Acetaldoxime - a promising reducing agent for Pu and Np ions in the Purex process

This paper discusses the properties of acetaldoxime as an example of a novel class of salt-free organic reductants for Np and Pu ions, the monoximes. The products of its reactions with Np(VI) and Pu(IV) are Np(V), Pu(III), N{sub 2}O, CH{sub 3}CHO and CH{sub 3}COOH. The rate of the Np(VI) - CH{sub 3}CHNOH reaction is first order relative to both reagents and negative first order relative to HNO{sub 3}. The rate constant is k{sub 1} = 254 {+-} 10 min{sup -1} at 26 deg. C and the activation energy is E = 62.6 {+-} 2.6 kJ/mol. The orders of the Pu(IV) - CH{sub 3}CHNOH reaction for Pu(IV), Pu(III), CH{sub 3}CHNOH and HNO{sub 3} are equal to 2, -1, 1.1 and -2.2, respectively, and the rate constant is k{sub 2} 25.3 {+-} 1.9 M{sup 1.1} min{sup -1} at 19.5 deg. C. The activation energy is 87.7 {+-} 2.8 kJ/mol. The likely mechanisms of these reactions are reviewed. Acetaldoxime is stable in HNO{sub 3} solutions when [HNO{sub 3}]<{approx} 3 M and temperature <{approx} 35 deg. C. When so-called 'critical' conditions are reached (e.g., [HNO{sub 3}] = 3.8 - 3.9 M at 35.5 deg. C) a rapid process of HNO{sub 2} formation and acetaldoxime oxidation occurs. Investigations were implemented to study the kinetics of the acetaldoxime oxidation with HNO{sub 2} when [HNO{sub 3}] < 1.4 M as well as with HNO{sub 3} under 'critical' conditions. (authors)