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| Identifiers | |
|---|---|
3D model (JSmol) | |
| ChemSpider |
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| UN number | 2909 |
| |
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| Properties | |
| UH 2O 4 | |
| Molar mass | 304.0424 g mol−1 |
| Related compounds | |
Related compounds | Sulfuric acid Chromic acid Uranium trioxide |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Uranyl hydroxide is ahydroxide ofuranium with the chemical formula UO2(OH)2 in the monomeric form and [(UO2)2(OH)4]2- in the dimeric; both forms may exist in normal aqueous media. In aerobic conditions, up to 5 hydroxides can bind to uranyl ([(UO2)2(OH)5]3-). Uranyl hydroxide hydrate is precipitated as acolloidalyellowcake from oxidized uranium liquors near neutral pH.[citation needed]
Uranyl hydroxide was once used in glassmaking andceramics in the colouring of thevitreous phases and the preparation of pigments for high temperature firing. The introduction ofalkaline diuranates (likesodium diuranate) intoglasses leads to yellow by transmission, green by reflection; moreover these glasses becomedichroic andfluorescent underultraviolet rays.[citation needed]
Uranyl hydroxide isteratogenic andradioactive.[citation needed]
The formation of uranyl hydroxide hydrate can occur via hydrated uranyl fluoride [(UO2F2)(H2O)]7·4H2O which is not stable at an elevated water vapor pressure. A complete loss of fluorine is undergone and the formation of uranyl hydroxide hydrate ([(UO2)4O(OH)6]·5H2O) occurs. This uranyl hydroxide species is structurally similar to the uranyl hydroxide hydrate minerals schoepite and metaschoepite. X-ray diffraction data was gathered and found that this species has expanded interlayer spacing suggesting there may be additional water molecules in between uranyl layers. Unlike metaschoepite, however, this species does not form UO2(OH)2 upon dehydration.[1]
UO2(OH)2 reacts with water in a hydration reaction to form [(UO2(OH)2)(H2O)]+ and the monohydrate form also reacted with water to form dihydrates [(UO2OH)(H2O)2]+ and trihydrates [(UO2OH)(H2O)3]+. The hydration reaction to form the monohydrate was significantly slower than if the hydroxide were replaced with acetate or nitrate. This could be due to the strongly basic (OH)− reducing the Lewis acidity of U or because the more complex acetate and nitrate anions provide more degrees of freedom. However, it was found that the formation of the dihydrate uranyl hydroxide hydrate (2) was nearly three times faster than the monohydrate (1).[2]
A mechanism for oxygen exchange between the UO22+ cations in a highly alkaline solution was proposed and investigated by Shamov et al. in theJournal of the American Chemical Society. An equilibrium between [UO2(OH)4]2- and [UO2(OH)5]3- was observed followed by the formation of the stable [UO3(OH)3·H2O]3- intermediate that formed from [UO2(OH)5]3- via intramolecular water elimination.[3]
