Investigation of U(VI), Th(IV), and Eu(III) ions' sorption behavior onto silica gel modified with anhydride

Modification of silica gel by butanedioic anhydride (SiO₂–BDAH) results in efficient adsorbents for removal of U(VI), Th(IV), and Eu(III) from aqueous solutions. SiO₂–BDAH was characterized by Fourier Transform infrared spectroscopy, elemental analysis, N₂ adsorption–desorption isotherms, thermogravimetic analysis, and potentiometric titration. The effect of contact time, pH, and initial concentration of radioactive solutions and temperature on the adsorption capacity of the sorbent was investigated. The sorption equilibrium times of U(VI), Th(IV), and Eu(III) onto SiO₂–BDAH were 1.5, 2, and about 10 h. The sorption percentages of U(VI), Th(IV), and Eu(III) increased with increased pH from 1 to 5. The sorption process of U(VI), Th(IV), and Eu(III) can be described by the Langmuir model, with sorption capacities of 5.10 × 10⁻⁵, 5.06 × 10⁻⁵, and 3.44 × 10⁻⁵ mol/L, respectively. The enthalpy and entropy changes were all positive, whereas the free energy changes were negative. This study indicated that SiO₂–BDAH can remove U(VI) and Th(IV) at the same time in the presence of multiple ions from waste water quickly.