Refining and conversion of uranium concentrates

The conversion and purification of uranium into UF₆ is carried out industrially along two possible routes: either preliminary refining by liquid/liquid extraction followed by conversion into UF₆ (wet route), or direct conversion into UF₆ followed by distillation (dry route).

In the wet process, uranium oxide is dissolved by nitric acid, then uranyl nitrate is selectively extracted by solvent in an acid medium. After aqueous phase re-extraction and denitration, the oxide is then reduced to UO₂ , then hydrofluorinated to UF₄ and, finally fluorinated to UF₆ . Various fluorination or hydrofluorination reactor techniques are possible: flame reactors, fluidized beds, rotary furnaces, flow bed furnaces.

In the case of dry conversion, U₃O₈ is reduced to UO₂, then further converted to UF₄ and then UF₆ in a succession of fluid beds. Finally, the liquid UF₆ is distilled under pressure in two columns in series.

Obtaining UF₆ is made possible by preparing molecular fluorine from HF electrolysis.

There are currently six UF₆ converters in the world, and installed industrial capacity is of the order of 73 kt U, with production of 61 kt U in 2009. The cost of conversion is low (2% of the fuel cycle), but it is an essential step between two important operations: uranium extraction and enrichment.