Zeolite T was synthesized from the molar chemical composition of 1SiO2:0.04Al2O3:0.26Na2O:0.09K2O:14H2O in the form of a homogenous milky solution in the presence of the two different structure-directing agents TMAOH and TEAOH respectively. Modification of the composition of silica was undertaken using metakaolin from calcined kaolin at 750 °C for 4 h, while the molar composition of each different SDA was variated from 0.05, 0.10, 0.15, 0.20 and 0.25. The homogenous mixture was left at room temperature for 24 h before undergoing hydrothermal synthesis at 100 °C for 168 h. The synthesized samples were filtered and aged at 120 °C for 2 h and each sample was calcined at high temperatures (545 °C for TMAOH and 520 °C for TEAOH) for template removal before characterization using XRD and SEM. Crystallization of the zeolite T in its major form only took place at a molar ratio of 0.10 of TMAOH, while TEAOH showed the species evolution of zeolite T into zeolite L and W for other molar ratios.

Free-template zeolite T crystals were synthesized via hydrothermal synthesis by utilizing the activated kaolin as silica and alumina source, with the molar composition of 1 SiO2: 0.04 Al2O3: 0.26 Na2O: 0.09 K2O: 14 H2O. Observation of the formation of free-template zeolite crystals were done at temperature 90°C, 100 °C and 110 °C respectively. It was therefore determined that during the 120 h of the synthesis at 90 °C, zeolite T nucleated and formed a first competitive phase with zeolite L. As temperature increases to 100 °C, zeolite T presented itself as a major phase in the system at time 168 h. Subsequently, development of Zeolite T with second competitive phase of zeolite W was observed at temperature 110 °C. In this study, XRD and SEM instruments were used to monitor the behavior of zeolite T crystals with respect of temperature and time. By using natural resource of kaolin clay as a starting material, this paper hence aims to provide new findings in synthesis of zeolite T using low energy consumption and low production cost.

Metakaolinite has been used as a silica and alumina precursor to synthesise kalsilite via the hydrothermal method with the addition of potassium hydroxide (KOH) as the potassium source. The effects of the KOH concentrations and reaction temperatures have been investigated. X-ray diffraction (XRD) diffractograms and field emission scanning electron microscope (FESEM) images showed the formation of hexagonal kalsilite after the hydrothermal reaction of metakaolinite at 190 °C in 1.25 M KOH for 24 hours. Kalsilite formed as a minor crystalline phase at a KOH concentration of less than 1.0 M KOH, while, at a higher KOH concentration, the crystallinity of the product increases. On the other hand, 190 °C was sufficient to convert metakaolinite to kalsilite. Besides, zeolite F and muscovite have been found as the dominant products at a lower KOH concentration and temperature, respectively.

Hydrothermal synthesis of kalsilite was facilitated by the inclusion of potassium carbonate (K 2 CO 3 ) as the source of the potassium ion. After a 24 h reaction at 220 °C, kaolin clay treated with 1.25 M K 2 CO 3 showed the most significant peaks at 2θ of 28.5° and 34.7° by X-ray diffraction corresponding to the hexagonal kalsilite. In addition, field emission scanning electron microscopy images also revealed hexagonal particles proving the formation of the desired mineral. The orthorhombic boehmite and monoclinic bayerite were formed as the dominant phases at lower K 2 CO 3 molarity (<1.0 M), whereas kalsilite was recognized as the minor crystalline phase. The crystallinity of hexagonal kalsilite increased at higher K 2 CO 3 concentration (>1.0 M) while the reaction temperature remained at 220 °C. Furthermore, the energy dispersive spectroscopy pattern of kalsilite showed a significant atomic percentage of potassium in the aluminosilicate material, indicating its formation.