Filtered Tailings (Dry Stack) Filtered tailings (often referred to as “dry stack” when deposited on surface) are produced by mechanical dewatering, typically using pressure filters or vacuum filters, to achieve low residual moisture (commonly in the range of 10–20% for sulphide ores, lower in some cases). The resulting cake is: • trafficable and stackable, • transported by conveyor or truck, • placed in thin lifts and compacted to achieve target density and shear strength. Large-scale case studies in Chile and Peru show filtered tailings dry stacks operating at tens of thousands of tonnes per day, with integrated truck or conveyor systems and progressive reclamation practices. Figure 2 Ongoing reclamation of filtered stack slope Figure 44 Water Recovery and Stability Filtered tailings provide the highest water recovery of the options considered. Studies of the water–energy nexus for copper mining show that filtered tailings can significantly reduce freshwater or desalinated water demand by returning most of the process water to the plant, thereby cutting both water and energy consumption. Geotechnically, dry stacks: • eliminate the large supernatant pond, • operate without large conventional dams, and • rely on compacted, unsaturated tailings with high matric suction and improved shear strength. This configuration reduces the potential for catastrophic dam breach events, although it introduces its own challenges, including maintaining trafficability under wet conditions and managing surface runoff and erosion. Cost and Operational Considerations From a cost perspective, filtered tailings are generally recognised as: • higher CAPEX, due to filter plant, structural, and materials handling infrastructure; and
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