Adsorption characteristics of natural zeolites as solid adsorbents for phenol removal from aqueous solutions: Kinetics, mechanism, and thermodynamics studies

Zeolitic tuff was used for the adsorption of phenol from aqueous solutions at different temperatures in a batch process. The adsorption characteristics, i.e., kinetics, mechanism, isotherms, and thermodynamics, of phenol from water onto zeolite were studied. Three different kinetic models, viz., pseudo-first-order, pseudo-second-order, and intraparticle diffusion were used to fit the kinetics data. The pseudo-second-order model best described the experimental data. Concerning the mechanism, the results indicated that the intraparticle diffusion is not the rate limiting step in the phenol adsorption process. The adsorption isotherms at different temperatures were determined and modeled using four different models. The best-fitted adsorption isotherm models were found to be in the order: Freundlich > Redlich-Peterson > Langmiur > Temkin for temperature range 25-45 degrees C. The Langmiur model fitted well the experimental data with a maximum adsorption capacity of 34.5, 24.9, 23.8, and 23.3 mg/g at 25, 35, 45, and 55 degrees C. Thermodynamically, it was determined that the adsorption of phenol onto zeolite is physical in nature and enthalpy driven with Delta H degrees = -10.2 kJ/mol. (C) 2011 Elsevier B.V. All rights reserved.