Aluminum and copper both occur naturally as oxides. Why is energy needed more to extract aluminium from its ores than to extract copper from its ores?
A glimpse at the general nature of metals andtheir compounds reveal that:
1) Reactive metals form compounds easily.
2) The compounds of reactive metals are difficult to split up.
Because aluminium is a reactive metal (it is placed in the higher end of the reactivity series for metals) it is difficult to separate it from the oxygen in the oxides. It cannot be reduced using carbon or carbon monoxide. Electrolytic reduction has to be resorted to for this purpose.
Copper is placed in the lower part of the activity series, its oxides are not that stable and hence can be reduced to the metal using carbon reduction at moderately elevated temperatures.
2Cu2O + C → 4Cu + CO2(g)
2CuO + C → 2Cu + CO2(g)
Aluminium oxide is more stable than copper oxide, meaning that it is much more difficult to extract from its ores (oxides) than copper.