The relationship between the electrochemical, mineralogical and flotation characteristics of pyrrhotite samples from different Ni Ores

The common sulphide mineral pyrrhotite (Fe_{(1-x )}S) occurs in varying crystallographic forms with each type exhibiting subtly different physical and chemical properties. Accounts in the literature suggest that the processing behaviour of magnetic and non-magnetic pyrrhotite differ from each other in their flotation properties, although limited agreement exists in terms of which is the more reactive pyrrhotite form. Since the flotation process is based on the surface properties of the sulphide minerals and pyrrhotite is a metallic conductor, it is of interest to characterise the surface properties of pyrrhotite with respect to its electrochemical state. This paper presents the results of electrochemical measurements performed on four pyrrhotite samples which have been characterised in terms of their mineralogical characteristics and flotation performance. Pyrrhotite samples from the Phoenix, Sudbury Copper Cliff North (CCN), Sudbury Gertrude West and Nkomati nickel mines were used for electrochemical measurements. Rest potential measurements, cyclic voltammetry and electrochemical impedance spectroscopy techniques were employed to characterise electrochemical behaviour of the samples. The electrochemical results showed that non-magnetic pyrrhotite was the least reactive towards oxidation and hence showed the best collectorless flotation performance, whereas the magnetic pyrrhotite samples were considerably more reactive. Due to the reactivity of the magnetic pyrrhotite samples, their collectorless flotation recovery was almost negligible due to the formation of hydrophilic ferric hydroxide species associated with the oxidation reaction. Differences in electrochemical reactivity were also noted for different magnetic pyrrhotite samples, suggesting the dependency of pyrrhotite reactivity on its provenance.