SELF-DIFFUSION COEFFICIENTS OF THE TRIVALENT LANTHANIDE IONS GD-153(III) AND TM-170(III) IN CONCENTRATED AQUEOUS-SOLUTIONS

The ionic self-diffusion coefficients D of the trivalent ions Gd-153(I II) and Tm-170(III), have been determined in aqueous solutions of La(N O3)(3)-HNO3 and Gd(NO3)(3)-HNO3 (pH=2.5) at 25 degrees C by the open-e nd capillary method (O.E.C.M.). The diffusion data obtained in large r ange of concentration as well as the physico-chemical properties, allo w to derive the following informations: The limiting Value D-o at zero ionic strength, respectively 6.04 10(-6) cm(2) s(-1) for Gd(III) and 5.96 10(-6) cm(2) s(-1) for Tm(III). The validity of the Onsager limit ing law. The ionic self-diffusion coefficient as a function of the ion ic strength for non-symmetrical 3:1 electrolytes in dilute solutions. A more extended law available for an intermediate range of concentrati on up to 0.1M.