A Quasi-Solid-Phase Approach to Activate Natural Minerals for Zeolite Synthesis

Synthesis of zeolites or zeolite/clay composites from natural aluminosilicate minerals has received extensive attention because of its great usefulness in greening the zeolite manufacturing process, in which effective activation of natural aluminosilicate minerals is crucially important. Herein, we present an energy saving and green approach, the quasi-solid-phase activation method, to efficiently destruct the natural minerals under the conditions of a temperature as low as 100 °C and an activation time as short as 30 min. Our strategy consists of the following three steps: (1) preparation of a mixture of a natural kaolin mineral, NaOH, and water by kneading, (2) extruding of the mixture into sticks, and (3) low-temperature calcination of the stick, featured by the combined use of mechanochemical actions. The results showed that 84.7% Si species and 69.0% Al species in the kaolin mineral underwent a large degree of depolymerization in the kneading and extruding steps, and following calcination at 100 °C resulted in the complete depolymerization of the kaolin mineral to monomer orthosilicate anions (Q0) and tetracoordinated aluminum (AlIV) species, which are highly active silica and alumina sources for synthesizing aluminosilicate zeolites. Using the activated kaolin mineral as a starting material, pure-phase NaY and NaA zeolites have been successfully synthesized.