The mixed potential plays a key role in leaching of chalcopyrite. Therefore, the impact of Fe2+ and Fe3+ on chalcopyrite leaching was investigated in this work. Simultaneously, the chalcopyrite passive film was studied by applying cyclic voltammetry (CV), potentiodynamic, potentiostatic, and Tafel polarization. X-ray photoelectron spectroscopy (XPS) was used to analyze the products formed during the electrochemical treatment of chalcopyrite. Furthermore, the band theory was used to analyze the oxidation and reduction of chalcopyrite. High copper extraction percentage was obtained at a low mixed potential or ratio of Fe3+/Fe2+. The empty states of chalcopyrite overlapped with filled states of Fe2+; chalcopyrite captured electrons from Fe2+ and was reduced to chalcocite, which was very easily oxidized by Fe3+. The Fe dissolves preferentially from the chalcopyrite surface in the potential range from 475 to 700 mV and leave behind a S-2(2-) and S-n(2-) passive film. The chalcopyrite transpassive dissolution occurs above 700 mV.