Thickened discharge is therefore seen as a risk-reduction approach relative to conventional slurry, but it still relies on containment structures whose long-term performance must be assured. Life-cycle cost studies for conceptual Western Australian operations show that thickened tailings can be an economically attractive option, especially when: water, land, and closure costs are partially internalised, but energy costs and carbon pricing remain moderate. Thickened systems incur higher CAPEX than slurry (for thickeners and associated infrastructure) but maintain largely familiar pumping and deposition practices. Operationally, they can face challenges in maintaining consistent rheology, especially under variable ore and climate conditions, but the technology is widely understood and has a strong operational track record. Paste Tailings Paste tailings are produced when tailings are thickened to very high solids concentrations, yielding a non-segregating, non-Newtonian material with a high yield stress. Paste can be deposited on surface (as thickened/paste discharge) or used underground as cemented paste backfill. Paste systems are attractive where: • deposition space is limited, • underground backfill can offset tailings storage requirements, or • there is a need to minimize free water at the deposition area while avoiding full filtration. Water and Stability Performance Water recovery for paste is generally higher than for thickened tailings but below that achieved by filtered tailings. Free water on the surface is significantly reduced; nonetheless, paste placed in surface impoundments still requires some containment and drainage infrastructure. From a stability perspective, paste exhibits high cohesiveness and low segregation potential, which can improve depositional control and stack geometry. When used underground, paste backfill contributes directly to ground support and reduces the volume of tailings requiring surface storage, thereby lowering surface TSF risk. 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.
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