The reduction of plutonium and neptunium ions by acetaldoxime in nitric acid

Abstract

The rate equations for the reduction of Np(V), Np(VI) and Pu(IV) ions by acetaldoxime in nitric acid have been determined as: -d[Np(V)]/dt = k 26 [Np(V)][CH 3 CHNOH][HNO 3 ] 1.2 - d[Np(VI)/dt = k 19 [Np(VI)][CH 3 CHNOH]/[HNO 3 ] - d[Pu(IV)/dt = k 6 [Pu(IV)] 2 [CH 3 CHNOH] 1.1 /[Pu(III)][HNO 3 ] 2.2 where respectively: k 26 = (9.2±0.2)×10 -4 l 2.2 mol -2.2 min -1 at 60° C; k 19 = 254±10 min -1 at 26.0° C; k 6 = 25.3±1.9 mol 1.1 l -1.1 min -1 at 19.5°C. The activation energies were found to be: E 19 = 62.6±2.6 kJmol -1 and E 26 = 87.7±9.8 kJmol -1 . Np(V) was generally found to be stable for long periods in nearly all the kinetic experiments and the reduction of Np(V) to Np(IV) could only be studied at elevated temperatures and reactant concentrations. Possible reaction mechanisms for the reduction of Np(VI) and Pu(IV) have been suggested; proceeding, in both cases, via the hydrolysis product and an intermediate CH 3 CHN¤O radical. Simple solvent extraction experiments have shown that Np(VI) and Pu(IV) can be reductively stripped from 30% TBP/n-dodecane in the presence of U(VI).