SOLUBILITY OF POTASSIUM FERRATE IN 12 M ALKALINE-SOLUTIONS BETWEEN 20-DEGREES-C AND 60-DEGREES-C

The solubility of potassium ferrate (K2FeO4) was measured in aqueous s olutions of NaOH and KOH of total concentration 12 M containing variou s molar ratios of KOH:NaOH in the range 12:0 to 3:9. Several analytica l methods were tested for the determination of ferrate concentration. The final method chosen consisted of potentiometric titration of the f errate sample with an alkaline solution of As2O3. The assumption was m ade that ferrate dissociates in concentrated KOH solutions predominant ly to KFeO4-. The solubility constant, S, defined as the product of th e molar concentration of the potassium ion, K+, and the ferrate anion, KFeO4- was found to be 0.044 +/- 0.006 mol(2) dm(-6) for 20 degrees C , 0.093 +/- 0.004 mol(2) dm(-6) for 40 degrees C and 0.15 +/- 0.09 mol (2) dm(-6) for 60 degrees C. From these results the heat of dissolutio n of K2FeO4 was calculated as -14.3 kJ mol(-1). At 60 degrees C the en hanced decomposition of the ferrate at the higher temperature led to a greater deviation in solubility values compared with data for either 20 degrees C or 40 degrees C.