Question

Why should we convert metal compounds into oxides and then extract it

Answer 1

 We always treat bauxite as if it was aluminium oxide for chemistry purposes, although it is actually more complicated than that in reality. ... Concentrating the ore. This simply means getting rid of as much of the unwanted rocky material as possible before the ore is converted into the metal.

Answer 2

it is easier to obtain a metal from its oxide as compared to its sulphide and carbonates therefore prior to reduction the metal sulfides and carbonates must be converted into metal oxides