Synthesis and characterization of zeolites produced by ultrasonication of coal fly ash/NaOH slurry filtrates

Abstract

Studies were conducted to determine if crystalline zeolites could be obtained from the filtrates of coal fly ash (CFA)/NaOH slurries through sonication. The CFA/NaOH slurries were obtained by aging CFA in 3 M NaOH for 24 h at 50 °C using a solid/liquid (S/L) ratio of 15 g/120 mL. FT-IR studies indicated that the ‘Lo’ regime ultrasonicated zeolite had higher intensities than that of the ‘Hi’ frequency ultrasonicated zeolite. The bands associated with the ‘Lo’ regime ultrasonicated zeolite were observed at 1066cm^–1, 1400cm^–1 and 3600cm^–1, which were identified as Si-Oasymmetric stretch, Al-Oasymmetric stretch, O-Hbend and O-H asymmetric stretch, respectively. Based on PXRD studies, the zeolitic phases were most intense for the 90 min ultrasonicated zeolite. Powder X-ray diffraction studies showed that the phases initially in CFA, such as quartz and aluminosilicate, were converted into gismodine zeolite Na-P1. Morphological changes were seen as ultrasonication period was increased. At short ultrasonication times, irregularly shaped fused-like grain structures were observed, while at longer times separate grain-like structures became more apparent. Energy dispersive X-ray spectroscopy studies on the 90 min ultrasonicated zeolite indicated the presence of Na, O, Si and Al, which were important building-blocks for the zeolites.