JP4115815B2 - Method and apparatus for treating fluorine-containing wastewater - Google Patents

Method and apparatus for treating fluorine-containing wastewater Download PDF

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JP4115815B2
JP4115815B2 JP2002346399A JP2002346399A JP4115815B2 JP 4115815 B2 JP4115815 B2 JP 4115815B2 JP 2002346399 A JP2002346399 A JP 2002346399A JP 2002346399 A JP2002346399 A JP 2002346399A JP 4115815 B2 JP4115815 B2 JP 4115815B2
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electrodialysis
fluorine
wastewater
concentration
hydrofluoric acid
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JP2004174439A (en
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悦二 立木
貞義 沢田
英明 米本
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松下環境空調エンジニアリング株式会社
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02ATECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A20/00Water conservation; Efficient water supply; Efficient water use
    • Y02A20/124Water desalination
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02ATECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A20/00Water conservation; Efficient water supply; Efficient water use
    • Y02A20/124Water desalination
    • Y02A20/131Reverse-osmosis

Description

【0001】
【発明の属する技術分野】
本発明は、半導体・液晶・電子部品製造に幅広く製造されるPFC(パーフロロコンパウンズ)ガスの除害後の排水処理とくに排水中のフッ素化合物の再利用方法およびそのための装置に関するものである。
【0002】
【従来の技術】
半導体製造工程などにおいて排出される各種のフッ素含有排水として、製造プロセスで使用されるフッ素含有の排ガスなどの処理水が挙げられる。この排水は、各種フッ素含有排水の中でも極めて希薄で大量に排出される。このフッ素含有排水においては、近年、フッ素の排水基準が厳しくなり、環境面からもフッ素を効率的に回収することが要望されている。またこの種の排水は、珪素(Si)成分を多く含むため次式に示すような反応によりSi分に対応するフッ素イオンは遊離のフッ素イオンとしてではなく、ヘキサフルオロ珪酸(SiF6 2-)塩として存在している。
SiO2+6HF→H2SiF6+2H2
このヘキサフルオロ珪酸を含むフッ素の再資源化は簡単ではなく、珪素(Si)分を有効に処理できる方法が要望されている。従来より、この種のフッ素含有排水の処理方法(および、その処理装置)として提案された代表的な方法として以下の方法が知られている。
【0003】
(凝集沈殿処理法)
フッ素イオンを溶解度の低いフッ化カルシウム、またはヒドロキシアパタイト類として沈殿させ、固液分離して処理水を得る方法である。
(カルサイト法)
炭酸カルシウム粒とフッ素廃液とを接触させ、炭酸カルシウム表面から炭酸ガスを奪い、フッ化カルシウム化させ、水中から分離して処理水を得る方法である。この方法により生成したフッ化カルシウム汚泥は、フッ酸原料として再利用可能な純度のものが得られるといわれている。
【0004】
(フッ化カルシウム晶析法)
フッ素イオンがフッ化カルシウム粒子となる状態を処理槽内で生成させ、その粒子を種粒子表面に結晶成長させて水中から分離し、処理水を得る方法である。
(イオン交換法)
イオン交換樹脂によりフッ素イオンをイオン交換反応により水中から分離除去し、処理水を得る方法である。
(電気透析法)
陽イオン交換膜および陰イオン交換膜を交互に配して濃縮室および希薄室を交互に備える構成の装置に、フッ素イオンを含む水を供給しつつ直流電気を印加することで、水中のフッ素イオンを濃縮し、フッ素濃度の低い処理水と高い濃縮液に分離・濃縮する方法である。
(晶析によるアパタイト化法)
カルシウム塩およびリン酸塩の共存下で反応させることにより、Ca5F(PO43として結晶成長させ、水中から分離し処理水を得る方法である。
【0005】
さらに近年の排水基準の強化に対応する提案として、処理水に含まれるフッ素以外のイオンであって、フッ化カルシウムの生成を抑制する難溶性塩を生成するイオンの量を測定して、このイオン量に基づいてカルシウム塩の添加量を制御し、これにより高度な処理水を得ることが開示されている(例えば、特開2001−212574号公報参照)。また、フッ化カルシウムを含む濃縮汚泥を一部反応槽へ返送して汚泥循環させることでフッ素の除去効率を高めることが開示されている(例えば、特開平6−114382号公報参照)。さらに、排水中の珪素濃度をSiO2として500mg/l以下に調整する技術が開示されている(例えば、特開平5−237481号公報参照)。また、フッ素を含む排水の回収に関しては、共存するカルシウム濃度により水の回収率、すなわちフッ素の濃縮倍率は制限されることが開示されている(例えば、特開2000−229289号公報参照)。
【0006】
【特許文献1】
特開2001−212574号公報(「0015」、「0027」)
【特許文献2】
特開平6−114382号公報(請求項1、「0009」)
【特許文献3】
特開平5−237481号公報(「0012」〜「0032」、図1)
【特許文献4】
特開2000−229289号公報(「0012」〜「0013」)
【0007】
【発明が解決しようとする課題】
しかしながら、このような従来の技術は、いずれも以下のような課題を備えている。
(凝集沈殿処理法)
第1の課題は、当該排水のフッ素濃度が希薄であるため通常のフッ素含有排水に比べ、単位フッ素量に対する固形廃棄物発生量多いことである。第2には、希薄であるがゆえ、その処理には無機凝集剤等の薬剤が必要となり、当該発生固形物中には、無機凝集剤に起因する不純物が含まれるため、再資源化の用途が限定され、セメント材料等の低付加価値のものとなり、リサイクルコストは割高になる。第3には、処理のために無機凝集剤等の薬剤を添加するため、処理水中に塩分が増加する。この水の回収には脱イオンが必要となり、また脱塩後の濃縮液の処理も必要になることが挙げられる。また第4の課題としては、処理水の再利用の際に、水中に残存するカルシウムイオンは、燃焼後のガス吸収液に吸収されるフッ素と反応し、不溶性固形物であるフッ化カルシウムを形成し、PFC除害後のガス吸収装置内に固着蓄積し、その機能に障害を与えるため高度に除去する必要があるという点である。
【0008】
また特開2001−212574号公報の方法は、難溶性塩を多量に含む場合には好適であるが、本来的にそのような塩を含まない処理液には適合しない。また処理水中のフッ素イオン濃度を低下させることができたものの大量の難溶性塩がフッ化カルシウム含有ケーキに含まれる恐れがある。加えて固形分としての反応生成物を得るために大規模な処理設備が必要となる。
【0009】
また、特開平6−114382号公報に記載の方法は、フッ化カルシウムの生成を促進させる点においては、効果的であるが、大量の汚泥を返送させる必要がある。このために得られるフッ化カルシウム含有ケーキには、フッ化カルシウム以外の固形分も濃縮されることになる。すなわち、従来のこれらの方法では、フッ素濃度が低減された処理水を得ることはできるものの、純度の高い再資源化できるフッ化カルシウム含有ケーキを得ることが困難であった。またこの種の排水には、Siを含む成分が多く含まれており、Siを含むフッ素化合物を再資源化可能とする方法は、提案されていない。
【0010】
(カルサイト法)
この方法の第1の課題は、粒状炭酸カルシウム表面に生じるフッ化カルシウムの内部にフッ酸が浸透することにより反応が進行するため反応速度が遅く、特にフッ素濃度が希薄な排水系については、不利になる点である。第2は、処理水中にカルシウムイオンの溶出がさけられず、処理水再利用にあたってカルシウムイオンが、ガス吸収液中のフッ素と反応して、不溶性固形物であるフッ化カルシウムを形成し、PFC除害後のガス吸収装置内に固着蓄積し、その機能に障害を与えるため高度に除去する必要があるという点である。第3の課題は、充填された炭酸カルシウムはフッ素で置換され、フッ化カルシウムとして再資源化可能となるが、粒状炭酸カルシウムの内部がフッ素によりフッ化カルシウムに完全に置換されていない場合は未反応の炭酸カルシウムが残存することとなる。これは回収物のフッ化カルシウムの純度低下させ、その価値を損ねるため、安定した有価物として再資源化することが困難であるという点である。
【0011】
(フッ化カルシウム晶析法)
この方法の課題は、第1に晶析反応では、薬液添加量の適正制御が不可欠であり、濃度変動の多い排水が対象の場合には、残存するカルシウム濃度が変動し、その濃度によりフッ化カルシウムは微細粒子として凝集する反応が晶析反応に優先して起こるため微細なフッ化物微粒子が流出し、処理水質が悪化するという点である。第2には、処理水中にカルシウムイオンの残存が避けられず、処理水再利用に当たって、そのカルシウムイオンは燃焼後のガス吸収液中のフッ素と反応し、不溶性固形物であるフッ化カルシウムを生じるので、上記の凝集沈殿処理法、カルサイト法と同様にこの場合も、高度に除去する必要があるという点である。第3の課題は、晶析されたフッ化カルシウムペレットは、再資源化可能であるが、排水中に共存する珪フッ化物を分離する技術は提唱されておらず、安定して有価物として再資源化することが困難であるという点である。
【0012】
(イオン交換法)
第1の課題は、飽和した樹脂は、薬液により再生し、再生廃液に上記の凝集沈殿処理法、カルサイト法、フッ化カルシウム晶析法等の新たな処理が必要になるという点である。第2には、既存のフッ素吸着樹脂の交換容量が少なく、再生には少なくとも1種類の薬液を必要とし、再生廃液量も多くなるため、水回収率及びランニングコストの面で不利になるという点である。第3には、再生廃液はフッ素処理が必要であり、しかも樹脂再生に使用した薬剤が含まれるため不純物が多く再資源化は困難といえる。通常は、前記凝集沈殿処理法の方法にて処理されるが、前記凝集沈殿処理法の課題を含み、さらにこの再生廃液の処理コストも付加され、一層不利となるということが挙げられる。
【0013】
(電気透析法)
第1の課題は特開2000−229289号公報に記載の方法は、電気透析装置に供給される水のカルシウム濃度[Ca](mg/L)とフッ素濃度[F](mg/L)と水の回収率[R](処理水/供給水)を[Ca]×[F]2×/{1−[R]}<50とし、過剰濃縮によるフッ化カルシウムスケールの形成を防ぐ方法である。この方法によるとフッ素濃度及びカルシウム濃度を数mg/L程度に低下させなければ電気透析装置が適応できないことを示し、当該排水に電気透析装置を適応する場合はこれらを低減化させる何らかの前処理を必要であることを意味する。第2の課題は電極循環液に移動するフッ素イオンが電極循環液に移動し、循環により濃縮され、濃縮室より濃度拡散等により移動してくる水素イオンと結合しフッ酸を形成し、正極を腐食劣化させることである。
【0014】
(アパタイト晶析法)
第1の課題は、反応を完結させるためには、過剰な薬液添加が必要であるという点である。第2の課題は、晶析は充填された種晶表面で進行するため、接触効率の向上を目的として種晶の単位表面積を大きくすると晶析した固形物が目詰まり・閉塞を起こし、処理不能となる点である。従って装置は目詰まり前に通液を止め機械式または空気(エアレーション)を用いて撹拌し、閉塞物を剥離後分離する機構を設けるか、攪拌を伴う反応後沈降分離させるバッチ式の処理が主体になり、装置が大型化してしまうという点である。
本発明は、このような問題点に鑑みなされたもので、希薄なフッ素含有排水からフッ素を濃縮することにより、処理水を有効利用すると共に、後段の効率的な排水処理、すなわち再資源化可能なフッ素含有排水の処理技術を提供することをその目的とする。またSi分の有効な処理技術を提供することもその目的とする。さらに全体的な処理システムの小型化や処理コストの経済性を考慮したフッ素含有の排水処理技術も提供するものである。
【0015】
【課題を解決するための手段】
前記課題を解決するために、本発明のフッ素含有排水の処理方法およびその処理装置は、フッ素含有排水を電気透析工程により、処理水(脱塩水)は排ガス除害装置への補給水として返送する工程、濃縮液は表面処理フッ酸液として再資源化する工程により処理するものである。フッ素含有排水を酸性(フッ酸酸性)のまま、電気透析工程で処理することにより、再使用可能な処理水および再資源化可能な濃縮液(フッ酸液)が得られるようにしたものである。本発明によれば、処理水循環使用により外部からのスケール成分持込をなくすことができ、またこれにより、フッ酸の濃縮倍率を高めることができ表面処理用のフッ酸液としての濃度にまで濃縮可能となった。
【0016】
この場合、電気透析工程においては、電極の耐食性や電気透析操作の安定性が課題となる。本発明のフッ素含有排水の処理方法(装置)においては、電気透析工程において、貯留装置に加えて濃縮液、処理水、電極循環液、遮断液の4つの循環系に対応した4つの槽および循環ポンプを備え、電気透析装置の負極部および中央部は、陽イオン交換膜および陰イオン交換膜を交互に配し、濃縮室および希薄室を交互に備えた構成であるが、特に正極部近傍には、陽イオン交換膜を複数枚連続して配し、正極負極の電極近傍および前記陽イオン交換膜を複数枚備えた構成としている。通常この部分には、数%の希薄な硫酸を電極循環液および遮断液として循環使用しフッ素イオンの移動を抑制しているが、フッ素イオンは濃度差拡散により透過してくる水素イオンと反応しフッ酸を形成せしめ、また、循環による濃縮によりその腐食性は徐々に高くなるため、定期的な更新が必要となり、フッ酸以外の廃酸の発生が避けられなかった。本発明は、電気透析装置に遮断室を設け、電気透析処理水を電極循環液および遮断液として、循環または通過させる構成を備えたものとした点にある。本発明によれば、前記遮断室に処理水を通液し、常時置換することで電極循環液および遮断液のフッ酸濃度を低く抑えられ、正極付近でのフッ酸発生による電極腐食が抑制でき装置稼動の長期安定性が確保できるようになった。また、その処理水の再利用先を排ガス除害装置とすればフッ素の混入は問題とならないことが明らかとなった。
【0018】
また本発明により見出された前記電気透析工程と前記晶析方法の組合せにより、フッ素の存在形態に適した再資源化方法が可能となった。フッ素含有排水を2段の電気透析工程を備え、初段の電気透析装置によりフッ酸を脱イオンおよび1次濃縮する工程、初段電気透析装置の処理水(脱塩水)を、排ガス除害装置への補給水として返送する工程、初段電気透析装置の濃縮液を再資源化可能な濃度に再濃縮する工程、この後段電気透析装置の濃縮液を表面処理用フッ酸液として再資源化する工程、この後段電気透析処理水中のフッ素を珪フッ化物として再資源化する工程を備える装置としたものである。すなわちフッ素含有排水中のフッ素分イオンフッ酸に、ヘキサフルオロ珪酸イオンを珪フッ化物として効率的に再資源化することができる。また電気透析工程により得られる処理水は、スケール成分としてトラブルを起こす懸念のあるカルシウムイオン等が十分に除去されているため排ガス除害装置への補給水として再利用することができる。このようにフッ素含有排水は、濃縮液および処理水を共に有効に再利用ができる。
【0019】
【発明の実施の形態】
本発明のフッ素含有排水の処理方法は、フッ素含有排水の処理および濃縮操作を行う電気透析工程において、処理水を排ガス除害装置への補給水として返送する工程と、濃縮液は表面処理用フッ酸液として再資源化利用する工程とを備えたものである。すなわち、フッ素含有排水の処理方法であって、フッ素含有排水の脱塩操作とフッ酸濃縮操作とを行う電気透析工程を備え、前記脱塩処理液を前記フッ素含有排水の発生源への補給水として再生し、前記フッ酸濃縮液を利用可能な濃度のフッ酸溶液として再生する程度に電気透析することを特徴とする方法である。また、フッ素含有排水の処理方法であって、フッ素含有排水の脱塩操作とフッ酸濃縮操作とを行い、フッ酸濃度が3重量%以上のフッ酸濃縮液を再生する電気透析工程を備える方法であり、さらに、フッ素含有排水の脱塩操作とフッ酸濃縮操作とを行い、前記濃縮液を酸性洗浄液として再生する電気透析工程、方法である。
前記電気透析工程による濃縮作用により、鉄鋼酸洗液等として用いることのできる3〜10Wt%の処理液を得ることができる。同時に処理水は、カルシウムイオンなどのスケール成分が除去されているため排ガス除害装置への補給水として返送する工程により再利用できる。
【0020】
本発明の処理技術は、半導体製造工程において発生するフッ素含有排水に適用できる。とりわけ、半導体製造工程の成膜工程などに使用されるフッ素を含有する各種ガス(デポジットガス、クリーニングガス、ドライエッチングガスなど)の熱分解等による除害工程で発生するフッ素含有排水の処理に適している。熱分解後のガスが、スクラバーなどにより洗浄される際、フッ酸などが溶解した洗浄水が発生する。この種の洗浄水に適用するのが好ましい。
【0021】
PFCガスの排ガス除害装置内での反応は、例えば4フッ化珪素の場合は以下の式に示すとおりである。
SiF4+O2+2H2O→SiO2+4HF
6HF+SiO2→H2SiF6+2H2
フッ素含有排水の特性としては、フッ素濃度が500mg/l以下から50mg/l以上の濃度範囲にあって、排水濃度は、生産プロセスの稼働状況により変動し、Si、B、Clなど、とくにSiを含む溶液であることが挙げられる

【0022】
半導体製造工程において、一般的に用いられるフッ素系ガスは、一般的に酸性であるが、除害処理した後にスクラバーから排出されるスクラバー排水は、経路内でアルカリが投入されてアルカリ性になっている場合もある。そのような場合には、処理水のpH値が2〜6の範囲にpH調整しておくことが必要になる。このようなpH条件下では、下記の反応式のようにフッ素イオンが遊離
し、電気透析によりフッ酸が濃縮ができる。
2SiF6+2H2O→SiO2+6H++6F-
pH調整の方法については、硫酸や各種有機酸も適用可能であるが、望ましくは、フッ酸を用いる。その理由は、再資源化するフッ素含有製品の純度を確
保するためである。
【0023】
この際、SiO2が沈殿物を形成したりする場合には、後工程で悪影響のな
いレベルまで予め濾過手段により、沈殿物を除去する必要がある。
電気透析工程では、H+、F-、SiF6 2-などのイオンが濃縮室側に移動 するが、SiO2は、電気泳動作用は受けにくく、希薄室をほぼそのままの濃 度で通過するため、結果、電気透析装置内で上記反応式は右辺に移行し、ヘキ サフロオロ珪酸からフッ酸を分離回収できることとなる。
電気透析工程の構成としては、所定の濃縮倍数を得るため複数の電気透析装置(ユニット)を直列に接続し、濃縮側、希薄側の一部を各ユニットの一部をそれぞれのユニットの入口に戻す部分循環式の連続式を採用しても良いし、バッチ式となるが、貯液タンクとポンプを用いて各流路を構成する循環式として用いても良い。また両者を併用しても良い。比較的濃縮率が高いことから、システムを小型化するため複数のユニットを直列接続する場合でも循環式を組み入れることが有利になる。この電気透析工程により、鉄鋼酸洗液等として最適の3〜10Wt%のフッ酸系溶液が得られる。この濃度範囲にあるフッ酸系溶液が通常鉄鋼業で酸洗液として用いられている。ここで濃縮された溶液は、浮
遊物等を濾過手段で除いて再資源化製品としての貯留槽に貯留される。
【0024】
また、第2の発明は、前記電気透析工程に用いる電気透析工程についてのもので、電気透析工程では、フッ素含有排水を貯留する貯留装置に加えて濃縮液、処理水、電極循環液、遮断液の4つの循環系に対応した4つの槽および循環ポンプを備え、電気透析部の負極部および中央部は、陽イオン交換膜および陰イオン交換膜を交互に配し、濃縮室および希薄室を交互に備えた構成であるが、特に正極部近傍には、陽イオン交換膜を複数枚連続して配し、正極負極の電極近傍および前記陽イオン交換膜を複数枚備えた部分には処理水を電極循環液および遮断液として循環させる構成よりなる。すなわち、おおよそ対向状に配置される負極部と正極部とを備える電気透析手段において、負極部及び中央部には、陽イオン交換膜と陰イオン交換膜とが交互に配置され、正極部近傍には、陽イオン交換膜が複数枚連続して配置されており、前記負極部と正極部に脱塩処理水を供給し、前記正極部近傍の陽イオン交換膜配置部位にも前記脱塩処
理液を供給する工程を含む方法である。
通常の電気透析装置(電気透析部)の場合は、電気透析操作中に正電極側にはフッ素イオンが集まり、一方水素イオンは濃度差拡散により正極液中に拡散透過し、フッ酸を形成するため正極は著しく腐食されやすい。従って、電極自体、このような環境に耐えうるDSA電極(すなわちチタンに酸化ルテニウムをコーティングした耐ハロゲン特性の良好なアノード用電極)などを用いる。但し耐久性の優れたDSA電極などは、ハロゲンの発生の過電圧が小さいという課題があるため、正極部近傍には、陽イオン交換膜を複数枚連続して配する構成によりフッ素イオンの正極への移動を抑制し、腐食防止を図っている。すなわち陽イオン交換膜を複数回通過させる遮断室を設けることでフッ素の阻止
率を高め、電極液中のフッ酸濃度を低減化するものである。
【0025】
一般的にこの遮断室は電極液同様0.5〜4%程度の硫酸液で循環されて、しかも遮断室循環液は循環によりフッ素濃度が暫時上昇するため電極液とは区分しでいる。また、運転を継続することにより遮断液にはフッ素が濃縮されるため、定期的に更新が必要であった。本発明では、この遮断液に処理水を利用し、定常的に置換することで正極の腐食防止と廃棄される遮断液更新廃液の問題を解決するものである。また、定常的に液が更新されるためそのフッ素濃度は常に5〜30mg/Lと低く、電極液との共有も可能となり、しかも後段の処理水再使用先である排ガス除害装置の性能にも影響を及ぼさないことが判明した。
【0026】
第3の本発明は、前記電気透析工程の濃縮液中におけるフッ素イオン濃度、および/もしくは、電解質濃度を計測し、濃度変動に応じて、処理時間を制御するものである。また部分循環式電気透析の場合には、最終段の濃縮液で、またバッチ式や、最終段が循環式の場合は、濃縮液槽のフッ素イオン濃度または電解質濃度を計測することで電気透析操作条件を制御する。フッ素イオン濃度の計測は、イオンクロマト法やイオン選択性電極にて、電解質濃度の場合は、pHと導電率で予め検量線を作成しておき、pHと導電率を計ることで電解質濃度を評価する方法で最終の3〜10Wt%のフッ酸濃度となっているかを評価する。電気透析工程の安定のために処理流量、印加電圧、電流密度条件などを定めた一定値で操作するとすれば、循環時間が制御要素になる。部分循環の場合には、戻し流量が制御要素になる。これらの要素の制御することで安定した動作で、鉄鋼酸洗液等として再資源化製品を得ることができる。また得られる処理水は、フッ素含有排水中の電解質分が脱塩されており、特にカルシウムなどのスケール成分を高度に脱塩しているのでスケール障害の懸念無く、排ガス除害装置への補給水として好適であり、有効に再利用できる。
【0029】
第4の発明は、フッ素含有排水の処理装置であって、フッ素含有排水の電気透析装置と濃縮液の回収経路と処理水の排ガス除害装置への返送経路とを備えて構成される。すなわち、フッ素含有排水の処理装置であって、フッ素含有排水を脱塩及び濃縮する電気透析手段と、前記脱塩処理液をフッ素含有排水発生源へ返送する経路と、前記濃縮液を回収する経路、とを備える、装置である。電気透析装置による濃縮作用により、鉄鋼酸洗液等として用いることのできる3〜10Wt%の濃縮液を得ることができる。同時に処理水は、カルシウムイオンなどのスケール成分が除去されているため排ガス除害装置への補給水として好適であり、返送する経路により再利用できる。
【0030】
第5の発明は、フッ素含有排水の処理装置であって、第4の発明の電気透析装置において、特にその耐久性および動作の安定性に優れた電気透析装置に関するもので、電気透析装置として、貯留装置に加えて濃縮液、処理水、電極循環液、遮断液の4つの循環系に対応した4つの槽および循環ポンプを備え、負極部および中央部は陽イオン交換膜および陰イオン交換膜を交互に配し、濃縮室および希薄室を交互に備えた構成であるが、特に正極部近傍には陽イオン交換膜を複数枚連続して配し、正極負極近傍および前記陽イオン交換膜を複数枚備えた部分には処理水を電極循環液および遮断液として循環させる構成を備えた電気透析装置を用いて構成されるものである。すなわち、おおよそ対向状に配置される負極部と正極部とを備える電気透析手段であり、負極部及び中央部には、陽イオン交換膜と陰イオン交換膜とが交互に配置され、正極部近傍には、陽イオン交換膜が複数枚連続して配置されており、少なくとも前記正極部近傍の陽イオン交換膜配置部位に当該電気透析手段において得られる脱塩処理液を供給する経路を備える、電気透析手段を備える、装置である。基本的に本電気透析装置は、ワンパス式でなく循環動作をさせるため高濃縮高脱塩が見込める。また循環式で用いると、電気透析装置の電極の正極(アノード)は耐食性が課題となり、負極(カソード)ではスケール生成が課題となる。本処理装置においては、正極側での耐食性を確保するため正極近傍にフッ素イオン等の陰イオンが集まりにくいように陽イオン交換膜を複数枚配し、電極近傍および前記陽イオン交換膜を複数枚配した部分には、処理水を通水させることで上記の課題の解決を図り、動作電流の安定化と電極劣化を防止しているものである。このようにして、フッ素含有排水の高倍率の濃縮と脱塩処理を有効に行うことができる。
【0031】
第6の発明は、フッ素含有排水の処理装置に関するものである。第4の発明の電気透析装置において、濃縮液中のフッ素イオン濃度、および/または、電解質濃度の計測手段および循環時間の制御手段を備えて構成される。最終段の濃縮流路系の溶液を採取またはモニタリングすることで、フッ素イオン濃度または電解質濃度は、例えば、イオン選択性電極、またはイオンクロマトグラフィ、またはpHと導電率などを計測することで把握することができる。電気透析装置の制御要素としては、電極間の印加電圧、電流密度、温度、循環流速、循環時間などある。これらを制御することで適切な濃縮倍率を実現できるが、電気透析装置の動作の安定化から他のパラメータは一定条件下で動作させることが望ましいので、循環時間を制御することで目的の濃縮倍率を実現することができる。
【0034】
さらに、本発明は、電気透析と晶析とを組み合わせた以下の手段も提供する。すなわち、フッ素含有排水の処理方法であって、フッ素含有排水を脱塩及び濃縮して、脱塩処理液をフッ素含有排水の発生源への補給水として再生する第1の電気透析工程と、第1の電気透析工程において得られるフッ酸濃縮液をさらに脱塩及び濃縮して、フッ酸濃縮液を利用な濃度のフッ酸溶液として再生する第2の電気透析工程と、第2の電気透析工程で得られた脱塩処理液を晶析する工程と、晶析工程の処理物を流動床で晶析分離する工程、とを備える、方法を提供する。
また、前記第1の電気透析工程を、フッ素含有排水の発生源に対応させた複数の電気透析工程を並列に組み合わせて実施し、これらの各第1の電気透析工程で得られたフッ酸濃縮液を合わせて第2の電気透析工程に供給する、方法も提供する。
さらに、フッ素含有排水の処理装置であって、フッ素含有排水を脱塩及び濃縮する第1の電気透析手段と、第1の電気透析手段において得られたフッ酸濃縮液を脱塩及び濃縮する第2の電気透析手段と、第2の電気透析手段において得られた脱塩処理液を晶析する手段と、晶析手段により得られる処理物が投入される充填槽であって、エアレーションをしながら膜分離操作により分離した水を系外へ放流する一方、充填槽にて前記処理物中の珪フッ化物を析出成長させる充填槽、とを備える、装置を提供する。また、前記第1の電気透析手段を、フッ素含有排水の発生源に対応して備え、これらの第1の電気透析手段から得られたフッ酸濃縮液を合わせて第2の電気透析手段に供給する構成を備える、装置も提供する。なお、電気透析と晶析とを行う方法及び装置においては、電気透析工程を2工程備え、電気透析手段を2個備えることが好ましいが、3工程以上の電気透析工程、3段以上の電気透析手段を備えていてもよい。また、必ずしも、電気透析工程を2工程以上、電気透析手段を2段以上備えなくてもよく、それぞれ1工程及び1段であってもよい。
【0035】
【実施例】
以下、本発明の実施例について図1〜5を参照しながら説明する。
(実施例1)
図1は、本発明に関わる一実施例のフッ素含有排水の処理方法およびその処理装置の概要を示すフロー図である。
図1において、1は排ガス除害装置(または、フッ酸系スクラバーであるが、以下、省略する。他語の説明も同じ)であり、この排ガス除害装置1からのフッ素含有排水2は、貯留装置3に保持される。予め、フッ素含有排水2の特性は把握されているが、もしフッ素含有排水2にアルカリが含まれていて、pH値が2〜6の範囲から逸脱している場合には、この貯留装置3でpH値が2〜6となるようにpH調整を実施しておく。このpH調整は酸を加えるが、フッ酸(HF)を用いるのが望ましい。
【0036】
フッ素含有排水2は、フィルター4を経て、電気透析装置(または、電気透析工程)5に送られ、処理および濃縮操作が為される。処理水(または、脱塩処理液)9は、熱交換器13を経て排ガス除害装置1へ返送14される。一方、濃縮液7は、2段に直列接続された電気透析装置(または、電気透析工程)6に送られる。電気透析装置6の処理水10は、電気透析装置5の前段に返されるが、濃縮液8は、導電率計(または、電解質濃度計)30、3方切替弁31を経て再資源化され、その一部の濃縮液8は電気透析装置6の前段に返される。つまり、それぞれ循環11および循環12とする構成を持ち、各電気透析工程による電解質の濃縮および処理操作は、複数段の一部循環の構成によって可能となる。
【0037】
ここに濃縮水8は、3方切替弁31等を介して採取し、もしくは経路内でそのフッ素イオン濃度(および/または、電解質濃度)を計測することで、所定の3〜10Wt%の適切な範囲値、例えば4Wt%に到達しているか否かを判定し、到達していなければ、循環12(処理水10は、循環11となる)させ電気透析操作を継続する。濃度が到達すれば、循環12を中止(採取することで工程条件を有効に制御することができる)する。フッ素イオン濃度の計測は、導電率計、イオン選択性電極等が好ましく、精度を要する場合はイオンクロマトグラフィーもしくは中和滴定などで分析する。また電解質濃度については、pHと導電率との検量線を作成しておき、pHと導電率を測ることで電解質濃度を推測することができる。このようにして、最適な電気透析装置・工程の管理ができる。
【0038】
一方、実験によると、フッ素含有排水2のフッ素分が100mg/lとすれば、5Wt%溶液を得るためには、500倍程度の高濃縮が必要で、2倍濃縮を9回循環させる程度の濃縮が必要でなる。ここでフッ素含有排水2は、所定の濃縮倍数が達成され、3〜10Wt%のフッ酸系溶液(回収酸)が得られる。これは、浮遊物等を除去して、鉄鋼酸洗液(スラグ除去)やブラウン管・すりガラスのエッチング等の再資源化として用いることができる。従って、最終段の濃縮液8は、フッ酸含有排水2中のフッ素成分をフッ酸(HF)及びヘキサフルオロ珪酸(H2SiF6)として再資源化でき、ゼロエミッションが可能となる。また、処理水9は、その電気電導率30ms/m以下となっており、熱交換器13によって温度調節されて排ガス除害装置1の補給水として再利用できる。とくにスケール生成が懸念されるカルシウムイオンなどは高度に除去されているので、排ガス除害装置1内でカルシウム障害を起こすことはない。また処理工程は、基本的に電気透析工程のみでコストのかかる薬品類を一切使用していないため再資源化の場合のコスト面でも有利である。このようにして、経済性と排水基準の遵守およびリサイクル化によるゼロエミッションを有効に成立させることができる。
【0039】
図2は、本発明に関わる上記一実施例を示す図1の中の電気透析装置(または、電気透析工程)5,6の詳細(電気透析部5a,6a)を示すフロー図で、特に高濃縮倍数を実現するための循環系に関する概要を示す図である。
図2において、例えば、排ガス除害装置1からのpH値が2〜6のフッ素含有排水2は、一旦貯留装置3に貯留される。貯留装置3に貯留されたフッ素含有排水2は、ポンプ15で脱塩水槽16に送られる。この動作は、バッチの操作となる。脱塩水槽16からのフッ素含有排水2は、ポンプ17により電気透析装置5の電気透析部5aの中央部において所定のパスを通過する循環流路24を巡って脱塩水槽16に戻る。この循環流路24は、電気透析装置5内の複数の流路をまとめて一つで代表している。
【0040】
電気透析部5aに脱塩水槽16から入ったフッ素含有排水2は、濃縮液7として濃縮流路25により濃縮液循環槽18へ入り貯留される。濃縮液循環槽18の濃縮液7は、ポンプ19により、循環して濃縮液循環槽18に戻る。とくに電気透析部5aの正極28側には、陽イオン交換膜を複数枚配した構成を備えており、フッ素イオンが正極28近傍には、集まらない構成を有し、かつ陽イオン交換膜を配した部分には、遮断液循環槽22より、ポンプ23を介して遮断液が通過し、循環ループ27を構成している。遮断液には、経路9aを介して処理水9を通過させ、電解質濃度が薄い溶液として、さらにフッ素イオンなどのアニオンの正極28への移動を起こりにくくしている。また正極28および負極29の近傍には、電極液循環槽20よりポンプ21を経て、電極循環液26が循環する。電極循環液26も経路9bを介して処理水9cを通水し、それぞれの極28,29での電極反応生成物の発生を抑制すると共に、電極反応により生成した酸素や水素などのガスを電極液循環槽20から速やかに系外へ排気させている。
【0041】
またこれらの構成により、正極28における電極の消耗および負極29でのスケール生成を抑制し、電気透析部5aとしての安定動作および長寿命化を図っている。さらにバッチ処理での循環時間を制御し、所定の濃縮倍数を確保する。所定の濃縮倍数に達したら電気透析操作を停止し、濃縮液7および処理水9を取り出し再利用される。このようにして濃縮液7は、3〜10Wt%の鉄鋼用酸洗液等再利用が可能となり、処理水9および処理水9cは、排ガス除害装置1への補給水として、それぞれの再資源化が実現できる。図2の電気透析装置5を複数の電気透析工程に組み入れることで、高濃縮倍数がコンパクトな装置で達成でき、また有効で効率の良い再資源化のための濃縮〜希薄処理構成が
できる。
なお、前記構成において、電極液循環槽20と遮断液循環槽22を別個の構成としているが、電極液循環槽20と遮断液循環槽22をひとつの槽で構成しても効果を得ることができる。また、処理水9cは電極液循環槽20へ供給し、その後、オーバーフロー等により遮断部(陽イオン交換膜配置部位)に供給するようにしてもよい。
【0042】
(参考例)
図3は、フッ素含有排水の別の処理方法として、フッ素含有排水を晶析する場合の工程およびその処理装置の概要を示すフロー図である。図3において、晶析装置35は、フッ素含有排水2のpH値をpH調整剤により6〜10(望ましくは7〜9)に調整する。このpH調整剤として、水酸化カルシウムなどのCa系アルカリを用いるのが望ましい。また、カルシウムイオンが不足する場合は塩化カルシウム等の水溶性カルシウム塩を用いる。これによりフッ酸は、フッ化カルシウムなどの懸濁液となる。このフッ素含有排水2に、Si含有量が不足する場合は、反応容器32において撹拌しながらSiO2粉末(または、Si粉末)33を添加し反応させてもよい。反応容器32において、反応の結果、ヘキサフルオロ珪酸(珪フッ酸)(または、ヘキサフルオロ珪酸塩(珪フッ化物))34が得られる。ここで用いるSiO2粉末(または、Si粉末)33は、半導体または液晶製造工程で廃棄物として発生しているものを適用することができる。
【0043】
さらにこれに晶析促進剤36として、例えばフルオロアパタイト(Ca5F(PO43)粒子を加え、この粒子表面にフッ化カルシウムや珪フッ化物を吸着させ析出成長させる。この吸着反応によりフッ素分は、0.8〜5mg/l以下の濃度レベルまで除去される。晶析促進剤36表面での結晶成長は、上部に浸漬型膜分離装置38を備えた種晶充填槽(または、流動床式晶析分離工程)37において、下部に配したバブリング装置39を通気し、発生する気泡の上昇に伴う流動により、種晶を流動させ、種晶充填槽37の目詰まりを防止しながら晶析反応を加速する。またその流動により液は上昇し、分離膜に対してクロスフローを形成し,分離操作に必要な膜表面上の流速を確保し、懸濁物の膜分離を有効に行わせる。これにより前記中和反応によりフッ化カルシウムとして沈殿し、液相中の濃度が0.8〜5mg/l以下となったフッ素含有排水2は分離され、放流路66を経て放流される。またフルオロアパタイト上に吸着し、結晶化したフッ化カルシウム、或いは珪フッ化カルシウムは種晶充填槽37の下部から抜き出され、脱水機40によりケーキ41として採取され、リン酸製造工程の原料等として再資源化される。また、スラリー42としても再資源化される。
【0044】
実施例2
図4は、本発明に関わる上記一実施例(実施例1)と、上記参考例とを組み合わせた構成の概要を示すフロー図である。図4についての説明は、実施例1、参考例を併せたものであるので省略する。すなわち、実施例1の後段電気透析装置6の濃縮液をフッ酸系溶液(回収酸)として再資源化し、またその脱塩処理液10の後に、参考例の晶析装置35と種晶充填槽37とを入れ、その膜ろ過水を放流し、晶析物を再資源化するものである。また、実施例2の作用・効果についても、上述の実施例1と参考例との各々を補いあって、かつ各々を併せたもの(相乗したもの)となるので,より高精度にフッ素含有排水(A)2を処理できることになる。
【0045】
実施例3
図5は、本発明に関わる上記一実施例(実施例1)を並列に複数組み合わせ、さらに上記他の参考例とを組み合わせた構成の概要を示すフロー図である。図5において、並列に複数組み合わせた排ガス除害装置(または、フッ酸系スクラバー)61、排ガス除害装置(または、フッ酸系スクラバー)81からのフッ素含有排水62、フッ素含有排水82が、電気透析装置(または、電気透析工程63、電気透析装置(または、電気透析工程)83を経て、共用の電気透析装置または、電気透析工程)64に送られる。65、84は、各々の熱交換器65、熱交換器84を示す。さらに、共用の電気透析装置の後は、各々共用の晶析装置67、種晶充填槽68、浸漬型膜分離装置69を経過して、所定の濃縮・希薄処理が為される。なお、上記各実施例において既に為された同一の説明は省略(符号も)する。多種にわたるフッ素含有排水62,82であっても、高効率に処理することができる。さらに、上記の後半の各装置(または、各工程)は共用することによって、コストや設置面積等において、省資源化、省エネルギー化等の効果を倍増することができる。なお、フッ素含有排水の発生源であるフッ素系スクラバーや排ガス除害装置は、2個として図5に例示したが、種類や個数を限定するものではなく、各種のフッ素含有排水発生源に対応させることができ、また、並列させる電気透析工程あるいは電気透析手段の数は必要に応じて3以上とすることもできる。
【0046】
【発明の効果】
以上のように本発明のフッ素含有排水の処理方法およびその装置によれば、以下のような効果を生ずる。
(1)電気透析装置(または、同工程)によりフッ酸(酸性)のまま濃縮し、特別な薬品の添加をすることがなく、処理水は排ガス除害装置(または、フッ酸スクラバー)の補給水として、フッ酸は再資源化として、それぞれに再利用することができ、工場のゼロエミッションに寄与できる。
(2)上記処理水(または、脱塩水)の再利用において、排ガス除害装置のスケール障害の原因となるカルシウムなどのスケール成分を高度に除去しているため、スケール発生の抑制に寄与できる。
(3)上記処理水(または、脱塩水)の再利用において、排ガス除害装置からの排水中にカルシウムなどのスケール成分を持ち込むことがなくなり、電気透析装置により高濃縮ができ、濃縮液を洗浄用フッ酸液として最資源化でき、工場のゼロエミッション化に寄与できる。
(4)晶析法において晶析剤に珪フッ化物として晶析分離することで珪素含有量の多いフッ酸排水中からのフッ素分を再資源化することが可能となった。
(5)アパタイト晶析法に膜分離を併用し、処理水水質を向上でき、同時に懸濁生成物を種晶充填槽内で循環させることで懸濁物の滞留時間を長くできるため薬剤の反応効率を上げ、その消費量を削減できる。またその際、結晶も粗大化し、分離性能が向上する効果を生ずる。
(6)とくに遮断室を持つ電気透析装置の遮断液などの構成により、電気透析工程において、新たな廃酸を発生させることなく、電極の耐久性と透析操作の安定動作を確保できる。
(7)電気透析装置の構成において処理水再利用を主眼とした装置とフッ酸濃縮を目的とした装置に分離することによって設備の効率的な設置が可能となる。また、後段電気透析装置の濃縮液を表面洗浄用フッ酸に、処理水中のフッ素を珪フッ化物として晶析分離し再資源化することで、排水中のフッ素形態に適した再資源化が可能となる。
【図面の簡単な説明】
【図1】本発明に関わる一実施例のフッ素含有排水の処理方法およびその処理装置の概要を示すフロー図(実施例1)である。
【図2】本発明に関わる上記一実施例を示す図1の中の電気透析装置(または、電気透析工程)の詳細を示すフロー図である。
【図3】フッ素含有排水の別の処理方法に関する工程およびその処理装置の概要を示すフロー図(参考例)である。
【図4】本発明に関わる上記一実施例と、上記参考例とを組み合わせた構成の概要を示すフロー図(実施例2)である。
【図5】本発明に関わる上記一実施例を並列に複数組み合わせ、さらに上記参考例とを組み合わせた構成の概要を示すフロー図(実施例3)である。
[0001]
BACKGROUND OF THE INVENTION
The present invention relates to wastewater treatment after detoxification of PFC (perfluorocompound) gas, which is widely produced in the manufacture of semiconductors, liquid crystals, and electronic components, and more particularly to a method for reusing fluorine compounds in wastewater and an apparatus therefor.
[0002]
[Prior art]
Examples of various fluorine-containing wastewater discharged in the semiconductor manufacturing process include treated water such as fluorine-containing exhaust gas used in the manufacturing process. This waste water is extremely dilute among various fluorine-containing waste waters and is discharged in large quantities. In this fluorine-containing wastewater, in recent years, the wastewater standards for fluorine have become stricter, and it has been demanded to recover fluorine efficiently from the environmental aspect. In addition, since this type of wastewater contains a large amount of silicon (Si) component, the fluorine ions corresponding to the Si component are not formed as free fluorine ions by the reaction shown in the following formula, but instead of hexafluorosilicic acid (SiF).6 2-) It exists as a salt.
SiO2+ 6HF → H2SiF6+ 2H2O
The recycling of fluorine containing hexafluorosilicic acid is not easy, and a method capable of effectively treating silicon (Si) content is desired. Conventionally, the following methods are known as typical methods proposed as a method for treating this type of fluorine-containing wastewater (and its treatment device).
[0003]
(Coagulation sedimentation method)
In this method, fluorine ions are precipitated as calcium fluoride or hydroxyapatites having low solubility, and solid-liquid separation is performed to obtain treated water.
(Calcite method)
In this method, calcium carbonate particles and fluorine waste liquid are brought into contact with each other, carbon dioxide is taken from the surface of calcium carbonate, converted into calcium fluoride, and separated from water to obtain treated water. The calcium fluoride sludge produced by this method is said to be of a purity that can be reused as a hydrofluoric acid raw material.
[0004]
(Calcium fluoride crystallization method)
This is a method in which a state in which fluorine ions become calcium fluoride particles is generated in a treatment tank, the particles are crystal-grown on the surface of seed particles and separated from water to obtain treated water.
(Ion exchange method)
This is a method of obtaining treated water by separating and removing fluorine ions from water by ion exchange reaction with an ion exchange resin.
(Electrodialysis method)
Fluorine ions in water by applying DC electricity while supplying water containing fluorine ions to an apparatus having a structure in which a cation exchange membrane and an anion exchange membrane are alternately arranged to alternately have a concentration chamber and a dilute chamber Is concentrated and separated and concentrated into treated water having a low fluorine concentration and concentrated liquid having a high fluorine concentration.
(Apatite formation method by crystallization)
By reacting in the presence of calcium salt and phosphate, CaFiveF (POFour)ThreeThe crystal is grown and separated from water to obtain treated water.
[0005]
Furthermore, as a proposal corresponding to the recent strengthening of wastewater standards, the amount of ions other than fluorine contained in the treated water, which forms a sparingly soluble salt that suppresses the formation of calcium fluoride, is measured. It has been disclosed that the amount of calcium salt added is controlled based on the amount, thereby obtaining highly treated water (see, for example, JP-A-2001-212574). Further, it has been disclosed that the concentration efficiency of fluorine is improved by partially returning the concentrated sludge containing calcium fluoride to the reaction tank and circulating the sludge (see, for example, JP-A-6-114382). Furthermore, the silicon concentration in the wastewater is reduced to SiO2For example, a technique for adjusting to 500 mg / l or less is disclosed (for example, see Japanese Patent Application Laid-Open No. 5-237482). Regarding the recovery of wastewater containing fluorine, it is disclosed that the water recovery rate, that is, the concentration ratio of fluorine is limited by the coexisting calcium concentration (see, for example, JP 2000-229289 A).
[0006]
[Patent Document 1]
JP 2001-212574 A ("0015", "0027")
[Patent Document 2]
JP-A-6-114382 (Claim 1, "0009")
[Patent Document 3]
Japanese Patent Laid-Open No. 5-237482 (“0012” to “0032”, FIG. 1)
[Patent Document 4]
JP 2000-229289 A ("0012" to "0013")
[0007]
[Problems to be solved by the invention]
However, all of these conventional techniques have the following problems.
(Coagulation sedimentation method)
The first problem is that the amount of solid waste generated per unit fluorine amount is larger than that of normal fluorine-containing wastewater because the fluorine concentration of the wastewater is dilute. Second, because it is dilute, it requires a chemical such as an inorganic flocculant for its treatment, and the generated solid contains impurities due to the inorganic flocculant. However, it becomes a low added value such as cement material, and the recycling cost becomes high. Third, since a chemical such as an inorganic flocculant is added for the treatment, the salt content increases in the treated water. It is mentioned that deionization is necessary for the recovery of this water, and that the concentrated solution after desalting is also required. As a fourth problem, when the treated water is reused, calcium ions remaining in the water react with fluorine absorbed in the gas absorption liquid after combustion to form calcium fluoride which is an insoluble solid. However, it is necessary to remove it to a high degree because it adheres and accumulates in the gas absorption device after PFC removal and impairs its function.
[0008]
In addition, the method disclosed in JP-A-2001-212574 is suitable when a large amount of a hardly soluble salt is contained, but is not suitable for a treatment solution that does not naturally contain such a salt. Moreover, although the fluoride ion concentration in treated water could be reduced, there is a possibility that a large amount of hardly soluble salt is contained in the calcium fluoride-containing cake. In addition, a large-scale processing facility is required to obtain a reaction product as a solid content.
[0009]
The method described in JP-A-6-114382 is effective in promoting the production of calcium fluoride, but it is necessary to return a large amount of sludge. For this reason, solid content other than calcium fluoride is also concentrated in the calcium fluoride-containing cake obtained. That is, with these conventional methods, although treated water with reduced fluorine concentration can be obtained, it has been difficult to obtain a calcium fluoride-containing cake that can be recycled with high purity. In addition, this kind of waste water contains a large amount of Si-containing components, and no method has been proposed for enabling the recycling of Si-containing fluorine compounds.
[0010]
(Calcite method)
The first problem of this method is that the reaction proceeds slowly due to the penetration of hydrofluoric acid into the calcium fluoride produced on the surface of the granular calcium carbonate, and the reaction rate is slow, especially for a drainage system with a low fluorine concentration. It is a point to become. Secondly, the elution of calcium ions in treated water is not avoided, and calcium ions react with fluorine in the gas absorption liquid to form calcium fluoride, which is an insoluble solid, in the reuse of treated water. It is a point that it needs to be removed to a high degree in order to adhere and accumulate in the gas absorption device after the damage and damage its function. The third problem is that the filled calcium carbonate is replaced with fluorine and can be recycled as calcium fluoride. However, if the inside of the granular calcium carbonate is not completely substituted with calcium fluoride by fluorine, it is not yet available. The reaction calcium carbonate remains. This is because it is difficult to recycle as a stable valuable material because the purity of the recovered calcium fluoride is reduced and its value is impaired.
[0011]
(Calcium fluoride crystallization method)
The problem with this method is that, first of all, in the crystallization reaction, appropriate control of the amount of chemical solution added is indispensable. When wastewater with a large concentration fluctuation is targeted, the remaining calcium concentration fluctuates, and fluorination depends on the concentration. Calcium has a reaction that agglomerates as fine particles in preference to the crystallization reaction, so that fine fluoride particles flow out and the quality of treated water deteriorates. Secondly, calcium ions remain unavoidable in the treated water, and when the treated water is reused, the calcium ions react with fluorine in the gas absorption liquid after combustion to produce calcium fluoride which is an insoluble solid. Therefore, in this case as well as the above-described coagulation-precipitation treatment method and calcite method, it is necessary to highly remove. The third problem is that crystallized calcium fluoride pellets can be recycled, but no technology for separating silicofluoride coexisting in wastewater has been proposed, and it can be reused as a valuable resource stably. It is difficult to recycle.
[0012]
(Ion exchange method)
The first problem is that a saturated resin is regenerated with a chemical solution, and a new treatment such as the above-described coagulation-precipitation method, calcite method, calcium fluoride crystallization method, or the like is required for the recycled waste solution. Secondly, there is a disadvantage in terms of water recovery rate and running cost because the exchange capacity of existing fluorine adsorption resin is small, at least one chemical solution is required for regeneration, and the amount of waste liquid for regeneration is also large. It is. Thirdly, the reclaimed waste liquid needs to be treated with fluorine, and since it contains chemicals used for resin regeneration, it can be said that there are many impurities and it is difficult to recycle. Usually, it is processed by the method of the coagulation-precipitation treatment method, but includes the problem of the coagulation-precipitation treatment method, and further, the processing cost of the recycled waste liquid is added, which is further disadvantageous.
[0013]
(Electrodialysis method)
The first problem is that the method described in Japanese Patent Application Laid-Open No. 2000-229289 is based on the calcium concentration [Ca] (mg / L), fluorine concentration [F] (mg / L) and water supplied to the electrodialyzer. Recovery rate [R] (treated water / feed water) is [Ca] × [F]2X / {1- [R]} <50 to prevent formation of calcium fluoride scale due to excessive concentration. According to this method, the electrodialysis apparatus cannot be adapted unless the fluorine concentration and calcium concentration are reduced to several mg / L. When applying the electrodialysis apparatus to the drainage, some pretreatment is required to reduce these. It means that it is necessary. The second problem is that fluorine ions that move to the electrode circulation liquid move to the electrode circulation liquid, are concentrated by circulation, combine with hydrogen ions that move by concentration diffusion, etc. from the concentration chamber to form hydrofluoric acid, Corrosion degradation.
[0014]
(Apatite crystallization method)
The first problem is that it is necessary to add an excessive amount of chemical solution in order to complete the reaction. The second problem is that since the crystallization proceeds on the surface of the filled seed crystal, if the unit surface area of the seed crystal is increased for the purpose of improving the contact efficiency, the crystallized solid is clogged and clogged and cannot be treated. This is the point. Therefore, the system is mainly batch-type processing that stops liquid flow before clogging and stirs using mechanical or air (aeration) to provide a mechanism to separate the clogged material after separation, or to precipitate and separate after reaction with stirring. Therefore, the apparatus becomes large.
The present invention has been made in view of such problems, and by concentrating fluorine from dilute fluorine-containing wastewater, it is possible to effectively use treated water and efficiently perform subsequent wastewater treatment, that is, recycling. The purpose is to provide a new treatment technology for fluorine-containing wastewater. Another object of the present invention is to provide an effective processing technique for Si. It also provides fluorine-containing wastewater treatment technology that takes into account the downsizing of the overall treatment system and the economics of treatment costs.
[0015]
[Means for Solving the Problems]
In order to solve the above-described problems, the fluorine-containing wastewater treatment method and treatment apparatus according to the present invention returns the treated water (demineralized water) as make-up water to the exhaust gas abatement device by the electrodialysis process. The process and the concentrated solution are processed by a step of recycling as a surface-treated hydrofluoric acid solution. By treating the fluorine-containing wastewater with acidity (hydrofluoric acid acidity) in the electrodialysis process, reusable treated water and a recyclable concentrate (hydrofluoric acid solution) can be obtained. . According to the present invention, it is possible to eliminate the introduction of scale components from the outside through the use of treated water circulation, thereby increasing the concentration ratio of hydrofluoric acid and concentrating it to a concentration as a hydrofluoric acid solution for surface treatment. It has become possible.
[0016]
In this case, in the electrodialysis step, the corrosion resistance of the electrode and the stability of the electrodialysis operation are problems. In the treatment method (apparatus) for fluorine-containing wastewater of the present invention, in the electrodialysis step, in addition to the storage device, four tanks and circulations corresponding to the four circulation systems of concentrated liquid, treated water, electrode circulation liquid, and blocking liquid. The pump is equipped with a negative electrode part and a central part of the electrodialyzer, in which a cation exchange membrane and an anion exchange membrane are alternately arranged, and a concentrating chamber and a dilute chamber are provided alternately. Has a configuration in which a plurality of cation exchange membranes are continuously arranged, and a plurality of cation exchange membranes are provided in the vicinity of the positive and negative electrodes. Normally, several percent of dilute sulfuric acid is circulated and used as an electrode circulating solution and a blocking solution in this part to suppress the movement of fluorine ions, but fluorine ions react with hydrogen ions that permeate through concentration difference diffusion. Since the formation of hydrofluoric acid and its corrosivity gradually increased by the concentration by circulation, periodic renewal was necessary, and generation of waste acid other than hydrofluoric acid was inevitable. The present invention resides in that a blocking chamber is provided in the electrodialysis apparatus and the electrodialyzed water is circulated or passed as an electrode circulating liquid and a blocking liquid. According to the present invention, the hydrofluoric acid concentration of the electrode circulation liquid and the blocking liquid can be kept low by passing the treated water through the blocking chamber and constantly replacing it, and the electrode corrosion due to the generation of hydrofluoric acid near the positive electrode can be suppressed. Long-term stability of equipment operation can be secured. In addition, it became clear that the contamination of fluorine would not be a problem if the treated water was reused as an exhaust gas abatement device.
[0018]
Further, the combination of the electrodialysis step and the crystallization method found by the present invention has enabled a recycling method suitable for the form of fluorine. Fluorine-containing wastewater is equipped with a two-stage electrodialysis process, hydrofluoric acid is deionized and primarily concentrated by the first-stage electrodialysis machine, and treated water (demineralized water) from the first-stage electrodialysis machine is sent to the exhaust gas abatement system. The step of returning it as make-up water, the step of re-concentrating the concentrate of the first-stage electrodialyzer to a recyclable concentration, the step of recycling the concentrate of the latter-stage electrodialyzer as the hydrofluoric acid solution for surface treatment, The apparatus includes a step of recycling fluorine in the latter-stage electrodialysis water as silicofluoride. That is, hexafluorosilicate ions can be efficiently recycled into the fluorine-containing ion hydrofluoric acid in the fluorine-containing wastewater as silicofluoride. Further, the treated water obtained by the electrodialysis step can be reused as makeup water for the exhaust gas abatement apparatus because calcium ions and the like that may cause trouble as scale components are sufficiently removed. As described above, the fluorine-containing waste water can effectively reuse both the concentrated liquid and the treated water.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The method for treating fluorine-containing wastewater according to the present invention comprises a step of returning treated water as makeup water to an exhaust gas abatement device in an electrodialysis step in which fluorine-containing wastewater is treated and concentrated, and the concentrate is used for surface treatment. And a step of recycling as an acid solution. That is, a method for treating fluorine-containing wastewater, comprising an electrodialysis process for performing desalting operation and hydrofluoric acid concentration operation of fluorine-containing wastewater, and supplying the desalination treatment liquid to the source of the fluorine-containing wastewater The hydrofluoric acid concentrate is electrodialyzed to such an extent that it can be regenerated as a hydrofluoric acid solution having a usable concentration. Also, a method for treating fluorine-containing wastewater, which comprises an electrodialysis step of regenerating a hydrofluoric acid concentrate having a hydrofluoric acid concentration of 3% by weight or more by performing a desalting operation and a hydrofluoric acid concentration operation on the fluorine-containing wastewater. And an electrodialysis step and method for regenerating the concentrated solution as an acidic washing solution by performing a desalting operation and a hydrofluoric acid concentration operation of the fluorine-containing waste water.
By the concentration action by the electrodialysis step, a treatment solution of 3 to 10 Wt% that can be used as a steel pickling solution or the like can be obtained. At the same time, the treated water can be reused in the process of returning it as make-up water to the exhaust gas abatement apparatus since scale components such as calcium ions have been removed.
[0020]
The treatment technique of the present invention can be applied to fluorine-containing wastewater generated in a semiconductor manufacturing process. Especially suitable for treatment of fluorine-containing wastewater generated in detoxification processes such as thermal decomposition of various fluorine-containing gases (deposit gas, cleaning gas, dry etching gas, etc.) used in film formation processes of semiconductor manufacturing processes, etc. ing. When the pyrolyzed gas is cleaned with a scrubber or the like, cleaning water in which hydrofluoric acid or the like is dissolved is generated. It is preferable to apply to this kind of washing water.
[0021]
The reaction of the PFC gas in the exhaust gas abatement apparatus is as shown in the following formula in the case of silicon tetrafluoride, for example.
SiFFour+ O2+ 2H2O → SiO2+ 4HF
6HF + SiO2→ H2SiF6+ 2H2O
The characteristics of the fluorine-containing wastewater are that the fluorine concentration is in the concentration range of 500 mg / l or less to 50 mg / l or more, and the wastewater concentration varies depending on the operation status of the production process, such as Si, B, Cl, especially Si. It is mentioned that it is a solution containing
.
[0022]
In a semiconductor manufacturing process, a fluorine-based gas that is generally used is generally acidic, but scrubber wastewater discharged from a scrubber after detoxification is made alkaline by adding alkali in the path. In some cases. In such a case, it is necessary to adjust the pH value of the treated water in the range of 2 to 6. Under such pH conditions, fluorine ions are liberated as shown in the following reaction formula.
Then, hydrofluoric acid can be concentrated by electrodialysis.
H2SiF6+ 2H2O → SiO2+ 6H++ 6F-
As a method for adjusting the pH, sulfuric acid and various organic acids can be applied, but preferably, hydrofluoric acid is used. The reason is to ensure the purity of the fluorine-containing products to be recycled.
It is for keeping.
[0023]
At this time, SiO2If a precipitate forms, it will not adversely affect the subsequent process.
It is necessary to remove the precipitate by a filtering means in advance to a high level.
In the electrodialysis process, H+, F-, SiF6 2-Ions move to the concentration chamber side, but SiO2Is less susceptible to electrophoretic action and passes through the lean chamber at almost the same concentration. As a result, the above reaction formula shifts to the right side in the electrodialysis machine, and hydrofluoric acid can be separated and recovered from hexafluorosilicate. .
The electrodialysis process is configured by connecting multiple electrodialyzers (units) in series to obtain a predetermined concentration factor, with a part of each unit on the concentrating side and lean side, and a part of each unit at the inlet of each unit. A returning partial circulation type continuous type may be employed, or a batch type may be employed, but a circulation type in which each flow path is configured using a liquid storage tank and a pump may be employed. Moreover, you may use both together. Since the concentration rate is relatively high, it is advantageous to incorporate a circulation system even when a plurality of units are connected in series in order to reduce the size of the system. By this electrodialysis step, an optimal 3 to 10 Wt% hydrofluoric acid-based solution as a steel pickling solution or the like is obtained. A hydrofluoric acid solution in this concentration range is usually used as a pickling solution in the steel industry. The concentrated solution
Playthings and the like are removed by filtration means and stored in a storage tank as a recycled product.
[0024]
The second invention relates to an electrodialysis step used in the electrodialysis step. In the electrodialysis step, in addition to a storage device for storing fluorine-containing wastewater, concentrated liquid, treated water, electrode circulating liquid, blocking liquid. 4 tanks and circulation pumps corresponding to the above four circulation systems, the negative electrode part and the central part of the electrodialysis part are alternately arranged with cation exchange membranes and anion exchange membranes, and the concentrating chambers and diluting chambers are alternately placed. In particular, a plurality of cation exchange membranes are continuously arranged in the vicinity of the positive electrode portion, and treated water is provided in the vicinity of the positive electrode and the negative electrode and a portion having the plurality of cation exchange membranes. It is configured to circulate as an electrode circulation liquid and a blocking liquid. That is, in an electrodialysis means comprising a negative electrode portion and a positive electrode portion that are arranged roughly opposite to each other, a cation exchange membrane and an anion exchange membrane are alternately arranged in the negative electrode portion and the central portion, and in the vicinity of the positive electrode portion. A plurality of cation exchange membranes are continuously arranged, demineralized water is supplied to the negative electrode portion and the positive electrode portion, and the demineralization treatment is also performed at the cation exchange membrane arrangement site in the vicinity of the positive electrode portion.
It is a method including the process of supplying a scientific liquid.
In the case of a normal electrodialysis apparatus (electrodialysis unit), fluorine ions gather on the positive electrode side during electrodialysis, while hydrogen ions diffuse and permeate into the cathode solution by concentration difference diffusion to form hydrofluoric acid. Therefore, the positive electrode is extremely susceptible to corrosion. Therefore, an electrode itself, such as a DSA electrode that can withstand such an environment (that is, an anode electrode having good halogen resistance characteristics in which titanium is coated with ruthenium oxide) or the like is used. However, since the DSA electrode having excellent durability has a problem that the overvoltage of the generation of halogen is small, a structure in which a plurality of cation exchange membranes are continuously arranged in the vicinity of the positive electrode portion allows the fluorine ion to be supplied to the positive electrode. The movement is controlled to prevent corrosion. In other words, fluorine is blocked by providing a blocking chamber that allows the cation exchange membrane to pass multiple times.
The rate is increased and the concentration of hydrofluoric acid in the electrode solution is reduced.
[0025]
Generally, this blocking chamber is circulated with about 0.5 to 4% sulfuric acid solution like the electrode solution, and the blocking chamber circulation solution is separated from the electrode solution because the fluorine concentration rises for a while due to the circulation. Further, since the fluorine is concentrated in the blocking liquid by continuing the operation, it is necessary to periodically update it. In the present invention, the treatment water is used as the blocking liquid and is constantly replaced to solve the problem of the positive electrode corrosion prevention and the discarded blocking liquid renewal waste liquid. In addition, since the solution is constantly renewed, the fluorine concentration is always as low as 5 to 30 mg / L, and it can be shared with the electrode solution. Was also found to have no effect.
[0026]
In the third aspect of the present invention, the fluorine ion concentration and / or the electrolyte concentration in the concentrated liquid in the electrodialysis step is measured, and the treatment time is controlled according to the concentration fluctuation. In the case of partial circulation electrodialysis, the electrodialysis operation is performed with the concentrate of the final stage, and when the batch system or the final stage is of the circulation type, the fluoride ion concentration or the electrolyte concentration in the concentrate tank is measured. Control the conditions. Fluorine ion concentration is measured by ion chromatography or ion-selective electrode. In the case of electrolyte concentration, a calibration curve is created in advance using pH and conductivity, and the electrolyte concentration is evaluated by measuring pH and conductivity. To evaluate whether the final hydrofluoric acid concentration is 3 to 10 Wt%. If the processing flow rate, applied voltage, current density conditions, etc. are operated at a fixed value to stabilize the electrodialysis process, the circulation time becomes a control factor. In the case of partial circulation, the return flow rate becomes the control element. By controlling these elements, a recycled product can be obtained as a steel pickling solution or the like with stable operation. In addition, the treated water obtained is desalted of the electrolyte content in the fluorine-containing wastewater, and in particular, scale components such as calcium are highly desalted. And can be effectively reused.
[0029]
  4thThe present invention is a treatment apparatus for fluorine-containing wastewater, comprising an electrodialyzer for fluorine-containing wastewater, a recovery path for the concentrated liquid, and a return path for the treated water to the exhaust gas abatement apparatus. That is, a treatment apparatus for fluorine-containing wastewater, an electrodialysis means for desalting and concentrating the fluorine-containing wastewater, a path for returning the desalination treatment liquid to a fluorine-containing wastewater generation source, and a path for collecting the concentrate , And an apparatus. By the concentration action by the electrodialyzer, a 3 to 10 Wt% concentrated solution that can be used as a steel pickling solution or the like can be obtained. At the same time, the treated water is suitable as make-up water to the exhaust gas abatement apparatus because scale components such as calcium ions have been removed, and can be reused by a return route.
[0030]
  5thThe invention is a treatment apparatus for fluorine-containing wastewater,Of the fourth inventionThe electrodialysis apparatus particularly relates to an electrodialysis apparatus that is excellent in durability and operational stability. As an electrodialysis apparatus, in addition to a storage apparatus, there are four circulations of concentrated liquid, treated water, electrode circulating liquid, and blocking liquid. The system is equipped with four tanks and circulation pumps corresponding to the system, and the negative electrode part and the central part are alternately arranged with cation exchange membranes and anion exchange membranes, and are provided with concentrating chambers and diluting chambers alternately. A plurality of cation exchange membranes are continuously arranged in the vicinity of the positive electrode part, and a configuration in which treated water is circulated as an electrode circulation liquid and a blocking liquid in the vicinity of the positive electrode negative electrode and a part having the plurality of cation exchange membranes is provided. The electrodialyzer is used. That is, it is an electrodialysis means having a negative electrode portion and a positive electrode portion that are arranged approximately opposite to each other, and a cation exchange membrane and an anion exchange membrane are alternately arranged in the negative electrode portion and the central portion, and in the vicinity of the positive electrode portion. A plurality of cation exchange membranes are continuously arranged, and at least an electric path provided with a path for supplying a desalting treatment liquid obtained in the electrodialysis means to a cation exchange membrane arrangement site near the positive electrode part. A device comprising dialysis means. Basically, this electrodialyzer is not a one-pass type, but it can be circulated and highly concentrated and highly desalted. When used in a circulating manner, the positive electrode (anode) of the electrode of the electrodialysis apparatus has a problem of corrosion resistance, and the negative electrode (cathode) has a problem of scale generation. In this treatment apparatus, in order to ensure corrosion resistance on the positive electrode side, a plurality of cation exchange membranes are arranged so that anions such as fluorine ions are unlikely to collect near the positive electrode, and a plurality of cation exchange membranes in the vicinity of the electrodes and the cation exchange membranes are arranged. In the disposed portion, treated water is made to flow to solve the above-described problems, and the operating current is stabilized and electrode deterioration is prevented. In this manner, high-concentration concentration and desalting treatment of fluorine-containing wastewater can be performed effectively.
[0031]
  6thThe present invention relates to an apparatus for treating fluorine-containing wastewater.4thThe electrodialysis apparatus of the invention is configured to include a measuring means for measuring the fluoride ion concentration and / or electrolyte concentration in the concentrate and a control means for the circulation time. By collecting or monitoring the solution in the final concentration channel system, the fluoride ion concentration or electrolyte concentration can be determined by measuring, for example, ion-selective electrodes, ion chromatography, or pH and conductivity. Can do. Control elements of the electrodialysis apparatus include applied voltage between electrodes, current density, temperature, circulation flow rate, circulation time, and the like. By controlling these, it is possible to achieve an appropriate concentration factor. However, it is desirable to operate other parameters under certain conditions in order to stabilize the operation of the electrodialyzer, so the target concentration factor can be controlled by controlling the circulation time. Can be realized.
[0034]
Furthermore, the present invention also provides the following means combining electrodialysis and crystallization. That is, a treatment method for fluorine-containing wastewater, which comprises desalting and concentrating fluorine-containing wastewater, and regenerating the desalination treatment liquid as makeup water to the source of fluorine-containing wastewater; A second electrodialysis step in which the hydrofluoric acid concentrate obtained in 1 electrodialysis step is further desalted and concentrated to regenerate the hydrofluoric acid concentrate as a hydrofluoric acid solution having a concentration of use, and a second electrodialysis step And a step of crystallizing and separating the treated product of the crystallization step in a fluidized bed.
The first electrodialysis step is performed by combining a plurality of electrodialysis steps corresponding to the generation source of fluorine-containing waste water in parallel, and the hydrofluoric acid concentration obtained in each of the first electrodialysis steps A method is also provided wherein the fluids are combined and fed to a second electrodialysis step.
Furthermore, it is a treatment apparatus for fluorine-containing wastewater, the first electrodialysis means for desalting and concentrating the fluorine-containing wastewater, and the first desalting and concentrating hydrofluoric acid concentrate obtained in the first electrodialysis means. 2 dialysis means, means for crystallization of the desalting treatment liquid obtained in the second electrodialysis means, and a filling tank into which the processed product obtained by the crystallization means is charged, with aeration There is provided an apparatus comprising: a filling tank that discharges water separated by a membrane separation operation to the outside of the system while depositing and growing silicofluoride in the treated product in the filling tank. The first electrodialysis means is provided corresponding to the source of fluorine-containing wastewater, and the hydrofluoric acid concentrate obtained from the first electrodialysis means is combined and supplied to the second electrodialysis means. There is also provided an apparatus comprising the arrangement of: In addition, in the method and apparatus for performing electrodialysis and crystallization, it is preferable to provide two electrodialysis steps and two electrodialysis means. However, the electrodialysis step includes three or more steps, and the electrodialysis includes three or more steps. Means may be provided. In addition, it is not always necessary to provide two or more electrodialysis steps and two or more stages of electrodialysis means, and may include one step and one step, respectively.
[0035]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
Example 1
FIG. 1 is a flowchart showing an outline of a treatment method and treatment apparatus for fluorine-containing wastewater according to one embodiment of the present invention.
In FIG. 1, 1 is an exhaust gas abatement device (or a hydrofluoric acid scrubber, but will be omitted hereinafter. The explanation of other words is the same), and the fluorine-containing waste water 2 from this exhaust gas abatement device 1 It is held in the storage device 3. The characteristics of the fluorine-containing wastewater 2 are known in advance, but if the fluorine-containing wastewater 2 contains alkali and the pH value deviates from the range of 2 to 6, this storage device 3 The pH is adjusted so that the pH value is 2-6. Although this pH adjustment adds an acid, it is desirable to use hydrofluoric acid (HF).
[0036]
The fluorine-containing wastewater 2 is sent to an electrodialysis apparatus (or electrodialysis step) 5 through a filter 4 and subjected to treatment and concentration operations. The treated water (or desalted solution) 9 is returned 14 to the exhaust gas abatement apparatus 1 via the heat exchanger 13. On the other hand, the concentrate 7 is sent to an electrodialysis apparatus (or electrodialysis step) 6 connected in series in two stages. The treated water 10 of the electrodialyzer 6 is returned to the previous stage of the electrodialyzer 5, but the concentrate 8 is recycled through the conductivity meter (or electrolyte concentration meter) 30 and the three-way switching valve 31, A part of the concentrated solution 8 is returned to the front stage of the electrodialyzer 6. That is, it has the structure of the circulation 11 and the circulation 12, respectively, and the concentration and treatment operation of the electrolyte in each electrodialysis step can be performed by a structure of partial circulation of a plurality of stages.
[0037]
Here, the concentrated water 8 is collected through the three-way switching valve 31 or the like, or the fluorine ion concentration (and / or the electrolyte concentration) is measured in the path, so that a predetermined 3 to 10 Wt% can be obtained. It is determined whether or not a range value, for example, 4 Wt% has been reached. If not, circulation 12 (treated water 10 becomes circulation 11) is performed and electrodialysis is continued. When the concentration reaches, the circulation 12 is stopped (the process condition can be effectively controlled by sampling). For measurement of the fluorine ion concentration, a conductivity meter, an ion-selective electrode or the like is preferable. When accuracy is required, analysis is performed by ion chromatography or neutralization titration. As for the electrolyte concentration, a calibration curve between pH and conductivity can be prepared, and the electrolyte concentration can be estimated by measuring pH and conductivity. In this way, optimal electrodialysis apparatus / process management can be performed.
[0038]
On the other hand, according to the experiment, if the fluorine content of the fluorine-containing waste water 2 is 100 mg / l, a high concentration of about 500 times is necessary to obtain a 5 Wt% solution, and the double concentration is circulated nine times. Concentration is required. Here, the fluorine-containing waste water 2 achieves a predetermined concentration factor, and a hydrofluoric acid solution (recovered acid) of 3 to 10 Wt% is obtained. This can remove suspended matters and the like, and can be used for recycling of steel pickling solution (slag removal), etching of cathode ray tubes and ground glass, and the like. Therefore, the concentrated liquid 8 in the final stage is obtained by converting the fluorine component in the hydrofluoric acid-containing waste water 2 into hydrofluoric acid (HF) and hexafluorosilicic acid (H2SiF6) Can be recycled and zero emission is possible. Further, the treated water 9 has an electric conductivity of 30 ms / m or less, and can be reused as makeup water for the exhaust gas abatement apparatus 1 after its temperature is adjusted by the heat exchanger 13. In particular, calcium ions and the like that are likely to cause scale formation have been removed to a high degree, so that no calcium damage occurs in the exhaust gas abatement apparatus 1. In addition, the treatment process is basically only an electrodialysis process and does not use any expensive chemicals, which is advantageous in terms of cost in the case of recycling. In this way, it is possible to effectively establish zero emission by complying with economic efficiency and drainage standards and recycling.
[0039]
FIG. 2 is a flowchart showing the details (electrodialysis units 5a, 6a) of the electrodialysis apparatus (or electrodialysis step) 5 and 6 in FIG. 1 showing the above-described embodiment according to the present invention. It is a figure which shows the outline | summary regarding the circulatory system for implement | achieving a concentration multiple.
In FIG. 2, for example, the fluorine-containing waste water 2 having a pH value of 2 to 6 from the exhaust gas abatement apparatus 1 is temporarily stored in the storage device 3. The fluorine-containing wastewater 2 stored in the storage device 3 is sent to a desalted water tank 16 by a pump 15. This operation is a batch operation. The fluorine-containing waste water 2 from the desalting water tank 16 returns to the desalting water tank 16 around the circulation flow path 24 that passes through a predetermined path at the center of the electrodialysis unit 5 a of the electrodialysis apparatus 5 by the pump 17. This circulation flow path 24 represents a plurality of flow paths in the electrodialysis apparatus 5 together.
[0040]
The fluorine-containing waste water 2 that has entered the electrodialysis unit 5 a from the desalted water tank 16 enters the concentrated liquid circulation tank 18 as a concentrated liquid 7 and is stored therein. The concentrate 7 in the concentrate circulating tank 18 is circulated by the pump 19 and returned to the concentrate circulating tank 18. In particular, the electrodialysis unit 5a has a configuration in which a plurality of cation exchange membranes are arranged on the positive electrode 28 side, and has a configuration in which fluorine ions do not collect near the positive electrode 28, and a cation exchange membrane is arranged. The blocking liquid passes from the blocking liquid circulation tank 22 through the pump 23 to the part where the circulation loop 27 is formed. In the blocking liquid, the treated water 9 is passed through the path 9a, and as a solution having a low electrolyte concentration, the movement of anions such as fluorine ions to the positive electrode 28 is made difficult to occur. Further, in the vicinity of the positive electrode 28 and the negative electrode 29, the electrode circulation liquid 26 circulates from the electrode liquid circulation tank 20 through the pump 21. The electrode circulating liquid 26 also passes the treated water 9c through the path 9b, suppresses the generation of electrode reaction products at the respective electrodes 28 and 29, and supplies gases such as oxygen and hydrogen generated by the electrode reaction to the electrode. The liquid circulation tank 20 is quickly exhausted out of the system.
[0041]
Also, with these configurations, consumption of the electrode in the positive electrode 28 and scale generation in the negative electrode 29 are suppressed, and stable operation and long life as the electrodialysis unit 5a are achieved. Furthermore, the circulation time in batch processing is controlled to ensure a predetermined concentration factor. When the predetermined concentration factor is reached, the electrodialysis operation is stopped, and the concentrated solution 7 and treated water 9 are taken out and reused. In this way, the concentrated liquid 7 can be reused for 3-10 Wt% of pickling solution for steel, etc., and the treated water 9 and the treated water 9c can be recycled as make-up water to the exhaust gas abatement device 1, respectively. Can be realized. By incorporating the electrodialysis apparatus 5 of FIG. 2 into a plurality of electrodialysis processes, a high concentration factor can be achieved with a compact apparatus, and a concentration-dilution treatment configuration for efficient and efficient recycling is achieved.
it can.
In addition, in the said structure, although the electrode liquid circulation tank 20 and the cutoff liquid circulation tank 22 are made into the separate structure, even if it comprises the electrode liquid circulation tank 20 and the cutoff liquid circulation tank 22 by one tank, an effect is acquired. it can. Further, the treated water 9c may be supplied to the electrode solution circulation tank 20 and then supplied to the blocking part (cation exchange membrane arrangement site) by overflow or the like.
[0042]
(Reference example)
  FIG.As another treatment method for fluorine-containing wastewater,It is a flowchart which shows the outline | summary of a process and its processing apparatus. In FIG. 3, the crystallizer 35 adjusts the pH value of the fluorine-containing wastewater 2 to 6 to 10 (preferably 7 to 9) with a pH adjuster. As this pH adjuster, it is desirable to use a Ca-based alkali such as calcium hydroxide. When calcium ions are insufficient, a water-soluble calcium salt such as calcium chloride is used. Thereby, hydrofluoric acid becomes a suspension of calcium fluoride or the like. If this fluorine-containing wastewater 2 has insufficient Si content, the reaction vessel 32 is stirred with SiO2Powder (or Si powder) 33 may be added and reacted. In the reaction vessel 32, hexafluorosilicic acid (silicic acid) (or hexafluorosilicate (silicofluoride)) 34 is obtained as a result of the reaction. SiO used here2As the powder (or Si powder) 33, one generated as waste in a semiconductor or liquid crystal manufacturing process can be applied.
[0043]
Further, as the crystallization accelerator 36, for example, fluoroapatite (CaFiveF (POFour)Three) Add particles and adsorb calcium fluoride and silicofluoride on the surface of the particles to cause precipitation. This adsorption reaction removes fluorine to a concentration level of 0.8 to 5 mg / l or less. Crystal growth on the surface of the crystallization accelerator 36 is performed by ventilating a bubbling device 39 disposed at the bottom in a seed crystal filling tank (or a fluidized bed crystallization separation step) 37 having an immersion type membrane separation device 38 at the top. The seed crystal is caused to flow by the flow accompanying the rising of the generated bubbles, and the crystallization reaction is accelerated while preventing the seed crystal filling tank 37 from being clogged. Also, the liquid rises due to the flow, forms a cross flow with respect to the separation membrane, secures a flow velocity on the membrane surface necessary for the separation operation, and effectively performs membrane separation of the suspension. As a result, the fluorine-containing waste water 2 precipitated as calcium fluoride by the neutralization reaction and having a concentration in the liquid phase of 0.8 to 5 mg / l or less is separated and discharged through the discharge channel 66. Further, calcium fluoride or calcium silicofluoride adsorbed and crystallized on the fluoroapatite is extracted from the lower part of the seed crystal filling tank 37, collected as a cake 41 by a dehydrator 40, and used as a raw material for the phosphoric acid production process. It is recycled as. Further, the slurry 42 is also recycled.
[0044]
(Example 2)
  FIG. 4 shows the above-described embodiment (embodiment 1) related to the present invention and the above-described embodiment.Reference exampleIt is a flowchart which shows the outline | summary of the structure which combined. 4 will be described in the first embodiment.Reference exampleAre omitted here. That is, the concentrated liquid of the latter-stage electrodialysis apparatus 6 of Example 1 is recycled as a hydrofluoric acid solution (recovered acid), and after the desalting treatment liquid 10,Reference exampleThe crystallizer 35 and the seed crystal filling tank 37 are put in, the membrane filtrate is discharged, and the crystallized product is recycled. Also,Example 2As for the function and effect of the first embodiment,Reference exampleTherefore, the fluorine-containing waste water (A) 2 can be treated with higher accuracy.
[0045]
(Example 3)
  FIG. 5 shows a combination of a plurality of the above-described one embodiment (embodiment 1) relating to the present invention in parallel,Reference exampleIt is a flowchart which shows the outline | summary of the structure which combined. In FIG. 5, an exhaust gas abatement device (or hydrofluoric acid scrubber) 61, a fluorine-containing waste water 62 and a fluorine-containing waste water 82 from an exhaust gas abatement device (or hydrofluoric acid scrubber) 81, which are combined in parallel, The dialysis apparatus (or electrodialysis process 63 and electrodialysis apparatus (or electrodialysis process) 83 is sent to a shared electrodialysis apparatus or electrodialysis process) 64. Reference numerals 65 and 84 denote the heat exchanger 65 and the heat exchanger 84, respectively. Further, after the common electrodialyzer, a predetermined concentration / dilution treatment is performed after passing through the common crystallizer 67, the seed crystal filling tank 68, and the submerged membrane separator 69, respectively. In addition, the same description already made in each said Example is abbreviate | omitted (code | symbol). Even a wide variety of fluorine-containing wastewater 62 and 82 can be treated with high efficiency. Furthermore, by sharing each device (or each process) in the latter half, the effects of resource saving and energy saving can be doubled in terms of cost, installation area, and the like. In addition, although the fluorine-type scrubber which is a generation source of fluorine-containing wastewater and an exhaust gas abatement apparatus were illustrated in FIG. 5 as two, it does not limit a kind and number, and it is made to respond to various fluorine-containing wastewater generation sources. In addition, the number of electrodialysis steps or electrodialysis means to be arranged in parallel can be 3 or more as required.
[0046]
【The invention's effect】
As described above, according to the method and apparatus for treating fluorine-containing wastewater of the present invention, the following effects are produced.
(1) Concentrate hydrofluoric acid (acidic) with an electrodialyzer (or the same process), add no special chemicals, and replenish treated water with an exhaust gas abatement device (or hydrofluoric acid scrubber) As water, hydrofluoric acid can be reused for recycling, which can contribute to zero emissions at factories.
(2) In the reuse of the treated water (or demineralized water), scale components such as calcium that cause the scale failure of the exhaust gas abatement apparatus are highly removed, which can contribute to the suppression of scale generation.
(3) In the reuse of the above treated water (or desalted water), scale components such as calcium are no longer brought into the waste water from the exhaust gas abatement device, and high concentration can be achieved with an electrodialyzer, and the concentrate is washed. It can be the most resourceful solution for hydrofluoric acid and can contribute to the zero emission of factories.
(4) In the crystallization method, it became possible to recycle the fluorine content from the hydrofluoric acid wastewater with a high silicon content by crystallization and separation as a silicofluoride in the crystallization agent.
(5) Combined with membrane separation in apatite crystallization method, the quality of treated water can be improved, and at the same time, the suspension product can be circulated in the seed crystal filling tank, so the residence time of the suspension can be lengthened, so the reaction of the drug Increase efficiency and reduce consumption. At that time, the crystal is also coarsened, and the effect of improving the separation performance is produced.
(6) The structure of the electrodialysis device having a shut-off chamber in particular can ensure the durability of the electrode and the stable operation of the dialysis operation without generating new waste acid in the electrodialysis process.
(7) In the configuration of the electrodialysis apparatus, it is possible to efficiently install the facilities by separating the apparatus mainly for reuse of treated water and the apparatus intended for hydrofluoric acid concentration. In addition, it is possible to recycle resources suitable for the form of fluorine in the wastewater by crystallizing and separating the concentrated solution of the latter-stage electrodialysis device into hydrofluoric acid for surface cleaning and fluorine in the treated water as silicofluoride. It becomes.
[Brief description of the drawings]
FIG. 1 is a flowchart (Example 1) showing an outline of a fluorine-containing wastewater treatment method and treatment apparatus according to an embodiment of the present invention.
FIG. 2 is a flowchart showing details of the electrodialysis apparatus (or electrodialysis step) in FIG. 1 showing the above-described embodiment according to the present invention.
[Fig. 3]]Of nitrogen-containing wastewateranotherFlow chart showing the outline of the process and its processing equipment related to the processing method (Reference example).
FIG. 4 shows one embodiment related to the present invention, andReference exampleFlow diagram showing the outline of the configuration combiningExample 2).
FIG. 5 shows a combination of a plurality of the above embodiments according to the present invention in parallel;Reference exampleFlow diagram showing the outline of the configuration combiningExample 3).

Claims (10)

フッ素含有排水の処理方法であって、
フッ素含有排水を脱塩及び濃縮する電気透析工程を備え、
前記電気透析工程には、おおよそ対向状に配置される負極部と正極部とを備える電気透析手段において、負極部及び中央部には、陽イオン交換膜と陰イオン交換膜とが交互に配置され、正極部近傍には、陽イオン交換膜が複数枚連続して配置されており、前記負極部と正極部に脱塩処理液を循環供給し、前記正極部近傍の陽イオン交換膜配置部位にも前記脱塩処理液を循環供給する工程を含み、
前記脱塩処理液を前記フッ素含有排水の発生源への補給水として再生し、前記フッ酸濃縮液を利用可能な濃度のフッ酸溶液として再生する程度に電気透析することを特徴とする方法。
A method for treating fluorine-containing wastewater,
An electrodialysis process for desalting and concentrating fluorine-containing wastewater,
In the electrodialysis step, in the electrodialysis means having a negative electrode portion and a positive electrode portion that are arranged approximately opposite to each other, a cation exchange membrane and an anion exchange membrane are alternately arranged in the negative electrode portion and the central portion. In the vicinity of the positive electrode part, a plurality of cation exchange membranes are continuously arranged, and a desalination treatment liquid is circulated and supplied to the negative electrode part and the positive electrode part, and the cation exchange membrane is arranged near the positive electrode part. Including a step of circulating and supplying the desalting treatment liquid,
The method is characterized in that the desalting solution is regenerated as make-up water to the fluorine-containing wastewater generation source, and electrodialyzed to such an extent that the hydrofluoric acid concentrate is regenerated as a hydrofluoric acid solution having an available concentration.
フッ素含有排水の処理方法であって、
前記電気透析工程により利用可能な濃度のフッ酸溶液として再生される、前記フッ酸濃縮液のフッ酸濃度が3重量%以上である請求項1に記載の方法。
A method for treating fluorine-containing wastewater,
The method according to claim 1 , wherein the hydrofluoric acid concentration of the hydrofluoric acid concentrate regenerated as a hydrofluoric acid solution having a concentration usable by the electrodialysis step is 3% by weight or more.
フッ素含有排水の処理方法であって、
前記フッ酸濃縮液酸性洗浄液として再生される、請求項1又は2に記載の方法。
A method for treating fluorine-containing wastewater,
The method according to claim 1, wherein the hydrofluoric acid concentrate is regenerated as an acidic cleaning solution.
前記電気透析工程において、前記濃縮液中のフッ素イオン濃度、および/または電解質濃度を計測し、この濃度変動に応じて濃縮倍率を制御する工程を含む、請求項1〜3のいずれかに記載の方法。  The said electrodialysis process WHEREIN: The fluorine ion concentration in the said concentrate and / or electrolyte concentration are measured, The process of controlling a concentration rate according to this density | concentration fluctuation | variation is included in any one of Claims 1-3. Method. フッ素含有排水の処理装置であって、
おおよそ対向状に配置される負極部と正極部とを備える電気透析手段であり、負極部及び中央部には、陽イオン交換膜と陰イオン交換膜とが交互に配置され、正極部近傍には、陽イオン交換膜が複数枚連続して配置されており、少なくとも前記正極部近傍の陽イオン交換膜配置部位に当該電気透析手段において得られる脱塩処理液を循環供給する経路を備える、電気透析手段を備える、装置。
A treatment apparatus for fluorine-containing wastewater,
It is an electrodialysis means comprising a negative electrode portion and a positive electrode portion that are arranged roughly opposite to each other. In the negative electrode portion and the central portion, cation exchange membranes and anion exchange membranes are alternately arranged, and in the vicinity of the positive electrode portion. Electrodialysis, wherein a plurality of cation exchange membranes are continuously arranged, and a path for circulating and supplying the desalting solution obtained in the electrodialysis means to at least the cation exchange membrane arrangement site in the vicinity of the positive electrode portion is provided. An apparatus comprising means .
電気透析された濃縮液中のフッ素イオン濃度もしくは電解質濃度の計測手段、および濃縮倍率の制御手段を備える、請求項5に記載の装置。 Electrodialyzed fluoride ion concentration or electrolyte concentration measuring means in the concentrate, and a control means for concentration ratio, according to claim 5. フッ素含有排水の処理方法であって、
フッ素含有排水を脱塩及び濃縮して、脱塩処理液をフッ素含有排水の発生源への補給水として再生する第1の電気透析工程と、
第1の電気透析工程において得られるフッ酸濃縮液をさらに脱塩及び濃縮して、フッ酸濃縮液を利用可能な濃度のフッ酸溶液として再生する第2の電気透析工程と、
第2の電気透析工程で得られた脱塩処理液を晶析する工程と、
晶析工程の処理物を流動床で晶析分離する工程、
とを備える方法。
A method for treating fluorine-containing wastewater,
A first electrodialysis step of desalinating and concentrating the fluorine-containing wastewater to regenerate the desalination treatment liquid as makeup water to the source of fluorine-containing wastewater;
A second electrodialysis step of further desalting and concentrating the hydrofluoric acid concentrate obtained in the first electrodialysis step to regenerate the hydrofluoric acid concentrate as a hydrofluoric acid solution having a usable concentration;
Crystallization of the desalting treatment liquid obtained in the second electrodialysis step;
A process of crystallizing and separating the treated product of the crystallization process in a fluidized bed,
A method comprising:
フッ素含有排水の処理装置であって、
フッ素含有排水を脱塩及び濃縮する第1の電気透析手段と、
第1の電気透析手段において得られたフッ酸濃縮液を脱塩及び濃縮する第2の電気透析手段と、
第2の電気透析手段において得られた脱塩処理液を晶析する手段と、
晶析手段により得られる処理物が投入される充填槽であって、エアレーションをしながら膜分離操作により分離した水を系外へ放流する一方、充填槽にて前記処理物中の珪フッ化物を析出成長させる充填槽、とを備える装置。
A treatment apparatus for fluorine-containing wastewater,
A first electrodialysis means for desalting and concentrating the fluorine-containing wastewater;
A second electrodialysis means for desalting and concentrating the hydrofluoric acid concentrate obtained in the first electrodialysis means;
Means for crystallizing the desalted solution obtained in the second electrodialysis means;
It is a filling tank into which the processed product obtained by the crystallization means is charged, and the water separated by the membrane separation operation while aeration is discharged to the outside of the system, while the silicofluoride in the processed product is discharged in the filling tank. A filling tank for precipitation growth.
前記第1の電気透析工程を、フッ素含有排水の発生源に対応させた複数の電気透析工程を並列に組み合わせて実施し、これらの各第1の電気透析工程で得られたフッ酸濃縮液を合わせて第2の電気透析工程に供給する、請求項7に記載の方法。  The first electrodialysis step is performed by combining in parallel a plurality of electrodialysis steps corresponding to the generation source of fluorine-containing waste water, and the hydrofluoric acid concentrate obtained in each of the first electrodialysis steps The method according to claim 7, wherein both are supplied to the second electrodialysis step. 前記第1の電気透析手段を、フッ素含有排水の発生源に対応して備え、これらの第1の電気透析手段から得られたフッ酸濃縮液を合わせて第2の電気透析手段に供給する構成を備える、請求項8に記載の装置。  The first electrodialysis means is provided corresponding to the generation source of fluorine-containing wastewater, and the hydrofluoric acid concentrate obtained from the first electrodialysis means is combined and supplied to the second electrodialysis means. 9. The apparatus of claim 8, comprising:
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