When the hydraulic properties of the ore that constitute a permanent heap leach do not allow proper percolation of solutions through its full height, intermediate drainage systems between different ore layers must be considered. These drainage systems commonly comprise an impervious liner deployed below a layer of drainage and collection pipes. Under this configuration, each layer is hydraulically isolated, thereby preventing the solution from flowing through ore layers that have gone through a process of densification and permeability reduction caused by overload of higher levels. One downside of this system is that it generates a series of weak planes in the contact interface between the impervious liner and the ore, generating several potential block failures. An alternative configuration has been considered in some operations that may decrease this adverse effect and reduce the costs associated with the impervious liner.
This alternative configuration consists of the compaction of the surface of certain layers, and leachate collection pipes on each compacted layer. The reduction of permeability on the subgrade of each layer aims to isolate the solution outflow of a set of lifts, similar to the condition with a geosynthetic inter-lift liner. However, depending on the densification degree and the geotechnical properties of the compacted ore, part of the applied solution may not be captured by the drain pipes due to infiltration into the lower layers of the heap leach, resulting in different saturation degrees in each of them, with negative consequences in terms of recovery and slopes stability.
Through numerical models, hydraulic behavior is analyzed on heap leach systems composed of intermediate drainage systems without an impermeable liner. The resulting phreatic level of each layer and the vertical infiltration flow is evaluated in relation to different initial conditions regarding irrigation rates and saturated ore properties for different geometrical configurations. Using the results of this analysis, the authors discuss the implications of the maximum irrigation rate and a maximum number of layers for a configuration comprised of an intermediate compacted layer, complemented with a collection piping system.
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