Investigation of the Self-Diffusion Coefficients of Trivalent Gd3+ in aqueous solutions: The Effect of Hydrolysis and nitrate ion association

Abstract

In recent work, we have deduced that berkelium and gadolinium, which have 4f and 5f with half-filled configurations, also display similar diffusion properties. Results, using self-diffusion coefficients to study thermodynamic properties, show very similar behavior, which is understood given their similarities in charge, ionic size, mobility, conductance, and hydration number. In this paper we undertook a study of Gd3+ as an aid for deducing the thermodynamics properties of the Bk3+ .

In first part we compare magnitudes of transport (self-diffusion coefficient) of the trivalent aquo ions of Gd III for two concentrations, C1 = 2 10-4 mol.L-1, C2 = 10-3 mol.L-1 , and in perchlorate and nitrate media . In second part, we studied the variation of D with the medium’s pH. Self-diffusion coefficients, D, of the trivalent f-elements aqua ions have been determined in an aqueous electrolyte support of Gd(NO3)3 and Nd(ClO4)3 and at a pH=2.5. (HNO3, HClO4 ) and at 25 °C using the open-end capillary method (O.E.C.M.).

The variation of D versus pH shows three zones

We changed the NO3- counter ion with ClO4- ,and found that measurements must be carried in perchloric acid medium so as to avoid pairing phenomena. Using association constants between Gd3+ and NO3- , and a hydration constant, we estimated self-diffusion coefficients for Gd(NO3)2+ and Gd(OH)2+ .

The results justified our choice of working at pH = 2.5 which constitute an optimum condition to avoid hydrolysis and pairing phenomena. Our results were confirmed by mobility measurements using an electro migration technique.