Reconstruction of the Chalcopyrite SurfacesA DFT Study

Chalcopyrite (CuFeS₂) is the main source of copper in the world. The development of hydrometallurgical processes to extract copper from chalcopyrite is challenging due to the low leaching kinetics. The main difficulty is in the fact that the kinetics of the leaching process decreases very rapidly, marginally stopping the reaction. A passivation process of the surface has been proposed for explaining the low reaction kinetics. However, the leaching mechanism and the reactants which are involved in the passivation process are still a matter of debate. Therefore, understanding the chalcopyrite surface reactivity and the intricate reaction occurring in the solid/solution interface is of fundamental importance. In the present study, DFT calculations within the plane wave framework were performed to understand the reconstruction of (001), (100), (111), (112), (101), and (110) chalcopyrite surfaces. Metal and sulfur terminated surfaces have been investigated. The structural and electronic properties of the reconstructed surfaces have been discussed in detail. Three different mechanisms of the chalcopyrite surface reconstructions emerged from this study. It is clear that the chalcopyrite surface undergoes important reconstruction in which the sulfide, S^2–, ions migrate to the surface which tend to oxidize, forming disulfides, S₂^2–, and, concomitantly, reducing the superficial Fe³⁺ to the Fe²⁺. It is also observed that the metal atom moves downward to the surface, forming metallic-like bidimensional alloys underneath the surface.