Transformation of Coal Gangue to Sodalite and Faujasite Using Alkali-hydrothermal Method

The coal gangue as the only source of silicon and aluminum was employed to synthesize sodalite and faujasite using hydrothermal method, which directly treated the mixture of pre-treated coal gangue and NaOH solution under hydrothermal environment. X-ray powder diffraction analysis (XRD), thermogravimetry analysis (TG) and differential thermogravimetry analysis (DTG), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), N2 adsorption-desorption technique, X-ray photoelectron spectroscopy (XPS), etc. were used to characterize the samples. Cd2+ ion was used to evaluate the heavy metal ions removal performance of the samples. The experimental results show that the coal gangue, which consists of quartz, calcium feldspar, potassium feldspar and kaolinite, can transform to sodalite and faujasite under alkali-hydrothermal condition at 150 and 180 °C, respectively. The as-prepared sodalite and faujasite can effectively remove the simulated Cd2+ ion wastewater and actual industrial wastewater containing As3+, Cd2+, and Cr3+ ions, and the good heavy metal ion removal performance of the zeolites is mainly attributed to their low Si/Al ratio and high Na+ content. This alkali-hydrothermal method appears to be a simple and efficient method for transformation of coal gangue to high purity zeolites.