Efficiently immobilizing uranium (VI) by oxidized carbon foam

Abstract

Oxidized carbon foam (oxidized CF) was prepared by using a facile chemical oxidation treatment at relatively low temperature of 450 °C and applied to capture uranyl cation [U(VI)] from aqueous solutions. The effects of pH, contact time, initial U(VI) concentration, and temperature on the U(VI) absorption performance of oxidized CF were investigated by batch experiments. The oxidized CF was illustrated to exhibit fast sorption kinetics (92% removal within 15 min and 98% removal in 2 h) and high sorption capacity (305.77 mg g−1 at pH 5) toward U(VI). Integrated analyses combining energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy were applied on the U(VI)-loaded oxidized CF, showing the introduction of carboxyl groups as U(VI) sorption sites on the surface of CF after oxidation treatment. Furthermore, extended X-ray absorption fine structure spectroscopy was employed to identify the binding modes of U(VI) indicating that each UO22+ cation is coordinated with one or two carboxyl groups on the equatorial plane. Notably, the low content of U(VI) in wastewater can be efficiently immobilized by the oxidized CF, and the immobilized U(VI) can be further concentrated and converted into Na2U2O7 or U3O8 by a simple sintering step. These findings presented in this work suggest the potential of using oxidized CF for further treatment of low concentration wastewater containing U(VI).