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- 저자 : ( Naoto Kakinoki ) (검색결과 1 건)
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Change in type of heavy metal compounds after oxygen exposure of fly ash
( Naoto Kakinoki ),( Shinya Suzuki ),( Ayako Tachifuji ) 한국폐기물자원순환학회(구 한국폐기물학회) 2019 한국폐기물자원순환학회 심포지움 Vol.2019 No.1
Under the revision of the Waste Management and Public Cleansing Law in 1991, it was regulated that the fly ash must be landfilled after chelate treatment or cement solidification for preventing from the heavy metal leaching. However, it was reported that Pb eluted again from such treated fly ash if it was left for a certain period under the wet and oxidative condition. Therefore, the O<sub>2</sub> exposure experiment was conducted to clarify the re-elution mechanism under such condition. As the results, the Pb concentration in the elution of leaching test increased after O<sub>2</sub> exposure (Fig. 2). It suggests that the chelate bond is cleaved or the insoluble Pb compounds (PbO<sub>2</sub>) change to the water soluble compounds (PbO, PbCl<sub>2</sub>) by H<sub>2</sub> generated by the alkali hydration reaction with Al. Whereas the concentration of soluble Zn, which is amphoteric metal same as Pb, was decreased. From these results, it was considered that Zn was related to such chemical change of Pb. In this study, the change in the Zn compounds of fly ash after O<sub>2</sub> exposure was investigated to clarify the influence of O<sub>2</sub> on the change of insoluble metal compounds to soluble one. In all three experiments, the content of soluble Zn compounds and Zn oxide decreased as that of organic Zn and Zn sulfide increased (Fig. 2). It means that the soluble Zn reacted with hydrogen sulfur produced by H<sub>2</sub> and formed the insoluble ZnS under alkaline conditions. Such mechanism is also expected from the slight decrease in the concentration of the SO<sub>4</sub> <sup>2- </sup>after the O<sub>2</sub> exposure. From these results, it is estimated that O<sub>2</sub> contribute to the change in the charge of metal compounds and consequently is increased the soluble metal compounds.
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