Thermodynamic modelling of aqueous Fe(II) sulfate solutions

The H(2)O-FeSO(4) system has been modelled using the Pitzer activity coefficient approach over a temperature interval of -2-220 degrees C and in concentrations from pure water to the solubility limit of ferrous sulfate hydrates, the maximum FeSO(4) molality being 3.58 mol/kg at the FeSO(4)center dot 7H(2)O(s) to FeSO(4)center dot H(2)O(s) transition temperature of 56.5 degrees C. The thermodynamic properties of FeSO(4) hydrates were refined and FeSO(4)center dot 4H(2)O(s) was found to be a metastable phase in the whole temperature range. The model in this work presents all the experimental data available, including the solubilities, mean activity coefficients, activities of water, enthalpy and heat capacity of solution, and hydrate dissociation pressure, with good accuracy and consistently up to 220 degrees C, but the model has limitations at temperatures higher than 100 degrees C due to lack of experimental data. (C) 2011 Elsevier Ltd. All rights reserved.