Flotation tests carried out with fluorite, magnesite and hematite using sodium oleate as collector confirmed acidic and alkaline ranges of good flotation. While the flotation results in acidic solutions depend strongly on the conditioning time and can be very much improved when longer conditioning times are utilized, the tests in the alkaline environment do not exhibit any significant dependence on conditioning. The observed effects provide additional evidence for the role of the colloidal species which appear in the acidic solutions of weak electrolyte type surfactants, such as fatty acids. The flotation properties of sodium oleate in the acidic pH region are determined by the properties of the precipitating oleic acid, and slow diffusion of such colloidal species toward mineral surfaces controls flotation kinetics. On the other hand, adsorption equilibrium is established quickly in alkaline environment in which the collector appears in the form of ions, and the flotation under such conditions depends very little on the conditioning time. One of the important features of such flotation systems is dependence of the maxima in the flotation recovery-pH curves on conditioning; the maximum shifts towards more acidic pH values when conditioning time is increased.