Biosorption of hexavalent chromium from aqueous solution by six brown macroalgae

The biosorption potential of six brown macroalgae viz. Nizamuddina zanardinii, Stoechospermum marginatum, Cystoseira indica, Dictyota cervicornis, Padina australis, and Sargassum glaucescens, for the removal of hexavalent chromium (Cr(VI)) was investigated in the present study. Optimum conditions were determined by studying the effect of initial solution pH, biomass dosage, initial Cr(VI) concentration, and contact time on Cr(VI) removal by the macroalgae. Cr(VI) sorption was found to be highly pH dependent and maximum sorption was obtained at pH 1.0. Freundlich isotherm model showed the best fit with the equilibrium data. The removal rate of Cr(VI) was relatively rapid during the first 30 min, although the rate decreased gradually and the sorption reached equilibrium in about 70 min for S. marginatum, 90 min for N. zanardinii, and 150 min for D. cervicornis, P. australis, S. glaucescens, and C. indica. Different kinetic models such as pseudo-first-order, pseudo-second-order, and intra-particle diffusion model were tested, and the experimental data was in agreement with the pseudo-second-order model. The results of the present study suggest that brown macroalgae could be used as effective biosorbents for Cr(VI) removal from aqueous solution.