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Abstract
The goal of this study was to investigate the effect of thermal treatment (200, 400, and 600 °C) on the adsorption capacity of a natural clinoptilolite-rich zeolite (NZ) of different particle sizes for methylene blue removal from aqueous solution. The physical properties and chemical composition of the natural zeolites treated at several temperatures were determined. Powder X-ray diffraction, Brunauer–Emmett–Teller, and scanning electron microscopy were used to characterize the thermally treated zeolites. X-ray diffraction showed that the main crystalline phases of the thermally treated zeolites were clinoptilolite-Na, quartz, muscovite, and albite. The equilibrium measurements were analyzed using Langmuir, Freundlich, and Dubinin-Radushkevich isotherms. The experimentally fitted Freundlich isotherm was a better fit than the Langmuir model for methylene blue adsorption onto the thermally treated zeolites. The adsorption of methylene blue on the thermally treated natural zeolites was shown to involve chemisorption.