Investigation of the Interaction between 1-Hydroxyethane-1,1‘-diphosphonic Acid (HEDP) and Uranium(VI)

A detailed study, using a panel of spectroscopic analytical methods, of the complexation between 1-hydroxyethane-1,1‘-diphosphonic acid (HEDP) and uranyl ion (UO₂²⁺) is reported. Results suggest that the metal complex is present as only 1:1 (metal/ligand) species at low concentration (<10^-4 M). The conditional constants of this complex were determined at various pH using time-resolved laser-induced fluorescence (TRLIF) and electrospray ionization mass spectrometry (ESI-MS). Further investigations indicate the presence of a 1:2 (metal/ligand) complex at higher concentrations (∼10^-2 M). Selectivity studies as well as structural aspects are presented.