SEM and AES studies of chalcopyrite bioleaching in the presence of catalytic ions

Scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) were used to study the surface changes occurring in chalcopyrite when the bioleaching medium contained Ag(I), Hg(II) and Bi(III) ions. The untreated sample revealed the presence of carbon and oxygen in addition to the chalcopyrite elements (Cu, Fe and S). AES spectra showed a sulphur enrichment on the chalcopyrite surface during bioleaching without catalytic cations. The results with catalytic cations showed that Ag(I), Hg(II) and Bi(III) are incorporated into the surface irrespective of the presence of bacteria. However, different interactions between the chalcopyrite and the cation take place, depending on the cation added to the leaching medium. Ag(I) and Hg(II) ions formed a coating of a silver sulphide and a mercury sulphide, respectively. Microorganisms oxidise the surface sulphur of this silver sulphide but not the mercury sulphide layer, so that its thickness did not increase during bioleaching. The observed changes in the shape of AES sulphur peak confirmed the formation of Ag2S in the surface. When Bi (III) is added to the bioleaching medium an oxidised compound is formed, which suggested a different pattern of interaction with respect to Ag(I) and Hg(II).