Sorption and desorption of hexavalent chromium using a novel brown marine algae Sargassum myriocystum

The present investigation deals with the sorption of Cr(VI) onto a marine brown algae Sargassum myriocystum in batch reactors. Response surface methodology (RSM) was used for the optimization of variables like pH, sorbent dosage (g/L), agitation speed (rpm) and contact time (min). A maximum percentage removal of Cr(VI) by Sargassum myriocystum occurs at the following conditions: pH - 5.2; sorbent dosage - 2.017 g/L; agitation speed - 120 rpm and contact time - 108 min. Before and after sorption, Sargassum myriocystum was characterized. Kinetic studies were performed using various kinetic models. It was found that the sorption process of Cr(VI) ions follows pseudo-second order, Elovich and power function kinetics. The data obtained were fitted to different isotherms. Sorption of Cr(VI) onto Sargassum myriocystum follows Langmuir and Toth isotherm models (R2=0.993 and 0.992), with a maximum sorption capacity of 66.66 mg/g. The calculated thermodynamic parameters such as ΔG°, ΔH° and ΔS° showed that the sorption of Cr(VI) ions onto Sargassum myriocystum biomass was feasible, spontaneous and endothermic. Desorption experiments show that the Sargassum myriocystum sorbent can be regenerated using 0.2 M HCl solutions with up to 80% recovery.