Kinetic and equilibrium study of the removal of reactive dye using modified walnut shell

Modified walnut shell (EAWNS) was prepared by reaction with epichlorohydrin and alkaline solution of aspartic acid and used to remove reactive dye (Reactive Brilliant Blue (KN-R)) from aqueous media. The isotherms, kinetics and thermodynamics of KN-R adsorption onto EAWNS were studied at 298-318 K. The isotherm data of KN-R adsorption onto EAWNS agreed closely with the Langmuir model. The theoretical monolayer adsorption capacity for KN-R was 224.42 mg/g at 318 K. The result from the Dubinin-Radushkevich model showed that the KN-R adsorption onto EAWNS is chemisorption. The adsorption rate of KN-R onto EAWNS conformed to the pseudo-second-order model. The diffusion mechanism was investigated by the intraparticle diffusion model. The mass-transfer coefficient calculated by the surface mass-transfer coefficient model was in range of 2.95 × 10^-5 to 2.93 × 10^-4cm/s. The thermodynamic results suggested that the adsorption of KN-R onto EAWNS is spontaneous and endothermic in nature. The design of a single-stage batch adsorption process based on EAWNS adsorbent was carried out. Furthermore, the recycled EAWNS maintains high adsorption capacity despite four cycles.