Decommissioning of Low-grade Uranium Mines in Canada: Current Status and Long-term Radium Mobility

Abstract

Low ore grade and uranium market conditions have lead to the closure of all low-grade uranium mines in Canada. With the exception some past historic and abandoned mine sites, all other inactive and recently closed-out mines and associated waste management sites have been rehabilitated and decommissioned. Acid mine drainage and contaminant migration, including uranium decay series radionuclides and trace heavy metals, from waste management areas are major environmental concerns at many of these sites. Hence, long-term prevention, control and treatment measures are required. In the past, many older and inactive surface-deposited waste management sites, having acidic drainage problems, were rehabilitated with vegetation covers. This has controlled surface erosion and greatly improved site aesthetics. However, acidic drainage continues and at these sites long-term effluent collection and treatment is required. The waste management areas at the newer, recently closed mines have been rehabilitated with shallow, in-situ water covers, having a minimum depth of approximately 1 m, to minimize acid generation and release of radon gas and its progeny. Acid generation at these sites has decreased significantly, and at most sites only a limited effluent treatment is required for pH control and radium removal. The mobility of Ra-226 from pyritic uranium tailings was evaluated for both on-land and underwater disposal scenarios. During the acid generation phase and/or in the presence of available sulphate ions, the dissolution and mobility of radium was very low due to sulphate ion solubility control. With the cessation of acid generation, and/or upon depletion of sulphate ion control, including microbial sulphate degradation, the solubility of radium was enhanced. Hence, further investigations are needed to improve the understanding of the long-term stability and control aspects of decommissioned uranium mine waste management sites.