Kinetic, Equilibrium and Thermodynamic Studies of Biosorption of Chromium (VI) from Aqueous Solutions using Azolla filiculoidus

Biosorption of Cr(VI) by Azolla Filiculoidus was studied in the present study. The batch experiments were carried out to investigate the effect of the significant process parameters such as pH, contact time, initial Cr(VI) concentration, and biomass dosage. The results of this study showed that higher chromium removal was observed at lower pH points, and maximum chromium removal (83.341 %) was obtained at pH of 2. Adsorption of chromium by Azolla Filiculoidus reached to equilibrium after 100 min and after that a little change of chromium removal efficiency was observed. Biosorption of chromium by Azolla Filiculoidus was decreased with increasing in initial chromium concentration and increased with increasing in biomass dosage. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models were applied to describe the biosorption isotherms. The maximum adsorption capacity obtained was 10.638 mg g(-1) at a pH value of 2. From the D R isotherm model, the mean free energy was calculated as 8.494 kj/mol, indicating that the biosorption of Cr(VI) the metal ions were taken place by chemisorptions. Biosorption process follows the second-order kinetics and the corresponding rate constants are obtained. The calculated thermodynamic parameters (Delta G degrees, Delta H degrees, and Delta S degrees) showed that the biosorption of Cr(VI) ions onto Azolla Filiculoidus was feasible, spontaneous and exothermic at 293-323 K. The results indicate that Azolla Filiculoidus can be employed as a low cost alternative to commercial adsorbents in the removal of Cr(VI) from industrial wastewater.