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

Abstract

Activity coefficients of FeO and FeO1.5 in CaO‐SiO2‐FeO‐Fe2O3 melts have been investigated from the perspective of the coordination structures of iron ions. The percentages of Fe2+ and Fe3+ in octahedral symmetry (Fe3+(oct)) and Fe3+ in tetrahedral symmetry (Fe3+(tetr)) were measured by Mössbauer spectroscopy. It has been found that both values of γFeO and monotonically increase with increasing and that the γFeO values are higher than the values suggesting that FeO is more readily released from the silicate network to precipitate FeOx‐bearing compound from the slag than FeO1.5. It has also been found that the value increases with increasing the ratio of Fe3+(oct) pct./Fe3+(tetr) pct., which indicates that the values of (oct) are higher than those of (tetr). Accordingly, the hierarchy of the activity coefficients, i.e., γFeO > (oct) > (tetr) holds in the present system. The magnitude of effective ionic radii is in the hierarchy of Fe2+ > Fe3+(oct) > Fe3+(tetr), and thereby the bond strength between iron ion and oxide ion is in the hierarchy of Fe3+(tetr) > Fe3+(oct) > Fe2+. This suggests that Fe2+ are more loosely and Fe3+(tetr) are more rigidly bound to the silicate skeleton.