From Columns to Industrial Heaps: Critical Design Considerations for Heap Leach Pilot Plants

Heap leaching has become a strategic approach for processing low-grade and mineralogically complexnickel ores; however, the transition from laboratory testing to full-scale industrial heaps remains one of the leaststructured and most risk-prone stages in hydrometallurgical project development. This review critically evaluatesthe role of pilot heap leach plants in reducing scale-up uncertainty, emphasizing that bottle-roll and column tests,while useful for estimating kinetics and acid consumption under controlled conditions, do not reproduce thehydraulic heterogeneity, permeability evolution, mechanical compaction, solution retention, and long-term hydrogeochemical feedback mechanisms that govern industrial heap performance. Key engineering variablesinfluencing pilot behavior are examined, including heap geometry, stacking strategy, agglomeration practices,irrigation system design, acid management, solution recycling, hydro-mechanical monitoring, and integration withdownstream processing. Recurrent failure mechanisms—undersized pilots, short operational campaigns,insufficient instrumentation, simplified irrigation layouts, and incomplete water–acid balance closure—areidentified as major contributors to scale-up errors. Persistent gaps in long-term pilot data reporting and in thevalidation of reactive transport models against field measurements are also discussed. A structured best-practiceframework is proposed that integrates geometallurgical characterization, reactive transport modeling, extendedduration pilot operation, and comprehensive monitoring, advancing the central thesis that pilot heaps must bedesigned as dynamic hydro-geochemical reactors rather than as enlarged laboratory columns to reduce technical,economic, and environmental risks in industrial nickel heap leaching.