Similarly





The line BC is the variation between log pSO₂ and log po₂ for  equilibrium.
The predominance area diagram can be constructed easily by writing  values for each reaction.
Utility of predominance – area diagram (PAD)

1. PAD shows the stable phase under different conditions (gas pressures)
2. PAD predicts possible processing routes.
3. One can predict the conditions for formation of a particular phase. In dead roasting of PbS, PbO can form several compounds  like  and .Dead roasting of  is likely to produce  and
4. It is possible thermodynamically to produce metal from sulphide by controlling .
   
   

Roasting of complex sulphide ores

Additional reactions may occur during the roasting of complex sulphide ore.
Differentsulphide may form solid solutions and even complex sulphides. In iron-copper sulphide ores, numberof ternary phases and also solid solutions of  in  may form during roasting.

Another phenomenon is the formation of  in roasting of sulphide ores. Since in a complex phase the chemical activity of a given compound is less than the pure compound, its predominance area will expand.