Kinetics of reaction between Np(VI) and hydroxysemicarbazide in nitric acid solution

The effects of c(HSC), c(H⁺), c(Fe³⁺), c(UO²⁺2⁾, ionic strength and temperature on the reduction rate of Np(VI) by hydroxysemicarbazide (HSC) were investigated. The results show that Np(VI) can be rapidly reduced to Np(V) by HSC. The reaction rate of Np(VI) with HSC can be accelerated by increasing concentration of HSC and temperature, decreasing concentration of HNO₃ and ionic strength. The kinetic equation for the reduction of Np(VI) by hydroxysemicarbazide is: -dc(Np(VI))/dt = kc(Np(VI))c^2.52 (HSC)c^-0.53 (H⁺) · c^-0.61 (NO^-₃) where k = (1037 ± 60) (mol/L)^-1.40 · s^-1 at 4.00℃. The activation energy is E_a = (64.03 ± 6.4) kJ/mol. No significant effect on the reduction of Np(VI) by hydroxysemicarbazide is observed when the concentration of Fe³⁺ is less than 1 × 10^-3 mol/L or in the presence of UO²⁺₂. (authors)