Transformation of natural uranium into uranium tetrafluoride

 During the first phase, the uranium is transformed into uranium tetrafluoride (UF₄).
The concentrated ore is dissolved by acid, then purified to yield. After precipitation and calcination, uranium trioxide powder (UO₃) is obtained, and is then hydrofluorated using hydrofluoric acid.
It is thus transformed into a green substance with a granular appearance called uranium tetrafluoride (UF₄).
These operations are carried out in the COMURHEX-Malvési plant in Narbonne, France.     

Transformation of uranium tetrafluoride into uranium hexafluoride

The UF₄ is then converted in a second phase of fluorination into uranium hexafluoride (UF₆), using fluorine obtained by electrolysis of hydrofluoric acid.
The UF₆ is made by contact of gaseous fluorine with the UF₄ powder. The chemical reaction makes very high-temperature in a reactor with flames.
A last stage consists in transforming the obtained UF6 of the solid state to the gaseous state. Thus, it's possible to enrich it. These operations are carried out in the COMURHEX plant in Tricastin.

http://www.areva.com/EN/operations-757/conversion-the-fluorination-of-uranium-in-2-stages.html