JP3896048B2

JP3896048B2 - Purification method for contaminated soil

Info

Publication number: JP3896048B2
Application number: JP2002220669A
Authority: JP
Inventors: 正郎小西; 茂亀田; 健太郎林; 佳範車田; 高永岡; 淳中根
Original assignee: Penta Ocean Construction Co Ltd; Okumura Corp
Current assignee: Penta Ocean Construction Co Ltd; Okumura Corp
Priority date: 2002-07-30
Filing date: 2002-07-30
Publication date: 2007-03-22
Anticipated expiration: 2022-07-30
Also published as: JP2004057953A

Description

【０００１】
【発明の属する技術分野】
本発明は、汚染土壌の浄化方法、特に汚染土壌の存する原位置において汚染物質が溶出し易い状態となるよう前処理を施し、浄化処理施設での土壌洗浄システムと併せて汚染土壌の浄化効率をより一層向上させる汚染土壌の浄化方法に関するものである。
【０００２】
【従来の技術】
わが国においては、近年、有害物質による土壌汚染事例の判明件数の増加が著しく、特に、都市部や比較的人口密集度の高い市街地に立地していた企業が移転又は廃業した後、工場跡地等における重金属や揮発性有機化合物等による土壌汚染が当該工場跡地等の再開発等に伴い顕在化するという状況にある。これらの有害物質を放置すれば人の健康に重大な影響が及ぶことが懸念されるため、先般、土壌汚染対策法が制定され、土壌に含まれることに起因して人の健康被害を生ずるおそれがあるもの、例えば鉛、砒素、トリクロロエチレンその他の物質を特定有害物質として取り上げている。また、該土壌汚染対策法によれば、都道府県知事はこれら特定有害物質が環境基準に適合しない区域を指定区域とし、さらに指定区域内で人の健康被害が生ずるおそれがあると認めるときは、当該土地の所有者又は汚染原因者に対し、摂食又は皮膚接触による直接摂取リスクの場合は立入制限、舗装、覆土、封じ込め、浄化により、また、地下水等への溶出リスクの場合は地下水のモニタリング、封じ込め、浄化により、汚染の除去等の措置を命ずることができるとしている。
【０００３】
かかる背景の下、汚染状況すなわち汚染物質の種類、汚染の程度や土地利用の現況と将来への見込みの見地から、汚染区域の地層条件、投入可能な処理経費、汚染対策の緊急度などを勘案の上、技術的、経済的又は社会的諸条件に見合うべく多くの土壌汚染対策の方法が提案又は実施されてきているところである。これらの方法については、汚染土壌を原位置から移動させて浄化処理施設まで搬送し該浄化処理施設内で処理する方法と、汚染土壌を移動させないで原位置で処理する方法とに大別することができる。
汚染土壌を移動させて処理する方法には、掘削した汚染土壌を焼却炉等により焼却処理したり、掘削した汚染土壌を浄化処理施設により洗浄する方法などがある。他方、汚染土壌を移動させないで原位置において処理する方法には、微生物を利用したバイオレメディエーション、コンクリート壁等の構築による汚染区域の封じ込めや固化物の流し込み等による固定安定化、汚染物質を気化させる曝気による除去方法又は地下水流を利用した汚染物質の洗浄などの方法がある。
【０００４】
これらの方法の一例を示せば次のとおりである。
（１）土壌を移動させて浄化処理施設内で処理する方法は、例えば図６のフロー構成図に示す方法である。すなわち、まず汚染区域に於ける汚染土壌Ｌを掘削（ステップ１）のうえダンプカー等の運搬車両に積込（ステップ２）し、浄化処理施設Ｓまで運搬（ステップ３）する。該浄化処理施設Ｓには、一旦仮置（ステップ４）された汚染土壌Ｌのうち該浄化処理施設Ｓの処理能力に見合った量を搬入し、まず該汚染土壌Ｌと水道水とをドラム式洗浄装置１等で攪拌混合（ステップ５）する。次に、該汚染土壌Ｌと水道水の混合物を振動フルイ分け等の分級装置２に投入して粗粒分と細粒分を分級（ステップ６）したうえで、該粗粒分を二次洗浄装置３にて洗浄液によりさらに洗浄（ステップ７）し、該細粒分は場外に最終的に処分（ステップ８）される。ここで、ドラム式洗浄装置１等からの排出水道水と二次洗浄装置３からの排出洗浄液は、回収して一旦貯留水槽４に貯留された後、水処理設備５にて汚染物質を分離する処理（ステップ９）が行われ、汚染物質を含む汚泥は定められた方法により適正に処分（ステップ１０）すると共に、処理された排水は下水道等に放流（ステップ１１）される。一方、前記二次洗浄装置３に於いて洗浄された粗粒分は、回収して元の汚染区域に運搬して埋め戻すなどの再利用（ステップ１２）が図られるものである。
【０００５】
また、他の例を示せば次のとおりである。
（２）土壌を移動させないで原位置で処理する方法は、例えば特開平７−８２７３０号に開示されているように、まず汚染区域内の地下水位の深さまで止水壁を打設して汚染土壌を側面から取囲み、その領域内に注入孔と揚水孔を掘削する。該注入孔から水又は洗浄液を注入して領域内の地下水位を上昇せしめて汚染土壌付近を飽和状態とし、他方で該揚水孔から地下水を揚水して人為的に地下水流を発生させ、そしてこの地下水流に汚染物質を捕捉、輸送させようとするものである。最後に、前記揚水孔から揚水した汚染物質を含んだ地下水を専用の施設にて処理する方法である。
【０００６】
【発明が解決しようとする課題】
従来の技術は上述した構成であるので、次の課題が存在した。
（１）上記浄化処理施設内で処理する方法では、汚染土壌を直接掘削して指定の浄化処理施設まで運搬する必要があり、その移動途上に於いて汚染土壌がダンプカー等の運搬車両から飛散等することにより、二次汚染を移動ルート沿線に生ぜしめることとなり、特に市街地内を移動せざるを得ない場合には二次汚染が一層深刻となる問題点があった。また、浄化処理施設での浄化前の仮置の際、対象となる汚染土壌が大量の場合には浄化処理施設の敷地内外の仮置場に於いて長期間に渉って汚染土壌が滞留することとなり、雨水による周辺地への汚染土壌の流出や地下水への汚染物質の浸透などにより、建設残土や産業廃棄物の埋立場又は仮置場と類似の二次汚染が惹起されるという問題点があった。更に、洗浄等の浄化処理を浄化処理施設内ですべて行うため、浄化処理施設が相対的に大規模化することとなり、その設置条件が限定され汚染区域内若しくは所望区域内に浄化処理施設を設置することが困難となるばかりか、汚染区域と浄化処理施設が遠距離化して移動ルートが伸長され、前述の二次汚染区域の拡大と共に浄化後の土壌埋め戻しも含め運送コストが増大するという問題点があった。
【０００７】
（２）上記原位置で処理する方法は、注入された水又は洗浄液により汚染物質を地下水流により捕捉しようとするものであるが、自然地盤内を通じての地下水循環、特に汚染区域が広範囲にわたる場合や不透水性地盤等である場合、この地下水循環は極めて緩慢であると共に、加圧注入したとしても注入した水又は洗浄液の浸透域を特定の汚染範囲に限定して制御することも困難であるという問題点があった。また、この方法によれば、地上においては土地利用を行いつつ地下では浄化を進め得るということは可能であるものの、環境基準を達成する程度に至るまでには多大な浄化処理時間ひいては多大な浄化処理費用が必要となるという問題点があった。また、汚染土壌の上で該汚染土壌の浄化処理と並行的に土地利用が行われる、すなわち人間活動が営まれることを想定しているため、例えば新規若しくは既存の上下水道設備が稼動した際に、該上下水道設備へ汚染物質を含んだ地下水が混入したり、汚染土壌の露出部分から飛散等により人体等へ思わぬ影響が出るなど、不測の事態が発生するとも限らないという問題点があった。
【０００８】
【課題を解決するための手段】
本発明は、汚染土壌の存する原位置において汚染物質が溶出し易い状態となるよう前処理を施したうえ、浄化処理施設での土壌洗浄システムと併せて汚染土壌の浄化効率をより一層向上させる汚染土壌の浄化方法を提供することを目的としたものであって、次の構成、手段から成立するものである。
【０００９】
請求項１記載の発明によれば、鉛又はカドミウムにより汚染された土壌の深さ方向の浸透程度に応じて透水性地盤の中に所望数及び所望深度の洗浄液注入孔を設け、該洗浄液注入孔にクエン酸水溶液でなる洗浄液を注入し又は所定区域の全域若しくは一部を所望深度に達するまで掘削し、掘削後の空間に前記クエン酸水溶液でなる洗浄液を満たした後に前記所定区域から掘削した前記鉛又はカドミウムにより汚染された土壌をクエン酸水溶液でなる洗浄液に投入して一定時間まで浸漬放置する前処理方法と、この前処理方法による前処理済み土壌及び前記クエン酸水溶液でなる洗浄液の混合物を分級装置に投入して粗粒分、細粒分を分級し、該混合物の細粒分の一部をドラム式洗浄装置で洗浄溶液によりさらに前処理済み土壌を洗浄し、ドラム式洗浄装置で不溶化処理を施す洗浄方法とでなることを特徴とする汚染土壌の浄化方法である。
【００１０】
請求項２記載の発明によれば、鉛又はカドミウムにより汚染された土壌の不透水性地盤でなる所定区域を所定面積に画成し、かつ所定深さを有する区画壁を前記汚染された土壌に打設し、該区画壁の打設完了後に該区画壁で取囲まれた各々の区画区分内にクエン酸水溶液でなる洗浄液を注入し、又は該区画壁内を掘削して前記クエン酸水溶液でなる洗浄液で満たした後に前記画成区分から掘削した前記鉛又はカドミウムにより汚染された土壌をクエン酸水溶液でなる洗浄液に投入して一定時間まで浸漬放置する前処理方法と、この前処理方法による前処理済み土壌及び前記クエン酸水溶液でなる洗浄液の混合物を分級装置に投入して粗粒分、細粒分を分級し、該混合物の細粒分の一部をドラム式洗浄装置で洗浄溶液によりさらに前処理済み土壌を洗浄し、ドラム式洗浄装置で不溶化処理を施す洗浄方法とでなることを特徴とする汚染土壌の浄化方法である。
【００１１】
請求項３記載の発明によれば、鉛又はカドミウムにより汚染された土壌の不透水性地盤でなる所定区域を所定面積に画成し、かつ所定深さを有する区画壁を前記汚染された土壌に打設し、該区画壁の打設完了後に該区画壁で取囲まれた各々の区画区分内の鉛又はカドミウムにより汚染された土壌を掘削除去して当該各画成区分内の底盤処理を施し、前記クエン酸水溶液でなる洗浄液と前記掘削された土壌を該画成区分内に混合投入して一定時間まで放置する前処理方法と、この前処理方法による前処理済み土壌及び前記クエン酸水溶液でなる洗浄液の混合物を分級装置に投入して粗粒分、細粒分を分級し、該混合物の細粒分の一部をドラム式洗浄装置で洗浄溶液によりさらに前処理済み土壌を洗浄し、ドラム式洗浄装置で不溶化処理を施す洗浄方法とでなることを特徴とする汚染土壌の浄化方法である。
【００１２】
請求項４記載の発明によれば、前記クエン酸水溶液でなる洗浄液が、鉛又はカドミウムにより汚染された土壌のＰＨ調整剤でなることを特徴とする請求項１、２又は３記載の汚染土壌の浄化方法である。
【００１３】
請求項５記載の発明によれば、前記区画壁が、止水壁で構成されたことを特徴とする請求項２又は３記載の汚染土壌の浄化方法である。
【００１４】
【発明の実施の形態】
本発明に係る汚染土壌の浄化方法の実施の形態について、添付図面に基づき詳細に説明する。
【００１５】
【発明の実施の形態１】
図１は、本発明に係る汚染土壌の理浄化方法の実施の形態１の一例を示しており、（ａ）は土壌汚染された所定区域の全域を示した平面図、（ｂ）は土壌汚染された所定区域を画成区分した際の一部を示す平面図、（ｃ）は（ｂ）の矢視Ａ−Ａ方向に於ける断面図、（ｄ）は汚染土壌の原位置の前処理を実施中の画成区分を中心に前処理工程の流れを示した断面図である。
【００１６】
本発明の実施の形態１は、土壌汚染された所定区域Ｂが透水性地盤Ｌ１である場合に於ける実施例である。図１（ａ）は、土壌汚染された該所定区域Ｂの面積、地質条件、汚染土壌の量又は周辺地の状況等により、該所定区域Ｂの全域を一つの区分として取扱う場合を示すものであって、ボーリング等の事前調査によって判明した土壌汚染の深さ方向の浸透程度に応じて、透水性地盤Ｌ１の中に所望数及び所望深度の洗浄液注入孔６を設けてある。当該図１（ａ）では洗浄液注入孔６を設けた場合を図示しているが、この他にも洗浄液注入孔６を設けることなく、該所定区域Ｂの全域若しくは一部を所望深度に達するまで掘削し、掘削後の空間に洗浄液を満たした後に該所定区域Ｂから掘削した汚染土壌を該洗浄液に投入して一定時間まで浸漬放置する方法でもよい（図示せず）。７は、土壌汚染された該所定区域Ｂすなわち浄化処理の対象区域と非汚染区域Ｃすなわち浄化処理の非対象区域を仕切る隔壁であって、処理に伴って溶出し易い状態となっている汚染物質が土壌汚染された該所定区域Ｂから非汚染区域Ｃへ流出することを防止するため、止水壁により構成されている。
尚、該隔壁７は、現場の条件によっては設けなくともよい。
【００１７】
図１（ｂ）は土壌汚染された前記所定区域Ｂを所定面積に画成した場合を示しており、８は区画壁であって、１区画の画成の大きさはボーリング等による事前調査によって判明した土壌汚染の深さ方向の浸透程度に応じて、掘削容量と処理施設の能力がバランスするように区画壁８の打設間隔Ｗ１、Ｗ２及び打設深度Ｈを設定している。また、区画壁８は、処理前の画成区分８１と処理中の画成区分８２若しくは処理後の画成区分８３との間で汚染物質が移動することを防止するため、止水壁で構成されている。図１（ｃ）では、区画壁８の打設深度Ｈを土壌汚染の浸透が及ばない不透水域Ｇまで区画壁８を貫入させた場合を図示しているが、事前調査の結果によっては不透水域Ｇの深さまで該区画壁８を貫入することなく、浄化処理に必要な深度までに設定してもよい。
【００１８】
９は浄化処理対象となる透水性の汚染土壌であって、前処理を施す順番に該当する画成区分８２内の汚染土壌９の中には、図１（ｂ）に示すように洗浄液注入孔６が設けられており、地上に配置された洗浄液タンク１０から洗浄液１１を注入する。この注入に際しては、汚染土壌９の物理特性により必要に応じてポンプ（図示せず）による加圧注入としてもよい。また、洗浄液注入孔６を設けることなく、該画成区分８２を所望深度に達するまで掘削し、掘削後の空間に洗浄液１１を満たした後に該画成区分８２から掘削した汚染土壌９を該洗浄液１１に投入して一定時間まで浸漬放置する方法でもよい（図示せず）。洗浄液１１の注入後又は洗浄液１１内への投入後所定の期間放置された汚染土壌９は、該汚染土壌９の中に浸透している鉛等の汚染物質が溶出し易い状態へと経時的変化を辿り、前処理済み土壌１２となる。図中、１３は該前処理済み土壌１２を浄化処理施設内で浄化した後の最終処理済み土壌であり、元の画成区分若しくは別の適宜な画成区分内に埋め戻して再利用するものである。
【００１９】
次に、本発明に係る汚染土壌の浄化方法の実施の形態１の動作について説明する。
土壌汚染された所定区域の存在につき情報が得られた後、まず次のような事前調査を行う。汚染原因の確認、汚染現場及び周辺地区の植生状況調査、被害発生の聞き取り等で概略を調査した後、ボーリングによる汚染土壌のサンプル採取や地下水採取を行い、汚染物質の種類、横方向及び縦方向の汚染範囲と濃度分布、浄化処理対象の汚染土壌の重量と容積等を把握し、これら基礎的な情報に基づき浄化処理計画を策定する。
【００２０】
該浄化処理計画に従い、図１（ａ）に示すように土壌汚染された前記所定区域Ｂの全域を囲む隔壁７を必要に応じて打設した後、洗浄液１１を注入する方法にあっては、汚染物質の横方向及び縦方向の濃度分布に適合するように所望数及び所望深度に設定した洗浄液注入孔６を掘削する。該洗浄液注入孔６の地上の開口部近傍には洗浄液タンク１０を配置し、浄化処理すべき汚染土壌の量、処理施設の処理能力に応じることができるように、一斉に若しくは順次に洗浄液注入孔６から洗浄液１１を注入する。洗浄液１１の注入後、洗浄液１１が汚染土壌９から汚染物質を溶出するに必要な一定時間そのまま放置し、経時的変化を観察して浄化処理施設に向け搬送可能な程度になった段階で所定量の前処理済み土壌１２を掘削する。
他方、洗浄液１１を満たした後に汚染土壌９を投入する方法にあっては、土壌汚染された前記所定区域Ｂの全域を囲む隔壁７を必要に応じて打設した後、該所定区域Ｂの全域若しくは一部を所望深度に達するまで掘削する。掘削後の空間に洗浄液１１を満たした後に該所定区域Ｂから掘削した汚染土壌９を該洗浄液１１に投入して一定時間まで浸漬放置し、経時的変化を観察して浄化処理施設に向け搬送可能な程度になった段階で所定量の前処理済み土壌１２を掘削する。（図示せず）。
【００２１】
次に、土壌汚染された所定区域Ｂを画成区分する場合の動作を説明する。土壌汚染された所定区域Ｂの全域を囲む隔壁７を必要に応じて打設した後、全域又は必要な一部区域について浄化処理すべき汚染土壌９の量、浄化処理施設の処理能力に応じることができるように、適切な大きさに画成するための区画壁８を図１（ｂ）ないし（ｄ）に示すように打設（ステップ１３）する。次に、洗浄液１１を注入する方法にあっては、汚染物質の横方向及び縦方向の濃度分布に適合するように所望数及び所望深度に設定した洗浄液注入孔６を掘削し、該洗浄液注入孔６の地上の開口部近傍に配置した洗浄液タンク１０から洗浄液１１を注入（ステップ１４）する。図１（ｄ）には１つの画成区分に１本の洗浄液注入孔６を図示しているが、必要に応じて複数本の洗浄液注入孔６を設けても差支えない。洗浄液１１の洗浄液注入孔６への注入後、洗浄液１１が汚染土壌９から汚染物質を溶出するに必要な一定時間そのまま放置し、経時的変化を観察して浄化処理施設に向け搬送可能な程度になった段階で所定量の前処理済み土壌１２を掘削（ステップ１５）する。以下、図１（ｄ）に示す上記ステップ１３からステップ１５のように、画成区分ごとに順次同様の動作を繰り返し実施する。
他方、洗浄液１１を満たした後に汚染土壌９を投入する方法にあっては、区画壁８を打設した後、該画成区分を所望深度に達するまで掘削する。掘削後の空間に洗浄液１１を満たした後に該画成区分から掘削した汚染土壌９を該洗浄液１１に投入して一定時間まで浸漬放置し、経時的変化を観察して浄化処理施設に向け搬送可能な程度になった段階で所定量の前処理済み土壌１２を掘削する。（図示せず）
【００２２】
次に、洗浄液の注入による汚染土壌の洗浄作用について、添付図面に基づき説明する。
図２は、汚染物質として鉛（Ｐｂ）、洗浄液１１として例えばクエン酸水溶液を用いた場合の試験結果を示す図であって、（ａ）は試験結果を示す図、（ｂ）は試験結果の数値を示す図である。図２（ａ）の左側縦軸及び縦棒グラフは汚染物質すなわち鉛（Ｐｂ）の除去率δ１（％）、同右側縦軸及び折れ線グラフは汚染土壌のｐＨ値、同横軸は洗浄液１１すなわちクエン酸水溶液の濃度及び汚染土壌と洗浄液１１の固液比αの組合せによる４つの試験条件を、それぞれ示している。ここで、鉛（Ｐｂ）の除去率δ１（％）＝{１−（Ｄ１／Ｄ２）}×１００である。但し、Ｄ１は前処理後の汚染土壌に含まれる汚染物質すなわち鉛（Ｐｂ）の濃度（ｍｇ／ｋｇ）、Ｄ２は前処理前の汚染土壌に含まれる汚染物質すなわち鉛（Ｐｂ）の濃度（ｍｇ／ｋｇ）である。固液比αは試験に供した汚染土壌の重量（ｇ）と、試験に供した洗浄液すなわちクエン酸水溶液の重量（ｇ）の比である。
【００２３】
試験は、汚染土壌９としては鉛濃度（Ｐｂ）が２７００（ｍｇ／ｋｇ）の実際の汚染現場から採取した土壌９を、洗浄液１１としてはクエン酸水溶液をそれぞれ使用し、クエン酸水溶液の濃度と前述の固液比αで表される添加量を変化させて４つの条件設定を行い、いずれも１４日間浸漬させることにより実施した。ここで、該試験に於いてクエン酸水溶液を洗浄液１１として使用した理由は、クエン酸が自然界の土壌中に含まれる有機酸の１つであって、適度な濃度であれば土壌環境に無害であること、同じく有機酸である酢酸が強臭気かつ通常液体であるのに対しクエン酸は無臭かつ粉末で扱い易いこと、大量生産が可能で安価であること、建設分野で地盤改良工事に於けるｐＨ調整剤として使用されていることなどから採用したものである。
尚、図２（ａ）、（ｂ）に示す条件のうちの１つに「（振）」とあるのは、浸漬した供試体を振盪させたことを意味しており、他の３つは振盪させていない。
【００２４】
試験結果をみると、洗浄液１１すなわちクエン酸水溶液の濃度が３．０（％ｗｔ）かつ固液比αが１：１．０の場合に、鉛（Ｐｂ）の残留濃度が１７５０（ｍｇ／ｋｇ）となり鉛（Ｐｂ）の除去率δ１が３５．２（％）と最も高くなるものの、一方でｐＨ値が６．１８と中性の７．０を下回り酸性が強くなるため地盤環境への悪影響が懸念される。従って、鉛（Ｐｂ）の除去率δ１が３０（％）前後であってｐＨ値も８．０以上となっている濃度１．０（％）程度のクエン酸水溶液を目安とするのが妥当と判断される。但し、土壌には緩衝作用と称する現象があり、浸漬期間を延長することによりｐＨ値が７．０〜８．０に収束することが知られており、浄化後の土壌の性状についてはクエン酸水溶液の濃度による問題は解消することができる。
而して、本発明によれば汚染土壌９に含まれる鉛（Ｐｂ）を大幅に除去でき、かつ、クエン酸水溶液による洗浄液１１により土壌のｐＨ値を調整することが判明した。
【００２５】
図３は、汚染物質としてカドミウム（Ｃｄ）、洗浄液１１として例えばクエン酸水溶液を用いた場合の試験結果を示す図であって、（ａ）は試験結果を示す図、（ｂ）は試験結果の数値を示す図である。図２（ａ）の左側縦軸及び縦棒グラフは汚染物質すなわちカドミウム（Ｃｄ）の除去率δ２（％）、同右側縦軸及び折れ線グラフは汚染土壌のｐＨ値、同横軸は洗浄液１１すなわちクエン酸水溶液の濃度及び汚染土壌と洗浄液１１の固液比αの組合せによる３つの試験条件を、それぞれ示している。ここで、カドミウム（Ｃｄ）の除去率δ２（％）＝{１−（Ｄ３／Ｄ４）}×１００である。但し、Ｄ３は前処理後の汚染土壌に含まれる汚染物質すなわちカドミウム（Ｃｄ）の濃度（ｍｇ／ｋｇ）、Ｄ４は前処理前の汚染土壌に含まれる汚染物質すなわちカドミウム（Ｃｄ）の濃度（ｍｇ／ｋｇ）である。固液比αは試験に供した汚染土壌の重量（ｇ）と、試験に供した洗浄液すなわちクエン酸水溶液の重量（ｇ）の比である。
【００２６】
試験は、汚染土壌９としてはカドミウム濃度（Ｃｄ）が０．８（ｍｇ／ｋｇ）の実際の汚染現場から採取した土壌９を、洗浄液１１としてはクエン酸水溶液をそれぞれ使用し、クエン酸水溶液の濃度と前述の固液比αで表される添加量を変化させて３つの条件設定を行い、いずれも１４日間浸漬させることにより実施した。ここで、該試験に於いてクエン酸水溶液を洗浄液１１として使用した理由は、クエン酸が自然界の土壌中に含まれる有機酸の１つであって、適度な濃度であれば土壌環境に無害であること、同じく有機酸である酢酸が強臭気かつ通常液体であるのに対しクエン酸は無臭かつ粉末で扱い易いこと、大量生産が可能で安価であること、建設分野で地盤改良工事に於けるｐＨ調整剤として使用されていることなどから採用したものである。
【００２７】
試験結果をみると、洗浄液１１すなわちクエン酸水溶液の濃度が３．０（％ｗｔ）かつ固液比αが１：１．０の場合と、それぞれが１．０（％ｗｔ）かつ１：１．５の場合が共に、カドミウム（Ｃｄ）の残留濃度が０．３（ｍｇ／ｋｇ）となりカドミウム（Ｃｄ）の除去率δ２が６２．５（％）と最も高くなるものの、一方で前者のｐＨ値が６．１８と中性の７．０を下回り酸性が強くなるため地盤環境への悪影響が懸念される。従って、カドミウム（Ｃｄ）の除去率δ２が５０〜６０（％）前後であってｐＨ値も７．０以上となっている濃度１．０（％）程度のクエン酸水溶液を目安とするのが妥当と判断される。但し、土壌には緩衝作用と称する現象があり、浸漬期間を延長することによりｐＨ値が７．０〜８．０に収束することが知られており、浄化後の土壌の性状についてはクエン酸水溶液の濃度による問題は解消することができる。
而して、本発明によれば汚染土壌９に含まれるカドミウム（Ｃｄ）を大幅に除去でき、かつ、クエン酸水溶液による洗浄液１１により土壌のｐＨ値を調整することが判明した。
【００２８】
【発明の実施の形態２】
図４は、本発明に係る汚染土壌の浄化方法の実施の形態２の一例を示しており、（ａ）は土壌汚染された所定区域を画成区分した際の一部を示す平面図、（ｂ）は（ａ）の矢視Ｅ−Ｅ方向に於ける断面図、（ｃ）は汚染土壌の原位置の前処理を実施中の画成区分を中心に前処理工程の流れを示した断面図である。
【００２９】
本発明の実施の形態２は、土壌汚染された所定区域Ｂが不透水性地盤Ｌ２である場合に於ける実施例である。図４（ａ）は土壌汚染された所定区域Ｂを所定面積に画成した場合を示しており、８は区画壁であって、１区画の画成の大きさはボーリング等による事前調査によって判明した土壌汚染の深さ方向の浸透程度に応じて、掘削容量と処理施設の能力がバランスするように区画壁８の打設間隔Ｗ１、Ｗ２及び打設深度Ｈを設定している。また、区画壁８は、処理前の画成区分８１と処理中の画成区分８２若しくは処理後の画成区分８３との間で汚染物質が移動することを防止するため、止水壁で構成されている。図１（ｃ）では、区画壁８の打設深度Ｈを土壌汚染の浸透が及ばない不透水域Ｇまで区画壁８を貫入させた場合を図示しているが、事前調査の結果によっては不透水域Ｇの深さまで該区画壁８を貫入することなく、浄化処理に必要な深度までとしてもよい。
【００３０】
１４は処理対象となる不透水性の汚染土壌であって、まず単数又は複数の特定の画成区分８２に於ける汚染土壌１４を掘削した後に該汚染土壌１４を近傍に一時仮置し、本発明の実施の形態２の動作にて後述するように、本発明の実施の形態２では当該画成区分８２を前処理専用のスペースとして使用するので、作業性及び安全性を確保するのに必要な底盤処理１５を、例えばセメントミルク注入による固化等の方法により施す。その後、掘削して近傍に一時仮置しておいた汚染土壌１４と、図４（ｃ）に示すように地上に配置された洗浄液タンク１０に充填されている洗浄液１１を混合して投入する。洗浄液１１と汚染土壌１４を混合投入後、所定の期間放置された汚染土壌１４は、該汚染土壌１４の中に浸透している鉛等の汚染物質が溶出し易い状態へと経時的変化を辿り、前処理済み土壌１２となる。１３は該前処理済み土壌１２を浄化処理施設内で完全処理した後の最終処理済み土壌であり、元の画成区分若しくは別の適宜な画成区分内に埋め戻すものである。
【００３１】
次に、本発明に係る汚染土壌の浄化方法の実施の形態２の動作について説明する。
土壌汚染された所定区域の存在につき情報が得られた後、まず前記本発明の実施の形態１に示したと同様の事前調査を行って、処理計画を策定する。
【００３２】
該処理計画に従い、図４（ｂ）に示すように、土壌汚染された所定区域Ｂの全域を囲む隔壁７を必要に応じて打設した後、全域又は必要な一部区域を画成するための区画壁８を打設（ステップ１６）する。画成区分が了した後、単数又は複数の画成区分を適宜に選択し、当該画成区分８２内の汚染土壌１４を掘削、一時仮置のうえ、当該画成区分８２の底面に例えばセメントミルク等の地盤固化材を投入して底盤処理１５を行った後、一時仮置した汚染土壌１４と洗浄液１１を当該画成区分内８２に混合投入（ステップ１７）する。
【００３３】
この底盤処理１５は、一旦汚染土壌１４を掘り返して洗浄液１１と共に混合投入する際の作業性及び安全性を確保するために必要となるものであるが、この底盤処理１５を全ての画成区分で行えば土壌汚染された所定区域Ｂの全域の地下に例えばセメント層が形成されることとなる。このことは、処理後すなわち浄化された土壌を埋め戻した後の土地利用に際し、土地利用の内容によっては不都合な作用をもたらすことが危惧されるため、底盤処理１５を施す画成区分を可能な限り限定することとし、単数又は複数の画成区分を処理専用スペースとして使用するものである。
【００３４】
前記単数又は複数の前処理専用画成区分内への汚染土壌１４と洗浄液１１の混合投入後、洗浄液１１が汚染土壌１４から汚染物質を溶出するに必要な一定時間そのまま放置し、経時的変化を観察して浄化処理施設に向け搬送可能な程度になった段階で前処理済み土壌１２を掘削（ステップ１８）する。当該前処理済み土壌１２を掘削し浄化処理施設に搬送した後、他の画成区分の汚染土壌１４を掘削して前記単数又は複数の前処理専用画成区分８２に洗浄液１１と共に混合投入する。以下、画成区分ごとに順次同様の動作を反復しすべての画成区分内の汚染土壌１４を処理する。
【００３５】
【発明の実施の形態３】
図５は、前処理済み土壌１２を処理する浄化処理施設Ｆ内の土壌洗浄システムを示すフロー構成図である。
前述の本発明の実施の形態１及び２で前処理を施された前処理済み土壌１２は、いずれも汚染物質が溶出し易い状態で図５に示すような浄化処理施設Ｆに搬入され、環境基準を満足する程度までに洗浄されることとなる。
まず、前記ステップ１５又はステップ１８にて汚染区域Ｂの画成区分から掘削された前処理済み土壌１２を、ダンプカー等の運搬車両にて浄化処理施設Ｆまで運搬（ステップ１９）する。この際、該浄化処理施設Ｆの処理能力に見合った量の前処理済み土壌１２が運搬されてくるので、該浄化処理施設Ｆの敷地内に前処理済み土壌１２がほとんど滞留することなく、円滑に該浄化処理施設Ｆに搬入されることとなる。
【００３６】
浄化処理施設Ｆ内の工程については、まず該前処理済み土壌１２と洗浄液１１の混合物を振動フルイ分け等の分級装置１６に投入して粗粒分と細粒分を分級（ステップ２０）したうえで、該粗粒分及び細粒分の一部を例えばドラム式洗浄装置１７にて洗浄溶液によりさらに洗浄（ステップ２１）し、細粒分の残りは場外に最終的に処分（ステップ２２）される。ステップ２１を経て環境基準を満足する程度にまで汚染物質の濃度が低下した粗粒分及び細粒分の一部は、浄化処理の一連の工程で汚染物質の可溶性が高まっており、このままでは埋め戻し等の再利用に供することができないので、ドラム式洗浄装置１８にて不溶化処理を最後に施す（ステップ２３）。
【００３７】
ここで、ドラム式洗浄装置１７からの排出洗浄溶液とドラム式洗浄装置１８からの排出不溶化溶液は、回収して一旦貯留水槽１９に貯留された後、各々の洗浄溶液処理設備２０、不溶化溶液処理設備２１に於いて処理（ステップ２４）され、再利用が図られることとなる。また、該再利用した後の廃液は、前記分級装置１６から回収された原位置による前処理で使用された洗浄液と併せて水処理設備２２にて汚染物質を分離する処理（ステップ２５）が行われ、汚染物質を含む汚泥は定められた方法により適正に処分（ステップ２６）すると共に、処理された排水は下水道等に放流（ステップ２７）される。一方、前記ドラム式洗浄装置１８に於いて不溶化処理された粗粒分及び細粒分の一部は、最終処理済み土壌１３として回収し元の汚染区域に運搬して埋め戻すなどの再利用（ステップ２８）が図られるものである。
【００３８】
【発明の効果】
本発明に係る汚染土壌の浄化方法は、叙上の構成、動作を有するので次の効果がある。
【００３９】
請求項１記載の発明によれば、鉛又はカドミウムにより汚染された土壌の深さ方向の浸透程度に応じて透水性地盤の中に所望数及び所望深度の洗浄液注入孔を設け、該洗浄液注入孔にクエン酸水溶液でなる洗浄液を注入し又は所定区域の全域若しくは一部を所望深度に達するまで掘削し、掘削後の空間に前記クエン酸水溶液でなる洗浄液を満たした後に前記所定区域から掘削した前記鉛又はカドミウムにより汚染された土壌をクエン酸水溶液でなる洗浄液に投入して一定時間まで浸漬放置する前処理方法と、この前処理方法による前処理済み土壌及び前記クエン酸水溶液でなる洗浄液の混合物を分級装置に投入して粗粒分、細粒分を分級し、該混合物の細粒分の一部をドラム式洗浄装置で洗浄溶液によりさらに前処理済み土壌を洗浄し、ドラム式洗浄装置で不溶化処理を施す洗浄方法とでなることを特徴とする汚染土壌の浄化方法を提供する。
このような構成としたので、鉛又はカドミウムにより汚染された土壌の深さ方向の浸透程度に応じて透水性地盤の中に設けた注入孔にクエン酸水溶液でなる洗浄液を所望量かつ所定時間注入し、又はクエン酸水溶液の中に鉛又はカドミウムにより汚染された土壌を投入して一定時間まで浸漬放置することにより、汚染された土壌を原位置から移動させることなく前処理方法を実施すると共に、浄化処理施設の全体を相対的に小規模化することができ、該浄化処理施設を土壌汚染された所定区域内若しくは近傍に設置することが可能となり、汚染土壌の搬送による飛散等がもたらす移動ルート沿線上への二次汚染を防止し運送コストの低減を図ると共に、浄化処理施設への汚染土壌の搬入に際して仮置場等に於ける管理がし易く二次汚染をも防止でき、最終処理済み土壌を原位置に埋め戻した後に、一連の浄化処理工程に於いて可溶化された汚染物質の一部が残留汚染物質として溶出することを防止できるという効果がある。
【００４０】
請求項２記載の発明によれば、鉛又はカドミウムにより汚染された土壌の不透水性地盤でなる所定区域を所定面積に画成し、かつ所定深さを有する区画壁を前記汚染された土壌に打設し、該区画壁の打設完了後に該区画壁で取囲まれた各々の区画区分内にクエン酸水溶液でなる洗浄液を注入し、又は該区画壁内を掘削して前記クエン酸水溶液でなる洗浄液で満たした後に前記画成区分から掘削した前記鉛又はカドミウムにより汚染された土壌をクエン酸水溶液でなる洗浄液に投入して一定時間まで浸漬放置する前処理方法と、この前処理方法による前処理済み土壌及び前記クエン酸水溶液でなる洗浄液の混合物を分級装置に投入して粗粒分、細粒分を分級し、該混合物の細粒分の一部をドラム式洗浄装置で洗浄溶液によりさらに前処理済み土壌を洗浄し、ドラム式洗浄装置で不溶化処理を施す洗浄方法とでなることを特徴とする汚染土壌の浄化方法を提供する。
このような構成としたので、請求項１記載の発明の効果に加えて、鉛又はカドミウムにより汚染された土壌の所定区域を所定面積に画成したうえで前処理を施すため、該所定区域が広範囲にわたって処理すべき汚染土壌が大量となる場合であっても、浄化処理施設の処理能力と適合させたきめ細かな浄化処理作業が可能となり、搬送や仮置場等での二次汚染をより一層防止できるという効果がある。
【００４１】
請求項３記載の発明によれば、鉛又はカドミウムにより汚染された土壌の不透水性地盤でなる所定区域を所定面積に画成し、かつ所定深さを有する区画壁を前記汚染された土壌に打設し、該区画壁の打設完了後に該区画壁で取囲まれた各々の区画区分内の鉛又はカドミウムにより汚染された土壌を掘削除去して当該各画成区分内の底盤処理を施し、前記クエン酸水溶液でなる洗浄液と前記掘削された土壌を該画成区分内に混合投入して一定時間まで放置する前処理方法と、この前処理方法による前処理済み土壌及び前記クエン酸水溶液でなる洗浄液の混合物を分級装置に投入して粗粒分、細粒分を分級し、該混合物の細粒分の一部をドラム式洗浄装置で洗浄溶液によりさらに前処理済み土壌を洗浄し、ドラム式洗浄装置で不溶化処理を施す洗浄方法とでなることを特徴とする汚染土壌の浄化方法を提供する。
このような構成としたので、請求項２記載の発明の効果に加えて、鉛又はカドミウムにより汚染された土壌に於ける不透水性地盤でなる所定区域にも適用できるという効果がある。
【００４２】
請求項４記載の発明によれば、前記クエン酸水溶液でなる洗浄液が、鉛又はカドミウムにより汚染された土壌のＰＨ調整剤でなることを特徴とする請求項１、２又は３記載の汚染土壌の浄化方法を提供する。
このような構成としたので、請求項１、２又は３記載の発明の効果に加えて、建設分野で地盤改良工事に於いて使用されているｐＨ調整剤として、自然界の土壌中に含まれる有機酸の１つであるクエン酸等を洗浄液として活用するため、適度な濃度であれば塩酸や硝酸のような強酸とは異なり土壌の成分や養分までも溶出することはなく自然環境に順応でき、また、クエン酸であれば無臭かつ粉末で扱い易くかつ汚染土壌の浄化処理の作業性を高めると同時に処理コストの低廉化を図ることができるという効果がある。
【００４３】
請求項５記載の発明によれば、前記区画壁が、止水壁で構成されたことを特徴とする請求項２又は３記載の汚染土壌の浄化方法を提供する。
このような構成としたので、請求項２又は３記載の発明の効果に加えて、前処理方法を実施する前の画成区分内の汚染物質が、洗浄液の効果により溶出して降雨や地下水により前処理中若しくは前処理後の画成区分内に浸入することが防止でき、画成区分ごとの汚染物質の濃度管理が正確かつ計画どおりに行えるという効果がある。
【図面の簡単な説明】
【図１】本発明に係る汚染土壌の浄化方法の実施の形態１の一例を示す構成図であって、（ａ）は土壌汚染された所定区域の全域を示した平面図、（ｂ）は土壌汚染された所定区域を画成区分した際の一部を示す平面図、（ｃ）は（ｂ）の矢視Ａ−Ａ方向に於ける断面図、（ｄ）は汚染土壌の原位置の前処理を実施中の画成区分を中心に前処理工程の流れを示した断面図である。
【図２】汚染物質として鉛（Ｐｂ）、洗浄液としてクエン酸水溶液を用いた場合の洗浄作用の試験結果を示す図であって、（ａ）は試験結果を示す図、（ｂ）は試験結果の数値を示す図である。
【図３】汚染物質としてカドミウム（Ｃｄ）、洗浄液としてクエン酸水溶液を用いた場合の洗浄作用の試験結果を示す図であって、（ａ）は試験結果を示す図、（ｂ）は試験結果の数値を示す図である。
【図４】本発明に係る汚染土壌の浄化方法の実施の形態２の一例を示す構成図であって、（ａ）は土壌汚染された所定区域を画成区分した際の一部を示す平面図、（ｂ）は（ａ）の矢視Ｅ−Ｅ方向に於ける断面図である。（ｃ）は汚染土壌の原位置の前処理を実施中の画成区分を中心に前処理工程の流れを示した断面図である。
【図５】前処理済み汚染土壌を処理する浄化処理施設内の土壌洗浄システムを示すフロー構成図である。
【図６】従来の技術に於ける土壌を移動させて浄化処理施設内で汚染土壌を浄化処理する方法の一例を示すフロー構成図である。
【符号の説明】
６洗浄液注入孔
７隔壁
８区画壁
８１浄化処理前の画成区分
８２浄化処理中の画成区分
８３浄化処理後の画成区分
９汚染土壌
１０洗浄液タンク
１１洗浄液
１２前処理済み土壌
１３最終処理済み土壌
１４汚染土壌
１５底盤処理
１６分級装置
１７ドラム式洗浄装置
１８ドラム式洗浄装置（不溶化処理用）
１９貯留水槽
２０洗浄溶液処理設備
２１不溶化溶液処理設備
２２水処理設備
Ｂ土壌汚染された所定区域
Ｃ非汚染区域
Ｆ浄化処理施設
Ｇ不透水域
Ｈ区画壁の打設深度
Ｌ１透水性地盤
Ｌ２不透水性地盤
Ｗ１、Ｗ２区画壁の打設間隔
δ１鉛（Ｐｂ）の除去率
δ２カドミウム（Ｃｄ）の除去率
α 固液比[0001]
BACKGROUND OF THE INVENTION
The present invention provides a purification method for contaminated soil, in particular, pretreatment is performed so that contaminants are likely to elute at the original position where the contaminated soil exists, and the purification efficiency of the contaminated soil is improved in combination with the soil cleaning system in the purification treatment facility. The present invention relates to a method for purifying contaminated soil to be further improved.
[0002]
[Prior art]
In Japan, the number of cases of soil contamination due to harmful substances has been increasing in recent years, especially after companies that have been located in urban areas or relatively densely populated urban areas have relocated or closed business, Soil pollution due to heavy metals, volatile organic compounds, etc. is becoming apparent with the redevelopment of the factory site. If these harmful substances are left unattended, there will be a serious impact on human health, so the Soil Contamination Countermeasures Law has recently been enacted and may cause human health damage due to inclusion in soil. Some substances, such as lead, arsenic, trichlorethylene, etc. are taken as specific hazardous substances. In addition, according to the Soil Contamination Countermeasures Law, when the prefectural governor finds that these specified harmful substances do not conform to the environmental standards as a designated area, and further recognizes that there is a risk of human health damage in the designated area, In the case of direct intake risk due to eating or skin contact, the land owner or the cause of contamination of the land is subject to restricted access, pavement, covering soil, containment, purification, and in the case of the risk of elution into groundwater, etc. It is said that measures such as removal of contamination can be ordered by containment and purification.
[0003]
Against this background, taking into account the pollution status, the type of pollutant, the degree of contamination, the current state of land use and the prospects for the future, the geological conditions of the contaminated area, the processing costs that can be input, the urgency of pollution measures, etc. In addition, many soil pollution countermeasures have been proposed or implemented to meet technical, economic or social conditions. These methods are roughly divided into a method of moving the contaminated soil from the original position, transporting it to the purification treatment facility and treating it within the purification treatment facility, and a method of treating the contaminated soil in the original position without moving. Can do.
Methods for moving contaminated soil include incineration of excavated contaminated soil with an incinerator or the like, and cleaning of excavated contaminated soil with a purification treatment facility. On the other hand, in-situ treatment without moving contaminated soil includes bioremediation using microorganisms, containment of contaminated areas by construction of concrete walls, etc., fixation stabilization by pouring solids, etc., and vaporizing pollutants There are methods such as removal by aeration or cleaning of pollutants using groundwater flow.
[0004]
An example of these methods is as follows.
(1) The method of moving the soil and processing in the purification treatment facility is, for example, the method shown in the flow configuration diagram of FIG. That is, first, the contaminated soil L in the contaminated area is excavated (step 1), loaded onto a transport vehicle such as a dump truck (step 2), and transported to the purification treatment facility S (step 3). An amount corresponding to the treatment capacity of the purification treatment facility S out of the contaminated soil L temporarily (step 4) is carried into the purification treatment facility S. First, the contaminated soil L and tap water are drum-typed. Stir and mix (step 5) with the cleaning device 1 or the like. Next, the mixture of the contaminated soil L and tap water is put into a classifier 2 such as a vibrating sieve to classify the coarse particles and fine particles (step 6), and then the coarse particles are subjected to secondary washing. The apparatus 3 is further washed with a washing solution (step 7), and the fine particles are finally disposed of outside the field (step 8). Here, the discharged tap water from the drum type cleaning device 1 and the like and the discharged cleaning liquid from the secondary cleaning device 3 are collected and temporarily stored in the storage tank 4, and then the contaminants are separated by the water treatment facility 5. The treatment (step 9) is performed, and the sludge containing the pollutant is appropriately disposed (step 10) by a predetermined method, and the treated waste water is discharged into the sewer or the like (step 11). On the other hand, the coarse particles washed in the secondary washing device 3 are collected, transported to the original contaminated area, and re-filled (step 12).
[0005]
Another example is as follows.
(2) The method of processing in situ without moving the soil is as follows. For example, as disclosed in Japanese Patent Application Laid-Open No. 7-82730, a water barrier is first placed to the depth of the groundwater level in the contaminated area. Surround the soil from the side and drill an injection hole and a pumping hole in the area. Water or cleaning liquid is injected from the injection hole to raise the groundwater level in the region to make the vicinity of the contaminated soil saturated, and on the other hand, groundwater is pumped from the pumping hole to artificially generate a groundwater flow, and It is intended to capture and transport pollutants in the groundwater flow. Finally, it is a method of treating groundwater containing contaminants pumped from the pumping hole in a dedicated facility.
[0006]
[Problems to be solved by the invention]
Since the conventional technology has the above-described configuration, the following problems existed.
(1) In the above treatment method, it is necessary to directly excavate the contaminated soil and transport it to the designated purification facility. The contaminated soil is scattered from a transport vehicle such as a dump truck during the movement. As a result, secondary pollution is caused along the movement route, and there is a problem that the secondary pollution becomes more serious especially when it is necessary to move in the urban area. In addition, if there is a large amount of contaminated soil during the temporary storage before purification at the purification treatment facility, the contaminated soil will stay for a long time at temporary storage sites inside and outside the purification treatment facility. There is a problem that secondary pollution similar to the landfill or temporary storage site of construction residual soil and industrial waste is caused by the outflow of contaminated soil to the surrounding area by rainwater and the penetration of pollutants into the groundwater. It was. Furthermore, since purification processing such as cleaning is all performed in the purification processing facility, the purification processing facility will be relatively large, and the installation conditions are limited, and the purification processing facility is installed in a contaminated area or a desired area. Not only is it difficult to do so, but the problem is that the contaminated area and the purification facility will be far away, and the movement route will be extended. There was a point.
[0007]
(2) The above in-situ treatment method is intended to capture the pollutant by the injected water or washing liquid by the groundwater flow, but the groundwater circulation through the natural ground, especially when the contaminated area is extensive, In the case of impermeable ground, etc., this groundwater circulation is extremely slow, and even if pressurized injection, it is difficult to control the infiltration area of the injected water or cleaning liquid to a specific contamination range. There was a problem. Also, according to this method, although it is possible to proceed with purification on the ground while using land on the ground, a large amount of purification processing time and a large amount of purification are required until the environmental standard is achieved. There was a problem that processing costs were required. In addition, since it is assumed that land use is performed on the contaminated soil in parallel with the purification treatment of the contaminated soil, that is, human activities are carried out, for example, when a new or existing water and sewage system is operated However, there is a problem that unforeseen circumstances may not occur, such as groundwater containing pollutants mixed into the water and sewage facilities, or unexpected effects on the human body due to scattering from exposed portions of contaminated soil. It was.
[0008]
[Means for Solving the Problems]
In the present invention, the pretreatment is performed so that the pollutant is easily eluted at the original position where the contaminated soil exists, and the contamination that further improves the purification efficiency of the contaminated soil in conjunction with the soil cleaning system in the purification treatment facility. The object is to provide a soil remediation method, which is composed of the following constitution and means.
[0009]
According to the first aspect of the present invention, the cleaning liquid injection holes having a desired number and a desired depth are provided in the water-permeable ground according to the depth of the soil contaminated with lead or cadmium in the depth direction. Injecting a cleaning solution made of an aqueous citric acid solution or excavating the whole or part of a predetermined area until reaching a desired depth, and filling the cleaning solution made of the aqueous citric acid solution in the space after excavation and excavating from the predetermined area A pretreatment method in which soil contaminated with lead or cadmium is put into a washing solution made of a citric acid aqueous solution and immersed for a certain time, and a mixture of the pretreated soil by this pretreatment method and the washing solution made of the citric acid aqueous solution The mixture is put into a classifier to classify coarse and fine particles, and a portion of the fine particles of the mixture is further washed with a washing solution using a drum-type washing device, and the pretreated soil is washed. A method of purifying contaminated soil characterized by comprising in the cleaning method of performing insolubilization treatment by the formula cleaning device.
[0010]
According to invention of Claim 2, the predetermined area which consists of the impervious ground of the soil contaminated with lead or cadmium is defined in the predetermined area, and the partition wall which has a predetermined depth in the said contaminated soil And after the placement of the partition wall is completed, a cleaning solution made of a citric acid aqueous solution is injected into each of the partition sections surrounded by the partition wall, or the interior of the partition wall is excavated with the citric acid aqueous solution. A pretreatment method in which the soil contaminated with the lead or cadmium excavated from the defined section after being filled with the cleaning solution is put into a cleaning solution made of an aqueous citric acid solution and immersed for a certain period of time; A mixture of the treated soil and the cleaning solution composed of the aqueous citric acid solution is put into a classifier to classify coarse and fine particles, and a portion of the fine particles of the mixture is further washed with a cleaning solution using a drum type cleaning device. Pretreated soil It washed, a method of purifying contaminated soil characterized by comprising in the cleaning method of performing insolubilization treatment drum cleaning device.
[0011]
According to invention of Claim 3, the predetermined area which consists of the impervious ground of the soil contaminated with lead or cadmium is defined in the predetermined area, and the partition wall which has a predetermined depth in the said contaminated soil After the placement of the partition wall, the soil contaminated with lead or cadmium in each of the partition sections surrounded by the partition wall is excavated and removed, and the bottom plate processing in each defined section is performed. A pretreatment method in which the cleaning solution composed of the citric acid aqueous solution and the excavated soil are mixed and charged into the defined section and left for a predetermined time, the pretreated soil by the pretreatment method, and the citric acid aqueous solution. The mixture of the cleaning liquid is put into a classifier, and the coarse and fine particles are classified, and a part of the fine particles of the mixture is further washed with the cleaning solution in the drum-type cleaning device, and the pretreated soil is washed with the drum. Washing with insolubilization treatment A method of purifying contaminated soil characterized by comprising in the method.
[0012]
According to invention of Claim 4, the washing | cleaning liquid which consists of the said citric acid aqueous solution consists of pH adjuster of the soil contaminated with lead or cadmium, The contaminated soil of Claim 1, 2 or 3 characterized by the above-mentioned. It is a purification method.
[0013]
According to invention of Claim 5, the said partition wall was comprised by the water stop wall, It is characterized by the above-mentioned. Claim 2 or 3 It is a purification method of contaminated soil.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of a purification method for contaminated soil according to the present invention will be described in detail with reference to the accompanying drawings.
[0015]
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1
FIG. 1 shows an example of Embodiment 1 of a method for rationalizing and purifying contaminated soil according to the present invention, wherein (a) is a plan view showing the entire area of the soil-contaminated area, and (b) is soil contamination. (C) is a cross-sectional view in the direction of arrow AA in (b), and (d) is a pretreatment of the contaminated soil in-situ. It is sectional drawing which showed the flow of the pre-processing process centering on the definition division in implementation.
[0016]
The first embodiment of the present invention is an example in the case where the predetermined area B contaminated with soil is the water-permeable ground L1. FIG. 1 (a) shows a case where the entire area of the predetermined area B is handled as one division according to the area of the predetermined area B contaminated with soil, geological conditions, the amount of contaminated soil, or the situation of the surrounding area. And according to the depth penetration | infiltration degree of the soil contamination discovered by prior investigations, such as a boring, the washing | cleaning liquid injection hole 6 of the desired number and desired depth is provided in the water-permeable ground L1. Although FIG. 1A shows the case where the cleaning liquid injection hole 6 is provided, the entire area or a part of the predetermined area B is reached to a desired depth without providing the cleaning liquid injection hole 6 in addition to this. A method may also be used in which the contaminated soil excavated from the predetermined area B is filled in the cleaning liquid after being excavated and the space after excavation is filled with the cleaning liquid, and is left immersed for a predetermined time (not shown). 7 is a partition wall that partitions the predetermined area B contaminated with soil, that is, a target area for purification treatment, and a non-contaminated area C, that is, a non-target area for purification treatment, and is easily contaminated with the treatment. In order to prevent the soil from flowing out from the predetermined area B contaminated with soil into the non-contaminated area C, a water blocking wall is used.
The partition wall 7 may not be provided depending on site conditions.
[0017]
FIG. 1B shows a case where the predetermined area B contaminated with soil is defined as a predetermined area, 8 is a partition wall, and the size of the definition of one section is based on a preliminary survey such as by boring. The placement intervals W1 and W2 and the placement depth H of the partition wall 8 are set so that the excavation capacity and the capacity of the treatment facility are balanced in accordance with the determined depth of soil contamination. In addition, the partition wall 8 is constituted by a water blocking wall in order to prevent contaminants from moving between the pre-treatment definition section 81 and the processing section 82 or the processing section 83. Has been. In FIG. 1 (c), the case where the partition wall 8 is penetrated to the impervious area G where the penetration of soil contamination does not reach is shown in FIG. 1C. You may set to the depth required for a purification process, without penetrating this partition wall 8 to the depth of the water-permeable region G. FIG.
[0018]
9 is a water-permeable contaminated soil to be purified, and in the contaminated soil 9 in the defined section 82 corresponding to the order in which pretreatment is performed, as shown in FIG. 6 is provided, and the cleaning liquid 11 is injected from the cleaning liquid tank 10 disposed on the ground. At the time of this injection, pressure injection by a pump (not shown) may be performed as necessary depending on the physical characteristics of the contaminated soil 9. Further, without providing the cleaning liquid injection hole 6, the defined section 82 is excavated until a desired depth is reached, and after the excavated space is filled with the cleaning liquid 11, the contaminated soil 9 excavated from the defined section 82 is washed with the cleaning liquid. 11 and may be left immersed for a certain time (not shown). The contaminated soil 9 left for a predetermined period after the injection of the cleaning liquid 11 or after the injection into the cleaning liquid 11 changes over time to a state in which contaminants such as lead penetrating into the contaminated soil 9 are likely to elute. , The pretreated soil 12 is obtained. In the figure, 13 is the final treated soil after the pretreated soil 12 has been purified in the purification treatment facility, and is backfilled in the original defined category or another appropriate defined category for reuse. It is.
[0019]
Next, operation | movement of Embodiment 1 of the purification method of the contaminated soil which concerns on this invention is demonstrated.
After obtaining information about the presence of a predetermined area contaminated with soil, the following preliminary survey is first conducted. After confirming the cause of contamination, surveying the vegetation situation in the contaminated site and surrounding area, hearing the occurrence of damage, etc., sampling the contaminated soil by boring and collecting groundwater, the type of contaminant, horizontal and vertical direction The pollution range and concentration distribution of the soil, the weight and volume of the contaminated soil subject to purification treatment, etc. are grasped, and a purification treatment plan is formulated based on these basic information.
[0020]
In the method of injecting the cleaning liquid 11 after placing the partition wall 7 surrounding the entire area of the predetermined area B contaminated with the soil as shown in FIG. The cleaning liquid injection holes 6 set to a desired number and a desired depth are excavated so as to conform to the horizontal and vertical concentration distributions of the contaminants. A cleaning liquid tank 10 is arranged in the vicinity of the opening on the ground of the cleaning liquid injection hole 6, and the cleaning liquid injection holes are arranged simultaneously or sequentially so as to be able to respond to the amount of contaminated soil to be purified and the processing capacity of the processing facility. The cleaning liquid 11 is injected from 6. After the injection of the cleaning liquid 11, the cleaning liquid 11 is left as it is for a certain period of time necessary to elute the pollutant from the contaminated soil 9, and is observed at a stage where it can be transported to the purification treatment facility by observing changes over time. The pretreated soil 12 is excavated.
On the other hand, in the method of charging the contaminated soil 9 after filling the cleaning liquid 11, the partition wall 7 surrounding the entire area of the predetermined area B contaminated with soil is cast as necessary, and then the entire area of the predetermined area B is placed. Or excavate a part until the desired depth is reached. After the excavated space is filled with the cleaning liquid 11, the contaminated soil 9 excavated from the predetermined area B is put into the cleaning liquid 11 and left immersed for a certain time, and can be transported to the purification treatment facility by observing changes over time. A predetermined amount of the pretreated soil 12 is excavated at a stage when it reaches a certain level. (Not shown).
[0021]
Next, an operation in the case where the predetermined area B contaminated with soil is defined is described. After placing the partition wall 7 surrounding the entire area of the predetermined area B contaminated with soil as necessary, comply with the amount of contaminated soil 9 to be purified for the entire area or a required partial area, and the processing capacity of the purification facility. The partition wall 8 for defining an appropriate size is placed as shown in FIGS. 1B to 1D (step 13). Next, in the method of injecting the cleaning liquid 11, the cleaning liquid injection holes 6 set to a desired number and a desired depth are excavated so as to conform to the horizontal and vertical concentration distributions of the contaminants, and the cleaning liquid injection holes are formed. The cleaning liquid 11 is injected from the cleaning liquid tank 10 disposed in the vicinity of the opening on the ground 6 (step 14). In FIG. 1 (d), one cleaning liquid injection hole 6 is shown in one defined section, but a plurality of cleaning liquid injection holes 6 may be provided as necessary. After the cleaning liquid 11 is injected into the cleaning liquid injection hole 6, the cleaning liquid 11 is left as it is for a certain period of time necessary to elute the pollutant from the contaminated soil 9, and the change over time is observed so that it can be transported to the purification treatment facility. At this stage, a predetermined amount of pretreated soil 12 is excavated (step 15). Thereafter, the same operation is sequentially repeated for each defined section as in Step 13 to Step 15 shown in FIG.
On the other hand, in the method in which the contaminated soil 9 is charged after the cleaning liquid 11 is filled, after the partition wall 8 is placed, the defined section is excavated until the desired depth is reached. After the excavated space is filled with the cleaning solution 11, the contaminated soil 9 excavated from the defined section is put into the cleaning solution 11 and left immersed for a certain period of time, and can be transported to the purification treatment facility by observing changes over time. A predetermined amount of the pretreated soil 12 is excavated at a stage when it reaches a certain level. (Not shown)
[0022]
Next, the cleaning action of the contaminated soil by the injection of the cleaning liquid will be described with reference to the attached drawings.
FIG. 2 is a diagram showing test results when lead (Pb) is used as a contaminant and, for example, a citric acid aqueous solution is used as the cleaning liquid 11, where (a) shows the test results and (b) shows the test results. It is a figure which shows a numerical value. In FIG. 2A, the left vertical axis and vertical bar graph indicate the removal rate δ1 (%) of the pollutant, that is, lead (Pb), the right vertical axis and line graph indicate the pH value of the contaminated soil, and the horizontal axis indicates the cleaning solution 11 or quencher. Four test conditions according to the combination of the concentration of the acid aqueous solution and the solid-liquid ratio α of the contaminated soil and the cleaning liquid 11 are shown. Here, the removal rate δ1 (%) of lead (Pb) = {1− (D1 / D2)} × 100. However, D1 is the concentration (mg / kg) of the pollutant or lead (Pb) contained in the contaminated soil after the pretreatment, and D2 is the concentration of the pollutant or lead (Pb) contained in the contaminated soil before the pretreatment (mg / Kg). The solid-liquid ratio α is a ratio between the weight (g) of the contaminated soil subjected to the test and the weight (g) of the cleaning liquid used for the test, that is, the citric acid aqueous solution.
[0023]
In the test, soil 9 collected from an actual contaminated site having a lead concentration (Pb) of 2700 (mg / kg) was used as the contaminated soil 9, and a citric acid aqueous solution was used as the cleaning solution 11, respectively. Four conditions were set by changing the addition amount represented by the above-mentioned solid-liquid ratio α, and all of the conditions were immersed for 14 days. Here, the reason for using the citric acid aqueous solution as the washing solution 11 in the test is that the citric acid is one of the organic acids contained in the natural soil, and is harmless to the soil environment if the concentration is appropriate. In addition, acetic acid, which is also an organic acid, has a strong odor and is usually liquid, whereas citric acid is odorless and easy to handle with powder, mass production is possible and it is inexpensive, and ground improvement works in the construction field It is adopted because it is used as a pH adjuster.
Incidentally, “(shake)” in one of the conditions shown in FIGS. 2 (a) and 2 (b) means that the immersed specimen was shaken, and the other three were Not shaken.
[0024]
The test results show that the residual concentration of lead (Pb) is 1750 (mg / kg) when the concentration of the cleaning solution 11, that is, the citric acid aqueous solution is 3.0 (% wt) and the solid-liquid ratio α is 1: 1.0. ) And lead (Pb) removal rate δ1 is the highest at 35.2 (%), but on the other hand, the pH value is below 6.18, which is neutral 7.0, and the acidity becomes stronger, so the negative impact on the ground environment Is concerned. Therefore, it is appropriate to use a citric acid aqueous solution with a concentration of about 1.0 (%) having a lead (Pb) removal rate δ1 of around 30 (%) and a pH value of 8.0 or more. To be judged. However, the soil has a phenomenon called buffering action, and it is known that the pH value converges to 7.0-8.0 by extending the soaking period. Problems due to the concentration of the aqueous solution can be solved.
Thus, according to the present invention, it has been found that lead (Pb) contained in the contaminated soil 9 can be largely removed, and the pH value of the soil is adjusted by the cleaning solution 11 using a citric acid aqueous solution.
[0025]
3A and 3B are diagrams showing test results when cadmium (Cd) is used as a contaminant and, for example, an aqueous citric acid solution is used as the cleaning liquid 11, wherein FIG. 3A shows the test results, and FIG. 3B shows the test results. It is a figure which shows a numerical value. In FIG. 2A, the left vertical axis and vertical bar graph indicate the removal rate δ2 (%) of the pollutant, that is, cadmium (Cd), the right vertical axis and line graph indicate the pH value of the contaminated soil, and the horizontal axis indicates the cleaning solution 11 or quencher. Three test conditions according to the combination of the concentration of the acid aqueous solution and the solid-liquid ratio α of the contaminated soil and the cleaning liquid 11 are shown. Here, the removal rate of cadmium (Cd) δ2 (%) = {1− (D3 / D4)} × 100. However, D3 is the density | concentration (mg / kg) of the pollutant, ie, cadmium (Cd), contained in the contaminated soil after pretreatment, and D4 is the density of the pollutant, ie, cadmium (Cd), contained in the contaminated soil before pretreatment (mg). / Kg). The solid-liquid ratio α is a ratio between the weight (g) of the contaminated soil subjected to the test and the weight (g) of the cleaning liquid used for the test, that is, the citric acid aqueous solution.
[0026]
In the test, soil 9 collected from an actual contamination site having a cadmium concentration (Cd) of 0.8 (mg / kg) was used as the contaminated soil 9, and an aqueous citric acid solution was used as the cleaning solution 11, respectively. Three conditions were set by changing the concentration and the addition amount represented by the above-mentioned solid-liquid ratio α, and all of the conditions were immersed for 14 days. Here, the reason for using the citric acid aqueous solution as the washing solution 11 in the test is that the citric acid is one of the organic acids contained in the natural soil, and is harmless to the soil environment if the concentration is appropriate. In addition, acetic acid, which is also an organic acid, has a strong odor and is usually liquid, whereas citric acid is odorless and easy to handle with powder, mass production is possible and it is inexpensive, and ground improvement works in the construction field It is adopted because it is used as a pH adjuster.
[0027]
The test results show that the concentration of the cleaning solution 11, that is, the citric acid aqueous solution is 3.0 (% wt) and the solid-liquid ratio α is 1: 1.0, and each is 1.0 (% wt) and 1: 1. In both cases, the residual concentration of cadmium (Cd) is 0.3 (mg / kg), and the removal rate δ2 of cadmium (Cd) is the highest at 62.5 (%). Since the value is 6.18, which is less than neutral 7.0 and the acidity becomes strong, there is a concern about adverse effects on the ground environment. Therefore, an aqueous citric acid solution having a concentration of about 1.0 (%) having a cadmium (Cd) removal rate δ2 of about 50 to 60 (%) and a pH value of 7.0 or more is used as a guide. It is judged appropriate. However, the soil has a phenomenon called buffering action, and it is known that the pH value converges to 7.0-8.0 by extending the soaking period. Problems due to the concentration of the aqueous solution can be solved.
Thus, according to the present invention, it has been found that cadmium (Cd) contained in the contaminated soil 9 can be largely removed, and the pH value of the soil is adjusted by the cleaning solution 11 using an aqueous citric acid solution.
[0028]
Second Embodiment of the Invention
FIG. 4 shows an example of Embodiment 2 of the purification method for contaminated soil according to the present invention, and (a) is a plan view showing a part when a predetermined area contaminated with soil is defined, (b) is a cross-sectional view in the direction of arrow EE in (a), (c) is a cross-section showing the flow of the pretreatment process centering on the defined section where the pretreatment of the contaminated soil is being performed in-situ. FIG.
[0029]
The second embodiment of the present invention is an example in the case where the predetermined area B contaminated with soil is the impermeable ground L2. Fig. 4 (a) shows a case where a predetermined area B contaminated with soil is defined as a predetermined area, 8 is a partition wall, and the size of the definition of one section is found by a preliminary survey such as by boring. The placement intervals W1 and W2 and the placement depth H of the partition wall 8 are set so as to balance the excavation capacity and the capacity of the treatment facility according to the degree of penetration of soil contamination in the depth direction. In addition, the partition wall 8 is constituted by a water blocking wall in order to prevent contaminants from moving between the pre-treatment definition section 81 and the processing section 82 or the processing section 83. Has been. In FIG. 1 (c), the case where the partition wall 8 is penetrated to the impervious area G where the penetration of soil contamination does not reach is shown in FIG. 1C. It is good also as a depth required for a purification process, without penetrating the partition wall 8 to the depth of the permeable region G.
[0030]
14 is impervious contaminated soil to be treated. First, after excavating the contaminated soil 14 in one or a plurality of specific defined sections 82, the contaminated soil 14 is temporarily placed in the vicinity, As will be described later in the operation of the second embodiment of the present invention, in the second embodiment of the present invention, the definition section 82 is used as a space dedicated for pre-processing, so that it is necessary to ensure workability and safety. The bottom board process 15 is performed by a method such as solidification by cement milk injection, for example. After that, the contaminated soil 14 that has been excavated and temporarily placed in the vicinity is mixed with the cleaning liquid 11 filled in the cleaning liquid tank 10 disposed on the ground as shown in FIG. 4C. After the cleaning solution 11 and the contaminated soil 14 are mixed and introduced, the contaminated soil 14 left for a predetermined period of time changes over time to a state in which contaminants such as lead penetrating into the contaminated soil 14 are easily eluted. The pretreated soil 12 is obtained. Reference numeral 13 denotes final treated soil after the pretreated soil 12 is completely treated in the purification treatment facility, and is backfilled in the original defined section or another appropriate defined section.
[0031]
Next, operation | movement of Embodiment 2 of the purification method of the contaminated soil which concerns on this invention is demonstrated.
After information about the presence of a predetermined area contaminated with soil is obtained, first, a pre-investigation similar to that shown in the first embodiment of the present invention is performed to formulate a treatment plan.
[0032]
According to the treatment plan, as shown in FIG. 4 (b), in order to define the whole area or a necessary partial area after placing the partition wall 7 surrounding the whole area of the predetermined area B contaminated with soil as necessary. The partition wall 8 is placed (step 16). After the defined section is completed, one or more defined sections are appropriately selected, and after the contaminated soil 14 in the defined section 82 is excavated and temporarily placed, the bottom of the defined section 82 is, for example, cemented. After the ground solidifying material such as milk is introduced and the bottom plate processing 15 is performed, the temporarily contaminated contaminated soil 14 and the cleaning liquid 11 are mixed and introduced into the defined section 82 (step 17).
[0033]
The bottom board processing 15 is necessary to ensure workability and safety when the contaminated soil 14 is dug once and mixed and introduced with the cleaning liquid 11. The bottom board processing 15 is classified into all the defined categories. If it does, a cement layer will be formed in the underground of the whole area of the predetermined area B contaminated with soil. This is because there is a concern that the land use after treatment, that is, after the purified soil is backfilled, may have an adverse effect depending on the contents of the land use. In this case, one or a plurality of defined sections are used as a processing-dedicated space.
[0034]
After the contaminated soil 14 and the cleaning liquid 11 are mixed and introduced into the one or more pretreatment dedicated definition sections, the cleaning liquid 11 is left as it is for a certain period of time necessary to elute the pollutant from the contaminated soil 14, and changes over time. The pre-treated soil 12 is excavated (step 18) when it is observed and transported to the purification treatment facility. After excavating the pretreated soil 12 and transporting it to the purification facility, the contaminated soil 14 of other defined sections is excavated and mixed and introduced into the single or plural pretreated dedicated defined sections 82 together with the cleaning liquid 11. Thereafter, the same operation is sequentially repeated for each defined section to process the contaminated soil 14 in all defined sections.
[0035]
Embodiment 3 of the Invention
FIG. 5 is a flow configuration diagram showing a soil cleaning system in the purification treatment facility F that processes the pretreated soil 12.
The pretreated soil 12 that has been pretreated in the above-described first and second embodiments of the present invention is carried into a purification treatment facility F as shown in FIG. It will be washed to the extent that it meets the standards.
First, the pretreated soil 12 excavated from the defined section of the contaminated area B in Step 15 or Step 18 is transported to the purification treatment facility F by a transport vehicle such as a dump truck (Step 19). At this time, since the pretreated soil 12 in an amount corresponding to the treatment capacity of the purification treatment facility F is transported, the pretreated soil 12 is hardly accumulated in the premises of the purification treatment facility F, so that smooth It will be carried into the purification treatment facility F.
[0036]
Regarding the process in the purification treatment facility F, first, the mixture of the pretreated soil 12 and the cleaning liquid 11 is put into a classifier 16 such as a vibration sieve to classify the coarse and fine particles (step 20). Then, the coarse particles and a part of the fine particles are further washed with a washing solution in, for example, the drum type washing device 17 (step 21), and the remainder of the fine particles is finally disposed of outside the field (step 22). The Part of the coarse and fine particles whose concentration of contaminants has been reduced to a level that satisfies the environmental standards through step 21 has increased the solubility of the contaminants in a series of purification processes. Since it cannot be used for reuse such as returning, insolubilization processing is finally performed in the drum type cleaning device 18 (step 23).
[0037]
Here, the discharged cleaning solution from the drum type cleaning device 17 and the discharged insolubilized solution from the drum type cleaning device 18 are collected and temporarily stored in the reservoir 19, and then each cleaning solution processing facility 20, insolubilized solution processing. It is processed (step 24) in the facility 21 and reused. In addition, the waste liquid after reuse is subjected to a process (step 25) for separating contaminants in the water treatment facility 22 together with the cleaning liquid used in the pre-treatment in-situ collected from the classifier 16. In addition, the sludge containing the pollutant is properly disposed of by a predetermined method (step 26), and the treated waste water is discharged into the sewer or the like (step 27). On the other hand, the coarse particles and a part of the fine particles insolubilized in the drum type cleaning device 18 are collected as the final treated soil 13 and transported to the original contaminated area to be reused (for example, refilled). Step 28) is intended.
[0038]
【The invention's effect】
The method for purifying contaminated soil according to the present invention has the following effects because it has the above-described configuration and operation.
[0039]
According to the first aspect of the present invention, the cleaning liquid injection holes having a desired number and a desired depth are provided in the water-permeable ground according to the depth of the soil contaminated with lead or cadmium in the depth direction. Injecting a cleaning solution made of an aqueous citric acid solution or excavating the whole or part of a predetermined area until reaching a desired depth, and filling the cleaning solution made of the aqueous citric acid solution in the space after excavation and excavating from the predetermined area A pretreatment method in which soil contaminated with lead or cadmium is put into a washing solution made of a citric acid aqueous solution and immersed for a certain time, and a mixture of the pretreated soil by this pretreatment method and the washing solution made of the citric acid aqueous solution The mixture is put into a classifier to classify coarse and fine particles, and a portion of the fine particles of the mixture is further washed with a washing solution using a drum-type washing device, and the pretreated soil is washed. It provides a method of purifying contaminated soil characterized by comprising in the cleaning method of performing insolubilization treatment by the formula cleaning device.
With this configuration, a desired amount of a cleaning solution made of a citric acid aqueous solution is injected into the injection hole provided in the water-permeable ground according to the depth of the soil contaminated with lead or cadmium for a predetermined time. Or, by putting the soil contaminated with lead or cadmium into an aqueous citric acid solution and leaving it immersed for a certain time, the pretreatment method is carried out without moving the contaminated soil from its original position, The entire purification treatment facility can be made relatively small, and the purification treatment facility can be installed in or near a predetermined area contaminated with soil. In addition to preventing secondary contamination along railway lines and reducing transportation costs, it is easy to manage temporary storage when carrying contaminated soil to a purification treatment facility, and also prevents secondary contamination. Can, the final treated soil after backfilling to the original position, there is an effect that a portion of the solubilized contaminants at a series of purification process can be prevented from eluting as residual contaminant.
[0040]
According to invention of Claim 2, the predetermined area which consists of the impervious ground of the soil contaminated with lead or cadmium is defined in the predetermined area, and the partition wall which has a predetermined depth in the said contaminated soil And after the placement of the partition wall is completed, a cleaning solution made of a citric acid aqueous solution is injected into each of the partition sections surrounded by the partition wall, or the interior of the partition wall is excavated with the citric acid aqueous solution. A pretreatment method in which the soil contaminated with the lead or cadmium excavated from the defined section after being filled with the cleaning solution is put into a cleaning solution made of an aqueous citric acid solution and immersed for a certain period of time; A mixture of the treated soil and the cleaning solution composed of the aqueous citric acid solution is put into a classifier to classify coarse and fine particles, and a portion of the fine particles of the mixture is further washed with a cleaning solution using a drum type cleaning device. Pretreated soil Washed, it provides a method of purifying contaminated soil characterized by comprising in the cleaning method of performing insolubilization treatment drum cleaning device.
Since it was set as such a structure, in addition to the effect of invention of Claim 1, in order to pre-process, after defining the predetermined area of the soil contaminated with lead or cadmium into the predetermined area, the predetermined area is Even when there is a large amount of contaminated soil to be treated over a wide area, it is possible to carry out fine purification processing that matches the processing capacity of the purification treatment facility, and further prevent secondary contamination in transportation and temporary storage. There is an effect that can be done.
[0041]
According to invention of Claim 3, the predetermined area which consists of the impervious ground of the soil contaminated with lead or cadmium is defined in the predetermined area, and the partition wall which has a predetermined depth in the said contaminated soil After the placement of the partition wall, the soil contaminated with lead or cadmium in each of the partition sections surrounded by the partition wall is excavated and removed, and the bottom plate processing in each defined section is performed. A pretreatment method in which the cleaning solution composed of the citric acid aqueous solution and the excavated soil are mixed and charged into the defined section and left for a predetermined time, the pretreated soil by the pretreatment method, and the citric acid aqueous solution. The mixture of the cleaning liquid is put into a classifier, and the coarse and fine particles are classified, and a part of the fine particles of the mixture is further washed with the cleaning solution in the drum-type cleaning device, and the pretreated soil is washed with the drum. Washing with insolubilization treatment It provides a method of purifying contaminated soil characterized by comprising in the method.
Since it was set as such a structure, in addition to the effect of the invention of Claim 2, it has the effect that it can apply also to the predetermined area which consists of a water-impermeable ground in the soil contaminated with lead or cadmium.
[0042]
According to invention of Claim 4, the washing | cleaning liquid which consists of the said citric acid aqueous solution consists of pH adjuster of the soil contaminated with lead or cadmium, The contaminated soil of Claim 1, 2 or 3 characterized by the above-mentioned. Provide a purification method.
Since it is such a configuration, in addition to the effect of the invention of claim 1, 2 or 3, as a pH adjuster used in the ground improvement work in the construction field, organic contained in natural soil Because citric acid, which is one of the acids, is used as a cleaning solution, it can be adapted to the natural environment without elution of soil components and nutrients, unlike strong acids such as hydrochloric acid and nitric acid, at moderate concentrations. In addition, citric acid has the effect of being odorless and easy to handle with powder, improving the workability of the purification treatment of contaminated soil, and at the same time reducing the processing cost.
[0043]
According to invention of Claim 5, the said partition wall was comprised by the water stop wall, It is characterized by the above-mentioned. Claim 2 or 3 A method for remediating contaminated soil is provided.
Because it was such a configuration, Claim 2 or 3 In addition to the effects of the invention of the present invention, the contaminants in the defined section before the pretreatment method is eluted by the effect of the cleaning liquid and enter the defined section during or after the pretreatment by rain or groundwater. This has the effect of being able to control the concentration of pollutants for each defined category accurately and as planned.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a configuration diagram showing an example of a first embodiment of a method for purifying contaminated soil according to the present invention, in which (a) is a plan view showing the entire area of a soil-contaminated area, and (b) is a plan view. A plan view showing a part of a predetermined area contaminated with soil, (c) is a cross-sectional view in the direction of arrow AA in (b), and (d) is the original position of the contaminated soil. It is sectional drawing which showed the flow of the pre-processing process centering on the definition division in which pre-processing is implemented.
FIGS. 2A and 2B are diagrams showing test results of cleaning action when lead (Pb) is used as a contaminant and a citric acid aqueous solution is used as a cleaning solution, where FIG. 2A shows the test results, and FIG. 2B shows the test results; It is a figure which shows the numerical value of.
FIGS. 3A and 3B are diagrams showing test results of cleaning action when cadmium (Cd) is used as a contaminant and citric acid aqueous solution is used as a cleaning solution, where FIG. 3A shows the test results and FIG. 3B shows the test results. It is a figure which shows the numerical value of.
FIG. 4 is a block diagram showing an example of a second embodiment of a method for purifying contaminated soil according to the present invention, wherein (a) is a plane showing a part when a predetermined area contaminated with soil is defined. FIG. 4B is a cross-sectional view in the direction of arrows EE in FIG. (C) is sectional drawing which showed the flow of the pre-processing process centering on the definition division in which the pre-processing of the original position of contaminated soil is implemented.
FIG. 5 is a flow configuration diagram showing a soil washing system in a purification treatment facility for treating pretreated contaminated soil.
FIG. 6 is a flow configuration diagram showing an example of a method for purifying contaminated soil in a purification treatment facility by moving the soil in the prior art.
[Explanation of symbols]
6 Cleaning liquid injection hole
7 Bulkhead
8 division wall
81 Classification before purification
82 Definition categories during the purification process
83 Definition categories after purification
9 Contaminated soil
10 Cleaning liquid tank
11 Cleaning liquid
12 Pretreated soil
13 Final treated soil
14 Contaminated soil
15 Bottom processing
16 classifier
17 Drum-type cleaning device
18 Drum-type cleaning device (for insolubilization)
19 Reservoir
20 Cleaning solution processing equipment
21 Insolubilized solution processing equipment
22 Water treatment facilities
B Specified area contaminated with soil
C Non-contaminated area
F Purification processing facility
G Impervious area
H Depth of partition wall
L1 permeable ground
L2 impervious ground
W1, W2 Partition wall placement interval
δ1 Lead (Pb) removal rate
δ2 Cadmium (Cd) removal rate
α Solid-liquid ratio

Claims

Depending on the depth of penetration of soil contaminated with lead or cadmium, a desired number and depth of cleaning liquid injection holes are provided in the permeable ground, and a cleaning liquid made of a citric acid aqueous solution is injected into the cleaning liquid injection hole. Or, excavate the entire area or a part of the predetermined area until the desired depth is reached, fill the space after excavation with the cleaning solution made of the citric acid aqueous solution, and then clean the soil contaminated with the lead or cadmium excavated from the predetermined area. A pretreatment method that is put into a cleaning solution made of an acid aqueous solution and left to stand for a predetermined time, and a mixture of the pretreated soil by this pretreatment method and the cleaning solution made of the citric acid aqueous solution is put into a classifier, and the coarse fraction, The fine particles are classified, and a part of the fine particles of the mixture is further washed with a washing solution using a drum-type washing device, and the soil is subjected to insolubilization with a drum-type washing device. Method of purifying contaminated soil characterized by comprising in the washing method.

A predetermined area composed of a water-impermeable ground of soil contaminated with lead or cadmium is defined in a predetermined area, and a partition wall having a predetermined depth is placed in the contaminated soil, and the partition wall is driven After the completion, the partition section surrounded by the partition wall is injected with a cleaning solution composed of a citric acid aqueous solution, or the partition section is excavated and filled with the cleaning solution composed of the citric acid aqueous solution. A pretreatment method in which the soil contaminated with lead or cadmium excavated from is put into a washing solution made of a citric acid aqueous solution and left to stand for a predetermined time, a pretreated soil by this pretreatment method and the citric acid aqueous solution The mixture of washing liquid is put into a classification device to classify coarse and fine particles, and a part of the fine particles of the mixture is further washed with a washing solution with a drum type washing device, and the pretreated soil is washed with a drum type. Cleaning device Method of purifying contaminated soil characterized by comprising in the cleaning method of performing insolubilization process.

A predetermined area composed of a water-impermeable ground of soil contaminated with lead or cadmium is defined in a predetermined area, and a partition wall having a predetermined depth is placed in the contaminated soil, and the partition wall is driven After completion, the soil contaminated with lead or cadmium in each of the compartments surrounded by the compartment wall is excavated and removed, and a bottom plate treatment is performed in each of the defined compartments, and the cleaning solution composed of the citric acid aqueous solution and the A pretreatment method in which the excavated soil is mixed and charged into the defined section and allowed to stand for a certain period of time, and a mixture of the pretreated soil by the pretreatment method and the cleaning solution composed of the citric acid aqueous solution is charged into the classifier. A washing method in which coarse and fine particles are classified, a part of the fine particles of the mixture is further washed with a washing solution in a drum-type washing device, and the pretreated soil is washed with a drum-type washing device. It is characterized by The method for remediation of contaminated soil.

4. The method for purifying contaminated soil according to claim 1, wherein the cleaning solution comprising the citric acid aqueous solution is a pH adjuster for soil contaminated with lead or cadmium.

The method for purifying contaminated soil according to claim 2 or 3 , wherein the partition wall is constituted by a water blocking wall.