Analysis of Long-term Stability of Filtered Tailings at the Cantung Mine, Northwest Territories, CanadaOnline pre-recorded
Tailings storage is a critical component of the mining process that must be properly conducted in order to mitigate environmental and social impacts. Failures of conventional tailings storage dams have resulted in catastrophic consequences, which have forced a shift in the design thinking of tailings management strategies. Filtered tailings storage involves dewatering and filtering tailings from less than 25% to greater than 80% solids content and is increasingly considered a more environmentally, socially, and economically sustainable option for tailings storage. However, the applicability of this method to potentially acid generating (PAG) tailings remains uncertain because of the potential for environmental harm caused by acid rock drainage. The balance between geotechnical strength and geochemical stability is a critical component of filtered tailings storage design. The water contents of filtered tailings are not high enough to limit oxidation by saturation, so testing the variation in oxidation rates with water content can help to optimize the design. The Cantung Mine, Northwest Territories, is a former tungsten mine currently under care and maintenance. Tungsten is classified as a critical metal in Canada, the USA and the EU, and the Cantung Mine is considered a world class tungsten deposit based on both grade and tonnage. Production ceased in 2015 with approximately 6.5 Mt of impounded tailings on site. Although static testing indicates that most talilings are PAG, the impounded tailings on the mine site exhibit limited oxidation and pH-neutral pore waters except for the Flat River tailings. Results also indicated that substantial concentrations of tungsten remain in the tailings. This project focuses on geochemical analysis of a filtered tailings storage configuration through column experiments of tailings at different water contents and with different compositions. The range of water contents is based on Standard Proctor Tests, with optimum determined to be 16%. Oxygen consumption, water content and pH have been monitored over 8 months for tailings with initial water contents of 11%, 16%, and 21%. Results show that the rate of oxidation decreases with time after tailings are initially exposed to the atmosphere. While oxidation is occurring, pH appears to remain circumneutral which is expected to be due to the presence of carbonate minerals in the tailings. Reprocessing tests will be conducted to determine if further tungsten recovery and/or sulfide separation is possible. The resulting products from these tests will also be used to investigate variations in geochemical stability. This research will help improve the understanding of how PAG tailings will behave under unsaturated conditions in a filtered tailings stack.