Thermodynamical and Structural Study of Protactinium(V) Oxalate Complexes in Solution

The complexation of protactinium(V) by oxalate is studied by X-ray absorption spectroscopy (XAS), capillary electrophoresis coupled with ICP-MS (CE-ICP-MS ) and solvent extraction. XAS measurements show unambiguously the presence of a short single oxo-bond. CE-ICP-MS results indicate the formation of a highly charged anionic complex. The formation constant of PaO(C2O4)+, PaO(C2O4)2– and PaO(C2O4)33– are determined from solvent extraction data by using protactinium at tracer scale (CPa < 10–10M) and different temperatures. Complexation reactions of Pa(V) with oxalate are found to be exothermic with relatively high positive entropic variation.