ELLIPSOMETRIC STUDY OF ANIONIC SURFACTANT ADSORPTION ON APATITE AND CALCITE ORE SURFACES

The adsorption of an anionic surfactant, disodium N-alkylsulfosuccinamate, onto polished apatite and calcite ore surfaces was studied by ellipsometry. Partial dissolution of the minerals in NaOH solutions at Ph 10.5 caused a roughening of the surfaces which, in the case of apatite, was optically modeled as a semi-infinite substrate with a porous surface layer. Solutions containing Ca2+ hindered the dissolution of the minerals, and contacting the surfactant with nondissolved surfaces in the presence of Ca2+ resulted in reversible adsorption of a surface film. On partially dissolved apatite surfaces, in the absence of Ca2+ in the solution, an irreversible absorption of the surfactant was observed in the porous interface zone. In the presence of 1.4 x 10(-4) M Ca2+ both surfactant absorption and calcium-surfactant salt precipitation was observed depending on the concentration of the surfactant. The calcium-surfactant salt could be washed away by flushing the cell with fresh Ca2+ solution while the absorbed surfactant remained in the porous surface layer. Results on calcite surfaces were similar to those for apatite, but quantitative analysis of the data was not possible because of optical anisotropy and a much higher degree of dissolution.