Milling, which is generally carried out close to a uranium mine, extracts the uranium from the ore. Most mining facilities include a mill, although where mines are close together, one mill may process the ore from several mines. Milling produces a uranium concentrate that has a smaller volume than the ore, and hence is less expensive to ship. In a mill, uranium is extracted from the ore by a combination of one or more chemical processes. The most common process is leaching, in which either a strong acid or a strong alkaline solution is used to dissolve the uranium, which is then precipitated from solution as a concentrate.
Some uranium is produced by direct chemical extraction rather than mining.
One method by which this is achieved is in situ leaching of uranium deposits. Where this method is employed, a chemical solution in which uranium will dissolve is introduced into the ground at or close to a deposit. Ground water is then extracted from the area using a well which has been located such that the uranium solvent is drawn through the ore body. This approach is only appropriate where geological conditions are such that ground water contamination can be avoided. The chemical solution dissolves the uranium and carries it to the well.