Contact angle measurements, ultraviolet (UV) spectroscopy and microflotation studies were carried out in order to investigate the effect of externally applied potential on the wettability of both synthetic and natural chalcopyrites in potassium amyl xanthate (PAX) solutions. The contact angle on the mineral electrode surface was measured after the mineral electrodes were conditioned at a fixed potential for 10 min. The effects of pH, concentration of PAX and depressants such as sodium cyanide, sodium sulfide and MAA (a mixture of magnesium chloride, ammonium chloride and ammonium hydroxide) on the contact angle of synthetic and natural chalcopyrites were also investigated. The hydrophobic film on the chalcopyrite surface was extracted using hexane and examined by UV spectroscopy. Collector and collectorless microflotation of natural chalcopyrite under controlled potential at pH 10 was performed in order to determine the floatable potential range of chalcopyrite. The contact angle results indicated that synthetic and natural chalcopyrites have similar wettability. Their floatable potential range in 7 x 10(-4) M PAX solution was -0.2 to 0.2 V vs. standard calomel electrode at pH 10 and was -0.25 to 0.3 V at pH 7. Sodium sulfide showed the strongest inhibiting effect among the three depressants investigated. The flotation results indicated that natural chalcopyrite floated in the pulp potential range of -0.087 to +0.2 V (vs. SCE and monitored by a platinum electrode) without collector and in the potential range of -0.2 to +0.205 V in the 7 x 10(-4) M PAX solution. (C) 2003 Elsevier Science Ltd. All rights reserved.