Conversion of coal fly ash to zeolite utilizing microwave and ultrasound energies: A review

The ever increasing consumption of coal around the world has given rise to the by-product coal fly ash that requires an urgent attention and is gaining much needed research attention. This paper introduces pioneering work on zeolitization of coal fly ash utilizing conventional heating methods and reviews the progress made in the conversion of coal fly ash to zeolite and its applications while strongly focusing on the utilization of microwave and ultrasound energies in achieving this goal. An introduction to coal fly ash and zeolitic materials is given and the conversion of the formal to the latter is discussed. Zeolites are multi-utility crystals that have attracted much attention in the research community. Zeolites synthesized from pure chemical precursors are inherently different from zeolites produced from coal fly ash therefore; published works which have investigated the application of zeolites produced from coal fly ash are also discussed. Microwave and ultrasound energies have been reported to dramatically decrease reaction times due to the influences on the induction periods and nucleation. In the last few years these novel energies have blossomed in a useful technique for many applications. As novel energies they hold great promise in rapid and efficient conversion of coal fly ash to value added materials such as zeolites.