Solutions of iron oxides in molten cryolite

All the iron oxides (FeO, Fe3O4, Fe2O3, and FeAl2O4) dissolve in cryolite-a lumina melts to give solutions containing both Fe(II) and Fe(III). The fact or controlling the Fe(II)/Fe(III) ratio is the oxygen pressure, and experim ental results are interpreted on that basis. Predictions are made of the va riation of solubility with oxygen pressure, and the standard potential of t he Fe2+/Fe3+ redox couple is calculated. The anode and anode gas of an indu strial Hall-Heroult cell appear to be insufficiently oxidizing to cause sig nificant conversion of Fe(II) to Fe(III). An anomaly in the liquidus diagra ms for FeF2 - Na3AlF6 and FeO - Na3AlF6 is accounted for in terms of solid solution of FeF2 in cryolite.