The influence of humic acid on U(VI) sequestration by calcium titanate

The influence of humic acid (HA) on U(VI) sequestration by calcium titanate (CaTiO3) was investigated by batch experiment and spectroscopic techniques. Various characterizations, including zeta potentials, average hydrodynamic diameters, specific surface area and pore volume, have been demonstrated that HA significantly changes the surface properties of CaTiO3. In addition, the obtained results revealed that HA enhanced U(VI) adsorption at pH < 5.0 attributed to the strong electrostatic attraction, the dispersion of particles exposed more adsorption sites and abundant oxygen-groups of surface loaded HA, whereas U(VI) sequestration was inhibited assigned to the stronger electrostatic repulsion between anionic U(VI) species and more negative surface of CaTiO3 at pH > 6.0. XPS analysis showed that the higher sequestration of U(VI) in the existence of HA, which was ascribed to the enhanced dispersity, decreased zeta potential and more abundant surface functional groups of CaTiO3 at low pH. In addition, HA inhibited the reduction of U(VI)-U(IV) at low pH under ambient conditions. These information are significant for the understanding the surface properties of perovskite-type titanate materials and its sequestration performance of uranium in HA-rich environments.