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Characterizing the Long-term Stability and Porewater Quality of Uranium Mine Tailings

SRK has been providing consulting services to Cameco Corporation for over 15 years. During this time, our geochemists have characterized and monitored geochemistry and water quality issues associated with all types of uranium mine tailings stored in the Above-Ground Tailings Management Facility at Key Lake Mine, the Deilmann In-Pit Tailings Management Facility at Key Lake, and the Rabbit Lake In-Pit Tailings Management Facility at Rabbit Lake Mine. Our work has supported regulatory approvals and licencing conditions at these facilities, addressing the requirements and standards of both the Provincial and Federal regulatory agencies, including the federal Canadian Nuclear Safety Commission (CNSC).

At both sites, sulphuric acid is used to extract the uranium from the ore. After recovery, the acidic solutions are neutralized with lime. Sulphate, arsenic, iron, uranium and other metals in the acidic solutions are removed during the neutralization process forming secondary mineral precipitates. These are combined with residues from the leaching process and then discharged to the tailings management facilities. The chemical stability of the secondary minerals is critical to the long-term geochemical performance of the facility, ensuring that these elements are not released back into the tailings porewater.

SRK’s predictions of long-term geochemical performance at these facilities rely on a combination of laboratory testing, equilibrium modeling, and site-specific monitoring data from earlier phases of tailings deposition. The laboratory tests typically include solids characterization to establish the elemental composition of the tailings, aging tests to assess the short-term solubility of the tailings, and mineralogical characterization to support the modeling assumptions.

Major improvements in mineralogical techniques have occurred in recent years, and, thanks to university research funded by Cameco Corporation and other mining companies operating in the region, many of the previously unknown phases controlling metal solubility have now been identified. Cameco completes drilling investigations at each of their tailings facilities every few years to monitor and assess the geochemical performance of the different types of tailings, and to confirm the results of the predictions. Typically, SRK is involved in the data review so that the predictions of long-term geochemical performance can be updated. Currently, Cameco is funding an Engineered Tailings Research Program at the University of Saskatchewan to better understand how the tailings characteristics can be improved to reduce concentrations in the porewater to even lower levels. Quarterly workshops are held to ensure that the results of these studies are reported back to the site operators, consultants and management in a timely fashion.

The design of the tailings facilities is also critical to the long-term geochemical performance. The Deilmann and Rabbit Lake facilities represent the third generation of tailings management in the area, and are situated in mined-out open pits. They benefit from the naturally low permeability of the surrounding rock, constructed features that allow improved tailings consolidation and groundwater bypass, and deposition methods that minimize the potential for oxidation. SRK’s work over the last fifteen years has helped Cameco Corporation understand the effect of these factors in minimizing long-term contaminant releases.

Kelly Sexsmith:

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