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 (1600 K) is very high. Hence the reduction process will be uneconomic and difficult.
` Fe_2 O_3 + 2Al overset( 1000-1500^@ C ) to Al_2 O_3 +2Fe `
The ignition helps to overcome the energy of activitation and hence the reaction is fast.