Chalcopyrite is known to be slow reacting mineral in hydrometallurgical systems and is considered one of the most inert
sulphide minerals with respect to leaching. Such character of chalcopyrite seems to be linked to a formation of a passive layer on its
surface. This work reports that freshly fractured chalcopyrite surfaces exhibit highly selective reactivity depending on the exposed
fracture planes. ToF-SIMS was used to qualitatively characterize various fracture planes in freshly fractured chalcopyrite particles,
prior to and after hydrometallurgical treatment. It was found that, prior to treatment, certain areas exhibited pronounced
contamination from atmospheric hydrocarbons; whereas, others were highly unreactive and remarkably free from adventitious
hydrocarbon contamination. The positive ion spectra recorded from these areas were found to be dominated by peaks from Fe- and
Cu-elements and related compounds. The negative ion spectra for the reactive areas on the other hand showed a high content of
oxidized (sulphur) species.
The differences between the areas of low and high reactivity, as detected after leaching, were more subtle than prior to leaching;
whereas, SEM analysis showed clear evidence for selective attack of ferric sulphate to specific planes. Furthermore, it was shown
that, when chalcopyrite is in intimate contact with pyrite, it experiences an enhanced oxidation compared to when there is no
electric contact with pyrite.
Attempts were made to explain the preferential oxidation observed based on the different chemistry of the fracture surfaces.