Integrated characterization for improvedleach design and performance

Heap leaching extracts valuable metals from low-grade ore by irrigating a stacked heap of crushed material with a leaching solution. Percolation leaching occurs under partial liquid saturation, a vadose zone hydrogeology principle (Chahbandour et al., 2000; Guzman et al., 2008), ensuring the stability of the rock mass while minimizing reagent and water use. Traditional metallurgical characterization lacks data on the physical, hydraulic and mechanical properties of the ore, as well as their evolution with heap height or rock decrepitation over multiple leach cycles. Key factors influencing metallurgical performance include (1) ore hydrodynamics, (2) compaction effects, (3) chemical decrepitation impacts and (4) reagent accessibility to mineral surfaces. Data from more than 50 active leaching operations and numerous design-stage projects reveal that most metallurgical performance issues stem from limited understanding of ore hydrodynamics. Common design errors include incorrect particle size distribution (PSD), lack of percolation and moisture retention data, and failure to account for compaction effects with heap height. The relationship between solution application rates, liquid saturation and their changes under multiple leach cycle is rarely considered — let alone quantified (Breitenbach and Smith, 2006; Guzman et al., 2008). Additionally, an incomplete understanding of the effect of reagent concentration and delivery schedule results in suboptimal leach cycles and reduced efficiency. Heap leach facility design is inherently complex due to data gaps and the trade-offs of optimizing parameters in isolation. Variability in ore mineralization, hydrodynamic behavior and geotechnical conditions often necessitate assumptions, introducing biases that propagate through the design, creating uncertainties in industrial-scale metallurgical performance. Figure 1: Copper recovery for original and improved design. Each design choice cascades into subsequent decisions, amplifying risks such as low percolation capacity, excessive solution and metal inventory, and reduced recovery efficiency — ultimately impacting economic viability and heap stability. The consequences of a partially informed design can be severe, both financially and environmentally. The 2024 heap failures at Çöpler Gold Mine in Turkey and Eagle Gold Mine in Canada serve as stark reminders of these risks, underscoring the critical need for a meticulous, data-driven approach to heap leach facility design. Building on 26 years of experience in heap leach optimization and the work of Scheffel et al. (2016), I developed an integrated characterization program to quantify key metal extraction mechanisms and provide a data-driven foundation for heap leach design. This program emphasizes early identification of real-world conditions as the most effective way to mitigate risk and is structured around five critical steps to support the design process effectively: Analytical characterization — Define the ore grade, mineralization and deportment with respect to the as-mined PSD. Additionally, quantify key impurities to assess their impact on processing efficiency. Ore preparation — Select the crushing method and level of crushing to produce the PSD that would support selected maximum heap height. The total heap height would be dictated by the type of facility to be constructed (dynamic or static). Ore conditioning — Determine if agglomeration is required, and the optimal reagent addition in terms of dosage and schedule. Optimal reagent addition promotes fast kinetics and maximum recovery. Optimal agglomeration improves solution-to-ore contact, minimizes solution and metal inventory, and promotes proper drainage. Leaching process — Select an irrigation scheme (rate and schedule) to maintain adequate liquid saturation and optimize reagent concentration for efficient extraction and delivery while minimizing consumption. Saturation must remain below 85 percent for slope stability or below 65 percent if aeration is required. The design must ensure these levels across the heap profile and multiple leach cycles in static heaps. Process optimization — Use data from the previous steps to determine optimal operational conditions, including target recovery, leach cycle duration and leach ratio. These conditions maximize economic return by balancing recovery, cycle time, reagent consumption and leach ratio through trade-off analysis. The integrated characterization program has been used to optimize copper, gold, silver, nickel, zinc, uranium, rare earth elements and lithium operations, leading to quantifiable improvements in leaching performance. The resulting process design, combined with real-time monitoring (Guzman et al., 2014), significantly reduces operational uncertainty and risk, providing a strong foundation for decision-making. Table 1 summarizes the benefits of the program in two of the 16 projects where it has been fully implemented: (1) a mixed oxide-secondary sulfide copper operation and (2) an exotic copper project in the design stage. Ore testing revealed the original design would not effectively support even the first lift at these sites. The values of the parameters in Table 1, except for the heap height, correspond to an operational condition where maximum copper recovery is the optimization target. The benefits of the integrated design are all-encompassing, enabling the construction of multiple lifts while ensuring the delivery of required solution application rates. This approach also mitigates the risk of high liquid saturation, reducing the potential for slope failure. Additionally, several operational improvements contribute to upgraded financial performance for these operations. Figure 1 shows the total copper recovery (CuT) versus leach ratio (m3/t) for the sites in Table 1. The data suggest that alternative optimization targets would yield different parameters values, further benefiting the operations. For example, in the mixed copper operation, selecting a 60 percent recovery target would reduce the leach ratio from 2.9 m³/t in the original design to 0.3 m³/t in the integrated design, significantly reducing water demand and acid consumption while shortening the leach cycle. A similar outcome would be derived for the exotic-oxide project. A trade-off study would determine the optimal copper recovery target to maximize financial performance. Conclusion A well-designed heap leach operation must balance metal recovery, financial returns, heap stability and environmental compliance to ensure long-term viability. Minimizing design uncertainties is crucial to preventing costly failures and maintaining safety and sustainability. Industrial experience shows that the integrated characterization approach provides the comprehensive data needed to develop a robust and reliable design. References Breitenbach, A. J., and Smith, M. 2006. Sustainable Issues Related to Heap Leaching Operations. Journal of the Southern African Institute of Mining and Metallurgy, 106(12), 857-868.Chahbandour, J., Guzman, A., Filippone, C., and Carrera, I. 2000. Hydrodynamic Characterization and Optimization of the Chuquicamata Ripios Mina Sur Aglomerados Heap Leach Project – Part 1, Cu Hydromet 2000, September 5-8, Tucson, Arizona, USA.Guzman, A., Scheffel, R.E. and Flaherty, S. 2008. The fundamentals of physical characterization of ore for leach. Sixth International Symposium on Hydrometallurgy, Edited by Y. A. Courtney et al., SME, Phoenix, AZ. August 2008.Scheffel, R.E., Guzman, A., and Dreier, J.E. 2016. Development of metallurgy guidelines for copper heap leach. Special Issue on Process Development Testing. Minerals & Metallurgical Processing, 2016, Vol. 33, No. 4, pp. 187-199. The Society for Mining, Metallurgy & Exploration Inc.

Integrated characterization for improvedleach design and performance

Authored by: Amado Guzman

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