Morphological and Chemical Properties of MSWI Bottom Ash with Respect to the Glassy Constituents

Abstract

MSWI bottom ash consists predominantly of x-ray amorphous, glassy constituents. A thorough characterization of the glassy constituents could provide insight into both long term leaching and suitability for technological applications of MSWI bottom ash. In this study the bottom ash glasses were examined using conventional and advanced microanalytical techniques. The glass content of the bottom ash sample used in this study was estimated at 75% (w/w). Although the identity of all crystalline phases was very difficult to establish, seven minerals were identified. Automated particle analysis revealed that the major element composition (Si, Al, Ca and Fe) varies little with particle size for particles smaller than 1000 μm diameter, which may indicate complete transformation in this particle range. Inter particle heterogeneity is observed in ash particle composition, with varying quantities of network formers and modifiers. Reducing the scale of observation reveals the existence of different phases within individual particles. Over 50% of the surface area of the ash particles belong to silicon rich, calcium-silicon rich, and aluminum-silicon rich particles types. From a morphological and chemical point of view volcanic ashes and MSWI bottom ash exhibit a close similarity. Knowledge of weathering processes based on studies of volcanic ashes can be used to predict long term leaching behaviour of MSWI bottom ash.