Nucleation and Growth Process of Sodalite and Cancrinite from Kaolinite-rich Clay under Low-temperature Hydrothermal Conditions

The synthesis of low-silica zeotypes by hydrothermal transformation of kaolinite-rich clay and the nucleation and growth processes of sodalite and cancrinite in the system Na2O-Al2O3-SiO2-H2O at 100 degrees C were investigated. The synthesis products were characterized by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Si-29 and Al-27 Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) and thermogravimetric analysis (TGA). Our data show that the sequence of the transformation of phases is: Poorly crystalline aluminosilicate -> zeolite LTA -> sodalite -> sodalite + cancrinite -> cancrinite. Synthesized materials appeared stable thermodynamically under the experimental conditions, with zeolite LTA (a metastable phase) occurring as a minor phase, compared with the presence of sodalite and cancrinite.