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 (R-2=0.993 and 0.992), with a maximum sorption capacity of 66.66 mg/g. The calculated thermodynamic parameters such as Delta GA degrees, Delta HA degrees and Delta SA degrees 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.