Wastes

Mining and milling waste

Mining activities produce large quantities of waste rock. If left on the surface indefinitely, some of this material could generate acid or release metals at rates that may harm the environment. This can potentially affect ground and surface waters. Today’s mines manage this waste rock by placing it in an environment similar to that from which it was excavated — that is, at the bottom of a flooded pit, surrounded by water and isolated from atmospheric conditions.

Another potential environmental risk at uranium mines is tailings — solid waste materials that remain after rock is milled and treated with chemicals to extract uranium. This material contains radon and toxic materials such as heavy metals. If improperly stored and managed, tailings can contaminate lakes and rivers and local ecosystems.

In the past, tailings were used as backfill in underground mines or placed in low areas on the surface and confined by man-made embankments, in accordance with mining practices at the time. Today tailings management must meet more stringent regulations to protect people and the environment. Containment structures (engineered dams or mined-out pits) are designed for long-term environmental protection. Other methods to manage mine tailings include:

• chemically treating the material
• controlling the release of radon and radioactive dust from tailings
• using liners to redirect groundwater flow around waste
• preventing seepage of heavy metals and acids into ground and surface water

In Canada, about 210 million tonnes of uranium mine and mill tailings have been produced since the mid-1950s. There are 24 tailings sites from past and operating mine and milling operations in Ontario, Saskatchewan and the Northwest Territories. All Canadian uranium mining now takes place in northern Saskatchewan, where three tailings management facilities are in operation.

Each year Canada’s uranium mining and milling activities produce around one million tonnes of waste rock and tailings.