Surface active species and their reaction schemes in extraction solution systems identified from practical behaviors of interfacial tension

The interfacial tensions in two-phase solution systems for extraction of me tallic ions from aqueous phase to organic phase by di(2-ethyl-hexyl) phosph oric acid were measured by the Wilhelmy plate method and partly by laser-li ght scattering method to confirm the accuracy. For copper and iron extracti on solution systems, the surface-active species and their interfacial conce ntrations were identified by comparing the actual behavior of interfacial t ension, the pH and extractant concentration dependencies, with the Gibbs-La ngmuir equation for adsorption. It was shown that the extractant molecules should be adsorbed at the interface in the form of monomer and its dehydrog enated anion and that in copper extraction solution system non-surface-acti ve 1:2 intermediate complexes should be formed, and in iron extraction solu tion system strongly surface-active 1:2 intermediate complexes should be fo rmed at the interface. Based on the insights related to the intermediate co mplexes, reaction schemes at the interface are also discussed. (C) 2000 Els evier Science B.V. All rights reserved.