Restoring the floatability of oxidised sulfides using sulfidisation

While sulfide minerals generally are easy to recover by flotation, surface oxidation can have a significant impact on both the recovery and selectivity. The extent of this impact depended upon the mineral type for oxidised Nkomati sulfides (chalcopyrite < pentlandite ∼ pyrrhotite). The floatability of these oxidised sulfides has been shown to be restored by sulfidisation with varying degrees of success (chalcopyrite < pyrrhotite < pentlandite). Electrophoretic measurements showed that the oxidised sulfides strongly adsorbed hydrosulfide ions during sulfidisation which corresponded with the onset of strong floatability. XPS analyses showed that the surface of the oxidised chalcopyrite was readily converted to a chalcocite-like stoichiometry through an electrochemical mechanism coupled with the oxidation of copper and iron. The sulfidisation of oxidised pyrrhotite proceeded through both an anionic exchange mechanism and a direct precipitation reaction to form a pyrrhotite-like surface, which was subsequently converted electrochemically to a pyrite-like composition via iron and copper oxidation. Under more intense sulfidisation, the precipitation reaction was more dominant and a more pyrrhotite-like surface was evident. For the sulfidisation of oxidised pentlandite, although small quantities of a millerite-like and a pyrite-like surface may have formed, significant flotation in the presence of other oxidised sulfides appears to have been achieved through either adsorbed ferric hydroxides that became sulfidised or precipitated iron sulfides generated from the oxidised pyrrhotite. A feature common to all the sulfidised surfaces was the presence of reasonable quantities of either polysulfides or elemental sulfur, which may well contribute to any subsequent flotation.