Kinetic and equilibrium studies on the removal of Congo red from aqueous solution using Eucalyptus wood (Eucalyptus globulus) saw dust

Eucalyptus wood (Eucalyptus globulus) saw dust (SD) was treated using sodium hydroxide to improve adsorption capacity for the removal of Congo red from aqueous solutions. The treated saw dusts using sodium hydroxide was evaluated through SEM, FTIR, TGA and XRD. The Brunauer–Emmett–Teller (BET) surface area, pore volume and average pore diameter of SD were 0.3742 m2/g, 0.00836 cm3/g and 893.6 Å. Average particle size of SD was 182.8 μm. Bulk density of SD was 212 kg/m3. The porosity of SD is 0.3. Equilibrium and kinetic adsorption studies were carried using SD. The effect of various operating parameters like initial pH, contact time, adsorbent dose, initial concentration and temperature on the removal of Congo red has been studied. The Congo red adsorption data were fitted to various isotherm models. It was found that Redlich and Peterson (R–P) model fitted well. The optimum pH for the adsorption was 7. The kinetics of adsorption showed that the Congo red adsorption on SD is a gradual process with quasi-equilibrium being attained in 4 h. The data obtained were also applied to pseudo first-order, pseudo second-order and Weber–Morris equations. The rates of adsorption were found to conform to pseudo second-order kinetics. The adsorption of the Congo red increased with increasing temperature indicating the endothermic nature of the adsorption process. Thermodynamic parameters such as free energy, enthalpy and entropy change were calculated. This adsorbent was found to be both effective and economically viable.

► Eucalyptus wood (Eucalyptus globulus) saw dust treated with NaOH has been investigated for the removal of Congo red.
► Adsorbent was evaluated through SEM, FTIR, TGA and XRD.
► Kinetic data were best described by the pseudo-second order model.
► Experimental equilibrium data were fitted to four different isotherm models.
► The adsorption was spontaneous and endothermic.