Uranium sorption on oxyhydroxide minerals by surface complexation and precipitation

During the chemical weathering of the uranium mill tailings, released uranium could be immobilized by the newly formed secondary minerals such as oxyhydroxides. A deeper understanding of the interaction between uranium and common oxyhydroxides under environmental conditions is necessary. In this work, uranium sorption behaviors on Al-, Mn- and Fe-oxyhydroxide minerals (boehmite, manganite, goethite, and lepidocrocite) were investigated by batch experiments. Results showed that the uranium sorption on Al-oxyhydroxide behaved significantly differently from the other three minerals. The sorption edge of the Mn- and Fe-oxyhydroxides located around pH 5, while the sorption edge of boehmite shifted about 1.5 pH unit to near neutral. The sorption isotherms of uranium on manganite, goethite and lepidocrocite at pH 5.0 could be well fitted by the Langmuir model. Instead of surface complexation, sorption on boehmite happened mainly by uranium-bearing carbonates and hydroxides precipitation as illustrated by the characterization results. Both carbonate and phosphate strongly affected the uranium sorption behavior. The removal efficiency of uranium by boehmite exceeded 98% after three sorption-desorption cycles, indicating it may be a potential material for uranium removal and recovery. (C) 2022 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.