title: Effects of anionic surfactants on ligand-promoted dissolution of iron and aluminum hydroxides.
abstract: We investigated the influence of the surfactants sodium dodecyl sulfate (SDS) and rhamnolipid (RhL) on ligand-promoted dissolution of goethite (alpha-FeOOH) and boehmite (gamma-AlOOH) at pH 6. The siderophore desferrioxamine B (DFOB), its derivate desferrioxamine D (DFOD), ethylenediaminetetraacetic acid (EDTA), and 8-hydroxyquinoline-5-sulfonic acid (HQS) were used as ligands. The rates of ligand-promoted dissolution of goethite were significantly increased in the presence of low concentrations of anionic surfactants (<80 microM SDS; <6 mg/L RhL). At higher surfactant concentrations, however, the effects of surfactants were negligible. The dissolution rates in the presence of surfactants were not correlated with adsorbed amounts of ligands. Three possible factors contributing to these observations were further investigated and discussed: (i) adsorbed surfactants may influence ligand adsorption by changes in the ligand's surface speciation, (ii) re-adsorption of Fe-DFOB or Fe-DFOD complexes may lead to an underestimation of siderophore-promoted dissolution rates at high surfactant concentrations, and (iii) co-adsorption of protons to goethite with SDS may influence the dissolution rates. However, our results show that none of these three factors can satisfactorily explain the observed effects of anionic surfactants on ligand-promoted dissolution rates of iron and aluminum hydroxides.
authors.affiliation: Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Sciences, ETH Zurich, CHN, CH-8092 Zurich, Switzerland.
authors.forename: Naraya
authors.initials: N
authors.lastname: Carrasco
authors.forename: Ruben
authors.initials: R
authors.lastname: Kretzschmar
authors.forename: Marie-Laure
authors.initials: ML
authors.lastname: Pesch
authors.forename: Stephan M
authors.initials: SM
authors.lastname: Kraemer
mesh_terms: D000327:Adsorption; D000536:Aluminum Hydroxide; D000537:Aluminum Oxide; D000838:Anions; D003676:Deferoxamine; D006017:Glycolipids; D006863:Hydrogen-Ion Concentration; D058085:Iron Compounds; D008024:Ligands; D008903:Minerals; D017262:Siderophores; D012967:Sodium Dodecyl Sulfate; D012995:Solubility; D013499:Surface Properties; D013501:Surface-Active Agents
chemical_list: D000838:Anions; D006017:Glycolipids; D058085:Iron Compounds; D008024:Ligands; D008903:Minerals; D017262:Siderophores; D013501:Surface-Active Agents; C418382:rhamnolipid; C094886:goethite; D012967:Sodium Dodecyl Sulfate; D000536:Aluminum Hydroxide; C069471:aluminum oxide hydroxide; D003676:Deferoxamine; D000537:Aluminum Oxide