Kinetic modeling of pentachlorophenol adsorption onto granular activated carbon

The overall rate of adsorption of pentachlorophenol (PCP) from an aqueous solution on a granular activated carbon (GAC) was investigated in this work. The adsorption isotherm data were obtained in a batch adsorber and the Prausnitz–Radke isotherm fitted reasonably well the equilibrium data. The concentration decay data were obtained in a rotating basket batch adsorber and the experimental data were interpreted by a diffusional model which takes into account adsorption, external mass transfer and intraparticle diffusion. It was assumed that the intraparticle diffusion is due to pore volume diffusion (Fick diffusion) and surface diffusion. The external mass transfer coefficient was estimated from the initial slope of the concentration decay curve. The effective diffusion coefficient was evaluated by matching the experimental concentration decay data with a numerical solution of the mathematical model. The effective pore volume diffusivity was greater than the molecular diffusivity of PCP in aqueous solution. The results indicated that the overall rate of adsorption is mainly controlled by intraparticle diffusion. Moreover, intraparticle diffusion was predominantly due to surface diffusion and that external mass transport resistance was negligible.