Kinetics of dyes adsorption at the solid-solution interfaces: a theoretical description based on the two-step kinetic model.

It is shown that the kinetics of dyes sorption from aqueous solutions by solids can be considered as a two-step process. The first initial kinetics is governed by the rate of surface reaction. When the adsorbed amount reaches about 80% of the equilibrium coverage, it switches to another kinetics governed by the rate of intraparticle diffusion. Equations we developed recently are used to calculate the whole composite kinetic isotherm, and a simple numerical procedure is proposed to use these equations in the quantitative analysis of experimental data. This procedure is illustrated by the analysis of kinetic isotherms of sorption of metal complex yellow by pine sawdust.