Two-step kinetic study on the adsorption and desorption of reactive dyes at cationic polymer/bentonite.

The adsorption kinetics of two reactive dyes, namely, Reactive Blue K-GL and Reactive Yellow K-4G onto the new cationic polymer/bentonite, i.e., polyepicholorohydrin-dimethylamine/bentonite (EPI-DMA/bentonite), were studied under different conditions. The result indicated that the adsorption processes were found to follow the two-step kinetic rate equation with two different adsorption rate constants (k(1) and k(2)) and also to follow the intraparticle diffusion model with two different diffusion rate constants (k(int,1) and k(int,2)). The corresponding values of energies of activation of adsorption, enthalpies of activation and entropies of activation for both the two adsorption kinetic steps have been calculated, suggesting that the adsorption processes were endothermic and physical. The desorption kinetics of two dyes from EPI-DMA/bentonite were studied in NaOH solution with different concentrations, which were also found to obey the two-step kinetic rate equation with two different desorption rate constants (k(d,1) and k(d,2)).