Self-diffusion coefficients and structure of the trivalent transplutonium ion curium and gadolinium in aqueous solution

Self-diffusion coefficients D of the trivalent aquo ion Cm³⁺ have been determined in aqueous Nd(ClO₄)₃?HClO₄ solutions (pH 2.5) at 25°C, by the open-end capillary method (O. E. C. M.). The variation of D versus the square root of the concentration of inactive solution is an exponential form in the studied range of concentration. The limiting value D₀ at zero ionic strength is 6.0·10^?6 cm²·s^?1. The curve (D = f(sqrt c )) relating to Cm³⁺ can be compared to those of²⁴¹Am³⁺ and¹⁵³Gd³⁺ obtained under similar conditions. We find a similar ionic structure of Cm³⁺ with Am³⁺ and Gd³⁺. They have the same hydration as a tripositive of 5f and 4f ions in the absence of hydrolysis, complexing, or pairing at pH 2.5. The present study contributes to show the analogy of the solvation structure of trivalent actinide ions in aqueous solution at pH 2.5 with that of the trivalent lanthanide ions as a help for predicting the thermodynamic properties.