Determination of kinetic and equilibrium parameters of the batch adsorption of Ni(II) from aqueous solutions by Na-mordenite

The potential to remove nickel(II) ions from aqueous solutions using Na-mordenite, a common zeolite mineral, was thoroughly investigated. The effects of relevant parameters solution pH, adsorbent dose, ionic strength, and temperature on nickel(II) adsorption capacity were examined. The sorption data followed the Langmuir, Freundlich, Langmuir-Freundlich and Dubinin-Radushkevich (D-R) isotherms. The maximum sorption capacity was found to be 5.324 mg/g at pH 6, initial concentration of 40 mg/L and temperature of 20 degrees C. Thermodynamic parameters, viz. changes in standard free energy (Delta G degrees), enthalpy (Delta H degrees) and entropy (Delta S degrees) have also been evaluated and the results show that the sorption process was spontaneous and endothermic in nature. Dynamics of the sorption process were studied and the values of rate constant of adsorption, rate constant of intraparticle, diffusion were calculated. The activation energy (E-a) was found to be 12.465 kJ/mol in the present study, indicating a chemical sorption process involving weak interactions between sorbent and sorbate. The sorption capacity increased with the increase of solution pH and the decrease of ionic strength and adsorbent dose. The nickel(II) ions sorption by the Na-mordenite is not completely attributable to ion exchange. Compared to the other adsorbents, the nickel(II) ions show a lower affinity towards the clay mineral adsorbents. (c) 2006 Elsevier B.V. All rights reserved.