Kinetics of Reduction of Np(Ⅴ) by U(Ⅳ) Ions in Nitric Acid Media

The reduction of NpO⁺₂ to Np⁴⁺ by U(Ⅳ) in nitric acid solution has been studied by spectrophotometric method, and the rate equation is described by: -dc(Np(Ⅴ))/dt=kc(Np(Ⅴ))c^0.7 (U(Ⅳ))c^1.9 (H⁺)c(NO^-₃) where  k =(6.37±0.49)×10^-3 L^3.6/(mol3.6•min) at 25℃. The activation energy is estimated to be 60.13 kJ/mol. U(Ⅵ) with the concentration of 0-4.2×10^-2 mol/L has little effect on the reaction. The possible mechanism is discussed.