The transformation of uranyl oxide hydrates: The effect of dehydration on synthetic metaschoepite and its alteration to becquerelite
The U(VI) solid phases schoepite, metaschoepite, and dehydrated schoepite are important reservoirs of mobile uranium in the environment. These simple uranyl oxide hydrates result from weathering of uranium minerals and the corrosion of anthropogenic uranium solids. The authors have studied the role of hydrational water among these phases and in subsequent transformation to other secondary metal-U(VI) oxide hydrates. Synthetic metaschoepite (MS, UO{sub 3}{center{underscore}dot}2.0H{sub 2}O), its dehydrated phases, and its secondary alteration products were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), and high-resolution thermogravimetric analysis (HRTGA). Drying MS at 105 C resulted in the formation of a dehydrated phase (UO{sub 3}{center{underscore}dot}0.9H{sub 2}O) that was structurally distinct from natural dehydrated schoepite (DS, UO{sub 3}{center{underscore}dot}0.75H{sub 2}O) reported by others. Unlike natural DS, their dehydrated material was easily rehydrated, although crystallinity of the rehydrated phase was reduced. The rates of transformation of synthetic MS and dehydrated MS in the presence of Ca{sup 2+} to form becquerelite (Ca[(UO{sub 2}){sub 6}O{sub 4}(OH){sub 6}]{center{underscore}dot}8H{sub 2}O) were determined. Alteration rates were significantly faster when the starting material had been dehydrated. These results are explained in the context of structural aspects of U(VI) solid phases, and the possible impact of hydration on long-term stability of U(VI) oxide hydrates in environmental systems is discussed.
- Research Organization:
- Washington State Univ., Pullman, WA (US)
- Sponsoring Organization:
- US Department of Energy
- DOE Contract Number:
- FC09-96SR18546
- OSTI ID:
- 20000729
- Journal Information:
- Environmental Science and Technology, Journal Name: Environmental Science and Technology Journal Issue: 20 Vol. 33; ISSN ESTHAG; ISSN 0013-936X
- Country of Publication:
- United States
- Language:
- English
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