Synthesis of Zeolite-A Using Silica from Rice Husk Ash

We describe the synthesis of zeolite-A using rice husk ash (RHA) as starting material. Synthesis comprised alkali activation at low temperature (<100 degrees C) using NaOH as reagent. We investigated the effect of experimental conditions on zeolite synthesis from RHA. The process was studied as a function of NaAlO2 addition, NaOH concentration, temperature, and reaction time. A stirred batch reactor was used under the following reaction conditions: SiO2/Al2O3 molar ratio, 1.7-2.8; NaOH concentration, 2-6 M; temperature, 50-80 degrees C; reaction time, 0-48 h. The obtained solids were identified by X-ray diffraction and characterized by scanning electron microscopy; specific surface areas and cation exchange capacity values were also determined. Concentrations of Si and Al in the solution were analyzed to monitor the reaction process. Single zeolite-A can be synthesized from RHA under all our experimental conditions. We proposed the formation mechanism of zeolite-A from RHA. The silicate ion dissolves in NaOH solution from RHA and reacts with aluminate in the solution to form aluminosilicate, from which zeolite-A crystals are generated. The high crystallinity was obtained rapidly when SiO2/Al2O3 ratio, NaOH concentration and temperate were high in this experimental conditions.