Distribution of an adsorbed anionic surfactant on the external and internal surfaces of a porous apatite mineral

Abstract The adsorption of an anionic surfactant, disodium N-alkylsulfosuccinamate, onto polished apatite ore surfaces was studied by ellipsometry. Surfaces of varying porosity were created by partially dissolving planar apatite surfaces to different degrees in NaOH solution at pH 10.6. Partially dissolved apatite was optically modelled as a semi-infinite substrate with a porous surface layer. The porous layer varied in thickness from 0 – 550 A and in degree of porosity from 0 – 12 volume %. Adsorption of the surfactant in Ca(OH) 2 solution on the non-porous surface resulted in formation of a thin film about 40 A thick which could be removed by flushing the measurement cell with fresh solution. Adsorption of the surfactant on the porous surfaces resulted in both revesible adsorption on the external surface and irreversible adsorption within the pores. The role of the pores in flotation is commented on and a proposal is made concerning how the selectivity for hydrophobization in apatite/calcite ore mixtures is possibly affected by solubility related differences in the microstructure of the minerals.