Abstract
Zeolite X powder was synthesized using natural low-grade diatomite as the main source of Si but only as a partial source of Al via a simple and green hydrothermal method. The microstructure and surface properties of the obtained samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), wavelength dispersive X-ray fluorescence (XRF), calcium ion exchange capacity (CEC), thermogravimetric-differential thermal (TG-DTA) analysis, and N2 adsorption-desorption technique. The influence of various synthesis factors, including aging time and temperature, crystallization time and temperature, Na2O/SiO2 and H2O/Na2O ratio on the CEC of zeolite, were systematically investigated. The as-synthesized zeolite X with binary meso-microporous structure possessed remarkable thermal stability, high calcium ion exchange capacity of 248 mg/g and large surface area of 453 m2/g. In addition, the calcium ion exchange capacity of zeolite X was found to be mainly determined by the crystallization degree. In conclusion, the synthesized zeolite X using diatomite as a cost-effective raw material in this study has great potential for industrial application such as catalyst support and adsorbent.
Highlights
IntroductionTraditional methods for synthesizing zeolites typically involve chemical reagents as starting materials or crystallization from a gel or clear solution under hydrothermal conditions, which have the disadvantages of high cost, excessive waste, and unfriendly nature to the environment
Zeolites are crystalline aluminosilicates built from TO4 tetrahedra (T = Si and Al) with excellent properties of high surface area, uniform and precise microporosity, shape selectivity, high ion-exchange capacity, strong Brønsted acidity and high thermal and hydrothermal stability [1]
The principle raw materials used for the synthesis of the zeolites are different sources of silica and alumina, which are usually composed of sodium silicates, sodium aluminate, aluminum salts or colloidal silica
Summary
Traditional methods for synthesizing zeolites typically involve chemical reagents as starting materials or crystallization from a gel or clear solution under hydrothermal conditions, which have the disadvantages of high cost, excessive waste, and unfriendly nature to the environment. Natural aluminosilicate and silicate minerals and industrial solid wastes have been explored as silica and/or alumina source because they are cost-effective precursors and can lead to reduction of the synthesis costs. Diatomite serves as the silica source in the synthesis of zeolites, which is cost-effective. We report on the synthesis of zeolite X from natural low-grade diatomite with high crystallization degree under hydrothermal conditions.
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