The Chemistry of Uranium

Uranium is located in the periodic table in actinides zone. His oxidation states are 3, 4, 5, and 6. A fresh surface of metallic uranium is white and lustrous, with a bluish tinge, but it soon tarnishes in air. There are three crystalline forms of metallic uranium; the usual form is orthorhombic, and is malleable and ductile. It can be cast, rolled and extruded, and is often produced in 1" diameter rods.

The metal oxidizes rapidly when heated to 200°C, and burns in air. This behavior is typical of all the heavy metals in this region of the periodic table, including radium and plutonium. When used as metals, they must be cladded with another metal, such as zirconium or aluminium, to protect them from moisture and oxygen. Uranium is soluble in mineral acids, and will displace hydrogen from water. Since the nitrates of uranium and its friends are soluble, chemistry is generally performed with them. A notable property of uranium is its high density, about 19 g/cc (sources give 18.9 and 19.04). This is about twice the density of lead (11 g/cc), and puts uranium up with the densest metals, such as platinum, osmium and iridium. Uranium melts at 1133°C with latent heat 2.5-3.0 kcal/mol, and boils at 3925°C with latent heat 110 kcal/mol. Its coefficient of thermal expansion is 15 x 10^-6 per °C, and its electrical resistivity is 29 μΩ-cm.

The oxidation state more stable is 6 and presents an oxide, UO₃ and a cation UO²⁺. Its reaction in acid environment is as fallow:

UO₃ + 2H⁺ = UO₂²⁺ + H₂O

The oxidation state 5 forms compounds with halogens and presents a cation U₂O⁺ which is very unstable and disproportionate in U⁶⁺ and U⁴⁺.

The oxidation state 4 is typical of actinides. 

UO₂ – 2e^- = UO₂²⁺

The oxidation state 3 presents ion U³⁺ which has red color and high reducing strength (electron donor). For this reason is easily oxidized to U⁴⁺.

On the field of uranium hydrometallurgy is very important two oxidation states: 4 and 6, because uranium can be usually found in those states, and also forms some complexes during its processing by leaching:

UO₂²⁺ + 3(SO₄)²⁺ = UO₂(SO₄)₃^{4 -}

UO₂²⁺ + 3(CO₃)²⁺ = UO₂(CO₃)₃^{4 -}

Uranium dose not exist as native metal and is usually combined with oxygen forming silicates, phosphates, carbonates, sulphates, arsenates, and vanadates, which are stable minerals.

Corundum Occurrence and Use Triclinic Section – Microcline Composition & Structure Flotation Collection Froth Flotation Depth Taconite - Magnetic Separation Method Smithsonite Composition, Crystallization & Structure Oligoclase Composition, Crystallization & Structure Nickel Elements, Alloys and Symbols EXPERIMENTAL FLOTATION Development and Production How much Frother is Required: Dosage Hidrous Silicates - Zeolite Division, Subdivision, Apophyllite Composition Uranium Precipitation into Yellow cake Formation Celestite Composition, Crystallization & Structure