Simple and rapid synthesis of zeolite W from K-feldspar via the improved hydrothermal method

Abstract

An improved hydrothermal method was proposed to rapidly synthesize zeolite W from alkali fusion-activated K-feldspar. The effects of m (KOH)/m (K-feldspar), n (SiO₂)/n (Al₂O₃), n (H₂O)/n (SiO₂), crystallization time, and crystallization temperature on the synthesis of the zeolite W were investigated. The optimal synthesis conditions were m (KOH)/m (K-feldspar) ratio of 1.5:1, the activation time of 2 h, and the activation temperature of 500°C, n (H₂O)/n (SiO₂) ratios of 42, n (K₂O)/n (SiO₂) of 0.90, n (SiO₂)/n (Al₂O₃) of 5, crystallization time of 6 h, and crystallization temperature of 150°C. The mechanism for rapid synthesis of zeolite W was illustrated. In this process, Na₂SiO₃·9H₂O and Al₂(SO₄)₃·18H₂O were first dissolved rapidly in the synthesis system to form an amorphous gel, which contributes to the accelerated crystallization process. Compared with the state-of-the-art synthesis method, this method remarkably decreases the water content to be added in the synthesis process and crystallization time, avoids the pre-preparation process of the xerogel, and enhances the utilization rate of K-feldspar. This work provides an industrial-friendly synthesis process of zeolite W and could realize the highly efficient utilization of K-feldspar.