Spectroscopic study of acetohydroxamic acid (AHA) hydrolysis in the presence of europium. Implications in the extraction system studies for lanthanide and actinide separation

Acetohydroxamic acid (AHA) has been widely used in the development of reprocessing processes for spent nuclear fuel (SNF) due to its ability to form hydrophilic complexes preferentially with tetravalent metals and to contribute to the control of their oxidation states. It is also well known that AHA undergoes hydrolytic degradation under acidic conditions used during reprocessing. In spite of the wide variety of already published studies concerning the use of AHA, a further analysis of the effect of its hydrolysis on the metal complexing capacity of the extraction system is still needed. In this work we present a spectroscopic study (Raman and fluorescence emission) with the aim of analyzing not only the hydrolysis of AHA in the presence of europium (Eu), but also the effect of its degradation with regard to the global extraction system behavior. Particularly, we have focused on the actinides (An) stripping from lanthanides (Ln) in a EURO-GANEX process. To analyze these effects we have first measured the influence on the An/Ln separation factor. Then, the hydrolysis rate constant and Eu(III) fluorescence as a function of the AHA hydrolysis time have been evaluated to explain these effects. Our results show a decrease in DM(III) values that should be considered for all those studies of process development taking more than 24 hours. An increase in the Eu complexation in the aqueous phase as a function of time has also been observed, which is not directly associated with the formation of AHA hydrolysis products. This behavior predicts that AHA degradation could have an additional effect on the coordination of some Ln when it is employed for An/Ln separation.