Competitive sorption of Cu(II), Eu(III) and U(VI) ions on TiO2 in aqueous solutions—A potentiometric study

The competitive sorption of Cu(II), Eu(III) and U(VI) ions in aqueous solutions by TiO2, has been investigated by potentiometry at I = 0.1 M NaClO4, 25 °C and under atmospheric conditions. For Cu(II) ions the investigation was performed directly by means of a Cu2+ ion selective electrode, whereas for the Eu(III) and U(VI) ions indirectly based on competition reactions between the Cu(II) ion and the Eu(III) and U(VI) ions. Numerical analysis of the experimental data supports the formation of inner-sphere surface complexes and allows the evaluation of the formation constant of the (TiO)2Cu, which is found to amount to log β* = 4.3 ± 0.4. Addition of competing Eu(III) and U(VI) ions in the aqueous system leads to replacement of the Cu(II) by the competitor metal ion. Evaluation of the potentiometric data obtained from competition experiments indicates on an ion exchange mechanism. The formation constant of the Eu(III) and U(VI) species adsorbed on TiO2 is found to be log β* = 4.4 ± 0.7 and 4.8 ± 0.8, respectively. The relative affinity of the TiO2 surface for the metal ions under investigation is U(VI) > Eu(III) > Cu(II).