Mining and milling uranium results in solid and liquid wastes or tailings that are radioactive. After the milling process, as much as 98% of the mined uranium ore could remain as solid waste. Because radioactivity remains in the tailings, these wastes could contaminate the environment for centuries if allowed to seep into natural water systems or if exposed to air.
Methods of handling wastes vary from mine to mine. In general, the tailings are in slurry form and are treated to remove chemicals and other impurities. They are then pumped to a containment area. After the solids settle, the liquid is collected and returned to the mill where it is reused or treated with barium chloride, and then tested for chemical and radioactivity levels. At this point, if the tested levels are acceptable, the liquid is discharged into the environment.
Solid waste management methods vary at different mines. For example, a specially constructed tailings pond is used at one mine. It uses bentonite clay and a plastic liner to help to prevent seepage into the groundwater. When the pond is full of solid waste, another layer of bentonite will be used to seal the pond and isolate it from the environment. The area will then be revegetated.
Another mine uses an older open pit mine for tailings disposal. The solid tailings are put in the layered sand and gravel lined pit. When the pit is no longer needed, it will be filled with sand and gravel to form a permeable (porous) layer. When the water table returns to normal, water will flow through the sand and gravel, avoiding the less permeable layer of wastes.