FOURIER-TRANSFORM INFRARED SPECTROSCOPIC STUDY OF ADSORPTION OF OLEIC-ACID OLEATE ON SURFACES OF APATITE AND DOLOMITE

The nature of the oleic acid species adsorbed on apatite and dolomite at pH 4 and pH 10 with and without NaCl was examined by Fourier transform infared (FT-IR) spectroscopy. In the case of apatite at pH 10, absence of the carboxyl stretching band at 1735 cm-1 and a moderate intensity of asymmetric carboxylate stretching band at 1560 cm-1 indicated that the predominant surfaces species is oleate. At pH 4, the intensity of the two bands reversed indicating oleic acid as the major adsorbed species. Intensity of the carbonyl stretching band increased in the presence of NaCl at pH 4. This is attributed to a shift in equilibrium toward oleic acid in the presence of sodium ions. In the case of dolomite at pH 10, none of the above bands were detected, presumably due to the small amount of oleate present at this pH value. At pH 4, although there is masking of the carboxylate band at 1560 cm-1 by the strong dolomite band in the 1350-1575 cm-1 region, based on the intensity of the carboxyl stretching band at 1735 cm-1 it is indicated that the nature of the adsorbed species is similar to the apatite-oleate system. Adsorption of various species was estimated by integrated intensity of the bands in accordance with Beer's law and compared with macroscopic adsorption data. A good agreement between the two adsorption trends was obtained except for dolomite at pH 10. Flotation results correlate with the adsorption trends estimated by FT-IR spectroscopic measurements.