940 Higher moisture leads to plasticity, instability, and poor mixing behaviour, while too-dry cake becomes brittle and loses cohesion. Maintaining consistent moisture—enabled by modern automated filtration—is therefore essential for effective co-disposal. 7.2.2 Filter Cake As A Fine Fraction For Geotechnical Improvement Filtered cake, when well-controlled, serves as an ideal fine material to fill voids in waste rock. Previous studies demonstrate: • improved structural stability at various blend ratios, • reduced compaction effort required during placement, • minimized transport and spreading challenges, and • better long-term deposit performance. These advantages make filtered tailings uniquely suited for hybrid waste storage designs. 7.3 Co-Disposal Approaches and Engineering Considerations Several co-disposal strategies appear in the documents: 7.3.1 Co-Mixing (Engineered Backfill Or Above-Ground Stacks) This involves blending waste rock and filtered tailings in controlled ratios such as 20:1, 5:1, or 1:1, as tested in the CONCEPTS FOR CO-MIXING study. In these trials: • hydraulic conductivity decreased dramatically, particularly when bentonite or compaction was added, • shear strength improved due to coarser rock fractions, and • controlled compaction increased stability. These enhanced geotechnical and hydraulic characteristics support safer and more resilient landforms. 7.3.2 Co-Disposal In Waste Rock Dumps Co-disposal can also be implemented by strategically incorporating filtered tailings into waste rock dumps, reducing: • oxygen ingress, • percolation pathways, and • the risk of ARD generation. Filtered tailings’ low permeability helps create oxygen diffusion barriers, which is a key mechanism for reducing ARD in sulphide-hosted deposits. 7.3.3 Staged Or In-Pit Blended Deposition Some mines use staged blending of filtered tailings with coarse rejects or mining byproducts in in-pit settings. Although not explicitly detailed in the uploaded files, the principles in (Palmer et al) and Co-Mixing studies directly support the viability of such approaches through consistent laboratory evidence. 7.4 Operational Challenges in Co-Disposal Despite their advantages, several challenges must be addressed for successful implementation: 7.4.1 Scale-Up Risk
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