Equilibrium, kinetics and mechanism for the removal of Rhodamine B by adsorption on Okoume (Aucoumea Klaineana) sawdust from aqueous media

The aim of the present work was to investigate the feasibility of Okoume (Aucoumea Klaineana) sawdust (OS) for Rhodamine B (RhB) adsorption from aqueous media. OS surface was characterized by the functional organic groups by the Boehm titration method, scanning electron microscopy (SEM) and isoelectric potential (pH(ZPC)). The adsorption of RhB on OS material was studied as a function of solution pH 2-10, sodium chloride (0-5000 mg/L), solution temperature (25-45 degrees C), contact time and initial concentration (5-30 mg/L). The influence of these parameters on the amount of RhB adsorbed was studied using the batch process. The results show that the increase of initial concentration, the temperature has a positive impact on the adsorption of RhB. However, the sodium chloride and pH have a negative effect to the dye removal, and a maximum adsorption was achieved at pH 3.0. Experimental kinetics data at different initial dye concentrations were analyzed using Lagergren pseudo-first-order, pseudo-second-order and Elovich models, and were found well described by the pseudo-second order model. The results for the mechanism adsorption, the intraparticle diffusion for all period was not the only rate-limiting step, it seems that other processes might implicate in control the rate. Equilibrium isotherm data at different temperatures (25-45 degrees C) were analyzed according to Langmuir and Freundlich equations, and the adsorption isotherm was found to follow the Langmuir model. The monolayer adsorption capacity (q(m)) was found to be 79.65 mg/g at 25 degrees C. Furthermore, thermodynamic parameters such as Delta G degrees,Delta S degrees and Delta H degrees were calculated, and the results suggest that the adsorption is spontaneous, a physical process and endothermic in nature.