Kinetic, Mechanistic, Thermodynamic and Equilibrium Studies on the Adsorption of Rhodamine B by Acid Activated Low Cost Carbon

Abstract

A carbonaceous adsorbent prepared from an indigenous waste by acid treatment was tested for its efficiency in removing Rhodamine B (RDB). The parameters studied include agitation time, initial dye concentration, carbon dose, pH and temperature. The adsorption followed first order reaction equation and the rate is mainly controlled by intra-particle diffusion. Freundlich and Langmuir isotherm models were applied to the equilibrium data. The adsorption capacity (Q_m) obtained from the Langmuir isotherm plots were 51.546, 47.236, 44.072 and 41.841 mg/g respectively at an initial pH of 7.0 at 30, 40, 50 and 60^°C. The temperature variation study showed that the Rhodamine B adsorption is endothermic and spontaneous with increased randomness at the solid solution interface. Significant effect on adsorption was observed on varying the pH of the Rhodamine B solutions. Almost 90% removal of Rhodamine B was observed at 60^°C. The Langmuir and Freundlich isotherms obtained, positive ΔH⁰ value, pH dependent results and desorption of dye in mineral acid suggest that the adsorption of Rhodamine B on PSC involves physisorption mechanism.