JP3818446B2 - Heavy metal fixing agent - Google Patents
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- JP3818446B2 JP3818446B2 JP2002191833A JP2002191833A JP3818446B2 JP 3818446 B2 JP3818446 B2 JP 3818446B2 JP 2002191833 A JP2002191833 A JP 2002191833A JP 2002191833 A JP2002191833 A JP 2002191833A JP 3818446 B2 JP3818446 B2 JP 3818446B2
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【０００１】
【発明の属する技術分野】
本発明は、汚染土壌、排水、地下水、都市ゴミ焼却灰、産業廃棄物等に含まれる重金属の不溶化あるいは固形化による封じ込めに使用する重金属固定化剤に関するものである。本発明の重金属固定化剤は、セメントや固化材に添加して重金属汚染土壌からの重金属の溶出抑制に使用される。
【０００２】
【従来の技術】
無機系物質による重金属の固定化剤には、対象とする重金属の種類により、大別して酸化剤、還元剤及び沈殿剤がある。酸化剤は、汚染土や排水中のＣＯＤやＢＯＤ低減、脱色、除鉄、除マンガン、シアン及び有機水銀の酸化分解、重金属の沈殿の前処理を目的として添加されるものであり、酸素、オゾン、金属酸化物・過酸化物、塩素酸塩、ハロゲン化物等が使用される。
還元剤は、例えば、六価クロムの難溶性三価クロムへの還元に使用され、水素化物（硫化水素）、二酸化硫黄、亜硫酸ナトリウム、硫黄（Ｓ）、硫化カルシウム（ＣａＳ）、多硫化カルシウム（ＣａＳｘ）、亜硫酸水素ナトリウム、硫酸第一鉄のほか、金属粉（Ｎａ、Ｋ、Ｍｇ、Ｆｅ、Ｚｎ）等が使用される。また、特開２００１−３４２４６１号公報には、多硫化カルシウム水溶液に固定化材（例えば、生石灰）を添加して粉状化した後、セメント系固化材に添加する方法も開示されている。
更に、沈殿剤は、カドミウム、鉛、砒素、水銀、等の有害重金属等を難溶性の硫化物、カルシウム塩、水酸化物として沈殿させる目的で添加されるものであり、硫化物、アルカリ、石灰等が使用されている。
【０００３】
しかし、汚染土壌、排水、地下水、都市ゴミ焼却灰、産業廃棄物中の可溶性重金属の固定化は、対象とする重金属の許容濃度限界をクリア出来なかったり、複数の重金属種が共存する複合汚染の場合には性能低下が生じることがあり、上記した従来用いられてきた還元剤や沈殿剤の性能には自ずと限界があった。また、硫化物として多く使用される硫化ナトリウムは潮解性があり、また比較的毒性も高く、使用方法が制限される問題点もあった。
一方、重金属等汚染土壌の恒久対策の一つとして、セメントあるいは固化材による固形化封じ込めがあるが、この方法は土壌の物理化学的固化によるものであって、その効果は土壌の性状（粒度、含水比、有機物量）の影響を大きく受けやすく、結果として、重金属の固定化にはやはり限界があった。
【０００４】
【発明が解決しようとする課題】
本発明の目的は、汚染土壌、排水、地下水、都市ゴミ焼却灰、産業廃棄物中の重金属の還元あるいは沈殿による無害化性能に優れた重金属固定化剤を提供することにある。また、該重金属固定化剤とセメント、固化材等とを併用することにより、セメント、固化材の固形化機能が更に付加されて、重金属の封じ込め性能が高められ、且つ封じ込め対象の重金属種が拡大した固化材の提供も目的とする。
【０００５】
【課題を解決するための手段】
発明者は、先ず、Ｃａ８Ｓ５(Ｓ２Ｏ３)(ＯＨ)１２・２０Ｈ２Ｏ及び水酸化カルシウムからなる重金属固定化剤が優れた封じ込め作用を有することを見出し、Ｃａ８Ｓ５(Ｓ２Ｏ３)(ＯＨ)１２・２０Ｈ２Ｏを３０〜８５質量％含有する重金属固定化剤を見出した。また、この重金属固定化剤は、消石灰と多硫化カルシウム水溶液とを混合・攪拌することによって得られたものであることが好ましく、さらに当該重金属固定化剤を０．５〜２０質量％含有するセメントまたは固化材が極めて優れた封じ込め材料と成ることを見出し、本発明を完成した。
【０００６】
【発明の実施の形態】
本発明の重金属固定化剤は、Ｃａ８Ｓ５(Ｓ２Ｏ３)(ＯＨ)１２・２０Ｈ２Ｏ及び水酸化カルシウムを主成分とするものである。Ｃａ８Ｓ５(Ｓ２Ｏ３)(ＯＨ)１２・２０Ｈ２Ｏで示される水和物は、図１に示したように粉末Ｘ線回折によって同定される。これらの構成成分の定量は、化学分析（硫黄分、遊離水酸化カルシウム等）からノルムにより行うことができる。すなわち、Ｘ線回折で同定される上記の水和物中の硫黄含有量は化学量論的には約２０質量％であり、換言すれば硫黄含有量に５を乗じた値が水和物量となる。しかし、本発明の重金属固定化剤中には上記の水和物以外の硫黄化合物も共存していることが推定され、単に硫黄含有量に５を乗じることによって水和物量を計算すると過大評価される。このため、本明細書では、定量された全硫黄分を３．５倍した値で水和物量を推定して記述した。
【０００７】
重金属固定化剤中のＣａ８Ｓ５(Ｓ２Ｏ３)(ＯＨ)１２・２０Ｈ２Ｏ（以下、水和物と称す）の含有量は３０〜８５質量％とするのが好ましい。
水和物含有量が３０質量％未満では、重金属の還元あるいは沈殿による無害化効果が小さくなり好ましくない。一方、８５質量％を超えると、水酸化カルシウムの適正量が確保できなくなり、重金属の難溶性水酸化物形成、あるいはカルシウム塩の生成等、消石灰に因ってもたらされる沈殿形成の複合効果の発現が不十分となるだけでなく、粉体流動性も低下し好ましくない結果を招く。本発明の重金属固定化剤は、５〜５５質量％の水酸化カルシウムを含有することが望ましいのである。
【０００８】
Ｃａ８Ｓ５(Ｓ２Ｏ３)(ＯＨ)１２・２０Ｈ２Ｏ水和物は市場には流通しておらず、消石灰と出来合いの水和物の単純混合で本発明の重金属固定化剤を調製することは困難である。したがって、本発明の重金属固定化剤は、多硫化カルシウム水溶液と消石灰との反応によって製造するのが好ましい実施形態である。
多硫化カルシウム水溶液は、固形分基準で約３０〜５５質量％のものが使用でき、消石灰は一般の工業製品が使用できる。尚、生石灰やセメント仮焼原料も、水を加えて予め消和したものを冷却した後、多硫化カルシウム水溶液と混合することにより原料として使用することができる。予め消和した原料を使用した場合には、生石灰を使用した場合とは異なり、消和に起因する発熱を伴わないことから、Ｃａ８Ｓ５(Ｓ２Ｏ３)(ＯＨ)１２・２０Ｈ２Ｏ水和物の生成・存在が可能となり、この点において特開２００１−３４２４６１号公報記載の、多硫化カルシウム水溶液に固定化材（例えば、生石灰を添加して粉状化）を添加する方法で得られるものとは、生成する化合物種及び重金属固定化能が大きく相違する。
【０００９】
重金属固定化剤中において前記した水和物含有量を確保するためには、多硫化カルシウム水溶液／消石灰 質量比（固形分基準）は、多硫化カルシウム水溶液中の固形分濃度に応じて変化するが、入手容易性等、実用的面を考慮すると０．２〜１．０の範囲から選択するのが好ましい。
【００１０】
多硫化カルシウム水溶液と消石灰の混合方法は一般に使用されているミキサー類を使用して行うことができる。この場合、Ｃａ８Ｓ５(Ｓ２Ｏ３)(ＯＨ)１２・２０Ｈ２Ｏ水和物が比較的簡単に分解・脱水されることから、混合・攪拌操作及び必要に応じて加える乾燥操作は５０℃以下で行うのが好ましく、窒素ガスパージによって重金属固定化剤の空気酸化を抑制するのは更に好ましい結果をもたらす。
【００１１】
本発明の重金属固定化剤は、処理対象物に単独で添加する重金属固定化剤としても使用できるが、セメントあるいは固化材と併用することがより効果的である。セメントは、各種ポルトランドセメント、混合セメント（高炉セメント、フライアッシュセメント、シリカセメント、シリカフュームセメント等）が使用可能であり、固化材は、セメント系（一般軟弱土用、高含水土用、高有機質土用、六価クロム対策用、発塵抑制型等）、石灰系（生石灰系、消石灰系）、マグネシア系（マグネシア、水酸化マグネシウム、塩基性炭酸マグネシウム）、せっこう系（半水、無水、二水）、高炉スラグ系の１種または２種以上を使用することができる。
【００１２】
これらセメントあるいは固化材中における重金属固定化剤の含有量は、処理の対象となる汚染土壌、都市ゴミ焼却灰あるいは産業廃棄物種によって異なり、また、固定化剤中における水和物含有量によって異なるが、０．５から２０質量％とするのが好ましい。０．５質量％未満では、還元、沈殿及び固形化による無害化効果が十分発揮されない場合があり、また２０質量％を超えると、セメントあるいは固化材量が少なくなりセメントあるいは固化材に因ってもたらされる固形化効果の発現が不充分となり好ましくない。
【００１３】
【実施例】
以下に具体例を示し、本発明を更に詳しく説明する。
重金属固定化剤は次のように調製した。
Ｓ（硫黄）源としては、石灰硫黄合剤市販品（固形分濃度３５質量％の多硫化カルシウム水溶液、以下「合剤」と記述）又こはの合剤からエバポレータで水分を蒸発させ、固形分濃度４９．５質量％とした濃縮液を使用した。
ホバートミキサー（容量 ５Ｌ）を用い、この石灰硫黄合剤またはその濃縮液を消石灰に添加する方法で、名称Ａ〜Ｆで示される重金属固定化剤を得た。Ａ〜Ｃでは合剤を使用し、Ｄ〜Ｆでは濃縮液を使用した。混合攪拌時間は２０分間、多硫化カルシウム水溶液はいずれも混合・攪拌開始から５分間かけて消石灰に添加した。また、比較対照用として、合剤と生石灰から還元性粉体Gを調製した。
重金属固定化剤は、単独またはセメント系固化材と併用して用いた。固化材を併用する場合、一般軟弱土用セメント系固化材（ユースタビラー １０）を使用した。
【００１４】
重金属の固定化処理対象物としては、次の３種を選択した。
（イ）砂質土（自然含水比 １８．２％） 環境庁告示第４６号による鉛溶出量：８２．３ ｍｇ／Ｌ
（ロ）砂質土（自然含水比 ２１．２％） 環境庁告示第４６号による砒素溶出量：１６．７ ｍｇ／Ｌ
（ハ）都市ゴミ焼却灰 調湿前の有姿の環境庁告示第１３号による溶出試験での溶出量：カドミウム２０．１ｍｇ／Ｌ、砒素０．２６ｍｇ／Ｌ、鉛０．８１ｍｇ／Ｌ、六価クロム０．９８ｍｇ／Ｌ 都市ゴミ焼却灰は、含水比が１８質量％になるように予め水を噴霧、攪拌して調湿した。
【００１５】
重金属固定化剤及び該固定化剤を含む固化材による、含重金属処理対象物の処理は次の様に行った。
すなわち、重金属固定化剤及び固化材を処理対象物に添加、攪拌混合し、型枠（径５cm×高さ１０cm）に充填したのち締固め、２０℃、湿度６０％の恒温室で密封養生した。７日経過後、脱型して供試体を得た。
【００１６】
脱型後の供試体については、次の評価試験を行った。
・圧縮強度：ＪＩＳ A １２１６により一軸圧縮強度を測定した。
・重金属の溶出量：汚染土壌については環境庁告示第４６号、都市ゴミ焼却灰については環境庁告示第１３号に則り、重金属の溶出量を測定した。
評価結果を、表１に示す。表１において、重金属固定化剤中のＣａ８Ｓ５(Ｓ２Ｏ３)(ＯＨ)１２・２０Ｈ２Ｏ水和物含有量は、全硫黄量の定量値に３．５を乗じた計算値を記載した。また、重金属溶出量については、重金属濃度が検出限界以下のものは「ＮＤ」と記載した。
【００１７】
【表１】
重金属固定化剤Ｅと一般軟弱土用セメント系固化材との併用による鉛汚染安定処理土の溶出試験結果から、セメント系固化材に対する重金属固定化剤の所要量は、内割質量基準で０．５〜２０．０％が好ましいことがわかる。４０質量％になると、セメント系固化材量が相対的に減少することもあって、鉛の封じ込め効果が低減する（Ｎｏ．１〜Ｎｏ．６）。
【００１９】
Ｎｏ．７〜１１は、重金属固定化剤中のＣａ８Ｓ５(Ｓ２Ｏ３)(ＯＨ)１２・２０Ｈ２Ｏ水和物含有量を変えたものであるが、重金属固定化剤中の水和物含有量が３０〜８５質量％の範囲では、良好な水溶性砒素封じ込め効果を示す。水和物含有量がこの範囲内に在っても、水酸化カルシウム含有量が低い場合には、水溶性砒素の封じ込め効果が大幅に小さくなる（Ｎｏ．１２）。また、消石灰に代え、合剤と生石灰より調製した還元性粉体Ｇ（Ｎｏ．１３）においても水溶性砒素に対する封じ込め効果は低くなる。
【００２０】
本発明の重金属固定化剤を、都市ゴミ焼却灰のように複数の重金属を含有する複合汚染物に重金属固定化剤を単独添加した場合には、種々の重金属に対して複合的、かつ十分な封じ込めが可能となる（Ｎｏ．１４〜１７）。しかし、合剤と生石灰より調製した還元性粉体Ｇでは、固化材と併用した時と同様、砒素や鉛に対する固形化機能が劣る（Ｎｏ．１８）。
【００２１】
【発明の効果】
本発明の重金属固定化剤は、重金属の還元による難溶化に、難溶性の水酸化物、カルシウム塩や硫化物形成による溶出抑制効果が加わることから、効果的な重金属溶出抑制が可能である。さらには、各種セメントや固化材と併用することにより固化効果が加わり、封じ込め効果を更に高めることができる。また、ハンドリング性に優れている。従って、本発明の重金属固定化剤は、カドミウム、水銀、鉛、砒素、六価クロム等の重金属により単独または複合汚染された土壌、排水、地下水、都市ゴミ焼却灰、下水汚泥焼却灰、その他各種産業廃棄物中の重金属の封じ込めに効果を発揮する。
【図面の簡単な説明】
【図１】重金属固定化剤のＸ線回折図である
下段：消石灰に多硫化カルシウム水溶液を添加した方法で製造され本発明の重金属固定化剤。
上段：生石灰に多硫化カルシウム水溶液を添加して製造された還元性粉体。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heavy metal immobilizing agent used for containment by insolubilization or solidification of heavy metals contained in contaminated soil, drainage, groundwater, municipal waste incineration ash, industrial waste, and the like. The heavy metal immobilizing agent of the present invention is used for suppressing elution of heavy metals from heavy metal-contaminated soil by adding to cement or solidifying material.
[0002]
[Prior art]
The heavy metal immobilizing agents based on inorganic substances are roughly classified into oxidizing agents, reducing agents, and precipitating agents, depending on the type of heavy metal to be used. Oxidizing agents are added for the purpose of pretreatment of COD and BOD reduction in contaminated soil and wastewater, decolorization, iron removal, manganese removal, cyanide and organic mercury oxidation, and heavy metal precipitation. Metal oxides / peroxides, chlorates, halides, etc. are used.
The reducing agent is used, for example, for the reduction of hexavalent chromium to sparingly soluble trivalent chromium, such as hydride (hydrogen sulfide), sulfur dioxide, sodium sulfite, sulfur (S), calcium sulfide (CaS), calcium polysulfide ( In addition to CaSx), sodium hydrogen sulfite, and ferrous sulfate, metal powder (Na, K, Mg, Fe, Zn) or the like is used. Japanese Patent Application Laid-Open No. 2001-342461 also discloses a method of adding a fixing material (for example, quicklime) to a calcium polysulfide aqueous solution and then adding it to a cement-based solidifying material.
Furthermore, the precipitant is added for the purpose of precipitating toxic heavy metals such as cadmium, lead, arsenic, mercury, etc. as sparingly soluble sulfides, calcium salts, hydroxides, sulfides, alkalis, limes. Etc. are used.
[0003]
However, the immobilization of soluble heavy metals in contaminated soil, drainage, groundwater, municipal waste incineration ash, and industrial waste cannot clear the permissible concentration limit of the target heavy metals, or complex contamination where multiple heavy metal species coexist. In some cases, performance degradation may occur, and the performance of the above-described reducing agents and precipitating agents that have been conventionally used is naturally limited. In addition, sodium sulfide, which is often used as a sulfide, has a deliquescent property, is relatively highly toxic, and has a problem that its method of use is limited.
On the other hand, solidification containment with cement or solidifying material is one of the permanent measures for contaminated soils such as heavy metals. This method is based on physicochemical solidification of soil, and the effect is the property of soil (particle size, It is easily affected by the water content and the amount of organic substances). As a result, there is still a limit to immobilization of heavy metals.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a heavy metal immobilizing agent excellent in detoxification performance by reduction or precipitation of heavy metals in contaminated soil, drainage, groundwater, municipal waste incineration ash, and industrial waste. In addition, by using the heavy metal fixing agent in combination with cement, solidifying material, etc., solidification function of cement and solidifying material is further added, and the containment performance of heavy metal is enhanced, and the heavy metal species to be contained is expanded. The purpose is to provide a solidified material.
[0005]
[Means for Solving the Problems]
The inventor first discovered that a heavy metal fixing agent composed of Ca 8 S 5 (S 2 O 3 ) (OH) 12 .20H 2 O and calcium hydroxide has an excellent containment action, and Ca 8 S 5 ( S 2 O 3) (OH) a 12 · 20H 2 O was found a heavy metal immobilizing agent containing 30 to 85 wt%. The heavy metal fixing agent is preferably obtained by mixing and stirring slaked lime and a calcium polysulfide aqueous solution, and further contains 0.5 to 20% by mass of the heavy metal fixing agent. Alternatively, the present inventors have found that the solidified material is an extremely excellent containment material and completed the present invention.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Heavy metal immobilizing agent of the present invention is mainly composed of Ca 8 S 5 (S 2 O 3) (OH) 12 · 20H 2 O and calcium hydroxide. The hydrate represented by Ca 8 S 5 (S 2 O 3 ) (OH) 12 .20H 2 O is identified by powder X-ray diffraction as shown in FIG. These components can be quantified by norm from chemical analysis (sulfur content, free calcium hydroxide, etc.). That is, the sulfur content in the hydrate identified by X-ray diffraction is about 20% by mass stoichiometrically, in other words, the value obtained by multiplying the sulfur content by 5 is the amount of hydrate. Become. However, it is presumed that sulfur compounds other than the above hydrates coexist in the heavy metal fixing agent of the present invention, and it is overestimated when the amount of hydrate is simply calculated by multiplying the sulfur content by 5. The For this reason, in this specification, the amount of hydrates was estimated and described by a value obtained by multiplying the quantified total sulfur content by 3.5.
[0007]
Ca 8 S 5 in a heavy metal immobilizing agent (S 2 O 3) (OH ) 12 · 20H 2 O ( hereinafter, referred to as a hydrate) content is preferably between 30-85 wt%.
When the hydrate content is less than 30% by mass, the detoxification effect due to reduction or precipitation of heavy metals is reduced, which is not preferable. On the other hand, if it exceeds 85% by mass, an appropriate amount of calcium hydroxide cannot be secured, and the combined effect of precipitation formation caused by slaked lime, such as formation of insoluble hydroxides of heavy metals or formation of calcium salts, etc. Not only becomes insufficient, but also the powder fluidity decreases, leading to undesirable results. The heavy metal fixing agent of the present invention desirably contains 5 to 55% by mass of calcium hydroxide.
[0008]
Ca 8 S 5 (S 2 O 3) (OH) 12 · 20H 2 O hydrate is not distributed on the market, a heavy metal immobilizing agent of the present invention in a simple mixing of the slaked lime and ready-made hydrate It is difficult to prepare. Therefore, it is preferable that the heavy metal fixing agent of the present invention is produced by a reaction between a calcium polysulfide aqueous solution and slaked lime.
A calcium polysulfide aqueous solution having a solid content of about 30 to 55% by mass can be used, and slaked lime can be a general industrial product. Quick lime and cement calcined raw materials can also be used as raw materials by mixing water with an aqueous solution of calcium polysulfide after cooling water previously added with water and cooling. Unlike the case of using quicklime, when using a raw material that has been preliminarily hydrated, there is no heat generated due to calcination, so Ca 8 S 5 (S 2 O 3 ) (OH) 12 · 20H 2 O hydrate can be generated and present, and in this respect, a method of adding a fixing material (for example, powdered by adding quick lime) to an aqueous solution of calcium polysulfide described in JP-A-2001-342461. The resulting compound species and heavy metal immobilization ability are greatly different from those obtained.
[0009]
In order to ensure the above-mentioned hydrate content in the heavy metal fixing agent, the calcium polysulfide aqueous solution / slaked lime mass ratio (solid content basis) varies depending on the solid content concentration in the calcium polysulfide aqueous solution. In view of practical aspects such as availability, it is preferable to select from the range of 0.2 to 1.0.
[0010]
The mixing method of calcium polysulfide aqueous solution and slaked lime can be performed using the mixers generally used. In this case, since Ca 8 S 5 (S 2 O 3 ) (OH) 12 · 20H 2 O hydrate is relatively easily decomposed and dehydrated, mixing / stirring operation and drying operation added as necessary are It is preferable to carry out at 50 ° C. or lower, and suppressing the air oxidation of the heavy metal immobilizing agent by nitrogen gas purge brings about a more preferable result.
[0011]
The heavy metal immobilizing agent of the present invention can be used as a heavy metal immobilizing agent added alone to the object to be treated, but it is more effective to use it together with cement or a solidifying material. As for the cement, various Portland cements and mixed cements (blast furnace cement, fly ash cement, silica cement, silica fume cement, etc.) can be used, and the solidifying material is cement type (general soft soil, high water content soil, high organic soil). , Anti-hexavalent chromium, dust control type, lime (quick lime, slaked lime), magnesia (magnesia, magnesium hydroxide, basic magnesium carbonate), gypsum (half water, anhydrous, two Water), one or more of blast furnace slag systems can be used.
[0012]
The content of the heavy metal fixing agent in these cements or solidification materials varies depending on the contaminated soil, municipal waste incineration ash or industrial waste species to be treated, and also varies depending on the hydrate content in the fixing agent. 0.5 to 20% by mass is preferable. If it is less than 0.5% by mass, the detoxification effect due to reduction, precipitation, and solidification may not be sufficiently exerted. If it exceeds 20% by mass, the amount of cement or solidified material will be reduced and depending on the cement or solidified material. The resulting solidification effect is insufficient, which is not preferable.
[0013]
【Example】
Hereinafter, the present invention will be described in more detail with reference to specific examples.
The heavy metal fixing agent was prepared as follows.
The S (sulfur) source is a commercial product of lime-sulfur mixture (solid calcium sulfide aqueous solution with a solid content of 35% by mass, hereinafter referred to as “mixture”). A concentrated solution having a partial concentration of 49.5% by mass was used.
Using a Hobart mixer (capacity 5 L), a heavy metal fixing agent represented by names A to F was obtained by a method of adding this lime-sulfur mixture or its concentrated liquid to slaked lime. A mixture was used in A to C, and a concentrated solution was used in D to F. The mixing stirring time was 20 minutes, and all the calcium polysulfide aqueous solutions were added to slaked lime over 5 minutes from the start of mixing and stirring. Moreover, reducing powder G was prepared from a mixture and quicklime as a comparative control.
The heavy metal fixing agent was used alone or in combination with a cement-based solidifying material. When a solidifying material was used in combination, a general soft soil cement-based solidifying material (Youth Tabira 10) was used.
[0014]
The following three kinds of heavy metal immobilization treatment objects were selected.
(I) Sandy soil (natural water content: 18.2%) Elution amount of lead according to Environment Agency Notification No. 46: 82.3 mg / L
(B) Sandy soil (natural water content 21.2%) Arsenic elution amount according to Environment Agency Notification No. 46: 16.7 mg / L
(C) Municipal waste incineration ash Elution amount in the elution test according to Notification No. 13 of the environmental agency before humidity control: Cadmium 20.1 mg / L, Arsenic 0.26 mg / L, Lead 0.81 mg / L, Six Chromium 0.98mg / L The municipal waste incineration ash was preconditioned by spraying water and stirring so that the water content ratio was 18% by mass.
[0015]
The heavy metal treatment object was treated with the heavy metal immobilizing agent and the solidifying material containing the immobilizing agent as follows.
That is, a heavy metal fixing agent and a solidifying material were added to the object to be treated, mixed with stirring, filled into a mold (
[0016]
For the specimen after demolding, the following evaluation test was performed.
Compressive strength: uniaxial compressive strength was measured according to JIS A 1216.
-Elution amount of heavy metals: The amount of elution of heavy metals was measured in accordance with Environment Agency Notification No. 46 for polluted soil and Environment Agency Notification No. 13 for municipal waste incineration ash.
The evaluation results are shown in Table 1. In Table 1, Ca 8 S 5 in a heavy metal immobilizing agent (S 2 O 3) (OH ) 12 · 20H 2 O hydrate content calculated value multiplied by 3.5 the quantitative value of the total sulfur content Was described. As for heavy metal elution amounts, those with heavy metal concentrations below the detection limit were described as “ND”.
[0017]
[Table 1]
Based on the results of dissolution test of lead-contaminated stabilized soil using a combination of heavy metal fixing agent E and general soft soil cement-based solidifying material, the required amount of heavy metal fixing agent for cement-based solidifying material is 0. It turns out that 5 to 20.0% is preferable. If it becomes 40 mass%, the amount of cement-based solidifying material may be relatively reduced, and the lead containment effect is reduced (No. 1 to No. 6).
[0019]
No. 7-11, but it is obtained by changing the Ca 8 S 5 (S 2 O 3) (OH) 12 · 20H 2 O hydrate content in the heavy metal immobilizing agent, hydrating in heavy metal immobilizing agent When the substance content is in the range of 30 to 85 mass%, a good water-soluble arsenic containment effect is exhibited. Even if the hydrate content is within this range, the containment effect of water-soluble arsenic is significantly reduced when the calcium hydroxide content is low (No. 12). Moreover, it replaces with slaked lime and the containment effect with respect to water-soluble arsenic becomes low also in the reducing powder G (No. 13) prepared from the mixture and quick lime.
[0020]
When the heavy metal fixing agent of the present invention is added alone to a composite contaminant containing a plurality of heavy metals such as municipal waste incineration ash, it is complex and sufficient for various heavy metals. Containment becomes possible (No. 14 to 17). However, the reducing powder G prepared from the mixture and quicklime has a poor solidifying function for arsenic and lead as in the case of using it together with the solidifying material (No. 18).
[0021]
【The invention's effect】
The heavy metal immobilizing agent of the present invention can effectively suppress elution of heavy metals because the elution suppression effect due to the formation of hardly soluble hydroxides, calcium salts and sulfides is added to the insolubilization by reduction of heavy metals. Furthermore, by using together with various cements and solidifying materials, a solidifying effect is added, and the containment effect can be further enhanced. Moreover, it is excellent in handling property. Therefore, the heavy metal immobilizing agent of the present invention includes soil, drainage, groundwater, municipal waste incineration ash, sewage sludge incineration ash, and other various types that are singly or combined with heavy metals such as cadmium, mercury, lead, arsenic, and hexavalent chromium. Effective for containment of heavy metals in industrial waste.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an X-ray diffraction diagram of a heavy metal immobilizing agent. Lower: the heavy metal immobilizing agent of the present invention produced by a method in which a calcium polysulfide aqueous solution is added to slaked lime.
Upper: Reducing powder produced by adding calcium polysulfide aqueous solution to quicklime.
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| JP2002191833A JP3818446B2 (en) | 2002-07-01 | 2002-07-01 | Heavy metal fixing agent |
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| JP2002191833A JP3818446B2 (en) | 2002-07-01 | 2002-07-01 | Heavy metal fixing agent |
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| JP4712483B2 (en) * | 2005-08-19 | 2011-06-29 | 宇部興産株式会社 | Treatment composition and treatment method for heavy metal contaminated soil |
| KR101026668B1 (en) * | 2005-12-01 | 2011-04-04 | 가부시키가이샤 간쿄 아네토스 | Method of fixing asbestos |
| JP5390975B2 (en) * | 2009-07-22 | 2014-01-15 | 吉弘 直彦 | Solidifying agent using fly ash and solidifying method using the solidifying agent |
| JP6482878B2 (en) * | 2015-01-15 | 2019-03-13 | デンカ株式会社 | Spray cement mortar and spray cement concrete |
| JP6497990B2 (en) * | 2015-03-13 | 2019-04-10 | デンカ株式会社 | Liquid admixture for ground stabilization, ground stabilization material, and ground stabilization method using the same |
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