Geochemistry of uranium mill tailings in the Athabasca Basin, Saskatchewan, Canada: A review

The Athabasca Basin, located in northern Saskatchewan, Canada, is a major source of global U and an important economic driver for the province and country. Athabasca Basin U deposits consist of uraninite and pitchblende dominated by quartz and aluminosilicates and varying amounts of sulfide and arsenide minerals associated with varying concentrations of As, Se, Mo, Ni, and 226Ra (elements of concern; EOCs). Processing these U ores results in tailings that are often enriched in EOCs. Mill treatment processes are designed to generate tailings that minimize the long-term environmental impact of U tailings, although many challenges exist in reaching this goal. Many studies have contributed to our understanding of the geochemistry of these tailings and EOCs and their potential impact on the surrounding hydrosphere. Using nearly two decades of data from tailings samples, mill sampling campaigns, and laboratory experiments, this review provides a comprehensive analysis of the geochemistry and long-term behavior of U tailings in the Athabasca Basin and develops a geochemical model of the tailings. Results of this review are applicable to tailings generated from other milling operations with comparable acid leaching hydrometallurgical processes. This holistic review also highlights the limitations to our current understanding of U tailings geochemistry.