Adsorption Kinetics and Thermodynamics of Acid Blue 25 and Methylene Blue Dye Solutions on Natural Sepiolite

Natural sepiolite was used as an adsorbent for the investigation of the adsorption kinetics, isotherms, thermodynamic parameters of an acid blue 25 (AB25), methylene blue (MB) from aqueous solution at various pHs, temperatures, the kinetics, and thermodynamics for the removal of the two dyes onto natural sepiolite have also been investigated. The adsorbed amounts of AB25 increased with decreasing pH and the optimum pH value for the AB25 and MB were found to be 3.0 and 9.0. respectively. The adsorption capacity of AB25 onto natural sepiolite increased with the increasing temperature, indicating that AB25 and MB dye adsorption on the natural sepiolite was an endothermic process, the second-order model is found to be more suitable to describe the adsorption kinetic data than the first-order model for natural sepiolite on the AB25 and MB and the adsorption process of AB25 and MB are showing pseudo–second-order kinetic behavior, respectively. The adsorption of AB25 and MB on natural sepiolite may be followed by an intraparticle diffusion up to 60 and 90 min, respectively, and the Langmuir equation represents the adsorption process better. The fit of the data for AB25 and MB adsorption onto natural sepiolite suggests that the D-R model gave slightly closer fittings than those of Langmuir and Freundlich models. The adsorption of AB25 on natural sepiolite has a low potential barrier, which is also indicates a physical adsorption. The negative values of ΔG 0 and positive ΔH 0 which has been obtained indicates that the MB adsorption process is a spontaneous and endothermic.