[en] When a solution containing ferric ions passes on cationic resin in U(IV) form, the substitution of uranium by iron is preceded by oxydation of U(IV) to U(VI). During the contact of U(VI) in solution with U(IV) in resin, an exchange reaction occurs, in which ²³⁵U is slightly concentrated in solution and ²³⁸U in resin phase. Since increase of temperature accelerates the exchange reaction, the apparent thermodynamic values of the exchange reaction were calculated, by taking into account the variation of the apparent equilibrium constant as a function of the reciprocal value of the temperature. The corresponding thermodynamic values in both pure aqueous and water-glycerine solution are: ΔH⁰=6.45 cal.mol^-1 and ΔS⁰=21.6x10^-3 cal.⁰K^-1. The use of glycerine containing solutions offers the important advantage to increase the stability versus hydrolysis of the ferric ions even at higher temperature