J. Eng . Te c hno l. Sc i., Vo l. 47, No . 6, 2015, 633-639 633 Received August 27 th , 2014, Revised April 14 th , 2015, Accepted for publication November 10 th , 2015. Copyright ©2015 Published by ITB Journal Publisher, ISSN: 2337-5779, DOI: 10.5614/j.eng.technol.sci.2015.47.6.4 Synthesis of NaY Zeolite Using Mixed Calcined Kaolins Subagjo, Endang Sri Rahayu, Tjokorde Walmiki Samadhi & Melia Laniwati Gunawan Chemical Engineering Program, Bandung Institute of Technology, Jalan Ganesha 10, Bandung 40132, Indonesia Email: subagjo@che.itb.ac.id Abstract. Kaolin is one of several types of clay minerals. The most common crystalline phase constituting kaolin minerals is kaolinite, with the chemical composition Al 2 Si 2 O 5 (OH) 4 . Kaolin is mostly used for manufacturing traditional ceramics and also to synthesize zeolites or molecular sieves. The Si-O and Al-O structures in kaolin are inactive and inert, so activation by calcination is required. This work studies the conversion of kaolin originating from Bangka island in Indonesia into calcined kaolin phase as precursor in NaY zeolite synthesis. In the calcination process, the kaolinite undergoes phase transformations from metakaolin to mullite. The Bangka kaolin is 74.3% crystalline, predominantly composed of kaolinite, and 25.7% amorphous, with an SiO 2 /Al 2 O 3 mass ratio of 1.64. Thermal characterization using simultaneous DSC/TGA identified an endothermic peak at 527 °C and an exothermic peak at 1013 °C. Thus, three calcination temperatures (700, 1013, and 1050 °C) were selected to produce calcined kaolins with different phase distributions. The best product, with 87.8% NaY zeolite in the 54.7% crystalline product and an SiO 2 /Al 2 O 3 molar ratio of 5.35, was obtained through hydrothermal synthesis using mixed calcined kaolins with a composition of K 700C : K 1013C : K 1050C = 10 : 85 : 5 in %-mass, with seed addition, at a temperature of 93 °C and a reaction time of 15 hours. Keywords: calcined kaolin phases; hydrothermal synthesis; kaolin; NaY zeolite. 1 Introduction Kaolin consists mainly of the kaolinite phase with the chemical composition of Al 2 Si 2 O 5 (OH) 4 and relatively inert Si-O and Al-O structures. Breck [1] stated that among clay minerals kaolin is the most commonly used in manufacturing traditional ceramics and is also used to synthesize zeolites or molecular sieves because of the reactivity of calcined kaolin to alkali solutions. Many researches have been carried out using treated kaolin to produce NaY zeolite. Brown [2] reacted calcined clay and aqueous alkali to produce a mixture of crystalline zeolitic aluminosilicate and a porous amorphous silica-alumina. Htay [3] obtained zeolite Y with an SiO 2 /Al 2 O 3 molar ratio of 3.53 by activation of kaolin and treatment using sodium hydroxide and hydrothermal crystallization. Zheng [4] observed that, due to the inert nature of kaolin, in the process of