Adsorption characteristics of metal-EDTA complexes onto hydrous oxides |
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| Authors: | A. R. Bowers C. P. Huang |
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| Affiliation: | 1. University of Patras, Department of Chemistry, GR-26504 Patras, Greece;2. Hellenic Open University, School of Science and Technology, GR-26222 Patras, Greece;3. Foundation for Research and Technology Hellas—Institute of Chemical Engineering Sciences (FORTH/ICE-HT), GR-26504 Rio, Patras, Greece;4. Institute of Catalysis and Petrochemistry, CSIC, Marie Curie 2, 28049 Madrid, Spain;1. Centre for Laser, Atomic and Molecular Sciences (CLAMS) and Physics Department, University of New Brunswick, 100 Tucker Park Road, Saint John, NB E2L 4L5, Canada;2. Canadian Light Source Inc., University of Saskatchewan, 44 Innovation Boulevard, Saskatoon, SK S7N 2V3, Canada;1. Department of Bioprocess Engineering, Faculty of Chemical Engineering, c/o Institute of Bioproduct Development (IBD), Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia;2. Department of Mechanical Engineering, Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia |
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| Abstract: | The adsorption characteristics of a variety of metal-EDTA complexes onto hydrous oxides, principally aluminum oxide (γ-Al2O3), were examined in aqueous solution. Adsorption of these complexes increased with increasing proton concentration due to the formation of surface complexes between EDTA and the surface hydroxo groups, specifically the AlOH2+ surface groups. The pH-dependent adsorptive behavior and the magnitude of adsorption of the “free” EDTA species were similar to those of the metal complexes. The results also showed that the adsorption of “free” EDTA was exothermic, while the adsorption of Ni(II)-EDTA complexes was endothermic in the lower pH region (3.5) and exothermic at higher pH values (6.0). This implied that the surface preferred the NiHEDTA−1 species rather than the NiEDTA−2 species. Specific adsorption of the metal complexes was evidenced by the charge reversal exhibited by the γ-Al2O3 particles at the highest surface loadings. A quantitative model was formulated based on the pH-dependent speciation of the oxide surface, speciation of the metal complexes in solution, and ζ potential measurements. This model proved valid over a wide range of pH (3–10) and for both high (>50% coverage) and low (<10% coverage) surface loadings. |
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