Thermal Treatment on MSWI Bottom Ash for the Utilisation in Alkali Activated Materials

At present, most municipal solid waste incineration (MSWI) bottom ash is directly landfilled, raising concerns about environmental issues and loss of resources. Due to its high mineral content, MSWI bottom ash is now being considered as a raw material to prepare alkali-activated materials (AAMs). However, the mineral fraction unavoidably contains metallic aluminium (Al) and zinc (Zn) scraps (<1 wt.%), which easily oxidise and generate H2gas under alkaline conditions. As a result, when using MSWI bottom ash to prepare AAMs, the formation of a porous structure, as well as expansive cracks (both detrimental to strength development) can be observed. In this research, thermal treatment of MSWI bottom ash, at temperatures of 500 and 1000 °C, was performed to deal with the issue caused by metallic Al/Zn. A series of tests, including Quantitative X-ray diffraction (QXRD) analysis, fineness measurements (particle size and surface area), and the dissolution test, were conducted to examine the effects of thermal treatment on as-received bottom ash. The results indicate that it is difficult to oxidise metallic Al/Zn at 500°C, but heating up to 1000 °C can realize the complete oxidation of Al/Zn, which in turn allows the wide utilisation of bottom ash in AAMs. Keywords: MSWI bottom ash, thermal treatment, alkali-activated materials.