HeapSim2D-A 2D axisymmetric model of heap leaching under drip emitters I. Hydrology and solute transport

Most modern heap leaching processes involve drip irrigation, which induces certain flow and dispersion patterns within the heap. However, this important aspect of heap leaching is overlooked in most mathematical models.This is the first in a planned series of papers presenting a two-dimensional comprehensive model of heap leaching under drip emitters, called HeapSim2D. In this paper, the fundamentals of heap leach modelling are discussed, with particular attention paid to the effect of drip irrigation on the flow of water and the dispersion of solutes within heaps. The mathematical and numerical foundations of a 2D axisymmetric model of heap irrigation under a single point source are developed in detail, and a sensitivity study is presented for the simple case of a first-order gangue acid dissolution reaction in a column under a single drip emitter, using hydrological parameters based on experimental work presented in a previous paper.Simulations show that the capillary head parameter hc,0 is the master parameter which determines the degree of solution spreading under drip emitters. Ores with high capillarity (such as agglomerated ores with significant fines) will spread the solution effectively, whereas ores with low capillarity (such as pebbles without fines) will confine the flow mostly to a channel below the drip emitter. Also, even ores with high capillarity will have a largely unwetted zone at the top of the heap or column.Simulations also show that solute dispersion has a relatively subtle effect on the rate of chemical reactions within heaps and columns, but that, presuming the solution is spread out, the chemical rate constant is the most important parameter in determining the degree of reaction within heaps and columns.In future papers, models for gas flow, gas species transport, heat transport, and various case studies involving custom networks of chemical and biological reactions with kinetics will be presented.