1. INTRODUCTION 1.1. MSWI bottom ash Municipal solid waste incineration (MSWI) is preferred as an alternative to landfilling. In this way, a significant reduction of both mass and volume, by approximately 70% and respectively 90% [1] is achieved. After collection of the municipal solid waste, incineration takes place in a waste-toenergy plant. Next to energy, the incineration process generates a variety of solid residual materials. 20% of these are carried from the incinerator by flue gasses, e.g. air pollution control residues, fly ash, and boiler ash. The remaining 80% of the total volume of by-products is accounted for by MWSI bottom ash (BA)