High silicon fly ash (HSFA) utilized as a source of silicon in synthesizing of Na-A, -X and -Y zeolites through alkali fusion followed by hydrothermal treatment at 100 degrees C for 12 h. Various types of zeolites with different degrees of purity were prepared by changing Si/Al ratio of the reaction mixture from 1.6 to 3.0. In addition, exact boundaries of this ratio for synthesis of each zeolite type were determined. Furthermore, the effect of NaOH amount utilized in alkaline fusion step on crystalinity of samples investigated. The synthesized zeolites were characterized using various techniques including; XRD, TGA, FTIR, SEM and BET. The ion-exchange behaviors of zeolitic samples tested with Co(2+). The obtained Na-X zeolite was crystaline, had a very high cation-exchange capability of 4.9 mequiv. g(-1) and possessed relatively high specific surface area of about 434 m(2) g(-1). (C) 2008 Elsevier Ltd. All rights reserved.