Studies of U(IV) Oxidation Kinetics in Nitric Acid and TBP Phases

Abstract

V(IV) is an important reagent in current reprocessing plants since it is used to reduce Pu(IV) to Pu(III), therefore, allowing the efficient separation of V and Pu in multi-stage counter-current solvent extraction contactors. The benefits of V(IV) are that it is a kinetically fast reductant and it is a salt free reagent, since V (IV) is oxidised to V (VI) and so does not add to the aqueous waste volumes. Many kinetic reactions ofV(IV) have been studied in the past and these are used by BNFL to model the behaviour ofV(IV) in process flowsheets. However, some reactions have either not been studied or have been previously studied but without conclusive resolution. Therefore, to expand our understanding of V(IV) in the process and to generate data that underpins process models, we are studying a series of V(IV) reactions, and this paper will summarise the results of our kinetic and mechanistic studies.

Molecular modification of a novel macroporous silica-based impregnated polymeric composite by tri-n-butyl phosphate and its application in the adsorption for some metals contained in a typical simulated HLLW

“…In Purex process and its modified process, 30% TBP in hydrocarbon diluent was usually used as an organic phase to extract U(VI) and Pu(VI) from 3.0 M HNO 3 . It was reported a series of the associated formations of TBP with HNO 3 such as HNO 3 ·TBP, HNO 3 ·2TBP, HNO 3 ·3TBP, and HNO 3 ·4TBP have been demonstrated [26][27][28][29][30]. So, the obvious decrease in the concentration of TBP leaked from 1.0 to 5.0 M HNO 3 was ascribed to the effective association of TBP with HNO 3 through hydrogen bonding.…”

Pulse radiolysis study on the reactivity of NO3˙ radical toward uranous(iv), hydrazinium nitrate and hydroxyl ammonium nitrate at room temperature and at 45 °C

“…The oxidation of U(IV) in nitric acid exhibits an initial induction period, in which oxidation of HNO 3 occurs producing HNO 2 , followed by an autocatalytic reaction, in which U(IV) is oxidized by the resulting HNO 2 . 38,73,74  …”