RE: Excellent piece (posted on ADVFN)23 Jun 2026 01:14
Interested to hear an assessment from anyone with a metallurgical background about the pilot processing risk. Below is the generalist Gemini take on the risk (final para is particularly interesting. Wondering if this has been done):
Pilot-scale recoveries falling materially below bench-scale results is a common metallurgical hurdle. While specific statistics vary by deposit, industry literature indicates that 15% to 30% of new projects experience this material shortfall during initial pilot testing, largely driven by batch-versus-continuous operation differences, unmapped feed variability, and scaling dynamics.Here is a breakdown of why these shortfalls occur and how they manifest:
1. Feed Variability & Sample Representativeness
Geological Diversity: Bench-scale tests typically use small, high-grade core intervals (e.g., <50 kg). These rarely capture the spatial mineralogical diversity (e.g., hard vs. soft rock, varied gangue minerals) encountered during bulk pilot operations.
Weathering and Alteration: Tailings or bulk samples used in pilots often exhibit rounded edges, oxidization, or surface-area porosity from long-term exposure, changing their chemical reactivity compared to freshly crushed drill core.
Interference: Trace gangue elements (such as talc or carbonaceous matter) that dilute concentrates are frequently masked in batch testing but become concentrated over extended continuous pilot runs.
2. Process Scaling & Continuous Dynamics
Batch vs. Continuous Operation: Bench tests are discontinuous, whereas pilot plants simulate dynamic, continuous processes. Elements like water quality, dissolved oxygen, and reagent residual levels reach steady-state limits in a pilot circuit that batch tests cannot replicate.
Recycle Loads: Continuous pilot plants involve closed-loop recycle streams (e.g., middlings returning to rougher cells). These create a build-up of fine particles and deleterious elements that artificially lower overall metallurgical recovery and concentrate grade.
Reagent Overdosing: Bench testing often involves flushing out mills with water to recover all particles, inadvertently diluting remaining reagents. At pilot scale, continuous milling lacks this flushing effect, leading to reagent overdosing and "froth drop-back" losses if not controlled.
3. Equipment & Hydrodynamic Discrepancies
Mixing and Kinetics: Parameters like oxygen mass transfer, localized turbulence, and slurry retention times scale non-linearly from small lab beakers to large industrial cells.
Froth Depth and Area: Bench cells rely on manual scraping to remove froth, whereas pilot and commercial cells rely on natural overflow. Inadequate froth depth or poor drainage in larger cells often results in entrained gangue minerals reporting to the concentrate.
To mitigate these pitfalls, testing standards such as those detailed by SGS advise geometallurgical variability mapping and conducting mass-balance kinetic models during the pre-feasibility pha
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