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】
【0113】
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】
【0117】
【表3】
【0118】
<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】
【0121】
【表5】
【0122】
<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]
[0113]
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]
[0117]
[Table 3]
[0118]
<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]
[0121]
[Table 5]
[0122]
<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)
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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 |
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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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 |
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