10.4. Uranium ores are found in many parts of the world, with the contained percentage of uranium varying widely. Rich ores contain about 2 percent uranium, chiefly in the form of oxide minerals. However, most commercially mined ore is of medium grade, in the range of 0.1 to 0.5 percent uranium in the form of minerals of complex composition. The practically recoverable grade depends on numerous economic factors, as is true for most ores.

10.5. Since medium-grade ores contain such a large fraction of inert material, a concentration operation is needed in a mill located close to the mining area. Typical operations utilize either chemical leaching or solvent extraction procedures. The product is yellow cake, containing about 80 percent of U3Os. The yellow cake is then shipped to a central purification facility where further chemical operations are used to remove impurities and produce either uranium dioxide or uranium hexafluoride feed for sub­sequent isotopic enrichment processes.