posted on 2016-02-21, 17:43authored byCláudio de Oliveira, Guilherme Ferreira de Lima, Heitor Avelino de Abreu, Hélio Anderson Duarte
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, S2–, ions migrate to the surface
which tend to oxidize, forming disulfides, S22–, 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.