Lawrence Berkeley National Laboratory

HEDPA (1-hydroxyethane-1,1-diphosphonic acid) and other diphosphonic acids are remarkably strong chelating agents in moderately acidic solutions and have found applications in separations and HEDPA has also been identified as a promising candidate for the decorporation of uranium from the human body. Consequently, the coordination chemistry of the lanthanides and actinides with HEDPA has been studied extensively in acidic solutions, and to a lesser extent at physiological pH. However, no studies have been carried out on the complexation of HEDPA with uranyl(VI) at higher pH. In this work, potentiometry and calorimetry were used to determine the thermodynamic parameters of the complexation of uranyl(VI) with HEDPA over a wide pH range. Spectroscopic techniques, including NMR, Laser-induced fluorescence and EXAFS, were used to obtain insight into the nature of the complexes.This work is supported by the Office of Science, Biological and Environmental Research, U.S. Department of Energy under Contract No. DE-AC03-76SF0098 at Lawrence Berkeley National Laboratory and Contract No. W-31-109-ENG-38 at Argonne National Laboratory.