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Modeling the adsorption of Cd(II) onto goethite in the presence of citric acid.
MedLine Citation:
PMID:  14651893     Owner:  NLM     Status:  PubMed-not-MEDLINE    
The adsorption of cadmium onto goethite in the presence of citric acid was measured as a function of pH and cadmium concentration at 25 degrees C. Potentiometric titrations were also performed on the system. Cadmium adsorption onto goethite was enhanced above pH 4 in the presence of 50 microM, 100 microM and 1 mM citric acid. While there was little difference between the enhancements caused by 50 and 100 microM citric acid below pH 6, above pH 6 further enhancement is seen in the presence of 100 microM citric acid. When 1 mM citric acid was present, the enhancement of cadmium adsorption was greater below pH 6, with increased Cd(II) adsorption down to pH 3.5. However, above pH 6, 1 mM of citric acid caused slightly less enhancement than the lower citric acid concentrations. ATR-FTIR spectra of soluble and adsorbed citrate-cadmium species were measured as a function of pH. At pH 4.6 there was very little difference between the ternary Cd(II)-citric acid-goethite spectrum and the binary citric acid-goethite spectrum. However, spectra of the ternary system at pH 7.0 and 8.7 indicated the presence of additional surface species. Further analysis of the spectra suggested that these were metal-ligand outer-sphere complexes. Data from the adsorption experiments and potentiometric titrations of the ternary Cd(II)-citric acid-goethite system were fitted by an extended constant-capacitance surface complexation model. The spectroscopic data were used to inform the choice of surface species. Three reactions in addition to those for the binary Cd(II)-goethite and citric acid-goethite systems were required to describe all of the data. They were [formula in text], [formula in text], and [formula in text]. Neither the spectroscopy nor the modeling suggested the formation of a ternary inner-sphere complex or a surface precipitate under the conditions used in this study.
Kurt Lackovic; Michael J Angove; John D Wells; Bruce B Johnson
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Journal of colloid and interface science     Volume:  269     ISSN:  0021-9797     ISO Abbreviation:  J Colloid Interface Sci     Publication Date:  2004 Jan 
Date Detail:
Created Date:  2003-12-03     Completed Date:  2004-08-19     Revised Date:  2009-11-11    
Medline Journal Info:
Nlm Unique ID:  0043125     Medline TA:  J Colloid Interface Sci     Country:  United States    
Other Details:
Languages:  eng     Pagination:  37-45     Citation Subset:  -    
Colloid and Environmental Chemistry Laboratory, La Trobe University, Bendigo, PO Box 199, Bendigo, Victoria 3552, Australia.
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