Highly effective removal of Pb²⁺ in aqueous solution by Na-X zeolite derived from coal gangue

The present study aimed to synthesize Na-X zeolite from coal gangue powder (CGP) via the alkali fusion hydrothermal method. The optimal synthetic conditions were investigated, the mass ratio of CGP/NaOH(s) was 1:1.25, and crystallization reaction time was 12 h. X-ray powder diffraction, scanning electron microscopy energy-dispersive X-ray spectrum, and Fourier transform infrared spectrometer techniques were used to test the properties of resultant zeolite product, which was highly identical to that of commercial zeolite. The efficiencies of the synthetic zeolite for Pb²⁺ adsorption were analyzed on factors including solution pH, adsorbent dosage, temperature, and contact time. Compared with the pseudo-first-order, Elovich, Freundlich, and Temkin models, the pseudo-second-order and Langmuir models were fitted more satisfactorily with the dynamic data and adsorption equilibrium data, respectively. The maximum Pb²⁺ adsorption capacity of synthetic zeolite (457 mg/g) could be reached when the pH, contact time, temperature, and initial Pb²⁺ concentration was 6, 40 min, 45 °C, and 200 mg/L. The adsorption capacity was higher than many of the natural and synthetic zeolites reported in previous literature.