JP2004216209A - Fly ash treatment method - Google Patents
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- JP2004216209A JP2004216209A JP2003003522A JP2003003522A JP2004216209A JP 2004216209 A JP2004216209 A JP 2004216209A JP 2003003522 A JP2003003522 A JP 2003003522A JP 2003003522 A JP2003003522 A JP 2003003522A JP 2004216209 A JP2004216209 A JP 2004216209A
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- fly ash
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、鉛、カドミウム、その他の重金属（これらの金属を総称して単に重金属という。）を含有する飛灰についてキレート剤を用いて不溶化する処理法であって、簡易な分析的手法により処理結果を判定して処理作業の効率化およびキレート剤添加量の最適化を図るものである。
【０００２】
【従来の技術】
産業廃棄物および一般廃棄物等の廃棄物を焼却または加熱酸化処理等を行うと、その反応に伴い炉内および炉からの排ガス中等に重金属等を含有する灰が発生する。これらの灰（総称して飛灰という。）の中には上記の種々の重金属などが含有されており、例えば鉛やカドミウム等の重金属は環境を汚染する恐れがあるため、これらの飛灰は中和処理、重金属の不溶化・無害化処理等が施される。
【０００３】
従来より、飛灰中の重金属の不溶化・無害化処理には、セメントやアスファルトによる固化方法、炭酸ガスによって不溶性の炭酸塩とする中和炭酸塩化の処理方法、還元溶融炉によってスラグに固化する方法、有機高分子系のキレート剤によって不溶化する方法などがある。
【０００４】
このうち、セメントやアスファルトによる固化方法では２０〜３０％程度体積増となってしまうことや酸性雨などによる再溶出の恐れがあり、また、炭酸ガスによる炭酸塩化法や溶融炉を用いるスラグ化法では処理設備が大掛かりなものとなり設備費が嵩むことなどがあって、処理設備、工程管理および処理コスト等において比較的有利な有機高分子系のキレート剤による処理法が多く実施されている。
【０００５】
上記のキレート剤による処理においては、飛灰の性状、重金属含有量、重金属溶出濃度等に応じてキレート剤および水を添加し、混練することによって処理飛灰を得るものである。この処理により重金属が確実に不溶化されて重金属溶出の恐れが無くなった処理飛灰は最終処分場に移送され、埋立処分などに供される。
【０００６】
処理飛灰中の重金属が確実に不溶化されたかどうかは、処理飛灰の溶出液中の重金属濃度を分析することで確認することができる。すなわち、環境省告示１３号法試験に基づき、処理飛灰を中性域の溶媒と混合してその溶出液を得、次いで工場排水試験方法（ＪＩＳ Ｋ ０１０２）に基づき、この溶出液を酸溶解した後に、ｐＨ調整、錯体形成、有機溶媒による分液抽出、塩酸による逆抽出などの工程を経て分析用溶出液を得る。さらにその溶出液について原子吸光法、ＩＣＰ発光分析法などのＪＩＳに基づいた定量分析法により重金属濃度を定量し、重金属濃度が埋立基準値以下であるかどうか、すなわちキレート剤による不溶化が確実になされたかどうかを判定する。
【０００７】
溶出液中の重金属濃度が基準値以下と判定されることにより、その処理ロットの処理飛灰が最終処分場に向けて出荷される。溶出液中の重金属濃度が基準値を上回る場合は、その処理ロットの処理飛灰は出荷停止され、さらにキレート剤を追加して再処理を行ない、溶出液中への重金属の溶出量が基準値以下になるように繰り返される。
【０００８】
なお、前記環境省告示１３号法試験の規定によれば、溶出液を得るための試料液は、「イ 埋立処分（海面埋立処分を除く）を行おうとする燃え殻、汚泥、鉱さい、ばいじん又はこれらの産業廃棄物を処分するために処理したものにあっては、試料（単位：グラム）と溶媒（純水に水酸化ナトリウムまたは塩酸を加えて、水素イオン濃度指数が５．８以上、６．３以下となるようにしたもの）（単位：ミリリットル）とを重量体積比１０％の割合で混合し、かつ、その混合液が５００ミリリットル以下となるようにしたものとする。」と規定され、溶出操作については、「常温（おおむね摂氏２０度）、常圧（おおむね１気圧）で振とう機（あらかじめ振とう回数を毎分約２００回に、振とう幅を４センチメートル以上、５センチメートル以下に調整したもの）を用いて、６時間連続して振とうする。」と規定されている。
【０００９】
【発明が解決しようとする課題】
しかしながら、従来は、キレート剤と混練して処理された処理飛灰に十分な量のキレート剤が添加され、重金属が確実に不溶化されたかどうかは、全処理飛灰中の重金属の溶出値をその溶出液についてＪＩＳの機器分析手法にしたがって測定する必要があった。また、その測定値をもとに再処理の必要の有無を判断し、キレート剤の過不足量を判断している状況にあった。
【００１０】
従来、処理工程においてＪＩＳの原子吸光法やＩＣＰ発光分析法など機器分析手法による溶出液中の重金属濃度の確認作業に際しては、前記溶出液から分析用のサンプル液を調製するまでの手順が多く、時間や分析費用が大きいという欠点があった。また、再処理飛灰の場合を含めて重金属濃度の確認作業の全てにＪＩＳの機器分析手法を適用するには、それらの機器を揃えて調整・管理をしなければならず、また分析にかかる時間や人手も大きいという問題があった。
【００１１】
さらには、前記溶出液は処理飛灰のサンプリングの場所や処理時間（混練、養生）の違い等も考慮し、また、処理飛灰の溶出液の分析によりキレート処理が不十分と判定された場合を考慮すると、必要なサンプル液の調製および分析を行なう時間およびコストの負担は著しく増加し、分析必要量が設備の処理能力を上回ったり、飛灰の処理量にも影響を及ぼすことがある。また、重金属無害化処理に用いたキレート剤がどれほど過剰であったかは正確には不明であった。
【００１２】
したがって、本発明の目的とするところは、前記の問題点に鑑み、飛灰のキレート剤による重金属不溶化処理の途上において、代用特性を用いて処理飛灰中の重金属の溶出の有無を簡易に判定できる方法を提供し、機器分析およびそのための分析用サンプル液の調製などに要する時間およびコスト負担の軽減を図り、前記重金属不溶化処理作業の効率化および分析コスト低減を図ること、ならびに、重金属再溶出防止に必要なキレート剤過剰添加の最適化によりキレート剤コスト低減を図ることにある。
【００１３】
【課題を解決するための手段】
この点を解決するため、本発明者は金属含有溶液を試薬として扱い、溶出液中の未反応キレート剤を定量的に判定する手法を見出した。すなわち、本発明は第１に、重金属を含有する飛灰にキレート剤を添加して混練し、該飛灰中の該重金属を不溶化する処理法であって、該処理後の飛灰に溶媒を添加してなるスラリーからの溶出液中に、金属イオンを含有する試験溶液を添加し、該試験溶液添加前後における該溶出液の色について該溶出液中に残留する前記キレート剤による変化が無くなるまでに要した該試験溶液の添加量によって該溶出液中に残留する前記キレート剤量を求めることを特徴とする飛灰の処理法であり、第２に、前記試験溶液の添加量が前記溶出液中に残留する未反応の前記キレート剤量に相当する、第１記載の飛灰の処理法である。
【００１４】
次に、本発明は第３に、前記試験溶液の添加量によって前記処理における前記キレート剤の添加量不足と判定した後、該処理後の飛灰に該判定結果に基づく不足量の該キレート剤をさらに添加して混練し該処理を継続する、第１または２に記載の飛灰の処理法であり、第４に、前記試験溶液の添加量によって前記処理における前記キレート剤の添加量不足と判定した後、該処理対象の次ロットの飛灰に該判定結果に基づく不足分の該キレート剤を増量して添加して混練し該処理を行う、第１〜３のいずれかに記載の飛灰の処理法である。
【００１５】
【発明の実施の形態】
キレート剤が添加された処理飛灰のサンプリング試料から得られる溶出液については、キレート剤がある一定の添加量を超えて添加された場合では、測定される重金属濃度はほぼゼロ付近で一定となる。キレート剤添加量が不足の場合には重金属溶出の原因になるため再処理が必要であり、この再処理を省くためには、キレート剤が過剰サイドで添加されていれば良いが、大過剰となることは処理コストおよび資源浪費の観点から悪影響を与えるので好ましくない。
【００１６】
すなわち、金属含有溶液の滴下によって溶出液中における未反応キレート剤および溶出性の重金属の有無を評価することにより、大過剰もしくは不足する未反応キレート剤量を知ることができる。未反応キレート剤が過剰に存在する場合は、前記のように、溶出液中の重金属はほぼゼロである。したがって、過剰の未反応キレート剤の存在を証明、判定できれば、溶出液中の重金属濃度は基準値以下であることがいえる。また、未反応キレート剤の過剰量を判定および調整できれば、コスト削減につながる。すなわち、キレート剤添加量が大過剰と判定された場合には次ロットの飛灰処理に用いるキレート剤量を削減して混練処理を行なうことができる。
【００１７】
試験溶液となる金属含有溶液はその金属イオンが銅イオンであれば青色を呈するが、この金属含有溶液が添加される溶出液中に未反応キレート剤が残存していれば、そのキレート剤との反応で褐色の錯体が形成される。この場合、重金属の溶出は殆ど無い。すなわち、キレート剤の量が重金属不溶化に対して過剰であると判定できる。
【００１８】
ただし、未反応キレート剤の処理飛灰中における経時失活（消費）による、重金属の再溶出作用を考慮する場合、再溶出を防止するための褐色錯体の必要生成量は飛灰により異なる。従って、経時再溶出に耐えうる未反応キレート剤量は、未反応キレート剤量と経時重金属の溶出値との関係を予め調査した統計的データから決定しておく。これは、飛灰の成分等の性状により異なるほか、他の要因として飛灰の保管環境（温度、湿度、その他）なども考慮されなければならないからである。
【００１９】
本発明における飛灰の処理工程の概略は次のとおりである。
焼却炉等においてごみ等を焼却した際に飛散するいわゆる飛灰は、電気集塵機やバグフィルターにて捕集され、飛灰ホッパーに一次貯留される。この飛灰は一般に乾燥した粉体である。この飛灰をサンプリングしてＪＩＳ法に則して重金属成分の定性分析または定量分析を行なう。飛灰は飛灰ホッパーからコンベアーによって混練機に搬送し、前記重金属成分の分析結果値に基づいた量のキレート剤および加湿水を添加して混練する。
【００２０】
混練作業の終了後、処理飛灰はコンテナに移す。この処理飛灰のサンプリングは飛灰のコンテナロット毎に行ない、得られたサンプリング試料から前記したように溶出液を得、前記金属含有溶液の滴定手法による本発明の簡易分析を行ない、溶出液中の金属イオンの有無および未反応キレート剤の量または有無の判定を行なう。この間、処理飛灰は分析結果の判定待ちの状態にある。判定結果で、搬出基準を達成しなかった処理飛灰については、判定結果に基づく不足分のキレート剤を添加して混練し、無害化処理を行うことになる。搬出基準を達成した処理飛灰については、その後、ＪＩＳ法に則して分析用サンプル液の調製と機器分析からなる出荷検査を行った後、最終処分場などに移送する。
なお、前記出荷検査は、経時変化を含めて処理飛灰が埋立基準を達成するものであることを対外的に証明するための出荷時の必要な分析作業である。
【００２１】
前記の混練処理後の処理飛灰サンプリング試料によって溶出液を得る手順は、前記環境省告示１３号法試験に則ったものである。すなわち、処理飛灰のサンプル５０ｇを取り、ｐＨ５．８〜６．３に調製された５００ｍｌの脱塩水を加え、常温、常圧において、振幅４〜５ｃｍ、２００ｒｐｍの振とう数で連続６時間振とうする。振とう後は、孔径１μｍのグラスファイバーフィルターペーパー（ＧＦＰということがある。）で吸引濾過した溶出液を抽出する。
【００２２】
さらに、着色変化を利用した判定検査においては、抽出された溶出液に硝酸銅溶液など着色銅含有溶液を滴下し、溶出液が青色に着色したままのサンプル液はキレート剤添加量が不十分であると判定する。この場合、既知の濃度のキレート剤を溶出液に褐色になるまで添加し、その後、銅含有液を添加し、溶出液の色が褐色になった時点での銅含有溶液の添加量により不足キレート剤量が推算される。
【００２３】
一方、溶出液が褐色に変色した場合は、この液を濾過し銅含有溶液を更に添加し、青色になるまで濾過および銅含有溶液の添加操作を繰り返す。添加した銅溶液の量から添加されたキレート剤のうちの未反応キレート剤量を判定する。未反応キレート剤量が不十分である場合には重金属の再溶出が起こりうるため再処理が必要となり、未反応キレート剤判定量から再処理に必要なキレート剤量を推算する。
【００２４】
【実施例】
以下に本発明の実施例を示すが、本発明の技術的範囲はこれらの実施例の記載によって限定されるものではない。
【００２５】
［実施例１］ キレート剤の必要添加量は主に鉛と銅の含有量に比例することが知られている。鉛および銅の含有量が既知の飛灰を混練機に移し、鉛および銅の含有量を基に予め算出した必要添加設定量の高分子液体キレート剤（ジチオカルバミン酸基を有する有機化合物）と水とを加えて混練し、キレート処理を行なった。その後養生コンテナに移し、養生コンテナを変えて１０ヶ所から処理飛灰Ａをサンプリングした。このサンプリングした処理飛灰Ａからそれぞれ５０ｇ取り、ｐＨ５．８〜６．３に調製された５００ｍｌの脱塩水を加え、常温、常圧において、振幅４〜５ｃｍ、２００ｒｐｍの振とう数で連続６時間振とうした。振とう後は、孔径１μｍのＧＦＰで吸引濾過し、溶出液を抽出した。
【００２６】
この溶出液に青色の硝酸銅溶液を添加して、銅−キレート錯体形成による褐色を呈さなくなるまでの硝酸銅溶液の添加量から、１０サンプルとも未反応キレート剤量は適量であることが分かり、重金属は不溶化されており、溶出の無いことが確認できた。この時溶出液抽出後に硝酸銅溶液の添加による判定に要した時間は１０サンプルで１５分であった。経時再溶出に耐えうる未反応キレート剤量は、未反応キレート剤量と経時重金属の溶出値との関係を予め調査した統計的データから決定しておく。
【００２７】
この後、処分場に移送する前に、埋立基準値を実際に達成しているのを証明するため、出荷検査として鉛、カドミウム等所定の重金属元素についてＪＩＳ法に準じて発光分析により定量分析を行なった。
【００２８】
この分析用サンプル液の液調製は、次のようにして行なった。
すなわち、溶出液５００ｍｌに塩酸を２ｍｌ、硝酸を１ｍｌ添加し、約１０分加熱後冷却し分液漏斗で濾過した。その液にクエン酸水素アンモニウム（１０％）１０ｍｌ、指示薬メタクレゾールパープル（０．１％）２、３滴、ＮＨ４ＯＨ（１＋１）で中和してｐＨ７．５〜９．０（青〜紫色）にする。さらに着色がピンク色から黄色、薄水色になった後、過剰にＮＨ４ＯＨを４ｍｌ加える。その後ＤＤＴＣ（ジエチルジチオカルバミン酸（ソーダ）、１％）を５ｍｌ添加し、手で振とうする。次いでＭＩＢＫ（メチルイソブチルケトン）約１０ｍｌを滴下して水２０ｍｌを加えて約２分間振とうし、その後分層するまでしばらく待つ。水層を捨て、ＭＩＢＫ層にＨＣｌ（１．５Ｎ）を正確に１０ｍｌ加えて約２分間振とうし、その後分層するまでしばらく待つ。次いで、ＭＩＢＫ層を捨て水層（ＨＣｌ）を三角フラスコに抜き取って分析用サンプル液とした。
【００２９】
その分析用サンプル液について原子吸光分析した結果、重金属は検出されなかった。なお、このサンプル液調製を含めて分析に要した時間は９０分であった。実施例１の結果を表１に記載した。
【００３０】
［実施例２］ 実施例１と別ロットの鉛および銅の含有量が既知の飛灰を混練機に移し、予め算出した必要設定量の高分子液体キレート剤（ジチオカルバミン酸基を有する有機化合物）と水とを加えて混練し、キレート処理を行なった。その後養生コンテナに移し、養生コンテナを変えて１０ヶ所から処理飛灰Ｂをサンプリングした。このサンプリングした処理飛灰Ｂからそれぞれ５０ｇ取り、ｐＨ５．８〜６．３に調製された５００ｍｌの脱塩水を加え、常温、常圧において、振幅４〜５ｃｍ、２００ｒｐｍの振とう数で連続６時間振とうした。振とう後は、孔径１μｍのＧＦＰで吸引濾過し、溶出液を抽出した。
【００３１】
この溶出液に青色の硝酸銅溶液を添加して、銅−キレート錯体形成による褐色を呈さなくなるまでの硝酸銅溶液の添加量から、１０サンプルとも未反応キレート剤残量は重金属の経時再溶出に対して不足であることが分かり、硝酸銅溶液の添加量を基に必要なキレート剤量を算出し、処理飛灰Ｂの再度無害化処理を実施した。また、次ロットの飛灰（実施例３）へ添加するキレート剤の添加量設定値についても、鉛および銅含有量から算出したものに対し硝酸銅溶液の判定量に基づく必要量を増量した。
【００３２】
再処理を行なった処理飛灰Ｂを１０ヶ所からサンプリングした。これらの溶出液に青色の硝酸銅溶液を添加して、銅−キレート錯体形成による褐色が消失して青色を呈するまでの硝酸銅溶液の添加量から、１０サンプルとも未反応キレート剤量は重金属の経時再溶出に対して十分であることが分かり、重金属は不溶化されており、溶出の無いことが確認できた。
【００３３】
この後、処分場に移送する前に、埋立基準値を実際に達成しているのを証明するため、出荷検査として鉛、カドミウム等所定の重金属元素についてＪＩＳ法に準じて原子吸光分析により定量分析を行なったところ、重金属の溶出は殆ど見られず埋立基準を十分に達成していることが分かった。
実施例２の結果を表１に記載した。
【００３４】
［実施例３］ さらに実施例１、２と別ロットの飛灰について実施例２に基づきキレート剤添加量を増量して無害化処理を行なった処理飛灰Ｃを１０ヶ所からサンプリングした。実施例１、２と同様に、これらの溶出液に青色の硝酸銅溶液を添加して銅−キレート錯体形成による褐色が呈さなくなるまでの硝酸銅溶液の添加量から、１０サンプルとも未反応キレート剤残量は重金属の経時再溶出に対して十分であることが分かり、重金属は不溶化されており、溶出の無いことが確認できた。
【００３５】
この後、処分場に移送する前に、埋立基準値を実際に達成しているのを証明するため、出荷検査として鉛、カドミウム等所定の重金属元素についてＪＩＳ法に準じて原子吸光分析により定量分析を行なったところ、重金属の溶出は殆ど見られず埋立基準を十分に達成していることが分かった。
実施例３の結果を表１に記載した。
【００３６】
［比較例１］ 実施例１の処理飛灰Ａについて、実施例１と同様に溶出液を抽出した。その後ＪＩＳ法に準じて原子吸光分析による重金属の定量分析を行なった。この時の分析用サンプル液の調製は、実施例１の処分場搬出前の出荷検査における原子吸光分析用サンプル液の調製手順によって行なった。
【００３７】
この結果、いずれのサンプルとも重金属はほぼゼロに近い値を示し、十分に環境基準値を達成していたが、この時、溶出液からの分析用サンプル液の調製から分析試験の終了まで、１０サンプルで３時間を要した。
【００３８】
この後、処分場に運ぶ前に、環境基準値を具体的に達成しているのを証明するため、出荷検査として前記の溶出液から分析用サンプル液を調製し、所定の重金属元素についてＪＩＳ法に準じて原子吸光分析により定量分析を行なった。その結果を表１に記載した。
【００３９】
【表１】
所定重金属は全て検出されなかったが、この出荷検査では、分析用サンプル液の調製から原子吸光分析の終了まで１時間を要した。また、この処理飛灰Ａが経時重金属溶出に対して未反応キレート剤が十分に残っているかは不明であった。
【００４１】
【発明の効果】
以上のように、本発明で示した無害化処理工程において未反応のキレート剤量を簡易的かつ定量的に判定できる方法を用いることにより、従来の分析に要する時間、コスト、手間およびキレート剤使用量を大幅に削減できる。また、この工程で原子吸光度測定装置や原子吸光分析装置などの大掛かりな測定装置を利用すること無く、振盪機、濾過器、銅含有溶液など最低限の機材と試薬により前記判定が可能になる上に、キレート剤添加量の不足した処理飛灰サンプルを簡単に分別できる。特に、検体サンプル数が多くても容易に適用できるので、従来必要とした全工程における原子吸光法や原子吸光分析法などによる正規の分析を行なう回数を大幅に低減することが可能になり、飛灰処理において時間や費用を削減することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for insolubilizing fly ash containing lead, cadmium, and other heavy metals (these metals are collectively referred to simply as heavy metals) using a chelating agent. The result is determined to improve the efficiency of the processing operation and optimize the amount of the chelating agent added.
[0002]
[Prior art]
When waste such as industrial waste and general waste is incinerated or heated and oxidized, ash containing heavy metals and the like is generated in the furnace and in exhaust gas from the furnace along with the reaction. These ashes (collectively referred to as fly ash) contain the above-mentioned various heavy metals and the like. For example, heavy metals such as lead and cadmium may pollute the environment. Neutralization treatment, heavy metal insolubilization / detoxification treatment, etc. are performed.
[0003]
Conventionally, heavy metals in fly ash have been insolubilized and made harmless by solidifying with cement or asphalt, by neutralizing carbonic acid to form insoluble carbonates with carbon dioxide gas, and by solidifying into slag with a reduction melting furnace. And a method of insolubilization with an organic polymer chelating agent.
[0004]
Among them, the solidification method using cement or asphalt may increase the volume by about 20 to 30%, may cause re-elution due to acid rain, and the like, and furthermore, a carbonation method using carbon dioxide gas or a slag conversion method using a melting furnace. In this case, the processing equipment becomes large-scale and the equipment cost increases. For this reason, many processing methods using organic polymer-based chelating agents, which are relatively advantageous in processing equipment, process management, processing cost, and the like, are being implemented.
[0005]
In the treatment with the above chelating agent, a chelating agent and water are added according to the properties of the fly ash, the heavy metal content, the heavy metal elution concentration, and the like, and kneaded to obtain the treated fly ash. The treated fly ash in which the heavy metal is surely insolubilized by this treatment and there is no danger of elution of the heavy metal is transferred to a final disposal site, where it is subjected to landfill disposal and the like.
[0006]
Whether or not the heavy metal in the treated fly ash has been surely insolubilized can be confirmed by analyzing the heavy metal concentration in the eluate of the treated fly ash. That is, based on the Ministry of the Environment Notification No. 13 test, treated fly ash is mixed with a solvent in the neutral region to obtain an eluate, and then this eluate is acid-dissolved based on a factory drainage test method (JIS K 0102). After that, an eluate for analysis is obtained through steps such as pH adjustment, complex formation, separation extraction with an organic solvent, and back extraction with hydrochloric acid. Further, the eluate is quantified for heavy metal concentration by a quantitative analysis method based on JIS such as atomic absorption spectrometry, ICP emission spectrometry, etc., and whether the heavy metal concentration is below a landfill standard value, that is, insolubilization by a chelating agent is ensured. Is determined.
[0007]
When the heavy metal concentration in the eluate is determined to be equal to or less than the reference value, the processing fly ash of the processing lot is shipped to the final disposal site. If the concentration of heavy metals in the eluate exceeds the standard value, the processing fly ash of the processing lot is suspended from shipment, and the chelating agent is added and reprocessed, and the amount of heavy metal eluted into the eluate is the standard value. It is repeated as follows.
[0008]
According to the provisions of the Ministry of the Environment Notification No. 13 test, the sample solution used to obtain the eluate may be “a cinder, sludge, ore, dust, or soot or the like for which landfill disposal (excluding sea surface landfill disposal) is to be performed. In the case where the industrial waste is treated for disposal, a sample (unit: gram) and a solvent (sodium hydroxide or hydrochloric acid are added to pure water to obtain a hydrogen ion concentration index of 5.8 or more; 3 or less) (unit: milliliter) at a weight / volume ratio of 10%, and the mixed liquid is 500 ml or less. " For the dissolution operation, refer to "A shaking machine at normal temperature (approximately 20 degrees Celsius) and normal pressure (approximately 1 atm) (shaking frequency is about 200 times per minute in advance, and the shaking width is 4 cm or more and 5 cm Less than And shake it continuously for 6 hours. "
[0009]
[Problems to be solved by the invention]
However, conventionally, a sufficient amount of the chelating agent was added to the treated fly ash that had been kneaded and treated with the chelating agent, and whether or not the heavy metal was surely insolubilized was determined by determining the elution value of the heavy metal in the entire treated fly ash. It was necessary to measure the eluate according to the instrumental analysis method of JIS. In addition, there is a situation in which the necessity of reprocessing is determined based on the measured value, and the excess or deficiency of the chelating agent is determined.
[0010]
Conventionally, in the processing step, when confirming the concentration of heavy metals in the eluate by instrumental analysis methods such as JIS atomic absorption method and ICP emission analysis method, there are many procedures until preparing a sample solution for analysis from the eluate, There is a disadvantage that time and analysis costs are large. In addition, in order to apply the JIS equipment analysis method to all the heavy metal concentration confirmation work including the case of reprocessed fly ash, it is necessary to coordinate and manage such equipment, and the analysis is required. There was a problem that time and labor were large.
[0011]
Furthermore, the eluate considers the difference in the sampling place of the processing fly ash and the processing time (kneading, curing), and the like. Also, when the analysis of the eluate of the processing fly ash determines that the chelate treatment is insufficient. In consideration of the above, the time and cost burden for preparing and analyzing the required sample solution are significantly increased, and the required amount of analysis may exceed the processing capacity of the facility, and may affect the throughput of fly ash. Also, it was unknown exactly how much the chelating agent used in the heavy metal detoxification treatment was excessive.
[0012]
Therefore, in view of the above problems, it is an object of the present invention to easily determine the presence or absence of elution of heavy metals in treated fly ash using substitute properties during the heavy metal insolubilization treatment with a fly ash chelating agent. To reduce the time and cost burden required for instrumental analysis and the preparation of a sample solution for analysis for the purpose, to improve the efficiency of the heavy metal insolubilization treatment and reduce the analysis cost, and to re-elute the heavy metal An object is to reduce the cost of the chelating agent by optimizing the excessive addition of the chelating agent necessary for prevention.
[0013]
[Means for Solving the Problems]
In order to solve this point, the present inventor has found a method of treating a metal-containing solution as a reagent and quantitatively determining an unreacted chelating agent in an eluate. That is, first, the present invention is a treatment method in which a chelating agent is added to a fly ash containing a heavy metal and kneaded to insolubilize the heavy metal in the fly ash, and a solvent is added to the fly ash after the treatment. In the eluate from the slurry to be added, a test solution containing a metal ion is added, and the color of the eluate before and after the addition of the test solution is no longer changed by the chelating agent remaining in the eluate. A method for treating fly ash, wherein the amount of the chelating agent remaining in the eluate is determined based on the amount of the test solution required for the method. 2. The method for treating fly ash according to claim 1, which corresponds to the amount of the unreacted chelating agent remaining therein.
[0014]
Next, the present invention thirdly determines that the amount of the chelating agent added in the treatment is insufficient based on the amount of the test solution added, and then the fly ash after the treatment has an insufficient amount of the chelating agent based on the determination result. Is further added and kneaded and the treatment is continued, the fly ash treatment method according to the first or the second, and fourthly, an insufficient amount of the chelating agent in the treatment depending on an amount of the test solution added. The method according to any one of claims 1 to 3, wherein after the determination, the insufficient amount of the chelating agent based on the determination result is added to the fly ash of the next lot to be processed and added, and the mixture is kneaded to perform the processing. Ash treatment method.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
For the eluate obtained from a sample of the treated fly ash to which the chelating agent has been added, when the chelating agent is added in a certain amount, the measured heavy metal concentration is constant at almost zero. . If the amount of the chelating agent is insufficient, re-treatment is necessary because it causes heavy metal elution.In order to eliminate this re-treatment, it is sufficient that the chelating agent is added on the excess side. This is not preferable because it adversely affects processing costs and waste of resources.
[0016]
That is, by evaluating the presence or absence of the unreacted chelating agent and the leaching heavy metal in the eluate by dropping the metal-containing solution, it is possible to know the amount of the unreacted chelating agent in a large excess or shortage. If the unreacted chelating agent is present in excess, as described above, the heavy metal in the eluate is almost zero. Therefore, if the presence of the excess unreacted chelating agent can be proved and determined, it can be said that the heavy metal concentration in the eluate is below the reference value. Further, if the excess amount of the unreacted chelating agent can be determined and adjusted, the cost can be reduced. That is, when it is determined that the added amount of the chelating agent is excessively large, the kneading process can be performed by reducing the amount of the chelating agent used for the fly ash processing of the next lot.
[0017]
The metal-containing solution serving as the test solution exhibits a blue color if the metal ion is copper ion, but if an unreacted chelating agent remains in the eluate to which the metal-containing solution is added, the chelating agent may be used. The reaction forms a brown complex. In this case, there is almost no elution of heavy metals. That is, it can be determined that the amount of the chelating agent is excessive with respect to the heavy metal insolubilization.
[0018]
However, in consideration of the re-elution effect of heavy metals due to deactivation (consumption) of unreacted chelating agent in the treated fly ash over time, the required amount of the brown complex to prevent re-elution differs depending on the fly ash. Therefore, the amount of the unreacted chelating agent that can withstand re-elution with time is determined from statistical data obtained by previously examining the relationship between the amount of the unreacted chelating agent and the elution value of heavy metal over time. This is because it depends on the properties of the fly ash components and the like, and other factors such as the storage environment (temperature, humidity, etc.) of the fly ash must be considered.
[0019]
The outline of the process for treating fly ash in the present invention is as follows.
So-called fly ash that is scattered when incinerating garbage or the like in an incinerator or the like is collected by an electric dust collector or a bag filter, and is temporarily stored in a fly ash hopper. This fly ash is generally a dry powder. The fly ash is sampled and subjected to qualitative or quantitative analysis of heavy metal components according to the JIS method. Fly ash is conveyed from a fly ash hopper to a kneading machine by a conveyor, and a chelating agent and humidifying water in an amount based on the analysis result of the heavy metal component are added and kneaded.
[0020]
After the completion of the kneading operation, the treated fly ash is transferred to a container. The sampling of the treated fly ash is performed for each container lot of the fly ash, an eluate is obtained from the obtained sampling sample as described above, and the simple analysis of the present invention is performed by the titration method of the metal-containing solution. The presence or absence of metal ions and the amount or presence of unreacted chelating agent are determined. During this time, the processing fly ash is in a state of waiting for determination of the analysis result. As for the processing fly ash that did not achieve the carry-out standard in the determination result, a shortage chelating agent based on the determination result is added and kneaded to perform detoxification processing. The processed fly ash that has achieved the carry-out standard is then subjected to a shipping inspection consisting of preparation of a sample liquid for analysis and equipment analysis in accordance with the JIS method, and then transferred to a final disposal site.
Note that the shipping inspection is a necessary analysis at the time of shipping for externally proving that the treated fly ash achieves the landfill standard, including changes over time.
[0021]
The procedure for obtaining the eluate from the sampled fly ash sample after the kneading process is in accordance with the aforementioned test method 13 of the Ministry of the Environment. That is, a 50 g sample of the treated fly ash was taken, 500 ml of demineralized water adjusted to pH 5.8 to 6.3 was added, and the mixture was shaken at ordinary temperature and ordinary pressure with an amplitude of 4 to 5 cm and a shaking number of 200 rpm for 6 hours. I will. After shaking, the eluate obtained by suction filtration using a glass fiber filter paper (sometimes referred to as GFP) having a pore size of 1 μm is extracted.
[0022]
Furthermore, in the judgment test using the change in coloration, a colored copper-containing solution such as a copper nitrate solution is dropped into the extracted eluate, and the sample solution in which the eluate is colored blue has insufficient chelating agent addition amount. It is determined that there is. In this case, a chelating agent of a known concentration is added to the eluate until it becomes brown, then a copper-containing solution is added, and the amount of the copper-containing solution at the time when the color of the eluate turns brown becomes insufficient chelation. The dose is estimated.
[0023]
On the other hand, if the eluate turns brown, this solution is filtered, a copper-containing solution is further added, and the filtration and addition of the copper-containing solution are repeated until the solution turns blue. The amount of the unreacted chelating agent among the added chelating agents is determined from the amount of the added copper solution. When the amount of the unreacted chelating agent is insufficient, re-elution of the heavy metal may occur, so that reprocessing is necessary. The amount of the chelating agent necessary for the reprocessing is estimated from the unreacted chelating agent determination amount.
[0024]
【Example】
Examples of the present invention will be described below, but the technical scope of the present invention is not limited by the description of these examples.
[0025]
[Example 1] It is known that the required addition amount of a chelating agent is mainly proportional to the contents of lead and copper. Fly ash with a known content of lead and copper is transferred to a kneader, and a required amount of a polymer liquid chelating agent (an organic compound having a dithiocarbamic acid group) and a water are added in a required addition amount calculated in advance based on the contents of lead and copper. Was added and kneaded, and a chelating treatment was performed. After that, it was transferred to a curing container, and the treated fly ash A was sampled from 10 places while changing the curing container. 50 g of each of the sampled treated fly ash A is taken, 500 ml of demineralized water adjusted to pH 5.8 to 6.3 is added, and at room temperature and pressure, amplitude is 4 to 5 cm, shaking number of 200 rpm for 6 hours continuously. Shake. After shaking, suction filtration was performed with GFP having a pore size of 1 μm to extract an eluate.
[0026]
A blue copper nitrate solution was added to this eluate, and the amount of the copper nitrate solution added until the copper-chelate complex did not exhibit a brown color showed that the amount of the unreacted chelating agent was an appropriate amount for all 10 samples. The heavy metal was insolubilized and no elution was confirmed. At this time, the time required for the determination by the addition of the copper nitrate solution after the extraction of the eluate was 15 minutes for 10 samples. The amount of the unreacted chelating agent that can withstand the re-elution with time is determined from statistical data obtained by examining the relationship between the amount of the unreacted chelating agent and the elution value of heavy metal with time.
[0027]
After that, before transfer to the disposal site, quantitative analysis by emission analysis according to the JIS method for specified heavy metal elements such as lead and cadmium as a shipping inspection to prove that the landfill standard value has actually been achieved. Done.
[0028]
The preparation of the sample liquid for analysis was performed as follows.
That is, 2 ml of hydrochloric acid and 1 ml of nitric acid were added to 500 ml of the eluate, heated for about 10 minutes, cooled, and filtered with a separating funnel. The solution was neutralized with 10 ml of ammonium hydrogen citrate (10%), a few drops of indicator meta-cresol purple (0.1%), and NH 4 OH (1 + 1) to pH 7.5 to 9.0 (blue to purple). ). Further, after the color changes from pink to yellow to light blue, 4 ml of NH 4 OH is added in excess. Thereafter, 5 ml of DDTC (diethyldithiocarbamic acid (soda), 1%) is added, and the mixture is shaken by hand. Next, about 10 ml of MIBK (methyl isobutyl ketone) is added dropwise, 20 ml of water is added, and the mixture is shaken for about 2 minutes. Discard the aqueous layer, add exactly 10 ml of HCl (1.5N) to the MIBK layer, shake for about 2 minutes, and then wait for a while until separating. Next, the MIBK layer was discarded, and the aqueous layer (HCl) was withdrawn into an Erlenmeyer flask to prepare a sample liquid for analysis.
[0029]
As a result of atomic absorption analysis of the sample solution for analysis, no heavy metal was detected. The time required for the analysis including the preparation of the sample solution was 90 minutes. Table 1 shows the results of Example 1.
[0030]
[Example 2] Fly ash of a different lot from Example 1 with a known lead and copper content was transferred to a kneader, and a required amount of a polymer liquid chelating agent (an organic compound having a dithiocarbamic acid group) calculated in advance and required. And water were added and kneaded to perform a chelate treatment. After that, it was transferred to a curing container, and the treated fly ash B was sampled from 10 places while changing the curing container. 50 g of each of the sampled treated fly ash B was taken, 500 ml of demineralized water adjusted to pH 5.8 to 6.3 was added, and at normal temperature and normal pressure, amplitude 4 to 5 cm, shaking number of 200 rpm, continuous 6 hours Shake. After shaking, the solution was subjected to suction filtration with GFP having a pore size of 1 μm to extract an eluate.
[0031]
A blue copper nitrate solution was added to this eluate, and from the amount of the copper nitrate solution added until the brown color due to the formation of the copper-chelate complex was no longer present, the remaining amount of the unreacted chelating agent in all 10 samples was due to the re-elution of heavy metals with time. On the other hand, it was found that the amount was insufficient, and the necessary amount of the chelating agent was calculated based on the addition amount of the copper nitrate solution, and the detoxification treatment of the treated fly ash B was performed again. Also, as for the set amount of the chelating agent to be added to the fly ash of the next lot (Example 3), the required amount based on the determination amount of the copper nitrate solution was increased from that calculated from the lead and copper contents.
[0032]
The reprocessed fly ash B was sampled from 10 locations. A blue copper nitrate solution was added to these eluates, and from the amount of the copper nitrate solution added until the brown color disappeared due to the formation of the copper-chelate complex and turned blue, the amount of the unreacted chelating agent in all 10 samples was heavy metal. It was found that it was sufficient for re-elution with time, and it was confirmed that the heavy metal was insolubilized and there was no elution.
[0033]
After that, before transferring to the disposal site, quantitative analysis of specified heavy metal elements such as lead and cadmium by atomic absorption spectrometry according to JIS method as a shipping inspection to prove that the landfill standard value has actually been achieved. As a result, the elution of heavy metals was hardly observed, and it was found that the landfill standard was sufficiently achieved.
Table 1 shows the results of Example 2.
[0034]
[Example 3] Further, with respect to fly ash of a different lot from Examples 1 and 2, treated fly ash C obtained by increasing the amount of a chelating agent and detoxifying it based on Example 2 was sampled from 10 places. In the same manner as in Examples 1 and 2, a blue copper nitrate solution was added to these eluates, and the amount of the copper nitrate solution added until the brown color due to the formation of the copper-chelate complex was not exhibited. It was found that the remaining amount was sufficient for heavy metal re-elution with time, and it was confirmed that the heavy metal was insolubilized and no elution was performed.
[0035]
After that, before transferring to the disposal site, quantitative analysis of specified heavy metal elements such as lead and cadmium by atomic absorption analysis according to the JIS method as a shipping inspection to prove that the landfill standard value has actually been achieved. As a result, the elution of heavy metals was hardly observed, and it was found that the landfill standard was sufficiently achieved.
Table 1 shows the results of Example 3.
[0036]
Comparative Example 1 An eluate was extracted from the treated fly ash A of Example 1 in the same manner as in Example 1. Thereafter, quantitative analysis of heavy metals was performed by atomic absorption analysis according to the JIS method. At this time, the preparation of the sample solution for analysis was performed according to the procedure for preparing the sample solution for atomic absorption analysis in the shipping inspection before carrying out of the disposal site in Example 1.
[0037]
As a result, in all samples, the heavy metal showed a value close to zero, and sufficiently achieved the environmental standard value. At this time, from the preparation of the sample solution for analysis from the eluate to the end of the analysis test, 10 minutes. The sample took 3 hours.
[0038]
After that, before transporting to the disposal site, in order to prove that the environmental standard values have been specifically achieved, a sample solution for analysis is prepared from the above eluate as a shipping inspection, and the specified heavy metal element is subjected to the JIS method. Quantitative analysis was performed by atomic absorption spectrometry according to the method described in Example 1. The results are shown in Table 1.
[0039]
[Table 1]
Although all the predetermined heavy metals were not detected, in this shipping inspection, it took one hour from preparation of the sample solution for analysis to completion of the atomic absorption analysis. In addition, it was unknown whether the treated fly ash A had a sufficient amount of unreacted chelating agent remaining with the elution of heavy metals over time.
[0041]
【The invention's effect】
As described above, by using a method that can easily and quantitatively determine the amount of the unreacted chelating agent in the detoxification treatment step shown in the present invention, the time, cost, labor, and use of the chelating agent required for the conventional analysis are determined. The amount can be greatly reduced. Further, in this step, without using a large-scale measuring device such as an atomic absorption spectrometer or an atomic absorption analyzer, the determination can be made with a minimum of equipment and reagents such as a shaker, a filter, and a copper-containing solution. Furthermore, the treated fly ash sample with an insufficient amount of the chelating agent can be easily separated. In particular, since it can be easily applied even when the number of sample samples is large, it is possible to greatly reduce the number of times of normal analysis, such as atomic absorption spectrometry or atomic absorption spectrometry, in all the steps required conventionally, and to reduce the number of times. Time and cost can be reduced in ash processing.
Claims (4)
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2009229146A (en) * | 2008-03-19 | 2009-10-08 | Oriental Giken Kogyo Kk | Method and device for determining proper addition amount of fixing agent for fixing heavy metal in incineration fly ash |
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| JP2009229146A (en) * | 2008-03-19 | 2009-10-08 | Oriental Giken Kogyo Kk | Method and device for determining proper addition amount of fixing agent for fixing heavy metal in incineration fly ash |
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