Kinetic study of the adsorption of dyes onto activated carbon

Four batch systems were applied to study the adsorption by activated carbon of methylene blue, methyl orange, crystal violet and rhodamine B from aqueous solution. The kinetics of the adsorption systems were evaluated by pseudo first-order and modified pseudo first-order models. The kinetics of dye adsorption on activated carbon have been studied at close to equilibrium conditions. From empirical kinetic data, it was shown that application of the pseudo first-order and modified pseudo first-order equations for modelling over the entire span of adsorption time causes large error near the initial time of adsorption. Comparison between the pseudo first-order and the modified pseudo first-order models has been provided. It was shown that adsorption of the system dyes/activated carbon proceeded in two steps; an initial step governed by the intra-particle diffusion model, which is followed by pseudo first-order models or modified pseudo first-order models.