Uranium mines and mill facilities

Canada’s operating uranium mining companies, Cameco Corporation and Areva Resources Canada Incorporated are not only leaders in uranium production, but they also lead in the development of environmentally sus­tainable uranium mining practices. They have developed new technologies to manage uranium mill tailings and reduce environmental impacts.

The tailings management strategy is based on two principles that underlie the containment of the tailings and their potential radionuclide and heavy metal contaminants:

1. Hydraulic containment during the operational phase: The pit is main­tained in a partially dewatered state throughout the operational life of the tailings facility to create a cone of depression in the groundwater system, which results in the natural flow being directed toward the pit from every direction. Since water has to be pumped continuously from the pit, current water treatment technology results in high-quality efflu­ent suitable for discharge to surface water.

2. Passive long-term containment, using the hydraulic conductivity con­trast between the tailings and their surrounding geologic materials: Long-term environmental protection is established through control of the tailings’ geochemical and geotechnical characteristics during tailings preparation and placement. This control creates future passive physical controls for groundwater movement in the system, which will exist after the decommissioning of operational facilities.

In addition to tailings from the milling process, uranium mining results in large quantities of waste rock being produced. The segregation of these materials according to their future management requirements is now a core management strategy. Material excavated from open pits is classified into three main categories: clean waste (both overburden and waste rock), special waste (containing sub-economic mineralization) and ore.

The clean waste refers to waste materials that are benign with respect to future environmental impact, and that can be disposed of in surface stockpiles or used on-site for construction purposes. The special waste is waste rock near ore bodies. This waste is potentially problematic, because it has some halo mineralization around the ore deposit, and is therefore potentially acid-generating in some instances and/or a source of contami­nated leachates when exposed to an oxidation environment. The disposal of this special waste in mined-out pits and flooding, to cut off the oxygen supply from the atmosphere and stop oxidation reactions, is now a widely recognized solution. If the pit is not suitable for the long-term management of the risk, engineered covers present an in-situ solution to impede the interaction of oxygen and moisture with the special waste. Typically, any waste material with uranium content greater than either 300 ppm U3O8 or 0.025% (250 ppm) uranium is categorized as special waste, and all material grading greater than 0.085% uranium has been classified as ore. The cut-off grade for the mill may vary depending on market condi­tions for uranium.

All mine and mill facilities provide water treatment systems to manage contaminated water collected from their tailings’ disposal facilities, as well as water inflows collected during open pit or underground mining, and problematic seepages from waste rock piles. The treatment processes vary from continuous to batch systems, and largely rely on conventional physical settling and chemical precipitation methods found in the metal mining industry.

Owners of closed uranium mines are also required to ensure that their sites are properly decommissioned, and that they have set the standard for decommissioning uranium mine sites. In instances where remedial actions are required at uranium mine and mill tailings facilities where the owner no longer exists, the Government of Canada and provincial governments ensure that the sites are safely decommissioned through cost-sharing arrangements.

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