DETERMINATION OF THE CONCENTRATION OF U(IV) AND U(VI) IN ANOXIC LEACHING SOLUTIONS OF URANIUM-DIOXIDE

Anoxic leaching of uranium dioxide, with stoichiometry UO2.2 in thin a ltered surface layers, leads to a mixture of U(IV)-U(VI) in near neutr al aqueous solutions. The Uranium oxidation states have been separated using a chromatographic method based on the exchange of uranium chlor ocomplexes between HCl 4.5 M and the anionic exchanger Dowex 1. This m ethod does not change the initial U(IV)-U(VI) ratio. The concentration of U(VI) was measured in the range of 10(-10) to 10(-8) M using laser fluorescence spectroscopy. U(IV) is not oxidized by tracer amount of Fe(III) or O2 at pH 5.5 over a 3 weeks leaching period. neither by Fe( III) 10(-5) M even after 2 weeks, In contrast, oxic leaching gives onl y U(VI). The results are interpreted according to the behaviour of ura nium at tracer level concentration.