報告書番号

U03064

タイトル（和文）

石炭灰中の砒素・セレンに関する溶出特性の検討

タイトル（英文）

A laboratory study on leaching characteristics of As and Se from fly ash

概要 （図表や脚注は「報告書全文」に掲載しております）

石炭灰からの溶出が懸念される砒素とセレンは、溶出機構が不明なため、これまで溶出挙動を予測することができなかった。本検討では、性状の異なる6種類の石炭灰を対象にバッチ試験を行い、溶出水のpHが10と5の場合について、砒素・セレン溶出特性を明らかにした。pH5の場合、石炭灰からの砒素・セレン溶出量は、石炭灰中の非晶質アルミニウム酸化物含有量に支配されていることを明らかにした。このため、非晶質アルミニウム酸化物含有量の少ない石炭灰ほど、弱酸性域における砒素・セレン溶出濃度が高くなると推定された。pH10の場合、砒素の溶出濃度はCa3(AsO4)2･6H2Oの溶解律速として規定されることを明らかにした。また、同pH領域においては、カルシウム含有量の高い石炭灰ほどセレンを多く保持する傾向がみられ、セレンの溶出が抑制されると考えられた。

概要 （英文）

To improve our understanding of As and Se leaching from fly ash, it is necessary to know the underlying geochemical processes. In natural systems, such as soils and sediments, As and Se have been shown to interact with Al oxides and/or iron oxides at acidic pH, with Ca compounds at alkaline pH. By analogy, it was compared the leaching of As and Se from 6 different coal fly ashes with the sorption of arsenate and selenite on Al oxides and Ca compounds. It was observed the leaching As and Se from fly ash were almost in the form of arsenate and selenite in the solution respectively. It was possible to describe the leaching of As was controlled by calcium arsenate (Ca3(AsO4)2:2H2O) at alkaline pH (pH 10). Se sorption on Ca compounds was observed at pH 10. For reason the above, it was considered that high calcium fly ash tended to have a strong decrease in leaching of As and Se at alkaline pH. In HCl extract tests, it was showed 10-90% of total As and Se in fly ash to be extractable. HCl extractable As and Se were assumed as the available leaching fraction of As and Se, it was possible to describe the leaching of these oxyanions with a simplified model of surface complexation with amorphous Al oxides at weak acidic pH (pH 5). For reason the above, fly ashes that had high contents of HCl extractable As and Se and low contents of amorphous Al oxides were considered to have high leaching potential for As and Se.

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