Ultrasound-assisted synthesis of zeolite from bentonite clay: optimization using response surface methodology

Abstract

This study synthesised zeolite from bentonite clay, utilizing an ultrasound-assisted technique and response surface methodology (RSM) to optimize the process. Bentonite clay was dehydrated by calcining at 800°C for 1 h. Thereafter, dehydrated bentonite clay was subjected to alkali dissolution using ultrasonication and hydrothermal treatment. In the alkali dissolution stage, optimum conditions of 2.5 M of NaOH at 2 h of sonication were determined using the RSM tool, showcasing a SiO₂ and Al₂O₃ composition of 26.93 and 4.64%, respectively. After alkali dissolution, the obtained residues from the remaining dehydrated bentonite clay were characterized using X-ray fluorescence (XRF) to observe the remaining silica and alumina composition. In hydrothermal treatment, the synthesized zeolites were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and fourier-transform infrared spectroscopy (FTIR). The RSM analysis indicated optimum hydrothermal treatment conditions of 105°C for temperature treated at 1 h 30 min. Furthermore, the RSM plots for hydrothermal treatment showed that the crystallinity of the obtained zeolite samples increased with hydrothermal temperature and time. Moreover, the characterisation results showed that lower hydrothermal temperatures and crystallization times exhibited zeolite NaP phases with uniform spherical morphology, whilst higher temperatures and times exhibited hydroxy sodalite phases and large irregular particles. This methodology offers a promising approach for efficient and controlled zeolite synthesis from bentonite clay with the assistance of RSM.