Activities of Iron Oxides in the Na₂O-Na₂CO₃-SiO₂-FeO-FeO_1.5 System

Abstract

The activities of FeO and FeO_1.5 in the Na₂O-Na₂CO₃-SiO₂-FeO-FeO_1.5 system in contact with solid iron were measured, equilibrating with CO-CO₂ gas mixtures. The isoactivity contours of FeO were shown to be similar to those in the CaO-SiO₂-FeO system, having the noses approximately at the line joining the compositions of FeO and 0.4Na₂O-0.6SiO₂. The addition of P₂O₅ to this system enhances the activities of both iron oxides. The activity of FeO_1.5 was observed to have a maximum at the same composition as the basicity varies.
These results were interpreted qualitatively by the regular solution model for FeO and the amphoteric property for FeO_1.5.
The result indicates that the significantly low oxygen potential prevailing at the metal-slag interface rather than the possibly singular thermodynamic property of FeO in this system accounts for the relatively small oxidation loss of iron on the soda ash treatment of hot metals for simultaneous removal of sulphur and phosphorus.