Adsorption of Different Reactive Dyes onto Surfactant-Modified Zeolite: Kinetic and Equilibrium Modeling

This study deals with the kinetic and equilibrium modeling of adsorption of the commercially important reactive azo dyes, Black B (C.I. Reactive Black 5), Red 3BS (C.I. Reactive Red 239) and Yellow 3RS H/C (C.I. Reactive Yellow 176) onto a Turkish zeolite mineral. To increase the adsorption capacity of the zeolite, the surface of natural samples was modified with a typical quaternary amine surfactant hexadecyltrimethylammonium bromide (HTAB). A series of batch adsorption tests were carried out at 298 K and the pseudo-first order, pseudo-second-order kinetic models and intraparticle diffusion model were used to evaluate the kinetic data. The pseudo-second-order model provided excellent kinetic data fitting (R-2 > 0.997) for these three dyes. The free energy changes Delta G for dye adsorption onto HTAB-zeolite were calculated. The negative values of Delta G indicate that the adsorption process is spontaneous and thermodynamically favorable. The Freundlich and Langmuir equations were also applied to describe the equilibrium isotherms for three reactive dyes and isotherm constants were determined. The Langmuir model agrees very well with experimental data while the adsorption behavior of all reactive dyes is favorable (0< R-L < 1).