The investigation into the ammonium removal performance of Yemeni natural zeolite: Modification, ion exchange mechanism, and thermodynamics

• Optimum modification condition of zeolite was 1 M NaCl, 80 °C and stirring time of 1 h.
• Zeolite performance for NH4+ removal was up to 99% depends on relevant parameters.
• The highest ion exchange capacity was obtained at 35 °C and pH of 8.
• Various ion exchange isotherms and kinetics calculations were applied.
• The ion exchange was spontaneous and exothermic as revealed by ΔG°, ΔH° value.

This paper present the first attempt to investigate the potential use of Yemeni (Al-Ahyuq) natural zeolite on the effectiveness of ammonium ion (NH4+) removal. The kinetics and isotherms of ion exchange were studied in a batch system. Important parameters which affect the ion exchange, such as optimal modified zeolite (SNZ), pH of solution, temperature, contact time, zeolite mass and initial ammonium concentration were investigated. The characteristics of modified zeolite (SNZ) and its mechanism of ammonium removal was investigated and compared with that of natural zeolite (NZ). Both zeolites were fully characterized by scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS) technique, zeta potential (Z-potential), X-ray diffraction (XRD), X-Ray Fluorescence (XRF),Fourier transform infrared spectroscopy (FTIR), thermogravimetry analyzes (TGA) and specific surface area (SSA) analysis. The results demonstrate that the SNZ has a high selectivity for NH4+ and had maximum removal efficiency reaching up to 99% based on relevant parameters. The highest ion exchange capacity was obtained at 35 °C and pH of 8. Moreover, the kinetic data followed more closely the pseudo-second order model whereas ion exchange isotherm was suitably described by the Langmuir model (LM). In addition to that, Kielland plots and thermodynamic parameters such as change in free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were also calculated. The parameters revealed that the exchange process of ammonium ion by zeolite is spontaneous and exothermic. The results indicate that the modified Yemeni zeolite has significant potential as an economic and effective adsorbent material for ammonium removal from aqueous solutions.

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