Reduction of Mn in slag

Conditions for reduction of MnO, that is reversal of reaction 2 is important. The reduction of MnO in slag transfers Mn from slag to metal and increases the concentration of manganese. The following are the conditions for the reduction of MnO in slag

• Low activity of FeO in slag which means a reducing slag
• High temperature which decreases

Illustration:
Consider a slag of basicity 1.8. At this basicity the activity coefficient of MnO in slag is 1.6. The mole fraction of FeO and MnO in slag is 0.25 and 0.05 respectively. Determine the equilibrium content of Mn and O in steel at 1873K. Given

        
Using equilibrium constant definition, we can write

(8)

Substituting the values, we get at 1873K

 

Using equations 10 of lecture 6

  
      
We get  

Hence

 

 
Calculations performed at 1773K shows that [wt% Mn] is 0.032. This means that decrease in temperature favours removal of manganese from metal to slag. The reader may perform calculations at 1973K and interpret the calculations.