Leaching Peculiarity of Uranium-Containing Layered Double Hydroxide Sediment Varied with Environmental Anions

In this research, we focus our attention on the leaching peculiarity of uranium-containing Mg-Al layered double hydroxide (LDH) which is one kind of waste sediment in uranium tailings, generated by the alkalinization of uranyl raffinate. The effect of inorganic (CO₃^2-, SO₄^2-, PO₄^3-) and organic (C₂O₄^2-, C₆H₆O₇^2-, C₆H₁₆O₂₄P₆^2-) anions were investigated. Atomic force microscopy result showed that the thickness of CO₃^2--LDH increased to 8.6 nm compared to original LDH whose thickness was 6.7 nm. Compared with the control sample (5.58 μm), the grain size with C₆H₁₆O₂₄P₆^2- anion grew to 7.04 μm. A large amount of CO₃^2- can stay in LDH, up to 1.78 mol percent, while the C₆H₁₆O₂₄P₆^2- anion was only 0.41 mol percent. X-ray diffraction results showed that the anions could change the crystal structure of LDH, especially the C₆H₁₈O₂₄P₆ anion, and theoretical calculation also conformed this result. The leaching tests showed that the introduction of anions improved the leaching efficiency of UO₂²⁺ from LDH. The introduction of anions destroyed the super buffer property of LDH. Theoretical calculation results indicated that the anions could grab UO₂²⁺ and help the UO₂²⁺ escape from the LDH. This research gave guidance for long-term disposal of uranium-containing tailings.