title: Heavy metal sorption by calcium alginate beads from Laminaria digitata.
abstract: Alginate with a high M/G ratio, extracted from Laminaria digitata, was evaluated for Cu(2+), Cd(2+) and Pb(2+) sorption in acidic solutions, in the form of calcium cross-linked beads. The high M/G ratio of alginate extracted from this algal species is most likely the determining factor for the increased adsorption capacity of the investigated metals, indicating that the mannuronic acid is responsible for the ion exchange mechanism. The data obtained from the batch experiments have been interpreted with Langmuir, Freundlich and Sips models. The Sips equation provided the best fit with the experimental results, indicating sorption sites heterogeneity for the material. The pH was found to have a significant effect on the process, with sorption capacity reaching a maximum at pH 4.5, indicating a competition mechanism between H(+) and metal ions. Kinetic experiments were performed at the optimum pH. For the interpretation of the kinetic experiments the Linear Adsorption Model was employed and diffusion coefficients were determined. The model fits the experimental data at higher concentrations, where the adsorbed quantity remains almost constant. Finally, a simplified expression of the batch kinetic adsorption model was employed. The model, predicts adequately, not only the diffusivity values, but also the concentration profiles inside the spherical particles.
authors.affiliation: Institute of Physical Chemistry, N.C.S.R. Demokritos, 15310 Ag. Paraskevi Attikis, Greece. spap@chem.demokritos.gr
authors.forename: Sergios K
authors.initials: SK
authors.lastname: Papageorgiou
authors.forename: Fotios K
authors.initials: FK
authors.lastname: Katsaros
authors.forename: Evangelos P
authors.initials: EP
authors.lastname: Kouvelos
authors.forename: John W
authors.initials: JW
authors.lastname: Nolan
authors.forename: Herve
authors.initials: H
authors.lastname: Le Deit
authors.forename: Nick K
authors.initials: NK
authors.lastname: Kanellopoulos
mesh_terms: D000327:Adsorption; D000464:Alginates / Q000737:chemistry* / Q000648:ultrastructure; D002104:Cadmium / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D020723:Glucuronic Acid / Q000737:chemistry; D006603:Hexuronic Acids / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry; D007700:Kinetics; D007795:Laminaria / Q000737:chemistry*; D007854:Lead / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D008956:Models, Chemical
chemical_list: D000464:Alginates; D006603:Hexuronic Acids; D007477:Ions; D002104:Cadmium; D007854:Lead; D003300:Copper; D020723:Glucuronic Acid