Characterization of coal gangue and coal gangue-based sodalite and their adsorption properties for Cd 2+ ion and methylene blue from aqueous solution

Synthesis and development of high-efficiency and low-cost adsorbents for treating of the wastewater containing heavy metal ions and/or dyes has been aroused worldwide attention in recent years. In this study, the coal gangue as the only supply of Si and Al was adopted to synthesize sodalite using hydrothermal method. Both the gangue and the synthesized sodalite were characterized in terms of composition and structure. Cd 2+ ions, methylene blue and their mixture were employed to evaluate the adsorption performance of the materials. The results showed that the gangue could be converted into sodalite with a small amount of impurity minerals. The as-prepared sodalite could effectively remove Cd 2+ ion, and methylene blue due to its low Si/Al ratio, relatively high specific surface area and exchangeable Na + ion content. The maximum adsorption capacities of the sodalite for Cd 2+ ions and methylene blue were up to 60 mg/g and 17.3 mg/g, respectively. The adsorption isotherm of the Cd 2+ ion and methylene blue could be described by Langmuir model, and the adsorption processes were more consistent with the pseudo-second-order kinetics. Relatively low-cost sodalite/gangue mixtures could be used instead of pure sodalite for the removal of Cd 2+ ion, methylene blue and their combined pollutants. The as-prepared sodalite and the sodalite/coal gangue mixtures appear to be good candidate for treating of the heavy metal ions and dye wastewater.