Design anion regulated layered double hydroxide and explore its theoretical mechanism of immobilizing uranium

Abstract

It is momentous to comprehensively understand the anion’s effect during the formation of Mg-Al layered double hydroxide (LDH), especially relating to the long-term disposal of uranium-containing (UO22+) residue. In this research, the CO32-, PO43- and SO42- anions were inserted into the LDH’s interlayer driven by its reconstructive memory effect. The UO22+ removal capacity increased in order (typically SO42- < PO43- < CO32-). This was further confirmed by the bond length of U-S, U-P and U-C data acquired by theoretical calculation. The SEM-EDS showed anion-regulated LDH materials got fleecy and facilitated the insertion of anions. The increased average pore size and volume of calcined LDH provided convenient access for anions to easily enter interlayer. XRD results showed inserted interlayer anions could increase the interlayer spacing and expose more active sites, which was conducive to the removal of UO22+. The FTIR combined with theoretical calculation results certified anions could grasp UO22+. XPS results gave a compelling evidence that the amount of anion insertion was proportional to UO22+ removal capacity. In short, the anions could significantly improve LDH to the removal of UO22+ by the mechanism of surface and interlayer complexation. What was discovered can better evaluate the environmental behavior of UO22+ influenced by anion factors.