Unravelling the nature differences of halide anions affecting the sorption of U(VI) by hydrous titanium dioxide supported waste polyacrylonitrile fibers in the presence of carbonates

Abstract

The co-occurrence of halides and carbonates with uranium in the natural water poses a challenge to the uranium recovery for nuclear power due to the potential complexation. Hydrated titanium dioxide (HTD) contains a lot of surface hydroxyl (–OH) groups and waste polyacrylonitrile fiber (WPANF) has the advantages of both weather and chemical resistances. Herein, the nature differences of halide anions affecting the sorption of U(VI) by WPANF/HTD was investigated in the presence of carbonates. The sorption capacity (qe) decreased with the increases of initial pH, total carbonates, and halides but increased at high temperature and initial U(VI) concentration. The U(VI) sorption was a spontaneous chemisorption, which mainly involved surface sorption rather than intra-particle diffusion. The order of inhibitory ability on U(VI) sorption for the four halides was F > I ∼ Br > Cl. The aqueous F− was shown to be the most strongly inhibited with the lowest qe value of 17.2 mg·g−1, due to the formation of U(VI)–F complex anions. The characteristic peaks with weakened relative intensity after U(VI) sorption for the surface –OH groups on HTD (HTD–OH), together with the results from DFT calculations, demonstrated a key role of HTD–OH in U(VI) sorption by WPANF/HTD via the coordination with U(VI) complex anions. This work unravels the nature differences of halide anions affecting U(VI) sorption in the presence of carbonates and provides a valuable reference for the U(VI) extraction toward halogen-rich natural uranium-containing water.