From comminution to pad design, miners are reviewing options for precious metals
By Steve Fiscor, Editor
While heap leach systems seem relatively simple at first glance, they can be quite complex. Basically, ore is crushed to a certain consistency and placed on the pad. A solution is distributed using an irrigation system, which percolates through the heap liberating the metals. The pregnant solution is collected and processed.
Pad designs vary, but there are predominantly two types of heaps: static and dynamic. With dynamic heaps (or on/off pads), the leached ore is removed and fresh ore is placed on the pad after each leach cycle. From a design perspective, the primary difference between dynamic and static heaps is the thickness of the liner. The pads for the dynamic heaps tend to use slightly thicker geomembranes and much thicker over-liner layers, which often consist of two layers. The bottom layer is similar to the over-liner layer for a static heap, and the upper layer consists of a coarse stone (primary crushed ore).