title: Competitive Adsorption of Cd(II), Cr(VI), and Pb(II) onto Nanomaghemite: A Spectroscopic and Modeling Approach.
abstract: A combined modeling and spectroscopic approach is used to describe Cd(II), Cr(VI), and Pb(II) adsorption onto nanomaghemite and nanomaghemite coated quartz. A pseudo-second order kinetic model fitted the adsorption data well. The sorption capacity of nanomaghemite was evaluated using a Langmuir isotherm model, and a diffuse double layer surface complexation model (DLM) was developed to describe metal adsorption. Adsorption mechanisms were assessed using X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Pb(II) adsorption occurs mainly via formation of inner-sphere complexes, whereas Cr(VI) likely adsorbs mainly as outer-sphere complexes and Cd(II) as a mixture of inner- and outer-sphere complexes. The simple DLM describes well the pH-dependence of single adsorption edges. However, it fails to adequately capture metal adsorption behavior over broad ranges of ionic strength or metal-loading on the sorbents. For systems with equimolar concentrations of Pb(II), Cd(II), and Cr(VI). Pb(II) adsorption was reasonably well predicted by the DLM, but predictions were poorer for Cr(VI) and Cd(II). This study demonstrates that a simple DLM can describe well the adsorption of the studied metals in mixed sorbate-sorbent systems, but only under narrow ranges of ionic strength or metal loading. The results also highlight the sorption potential of nanomaghemite for metals in complex systems.
authors.affiliation: Department of Environmental Geosciences, Faculty of Environmental Sciences, Czech University of Life Sciences Prague , Kamýcká 129, Prague 6 - Suchdol, 165 21, Czech Republic.
authors.forename: Michael
authors.initials: M
authors.lastname: Komárek
authors.affiliation: Department of Geosciences, Western Michigan University , 1187 Rood Hall, Kalamazoo, Michigan 49008, United States.
authors.forename: Carla M
authors.initials: CM
authors.lastname: Koretsky
authors.affiliation: Department of Geosciences, Western Michigan University , 1187 Rood Hall, Kalamazoo, Michigan 49008, United States.
authors.forename: Krishna J
authors.initials: KJ
authors.lastname: Stephen
authors.affiliation: Department of Earth and Atmospheric Sciences, University of Alberta , 1-26 Earth Sciences Building, Edmonton, Alberta, T6G 2E3, Canada.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Alessi
authors.affiliation: Department of Environmental Geosciences, Faculty of Environmental Sciences, Czech University of Life Sciences Prague , Kamýcká 129, Prague 6 - Suchdol, 165 21, Czech Republic.|Department of Geochemistry, Czech Geological Survey, Geologická 6, 152 00, Prague 5, Czech Republic.
authors.forename: Vladislav
authors.initials: V
authors.lastname: Chrastný
mesh_terms: D000327:Adsorption; D002104:Cadmium / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007854:Lead / Q000737:chemistry*; D008962:Models, Theoretical; D049329:Nanostructures / Q000737:chemistry; D009994:Osmolar Concentration; D056951:Photoelectron Spectroscopy; D011791:Quartz / Q000737:chemistry; D056928:X-Ray Absorption Spectroscopy
chemical_list: D005290:Ferric Compounds; D002104:Cadmium; D002857:Chromium; D011791:Quartz; C074702:chromium hexavalent ion; C000499:ferric oxide; D007854:Lead