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Outer-sphere adsorption of Pb(II)EDTA on goethite

Bargar, J. R.; Persson, Per LU and Brown, G. E. (1999) In Geochimica et Cosmochimica Acta 63. p.2957-2969
Abstract
Fourier transform infrared (FTIR) and extended X-ray absorption fine structure (EXAPS) spectroscopic measurements were performed on Pb(II)ethylenediaminetetraacetic (EDTA) adsorbed on goethite as a function of pH (4-6), Pb(II)EDTA concentration (0.11-72 mu M), and ionic strength (16 mu M-0.5 M). FTIR measurements show no evidence for carboxylate-Fe(III) bonding or protonation of EDTA at Pb:EDTA = 1:1. Both FTIR and EXAFS spectroscopic measurements suggest that EDTA acts as a hexadentate ligand, with all four of its carboxylate and both of its amine groups bonded to Pb(II). No evidence was observed for inner-sphere Pb(II)-goethite bonding at Pb:EDTA = 1:1. Hence, the adsorbed complexes should have composition Pb(II)EDTA(2-). Because... (More)
Fourier transform infrared (FTIR) and extended X-ray absorption fine structure (EXAPS) spectroscopic measurements were performed on Pb(II)ethylenediaminetetraacetic (EDTA) adsorbed on goethite as a function of pH (4-6), Pb(II)EDTA concentration (0.11-72 mu M), and ionic strength (16 mu M-0.5 M). FTIR measurements show no evidence for carboxylate-Fe(III) bonding or protonation of EDTA at Pb:EDTA = 1:1. Both FTIR and EXAFS spectroscopic measurements suggest that EDTA acts as a hexadentate ligand, with all four of its carboxylate and both of its amine groups bonded to Pb(II). No evidence was observed for inner-sphere Pb(II)-goethite bonding at Pb:EDTA = 1:1. Hence, the adsorbed complexes should have composition Pb(II)EDTA(2-). Because substantial uptake of PbEDTA(II)(2-) occurred in the samples, we interpret that Pb(II)EDTA(2-) adsorbed as outer-sphere complexes and/or as complexes that lose part of their solvation shells and hydrogen bond directly to goethite surface sites. We propose the term "hydration-sphere" for the latter type of complexes because they should occupy space in the primary hydration spheres of goethite surface functional groups and to distinguish this mode of sorption from common structural definitions of inner- and outer-sphere complexes. The lack of evidence for inner-sphere EDTA-Fe(III) bonding suggests that previously proposed metal/ligand-promoted dissolution mechanisms should be modified, specifically to account for the presence of outer-sphere precursor species. Copyright (C) 1999 Elsevier Science Ltd. (Less)
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author
publishing date
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Contribution to journal
publication status
published
subject
in
Geochimica et Cosmochimica Acta
volume
63
pages
2957 - 2969
publisher
Elsevier
external identifiers
  • scopus:0033379761
ISSN
0016-7037
DOI
10.1016/S0016-7037(99)00264-1
language
English
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no
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e04a250b-15ca-4ee0-afbd-b8ea997ebd08 (old id 4332631)
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2014-03-04 09:43:50
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@article{e04a250b-15ca-4ee0-afbd-b8ea997ebd08,
  abstract     = {Fourier transform infrared (FTIR) and extended X-ray absorption fine structure (EXAPS) spectroscopic measurements were performed on Pb(II)ethylenediaminetetraacetic (EDTA) adsorbed on goethite as a function of pH (4-6), Pb(II)EDTA concentration (0.11-72 mu M), and ionic strength (16 mu M-0.5 M). FTIR measurements show no evidence for carboxylate-Fe(III) bonding or protonation of EDTA at Pb:EDTA = 1:1. Both FTIR and EXAFS spectroscopic measurements suggest that EDTA acts as a hexadentate ligand, with all four of its carboxylate and both of its amine groups bonded to Pb(II). No evidence was observed for inner-sphere Pb(II)-goethite bonding at Pb:EDTA = 1:1. Hence, the adsorbed complexes should have composition Pb(II)EDTA(2-). Because substantial uptake of PbEDTA(II)(2-) occurred in the samples, we interpret that Pb(II)EDTA(2-) adsorbed as outer-sphere complexes and/or as complexes that lose part of their solvation shells and hydrogen bond directly to goethite surface sites. We propose the term "hydration-sphere" for the latter type of complexes because they should occupy space in the primary hydration spheres of goethite surface functional groups and to distinguish this mode of sorption from common structural definitions of inner- and outer-sphere complexes. The lack of evidence for inner-sphere EDTA-Fe(III) bonding suggests that previously proposed metal/ligand-promoted dissolution mechanisms should be modified, specifically to account for the presence of outer-sphere precursor species. Copyright (C) 1999 Elsevier Science Ltd.},
  author       = {Bargar, J. R. and Persson, Per and Brown, G. E.},
  issn         = {0016-7037},
  language     = {eng},
  pages        = {2957--2969},
  publisher    = {Elsevier},
  series       = {Geochimica et Cosmochimica Acta},
  title        = {Outer-sphere adsorption of Pb(II)EDTA on goethite},
  url          = {http://dx.doi.org/10.1016/S0016-7037(99)00264-1},
  volume       = {63},
  year         = {1999},
}