Synthesis of zeolites from the low-grade Tunisian natural illite by two different methods

Na-zeolites were successfully synthesised for the first time from Tunisian natural illite clay by two different methods: (1) alkaline fusion prior to hydrothermal reaction and (2) conventional hydrothermal alkaline activation. Both processes have been evaluated at different conditions of temperature and reaction time in order to optimise the synthesis. Products have been identified by X-ray diffraction and characterised by Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy (SEM). The textural properties were investigated by BET measurements, and also the cation exchange capacity (CEC) was determined. By fusion with NaOH followed by hydrothermal reaction, illite was converted into zeolite X. Using the second method, sodalite mixed with quartz and unreacted clay was formed during the treatment of illite in NaOH solution. In both cases, the synthetic zeolite products displayed significantly increased cationic exchange capacities compared to the raw material. However, the fusion method yielded better results in terms of shorter reaction times necessary to obtain a product with high crystallinity and excellent performance as a cation exchanger and surface area. The maximum surface area and CEC of the products were found to be 293 m2/g and 342 meq/100 g, respectively.

Research Highlights
► We study the synthesis of Na-zeolite from natural illite by two methods.
► Fusion prior hydrothermal treatment enables the crystallisation of X zeolite.
► Zeolite products without quartz and gypse impurities were synthesised.
► High cationic exchange capacity and surface area were obtained.
► Hydroxysodalite mixed with unreacted illite was prepared by hydrothermal method.