Homogeneous Surface Diffusion Model for the Adsorption of Basic Dyestuffs onto Natural Clay in Batch Adsorbers

Abstract

The adsorption of basic dyestuffs (Basic Blue 69 and Basic Red 22) onto natural clay has been studied using a series of batch adsorption runs. The homogeneous surface diffusion model (HSDM) has been developed based on external mass transfer and surface diffusion to explain the concentration–time curves. A computer program has been used to generate theoretical concentration–time curves and these results have been adjusted to the experimental data by means of a ‘best fit’ approach. The HSDM has been successfully used to model the dynamics of the adsorption process for basic dyestuffs onto natural clay. The model predicts a single external mass-transfer coefficient, Ks, and a single surface diffusion coefficient, Ds, with initial dye concentration or natural clay mass. The Ks values are 3.4×10–3 and 2.6×10–3 cm/s for Basic Blue 69 and Basic Red 22, respectively. The Ds values are 2.3×10–8 and 1.9×10–8 cm2/s for Basic Blue 69 and Basic Red 22, respectively.