We have covered what happens after uranium is mined -- it goes to a uranium recovery facility that produces concentrated uranium called yellowcake. These mills (uranium recovery facilities) usually are located at or very near the uranium mine.
However, for most nuclear purposes the yellowcake must be further processed. For example, it cannot be enriched in a solid form. The next step is called the conversion process and involves a bit of chemistry.
After the yellowcake is produced at the mill it is converted into uranium hexafluoride (UF6) gas suitable for use in enrichment operations. During this conversion, impurities are removed and the uranium is combined with fluorine to create the UF6 gas.
The UF6 is then pressurized and cooled to a liquid. The liquid then is pumped into cylinders where it solidifies after cooling for approximately five days. The UF6 cylinder, in the solid form, is then shipped to an enrichment plant. UF6 is the only uranium compound that exists as a gas at a suitable temperature.
The enrichment process requires reconversion to a liquid. The solid state is used only for transport and storage.
Iran has one or more conversion facilities, probably located adjacent to its enrichment plants (centrifuges).
One uranium conversion plant is operating in the United States: Honeywell International Inc. in Metropolis, Illinois.