Iron(III) solubility and speciation in aqueous solutions.: Experimental study and modelling:: Part 1.: Hematite solubility from 60 to 300°C in NaOH-NaCl solutions and thermodynamic properties of Fe(OH)4-(aq)

The solubility of natural and synthetic hematite (alpha-Fe2O3) was measured in NaOH-NaCI solutions (0.007 less than or equal to m(NaOH) less than or equal to 2.0) between 60 and 300 degrees C at saturated water vapour pressure and under excess oxygen. Solubility constants determined in the present study and by Yishan et al. (1986) at 300 degrees C were combined with the thermodynamic properties of hematite (Hemin,away, 1990) and water (SUPCRT92, Johnson ct al., 1992) to generate within the framework of the revised Helgeson-Kirkham-Flowers (HKF) model the standard partial molal thermodynamic properties at 25 degrees C and 1 bar, and the revised HKF equations of state parameters of Fe(OH)(4)-. The extrapolated value for the Gibbs energy of formation for Fe(OH)(4)- at 25 degrees C is -201.97 kcal/mol. Thermodynamic calculations show that Fe(OH)(4)- exhibits a chemical behaviour different from that of Ga(OH)(4)- and Al(OH)(4)-. Copyright (C) 1999 Elsevier Science Ltd.