Effect of Coordination Structure of Iron Ions on Iron Oxide Activity Coefficients in the CaO‐SiO₂‐FeO‐Fe₂O₃ Slags at 1573 K Under Oxygen Partial Pressures Between 10⁻⁹ and 10⁻⁴ atm

Activity coefficients of FeO and FeO 1.5 in CaO‐SiO 2 ‐FeO‐Fe 2 O 3 melts have been investigated from the perspective of the coordination structures of iron ions. The percentages of Fe 2+ and Fe 3+ in octahedral symmetry (Fe 3+ (oct)) and Fe 3+ in tetrahedral symmetry (Fe 3+ (tetr)) were measured by Mössbauer spectroscopy. It has been found that both values of γ FeO and monotonically increase with increasing and that the γ FeO values are higher than the values suggesting that FeO is more readily released from the silicate network to precipitate FeO x ‐bearing compound from the slag than FeO 1.5 . It has also been found that the value increases with increasing the ratio of Fe 3+ (oct) pct./Fe 3+ (tetr) pct., which indicates that the values of (oct) are higher than those of (tetr). Accordingly, the hierarchy of the activity coefficients, i.e., γ FeO > (oct) > (tetr) holds in the present system. The magnitude of effective ionic radii is in the hierarchy of Fe 2+ > Fe 3+ (oct) > Fe 3+ (tetr), and thereby the bond strength between iron ion and oxide ion is in the hierarchy of Fe 3+ (tetr) > Fe 3+ (oct) > Fe 2+ . This suggests that Fe 2+ are more loosely and Fe 3+ (tetr) are more rigidly bound to the silicate skeleton.