Morphological and Chemical Characterization of Calcium-Hydrate Phases Formed in Alteration Processes of Deposited Municipal Solid Waste Incinerator Bottom Ash

During a study which investigates the exothermal heating of municipal solid waste incinerator bottom ash (MSWI) in a landfill samples were taken at a solid waste incinerator in southern Germany operating at ∼1000 °C. The chemical and mineralogical bulk composition was determined by X-ray fluorescence (XRF) and X-ray diffraction (XRD). Single bottom ash particles were investigated by optical microscopy and scanning electron microscopy with quantitative energy-dispersive X-ray microanalysis (SEM/EDX). The fresh bottom ash consists of ash (42%), melting products (40%), metallic components (8%), usually aluminum, iron, and copper, and residual parts (10%). The main phase of the bottom ash is glass (∼ 40%) with relics (e.g. quartz) and quench phases (e.g. gehlenite). The main crystalline phases are silicates (e.g. gehlenite, augite, diopside, quartz), oxides (e.g. magnetite, spinel, hematite), carbonates (e.g. calcite, metal-carbonates), and salts (e.g. chlorides and sulfides). In the deposited bottom ash endo...