The raw uranium ore is brought to the surface and crushed into a fine sand. The valuable uranium -bearing minerals are then removed via heap leaching with the use of acids or bases, and the remaining radioactive sludge, called "uranium tailings", is stored in huge impoundments. A short ton (907 kg) of ore yields one to five pounds (0.45 to 2.3 kg) of uranium depending on the uranium content of the mineral. Uranium tailings can retain up to 85% of the ore's original radioactivity.