[en] Full text: Zeolites are natural or synthetic minerals that have attractive structural characteristics for industrial application. They are usually found in nature in regions rich in volcanic rocks being formed by alkaline activation [1]. The natural zeolites have a high content of impurities and/or do not have the necessary properties for some of their applications. These facts awoke the interest in theirs syntheses [2]. Usually they are form from supersaturated solutions of silicates and aluminates under strict experimental conditions [1]. The fly ash has a high content of silicon in its composition and, in addition, it has a fine particle size which favors the use of synthesis by hydrothermal treatment (in aqueous solution) under controlled temperature [2]. This work studied the alkaline hydrothermal process for the synthesis of zeolites using coal ash as an alternative source of silicon. The variables studied were: the concentration of the reaction medium (0.23 and 3.5 mol/L NaOH), reaction time (1, 2, 3, 4, 5 and 6 days) and the Si/Al ratio in the gel synthesis. The methodology used for the synthesis was performed as described by IZA (International Zeolite Association)[3]. The results (XRD, TEM, SEM) showed that it was possible to synthesize zeolites (sodalite) and other structures such as quartz and mullite, with an average specific surface area of 6 m² /g. References: [1] J. C.Izidoro, Estudo sobre remoção de íons metálicos em água usando zeólitas sintetizadas a partir de cinzas de carvão. Dissertação (Mestrado). Instituto de Pesquisas Energéticas e Nucleares - IPEN. São Paulo, 2008. [2] L.S.Ferret, Zeólitas de cinzas de carvão: síntese e uso. Tese (Doutorado). Universidade Federal do Rio Grande do Sul, Porto Alegre, 2004. [3] Portal web on-line da (International Zeolite Association) disponível em: < http://www.iza-online.org/>. Acessado em Maio de 2013.(author)