Abstract
Xβray photoelectron spectroscopy (XPS) and electrochemical techniques have been applied to the investigation of the surface oxidation of pentlandite. Photoelectron spectra indicate that the initial reaction on exposure to air is removal of iron from the pentlandite lattice to form a hydrated iron oxide overlayer and leave a metalβdeficient pentlandite in addition to a restructured nickelβiron sulphide. Further oxidation resulted in some nickel being transferred to the oxide. In dilute acetic acid, the oxide layer was largely soluble. In basic media, the products were the same as in air but the reaction rate was greater. The voltammetric characteristics of pentlandite in solutions of pH 4.6, 9.2 and 13 were consistent with the XPS findings. Pentlandite behaved in a manner similar to that established previously for pyrrhotite indicating that the iron in pentlandite is preferentially removed on anodic oxidation to leave a metalβdeficient sulphide layer. There was evidence for the additional removal of nickel from the sulphide lattice. The formation of sulphate as also indicated on scans to high potentials in basic media.