The present study addressed the investigation of the basic fundamentals of the behaviour of celestite (SrSO4), strontianite (SrCO3) and calcite (CaCO3) in aqueous solutions in the presence and absence of sodium oleate. The results showed that the isoelectric point (IEP((aq))) of aqueous suspensions of strontianite and calcite takes place at pH 8 and 8.2, respectively; from thermodynamics, the IEP((aq)) of the minerals takes place at pH 8 and 8.3, respectively. Similarly, a thermodynamic analysis of the celestite-aqueous solution equilibrium open to the atmosphere showed celestite transforms to strontium carbonate in alkaline slurries (pH greater than or equal to 7.75). This phenomenon is due to the chemical reaction of celestite with the carbonate ion that forms in the solution as a result of the dissolution of the atmospheric CO2. The results of the mineral-aqueous solution equilibrium, electrokinetic and infrared spectroscopy studies appear to confirm such a superficial transformation. The electrokinetic studies showed the isoelectric point (IEP) of celestite and strontianite takes place at pH 5.4 and 7.4, respectively. The floatability of the minerals was investigated in the pH range 5 to 11 and varying the concentration of sodium oleate from 10(-6) to 10(-4) M. The results showed that celestite floatability had a maximum in the pH range 7 to 9; at higher pH values its floatability tended to decrease as a result of its surface transformation to strontium carbonate. The floatability of strontianite and calcite was substantially lower than that of celestite and tended to increase with the pH (pH greater than or equal to 7) and concentration of sodium oleate. It is proposed that in alkaline slurries sodium oleate was adsorbed on the celestite, strontianite and calcite surfaces by a chemisorption mechanism.