Mine developers and operators are evaluating filtered tailings, also known as dry stack tailings, as an alternative to whole slurry, thickened, and paste tailings. Focus on enhancing physical stability and reducing short- and long-term liability associated with tailings storage facilities has increased, in part due to the failure of the perimeter embankment and subsequent release of slurry tailings at Mount Polley, British Columbia. In order to prevent future releases of tailings, the Independent Expert Investigation and Review Panel recommended three key principles for tailings management going forward: eliminate surface water from tailings impoundments, promote unsaturated conditions within tailings, and achieve dilatant conditions within the tailings deposit. Filtered tailings provide an opportunity to meet these three objectives. In addition, filtered tailings provide opportunities for reduced tailings facility footprints, lower capital costs, flexibility in stack shape, decreased seepage through tailings, and reduced post-closure care requirements. Constraints that must be considered when evaluating filtered tailings include potential difficulties dewatering finer grinds, current limitations on daily throughput, increased operating costs, and increased potential for oxidation of potentially acid generating tailings.
Filtered tailings stacks are in operation at cold regions mines including Pogo and Greens Creek in Alaska and Raglan in Quebec. Filtered tailings stacks at Minto and Bellekeno in the Yukon are in closure. Filtered tailings can offer specific opportunities for cold regions tailings management relative to other approaches, including increased tolerance for differential thaw settlement associated with a degrading permafrost foundation, increased physical and chemical stability from permafrost within the stack, and reduced difficulties with water management in the winter. Constraints that must be considered for filtered tailings in cold regions include tailings placement in freezing or wet conditions, surface water diversion, installation of erosion protection to deal with the freshet, foundation stability and drain integrity in ice-rich soils, and management of the tailings surface during extended wet or dry periods, i.e., management of snow or dust.
Filtered tailings provide many opportunities for developers and operators of cold regions mines. There are also constraints that must be considered when evaluating the use of filtered tailings for cold regions projects. As mineral development expands in cold regions, and operators strive to increase physical stability and decrease risks associated with tailings storage, filtered tailings is one tailings management strategy that can accomplish these objectives.
