Biosorption of Cr(VI) using a novel microalga Rhizoclonium hookeri: equilibrium, kinetics and thermodynamic studies

Heavy metal pollution is a major environmental concern in many countries. Among heavy metals, chromium is one of the widely used despite being one of the most toxic metal ions. The present study deals with the evaluation of Cr(VI) biosorption using a novel fresh water alga Rhizoclonium hookeri. Batch experiments were conducted and the maximum adsorption capacity was evaluated as 67.3mg/g at pH 2 at a biomass dosage of 1g/L and 1,000mg/L initial Cr(VI) concentration. Fourier transform infrared spectroscopy analysis of alga before and after biosorption revealed a shift in the carboxylic O-H stretching vibration from 3,401 to 3,373cm(-1), which confirmed its involvement in biosorption of Cr(VI) by R. hookeri. Surface morphology of alga was examined using the scanning electron microscopy, which indicated the highly porous nature of biomass. Non-linear regression analyses of isotherm models revealed that the three-parameter model isotherms (Redlich-Peterson and Sips) better described the experimental data compared with two-parameter model isotherms (Langmuir and Freundlich). An analysis of the kinetic models (pseudo-first-order, pseudo-second-order and Elovich models) indicated that the experimental data followed pseudo-second-order kinetics. The thermodynamic parameters such as free energy, enthalpy and entropy were calculated and Cr(VI) biosorption was found to be a spontaneous and endothermic process.