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

Abstract

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 CH3COOK solution at pH 7, 1 M CH3COONa solution at pH 5 (WIorgan's solution), and TAO solution (10.9 gl-' oxalic acidS16.1 g.Z-' ammonium oxalate).Under the static condition, the fraction of uranium desorbed by a 1 M CH3COOK 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 hactional 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.

Dissolution of uranyl microprecipitates in subsurface sediments at Hanford Site, USA

“…The desorption rate of U from laboratory-spiked pristine materials (Fuhrmann et al, 1997;Ohnuki et al, 1997;Giammar and Hering, 2001) and U-contaminated sediments (Braithwaite et al, 1997;Mason et al, 1997) was found to decrease with increasing exposure time to uranium contamination. For example, desorption equilibrium of U(VI) from goethite after aging for 1 month was achieved rapidly, but much slower desorption was observed after aging for 6 months (Giammar and Hering, 2001).…”

Uranium co-precipitation with iron oxide minerals

“…Uranium is not thought to be incorporated into the α-FeOOH (goethite) structure (GERTH, 1990). However, studies report the uptake of U during the formation of crystalline and amorphous Fe oxides (OHNUKI et al, 1997;PLOTNIKOV and BANNYKH, 1997;SATO et al, 1997;BRUNO et al, 1995).…”

“…Uranium sorption and co-precipitation processes with Fe minerals are studied in lieu of repository assessment, nuclear waste treatment and U biogeochemistry (MOYES et al, 2000;OHNUKI et al, 1997;PLOTNIKOV and BANNYKH, 1997;SATO et al, 1997;HOBBS and KARRAKER, 1996;BRUNO et al, 1995;PEARCY et al, 1994;WAITE et al, 1994 and many others). As part of the Poços de Caldas natural analogue study (Brazil), researchers evaluated the co-precipitation and precipitation equilibrium of U(VI) with Fe(III) oxides (BRUNO et al, 1995).…”

Uranium and other trace elements’ distribution in Korean granite: implications for the influence of iron oxides on uranium migration

“…Similarly, Sato et al (1997) reported that the decreasing trend of U content in Fe-(hydr)oxide nodules corresponds to the order of decreasing crystallinity of Fe oxides at the Koongarra U ore deposit site, Australia. Ohnuki et al (1997) also extracted U that had been From the observed facts, we can deduce that the amorphous phases may initially be prominent at immediate uptake of U over their surfaces, but there could be a lack of tight bounding between them due to their low structural stability, leading U to be desorbed during geologic time. Thus, it is not easy for some accumulated U to be found in them.…”