Abstract Incineration is an important municipal solid waste management process in Singapore. The incineration bottom ash (IBA) generated may contain heavy metals (HMs) and rare earth elements (REEs) that can cause environmental concerns upon reutilization. In this study, the particle size distribution, density, circularity, and chemical composition of the overall IBA as well as individual size ranges were determined. The particle size reduction characteristics and the mobility of HMs and REEs among different size ranges through ball milling and fluidization processes were examined. Certain HMs were found to present in high concentrations at particular particle size ranges. Mechanisms concerning the mobility of HMs and REEs were revealed.