The flotation behaviour of a Western Australian nickel ore was characterised by size-by-size flotation rate tests to extract rate constant information. The aim was to identify the effect of surface interactions on the flotation of the nickel sulphide mineral, pentlandite, with magnesium-silicate bearing minerals (predominantly serpentines). Flotation tests were carried out using collector (amyl xanthate), both with and without the other standard reagents for this ore. In this study the latter were carboxy-methyl cellulose (CMC) and soda ash. The addition of soda ash and CMC was shown to improve pentlandite flotation rate and recovery. Soda ash addition was found to be essential for improving flotation performance, as without it nickel recovery was unacceptably low. It is proposed that carbonate ions, derived from soda ash addition, enhance dispersion in the pulp and that CMC may assist removal of adhering slime particles from pentlandite surfaces. Drawing on the literature in this area, a number of mechanisms are proposed to explain the observed flotation behaviour of gangue magnesium-silicate bearing minerals.