Kinetic and Thermodynamic Studies for Phosphate Removal Using Natural Adsorption Materials

Batch adsorption experiments were carried out to study the kinetics and thermodynamics of phosphate removal from model solutions on the surfaces of some selected adsorbents. The data obtained were analyzed using two reaction-based kinetic models and a diffusion-based model. In order to examine the extent to which diffusion participates in this adsorption process, the data were processed by the Weber-Morris mass transfer model. The Freundlich model represented a slightly better description of phosphate adsorption onto slovakite and GEH104 than onto clinoptilolite-rich tuff, while the Redlich-Peterson model yields a better fit for phosphate adsorption onto clinoptilolite-rich tuff. Adsorption onto montmorillonite proceeds best using the Sips isotherm model. The calculated ΔG° values show that under standard conditions the adsorption of phosphate onto all adsorbents examined occurs spontaneously.