Co–Fe, Ni–Fe, and Zn–Ti Layered Double Hydroxides for Sorptive Extraction of U(VI) From Aqueous Solutions of Medium Salinity

The paper describes the synthesis of sorbents based on Co–Fe, Ni–Fe, and Zn–Ti layered double hydroxides (LDHs) obtained by the most reproducible and environmentally benign homogeneous co-precipitation method. This method provide dispersed materials with a particle size of not more than 10 μm and crystallite size of up to 10 nm for Co–Fe and Ni–Fe LDHs. This combination of transition metals gives rise to compounds possessing mechanical and chemical stability in harsh media and actively participating in redox reactions in the liquid phase. The physicochemical and sorption properties of the obtained materials were studied, regarding the removal of uranyl ions U(VI) from aqueous solutions, including salt solutions such as Na₂CO₃, Na₂SO₄, KNO₃, NaCl, K₃PO₄, and NaHCO₃ containing competing ions. The removal efficiency of uranyl ions from the salt solutions reached 99% and the partition ratios K_d were up to 10⁵ mL/g, indicating high selectivity to the extracted component. The Co–Fe LDH demonstrated the highest maximum sorption (G_max) of 101.6 mg/g in seawater and 114.1 mg/g in distilled water. The plots for the residual content of uranyl ions after the sorption as a function of the total volume of the starting solution that passed through the column are presented; the curves reach a plateau for Co–Fe and Fe–Ni LDH samples, which is caused by the saturation of the material with the extracted component. The total dynamic sorption capacity of the LDH-based sorption materials reaches 101.4 mg/g for Co–Fe LDH sample and only 40.2 mg/g Zn–Ti LDH. According to the results, the obtained materials based on Co–Fe, Ni–Fe, and Zn–Ti layered double hydroxides have a considerable potential for the sorptive extraction of uranyl U(VI) ions from aqueous solutions of medium salinity.