Study of the kinetics and thermodynamics of the adsorption of a basic dye on sawdust
The adsorption of a basic dye (Neutral red RBNR) on wood sawdust was studied. The kinetics, thermodynamics and isotherms of the adsorption were used to identify the retention mechanisms. For the kinetics study, perfectly stirred batch experiments were carried out after adjustment of the parameters influencing the system, such as the pH, adsorbent dosage and initial dye concentration. Experimental results were modelled according to kinetic equations representing pseudo-first order, pseudo-second order reactions, as well as equations for external and intra-particle diffusion. The chemical surface reaction was fitted to a pseudo-second order equation, with very high regression coefficients. Intra-particle diffusion is the rate-limiting step in the process of adsorption beyond 60 min contact time. The adsorption thermodynamics and isotherms are consistent with a spontaneous exothermic chemisorption reaction, leading to an organized monolayer of the dye molecules on the sorbent surface.