山」とも言える廃棄物焼却炉からの焼却残渣（人工の火山灰）もまた、土壌生成因子が作用することによって土壌化していくことが、充分に期待される。
【００３２】
本発明者らは、焼却残渣に上記の土壌生成因子として、水分（湿潤・乾燥の繰り返し）、温度、圧力（高温・高圧状態への暴露）を作用させ、それらに伴って、焼却残渣中の鉛等の重金属類の不溶化現象が大きく生じることを見出した。
【００３３】
本発明による焼却残渣に含まれる重金属類の安定化処理方法の第１は、鉛等の重金属類を含む焼却残渣（焼却主灰及び／又は焼却飛灰）を湿潤する処理と、乾燥する処理とを繰り返すものである。
【００３４】
ここで、焼却残渣の湿潤処理が、焼却残渣を含水率５〜３５％に湿潤する処理であり、焼却残渣の乾燥処理が、湿潤状態の焼却残渣を５０℃以上１１５℃以下の温度で乾燥させる処理であるのが、好ましい。
【００３５】
この焼却残渣の湿潤処理において、焼却残渣の含水率が５％未満であれば、鉛等重金属類の不溶化に寄与しないので、好ましくない。また焼却残渣の含水率が３５％を超えると、湿潤処理後の乾燥処理に時間がかゝるとともに、乾燥のためのエネルギーコストが高くつくので、好ましくない。また、焼却残渣の乾燥処理において、焼却残渣の乾燥温度が５０℃未満であれば、鉛等重金属類の不溶化が生じにくいので、好ましくない。また焼却残渣の乾燥温度が１１５℃を超えると、鉛等重金属類の不溶化は充分に生じるが、加熱乾燥のためのエネルギーコストが高くつくので、好ましくない。
【００３６】
なお、焼却残渣を湿潤する処理と、乾燥する処理とを繰り返す回数は、特に制限はないが、２〜１０回程度が好ましい。
【００３７】
また、本発明による焼却残渣に含まれる重金属類の安定化処理方法の第２は、鉛等の重金属類を含む焼却残渣（焼却主灰及び／又は焼却飛灰）を、高温・高圧で処理するものである。
【００３８】
ここで、焼却残渣の高温・高圧処理を、温度１１５℃以上１５０℃以下、及び圧力２００ｋＰａ以上５００ｋＰａ以下の条件で行なうのが、好ましい。
【００３９】
この焼却残渣の高温・高圧処理において、温度が１１５℃未満、及び圧力が２００ｋＰａ未満であれば、鉛等重金属類の不溶化が充分に生じないので、好ましくない。また温度が１５０℃を超え、及び圧力が５００ｋＰａを超えると、鉛等重金属類の不溶化は充分に生じるが、加熱・加圧のためのエネルギーコストが高くつくので、好ましくない。
【００４０】
本発明の上記第１の方法と第２の方法によれば、いずれの場合にも、焼却主灰及び／又は焼却飛灰よりなる焼却残渣に含まれる鉛等の重金属類を、簡易な方法で、しかも高効率で容易に不溶化して安定化することができて、従来のキレート剤等の薬剤が不要であるとともに、電気代等が少なくてすみ、ランニングコストを大幅に低減することができる。
【００４１】
つぎに、本発明による焼却残渣に含まれる重金属類の安定化処理方法の第３は、上記第１の方法と第２の方法とを組み合わせたものであり、鉛等の重金属類を含む焼却残渣（焼却主灰及び／又は焼却飛灰）の湿潤処理と乾燥処理とを繰り返した後、焼却残渣を、高温・高圧で処理するものである。
【００４２】
ここで、焼却残渣の湿潤処理が、焼却残渣を含水率５〜３５％に湿潤する処理であり、焼却残渣の乾燥処理が、湿潤状態の焼却残渣を５０℃以上１１５℃以下の温度で乾燥させる処理であり、焼却残渣の高温・高圧処理が、温度１１５℃以上１５０℃以下、及び圧力２００ｋＰａ以上５００ｋＰａ以下の条件で行なう処理であるのが、好ましい。
【００４３】
この場合、焼却残渣の湿潤処理において、焼却残渣の含水率が５％未満であれば、鉛等重金属類の不溶化に寄与しないので、好ましくない。また焼却残渣の含水率が３５％を超えると、湿潤処理後の乾燥処理に時間がかゝるとともに、乾燥のためのエネルギーコストが高くつくので、好ましくない。また、焼却残渣の乾燥処理において、焼却残渣の乾燥温度が５０℃未満であれば、鉛等重金属類の不溶化が生じにくいので、好ましくない。また焼却残渣の乾燥温度が１１５℃を超えると、鉛等重金属類の不溶化は充分に生じるが、加熱乾燥のためのエネルギーコストが高くつくので、好ましくない。また、焼却残渣の高温・高圧処理において、温度が１１５℃未満、及び圧力が２００ｋＰａ未満であれば、鉛等重金属類の不溶化が充分に生じないので、好ましくない。また温度が１５０℃を超え、及び圧力が５００ｋＰａを超えると、鉛等重金属類の不溶化は充分に生じるが、加熱・加圧のためのエネルギーコストが高くつくので、好ましくない。
【００４４】
本発明の上記第３の方法によれば、焼却主灰及び／又は焼却飛灰よりなる焼却残渣に含まれる鉛等の重金属類を、簡易な方法で、しかもより一層、高効率で容易に不溶化して安定化することができて、従来のキレート剤等の薬剤が不要であるとともに、電気代等が少なくてすみ、ランニングコストを大幅に低減することができる。
【００４５】
【実施例】
つぎに、本発明の実施例を説明するが、本発明は、これらの実施例に限定されるものではない。
【００４６】
実施例１
この実施例では、都市の乾式排ガス処理を行なっている清掃工場の電気集塵機で集められた飛灰、及び都市廃棄物の焼却灰を試料とした。各試料の成分分析と環境庁告示第４６号法に基づくに溶出試験（ＪＬＴ４６）の結果を、下記の表１に示す。
【００４７】
【表１】

最初に、鉛の含有量が多く、不溶化現象の等の把握が比較的容易である飛灰を用いて実験を行ない、つぎに、焼却灰を用いて同様の現象が生じるかを検討した。
【００４８】
本発明において、湿潤・乾燥工程の繰り返しが鉛の溶出に与える影響を調べるために、以下の実験を行なった。まず、各温度における乾燥時間を決定するために、含水率３０％に調整した試料をシャーレに所定の量を計り取り、６０℃（条件Ａ１）または１１０℃（条件Ａ２）で乾燥させた。１時間ごとに試料の含水率を測定し、同時に溶出試験に供した。この実験の結果より絶乾状態となる最小の時間を決定した。
【００４９】
この実施例では、試料をバットに取り、純水を加えて、含水率３０％に調整した後、各温度に設定した乾燥器で乾燥させ、再び含水率が３０％となるように純水を加えるという操作を１工程とし、この工程を繰り返す実験を行なった。
【００５０】
また、この実施例では、実験を同じにするために、試料の厚さは１．５センチとした。１工程終了後の試料から５０ｇを採取し、溶出試験（ＪＬＴ４６）、ｐＨ依存性試験を行なった。ｐＨ依存性試験は、初期の液固化比を１０とし、１Ｎの硝酸で滴定し、ｐＨをそれぞれ４，６，８，１０，１２に設定しながら、６時間スターラーで攪拌し、０．４５μｍの濾紙で濾過した。また、対照試験として、含水率３０％に調整した試料を室温１７℃の室内に放置する実験（条件Ｂ１）も行なった。濾液は、ｐＨと鉛の濃度を測定した。
【００５１】
さらに、上記の飛灰、及び焼却灰を試料とし、これらの焼却残渣を高温・高圧下に暴露した際の鉛溶出量を調べるため、以下の実験を行なった。
【００５２】
純水を用いて含水率３０％に調整した焼却残渣を５００ｍｌの三角フラスコに入れ、１２０℃、（２２３ｋＰａ）に設定した滅菌用オートクレーブに配置した（条件Ｃ１，Ｃ２）。実験中、含水率をほゞ一定に保つため、１００ｍｍビーカーで三角フラスコに蓋をした。含水率の増加は、実験前後で１〜２％以下に抑えられた。
【００５３】
加熱・加圧後、焼却残渣の試料は、湿潤・乾燥実験と同様に溶出試験（ＪＬＴ４６）、ｐＨ依存性試験に供し、濾液のｐＨと、鉛の濃度を測定した。
【００５４】
以上の実験条件を、下記の表２にまとめて示した。
【００５５】
【表２】

実験結果と考察
＜異なる乾燥温度における含水率の変化と鉛の不溶化＞
図１に、飛灰の含水率と乾燥時間の関係を、図２に、鉛の溶出濃度と乾燥時間の関係を示す。
【００５６】
これらの図から明らかなように、６０℃で乾燥させた場合は、１１０℃の場合と比較して乾燥速度は遅くなり、８時間経過後に、ほゞ含水率０％となった。鉛の溶出濃度は、初めの１時間で急激に低下した後、緩慢に低下し続け、乾燥開始から８時間目で値は落ち着いた。１１０℃で乾燥させた場合、含水率は２時間目でほゞ０％となり、Ｐｂの溶出濃度は、３時間経過後に最小値を示した。これより、鉛の不溶化が進行するのに充分かつ最短の時間として、６０℃では８時間を、１１０℃の乾燥では、３時間を乾燥工程１回とした。
【００５７】
本実験の結果から、６０℃で乾燥させた場合と、１１０℃で乾燥させた場合の溶出濃度を同じ乾燥時間で比較すると、６０℃で乾燥させた場合の方が鉛の不溶化が進行していることが判る。
【００５８】
以上のことから、鉛の不溶化と含水率や乾燥速度は密接に関係しており、鉛の不溶化現象には、水分の存在が必須であることが判明した。
【００５９】
＜湿潤・乾燥工程における鉛の不溶化現象＞
飛灰を用いた実験（条件Ａ１，Ａ２，Ｂ１）における鉛の溶出濃度の経時変化を図３に示す。湿潤・乾燥工程を繰り返すことよって、著しく鉛の不溶化が進行していることが判る。湿潤状態では、室内に放置したものは４８時間後、６０℃では、４０時間後、１１０℃では、１５時間後に、鉛の土壌環境基準値（０．０１ｍｇ／ｌ）以下となった。先にのべた実験では、鉛の不溶化現象には、水分の存在が大きく関与していると推測されたが、含水率を一定に保ったものと比較して、１１０℃で乾燥させたものの方が鉛の不溶化が進行していたため、温度が与える影響も示唆された。
【００６０】
つぎに、焼却灰を用いた実験（条件Ａ３，Ａ４）の結果を図４に示す。焼却灰の鉛の溶出濃度は、比較的低い濃度ではあったが、湿潤・乾燥工程を繰り返すことよって、飛灰と同様に鉛の不溶化現象が見られ、土壌環境基準を満たした。
【００６１】
＜高温・高圧下における鉛の不溶化現象＞
高温・高圧下に放置した際の鉛の溶出濃度の経時変化を図５に示す。飛灰（条件Ｃ１）、及び焼却灰（条件Ｃ２）ともに加熱・加圧時間の経過とともに、鉛の溶出濃度が減少した。焼却灰は、２時間後に鉛の土壌環境基準値（０．０１ｍｇ／ｌ）以下となった。しかし、飛灰は、鉛の土壌環境基準値（０．０１ｍｇ／ｌ）を下回ることはなかった。高温・高圧状態で２時間加熱した飛灰の鉛溶出濃度は、０．２９ｍｇ／ｌであり、１１０℃での湿潤・乾燥工程を３回（計９時間）繰り返した時の鉛溶出濃度１．５ｍｇ／ｌよりは小さかった。この結果から、湿潤状態に保持したまま圧力を加えながら加熱する方が、湿潤・乾燥を繰り返すことよりも、鉛の不溶化を促進させることが示された。
【００６２】
＜濾液のｐＨと鉛の不溶化率の関係＞
湿潤・乾燥実験、高温・高圧実験では、環境条件を急激に変化させることよって鉛の不溶化現象が認められたが、同時に濾液のｐＨも変化していた。各種の環境条件を与えたときの鉛の不溶化率と、そのときの濾液のｐＨの関係を図６に示す。鉛の不溶化率とは、初期の鉛の溶出濃度に対する減少濃度の割合を百分率で表わしたものである。湿潤・乾燥条件下では、鉛の不溶化率が上昇するにつれ、ｐＨが低下した。一方、高温・高圧条件下では、ｐＨがあまり変化しないにもかゝわらず、鉛の不溶化率が上昇していた。このことから、焼却残渣を高温・高圧下に放置した際の鉛の不溶化現象は、ｐＨの要因よりも、他の要因、例えば鉛の化合形態の変化の可能性があることが判る。
【００６３】
＜ｐＨの依存性試験による鉛の溶出特性＞
鉛の不溶化現象が認められた試料について、ｐＨの依存性試験を行なうことよって、酸性領域、強アルカリ領域での鉛の溶出量を調べた。試験には、不溶化の初期段階と最終段階として、湿潤・乾燥実験（条件Ａ１，Ａ２）の２回目と５回目、高温・高圧実験（条件Ｃ１）の０．５時間と２時間後の試料を用いた。ここで、飛灰（条件Ａ１，Ａ２）についてのｐＨ依存性試験の結果を図７に示す。
【００６４】
ｐＨ１２の強アルカリ領域では、原灰と比較して処理を加えた試料は、鉛の溶出濃度が減少していることが判る。減少の程度は、各試料の溶出試験（ＪＬＴ４６）の結果と類似しており、強アルカリ領域では鉛の不溶化の進行によりｐＨの影響を受けにくい形態の鉛に変化していることが考えられる。しかし、ｐＨ４の酸性領域では、処理を加えた試料について飛灰原灰と比較すると、鉛の溶出量が増加する傾向が見られる。特に、不溶化の進んでいない試料での溶出量が大きくなる傾向が見られ、低ｐＨで再溶解する形態の鉛も多く含まれていることが判る。
【００６５】
Ｘ線回析により、飛灰原灰とオートクレーブで１時間加熱した試料の化学形態について分析したところ、原灰中の鉛は不溶性の形態として、金属鉛、ＰｂＳ、ＰｂＳＯ_４の形で存在していたが、加熱・加圧後にはＰｂＳＯ_４がＰｂＣＯ_３に変化していることが確認された。しかし、この２つの結晶物の酸性領域出の溶解特性を考えると、鉛の不溶化現象は、鉛の化合形態の変化だけなく、共存物質の影響など、より複雑なメカニズムによって生じていることが考えられる。
【００６６】
上記の本発明の実施例によれば、焼却残渣に土壌生成因子として、水分（湿潤・乾燥の繰り返し）、温度、圧力（高温・高圧状態への暴露）を作用させることにより、以下のような結果が得られた。
【００６７】
（１）鉛の不溶化現象には、水分の存在が必須である。
【００６８】
（２）一定の湿潤状態で放置する場合に比較して、湿潤・乾燥を繰り返すと、鉛の不溶化が促進される。
【００６９】
（３）鉛の不溶化現象は、ｐＨの影響のみではなく、結晶物の変化など、鉱物学的な変化にも起因することが判明した。
【００７０】
（４）湿潤・乾燥、高温・高圧条件を作用させた場合、酸性領域では、鉛が溶出しやすくなることが認められた。
【００７１】
なお、将来的には、酸性領域での鉛の不溶化を生じさせるためにも、上記実施例で得られた鉛の不溶化現象のメカニズムを、機器分析、熱力学平衡計算等の手法を用いて解明するのが、望ましい。
【００７２】
【発明の効果】
本発明の請求項１記載の焼却残渣に含まれる重金属類の安定化処理方法は、上述のように、鉛等の重金属類を含む焼却残渣（焼却主灰及び／又は焼却飛灰）を湿潤する処理と、乾燥する処理とを繰り返すことを特徴とするもので、本発明によれば、焼却主灰及び／又は焼却飛灰よりなる焼却残渣に含まれる鉛等の重金属類を、簡易な方法で、しかも高効率で容易に不溶化して安定化することができて、従来のキレート剤等の薬剤、電気代等が不要で、ランニングコストを大幅に低減することができるという効果を奏する。
【００７３】
また、本発明の請求項３記載の焼却残渣に含まれる重金属類の安定化処理方法は、鉛等の重金属類を含む焼却残渣（焼却主灰及び／又は焼却飛灰）を、高温・高圧で処理することを特徴とするもので、本発明によれば、焼却主灰及び／又は焼却飛灰よりなる焼却残渣に含まれる鉛等の重金属類を、簡易な方法で、しかも高効率で容易に不溶化して安定化することができて、従来のキレート剤等の薬剤が不要であるとともに、電気代等が少なくてすみ、ランニングコストを大幅に低減することができるという効果を奏する。
【００７４】
本発明の請求項５記載の焼却残渣に含まれる重金属類の安定化処理方法は、鉛等の重金属類を含む焼却残渣（焼却主灰及び／又は焼却飛灰）の湿潤処理と乾燥処理とを繰り返した後、焼却残渣を、高温・高圧で処理することを特徴とするもので、本発明によれば、焼却主灰及び／又は焼却飛灰よりなる焼却残渣に含まれる鉛等の重金属類を、簡易な方法で、しかもより一層、高効率で容易に不溶化して安定化することができて、従来のキレート剤等の薬剤が不要であるとともに、電気代等が少なくてすみ、ランニングコストを大幅に低減することができるという効果を奏する。
【図面の簡単な説明】
【図１】本発明の実施形態において、飛灰の含水率と乾燥時間の関係を示すグラフである。
【図２】本発明の実施形態において、鉛の溶出濃度と乾燥時間の関係を示すグラフである。
【図３】本発明の実施形態において、飛灰を用いた実験における鉛の溶出濃度の経時変化を示すグラフである。
【図４】本発明の実施形態において、焼却灰を用いた実験における鉛の溶出濃度の経時変化を示すグラフである。
【図５】本発明の実施形態において、高温・高圧下に放置した際の鉛の溶出濃度の経時変化を示すグラフである。
【図６】本発明の実施形態において、鉛の不溶化率と、そのときの濾液のｐＨとの関係を示すグラフである。
【図７】本発明の実施形態において、飛灰についてのｐＨ依存性試験の結果を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for stabilizing heavy metals contained in incineration residues, and is applied to, for example, stabilizing treatment of heavy metals such as lead contained in incineration residues discharged from municipal waste incineration plants, industrial waste treatment plants, etc. It is what is done. Here, the incineration residue means incineration main ash and / or incineration fly ash.
[0002]
The present invention is also applicable to stabilization of heavy metals such as incineration residues discharged from gasification melting furnaces and ash melting furnace plants, or sludge incineration residues discharged from sewage treatment and human waste processing, etc. It is what is done.
[0003]
[Prior art]
Of industrial waste and waste from city life, combustibles are recovered and then incinerated in an incinerator and dumped in the form of incinerated ash (incinerated main ash, also simply referred to as incinerated ash) or buried It is attached.
[0004]
However, these incineration ash (incineration main ash) contains harmful heavy metals such as lead (Pb), cadmium (Cd), chromium (Cr), mercury (Hg), and arsenic (As). The regulations became stricter, and it was impossible to dump in the soil unless it was below a certain level in various elution tests, and it was necessary to clear the elution standard value of landfill. Moreover, when reusing as roadbed material, it was necessary to clear the soil environment standard value.
[0005]
On the other hand, when such waste is burned, low-boiling substances in various components are volatilized to form so-called incineration fly ash (hereinafter also simply referred to as fly ash). It contains a lot of harmful heavy metals, so it can not be landfilled like ordinary waste, and it is collected in a bag filter that carries slaked lime so that it does not diffuse into the external environment. . Such fly ash requires strict management in terms of environmental sanitation, and cannot be dumped or used as landfill as it is.
[0006]
However, in recent years, the amount of industrial waste and household waste has been increasing, and it has become difficult to secure land for disposal due to problems such as saturation of existing disposal sites and environmental pollution. It has been studied to use ash, fly ash, etc. as a concrete molded body as a basis for various civil engineering and construction work, or as a roadbed material.
[0007]
In addition, the incineration ash and fly ash from the incinerator are melted to reduce the volume and to thermally decompose dioxins. However, in the above melting process, lead or cadmium with a high vapor pressure is used. The heavy metal volatilizes in the furnace and enters the exhaust gas, and the heavy metal contained in the exhaust gas condenses in the exhaust gas treatment facility and becomes fly ash again.
[0008]
Conventionally, the following five treatments have been put to practical use as methods for stabilizing heavy metals such as lead contained in such incineration residues.
[0009]
(1) Melt-solidification treatment: Melt-solidification involves heating the dust and incineration ash etc. with the heat energy of fuel, the heat energy obtained from electricity, or other energy, and burning the organic matter at a high temperature of 1200-1400 ° C. This is a processing method of gasifying, melting an inorganic substance, and recovering it as a glassy slag.
[0010]
(2) Cement solidification: Cement solidification is the process of adsorption and solidification of harmful substances in incineration residues in the process where tissue minerals such as calcium silicate in cement combine with water to form hydrate crystals and harden. In addition, it is a processing method in which a hardly soluble compound of a harmful substance is generated by the strong alkalinity of cement, and is deposited and fixed in a solidified body.
[0011]
Here, there are the following prior patent documents in the method for stabilizing the incineration residue by cement solidification.
[0012]
[Patent Document 1]
"JP 2002-86100 A"
An object of the invention described in Patent Document 1 is to provide a heavy metal elution prevention method that can be easily and stably prevented from elution of heavy metals in fly ash, particularly lead, within the optimum pH value range without performing pH control. In the invention described in

Patent Document

1, 1 to 100% of cement per fly ash is added to and mixed with molten fly ash and / or calcined fly ash, and then iron salt is converted to Fe in terms of Fe per fly ash. Add 1% or more, add water, knead and wet or granulate, or pass the exhaust gas containing the fly ash through the bag filter in the previous stage to collect the fly ash When spraying slaked lime on the collected exhaust gas and treating the exhaust gas through the subsequent bag filter, the fly ash collected by the preceding bag filter is mixed with 1-100% cement per fly ash and the latter bug After adding the ash collected by the filter and mixing, Salts adding the fly ash per Fe converted at least 0.1%, by adding water and kneaded wet state, or is set to be granulated.
[0013]
(3) Chemical treatment: The chemical treatment is a treatment method in which the incineration residue is treated with a chemical such as a chelating agent and stabilized by a reaction with the chemical.
[0014]
Here, there are the following prior patent literatures as methods for stabilizing the incineration residue by this chemical treatment.
[0015]
[Patent Document 2]
"JP 2001-137823 A"
The invention described in Patent Document 2 suppresses the volume expansion of municipal waste incineration fly ash, in particular fluidized bed furnace fly ash, improves the solidification state, and suppresses lead elution to a reference value or less to perform the treatment. The purpose of this is to mix together a liquid chelating agent, Portland cement, an alkali metal silicate and an alkali carbonate carbonate to municipal waste incineration fly ash and knead with water.
[0016]
(4) Stabilization treatment with acid and other solvents: Stabilization treatment with acid extraction / hydroxide method / acid extraction / sulfide method / acid extraction / heavy metal fixing method / exhaust gas neutralization method.
[0017]
Here, there are the following prior patent documents for the stabilization treatment method using an acid or other solvent.
[0018]
[Patent Document 3]
"JP 2001-49360 A"
The invention described in Patent Document 3 provides a method for recovering lead in fly ash that stabilizes fly ash by removing lead contained in fly ash at a low cost and collects the removed lead. In addition, sulfuric acid is added to fly ash containing heavy metals such as lead discharged from an incinerator or melting furnace, and then heavy metals other than lead are extracted, followed by solid-liquid separation, and then solid-liquid separation. After adding lead thiosulfate alkali salt to the resulting lead-containing residue and extracting lead, it is separated into solid and liquid, and further, a sulfide is added to the filtrate obtained by solid-liquid separation to make lead insolubilized. Solid-liquid separation.
[0019]
(5) Solidification by firing: After incineration residue is added alone or clay is added to form a granular or brick shape, the solid particles are melted and fixed to each other by heating, by firing at a high temperature of approximately 1000 ° C. or higher. This is a treatment method for solidifying and stabilizing by accompanying shrinkage, densification, recrystallization and the like.
[0020]
[Problems to be solved by the invention]
However, among the conventional methods for stabilizing heavy metals such as lead contained in the above incineration residue, (1) the melt-solidifying method has the problem that the energy cost of fuel combustion heat and electricity is very high. there were. In addition, the above (2) cement solidification treatment method has a problem that a cement cost is required and the amount of treated material increases due to the addition of cement. Further, the above (3) chemical treatment method has a problem that the cost of chemicals such as liquid chelating agents is very high. In addition, the above-mentioned (4) stabilization method using an acid or other solvent has a problem that a chemical (acid) and water treatment equipment are required. Further, the above-mentioned (5) calcination solidification treatment method has a problem that equipment for molding by calcination solidification and high-temperature treatment are required, and the equipment cost is high.
[0021]
The object of the present invention is to solve the above-mentioned problems of the prior art, and to easily remove heavy metals such as lead contained in the incineration residue composed of incineration main ash and / or incineration fly ash by a simple method and with high efficiency. A method for stabilizing heavy metals contained in incineration residues that can be insolubilized and stabilized, eliminates the need for conventional chelating agents and other chemicals, electricity costs, etc., and significantly reduces running costs. Try to offer.
[0022]
[Means for Solving the Problems]
In view of the above points, as a result of intensive studies, the present inventors have conducted a wet treatment and a dry treatment rather than leaving incineration residues (incineration main ash and / or incineration fly ash) containing heavy metals such as lead in a wet state. It was found that the insolubilization of lead and the like was promoted by repeating the above. On the other hand, it was found that insolubilization of lead and the like was promoted by treating the incineration residue containing heavy metals such as lead at a high temperature and high pressure. Furthermore, the present inventors combine the first method and the second method, and wet treatment and drying treatment of incineration residues (incineration main ash and / or incineration fly ash) containing heavy metals such as lead, etc. After repeating the above, the incineration residue was treated at a high temperature and a high pressure to find that further insolubilization of heavy metals such as lead was promoted, and the present invention was completed.
[0023]
The stabilization method of heavy metals contained in the incineration residue according to claim 1 of the present invention is a treatment for wetting incineration residue (incineration main ash and / or incineration fly ash) containing heavy metals such as lead and drying. It is characterized by repeating the process.
[0024]
In the method for stabilizing heavy metals contained in the incineration residue according to claim 1, the incineration residue wetting treatment is a treatment for wetting the incineration residue to a moisture content of 5 to 35%, and the incineration residue drying treatment is performed. This is a treatment for drying a wet incineration residue at a temperature of 50 ° C. or higher and 115 ° C. or lower.
[0025]
Moreover, the stabilization processing method of heavy metals contained in the incineration residue according to claim 3 of the present invention is a method for treating incineration residues (incineration main ash and / or incineration fly ash) containing heavy metals such as lead at high temperature and high pressure. It is characterized by processing.
[0026]
In the stabilization method of heavy metals contained in the incineration residue according to claim 3, the high temperature and high pressure treatment of the incineration residue is performed under conditions of a temperature of 115 ° C to 150 ° C and a pressure of 200 kPa to 500 kPa. is there.
[0027]
The stabilization method of heavy metals contained in the incineration residue according to claim 5 of the present invention includes a wet treatment and a drying treatment of the incineration residue (incineration main ash and / or incineration fly ash) containing heavy metals such as lead. After the repetition, the incineration residue is treated at high temperature and high pressure.
[0028]
In the method for stabilizing heavy metals contained in the incineration residue according to claim 5, the incineration residue wet treatment is a treatment of wetting the incineration residue to a moisture content of 5 to 35%, and the incineration residue drying treatment is performed. The incineration residue in a wet state is dried at a temperature of 50 ° C. or higher and 115 ° C. or lower, and the high temperature and high pressure treatment of the incineration residue is performed at a temperature of 115 ° C. or higher and 150 ° C. or lower and a pressure of 200 kPa or higher and 500 kPa or lower. It is.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described.
[0030]
In order to effectively use the incineration residue (incineration main ash and / or incineration fly ash) of general waste, it is indispensable to deal with elution of toxic substances such as heavy metals. One of the methods is to use the insolubilization phenomenon of heavy metals due to aging.
[0031]
For example, focusing on the fact that about 40% of the surface soil in Japan is derived from volcanic ash, the incineration residue (artificial volcanic ash) from a waste incinerator, which can be called an “artificial volcano”, is also affected by soil formation factors. It is fully expected that it will become soil.
[0032]
The present inventors acted moisture (repetition of wet and dry), temperature and pressure (exposure to high temperature and high pressure) on the incineration residue as the above-mentioned soil formation factors, and accordingly, in the incineration residue It has been found that the insolubilization phenomenon of heavy metals such as lead occurs greatly.
[0033]
A first method for stabilizing heavy metals contained in incineration residues according to the present invention is a treatment for wetting incineration residues (incineration main ash and / or incineration fly ash) containing heavy metals such as lead, and a treatment for drying. Is repeated.
[0034]
Here, the wetting treatment of the incineration residue is a treatment of wetting the incineration residue to a moisture content of 5 to 35%, and the drying treatment of the incineration residue is drying the incineration residue in a wet state at a temperature of 50 ° C. or more and 115 ° C. or less. A treatment is preferred.
[0035]
In the wet treatment of the incineration residue, if the water content of the incineration residue is less than 5%, it does not contribute to insolubilization of heavy metals such as lead, which is not preferable. Further, if the moisture content of the incineration residue exceeds 35%, it takes a long time for the drying treatment after the wet treatment, and the energy cost for drying is high, which is not preferable. In addition, if the drying temperature of the incineration residue is less than 50 ° C. in the incineration residue drying process, insolubilization of heavy metals such as lead is unlikely to occur. Further, if the drying temperature of the incineration residue exceeds 115 ° C., heavy metals such as lead are sufficiently insolubilized, but this is not preferable because the energy cost for heat drying is high.
[0036]
In addition, the frequency | count of repeating the process which wets an incineration residue, and the process to dry is although there is no restriction | limiting in particular, About 2 to 10 times is preferable.
[0037]
The second method for stabilizing heavy metals contained in incineration residues according to the present invention is to treat incineration residues (incineration main ash and / or incineration fly ash) containing heavy metals such as lead at high temperature and high pressure. Is.
[0038]
Here, it is preferable to perform the high-temperature and high-pressure treatment of the incineration residue under conditions of a temperature of 115 ° C. to 150 ° C. and a pressure of 200 kPa to 500 kPa.
[0039]
In the high-temperature and high-pressure treatment of the incineration residue, if the temperature is less than 115 ° C. and the pressure is less than 200 kPa, insolubilization of heavy metals such as lead does not occur sufficiently, which is not preferable. On the other hand, if the temperature exceeds 150 ° C. and the pressure exceeds 500 kPa, heavy metals such as lead are sufficiently insolubilized, but this is not preferable because the energy cost for heating and pressurization is high.
[0040]
According to the first method and the second method of the present invention, in any case, heavy metals such as lead contained in the incineration residue composed of incineration main ash and / or incineration fly ash can be obtained by a simple method. In addition, it can be easily insolubilized and stabilized with high efficiency, and a conventional agent such as a chelating agent is not required, and an electric bill and the like can be reduced, and the running cost can be greatly reduced.
[0041]
Next, the third of the stabilization methods for heavy metals contained in the incineration residue according to the present invention is a combination of the first method and the second method, and the incineration residue containing heavy metals such as lead. The incineration residue is treated at a high temperature and a high pressure after the wet treatment and the drying treatment of (incineration main ash and / or incineration fly ash) are repeated.
[0042]
Here, the wetting treatment of the incineration residue is a treatment of wetting the incineration residue to a moisture content of 5 to 35%, and the drying treatment of the incineration residue is drying the incineration residue in a wet state at a temperature of 50 ° C. or more and 115 ° C. or less. Preferably, the high-temperature and high-pressure treatment of the incineration residue is performed under conditions of a temperature of 115 ° C. to 150 ° C. and a pressure of 200 kPa to 500 kPa.
[0043]
In this case, in the wet treatment of the incineration residue, if the moisture content of the incineration residue is less than 5%, it does not contribute to insolubilization of heavy metals such as lead, which is not preferable. Further, if the moisture content of the incineration residue exceeds 35%, it takes a long time for the drying treatment after the wet treatment, and the energy cost for drying is high, which is not preferable. In addition, if the drying temperature of the incineration residue is less than 50 ° C. in the incineration residue drying process, insolubilization of heavy metals such as lead is unlikely to occur. Further, if the drying temperature of the incineration residue exceeds 115 ° C., heavy metals such as lead are sufficiently insolubilized, but this is not preferable because the energy cost for heat drying is high. In addition, in the high-temperature and high-pressure treatment of incineration residues, if the temperature is less than 115 ° C. and the pressure is less than 200 kPa, insolubilization of heavy metals such as lead does not occur sufficiently, such being undesirable. On the other hand, if the temperature exceeds 150 ° C. and the pressure exceeds 500 kPa, heavy metals such as lead are sufficiently insolubilized, but this is not preferable because the energy cost for heating and pressurization is high.
[0044]
According to the third method of the present invention, heavy metals such as lead contained in the incineration residue composed of incineration main ash and / or incineration fly ash can be easily insolubilized with a simple method, yet with higher efficiency. Thus, the conventional chelating agent and other chemicals are not necessary, and the electricity cost and the like can be reduced, and the running cost can be greatly reduced.
[0045]
【Example】
Next, examples of the present invention will be described, but the present invention is not limited to these examples.
[0046]
Example 1
In this example, fly ash collected by an electric dust collector of a cleaning factory that performs dry exhaust gas treatment in cities and incineration ash of city wastes were used as samples. Table 1 below shows the results of the dissolution analysis (JLT46) based on the component analysis of each sample and the Environmental Agency Notification No. 46.
[0047]
[Table 1]

First, an experiment was conducted using fly ash, which contains a large amount of lead and it is relatively easy to grasp the insolubilization phenomenon. Next, it was examined whether the same phenomenon would occur using incinerated ash.
[0048]
In the present invention, the following experiment was conducted in order to investigate the influence of repeated wet and dry processes on lead elution. First, in order to determine the drying time at each temperature, a predetermined amount of a sample adjusted to a moisture content of 30% was measured in a petri dish and dried at 60 ° C. (condition A1) or 110 ° C. (condition A2). The moisture content of the sample was measured every hour and simultaneously subjected to a dissolution test. Based on the results of this experiment, the minimum time for an absolutely dry state was determined.
[0049]
In this example, a sample is taken into a vat, pure water is added to adjust the moisture content to 30%, and then dried with a drier set to each temperature, and pure water is added again so that the moisture content becomes 30%. The operation of adding was taken as one step, and this step was repeated.
[0050]
In this example, the thickness of the sample was 1.5 cm in order to make the experiment the same. 50 g was collected from the sample after completion of one step, and a dissolution test (JLT46) and a pH dependence test were performed. In the pH dependence test, the initial liquid solidification ratio was 10, and titration with 1N nitric acid was performed. The pH was set to 4, 6, 8, 10, and 12, respectively, and the mixture was stirred with a stirrer for 6 hours. Filter with filter paper. As a control test, an experiment (condition B1) was also conducted in which a sample adjusted to a moisture content of 30% was left in a room at a room temperature of 17 ° C. The filtrate was measured for pH and lead concentration.
[0051]
Furthermore, the following experiment was conducted in order to investigate the amount of lead elution when the above-mentioned fly ash and incineration ash were used as samples and these incineration residues were exposed to high temperature and high pressure.
[0052]
The incineration residue adjusted to a water content of 30% using pure water was placed in a 500 ml Erlenmeyer flask and placed in a sterilization autoclave set at 120 ° C. (223 kPa) (conditions C1, C2). During the experiment, the Erlenmeyer flask was covered with a 100 mm beaker in order to keep the water content almost constant. The increase in moisture content was suppressed to 1 to 2% or less before and after the experiment.
[0053]
After heating and pressurizing, the incineration residue sample was subjected to a dissolution test (JLT46) and a pH dependence test in the same manner as the wet / dry experiment, and the pH of the filtrate and the lead concentration were measured.
[0054]
The above experimental conditions are summarized in Table 2 below.
[0055]
[Table 2]

Experimental results and discussion
<Change in moisture content and insolubilization of lead at different drying temperatures>
FIG. 1 shows the relationship between the water content of fly ash and the drying time, and FIG. 2 shows the relationship between the elution concentration of lead and the drying time.
[0056]
As is apparent from these figures, when dried at 60 ° C., the drying rate was lower than at 110 ° C., and after 8 hours, the water content was almost 0%. The elution concentration of lead decreased rapidly after the first hour, and then continued to decrease slowly. The value settled at 8 hours after the start of drying. When dried at 110 ° C., the moisture content was about 0% at 2 hours, and the elution concentration of Pb showed a minimum value after 3 hours. As a result, as the shortest time sufficient and sufficient for lead insolubilization to proceed, 8 hours at 60 ° C. and 3 hours for 110 ° C. drying were defined as one drying step.
[0057]
From the results of this experiment, when the elution concentration when dried at 60 ° C. and when dried at 110 ° C. are compared with the same drying time, lead insolubilization progresses when dried at 60 ° C. I know that.
[0058]
From the above, it was found that the insolubilization of lead and the moisture content and drying rate are closely related, and the presence of moisture is essential for the insolubilization phenomenon of lead.
[0059]
<Lead insolubilization phenomenon in wet and dry process>
FIG. 3 shows changes with time in the elution concentration of lead in experiments using fly ash (conditions A1, A2, and B1). It can be seen that lead insolubilization has advanced remarkably by repeating the wetting and drying steps. In the wet state, the sample left in the room was 48 hours later, 60 ° C., 40 hours later, and 110 ° C., 15 hours later, the lead soil soil environmental standard value (0.01 mg / l) or less. In the previous experiment, it was speculated that the presence of moisture greatly contributed to the insolubilization phenomenon of lead, but the one dried at 110 ° C compared to the one in which the moisture content was kept constant. However, since lead insolubilization was in progress, the effect of temperature was also suggested.
[0060]
Next, the result of the experiment using the incinerated ash (conditions A3 and A4) is shown in FIG. Although the elution concentration of lead in incineration ash was relatively low, by repeating the wet and dry process, lead insolubilization phenomenon was observed in the same way as fly ash, and the soil environmental standards were satisfied.
[0061]
<Lead insolubilization phenomenon under high temperature and pressure>
FIG. 5 shows changes with time in the elution concentration of lead when left under high temperature and high pressure. In both fly ash (condition C1) and incineration ash (condition C2), the elution concentration of lead decreased with the lapse of heating and pressurizing time. The incinerated ash became lead soil environmental standard value (0.01 mg / l) or less after 2 hours. However, fly ash did not fall below the soil soil environmental standard value (0.01 mg / l). The lead elution concentration of fly ash heated at high temperature and high pressure for 2 hours is 0.29 mg / l, and the lead elution concentration when the wet / dry process at 110 ° C. is repeated 3 times (9 hours in total). It was less than 5 mg / l. From this result, it was shown that heating while applying pressure while keeping the wet state promoted insolubilization of lead rather than repeating wet and dry.
[0062]
<Relationship between pH of filtrate and insolubilization rate of lead>
In wet / dry experiments and high-temperature / high-pressure experiments, lead insolubilization was observed by rapidly changing environmental conditions, but at the same time, the pH of the filtrate also changed. FIG. 6 shows the relationship between the insolubilization rate of lead when various environmental conditions are given and the pH of the filtrate at that time. The insolubilization rate of lead is a percentage of the decrease concentration relative to the initial lead elution concentration. Under wet and dry conditions, the pH decreased as the lead insolubilization rate increased. On the other hand, under high temperature and high pressure conditions, the insolubilization rate of lead increased even though the pH did not change much. From this, it is understood that the insolubilization phenomenon of lead when the incineration residue is left under high temperature and high pressure may change other factors than the factor of pH, for example, the compound form of lead.
[0063]
<Lead elution characteristics by pH dependence test>
About the sample in which the insolubilization phenomenon of lead was recognized, the elution amount of lead in the acidic region and the strong alkali region was examined by conducting a pH dependency test. In the test, as the initial stage and the final stage of insolubilization, the second and fifth times of the wet / dry experiment (Conditions A1, A2) and the samples after 0.5 hours and 2 hours of the high temperature / high pressure experiment (Condition C1) were used. Using. Here, the result of the pH dependence test about fly ash (conditions A1 and A2) is shown in FIG.
[0064]
It can be seen that in the strongly alkaline region of pH 12, the lead elution concentration decreased in the sample subjected to the treatment as compared with the raw ash. The degree of decrease is similar to the results of the elution test (JLT46) of each sample, and it is considered that the lead is in a form that is hardly affected by pH due to the progress of insolubilization of lead in the strong alkali region. However, in the acidic region of pH 4, there is a tendency for the amount of lead elution to increase when the treated sample is compared with the fly ash ash. In particular, it can be seen that the amount of elution in a sample that has not been insolubilized tends to increase, and a large amount of lead that is redissolved at a low pH is also contained.
[0065]
Analysis of the chemical form of the fly ash raw ash and the sample heated in an autoclave for 1 hour by X-ray diffraction revealed that the lead in the raw ash was insoluble, and metal lead, PbS, PbSO ₄ It was present in the form of PbSO after heating and pressurization. ₄ Is PbCO ₃ It has been confirmed that However, considering the dissolution characteristics of these two crystals in the acidic region, it is considered that the insolubilization phenomenon of lead is caused not only by the change in the compound form of lead but also by more complicated mechanisms such as the influence of coexisting substances. It is done.
[0066]
According to the above-described embodiment of the present invention, moisture (repeated wet and dry), temperature, and pressure (exposure to high temperature and high pressure) are applied to the incineration residue as a soil formation factor. Results were obtained.
[0067]
(1) The presence of moisture is essential for the insolubilization phenomenon of lead.
[0068]
(2) Lead insolubilization is promoted when wetting and drying are repeated as compared with the case of leaving in a constant moist state.
[0069]
(3) It has been found that the insolubilization phenomenon of lead is caused not only by the influence of pH but also by mineralogical changes such as changes in crystalline substances.
[0070]
(4) When wet / dry, high temperature / high pressure conditions were applied, it was found that lead is likely to elute in the acidic region.
[0071]
In the future, in order to cause insolubilization of lead in the acidic region, the mechanism of the insolubilization phenomenon of lead obtained in the above examples will be elucidated using methods such as instrumental analysis and thermodynamic equilibrium calculation. It is desirable to do.
[0072]
【The invention's effect】
The method for stabilizing heavy metals contained in the incineration residue according to claim 1 of the present invention wets the incineration residue (incineration main ash and / or incineration fly ash) containing heavy metals such as lead as described above. According to the present invention, heavy metals such as lead contained in the incineration residue composed of incineration main ash and / or incineration fly ash can be obtained by a simple method. In addition, it can be easily insolubilized and stabilized with high efficiency, and there is no need for conventional chemicals such as chelating agents, electricity bills, etc., and the running cost can be greatly reduced.
[0073]
Moreover, the stabilization processing method of heavy metals contained in the incineration residue according to claim 3 of the present invention is a method for treating incineration residues (incineration main ash and / or incineration fly ash) containing heavy metals such as lead at high temperature and high pressure. According to the present invention, heavy metals such as lead contained in the incineration residue composed of incineration main ash and / or incineration fly ash can be easily and efficiently processed. It can be insolubilized and stabilized, and there is an effect that a conventional agent such as a chelating agent is not necessary, an electricity bill is reduced, and a running cost can be greatly reduced.
[0074]
The stabilization method of heavy metals contained in the incineration residue according to claim 5 of the present invention includes a wet treatment and a drying treatment of the incineration residue (incineration main ash and / or incineration fly ash) containing heavy metals such as lead. After repeating, the incineration residue is treated at high temperature and high pressure. According to the present invention, heavy metals such as lead contained in the incineration residue composed of incineration main ash and / or incineration fly ash In addition, it can be easily insolubilized and stabilized with a simple method, and can be stabilized with no need for conventional chelating agents and other chemicals. There is an effect that it can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between fly ash moisture content and drying time in an embodiment of the present invention.
FIG. 2 is a graph showing the relationship between lead elution concentration and drying time in an embodiment of the present invention.
FIG. 3 is a graph showing a change with time in the elution concentration of lead in an experiment using fly ash in the embodiment of the present invention.
FIG. 4 is a graph showing a change with time in the elution concentration of lead in an experiment using incinerated ash in the embodiment of the present invention.
FIG. 5 is a graph showing a change with time in the elution concentration of lead when left under high temperature and high pressure in an embodiment of the present invention.
FIG. 6 is a graph showing the relationship between the insolubilization rate of lead and the pH of the filtrate at that time in the embodiment of the present invention.
FIG. 7 is a graph showing the results of a pH dependence test on fly ash in the embodiment of the present invention.

Claims

A method for stabilizing heavy metals contained in incineration residues, characterized by repeating a process of wetting and drying an incineration residue (incineration main ash and / or incineration fly ash) containing heavy metals such as lead. .

The incineration residue wetting process is a process of wetting the incineration residue to a moisture content of 5 to 35%, and the incineration residue drying process is a process of drying the wet incineration residue at a temperature of 50 ° C. or higher and 115 ° C. or lower. A method for stabilizing heavy metals contained in the incineration residue according to claim 1.

A method for stabilizing heavy metals contained in incineration residues, comprising treating incineration residues (incineration main ash and / or incineration fly ash) containing heavy metals such as lead at high temperature and high pressure.

The method for stabilizing heavy metals contained in an incineration residue according to claim 3, wherein the incineration residue is subjected to high temperature and high pressure treatment under conditions of a temperature of 115 ° C to 150 ° C and a pressure of 200 kPa to 500 kPa. .

Incineration residue, characterized by treating the incineration residue at high temperature and high pressure after wetting and drying of the incineration residue (incineration main ash and / or incineration fly ash) containing heavy metals such as lead Of stabilization of heavy metals contained in the above.

The incineration residue wetting process is a process of wetting the incineration residue to a moisture content of 5 to 35%, and the incineration residue drying process is a process of drying the wet incineration residue at a temperature of 50 ° C. to 115 ° C. The high-temperature and high-pressure treatment of the incineration residue is a treatment performed under the conditions of a temperature of 115 ° C or higher and 150 ° C or lower and a pressure of 200 kPa or higher and 500 kPa or lower. Stabilization method.