Roles of oxidants and reductants in bioleaching system of chalcopyrite at normal atmospheric pressure and 45 °C

In this work, the roles of dissolved oxygen (O₂), Fe^3 + and Fe^2 + and their interactions during chalcopyrite leaching in basic culture medium at normal atmospheric pressure and 45 °C were investigated by leaching experiments, XPS and electrochemistry analysis. Results showed that Fe^3 + 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 Fe^2 + cannot promote chalcopyrite dissolution in N₂ atmosphere, while significantly promoted chalcopyrite dissolution in O₂ atmosphere. XPS and electrochemistry further proved that Fe^2 + cannot directly react with chalcopyrite, Fe^2 + was steadily oxidized to Fe^3 + by O₂ 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, Fe^3 +, rather than O₂ 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 °C.