Comment on "Behaviour of Europium(III) and its Hydroxo and Carbonate Complexes in a Solvent Extraction System with HDBM in 2 M NaCl at 303 K" by M. Jiménez-Reyes, M. Solache-Rios and A. Rojas-Hernández.

In a recent paper [1] the hydrolysis and carbonate complexation of Eu(III) was studied by potentiometric titration of 2 ´ 10-4 M Eu(III) solutions in the range pH = 7 - 13. Under the experimental conditions applied in this study, the Eu(III) concentration exceeds the solubility of Eu(OH)3(s) or EuOHCO3(s) by several orders of magnitude. The formation constants derived for numerous aqueous Eu(III) hydrolysis species and ternary hydroxo-carbonate complexes constants must be considered as erroneous. They are the result of misinterpreting the formation of solid Eu(III) particles as hydrolysis or carbonate complexation in solution.