Evaluation of the Efficiency of Natural Clinoptilolite Zeolites in the Removal of Magnesium Ions from Aqueous Solution

In this research, the adsorption of Mg (II) was studied in a batch system by using zeolite, and the influence of effective parameters on the adsorption, such as initial pH, adsorbent dosage, contact time, initial Mg (II) concentration and temperature were investigated. Also, the surface characteristics and structure of the adsorbents were respectively obtained by SEM and FT-IR. The pH experimental results showed that the maximum adsorption efficiency of Mg (II) ion occurs at pH=7. By increasing the contact time between the adsorbent and solution, adsorption efficiency was raised, and after 60 minutes, equilibrium is reached. Results showed the adsorption efficiency decreased by increasing the initial concentrations of Mg (II) in the range of 50-250 ppm in solution, and the effect of adsorbent dosage showed that adsorption efficiency increased by increasing the adsorbent dosage from 0.5g to 2.5g. In addition, the higher adsorption of Mg (II) was observed at higher temperatures, which proves the endothermic behavior of the adsorption process. Thermodynamic parameters were investigated in three temperatures 25, 35, and, 45°Ϲ. The negative value of the Gibbs free energy (ΔG˚) showed that the adsorption process was spontaneous. Positive value enthalpy (ΔH˚) indicated that the adsorption process was endothermic, and positive value entropy (ΔS˚) can be attributed to the increased randomness at the interface of the adsorbent and the solution. The experimental results for the effect of exposure time were examined for the kinetic study with three different models: Pseudo-First order, Pseudo-Second order, and Intra-Particle diffusion. Among these models, the best fit was observed for pseudo-second-order. The study for initial concentration of Mg (II) in the solution was studied by Langmuir, Freundlich, Temkin, and Dubnin-Radushkevich isotherms, and the best fit for the adsorbent was observed by Langmuir isotherm and the Langmuir maximum sorption capacity was found to be 4.77 mg/g at 45°C.