A green process for zeolite synthesis: low-temperature vapor phase treatment of natural bauxites

In this work, three samples of bauxite were used as inexpensive sources for the zeolite formation by a green process based on vapor-phase crystallization (VPC) method. The synthesis was carried out using a water bath with deionized water heated at 35, 45, 60 or 90 °C. During the process, NaOH pre-fused bauxites were contacted only with vapor from the liquid. The results indicate that sodalite formed in all the samples after VPC at higher temperatures (60 °C and 90 °C). Large amount of zeolite A was instead synthesized in the sample characterized by SiO2/Al2O3 ratio next to 1 and after vapor treatment at 35 °C and 45 °C. These data highlight the determining role of both raw material chemical composition and amount of water molecules in type of zeolite formed by vapor crystallization method. Moreover, the results indicate that VPC process made it possible to synthesize zeolite generating no water waste.