Synthesis and application of geopolymers from municipal waste incineration fly ash (MSWI FA) as raw ingredient - A review

Municipal solid waste incineration fly ash (MSWI FA) is classified as hazardous waste in many countries around the world.Application of MSWI FA as a precursor into geopolymers can effectively reduce or even eliminate the environmental hazards. It also enables resource utilization of MSWI FA, while avoiding the limitation of insufficient space for landfill disposal. This paper critically reviewed the MSWI FA base geopolymers used as low-carbon cementitious materials and stabilization/solidification. The effects of the different technologies and changes in process parameters on the material properties were analyzed. The synthesis process parameters such as raw material mixing ratio, properties of alkali activator, liquid-to-solid (L/S) ratio and curing conditions have significant effects on the mechanical properties of products. MSWI FA based geopolymer preserved excellent durability under acidic or alkaline conditions. The techniques such as incorporation of silica-aluminum oxide precursors, moulded, mechanochemical and electrochemical effectively promote the solidification of heavy metals in the raw material and reduce the heavy metal leaching concentration. In addition, the MSWI FA based geopolymer can be used as an excellent solidification material for radioactive substances and organic contaminants. The future research requirements are outlined based on the current state of research.