JP5024643B2

JP5024643B2 - Method and apparatus for reducing permanganate-containing water

Info

Publication number: JP5024643B2
Application number: JP2001254710A
Authority: JP
Inventors: 勇加藤
Original assignee: Kurita Water Industries Ltd
Current assignee: Kurita Water Industries Ltd
Priority date: 2001-08-24
Filing date: 2001-08-24
Publication date: 2012-09-12
Anticipated expiration: 2021-08-24
Also published as: JP2003062584A

Description

【０００１】
【発明の属する技術分野】
本発明は、過マンガン酸塩含有水の還元処理方法及び装置に関する。さらに詳しくは、本発明は、少量の第一鉄塩を用いて水中の過マンガン酸イオンを難溶性のマンガン(IV)又はマンガン(III)化合物まで還元し、発生汚泥量が少なく、可溶性のマンガン(II)の生成を防ぐことができる過マンガン酸塩含有水の還元処理方法及び装置に関する。
【０００２】
【従来の技術】
過マンガン酸塩を使用したステンレス製電子部品エッチング工程からの廃水や、有機塩素化合物含有廃水を過マンガン酸塩により酸化分解した後の廃水には、過マンガン酸塩が含まれる。過マンガン酸塩は水溶性であり、水中にＭｎ(VII)として１〜２mg／Ｌ含まれるだけでも赤紫色を呈し、また、中性ないしアルカリ性でも強い酸化力を有するために、そのまま放流することができない。このために、Ｍｎ(VII)を、Ｍｎ(IV)、Ｍｎ(III)又はＭｎ(II)に還元したのち、難溶性の沈澱物として廃水中から分離する必要がある。
Ｍｎ(IV)は、ＭｎＯ₂・ｎＨ₂Ｏの沈澱物であり、酸性でも難溶性である。Ｍｎ(III)は、Ｍｎ(ＯＨ)₃又はＭｎ₂Ｏ₃・ｎＨ₂ＯとしてpH３以上で沈殿する。Ｍｎ(II)は、Ｍｎ(ＯＨ)₂としてpH１０以上で沈殿する。したがって、高次の還元状態の沈澱物、すなわちＭｎＯ₂・ｎＨ₂ＯやＭｎ(ＯＨ)₃が得られれば、pH６〜８の中性域で分離可能であり、Ｍｎ(II)に還元するより還元剤の使用量が少なくてすみ、わざわざpH１０以上のアルカリ性にする必要もない。第一鉄塩を使用して還元する場合、Ｍｎ(II)の生成がなく、中性で還元可能であれば、生成する還元物であるＭｎＯ₂とＭｎ₂Ｏ₃は、中性で沈澱するために、還元反応、凝集処理、沈殿処理を一連の同じpHで行うことができ、処理水をそのままで、あるいは、処理水のpHを微調整するだけで放流することができる。
特許第２８４７８６４号公報には、中性で酸化性重金属を還元し、水酸化物として沈殿分離する方法として、６価クロムを含有する廃水のpHを４以上に調整し、溶存酸素が２mg／Ｌ以下になるように第一鉄イオンを添加し、３価クロムに還元して不溶性化合物として沈殿除去する方法が提案されている。過マンガン酸塩に第一鉄塩を添加して還元処理すると、マンガンは酸化数の高い順位から、第一鉄塩の添加量に応じて、Ｍｎ(VII)（ＭｎＯ^4-）→ Ｍｎ(IV)（ＭｎＯ₂）→ Ｍｎ(III)（Ｍｎ₂Ｏ₃）→ Ｍｎ(II)（ＭｎＯ）と還元される。一方、第一鉄イオンは溶存酸素と反応して、４Ｆｅ²⁺＋Ｏ₂＋２Ｈ₂Ｏ → ４Ｆｅ³⁺＋４ＯＨ^-の反応により、液中の溶存酸素を消費するために、溶存酸素濃度を指標として第一鉄塩の添加量を制御することができる。しかし、マンガンのどの還元段階で第一鉄イオンと溶存酸素の反応が起きるかは明らかではなく、過マンガン酸塩の第一鉄塩による還元処理において、溶存酸素による制御を適用すると、第一鉄塩が多量に必要であり、その結果、処理コストが高くなり、発生汚泥量が多くなるという問題があった。
【０００３】
【発明が解決しようとする課題】
本発明は、少量の第一鉄塩を用いて水中の過マンガン酸イオンを難溶性のマンガン(IV)又はマンガン(III)化合物まで還元し、発生汚泥量が少なく、可溶性のマンガン(II)の生成を防ぐことができる過マンガン酸塩含有水の還元処理方法及び装置を提供することを目的としてなされたものである。
【０００４】
【課題を解決するための手段】
本発明者は、上記の課題を解決すべく鋭意研究を重ねた結果、過マンガン酸塩を含有する被処理水に第一鉄塩を添加して還元処理するとき、溶存酸素の代わりに酸化還元電位により第一鉄塩の添加量を制御し、第一鉄塩の添加量と酸化還元電位の関係を示す曲線の変曲点において第一鉄塩の添加を停止することにより、少量の第一鉄塩の添加量でマンガンがＭｎ(IV)又はＭｎ(III)の状態となり、この状態で固液分離すれば処理水中のマンガン濃度は１ｍｇ／Ｌ以下となり、発生する汚泥量も少ないことを見いだし、この知見に基づいて本発明を完成するに至った。
すなわち、本発明は、
（１）被処理水のｐＨを測定するｐＨ計及び被処理水の酸化還元電位を測定する酸化還元電位計を備えた還元処理装置に過マンガン酸塩を含有する被処理水を導入し、該被処理水に第一鉄塩を添加して、マンガン(II)化合物を生成させることなく、難溶性のマンガン(IV)化合物又はマンガン(III)化合物に還元処理する方法において、還元処理装置内における被処理水のｐＨを４〜１０の範囲にｐＨ調整剤により維持しながら第一鉄塩を被処理水に添加して、該被処理水の酸化還元電位を酸化還元電位計により測定して、被処理水の酸化還元電位が第一鉄塩の添加量と酸化還元電位の関係を示す曲線の変曲点における値に達したときに、第一鉄塩の添加を停止し、次いで、被処理水を固液分離することを特徴とする過マンガン酸塩含有水の還元処理方法、
（２）被処理水のｐＨを測定するｐＨ計及び被処理水の酸化還元電位を測定する酸化還元電位計を備えた還元処理装置に過マンガン酸塩を含有する被処理水を導入し、該被処理水に第一鉄塩を添加して、マンガン(II)化合物を生成させることなく、難溶性のマンガン(IV)化合物又はマンガン(III)化合物に還元処理する連続式処理方法において、反応槽に連続的に過マンガン酸塩含有水を送り込み、該過マンガン酸塩含有水のｐＨを４〜１０の範囲にｐＨ調整剤により維持しながら、第一鉄塩の反応槽への添加を、第一鉄塩の添加量と酸化還元電位の関係を示す曲線の変曲点を目安として、被処理水の酸化還元電位が前記変曲点での電位より下方の設定値に達したとき第一鉄塩の添加を停止し、被処理水の酸化還元電位が前記変曲点での電位より上方の設定値に達したとき第一鉄塩の添加を再開し、反応槽から還元処理された水を連続的に後段の固液分離工程に送り出すことを特徴とする過マンガン酸塩含有水の還元処理方法、
（３）過マンガン酸塩を含有する被処理水の酸化還元電位を測定する酸化還元電位計及び第一鉄塩供給装置並びに還元処理装置内の被処理水のｐＨを測定するｐＨ計及び被処理水のｐＨ調整剤供給装置を備え、該被処理水に第一鉄塩を添加して、マンガン(II)化合物を生成させることなく、難溶性のマンガン(IV)化合物又はマンガン(III)化合物に還元処理する還元処理装置であって、還元処理装置内の被処理水のｐＨを４〜１０の範囲に維持しながら、第一鉄塩の被処理水への供給を続けて、被処理水の酸化還元電位が第一鉄塩の添加量と酸化還元電位の関係を示す曲線の変曲点に達したときに、第一鉄塩の添加を停止する手段を有し、還元処理装置内の還元後の被処理水を凝集槽に送り出す手段、凝集槽から排出される被処理水を固液分離する手段を有することを特徴とする過マンガン酸塩含有水の還元処理装置、及び、
（４）過マンガン酸塩を含有する被処理水の酸化還元電位を測定する酸化還元電位計及び第一鉄塩供給装置並びに被処理水のｐＨを測定するｐＨ計及び被処理水のｐＨ調整剤供給装置を備え、該被処理水に第一鉄塩を添加して、マンガン(II)化合物を生成させることなく、難溶性のマンガン(IV)化合物又はマンガン(III)化合物に還元処理する連続式還元処理装置であって、還元処理装置内の被処理水のｐＨを４〜１０の範囲に維持しながら、第一鉄塩の添加量と酸化還元電位の関係を示す曲線の変曲点を目安として、酸化還元電位が前記変曲点より下方の酸化還元電位の設定値に達したとき第一鉄塩の添加を停止し、酸化還元電位が前記変曲点より上方の酸化還元電位の設定値に達したとき第一鉄塩の添加を再開する手段を有し、還元処理装置内の還元後の被処理水を凝集槽に送り出す手段、凝集槽から排出される被処理水を固液分離する手段を有することを特徴とする過マンガン酸塩含有水の還元処理装置、
を提供するものである。
【０００５】
【発明の実施の形態】
本発明の過マンガン酸塩含有水の還元処理方法においては、過マンガン酸塩を含有する被処理水に、第一鉄塩を添加して還元処理する方法において、第一鉄塩が添加された被処理水の酸化還元電位が所定の値に達するまで第一鉄塩を添加する。本発明の過マンガン酸塩含有水の還元処理装置は、酸化還元電位計及び第一鉄塩供給装置を備えた還元処理装置であって、酸化還元電位計の測定値に基づいて第一鉄塩の供給を制御する装置である。
過マンガン酸塩含有水に第一鉄塩を添加して還元処理すると、過マンガン酸イオンは下記のように反応して、Ｍｎ(IV)、Ｍｎ(III)又はＭｎ(II)まで還元される。
Ｍｎ(IV)への還元：
ＭｎＯ₄ ^- ＋３Ｆｅ²⁺ ＋２Ｈ₂Ｏ → ＭｎＯ₂ ＋３Ｆｅ³⁺ ＋４ＯＨ^-…［１］
Ｍｎ(III)への還元：
ＭｎＯ₄ ^- ＋４Ｆｅ²⁺ ＋４Ｈ₂Ｏ → Ｍｎ(ＯＨ)₃ ＋４Ｆｅ³⁺ ＋５ＯＨ^-…［２］
Ｍｎ(II)への還元：
ＭｎＯ₄ ^- ＋５Ｆｅ²⁺ ＋４Ｈ₂Ｏ → Ｍｎ(ＯＨ)₂ ＋５Ｆｅ³⁺ ＋６ＯＨ^-…［３］
過マンガン酸塩をマンガンとして６０mg／Ｌ含有する過マンガン酸塩含有水を第一鉄塩を用いて還元する場合、上記の化学反応式にしたがって計算すると、第一鉄イオンの必要な理論当量は、Ｍｎ(IV)への還元の場合１８３mg／Ｌ、Ｍｎ(III)への還元の場合２４４mg／Ｌ、Ｍｎ(II)への還元の場合３０５mg／Ｌとなる。
【０００６】
マンガン化合物の水に対する溶解性は、Ｍｎ(VII)化合物であるＫＭｎＯ₄は、２０℃において水１００ｇに５.９６ｇ溶解し、Ｍｎ(IV)化合物であるＭｎＯ₂は、水にほとんど溶解しない。さらに、Ｍｎ(III)化合物であるＭｎ(ＯＨ)₃は、溶解度積１０^-36より、pH３以上でマンガン濃度１mg／Ｌ以下となり、Ｍｎ(II)化合物であるＭｎ(ＯＨ)₂は、溶解度積１０^-12.8より、pH１０以上でマンガン濃度１mg／Ｌ以下となる。したがって、中性領域で過マンガン酸塩の還元処理を行う場合、還元をＭｎ(IV)又はＭｎ(III)の段階にとどめ、Ｍｎ(II)を生成させなければ、固液分離によりマンガン濃度の低い良好な水質の処理水を得ることができる。
図１は、過マンガン酸塩含有水を第一鉄塩を用いて還元処理したときの第一鉄イオンの添加量と、溶存酸素、酸化還元電位、処理水をろ過して得られるろ液中のマンガン濃度及び鉄濃度との関係を示すグラフの一例である。本例においては、過マンガン酸カリウムをマンガン濃度として６０mg／Ｌ含む被処理水を、pH７に保ち、硫酸第一鉄を添加して還元処理している。本図に見られるように、pH７に保った場合、第一鉄イオンの添加量と溶存酸素の関係を示す曲線の変曲点は、式［１］で求められるＭｎ(IV)への還元の場合の理論当量より過剰側へずれているが、第一鉄イオンの添加量と酸化還元電位の関係を示す曲線の変曲点は、式［１］で求められるＭｎ(IV)への還元の場合の理論当量とほぼ一致する添加量のところに現れる。したがって、酸化還元電位を測定しつつ過マンガン酸塩含有水に第一鉄塩を添加し、変曲点に達したときに第一鉄塩の添加を停止することにより、Ｍｎ(II)を生成させることなく、過マンガン酸イオンをＭｎ(IV)又はＭｎ(III)まで還元することができる。
【０００７】
本発明方法において、第一鉄塩の添加による還元処理方法に特に制限はなく、例えば、回分式、連続式のいずれの方式によっても処理することができる。回分式処理の場合には、反応槽に過マンガン酸塩含有水を導入し、好ましくはpHを調整しつつ、酸化還元電位が所定の値に達するまで、第一鉄塩を添加して処理することができる。連続式処理の場合には、反応槽に連続的に過マンガン酸塩含有水を送り込み、好ましくはpHを調整しつつ、第一鉄塩の添加量と酸化還元電位の関係を示す曲線の変曲点を目安として、酸化還元電位が下方の設定値に達したとき第一鉄塩の添加を停止し、酸化還元電位が上方の設定値に達したとき第一鉄塩の添加を再開し、反応槽から還元処理された水を連続的に後段の固液分離工程に送り出すことができる。あるいは、第一鉄塩の所定の基礎量を常時添加し、酸化還元電位値により追加量の停止、供給を制御することもできる。
本発明方法においては、被処理水のpHを４〜１０の範囲に維持しつつ第一鉄塩を添加することが好ましい。被処理水のpHが４未満であると、第一鉄塩の添加量と酸化還元電位の関係を示す曲線の変曲点が、理論当量よりも過剰側に移行し、変曲点を目安として制御したとき、過剰量の第一鉄塩を供給することになり、一部Ｍｎ(II)化合物が生成し、かつpH４未満ではＭｎ(II)化合物の水に対する溶解性が大きいので、処理水中にマンガンが漏出するおそれがある。被処理水のpHが１０を超えても、変曲点を目安にして第一鉄塩の添加を制御し、マンガンを難溶性のＭｎ(III)化合物まで還元するという本発明の目的は達せられるが、処理水を放流するためには中和剤を用いる中和が必要になる。被処理水のpHを４〜１０の範囲に維持することにより、第一鉄塩の理論当量と変曲点が一致して、最少必要量の第一鉄塩の添加で、Ｍｎ(II)化合物を生成することなく、マンガンを難溶性のＭｎ(IV)又はＭｎ(III)まで還元し、処理水はそのまま、あるいは、pHの微調整をするだけで放流することができる。
【０００８】
本発明方法に用いる第一鉄塩に特に制限はなく、例えば、塩化第一鉄、臭化第一鉄、硫酸第一鉄、硝酸第一鉄、チオシアン酸第一鉄などを挙げることができる。これらの中で、硫酸第一鉄は、安定で取り扱いが容易であり、副次的な環境汚染を引き起こすおそれがないので、好適に用いることができる。第一鉄塩の添加方法に特に制限はないが、作業性の面からは、水溶液として添加することが好ましい。
本発明方法により、第一鉄塩を添加してマンガンが還元された被処理水は、水中に不溶化したＭｎ(IV)又はＭｎ(III)化合物が懸濁状態で存在するので、凝集処理及び固液分離により懸濁物質を除去することが好ましい。凝集処理方法に特に制限はなく、無機凝集剤及び／又は高分子凝集剤を用いて凝集処理することができ、例えば、無機凝集剤を添加し、必要に応じてpHを６〜８に調整したのち、高分子凝集剤を添加することができる。含まれるマンガン量が少ない場合は、無機凝集剤を添加することにより、Ｍｎ(IV)又はＭｎ(III)化合物からなる懸濁粒子の表面荷電を中和して、微小フロックを形成し、さらに高分子凝集剤を添加することにより、微小フロックを凝集して粗大フロックとすることができる。
凝集処理により形成されたＭｎ(IV)又はＭｎ(III)化合物の凝集フロックは、固液分離により除去することができる。固液分離方法に特に制限はなく、例えば、沈殿処理、ろ過、膜分離などを挙げることができる。沈殿処理方法に特に制限はなく、例えば、沈殿槽などを用いる自然沈殿処理と遠心分離機などを用いる強制沈殿処理のいずれをも行うことができる。ろ過方法にも特に制限はなく、例えば、重力式、圧力式、サイフォン式、上向流式、ろ材循環式、連続ろ過式などのろ過器と、アンスラサイト、砂、けい砂、砂利、活性炭、プラスチックなどのろ材を用いてろ過することができる。膜分離方法にも特に制限はなく、例えば、精密ろ過膜、限外ろ過膜などを用いて膜分離することができる。
【０００９】
図２は、本発明方法の実施の一態様の工程系統図である。本態様においては、pH計１、酸化還元電位計２を備えた還元処理装置３に、過マンガン酸塩含有水が導入される。pH計の測定値に基づいて、pH制御器４からポンプ５に信号が送られ、槽内において所定のpH値が維持されるようにpH調整剤槽６からpH調整剤が供給される。また、酸化還元電位計の測定値に基づいて、酸化還元電位制御器７からポンプ８に信号が送られ、槽内において所定の酸化還元電位範囲が維持されるように、第一鉄塩水溶液槽９から第一鉄塩水溶液が供給される。マンガンが難溶性のＭｎ(IV)又はＭｎ(III)化合物まで還元された被処理水は、第１の凝集槽１０に送られ、無機凝集剤が添加されて凝集し、さらに第２の凝集槽１１に送られ、高分子凝集剤が添加されて、凝集フロックが粗大化する。粗大フロックが形成された被処理水は、次いで固液分離槽１２に送られ、沈降したマンガン化合物が汚泥として槽底から抜き出され、上澄水は無害な処理水として放流される。
本発明方法及び装置によれば、過マンガン酸塩を含有する被処理水に第一鉄塩を添加して還元処理するに際し、被処理水の酸化還元電位を測定し、酸化還元電位が所定の値に達するまで第一鉄塩を添加するように制御することにより、還元の段階を難溶性のＭｎ(IV)又はＭｎ(III)化合物でとどめ、マンガン濃度の低い良好な水質の処理水を得ることができる。
【００１０】
【実施例】
以下に、実施例を挙げて本発明をさらに詳細に説明するが、本発明はこれらの実施例によりなんら限定されるものではない。
実施例１
過マンガン酸カリウム（試薬特級）を水道水に溶解し、マンガン濃度６０mg／Ｌの水溶液を調製した。この過マンガン酸カリウム水溶液を１Ｌビーカーにとり、pH７に保ちながら、第一鉄イオン濃度２０ｇ／Ｌの硫酸第一鉄水溶液を添加して過マンガン酸イオンを還元し、溶存酸素と酸化還元電位を測定した。また、第一鉄イオン添加量１００、１７０、２００、２４０、２８０及び３００mg／Ｌのとき、液をサンプリングして化学分析用５種Ａろ紙を用いてろ過し、その色相を観察するとともに、フレーム原子吸光法によりろ液中のマンガン濃度と鉄濃度を測定した。結果を、第１表及び図１に示す。
【００１１】
【表１】

【００１２】
第１表及び図１に見られるように、第一鉄イオン添加量と溶存酸素の関係を示す曲線は、第一鉄イオン添加量２８０mg／Ｌ付近に変曲点を有し、第一鉄イオン添加量と酸化還元電位の関係を示す曲線は、第一鉄イオン添加量２００mg／Ｌ付近に変曲点を有する。
Ｍｎ(VII)６０mg／ＬをＭｎ(IV)に還元するために必要な第一鉄イオンは１８３mg／Ｌ、Ｍｎ(III)に還元するために必要な第一鉄イオンは２４４mg／Ｌ、Ｍｎ(II)還元するために必要な第一鉄イオンは３０５mg／Ｌである。
第一鉄イオン添加量２００mg／Ｌのとき、ろ液のマンガン濃度が０.２mg／Ｌとなり、ろ液の色相も無色となることから、Ｍｎ(VII)の還元反応は終了していることが分かる。また、このとき、第一鉄イオンの添加量と酸化還元電位の関係を示す曲線は変曲点を示すので、この曲線の変曲点を目安として第一鉄イオンの添加を制御することができる。
一方、第一鉄イオンの添加量と溶存酸素の関係を示す曲線は、第一鉄イオン添加量２８０mg／Ｌ付近に変曲点があり、この曲線の変曲点を目安として第一鉄イオンを添加すると、Ｍｎ(VII)をＭｎ(III)に還元するために必要な量よりも過剰に添加することになる。しかし、第一鉄イオン添加量２８０mg／Ｌのとき、ろ液中のマンガン濃度は、わずかに上昇する傾向の０.５mg／Ｌであり、そのまま増加する傾向である。これは、第一鉄イオンとＭｎ(VII)との反応、すなわちＭｎ(VII)→Ｍｎ(IV)→Ｍｎ(III)の反応は、溶存酸素との反応、すなわちＦｅ²⁺→Ｆｅ³⁺の反応に優先して起きるが、Ｍｎ(III)→Ｍｎ(II)の反応は、溶存酸素との反応も並発しており、大部分のマンガンの還元状態はなおＭｎ(III)であろうと推定される。
【００１３】
【発明の効果】
本発明方法によれば、過マンガン酸塩含有水中のＭｎ(VII)をＭｎ(III)に還元するために必要な最小限の第一鉄塩を添加して処理することができるので、経済的に有利である、また、過マンガン酸塩含有水を中性で還元処理することができ、処理水中のマンガンと鉄の濃度は十分に低いので、沈殿処理後、処理水をそのまま放流することができる。
【図面の簡単な説明】
【図１】図１は、過マンガン酸塩含有水を第一鉄塩を用いて還元処理したときの第一鉄イオンの添加量と、溶存酸素、酸化還元電位、処理水中のマンガン濃度及び鉄濃度との関係を示すグラフの一例である。
【図２】図２は、本発明方法の実施の一態様の工程系統図である。
【符号の説明】
１ pH計
２酸化還元電位計
３還元処理装置
４ pH制御器
５ポンプ
６ pH調整剤槽
７酸化還元電位制御器
８ポンプ
９第一鉄塩水溶液槽
１０第１の凝集槽
１１第２の凝集槽
１２固液分離槽[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for reducing permanganate-containing water. More specifically, the present invention reduces permanganate ions in water to a sparingly soluble manganese (IV) or manganese (III) compound using a small amount of ferrous salt, and generates a small amount of sludge and soluble manganese. The present invention relates to a reduction treatment method and apparatus for permanganate-containing water that can prevent the formation of (II).
[0002]
[Prior art]
Permanganate is contained in the wastewater from the etching process of stainless steel electronic components using permanganate and the wastewater after oxidative decomposition of the organic chlorine compound-containing wastewater with permanganate. Permanganate is water-soluble, and even if it contains 1-2 mg / L of Mn (VII) in water, it exhibits a reddish purple color, and it is neutral or alkaline and has strong oxidizing power. I can't. For this purpose, Mn (VII) must be reduced to Mn (IV), Mn (III) or Mn (II) and then separated from the wastewater as a hardly soluble precipitate.
Mn (IV) is a precipitate of MnO ₂ · nH ₂ O and is hardly soluble even when acidic. Mn (III) precipitates as Mn (OH) ₃ or Mn ₂ O ₃ .nH ₂ O at pH 3 or higher. Mn (II) precipitates as Mn (OH) ₂ at pH 10 or higher. Therefore, if a precipitate in a higher-order reduced state, that is, MnO ₂ · nH ₂ O or Mn (OH) ₃ is obtained, it can be separated in the neutral range of pH 6 to 8, and is reduced to Mn (II). The amount of reducing agent used is small, and there is no need to make it alkaline with a pH of 10 or more. When reducing using ferrous salt, if there is no formation of Mn (II) and it is neutral and reducible, the resulting reduction products MnO ₂ and Mn ₂ O ₃ are neutral and precipitate. Therefore, the reduction reaction, the coagulation treatment, and the precipitation treatment can be performed at a series of the same pH, and the treated water can be discharged as it is or by just finely adjusting the pH of the treated water.
In Japanese Patent No. 2847864, as a method of reducing neutral and oxidizing heavy metals and precipitating and separating them as hydroxides, the pH of wastewater containing hexavalent chromium is adjusted to 4 or more, and dissolved oxygen is 2 mg / L. A method has been proposed in which ferrous ions are added so as to reduce the amount to trivalent chromium and precipitate is removed as an insoluble compound. When ferrous salt is added to permanganate and reduction treatment is performed, manganese becomes Mn (VII) (MnO ⁴⁻ ) → Mn (IV) according to the amount of ferrous salt added in order of higher oxidation number. ) (MnO ₂ ) → Mn (III) (Mn ₂ O ₃ ) → Mn (II) (MnO). On the other hand, ferrous ion reacts with dissolved oxygen and consumes dissolved oxygen in the liquid by the reaction of 4Fe ²⁺ + O ₂ + 2H ₂ O → 4Fe ³⁺ + 4OH ⁻ . The amount of ferrous salt added can be controlled. However, it is not clear at which reduction stage of manganese the reaction between ferrous ions and dissolved oxygen occurs. When control with dissolved oxygen is applied in the reduction treatment of permanganate with ferrous salt, ferrous iron There was a problem that a large amount of salt was required, resulting in an increase in processing cost and an increase in the amount of generated sludge.
[0003]
[Problems to be solved by the invention]
The present invention reduces permanganate ions in water to a sparingly soluble manganese (IV) or manganese (III) compound using a small amount of ferrous salt, and generates a small amount of sludge and generates soluble manganese (II). An object of the present invention is to provide a reduction treatment method and apparatus for permanganate-containing water that can prevent formation.
[0004]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventor, when reducing treatment by adding ferrous salt to water to be treated containing permanganate, redox instead of dissolved oxygen By controlling the amount of ferrous salt added by the potential and stopping the addition of ferrous salt at the inflection point of the curve indicating the relationship between the amount of ferrous salt added and the redox potential, It is found that manganese is in the state of Mn (IV) or Mn (III) with the amount of iron salt added, and if solid-liquid separation is performed in this state, the manganese concentration in the treated water will be 1 mg / L or less, and the amount of generated sludge will be small. Based on this finding, the present invention has been completed.
That is, the present invention
(1) introducing water to be treated containing permanganate into a reduction treatment apparatus equipped with a pH meter for measuring the pH of the water to be treated and a redox potentiometer for measuring the oxidation-reduction potential of the water to be treated ; by adding a ferrous salt to the water to be treated, manganese (II) without generating compound, a method of reduction treatment of manganese (IV) compound or manganese (III) compound slightly soluble, in the reduction treatment apparatus Ferrous salt is added to the water to be treated while maintaining the pH of the water to be treated in the range of 4 to 10 with a pH adjuster , and the redox potential of the water to be treated is measured with a redox potentiometer , When the oxidation-reduction potential of the water to be treated reaches a value at the inflection point of the curve indicating the relationship between the addition amount of ferrous salt and the oxidation-reduction potential, the addition of ferrous salt is stopped and then treated Reduction treatment of permanganate-containing water characterized by solid-liquid separation of water Method,
(2) introducing water to be treated containing permanganate into a reduction treatment apparatus equipped with a pH meter for measuring the pH of the water to be treated and a redox potential meter for measuring the oxidation-reduction potential of the water to be treated ; In a continuous treatment method in which ferrous salt is added to water to be treated to produce a manganese (II) compound and reduced to a sparingly soluble manganese (IV) compound or manganese (III) compound, a reaction tank The permanganate-containing water was continuously fed to the reactor , and the pH of the permanganate-containing water was maintained in the range of 4 to 10 with a pH adjuster while adding ferrous salt to the reaction vessel . Using the inflection point of the curve showing the relationship between the amount of ferrous salt added and the oxidation-reduction potential as a guide, ferrous iron when the oxidation-reduction potential of the water to be treated reaches a set value lower than the potential at the inflection point. Stop adding salt and the redox potential of the water to be treated is above the potential at the inflection point. The ferrous salt-containing water is characterized by restarting the addition of ferrous salt when reaching the set value of the other, and continuously sending the reduced water from the reaction tank to the subsequent solid-liquid separation step Reduction treatment method,
(3) pH meter and the processing for measuring the pH of the water to be treated in the oxidation-reduction potentiometer and ferrous salt supply unit and the reduction treatment apparatus for measuring the oxidation-reduction potential of the water to be treated containing permanganate A water pH adjuster supply device is provided, and a ferrous salt is added to the water to be treated to form a hardly soluble manganese (IV) compound or manganese (III) compound without producing a manganese (II) compound. A reduction treatment device for reduction treatment, maintaining the pH of the water to be treated in the reduction treatment device in the range of 4 to 10, while continuing to supply ferrous salt to the water to be treated, When the oxidation-reduction potential reaches the inflection point of the curve indicating the relationship between the addition amount of the ferrous salt and the oxidation-reduction potential, there is means for stopping the addition of the ferrous salt, and the reduction in the reduction treatment apparatus A means for sending the treated water afterwards to the coagulation tank, and the treated water discharged from the coagulation tank is separated into solid and liquid. A reduction treatment apparatus for permanganate-containing water, characterized by comprising:
(4) Redox potential meter and ferrous salt feeder for measuring redox potential of water to be treated containing permanganate, pH meter for measuring pH of water to be treated, and pH adjuster for water to be treated A continuous system comprising a supply device, wherein ferrous salt is added to the water to be treated, and reduced to a sparingly soluble manganese (IV) compound or manganese (III) compound without producing a manganese (II) compound An inflection point of a curve indicating the relationship between the amount of ferrous salt added and the oxidation-reduction potential while maintaining the pH of the water to be treated in the reduction treatment device in the range of 4 to 10 as the addition of the ferrous salt when redox potential reaches the set value of the redox potential of lower than the inflection point stops, redox potential of the redox potential of above said inflection point setting value Has means to resume the addition of ferrous salt when it reaches A reduction treatment apparatus for permanganate-containing water, characterized by having means for sending the treated water after reduction to the coagulation tank, means for solid-liquid separation of the treated water discharged from the coagulation tank,
Is to provide.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
In the method for reducing permanganate-containing water according to the present invention, ferrous salt is added in the method of adding ferrous salt to the water to be treated containing permanganate and performing the reduction treatment. Ferrous salt is added until the redox potential of the water to be treated reaches a predetermined value. The reduction treatment apparatus for permanganate-containing water of the present invention is a reduction treatment apparatus provided with an oxidation-reduction potentiometer and a ferrous salt supply device, and the ferrous salt based on the measured value of the oxidation-reduction potentiometer Is a device for controlling the supply of.
When ferrous salt is added to permanganate-containing water for reduction treatment, permanganate ions react as follows and are reduced to Mn (IV), Mn (III), or Mn (II). .
Reduction to Mn (IV):
_{^{^{MnO 4 - + 3Fe 2+ + 2H}}} 2 O → MnO 2 + 3Fe 3+ + 4OH - ... [1]
Reduction to Mn (III):
_{^{^{MnO 4 - + 4Fe 2+ + 4H}}} 2 O → Mn (OH) 3 + 4Fe 3+ + 5OH - ... [2]
Reduction to Mn (II):
_{^{^{MnO 4 - + 5Fe 2+ + 4H}}} 2 O → Mn (OH) 2 + 5Fe 3+ + 6OH - ... [3]
When permanganate-containing water containing 60 mg / L of permanganate as manganese is reduced using ferrous salt, the required theoretical equivalent of ferrous ion is calculated according to the above chemical reaction formula. In the case of reduction to Mn (IV), 183 mg / L, in the case of reduction to Mn (III), 244 mg / L, and in the case of reduction to Mn (II), 305 mg / L.
[0006]
As for the solubility of manganese compounds in water, KMnO ₄ which is a Mn (VII) compound dissolves 5.96 g in 100 g of water at 20 ° C., and MnO ₂ which is a Mn (IV) compound hardly dissolves in water. Further, Mn (OH) ₃ which is a Mn (III) compound has a manganese concentration of 1 mg / L or less at a pH of 3 or more from a solubility product of 10 ⁻³⁶ , and Mn (OH) ₂ which is a Mn (II) compound is a solubility product. From 10 ^−12.8 , the manganese concentration is 1 mg / L or less at pH 10 or more. Therefore, when the reduction treatment of permanganate is performed in the neutral region, if the reduction is not limited to Mn (IV) or Mn (III) and Mn (II) is not generated, the manganese concentration can be reduced by solid-liquid separation. Low and good quality treated water can be obtained.
Fig. 1 shows the amount of ferrous ion added when permanganate-containing water is reduced with ferrous salt, dissolved oxygen, redox potential, and filtrate obtained by filtering the treated water. It is an example of the graph which shows the relationship between manganese concentration and iron concentration. In this example, water to be treated containing 60 mg / L of potassium permanganate as a manganese concentration is kept at pH 7, and reduced by adding ferrous sulfate. As can be seen from this figure, when the pH is maintained at 7, the inflection point of the curve indicating the relationship between the added amount of ferrous ions and dissolved oxygen is the reduction of Mn (IV) obtained by equation [1]. The inflection point of the curve indicating the relationship between the addition amount of ferrous ions and the oxidation-reduction potential is deviated from the theoretical equivalent of the case, but the reduction to Mn (IV) obtained by the equation [1] It appears at the amount of addition that almost matches the theoretical equivalent of the case. Therefore, Mn (II) is generated by adding ferrous salt to permanganate-containing water while measuring the redox potential and stopping the addition of ferrous salt when the inflection point is reached. Without making it possible, permanganate ions can be reduced to Mn (IV) or Mn (III).
[0007]
In the method of the present invention, there is no particular limitation on the reduction treatment method by adding ferrous salt, and for example, the treatment can be carried out by either a batch system or a continuous system. In the case of batch-type treatment, ferrous salt-containing water is introduced into the reaction vessel, and preferably ferrous salt is added until the redox potential reaches a predetermined value while adjusting the pH. be able to. In the case of continuous treatment, perovate-containing water is continuously fed into the reaction vessel, preferably while adjusting the pH, and the curve inflection showing the relationship between the ferrous salt addition amount and the oxidation-reduction potential. Using the point as a guide, the addition of ferrous salt is stopped when the redox potential reaches the lower set value, and the addition of ferrous salt is resumed when the redox potential reaches the upper set value. Water reduced from the tank can be continuously sent to the subsequent solid-liquid separation step. Alternatively, a predetermined basic amount of ferrous salt can be constantly added, and the stop and supply of the additional amount can be controlled by the oxidation-reduction potential value.
In the method of the present invention, it is preferable to add the ferrous salt while maintaining the pH of the water to be treated in the range of 4 to 10. If the pH of the water to be treated is less than 4, the inflection point of the curve indicating the relationship between the addition amount of ferrous salt and the oxidation-reduction potential shifts to the excess side of the theoretical equivalent, and the inflection point is taken as a guide. When controlled, an excessive amount of ferrous salt is supplied, and a part of the Mn (II) compound is produced, and if the pH is less than 4, the solubility of the Mn (II) compound in water is large. Manganese may leak out. Even if the pH of the water to be treated exceeds 10, the object of the present invention can be achieved in which the addition of ferrous salt is controlled using the inflection point as a guide to reduce manganese to a sparingly soluble Mn (III) compound. However, neutralization using a neutralizing agent is required to discharge the treated water. By maintaining the pH of the water to be treated in the range of 4 to 10, the theoretical equivalent of ferrous salt and the inflection point coincide with each other, and the minimum required amount of ferrous salt can be added. Without producing manganese, manganese can be reduced to poorly soluble Mn (IV) or Mn (III), and the treated water can be discharged as it is or just by fine adjustment of pH.
[0008]
There is no restriction | limiting in particular in the ferrous salt used for this invention method, For example, ferrous chloride, ferrous bromide, ferrous sulfate, ferrous nitrate, ferrous thiocyanate etc. can be mentioned. Among these, ferrous sulfate is stable and easy to handle, and can be suitably used because it does not cause secondary environmental pollution. Although there is no restriction | limiting in particular in the addition method of a ferrous salt, It is preferable to add as aqueous solution from the surface of workability | operativity.
In the water to be treated in which ferrous salt is added and manganese is reduced by the method of the present invention, the Mn (IV) or Mn (III) compound insolubilized in water exists in a suspended state. It is preferable to remove suspended substances by liquid separation. There is no particular limitation on the coagulation treatment method, and the coagulation treatment can be performed using an inorganic coagulant and / or a polymer coagulant. For example, an inorganic coagulant is added, and the pH is adjusted to 6 to 8 as necessary. Thereafter, a polymer flocculant can be added. When the amount of manganese contained is small, an inorganic flocculant is added to neutralize the surface charge of suspended particles composed of Mn (IV) or Mn (III) compounds, forming micro flocs, By adding a molecular flocculant, fine flocs can be aggregated into coarse flocs.
Aggregated flocs of Mn (IV) or Mn (III) compound formed by the aggregation treatment can be removed by solid-liquid separation. There is no restriction | limiting in particular in a solid-liquid separation method, For example, precipitation process, filtration, membrane separation etc. can be mentioned. There is no restriction | limiting in particular in the precipitation processing method, For example, both the natural precipitation process using a precipitation tank etc. and the forced precipitation process using a centrifuge etc. can be performed. There is no particular limitation on the filtration method, for example, gravity type, pressure type, siphon type, upward flow type, filter medium circulation type, continuous filtration type, etc., anthracite, sand, silica sand, gravel, activated carbon, It can be filtered using a filter medium such as plastic. The membrane separation method is not particularly limited, and for example, membrane separation can be performed using a microfiltration membrane, an ultrafiltration membrane, or the like.
[0009]
FIG. 2 is a process flow diagram of one embodiment of the method of the present invention. In this embodiment, permanganate-containing water is introduced into a reduction treatment device 3 including a pH meter 1 and a redox potential meter 2. Based on the measured value of the pH meter, a signal is sent from the pH controller 4 to the pump 5, and the pH adjusting agent is supplied from the pH adjusting agent tank 6 so that a predetermined pH value is maintained in the tank. Further, based on the measured value of the redox potentiometer, a signal is sent from the redox potential controller 7 to the pump 8 so that a predetermined redox potential range is maintained in the tank. A ferrous salt aqueous solution is supplied from 9. Water to be treated in which manganese is reduced to slightly soluble Mn (IV) or Mn (III) compound is sent to the first flocculation tank 10 and added with an inorganic flocculant to flocculate, and further to the second flocculation tank. 11 and the polymer flocculant is added to coarsen the floc flocs. The treated water in which the coarse flocs are formed is then sent to the solid-liquid separation tank 12, where the precipitated manganese compound is extracted from the tank bottom as sludge, and the supernatant water is discharged as harmless treated water.
According to the method and apparatus of the present invention, when the ferrous salt is added to the treated water containing permanganate for reduction treatment, the oxidation-reduction potential of the treated water is measured, and the oxidation-reduction potential is a predetermined value. By controlling the addition of ferrous salt until the value is reached, the reduction stage is limited to the hardly soluble Mn (IV) or Mn (III) compound, and a good quality water with low manganese concentration is obtained. be able to.
[0010]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
Example 1
Potassium permanganate (special reagent grade) was dissolved in tap water to prepare an aqueous solution having a manganese concentration of 60 mg / L. While taking this potassium permanganate aqueous solution in a 1 L beaker and maintaining pH 7, ferrous sulfate aqueous solution with ferrous ion concentration of 20 g / L is added to reduce permanganate ions and measure dissolved oxygen and redox potential. did. In addition, when the ferrous ion addition amount is 100, 170, 200, 240, 280 and 300 mg / L, the liquid is sampled and filtered using 5 kinds of A filter paper for chemical analysis, and its hue is observed, The manganese concentration and iron concentration in the filtrate were measured by atomic absorption method. The results are shown in Table 1 and FIG.
[0011]
[Table 1]

[0012]
As seen in Table 1 and FIG. 1, the curve showing the relationship between the ferrous ion addition amount and dissolved oxygen has an inflection point in the vicinity of the ferrous ion addition amount of 280 mg / L. The curve showing the relationship between the addition amount and the oxidation-reduction potential has an inflection point near the ferrous ion addition amount of 200 mg / L.
The ferrous ion required to reduce Mn (VII) 60 mg / L to Mn (IV) is 183 mg / L, the ferrous ion required to reduce Mn (III) is 244 mg / L, Mn ( II) The ferrous ion necessary for reduction is 305 mg / L.
When the ferrous ion addition amount is 200 mg / L, the manganese concentration in the filtrate is 0.2 mg / L, and the hue of the filtrate is also colorless, so that the reduction reaction of Mn (VII) is completed. I understand. At this time, the curve indicating the relationship between the addition amount of ferrous ions and the oxidation-reduction potential indicates an inflection point, and therefore the addition of ferrous ions can be controlled using the inflection point of the curve as a guide. .
On the other hand, the curve indicating the relationship between the addition amount of ferrous ions and dissolved oxygen has an inflection point in the vicinity of the addition amount of ferrous ions of 280 mg / L. When added, Mn (VII) will be added in excess of the amount necessary for reducing Mn (VII) to Mn (III). However, when the ferrous ion addition amount is 280 mg / L, the manganese concentration in the filtrate is 0.5 mg / L, which tends to increase slightly, and tends to increase as it is. This is because the reaction between ferrous ions and Mn (VII), that is, the reaction of Mn (VII) → Mn (IV) → Mn (III) is the reaction with dissolved oxygen, that is, Fe ²⁺ → Fe ³⁺ Although it occurs in preference to the reaction, the reaction of Mn (III) → Mn (II) is also accompanied by a reaction with dissolved oxygen, and it is estimated that most of the reduced state of manganese is still Mn (III). The
[0013]
【Effect of the invention】
According to the method of the present invention, since the minimum ferrous salt necessary for reducing Mn (VII) in permanganate-containing water to Mn (III) can be added, it is economical. In addition, the permanganate-containing water can be neutralized and reduced, and the concentration of manganese and iron in the treated water is sufficiently low, so that the treated water can be discharged as it is after the precipitation treatment. it can.
[Brief description of the drawings]
FIG. 1 shows the amount of ferrous ion added when permanganate-containing water is reduced with ferrous salt, dissolved oxygen, redox potential, manganese concentration in treated water and iron. It is an example of the graph which shows the relationship with a density | concentration.
FIG. 2 is a process flow diagram of one embodiment of the method of the present invention.
[Explanation of symbols]
1 pH meter 2 Redox potential meter 3 Reduction treatment device 4 pH controller 5 Pump 6 pH adjuster tank 7 Redox potential controller 8 Pump 9 Ferrous salt aqueous solution tank 10 First coagulation tank 11 Second coagulation tank 12 Solid-liquid separation tank

Claims

The treated water containing permanganate is introduced into a reduction treatment apparatus equipped with a pH meter for measuring the pH of the treated water and a redox potential meter for measuring the oxidation-reduction potential of the treated water, and the treated water In the method of reducing to a sparingly soluble manganese (IV) compound or manganese (III) compound without adding ferrous salt to producing a manganese (II) compound, water to be treated in the reduction treatment apparatus The ferrous salt was added to the water to be treated while maintaining the pH of the water to be treated in the range of 4 to 10, and the redox potential of the water to be treated was measured with a redox potentiometer. When the oxidation-reduction potential of the iron reached the value at the inflection point of the curve indicating the relationship between the addition amount of ferrous salt and the oxidation-reduction potential, the addition of ferrous salt was stopped, and then the water to be treated was solidified. A method for reducing permanganate-containing water, which comprises liquid separation.

The treated water containing permanganate is introduced into a reduction treatment apparatus equipped with a pH meter for measuring the pH of the treated water and a redox potential meter for measuring the oxidation-reduction potential of the treated water, and the treated water In a continuous treatment method in which ferrous salt is added to reduce the insoluble manganese (IV) compound or manganese (III) compound without producing a manganese (II) compound, The permanganate-containing water was fed into the reactor, and the ferrous salt was added to the reaction vessel while maintaining the pH of the permanganate-containing water in the range of 4 to 10 with a pH adjuster. The ferrous salt is added when the redox potential of the water to be treated reaches a set value lower than the potential at the inflection point, using the inflection point of the curve indicating the relationship between the addition amount of the redox potential and the redox potential as a guide. The redox potential of the water to be treated is set higher than the potential at the inflection point. The method of reducing permanganate-containing water, wherein the addition of ferrous salt is resumed when a fixed value is reached, and the reduced water from the reaction tank is continuously sent to the subsequent solid-liquid separation step .

A redox potentiometer for measuring the redox potential of water to be treated containing permanganate, a ferrous salt supply device, a pH meter for measuring the pH of the water to be treated in the reduction treatment device, and the pH of the water to be treated A regulator supply device is provided, and ferrous salt is added to the water to be treated, and reduced to a hardly soluble manganese (IV) compound or manganese (III) compound without producing a manganese (II) compound. It is a reduction treatment device, and the supply of ferrous salt to the treatment water is continued while maintaining the pH of the treatment water in the reduction treatment device in the range of 4 to 10, and the oxidation-reduction potential of the treatment water Has a means for stopping the addition of ferrous salt when it reaches the inflection point of the curve indicating the relationship between the addition amount of ferrous salt and the oxidation-reduction potential, Means for sending treated water to the coagulation tank, means for solid-liquid separation of water to be treated discharged from the coagulation tank A reduction treatment apparatus for permanganate-containing water, comprising:

An oxidation-reduction potentiometer and ferrous salt supply device for measuring the oxidation-reduction potential of water to be treated containing permanganate, a pH meter for measuring the pH of water to be treated, and a pH adjuster supply device for water to be treated A continuous reduction treatment apparatus for reducing to a sparingly soluble manganese (IV) compound or manganese (III) compound without adding a ferrous salt to the treated water and generating a manganese (II) compound In addition, while maintaining the pH of the water to be treated in the reduction treatment apparatus in the range of 4 to 10, oxidation is performed using the inflection point of the curve indicating the relationship between the addition amount of ferrous salt and the oxidation-reduction potential as a guide. When the reduction potential reaches the set value of the redox potential below the inflection point, the addition of ferrous salt is stopped, and the redox potential reaches the set value of the redox potential above the inflection point . When there is a means to resume the addition of ferrous salt, An apparatus for reducing permanganate-containing water, comprising: means for sending the water to be treated later to the coagulation tank; and means for solid-liquid separation of the water to be treated discharged from the coagulation tank.