Uranium Mining and Milling cont'd - doe-hdbk-1113-98_reaffirm_2005

DOE-HDBK-1113-98

Radiological Safety Training for Uranium Facilities

Module 102 The Nuclear Fuel Cycle

processing and a mixture of low-grade crushed rock and sand called "mill

tailings."

Only about 3 percent of the actual material removed from the mine ends

up as yellowcake, which means that millions of tons of mill tailings are

leftover. Yellowcake contains 70-90% by weight of uranium oxides. The

leftover mill tailings are a concern because they still contain some of the

uranium ore. Additional hazards exist due to the chemicals added.

It is estimated that the uranium milling in the United States left

approximately 138 million tons of mill tailings covering about 3,000 acres

of land.

The yellowcake slurry is then purified by either ion exchange or solvent

extraction.

Following purification, the yellowcake slurry is dried, forming a

concentrated yellowcake compound that contains 75 - 98 percent uranium.

The yellow color is caused by the addition of leaching chemicals and their

eventual removal during the drying step. The final color can range from

yellow to orange to black depending on the chemicals used and the drying

temperature.

The final color is a good indicator of solubility, and thus of biological

effects if uranium in this form is taken into the body. Less soluble uranium

compounds tend both to remain in the body longer and to be darker in

color. More soluble uranium compounds are removed from the body more

quickly by normal body functions, and tend to be lighter in color.