Synthesis of binder-free granulated low-modular zeolites using ultrasound

Synthesis of binder-free granulated low-modular zeolites has been studied. As starting material, the aqueous suspensions of Na2SiO3 center dot 5H(2)O, A1(2)O(3), and SiO2 have been used. The mixtures with atomic ratios Si:Al equal 1 and 2 have been prepared. For the pre-activation of the reaction mixtures, the ultrasound with a frequency of 22 kHz has been used. Moulding pastes have been prepared from the suspensions and then the pellets of 3 mm diameter have been extruded. The pellets have been calcined at 650 degrees C and then have been subjected to the hydrothermal crystallization in NaOH solutions with concentrations of 2 and 6 mol l(-1).XRD, SEM, and FT-IR have been used for testing. It was found that at the ratio of Si: Al =1 after the thermal treatment, sodium aluminosilicates of cubic syngony have been synthesized, and with an atomic ratio of 2, orthorhombic and monoclinic Na2Si2O3 have been formed. The hydrothermal crystallization of the pellets with an Si:Al = 1 resulted in forming three types of zeolites (NaP, sodalite, NaA). When the ratio Si:Al in the pellets was 2, NaP and sodalite have been synthesized. It was found that ultrasonic treatment caused a change in the morphology of the solid phase, which was traced at all stages of the preparation of granulated zeolites. The morphological differences determined the phase composition and crystallite size after hydrothermal crystallization. It was shown that at the ratio of Si:Al = 2 using sonication of the suspension and crystallization pellets in 2 M alkali solution, the pure phase of NaP zeolite has been synthesized, and the solid phase had a wool-like morphology. (C) 2017 Elsevier Inc. All rights reserved.