Green Synthesis of Coal Gangue-Derived NaX Zeolite for Enhanced Adsorption of Cu2+ and CO2

The accumulation of coal gangue (CG), a byproduct of coal mining, poses severe environmental challenges. This study presents a green strategy to convert CG into high-value NaX zeolite via an alkali fusion–hydrothermal method. Through orthogonal experiments, the optimal synthesis conditions (solid–liquid ratio 1:8, crystallization temperature 110 °C, time 12 h) were identified, yielding NaX zeolite with exceptional crystallinity (98%), specific surface area (703.5 m2/g), and pore volume (0.28 cm3/g). Comprehensive characterization (XRD, SEM-EDS, BET, etc.) confirmed its structural integrity and thermal stability. The synthesized zeolite exhibited remarkable adsorption capacities for Cu2+(185.35 mg/g) and CO2(5.51 mmol/g), following the Langmuir isotherm model. This work not only addresses gangue disposal challenges but also demonstrates a cost-effective route for producing high-performance adsorbents, aligning with circular economy and carbon neutrality goals.