title: Application of the Nernst-Planck approach to lead ion exchange in Ca-loaded Pelvetia canaliculata.
abstract: Ca-loaded Pelvetia canaliculata biomass was used to remove Pb(2+) in aqueous solution from batch and continuous systems. The physicochemical characterization of algae Pelvetia particles by potentiometric titration and FTIR analysis has shown a gel structure with two major binding groups - carboxylic (2.8 mmol g(-1)) and hydroxyl (0.8 mmol g(-1)), with an affinity constant distribution for hydrogen ions well described by a Quasi-Gaussian distribution. Equilibrium adsorption (pH 3 and 5) and desorption (eluents: HNO(3) and CaCl(2)) experiments were performed, showing that the biosorption mechanism was attributed to ion exchange among calcium, lead and hydrogen ions with stoichiometry 1:1 (Ca:Pb) and 1:2 (Ca:H and Pb:H). The uptake capacity of lead ions decreased with pH, suggesting that there is a competition between H(+) and Pb(2+) for the same binding sites. A mass action law for the ternary mixture was able to predict the equilibrium data, with the selectivity constants alpha(Ca)(H)=9+/-1 and alpha(Ca)(Pb)=44+/-5, revealing a higher affinity of the biomass towards lead ions. Adsorption (initial solution pH 4.5 and 2.5) and desorption (0.3M HNO(3)) kinetics were performed in batch and continuous systems. A mass transfer model using the Nernst-Planck approximation for the ionic flux of each counter-ion was used for the prediction of the ions profiles in batch systems and packed bed columns. The intraparticle effective diffusion constants were determined as 3.73x10(-7)cm(2)s(-1) for H(+), 7.56x10(-8)cm(2)s(-1) for Pb(2+) and 6.37x10(-8)cm(2)s(-1) for Ca(2+).
authors.affiliation: LSRE - Laboratory of Separation and Reaction Engineering, Departamento de Engenharia Química, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal.
authors.forename: Joana F de Sá S
authors.initials: JF
authors.lastname: Costa
authors.forename: Vítor J P
authors.initials: VJ
authors.lastname: Vilar
authors.forename: Cidália M S
authors.initials: CM
authors.lastname: Botelho
authors.forename: Eduardo A B
authors.initials: EA
authors.lastname: da Silva
authors.forename: Rui A R
authors.initials: RA
authors.lastname: Boaventura
mesh_terms: D000327:Adsorption; D001673:Biodegradation, Environmental; D018533:Biomass; D019149:Bioreactors; D002118:Calcium / Q000737:chemistry*; D006859:Hydrogen / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D007477:Ions; D007700:Kinetics; D007854:Lead / Q000302:isolation & purification*; D008956:Models, Chemical; D000459:Phaeophyceae / Q000254:growth & development / Q000378:metabolism*; D011199:Potentiometry; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D007477:Ions; D007854:Lead; D006859:Hydrogen; D002118:Calcium