Lawrence Berkeley National Laboratory

Diphosphonic acid ligands such as HEDPA (1-hydroxyethane-1,1-diphosphonic acid) have been found to have superior complexation properties in acidic media over carboxylic acids. Consequently, they have been incorporated in a number of actinide separation processes: for example, surface decontamination and solvent extraction. Though these systems are well understood in the acidic region, relatively little work has been carried out with regards to the interaction between these ligands and metals in neutral and alkaline solutions. Recently we have started studies on the coordination of HEDPA with uranyl(VI), with emphasis on the complexation in neutral to basic solutions. Thermodynamic results from potentiometry and calorimetry and structural information from spectroscopic techniques are presented.