Removal of Direct Red 81 Dye from Aqueous Solution by Native and Citric Acid Modified Bamboo Sawdust - Kinetic Study and Equilibrium Isotherm Analyses

Adsorption of Direct Red 81 (DR81) dye was investigated using Bamboo Sawdust (BSD) and Treated Bamboo Sawdust (TBSD) in a batch system with respect to initial dye concentration, adsorbent dose, pH, temperature and contact time. Maximum adsorption capacity (qm) obtained from the Langmuir isotherm plots were 6.43 mg/g (89%) (DR81-BSD) and 13.83 mg/g (92%) (DR81-TBSD) at 303 K. Freundlich and Halsey models described the data more appropriately as compared to Langmuir, Dubinin-Kaganer-Radushkevich (DKR), Harkin-Jura and Temkin models. The adsorption dynamics conformed well to pseudo-second order kinetic equation. The adsorption process was controlled by both liquid-film and intra-particle diffusions. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) suggested the adsorption process to be spontaneous, endothermic with increase in randomness at solid-solution interface.