Synthesis of Na-A zeolite from coal gangue with the in-situ crystallization technique

•Na-A zeolite (NAZ) was prepared using coal gangue as the raw material via in-situ crystallization technique.•Optimum synthesis conditions of pure, single phase and high-crystalline NAZ were determined.•The synthetic NAZ exhibited excellent calcium binding capacity compared to the commercial-grade NAZ.

Coal gangue (CG), a complex solid waste from coal industry, is still underutilized, thus leading to disposal problems. However, high contents of silica and alumina in this material make it a potential zeolite precursor. In this paper, pure, single-phase and highly crystalline Na-A zeolite (NAZ) with high Ca2+-exchange capacity (CEC) was successfully synthesized with coal gangue as raw materials via the in-situ crystallization technique. Firstly, in order to provide part or all of active SiO2 and Al2O3 species, CG was decarbonized at 800 °C to form an X-ray amorphous material. Secondly, hydrothermal treatment was performed in aqueous alkali to form the NAZ crystal. Moreover, we explored several factors in the formation of NAZ:NaOH concentration, crystallization temperature, and crystallization time. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N2-adsorption–desorption measurements, and CEC testing. Compared to the commercial-grade NAZ, the NAZ prepared from CG could be an alternative material for the phosphorus-containing additives in the detergent industry.

Graphical abstractPure, single-phase and highly-crystalline NAZ with high Ca2+-exchange capacity was successfully synthesized with coal gangue as raw materials via the in-situ crystallization technique.Figure optionsDownload full-size imageDownload as PowerPoint slide