6.3 Why is the extraction of copper from pyrites more difficult than that from its oxide ore through reduction?


The Gibbs free energy of formation (∆fG) of Cu2S is less than that of H2S and CS2.

Therefore, H2 and C cannot reduce Cu2S to Cu.

On the other hand, the Gibbs free energy of formation of Cu2S is greater than that of CO. Hence, C can reduce Cu2S  to Cu. 

                      C(s) + Cu2O(s)    2Cu(s) + CO(g)

Hence, the extraction of copper from its pyrite ore is difficult than from its oxide ore through reduction.