Studies on room-temperature synthesis of zeolite NaA

Zeolites NaA were prepared by hydrothermal synthesis under room-temperature conditions. The effects of crystallization time, Na2O/SiO2, H2O/SiO2, silicon and aluminum from different sources on the end products were studied. The results indicated that although 7 days product was fully crystalline according to the XRD investigation, further prolonging the crystallization time more, the crystals transferred from spherical to cubic in shape. The products synthesized at room temperature showed much smaller crystal sizes than those synthesized at high temperature, with the mean particle sizes of about 346 and 1374 nm, respectively. Mild alkalinity circumstance was favorable for the crystallization of zeolite NaA. However, higher Na2O/SiO2 molar ratio resulted in the formation of sodalite. Furthermore, the silicon and aluminum sources determined whether or not zeolites NaA were formed. Well-developed zeolite NaA crystals were obtained with water glass, fumed silica as silicon sources and aluminum sulphate, aluminum isopropoxide, aluminum powder as aluminum sources.