TAILINGS
Rethinking tailings
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hen a tonne of is ore processed, only a fraction becomes a saleable product while the rest becomes tailings: the finely ground waste material left behind after mineral extraction. Managing those tailings has long been one of mining’s biggest operational challenges. While conventional tailings storage facilities remain the dominant solution worldwide, growing pressure on water resources and increasing scrutiny of storage practices are pushing miners to consider alternative approaches. Speaking on McLanahan’s Groundwork podcast, thickener group specialist Mark Taylor said the scale of tailings generation is often overlooked. Using gold mining as an example, Taylor said operators may recover only a few grams of gold from every tonne of ore processed. “That means virtually all of the material becomes tailings,” he said. The challenge becomes even greater at large copper operations, where millions of tonnes of material can be processed each year. “You can’t mine without putting your tailings somewhere,” Taylor said. “If you’re having problems with your tailings, you’re not getting any mineral out.” Historically, tailings dams became the preferred option because they could
accommodate large volumes at relatively low cost. Tailings are thickened and pumped as a slurry into a storage facility, allowing solids to settle while water is recovered and recycled back into the plant. While that approach remains common, water recovery has become an increasingly important consideration, particularly in regions where supply is limited. Taylor pointed to Chile’s Atacama Desert, home to some of the world’s largest copper mines. “Whatever water they get has to be recycled and used as many times as possible,” he said. That need to maximise water recovery has fuelled interest in dry stack tailings. Unlike conventional disposal methods, dry stack systems use filtration to remove substantially more water before the material reaches storage. The filtered tailings can then be transported by conveyor and stacked in layers rather than pumped into a dam. Taylor said conventional tailings disposal typically achieves solids concentrations of around 60–65 per cent, while filtration can increase that figure to 80–85 per cent. “The difference is significant when you physically see the material,” he said. “It looks like a dry product and can generally be walked on almost immediately.”
Images: McLanahan
As miners face growing pressure to improve water recovery and reduce storage risks, tailings management is becoming a key consideration.
The right thickener can eliminate the need for ponds or tailings storage facilities altogether.
The benefits are more water is recovered for reuse and less remains within the storage facility, but those gains come at a cost. “It’s easy to add the water. It’s much more difficult to remove the water afterwards,” Taylor said. Large filtration plants, conveyors and stacking systems can represent a significant capital investment, particularly for operations processing thousands of tonnes per hour. As a result, many miners are pursuing a middle ground through thickened tailings technology. High-density and paste thickeners increase solids concentration before disposal, producing a more stable material while avoiding much of the expense associated with full filtration. Taylor said thickened tailings can be a practical compromise between conventional storage facilities and dry stack operations.
Thickeners are essential for liquid–solid separation in mining operations.
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“Thickeners use the cheapest form of energy available – gravity,” he said. Underground mines often take a different path again through paste backfill systems, where thickened tailings are mixed with a binder and returned underground to fill mined-out voids. The process provides ground support while reducing the volume of material requiring surface storage. For Australian miners, the choice between conventional storage, thickened tailings, dry stacking and paste backfill is rarely straightforward. Water availability, site conditions, production rates and project economics all play a role. “There is no one right answer,” Taylor said. “Every country and every operation has different requirements.” As miners seek to many variables, tailings management is increasingly becoming a site-specific decision rather than a one-size-fits-all solution. AM