ADSORPTIVE LAYERS OF DI(2-ETHYLHEXYL)PHOSPHORIC ACID ON THE FREE-SURFACE OF AQUEOUS CU(II), CO(II), NI(II), AND K(I)

The surface tension and electrical surface potential were determined for aqueous solutions of di(2-ethylhexyl)phosphoric acid (D2EHPA) containing KC1, CuSO4, NiSO4, or COSO4, at various concentrations of D2EHPA and constant concentration of the electrolyte. The surface excesses for the systems studied as well as the limit surface area per adsorbed molecule were calculated. The dependence of the electrical surface potential on the surface excess confirmed a neutral character of adsorptive layers on the free surface of the solutions examined. From both these magnitudes the effective dipole moments for adsorbed molecules were calculated. All surface properties of D2EHPA solutions with KC1 and CuSO4 were found to be different from those with COSO4 and NiSO4. Adsorptive layers consisting of plane square Cu(D2EHP)2, octahedral Ni(D2EHP)2(H20)2, and tetrahedral Co(D2EHP)2 were suggested for D2EHPA solutions conraining CuSO4, NiSO4, and COSO4, respectively. It has also been found that the surface activity of the first compound was substantially lower than in the remaining ones. The results obtained allow one to explain the differences which were found previously in the course of copper, cobalt, and nickel separation from their aqueous solutions by a liquid surfactant membrane containing D2EHPA. © 1980 by Academic Press, Inc.