Change in Sorption Characteristics of Uranium during Crystallization of Amorphous Iron Minerals

摘要

Sorption behavior of uranium (Ⅵ) during crystallization of amorphous iron (A.Fe) minerals to crystalline iron (C.Fe) minerals have been investigated. Two different sorption conditions are applied for the experiments. One is the condition in which uranium is sorbed on A.Fe minerals before the crystallization (dynamic condition). The other is the condition in which uranium is sorbed on the A.Fe minerals and C.Fe minerals of goethite (static condition). Associations of uranium with the iron minerals are examined by a selective extraction test using a 1 M CH_3COOK solution at pH 7, 1 M CH_3COONa solution at pH 5 (Morgan's solution), and TAO solution (10.9 g·l~(-1) oxalic acid+16.1 g·l~(-1) ammonium oxalate). Under the static condition, the fraction of uranium desorbed by a 1 M CH_3COOK solution at pH 7 from A.Fe minerals is lower than that from goethite. And all of uranium are desorbed by the TAO solution from both A.Fe minerals and goethite. Contrary, under the dynamic condition, fractional uranium is remained after the TAO solution extraction. The fractional uranium remained after the TAO solution extraction from the iron minerals increases with increase in the crystallinity of the iron minerals. The concentrations of uranium in the solutions are less than 1%. These show that during the crystallization of amorphous to crystalline iron minerals most of uranium associated with the amorphous iron minerals is not released into the solution, and some fractional uranium move to be fixed to crystalline iron minerals.