Preferential flow behaviour in unsaturated packed beds and heaps: Incorporating into a CFD model

Heap leach stockpiles inevitably contain local voidage heterogeneities due to non-uniform particle size distributions of the ore and other factors that lead to preferential flow paths and solution channelling. The stockpile can also encounter diverse flow conditions due to a number of factors, including storm events, infiltration into dry ore material, cyclic drain down, compaction, migration of fines, all contributing to large variations in local ore permeability and the creation of preferential flow pathways. Non-uniform and adverse flow behaviour within the heap reduces the leaching efficiency which can lead to lower metal recoveries. Therefore, capturing the local flow variations that affect the transport of leach solution within the heap is critical to accurately predicting the leaching kinetics. Experimental data shows how channelling develops due to local heterogeneities that cannot be eliminated by packing alone. Thus, effective modelling of heap leach stockpiles should account for these channelling affects. This paper utilises a robust computational fluid dynamics (CFD) framework that incorporates techniques to account for local preferential flow paths in the heap leach system. The results are compared against liquid flow behaviour in a pseudo two-dimensional column of narrowly sized particles and a more realistic particle size distribution. The methods are then applied to a hypothetical leach to assess the impact of accounting for the flow variability in the heap.