Atmospheric ferric sulfate leaching of chalcopyrite: Thermodynamics, kinetics and electrochemistry

- CuFeS2 dissolution rates are not a simple function of [Fe3 +] or [Fe3 +]/[Fe2 +].
- Mineral semiconducting properties (bulk and/or film) must be considered.
- Altering the mineral semiconducting properties can influence the kinetics.
- Electrochemical results cannot be directly related to leaching operations.

The dissolution of chalcopyrite has been studied from an integrated point of view where the thermodynamics, dissolution kinetics and electrochemical behavior have been considered together.The variations in mixed potential and dissolution current density were interpreted considering the aqueous speciation of the electrolyte and the semiconductor properties of the chalcopyrite. This leads to the conclusion that CuFeS2 dissolution rates are not a simple function of the nominal ferric concentration or of the nominal ratio of ferric to ferrous.The differences observed in the anodic charge transfer coefficient for the dissolution of chalcopyrite and the limiting current densities observed in potentiodynamic experiments at different temperatures have been explained in terms of the semiconductor properties of chalcopyrite (and/or its reaction product surface film).The differences between studying the electrochemistry of chalcopyrite by imposing an electrode potential using a potentiostat and by using a solution of known redox potential, as well as the differences in the interpretation of experimental results when redox potential is used instead of mixed potential are also discussed. It is shown that extrapolation of electrochemically-obtained results to leaching operations should be done with care.