Uranium

Chemical reactions

Reaction of uranium with acids


Uranium is dissolved by acids [3]

U(s) + 2 H+(aq) + 2 H2O(l) UO22+(aq) + 3 H2(g)

U(VI) exist as yellow uranyle ions, UO22+, at [H+]> 10-2 M. At around pH 3, the uranyle ion hydrolyses further and dimerizes to [UO2(OH)]22+. At pH 5 the dominating entity is [(UO2)3(OH)5]+.


Reaction of uranium with air


Uranium reacts wit oxygen, O2, and becomes covered by a thin layer of uranium oxide

3 U(s) + 4 O2(g) U3O8(s) [white]


U(s) + 2 H+(aq) + 2 H2O(l) UO22+(aq) + 3 H2(g)

U(VI) exist as yellow uranyle ions, UO22+, at [H+]> 10-2 M. At around pH 3, the uranyle ion hydrolyses further and dimerizes to [UO2(OH)]22+. At pH 5 the dominating entity is [(UO2)3(OH)5]+.


Reaction of uranium with carbonate


U(VI) is not precipitated by carbonate, but exist as complexes like [UO2(CO3)3]4−. Excess carbonate precipitates the uranyle as UO2(OH)2.


Reaction of uranium with hexacyanoferrate


UO22+ is precipitated by potassium hexacyanoferrate under acidic conditions as (UO2)2[Fe(CN)6] or UO2K2[Fe(CN)6] or a mixture thereof.

2 UO22+(aq) + Fe(CN)64−(aq) (UO2)2[Fe(CN)6](s) (red brown)
(UO2)2[Fe(CN)6](s) + 2 Na+(aq) + 6 OH−(aq) Na2U2O7(aq) + Fe(CN)64−(aq) + 3 H2O(l)


Reaction of uranium with hydrogen peroxide


UO22+ is precipitated by hydrogen peroxide under slightly acidic conditions as UO2(O2)·H2O [yellow]. Under alkaline conditions UO22+ forms peroxouranate ions [UO2(O2)3]4− [yellow/red yellow] or other peroxide ions containing ligands like carbonate, [UO2(O2)2CO3]4−.


Reaction of uranium with hydroxide ions


Uranium is usually unaffected by alkalis [3].


The uranyle ion is precipitated by hydroxide ions.

UO22+(aq) + 2 OH-(aq) UO2(OH)2(s) [yellow]

Excess hydroxide ions converts the uranyle to di- and polyuranates

UO2(OH)2(s) + 2 Na+(aq) + 2 OH−(aq) Na2U2O7(aq) + 3 H2O(l)


Reaction of uranium with metals/metal ions


UO22+ is only reduced to U(IV) by strong reducing agents like Zn

UO22+(aq) + Zn(s) + 4 H+(aq) U(IV)(aq) + Zn2+(aq) + 2 H2O(l)


Reaction of uranium with sulfide


Uranyle is not precipitated by sulfide at 0.4 M hydrochloric acid.


Reaction of uranium with water


Finely divided uranium reacts with liquid water and oxygen free water vapor [4]

U(s) + 2 H2O(l) UO2(s) + 2 H2(g)
2 U(s) + 3 H2(g) 2 UH3(s)