Solid State Science and Technology, Vol. 19, No 1 (2011) 88-100

ISSN 0128-7389





Abdul Salam Matlob1,*, Rose Aini Kamarudin1, Zaemah Jubri1 and Zainab Ramli2

1Department of Engineering Sciences & Mathematic, College of Engineering,

Universiti Tenaga Nasional, Km 7 Jalan Kajang-Puchong,

43009 Kajang, Selangor, Malaysia

2Department of Chemistry, Faculty of Science,

Universiti Teknologi Malaysia, 80990 Skudai, Johor, Malaysia

*Corresponding Author:



Response Surface Methodology (RSM) was used in this study to determine the

optimum conditions for the synthesis of Na-A zeolites from coal fly ash (CFA).

Application of this methodology allows a better understanding of the influence of

various factors (Si/Al ratio (0.5-1.5), incubation temperature (70-120 °C) and time of

incubation (2–4 days)) on the synthesis of zeolites. The Box–Behnken design was

applied with different levels of the factors, determining its influence on yield percent in

order to obtain contour plots. The silicates and aluminates were extracted from coal fly

ash (CFA) with 4M NaOH solution assisted by microwave irradiation (power level 100

watts) for 6 minutes followed by incubation at various temperatures. The products

isolated were characterized by their XRD images and found to be Na-A zeolites,

sodalite octahydrate and gibbsite. The highest percent yield of product was obtained at

0.5 SiO2/Al2O3 molar ratio, 70 °C incubation temperature for 3 days, the product

however, was not a zeolite. It was gibbsite which contains Al(OH)3. Na-A zeolite was

formed at SiO2/Al2O3 molar ratio 1-1.5, incubation temperature was 70 – 95 °C and 2-4

days of incubation and the highest yield was observed at SiO2\Al2O3 ratio = 1,

incubation temperature 70 oC for 4 days. The contour plots showed that the yield

percent of the product was inversely proportional to the three factors used. The order of

effectiveness of the factors on yield percent is: SiO2/Al2O3 molar ratio > incubation

temperature > duration of incubation.



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