h i g h l i g h t s " Insights into Cr(III) biosorption onto protonated brown algae Pelvetia canaliculata. " Carboxylic groups are the major binding sites present in the surface of biomass. " Distribution of chromium ionic species in the solution and on the binding sites. a b s t r a c t In the present study, biosorption of trivalent chromium by protonated brown algae, Pelvetia canaliculata, was studied in batch system. FTIR analyses provided information about the possible binding groups pres-ent in the algae, as carboxylic, hydroxyl and sulfonate groups. Potentiometric acid–base titrations showed a heterogeneous distribution of two major binding groups, carboxyl and hydroxyl ones, following the Quasi-Gaussian affinity constant distribution suggested by Sips, which allowed to estimate the maximum amount of acidic functional groups (2.26 ± 0.02 mmol g À1) and proton binding parameters (pK 0 H ¼ 3:18 AE 0:01; m H ¼ 0:78 AE 0:03) for an ionic strength of 0.2 M. The trivalent chromium removal was found to increase with pH and the maximum chromium uptake was observed at pH 4.0 ($0.6 mmol/g), corresponding to 1.34 meq/g, since at that pH, 25.8% of total chromium is in the Cr 3+ form and 72.7% as CrOH 2+ . An equilibrium model incorporating the hydrolysis reactions that chromium under-goes in the aqueous phase was able to predict the chromium biosorption at different pH values and chro-mium concentrations, enabling the prediction of the distribution of chromium ionic species on the binding sites. A mass transfer model provided a good representation of the chromium biosorption kinet-ics, resulting in intraparticle homogeneous diffusion coefficients of 4.6 Â 10 À7 cm 2 /s for Cr 3+ and 1.8 Â 10 À8 cm 2 /s for CrOH 2+ . The distribution of chromium ionic species in the solution and on the bind-ing sites was also predicted by the kinetic model. Ó 2012 Elsevier B.V. All rights reserved.