Mesoscale depolymerization of natural rectorite mineral via a quasi-solid-phase approach for zeolite synthesis

Abstract

Synthesis of zeolites from natural aluminosilicate minerals is a green and sustainable technology. One major challenge in the synthesis is how to enhance the reactivity of the natural minerals. Herein we developed a facile quasi-solid-phase method to efficiently depolymerize natural rectorite into its corresponding mesoscale building blocks, i.e., TO4 (T = Si or Al) monomers or oligomeric species. Natural rectorite can be completely and efficiently depolymerized at 170 °C within 60 min, which is substantially lower than temperatures (>900 °C) used in industrial depolymerization methods. The transformation of Si and Al species in the QSP depolymerization mainly undergoes three stages: (1) the layer of Na6AlVI4AlIV2Si6O24·nH2O is dissociated and converted into Na6AlVI2AlIV4Si6O24; (2) Na6AlVI2AlIV4Si6O24 is further depolymerized into Na4AlIV4Si6O20 and monomer NaAlIVO2; (3) Na4AlIV4Si6O20 is finally decomposed into mesoscale monomers (Na4SiO4 and NaAlIVO2), dimers (Na6Si2O7), and chains (Na2SiO3). Moreover, the depolymerized rectorites exhibits high reactivity for synthesizing highly crystalline ZSM-5 zeolite.