Kinetics of tetravalent plutonium oxidation by cerium (4)

Stoichiometry and kinetics of the Pu(4) + Ce(4) reaction is studied by spectrophotometric method at 5-30 deg C in nitric acid solutions (μ=[HNO3]+[NaNO3] = 1.0 - 5.7; [Ce(4)] = 5.10-5 - 1.2.10-3 g-ion/1, [Pu(4)] =1.10-5 - 8.5.10-4 g-ion/1. Oxidation of one Pu(4) ion to a hexavalent state requiers two Ce(4) ions. The plutonium oxidation is not is not complicated by by-processes. Reverse Ce(3) + PuO2+ reaction does not contribute essentially to the process at [Ce(3)] 2.6.10-2 g-ion/1. The reaction rate obeys the kinetic equation - d[Pu(4)]/dt = ksub(eff)[Pu(4)][Ce(4)]/a sub(+-HNO3). The thermodynamical activation parameters are found for solutions at the varied nitric acid concentrations:ΔGsup(not equal) = 17.0+-0.2 and ΔHsup(not equal) = 21.8+-2 kcal/mole(μ=1.0); ΔGsup(not equal) = 19.1+-0.1 and ΔHsup(not equal) = 23.1+-1 kcal/mole(μ=4.9). The reaction mechanism is discussed in terms of the theory of absolute reaction rates and the model of long-range charge transfer