Synthesis of ZSM-5 Microspheres Made of Nanocrystals from Iron Ore Tailings by the Solid-Phase Conversion Method.

ZSM-5 microspheres made of nanocrystals are successfully synthesized from iron ore tailings (IOTs) using a novel and environmentally friendly method, which have a well-defined microporous and mesoporous structure with a large surface area and high acidic strength. In the absence of the liquid water phase during the solid-phase conversion, the phase separation between the surfactant and the solid silica phase is able to be bypassed. Compared to conventional methods, such as hydrothermal and steam-assisted conversion methods, this approach enhances the utilization of autoclaves, considerably reduces pollutants, and simplifies the synthetic process, which saves both energy and time. Furthermore, the crystallization of ZSM-5 microspheres via the solid-phase conversion was examined at 413, 433, and 453 K. The results of the kinetic study suggest that the experimental values obtained conform to those of the nonlinear regression model of Kolmogorov-Johnson-Mehl-Avrami for crystallization and nucleation. For the induction, transition, and crystallization stages, the activation energies are 70.96, 39.76, and 36.23 kJ·mol, respectively. The new method is economical and offers a valuable industrially applicable route for the reuse of IOTs to synthesize ZSM-5 microspheres. This synthetic concept could also be expanded to obtain other types of mesoporous zeolites.