Authors: van Zyl, D

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van Zyl, D 2008, 'Integrated Heap Leach Design — Incorporating Unsaturated Material Considerations', in AB Fourie (ed.), Rock Dumps 2008: Proceedings of the First International Seminar on the Management of Rock Dumps, Stockpiles and Heap Leach Pads, Australian Centre for Geomechanics, Perth, pp. 153-166,

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Heap leaching of gold/silver and copper ores are carried out under unsaturated flow conditions. While the mechanics of unsaturated flow through porous media is well understood, the large diameter particles typically present in heap leach operations present special challenges. The unsaturated flow characterisation of these materials is one such challenge. This paper will review unsaturated flow observations in heap leach materials under laboratory and field conditions. Specific attention will be paid to characterising the parameters for unsaturated flow through coarse heap leach materials and its impact on the subsequent modelling of unsaturated flow. Flow conditions during closure will also be evaluated as the drain down rate of heap leach facilities is dependent on the heap material characteristics. Recent observations and evaluations of the unsaturated behaviour of materials removed from dynamic (on off pad) heap leach operations for placement in spent ore disposal areas will be presented. These materials must be sufficiently dry to provide the shear strength and trafficability required for stacking conveyors typically used in the spent ore disposal area. A range of geotechnical and unsaturated flow evaluations can be used to evaluate the material behaviour. It is concluded that 21st century designers of heap leach facilities must include full consideration of the unsaturated behaviour of the heap leach materials, both as it relates to flow and strength of such materials. Recommendations are made for the integrated development of heap leach projects incorporating unsaturated material considerations.

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