Iron(III) solubility and speciation in aqueous solutions. Experimental study and modelling: Part 1. Hematite solubility from 60 to 300 deg C in NaOH-NaCl solutions and thermodynamic properties of Fe(OH)_4-(aq)

摘要

The solubility of natural and synthetic hematite (#alpha#-Fe_2O_3) was measured in NaOH-NaCl solutions (0.007<=m(NaOH)<=2.0) between 60 and 300 deg 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 deg C were combined with the thermodynamic properties of hematite (Hemingway, 1990) and water (SUPCRT92, Johnson et al., 1992) to generate within the framework of the revised Helgeson-Kirkham-Flower (HKF) model the standard partial molal thermodynamic properties at 25 deg 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 deg 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-.