Separation of lanthanides(III) by inorganic nanofiltration membranes using a water soluble complexing agent

First separation of Ln(III) using an inorganic nanofiltration membrane has been achieved. Ln(III) ions are strongly repelled by the ZrO2/TiO2 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 Eu3+ is higher than the one with La3+. 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 Eu3+ and La3+, a La3+/Eu3+ 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 La3+/Eu3+ separation factor has been obtained with HEDTA. In that case, the La3+/Eu3+ separation factor is 7.5 at pH 2.3. All these ligands have been also evaluated with a TiO2 nanofiltration membrane and results are comparable.