A consistent set of thermodynamic data for iron and reevaluation of green rusts and fougeraie solubilities
2016
Trolard, Fabienne | Ben Nacib, Jihaine | Bourrie, Guilhem | Ben Taher, Bechir | Environnement Méditerranéen et Modélisation des Agro-Hydrosystèmes (EMMAH) ; Avignon Université (AU)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE) | traitement des eaux, ISO et gestion de l'environnement ; Ecole Supérieure des Ingénieurs de l'Equipement Rural
Over the last ten years, several comprehensive reviews of iron thermodynamics data were published. This work aims to: (i) propose a consistent set of Gibbs free energies (ΔfG0) of ferrous hydroxide, Fe(OH)2,cr and of synthetic Green rusts I and II; (ii) check the consistency of the data of these isostructural compounds by means of a correlation obtained with electronegativities of the anions. Experimental data are concentrations in aqueous solutions and pH, and must be processed to obtain ionic activity products (IAP). The model of Specific Interaction Theory (SIT) was used here. Firstly, some complexes whose existences are doubtful were removed from the SIT database. The new modified database is given here. Secondly, experimental data were processed. Thirdly, the following relation of regression between Gibbs free energies of formation of Green rusts and normalized Allred-Rochow electronegativities of anions was obtained as: ΔfG0 = -488.354 -353.11 (χ/n), r = -0.994. This relation was then used to assess the Gibbs free energy of formation for GR1-OH, simply written as Fe3(OH)7.
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