| Carboxylic acids have played an important role in the field of actinide (An) and lanthanide (Ln) separations and the reprocessing of irradiated nuclear fuel. Recent bench-scale experiments have demonstrated that 3-carboxy-3-hydroxypentanedioic acid (citric acid) is a promising aqueous complexant that can effectively aid in the separation of transition metals from f-element mixtures. Furthermore, citric acid was found to be a suitable buffer for the nitrogen donating ligand diethylenetriamine-N,N,N',N'',N''-pentaacetic acid (DTPA) which has a higher complexation affinity for An over Ln.;The complexation of Ln and An with anions of citric acid and DTPA have been previously studied with conflicting results regarding the coordination of metal ions between carboxylic groups, the feasibility of protonated metal complexes, and the formation constants themselves. Using potentiometry, spectrophotometry, microcalorimetry, and specific ion interaction modeling, we investigated metal complexes of citric acid and DTPA with selected trivalent and tetravalent Ln and An ions. The complexes were investigated with respects to stability constants, thermodynamics of complexation, oxidation states, the concentration of electrolyte, ligand size, and metal ionic radius. |
