Synthesis of Zeolite-A Using Silica from Rice Husk Ash

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We describe the synthesis of zeolite-A using rice husk ash (RHA)as starting material. Synthesis comprised alkali activation at low temperature (<100°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°C; reaction time, 0–48 h. The obtained solids were identi fied 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.