Biosorption performance of two brown marine algae for removal of chromium and cadmium

The brown marine algae Sargassum sp. and Padina sp., harvested locally, are used for the removal of cations (Cd2+ and Cr3+) and anion (Cr2O72-) from dilute aqueous solutions. It is found that the biosorption capacities are significantly affected by solution pH. Higher pH favors higher cation removal, whereas higher uptake of anion is observed as the pH is decreased, with the optimal uptake at pH 2. It is demonstrated that the removal rate of the cations is much faster than that of the anion. For cations, 90% of the total adsorption occurs within 60 min, but it takes min for the Cr2O72- to reach 90% of the maximum uptake. A series of isotherm experiments are carried out at the optimal pH of 5.5 for Cd2+, 3.8 for Cr3+, and 2.0 for Cr2O72-. The results are well represented by Freundlich and Langmuir equations. Finally, it is observed that reduction of Cr(VI) to Cr(III) and biosorption of these two species occur simultaneously during the process.