KINETIC, EQUILIBRIUM AND THERMODYNAMIC MODELING OF DISPERSE DYE ADSORPTION ONTO FLY ASH.

Fly ash has been employed as adsorbent for the removal of an azo dye; disperse blue 79 from aqueous solution. The fly ash has been characterized by means of X-ray diffraction and Fourier transform infrared spectroscopy. Adsorption studies were performed at different temperatures, adsorbent doses, pH?s and dye initial concentrations. It was found that increasing temperature increases the adsorption process thereby indicating an endothermic process, as for the pH, it had no significant influence on the dye adsorption onto the fly ash. Increasing dye concentration leaded to a decrease in the adsorption removal percentage. The Langmuir and Freundlich isotherm models were utilized to understand the nature of the adsorption process; the results suggested that Langmuir model fitted the adsorption data better than the Freundlich isotherm model. Further, the kinetic data were better correlated with the pseudo second order model than the pseudo first model. The thermodynamic parameters such as the free energy, enthalpy and entropies of adsorption of the dye-fly ash system were also evaluated; the negative value of ΔS0 suggested that the system exhibits random behavior, the value of ΔG? is negative, which indicates that the adsorption process is spontaneous and feasible on the fly ash.