Synthesis and characterization of zeolite 4A from soft kaolin

Abstract

The synthesis of zeolite 4A from soft kaolin has been studied. Kaolin was converted to metakaolin by firing at 550 °C for 2 h, which was then added to NaOH solutions of appropriate concentration. The optimum molar ratios for the main constituents in the starting gel were SiO2/Al2O3 = 1.7, Na2O/SiO2 = 2.8 and H2O/Na2/O = 61.7. The gels were vigorously stirred at 70 °C for 2 h and aged under the room temperature for 24 h, then stirred again with intermediate speed at 90 °C. After 4 h, the product was centrifugated and washed till pH 10˜11. Examination with XRD, IR and SEM proved that the product was zeolite 4A.