A kinetic analysis of the flotation of various nickel-copper sulphide samples is presented. Two approaches of first order kinetics have been used to estimate the flotation rate constants of pentlandite and pyrrhotite for stockpile samples and fresh sample as a reference. Stockpile oxidation of samples was characterized by variations of the rate constants for fast (k(f)) and slow floating fractions (k(s)) as well as the slow floating fraction (Phi) according to the Kelsall approach. An overall rate constant along with parameters, ultimate recovery (RI) and time correction factor (theta) was determined according to the Agar approach. Selectivity index for pentlandite-pyrrhotite separation was also determined for all cases investigated. Both the collectorless flotation and collector induced flotation were investigated for a more complete view on the behaviour of these minerals. Fundamental differences in behaviour of these two minerals have been discussed with respect to development of floatability based on metal ion activation and elemental sulphur/polysulphide induced hydrophobicity. While both of these primary effects promote fast flotation kinetics, the former mechanism appears to be more important in practice. Over-oxidation results in flotation losses by transforming the fast floating particles into slow floating particles and those in turn into non-floatable particles. The values of Phi estimated from the kinetic analysis have been shown to correlate with nickel losses. (c) 2007 Elsevier B.V. All rights reserved.