Synthesis of analcime from sericite and pyrophyllite by microwave-assisted hydrothermal processes

This paper reports the synthesis of analcime from sericite and pyrophyllite by hydrothermal reactions. Commercial mica powders, composed of sericite and pyrophyllite, were treated by microwave-assisted hydrothermal reactions using Na₂SiO₃ as the mineralizer. Besides the as-received, the mica powders were ground in a beads-mill so as to obtain starting materials with different sizes. At 240 °C with 0.5–5 M Na₂SiO₃, the “as-received” and “ground” were transformed to analcime with typical trapezohedron crystal form. Pyrophyllite disappeared faster than sericite indicating that pyrophyllite is more reactive than sericite in the process of analcime synthesis. At higher concentrations of Na₂SiO₃, however, the two minerals eventually transformed to analcime. The synthesis of analcime from pyrophyllite was a one-way type reaction without the appearance of intermediate phases. A similar reaction also proceeded for sericite. The particle sizes of the analcime were in proportional to the starting material, i.e. the size of analcime particles can be controlled by choosing proper starting material sizes. Fine starting material size facilitates the reaction rate and the analcime synthesis can be completed in shorter times.