JP4639029B2 - Soil contaminated with toxic substances such as heavy metals, iron composite particle powder for purification treatment of soil and groundwater, its manufacturing method, purification agent containing the iron composite particle powder, its manufacturing method and soil contaminated with toxic substances such as heavy metals Groundwater purification method - Google Patents
Soil contaminated with toxic substances such as heavy metals, iron composite particle powder for purification treatment of soil and groundwater, its manufacturing method, purification agent containing the iron composite particle powder, its manufacturing method and soil contaminated with toxic substances such as heavy metals Groundwater purification method Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、土壌又は地下水中のカドミウム、鉛、六価クロム、砒素、セレン、シアン等の重金属等からなる有害物質を効率よく、かつ、持続的に、不溶化できる浄化処理用鉄複合粒子粉末及び該粉末を有効成分とする浄化剤を提供するものである。
【０００２】
【従来の技術】
近年、環境意識の向上から、土壌・地下水の汚染が注目されている。特に、カドミウム、鉛、六価クロム、砒素、セレン、シアン等の重金属等からなる有害物質による汚染は人体又は生態系に対して有害であるため、前記有害物質の浄化・除去処理が急務とされている。
【０００３】
周知のとおり、重金属等の有害物質で汚染された土壌又は地下水の対策技術は「浄化技術」と「封じ込め」に分類され、浄化技術は「原位置浄化」と対象地から汚染土壌を掘削する「掘削除去」とに分類される。「原位置浄化」は更に、汚染土壌・地下水に含まれる重金属等を地下（原位置）で分解する「原位置分解」と汚染土壌・地下水を抽出または掘削した中の重金属等を取り除く「原位置抽出」に分けられる。
【０００４】
「原位置抽出」は、重金属等に分類される対象物質のうち、シアン、農薬などの化合物を熱化学的に分解する「分解」と物理的な分離によって濃縮された重金属等を土壌・地下水から分離する「分離」とがある。
【０００５】
一方、「封じ込め」は「原位置封じ込め」と「掘削除去後封じ込め」に分類される。原位置封じ込めは、汚染土壌に固化剤を混合して固型化し、その後現場の土壌を移動させずに原位置で汚染土壌を封じ込める技術である。また、掘削除去後封じ込めは、前処理として汚染土壌に不溶化剤を混合し、難溶化させ、その後一度掘削してから、改めて汚染土壌を封じ込める技術である。
【０００６】
「浄化技術」に係る施工法としては、土壌洗浄法、熱脱着法などが挙げられ、例えば、薬品を添加し、重金属等を溶解して分離する化学溶解法、水で土壌を洗浄・分級し、重金属等を多く含んだ微粒子を分離する水洗浄法、土壌粒子の表面に付着した汚染物質を洗浄剤で洗浄し、更に粒子の大きさと比重によって清浄な大粒子と汚染物の微粒子に分級する土壌湿式洗浄法などが挙げられる。
【０００７】
また、「封じ込め」に係る施工法は、「原位置封じ込め」では汚染土壌にセメント等の固化剤を混合して不透水層と鋼矢板等によって封じ込める方法があり、「掘削除去後封じ込め」では、汚染土壌に対して薬剤によって不溶化処理して汚染土壌を溶出しにくい形態に変化させた後に遮断工、遮水工で封じ込める方法がある。
【０００８】
しかしながら、前記各処理技術は、処理コストが高く、長期間を要するものであり、重金属等の有害物質を効率よく、かつ、持続的に、低減する技術とは言い難いものである。
【０００９】
最近では、主に鉄粉の還元作用を利用し重金属の価数を低減し無害化、安定化する低コストの処理技術が開発されている。例えば、鉄粉の還元作用（金属の価数低減）を利用した技術（特許文献１）、砒素に対して鉄粉の還元作用や吸着作用を利用した技術（特許文献２）、熱処理と鉄粉の還元作用（金属の価数低減）を併用した技術（特許文献３）、六価クロムに対して鉄粉の還元作用（金属の価数低減）を利用した技術（特許文献４）、鉄粉の還元作用（金属の価数低減）を利用した技術（特許文献５）等が挙げられる。
【００１０】
また、重金属含有廃水における処理技術として、鉄塩の添加によるフェライト化処理法と鉄粉の還元作用に基づく安定化法が提案されている。
【００１１】
鉄塩の添加によるフェライト化処理法は、Ｆｅ２＋、Ｆｅ３＋をアルカリで中和し、空気通気あるいは酸化剤で酸化し、加熱（〜常温）によりスピネルフェライト化させ重金属を結晶内部に取り込むか、吸着させる方法である。また、一部、α、γ、δ−ＦｅＯＯＨなどの水酸化鉄として結晶内部に取り込むか、吸着することも知られている（非特許文献１、特許文献６乃至８）。
【００１２】
鉄粉の還元作用に基づく安定化法は、重金属の価数低減による無害化、安定化する方法である。なお、一部、酸性領域で鉄粉が少量溶解しゲーサイトもしくはスピネルフェライト化し結晶内部に取り込むか、吸着することも知られている。
【００１３】
例えば、特許文献９には、重金属イオンを含む溶液をｐＨ５〜６程度に調整し、鉄粉を加えて攪拌すると、鉄粉の一部が溶解して、水酸化第２鉄が沈殿し、ｐＨの上昇とともにゲーサイト、レピッドクロサイトが生成し、この際重金属の一部は共沈して大部分は鉄粉へ吸着することが記載されており、また、低いｐＨでは鉄粉の溶出が増大し、吸着除去効果は劣化することが記載されている。
【００１４】
特許文献１０には、重金属キレート錯体を含む溶液をｐＨ２〜６に調整し、鉄粉を加えて空気を巻き込むような強力攪拌あるいは攪拌時空気を送入して反応させ、ｐＨをほぼ中性に自然に上昇させると、鉄粉表面が活性化されて、重金属が吸着されることが記載されて、また、一部ゲーサイト、レピッドクロサイト、マグネタイトが生成し取り込まれることが記載されている。
【００１５】
特許文献１１には、鉄シアン錯体を含有する溶液のｐＨを５未満に調整し、鉄粉を添加し攪拌し、これにより鉄粉の一部を溶解させながら鉄シアン錯体を鉄体に吸着させることが記載されていると共に、還元反応（金属の価数低減）、置換析出（イオン化傾向）、鉄粉への吸着反応、酸化鉄生成での取り込み、中和による水酸化物析出、共沈反応（フェライト化）などの該反応が記載されている。
【００１６】
非特許文献２には鉄粉の溶解からスピネル化合物が生成することが記載されている。
【００１７】
【特許文献１】
特開平１０−７１３８６
【特許文献２】
特開平１０−２４４２４８
【特許文献３】
特開２０００−１５７９６１
【特許文献４】
特開２００１−１９８５６７
【特許文献５】
特開２００２−２００４７８
【特許文献６】
特開昭５０−３６３７０
【特許文献７】
特開昭５０−１３３６５４
【特許文献８】
特開昭５０−１５４１６４
【特許文献９】
特公昭５２−４５６６５
【特許文献１０】
特公昭５４−１１６１４
【特許文献１１】
特開昭５７−７７９５
【非特許文献１】
ＮＥＣ技報Ｖｏｌ．３７，Ｎｏ．９／１９８４の「フェライト法による重金属廃水の処理」
【非特許文献２】
Ｂｕｌｌ．Ｉｎｓｔ．Ｃｈｅｍ．Ｒｅｓ．Ｋｙｏｔｏ Ｕｎｉｖ．Ｖｏｌ７１，Ｎｏ．２．１９９３「Ａｉｒ Ｏｘｉｄａｔｉｏｎ ｏｆ Ｉｒｏｎ Ｐｏｗｄｅｒ Ｄｉｓｐｅｒｓｅｄ ｉｎ Ａｑｕｅｏｕｓ Ｓｏｌｕｔｉｏｎ ｏｆ Ｓｏｄｉｕｍ Ｈｙｄｒｏｘｉｄｅ」
【００１８】
【発明が解決しようとする課題】
【００１９】
前出特許文献１乃至５記載の各技術は、鉄粉の還元作用（価数低減）を利用した無害化、安定化処理方法であり、年数が経つと鉄粉の還元作用の持続性に問題を生じ、重金属が無害で安定な価数になっていても再度価数が上がり有害な金属に変わる可能性がり、恒久的な対策とは言い難いものである。
【００２０】
前出特許文献６乃至１１記載の何れの技術においても、鉄粉の作用は還元もしくは吸着が主である。一部溶解による作用もあるが、全て酸性領域での鉄粉の溶出を経由して、ゲーサイト、レピッドクロサイト、マグネタイトが生成し取り込まれるメカニズムであり、鉄粉を利用した処理技術においてＦｅ２＋もしくはＦｅ３＋の溶解により重金属を取り込みながらスピネルフェライト化する現象を積極的に利用した技術ではない。
【００２１】
前出非特許文献２記載の技術は、アルカリを添加することによるｐＨ調整、加熱及び強制酸化が必須となっている。
【００２２】
そこで、本発明は、「封じ込め」に関連するものであり、鉄粉を用いてカドミウム、鉛、六価クロム、砒素、セレン及びシアン等の重金属等の有害物質を効率よく、且つ持続的に不溶化させることを技術的課題とする。
【００２３】
【課題を解決するための手段】
前記技術的課題は次のとおりの本発明により達成できる。
【００２４】
即ち、本発明は、α−Ｆｅとマグネタイトとからなる鉄複合粒子粉末であって、該鉄複合粒子粉末の平均粒子径が０．０５〜０．５０μｍであり、かつ、α−Ｆｅ含有量が３０〜９９重量％であり、Ｓ含有量が３５００〜１００００ｐｐｍであることを特徴とする重金属等の有害物質で汚染された土壌・地下水浄化処理用鉄複合粒子粉末である（本発明１）。
【００２５】
また、本発明は、α−Ｆｅとマグネタイトとからなる平均粒子径が０．０５〜０．５０μｍの鉄複合粒子粉末であって、Ｓ含有量が３５００〜１００００ｐｐｍであり、該鉄複合粒子粉末のＸ線回折スペクトルにおいてα−Ｆｅの（１１０）面の回折強度Ｄ１１０とマグネタイトの（３１１）面の回折強度Ｄ３１１との強度比（Ｄ１１０／（Ｄ１１０＋Ｄ３１１））が０．２０〜０．９８であることを特徴とする重金属等の有害物質で汚染された土壌・地下水浄化処理用鉄複合粒子粉末である（本発明２）。
【００２６】
また、本発明は、飽和磁化値が９０〜１９０Ａｍ２／ｋｇであり、ＢＥＴ比表面積が５．０〜６０．０ｍ２／ｇであり、α−Ｆｅの（１１０）面の結晶子サイズが２００〜４００Åである本発明１又は本発明２の重金属等の有害物質で汚染された土壌・地下水浄化処理用鉄複合粒子粉末である（本発明３）。
【００２７】
また、本発明は、粒子形状が米粒状であって軸比が１．０を越え２．０以下である本発明１乃至３の重金属等の有害物質で汚染された土壌・地下水浄化処理用鉄複合粒子粉末である（本発明４）。
【００２８】
また、本発明は、本発明１乃至本発明４のいずれかの重金属等の有害物質で汚染された土壌・地下水の浄化処理用鉄複合粒子粉末を有効成分として含有する水懸濁液からなることを特徴とする重金属等の有害物質で汚染された土壌・地下水の浄化剤である（本発明５）。
【００２９】
また、本発明は、平均長軸径が０．０５〜０．５０μｍのゲータイト粒子粉末又は該ゲータイト粒子粉末を２５０〜３５０℃の温度範囲で加熱脱水した平均長軸径が０．０５〜０．５０μｍのヘマタイト粒子粉末を３００〜６００℃の温度範囲で加熱還元して鉄粒子粉末とし、冷却後、該鉄粒子粉末を気相中で表面酸化被膜を形成することなく水中に取り出し、次いで、水中で当該鉄粒子粉末の粒子表面に酸化被膜を形成した後に乾燥することを特徴とする本発明１乃至本発明４の重金属等の有害物質で汚染された土壌・地下水の浄化処理用鉄複合粒子粉末の製造法である（本発明６）。
【００３０】
また、本発明は、平均長軸径が０．０５〜０．５０μｍのゲータイト粒子粉末又は該ゲータイト粒子粉末を２５０〜３５０℃の温度範囲で加熱脱水した平均長軸径が０．０５〜０．５０μｍのヘマタイト粒子粉末を３００〜６００℃の温度範囲で加熱還元して鉄粒子粉末とし、冷却後、該鉄粒子粉末を気相中で表面酸化被膜を形成することなく水中に取り出し、次いで、水中で当該鉄粒子粉末の粒子表面に酸化被膜を形成して鉄複合粒子粉末を含有する水懸濁液を得ることを特徴とする本発明５の重金属等の有害物質で汚染された土壌・地下水の浄化剤の製造法である（本発明７）。
【００３１】
また、本発明は、本発明１乃至本発明４のいずれかに記載の重金属等の有害物質で汚染された土壌・地下水浄化処理用鉄複合粒子粉末と重金属等の有害物質で汚染された土壌又は重金属等の有害物質で汚染された地下水とを混合接触させることを特徴とする重金属等の有害物質で汚染された土壌・地下水の浄化処理方法である（本発明８）。
【００３２】
また、本発明は、本発明５の重金属等の有害物質で汚染された土壌・地下水の浄化剤と重金属等の有害物質で汚染された土壌又は重金属等の有害物質で汚染された地下水とを混合接触させることを特徴とする重金属等の有害物質で汚染された土壌・地下水の浄化処理方法である（本発明９）。
【００３３】
また、本発明は、重金属等の有害物質がカドミウム、鉛、六価クロム、砒素、セレン、シアンであることを特徴とする本発明８又は本発明９の重金属等の有害物質で汚染された土壌・地下水の浄化処理方法である（本発明１０）。
【００３４】
本発明の構成を詳しく説明すれば、次の通りである。
【００３５】
先ず、本発明１乃至４に係る重金属等の有害物質で汚染された土壌・地下水の浄化処理用鉄複合粒子粉末（以下、「浄化処理用鉄複合粒子粉末」という）について述べる。
【００３６】
本発明に係る浄化処理用鉄複合粒子粉末の平均粒子径は０．０５〜０．５０μｍである。平均粒子径が０．０５μｍ未満の場合にはα−Ｆｅ相が不安定であるため表面に厚い酸化被膜が形成されα−Ｆｅ含有量を高くすることが困難となりα−Ｆｅ量が少なくなるため、浄化処理においてα−Ｆｅの溶解反応が不十分となり、本発明の目的とする効果を得ることが困難となる。０．５０μｍを越える場合にはα−Ｆｅ含有量は高くできるが、ＢＥＴ比表面積が小さくなり、本発明の目的とする効果を得ることが困難となる。より好ましくは０．０５〜０．３０μｍである。
【００３７】
本発明に係る浄化処理用鉄複合粒子粉末は、α−Ｆｅ相を３０〜９９重量％含有する。α−Ｆｅ相が３０重量％未満の場合には、α−Ｆｅ量が少ないために浄化処理においてα−Ｆｅの溶解反応が不十分となり、重金属等とのフェライト化反応が不十分となり、本発明の目的とする効果が得られない。α−Ｆｅ相が９９重量％を越える場合には、粒子サイズが極端に大きいか又はＢＥＴ比表面積が極端に小さく空気中で安定な状態であり、後出比較例に示すように、浄化処理においてα−Ｆｅの溶解反応が不十分となり重金属等とのフェライト化反応が十分に進行しないため、本発明の目的とする効果が得られない。好ましくは４０〜９９重量％である。
【００３８】
浄化処理用鉄複合粒子粉末の構成相はα−Ｆｅ相とともに、マグネタイト相を含有する。マグネタイトを含有することによってフェライト化反応を容易に進行させることができる。マグネタイトの含有割合は、鉄複合粒子粉末のＸ線回折スペクトルにおいてα−Ｆｅの（１１０）面の回折強度Ｄ１１０とマグネタイトの（３１１）面の回折強度Ｄ３１１との強度比（Ｄ１１０／（Ｄ１１０＋Ｄ３１１））が０．２０〜０．９８であることが好ましく、より好ましくは０．３０〜０．９８である。また、マグネタイトは浄化処理用鉄複合粒子粉末の粒子表面に存在することが好ましく、マグネタイトが粒子表面に存在することによって、鉄複合粒子をシードとしてフェライト化反応がエピタキシャルに進行することができる。
【００３９】
本発明に係る浄化処理用鉄複合粒子粉末の粒子形状は米粒状が好ましく、軸比は１．０を越え２．０以下が好ましい。軸比が１．０の場合、球状粒子であり粒子サイズが同じであればＢＥＴ比表面積が小さくなり、浄化処理においてα−Ｆｅの溶解反応が不十分となり好ましくない。２．０を越える場合、ＢＥＴ比表面積が大きくなりα−Ｆｅ相が不安定になり表面に厚い酸化被膜が形成されやすく、α−Ｆｅ含有量を高くすることが困難となりα−Ｆｅ量が少なくなるため、浄化処理においてα−Ｆｅの溶解反応が不十分となり、本発明の目的とする効果が得られ難い。より好ましくは１．２〜１．８である。
【００４０】
本発明に係る浄化処理用鉄複合粒子粉末の結晶子サイズ（α−Ｆｅの（１１０）面）は２００〜４００Åが好ましい。２００Å未満の場合にはＢＥＴ比表面積は大きいがα−Ｆｅ相が不安定であるため表面に厚い酸化被膜が形成されα−Ｆｅ含有量を高くすることが困難となりα−Ｆｅ量が少なくなるため、浄化処理においてα−Ｆｅの溶解反応が不十分となり、本発明の目的とする効果を得ることが困難となる。４００Åを越える場合には、α−Ｆｅ含有量は高くできるが、ＢＥＴ比表面積が小さくなり、本発明の目的とする効果を得ることが困難となる。より好ましくは２００〜３５０Åである。
【００４１】
本発明に係る浄化処理用鉄複合粒子粉末のＢＥＴ比表面積値は５．０〜６０．０ｍ２／ｇが好ましい。５．０ｍ２／ｇ未満の場合には、接触面積が小さくなり、浄化処理においてα−Ｆｅの溶解反応が不十分となる。６０．０ｍ２／ｇを越える場合には、α−Ｆｅ相が不安定であるため表面に厚い酸化被膜が形成されα−Ｆｅ含有量を高くすることが困難となりα−Ｆｅ量が少なくなるため、浄化処理においてα−Ｆｅの溶解反応が不十分となり、本発明の目的とする効果を得ることが困難となる。より好ましくは７．０〜５５．０ｍ２／ｇである。
【００４２】
本発明に係る浄化処理用鉄複合粒子粉末の全Ｆｅ含有量は全粒子粉末に対して７５重量％以上が好ましい。７５重量％未満の場合にはα−Ｆｅ含有量が少なくなり、浄化処理においてα−Ｆｅの溶解反応が不十分となるため、本発明の目的とする効果を得ることが困難となる。より好ましくは７５〜９８重量％である。
【００４３】
本発明に係る浄化処理用鉄複合粒子粉末は、Ｐｂ、Ｃｄ、Ａｓ、Ｈｇ、Ｓｎ、Ｓｂ、Ｂａ、Ｚｎ、Ｃｒ、Ｎｂ、Ｃｏ、Ｂｉ等のＦｅ以外の金属元素は毒性のある金属であるため極力含有しない方がよく、特にＰｂ、Ｃｄ、Ａｓ、Ｈｇを実質的に含有しないことが好ましい。
【００４４】
本発明に係る浄化処理用鉄複合粒子粉末のＳ含有量は３５００〜１００００ｐｐｍが好ましい。
【００４５】
本発明に係る浄化処理用鉄複合粒子粉末の飽和磁化値は９０〜１９０Ａｍ２／ｋｇ（９０〜１９０ｅｍｕ／ｇ）が好ましい。９０Ａｍ２／ｋｇ未満の場合には、α−Ｆｅ含有量が少ないものであり、浄化処理においてα−Ｆｅの溶解反応が不十分となるため好ましくない。１９０Ａｍ２／ｋｇを越える場合にはＦｅ含有量が高いもののＢＥＴ比表面積が低くなり、浄化処理においてα−Ｆｅの溶解反応が不十分となるため好ましくない。より好ましくは９５〜１９０Ａｍ２／ｋｇ（９５〜１９０ｅｍｕ／ｇ）である。
【００４６】
なお、本発明に係る浄化処理用鉄複合粒子粉末は、造粒物の形態であってもよい。
【００４７】
次に、本発明５に係る重金属等の有害物質で汚染された土壌・地下水の浄化剤（以下、「浄化剤」という）について述べる。
【００４８】
本発明に係る浄化剤は、本発明１乃至本発明４に係る浄化処理用鉄複合粒子粉末を有効成分として含有する水懸濁液であり、浄化処理用鉄複合粒子粉末の水懸濁液中の含有量は０．５〜５０重量部の範囲内で適宜選択することができる。
【００４９】
本発明に係る浄化剤のｐＨ値は７〜１２が好ましく、より好ましくは８〜１２である。本発明において、浄化剤のｐＨ値は時間の推移に伴い８から１１程度へ上昇することが確認されており、ｐＨがアルカリ領域であることによりα−Ｆｅが少量ずつ徐々に溶解しているものと推定され、重金属等とのフェライト化反応が持続的に進行するものと推定される。
【００５０】
次に、本発明６に係る重金属等の有害物質で汚染された土壌・地下水の浄化処理用鉄複合粒子粉末の製造法について述べる。
【００５１】
ゲータイト粒子粉末は、常法に従って、例えば、第一鉄塩と、水酸化アルカリ、炭酸アルカリ又はアンモニアから選ばれる１種又は２種以上とを反応させて得られる鉄の水酸化物や炭酸鉄等の第一鉄含有沈殿物を含む懸濁液中に空気等の酸素含有ガスを通気することにより得ることができる。
【００５２】
ゲータイト粒子粉末の平均長軸径は０．０５〜０．５０μｍであり、粒子形状は紡錘状又は針状のどちらでも良い。軸比は４〜３０が好ましく、より好ましくは５〜２５であり、ＢＥＴ比表面積は２０〜２００ｍ２／ｇが好ましく、より好ましくは２５〜１８０ｍ２／ｇである。Ｓ含有量は１〜８０００ｐｐｍが好ましく、殊に、ゲータイト粒子粉末を直接加熱還元する場合には、Ｓ含有量は２２００〜８０００ｐｐｍが好ましい。
【００５３】
また、鉄複合粒子におけるα−Ｆｅ含有量を高い割合で維持すると共に形状を破壊して粒状に結晶成長させるには、ゲータイト粒子粉末に対して焼結防止処理などの表面処理を行わないことが好ましい。
【００５４】
ゲータイト粒子粉末は、常法に従って、造粒しておくことが好ましい。造粒することによって、固定層方式の還元炉を使用できるほか、鉄複合粒子とした場合でも還元条件によってはそのまま造粒物の形態を保つことが可能となり、カラム等に充填して使用する場合には好ましい。
【００５５】
得られたゲータイト粒子粉末は２５０〜３５０℃の温度範囲で加熱脱水したヘマタイト粒子粉末にすることが好ましい。
【００５６】
本発明におけるヘマタイト粒子粉末は、あらかじめＳ含有量が高いゲータイト粒子を用いるか、又は、Ｓ含有量が低いゲータイト粒子の場合には、ヘマタイト粒子粉末の水懸濁液に硫酸を添加することで、ヘマタイト粒子粉末のＳ含有量を制御することが好ましい。
【００５７】
ヘマタイト粒子粉末の平均長軸径は０．０５〜０．５０μｍであり、Ｓ含有量は２４００〜８５００ｐｐｍが好ましい。
【００５８】
前記ゲータイト粒子粉末又は前記ヘマタイト粒子粉末を３００〜６００℃の温度範囲で加熱還元することによって鉄粒子（α−Ｆｅ）粉末とする。
【００５９】
加熱還元温度が３００℃未満である場合には、還元反応の進行が遅く、還元反応に長時間を要する。また、ＢＥＴ比表面積を大きくすることができるが、結晶成長を十分に行うことができず、α−Ｆｅ相が不安定となり粒子表面に酸化被膜が厚く形成されたり、またマグネタイト相からα−Ｆｅ相への相変化が不十分のため、α−Ｆｅ含有量を高くすることが困難となり、浄化処理においてα−Ｆｅの溶解反応が不十分となる。６００℃を超える場合には、還元反応が急激に進行して粒子及び粒子相互間の焼結が過度に促進され粒子径が大きくなり、ＢＥＴ比表面積も小さくなるため好ましくない。
【００６０】
なお、還元反応の昇温時の雰囲気は水素ガス、窒素ガス等が利用できるが、工業的には水素ガスが好ましい。
【００６１】
加熱還元後の鉄粒子粉末は冷却した後、該鉄粒子粉末を気相中で表面酸化被膜を形成することなく水中に取り出し、水中で当該鉄粒子粉末の粒子表面に表面酸化被膜を形成し、次いで、乾燥する。
【００６２】
冷却時の雰囲気は窒素又は水素のいずれでもよいが、最終的には窒素に切り替えることが好ましい。また、水中に取り出す時には１００℃以下まで冷却されていることが好ましい。
【００６３】
乾燥雰囲気は、窒素、空気中、真空中等適宜選択できるが、温度は１００℃以下が好ましい。
【００６４】
なお、前記加熱還元処理において、粒子全体はα−Ｆｅ相からなる鉄粒子となり、これを水中に取り出すことによってα−Ｆｅの触媒活性により水が分解されて、水素の発生と共に生成した水酸基、酸素又は水中の溶存酸素等によりα−Ｆｅが酸化されて、粒子表面にマグネタイトからなる酸化被膜が形成されるものと推定できる。
【００６５】
次に、本発明７に係る重金属等の有害物質で汚染された土壌・地下水の浄化剤の製造法について述べる。
【００６６】
本発明７に係る重金属等の有害物質で汚染された土壌・地下水の浄化剤は、本発明６における加熱還元後の鉄粒子粉末を冷却後、水中に取り出し、そのまま鉄複合粒子粉末を含有する水懸濁液からなる浄化剤とするものである。
【００６７】
本発明の浄化剤においては鉄複合粒子粉末の二次凝集体を粉砕して分散させておくことが好ましい。
【００６８】
次に、本発明８乃至本発明１０に係る重金属等の有害物質で汚染された土壌・地下水の浄化処理方法ついて述べる。
【００６９】
本発明に係る重金属等の有害物質で汚染された土壌・地下水の浄化処理方法は、「封じ込め」による方法であり、「原位置封じ込め」又は「掘削後封じ込め」のいずれにも適用できる。
【００７０】
「原位置封じ込め」においては、浄化処理用鉄複合粒子粉末と水との混合物又は浄化剤を高圧の空気、窒素等のガスを媒体にしてそのまま浸透もしくはボーリング孔から地下に導入する方法である。浄化剤を用いる場合には、水懸濁液であるのでそのまま使用するか必要に応じて希釈すれば良い。
【００７１】
「掘削後封じ込め」においては、浄化処理用鉄複合粒子粉末と水との混合物又は浄化剤を、サンドミル、ヘンシェルミキサー、コンクリートミキサー、ナウターミキサー、一軸又は二軸式のニーダー型混合器等を用いて汚染土壌と混合攪拌して、土壌中の重金属等をフェライト化した後、封じ込める方法である。なお、必要に応じて、重金属等を取り込んだフェライトを磁気分離することもできる。
【００７２】
浄化処理用鉄複合粒子粉末あるいは浄化剤（固形分換算）の添加量は、土壌・地下水中における重金属等の有害物質の汚染の程度に応じて適宜選択することができるが、汚染土壌を対象とする場合には、通常土壌１００重量部に対して０．５〜５０重量部が好ましく、より好ましくは１〜３０重量部である。０．５重量部未満の場合には、本発明の目的とする効果が充分得られない。５０重量部を超える場合には、浄化効果は向上するが経済的ではない。また、汚染地下水を対象とする場合には、地下水１００重量部に対して０．５〜５０重量部添加することが好ましく、より好ましくは１〜３０重量部である。
【００７３】
本発明に係る浄化処理用鉄複合粒子粉末又は本発明に係る浄化剤を用いた場合には、後述する評価法において、汚染土壌中又は汚染地下水中のカドミウムを０．０１ｍｇ／ｌ以下、鉛を０．０１ｍｇ／ｌ以下、六価クロムを０．０５ｍｇ／ｌ以下、砒素を０．０１ｍｇ／ｌ以下、セレンを０．０１ｍｇ／ｌ以下、シアンを未検出にまでそれぞれ低減することができる。
【００７４】
【発明の実施の形態】
本発明の代表的な実施の形態は次の通りである。
【００７５】
ゲータイト粒子粉末の平均長軸径及び軸比は透過型電子顕微鏡写真で測定した。ヘマタイト粒子粉末及び鉄複合粒子粉末の平均粒子径は走査型電子顕微鏡写真を用いて測定した。
【００７６】
鉄複合粒子粉末の全Ｆｅ量は、「誘導結合プラズマ発光分光分析装置ＳＰＳ４０００」（セイコー電子工業（株）製）を使用して測定した。
【００７７】
各粒子粉末の結晶相は前記Ｘ線回折装置によって１０〜９０°の範囲で測定して同定した。
【００７８】
鉄複合粒子粉末のα−Ｆｅ含有量は、あらかじめ各種混合割合の鉄とマグネタイト（α−Ｆｅを水中に取り出し変態させた）とからなる混合粉末のＸ線回折を測定し、α−Ｆｅの（１１０）面の回折強度Ｄ１１０、マグネタイトの（３１１）面の回折強度Ｄ３１１と混合割合との関係式を作成して検量線として用いることによって算出した。検量線である関係式は下記の通りである。
【００７９】
α−Ｆｅ含有量＝−５１．３８７Ｘ２＋１５１．８８Ｘ
Ｘ：強度比率（Ｄ１１０／（Ｄ１１０＋Ｄ３１１））
【００８０】
各粒子粉末中に存在する鉄以外の金属元素のうち、Ｐｂ及びＣｄについては「フレーム原子吸光光度計 ＡＡ−６５００Ｓ」（島津製作所製）を、Ａｓについては「水素化合物発生原子吸光光度計 ＨＶＧ−１」（島津製作所製）を、Ｈｇについては「還元気化原子吸光光度計 ＭＶＵ−１Ａ」（島津製作所製）を用いてそれぞれ測定した。Ｓ含有量は、「カーボン・サルファーアナライザー：ＥＭＩＡ−２２００」（ＨＯＲＩＢＡ製）を使用して測定した。
【００８１】
鉄複合粒子粉末の結晶子サイズ（α−Ｆｅの（１１０）面）は、Ｘ線回折法で測定される結晶粒子の大きさを、各粒子の結晶面のそれぞれに垂直な方向における結晶粒子の厚さを表したものであり、各結晶面についての回折ピーク曲線から、下記シェラーの式を用いて計算した値で示したものである。
【００８２】
結晶子サイズ＝Ｋλ／βｃｏｓθ
但し、β＝装置に起因する機械幅を補正した真の回折ピークの半値幅（ラジアン単位）。
Ｋ＝シェラー定数（＝０．９）。
λ＝Ｘ線の波長（Ｃｕ Ｋα線 ０．１５４２ｎｍ）。
θ＝回折角（各結晶面の回折ピークに対応）。
【００８３】
各粒子粉末の比表面積は、「モノソーブＭＳ−１１」（カンタクロム（株）製）を使用し、ＢＥＴ法により測定した値で示した。
【００８４】
鉄複合粒子粉末の飽和磁化値は、「振動試料磁力計ＶＳＭ−３Ｓ−１５」（東英工業（株）製）を使用し、外部磁場７９５．８ｋＡ／ｍ（１０ｋＯｅ）で測定した。
【００８５】
浄化処理における重金属等の有害物質の測定は、汚染土壌の固形分については、環境庁告示第４６号「土壌の汚染に係る環境基準について」に基づいて、汚染地下水については、環境庁告示第１０号「地下水の水質汚濁に係る環境基準について」に基づいて分析した。
【００８６】
＜浄化処理用鉄複合粒子粉末及び浄化剤の製造＞
毎秒３．４ｃｍの割合でＮ２ガスを流すことによって非酸化性雰囲気に保持された反応容器中に、１．１６ｍｏｌ／ｌのＮａ２ＣＯ３水溶液７０４ｌを添加した後、Ｆｅ２＋１．３５ｍｏｌ／ｌを含む硫酸第一鉄水溶液２９６ｌを添加、混合（Ｎａ２ＣＯ３量は、Ｆｅに対し２．０倍当量に該当する。）し、温度４７℃においてＦｅＣＯ３を生成させた。
【００８７】
ここに得たＦｅＣＯ３を含む水溶液中に、引き続き、Ｎ２ガスを毎秒３．４ｃｍの割合で吹き込みながら、温度４７℃で７０分間保持した後、当該ＦｅＣＯ３を含む水溶液中に、温度４７℃において毎秒２．８ｃｍの空気を５．０時間通気してゲータイト粒子を生成させた。なお、空気通気中におけるｐＨは８．５〜９．５であった。
【００８８】
ここに得たゲータイト粒子を含有する懸濁液をフィルタープレスで水洗し、得られたプレスケーキを圧縮成型機を用いて孔径４ｍｍの成型板で押し出し成型して１２０℃で乾燥してゲータイト粒子粉末の造粒物とした。
【００８９】
ここに得た造粒物を構成する含有するゲータイト粒子粉末は、平均長軸径０．３０μｍ、軸比（長軸径／短軸径）１２．５の紡錘状を呈した粒子であった。ＢＥＴ比表面積は８５ｍ２／ｇ、Ｓ含有量は４００ｐｐｍであった。
【００９０】
前記造粒物を３００℃で加熱しヘマタイト粒子とし乾式粉砕する。その後水に邂逅し７０％硫酸を１０ｍｌ／ｋｇの割合で添加し攪拌する。その後、脱水しプレスケーキとし、圧縮成型機を用いて孔径３ｍｍの成型板で押し出し成型して１２０℃で乾燥してヘマタイト粒子粉末の造粒物とした。
【００９１】
ここに得た造粒物を構成するヘマタイト粒子粉末は、平均長軸径０．２４μｍ、軸比（長軸径／短軸径）１０．５の紡錘形を呈した粒子であった。Ｓ含有量は３１００ｐｐｍであった。
【００９２】
前記ゲータイト粒子粉末の造粒物１００ｇを固定層還元装置に導入し、Ｈ２ガスを通気させながら、４５０℃で１８０分間、完全にα−Ｆｅとなるまで還元した。次に、Ｎ２ガスに切替え室温まで冷却させた後、イオン交換水３００ｍｌを直接還元炉に導入し、そのまま１８重量％の鉄複合粒子粉末を含有する水懸濁液として取り出した（なお、この水懸濁液が本発明に係る浄化剤である）。
【００９３】
次いで、前記水懸濁液を濾過し、４０℃で３時間、大気中で乾燥し、浄化処理用鉄複合粒子粉末を得た。
【００９４】
得られた浄化処理用鉄複合粒子粉末は、走査型電子顕微鏡（３００００倍）で観察した結果、米粒状であり、平均粒子径が０．１０μｍであり、α−Ｆｅを主体としており、飽和磁化値１６０Ａｍ２／ｋｇ（１６０ｅｍｕ／ｇ）、ＢＥＴ比表面積２６ｍ２／ｇ、結晶子サイズ２９０Å、Ｆｅ含有量は８９．５重量％であった。Ｓ含有量は３８００ｐｐｍ、炭素量は０．０９重量％であった。Ｃｄ、Ｐｂ、Ａｓ及びＨｇはいずれも検出されなかった。Ｘ線回折の結果、α−Ｆｅとマグネタイトとが存在することが確認された。また、検量線から求めたα−Ｆｅ含有量は９５．７重量％であり、そのＤ１１０（α−Ｆｅ）とＤ３１１（マグネタイト）の強度比Ｄ１１０／（Ｄ１１０＋Ｄ３１１）は０．９１であった。
【００９５】
＜重金属等の有害物質で汚染された土壌の鉄複合粒子による浄化処理＞
バイアル瓶に、あらかじめ湿った砂質土壌２０ｇ（目開き２ｍｍ篩い下）とここに得た浄化処理用鉄複合粒子粉末１ｇと２７．０ｍｌのイオン交換水とを注入し、カドミウム、鉛、砒素、セレン及びシアンを各１０ｐｐｍとなるように１０００ｐｐｍ標準液（関東化学（株）製）より各０．３ｍｌ注入し、六価クロムを５０ｐｐｍとなるように１０００ｐｐｍ標準液（関東化学（株）製）より１．５ｍｌ注入し、全量で１００ｐｐｍになるように合計３．０ｍｌ注入した。直ぐにフッ素樹脂ライナー付きゴム栓で蓋をし、その上からアルミシールで強固に締め付けた。前記バイアル瓶をペイントコンディショナー（レッドデビル社製）で１６時間振とうした後、０．４５μｍメンブランフィルターを使用して固液分離した。
【００９６】
次いで、測定に必要な量の固形分（５０ｇ）及び濾液（３００ｍｌ）が得られるまで、同様の処理を行った。濾液はそのまま環境庁告示第１０号「地下水の水質汚濁に係る環境基準について」に基づき、固形分については４０℃で３時間、大気中で乾燥し試料を得て、環境庁告示第４６号「土壌の汚染に係る環境基準について」に基づき分析した。その結果、溶液中のカドミウム０．００１ｍｇ／ｌ未満、鉛０．００５ｍｇ／ｌ未満、六価クロム０．０４ｍｇ／ｌ未満、砒素０．００１ｍｇ／ｌ未満、セレン０．００２ｍｇ／ｌ未満、シアンは未検出であり、固体からの溶出量はカドミウム０．００１ｍｇ／ｌ未満、鉛０．００５ｍｇ／ｌ未満、六価クロム０．０４ｍｇ／ｌ未満、砒素０．００１ｍｇ／ｌ未満、セレン０．００２ｍｇ／ｌ未満、シアンは未検出であった。
【００９７】
＜重金属等の有害物質で汚染された地下水の鉄複合粒子粉末による浄化処理＞
褐色バイアル瓶５０ｍｌ（実容積６８ｍｌ）に、ここに得られた浄化処理用鉄複合粒子粉末１ｇと２７．０ｍｌのイオン交換水とを注入し、カドミウム、鉛、砒素、セレン及びシアンを各１０ｐｐｍとなるように１０００ｐｐｍ標準液(関東化学（株）製)より各０．３ｍｌ注入し、六価クロムを５０ｐｐｍとなるように１０００ｐｐｍ標準液(関東化学（株）製)より１．５ｍｌ注入し、全量で１００ｐｐｍになるように合計３．０ｍｌ注入した。直ぐにフッ素樹脂ライナー付きゴム栓で蓋をし、その上からアルミシールで強固に締め付けた。前記バイアル瓶をペイントコンディショナー（レッドデビル社製）で１６時間振とうした後、０．４５μｍメンブランフィルターを使用して固液分離した。
【００９８】
次いで、測定に必要な量の固形分及び濾液が得られるまで、同様の処理を行った。濾液はそのまま環境庁告示第１０号「地下水の水質汚濁に係る環境基準について」に基づき、固形分については４０℃で３時間、大気中で乾燥し試料を得て、環境庁告示第４６号「土壌の汚染に係る環境基準について」に基づき分析した。その結果、溶液中のカドミウム０．００１ｍｇ／ｌ未満、鉛０．００５ｍｇ／ｌ未満、六価クロム０．０４ｍｇ／ｌ未満、砒素０．００１ｍｇ／ｌ未満、セレン０．００２ｍｇ／ｌ未満、シアンは未検出であり、固体からの溶出量はカドミウム０．００１ｍｇ／ｌ未満、鉛０．００５ｍｇ／ｌ未満、六価クロム０．０４ｍｇ／ｌ未満、砒素０．００１ｍｇ／ｌ未満、セレン０．００２ｍｇ／ｌ未満、シアンは未検出であった。
【００９９】
＜重金属等の有害物質で汚染された土壌の浄化剤による浄化処理＞
バイアル瓶に、あらかじめ湿った砂質土壌２０ｇ（目開き２ｍｍ篩い下）とここに得られた前記浄化剤（鉄複合粒子粉末１８重量％含有）５．６ｇとイオン交換水２２．４ｍｌを注入し、さらに、カドミウム、鉛、砒素、セレン及びシアンを各１０ｐｐｍとなるように１０００ｐｐｍ標準液（関東化学（株）製）より各０．３ｍｌ注入し、六価クロムを５０ｐｐｍとなるように１０００ｐｐｍ標準液（関東化学（株）製）より１．５ｍｌ注入し、全量で１００ｐｐｍになるように合計３．０ｍｌ注入した。直ぐにフッ素樹脂ライナー付きゴム栓で蓋をし、その上からアルミシールで強固に締め付けた。前記バイアル瓶をペイントコンディショナー（レッドデビル社製）で１６時間振とうした後、０．４５μｍメンブランフィルターを使用して固液分離した。
【０１００】
次いで、測定に必要な量の固形分及び濾液が得られるまで、同様の処理を行った。濾液はそのまま環境庁告示第１０号「地下水の水質汚濁に係る環境基準について」に基づき、固形分については４０℃で３時間、大気中で乾燥し試料を得て、環境庁告示第４６号「土壌の汚染に係る環境基準について」に基づき分析した。その結果、溶液中のカドミウム０．００１ｍｇ／ｌ未満、鉛０．００５ｍｇ／ｌ未満、六価クロム０．０４ｍｇ／ｌ未満、砒素０．００１ｍｇ／ｌ未満、セレン０．００２ｍｇ／ｌ未満、シアンは未検出であり、固体からの溶出量はカドミウム０．００１ｍｇ／ｌ未満、鉛０．００５ｍｇ／ｌ未満、六価クロム０．０４ｍｇ／ｌ未満、砒素０．００１ｍｇ／ｌ未満、セレン０．００２ｍｇ／ｌ未満、シアンは未検出であった。
【０１０１】
＜重金属等の有害物質で汚染された地下水の浄化剤による浄化処理＞
褐色バイアル瓶５０ｍｌ（実容積６８ｍｌ）に前記浄化剤（鉄複合粒子粉末１８重量％含有）５．６ｇとイオン交換水２２．４ｍｌを注入し、さらに、カドミウム、鉛、砒素、セレン及びシアンを各１０ｐｐｍとなるように１０００ｐｐｍ標準液(関東化学（株）製)より各０．３ｍｌ注入し、六価クロムを５０ｐｐｍとなるように１０００ｐｐｍ標準液(関東化学（株）製)より１．５ｍｌ注入し、全量で１００ｐｐｍになるように合計３．０ｍｌ注入した。直ぐにフッ素樹脂ライナー付きゴム栓で蓋をし、その上からアルミシールで強固に締め付けた。前記バイアル瓶をペイントコンディショナー（レッドデビル社製）で１６時間振とうした後、０．４５μｍメンブランフィルターを使用して固液分離した。
【０１０２】
次いで、測定に必要な量の固形分及び濾液が得られるまで、同様の処理を行った。濾液はそのまま環境庁告示第１０号「地下水の水質汚濁に係る環境基準について」に基づき、固形分については４０℃で３時間、大気中で乾燥し試料を得て、環境庁告示第４６号「土壌の汚染に係る環境基準について」に基づき分析した。その結果、溶液中のカドミウム０．００１ｍｇ／ｌ未満、鉛０．００５ｍｇ／ｌ未満、六価クロム０．０４ｍｇ／ｌ未満、砒素０．００１ｍｇ／ｌ未満、セレン０．００２ｍｇ／ｌ未満、シアンは未検出であり、固体からの溶出量はカドミウム０．００１ｍｇ／ｌ未満、鉛０．００５ｍｇ／ｌ未満、六価クロム０．０４ｍｇ／ｌ未満、砒素０．００１ｍｇ／ｌ未満、セレン０．００２ｍｇ／ｌ未満、シアンは未検出であった。
【０１０３】
【作用】
本発明に係る浄化処理用鉄複合粒子は、鉄複合粒子のα−Ｆｅが溶解し、溶解したα−Ｆｅと重金属等とがフェライト化反応することによって、重金属等を不溶化するものである。
【０１０４】
即ち、本発明に係る浄化処理用鉄複合粒子は、粒子サイズが微細であり高い活性を保持しているため、加熱することなく常温でα−Ｆｅが溶解しやすく、更に、土壌中に含有されている水又は地下水を効率よく分解して水素又は水酸基を生じさせ局所的に常にアルカリ領域となるため、α−Ｆｅの溶解反応が徐々に進行する。次いで、溶解したα−Ｆｅと重金属等の有害物質とが鉄複合粒子の界面で、水の分解による水酸基、酸素又は溶存酸素等を取り込みスピネルフェライト化が持続的に進行し重金属等の有害物質を不溶化するものと本発明者は推定している。また、鉄複合粒子中に含有するＳも局所的にα−Ｆｅの溶解に寄与しているものと推定される。
【０１０５】
また、溶解したα−Ｆｅと重金属等の有害物質とのフェライト化反応が、スピネル構造である表層マグネタイトをシードとし、エピタキシャルに粒子が成長するため、効率よく重金属等の有害物質を不溶化できるものと本発明者は推定している。
【０１０６】
本発明においては、酸又はアルカリを添加してｐＨを調整する処理、加熱処理及び空気吹き込みなどによる強制的な酸化処理も不要であることからも、効率よく重金属等の有害物質を不溶化できるものであり、また、浄化処理用鉄複合粒子は経時による特性の変化がないので、長期に亘って重金属等の有害物質を不溶化できるものである。
【０１０７】
【実施例】
次に、本発明の実施例及び比較例を挙げる。
【０１０８】
＜ゲータイト粒子＞
ゲータイト粒子として表１に示すゲータイト粒子を用意した。
【０１０９】
ゲータイト粒子２
Ｆｅ２＋１．５０ｍｏｌ／ｌを含む硫酸第一鉄水溶液１２．８ｌと０．４４−ＮのＮａＯＨ水溶液３０．２ｌ（硫酸第一鉄水溶液中のＦｅ２＋に対し０．３５当量に該当する。）とを混合し、ｐＨ６．７、温度３８℃においてＦｅ（ＯＨ）２を含む硫酸第一鉄水溶液の生成を行なった。次いで、Ｆｅ（ＯＨ）２を含む硫酸第一鉄水溶液に温度４０℃において毎分１３０ｌの空気を３．０時間通気してゲータイト核粒子を生成させた。
【０１１０】
前記ゲータイト核粒子を含む硫酸第一鉄水溶液（ゲータイト核粒子の存在量は生成ゲータイト粒子に対し３５ｍｏｌ％に該当する。）に、５．４ＮのＮａ２ＣＯ３水溶液７．０ｌ（残存硫酸第一鉄水溶液中のＦｅ２＋に対し１．５当量に該当する。）を加え、ｐＨ９．４、温度４２℃において毎分１３０ｌの空気を４時間通気してゲータイト粒子粉末を生成させた。ここに得たゲータイト粒子を含有する懸濁液をフィルタープレスで水洗し、得られたプレスケーキを圧縮成型機を用いて孔径４ｍｍの成型板で押し出し成型して１２０℃で乾燥してゲータイト粒子粉末の造粒物とした。
【０１１１】
ここに得た造粒物を構成する含有するゲータイト粒子粉末は、平均長軸径０．３３μｍ、軸比（長軸径／短軸径）２５．０の針状を呈した粒子であった。ＢＥＴ比表面積は７０ｍ２／ｇ、Ｓ含有量は４０００ｐｐｍであった。
【０１１２】
【表１】
浄化処理用鉄複合粒子粉末：実施例１〜８、比較例１；
ゲータイト粒子の種類、加熱脱水の温度、ヘマタイト粒子を含有する懸濁液への硫酸の添加の有無及び添加量、加熱還元の温度、水中での保持時間（日数）を種々変化させた以外は前記発明の実施の形態と同様にして浄化処理用鉄複合粒子粉末を得た。
【０１１４】
このときの製造条件を表２に、得られた浄化処理用鉄複合粒子粉末の諸特性を表３に示す。
【０１１５】
比較例２は、前記ゲータイト粒子粉末２の造粒物１００ｇを転動還元装置に導入し、Ｈ２ガスを通気させながら、３００℃で１８０分間、完全にマグネタイトとなるまで還元した、α−Ｆｅを全く含まないマグネタイト粒子粉末である。
比較例３及び比較例４は電解鉄粉である。
【０１１６】
【表２】
【表３】
＜汚染土壌・汚染地下水の浄化処理＞
実施例９〜１６、比較例５〜８；
浄化処理用鉄複合粒子粉末の種類及び浄化剤の種類を種々変化させた以外は、前記発明の実施の形態と同様にして汚染土壌又は汚染地下水の処理を行った。
【０１１９】
このときの処理条件及び測定結果を表４及び表５に示す。
【０１２０】
【表４】
【表５】
＜触媒活性の持続性＞
浄化処理用鉄複合粒子を水中に４日（実施例３及び実施例７）及び３０日（実施例４及び実施例８）保持した各浄化剤を前記評価方法と同様にして浄化処理を行った結果、本発明に係る浄化剤を用いた場合にはいずれも土壌中及び地下水中の重金属等の有害物質を取り込み、重金属等の有害物質とのフェライト化が長期にわたって進行していることから、本発明に係る浄化剤は重金属等の有害物質の不溶化効果が長期に亘って維持されることが明らかである。
【０１２３】
【発明の効果】
本発明に係る浄化処理用鉄複合粒子粉末及び該粉末を有効成分とする浄化剤は、カドミウム、鉛、六価クロム、砒素、セレン、シアン等の重金属等の有害物質を効率よく、且つ持続的に不溶化できるので、重金属等の有害物質によって汚染された土壌・地下水の浄化に好適である。
【０１２４】
従って、本発明の産業利用性は非常に大きいといえる。[0001]
BACKGROUND OF THE INVENTION
The present invention provides an iron composite particle powder for purification treatment that can efficiently and continuously insolubilize harmful substances composed of heavy metals such as cadmium, lead, hexavalent chromium, arsenic, selenium, and cyanide in soil or groundwater, and The present invention provides a cleaning agent comprising the powder as an active ingredient.
[0002]
[Prior art]
In recent years, contamination of soil and groundwater has attracted attention due to the improvement of environmental awareness. In particular, since contamination by harmful substances such as cadmium, lead, hexavalent chromium, arsenic, selenium, and cyanide is harmful to the human body and ecosystem, there is an urgent need to clean up and remove the harmful substances. ing.
[0003]
As is well known, the countermeasure technology for soil or groundwater contaminated with heavy metals and other hazardous substances is classified as “purification technology” and “containment”, and the purification technology is “in-situ purification” and excavating contaminated soil from the target site. “Excavation removal”. “In-situ purification” further includes “in-situ decomposition” in which heavy metals contained in contaminated soil and groundwater are decomposed underground (in-situ), and “in-situ removal” that removes heavy metals from extracted or excavated contaminated soil and groundwater. It is divided into “extraction”.
[0004]
“In-situ extraction” refers to “decomposition” that decomposes compounds such as cyanide and pesticides among the target substances classified as heavy metals, etc., and heavy metals concentrated by physical separation from soil and groundwater. There is "separation" to separate.
[0005]
On the other hand, “containment” is classified into “in-situ containment” and “containment after excavation and removal”. In-situ containment is a technique in which a contaminated soil is mixed with a solidifying agent and solidified, and then the contaminated soil is contained in-situ without moving on-site soil. Containment after excavation and removal is a technique in which an insolubilizing agent is mixed in the contaminated soil as a pretreatment to make it insoluble, and after excavation is performed once, the contaminated soil is contained again.
[0006]
Construction methods related to “Purification Technology” include soil washing method, thermal desorption method, etc., for example, chemical dissolution method that adds chemicals and dissolves and separates heavy metals, etc., washing and classifying soil with water , Water washing method for separating fine particles containing a lot of heavy metals, etc., cleaning contaminants adhering to the surface of soil particles with a cleaning agent, and classifying them into clean large particles and contaminant fine particles according to the size and specific gravity of the particles Examples include soil wet cleaning.
[0007]
In addition, the construction method related to “containment” is “in-situ containment”, where there is a method of mixing a solidifying agent such as cement into the contaminated soil and containing it with an impermeable layer and a steel sheet pile, etc. There is a method in which the contaminated soil is insolubilized with a chemical to change the contaminated soil into a form in which it is difficult to elute, and is then contained by a barrier or water barrier.
[0008]
However, each processing technique is expensive and requires a long period of time, and it is difficult to say that it is a technique that efficiently and continuously reduces harmful substances such as heavy metals.
[0009]
Recently, low-cost processing technology has been developed that mainly uses the reducing action of iron powder to reduce the valence of heavy metals, making them harmless and stabilizing. For example, a technique using a reduction action of iron powder (reduction of metal valence) (Patent Document 1), a technique using an iron powder reduction action or adsorption action against arsenic (Patent Document 2), heat treatment and iron powder (Patent document 3) that uses the reduction action (reduction of metal valence) of iron, technology that uses the reduction action (reduction of metal valence) of iron powder against hexavalent chromium (patent document 4), iron powder And the like (Patent Document 5) using the reduction action (reduction of metal valence).
[0010]
In addition, as a treatment technique for heavy metal-containing wastewater, a ferritization treatment method by adding iron salt and a stabilization method based on the reduction action of iron powder have been proposed.
[0011]
Ferritic treatment by adding iron salt is Fe 2+ , Fe 3+ Is neutralized with an alkali, oxidized with an air vent or an oxidizing agent, and converted into spinel ferrite by heating (up to room temperature) to take in or adsorb heavy metal into the crystal. In addition, it is also known that iron hydroxide such as α, γ, and δ-FeOOH is partially incorporated or adsorbed inside the crystal (Non-patent Documents 1 and 6 to 8).
[0012]
The stabilization method based on the reducing action of iron powder is a method of detoxifying and stabilizing by reducing the valence of heavy metals. In some cases, it is also known that a small amount of iron powder dissolves in an acidic region and turns into goethite or spinel ferrite, which is taken into the crystal or adsorbed.
[0013]
For example, in Patent Document 9, when a solution containing heavy metal ions is adjusted to about pH 5-6, and iron powder is added and stirred, part of the iron powder dissolves and ferric hydroxide precipitates, and pH It is described that goethite and rapid crosite are formed with the rise in the temperature, and in this case, a part of heavy metals are co-precipitated and most of them are adsorbed to the iron powder. It is described that it increases and the adsorption removal effect deteriorates.
[0014]
In Patent Document 10, a solution containing a heavy metal chelate complex is adjusted to pH 2 to 6, and the reaction is carried out by supplying air at the time of strong stirring such as adding iron powder or engulfing air or stirring, so that the pH becomes almost neutral. It is described that, when naturally raised, the iron powder surface is activated and heavy metals are adsorbed, and that some goethite, rapid crosite, and magnetite are generated and taken up. .
[0015]
In Patent Document 11, the pH of a solution containing an iron cyanide complex is adjusted to less than 5, and iron powder is added and stirred, whereby the iron cyanide complex is adsorbed to the iron body while part of the iron powder is dissolved. Reduction reaction (metal valence reduction), displacement precipitation (ionization tendency), adsorption reaction to iron powder, incorporation in iron oxide formation, hydroxide precipitation by neutralization, coprecipitation reaction Such reactions such as (ferritization) are described.
[0016]
Non-Patent Document 2 describes that a spinel compound is generated from dissolution of iron powder.
[0017]
[Patent Document 1]
JP-A-10-71386
[Patent Document 2]
JP-A-10-244248
[Patent Document 3]
JP 2000-157961 A
[Patent Document 4]
JP 2001-198567 A
[Patent Document 5]
JP2002-200478
[Patent Document 6]
JP-A-50-36370
[Patent Document 7]
JP 50-133654 A
[Patent Document 8]
JP-A-50-154164
[Patent Document 9]
Shoko 52-45665
[Patent Document 10]
Shoko 54-11614
[Patent Document 11]
JP-A-57-7795
[Non-Patent Document 1]
NEC Technical Report Vol. 37, no. 9/1984 "Treatment of heavy metal wastewater by ferrite method"
[Non-Patent Document 2]
Bull. Inst. Chem. Res. Kyoto Univ. Vol 71, no. 2.1993 "Air Oxidation of Iron Dispersed in Aqueous Solution of Sodium Hydroxide"
[0018]
[Problems to be solved by the invention]
[0019]
Each of the technologies described in Patent Documents 1 to 5 described above is a detoxification and stabilization treatment method that uses the reduction action (valence reduction) of iron powder, and problems with the sustainability of the reduction action of iron powder over the years. Even if the heavy metal is harmless and has a stable valence, the valence rises again and may be changed into a harmful metal, which is not a permanent measure.
[0020]
In any of the techniques described in Patent Documents 6 to 11, the action of the iron powder is mainly reduction or adsorption. Although there is an effect due to partial dissolution, it is a mechanism in which goethite, rapid crosite and magnetite are generated and taken in via the elution of iron powder in the acidic region, and in the processing technology using iron powder, Fe 2+ Or Fe 3+ It is not a technology that positively utilizes the phenomenon of spinel ferrite while taking in heavy metals by dissolution of.
[0021]
In the technique described in the aforementioned Non-Patent Document 2, pH adjustment, heating, and forced oxidation by adding an alkali are essential.
[0022]
Therefore, the present invention relates to "containment", and uses iron powder to efficiently and continuously insolubilize toxic substances such as cadmium, lead, hexavalent chromium, arsenic, selenium and cyanide, etc. Making it a technical issue.
[0023]
[Means for Solving the Problems]
The technical problem can be achieved by the present invention as follows.
[0024]
That is, the present invention is an iron composite particle powder comprising α-Fe and magnetite, the iron composite particle powder has an average particle size of 0.05 to 0.50 μm, and the α-Fe content is 30-99% by weight S content is 3500-10000ppm This is an iron composite particle powder for soil / groundwater purification treatment contaminated with harmful substances such as heavy metals (Invention 1).
[0025]
The present invention also relates to an iron composite particle powder having an average particle diameter of 0.05 to 0.50 μm composed of α-Fe and magnetite. And the S content is 3500-10000 ppm The diffraction intensity D of the (110) plane of α-Fe in the X-ray diffraction spectrum of the iron composite particle powder 110 And magnetite (311) plane diffraction intensity D 311 Intensity ratio (D 110 / (D 110 + D 311 )) Is 0.20 to 0.98, and is an iron composite particle powder for soil / groundwater purification treatment contaminated with harmful substances such as heavy metals (Invention 2).
[0026]
In the present invention, the saturation magnetization value is 90 to 190 Am. 2 / Kg and a BET specific surface area of 5.0 to 60.0 m 2 / G and α-Fe (110) crystallite size of 200 to 400 mm of iron composite particle powder for purification of soil and groundwater contaminated with hazardous substances such as heavy metals of the present invention 1 or 2 (Invention 3).
[0027]
In addition, the present invention provides iron for soil / groundwater purification treatment contaminated with harmful substances such as heavy metals according to the first to third aspects of the present invention having a grain shape of rice grains and an axial ratio of more than 1.0 and not more than 2.0. It is a composite particle powder (Invention 4).
[0028]
Further, the present invention comprises an aqueous suspension containing iron composite particles for purification treatment of soil and groundwater contaminated with a hazardous substance such as heavy metal according to any one of the present inventions 1 to 4 as an active ingredient. It is a purification agent for soil and groundwater contaminated with harmful substances such as heavy metals (Invention 5).
[0029]
The present invention also provides a goethite particle powder having an average major axis diameter of 0.05 to 0.50 μm or an average major axis diameter obtained by heating and dehydrating the goethite particle powder in a temperature range of 250 to 350 ° C. A 50 μm hematite particle powder is heated and reduced to a temperature of 300 to 600 ° C. to obtain an iron particle powder. After cooling, the iron particle powder is taken out in water without forming a surface oxide film in the gas phase, The iron composite particle powder for purification treatment of soil and groundwater contaminated with a hazardous substance such as heavy metal according to the present invention 1 to the present invention 4, wherein an oxide film is formed on the surface of the iron particle powder and then dried. (Invention 6).
[0030]
The present invention also provides a goethite particle powder having an average major axis diameter of 0.05 to 0.50 μm or an average major axis diameter obtained by heating and dehydrating the goethite particle powder in a temperature range of 250 to 350 ° C. A 50 μm hematite particle powder is heated and reduced to a temperature of 300 to 600 ° C. to obtain an iron particle powder. After cooling, the iron particle powder is taken out in water without forming a surface oxide film in the gas phase, A water suspension containing an iron composite particle powder is obtained by forming an oxide film on the surface of the iron particle powder, and soil or groundwater contaminated with a hazardous substance such as heavy metal according to the present invention 5 It is a manufacturing method of a cleaning agent (this invention 7).
[0031]
In addition, the present invention is a soil contaminated with a harmful substance such as heavy metal according to any one of the first to fourth aspects of the present invention. A method for purifying soil and groundwater contaminated with a hazardous substance such as heavy metal (mixed contact with groundwater contaminated with a hazardous substance such as heavy metal) (Invention 8).
[0032]
In addition, the present invention is a mixture of the soil / groundwater purification agent contaminated with a hazardous substance such as heavy metal of the present invention and the soil contaminated with a hazardous substance such as heavy metal or groundwater contaminated with a hazardous substance such as heavy metal. A method for purifying soil and groundwater contaminated with a hazardous substance such as heavy metal, which is characterized by contacting (present invention 9).
[0033]
Further, the present invention provides a soil contaminated with a hazardous substance such as heavy metal according to the present invention 8 or 9, wherein the hazardous substance such as heavy metal is cadmium, lead, hexavalent chromium, arsenic, selenium, or cyan. -It is a purification process of groundwater (this invention 10).
[0034]
The configuration of the present invention will be described in detail as follows.
[0035]
First, the iron composite particle powder for purification treatment of soil and groundwater contaminated with harmful substances such as heavy metals according to the present invention 1 to 4 (hereinafter referred to as “iron composite particle powder for purification treatment”) will be described.
[0036]
The average particle diameter of the iron composite particle powder for purification treatment according to the present invention is 0.05 to 0.50 μm. When the average particle diameter is less than 0.05 μm, the α-Fe phase is unstable, so a thick oxide film is formed on the surface, making it difficult to increase the α-Fe content and reducing the α-Fe amount. In the purification treatment, the dissolution reaction of α-Fe becomes insufficient, and it becomes difficult to obtain the intended effect of the present invention. If it exceeds 0.50 μm, the α-Fe content can be increased, but the BET specific surface area becomes small, making it difficult to obtain the intended effect of the present invention. More preferably, it is 0.05-0.30 micrometer.
[0037]
The iron composite particle powder for purification treatment according to the present invention contains 30 to 99% by weight of an α-Fe phase. When the α-Fe phase is less than 30% by weight, the amount of α-Fe is small, so that the dissolution reaction of α-Fe becomes insufficient in the purification treatment, and the ferritization reaction with heavy metals and the like becomes insufficient. The intended effect cannot be obtained. When the α-Fe phase exceeds 99% by weight, the particle size is extremely large or the BET specific surface area is extremely small and stable in the air. Since the α-Fe dissolution reaction is insufficient and the ferritization reaction with a heavy metal or the like does not proceed sufficiently, the intended effect of the present invention cannot be obtained. Preferably it is 40 to 99% by weight.
[0038]
The constituent phase of the iron composite particle powder for purification treatment contains a magnetite phase together with the α-Fe phase. By containing magnetite, the ferritization reaction can easily proceed. The content ratio of magnetite is the diffraction intensity D of the (110) plane of α-Fe in the X-ray diffraction spectrum of the iron composite particle powder. 110 And magnetite (311) plane diffraction intensity D 311 Intensity ratio (D 110 / (D 110 + D 311 )) Is preferably 0.20 to 0.98, more preferably 0.30 to 0.98. Magnetite is preferably present on the particle surface of the iron composite particle powder for purification treatment, and the presence of magnetite on the particle surface allows the ferritization reaction to proceed epitaxially using the iron composite particle as a seed.
[0039]
The particle shape of the iron composite particle powder for purification treatment according to the present invention is preferably a rice grain shape, and the axial ratio is preferably more than 1.0 and not more than 2.0. When the axial ratio is 1.0, if the particles are spherical and have the same particle size, the BET specific surface area becomes small, and the α-Fe dissolution reaction becomes insufficient in the purification treatment, which is not preferable. If it exceeds 2.0, the BET specific surface area becomes large, the α-Fe phase becomes unstable, and a thick oxide film tends to be formed on the surface, making it difficult to increase the α-Fe content and reducing the α-Fe amount. Therefore, the dissolution reaction of α-Fe becomes insufficient in the purification treatment, and it is difficult to obtain the intended effect of the present invention. More preferably, it is 1.2-1.8.
[0040]
The crystallite size (α-Fe (110) plane) of the iron composite particle powder for purification treatment according to the present invention is preferably 200 to 400 mm. If it is less than 200 mm, the BET specific surface area is large, but the α-Fe phase is unstable, so a thick oxide film is formed on the surface, making it difficult to increase the α-Fe content and reducing the α-Fe amount. In the purification treatment, the α-Fe dissolution reaction becomes insufficient, making it difficult to obtain the intended effect of the present invention. If it exceeds 400%, the α-Fe content can be increased, but the BET specific surface area becomes small, making it difficult to obtain the intended effect of the present invention. More preferably, it is 200-350cm.
[0041]
The BET specific surface area value of the iron composite particle powder for purification treatment according to the present invention is 5.0 to 60.0 m. 2 / G is preferred. 5.0m 2 If it is less than / g, the contact area becomes small, and the dissolution reaction of α-Fe becomes insufficient in the purification treatment. 60.0m 2 In the case of exceeding / g, since the α-Fe phase is unstable, a thick oxide film is formed on the surface, making it difficult to increase the α-Fe content and reducing the α-Fe content. The α-Fe dissolution reaction becomes insufficient, making it difficult to obtain the intended effect of the present invention. More preferably 7.0-55.0m 2 / G.
[0042]
The total Fe content of the iron composite particle powder for purification treatment according to the present invention is preferably 75% by weight or more based on the total particle powder. If it is less than 75% by weight, the α-Fe content decreases, and the α-Fe dissolution reaction becomes insufficient in the purification treatment, making it difficult to obtain the intended effect of the present invention. More preferably, it is 75 to 98% by weight.
[0043]
In the iron composite particle powder for purification treatment according to the present invention, metallic elements other than Fe, such as Pb, Cd, As, Hg, Sn, Sb, Ba, Zn, Cr, Nb, Co, and Bi, are toxic metals. Therefore, it is better not to contain as much as possible, and it is particularly preferable that Pb, Cd, As, and Hg are not substantially contained.
[0044]
The S content of the iron composite particle powder for purification treatment according to the present invention is preferably 3500 to 10,000 ppm.
[0045]
The saturation magnetization value of the iron composite particle powder for purification treatment according to the present invention is 90 to 190 Am. 2 / Kg (90-190 emu / g) is preferred. 90 Am 2 If it is less than / kg, the α-Fe content is low, and the α-Fe dissolution reaction becomes insufficient in the purification treatment, which is not preferable. 190Am 2 When the amount exceeds / kg, the BET specific surface area is low although the Fe content is high, and the α-Fe dissolution reaction becomes insufficient in the purification treatment, which is not preferable. More preferably 95-190 Am 2 / Kg (95-190 emu / g).
[0046]
The iron composite particle powder for purification treatment according to the present invention may be in the form of a granulated product.
[0047]
Next, the soil / groundwater purification agent (hereinafter referred to as “purification agent”) contaminated with hazardous substances such as heavy metals according to the present invention 5 will be described.
[0048]
The purification agent according to the present invention is a water suspension containing the iron composite particle powder for purification treatment according to the first to fourth aspects of the present invention as an active ingredient, and in the water suspension of the iron composite particle powder for purification treatment. The content of can be appropriately selected within the range of 0.5 to 50 parts by weight.
[0049]
The pH value of the purifier according to the present invention is preferably 7-12, more preferably 8-12. In the present invention, it has been confirmed that the pH value of the purifier increases from about 8 to about 11 with the passage of time, and α-Fe is gradually dissolved little by little because the pH is in the alkaline region. It is estimated that the ferritization reaction with heavy metals and the like proceeds continuously.
[0050]
Next, the manufacturing method of the iron composite particle powder for purification treatment of soil and groundwater contaminated with hazardous substances such as heavy metals according to the present invention 6 will be described.
[0051]
The goethite particle powder is obtained by reacting ferrous salt with one or more selected from alkali hydroxide, alkali carbonate or ammonia according to a conventional method, such as iron hydroxide or iron carbonate. This can be obtained by ventilating an oxygen-containing gas such as air into a suspension containing the ferrous iron-containing precipitate.
[0052]
The average major axis diameter of the goethite particle powder is 0.05 to 0.50 μm, and the particle shape may be either a spindle shape or a needle shape. The axial ratio is preferably 4 to 30, more preferably 5 to 25, and the BET specific surface area is 20 to 200 m. 2 / G is preferable, more preferably 25 to 180 m. 2 / G. The S content is preferably 1 to 8000 ppm. In particular, when the goethite particle powder is directly heated and reduced, the S content is preferably 2200 to 8000 ppm.
[0053]
Also, in order to maintain the α-Fe content in the iron composite particles at a high rate and destroy the shape and grow the crystals in a granular form, the goethite particle powder may not be subjected to surface treatment such as sintering prevention treatment. preferable.
[0054]
The goethite particle powder is preferably granulated according to a conventional method. By granulating, a fixed bed type reduction furnace can be used, and even when iron composite particles are used, it is possible to maintain the shape of the granulated product as it is depending on the reducing conditions. Is preferred.
[0055]
The obtained goethite particle powder is preferably a hematite particle powder that has been heat-dehydrated in a temperature range of 250 to 350 ° C.
[0056]
The hematite particle powder in the present invention uses goethite particles having a high S content in advance, or in the case of goethite particles having a low S content, by adding sulfuric acid to an aqueous suspension of the hematite particle powder, It is preferable to control the S content of the hematite particle powder.
[0057]
The average major axis diameter of the hematite particle powder is 0.05 to 0.50 μm, and the S content is preferably 2400 to 8500 ppm.
[0058]
The goethite particle powder or the hematite particle powder is heated and reduced in a temperature range of 300 to 600 ° C. to obtain iron particles (α-Fe) powder.
[0059]
When the heating reduction temperature is less than 300 ° C., the reduction reaction proceeds slowly and takes a long time for the reduction reaction. Further, although the BET specific surface area can be increased, the crystal growth cannot be sufficiently performed, the α-Fe phase becomes unstable, and a thick oxide film is formed on the particle surface, or the α-Fe phase is changed from the magnetite phase. Since the phase change to the phase is insufficient, it is difficult to increase the α-Fe content, and the α-Fe dissolution reaction becomes insufficient in the purification treatment. When the temperature exceeds 600 ° C., the reduction reaction proceeds rapidly, the sintering between the particles and the particles is excessively promoted, the particle diameter is increased, and the BET specific surface area is also decreased.
[0060]
In addition, although hydrogen gas, nitrogen gas, etc. can utilize the atmosphere at the time of temperature increase of a reductive reaction, hydrogen gas is preferable industrially.
[0061]
After cooling the iron particle powder after heat reduction, the iron particle powder is taken out in water without forming a surface oxide film in the gas phase, and a surface oxide film is formed on the particle surface of the iron particle powder in water, Then it is dried.
[0062]
The atmosphere during cooling may be either nitrogen or hydrogen, but is preferably switched to nitrogen finally. Moreover, when taking out in water, it is preferable to be cooled to 100 degrees C or less.
[0063]
The drying atmosphere can be selected as appropriate, such as nitrogen, air, or vacuum, but the temperature is preferably 100 ° C. or lower.
[0064]
In the heat reduction treatment, the whole particle becomes an iron particle composed of an α-Fe phase, and the water is decomposed by the catalytic activity of α-Fe by taking it out into water. Alternatively, it can be presumed that α-Fe is oxidized by dissolved oxygen or the like in water to form an oxide film made of magnetite on the particle surface.
[0065]
Next, a method for producing a purification agent for soil and groundwater contaminated with hazardous substances such as heavy metals according to the present invention 7 will be described.
[0066]
The purification agent for soil and groundwater contaminated with hazardous substances such as heavy metals according to the present invention 7 is a water containing iron composite particle powder as it is after cooling the iron particle powder after heating and reduction in the present invention 6 into water. A purification agent comprising a suspension is obtained.
[0067]
In the cleaning agent of the present invention, it is preferable to pulverize and disperse the secondary aggregates of the iron composite particle powder.
[0068]
Next, the method for purifying soil and groundwater contaminated with hazardous substances such as heavy metals according to the present invention 8 to the present invention 10 will be described.
[0069]
The method for purifying soil and groundwater contaminated with toxic substances such as heavy metals according to the present invention is a method of “containment” and can be applied to either “in-situ containment” or “containment after excavation”.
[0070]
“In-situ containment” is a method in which a mixture or a purification agent of iron composite particle powder for purification treatment and water or a gas such as nitrogen or the like is permeated or introduced into a basement through a borehole as it is. When using a cleaning agent, since it is a water suspension, it may be used as it is or may be diluted as necessary.
[0071]
In "containment after excavation", use a sand mill, Henschel mixer, concrete mixer, nauter mixer, uniaxial or biaxial kneader type mixer, etc. This is a method of mixing and agitation with contaminated soil to ferritize heavy metals in the soil and then contain them. In addition, if necessary, it is possible to magnetically separate ferrite incorporating heavy metal or the like.
[0072]
The amount of iron composite particles for purification treatment or the amount of purification agent (solid content conversion) can be selected as appropriate according to the degree of contamination of hazardous substances such as heavy metals in the soil and groundwater. When doing, 0.5-50 weight part is normally preferable with respect to 100 weight part of soil, More preferably, it is 1-30 weight part. When the amount is less than 0.5 part by weight, the intended effect of the present invention cannot be obtained sufficiently. If it exceeds 50 parts by weight, the purification effect is improved, but it is not economical. When contaminated groundwater is targeted, it is preferably added in an amount of 0.5 to 50 parts by weight, more preferably 1 to 30 parts by weight with respect to 100 parts by weight of the groundwater.
[0073]
When the iron composite particle powder for purification treatment according to the present invention or the purification agent according to the present invention is used, 0.01 mg / l or less of cadmium in the contaminated soil or the contaminated groundwater, It is possible to reduce 0.01 mg / l or less, hexavalent chromium 0.05 mg / l or less, arsenic 0.01 mg / l or less, selenium 0.01 mg / l or less, and cyan undetected.
[0074]
DETAILED DESCRIPTION OF THE INVENTION
A typical embodiment of the present invention is as follows.
[0075]
The average major axis diameter and axial ratio of the goethite particle powder were measured with a transmission electron micrograph. The average particle diameter of the hematite particle powder and the iron composite particle powder was measured using a scanning electron micrograph.
[0076]
The total amount of Fe in the iron composite particle powder was measured using an “inductively coupled plasma emission spectrometer SPS4000” (manufactured by Seiko Denshi Kogyo Co., Ltd.).
[0077]
The crystalline phase of each particle powder was identified by measuring in the range of 10 to 90 ° with the X-ray diffractometer.
[0078]
The α-Fe content of the iron composite particle powder was measured in advance by measuring the X-ray diffraction of a mixed powder composed of iron and magnetite in various mixing ratios (α-Fe was taken out into water and transformed). 110) Diffraction intensity D of the surface 110 Diffraction intensity D of (311) plane of magnetite 311 It was calculated by creating a relational expression between the mixing ratio and the mixing ratio and using it as a calibration curve. The relational expression which is a calibration curve is as follows.
[0079]
α-Fe content = −51.387X 2 + 151.88X
X: Strength ratio (D 110 / (D 110 + D 311 ))
[0080]
Of the metal elements other than iron present in each particle powder, “Frame atomic absorption photometer AA-6500S” (manufactured by Shimadzu Corporation) is used for Pb and Cd, and “Hydrogen compound generation atomic absorption photometer HVG-” is used for As. 1 ”(manufactured by Shimadzu Corporation) was measured for Hg using“ reduction vaporization atomic absorption photometer MVU-1A ”(manufactured by Shimadzu Corporation). The S content was measured using “Carbon Sulfur Analyzer: EMIA-2200” (manufactured by HORIBA).
[0081]
The crystallite size (α-Fe (110) plane) of the iron composite particle powder is the size of the crystal particle measured by X-ray diffractometry, and the crystal particle size in the direction perpendicular to the crystal plane of each particle. The thickness is expressed by a value calculated from the diffraction peak curve for each crystal plane using the following Scherrer equation.
[0082]
Crystallite size = Kλ / βcosθ
Where β = half-value width (in radians) of the true diffraction peak corrected for machine width due to the device.
K = Scherrer constant (= 0.9).
λ = wavelength of X-ray (Cu Kα ray 0.1542 nm).
θ = Diffraction angle (corresponding to the diffraction peak of each crystal plane).
[0083]
The specific surface area of each particle powder was represented by a value measured by BET method using “Monosorb MS-11” (manufactured by Kantachrome Co., Ltd.).
[0084]
The saturation magnetization value of the iron composite particle powder was measured using an “vibrating sample magnetometer VSM-3S-15” (manufactured by Toei Industry Co., Ltd.) with an external magnetic field of 795.8 kA / m (10 kOe).
[0085]
Measurements of hazardous substances such as heavy metals in the purification treatment are based on the Environmental Agency Notification No. 46 “Environmental Standards Concerning Soil Contamination” for the solid content of contaminated soil, and the Environmental Agency Notification No. 10 for contaminated groundwater. No. “Environmental standards for groundwater pollution” was analyzed.
[0086]
<Manufacture of iron composite particle powder and purification agent for purification treatment>
N at a rate of 3.4 cm per second 2 In a reaction vessel maintained in a non-oxidizing atmosphere by flowing gas, 1.16 mol / l Na 2 CO 3 After adding 704 l of aqueous solution, Fe 2+ Add 296 l of ferrous sulfate aqueous solution containing 1.35 mol / l and mix (Na 2 CO 3 The amount corresponds to 2.0 times equivalent to Fe. And FeCO at a temperature of 47 ° C. 3 Was generated.
[0087]
The obtained FeCO 3 In an aqueous solution containing 2 While maintaining gas at a temperature of 47 ° C. for 70 minutes while blowing gas at a rate of 3.4 cm per second, the FeCO 3 Into an aqueous solution containing 2.8 g of air, 2.8 cm of air was aerated at a temperature of 47 ° C. for 5.0 hours to generate goethite particles. The pH during air ventilation was 8.5 to 9.5.
[0088]
The suspension containing the obtained goethite particles was washed with a filter press, and the obtained press cake was extruded with a molding plate having a pore diameter of 4 mm using a compression molding machine and dried at 120 ° C. to obtain a goethite particle powder. It was set as the granulated material.
[0089]
The goethite particles contained in the granulated product thus obtained were particles having a spindle shape with an average major axis diameter of 0.30 μm and an axial ratio (major axis diameter / minor axis diameter) of 12.5. BET specific surface area is 85m 2 / G, S content was 400 ppm.
[0090]
The granulated product is heated at 300 ° C. to form hematite particles and dry pulverized. Then, it is poured into water and 70% sulfuric acid is added at a rate of 10 ml / kg and stirred. Thereafter, it was dehydrated into a press cake, extruded using a molding plate having a pore diameter of 3 mm using a compression molding machine, and dried at 120 ° C. to obtain a granulated product of hematite particles.
[0091]
The hematite particle powder constituting the granulated product obtained here was a spindle-shaped particle having an average major axis diameter of 0.24 μm and an axial ratio (major axis diameter / minor axis diameter) of 10.5. The S content was 3100 ppm.
[0092]
100 g of the granulated product of the goethite particle powder is introduced into a fixed bed reducing device, and H 2 While the gas was bubbled, the mixture was reduced at 450 ° C. for 180 minutes until it was completely α-Fe. Next, N 2 After switching to gas and allowing to cool to room temperature, 300 ml of ion-exchanged water was directly introduced into the reduction furnace and taken out as it was as an aqueous suspension containing 18% by weight of iron composite particle powder. It is a purifying agent according to the present invention).
[0093]
Next, the aqueous suspension was filtered and dried in the air at 40 ° C. for 3 hours to obtain iron composite particle powder for purification treatment.
[0094]
The obtained iron composite particle powder for purification treatment was observed with a scanning electron microscope (30000 times). As a result, it was rice-grained, the average particle diameter was 0.10 μm, mainly α-Fe, and saturated magnetization. Value 160 Am 2 / Kg (160 emu / g), BET specific surface area 26 m 2 / G, crystallite size of 290 kg, Fe content was 89.5% by weight. The S content was 3800 ppm and the carbon content was 0.09% by weight. Cd, Pb, As, and Hg were not detected. As a result of X-ray diffraction, it was confirmed that α-Fe and magnetite were present. The α-Fe content obtained from the calibration curve is 95.7% by weight. 110 (Α-Fe) and D 311 (Magnetite) strength ratio D 110 / (D 110 + D 311 ) Was 0.91.
[0095]
<Purification of soil contaminated with heavy metals and other harmful substances with iron composite particles>
Into a vial, Pre-moist sandy soil 20g (under 2mm mesh sieve) When 1 g of the obtained iron composite particle powder for purification treatment and 27.0 ml of ion-exchanged water were injected, and a 1000 ppm standard solution (Kanto Chemical Co., Ltd.) was added so that cadmium, lead, arsenic, selenium, and cyan were each 10 ppm. 0.3 ml each, and 1.5 ml from a 1000 ppm standard solution (manufactured by Kanto Chemical Co., Ltd.) so that hexavalent chromium is 50 ppm, and a total of 3.0 ml is injected so that the total amount is 100 ppm. . The lid was immediately covered with a rubber stopper with a fluororesin liner, and the top was firmly tightened with an aluminum seal. The vial was shaken with a paint conditioner (manufactured by Red Devil) for 16 hours, and then solid-liquid separated using a 0.45 μm membrane filter.
[0096]
Then, the same treatment was performed until a solid content (50 g) and a filtrate (300 ml) required for the measurement were obtained. Based on the Environmental Agency Notification No. 10 “Environmental Standards Concerning Groundwater Water Pollution”, the filtrate was dried in the atmosphere at 40 ° C. for 3 hours to obtain a sample, and the Environmental Agency Notification No. 46 “ The analysis was based on the “environmental standards for soil contamination”. As a result, cadmium in the solution is less than 0.001 mg / l, lead is less than 0.005 mg / l, hexavalent chromium is less than 0.04 mg / l, arsenic is less than 0.001 mg / l, selenium is less than 0.002 mg / l, cyan is Undetected, elution amount from solid was less than 0.001 mg / l cadmium, less than 0.005 mg / l lead, less than 0.04 mg / l hexavalent chromium, less than 0.001 mg / l arsenic, 0.002 mg / selenium Less than l and cyan were not detected.
[0097]
<Purification treatment with iron composite particles of groundwater contaminated with toxic substances such as heavy metals>
Into a 50 ml brown vial (actual volume 68 ml), 1 g of the iron composite particle powder for purification treatment obtained here and 27.0 ml of ion-exchanged water were injected, and 10 ppm each of cadmium, lead, arsenic, selenium and cyanide. Inject 0.3 ml each from 1000 ppm standard solution (manufactured by Kanto Chemical Co., Ltd.) and inject 1.5 ml from 1000 ppm standard solution (manufactured by Kanto Chemical Co., Ltd.) to 50 ppm hexavalent chromium. A total of 3.0 ml was injected to 100 ppm. The lid was immediately covered with a rubber stopper with a fluororesin liner, and the top was firmly tightened with an aluminum seal. The vial was shaken with a paint conditioner (manufactured by Red Devil) for 16 hours, and then solid-liquid separated using a 0.45 μm membrane filter.
[0098]
Next, the same treatment was performed until a solid content and a filtrate required for measurement were obtained. Based on the Environmental Agency Notification No. 10 “Environmental Standards for Groundwater Water Pollution”, the filtrate was dried in the atmosphere at 40 ° C. for 3 hours to obtain a sample. The analysis was based on the “environmental standards for soil contamination”. As a result, cadmium in the solution is less than 0.001 mg / l, lead is less than 0.005 mg / l, hexavalent chromium is less than 0.04 mg / l, arsenic is less than 0.001 mg / l, selenium is less than 0.002 mg / l, cyan is Undetected, elution amount from solid was less than 0.001 mg / l cadmium, less than 0.005 mg / l lead, less than 0.04 mg / l hexavalent chromium, less than 0.001 mg / l arsenic, 0.002 mg / selenium Less than l and cyan were not detected.
[0099]
<Purification treatment of soil contaminated with toxic substances such as heavy metals>
Into a vial, Pre-moist sandy soil 20g (under 2mm mesh sieve) When 5.6 g of the purification agent (containing 18% by weight of iron composite particle powder) and 22.4 ml of ion-exchanged water thus obtained were injected, and cadmium, lead, arsenic, selenium and cyan were each 10 ppm. Inject 0.3 ml each from 1000 ppm standard solution (manufactured by Kanto Chemical Co., Ltd.), and inject 1.5 ml from 1000 ppm standard solution (manufactured by Kanto Chemical Co., Ltd.) so that hexavalent chromium is 50 ppm. A total of 3.0 ml was injected. The lid was immediately covered with a rubber stopper with a fluororesin liner, and the top was firmly tightened with an aluminum seal. The vial was shaken with a paint conditioner (manufactured by Red Devil) for 16 hours, and then solid-liquid separated using a 0.45 μm membrane filter.
[0100]
Next, the same treatment was performed until a solid content and a filtrate required for measurement were obtained. Based on the Environmental Agency Notification No. 10 “Environmental Standards Concerning Groundwater Water Pollution”, the filtrate was dried in the atmosphere at 40 ° C. for 3 hours to obtain a sample, and the Environmental Agency Notification No. 46 “ The analysis was based on the “environmental standards for soil contamination”. As a result, cadmium in the solution is less than 0.001 mg / l, lead is less than 0.005 mg / l, hexavalent chromium is less than 0.04 mg / l, arsenic is less than 0.001 mg / l, selenium is less than 0.002 mg / l, cyan is Undetected, elution amount from solid was less than 0.001 mg / l cadmium, less than 0.005 mg / l lead, less than 0.04 mg / l hexavalent chromium, less than 0.001 mg / l arsenic, 0.002 mg / selenium Less than l and cyan were not detected.
[0101]
<Purification treatment with a purification agent for groundwater contaminated with toxic substances such as heavy metals>
5.6 g of the cleaning agent (containing 18% by weight of iron composite particle powder) and 22.4 ml of ion-exchanged water are injected into 50 ml of brown vial (actual volume 68 ml), and each of cadmium, lead, arsenic, selenium and cyanide is added. Inject 0.3 ml each from 1000 ppm standard solution (manufactured by Kanto Chemical Co., Ltd.) to 10 ppm, and inject 1.5 ml from 1000 ppm standard solution (manufactured by Kanto Chemical Co., Ltd.) to 50 ppm hexavalent chromium. A total of 3.0 ml was injected so that the total amount was 100 ppm. The lid was immediately covered with a rubber stopper with a fluororesin liner, and the top was firmly tightened with an aluminum seal. The vial was shaken with a paint conditioner (manufactured by Red Devil) for 16 hours, and then solid-liquid separated using a 0.45 μm membrane filter.
[0102]
Next, the same treatment was performed until a solid content and a filtrate required for measurement were obtained. Based on the Environmental Agency Notification No. 10 “Environmental Standards Concerning Groundwater Water Pollution”, the filtrate was dried in the atmosphere at 40 ° C. for 3 hours to obtain a sample, and the Environmental Agency Notification No. 46 “ The analysis was based on the “environmental standards for soil contamination”. As a result, cadmium in the solution is less than 0.001 mg / l, lead is less than 0.005 mg / l, hexavalent chromium is less than 0.04 mg / l, arsenic is less than 0.001 mg / l, selenium is less than 0.002 mg / l, cyan is Undetected, elution amount from solid was less than 0.001 mg / l cadmium, less than 0.005 mg / l lead, less than 0.04 mg / l hexavalent chromium, less than 0.001 mg / l arsenic, 0.002 mg / selenium Less than l and cyan were not detected.
[0103]
[Action]
In the iron composite particles for purification treatment according to the present invention, α-Fe of the iron composite particles dissolves, and the dissolved α-Fe reacts with a heavy metal to insolubilize the heavy metal and the like.
[0104]
That is, since the iron composite particles for purification treatment according to the present invention have a fine particle size and retain high activity, α-Fe is easily dissolved at room temperature without heating, and is further contained in soil. The water or groundwater is efficiently decomposed to generate hydrogen or a hydroxyl group and always become an alkaline region locally, so that the dissolution reaction of α-Fe proceeds gradually. Next, dissolved α-Fe and heavy metals and other harmful substances are taken at the interface of the iron composite particles, and hydroxyl groups, oxygen or dissolved oxygen, etc. due to decomposition of water are taken in and spinel ferrite formation proceeds continuously, and harmful substances such as heavy metals are removed. The inventor presumes that it is insolubilized. It is also presumed that S contained in the iron composite particles also contributes to the dissolution of α-Fe locally.
[0105]
In addition, the ferritization reaction between dissolved α-Fe and toxic substances such as heavy metals can be used to efficiently insolubilize toxic substances such as heavy metals because the grains grow epitaxially with the surface layer magnetite having a spinel structure as a seed. The inventor estimates.
[0106]
In the present invention, the process of adjusting the pH by adding an acid or alkali, the heat treatment, and the forced oxidation treatment by air blowing, etc. are also unnecessary, so that harmful substances such as heavy metals can be efficiently insolubilized. In addition, since the iron composite particles for purification treatment do not change their characteristics over time, they can insolubilize harmful substances such as heavy metals over a long period of time.
[0107]
【Example】
Next, examples and comparative examples of the present invention will be given.
[0108]
<Goethite particles>
The goethite particles shown in Table 1 were prepared as goethite particles.
[0109]
Goethite particles 2
Fe 2+ 1.28 l of ferrous sulfate aqueous solution containing 1.50 mol / l and 30.2 l of 0.44-N NaOH aqueous solution (Fe in ferrous sulfate aqueous solution) 2+ This corresponds to 0.35 equivalents. And a ferrous sulfate aqueous solution containing Fe (OH) 2 at a pH of 6.7 and a temperature of 38 ° C. was produced. Next, Fe (OH) 2 Into the aqueous ferrous sulfate solution containing 130 g of air, 130 l / min of air was passed at a temperature of 40 ° C. for 3.0 hours to generate goethite core particles.
[0110]
5.4N Na was added to the ferrous sulfate aqueous solution containing the goethite core particles (the amount of the goethite core particles was 35 mol% with respect to the generated goethite particles). 2 CO 3 7.0 l of aqueous solution (Fe in residual ferrous sulfate aqueous solution 2+ This corresponds to 1.5 equivalents. ) Was added, and 130 liters of air was aerated for 4 hours at a pH of 9.4 and a temperature of 42 ° C. to produce goethite particles. The suspension containing the obtained goethite particles was washed with a filter press, and the obtained press cake was extruded with a molding plate having a pore diameter of 4 mm using a compression molding machine and dried at 120 ° C. to obtain a goethite particle powder. It was set as the granulated material.
[0111]
The goethite particle powder contained in the granulated product thus obtained was a needle-like particle having an average major axis diameter of 0.33 μm and an axial ratio (major axis diameter / minor axis diameter) of 25.0. BET specific surface area is 70m 2 / G, S content was 4000 ppm.
[0112]
[Table 1]
Iron composite particle powder for purification treatment: Examples 1 to 8, Comparative Example 1;
Except for various changes in the types of goethite particles, the temperature of heat dehydration, the presence or absence and addition amount of sulfuric acid to the suspension containing hematite particles, the temperature of heat reduction, and the retention time in water (days) The iron composite particle powder for purification treatment was obtained in the same manner as the embodiment of the invention.
[0114]
The production conditions at this time are shown in Table 2, and the properties of the obtained iron composite particle powder for purification treatment are shown in Table 3.
[0115]
In Comparative Example 2, 100 g of the granulated product of the goethite particle powder 2 was introduced into a rolling reduction device, 2 It is a magnetite particle powder that does not contain α-Fe and has been reduced to 300% at 300 ° C. for 180 minutes while allowing gas to pass.
Comparative Example 3 and Comparative Example 4 are electrolytic iron powders.
[0116]
[Table 2]
[Table 3]
<Purification treatment of contaminated soil and contaminated groundwater>
Examples 9-16, Comparative Examples 5-8;
Contaminated soil or contaminated groundwater was treated in the same manner as in the above-described embodiment except that the type of the iron composite particle powder for purification treatment and the type of the purification agent were variously changed.
[0119]
The processing conditions and measurement results at this time are shown in Tables 4 and 5.
[0120]
[Table 4]
[Table 5]
<Durability of catalyst activity>
Purifying treatment was performed in the same manner as the evaluation method described above for each purifying agent retained in water for 4 days (Example 3 and Example 7) and 30 days (Example 4 and Example 8). As a result, when the purifying agent according to the present invention is used, harmful substances such as heavy metals in soil and groundwater are taken in and ferritization with harmful substances such as heavy metals has progressed for a long time. It is clear that the purifying agent according to the invention maintains the insolubilizing effect of harmful substances such as heavy metals over a long period of time.
[0123]
【The invention's effect】
The iron composite particle powder for purification treatment according to the present invention and the purification agent comprising the powder as an active ingredient are effective and sustainable for harmful substances such as heavy metals such as cadmium, lead, hexavalent chromium, arsenic, selenium, and cyanide. Therefore, it is suitable for the purification of soil and groundwater contaminated by toxic substances such as heavy metals.
[0124]
Therefore, it can be said that the industrial applicability of the present invention is very large.
Claims (8)
Priority Applications (8)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2002311957A JP4639029B2 (en) | 2002-10-25 | 2002-10-25 | Soil contaminated with toxic substances such as heavy metals, iron composite particle powder for purification treatment of soil and groundwater, its manufacturing method, purification agent containing the iron composite particle powder, its manufacturing method and soil contaminated with toxic substances such as heavy metals Groundwater purification method |
| KR1020020075808A KR100921261B1 (en) | 2001-12-04 | 2002-12-02 | Iron Particles for Purifying Contaminated Soil or Ground Water, Process for Producing the Iron Particles, Purifying Agent Comprising the Iron Particles, Process for Producing the Purifying Agent and Method of Purifying Contaminated Soil or Ground Water |
| US10/308,175 US7022256B2 (en) | 2001-12-04 | 2002-12-03 | Iron particles for purifying contaminated soil or ground water |
| EP02258342A EP1318103B1 (en) | 2001-12-04 | 2002-12-03 | Iron particles for purifying contaminated soil or ground water |
| ES02258342T ES2336429T3 (en) | 2001-12-04 | 2002-12-03 | IRON PARTICLES TO PURIFY EARTH OR CONTAMINATED GROUNDWATER. |
| DE60234568T DE60234568D1 (en) | 2001-12-04 | 2002-12-03 | Iron particles for the remediation of contaminated soil or groundwater |
| AT02258342T ATE450478T1 (en) | 2001-12-04 | 2002-12-03 | IRON PARTICLES FOR REMEDIATION OF CONTAMINATED SOIL OR GROUNDWATER |
| US11/324,369 US7220366B2 (en) | 2001-12-04 | 2006-03-07 | Process for purifying contaminated soil or groundwater with iron particles |
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| JP2002311957A JP4639029B2 (en) | 2002-10-25 | 2002-10-25 | Soil contaminated with toxic substances such as heavy metals, iron composite particle powder for purification treatment of soil and groundwater, its manufacturing method, purification agent containing the iron composite particle powder, its manufacturing method and soil contaminated with toxic substances such as heavy metals Groundwater purification method |
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| JP2006116477A (en) * | 2004-10-22 | 2006-05-11 | Miura Co Ltd | Arsenic removing agent and arsenic removing method |
| JP2006152126A (en) * | 2004-11-29 | 2006-06-15 | Miura Co Ltd | Cadmium elution inhibitor and method for inhibiting cadmium elution |
| JP4519665B2 (en) * | 2005-01-27 | 2010-08-04 | 関東電化工業株式会社 | Recovery method for heavy metal components |
| JP4861718B2 (en) * | 2006-02-16 | 2012-01-25 | 国立大学法人群馬大学 | Treatment of processing object containing heavy metal component and method for recovering heavy metal component from the processing object |
| JP5887972B2 (en) * | 2012-02-10 | 2016-03-16 | 宇部興産株式会社 | Treatment method of contaminated soil |
| KR102544214B1 (en) * | 2020-02-20 | 2023-06-16 | 고려대학교 산학협력단 | Iron carbonate composites for removing heavy metal and preparation method thereof |
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