A dried Azolla filiculoides (A. filiculoides) biomass was used to remove Cr(VI) from aqueous solution using batch experiments. The influence of pH, algal dosage, initial Cr(VI) concentration, contact time, and temperature were studied and analyzed using response surface methodology (RSM). The optimum biosorption conditions were determined as initial pH 2, at temperature 25°C, biosorbent concentration 0.2 g/l and initial Cr(VI) concentration 200 mg/l. The maximum capacity of A. filiculoides for Cr(VI) ions was found to be 200 mg/g at optimum conditions. The properties of the biosorbent were determined and the nature of biomass–metal ions interactions were evaluated by FTIR analysis, which showed the participation of COOH, OH, SO3, and NH2 groups in the biosorption process. The thermodynamic properties ΔG°, ΔH°, and ΔS° by the Cr(VI) ions for biosorption were analyzed using the equilibrium constant value obtained from experimented data at different temperatures. The results showed that biosorption of Cr(VI) ions by A. filiculoides adsorbent are more endothermic and spontaneous. Kinetic of the system was described by second-order rate equation. The Langmuir and Freundlich isotherm models were applied to the equilibrium of system, data fit with the Freundlich isotherm
