Study of Chromium Oxide Activities in EAF Slags

Abstract

The activity coefficients of chromium in Cu-Cr melts were determined by equilibrating liquid copper with solid Cr₂O₃ in CO-CO₂ atmosphere. The temperature dependence of the activity coefficients of chromium in Cu-Cr melts could be expressed as

$$ \lg \gamma_{{{\text{Cr}}\left( {\text{s}} \right)}}^{ 0} = \frac{{ 3 2 5 9\left( { \pm 1 8 6} \right)}}{T} - 0. 5 9\left( { \pm 0. 1} \right). $$

Based on the above results, the activities of bivalent and trivalent chromium oxide in some slags at 1873 K (1600 °C) were measured. The slags were equilibrated with Cu-Cr melts under two oxygen partial pressures (${p_{{{\text{O}}_{ 2} }} }$ = 6.9 × 10⁻⁴ and 1.8 × 10⁻⁶ Pa, respectively). The morphology of the quenched slags and the solubility of chromium oxide in the melts were investigated by EPMA, SEM, and XRD. Under both oxygen partial pressures, the slags were saturated by the solid solution MgAl_2−x Cr _x O_4−δ . At the low oxygen partial pressure (1.8 × 10⁻⁶ Pa), the content of Cr in the liquid phase varied from 0.4 to 1.6 mass pct with the total Cr content in the slags increasing from 1.3 to 10.8 mass pct. At the high oxygen partial pressure (6.9 × 10⁻⁴ Pa), the content of Cr in the liquid phase decreased to the level of 0.2 to 0.6 mass pct. Both the activities of CrO and Cr₂O₃ in slag were found to increase approximately linearly with the increase of the total Cr content in slag. While the oxygen partial pressure had minor effect on the activity of Cr₂O₃ in the slag, it had significant effect on the activity of CrO.