Engineering & Mining Journal

APR 2018

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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Page 53 of 91

HEAP LEACH 52 E&MJ • APRIL 2018 While heap leach systems seem rel- atively 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 distrib- uted using an irrigation system, which percolates through the heap liberating the metals. The pregnant solution is col- lected and processed. Pad designs vary, but there are pre- dominantly 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). Among the world's gold producers, Peru has some of the most rugged ter- rain and those operations tend to use val- ley leach pads, where the ore is stacked against the mountain. These mines will also use a compacted clay liner or a geo- synthetic clay liner, or in some cases, both. Valley leach pads also use geocom- posites under the geomembrane to protect the liner from an aggressive subgrade. The technique for placing ore on the pad can also vary, but many mines pre- Get Better Recovery From Heap-leach Systems From comminution to pad design, miners are reviewing options for precious metals By Steve Fiscor, Editor Despite constant high winds and steep slopes, an 11-man crew installs more than 375,000 ft 2 of GCL and 80 mil HDPE geomembrane. (Photo: Comanco)

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