Bifunctional Amidophosphonate Molecules for Uranium Extraction in Nitrate Acidic Media

Bifunctional amidophosphonate derivatives, already known as efficient ligands in uranium extraction from phosphoric media, have been evaluated and compared to the conventional tri-n-butyl phosphate (TBP) for uranium extraction from nitrate medium. The efficiency of U extraction and its selectivity towards competing elements such as Th, Zr, Mo, Fe, and V was evaluated with various ligand structures. It was found that extractant molecules containing a monosaponified phosphonate moiety instead of phosphonate moieties are less effective and selective. Furthermore, it was observed that the alkylation of the methylene bridge linking the two functional groups prevents the formation of precipitates during the uranium loading. Effects of acidity as well as ligand concentration were also investigated in order to estimate the loading capacity of the molecules. More detailed stoichiometry and transfer energy were further determined by the slope analysis method and a thermodynamic study. The possible uranium recovery from the organic phase has moreover been demonstrated thanks to stripping steps at low nitric acid concentration.