This study investigated the effect of the pulp chemistry conditions during milling on the flotation performance of an Nkomati ore. The results have shown that there was approximately 10% increase in Ni recovery, when the ore was ground at dissolved oxygen (DO) concentration of 0 ppm in comparison to a condition where oxygen was allowed to access the slurry during the grinding stage. However, when the pH was changed from 9 to 11, the presence of oxygen resulted in a 20% decrease in the Ni recovery as compared to only 5% decrease in the Ni recovery at DO=0 ppm. A noteworthy observation is that controlling a combination of DO and pH during grinding can have a significant effect on selectivity in the flotation of such ores. It was shown that grinding at lower DO levels/redox potentials (Eh) in the presence of xanthate significantly improved the recoveries of pentlandite and pyrrhotite. (C) 2013 Elsevier B.V. All rights reserved.