Superior sorption capacities of Ca-Ti and Ca-Al bimetallic oxides for U(VI) from aqueous solutions

Herein the novel natural bimetallic oxides of perovskite oxides (CaTiO_x) and calcium aluminum oxides (CaAlO_x) were fabricated by one-step calcination-oxidation process under air conditions and were characterized using zeta potential, FT-IR, SEM, TEM, XRD, and XPS techniques. Porous and cotton-shaped irregular surface morphologies of CaTiO_xand CaAlO_xcould provide excellent active sites and large specific surface area for the removal of U(VI) from wastewater. Based on FT-IR, XRD and XPS analyses, the enrichment of U(VI) was attributed to the abundant adsorption sites (e.g., M-O groups) of CaTiO_xand CaAlO_x. The consequences demonstrated that the sorption of U(VI) on CaTiO_xand CaAlO_xwere strongly dependent on pH and weakly dependent on ionic strength at pH < 4.0, while strongly dependent on pH and ionic strength at pH > 4.0. The accordance of sorption kinetic data with the pseudo-second order model suggested that the sorption reaction was multi-stage controlled chemical process. The sorption isotherms of U(VI) can be satisfactorily simulated by the Langmuir model and the maximum monolayer sorption capacities of U(VI) were 241.71 mg·g⁻¹on CaTiO_xand 258.29 mg·g⁻¹on CaAlO_xat 298.15 K. In addition, the thermodynamic results pointed out that the sorption reaction was spontaneous and endothermic process. The sorption mechanism was interpreted as surface complexation and electrostatic interactions. The results demonstrated that CaTiO_xand CaAlO_xcould be widely used as promising and cost-effective materials for the treatment of U(VI) of aqueous solutions in environmental management and pollution prevention and cure.