The sulfidisation of a thermally oxidised Nkomati massive sulfide ore was successful in restoring the flotation recoveries of the oxidised sulfide minerals including pentlandite. As a single mineral, however, oxidised pentlandite was not readily sulfidised and XPS analyses failed to identify any sulfidised surface species. A sulfidisation mechanism for oxidised pentlandite is proposed whereby iron and copper species from the oxidised Nkomati mineral surfaces form sulfides on the oxidised pentlandite surfaces, either through a precipitation process or the conversion of adsorbed iron and copper hydroxides, and subsequently confer floatability. To evaluate this proposal, the role of base-metal ions during the sulfidisation process was studied for oxidised pentlandite as a single mineral. The addition of iron during sulfidisation was found to be effective in improving the subsequent flotation recovery and was a maximum after sulfidisation at a sulfide ion electrode potential of -650 mV (-315 SHE). While this corresponded to that found for pentlandite during the sulfidisation of oxidised Nkomati ores, the sulfidised pentlandite floated more slowly as a single mineral. Iron was more effective than copper, most likely due to a significantly higher concentration. The significance of the sulfidisation potential at lower hydrosulfide concentrations is related to hydrosulfide ion availability while at higher sulfidisation potentials, it is associated with the depressive effect of adsorbed base-metal hydrosulfide ion complexes. A technique is presented whereby base-metal ions additions during sulfidisation improved the flotation recovery of a difficult to sulfidise mineral species, such as oxidised pentlandite. (C) 2007 Elsevier Ltd. All rights reserved.