Competitive Adsorption of Cd(II), Cr(VI), and Pb(II) onto Nanomaghemite: A Spectroscopic and Modeling Approach

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 i...

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Bibliographic Details
Published in:Environmental science & technology 2015-11, Vol.49 (21), p.12851-12859
Main Authors: Komárek, Michael, Koretsky, Carla M, Stephen, Krishna J, Alessi, Daniel S, Chrastný, Vladislav
Format: Article
Language:English
Subjects:
Adsorption
Cadmium - chemistry
Chemical elements
Chromium - chemistry
Complex systems
Ferric Compounds - chemistry
Hydrogen-Ion Concentration
Ions
Kinetics
Lead - chemistry
Models, Theoretical
Nanostructures - chemistry
Osmolar Concentration
Photoelectron Spectroscopy
Quartz
Quartz - chemistry
Sorption
Spectrum analysis
X-Ray Absorption Spectroscopy
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Summary: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.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.5b03063