Rate determining step of reduction Np(VI) by organic reagents from 30%TBP/Kerosene to nitrate solution

Abstract

A series of single stage trials were conducted using six reducing reagents to investigate the rate determining step during Np(VI) reduction back-extraction from 30%TBP/Kerosene to HNO3 solution under the same conditions. The six reducing reagents included: acetohydroxamic acid, N,N-dimethylhydroxylamine, N,N-diethylhydroxylamine, 2-hydroxyethylhydrazine, methylhydrazine and N,N-dimethylhydrazine. Moreover, the back-extraction of Np(V) from 30%TBP/Kerosene to HNO3 solution without reducing reagent was conducted with the same concentrations of Np and HNO3. The experimental results indicate the rate of Np(VI) reduction in the two-phase system is determined mainly by the rate of Np(V) mass transfer from 30%TBP/Kerosene to HNO3 solution, whose mass transfer kinetics is far slower than previously estimated. The rate determining step is a slow chemical reaction as: NpO2NO3 center dot TBP = NpO2++ NO3- + TBP.