The speciation and solubility of iron under reducing, hyperalkaline conditions was investigated through undersaturation solubility experiments in combination with solid phase characterization by XRD. The solubility of a well-defined Fe (OH) ₂ (cr) solid phase was studied at T = (25 ± 2) °C in aqueous solutions containing 0. 10 to 4. 20 m KOH and 1. 06 to 22. 73 m NaOH. Experimental data were used to derive chemical, thermodynamic and (Specific Ion Interaction Theory (SIT), Pitzer) activity models that accurately describe iron solubility under these conditions. These results support Fe (OH) ₃^− as the main aqueous iron (II) species up to 1 m NaOH/KOH, while Fe (OH) ₄^2− dominates at higher hydroxide concentrations.
Fürst et al. (Wed,) studied this question.