Influence of crystallization time for synthesis of zeolite a and zeolite x from natural kaolin

Zeolite A and zeolite X were successfully synthesized from natural kaolin from Lampang province using calcination and a two-step hydrothermal method. First, metakaolin was obtained by calcining the kaolin at 700 °C for 2 h. Hydrothermal experiments can be separated into two types, being high temperature and short time or lower temperature long time. For high temperature hydrothermal treatment, metakaolin was mixed with NaOH to form hydrous sodium aluminosilicate. This was dissolved in dilute HCl. After filtration, the pH was adjusted with deionized water to pH = 7. This formed an amorphous aluminosilicate gel. For low temperature and longtime hydrothermal treatment aluminosilicate gel was mixed with NaOH to form zeolite A and zeolite X. The optimum condition for the first step in the synthesis of zeolite A is high temperature and short time of hydrothermal treatment with NaOH 8 M at 200 °C for 3 hours. This is followed by low temperature and longtime of hydrothermal treatment with NaOH 1 M carried out at 90 °C for 72 hours. The optimum conditions for the first step of synthesis of zeolite X is the high temperature, short time hydrothermal treatment with NaOH 8 M at 200 °C for 3 hours and low temperature, longtime hydrothermal treatment with NaOH 1 M at 90 °C for 120 hours. The characterizations of zeolite A and zeolite X were carried out by x-ray diffraction (XRD), scanning electron microscopy (SEM), and infrared spectroscopy (FT-IR).