Concentration-dependent surface diffusivity model (CDSDM): Numerical Development and Application

In this paper. the film-solid diffusion model (FSDM) combined with a concentration-dependent surface diffusivity D-s = D-0 exp {k(q/q(sat))} was presented to describe the kinetics of adsorption of reactive dye from aqueous solution onto activated carbon in a batch reactor. A finite-difference scheme was employed to solve the partial differential equations which govern the entire adsorption process in the batch reactor and the resulting kinetic data was presented in terms of the concentration decay curve. It was found that, for the investigated adsorption system, one set of mass transfer parameters was adequate to describe the adsorption rate at different initial solute concentrations. Compared with the constant surface diffusivity model (CSDM), the concentration-dependent surface diffusivity model (CDSDM) yielded a steeper solid-phase concentration profile due to the concentration dependence of D-s. Parametric sensitivity analysis was also carried out in order to facilitate understanding of the effect of each parameter on the shape of the concentration decay curve. (C) 2003 Elsevier Science B.V. All rights reserved.