JP2004269822A - Process for preparing calcium sulfide-based heavy metal fixing agent - Google Patents
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- JP2004269822A JP2004269822A JP2003066259A JP2003066259A JP2004269822A JP 2004269822 A JP2004269822 A JP 2004269822A JP 2003066259 A JP2003066259 A JP 2003066259A JP 2003066259 A JP2003066259 A JP 2003066259A JP 2004269822 A JP2004269822 A JP 2004269822A
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Abstract
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【０００１】
【発明の属する技術分野】本発明は、石膏廃材を利用し、硫化カルシウムを作用主成分とする硫化カルシウム系重金属固定化剤の製造方法に関するものである。更に詳しくは、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に使用可能な、さらに、セメントや固化材に添加してそれらの固形化による封じ込めに使用する重金属固定化剤として機能する、硫化カルシウムを主成分とする重金属固定化剤を、石膏廃材を焼成して製造する方法に関するものである。
【０００２】
【従来の技術】石膏は極めて短時間で硬化する水硬性材料であり、成形・加工性に優れ、寸法安定性が高く、防火性・耐火性に優れる等の特性を有し、また安価な材料であることから、石膏ボードや原型もしくは成型用の型材等として広く使用されているが、その生産量が増大するにつれて、その廃材の処理が大きな問題となってきている。例えば、代表的な石膏製品である石膏ボードは、建物の解体工事等で年間に１００万トン程度排出されている。しかし、石膏ボード廃材は、建物の内装材として使用されたものであることから、表面に左官材料（石膏プラスター、土塗り仕上材、砂壁仕上材等）や、壁紙、塗料等の表面化粧材が施され、また木材や鋼製の下地材等が付着したものも多く含まれており、これらの夾雑物を除去・分離することが技術的に困難なことから、其のほとんどが有効利用されずに、埋立処理されているが、埋立可能な処分地の減少に伴い、埋立に変わる方法の開発は避けて通れないものとなっている。
【０００３】当然のことながら、従来から石膏ボード廃材の有効利用方法について種々の提案がなされて来た。石膏ボードは、石膏を主体とする芯材を紙で被覆した板状の構造であるため、その多くは破砕処理や加熱処理により石膏と紙を分離し、さらには石膏中に含まれる混和材を加熱分解する事により、石膏ボード用の原料やセメント添加用の石膏として利用するものである（例えば、特許文献１及び２、非特許文献１）。
しかしながら、これらの方法は、石膏ボード廃材から単に元の石膏を回収するためだけの有効利用方法にすぎないものである。バージン材の石膏が安価に入手できるのに対し、廃石膏は、夾雑物の存在と発生個所が集中していないことにより、回収処理に必要な設備投資やランニングコストが高くなり、経済性の面からバージン材には太刀打ちできないのが現状である。
そのため、視点を変えた、実用的な有効利用法の開発が急務となっていた。
【０００４】一方、重金属等汚染土壌に対する対応も現代社会の抱える大きな問題の一つである。そ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限界があった。また、土質よっては、セメントに由来する六価クロムが土壌環境基準を超えて溶出するといった問題があった。
セメント系固化材による固化処理土からの六価クロム溶出抑制対策としては、各種の還元剤の添加が知られている。還元剤としては、硫酸第一鉄、亜硫酸塩、チオ硫酸塩、硫黄、硫化物、高炉スラグ、水素化物（硫化水素）、金属粉（Ｎａ、Ｋ、Ｍｇ、Ｆｅ、Ｚｎ）等が使用される。しかし、固化処理土における中・長期的な還元作用の持続性、セメント系固化材と還元剤との均一混合性の確保の困難さ、さらには固化処理土の強度発現性の低下等に問題があった。
【０００５】また、無機系物質による重金属の固定化剤には、上述の還元剤の他に、対象とする重金属の種類により、大別して酸化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。
【０００６】一方、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。
しかし、汚染土壌、汚泥、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。
【０００７】本発明者は、これらの中にあって硫化カルシウムが固化処理土からの六価クロム溶出抑制剤や重金属不溶化剤として優れた効果を示すものであることを見出した。
しかしながら、硫化カルシウムは、現在、高純度の試薬が市場に流通しているだけであり、コストが高く、上記の用途への適用は困難であり、実用的な製造方法の開発が望まれていたものである。
【０００８】
【特許文献１】
特開平６−１４２６３８号公報（２ページ）
【特許文献２】
特開平１０−３６１４９号公報（２ページ）
【非特許文献１】
環境省編「廃石膏ボードのリサイクルの推進に関する検討調査（平成１４年１２月）」（２３ページ）
【０００９】
【発明が解決しようとする課題】本発明の目的は、年々排出量が増加し、その有効利用方法の開発が望まれている石膏廃材を原料に用いて、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無害化性能に優れた、硫化カルシウム系重金属固定化剤の実用的な製造方法を提供することに在る。
【００１０】
【課題を解決するための手段】発明者は、石膏廃材を還元雰囲気中で加熱処理する事により優れた重金属固定化性能を持つ硫化カルシウム系固定化剤が製造できる事を見出し、本発明を完成した。
すなわち、本発明は、石膏廃材を還元雰囲気で加熱処理する事を特徴とする、重金属固定化剤用途の硫化カルシウム系固定化剤の製造方法に関する。
【００１１】
【発明の実施の形態】以下に、本発明を詳細に説明する。
本発明における石膏廃材は、石膏を主成分として含有するものであれば特に限定されず、石膏ボード、鋳込み成型用石膏型、工業模型用石膏型等が使用できる。この内、現在、石膏廃材として量的に最も多く排出されている石膏ボードには約７質量％の紙が付着しているが、石膏廃材を還元雰囲気で焼成する本発明においては、紙を分離する必要は無く、石膏廃材に添加する還元剤の一部として有効に機能する。
また、本発明で使用する石膏廃材は、粉砕されて使用されるが、石膏の還元反応を効率良く進めるためには、５ｍｍ以下に粉砕することが望ましい。粉砕方法は、特に限定されない。
【００１２】金属類は、粉砕処理後、磁選機、篩を用いて大きなものを除去することになるが、小さなものの残留は構わない。
【００１３】石膏廃材の粉砕物を還元雰囲気で焼成するための手段としては、石膏廃材に還元剤となる炭素および／または有機化合物を含有する物質を混合して焼成するのが好ましい。還元剤として働く物質としては、石炭、コークス、木炭、木材等のほか、石炭火力発電所から排出する未燃炭素を含む石炭灰、石炭ガス化炉から排出するガス化スラグ、製紙工場から排出するパルプスラッジや廃プラスチック、廃木材、伐採木等の廃棄物を挙げることが出来る。
【００１４】
石膏廃材に対する還元剤の添加量は、例えば、カーボン等は、還元等量の計算が容易なものについては、計算された還元等量値以上の還元剤を添加するのが好ましい。木材や廃プラスチックにおいては、炭化して生成したカーボン以外に、炭化水素、Ｈ２、ＣＯ等の乾留ガスによる還元も考慮して還元等量を計算し、その値以上の還元剤を存在させることが好ましい。
【００１５】本発明において、全石膏が硫化カルシウムに変換されることは必ずしも必要ではないが、全石膏の２０質量％以上が、硫化カルシウムに変換されることが好ましい。
【００１６】石膏廃材の粉砕物を焼成する温度は、６００〜１１００℃とする。焼成温度が６００℃よりも低いと、石膏の還元に時間が掛かり過ぎ生産効率が低下するので好ましくない。また、１１００℃よりも高いと、生成した硫化カルシウムの分解が激しくなり、収率が低下するだけでなく、ＳＯｘガスの発生による環境対策が必要となる。
【００１７】廃石膏を焼成するための加熱炉は、内燃バーナー式ロータリーキルン、外熱式ロータリーキルン、二重筒ロータリーキルン式炭化炉、バッチ式炭化炉等、所定の温度に加熱できるものであれば特に限定されない。
なお、セメントや軽量骨材の焼成に使用される内燃バーナー式ロータリーキルンの様に、構造上内部を完全に還元雰囲気にすることが出来ない加熱炉を使用する場合には、バーナーの焼点部からキルン落ち口部にかけて、焼成物が高温で、かつ酸素濃度の高い大気と接触するために、硫化カルシウムの分解が起こりやすくなる。硫化カルシウムの分解を最小限に抑えるためには、予め原料を１０〜３０ｍｍ程度に造粒して、焼成することが望ましい。
【００１８】この造粒に用いる造粒方法としては、例えば、押出し造粒、ブリケット造粒、撹拌造粒等、いずれの方法でも良く、特に限定されない。
なお、炭化炉の様に、内部を還元雰囲気に保持できる構造の焼成炉を使用すれば、この造粒工程は当然省略できる。
【００１９】得られた焼成物は、ボールミル、竪型ローラーミル、振動ミル、ピンミル等公知の方法により粉砕し、硫化カルシウム系重金属固定化剤を得ることができる。なお、重金属固定化剤用途として使うことから、平均粒径１００μｍ以下に粉砕するのが好ましい。
【００２０】得られた硫化カルシウム系重金属固定化剤は、単に、重金属の固定化に使用するのであれば、粉体のみを処理対象物に添加することになるが、処理対象物の固化処理も必要であれば、セメントまたは固化材と併用使用することになる。
【００２１】
【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。
建物の解体工事現場から回収した石膏ボード廃材（厚さ９．５ｍｍの石膏ボード、石膏量約９４質量％、紙約６質量％）を、ジョークラッシャーおよびアトマイザーを用いて、紙ごと３ｍｍ篩を全通する粒度に粉砕した。また、建設現場から回収した廃木材を、チッパーシュレッダーで一次破砕後、竪型ローラーミルを用いて３ｍｍ篩を全通する粒度に粉砕し、廃石膏ボード粉砕物と廃木材粉砕物を質量比で６：４になるように混合した。さらに、混合物２０ｇを船形るつぼ入れ、ガス流通式の管状電気炉（径６０ｍｍ×高さ１０００ｍｍ）内で、窒素ガスを０．５Ｌ／分で流しながら、５００℃〜１２００℃で４時間加熱した。焼成中に発生したガス中のＳＯｘ濃度を、ガス検知管を用いて測定した。
【００２２】得られた焼成物は、ＪＩＳ Ｒ ５２０２により硫化物形態の硫黄及び三酸化硫黄量を測定した。硫化カルシウム量及び硫酸カルシウム量は次式より算出し、石膏から硫化カルシウムへの反応率を求めた。
硫化カルシウム量＝硫化物形態硫黄量×（７２．１４／３２．０６）
硫酸カルシウム量＝三酸化硫黄量×（１３６．１４／８０．０６）
反応率＝（硫化カルシウム量／７２．１４）／（（硫化カルシウム量／７２．１４）＋（硫酸カルシウム量／１３６．１４））
【００２３】さらに、得られた焼成物を、ボールミルを用いて平均粒径１０μｍに粉砕し、セメント系固化材との併用または単独で使用して重金属の固定化効果を確認した。なお、固化材を併用する場合、一般軟弱土用セメント系固化材を使用した。
焼成物の特性を表１に示す。
【００２４】得られた焼成物の重金属の固定化効果の評価は、次のように行った。
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）火山灰質粘性土（自然含水比 １０４．６％） 非汚染土
（ロ）砂質土（自然含水比 １８．５％） 六価クロム汚染土：環境庁告示第４６号による六価クロム溶出量：１．０２ ｍｇ／Ｌ
（ハ）都市ゴミ焼却灰 複合汚染物：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。
【００２５】重金属固定化剤及び固化材による、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）に充填した後締固め、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。
【００２６】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：非汚染土（火山灰質粘性土）は、固化材による固化改良土からのセメントに由来する六価クロムの溶出量を環境庁告示４６号法により測定。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２に示す。なお、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「＜（検出限界値）」と記載した。
【００２７】表１に示す様に、焼成温度１２００℃では二酸化硫黄ガスの濃度が著しく増加することが分かる。
また、表２のＮｏ．１〜９は、５００〜１２００℃で焼成して得られた硫化カルシウムＡ〜Ｈと一般軟弱土用セメント系固化材を使用して固化処理した火山灰質粘性土からの六価クロム溶出試験結果であるが、焼成温度５００℃の重金属固定化剤Ａを使用した場合は、硫化カルシウムの生成量が少ないため、セメント等からの六価クロム溶出抑制効果は充分でない。
【００２８】Ｎｏ．１０〜１３は、７００℃で焼成して得られた硫化カルシウムＣと一般軟弱土用セメント系固化材を使用して重金属の固定化処理をした六価クロム汚染土からの溶出試験結果であり、汚染土への添加量１．０ｋｇ／ｍ３でも、汚染土からの六価クロム溶出抑制効果が認められた。
【００２９】
Ｎｏ．１４〜１６は、カドミウム、砒素、鉛、六価クロムを含む複合汚染物である都市ゴミ焼却灰に、８００℃で焼成して得られた硫化カルシウムＤを単独添加した場合の溶質試験結果であり、処理対象物に対し２．０ｋｇ／ｍ３以上の添加で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。
【００３０】
【表１】
【発明の効果】本発明は、石膏廃材を原料にして、重金属固定化剤として使用可能な硫化カルシウム系重金属固定化剤を製造する方法を提供するものである。廃棄物の有効利用と重金属による土壌汚染防止の両面から環境負荷の低減に寄与できるため、本発明の効果は極めて大きい。[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a calcium sulfide-based heavy metal fixing agent containing calcium sulfide as a main component, using waste gypsum. More specifically, it can be used for insolubilization of heavy metals contained in contaminated soil, wastewater, groundwater, municipal waste incineration ash, industrial waste, etc. Further, it is added to cement and solidification materials and used for containment by solidification. The present invention relates to a method for producing a heavy metal fixing agent containing calcium sulfide as a main component, which functions as a heavy metal fixing agent, by firing gypsum waste material.
[0002]
2. Description of the Related Art Gypsum is a hydraulic material that cures in an extremely short time, has properties such as excellent moldability and workability, high dimensional stability, excellent fire resistance and fire resistance, and is an inexpensive material. Therefore, it is widely used as a gypsum board, a prototype, or a molding material, but as the production amount increases, disposal of the waste material has become a major problem. For example, gypsum board, which is a typical gypsum product, is discharged about 1 million tons per year due to demolition work of buildings and the like. However, since gypsum board waste is used as an interior material for buildings, plastering materials (plaster plaster, earthen finishing material, sand wall finishing material, etc.) and surface decorative materials such as wallpaper and paint are used on the surface. Many of these materials are attached with wood or steel base materials, etc., and it is technically difficult to remove and separate these contaminants. In addition, landfills are being disposed of, but with the reduction of landfill sites that can be landfilled, the development of a method that replaces landfills has become unavoidable.
[0003] Naturally, various proposals have been made on methods for effectively using gypsum board waste materials. Gypsum board has a plate-like structure in which a core material mainly composed of gypsum is covered with paper, so most of the gypsum board separates gypsum and paper by crushing or heat treatment, and further removes the admixture contained in the gypsum. It is used as a raw material for gypsum board or gypsum for adding cement by thermal decomposition (for example, Patent Documents 1 and 2, Non-Patent Document 1).
However, these methods are merely effective utilization methods for simply recovering the original gypsum from the gypsum board waste material. Whereas virgin gypsum can be obtained at low cost, waste gypsum increases the capital investment and running costs required for the collection process due to the presence of contaminants and the lack of concentration of generated parts, and is economical. At present, virgin materials cannot be competed with.
Therefore, there has been an urgent need to develop a practical and effective use method from a different viewpoint.
On the other hand, dealing with contaminated soil such as heavy metals is also one of the major problems in modern society. As one of the permanent measures, there is solidification containment with cement or solidification material, but this method is based on physicochemical solidification of the soil, and the effect is the properties of the soil (particle size, water content ratio, organic matter content). Therefore, the immobilization of heavy metals is limited. Further, depending on the soil quality, there is a problem that hexavalent chromium derived from cement elutes in excess of the soil environmental standard.
As a measure for suppressing the elution of hexavalent chromium from the solidified soil by the cement-based solidifying material, addition of various reducing agents is known. As the reducing agent, ferrous sulfate, sulfite, thiosulfate, sulfur, sulfide, blast furnace slag, hydride (hydrogen sulfide), metal powder (Na, K, Mg, Fe, Zn) and the like are used. . However, there are problems with the medium- to long-term sustainability of the reducing action in the solidified soil, the difficulty in ensuring uniform mixing of the cement-based solidifying material and the reducing agent, and the reduction in the strength development of the solidified soil. there were.
[0005] In addition to the above-mentioned reducing agents, heavy metal-fixing agents made of inorganic substances are roughly classified into oxidizing agents and precipitating agents depending on the type of the target heavy metal. The oxidizing agent is added for the purpose of reducing COD and BOD in contaminated soil and wastewater, decolorizing, removing iron, removing manganese, oxidizing decomposition of cyanide and organic mercury, and pretreating heavy metal precipitation. , Metal oxides / peroxides, chlorates, halides and the like are used.
On the other hand, a precipitant is added for the purpose of precipitating harmful heavy metals such as cadmium, lead, arsenic and mercury as hardly soluble sulfides, calcium salts and hydroxides. Alkali, lime, etc. are used.
However, the immobilization of soluble heavy metals in contaminated soil, sludge, wastewater, groundwater, municipal waste incineration ash, and industrial waste cannot meet the allowable concentration limits of the target heavy metals, or the complex where multiple heavy metal species coexist. In the case of contamination, the performance may decrease, and the performance of the above-described conventionally used reducing agents and precipitants is naturally limited.
The present inventors have found that, among these, calcium sulfide exhibits excellent effects as a hexavalent chromium elution inhibitor and heavy metal insolubilizer from the solidified soil.
However, calcium sulfide is currently only available in high-purity reagents on the market, is expensive, is difficult to apply to the above-mentioned applications, and has been desired to develop a practical production method. Things.
[0008]
[Patent Document 1]
JP-A-6-142638 (page 2)
[Patent Document 2]
JP-A-10-36149 (page 2)
[Non-patent document 1]
Ministry of the Environment, “Survey on Waste Gypsum Board Recycling (December 2002)” (page 23)
[0009]
SUMMARY OF THE INVENTION An object of the present invention is to use a gypsum waste material whose emission amount is increasing year by year and development of an effective utilization method thereof is required as a raw material, thereby contaminating soil, drainage, groundwater, and municipal waste. It is an object of the present invention to provide a practical method for producing a calcium sulfide-based heavy metal fixing agent which is excellent in detoxifying performance of heavy metals in incinerated ash and industrial waste.
[0010]
Means for Solving the Problems The present inventors have found that a calcium sulfide-based fixing agent having excellent heavy metal fixing performance can be produced by subjecting gypsum waste material to heat treatment in a reducing atmosphere, and completed the present invention. did.
That is, the present invention relates to a method for producing a calcium sulfide-based fixing agent for use as a heavy metal fixing agent, which comprises subjecting gypsum waste material to heat treatment in a reducing atmosphere.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The gypsum waste material in the present invention is not particularly limited as long as it contains gypsum as a main component, and a gypsum board, a gypsum mold for casting and a gypsum mold for an industrial model can be used. Of these, about 7% by mass of paper is attached to the gypsum board, which is currently discharged most in quantity as gypsum waste, but in the present invention in which gypsum waste is fired in a reducing atmosphere, paper is separated. It does not need to be performed, and functions effectively as a part of the reducing agent added to the gypsum waste material.
The gypsum waste used in the present invention is used after being pulverized, but it is preferable that the gypsum waste be pulverized to 5 mm or less in order to promote the reduction reaction of gypsum efficiently. The grinding method is not particularly limited.
After pulverization, large metals are removed using a magnetic separator and a sieve, but small ones may remain.
[0013] As a means for baking the ground gypsum waste material in a reducing atmosphere, it is preferable to mix a gypsum waste material containing a carbon and / or organic compound as a reducing agent and bake it. Substances that act as reducing agents include coal, coke, charcoal, wood, etc., as well as coal ash containing unburned carbon emitted from coal-fired power plants, gasified slag emitted from coal gasifiers, and discharged from paper mills. Examples of the waste include pulp sludge, waste plastic, waste wood, and felled trees.
[0014]
As for the amount of the reducing agent added to the gypsum waste material, for example, it is preferable to add a reducing agent having a calculated reduction equivalent value or more for carbon or the like for which the calculation of the reduction equivalent amount is easy. For wood and waste plastics, in addition to carbon generated by carbonization, calculate the reduction equivalent taking into account reduction by carbonization gas such as hydrocarbons, H 2 , CO, etc. Is preferred.
In the present invention, it is not always necessary that the total gypsum be converted into calcium sulfide, but it is preferable that at least 20% by mass of the total gypsum be converted into calcium sulfide.
The temperature for firing the ground gypsum waste is 600 to 1100 ° C. If the firing temperature is lower than 600 ° C., it takes too much time to reduce the gypsum, and the production efficiency is undesirably reduced. If the temperature is higher than 1100 ° C., the generated calcium sulfide is greatly decomposed, which not only reduces the yield, but also requires environmental measures by generating SOx gas.
The heating furnace for burning waste gypsum is not particularly limited as long as it can be heated to a predetermined temperature, such as an internal combustion burner type rotary kiln, an external heating type rotary kiln, a double cylinder rotary kiln type carbonization furnace, and a batch type carbonization furnace. Not done.
When using a heating furnace that cannot completely reduce the inside to a reducing atmosphere, such as an internal combustion burner type rotary kiln used for sintering cement and lightweight aggregates, the burning point of the burner is Since the calcined product contacts the atmosphere having a high temperature and a high oxygen concentration at the kiln outlet, the decomposition of calcium sulfide tends to occur. In order to minimize the decomposition of calcium sulfide, it is desirable to granulate the raw material to about 10 to 30 mm in advance and fire it.
The granulation method used for this granulation may be any of extrusion granulation, briquette granulation, and stirring granulation, and is not particularly limited.
If a firing furnace having a structure capable of holding the inside in a reducing atmosphere, such as a carbonizing furnace, is used, the granulating step can be omitted.
The obtained calcined product is pulverized by a known method such as a ball mill, a vertical roller mill, a vibration mill, and a pin mill to obtain a calcium sulfide-based heavy metal fixing agent. In addition, since it is used as a heavy metal fixing agent, it is preferable to pulverize the particles to an average particle diameter of 100 μm or less.
If the obtained calcium sulfide-based heavy metal fixing agent is simply used for fixing a heavy metal, only the powder is added to the object to be treated. If necessary, it will be used in combination with cement or solidifying material.
[0021]
The present invention will be described in more detail with reference to specific examples below.
Gypsum board waste material (9.5 mm thick gypsum board, plaster amount about 94% by mass, paper about 6% by mass) collected from the demolition work site of the building was sieved with a 3 mm sieve together with paper using a jaw crusher and an atomizer. Milled to a passing particle size. In addition, waste wood collected from the construction site is first crushed by a chipper shredder and then crushed using a vertical roller mill to a particle size that passes through a 3 mm sieve, and the crushed waste gypsum board and crushed waste wood are measured in mass ratio. 6: 4. Further, 20 g of the mixture was put in a boat-shaped crucible and heated at 500 ° C. to 1200 ° C. for 4 hours in a gas flow type tubular electric furnace (diameter 60 mm × height 1000 mm) while flowing nitrogen gas at 0.5 L / min. The concentration of SOx in the gas generated during firing was measured using a gas detector tube.
The obtained fired product was measured for the amount of sulfur in the form of sulfide and sulfur trioxide in accordance with JIS R5202. The amount of calcium sulfide and the amount of calcium sulfate were calculated from the following formula, and the reaction rate from gypsum to calcium sulfide was determined.
Calcium sulfide content = sulfide form sulfur content x (72.14 / 32.06)
The amount of calcium sulfate = the amount of sulfur trioxide x (136.14 / 80.06)
Reaction rate = (amount of calcium sulfide / 72.14) / ((amount of calcium sulfide / 72.14) + (amount of calcium sulfate / 136.14))
Further, the obtained fired product was pulverized to an average particle size of 10 μm using a ball mill, and the effect of immobilizing heavy metals was confirmed by using it together with a cement solidifying material or by using it alone. When a solidifying material was used in combination, a cement-type solidifying material for general soft soil was used.
Table 1 shows the properties of the fired product.
The evaluation of the effect of immobilizing heavy metals on the obtained fired product was performed as follows.
The following three types were selected as the objects to be subjected to the heavy metal immobilization treatment.
(A) Volcanic ash cohesive soil (natural water content: 104.6%) Non-contaminated soil (b) Sandy soil (natural water content: 18.5%) Hexavalent chromium contaminated soil: Hexavalent chromium according to Environment Agency Notification No. 46 Elution amount: 1.02 mg / L
(C) Municipal garbage incineration ash Complex contaminants: Dissolution amount in dissolution test according to No. 13 of the Environmental Agency Notification No. 13 before humidification: Cadmium 20.1 mg / L, arsenic 0.26 mg / L, lead 0.81 mg / L, hexavalent chromium 0.98mg / L
The municipal waste incineration ash was previously humidified by spraying and stirring water so that the water content was 18% by mass.
The treatment of the heavy metal-containing object with the heavy metal fixing agent and the solidifying material was performed as follows.
That is, the heavy metal fixing agent and the solidifying agent were added to the object to be treated, mixed with stirring, filled in a mold (diameter 5 cm × height 10 cm), compacted, and sealed and cured in a constant temperature room at 20 ° C. and 60% humidity. . After a lapse of 7 days, the sample was demolded to obtain a specimen.
The following evaluation test was performed on the specimen after demolding.
Compressive strength: Uniaxial compressive strength was measured according to JIS A1216.
・ Eluted amount of heavy metals: For non-contaminated soil (volcanic ash clayey soil), the amount of hexavalent chromium eluted from cement from solidified improved soil with solidified material was measured by the Environmental Agency Notification No. 46 method. For the polluted soil, the elution amount of heavy metals was measured in accordance with the Notification of the Environment Agency No. 46, and for the incineration ash of municipal waste in accordance with the Notification No. 13 of the Environment Agency.
Table 2 shows the evaluation results. In addition, about the heavy metal elution amount, when the heavy metal concentration was below the detection limit, it described as "<(detection limit value)."
As shown in Table 1, it can be seen that the concentration of sulfur dioxide gas is significantly increased at a sintering temperature of 1200 ° C.
Further, in Table 2, No. 1 to 9 are hexavalent chromium elution test results from volcanic ash cohesive soil solidified using calcium sulfide A to H obtained by calcining at 500 to 1200 ° C. and a cement-based solidifying material for general soft soil. However, when heavy metal fixing agent A having a calcination temperature of 500 ° C. is used, the effect of suppressing hexavalent chromium elution from cement or the like is not sufficient because the amount of generated calcium sulfide is small.
No. 10 to 13 are the results of a dissolution test from hexavalent chromium-contaminated soil obtained by fixing heavy metals using calcium sulfide C obtained by calcining at 700 ° C. and a cement-based solidifying material for general soft soil, Even with the addition amount of 1.0 kg / m 3 to the contaminated soil, the effect of suppressing the elution of hexavalent chromium from the contaminated soil was observed.
[0029]
No. 14 to 16 are solute test results when calcium sulfide D obtained by firing at 800 ° C. was solely added to municipal waste incineration ash, which is a composite contaminant containing cadmium, arsenic, lead, and hexavalent chromium. By adding 2.0 kg / m 3 or more to the object to be treated, complex and sufficient containment of various heavy metals can be achieved.
[0030]
[Table 1]
The present invention provides a method for producing a calcium sulfide-based heavy metal fixing agent which can be used as a heavy metal fixing agent by using gypsum waste as a raw material. The effect of the present invention is extremely large because it can contribute to the reduction of environmental load from both sides of effective use of waste and prevention of soil contamination by heavy metals.
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2005306911A (en) * | 2004-04-16 | 2005-11-04 | Mitsubishi Materials Corp | Heavy metal fixation material, manufacturing method for heavy metal fixation material, manufacturing method for ground improving material, and treatment method for soil to be treated |
| JP2006102643A (en) * | 2004-10-05 | 2006-04-20 | Ube Ind Ltd | Calcium sulfide heavy metal solidifying agent, its production method, method for producing soil modification material and method for treating object to be treated |
| JP2010065158A (en) * | 2008-09-11 | 2010-03-25 | Nippon Steel & Sumikin Stainless Steel Corp | Soil-based solidifying material |
| US20120253094A1 (en) * | 2011-03-29 | 2012-10-04 | Heritage Environmental Services, Llc | Stabilizing hazardous wastes using waste byproducts |
| US20130060076A1 (en) * | 2011-09-01 | 2013-03-07 | Keith E. Forrester | Method to reduce pcb content and/or lead tclp solubility |
| CN115595157A (en) * | 2022-08-15 | 2023-01-13 | 浙江省地质调查院（Cn） | Cadmium-mercury polluted soil passivator and application thereof |
| CN115678562A (en) * | 2022-11-05 | 2023-02-03 | 昆明理工大学 | Method for preparing soil heavy metal passivator by using phosphogypsum |
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2003
- 2003-03-12 JP JP2003066259A patent/JP4209224B2/en not_active Expired - Lifetime
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2005306911A (en) * | 2004-04-16 | 2005-11-04 | Mitsubishi Materials Corp | Heavy metal fixation material, manufacturing method for heavy metal fixation material, manufacturing method for ground improving material, and treatment method for soil to be treated |
| JP4516780B2 (en) * | 2004-04-16 | 2010-08-04 | 三菱マテリアル株式会社 | Heavy metal fixing material, cement-based solidifying material, manufacturing method of heavy metal fixing material, manufacturing method of ground improvement material, and processing method of soil to be processed |
| JP2006102643A (en) * | 2004-10-05 | 2006-04-20 | Ube Ind Ltd | Calcium sulfide heavy metal solidifying agent, its production method, method for producing soil modification material and method for treating object to be treated |
| JP2010065158A (en) * | 2008-09-11 | 2010-03-25 | Nippon Steel & Sumikin Stainless Steel Corp | Soil-based solidifying material |
| US20120253094A1 (en) * | 2011-03-29 | 2012-10-04 | Heritage Environmental Services, Llc | Stabilizing hazardous wastes using waste byproducts |
| US20130060076A1 (en) * | 2011-09-01 | 2013-03-07 | Keith E. Forrester | Method to reduce pcb content and/or lead tclp solubility |
| CN115595157A (en) * | 2022-08-15 | 2023-01-13 | 浙江省地质调查院（Cn） | Cadmium-mercury polluted soil passivator and application thereof |
| CN115678562A (en) * | 2022-11-05 | 2023-02-03 | 昆明理工大学 | Method for preparing soil heavy metal passivator by using phosphogypsum |
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