Equilibrium, kinetic and thermodynamic studies of Na+ adsorption from aqueous solutions on homo-ionized K- and NH4-kaolin

Document Type : Original Article

Authors

1 Soils, water and environment research institute, Agriculture Research Centre, Egypt.

2 Department of Inorganic Chemistry, National Research Centre, 33 El Bohouth st. (former Eltahrir st.), P.O. 12622, Dokki, Giza, Egypt.

3 Department of Chemistry, Faculty of Science, Mansoura University, (2), P.O.Box 70, Mansoura- Egypt

Abstract

Egyptian kaolin clay (UnK) was homo-ionized with K+and NH4+ to obtain K-K and N-K, respectively. The analysis of the molar leaching solutions of KCl, NH4Cl or HCl revealed anoriginal cation exchange capacity of UnK up to 6.08meq per 100 g. The adsorption parameters of Na+ on K-K and N-K were examined in aqueous solutions. The equilibrium adsorption data were evaluatedusing Langmuir, Freundlich adsorption and Dubinin–Radushkevich-Kaganer isotherm models. Freundlich model was the best that described the adsorption process and the maximum capacities (qmax) are found to be enhanced to 75.6 and 17.5 mg g-1, respectively. The experimental data fitted well the pseudo-second-order kinetics model. The thermodynamic parameters such as standard Gibbs free energy (∆Gads), enthalpy (∆Hads) and entropy changes (∆Sads) for the adsorption process were calculated. The negative values of the Gibbs free energy confirm that the adsorption processes are spontaneous and thermodynamically favorable while the negative value of ∆Hads supports the exothermic physicochemisorption of the adsorption process. Both homo-ionized kaolin samples are promising cheap adsorbents for lowering the sodicity of soil while gradually exchanging valuable nutrients for plants

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