An Aqueous Thermodynamic Model for the Solubility of Potassium Ferrate in Alkaline Solutions to High Ionic Strengths from 283.15 to 333.15 K

Abstract

Potassium ferrate, K2FeO4(cr), has numerous promising environmental applications. An aqueous thermodynamic model applicable to high ionic strengths is essential for guiding its applications. In this study, a thermodynamic model is developed for the solubility of K2FeO4(cr) in aqueous alkali metal hydroxide solutions, from 283.15 to 333.15 K to high ionic strengths, up to saturation of KOH and NaOH, based on the Pitzer activity coefficient model for aqueous species. The solubility products for K2FeO4(cr) at infinite dilution in the temperature range from 283.15 to 333.15 K were obtained. Based on the thermodynamic solubility product of K2FeO4(cr) at 298.15 and its temperature dependence, in combination with thermodynamic properties for $$ {\text{FeO}}_{4}^{2 - } $$ and K+ from the literature, standard thermodynamic properties of K2FeO4(cr) at 298.15 K and 0.1 MPa (1 bar) are derived for the first time as follows: Δf G 0 = −(896 ± 8) kJ·mol−1, Δf H 0 = −(1026 ± 4) kJ·mol−1, and S 0 = (130 ± 17) J·mol−1·K−1. Using the above thermodynamic properties for K2FeO4(cr), the potential presence or preservation of K2FeO4(cr) in the Martian soils under the conditions relevant to Mars were quantitatively evaluated. Thermodynamic calculations pertaining to the Martian conditions indicate that the presence or preservation of K2FeO4(cr) as a strong oxidant in the Martian soils can be supported.