Ammonium removal from aqueous solution by zeolite X synthesized from halloysite mineral.Water Sci Technol. 2010; 62(4):937-46.WS
Zeolite X was successfully synthesized from natural halloysite mineral by hydrothermal method. The synthesized zeolite X was characterized by XRD, SEM, TEM and HRTEM. The characterization indicated that zeolite X had high crystallinity together with symmetrical and uniform pore channels. Ammonium (NH₄+) adsorption properties of zeolite X were studied using batch experiments. The results revealed that high initial concentration and low temperature favored NH₄+ adsorption on zeolite X. Both Langmuir and Freundlich isotherms fit well with the equilibrium data. Kinetic studies showed that the adsorption followed pseudo-second-order model. Intra-particle diffusion analysis demonstrated that NH₄+ diffused quickly among the particles at the initial 20 min of the adsorption process, and then the diffusion slowed down and stabilized. Thermodynamic parameters such as change in free energy (ΔG⁰), enthalpy (ΔH⁰) and entropy (ΔS⁰) indicated that the adsorption was spontaneous and exothermic at ambient conditions. The reusable ability of zeolite X was also evaluated. Due to its low cost, high adsorption capacity and fast adsorption rate, zeolite X synthesized from halloysite could be used as an effective and environmental-friendly adsorbent for NH₄+ removal.