(a) Suggest a condition under which magnesium could reduce alumina.
(b) Although thermodynamically feasible, in practice magnesium metal is not used for the reduction of alumina in the metallurgy of aluminium. Why ?
( c) What is the reduction of a metal oxide easier if the metal formed is in liquid state at the temperature of reduction ?
(d) At a site, low grade copper ores oare available and zinc and iron scraps are also available. Which of the two scraps would be more suitable for reducing the leached copper ore and why ?

Explanation

The two equations are:
(a) `(4)/(3) Al +O_(2)to (2)/(3) Al_(2)O_(3) " "(b) 2 Mg +O_(2)to 2 MgO`
At the point of intersection of the `Al_(2)O_(3)` and MgO curves (marked “A”in diagram 6.4), the`Delta _(r)G^(Ө)` becomes ZERO for the reaction:
`(2/(3) Al_(2)O_(3) +2 Mg O+(4)/(3) Al`
Below that point magnesium can reduce aluumina .