Sodalite, faujasite and A-type zeolite from 2:1dioctahedral and 2:1:1 trioctahedral clay minerals. A singular review of synthesis methods through laboratory trials at a low incubation temperature

This paper reviews different methods to synthesise zeolite from clay minerals through experiments at a low incubation temperature (40 °C). Ca-montmorillonite, Na-montmorillonite, illite and chlorite from Source Clay Repository of Clay Minerals Society were used as raw materials. These samples were acid- treated, calcined and NaOH pre-fused, in separate experiments. Zeolite synthesis was performed by means of: i) a conventional alkaline hydrothermal method and ii) a pre-fusion hydrothermal method. Both were also carried out with the addition of Al(OH)3 to the hydrothermal solution. The results indicate that HCl treatment acts on the chemical dissolution of clays, while the breaking down of clay structure induced by calcinations together with the amorphization process (both on natural and acid pre-treated samples), has an important role in clay mineral activation. However, zeolites do not form by means of the conventional hydrothermal method, instead, they crystallize by a pre-fusion hydrothermal process, thus confirming the action of alkaline pre-fusion to improve raw material reactivity.