JP3907949B2 - Determination method of optimum addition rate of heavy metal elution inhibitor to incineration fly ash and treatment method of incineration fly ash - Google Patents
Determination method of optimum addition rate of heavy metal elution inhibitor to incineration fly ash and treatment method of incineration fly ash Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、ごみ焼却炉などの各種焼却炉やボイラ等の燃焼炉から排出される飛灰及び焼却灰（以下、これらを併せて「焼却飛灰」と称する）の重金属溶出防止処理において用いる液体キレート剤の最適添加率の決定方法、並びにかかる方法によって決定された最適添加率に基づいて焼却飛灰を処理する方法に関する。
【０００２】
【従来の技術】
ごみ焼却炉などの各種焼却炉やボイラ等の燃焼炉から排出される焼却飛灰には、鉛、カドミウム、クロム、水銀、亜鉛、銅等の人体に有害な重金属類が高濃度に含有されている。これらは雨水等の環境水と接触すると溶出を起こし、土壌や地下水、河川、海水等を汚染する。したがって、焼却飛灰からのこれらの重金属類の溶出を防止することが必要である。
【０００３】
従来、焼却炉から排出される焼却飛灰中の重金属類の処理方法として、焼却飛灰をジチオカルバミン酸塩などの液体キレート剤に代表される重金属溶出防止剤で処理する方法が採用されている。このような液体キレート剤による焼却飛灰の処理においては、まず実験室並びに実施設において、焼却飛灰に対して種々の添加率で液体キレート剤を加えて数回試験を行い、その結果をもとに重金属類の埋立基準値を満たす添加率をもって最適添加率としていた。
【０００４】
【発明が解決しようとする課題】
しかしながら、焼却飛灰中の重金属類の濃度は一定ではなく、時々刻々と、燃焼条件やごみの質等にも影響されて変動している。したがって、上記で決定された最適添加率で重金属溶出防止剤を加えた場合、実際の処理時においては必要量以上の薬剤が加えられている可能性が極めて高く、薬剤費等のランニングコストの増大につながっている。
【０００５】
したがって、焼却飛灰処理の現場で簡便に焼却飛灰中の重金属濃度を測定して、その濃度に見合った最適の重金属溶出防止剤添加量を決定することができれば、効率的に焼却飛灰からの重金属の溶出を防止することができ、コスト的にも極めて有利である。
【０００６】
【課題を解決するための手段】
本発明者らは、ストーカ炉及び流動床炉から排出された焼却飛灰の３０検体ずつ、合計６０検体について調査を行った結果、焼却飛灰中の鉛含有量と、重金属溶出防止に必要な薬剤の添加率との間に、強い相関関係があることを見出した。この結果を図１及び図２に示す。図１はストーカ炉に関して得られた結果を示す図であり、図２は流動床炉に関して得られた結果を示す図である。ここで、焼却飛灰中の鉛含有量の値は、「環境庁水質保全局水質管理課編底質調査方法」に基づく精密測定法（以下、従来法という）によって測定された値である。また、必要薬剤添加率の値は、当該焼却飛灰試料に種々の量の重金属溶出防止剤を加えて処理を行なって、それぞれの場合の鉛の溶出濃度を測定することによって、薬剤添加量と鉛溶出濃度との関係図を作成して、この関係図に基づき、鉛の溶出濃度が環境庁告示第１３号或いは総理府令第５号で定められている埋立基準値である０．３(mg/L)以下となる薬剤の添加率を求めたものである。なお、図１及び図２の作成において、重金属溶出防止剤としてはジエチルジチオカルバミン酸カリウムの５０％水溶液を用いた。
【０００７】
図１及び図２に示されている相関関係から、焼却飛灰中の鉛の含有量が分かれば、最適な薬剤添加率を決定することができると考えられる。しかしながら、上述の従来法による鉛含有量の定量は、焼却飛灰試料を王水、硝酸、塩酸で逐次熱抽出して鉛を溶出させるというもので、一検体あたり凡そ２０時間の分析時間を必要とする。このため、短時間で焼却飛灰中の鉛含有量を定量することができない。これでは焼却飛灰を排出する燃焼炉の現場において焼却飛灰中の鉛濃度を測定し、その値に基づいて薬剤添加率を決定するということができない。
【０００８】
そこで、まず本発明者らは、焼却飛灰中の鉛含有量を簡便に且つ迅速に定量する方法を見出すべく鋭意研究を行った結果、以下のような方法を見出した。即ち、本発明の第１の態様は、燃焼炉からの焼却飛灰をアルカリ水溶液と混合し、加熱して焼却飛灰中の鉛を溶出させ、得られた水溶液中の鉛濃度を測定することにより焼却飛灰中の鉛濃度を算出することを特徴とする、焼却飛灰中の鉛の濃度を測定する方法に関する。
【０００９】
【発明の実施の形態】
以下において、本発明に係る焼却飛灰中の鉛含有量を測定する方法について説明する。
【００１０】
排ガス処理には一般に乾式処理（消石灰噴霧）が用いられているので、焼却飛灰の殆どはアルカリ性を示す。また、湿式処理を採用している施設においては、焼却飛灰は中性〜アルカリ性を示す。これらの焼却飛灰を重金属溶出防止剤である液体キレート剤を用いて処理すると、市場にある液体キレート剤の殆どがｐＨ＝１２以上のアルカリ性を示すため、処理された焼却飛灰はアルカリ性となる。したがって、環境庁告示１３号法による重金属溶出試験を行うと、溶出液はｐＨ＝１２前後となり、処理対象となる重金属類の殆どは両性金属である鉛となる。
【００１１】
本発明に係る焼却飛灰中の鉛含有量の測定方法においては、まず焼却飛灰をアルカリ性化合物の水溶液中に混合して、加熱することによって焼却飛灰から鉛を溶出させる。
【００１２】
ここで、「溶出」という現象は、固形物と液体とが接触して固形物中の可溶出成分が液体（溶媒）中に溶け出してくることを言う。しかしながら、この現象は、可溶出成分の溶媒への溶解度が大きな制限因子となるため、固形物に対する液体の量が少なすぎると、目的とする成分は全て溶出しきれない。また、共存物質による影響も極めて大きいことが知られている。
【００１３】
上述の環境庁告示１３号法では、固液比１：１０で溶出試験を行っているが、この固液比では共存物質による溶解度への影響が非常に大きく、固形物からの可溶出成分の溶出量の判断には不十分である、ということが当該技術において既知となっている。これに対して、オランダの公定試験法に見られるような固液比１：１００の溶出試験では、共存物質による溶解度への影響が小さく、固形物からの可溶出成分の溶出量を比較的正確に判断できるということが知られている。したがって、本発明に係る焼却飛灰中の鉛含有量の測定方法において、焼却飛灰からの鉛の溶出工程の際の焼却飛灰とアルカリ性化合物の水溶液との混合比率は、１：５０〜１０００、より好ましくは１：１００〜５００程度、例えば１：１００（重量比）とすることが好ましい。この目的で用いることのできるアルカリ性化合物としては、水酸化ナトリウム、炭酸ナトリウムなどを挙げることができる。また、用いるアルカリ性化合物水溶液の濃度は、鉛が溶出し易いアルカリ性条件を構築するためには、０．０１〜１０Ｎ、より好ましくは０．０５〜５Ｎ、例えば０．５Ｎであることが好ましい。アルカリ水溶液の濃度がこの範囲よりも高いと、アルカリ金属が鉛溶出の制限因子となる可能性もあり、更にアルカリ金属は鉛濃度測定の際に測定機器への妨害物質となる可能性もあるので好ましくない。
【００１４】
次に、鉛が溶出されたアルカリ水溶液中の溶解鉛濃度を定量する。この目的で用いることのできる鉛の定量法としては、フレーム原子吸光法、吸光光度法、ＩＣＰ発光分析法、イオン電極測定法などを挙げることができる。なお、フレーム原子吸光法による定量では、水溶液に硝酸を加えて系を０．１〜１mol/Lの硝酸酸性とする。また、ＩＣＰ発光分析法による定量では、水溶液に塩酸又は硝酸を加えて、系を０．１〜０．５mol/Lの塩酸又は硝酸酸性とする。吸光光度法及びイオン電極測定法による定量では、上述で得られた鉛含有アルカリ水溶液を、それぞれｐＨ９前後、ｐＨ４．５〜６．５程度に調整した後に分析にかけることができる。これらの定量分析法によって、水溶液中の溶解鉛濃度(mg/L)が得られる。なお、これらの定量分析を行うにあたっては、予め幾つかの既知濃度の鉛溶液の吸光度を測定して検量線を作成して、この検量線に基づいて水溶液試料中の溶解鉛濃度を算出する。
【００１５】
上記の溶出処理によって焼却飛灰中の鉛が全て溶出されたと考えると、得られた水溶液試料中の溶解鉛濃度(mg/L)を、焼却飛灰の希釈倍率に基づいて換算することによって、焼却飛灰中の鉛濃度(mg/kg)を算出することができる。
【００１６】
なお、上記の簡易法で求められる鉛濃度は、アルカリ溶出処理によって焼却飛灰中の鉛が全て溶出されたという前提に基づいた推定値である。したがって、より正確な焼却飛灰中の鉛濃度を求めるためには、測定対象の各焼却施設ごとに、同じ焼却飛灰試料について、本発明に係る簡易測定法と従来の精密測定法（例えば上述の環境庁規定の測定方法）とによって予め鉛濃度の測定値を求める予備試験を行って両者の値を対比することにより、本発明に係る簡易測定法で得られた鉛濃度の値から正確な鉛濃度を算出するための補正係数αを求めておくことが望ましい。
【００１７】
本発明によれば、このようにして、焼却飛灰中の鉛の濃度を、従来法に比べて極めて簡便且つ迅速な方法で測定することができる。このようにして測定された鉛濃度から、対象となる焼却施設に関して予め求めておいた鉛含有量と必要薬剤添加率との関係図に基づいて、重金属類の溶出防止処理に必要な溶出防止剤の添加率を決定し、これから求められた必要量の溶出防止剤を焼却飛灰に添加して溶出防止処理を行うことにより、過剰に溶出防止剤を用いることなく、極めて効率的に焼却飛灰からの重金属類の溶出防止処理を行うことができる。したがって、本発明の他の態様は、処理対象の燃焼炉について、予め、焼却飛灰中の鉛濃度と、焼却飛灰中に含まれている重金属類の溶出防止に必要な重金属類溶出防止剤の必要量との相関関係を求め、上記記載の本発明に係る測定方法によって求められた焼却飛灰中の鉛濃度によって、上記相関関係に基づいて焼却飛灰中に含まれている重金属類の溶出防止に必要な重金属類溶出防止剤の必要量を決定し、決定された必要量の重金属類溶出防止剤を焼却飛灰に添加して混練することを特徴とする、燃焼炉からの焼却飛灰の処理方法に関する。本発明のかかる態様において用いることのできる重金属類溶出防止剤としては、重金属捕捉剤として当該技術において従来公知のジチオカルバミン酸基を有する化合物などの液体キレート剤を挙げることができる。本発明において重金属類の溶出防止剤として用いることのできる具体的な化合物としては、ジエチルジチオカルバミン酸ナトリウム、ジエチルジチオカルバミン酸カリウム、Ｎ1,Ｎ2,Ｎ3,Ｎ5−テトラ（ジチオカルボキシ）テトラエチレンペンタミンの４ナトリウム塩、ピペリジン−Ｎ−ジチオカルバミン酸（ペンタメチレンジチオカルバミン酸）カリウムなどを挙げることができる。なお、使用の際には、この液体キレート剤を水で希釈して用いるが、好ましい希釈倍率は、１〜２５重量％濃度である。
【００１８】
上記に示すような液体キレート剤希釈液を焼却飛灰に加えて混練することによって、焼却飛灰中に含まれている重金属類が液体キレート剤と結合して水に不溶性の化合物が生成する。これによって、焼却飛灰からの重金属類の溶出が防止される。
【００１９】
焼却飛灰と液体キレート剤とを混練するために使用される混練機としては、当該技術において周知の混練機、例えば、押出造粒機、転動造粒機などを用いることができる。混練りは、常温〜８０℃程度の温度で、混合物が均一な状態に混合されるまで行うことが好ましい。なお、混練りにより発熱が起こるので、混練機に加熱手段を用いる必要性はない。
【００２０】
【発明の効果】
本発明方法によれば、焼却飛灰中に含まれる鉛濃度を極めて簡便且つ迅速に測定することができる。したがって、焼却飛灰が排出される燃焼炉施設の現場において焼却飛灰中の鉛濃度を測定し、その測定値に基づいて、焼却飛灰からの重金属類の溶出防止処理に必要な溶出防止剤の添加率を決定することにより、過剰な重金属類溶出防止剤を用いることなく、極めて効率的に焼却飛灰からの重金属類の溶出防止処理を行うことが可能になる。
【００２１】
【実施例】
以下の実施例によって、本発明をより具体的に説明する。以下の実施例は、本発明の好ましい態様の例示であり、本発明を限定するものではない。
【００２２】
以下の実施例において、焼却飛灰試料としては、ストーカ炉Ａ及びＢから採取した焼却飛灰試料Ａ及び焼却飛灰試料Ｂ、流動床炉Ｃ及びＤから採取した焼却飛灰試料Ｃ及び焼却飛灰試料Ｄを用いた。それぞれの焼却飛灰試料の重金属類含有量を表１に、重金属類溶出濃度を表２に示す。なお、重金属類溶出濃度は、環境庁告示１３号法に準じた溶出試験によって求めた。
【００２３】
【表１】
【表２】
実施例１
本発明方法による焼却飛灰中の鉛濃度の測定
ストーカ炉Ａから焼却飛灰Ａを合計で２０検体採取し、本発明方法による鉛濃度の測定を行った。▲１▼まず、焼却飛灰検体１ｇと、０．５ＮのＮａＯＨ水溶液１００ｍｌとを、容量２００ｍｌの三角フラスコに入れ、よく振り混ぜて混合した。▲２▼次に、三角フラスコをウォーターバス中で時折振り混ぜながら、１０〜６０分、好ましくは３０分間、８０〜９５℃、好ましくは９５℃に加熱して、焼却飛灰中の鉛を水溶液中に溶出させた。▲３▼水溶液を放冷した後、孔径１．０μｍのガラスフィルターで吸引濾過した。▲４▼濾液を１００ｍｌメスフラスコに取り、蒸留水を標線まで加えてメスアップすることにより、加熱で蒸発した分を補充した。▲５▼試料液を１ｍｌホールピペットでとり、５０ｍｌメスフラスコに入れた。▲６▼濃硝酸：水＝１：１（体積比）の酸水溶液６ｍｌを駒込ピペットで取ってメスフラスコ中に入れ、蒸留水を標線まで加えてメスアップした（これにより試料液は５０倍に希釈された）。▲７▼試料液を５０ｍｌガラスバイアルに移し、フレーム原子吸光光度計によって試料液中の鉛濃度(mg/L)を分析した。
【００２６】
得られた試料液中の鉛濃度Ｃ(mg/L)から、以下のような計算によって焼却飛灰中の鉛濃度ｐ(mg/kg)を算出することができる。
p(mg/kg)＝C(mg/L)×0.1(L)÷1(g)×50＝5・C(mg/g)＝5000・C(mg/kg)
（上記式において、0.1(L)は焼却飛灰と混合したアルカリ水溶液の量；1(g)はアルカリ水溶液と混合した焼却飛灰の量；×50は上記▲６▼工程での試料液の希釈倍率；である）
なお、試料液中の鉛濃度の分析方法として吸光光度法を用いる場合には、上記▲４▼工程で得られた試料液を一般的な吸光光度法による手順にかけることによって液中の鉛濃度を求めることができる。また、イオン電極測定法を用いる場合には、上記▲３▼の放冷後に、ｐＨ４．５〜６．５に調整し、水溶液中に電極を挿入して測定を行うことにより、液中の鉛濃度を求めることができる。
【００２７】
同じ焼却飛灰検体について、「環境庁水質保全局水質管理課編底質調査方法」に基づく精密分析法によって、飛灰中の鉛濃度を測定した。それぞれの検体に関して、本発明方法によって求められた鉛濃度と従来の精密分析法によって求められた鉛濃度とを対比することにより、補正係数αを求めた。なお、補正係数αは、従来の精密分析法によって求められた鉛濃度を本発明方法によって求められた鉛濃度で割った値である。
【００２８】
なお、従来の精密分析法とは、「環境庁水質保全局水質管理課編底質調査方法」に基づく方法であり、本発明の実施例で行った具体的な手順は以下のようなものであった。まず、乾燥させた焼却飛灰の微粉砕試料５ｇをビーカーに秤量し、純水約５０ｍｌを加えて１５分間撹拌した。王水（硝酸：塩酸＝１：３の混合酸溶液）１０ｍｌを加え、５分間撹拌した。これをウォーターバスで乾固近くまで蒸発させた。次に、濃硝酸１０ｍｌを加えて再び乾固近くまで蒸発させた。次に、ビーカーに濃塩酸：水＝１：５の塩酸水溶液２５ｍｌを加え、ビーカーの上に時計皿をのせて蓋をして、ホットプレート上で５分間加熱した。時計皿とビーカーの内壁を純水で洗浄し、Ｎｏ．５Ｂの濾紙で濾過した。濾紙上の残留物を純水で洗浄し、洗浄液を濾液に加えた。洗浄液を加えた濾液を２００ｍｌメスフラスコに移し、蒸留水でメスアップして試料液を調製し、この試料液についてフレーム原子吸光法によって溶液中の鉛濃度の定量を行った。次式によって、得られた鉛濃度Ｃ(mg/L)を焼却飛灰中の鉛濃度(mg/kg)に換算した。
【００２９】
飛灰中鉛濃度(mg/kg)＝Ｃ(mg/L)×0.2(L)÷5(g)=0.04Ｃ(mg/g)=40Ｃ(mg/kg)
（上式において、0.2(L)はフレーム原子吸光法で測定した試料液の量(200ml)；5(g)は焼却飛灰試料の量である）
２０検体のそれぞれに関して求められた補正係数αの平均値を求めると、１．１２であり、９５％信頼区間は±０．０２であった。即ち、補正係数αの真の値は、１．１２±０．０２の範囲内に９５％以上の確率で入ることが分かった。したがって、本発明方法によって測定された焼却飛灰中の鉛含有量ｐに補正係数α＝１．１２、より安全性を考慮すれば１．１４をかけることにより、焼却飛灰中の正確な鉛濃度Ｐ(mg/kg)を求めることができることが分かった。結果を表３に示す。
【００３０】
【表３】
焼却飛灰の重金属類溶出防止処理
ストーカ炉Ａから採取した焼却飛灰試料Ａの１検体について、本発明による鉛濃度測定方法によって鉛含有量を定量した結果、１５２０mg/kgと算出された（補正係数による補正後の値）。図１に示されているストーカ炉に関する焼却飛灰中の鉛含有量と重金属溶出防止に必要な薬剤の添加率との関係図から、鉛含有量＝１５２０mg/kgに対する必要な重金属類溶出防止剤の量は２．１(w/w%)と読み取った。
【００３２】
焼却飛灰試料Ａに、加湿水を３０(w/w%)と、液体キレート剤としてジエチルジチオカルバミン酸カリウムの５０％水溶液を２．１(w/w%)加えて、混練り処理を行った。２４時間養生後、環境庁告示１３号法に準じた重金属類溶出試験を行って、鉛の溶出濃度を定量した。また、溶出液のｐＨを測定した。鉛の溶出濃度は０．１９mg/L、溶出液のｐＨは１２．１であった。
【００３３】
実施例２
本発明方法による焼却飛灰中の鉛濃度の測定
ストーカ炉Ｂから焼却飛灰Ｂを合計で２０検体採取し、実施例１と同様に、本発明方法による鉛濃度の測定を行った。また、同じ焼却飛灰検体について、「環境庁水質保全局水質管理課編底質調査方法」に基づく精密分析法によって、飛灰中の鉛濃度を測定した。それぞれの検体に関して、実施例１と同様に補正係数αを求めた。補正係数αの平均値は１．１３、９５％信頼区間は±０．０２であった。結果を表４に示す。
【００３４】
【表４】
焼却飛灰の重金属類溶出防止処理
ストーカ炉Ｂから採取した焼却飛灰試料Ｂの１検体について、本発明による鉛濃度測定方法によって鉛含有量を定量した結果、１２４０mg/kgと算出された。図１に示されているストーカ炉に関する焼却飛灰中の鉛含有量と重金属溶出防止に必要な薬剤の添加率との関係図から、鉛含有量＝１２４０mg/kgに対する必要な重金属類溶出防止剤の量は１．７(w/w%)と読み取った。
【００３６】
焼却飛灰試料Ｂに、加湿水を３０(w/w%)と、液体キレート剤としてジエチルジチオカルバミン酸カリウムの５０％水溶液を１．７(w/w%)加えて、混練り処理を行った。２４時間養生後、環境庁告示１３号法に準じた重金属類溶出試験を行って、鉛の溶出濃度を定量した。また、溶出液のｐＨを測定した。鉛の溶出濃度は０．２１mg/L、溶出液のｐＨは１２．０であった。
【００３７】
実施例３
本発明方法による焼却飛灰中の鉛濃度の測定
流動床炉Ｃから焼却飛灰Ｃを合計で２０検体採取し、実施例１と同様に、本発明方法による鉛濃度の測定を行った。また、同じ焼却飛灰検体について、「環境庁水質保全局水質管理課編底質調査方法」に基づく精密分析法によって、飛灰中の鉛濃度を測定した。それぞれの検体に関して、実施例１と同様に補正係数αを求めた。補正係数αの平均値は１．２３、９５％信頼区間は±０．０２であった。結果を表５に示す。
【００３８】
【表５】
焼却飛灰の重金属類溶出防止処理
流動床炉Ｃから採取した焼却飛灰試料Ｃの１検体について、本発明による鉛濃度測定方法によって鉛含有量を定量した結果、２６７０mg/kgと算出された。図２に示されているストーカ炉に関する焼却飛灰中の鉛含有量と重金属溶出防止に必要な薬剤の添加率との関係図から、鉛含有量＝２６７０mg/kgに対する必要な重金属類溶出防止剤の量は４．１(w/w%)と読み取った。
【００４０】
焼却飛灰試料Ｂに、加湿水を３０(w/w%)と、液体キレート剤としてジエチルジチオカルバミン酸カリウムの５０％水溶液を４．１(w/w%)加えて、混練り処理を行った。２４時間養生後、環境庁告示１３号法に準じた重金属類溶出試験を行って、鉛の溶出濃度を定量した。また、溶出液のｐＨを測定した。鉛の溶出濃度は０．２４mg/L、溶出液のｐＨは１２．１であった。
【００４１】
実施例４
本発明方法による焼却飛灰中の鉛濃度の測定
流動床炉Ｄから焼却飛灰Ｄを合計で２０検体採取し、実施例１と同様に、本発明方法による鉛濃度の測定を行った。また、同じ焼却飛灰検体について、「環境庁水質保全局水質管理課編底質調査方法」に基づく精密分析法によって、飛灰中の鉛濃度を測定した。それぞれの検体に関して、実施例１と同様に補正係数αを求めた。補正係数αの平均値は１．２６、９５％信頼区間は±０．０２であった。結果を表６に示す。
【００４２】
【表６】
焼却飛灰の重金属類溶出防止処理
流動床炉Ｄから採取した焼却飛灰試料Ｄの１検体について、本発明による鉛濃度測定方法によって鉛含有量を定量した結果、３０５０mg/kgと算出された。図２に示されている流動床炉に関する焼却飛灰中の鉛含有量と重金属溶出防止に必要な薬剤の添加率との関係図から、鉛含有量＝３０５０mg/kgに対する必要な重金属類溶出防止剤の量は４．８(w/w%)と読み取った。
【００４４】
焼却飛灰試料Ｄに、加湿水を３０(w/w%)と、液体キレート剤としてジエチルジチオカルバミン酸カリウムの５０％水溶液を４．０(w/w%)加えて、混練り処理を行った。２４時間養生後、環境庁告示１３号法に準じた重金属類溶出試験を行って、鉛の溶出濃度を定量した。また、溶出液のｐＨを測定した。鉛の溶出濃度は０．１７mg/L、溶出液のｐＨは１２．０であった。
【００４５】
以上の結果から、いずれの実施例においても、焼却飛灰からの鉛の溶出濃度を０．３mg/L以下に抑制することができたことが確認された。
【図面の簡単な説明】
【図１】ストーカ炉から排出された焼却飛灰中の鉛含有量と重金属溶出防止に必要な薬剤の添加率との間の相関関係を示すグラフである。
【図２】流動床炉から排出された焼却飛灰中の鉛含有量と重金属溶出防止に必要な薬剤の添加率との間の相関関係を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention is a liquid used in heavy metal elution prevention treatment of fly ash and incineration ash (hereinafter collectively referred to as “incineration fly ash”) discharged from various incinerators such as garbage incinerators and combustion furnaces such as boilers. The present invention relates to a method for determining the optimum addition rate of a chelating agent, and a method for treating incineration fly ash based on the optimum addition rate determined by such a method.
[0002]
[Prior art]
Incineration fly ash discharged from various incinerators such as garbage incinerators and combustion furnaces such as boilers contains high concentrations of heavy metals harmful to the human body such as lead, cadmium, chromium, mercury, zinc and copper. Yes. When they come into contact with environmental water such as rainwater, they are eluted and contaminate soil, groundwater, rivers, seawater and the like. Therefore, it is necessary to prevent elution of these heavy metals from the incineration fly ash.
[0003]
Conventionally, as a method for treating heavy metals in incineration fly ash discharged from an incinerator, a method of treating incineration fly ash with a heavy metal elution inhibitor typified by a liquid chelating agent such as dithiocarbamate has been adopted. In the treatment of incineration fly ash with such a liquid chelating agent, first, in the laboratory and the implementation facility, the liquid chelating agent was added to the incineration fly ash at various addition rates, and the test was conducted several times. At the same time, the optimum addition rate was determined with the addition rate satisfying the landfill standard value for heavy metals.
[0004]
[Problems to be solved by the invention]
However, the concentration of heavy metals in the incineration fly ash is not constant, and fluctuates from time to time by being influenced by combustion conditions and the quality of garbage. Therefore, when the heavy metal dissolution inhibitor is added at the optimum addition rate determined above, there is a high possibility that more than the required amount of chemicals has been added during actual processing, which increases the running costs such as chemical costs. Connected to.
[0005]
Therefore, if the concentration of heavy metals in incineration fly ash can be measured easily at the site of incineration fly ash treatment and the optimum amount of heavy metal dissolution inhibitor added to the concentration can be determined, the incineration fly ash can be efficiently used. Of heavy metals can be prevented, which is extremely advantageous in terms of cost.
[0006]
[Means for Solving the Problems]
As a result of investigating 30 samples of incinerated fly ash discharged from the stoker furnace and fluidized bed furnace, a total of 60 samples, the present inventors have found that the lead content in the incinerated fly ash and heavy metal elution prevention are necessary. It was found that there is a strong correlation with the rate of drug addition. The results are shown in FIGS. FIG. 1 is a diagram showing the results obtained for a stoker furnace, and FIG. 2 is a diagram showing the results obtained for a fluidized bed furnace. Here, the value of the lead content in the incineration fly ash is a value measured by a precision measurement method (hereinafter referred to as a conventional method) based on the “Environment Agency Water Quality Conservation Bureau Water Quality Management Section edited by bottom sediment investigation method”. In addition, the value of the required drug addition rate is calculated by adding various amounts of heavy metal elution inhibitor to the incinerated fly ash sample and measuring the lead elution concentration in each case. A relationship diagram with lead elution concentration was prepared, and based on this relationship diagram, the elution concentration of lead was 0.3 (mg), which is the landfill standard value determined by the Environment Agency Notification No. 13 or Prime Minister's Ordinance No. 5 / L) The rate of addition of the following drug was obtained. 1 and 2, a 50% aqueous solution of potassium diethyldithiocarbamate was used as the heavy metal elution inhibitor.
[0007]
From the correlation shown in FIG. 1 and FIG. 2, if the content of lead in the incineration fly ash is known, it is considered that the optimum drug addition rate can be determined. However, quantification of lead content by the above-mentioned conventional method involves the sequential heat extraction of incinerated fly ash samples with aqua regia, nitric acid, and hydrochloric acid to elute lead, requiring an analysis time of approximately 20 hours per sample. And For this reason, lead content in incineration fly ash cannot be quantified in a short time. In this case, it is impossible to measure the lead concentration in the incineration fly ash at the site of the combustion furnace that discharges the incineration fly ash and determine the chemical addition rate based on the value.
[0008]
Therefore, first, the present inventors conducted intensive research to find a method for easily and quickly quantifying the lead content in incineration fly ash, and as a result, found the following method. That is, in the first aspect of the present invention, incineration fly ash from a combustion furnace is mixed with an alkaline aqueous solution, heated to elute lead in the incineration fly ash, and the lead concentration in the obtained aqueous solution is measured. It is related with the method of measuring the density | concentration of lead in incineration fly ash characterized by calculating the lead density | concentration in incineration fly ash by.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a method for measuring the lead content in the incineration fly ash according to the present invention will be described.
[0010]
In general, dry treatment (slaked lime spraying) is used for exhaust gas treatment, so most of the incinerated fly ash is alkaline. Moreover, in the facility which employ | adopts a wet process, incineration fly ash shows neutrality-alkalinity. When these incineration fly ash is treated with a liquid chelating agent that is a heavy metal elution inhibitor, most of the liquid chelating agents on the market exhibit an alkalinity of pH = 12 or more, so that the treated incineration fly ash becomes alkaline. . Therefore, when the heavy metal elution test by the Environmental Agency Notification No. 13 method is performed, the eluate has a pH of around 12, and most of the heavy metals to be treated are lead which is an amphoteric metal.
[0011]
In the method for measuring the lead content in incineration fly ash according to the present invention, first, incineration fly ash is mixed in an aqueous solution of an alkaline compound and heated to elute lead from the incineration fly ash.
[0012]
Here, the phenomenon of “elution” means that a solid and a liquid come into contact with each other, and a soluble component in the solid is dissolved in the liquid (solvent). However, since this phenomenon is a great limiting factor due to the solubility of the soluble component in the solvent, if the amount of the liquid relative to the solid is too small, the target component cannot be completely eluted. It is also known that the influence of coexisting substances is extremely large.
[0013]
In the Environmental Agency Notification No. 13 described above, the dissolution test is performed at a solid-liquid ratio of 1:10. However, at this solid-liquid ratio, the influence of coexisting substances on the solubility is very large, It is known in the art that it is insufficient for determining the amount of elution. On the other hand, in the elution test with a solid-liquid ratio of 1: 100 as seen in the official test method in the Netherlands, the influence of the coexisting substance on the solubility is small, and the elution amount of the soluble component from the solid substance is relatively accurate. It is known that it can be judged. Therefore, in the method for measuring the lead content in the incinerated fly ash according to the present invention, the mixing ratio of the incinerated fly ash to the aqueous solution of the alkaline compound in the lead elution step from the incinerated fly ash is 1:50 to 1000. More preferably, it is about 1: 100 to 500, for example, 1: 100 (weight ratio). Examples of the alkaline compound that can be used for this purpose include sodium hydroxide and sodium carbonate. The concentration of the aqueous alkaline compound solution used is preferably 0.01 to 10N, more preferably 0.05 to 5N, for example 0.5N, in order to establish an alkaline condition in which lead is easily eluted. If the concentration of the aqueous alkali solution is higher than this range, the alkali metal may be a limiting factor for lead elution, and further, the alkali metal may be an interfering substance for the measuring instrument when measuring the lead concentration. It is not preferable.
[0014]
Next, the dissolved lead concentration in the alkaline aqueous solution from which lead is eluted is quantified. Examples of lead quantification methods that can be used for this purpose include flame atomic absorption spectrometry, absorptiometry, ICP emission analysis, and ion electrode measurement. In the determination by flame atomic absorption, nitric acid is added to the aqueous solution to make the system acidic with 0.1 to 1 mol / L nitric acid. In the determination by ICP emission analysis, hydrochloric acid or nitric acid is added to the aqueous solution to make the system acidic with 0.1 to 0.5 mol / L hydrochloric acid or nitric acid. In the quantification by the absorptiometric method and the ion electrode measurement method, the lead-containing alkaline aqueous solution obtained above can be subjected to analysis after being adjusted to about pH 9 and about pH 4.5 to 6.5, respectively. By these quantitative analysis methods, the concentration of dissolved lead (mg / L) in the aqueous solution is obtained. In performing these quantitative analyses, the absorbance of several known concentrations of lead solution is measured in advance to create a calibration curve, and the concentration of dissolved lead in the aqueous solution sample is calculated based on the calibration curve.
[0015]
Assuming that all of the lead in the incineration fly ash was eluted by the above elution treatment, by converting the dissolved lead concentration (mg / L) in the obtained aqueous solution sample based on the dilution rate of the incineration fly ash, Lead concentration (mg / kg) in incineration fly ash can be calculated.
[0016]
In addition, the lead concentration calculated | required by said simple method is an estimated value based on the premise that all the lead in incineration fly ash was eluted by the alkali elution process. Therefore, in order to obtain a more accurate lead concentration in the incineration fly ash, the simple measurement method according to the present invention and the conventional precision measurement method (for example, the above-mentioned) The measurement method prescribed by the Environmental Agency of Japan) was conducted in advance to determine the lead concentration measurement value, and by comparing the two values, the lead concentration value obtained by the simplified measurement method according to the present invention was accurately determined. It is desirable to obtain a correction coefficient α for calculating the lead concentration.
[0017]
According to the present invention, in this way, the concentration of lead in the incineration fly ash can be measured by an extremely simple and rapid method as compared with the conventional method. From the lead concentration measured in this way, based on the relationship between the lead content and the required chemical addition rate determined in advance for the target incineration facility, the elution inhibitor required for the elution prevention treatment of heavy metals By adding the required amount of elution inhibitor obtained from this to the incineration fly ash and carrying out the elution prevention treatment, the incineration fly ash is extremely efficiently used without excessive use of the elution inhibitor. The elution prevention process of heavy metals from can be performed. Accordingly, another aspect of the present invention relates to a lead concentration in incineration fly ash and a heavy metal elution inhibitor necessary for preventing elution of heavy metals contained in the incineration fly ash in advance for the combustion furnace to be treated. Of the heavy metals contained in the incineration fly ash based on the above correlation by the lead concentration in the incineration fly ash determined by the measurement method according to the present invention described above. Determine the required amount of heavy metal elution inhibitor necessary to prevent elution, add the determined required amount of heavy metal elution inhibitor to the incineration fly ash, and knead it. It is related with the processing method of ash. Examples of the heavy metal elution preventing agent that can be used in this aspect of the present invention include liquid chelating agents such as compounds having a dithiocarbamic acid group conventionally known in the art as a heavy metal scavenger. Specific compounds which can be used as an elution preventive agent of heavy metals in the present invention, sodium diethyldithiocarbamate, potassium diethyldithiocarbamate, N 1, N 2, N 3, N 5 - tetra (dithiocarboxy) tetraethylene Examples thereof include tetrasodium salt of pentamine, potassium piperidine-N-dithiocarbamic acid (pentamethylenedithiocarbamic acid), and the like. In use, the liquid chelating agent is diluted with water and used. The preferred dilution ratio is 1 to 25% by weight.
[0018]
By adding the liquid chelating agent diluent as described above to the incineration fly ash and kneading, the heavy metals contained in the incineration fly ash are combined with the liquid chelating agent to produce a water-insoluble compound. This prevents elution of heavy metals from the incineration fly ash.
[0019]
As a kneader used for kneading the incinerated fly ash and the liquid chelating agent, a kneader well known in the art, for example, an extrusion granulator, a rolling granulator, or the like can be used. The kneading is preferably performed at a temperature of about room temperature to about 80 ° C. until the mixture is mixed in a uniform state. In addition, since heat_generation | fever occurs by kneading | mixing, it is not necessary to use a heating means for a kneading machine.
[0020]
【The invention's effect】
According to the method of the present invention, the concentration of lead contained in incineration fly ash can be measured very simply and quickly. Therefore, the lead concentration in the incineration fly ash is measured at the site of the combustion furnace facility where the incineration fly ash is discharged, and based on the measured value, the elution inhibitor necessary for the elution prevention treatment of heavy metals from the incineration fly ash By determining the addition rate, it becomes possible to perform the elution prevention treatment of heavy metals from the incineration fly ash very efficiently without using an excessive heavy metal elution inhibitor.
[0021]
【Example】
The following examples illustrate the present invention more specifically. The following examples are illustrative of preferred embodiments of the invention and are not intended to limit the invention.
[0022]
In the following examples, the incineration fly ash samples are the incineration fly ash sample A and the incineration fly ash sample B collected from the stoker furnaces A and B, the incineration fly ash sample C and the incineration fly collected from the fluidized bed furnaces C and D, respectively. Ash sample D was used. Table 1 shows the heavy metal content of each incineration fly ash sample, and Table 2 shows the elution concentration of heavy metals. The elution concentration of heavy metals was determined by an elution test according to the Environmental Agency Notification No. 13 method.
[0023]
[Table 1]
[Table 2]
Example 1
Measurement of lead concentration in incinerated fly ash by the method of the present invention A total of 20 samples of incinerated fly ash A were collected from the stoker furnace A, and the lead concentration was measured by the method of the present invention. (1) First, 1 g of incinerated fly ash specimen and 100 ml of 0.5N NaOH aqueous solution were put into a 200 ml Erlenmeyer flask, and well shaken and mixed. (2) Next, while stirring the Erlenmeyer flask in a water bath occasionally, heat for 10 to 60 minutes, preferably 30 minutes, 80 to 95 ° C., preferably 95 ° C. Elute in. (3) The aqueous solution was allowed to cool and then filtered with suction through a glass filter having a pore size of 1.0 μm. (4) The filtrate was placed in a 100 ml volumetric flask, and distilled water was added up to the marked line to make up the volume, thereby supplementing the amount evaporated by heating. (5) The sample solution was taken with a 1 ml whole pipette and put into a 50 ml volumetric flask. (6) Concentrated nitric acid: water = 1: 1 (volume ratio) 6 ml of an acid aqueous solution was taken with a Komagome pipette and placed in a measuring flask, and distilled water was added up to the marked line to increase the volume. Diluted). (7) The sample solution was transferred to a 50 ml glass vial, and the lead concentration (mg / L) in the sample solution was analyzed by a flame atomic absorption photometer.
[0026]
From the lead concentration C (mg / L) in the obtained sample solution, the lead concentration p (mg / kg) in the incineration fly ash can be calculated by the following calculation.
p (mg / kg) = C (mg / L) x 0.1 (L) ÷ 1 (g) x 50 = 5 · C (mg / g) = 5000 · C (mg / kg)
(In the above formula, 0.1 (L) is the amount of alkaline aqueous solution mixed with incinerated fly ash; 1 (g) is the amount of incinerated fly ash mixed with alkaline aqueous solution; × 50 is the amount of the sample solution in step (6) above. Dilution ratio;
When the spectrophotometric method is used as a method for analyzing the lead concentration in the sample solution, the sample solution obtained in the above step (4) is subjected to a general absorptiometric procedure to obtain the lead concentration in the solution. Can be requested. Moreover, when using the ion electrode measurement method, after allowing to cool in the above (3), the pH is adjusted to 4.5 to 6.5, and measurement is performed by inserting the electrode into an aqueous solution, thereby measuring lead in the liquid. The concentration can be determined.
[0027]
For the same incineration fly ash sample, the lead concentration in the fly ash was measured by a precision analysis method based on the “Survey of bottom sediment investigation method edited by Water Quality Management Division, Water Quality Conservation Bureau, Environment Agency”. For each specimen, the correction coefficient α was determined by comparing the lead concentration determined by the method of the present invention with the lead concentration determined by the conventional precision analysis method. The correction coefficient α is a value obtained by dividing the lead concentration obtained by the conventional precision analysis method by the lead concentration obtained by the method of the present invention.
[0028]
The conventional precision analysis method is a method based on “Environment Agency Water Quality Conservation Bureau Water Quality Management Section edited bottom sediment investigation method”, and the specific procedure performed in the embodiment of the present invention is as follows. there were. First, 5 g of a finely pulverized sample of incinerated fly ash that had been dried was weighed into a beaker, and about 50 ml of pure water was added and stirred for 15 minutes. 10 ml of aqua regia (mixed acid solution of nitric acid: hydrochloric acid = 1: 3) was added and stirred for 5 minutes. This was evaporated to near dryness in a water bath. Next, 10 ml of concentrated nitric acid was added and evaporated again to near dryness. Next, 25 ml of a hydrochloric acid aqueous solution of concentrated hydrochloric acid: water = 1: 5 was added to the beaker, a watch glass was placed on the beaker, the lid was placed, and the plate was heated on a hot plate for 5 minutes. Wash the watch glass and the inner wall of the beaker with pure water. Filter through 5B filter paper. The residue on the filter paper was washed with pure water, and the washing solution was added to the filtrate. The filtrate to which the washing solution was added was transferred to a 200 ml volumetric flask, diluted with distilled water to prepare a sample solution, and the lead concentration in the solution was determined by flame atomic absorption spectrometry for this sample solution. The obtained lead concentration C (mg / L) was converted to the lead concentration (mg / kg) in the incineration fly ash by the following formula.
[0029]
Lead concentration in fly ash (mg / kg) = C (mg / L) x 0.2 (L) ÷ 5 (g) = 0.04C (mg / g) = 40C (mg / kg)
(In the above formula, 0.2 (L) is the amount of sample solution measured by flame atomic absorption (200 ml); 5 (g) is the amount of incinerated fly ash sample)
The average value of the correction coefficients α obtained for each of the 20 samples was 1.12, and the 95% confidence interval was ± 0.02. That is, it was found that the true value of the correction coefficient α falls within the range of 1.12 ± 0.02 with a probability of 95% or more. Therefore, the correct lead in the incineration fly ash is calculated by multiplying the lead content p in the incineration fly ash measured by the method of the present invention by a correction coefficient α = 1.12 and 1.14 if safety is taken into consideration. It was found that the concentration P (mg / kg) can be determined. The results are shown in Table 3.
[0030]
[Table 3]
As a result of quantifying the lead content of one sample of the incineration fly ash sample A collected from the stoker furnace A from the incineration fly ash heavy metal elution prevention method, it was calculated to be 1520 mg / kg (correction) Value after correction by coefficient). Figure 1 shows the relationship between the lead content in incineration fly ash and the addition rate of chemicals necessary to prevent heavy metal elution for the stoker furnace shown in Fig. 1, and the necessary heavy metal elution inhibitor for lead content = 1520 mg / kg. Was read as 2.1 (w / w%).
[0032]
30% (w / w%) of humidified water and 2.1% (w / w%) of a 50% aqueous solution of potassium diethyldithiocarbamate as a liquid chelating agent were added to the incinerated fly ash sample A and kneaded. . After curing for 24 hours, the elution concentration of lead was quantified by conducting a heavy metal elution test according to the Environmental Agency Notification No. 13 method. Further, the pH of the eluate was measured. The elution concentration of lead was 0.19 mg / L, and the pH of the eluate was 12.1.
[0033]
Example 2
Measurement of Lead Concentration in Incinerated Fly Ash by the Method of the Present Invention A total of 20 samples of incinerated fly ash B were collected from the stoker furnace B, and the lead concentration was measured by the method of the present invention in the same manner as in Example 1. In addition, for the same incinerated fly ash sample, the lead concentration in the fly ash was measured by a precision analysis method based on the “Investigation Method of Bottom Quality by Water Quality Management Division, Water Quality Conservation Bureau, Environment Agency”. For each specimen, the correction coefficient α was determined in the same manner as in Example 1. The average value of the correction coefficient α was 1.13, and the 95% confidence interval was ± 0.02. The results are shown in Table 4.
[0034]
[Table 4]
As a result of quantifying the lead content by the lead concentration measurement method according to the present invention for one sample of the incineration fly ash sample B collected from the stoker furnace B, which was treated with the incineration fly ash to prevent elution of heavy metals, it was calculated to be 1240 mg / kg. Figure 1 shows the relationship between the lead content in the incineration fly ash and the addition rate of chemicals required to prevent elution of heavy metals for the stoker furnace shown in Fig. 1, and the necessary elution inhibitor for heavy metals required for lead content = 1240 mg / kg. The amount of was read as 1.7 (w / w%).
[0036]
30% (w / w%) of humidified water and 1.7% (w / w%) of a 50% aqueous solution of potassium diethyldithiocarbamate as a liquid chelating agent were added to the incinerated fly ash sample B and kneaded. . After curing for 24 hours, the elution concentration of lead was quantified by conducting a heavy metal elution test according to the Environmental Agency Notification No. 13 method. Further, the pH of the eluate was measured. The elution concentration of lead was 0.21 mg / L, and the pH of the eluate was 12.0.
[0037]
Example 3
Measurement of Lead Concentration in Incinerated Fly Ash Using the Method of the Present Invention A total of 20 samples of incinerated fly ash C were collected from the fluidized bed furnace C, and the lead concentration was measured using the method of the present invention in the same manner as in Example 1. In addition, for the same incinerated fly ash sample, the lead concentration in the fly ash was measured by a precision analysis method based on the “Investigation Method of Bottom Quality by Water Quality Management Division, Water Quality Conservation Bureau, Environment Agency”. For each specimen, the correction coefficient α was determined in the same manner as in Example 1. The average value of the correction coefficient α was 1.23, and the 95% confidence interval was ± 0.02. The results are shown in Table 5.
[0038]
[Table 5]
As a result of quantifying the lead content of the incinerated fly ash sample C collected from the fluidized bed furnace C from the incineration fly ash by the fluidized bed furnace C, the lead concentration was calculated to be 2670 mg / kg. Figure 2 shows the relationship between the lead content in the incineration fly ash and the addition rate of chemicals required to prevent elution of heavy metals for the stoker furnace shown in Fig. 2, and the necessary elution inhibitor for heavy metals required for lead content = 2670 mg / kg. Was read as 4.1 (w / w%).
[0040]
30% (w / w%) of humidified water and 4.1% (w / w%) of a 50% aqueous solution of potassium diethyldithiocarbamate as a liquid chelating agent were added to the incinerated fly ash sample B and kneaded. . After curing for 24 hours, the elution concentration of lead was quantified by conducting a heavy metal elution test according to the Environmental Agency Notification No. 13 method. Further, the pH of the eluate was measured. The elution concentration of lead was 0.24 mg / L, and the pH of the eluate was 12.1.
[0041]
Example 4
Measurement of lead concentration in incinerated fly ash by the method of the present invention A total of 20 samples of incinerated fly ash D were collected from the fluidized bed furnace D, and the lead concentration by the method of the present invention was measured in the same manner as in Example 1. In addition, for the same incinerated fly ash sample, the lead concentration in the fly ash was measured by a precision analysis method based on the “Investigation Method of Bottom Quality by Water Quality Management Division, Water Quality Conservation Bureau, Environment Agency”. For each specimen, the correction coefficient α was determined in the same manner as in Example 1. The average value of the correction coefficient α was 1.26, and the 95% confidence interval was ± 0.02. The results are shown in Table 6.
[0042]
[Table 6]
As a result of quantifying the lead content of the incinerated fly ash sample D collected from the fluidized bed furnace D from the incineration fly ash by the fluidized bed furnace D, the lead concentration was calculated to be 3050 mg / kg. Figure 2 shows the relationship between the lead content in incineration fly ash and the addition rate of chemicals necessary to prevent heavy metal elution for the fluidized bed furnace shown in Fig. 2, and the necessary heavy metal elution prevention for lead content = 3050 mg / kg. The amount of the agent was read as 4.8 (w / w%).
[0044]
The incinerated fly ash sample D was kneaded by adding 30 (w / w%) humidified water and 4.0 (w / w%) 50% aqueous solution of potassium diethyldithiocarbamate as a liquid chelating agent. . After curing for 24 hours, the elution concentration of lead was quantified by conducting a heavy metal elution test according to the Environmental Agency Notification No. 13 method. Further, the pH of the eluate was measured. The elution concentration of lead was 0.17 mg / L, and the pH of the eluate was 12.0.
[0045]
From the above results, it was confirmed that the lead elution concentration from the incineration fly ash could be suppressed to 0.3 mg / L or less in any of the examples.
[Brief description of the drawings]
FIG. 1 is a graph showing the correlation between the lead content in incineration fly ash discharged from a stoker furnace and the addition rate of chemicals necessary for preventing heavy metal elution.
FIG. 2 is a graph showing the correlation between the lead content in incineration fly ash discharged from a fluidized bed furnace and the addition rate of chemicals necessary for preventing heavy metal elution.
Claims (4)
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