Abstract In flotation, regrinding is used to increase the liberation of value minerals, such as chalcopyrite, from gangue minerals. As a result of the significant decrease in particle size following regrinding, flotation efficiency is generally worst. In this study it is shown that the flotation recovery (and rate) of chalcopyrite in chalcopyrite–pyrite mineral mixtures, which is lower after regrinding, could be partially restored with aeration. The increase in Cp flotation upon aeration was attributed to the creation of a more favourable environment for xanthate adsorption and dixanthogen formation whereas the decrease in Cp flotation after prolonged aeration is due to its increased oxidation as a result of galvanic interactions with pyrite upon regrinding. The amount of aeration required for maximum flotation decreased monotonically with increasing feed grind particle size. To rationalize the observed chalcopyrite flotation trends, a simple model which involves competitive adsorption of xanthate and oxygen on chalcopyrite and pyrite surface sites and underpinning oxygen consumption and mineral oxidation effect is proposed.