Abstract
Mineralogical and physical immobilization effects of secondary minral formation by chelate treatment for hazardous elements contained in municipal solid waste incineration (MSWI) fly ash particles were investigated. SEM observation showed that ettringite, which can incorporate heavy metals into its structure, was generated on the surface of fly ash particles after chelate treatment. However, SEM-EDX analysis could not find concentrated spots of hazardous elements on ettringite. This means that mineralogical immobilization of hazardous elements by ettringite is negligible. The same MSWI fly ash particles were observed before and after the moistening treatment in order to investigate physical immobilization effect. These observation showed that soluble components transferred on fly ash particle surfaces and such elemental transfer was inhibited by insoluble mineral formation like gypsum. This means that physical immobilization by insoluble secondary mineral formation can contribute to hazardous elements immobilization to some extent. However, such mineralogical and physical immobilization by secondary mineral formation, which is promoted by fly ash moistening owing to chelate treatment, were limited. Therefore, toxic element immobilization by chelate treatment and its stability would depend mainly on the stability of complexation between toxic elements and chelate reagent.
