From natural aluminosilicate minerals to zeolites: synthesis of ZSM-5 from rectorites activated via different methods

The key to success in synthesizing zeolites from natural aluminosilicate minerals is the effective activation. This article presents an energy-saving and high-efficient method based on a submolten salt (SMS) system. Taking rectorite as an example, the effects of various activation methods on the reactivity of the resulting minerals were investigated. The results showed that after being thermally treated at 900 degrees C, the rectorite was transformed into meta-rectorite consisting of distorted crystallized AlO6 and SiO4/AlO4 units; after being alkali-fused at 900 degrees C the crystallized SiO4 units were depolymerized into disilicates (Na2SiO3/Na2Si2O2) and monosilicates (Na4SiO4), and the AlO6/AlO4 units were converted into sodium aluminates (NaAlO2/Na2Al2O4); after being SMS-activated at 250 degrees C, the SiO4 units were exclusively depolymerized into monosilicates, and the AlO6/AlO4 units were converted into NaAlO2 and/or Na2Al2O4. As a result, when taking the alkali-fused or SMS-activated minerals as the starting materials, pure-phase ZSM-5 zeolites were obtained. (C) 2015 Elsevier B.V. All rights reserved.