Adsorption of Ni2+ Ions onto NaX and NaY Zeolites: Equilibrium, Kinetics, Intra Crystalline Diffusion, and Thermodynamic Studies

Abstract

This paper focuses on intra crystalline diffusion of Ni2+ ions onto NaX and NaY zeolites. The zeolites are obtained by the hydrothermal synthesis method. The samples were characterized by several techniques: X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) and InfraRed Spectroscopy (FT-IR). Physical parameters such as pH solution (2 - 7), adsorbent dose (0.25 - 2 g/L), initial concentration of Ni (II) ions (50 - 200 mg/L) and temperature (298 - 323 K) are optimized. The maximum uptake is 99% and 97% for NaX and NaY zeolite respectively under the optimum conditions: pH ∼ 7 and adsorbent dose of 1 g/L for initial concentration of 50 mg/L at 298 K. The best interpretation of the experimental data is obtained by the Langmuir isotherm with a maximum adsorption capacity of 111.85 and 77.57 mg/g for NaX and NaY respectively. The results show that the kinetic data for both zeolites follow the pseudo-second-order model, indicating the presence of physical adsorption. The free energy (DGo), enthalpy (DHo), and entropy (DS°) are evaluated. The process has proved it's spontaneous and endothermic. Diffusion mechanisms of Ni (II)ions adsorption onto NaX and NaY has shown that intraparticle diffusion is the limiting step of the process. The NaX and NaY have been applied to wastewater from the Algerian industrial zone to eliminate the Ni2+ effluents using the optimal parameters. It has been found that the Ni2+ ions removal yield was 77.81% for NaX and 83.86% for NaY.

Keywords

• adsorption
• nickel ions
• zeolite
• kinetic
• diffusion
• thermodynamic