Prediction of the thermodynamic properties of metal–chromate aqueous complexes to high temperatures and pressures and implications for the speciation of hexavalent chromium in some natural waters |
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| Authors: | Marina Accornero Luigi Marini Matteo Lelli |
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| Institution: | 1. D’Appolonia S.p.A., Via San Nazaro, 19, 16145 Genova, Italy;2. Laboratory of Geochemistry, Dip.Te.Ris., University of Genova, Corso Europa 26, 16132 Genova, Italy;3. Institute of Geosciences and Georesources, CNR, Area della Ricerca, Via G. Moruzzi 1, I-56124 Pisa, Italy |
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| Abstract: | Log–log correlation plots between the dissociation constants of known metal–chromate complexes and those of corresponding metal–sulfate complexes at 25 °C, 1 bar were used to derive the standard partial molal Gibbs free energies of formation of unknown metal–chromate complexes involving either (i) monovalent cations, divalent cations, and trivalent lanthanides or (ii) trivalent cations (excluding those of rare earth elements, REE) and tetravalent cations. For each of these two classes of ionic associations, empirical relationships between the standard partial molal volumes, isobaric heat capacities and entropies of known metal–chromate complexes and the corresponding thermodynamic properties of metal ions have been found. These data were utilized to evaluate the solute-characteristic parameters of the revised Helgeson–Kirkham–Flowers equation of state and to compute the thermodynamic properties of the dissociation reactions of metal–chromate complexes at high temperatures and pressures. |
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