Synthesis of Na-X zeolite from Longkou oil shale ash by alkaline fusion hydrothermal method

Abstract

Na-X zeolites were synthesized by Longkou oil shale ash with the alkaline fusion hydrothermal method. The effects of fusion temperature, ash to NaOH ratio, solid-liquid ratio, crystallization time and crystallization temperature on the crystallinity of zeolites were investigated. The synthetic products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), 29Si nuclear magnetic resonance spectroscopy (29Si NMR) and N2 adsorption-desorption. The results showed that the conditions to synthesize Na-X zeolite were: Longkou oil shale ash to sodium hydroxide ratio 1:1.2 g·g−1, fusion temperature 600 °C, solid-liquid ratio 1:4 g·mL−1, crystallization time 24 h and crystallization temperature 80 °C. The zeolite with high crystallinity (91.32%) was synthesized: the product exhibiting octahedral particles observed by SEM, and the calculated Si/Al ratio in Na-X zeolite being 1.23 from 29Si MAS NMR spectra, which was consistent with the observation from XRD. Keywords: Na-X zeolite, Oil shale ash, Fusion, Crystallization, Hydrothermal