At first glance, heap leaching can appear an extremely simple technology; however, without proper characterisation, engineering and design, heap leaching faces significant issues that can affect the overall economic viability of the project. Combined with compartmentalising the project and pressures to skip conventional steps in the normal project development process (advancing from the conceptual or scoping study phase to feasibility or final design), the overall project viability and economics can be inadvertently affected or constrained during operations.
With lessons learned from the design, construction and operation of numerous heap leach pads worldwide, SRK recommends the following for a successful heap leach facility:
• Develop a site specific design that accounts for such conditions as metallurgy, topography, climate, geotechnics, environmental and closure conditions;
• Develop a rigorous program for sampling and metallurgical characterisation that assesses the variability of the ore;
• Select the appropriate heap leach pad (HLP) type, containment, and ore loading system;
• Consider adjacent facilities and anticipate potential facility changes in the heap leach life cycle, including closure conditions;
• Select the system for solution management (including irrigation, solution collection and water balance system), that considers upsets, such as extremely wet or dry conditions;
• Monitor the operational kinetics against those used in the design process, update with metallurgical testing performed during operations, and
• Perform a risk assessment at numerous stages of the design process. In addition to these technical recommendations, SRK suggests that the design process should:
• Benchmark with other projects;
• Implement a peer review program;
• Follow a staged design process that covers the entire HLP Life cycle;
• Allow for construction and operational flexibility in the design;
• Exceed minimum requirements and define battery limits early on; and
• Document the process to provide transparency and allow for regular reviews of key decisions.
