Geochemical modelling and identification of leaching processes in MSWI bottom ash : implications for the short-term and long-term release of contaminants

Abstract

Municipal Solid Waste Incinerator (MSWI) bottom ash is the major residue that remains after the incineration of Municipal Solid Waste. The slag-like material is produced world-wide in very large and everincreasing quantities. In the past the bottom ash was usually disposed, nowadays it is increasingly being used as a construction material. Incineration concentrates the mineral components of the original waste, including elements of environmental concern such as heavy metals, oxyanions, and salts. To ensure an environmentally safe utilisation or disposal of MSWI bottom ash it is, therefore, necessary to investigate its leaching properties. It is in particular necessary to identify the mechanisms that control leaching, because only then reliable predictions of the long-term leaching can be made. This thesis focuses on the geochemical processes that control the shortterm and long-term leaching of major and minor elements from MSWI bottom ash. The research is based on (I) carefully controlled laboratory leaching experiments on MSWI bottom ash at different stages of weathering, (II) geochemical modelling of aqueous (in)organic complexation, precipitation/dissolution, and sorption processes, (III) specific experiments to obtain parameters for the modelling of sorption reactions and organic complexation reactions, (IV) spectroscopic analyses of bottom ash samples, and (V) a field investigation of a 20-year old disposal of MSWI residues.