A by-product fly ash from oil shale processing was converted into zeolite by alkali hydrothermal activation using sodium hydroxide. The activation was performed at different activation temperatures using 8 M sodium hydroxide. The obtained cation exchange capacity (CEC) showed that the best condition for synthesis of zeolite performed in a closed reactor at 160 degreesC for 24 h. Powder patterns of X-ray diffraction analysis have shown that zeolite of type Na-PI was successfully synthesized at 29.5, 32.2 and 34.4degrees. The produced zeolite was used as an ion exchanger for the treatment of wastewater for metal ions. Lead and cadmium were chosen as target metal ions. The adsorption capacity was estimated to be 70.58 mg lead/g-zeolite and 95.6 mg cadmium/g-zeolite when the initial concentration for both ions was 100 mg/l. The results were correlated using Redlich-Peterson and Sips models. For cadmium the best fit was obtained with the Sips model while, for lead the Sips models fits the experimental data adequately. Based on such results, it is concluded that the treated ash may possess strong potentials for zeolite production used in wastewater treatment. (C) 2003 Elsevier Ltd. All fights reserved.