| Abstract: |
Sorption behaviors of neptunium (V) on naturally-occurring magnetite (Fe3O4) and goethite (α-FeOOH) in 0.1M NaNO3 electrolyte solution under aerobic conditions were interpreted using the surface complexation model (SCM). The surface properties of these materials were experimentally investigated by CO2-free potentiometric titration, and SCM parameters for the constant capacitance model, such as protonation/deprotonation constants of the surface hydroxyl group, were determined. The number of negatively charged sorption sites of goethite rapidly increased with the increase of the bulk solution pH compared with that of magnetite and this tendency was similar to the pH dependence of neptunium sorption. This implies that the neptunyl cation, NpO2+, plays a dominant role in possible sorption reactions. Assuming that the dominant surface complex is XO-NpO2, modeling by means of SCM was carried out, and the results were found to agree with experimental data. |
