First separation of Ln(III) using an inorganic nanofiltration membrane has been achieved. Ln(III) ions are strongly repelled by the ZrO(2)/TiO(2) membrane. When diethylenetriaminepentaacetic acid (DTPA) is used as water soluble complexing agent, the complexes formed with Ln(III), surprisingly passes through the membrane. The stability constant of DTPA with Eu(3+) is higher than the one with La(3+). Thus [EuDTPA](2-) complex is formed at lower pH than [LaDTPA](2-) and so these two elements can be separated. With an equimolar mixture of Eu(3+) and La(3+), a La(3+)/Eu(3+) separation factor of 2.5 is obtained at pH 1.9. Other polyaminocarboxylic acids have been used such as EDTA and HEDTA and similar phenomenon occur. The best La(3+)/Eu(3+) separation factor has been obtained with HEDTA. In that case, the La(3+)/Eu(3+) separation factor is 7.5 at pH 2.3. All these ligands have been also evaluated with a TiO(2) nanofiltration membrane and results are comparable. (C) 2009 Elsevier B.V. All rights reserved.