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

Although thermodynamically feasible, in practice, Magnesium metal is not used for the reduction of Alumina in the metallurgy of aluminium.Why?
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Ans. : Below the temperature(1623 K) correspoinding to the point of intersection of Al 2O3 and MgO curves in Ellingham diagram, Magnesium can reduce Alumina because the ΔfG o value of Al2O3 at temperatures below 1623 K, is less negative than that of MgO. Therefore below 1623 K Mg can reduce Al2O3 to Al. But Magnesium is much costier metal than Aluminium and hence the process will be uneconomical.
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