Solubility of Ferrate(VI) in NaOH-KOH Mixtures at Different Temperatures

The solubility of potassium ferrate(VI) (K2FeO4) was measured in a mixture solution containing various molar ratios of KOH and NaOH at a total concentration of 14 M from (10 to 60) degrees C. The solubility of K2FeO4 decreased necause of the presence of K+ in the solution mixture. The solubility (S*) was expressed as log S* = 5.830 - 2019/T - 5.845X(K+)(0.5) + 1.595X(K+) + 724X(K+)(0.5)/T (sigma = 0.024), where XK+ is the mole fraction of K+ in the solution mixture and T is in Kelvin. A comparison of the values of S* in different alkali metal hydroxide solutions showed that the solubility of K2FeO4 was diminished in KOH and CsOH and similarly in LiOH and NaOH solutions. The solubility product constant (K-sp*), calculated from the solubility measurements, was given as log K-sp* = 18.10 - 6055/T - 17.535X(K+)(0.5) + 4.785X(K+) + 2171X(K+)(0.5)/T (sigma = 0.061). The heat of dissolution (Delta H-diss) decreased linearly with an increase in the mole fraction of K+ ions. The significance of the solubility results is briefly discussed.