Application of kinetic models to the sorption of disperse dyes onto alunite

The sorption of three disperse dyes, namely, Disperse Blue 56 (DB56), Disperse Red 74 (DR74) and Disperse Yellow 119 (DY119), onto alunite has been studied in terms of pseudo-first- and second-order sorptions and intraparticle diffusion processes thus comparing chemical sorption and diffusion sorption processes. The pseudo-second-order model provided a high degree of correlation with the experimental data for the sorption processes. There was a small discrepancy at the beginning of the experiments (5–30 min) which suggested that intraparticle diffusion may be involved up to 30 min of the sorption process. The kinetics of sorption, based on the sorption capacities of disperse dyes on alunite, were followed at various time intervals. Results show that the intraparticle diffusion may be rate-limiting, followed by the pseudo-second-order kinetic model in the sorption of disperse dyes onto alunite during agitated batch contact time experiments. The rate constant, the equilibrium sorption capacity and the initial sorption rate were calculated as a function of the effect of alunite particle size, alunite dose, initial dye concentration and pH of the solution.