Self-diffusion coefficients and structure of the trivalent f-element ions, Eu, Gd, Am, Bk, Cf and Es in aqueous diluted and concentrated solutions

Self-diffusion coefficients D of the trivalent ions in aqueous solutions of Eu and Gd have been determined in electrolyte support Gd(NO3)3, and of Am, Bk, Cf and Es in electrolyte support Nd(ClO4)3, in concentrated solutions at (pH = 2.5) HNO3, HClO4 and at 25 °C using the open end capillary method (O.E.C.M.). This method measures the transportation time of ions across a fixed distance. In this paper we complete a measurement of self-diffusion coefficient at concentrated solution (1.5 M). We optimized the pH in order to avoid the hydrolysis, pairing and complexing trivalent 4f and 5f ions. The behavior of D and Dη are plotted versus √C. The similarities observed of self-diffusion coefficients of trivalent f-elements ions can be explained by a similar electronic configuration and same hydration number. The variation of D versus the square root of the concentration of the solution was found to be quasi-linear in the studied concentration range (C ≤ 1.5 M). Results of the diffusion for the two couples (Am-Eu) and (Bk-Gd) show us that 4f and 5f elements, having similar electronic configuration and/or sub shell half-filled configuration of trivalent ions, have the same behavior. We compared variation of D/D° versus √C for all studied 4f and 5f elements from concentration 0 to 1.5 M and we obtained the same variation with √C for all studied elements. We have estimated activity coefficients for both 4f and 5f trivalent ion elements using Nernst-Hartley expression. We deduced that we can achieve self-diffusion experience using 4f support electrolyte as Nd(ClO4)3 in acid medium and needing only some 5f element tracer element. This method is adequate for the study of 5f element which is not available as a macro element such as heavy 5f elements fermium Fm3+ and mendelevium Md3+.