Microwave synthesis of zeolites from waste glass cullet using indirect fusion and direct hydrothermal methods: A comparative study

Abstract The present work studied the conversion of waste glass (WG) cullet into zeolite using microwave (MW) radiation technique. The temperature and power of radiation were monitored through constant temperature (MWCT) and constant power (MWCP) modes. Indirect fusion synthesis (IFS) and direct hydrothermal synthesis (DHS) conversion methods were studied and the zeolites synthesized by these methods were compared in terms of their characteristics using various techniques including XRD, EDX, SEM, FTIR, TGA, and cation exchange capacity (CEC). IFS was an efficacious synthesis technique and produced zeolites with a much higher crystal growth efficiency compared with those synthesized by DHS method. The IFS method was better than the DHS method as it eliminated the inhibitive effect of soluble aluminates on Si release. The IFS zeolites also provided lower Si/Al ratio and consequently higher cation exchange and water holding capacities compared to DHS zeolites, as validated by EDX, TGA, and CEC results. In addition, high pressure and high-temperature environment deteriorated the zeolite structure and diminished the crystal growth performance. The application of cooling air jet (CAJ) through MWCP mode provided efficient monitoring of temperature overshoot and excessive pressure generation by cooling the excessive generated hot spot zones. Therefore, the CAJ application improved the crystal growth in IFS method as higher radiation powers were applied.