JP3965542B2 - Method for treating chromium oxide-containing soil - Google Patents

Description

【００１９】
表１においては、還元能力として、未エージング高炉徐冷スラグまたは溶銑予備処理スラグそれぞれ１kg当たりの、溶液中Cr⁶⁺の減少量を、還元能力として示した。
表１に示すように、未エージング高炉徐冷スラグ、溶銑予備処理スラグがCr⁶⁺を還元する能力を有することが分かる。
【００２０】
未エージング高炉徐冷スラグ、溶銑予備処理スラグがCr⁶⁺の還元能力を有する理由は、これらの物質中に存在するＳ、S^2- 、S₂O₃ ^2-などの酸化数が＋５価以下の還元性硫黄が酸化することによってCr⁶⁺が還元されるためと考えられる。
次に、本発明者らは、試薬のCrO₃を純水に溶解し、Cr⁶⁺濃度を100mg/l とした溶液10リットルに、酸化数が＋５価以下の還元性硫黄を0.05重量％含有する高炉スラグ溶出水100gを添加し、６時間震盪後、溶液中のCr⁶⁺の濃度の測定結果からCr⁶⁺の減少量を調査した。
【００２１】
表２に調査結果を示す。
【００２２】
【表２】

【００２３】
表２においては、還元能力として、高炉スラグ溶出水１kgあたりの、溶液中Cr⁶⁺の減少量を、還元能力として示した。
表２に示すように、高炉スラグ溶出水を用いた場合も、単位重量当たり、未エージング高炉徐冷スラグと同等のCr⁶⁺の還元能力を有することが分かる。
以上の実験結果および土壌の処理実験結果に基づき、本発明者らは、クロム酸化物含有土壌中のCr⁶⁺を効果的かつ経済性に優れた方法でCr³⁺などに還元する方法として、好ましくは▲１▼スラグ、高炉スラグ溶出水を土壌と混合する方法、▲２▼スラグ、高炉スラグ溶出水を土壌に注入する方法によって、クロム酸化物含有土壌とスラグ、高炉スラグ溶出水とを接触せしめる本発明に想到した。
【００２４】
以下、本発明における[I] クロム酸化物含有土壌、[II]スラグ、[III] 高炉スラグ溶出水、[IV]クロム酸化物含有土壌の処理方法の順に説明する。
[I] クロム酸化物含有土壌：
クロム酸化物含有土壌とは、クロム鉱滓やCr⁶⁺廃液などで汚染されたCrO₃、CrO₄ ^2-などCr⁶⁺を含有する土壌である。
【００２５】
[II]スラグ：
本発明で用いられるスラグは未エージング高炉徐冷スラグおよび／または溶銑予備処理スラグであるが、酸化数が＋５価以下の硫黄を含有することが好ましい。
これは、クロム酸化物含有土壌と酸化数が＋５価以下の硫黄を含有するスラグとを接触せしめることによって、スラグ中の酸化数が＋５価以下の硫黄とCr⁶⁺が反応し、クロム酸化物含有土壌中のCr⁶⁺が還元されるためである。
【００２６】
本発明においては、スラグとして、未エージング高炉徐冷スラグおよび／または溶銑予備処理スラグを用いる。
なお、上記した未エージング高炉徐冷スラグとは、黄濁水を発生するスラグ、すなわち、JIS A 5015付属書１の呈色判定試験方法により、呈色があるスラグのことであり、概ね、自然エージング３ヶ月未満の高炉徐冷スラグである。
【００２７】
さらには、冷却、破砕直後、すなわち破砕後１週間以内の高炉徐冷スラグである未エージング高炉徐冷スラグを用いることが、より好ましい。
また、上記した溶銑予備処理スラグは、高炉において溶銑の脱硫、脱燐を行う際に得られるスラグである。
上記したスラグを用いる利点として、下記▲１▼、▲２▼が挙げられる。
【００２８】
▲１▼処理時間の短縮：
上記したスラグを用いることによって、短時間で、クロム酸化物含有土壌のCr⁶⁺溶出量が、環境基準値である0.05mg/l以下を達成できる。
これに対して、還元剤として単体硫黄を用いた場合、クロム酸化物含有土壌のCr⁶⁺溶出量は、環境基準値である0.05mg/l以下を達成することができない。
【００２９】
これは、単体硫黄の場合、空気中の酸素で酸化され還元能力が低下するのに対して、スラグ中のS^2- 、S₂O₃ ^2-などの還元性硫黄成分は、空気中の酸素によって酸化されにくいためと考えられる。
▲２▼還元されて生成したCr³⁺の安定化：
前記したスラグは、アルカリ性であるため、還元されて生成したCr³⁺がCr(OH)₃ の形態となって安定化される。
【００３０】
[III] 高炉スラグ溶出水：
高炉スラグ溶出水としては、酸化数が＋５価以下の硫黄を含有する高炉スラグ溶出水を用いることが好ましい。
これは、クロム酸化物含有土壌と酸化数が＋５価以下の硫黄を含有する高炉スラグ溶出水とを接触せしめることによって、高炉スラグ溶出水中の酸化数が＋５価以下の硫黄とCr⁶⁺が反応し、クロム酸化物含有土壌中のCr⁶⁺が還元されるためである。
【００３１】
また、高炉スラグ溶出水としては、酸化数が＋５価以下の硫黄の含有量が合計量で0.03重量％超えである高炉スラグ溶出水を用いることが好ましい。
これは、酸化数が＋５価以下の硫黄の含有量が合計量で0.03重量％超えの高炉スラグ溶出水を用いることによって、クロム酸化物含有土壌中のCr⁶⁺を効果的に還元できるためである。
【００３２】
なお、本発明において、酸化数が＋５価以下の硫黄の量とは、全硫黄量からSO₄ ²⁺ 中のＳ分を差し引いた硫黄の量を示す。
さらに、高炉スラグ溶出水としては、例えば、未エージング高炉徐冷スラグに水を散水して得られた溶出水、例えば高炉から排出された高温状態の高炉スラグに水を散水して得られた溶出水が好ましい。
【００３３】
また、高炉スラグ溶出水としては、概ね、自然エージング３個月未満の高炉徐冷スラグに水を散水して得られた溶出水を用いることが好ましく、例えば、高温状態の高炉スラグに水を散水して得られた溶出水が好ましい。
上記した高炉スラグ溶出水を用いることによって、短時間で、クロム酸化物含有土壌のCr⁶⁺溶出量を、環境基準値である0.05mg/l以下とすることができる。
【００３４】
これは、高炉スラグ溶出水中のS^2- 、S₂O₃ ^2-などの還元性硫黄成分が、空気中の酸素によって酸化されにくいためと考えられる。
高炉スラグ溶出水を用いる場合は、アルカリ性化合物と併用することが好ましい。
これは、アルカリ性化合物と併用することによって、還元されて生成したCr³⁺がCr(OH)₃ の形態となって安定化されるためである。
【００３５】
アルカリ性化合物としては、特に制限は受けないが、還元されて生成したCr³⁺の安定化に対する効果、および経済性の面から、転炉スラグ、Ca(OH)₂ 、CaCO₃ 、石灰石およびドロマイトなどから選ばれる１種または２種以上を用いることが好ましい。
[IV]クロム酸化物含有土壌の処理方法：
以下、前記した第１の発明〜第３の発明および各発明のより好適な態様について説明する。
【００３６】
(1)第１の発明：
第１の発明は、クロム酸化物含有土壌と、未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上とを接触せしめるクロム酸化物含有土壌の処理方法である。
上記した第１の発明の第１の好適態様は、クロム酸化物含有土壌と、未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上とを混合、接触せしめるクロム酸化物含有土壌の処理方法である。
【００３７】
上記した第１の発明の第１の好適態様によれば、クロム酸化物含有土壌と未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上とを混合することによって、クロム酸化物含有土壌が均一にスラグ、高炉スラグ溶出水と接触し、この結果スラグ、高炉スラグ溶出水の使用量を削減しつつ、クロム酸化物含有土壌のCr⁶⁺溶出量を環境基準値以下とすることが可能となった。
【００３８】
(2)第２の発明：
第２の発明は、クロム酸化物含有土壌と、未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上とを混合し、得られた混合物を埋設するクロム酸化物含有土壌の処理方法である。
上記した第２の発明の第１の好適態様は、クロム酸化物含有土壌層を掘削した後、掘削したクロム酸化物含有土壌と未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上とを混合し、埋め戻すクロム酸化物含有土壌の処理方法である。
【００３９】
(3)第３の発明：
第３の発明は、クロム酸化物含有土壌に、未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上を注入するクロム酸化物含有土壌の処理方法である。
すなわち、第３の発明は、未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上を、クロム酸化物含有土壌に注入することによって、未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上をクロム酸化物含有土壌と接触させて、クロム酸化物含有土壌中のCr⁶⁺を還元する方法である。
【００４０】
前記した第３の発明の第１の好適態様は、クロム酸化物含有土壌層に管を埋設するかまたは穴を穿設するかまたはその両者を施工し、管および／または穴によって、未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上を注入するクロム酸化物含有土壌の処理方法である。
なお、上記した第３の発明、第３の発明の第１の好適態様における未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上の注入速度および注入期間は特に制限されるものではない。
【００４１】
これは、クロム酸化物含有土壌の量、Cr⁶⁺含有量により最適注入速度、必要となる注入期間が異なるためである。
また、第３の発明の第１の好適態様における管および穴の本数は特に制限されるものではない。
これは、クロム酸化物含有土壌の量、Cr⁶⁺含有量により最適本数が異なるためである。
【００４２】
前記した第３の発明の第２の好適態様、第３の好適態様は、それぞれ、前記した第３の発明、第３の発明の第１の好適態様において、少なくとも高炉スラグ溶出水を注入すると共に、クロム酸化物含有土壌中の水を排出するクロム酸化物含有土壌の処理方法である。
すなわち、第３の発明の第２の好適態様、第３の好適態様は、高炉スラグ溶出水を注入するだけでなく、クロム酸化物含有土壌中の水を汲み上げ、排出することによって、注入した高炉スラグ溶出水の土壌中での拡散速度が向上し、短時間での還元処理を可能にするものである。
【００４３】
上記した第３の発明の第２の好適態様、第３の好適態様においては、クロム酸化物含有土壌層に２本以上の管を埋設するかまたは２本以上の穴を穿設するかまたは管の埋設および穴の穿設の両者を施工し、少なくとも１本の管または穴によって、クロム酸化物含有土壌に高炉スラグ溶出水を注入すると共に、他の少なくとも１本の管または穴によって、クロム酸化物含有土壌中の水を排出することが好ましい（第３の発明の第４の好適態様、第５の好適態様）。
【００４４】
なお、上記した第３の発明の第４の好適態様、第５の好適態様における管および／または穴は、少なくとも、注入用に１本、汲み上げ用に１本を配設し、その本数は特に限定されるものではない。
これは、クロム酸化物含有土壌の量、Cr⁶⁺含有量により最適本数が異なるためである。
【００４５】
また、上記した第３の発明の第２の好適態様〜第５の好適態様においては、クロム酸化物含有土壌への高炉スラグ溶出水の注入と該クロム酸化物含有土壌中からの水の排出は同時に行うこともでき、経時的に別の時間に行うこともでき、その順序は特に制限されるものではないが、クロム酸化物含有土壌に高炉スラグ溶出水を注入しつつ該クロム酸化物含有土壌中から水を排出することがより好ましい（第３の発明の第６の好適態様〜第９の好適態様）。
【００４６】
これは、高炉スラグ溶出水の注入と排出を経時的に並行して行うことによって、クロム酸化物含有土壌の処理時に、常に高炉スラグ溶出水の土壌中での拡散速度を大とすることが可能となり、さらに短時間で還元処理を行うことができるためである。
なお、上記した第３の発明の第６の好適態様〜第９の好適態様における、クロム酸化物含有土壌中の水を排出する速度は、高炉スラグ溶出水の注入速度とほぼ同一速度とすることが好ましく、排出速度が注入速度の0.5 〜２倍であることが好ましい。
【００４７】
これは、水を排出する速度が、高炉スラグ溶出水の注入速度よりも極端に遅いと、高炉スラグ溶出水の拡散速度が低下し、必要な処理時間が長くなり、逆に高炉スラグ溶出水の注入速度よりも極端に速いと、高炉スラグ溶出水のクロム酸化物含有土壌層中での滞留時間が短くなり効果が低下するためである。
(4)第４の発明：
第４の発明は、前記した第１の発明〜第３の発明、第１の発明〜第３の発明のそれぞれの好適態様のクロム酸化物含有土壌の処理方法において、クロム酸化物含有土壌に、さらに、アルカリ性化合物を接触もしくは混合もしくは注入することを特徴とするクロム酸化物含有土壌の処理方法である。
【００４８】
上記した第４の発明によれば、好ましくは転炉スラグ、Ca(OH)₂ 、CaCO₃ 、石灰石およびドロマイトなどから選ばれる１種または２種以上であるアルカリ性化合物を、クロム酸化物含有土壌層に注入することによって、Ca²⁺などのアルカリ土類金属、アルカリ金属のイオンが水分中に溶解し、クロム酸化物含有土壌層に拡散し、クロム酸化物含有土壌層がアルカリ性となる。
【００４９】
この結果、未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上によって還元されて生成したCr³⁺を、Cr(OH)₃ として安定化させ、Cr³⁺の再酸化を防止することができる。
なお、高炉スラグ溶出水はpHが10〜11のアルカリ性であり、高炉スラグ溶出水を大量にクロム酸化物含有土壌層に注入する場合は、クロム酸化物含有土壌層は、転炉スラグまたは消石灰などのアルカリ性化合物を注入しなくてもアルカリ性となり、Cr³⁺がCr(OH)₃ として安定化される。
【００５０】
したがって、第４の発明は、高炉スラグ溶出水などの注入量が少ないなどの原因により、クロム酸化物含有土壌層がアルカリ性とならない場合に効果的である。
なお、第４の発明における転炉スラグ、消石灰などアルカリ性化合物の粒径は注入可能な粒径であれば特に限定しないが、粒径が小さいほど好ましい。
【００５１】
これは、粒径が小さいほどCa²⁺などアルカリ土類金属、アルカリ金属のイオンの水分中への溶解速度が速く、少量で効果を発揮するからである。
なお、本発明におけるアルカリ性とは、環境庁告示46号法による溶出試験における溶出水のpHが８以上、より好ましくは該溶出水のpHが8.5 以上、さらに好ましくは該溶出水のpHが９以上のことを示す。
【００５２】
これは、pHが８以上において、Cr³⁺がCr(OH)₃ として安定化されるためである。
したがって、対象となる土壌の環境庁告示46号法による溶出試験における溶出水のpHが８以上、より好ましくは8.5 以上、さらに好ましくは９以上となるように転炉スラグ、消石灰などのアルカリ性化合物を添加することが好ましい。
【００５３】
なお、転炉スラグ、消石灰について、環境庁告示46号法による溶出試験をおこなった際の溶出液のpHは、転炉スラグの場合、pH＝12、消石灰の場合、pH＝13である。
なお、前記した第４の発明においてクロム酸化物含有土壌にアルカリ性化合物を混合する場合は、クロム酸化物含有土壌と未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上とアルカリ性化合物とを混合した後、得られた混合物を埋設することが好ましい。
【００５４】
また、前記した第４の発明においてクロム酸化物含有土壌にアルカリ性化合物を混合する場合は、クロム酸化物含有土壌層を掘削した後、掘削したクロム酸化物含有土壌と未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上とアルカリ性化合物とを混合し、埋め戻すことが好ましい。
また、前記した第４の発明においてクロム酸化物含有土壌にアルカリ性化合物を注入する場合は、クロム酸化物含有土壌層に管を埋設するかまたは穴を穿設するかまたはその両者を施工し、管および／または穴によってアルカリ性化合物を注入することが好ましい。
【００５５】
さらには、アルカリ性化合物を注入する場合は、アルカリ性化合物を添加した高炉スラグ溶出水を注入することがより好ましい。
なお、前記した第１の発明〜第４の発明、第１の発明〜第４の発明の各好適態様における未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上の好適な使用量は、土壌の密度、pH、Cr⁶⁺含有量などに依存するため、特に限定はされないが、クロム酸化物含有土壌100 重量部に対して使用する未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水から選ばれる１種以上中の酸化数が＋５価以下の硫黄の量が合計量として0.05重量部以上、さらに好ましくは0.5 〜５重量部を満足することが好ましい。
【００５６】
上記した合計量が少なすぎる場合は、クロム酸化物含有土壌のCr⁶⁺溶出量の低減効果が必ずしも十分得られず、逆に多すぎる場合は、Cr⁶⁺溶出量の低減効果が飽和し経済的でない。
【００５７】
【実施例】
以下、本発明を実施例に基づいてさらに具体的に説明する。
本実施例においては、重クロム酸ナトリウム製造の際に発生したクロム鉱滓またはCr⁶⁺含有廃液によって汚染された表３に示すCr⁶⁺汚染土壌−Ａ、Ｂ、Ｃの処理実験を行った。
【００５８】
還元剤としては、下記の還元剤▲１▼〜▲３▼（実施例）、▲４▼、▲５▼（比較例）を用いた。
▲１▼未エージング高炉徐冷スラグ：冷却、破砕後、１週間以内の高炉スラグ、粒径≦25mm
▲２▼溶銑予備処理スラグ：高炉における溶銑の脱硫、脱燐で得られたスラグ、粒径≦25mm
▲３▼高炉スラグ溶出水：高温状態の高炉スラグに水を散水して得られた溶出水、酸化数が＋５価以下の硫黄の含有量＝0.05wt％
▲４▼硫黄化合物：亜硫酸ナトリウム
▲５▼硫酸第一鉄
また、アルカリ性化合物としては、いずれも粒径が5mm 以下の転炉スラグまたは消石灰を用いた。
【００５９】
なお、本実施例におけるCr⁶⁺溶出量は、環境庁告示４６号法による溶出試験方法に基づいて測定した。
また、酸化数が＋５価以下の硫黄の量は、全硫黄量からSO₄ ²⁺ 中のＳ分を差し引いた硫黄の量を示す。
（実施例１〜７）
表３に示すCr⁶⁺溶出量がそれぞれ12.3mg/l、1.5mg/l 、0.2mg/l のCr⁶⁺汚染土壌−Ａ、Ｂ、Ｃを掘削した後、掘削した土壌−Ａ、土壌−Ｂ、土壌−Ｃと未エージング高炉徐冷スラグまたは溶銑予備処理スラグまたは高炉スラグ溶出水とを混合し、得られた混合物を埋設した。
【００６０】
なお、実施例６、７においては、さらにアルカリ性化合物として転炉スラグ、消石灰を上記した還元剤と併用した。
埋設後、経時的に、埋設した土壌をサンプリングし溶出量を測定し、土壌のCr⁶⁺溶出量が環境基準値である0.05mg/l以下となるのに必要な日数を調査した。
実験条件および実験結果を、表４に示す。
（実施例８、９、10）
表３に示すCr⁶⁺溶出量が12.3mg/lのCr⁶⁺汚染土壌−Ａの地層に管を埋め込み、高炉スラグ溶出水、または５mm以下に粉砕した転炉スラグを添加した高炉スラグ溶出水、または５mm以下に粉砕した消石灰を添加した高炉スラグ溶出水を管を通じてCr⁶⁺汚染土壌−Ａの地層に注入した。
【００６１】
注入量は、一日当たりの注入量(t) として、0.05×〔汚染土壌量(t) 〕／日とした。
注入開始後、前記した実施例１〜７と同様に、土壌のCr⁶⁺溶出量が0.05mg/l以下となるのに必要な日数を調査した。
実験条件および実験結果を、表４に示す。
（実施例11、12）
表３に示すCr⁶⁺溶出量が12.3mg/lのCr⁶⁺汚染土壌−Ａの地層に管を埋め込み、高炉スラグ溶出水または転炉スラグを添加した高炉スラグ溶出水を管を通じてCr⁶⁺汚染土壌−Ａの地層に注入すると共に、水平方向において上記した注入用の管から10ｍ離れた地層に埋め込んだ管から注入量と同量の水を汲み上げCr⁶⁺汚染土壌の水を排出した。
【００６２】
注入量および排出量は、一日当たりの注入量(t) 、排出量(t) として、0.1 ×〔汚染土壌量(t) 〕／日とした。
注入開始後、前記した実施例１〜７と同様に、土壌のCr⁶⁺溶出量が0.05mg/l以下となるのに必要な日数を調査した。
実験条件および実験結果を、表４に示す。
（比較例１、２）
表３に示すCr⁶⁺溶出量が12.3mg/lのCr⁶⁺汚染土壌−Ａを掘削した後、掘削した土壌−Ａと亜硫酸ナトリウムまたは硫酸第一鉄とを混合し、得られた混合物を埋設した。
【００６３】
埋設後、経時的に、埋設した土壌をサンプリングし溶出量を測定し、土壌のCr⁶⁺溶出量が0.05mg/l以下となるのに必要な日数を調査した。
実験条件および実験結果を、表４に示す。
（比較例３）
表３に示すCr⁶⁺溶出量が12.3mg/lのCr⁶⁺汚染土壌−Ａの地層に管を埋め込み、亜硫酸ナトリウムを溶解させた水を、管を通じてCr⁶⁺汚染土壌−Ａの地層に注入した。
【００６４】
注入量は、一日当たりの注入量(t) として、0.05×〔汚染土壌量(t) 〕／日とした。
注入開始後、前記した実施例１〜７と同様に、土壌のCr⁶⁺溶出量が0.05mg/l以下となるのに必要な日数を調査した。
実験条件および実験結果を、表４に示す。
（比較例４）
表３に示すCr⁶⁺溶出量が12.3mg/lのCr⁶⁺汚染土壌−Ａの地層に管を埋め込み、亜硫酸ナトリウムを溶解させた水を、管を通じてCr⁶⁺汚染土壌−Ａの地層に注入すると共に、水平方向において上記した注入用の管から10ｍ離れた地層に埋め込んだ管から注入量と同量の水を汲み上げCr⁶⁺汚染土壌の水を排出した。
【００６５】
注入量および排出量は、一日当たりの注入量(t) 、排出量(t) として、0.1 ×〔汚染土壌量(t) 〕／日とした。
注入開始後、前記した実施例１〜７と同様に、土壌のCr⁶⁺溶出量が0.05mg/l以下となるのに必要な日数を調査した。
実験条件および実験結果を、表４に示す。
【００６６】
表４に示されるように、本発明のクロム酸化物含有土壌の処理方法によれば、下記の効果が得られる。
(1)クロム酸化物含有土壌と還元剤との混合、埋設による、汚染土壌のCr⁶⁺溶出量の大幅な低減：
クロム酸化物含有土壌と、酸化数が＋５価以下の硫黄を含有する未エージング高炉徐冷スラグ、溶銑予備処理スラグ、高炉スラグ溶出水とを混合し、埋設することによって、スラグ、高炉スラグ溶出水の使用量を削減しつつ、クロム酸化物含有土壌のCr⁶⁺の溶出量を環境基準値以下にすることができる。
【００６７】
(2)クロム酸化物含有土壌への高炉スラグ溶出水の注入による、汚染土壌のCr⁶⁺溶出量の短時間かつ大幅な低減：
クロム酸化物含有土壌に高炉スラグ溶出水を注入することによって、上記した混合、埋設法に対してさらに短時間で、クロム酸化物含有土壌のCr⁶⁺の溶出量を環境基準値以下にすることができる。
【００６８】
(3)クロム酸化物含有土壌への高炉スラグ溶出水の注入および排出による、汚染土壌のCr⁶⁺溶出量の短時間かつ大幅な低減：
クロム酸化物含有土壌に高炉スラグ溶出水を注入するだけでなく、隣接した地層から水を汲み上げ、排出することによって、上記した注入法のみの場合よりもさらに短時間で、クロム酸化物含有土壌のCr⁶⁺の溶出量を環境基準値以下にすることができる。
【００６９】
(4)アルカリ性化合物との併用による酸性汚染土壌のCr⁶⁺溶出量の大幅な低減：還元剤とアルカリ性化合物を併用することによって、Cr⁶⁺の還元によって生成したCr³⁺をCr(OH)₃ の形態とし安定化することができ、その結果、酸性汚染土壌のCr⁶⁺溶出量を環境基準値以下にすることができる。
【００７０】
【表３】

【００７１】
【表４】

【００７２】
【表５】

【００７３】
【発明の効果】
本発明によれば、クロム鉱滓、Cr⁶⁺イオン含有廃液などによって汚染されたクロム酸化物含有土壌中のCr⁶⁺を短時間で完全に還元し、クロム酸化物含有土壌のCr⁶⁺の溶出量を環境基準値以下にすることが可能となった。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating chromium oxide-containing soil, and more specifically, Cr in chromium oxide-containing soil.⁶⁺Cr³⁺The present invention relates to a method for treating chromium oxide-containing soil that is reduced to the above.
[0002]
[Prior art]
Chromium slag generated during the production of chromium compounds such as sodium dichromate contains several percent of chromium oxide, some of which is chromium peroxide, ie Cr⁶⁺Exists as.
At present, chrome ore is reduced to roasted and Cr⁶⁺Cr³⁺There are known methods of detoxifying and detoxifying them by mixing them with chromium ore, contaminated soil, and ferrous sulfate (city and waste, Vol.7, No.2, p. .43).
[0003]
In addition, by spraying dead leaves on chromium elution water, Cr⁶⁺There is known a method for performing reduction (see Water, Vol. 34, No. 11, p. 18, 1992).
However, the treatment method using the above-described reduction roasting requires a large-scale facility, and the treatment method using ferrous sulfate easily loses the reduction ability because ferrous sulfate easily reacts with oxygen in the atmosphere. From, chrome ore, Cr⁶⁺Cr by the Environment Agency Notification No. 46 of Contaminated Soil Contained⁶⁺A large amount of ferrous sulfate is required to reduce the elution amount of selenium to below the environmental standard value, that is, 0.05 mg / l or less.
[0004]
Moreover, although the treatment method with dead leaves is effective in the elution water, there is a problem that a large amount of dead leaves are required, and the effect on solid matter such as soil is unknown.
[0005]
[Problems to be solved by the invention]
The present invention solves the above-mentioned problems of the prior art, and produces chromium slag and Cr generated in the production of chromium compounds such as sodium dichromate.⁶⁺Cr in soil containing chromium oxide contaminated by waste liquid containing ions⁶⁺It aims at providing the processing method of the chromium oxide containing soil which can perform the reduction | restoration process of this in a short time.
[0006]
[Means for Solving the Problems]
  The first invention is a chromium oxide-containing soil,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIt is the processing method of the chromium oxide containing soil characterized by making it contact.
  The first preferred embodiment of the first invention described above is a chromium oxide-containing soil,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slagElutionwater1 or more types selected fromIs a method for treating a chromium oxide-containing soil.
[0007]
  The second invention is a chromium oxide-containing soil,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromAnd burying the obtained mixture. A method for treating chromium oxide-containing soil.
  In the first preferred embodiment of the second invention described above, after excavating the chromium oxide-containing soil layer, the excavated chromium oxide-containing soil andUnaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIs a method for treating a chromium oxide-containing soil, characterized by mixing and backfilling.
[0008]
  3rd invention is to chromium oxide containing soil,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIs a method for treating a chromium oxide-containing soil.
  According to the first preferred embodiment of the third invention described above, a tube is embedded in the chromium oxide-containing soil layer or a hole is drilled or both are constructed, and the tube and / or the hole are used.Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIs a method for treating a chromium oxide-containing soil.
[0009]
The second preferred embodiment and the third preferred embodiment of the third invention are the same as the third preferred embodiment of the third invention and the first preferred embodiment of the third invention, respectively, while injecting at least blast furnace slag elution water. And a method for treating chromium oxide-containing soil, characterized in that water in the chromium oxide-containing soil is discharged.
In the second preferred embodiment and the third preferred embodiment of the third invention described above, whether two or more pipes are embedded in the chromium oxide-containing soil layer or two or more holes are drilled. Alternatively, both burial of the pipe and drilling of the hole are performed, and blast furnace slag elution water is injected into the chromium oxide-containing soil through at least one pipe or hole, and at least one other pipe or hole is used. It is preferable to discharge the water in the chromium oxide-containing soil (fourth preferred embodiment of the third invention, fifth preferred embodiment).
[0010]
In the second to fifth preferred embodiments of the third invention described above, water is discharged from the chromium oxide-containing soil while injecting blast furnace slag elution water into the chromium oxide-containing soil. Is more preferable (sixth to ninth preferred embodiments of the third invention).
4th invention is the processing method of chromium oxide containing soil of each suitable aspect of above-described 1st invention-3rd invention, 1st invention-3rd invention, In chromium oxide containing soil, Furthermore, it is the processing method of the chromium oxide containing soil characterized by contacting, mixing, or inject | pouring an alkaline compound.
[0011]
  In the above-described fourth invention, chromium oxide-containing soil,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIn contact with the alkaline compound, and when contacting the alkaline compound, soil containing chromium oxide,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIt is preferable to contact three or four of the alkaline compounds at the same time, but the order of contact is not particularly limited.
[0012]
  Moreover, in the above-mentioned 4th invention, chromium oxide containing soil,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromAnd mixing the alkaline compound with the chromium oxide-containing soil,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIn addition, it is preferable to mix three or four of the alkaline compounds at the same time and embed the obtained mixture, but the order of mixing and burying is not particularly limited.
[0013]
  Moreover, in the above-mentioned 4th invention, in chromium oxide containing soil,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromAnd then injecting the alkaline compound into the soil containing chromium oxide,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIt is preferable to inject two or three of the alkaline compounds at the same time, but the order of injection is not particularly limited.
[0014]
  The first to fourth inventions, the first preferred embodiment of the first invention, the first preferred embodiment of the second invention, the first preferred embodiment to the ninth invention of the third invention. In the preferred embodiment, the fourth invention, as described above.Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIt is preferable that at least one of the above contains sulfur having an oxidation number of +5 or less (second preferred embodiment of the first invention, third preferred embodiment, second preferred embodiment of the second invention, second 3 preferred embodiments, tenth preferred embodiment to nineteenth preferred embodiment of the third invention, and first preferred embodiment of the fourth invention).
[0015]
  Furthermore, the first to fourth inventions described above, the first preferred embodiment to the third preferred embodiment of the first invention, the first preferred embodiment to the third preferred embodiment of the second invention, and the third preferred embodiment. In the first preferred embodiment to the nineteenth preferred embodiment of the present invention and the first preferred embodiment of the fourth invention, the slag described above is used.The, Unaged blast furnace slow cooling slag and / or hot metal pretreatment slagWasCanIt is characteristic.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
We have used the reagent CrO_ThreeIs dissolved in pure water, Cr⁶⁺Add 100g of unaged blast furnace slow-cooled slag or hot metal pre-treated slag immediately after cooling and crushing to 10 liter of solution with a concentration of 100mg / l, shake for 6 hours, and then add Cr in the solution.⁶⁺From the concentration measurement result of Cr⁶⁺The amount of decrease was investigated.
[0017]
Table 1 shows the survey results.
[0018]
[Table 1]

[0019]
In Table 1, as reducing capacity, Cr in solution per kg of unaged blast furnace slow-cooled slag or hot metal pretreated slag⁶⁺The amount of decrease was shown as the reducing ability.
As shown in Table 1, unaged blast furnace slag and hot metal pretreatment slag are Cr⁶⁺It can be seen that it has the ability to reduce
[0020]
Unaged blast furnace slag, hot metal pretreatment slag is Cr⁶⁺The reason for having the reducing ability of S, S present in these substances is^2-, S₂O_Three ^2-As a result of oxidation of reducing sulfur with an oxidation number of +5 or less, such as Cr⁶⁺Is considered to be reduced.
Next, we will use the CrO reagent._ThreeIs dissolved in pure water, Cr⁶⁺To 10 liters of a solution with a concentration of 100 mg / l, 100 g of blast furnace slag elution water containing 0.05% by weight of reducing sulfur with an oxidation number of +5 or less was added, and after shaking for 6 hours, Cr in the solution⁶⁺From the concentration measurement result of Cr⁶⁺The amount of decrease was investigated.
[0021]
Table 2 shows the survey results.
[0022]
[Table 2]

[0023]
In Table 2, as reducing capacity, Cr in solution per kg of blast furnace slag elution water⁶⁺The amount of decrease was shown as the reducing ability.
As shown in Table 2, even when blast furnace slag elution water is used, Cr equivalent to unaged blast furnace slow-cooled slag per unit weight⁶⁺It can be seen that it has a reducing ability.
Based on the above experimental results and soil treatment experimental results, the present inventors have developed Cr in chromium oxide-containing soil.⁶⁺In an effective and economical way³⁺As a method of reducing to, etc., preferably, (1) slag, blast furnace slag elution water is mixed with soil, (2) slag, blast furnace slag elution water is injected into the soil, chromium oxide-containing soil and slag, The present invention has been conceived in which the effluent from blast furnace slag is brought into contact.
[0024]
Hereinafter, [I] chromium oxide-containing soil, [II] slag, [III] blast furnace slag elution water, and [IV] chromium oxide-containing soil will be described in this order.
[I] Chromium oxide-containing soil:
Chromium oxide-containing soil is chromium ore and Cr⁶⁺CrO contaminated with waste liquid_Three, CrO_Four ^2-Cr⁶⁺It contains soil.
[0025]
  [II] Slag:
  The slag used in the present invention isUnaged blast furnace slag and / or hot metal pretreatment slagHowever, it is preferable to contain sulfur having an oxidation number of +5 or less.
  This is due to the contact between the chromium oxide-containing soil and slag containing sulfur with an oxidation number of +5 or less, and sulfur with an oxidation number of +5 or less and Cr in the slag.⁶⁺Reacts with Cr in chromium oxide-containing soil⁶⁺This is because is reduced.
[0026]
  In the present invention, as the slag, unaged blast furnace slow cooling slag and / or hot metal pretreatment slag is used.Ru.
  The above-mentioned non-aging blast furnace slow cooling slag is a slag that generates yellow water, that is, a slag that is colored by the color judgment test method of Appendix 1 of JIS A 5015, and is generally natural aging. Blast furnace slow cooling slag for less than 3 months.
[0027]
Furthermore, it is more preferable to use unaged blast furnace chilled slag immediately after cooling and crushing, that is, blast furnace chilled slag within one week after crushing.
The hot metal pretreatment slag described above is slag obtained when desulfurizing and dephosphorizing the hot metal in a blast furnace.
Advantages of using the above-described slag include the following (1) and (2).
[0028]
(1) Reduction of processing time:
By using the above slag, Cr in the chromium oxide-containing soil can be obtained in a short time.⁶⁺The elution amount can achieve the environmental standard value of 0.05 mg / l or less.
In contrast, when elemental sulfur is used as the reducing agent, Cr in the soil containing chromium oxide⁶⁺The elution amount cannot achieve the environmental standard value of 0.05 mg / l or less.
[0029]
This is because, in the case of simple sulfur, it is oxidized by oxygen in the air and the reducing ability is reduced, while S in the slag is reduced.^2-, S₂O_Three ^2-It is considered that reductive sulfur components such as are difficult to be oxidized by oxygen in the air.
(2) Cr produced by reduction³⁺Stabilization:
Since the above-mentioned slag is alkaline, it is produced by reducing Cr.³⁺Is Cr (OH)_ThreeTo be stabilized.
[0030]
[III] Blast furnace slag elution water:
As the blast furnace slag elution water, it is preferable to use blast furnace slag elution water containing sulfur having an oxidation number of +5 or less.
This is because the blast furnace slag elution water containing sulfur with an oxidation number of +5 or less is brought into contact with the chromium oxide-containing soil, and sulfur with an oxidation number of +5 or less and Cr⁶⁺Reacts with Cr in chromium oxide-containing soil⁶⁺This is because is reduced.
[0031]
Further, as the blast furnace slag elution water, it is preferable to use blast furnace slag elution water having a total content of sulfur having an oxidation number of +5 or less and exceeding 0.03% by weight.
This is because the blast furnace slag elution water with a total oxidation amount of sulfur with an oxidation number of +5 valence or less exceeds 0.03% by weight,⁶⁺This is because it can be effectively reduced.
[0032]
In the present invention, the amount of sulfur having an oxidation number of +5 or less is defined as SO_Four ²⁺The amount of sulfur after subtracting the S content is shown.
Furthermore, as blast furnace slag elution water, for example, elution obtained by sprinkling water into unaged blast furnace slow-cooled slag, for example, elution obtained by watering high temperature blast furnace slag discharged from the blast furnace Water is preferred.
[0033]
As the blast furnace slag elution water, it is generally preferable to use elution water obtained by sprinkling water into a blast furnace slow-cooled slag of less than 3 months of natural aging. For example, water is sprinkled into blast furnace slag in a high temperature state. The elution water obtained in this way is preferred.
By using the blast furnace slag elution water described above, Cr in the chromium oxide-containing soil can be obtained in a short time.⁶⁺The elution amount can be set to 0.05 mg / l or less which is the environmental standard value.
[0034]
This is because S in the effluent of blast furnace slag^2-, S₂O_Three ^2-This is probably because reductive sulfur components such as are difficult to be oxidized by oxygen in the air.
When using blast furnace slag elution water, it is preferable to use together with an alkaline compound.
This is because Cr is produced by reduction by using in combination with an alkaline compound.³⁺Is Cr (OH)_ThreeIt is because it becomes the form of and is stabilized.
[0035]
The alkaline compound is not particularly limited, but is produced by reducing Cr.³⁺Converter stabilization slag, Ca (OH)₂, CaCO_ThreeIt is preferable to use one or more selected from limestone and dolomite.
[IV] Method for treating soil containing chromium oxide:
Hereinafter, the above-described first to third inventions and more preferable aspects of each invention will be described.
[0036]
(1) First invention:
  The first invention is a chromium oxide-containing soil,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIt is the processing method of the chromium oxide containing soil which is made to contact.
  The first preferred embodiment of the first invention described above is a chromium oxide-containing soil,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIs a method of treating a chromium oxide-containing soil that is mixed and brought into contact with each other.
[0037]
  According to the first preferred embodiment of the first invention described above, the chromium oxide-containing soil andUnaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromThe chromium oxide-containing soil uniformly contacts the slag and blast furnace slag elution water, and as a result, the amount of slag and blast furnace slag elution water is reduced, while the chromium oxide-containing soil Cr is reduced.⁶⁺It became possible to make the elution amount below the environmental standard value.
[0038]
(2) Second invention:
  The second invention is a chromium oxide-containing soil,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromAnd a chromium oxide-containing soil treatment method in which the resulting mixture is embedded.
  In the first preferred embodiment of the second invention described above, after excavating the chromium oxide-containing soil layer, the excavated chromium oxide-containing soil andUnaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIt is a processing method of the chromium oxide containing soil which mixes and backfills.
[0039]
(3) Third invention:
  3rd invention is to chromium oxide containing soil,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIt is the processing method of the chromium oxide containing soil which inject | pours.
  That is, the third inventionUnaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromBy injecting into the chromium oxide containing soilUnaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIn the chromium oxide-containing soil⁶⁺Is a method of reducing
[0040]
  According to the first preferred embodiment of the third invention described above, a tube is embedded in the chromium oxide-containing soil layer or a hole is drilled or both are constructed, and the tube and / or the hole are used.Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIt is the processing method of the chromium oxide containing soil which inject | pours.
  In the above-described third invention, the first preferred embodiment of the third inventionUnaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromThe injection rate and the injection period are not particularly limited.
[0041]
This is the amount of chromium oxide-containing soil, Cr⁶⁺This is because the optimum injection rate and the required injection period differ depending on the content.
Further, the number of tubes and holes in the first preferred embodiment of the third invention is not particularly limited.
This is the amount of chromium oxide-containing soil, Cr⁶⁺This is because the optimum number varies depending on the content.
[0042]
The second preferred embodiment and the third preferred embodiment of the third invention are the same as the third preferred embodiment of the third invention and the first preferred embodiment of the third invention, respectively, while injecting at least blast furnace slag elution water. This is a method for treating chromium oxide-containing soil that discharges water in the chromium oxide-containing soil.
That is, the second preferred embodiment and the third preferred embodiment of the third invention are not only injecting blast furnace slag elution water, but also pumping up and discharging the water in the chromium oxide-containing soil. The diffusion rate of slag elution water in the soil is improved, and reduction treatment in a short time is enabled.
[0043]
In the second preferred embodiment and the third preferred embodiment of the third invention described above, two or more pipes are buried in the chromium oxide-containing soil layer, or two or more holes are bored or pipes. The blast furnace slag elution water is injected into the chromium oxide-containing soil through at least one pipe or hole, and chrome oxidation is performed through at least one other pipe or hole. It is preferable to discharge the water in the soil containing material (fourth preferred embodiment of the third invention, fifth preferred embodiment).
[0044]
It should be noted that at least one tube and / or hole is provided for injection and one for pumping in the fourth and fifth preferred embodiments of the third invention described above, and the number of tubes and / or holes is particularly large. It is not limited.
This is the amount of chromium oxide-containing soil, Cr⁶⁺This is because the optimum number varies depending on the content.
[0045]
In the second to fifth preferred embodiments of the third invention described above, injection of blast furnace slag elution water into the chromium oxide-containing soil and discharge of water from the chromium oxide-containing soil are performed as follows: It can be performed at the same time, and can be performed at different times over time, the order of which is not particularly limited, while the blast furnace slag elution water is injected into the chromium oxide-containing soil, the chromium oxide-containing soil It is more preferable to discharge water from the inside (sixth to ninth preferred embodiments of the third invention).
[0046]
By injecting and discharging blast furnace slag elution water in parallel over time, it is possible to always increase the diffusion rate of blast furnace slag elution water in the soil when treating chromium oxide-containing soil. This is because the reduction treatment can be performed in a shorter time.
In addition, the speed | rate which discharges the water in chromium oxide containing soil in the above-mentioned 6th suitable aspect-9th suitable aspect of 3rd invention shall be substantially the same speed as the injection speed of blast furnace slag elution water. The discharge rate is preferably 0.5 to 2 times the injection rate.
[0047]
This is because if the rate of discharging water is extremely slower than the injection rate of blast furnace slag elution water, the diffusion rate of blast furnace slag elution water will decrease, and the required treatment time will be longer. If the rate is extremely higher than the injection rate, the residence time in the chromium oxide-containing soil layer of blast furnace slag elution water is shortened and the effect is reduced.
(4) Fourth invention:
4th invention is the processing method of chromium oxide containing soil of each suitable aspect of above-described 1st invention-3rd invention, 1st invention-3rd invention, In chromium oxide containing soil, Furthermore, it is the processing method of the chromium oxide containing soil characterized by contacting, mixing, or inject | pouring an alkaline compound.
[0048]
According to the fourth invention described above, preferably converter slag, Ca (OH)₂, CaCO_ThreeBy injecting an alkaline compound that is one or more selected from limestone and dolomite into a chromium oxide-containing soil layer,²⁺Alkaline earth metals such as alkaline metal ions are dissolved in moisture and diffused into the chromium oxide-containing soil layer, and the chromium oxide-containing soil layer becomes alkaline.
[0049]
  As a result,Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromCr produced by reduction by³⁺Cr (OH)_ThreeStabilized as Cr³⁺Can be prevented from being reoxidized.
  The blast furnace slag elution water is alkaline with a pH of 10 to 11, and when injecting a large amount of blast furnace slag elution water into the chromium oxide-containing soil layer, the chromium oxide-containing soil layer is converted into converter slag or slaked lime, etc. It becomes alkaline without injecting alkaline compound of Cr, Cr³⁺Is Cr (OH)_ThreeAs stabilized.
[0050]
Therefore, the fourth invention is effective when the chromium oxide-containing soil layer does not become alkaline due to a small injection amount of blast furnace slag elution water or the like.
In addition, although the particle size of alkaline compounds, such as converter slag and slaked lime in 4th invention, will not be specifically limited if it is a particle size which can be inject | poured, it is so preferable that a particle size is small.
[0051]
This is because the smaller the particle size,²⁺This is because the alkaline earth metal and alkali metal ions are rapidly dissolved in water, and the effect is exhibited in a small amount.
The alkalinity in the present invention means that the pH of the elution water in the elution test by the Environmental Agency Notification No. 46 method is 8 or more, more preferably the pH of the elution water is 8.5 or more, more preferably the pH of the elution water is 9 or more. It shows that.
[0052]
This is because when the pH is 8 or more, Cr³⁺Is Cr (OH)_ThreeIt is because it is stabilized as.
Therefore, alkaline compounds such as converter slag and slaked lime should be used so that the pH of the elution water in the dissolution test according to the Environmental Agency Notification No. 46 method of the target soil is 8 or more, more preferably 8.5 or more, and even more preferably 9 or more. It is preferable to add.
[0053]
  Regarding converter slag and slaked lime, the pH of the eluate when the dissolution test is conducted by the Environmental Agency Notification No. 46 method is pH = 12 for converter slag and pH = 13 for slaked lime.
  In addition, when mixing an alkaline compound with chromium oxide containing soil in the above-mentioned 4th invention, chromium oxide containing soil andUnaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIt is preferable to embed the obtained mixture after mixing the alkaline compound.
[0054]
  Moreover, when mixing an alkaline compound with chromium oxide containing soil in the above-mentioned 4th invention, after excavating the chromium oxide containing soil layer, the excavated chromium oxide containing soil andUnaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromIt is preferable to mix and backfill the alkaline compound.
  In addition, when the alkaline compound is injected into the chromium oxide-containing soil in the fourth invention described above, a pipe is embedded in the chromium oxide-containing soil layer or a hole is drilled, or both are constructed, It is preferable to inject the alkaline compound through the holes.
[0055]
  Furthermore, when injecting an alkaline compound, it is more preferable to inject blast furnace slag elution water to which an alkaline compound is added.
  In the preferred embodiments of the first to fourth inventions and the first to fourth inventions described above.Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromThe preferred amount of use is soil density, pH, Cr⁶⁺Since it depends on the content, etc., it is not particularly limited, but it is used for 100 parts by weight of chromium oxide-containing soil.Unaged blast furnace slag, hot metal pretreatmentSlug,Blast furnace slag elution water1 or more types selected fromThe amount of sulfur having an oxidation number of +5 or less is preferably 0.05 parts by weight or more, more preferably 0.5 to 5 parts by weight as a total amount.
[0056]
If the total amount is too small, Cr in the chromium oxide-containing soil⁶⁺If the elution amount reduction effect is not always sufficiently obtained,⁶⁺The effect of reducing the elution amount is saturated and not economical.
[0057]
【Example】
Hereinafter, the present invention will be described more specifically based on examples.
In this example, chromium ore generated during the production of sodium dichromate or Cr⁶⁺Cr as shown in Table 3 contaminated with waste liquid⁶⁺Treatment experiment of contaminated soil-A, B, and C was conducted.
[0058]
As the reducing agent, the following reducing agents (1) to (3) (Examples), (4) and (5) (Comparative Examples) were used.
(1) Unaged blast furnace slag: blast furnace slag within 1 week after cooling and crushing, grain size ≤25mm
(2) Hot metal pretreatment slag: Slag obtained by desulfurization and dephosphorization of hot metal in a blast furnace, particle size ≤ 25 mm
(3) Blast furnace slag elution water: Elution water obtained by sprinkling water into high temperature blast furnace slag, content of sulfur whose oxidation number is +5 or less = 0.05wt%
(4) Sulfur compounds: sodium sulfite
(5) Ferrous sulfate
In addition, as the alkaline compound, converter slag or slaked lime having a particle size of 5 mm or less was used.
[0059]
In this example, Cr⁶⁺The amount of dissolution was measured based on the dissolution test method according to the Environmental Agency Notification No. 46 method.
Also, the amount of sulfur with an oxidation number of +5 or less is calculated from the total sulfur_Four ²⁺The amount of sulfur after subtracting the S content is shown.
(Examples 1-7)
Cr shown in Table 3⁶⁺Elution amounts of 12.3 mg / l, 1.5 mg / l and 0.2 mg / l Cr⁶⁺After excavating the contaminated soil-A, B, C, the excavated soil-A, soil-B, soil-C and unaged blast furnace slow-cooled slag or hot metal pretreated slag or blast furnace slag elution water are mixed and obtained The mixture was buried.
[0060]
In Examples 6 and 7, converter slag and slaked lime were further used in combination with the reducing agent described above as alkaline compounds.
After embedding, over time, the buried soil was sampled and the amount of elution was measured.⁶⁺The number of days required for the elution amount to be 0.05 mg / l or less, which is the environmental standard value, was investigated.
Table 4 shows experimental conditions and experimental results.
(Examples 8, 9, and 10)
Cr shown in Table 3⁶⁺Elution amount of 12.3mg / l Cr⁶⁺Tubes are buried in the soil layer of contaminated soil-A, blast furnace slag elution water, blast furnace slag elution water added with converter slag crushed to 5 mm or less, or blast furnace slag elution water added with slaked lime crushed to 5 mm or less through the pipe. Cr⁶⁺Injected into the soil layer of contaminated soil-A.
[0061]
The injection amount was 0.05 × [contaminated soil amount (t)] / day as the injection amount per day (t).
After the start of injection, as in Examples 1 to 7, the soil Cr⁶⁺The number of days required for the elution amount to be 0.05 mg / l or less was investigated.
Table 4 shows experimental conditions and experimental results.
(Examples 11 and 12)
Cr shown in Table 3⁶⁺Elution amount of 12.3mg / l Cr⁶⁺Pipes were embedded in the soil layer of contaminated soil-A, and blast furnace slag elution water or blast furnace slag elution water added with converter slag was added through the pipe to Cr.⁶⁺Infused into the soil layer of contaminated soil-A, the same amount of water is pumped up from the tube embedded in the formation 10m away from the above-mentioned injection tube in the horizontal direction.⁶⁺Drained contaminated soil water.
[0062]
The injection amount and discharge amount were set to 0.1 × [contaminated soil amount (t)] / day as the injection amount (t) and discharge amount (t) per day.
After the start of injection, as in Examples 1 to 7, the soil Cr⁶⁺The number of days required for the elution amount to be 0.05 mg / l or less was investigated.
Table 4 shows experimental conditions and experimental results.
(Comparative Examples 1 and 2)
Cr shown in Table 3⁶⁺Elution amount of 12.3mg / l Cr⁶⁺After excavating the contaminated soil-A, the excavated soil-A and sodium sulfite or ferrous sulfate were mixed, and the resulting mixture was buried.
[0063]
After embedding, over time, the buried soil was sampled and the amount of elution was measured.⁶⁺The number of days required for the elution amount to be 0.05 mg / l or less was investigated.
Table 4 shows experimental conditions and experimental results.
(Comparative Example 3)
Cr shown in Table 3⁶⁺Elution amount of 12.3mg / l Cr⁶⁺A tube is embedded in the soil layer of contaminated soil-A, and water in which sodium sulfite is dissolved is added to the Cr through the tube.⁶⁺Injected into the soil layer of contaminated soil-A.
[0064]
The injection amount was 0.05 × [contaminated soil amount (t)] / day as the injection amount per day (t).
After the start of injection, as in Examples 1 to 7, the soil Cr⁶⁺The number of days required for the elution amount to be 0.05 mg / l or less was investigated.
Table 4 shows experimental conditions and experimental results.
(Comparative Example 4)
Cr shown in Table 3⁶⁺Elution amount of 12.3mg / l Cr⁶⁺A tube is embedded in the soil layer of contaminated soil-A, and water in which sodium sulfite is dissolved is added to the Cr through the tube.⁶⁺Infused into the soil layer of contaminated soil-A, the same amount of water is pumped up from the tube embedded in the formation 10m away from the above-mentioned injection tube in the horizontal direction.⁶⁺Drained contaminated soil water.
[0065]
The injection amount and discharge amount were set to 0.1 × [contaminated soil amount (t)] / day as the injection amount (t) and discharge amount (t) per day.
After the start of injection, as in Examples 1 to 7, the soil Cr⁶⁺The number of days required for the elution amount to be 0.05 mg / l or less was investigated.
Table 4 shows experimental conditions and experimental results.
[0066]
  As shown in Table 4, according to the method for treating chromium oxide-containing soil of the present invention, the following effects are obtained.
(1) Cr in contaminated soil by mixing and burying chromium oxide-containing soil and reducing agent⁶⁺Significant reduction of elution volume:
  Chromium oxide-containing soil, unaged blast furnace chilled slag containing sulfur with an oxidation number of +5 or less, hot metal pretreated slurryGroupBy mixing and embedding blast furnace slag elution water, while reducing the amount of slag and blast furnace slag elution water used, Cr in the chromium oxide-containing soil⁶⁺The amount of elution can be reduced below the environmental standard value.
[0067]
(2) Cr in soil contaminated with blast furnace slag effluent injected into chromium oxide-containing soil⁶⁺Short and significant reduction of elution volume:
By injecting blast furnace slag elution water into the chromium oxide-containing soil, the Cr in the chromium oxide-containing soil is further reduced in a shorter time than the mixing and burying methods described above.⁶⁺The amount of elution can be reduced below the environmental standard value.
[0068]
(3) Cr in contaminated soil by injection and discharge of blast furnace slag elution water to and from chromium oxide-containing soil⁶⁺Short and significant reduction of elution volume:
Not only injecting blast furnace slag elution water into the chromium oxide-containing soil, but also pumping and discharging water from the adjacent formations in a shorter time than the above-mentioned injection method alone, Cr⁶⁺The amount of elution can be reduced below the environmental standard value.
[0069]
(4) Cr in acid-contaminated soil combined with alkaline compounds⁶⁺Significant reduction of elution amount: By using reducing agent and alkaline compound together, Cr⁶⁺Produced by reduction of Cr³⁺Cr (OH)_ThreeAs a result, the acid-contaminated soil Cr can be stabilized⁶⁺The amount of elution can be reduced below the environmental standard value.
[0070]
[Table 3]

[0071]
[Table 4]

[0072]
[Table 5]

[0073]
【The invention's effect】
According to the present invention, the chromium slag, Cr⁶⁺Cr in chromium oxide-containing soil contaminated with ion-containing waste liquid⁶⁺Can be completely reduced in a short time, and Cr in soil containing chromium oxide⁶⁺It became possible to make the amount of leaching below the environmental standard value.

Claims (4)

A method for treating chromium oxide-containing soil, comprising bringing chromium oxide-containing soil into contact with at least one selected from unaged blast furnace slag, hot metal pretreated slag , and blast furnace slag elution water. Chromium oxide-containing soil mixed with one or more types selected from unaged blast furnace chilled slag, hot metal pretreated slag , and blast furnace slag elution water, and embedded in the resulting mixture Soil treatment method. A method for treating chromium oxide-containing soil, wherein one or more selected from unaged blast furnace slow-cooled slag, hot metal pretreatment slag , and blast furnace slag elution water are injected into chromium oxide-containing soil.   The chromium treatment method for chromium oxide-containing soil according to any one of claims 1 to 3, wherein the alkaline compound is further contacted, mixed, or injected into the chromium oxide-containing soil. Method for treating oxide-containing soil.