JP3813052B2

JP3813052B2 - Method for processing fly ash containing heavy metals

Info

Publication number: JP3813052B2
Application number: JP2000198464A
Authority: JP
Inventors: 三雄鐙屋; 隆史黒川; 俊章徳光; 正久宮崎
Original assignee: Dowa Holdings Co Ltd; Dowa Mining Co Ltd
Current assignee: Dowa Holdings Co Ltd
Priority date: 1999-08-12
Filing date: 2000-06-30
Publication date: 2006-08-23
Anticipated expiration: 2020-06-30
Also published as: JP2001113242A

Description

【０００１】
【発明の属する技術分野】
本発明は、都市ゴミ焼却施設や産業廃棄物焼却場等における焼却炉や溶融炉あるいは汚泥を処理するセメントキルン等から発生する銅、鉛、亜鉛等重金属の他、塩素及びセレンを含有する飛灰の処理方法に関する。
【０００２】
【従来の技術】
一般事業所や一般家庭から排出されるゴミ（「都市ゴミ」または「一般廃棄物」と称されている）は都市ゴミ焼却施設や産業廃棄物焼却工場等に集められ焼却処分されている。その際に焼却炉から発生する焼却灰や飛灰は薬剤処理、または、溶融炉、セメントキルン処理等の中間処理を施し最終処分場に堆積されている。
【０００３】
しかしながら、上記溶融炉やセメントキルン等での中間処理では、蒸気圧の高い鉛、亜鉛およびカドミウム等の重金属は炉内で揮発して排ガスに入り、この排ガスに入った重金属は排ガス処理設備のなかで凝縮して再び飛灰となってしまうという問題があった。
この再度の飛灰中には、塩素、ナトリウム、カルシウム、セレンと共に鉛、銅、亜鉛、カドミウム等の重金属が多量に含まれれており、これらの回収を含めた安定した処理方法が求められていた。
【０００４】
このような飛灰について、特開平７−１０９５３３号公報には、飛灰を槽内の水に懸濁し、この懸濁液を酸またはアルカリの添加によりアルカリ域の適当値にｐＨ調整することによって飛灰中の重金属を水酸化物として沈殿させ、その沈殿を回収する方法について開示している。また本出願人も、先に、湿式処理方式によって対処する方法を出願している（特開平８−１１７７２７号公報および特開平８−１４１５３９号公報）。
【０００５】
特開平８−１１７７２４号公報には、飛灰を水でスラリー化し、ｐＨ調整して固液分離する第１工程と、該第１工程からの殿物を酸液でリパルプし、ｐＨ３以下に調整した後、固液分離して鉛残渣を得る第２工程と、前記第１工程と前記第２工程からの酸性濾液に中和剤またさらに水硫化ソーダを加えて亜鉛、銅を含む殿物を濾別し、濾過水を排水液とする第３工程とからなる方法が開示されており、特開平８−１４１５３９号公報には、飛灰を水と中和剤で中和して固液分離する第１工程と、該第１工程からの殿物をリパルプし、硫酸によりｐＨ３前後に調整した後、固液分離して鉛残渣を得る第２工程と、該第２工程からの濾液にアルカリ中和剤を加えて亜鉛、銅を含む殿物を濾別する第３工程と、該第３工程の濾過水を該第１工程の中和液として繰り返し、該第１工程からの濾液について硫化剤を添加して排液処理する方法が開示されている。
【０００６】
このような湿式処理方法により、飛灰に含まれている重金属を安定な形で分離し、重金属資源として有効に回収すると共に、飛灰を湿式処理した後の排水を、国の排水基準すなわち水質汚濁防止法第３条第１項の規制に沿って無害化できるようになった。
【０００７】
【発明が解決しようとする課題】
しかしながら、前記特開平７−１０９５３３号公報にみられるように回収した重金属殿物中に塩化カルシウム等の塩類が多量に入り込む場合があり、製錬工程では、塩素の持ち込みを嫌うことから重金属のリサイクルという面では、なお問題を残していた。また、処理排水についても、近年、地域によっては環境公害に対する懸念からさらに規制を強化し、上記の国の排水基準値を上回る厳しい基準値で上乗せ規制を課すところがでている。例えば、地方条例（Ｉ市の上乗せ基準値）によれば、カドミウム０．０１ｍｇ／ｌ（国の排水基準値０．１ｍｇ／ｌ，以下同様）、フッ素１０ｍｇ／ｌ（１５ｍｇ／ｌ）、水銀０．０００５ｍｇ／ｌ（０．００５ｍｇ／ｌ）、ＣＯＤ２０ｍｇ／ｌ（１２０ｍｇ／ｌ）を上限とするように厳しく規制されるような状況にある。
【０００８】
さらに、飛灰を湿式処理した排水は、２０〜５０ｇ／ｌにも及ぶ多量の塩素が含まれ、溶存する重金属類は塩化物錯イオンを形成し易く、その除去が非常に困難な特異的な排水になっており、従来の技術では上記の地域の上乗せ規制に対応できない場合が生じているのが現状である。また、前記排水にセレンが混入した場合についても、従来法では国の排水基準値（０．１ｍｇ／ｌ）以下に除去するのは非常に困難で、多くの工数やコストをかけている状況にある。
【０００９】
排水中のセレンを除去する方法としては、鉄粉置換処理方法や水酸化第２鉄を用いた吸着処理方法等が知られているが。前記の鉄粉置換処理法では、ＳｅＯ₃ ^2- （亜セレン酸イオン；以下４価セレンという）の除去に関しては、ほぼ排水基準値以下にまで低減が可能であったが、ＳｅＯ₄ ^2- （セレン酸イオン；以下６価セレンという）の除去に関しては、除去能力が乏しいという問題があり、また、水酸化第２鉄の凝集フロックにセレンを吸着させて除去する吸着処理方法では、吸着可能な微量濃度でのみ適用可能な方法であり、したがって上述のような従来の除去法においては、いずれも比較的濃度が高い６価セレンを含有する排水処理の場合の適用に問題があった。
【００１０】
また例えば、特開平６−７９２８６号公報には、排水にセレン量に見合う多量の硫酸第１鉄塩を加えた後、中和剤を添加し、セレンを凝集する水酸化第２鉄に吸着させて除去する方法が開示されている。しかし、この方法は６価セレンの除去効率が悪く、また、コストがかかるという問題があった。
【００１１】
さらに、特開平８−１３２０７４号公報には、排水を、塩化第１鉄等、遷移金属化合物の存在下で、ｐＨ９以上に、かつ温度７０℃以上に保持してセレンを殿物として除去する方法が開示されている。しかし、この方法においては実質的に液温を８０℃以上に昇温させないと６価セレンの効率的な除去ができないので、昇温のためのコストがかかり、また、排水が高温度となる点に問題があった。
【００１２】
一方、本発明者等が提案した技術として、特開平８−２６７０７６号公報に開示された方法がある。この方法は、セレンを含有する排水に、２価鉄イオンを溶存させ、大気中で液温を３０℃以上に加温維持しつつ、アルカリ剤を添加してｐＨ８〜１０に中和し、固液分離して殿物を除くか、また、好ましくは大気遮断下、３０℃以上に加温維持しつつアルカリ剤を添加してｐＨを８〜１０に中和した後、固液分離して殿物を除くことにより排水中のセレン量を０．１ｍｇ／ｌ以下にまで低下させる方法である。
【００１３】
【発明が解決しようとする課題】
前記特開平８−２６７０７６号公報に開示された方法は、６価セレンをも容易に０．１ｍｇ／ｌ以下にまで除去が可能であったが、前記特開平８−１３２０７４号公報の発明の場合程の高温度ではないが、液の加温処理が必要である等作業性や経済性に問題が残っている。
【００１４】
本発明は、このような状況に鑑み、飛灰中の有用重金属を塩素、カルシウム等の塩類と分離し、製錬工程において再利用可能な形で分離回収でき、且つ飛灰処理の多量に塩素を含有する排水について６価セレンが混入しても他の重金属等と共に、室温でも容易に除去でき、厳しい地域排水規制に対応できる飛灰処理方法の提供を目的とする。
【００１５】
【課題を解決するための手段】
上記の目的を達成するため、本発明は、第１に、亜鉛、銅、鉛の少なくとも１種と塩素及びセレンとを含む飛灰の処理方法であって、前記飛灰に鉱酸を加えてスラリー化し、ｐＨを５以下に調整して塩類を溶出させる塩類溶出工程と、該塩類溶出工程のスラリーに中和剤を添加してｐＨを８〜１２に調整し、重金属含有殿物と塩類含有濾液とに固液分離する重金属分離工程と、該重金属分離工程で得られた塩類含有濾液から溶存酸素を除去する溶存酸素除去工程と、該溶存酸素除去工程の処理液に第１鉄塩を添加し、引き続きアルカリ剤を添加してｐＨを８〜１１に調整し、鉄塩共沈殿物と濾過水とに固液分離する鉄塩共沈工程とからなる重金属等を含有する飛灰の処理方法であり；第２に、前記鉄塩共沈工程は、前記重金属分離工程で得られた塩類含有濾液に第１鉄塩を添加した後、該塩類含有濾液から溶存酸素を除去する溶存酸素除去工程を経て、該溶存酸素除去工程の処理液に、アルカリ剤を添加してｐＨを８〜１１に調整し、鉄塩共沈殿物と濾過水とに固液分離する工程であることを特徴とする前記第１に記載の飛灰の処理方法であり；第３に、前記鉄塩共沈工程は、前記重金属分離工程で得られた塩類含有濾液から溶存酸素を除去する溶存酸素除去工程を経て、該溶存酸素除去工程の処理液に、第１鉄塩を添加し、引き続きアルカリ剤を添加してｐＨを８〜９に調整し、次いで、ｐＨを９〜１１に調整して鉄塩共沈殿物と濾過水とに固液分離する工程であることを特徴とする前記第１に記載の飛灰の処理方法であり；第４に、前記鉄塩共沈工程は、前記重金属分離工程で得られた塩類含有濾液に第１鉄塩を添加した後、該塩類含有濾液から溶存酸素を除去する溶存酸素除去工程を経て、該溶存酸素除去工程の処理液に、引き続きアルカリ剤を添加してｐＨを８〜９に調整し、次いで、ｐＨを９〜１１に調整した後、鉄塩共沈殿物と濾過水を固液分離する工程であることを特徴とする前記第１に記載の飛灰の処理方法であり；第５に、前記溶存酸素を除去する方法が、前記塩類含有濾液をｐＨが７以下で金属と接触させる手段を含むことを特徴とする前記第１〜第４のいずれかに記載の飛灰の処理方法であり；第６に、前記金属が鉄粉であることを特徴とする前記第５に記載の飛灰の処理方法であり；第７に、前記鉄塩共沈工程における鉄塩共沈殿物を含有する被処理水から鉄粉を磁気選別により回収して前記溶存酸素除去工程に供すると共に、鉄粉を除去した前記被処理水を鉄塩共沈殿物と濾過水とに固液分離し、得られた鉄塩共沈殿物をｐＨ４以下の酸性液で溶解し、濾別して得られた濾過液を２価鉄源として前記第１鉄塩の添加処理に供することを特徴とする前記第６に記載の飛灰の処理方法であり；第８に、前記鉄塩共沈工程において固液分離して得られた鉄塩共沈殿物をｐＨ４以下の酸性液で溶解した後、溶解液中の鉄粉を磁気選別により回収して前記溶存酸素除去工程に供すると共に、鉄粉を除去した前記溶解液を濾過して得られる濾過液を２価鉄源として前記第１鉄塩の添加処理に供することを特徴とする前記第６に記載の飛灰の処理方法であり；第９に、前記溶存酸素を除去する方法が、少なくとも、前記塩類含有濾液を非酸化性ガスでバブリングする手段を含むことを特徴とする前記第１〜第４のいずれかに記載の飛灰の処理方法であり；第１０に、前記溶存酸素を除去する方法が、少なくとも、前記塩類含有濾液を減圧処理する手段を含むことを特徴とする前記第１〜第４のいずれかに記載の飛灰の処理方法であり；第１１に、前記溶存酸素を除去する方法が、少なくとも、前記塩類含有濾液に溶存酸素除去剤を添加する手段を含むことを特徴とする前記第１〜第４のいずれかに記載の飛灰の処理方法であり；第１２に、前記溶存酸素の除去を前記塩類含有濾液の溶存酸素が０．５ｍｇ／ｌ以下になるまで行うことを特徴とする前記第１〜第１１のいずれかに記載の飛灰の処理方法であり；第１３に、前記鉄塩共沈工程における前記塩類含有濾液の処理温度が２０〜３０℃であることを特徴とする前記第１〜第１２のいずれかに記載の飛灰の処理方法であり；第１４に、前記鉄塩共沈工程からの濾過水に、吸着剤を接触させてＣＯＤ成分と重金属とを吸着させる吸着処理を施して清浄排水を得るＣＯＤ成分及び重金属吸着工程を有することを特徴とする前記第１〜第１３のいずれかに記載の飛灰の処理方法であり；第１５に、前記重金属分離工程で得られた前記塩類含有濾液に、アルミニウム塩を添加してｐＨを５〜８に調整し、アルミ塩共沈殿物と濾過水とに固液分離するアルミ塩共沈工程を設けることを特徴とする前記第１〜第１４のいずれかに記載の飛灰の処理方法であり；第１６に、前記重金属分離工程で得られた前記重金属含有殿物に鉱酸を加えてリパルプすると共に、ｐＨを５以下に調整し、鉛を主体とする鉛産物と濾液とに固液分離する鉛産物回収工程と、該鉛産物回収工程で得られた濾液に中和剤を添加してｐＨを８以上に調整し、銅と亜鉛を主体とする銅・亜鉛産物と濾過水とに固液分離する銅・亜鉛産物回収工程とを有することを特徴とする前記第１〜第１５のいずれかに記載の飛灰の処理方法であり；第１７に、前記重金属分離工程で得られた前記重金属含有殿物に鉱酸を加えてリパルプすると共に、ｐＨを５以下に調整し、引き続き中和剤を添加してｐＨを８以上に調整した後、重金属産物と濾過水とに固液分離する重金属産物回収工程を有することを特徴とする前記第１〜第１５のいずれかに記載の飛灰の処理方法であり；第１８に、前記重金属産物を水で洗浄する洗浄工程を有することを特徴とする前記１７に記載の飛灰の処理方法であり；第１９に、前記溶存酸素除去工程が、非酸化性雰囲気中で行われることを特徴とする前記第１〜第１８のいずれかに記載の飛灰の処理方法であり；第２０に、前記第１鉄塩の添加処理と前記鉄塩共沈工程が非酸化性雰囲気中で行われることを特徴とする前記第１〜第１９のいずれかに記載の飛灰の処理方法である。
【００１６】
【発明の実施の形態】
本発明の実施の形態を、都市ゴミ焼却施設等の焼却灰処理で発生する二次飛灰の処理方法の場合を例に図１の全処理工程図と、処理の具体例を示す図２〜図５の部分工程図を参照して説明する。先ず、図１に示すように、飛灰は、塩類溶出工程と重金属分離工程を経て、塩類含有濾液と重金属含有殿物とに分離する。すなわち、図２のように、飛灰を水と混合させてスラリー化させ、このスラリーを攪拌しながら、塩酸または硫酸等の鉱酸を添加してｐＨを５以下、好ましくは、ｐＨ４程度に調整し、塩素、ナトリウム、カルシウム等の塩類、特に塩化物を液側に移行させる（塩類溶出工程）。なお、前記スラリーのｐＨは、飛灰の組成によって異なるため、鉱酸の添加量は飛灰に応じて調整する。したがって、前記スラリーのｐＨがすでに最適ｐＨにある場合には鉱酸を加える必要はない。
【００１７】
次いで、スラリーに水酸化ナトリウムまたは炭酸ナトリウム等のアルカリ中和剤を添加してｐＨを８〜１２の間に調整した後、固液分離することによって重金属含有殿物と、セレンを含む塩素、ナトリウム、カルシウム等を含有する塩類含有濾液とに固液分離する（重金属分離工程）。以上のように、塩類溶出工程で飛灰中の塩類を酸性側において十分に溶出させた後、重金属分離工程でこの酸性の溶出液を中和することにより、重金属含有殿物中の塩素等の塩類の含有率を著しく減少させることが可能となる。この塩素含有率の低い重金属含有殿物は水洗後、製錬工程の原料とすることができる。塩類含有濾液については、第１鉄塩の添加による鉄塩凝集処理を行ってセレンや重金属を含む鉄塩共沈殿物とに濾過水に分別する（鉄塩共沈工程）。
【００１８】
前記塩類含有濾液がフッ素を含有する場合は、鉄塩共沈工程前後に除去を図る必要があるが、鉄塩共沈行程に先立って除去すると効果的である。すなわち、前記塩類含有濾液に塩化アルミニウム等のアルミニウム塩を添加してｐＨを５〜８程度に調整することにより、溶存するフッ素を凝集する水酸化アルミニウム（Ａｌ（ＯＨ）₃）と共沈させ、固液分離することにより、アルミニウム塩共沈殿物と濾過水を得ることができる（アルミ塩共沈工程）。このアルミ塩共沈工程において、水酸化物の沈降濾過を促進させるために、凝集剤と共に、珪藻土等の濾過助剤を添加するのが好ましい。
なお、前記重金属分離工程からの塩類含有濾液が問題になる程度のフッ素を含まない場合は、このアルミ塩共沈工程を省略し、前記塩類含有濾液をそのまま溶存酸素除去工程に供することができる。
【００１９】
次に、図１に示したように、前記アルミ塩共沈工程からの濾過水から残存重金属の除去を行う鉄塩共沈工程において、特に、含有セレンの共沈を図るため、鉄塩共沈工程に先んじて、溶存酸素除去工程を実施する。また、鉄塩共沈工程においては、第１鉄塩の存在下で、溶存酸素が除去された室温の、好ましくは２０〜３０℃の処理液をｐＨ８〜１１にｐＨ調整操作することにより、溶存する６価セレンを還元すると共に、同時に生成する水酸化第一鉄の凝集フロックに吸着させて鉄塩共沈殿物を得るものである。
【００２０】
前記塩類含有濾液またはアルミ塩共沈工程からの濾過水の溶存酸素は、０．５ｍｇ／ｌ以下にまで低減しないと、前記水酸化第一鉄の安定性の面から、処理排水のセレンを排水基準値の０．１ｍｇ／ｌ以下にまで低減させるのは困難である。また、この溶存酸素の除去工程及び鉄塩共沈工程は、大気雰囲気下で実施できるが、好ましくは非酸化性雰囲気下において実施する方がより高濃度のセレン含有量まで対応が可能となる。
【００２１】
溶存酸素を除去するには、(1) ｐＨ７以下の酸性域において、被処理水を鉄粉等金属と接触させる手段、(2) Ｎ₂ガス等非酸化性ガスで被処理水をバブリングする手段、(3) 被処理水に２価鉄塩を溶解して中和する手段や亜硫酸ソーダ等溶存酸素除去試薬（還元剤）を添加する手段、(4) 被処理水を減圧処理する手段等がある。それ以外の溶存酸素を除去する処理手段も当然本発明に含まれるものであり、また、これらの手段は１つまたは２つ以上に組合わせて利用することができる。
【００２２】
非酸化性雰囲気は、反応液槽に被処理水を入れた後、その反応液槽の上部空間にＮ₂等非酸化性ガスを流入させて空気と置換させ、被処理水を上部シールすることで得られる。非酸化性ガスは、Ｎ₂ガス以外にアルゴン、ヘリウム等の不活性ガス等を用いることができるが、Ｎ₂ガスがコスト的に有利である。Ｎ₂ガス等非酸化性ガスによるバブリング処理の場合は、蓋付きの反応槽を用いて行うことにより、実質的に上部空間は置換状況すなわち非酸化性雰囲気状況となるので、バブリング処理時は、特に上部シールを行う必要はない。
【００２３】
溶存酸素の除去がセレンの除去に及ぼす効果は顕著であり、例えば、純水に試薬を添加して６価セレンの濃度を高濃度の３４ｍｇ／ｌにした液を用い、スターラーでの攪拌下で液温を２５℃に保持させるようにし、５００ｍｇ／ｌのＦｅ²⁺を存在させ、ｐＨ９のアルカリ域で３０分反応させて水酸化第１鉄を凝集させた場合において、液残留セレン濃度は２０ｍｇ／ｌであったのに対し、液槽底部からＮ₂ガスをバブリングさせて溶存酸素を除去した場合、同じ液温２５℃の同じ処理で、セレン濃度は、１．９ｍｇ／ｌとなった。また、溶存酸素を除去することなく、液温を比較的高温度の４５℃で液槽をＮ₂ ガスで上部シールした場合、セレン濃度は２．０ｍｇ／ｌであった。すなわち、溶存酸素を除去して鉄塩共沈処理を行う本発明によれば、室温処理で十分な脱セレン効果を得ることができる。
【００２４】
被処理排水の溶存酸素と処理排水のセレン濃度とは密接に関連しており、溶存酸素の除去は、６価セレンの還元、水酸化第１鉄の安定とその吸着性等に顕著な影響力を及ぼしている。
飛灰の処理では、カルシウムや塩素等を多量に含む高塩濃度の排水が得られるが、このような高塩濃度排水は塩類の少ない排水に比べて６価セレンが除去し難いという問題がある。このような高塩濃度排水を元液として溶存酸素の影響力を調査したところでは、３０℃以下の室温処理で処理排水のセレンを排水基準の０．１ｍｇ／ｌ以下とするには、溶存酸素除去処理で、被処理水の溶存酸素を０．５ｍｇ／ｌ以下にまで低減すればよいことが見出された。
【００２５】
また、本発明では、鉄塩共沈工程において、６価セレンの還元と水酸化第一鉄の凝集フロックへのセレンの吸着のため、第１鉄塩を添加する。この被処理濾過水への第１鉄塩の添加は、被処理濾過水の溶存酸素除去工程の前であっても、後であってもよいが、この溶存酸素除去工程を含めて全工程を非酸化性雰囲気下で処理するのが好ましい。また、溶存酸素除去用鉄塩として第１鉄塩を使用する場合は、第１鉄塩の使用はセレン除去のための鉄塩共沈処理の場合との２段階使用になる。
【００２６】
被処理水への第１鉄塩の添加は、通常、反応促進のため過剰に行われるので、セレンの共沈のための好適なｐＨ９前後におけるセレンの除去後も、鉄イオンがその排出基準値１０ｍｇ／ｌ以下を若干上回る量で残留する場合がある。この過剰量の残留鉄イオンの除去のため、セレンの共沈反応後、さらにｐＨ値を高めて水酸化鉄の生成を進める２段階の鉄塩共沈法を行うことが好ましい。
【００２７】
飛灰処理による高塩濃度排水を元液としてｐＨ値と残留セレンと残留鉄イオンとの関係を調査したところでは、第１段階でｐＨ８〜９、好ましくはｐＨ９で効率的にセレンを共沈させた後、その共沈殿物を含有したままで、第２段階として被処理液をｐＨ９〜１１に、好ましくは、約１０．５に再調整し、水酸化鉄の二次凝集を行わせることにより、セレンと鉄を共に排水基準値以下に抑えることができ、また、同時に、排水中に残存するカドミウム、アンチモン、水銀、鉛等の重金属も排水基準値以下に抑えることができることが確認された。なお、前記水酸化第１鉄の二次凝集の際、ｐＨを１１以上にしても、水酸化第１鉄の沈殿量は増えず、一方、吸着セレンが若干再溶解する傾向がみられるので、ｐＨは１１以下、好ましくは１０．５程度に止めたほうがよい。
【００２８】
以下、図３の部分工程図により、被処理水に金属（鉄粉）を接触させる溶存酸素除去工程と第１鉄塩を添加する鉄塩共沈工程の具体例を説明する。
なお、図示の工程は、鉄塩の凝集を２段階で行うものであるが、ｐＨ８〜１１での１段凝集に止めてもよい。
先ず、アルミ塩共沈工程からの濾過水を反応槽に供給する。反応槽は完全密閉槽である必要はなく、非酸化性ガスの連続供給で上部空間を非酸化性雰囲気とすることが可能で、ガス供給管及び薬剤等の供給口と共に攪拌装置を具備する蓋体を有するものであればよい。
【００２９】
濾過水即ち被処理水を反応槽に供給した後、反応槽上部の空間に、非酸化性ガスとしてＮ₂ガスを一定の供給速度で供給して空気と置換させ、被処理水をシール状態とすることにより、非酸化性雰囲気の形成を行う。次いで、この被処理水を塩酸等酸性剤によりｐＨ３程度の酸性域に保持し、鉄粉を例えば０．３〜１．０ｇ／ｌ供給し、攪拌機により強く攪拌する。鉄粉は少量が溶けて液中の酸素と反応し、０．１ｍｇ／ｌ以下にまで溶存酸素を低減させることができる。
【００３０】
溶存酸素計により、０．５ｍｇ／ｌ以下、好ましくは、０．１ｍｇ／ｌ以下にまで溶存酸素が低減したことを確認した後、引き続き非酸化性雰囲気中で、被処理水にＦｅＣｌ₂、ＦｅＳＯ₄等２価鉄塩をＦｅとして５００ｍｇ／ｌ程度を投入し、攪拌して溶解させた後、ＮａＯＨ等アルカリ剤を添加し、ｐＨ８〜９とし、このｐＨを維持したまま中和反応させることにより、２価の鉄イオン（Ｆｅ²⁺）はＦｅ（ＯＨ）₂となって凝集（一次凝集）し、液中のセレンはこのＦｅ（ＯＨ）₂で還元され、吸着されて共沈する。３０分程度でセレンは殆ど沈殿となるが、液中に残存するＦｅ²⁺が多く鉄分の排水基準値を越える場合、さらに、ＮａＯＨ等アルカリ剤によりｐＨ９〜１１程度に上げ、Ｆｅ（ＯＨ）₂ の二次凝集を促進させる。この時、凝集剤と共に、沈降濾過助剤として珪藻土を添加することが好ましい。
【００３１】
得られたパルプ状の殿物含有処理水は沈降装置、フィルタープレス等の手段でセレンと重金属を含む鉄塩共沈殿物と濾過水とに固液分離する。これによって、セレンが容易に０．１ｍｇ／ｌ以下に低減された清浄な濾過水を得ることができる。
【００３２】
すなわち、第１鉄塩を添加してｐＨ調整することにより、高い溶存塩素に拘らず、第１鉄イオンが総て水酸化第１鉄を生成し、この晶出初期の活性な水酸化第１鉄がその沈殿過程でセレンの他、液中の残存重金属例えば水銀、銅、鉛、亜鉛、カドミウム、クロム、砒素、アンチモン、ニッケル等を取り込んで共沈させるものと考えられ、重金属を極低レベルまで低減できる等除去効率を飛躍的に高めることができる。例えば、従来の技術では活性炭等吸着剤による吸着処理を必要としていた水銀についても、本方法の鉄塩共沈処理で十分に処理可能となっている。
【００３３】
また、前記のように溶存酸素の除去に還元剤として鉄粉を使用する場合、作業効率の点から、過剰量の鉄粉が添加されるが、ｐＨ調整による水酸化鉄凝集反応の終了後、固液分離に先立ち、殿物含有処理水（パルプ水）から磁気選別等により過剰量の鉄粉が回収でき、再度溶存酸素の除去処理に供することができる。さらに、鉄粉を磁気選別により回収した後、前記殿物含有処理水を固液分離し、得られた鉄塩共沈殿物を、図示のように、ｐＨ１〜４、好ましくは２〜４の酸性液で溶解し、セレンを含む不溶解残渣を濾別し、得られた濾過液を２価鉄源として再度前記第１鉄塩の添加処理に利用することができる。この場合、殿物溶解用の前記酸性液がｐＨ１より低いと、セレンが微量溶け出すことがあり、ｐＨが４より高いと、鉄塩の溶解が不十分である。
【００３４】
あるいは、前記水酸化鉄凝集反応の終了後、殿物含有処理水をそのまま固液分離し、得られた鉄塩共沈殿物をｐＨ４以下の酸性液で溶解した後、溶解液中に残留する鉄粉を磁気選別で回収し、再度前記溶存酸素の除去処理に供すると共に、さらに鉄粉を除いた溶解液を濾過し、セレンを含む不溶解物を濾別し、得られた濾過液を２価の鉄源として再度前記第１鉄塩の添加工程に供することもできる。
【００３５】
なお、溶存酸素除去処理を非酸化性ガスのバブリングによって行う場合は、蓋体を備える反応槽に、処理水を供給し、この被処理水中に槽底に設けた給気管を通してＮ₂ガス等非酸化性ガスを吹き込むバブリング操作により、被処理水中の溶存酸素を非酸化性ガスに同伴させる形で、０．１ｍｇ／ｌ以下にまで低減させることができる。この場合、非酸化性ガスによるバブリングが反応槽上部空間のガス置換を兼ねて非酸化性雰囲気の形成を行うことになるので、鉄粉等金属や試薬を添加する場合のように、特に上部空間のガス置換操作は必要ではない。ただし、バブリング終了後すなわち溶存酸素の除去後の中和処理や鉄塩共沈処理は非酸化性雰囲気中で行う方が好ましく、前記バブリング処理後、反応槽の上部空間に非酸化性ガスを吹き込む上部シール処理を行うとより効果的である。
【００３６】
また、水酸化物の凝集を３段階で行う鉄塩共沈工程の具体例を説明する（図示せず）。
被処理水を、攪拌装置を具備する反応槽に供給し、空気を巻き込まない程度の攪拌を行う。この攪拌は反応終了まで継続する。なお、Ｎ₂ ガスで上部シールする場合は、強攪拌しても構わない。液温は好ましくは２５〜３０℃とする。反応槽を大気開放下、好ましくはＮ₂ シール状態下におき、被処理水にＦｅＳＯ₄ ・７Ｈ₂ Ｏ等２価鉄塩をＦｅ²⁺として４００ｍｇ／ｌ程度を投入し、ＮａＯＨ等アルカリ剤によりｐＨを８〜９好ましくは９程度に調整して１５分間程度保持させ、水酸化鉄（Ｆｅ（ＯＨ）₂ ）の生成を図ることにより（一次凝集）、溶存酸素を低減させることができる。この時凝集する水酸化鉄により、液中のセレンもある程度共沈する。
【００３７】
次いで、塩酸等酸性液によりｐＨを７に調整し、再度ＦｅＳＯ₄ ・７Ｈ₂ Ｏ等２価鉄塩をＦｅ²⁺として４００ｍｇ／ｌ程度添加し、ＮａＯＨ等アルカリ剤によりｐＨを８〜９好ましくは９に調整し、１５〜３０分間好ましくは約３０分間保持することにより、水酸化鉄を凝集させ（二次凝集）、セレンを吸着・共沈させることができ、液中のセレンは０．１ｍｇ／ｌ以下にまで十分に除去される。
【００３８】
次に、液中に残存する鉄イオンを除去するため、水酸化鉄殿物を除去することなく、被処理水をＮａＯＨ等アルカリ剤でｐＨ９〜１１好ましくはｐＨ１０．５に調整し約１０分間保持させることにより新たな水酸化鉄の凝集を図る（三次凝集）。１０分経過後、凝集剤と共に沈降濾過助剤として珪藻土を添加し、凝集物を十分に沈降させた後、固液分離し、セレン共沈殿物を回収する。
以上の処理により、セレンおよび鉄をそれぞれ排水基準以下にまで低減した清浄排水を得ることができる。また、水酸化物の凝集は３段以上の多段で行えばより効果が大きい。なお、本反応はバッチ式でも連続式でも可能である。
【００３９】
また、前記鉄塩共沈工程からの濾過水が、なお問題となる程度にＣＯＤ成分または重金属を含む場合は、さらに、図３に示したように、活性炭あるいはキレート剤等の吸着剤によるＣＯＤ成分及び重金属吸着処理に供することにより、ＣＯＤ成分と共に残存する微量の重金属を吸着除去させて清浄排水を得ることができる（ＣＯＤ・重金属吸着工程）。この活性炭等の吸着処理は、勿論カラムを使用してもよいが、前工程の鉄塩共沈液に、顆粒状あるいは粉状で加えて固液分離してもよい。勿論液中のＣＯＤ成分や重金属は除去され、また水酸化鉄の濾過性を極度に改善することができる。
【００４０】
さらに、図４に示したように、前記重金属分離工程からの重金属含有殿物はリパルプあるいはフィルタープレス中での通水洗浄（正洗、逆洗）による水洗浄を行うことにより、塩素、ナトリウム、カルシウム等塩類をさらにこの重金属含有殿物より分離することができ、固液分離後の洗浄濾過水は飛灰のスラリー化用水として前記塩類溶出工程に循環させることができる（殿物洗浄工程）。
【００４１】
得られた洗浄殿物はそのまま製錬工程の原料とすることもできるが、さらに分別あるいは塩類のさらなる低減を図っておくと製錬工程の処理の負担が軽減される。すなわち、さらにこの洗浄殿物に水を加えてリパルプし、塩酸または硫酸等の鉱酸を添加してｐＨを５以下好ましくはｐＨ４以下に調整し、亜鉛、銅、カドミウムを主成分とする重金属を溶解させ、固液分離により、鉱酸に難溶の鉛を主成分とする重金属を回収鉛産物として回収する（鉛産物回収工程）。
【００４２】
前記鉛産物回収工程からの濾液には、アルカリ中和剤を添加してｐＨを８以上好ましくはｐＨ９程度に調整することにより、亜鉛、銅、カドミウムを主成分とする重金属の水酸化物を生成させ、固液分離することにより、銅・亜鉛産物と濾過水を得ることができる（銅・亜鉛産物回収工程）。濾過水は、前記殿物洗浄工程からの洗浄濾過水と併せて、塩類溶出工程における飛灰のスラリー化用水として繰り返すことにより、重金属の回収性と共に飛灰処理の経済性を高めることができる。
【００４３】
前記のように、殿物洗浄工程からの洗浄殿物を鉛産物回収工程と銅・亜鉛産物回収工程の２段階工程で分別処理し、鉛産物と銅・亜鉛産物との２産物を得ることができるが、一方、前記の２段階工程を１段階工程にまとめ、重金属産物の１産物を回収するようにし、重金属回収処理の作業性を高めることもできる。すなわち、図５に示したように、前記洗浄殿物に水を加えてリパルプし、硫酸等鉱酸を添加してｐＨを５以下、好ましくはｐＨ４以下に調整した後、固液分離することなく、さらにその殿物含有液にアルカリ中和剤を添加してｐＨを８以上、好ましくはｐＨ９〜１１に調整した後、固液分離する（重金属産物回収工程）。得られる回収殿物については、さらに水で洗浄して固液分離して塩類を低減した重金属産物を得る（洗浄工程）。洗浄工程からの洗浄濾過水は前記殿物洗浄工程からの洗浄濾過水及び前記重金属産物回収工程からの濾過水と共に、飛灰の塩類抽出工程のスラリー化用水として返戻する。
【００４４】
以上のように、本発明においては、ゴミ焼却施設等からの飛灰を処理して、含まれている銅、亜鉛、鉛等重金属を、塩類と分別して製錬原料として利用できる状態で回収し、さらに、排水としては、従来、除去手段に問題があったセレンを含めて重金属や有害元素が十分に除去され、国の排水規制は勿論、地域の上乗せ規制をも満足できる清浄な濾過水を得ることができるものである。
【００４５】
【実施例】
［実施例１］
＜図２及び図４参照＞１０リットルビーカーに純水８リットルを入れて攪拌しながら、原料としてＡ処理工場の飛灰８００ｇを入れてスラリーとし、１０分間攪拌しながら、鉱酸として３６％塩酸を添加してｐＨを４に調整・維持し、３０分間溶解処理を行い（塩類溶出工程）、次いで、アルカリ中和剤として２００ｇ／ｌのＮａＯＨ液を添加してｐＨを１１に調整し３０分間維持した後、濾過操作により重金属を主とする重金属含有殿物と塩類を主とする塩類含有濾液とに分離した（重金属分離工程）。次に、得られた重金属含有殿物を５リットルビーカーに移し、純水を２．０リットル入れてスラリーとし３０分間攪拌維持した後、洗浄殿物と洗浄濾液を得た（殿物洗浄工程）。
表１に原料飛灰の組成および殿物洗浄工程で得られた洗浄殿物の品位を、また、表２に前記重金属分離工程からの塩類含有濾液の組成を示した。
【００４６】
殿物洗浄工程から得られた前記洗浄殿物を１０リットルビーカーに移し、純水５リットルでリパルプし、９５％Ｈ₂ＳＯ₄を添加し、ｐＨを４に調整して鉛以外の重金属を溶出せしめ、鉛を主とした鉛産物を得た（鉛産物回収工程）。得られた鉛産物の品位を表１に併記した。
さらに鉛産物回収工程で分別された濾液に２００ｇ／ｌのＮａＯＨ液をアルカリ中和剤として添加してｐＨを１１に調整し、銅・亜鉛を主成分とする水酸化物態の銅・亜鉛産物と濾過水とに固液分離した（銅・亜鉛産物回収工程）。得られた銅・亜鉛産物の品位を表１に併記した。
【００４７】
【表１】

【００４８】
【表２】

すなわち、飛灰中の重金属を、鉛を主体とし、塩素等塩類を低減した鉛産物と、銅、亜鉛、カドミウムを主体とし、同様に塩類を低減した銅・亜鉛産物とに分別した製錬原料を得ることができた。
【００４９】
［実施例２］
＜図５参照＞実施例１の殿物洗浄工程で得られた洗浄殿物を１０リットルビーカーに移し、純水５リットルでリパルプし、９５％Ｈ₂ＳＯ₄を添加し、ｐＨを４に調整して攪拌し、３０分後、固液分離することなく、２００ｇ／ｌのＮａＯＨ液を添加してｐＨを９に調整した。１０分後、固液分離して重金属産物と濾過水とを得た（重金属産物回収工程）。
この２段連続ｐＨ調整による洗浄殿物の処理によって得られた重金属産物の成分値を前記表１に併記した。
すなわち、前記鉛産物と前記銅・亜鉛産物を分別することなく、非鉄重金属を塩類と分離して効率的に濃縮して回収することができた。
【００５０】
［実施例３］
＜図２参照＞飛灰を塩類溶出工程と重金属分離工程を経て処理して得られた表３に示す成分値の塩類含有濾液を元液として、処理試験を行った。
この元液２．５リットルを３リットルビーカーに採り、脱フッ素を目的とし、アルミニウム塩として、塩化アルミニウムをアルミニウム量で５０ｍｇ／ｌ分を添加し、２５℃に保持し、ｐＨを７に調整し、３０分間反応させた後、Ｃ濾紙を使用し吸引濾過することによりアルミ塩共沈殿物と濾過水とに分離した（アルミ塩共沈工程）。この濾過水即ち脱フッ素濾液（アルミ塩共沈濾液と表示）のフッ素成分値を表３に併記した。すなわち、十分にフッ素が低減された濾液が得られた。
【００５１】
＜図３参照＞次に、得られた濾過水（脱フッ素濾液）９００ｍｌを１リットルビーカーにとり、蓋をして上部空間にＮ₂ガスを５００ｍｌ／ｍｉｎの割合で流し、上部シール状態とし、スターラー攪拌を行った。反応温度は室温の２５℃に保持するようにした。塩酸液により液のｐＨを３に調整した後、鉄粉を０．５ｇ／ｌの割合で添加し、強い攪拌を行った。１０分間で溶存酸素が０．１ｍｇ／ｌ以下となったことが溶存酸素計により確認された。
引き続き、Ｎ₂ガスによる上部シールを続けながら、第１鉄塩としてＦｅＳＯ₄・７Ｈ₂ＯをＦｅ²⁺の換算量で５００ｍｇ／ｌを添加し、４分間攪拌して溶解させた。
【００５２】
さらに、ＮａＯＨ液でｐＨ９に調整して３０分間保持させ、水酸化第１鉄を凝集させた。次ぎに、ＮａＯＨ液でｐＨを９．５に調整し、１０分間保持させ、再び水酸化第１鉄を凝集させると共に凝集剤と珪藻土を添加した。得られたパルプ液をブフナーで吸引濾過した（鉄塩共沈工程）。
前記凝集処理（鉄塩共沈工程）における１段目のｐＨ＝９の調整反応後に採取した処理水（鉄塩共沈(1)と表示）の成分値と、２段目のｐＨ＝９．５に調整反応後に採取した処理水（鉄塩共沈(2)と表示）のＺｎ、Ｓｅ、Ｆｅ成分値を表３に併記した。
すなわち、セレンと共に、鉄以外の重金属は、１段目のｐＨ調整（ｐＨ＝９）で十分に低減されたが、鉄分は多量に残存した。この残留鉄分は、２段目のｐＨ調整（ｐＨ＝９．５）で十分凝集沈降したことがわかる。
【００５３】
【表３】

【００５４】
［比較例］
［実施例３］と同じ塩類含有濾液を元液として、アルミ塩共沈処理と鉄塩共沈処理を行った。
ただし、［実施例３］で得られたアルミ塩共沈濾液を対象に鉄塩共沈処理を行った。また、この濾液について溶存酸素の除去処理を行わなかった。鉄塩共沈処理は大気開放下で行うと共に、反応液の温度を常温以上の４５℃に保持した。その他については、［実施例３］と同一条件で処理した。
元液の塩類含有濾液の成分値、アルミ塩共沈濾液のフッ素成分値、鉄塩共沈処理における１段目のｐＨ調整（ｐＨ＝９）で反応させた後の処理水（鉄塩共沈(1)と表示）の各成分値、及び、２段目のｐＨ調整（ｐＨ＝９．５）で反応させた後の処理水（鉄塩共沈(2)と表示）のＣｄ、Ｓｅの含有量を表４に示した。
【００５５】
【表４】

【００５６】
すなわち、本発明の［実施例３］は、常温での処理でありながら４５℃以上で処理した［比較例］の場合と同等の結果が得られている。
この結果から、溶存酸素の除去を行い、室温で鉄塩の添加処理を行う本発明の方法は、液の加温下で行う鉄塩共沈処理とほぼ同等の効果を有しており、加温処理のための設備や操作を必要としない有利面を備えているのがわかる。
【００５７】
【発明の効果】
飛灰中の塩類を酸により十分に溶解した後、中和して重金属含有殿物を回収すると共に、得られた高塩濾液について溶存酸素の除去と鉄塩との共沈を図る本発明によれば、塩素等塩類が除かれて製錬工程の原料となり得る重金属含有殿物の回収が可能となり、また、６価セレンが混入した高塩濾液についても、セレンの他、鉄、銅、鉛等の残留重金属を同時に極低レベルまで低減でき、厳しい排水規制にも対応できる清浄排水が得られるという効果を奏する。
特に前記高塩濾液からのセレンの除去が室温処理で可能となったことから、作業性が向上し、また液の加温設備を必要とせず、設備コストも安価にすむという効果を奏する。
【００５８】
重金属分離工程からの塩類含有濾液またはアルミ塩共沈工程からの濾過水を被処理水としてその溶存酸素を除去する手段としては、金属、特に鉄粉を用いる手段は、鉄粉が安価で、溶存酸素除去薬剤と共に取扱い性がよいという利点を有し、バブリングや減圧手段によるものは、作業効率がよいという利点を有する。また、鉄粉を用いた場合にあっては、鉄塩共沈反応後、容易に鉄粉と鉄塩の回収再利用が図れるという効果を奏する。
【００５９】
さらに、前記重金属含有殿物を洗浄し、またこの洗浄殿物を酸液処理した後中和処理して重金属産物を得る工程を有するものにあっては、さらなる塩類の除去を行い、また、重金属の分別回収を可能とし、製錬工程における重金属の回収処理作業の負担を軽減できる効果を奏する。
【図面の簡単な説明】
【図１】本発明の重金属等を含有する飛灰の処理方法を示す全工程図である。
【図２】図１の飛灰の処理方法における塩類溶出工程からアルミ塩共沈工程に至る処理法の具体例を示す部分工程図である。
【図３】図１の飛灰処理方法におけるアルミ塩共沈工程からの濾過水の処理法の具体例を示す部分工程図である。
【図４】図１の飛灰処理方法における重金属含有殿物の処理法の具体例を示す部分工程図である。
【図５】図１の飛灰処理方法における重金属含有殿物の処理法の別の具体例を示す部分工程図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to fly ash containing chlorine and selenium in addition to heavy metals such as copper, lead and zinc generated from incinerators, melting furnaces or cement kilns for treating sludge in municipal waste incineration facilities and industrial waste incinerators. It relates to the processing method.
[0002]
[Prior art]
Garbage discharged from general offices and households (referred to as “urban waste” or “general waste”) is collected and incinerated at municipal waste incineration facilities, industrial waste incineration plants, and the like. Incineration ash and fly ash generated from the incinerator at that time are subjected to chemical treatment or intermediate treatment such as melting furnace and cement kiln treatment, and are deposited in the final disposal site.
[0003]
However, in the intermediate treatment in the above melting furnace, cement kiln, etc., heavy metals such as lead, zinc, and cadmium with high vapor pressure volatilize in the furnace and enter the exhaust gas. There was a problem that it would condense and become fly ash again.
This second fly ash contained a large amount of heavy metals such as lead, copper, zinc and cadmium together with chlorine, sodium, calcium and selenium, and a stable treatment method including recovery of these was required. .
[0004]
JP-A-7-109533 discloses such fly ash by suspending fly ash in water in a tank and adjusting the pH of the suspension to an appropriate value in the alkali range by adding acid or alkali. It discloses a method for precipitating heavy metals in fly ash as hydroxides and recovering the precipitates. The present applicant has also filed a method for coping with the wet processing method (Japanese Patent Laid-Open Nos. 8-117727 and 8-141539).
[0005]
JP-A-8-117724 discloses a first step in which fly ash is slurried with water, pH-adjusted and solid-liquid separated, and the residue from the first step is repulped with an acid solution and adjusted to pH 3 or lower. After that, a second step of solid-liquid separation to obtain a lead residue, and a neutralizer or further sodium hydrosulfide added to the acidic filtrate from the first step and the second step to add a residue containing zinc and copper A method comprising a third step of separating by filtration and using filtered water as a drainage liquid is disclosed. JP-A-8-141539 discloses solid-liquid separation by neutralizing fly ash with water and a neutralizing agent. A first step of repulping the residue from the first step and adjusting the pH to about 3 with sulfuric acid, followed by solid-liquid separation to obtain a lead residue, and an alkali in the filtrate from the second step A third step of adding a neutralizing agent to filter the precipitate containing zinc and copper, and the filtered water of the third step in the first step Repeated as a liquid, a method of draining process by adding a sulfurizing agent are disclosed for filtrate from the first step.
[0006]
By such a wet treatment method, heavy metals contained in fly ash are stably separated and effectively recovered as heavy metal resources, and waste water after wet treatment of fly ash is treated with national wastewater standards, that is, water quality. It has become possible to detoxify in accordance with the regulations of Article 3, Paragraph 1 of the Pollution Control Law.
[0007]
[Problems to be solved by the invention]
However, as seen in the above-mentioned JP-A-7-109533, a large amount of salts such as calcium chloride may get into the recovered heavy metal deposits, and in the smelting process, heavy metals are recycled because they dislike the introduction of chlorine. On the other hand, there was still a problem. In recent years, treatment wastewater has become more restrictive due to concerns over environmental pollution in some regions, and is subject to additional regulations with stricter standards that exceed the national wastewater standards. For example, according to the local ordinance (I city additional standard value), cadmium 0.01 mg / l (national wastewater standard value 0.1 mg / l, the same applies hereinafter), fluorine 10 mg / l (15 mg / l), mercury 0 .0005 mg / l (0.005 mg / l) and COD 20 mg / l (120 mg / l) are severely regulated.
[0008]
Furthermore, wastewater obtained by wet-treating fly ash contains a large amount of chlorine ranging from 20 to 50 g / l, and dissolved heavy metals easily form chloride complex ions, which are very difficult to remove. The current situation is that there is a case where the conventional technology cannot cope with the above-mentioned additional regulations. In addition, even when selenium is mixed in the wastewater, it is very difficult to remove it below the national wastewater standard value (0.1 mg / l) by the conventional method, and it takes a lot of man-hours and costs. is there.
[0009]
As a method for removing selenium in waste water, an iron powder replacement treatment method, an adsorption treatment method using ferric hydroxide, and the like are known. In the iron powder replacement treatment method, SeO_Three ^2- Regarding the removal of selenite ion (hereinafter referred to as tetravalent selenium), it was possible to reduce it to below the effluent standard value, but SeO_Four ^2- Regarding the removal of (selenate ion; hereinafter referred to as hexavalent selenium), there is a problem that the removal ability is poor, and the adsorption treatment method in which selenium is adsorbed and removed by the aggregated floc of ferric hydroxide can be adsorbed. Therefore, the conventional removal methods as described above have problems in application to wastewater treatment containing hexavalent selenium having a relatively high concentration.
[0010]
Further, for example, in JP-A-6-79286, after adding a large amount of ferrous sulfate suitable for the amount of selenium to the waste water, a neutralizing agent is added to adsorb the selenium to the ferric hydroxide which aggregates. And a method for removing them is disclosed. However, this method has a problem that the removal efficiency of hexavalent selenium is poor and the cost is high.
[0011]
Further, JP-A-8-132074 discloses a method of removing selenium as a residue by maintaining waste water at a pH of 9 or higher and a temperature of 70 ° C. or higher in the presence of a transition metal compound such as ferrous chloride. Is disclosed. However, in this method, since the hexavalent selenium cannot be efficiently removed unless the liquid temperature is substantially raised to 80 ° C. or more, the temperature is increased, and the temperature of the waste water becomes high. There was a problem.
[0012]
On the other hand, as a technique proposed by the present inventors, there is a method disclosed in JP-A-8-267076. In this method, divalent iron ions are dissolved in selenium-containing waste water, and while maintaining the liquid temperature at 30 ° C. or higher in the atmosphere, an alkali agent is added to neutralize the solution to pH 8 to 10 to obtain a solid solution. Liquid separation is performed to remove the residue, or preferably, the mixture is neutralized to pH 8 to 10 by adding an alkali agent while maintaining the temperature at 30 ° C. or higher while blocking air, and then solid-liquid separation is performed. In this method, the amount of selenium in the waste water is reduced to 0.1 mg / l or less by removing the substances.
[0013]
[Problems to be solved by the invention]
The method disclosed in the above-mentioned JP-A-8-267076 can easily remove hexavalent selenium to 0.1 mg / l or less, but in the case of the invention in the above-mentioned JP-A-8-132004 Although the temperature is not so high, problems remain in workability and economy, such as the necessity of heating the liquid.
[0014]
In view of such a situation, the present invention can separate useful heavy metals in fly ash from salts such as chlorine and calcium, and can be separated and recovered in a form that can be reused in the smelting process, and a large amount of fly ash can be treated with chlorine. The purpose of the present invention is to provide a fly ash treatment method that can be easily removed at room temperature together with other heavy metals even when hexavalent selenium is mixed in wastewater containing selenium, and can comply with strict regional drainage regulations.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, first, the present invention is a method for treating fly ash comprising at least one of zinc, copper and lead, chlorine and selenium, wherein a mineral acid is added to the fly ash. Slurry, adjust the pH to 5 or less and elute the salt, and adjust the pH to 8-12 by adding a neutralizing agent to the slurry of the salt elution step. A heavy metal separation step for solid-liquid separation into a filtrate, a dissolved oxygen removal step for removing dissolved oxygen from the salt-containing filtrate obtained in the heavy metal separation step, and a ferrous salt added to the treatment liquid of the dissolved oxygen removal step Subsequently, an alkali agent is added to adjust the pH to 8 to 11, and a method for treating fly ash containing heavy metals and the like comprising an iron salt coprecipitation step of solid-liquid separation into an iron salt coprecipitate and filtered water Second, the iron salt coprecipitation step is obtained in the heavy metal separation step. After adding ferrous salt to the salt-containing filtrate, a dissolved oxygen removal step is performed to remove dissolved oxygen from the salt-containing filtrate, and an alkaline agent is added to the treatment liquid of the dissolved oxygen removal step to adjust the pH to 8 The method for treating fly ash according to the first aspect, characterized in that the method is a step of solid-liquid separation into an iron salt coprecipitate and filtered water; In the precipitation step, a ferrous salt is added to the treatment liquid of the dissolved oxygen removal step through the dissolved oxygen removal step of removing dissolved oxygen from the salt-containing filtrate obtained in the heavy metal separation step, and then the alkaline agent is added. The first step is characterized in that it is a step of adding and adjusting the pH to 8 to 9, and then adjusting the pH to 9 to 11 and solid-liquid separation into an iron salt coprecipitate and filtered water. 4th, the iron salt coprecipitation step is the heavy metal separation step. After adding a ferrous salt to the obtained salt-containing filtrate, a dissolved oxygen removing step of removing dissolved oxygen from the salt-containing filtrate, and subsequently adding an alkaline agent to the treatment liquid of the dissolved oxygen removing step to adjust the pH After adjusting the pH to 8-9 and then adjusting the pH to 9-11, it is a step of solid-liquid separation of the iron salt coprecipitate and filtered water. Fifth, fifth, the method for removing dissolved oxygen includes means for bringing the salt-containing filtrate into contact with a metal having a pH of 7 or less. The fly ash treatment method according to claim 5; sixth, the fly ash treatment method according to claim 5, wherein the metal is iron powder; and seventh, the iron salt coprecipitation step. Iron powder is recovered from the water to be treated containing iron salt coprecipitate in Japan by magnetic separation and dissolved. While being subjected to an oxygen removal step, the treated water from which iron powder has been removed is solid-liquid separated into an iron salt coprecipitate and filtered water, and the obtained iron salt coprecipitate is dissolved in an acidic solution having a pH of 4 or less, The method for treating fly ash according to the sixth aspect, wherein the filtrate obtained by filtration is subjected to a treatment for adding the ferrous salt as a divalent iron source; After the iron salt coprecipitate obtained by solid-liquid separation in the precipitation step is dissolved in an acidic solution having a pH of 4 or less, the iron powder in the solution is recovered by magnetic sorting and used for the dissolved oxygen removal step, The fly ash treatment method according to the sixth aspect, wherein the filtrate obtained by filtering the solution from which the powder has been removed is subjected to an addition treatment of the ferrous salt using a divalent iron source; Ninth, the method for removing dissolved oxygen includes at least removing the salt-containing filtrate with a non-oxidizing gas. The fly ash treatment method according to any one of the first to fourth aspects, further comprising a means for bringing about; tenth, the method for removing dissolved oxygen includes at least the salt-containing filtrate. The method for treating fly ash according to any one of the first to fourth aspects, comprising means for performing a decompression treatment; eleventh, the method for removing dissolved oxygen includes at least the salt-containing filtrate. The method for treating fly ash according to any one of the first to fourth aspects, further comprising means for adding a dissolved oxygen removing agent to the ash; and twelfth, the salt-containing filtrate for removing the dissolved oxygen. The fly ash treatment method according to any one of the first to eleventh aspects, wherein the dissolved oxygen is reduced to 0.5 mg / l or less; thirteenth, in the iron salt coprecipitation step The processing temperature of the salt-containing filtrate is 20-30 ° C. 14. The fly ash treatment method according to any one of the first to twelfth aspects, wherein the COD component is obtained by bringing an adsorbent into contact with the filtered water from the iron salt coprecipitation step. The fly ash treatment method according to any one of the first to thirteenth aspects, further comprising: a COD component that obtains clean wastewater by performing an adsorption treatment for adsorbing heavy metal and heavy metal; and a heavy metal adsorption step; Further, an aluminum salt coprecipitation step for adjusting the pH to 5 to 8 by adding an aluminum salt to the salt-containing filtrate obtained in the heavy metal separation step and solid-liquid separation into an aluminum salt coprecipitate and filtered water The method for treating fly ash according to any one of the first to fourteenth aspects, comprising: adding a mineral acid to the heavy metal-containing residue obtained in the heavy metal separation step. While repulping, adjust the pH to 5 or less, mainly lead A lead product recovery step for solid-liquid separation into a lead product and a filtrate, a neutralizer is added to the filtrate obtained in the lead product recovery step to adjust the pH to 8 or more, and copper and zinc are mainly used. A method for treating fly ash according to any one of the first to fifteenth aspects, further comprising: a copper / zinc product recovery step for solid-liquid separation between the copper / zinc product and the filtered water. In addition, after adding mineral acid to the heavy metal containing residue obtained in the heavy metal separation step and repulping, adjusting the pH to 5 or less, and subsequently adjusting the pH to 8 or more by adding a neutralizer, The method for treating fly ash according to any one of the first to fifteenth aspects, further comprising a heavy metal product recovery step for solid-liquid separation into a heavy metal product and filtered water; The fly ash according to 17 above, further comprising a washing step of washing with water. Nineteenth, the fly ash treatment method according to any one of the first to eighteenth aspects, wherein the dissolved oxygen removal step is performed in a non-oxidizing atmosphere; 20. The fly ash treatment method according to any one of the first to nineteenth aspects, wherein the addition treatment of the first iron salt and the iron salt coprecipitation step are performed in a non-oxidizing atmosphere. is there.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The embodiment of the present invention is an example of a method for treating secondary fly ash generated by incineration ash treatment at a municipal waste incineration facility or the like, and an example of the entire treatment process of FIG. This will be described with reference to the partial process diagram of FIG. First, as shown in FIG. 1, fly ash is separated into a salt-containing filtrate and a heavy metal-containing residue through a salt elution step and a heavy metal separation step. That is, as shown in FIG. 2, fly ash is mixed with water to form a slurry, and while stirring this slurry, a mineral acid such as hydrochloric acid or sulfuric acid is added to adjust the pH to 5 or less, preferably about pH 4. Then, salts such as chlorine, sodium, calcium, etc., especially chloride are transferred to the liquid side (salt elution step). In addition, since the pH of the slurry varies depending on the fly ash composition, the amount of mineral acid added is adjusted according to the fly ash. Therefore, it is not necessary to add mineral acid when the pH of the slurry is already at the optimum pH.
[0017]
Next, an alkali neutralizing agent such as sodium hydroxide or sodium carbonate is added to the slurry to adjust the pH to between 8 and 12, followed by solid-liquid separation, and heavy metal-containing residue, selenium-containing chlorine and sodium Solid-liquid separation into a salt-containing filtrate containing calcium and the like (heavy metal separation step). As described above, after the salts in the fly ash are sufficiently eluted on the acidic side in the salt elution step, the acidic eluate is neutralized in the heavy metal separation step, so that It becomes possible to significantly reduce the salt content. This heavy metal-containing porcelain having a low chlorine content can be used as a raw material for the smelting process after washing with water. The salt-containing filtrate is subjected to iron salt aggregation treatment by addition of ferrous salt and separated into filtered water into iron salt coprecipitates containing selenium and heavy metals (iron salt coprecipitation step).
[0018]
When the salt-containing filtrate contains fluorine, it is necessary to remove it before and after the iron salt coprecipitation step, but it is effective to remove it before the iron salt coprecipitation step. That is, aluminum hydroxide (Al (OH)) that aggregates dissolved fluorine by adding an aluminum salt such as aluminum chloride to the salt-containing filtrate and adjusting the pH to about 5-8._Three) And solid-liquid separation, an aluminum salt coprecipitate and filtered water can be obtained (aluminum salt coprecipitation step). In this aluminum salt coprecipitation step, it is preferable to add a filter aid such as diatomaceous earth together with the flocculant in order to promote precipitation filtration of the hydroxide.
In addition, when the salt containing filtrate from the said heavy metal separation process does not contain the fluorine which is a problem, this aluminum salt coprecipitation process can be abbreviate | omitted and the said salt containing filtrate can be used for a dissolved oxygen removal process as it is.
[0019]
Next, as shown in FIG. 1, in the iron salt coprecipitation step of removing residual heavy metals from the filtered water from the aluminum salt coprecipitation step, in particular, in order to coprecipitate the contained selenium, Prior to the process, a dissolved oxygen removing process is performed. Further, in the iron salt coprecipitation step, the dissolution is performed by adjusting the pH of the treatment solution at room temperature, preferably 20 to 30 ° C. from which dissolved oxygen has been removed, to pH 8 to 11 in the presence of the ferrous salt. The iron salt coprecipitate is obtained by reducing the hexavalent selenium to be adsorbed on the coagulated flocs of ferrous hydroxide produced at the same time.
[0020]
If the dissolved oxygen of the filtrate from the salt-containing filtrate or aluminum salt coprecipitation step is not reduced to 0.5 mg / l or less, the selenium of the treated wastewater is drained from the viewpoint of stability of the ferrous hydroxide. It is difficult to reduce it to a reference value of 0.1 mg / l or less. In addition, the dissolved oxygen removal step and the iron salt coprecipitation step can be carried out in an air atmosphere, but it is possible to cope with a higher concentration of selenium content preferably in a non-oxidizing atmosphere.
[0021]
To remove dissolved oxygen, (1) means for bringing the water to be treated into contact with a metal such as iron powder in an acidic region of pH 7 or lower; (2) N₂Means for bubbling treated water with non-oxidizing gas such as gas, (3) Means for dissolving and neutralizing divalent iron salt in treated water, and means for adding dissolved oxygen removal reagent (reducing agent) such as sodium sulfite (4) There are means for decompressing the water to be treated. Naturally, other treatment means for removing dissolved oxygen is also included in the present invention, and these means can be used alone or in combination of two or more.
[0022]
A non-oxidizing atmosphere is created by adding water to be treated to a reaction tank and then adding N in the upper space of the reaction tank.₂The non-oxidizing gas is allowed to flow in to replace air, and the water to be treated is sealed at the top. Non-oxidizing gas is N₂In addition to gas, inert gas such as argon and helium can be used.₂Gas is advantageous in terms of cost. N₂In the case of bubbling treatment with a non-oxidizing gas such as gas, the upper space is substantially replaced or non-oxidizing atmosphere by using a reaction vessel with a lid. There is no need to seal.
[0023]
The effect of removing dissolved oxygen on the removal of selenium is remarkable. For example, using a solution in which a reagent is added to pure water to make the concentration of hexavalent selenium 34 mg / l, and stirring with a stirrer The liquid temperature was kept at 25 ° C., and 500 mg / l Fe²⁺In the case where ferrous hydroxide was agglomerated by reacting in an alkaline region at pH 9 for 30 minutes, the liquid residual selenium concentration was 20 mg / l, whereas N from the bottom of the liquid tank₂When the dissolved oxygen was removed by bubbling the gas, the selenium concentration was 1.9 mg / l by the same treatment at the same liquid temperature of 25 ° C. In addition, without removing dissolved oxygen, the liquid bath is kept at a relatively high temperature of 45 ° C.₂ When the top was sealed with gas, the selenium concentration was 2.0 mg / l. That is, according to the present invention in which dissolved oxygen is removed and the iron salt coprecipitation treatment is performed, a sufficient deselenium effect can be obtained by room temperature treatment.
[0024]
The dissolved oxygen in the treated wastewater and the selenium concentration in the treated wastewater are closely related, and the removal of dissolved oxygen has a significant impact on the reduction of hexavalent selenium, the stability of ferrous hydroxide and its adsorption properties, etc. Is exerting.
In the treatment of fly ash, wastewater with a high salt concentration containing a large amount of calcium, chlorine, etc. can be obtained, but such high salt concentration wastewater has a problem that hexavalent selenium is difficult to remove compared to wastewater with less salt. . When investigating the influence of dissolved oxygen using such high-salt concentration wastewater as the base solution, dissolved oxygen is required to reduce the selenium of the treated wastewater to 0.1 mg / l or less of the wastewater standard at room temperature treatment of 30 ° C. or lower. It has been found that it is sufficient to reduce the dissolved oxygen in the water to be treated to 0.5 mg / l or less in the removal treatment.
[0025]
In the present invention, in the iron salt coprecipitation step, ferrous salt is added for the reduction of hexavalent selenium and the adsorption of selenium to the aggregated floc of ferrous hydroxide. The addition of the ferrous salt to the treated filtered water may be before or after the dissolved oxygen removing step of the treated filtered water, but the entire process including the dissolved oxygen removing step is performed. The treatment is preferably performed in a non-oxidizing atmosphere. Moreover, when using a ferrous salt as an iron salt for removing dissolved oxygen, the use of the ferrous salt is used in two stages, as in the case of iron salt coprecipitation treatment for removing selenium.
[0026]
Since the addition of ferrous salt to the water to be treated is usually carried out excessively for promoting the reaction, iron ions remain in the emission standard value even after removal of selenium at a pH of about 9 suitable for coprecipitation of selenium. It may remain in an amount slightly exceeding 10 mg / l or less. In order to remove this excessive amount of residual iron ions, it is preferable to perform a two-stage iron salt coprecipitation method in which the pH value is further increased to promote the production of iron hydroxide after the coprecipitation reaction of selenium.
[0027]
When the relationship between pH value, residual selenium and residual iron ions was investigated using high salt concentration wastewater by fly ash treatment as the original solution, selenium was efficiently coprecipitated at pH 8-9, preferably pH 9, in the first stage. After that, the liquid to be treated is readjusted to pH 9-11, preferably about 10.5, and the secondary aggregation of iron hydroxide is performed while the coprecipitate is contained. It was confirmed that both selenium and iron could be kept below the effluent standard value, and at the same time, heavy metals such as cadmium, antimony, mercury and lead remaining in the effluent could be kept below the effluent standard value. In addition, during the secondary aggregation of the ferrous hydroxide, even if the pH is 11 or more, the precipitation amount of ferrous hydroxide does not increase, while the adsorbed selenium tends to re-dissolve slightly. The pH should be 11 or less, preferably about 10.5.
[0028]
Hereinafter, with reference to the partial process diagram of FIG. 3, a specific example of a dissolved oxygen removing process in which metal (iron powder) is brought into contact with water to be treated and an iron salt coprecipitation process in which a first iron salt is added will be described.
In the illustrated process, the iron salt is aggregated in two stages, but it may be limited to one-stage aggregation at pH 8-11.
First, the filtered water from the aluminum salt coprecipitation step is supplied to the reaction tank. The reaction tank does not need to be a completely sealed tank, and the upper space can be made into a non-oxidizing atmosphere by continuous supply of non-oxidizing gas, and a lid provided with a stirring device together with a gas supply pipe and a supply port for chemicals, etc. What is necessary is just to have a body.
[0029]
After supplying filtered water, that is, water to be treated, to the reaction tank, in the space above the reaction tank, N is added as a non-oxidizing gas.₂A non-oxidizing atmosphere is formed by supplying gas at a constant supply rate and replacing it with air to bring the water to be treated into a sealed state. Next, the water to be treated is maintained in an acidic region of about pH 3 with an acid such as hydrochloric acid, and iron powder is supplied at 0.3 to 1.0 g / l, for example, and stirred vigorously with a stirrer. A small amount of iron powder dissolves and reacts with oxygen in the liquid, and the dissolved oxygen can be reduced to 0.1 mg / l or less.
[0030]
After confirming that the dissolved oxygen was reduced to 0.5 mg / l or less, preferably 0.1 mg / l or less by a dissolved oxygen meter, subsequently, in a non-oxidizing atmosphere, FeCl was added to the water to be treated.₂, FeSO_FourBy adding about 500 mg / l of Fe as an equivalent divalent iron salt and stirring to dissolve it, an alkaline agent such as NaOH is added to adjust the pH to 8-9, and neutralizing while maintaining this pH, Divalent iron ions (Fe²⁺) Is Fe (OH)₂And aggregated (primary aggregation), and the selenium in the liquid is Fe (OH)₂It is reduced by, adsorbed and co-precipitated. Selenium almost precipitates in about 30 minutes, but Fe remaining in the liquid²⁺If it exceeds the standard value of iron wastewater, the pH is raised to about 9-11 with an alkaline agent such as NaOH, and Fe (OH)₂ Promotes secondary aggregation. At this time, it is preferable to add diatomaceous earth as a sedimentation filter aid together with the flocculant.
[0031]
The obtained pulp-like residue-containing treated water is solid-liquid separated into an iron salt coprecipitate containing selenium and heavy metals and filtered water by means of a settling device, a filter press or the like. Thereby, clean filtered water in which selenium is easily reduced to 0.1 mg / l or less can be obtained.
[0032]
That is, by adjusting the pH by adding a ferrous salt, all ferrous ions produce ferrous hydroxide regardless of high dissolved chlorine, and this active first active hydration hydroxide is crystallized. In addition to selenium, iron is considered to take in and co-precipitate residual heavy metals such as mercury, copper, lead, zinc, cadmium, chromium, arsenic, antimony and nickel in the precipitation process. The removal efficiency can be drastically increased. For example, mercury that requires an adsorption treatment with an adsorbent such as activated carbon in the prior art can be sufficiently treated by the iron salt coprecipitation treatment of this method.
[0033]
In addition, when iron powder is used as a reducing agent to remove dissolved oxygen as described above, an excessive amount of iron powder is added from the viewpoint of work efficiency, but after completion of the iron hydroxide aggregation reaction by pH adjustment, Prior to solid-liquid separation, an excess amount of iron powder can be recovered from the residue-containing treated water (pulp water) by magnetic sorting or the like, and can be used again for the removal of dissolved oxygen. Further, after the iron powder is recovered by magnetic sorting, the processed water containing the residue is separated into solid and liquid, and the obtained iron salt coprecipitate is acidified at pH 1 to 4, preferably 2 to 4, as shown in the figure. The insoluble residue containing selenium is separated by filtration, and the obtained filtrate can be used again for the addition of the ferrous salt as a divalent iron source. In this case, if the acidic solution for dissolving the porridge is lower than pH 1, selenium may be dissolved in a small amount, and if the pH is higher than 4, the iron salt is not sufficiently dissolved.
[0034]
Alternatively, after completion of the iron hydroxide agglomeration reaction, the residue-containing treated water is solid-liquid separated as it is, and the obtained iron salt coprecipitate is dissolved in an acidic solution having a pH of 4 or less, and then the iron remaining in the solution is retained. The powder is recovered by magnetic sorting and again used for the removal of the dissolved oxygen. Further, the solution from which iron powder has been removed is filtered, insoluble matter containing selenium is filtered off, and the resulting filtrate is divalent. The iron source can be used again for the ferrous salt addition step.
[0035]
In addition, when performing a dissolved oxygen removal process by bubbling of a non-oxidizing gas, treated water is supplied to the reaction tank provided with a cover body, and N is supplied through the supply pipe provided in this tank under the treated water.₂By bubbling operation in which a non-oxidizing gas such as gas is blown, dissolved oxygen in the water to be treated can be reduced to 0.1 mg / l or less in the form of accompanying the non-oxidizing gas. In this case, bubbling with a non-oxidizing gas also forms a non-oxidizing atmosphere that also serves as a gas replacement in the reaction tank upper space. This gas replacement operation is not necessary. However, it is preferable to perform neutralization treatment or iron salt coprecipitation treatment after the completion of bubbling, that is, removal of dissolved oxygen, in a non-oxidizing atmosphere. After the bubbling treatment, a non-oxidizing gas is blown into the upper space of the reaction vessel. It is more effective to perform the top sealing process.
[0036]
A specific example of an iron salt coprecipitation step in which hydroxide aggregation is performed in three stages will be described (not shown).
Water to be treated is supplied to a reaction vessel equipped with a stirring device, and stirring is performed to such an extent that air is not involved. This stirring is continued until the end of the reaction. N₂ When the upper part is sealed with gas, it may be vigorously stirred. The liquid temperature is preferably 25 to 30 ° C. The reactor is open to the atmosphere, preferably N₂ Put it in a sealed state and add FeSO_Four ・ 7H₂ Divalent iron salt such as O²⁺About 400 mg / l, and the pH is adjusted to about 8-9, preferably about 9, with an alkaline agent such as NaOH, and kept for about 15 minutes. Iron hydroxide (Fe (OH)₂ ) (Primary aggregation), the dissolved oxygen can be reduced. At this time, selenium in the liquid coprecipitates to some extent due to the iron hydroxide aggregated.
[0037]
Next, the pH is adjusted to 7 with an acidic solution such as hydrochloric acid, and again FeSO 4._Four ・ 7H₂ Divalent iron salt such as O²⁺As about 400 mg / l, adjust the pH to 8-9, preferably 9 with an alkaline agent such as NaOH, and hold it for 15-30 minutes, preferably about 30 minutes, to aggregate iron hydroxide (secondary aggregation) Selenium can be adsorbed and co-precipitated, and selenium in the liquid is sufficiently removed to 0.1 mg / l or less.
[0038]
Next, in order to remove the iron ions remaining in the solution, the water to be treated is adjusted to pH 9-11, preferably pH 10.5, with an alkali agent such as NaOH without removing the iron hydroxide, and held for about 10 minutes. By doing so, the new iron hydroxide is agglomerated (tertiary agglomeration). After 10 minutes, diatomaceous earth is added as a settling filter aid together with the flocculant, and the flocculent is sufficiently settled, followed by solid-liquid separation to recover the selenium coprecipitate.
Through the above treatment, clean waste water in which selenium and iron are reduced to below the waste water standard can be obtained. Further, the effect of the agglomeration of hydroxide is greater if it is performed in three or more stages. This reaction can be performed either batchwise or continuously.
[0039]
Further, when the filtered water from the iron salt coprecipitation step still contains a COD component or heavy metal to the extent that it causes a problem, as shown in FIG. 3, the COD component by an adsorbent such as activated carbon or chelating agent And by subjecting it to heavy metal adsorption treatment, it is possible to adsorb and remove a trace amount of heavy metal remaining together with the COD component to obtain clean wastewater (COD / heavy metal adsorption step). Of course, a column may be used for the adsorption treatment of the activated carbon or the like, but it may be added to the iron salt coprecipitation liquid in the previous step in the form of granules or powder and solid-liquid separated. Of course, COD components and heavy metals in the liquid are removed, and the filterability of iron hydroxide can be extremely improved.
[0040]
Furthermore, as shown in FIG. 4, the heavy metal-containing residue from the heavy metal separation step is subjected to water washing by re-pulping or water-washing (normal washing, back washing) in a filter press, so that chlorine, sodium, Salts such as calcium can be further separated from this heavy metal-containing residue, and the washed filtered water after solid-liquid separation can be circulated in the salt elution step as slurry for fly ash slurry (a residue washing step).
[0041]
The resulting washed residue can be used as a raw material for the smelting process as it is, but if the fractionation or further reduction of salts is attempted, the burden of processing in the smelting process is reduced. In other words, water is further added to this washing porridge and repulped, and a mineral acid such as hydrochloric acid or sulfuric acid is added to adjust the pH to 5 or less, preferably 4 or less, and heavy metals mainly composed of zinc, copper and cadmium are added. A heavy metal mainly composed of lead that is hardly soluble in mineral acid is recovered as a recovered lead product by dissolving and solid-liquid separation (lead product recovery step).
[0042]
In the filtrate from the lead product recovery step, an alkali neutralizer is added to adjust the pH to 8 or more, preferably about pH 9, thereby producing a heavy metal hydroxide mainly composed of zinc, copper, and cadmium. The copper / zinc product and filtered water can be obtained by solid-liquid separation (copper / zinc product recovery step). By repeating the filtered water together with the washed filtered water from the porridge washing step as water for slurrying fly ash in the salt elution step, it is possible to improve the economics of fly ash treatment as well as the recovery of heavy metals.
[0043]
As described above, the cleaning product from the cleaning process of the porcelain is separated in two steps, the lead product recovery process and the copper / zinc product recovery process, to obtain two products of the lead product and the copper / zinc product. However, it is also possible to improve the workability of the heavy metal recovery process by combining the two-stage process into a single-stage process and recovering one heavy metal product. That is, as shown in FIG. 5, water is added to the washed residue and repulped, and a mineral acid such as sulfuric acid is added to adjust the pH to 5 or less, preferably pH 4 or less, and then solid-liquid separation is not performed. Further, an alkali neutralizing agent is added to the residue-containing liquid to adjust the pH to 8 or more, preferably pH 9 to 11, and then solid-liquid separation (heavy metal product recovery step). The recovered residue obtained is further washed with water and subjected to solid-liquid separation to obtain a heavy metal product with reduced salts (washing step). The washed filtered water from the washing step is returned as slurry water for the fly ash salt extraction step together with the washed filtered water from the porridge washing step and the filtered water from the heavy metal product recovery step.
[0044]
As described above, in the present invention, fly ash from a garbage incineration facility or the like is treated, and the contained heavy metals such as copper, zinc and lead are recovered in a state where they can be separated from salts and used as smelting raw materials. Furthermore, as the drainage, clean filtered water that has been well removed from heavy metals and harmful elements, including selenium, which has had a problem with conventional means of removal, and that satisfies not only the national drainage regulations but also local restrictions. It can be obtained.
[0045]
【Example】
[Example 1]
<Refer to FIG. 2 and FIG. 4> While adding 8 liters of pure water to a 10 liter beaker and stirring, add 800 g of fly ash from the A treatment plant as a raw material to make a slurry, and stirring for 10 minutes, 36% hydrochloric acid as a mineral acid PH is adjusted and maintained at 4 and dissolved for 30 minutes (salt elution step), then 200 g / l NaOH solution is added as an alkali neutralizer to adjust the pH to 11 and 30 minutes After the maintenance, a heavy metal-containing residue mainly containing heavy metals and a salt-containing filtrate mainly containing salts were separated by a filtration operation (heavy metal separation step). Next, the resulting heavy metal-containing porcelain was transferred to a 5-liter beaker, and 2.0 liters of pure water was added to form a slurry, which was then stirred and maintained for 30 minutes. .
Table 1 shows the composition of the raw fly ash and the quality of the washed residue obtained in the residue washing step, and Table 2 shows the composition of the salt-containing filtrate from the heavy metal separation step.
[0046]
Transfer the washed porridge obtained from the porridge washing process to a 10 liter beaker and repulp with 5 liters of pure water.₂SO_FourWas added and the pH was adjusted to 4 to elute heavy metals other than lead to obtain lead products mainly containing lead (lead product recovery step). Table 1 shows the quality of the lead products obtained.
Further, a 200 g / l NaOH solution is added as an alkali neutralizing agent to the filtrate separated in the lead product recovery step to adjust the pH to 11, and a copper / zinc product in a hydroxide state mainly composed of copper / zinc. And solid-liquid separation into filtered water (copper / zinc product recovery step). Table 1 shows the quality of the obtained copper / zinc products.
[0047]
[Table 1]

[0048]
[Table 2]

In other words, smelting raw materials in which heavy metals in fly ash are separated into lead products mainly composed of lead and reduced salt such as chlorine, and copper and zinc products mainly composed of copper, zinc and cadmium and similarly reduced in salt Could get.
[0049]
[Example 2]
<Refer to FIG. 5> The washed residue obtained in the washed step of Example 1 is transferred to a 10-liter beaker, repulped with 5 liters of pure water, and 95% H₂SO_FourThe pH was adjusted to 4 and stirred, and after 30 minutes, 200 g / l NaOH solution was added to adjust the pH to 9 without solid-liquid separation. After 10 minutes, solid-liquid separation was performed to obtain a heavy metal product and filtered water (heavy metal product recovery step).
The component values of the heavy metal product obtained by the treatment of the washed residue by the two-stage continuous pH adjustment are shown in Table 1 above.
That is, non-ferrous heavy metals were separated from salts and efficiently concentrated and recovered without separating the lead product and the copper / zinc product.
[0050]
[Example 3]
<Refer FIG. 2> A treatment test was conducted using a salt-containing filtrate having component values shown in Table 3 obtained by treating fly ash through a salt elution step and a heavy metal separation step as a base solution.
Take 2.5 liters of the original solution in a 3 liter beaker, add 50 mg / l of aluminum chloride as an aluminum salt in the amount of aluminum as an aluminum salt, maintain at 25 ° C., and adjust the pH to 7. After reacting for 30 minutes, it was separated into an aluminum salt coprecipitate and filtered water by suction filtration using C filter paper (aluminum salt coprecipitation step). Table 3 shows the fluorine component values of this filtered water, that is, the defluorinated filtrate (shown as aluminum salt coprecipitate filtrate). That is, a filtrate with sufficiently reduced fluorine was obtained.
[0051]
<See FIG. 3> Next, 900 ml of the obtained filtered water (defluorinated filtrate) is placed in a 1 liter beaker and covered with N in the upper space.₂Gas was allowed to flow at a rate of 500 ml / min to obtain an upper sealed state, and stirring was performed. The reaction temperature was kept at 25 ° C., which is room temperature. After adjusting the pH of the solution to 3 with hydrochloric acid solution, iron powder was added at a rate of 0.5 g / l and strong stirring was performed. It was confirmed by a dissolved oxygen meter that dissolved oxygen became 0.1 mg / l or less in 10 minutes.
Continue N₂FeSO as the ferrous salt while continuing the top seal with gas_Four・ 7H₂O for Fe²⁺500 mg / l was added, and the mixture was dissolved by stirring for 4 minutes.
[0052]
Further, the pH was adjusted to 9 with an NaOH solution and held for 30 minutes to aggregate ferrous hydroxide. Next, the pH was adjusted to 9.5 with NaOH solution and held for 10 minutes to again coagulate ferrous hydroxide and add the coagulant and diatomaceous earth. The obtained pulp liquid was subjected to suction filtration with a Buchner (iron salt coprecipitation step).
Component values of treated water (labeled as iron salt coprecipitation (1)) collected after the adjustment reaction of pH = 9 in the first stage in the agglomeration process (iron salt coprecipitation process), and pH = 9 in the second stage. Table 3 also shows the Zn, Se, and Fe component values of the treated water collected after the adjustment reaction (indicated as iron salt coprecipitation (2)).
That is, along with selenium, heavy metals other than iron were sufficiently reduced by the first stage pH adjustment (pH = 9), but a large amount of iron remained. It can be seen that this residual iron content was sufficiently agglomerated and precipitated by the second stage pH adjustment (pH = 9.5).
[0053]
[Table 3]

[0054]
[Comparative example]
Aluminum salt coprecipitation treatment and iron salt coprecipitation treatment were performed using the same salt-containing filtrate as in [Example 3] as the original solution.
However, an iron salt coprecipitation treatment was performed on the aluminum salt coprecipitation filtrate obtained in [Example 3]. Moreover, the removal process of dissolved oxygen was not performed about this filtrate. The iron salt coprecipitation treatment was carried out in the open air, and the temperature of the reaction solution was kept at 45 ° C., which is normal temperature or higher. Others were processed under the same conditions as in [Example 3].
Component value of the salt-containing filtrate of the original solution, fluorine component value of the aluminum salt coprecipitation filtrate, treated water (iron salt coprecipitation) after reaction in the first stage pH adjustment (pH = 9) in the iron salt coprecipitation treatment (Indicated as (1)) and Cd and Se of treated water (represented as iron salt coprecipitation (2)) after reacting with pH adjustment (pH = 9.5) in the second stage The content is shown in Table 4.
[0055]
[Table 4]

[0056]
That is, the result of [Example 3] of the present invention is the same as the case of [Comparative Example] in which the treatment was performed at 45 [deg.] C. or higher while being treated at room temperature.
From this result, the method of the present invention, in which dissolved oxygen is removed and the iron salt is added at room temperature, has almost the same effect as the iron salt coprecipitation treatment performed under heating of the solution. It can be seen that it has the advantage of not requiring equipment and operation for temperature treatment.
[0057]
【The invention's effect】
In the present invention, the salt in the fly ash is sufficiently dissolved with acid, and then neutralized to recover the heavy metal-containing residue, and the resulting high salt filtrate is subjected to removal of dissolved oxygen and coprecipitation with iron salt. According to this, it is possible to recover heavy metal-containing materials that can be used as raw materials for smelting processes by removing salts such as chlorine, and high salt filtrate mixed with hexavalent selenium can be used for iron, copper, lead in addition to selenium. Residual heavy metals such as can be reduced to an extremely low level at the same time, and there is an effect that clean wastewater that can meet strict drainage regulations can be obtained.
In particular, since selenium can be removed from the high-salt filtrate by room temperature treatment, the workability is improved, the liquid heating equipment is not required, and the equipment cost can be reduced.
[0058]
As a means for removing dissolved oxygen from the salt-containing filtrate from the heavy metal separation process or the filtered water from the aluminum salt coprecipitation process as the treated water, the means using metal, particularly iron powder, the iron powder is inexpensive and dissolved. It has the advantage that it is easy to handle together with the oxygen-removing agent, and the bubbling or decompression means has the advantage of good working efficiency. Further, when iron powder is used, the iron powder and iron salt can be easily recovered and reused after the iron salt coprecipitation reaction.
[0059]
Further, in the case where the heavy metal-containing residue is washed, and the washed residue is treated with an acid solution and then neutralized to obtain a heavy metal product, further removal of salts is performed. This makes it possible to separate and collect the heavy metals in the smelting process, thereby reducing the burden of heavy metal recovery processing work.
[Brief description of the drawings]
FIG. 1 is an overall process diagram showing a method for treating fly ash containing heavy metals according to the present invention.
2 is a partial process diagram showing a specific example of a treatment method from a salt elution step to an aluminum salt coprecipitation step in the fly ash treatment method of FIG. 1. FIG.
FIG. 3 is a partial process diagram showing a specific example of a method for treating filtered water from an aluminum salt coprecipitation step in the fly ash treatment method of FIG. 1;
FIG. 4 is a partial process diagram showing a specific example of a method for treating heavy metal-containing residue in the fly ash treatment method of FIG. 1;
FIG. 5 is a partial process diagram illustrating another specific example of the method for treating heavy metal-containing residue in the fly ash treatment method of FIG. 1;

Claims

A method for treating fly ash containing at least one of zinc, copper and lead, chlorine and selenium, and adding a mineral acid to the fly ash to make a slurry, adjusting the pH to 5 or less and eluting the salts An elution step, a heavy metal separation step of adjusting the pH to 8 to 12 by adding a neutralizing agent to the slurry of the salt elution step, and solid-liquid separation into a heavy metal-containing residue and a salt-containing filtrate, and the heavy metal separation step In the dissolved oxygen removing step for removing dissolved oxygen from the salt-containing filtrate obtained in Step 1, and to the treatment liquid in the dissolved oxygen removing step, ferrous salt is added, and then an alkaline agent is added to adjust the pH to 8-11. A method for treating fly ash containing heavy metal or the like, characterized by comprising an iron salt coprecipitation step of adjusting and solid-liquid separating an iron salt coprecipitate and filtered water.

In the iron salt coprecipitation step, after adding ferrous salt to the salt-containing filtrate obtained in the heavy metal separation step, the dissolved oxygen removal step is performed through a dissolved oxygen removal step of removing dissolved oxygen from the salt-containing filtrate. The heavy metal or the like according to claim 1, which is a step of solid-liquid separation into an iron salt coprecipitate and filtered water by adding an alkali agent to the treatment liquid of the step to adjust the pH to 8 to 11. For treating fly ash containing sucrose.

In the iron salt coprecipitation step, a ferrous salt is added to the treatment liquid of the dissolved oxygen removal step through a dissolved oxygen removal step of removing dissolved oxygen from the salt-containing filtrate obtained in the heavy metal separation step, The step of adjusting the pH to 8 to 9 by adding an alkali agent and then adjusting the pH to 9 to 11 and solid-liquid separation into an iron salt coprecipitate and filtered water. A method for treating fly ash containing the heavy metal according to Item 1.

In the iron salt coprecipitation step, after adding ferrous salt to the salt-containing filtrate obtained in the heavy metal separation step, the dissolved oxygen removal step is performed through a dissolved oxygen removal step of removing dissolved oxygen from the salt-containing filtrate. It is a step of solid-liquid separation of the iron salt coprecipitate and filtered water after adjusting the pH to 8 to 9 by subsequently adding an alkaline agent to the treatment liquid of the step and then adjusting the pH to 9 to 11. The processing method of the fly ash containing the heavy metal etc. of Claim 1 characterized by the above-mentioned.

The method for removing dissolved oxygen includes means for bringing the salt-containing filtrate into contact with a metal having a pH of 7 or less, wherein the fly ash containing heavy metal or the like according to any one of claims 1 to 4 is used. Processing method.

The said metal is iron powder, The processing method of the fly ash containing the heavy metal etc. of Claim 5 characterized by the above-mentioned.

The iron powder is recovered from the treated water containing the iron salt coprecipitate in the iron salt coprecipitation step by magnetic sorting and used for the dissolved oxygen removal step, and the treated water from which the iron powder has been removed is recovered from the iron salt coprecipitation step. Solid-liquid separation into precipitate and filtered water, the obtained iron salt coprecipitate is dissolved with an acidic solution having a pH of 4 or less, and the filtrate obtained by filtration is added as a divalent iron source. It uses for a process, The processing method of the fly ash containing the heavy metal etc. of Claim 6 characterized by the above-mentioned.

After the iron salt coprecipitate obtained by solid-liquid separation in the iron salt coprecipitation step is dissolved in an acidic solution having a pH of 4 or less, the iron powder in the solution is recovered by magnetic separation and is used in the dissolved oxygen removal step. The heavy metal or the like according to claim 6, wherein the heavy metal is added to the ferrous salt as a divalent iron source using a filtrate obtained by filtering the solution from which the iron powder has been removed. To fly fly ash.

The method for removing the dissolved oxygen includes at least means for bubbling the salt-containing filtrate with a non-oxidizing gas, wherein the fly ash containing heavy metal or the like according to any one of claims 1 to 4 is used. Processing method.

The method for treating fly ash containing heavy metal or the like according to any one of claims 1 to 4, wherein the method for removing dissolved oxygen includes at least means for subjecting the salt-containing filtrate to reduced pressure treatment.

The method for removing dissolved oxygen includes at least means for adding a dissolved oxygen removing agent to the salt-containing filtrate, wherein the fly ash containing heavy metal or the like according to any one of claims 1 to 4 is used. Processing method.

The method for treating fly ash containing heavy metal or the like according to any one of claims 1 to 11, wherein the dissolved oxygen is removed until the dissolved oxygen in the salt-containing filtrate becomes 0.5 mg / l or less. .

The processing temperature of the said salt containing filtrate in the said iron salt coprecipitation process is 20-30 degreeC, The processing method of the fly ash containing the heavy metal etc. in any one of Claims 1-12 characterized by the above-mentioned.

The filtered water from the iron salt coprecipitation step includes a COD component and a heavy metal adsorption step for obtaining clean wastewater by performing an adsorption treatment for adsorbing a COD component and a heavy metal by bringing an adsorbent into contact therewith. The processing method of the fly ash containing the heavy metal etc. in any one of 1-13.

An aluminum salt coprecipitation step for solid-liquid separation into an aluminum salt coprecipitate and filtered water is provided by adding an aluminum salt to the salt-containing filtrate obtained in the heavy metal separation step to adjust the pH to 5-8. The processing method of the fly ash containing the heavy metal etc. in any one of Claims 1-14 characterized by the above-mentioned.

A lead product recovery step in which a mineral acid is added to the heavy metal-containing residue obtained in the heavy metal separation step and repulped, and the pH is adjusted to 5 or less, and the lead product and filtrate are mainly separated from lead. Then, a neutralizer is added to the filtrate obtained in the lead product recovery step to adjust the pH to 8 or more, and the copper / zinc product mainly containing copper and zinc is separated into solid and liquid into filtered water. It has a zinc product collection | recovery process, The processing method of the fly ash containing the heavy metal etc. in any one of Claims 1-15 characterized by the above-mentioned.

Mineral acid is added to the heavy metal-containing porcelain obtained in the heavy metal separation step and repulped, and the pH is adjusted to 5 or lower, and then the neutralizer is added to adjust the pH to 8 or higher. The processing method of the fly ash containing the heavy metal etc. in any one of Claims 1-15 characterized by having a heavy metal product collection | recovery process solid-liquid-separated into filtered water.

The method for treating fly ash containing heavy metal or the like according to claim 17, further comprising a washing step of washing the heavy metal product with water.

The method for treating fly ash containing heavy metal or the like according to any one of claims 1 to 18, wherein the dissolved oxygen removing step is performed in a non-oxidizing atmosphere.

The method for treating fly ash containing heavy metal according to claim 1, wherein the ferrous salt addition treatment and the iron salt coprecipitation step are performed in a non-oxidizing atmosphere. .