Upgrading Coal Gangue Waste into Molecular Sieves for Sustainable Wastewater Purification

Abstract

The disposal and management of coal gangue (CG) waste from coal mining pose significant environmental pollution challenges. Here, we propose utilizing CG as raw material to synthesize CG-based NaA-type molecular sieves (CG@NaA MS) through a high-temperature alkali fusion combined with a hydrothermal process. This approach enables the sustainable treatment of copper ions and methylene blue (MB) in wastewater. Semi-in situ characterization reveals that grains are formed by energy-driven directional attachment of seeds, followed by anisotropic crystallization to produce a highly crystalline cubic structure. The maximum adsorption capacities of CG@NaA MS for copper ions and MB are 107.8 and 20.3 mg/g, respectively, surpassing commercial MSs and most similar materials reported in the literature. This enhanced adsorption is attributed to ion exchange and electrostatic interactions between Na⁺, Si-O, and Al-O sites within the MS and the adsorbed copper ions or MB. This study presents a straightforward, eco-friendly method for CG and wastewater treatment, advancing a sustainable "waste treatment with waste" solution.