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Optimal Mixture Designs for Heavy Metal Encapsulation in Municipal Solid Waste Incineration Fly Ash

Mixing municipal solid waste incineration fly ash (MSWIFA) with industrial by-products such as ground granulated blast furnace slag (GGBFS) and ladle furnace slag (LFS) can lead to a hardened system which can encapsulate the heavy metals present in the MSWIFA. The objective of this study is to find optimal mixture designs to effectively encapsulate these heavy metals. The nature of the hydrates and the strength of the mixtures are studied to develop a sustainable and practical construction material incorporating MSWIFA. Heavy metals including Cr, Cu, Zn and Cd are safely encapsulated in several developed mixtures with leachate concentration below EPA drinking water limit. The encapsulation behavior is complex and depends on metal type, age of testing, and hydration products. In general, mixtures containing LFS have more aluminate hydrates, and show greater encapsulation capacity for most heavy metals. However, they also generally show significant Sb leaching. Mixtures which show satisfactory encapsulation for all ions and adequate strength development are identified. Three ideal mixtures, including one containing zero cement, are identified which satisfy both leaching and strength requirements.