The effect of sulphite and ferric species on the collector-induced flotation of chalcopyrite has been studied, while the effect of these species on the rate of dicresyl dithiophosphate (DCDTP) adsorption has been monitored in situ using UV spectroscopy. Chalcopyrite, which had been previously conditioned with Fe(III) species, exhibited decreased affinity for DCDTP adsorption. Under these conditions, the flotation rate and recovery of chalcopyrite was reduced. The extent of flotation depression by iron oxyhydroxide depended on pH, conditioning gas, and the presence of adsorbed collector on chalcopyrite. Prior interaction of the chalcopyrite surface with sulphite significantly increased both the adsorption rate as well as the surface coverage of DCDTP on chalcopyrite. Sulphite removes adsorbed iron oxyhydroxide, present due to its specific introduction or oxidation of chalcopyrite, from the chalcopyrite surface and promotes the formation of an iron-deficient chalcopyrite. The rate of DCDTP adsorption onto chalcopyrite was increased due to both removal of iron oxyhydroxide previously existing on the chalcopyrite surface and the formation of an iron-deficient chalcopyrite. Under these conditions, the flotation rate and recovery of chalcopyrite was increased. Reasons why the surface modified chalcopyrite exhibited enhanced DCDTP adsorption are discussed.