Synthesis and characterization of Faujasite-Na from fly ash by the fusion-hydrothermal method

Abstract

This research focused on the synthesis and characterization of Faujasite-Na zeolites from fly ash (FA). The FA was subjected to pretreatment processes, washings with hydrochloric acid solutions and heat treatments at 700 °C for 3 h, to remove unburned carbon that would affect the synthetic process. After a fusion with NaOH at 550 °C for 3 h, the resulting material was disposed in a hydrothermal reactor at 100 °C for 12 h to obtain the corresponding zeolite. The products were characterized by XRD analysis, where quartz, mullite, sillimanite and lime phases were identified for the fly ash; quartz, mullite and in higher proportion Faujasite-Na for the synthesized material. The average size of the crystals of the fly ash and zeolite Faujasite-Na was 35.0 and 38.7 nm respectively, while the FTIR results allowed the identification of vibrational bands, characteristic of SiOSi and SiO bonds. The TGA-DTA analysis, allowed the identification of signals associated with exothermic and endothermic processes related to water removal and Faujasite-Na formation, while the EDX analysis coupled to SEM allowed verifying that the composition of the samples is consistent with the results sought and that the morphological characteristics validate the proposed methodology. The XRF results confirm the composition of the fly ash and the obtained Faujasite in accordance with some previous results and an improved composition. Surface area analyses (BET) showed that synthesized Faujasite possess an active area of 460 m² g⁻¹ while the fly ash for its physicochemical properties just an area of 6 m² g⁻¹. The overall results confirmed the efficiency of Faujasite-Na synthesis from FA by the proposed fusion-hydrothermal method.