Study of the mechanism of pore diffusion in batch adsorption systems

In this study the film‐pore diffusion model was applied to describe system transport kinetics of three basic dye‐carbon systems, namely Basic Blue 69, Basic Red 22 and Basic Yellow 21. The mass transfer parameters evaluated were the external mass transfer coefficient k_f (cm s⁻¹) and the effective diffusivity D_eff (cm² s⁻¹). A single k_f value was sufficient to describe each dye system: these were 0.15 × 10⁻², 0.20 × 10⁻² and 0.50 × 10⁻² cm s⁻¹ for BB69, BR22 and BY21, respectively. The effective diffusivity was found to have values much larger than those of pore diffusivities calculated from liquid diffusivities and its value decreased with increasing initial dye concentration. This was attributed to the effect of surface diffusion, hence pore diffusivity was exchanged by the effective pore diffusivity in the model. The present model was solved by the exponential curve fit technique; results were expressed in the form of experimental and theoretical Sherwood Numbers compared in terms of the residual.