Although thermodynamically feasible, in practice , magnesium metal is not used for the reduction of alumina in the metallurgy of aluminium .Why?

Explanation

Temperature above the point of intersection of `Al_(2) O_(3)` and MgO curves, Mg can reduce `Al_(2) O_(3)` . But the temperature required (1600K) is very high. Hence the reduction process will be uneconomic and difficult.
`Fe_(2)O_(3) + 2A1 overset (1000-1500^(0)C) to A1_(2) O_(3) + 2Fe`
The ignition helps to overcome the energy of activitation and hence the reaction is fast.