MECHANISM OF REDOX DISSOLUTION OF TRANSURANIUM AND RARE-EARTH DIOXIDES .1. FORMAL KINETICS OF CERIUM DIOXIDE REDUCTION WITH IRON(II)

Stoichiometry and formal kinetics of cerium dioxide reduction with Fe( II) in sulfuric acid solutions have been systematically studied. In Ce O2 + Fe(II) reaction, one mole of Fe(II) is consumed per mole of CeO2. The initial reaction rate is described by the equation -(d[Fe(II)]/d tau)(tau-->0) = -(d{CeO2}/dtau>)-->0 = (k')(eff){CeO2})[Fe(II)](0)a(+H 2SO4) in the region {CeO2}, [Fe(II)] = (0.03-7)x 10(-2) M, [H2SO4] = 0 .5-2 M, and t = 10-40 degrees C. With {CeO2}(0) [Fe(II)](0) = (0.03-1. 0)x 10(-2) M, the activation energy, activation free energy, and activ ation enthalpy are equal to 59+/-3 kJ mol(-1), 80.8+/-1.2 kJ mol(-1) a nd -81 J mol(-1) K-1, respectively. With [H2SO4] = const and {CeO2}, [ Fe(II)] = (1-7) x 10(-2) M, the dissolution process can be formally de scribed both in terms of mass: -(d{CeO2}/d tau)(tau greater than or eq ual to 0) = k'(eff){CeO2}tau[Fe(II)](tau), and in terms of surface:-(d {CeO2}/d tau)(tau greater than or equal to) = k(eff)(''){CeO2}(2/3)(ta u)[Fe(II)]tau.