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 similar to 1000 de greesC. The chemical and mineralogical bulk composition was determined by X -ray fluorescence (XRF) and X-ray diffraction (XRD). Single bottom ash part icles were investigated by optical microscopy and scanning electron microsc opy with quantitative energy-dispersive X-ray microanalysis (SEMI EDX). The fresh bottom ash consists of ash (42%), melting products (40%), metallic c omponents (8%), usually aluminum, iron, and copper, and residual parts (10% ). The main phase of the bottom ash is glass (similar to 40%) with relics ( e.g, quartz) and quench phases (e.g. gehlenite). The main crystalline phase s are silicates (e.g. gehlenite, augite, diopside, quartz), oxides (e.g. ma gnetite, spinel, hematite), carbonates (e.g. calcite, metal-carbonates), an d salts (e.g, chlorides and sulfides). In the deposited bottom ash endother mic and exothermic alteration processes are observed (dissolution/precipita tion of salts, glass corrosion, hydration and oxidation reactions of metals , slaking of lime, cementation and carbonation processes). In the course of these processes new mineralogical phases are formed. Among these are e.g. anhydrite, portlandite, calcite, iron oxides and hydroxides, or gibbsite. T hese minerals are always accompanied by different calcium-hydrate phases wi th different mineralogical and chemical properties. The hydrate phases were morphologically and chemically characterized by SEM/EDX. The single crysta ls have a fibrous, ribbonlike, or tabular habit. Ca, Al, Si, and Fe were fo und as main components, with minor amounts of Na, K, Mg, Cu, Zn, Ti, Mn, an d CI, S, P.