Uranium sulfate
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3D model (JSmol)
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| U(SO4)2 | |
| Molar mass | 430.15 g/mol |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Uranium sulfate (U(SO4)2) is a water-soluble salt of uranium. It is a very toxic compound. Uranium sulfate minerals commonly are widespread around uranium bearing mine sites, where they usually form during the evaporation of acid sulfate-rich mine tailings which have been leached by oxygen-bearing waters. Uranium sulfate is a transitional compound in the production of Uranium hexafluoride. It was also used to fuel aqueous Homogeneous Reactors.
Uranyl sulfate in solution is readily reduced to uranium(IV) sulfate. The photoreduction can be carried out in the sunshine and this requires the addition of ethanol as a reducing agent. Uranium(IV) crystallizes or is precipitated by ethanol in excess. It can be obtained with different degrees of hydration. U(SO4)2 can also be prepared through electrochemical reduction of U(VI) and the addition of sulfates. Reduction of U(VI) to U(IV) occurs naturally through a variety of means, including through the actions of microorganisms. Formation of U(SO4)2 is an entropically and thermodynamically favorable reaction.
In situ leaching (ISL), a widespread technique used to mine uranium, is implicated in the artificial increase of uranium sulfate compounds. ISL was the most widely used method to mine uranium in the United States during the 1990s. The method involves pumping an extraction liquid (either sulfuric acid or an alkaline carbonate solution) into an ore deposit, where it complexes with the uranium, then removing the liquid and purifying the uranium. This synthetic addition of sulfuric acid unnaturally raises the abundance of uranium sulfate complexes at the site. The lower pH caused by the introduction of acid increases the solubility of U(IV), which is typically relatively insoluble and precipitates out of solution at neutral pH. While oxidation states for uranium range from U3+ to U6+, U(III) and U(V) are rarely found, and U(VI) and U(IV) predominate. U(VI) forms stable aqueous complexes and is thus fairly mobile. Preventing the spread of toxic uranium compounds from mining sites often involves reduction of U(VI) to the far less soluble U(IV). The presence of sulfuric acid and sulfates prevents this sequestration, however, by both lowering the pH and through the formation of uranium salts. U(SO4)2 is soluble in water, and thus far more mobile. Uranium sulfate complexes also form quite readily.
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