Distribution of Bi Between Slags and Liquid Copper

The distribution of Bi between liquid copper and calcium ferrite slag containing 24 wt pct CaO, iron silicate slag with 25 wt pct SiO₂, and calcium iron silicate slags was measured at 1573 K (1300 °C) under controlled CO-CO₂ atmosphere. The experimental results showed that bismuth distribution is affected by the oxygen partial pressure, and bismuth is likely to exist in slags in the 2+ oxidation state, i.e., as BiO. The distribution ratio between calcium ferrite slag and metal was found to be close to that of iron silicate slag. The Bi distribution ratio was found to decrease with increasing SiO₂ and Al₂O₃ content in slag. Increasing temperature was found to decrease the Bi distribution ratio between slag and metal. Using the measured equilibrium data on Bi content of the metal and slag and composition dependence of the activity of Bi in liquid copper, the activity and hence activity coefficient of BiO in the slag was calculated. The close value of activity coefficient of BiO in both slags at the same oxygen partial pressure indicates that the CaO-BiO and SiO₂-BiO interactions are likely to be at the same level, or the FeO _x -BiO interaction is the predominant interaction for BiO in the slag. Therefore at a constant FeO _x content in the slag, the CaO-BiO and SiO₂-BiO interactions doesn’t affect \( \gamma_{\text{BiO}} \) significantly.