Separation of ²³⁹U(IV) and ²³⁹U(VI) by HPLC

Abstract

The oxidation states of 239 U formed by the 238 U(n,y) 239 U nuclear reaction have been determined in various solid salts by HPLC. Optimal conditions of separation were obtained with an equimolar (0.125 M) solution of oxalic and nitric acids. U(IV) and U(VI) are eluted within 3.6 and 9 min., respectively.

Chemical Effects of the 238U(n,y)239U Reaction and of the 239U→β– 239Np Decay in Solid Uranium Compounds

“…It is deduced that in 0.125 Μ oxalic acid solutions, neglecting the ionic strength effects, the most abundant complexes are the following: 99% U(C 2 0 4 )r for U(IV), 93% U0 2 (C 2 0 4 )r for U(VI), 99% Np(C 2 0 4 )r for Np(IV) and 58% Np0 2 (C 2 0 4 )|" for Np(V). As discussed previously [16], the stronger adsorption of U0 2 + on the column as compared to U 4+ arises from steric hindrance factors, as the former ion can only accommodate 3 oxalato ligands while the latter is complexed by 4 oxalato groups, with the same total negative charge.…”

“…The HPLC assembly and the experimental procedure have been described previously [16]. The activity of the eluted 239 U(IV), 239 U(VI), 239 Np(IV) and 239 Np(V) fractions was measured by γ spectrometry using a Nal(Tl) scintillator.…”

“…The high retention in ammonium diuranate is unexpected [16]. The structure of this compound is not well known, but it is suspected that the ammonium group is not directly bound to the uranium atom [25].…”

“…This proportion increases in the order oxalate < acetate < formate. In ammonium diuranate, the striking absence of reducing effects due to the ammonium ions for the 239 U [16], is no more found during the 239 Np speciation, as 43% of 239 Np end up in the form of Np(IV). Quite generally, in the presence of inorganic ions, the proportion of the reduced 239 U(IV) form is very small; the fraction of 239 Np(IV) is only slightly higher.…”