In previous study, it has been found that the grinding conditions have a great effect on the flotation of chalcopyrite and galena as well as their separation from pyrite (Peng et al., 2003a,b). In this study, the effect of the grinding conditions on the activation of pyrite by Cu(2+) and Pb(2+) were investigated. Based on flotation behaviour, EDTA (ethylene diamine-tetra acid) extraction, pulp potential measurement and electrokinetic study, it is found that the activation of pyrite flotation by Cu(2+) and Pb(2+) involves different mechanisms. Reduction of copper(II) to copper(I) and the formation of new copper sulphide phases are responsible for the activation of pyrite flotation by Cu(2+). This is an electrochemical process. However, adsorption of lead hydroxide on pyrite surface is principally responsible for the activation of pyrite flotation by Pb(2+). The effect of grinding media on the flotation of pyrite activated by Cu(2+) or Pb(2+) is through the change of pulp potential and iron oxidation species emanating from the media. The iron oxidation species from grinding media is electrostatically repulsive with respect to copper-activated pyrite and therefore, reducing conditions produced by mild steel medium promotes pyrite flotation in the presence of Cu(2+). However, iron oxidation species from grinding media is electrostatically attractive with respect to lead-activated pyrite and therefore inert grinding medium favours pyrite flotation in the presence of Pb(2+). This study provides a clear picture of how to increase or decrease pyrite flotation through a smart selection of grinding media. (C) 2010 Elsevier Ltd. All rights reserved.