Marine macroalgae Pelvetia canaliculata (Phaeophyceae) as a natural cation exchanger for cadmium and lead ions separation in aqueous solutions Fabíola V. Hackbarth a , Franciélle Girardi a , Selene M.A. Guelli U. de Souza a , Antônio Augusto U. de Souza a , Rui A.R. Boaventura b , Vítor J.P. Vilar b,⇑ a Laboratório de Transferência de Massa e Simulação Numérica de Sistemas Químicos, Federal University of Santa Catarina, PO Box 476, CEP 88040-900 Florianópolis, SC, Brazil b LSRE – Laboratory of Separation and Reaction Engineering – Associate Laboratory LSRE/LCM, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal highlights  Marine macroalgae Pelvetia canaliculata showed to be a natural cation exchanger.  Weakly acidic (carboxylic groups) and strongly acidic (sulfonic groups) functional groups.  Trapping of Cd 2+ and Pb 2+ by raw biomass occurs by the release of light metals.  Binding strength between light metals and O donors increases as Na + <K + < Mg 2+ < Ca 2+ .  Selectivity coefficients of the natural exchanger increases as Na + <H + < Cd 2+ < Pb 2+ . graphical abstract article info Article history: Received 31 October 2013 Received in revised form 13 December 2013 Accepted 17 December 2013 Available online 28 December 2013 Keywords: Natural cation exchanger Macro-algae Lead and cadmium ions Mass action law Mass transfer model abstract This work aims to add value to marine brown macro-algae Pelvetia canaliculata (Linnaeus) Decaisne and Thuret through its use as cation exchanger for separation and recovery of cadmium and lead ions in aqueous solution, as a cost effective and environmental friendly process. Raw algae was established as a cation exchanger, in which cadmium and lead ions present in the solution exchange with Na + ,K + , Ca 2+ and Mg 2+ , bound to the negatively functional groups existing on the algae surface, with a stoichiometric ratio of 1:1 between ions of the same charge and 2:1 between monovalent and divalent ions. Batch equilibrium and kinetic experiments were conducted at different pH values using Na-loaded algae. The main functional groups present on the surface of the algae responsible for binding metals, as determined by Fourier Trans- form Infrared (FTIR) analysis, are weakly acidic carboxylic groups and strongly acidic sulfonic groups. Con- sidering the potentiometric titration and biomass esterification results, the amount of sulfonic and carboxylic groups is 1.0 mmol/g and 1.5 mmol/g, respectively, which is in agreement with the total amount of Na + present at the surface of Na-loaded biomass (2.5 mEq/g) and total amount of light metals present at the surface of raw biomass (2.5 mEq/g). Maximum biosorption capacity of Pb 2+ at pH 4.0 was 1.25 mmol/g (2.5 mEq/g; 259 mg/g) and for Cd 2+ at pH 4.5 was 1.25 mmol/g (2.5 mEq/g; 140 mg/g). The mass action law for the ternary mixture was able to predict the equilibrium data, with the selectivity coefficients a Cd Na ¼ 337 1385-8947/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2013.12.043 ⇑ Corresponding author. Tel.: +351 918257824; fax: +351 225081674. E-mail address: vilar@fe.up.pt (V.J.P. Vilar). Chemical Engineering Journal 242 (2014) 294–305 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej