Properties and microstructure of sintered incinerator bottom ash

The fraction of incinerator bottom ash with a particle size less than 8 mm produced at a commercial municipal solid waste incinerator was wet milled, dried, compacted and sintered at a range of temperatures to form ceramic materials. The effects of milled ash particle size distribution, powder compaction pressure and sintering temperature were investigated, and the materials formed characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis (TG/DTA). The main minerals present in the milled ash were quartz (SiO2) and calcite (CaCO3). Sintered densities of materials produced from ash milled to 95% less than 27 μm increased from 1.38 to 2.63 g/cm3 on increasing the sintering temperature from 1020 to 1080 °C. Firing above 1080 °C caused a rapid decrease in density and sample expansion. The principal crystalline phase present in the high-density material was diopside (CaMgSi2O6). This work shows that a significant fraction of incinerator bottom ash can be processed to form sintered materials with properties controlled by ash particle size distribution and sintering conditions.