The solid by-product of oil shale processing (PETROBRAS-Brazil) was used as a raw material to synthesize Na-A and -X zeolites. Two preparation methods using the same starting material composition were carried out. In Method (1), alkaline fusion was used to prepare a glass, which was then hydrated by refluxing. The largest amount of crystallinity was reached with 2 h 30 min of refluxing. In Method (2), alkaline fusion was followed by hydrothermal treatment. The most crystalline sample was obtained after 12 h of heat treatment, and after 96 h hydroxysodalite zeolite was formed. In both procedures, the synthesis products were mainly composed of Na-X zeolite, whose content was influenced by the crystallization time, and of Na-A zeolite, with a practically constant content. (c) 2005 Elsevier Ltd. All rights reserved.