In this work, the roles of dissolved oxygen (O-2), Fe3+ and Fe2+ and their interactions during chalcopyrite leaching in basic culture medium at normal atmospheric pressure and 45 degrees C were investigated by leaching experiments, XPS and electrochemistry analysis. Results showed that Fe3+ remarkably promoted chalcopyrite dissolution at the initial stage of leaching process, while easily caused the final passivation at the later stage. Leaching experiments showed that Fe2+ cannot promote chalcopyrite dissolution in N-2 atmosphere, while significantly promoted chalcopyrite dissolution in O-2 atmosphere. XPS and electrochemistry further proved that Fe2+ cannot directly react with chalcopyrite, Fe2+ was steadily oxidized to Fe3+ by O-2 and caused redox potential at an appropriate range (about 380-480 mV vs. Ag/AgCl), thus eliminating passivation species of polysulfide (S-n(2-)) and promoting chalcopyrite dissolution. Dissolved oxygen can directly oxidize chalcopyrite when with no addition of metal ions. In addition, Fe3+, rather than O-2 was the main oxidant in leaching system of chalcopyrite at normal atmospheric pressure. Band theory was used to further interpret the roles of oxidants and reductants in bioleaching system of chalcopyrite. This work is potentially useful in interpreting the roles of oxidants and reductants in bioleaching system of chalcopyrite at normal atmospheric pressure and 45 degrees C. (C) 2017 Published by Elsevier B.V.