Ternary complex formation of Eu(III) and Am(III) with pyridine-2,6-dicarboxylate in aqueous solutions

Abstract

Ternary hydroxo complex formation of Eu(III) with pyridine-2,6-dicarboxylate (PDA) was investigated by potentiometry and fluorescence spectrophotometry. Curves of equilibrium pH versus amount of OH − added showed that the pH for the precipitation of Eu(III) was decreased due to the formation of ternary hydroxo complex, EuOHL(s) (L = PDA), which was confirmed by the enhancement of fluorescence intensity of Eu(III) in precipitate with PDA excitation wavelength. The ternary hydroxo complex species was also confirmed by the analysis of concentrations of the Eu(III), OH − and PDA in the precipitate. Solubility products of EuOHL(s) and Eu(OH) 3 were determined as p K sp 0 = 19.2 ± 0.2 and 24.5 ± 0.1, respectively. Similar behavior for the ternary hydroxo complex formation was observed for trace 241Am(III) added to Eu(III).