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Antimony(V) complexing with O-bearing organic ligands in aqueous solution: an X-ray absorption fine structure spectroscopy and potentiometric study

Published online by Cambridge University Press:  05 July 2018

M. Tella  and
G. S. Pokrovski
M. Tella*
Affiliation:
Experimental Geochemistry and Biogeochemistry Group, Laboratoire des Mécanismes et Transfert en Géologie, LMTG, Université de Toulouse, CNRS, IRD, OMP, 14 Av. E. Belin, F-31400 Toulouse, France
G. S. Pokrovski
Affiliation:
Experimental Geochemistry and Biogeochemistry Group, Laboratoire des Mécanismes et Transfert en Géologie, LMTG, Université de Toulouse, CNRS, IRD, OMP, 14 Av. E. Belin, F-31400 Toulouse, France
*
*E-mail: [email protected]
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Abstract

The stabilityand structure of aqueous complexes formed by pentavalent antimony (SbV) with simple organic ligands (acetic, adipic, oxalic, citric acids, catechol and xylitol) having O-functional groups (carboxyl, alcoholic hydroxyl, aliphatic and aromatic hydroxyl) typical of natural organic matter (NOM), were determined at 25°C from potentiometric and X-ray absorption fine structure spectroscopy (XAFS) measurements. In organic-free aqueous solutions, spectroscopic data are consistent with the dominant formation of SbV hydroxide species, Sb(OH)5 and Sb(OH)6-, at acid and near-neutral to basic pH, respectively. Potentiometric measurements demonstrate negligible complexing with mono-functional organic ligands (acetic) or those having non-adjacent carboxylic groups (adipic). In contrast, in the presence of poly-functional carboxylic, hydroxyl carboxylic acids and aliphatic and phenolic hydroxyl, SbV forms stable 1:1 or 1:3 complexes in coordination 6 with the studied organic ligands, over a wide pH range pertinent to natural waters (3 ≤ pH ≤ 9). The XAFS measurements show that in these species the central SbV atom has an octahedral geometry with 6 oxygen atoms from hydroxyl moieties and adjacent functional groups (O = C—OH and/or C—OH) of the ligand, forming bidendate chelate cycles. Stability constants for SbV-oxalate complexes generated from potentiometric experiments were used to model SbV complexing with di-carboxylic functional groups of natural humic acids. Our predictions show that in an aqueous solution of pH between 1 and 4 containing 1 μg/l of Sb and 5 mg/l of dissolved organic carbon (DOC), up to 15% of total dissolved Sb maybe bound to aqueous organic matter via di-carboxylic groups.

Keywords

antimonyaqueous complexesXAFSorganic ligandspotentiometry
Type
Research Article
Information
Mineralogical Magazine , Volume 72 , Issue 1 , February 2008 , pp. 205 - 209
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2008

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