Thermodynamics of actinide redox reactions in potassium phosphotungstate solutions

Abstract

The paper represents the results of the investigation of kinetics and thermodynamics of the M(IV) reduction reactions (M=Am, Cm, Bk, Cf) and also those of the Am(V) disproportionation reaction and the reaction between Am(V) and Am(III) in aqueous solutions of potassium phosphotungstate, K 10P 2W 17O 61 (KPW). From experimental data the thermodynamic parameters of activated complex formation for the M(IV) ions reduction process through the chemical route have been calculated. Linear correlation has been ascertained between the Δ G 298 ≠ values and the oxidation potentials of the M(IV)–M(III) pairs in KPW solutions and on this basis the estimation of the Δ G 298 ≠ values has been made for U, Pu and Np. In the case of the Am(V) disproportionation and the reaction of the interaction between Am(V) and Am(III) ions the enthalpy component introduces the main contribution into the Δ G 298 ≠ change. At the same time the contribution of the entropy component into the Δ G 298 ≠ change in KPW solutions is considerably lower than for perchloric acid solutions.