926 3.3.2 Cost And Operational Complexity Paste systems often involve: • higher CAPEX than thickened-only systems (due to the need for paste mixers, positive displacement pumps, and potentially binder infrastructure), and • higher OPEX associated with pumping high-yield-stress material and, where applicable, binder costs for backfill. As reported in comparative cost studies and industry experience, paste can be cost-effective when underground backfill benefits are fully credited. However, paste transport over long distances or steep gradients can be technically challenging and requires tight operational control to avoid plugging and excessive wear. 3.4 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 2Ongoing reclamation of filtered stack slope Figure 64 3.4.1 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.
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